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1.  Increased cortical expression of FK506 binding protein-51 in HIV-associated neurocognitive disorders 
Journal of Neurovirology  2012;18(4):313-322.
FK506 binding protein (FKBP)-51 and FKBP52 act as molecular chaperones to control glucocorticoid receptor (GR) sensitivity. Dysregulation of proteins involved in GR-mediated signaling can lead to maladaptive stress response and aging-related cognitive decline. As HIV infection is related to chronic stress, we hypothesized that altered cortical expression of these proteins was associated with HIV-associated neurocognitive disorders (HAND). We used quantitative immunohistochemistry to assess expression levels of these proteins in the mid-frontal gyrus of 55 HIV-infected subjects free of cerebral opportunistic diseases compared to 20 age-matched non-HIV controls. The immunoreactivity normalized to the neuroanatomic area measured (IRn) for FKBP51 was increased in HIV subjects both in the cortex and subcortical white matter (p<0.0001, U test), while no significant alterations were observed for GR or FKBP52. Notably, the cortical FKBP51 IRn was higher in HAND subjects than in cognitively normal HIV subjects (p=0.02, U test). There was also a trend for increasing cortical FKBP51 IRn with the increasing severity of HAND (p=0.08, Kruskal-Wallis test). No significant changes in FKBP51 IRn were found with respect to hepatitis C virus infection, lifetime methamphetamine use, or antiretroviral treatment in HIV subjects. In conclusion, the increased cortical expression of FKBP51 (an inhibitor for GR activity) might represent negative feedback in an attempt to reduce GR sensitivity in the setting of chronic stress-induced elevation of GR-mediated signaling inherent in HIV infection. The further increased FKBP51 expression might lead to maladaptive stress response and HAND.
PMCID: PMC3374917  PMID: 22234543
FKBP4; FKBP5; HIV dementia; Immunophilin; NR3C1
2.  Association of FKBP51 with Priming of Autophagy Pathways and Mediation of Antidepressant Treatment Response: Evidence in Cells, Mice, and Humans 
PLoS Medicine  2014;11(11):e1001755.
Theo Rein and colleagues examine the role of FKBP51 in the actions of antidepressants, with a particular focus on pathways of autophagy.
Please see later in the article for the Editors' Summary
FK506 binding protein 51 (FKBP51) is an Hsp90 co-chaperone and regulator of the glucocorticoid receptor, and consequently of stress physiology. Clinical studies suggest a genetic link between FKBP51 and antidepressant response in mood disorders; however, the underlying mechanisms remain elusive. The objective of this study was to elucidate the role of FKBP51 in the actions of antidepressants, with a particular focus on pathways of autophagy.
Methods and Findings
Established cell lines, primary neural cells, human blood cells of healthy individuals and patients with depression, and mice were treated with antidepressants. Mice were tested for several neuroendocrine and behavioral parameters. Protein interactions and autophagic pathway activity were mainly evaluated by co-immunoprecipitation and Western blots. We first show that the effects of acute antidepressant treatment on behavior are abolished in FKBP51 knockout (51KO) mice. Autophagic markers, such as the autophagy initiator Beclin1, were increased following acute antidepressant treatment in brains from wild-type, but not 51KO, animals. FKBP51 binds to Beclin1, changes decisive protein interactions and phosphorylation of Beclin1, and triggers autophagic pathways. Antidepressants and FKBP51 exhibited synergistic effects on these pathways. Using chronic social defeat as a depression-relevant stress model in combination with chronic paroxetine (PAR) treatment revealed that the stress response, as well as the effects of antidepressants on behavior and autophagic markers, depends on FKBP51. In human blood cells of healthy individuals, FKBP51 levels correlated with the potential of antidepressants to induce autophagic pathways.
Importantly, the clinical antidepressant response of patients with depression (n = 51) could be predicted by the antidepressant response of autophagic markers in patient-derived peripheral blood lymphocytes cultivated and treated ex vivo (Beclin1/amitriptyline: r = 0.572, p = 0.003; Beclin1/PAR: r = 0.569, p = 0.004; Beclin1/fluoxetine: r = 0.454, p = 0.026; pAkt/amitriptyline: r = −0.416, p = 0.006; pAkt/PAR: r = −0.355, p = 0.021; LC3B-II/PAR: r = 0.453, p = 0.02), as well as by the lymphocytic expression levels of FKBP51 (r = 0.631, p<0.0001), pAkt (r = −0.515, p = 0.003), and Beclin1 (r = 0.521, p = 0.002) at admission. Limitations of the study include the use of male mice only and the relatively low number of patients for protein analyses.
To our knowledge, these findings provide the first evidence for the molecular mechanism of FKBP51 in priming autophagic pathways; this process is linked to the potency of at least some antidepressants. These newly discovered functions of FKBP51 also provide novel predictive markers for treatment outcome, consistent with physiological and potential clinical relevance.
Please see later in the article for the Editors' Summary
Editors' Summary
Everyone feels miserable sometimes, but about one in six people will have an episode of clinical depression during their lifetime. For people who are clinically depressed, overwhelming feelings of sadness, anxiety, and hopelessness can last for months or years. Affected individuals lose interest in activities they used to enjoy, they sometimes have physical symptoms such as disturbed sleep, and they may contemplate suicide. Clinicians diagnose depression and determine its severity using questionnaires (“depression rating scales”) that explore the patient's feelings and symptoms. Mild depression is often treated with talking therapies (psychotherapy) such as cognitive behavioral therapy, which helps people change negative ways of thinking. For more severe depression, patients are also usually prescribed an antidepressant, most commonly a “selective serotonin reuptake inhibitor” such as paroxetine or a tricyclic antidepressant such as amitriptyline.
Why Was This Study Done?
Unfortunately, antidepressants don't work for more than half of patients. Moreover, because it is unclear how antidepressants work, it is not possible to predict which patients will respond to which antidepressants. Thus, matching patient to drug can be a lengthy, sometimes unsuccessful, process. Here, the researchers use several approaches to test the hypothesis that a protein called FK506 binding protein 51 (FKBP51) is involved in the actions of antidepressants and to investigate whether the ability of both FKBP51 and antidepressants to regulate a process called autophagy underlies the impact of FKBP51 on antidepressant responses. FKBP51 is a regulator of stress physiology, which is connected to the development and treatment of depression; genetic studies have suggested a link between FKBP51 expression and the antidepressant response rate. Some antidepressants are known to alter the initial steps in the autophagy pathway, a multistep process that maintains the integrity of cells through regulated degradation and recycling of cellular components; however, the potential synergistic role of FKBP51 and antidepressants in regulating pathways of autophagy are unknown.
What Did the Researchers Do and Find?
The researchers first treated wild-type mice and FKBP51 knockout mice (genetically altered animals that make no FKBP51) with an acute dose of antidepressant and compared their behavior in a forced swim test, an assay that measures the action of antidepressants in mice by determining how long the mice struggle or float inertly when placed in deep water. As expected, acute antidepressant treatment increased the time that wild-type mice spent struggling. However, this effect of antidepressant treatment was greatly attenuated in the FKBP51 knockout mice. Moreover, the levels of several autophagy markers increased in the brains of wild-type mice following antidepressant treatment but not in the brains of FKBP51 knockout mice. Next, using “chronic social defeat stress” to model the “endophenotype” of depression (a combination of physiological, hormonal, and behavioral traits seen in people with depression) in mice, the researchers showed that the stress response and the effect of chronic antidepressants on behavior and on autophagic markers all depend on FKBP51. Using cell-based assays, the researchers showed that antidepressants and FKBP51 had synergistic (interactive) effects on the autophagic pathway and that, in human blood cells, FKBP51 levels correlated with the potential of antidepressants to induce autophagic pathways. Finally, the researchers report that the clinical response to antidepressant treatment in 51 patients with depression was associated with the response of autophagic markers in their peripheral blood lymphocytes to antidepressant treatment in test tubes, and that the expression levels of FKBP51 and autophagy markers in patient lymphocytes at admission were associated with subsequent clinical responses to antidepressants.
What Do These Findings Mean?
These findings suggest that the protein FKBP51 is required for the effects of both acute and chronic treatment with some antidepressants on behavior and on autophagic pathways in mice. These findings also reveal an association between antidepressant treatment responses in patients and both the expression levels of FKBP51 and autophagy markers in lymphocytes at admission and the response of autophagic markers to antidepressant treatment in patient lymphocytes. The accuracy of these findings is limited by the small number of clinical samples available for analysis, by the use of only male mice in the animal experiments, and by the inability of animal models of depression to fully replicate the human condition. Nevertheless, these findings identify the early stages of autophagy as potential targets for the development of new antidepressants and identify several potential biomarkers that might, after further clinical validation, help clinicians predict antidepressant efficacy in patients with depression.
Additional Information
Please access these websites via the online version of this summary at
The US National Institute of Mental Health provides information on all aspects of depression (in English and Spanish), including information on antidepressants
The UK National Health Service Choices website provides detailed information about depression and about antidepressants; it also provides personal stories about depression
The UK charity Mind provides information on depression, including some personal stories about depression
More personal stories about depression are available from
MedlinePlus provides links to other resources about depression
Wikipedia has a page on autophagy (note that Wikipedia is a free online encyclopedia that anyone can edit; available in several languages)
The patients included in this study were all enrolled in the Munich Antidepressant Response Signature project, which aims to identify gene variants and biomarkers that predict treatment outcomes with antidepressants
PMCID: PMC4227651  PMID: 25386878
3.  Age-Associated Epigenetic Upregulation of the FKBP5 Gene Selectively Impairs Stress Resiliency 
PLoS ONE  2014;9(9):e107241.
Single nucleotide polymorphisms (SNPs) in the FK506 binding protein 5 (FKBP5) gene combine with traumatic events to increase risk for post-traumatic stress and major depressive disorders (PTSD and MDD). These SNPs increase FKBP51 protein expression through a mechanism involving demethylation of the gene and altered glucocorticoid signaling. Aged animals also display elevated FKBP51 levels, which contribute to impaired resiliency to depressive-like behaviors through impaired glucocorticoid signaling, a phenotype that is abrogated in FKBP5−/− mice. But the age of onset and progressive stability of these phenotypes remain unknown. Moreover, it is unclear how FKBP5 deletion affects other glucocorticoid-dependent processes or if age-associated increases in FKBP51 expression are mediated through a similar epigenetic process caused by SNPs in the FKBP5 gene. Here, we show that FKBP51-mediated impairment in stress resiliency and glucocorticoid signaling occurs by 10 months of age and this increased over their lifespan. Surprisingly, despite these progressive changes in glucocorticoid responsiveness, FKBP5−/− mice displayed normal longevity, glucose tolerance, blood composition and cytokine profiles across lifespan, phenotypes normally associated with glucocorticoid signaling. We also found that methylation of Fkbp5 decreased with age in mice, a process that likely explains the age-associated increases in FKBP51 levels. Thus, epigenetic upregulation of FKBP51 with age can selectively impair psychological stress-resiliency, but does not affect other glucocorticoid-mediated physiological processes. This makes FKBP51 a unique and attractive therapeutic target to treat PTSD and MDD. In addition, aged wild-type mice may be a useful model for investigating the mechanisms of FKBP5 SNPs associated with these disorders.
PMCID: PMC4156438  PMID: 25191701
4.  Early life stress and serotonin transporter gene variation interact to affect the transcription of the glucocorticoid and mineralocorticoid receptors, and the co-chaperone FKBP5, in the adult rat brain 
The short allelic variant of the serotonin transporter (5-HTT) promoter-linked polymorphic region (5-HTTLPR) has been associated with the etiology of major depression by interaction with early life stress (ELS). A frequently observed endophenotype in depression is the abnormal regulation of levels of stress hormones such as glucocorticoids. It is hypothesized that altered central glucocorticoid influence on stress-related behavior and memory processes could underlie the depressogenic interaction of 5-HTTLPR and ELS. One possible mechanism could be the altered expression of the genes encoding the glucocorticoid and mineralocorticoid receptors (GR, MR) and their inhibitory regulator FK506-binding protein 51 (FKBP5) in stress-related forebrain areas. To test this notion, we exposed heterozygous (5-HTT+/−) and homozygous (5-HTT−/−) serotonin transporter knockout rats and their wildtype littermates (5-HTT+/+) to daily 3 h maternal separations from postnatal day 2 to 14. In the medial prefrontal cortex (mPFC) and hippocampus of the adult male offspring, we found that GR, MR, and FKBP5 mRNA levels were affected by ELS × 5-HTT genotype interaction. Specifically, 5-HTT+/+ rats exposed to ELS showed decreased GR and FKBP5 mRNA in the dorsal and ventral mPFC, respectively. In contrast, 5-HTT+/− rats showed increased MR mRNA levels in the hippocampus and 5-HTT−/− rats showed increased FKBP5 mRNA in the ventral mPFC after ELS exposure. These findings indicate that 5-HTT genotype determines the specific adaptation of GR, MR, and FKBP5 expression in response to early life adversity. Therefore, altered extra-hypothalamic glucocorticoid signaling should be considered to play a role in the depressogenic interaction of ELS and 5-HTTLPR.
PMCID: PMC4195371  PMID: 25352794
early life stress; serotonin transporter; depression; glucocorticoid receptor; mineralocorticoid receptor; FKBP5; hippocampus; medial prefrontal cortex
5.  FKBP51 increases the tumour-promoter potential of TGF-beta 
FKBP51 (FKBP5 Official Symbol) is a large molecular weight component of the family of FK506 binding proteins (FKBP). In recent years, research studies from our laboratory highlighted functions for FKBP51 in the control of apoptosis and melanoma progression. FKBP51 expression correlated with the invasiveness and aggressiveness of melanoma. Since a role for TGF-β in the enhanced tumorigenic potential of melanoma cells is widely described, we hypothesized a cooperative effect between FKBP51 and TGF-β in melanoma progression.
SAN and A375 melanoma cell lines were utilized for this study. Balb/c IL2γ NOD SCID served to assess the ability to colonize organs and metastasize of different cell lines, which was evaluated by in vivo imaging. Realtime PCR and western blot served for measurement of mRNA and protein expression, respectively.
By comparing the metastatic potential of two melanoma cell lines, namely A375 and SAN, we confirmed that an increased capability to colonize murine organs was associated with increased levels of FKBP51. A375 melanoma cell line expressed FKBP51 mRNA levels 30-fold higher in comparison to the SAN mRNA level and appeared more aggressive than SAN melanoma cell line in an experimental metastasis model. In addition, A375 expressed, more abundantly than SAN, the TGF-β and the pro angiogenic TGF-β receptor type III (TβRIII) factors. FKBP51 silencing produced a reduction of TGF-β and TβRIII gene expression in A375 cell line, in accordance with previous studies. We found that the inducing effect of TGF-β on Sparc and Vimentin expression was impaired in condition of FKBP51 depletion, suggesting that FKBP51 is an important cofactor in the TGF-β signal. Such a hypothesis was supported by co immunoprecipitation assays, showing that FKBP51 interacted with either Smad2,3 and p300. In normal melanocytes, FKBP51 potentiated the effect of TGF-β on N-cadherin expression and conferred a mesenchymal-like morphology to such round-shaped cells.
Overall, our findings show that FKBP51 enhances some pro oncogenic functions of TGF-β, suggesting that FKBP51-overexpression may help melanoma to take advantage of the tumor promoting activities of the cytokine.
PMCID: PMC3906759  PMID: 24460977
Melanoma; TGF-β; FKBP51; Metastasis
6.  Disrupting Function of FK506-Binding Protein 1b/12.6 Induces the Ca2+-Dysregulation Aging Phenotype in Hippocampal Neurons 
With aging, multiple Ca2+-associated electrophysiological processes exhibit increased magnitude in hippocampal pyramidal neurons, including the Ca2+-dependent slow afterhyperpolarization (sAHP), L-type voltage-gated Ca2+channel (L-VGCC) activity, Ca2+-induced Ca2+ release (CICR) from ryanodine receptors (RyRs), and Ca2+ transients. This pattern of Ca2+ dysregulation correlates with reduced neuronal excitability/plasticity and impaired learning/memory and has been proposed to contribute to unhealthy brain aging and Alzheimer’s disease. However, little is known about the underlying molecular mechanisms. In cardiomyocytes, FK506-binding protein 1b/12.6 (FKBP1b) binds and stabilizes RyR2 in the closed state, inhibiting RyR-mediated Ca2+release. Moreover, we recently found that hippocampal Fkbp1b expression is downregulated, whereas Ryr2 and Frap1/Mtor (mammalian target of rapamycin) expression is up-regulated with aging in rats. Here, we tested the hypothesis that disrupting FKBP1b function also destabilizes Ca2+ homeostasis in hippocampal neurons and is sufficient to induce the aging phenotype of Ca2+ dysregulation in young animals. Selective knockdown of Fkbp1b with interfering RNA in vitro (96 h) enhanced voltage-gated Ca2+ current in cultured neurons, whereas in vivo Fkbp1b knock-down by microinjection of viral vector (3–4 weeks) dramatically increased the sAHP in hippocampal slice neurons from young-adult rats. Rapamycin, which displaces FKBP1b from RyRs in myocytes, similarly enhanced VGCC current and the sAHP and also increased CICR. Moreover, FKBP1b knockdown in vivo was associated with upregulation of RyR2 and mTOR protein expression. Thus, disruption of FKBP1b recapitulated much of the Ca2+-dysregulation aging phenotype in young rat hippocampus, supporting a novel hypothesis that declining FKBP function plays a major role in unhealthy brain aging.
PMCID: PMC3092371  PMID: 21289178
7.  Control of Alzheimer's Amyloid Beta Toxicity by the High Molecular Weight Immunophilin FKBP52 and Copper Homeostasis in Drosophila 
PLoS ONE  2010;5(1):e8626.
FK506 binding proteins (FKBPs), also called immunophilins, are prolyl-isomerases (PPIases) that participate in a wide variety of cellular functions including hormone signaling and protein folding. Recent studies indicate that proteins that contain PPIase activity can also alter the processing of Alzheimer's Amyloid Precursor Protein (APP). Originally identified in hematopoietic cells, FKBP52 is much more abundantly expressed in neurons, including the hippocampus, frontal cortex, and basal ganglia. Given the fact that the high molecular weight immunophilin FKBP52 is highly expressed in CNS regions susceptible to Alzheimer's, we investigated its role in Aβ toxicity. Towards this goal, we generated Aβ transgenic Drosophila that harbor gain of function or loss of function mutations of FKBP52. FKBP52 overexpression reduced the toxicity of Aβ and increased lifespan in Aβ flies, whereas loss of function of FKBP52 exacerbated these Aβ phenotypes. Interestingly, the Aβ pathology was enhanced by mutations in the copper transporters Atox1, which interacts with FKBP52, and Ctr1A and was suppressed in FKBP52 mutant flies raised on a copper chelator diet. Using mammalian cultures, we show that FKBP52 (−/−) cells have increased intracellular copper and higher levels of Aβ. This effect is reversed by reconstitution of FKBP52. Finally, we also found that FKBP52 formed stable complexes with APP through its FK506 interacting domain. Taken together, these studies identify a novel role for FKBP52 in modulating toxicity of Aβ peptides.
PMCID: PMC2801609  PMID: 20084280
Hypertension  2011;57(6):1167-1175.
Patients treated with the immunosuppressive drug tacrolimus (FK506), which binds FK506 Binding Protein 12 (FKBP12) then inhibits the calcium-dependent phosphatase calcineurin, exhibit decreased regulatory T cells, endothelial dysfunction, and hypertension; however the mechanisms and whether altered T cell polarization play a role are unknown. Tacrolimus treatment of mice for 1 week dose-dependently decreased CD4+/FoxP3+ (regulatory T cells) and increased CD4+/IL-17+ (T helper 17) cells in the spleen, and caused endothelial dysfunction and hypertension. To determine the mechanisms, we crossed floxed FKBP12 mice with Tie2-Cre mice to generate offspring lacking FKBP12 in endothelial and hematopoietic cells only (FKBP12EC KO). Given FKBP12’s role in inhibiting TGF-β receptor activation, Tie2-Cre-mediated deletion of FKBP12 increased TGF-β receptor activation and SMAD2/3 signaling. FKBP12EC KO mice exhibited increased vascular expression of genes and proteins related to endothelial cell activation and inflammation. Serum levels of the pro-inflammatory cytokines IL-2, IL-6, IFNγ, IL-17a, IL-21, and IL-23 were increased significantly suggesting a Th17 cell-mediated inflammatory state. Flow cytometry studies confirmed this as splenocyte levels of CD4+/IL-17+ cells were increased significantly while CD4+/FoxP3+ cells were decreased in FKBP12EC KO mice. Furthermore, spleens from FKBP12EC KO mice showed increased STAT3 activation, involved in Th17 cell induction, and decreased STAT5 activation, involved in regulatory T cell induction. FKBP12EC KO mice also exhibited endothelial dysfunction and hypertension. These data suggest that tacrolimus, through its activation of TGF-β receptors in endothelial and hematopoietic cells, may cause endothelial dysfunction and hypertension by activating endothelial cells, reducing Tregs, and increasing Th17 cell polarization and inflammation.
PMCID: PMC3108179  PMID: 21518963
endothelium; hypertension; experimental; inflammation; lymphocytes; T cells; FK506 (tacrolimus)
9.  Intracellular calcium leak due to FKBP12.6 deficiency in mice facilitates the inducibility of atrial fibrillation 
Although defective Ca2+ homeostasis may contribute to arrhythmogenesis in atrial fibrillation (AF), the underlying molecular mechanisms remain poorly understood. Studies in patients with AF revealed that impaired diastolic closure of SR Ca2+-release channels (ryanodine receptors, RyR2) is associated with reduced levels of the RyR2-inhibitory subunit FKBP12.6.
Objective of the present study was to test the hypothesis that Ca2+ leak from the sarcoplasmic reticulum (SR) through RyR2 increases the propensity for AF in FKBP12.6 deficient (−/−) mice.
Surface ECG and intracardiac electrograms were recorded simultaneously in FKBP12.6−/− mice and wildtype (WT) littermates. Right atrial programmed stimulation was performed before and after injection of RyR2 antagonist tetracaine (0.5 mg/kg). Intracellular Ca2+ transients were recorded in atrial myocytes from FKBP12.6−/− and WT mice.
FKBP12.6−/− mice had structurally normal atria and unaltered expression of key Ca2+-handling proteins. AF episodes were inducible in 81% of FKBP12.6−/−, but in only 7% of WT mice (P<0.05), and were prevented by tetracaine in all FKBP12.6−/− mice. SR Ca2+ leak in FKBP12.6−/− myocytes was 53% larger than in WT myocytes, and FKBP12.6−/− myocytes exhibited increased incidence of spontaneous SR Ca2+ release events, which could be blocked by tetracaine.
The increased vulnerability to AF in FKBP12.6−/− mice substantiates the notion that defective SR Ca2+ release due to abnormal RyR2 and FKBP12.6 interactions may contribute to the initiation or maintenance of atrial fibrillation.
PMCID: PMC2525570  PMID: 18598963
Atrial fibrillation; calcium; electrical remodeling; focal activity; ryanodine receptors
10.  FKBP12 is a Critical Regulator of the Heart Rhythm and the Cardiac Voltage-Gated Sodium Current in Mice 
Circulation research  2011;108(9):1042-1052.
FK506 binding protein 12 (FKBP12) is a known cis-trans peptidyl prolyl isomerase and highly expressed in the heart. Its role in regulating postnatal cardiac function remains largely unknown.
Methods and Results
We generated FKBP12 overexpressing transgenic (αMyHC-FKBP12) mice and cardiomyocyte-restricted FKBP12 conditional knockout (FKBP12f/f/αMyHC-Cre) mice, and analyzed their cardiac electrophysiology in vivo and in vitro. A high incidence (38%) of sudden death was found in αMyHC-FKBP12 mice. Surface and ambulatory ECGs documented cardiac conduction defects, which were further confirmed by electrical measurements and optical mapping in Langendorff-perfused hearts. αMyHC-FKBP12 hearts had slower action potential upstrokes, and longer action potential durations. Whole-cell patch-clamp analyses demonstrated an ~80% reduction in peak density of the tetrodotoxin-resistant, voltage-gated sodium current, INa, in αMyHC-FKBP12 ventricular cardiomyocytes, a slower recovery of INa from inactivation, shifts of steady-state activation and inactivation curves of INa to more depolarized potentials, and augmentation of late INa, suggesting that the arrhythmogenic phenotype of αMyHC-FKBP12 mice is due to abnormal INa. Ventricular cardiomyocytes isolated from FKBP12f/f/αMyHC-Cre hearts showed faster action potential upstrokes and a more than 2-fold increase in peak INa density. Dialysis of exogenous recombinant FKBP12 protein into FKBP12-deficient cardiomyocytes promptly recapitulated alterations in INa seen in αMyHC-FKBP12 myocytes.
FKBP12 is a critical regulator of INa and is important to cardiac arrhythmogenic physiology. FKPB12-mediated dysregulation of INa may underlie clinical arrhythmias associated with FK506 administration.
PMCID: PMC3092589  PMID: 21372286
proteins; ion channels; conduction; heart block; long-QT syndrome
11.  Prenatal Alcohol Exposure Is Associated with Altered Subcellular Distribution of Glucocorticoid and Mineralocorticoid Receptors in the Adolescent Mouse Hippocampal Formation 
Accumulating evidence indicates that several of the long-term consequences of prenatal alcohol exposure (PAE) are the result of changes in the development and function of cortico-limbic structures, including the hippocampal formation. The glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) are key regulators of hippocampal formation development, structure, and functioning and, thus, are potential mediators of PAE’s effects on this brain region. In the present studies, we assessed the impact of PAE on components of corticosteroid signaling pathways in the mouse hippocampal formation.
Throughout pregnancy, mouse dams were offered either 10% (w/v) ethanol sweetened with 0.066% (w/v) saccharin (SAC) or 0.066% (w/v) SAC alone using a limited (4-hour) access, drinking-in-the-dark paradigm. The hippocampal formation was isolated from naïve postnatal day 40 to 50 offspring, and subcellular fractions were prepared. Using immunoblotting techniques, we measured the levels of GR, MR, 11-β-hydroxysteroid dehydrogenase 1 (11β-HSD1), and the FK506-binding proteins 51 (FKBP51, FKBP5) and 52 (FKBP52, FKBP4). Finally, we determined the effect of PAE on context discrimination, a hippocampal-dependent learning/memory task.
PAE was associated with reduced MR and elevated GR nuclear localization in the hippocampal formation, whereas cytosolic levels of both receptors were not significantly altered. FKBP51 levels were reduced, while FKBP52 levels were unaltered, and 11β-HSD1 levels were increased in postnuclear fractions isolated from PAE mouse hippocampal formation. These neurochemical alterations were associated with reduced context discrimination.
The data support a model in which PAE leads to increased nuclear localization of GRs secondary to reductions in FKBP51 and increases in 11β-HSD1 levels in the adolescent mouse hippocampal formation. Persistent dysregulation of GR subcellular distribution is predicted to damage the hippocampal formation and may underlie many of the effects of PAE on hippocampal-dependent functioning.
PMCID: PMC3864567  PMID: 23992407
Prenatal; Alcohol; Glucocorticoid; Mineralocorticoid; 11β-HSD1; Hippocampus
12.  Expression and Regulation of the Fkbp5 Gene in the Adult Mouse Brain 
PLoS ONE  2011;6(2):e16883.
Chronic stress has been found to be a major risk factor for various human pathologies. Stress activates the hypothalamic-pituitary-adrenal (HPA) axis, which is tightly regulated via, among others, the glucocorticoid receptor (GR). The activity of the GR is modulated by a variety of proteins, including the co-chaperone FK506 binding protein 51 (FKBP5). Although FKBP5 has been associated with risk for affective disorders and has been implicated in GR sensitivity, previous studies focused mainly on peripheral blood, while information about basal distribution and induction in the central nervous system are sparse.
Methodology/Principal Findings
In the present study, we describe the basal expression pattern of Fkbp5 mRNA in the brain of adult male mice and show the induction of Fkbp5 mRNA via dexamethasone treatment or different stress paradigms. We could show that Fkbp5 is often, but not exclusively, expressed in regions also known for GR expression, for example the hippocampus. Furthermore, we were able to induce Fkbp5 expression via dexamethasone in the CA1 and DG subregions of the hippocampus, the paraventricular nucleus (PVN) and the central amygdala (CeA). Increase of Fkbp5 mRNA was also found after restrained stress and 24 hours of food deprivation in the PVN and the CeA, while in the hippocampus only food deprivation caused an increase in Fkbp5 mRNA.
Interestingly, regions with a low basal expression showed higher increase in Fkbp5 mRNA following induction than regions with high basal expression, supporting the hypothesis that GR sensitivity is, at least partly, mediated via Fkbp5. In addition, this also supports the use of Fkbp5 gene expression as a marker for GR sensitivity. In summary, we were able to give an overview of the basal expression of fkbp5 mRNA as well as to extend the findings of induction of Fkbp5 and its regulatory influence on GR sensitivity from peripheral blood to the brain.
PMCID: PMC3036725  PMID: 21347384
13.  Differential Expression of Immunophilins FKBP51 and FKBP52 in the Frontal Cortex of HIV-Infected Patients with Major Depressive Disorder 
Patients infected with human immunodeficiency virus (HIV) have a higher risk of developing major depressive disorder (MDD) than the general population. Immunophilins FKBP51 and FKBP52 are expressed in cortical neurons and regulate the function of the glucocorticoid receptor (GR). Previous reports have shown that genetic variants in the FKBP5 gene encoding FKBP51 are linked to psychiatric disorders. We sought to determine whether immunophilins are upregulated in HIV infection. To determine whether FKBP52 and FKBP51 are associated with MDD and/or HIV, we compared protein and gene expression in autopsy tissues from the frontal cortical gray matter. The study cases were divided into five groups: control, MDD, MDD with psychosis, HIV+, and HIV+ with MDD. Gene expression and protein levels were determined by real-time PCR and Western blot analysis of fresh frozen tissues. Genotyping of previously published alleles of the FKBP5 gene was also performed. We found correlation of upregulation of both immunophilins in the HIV-infected groups. In the HIV+ population with MDD, FKBP4 expression is significantly higher while FKBP5 is more variable. After analyzing the FKBP5 gene for single nucleotide polymorphisms, we found that rs3800373 CC genotype is more frequent in the MDD and MDD/Psychosis groups. We hypothesized that the levels of FKBP51, as modulator of the nuclear translocation of GR, would be lower in MDD. Instead, an increase in FKBP51 at both the transcript (FKBP5) and protein level correlated with MDD. Increased FKBP4 expression of correlated to HIV+MDD but not to HIV without MDD.
PMCID: PMC2929573  PMID: 19199039
HIV; immunophilins; major depressive disorder; glucocorticoid receptor
14.  Caspase-mediated pro-apoptotic interaction of panaxadiol and irinotecan in human colorectal cancer cells 
Panaxadiol (PD) is a purified sapogenin of ginseng saponins that exhibits anticancer activity. Irinotecan (IRN) is a second line anticancer drug, but clinical treatment with IRN is limited due to side effects. In this study, we investigated the possible synergistic anticancer effects of PD and IRN on human colorectal cancer cells and explored the potential role of apoptosis in the synergistic activities.
Key findings
The combination of PD and IRN significantly enhanced antiproliferative effects in HCT-116 cells (P < 0.05). Cell cycle analysis demonstrated that combining IRN treatment with PD significantly increased the G1-phase fractions of cells, compared with IRN treatment alone. In apoptotic assays, the combination of PD and IRN significantly increased the percentage of apoptotic cells compared with IRN alone (P < 0.01). Increased caspase 3 and caspase 9 activities were observed after treating with PD and IRN. The synergistic apoptotic effects were also supported by docking analysis, which demonstrated that PD and IRN bound two different chains of the caspase 3 protein.
Data from this study suggested that caspase 3- and caspase 9-mediated apoptosis may play an important role in the PD enhanced antiproliferative effects of IRN on human colorectal cancer cells.
PMCID: PMC3349342  PMID: 22471369
Irinotecan; panaxadiol; apoptosis; cell cycle; human colorectal cancer
15.  Genome-Wide Association Study Implicates Testis-Sperm Specific FKBP6 as a Susceptibility Locus for Impaired Acrosome Reaction in Stallions 
PLoS Genetics  2012;8(12):e1003139.
Impaired acrosomal reaction (IAR) of sperm causes male subfertility in humans and animals. Despite compelling evidence about the genetic control over acrosome biogenesis and function, the genomics of IAR is as yet poorly understood, providing no molecular tools for diagnostics. Here we conducted Equine SNP50 Beadchip genotyping and GWAS using 7 IAR–affected and 37 control Thoroughbred stallions. A significant (P<6.75E-08) genotype–phenotype association was found in horse chromosome 13 in FK506 binding protein 6 (FKBP6). The gene belongs to the immunophilins FKBP family known to be involved in meiosis, calcium homeostasis, clathrin-coated vesicles, and membrane fusions. Direct sequencing of FKBP6 exons in cases and controls identified SNPs g.11040315G>A and g.11040379C>A (p.166H>N) in exon 4 that were significantly associated with the IAR phenotype both in the GWAS cohort (n = 44) and in a large multi-breed cohort of 265 horses. All IAR stallions were homozygous for the A-alleles, while this genotype was found only in 2% of controls. The equine FKBP6 was exclusively expressed in testis and sperm and had 5 different transcripts, of which 4 were novel. The expression of this gene in AC/AG heterozygous controls was monoallelic, and we observed a tendency for FKBP6 up-regulation in IAR stallions compared to controls. Because exon 4 SNPs had no effect on the protein structure, it is likely that FKBP6 relates to the IAR phenotype via regulatory or modifying functions. In conclusion, FKBP6 was considered a susceptibility gene of incomplete penetrance for IAR in stallions and a candidate gene for male subfertility in mammals. FKBP6 genotyping is recommended for the detection of IAR–susceptible individuals among potential breeding stallions. Successful use of sperm as a source of DNA and RNA propagates non-invasive sample procurement for fertility genomics in animals and humans.
Author Summary
Impaired acrosomal reaction (IAR) of sperm causes male subfertility in humans and animals, and currently the molecular causes of the condition are not known. Here we report the mapping, identification, and functional analysis of a susceptibility locus for IAR in stallions. The candidate region was mapped to horse chromosome 13 by SNP genotyping and GWAS of 7 IAR affected and 44 control Thoroughbred stallions. Re-sequencing and case-control analysis of functionally relevant candidate genes in the region identified FKBP6 gene as a significantly associated locus. The association was confirmed by genotyping 265 male horses of multiple breeds. FKBP6 belongs to the immunophilins FKBP family known to be involved in meiosis, calcium homeostasis, clathrin-coated vesicles, and membrane fusions. We showed that the equine FKBP6 is exclusively and monoallelically expressed in testis and sperm and has 5 different transcripts, of which 4 were novel. Overall, FKBP6 was considered a susceptibility gene of incomplete penetrance for IAR in stallions and a candidate gene for male subfertility in other mammals. Successful use of sperm as a source of DNA and RNA propagates non-invasive sample procurement for fertility genomics in animals and humans.
PMCID: PMC3527208  PMID: 23284302
16.  Essential Role for Co-Chaperone FKBP52 but not FKBP51 in Androgen Receptor-Mediated Signaling and Physiology 
The Journal of biological chemistry  2006;282(7):5026-5036.
FKBP52 and FKBP51 are tetratricopeptide repeat (TPR) proteins found in steroid receptor complexes and FKBP51 is an androgen receptor (AR) target gene. Although in vitro studies suggest that FKBP52 and FKBP51 regulate hormone-binding and/or subcellular trafficking of receptors, the roles of FKBP52 and FKBP51 in vivo have not been extensively investigated. Here, we evaluate their physiological roles in FKBP52-deficient and FKBP51-deficient mice. FKBP52-deficient males developed defects in select reproductive organs (e.g., penile hypospadias, prostate dysgenesis, but normal testis), pointing to a role for FKBP52 in AR-mediated signaling and function. Surprisingly, ablation of FKBP52 did not affect AR hormone-binding or nuclear translocation in vivo and in vitro. Molecular studies in MEF cells uncovered that FKBP52 is critical to AR transcriptional activity. Interestingly, FKBP51 expression was down-regulated in FKBP52-deficient males but only in affected tissues, providing further evidence of tissue-specific loss of AR activity and suggesting that FKBP51 is an AR target gene essential to penile and prostate development. However, FKBP51-deficient mice were normal, showing no defects in AR-mediated reproductive function. Our work demonstrates that FKBP52 but not FKBP51 is essential to AR-mediated signaling, and provides evidence for an unprecedented FKBP52 function – direct control of steroid receptor transcriptional activity.
PMCID: PMC2577319  PMID: 17142810
17.  Developmental regulation and coordinate reexpression of FKBP65 with extracellular matrix proteins after lung injury suggest a specialized function for this endoplasmic reticulum immunophilin 
Cell Stress & Chaperones  2005;10(4):285-295.
FKBP65 (65-kDa FK506-binding protein) is an endoplasmic reticulum (ER)–localized peptidyl-prolyl cis-trans isomerase predicted to play a role in the folding and trafficking of secretory proteins. In previous studies, we have shown that FKBP65 is developmentally regulated and associates with the extracellular matrix protein, tropoelastin, during its maturation and transport through the ER. In this study, we show that FKBP65 is expressed in the lung with the same developmental pattern as tropoelastin and other matrix proteins. To test the hypothesis that FKBP65 is upregulated at times when extracellular matrix proteins are being actively synthesized and assembled, adult mice were treated with bleomycin to cause reinitiation of matrix protein production during the ensuing development of pulmonary fibrosis. After bleomycin instillation, FKBP65 expression was reactivated in the lung with a pattern similar to that observed for tropoelastin and type I collagen. Using human lung fibroblast cultures, we showed that FKBP65 does not undergo the unfolded protein response, a response associated with an upregulation of resident ER proteins that occurs after increased ER stress. When fibroblasts were treated with transforming growth factor (TGF)-β1, which is upregulated during the development of pulmonary fibrosis and known to induce matrix production, FKBP65 expression and synthesis was also increased. Similar to type I collagen and tropoelastin, this response was completely inhibited in a dose-dependent manner by GGTI-298, a geranylgeranyl transferase I inhibitor. Treatment of fibroblasts with an inhibitor of ribonucleic acid (RNA) polymerase II after TGF-β1 treatment showed that the effect of TGF-β1 was not because of increased stabilization of the FKBP65 messenger RNA. In summary, we have shown that FKBP65 is highly expressed in lung development, downregulated in the adult, and can be reactivated in a coordinated manner with extracellular matrix proteins after lung injury. The expression pattern of FKBP65, which is atypical for general ER foldases, suggests that FKBP65 has a distinct set of developmentally regulated protein ligands. The response to injury, which may be in part a direct response to TGF-β1, assures the presence of FKBP65 in the ER of cells actively producing components of the extracellular matrix.
PMCID: PMC1283874  PMID: 16333983
18.  Removal of FKBP12 Enhances mTOR-Raptor Interactions, LTP, Memory, and Perseverative/Repetitive Behavior 
Neuron  2008;60(5):832-845.
FK506 binding protein 12 (FKBP12) binds the immunosuppressant drugs FK506 and rapamycin and regulates several signaling pathways, including mammalian target of rapamycin (mTOR) signaling. We determined whether the brain-specific disruption of the FKBP12 gene altered mTOR signaling, synaptic plasticity, and memory. Biochemically, the FKBP12-deficient mice displayed increases in basal mTOR phosphorylation, mTOR-Raptor interactions, and p70 S6 kinase (S6K) phosphorylation. Electrophysiological experiments revealed that FKBP12 deficiency was associated with an enhancement in long-lasting hippocampal long-term potentiation (LTP). The LTP enhancement was resistant to rapamycin, but not anisomycin, suggesting that altered translation control is involved in the enhanced synaptic plasticity. Behaviorally, FKBP12 conditional knockout (cKO) mice displayed enhanced contextual fear memory, and autistic/obsessive-compulsive-like perseveration in several assays including the water maze, Y-maze reversal task, and the novel object recognition task. Our results indicate that FKBP12 plays a critical role in the regulation of mTOR-Raptor interactions, LTP, memory, and perseverative behaviors.
PMCID: PMC2630531  PMID: 19081378
19.  Differential conformational dynamics in the closely homologous FK506-binding domains of FKBP51 and FKBP52 
Biochemical Journal  2014;461(Pt 1):115-123.
As co-chaperones of Hsp90 (heat-shock protein 90), FKBP51 (FK506-binding protein of 51 kDa) and FKBP52 (FK506-binding protein of 52 kDa) act as antagonists in regulating the hormone affinity and nuclear transport of steroid receptor complexes. Exchange of Leu119 in FKBP51 for Pro119 in FKBP52 has been shown to largely reverse the steroid receptor activities of FKBP51 and FKBP52. To examine whether differences in conformational dynamics/plasticity might correlate with changes in the reported receptor activities, 15N-NMR relaxation measurements were carried out on the N-terminal FKBP domains of FKBP51 and FKBP52 as well as their residue-swapped variants. Both proteins exhibit a similar pattern of motion in the picosecond–nanosecond timeframe as well as a small degree of 15N line-broadening, indicative of motion in the microsecond–millisecond timeframe, in the β3a strand of the central sheet. Only the FKBP51 domain exhibits much larger line-broadening in the adjacent β3 bulge (40′s loop of FKBP12) and throughout the long β4–β5 loop (80′s loop of FKBP12). The L119P mutation at the tip of the β4–β5 loop completely suppressed the line-broadening in this loop while partially suppressing the line-broadening in the neighbouring β2 and β3a strands. The complementary P119L and P119L/P124S variants of FKBP52 yielded similar patterns of line-broadening for the β4–β5 loop as that for FKBP51, although only 20% and 60% as intense respectively. However, despite the close structural similarity in the packing interactions between the β4–β5 loop and the β3a strand for FKBP51 and FKBP52, the line-broadening in the β3a strand is unaffected by the P119L or P119L/P124S mutations in FKBP52.
Unlike FKBP52, the FK1 domain of FKBP51 exhibits microsecond–millisecond conformational dynamics in the β3 bulge and the β4–β5 loop, known sites of protein signalling interactions. Swapping residue 119 yields altered conformational dynamics in a pattern reminiscent of reported modulations in steroid receptor activity.
PMCID: PMC4060953  PMID: 24749623
conformational dynamics; differential line-broadening; FK506-binding protein of 51 kDa (FKBP51); FK506-binding protein of 52 kDa (FKBP52); mutational analysis; nuclear magnetic resonance (NMR); FKBP, FK506-binding protein; FRB, FKBP12–rapamycin-binding; Hsp, heat-shock protein; LBD, ligand-binding domain; NF-κB, nuclear factor κB; TPR, tetratricopeptide
20.  Isorhynchophylline Protects PC12 Cells Against Beta-Amyloid-Induced Apoptosis via PI3K/Akt Signaling Pathway 
The neurotoxicity of amyloid-β (Aβ) has been implicated as a critical cause of Alzheimer's disease. Isorhynchophylline (IRN), an oxindole alkaloid isolated from Uncaria rhynchophylla, exerts neuroprotective effect against Aβ25–35-induced neurotoxicity in vitro. However, the exact mechanism for its neuroprotective effect is not well understood. The present study aimed to investigate the molecular mechanisms underlying the protective action of IRN against Aβ25–35-induced neurotoxicity in cultured rat pheochromocytoma (PC12) cells. Pretreatment with IRN significantly increased the cell viability, inhibited the release of lactate dehydrogenase and the extent of DNA fragmentation in Aβ25–35-treated cells. IRN treatment was able to enhance the protein levels of phosphorylated Akt (p-Akt) and glycogen synthase kinase-3β (p-GSK-3β). Lithium chloride blocked Aβ25–35-induced cellular apoptosis in a similar manner as IRN, suggesting that GSK-3β inhibition was involved in neuroprotective action of IRN. Pretreatment with LY294002 completely abolished the protective effects of IRN. Furthermore, IRN reversed Aβ25–35-induced attenuation in the level of phosphorylated cyclic AMP response element binding protein (p-CREB) and the effect of IRN could be blocked by the PI3K inhibitor. These experimental findings unambiguously suggested that the protective effect of IRN against Aβ25–35-induced apoptosis in PC12 cells was associated with the enhancement of p-CREB expression via PI3K/Akt/GSK-3β signaling pathway.
PMCID: PMC3836301  PMID: 24319473
21.  FK506 Binding Protein Mediates Glioma Cell Growth and Sensitivity to Rapamycin Treatment by Regulating NF-κB Signaling Pathway1 
Neoplasia (New York, N.Y.)  2008;10(3):235-243.
FK506 binding protein 5 (FKBP5) belongs to a family of immunophilins named for their ability to bind immunosuppressive drugs, also known as peptidyl-prolyl cis-trans isomerases, and also with chaperones to help protein folding. Using glioma cDNA microarray analysis, we found that FKBP5 was overexpressed in glioma tumors. This finding was further validated by real-time reverse transcription-polymerase chain reaction and Western blot analysis. The roles of FKBP5 in glioma cells were then examined. We found that cell growth was suppressed after FKBP5 expression was inhibited by short interfering RNA transfection and enhanced by FKBP5 overexpression. Electrophoretic mobility shift assay showed that nuclear factor-kappa B (NF-κB) and DNA binding was enhanced by FKBP5 overexpression. The expression level of I-kappa B alpha and phosphorylated NF-κB was regulated by the expression of FKBP5. These data suggest that FKBP5 is involved in NF-κB pathway activation in glioma cells. In addition, FKBP5 overexpression in rapamycin-sensitive U87 cells blocked the cells' response to rapamycin treatment, whereas rapamycin-resistant glioma cells, both PTEN-positive and -negative, were synergistically sensitive to rapamycin after FKBP5 was knocked down, suggesting that the FKBP5 regulates glioma cell response to rapamycin treatment. In conclusion, our study demonstrates that FKBP5 plays an important role in glioma growth and chemoresistance through regulating signal transduction of the NF-κB pathway.
PMCID: PMC2259453  PMID: 18320068
22.  Hypoxia Induces Intracellular Ca2+ Release by Causing Reactive Oxygen Species-Mediated Dissociation of FK506-Binding Protein 12.6 from Ryanodine Receptor 2 in Pulmonary Artery Myocytes 
Antioxidants & Redox Signaling  2011;14(1):37-47.
Here we attempted to test a novel hypothesis that hypoxia may induce Ca2+ release through reactive oxygen species (ROS)-mediated dissociation of FK506-binding protein 12.6 (FKBP12.6) from ryanodine receptors (RyRs) on the sarcoplasmic reticulum (SR) in pulmonary artery smooth muscle cells (PASMCs). The results reveal that hypoxic exposure significantly decreased the amount of FKBP12.6 on the SR of PAs and increased FKBP12.6 in the cytosol. The colocalization of FKBP12.6 with RyRs was decreased in intact PASMCs. Pharmacological and genetic inhibition of intracellular ROS generation prevented hypoxia from decreasing FKBP12.6 on the SR and increasing FKBP12.6 in the cytosol. Exogenous ROS (H2O2) reduced FKBP12.6 on the SR and augmented FKBP12.6 in the cytosol. Oxidized FKBP12.6 was absent on the SR from PAs pretreated with and without hypoxia, but it was present with a higher amount in the cytosol from PAs pretreated with than without hypoxia. Hypoxia and H2O2 diminished the association of FKBP12.6 from type 2 RyRs (RyR2). The activity of RyRs was increased in PAs pretreated with hypoxia or H2O2. FKBP12.6 removal enhanced, whereas RyR2 gene deletion blocked the hypoxic increase in [Ca2+]i in PASMCs. Collectively, we conclude that hypoxia may induce Ca2+ release by causing ROS-mediated dissociation of FKBP12.6 from RyR2 in PASMCs. Antioxid. Redox Signal. 14, 37–47.
PMCID: PMC3000638  PMID: 20518593
23.  Dissociation of FKBP12.6 from ryanodine receptor type 2 is regulated by cyclic ADP-ribose but not β-adrenergic stimulation in mouse cardiomyocytes 
Cardiovascular Research  2009;84(2):253-262.
β-Adrenergic augmentation of Ca2+ sparks and cardiac contractility has been functionally linked to phosphorylation-dependent dissociation of FK506 binding protein 12.6 (FKBP12.6) regulatory proteins from ryanodine receptors subtype 2 (RYR2). We used FKBP12.6 null mice to test the extent to which the dissociation of FKBP12.6 affects Ca2+ sparks and mediates the inotropic action of isoproterenol (ISO), and to investigate the underlying mechanisms of cyclic ADP-ribose (cADPR) regulation of Ca2+ sparks.
Methods and results
Ca2+ sparks and contractility were measured in cardiomyocytes and papillary muscle segments from FKBP12.6 null mice, and western blot analysis was carried out on sarcoplasmic reticulum microsomes prepared from mouse heart. Exposure to ISO resulted in a three- and two-fold increase in Ca2+ spark frequency in wild-type (WT) and FKBP12.6 knockout (KO) myocytes, respectively, and Ca2+ spark kinetics were also significantly altered in both types of cells. The effects of ISO on Ca2+ spark properties in KO cells were inhibited by pre-treatment with thapsigargin or phospholamban inhibitory antibody, 2D12. Moreover, twitch force magnitude and the rate of force development were not significantly different in papillary muscles from WT and KO mice. Unlike β-adrenergic stimulation, cADPR stimulation increased Ca2+ spark frequency (2.8-fold) and altered spark kinetics only in WT but not in KO mice. The effect of cADPR on spark properties was not entirely blocked by pre-treatment with thapsigargin or 2D12. In voltage-clamped cells, cADPR increased the peak Ca2+ of the spark without altering the decay time. We also noticed that basal Ca2+ spark properties in KO mice were markedly altered compared with those in WT mice.
Our data demonstrate that dissociation of FKBP12.6 from the RYR2 complex does not play a significant role in β-adrenergic-stimulated Ca2+ release in heart cells, whereas this mechanism does underlie the action of cADPR.
PMCID: PMC2761199  PMID: 19578067
β-Adrenergic stimulation; cADPR; FKBP126 null cardiac myocytes; Ryanodine receptor; Ca2+ spark; Cardiac contractility
24.  Regulation of Steroid Hormone Receptor Function By the 52-kDa FK506-Binding Protein (FKBP52) 
Current opinion in pharmacology  2011;11(4):314-319.
The large FK506-binding protein FKBP52 has been characterized as an important positive regulator of androgen, glucocorticoid and progesterone receptor signaling pathways. FKBP52 associates with receptor-Hsp90 complexes and is proposed to have roles in both receptor hormone binding and receptor subcellular localization. Data from biochemical and cellular studies has been corroborated in whole animal models as fkbp52-deficient male and female mice display characteristics of androgen, glucocorticoid and/or progesterone insensitivity. FKBP52 receptor specificity and the specific phenotypes displayed by the fkbp52-deficient mice have firmly established FKBP52 as a promising target for the treatment of a variety of hormone-dependent diseases. Recent studies demonstrated that the FKBP52 FK1 domain and the proline-rich loop within this domain are functionally important for FKBP52 regulation of receptor function. Based on these data, efforts are currently underway to target the FKBP52 FK1 domain and the proline-rich loop with small molecule inhibitors.
PMCID: PMC3156321  PMID: 21511531
25.  Increased hippocampal accumulation of autophagosomes predicts short-term recognition memory impairment in aged mice 
Age  2011;34(2):305-316.
Constitutive macroautophagy involved in the turnover of defective long-lived proteins and organelles is crucial for neuronal homeostasis. We hypothesized that macroautophagic dysregulation in selective brain regions was associated with memory impairment in aged mice. We used the single-trial object recognition test to measure short-term memory in 18 aged mice compared to 22 young mice and employed immunohistochemistry to assess cellular distribution of proteins involved in the selective degradation of ubiquitinated proteins via macroautophagy. Values of the discrimination ratio (DR, a measure of short-term recognition memory performance) in aged mice were significantly lower than those in young mice (median, 0.54 vs. 0.67; p = 0.005, U test). Almost exclusively in aged mice, there were clusters of puncta immunoreactive for microtubule-associated protein 1 light chain 3 (LC3), ubiquitin- and LC3-binding protein p62, and ubiquitin in neuronal processes predominantly in the hippocampal formation, olfactory bulb/tubercle, and cerebellar cortex. The hippocampal burden of clustered puncta immunoreactive for LC3 and p62 exhibited inverse linear correlations with DR in aged mice (ρ = −0.48 and −0.55, p = 0.044 and 0.018, respectively, Spearman’s rank correlation). These findings suggest that increased accumulation of autophagosomes within neuronal processes in selective brain regions is characteristic of aging. The dysregulation of macroautophagy can adversely affect the turnover of aggregate-prone proteins and defective organelles, which may contribute to memory impairment in aged mice.
PMCID: PMC3312638  PMID: 21431350
Autophagy; Brain aging; MAP1LC3; Object recognition test; p62; Ubiquitin

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