Induction of tolerance against grafted organs is achieved by the immunosuppressive agent cyclosporine, a prominent member of the calcineurin inhibitors. Unfortunately, its lifetime use is associated with hypertension and nephrotoxicity. Several mechanism for cyclosporine induced hypertension have been proposed, i.e. activation of the sympathetic nervous system, endothelin-mediated systemic vasoconstriction, impaired vasodilatation secondary to reduction in prostaglandin and nitric oxide, altered cytosolic calcium translocation, and activation of the renin-angiotensin system (RAS). In this regard the molecular basis for undue RAS activation and an increased signaling of the vasoactive oligopeptide angiotensin II (AngII) remain elusive. Notably, angiotensinogen (AGT) is the precursor of AngII and transcriptional regulation of AGT is controlled by the hepatic nuclear factor HNF4alpha. To better understand the molecular events associated with cyclosporine induced hypertension, we investigated the effect of cyclosporine on HNF4alpha expression and activity and searched for novel HNF4alpha target genes among members of the RAS cascade. Using bioinformatic algorithm and EMSA bandshift assays we identified angiotensin II receptor type 1 (AGTR1), angiotensin I converting enzyme (ACE), and angiotensin I converting enzyme 2 (ACE2) as genes targeted by HNF4alpha. Notably, cyclosporine represses HNF4alpha gene and protein expression and its DNA-binding activity at consensus sequences to AGT, AGTR1, ACE, and ACE2. Consequently, the gene expression of AGT, AGTR1, and ACE2 was significantly reduced as evidenced by quantitative real-time RT-PCR. While RAS is composed of a sophisticated interplay between multiple factors we propose a decrease of ACE2 to enforce AngII signaling via AGTR1 to ultimately result in vasoconstriction and hypertension. Taken collectively we demonstrate cyclosporine to repress HNF4alpha activity through calcineurin inhibitor mediated inhibition of nuclear factor of activation of T-cells (NFAT) which in turn represses HNF4alpha that leads to a disturbed balance of RAS.
Cyclooxygenase (COX)-2, the inducible isoform of cyclooxygenase, plays a role in the process of uterine decidualization and blastocyst attachment. On the other hand, overexpression of COX-2 is involved in the proliferation of the endometrial tissue during endometriosis. Deregulation of the renin-angiotensin-system plays a role in the pathophysiology of endometriosis and pre-eclampsia. Angiotensin II increases intracellular Ca2+ concentration by targeting phospholypase C-gamma in endometrial stromal cells (ESC). A key element of the cellular response to Ca2+ signals is the activity of the Ca2+- and calmodulin-dependent phosphatase calcineurin. Our first aim was to study whether angiotensin II stimulated Cox-2 gene expression in rat ESC and to analyze whether calcineurin activity was involved. In cells isolated from non-pregnant uteri, COX-2 expression -both mRNA and protein- was induced by co-stimulation with phorbol ester and calcium ionophore (PIo), as well as by angiotensin II. Pretreatment with the calcineurin inhibitor cyclosporin A inhibited this induction. We further analyzed the role of the calcineurin/NFAT signaling pathway in the induction of Cox-2 gene expression in non-pregnant rat ESC. Cyclosporin A abolished NFATc1 dephosphorylation and translocation to the nucleus. Cyclosporin A also inhibited the transcriptional activity driven by the Cox-2 promoter. Exogenous expression of the peptide VIVIT -specific inhibitor of calcineurin/NFAT binding- blocked the activation of Cox-2 promoter and the up-regulation of COX-2 protein in these cells. Finally we analyzed Cox-2 gene expression in ESC of early-pregnant rats. COX-2 expression -both mRNA and protein- was induced by stimulation with PIo as well as by angiotensin II. This induction appears to be calcineurin independent, since it was not abrogated by cyclosporin A. In conclusion, angiotensin II induced Cox-2 gene expression by activating the calcineurin/NFAT signaling pathway in endometrial stromal cells of non-pregnant but not of early-pregnant rats. These results might be related to differential roles that COX-2 plays in the endometrium.
Pulmonary arterial hypertension (PAH) is associated with aberrant pulmonary vascular remodeling that leads to increased pulmonary artery pressure, pulmonary vascular resistance, and right ventricular dysfunction. There is now accumulating evidence that the renin-angiotensin-aldosterone system is activated and contributes to cardiopulmonary remodeling that occurs in PAH. Increased plasma and lung tissue levels of angiotensin and aldosterone have been detected in experimental models of PAH and shown to correlate with cardiopulmonary hemodynamics and pulmonary vascular remodeling. These processes are abrogated by treatment with angiotensin receptor or mineralocorticoid receptor antagonists. At a cellular level, angiotensin and aldosterone activate oxidant stress signaling pathways that decrease levels of bioavailable nitric oxide, increase inflammation, and promote cell proliferation, migration, extracellular matrix remodeling, and fibrosis. Clinically, enhanced renin-angiotensin activity and elevated levels of aldosterone have been detected in patients with PAH, which suggests a role for angiotensin and mineralocorticoid receptor antagonists in the treatment of PAH. This review will examine the current evidence linking renin-angiotensin-aldosterone system activation to PAH with an emphasis on the cellular and molecular mechanisms that are modulated by aldosterone and may be of importance for the pathobiology of PAH.
aldosterone; angiotensin II; mineralocorticoid receptor; pulmonary arterial hypertension; spironolactone
Vascular injury and remodeling are common pathological sequelae of hypertension. Previous studies have suggested that the renin-angiotensin system (RAS) acting through the type I (AT1) angiotensin (AT1)-receptor promotes vascular pathology in hypertension. To study the role of AT1-receptors in this process, we generated mice with cell-specific deletion of AT1-receptors in VSMCs using Cre/Loxp technology. We crossed the SM22α-Cre transgenic mouse line expressing Cre recombinase in smooth muscle cells with a mouse line bearing a conditional allele of the Agtr1a gene (Agtr1a flox), encoding the major murine AT1-receptor isoform (AT1A). In SM22α-Cre+Agtr1a flox/flox (SMKO) mice, AT1A-receptors were efficiently deleted from VSMCs in larger vessels, but not from resistance vessels such as pre-glomerular arterioles. Thus, vasoconstrictor responses to angiotensin II were preserved in SMKOs. To induce hypertensive vascular remodeling, mice were continuously infused with angiotensin II for 4 weeks. During infusion of angiotensin II, blood pressures increased significantly and to a similar extent in SMKOs and controls. In control mice, there was evidence of vascular oxidative stress indicated by enhanced nitrated tyrosine residues in segments of aorta; this was significantly attenuated in SMKOs. Despite these differences in oxidative stress, the extent of aortic medial expansion induced by angiotensin II infusion was virtually identical in both groups. Thus, vascular AT1A-receptors promote oxidative stress in the aortic wall but are not required for remodeling in angiotensin II-dependent hypertension.
angiotensin II; hypertrophy; hyperplasia; aorta; smooth muscle; hypertension
Angiotensin II type 2 (AT2) receptor is abundantly expressed in vascular smooth muscle cells (VSMC) of the fetal vasculature during late gestation (embryonic day 15–20), during which the blood vessels undergo remodeling. To examine directly the influence of AT2 receptor expression in the developmental biology of VSMC, we studied cultures of VSMC from fetal and postnatal wild-type (Agtr2+) and AT2 receptor null (Agtr2–) mice. Consistent with in vivo data, AT2 receptor binding in cultured Agtr2+ VSMC increased by age, peaking at embryonic day 20, and decreased dramatically after birth. Angiotensin II–induced growth in Agtr2+ VSMC (embryonic day 20) was increased by the AT2 receptor blocker PD123319, indicating that the AT2 receptors are functional and exert an antigrowth effect in Agtr2+ VSMC. Growth of VSMC in response to serum decreased age dependently and was higher in Agtr2– than in Agtr2+, inversely correlating with AT2 receptor expression. However, serum-induced growth in Agtr2+ and Agtr2– VSMC and the exaggerated Agtr2– VSMC growth was maintained even in the presence of PD123319 or losartan, an AT1 receptor blocker. Moreover, Agtr2– VSMC showed greater growth responses to platelet-derived growth factor and basic fibroblast growth factor, indicating that Agtr2– cells exhibit a generalized exaggerated growth phenotype. We studied the mechanism responsible for this phenotype and observed that extracellular signal-regulated kinase (ERK) activity was higher in Agtr2– VSMC at baseline and also in response to serum. ERK kinase inhibitor PD98059 inhibited both growth and ERK phosphorylation dose–dependently, while the regression lines between growth and ERK phosphorylation were identical in Agtr2+ and Agtr2– VSMC, suggesting that increased ERK activity in Agtr2– VSMC is pivotal in the growth enhancement. Furthermore, the difference in ERK phosphorylation between Agtr2+ and Agtr2– was abolished by vanadate but not by okadaic acid, implicating tyrosine phosphatase in the difference in ERK activity. These results suggest that the AT2 receptor expression during the fetal vasculogenesis influences the growth phenotype of VSMC via the modulation of ERK cascade.
We have previously found that T lymphocytes are essential for development of angiotensin II-induced hypertension however the mechanisms responsible for T cell activation in hypertension remain undefined.
To study the roles of the central nervous system and pressure elevation in T cell activation and vascular inflammation caused by angiotensin II.
Methods and Results
To prevent the central actions of angiotensin II we created anteroventral third cerebral ventricle (AV3V) lesions in mice. The elevation in blood pressure in response to angiotensin II was virtually eliminated by AV3V lesions, as was activation of circulating T cells and the vascular infiltration of leukocytes. In contrast, AV3V lesioning did not prevent the hypertension and T cell activation caused by the peripheral acting agonist norepinephrine. To determine if T cell activation and vascular inflammation are due to central influences or are mediated by blood pressure elevation, we administered hydralazine (250 mg/L) in the drinking water. Hydralazine prevented the hypertension, and abrogated the increase in circulating activated T cells and vascular infiltration of leukocytes caused by angiotensin II.
We conclude that the central and pressor effects of angiotensin II are critical for T cell activation and development of vascular inflammation. These findings also support a feed forward mechanism in which modest degrees of blood pressure elevation lead to T cell activation, which in turn promotes inflammation and further raises blood pressure, leading to severe hypertension.
We have previously shown that T cells are important for the development of hypertension and others have shown that CNS lesions such as AV3V disruption prevent hypertension. We examined the relationship between central actions of angiotensin II, T cell activation and hypertension by determining how AV3V lesions affect T cell activation and hypertensive responses to angiotensin II and norepinephrine. Our data are compatible with a scenario in which modest degrees of pressure elevation, mediated either directly by norepinephrine or via central actions of angiotensin II, promote an inflammatory response that leads to severe hypertension. These studies provide new insight into how the central nervous system contributes to systemic inflammation in hypertension.
Hypertension; vascular inflammation; T cells; central nervous system
The phosphatase calcineurin, target of the immunosuppressants cyclosporin A and FK506, dephosphorylates NFAT transcription factors to promote immune activation and development of the vascular and nervous systems. NFAT interacts with calcineurin through distinct binding motifs: the PxIXIT and LxVP sites. While many calcineurin substrates contain PxIxIT motifs, the generality of LxVP-mediated interactions is unclear. We define critical residues in the LxVP motif, and demonstrate its binding to a hydrophobic pocket at the interface of the two calcineurin subunits. Mutations in this region disrupt binding of mammalian calcineurin to NFATc1, and interaction of yeast calcineurin with substrates including Rcn1, which contains an LxVP motif. These mutations also interfere with calcineurin-immunosuppressant binding, and an LxVP-based peptide competes with immunosuppressant-immunophilin complexes for binding to calcineurin. These studies suggest that LxVP-type sites are a common feature of calcineurin substrates and that immunosuppressant-immunophilin complexes inhibit calcineurin by interfering with this mode of substrate recognition.
We have developed chimeric mice carrying 'regional' null mutation of the angiotensin type 1A (AT1A) receptor, the AT1 receptor subtype exclusively present in mouse juxtaglomerular (JG) cells. The chimeric mouse (Agtr1a -/- <--> +/+) is made up of wild-type (Agtr1a +/+) cells or cells homozygous for Agtr1a deletion (Agtr1a -/-). In the latter, the AT1A coding exon was replaced with a reporter gene, lacZ. In Agtr1a -/- <--> +/+ mice, these two clones of cells are found to be clustered and display patchy distributions in the kidney and heart. Tracking of lacZ activities in hetero- (Agtr1a +/-) and homozygous (Agtr1a -/-) deletion mutant offspring from Agtr1a -/- <--> +/+ mice revealed that the promoter activity of Agtr1a is localized in JG cells, afferent arteriolar walls, glomerular mesangial region and endothelial cells, and apical and basolateral proximal tubule membranes. The JG apparatuses of Agtr1a -/- mice are markedly enlarged with intense expression of renin mRNA and protein. In Agtr1a -/- <--> +/+ mice, these changes were proportional to the degree of chimerism. Within a given Agtr1a -/- <--> +/+ mouse, however, the degree of JG hypertrophy/hyperplasia and the expression of renin mRNA and protein were identical between Agtr1a +/+ and Agtr1a -/- cells. Thus, in the in vivo condition tested, the local interaction between angiotensin and the AT1 receptor on the JG cells has little functional contribution to the feedback regulation of JG renin synthesis.
Peroxisome proliferator activated receptor γ (PPARγ) has been reported to play a protective role in the vasculature; however, the underlying mechanisms involved are not entirely known. We previously showed that vascular smooth muscle-specific overexpression of a dominant negative human PPARγ mutation in mice (S-P467L) leads to enhanced myogenic tone and increased angiotensin-II-dependent vasoconstriction. S-P467L mice also exhibit increased arterial blood pressure. Here we tested the hypotheses that a) mesenteric smooth muscle cells isolated from S-P467L mice exhibit enhanced angiotensin-II AT1 receptor signaling, and b) the increased arterial pressure of S-P467L mice is angiotensin-II AT1 receptor dependent. Phosphorylation of mitogen-activated protein/extracellular signal-regulated kinase (ERK1/2) was robustly increased in mesenteric artery smooth muscle cell cultures from S-P467L in response to angiotensin-II. The increase in ERK1/2 activation by angiotensin-II was blocked by losartan, a blocker of AT1 receptors. Angiotensin-II-induced ERK1/2 activation was also blocked by Tempol, a scavenger of reactive oxygen species, and correlated with increased Nox4 protein expression. To investigate whether endogenous renin-angiotensin system activity contributes to the elevated arterial pressure in S-P467L, non-transgenic and S-P467L mice were treated with the AT1 receptor blocker, losartan (30 mg/kg per day), for 14-days and arterial pressure was assessed by radiotelemetry. At baseline S-P467L mice showed a significant increase of systolic arterial pressure (142.0±10.2 vs 129.1±3.0 mmHg, p<0.05). Treatment with losartan lowered systolic arterial pressure in S-P467L (132.2±6.9 mmHg) to a level similar to untreated non-transgenic mice. Losartan also lowered arterial pressure in non-transgenic (113.0±3.9 mmHg) mice, such that there was no difference in the losartan-induced depressor response between groups (−13.53±1.39 in S-P467L vs −16.16±3.14 mmHg in non-transgenic). Our results suggest that interference with PPARγ in smooth muscle: a) causes enhanced angiotensin-II AT1 receptor-mediated ERK1/2 activation in resistance vessels, b) and may elevate arterial pressure through both angiotensin-II AT1 receptor-dependent and -independent mechanisms.
Structural analyses show that a viral protein and immunosuppressant drugs inhibit the phosphatase calcineurin by preventing substrate binding, and provide a model of a phosphatase engaged with its substrate.
Ser/thr phosphatases dephosphorylate their targets with high specificity, yet the structural and sequence determinants of phosphosite recognition are poorly understood. Calcineurin (CN) is a conserved Ca2+/calmodulin-dependent ser/thr phosphatase and the target of immunosuppressants, FK506 and cyclosporin A (CSA). To investigate CN substrate recognition we used X-ray crystallography, biochemistry, modeling, and in vivo experiments to study A238L, a viral protein inhibitor of CN. We show that A238L competitively inhibits CN by occupying a critical substrate recognition site, while leaving the catalytic center fully accessible. Critically, the 1.7 Å structure of the A238L-CN complex reveals how CN recognizes residues in A238L that are analogous to a substrate motif, “LxVP.” The structure enabled modeling of a peptide substrate bound to CN, which predicts substrate interactions beyond the catalytic center. Finally, this study establishes that “LxVP” sequences and immunosuppressants bind to the identical site on CN. Thus, FK506, CSA, and A238L all prevent “LxVP”-mediated substrate recognition by CN, highlighting the importance of this interaction for substrate dephosphorylation. Collectively, this work presents the first integrated structural model for substrate selection and dephosphorylation by CN and lays the groundwork for structure-based development of new CN inhibitors.
Transplantation medicine was revolutionized by the introduction of the immunosuppressant drugs cyclosporin A and FK506 that prevent rejection of transplanted organs by the recipient's immune system. These drugs work by inhibiting calcineurin, a conserved protein phosphatase. Calcineurin regulates the immune response by dephosphorylating and activating the members of the NFAT family of transcription factors, which in turn activate genes required for the antigen-dependent stimulation of T-cells. Despite its biological and clinical importance, we have only a limited understanding of how calcineurin and other protein phosphatases interact with their substrates and target specific phosphorylated residues for dephosphorylation. Here, we determined the structure of calcineurin in complex with A238L, a viral peptide inhibitor of its function. This study shows that the viral peptide inhibits calcineurin not by targeting its active site but rather by occupying two critical substrate-binding regions of calcineurin (distant from each other and from the active site), thereby preventing its interaction with protein substrates. These findings allow us to present the first computational model of calcineurin bound to a phospho-substrate at its active site. Furthermore, by elucidating the structural basis for one particular mode of substrate–calcineurin interaction, this study reveals that both this viral peptide and immunosuppressant drugs inhibit calcineurin by blocking substrate access to a single critical region of the enzyme.
Calcineurin is responsible for mediating a wide variety of cellular processes in response to dynamic calcium (Ca2+) signals, yet the precise mechanisms involved in the spatiotemporal control of calcineurin signaling are poorly understood. Here, we use genetically encoded fluorescent biosensors to directly probe the role of cytosolic Ca2+ oscillations in modulating calcineurin activity dynamics in insulin-secreting MIN6 β-cells. We show that Ca2+ oscillations induce distinct temporal patterns of calcineurin activity in the cytosol and plasma membrane vs at the ER and mitochondria in these cells. Furthermore, we found that these differential calcineurin activity patterns are determined by variations in the subcellular distribution of calmodulin (CaM), indicating that CaM plays an active role in shaping both the spatial and temporal aspects of calcineurin signaling. Together, our findings provide new insights into the mechanisms by which oscillatory signals are decoded to generate specific functional outputs within different cellular compartments.
Cells need to be able to communicate with other cells, and they employ a variety of molecules and ions to send messages to each other. When calcium ions are used for these communications, the concentration of the ions typically rises and falls in a wave-like pattern. The size and shape of these ‘calcium waves’ contains information that is needed by organs as diverse as the heart and the brain.
Most cells detect calcium waves using a sensor molecule called calmodulin. This, in turn, activates an enzyme called calcineurin. However, relatively little is known about the ways in which calcium waves shape the activity of calcineurin, even though calcium signaling is very common.
Mehta et al. have now clarified this relationship by studying how calcium ions affect the activity of calcineurin molecules inside pancreatic cells. The response of calcineurin to calcium depends on position inside the cell. In the cytosol and at the plasma membrane that encloses the cell, calcium waves trigger a very fast ‘step-like’ increase in calcineurin activity. By contrast, at the surface of certain organelles within the cell, the calcium waves cause the calcineurin activity to rise and fall in a wave-like pattern.
Experiments designed to identify the molecular mechanism behind this difference revealed that the answer lies in the distribution of calmodulin, the intermediate between calcium and calcineurin. At the surface of organelles, there is less calmodulin available to activate calcineurin than in the cytosol or at the plasma membrane. As a result, calcineurin activity in the vicinity of organelles is vulnerable to being canceled out by the actions of other enzymes. When more calmodulin is available, this canceling out does not occur, which is how wave-like input can lead to step-like output.
By identifying the mechanism by which a single signal—a calcium wave—generates distinct responses in the same target molecule—calcineurin—depending on subcellular location, Mehta et al. have identified a process that is relevant to a wide range of biological systems.
calcium; oscillation; FRET; live-cell imaging; other
The chorionic villi in the placenta are responsible for the regulation of fetal oxygen and nutrient transport. Although the peripheral renin-angiotensin system is activated during normal pregnancy, the regulation of the local chorionic villi renin-angiotensin system remains unknown. Therefore, placental chorionic villous tissue was collected from nulliparous third-trimester normotensive or preeclamptic subjects and was analyzed for angiotensin peptide content, angiotensinogen, renin, angiotensin-converting enzyme (ACE), ACE2, neprilysin, angiotensin II type 1 (AT1), angiotensin II type 2, Mas receptor mRNAs, and angiotensin receptor density and subtype. Angiotensin II in chorionic villi was significantly higher in preeclamptic subjects, whereas angiotensin (1–7) was not different. Angiotensinogen and AT1 receptor gene expression was significantly higher in preeclamptic subjects. No differences were observed in renin, ACE, ACE2, or neprilysin gene expression. Mas receptor mRNA in preeclamptic subjects was decreased. The AT1 receptor was the predominant receptor subtype in normal and preeclamptic chorionic villi. There was no difference in the density of the AT1, angiotensin II type 2, and angiotensin (1–7) receptors. These results indicate that enhanced chorionic villous expression of angiotensin II may result from increased angiotensinogen. Elevated angiotensin II, acting through the AT1 receptor, may favor vasoconstriction in placental chorionic villi and contribute to impaired fetal blood flow and decreased fetal nutrition observed during preeclampsia.
preeclampsia; renin angiotensin system; pregnancy; placenta; angiotensin receptors; Mas receptor; angiotensin (1–7)
The immunosuppressive drugs FK506 and cyclosporin A block T-lymphocyte proliferation by inhibiting calcineurin, a critical signaling molecule for activation. Multiple intracellular receptors (immunophilins) for these drugs that specifically bind either FK506 and rapamycin (FK506-binding proteins [FKBPs]) or cyclosporin A (cyclophilins) have been identified. We report the cloning and characterization of a new 51-kDa member of the FKBP family from murine T cells. The novel immunophilin, FKBP51, is distinct from the previously isolated and sequenced 52-kDa murine FKBP, demonstrating 53% identity overall. Importantly, Western blot (immunoblot) analysis showed that unlike all other FKBPs characterized to date, FKBP51 expression was largely restricted to T cells. Drug binding to recombinant FKBP51 was demonstrated by inhibition of peptidyl prolyl isomerase activity. As judged from peptidyl prolyl isomerase activity, FKBP51 had a slightly higher affinity for rapamycin than for FK520, an FK506 analog. FKBP51, when complexed with FK520, was capable of inhibiting calcineurin phosphatase activity in an in vitro assay system. Inhibition of calcineurin phosphatase activity has been implicated both in the mechanism of immunosuppression and in the observed toxic side effects of FK506 in nonlymphoid cells. Identification of a new FKBP that can mediate calcineurin inhibition and is restricted in its expression to T cells suggests that new immunosuppressive drugs may be identified that, by virtue of their specific interaction with FKBP51, would be targeted in their site of action.
Astrocyte reactivity (i.e., activation) and associated neuroinflammation are increasingly thought to contribute to neurodegenerative disease. However, the mechanisms that trigger astrocyte activation are poorly understood. Here, we studied the Ca2+-dependent phosphatase calcineurin, which regulates inflammatory signaling pathways in immune cells, for a role in astrogliosis and brain neuroinflammation. Adenoviral transfer of activated calcineurin to primary rat hippocampal cultures resulted in pronounced thickening of astrocyte somata and processes compared with uninfected or virus control cultures, closely mimicking the activated hypertrophic phenotype. This effect was blocked by the calcineurin inhibitor cyclosporin A. Parallel microarray studies, validated by extensive statistical analyses, showed that calcineurin overexpression also induced genes and cellular pathways representing most major markers associated with astrocyte activation and recapitulated numerous changes in gene expression found previously in the hippocampus of normally aging rats or in Alzheimer’s disease (AD). No genomic or morphologic evidence of apoptosis or damage to neurons was seen, indicating that the calcineurin effect was mediated by direct actions on astrocytes. Moreover, immunocytochemical studies of the hippocampus/neocortex in normal aging and AD model mice revealed intense calcineurin immunostaining that was highly selective for activated astrocytes. Together, these studies show that calcineurin overexpression is sufficient to trigger essentially the full genomic and phenotypic profiles associated with astrocyte activation and that hypertrophic astrocytes in aging and AD models exhibit dramatic upregulation of calcineurin. Thus, the data identify calcineurin upregulation in astrocytes as a novel candidate for an intracellular trigger of astrogliosis, particularly in aging and AD brain.
Ca2+ regulation; hypertrophy; microarray; phosphatase; reactive; glia
Recombinant adenovirus vectors (AdV) have been considered a potential vehicle for performing gene therapy in patients suffering from Duchenne muscular dystrophy but are limited by a cellular and humoral immune response that prevents long-term transgene expression as well as effective transduction after AdV readministration. Conventional immunosuppressive agents such as cyclosporine and FK506, which act by interfering with CD3-T-cell receptor-mediated signaling via calcineurin, are only partially effective in reversing these phenomena and may also produce substantial organ toxicity. We hypothesized that activation of redundant T-cell activation pathways could limit the effectiveness of these drugs at clinically tolerable doses. Therefore, we have tested the ability of immunomodulatory immunoglobulins (Ig) with different modes of action to facilitate AdV-mediated gene transfer to adult dystrophic (mdx) mice. When used in isolation, immunomodulatory Ig (anti-intercellular adhesion molecule-1, anti-leukocyte function-associated antigen-1, anti-CD2, and CTLA4Ig) were only mildly effective in mitigating cellular and/or humoral immunity against adenovirus capsid proteins and the therapeutic transgene product, dystrophin. However, the combination of FK506 plus CTLA4Ig abrogated the immune response against adenovirus proteins and dystrophin to a degree not achievable with the use of either agent alone. At 30 days after AdV injection, >90% of myofibers could be found to express dystrophin with little or no evidence of a cellular immune response against transduced fibers. In addition, the humoral immune response was markedly suppressed, and this was associated with increased transduction efficiency following vector readministration. These data suggest that by facilitating both primary and secondary transduction after AdV administration, combined targeting of CD3-T-cell receptor-mediated signaling via calcineurin and the B7:CD28 costimulatory pathway could greatly increase the potential utility of AdV-mediated gene transfer as a therapeutic modality for genetic diseases such as Duchenne muscular dystrophy that will require long-term transgene expression and repeated vector delivery.
Maternal endothelial dysfunction in preeclampsia is associated with increased soluble fms-like tyrosine kinase-1 (sFlt-1), a circulating antagonist of vascular endothelial growth factor and placental growth factor. Angiotensin II (Ang II) is a potent vasoconstrictor that increases concomitant with sFlt-1 during pregnancy. Therefore, we speculated that Ang II may promote the expression of sFlt-1 in pregnancy. Here we report that infusion of Ang II significantly increases circulating levels of sFlt-1 in pregnant mice, thereby demonstrating that Ang II is a regulator of sFlt-1 secretion in vivo. Furthermore, Ang II stimulated sFlt-1 production in a dose- and time-dependent manner from human villous explants and cultured trophoblasts but not from endothelial cells, suggesting that trophoblasts are the primary source of sFlt-1 during pregnancy. As expected, Ang II–induced sFlt-1 secretion resulted in the inhibition of endothelial cell migration and in vitro tube formation. In vitro and in vivo studies with losartan, small interfering RNA specific for calcineurin and FK506 demonstrated that Ang II–mediated sFlt-1 release was via Ang II type 1 receptor activation and calcineurin signaling, respectively. These findings reveal a previously unrecognized regulatory role for Ang II on sFlt-1 expression in murine and human pregnancy and suggest that elevated sFlt-1 levels in preeclampsia may be caused by a dysregulation of the local renin/angiotensin system.
sFlt-1; angiotensin II; AT1 receptor; pregnancy; placenta; calcineurin
The renin-angiotensin system regulates normal cardiovascular homeostasis and is activated in certain forms of hypertension and in heart failure. Angiotensin II has multiple physiological effects and we have shown recently that its growth-promoting effects on vascular smooth muscle require autocrine activation of the IGF I receptor. To study the effect of angiotensin II on circulating IGF I, we infused rats with 500 ng/kg/min angiotensin II for up to 14 d. Angiotensin II markedly reduced plasma IGF I levels (56 and 41% decrease at 1 and 2 wk, respectively) and IGF binding protein-3 levels, and increased IGF binding protein-2 levels, a pattern suggestive of dietary restriction. Compared with sham, angiotensin II-infused hypertensive rats lost 18-26% of body weight by 1 wk, and pair-feeding experiments indicated that 74% of this loss was attributable to a reduction in food intake. The vasodilator hydralazine and the AT1 receptor antagonist losartan had comparable effects to reverse angiotensin II-induced hypertension, but only losartan blocked the changes in body weight and in circulating IGF I and its binding proteins produced by angiotensin II. Moreover, in Dahl rats that were hypertensive in response to a high-salt diet, none of these changes occurred. Thus, angiotensin II produces weight loss through a pressor-independent mechanism that includes a marked anorexigenic effect and an additional (likely metabolic) effect. These findings have profound implications for understanding the pathophysiology of conditions, such as congestive heart failure, in which the renin-angiotensin system is activated.
Hyperthyroidism is characterized by increased vascular relaxation and decreased vascular contraction and is associated with augmented levels of triiodothyronine (T3) that contribute to the diminished systemic vascular resistance found in this condition. T3 leads to augmented NO production via PI3K/Akt signaling pathway, which in turn causes vascular smooth muscle cell (VSMC) relaxation; however, the underlying mechanisms involved remain largely unknown. Evidence from human and animal studies demonstrates that the renin-angiotensin system (RAS) plays a crucial role in vascular function and also mediates some of cardiovascular effects found during hyperthyroidism. Thus, in this study, we hypothesized that type 2 angiotensin II receptor (AT2R), a key component of RAS vasodilatory actions, mediates T3 induced-decreased vascular contraction. Marked induction of AT2R expression was observed in aortas from T3-induced hyperthyroid rats (Hyper). These vessels showed decreased protein levels of the contractile apparatus: α-actin, calponin and phosphorylated myosin light chain (p-MLC). Vascular reactivity studies showed that denuded aortic rings from Hyper rats exhibited decreased maximal contractile response to angiotensin II (AngII), which was attenuated in aortic rings pre-incubated with an AT2R blocker. Further study showed that cultured VSMC stimulated with T3 (0.1 µmol/L) for 24 hours had increased AT2R gene and protein expression. Augmented NO levels and decreased p-MLC levels were found in VSMC stimulated with T3, both of which were reversed by a PI3K/Akt inhibitor and AT2R blocker. These findings indicate for the first time that the AT2R/Akt/NO pathway contributes to decreased contractile responses in rat aorta, promoted by T3, and this mechanism is independent from the endothelium.
Metabolic actions of insulin to promote glucose disposal are augmented by nitric oxide (NO)-dependent increases in microvascular blood flow to skeletal muscle. The balance between NO-dependent vasodilator actions and endothelin-1-dependent vasoconstrictor actions of insulin is regulated by phosphatidylinositol 3-kinase-dependent (PI3K) - and mitogen-activated protein kinase (MAPK)-dependent signaling in vascular endothelium, respectively. Angiotensin II acting on AT2 receptor increases capillary blood flow to increase insulin-mediated glucose disposal. In contrast, AT1 receptor activation leads to reduced NO bioavailability, impaired insulin signaling, vasoconstriction, and insulin resistance. Insulin-resistant states are characterized by dysregulated local renin-angiotensin-aldosterone system (RAAS). Under insulin-resistant conditions, pathway-specific impairment in PI3K-dependent signaling may cause imbalance between production of NO and secretion of endothelin-1, leading to decreased blood flow, which worsens insulin resistance. Similarly, excess AT1 receptor activity in the microvasculature may selectively impair vasodilation while simultaneously potentiating the vasoconstrictor actions of insulin. Therapeutic interventions that target pathway-selective impairment in insulin signaling and the imbalance in AT1 and AT2 receptor signaling in microvascular endothelium may simultaneously ameliorate endothelial dysfunction and insulin resistance. In the present review, we discuss molecular mechanisms in the endothelium underlying microvascular and metabolic actions of insulin and Angiotensin II, the mechanistic basis for microvascular endothelial dysfunction and insulin resistance in RAAS dysregulated clinical states, and the rationale for therapeutic strategies that restore the balance in vasodilator and constrictor actions of insulin and Angiotensin II in the microvasculature.
Nitric Oxide; Insulin Resistance; Endothelial Dysfunction; Angiotensin II
The calcineurin/nuclear factor of activated T cells (NFATs) signaling pathway plays a central role in T cell mediated adaptive immune responses, but a number of recent studies demonstrated that calcineurin/NFAT signaling also plays a key role in the control of the innate immune response by myeloid cells. Calcineurin inhibitors, such as cyclosporine A (CsA) and tacrolimus (FK506), are commonly used in organ transplantation to prevent graft rejection and in a variety of immune diseases. These immunosuppressive drugs have adverse effects and significantly increase host’s susceptibility towards bacterial or fungal infections. Recent studies highlighted the role of NFAT signaling in fungal infection and in the control of the pattern recognition receptor nucleotide-binding oligomerization domain-containing protein 1 (NOD1), which predominantly senses invasive Gram-negative bacteria and mediates neutrophil phagocytic functions. This review summarises some of the current knowledge concerning the role of NFAT signaling in the innate immune response and the recent advances on NFAT-dependent inhibition of NOD1-mediated innate immune response caused by CsA, which may contribute to sensitizing transplant recipients to bacterial infection.
NFAT; Calcineurin inhibitors; NOD1; Bacterial phagocytosis
The role played by several vasoactive mediators that are synthesized and released by the pulmonary vascular endothelium in the regulation of hypoxic pulmonary vasoconstriction (HPV) remains unclear. As a potent vasoconstrictor, angiotensin II could be involved. We tested the hypothesis that angiotensin-converting enzyme inhibition by enalaprilat and type 1 angiotensin II receptor blockade by candesartan would inhibit HPV.
HPV was evaluated in anaesthetized dogs, with an intact pulmonary circulation, by examining the increase in the Ppa–Ppao gradient (mean pulmonary artery pressure minus occluded pulmonary artery pressure) that occurred in response to hypoxia (inspiratory oxygen fraction of 0.1) at constant pulmonary blood flow. Plasma renin activity and angiotensin II immunoreactivity were measured to determine whether activation or inhibition of the renin–angiotensin system was present.
Administration of enalaprilat and candesartan did not affect the Ppa–Ppao gradient at baseline or during hypoxia. Plasma renin activity and angiotensin II immunoreactivity increased during hypoxia, and subsequent measurements were consistent with effective angiotensin-converting enzyme inhibition after administration of enalaprilat, and with angiotensin receptor blockade after administration of candesartan.
These results suggest that, although the renin–angiotensin system was activated in hypoxia, angiotensin II is not normally involved in mediating acute HPV.
angiotensin II; angiotensin-converting enzyme inhibition; angiotensin receptor antagonism; hypoxic pulmonary vasoconstriction; renin–angiotensin system
Purpose of the review
The renin-angiotensin system (RAS) is critical for cardiovascular control, impacting normal physiology and disease pathogenesis. Although several biologically active peptides are generated by this system, its major actions are mediated by angiotensin II acting through its type 1 (AT1) and type 2 (AT2) receptors. Along with their effects to influence blood pressure and hemodynamics, recent studies have provided evidence that angiotensin receptors influence a range of processes independent from hemodynamic effects.
This review is focused on new molecular mechanisms underlying actions of AT1 receptors to influence vasoconstriction, inflammation, immune responses, and longevity. Moreover, we also highlight new advances in understanding functions of the AT2 receptor in end-organ damage, emphasizing the AT2 receptor as a potential therapeutic target in cardiovascular diseases.
Here we review recent advances in understanding the role of angiotensin receptors in normal physiology and disease states, focusing on their properties that may contribute to blood pressure regulation, end-organ damage, autoimmune disease and longevity.
Angiotensin receptors; hypertension; aging; vascular function; immunity
Recent knowledge demonstrated that the renin-angiotensin system (RAS) functions as a local renal paracrine system. All components of the RAS are present within the kidney and include angiotensinogen, renin, angiotensin I, angiotensin-converting enzymes, angiotensin II, the angiotensin II type 1 (AT1) receptor and the angiotensin II type 2 (AT2) receptor. Angiotensin II is the major effector hormone of the RAS and contributes to a variety of renal and cardiovascular physiologic and pathologic mechanisms through stimulation of AT1 and AT2 receptors. Angiotensin receptor blockers were developed based on the advanced knowledge of the AT1 receptor contribution to development of a variety of kidney, vascular and cardiac diseases including but not limited to hypertension, diabetic nephropathy, heart failure, myocardial infarction and atherosclerosis. In contrast, knowledge concerning the role of the AT2 receptor in health and disease is still emerging. The AT2 receptor is believed to counterbalance the effects of the AT1 receptor through influencing cellular differentiation, vasodilation, inhibition of cellular proliferation and hypertrophy, nitric oxide production and natriuresis. Thus, the pursuit of a specific AT2 receptor agonist is a potentially fruitful area for combating renal and cardiovascular diseases. This review focuses on the role of the AT2 receptor in the kidney.
AT2 receptors; cGMP; kidney; nitric oxide
We have previously shown that in rat renal cortex, cyclooxygenase-2 (COX-2) expression is localized to cTALH cells in the region of the macula densa, and that dietary salt restriction increases COX-2 expression. Administration of the angiotensin converting inhibitor, captopril, further increased COX-2 mRNA and renal cortical COX-2 immunoreactivity, with the most pronounced expression in the macula densa. Administration of an AT1 receptor antagonist, losartan, also significantly increased cortical COX-2 mRNA expression and COX-2 immunoreactivity. Mutant mice homozygous for both Agtr1a and Agtr1b null mutations (Agtr1a–/–,Agtr1b–/–) demonstrated large increases in immunoreactive COX-2 expression inthe cTALH/macula densa. To determine whether increased COX-2expression in response to ACE inhibition mediated increases in renin production, rats were treated with captopril for one week with or without the specific COX-2 inhibitor, SC58236. Plasma renin activity increased significantly in the captropril group, and this increase was significantly inhibited by simultaneous treatment with SC58236. Thus, these studies indicated that angiotensin II inhibitors augment upregulation of renal cortical COX-2 in states of volume depletion, suggesting that negative feedback by the renin-angiotensin system modulates renal cortical COX-2 expression and that COX-2 is a mediator of increased renin production in response to inhibition of angiotension II production.
Cyclosporin A (CsA) has direct effects on neural stem and progenitor cells (together termed neural precursor cells; NPCs) in the adult central nervous system. Administration of CsA in vitro or in vivo promotes the survival of NPCs and expands the pools of NPCs in mice. Moreover, CsA administration is effective in promoting NPC activation, tissue repair and functional recovery in a mouse model of cortical stroke. The mechanism(s) by which CsA mediates this cell survival effect remains unknown. Herein, we examined both calcineurin-dependent and calcineurin-independent pathways through which CsA might mediate NPC survival. To examine calcineurin-dependent pathways, we utilized FK506 (Tacrolimus), an immunosuppressive molecule that inhibits calcineurin, as well as drugs that inhibit cyclophilin A-mediated activation of calcineurin. To evaluate the calcineurin-independent pathway, we utilized NIM811, a non-immunosuppressive CsA analog that functions independently of calcineurin by blocking mitochondrial permeability transition pore formation. We found that only NIM811 can entirely account for the pro-survival effects of CsA on NPCs. Indeed, blocking signaling pathways downstream of calcineurin activation using nNOS mice did not inhibit CsA-mediated cell survival, which supports the proposal that the effects are calcinuerin-independent. In vivo studies revealed that NIM811 administration mimics the pro-survival effects of CsA on NPCs and promotes functional recovery in a model of cortical stroke, identical to the effects seen with CsA administration. We conclude that CsA mediates its effect on NPC survival through calcineurin-independent inhibition of mitochondrial permeability transition pore formation and suggest that this pathway has potential therapeutic benefits for developing NPC-mediated cell replacement strategies.
Cyclosporin A; Adult neural precursors; Mitochondrial permeability transition pore formation; Cyclophilin D; Calcineurin-independent signaling; FK506; Stroke