The present paper reviews astrocyte pathology in major depressive disorder (MDD) and proposes that reductions in astrocytes and related markers are key features in the pathology of MDD. Astrocytes are the most numerous and versatile of all types of glial cells. They are crucial to the neuronal microenvironment by regulating glucose metabolism, neurotransmitter uptake (particularly for glutamate), synaptic development and maturation and the blood brain barrier. Pathology of astrocytes has been consistently noted in MDD as well as in rodent models of depressive-like behavior. This review summarizes evidence from human postmortem tissue showing alterations in the expression of protein and mRNA for astrocyte markers such as glial fibrillary acidic protein (GFAP), gap junction proteins (connexin 40 and 43), the water channel aquaporin-4 (AQP4), a calcium-binding protein S100B and glutamatergic markers including the excitatory amino acid transporters 1 and 2 (EAAT1, EAAT2) and glutamine synthetase. Moreover, preclinical studies are presented that demonstrate the involvement of GFAP and astrocytes in animal models of stress and depressive-like behavior and the influence of different classes of antidepressant medications on astrocytes. In light of the various astrocyte deficits noted in MDD, astrocytes may be novel targets for the action of antidepressant medications. Possible functional consequences of altered expression of astrocytic markers in MDD are also discussed. Finally, the unique pattern of cell pathology in MDD, characterized by prominent reductions in the density of astrocytes and in the expression of their markers without obvious neuronal loss, is contrasted with that found in other neuropsychiatric and neurodegenerative disorders.
Glia; Fronto-limbic; Depression; Glutamate; Postmortem
Investigations of the molecular mechanisms underlying major depressive disorder (MDD) have been hampered by the complexity of brain tissue and sensitivity of gene expression profiling approaches. To address these issues, we used discrete microdissections of postmortem dorsolateral prefrontal cortex (DLPFC) (area 9) and an oligonucleotide (60mer) microarray hybridization procedure that increases sensitivity without RNA amplification. Mixed-effects statistical methods were used to rigorously control for medication usage in the subset of medicated depressed subjects. These analyses yielded a rich profile of dysregulated genes. Two of the most highly dysregulated genes of interest were stresscopin, a neuropeptide involved in stress responses, and Forkhead box D3 (FOXD3), a transcription factor. Secondary cell-based analysis demonstrated that stresscopin and FoxD3 are increased in neurons of DLPFC gray matter of MDD subjects. These findings identify abnormal gene expression in a discrete region of MDD subjects and contribute to further elucidation of the molecular alterations of this complex mood disorder.
microarray; stresscopin; urocortin III; stress; corticotrophin releasing hormone; FoxD3; fibroblast growth factor
The relationship between serotonin (5-HT) and major depressive disorder (MDD) has been extensively studied but certain aspects are still ambiguous. Given the evidence that 5-HT neurotransmission is reduced in depressed subjects, it is possible that one or more of the 5-HT regulators may be altered in the dorsal raphe nucleus (DR) of depressed subjects. Candidates that regulate 5-HT synthesis and neuronal activity of 5-HT neurons include intrinsic regulators such as tryptophan hydroxylase 2 (TPH2), 5-HT autoreceptors, 5-HT transporter (SERT) and transcription factors, as well as afferent regulators such as estrogen and brain-derived neurotrophic factor (BDNF). The present study was designed to quantify mRNA concentrations of the above 5-HT regulators in an isolated population of 5-HT-containing DR neurons of MDD subjects and gender-matched psychiatrically normal control subjects. We found that mRNA concentrations of the 5-HT1D receptor and the transcription factors, NUDR and REST, were significantly increased in DR-captured neurons of female MDD subjects compared to female control subjects. No significant differences were found for the transcripts in male MDD subjects compared to male controls. This study reveals sex-specific alterations in gene expression of the presynaptic 5-HT1D autoreceptors and 5-HT-related transcription factors, NUDR and REST, in DR neurons of women with MDD.
Dorsal raphe nucleus; Laser capture microdissection; Major depressive disorder; messenger RNA; Serotonin receptors; Transcription factors
Norepinephrine and glutamate are among several neurotransmitters implicated in the neuropathology of major depressive disorder (MDD). Glia deficits have also been demonstrated in people with MDD, and glia are critical modulators of central glutamatergic transmission. We studied glia in men with MDD in the region of the brain (locus coeruleus; LC) where noradrenergic neuronal cell bodies reside and receive glutamatergic input.
The expression of 3 glutamate-related genes (SLC1A3, SLC1A2, GLUL) concentrated in glia and a glia gene (GFAP) were measured in postmortem tissues from men with MDD and from paired psychiatrically healthy controls. Initial gene expression analysis of RNA isolated from homogenized tissue (n = 9–10 pairs) containing the LC were followed by detailed analysis of gene expressions in astrocytes and oligodendrocytes (n = 6–7 pairs) laser captured from the LC region. We assessed protein changes in GFAP using immunohistochemistry and immunoblotting (n = 7–14 pairs).
Astrocytes, but not oligodendrocytes, demonstrated robust reductions in the expression of SLC1A3 and SLC1A2, whereas GLUL expression was unchanged. GFAP expression was lower in astrocytes, and we confirmed reduced GFAP protein in the LC using immunostaining methods.
Reduced expression of protein products of SLC1A3 and SLC1A2 could not be confirmed because of insufficient amounts of LC tissue for these assays. Whether gene expression abnormalities were associated with only MDD and not with suicide could not be confirmed because most of the decedents who had MDD died by suicide.
Major depressive disorder is associated with unhealthy astrocytes in the noradrenergic LC, characterized here by a reduction in astrocyte glutamate transporter expression. These findings suggest that increased glutamatergic activity in the LC occurs in men with MDD.
Major depressive disorder (MDD) has been linked to changes in function and activity of the hippocampus, one of the central limbic regions involved in regulation of emotions and mood. The exact cellular and molecular mechanisms underlying hippocampal plasticity in response to stress are yet to be fully characterized. In this study, we examined the genetic profile of micro-dissected subfields of post-mortem hippocampus from subjects diagnosed with MDD and comparison subjects matched for sex, race and age. Gene expression profiles of the dentate gyrus and CA1 were assessed by 48K human HEEBO whole genome microarrays and a subgroup of identified genes was confirmed by real-time polymerase chain reaction (qPCR). Pathway analysis revealed altered expression of several gene families, including cytoskeletal proteins involved in rearrangement of neuronal processes. Based on this and evidence of hippocampal neuronal atrophy in MDD, we focused on the expression of cytoskeletal, synaptic and glutamate receptor genes. Our findings demonstrate significant dysregulation of synaptic function/structure related genes SNAP25, DLG2 (SAP93), and MAP1A, and 2-amino-3-(5-methyl-3-oxo-1,2-oxazol-4-yl)propanoic acid receptor subunit genes GLUR1 and GLUR3. Several of these human target genes were similarly dysregulated in a rat model of chronic unpredictable stress and the effects reversed by antidepressant treatment. Together, these studies provide new evidence that disruption of synaptic and glutamatergic signalling pathways contribute to the pathophysiology underlying MDD and provide interesting targets for novel therapeutic interventions.
AMPA; depression; hippocampus; post-mortem; stress
Restorative/protective therapies to restore dopamine neurons in the substantia nigra pars compacta (SNpc) are greatly needed to effectively change the debilitating course of Parkinson's disease. In this study, we tested the therapeutic potential of a neurogenic neurosteroid, allopregnanolone, in the restoration of the components of the nigrostriatal pathway in MPTP-lesioned mice by measuring striatal dopamine levels, total and tyrosine hydroxylase immunoreactive neuron numbers and BrdU-positive cells in the SNpc. An acute treatment (once/week for two weeks) with allopregnanolone restored the number of tyrosine hydroxylase-positive and total cell numbers in the SNpc of MPTP-lesioned mice, even though this did not increase striatal dopamine. It was also noted that MPTP treated mice to which allopregnanolone was administered had an increase in BrdU-positive cells in the SNpc. The effects of allopregnanolone in MPTP-lesioned mice were more apparent in mice that underwent behavioral tests. Interestingly, mice treated with allopregnanolone after MPTP lesion were able to perform at levels similar to that of non-lesioned control mice in a rotarod test. These data demonstrate that allopregnanolone promotes the restoration of tyrosine hydroxylase immunoreactive neurons and total cells in the nigrostriatal tract, improves the motor performance in MPTP-treated mice, and may serve as a therapeutic strategy for Parkinson's disease.
The novel transcriptional repressor protein, R1 (JPO2/CDCA7L/RAM2), inhibits monoamine oxidase A (MAO A) gene expression and influences cell proliferation and survival. MAO A is implicated in several neuropsychiatric illnesses and highly elevated in major depressive disorder (MDD); however, whether R1 is involved in these disorders is unknown. This study evaluates the role of R1 in depressed subjects either untreated or treated with antidepressant drugs. R1 protein levels were determined in the postmortem prefrontal cortex of 18 untreated MDD subjects and 12 medicated MDD subjects compared with 18 matched psychiatrically normal control subjects. Western blot analysis showed that R1 was significantly decreased by 37.5% (p<0.005) in untreated MDD subjects. The R1 level in medicated MDD subjects was also significantly lower (by 30% p<0.05) compared with control subjects, but was not significantly different compared with untreated MDD subjects. Interestingly, the reduction in R1 was significantly correlated with an increase (approximately 40% p<0.05) in MAO A protein levels within the MDD groups compared with controls. Consistent with the change in MAO A protein expression, the MAO A catalytic activity was significantly greater in both MDD groups compared with controls. These results suggest that reduced R1 may lead to elevated MAO A levels in untreated and treated MDD subjects; moreover, the reduction of R1 has been implicated in apoptotic cell death and apoptosis has also been observed in the brains of MDD subjects. Therefore, modulation of R1 levels may provide a new therapeutic target in the development of more effective strategies to treat MDD.
major depressive disorder; transcriptional repressor protein; monoamine oxidase; treatment; selective serotonin reuptake inhibitor; prefrontal cortex; molecular & cellular neurobiology; depression; unipolar/bipolar; drug discovery/development; biological psychiatry; major depressive disorder; transcriptional repressor protein; monoamine oxidase; treatment; prefrontal cortex
A-to-I RNA editing is a post-transcriptional modification of single nucleotides in RNA by adenosine deamination, which thereby diversifies the gene products encoded in the genome. Thousands of potential RNA editing sites have been identified by recent studies (e.g. see Li et al, Science 2009); however, only a handful of these sites have been independently confirmed. Here, we systematically and quantitatively examined 109 putative coding region A-to-I RNA editing sites in three sets of normal human brain samples by ultra-high-throughput sequencing (uHTS). Forty of 109 putative sites, including 25 previously confirmed sites, were validated as truly edited in our brain samples, suggesting an overestimation of A-to-I RNA editing in these putative sites by Li et al (2009). To evaluate RNA editing in human disease, we analyzed 29 of the confirmed sites in subjects with major depressive disorder and schizophrenia using uHTS. In striking contrast to many prior studies, we did not find significant alterations in the frequency of RNA editing at any of the editing sites in samples from these patients, including within the 5HT2C serotonin receptor (HTR2C). Our results indicate that uHTS is a fast, quantitative and high-throughput method to assess RNA editing in human physiology and disease and that many prior studies of RNA editing may overestimate both the extent and disease-related variability of RNA editing at the sites we examined in the human brain.
Recent studies demonstrate that rapid antidepressant response to ketamine is mediated by activation of the mammalian target of rapamycin (mTOR) signaling pathway, leading to increased synaptic proteins in the prefrontal cortex (PFC) of rats. Our postmortem studies indicate robust deficits in prominent postsynaptic proteins including N-methyl-D-aspartate (NMDA) receptor subunits (NR2A, NR2B), metabotropic glutamate receptor subtype 5 (mGluR5) and postsynaptic density protein 95 kDa (PSD-95) in the PFC in major depressive disorder (MDD). We hypothesize that deficits in the mTOR-dependent translation initiation pathway contribute to the molecular pathology seen in the PFC of MDD subjects, and that a rapid reversal of these abnormalities may underlie antidepressant activity. The majority of known translational regulation occurs at the level of initiation. mTOR regulates translation initiation via its downstream components: p70-kDa ribosomal protein S6 kinase (p70S6K), and eukaryotic initiation factors 4E and 4B (eIF4E, eIF4B). In this study, we examined the expression of mTOR and its core downstream signaling targets: p70S6K, eIF4E, eIF4B in the PFC of 12 depressed subjects and 12 psychiatrically healthy controls using Western blot. Levels of eIF4E phosphorylated at serine 209 (p-eIF4E-Ser209) and eIF4B phosphorylated at serine 504 (p-eIF4B-Ser504) were also examined. Adjacent cortical tissue samples from both cohorts of subjects were used in our previous postmortem analyses. There was a significant reduction in mTOR, p70S6K, eIF4B and p-eIF4B protein expression in MDD subjects relative to controls. No group differences were observed in eIF4E, p-eIF4E or actin levels. Our findings show deficits in mTOR-dependent translation initiation in MDD particularly via the p70S6K/eIF4B pathway, and indicate a potential association between marked deficits in synaptic proteins and dysregulation of mTOR signaling in MDD.
prefrontal cortex; translation initiation pathway; major depressive disorder; postmortem
Vascular and immune alterations in the prefrontal cortex may contribute to major depression in elderly subjects. Intercellular adhesion molecule-1 (ICAM-1), major inflammatory mediator in vessels and astrocytes, could be altered in geriatric depression, but little is known about its age-dependent expression in subjects with depression and its relationship to astrocytes identified by the marker glial fibrillary acidic protein (GFAP), found to be reduced in depression.
We measured the percentage of gray matter area fraction covered by ICAM-1 immunoreactivity in blood vessels and in extravascular accumulations of ICAM-1 immunoreactivity in 19 non-psychiatric comparison subjects and 18 subjects with major depression, all characterized by postmortem psychological diagnosis. Association of extravascular ICAM-1 to GFAP-positive astrocytes was investigated by double-labeling immunofluorescence.
Vascular and extravascular fractions of ICAM-1 immunoreactivity were lower in subjects with MDD than in non-psychiatric comparison subjects. Non-psychiatric comparison subjects older than 60 experienced dramatic increase in extravascular ICAM-1 immunoreactivity, but this increase was attenuated in elderly subjects with MDD, particularly in those dying by suicide. Most extracellular ICAM-1 immunoreactivity was coextensive with GFAP-immunoreactive astrocytes in both groups.
Heterogeneity in type and dosage of antidepressant medication. Difficulty in determining the exact onset of depression in subjects older than 60 at the time of death. Routine cerebrovascular pathological screening may miss subtle subcellular and molecular changes.
There is significant attenuation of extravascular and vascular ICAM-1 immunoreactivity in elderly subjects with major depression suggesting an astrocyte-associated alteration in immune function in the aging orbitofrontal cortex of subjects with MDD.
Depression; prefrontal cortex; astrocytes; GFAP; ICAM-1; postmortem
Clinical and preclinical evidence suggest a hyperactive glutamatergic system in clinical depression. Recently, the metabotropic glutamate receptor 5 (mGluR5) has been proposed as an attractive target for discovery of novel therapeutic approaches against depression. The goal of this study was to compare mGluR5 binding (PET study) and mGluR5 protein expression (postmortem study) between subjects with major depressive disorder and healthy controls.
Images of mGluR5 receptor binding were acquired using PET and [11C]ABP688 that binds to an allosteric site with high specificity in 11 unmedicated subjects with major depression and 11 matched healthy controls; the amount of mGluR5 protein was investigated using Western blot method in brain samples of 15 depressed subjects and 15 matched controls (postmortem study).
The PET study revealed decreased regional mGluR5 binding in the prefrontal cortex, the cingulate cortex, the insula, the thalamus and the hippocampus of the depressed individuals (uncorrected p<0.001). Severity of depression correlated negatively with mGluR5 binding in the hippocampus (cluster-level corrected p=0.029). The postmortem study showed reduced mGluR5 protein expression in the prefrontal cortex (Brodmann's area 10) in depression (p<0.014), while prefrontal mGluR1 protein expression was unchanged.
The reductions in mGluR5 binding found in the depressed sample are compatible with reduced protein expression in postmortem tissue. Thus, both studies suggest that basal or compensatory changes in excitatory neurotransmission play roles in the pathophysiology of major depression.
More than a third of Alzheimer’s disease (AD) patients show nigrostriatal pathway disturbances, resulting in akinesia (inability to initiate movement) and bradykinesia (slowness of movement). The high prevalence of this dysfunction of dopaminergic neuron in the nigrostriatal pathway in AD suggests that the risk factors for AD appear also significant risk factors for substantia nigra pars compacta (SNpc) lesions. Previously, we have demonstrated that allopregnanolone (APα) promotes neurogenesis and improves the cognitive function in a triple transgenic mouse model of AD (3xTgAD). In this study, we sought to exam 1) the SNpc lesions in 3xTgAD mice and 2) the impact of APα on promoting the regeneration of new dopaminergic neurons in SNpc of the 3xTgAD mice. The number of Nissl-stained total neurons, tyrosine hydroxylase (TH) positive neurons, and BrdU/TH double positive newly formed neurons were analyzed with unbiased stereology. In the SNpc of 3xTgAD mice, TH positive neurons was 47 ± 18 % (p = 0.007), total neurons was 62 ± 11.6 % (p = 0.016), of those in the SNpc of non-Tg mice, respectively. APα treatment increased the TH positive neurons in the SNpc of 3xTgAD mice to 93.2 ± 18.5 % (p = 0.021 vs. 3xTgAD vehicle) and the total neurons to 84.9 ± 6.6 (p = 0.046 vs. 3xTgAD vehicle) of non-Tg mice. These findings indicate that there is a loss of neurons, specifically the TH positive neurons in SNpc of 3xTgAD mice, and that APα reverses the lesion in SNpc of 3xTgAD by increasing the formation of new TH neurons.
Allopregnanolone; neurogenesis; tyrosine hydroxylase (TH); substantia nigra; dopaminergic neurons
The molecular mechanisms for the discrepancy in outcome of initiating estrogen therapy (ET) around peri-menopause or several years after menopause in women are unknown. We hypothesize that the level of expression of a dominant negative estrogen receptor (ER) β variant, ERβ2, may be a key factor determining the effectiveness of ET in post-menopausal women. We tested this hypothesis in ovariectomized nine month-old (an age when irregular estrous cycles occur) female Sprague Dawley rats. Estradiol treatment was initiated either 6 days (Early ET, analogous to 4 months post-menopause in humans), or 180 days (Late ET, analogous to 11 years post-menopause in humans) after ovariectomy. Although ERβ2 expression increased in all OVX rats, neurogenic and neuroprotective responses to estradiol differed in Early and Late ET. Early ET reduced ERβ2 expression in both hippocampus and white blood cells, increased the hippocampal cell proliferation as assessed by Ki-67 expression, and improved mobility in the forced swim test. Late ET resulted in either no or modest effects on these parameters. There was a close correlation between the degree of ERβ2 expression and the preservation of neural effects by ET after OVX in rats, supporting the hypothesis that persistent elevated levels of ERβ2 are a molecular basis for the diminished effectiveness of ET in late post-menopausal women. The correlation between the expression of ERβ2 in circulating white blood cells and brain cells suggests that ERβ2 expression in peripheral blood cells may be an easily accessible marker to predict the effective window for ET in the brain.
The density of glial cells is reduced in certain layers of the dorsolateral prefrontal cortex in major depressive disorder (MDD). Moreover, there are reductions in the packing density of glial fibrillary acidic protein (GFAP) immunoreactive astrocytes in the same cortical layers in younger subjects with MDD. The objective of the present study was to test if the level of GFAP is preferentially decreased in younger subjects with MDD, and whether GFAP levels are correlated with the age of onset of depression. Post-mortem brain tissue punches from dorsolateral prefrontal cortex were collected from 15 subjects with MDD and 15 age-matched psychiatrically normal control subjects. Western blots were performed on gels containing duplicated samples from both subjects of each matched pair, and on gels containing samples at different ages from either the MDD or the control group. The GFAP level was calculated as the ratio of the optical density of GFAP bands to actin bands in subjects with MDD and nonpsychiatric controls. Levels of GFAP were significantly lower in subjects with MDD as compared to controls and this decrease was most prominent in subjects less than 60 years old at the time of death. In the MDD group, GFAP levels were positively correlated with age at the time of death and show a trend toward correlation with the age of onset of depression. These findings indicate that a decrease in levels of GFAP may contribute to the pathophysiology of MDD, particularly in subjects of relatively young age.
depression; glia; astrocytes; Western blotting; frontal lobe; aging
Morphometric changes in the general population of Nissl-stained neurons in area 9 of the dorsolateral prefrontal cortex have been reported in major depressive disorder (MDD) and schizophrenia. These alterations include lamina-specific reductions in the packing density of neuronal somata in MDD, increases or reductions in the density of neuronal somata in schizophrenia, and reductions in average size of neuronal somata in both MDD and schizophrenia. These changes are prominent in deep layer III, where pyramidal excitatory neurons establishing cortico-cortical association connections are localized. To test whether deep layer III pyramidal neurons are differentially affected in MDD or schizophrenia, an antibody was used that labels both phosphorylated and non-phosphorylated forms of the 200 kD neurofilament protein (NF200) in pyramidal cells of layer III in area 9. The packing density and somal size of NF200-immunoreactive (IR) pyramidal neurons were measured in area 9 in 13 subjects with nonpsychotic MDD, 11 subjects with schizophrenia and 13 psychiatrically normal controls. Analysis of covariance did not reveal a difference in packing density among groups. However, the mean size of NF200-IR somata was significantly larger in subjects with schizophrenia than in controls. These results indicate that this neuronal subpopulation does not contribute to the smaller average size of neuronal somata in layer III of prefrontal cortical area 9 in schizophrenia or MDD. In addition, the enlarged somal size in schizophrenia as compared to controls suggests that NF200 neurons may contribute differentially to unique cognitive disturbances present in schizophrenia and not in MDD subjects.
Postmortem; Immunohistochemistry; Brodmann’s area 9; Human; Psychiatry
Suicide attempters and completers may represent different but overlapping groups of distressed individuals. Although depression is related to an increased risk of suicide, the presence of depression may not discriminate suicide attempters from completers. The present study compared suicide attempters and suicide completers on symptoms of depression, the presence of suicide-related variables and stressful life events.
The present study sought to identify the key differences between 50 suicide attempters and 50 completers, all diagnosed with a Major Depressive Disorder at the time of their suicidal act.
Suicide attempters and family member informants of suicide completers participated in a thorough psychosocial evaluation. To maximize comparisons with completers, suicide attempters were subclassifed based on the lethality of their attempt.
Suicide attempters and completers were similar on most measures of depressive symptoms. However, suicide completers were significantly more likely to use alcohol or drugs prior to their suicidal act and they were more likely to leave a suicide note. Suicide completers were significantly more likely to have encountered significant job stress and financial problems.
The present findings have documented several similarities and differences between suicide attempters and suicide completers. Future research may help to clarify the key warning signs that reflect the risk of completed suicide in adults who have been diagnosed with a Major Depressive Disorder.
Suicide; suicide attempt; suicide completion
Reductions in glial density and enlargement of glial nuclei have been reported in the dorsolateral prefrontal cortex (dlPFC) in mood disorders. In alcohol dependence, often comorbid with depression, it is unclear whether there are changes in the density and size of glial cells in the dlPFC.
The packing density and size of Nissl-stained glial cell nuclei were analyzed postmortem in the cortical layers of the dlPFC from 21 control and 17 alcohol-dependent (Alc) subjects without Wernicke or Korsakoff syndromes. Eight Alc subjects had depressive symptoms. The density of glial cells was measured with a three-dimensional cell counting method, and the areal fraction of glial fibrillary acidic protein immunoreactivity (GFAP) was also determined.
Glial density was reduced by 11–14% in layers V and VI and in all layers combined in the Alc group. The size of glial nuclei was decreased by 3.2% in Alc subjects. The Alc subjects with depressive symptoms showed the lowest values of density and size. There was no difference in GFAP immunoreactivity, although the lowest values were in the Alc group.
Alcohol dependence is characterized by decreases in both density and size of glia in the dlPFC. Glial pathology may be more severe in Alc subjects with depressive symptoms.
Alcoholism; neuropathology; postmortem; comorbidity; morphometry; immunohistochemistry
Serotonin1A (5-HT1A) receptors are reported altered in the brain of subjects with major depressive disorder (MDD). Recent studies have identified transcriptional regulators of the 5-HT1A receptor and have documented gender-specific alterations in 5-HT1A transcription factor and 5-HT1A receptors in female MDD subjects. The 5′ repressor element under dual repression binding protein-1 (Freud-1) is a calcium-regulated repressor that negatively regulates the 5-HT1A receptor gene. This study documented the cellular expression of Freud-1 in the human prefrontal cortex (PFC) and quantified Freud-1 protein in the PFC of MDD and control subjects as well as in the PFC of rhesus monkeys chronically treated with fluoxetine. Freud-1 immunoreactivity was present in neurons and glia and was co-localized with 5-HT1A receptors. Freud-1 protein level was significantly decreased in the PFC of male MDD subjects (37%, p=0.02) relative to gender-matched control subjects. Freud-1 protein was also reduced in the PFC of female MDD subjects (36%, p=0.18) but was not statistically significant. When the data was combined across genders and analysed by age, the decrease in Freud-1 protein level was greater in the younger MDD subjects (48%, p=0.01) relative to age-matched controls as opposed to older depressed subjects. Similarly, 5-HT1A receptor protein was significantly reduced in the PFC of the younger MDD subjects (48%, p=0.01) relative to age-matched controls. Adult male rhesus monkeys administered fluoxetine daily for 39 wk revealed no significant change in cortical Freud-1 or 5-HT1A receptor proteins compared to vehicle-treated control monkeys. Reduced protein expression of Freud-1 in MDD subjects may reflect dysregulation of this transcription factor, which may contribute to the altered regulation of 5-HT1A receptors observed in subjects with MDD. These data may also suggest that reductions in Freud-1 protein expression in the PFC may be associated with early onset of MDD.
Major depression; prefrontal cortex; 5-HT1A receptors; serotonin; transcription factor
Alcoholism is a major psychiatric condition at least partly associated with ethanol-induced cell damage. Although brain cell loss has been reported in subjects with alcoholism, the molecular mechanism is unclear. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and monoamine oxidase B (MAO B) reportedly play a role in cellular dysfunction under stressful conditions and may contribute to ethanol-induced cell damage.
Expression of GAPDH and MAO B protein was studied in human glioblastoma and neuroblastoma cell lines exposed to physiological concentrations of ethanol. Expression of these proteins was also examined in the prefrontal cortex from human subjects with alcohol dependence and in rats fed with an ethanol diet. Co-immunoprecipitation, subcellular fractionation, and luciferase assay were used to address nuclear GAPDH-mediated MAO B activation. To test the effects of inactivation, RNAi and pharmacological intervention were used, and cell damage was assessed by TUNEL and H2O2 measurements.
Ethanol significantly increases levels of GAPDH, especially nuclear GAPDH, and MAO B in neuronal cells as well as in human and rat brains. Nuclear GAPDH interacts with the transcriptional activator, transforming growth factor-beta-inducible early gene 2 (TIEG2), and augments TIEG2-mediated MAO B transactivation, which results in cell damage in neuronal cells exposed to ethanol. Knockdown expression of GAPDH or treatment with MAO B inhibitors selegiline (Deprenyl) and rasagiline (Azilect) can block this cascade.
Ethanol-elicited nuclear GAPDH augments TIEG2-mediated MAO B, which may play a role in brain damage in subjects with alcoholism. Compounds that block this cascade are potential candidates for therapeutic strategies.
alcoholism; human brain tissues; rats-fed with an ethanol diet; ethanol-induced brain cell dysfunction; monoamine oxidase B; glyceraldehyde-3-phosphate dehydrogenase
Lifetime prevalence (~16%)1 and the economic burden ($100 billion annually)2,3 associated with major depressive disorder (MDD) make it one of the most common and debilitating neurobiological illnesses. To date, the exact cellular and molecular mechanisms underlying the pathophysiology of MDD have not been identified. Here we use whole genome expression profiling of postmortem tissue and demonstrate significantly increased expression of mitogen-activated protein kinase (MAPK) phosphatase-1 (MKP-1) in the hippocampal subfields of MDD subjects compared to matched controls. MKP-1, also known as DUSP1, is a member of a family of dual-specificity phosphatases (DUSP) that dephosphorylate both threonine and tyrosine residues and thereby serves as a key negative regulator of MAPK cascade4, a major signaling pathway involved in neuronal plasticity, function and survival5,6. The significance of altered MKP-1 was tested in rodent models of depression and demonstrates that increased hippocampal MKP-1 expression, as a result of stress or viral-mediated gene transfer, causes depressive behaviors. Conversely, chronic antidepressant treatment normalizes the stress-induced MKP-1 expression and behavior, and mice lacking MKP-1 are resilient to stress. These postmortem and preclinical studies identify MKP-1 as a critical factor in MDD pathophysiology and as a novel target for therapeutic interventions.
depression; hippocampus; postmortem; stress; rat; mouse
Clinical, postmortem and preclinical research strongly implicates dysregulation of glutamatergic neurotransmission in major depressive disorder (MDD). Recently, metabotropic glutamate receptors (mGluRs) have been proposed as attractive targets for discovery of novel therapeutic approaches against depression. The aim of this study was to examine mGluR2/3 protein levels in the prefrontal cortex (PFC) from depressed subjects. In addition, to test whether antidepressants influence mGluR2/3 expression we also studied levels of mGluR2/3 in fluoxetine treated monkeys. Postmortem human prefrontal samples containing Brodmann’s area 10 (BA 10) were obtained from 11 depressed and 11 psychiatrically healthy controls. Male rhesus monkeys were treated chronically with fluoxetine (dose escalated to 3mg/kg, p.o; n=7) or placebo (n=6) for 39 weeks. The mGluR2/3 immunoreactivity was investigated using Western blot method. There was a robust (+67%) increase in the expression of the mGlu2/3 protein in the PFC of depressed subjects relative to healthy controls. The expression of mGlu2/3 was unchanged in the PFC of monkeys treated with fluoxetine. Our findings provide the first evidence that mGluR2/3 is elevated in the PFC in MDD. This observation is consistent with reports showing that mGluR2/3 antagonists exhibit antidepressant-like activity in animal models and demonstrates that these receptors are promising targets for the discovery of novel antidepressants.
prefrontal cortex; metabotropic glutamate receptor; major depression; postmortem; fluoxetine; rhesus monkey
Alteration of glutamatergic neurotransmission in the prefrontal cortex (PFC) may contribute to the pathophysiology of alcoholism and major depressive disorder (MDD). Among glial cells, astrocytes are mostly responsible for recycling synaptic glutamate by uptake through excitatory amino acid transporters 1 and 2 (EAAT1 and EAAT2), and conversion to glutamine with glutamine synthetase (GS). Low density of astrocytes in the PFC of “uncomplicated’ alcoholics and MDD subjects may parallel altered glutamate transporters and GS in the PFC.
Immunohistochemistry and Western blotting for glutamate transporters, GS and glial fibrillary acidic protein (GFAP) were applied to postmortem tissue of the left orbitofrontal cortex from 13 subjects with MDD, 13 with alcoholism, 10 with comorbid alcoholism plus MDD (MDA), and 13 non-psychiatric controls. Area fraction of immunoreactivity was measured in sections, and protein levels in Western blots.
EAAT2 immunoreactivity was significantly lower in MDD and MDA subjects than in controls. EAAT1 levels were lower in MDA and MDD subjects as compared to controls, while GS levels in MDA were significantly lower than in alcoholics and controls, and lower in MDD subjects than in alcoholics. Area fraction of GFAP was lower in MDD, but not in MDA subjects as compared to controls or alcoholics.
High variability of protein levels in some groups and effects of antidepressant treatment, although appearing to be limited, cannot be fully evaluated.
There are differential changes in the expression of glial glutamatergic markers in depression and alcoholism, suggesting a depletion of certain aspects of glutamatergic processing in depression.
Astrocytes; Alcohol dependence; Major depressive disorder; Orbitofrontal cortex; Postmortem; Human
Imaging studies report that hippocampal volume is decreased in major depressive disorder (MDD). A cellular basis for reduced hippocampal volume in MDD has not been identified.
Sections of right hippocampus were collected in 19 subjects with MDD and 21 normal control subjects. The density of pyramidal neurons, dentate granule cell neurons, glia, and the size of the neuronal somal area were measured in systematic, randomly placed three-dimensional optical disector counting boxes.
In MDD, cryostat-cut hippocampal sections shrink in depth a significant 18% greater amount than in control subjects. The density of granule cells and glia in the dentate gyrus and pyramidal neurons and glia in all cornv ammonis (CA)/hippocampal subfields is significantly increased by 30% –35% in MDD. The average soma size of pyramidal neurons is significantly decreased in MDD.
In MDD, the packing density of glia, pyramidal neurons, and granule cell neurons is significantly increased in all hippocampal subfields and the dentate gyrus, and pyramidal neuron soma size is significantly decreased as well. It is suggested that a significant reduction in neuropil in MDD may account for decreased hippocampal volume detected by neuroimaging. In addition, differential shrinkage of frozen sections of the hippocampus suggests differential water content in hippocampus in MDD.
Depression; glia; hippocampus; pyramidal neurons
Elderly depressed patients have more vascular hyperintensities in frontal white matter and basal ganglia than elderly control subjects. Cell pathology that might be related to increased vascular hyperintensities has not been examined.
Postmortem samples from the orbitofrontal cortex (ORB) were collected in 15 elderly subjects with major depressive disorder (MDD) and 11 age-matched control subjects. Cell packing density of neurons and glia, density of pyramidal and nonpyramidal neurons, and cortical and laminar width were measured.
The overall (layers I–VI) packing density of ORB neurons with pyramidal morphology was markedly decreased in MDD (by 30%) as compared with control subjects. Further laminar analysis of pyramidal neurons density revealed significant reductions in layers IIIc and V in MDD. In contrast, in MDD the density of nonpyramidal neurons and glia and cortical and laminar width were comparable to control values.
In elderly subjects with depression, the density of pyramidal neurons in the ORB was particularly low in cortical layers V and III, the origin of prefronto–striatal and prefronto–cortical and prefronto–amygdalar projections. Degeneration of neurons furnishing these projections might be related to the white matter hyperintensities previously observed. Neuronal pathology seems to be more severe in elderly than in younger subjects with MDD.
Postmortem; morphometry; glial cells; major depression; late-life depression; aging
Low levels of the intracellular mediator of glutamate receptor activation, neuronal nitric oxide synthase (nNOS) were previously observed in locus coeruleus (LC) from subjects diagnosed with major depression. This finding implicates abnormalities in glutamate signaling in depression. Receptors responding to glutamate in the LC include ionotropic N-methyl-d-aspartate receptors (NMDARs). The functional NMDAR is a hetero-oligomeric structure composed of NR1 and NR2 (A–D) subunits. Tissue containing the LC and a nonlimbic LC projection area (cerebellum) was obtained from 13 and 9 matched pairs, respectively, of depressed subjects and control subjects lacking major psychiatric diagnoses. NMDAR subunit composition in the LC was evaluated in a psychiatrically normal subject. NR1 and NR2C subunit immunoreactivities in LC homogenates showed prominent bands at 120 and 135 kDa, respectively. In contrast to NR1 and NR2C, very weak immunoreactivity of NR2A and NR2B subunits was observed in the LC. Possible changes in concentrations of NR1 and NR2C that might occur in depression were assessed in the LC and cerebellum. The overall amount of NR1 immunoreactivity was normal in the LC and cerebellum in depressed subjects. Amounts of NR2C protein were significantly higher (+61%, p = 0.003) in the LC and modestly, but not significantly, elevated in the cerebellum (+35%) of depressives as compared to matched controls. Higher levels of NR2C subunit implicate altered glutamatergic input to the LC in depressive disorders.
depression; locus coeruleus; cerebellum; glutamate; NMDA receptor