Protein kinase C in platelets of depressed patients

Comprehensive analysis of key genes and pathways for biological and clinical implications in thyroid-associated ophthalmopathy

Background

Thyroid-associated ophthalmopathy (TAO) is a common and organ-specific autoimmune disease. Early diagnosis and novel treatments are essential to improve the prognosis of TAO patients. Therefore, the current work was performed to identify the key genes and pathways for the biological and clinical implications of TAO through comprehensive bioinformatics analysis and a series of clinical validations.

Methods

GSE105149 and GSE185952 were obtained from the Gene Expression Omnibus (GEO) database for analysis. The data were normalized to identify the common differentially expressed genes (DEGs) between the two datasets, and the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were conducted to assess key pathways in TAO. Protein–protein interaction (PPI) networks and hub genes among the common DEGs were identified. Furthermore, we collected the general information and blood samples from 50 TAO patients and 20 healthy controls (HCs), and the expression levels of the proteins encoded by hub genes in serum were detected by enzyme-linked immunosorbent assay (ELISA). Then we further assessed the relationship between the ELISA data and the TAO development.

Results

Several common pathways, including neuroactive ligand-receptor interaction, the IL-17 signaling pathway, and the TNF signaling pathway, were identified in both datasets. In parallel, 52 common DEGs were identified. The KEGG analysis showed that these common DEGs are mainly enriched in long-term depression, the VEGF signaling pathway, the IL-17 signaling pathway, the TNF signaling pathway, and cytokine-cytokine receptor interactions. The key hub genes PRKCG, OSM, DPP4, LRRTM1, CXCL6, and CSF3R were screened out through the PPI network. As confirmation, the ELISA results indicated that protein expression levels of PRKCG, OSM, CSF3R, and DPP4 were significantly upregulated in TAO patients compared with HCs. In addition, PRKCG and DPP4 were verified to show value in diagnosing TAO, and CSF3R was found to be a valuable diagnostic marker in distinguishing active TAO from inactive TAO.

Conclusions

Inflammation- and neuromodulation-related pathways might be closely associated with TAO. Based on the clinical verification, OSM, CSF3R, CXCL6, DPP4, and PRKCG may serve as inflammation- or neuromodulation-related biomarkers for TAO, providing novel insights for the diagnosis and treatment of TAO.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08854-5.

The α1-adrenergic receptors in the amygdala regulate the induction of learned despair through protein kinase C-beta signaling

Hyperactivity of amygdala is observed in patients with major depressive disorder. Although the role of α1-adrenoceptor in amygdala on fear memory has been well studied, the role of α1-adrenoceptor in amygdala on depression-like behaviors remains unclear. Therefore, we investigated the effect of α1A-adrenoreceptor in amygdala on despair behavior, evaluated by the immobility time during tail suspension test (TST), pharmacological intervention, and immunohistological methods. C57BL6/J mice given a bilateral intra-amygdala injection of artificial cerebrospinal fluid exhibited an increased duration of immobility in the latter half of both trials of TST with a 24-h interval, a phenomenon known as learned despair. Intra-amygdala injection of WB4101 (1.7 nmol/0.1 µl), an α1 adrenoreceptor antagonist, but not propranolol (250 pmol/0.1 µl), a β-adrenoreceptor antagonist, blocked the induction of learned despair during TST. Immunostaining experiments revealed that ~61-75% of α1A-adrenoreceptor-positive neurons were colocalized with GAD65/67 in amygdala, implying that the α1-adrenoceptors in amygdala may enormously regulate the GABA release. Protein kinase C-beta (PKCβ) was predominantly expressed in the α1A-adrenoreceptor-positive neurons in the BLA, whereas protein kinase C-epsilon (PKCε) was highly expressed with the α1A-adrenoreceptor in the Central nucleus of amygdala. Intra-amygdala injection of ruboxistaurin (10 pmol/0.1 µl), a PKCβ inhibitor, blocked the induction of learned despair during TST, whereas neither TAT-εV1-2 (500 ng/0.1 μl), a cell-permeant PKCε inhibitory peptide, nor HBDDE (50 pmol/0.1 µl), an inhibitor of PKCα and -γ, affected the duration of immobility during TST. These data suggest that the α1-adrenoreceptor in amygdala regulates the induction of learned despair via PKCβ.

Dysregulation of Protein Kinase C in Adult Depression and Suicide: Evidence From Postmortem Brain Studies

BACKGROUND

Several lines of evidence suggest the abnormalities of protein kinase C (PKC) signaling system in mood disorders and suicide based primarily on the studies of PKC and its isozymes in the platelets and postmortem brain of depressed and suicidal subjects. In this study, we examined the role of PKC isozymes in depression and suicide.

METHODS

We determined the protein and mRNA expression of various PKC isozymes in the prefrontal cortical region (Brodmann area 9) in 24 normal control subjects, 24 depressed suicide (DS) subjects, and 12 depressed nonsuicide (DNS) subjects. The levels of mRNA in the prefrontal cortex were determined by quantitative real-time reverse transcription PCR, and the protein expression was determined by western blotting.

RESULTS

We observed a significant decrease in mRNA expression of PKCα, PKCβI, PKCδ, and PKCε and decreased protein expression in either the membrane or the cytosol fraction of PKC isozymes PKCα, PKCβI, PKCβII, and PKCδ in DS and DNS subjects compared with normal control subjects.

CONCLUSIONS

The current study provides detailed evidence of specific dysregulation of certain PKC isozymes in the postmortem brain of DS and DNS subjects and further supports earlier evidence for the role of PKC in the platelets and brain of the adult and teenage depressed and suicidal population. This comprehensive study may lead to further knowledge of the involvement of PKC in the pathophysiology of depression and suicide.

The Role of MAPK and Dopaminergic Synapse Signaling Pathways in Antidepressant Effect of Electroacupuncture Pretreatment in Chronic Restraint Stress Rats

Acupuncture has demonstrated the function in ameliorating depressive-like behaviors via modulating PKA/CREB signaling pathway. To further confirm the antidepressant mechanism of EA on the mitogen-activated protein kinase (MAPK) and dopaminergic synapse signaling pathways, 4 target proteins were detected based on our previous iTRAQ analysis. Rats were randomly divided into control group, model group, and electroacupuncture (EA) group. Except for the control group, all rats were subjected to 28 days of chronic restraint stress (CRS) protocols to induce depression. In the EA group, EA pretreatment at Baihui (GV20) and Yintang (GV29) was performed daily (1 mA, 2 Hz, discontinuous wave, 20 minutes) prior to restraint. The antidepressant-like effect of EA was measured by body weight and open-field test. The protein levels of DAT, Th, Mapt, and Prkc in the hippocampus were examined by using Western blot. The results showed EA could ameliorate the depression-like behaviors and regulate the expression levels of Prkc and Mapt in CRS rats. The effect of EA on DAT and Th expression was minimal. These findings implied that EA pretreatment could alleviate depression through modulating MAPK signaling pathway. The role of EA on dopaminergic synapse signaling pathways needs to be further explored.

The interaction of combined effects of the BDNF and PRKCG genes and negative life events in major depressive disorder

Major depressive disorder (MDD) is a mental disorder that results from complex interplay between multiple and partially overlapping sets of susceptibility genes and environmental factors. The brain derived neurotrophic factor (BDNF) and Protein kinase C gamma type (PRKCG) are logical candidate genes in MDD. Among diverse environmental factors, negative life events have been suggested to exert a crucial impact on brain development. In the present study, we hypothesized that interactions between genetic variants in BDNF and PRKCG and negative life events may play an important role in the development of MDD. We recruited a total of 406 patients with MDD and 391 age- and gender-matched control subjects. Gene-environment interactions were analyzed using generalized multifactor dimensionality reduction (GMDR). Under a dominant model, we observed a significant three-way interaction among BDNF rs6265, PRKCG rs3745406, and negative life events. The gene-environment combination of PRKCG rs3745406 C allele, BDNF rs6265 G allele and high level of negative life events (C-G-HN) was significantly associated with MDD (OR, 5.97; 95% CI, 2.71-13.15). To our knowledge, this is the first report of evidence that the BDNF-PRKCG interaction may modify the relationship between negative life events and MDD in the Chinese population.

Protein kinase Mζ is involved in the modulatory effect of fluoxetine on hippocampal neurogenesis in vitro

The efficacy of chronic selective serotonin reuptake inhibitors (SSRIs) on depression is paralleled by the recovery of deficits in hippocampal neurogenesis related to sustained stress and elevated glucocorticoids. Previous studies have shown that atypical protein kinase C (aPKC) is implicated in the regulation of neurogenesis and the antidepressant response. Whether the specific aPKC isoforms (PKCζ, PKMζ and PKCι) are involved in SSRI-induced hippocampal neurogenesis and the underlying mechanisms is unknown. The present study shows that PKMζ and PKCι but not PKCζ are expressed in rat embryonic hippocampal neural stem cells (NSCs), whereas PKMζ but not PKCι expression is increased by the SSRI fluoxetine both in the absence and presence of the glucocorticoid receptor agonist dexamethasone. PKMζ shRNA significantly decreased neuronal proliferation and neuron-oriented differentiation, increased NSC apoptosis, and blocked the stimulatory effect of fluoxetine on NSC neurogenesis. Fluoxetine significantly increased PKMζ expression in hippocampal NSCs in a 5-hydroxytryptamine-1A (5-HT1A) receptor-dependent manner in both the absence and presence of dexamethasone. The PKMζ peptide blocker ZIP and MEK inhibitor U0126 significantly inhibited the increase in extracellular signal-regulated kinase 1/2 and cyclic adenosine monophosphate response element binding protein phosphorylation in the mitogen-activated protein kinase (MAPK) pathway and hippocampal NSC neurogenesis in response to fluoxetine and the 5-HT1A receptor agonist 8-OH DPAT. Collectively, our results suggest that the SSRI fluoxetine increases hippocampal NSC neurogenesis via a PKMζ-mediated mechanism that links 5-HT1A receptor activation with the phosphorylation of the downstream MAPK signaling pathway.

Oxidative stress and glutathione response in tissue cultures from persons with major depression

There is evidence that major depressive disorder (MDD) is associated with increased peripheral markers of oxidative stress. To explore oxidation and antioxidant response in MDD, we assayed human dermal fibroblast cultures derived from skin biopsies of age-, race-, and sex-matched individuals in depressed and normal control groups (n = 16 each group), cultured in glucose and galactose conditions, for relative protein carbonylation (a measure of oxidative stress), glutathione reductase (GR) expression, and total glutathione concentration. In control-group fibroblasts, galactose induced a significant increase from the glucose condition in both protein carbonylation and GR. The cells from the MDD group showed total protein carbonylation and GR expression in the glucose condition that was significantly higher than control cells in glucose and equivalent to controls in galactose. There was a small decrease in protein carbonylation in MDD cells from glucose to galactose and no significant change in GR. There was no difference in total glutathione among any of the groups. Increased protein carbonylation and GR expression, cellular responses to oxidative stress induced by galactose in control fibroblasts, are present in fibroblasts derived from MDD patients and are not explainable by reduced GR or total glutathione in the depressed patients. These studies support the role of oxidative stress in the pathophysiology of MDD. Further confirmation of these findings could lead to the development of novel antioxidant approaches for the treatment of depression.

Platelet protein kinase C and brain-derived neurotrophic factor levels in borderline personality disorder patients

Borderline personality disorder (BPD) is a prevalent and difficult to treat psychiatric condition characterized by abrupt mood swings, intense anger and depression, unstable interpersonal relationships, impulsive self-destructive behavior and a suicide rate of approximately 10%. Possible underlying molecular dysregulations in BPD have not been well explored. Protein kinase C (PKC) and brain-derived neurotrophic factor (BDNF) have both been implicated in affective disorders, but their role in BPD has not been examined. Platelets were isolated from blood obtained from 24 medication-free BPD patients and 18 healthy control subjects. PKC-α, phosphorylated-PKC-α (p-PKCα), PKC-βII, and BDNF were measured in platelet homogenates by immunoblotting. In the males, platelet BDNF and PKC-α levels were lower in patients than controls. p-PKC-α and PKC-βII were lower at trend levels. In the entire sample, platelet p-PKCα and PKC-α activity were lower, at a trend level, in patients compared to controls. This is the first report to our knowledge of PKC and BDNF activity in BPD and calls for replication. These findings are consistent with altered PKC and BDNF activity in a range of neuropsychiatric conditions including bipolar disorder, depression and suicide.

Regionally selective activation and differential regulation of ERK, JNK and p38 MAP kinase signalling pathway by protein kinase C in mood modulation

A growing body of evidence indicates that the extracellular signal-regulated kinase (ERK) pathway may participate in the neuronal modulation of depression. p38MAPK and c-Jun-N-terminal kinase/stress-activated protein kinase (JNK/SAPK) also belong to the MAPK family which mainly function as mediators of cellular stresses. Since increasing evidence implicates stress as an important factor in vulnerability to depressive illnesses, the involvement of ERK, JNK and p38MAPK pathways in the modulation of mood was investigated in the forced swim test (FST) and tail suspension test (TST). The effect produced by a single acute session of FST and TST on hippocampal and cortical MAPK expression and phosphorylation was investigated by immunoblotting experiments. In the hippocampus of animals exposed to FST and TST, an intensive, PKC-dependent, ERK1, ERK2, JNK, and p38MAPK phosphorylation was observed. In the frontal cortex, the FST and TST produced a PKC-dependent increase of ERK2 and p38MAPK phosphorylation, a PKC-independent activation of JNK and cAMP response element-binding protein (CREB) whereas any involvement of ERK1 was detected. The PKC blocker calphostin C (0.05-0.1 μg i.c.v.), the MEK inhibitor U0126 (10-20 μg i.c.v.), the p38MAPK inhibitor SB203580 (5-20 μg i.c.v.) and the JNK inhibitor II (0.5-5 μg i.c.v.), produced antidepressant-like behaviour without altering locomotor activity. These results illustrate a differentially mediated activation of MAPK in hippocampus and frontal cortex of animals exposed to behavioural despair paradigms. An antidepressant-like phenotype produced by acute blockade of MAPK signalling was also demonstrated.

Glycosides, depression and suicidal behaviour: the role of glycoside-linked proteins

Nowadays depression and suicide are two of the most important worldwide public health problems. Although their specific molecular mechanisms are still largely unknown, glycosides can play a fundamental role in their pathogenesis. These molecules act presumably through the up-regulation of plasticity-related proteins: probably they can have a presynaptic facilitatory effect, through the activation of several intracellular signaling pathways that include molecules like protein kinase A, Rap-1, cAMP, cADPR and G proteins. These proteins take part in a myriad of brain functions such as cell survival and synaptic plasticity. In depressed suicide victims, it has been found that their activity is strongly decreased, primarily in hippocampus and prefrontal cortex. These studies suggest that glycosides can regulate neuroprotection through Rap-1 and other molecules, and may play a crucial role in the pathophysiology of depression and suicide.

Elevated 5-HT 2A receptors in postmortem prefrontal cortex in major depression is associated with reduced activity of protein kinase A

Previous human postmortem brain tissue research has implicated abnormalities of 5-HT receptor availability in depression and suicide. Although altered abundance of 5-HT 1A, 5-HT 2A, and 5-HT 2C receptors (5-HT(1A), 5-HT(2A), and 5-HT(2C)) has been reported, the causes remain obscure. This study evaluated the availability of these three receptor subtypes in postmortem brain tissue specimens from persons with a history of major depression (MDD) and normal controls and tested the relationships to protein kinases A and C (PKA, PKC). Samples were obtained from postmortem brain tissue (Brodmann area 10) from 20 persons with a history of MDD and 20 matched controls as determined by a retrospective diagnostic evaluation obtained from family members. Levels of 5-HT(1A), 5-HT(2A), and 5-HT(2C) receptor were quantitated via Western blot analyses. Basal and stimulated PKA and PKC activity were also determined. The depressed samples showed significantly increased 5-HT(2A) receptor abundance relative to controls, but no differences in 5-HT(1A) or 5-HT(2C) receptors. Basal and cyclic AMP-stimulated PKA activity was also reduced in the depressed sample; PKC activity was not different between groups. 5-HT(2A) receptor availability was significantly inversely correlated with PKC activity in controls, but with PKA activity in the depressed sample. Increased 5-HT(2A) receptor abundance and decreased PKA activity in the depressed sample are consistent with prior reports. The correlation of 5-HT(2A) receptor levels with PKA activity in the depressed group suggests that abnormalities of 5-HT(2A) receptor abundance may depend on receptor uncoupling and heterologous regulation by PKA.

Glutamate receptors as targets of protein kinase C in the pathophysiology and treatment of animal models of mania

Considerable biochemical evidence suggests that the protein kinase C (PKC) signaling cascade may be a convergent point for the actions of anti-manic agents, and that excessive PKC activation can disrupt prefrontal cortical regulation of thinking and behavior. To date, however, brain protein targets of PKC's anti-manic effects have not been fully identified. Here we showed that PKC activity was enhanced in the prefrontal cortex of animals treated with the psychostimulant amphetamine. Phosphorylation of MARCKS, a marker of PKC activity, was increased in the prefrontal cortex of animals treated with the psychostimulant amphetamine, as well as in sleep-deprived animals (another animal model of mania), but decreased in lithium-treated animals. The antidepressant imipramine, which shows pro-manic properties in patients with bipolar disorder (BPD), also enhanced phospho-MARCKS in prefrontal cortex in vivo. We further explored the functional targets of PKC in mania-associated behaviors. Neurogranin is a brain-specific, postsynaptically located PKC substrate. PKC phosphorylation of neurogranin was robustly increased by pro-manic manipulations and decreased by anti-manic agents. PKC phosphorylation of the NMDA receptor site GluN1S896 and the AMPA receptor site GluA1T840 was also enhanced in the prefrontal cortex of animals treated with the antidepressant imipramine, as well as in behaviorally sleep-deprived animals, in striking contrast to the reduced activity seen in lithium-treated animals. These results suggest that PKC may play an important role in regulating NMDA and AMPA receptor functions. The biochemical profile of the PKC pathway thus encompasses both pro- and anti-manic effects on behavior. These results suggest that PKC modulators or their intracellular targets may ultimately represent novel avenues for the development of new therapeutics for mood disorders.

Diverse antidepressants increase CDP-diacylglycerol production and phosphatidylinositide resynthesis in depression-relevant regions of the rat brain

Background

Major depression is a serious mood disorder affecting millions of adults and children worldwide. While the etiopathology of depression remains obscure, antidepressant medications increase synaptic levels of monoamine neurotransmitters in brain regions associated with the disease. Monoamine transmitters activate multiple signaling cascades some of which have been investigated as potential mediators of depression or antidepressant drug action. However, the diacylglycerol arm of phosphoinositide signaling cascades has not been systematically investigated, even though downstream targets of this cascade have been implicated in depression. With the ultimate goal of uncovering the primary postsynaptic actions that may initiate cellular antidepressive signaling, we have examined the antidepressant-induced production of CDP-diacylglycerol which is both a product of diacylglycerol phosphorylation and a precursor for the synthesis of physiologically critical glycerophospholipids such as the phosphatidylinositides. For this, drug effects on [³H]cytidine-labeled CDP-diacylglycerol and [³H]inositol-labeled phosphatidylinositides were measured in response to the tricyclics desipramine and imipramine, the selective serotonin reuptake inhibitors fluoxetine and paroxetine, the atypical antidepressants maprotiline and nomifensine, and several monoamine oxidase inhibitors.

Results

Multiple compounds from each antidepressant category significantly stimulated [³H]CDP-diacylglycerol accumulation in cerebrocortical, hippocampal, and striatal tissues, and also enhanced the resynthesis of inositol phospholipids. Conversely, various antipsychotics, anxiolytics, and non-antidepressant psychotropic agents failed to significantly induce CDP-diacylglycerol or phosphoinositide synthesis. Drug-induced CDP-diacylglycerol accumulation was independent of lithium and only partially dependent on phosphoinositide hydrolysis, thus indicating that antidepressants can mobilize CDP-diacylglycerol from additional pools lying outside of the inositol cycle. Further, unlike direct serotonergic, muscarinic, or α-adrenergic agonists that elicited comparable or lower effects on CDP-diacylglycerol versus inositol phosphates, the antidepressants dose-dependently induced significantly greater accumulations of CDP-diacylglycerol.

Conclusion

Chemically divergent antidepressant agents commonly and significantly enhanced the accumulation of CDP-diacylglycerol. The latter is not only a derived product of phosphoinositide hydrolysis but is also a crucial intermediate in the biosynthesis of several signaling substrates. Hence, altered CDP-diacylglycerol signaling might be implicated in the pathophysiology of depression or the mechanism of action of diverse antidepressant medications.

The molecular neurobiology of depression

Depression is a condition with a complex biologic pattern in etiology. Environmental stressors modulate subsequent vulnerability to depression. In particular, early adversity seems to induce heightened reactivity to stress through several possible mechanisms, both biologic and psychologic. This increased reactivity results in an enhancement of biologic stress-response mechanisms, especially the HPA axis. Regulators of this system, particularly signal transduction pathways involving PKA and PKC, may be important in the regulation of key genes in this system including genes for GR, BDNF, and trk-b. This system potentially is vulnerable to ROS and therefore, indirectly, to the effects of cytokines. Finally, some of these effects may be controlled by chemical modification of DNA, specifically, methylation of promoters or other gene regions. This modification is a mechanism by which long-term biologic change can be induced by environmental stressors. The brain is homeostatic, and it is possible that alterations at multiple points in this system may induce dysregulation and, as a result, vulnerability to stress. Therefore, a person may be vulnerable to depression, which may be a final common "pathway" for this family of conditions. Individuals may very considerably with regard to the locus of the problem, however. For example, functional variants in a set of genes might predispose some people to depression; others may have epigenetic imprinting; and yet different causes may be at work in others. Although this mix is complicated, it can be unraveled. Doing so could lead to the development of novel interventions that could target specific points of vulnerability, allowing an improved matching of patient to treatment based on differential abnormalities at the cellular level.

Effects of calmodulin and protein kinase C modulators on transient Ca2+ increase and capacitative Ca2+ entry in human platelets: relevant to pathophysiology of bipolar disorder

Disturbed intracellular calcium (Ca(2+)) homeostasis has been implicated in bipolar disorder, which mechanisms may be involved in the dysregulation of protein kinase C (PKC) and calmodulin systems. In this study, we investigated a transient intracellular Ca(2+) increase induced by thapsigargin, an inhibitor of sarco/endoplasmic reticulum Ca(2+)-ATPase pump (SERCA), and a capacitative Ca(2+) entry followed by addition of extracellular Ca(2+), in the presence or absence of PKC/calmodulin modulators in the platelets of healthy subjects in order to elucidate the role of SERCA in Ca(2+) homeostasis and to assess how both PKC and calmodulin systems regulate the two Ca(2+) responses. Moreover, we also examined the thapsigargin-elicited transient Ca(2+) increase and capacitative Ca(2+) entry in patients with mood disorders. PKC and calmodulin systems have opposite regulatory effects on the transient Ca(2+) increase and capacitative Ca(2+) entry in the platelets of normal subjects. The inhibitory effect of PKC activation on capacitative Ca(2+) entry is significantly increased and the stimulatory effect of PKC inhibition is significantly decreased in bipolar disorder compared to major depressive disorder and normal controls. These results suggest the possibility that increased PKC activity may activate the inhibitory effect of capacitative Ca(2+) entry in bipolar disorder. However, this is a preliminary study using a small sample, thus further studies are needed to examine the PKC and calmodulin modulators on the capacitative Ca(2+) entry in a larger sample.

Modulation of phosphoinositide-protein kinase C signal transduction by omega-3 fatty acids: implications for the pathophysiology and treatment of recurrent neuropsychiatric illness

The phosphoinositide (PI)-protein kinase C (PKC) signal transduction pathway is initiated by pre- and postsynaptic Galphaq-coupled receptors, and regulates several clinically relevant neurochemical events, including neurotransmitter release efficacy, monoamine receptor function and trafficking, monoamine transporter function and trafficking, axonal myelination, and gene expression. Mounting evidence for PI-PKC signaling hyperactivity in the peripheral (platelets) and central (premortem and postmortem brain) tissues of patients with schizophrenia, bipolar disorder, and major depressive disorder, coupled with evidence that PI-PKC signal transduction is down-regulated in rat brain following chronic, but not acute, treatment with antipsychotic, mood-stabilizer, and antidepressant medications, suggest that PI-PKC hyperactivity is central to an underlying pathophysiology. Evidence that membrane omega-3 fatty acids act as endogenous antagonists of the PI-PKC signal transduction pathway, coupled with evidence that omega-3 fatty acid deficiency is observed in peripheral and central tissues of patients with schizophrenia, bipolar disorder, and major depressive disorder, support the hypothesis that omega-3 fatty acid deficiency may contribute to elevated PI-PKC activity in these illnesses. The data reviewed in this paper outline a potential molecular mechanism by which omega-3 fatty acids could contribute to the pathophysiology and treatment of recurrent neuropsychiatric illness.

Initial conditions of psychotropic drug response: studies of serotonin transporter long promoter region (5-HTTLPR), serotonin transporter efficiency, cytokine and kinase gene expression relevant to depression and antidepressant outcome

The Hypothesis of Initial Conditions posits that differences in psychotropic drug response result from individual differences in receptor site kinetics, and differences in the sensitivity of downstream receptor-linked responses. This work examines data consistent with the hypothesis, specific to genetic and kinetic differences of the serotonin (5-HT) transporter (SERT), as they may be linked to divergent antidepressant response (ADR). The mechanisms for divergent ADR in association with different initial SERT function are considered within the context of SERT trafficking as sensitive to various different kinase and cytokine signals, some of which are dependent on the 5-HTTLPR polymorphism of the SERT gene. Pilot data suggest that human lymphocytes show kinase changes similar to those found in rat brain with ADT. These studies additionally suggest that ADT prompts a shift in cytokine gene expression toward a greater anti-inflammatory/inflammatory ratio. These latter findings are discussed within the context of a literature suggesting increased inflammatory cytokine levels in depression, and recent observations of increased temperature associated with depression. In sum, the data suggest the opportunity to identify response dependent protein (RDP) expression patterns that may differ with dichotomous ADR, and suggest new insights into understanding the mechanisms of psychotropic drug response through an understanding of initial differences in potential for psychotropic drug target regulation during therapy.

Neurobiological findings in bipolar II disorder compared with findings in bipolar I disorder

OBJECTIVE

To determine whether there are consistent neurobiological differences between patients with bipolar I disorder (BD I) and those with bipolar II disorder (BD II).

METHOD

We reviewed the literature in areas where the most consistent neurobiological findings have been reported for bipolar disorder, specifically, neuroimaging and brain metabolism. The imaging studies reviewed examined structure, using magnetic resonance imaging (MRI), and function, using functional MRI, positron emission tomography, and single photon emission computed tomography. We used magnetic resonance spectroscopy to examine brain chemistry. We reviewed those metabolic studies that examined cell calcium, 3-methoxy-4-hydroxyphenylglycol, and protein kinase C.

RESULTS

Some genetic studies suggest that there may be differences between BD II and BD I patients. However, our review of the imaging and metabolic studies identified few studies directly comparing these 2 groups. In those studies, there were few differences, if any, and these were not consistent.

CONCLUSIONS

While genetic data suggest there may be differences between BD II patients and BD I patients, the neurobiological findings to date do not provide support. However, this may be owing to the small number of studies directly comparing the 2 groups and also to the fact that those carried out have not been adequately powered to detect possible small true differences. This is an important issue because, if there are no neurobiological differences, it would be anticipated that similar treatments would be similarly effective in both groups. Given the importance of understanding whether there are neurochemical differences between these groups, further research in this area is clearly needed.

Serotonin-mediated phosphorylation of extracellular regulated kinases in platelets of patients with panic disorder versus controls

Phosphorylation of extracellular signal-regulated kinases (ERK 1/2) represents a converging intracellular signalling pathway which is involved in the modulation of gene transcription and may contribute to the feed-back regulation of neurotransmitter receptor functioning. The purpose of the current study was to investigate the serotonin-mediated phosphorylation of ERK 1/2 in platelets from patients (n = 17) with panic disorder, with respect to healthy volunteers (n = 17). Patients presented a severe symptomatology as assessed by the self-report rating scales for panic-agoraphobic (PAS-SR) and mood (MOOD-SR) spectrum, and by Clinical Global Impression Severity Scale (CGI-S). In platelets from healthy volunteers, serotonin induced a rapid increase of ERK 1/2 phosphorylation with a transient monophasic kinetic. The dose-response curves showed this effect was concentration dependent with an average of the EC(50) value of 22.8 +/- 2.4 microM. Platelet pre-incubation with 5HT(1A) and 5HT(2A) antagonists, pindobind and ritanserin, significantly inhibited serotonin-mediated kinase activation with an EC(50) of 3.2 +/- 0.2 and 1.99 +/- 0.08 nM, respectively, suggesting an involvement of these specific receptor subtypes in serotonin-mediated response. Furthermore, the 5HT(1A) and 5HT(2A) agonists, 8-hydroxy-N,N-dipropyl-aminotetralin (8OH-DPAT) and 1-(2,5-dimethoxy)-4-iodophenyl-2-aminopropane (DOI), were able to modulate ERK 1/2 phosphorylation in a concentration-dependent manner with an EC(50) value of 3.1 +/- 0.2 and 76 +/- 4.5 nM, respectively. ERK 1/2 phosphorylation was not observed after serotonin treatment of platelets from drug-free panic disorder patients, suggesting an alteration in intracellular phosphorylative pathways. Since ERK 1/2 responsiveness to other stimulus, such as collagen and thrombin, was comparable in platelets from healthy volunteers and patients, our results suggested that a specific alteration of serotonergic system occurred in panic disorder. Further studies to investigate 5HT(1A) and 5HT(2A) receptor expression and threonine phosphorylation levels showed that, nevertheless no significant differences in the receptor expression levels were detected, an increase of both 5HT receptor phosphorylation, on threonine residues, occurred in platelet from panic patients with respect to controls, suggesting that a reduction of serotonin receptor functioning was involved in the loss of serotonin responsiveness in panic.

Altered expression and phosphorylation of myristoylated alanine-rich C kinase substrate (MARCKS) in postmortem brain of suicide victims with or without depression

Myristoylated alanine-rich C kinase substrate (MARCKS), an acidic, heat-stable protein, is involved in important physiological functions such as neurotransmitter release and re-uptake. It is also a substrate for phosphorylation by protein kinase C (PKC) and has been shown to play a role in the pathophysiology of mood disorders. In this study, protein and mRNA expression of MARCKS as well as phosphorylation of MARCKS were determined in the prefrontal cortex (PFC) and hippocampus of postmortem brain obtained from suicide victims, with or without depression, and normal control subjects. There were no significant differences in mRNA and protein levels of MARCKS between suicide subjects and controls. However, protein levels of MARCKS were significantly increased in the membrane but not in cytosol fraction of PFC and hippocampus obtained from depressed suicide subjects as compared to normal controls. When PKC-mediated MARCKS phosphorylation was determined, it was observed that MARCKS phosphorylation was significantly decreased in the membrane fraction of PFC and hippocampus obtained from total suicide subjects as well as depressed and non-depressed suicide subjects compared with control population. Although the mechanism of such alterations in MARCKS in depressed and non-depressed suicide subjects is not clear, results of the present study indicate that an increase in membrane MARCKS is associated with depressed suicide victims and a decrease in MARCKS phosphorylation may be a common feature of suicide victims independent of diagnosis.

Altered 5-HT-induced calcium response in the presence of staurosporine in blood platelets from bipolar disorder patients

We have reported that the platelet intracellular calcium (Ca) mobilization after stimulation by serotonin (5-HT) is specifically enhanced in bipolar disorder among various psychiatric disorders, compared with that in normal control. To explore the mechanisms of enhanced Ca response to 5-HT in the platelets, we first examined the relation between the 5HT-elicited Ca mobilization and 5-HT(2A) receptor density using the platelets from 13 normal subjects. From this study, we found no significant correlation between two measures. Then, we investigated the effects of staurosporine, a protein kinase C (PKC) inhibitor, on Ca response to 5-HT in platelets from patients with major depressive disorder (unipolar), bipolar disorder, and normal controls. While 5-HT-induced Ca mobilization, in the presence of 100 nM staurosporine, was significantly attenuated in normal controls and patients with major depressive disorder, the inhibitory effect of staurosporine was not observed in bipolar disorder. These results suggest that the failure in inhibiting the platelet intracellular Ca response to 5-HT in bipolar disorder may be related to increased activity of PKC rather than increased 5-HT(2A) receptor number. Moreover, the trend of the Ca response towards staurosporine may become a specific biological marker for unipolar-bipolar dichotomy.

Congenitally learned helpless rats show abnormalities in intracellular signaling

BACKGROUND

Affective disorders and the drugs used to treat them lead to changes in intracellular signaling. We used a genetic animal model to investigate to what extent changes in intracellular signal transduction confer a vulnerability to mood or anxiety disorders.

METHODS

Levels of gene expression in a selectively bred strain of rats with a high vulnerability to develop congenitally learned helplessness (cLH), a strain highly resistant to the same behavior (cNLH) and outbred Sprague-Dawley (SD) control animals were compared using quantitative reverse transcription polymerase chain reaction.

RESULTS

Congenitally learned helpless animals had a 24%-30% reduced expression of the cyclic adenosine monophosphate response element binding protein messenger ribonucleic acid (mRNA) in the hippocampus and a 40%-41% increased level of the antiapoptotic protein bcl-2 mRNA in the prefrontal cortex compared to cNLH and SD rats. Other significant changes included changes in the expression levels of the alpha catalytic subunit of protein kinase A, glycogen synthase kinase 3beta, and protein kinase C epsilon.

CONCLUSIONS

Congenitally learned helpless animals show evidence of altered signal transduction and regulation of apoptosis compared to cNLH and SD control animals.

Purinergic dysfunction in mania: an integrative model

The purinergic system, which includes the anticonvulsant and antikindling neuromodulator adenosine and the neurotransmitter ATP, modulates second messenger systems, neurotransmitters, energy metabolism and different behaviors, such as sleep, motor activity, cognition, memory, aggressive behavior and social interaction. At the same time, mania is characterized by similar behavioral changes and a molecular basis to explain the pathological activation observed during manic episodes has been also associated with second messenger systems dysfunction and kindling. This hypothesis put forward an integrative model of neuronal communication, associating a reduced adenosinergic activity, mostly at A1 receptors, with the complex network of changes on neurotransmitters pathways related to manic behavior.

The neurobiology of bipolar disorder: focus on signal transduction pathways and the regulation of gene expression

OBJECTIVE

This article presents an overview of signal transduction pathways and reviews the research undertaken to study these systems in clinically relevant samples from patients with bipolar disorder (BD).

METHOD

We reviewed the published findings from studies of postmortem brain tissue and blood samples from patients with BD.

RESULTS

Although the exact biochemical abnormalities have yet to be identified, the presented findings strongly suggest that BD may be due, at least in part, to abnormalities in signal transduction mechanisms. In particular, altered levels or function, or both, of G-protein alpha subunits and effector molecules such as protein kinase A (PKA) and protein kinase C (PKC) have consistently been associated with BD both in peripheral cells and in postmortem brain tissue, while more recent studies implicate disruption in novel second-messenger cascades, such as the ERK/MAPK pathway.

CONCLUSIONS

Despite the difficulties inherent in biochemical studies of clinically relevant tissue samples, numerous investigations have illuminated the signal transduction mechanisms in patients with BD. These studies also suggest that BD may be due to the interaction of many abnormalities. In this context, novel techniques enabling the study of gene expression promise to assist in untangling these complex interactions, through visualizing the end result of these changes at the level of gene transcription.

Serotonin-induced platelet intracellular calcium mobilization in various psychiatric disorders: is it specific to bipolar disorder?

BACKGROUND

Serotonin (5-HT)-stimulated platelet intracellular calcium (Ca) mobilization has been reported to be enhanced in unmedicated depressive patients compared to those of normal healthy subjects, which suggests increased 5-HT2A receptor function in these patients. It has not been ascertained whether this enhanced response is specific to some type of affective disorders among various mental disorders.

METHODS

We examined 5-HT-induced platelet intracellular Ca response in 152 unmedicated outpatients with various psychiatric disorders including bipolar disorder (BD), major depressive disorder with melancholia (DM), major depressive disorder without melancholia (DN), schizophrenia (SCH), panic disorder (PD), obsessive-compulsive disorder (OCD), social phobia (SP) and bulimia nervosa (BN), and 30 normal controls.

RESULTS

We observed no significant differences in basal intracellular Ca concentration among all patient subgroups and normal controls. While the 5-HT-induced Ca response was significantly and specifically higher in patients with BD than in normal controls, no significant differences were found in the Ca response to 5-HT between patients with DM, DN, SCH, PD, OCD, SP and BN, and normal controls.

LIMITATIONS

The sample sizes of each group are still small. Therefore, they have to be enlarged in the continuation of the study so as to increase the power of the statistical tests.

CONCLUSION

These results indicate the possibility that enhanced signal transduction, mediated by the 5-HT2A receptor, may be specific to bipolar disorder.

Increased platelet membrane phosphatidylinositol-4,5-bisphosphate in drug-free depressed bipolar patients

Prior investigations in bipolar disorder patients have suggested abnormalities in the cellular phosphoinositide second messenger system. This study was conducted to examine the levels of platelet membrane phosphoinositides in drug-free bipolar patients in the depressed state (n=9) and healthy controls (n=19). Bipolar patients had significantly increased levels of platelet membrane phosphatidylinositol-4,5-bisphosphate (PIP(2)) compared to healthy individuals (0.67+/-0.14 and 0.44+/-0.17%, respectively, t-test=3.71, d.f.=26, P=0.001). No significant differences in the levels of phosphatidylinositol-4-phosphate (PIP) (0.65+/-0.17 and 0.58+/-0.20%, respectively, t-test=1.02; d.f.=26; P=0.32) or phosphatidylinositol (PI) (5.92+/-1.23 and 5.56+/-1.45%, respectively, t-test=0.68; d.f.=26; P=0.51) were found. These findings provide the first demonstration of increased PIP(2) platelet levels in bipolar patients in the depressed state, and provide additional evidence that the phosphoinositide second messenger system may be a site of abnormality in bipolar disorder.

Protein kinase A and Rap1 levels in platelets of untreated patients with major depression

We have recently reported altered levels of protein kinase A and Rap1 in patients with bipolar disorder. The purpose of the current investigation was to assess the levels of these proteins in platelets from untreated euthymic and depressed patients with major unipolar depression. Platelets were collected from 45 drug-free unipolar patients (13 euthymic and 32 depressed) and 45 healthy subjects. The levels of protein kinase A and Rap1 were assessed by Western blot analysis, immunostaining and computer-assisted imaging. The immunolabeling of the regulatory subunit type II of protein kinase A and that of Rap1 was significantly lower in untreated depressed patients compared with untreated euthymic patients and healthy subjects. No significant differences were found in the immunolabeling of both the regulatory type I and the catalytic subunits of protein kinase A among groups. Levels of the regulatory subunit type II of protein kinase A and Rap1 are altered in platelets of unipolar depressive patients. These findings may provide new insight about the relationship between components of cAMP signaling and affective disorders.

Altered 5-HT(2A) binding sites and second messenger inositol trisphosphate (IP(3)) levels in hippocampus but not in frontal cortex from depressed suicide victims

The binding parameters of 5-HT(2A) and levels of its second messenger, 1,4,5-trisphosphate (IP(3)), were simultaneously studied in frontal cortex and hippocampus from the brains of 18 control subjects and 18 depressed suicide victims. All suicides met DSM-III-R criteria for depressive symptoms, suffered a violent death and had not taken any antidepressant drugs for at least 6 months prior to death. A significant decrease in the number of 5-HT(2A) binding sites (154+/-22 vs. 254+/-36 fmol/mg), together with a significantly lower apparent affinity constant (1.02+/- 0.08 vs. 1. 36+/-0.09 nM), was detected in hippocampus but not in frontal cortex from the depressed suicides compared to the control subjects. Furthermore, IP(3) concentrations were significantly increased in hippocampus (3.2+/-0.3 vs. 2.1+/-0.3 pmol/g) but not in frontal cortex (1.3+/-0.3 vs. 2.7+/-0.5 pmol/g) from the suicide victims. The reported results may indicate a significant hypersensitivity of the 5-HT(2A) postsynaptic receptor located in the hippocampus from depressed suicide victims, giving rise to an enhancement of its intracellular signaling system with higher IP(3) production.

Concurrent measures of protein kinase C and phosphoinositides in lithium-treated bipolar patients and healthy individuals: a preliminary study

This study examined the hypothesis that lithium inhibits the PI signaling pathway in humans during in vivo administration by concurrently measuring PKC isozymes and platelet membrane phosphoinositides in lithium-treated patients and healthy individuals. The platelet membrane and cytosolic levels of PKC alpha, beta I, beta II, delta, and epsilon were measured using Western blotting. The relative platelet membrane contents of phosphatidylinositol (PI), phosphatidylinositol-4-phosphate (PIP), and phosphatidylinositol-4,5-bisphosphate (PIP(2)) were measured with two-dimensional thin-layer chromatography. Nine euthymic lithium-treated bipolar subjects and 11 healthy control subjects were studied. Compared to control subjects, lithium-treated bipolar patients had significantly lower levels of cytosolic PKC alpha isozyme (t-test=-3.24, d.f.=17, P=0.01) and PIP(2) platelet membrane levels (t-test=-2.51, d.f.=18, P=0.02), and a trend toward reduced levels of cytosolic PKC beta II isozyme (t=-2.17, d.f.=17, P=0.05). There was no significant correlation between PIP(2) and any of the PKC isozymes. These preliminary findings suggest that chronic lithium treatment may decrease the levels of both cytosolic PKC alpha isozyme and membrane PIP(2) in platelets of bipolar disorder patients.

Altered brain protein kinase C in depression: a post-mortem study

[(3)H]Phorbol 12,13-dibutyrate (PDBu) binding was measured in soluble and particulate fractions of frontal cortex and hippocampus from suicides, with a firm retrospective diagnosis of depression, and individually matched controls. Suicides were divided into those who had been free of antidepressant drugs for at least 3 months and those in whom prescription of antidepressants was clearly documented. In frontal cortex, there was a significantly higher number (by 75%) of [(3)H]PDBu binding sites in the soluble fraction in antidepressant-free suicides compared to controls; significant differences were also seen in the proportion of sites in the soluble and particulate fractions. Higher numbers of [(3)H]PDBu binding sites in the particulate fraction of hippocampus in antidepressant-free suicides was restricted to those who died by violent means. No significant differences in the number of [(3)H]PDBu binding sites were found in antidepressant-treated suicides compared to controls. This study provides evidence for the involvement of protein kinase C in the pathophysiology of depression.

Abnormalities of cAMP signaling in affective disorders: implication for pathophysiology and treatment

OBJECTIVE

During the last decade, much attention has been given to the role of signal transduction pathways in affective disorders. This review describes the possible role of the cAMP signaling in such disorders.

METHODS

Among the components of cAMP signaling, this review focuses on the cAMP-dependent phosphorylation system. We analyzed the basic components of the cAMP-dependent phosphorylation system and the preclinical evidence supporting their involvement in the biochemical action of antidepressants and mood stabilizers. The clinical data available until now, concerning the possible link between the cAMP-dependent phosphorylation system and the pathophysiology of affective disorders, are also reviewed.

RESULTS

The studies herein presented demonstrated that the levels and the activity of cAMP-dependent protein kinase are altered by antidepressants and mood stabilizers. Furthermore. these medications are able to modify the phosphorylation state, as well as the levels of some of the cAMP-dependent protein kinase substrates. More recently, clinical studies have reported abnormalities in the cAMP-dependent phosphorylation system in both peripheral cells and the postmortem brain of patients with affective disorders.

CONCLUSIONS

Overall, these studies support an involvement of cAMP signaling in affective disorders. The precise knowledge of the findings has the potential to improve the understanding of pharmacotherapy and to provide directions for the development of novel biochemical and genetic research strategies on the pathogenesis of affective disorders.

Ziskind-Somerfeld Research Award. Protein kinase C signaling in the brain: molecular transduction of mood stabilization in the treatment of manic-depressive illness

Understanding the biology of the pharmacological stabilization of mood will undoubtedly serve to provide significant insight into the pathophysiology of manic-depressive illness (MDI). Accumulating evidence from our laboratories and those of other researchers has identified the family of protein kinase C isozymes as a shared target in the brain for the long-term action of both lithium and valproate. In rats chronically treated with lithium, there is a reduction in the hippocampus of the expression of two protein kinase isozymes, alpha and epsilon, as well as a reduction in the expression of a major PKC substrate, MARCKS, which has been implicated in long-term neuroplastic events in the developing and adult brain. In addition, we have been investigating the down-stream impact of these mood stabilizers on another kinase system, GSK-3 beta and on the AP-1 family of transcription factors. Further studies have generated promising preliminary data in support of the antimanic action of tamoxifen, and antiestrogen that is also a PKC inhibitor. Future studies must address the therapeutic relevance of these protein targets in the brain using innovative strategies in both animal and clinical investigations to ultimately create opportunities for the discovery of the next generations of mood stabilizers for the treatment of MDI.

Repeated administration of dexamethasone increases phosphoinositide-specific phospholipase C activity and mRNA and protein expression of the phospholipase C beta 1 isozyme in rat brain

Altered hypothalamic-pituitary-adrenal (HPA) function has been shown to be associated with changes in mood and behavior. The enzyme phosphoinositide-specific phospholipase C (PI-PLC), an important component of the PI signal transduction system, plays a major role in mediating various physiological functions. In the present study, we investigated the effects of a single dose and of repeated administration (0.5 or 1.0 mg/kg for 10 days) of dexamethasone (DEX), a synthetic glucocorticoid, on PI-PLC activity and on expression of PLC isozymes (beta1, delta1, and gamma1) in rat brain. Repeated administration of DEX (1.0 mg/kg) caused a significant increase in PI-PLC activity and in protein expression of the PLC beta1 isozyme in both membrane and cytosol fractions of cortex and hippocampus; however, the repeated administration of a smaller dose of DEX (0.5 mg/kg) caused these changes only in hippocampus but not in cortex. The increase in PLC beta1 protein was associated with an increase in its mRNA level, as measured by competitive RT-PCR. A single administration of DEX (0.5 or 1.0 mg/kg) to rats had no significant effects on PI-PLC activity or on the protein expression of PLC isozymes. These results suggest that DEX up-regulates PI-PLC in rat brain, which presumably is due to a selective increase in expression of the PLC beta1 isozyme, and that these changes in PI-PLC may be related to HPA axis-mediated changes in mood and behavior.

Administration of dexamethasone up-regulates protein kinase C activity and the expression of gamma and epsilon protein kinase C isozymes in the rat brain

Altered hypothalamic-pituitary-adrenal (HPA) function (increased plasma cortisol level) has been shown to be associated with mood and behavior. Protein kinase C (PKC), an important component of the phosphatidyl-inositol signal transduction system, plays a major role in mediating various physiological functions. The present study investigates the effects of acute (single) and repeated (10-day) administrations of 0.5 or 1.0 mg/kg doses of dexamethasone (DEX), a synthetic glucocorticoid, on Bmax and KD of [3H]phorbol 12,13-dibutyrate ([3H]PDBu) binding, PKC activity, and protein expression of PKC isozymes alpha, beta, gamma, delta, and epsilon in the membrane and the cytosolic fractions of rat cortex and hippocampus. It was observed that repeated administration of 1.0 mg/kg DEX for 10 days caused a significant increase in Bmax of [3H]PDBu binding to PKC, in PKC activity, and in expressed protein levels of the gamma and epsilon isozymes in both the cytosolic and the membrane fractions of the cortex and the hippocampus, whereas a lower dose of DEX (0.5 mg/kg for 10 days) caused these changes only in the hippocampus. On the other hand, a single administration of DEX (0.5 or 1.0 mg/kg) had no significant effect on PKC in the cortex or in the hippocampus. These results suggest that alterations in HPA function from repeated administration of glucocorticoids may modulate PKC-mediated functions.