Gene expression profiling in the midbrain of striatal 6-hydroxydopamine-injected mice

Serum/glucocorticoid regulated kinase 1 (SGK1) in neurological disorders: pain or gain

Serum/Glucocorticoid Regulated Kinase 1 (SGK1), a serine/threonine kinase, is ubiquitous across a wide range of tissues, orchestrating numerous signaling pathways and associated with various human diseases. SGK1 has been extensively explored in diverse types of immune and inflammatory diseases, cardiovascular disorders, as well as cancer metastasis. These studies link SGK1 to cellular proliferation, survival, metabolism, membrane transport, and drug resistance. Recently, increasing research has focused on SGK1's role in neurological disorders, including a variety of neurodegenerative diseases (e.g., Alzheimer's disease, Huntington's disease and Parkinson's disease), brain injuries (e.g., cerebral ischemia and traumatic brain injury), psychiatric conditions (e.g., depression and drug addiction). SGK1 is emerging as an increasingly compelling therapeutic target across the spectrum of neurological disorders, supported by the availability of several effective agents. However, the conclusions of many studies observing the prevalence and function of SGK1 in neurological disorders are contradictory, necessitating a review of the SGK1 research within neurological disorders. Herein, we review recent literature on SGK1's primary functions within the nervous system and its impacts within different neurological disorders. We summarize significant findings, identify research gaps, and outline possible future research directions based on the current understanding of SGK1 to help further progress the understanding and treatment of neurological disorders.

Chronic hyperactivation of midbrain dopamine neurons causes preferential dopamine neuron degeneration

Parkinson's disease (PD) is characterized by the death of substantia nigra (SNc) dopamine (DA) neurons, but the pathophysiological mechanisms that precede and drive their death remain unknown. The activity of DA neurons is likely altered in PD, but we understand little about if or how chronic changes in activity may contribute to degeneration. To address this question, we developed a chemogenetic (DREADD) mouse model to chronically increase DA neuron activity, and confirmed this increase using ex vivo electrophysiology. Chronic hyperactivation of DA neurons resulted in prolonged increases in locomotor activity during the light cycle and decreases during the dark cycle, consistent with chronic changes in DA release and circadian disturbances. We also observed early, preferential degeneration of SNc projections, recapitulating the PD hallmarks of selective vulnerability of SNc axons and the comparative resilience of ventral tegmental area axons. This was followed by eventual loss of midbrain DA neurons. Continuous DREADD activation resulted in a sustained increase in baseline calcium levels, supporting an important role for increased calcium in the neurodegeneration process. Finally, spatial transcriptomics from DREADD mice examining midbrain DA neurons and striatal targets, and cross-validation with human patient samples, provided insights into potential mechanisms of hyperactivity-induced toxicity and PD. Our results thus reveal the preferential vulnerability of SNc DA neurons to increased neural activity, and support a potential role for increased neural activity in driving degeneration in PD.

Identification of a new structural family of SGK1 inhibitors as potential neuroprotective agents

SGK1 is a serine/threonine kinase involved in several neurodegenerative-related pathways such as apoptosis, neuroinflammation, ionic channel regulation, and autophagy, among others. Despite its potential role as a pharmacological target against this kind of diseases, there are no reported inhibitors able to cross the BBB so far, being a field yet to be explored. In this context, a structure-based virtual screening against this kinase was performed, pointing out the deazapurine moiety as an interesting and easy-to-derivatize scaffold. Moreover, these inhibitors are able to i) exert neuroprotection in an in vitro model of AD and ii) block mitophagy in a PRKN-independent manner, reinforcing the hypothesis of SGK1 inhibitors as neuroprotective chemical tools.

SGK1 inhibition in glia ameliorates pathologies and symptoms in Parkinson disease animal models

Astrocytes and microglia are brain-resident glia that can establish harmful inflammatory environments in disease contexts and thereby contribute to the progression of neuronal loss in neurodegenerative disorders. Correcting the diseased properties of glia is therefore an appealing strategy for treating brain diseases. Previous studies have shown that serum/ glucocorticoid related kinase 1 (SGK1) is upregulated in the brains of patients with various neurodegenerative disorders, suggesting its involvement in the pathogenesis of those diseases. In this study, we show that inhibiting glial SGK1 corrects the pro-inflammatory properties of glia by suppressing the intracellular NFκB-, NLRP3-inflammasome-, and CGAS-STING-mediated inflammatory pathways. Furthermore, SGK1 inhibition potentiated glial activity to scavenge glutamate toxicity and prevented glial cell senescence and mitochondrial damage, which have recently been reported as critical pathologic features of and therapeutic targets in Parkinson disease (PD) and Alzheimer disease (AD). Along with those anti-inflammatory/neurotrophic functions, silencing and pharmacological inhibition of SGK1 protected midbrain dopamine neurons from degeneration and cured pathologic synuclein alpha (SNCA) aggregation and PD-associated behavioral deficits in multiple in vitro and in vivo PD models. Collectively, these findings suggest that SGK1 inhibition could be a useful strategy for treating PD and other neurodegenerative disorders that share the common pathology of glia-mediated neuroinflammation.

Serum- and glucocorticoid-induced kinase 1, a new therapeutic target for autophagy modulation in chronic diseases

Introduction: Autophagy, a basic cellular degradation pathway essential for survival, is altered both in aging and in many chronic human diseases, including infections, cancer, heart disease, and neurodegeneration. Identifying new therapeutic targets for the control and modulation of autophagy events is therefore of utmost importance in drug discovery. Serum and glucocorticoid activated kinase 1 (SGK1), known for decades for its role in ion channel modulation, is now known to act as a switch for autophagy homeostasis, and has emerged as a novel and important therapeutic target likely to attract considerable research attention in the coming years.Areas covered: In this general review of SGK1 we describe the kinase's structure and its roles in physiological and pathological contexts. We also discuss small-molecule modulators of SGK1 activity. These modulators are of particular interest to medicinal chemists and pharmacists seeking to develop more potent and selective drug candidates for SGK1, which, despite its key role in autophagy, remains relatively understudied.Expert opinion: The main future challenges in this area are (i) deciphering the role of SGK1 in selective autophagy processes (e.g. mitophagy, lipophagy, and aggrephagy); (ii) identifying selective allosteric modulators of SGK1 with specific biological functions; and (iii) conducting first-in-man clinical studies.

Acupuncture Inhibits the Increase in Alpha-Synuclein by Modulating SGK1 in an MPTP Induced Parkinsonism Mouse Model

Parkinson’s disease (PD), a progressive neurodegenerative disease, is caused by the loss of dopaminergic neurons in the substantia nigra (SN). It is characterized by the formation of intracytoplasmic Lewy bodies that are primarily composed of the protein alpha-synuclein ([Formula: see text]-syn) along with dystrophic neurites. Acupuncture stimulation results in an enhanced survival of dopaminergic neurons in the SN in parkinsonism animal models. We investigated the role of acupuncture in inhibiting the increase in [Formula: see text]-syn expression that is related with dopaminergic cell loss in the SN in a chronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) parkinsonism mouse model. In this model, acupuncture stimulation at GB34 and LR3 attenuated the decrease in tyrosine hydroxylase. Moreover, acupuncture stimulation attenuated the increase in [Formula: see text]-syn. We identified that serum- and glucocorticoid-dependent kinase 1 (SGK1) is evidently downregulated in chronic MPTP-intoxication and acupuncture stimulation maintained SGK1 expression at levels similar to the control group. For an examination of the expression correlation between SGK1 and [Formula: see text]-syn, SH-SY5Y cells were knocked down with SGK1 siRNA then, the downregulation of dopaminergic cells and the increase in the expression of [Formula: see text]-syn were observed. Our findings indicate that the acupuncture-mediated inhibition in the [Formula: see text]-syn increase induced by MPTP may be responsible for modulating SGK1 expression.

Decreased expression of serum- and glucocorticoid-inducible kinase 1 (SGK1) promotes alpha-synuclein increase related with down-regulation of dopaminergic cell in the Substantia Nigra of chronic MPTP-induced Parkinsonism mice and in SH-SY5Y cells

Parkinson's disease (PD) is a chronically progressive neurodegenerative disease, with its main pathological hallmarks being a dramatic loss of dopaminergic neurons predominantly in the Substantia Nigra (SN), and the formations of intracytoplasmic Lewy bodies and dystrophic neurites. Alpha-synuclein (α-syn), widely recognized as the most prominent element of the Lewy body, is one of the representative hallmarks in PD. However, the mechanisms behind the increased α-syn expression and aggregation have not yet been clarified. To examine what causes α-syn expression to increase, we analyzed the pattern of gene expression in the SN of mice intoxicated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), where down-regulation of dopaminergic cells occurred. We identified serum- and glucocorticoid-dependent kinase 1 (SGK1) as one of the genes that is evidently downregulated in chronic MPTP-intoxication. The results of Western blot analyses showed that, together with the down-regulation of dopaminergic cells, the decrease in SGK1 expression increased α-syn expression in the SN in a chronic MPTP-induced Parkinsonism mouse. For an examination of the expression correlation between SGK1 and α-syn, SH-5YSY cells were knocked down with SGK1 siRNA then, the downregulation of dopaminergic cells and the increase in the expression of α-syn were observed. These results suggest that decreased expression of SGK1 may play a critical role in increasing the expression of α-syn, which is related with dopaminergic cell death in the SN of chronic MPTP-induced Parkinsonism mice and in SH-SY5Y cells.

Disturbance of oligodendrocyte function plays a key role in the pathogenesis of schizophrenia and major depressive disorder

The major psychiatric disorders such as schizophrenia (SZ) and major depressive disorder (MDD) are thought to be multifactorial diseases related to both genetic and environmental factors. However, the genes responsible and the molecular mechanisms underlying the pathogenesis of SZ and MDD remain unclear. We previously reported that abnormalities of disrupted-in-Schizophrenia-1 (DISC1) and DISC1 binding zinc finger (DBZ) might cause major psychiatric disorders such as SZ. Interestingly, both DISC and DBZ have been further detected in oligodendrocytes and implicated in regulating oligodendrocyte differentiation. DISC1 negatively regulates the differentiation of oligodendrocytes, whereas DBZ plays a positive regulatory role in oligodendrocyte differentiation. We have reported that repeated stressful events, one of the major risk factors of MDD, can induce sustained upregulation of plasma corticosterone levels and serum/glucocorticoid regulated kinase 1 (Sgk1) mRNA expression in oligodendrocytes. Repeated stressful events can also activate the SGK1 cascade and cause excess arborization of oligodendrocyte processes, which is thought to be related to depressive-like symptoms. In this review, we discuss the expression of DISC1, DBZ, and SGK1 in oligodendrocytes, their roles in the regulation of oligodendrocyte function, possible interactions of DISC1 and DBZ in relation to SZ, and the activation of the SGK1 signaling cascade in relation to MDD.

Gene expression profiling in the striatum of amphetamine-treated spontaneously hypertensive rats which showed amphetamine conditioned place preference and self-administration

Attention-deficit/hyperactivity disorder (ADHD), the most commonly diagnosed neurobehavioral disorder of childhood, is usually treated with psychostimulants (e.g., amphetamine). Little is known about the neuronal and behavioral consequences of chronic amphetamine use or abuse in individuals with ADHD. Of all ADHD animal models, the spontaneously hypertensive rat (SHR) is the most validated and widely used. Here, we analyzed striatal transcriptomes in amphetamine-pretreated SHRs (5 mg/kg, i.p. for 7 days [twice daily]), which showed a conditioned place preference to and self-administration of amphetamine. Microarray analyses revealed increased mRNA expression of 55 genes (>1.65-fold increase), while 17 genes were downregulated (<0.6-fold) in the striatum of SHRs. The main functional categories overrepresented among the differentially expressed genes in the striatum include those involved in transcription (e.g., Cebpb, Per2), genes associated with angiogenesis (e.g., Kdr, Klf5), cell adhesion (e.g., Col11a1, Ctgf), apoptosis (e.g., Nfkbia, Perp) and neuronal development (e.g., Egr2, Nr4a3). In conclusion, we dissected the striatal transcriptional responses to the reinforcing effects of repeated amphetamine treatment in the SHR model of ADHD. Future studies should determine the influence of these altered transcripts on amphetamine reinforcement in amphetamine-treated SHRs, and the clinical relevance of the present findings with regard to amphetamine use/abuse in ADHD individuals.

Time course of dopamine neuron loss and glial response in the 6-OHDA striatal mouse model of Parkinson's disease

The 6-hydroxydopamine (6-OHDA) neurotoxic lesion of the midbrain dopamine (DA) system is one of the most widely used techniques for modelling Parkinson's disease in rodents. The majority of studies using this approach, however, largely limit their analysis to lesioning acutely, and looking at behavioural deficits and the number of surviving tyrosine hydroxylase (TH)-stained cells in the midbrain. Here we have analysed additional characteristics that occur following intrastriatal delivery of 6-OHDA, providing better understanding of the neurodegenerative process. Female C57/Black mice were given lesions at 10 weeks old, and killed at several different time points postoperatively (3 and 6 h, 1, 3, 6, 9 and 12 days). While the detrimental effect of the toxin on the TH+ fibres in the striatum was immediate, we found that the loss of TH+ dendritic fibres, reduction in cell size and intensity of TH expression, and eventual reduction in the number of TH+ neurons in the substantia nigra was delayed for several days post-surgery. We also investigated the expression of various transcription factors and proteins expressed by midbrain DA neurons following lesioning, and observed changes in the expression of Aldh1a1 (aldehyde dehydrogenase 1 family, member A1) as the neurodegenerative process evolved. Extracellularly, we looked at microglia and astrocytes in reaction to the 6-OHDA striatal lesion, and found a delay in their response and proliferation in the substantia nigra. In summary, this work highlights aspects of the neurodegenerative process in the 6-OHDA mouse model that can be applied to future studies looking at therapeutic interventions.

Activation of GSK-3β and caspase-3 occurs in Nigral dopamine neurons during the development of apoptosis activated by a striatal injection of 6-hydroxydopamine

The 6-Hydroxydopamine (6-OHDA) rat model of Parkinson's disease is essential for a better understanding of the pathological processes underlying the human disease and for the evaluation of promising therapeutic interventions. This work evaluated whether a single striatal injection of 6-OHDA causes progressive apoptosis of dopamine (DA) neurons and activation of glycogen synthase kinase 3β (GSK-3β) and caspase-3 in the substantia nigra compacta (SNc). The loss of DA neurons was shown by three neuron markers; tyrosine hydroxylase (TH), NeuN, and β-III tubulin. Apoptosis activation was determined using Apostain and immunostaining against cleaved caspase-3 and GSK-3β pY216. We also explored the possibility that cleaved caspase-3 is produced by microglia and astrocytes. Our results showed that the 6-OHDA caused loss of nigral TH(+) cells, progressing mainly in rostrocaudal and lateromedial directions. In the neostriatum, a severe loss of TH(+) terminals occurred from day 3 after lesion. The disappearance of TH(+) cells was associated with a decrease in NeuN and β-III tubulin immunoreactivity and an increase in Apostain, cleaved caspase-3, and GSK-3β pY216 in the SNc. Apostain immunoreactivity was observed from days 3 to 21 postlesion. Increased levels of caspase-3 immunoreactivity in TH(+) cells were detected from days 1 to 15, and the levels then decreased to day 30 postlesion. The cleaved caspase-3 also collocated with microglia and astrocytes indicating its participation in glial activation. Our results suggest that caspase-3 and GSK-3β pY216 activation might participate in the DA cell death and that the active caspase-3 might also participate in the neuroinflammation caused by the striatal 6-OHDA injection.

Therapeutic potential of serum and glucocorticoid inducible kinase inhibition

INTRODUCTION

Expression of serum-and-glucocorticoid-inducible kinase-1 (SGK1) is low in most cells, but dramatically increases under certain pathophysiological conditions, such as glucocorticoid or mineralocorticoid excess, inflammation with TGFβ release, hyperglycemia, cell shrinkage and ischemia. SGK1 is activated by insulin and growth factors via phosphatidylinositide-3-kinase, 3-phosphoinositide-dependent kinase and mammalian target of rapamycin. SGK1 sensitive functions include activation of ion channels (including epithelial Na(+) channel ENaC, voltage gated Na(+) channel SCN5A transient receptor potential channels TRPV4 - 6, Ca(2+) release activated Ca(2+) channel Orai1/STIM1, renal outer medullary K(+) channel ROMK, voltage gated K(+) channels KCNE1/KCNQ1, kainate receptor GluR6, cystic fibrosis transmembrane regulator CFTR), carriers (including Na(+),Cl(-) symport NCC, Na(+),K(+),2Cl(-) symport NKCC, Na(+)/H(+) exchangers NHE1 and NHE3, Na(+), glucose symport SGLT1, several amino acid transporters), and Na(+)/K(+)-ATPase. SGK1 regulates several enzymes (e.g., glycogen synthase kinase-3, ubiquitin-ligase Nedd4-2) and transcription factors (e.g., forkhead transcription factor 3a, β-catenin, nuclear factor kappa B).

AREAS COVERED

The phenotype of SGK1 knockout mice is mild and SGK1 is apparently dispensible for basic functions. Excessive SGK1 expression and activity, however, contributes to the pathophysiology of several disorders, including hypertension, obesity, diabetes, thrombosis, stroke, fibrosing disease, infertility and tumor growth. A SGK1 gene variant (prevalence ∼ 3 - 5% in Caucasians and ∼ 10% in Africans) is associated with hypertension, stroke, obesity and type 2 diabetes. SGK1 inhibitors have been developed and shown to reduce blood pressure of hyperinsulinemic mice and to counteract tumor cell survival.

EXPERT OPINION

Targeting SGK1 may be a therapeutic option in several clinical conditions, including metabolic syndrome and tumor growth.

Astrocytes are a neural target of morphine action via glucocorticoid receptor-dependent signaling

Chronic opioid use leads to the structural reorganization of neuronal networks, involving genetic reprogramming in neurons and glial cells. Our previous in vivo studies have revealed that a significant fraction of the morphine-induced alterations to the striatal transcriptome included glucocorticoid (GC) receptor (GR)-dependent genes. Additional analyses suggested glial cells to be the locus of these changes. In the current study, we aimed to differentiate the direct transcriptional effects of morphine and a GR agonist on primary striatal neurons and astrocytes. Whole-genome transcriptional profiling revealed that while morphine had no significant effect on gene expression in both cell types, dexamethasone significantly altered the transcriptional profile in astrocytes but not neurons. We obtained a complete dataset of genes undergoing the regulation, which includes genes related to glucose metabolism (Pdk4), circadian activity (Per1) and cell differentiation (Sox2). There was also an overlap between morphine-induced transcripts in striatum and GR-dependent transcripts in cultured astrocytes. We further analyzed the regulation of expression of one gene belonging to both groups, serum and GC regulated kinase 1 (Sgk1). We identified two transcriptional variants of Sgk1 that displayed selective GR-dependent upregulation in cultured astrocytes but not neurons. Moreover, these variants were the only two that were found to be upregulated in vivo by morphine in a GR-dependent fashion. Our data suggest that the morphine-induced, GR-dependent component of transcriptome alterations in the striatum is confined to astrocytes. Identification of this mechanism opens new directions for research on the role of astrocytes in the central effects of opioids.

Neurotrophic effects of serum- and glucocorticoid-inducible kinase on adult murine mesencephalic dopamine neurons

Mesencephalic dopamine neurons are central to many aspects of human cognition, motivational, and motor behavior, and they are uniquely vulnerable to degenerative neurologic disorders such as Parkinson's disease. There is growing evidence that in the mature brain these neurons not only remain responsive to neurotrophic support, but are dependent on it for viability and function. Little is known of the cellular signaling pathways that mediate this support, although some evidence suggests that protein kinase Akt/PKB may play such a role. Another candidate for such a role is serum- and glucocorticoid-inducible kinase (SGK), a member of the AGC kinase family that is closely related to Akt. We have herein examined the responsiveness of adult mouse dopamine neurons in vivo to overexpression of wild-type and a constitutively active form of SGK by use of viral vector transfer in normal mice and both before and after 6-OHDA lesion. We find that SGK induces a broad spectrum of neurotrophic effects on these neurons, including induction of neuronal hypertrophy, protection from both neuron death and neurotoxin-induced retrograde axonal degeneration, and axon regeneration. Given the diverse and robust effects of SGK on these neurons, and its abundant expression in them, we suggest that SGK, like closely related Akt, may play a role in their responsiveness to neurotrophic factors and in adult maintenance. It therefore offers a novel target for therapeutic development.

Differential gene expression in the nucleus accumbens and frontal cortex of lewis and Fischer 344 rats relevant to drug addiction

Drug addiction results from the interplay between social and biological factors. Among these, genetic variables play a major role. The use of genetically related inbred rat strains that differ in their preference for drugs of abuse is one approach of great importance to explore genetic determinants. Lewis and Fischer 344 rats have been extensively studied and it has been shown that the Lewis strain is especially vulnerable to the addictive properties of several drugs when compared with the Fischer 344 strain. Here, we have used microarrays to analyze gene expression profiles in the frontal cortex and nucleus accumbens of Lewis and Fischer 344 rats. Our results show that only a very limited group of genes were differentially expressed in Lewis rats when compared with the Fischer 344 strain. The genes that were induced in the Lewis strain were related to oxygen transport, neurotransmitter processing and fatty acid metabolism. On the contrary genes that were repressed in Lewis rats were involved in physiological functions such as drug and proton transport, oligodendrocyte survival and lipid catabolism.

These data might be useful for the identification of genes which could be potential markers of the vulnerability to the addictive properties of drugs of abuse.

In vivo quantification of dopamine transporters in mice with unilateral 6-OHDA lesions using [11C]methylphenidate and PET

Quantification of the binding of [11C]methylphenidate to the dopamine transporter (DAT) using positron emission tomography (PET) is often used to evaluate the integrity of dopaminergic neurons in the striatal regions of the brain. Over the past decade, many genetically engineered mouse models of human disease have been developed and have become particularly useful for the study of disease onset and progression over time. Quantitative imaging of small structures such as the mouse brain is especially challenging. Thus, the aims of this study were (1) to evaluate the accuracy of quantifying DAT binding using in vivo PET and (2) to examine the impact of different methodologies.

METHODS

Eight mice were scanned with [11C]methylphenidate under true or transient equilibrium conditions using a bolus and constant infusion protocol or a bolus injection protocol to evaluate the accuracy of the Logan graphical approach for [11C]methylphenidate imaging in mice. Displacement with unlabeled methylphenidate (0.1, 3 and 10 mg/kg) was used to verify specific binding. In a second experiment, 30 mice were lesioned by injection of 6-hydroxydopamine (6-OHDA) at doses of 0, 2 or 4 μg (n=10) into the right striatum to assess the dose-dependent correlation between the PET signal and dopaminergic degeneration. In addition, we performed test-retest experiments and used ex vivo autoradiography (AR) to validate the effect of partial volume on the accuracy of the [11C]methylphenidate PET quantification in the mouse striatum.

RESULTS

The binding potentials (BPND) calculated from the Logan graphical analysis under transient equilibrium conditions (1.03±0.1) were in excellent agreement with those calculated at true equilibrium (1.07±0.1). Displacement of specific binding with 0.1, 3 and 10mg/kg methylphenidate resulted in 38%, 77% and 81% transporter occupancy in the striatum. Intra-striatal injections of 6-OHDA caused a dose-dependent decrease in the specific binding of [11C]methylphenidate to the DAT in the striatum. The BPND was reduced by 49% and 61% after injection with 2 and 4 μg of 6-OHDA, respectively. The test-retest reproducibility was 6% in the healthy striatum and 27% in the lesioned striatum. In addition, only a small (15%) difference was found between the [11C]methylphenidate DVR-1 values determined by PET and AR on the healthy side, and no differences were observed on the lesioned side.

CONCLUSION

The present work demonstrates for the first time that [11C]methylphenidate PET is useful for the quantification of striatal dopamine transporters at the dopaminergic nerve terminals in the mouse striatum; therefore, this marker may be used as a biomarker in genetically engineered mouse models of neurodegenerative disorders. However, only changes resulting in greater than 10% differences in BPND values can reliably be detected in vivo.

Hydration-sensitive gene expression in brain

Dehydration has a profound influence on neuroexcitability. The mechanisms remained, however, incompletely understood. The present study addressed the effect of water deprivation on gene expression in the brain. To this end, animals were exposed to a 24 hours deprivation of drinking water and neuronal gene expression was determined by microarray technology with subsequent confirmation by RT-PCR. As a result, water deprivation was followed by significant upregulation of clathrin (light polypeptide Lcb), serum/glucocorticoid-regulated kinase (SGK) 1, and protein kinase A (PRKA) anchor protein 8-like. Water deprivation led to downregulation of janus kinase and microtubule interacting protein 1, neuronal PAS domain protein 4, thrombomodulin, purinergic receptor P2Y - G-protein coupled 13 gene, gap junction protein beta 1, neurotrophin 3, hyaluronan and proteoglycan link protein 1, G protein-coupled receptor 19, CD93 antigen, forkhead box P1, suppressor of cytokine signaling 3, apelin, immunity-related GTPase family M, serine (or cysteine) peptidase inhibitor clade B member 1a, serine (or cysteine) peptidase inhibitor clade H member 1, glutathion peroxidase 8 (putative), discs large (Drosophila) homolog-associated protein 1, zinc finger and BTB domain containing 3, and H2A histone family member V. Western blotting revealed the downregulation of forkhead box P1, serine (or cysteine) peptidase inhibitor clade H member 1, and gap junction protein beta 1 protein abundance paralleling the respective alterations of transcript levels. In conclusion, water deprivation influences the transcription of a wide variety of genes in the brain, which may participate in the orchestration of brain responses to water deprivation.

Plasma corticosterone activates SGK1 and induces morphological changes in oligodendrocytes in corpus callosum

Repeated stressful events are known to be associated with onset of depression. Further, stress activates the hypothalamic–pituitary–adrenocortical (HPA) system by elevating plasma cortisol levels. However, little is known about the related downstream molecular pathway. In this study, by using repeated water-immersion and restraint stress (WIRS) as a stressor for mice, we attempted to elucidate the molecular pathway induced by elevated plasma corticosterone levels. We observed the following effects both, in vivo and in vitro: (1) repeated exposure to WIRS activates the 3-phosphoinositide-dependent protein kinase (PDK1)–serum glucocorticoid regulated kinase (SGK1)–N-myc downstream-regulated gene 1 (NDRG1)–adhesion molecule (i.e., N-cadherin, α-catenin, and β-catenin) stabilization pathway via an increase in plasma corticosterone levels; (2) the activation of this signaling pathway induces morphological changes in oligodendrocytes; and (3) after recovery from chronic stress, the abnormal arborization of oligodendrocytes and depression-like symptoms return to the control levels. Our data strongly suggest that these abnornalities of oligodendrocytes are possibly related to depression-like symptoms.

Sgk1 activates MDM2-dependent p53 degradation and affects cell proliferation, survival, and differentiation

Serum and glucocorticoid regulated kinase 1 (Sgk1) is a serine-threonine kinase that is activated by serum, steroids, insulin, vasopressin, and interleukin 2 at the transcriptional and post-translational levels. Sgk1 is also important in transduction of growth factors and steroid-dependent survival signals and may have a role in the development of resistance to cancer chemotherapy. In the present paper, we demonstrate that Sgk1 activates MDM2-dependent p53 ubiquitylation. The results were obtained in RKO cells and other cell lines by Sgk1-specific RNA silencing and were corroborated in an original mouse model as well as in transiently and in stably transfected HeLa cells expressing wild-type or dominant negative Sgk1 mutant. Sgk1 contributes to cell survival, cell-cycle progression, and epithelial de-differentiation. We also show that the effects of Sgk1 on the clonogenic potential of different cancer cells depend on the expression of wild-type p53. Since transcription of Sgk1 is activated by p53, we propose a finely tuned feedback model where Sgk1 down-regulates the expression of p53 by enhancing its mono- and polyubiquitylation.

Mu-opioid receptor activation induces transcriptional plasticity in the central extended amygdala

Addiction develops from the gradual adaptation of the brain to chronic drug exposure, and involves genetic reprogramming of neuronal function. The central extended amygdala (EAc) is a network formed by the central amygdala and the bed nucleus of the stria terminalis. This key site controls drug craving and seeking behaviors, and has not been investigated at the gene regulation level. We used Affymetrix microarrays to analyze transcriptional activity in the murine EAc, with a focus on mu-opioid receptor-associated events because these receptors mediate drug reward and dependence. We identified 132 genes whose expression is regulated by a chronic escalating morphine regimen in the EAc from wild-type but not mu-opioid receptor knockout mice. These modifications are mostly EAc-specific. Gene ontology analysis reveals an overrepresentation of neurogenesis, cell growth and signaling protein categories. A separate quantitative PCR analysis of genes in the last of these groups confirms the dysregulation of both orphan (Gpr88) and known (DrD1A, Adora2A, Cnr1, Grm5, Gpr6) G protein-coupled receptors, scaffolding (PSD95, Homer1) and signaling (Sgk, Cap1) proteins, and neuropeptides (CCK, galanin). These transcriptional modifications do not occur following a single morphine injection, and hence result from long-term adaptation to excessive mu receptor activation. Proteins encoded by these genes are classically associated with spine modules function in other brain areas, and therefore our data suggest a remodeling of EAc circuits at sites where glutamatergic and monoaminergic afferences interact. Together, mu receptor-dependent genes identified in this study potentially contribute to drug-induced neural plasticity, and provide a unique molecular repertoire towards understanding drug craving and relapse.

A brain-specific SGK1 splice isoform regulates expression of ASIC1 in neurons

Neurodegenerative diseases and noxious stimuli to the brain enhance transcription of serum- and glucocorticoid-induced kinase-1 (SGK1). Here, we report that the SGK1 gene encodes a brain-specific additional isoform, SGK1.1, which exhibits distinct regulation, properties, and functional effects. SGK1.1 decreases expression of the acid-sensing ion channel-1 (ASIC1); thereby, SGK1.1 may limit neuronal injury associated to activation of ASIC1 in ischemia. Given that neurons express at least two splice isoforms, SGK1 and SGK1.1, driven by distinct promoters, any changes in SGK1 transcript level must be examined to define the isoform induced by each stimulus or neurological disorder.

Broad spectrum neuroprotection profile of phosphodiesterase inhibitors as related to modulation of cell-cycle elements and caspase-3 activation

Cellular injury can involve the aberrant stimulation of cell cycle proteins in part through activation of phosphodiesterases (PDEs) and downstream expression of cell-cycle components such as cyclin D1. In mature non-proliferating cells activation of the cell cycle can lead to the induction of programmed cell death. In the present study, we investigated the in vitro neuroprotective efficacy and mechanism of action of vinpocetine (PDE1 inhibitor), trequinsin (PDE3 inhibitor), and rolipram (PDE4 inhibitor) in four mechanistically-distinct models of injury to primary rat cortical neurons as related to cell cycle regulation and apoptosis. Cellular injury was induced by hypoxia/hypoglycemia, veratridine (10 microM), staurosporine (1 microM), or glutamate (100 microM), resulting in average neuronal cell death rates of 43-48% as determined by MTT assay. Treatment with each PDE inhibitor (PDEI) resulted in a similar concentration-dependent neuroprotection profile with maximal effective concentrations of 5-10 microM (55-77% neuroprotection) in all four neurotoxicity models. Direct cytotoxicity due to PDE inhibition alone was not observed at concentrations below 100 microM. Further studies indicated that PDEIs can suppress the excitotoxic upregulation of cyclin D1 similar to the effects of flavopiridol, a cyclin-dependent kinase inhibitor, including suppression of pro-apoptotic caspase-3 activity. Overall, these data indicate that PDEIs are broad-spectrum neuroprotective agents acting through modulation of cell cycle elements and may offer a novel mode of therapy against acute injury to the brain.

(Patho)physiological significance of the serum- and glucocorticoid-inducible kinase isoforms

The serum- and glucocorticoid-inducible kinase-1 (SGK1) is ubiquitously expressed and under genomic control by cell stress (including cell shrinkage) and hormones (including gluco- and mineralocorticoids). Similar to its isoforms SGK2 and SGK3, SGK1 is activated by insulin and growth factors via phosphatidylinositol 3-kinase and the 3-phosphoinositide-dependent kinase PDK1. SGKs activate ion channels (e.g., ENaC, TRPV5, ROMK, Kv1.3, KCNE1/KCNQ1, GluR1, GluR6), carriers (e.g., NHE3, GLUT1, SGLT1, EAAT1-5), and the Na+-K+-ATPase. They regulate the activity of enzymes (e.g., glycogen synthase kinase-3, ubiquitin ligase Nedd4-2, phosphomannose mutase-2) and transcription factors (e.g., forkhead transcription factor FKHRL1, beta-catenin, nuclear factor kappaB). SGKs participate in the regulation of transport, hormone release, neuroexcitability, cell proliferation, and apoptosis. SGK1 contributes to Na+ retention and K+ elimination of the kidney, mineralocorticoid stimulation of salt appetite, glucocorticoid stimulation of intestinal Na+/H+ exchanger and nutrient transport, insulin-dependent salt sensitivity of blood pressure and salt sensitivity of peripheral glucose uptake, memory consolidation, and cardiac repolarization. A common ( approximately 5% prevalence) SGK1 gene variant is associated with increased blood pressure and body weight. SGK1 may thus contribute to metabolic syndrome. SGK1 may further participate in tumor growth, neurodegeneration, fibrosing disease, and the sequelae of ischemia. SGK3 is required for adequate hair growth and maintenance of intestinal nutrient transport and influences locomotive behavior. In conclusion, the SGKs cover a wide variety of physiological functions and may play an active role in a multitude of pathophysiological conditions. There is little doubt that further targets will be identified that are modulated by the SGK isoforms and that further SGK-dependent in vivo physiological functions and pathophysiological conditions will be defined.

Puma and p53 play required roles in death evoked in a cellular model of Parkinson disease

6-Hydroxydopamine (6-OHDA) is widely used in vivo and in vitro to mimic the selective neuronal degeneration that characterizes Parkinson disease (PD). To uncover candidate genes that may mediate neuron death in PD, we previously used SAGE to identify transcripts that are rapidly induced by 6-OHDA in neuronally differentiated PC12 cells. Among induced pro-apoptotic genes was that encoding the BH3-only protein PUMA. Here, we confirm that 6-OHDA induces both PUMA mRNA and protein. 6-OHDA additionally induced Bim, another pro-apoptotic BH3-only protein. Using specific siRNAs, we demonstrate that PUMA, but not Bim, is required for death evoked by 6-OHDA. PUMA is a target of p53, a transcription factor activated by 6-OHDA. Involvement of p53 in 6-OHDA evoked death was confirmed by the protective actions of a DN p53 and pifithrin alpha, inhibitors of p53 signaling. Our findings thus indicate that p53 and PUMA play required roles in a cellular model of PD.

Early induction of calpains in rotenone-mediated neuronal apoptosis

Rotenone is an inhibitor of mitochondrial complex I that produces a model of Parkinson's disease (PD), where neurons undergo apoptosis by caspase-dependent and/or caspase-independent pathways. Inhibition of calpains has recently been shown to attenuate neuronal apoptosis. This study aims to establish for the first time, the time-point of calpain activation with respect to the caspase activation and the possibility of cell cycle re-entry in rotenone-mediated cell death. Immunoblot results revealed calpain activation occurred at 5, 10h prior to caspase-3 activation (at 15 h), suggesting calpain activation was an earlier cellular event compared to caspase activation in the rotenone-mediated apoptosis. In addition, an upregulation of phospho-p53 was observed at 21 h. However, no expression or upregulation of cell cycle regulatory proteins including cdc25a, cyclin-D1 and cyclin-D3 were observed, strongly suggesting that cell cycle re-entry did not occur. These findings provide new insights into the differential patterns of calpain and caspase activation that result from rotenone poisoning and which may be relevant to the therapeutic management of PD.

Molecular basis of programmed cell death involved in neurodegeneration

Rapid progress in understanding the molecular basis of neurodegeneration has been tightly linked with recent discoveries in the field of programmed cell death (PCD). Analysis of PCD in neuronal demise has led to identification of several associated phenomena, such as re-initiation of the cell cycle and the key role of oxidative stress, although putative causal relationships between these events are still debatable. These issues are reviewed here in the context of acute and chronic neurodegenerative processes. In addition, newly emerging concepts concerning cell-cycle re-initiation are discussed in terms of their potential impact on the development of more effective therapeutic strategies.

Sgk1, a cell survival response in neurodegenerative diseases

Serum and glucocorticoid-regulated kinase 1 (sgk1) belongs to a family of serine/threonine kinases that is under acute transcriptional control by serum and glucocorticoids. An expanding set of receptors and cellular stress pathways has been shown to enhance sgk1 expression, which is implicated in the regulation of ion channel conductance, cell volume, cell cycle progression, and apoptosis. Recent evidence for the involvement of sgk1 in the early pathogenesis of MPTP-induced Parkinson's disease (PD) prompted us to investigate in more detail its expression and role in animal models of different neurodegenerative diseases. Here, we show that transcription of sgk1 is increased in several animal models of PD and a transgenic model of amyotrophic lateral sclerosis (ALS). The upregulation of sgk1 strongly correlates with the occurrence of cell death. Furthermore, we provide evidence that the Forkhead transcription factor FKHRL1 and some of the voltage-gated potassium channels are physiological substrates of sgk1 in vivo. Using a small interfering RNA approach to silence sgk1 transcripts in vitro, we give evidence that sgk1 exerts a protective role in oxidative stress situations. These findings underline a key role for sgk1 in the molecular pathway of cell death, in which sgk1 seems to exert a protective role.

p53 in neuronal apoptosis

The tumor suppressor and transcription factor p53 is a key modulator of cellular stress responses, and activation of p53 can trigger apoptosis in many cell types including neurons. Apoptosis is a form of programmed cell death that occurs in neurons during development of the nervous system and may also be responsible for neuronal deaths that occur in neurological disorders such as stroke, and Alzheimer's and Parkinson's diseases. p53 production is rapidly increased in neurons in response to a range of insults including DNA damage, oxidative stress, metabolic compromise, and cellular calcium overload. Target genes induced by p53 in neurons include those encoding the pro-apoptotic proteins Bax and the BH3-only proteins PUMA and Noxa. In addition to such transcriptional control of the cell death machinery, p53 may more directly trigger apoptosis by acting at the level of mitochondria, a process that can occur in synapses (synaptic apoptosis). Preclinical data suggest that agents that inhibit p53 may be effective therapeutics for several neurodegenerative conditions.

Analysis of gene expression changes in a cellular model of Parkinson disease

We employed Serial Analysis of Gene Expression to identify transcriptional changes in a cellular model of Parkinson Disease (PD). The model consisted of neuronally differentiated PC12 cells compared before and after 8 hours' exposure to 6-hydroxydopamine. Approximately 1200 transcripts were significantly induced by 6-OHDA and approximately 500 of these are currently matched to known genes. Here, we categorize the regulated genes according to known functional activities and discuss their potential roles in neuron death and survival and in PD. We find induction of multiple death-associated genes as well as many with the capacity for neuroprotection. This suggests that survival or death of individual neurons in PD may reflect an integrated response to both protective and destructive gene changes. Our findings identify a number of regulated genes as candidates for involvement in PD and therefore as potential targets for therapeutic intervention. Such intervention may include both inhibiting the induction/activity of death-promoting genes and enhancing those with neuroprotective activity.

sgk1, a member of an RNA cluster associated with cell death in a model of Parkinson's disease

In an effort to gain deeper insight into the molecular processes underlying neurodegeneration in Parkinson's disease, we performed gene expression profiling at several early time points after MPTP-injection into old (1-year) mice. We used a PCR-based gene expression profiling method, digital expression pattern display (DEPD), a method of very high sensitivity and reproducibility, which displays almost all transcripts of a tissue. To identify cell death-associated genes, we defined clusters of differentially expressed transcripts with expression behaviour that correlated with the temporal profile of cell death progression and characterized one of these cell death clusters further. We selected one of the strongest regulated genes, the serum and glucocorticoid-regulated kinase 1 (sgk1), and validated its differential expression by Northern blot analysis, semiquantitative PCR and in situ hybridization. Up-regulation of sgk1 (i) coincides with the onset of dopaminergic cell death in both the 8-week acute and 1-year subacute MPTP models, (ii) spans the entire brain, (iii) is attenuated by the l-deprenyl-mediated inhibition of the MPTP conversion to its active metabolite MPP+ and (iv) is not induced by dehydration. This study demonstrated that the combination of the DEPD technology, clustering analysis and a detailed histopathology is a useful tool for elucidating molecular pathways in neurodegenerative diseases.

Administration of haloperidol with biperiden reduces mRNAs related to the ubiquitin-proteasome system in mice

In order to find molecules affected by administration of an antipsychotic drug with an antimuscarinic drug, which is a common prescription used to prevent extrapyramidal adverse effects caused by the antipsychotic drugs, gene expression profiling in the frontal cortex was studied in mice. After 14 days of administration with 2 mg/kg haloperidol, a typical antipsychotic drug, and 2 mg/kg biperiden, a high-affinity antagonist for muscarinic receptors in the brain, approximately 500 mRNAs related to synaptic function were investigated. The levels of the mRNAs related to the ubiquitin-related systems were significantly reduced after the combined administration. However, the separate administration of either haloperidol or biperiden had little effect on the levels of the mRNAs. This result suggests that coadministration of haloperidol and biperiden specifically affects the ubiquitin-related system.