Inhibition of p38 mitogen-activated protein kinase-induced apoptosis in cultured mature oligodendrocytes using SB202190 and SB203580

Icaritin Promotes Myelination by Simultaneously Enhancing the Proliferation and Differentiation of Oligodendrocyte Precursor Cells

Myelin repair, which is known as remyelination, is critical to the treatment of neurodegenerative diseases, and myelination depends on not only the differentiation of oligodendrocyte precursor cells toward oligodendrocytes but also the renewal of oligodendrocyte precursor cells under pathological conditions. However, simultaneously promoting the differentiation and proliferation of oligodendrocyte precursor cells in lesions remains an unmet challenge and might affect demyelinating diseases. Kidney-tonifying herbs of traditional Chinese medicine (TCM) are effective in improving the symptoms of degenerative patients. However, herbs or compounds with dual functions are unverified. The purpose of this study was to find a kidney-tonifying TCM that synchronously improved the differentiation and proliferation of oligodendrocyte precursor cells under pathological conditions. Compounds with dual functions were screened from highly frequently used kidney-tonifying TCM, and the effects of the obtained compound on remyelination were investigated in an in vitro oligodendrocyte precursor cell differentiation model under pathological conditions and in demyelinating mice in vivo. The compound icaritin, which is an active component of Yin-Yang-Huo (the leaves of Epimedium brevicornu Maxim), demonstrated multiple effects on the remyelination process, including enhancing oligodendrocyte precursor cell proliferation, facilitating the differentiation of neural progenitor cells toward oligodendrocyte precursor cells and further toward oligodendrocytes, and maturation of oligodendrocytes under corticosterone- or glutamate-induced pathological conditions. Importantly, icaritin effectively rescued behavioral functions and increased the formation of myelin in a cuprizone-induced demyelination mouse model. The multiple effects of icaritin make it a promising lead compound for remyelination therapy.

Understanding Abnormal c-JNK/p38MAPK Signaling Overactivation Involved in the Progression of Multiple Sclerosis: Possible Therapeutic Targets and Impact on Neurodegenerative Diseases

Demyelination, immune dysregulation, and neuroinflammation are the most common triggers of motor neuron disorders such as multiple sclerosis (MS). MS is a chronic demyelinating neurodegenerative disease of the central nervous system caused by abnormal immune activation, which causes myelin sheath damage. Cell signal transduction pathways are required for a variety of physiological and pathological processes in the brain. When these signaling systems become overactive, they can lead to disease progression. In various physiological conditions, abnormal mitogen-activated protein kinase (MAPK) activation is associated with several physiological dysfunctions that cause neurodegeneration. Previous research indicates that c-JNK and p38MAPK signaling play critical roles in neuronal growth and differentiation. c-JNK/p38MAPK is a member of the MAPK family, which regulates metabolic pathways, cell proliferation, differentiation, and apoptosis that control certain neurological activities. During brain injuries, c-JNK/p38MAPK also affects neuronal elastic properties, nerve growth, and cognitive processing. This review systematically linked abnormal c-JNK/p38MAPK signaling activation to multiple neuropathological pathways in MS and related neurological dysfunctions. MS progression is linked to genetic defects, oligodendrocyte destruction, glial overactivation, and immune dysregulation. We concluded that inhibiting both the c-JNK/p38MAPK signaling pathways can promote neuroprotection and neurotrophic effects against the clinical-pathological presentation of MS and influence other neurological disorders. As a result, the potential benefits of c-JNK/p38MAPK downregulation for the development of disease-modifying treatment interventions in the future could include MS prevention and related neurocomplications.

Cell-permeable p38 MAP kinase protects adult hippocampal neurons from cell death

p38 mitogen-activated protein (MAP) kinase (p38) is a member of the MAP kinase family. Previous reports using p38 chemical inhibitors have suggested that its activation contributes to hippocampal neuronal cell death rather than cell survival. In this study, we used both a cell-permeable p38 protein containing the HIV protein transduction domain (PTD) and cultured adult hippocampal neurons, which were differentiated from cultured adult hippocampal neural stem/progenitor cells (NPCs), to evaluate the direct function of p38 on adult hippocampal neurons. Our immunocytochemical experiments demonstrated that wild-type cell-permeable p38 protein prevents cell death of adult hippocampal neurons induced by a low glucose condition. Our findings indicate that cell-permeable p38 protein may be useful in preventing the degeneration of higher brain function occurring through hippocampal neuronal cell death, and furthermore, that the maintenance of intracellular p38 levels could be another therapeutic target for neurodegenerative diseases such as Alzheimer's disease (AD).

The p38α MAPK Deletion in Oligodendroglia does not Attenuate Myelination Defects in a Mouse Model of Periventricular Leukomalacia

Periventricular leukomalacia (PVL) is a severe type of white matter damage in premature infants and the most common cause of cerebral palsy. It is generally known to be caused by hypoxia and inflammation. Currently there is no effective treatment available, in part due to that the pathogenesis of the disease has not been well understood. The p38α mitogen-activated protein kinase (MAPK) is the serine/threonine kinase and several in vitro studies demonstrated that p38 MAPK is essential for oligodendroglial differentiation and myelination. Indeed, our nerve/glial antigen 2 (NG2)-specific oligodendroglial p38α MAPK conditional knockout (CKO) mice revealed its complex roles in myelination and remyelination. To identify the specific in vivo roles of oligodendroglial p38α MAPK in PVL, we generated a mouse PVL model by combination of LPS-mediated inflammation and hypoxia-ischemia in NG2-p38α MAPK CKO mice. Our results demonstrate that a selective deletion of p38α MAPK in oligodendrocyte did not attenuate myelination defects in the mouse model of PVL. Myelination phenotype revealed by MBP immunostaining was not significantly affected in the p38α MAPK CKO mice compared to the wildtype after PVL induction. The electron microscopic images demonstrated that the microstructure of myelin structures was not significantly different between the wild-type and p38α MAPK CKO mice. In addition, oligodendrocyte degeneration in the corpus callosum white matter area was unaffected in the p38α MAPK CKO during and after the PVL induction. These data indicate that p38α MAPK in oligodendrocyte has minimal effect on myelination and oligodendrocyte survival in the mouse PVL model.

Suppression of Nestin reveals a critical role for p38-EGFR pathway in neural progenitor cell proliferation

The expression of intermediate filament Nestin is necessary for the neural progenitor cells (NPCs) to maintain stemness, but the underlying cellular and molecular mechanism remains unclear. In this study, we demonstrated that Nestin is required for the self-renew of NPCs through activating MAPK and EGFR pathways. Knockdown of Nestin by shRNA inhibited cell cycle progression and proliferation in mouse NPCs. Moreover, suppression of Nestin reduced expression of the epidermal growth factor receptor (EGFR) in NPCs and inhibited the mitogenic effects of EGF on these cells. Treatment of NPCs with p38-MAPK inhibitor PD169316 reversed cell cycle arrest caused by the knockdown of Nestin. Our findings indicate that Nestin promotes NPC proliferation via p38-MAPK and EGFR pathways, and reveals the necessity of these pathways in NPCs self-renewal.

Cell-permeable p38 MAP kinase promotes migration of adult neural stem/progenitor cells

Endogenous neural stem/progenitor cells (NPCs) can migrate toward sites of injury, but the migration activity of NPCs is insufficient to regenerate damaged brain tissue. In this study, we showed that p38 MAP kinase (p38) is expressed in doublecortin-positive adult NPCs. Experiments using the p38 inhibitor SB203580 revealed that endogenous p38 participates in NPC migration. To enhance NPC migration, we generated a cell-permeable wild-type p38 protein (PTD-p38WT) in which the HIV protein transduction domain (PTD) was fused to the N-terminus of p38. Treatment with PTD-p38WT significantly promoted the random migration of adult NPCs without affecting cell survival or differentiation; this effect depended on the cell permeability and kinase activity of the fusion protein. These findings indicate that PTD-p38WT is a novel and useful tool for unraveling the roles of p38, and that this protein provides a reasonable approach for regenerating the injured brain by enhancing NPC migration.

Clematichinenoside Serves as a Neuroprotective Agent Against Ischemic Stroke: The Synergistic Action of ERK1/2 and cPKC Pathways

There are numerous evidences suggesting that inhibition of apoptosis of neurons play a critical role in preventing the damage and even death of neurons after brain ischemia/reperfusion, which shows therapeutic potential for clinical treatment of brain injury induced by stroke. In this study, we aimed to investigate the neuroprotective effect of Clematichinenoside (AR) and its underlying mechanisms. MCAO mode was performed in rats and OGD/R model in primary cortical neurons to investigate the neuroprotective effect of AR. The rate of apoptotic cells was measured using TUNEL assay in cerebral cortex and flow cytometric assay in cortical neurons. Apoptosis-related proteins such as bcl-2, bcl-xl, and bax and the phosphorylation of ERK1/2, cPKC, p90RSK, and CREB in ischemic penumbra were assayed by western blot. Furthermore, we made a thorough inquiry about how these proteins play roles in the anti-apoptotic mechanism using targets-associated inhibitors step by step. The results revealed that AR could activate both ERK1/2 and cPKC which resulted in p90RSK phosphorylation and translocation into the nucleus. Moreover, CREB, a downstream target of p90RSK, was phosphorylated and then bound to cAMP-regulated enhancer (CRE) to activate apoptosis-related genes, and finally ameliorate ischemic stroke through preventing neuron death. In conclusion, these data strongly suggest that AR could be used as an effective neuroprotective agent to protect against ischemic stroke after cerebral I/R injury through regulating both ERK1/2 and cPKC mediated p90RSK/CREB apoptotic pathways.

Neuroprotection effect of Y-27632 against H2O2-induced cell apoptosis of primary cultured cortical neurons

Y-27632 protects the cortical neurons from H₂O₂-induced apoptosis by inhibiting oxidative stress and activation of JNK and p38 MAPKs pathways.

The p38α mitogen-activated protein kinase is a key regulator of myelination and remyelination in the CNS

The p38α mitogen-activated protein kinase (MAPK) is one of the serine/threonine kinases regulating a variety of biological processes, including cell-type specification, differentiation and migration. Previous in vitro studies using pharmacological inhibitors suggested that p38 MAPK is essential for oligodendrocyte (OL) differentiation and myelination. To investigate the specific roles of p38α MAPK in OL development and myelination in vivo, we generated p38α conditional knockout (CKO) mice under the PLP and nerve/glial antigen 2 (NG2) gene promoters, as these genes are specifically expressed in OL progenitor cells (OPCs). Our data revealed that myelin synthesis was completely inhibited in OLs differentiated from primary OPC cultures derived from the NG2 Cre-p38α CKO mouse brains. Although an in vivo myelination defect was not obvious after gross examination of these mice, electron microscopic analysis showed that the ultrastructure of myelin bundles was severely impaired. Moreover, the onset of myelination in the corpus callosum was delayed in the knockout mice compared with p38α fl/fl control mice. A delay in OL differentiation in the central nervous system was observed with concomitant downregulation in the expression of OPC- and OL-specific genes such as Olig1 and Zfp488 during early postnatal development. OPC proliferation was not affected during this time. These data indicate that p38α is a positive regulator of OL differentiation and myelination. Unexpectedly, we observed an opposite effect of p38α on remyelination in the cuprizone-induced demyelination model. The p38α CKO mice exhibited better remyelination capability compared with p38α fl/fl mice following demyelination. The opposing roles of p38α in myelination and remyelination could be due to a strong anti-inflammatory effect of p38α or a dual reciprocal regulatory action of p38α on myelin formation during development and on remyelination after demyelination.

The role of mitogen-activated protein kinase in cadmium-induced primary rat cerebral cortical neurons apoptosis via a mitochondrial apoptotic pathway

Cadmium (Cd) is an extremely toxic metal capable of severely damaging several organs, including the brain. Studies have shown that Cd induces neuronal apoptosis partially by activating the mitogen-activated protein kinase (MAPK) pathways. However, the underlying mechanism of MAPK involving the mitochondrial apoptotic pathway in neurons remains unclear. In this study, primary rat cerebral cortical neurons were exposed to Cd, which significantly decreased cell viability and the B-cell lymphoma 2/Bcl-2 associate X protein (Bcl-2/Bax) ratio and increased the percentage of apoptotic cells, release of cytochrome c, cleavages of caspase-3 and poly (ADP-ribose) polymerase (PARP), and nuclear translocation of apoptosis-inducing factor (AIF). In addition, Cd induced phosphorylation of extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK) and p38 MAPK. Inhibition of ERK and JNK, but not p38 MAPK, partially protected the cells from Cd-induced apoptosis. ERK and JNK inhibition also blocked alteration of the Bcl-2/Bax ratio, release of cytochrome c, cleavages of caspase-3 and PARP, and nuclear translocation of AIF. Taken together, these data suggest that the ERK- and JNK-mediated mitochondrial apoptotic pathways play important roles in Cd-induced neuronal apoptosis.

Activation of PPAR-γ and PTEN cascade participates in lovastatin-mediated accelerated differentiation of oligodendrocyte progenitor cells

Previously, we and others documented that statins including-lovastatin (LOV) promote the differentiation of oligodendrocyte progenitor cells (OPCs) and remyelination in experimental autoimmune encephalomyelitis (EAE), an multiple sclerosis (MS) model. Conversely, some recent studies demonstrated that statins negatively influence oligodendrocyte (OL) differentiation in vitro and remyelination in a cuprizone-CNS demyelinating model. Therefore, herein, we first investigated the cause of impaired differentiation of OLs by statins in vitro settings. Our observations indicated that the depletion of cholesterol was detrimental to LOV treated OPCs under cholesterol/serum-deprived culture conditions similar to that were used in conflicting studies. However, the depletion of geranylgeranyl-pp under normal cholesterol homeostasis conditions enhanced the phenotypic commitment and differentiation of LOV-treated OPCs ascribed to inhibition of RhoA-Rho kinase. Interestingly, this effect of LOV was associated with increased activation and expression of both PPAR-γ and PTEN in OPCs as confirmed by various pharmacological and molecular based approaches. Furthermore, PTEN was involved in an inhibition of OPCs proliferation via PI3K-Akt inhibition and induction of cell cycle arrest at G1 phase, but without affecting their cell survival. These effects of LOV on OPCs in vitro were absent in the CNS of normal rats chronically treated with LOV concentrations used in EAE indicating that PPAR-γ induction in normal brain may be tightly regulated-providing evidences that statins are therapeutically safe for humans. Collectively, these data provide initial evidence that statin-mediated activation of the PPAR-γ-PTEN cascade participates in OL differentiation, thus suggesting new therapeutic-interventions for MS or related CNS-demyelinating diseases.

Mechanisms of regulation of oligodendrocyte development by p38 mitogen-activated protein kinase

Many extracellular and intrinsic factors regulate oligodendrocyte development, but their signaling pathways remain poorly understood. Although the p38 mitogen-activated protein kinase (MAPK)-dependent pathway is implicated in oligodendrocyte progenitor cell (OPC) lineage progression, its molecular targets involved in myelinogenesis are mostly unidentified. We have analyzed mechanisms by which p38MAPK regulates oligodendrocyte development and demonstrate that p38MAPK inhibition prevents OPC lineage progression and inhibits MBP (myelin basic protein) promoter activity and Sox10 function. In white-matter tissue, differential levels of MAPK phosphorylation are observed in oligodendrocyte lineage cells. Phosphorylated p38MAPK was found in CC1- and CNP-expressing differentiated oligodendrocytes of the adult brain and was temporally associated with a decline in the levels of phosphorylated extracellular signal-regulated kinase (ERK) in cells of this lineage. PDGF stimulates the phosphorylation of ERK, p38MAPK, and c-Jun N-terminal kinase (JNK), and p38MAPK inhibition was associated with increased ERK, JNK, and c-Jun phosphorylation. In the presence of PDGF, simultaneous inhibition of p38MAPK and either MAPK kinase (MEK) or JNK significantly alleviates the repression of myelin gene expression and lineage progression induced by p38MAPK inhibition alone. Dominant-negative c-Jun reverses the inhibition of myelin promoter activity by active MEK1 or dominant-negative p38MAPKalpha mutants, and phosphorylated c-Jun was detected at the MBP promoter after p38MAPK inhibition, indicating c-Jun as a negative mediator of p38MAPK action. Our findings indicate that p38MAPK activity in the brain supports myelin gene expression through distinct mechanisms via positive and negative regulatory targets. We show that oligodendrocyte differentiation involves p38-mediated Sox10 regulation and cross talk with parallel ERK and JNK pathways to repress c-Jun activity.

The role of p38 MAPK in valproic acid induced microglia apoptosis

Valproic acid (VPA), a widely prescribed drug for seizures and bipolar disorder, induces apoptosis in microglia, but the underlying mechanism by which microglia apoptosis in response to VPA is not yet known. In this study, we found that the mitochondrial pathway played an important role in VPA-induced apoptosis in both BV-2 microglia and mouse primary microglial cells. In addition, VPA increased the level of phospho-p38 mitogen-activated protein kinase (MAPK), but had no effects on phospho-ERK and phospho-JNK MAPKs. Moreover, p38 inhibitor SB203580 strongly inhibited VPA-induced apoptosis and caspase-3 activation. Taken together, our results clearly demonstrated that VPA could induce apoptosis of microglia via p38 MAPK and mitochondrial apoptosis pathway.

p38 mitogen-activated protein kinase promotes cell survival in response to DNA damage but is not required for the G(2) DNA damage checkpoint in human cancer cells

p38 mitogen-activated protein kinase (MAPK) is rapidly activated by stresses and is believed to play an important role in the stress response. While Chk1 is known to mediate G(2) DNA damage checkpoint control, p38 was also reported to have an essential function in this checkpoint control. Here, we have investigated further the roles of p38 and Chk1 in the G(2) DNA damage checkpoint in cancer cells. We find that although p38 activation is strongly induced by DNA damage, its activity is not required for the G(2) DNA damage checkpoint. In contrast, Chk1 kinase is responsible for the execution of G(2) DNA damage checkpoint control in p53-deficient cells. The inhibition of p38 activity has no effect on Chk1 activation and gamma-H2AX expression. Global gene expression profiling of cancer cells in response to tumor necrosis factor alpha (TNF-alpha) revealed that p38 plays a strong prosurvival role through the coordinated downregulation of proapoptotic genes and upregulation of prosurvival genes. We show that the inhibition of p38 activity during G(2) DNA damage checkpoint arrest triggers apoptosis in a p53-independent manner with a concurrent decrease in the level of Bcl2 family proteins. Our results suggest that although p38 MAPK is not required for the G(2) DNA damage checkpoint function, it plays an important prosurvival role during the G(2) DNA damage checkpoint response through the upregulation of the Bcl2 family proteins.

A role for the MAPK/ERK pathway in oligodendroglial differentiation in vitro: stage specific effects on cell branching

The mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) pathway is important for both long-term survival and timing of the progression of oligodendrocyte differentiation. Oligodendroglial cells treated with MEK inhibitor were distinguished by using stage specific markers: NG2 proteoglycan, A2B5, 2'3'nucleotide-cyclic 3'phosphodiesterase (CNPase) and myelin basic protein (MBP), and classified according to their morphology into different developmental stages. Treatment significantly increased the number of cells with more immature morphologies and decreased the number of mature cells. Furthermore, it increased the number of rounded cells that could not be classified into any of the oligodendroglial developmental stages. The strongest effects were usually observed shortly after treatment. Rounded cells were CNPase/MBP positive and they were not stained by anti-NG2 or A2B5, indicating that they were mature cells unable either to extend and/or to maintain their processes. These data showed an effect of the MAPK/ERK pathway on oligodendroglial branching, with possible consequences for the formation of the myelin sheath.

Simultaneous PKC and cAMP activation induces differentiation of human dental pulp stem cells into functionally active neurons

The plasticity of dental pulp stem cells (DPSCs) has been demonstrated by several studies showing that they appear to self-maintain through several passages, giving rise to a variety of cells. The aim of the present study was to differentiate DPSCs to mature neuronal cells showing functional evidence of voltage gated ion channel activities in vitro. First, DPSC cultures were seeded on poly-l-lysine coated surfaces and pretreated for 48h with a medium containing basic fibroblast growth factor and the demethylating agent 5-azacytidine. Then neural induction was performed by the simultaneous activation of protein kinase C and the cyclic adenosine monophosphate pathway. Finally, maturation of the induced cells was achieved by continuous treatment with neurotrophin-3, dibutyryl cyclic AMP, and other supplementary components. Non-induced DPSCs already expressed vimentin, nestin, N-tubulin, neurogenin-2 and neurofilament-M. The inductive treatment resulted in decreased vimentin, nestin, N-tubulin and increased neurogenin-2, neuron-specific enolase, neurofilament-M and glial fibrillary acidic protein expression. By the end of the maturation period, all investigated genes were expressed at higher levels than in undifferentiated controls except vimentin and nestin. Patch clamp analysis revealed the functional activity of both voltage-dependent sodium and potassium channels in the differentiated cells. Our results demonstrate that although most surviving cells show neuronal morphology and express neuronal markers, there is a functional heterogeneity among the differentiated cells obtained by the in vitro differentiation protocol described herein. Nevertheless, this study clearly indicates that the dental pulp contains a cell population that is capable of neural commitment by our three step neuroinductive protocol.

The p38(MAPK) signaling pathway regulates neuronal apoptosis through the phosphorylation of the retinoblastoma protein

We investigated the role of SB202190, a selective p38 mitogen-activated protein kinase (MAPK) inhibitor in cerebellar granule neurons (CGC) in response to serum potassium deprivation (S/K deprivation), an apoptotic stimulus. CGC apoptosis after S/K deprivation was shown to be mediated through cell cycle re-entry and the induction of transcription factor E2F-1. We found that SB 202190 (10muM) inhibits retinoblastoma protein (pRb) phosphorylation, in response to S/K deprivation. Moreover, the expression of cyclin E and E2F-1 were also significantly decreased. Interestingly, SB202190 did not affect or modulate the increase in the protein expression levels of cyclin D1. Similarly, p-Akt and p-GSK3 protein levels, measured after 12h S/K deprivation, did not appear to be regulated by SB 202190 (10muM). These data indicate that the neuroprotective effects of the p38 inhibitor were not mediated via Akt activation. In conclusion, these results suggest that p38MAPK converged with the cell cycle in S/K deprivation-induced apoptosis through pRb phosphorylation.

Lectin panning method: the prospective isolation of mouse neural progenitor cells by the attachment of cell surface N-glycans to Phaseolus vulgaris erythroagglutinating lectin-coated dishes

Retrospective isolation of neural progenitor cells (NPCs) may cause deterioration of the phenotype during the long-term cultivation. Therefore, prospective isolation is essential for understanding the exact characteristics of intact NPCs in the brain. However, few suitable specific cell surface antigens on NPCs that could be used for their prospective isolation are available. The present study demonstrated that within 60 min after initial plating, embryonic day 12 (E12) brain cells firmly attach to several types of lectin-coated culture wells, including Phaseolus vulgaris erythroagglutinating lectin (E-PHA), concanavalin A (Con A) and wheat germ agglutinin (WGA). Approximately 80% of the cells isolated from E-PHA-coated wells expressed the nestin antigen, which is a specific intracellular marker for NPCs and the ratio of 5-bromo-2'-deoxyuridine (BrdU)-positive/nestin-positive cells to the cells attached on the E-PHA-coated wells was significantly higher than that of the cells attached on the wells coated with other adhesive substrates. The cells that were isolated from the E-PHA-coated wells continued to attach to the well for 1 week, while those isolated from Con A- and WGA-coated wells lost their attachment after 6 days and 1 day, respectively. Furthermore, the cells isolated from the E-PHA-coated wells grew quite satisfactorily and formed numerous attached neurospheres. Their growth rate was almost equal to that observed in suspension cultures. These results indicate that the lectin panning method enables the prospective, quick and easy isolation of mouse NPCs without requiring a fluorescence-activated cell sorter (FACS) system.

Inhibitors of p38 mitogen-activated protein kinase enhance proliferation of mouse neural stem cells

The p38 mitogen-activated protein kinase (MAPK) is induced in response to environmental stress. Although p38 MAPK has been implicated in diverse cellular processes, including cell proliferation, differentiation, and survival of differentiated cells in the central nervous system (CNS), the expression profile and roles of p38 MAPK in the developing brain remain largely unknown. In the present study, we demonstrate that p38 MAPK is expressed predominantly in nestin-positive cells in the cerebral cortex in embryonic day 10 (E10) brain and that expression of the protein decreases gradually during development. To investigate the roles of p38 MAPK in the embryonic brain, two selective p38 MAPK inhibitors, SB202190 and SB203580, were added to the primary neuronal cultures from E10-E14 brains. After 7 days of exposure to these inhibitors, but not SB202474, a negative analog of SB203580, numerous large neurospheres were present. MAPK inhibitors also selectively increased the growth rate of neural stem cells (NSCs) purified from secondary neurospheres and the number of bromodeoxyuridine-positive NSCs. Thus, p38 MAPK inhibitors are potent stimulators of NSC proliferation, and p38 MAPK may be an intrinsic negative regulator of NSC proliferation during early brain development.

Differential crosstalk between P2X7 and arachidonic acid in activation of mitogen-activated protein kinases

Accumulating evidence indicates that astroglial syncytium plays key role in normal and pathological brain functions. Astrocytes both in vitro and in situ respond to extracellular adenine-based nucleotides via the activation of P2 receptors. Massive release of ATP from neurons and glial cells occurs as a result of pathological conditions of the brain leading to neuroinflammation and involving P2X7 receptors. In this study, we investigated whether P2X7 stimulation on cultured cortical astrocytes promoted a differential activation of mitogen-activated protein kinases (MAPKs), and whether the second messenger arachidonic acid (AA), which is also a key modulator of neuroinflammation, affected the P2X7-mediated MAPK phosphorylation. The results show that the synthetic P2X7 receptor agonist 2',3'-O-(4-benzoyl)benzoyl-ATP (BzATP), induced a concentration-dependent phosphorylation of MAPK ERK1/2, JNK and p38. Stimulation of ERK1/2, JNK and p38 phosphorylation was also obtained by pathophysiological levels of extracellularly applied AA. Interestingly, a robust potentiation of ERK1/2 phosphorylation was elicited by co-application of BzATP and AA, whereas no differences were observed in JNK or p38 phosphosignals. The kinases activation showed a differential dependence on the presence of extracellular Ca(2+). The potentiation of BzATP-mediated ERK1/2 phosphorylation was also observed in human embryonic kidney cells (HEK293) stably transfected with rat P2X7, but not in HEK cells expressing truncated P2X7 receptor lacking the full cytoplasmic carboxy-terminal or in those carrying the structurally related rat P2X2. AA and BzATP synergism in ERK1/2 activation was abolished by cyclo-oxygenase and lipoxygenase pathway inhibitors. The result that ERK1/2-mediated transduction pathway is synergistically modulated by ATP and AA signalling depicts possible novel pharmacological targets for interfering with pathological activation of astroglial cells.

The alpha1D-adrenergic receptor induces vascular smooth muscle apoptosis via a p53-dependent mechanism

Activation of the endogenous alpha1-adrenergic receptor (AR) associated with human aortic smooth muscle cells resulted in a dose- and time-dependent increase in the levels of mitochondrial reactive oxygen species (ROS). ROS increases were apparent within 10 min and maximal after 45 min. Prolonged activation (>4 h) of the alpha1-AR resulted in smooth muscle cell apoptosis. Both the increase in ROS and apoptotic cell death were blocked by the nonselective alpha1-AR antagonist prazosin as well as the selective alpha1D-AR antagonist 8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4.5]decane-7, 9-dione (BMY 7378). Increases in ROS and apoptosis produced by alpha1-AR activation were also blocked by the p38 mitogen-activated protein kinase inhibitor 4-(4-fluorophenyl)-2-(4-hydroxyphenyl)-5-(4-pyridyl)-1H-imidazole (SB 202190) and the NAPDH oxidase inhibitor apocynin. The extracellular signal-regulated kinase 1/2 inhibitor 2'-amino-3'-methoxyflavone (PD 98059) or the c-Jun NH2-terminal kinase inhibitor 1, 9-pyrazoloanthrone anthra(1, 9-cd)pyrazol-6(2H)-one (SP 600125) was without effect on increases in ROS levels or apoptosis. Pifithrin-alpha, an inhibitor of the tumor suppressor protein p53, had no effect on ROS generation but did block alpha1D-AR-induced apoptosis. Activation of the alpha1D-AR resulted in translocation of p53 to the mitochondria. The mitochondrial translocation of p53 was blocked by prazosin, BMY 7378, apocynin, SB 202190, and pifithrin-alpha. Apoptosis was also blocked by small interfering RNA directed against p53. These data show that the alpha1D-AR is coupled to the generation of mitochondrial ROS by a pathway involving p38 and NADPH oxidase. Sustained activation of the alpha1D-AR results in smooth muscle cell apoptosis in a pathway that involves the tumor suppressor protein p53 and the mitochondrial translocation of p53. The data also provide evidence of a linkage between the alpha1D-AR and p53.

p38 Mitogen-activated protein kinase regulates myelination

The p38 mitogen-activated protein kinase family is emerging as a crucial signaling molecule for a vast number of cellular functions including cell migration, proliferation, and differentiation. The function of p38 in myelination has only been recently addressed. Using pyridinyl imidazole-based p38 alpha/beta selective inhibitors, we have reported a critical role for this kinase in the regulation of myelination, specifically, in controlling the differentiation of Schwann cells, and oligodendrocytes, the myelinating glia of the peripheral and central nervous systems, respectively. These compounds inhibited the accumulation of myelin-cell-specific markers, including myelin-specific glycosphingolipids, myelin-associated glycoprotein, and myelin basic protein. More significantly, myelination of dorsal root ganglia neurons by oligodendrocytes was irreversibly blocked by p38 inhibitors. Our current studies are focusing on the molecular mechanisms by which p38 regulates oligodendrocyte and Schwann cell differentiation and its role in models of myelination and remyelination.

JC virus agnoprotein inhibits in vitro differentiation of oligodendrocytes and promotes apoptosis

Productive infection of oligodendrocytes, which are responsible for the formation of myelin sheath in the central nervous system, with the human neurotropic virus JC virus (JCV) causes the fatal demyelinating disease progressive multifocal leukoencephalopathy (PML). In addition to encoding T antigen and the capsid proteins, which are produced at the early and late phases of the infection cycle, respectively, JCV encodes a small regulatory protein named agnoprotein that is important for successful completion of the virus life cycle. Here we used bipotential CG-4 cells to examine the impact of agnoprotein on oligodendrocyte differentiation and survival in the absence of JCV lytic infection. We demonstrate that the expression of agnoprotein delayed the formation of complex outgrowth networks of the cells during oligodendrocyte differentiation. These alterations were accompanied by high levels of DNA damage, induction of proapoptotic proteins, and suppression of prosurvival signaling. Accordingly, apoptosis was significantly increased upon the induction of CG-4 cells toward differentiation in cells expressing agnoprotein. These observations provide the first evidence for the possible involvement of agnoprotein, independent from its role in viral replication, in a series of biological events that may contribute to the pathological features seen in PML lesions.