Interleukin-1alpha stimulates non-amyloidogenic pathway by alpha-secretase (ADAM-10 and ADAM-17) cleavage of APP in human astrocytic cells involving p38 MAP kinase

Interleukin-1alpha (IL-1alpha) stimulates a disintegrin and metalloproteinase, ADAM-17 synthesis, consistent with activation of the soluble fragment of Amyloid Precursor Protein, APP, (sAPPalpha) in human primary astrocytes. To characterize the mechanism by which IL-1alpha promotes the non-amyloidogenic pathway of APP metabolism, we used U373 MG astrocytoma cells. IL-1alpha significantly increased levels of ADAM-10 and ADAM-17 mRNA in 16 hr. Upregulation of ADAM-17 mRNA by IL-1alpha was more pronounced despite higher basal levels of ADAM-10 mRNA. This pattern was also observed at the protein level with the upregulation of alpha-secretase. RNA interference (RNAi) of ADAM-10 and ADAM-17 inhibited IL-1alpha-stimulated sAPPalpha release and the effect was more pronounced with ADAM-17 RNAi. Concomitantly, the level of sAPPalpha was significantly increased by IL-1alpha in 48 hr; however, IL-1alpha stimulated cell-associated APP levels maximally at 6 h but the induction declined at 48 hr. IL-1alpha treatment of cells for 48 h reduced both intracellular and secreted levels of amyloid-beta, Abeta-40, and Abeta-42 peptides. Multiple MAP kinases (MAPK), including MEK/ERK, p38 kinase, PI3 kinase (PI3K) but not JNK were involved in the regulation of IL-1alpha-stimulated alpha-secretase activity and sAPPalpha release. p38 MAPK seems to be the most proximal of these MAPKs, as it was the earliest to be activated by IL-1alpha and blocking this pathway attenuated activation of IL-1alpha-induced MEK and PI3K pathways. Our data show a complex mechanism of sAPPalpha regulation by IL-1alpha that involves ADAM-10, ADAM-17 and p38 MAPK upstream of MEK and PI3K.     

Vitamin E suppression of microglial activation is neuroprotective

Neurotoxic microglial-neuronal interactions have been implicated in the pathogenesis of various neurodegenerative diseases such as Alzheimer's disease, and vitamin E has been shown to have direct neuroprotective effects. To determine whether vitamin E also has indirect neuroprotective effects through suppression of microglial activation, we used a microglial-neuronal coculture. Lipopolysaccharide (LPS) treatment of a microglial cell line (N9) induced a time-dependent activation of both p38 mitogen-activated protein kinase (p38 MAPK) and nuclear factor-kappaB (NFkappaB), with consequent increases in interleukin-1alpha (IL-1alpha), tumor necrosis factor-alpha (TNF-alpha), and nitric oxide (NO) production. Differentiated neuronal cells (PC12 cells treated with nerve growth factor) exhibited marked loss of processes and decreased survival when cocultured with LPS-activated microglia. Preincubation of microglia with vitamin E diminished this neurotoxic effect, independently of direct effects of the antioxidant on the neuronal cells. Microglial NO production and the induction of IL-1alpha and TNFalpha expression also were attenuated by vitamin E. Such antiinflammatory effects of vitamin E were correlated with suppression of p38 MAPK and NFkappaB activation and were mimicked by an inhibition of either p38 MAPK (by SB203580) or NFkappaB (by decoy oligonucleotides). These results suggest that, in addition to the beneficial effects of providing direct antioxidant protection to neurons reported by others, vitamin E may provide neuroprotection in vivo through suppression of signaling events necessary for microglial activation.     

Heat shock induces neurite outgrowth in PC12m3 cells via the p38 mitogen-activated protein kinase pathway

We investigated the role of the p38 mitogen-activated protein kinase (MAPK) pathway in heat-shock-induced neurite outgrowth of PC12 mutant cells in which nerve growth factor (NGF)-induced neurite outgrowth is impaired. When cultures of the PC12 mutant (PC12m3) cells were exposed to heat stress at 44 degrees C for 10 min, activity of p38 MAPK increased and neurite outgrowth was greatly enhanced. The neurite extension was inhibited by the p38 MAPK inhibitor BS203580. Longer heat treatment of PC12m3 cells provoked cell death, which was enhanced by SB203580. These findings suggest that heat-induced activation of p38 MAPK is responsible for the neurite outgrowth and survival of PC12m3 cells.     

Inhibition of p38 mitogen activated protein kinase activation and mutant SOD1(G93A)-induced motor neuron death

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder characterized by the selective loss of motor neurons. Stress activated protein kinases (SAPK) have been suggested to play a role in the pathogenesis of ALS. We studied the relevance of p38 MAPK for motor neuron degeneration in the mutant SOD1 mouse. Increased levels of phospho-p38 MAPK were present in the motor neurons and microglia of the ventral spinal cord. The p38 MAPK-inhibitor, SB203580, completely inhibited mutant SOD1-induced apoptosis of motor neurons and blocked LPS-induced activation of microglia. Semapimod, a p38 MAPK inhibitor suitable for clinical use, prolonged survival of mutant SOD1 mice to a limited extent, but largely protected motor neurons and proximal axons from mutant SOD1-induced degeneration. Our data confirm the abnormal activation of p38 MAPK in mutant SOD1 mice and the involvement of p38 MAPK in mutant SOD1-induced motor neuron death. We demonstrate the effect of p38 MAPK inhibition on survival of mutant SOD1 mice and reveal a dissociation between the effect on survival of motor neurons and that on survival of the animal, the latter likely depending on the integrity of the entire motor axon.     

Administration of the p38 MAPK inhibitor SB203580 affords brain protection with a wide therapeutic window against focal ischemic insult

We have reported previously the delayed and differential induction of p38alpha and p38beta mitogen-activated protein kinases (MAPKs) in microglia and astrocytes, respectively, in brain after transient global ischemia. We report here the sustained induction and activation of p38alpha MAPK in activating microglia in rat brain after transient middle cerebral artery occlusion (MCAO). The intraventricular administration of SB203580, a p38 MAPK inhibitor, 30 min before MCAO reduced the infarct volume to 50% of the control, which was accompanied by the significant improvement of neurological deficits. More interestingly, the infarct volume was reduced to 72% and 77% when SB203580 was administered 6 hr and 12 hr after MCAO, respectively. The induction of various factors involved in inflammatory processes, such as inducible nitric oxide synthase (iNOS), tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta) and cyclooxygenase-2 (COX-2), was suppressed by the administration of SB203580 at 6 hr after MCAO. These results suggest that sustained activation of p38 MAPK pathway and p38 MAPK-associated inflammatory processes play a crucial role in postischemic brain.     

Inhibition of delayed induction of p38 mitogen-activated protein kinase attenuates kainic acid-induced neuronal loss in the hippocampus

The activation of p38 mitogen-activated protein kinase (MAPK) has been implicated in the pathological changes accompanying inflammatory and apoptotic processes of various cell types including neurons. In a kainic acid (KA)-induced mouse seizure model, p38 MAPK is induced in reactive astrocytes in the CA3 region of the hippocampus where severe neuronal loss occurs. Here we report the delayed and protracted activation of p38 MAPK in the CA3 region of the hippocampus of mice treated with KA. In this model, the inhibition of p38 MAPK isoforms by SB203580, a specific inhibitor, attenuated neuronal loss in the CA3 and CA1 regions of the hippocampus, which was accompanied by the suppression of the p38 MAPK activation as well as astrogliosis. Thus, the delayed and sustained induction of p38 MAPK plays a crucial role in the neuronal damage of KA-induced brain seizures.     

Retinoic acid increases glucocorticoid receptor phosphorylation via cyclin-dependent kinase 5

Glucocorticoid receptor (GR) function is modulated by phosphorylation. As retinoic acid (RA) can activate some cytoplasmic kinases able to phosphorylate GR, we investigated whether RA could modulate GR phosphorylation in neuronal cells in a context of long-term glucocorticoid exposure.A 4-day treatment of dexamethasone (Dex) plus RA, showed that RA potentiated the (Dex)-induced phosphorylation on GR Serine 220 (_pSer220GR) in the nucleus of a hippocampal HT22 cell line. This treatment increased the cytoplasmic ratio of p35/p25 proteins, which are major CDK5 cofactors. Roscovitine, a pharmacological CDK5 inhibitor, or a siRNA against CDK5 prevented RA potentiation of GR phosphorylation.Furthermore, roscovitine counter-acted the effect of RA on GR sensitive target proteins such as BDNF or tissue-transglutaminase.These data help understanding the interaction between RA- and glucocorticoid-signalling pathways, both of which have strong influences on the adult brain.     

Polymorphonuclear leukocyte apoptosis is inhibited by platelet-released mediators, role of TGFbeta-1

Platelets regulate several polymorphonuclear leukocyte (PMN) functions. We have found that thrombin-stimulated platelets potently inhibited PMN apoptosis. Cell-free supernatant from increasing concentrations of stimulated platelets inhibited PMN apoptosis in a dose-dependent manner, with an effect similar to that of corresponding concentrations of platelets. At the plateau, platelet supernatant inhibited PMN apoptosis by 54.6 +/- 6.8%, the anti-apoptotic activity being higher than that of GM-CSF and comparable to that of LPS. Neither IL-1ra nor a combination of anti-IL1alpha + betamAb affected the activity of platelet supernatant. In contrast a mAb recognizing the active form of TGF-beta1 significantly decreased this activity. Moreover, exogenous TGF-beta1 inhibited PMN apoptosis in a dose-dependent manner. The active form of this cytokine was indeed present in the supernatant of stimulated platelets at a concentration able to elicit an anti-apoptotic effect. The p38 MAPK inhibitor SB203580 prevented the anti-apoptotic effect of TGF-beta1 in a dose-dependent manner. Interestingly, it also prevented the anti-apoptotic effect of IL-1alpha, but not that of GM-CSF, LPS and dexamethasone. In conclusion, we report for the first time that PMN apoptosis is potently inhibited by platelet-released mediators, that TGF-beta1 mediates an important part of this effect, and that p38 MAPK is involved in the TGF-beta1 signaling leading to its anti-apoptotic effect. These results provide novel evidence to support the central role of platelets in inflammation.     

Somatostatin and gamma-aminobutyric acid inhibit interleukin-1 beta-stimulated release of interleukin-6 from rat C6 glioma cells

OBJECTIVE: We investigated the ability of inhibitory neurotransmitters to alter the interleukin-1 beta (IL-1 beta)-stimulated release of interleukin-6 (IL-6) from cultured glial tumor cells. METHODS: C6 rat glioblastoma cells were exposed to either IL-1 beta or its putative second messenger lysophosphatidylcholine (LPC) in the absence or presence of the inhibitory neurotransmitters somatostatin (SRIF) or gamma-aminobutyric acid (GABA). Alternatively, C6 cells were pretreated with selective inhibitors of JNK or p38 and then exposed to either IL-1 beta or LPC to determine the relative involvement of these terminal stress kinases in the stimulation of IL-6 release. RESULTS: IL-1 beta promoted the release of IL-6 with a maximally effective concentration of 25 ng/ml. Both SRIF-14 and SRIF-28 comparably suppressed stimulated IL-6 release with an ED(50) of approximately 50 nM. GABA also prevented IL-1 beta-driven IL-6 release (ED(50) = 100 microM). IL-1 beta and LPC synergistically enhanced release of IL-6 in the presence of the beta-adrenergic receptor agonist isoproterenol (ISO); these effects were largely reversed by SRIF or GABA. The pyridinylimidazole inhibitor of p38, SB-203580, completely blocked stimulation of IL-6 release by IL-1 beta or LPC; conversely, the anthrapyrazolone JNK inhibitor, SP-600125, was ineffective in modifying stimulated IL-6 release. CONCLUSIONS: The effects of IL-1 beta and LPC on IL-6 release from glioma cells are effectively antagonized by the inhibitory neurotransmitters SRIF and GABA. On the basis of correlative studies, we propose that the ability of inhibitory transmitters such as SRIF and GABA to counter the induction of IL-6 release may entail suppression of p38 activity.     

Role of mitogen-activated protein kinases in inducible nitric oxide synthase and TNFalpha expression in human fetal astrocytes

Astrocytes are important sources of proinflammatory mediators such as iNOS and TNFalpha in the diseased central nervous system. In previous studies, we showed that the cytokine IL-1 plays a critical role in the activation of human astrocytes to express TNFalpha and the inducible form of nitric oxide synthase (iNOS). In the present study, we have addressed the role of the MAP-kinase pathway in the signaling events leading to the induction of these genes. Treatment with SB203580, a specific inhibitor of p38 mitogen-activated protein kinases (MAPK), potently inhibited IL-1-mediated induction of iNOS and TNFalpha in cultures of human fetal astrocytes. In contrast, PD98059, an upstream inhibitor of the extracellular regulated kinase (ERK)1/2 pathway, had little or no effect. Interestingly, SB203580 reduced the mRNA expression for iNOS, TNFalpha, and IL-6, indicating inhibition prior to translation. Transfection of astrocytes with a dominant-negative Jun-NH(2)-terminal kinase (JNK) construct also reduced iNOS expression. Western blot analysis showed phosphorylated p38 and JNK in IL-1-activated astrocytes, and phosphorylated ERK in both resting and activated cells. Electrophoretic mobility shift assay (EMSA) showed that IL-1 induced NF-kappaB and AP-1 DNA complex formation in astrocytes, and that SB203580 inhibited AP-1 complex formation. Taken together, these results demonstrate the differential roles played by the three MAP kinases in human astrocyte inflammatory gene activation and point to a crucial function of p38 and JNK MAP kinases in IL-1-mediated astrocyte activation.     

Regulation of the cyclooxygenase-2 system by interleukin-1beta through mitogen-activated protein kinase signaling pathways: a comparative study of human neuroglioma and neuroblastoma cells

Glial activation and inflammation following brain injury may initiate and maintain the process of neurodegeneration. Both glia and neurons synthesize proinflammatory mediators such as interleukin 1 beta (IL-1beta), cytosolic phospholipase A2 (cPLA2), cyclooxygenase-2 (COX-2), and prostaglandins. The molecular mechanisms by which IL-1beta regulates inflammatory genes such as cPLA2 and COX-2 in glial and neuronal cells are poorly understood. We have studied IL-1beta-mediated gene regulation in an established glial and neuronal human cell lines. We report that IL-1beta induced cPLA2 and COX-2 mRNA and protein expression and subsequent prostaglandin E2 (PGE2) release in a time-dependent manner in H4 neuroglioma cells. Both SB203580 and PD98059 [p38 and p42/44 mitogen-activated protein kinase (MAPKs) inhibitors, respectively] reduced IL-1beta-induced PGE2 production, while only SB203580 reduced both cPLA2 and COX-2 expression. Similarly, in SKNSH neuroblastoma cells, both SB203580 and PD98059 reduced IL-1beta-induced PGE2 release, with no detectable COX-2 and cPLA2 protein expression in these cells. Our results indicate that the signaling mechanisms of p38 and p42/44 MAPKs play a role in IL-1beta-mediated PGE2 release in both of these cell lines, with differences upstream at the level of cPLA(2)/COX-2 expression. IL-1beta-induced cPLA2 and COX-2 gene expression is modulated through the p38 MAPK pathway in both neuroglioma and neuroblastoma cells. Understanding the signaling mechanisms involved in IL-1beta-mediated inflammatory processes in both glia and neuronal cells may provide potential targets for therapeutic intervention for neurological disorders.     

Differential activation of MAPK in injured and uninjured DRG neurons following chronic constriction injury of the sciatic nerve in rats

To investigate the intracellular signal transduction pathways involved in the pathophysiological mechanisms of neuropathic pain after partial nerve injury, we examined the activation of extracellular signal-regulated protein kinase (ERK) and p38 mitogen-activated protein kinase (MAPK) in the dorsal root ganglion (DRG) in the chronic constriction injury (CCI) model. The CCI induced an increase in the phosphorylation of ERK in predominantly injured medium-sized and large-sized DRG neurons and in satellite glial cells. Treatment with the MAPK kinase 1/2 inhibitor, U0126, suppressed CCI-induced mechanical allodynia and partially reversed the increase in neuropeptide Y (NPY) expression in damaged DRG neurons. In contrast, the CCI induced the activation of p38, mainly in uninjured small-to-medium-diameter DRG neurons and in satellite glial cells. The p38 inhibitor, SB203580, reversed the CCI-induced heat hyperalgesia and also the increase in brain-derived neurotrophic factor (BDNF) expression in intact DRG neurons. On the other hand, the nerve growth factor (NGF)-induced increase in BDNF expression in small-to-medium-diameter neurons was reversed by SB203580, whereas the anti-NGF-induced increase in NPY in medium-sized and large-sized neurons was partially blocked by U0126. Taken together, our results demonstrate that the activation of ERK and p38 and also the changes in NPY and BDNF expression may occur in different populations of DRG neurons after CCI, partially through alterations in the target-derived NGF. These changes in injured and intact primary afferents are likely to have a substantial role in pathological states, and MAPK pathways in nociceptors may be potential targets for the development of novel analgesics.     

IL-2 and IL-10 production by human CD4+T cells is differentially regulated by p38: mode of stimulation-dependent regulation of IL-2

Antigenic stimulation of T cells initiates a complex series of intracellular signaling pathways that target and activate different cytokine genes. The participation of mitogen-activated protein kinases (MAPKs) in these processes has not been studied thoroughly and in some instances conflicting results have been reported. Here we have examined the role of p38 MAPK on IL-2 and IL-10 production following activation of human CD4+ T cells or of the leukemic cell line Hut-78, with either plate-bound anti-CD3 in the presence or absence of soluble anti-CD28 (plCD3, plCD3/sCD28), or with cross-linked anti-CD3 and anti-CD28 (crsCD3+CD28), or with PMA plus ionomycin. Pharmacological inhibition of the p38 pathway with either SB203580, SB202190, or SKF86002 strongly downregulated IL-10 production by T cells stimulated with any of the above treatments. In contrast the effect of p38 inhibition on IL-2 was stimulus dependent. Thus, p38 inhibition strongly upregulated IL-2 production (up to 10-fold) in the plCD3- and plCD3/sCD28-stimulated cultures while it had minimal or no effect in the other two stimulation protocols. Intracellular and mRNA levels of IL-2 and IL-10 were also upregulated and downregulated, respectively, by p38 inhibitors in the plCD3/sCD28-stimulated CD4+ T cells. Also, the induction of IL-2 and the parallel suppression of IL-10 by p38 inhibitors were independent of the balance between these two cytokines, as demonstrated by the addition of exogenous IL-10 or blocking anti-IL-10 antibody in CD4+ and Hut-78 cell cultures. These results show that p38 acts as a molecular switch that changes the balance between IL-2 and IL-10. This is especially important considering the opposing role of these cytokines in peripheral immune tolerance.     

Neurotoxicity of cadmium on immature hippocampus and a neuroprotective role for p38 MAPK

The developing brain is very sensitive to damage by toxic agents, many of which only manifest in adulthood. Cadmium [Cd(II)] is an environmental pollutant which is widely used in industry and is a constituent of tobacco smoke. Exposure to Cd(II) has been linked to detrimental effects on mammalian cells including neural cells. We have investigated the action of Cd(II) on immature hippocampus by assessing cell viability and modulation of AKT/PKB and mitogen-activated protein kinase (MAPK) family members including extracellular signal-regulated kinase (ERK)-1/2, p38 MAPK and c-Jun N-terminal kinases (JNK). Hippocampal slices from immature rats (postnatal day 14; PN14) were incubated with Cd(II) (5-200 microM) for 3h and the effects on protein phosphorylation were analyzed by western blotting. Phosphorylation of p38(MAPK) was enhanced by Cd(II) at all doses tested. Cd(II) also stimulated the phosphorylation of ERK1/2 in a concentration-dependent manner. However, the phosphorylation of JNK and AKT was not altered by the metal. Moreover, Cd(II) reduced cell viability, as measured by MTT reduction. Inhibition of p38 MAPK by SB203580 aggravated the acute Cd(II)-induced impairment of cell viability, whereas inhibition of MEK by PD98059 did not alter the effects of Cd(II). The present data suggest that in immature hippocampal cells p38 MAPK may be a part of signaling pathway that counteracts acute Cd(II) neurotoxicity. In conclusion, our results showed that Cd(II) impairs cell viability and disturbs MAPKs pathways in an important developmental stage for synaptic organization.     

Role of p38 MAPK and pro-inflammatory cytokines expression in glutamate-induced neuronal death of neonatal rats

Pro-inflammatory cytokines TNF-, IL-1β and IL-6 rises significantly during neuronal damage and activate the signaling p38 MAPK pathway, which is involved in the apoptotic (AP) neuronal death. Systemic administration of glutamate as monosodium salt (MSG) to newborn animals induces neuronal death, however whether neurons die by AP or necrosis through MAPK p38 pathway activation it is unknown. In this study, TNF-, IL-1β and IL-6 expression levels, AP neuronal death and cellular type that produces TNF- was also identified in the cerebral cortex (CC) and striatum (St) of rats at 8, 10, and 14 days of age after neonatal exposure to MSG. TNF- production and AP neuronal death was significantly increased in the CC at PD8–10, and in the St in all ages studied by excitotoxicity effect induced with MSG. This effect was completely inhibited by SB203580 (p38 inhibitor) in both regions studied. TNF-, IL-1β and IL-6 RNAm increased after MSG administration, whereas SB203580 did not modify their expression. These data indicates that neuronal death induced by excitotoxicity appears to be mediated through p38 signaling pathway activated by TNF- and their inhibition may have an important neuroprotective role as part of anti-inflammatory therapeutic strategy.     

Inhibition of p38 MAP kinase activity enhances axonal regeneration

Tumor necrosis factor alpha (TNF)-induced cellular signaling through the p38 mitogen-activated protein kinase (p38 MAPK) pathway plays a critical role in Wallerian degeneration and subsequent regeneration, processes that depend on Schwann cell (SC) activity. TNF dose-dependently induces Schwann cell and macrophage activation in vivo and apoptosis in primary SC cultures in vitro, while inhibition of p38 MAPK is thought to block these cellular processes. We show with Western blots that after sciatic nerve crush injury, phosphorylated p38 (p-p38) MAPK is significantly increased (P < 0.01) in distal nerve segments. In tissue sections, p38 co-localized immunohistochemically with activated Schwann cells (GFAP) and to a lesser degree with macrophages (ED-1). In other experiments, animals were gavaged with Scios SD-169 (10 or 30 mg/kg) or excipient (PEG300) 1 day before and daily after crush injury to the sciatic nerve. SD-169 is a proprietary oral inhibitor of p38 MAPK activity. The rate of axonal regeneration was determined by the functional pinch test and was significantly increased in treated animals 8 days after crush injury (P < 0.05; 30 mg/kg dose). In SD-169-treated animals with nerve transection, nerve fibers regenerating through a silicone chamber were morphologically more mature than untreated nerves when observed 28 days after transection. TNF immunofluorescence of distal nerve segments after crush injury suggested that SD-169 reduced SC TNF protein. In support of these findings, SD-169 significantly reduced (P < 0.05) TNF-mediated primary SC death in culture experiments. We conclude that inhibition of p38 activity promotes axonal regeneration through interactions with SC signaling and TNF activity.     

Transforming growth factor-β1 acts via TβR-I on microglia to protect against MPP+-induced dopaminergic neuronal loss

Neuroinflammation is associated with pathogenesis of Parkinson’s disease (PD), a neurodegenerative disorder characterized by a progressive loss of dopaminergic (DAergic) neurons within the substantia nigra. Transforming growth factor (TGF)-β1 exerts anti-inflammatory and neuroprotective properties. However, it is unclear if microglia are required for TGF-β1 neuroprotection in PD. Here we used both shRNA and pharmacologic inhibition to determine the role of microglial TGF-β receptor (TβR)-I and its downstream signaling pathways in 1-methyl-4-phenylpyridinium (MPP⁺)-induced DAergic neuronal toxicity. As expected, MPP⁺ reduced the number of tyrosine hydroxylase (TH)-immunoreactive cells in ventral mesencephalic cell cultures. We found that MPP⁺ activated microglia as determined by an upregulation in expression of CD11b and inducible nitric oxide synthase (iNOS), an increase in expression and secretion of tumor necrosis factor (TNF)-α and interleukin (IL)-1β, and a decrease in expression and secretion of the neurotrophic factor, insulin-like growth factor (IGF)-1. Pretreatment with TGF-β1 significantly inhibited all these changes caused by MPP⁺. Expression of microglial TβR-I was upregulated by TGF-β1. Silencing of the TβR-I gene in microglia abolished both the neuroprotective and anti-inflammatory properties of TGF-β1. TGF-β1 increased microglial p38 MAPK and Akt phosphorylation, both of which were blocked by the p38 inhibitor SB203580 and the PI3K inhibitor LY294002, respectively. Pretreatment of microglia with either SB203580 or LY294002 impaired the ability of TGF-β1 to inhibit MPP⁺-induced DAergic neuronal loss and microglial activation. These findings establish that TGF-β1 activates TβR-I and its downstream p38 MAPK and PI3K–Akt signaling pathways in microglia to protect against DAergic neuronal loss that characterizes in PD.     

p38 mitogen-activated protein kinase modulates expression of tumor necrosis factor-related apoptosis-inducing ligand induced by interferon-gamma in fetal brain astrocytes

This study describes the involvement of the p38 mitogen-activated protein kinase (MAPK) during interferon-gamma (IFN-gamma) signaling in fetal brain astrocytes. In some pathological conditions of brain, p38 MAPK transduces stress-related signals, increases expression of proinflammatory cytokines, and induces cellular damage or apoptosis. In astrocytes, the tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) expression level was increased by IFN-gamma. AG490, a JAK inhibitor, blocked TRAIL expression induced by IFN-gamma. SB203580, a specific p38alpha and p38beta2 MAPK inhibitor, decreased the TRAIL expression induced by IFN-gamma. The phosphorylation of the Ser727 site of STAT1, but not the Tyr701 site, was inhibited by SB203580. These results suggest that p38 MAPK modulates STAT1 phosphorylation in IFN-gamma signaling in fetal brain astrocytes.