P38α Deficiency Research Articles

P38α deficiency ameliorates psoriasis development by downregulating STAT3-mediated keratinocyte proliferation and cytokine production

Psoriasis is characterized by keratinocyte (KC) hyperproliferation and inflammatory cell infiltration, but the mechanisms remain unclear. In an imiquimod-induced mouse psoriasiform model, p38 activity is significantly elevated in KCs and p38α specific deletion in KCs ameliorates skin inflammation. p38α signaling promotes KC proliferation and psoriasis-related proinflammatory gene expression during psoriasis development. Mechanistically, p38α enhances KC proliferation and production of inflammatory cytokines and chemokines by activating STAT3. While p38α signaling in KCs does not affect the expression of IL-23 and IL-17, it substantially amplifies the IL-23/IL-17 pathogenic axis in psoriasis. The therapeutic effect of IL-17 neutralization is associated with decreased p38 and STAT3 activities in KCs and targeting the p38α-STAT3 axis in KCs ameliorates the severity of psoriasis. As IL-17 also highly activates p38 and STAT3 in KCs, our findings reveal a sustained signaling circuit important for psoriasis development, highlighting p38α-STAT3 axis as an important target for psoriasis treatment.

P38α in the preoptic area inhibits brown adipose tissue thermogenesis

Elevation of energy expenditure through an increase of brown adipose tissue (BAT) thermogenesis is regarded as one of the most promising ways to prevent obesity development. The preoptic area (POA) of the hypothalamus is a critical area for control of BAT thermogenesis. However, the intracellular signaling cascades in the POA for regulation of BAT thermogenesis are poorly understood. Phosphorylation proteomics (phosphoproteomics) and bioinformatics approaches were used to disclose numerous hypothalamic signaling pathways involved in the regulation of BAT thermogenesis. Conditional manipulation of the p38α gene in mouse POA was performed by stereotaxic injection of adeno-associated virus 9 vector to explore the role of p38α in BAT thermogenesis. Multiple hypothalamic signaling pathways were triggered by cold exposure, especially the mitogen-activated protein kinase (MAPK) signaling pathway. The p38α activation, but not extracellular signal-regulated kinase 1/2 (ERK1/2) and c-Jun NH2-terminal kinase (JNK), in the hypothalamus was significantly decreased during cold exposure. p38α deficiency in the POA dramatically elevated energy expenditure owing to a marked increase in BAT thermogenesis, resulting in significantly decreased body weight gain and fat mass. Overexpression of p38α in the POA led to a dramatic increase in weight gain. These results demonstrate that p38α in the POA exacerbates obesity development, at least in part owing to a decrease in BAT thermogenesis.

P38α deficiency in macrophages ameliorates murine experimental colitis by regulating inflammation and immune process

IntroductionP38α is a mitogen-activated protein kinase (MAPK) that mediates inflammatory responses. P38α alterations have been associated with the inflammation-related diseases. However, the role of macrophages-derived p38α in dextran sulfate sodium (DSS)-induced murine experimental colitis remains unclear. ObjectivesWe characterized the role of macrophages-derived p38α in DSS-induced colitis. MethodsThe expression of macrophage-derived p38α in human colitis and normal tissues was measured by immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) analysis. Macrophage-specific p38α knockout (p38αΔMφ) and wild type (WT) mice administrated by 3% DSS were used to establish experimental colitis. The alterations in inflammatory cytokines, intestinal epithelial barrier, cell proliferation and cell apoptosis between p38αΔMφ and WT groups were determined by IHC, immunofluorescence (IF), TdT-mediated dUTP Nick-End Labeling (TUNEL) and Western blot analyses. The enriched pathways between p38αΔMφ and WT groups were identified by RNA-seq and KEGG analysis. SB203580 and BIRB796 as the p38 MAPK inhibitors were used to treat DSS-induced colitis. Resultsp38α was co-localized with CD68 in the cytoplasm and their co-expression indicated an increased level in colitis tissues as compared with the normal tissues. P38α deficiency in macrophages was sufficient to suppress the exacerbated clinical symptoms and inflammation responses in experimental colitis, followed by reducing cytokine release, increasing MUC-2 and Claudin-2 secretion and promoting colonic mucosa repair. Further investigations validated that the immune process-related factors such as Lgals9, Rtp4, Ddx60, Nlrp1b, Hsh2d, Oas2 and Oas3 were upregulated in colon tissues from p38αΔMφ group as compared with the WT group. Inhibition of p38 MAPK attenuated DSS-induced colitis. ConclusionOur findings demonstrated that p38α deficiency in macrophages ameliorated murine experimental colitis by regulating inflammation and immune process.

P38α Deficiency in T Cells Ameliorates Diet-Induced Obesity, Insulin Resistance, and Adipose Tissue Senescence.

Adipose tissue-resident T cells play vital roles in regulating inflammation and metabolism in obesity, but the underlying mechanisms remain unclear. Here, we show that high-fat diet (HFD) feeding enhances p38 activity in adipose-resident T cells. T cell-specific deletion of p38α, an essential subunit of p38 expressed in most immune cells, protected mice from HFD-induced obesity, hepatic steatosis, adipose tissue inflammation, and insulin resistance. Mice with p38α deletion in T cells exhibited higher energy expenditure. Mechanistically, p38α promoted T-cell glycolysis through mechanistic target of rapamycin signaling, leading to enhanced Th1 differentiation. Accordingly, genetic deletion of p38α alleviated ongoing diet-induced obesity. Unexpectedly, p38α signaling in T cells promoted adipose tissue senescence during obesity and aging. Taken together, our results identify p38α in T cells as an essential regulator of obesity, insulin resistance, and adipose tissue senescence, and p38α may be a therapeutic target for obese- or aging-associated diseases.

Perturbation of p38α MAPK as a Novel Strategy to Effectively Sensitize Chronic Myeloid Leukemia Cells to Therapeutic BCR-ABL Inhibitors.

Chronic myeloid leukemia (CML) is a hematopoietic malignancy characterized by the presence of the BCR-ABL oncogene. Therapeutic regimens with tyrosine kinase inhibitors (TKIs) specifically targeting BCR-ABL have greatly improved overall survival of CML. However, drug intolerance and related toxicity remain. Combined therapy is effective in reducing drug magnitude while increasing therapeutic efficacy and, thus, lowers undesired adverse side effects. The p38 MAPK activity is critically linked to the pathogenesis of a number of diseases including hematopoietic diseases; however, the role of each isozyme in CML and TKI-mediated effects is still elusive. In this study, we used specific gene knockdown to clearly demonstrate that the deficiency of p38α greatly enhanced the therapeutic efficacy in growth suppression and cytotoxicity of TKIs, first-generation imatinib, and second generation dasatinib by approximately 2.5–3.0-fold in BCR-ABL-positive CML-derived leukemia K562 and KMB5 cells. Knockdown of p38β, which displays the most sequence similarity to p38α, exerted distinct and opposite effects on the TKI-mediated therapeutic efficacy. These results show the importance of isotype-specific intervention in enhancing the therapeutic efficacy of TKI. A highly specific p38α inhibitor, TAK715, also significantly enhanced the imatinib- and dasatinib-mediated therapeutic efficacy, supporting the feasibility of p38α deficiency in future clinic application. Taken together, our results demonstrated that p38α is a promising target for combined therapy with BCR-ABL-targeting tyrosine kinase inhibitors for future application to increase therapeutic efficacy.

P38 MAP Kinase Signaling in Microglia Plays a Sex-Specific Protective Role in CNS Autoimmunity and Regulates Microglial Transcriptional States.

Multiple sclerosis (MS) is an autoimmune demyelinating disease of the central nervous system, representing the leading cause of non-traumatic neurologic disease in young adults. This disease is three times more common in women, yet more severe in men, but the mechanisms underlying these sex differences remain largely unknown. MS is initiated by autoreactive T helper cells, but CNS-resident and CNS-infiltrating myeloid cells are the key proximal effector cells regulating disease pathology. We have previously shown that genetic ablation of p38α MAP kinase broadly in the myeloid lineage is protective in the autoimmune model of MS, experimental autoimmune encephalomyelitis (EAE), but only in females, and not males. To precisely define the mechanisms responsible, we used multiple genetic approaches and bone marrow chimeras to ablate p38α in microglial cells, peripheral myeloid cells, or both. Deletion of p38α in both cell types recapitulated the previous sex difference, with reduced EAE severity in females. Unexpectedly, deletion of p38α in the periphery was protective in both sexes. In contrast, deletion of p38α in microglia exacerbated EAE in males only, revealing opposing roles of p38α in microglia vs. periphery. Bulk transcriptional profiling revealed that p38α regulated the expression of distinct gene modules in male vs. female microglia. Single-cell transcriptional analysis of WT and p38α-deficient microglia isolated from the inflamed CNS revealed a diversity of complex microglial states, connected by distinct convergent transcriptional trajectories. In males, microglial p38α deficiency resulted in enhanced transition from homeostatic to disease-associated microglial states, with the downregulation of regulatory genes such as Atf3, Rgs1, Socs3, and Btg2, and increased expression of inflammatory genes such as Cd74, Trem2, and MHC class I and II genes. In females, the effect of p38α deficiency was divergent, exhibiting a unique transcriptional profile that included an upregulation of tissue protective genes, and a small subset of inflammatory genes that were also upregulated in males. Taken together, these results reveal a p38α-dependent sex-specific molecular pathway in microglia that is protective in CNS autoimmunity in males, suggesting that autoimmunity in males and females is driven by distinct cellular and molecular pathways, thus suggesting design of future sex-specific therapeutic approaches.

P38 MAP kinase signaling in microglia plays a sex-specific protective role in CNS autoimmunity and regulates microglial transcriptional states

Abstract Multiple sclerosis (MS) is an autoimmune demyelinating disease of the central nervous system. MS is three times more common in women, yet more severe in men. The mechanisms underlying these sex differences remain largely unknown. MS is initiated by autoreactive T cells, but CNS-infiltrating myeloid cells are key effector cells driving pathology. The role of CNS-resident microglial cells is less clear. We have previously shown that genetic ablation of p38α MAP kinase broadly in the myeloid lineage is protective in the autoimmune model of MS, experimental autoimmune encephalomyelitis (EAE), but only in females, and not males. Here, we sought to define the mechanisms responsible, using genetic approaches and bone marrow chimeras to ablate p38α in microglial cells, peripheral myeloid cells, or both. Deletion of p38α in both cell types recapitulated the previous sex difference, with reduced EAE severity in females. Unexpectedly, deletion of p38α in the periphery was protective in both sexes. In contrast, deletion of p38α in microglia exacerbated EAE in males only, revealing opposing roles of p38α in microglia vs. periphery. Single-cell RNAseq revealed a diversity of microglial states, connected by distinct convergent transcriptional trajectories. Microglial p38α deficiency resulted in enhanced transition from homeostatic to disease-associated microglia, with downregulation of regulatory genes such as Atf3, Rgs1, and Btg2, and upregulation of inflammatory genes such as Cd74, Trem2, and MHC class I and II. These results reveal a p38α-dependent male-specific molecular pathway in microglia that is protective in CNS autoimmunity, suggesting that autoimmunity in males and females may be driven by distinct cellular and molecular pathways.

P38\u03b1 deficiency restrains liver regeneration after partial hepatectomy triggering oxidative stress and liver injury

p38α MAPK negatively regulates the G1/S and G2/M cell cycle transitions. However, liver-specific p38α deficiency impairs cytokinesis and reduces hepatocyte proliferation during cirrhosis and aging in mice. In this work, we have studied how p38α down-regulation affects hepatocyte proliferation after partial hepatectomy, focusing on mitotic progression, cytokinesis and oxidative stress. We found that p38α deficiency triggered up-regulation of cyclins A1, B1, B2, and D1 under basal conditions and after hepatectomy. Moreover, p38α-deficient hepatocytes showed enhanced binucleation and increased levels of phospho-histone H3 but impaired phosphorylation of MNK1 after hepatectomy. The recovery of liver mass was transiently delayed in mice with p38α-deficient hepatocytes vs wild type mice. We also found that p38α deficiency caused glutathione oxidation in the liver, increased plasma aminotransferases and lactate dehydrogenase activities, and decreased plasma protein levels after hepatectomy. Interestingly, p38α silencing in isolated hepatocytes markedly decreased phospho-MNK1 levels, and silencing of either p38α or Mnk1 enhanced binucleation of hepatocytes in culture. In conclusion, p38α deficiency impairs mitotic progression in hepatocytes and restrains the recovery of liver mass after partial hepatectomy. Our results also indicate that p38α regulates cytokinesis by activating MNK1 and redox modulation.

P38α/JNK Signaling Restrains Erythropoiesis By Suppressing Ezh2-Mediated Epigenetic Silencing of Bim

A remarkable feature of erythropoiesis is the coordination of proliferation, differentiation and apoptosis of erythroid cells to precisely achieve erythropoietic homeostasis to avoid anemia and polycythemia. Anemia is a common disease arising from various causes, including Myelodysplastic syndromes, thalassemia, cancer chemotherapy, chronic kidney disease and hemorrhage. The pro-erythropoietic factor erythropoietin (EPO) is often employed for anemia therapy. However, questions have been raised about the safety of EPO given its potential for tumor promotion in cancer-related anemia. Moreover, many acute and chronic anemias, including hemolysis, sepsis and genetic bone marrow failure diseases such as Diamond-Blackfan anemia are untreatable with EPO. To overcome these hurdles, new molecular mechanisms need to be identified that physiologically restrain erythropoiesis by acting as molecular brakes to prevent over-active erythropoiesis caused by pro-erythropoietic signals. Inhibiting these restraining mechanisms could provide alternative approaches to treat anemia in an EPO-independent fashion. P38 MAPK (Mitogen-activated protein kinase) is an important pathway involved in diverse biological processes. P38 modulates cell proliferation, controls cell survival and decides cell fate during differentiation. P38 pathway functions mainly by phosphorylating and activating important transcription factors in response to different stimuli, including ATF2, CREB, and MEF2. There are four members within the P38 MAPK family, including P38α, P38β, P38γ, and P38δ. These members are encoded by different genes and have different tissue expression patterns. Among them, P38α is ubiquitously expressed. P38α modulates the function of different cell types. There are two distinct developmental defects reported in global P38α knockout mice by two separate groups using different mouse strains. One displayed embryonic death with highly anemic appearance due to reduced EPO production and another showed even earlier embryonic lethality due to placental developmental defects. In a P38α conditional mice model in which Cre recombinase was expressed in the whole mouse embryo but not in the placenta by crossing to MORE-Cre mice, no anemia or EPO defects were observed. However, the intrinsic and cell autonomous role of P38α in adult steady-state or stressful erythropoiesis has not been established. Loss of P38α causes activation of JNK in the liver. P38 inhibitors are in clinical trials and have the potential for the treatment of human disease. Therefore, it is important to understand the down-stream targets and functional outcomes induced by P38α deficiency. Using primary human erythroblasts derived from human CD34+ hematopoietic stem and progenitor cells (HSPCs) and P38α conditional knockout mice, we find that P38α acts as a molecular brake during anemia recovery through integrating apoptotic signals and by shortening the lifespan of erythroblasts to prevent potential over-active erythropoiesis caused by pro-erythropoietic signaling. Loss of P38α in erythroblasts activates JNK through augmented Map3k4 via a negative feedback circuit revealed by gene expression profiling. Functionally, JNK serves as a pro-survival signal independent of EPO by compromising Bim expression via stabilizing the epigenetic silencer Ezh2 in erythroblasts. JNK-controlled Cdk1 activity modulates full interaction of Ezh2 to the E3 ligase Smurf2 through multiple threonine phosphorylation sites within Ezh2. Our findings identify a key signaling cascade involving P38α/JNK/Cdk1/smurf2/Ezh2/Bim in fine tuning stress erythropoiesis. We propose that inhibition of P38α may provide an alternative strategy for the treatment of anemia. DisclosuresNo relevant conflicts of interest to declare.

P38\u03b1/JNK signaling restrains erythropoiesis by suppressing Ezh2-mediated epigenetic silencing of Bim

While erythropoietin (EPO) constitutes the major treatment for anemia, a range of anemic disorders remain resistant to EPO treatment. The need for alternative therapeutic strategies requires the identification of mechanisms that physiologically restrain erythropoiesis. Here we show that P38α restrains erythropoiesis in mouse and human erythroblasts independently of EPO by integrating apoptotic signals during recovery from anemia. P38α deficiency promotes JNK activation through increased expression of Map3k4 via a negative feedback mechanism. JNK prevents Cdk1-mediated phosphorylation and subsequent degradation by Smurf2 of the epigenetic silencer Ezh2. Stabilized Ezh2 silences Bim expression and protects erythroblasts from apoptosis. Thus, we identify P38α/JNK signaling as a molecular brake modulating erythropoiesis through epigenetic silencing of Bim. We propose that inhibition of P38α, by enhancing erythropoiesis in an EPO-independent fashion, may provide an alternative strategy for the treatment of anemia.

Metabolic benefits of inhibition of p38α in white adipose tissue in obesity.

p38 has long been known as a central mediator of protein kinase A (PKA) signaling in brown adipocytes, which positively regulate the transcription of uncoupling protein 1 (UCP-1). However, the physiological role of p38 in adipose tissues, especially the white adipose tissue (WAT), is largely unknown. Here, we show that mice lacking p38α in adipose tissues display a lean phenotype, improved metabolism, and resistance to diet-induced obesity. Surprisingly, ablation of p38α causes minimal effects on brown adipose tissue (BAT) in adult mice, as evident from undetectable changes in UCP-1 expression, mitochondrial function, body temperature (BT), and energy expenditure. In contrast, genetic ablation of p38α in adipose tissues not only markedly facilitates the browning in WAT upon cold stress but also prevents diet-induced obesity. Consistently, pharmaceutical inhibition of p38α remarkably enhances the browning of WAT and has metabolic benefits. Furthermore, our data suggest that p38α deficiency promotes white-to-beige adipocyte reprogramming in a cell-autonomous manner. Mechanistically, inhibition of p38α stimulates the UCP-1 transcription through PKA and its downstream cAMP-response element binding protein (CREB), which form a positive feedback loop that functions to reinforce the white-to-beige phenotypic switch during cold exposure. Together, our study reveals that inhibition of p38α is able to promote WAT browning and confer metabolic benefits. Our study also indicates that p38α in WAT represents an exciting pharmacological target to combat obesity and metabolic diseases.

Age-dependent regulation of antioxidant genes by p38α MAPK in the liver

p38α is a redox sensitive MAPK activated by pro-inflammatory cytokines and environmental, genotoxic and endoplasmic reticulum stresses. The aim of this work was to assess whether p38α controls the antioxidant defense in the liver, and if so, to elucidate the mechanism(s) involved and the age-related changes. For this purpose, we used liver-specific p38α-deficient mice at two different ages: young-mice (4 months-old) and old-mice (24 months-old). The liver of young p38α knock-out mice exhibited a decrease in GSH levels and an increase in GSSG/GSH ratio and malondialdehyde levels. However, old mice deficient in p38α had higher hepatic GSH levels and lower GSSG/GSH ratio than young p38α knock-out mice. Liver-specific p38α deficiency triggered a dramatic down-regulation of the mRNAs of the key antioxidant enzymes glutamate cysteine ligase, superoxide dismutase 1, superoxide dismutase 2, and catalase in young mice, which seems mediated by the lack of p65 recruitment to their promoters. Nrf-2 nuclear levels did not change significantly in the liver of young mice upon p38α deficiency, but nuclear levels of phospho-p65 and PGC-1α decreased in these mice. p38α-dependent activation of NF-κB seems to occur through classical IκB Kinase and via ribosomal S6 kinase1 and AKT in young mice. However, unexpectedly the long-term deficiency in p38α triggers a compensatory up-regulation of antioxidant enzymes via NF-κB activation and recruitment of p65 to their promoters. In conclusion, p38α MAPK maintains the expression of antioxidant genes in liver of young animals via NF-κΒ under basal conditions, whereas its long-term deficiency triggers compensatory up-regulation of antioxidant enzymes through NF-κΒ.

Deficiency of p38α in macrophage ameliorates d-galactosamine/TNF-α-induced acute liver injury in mice.

Growing evidence suggests that hepatic macrophages play an important role in tissue repair after liver injury by coordinating the induction and resolution of inflammation, removing apoptotic cells, and promoting hepatocyte proliferation. Understanding the role of macrophages in the pathogenesis of liver injury will help pave the way to future therapeutics. Here, we investigated whether macrophage p38α plays a regulatory role in the tissue repair following d-galactosamine (GalN)/tumor necrosis factor-α (TNF-α)-induced acute liver injury. We found that macrophage p38α-deficient mice displayed decreased mortality and relieved liver injury as evident from less apoptosis, accelerated regeneration, decreased granulocytes recruitment, monocytes infiltration, and cytokine production after GalN/TNF-α treatment. Mechanistically, we found that p38 signaling was activated by lipopolysaccharide/interferon-γ treatment but not by inteleukin-4 stimulation, while pharmaceutical inhibition of p38α induced a shift in polarization from M1 macrophages to M2 macrophages. Together, our results indicated that macrophage p38α signaling is involved in the pathogenesis of liver injury induced by GalN/TNF-α, and inhibition of p38α signaling in macrophage could ameliorate liver injury and accelerate regeneration, probably by promoting the polarization of macrophages from the M1 phenotype to the M2 phenotype.

P38α regulates cytokine‐induced IFNγ secretion via the Mnk1/eIF4E pathway in Th1 cells

The p38 mitogen-activated protein kinase (MAPK) pathway is involved in the regulation of immune and inflammatory processes. We used p38α-conditional, p38β-deficient and p38α/β double-null mouse models to address the role of these two p38 MAPK in CD4+ T cells, and found that p38α deficiency causes these cells to hyperproliferate. Our studies indicate that both p38α and p38β are dispensable for T helper cell type 1 (Th1) differentiation but, by controlling interferon (IFN)γ and tumor necrosis factor (TNF)α production, are critical for normal Th1 effector function. We found that both p38α and p38β modulate T-cell receptor-induced IFNγ and TNFα production, whereas only p38α regulates cytokine-induced IFNγ production. The lack of p38α and p38β did not affect transcription and mRNA stability of Ifng. However, the absence of p38α in Th1 cells resulted in a decreased MNK1 phosphorylation after cytokine activation, and MNK1 inhibition blocked IFNγ production. Our results indicate that p38α regulates IFNγ secretion through the activation of the MNK1/eIF4E pathway of translation initiation and identify specific functions for p38α and p38β in T-cell proliferation.

P 088 - p38α and NF-κB regulate antioxidant defense in the liver through an age-dependent mechanism

p38α MAPK is a sensor of oxidative stress. The aim of this work was to assess the role of p38α in the regulation of the antioxidant defense in the liver with aging. Livers ofyoung and old wild type (WT) and p38α liver-specific knock out (KO) mice were used to determine glutathione redox status by mass spectrometry; malondialdehyde (MDA) levels by HPLC; mRNA expression of glutamate cysteine ligase (Gclc), Sod1, Sod2 and catalase by RT-PCR and nuclear levels of NF-κB subunit p65 by western-blotting. Chromatin immunoprecipitation (ChIP) assay of p65 was performed. Young KO liver exhibited increased in GSSG/GSH ratio and MDA levels when are compared with young WT mice. However, old KO mice had lower hepatic GSSG/GSH ratio and MDA levels than young KO mice. The mRNA expression of Gclc, Sod1, Sod2 and catalase was decreased in young KO mice compared with WT young mice. In contrast, these antioxidant enzymes were up-regulated in KO old mice regard to WT. p65 was markedly phosphorylated in the nucleus of WT young and old KO mice. ChIP assay of p65 confirmed the recruitment of p65 to the promoters of antioxidant genes in WT young and KO old mice. Deficiency of p38α in the liver causes dramatic down-regulation of antioxidant enzymes in young mice, but triggers adaptive up-regulation in the long term via NF-κB to enhance the antioxidant defense in old p38α KO mice.

P38\u03b1 MAPK regulates proliferation and differentiation of osteoclast progenitors and bone remodeling in an aging-dependent manner

Bone mass is determined by the balance between bone formation, carried out by mesenchymal stem cell-derived osteoblasts, and bone resorption, carried out by monocyte-derived osteoclasts. Here we investigated the potential roles of p38 MAPKs, which are activated by growth factors and cytokines including RANKL and BMPs, in osteoclastogenesis and bone resorption by ablating p38α MAPK in LysM+monocytes. p38α deficiency promoted monocyte proliferation but regulated monocyte osteoclastic differentiation in a cell-density dependent manner, with proliferating p38α−/− cultures showing increased differentiation. While young mutant mice showed minor increase in bone mass, 6-month-old mutant mice developed osteoporosis, associated with an increase in osteoclastogenesis and bone resorption and an increase in the pool of monocytes. Moreover, monocyte-specific p38α ablation resulted in a decrease in bone formation and the number of bone marrow mesenchymal stem/stromal cells, likely due to decreased expression of PDGF-AA and BMP2. The expression of PDGF-AA and BMP2 was positively regulated by the p38 MAPK-Creb axis in osteoclasts, with the promoters of PDGF-AA and BMP2 having Creb binding sites. These findings uncovered the molecular mechanisms by which p38α MAPK regulates osteoclastogenesis and coordinates osteoclastogenesis and osteoblastogenesis.

P38α regulates actin cytoskeleton and cytokinesis in hepatocytes during development and aging.

BackgroundHepatocyte poliploidization is an age-dependent process, being cytokinesis failure the main mechanism of polyploid hepatocyte formation. Our aim was to study the role of p38α MAPK in the regulation of actin cytoskeleton and cytokinesis in hepatocytes during development and aging.MethodsWild type and p38α liver-specific knock out mice at different ages (after weaning, adults and old) were used.ResultsWe show that p38α MAPK deficiency induces actin disassembly upon aging and also cytokinesis failure leading to enhanced binucleation. Although the steady state levels of cyclin D1 in wild type and p38α knock out old livers remained unaffected, cyclin B1- a marker for G2/M transition- was significantly overexpressed in p38α knock out mice. Our findings suggest that hepatocytes do enter into S phase but they do not complete cell division upon p38α deficiency leading to cytokinesis failure and binucleation. Moreover, old liver-specific p38α MAPK knock out mice exhibited reduced F-actin polymerization and a dramatic loss of actin cytoskeleton. This was associated with abnormal hyperactivation of RhoA and Cdc42 GTPases. Long-term p38α deficiency drives to inactivation of HSP27, which seems to account for the impairment in actin cytoskeleton as Hsp27-silencing decreased the number and length of actin filaments in isolated hepatocytes.Conclusionsp38α MAPK is essential for actin dynamics with age in hepatocytes.

Loss of Functionally Redundant p38 Isoforms in T Cells Enhances Regulatory T Cell Induction

The evolutionarily conserved protein kinase p38 mediates innate resistance to environmental stress and microbial infection. Four p38 isoforms exist in mammals and may have been co-opted for new roles in adaptive immunity. Murine T cells deficient in p38α, the ubiquitously expressed p38 isoform, showed no readily apparent cell-autonomous defects while expressing elevated amounts of another isoform, p38β. Mice with T cells simultaneously lacking p38α and p38β displayed lymphoid atrophy and elevated Foxp3+ regulatory T cell frequencies. Double deficiency of p38α and p38β in naïve CD4+ T cells resulted in an attenuation of MAPK-activated protein kinase (MK)-dependent mTOR signaling after T cell receptor engagement, and enhanced their differentiation into regulatory T cells under appropriate inducing conditions. Pharmacological inhibition of the p38-MK-mTOR signaling module produced similar effects, revealing potential for therapeutic applications.

P38α has an important role in antigen cross-presentation by dendritic cells.

The role of the p38 signaling pathway in the innate and adaptive immune responses has been well documented, especially in inflammatory cytokine production by dendritic cells (DCs). However, whether the p38 signaling pathway affects the important antigen (Ag) presentation function of DCs remains largely unknown. In this study, we reported that the deletion of p38α resulted in an impaired cross-presentation ability of CD8+ conventional DCs (cDCs) and a reduction in the direct presentation ability of CD8- cDCs ex vivo. Further study revealed that p38α had a crucial role in Ag processing by CD8+ cDCs but did not affect the Ag uptake or co-stimulation of T cells. Moreover, p38α deficiency led to reduced cross-priming of T cells in vivo. The production of the IL-12p40 and IL-12p70 cytokines by p38α-deficient cDCs was also significantly reduced. Our study identified a new role for p38α in modulating the important antigen cross-presentation function of DCs.

Tissue-Specific Regulation of p38α-Mediated Inflammation in Con A-Induced Acute Liver Damage.

Because p38α plays a critical role in inflammation, it has been an attractive target for the development of anti-inflammation therapeutics. However, p38α inhibitors showed side effects, including severe liver toxicity, that often prevailed over the benefits in clinical studies, and the mechanism of toxicity is not clear. In this study, we demonstrate that p38α regulates the inflammatory responses in acute liver inflammation in a tissue-specific manner, and liver toxicity by p38α inhibitors may be a result of the inhibition of protective activity of p38α in the liver. Genetic ablation of p38α in T and NKT cells protected mice from liver injury in Con A-induced liver inflammation, whereas liver-specific deletion of p38α aggravated liver pathology. We found that p38α deficiency in the liver increased the expression of chemokines to recruit more inflammatory cells, indicating that p38α in the liver plays a protective anti-inflammatory role during acute liver inflammation. Therefore, our results suggest that p38α regulates the inflammatory responses in a tissue-specific manner, and that the tissue-specific p38α targeting strategies can be used for the development of an effective anti-inflammation treatment with an improved side-effect profile.