Essential role for p38alpha MAPK but not p38gamma MAPK in Igf2 expression and myoblast differentiation

Edaravone Dexborneol ameliorates the cognitive deficits of APP/PS1 mice by inhibiting TLR4/MAPK signaling pathway via upregulating TREM2

Currently, there are no effective therapeutic agents available to treat Alzheimer's disease (AD). However, edaravone dexborneol (EDB), a novel composite agent used to treat acute ischemic stroke, has recently been shown to exert efficacious neuroprotective effects. However, whether EDB can ameliorate cognitive deficits in AD currently remains unclear. To this end, we explored the effects of EDB on AD and its potential mechanisms using an AD animal model (male APP/PS1 mice) treated with EDB for 10 weeks starting at 6 months of age. Subsequent analyses revealed that EDB-treated APP/PS1 mice exhibited improved cognitive abilities compared to untreated APP/PS1 mice. Administration of EDB in APP/PS1 mice further alleviated neuropathological alterations of the hippocampus, including Aβ deposition, pyramidal cell karyopyknosis, and oxidative damage, and significantly decreased the levels of inflammatory cytokines (IL-1β, IL-6 and TNF-α) and COX-2 in the hippocampus of APP/PS1 mice. Transcriptome sequencing analysis demonstrated the critical role of the inflammatory reaction in EDB treatment in APP/PS1 mice, indicating that the alleviation of the inflammatory reaction by EDB in the hippocampus of APP/PS1 mice was linked to the action of the TREM2/TLR4/MAPK signaling pathway. Further in vitro investigations showed that EDB suppressed neuroinflammation in LPS-stimulated BV2 cells by inhibiting the TLR4/MAPK signaling pathway and upregulating TREM2 expression. Thus, the findings of the present study demonstrate that EDB is a promising therapeutic agent for AD-related cognitive dysfunction.

G-quadruplex structural dynamics at MAPK12 promoter dictates transcriptional switch to determine stemness in breast cancer

P38γ (MAPK12) is predominantly expressed in triple negative breast cancer cells (TNBC) and induces stem cell (CSC) expansion resulting in decreased survival of the patients due to metastasis. Abundance of G-rich sequences at MAPK12 promoter implied the functional probability to reverse tumorigenesis, though the formation of G-Quadruplex (G4) structures at MAPK12 promoter is elusive. Here, we identified two evolutionary consensus adjacent G4 motifs upstream of the MAPK12 promoter, forming parallel G4 structures. They exist in an equilibria between G4 and duplex, regulated by the binding turnover of Sp1 and Nucleolin that bind to these G4 motifs and regulate MAPK12 transcriptional homeostasis. To underscore the gene-regulatory functions of G4 motifs, we employed CRISPR-Cas9 system to eliminate G4s from TNBC cells and synthesized a naphthalene diimide (NDI) derivative (TGS24) which shows high-affinity binding to MAPK12-G4 and inhibits MAPK12 transcription. Deletion of G4 motifs and NDI compound interfere with the recruitment of the transcription factors, inhibiting MAPK12 expression in cancer cells. The molecular basis of NDI-induced G4 transcriptional regulation was analysed by RNA-seq analyses, which revealed that MAPK12-G4 inhibits oncogenic RAS transformation and trans-activation of NANOG. MAPK12-G4 also reduces CD44High/CD24Low population in TNBC cells and downregulates internal stem cell markers, arresting the stemness properties of cancer cells.

ZSWIM8 is a myogenic protein that partly prevents C2C12 differentiation

Cell adhesion molecule-related/downregulated by oncogenes (Cdon) is a cell-surface receptor that mediates cell–cell interactions and positively regulates myogenesis. The cytoplasmic region of Cdon interacts with other proteins to form a Cdon/JLP/Bnip-2/CDC42 complex that activates p38 mitogen-activated protein kinase (MAPK) and induces myogenesis. However, Cdon complex may include other proteins during myogenesis. In this study, we found that Cullin 2-interacting protein zinc finger SWIM type containing 8 (ZSWIM8) ubiquitin ligase is induced during C2C12 differentiation and is included in the Cdon complex. We knocked-down Zswim8 in C2C12 cells to determine the effect of ZSWIM8 on differentiation. However, we detected neither ZSWIM8-dependent ubiquitination nor the degradation of Bnip2, Cdon, or JLP. In contrast, ZSWIM8 knockdown accelerated C2C12 differentiation. These results suggest that ZSWIM8 is a Cdon complex-included myogenic protein that prevents C2C12 differentiation without affecting the stability of Bnip2, Cdon, and JLP.

Testosterone-mediated activation of androgenic signalling sustains in vitro the transformed and radioresistant phenotype of rhabdomyosarcoma cell lines

PURPOSE

Rhabdomyosarcoma (RMS), the most common soft-tissue sarcoma in childhood, rarely affects adults, preferring male. RMS expresses the receptor for androgen (AR) and responds to androgen; however, the molecular action of androgens on RMS is unknown.

METHODS

Herein, testosterone (T) effects were tested in embryonal (ERMS) and alveolar (ARMS) RMS cell lines, by performing luciferase reporter assay, RT-PCR, and western blotting experiments. RNA interference experiments or bicalutamide treatment was performed to assess the specific role of AR. Radiation treatment was delivered to characterise the effects of T treatment on RMS intrinsic radioresistance.

RESULTS

Our study showed that RMS cells respond to sub-physiological levels of T stimulation, finally promoting AR-dependent genomic and non-genomic effects, such as the transcriptional regulation of several oncogenes, the phosphorylation-mediated post-transductional modifications of AR and the activation of ERK, p38 and AKT signal transduction pathway mediators that, by physically complexing or not with AR, participate in regulating its transcriptional activity and the expression of T-targeted genes. T chronic daily treatment, performed as for the hormone circadian rhythm, did not significantly affect RMS cell growth, but improved RMS clonogenic and radioresistant potential and increased AR mRNA both in ERMS and ARMS. AR protein accumulation was evident in ERMS, this further developing an intrinsic T-independent AR activity.

CONCLUSIONS

Our results suggest that androgens sustain and improve RMS transformed and radioresistant phenotype, and therefore, their therapeutic application should be avoided in RMS post puberal patients.

Insights of Crosstalk between p53 Protein and the MKK3/MKK6/p38 MAPK Signaling Pathway in Cancer

TP53 is universally recognized as a pivotal protein in cell-cycle fate and apoptotic induction and, unsurprisingly, it is one of the most commonly hijacked control mechanisms in cancer. Recently, the kinase MKK3 emerged as a potential therapeutic target in different types of solid tumor being linked to mutant p53 gain-of-function. In this review, we summarize the delicate relationship among p53 mutational status, MKK3/MKK6 and the downstream activated master kinase p38MAPK, dissecting a finely-tuned crosstalk, in a potentially cell-context dependent scenario that urges towards a deeper characterization of the different molecular players involved in this signaling cascade and their interactions.

Mice overexpressing growth hormone exhibit increased skeletal muscle myostatin and MuRF1 with attenuation of muscle mass

Background

In contrast to the acute effects of growth hormone (GH) on skeletal muscle protein synthesis, long-term GH treatment appears to have negligible effects on muscle mass. Despite this knowledge, little is known regarding the chronic effects of GH on skeletal muscle protein synthesis and atrophy signaling pathways. The purpose of this study was to determine if protein synthesis pathways are attenuated and/or muscle atrophy intracellular signaling pathways are altered in the skeletal muscle of transgenic bovine GH (bGH) mice.

Methods

The gastrocnemius and soleus from 5-month-old male bGH mice (n = 9) and wild type (WT) controls (n = 9) were harvested and analyzed for proteins involved in the protein synthesis (Akt/mTOR), growth and proliferation (MAPK), and muscle atrophy (MuRF1 and myostatin) pathways.

Results

Total body mass was significantly increased in bGH mice compared to WT controls (49%, P < 0.0001). When expressed relative to total body mass, the gastrocnemius (− 28%, P < 0.0001), but not the soleus, was significantly lower in mice overexpressing GH, compared to controls. Transgenic bGH mice had elevated phosphorylation levels of protein kinase b (Akt1), 4E-binding protein 1 (4E-BP1), p70 S6 kinase, p42/44, and p38 (P < 0.05) compared to WT littermates. Mature myostatin (26 kDa), premature myostatin (52 kDa), and activin receptor type IIB (AcvR2B) protein levels were increased in bGH mice (P < 0.05), along with elevated phosphorylation levels of mothers against decapentaplegic homolog (Smad2) (59%, P < 0.0001). Mice overexpressing GH had increased MuRF1 expression (30%, P < 0.05) and insulin receptor substrate 1 (IRS1) serine phosphorylation (44%, P < 0.05) in the gastrocnemius, but not the soleus, when compared to controls.

Conclusions

These findings demonstrate that chronic elevations in circulating GH have a critical impact on signaling pathways involved in skeletal muscle protein synthesis and atrophy, and suggest that MuRF1, myostatin, and IRS1 serine phosphorylation may act to inhibit exaggerated glycolytic muscle growth, in environments of chronic GH/IGF-1 excess.

p38α 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 MAPK disables KMT1A-mediated repression of myogenic differentiation program

BACKGROUND

Master transcription factor MyoD can initiate the entire myogenic gene expression program which differentiates proliferating myoblasts into multinucleated myotubes. We previously demonstrated that histone methyltransferase KMT1A associates with and inhibits MyoD in proliferating myoblasts, and must be removed to allow differentiation to proceed. It is known that pro-myogenic signaling pathways such as PI3K/AKT and p38α MAPK play critical roles in enforcing associations between MyoD and transcriptional activators, while removing repressors. However, the mechanism which displaces KMT1A from MyoD, and the signals responsible, remain unknown.

METHODS

To investigate the role of p38α on MyoD-mediated differentiation, we utilized C2C12 myoblast cells as an in vitro model. p38α activity was either augmented via overexpression of a constitutively active upstream kinase or blocked via lentiviral delivery of a specific p38α shRNA or treatment with p38α/β inhibitor SB203580. Overexpression of KMT1A in these cells via lentiviral delivery was also used as a system wherein terminal differentiation is impeded by high levels of KMT1A.

RESULTS

The association of KMT1A and MyoD persisted, and differentiation was blocked in C2C12 myoblasts specifically after pharmacologic or genetic blockade of p38α. Conversely, forced activation of p38α was sufficient to activate MyoD and overcome the differentiation blockade in KMT1A-overexpressing C2C12 cells. Consistent with this finding, KMT1A phosphorylation during C2C12 differentiation correlated strongly with the activation of p38α. This phosphorylation was prevented by the inhibition of p38α. Biochemical studies further revealed that KMT1A can be a direct substrate for p38α. Importantly, chromatin immunoprecipitation (ChIP) studies show that the removal of KMT1A-mediated transcription repressive histone tri-methylation (H3K9me3) from the promoter of the Myogenin gene, a critical regulator of muscle differentiation, is dependent on p38α activity in C2C12 cells. Elevated p38α activity was also sufficient to remove this repressive H3K9me3 mark. Moreover, ChIP studies from C2C12 cells show that p38α activity is necessary and sufficient to establish active H3K9 acetylation on the Myogenin promoter.

CONCLUSIONS

Activation of p38α displaces KMT1A from MyoD to initiate myogenic gene expression upon induction of myoblasts differentiation.

Ex Vivo Expansion and In Vivo Self-Renewal of Human Muscle Stem Cells

Adult skeletal muscle stem cells, or satellite cells (SCs), regenerate functional muscle following transplantation into injured or diseased tissue. To gain insight into human SC (huSC) biology, we analyzed transcriptome dynamics by RNA sequencing of prospectively isolated quiescent and activated huSCs. This analysis indicated that huSCs differentiate and lose proliferative potential when maintained in high-mitogen conditions ex vivo. Further analysis of gene expression revealed that p38 MAPK acts in a transcriptional network underlying huSC self-renewal. Activation of p38 signaling correlated with huSC differentiation, while inhibition of p38 reversibly prevented differentiation, enabling expansion of huSCs. When transplanted, expanded huSCs differentiated to generate chimeric muscle and engrafted as SCs in the sublaminar niche with a greater frequency than freshly isolated cells or cells cultured without p38 inhibition. These studies indicate characteristics of the huSC transcriptome that promote expansion ex vivo to allow enhanced functional engraftment of a defined population of self-renewing huSCs.

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Prospective isolation of highly pure huSCs from diverse muscles

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RNA sequencing resource for studying the huSC transcriptome

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Core transcription factor regulatory network of huSC differentiation

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Expanded huSCs that are genetically manipulable and self-renew in vivo

Selective inhibition of ATPase activity during contraction alters the activation of p38 MAP kinase isoforms in skeletal muscle

Muscle contractions strongly activate p38 MAP kinases, but the precise contraction-associated sarcoplasmic event(s) (e.g., force production, energetic demands, and/or calcium cycling) that activate these kinases are still unclear. We tested the hypothesis that during contraction the phosphorylation of p38 isoforms is sensitive to the increase in ATP demand relative to ATP supply. Energetic demands were inhibited using N-benzyl-p-toluene sulphonamide (BTS, type II actomyosin) and cyclopiazonic acid (CPA, SERCA). Extensor digitorum longus muscles from Swiss Webster mice were incubated in Ringer's solution (37°C) with or without inhibitors and then stimulated at 10 Hz for 15 min. Muscles were immediately freeze-clamped for metabolite and Western blot analysis. BTS and BTS + CPA treatment decreased force production by 85%, as measured by the tension time integral, while CPA alone potentiated force by 310%. In control muscles, contractions resulted in a 73% loss of ATP content and a concomitant sevenfold increase in IMP content, a measure of sustained energetic imbalance. BTS or CPA treatment lessened the loss of ATP, but BTS + CPA treatment completely eliminated the energetic imbalance since ATP and IMP levels were nearly equal to those of non-stimulated muscles. The independent inhibition of cytosolic ATPase activities had no effect on contraction-induced p38 MAPK phosphorylation, but combined treatment prevented the increase in phosphorylation of the γ isoform while the α/β isoforms unaffected. These observations suggest that an energetic signal may trigger phosphorylation of the p38γ isoform and also may explain how contractions differentially activate signaling pathways.

Acute low-load resistance exercise with and without blood flow restriction increased protein signalling and number of satellite cells in human skeletal muscle

PURPOSE

To investigate hypertrophic signalling after a single bout of low-load resistance exercise with and without blood flow restriction (BFR).

METHODS

Seven subjects performed unilateral knee extensions at 30 % of their one repetition maximum. The subjects performed five sets to failure with BFR on one leg, and then repeated the same amount of work with the other leg without BFR. Biopsies were obtained from m. vastus lateralis before and 1, 24 and 48 h after exercise.

RESULTS

At 1-h post-exercise, phosphorylation of p70S6KThr389 and p38MAPKThr180/Tyr182 was elevated in the BFR leg, but not in the free-flow leg. Phospho-p70S6KThr389 was elevated three- to fourfold in both legs at 24-h post-exercise, but back to baseline at 48 h. The number of visible satellite cells (SCs) per muscle fibre was increased for all post-exercise time points and in both legs (33–53 %). The proportion of SCs with cytoplasmic extensions was elevated at 1-h post in the BFR leg and the number of SCs positive for myogenin and/or MyoD was increased at 1- and 24-h post-exercise for both legs combined.

CONCLUSION

Acute low-load resistance exercise with BFR resulted in early (1 h) and late (24 h) enhancement of phospho-p70S6KThr389, an early response of p38MAPK, and an increased number of SCs per muscle fibre. Enhanced phospho-p70S6KThr389 at 24-h post-exercise and increases in SC numbers were seen also in the free-flow leg. Implications of these findings for the hypertrophic effects of fatiguing low-load resistance exercise with and without BFR are discussed.

p38α MAPK regulates adult muscle stem cell fate by restricting progenitor proliferation during postnatal growth and repair

Stem cell function is essential for the maintenance of adult tissue homeostasis. Controlling the balance between self-renewal and differentiation is crucial to maintain a receptive satellite cell pool capable of responding to growth and regeneration cues. The mitogen-activated protein kinase p38α has been implicated in the regulation of these processes but its influence in adult muscle remains unknown. Using conditional satellite cell p38α knockout mice we have demonstrated that p38α restricts excess proliferation in the postnatal growth phase while promoting timely myoblast differentiation. Differentiation was still able to occur in the p38α-null satellite cells, however, but was delayed. An absence of p38α resulted in a postnatal growth defect along with the persistence of an increased reservoir of satellite cells into adulthood. This population was still capable of responding to cardiotoxin-induced injury, resulting in complete, albeit delayed, regeneration, with further enhancement of the satellite cell population. Increased p38γ phosphorylation accompanied the absence of p38α, and inhibition of p38γ ex vivo substantially decreased the myogenic defect. We have used genome-wide transcriptome analysis to characterize the changes in expression that occur between resting and regenerating muscle, and the influence p38α has on these expression profiles. This study provides novel evidence for the fundamental role of p38α in adult muscle homeostasis in vivo.

Differential regulation of IGF-I and IGF-II gene expression in skeletal muscle cells

Insulin-like growth factor (IGF)-I and IGF-II play major roles in the regulation of skeletal muscle growth and differentiation, and both are locally expressed in muscle cells. Recent studies have demonstrated that IGF-II up-regulates its own gene expression during myogenesis and this auto-regulatory loop is critical for muscle differentiation. How local IGF-I is regulated in this process is unclear. Here, we report that while IGF-II up-regulated its own gene expression, it suppressed IGF-I gene expression during myogenesis. These opposite effects of IGF-II on IGF-I and IGF-II genes expression were time dependent and dose dependent. It has been shown that IGFs activate the PI3K-Akt-mTOR, p38 MAPK, and Erk1/2 MAPK pathways. In myoblasts, we examined their role(s) in mediating the opposite effects of IGF-II. Our results showed that both the PI3K-Akt-mTOR and p38 MAPK pathways played critical roles in increasing IGF-II mRNA expression. In contrast, mTOR was required for down-regulating the IGF-I gene expression by IGF-II. In addition, Akt, Erk1/2 MAPK, and p38 MAPK pathways were also involved in the regulation of basal levels of IGF-I and IGF-II genes during myogenesis. These findings reveal a previously unrecognized negative feedback mechanism and extend our knowledge of IGF-I and IGF-II gene expression and regulation during myogenesis.

Loss of emerin alters myogenic signaling and miRNA expression in mouse myogenic progenitors

Emerin is an integral membrane protein of the inner nuclear membrane. Mutations in emerin cause X-linked Emery-Dreifuss muscular dystrophy (EDMD), a disease characterized by skeletal muscle wasting and dilated cardiomyopathy. Current evidence suggests the muscle wasting phenotype of EDMD is caused by defective myogenic progenitor cell differentiation and impaired muscle regeneration. We obtained genome-wide expression data for both mRNA and micro-RNA (miRNA) in wildtype and emerin-null mouse myogenic progenitor cells. We report here that emerin-null myogenic progenitors exhibit differential expression of multiple signaling pathway components required for normal muscle development and regeneration. Components of the Wnt, IGF-1, TGF-β, and Notch signaling pathways are misexpressed in emerin-null myogenic progenitors at both the mRNA and protein levels. We also report significant perturbations in the expression and activation of p38/Mapk14 in emerin-null myogenic progenitors, showing that perturbed expression of Wnt, IGF-1, TGF-β, and Notch signaling components disrupts normal downstream myogenic signaling in these cells. Collectively, these data support the hypothesis that emerin is essential for proper myogenic signaling in myogenic progenitors, which is necessary for myogenic differentiation and muscle regeneration.

Non-genomic actions of aldosterone: from receptors and signals to membrane targets

In tissues which express the mineralocorticoid receptor (MR), aldosterone modulates the expression of membrane targets such as the subunits of the epithelial Na(+) channel, in combination with important signalling intermediates such as serum and glucocorticoid-regulated kinase-1. In addition, the rapid 'non-genomic' activation of protein kinases and secondary messenger signalling cascades has also been detected in aldosterone-sensitive tissues of the nephron, distal colon and cardiovascular system. These rapid actions are variously described as being coupled to MR or to an as yet unidentified, membrane-associated aldosterone receptor. The rapidly activated signalling cascades add a level of fine-tuning to the activity of aldosterone-responsive membrane transporters and also modulate the aldosterone-induced changes in gene expression through receptor and transcription factor phosphorylation.

The myogenic kinome: protein kinases critical to mammalian skeletal myogenesis

Myogenesis is a complex and tightly regulated process, the end result of which is the formation of a multinucleated myofibre with contractile capability. Typically, this process is described as being regulated by a coordinated transcriptional hierarchy. However, like any cellular process, myogenesis is also controlled by members of the protein kinase family, which transmit and execute signals initiated by promyogenic stimuli. In this review, we describe the various kinases involved in mammalian skeletal myogenesis: which step of myogenesis a particular kinase regulates, how it is activated (if known) and what its downstream effects are. We present a scheme of protein kinase activity, similar to that which exists for the myogenic transcription factors, to better clarify the complex signalling that underlies muscle development.

WITHDRAWN: Activation of p38 MAPK attenuates endoplasmic reticulum stress by up-regulating XBP1s

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