p21-activated kinase 4 counteracts PKA-dependent lipolysis by phosphorylating FABP4 and HSL.

Adipose tissue lipolysis is mediated by cAMP-protein kinase A (PKA)-dependent intracellular signalling. Here, we show that PKA targets p21-activated kinase 4 (PAK4), leading to its protein degradation. Adipose tissue-specific overexpression of PAK4 in mice attenuates lipolysis and exacerbates diet-induced obesity. Conversely, adipose tissue-specific knockout of Pak4 or the administration of a PAK4 inhibitor in mice ameliorates diet-induced obesity and insulin resistance while enhancing lipolysis. Pak4 knockout also increases energy expenditure and adipose tissue browning activity. Mechanistically, PAK4 directly phosphorylates fatty acid-binding protein 4 (FABP4) at T126 and hormone-sensitive lipase (HSL) at S565, impairing their interaction and thereby inhibiting lipolysis. Levels of PAK4 and the phosphorylation of FABP4-T126 and HSL-S565 are enhanced in the visceral fat of individuals with obesity compared to their lean counterparts. In summary, we have uncovered an important role for FABP4 phosphorylation in regulating adipose tissue lipolysis, and PAK4 inhibition may offer a therapeutic strategy for the treatment of obesity.

Cannabidiol Inhibits IgE-Mediated Mast Cell Degranulation and Anaphylaxis in Mice.

SCOPE: Cannabidiol (CBD), the most abundant non-psychoactive constituent of the plant Cannabis sativa, is known to possess immune modulatory properties. This study investigates the effects of CBD on mast cell degranulation in human and mouse primary mast cells and passive cutaneous anaphylaxis in mice. METHODS AND RESULTS: Mouse bone marrow-derived mast cells and human cord-blood derived mast cells are generated. CBD suppressed antigen-stimulated mast cell degranulation in a concentration-dependent manner. Mechanistically, CBD inhibited both the phosphorylation of FcεRI downstream signaling molecules and calcium mobilization in mast cells, while exerting no effect on FcεRI expression and IgE binding to FcεRI. These suppressive effects are preserved in the mast cells that are depleted of type 1 (CB1) and type 2 (CB2) cannabinoid receptors, as well as in the presence of CB1 agonist, CB2 agonist, CB1 inverse agonist, and CB2 inverse agonist. CBD also inhibited the development of mast cells in a long-term culture. The intraperitoneal administration of CBD suppressed passive cutaneous anaphylaxis in mice as evidenced by a reduction in ear swelling and decrease in the number of degranulated mast cells. CONCLUSION: Based on these results, the administration of CBD is a new therapeutic intervention in mast cell-associated anaphylactic diseases.

p21-activated kinase 4 suppresses fatty acid ß-oxidation and ketogenesis by phosphorylating NCoR1.

PPARα corepressor NCoR1 is a key regulator of fatty acid ß-oxidation and ketogenesis. However, its regulatory mechanism is largely unknown. Here, we report that oncoprotein p21-activated kinase 4 (PAK4) is an NCoR1 kinase. Specifically, PAK4 phosphorylates NCoR1 at T1619/T2124, resulting in an increase in its nuclear localization and interaction with PPARα, thereby repressing the transcriptional activity of PPARα. We observe impaired ketogenesis and increases in PAK4 protein and NCoR1 phosphorylation levels in liver tissues of high fat diet-fed mice, NAFLD patients, and hepatocellular carcinoma patients. Forced overexpression of PAK4 in mice represses ketogenesis and thereby increases hepatic fat accumulation, whereas genetic ablation or pharmacological inhibition of PAK4 exhibites an opposite phenotype. Interestingly, PAK4 protein levels are significantly suppressed by fasting, largely through either cAMP/PKA- or Sirt1-mediated ubiquitination and proteasome degradation. In this way, our findings provide evidence for a PAK4-NCoR1/PPARα signaling pathway that regulates fatty acid ß-oxidation and ketogenesis.

Multiple Roles of Sirtuin 6 in Adipose Tissue Inflammation.

Adipose tissue (AT) inflammation is strongly associated with obesity-induced insulin resistance. When subjected to metabolic stress, adipocytes become inflamed and secrete a plethora of cytokines and chemokines, which recruit circulating immune cells to AT. Although sirtuin 6 (Sirt6) is known to control genomic stabilization, aging, and cellular metabolism, it is now understood to also play a pivotal role in the regulation of AT inflammation. Sirt6 protein levels are reduced in the AT of obese humans and animals and increased by weight loss. In this review, we summarize the potential mechanism of AT inflammation caused by impaired action of Sirt6 from the immune cells' point of view. We first describe the properties and functions of immune cells in obese AT, with an emphasis on discrete macrophage subpopulations which are central to AT inflammation. We then highlight data that links Sirt6 to functional phenotypes of AT inflammation. Importantly, we discuss in detail the effects of Sirt6 deficiency in adipocytes, macrophages, and eosinophils on insulin resistance or AT browning. In our closing perspectives, we discuss emerging issues in this field that require further investigation.

LDHA Desuccinylase Sirtuin 5 as A Novel Cancer Metastatic Stimulator in Aggressive Prostate Cancer.

Prostate cancer (PCa) is the most commonly diagnosed genital cancer in men worldwide. Around 80% of the patients who developed advanced PCa suffered from bone metastasis, with a sharp drop in the survival rate. Despite great efforts, the detailed mechanisms underlying castration-resistant PCa (CRPC) remain unclear. Sirtuin 5 (SIRT5), an NAD+-dependent desuccinylase, is hypothesized to be a key regulator of various cancers. However, compared to other SIRTs, the role of SIRT5 in cancer has not been extensively studied. Here, we revealed significantly decreased SIRT5 levels in aggressive PCa cells relative to the PCa stages. The correlation between the decrease in the SIRT5 level and the patient's reduced survival rate was also confirmed. Using quantitative global succinylome analysis, we characterized a significant increase in the succinylation at lysine 118 (K118su) of lactate dehydrogenase A (LDHA), which plays a role in increasing LDH activity. As a substrate of SIRT5, LDHA-K118su significantly increased the migration and invasion of PCa cells and LDH activity in PCa patients. This study reveals the reduction of SIRT5 protein expression and LDHA-K118su as a novel mechanism involved in PCa progression, which could serve as a new target to prevent CPRC progression for PCa treatment.

Limonium tetragonum Promotes Running Endurance in Mice through Mitochondrial Biogenesis and Oxidative Fiber Formation.

The purpose of this study was to examine whether Limonium tetragonum, cultivated in a smart-farming system with LED lamps, could increase exercise capacity in mice. C57BL/6 male mice were orally administered vehicle or Limonium tetragonum water extract (LTE), either 30 or 100 mg/kg, and were subjected to moderate intensity treadmill exercise for 4 weeks. Running distance markedly increased in the LTE group (100 mg/kg) by 80 ± 4% compared to the vehicle group, which was accompanied by a higher proportion of oxidative fibers (6 ± 6% vs. 10 ± 4%). Mitochondrial DNA content and gene expressions related to mitochondrial biogenesis were significantly increased in LTE-supplemented gastrocnemius muscles. At the molecular level, the expression of PGC-1α, a master regulator of fast-to-slow fiber-type transition, was increased downstream of the PKA/CREB signaling pathway. LTE induction of the PKA/CREB signaling pathway was also observed in C2C12 cells, which was effectively suppressed by PKA inhibitors H89 and Rp-cAMP. Altogether, these findings indicate that LTE treatment enhanced endurance exercise capacity via an improvement in mitochondrial biosynthesis and the increases in the formation of oxidative slow-twitch fibers. Future study is warranted to validate the exercise-enhancing effect of LTE in the human.

Supplementation with Vitis vinifera Jingzaojing Leaf and Shoot Extract Improves Exercise Endurance in Mice.

Switching myofibers from the fast-glycolytic type to the slow-oxidative type is associated with an alleviation of the symptoms associated with various cardiometabolic diseases. This study investigates the effect of Vitis vinifera Jingzaojing leaf and shoot extract (JLSE), which is rich in phenolic compounds, on the regulation of skeletal muscle fiber-type switching, as well as the associated underlying mechanism. Male C57BL/6N mice were supplemented orally with vehicle or JLSE (300 mg/kg) and subjected to treadmill exercise training. After four weeks, mice in the JLSE-supplemented group showed significantly improved exercise endurance and mitochondrial oxidative capacity. JLSE supplementation increased the expression of sirtuin 6 and decreased Sox6 expression, thereby elevating the number of mitochondria and encouraging fast-to-slow myofiber switching. The results of our experiments suggest that JLSE supplementation reprograms myofiber composition to favor the slow oxidative type, ultimately enhancing exercise endurance.

Targeting p21-activated kinase 4 (PAK4) with pyrazolo[3,4-d]pyrimidine derivative SPA7012 attenuates hepatic ischaemia-reperfusion injury in mice.

p21-Activated kinase 4 (PAK4), one of the serine/threonine kinases activated by Rho-family GTPases, has been widely studied as an oncogenic protein that is overexpressed in many types of cancers. In our recent study, PAK4 upregulation was observed in mice exhibiting hepatic ischaemia-reperfusion (I/R) and in liver transplantation patients. Liver I/R injury was also attenuated in Pak4 KO mice. Herein, we report a novel series of pyrazolo[3,4-d]pyrimidine derivatives of type I ½ PAK4 inhibitors. The most potent compound SPA7012 was evaluated to determine the pharmacological potential of PAK4 inhibitor in I/R injury in mice. Mice with I/R injury showed typical patterns of liver damage, as demonstrated by increases in serum levels of aminotransferases and proinflammatory cytokines, hepatocellular necrosis and apoptosis, and inflammatory cell infiltration, relative to sham mice. Conversely, intraperitoneal administration of SPA7012 dramatically attenuated biochemical and histopathologic changes. Mechanistically, stabilisation of nuclear factor-erythroid 2-related factor 2 (Nrf2), a master regulator of anti-oxidative response, was observed following SPA7012 treatment. SPA7012 treatment in primary hepatocytes also attenuated hypoxia-reoxygenation-induced apoptotic cell death and inflammation. Together, these results provide experimental evidence supporting the use of PAK4 inhibitors for alleviation of I/R-induced liver damage.

Therapeutic Effect of Acer tegmentosum Maxim Twig Extract in Bile Duct Ligation-Induced Acute Cholestasis in Mice.

Cholestatic liver disease, or cholestasis, is a condition characterized by liver inflammation and fibrosis following a bile duct obstruction and an intrahepatic accumulation of bile acids. Inhibiting inflammation is a promising therapeutic strategy for cholestatic liver diseases. Acer tegmentosum Maxim extract (ATE) is best known for its anti-inflammatory and antioxidative properties. In this study, we investigated the effects of ATE on liver injury and fibrosis in mice with bile duct ligation (BDL)-induced cholestasis through analysis of gene expression, cytokines, and histological examination. Oral administration of ATE (20 or 50 mg/kg) for 14 days significantly attenuated hepatocellular necrosis compared to vehicle-treated BDL mice, which was accompanied by the reduced level of serum bile acids and bilirubin. We determined that ATE treatment reduced liver inflammation, oxidative stress, and fibrosis. These beneficial effects of ATE were concurrent with the decreased expression of genes involved in the NF-κB pathway, suggesting that the anti-inflammatory effect of ATE could be a possible mechanism against cholestasis-associated liver injury. Our findings substantiate ATE's role as an alternative therapeutic agent for cholestasis-induced liver injury and fibrosis.

NAD+-boosting molecules suppress mast cell degranulation and anaphylactic responses in mice.

Nicotinamide adenine dinucleotide (NAD+) acts as a cofactor for multiple biological processes. While previous research has revealed that the NAD+ declines associated with aging contributes to an impairment of immune cells, its role in mast cell function, especially in response to an anaphylactic condition, has remained unexplored. We tested whether the restoration of cellular NAD+ concentration by the supplementation of NAD+ boosting molecules prevented mast cell degranulation and anaphylactic responses. Methods: Bone marrow derived mast cells (BMMCs) and human cord blood derived mast cells were treated with NAD+ precursors nicotinamide mononucleotide (NMN) and nicotinamide riboside (NR), and FcεRI downstream signaling was assessed. Animal models of passive systemic anaphylaxis (PSA) and passive cutaneous anaphylaxis (PCA) were used to investigate the effects of NAD+ precursors in the anaphylactic responses of mice. Results: Treatment of murine BMMCs and human cord blood derived mast cells with NAD+ precursors repressed intracellular signaling downstream of FcεRI, as well as the release of inflammatory cytokines and lipid mediators. The intraperitoneal administration of NMN or NR also markedly attenuated IgE-mediated anaphylactic responses in mouse models of PSA and PCA. These beneficial effects of NAD+ precursors, however, were attenuated in mast cell-specific Sirt6 knockout mice, indicating a Sirt6 dependency for their action. Conclusion: NAD+ precursors may serve as an effective therapeutic strategy that limits mast cell-mediated anaphylactic responses.

Angelica keiskei Root Extract Attenuates Bile Duct Ligation-Induced Liver Injury in Mice.

Although multiple studies have shown that Angelica keiskei of the Umbelliferae family has potent anti-inflammatory and antioxidative activities and that it reduces the serum bile acids in humans, whether A. keiskei has protective effects against cholestasis-induced liver injury remains unexplored until now. This study tests the hypothesis that Angelica keiskei root extract (AKE) alleviates liver injury, inflammation, and fibrosis in mouse models of acute cholestasis induced by bile duct ligation (BDL). Oral administration of AKE (200 or 500 mg/kg) attenuated hepatocellular necrosis and significantly reduced serum levels of bile acids and bilirubin in BDL mice. The critical enzyme of bile acid synthesis, CYP7A1, was repressed by AKE, suggesting that reduced bile acid production may contribute to liver protection. Moreover, we determined through gene expression and cytokine analysis and histological examination that AKE treatment decreased liver inflammation, oxidative stress, and fibrosis. AKE also suppressed the NF-κB pathway, suggesting this as a possible mediator of its anti-inflammatory effect. Our findings substantiate that AKE may be promising for treating cholestatic liver diseases in the future.

Loss of ERdj5 exacerbates oxidative stress in mice with alcoholic liver disease via suppressing Nrf2.

Alcoholic liver disease is the major cause of chronic liver diseases. Excessive alcohol intake results in endoplasmic reticulum (ER) stress. ERdj5, a member of DNAJ family, is an ER-resident chaperone protein, whose role in alcoholic liver disease remains to be investigated. In this study, we aim to address the effect of ERdj5 on alcoholic liver disease and the underlying mechanism. Hepatic Dnajc10 (ERdj5) mRNA expression was elevated in both human and mouse alcoholic hepatitis. In mice subjected to chronic and binge ethanol feeding, ERdj5 levels were also markedly increased. Hepatic Dnajc10 correlated with Xbp1s mRNA. Tunicamycin, an ER stress inducer, increased ERdj5 levels. Dnajc10 knockout mice exhibited exacerbated alcohol-induced liver injury and hepatic steatosis. However, the macrophage numbers and chemokine levels were similar to those in wild-type mice. Depletion of Dnajc10 promoted oxidative stress. Ethanol feeding increased hepatic H2O2 levels, and these were further increased in Dnajc10 knockout mice. Additionally, Dnajc10-deficient hepatocytes produced large amounts of reactive oxygen species. Notably, Nrf2, a central regulator of oxidative stress, was decreased by depletion of Dnajc10 in the nuclear fraction of ethanol-treated mouse liver. Consistently, liver tissues from ethanol-fed Dnajc10 knockout mice had reduced expression of downstream antioxidant genes. Furthermore, hepatic glutathione content in the liver of knockout mice declined compared to wild-type mice. In conclusion, our results demonstrate that ethanol-induced ERdj5 may regulate the Nrf2 pathway and glutathione contents, and have protective effects on liver damage and alcohol-mediated oxidative stress in mice. These suggest that ERdj5 has the potential to protect against alcoholic liver disease.

Sirt6 reprograms myofibers to oxidative type through CREB-dependent Sox6 suppression.

Expanding the exercise capacity of skeletal muscle is an emerging strategy to combat obesity-related metabolic diseases and this can be achieved by shifting skeletal muscle fibers toward slow-twitch oxidative type. Here, we report that Sirt6, an anti-aging histone deacetylase, is critical in regulating myofiber configuration toward oxidative type and that Sirt6 activator can be an exercise mimetic. Genetic inactivation of Sirt6 in skeletal muscle reduced while its transgenic overexpression increased mitochondrial oxidative capacity and exercise performance in mice. Mechanistically, we show that Sirt6 downregulated Sox6, a key repressor of slow fiber specific gene, by increasing the transcription of CREB. Sirt6 expression is elevated in chronically exercised humans, and mice treated with an activator of Sirt6 showed an increase in exercise endurance as compared to exercise-trained controls. Thus, the current study identifies Sirt6 as a molecular target for reprogramming myofiber composition toward the oxidative type and for improving muscle performance.

p21-activated kinase 4 inhibition protects against liver ischemia/reperfusion injury: Role of nuclear factor erythroid 2-related factor 2 phosphorylation.

BACKGROUND AND AIMS: p21-activated kinase 4 (PAK4), an oncogenic protein, has emerged as a promising target for anticancer drug development. Its role in oxidative stress conditions, however, remains elusive. We investigated the effects of PAK4 signaling on hepatic ischemia/reperfusion (I/R) injury. APPROACH AND RESULTS: Hepatocyte- and myeloid-specific Pak4 knockout (KO) mice and their littermate controls were subjected to a partial hepatic I/R (HIR) injury. We manipulated the catalytic activity of PAK4, either through genetic engineering (gene knockout, overexpression of wild-type [WT] or dominant-negative kinase) or pharmacological inhibitor, coupled with a readout of nuclear factor erythroid 2-related factor 2 (Nrf2) activity, to test the potential function of PAK4 on HIR injury. PAK4 expression was markedly up-regulated in liver during HIR injury in mice and humans. Deletion of PAK4 in hepatocytes, but not in myeloid cells, ameliorated liver damages, as demonstrated in the decrease in hepatocellular necrosis and inflammatory responses. Conversely, the forced expression of WT PAK4 aggravated the pathological changes. PAK4 directly phosphorylated Nrf2 at T369, and it led to its nuclear export and proteasomal degradation, all of which impaired antioxidant responses in hepatocytes. Nrf2 silencing in liver abolished the protective effects of PAK4 deficiency. A PAK4 inhibitor protected mice from HIR injury. CONCLUSIONS: PAK4 phosphorylates Nrf2 and suppresses its transcriptional activity. Genetic or pharmacological suppression of PAK4 alleviates HIR injury. Thus, PAK4 inhibition may represent a promising intervention against I/R-induced liver injury.

SIRT5 Directly Inhibits the PI3K/AKT Pathway in Prostate Cancer Cell Lines.

BACKGROUND/AIM: Prostate cancer (PCa) is the most commonly diagnosed genital cancer in men globally. Among patients who develop advanced PCa, 80% are affected by bone metastasis, with a sharp drop in survival rate. Despite efforts, the details of mechanisms of metastasis of PCa remain unclear. SIRT5, an NAD+-dependent deacylase, is hypothesized to be a crucial regulator of various cancers. The role of SIRT5 in cancer has not been extensively studied compared to other SIRTs. In this study, we showed significantly decreased levels of SIRT5 in PC-3M, a highly aggressive PC-3 cell variant. MATERIALS AND METHODS: We characterized the differentially expressed proteins between parental and SIRT5 KO PC-3 cells using quantitative proteomics analysis. RESULTS: A significant increase in expression of interleukin-1ß (IL-1ß) in SIRT5 KO cells was observed, and the PI3K/AKT/NF-ĸB signaling pathway was found significantly elevated in SIRT5 KO cells by the Gene Ontology annotation and KEGG pathway functional enrichment analysis. Moreover, we confirmed that SIRT5 can bind PI3K by immunoprecipitation analysis. CONCLUSION: This study is the first to demonstrate a relationship between SIRT5 and PCa metastasis, suggesting that SIRT5-mediated inhibition of the PI3K/AKT/NK-kB pathway is reduced for secondary metastasis from bone to other tissues.

Loss of Sirt6 in adipocytes impairs the ability of adipose tissue to adapt to intermittent fasting.

Intermittent fasting (IF) is gaining popularity for its effectiveness in improving overall health, including its effectiveness in achieving weight loss and euglycemia. The molecular mechanisms of IF, however, are not well understood. This study investigated the relationship between adipocyte sirtuin 6 (Sirt6) and the metabolic benefits of IF. Adipocyte-specific Sirt6-knockout (aS6KO) mice and wild-type littermates were fed a high-fat diet (HFD) ad libitum for four weeks and then subjected to 12 weeks on a 2:1 IF regimen consisting of two days of feeding followed by one day of fasting. Compared with wild-type mice, aS6KO mice subjected to HFD + IF exhibited a diminished response, as reflected by their glucose and insulin intolerance, reduced energy expenditure and adipose tissue browning, and increased inflammation of white adipose tissue. Sirt6 deficiency in hepatocytes or in myeloid cells did not impair adaptation to IF. Finally, the results indicated that the impaired adipose tissue browning and reduced expression of UCP1 in aS6KO mice were accompanied by downregulation of p38 MAPK/ATF2 signaling. Our findings indicate that Sirt6 in adipocytes is critical to obtaining the improved glucose metabolism and metabolic profiles conferred by IF and that maintaining high levels of Sirt6 in adipocytes may mimic the health benefits of IF.

Repurposing the anthelmintic praziquantel to treat psoriasis.

BACKGROUND AND PURPOSE: The anthelmintic drug praziquantel has been used as a standard treatment for schistosomiasis for over 40 years. This study aimed to repurpose praziquantel to treat psoriasis. EXPERIMENTAL APPROACH: Psoriasis-like skin inflammation was induced in mice (C57 and Balb/C) by topical application of imiquimod or intradermal injection of recombinant IL-23. Praziquantel was either orally or topically administered during the psoriasis induction period. KEY RESULTS: Mice treated with either oral or topical praziquantel exhibited markedly improved psoriasiform skin symptoms when compared with control mice, as judged by disease severity score, epidermal thickening, inflammatory cell infiltration and spleen size. Flow cytometric analysis of infiltrating immune cells from mouse skin displayed reduced infiltration of Th17 cells. In vitro experiments revealed that praziquantel inhibited STAT3 phosphorylation and RORγt expression in splenic CD4+ T-cells. Praziquantel also decreased STAT3 phosphorylation in HEK-A/F cells. Down-regulation of STAT3 phosphorylation in these cells accounts for the decreased number of Th17 cells and keratinocytes. CONCLUSION AND IMPLICATIONS: These results provide the first preclinical evidence that praziquantel may effectively treat psoriasis, and suggest that praziquantel alleviates symptoms in mice by inhibiting STAT3 phosphorylation, thereby suppressing Th17 immune responses.

p21-activated kinase 4 phosphorylates peroxisome proliferator-activated receptor Υ and suppresses skeletal muscle regeneration.

BACKGROUND: Skeletal muscle regeneration is an adaptive response to injury that is crucial to the maintenance of muscle mass and function. A p21-activated kinase 4 (PAK4) serine/threonine kinase is critical to the regulation of cytoskeletal changes, cell proliferation, and growth. However, PAK4's role in myoblast differentiation and regenerative myogenesis remains to be determined. METHODS: We used a mouse model of myotoxin (notexin)-induced muscle regeneration. In vitro myogenesis was performed in the C2C12 myoblast cell line, primary myoblasts, and primary satellite cells. In vivo overexpression of PAK4 or kinase-inactive mutant PAK4S474A was conducted in skeletal muscle to examine PAK4's kinase-dependent effect on muscle regeneration. The regeneration process was evaluated by determining the number and size of multinucleated myofibres and expression patterns of myogenin and eMyHC. To explore whether PAK4 inhibition improves muscle regeneration, mice were injected intramuscularly with siRNA that targeted PAK4 or orally administered with a chemical inhibitor of PAK4. RESULTS: p21-activated kinase 4 was highly expressed during the myoblast stage, but expression gradually and substantially decreased as myoblasts differentiated into myotubes. PAK4 overexpression, but not kinase-inactive mutant PAK4S474A overexpression, significantly impeded myoblast fusion and MyHC-positive myotube formation in C2C12 cells, primary myoblasts, and satellite cells (P < 0.01). Conversely, PAK4 silencing led to an 8.7% and a 20.3% increase in the number of multinucleated larger myotubes in C2C12 cells and primary myoblasts. Further, in vivo overexpression of PAK4 by adenovirus injection to mice prior to and after myotoxin-induced injury led to a 52.6% decrease in the number of eMyHC-positive myofibres on Day 5 in tibialis anterior muscles as compared with those injected with control adenoviruses (P < 0.01), while Ad-PAK4S474A showed comparable muscle regeneration parameters. PAK4-induced repression of muscle regeneration coincided with an increase in phosphatase and tensin homologue (PTEN) expression and a decrease in phosphoinositide 3-kinase-Akt signalling. In contrast, PAK4 silencing reduced PTEN expression in mice. Consistent with these findings, prodrug of PAK4 inhibitor CZh-226 (30 mg/kg) orally administered to mice repressed PTEN expression and accelerated myotube formation. Subsequent mechanistic studies revealed that PAK4 directly phosphorylates PPARγ at S273 to increase its transcription activity, thereby up-regulating PTEN expression. Importantly, an analysis of the Genotype-Tissue Expression database showed a positive correlation between PAK4 and PTEN in human skeletal muscle tissues (P < 0.01). CONCLUSIONS: p1-activated kinase 4 is a new member of PPARγ kinase, and PAK4 inhibition may have a therapeutic role as an accelerant of muscle regeneration.

Sirtuin 6 promotes eosinophil differentiation by activating GATA-1 transcription factor.

There is evidence emerging that exposure to cold temperatures enhances alternative activation of macrophages in white adipose tissue (WAT), which promotes adipocyte beiging and adaptive thermogenesis. Although we recently reported that NAD+ -dependent deacetylase sirtuin 6 (Sirt6) drives alternatively activated (M2) macrophage polarization, the role of myeloid Sirt6 in adaptive thermogenesis had remained elusive. In this study, we demonstrate that myeloid Sirt6 deficiency impaired both thermogenic responses and M2 macrophage infiltration in subcutaneous WAT (scWAT) during cold exposure. Moreover, the infiltration of Siglec-F-positive eosinophils in scWAT and Th2 cytokines levels was reduced in myeloid Sirt6 knockout mice. An ex vivo bone marrow-derived cell culture experiment indicated that Sirt6 was required for eosinophil differentiation independent of its deacetylase activity. Data from our in vitro experiments show that Sirt6 acted as a transcriptional cofactor of GATA-1, independent of its catalytic function as a deacetylase or ADP-ribosyltransferase. Specifically, Sirt6 physically interacted with GATA-1, and enhanced GATA-1's acetylation and transcriptional activity by facilitating its cooperation with p300. Overall, our results suggest that myeloid Sirt6 plays an important role in eosinophil differentiation and fat beiging/adaptive thermogenesis, which is at least in part due to its ability to bind GATA-1 and stimulate its transcriptional activity.