Lysine Deacetylation Is a Key Function of the Lysyl Oxidase Family of Proteins in Cancer.

Mammalian members of the lysyl oxidase (LOX) family of proteins carry a copper-dependent monoamine oxidase domain exclusively within the C-terminal region, which catalyzes ε-amine oxidation of lysine residues of various proteins. However, recent studies have demonstrated that in LOX-like (LOXL) 2-4 the C-terminal canonical catalytic domain and N-terminal scavenger receptor cysteine-rich (SRCR) repeats domain exhibit lysine deacetylation and deacetylimination catalytic activities. Moreover, the N-terminal SRCR repeats domain is more catalytically active than the C-terminal oxidase domain. Thus, LOX is the third family of lysine deacetylases in addition to histone deacetylase and sirtuin families. In this review, we discuss how the LOX family targets different cellular proteins for deacetylation and deacetylimination to control the development and metastasis of cancer.

Inhibition of integrin alpha v/beta 5 mitigates the protective effect induced by irisin in hemorrhage.

INTRODUCTION: Irisin plays an important role in regulating tissue stress, cardiac function, and inflammation. Integrin αvß5 was recently identified as a receptor for irisin to elicit its physiologic function. It remains unknown whether integrin αvß5 is required for irisin's function in modulating the physiologic response to hemorrhage. The objective of this study is to examine if integrin αvß5 contributes to the effects of irisin during the hemorrhagic response. METHODS: Hemorrhage was induced in mice by achieving a mean arterial blood pressure of 35-45 mmHg for one hour, followed by two hours of resuscitation. Irisin (0.5  µg/kg) was administrated to assess its pharmacologic effects in hemorrhage. Cilengitide, a cyclic Arg-Gly-Asp peptide (cRGDyK) which is an inhibitor of integrin αvß5, or control RGDS (1 mg/kg) was administered with irisin. In another cohort of mice, the irisin-induced protective effect was examined after knocking down integrin ß5 with nanoparticle delivery of integrin ß5 sgRNA using CRSIPR/Cas-9 gene editing. Cardiac function and hemodynamics were measured using echocardiography and femoral artery catheterization, respectively. Systemic cytokine releases were measured using Enzyme-linked immunosorbent assay (ELISA). Histological analyses were used to determine tissue damage in myocardium, skeletal muscles, and lung tissues. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) was carried out to assess apoptosis in tissues. RESULTS: Hemorrhage induced reduction of integrin αvß5 in skeletal muscles and repressed recovery of cardiac performance and hemodynamics. Irisin treatment led to significantly improved cardiac function, which was abrogated by treatment with Cilengitide or knockdown of integrin ß5. Furthermore, irisin resulted in a marked suppression of tumor necrosis factor-α (TNF-α) and interleukin-1 (IL-1), muscle edema, and inflammatory cells infiltration in myocardium and skeletal muscles, which was attenuated by Cilengitide or knockdown of integrin ß5. Irisin-induced reduction of apoptosis in the myocardium, skeletal muscles, and lung, which were attenuated by either the inhibition of integrin αvß5, or knockdown of integrin ß5. CONCLUSION: Integrin αvß5 plays an important role for irisin in modulating the protective effect during hemorrhage.

Irisin deficiency exacerbates diet-induced insulin resistance and cardiac dysfunction in type II diabetes in mice.

Irisin is involved in the regulation of a variety of physiological conditions, metabolism, and survival. We and others have demonstrated that irisin contributes critically to modulation of insulin resistance and the improvement of cardiac function. However, whether the deletion of irisin will regulate cardiac function and insulin sensitivity in type II diabetes remains unclear. We utilized the CRISPR/Cas-9 genome-editing system to delete irisin globally in mice and high-fat diet (HFD)-induced type II diabetes model. We found that irisin deficiency did not result in developmental abnormality during the adult stage, which illustrates normal cardiac function and insulin sensitivity assessed by glucose tolerance test in the absence of stress. The ultrastructural analysis of the transmission electronic microscope (TEM) indicated that deletion of irisin did not change the morphology of mitochondria in myocardium. Gene expression profiling showed that several key signaling pathways related to integrin signaling, extracellular matrix, and insulin-like growth factors signaling were coordinately downregulated by deletion of irisin. However, when mice were fed a high-fat diet and chow food for 16 wk, ablation of irisin in mice exposed to HFD resulted in much more severe insulin resistance, metabolic derangements, profound cardiac dysfunction, and hypertrophic response and remodeling as compared with wild-type control mice. Taken together, our results indicate that the loss of irisin exacerbates insulin resistance, metabolic disorders, and cardiac dysfunction in response to HFD and promotes myocardial remodeling and hypertrophic response. This evidence reveals the molecular evidence and the critical role of irisin in modulating insulin resistance and cardiac function in type II diabetes.NEW & NOTEWORTHY By utilizing the CRISPR/Cas-9 genome-editing system and high-fat diet (HFD)-induced type II diabetes model, our results provide direct evidence showing that the loss of irisin exacerbates cardiac dysfunction and insulin resistance while promoting myocardial remodeling and a hypertrophic response in HFD-induced diabetes. This study provides new insight into understanding the molecular evidence and the critical role of irisin in modulating insulin resistance and cardiac function in type II diabetes.

Protein Kinase C Modulation Determines the Mesoderm/Extraembryonic Fate Under BMP4 Induction From Human Pluripotent Stem Cells.

The interplay among mitogenic signaling pathways is crucial for proper embryogenesis. These pathways collaboratively act through intracellular master regulators to determine specific cell fates. Identifying the master regulators is critical to understanding embryogenesis and to developing new applications of pluripotent stem cells. In this report, we demonstrate protein kinase C (PKC) as an intrinsic master switch between embryonic and extraembryonic cell fates in the differentiation of human pluripotent stem cells (hPSCs). PKCs are essential to induce the extraembryonic lineage downstream of BMP4 and other mitogenic modulators. PKC-alpha (PKCα) suppresses BMP4-induced mesoderm differentiation, and PKC-delta (PKCδ) is required for trophoblast cell fate. PKC activation overrides mesoderm induction conditions and leads to extraembryonic fate. In contrast, PKC inhibition leads to ß-catenin (CTNNB1) activation, switching cell fate from trophoblast to mesoderm lineages. This study establishes PKC as a signaling boundary directing the segregation of extraembryonic and embryonic lineages. The manipulation of intrinsic PKC activity could greatly enhance cell differentiation under mitogenic regulation in stem cell applications.

NF-κB represses retinoic acid receptor-mediated GPRC5A transactivation in lung epithelial cells to promote neoplasia.

Chronic inflammation is associated with lung tumorigenesis, in which NF-κB-mediated epigenetic regulation plays a critical role. Lung tumor suppressor G protein-coupled receptor, family C, member 5A (GPRC5A), is repressed in most non-small cell lung cancer (NSCLC); however, the mechanisms remain unclear. Here, we show that NF-κB acts as a transcriptional repressor in suppression of GPRC5A. NF-κB induced GPRC5A repression both in vitro and in vivo. Intriguingly, transactivation of NF-κB downstream targets was not required, but the transactivation domain of RelA/p65 was required for GPRC5A repression. NF-κB did not bind to any potential cis-element in the GPRC5A promoter. Instead, p65 was complexed with retinoic acid receptor α/ß (RARα/ß) and recruited to the RA response element site at the GPRC5A promoter, resulting in disrupted RNA polymerase II complexing and suppressed transcription. Notably, phosphorylation on serine 276 of p65 was required for interaction with RARα/ß and repression of GPRC5A. Moreover, NF-κB-mediated epigenetic repression was through suppression of acetylated histone H3K9 (H3K9ac), but not DNA methylation of the CpG islands, at the GPRC5A promoter. Consistently, a histone deacetylase inhibitor, but not DNA methylation inhibitor, restored GPRC5A expression in NSCLC cells. Thus, NF-κB induces transcriptional repression of GPRC5A via a complex with RARα/ß and mediates epigenetic repression via suppression of H3K9ac.

Anti-tumour potential of PD-L1/PD-1 post-translational modifications.

The immune checkpoint programmed death receptor 1 (PD-1) and programmed death ligand 1 (PD-L1) are biologically important immunosuppressive molecules, and the PD-L1/PD-1-mediated signalling pathway is currently considered one of the main mechanisms of tumour escape immune surveillance. PD-L1 is highly expressed on the cytomembrane of tumour cell and binds to PD-1 receptor of activated T cells. This interaction activates PD-L1/PD-1 downstream signal transduction, inhibiting T cells anti-tumour activity. Therefore, inhibitors of PD-L1/PD-1 activation, showing significant efficacy in some types of tumours, have been widely approved in clinical tumour therapy. Recent research on PD-L1/PD-1 signalling pathway regulation has shown post-translational modifications (PTMs) form of PD-L1 or PD-1, including glycosylation, ubiquitination, phosphorylation, and acetylation, which may play an important role in PD-L1/PD-1 signalling pathway regulation and anti-tumour function of T cells. In this review, we focused on PTMs of PD-L1/PD-1 research and potential applications in tumour immunotherapy.

S1P defects cause a new entity of cataract, alopecia, oral mucosal disorder, and psoriasis-like syndrome.

In this report, we discovered a new entity named cataract, alopecia, oral mucosal disorder, and psoriasis-like (CAOP) syndrome in two unrelated and ethnically diverse patients. Furthermore, patient 1 failed to respond to regular treatment. We found that CAOP syndrome was caused by an autosomal recessive defect in the mitochondrial membrane-bound transcription factor peptidase/site-1 protease (MBTPS1, S1P). Mitochondrial abnormalities were observed in patient 1 with CAOP syndrome. Furthermore, we found that S1P is a novel mitochondrial protein that forms a trimeric complex with ETFA/ETFB. S1P enhances ETFA/ETFB flavination and maintains its stability. Patient S1P variants destabilize ETFA/ETFB, impair mitochondrial respiration, decrease fatty acid ß-oxidation activity, and shift mitochondrial oxidative phosphorylation (OXPHOS) to glycolysis. Mitochondrial dysfunction and inflammatory lesions in patient 1 were significantly ameliorated by riboflavin supplementation, which restored the stability of ETFA/ETFB. Our study discovered that mutations in MBTPS1 resulted in a new entity of CAOP syndrome and elucidated the mechanism of the mutations in the new disease.

Identification of Immune-Related Gene Signature and Prediction of CeRNA Network in Active Ulcerative Colitis.

Background: Ulcerative colitis (UC) is an inflammatory disease of the intestinal mucosa, and its incidence is steadily increasing worldwide. Intestinal immune dysfunction has been identified as a central event in UC pathogenesis. However, the underlying mechanisms that regulate dysfunctional immune cells and inflammatory phenotype remain to be fully elucidated. Methods: Transcriptome profiling of intestinal mucosa biopsies were downloaded from the GEO database. Robust Rank Aggregation (RRA) analysis was performed to identify statistically changed genes and differentially expressed genes (DEGs). Gene Set Enrichment Analysis (GSEA), Gene Ontology (GO), and Kyoto Encyclopedia of Genes and Genomes (KEGG) were used to explore potential biological mechanisms. CIBERSORT was used to evaluate the proportion of 22 immune cells in biopsies. Weighted co-expression network analysis (WGCNA) was used to determine key module-related clinical traits. Protein-Protein Interaction (PPI) network and Cytoscape were performed to explore protein interaction network and screen hub genes. We used a validation cohort and colitis mouse model to validate hub genes. Several online websites were used to predict competing endogenous RNA (ceRNA) network. Results: RRA integrated analysis revealed 1838 statistically changed genes from four training cohorts (adj. p-value < 0.05). GSEA showed that statistically changed genes were enriched in the innate immune system. CIBERSORT analysis uncovered an increase in activated dendritic cells (DCs) and M1 macrophages. The red module of WGCNA was considered the most critical module related to active UC. Based on the results of the PPI network and Cytoscape analyses, we identified six critical genes and transcription factor NF-κB. RT-PCR revealed that andrographolide (AGP) significantly inhibited the expression of hub genes. Finally, we identified XIST and three miRNAs (miR-9-5p, miR-129-5p, and miR-340-5p) as therapeutic targets. Conclusions: Our integrated analysis identified four hub genes (CXCL1, IL1B, MMP1, and MMP10) regulated by NF-κB. We further revealed that AGP decreased the expression of hub genes by inhibiting NF-κB activation. Lastly, we predicted the involvement of ceRNA network in the regulation of NF-κB expression. Collectively, our results provide valuable information in understanding the molecular mechanisms of active UC. Furthermore, we predict the use of AGP and small RNA combination for the treatment of UC.

Rapamycin recruits SIRT2 for FKBP12 deacetylation during mTOR activity modulation in innate immunity.

The mammalian target of rapamycin (mTOR) is a serine-threonine kinase involved in cellular innate immunity, metabolism, and senescence. FK506-binding protein 12 (FKBP12) inhibits mTOR kinase activity via direct association. The FKBP12-mTOR association can be strengthened by the immunosuppressant rapamycin, but the underlying mechanism remains elusive. We show here that the FKBP12-mTOR association is tightly regulated by an acetylation-deacetylation cycle. FKBP12 is acetylated on the lysine cluster (K45/K48/K53) by CREB-binding protein (CBP) in mammalian cells in response to nutrient treatment. Acetyl-FKBP12 associates with CBP acetylated Rheb. Rapamycin recruits SIRT2 with a high affinity for FKBP12 association and deacetylation. SIRT2-deacetylated FKBP12 then switches its association from Rheb to mTOR. Nutrient-activated mTOR phosphorylates IRF3S386 for the antiviral response. In contrast, rapamycin strengthening FKBP12-mTOR association blocks mTOR antiviral activity by recruiting SIRT2 to deacetylate FKBP12. Hence, on/off mTOR activity in response to environmental nutrients relies on FKBP12 acetylation and deacetylation status in mammalian cells.

Roles of Mitochondrial Serine Hydroxymethyltransferase 2 (SHMT2) in Human Carcinogenesis.

In the last few years, cellular metabolic reprogramming has been acknowledged as a hallmark of human cancer and evaluated for its crucial role in supporting the proliferation and survival of human cancer cells. In a variety of human tumours, including hepatocellular carcinoma (HCC), breast cancer and non-small-cell lung cancer (NSCLC), a large amount of carbon is reused in serine/glycine biosynthesis, accompanied by higher expression of the key glycine synthetic enzyme mitochondrial serine hydroxymethyltransferase 2 (SHMT2). This enzyme can convert serine into glycine and a tetrahydrofolate-bound one-carbon unit, ultimately supporting thymidine synthesis and purine synthesis and promoting tumour growth. In tumour samples, elevated expression of SHMT2 was found to be associated with poor prognosis. In this review, the pivotal roles of SHMT2 in human carcinogenesis are described, highlighting the underlying regulatory mechanisms through promotion of tumour progression. In conclusion, SHMT2 may serve as a prognostic marker and a target for anticancer therapies.

The Essential Role of PRAK in Preserving Cardiac Function and Insulin Resistance in High-Fat Diet-Induced Diabetes.

Regulated/activated protein kinase (PRAK) plays a crucial role in modulating biological function. However, the role of PRAK in mediating cardiac dysfunction and metabolic disorders remains unclear. We examined the effects of deletion of PRAK on modulating cardiac function and insulin resistance in mice exposed to a high-fat diet (HFD). Wild-type and PRAK-/- mice at 8 weeks old were exposed to either chow food or HFD for a consecutive 16 weeks. Glucose tolerance tests and insulin tolerance tests were employed to assess insulin resistance. Echocardiography was employed to assess myocardial function. Western blot was used to determine the molecular signaling involved in phosphorylation of IRS-1, AMPKα, ERK-44/42, and irisin. Real time-PCR was used to assess the hypertrophic genes of the myocardium. Histological analysis was employed to assess the hypertrophic response, interstitial myocardial fibrosis, and apoptosis in the heart. Western blot was employed to determine cellular signaling pathway. HFD-induced metabolic stress is indicated by glucose intolerance and insulin intolerance. PRAK knockout aggravated insulin resistance, as indicated by glucose intolerance and insulin intolerance testing as compared with wild-type littermates. As compared with wild-type mice, hyperglycemia and hypercholesterolemia were manifested in PRAK-knockout mice following high-fat diet intervention. High-fat diet intervention displayed a decline in fractional shortening and ejection fraction. However, deletion of PRAK exacerbated the decline in cardiac function as compared with wild-type mice following HFD treatment. In addition, PRAK knockout mice enhanced the expression of myocardial hypertrophic genes including ANP, BNP, and ßMHC in HFD treatment, which was also associated with an increase in cardiomyocyte size and interstitial fibrosis. Western blot indicated that deletion of PRAK induces decreases in phosphorylation of IRS-1, AMPKα, and ERK44/42 as compared with wild-type controls. Our finding indicates that deletion of PRAK promoted myocardial dysfunction, cardiac remodeling, and metabolic disorders in response to HFD.

Furin Enzyme and pH Synergistically Triggered Aggregation of Gold Nanoparticles for Activated Photoacoustic Imaging and Photothermal Therapy of Tumors.

Specific and effective accumulation of nanoparticles within tumors is highly crucial for precise cancer diagnosis and treatment. Therefore, spatiotemporally manipulating the aggregation of small gold nanoparticles (AuNPs) in a tumor microenvironment is of great significance for enhancing the diagnostic and therapeutic efficacy of tumors. Herein, we reported a novel furin enzyme/acidic pH synergistically triggered small AuNP aggregation strategy for activating the photoacoustic (PA) imaging and photothermal (PTT) functions of AuNPs in vivo. Smart gold nanoparticles decorated with furin-cleavable RVRR (Arg-Val-Arg-Arg) peptides (Au-RRVR) were rationally designed and fabricated. Both in vitro and in vivo experiments demonstrated that such Au-RRVR nanoparticles could be simultaneously induced by furin and acidic pH to form large aggregates within tumorous tissue resulting in improved tumor accumulation and retention, which can further activate the PA and PTT effect of AuNPs for sensitive imaging and efficient therapy of tumors. Thus, we believe that this dual-stimuli-responsive aggregation system may offer a universal platform for effective cancer diagnosis and treatment.

Myristoylation-mediated phase separation of EZH2 compartmentalizes STAT3 to promote lung cancer growth.

N-myristoylation is a crucial signaling and pathogenic modification process that confers hydrophobicity to cytosolic proteins. Although different large-scale approaches have been applied, a large proportion of myristoylated proteins remain to be identified. EZH2 is overexpressed in lung cancer cells and exerts oncogenic effects via its intrinsic methyltransferase activity. Using a well-established click chemistry approach, we found that EZH2 can be modified by myristoylation at its N-terminal glycine in lung cancer cells. Hydrophobic interaction is one of the main forces driving or stabilizing liquid-liquid phase separation (LLPS), raising the possibility that myristoylation can modulate LLPS by mediating hydrophobic interactions. Indeed, myristoylation facilitates EZH2 to form phase-separated liquid droplets in lung cancer cells and in vitro. Furthermore, we provide evidence that myristoylation-mediated LLPS of EZH2 compartmentalizes its non-canonical substrate, STAT3, and activates STAT3 signaling, ultimately resulting in accelerated lung cancer cell growth. Thus, targeting EZH2 myristoylation may have significant therapeutic efficacy in the treatment of lung cancer. Altogether, these observations not only extend the list of myristoylated proteins, but also indicate that hydrophobic lipidation may serve as a novel incentive to induce or maintain LLPS.

Acetylation-dependent glutamate receptor GluR signalosome formation for STAT3 activation in both transcriptional and metabolism regulation.

Besides their original regulating roles in the brain, spinal cord, retina, and peripheral nervous system for mediating fast excitatory synaptic transmission, glutamate receptors consisting of metabotropic glutamate receptors (GluRs) and ionotropic glutamate receptors (iGluRs) have emerged to have a critical role in the biology of cancer initiation, progression, and metastasis. However, the precise mechanism underpinning the signal transduction mediated by ligand-bound GluRs is not clearly elucidated. Here, we show that iGluRs, GluR1 and GluR2, are acetylated by acetyltransferase CREB-binding protein upon glutamate stimulation of cells, and are targeted by lysyl oxidase-like 2 for deacetylation. Acetylated GluR1/2 recruit ß-arrestin1/2 and signal transducer and activator of transcription 3 (STAT3) to form a protein complex. Both ß-arrestin1/2 and STAT3 are subsequently acetylated and activated. Simultaneously, activated STAT3 acetylated at lysine 685 translocates to mitochondria to upregulate energy metabolism-related gene transcription. Our results reveal that acetylation-dependent formation of GluR1/2-ß-arrestin1/2-STAT3 signalosome is critical for glutamate-induced cell proliferation.

LOXL1 modulates the malignant progression of colorectal cancer by inhibiting the transcriptional activity of YAP.

BACKGROUND: LOX-like 1 (LOXL1) is a lysyl oxidase, and emerging evidence has revealed its effect on malignant cancer progression. However, its role in colorectal cancer (CRC) and the underlying molecular mechanisms have not yet been elucidated. METHODS: LOXL1 expression in colorectal cancer was detected by immunohistochemistry, western blotting and real-time PCR. In vitro, colony formation, wound healing, migration and invasion assays were performed to investigate the effects of LOXL1 on cell proliferation, migration and invasion. In vivo, metastasis models and mouse xenografts were used to assess tumorigenicity and metastasis ability. Molecular biology experiments were utilized to reveal the underlying mechanisms by which LOXL1 modulates the Hippo pathway. RESULTS: LOXL1 was highly expressed in normal colon tissues compared with cancer tissues. In vitro, silencing LOXL1 in CRC cell lines dramatically enhanced migration, invasion, and colony formation, while overexpression of LOXL1 exerted the opposite effects. The results of the in vivo experiments demonstrated that the overexpression of LOXL1 in CRC cell lines drastically inhibited metastatic progression and tumour growth. Mechanistically, LOXL1 inhibited the transcriptional activity of Yes-associated protein (YAP) by interacting with MST1/2 and increasing the phosphorylation of MST1/2. CONCLUSIONS: LOXL1 may function as an important tumour suppressor in regulating tumour growth, invasion and metastasis via negative regulation of YAP activity. Video abstract.

SQR mediates therapeutic effects of H2S by targeting mitochondrial electron transport to induce mitochondrial uncoupling.

Hydrogen sulfide (H2S) is a gasotransmitter and a potential therapeutic agent. However, molecular targets relevant to its therapeutic actions remain enigmatic. Sulfide-quinone oxidoreductase (SQR) irreversibly oxidizes H2S. Therefore, SQR is assumed to inhibit H2S signaling. We now report that SQR-mediated oxidation of H2S drives reverse electron transport (RET) at mitochondrial complex I, which, in turn, repurposes mitochondrial function to superoxide production. Unexpectedly, complex I RET, a process dependent on high mitochondrial membrane potential, induces superoxide-dependent mitochondrial uncoupling and downstream activation of adenosine monophosphate-activated protein kinase (AMPK). SQR-induced mitochondrial uncoupling is separated from the inhibition of mitochondrial complex IV by H2S. Moreover, deletion of SQR, complex I, or AMPK abolishes therapeutic effects of H2S following intracerebral hemorrhage. To conclude, SQR mediates H2S signaling and therapeutic effects by targeting mitochondrial electron transport to induce mitochondrial uncoupling. Moreover, SQR is a previously unrecognized target for developing non-protonophore uncouplers with broad clinical implications.

Senescent Stromal Cells Promote Cancer Resistance through SIRT1 Loss-Potentiated Overproduction of Small Extracellular Vesicles.

Cellular senescence is a potent tumor-suppressive program that prevents neoplastic events. Paradoxically, senescent cells develop an inflammatory secretome, termed the senescence-associated secretory phenotype, which is implicated in age-related pathologies including cancer. Here, we report that senescent cells actively synthesize and release small extracellular vesicles (sEV) with a distinctive size distribution. Mechanistically, SIRT1 loss supported accelerated sEV production despite enhanced proteome-wide ubiquitination, a process correlated with ATP6V1A downregulation and defective lysosomal acidification. Once released, senescent stromal sEVs significantly altered the expression profile of recipient cancer cells and enhanced their aggressiveness, specifically drug resistance mediated by expression of ATP-binding cassette subfamily B member 4 (ABCB4). Targeting SIRT1 with agonist SRT2104 prevented development of cancer resistance by restraining sEV production by senescent stromal cells. In clinical oncology, sEVs in peripheral blood of posttreatment cancer patients were readily detectable by routine biotechniques, presenting an exploitable biomarker to monitor therapeutic efficacy and predict long-term outcome. Together, this study identifies a distinct mechanism supporting pathologic activities of senescent cells and provides a potent avenue to circumvent advanced human malignancies by cotargeting cancer cells and their surrounding microenvironment, which contributes to drug resistance via secretion of sEVs from senescent stromal cells. SIGNIFICANCE: Senescent stromal cells produce a large number of sEVs to promote cancer resistance in therapeutic settings, a process driven by SIRT1 decline in stromal cells and ABCB4 augmentation in cancer cells.See related commentary by Wiley, p. 3193 GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/16/3383/F1.large.jpg.

Irisin counteracts high glucose and fatty acid-induced cytotoxicity by preserving the AMPK-insulin receptor signaling axis in C2C12 myoblasts.

Irisin, a newly identified myokine, is critical to modulating body metabolism and biological homeostasis. However, whether irisin protects the skeletal muscles against metabolic stresses remains unknown. In this study, we determine the effect of irisin on high glucose and fatty acid-induced damages using irisin-overexpressed mouse C2C12 (irisin-C2C12) myoblasts and skeletal muscle from irisin-injected mice. Compared with empty vector-transfected control C2C12 cells, irisin overexpression resulted in a marked increase in cell viability and decrease in apoptosis under high-glucose stress. Progression of the cell cycle into the G2/M phase in the proliferative condition was also observed with irisin overexpression. Furthermore, glucose uptake, glycogen accumulation, and phosphorylation of AMPKα/insulin receptor (IR) ß-subunit/Erk1/2 in response to insulin stimulation were enhanced by irisin overexpression. In irisin-C2C12 myoblasts, these responses of phosphorylation were preserved under palmitate treatment, which induced insulin resistance in the control cells. These effects of irisin were reversed by inhibiting AMPK with compound C. In addition, high glucose-induced suppression of the mitochondrial membrane potential was also prevented by irisin. Moreover, suppression of IR in irisin-C2C12 myoblasts by cotransfection of shRNA against IR also mitigated the effects of irisin while not affecting AMPKα phosphorylation. As an in vivo study, soleus muscles from irisin-injected mice showed elevated phosphorylation of AMPKα and Erk1/2 and glycogen contents. Our results indicate that irisin counteracts the stresses generated by high glucose and fatty acid levels and irisin overexpression serves as a novel approach to elicit cellular protection. Furthermore, AMPK activation is a crucial factor that regulates insulin action as a downstream target.