Deficient leukemia inhibitory factor signaling in muscle precursor cells from patients with type 2 diabetes

Signaling pathways of adipose stem cell-derived exosomes promoting muscle regeneration

ABSTRACT

Severe muscle injury is still a challenging clinical problem. Exosomes derived from adipose stem cells (ASC-exos) may be a potential therapeutic tool, but their mechanism is not completely clear. This review aims to elaborate the possible mechanism of ASC-exos in muscle regeneration from the perspective of signal pathways and provide guidance for further study. Literature cited in this review was acquired through PubMed using keywords or medical subject headings, including adipose stem cells, exosomes, muscle regeneration, myogenic differentiation, myogenesis, wingless/integrated (Wnt), mitogen-activated protein kinases, phosphatidylinositol-4,5-bisphosphate 3-kinase/protein kinase B (PI3K/Akt), Janus kinase/signal transducers and activators of transcription, and their combinations. We obtained the related signal pathways from proteomics analysis of ASC-exos in the literature, and identified that ASC-exos make different contributions to multiple stages of skeletal muscle regeneration by those signal pathways.

Mechanisms by Which Skeletal Muscle Myokines Ameliorate Insulin Resistance

The skeletal muscle is the largest organ in the body and secretes circulating factors, including myokines, which are involved in various cellular signaling processes. Skeletal muscle is vital for metabolism and physiology and plays a crucial role in insulin-mediated glucose disposal. Myokines have autocrine, paracrine, and endocrine functions, serving as critical regulators of myogenic differentiation, fiber-type switching, and maintaining muscle mass. Myokines have profound effects on energy metabolism and inflammation, contributing to the pathophysiology of type 2 diabetes (T2D) and other metabolic diseases. Myokines have been shown to increase insulin sensitivity, thereby improving glucose disposal and regulating glucose and lipid metabolism. Many myokines have now been identified, and research on myokine signaling mechanisms and functions is rapidly emerging. This review summarizes the current state of the field regarding the role of myokines in tissue cross-talk, including their molecular mechanisms, and their potential as therapeutic targets for T2D.

Exercise Therapy for People With Sarcopenic Obesity: Myokines and Adipokines as Effective Actors

Sarcopenic obesity is defined as a multifactorial disease in aging with decreased body muscle, decreased muscle strength, decreased independence, increased fat mass, due to decreased physical activity, changes in adipokines and myokines, and decreased satellite cells. People with sarcopenic obesity cause harmful changes in myokines and adipokines. These changes are due to a decrease interleukin-10 (IL-10), interleukin-15 (IL-15), insulin-like growth factor hormone (IGF-1), irisin, leukemia inhibitory factor (LIF), fibroblast growth factor-21 (FGF-21), adiponectin, and apelin. While factors such as myostatin, leptin, interleukin-6 (IL-6), interleukin-8 (IL-8), and resistin increase. The consequences of these changes are an increase in inflammatory factors, increased degradation of muscle proteins, increased fat mass, and decreased muscle tissue, which exacerbates sarcopenia obesity. In contrast, exercise, especially strength training, reverses this process, which includes increasing muscle protein synthesis, increasing myogenesis, increasing mitochondrial biogenesis, increasing brown fat, reducing white fat, reducing inflammatory factors, and reducing muscle atrophy. Since some people with chronic diseases are not able to do high-intensity strength training, exercises with blood flow restriction (BFR) are newly recommended. Numerous studies have shown that low-intensity BFR training produces the same increase in hypertrophy and muscle strength such as high-intensity strength training. Therefore, it seems that exercise interventions with BFR can be an effective way to prevent the exacerbation of sarcopenia obesity. However, due to limited studies on adipokines and exercises with BFR in people with sarcopenic obesity, more research is needed.

Differences in the expression profiles of lncRNAs and mRNAs in partially injured anterior cruciate ligament and medial collateral ligament of rabbits

Long noncoding RNAs (lncRNAs), as a novel regulatory factor, are considered to play a vital role in various biological processes and diseases. However, the overall expression profile and biological functions of lncRNAs in the partially injured anterior cruciate ligament (ACL) and medial collateral ligament (MCL) have not been clearly explored. Partially injured models of ACL and MCL were established in 3-month-old healthy male New Zealand white rabbits. Expression of lncRNAs and mRNAs in the ligament tissue was detected by high-throughput sequencing technology, and biological functions of differentially expressed RNAs were evaluated by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. Validation of several differentially expressed RNAs was performed using quantitative real-time PCR (qRT-PCR). Protein-protein interaction (PPI) analysis and competitive endogenous RNA (ceRNA) prediction were used to identify interactions among hub genes and the interaction among lncRNAs, miRNAs, and mRNAs. The results showed that compared with the normal group, there were 267 mRNAs and 329 lncRNAs differentially expressed in ACL and 726 mRNAs and 609 lncRNAs in MCL in the injured group. Compared with MCL, 420 mRNAs and 470 lncRNAs were differentially expressed in ACL in the normal group; 162 mRNAs and 205 lncRNAs were differentially expressed in ACL in the injured group. Several important lncRNAs and genes were identified, namely, COL7A1, LIF, FGFR2, EPHA2, CSF1, MMP2, MMP9, SOX5, LOX, MSTRG.1737.1, MSTRG.26038.25, MSTRG.20209.5, MSTRG.22764.1, and MSTRG.18113.1, which are closely related to inflammatory response, tissue damage repair, cell proliferation, differentiation, migration, and apoptosis. Further study of the functions of these genes may help to better understand the specific molecular mechanisms underlying the occurrence of endogenous repair disorders in ACL, which may provide new ideas for further exploration of effective means to promote endogenous repair of ACL injury.

New insights into IL-6 family cytokines in metabolism, hepatology and gastroenterology

IL-6 family cytokines are defined by the common use of the signal-transducing receptor chain glycoprotein 130 (gp130). Increasing evidence indicates that these cytokines are essential in the regulation of metabolic homeostasis as well as in the pathophysiology of multiple gastrointestinal and liver disorders, thus making them attractive therapeutic targets. Over the past few years, therapies modulating gp130 signalling have grown exponentially in several clinical settings including obesity, cancer and inflammatory bowel disease. A newly engineered gp130 cytokine, IC7Fc, has shown promising preclinical results for the treatment of type 2 diabetes, obesity and liver steatosis. Moreover, drugs that modulate gp130 signalling have shown promise in refractory inflammatory bowel disease in clinical trials. A deeper understanding of the main roles of the IL-6 family of cytokines during homeostatic and pathological conditions, their signalling pathways, sources of production and target cells will be crucial to the development of improved treatments. Here, we review the current state of the role of these cytokines in hepatology and gastroenterology and discuss the progress achieved in translating therapeutics targeting gp130 signalling into clinical practice.

VPS39-deficiency observed in type 2 diabetes impairs muscle stem cell differentiation via altered autophagy and epigenetics

Insulin resistance and lower muscle quality (strength divided by mass) are hallmarks of type 2 diabetes (T2D). Here, we explore whether alterations in muscle stem cells (myoblasts) from individuals with T2D contribute to these phenotypes. We identify VPS39 as an important regulator of myoblast differentiation and muscle glucose uptake, and VPS39 is downregulated in myoblasts and myotubes from individuals with T2D. We discover a pathway connecting VPS39-deficiency in human myoblasts to impaired autophagy, abnormal epigenetic reprogramming, dysregulation of myogenic regulators, and perturbed differentiation. VPS39 knockdown in human myoblasts has profound effects on autophagic flux, insulin signaling, epigenetic enzymes, DNA methylation and expression of myogenic regulators, and gene sets related to the cell cycle, muscle structure and apoptosis. These data mimic what is observed in myoblasts from individuals with T2D. Furthermore, the muscle of Vps39+/- mice display reduced glucose uptake and altered expression of genes regulating autophagy, epigenetic programming, and myogenesis. Overall, VPS39-deficiency contributes to impaired muscle differentiation and reduced glucose uptake. VPS39 thereby offers a therapeutic target for T2D.

Evaluation of vascular endothelial growth factor A and leukemia inhibitory factor expressions at the time of implantation in diabetic rats following treatment with Metformin and Pioglitazone

Background

Implantation requires intimate crosstalk between the embryo and uterus for a successful establishment of pregnancy. Type 2 diabetes mellitus may lead to implantation failure. The effect of diabetes and its therapeutic drugs on implantation is still largely unclear.

Objective

To assess the endometrial expression changes of vascular endothelial growth factor A (VEGFA) and leukemia inhibitory factor (LIF), at the time of implantation in diabetic rats following treatment with Metformin and Pioglitazone.

Materials and Methods

Twenty-eight 6-8-wk-old Wistar female rats weighing 200-250 gr were divided into four groups (n = 7/each). Type 2 diabetes was induced and Metformin and Pioglitazone were applied for 4 wk. The expression of VEGFA and LIF was measured by real-time reverse transcription-polymerase chain reaction and Western blot.

Results

The relative expression of VEGFA transcript was higher in the diabetic (p = 0.02) and Metformin-treated (p = 0.04) rats compared to the control group. Furthermore, the VEGFA transcript level significantly reduced in Pioglitazone-treated diabetic rats (p = 0.03). LIF expression was elevated in the Metformin- and the Pioglitazone-treated rats and reduced in the diabetic group in comparison with the control group. Compared to the diabetic rats, the expression of LIF was significantly elevated in the Metformin- (p = 0.01) and Pioglitazone-treated (p = 0.03) groups.

Conclusion

The expressions of LIF and VEGFA were altered in diabetic rats during implantation which may be associated with diabetic-related infertility. Pioglitazone is able to restore the VEGFA and LIF expressions to their baseline levels more efficiently than Metformin.

Sarcopenic obesity: Myokines as potential diagnostic biomarkers and therapeutic targets?

Sarcopenic obesity (SO) is a condition characterized by the occurrence of both sarcopenia and obesity and imposes a heavy burden on the health of the elderly. Controversies and challenges regarding the definition, diagnosis and treatment of SO still remain because of its complex pathogenesis and limitations. Over the past few decades, numerous studies have revealed that myokines secreted from skeletal muscle play significant roles in the regulation of muscle mass and function as well as metabolic homeostasis. Abnormalities in myokines may trigger and promote the pathogenesis underlying age-related and metabolic diseases, including obesity, sarcopenia, type 2 diabetes (T2D), and SO. This review mainly focuses on the role of myokines as potential biomarkers for the early diagnosis and therapeutic targets in SO.

Cigarette smoke exposure reduces leukemia inhibitory factor levels during respiratory syncytial viral infection

Background: Viral infections are considered a major driving factor of chronic obstructive pulmonary disease (COPD) exacerbations and thus contribute to disease morbidity and mortality. Respiratory syncytial virus (RSV) is a frequently detected pathogen in the respiratory tract of COPD patients during an exacerbation. We previously demonstrated in a murine model that leukemia inhibitory factor (LIF) expression was increased in the lungs during RSV infection. Subduing LIF signaling in this model enhanced lung injury and airway hypersensitivity. In this study, we investigated lung LIF levels in COPD patient samples to determine the impact of disease status and cigarette smoke exposure on LIF expression. Materials and methods: Bronchoalveolar lavage fluid (BALF) was obtained from healthy never smokers, smokers, and COPD patients, by written informed consent. Human bronchial epithelial (HBE) cells were isolated from healthy never smokers and COPD patients, grown at the air-liquid interface and infected with RSV or stimulated with polyinosinic:polycytidylic acid (poly (i:c)). Mice were exposed to cigarette smoke daily for 6 months and were subsequently infected with RSV. LIF expression was profiled in all samples. Results: In human BALF, LIF protein was significantly reduced in both smokers and COPD patients compared to healthy never smokers. HBE cells isolated from COPD patients produced less LIF compared to never smokers during RSV infection or poly (i:c) stimulation. Animals exposed to cigarette smoke had reduced lung levels of LIF and its corresponding receptor, LIFR. Smoke-exposed animals had reduced LIF expression during RSV infection. Two possible factors for reduced LIF levels were increased LIF mRNA instability in COPD epithelia and proteolytic degradation of LIF protein by serine proteases. Conclusions: Cigarette smoke is an important modulator for LIF expression in the lungs. Loss of LIF expression in COPD could contribute to a higher degree of lung injury during virus-associated exacerbations.

Role of myokines in the development of skeletal muscle insulin resistance and related metabolic defects in type 2 diabetes

Due to its mass, skeletal muscle is the major site of glucose uptake and an important tissue in the development of type 2 diabetes (T2D). Muscles of patients with T2D are affected with insulin resistance and mitochondrial dysfunction, which result in impaired glucose and fatty acid metabolism. A well-established method of managing the muscle metabolic defects occurring in T2D is physical exercise. During exercise, muscles contract and secrete factors called myokines which can act in an autocrine/paracrine fashion to improve muscle energy metabolism. In patients with T2D, plasma levels as well as muscle levels (mRNA and protein) of some myokines are upregulated, while others are downregulated. The signalling pathways of certain myokines are also altered in skeletal muscle of patients with T2D. Taken together, these findings suggest that myokine secretion is an important factor contributing to the development of muscle metabolic defects during T2D. It is also of interest considering that lack of physical activity is closely linked to the occurrence of this disease. The causal relationships between sedentary behavior, factors secreted by skeletal muscle at rest and during contraction and the development of T2D remain to be elucidated. Many myokines shown to influence muscle energy metabolism still have not been characterized in the context of T2D in skeletal muscle specifically. The purpose of this review is to highlight what is known and what remains to be determined regarding myokine secretion in patients with T2D to uncover potential therapeutic targets for the management of this disease.

miR-181c-3p and -5p promotes high-glucose-induced dysfunction in human umbilical vein endothelial cells by regulating leukemia inhibitory factor

Diabetes mellitus is a chronic metabolic disease with high blood glucose level and closely related to endothelial dysfunction, an important factor in the pathogenesis of vascular changes. Several miRNAs have been reported to be altered in a diabetic environment including miR-181c. In the article, we found that the expression of miR-181c-3p and miR-181c-5p was significantly downregulated under glucose treatment in a dose-dependent manner and in peripheral blood from diabetic patients compared with healthy participants. We explored the role of miR-181c-3p and miR-181c-5p in high glucose (HG)-induced dysfunction in human umbilical vein endothelial cells (HUVECs) by regulating leukemia inhibitory factor (LIF), their potential target with binding sites in 3-UTR region, that is also closely related to glucose metabolism. In addition, miR-181c-3p and miR-181c-5p significantly enhanced HG-induced oxidative stress injury by increasing malondialdehyde (MDA) and reactive oxygen species (ROS) production and promoted HG-induced HUVECs apoptosis, confirmed by TUNEL staining. LIF partially reduced those effects by decreasing oxidative stress and inhibiting cell apoptosis. Therefore, knocking down of LIF in HUVECs by LIF siRNA transfection, significantly increased HG-induced MDA and ROS production and induced more intense HUVECs apoptosis. Our results indicate that miR-181c-3p and miR-181c-5p promote HG-induced HUVECs injury through their target LIF.

DNA methylation in the pathogenesis of type 2 diabetes in humans

Background

Type 2 diabetes (T2D) is a multifactorial, polygenic disease caused by impaired insulin secretion and insulin resistance. Genome-wide association studies (GWAS) were expected to resolve a large part of the genetic component of diabetes; yet, the single nucleotide polymorphisms identified by GWAS explain less than 20% of the estimated heritability for T2D. There was subsequently a need to look elsewhere to find disease-causing factors. Mechanisms mediating the interaction between environmental factors and the genome, such as epigenetics, may be of particular importance in the pathogenesis of T2D.

Scope of Review

This review summarizes knowledge of the impact of epigenetics on the pathogenesis of T2D in humans. In particular, the review will focus on alterations in DNA methylation in four human tissues of importance for the disease; pancreatic islets, skeletal muscle, adipose tissue, and the liver. Case–control studies and studies examining the impact of non-genetic and genetic risk factors on DNA methylation in humans will be considered. These studies identified epigenetic changes in tissues from subjects with T2D versus non-diabetic controls. They also demonstrate that non-genetic factors associated with T2D such as age, obesity, energy rich diets, physical activity and the intrauterine environment impact the epigenome in humans. Additionally, interactions between genetics and epigenetics seem to influence the pathogenesis of T2D.

Conclusions

Overall, previous studies by our group and others support a key role for epigenetics in the growing incidence of T2D.

PHYSIOLOGY AND ENDOCRINOLOGY SYMPOSIUM:The effects of poor maternal nutrition during gestation on offspring postnatal growth and metabolism

Poor maternal nutrition during gestation has been linked to poor growth and development, metabolic dysfunction, impaired health, and reduced productivity of offspring in many species. Poor maternal nutrition can be defined as an excess or restriction of overall nutrients or specific macro- or micronutrients in the diet of the mother during gestation. Interestingly, there are several reports that both restricted- and over-feeding during gestation negatively affect offspring postnatal growth with reduced muscle and bone deposition, increased adipose accumulation, and metabolic dysregulation through reduced leptin and insulin sensitivity. Our laboratory and others have used experimental models of restricted- and over-feeding during gestation to evaluate effects on early postnatal growth of offspring. Restricted- and over-feeding during gestation alters body size, circulating growth factors, and metabolic hormones in offspring postnatally. Both restricted- and over-feeding alter muscle growth, increase lipid content in the muscle, and cause changes in expression of myogenic factors. Although the negative effects of poor maternal nutrition on offspring growth have been well characterized in recent years, the mechanisms contributing to these changes are not well established. Our laboratory has focused on elucidating these mechanisms by evaluating changes in gene and protein expression, and stem cell function. Through RNA-Seq analysis, we observed changes in expression of genes involved in protein synthesis, metabolism, cell function, and signal transduction in muscle tissue. We recently reported that satellite cells, muscle stem cells, have altered expression of myogenic factors in offspring from restricted-fed mothers. Bone marrow derived mesenchymal stem cells, multipotent cells that contribute to development and maintenance of several tissues including bone, muscle, and adipose, have a 50% reduction in cell proliferation and altered metabolism in offspring from both restricted- and over-fed mothers. These findings indicate that poor maternal nutrition may alter offspring postnatal growth by programming stem cell populations. In conclusion, poor maternal nutrition during gestation negatively affects offspring postnatal growth, potentially through impaired stem and satellite cell function. Therefore, determining the mechanisms that contribute to fetal programming is critical to identifying effective management interventions for these offspring and improving efficiency of production.

Type 2 diabetes and obesity induce similar transcriptional reprogramming in human myocytes

BACKGROUND

Skeletal muscle is one of the primary tissues involved in the development of type 2 diabetes (T2D). The close association between obesity and T2D makes it difficult to isolate specific effects attributed to the disease alone. Therefore, here we set out to identify and characterize intrinsic properties of myocytes, associated independently with T2D or obesity.

METHODS

We generated and analyzed RNA-seq data from primary differentiated myotubes from 24 human subjects, using a factorial design (healthy/T2D and non-obese/obese), to determine the influence of each specific factor on genome-wide transcription. This setup enabled us to identify intrinsic properties, originating from muscle precursor cells and retained in the corresponding myocytes. Bioinformatic and statistical methods, including differential expression analysis, gene-set analysis, and metabolic network analysis, were used to characterize the different myocytes.

RESULTS

We found that the transcriptional program associated with obesity alone was strikingly similar to that induced specifically by T2D. We identified a candidate epigenetic mechanism, H3K27me3 histone methylation, mediating these transcriptional signatures. T2D and obesity were independently associated with dysregulated myogenesis, down-regulated muscle function, and up-regulation of inflammation and extracellular matrix components. Metabolic network analysis identified that in T2D but not obesity a specific metabolite subnetwork involved in sphingolipid metabolism was transcriptionally regulated.

CONCLUSIONS

Our findings identify inherent characteristics in myocytes, as a memory of the in vivo phenotype, without the influence from a diabetic or obese extracellular environment, highlighting their importance in the development of T2D.

ANTI-DIABETIC EFFECTS OF ZHUODUQING FORMULA, A CHINESE HERBAL DECOCTION, ON A RAT MODEL OF TYPE 2 DIABETES

Background:

Zhuoduqing formula (ZDQ) is a Chinese herbal decoction and used to treat type 2 diabetes in clinical practice, but the potential evidence needs to be provided.

Materials and Methods:

Type 2 diabetic model rats were induced by feeding high fat diet (HFD) and intraperitoneal injection of streptozotocin (STZ). The model rats were given ZDQ for 4 weeks. Insulin sensitivity was evaluated by homeostasis model assessment of basal insulin resistance (HOMA-IR) and intraperitoneal glucose tolerance test (IPGTT). Blood insulin and tumour necrosis factor-α (TNF-α) levels as well as SOCS-3 levels in skeletal muscles were analyzed by ELISA.

Results:

ZDQ significantly decreased fasting blood glucose, ameliorated HOMA-IR and IPGTT, and reduced triglyceride and total cholesterol in type 2 diabetic rats. Moreover, ZDQ remarkably lowered blood TNF-α levels and inhibited SOCS-3 levels in skeletal muscles.

Conclusion:

The results display that ZDQ performs anti-diabetic functions in type 2 diabetic rats induced by feeding HFD and intraperitoneal injection of STZ.

Abbreviations: ZDQ, zhuoduqing formula; ROS, rosiglitazone; HOMA-IR, homeostasis model assessment of basal insulin resistance; IPGTT, intraperitoneal glucose tolerance test; HFD, high fat diet; SOCS-3, suppressor of cytokine signaling-3; TNF-α, tumour necrosis factor-α.

Abnormal epigenetic changes during differentiation of human skeletal muscle stem cells from obese subjects

BACKGROUND

Human skeletal muscle stem cells are important for muscle regeneration. However, the combined genome-wide DNA methylation and expression changes taking place during adult myogenesis have not been described in detail and novel myogenic factors may be discovered. Additionally, obesity is associated with low relative muscle mass and diminished metabolism. Epigenetic alterations taking place during myogenesis might contribute to these defects.

METHODS

We used Infinium HumanMethylation450 BeadChip Kit (Illumina) and HumanHT-12 Expression BeadChip (Illumina) to analyze genome-wide DNA methylation and transcription before versus after differentiation of primary human myoblasts from 14 non-obese and 14 obese individuals. Functional follow-up experiments were performed using siRNA mediated gene silencing in primary human myoblasts and a transgenic mouse model.

RESULTS

We observed genome-wide changes in DNA methylation and expression patterns during differentiation of primary human muscle stem cells (myoblasts). We identified epigenetic and transcriptional changes of myogenic transcription factors (MYOD1, MYOG, MYF5, MYF6, PAX7, MEF2A, MEF2C, and MEF2D), cell cycle regulators, metabolic enzymes and genes previously not linked to myogenesis, including IL32, metallothioneins, and pregnancy-specific beta-1-glycoproteins. Functional studies demonstrated IL-32 as a novel target that regulates human myogenesis, insulin sensitivity and ATP levels in muscle cells. Furthermore, IL32 transgenic mice had reduced insulin response and muscle weight. Remarkably, approximately 3.7 times more methylation changes (147,161 versus 39,572) were observed during differentiation of myoblasts from obese versus non-obese subjects. In accordance, DNMT1 expression increased during myogenesis only in obese subjects. Interestingly, numerous genes implicated in metabolic diseases and epigenetic regulation showed differential methylation and expression during differentiation only in obese subjects.

CONCLUSIONS

Our study identifies IL-32 as a novel myogenic regulator, provides a comprehensive map of the dynamic epigenome during differentiation of human muscle stem cells and reveals abnormal epigenetic changes in obesity.

Activation of the Pro-Oxidant PKCβII-p66Shc Signaling Pathway Contributes to Pericyte Dysfunction in Skeletal Muscles of Patients With Diabetes With Critical Limb Ischemia

Critical limb ischemia (CLI), foot ulcers, former amputation, and impaired regeneration are independent risk factors for limb amputation in subjects with diabetes. The present work investigates whether and by which mechanism diabetes negatively impacts on functional properties of muscular pericytes (MPs), which are resident stem cells committed to reparative angiomyogenesis. We obtained muscle biopsy samples from patients with diabetes who were undergoing major limb amputation and control subjects. Diabetic muscles collected at the rim of normal tissue surrounding the plane of dissection showed myofiber degeneration, fat deposition, and reduction of MP vascular coverage. Diabetic MPs (D-MPs) display ultrastructural alterations, a differentiation bias toward adipogenesis at the detriment of myogenesis and an inhibitory activity on angiogenesis. Furthermore, they have an imbalanced redox state, with downregulation of the antioxidant enzymes superoxide dismutase 1 and catalase, and activation of the pro-oxidant protein kinase C isoform β-II (PKCβII)-dependent p66^Shc signaling pathway. A reactive oxygen species scavenger or, even more effectively, clinically approved PKCβII inhibitors restore D-MP angiomyogenic activity. Inhibition of the PKCβII-dependent p66^Shc signaling pathway could represent a novel therapeutic approach for the promotion of muscle repair in individuals with diabetes.

Epigenetic Alterations in Human Liver From Subjects With Type 2 Diabetes in Parallel With Reduced Folate Levels

OBJECTIVE

Epigenetic variation may contribute to the development of complex metabolic diseases such as type 2 diabetes (T2D). Hepatic insulin resistance is a hallmark of T2D. However, it remains unknown whether epigenetic alterations take place in the liver from diabetic subjects. Therefore, we investigated the genome-wide DNA methylation pattern in the liver from subjects with T2D and nondiabetic controls and related epigenetic alterations to gene expression and circulating folate levels.

RESEARCH DESIGN AND METHODS

Liver biopsies were obtained from 35 diabetic and 60 nondiabetic subjects, which are part of the Kuopio Obesity Surgery Study. The genome-wide DNA methylation pattern was analyzed in the liver using the HumanMethylation450 BeadChip. RNA expression was analyzed from a subset of subjects using the HumanHT-12 Expression BeadChip.

RESULTS

After correction for multiple testing, we identified 251 individual CpG sites that exhibit differential DNA methylation in liver obtained from T2D compared with nondiabetic subjects (Q < .05). These include CpG sites annotated to genes that are biologically relevant to the development of T2D such as GRB10, ABCC3, MOGAT1, and PRDM16. The vast majority of the significant CpG sites (94%) displayed decreased DNA methylation in liver from subjects with T2D. The hypomethylation found in liver from diabetic subjects may be explained by reduced folate levels. Indeed, subjects with T2D had significantly reduced erythrocyte folate levels compared with nondiabetic subjects. We further identified 29 genes that displayed both differential DNA methylation and gene expression in human T2D liver including the imprinted gene H19.

CONCLUSIONS

Our study highlights the importance of epigenetic and transcriptional changes in the liver from subjects with T2D. Reduced circulating folate levels may provide an explanation for hypomethylation in the human diabetic liver.

Leukemia inhibitory factor increases glucose uptake in mouse skeletal muscle

Members of the IL-6 family, IL-6 and ciliary neurotrophic factor (CNTF), have been shown to increase glucose uptake and fatty acid oxidation in skeletal muscle. However, the metabolic effects of another family member, leukemia inhibitory factor (LIF), are not well characterized. Effects of LIF on skeletal muscle glucose uptake and palmitate oxidation and signaling were investigated in ex vivo incubated mouse soleus and EDL muscles from muscle-specific AMPKα2 kinase-dead, muscle-specific SOCS3 knockout, and lean and high-fat-fed mice. Inhibitors were used to investigate involvement of specific signaling pathways. LIF increased muscle glucose uptake in dose (50-5,000 pM/l) and time-dependent manners with maximal effects at the 30-min time point. LIF increased Akt Ser(473) phosphorylation (P) in soleus and EDL, whereas AMPK Thr(172) P was unaffected. Incubation with parthenolide abolished LIF-induced glucose uptake and STAT3 Tyr(705) P, whereas incubation with LY-294002 and wortmannin suppressed both basal and LIF-induced glucose uptake and Akt Ser(473) P, indicating that JAK and PI 3-kinase signaling is required for LIF-stimulated glucose uptake. Incubation with rapamycin and AZD8055 indicated that mammalian target of rapamycin complex (mTORC)2, but not mTORC1, also is required for LIF-stimulated glucose uptake. In contrast to CNTF, LIF stimulation did not alter palmitate oxidation. LIF-stimulated glucose uptake was maintained in EDL from obese insulin-resistant mice, whereas soleus developed LIF resistance. Lack of SOCS3 and AMPKα2 did not affect LIF-stimulated glucose uptake. In conclusion, LIF acutely increased muscle glucose uptake by a mechanism potentially involving the PI 3-kinase/mTORC2/Akt pathway and is not impaired in EDL muscle from obese insulin-resistant mice.

Proteome- and transcriptome-driven reconstruction of the human myocyte metabolic network and its use for identification of markers for diabetes

Skeletal myocytes are metabolically active and susceptible to insulin resistance and are thus implicated in type 2 diabetes (T2D). This complex disease involves systemic metabolic changes, and their elucidation at the systems level requires genome-wide data and biological networks. Genome-scale metabolic models (GEMs) provide a network context for the integration of high-throughput data. We generated myocyte-specific RNA-sequencing data and investigated their correlation with proteome data. These data were then used to reconstruct a comprehensive myocyte GEM. Next, we performed a meta-analysis of six studies comparing muscle transcription in T2D versus healthy subjects. Transcriptional changes were mapped on the myocyte GEM, revealing extensive transcriptional regulation in T2D, particularly around pyruvate oxidation, branched-chain amino acid catabolism, and tetrahydrofolate metabolism, connected through the downregulated dihydrolipoamide dehydrogenase. Strikingly, the gene signature underlying this metabolic regulation successfully classifies the disease state of individual samples, suggesting that regulation of these pathways is a ubiquitous feature of myocytes in response to T2D.

Suppressors of cytokine signaling (SOCS) and type 2 diabetes

The suppressors of cytokine signaling (SOCS) proteins are originally identified as negative regulators of cytokine-activated Janus kinase/signal transducers and activators of transcription signaling pathway, but increasing evidence reveals that SOCS proteins play an important role in the development of type 2 diabetes involving regulation of the insulin signaling and pancreatic β-cell function, and that SOCS are promising to be the targets for the treatment of type 2 diabetes. In this review, we focus on the emerging role for SOCS and the potential drugs targeting SOCS for type 2 diabetes.

Diabetic myopathy: impact of diabetes mellitus on skeletal muscle progenitor cells

Diabetes mellitus is defined as a group of metabolic diseases that are associated with the presence of a hyperglycemic state due to impairments in insulin release and/or function. While the development of each form of diabetes (Type 1 or Type 2) drastically differs, resultant pathologies often overlap. In each diabetic condition, a failure to maintain healthy muscle is often observed, and is termed diabetic myopathy. This significant, but often overlooked, complication is believed to contribute to the progression of additional diabetic complications due to the vital importance of skeletal muscle for our physical and metabolic well-being. While studies have investigated the link between changes to skeletal muscle metabolic health following diabetes mellitus onset (particularly Type 2 diabetes mellitus), few have examined the negative impact of diabetes mellitus on the growth and reparative capacities of skeletal muscle that often coincides with disease development. Importantly, evidence is accumulating that the muscle progenitor cell population (particularly the muscle satellite cell population) is also negatively affected by the diabetic environment, and as such, likely contributes to the declining skeletal muscle health observed in diabetes mellitus. In this review, we summarize the current knowledge surrounding the influence of diabetes mellitus on skeletal muscle growth and repair, with a particular emphasis on the impact of diabetes mellitus on skeletal muscle progenitor cell populations.

Lifelong Physical Activity Prevents Aging-Associated Insulin Resistance in Human Skeletal Muscle Myotubes via Increased Glucose Transporter Expression

Both aging and physical inactivity are associated with increased development of insulin resistance whereas physical activity has been shown to promote increased insulin sensitivity. Here we investigated the effects of physical activity level on aging-associated insulin resistance in myotubes derived from human skeletal muscle satellite cells. Satellite cells were obtained from young (22 yrs) normally active or middle-aged (56.6 yrs) individuals who were either lifelong sedentary or lifelong active. Both middle-aged sedentary and middle-aged active myotubes had increased p21 and myosin heavy chain protein expression. Interestingly MHCIIa was increased only in myotubes from middle-aged active individuals. Middle-aged sedentary cells had intact insulin-stimulated Akt phosphorylation however, the same cell showed ablated insulin-stimulated glucose uptake and GLUT4 translocation to the plasma membrane. On the other hand, middle-aged active cells retained both insulin-stimulated increases in glucose uptake and GLUT4 translocation to the plasma membrane. Middle-aged active cells also had significantly higher mRNA expression of GLUT1 and GLUT4 compared to middle-aged sedentary cells, and significantly higher GLUT4 protein. It is likely that physical activity induces a number of stable adaptations, including increased GLUT4 expression that are retained in cells ex vivo and protect, or delay the onset of middle-aged-associated insulin resistance. Additionally, a sedentary lifestyle has an impact on the metabolism of human myotubes during aging and may contribute to aging-associated insulin resistance through impaired GLUT4 localization.

Physical activity is associated with retained muscle metabolism in human myotubes challenged with palmitate

  The aim of this study was to investigate whether physical activity is associated with preserved muscle metabolism in human myotubes challenged with saturated fatty acids. Human muscle satellite cells were isolated from sedentary or active individuals and differentiated into myocytes in culture. Metabolic differences were then investigated in the basal state or after chronic palmitate treatment. At basal, myocytes from sedentary individuals exhibited higher CD36 and HSP70 protein expression as well as elevated phosphorylation of c-Jun NH2-terminal kinase (JNK) and insulin receptor substrate 1 (IRS1) serine(307) compared to myocytes from active individuals. Despite equal lipid accumulation following palmitate treatment, myocytes from sedentary individuals exhibited delayed acetyl coenzyme A carboxylase phosphorylation compared to the active group. Myocytes from sedentary individuals had significantly higher basal glucose uptake and palmitate promoted insulin resistance in sedentary myocytes. Importantly, myocytes from active individuals were partially protected from palmitate-induced insulin resistance. Palmitate treatment enhanced IRS1 serine307 phosphorylation in myocytes from sedentary individuals and correlated positively to JNK phosphorylation. In conclusion, muscle satellite cells retain metabolic differences associated with physical activity. Physical activity partially protects myocytes from fatty acid-induced insulin resistance and inactivity is associated with dysregulation of metabolism in satellite cells challenged with palmitate. Although the benefits of physical activity on whole body physiology have been well investigated, this paper presents novel findings that both diet and exercise impact satellite cells directly. Given the fact that satellite cells are important for muscle maintenance, a dysregulated function could have profound effects on health. Therefore the effects of lifestyle on satellite cells needs to be delineated.

Glucagon like peptide-1-induced glucose metabolism in differentiated human muscle satellite cells is attenuated by hyperglycemia

BACKGROUND

Glucagon like peptide-1 (GLP-1) stimulates insulin secretion from the pancreas but also has extra-pancreatic effects. GLP-1 may stimulate glucose uptake in cultured muscle cells but the mechanism is not clearly defined. Furthermore, while the pancreatic effects of GLP-1 are glucose-dependent, the glucose-dependency of its extra-pancreatic effects has not been examined.

METHODS

Skeletal muscle satellite cells isolated from young (22.5 ± 0.97 yr), lean (BMI 22.5 ± 0.6 kg/m(2)), healthy males were differentiated in media containing either 22.5 mM (high) or 5 mM (normal) glucose for 7 days in the absence or presence of insulin and/or various GLP-1 concentrations. Myocellular effects of GLP-1, insulin and glucose were assessed by western-blot, glucose uptake and glycogen synthesis.

RESULTS

We firstly show that the GLP-1 receptor protein is expressed in differentiated human muscle satellite cells (myocytes). Secondly, we show that in 5 mM glucose media, exposure of myocytes to GLP-1 results in a dose dependent increase in glucose uptake, GLUT4 amount and subsequently glycogen synthesis in a PI3K dependent manner, independent of the insulin signaling cascade. Importantly, we provide evidence that differentiation of human satellite cells in hyperglycemic (22.5 mM glucose) conditions increases GLUT1 expression, and renders the cells insulin resistant and interestingly GLP-1 resistant in terms of glucose uptake and glycogen synthesis. Hyperglycemic conditions did not affect the ability of insulin to phosphorylate downstream targets, PKB or GSK3. Interestingly we show that at 5 mM glucose, GLP-1 increases GLUT4 protein levels and that this effect is abolished by hyperglycemia.

CONCLUSIONS

GLP-1 increases glucose uptake and glycogen synthesis into fully-differentiated human satellite cells in a PI3-K dependent mechanism potentially through increased GLUT4 protein levels. The latter occurs independently of the insulin signaling pathway. Attenuation of both GLP-1 and insulin-induced glucose metabolism by hyperglycemia is likely to occur downstream of PI3K.