MyomiRs as Markers of Insulin Resistance and Decreased Myogenesis in Skeletal Muscle of Diet-Induced Obese Mice

Pharmaceutical Agents for Contractile-Metabolic Dysfunction After Volumetric Muscle Loss

Volumetric muscle loss (VML) injuries represent a majority of military service member casualties and are common in civilian populations following blunt and/or penetrating traumas. Characterized as a skeletal muscle injury with permanent functional impairments, there is currently no standard for rehabilitation, leading to lifelong disability. Toward developing rehabilitative strategies, previous research demonstrates that the remaining muscle after a VML injury lacks similar levels of plasticity or adaptability as healthy, uninjured skeletal muscle. This may be due, in part, to impaired innervation and vascularization of the remaining muscle, as well as disrupted molecular signaling cascades commonly associated with muscle adaptation. The primary objective of this study was to assess the ability of four pharmacological agents with a strong record of modulating muscle contractile and metabolic function to improve functional deficits in a murine model of VML injury. Male C57BL/6 mice underwent a 15% multimuscle VML injury of the posterior hindlimb and were randomized into drug treatment groups (formoterol [FOR], 5-aminoimidazole-4-carboxamide riboside [AICAR], pioglitazone [PIO], or sildenafil [SIL]) or untreated VML group. At the end of 60 days, the injury model was first validated by comparison to age-matched injury-naive mice. Untreated VML mice had 22% less gastrocnemius muscle mass, 36% less peak-isometric torque, and 27% less maximal mitochondrial oxygen consumption rate compared to uninjured mice (p < 0.01). Experimental drug groups were, then, compared to VML untreated, and there was minimal evidence of efficacy for AICAR, PIO, or SIL in improving contractile and metabolic functional outcomes. However, FOR-treated VML mice had 18% greater peak isometric torque (p < 0.01) and permeabilized muscle fibers had 36% greater State III mitochondrial oxygen consumption rate (p < 0.01) compared to VML untreated mice, suggesting an overall improvement in muscle condition. There was minimal evidence that these benefits came from greater mitochondrial biogenesis and/or mitochondrial complex protein content, but could be due to greater enzyme activity levels for complex I and complex II. These findings suggest that FOR treatment is candidate to pair with a rehabilitative approach to maximize functional improvements in VML-injured muscle. Impact statement Volumetric muscle loss (VML) injuries result in deficiencies in strength and mobility, which have a severe impact on patient quality of life. Despite breakthroughs in tissue engineering, there are currently no treatments available that can restore function to the affected limb. Our data show that treatment of VML injuries with clinically available and FDA-approved formoterol (FOR), a beta-agonist, significantly improves strength and metabolism of VML-injured muscle. FOR is therefore a promising candidate for combined therapeutic approaches (i.e., regenerative rehabilitation) such as pairing FOR with structured rehabilitation or cell-seeded biomaterials as it may provide greater functional improvements than either strategy alone.

Extracellular miRNAs as mediators of obesity-associated disease

Extracellular miRNAs are found in a variety of body fluids and mediate intercellular and interorgan communication, thus regulating gene expression and cellular metabolism. These miRNAs are secreted either in small vesicles/exosomes (sEV) or bound to proteins such as Argonaute and high-density lipoprotein. Both exosomal and protein-bound circulating miRNAs are altered in obesity. Although all tissues can contribute to changes in circulating miRNAs, adipose tissue itself is an important source of these miRNAs, especially those in sEVs. These are derived from both adipocytes and macrophages and participate in crosstalk between these cells, as well as peripheral tissues, including liver, skeletal muscle and pancreas, whose function may be impaired in obesity. Changes in levels of circulating miRNAs have also been linked to the beneficial effects induced by weight loss interventions, including diet, exercise and bariatric surgery, further indicating a role for these miRNAs as mediators of disease pathogenesis. Here, we review the role of circulating miRNAs in the pathophysiology of obesity and explore their potential use as biomarkers and in therapy of obesity-associated metabolic syndrome.

PDIA4, a new endoplasmic reticulum stress protein, modulates insulin resistance and inflammation in skeletal muscle

INTRODUCTION

Endoplasmic reticulum (ER) stress has emerged as a key player in insulin resistance (IR) progression in skeletal muscle. Recent reports revealed that ER stress-induced the expression of protein disulfide isomerase family a member 4 (PDIA4), which may be involved in IR-related diseases. A previous study showed that metformin modulated ER stress-induced IR. However, it remained unclear whether metformin alleviated IR by regulating PDIA4 expression in skeletal muscle.

METHODS

Herein, we used palmitate-induced IR in C2C12 cells and a high-fat diet-induced IR mouse model to document the relations between metformin, IR, and PDIA4.

RESULTS

In C2C12 cells, palmitate-induced IR increased inflammatory cytokines and PDIA4 expression. Besides, knocking down PDIA4 decreased palmitate-induced IR and inflammation in C2C12 cells. Furthermore, metformin modulated PDIA4 expression and alleviated IR both in vitro and in vivo. In addition, serum PDIA4 concentrations are associated with IR and inflammatory cytokines levels in human subjects.

DISCUSSION

Thus, this study is the first to demonstrate that PDIA4 participates in the metformin-induced effects on skeletal muscle IR and indicates that PDIA4 is a potential novel therapeutic target for directly alleviating IR.

Intramuscular Injection of miR-1 Reduces Insulin Resistance in Obese Mice

The role of microRNAs in metabolic diseases has been recognized and modulation of them could be a promising strategy to treat obesity and obesity-related diseases. The major purpose of this study was to test the hypothesis that intramuscular miR-1 precursor replacement therapy could improve metabolic parameters of mice fed a high-fat diet. To this end, we first injected miR-1 precursor intramuscularly in high-fat diet-fed mice and evaluated glucose tolerance, insulin sensitivity, and adiposity. miR-1-treated mice did not lose weight but had improved insulin sensitivity measured by insulin tolerance test. Next, using an in vitro model of insulin resistance by treating C2C12 cells with palmitic acid (PA), we overexpressed miR-1 and measured p-Akt content and the transcription levels of a protein related to fatty acid oxidation. We found that miR-1 could not restore insulin sensitivity in C2C12 cells, as indicated by p-Akt levels and that miR-1 increased expression of Pgc1a and Cpt1b in PA-treated cells, suggesting a possible role of miR-1 in mitochondrial respiration. Finally, we analyzed mitochondrial oxygen consumption in primary skeletal muscle cells treated with PA and transfected with or without miR-1 mimic. PA-treated cells showed reduced basal respiration, oxygen consumption rate-linked ATP production, maximal and spare capacity, and miR-1 overexpression could prevent impairments in mitochondrial respiration. Our data suggest a role of miR-1 in systemic insulin sensitivity and a new function of miR-1 in regulating mitochondrial respiration in skeletal muscle.

Palmitic Acid Impairs Myogenesis and Alters Temporal Expression of miR-133a and miR-206 in C2C12 Myoblasts

Palmitic acid (PA), a saturated fatty acid enriched in high-fat diet, has been implicated in the development of sarcopenic obesity. Herein, we chose two non-cytotoxic concentrations to better understand how excess PA could impact myotube formation or diameter without inducing cell death. Forty-eight hours of 100 µM PA induced a reduction of myotube diameter and increased the number of type I fibers, which was associated with increased miR-206 expression. Next, C2C12 myotube growth in the presence of PA was evaluated. Compared to control cells, 150 µM PA reduces myoblast proliferation and the expression of MyoD and miR-206 and miR-133a expression, leading to a reduced number and diameter of myotubes. PA (100 µM), despite not affecting proliferation, impairs myotube formation by reducing the expression of Myf5 and miR-206 and decreasing protein synthesis. Interestingly, 100 and 150 µM PA-treated myotubes had a higher number of type II fibers than control cells. In conclusion, PA affects negatively myotube diameter, fusion, and metabolism, which may be related to myomiRs. By providing new insights into the mechanisms by which PA affects negatively skeletal muscle, our data may help in the discovery of new targets to treat sarcopenic obesity.

Centennial Review: Metabolic microRNA - shifting gears in the regulation of metabolic pathways in poultry

Over 20 yr ago, a small noncoding class of RNA termed microRNA (miRNA) that was able to recognize sequences in mRNAs and inhibit their translation was discovered in Caenorhabditis elegans. In the intervening years, miRNA have been discovered in most eukaryotes and are now known to regulate the majority of protein-coding genes. It has been discovered that disruption of miRNA function often leads to the development of pathological conditions. One physiological system under extensive miRNA-mediated regulation is metabolism. Metabolism is one of the most dynamic of biological networks within multiple organs, including the liver, muscle, and adipose tissue, working in concert to respond to ever-changing nutritional cues and energy demands. Therefore, it is not surprising that miRNA regulate virtually all aspects of eukaryotic metabolism and have been linked to metabolic disorders, such as obesity, fatty liver diseases, and diabetes, just to name a few. Chickens, and birds in general, face their own unique metabolic challenges, particularly after hatching, when their metabolism must completely transform from using lipid-rich yolk to carbohydrate-rich feed as fuel in a very short period of time. Furthermore, commercial poultry breeds have undergone extensive selection over the last century for more desirable production traits, which has resulted in numerous metabolic consequences. Here, we review the current knowledge of miRNA-mediated regulation of metabolic development and function in chickens.

Expression and clinical significance of miR-1 and miR-133 in pre-diabetes

Pre-diabetes represents an intermediate state of altered glucose metabolism between normal glucose levels and type 2 diabetes mellitus (T2D), and is considered a significant risk factor for the development of T2D and related complications. Early detection of pre-diabetes may allow for the use of timely and effective treatment strategies to prevent its progression. Circulating microRNAs (miRNAs/miRs) that reflect changes in diabetes-related tissues, including the pancreas, liver, skeletal and heart muscle, and adipose tissue are promising biomarkers of disease progression. In our previous study, it was demonstrated that the cardiac and skeletal muscle specific miR-1 and miR-133 are upregulated in the blood of patients with T2D and cardiovascular disease. Since both miRNAs have been shown to be implicated in insulin resistance, an important feature of pre-diabetes, we hypothesised that their expression may be increased prior to clinical diagnosis of T2D, and may thus serve as biomarkers for pre-diabetes. The expression levels of circulating miRNAs were evaluated by reverse transcription-quantitative PCR in whole blood samples from 55 subjects, including 28 pre-diabetes individuals with impaired fasting glucose (FG) and impaired glucose tolerance, and 27 healthy controls. The individuals with pre-diabetes exhibited significantly higher expression levels of miR-1 and miR-133 compared with the controls (P<0.05). Target prediction search revealed that both miR-1 and miR-133 target several pathways involved in the pathophysiology of diabetes. Pearson's correlation analysis revealed that the two miRNAs were positively correlated with blood glucose parameters, including FG, 2-h oral glucose tolerance test and glycated haemoglobin A1c levels, as well as with insulin resistance (P<0.05). Multivariate logistic regression analysis revealed that the two miRNAs were significantly and directly associated with pre-diabetes, and this association remained significant after adjustment for several confounding variables (P<0.05). Moreover, linear regression analysis showed that the Homeostatic Model Assessment-Insulin Resistance was the only significant predictor to be significantly associated with both miRNAs (P<0.05). In discriminating pre-diabetes individuals from healthy controls, the area under the curves (AUCs) of the receiver operating characteristic curves (ROCs) were 0.813 and 0.810 for miR-1 and miR-133 respectively (P<0.05). Despite the relatively small number of participants, the present study showed for the first time that circulating levels of miR-1 and miR-133 were increased in individuals with pre-diabetes, and they were associated with important features of pre-diabetes. Thus, they may serve as clinical biomarkers for the early-stages of T2D.

Recent advances and future avenues in understanding the role of adipose tissue cross talk in mediating skeletal muscle mass and function with ageing

Sarcopenia, broadly defined as the age-related decline in skeletal muscle mass, quality, and function, is associated with chronic low-grade inflammation and an increased likelihood of adverse health outcomes. The regulation of skeletal muscle mass with ageing is complex and necessitates a delicate balance between muscle protein synthesis and degradation. The secretion and transfer of cytokines, long non-coding RNAs (lncRNAs) and microRNAs (miRNAs), both discretely and within extracellular vesicles, have emerged as important communication channels between tissues. Some of these factors have been implicated in regulating skeletal muscle mass, function, and pathologies and may be perturbed by excessive adiposity. Indeed, adipose tissue participates in a broad spectrum of inter-organ communication and obesity promotes the accumulation of macrophages, cellular senescence, and the production and secretion of pro-inflammatory factors. Pertinently, age-related sarcopenia has been reported to be more prevalent in obesity; however, such effects are confounded by comorbidities and physical activity level. In this review, we provide evidence that adiposity may exacerbate age-related sarcopenia and outline some emerging concepts of adipose-skeletal muscle communication including the secretion and processing of novel myokines and adipokines and the role of extracellular vesicles in mediating inter-tissue cross talk via lncRNAs and miRNAs in the context of sarcopenia, ageing, and obesity. Further research using advances in proteomics, transcriptomics, and techniques to investigate extracellular vesicles, with an emphasis on translational, longitudinal human studies, is required to better understand the physiological significance of these factors, the impact of obesity upon them, and their potential as therapeutic targets in combating muscle wasting.

The Changes of Heart miR-1 and miR-133 Expressions following Physiological Hypertrophy Due to Endurance Training

Objective

MicroRNAs (miRNAs) play a key role in the development of the heart. Recent studies have shown that miR- 1 and miR-133 are key regulators of cardiac hypertrophy. Therefore, we aimed to evaluate the effect of an endurance training (ET) program on the expressions of these miRNAs and their transcriptional network.

Materials and Methods

In this experimental study, cardiac hypertrophy was induced by 14 weeks of ET for 1 hour per day, 6 days per week at 75% VO2 max). The rats (221 ± 23 g) in the experimental (n=7) and control (n=7) groups were anesthetized to evaluate heart morphology changes by echocardiography. Next, we evaluated expressions of miR-1 and miR-133, and heart and neural crest derivatives express 2 (Hand2), Mef2c, histone deacetylase 4 (Hdac4) and serum response factor (Srf) gene expressions by real-time polymerase chain reaction (PCR). Finally, the collected data were evaluated by the independent t test to determine differences between the groups

Results

The echocardiography result confirmed physiological hypertrophy in the experimental group that underwent ET as shown by the increased left ventricular weight/body surface area (LVW/BSA) (P=0.004), LVW/body weight (BW) (P=0.011), left ventricular diameter end-diastolic (LVDd) (P=0.003), and improvements in heart functional indexes such as fractional shortness (FS) (P=0.036) and stroke volume (SV) (P=0.002). There were significant increases in the expressions of miR-1 (P=0.001) and miR-133 (P=0.004). The expressions of Srf, Hdac4, and Hand2 genes significantly increased (P<0.001) in the experimental group Compared with the control group. The expression of Mef2c did not significantly change.

Conclusion

The expressions of miR-1 and miR-133 and their target genes appeared to be involved in physiological hypertrophy induced by ET in these rats.

Association of Genetic Polymorphisms in MicroRNAs With Type 2 Diabetes Mellitus in a Chinese Population

INTRODUCTION

MicroRNAs (miRNA) involved in the insulin signaling pathways deeply affect the pathogenesis of T2DM. The aim of this study was to assess the association between single nucleotide polymorphisms (SNP) of the related miRNAs (let-7f rs10877887, let-7a-1 rs13293512, miR-133a-1 rs8089787, miR-133a-2 rs13040413, and miR-27a rs895819) and susceptibility to type 2 diabetes mellitus (T2DM), and its possible mechanisms.

METHODS

Five SNPs in miRNAs (let-7f rs10877887, let-7a-1 rs13293512, miR-133a-1 rs8089787, miR-133a-2 rs13040413, and miR-27a rs895819) involved in the insulin signaling pathways were selected and genotyped in a case-control study that enrolled 371 T2DM patients and 381 non-diabetic controls. The individual SNP association analyses, interaction analyses of SNP-SNP, SNP-environmental factors were performed. The effect the risk-associated polymorphism on regulating its mature miRNA expression was also evaluated.

RESULTS

In overall analyses, miR-133a-2 rs13040413 and let-7a-1 rs13293512 were related to the susceptibility to T2DM. In stratified analyses, miR-133a-2 rs13040413, let-7a-1 rs13293512 and miR-27a rs895819 showed associations with T2DM in the age ≥ 60 years subgroup. Moreover, let-7a-1 rs13293512 and miR-27a rs895819 showed associations with T2DM in male subgroup. In SNP-environmental factors interaction analyses, there were interaction effects of miR-133a-2 rs13040413 with dyslipidemia, let-7a-1 rs13293512 with smoking, and let-7a-1 rs13293512 with dyslipidemia on T2DM. In SNP-SNP interaction analyses, there were also interaction effects of miR-133a-1 rs8089787 with let-7a-1 rs13293512, and miR-133a-1 rs8089787 with let-7f rs10877887 on T2DM. Furthermore, for miR-133a-2 rs13040413, the variant T allele showed a trend toward decreased miR-133a expression in comparison with the wild C allele. For let-7a-1 rs13293512, the variant C allele expressed a lower let-7a compared to the wild T allele.

CONCLUSION

MiRNAs polymorphisms involved in the insulin signaling pathways and the interaction effects of SNP-SNP, SNP-environmental factors were related to T2DM susceptibility in a Chinese population.

A new hypoglycemic mechanism of catalpol revealed by enhancing MyoD/MyoG-mediated myogenesis

AIMS

Enhancing myogenesis has been identified as a possible target to improve insulin sensitivity and protect against metabolic diseases. Catalpol, an iridoid glycoside, has been shown to exert a hypoglycaemic effect by improvement of insulin sensitivity; however, the underlying mechanism remains unknown. In this study, we tested whether catalpol has the potential to improve insulin sensitivity by augmenting myogenesis.

MAIN METHODS

We examined the hypoglycaemic mechanism of catalpol in db/db mice and C2C12 cells. db/db mice were treated with catalpol (200 mg/kg) for 8 consecutive weeks. Serum analysis, skeletal muscle performance and histology, and gene and protein expression were performed. In vitro glucose uptake, gene and protein expression were determined, and small interfering RNA was used to identify the underlying hypoglycaemic mechanism of catalpol.

KEY FINDINGS

In this study, we tested whether catalpol has the potential to improve skeletal insulin sensitivity by augmenting myogenesis, in which we found that, catalpol treatment in db/db mice lowered blood glucose and improved insulin sensitivity via activation of phosphatidylinositol‑3‑Kinase (PI3K)/protein kinase B (AKT) pathway. Moreover, catalpol-treated mice exhibited enhanced myogenesis, as evidenced by increased myogenic differentiation (MyoD), myogenin (MyoG) and myosin heavy chain (MHC) expressions. The in vitro experimental results showed that both catalpol and metformin enhanced glucose uptake via activation of PI3K/AKT pathway. However, unlike metformin, the PI3K/AKT pathway activation by catalpol was dependent on enhanced MyoD/MyoG-mediated myogenesis.

SIGNIFICANCE

Improvement of insulin sensitivity by enhancing MyoD/MyoG-mediated myogenesis may constitute a new therapeutic approach for treating type 2 diabetes.