The effect of type 2 diabetes mellitus and obesity on muscle progenitor cell function

Glucagon-like peptide-1 receptor agonist-based agents and weight loss composition: Filling the gaps

Excess adiposity is at the root of type 2 diabetes (T2D). Glucagon-like peptide-1 receptor agonists (GLP-1RAs) have emerged as first-line treatments for T2D based on significant weight loss results. The composition of weight loss using most diets consists of <25% fat-free mass (FFM) loss, with the remainder from fat stores. Higher amounts of weight loss (achieved with metabolic bariatric surgery) result in greater reductions in FFM. Our aim was to assess the impact that GLP-1RA-based treatments have on FFM. We analysed studies that reported changes in FFM with the following agents: exenatide, liraglutide, semaglutide, and the dual incretin receptor agonist tirzepatide. We performed an analysis of various weight loss interventions to provide a reference for expected changes in FFM. We evaluated studies using dual-energy X-ray absorptiometry (DXA) for measuring FFM (a crude surrogate for skeletal muscle). In evaluating the composition of weight loss, the percentage lost as fat-free mass (%FFML) was equal to ΔFFM/total weight change. The %FFML using GLP-1RA-based agents was between 20% and 40%. In the 28 clinical trials evaluated, the proportion of FFM loss was highly variable, but the majority reported %FFML exceeding 25%. Our review was limited to small substudies and the use of DXA, which does not measure skeletal muscle mass directly. Since FFM contains a variable amount of muscle (approximately 55%), this indirect measure may explain the heterogeneity in the data. Assessing quantity and quality of skeletal muscle using advanced imaging (magnetic resonance imaging) with functional testing will help fill the gaps in our current understanding.

Impaired skeletal muscle regeneration in diabetes: From cellular and molecular mechanisms to novel treatments

Diabetes represents a major public health concern with a considerable impact on human life and healthcare expenditures. It is now well established that diabetes is characterized by a severe skeletal muscle pathology that limits functional capacity and quality of life. Increasing evidence indicates that diabetes is also one of the most prevalent disorders characterized by impaired skeletal muscle regeneration, yet underlying mechanisms and therapeutic treatments remain poorly established. In this review, we describe the cellular and molecular alterations currently known to occur during skeletal muscle regeneration in people with diabetes and animal models of diabetes, including its associated comorbidities, e.g., obesity, hyperinsulinemia, and insulin resistance. We describe the role of myogenic and non-myogenic cell types on muscle regeneration in conditions with or without diabetes. Therapies for skeletal muscle regeneration and gaps in our knowledge are also discussed, while proposing future directions for the field.

Investigating the Effects of Diet-Induced Prediabetes on Skeletal Muscle Strength in Male Sprague Dawley Rats

Type 2 diabetes mellitus, a condition preceded by prediabetes, is documented to compromise skeletal muscle health, consequently affecting skeletal muscle structure, strength, and glucose homeostasis. A disturbance in skeletal muscle functional capacity has been demonstrated to induce insulin resistance and hyperglycemia. However, the modifications in skeletal muscle function in the prediabetic state are not well elucidated. Hence, this study investigated the effects of diet-induced prediabetes on skeletal muscle strength in a prediabetic model. Male Sprague Dawley rats were randomly assigned to one of the two groups (n = 6 per group; six prediabetic (PD) and six non-pre-diabetic (NPD)). The PD group (n = 6) was induced with prediabetes for 20 weeks. The diet that was used to induce prediabetes consisted of fats (30% Kcal/g), proteins (15% Kcal/g), and carbohydrates (55% Kcal/g). In addition to the diet, the experimental animals (n = 6) were supplied with drinking water that was supplemented with 15% fructose. The control group (n = 6) was allowed access to normal rat chow, consisting of 35% carbohydrates, 30% protein, 15% fats, and 20% other components, as well as ordinary tap water. At the end of week 20, the experimental animals were diagnosed with prediabetes using the American Diabetes Association (ADA) prediabetes impaired fasting blood glucose criteria (5.6-6.9 mmol/L). Upon prediabetes diagnosis, the animals were subjected to a four-limb grip strength test to assess skeletal muscle strength at week 20. After the grip strength test was conducted, the animals were euthanized for blood and tissue collection to analyze glycated hemoglobin (HbA1c), plasma insulin, and insulin resistance using the homeostatic model of insulin resistance (HOMA-IR) index and malondialdehyde (MDA) concentration. Correlation analysis was performed to examine the associations of skeletal muscle strength with HOMA-IR, plasma glucose, HbA1c, and MDA concentration. The results demonstrated increased HbA1c, FBG, insulin, HOMA-IR, and MDA concentrations in the PD group compared to the NPD group. Grip strength was reduced in the PD group compared to the NPD group. Grip strength was negatively correlated with HbA1c, plasma glucose, HOMA-IR, and MDA concentration in the PD group. These observations suggest that diet-induced prediabetes compromises muscle function, which may contribute to increased levels of sedentary behavior during prediabetes progression, and this may contribute to the development of hyperglycemia in T2DM.

Semi-quantitative thigh magnetic resonance imaging scores in assessing disease activity and determining long-term clinical outcome in idiopathic inflammatory myopathies: a causal mediation analysis

OBJECTIVES

To evaluate the relationship of thigh MRI (t-MRI) with manual muscle testing-8 (MMT-8), muscle enzymes and autoantibodies. To determine the causal and mediating factors resulting in poor recovery of MMT-8 in inflammatory myositis (IIM).

METHODS

This was a single-centre retrospective study in IIM patients. t-MRI was semi-quantitatively scored for muscle oedema, fascial oedema, muscle atrophy and fatty infiltration. Spearman correlation of t-MRI scores was done with muscle enzymes at baseline, and MMT-8 at baseline and on follow-up. Causal mediation analysis was performed with age, sex, symptom duration, autoantibodies, diabetes and BMI as independent variables, follow-up MMT-8 as dependent and t-MRI scores as mediating variables.

RESULTS

Baseline evaluation was done on 59 and follow-up on 38 patients. Median follow-up of the cohort was 31 (10-57) months. Baseline MMT-8 negatively correlated with muscle oedema (r = -0755), fascial oedema (r = -0.443) and muscle atrophy (r = -0.343). Creatinine kinase (r = 0.422) and aspartate transaminase (r = 0.480) positively correlated with muscle oedema. Follow-up MMT-8 correlated negatively with baseline atrophy (r = -0.497) and fatty infiltration (r = -0.531). On follow-up, MMT-8 males had positive total effect (estimate (95%CI)) via atrophy [2.93 (0.44, 4.89)] and fatty infiltration [2.08 (0.54, 3.71)]. Antisynthetase antibody had a positive total effect via fatty infiltration [4.50 (0.37, 7.59)]. Age had a negative total effect via atrophy [-0.09 (0.19, -0.01)] and fatty infiltration [-0.07 (-0.15, -0.01)]. Disease duration had a negative total effect via fatty infiltration [-0.18 (-0.27, -0.02)].

CONCLUSION

Baseline fatty infiltration and muscle atrophy resulting from older age, female sex, longer disease duration and absent anti-synthetase antibodies, partly mediate muscle recovery in IIM.

The first exome wide association study in Tunisia: identification of candidate loci and pathways with biological relevance for type 2 diabetes

Introduction

Type 2 diabetes (T2D) is a multifactorial disease involving genetic and environmental components. Several genome-wide association studies (GWAS) have been conducted to decipher potential genetic aberrations promoting the onset of this metabolic disorder. These GWAS have identified over 400 associated variants, mostly in the intronic or intergenic regions. Recently, a growing number of exome genotyping or exome sequencing experiments have identified coding variants associated with T2D. Such studies were mainly conducted in European populations, and the few candidate-gene replication studies in North African populations revealed inconsistent results. In the present study, we aimed to discover the coding genetic etiology of T2D in the Tunisian population.

Methods

We carried out a pilot Exome Wide Association Study (EWAS) on 50 Tunisian individuals. Single variant analysis was performed as implemented in PLINK on potentially deleterious coding variants. Subsequently, we applied gene-based and gene-set analyses using MAGMA software to identify genes and pathways associated with T2D. Potential signals were further replicated in an existing large in-silico dataset, involving up to 177116 European individuals.

Results

Our analysis revealed, for the first time, promising associations between T2D and variations in MYORG gene, implicated in the skeletal muscle fiber development. Gene-set analysis identified two candidate pathways having nominal associations with T2D in our study samples, namely the positive regulation of neuron apoptotic process and the regulation of mucus secretion. These two pathways are implicated in the neurogenerative alterations and in the inflammatory mechanisms of metabolic diseases. In addition, replication analysis revealed nominal associations of the regulation of beta-cell development and the regulation of peptidase activity pathways with T2D, both in the Tunisian subjects and in the European in-silico dataset.

Conclusions

The present study is the first EWAS to investigate the impact of single genetic variants and their aggregate effects on T2D risk in Africa. The promising disease markers, revealed by our pilot EWAS, will promote the understanding of the T2D pathophysiology in North Africa as well as the discovery of potential treatments.

Population-scale skeletal muscle single-nucleus multi-omic profiling reveals extensive context specific genetic regulation

Skeletal muscle, the largest human organ by weight, is relevant to several polygenic metabolic traits and diseases including type 2 diabetes (T2D). Identifying genetic mechanisms underlying these traits requires pinpointing the relevant cell types, regulatory elements, target genes, and causal variants. Here, we used genetic multiplexing to generate population-scale single nucleus (sn) chromatin accessibility (snATAC-seq) and transcriptome (snRNA-seq) maps across 287 frozen human skeletal muscle biopsies representing 456,880 nuclei. We identified 13 cell types that collectively represented 983,155 ATAC summits. We integrated genetic variation to discover 6,866 expression quantitative trait loci (eQTL) and 100,928 chromatin accessibility QTL (caQTL) (5% FDR) across the five most abundant cell types, cataloging caQTL peaks that atlas-level snATAC maps often miss. We identified 1,973 eGenes colocalized with caQTL and used mediation analyses to construct causal directional maps for chromatin accessibility and gene expression. 3,378 genome-wide association study (GWAS) signals across 43 relevant traits colocalized with sn-e/caQTL, 52% in a cell-specific manner. 77% of GWAS signals colocalized with caQTL and not eQTL, highlighting the critical importance of population-scale chromatin profiling for GWAS functional studies. GWAS-caQTL colocalization showed distinct cell-specific regulatory paradigms. For example, a C2CD4A/B T2D GWAS signal colocalized with caQTL in muscle fibers and multiple chromatin loop models nominated VPS13C, a glucose uptake gene. Sequence of the caQTL peak overlapping caSNP rs7163757 showed allelic regulatory activity differences in a human myocyte cell line massively parallel reporter assay. These results illuminate the genetic regulatory architecture of human skeletal muscle at high-resolution epigenomic, transcriptomic, and cell state scales and serve as a template for population-scale multi-omic mapping in complex tissues and traits.

Melatonin Improves Skeletal Muscle Structure and Oxidative Phenotype by Regulating Mitochondrial Dynamics and Autophagy in Zücker Diabetic Fatty Rat

Obesity-induced skeletal muscle (SKM) inflexibility is closely linked to mitochondrial dysfunction. The present study aimed to evaluate the effects of melatonin on the red vastus lateralis (RVL) muscle in obese rat models at the molecular and morphological levels. Five-week-old male Zücker diabetic fatty (ZDF) rats and their age-matched lean littermates (ZL) were orally treated either with melatonin (10 mg/kg body weight (BW)/24 h) (M-ZDF and M-ZL) or non-treated (control) (C-ZDF and C-ZL) for 12 weeks. Western blot analysis showed that mitochondrial fission, fusion, and autophagy were altered in the C-ZDF group, accompanied by reduced SIRT1 levels. Furthermore, C-ZDF rats exhibited depleted ATP production and nitro-oxidative stress, as indicated by increased nitrites levels and reduced SOD activity. Western blotting of MyH isoforms demonstrated a significant decrease in both slow and fast oxidative fiber-specific markers expression in the C-ZDF group, concomitant with an increase in the fast glycolytic fiber markers. At the tissue level, marked fiber atrophy, less oxidative fibers, and excessive lipid deposition were noted in the C-ZDF group. Interestingly, melatonin treatment partially restored mitochondrial fission/fusion imbalance in the RVL muscle by enhancing the expression of fission (Fis1 and DRP1) markers and decreasing that of fusion (OPA1 and Mfn2) markers. It was also found to restore autophagy, as indicated by increased p62 protein level and LC3BII/I ratio. In addition, melatonin treatment increased SIRT1 protein level, mitochondrial ATP production, and SOD activity and decreased nitrites production. These effects were associated with enhanced oxidative phenotype, as evidenced by amplified oxidative fiber-specific markers expression, histochemical reaction for NADH enzyme, and muscular lipid content. In this study, we showed that melatonin might have potential therapeutic implications for obesity-induced SKM metabolic inflexibility among patients with obesity and T2DM.

Activation of PDGF Signaling in the Adult Muscle Stem Cell Niche in Patients With Type 2 Diabetes Mellitus

CONTEXT

Type 2 diabetes mellitus (T2D) negatively affects muscle mass and function throughout life. Whether adult muscle stem cells contribute to the decrease in muscle health is not clear and insights into the stem cell niche are difficult to obtain.

OBJECTIVE

To establish the upstream signaling pathway of microRNA (miR)-501, a marker of activated myogenic progenitor cells, and interrogate this pathway in muscle biopsies from patients with T2D.

METHODS

Analysis of primary muscle cell cultures from mice and 4 normoglycemic humans and muscle biopsies from 7 patients with T2D and 7 normoglycemic controls using gene expression, information on histone methylation, peptide screening, and promoter assays.

RESULTS

miR-501 shares the promoter of its host gene, isoform 2 of chloride voltage-gated channel 5 (CLCN5-2), and miR-501 expression increases during muscle cell differentiation. We identify platelet-derived growth factor (PDGF) as an upstream regulator of CLCN5-2 and miR-501 via Janus kinase/signal transducer and activator of transcription. Skeletal muscle biopsies from patients with T2D revealed upregulation of PDGF (1.62-fold, P = .002), CLCN5-2 (2.85-fold, P = .03), and miR-501 (1.73-fold, P = .02) compared with normoglycemic controls. In addition, we observed a positive correlation of PDGF and miR-501 in human skeletal muscle (r = 0.542, P = .045, n = 14).

CONCLUSIONS

We conclude that paracrine signaling in the adult muscle stem cells niche is activated in T2D. Expression analysis of the PDGF-miR-501 signaling pathway could represent a powerful tool to classify patients in clinical trials that aim to improve muscle health and glucose homeostasis in patients with diabetes.

The combined role of diabetes and obesity in susceptibility to musculoskeletal disorders and its subtypes in older men and women in India

Background and aims

In later life, diabetes and obesity can cause a change in musculoskeletal systems that can lead to aching joints and a myriad of other musculoskeletal disorders such as arthritis, osteoporosis, rheumatism, bone fractures etc., resulting in significant morbidity including pain and disability. There is a paucity of research to know how comorbidity of diabetes and obesity increase musculoskeletal disorders among older people. Therefore, the present study used nationally representative data to examine the interaction of diabetes and obesity on musculoskeletal disorders and its subtypes including arthritis, osteoporosis, and rheumatism among older men and women in India.

Methods

Data were extracted from the first wave of the nationally representative survey Longitudinal Aging Study in India (LASI) conducted in 2017-18. The final sample includes 31,464 people aged 60 years or above. Primary outcome variable was any listed musculoskeletal disorders and secondary outcomes were its subtypes including arthritis, osteoporosis, and rheumatism based on self-reported questions. Diabetes and obesity based on anthropometric index of weight and height (i.e., body mass index (BMI) with a standard cut-off of 30 kg/m2 or over) were considered as explanatory variables of interest. Logistic regression was used to assess the relationship between diabetes and musculoskeletal disorders. Interaction analysis was performed by both additive and multiplicative scales.

Results

Comparing older people without diabetes, the prevalence of musculoskeletal disorders and its subtypes were higher among those with diabetes, particularly arthritis disorders in older women. Diabetes was significantly correlated with the risk of musculoskeletal disorders and its subtypes including arthritis and osteoporosis even after controlling potential factors. The combination of diabetes and obesity was significantly and positively associated with musculoskeletal disorders (aOR: 4.14; p-value < 0.0001; 95% CI: 1.96 to 8.74) and its subtype only arthritis (aOR: 4.36; p-value < 0.0001; 95% CI: 1.76 to 10.8) comparing to those without both the conditions. However, the association was strong for older women as compared to older men. Notwithstanding, multiplicative scale interaction showed statistically significant for musculoskeletal disorders and its three subtypes among older women, however it was not significant for osteoporosis and rheumatism disorders among older men. When we analyzed interaction on additive scale, we found it only for arthritis disorder among older women suggesting the risk from obesity (relative excess risk due to interaction (RERI): -0.83, 95% CI: -1.44 to -0.22, attributable proportion due to interaction (AP): -0.54, 95% CI: -1.05 to -0.03, synergy index (S): 0.39, 95% CI: 0.16 to 0.93) was additive to the risk from diabetes.

Conclusions

This study suggests an elevated risk of musculoskeletal disorders among Indian older adults with diabetes. The result of this study also suggests an interactive association of diabetes and obesity with musculoskeletal disorders, particularly with arthritis disorder. There is a need to pay attention to the BMI level while treating diabetes in Indian older population.

Platelet-derived chemokines promote skeletal muscle regeneration by guiding neutrophil recruitment to injured muscles

Skeletal muscle regeneration involves coordinated interactions between different cell types. Injection of platelet-rich plasma is circumstantially considered an aid to muscle repair but whether platelets promote regeneration beyond their role in hemostasis remains unexplored. Here, we find that signaling via platelet-released chemokines is an early event necessary for muscle repair in mice. Platelet depletion reduces the levels of the platelet-secreted neutrophil chemoattractants CXCL5 and CXCL7/PPBP. Consequently, early-phase neutrophil infiltration to injured muscles is impaired whereas later inflammation is exacerbated. Consistent with this model, neutrophil infiltration to injured muscles is compromised in male mice with Cxcl7-knockout platelets. Moreover, neo-angiogenesis and the re-establishment of myofiber size and muscle strength occurs optimally in control mice post-injury but not in Cxcl7ko mice and in neutrophil-depleted mice. Altogether, these findings indicate that platelet-secreted CXCL7 promotes regeneration by recruiting neutrophils to injured muscles, and that this signaling axis could be utilized therapeutically to boost muscle regeneration.

Induction of miR-665-3p Impairs the Differentiation of Myogenic Progenitor Cells by Regulating the TWF1-YAP1 Axis

Actin dynamics are known to orchestrate various myogenic processes in progenitor cells. Twinfilin-1 (TWF1) is an actin-depolymerizing factor that plays a crucial role in the differentiation of myogenic progenitor cells. However, little is known about the mechanisms underlying the epigenetic regulation of TWF1 expression and impaired myogenic differentiation in the background of muscle wasting. This study investigated how miR-665-3p affects TWF1 expression, actin filaments' modulation, proliferation, and myogenic differentiation in progenitor cells. Palmitic acid, the most prevalent saturated fatty acid (SFA) in food, suppressed TWF1 expression and inhibited the myogenic differentiation of C2C12 cells while increasing the level of miR-665-3p expression. Interestingly, miR-665-3p inhibited TWF1 expression by targeting TWF1 3'UTR directly. In addition, miR-665-3p accumulated filamentous actin (F-actin) and enhanced the nuclear translocation of Yes-associated protein 1 (YAP1), consequently promoting cell cycle progression and proliferation. Furthermore, miR-665-3p suppressed the expressions of myogenic factors, i.e., MyoD, MyoG, and MyHC, and consequently impaired myoblast differentiation. In conclusion, this study suggests that SFA-inducible miR-665-3p suppresses TWF1 expression epigenetically and inhibits myogenic differentiation by facilitating myoblast proliferation via the F-actin/YAP1 axis.

Role of Hydroxytyrosol and Oleuropein in the Prevention of Aging and Related Disorders: Focus on Neurodegeneration, Skeletal Muscle Dysfunction and Gut Microbiota

Aging is a multi-faceted process caused by the accumulation of cellular damage over time, associated with a gradual reduction of physiological activities in cells and organs. This degeneration results in a reduced ability to adapt to homeostasis perturbations and an increased incidence of illnesses such as cognitive decline, neurodegenerative and cardiovascular diseases, cancer, diabetes, and skeletal muscle pathologies. Key features of aging include a chronic low-grade inflammation state and a decrease of the autophagic process. The Mediterranean diet has been associated with longevity and ability to counteract the onset of age-related disorders. Extra virgin olive oil, a fundamental component of this diet, contains bioactive polyphenolic compounds as hydroxytyrosol (HTyr) and oleuropein (OLE), known for their antioxidant, anti-inflammatory, and neuroprotective properties. This review is focused on brain, skeletal muscle, and gut microbiota, as these systems are known to interact at several levels. After the description of the chemistry and pharmacokinetics of HTyr and OLE, we summarize studies reporting their effects in in vivo and in vitro models of neurodegenerative diseases of the central/peripheral nervous system, adult neurogenesis and depression, senescence and lifespan, and age-related skeletal muscle disorders, as well as their impact on the composition of the gut microbiota.

Sodium ferrous citrate and 5-aminolevulinic acid improve type 2 diabetes by maintaining muscle and mitochondrial health

OBJECTIVE

Improving mitochondrial function is a promising strategy for intervention in type 2 diabetes mellitus. This study investigated the preventive effects of sodium ferrous citrate (SFC) and 5-aminolevulinic acid phosphate (ALA) on several metabolic dysfunctions associated with obesity because they have been shown to alleviate abnormal glucose metabolism in humans.

METHODS

Six-week-old male C57BL/6J mice were fed with a normal diet, a high-fat diet, or a high-fat diet supplemented with SFC and ALA for 15 weeks.

RESULTS

The simultaneous supplementation of SFC + ALA to high-fat diet-fed mice prevented loss of muscle mass, improved muscle strength, and reduced obesity and insulin resistance. SFC + ALA prevented abnormalities in mitochondrial morphology and reverted the diet effect on the skeletal muscle transcriptome, including the expression of glucose uptake and mitochondrial oxidative phosphorylation-related genes. In addition, SFC + ALA prevented the decline in mitochondrial DNA copy number by enhancing mitochondrial DNA maintenance and antioxidant transcription activity, both of which are impaired in high-fat diet-fed mice during long-term fasting.

CONCLUSIONS

These findings suggest that SFC + ALA supplementation exerts its preventive effects in type 2 diabetes mellitus via improved skeletal muscle and mitochondrial health, further validating its application as a promising strategy for the prevention of obesity-induced metabolic disorders.

Mir-302a/TWF1 Axis Impairs the Myogenic Differentiation of Progenitor Cells through F-Actin-Mediated YAP1 Activation

Actin cytoskeleton dynamics have been found to regulate myogenesis in various progenitor cells, and twinfilin-1 (TWF1), an actin-depolymerizing factor, plays a vital role in actin dynamics and myoblast differentiation. Nevertheless, the molecular mechanisms underlying the epigenetic regulation and biological significance of TWF1 in obesity and muscle wasting have not been explored. Here, we investigated the roles of miR-302a in TWF1 expression, actin filament modulation, proliferation, and myogenic differentiation in C2C12 progenitor cells. Palmitic acid, the most prevalent saturated fatty acid (SFA) in the diet, decreased the expression of TWF1 and impeded myogenic differentiation while increasing the miR-302a levels in C2C12 myoblasts. Interestingly, miR-302a inhibited TWF1 expression directly by targeting its 3′UTR. Furthermore, ectopic expression of miR-302a promoted cell cycle progression and proliferation by increasing the filamentous actin (F-actin) accumulation, which facilitated the nuclear translocation of Yes-associated protein 1 (YAP1). Consequently, by suppressing the expressions of myogenic factors, i.e., MyoD, MyoG, and MyHC, miR-302a impaired myoblast differentiation. Hence, this study demonstrated that SFA-inducible miR-302a suppresses TWF1 expression epigenetically and impairs myogenic differentiation by facilitating myoblast proliferation via F-actin-mediated YAP1 activation.

Characterizing conventional ankle MRI findings of nerve and muscle changes in diabetic patients: a case-control study

BACKGROUND

Foot and ankle amputation is a feared complication of diabetic neuropathy and diabetes mellitus (DM) accounts for 80% of all in-hospital amputations. Magnetic resonance neurography is an effective tool in characterizing neuromuscular sequelae of the disease. However, conventional ankle MRI is more commonly performed and has not been studied to assess neuromuscular changes of DM.

OBJECTIVE

The objective is to characterize neuromuscular changes of diabetic patients in a case-control study using conventional ankle MRI.

METHODS

Between November 2019 and July 2021, 110 consecutive ankle MRI scans (n = 102 patients) at our county hospital were reviewed and met the inclusion criteria. Patients were divided into two cohorts, diabetic (N = 63) and non-diabetic (N = 39). Demographics, HgbA1c, and reason for MRI study were collected via retrospective chart review. The presence of intramuscular edema-like signal, pattern of the edema, muscle fatty infiltration, and measurements of the cross-sectional area of the posterior, medial, and lateral tibial nerves (PTN, MPN, and LPN) was recorded blinded to the clinical findings by two readers.

RESULTS

Muscle edema-like signal was much more likely to be found in DM (odds ratio 19.5, 95% CI 7.0-54.6, p < 0.001). DM also showed increase of 0.87 in the mean grade of muscle fatty infiltration (p < 0.001). There were higher rates of nerve T2 hyperintensity (odds ratio 14.0, 95% CI 3.1-62.7, p < 0.001) and the measured areas of the PTN, MPN, and LPN were also larger in DM compared to their non-diabetic counterparts (PTN: 0.16 cm² vs. 0.10 cm², p < 0.01; MPN: 0.09 cm² vs. 0.05 cm², p < 0.01; LPN: 0.07 cm² vs. 0.04 cm², p < 0.05).

CONCLUSION

Conventional ankle MRIs can be used to detect DM-related neuromuscular changes.

Diabetic sarcopenia: metabolic and molecular appraisal

Myopathy is the missing slot from the routine clinical checkup for diabetic complications. Similarly, its pathophysiological, metabolic, and molecular bases are insufficiently explored. In this review, the above issues are highlighted with a focus on skeletal muscle atrophy (also described as diabetic sarcopenia), in contrast to the normal histological, physiological, and molecular features of the muscles. Literature search using published data from different online resources was used. Several diabetic myopathy etiological factors are discussed explicitly including; inflammation and immunological responses, with emphasis on TNFα and IL-6 overproduction, oxidative stress, neuropathy and vasculopathy, aging sarcopenia, antidiabetic drugs, and insulin resistance as a denominator. The pathophysiological hallmark of diabetic muscle atrophy is the decreased muscle proteins synthesis and increased degradation. The muscle protein degradation is conveyed by 4 systems; ubiquitin-proteasome, lysosomal autophagy, caspase-3, and calpain systems, and is mostly mediated via the IL6/STAT, TNF&IL6/NFκB, myostatin/Smad2/3, and FOXO1/3 signaling pathways, while the protein synthesis inhibition is mediated via suppression of the IGF1-PI3K-Akt-mTOR, and SC-Gαi2-pathways. Moreover, the satellite cells and multilineage muscle mesenchymal progenitor cells differentiation plays a major role on the fate of the affected muscle cells by taking an adipogenic, fibrogenic, or connective tissue lineage. As a conclusion, in this article, the pathological features of diabetic sarcopenia are reviewed at gross level, while at a molecular level the normal protein turnover, signal transduction, and pathways involved in muscle atrophy are described. Finally, an integrated network describing the molecular partakers in diabetic sarcopenia is presented.

Regenerating islet-derived protein 3α: A promising therapy for diabetes. Preliminary data in rodents and in humans

The aim of our study was to test the hypothesis that administration of Regenerating islet-derived protein 3α (Reg3α), a protein described as having protective effects against oxidative stress and anti-inflammatory activity, could participate in the control of glucose homeostasis and potentially be a new target of interest in the treatment of type 2 diabetes. To that end the recombinant human Reg3α protein was administered for one month in insulin-resistant mice fed high fat diet. We performed glucose and insulin tolerance tests, assayed circulating chemokines in plasma and measured glucose uptake in insulin sensitive tissues. We evidenced an increase in insulin sensitivity during an oral glucose tolerance test in ALF-5755 treated mice vs controls and decreased the pro-inflammatory cytokine C-X-C Motif Chemokine Ligand 5 (CXCL5). We also demonstrated an increase in glucose uptake in skeletal muscle. Finally, correlation studies using human and mouse muscle biopsies showed negative correlation between intramuscular Reg3α mRNA expression (or its murine isoform Reg3γ) and insulin resistance. Thus, we have established the proof of concept that Reg3α could be a novel molecule of interest in the treatment of T2D by increasing insulin sensitivity via a skeletal muscle effect.

Human Tissue-Engineered Skeletal Muscle: A Tool for Metabolic Research

Skeletal muscle is now regarded as an endocrine organ based on its secretion of myokines and exerkines, which, in response to metabolic stimuli, regulate the crosstalk between the skeletal muscle and other metabolic organs in terms of systemic energy homeostasis. This conceptual basis of skeletal muscle as a metabolically active organ has provided insights into the potential role of physical inactivity and conditions altering muscle quality and quantity in the development of multiple metabolic disorders, including insulin resistance, obesity, and diabetes. Therefore, it is important to understand human muscle physiology more deeply in relation to the pathophysiology of metabolic diseases. Since monolayer cell lines or animal models used in conventional research differ from the pathophysiological features of the human body, there is increasing need for more physiologically relevant in vitro models of human skeletal muscle. Here, we introduce recent studies on in vitro models of human skeletal muscle generated from adult myogenic progenitors or pluripotent stem cells and summarize recent progress in the development of three-dimensional (3D) bioartificial muscle, which mimics the physiological complexity of native skeletal muscle tissue in terms of maturation and functionality. We then discuss the future of skeletal muscle 3D-organoid culture technology in the field of metabolic research for studying pathological mechanisms and developing personalized therapeutic strategies.

Whole body vibration remodels skeletal muscle via autophagy and energy metabolism in diabetic mice

Hyperglycemia occurs due to a defect in insulin secretion or impaired biological functions, or both. The long-term hyperglycemia during diabetes causes chronic damage and dysfunction of various tissues. Whole body vibration (WBV) has significant effects on lipid and glucose metabolism and endocrine and motor systems. In order to explore the effects of WBV on skeletal muscle, mice trained for 12 weeks with WBV (15 Hz, 30 min) were used as experimental subjects and their skeletal muscle morphology under the pathological state of diabetes was observed. In addition, the blood lipids, blood glucose, gastrocnemius muscle glycogen and mRNA and protein levels of autophagy and glucose metabolism biomarkers were compared among the three groups of mice via western blot and RT-qPCR. The results showed that WBV can significantly reshape skeletal muscle morphology and upregulate high density lipoprotein. The expression of glucose-6-phosphatase (G6P), Beclin1 and Atg7 in the gastrocnemius muscle of the WBV group was significantly increased. Therefore, it can be concluded that WBV promotes skeletal muscle remodeling in diabetic mice. The present study confirmed that WBV can attenuate the development of diabetes melitus (DM) and lead to lower level low density lipoprotein in the blood. In addition, G6P level plays an important role in WBV-treated DM model and may be used to monitor the effect of WBV in patients. The findings of the present study may provide a new molecular basis for WBV to play a therapeutic role in the treatment of diabetes and may have potential clinical applications in the future.

Dual Beneficial Effects of α-Spinasterol Isolated from Aster pseudoglehnii on Glucose Uptake in Skeletal Muscle Cells and Glucose-Stimulated Insulin Secretion in Pancreatic β-Cells

Herein, we determined whether α-Spinasterol, a stigmastane-type phytosterol isolated from Aster pseudoglehnii, potentially impacts glucose uptake and glucose-stimulated insulin secretion in skeletal muscle cells and pancreatic β-cells, respectively. We observed that A. pseudoglehnii and its fractions enhanced glucose uptake, with no toxic effects on C2C12 cells, with the n-hexane fraction exhibiting the most potent effect. α-Spinasterol, isolated from the n-hexane fraction, enhanced glucose uptake with no toxic effects on C2C12 cells. Additionally, α-Spinasterol increased the expression of associated proteins, including insulin receptor substrate-1, AMP-activated protein kinase, and glucose transporter type 4, as determined by Western blotting. Furthermore, α-Spinasterol enhanced insulin secretion in response to high glucose concentrations, with no toxic effects on INS-1 cells; this effect was superior to that demonstrated by gliclazide (positive control), commonly prescribed to treat type 2 diabetes (T2D). α-Spinasterol enhanced the expression of associated proteins, including insulin receptor substrate-2, peroxisome proliferator-activated receptor γ, and pancreatic and duodenal homeobox 1, as determined using Western blotting. The insulin secretory effect of α-Spinasterol was enhanced by a K⁺ channel blocker and L-type Ca²⁺ channel agonist and was suppressed by a K⁺ channel activator and L-type Ca²⁺ channel blocker. α-Spinasterol isolated from A. pseudoglehnii may improve hyperglycemia by improving glucose uptake into skeletal muscle cells and enhancing insulin secretion in pancreatic β-cells. Accordingly, α-Spinasterol could be a potential candidate for anti-T2D therapy.

Preserved stem cell content and innervation profile of elderly human skeletal muscle with lifelong recreational exercise

Abstract

Muscle fibre denervation and declining numbers of muscle stem (satellite) cells are defining characteristics of ageing skeletal muscle. The aim of this study was to investigate the potential for lifelong recreational exercise to offset muscle fibre denervation and compromised satellite cell content and function, both at rest and under challenged conditions. Sixteen elderly lifelong recreational exercisers (LLEX) were studied alongside groups of age‐matched sedentary (SED) and young subjects. Lean body mass and maximal voluntary contraction were assessed, and a strength training bout was performed. From muscle biopsies, tissue and primary myogenic cell cultures were analysed by immunofluorescence and RT‐qPCR to assess myofibre denervation and satellite cell quantity and function. LLEX demonstrated superior muscle function under challenged conditions. When compared with SED, the muscle of LLEX was found to contain a greater content of satellite cells associated with type II myofibres specifically, along with higher mRNA levels of the beta and gamma acetylcholine receptors (AChR). No difference was observed between LLEX and SED for the proportion of denervated fibres or satellite cell function, as assessed in vitro by myogenic cell differentiation and fusion index assays. When compared with inactive counterparts, the skeletal muscle of lifelong exercisers is characterised by greater fatigue resistance under challenged conditions in vivo, together with a more youthful tissue satellite cell and AChR profile. Our data suggest a little recreational level exercise goes a long way in protecting against the emergence of classic phenotypic traits associated with the aged muscle.

Key points

The detrimental effects of ageing can be partially offset by lifelong self‐organized recreational exercise, as evidence by preserved type II myofibre‐associated satellite cells, a beneficial muscle innervation status and greater fatigue resistance under challenged conditions.

Satellite cell function (in vitro), muscle fibre size and muscle fibre denervation determined by immunofluorescence were not affected by recreational exercise.

Individuals that are recreationally active are far more abundant than master athletes, which sharply increases the translational perspective of the present study. Future studies should further investigate recreational activity in relation to muscle health, while also including female participants.

MiR-320-3p Regulates the Proliferation and Differentiation of Myogenic Progenitor Cells by Modulating Actin Remodeling

Skeletal myogenesis is essential for the maintenance of muscle quality and quantity, and impaired myogenesis is intimately associated with muscle wasting diseases. Although microRNA (miRNA) plays a crucial role in myogenesis and relates to muscle wasting in obesity, the molecular targets and roles of miRNAs modulated by saturated fatty acids (SFA) are largely unknown. In the present study, we investigated the role of miR-320-3p on the differentiation of myogenic progenitor cells. Palmitic acid (PA), the most abundant dietary SFA, suppressed myogenic factors expression and impaired differentiation in C2C12 myoblasts, and these effects were accompanied by CFL2 downregulation and miR-320-3p upregulation. In particular, miR-320-3p appeared to target CFL2 mRNA directly and suppress the expression of CFL2, an essential factor for filamentous actin (F-actin) depolymerization. Transfection of myoblasts with miR-320-3p mimic increased F-actin formation and nuclear translocation of Yes-associated protein 1 (YAP1), a key component of mechanotransduction. Furthermore, miR-320-3p mimic increased myoblast proliferation and markedly impeded the expression of MyoD and MyoG, consequently inhibiting myoblast differentiation. In conclusion, our current study highlights the role of miR-320-3p on CFL2 expression, YAP1 activation, and myoblast differentiation and suggests that PA-inducible miR-320-3p is a significant mediator of muscle wasting in obesity.

Role of MiR-325-3p in the Regulation of CFL2 and Myogenic Differentiation of C2C12 Myoblasts

Skeletal myogenesis is required to maintain muscle mass and integrity, and impaired myogenesis is causally linked to the etiology of muscle wasting. Recently, it was shown that excessive uptake of saturated fatty acids (SFA) plays a significant role in the pathogenesis of muscle wasting. Although microRNA (miRNA) is implicated in the regulation of myogenesis, the molecular mechanism whereby SFA-induced miRNAs impair myogenic differentiation remains largely unknown. Here, we investigated the regulatory roles of miR-325-3p on CFL2 expression and myogenic differentiation in C2C12 myoblasts. PA impeded myogenic differentiation, concomitantly suppressed CFL2 and induced miR-325-3p. Dual-luciferase analysis revealed that miR-325-3p directly targets the 3'UTR of CFL2, thereby suppressing the expression of CFL2, a crucial factor for actin dynamics. Transfection with miR-325-3p mimic resulted in the accumulation of actin filaments (F-actin) and nuclear Yes-associated protein (YAP) in myoblasts and promoted myoblast proliferation and cell cycle progression. Consequently, miR-325-3p mimic significantly attenuated the expressions of myogenic factors and thereby impaired the myogenic differentiation of myoblasts. The roles of miR-325-3p on CFL2 expression, F-actin modulation, and myogenic differentiation suggest a novel miRNA-mediated regulatory mechanism of myogenesis and PA-inducible miR-325-3p may be a critical mediator between obesity and muscle wasting.

Palmitic Acid-Induced miR-429-3p Impairs Myoblast Differentiation by Downregulating CFL2

MicroRNAs are known to play a critical role in skeletal myogenesis and maintenance, and cofilin-2 (CFL2) is necessary for actin cytoskeleton dynamics and myogenic differentiation. Nonetheless, target molecules and the modes of action of miRNAs, especially those responsible for the inhibitory mechanism on the myogenesis by saturated fatty acids (SFA) or obesity, still remain unclear. Here, we reported the role played by miR-429-3p on CFL2 expression, actin filament dynamics, myoblast proliferation, and myogenic differentiation in C2C12 cells. Palmitic acid (PA), the most abundant SFA in diet, inhibited the myogenic differentiation of myoblasts, accompanied by CFL2 reduction and miR-429-3p induction. Interestingly, miR-429-3p suppressed the expression of CFL2 by targeting the 3'UTR of CFL2 mRNA directly. Transfection of miR-429-3p mimic in myoblasts increased F-actin formation and augmented nuclear YAP level, thereby promoting cell cycle progression and myoblast proliferation. Moreover, miR-429-3p mimic drastically suppressed the expressions of myogenic factors, such as MyoD, MyoG, and MyHC, and impaired myogenic differentiation of C2C12 cells. Therefore, this study unveiled the crucial role of miR-429-3p in myogenic differentiation through the suppression of CFL2 and provided implications of SFA-induced miRNA in the regulation of actin dynamics and skeletal myogenesis.

Importance of Nutrient Availability and Metabolism for Skeletal Muscle Regeneration

Skeletal muscle is fundamentally important for quality of life. Deterioration of skeletal muscle, such as that observed with advancing age, chronic disease, and dystrophies, is associated with metabolic and functional decline. Muscle stem/progenitor cells promote the maintenance of skeletal muscle composition (balance of muscle mass, fat, and fibrotic tissues) and are essential for the regenerative response to skeletal muscle damage. It is increasing recognized that nutrient and metabolic determinants of stem/progenitor cell function exist and are potential therapeutic targets to improve regenerative outcomes and muscle health. This review will focus on current understanding as well as key gaps in knowledge and challenges around identifying and understanding nutrient and metabolic determinants of skeletal muscle regeneration.

Association of Appendicular Skeletal Muscle to Trunk Fat Ratio with Type 2 Diabetes Mellitus in Older Adults

INTRODUCTION

Mounting evidence has demonstrated that skeletal muscle and visceral adiposity play crucial roles in glucose metabolism. The purpose of this study was to investigate whether the appendicular skeletal muscle mass index (ASMI) to trunk fat mass (TFM) ratio (ASMI/TFM) is a more specific and identifiable factor for type 2 diabetes mellitus (T2DM) in older adults than conventional anthropometric measures.

METHODS

This cross-sectional study included 1,370 older adults from the Tianjin Chronic Low-Grade Systemic Inflammation and Health (TCLSIH) cohort. ASMI and TFM were measured by using a bioelectrical impedance analyzer, and T2DM was defined with the criteria of the American Diabetes Association. Odds ratios (ORs) were evaluated using multivariable logistic analysis.

RESULTS

The prevalence of T2DM is 20.0% in this study. The multivariable-adjusted ORs (95% confidence interval) of T2DM for increasing categories of ASMI/TFM, BMI, and waist circumference (WC) were 1.00 (reference), 0.70 (0.49, 1.02), 0.61 (0.42, 0.89), and 0.45 (0.30, 0.67; p for trend <0.0001); 1.00 (reference), 1.15 (0.83, 1.60), and 1.37 (0.94, 2.01; p for trend = 0.10); and 1.00 (reference) and 1.78 (1.19, 2.74; p < 0.01), respectively.

CONCLUSIONS

Higher ASMI/TFM was associated with a lower prevalence of T2DM in this study of older adults. The T2DM predictive value of ASMI/TFM may be stronger than BMI and WC in this population.

Comparative Analysis of MicroRNA Expression Profiles Between Skeletal Muscle- and Adipose-Derived Exosomes in Pig

Skeletal muscle and adipose tissues are both involved in regulation of metabolism. In the skeletal muscle-adipose tissue crosstalk, exosomes may play an important role but the main components of exosomes are not clear. In this study, we found skeletal muscle-derived exosomes can inhibit adipogenesis of porcine preadipocytes. We identified microRNA expression profiles of muscle exosomes and adipose exosomes by high-throughput sequencing. There were 104 (both novel and known microRNAs) microRNAs differentially expressed (DE miRNAs) between M-EXO (muscle-derived exosomes) and A-EXO (adipose–derived exosomes) groups. A total of 2,137 target genes of DE miRNAs for M-EXO and 2,004 target genes of DE miRNAs for A-EXO were detected. Bioinformatic analyses revealed that some DE miRNAs of M-EXO (especially miR-221-5p) were mainly enriched in lipid-related metabolism processes. The findings may serve as a fundamental resource for understanding the detailed functions of exosomes between the skeletal muscle-adipose crosstalk and the potential relationship between skeletal muscle atrophy and obesity.

Myogenetic Oligodeoxynucleotide (myoDN) Recovers the Differentiation of Skeletal Muscle Myoblasts Deteriorated by Diabetes Mellitus

Skeletal muscle wasting in patients with diabetes mellitus (DM) is a complication of decreased muscle mass and strength, and is a serious risk factor that may result in mortality. Deteriorated differentiation of muscle precursor cells, called myoblasts, in DM patients is considered to be one of the causes of muscle wasting. We recently developed myogenetic oligodeoxynucleotides (myoDNs), which are 18-base single-strand DNAs that promote myoblast differentiation by targeting nucleolin. Herein, we report the applicability of a myoDN, iSN04, to myoblasts isolated from patients with type 1 and type 2 DM. Myogenesis of DM myoblasts was exacerbated concordantly with a delayed shift of myogenic transcription and induction of interleukins. Analogous phenotypes were reproduced in healthy myoblasts cultured with excessive glucose or palmitic acid, mimicking hyperglycemia or hyperlipidemia. iSN04 treatment recovered the deteriorated differentiation of plural DM myoblasts by downregulating myostatin and interleukin-8 (IL-8). iSN04 also ameliorated the impaired myogenic differentiation induced by glucose or palmitic acid. These results demonstrate that myoDNs can directly facilitate myoblast differentiation in DM patients, making them novel candidates for nucleic acid drugs to treat muscle wasting in patients with DM.

The many actions of insulin in skeletal muscle, the paramount tissue determining glycemia

As the principal tissue for insulin-stimulated glucose disposal, skeletal muscle is a primary driver of whole-body glycemic control. Skeletal muscle also uniquely responds to muscle contraction or exercise with increased sensitivity to subsequent insulin stimulation. Insulin's dominating control of glucose metabolism is orchestrated by complex and highly regulated signaling cascades that elicit diverse and unique effects on skeletal muscle. We discuss the discoveries that have led to our current understanding of how insulin promotes glucose uptake in muscle. We also touch upon insulin access to muscle, and insulin signaling toward glycogen, lipid, and protein metabolism. We draw from human and rodent studies in vivo, isolated muscle preparations, and muscle cell cultures to home in on the molecular, biophysical, and structural elements mediating these responses. Finally, we offer some perspective on molecular defects that potentially underlie the failure of muscle to take up glucose efficiently during obesity and type 2 diabetes.

1-Deoxysphingolipids, Early Predictors of Type 2 Diabetes, Compromise the Functionality of Skeletal Myoblasts

Metabolic dysfunction, dysregulated differentiation, and atrophy of skeletal muscle occur as part of a cluster of abnormalities associated with the development of Type 2 diabetes mellitus (T2DM). Recent interest has turned to the attention of the role of 1-deoxysphingolipids (1-DSL), atypical class of sphingolipids which are found significantly elevated in patients diagnosed with T2DM but also in the asymptomatic population who later develop T2DM. In vitro studies demonstrated that 1-DSL have cytotoxic properties and compromise the secretion of insulin from pancreatic beta cells. However, the role of 1-DSL on the functionality of skeletal muscle cells in the pathophysiology of T2DM still remains unclear. This study aimed to investigate whether 1-DSL are cytotoxic and disrupt the cellular processes of skeletal muscle precursors (myoblasts) and differentiated cells (myotubes) by performing a battery of in vitro assays including cell viability adenosine triphosphate assay, migration assay, myoblast fusion assay, glucose uptake assay, and immunocytochemistry. Our results demonstrated that 1-DSL significantly reduced the viability of myoblasts in a concentration and time-dependent manner, and induced apoptosis as well as cellular necrosis. Importantly, myoblasts were more sensitive to the cytotoxic effects induced by 1-DSL rather than by saturated fatty acids, such as palmitate, which are critical mediators of skeletal muscle dysfunction in T2DM. Additionally, 1-DSL significantly reduced the migration ability of myoblasts and the differentiation process of myoblasts into myotubes. 1-DSL also triggered autophagy in myoblasts and significantly reduced insulin-stimulated glucose uptake in myotubes. These findings demonstrate that 1-DSL directly compromise the functionality of skeletal muscle cells and suggest that increased levels of 1-DSL observed during the development of T2DM are likely to contribute to the pathophysiology of muscle dysfunction detected in this disease.

MiR-96-5p Induced by Palmitic Acid Suppresses the Myogenic Differentiation of C2C12 Myoblasts by Targeting FHL1

Skeletal myogenesis is a multi-stage process that includes the cell cycle exit, myogenic transcriptional activation, and morphological changes to form multinucleated myofibers. Recent studies have shown that saturated fatty acids (SFA) and miRNAs play crucial roles in myogenesis and muscle homeostasis. Nevertheless, the target molecules and myogenic regulatory mechanisms of miRNAs are largely unknown, particularly when myogenesis is dysregulated by SFA deposition. This study investigated the critical role played by miR-96-5p on the myogenic differentiation in C2C12 myoblasts. Long-chain SFA palmitic acid (PA) significantly reduced FHL1 expression and inhibited the myogenic differentiation of C2C12 myoblasts but induced miR-96-5p expression. The knockdown of FHL1 by siRNA stimulated cell proliferation and inhibited myogenic differentiation of myoblasts. Interestingly, miR-96-5p suppressed FHL1 expression by directly targeting the 3’UTR of FHL1 mRNA. The transfection of an miR-96-5p mimic upregulated the expressions of cell cycle-related genes, such as PCNA, CCNB1, and CCND1, and increased myoblast proliferation. Moreover, the miR-96-5p mimic inhibited the expressions of myogenic factors, such as myoblast determination protein (MyoD), myogenin (MyoG), myocyte enhancer factor 2C (MEF2C), and myosin heavy chain (MyHC), and dramatically impeded differentiation and fusion of myoblasts. Overall, this study highlights the role of miR-96-5p in myogenesis via FHL1 suppression and suggests a novel regulatory mechanism for myogenesis mediated by miRNA in a background of obesity.

Effects of rehabilitation methods on lower-limb muscle function and functional performance in patients with cystic fibrosis: A systematic review

OBJECTIVE

To investigate the effects of rehabilitation methods on leg muscle function and functional performance in cystic fibrosis.

DATA SOURCES

A literature search was conducted in PubMed (MEDLINE), Scopus and the Cochrane Library from inception to October 12, 2020. A secondary hand search through reference lists from identified articles was conducted.

REVIEW METHODS

Three authors independently checked the full-text copies for eligibility of relevant articles. Randomized controlled trials were included. Methodological quality was assessed using the Physiotherapy Evidence Database scale. The PRISMA guidelines were followed. Results suggestive of leg muscle function (e.g. strength, power, endurance, and fatigue) and functional performance were reported.

RESULTS

The search identified 8 studies (233 patients). The overall quality of these articles was good. Rehabilitation modalities investigated were physical exercises (aerobic, anaerobic and resistance training) (n = 7) and neuromuscular electrical stimulation (n = 1). Most studies (n = 4) reported on the effects of combined aerobic and resistance training and showed improvement on leg strength when exercises were supervised. Aerobic training alone or the use of neuromuscular electrical stimulation also enhanced leg strength, whereas anaerobic training did not. Two studies evaluated leg fatigue and found no improvement compared to standard care. One study assessed the effect of exercises on functional performance and found no improvement when compared to standard care. No studies emphasized the impact of rehabilitation methods on leg muscle endurance or power.

CONCLUSION

Combined aerobic and resistance training enhances leg muscle strength in cystic fibrosis. There is insufficient data on other leg muscle outcomes, nor on alternative rehabilitation strategies.

High-fat diet pre-conditioning improves microvascular remodelling during regeneration of ischaemic mouse skeletal muscle

AIM

Critical limb ischaemia (CLI) is characterized by inadequate angiogenesis, arteriolar remodelling and chronic myopathy, which are most severe in type 2 diabetic patients. Hypertriglyceridaemia, commonly observed in these patients, compromises macrovascular function. However, the effects of high-fat diet-induced increases in circulating lipids on microvascular remodelling are not established. Here, we investigated if high-fat diet would mimic the detrimental effect of type 2 diabetes on post-ischaemia vascular remodelling and muscle regeneration, using a mouse model of hindlimb ischaemia.

METHODS

Male C57Bl6/J mice were fed with normal or high-fat diets for 8 weeks prior to unilateral femoral artery ligation. Laser doppler imaging was used to assess limb perfusion recovery. Vascular recovery, inflammation, myofibre regeneration and fibrosis were assessed at 4 or 14 days post-ligation by histology and RNA analyses. Capillary-level haemodynamics were assessed by intravital microscopy of control and regenerating muscles 14 days post-ligation.

RESULTS

High-fat diet increased muscle succinate dehydrogenase activity and capillary-level oxygen supply. At 4 days post-ligation, no diet differences were detected in muscle damage, inflammatory infiltration or capillary activation. At 14 days post-ligation, high fat-fed mice displayed accelerated limb blood flow recovery, elevated capillary and arteriole densities as well as greater red blood cell supply rates and capillary-level oxygen supply. Regenerating muscles from high fat-fed mice displayed lower interstitial fat and collagen deposition.

CONCLUSION

The muscle-level adaptations to high-fat diet improved multiple aspects of muscle recovery in response to ischaemia and did not recapitulate the worse outcomes seen in diabetic CLI patients.

Metabolic Coordination of Pericyte Phenotypes: Therapeutic Implications

Pericytes are mural vascular cells found predominantly on the abluminal wall of capillaries, where they contribute to the maintenance of capillary structural integrity and vascular permeability. Generally quiescent cells in the adult, pericyte activation and proliferation occur during both physiological and pathological vascular and tissue remodeling. A considerable body of research indicates that pericytes possess attributes of a multipotent adult stem cell, as they are capable of self-renewal as well as commitment and differentiation into multiple lineages. However, pericytes also display phenotypic heterogeneity and recent studies indicate that lineage potential differs between pericyte subpopulations. While numerous microenvironmental cues and cell signaling pathways are known to regulate pericyte functions, the roles that metabolic pathways play in pericyte quiescence, self-renewal or differentiation have been given limited consideration to date. This review will summarize existing data regarding pericyte metabolism and will discuss the coupling of signal pathways to shifts in metabolic pathway preferences that ultimately regulate pericyte quiescence, self-renewal and trans-differentiation. The association between dysregulated metabolic processes and development of pericyte pathologies will be highlighted. Despite ongoing debate regarding pericyte classification and their functional capacity for trans-differentiation in vivo, pericytes are increasingly exploited as a cell therapy tool to promote tissue healing and regeneration. Ultimately, the efficacy of therapeutic approaches hinges on the capacity to effectively control/optimize the fate of the implanted pericytes. Thus, we will identify knowledge gaps that need to be addressed to more effectively harness the opportunity for therapeutic manipulation of pericytes to control pathological outcomes in tissue remodeling.

Impaired Regeneration Contributes to Poor Outcomes in Diabetic Peripheral Artery Disease

Diabetes mellitus increases the risk and accelerates the course of peripheral artery disease, making patients more susceptible to ischemic events and infections and delaying tissue healing. Current understanding of pathogenic mechanisms is mainly based on the negative influence of diabetes mellitus on atherosclerotic disease and inflammation. In recent years, the novel concept that diabetes mellitus can impinge on endogenous regenerative processes has been introduced. Diabetes mellitus affects regeneration at the local level, disturbing proper angiogenesis, collateral artery formation, and muscle repair. Recent evidence indicates that an impairment in vascular mural cells, alias pericytes, may participate in diabetic peripheral vasculopathy. Moreover, the bone marrow undergoes a global remodeling, consisting of microvessels and sensory neurons rarefaction and fat accumulation, which creates a hostile microenvironment for resident stem cells. Bone marrow remodeling is also responsible for detrimental systemic effects. In particular, the aid of reparative cells from the bone marrow is compromised: these elements are released in an improper manner and become harmful vectors of inflammatory and antiangiogenic molecules and noncoding RNAs. This new understanding of impaired regeneration is inspiring new therapeutic options for the treatment of ischemic complications in people with diabetes mellitus.

Tyrosol Facilitates Neovascularization by Enhancing Skeletal Muscle Cells Viability and Paracrine Function in Diabetic Hindlimb Ischemia Mice

As one of the most severe manifestations of diabetes, vascular complications are the main causes of diabetes-related morbidity and mortality. Hyperglycemia induces systemic abnormalities, including impaired angiogenesis, causing diabetic patients to be highly susceptible in suffering hindlimb ischemia (HLI). Despite its severe prognosis, there is currently no effective treatment for diabetic HLI. Skeletal muscle cells secrete multiple angiogenic factors, hence, recently are reported to be critical for angiogenesis; however, hyperglycemia disrupted the paracrine function in skeletal muscle cells, leading to the impaired angiogenesis potential observed in diabetic patients. The present study showed that tyrosol, a phenylethanoid compound, suppresses accumulation of intracellular reactive oxygen species (ROS) caused by hyperglycemia, most plausibly by promoting heme oxygenase-1 (HO-1) expression in skeletal muscle cells. Consequently, tyrosol exerts cytoprotective function against hyperglycemia-induced oxidative stress in skeletal muscle cells, increases their proliferation vigorously, and simultaneously suppresses apoptosis. Furthermore, tyrosol grossly increases the secretion of vascular endothelial growth factor-A (VEGF-A) and platelet-derived growth factor-BB (PDGF-BB) from skeletal muscle cells. This leads to enhanced proliferation and migration capabilities of vascular endothelial and smooth muscle cells, two types of cells that are responsible in forming blood vessels, through cell-cell communication. Finally, in vivo experiment using the diabetic HLI mouse model showed that tyrosol injection into the gastrocnemius muscle of the ischemic hindlimb significantly enhances the formation of functional blood vessels and subsequently leads to significant recovery of blood perfusion. Overall, our findings highlight the potential of the pharmacological application of tyrosol as a small molecule drug for therapeutic angiogenesis in diabetic HLI patients.