Dual effects of obesity on satellite cells and muscle regeneration

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.

Aged black garlic (Allium sativum L.) and aged black elephant garlic (Allium ampeloprasum L.) alleviate obesity and attenuate obesity-induced muscle atrophy in diet-induced obese C57BL/6 mice

Garlic (Allium sativum L.) is a primary dietary component worldwide because of its health benefits and use as a traditional medicine. Elephant garlic (Allium ampeloprasum L.), a related species in the same genus, is less intense and sweeter than A. sativum. The object of this study was to investigate the alleviative effects of aged black garlic (ABG) and aged black elephant garlic (ABEG) on obesity and muscle atrophy induced by obesity in high fat diet-induced obese mice. We demonstrated that ABG and ABEG alleviated obesity and muscle atrophy and enhanced myogenic differentiation and myotube hypertrophy, and this effect was mediated by the upregulation of Akt/mTOR/p70^S6K signaling. Furthermore, a candidate bioactive compound of ABG and ABEG was suggested in this study through analysis using gas chromatography-mass spectroscopy and ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectroscopy. In conclusion, ABG and ABEG may alleviate obesity and treat obesity-induced muscle atrophy.

Melatonin and Exercise Counteract Sarcopenic Obesity through Preservation of Satellite Cell Function

Sarcopenic obesity (SO) is characterized by atrophic skeletal muscle impairment (sarcopenia) and obesity, which is associated with adverse outcomes of morbidity and mortality in elderly people. We investigated the effects of melatonin and exercise training on SO in 32-week-old senescence-accelerated mouse-prone-8 (SAMP8) mice fed a normal diet or a high-fat diet for 16 weeks. Melatonin, exercise, or melatonin and exercise for 8 weeks displayed reductions in the SO-induced impairment of skeletal muscle function and atrophy. Specifically, a decrease in mitochondrial calcium retention capacity in skeletal muscles observed in the HFD-con group was attenuated in melatonin and/or exercise intervention groups. More importantly, HFD-con mice displayed a lower number of Pax7+ satellite cells (SCs) and higher expression of p16^ink than P8ND mice, which were attenuated by melatonin and/or exercise interventions. The cellular senescence in SC-derived primary myoblasts from HFD-con mice was significantly attenuated in myoblasts from the melatonin and/or exercise groups, which was reproduced in a senescence model of H₂O₂-treated C2C12 myoblasts. Our results suggest that melatonin and exercise training attenuate SO-induced skeletal muscle dysfunction, at least in part, through preserving the SC pool by inhibiting cellular senescence and attenuating mitochondrial dysfunction.

Deciphering the "obesity paradox" in the elderly: A systematic review and meta-analysis of sarcopenic obesity

Aging and obesity are two global concerns in public health. Sarcopenic obesity (SO), defined as the combination of age-related sarcopenia and obesity, has become a pressing issue. This systematic review and meta-analysis summarize the current clinical evidence relevant to SO. PubMed, Embase, and Web of Science were searched, and 106 clinical studies with 167,151 elderlies were included. The estimated prevalence of SO was 9% in both men and women. Obesity was associated with 34% reduced risk of sarcopenia (odds ratio [OR] 0.66, 95% CI 0.48-0.91; p < 0.001). The pooled hazard ratio (HR) of all-cause mortality was 1.51 (95% CI 1.14-2.02; p < 0.001) for people with SO compared with healthy individuals. SO was associated with increased risk of cardiovascular disease and related mortality, metabolic disorders, cognitive impairment, arthritis, functional limitation, and lung diseases (all ORs > 1.0, p < 0.05). The attenuated risk of sarcopenia in elderlies with obesity ("obesity paradox") was dependent on higher muscle mass and strength. Apart from unifying the diagnosis of SO, more research is needed to subphenotype people with obesity and sarcopenia for individualized treatment. Meanwhile, the maintenance of proper body composition of muscle and fat may delay or attenuate the adverse outcomes of aging.

Cell shape characteristics of human skeletal muscle cells as a predictor of myogenic competency: A new paradigm towards precision cell therapy

Skeletal muscle-derived cells (SMDC) hold tremendous potential for replenishing dysfunctional muscle lost due to disease or trauma. Current therapeutic usage of SMDC relies on harvesting autologous cells from muscle biopsies that are subsequently expanded in vitro before re-implantation into the patient. Heterogeneity can arise from multiple factors including quality of the starting biopsy, age and comorbidity affecting the processed SMDC. Quality attributes intended for clinical use often focus on minimum levels of myogenic cell marker expression. Such approaches do not evaluate the likelihood of SMDC to differentiate and form myofibres when implanted in vivo, which ultimately determines the likelihood of muscle regeneration. Predicting the therapeutic potency of SMDC in vitro prior to implantation is key to developing successful therapeutics in regenerative medicine and reducing implementation costs. Here, we report on the development of a novel SMDC profiling tool to examine populations of cells in vitro derived from different donors. We developed an image-based pipeline to quantify morphological features and extracted cell shape descriptors. We investigated whether these could predict heterogeneity in the formation of myotubes and correlate with the myogenic fusion index. Several of the early cell shape characteristics were found to negatively correlate with the fusion index. These included total area occupied by cells, area shape, bounding box area, compactness, equivalent diameter, minimum ferret diameter, minor axis length and perimeter of SMDC at 24 h after initiating culture. The information extracted with our approach indicates live cell imaging can detect a range of cell phenotypes based on cell-shape alone and preserving cell integrity could be used to predict propensity to form myotubes in vitro and functional tissue in vivo.

Apol9a regulates myogenic differentiation via the ERK1/2 pathway in C2C12 cells

Background: The rising prevalence of obesity and its complications is a big challenge for the global public health. Obesity is accompanied by biological dysfunction of skeletal muscle and the development of muscle atrophy. The deep knowledge of key molecular mechanisms underlying myogenic differentiation is crucial for discovering novel targets for the treatment of obesity and obesity-related muscle atrophy. However, no effective target is currently known for obesity-induced skeletal muscle atrophy. Methods: Transcriptomic analyses were performed to identify genes associated with the regulation of myogenic differentiation and their potential mechanisms of action. C2C12 cells were used to assess the myogenic effect of Apol9a through immunocytochemistry, western blotting, quantitative polymerase chain reaction, RNA interference or overexpression, and lipidomics. Results: RNA-seq of differentiated and undifferentiated C2C12 cells revealed that Apol9a expression significantly increased following myogenic differentiation and decreased during obesity-induced muscle atrophy. Apol9a silencing in these C2C12 cells suppressed the expression of myogenesis-related genes and reduced the accumulation of intracellular triglycerides. Furthermore, RNA-seq and western blot results suggest that Apol9a regulates myogenic differentiation through the activation of extracellular signal-regulated kinase 1/2 (ERK1/2). This assumption was subsequently confirmed by intervention with PD98059. Conclusion: In this study, we found that Apol9a regulates myogenic differentiation via the ERK1/2 pathway. These results broaden the putative function of Apol9a during myogenic differentiation and provide a promising therapeutic target for intervention in obesity and obesity-induced muscle atrophy.

In Vitro Mimicking of Obesity-Induced Biochemical Environment to Study Obesity Impacts on Cells and Tissues

Obesity represents a heavy burden for modern healthcare. The main challenge facing obesity research progress is the unknown underlying pathways, which limits our understanding of the pathogenesis and developing therapies. Obesity induces specific biochemical environments that impact the different cells and tissues. In this piece of writing, we suggest mimicking obesity-induced in vivo biochemical environments including pH, lipids, hormones, cytokines, and glucose within an in vitro environment. The concept is to reproduce such biochemical environments and use them to treat the tissue cultures, explant cultures, and cell cultures of different biological organs. This will allow us to clarify how the obesity-induced biochemistry impacts such biological entities. It would also be important to try different environments, in terms of the compositions and concentrations of the constitutive elements, in order to establish links between the effects (impaired regeneration, cellular inflammation, etc.) and the factors constituting the environment (hormones, cytokines, etc.) as well as to reveal dose-dependent effects. We believe that such approaches will allow us to elucidate obesity mechanisms, optimize animal models, and develop therapies as well as novel tissue engineering applications.

Cellular and Molecular Variations in Male and Female Murine Skeletal Muscle after Long-Term Feeding with a High-Fat Diet

Current information regarding the effects of a high-fat diet (HFD) on skeletal muscle is contradictory. This study aimed to investigate the effects of a long-term HFD on skeletal muscle in male and female mice at the morphological, cellular, and molecular levels. Adult mice of the C57BL/6 strain were fed standard chow or an HFD for 20 weeks. The tibialis anterior muscles were dissected, weighed, and processed for cellular and molecular analyses. Immunocytochemical and morphometric techniques were applied to quantify fiber size, satellite cells (SCs), and myonuclei. Additionally, PCR array and RT-qPCR tests were performed to determine the expression levels of key muscle genes. Muscles from HFD mice showed decreases in weight, SCs, and myonuclei, consistent with the atrophic phenotype. This atrophy was associated with a decrease in the percentage of oxidative fibers within the muscle. These findings were further confirmed by molecular analyses that showed significant reductions in the expression of Pax7, Myh1, and Myh2 genes and increased Mstn gene expression. Male and female mice showed similar trends in response to HFD-induced obesity. These findings indicate that the long-term effects of obesity on skeletal muscle resemble those of age-related sarcopenia.

Obesity impairs skeletal muscle repair through NID-1 mediated extracellular matrix remodeling by mesenchymal progenitors

Obesity triggers skeletal muscle physio-pathological alterations. However, the crosstalk between adipose tissue and myogenic cells remains poorly understood during obesity. We identified NID-1 among the adipose tissue secreted factors impairing myogenic potential of human myoblasts and murine muscle stem cells in vitro. Mice under High Fat Diet (HFD) displayed increased NID-1 expression in the skeletal muscle endomysium associated with intramuscular fat adipose tissue expansion and compromised muscle stem cell function. We show that NID-1 is highly secreted by skeletal muscle fibro-adipogenic/mesenchymal progenitors (FAPs) during obesity. We demonstrate that increased muscle NID-1 impairs muscle stem cells proliferation and primes the fibrogenic differentiation of FAPs, giving rise to an excessive deposition of extracellular matrix. Finally, we propose a model in which obesity leads to skeletal muscle extracellular matrix remodeling by FAPs, mediating the alteration of myogenic function by adipose tissue and highlighting the key role of NID-1 in the crosstalk between adipose tissue and skeletal muscle.

Obesity as a premature aging phenotype - implications for sarcopenic obesity

Obesity and aging have both seen dramatic increases in prevalence throughout society. This review seeks to highlight common pathologies that present with obesity, along with the underlying risk factors, that have remarkable similarity to what is observed in the aged. These include skeletal muscle dysfunction (loss of quantity and quality), significant increases in adiposity, systemic alterations to autonomic dysfunction, reduction in nitric oxide bioavailability, increases in oxidant stress and inflammation, dysregulation of glucose homeostasis, and mitochondrial dysfunction. This review is organized by the aforementioned indices and succinctly highlights literature that demonstrates similarities between the aged and obese phenotypes in both human and animal models. As aging is an inevitability and obesity prevalence is unlikely to significantly decrease in the near future, these two phenotypes will ultimately combine as a multidimensional syndrome (a pathology termed sarcopenic obesity). Whether the pre-mature aging indices accompanying obesity are additive or synergistic upon entering aging is not yet well defined, but the goal of this review is to illustrate the potential consequences of a double aged phenotype in sarcopenic obesity. Clinically, the modifiable risk factors could be targeted specifically in obesity to allow for increased health span in the aged and sarcopenic obese populations.

Exercise, Diet and Sleeping as Regenerative Medicine Adjuvants: Obesity and Ageing as Illustrations

Regenerative medicine uses the biological and medical knowledge on how the cells and tissue regenerate and evolve in order to develop novel therapies. Health conditions such as ageing, obesity and cancer lead to an impaired regeneration ability. Exercise, diet choices and sleeping pattern have significant impacts on regeneration biology via diverse pathways including reducing the inflammatory and oxidative components. Thus, exercise, diet and sleeping management can be optimized towards therapeutic applications in regenerative medicine. It could allow to prevent degeneration, optimize the biological regeneration and also provide adjuvants for regenerative medicine.

Post-Coronavirus Disease-2019 (COVID-19): Toward a Severe Multi-Level Health Crisis?

There were already numerous challenges facing the healthcare system prior to the ongoing coronavirus disease-2019 (COVID-19) pandemic. Although we look forward to ending this pandemic, it is still expected that the healthcare system will face further challenges leading to a multi-level health crisis. Indeed, after the COVID-19 pandemic, there will still be COVID-19 active cases and those left with health problems following COVID-19 infection who will be of a particular impact. In addition, we also have the health problems that either emerged or worsened during COVID-19, especially with the reduced ability of the healthcare system to take care of many non COVID-19 patients during the COVID-19 pandemic. Such expected evolution of the situation highlights the necessity for the decision-makers to consider applying serious reforms and take quick measures to prevent a post-COVID-19 health crisis.

The effects of diet composition and chronic obesity on muscle growth and function

Diet-induced obesity (DIO) is associated with glucose intolerance, insulin resistance (IR), and an increase in intramyocellular lipids (IMCL), which may lead to disturbances in glucose and protein metabolism. To this matter, it has been speculated that chronic obesity and elevated IMCL may contribute to skeletal muscle loss and deficits in muscle function and growth capacity. Thus, we hypothesized that diets with elevated fat content would induce obesity and insulin resistance, leading to a decrease in muscle mass and an attenuated growth response to increased external loading in adult male mice. Male C57BL/6 mice (8 wk of age) were subjected to five different diets, namely, chow, low-dat-diet (LFD), high-fat-diet (HFD), sucrose, or Western diet, for 28 wk. At 25 wk, HFD and Western diets induced a 60.4% and 35.9% increase in body weight, respectively. Interestingly, HFD, but not Western or sucrose, induced glucose intolerance and insulin resistance. Measurement of isometric torque (ankle plantar flexor and ankle dorsiflexor muscles) revealed no effect of DIO on muscle function. At 28 wk of intervention, muscle area and protein synthesis were similar across all diet groups, despite insulin resistance and increased IMCL being observed in HFD and Western diet groups. In response to 30 days of functional overload, an attenuated growth response was observed in only the HFD group. Nevertheless, our results show that DIO alone is not sufficient to induce muscle atrophy and contractile dysfunction in adult male C57BL/6 mice. However, diet composition does have an impact on muscle growth in response to increased external loading.NEW & NOTEWORTHY The effects of diet-induced obesity on skeletal muscle mass are complex and dependent on diet composition and diet duration. The present study results show that chronic exposure to high levels of fatty acids does not affect muscle mass, contractile function, or protein synthesis in obese C57BL/6 mice compared with the consumption of chow. Obesity did result in a delay in load-induced growth; however, only a 45% HFD resulted in attenuated growth following 30 days of functional overload.

High-Fat Diet-Induced Mitochondrial Dysfunction Promotes Genioglossus Injury - A Potential Mechanism for Obstructive Sleep Apnea with Obesity

PURPOSE

Obesity is a worldwide metabolic disease and a critical risk factor for several chronic conditions. Obstructive sleep apnea (OSA) is an important complication of obesity. With the soaring morbidity of obesity, the prevalence of OSA has markedly increased. However, the underlying mechanism of the high relevance between obesity and OSA has not been elucidated. This study investigated the effects of obesity on the structure and function of the genioglossus to explore the possible mechanisms involved in OSA combined with obesity.

METHODS

Six-week-old male C57BL/6J mice were fed high-fat diet (HFD, 60% energy) or normal diet (Control, 10% energy) for 16 weeks. The muscle fibre structure and electromyography (EMG) activity of genioglossus were measured. The ultrastructure and function of mitochondrial, oxidative damage and apoptosis in genioglossus were detected by transmission electron microscopy (TEM), qPCR, Western blotting, immunohistochemistry and TUNEL staining. We further studied the influence of palmitic acid (PA) on the proliferation and myogenic differentiation of C2C12 myoblasts, as well as mitochondrial function, oxidative stress, and apoptosis in C2C12 myotubes.

RESULTS

Compared with the control, the number of muscle fibres was decreased, the fibre type was remarkably changed, and the EMG activity had declined in genioglossus. In addition, a HFD also reduced mitochondria quantity and function, induced excessive oxidative stress and increased apoptosis in genioglossus. In vitro, PA treatment significantly inhibited the proliferation and myogenic differentiation of C2C12 myoblasts. Moreover, PA decreased the mitochondrial membrane potential, upregulated mitochondrial reactive oxygen species (ROS) levels, and activated the mitochondrial-related apoptotic pathway in myotubes.

CONCLUSION

Our findings suggest that a HFD caused genioglossus injury in obese mice. The mitochondrial dysfunction and the accompanying oxidative stress were involved in the genioglossus injury, which may provide potential therapeutic targets for OSA with obesity.

Regeneration during Obesity: An Impaired Homeostasis

Simple Summary

Regeneration represents the biological processes that allow cells and tissues to renew and develop. During obesity, a variety of changes and reactions are seen. This includes inflammation and metabolic disorders. These obesity-induced changes do impact the regeneration processes. Such impacts that obesity has on regeneration would affect tissues and organs development and would also have consequences on the outcomes of therapies that depend on cells regeneration (such as burns, radiotherapy and leukemia) given to patients suffering from obesity. Therefore, a particular attention should be given to patients suffering from obesity in biological, therapeutic and clinical contexts that depend on regeneration ability.

Abstract

Obesity is a health problem that, in addition to the known morbidities, induces the generation of a biological environment with negative impacts on regeneration. Indeed, factors like DNA damages, oxidative stress and inflammation would impair the stem cell functions, in addition to some metabolic and development patterns. At the cellular and tissulaire levels, this has consequences on growth, renewal and restoration which results into an impaired regeneration. This impaired homeostasis concerns also key metabolic tissues including muscles and liver which would worsen the energy balance outcome towards further development of obesity. Such impacts of obesity on regeneration shows the need of a specific care given to obese patients recovering from diseases or conditions requiring regeneration such as burns, radiotherapy and leukemia. On the other hand, since stem cells are suggested to manage obesity, this impaired regeneration homeostasis needs to be considered towards more optimized stem cells-based obesity therapies within the context of precision medicine.