Intermuscular and perimuscular fat expansion in obesity correlates with skeletal muscle T cell and macrophage infiltration and insulin resistance

How Can Promoting Skeletal Muscle Health and Exercise in Children and Adolescents Prevent Insulin Resistance and Type 2 Diabetes?

Skeletal muscle secretome, through its paracrine and endocrine functions, contributes to the maintenance and regulation of overall physiological health. We conducted a narrative review on the role of skeletal muscle and exercise in maintaining glucose homeostasis, driving insulin resistance (IR), and preventing type 2 diabetes in pediatric populations, especially in the context of overweight and obesity. Myokines such as interleukin (IL)-6, IL-8, and IL-15, as well as irisin, myonectin, and myostatin, appear to play a crucial role in IR. Skeletal muscle can also become a target of obesity-induced and IR-induced inflammation. In the correlation between muscle, IR, and inflammation, the role of infiltration of the immune cells and the microvasculature may also be considered. It remains unclear which exercise approach is the best; however, combining aerobic exercise with resistance training seems to be the most effective strategy for managing IR, with high-intensity activities offering superior metabolic benefits and long-term adherence. Encouraging daily participation in enjoyable and engaging exercise is key for long-term commitment and effective glucose metabolism management. Promoting physical activity in children and adolescents must be a top priority for public health, not only in terms of individual quality of life and well-being but also for community health.

Endothelial metabolic control of insulin sensitivity through resident macrophages

Endothelial cells (ECs) not only form passive blood conduits but actively contribute to nutrient transport and organ homeostasis. The role of ECs in glucose homeostasis is, however, poorly understood. Here, we show that, in skeletal muscle, endothelial glucose transporter 1 (Glut1/Slc2a1) controls glucose uptake via vascular metabolic control of muscle-resident macrophages without affecting transendothelial glucose transport. Lowering endothelial Glut1 via genetic depletion (Glut1ΔEC) or upon a short-term high-fat diet increased angiocrine osteopontin (OPN/Spp1) secretion. This promoted resident muscle macrophage activation and proliferation, which impaired muscle insulin sensitivity. Consequently, co-deleting Spp1 from ECs prevented macrophage accumulation and improved insulin sensitivity in Glut1ΔEC mice. Mechanistically, Glut1-dependent endothelial glucose metabolic rewiring increased OPN in a serine metabolism-dependent fashion. Our data illustrate how the glycolytic endothelium creates a microenvironment that controls resident muscle macrophage phenotype and function and directly links resident muscle macrophages to the maintenance of muscle glucose homeostasis.

The immunology of sickness metabolism

Everyone knows that an infection can make you feel sick. Although we perceive infection-induced changes in metabolism as a pathology, they are a part of a carefully regulated process that depends on tissue-specific interactions between the immune system and organs involved in the regulation of systemic homeostasis. Immune-mediated changes in homeostatic parameters lead to altered production and uptake of nutrients in circulation, which modifies the metabolic rate of key organs. This is what we experience as being sick. The purpose of sickness metabolism is to generate a metabolic environment in which the body is optimally able to fight infection while denying vital nutrients for the replication of pathogens. Sickness metabolism depends on tissue-specific immune cells, which mediate responses tailored to the nature and magnitude of the threat. As an infection increases in severity, so do the number and type of immune cells involved and the level to which organs are affected, which dictates the degree to which we feel sick. Interestingly, many alterations associated with metabolic disease appear to overlap with immune-mediated changes observed following infection. Targeting processes involving tissue-specific interactions between activated immune cells and metabolic organs therefore holds great potential for treating both people with severe infection and those with metabolic disease. In this review, we will discuss how the immune system communicates in situ with organs involved in the regulation of homeostasis and how this communication is impacted by infection.

Exercise as a tool to mitigate metabolic disease

Metabolic diseases, notably obesity and type 2 diabetes (T2D), have reached alarming proportions and constitute a significant global health challenge, emphasizing the urgent need for effective preventive and therapeutic strategies. In contrast, exercise training emerges as a potent intervention, exerting numerous positive effects on metabolic health through adaptations to the metabolic tissues. Here, we reviewed the major features of our current understanding with respect to the intricate interplay between metabolic diseases and key metabolic tissues, including adipose tissue, skeletal muscle, and liver, describing some of the main underlying mechanisms driving pathogenesis, as well as the role of exercise to combat and treat obesity and metabolic disease.

Obesity-associated Inflammation and Alloimmunity

Obesity is a worldwide health problem with a rapidly rising incidence. In organ transplantation, increasing numbers of patients with obesity accumulate on waiting lists and undergo surgery. Obesity is in general conceptualized as a chronic inflammatory disease, potentially impacting alloimmune response and graft function. Here, we summarize our current understanding of cellular and molecular mechanisms that control obesity-associated adipose tissue inflammation and provide insights into mechanisms affecting transplant outcomes, emphasizing on the beneficial effects of weight loss on alloimmune responses.

The multifaceted life of macrophages in white adipose tissue: Immune shift couples with metabolic switch

White adipose tissue (WAT) is a vital endocrine organ that regulates energy balance and metabolic homeostasis. In addition to fat cells, WAT harbors macrophages with distinct phenotypes that play crucial roles in immunity and metabolism. Nutrient demands cause macrophages to accumulate in WAT niches, where they remodel the microenvironment and produce beneficial or detrimental effects on systemic metabolism. Given the abundance of macrophages in WAT, this review summarizes the heterogeneity of WAT macrophages in physiological and pathological conditions, including their alterations in quantity, phenotypes, characteristics, and functions during WAT growth and development, as well as healthy or unhealthy expansion. We will discuss the interactions of macrophages with other cell partners in WAT including adipose stem cells, adipocytes, and T cells in the context of various microenvironment niches in lean or obese condition. Finally, we highlight how adipose tissue macrophages merge immunity and metabolic changes to govern energy balance for the organism.

n-3 and n-6 Polyunsaturated Fatty Acids Modulate Macrophage-Myocyte Inflammatory Crosstalk and Improve Myocyte Insulin Sensitivity

In obesity, circulating saturated fatty acids (SFAs) and inflammatory cytokines interfere with skeletal muscle insulin signaling, leading to whole body insulin resistance. Further, obese skeletal muscle is characterized by macrophage infiltration and polarization to the inflammatory M1 phenotype, which is central to the development of local inflammation and insulin resistance. While skeletal muscle-infiltrated macrophage-myocyte crosstalk is exacerbated by SFA, the effects of other fatty acids, such as n-3 and n-6 polyunsaturated fatty acids (PUFAs), are less studied. Thus, the objective of this study was to determine the effects of long-chain n-3 and n-6 PUFAs on macrophage M1 polarization and subsequent effects on myocyte inflammation and metabolic function compared to SFA. Using an in vitro model recapitulating obese skeletal muscle cells, differentiated L6 myocytes were cultured for 24 h with RAW 264.7 macrophage-conditioned media (MCM), followed by insulin stimulation (100 nM, 20 min). MCM was generated by pre-treating macrophages for 24 h with 100 μM palmitic acid (16:0, PA-control), arachidonic acid (20:4n-6, AA), or docosahexaenoic acid (22:6n-3, DHA). Next, macrophage cultures were stimulated with a physiological dose (10 ng/mL) of lipopolysaccharide for an additional 12 h to mimic in vivo obese endotoxin levels. Compared to PA, both AA and DHA reduced mRNA expression and/or secreted protein levels of markers for M1 (TNFα, IL-6, iNOS; p < 0.05) and increased those for M2 (IL-10, TGF-β; p < 0.05) macrophage polarization. In turn, AA- and DHA-derived MCM reduced L6 myocyte-secreted cytokines (TNFα, IL-6; p < 0.05) and chemokines (MCP-1, MIP-1β; p < 0.05). Only AA-derived MCM increased L6-myocyte phosphorylation of Akt (p < 0.05), yet this was inconsistent with improved insulin signaling, as only DHA-derived MCM improved L6 myocyte glucose uptake (p < 0.05). In conclusion, dietary n-3 and n-6 PUFAs may be a useful strategy to modulate macrophage-myocyte inflammatory crosstalk and improve myocyte insulin sensitivity in obesity.

Skeletal muscle as a pro- and anti-inflammatory tissue: insights from children to adults and ultrasound findings

Previously regarded as a movement and posture control agent, the skeletal muscle is now recognized as an endocrine organ that may affect systemic inflammation and metabolic health. The discovery of myokines such as IL-6, released from skeletal muscle in response to physical exercise, is now one of the most recent insights. Myokines are the mediators of the balance between the pro-inflammatory and anti-inflammatory responses. This underscores the muscle function as a determinant of good health and prevention of diseases. Advances in ultrasound technology improved evaluation of muscle thickness, composition, and determining fat distribution. Combining imaging with molecular biology, researchers discovered the complicated interplay between muscle function, cytokine production and general health effects.The production of myokines with exercise showcasing the adaptability of muscles to high-stress conditions and contributing to metabolism and inflammation regulation. These findings have significant implications in order to provide improvement in metabolic and inflammatory diseases.

Integrated assessment of computed tomography density in pectoralis and erector spinae muscles as a prognostic biomarker for coronavirus disease 2019

BACKGROUND ＆ AIMS: Muscle quantification using chest computed tomography (CT) is a useful prognostic biomarker for coronavirus disease 2019 (COVID-19). However, no studies have evaluated the clinical course through comprehensive assessment of the pectoralis and erector spinae muscles. Therefore, we compared the impact of the areas and densities of these muscles on COVID-19 infection outcome.

METHODS

This multicenter retrospective cohort study was conducted by the COVID-19 Task Force. A total of 1410 patients with COVID-19 were included, and data on the area and density of the pectoralis and erector spinae muscles on chest CT were collected. The impact of each muscle parameter on the clinical outcome of COVID-19 was stratified according to sex. The primary outcome was the percentage of patients with severe disease, including those requiring oxygen supplementation and those who died. Additionally, 167 patients were followed up for changes in muscle parameters at three months and for the clinical characteristics in case of reduced CT density.

RESULTS

For both muscles, low density rather than muscle area was associated with COVID-19 severity. Regardless of sex, lower erector spinae muscle density was associated with more severe disease than pectoralis muscle density. The muscles were divided into two groups using the receiver operating characteristic curve of CT density, and the population was classified into four (Group A: high CT density for both muscles, Group B: low CT density for pectoralis and high for erector spinae muscle. Group C: high CT density for pectoralis and low for erector spinae muscle, Group D: low CT density for both muscles). In univariate analysis, Group D patients exhibited worse outcomes than Group A (OR: 2.96, 95% CI: 2.03-4.34 in men; OR: 3.02, 95% CI: 2.66-10.4 in women). Multivariate analysis revealed that men in Group D had a significantly more severe prognosis than those in Group A (OR: 1.82, 95% CI: 1.16-2.87). Moreover, Group D patients tended to have the highest incidence of other complications due to secondary infections and acute kidney injury during the clinical course. Longitudinal analysis of both muscle densities over three months revealed that patients with decreased muscle density over time were more likely to have severe cases than those who did not.

CONCLUSIONS

Muscle density, rather than muscle area, predicts the clinical outcomes of COVID-19. Integrated assessment of pectoralis and erector spinae muscle densities demonstrated higher accuracy in predicting the clinical course of COVID-19 than individual assessments.

Caloric restriction for the immunometabolic control of human health

Nutrition affects all physiological processes occurring in our body, including those related to the function of the immune system; indeed, metabolism has been closely associated with the differentiation and activity of both innate and adaptive immune cells. While excessive energy intake and adiposity have been demonstrated to cause systemic inflammation, several clinical and experimental evidence show that calorie restriction (CR), not leading to malnutrition, is able to delay aging and exert potent anti-inflammatory effects in different pathological conditions. This review provides an overview of the ability of different CR-related nutritional strategies to control autoimmune, cardiovascular, and infectious diseases, as tested by preclinical studies and human clinical trials, with a specific focus on the immunological aspects of these interventions. In particular, we recapitulate the state of the art on the cellular and molecular mechanisms pertaining to immune cell metabolic rewiring, regulatory T cell expansion, and gut microbiota composition, which possibly underline the beneficial effects of CR. Although studies are still needed to fully evaluate the feasibility and efficacy of the nutritional intervention in clinical practice, the experimental observations discussed here suggest a relevant role of CR in lowering the inflammatory state in a plethora of different pathologies, thus representing a promising therapeutic strategy for the control of human health.

Exercise, mitochondrial dysfunction and inflammasomes in skeletal muscle

In the broad field of inflammation, skeletal muscle is a tissue that is understudied. Yet it represents about 40% of body mass in non-obese individuals and is therefore of fundamental importance for whole body metabolism and health. This article provides an overview of the unique features of skeletal muscle tissue, as well as its adaptability to exercise. This ability to adapt, particularly with respect to mitochondrial content and function, confers a level of metabolic "protection" against energy consuming events, and adds a measure of quality control that determines the phenotypic response to stress. Thus, we describe the particular role of mitochondria in promoting inflammasome activation in skeletal muscle, contributing to muscle wasting and dysfunction in aging, disuse and metabolic disease. We will then discuss how exercise training can be anti-inflammatory, mitigating the chronic inflammation that is observed in these conditions, potentially through improvements in mitochondrial quality and function.

Targeting IL-12 family cytokines: A potential strategy for type 1 and type 2 diabetes mellitus

Diabetes is a common metabolic disease characterized by an imbalance in blood glucose levels. The pathogenesis of diabetes involves the essential role of cytokines, particularly the IL-12 family cytokines. These cytokines, which have a similar structure, play multiple roles in regulating the immune response. Recent studies have emphasized the importance of IL-12 family cytokines in the development of both type 1 and type 2 diabetes mellitus. As a result, they hold promise as potential therapeutic targets for the treatment of these conditions. This review focuses on the potential of targeting IL-12 family cytokines for diabetes therapy based on their roles in the pathogenesis of both types of diabetes. We have summarized various therapies that target IL-12 family cytokines, including drug therapy, combination therapy, cell therapy, gene therapy, cytokine engineering therapy, and gut microbiota modulation. By analyzing the advantages and disadvantages of these therapies, we have evaluated their feasibility for clinical application and proposed possible solutions to overcome any challenges. In conclusion, targeting IL-12 family cytokines for diabetes therapy provides updated insights into their potential benefits, such as controlling inflammation, preserving islet β cells, reversing the onset of diabetes, and impeding the development of diabetic complications.

Intermuscular adipose tissue in obesity and related disorders: cellular origins, biological characteristics and regulatory mechanisms

Intermuscular adipose tissue (IMAT) is a unique adipose depot interspersed between muscle fibers (myofibers) or muscle groups. Numerous studies have shown that IMAT is strongly associated with insulin resistance and muscular dysfunction in people with metabolic disease, such as obesity and type 2 diabetes. Moreover, IMAT aggravates obesity-related muscle metabolism disorders via secretory factors. Interestingly, researchers have discovered that intermuscular brown adipocytes in rodent models provide new hope for obesity treatment by acting on energy dissipation, which inspired researchers to explore the underlying regulation of IMAT formation. However, the molecular and cellular properties and regulatory processes of IMAT remain debated. Previous studies have suggested that muscle-derived stem/progenitor cells and other adipose tissue progenitors contribute to the development of IMAT. Adipocytes within IMAT exhibit features that are similar to either white adipocytes or uncoupling protein 1 (UCP1)-positive brown adipocytes. Additionally, given the heterogeneity of skeletal muscle, which comprises myofibers, satellite cells, and resident mesenchymal progenitors, it is plausible that interplay between these cellular components actively participate in the regulation of intermuscular adipogenesis. In this context, we review recent studies associated with IMAT to offer insights into the cellular origins, biological properties, and regulatory mechanisms of IMAT. Our aim is to provide novel ideas for the therapeutic strategy of IMAT and the development of new drugs targeting IMAT-related metabolic diseases.

Peripheral and central macrophages in obesity

Obesity is associated with chronic, low-grade inflammation. Excessive nutrient intake causes adipose tissue expansion, which may in turn cause cellular stress that triggers infiltration of pro-inflammatory immune cells from the circulation as well as activation of cells that are residing in the adipose tissue. In particular, the adipose tissue macrophages (ATMs) are important in the pathogenesis of obesity. A pro-inflammatory activation is also found in other organs which are important for energy metabolism, such as the liver, muscle and the pancreas, which may stimulate the development of obesity-related co-morbidities, including insulin resistance, type 2 diabetes (T2D), cardiovascular disease (CVD) and non-alcoholic fatty liver disease (NAFLD). Interestingly, it is now clear that obesity-induced pro-inflammatory signaling also occurs in the central nervous system (CNS), and that pro-inflammatory activation of immune cells in the brain may be involved in appetite dysregulation and metabolic disturbances in obesity. More recently, it has become evident that microglia, the resident macrophages of the CNS that drive neuroinflammation, may also be activated in obesity and can be relevant for regulation of hypothalamic feeding circuits. In this review, we focus on the action of peripheral and central macrophages and their potential roles in metabolic disease, and how macrophages interact with other immune cells to promote inflammation during obesity.

Effects of Physical Activity Program on Body Composition, Physical Performance, and Neuromuscular Strategies during Walking in Older Adults with Sarcopenic Obesity: Randomized Controlled Trial

The potential impact of a specific physical activity program on biomechanical gait parameters and neuromuscular strategies around the ankle joint in older adults with sarcopenic obesity (SO) remains largely unexplored. The objective of this study was to investigate the effectiveness of a 24-week posture, strengthening, and motricity (PSM) program on improving neuromuscular strategies and biomechanical gait parameters in older adults with SO. 40 participants were randomly assigned to either the trained group (TG) and the control group (CG). Only the TG received the PSM program. Standardized evaluations were performed before and after the intervention, including walking tests on an instrumented gait analysis treadmill to evaluate biomechanical gait parameters and EMG activity of ankle muscles. After the PSM program, TG exhibited an increase in comfortable walking speed (+80%, p < 0.001) and step length (+38%, p < 0.05). Moreover, TG demonstrated a reduction in CoP velocity (-26%, p < 0.01). These gait modifications were associated with decreased muscle activity during the different gait phases (p < 0.05). The PSM program effectively improved gait and neuromuscular capacities in older adults with SO. Notably, these results shed light on the remarkable trainability of neuromuscular capacities in older adults with SO, despite the adverse effects of aging and obesity.

Central and Peripheral Inflammation: A Common Factor Causing Addictive and Neurological Disorders and Aging-Related Pathologies

Many diseases and degenerative processes affecting the nervous system and peripheral organs trigger the activation of inflammatory cascades. Inflammation can be triggered by different environmental conditions or risk factors, including drug and food addiction, stress, and aging, among others. Several pieces of evidence show that the modern lifestyle and, more recently, the confinement associated with the COVID-19 pandemic have contributed to increasing the incidence of addictive and neuropsychiatric disorders, plus cardiometabolic diseases. Here, we gather evidence on how some of these risk factors are implicated in activating central and peripheral inflammation contributing to some neuropathologies and behaviors associated with poor health. We discuss the current understanding of the cellular and molecular mechanisms involved in the generation of inflammation and how these processes occur in different cells and tissues to promote ill health and diseases. Concomitantly, we discuss how some pathology-associated and addictive behaviors contribute to worsening these inflammation mechanisms, leading to a vicious cycle that promotes disease progression. Finally, we list some drugs targeting inflammation-related pathways that may have beneficial effects on the pathological processes associated with addictive, mental, and cardiometabolic illnesses.

Association between obesity, inflammation and insulin resistance: Insights into signaling pathways and therapeutic interventions

Obesity, a metabolic disorder, is becoming a worldwide epidemic that predominantly increases the risk for various diseases including metabolic inflammation, insulin resistance, and cardiovascular diseases. However, the mechanisms that link obesity with other metabolic diseases are not completely understood. In obesity, various inflammatory pathways that cause inflammation in adipose tissue of an obese individual become activated and exacerbate the disease. Obesity-induced low-grade metabolic inflammation perturbates the insulin signaling pathway and leads to insulin resistance. Researchers have identified several pathways that link the impairment of insulin resistance through obesity-induced inflammation like activation of Nuclear factor kappa B (NF-κB), suppressor of cytokine signaling (SOCS) proteins, cJun-N-terminal Kinase (JNK), Wingless-related integration site (Wnt), and Toll-like receptor (TLR) signaling pathways. In this review article, the published studies have been reviewed to identify the potential and influential role of different signaling pathways in the pathogenesis of obesity-induced metabolic inflammation and insulin resistance along with the discussion on potential therapeutic strategies. Therapies targeting these signaling pathways show improvements in metabolic diseases associated with obesity, but require further testing and confirmation through clinical trials.

Mechanism of immune attack in the progression of obesity-related type 2 diabetes

Obesity and overweight are widespread issues in adults, children, and adolescents globally, and have caused a noticeable rise in obesity-related complications such as type 2 diabetes mellitus (T2DM). Chronic low-grade inflammation is an important promotor of the pathogenesis of obesity-related T2DM. This proinflammatory activation occurs in multiple organs and tissues. Immune cell-mediated systemic attack is considered to contribute strongly to impaired insulin secretion, insulin resistance, and other metabolic disorders. This review focused on highlighting recent advances and underlying mechanisms of immune cell infiltration and inflammatory responses in the gut, islet, and insulin-targeting organs (adipose tissue, liver, skeletal muscle) in obesity-related T2DM. There is current evidence that both the innate and adaptive immune systems contribute to the development of obesity and T2DM.

Heterogeneity of circulating CXCR5-PD-1hiTph cells in patients of type 2 and type 1 diabetes in Chinese population

AIMS

Circulating peripheral helper T (Tph) cells are shown to promote the progression of autoimmune diseases. However, the role of Tph cells in inflammatory diseases such as type 2 diabetes mellitus (T2DM) and the differences between T2DM and autoimmune diabetes remain unclear.

METHODS

We recruited 92 T2DM patients, 106 type 1 diabetes mellitus (T1DM) patients and 84 healthy control individuals. Peripheral blood mononucleated cells were isolated and examined by multicolor flow cytometry. We further evaluated the correlations between circulating Tph cells and clinical biochemical parameters, islet function, disease progression and islet autoantibodies.

RESULTS

Circulating Tph cells were significantly higher in both T2DM and T1DM patients than in healthy control individuals. A significant positive correlation was observed between Tph cells and B cells in T1DM patients and overweight T2DM patients. Furthermore, Tph cells were negatively correlated with the area under the C-peptide curve (C-PAUC), and Tph cells were significantly positively correlated with fasting glucose and glycated hemoglobin levels in T2DM patients. However, no correlation was found between Tph cells and the above clinical indicators in T1DM patients. The frequency of Tph cells positively correlated with the titer of GAD autoantibodies and duration of disease in T1DM patients. In addition, we demonstrated that the frequency of Tph cells was decreased after rituximab therapy in T1DM patients.

CONCLUSIONS

Circulating Tph cells are associated with blood glucose levels and islet function in T2DM patients. In T1DM patients, circulating Tph cells are associated with B cells and islet autoantibodies. This may suggest that Tph cells have different pathogenic mechanisms in the two types of diabetes.

CLINICAL TRIAL INFORMATION

http://ClinicalTrials.gov NCT01280682 (registered July, 2010).

The interactions between inflammation and insulin resistance: molecular mechanisms in insulin-producing and insulin-dependent tissues

In the modern world the prevalence of obesity and type 2 diabetes mellitus (T2DM) significantly increases. In this light the risks of obesity-associated complications also grow up. The crucial linkage between obesity and its metabolic and cardiovascular complications is inflammatory process. The mechanism of this linkage is similar in pancreas and insulin-dependent tissues both on cells, cell-to-cell communication and signaling pathway levels: the catalysts are different lipids (cholesterol, free fatty acids, triglycerides), which are able to activate Toll-like receptors of innate immunity and inflammation. Nextly, IKK- and JNK-dependent cascades activate the secretion of inflammatory cytokines TNFa, IL-1b, IL-6 and others, which act by paracrine and autocrine manner and support inflammation both in local and systemic levels. Thus, insulin-producing and insulin-dependent tissues, which are involved in T2DM pathogenesis, through the inflammatory process integrate in pathogenic and self-maintaining cycle, which leads to the suppression of insulin secretion, pancreatic β-cell failure and the development of insulin-dependent tissues insulin resistance.

The antigen CD300e drives T cell inflammation in adipose tissue and elicits an antibody response predictive of the insulin sensitivity recovery in obese patients

Obesity and insulin resistance (IR), the key features of metabolic syndrome, are closely associated with a state of chronic, low-grade inflammation. Bariatric surgery leads to a considerable reduction in the adipose tissue mass and systemic inflammation along with a reduction of IR, with a whole-body metabolic improvement. However, a sizable portion of people experience an IR relapse within few years of remission.Numerous studies have attempted to explore the best clinical predictors of the improvement of insulin sensitivity and the maintenance of glucose homeostasis after bariatric surgery, but no simple fasting blood test has been found to be effective in predicting the short and long-term beneficial effects on glycaemia.With the present study, we investigated T-cell and antibody responses against CD300e, an antigen highly expressed in the adipose tissue of patients with obesity before the bariatric surgery-induced weight loss. We found both in fat tissue and in peripheral blood anti-CD300e-specific T helper 1 responses. Moreover, we evidenced in the sera of individuals with obesity an antibody response towards CD300e and revealed the existence of a significant correlation between the level of antibodies before surgery and the maintenance of glucose control after the intervention.

Intermuscular adipose tissue in patients with systemic lupus erythematosus

OBJECTIVE

Patients with SLE frequently have debilitating fatigue and reduced physical activity. Intermuscular adipose tissue (IMAT) accumulation is associated with reduced physical exercise capacity. We hypothesised that IMAT is increased in patients with SLE and associated with increased fatigue, reduced physical activity and increased inflammation.

METHODS

In a cross-sectional study, 23 patients with SLE and 28 control participants were evaluated. IMAT was measured in the calf muscles using sequential T ₁-weighted MRI. Patient-reported physical activity and fatigue were measured and a multiplex proteomic assay was used to measure markers and mediators of inflammation.

RESULTS

IMAT accumulation (percentage of IMAT area to muscle area) was significantly higher in SLE versus control participants (7.92%, 4.51%-13.39% vs 2.65%, 1.15%-4.61%, median, IQR, p<0.001) and remained significant after adjustment for age, sex, race and body mass index (p<0.001). In patients with SLE, IMAT accumulation did not differ significantly among corticosteroid users and non-users (p=0.48). In the study cohort (patients and controls), IMAT was positively correlated with self-reported fatigue score (rho=0.52, p<0.001) and inversely correlated with self-reported walking distance (rho=-0.60, p<0.001). Several markers of inflammation were associated with IMAT accumulation in patients with SLE, and gene ontology analysis showed significant enrichment for pathways associated with macrophage migration and activation in relation to IMAT.

CONCLUSION

Patients with SLE have greater IMAT accumulation than controls in the calf muscles. Increased IMAT is associated with greater fatigue and lower physical activity. Future studies should evaluate the effectiveness of interventions that improve muscle quality to alleviate fatigue in patients with SLE.

Adipose-Secreted Exosomes and Their Pathophysiologic Effects on Skeletal Muscle

Due to its prominent secretory activity, adipose tissue (AT) is now considered a major player in the crosstalk between organs, especially with skeletal muscle. In which, exosomes are effective carriers for the intercellular material transfer of a wide range of molecules that can influence a series of physiological and pathological processes in recipient cells. Considering their underlying roles, the regulatory mechanisms of adipose-secreted exosomes and their cellular crosstalk with skeletal muscle have received great attention in the field. In this review, we describe what is currently known of adipose-secreted exosomes, as well as their applications in skeletal muscle pathophysiology.

Macrophages, Chronic Inflammation, and Insulin Resistance

The prevalence of obesity has reached alarming levels, which is considered a major risk factor for several metabolic diseases, including type 2 diabetes (T2D), non-alcoholic fatty liver, atherosclerosis, and ischemic cardiovascular disease. Obesity-induced chronic, low-grade inflammation may lead to insulin resistance, and it is well-recognized that macrophages play a major role in such inflammation. In the current review, the molecular mechanisms underlying macrophages, low-grade tissue inflammation, insulin resistance, and T2D are described. Also, the role of macrophages in obesity-induced insulin resistance is presented, and therapeutic drugs and recent advances targeting macrophages for the treatment of T2D are introduced.

Aerobic Exercise Prevents Chronic Inflammation and Insulin Resistance in Skeletal Muscle of High-Fat Diet Mice

Obesity is commonly accompanied by chronic tissue inflammation and leads to insulin resistance. Aerobic exercise is an essential treatment for insulin resistance and has anti-inflammatory effects. However, the molecular mechanisms of exercise on obesity-associated inflammation and insulin resistance remain largely unknown. Here, we evaluated the effects of aerobic exercise on inflammation and insulin resistance in skeletal muscles of high-fat diet (HFD) mice. Male C57BL/6J mice were fed a high-fat diet or a normal diet for 12 weeks, and then aerobic training was performed on a treadmill for 8 weeks. Body weight, fasting blood glucose, food intake levels, and glucose and insulin tolerance were evaluated. The levels of cytokines, skeletal muscle insulin resistance, and inflammation were also analyzed. Eight weeks of aerobic exercise attenuated HFD-induced weight gain and glucose intolerance, and improved insulin sensitivity. This was accompanied by enhanced insulin signaling. Exercise directly resulted in a significant reduction of lipid content, inflammation, and macrophage infiltration in skeletal muscles. Moreover, exercise alleviated HFD-mediated inflammation by suppressing the activation of the NF-κB pathway within skeletal muscles. These results revealed that aerobic exercise could lead to an anti-inflammatory phenotype with protection from skeletal muscle insulin resistance in HFD-induced mice.

Bidirectional roles of skeletal muscle fibro-adipogenic progenitors in homeostasis and disease

Sarcopenia and myopathies cause progressive muscle weakness and degeneration, which are closely associated with fat infiltration and fibrosis in muscle. Recently, experimental research has shed light on fibro-adipogenic progenitors (FAPs), also known as muscle-resident mesenchymal progenitors with multiple differentiation potential for adipogenesis, fibrosis, osteogenesis and chondrogenesis. They are considered key regulators of muscle homeostasis and integrity. They play supportive roles in muscle development and repair by orchestrating the regulatory interplay between muscle stem cells (MuSCs) and immune cells. Interestingly, FAPs also contribute to intramuscular fat infiltration, fibrosis and other pathologies when the functional integrity of the network is compromised. In this review, we summarize recent insights into the roles of FAPs in maintenance of skeletal muscle homeostasis, and discuss the underlying mechanisms regulating FAPs behavior and fate, highlighting their roles in participating in efficient muscle repair and fat infiltrated muscle degeneration as well as during muscle atrophy. We suggest that controlling and predicting FAPs differentiation may become a promising strategy to improve muscle function and prevent irreparable muscle damage.

Muscle and Adipose Tissue Communicate with Extracellular Vesicles

In numerous body locations, muscle and adipose tissue are in close contact. Both tissues are endocrine organs that release cytokines, playing a crutial role in the control of tissue homeostasis in health and diseases. Within this context, the identification of the signals involved in muscle–fat crosstalk has been a hot topic over the last 15 years. Recently, it has been discovered that adipose tissue and muscles can release information embedded in lipid-derived nanovesicles called ‘extracellular vesicles’ (EVs), which can modulate the phenotype and the homeostasis of neighboring recipient cells. This article reviews knowledge on EVs and their involvement in the communication between adipose tissue and muscle in several body locations. Even if the works are scarce, they have revolutionized our vision in the field of metabolic and cardiovascular diseases.

Meta-analysis of gene expression data in adipose tissue reveals new obesity associated genes

High-throughput transcriptomic and proteomic data like microarray data are deposited in public databases such as Gene Expression Omnibus (GEO). Omics data integration and processing from different and independent studies is achieved by using efficient and effective computational tools through meta-analysis. Meta-analysis is a statistical powerful tool combining data from numerous studies, minimizes bias and increases statistical power by increasing sample size compared to individual studies. Therefore, we performed a meta-analysis of gene expression data in adipose tissue to identify genes that are differentially expressed between obese and non-obese subjects as well as to detect gene expression signatures, pathways and networks associated with obesity. We identified 821 differentially expressed genes (DEGs) in adipose tissue of obese subjects compared to non-obese. A protein-protein interactions (PPIs) network was reconstructed consisting of 168 proteins. Functional enrichment analysis in the network revealed proteins involved in RNA and energy metabolism. The KEGG pathway analysis revealed 15 enriched pathway terms. Furthermore, multiple testing correction methods identified five statistically significant obesity associated genes (NDUFA12, SFI1, SSB, FAR2 and LACE1) that require further investigation.

Keeping It Local in Metabolic Disease: Adipose Tissue Paracrine Signaling and Insulin Resistance

Alterations in adipose tissue composition and function are associated with obesity and contribute to the development of type 2 diabetes. While the significance of this relationship has been cemented, our understanding of the multifaceted role of adipose tissue in metabolic heath and disease continues to evolve and expand. Heterogenous populations of cells that make up adipose tissue throughout the body generate diverse secretomes containing a mosaic of bioactive compounds with vast structural and signaling capabilities. While there are many reports highlighting the important role of adipose tissue endocrine signaling in insulin resistance and type 2 diabetes, the direct, local, paracrine effect of adipose tissue has received less attention. Recent studies have begun to underscore the importance of considering anatomically discrete adipose depots for their specific impact on local microenvironments and metabolic function in neighboring tissues as well as regulation of whole-body physiology. This article highlights the important role of adipose tissue paracrine signaling on metabolic function and insulin sensitivity in nearby tissues and organs, specifically focusing on visceral, pancreatic, subcutaneous, intermuscular, and perivascular adipose tissue depots.

A High Triglyceride-Glucose Index Value Is Associated With an Increased Risk of Carotid Plaque Burden in Subjects With Prediabetes and New-Onset Type 2 Diabetes: A Real-World Study

Background

The triglyceride-glucose (TyG) index has been proposed as a convincing indicator of insulin resistance and has been found to be associated with atherosclerosis among diabetic patients. However, the relationship between the TyG index and arteriosclerosis in subjects with prediabetes and new-onset type 2 diabetes (T2D) remains uncertain. The purpose of this study was to assess the degree of carotid plaque burden in patients with prediabetes and new-onset T2D and to investigate the association between the TyG index and the degree of carotid plaque burden in this population.

Methods

This was a cross-sectional observational study that included 716 subjects aged 40–70 years old with prediabetes or new-onset T2D. Demographic, anthropometric, and laboratory measurements were collected. Participants underwent carotid arteriosclerosis evaluation by ultrasonography, and the degree of atherosclerosis was evaluated according to the carotid plaque burden. The TyG index was calculated.

Results

The population was stratified into high or low TyG index groups according to the median TyG index value. Higher values were associated with a higher BMI and waist circumference as well as higher total cholesterol, triglyceride, low-density lipoprotein cholesterol, plasma glucose, glycated hemoglobin, fasting C-peptide, and C-reactive protein levels (P < 0.001). The high TyG index group had a higher atherosclerotic plaque burden than the low TyG index group (P < 0.001). Multiclassification logistic regression analysis showed that the TyG index was positively associated with a high plaque burden [odds ratio (OR): 16.706, 95% confidence interval (CI): 3.988–69.978, P = 0.000], while no association was found between the TyG index and a low/moderate plaque burden. This association remained consistent in the subgroup analysis. In multiple linear regression analysis, sex, age, and the TyG index were found to be independently associated with carotid plaque burden. For each unit increase in the TyG index, the risk of a high carotid plaque burden increased 1.595-fold.

Conclusion

A high TyG index was positively associated with a high carotid plaque burden in subjects with prediabetes and new-onset T2D. Clinicians should pay close attention to the TyG index to help these patients receive the greatest benefit from early intervention.

Inflammation in obesity, diabetes, and related disorders

Obesity leads to chronic, systemic inflammation and can lead to insulin resistance (IR), β-cell dysfunction, and ultimately type 2 diabetes (T2D). This chronic inflammatory state contributes to long-term complications of diabetes, including non-alcoholic fatty liver disease (NAFLD), retinopathy, cardiovascular disease, and nephropathy, and may underlie the association of type 2 diabetes with other conditions such as Alzheimer's disease, polycystic ovarian syndrome, gout, and rheumatoid arthritis. Here, we review the current understanding of the mechanisms underlying inflammation in obesity, T2D, and related disorders. We discuss how chronic tissue inflammation results in IR, impaired insulin secretion, glucose intolerance, and T2D and review the effect of inflammation on diabetic complications and on the relationship between T2D and other pathologies. In this context, we discuss current therapeutic options for the treatment of metabolic disease, advances in the clinic and the potential of immune-modulatory approaches.

Magnetic Resonance Imaging Assessment of Abdominal Ectopic Fat Deposition in Correlation With Cardiometabolic Risk Factors

PURPOSE

Ectopic fat accumulation and abdominal fat distribution may have different cardiometabolic risk profiles. This study aimed to assess the associations between various magnetic resonance imaging (MRI)-acquired fat depots and cardiometabolic risk factors.

METHODS

A total of 320 subjects with median age of 59 years, 148 men and 172 women, were enrolled in the study. Visceral adipose tissue (VAT) area and fat fraction (FF), subcutaneous adipose tissue (SAT) area and FF at the L1-L2 levels, preperitoneal adipose tissue (pPAT) area and FF, hepatic FF, pancreatic FF, and intramuscular FF were assessed by MRI FF maps. The associations of various MRI-acquired fat depots with blood pressure, glucose, and lipid were examined using sex-stratified linear regression. Logistic regression stratified by sex was used to analyze the association of various MRI-acquired fat depots with the risk of hypertension, T2DM, and dyslipidemia.

RESULTS

The intraclass correlation coefficient (ICC) values were >0.9, which suggested good interobserver and intraobserver agreement. VAT area, V/S, hepatic fat, pancreatic fat, and pPAT rather than SAT area were significantly associated with multiple cardiometabolic risk factors (all p < 0.05). However, the patterns of these correlations varied by sex and specific risk factors. Also, VAT and SAT FF were only significantly associated with multiple cardiometabolic risk factors in women (all p < 0.05).

CONCLUSIONS

VAT, hepatic fat, pancreatic fat, and pPAT were associated with cardiovascular metabolic risk factors independent of BMI. The patterns of these correlations were related to gender. These findings further the understanding of the association between ectopic fat deposition and cardiometabolic risk factors and help to better understand the obesity heterogeneity.

Adaptive immune cells shape obesity-associated type 2 diabetes mellitus and less prominent comorbidities

Obesity and type 2 diabetes mellitus (T2DM) are increasing in prevalence owing to decreases in physical activity levels and a shift to diets that include addictive and/or high-calorie foods. These changes are associated with the adoption of modern lifestyles and the presence of an obesogenic environment, which have resulted in alterations to metabolism, adaptive immunity and endocrine regulation. The size and quality of adipose tissue depots in obesity, including the adipose tissue immune compartment, are critical determinants of overall health. In obesity, chronic low-grade inflammation can occur in adipose tissue that can progress to systemic inflammation; this inflammation contributes to the development of insulin resistance, T2DM and other comorbidities. An improved understanding of adaptive immune cell dysregulation that occurs during obesity and its associated metabolic comorbidities, with an appreciation of sex differences, will be critical for repurposing or developing immunomodulatory therapies to treat obesity and/or T2DM-associated inflammation. This Review critically discusses how activation and metabolic reprogramming of lymphocytes, that is, T cells and B cells, triggers the onset, development and progression of obesity and T2DM. We also consider the role of immunity in under-appreciated comorbidities of obesity and/or T2DM, such as oral cavity inflammation, neuroinflammation in Alzheimer disease and gut microbiome dysbiosis. Finally, we discuss previous clinical trials of anti-inflammatory medications in T2DM and consider the path forward.

Physiological Changes and Pathological Pain Associated with Sedentary Lifestyle-Induced Body Systems Fat Accumulation and Their Modulation by Physical Exercise

A sedentary lifestyle is associated with overweight/obesity, which involves excessive fat body accumulation, triggering structural and functional changes in tissues, organs, and body systems. Research shows that this fat accumulation is responsible for several comorbidities, including cardiovascular, gastrointestinal, and metabolic dysfunctions, as well as pathological pain behaviors. These health concerns are related to the crosstalk between adipose tissue and body systems, leading to pathophysiological changes to the latter. To deal with these health issues, it has been suggested that physical exercise may reverse part of these obesity-related pathologies by modulating the cross talk between the adipose tissue and body systems. In this context, this review was carried out to provide knowledge about (i) the structural and functional changes in tissues, organs, and body systems from accumulation of fat in obesity, emphasizing the crosstalk between fat and body tissues; (ii) the crosstalk between fat and body tissues triggering pain; and (iii) the effects of physical exercise on body tissues and organs in obese and non-obese subjects, and their impact on pathological pain. This information may help one to better understand this crosstalk and the factors involved, and it could be useful in designing more specific training interventions (according to the nature of the comorbidity).

Poorer Muscle Quality and Quantity With ART Initiation Is Associated With Greater Inflammation and Immune Activation

BACKGROUND

We have previously shown that the initiation of antiretroviral therapy (ART) is associated with a decrease in skeletal muscle density (greater fat accumulation), suggesting that gains in lean body mass seen in many ART studies may reflect gains in low quality, fatty muscle. Here, we explore whether skeletal muscle density and area are associated with markers of inflammation and immune activation.

METHODS

ART-naïve people with HIV were randomized to raltegravir or ritonavir-boosted atazanavir or darunavir, each with tenofovir disoproxil fumarate/emtricitabine. Abdominal computed tomography scans from baseline and week 96 were reanalyzed for psoas density and area and correlations explored with inflammation [interleukin-6 (IL-6) and high-sensitivity C-reactive protein] and immune activation [soluble CD14 (sCD14), soluble CD163 (sCD163), and %CD38+HLADR+ on CD4+ or CD8+ T cells].

RESULTS

Two hundred twenty-two participants had available inflammation/immune activation markers and paired computed tomography scans. At baseline, lower psoas density (greater fat) correlated with higher IL-6 (r = -0.26, P < 0.001) and sCD163 (r -0.15, P = 0.03) and lower lean psoas area correlated with higher IL-6, high-sensitivity C-reactive protein, sCD14, sCD163, and %CD38+HLADR+ on CD4+ T cells (r = -0.30-0.13; all P ≤ 0.05). From baseline to week 96, greater percent decrease in total psoas density (more fat) correlated with greater increase in IL-6 (r = -0.14; P = 0.04); greater % decrease in lean psoas area correlated greater increases in IL-6, sCD14, sCD163, and %CD38+HLADR+ on CD8+ T cells (r = -0.15 to -0.18; all P < 0.04).

CONCLUSIONS

Greater fat infiltration within the psoas muscle (lower density) and greater loss in lean psoas muscle area were associated with higher inflammation and immune activation, which may portend important effects on muscle function and cardiometabolic risk.

Fibro-Adipogenic Progenitors: Versatile keepers of skeletal muscle homeostasis, beyond the response to myotrauma

While Fibro-Adipogenic Progenitors (FAPs) have been originally identified as muscle-interstitial mesenchymal cells activated in response to muscle injury and endowed with inducible fibrogenic and adipogenic potential, subsequent studies have expanded their phenotypic and functional repertoire and revealed their contribution to skeletal muscle response to a vast range of perturbations. Here we review the emerging contribution of FAPs to skeletal muscle responses to motor neuron injuries and to systemic physiological (e.g., exercise) or pathological metabolic (e.g., diabetes) perturbations. We also provide an initial blueprint of discrete sub-clusters of FAPs that are activated by specific perturbations and discuss their role in muscle adaptation to these conditions.

Chronic tissue inflammation and metabolic disease

In this review, Lee and Olefsky discuss the characteristics of chronic inflammation in the major metabolic tissues and how obesity triggers these events, including a focus on the role of adipose tissue hypoxia and macrophage-derived exosomes.

Obesity is the most common cause of insulin resistance, and the current obesity epidemic is driving a parallel rise in the incidence of T2DM. It is now widely recognized that chronic, subacute tissue inflammation is a major etiologic component of the pathogenesis of insulin resistance and metabolic dysfunction in obesity. Here, we summarize recent advances in our understanding of immunometabolism. We discuss the characteristics of chronic inflammation in the major metabolic tissues and how obesity triggers these events, including a focus on the role of adipose tissue hypoxia and macrophage-derived exosomes. Last, we also review current and potential new therapeutic strategies based on immunomodulation.

Adipose Tissue Dendritic Cells: Critical Regulators of Obesity-Induced Inflammation and Insulin Resistance

Chronic inflammation of the adipose tissue (AT) is a critical component of obesity-induced insulin resistance and type 2 diabetes. Adipose tissue immune cells, including AT macrophages (ATMs), AT dendritic cells (ATDCs), and T cells, are dynamically regulated by obesity and participate in obesity-induced inflammation. Among AT resident immune cells, ATDCs are master immune regulators and engage in crosstalk with various immune cells to initiate and regulate immune responses. However, due to confounding markers and lack of animal models, their exact role and contribution to the initiation and maintenance of AT inflammation and insulin resistance have not been clearly elucidated. This paper reviews the current understanding of ATDCs and their role in obesity-induced AT inflammation. We also provide the potential mechanisms by which ATDCs regulate AT inflammation and insulin resistance in obesity. Finally, this review offers perspectives on ways to better dissect the distinct functions and contributions of ATDCs to obesity.

C. Silva T, Bluemke DA, Budoff M, Barr RG, Allison MA, Bertoni AG, Post WS, Lima JAC, Demehri S. Adipose tissue biomarkers and type 2 diabetes incidence in normoglycemic participants in the MESArthritis Ancillary Study: A cohort study

BACKGROUND

Given the central role of skeletal muscles in glucose homeostasis, deposition of adipose depots beneath the fascia of muscles (versus subcutaneous adipose tissue [SAT]) may precede insulin resistance and type 2 diabetes (T2D) incidence. This study was aimed to investigate the associations between computed tomography (CT)-derived biomarkers for adipose tissue and T2D incidence in normoglycemic adults.

METHODS AND FINDINGS

This study was a population-based multiethnic retrospective cohort of 1,744 participants in the Multi-Ethnic Study of Atherosclerosis (MESA) with normoglycemia (baseline fasting plasma glucose [FPG] less than 100 mg/dL) from 6 United States of America communities. Participants were followed from April 2010 and January 2012 to December 2017, for a median of 7 years. The intermuscular adipose tissue (IMAT) and SAT areas were measured in baseline chest CT exams and were corrected by height squared (SAT and IMAT indices) using a predefined measurement protocol. T2D incidence, as the main outcome, was based on follow-up FPG, review of hospital records, or self-reported physician diagnoses. Participants' mean age was 69 ± 9 years at baseline, and 977 (56.0%) were women. Over a median of 7 years, 103 (5.9%) participants were diagnosed with T2D, and 147 (8.4%) participants died. The IMAT index (hazard ratio [HR]: 1.27 [95% confidence interval [CI]: 1.15-1.41] per 1-standard deviation [SD] increment) and the SAT index (HR: 1.43 [95% CI: 1.16-1.77] per 1-SD increment) at baseline were associated with T2D incidence over the follow-up. The associations of the IMAT and SAT indices with T2D incidence were attenuated after adjustment for body mass index (BMI) and waist circumference, with HRs of 1.23 (95% CI: 1.09-1.38) and 1.29 (95% CI: 0.96-1.74) per 1-SD increment, respectively. The limitations of this study include unmeasured residual confounders and one-time measurement of adipose tissue biomarkers.

CONCLUSIONS

In this study, we observed an association between IMAT at baseline and T2D incidence over the follow-up. This study suggests the potential role of intermuscular adipose depots in the pathophysiology of T2D.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00005487.

High extracellular ATP levels released through pannexin-1 channels mediate inflammation and insulin resistance in skeletal muscle fibres of diet-induced obese mice

AIMS/HYPOTHESIS

Skeletal muscle is a key target organ for insulin's actions and is the main regulator of blood glucose. In obese individuals and animal models, there is a chronic low-grade inflammatory state affecting highly metabolic organs, leading to insulin resistance. We have described that adult skeletal muscle fibres can release ATP to the extracellular medium through pannexin-1 (PANX1) channels. Besides, it is known that high extracellular ATP concentrations can act as an inflammatory signal. Here, we propose that skeletal muscle fibres from obese mice release high levels of ATP, through PANX1 channels, promoting inflammation and insulin resistance in muscle cells.

METHODS

C57BL/6J mice were fed with normal control diet (NCD) or high-fat diet (HFD) for 8 weeks. Muscle fibres were isolated from flexor digitorum brevis (FDB) muscle. PANX1-knockdown FDB fibres were obtained by in vivo electroporation of a short hairpin RNA Panx1 plasmid. We analysed extracellular ATP levels in a luciferin/luciferase assay. Gene expression was studied with quantitative real-time PCR (qPCR). Protein levels were evaluated by immunoblots, ELISA and immunofluorescence. Insulin sensitivity was analysed in a 2-NBDG (fluorescent glucose analogue) uptake assay, immunoblots and IPGTT.

RESULTS

HFD-fed mice showed significant weight gain and insulin resistance compared with NCD-fed mice. IL-6, IL-1β and TNF-α protein levels were increased in FDB muscle from obese mice. We observed high levels of extracellular ATP in muscle fibres from obese mice (197 ± 55 pmol ATP/μg RNA) compared with controls (32 ± 10 pmol ATP/μg RNA). ATP release in obese mice fibres was reduced by application of 100 μmol/l oleamide (OLE) and 5 μmol/l carbenoxolone (CBX), both PANX1 blockers. mRNA levels of genes linked to inflammation were reduced using OLE, CBX or 2 U/ml ATPase apyrase in muscle fibres from HFD-fed mice. In fibres from mice with pannexin-1 knockdown, we observed diminished extracellular ATP levels (78 ± 10 pmol ATP/μg RNA vs 252 ± 37 pmol ATP/μg RNA in control mice) and a lower expression of inflammatory markers. Moreover, a single pulse of 300 μmol/l ATP to fibres from control mice reduced insulin-mediated 2-NBDG uptake and promoted an elevation in mRNA levels of inflammatory markers. PANX-1 protein levels were increased two- to threefold in skeletal muscle from obese mice compared with control mice. Incubation with CBX increased Akt activation and 2-NBDG uptake in HFD fibres after insulin stimulation, rescuing the insulin resistance condition. Finally, in vivo treatment of HFD-fed mice with CBX (i.p. injection of 10 mg/kg each day) for 14 days, compared with PBS, reduced extracellular ATP levels in skeletal muscle fibres (51 ± 10 pmol ATP/μg RNA vs 222 ± 28 pmol ATP/μg RNA in PBS-treated mice), diminished inflammation and improved glycaemic management.

CONCLUSIONS/INTERPRETATION

In this work, we propose a novel mechanism for the development of inflammation and insulin resistance in the skeletal muscle of obese mice. We found that high extracellular ATP levels, released by overexpressed PANX1 channels, lead to an inflammatory state and insulin resistance in skeletal muscle fibres of obese mice.

Skeletal Lipocalin-2 Is Associated with Iron-Related Oxidative Stress in ob/ob Mice with Sarcopenia

Obesity and insulin resistance accelerate aging-related sarcopenia, which is associated with iron load and oxidative stress. Lipocalin-2 (LCN2) is an iron-binding protein that has been associated with skeletal muscle regeneration, but details regarding its role in obese sarcopenia remain unclear. Here, we report that elevated LCN2 levels in skeletal muscle are linked to muscle atrophy-related inflammation and oxidative stress in leptin-deficient ob/ob mice. RNA sequencing analyses indicated the LCN2 gene expression is enhanced in skeletal muscle of ob/ob mice with sarcopenia. In addition to muscular iron accumulation in ob/ob mice, expressions of iron homeostasis-related divalent metal transporter 1, ferritin, and hepcidin proteins were increased in ob/ob mice compared to lean littermates, whereas expressions of transferrin receptor and ferroportin were reduced. Collectively, these findings demonstrate that LCN2 functions as a potent proinflammatory factor in skeletal muscle in response to obesity-related sarcopenia and is thus a therapeutic candidate target for sarcopenia treatment.

The Effect of Obstructive Sleep Apnea and Continuous Positive Airway Pressure Therapy on Skeletal Muscle Lipid Content in Obese and Nonobese Men

Obstructive sleep apnea (OSA), independently of obesity (OBS), predisposes to insulin resistance (IR) for largely unknown reasons. Because OSA-related intermittent hypoxia triggers lipolysis, overnight increases in circulating free fatty acids (FFAs) including palmitic acid (PA) may lead to ectopic intramuscular lipid accumulation potentially contributing to IR. Using 3-T-¹H-magnetic resonance spectroscopy, we therefore compared intramyocellular and extramyocellular lipid (IMCL and EMCL) in the vastus lateralis muscle at approximately 7 am between 26 male patients with moderate-to-severe OSA (17 obese, 9 nonobese) and 23 healthy male controls (12 obese, 11 nonobese). Fiber type composition was evaluated by muscle biopsies. Moreover, we measured fasted FFAs including PA, glycated hemoglobin A_1c, thigh subcutaneous fat volume (ScFAT, 1.5-T magnetic resonance tomography), and maximal oxygen uptake (VO₂max). Fourteen patients were reassessed after continuous positive airway pressure (CPAP) therapy. Total FFAs and PA were significantly (by 178% and 166%) higher in OSA patients vs controls and correlated with the apnea-hypopnea index (AHI) (r ≥ 0.45, P < .01). Moreover, IMCL and EMCL were 55% (P < .05) and 40% (P < .05) higher in OSA patients, that is, 114% and 103% in nonobese, 24.4% and 8.4% in obese participants (with higher control levels). Overall, PA, FFAs (minus PA), and ScFAT significantly contributed to IMCL (multiple r = 0.568, P = .002). CPAP significantly decreased EMCL (–26%) and, by trend only, IMCL, total FFAs, and PA. Muscle fiber composition was unaffected by OSA or CPAP. Increases in IMCL and EMCL are detectable at approximately 7 am in OSA patients and are partly attributable to overnight FFA excesses and high ScFAT or body mass index. CPAP decreases FFAs and IMCL by trend but significantly reduces EMCL.

Obesity-induced alterations to the immunoproteasome: a potential link to intramuscular lipotoxicity

Although the mechanisms are unclear, inflammation and/or lipotoxicity likely contribute to obese muscle pathology. The immunoproteasome is known to respond to inflammation and oxidative damage and may aid muscle regeneration. We sought to determine whether diet-induced obesity (DIO) influences the immunoproteasome subunits LMP7 and MECL-1 in mouse muscle with and without exercise-induced muscle damage (EIMD). Muscle mass, regeneration, macrophage content and lipid peroxidation (8-isoprostane) were also assessed. Sixty male, 4-week-old C57BL/6J mice were fed a high-fat (HFD) or low-fat diet for 12 weeks. Mice were then subdivided into EIMD or no muscle damage (NMD) groups. The gastrocnemius muscle was excised 1 or 5 days after EIMD, producing 6 groups (n = 10/group). Body mass was greater; however, relative gastrocnemius mass was lower in HFD-fed mice. Despite no macrophage or MECL-1 alterations, LMP7 and 8-isoprostane were increased in obese mice in the NMD and 1 day post-EIMD groups. However, 8-isoprostane was reduced in obese mice 5 days post-EIMD, and accompanied by increased muscle LMP7, MECL-1 and macrophage content. Consequently, DIO may impair the immunoproteasome's ability to control muscle lipid peroxidation but is reversed with eccentric exercise. Although muscle regeneration was unchanged, immunoproteasome dysregulation occurs in obese muscle and may contribute to muscle pathology. Novelty: DIO may impair the intramuscular immunoproteasome response to lipid peroxidation. Acute eccentric exercise may protect obese individuals from muscle lipotoxicity via immunoproteasome upregulation.

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.

Effects of 16 months of high intensity resistance training on thigh muscle fat infiltration in elderly men with osteosarcopenia

Osteosarcopenia is characterized by a progressive decline in muscle function and bone strength and associated with muscle fat accumulation. This study aimed to determine the effect of long-term high intensity resistance training (HIRT) on thigh muscle fat infiltration in older men with osteosarcopenia. Forty-three community-dwelling men (72 years and older) were randomly assigned to either an exercise group (EG, n = 21) or an inactive control group (CG, n = 22). EG participants performed a supervised single-set exercise training with high effort two times per week. Participants of both groups were individually provided with dietary protein to reach a cumulative intake of 1.5-1.6 g/kg/day or 1.2-1.3 g/kg/day (EG/CG), respectively, and Up to 10,000 IE/week of Vitamin-D were supplemented in participants with 25 OH Vitamin-D 3 levels below 100 nmol/l. Magnetic resonance (MR) imaging was performed to determine muscle and adipose tissue volume and fat fraction of the thigh. At baseline, there were no significant differences between the two groups. After 16 month,, there were significant training effects of 15% (p = 0.004) on intermuscular adipose tissue (IMAT) volume, which increased in the CG (p = 0.012) and was stable in the EG. In parallel, fat fraction within the deep fascia of the thigh (Baseline, EG: 18.2 vs CG: 15.5, p = 0.16) significantly differed between the groups (Changes, EG: 0.77% vs. CG: 7.7%, p = 0.009). The study confirms the role of fat infiltration of the muscles as an advanced imaging marker in osteosarcopenia and the favorable effects of HIRT on adipose tissue volume of the thigh, in men with osteosarcopenia.

NLRP3 Inflammasome: Potential Role in Obesity Related Low-Grade Inflammation and Insulin Resistance in Skeletal Muscle

Among multiple mechanisms, low-grade inflammation is critical for the development of insulin resistance as a feature of type 2 diabetes. The nucleotide-binding oligomerization domain-like receptor family (NOD-like) pyrin domain containing 3 (NLRP3) inflammasome has been linked to the development of insulin resistance in various tissues; however, its role in the development of insulin resistance in the skeletal muscle has not been explored in depth. Currently, there is limited evidence that supports the pathological role of NLRP3 inflammasome activation in glucose handling in the skeletal muscle of obese individuals. Here, we have centered our focus on insulin signaling in skeletal muscle, which is the main site of postprandial glucose disposal in humans. We discuss the current evidence showing that the NLRP3 inflammasome disturbs glucose homeostasis. We also review how NLRP3-associated interleukin and its gasdermin D-mediated efflux could affect insulin-dependent intracellular pathways. Finally, we address pharmacological NLRP3 inhibitors that may have a therapeutical use in obesity-related metabolic alterations.

Association of Inflammatory Metabolic Activity of Psoas Muscle and Acute Myocardial Infarction: A Preliminary Observational Study with 18F-FDG PET/CT

Inflamed skeletal muscle promotes chronic inflammation in atherosclerotic plaques, thereby contributing to the increased risk of coronary artery disease (CAD). In this study, we evaluated the metabolic activity of psoas muscle, using ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT), and its association with carotid artery inflammation and acute myocardial infarction (AMI). In total, 90 participants (32 AMI, 33 chronic stable angina (CSA), and 25 control) were enrolled in this prospective study. Metabolic activity of skeletal muscle (SM) was measured by using maximum standardized uptake value (SUVmax) of psoas muscle, and corresponding psoas muscle area (SM area) was also measured. Carotid artery inflammation was evaluated by using the target-to background ratio (TBR) of carotid artery. SM SUVmax was highest in AMI, intermediate in CSA, and lowest in control group. SM SUVmax was significantly correlated with carotid artery TBR and systemic inflammatory surrogate markers. Furthermore, SM SUVmax was independently associated with carotid artery TBR and showed better predictability than SM area for the prediction of AMI. Metabolic activity of psoas muscle assessed by ¹⁸F-FDG PET/CT was associated with coronary plaque vulnerability and synchronized with the carotid artery inflammation in the participants with CAD. Furthermore, it may also be useful to predict AMI.

Mechanism and Basis of Traditional Chinese Medicine Against Obesity: Prevention and Treatment Strategies

In the last few decades, the incidences of obesity and related metabolic disorders worldwide have increased dramatically. Major pathophysiology of obesity is termed "lipotoxicity" in modern western medicine (MWM) or "dampness-heat" in traditional Chinese medicine (TCM). "Dampness-heat" is a very common and critically important syndrome to guild clinical treatment in TCM. However, the pathogenesis of obesity in TCM is not fully clarified, especially by MWM theories compared to TCM. In this review, the mechanism underlying the action of TCM in the treatment of obesity and related metabolic disorders was thoroughly discussed, and prevention and treatment strategies were proposed accordingly. Hypoxia and inflammation caused by lipotoxicity exist in obesity and are key pathophysiological characteristics of "dampness-heat" syndrome in TCM. "Dampness-heat" is prevalent in chronic low-grade systemic inflammation, prone to insulin resistance (IR), and causes variant metabolic disorders. In particular, the MWM theories of hypoxia and inflammation were applied to explain the "dampness-heat" syndrome of TCM, and we summarized and proposed the pathological path of obesity: lipotoxicity, hypoxia or chronic low-grade inflammation, IR, and metabolic disorders. This provides significant enrichment to the scientific connotation of TCM theories and promotes the modernization of TCM.