Leptin administration favors muscle mass accretion by decreasing FoxO3a and increasing PGC-1alpha in ob/ob mice

Overexpression of PRDM16 improves muscle function after rotator cuff tears

BACKGROUND

Muscle atrophy, fibrosis, and fatty infiltration are commonly seen in rotator cuff tears (RCTs), which are critical factors that directly determine the clinical outcomes for patients with this injury. Therefore, improving muscle quality after RCT is crucial in improving the clinical outcome of tendon repair. In recent years, it has been discovered that adults have functional beige/brown adipose tissue (BAT) that can secrete batokines to promote muscle growth. PRDM16, a PR-domain-containing protein, was discovered with the ability to determine the brown fat cell fate and stimulate its development. Thus, the goal of this study was to discover the role of PRDM16 in improving muscle function after massive tendon tears using a transgenic mouse model with an elevated level of PRDM16 expression.

METHODS

Transgenic aP2-driven PRDM16-overexpressing mice and C57BL/6J mice underwent unilateral supraspinatus (SS) tendon transection and suprascapular nerve transection (TTDN) as described previously (n = 8 in each group). DigiGait was performed to evaluate forelimb function at 6 weeks post the TTDN injury. Bilateral SS muscles, interscapular brown fat, epididymal white fat, and inguinal beige fat were harvested for analysis. The expression of PRDM16 in adipose tissue was detected by Western blot. Masson Trichrome staining was conducted to evaluate the muscle fibrosis, and Oil Red O staining was used to determine the fat infiltration. Muscle fiber type was determined by major histocompatibility complex (MHC) expression via immunostaining. All data were presented in the form of mean ± standard deviation. t test and 2-way analysis of variance was performed to determine a statistically significant difference between groups. Significance was considered when P < .05.

RESULTS

Western blot data showed an increased expression of PRDM16 protein in both white and brown fat in PRDM16-overexpressing mice compared with wild-type (WT) mice. Even though PRDM16 overexpression had no effect on increasing muscle weight, it significantly improved the forelimbs function with longer brake, stance, and stride time and larger stride length and paw area in mice after RCT. Additionally, PRDM16-overexpressing mice showed no difference in the amount of fibrosis when compared to WT mice; however, they had a significantly reduced area of fatty infiltration. These mice also exhibited abundant MHC-IIx fiber percentage in the supraspinatus muscle after TTDN.

CONCLUSION

Overexpression of PRDM16 significantly improved muscle function and reduced fatty infiltration after rotator cuff tears. Promoting BAT activity is beneficial in improving rotator cuff muscle quality and shoulder function after RCT.

Control of muscle satellite cell function by specific exercise-induced cytokines and their applications in muscle maintenance

Exercise is recognized to play an observable role in improving human health, especially in promoting muscle hypertrophy and intervening in muscle mass loss-related diseases, including sarcopenia. Recent rapid advances have demonstrated that exercise induces the release of abundant cytokines from several tissues (e.g., liver, muscle, and adipose tissue), and multiple cytokines improve the functions or expand the numbers of adult stem cells, providing candidate cytokines for alleviating a wide range of diseases. Muscle satellite cells (SCs) are a population of muscle stem cells that are mitotically quiescent but exit from the dormancy state to become activated in response to physical stimuli, after which SCs undergo asymmetric divisions to generate new SCs (stem cell pool maintenance) and commit to later differentiation into myocytes (skeletal muscle replenishment). SCs are essential for the postnatal growth, maintenance, and regeneration of skeletal muscle. Emerging evidence reveals that exercise regulates muscle function largely via the exercise-induced cytokines that govern SC potential, but this phenomenon is complicated and confusing. This review provides a comprehensive integrative overview of the identified exercise-induced cytokines and the roles of these cytokines in SC function, providing a more complete picture regarding the mechanism of SC homeostasis and rejuvenation therapies for skeletal muscle.

Pathophysiology of sarcopenia: Genetic factors and their interplay with environmental factors

Sarcopenia is a geriatric disorder characterized by a progressive decline in muscle mass and function. This disorder has been associated with a range of adverse health outcomes, including fractures, functional deterioration, and increased mortality. The pathophysiology of sarcopenia is highly complex and multifactorial, involving both genetic and environmental factors as key contributors. This review consolidates current knowledge on the genetic factors influencing the pathogenesis of sarcopenia, particularly focusing on the altered gene expression of structural and metabolic proteins, growth factors, hormones, and inflammatory cytokines. While the influence of environmental factors such as physical inactivity, chronic diseases, smoking, alcohol consumption, and sleep disturbances on sarcopenia is relatively well understood, there is a dearth of studies examining their mechanistic roles. Therefore, this review emphasizes the interplay between genetic and environmental factors, elucidating their cumulative role in exacerbating the progression of sarcopenia beyond their individual effects. The unique contribution of this review lies in synthesizing the latest evidence on the genetic factors and their interaction with environmental factors, aiming to inform the development of novel therapeutic or preventive interventions for sarcopenia.

Preclinical, randomized phase 1, and compassionate use evaluation of REGN4461, a leptin receptor agonist antibody for leptin deficiency

Deficiency in the adipose-derived hormone leptin or leptin receptor signaling causes class 3 obesity in individuals with genetic loss-of-function mutations in leptin or its receptor LEPR and metabolic and liver disease in individuals with hypoleptinemia secondary to lipoatrophy such as in individuals with generalized lipodystrophy. Therapies that restore leptin-LEPR signaling may resolve these metabolic sequelae. We developed a fully human monoclonal antibody (mAb), REGN4461 (mibavademab), that activates the human LEPR in the absence or presence of leptin. In obese leptin knockout mice, REGN4461 normalized body weight, food intake, blood glucose, and insulin sensitivity. In a mouse model of generalized lipodystrophy, REGN4461 alleviated hyperphagia, hyperglycemia, insulin resistance, dyslipidemia, and hepatic steatosis. In a phase 1, randomized, double-blind, placebo-controlled two-part study, REGN4461 was well tolerated with an acceptable safety profile. Treatment of individuals with overweight or obesity with REGN4461 decreased body weight over 12 weeks in those with low circulating leptin concentrations (<8 ng/ml) but had no effect on body weight in individuals with higher baseline leptin. Furthermore, compassionate-use treatment of a single patient with atypical partial lipodystrophy and a history of undetectable leptin concentrations associated with neutralizing antibodies to metreleptin was associated with noteable improvements in circulating triglycerides and hepatic steatosis. Collectively, these translational data unveil an agonist LEPR mAb that may provide clinical benefit in disorders associated with relatively low leptin concentrations.

Incident low muscle mass is associated with greater lung disease and lower circulating leptin in a tobacco-exposed longitudinal cohort

BACKGROUND

Muscle loss is prevalent in chronic obstructive pulmonary disease (COPD). Prior studies evaluating musculoskeletal dysfunction in COPD have focused on individuals with baseline low muscle mass. Currently, there is limited data evaluating clinical characteristics and outcomes associated with progression to incident low muscle mass in a tobacco-exposed cohort of individuals with baseline normal muscle mass.

METHODS

We evaluated 246 participants from a single-center longitudinal tobacco-exposed cohort with serial spirometry, thoracic imaging, dual energy x-ray absorptiometry (DXA) measurements, walk testing, and plasma adipokine measurements. DXA-derived fat free mass index (FFMI) and appendicular skeletal mass index (ASMI) were used as surrogates for muscle mass. Participants with incident low muscle mass (LM) at follow-up were characterized by FFMI < 18.4 kg/m2 in males and < 15.4 kg/m2 in females and/or ASMI < 7.25 kg/m2 in males and < 5.67 kg/m2 in females.

RESULTS

Twenty-five (10%) participants progressed to incident low muscle mass at follow-up. At baseline, the LM subgroup had greater active smoking prevalence (60% v. 38%, p = 0.04), lower FFMI (17.8 ± 1.7 kg/m2 v. 19.7 ± 2.9 kg/m2, p = 0.002), lower ASMI (7.3 ± 0.9 kg/m2 v. 8.2 ± 1.2 kg/m2, p = 0.0003), and lower plasma leptin (14.9 ± 10.1 ng/mL v. 24.0 ± 20.9 ng/mL, p = 0.04). At follow-up, the LM subgroup had higher COPD prevalence (68% v. 43%, p = 0.02), lower FEV1/FVC (0.63 ± 0.12 v. 0.69 ± 0.12, p = 0.02), lower %DLco (66.5 ± 15.9% v. 73.9 ± 16.8%, p = 0.03), and higher annual rate of FFMI decline (-0.17 kg/m2/year v. -0.04 kg/m2/year, p = 0.006). There were no differences in age, gender distribution, pack years smoking history, or walk distance.

CONCLUSIONS

We identified a subgroup of tobacco-exposed individuals with normal baseline muscle mass who progressed to incident DXA-derived low muscle mass. This subgroup demonstrated synchronous lung disease and persistently low circulating leptin levels. Our study suggests the importance of assessing for muscle loss in conjunction with lung function decline when evaluating individuals with tobacco exposure.

Role of adipokines in sarcopenia

ABSTRACT

Sarcopenia is an age-related disease that mainly involves decreases in muscle mass, muscle strength and muscle function. At the same time, the body fat content increases with aging, especially the visceral fat content. Adipose tissue is an endocrine organ that secretes biologically active factors called adipokines, which act on local and distant tissues. Studies have revealed that some adipokines exert regulatory effects on muscle, such as higher serum leptin levels causing a decrease in muscle function and adiponectin inhibits the transcriptional activity of Forkhead box O3 (FoxO3) by activating peroxisome proliferators-activated receptor-γ coactivator -1α (PGC-1α) and sensitizing cells to insulin, thereby repressing atrophy-related genes (atrogin-1 and muscle RING finger 1 [MuRF1]) to prevent the loss of muscle mass. Here, we describe the effects on muscle of adipokines produced by adipose tissue, such as leptin, adiponectin, resistin, mucin and lipocalin-2, and discuss the importance of these adipokines for understanding the development of sarcopenia.

Interplay of skeletal muscle and adipose tissue: sarcopenic obesity

Sarcopenic obesity is becoming a global health concern, owing to the rising older population, causing cardiometabolic morbidity and mortality. Loss of muscle exceeding normal age-related changes has been revealed to be associated with obesity, aggravating each other through complex interactions. Physiological regeneration and proliferation of muscle tissue are achieved through harmonious processes of regulated inflammation, autophagy, muscle satellite cell proliferation, and signaling molecule function. Adipokines and myokines are signaling molecules from adipose tissue and muscle, respectively, that exert autocrine, paracrine, and endocrine effects on fat and muscle tissues. These signaling molecules interact with each other to regulate metabolic homeostasis. However, excessive adiposity creates pro-inflammatory conditions, leading to metabolic disorders and the disorganization of systemic homeostasis. Therefore, obesity impedes muscle tissue regeneration and induces the loss of muscle mass and function. Numerous studies have attempted to demonstrate the pathophysiological interaction between sarcopenia and obesity, but the interwoven matrix of the relationship between myokines and adipokines has made it difficult for researchers to understand them. This review briefly describes updated information about the crosstalk between muscle and adipose tissue.

The crosstalk between BAT thermogenesis and skeletal muscle dysfunction

Metabolic defects increase the risk of skeletal muscle diseases, and muscle impairment might worsen metabolic disruption, leading to a vicious cycle. Both brown adipose tissue (BAT) and skeletal muscle play important roles in non-shivering thermogenesis to regulate energy homeostasis. BAT regulates body temperature, systemic metabolism, and seretion of batokines that have positive or negative impacts on skeletal muscle. Conversely, muscle can secrete myokines that regulate BAT function. This review explained the crosstalk between BAT and skeletal muscle, and then discussed the batokines and highlighted their impact on skeletal muscle under physiological conditions. BAT is now considered a potential therapeutic target for obesity and diabetes treatment. Moreover, manipulation of BAT may be an attractive approach for the treatment of muscle weakness by correcting metabolic deficits. Therefore, exploring BAT as a potential treatment for sarcopenia could be a promising avenue for future research.

Comparative transcriptome analysis of longissimus dorsi tissues with different intramuscular fat contents from Guangling donkeys

Background

Donkey meat has low fat and high protein contents and is rich in various unsaturated fatty acids and trace elements that are beneficial to human digestion and absorption. IMF (intramuscular fat), also known as marbling, is an important indicator of the lean meat to fat ratio, which directly affects the tenderness and juiciness of the meat. At present, the underlying molecular variations affecting IMF content among donkey breeds are unclear. The Guangling donkey is an indigenous species in China. This study explored candidate regulatory genes that affect IMF content in Guangling donkeys. The IMF content of the longissimus dorsi muscle in 30 Guangling donkeys was measured. Six donkeys of similar age were selected according to age factors and divided into two groups, the high (H) and low (L) fat groups, according to their IMF content.

Results

RNA-seq technology was used to compare the muscle transcriptome between the two groups. More than 75.0% of alternative splicing (AS) events were of the skipped exon (SE) type. A total of 887 novel genes were identified; only 386 novel genes were aligned to the annotation information of various databases. Transcriptomics analysis revealed 167 differentially expressed genes (DEGs), of which 64 were upregulated and 103 were downregulated between the H and L groups. Gene ontology analysis showed that the DEGs were enriched in multiple biological processes and pathways that are related to adipocyte differentiation, lipid synthesis, and neutral lipid metabolism. KEGG pathway analysis suggested that arachidonic acid metabolism, the HIF-1 signalling pathway, fructose and mannose metabolism, glycerophospholipid metabolism, and the AMPK signalling pathway were involved in lipid deposition. In addition, a gene–gene interaction network was constructed that revealed that the DEGs, including SCD, LEPR, CIDEA, DLK1, DGAT2, ITGAL, HMOX1, WNT10B, and DGKA, had significant roles in adipocyte differentiation and adipogenesis. The selected DEGs were further validated by qRT–PCR.

Conclusion

This study improves the in-depth understanding of gene regulation and protein expression regarding IMF deposition and lays a basis for subsequent molecular breeding studies in Guangling donkeys.

Leptin mediates the regulation of muscle mass and strength by adipose tissue

Adipose tissue secretes numerous cytokines (termed 'adipokines') that have known or hypothesized actions on skeletal muscle. The majority of adipokines have been implicated in the pathological link between excess adipose and muscle insulin resistance, but approximately half also have documented in vitro effects on myogenesis and/or hypertrophy. This complexity suggests a potential dual role for adipokines in the regulation of muscle mass in homeostasis and the development of pathology. In this study, we used lipodystrophic 'fat-free' mice to demonstrate that adipose tissue is indeed necessary for the development of normal muscle mass and strength. Fat-free mice had significantly reduced mass (∼15%) and peak contractile tension (∼20%) of fast-twitch muscles, a slowing of contractile dynamics and decreased cross-sectional area of fast twitch fibres compared to wild-type littermates. These deficits in mass and contractile tension were fully rescued by reconstitution of ∼10% of normal adipose mass, indicating that this phenotype is the direct consequence of absent adipose. We then showed that the rescue is solely mediated by the adipokine leptin, as similar reconstitution of adipose from leptin-knockout mice fails to rescue mass or strength. Together, these data indicate that the development of muscle mass and strength in wild-type mice is dependent on adipose-secreted leptin. This finding extends our current understanding of the multiple roles of adipokines in physiology as well as disease pathophysiology to include a critical role for the adipokine leptin in muscle homeostasis. KEY POINTS: Adipose-derived cytokines (adipokines) have long been implicated in the pathogenesis of insulin resistance in obesity but likely have other under-appreciated roles in muscle physiology. Here we use a fat-free mouse to show that adipose tissue is necessary for the normal development of muscle mass and strength. Through add-back of genetically modified adipose tissue we show that leptin is the key adipokine mediating this regulation. This expands our understanding of leptin's role in adipose-muscle signalling to include development and homeostasis and adds the surprising finding that leptin is the sole mediator of the maintenance of muscle mass and strength by adipose tissue.

Role of insulin resistance and the gut microbiome on urine oxalate excretion in ob/ob mice

Ob/ob mice have recently emerged as a model for obesity-related hyperoxaluria as they are obese and excrete more urine oxalate compared to wild type mice. Ob/ob mice are deficient of leptin and develop obesity with hyperphagia and hyperinsulinemia. We hypothesized that insulin resistance and the gut microbiome contribute to hyperoxaluria in ob/ob mice. We developed a new liquid chromatography-mass spectrometry assay for urine oxalate and first compared urine oxalate excretion in ob/ob mice before and after ablation of intestinal bacteria with a standard antibiotic cocktail. We then compared urine oxalate excretion in ob/ob mice before and after leptin replacement or pioglitazone treatment, two maneuvers that reduce insulin resistance in ob/ob mice. Ob/ob mice excreted more oxalate into the urine in a 24-h period compared to wild type mice, but antibiotic, leptin, or pioglitazone treatment did not change urine oxalate excretion in ob/ob mice. Unexpectedly, we found that when food intake was carefully matched between ob/ob and wild type mice, the amount of 24-h urine oxalate excretion did not differ between the two mouse strains, suggesting that ob/ob mice excrete more urine oxalate because of hyperphagia. Since the level of urine oxalate excretion in wild type mice in our study was higher than those reported in prior studies, future work will be needed to standardize the measurement of urine oxalate and to define the range of urine oxalate excretion in wild type mice so that accurate and valid comparisons can be made between wild type mice and ob/ob mice or other mouse models.

Obesity attenuates inflammation, protein catabolism, dyslipidaemia, and muscle weakness during sepsis, independent of leptin

BACKGROUND

Muscle weakness is a frequently occurring complication of sepsis, associated with increased morbidity and mortality. Interestingly, obesity attenuates sepsis-induced muscle wasting and weakness. As the adipokine leptin is strongly elevated in obesity and has been shown to affect muscle homeostasis in non-septic conditions, we aimed to investigate whether leptin mediates the protective effect of obesity on sepsis-induced muscle weakness.

METHODS

In a mouse model of sepsis, we investigated the effects of genetic leptin inactivation in obese mice (leptin-deficient obese mice vs. diet-induced obese mice) and of leptin supplementation in lean mice (n = 110). We assessed impact on survival, body weight and composition, markers of muscle wasting and weakness, inflammation, and lipid metabolism. In human lean and overweight/obese intensive care unit (ICU) patients, we assessed markers of protein catabolism (n = 1388) and serum leptin (n = 150).

RESULTS

Sepsis mortality was highest in leptin-deficient obese mice (53% vs. 23% in diet-induced obese mice and 37% in lean mice, P = 0.03). Irrespective of leptin, after 5 days of sepsis, lean mice lost double the amount of lean body mass than obese mice (P < 0.0005). Also, irrespective of leptin, obese mice maintained specific muscle force up to healthy levels (P = 0.3) whereas lean mice suffered from reduced specific muscle force (72% of healthy controls, P < 0.0002). As compared with lean septic mice, both obese septic groups had less muscle atrophy, liver amino acid catabolism, and inflammation with a 50% lower plasma TNFα increase (P < 0.005). Conversely, again mainly irrespective of leptin, obese mice lost double amount of fat mass than lean mice after 5 days of sepsis (P < 0.0001), showed signs of increased lipolysis and ketogenesis, and had higher plasma HDL and LDL lipoprotein concentrations (P ≤ 0.01 for all). Muscle fibre type composition was not altered during sepsis, but a higher atrophy sensitivity of type IIb fibres compared with IIa and IIx fibres was observed, independent of obesity or leptin. After 5 days of critical illness, serum leptin was higher (P < 0.0001) and the net waste of nitrogen (P = 0.006) and plasma urea-to-creatinine ratio (P < 0.0001) was lower in overweight/obese compared with lean ICU human patients.

CONCLUSIONS

Leptin did not mediate the protective effect of obesity against sepsis-induced muscle wasting and weakness in mice. Instead, obesity-independent of leptin-attenuated inflammation, protein catabolism, and dyslipidaemia, pathways that may play a role in the observed muscle protection.

Higher Serum Leptin Levels are Associated with a Reduced Risk of Sarcopenia but a Higher Risk of Dynapenia Among Older Adults

Background

Leptin plays an important role in regulating the energy homeostasis of fat and muscle. Paradoxical findings existed between serum leptin levels and muscle health conditions. Here, we aimed to investigate the relationship between serum leptin levels and the risk of sarcopenia or dynapenia among older adults.

Methods

Adults aged 65 and older living in the community were recruited at annual health checkups. Body composition, gait speed, and handgrip strength were examined. The cutoff values of muscle mass and strength to define sarcopenia and dynapenia were based on the consensus by the Asia Working Group of Sarcopenia in 2019. Serum leptin level was measured by an immunoassay.

Results

Four hundred sixty participants (55.65% females) were enrolled. There were 16.08% and 23.91% with sarcopenia and dynapenia, respectively. Higher serum leptin levels were positively associated with muscle and fat mass but negatively associated with handgrip strength and gait speed for both sexes. In the logistic regression models adjusted for various confounders, a higher serum leptin level was associated with an increased risk of dynapenia with dose-response effects among both male and female participants (odds ratio [OR]=3.74, 95% confidence interval [CI]= 0.99–14.17; OR= 3.32, 95% CI=1.03–10.74, respectively), and a positive trend existed in both genders (p for trend=0.040 and 0.042, respectively). In contrast, a higher leptin level was associated with a reduced risk of sarcopenia with dose-response trends for both sexes (OR= 0.06, 95% CI=0.01–0.48; OR= 0.26, 95% CI=0.06–1.17, respectively) in models of multivariate logistic regression analyses, and a negative trend existed in both genders (p for trend = 0.002 and 0.023, respectively).

Conclusion

A positive trend existed between the serum leptin level and the dynapenia risk, whereas it revealed a negative trend in the serum leptin level and sarcopenia risk in both male and female elderly individuals. The biological mechanisms underlying its negative association with muscle strength but its positive association with muscle mass warrants further investigation.

Modified UCN2 peptide treatment improves skeletal muscle mass and function in mouse models of obesity-induced insulin resistance

BACKGROUND

Type 2 diabetes and obesity are often seen concurrently with skeletal muscle wasting, leading to further derangements in function and metabolism. Muscle wasting remains an unmet need for metabolic disease, and new approaches are warranted. The neuropeptide urocortin 2 (UCN2) and its receptor corticotropin releasing factor receptor 2 (CRHR2) are highly expressed in skeletal muscle and play a role in regulating energy balance, glucose metabolism, and muscle mass. The aim of this study was to investigate the effects of modified UCN2 peptides as a pharmaceutical therapy to counteract the loss of skeletal muscle mass associated with obesity and casting immobilization.

METHODS

High-fat-fed mice (C57Bl/6J; 26 weeks old) and ob/ob mice (11 weeks old) were injected daily with a PEGylated (Compound A) and non-PEGylated (Compound B) modified human UCN2 at 0.3 mg/kg subcutaneously for 14 days. A separate group of chow-fed C57Bl/6J mice (12 weeks old) was subjected to hindlimb cast immobilization and, after 1 week, received daily injections with Compound A. In vivo functional tests were performed to measure protein synthesis rates and skeletal muscle function. Ex vivo functional and molecular tests were performed to measure contractile force and signal transduction of catabolic and anabolic pathways in skeletal muscle.

RESULTS

Skeletal muscles (extensor digitorum longus, soleus, and tibialis anterior) from high-fat-fed mice treated with Compound A were ~14% heavier than muscles from vehicle-treated mice. Chronic treatment with modified UCN2 peptides altered the expression of structural genes and transcription factors in skeletal muscle in high-fat diet-induced obesity including down-regulation of Trim63 and up-regulation of Nr4a2 and Igf1 (P < 0.05 vs. vehicle). Signal transduction via both catabolic and anabolic pathways was increased in tibialis anterior muscle, with increased phosphorylation of ribosomal protein S6 at Ser^235/236 , FOXO1 at Ser²⁵⁶ , and ULK1 at Ser³¹⁷ , suggesting that UCN2 treatment modulates protein synthesis and degradation pathways (P < 0.05 vs. vehicle). Acutely, a single injection of Compound A in drug-naïve mice had no effect on the rate of protein synthesis in skeletal muscle, as measured via the surface sensing of translation method, while the expression of Nr4a3 and Ppargc1a4 was increased (P < 0.05 vs. vehicle). Compound A treatment prevented the loss of force production from disuse due to casting. Compound B treatment increased time to fatigue during ex vivo contractions of fast-twitch extensor digitorum longus muscle. Compound A and B treatment increased lean mass and rates of skeletal muscle protein synthesis in ob/ob mice.

CONCLUSIONS

Modified human UCN2 is a pharmacological candidate for the prevention of the loss of skeletal muscle mass associated with obesity and immobilization.

The role of endocrine hormones in the pathogenesis of adolescent idiopathic scoliosis

Adolescent idiopathic scoliosis (AIS) is a common spinal deformity characterized by changes in the three-dimensional structure of the spine. It usually initiates during puberty, the peak period of human growth when the secretion of numerous hormones is changing, and it is more common in females than in males. Accumulating evidence shows that the abnormal levels of many hormones including estrogen, melatonin, growth hormone, leptin, adiponectin and ghrelin, may be related to the occurrence and development of AIS. The purpose of this review is to provide a summary and critique of the research published on each hormone over the past 20 years, and to highlight areas for future study. It is hoped that the presentation will help provide a better understanding of the role of endocrine hormones in the pathogenesis of AIS.

Benchmarking the Discriminatory Performance of Body Mass Index and Body Fat for Obesity Detection in Patients Treated by Intragastric Balloon

INTRODUCTION/PURPOSE

The accuracy of body mass index (BMI) in detecting obesity in patients treated by intragastric balloon (IGB) remains still speculative. We aimed to determine the discriminatory performance of BMI as an estimate of excess body fat (%BF) in an IGB-treated population.

MATERIAL AND METHODS

Retrospective analysis of prospectively collected data of 476 patients who completed the 6-month IGB treatment period and were subjected to body composition analysis. We evaluated the relationship between BMI and %BF or lean mass and the diagnostic performance of BMI ≥ 30 kg/m² for adipose tissue detection, stratified by age (< 40 and ≥ 40 years) and gender. Moreover, we identified anthropometric and body composition parameters serving as predictors of obesity according to %BF-based criteria (> 25% in men or > 35% in women).

RESULTS

Gender emerged as an effect modifier in the quadratic polynomial relationship between BMI and %BF (R² = 0.849 for men, R² = 0.715 for women), while BMI was linearly associated with %BF in both age groups (R² = 0.435 for men, R² = 0.474 for women). BMI was strongly correlated with both %BF (r = 0.67) and lean mass (r = - 0.65). The overall area under the ROC curve for BMI ≥ 30 kg/m² to detect %BF was 0.87 (95%CI 0.85-0.90). A regression model including lean mass, total body water, age, BMI, and female gender explained 0.970 of the variance in %BF.

CONCLUSION

The discriminatory performance of BMI as an estimate of excess body fat is enhanced by the implementation of gender- and age-specific BMI thresholds for defining obesity, in IGB-treated patients.

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.

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

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

Elevated serum leptin levels are associated with low muscle strength and muscle quality in male patients undergoing chronic hemodialysis

Objectives:

Low muscle strength and poor muscle quality are highly prevalent in patients with chronic hemodialysis (HD), which lead to an increased risk of poor clinical outcomes. Leptin dysregulation is common in HD patients. Given that leptin receptors are abundant in skeletal muscle, there may be a link between leptin and muscle strength. The cross-sectional study aimed to explore the correlation of serum leptin levels with muscle strength and muscle quality in patients with chronic HD.

Materials and Methods:

A total of 118 chronic HD patients were included in this study. Basic characteristics, handgrip strength, body composition were assessed, and blood samples for serum leptin levels and other biochemical test were obtained. We defined skeletal muscle index (SMI) as skeletal muscle mass/height² (kg/m²) and muscle quality as handgrip strength divided by mid-arm muscle circumference (MAMC). Patients were classified into tertile groups, according to sex-specific leptin levels.

Results:

We observed that patients in the higher leptin tertile tend to have a higher body weight, body mass index (BMI), body fat mass, MAMC, and SMI, while the handgrip strength and muscle quality were significantly lower. Bodyweight (r = 0.30; P = 0.001), BMI (r = 0.45; P = 0.001), body fat mass (r = 0.57;P < 0.001), and SMI (r = 0.22; P = 0.018) were positively and handgrip strength (r = −0.27; P = 0.003) and muscle quality (r = −0.35;P < 0.001) were negatively correlated with serum leptin levels, respectively. After adjusting multiple confounding factors, logarithmically transformed serum leptin levels were independently associated with handgrip strength (β = −3.29, P = 0.005) and muscle quality (β = −0.14, P = 0.009). However, gender-stratified models showed the associations were observed only in male, but not in female.

Conclusion:

We concluded that higher serum leptin levels are associated with low handgrip strength and poor muscle quality in male patients on chronic HD. Further studies are needed to clarify the gender differences and to evaluate the casual relationship between circulating leptin levels and muscle strength.

Role of hormones in sarcopenia

Aging involves numerous changes in body composition that include a decrease in skeletal muscle mass. The gradual reduction in muscle mass is associated with a simultaneous decrease in muscle strength, which leads to reduced mobility, fragility and loss of independence. This process called sarcopenia is secondary to several factors such as sedentary lifestyle, inadequate nutrition, chronic inflammatory state and neurological alterations. However, the endocrine changes associated with aging seem to be of special importance in the development of sarcopenia. On one hand, advancing age is associated with a decreased secretion of the main hormones that stimulate skeletal muscle mass and function (growth hormone, insulin-like growth factor 1 (IGFI), testosterone and estradiol). On the other hand, the alteration of the IGF-I signaling along with decreased insulin sensitivity also have an important impact on myogenesis. Other hormones that decline with aging such as the adrenal-derived dehydroepiandrosterone, thyroid hormones and vitamin D seem to also be involved in sarcopenia. Adipokines released by adipose tissue show important changes during aging and can affect muscle physiology and metabolism. In addition, catabolic hormones such as cortisol and angiotensin II can accelerate aged-induced muscle atrophy, as they are involved in muscle wasting and their levels increase with age. The role played by all of these hormones and the possible use of some of them as therapeutic tools for treating sarcopenia will be discussed.

Muscular Contribution to Adolescent Idiopathic Scoliosis from the Perspective of Stem Cell-Based Regenerative Medicine

Adolescent idiopathic scoliosis (AIS) is a relatively frequent disease within a range 0.5%-5.0% of population, with higher frequency in females. While a resultant spinal deformity is usually medically benign condition, it produces far going psychosocial consequences, which warrant attention. The etiology of AIS is unknown and current therapeutic approaches are symptomatic only, and frequently inconvenient or invasive. Muscular contribution to AIS is widely recognized, although it did not translate to clinical routine as yet. Muscle asymmetry has been documented by pathological examinations as well as systemic muscle disorders frequently leading to scoliosis. It has been also reported numerous genetic, metabolic and radiological alterations in patients with AIS, which are linked to muscular and neuromuscular aspects. Therefore, muscles might be considered an attractive and still insufficiently exploited therapeutic target for AIS. Stem cell-based regenerative medicine is rapidly gaining momentum based on the tremendous progress in understanding of developmental biology. It comes also with a toolbox of various stem cells such as satellite cells or mesenchymal stem cells, which could be transplanted; also, the knowledge acquired in research on regenerative medicine can be applied to manipulation of endogenous stem cells to obtain desired therapeutic goals. Importantly, paravertebral muscles are located relatively superficially; therefore, they can be an easy target for minimally invasive approaches to treatment of AIS. It comes in pair with a fast progress in image guidance, which allows for precise delivery of therapeutic agents, including stem cells to various organs such as brain, muscles, and others. Summing up, it seems that there is a link between AIS, muscles, and stem cells, which might be worth of further investigations with a long-term goal of setting foundations for eventual bench-to-bedside translation.

Gene polymorphisms of Patatin-like phospholipase domain containing 3 (PNPLA3), adiponectin, leptin in diabetic obese patients

Obesity leads a crucial importance in metabolic disorders, as well as type 2 diabetes mellitus. Our present study was designed to assess the potential role of irisin, adiponectin, leptin and gene polymorphism of PNPLA3, leptin and adiponectin as predictive markers of diabetes associated with obesity. One hundred eighty subjects were distributed to three groups including; healthy non-diabetic non obese volunteers as a control group, diabetic non obese group, and diabetic obese group (n = 60 for each group). Fasting blood samples of all groups were collected to determine fasting blood glucose, insulin levels, insulin resistance, total cholesterol, high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C), triacylglycerol, irisin, adiponectin, leptin; as well as, polymorphism of PNPLA3, adiponectin and leptin. The results showed that glucose, insulin resistance, total cholesterol, irisin, leptin, LDL-C, triacylglycerol concentrations were significantly increased, however, insulin, HDL-C, adiponectin were significantly decreased in diabetic obese patients in relation to diabetic non-obese patients as well as in healthy volunteers. The polymorphism of PNPLA3 rs738409 was linearly related to irisin and leptin but was not related with circulating concentrations of adiponectin. We concluded that increased irisin and leptin levels can predict the insulin resistance in obese patients. Moreover, patients who have mutant genotype of PNPLA3 I148 gene (rs738409) C>G, ADIPOQ gene (rs266729) G>C and LEP gene (rs2167270) G>A showed a significant higher susceptibility rate for DM in obese people than those with wild type. This could be considered as an adjustable retort to counter the impact of obesity on glucose homeostasis.

Delayed access to feed alters gene expression associated with hormonal signaling, cellular differentiation, and protein metabolism in muscle of newly hatch chicks

Birds rely solely on utilization of the yolk sac as a means of nutritional support throughout embryogenesis and early post-hatch, before first feeding occurs. Newly hatched broiler (meat-type) chickens are frequently not given immediate access to feed, and this can result in numerous alterations to developmental processes, including those that occur in muscle. The objective of this study was to characterize the gene expression profile of newly hatched chicks' breast muscle with regards to hormonal regulation of growth and metabolism and development and differentiation of muscle tissue, and determine impacts of delayed access to feed on these profiles. Within 3 h of hatch, birds were placed in battery pens and given immediate access to feed (Fed) or delayed access to feed for 48 h (Delayed Fed). Breast muscle collected from male birds at hatch, or 4 h, 1 day (D), 2D, 4D, and 8D after hatch was used for analysis of mRNA expression by reverse transcription-quantitative PCR. Under fully fed conditions, insulin-like growth factor receptor and leptin receptor mRNA expression decreased as birds aged; however, delayed access to feed resulted in prolonged upregulation of these genes so their mRNA levels were higher in Delayed Fed birds at 2D. These expression profiles suggest that delayed feed access alters sensitivity to hormones that may regulate muscle development. Myogenin, a muscle differentiation factor, showed increasing mRNA expression in Fed birds through 2D, after which expression decreased. A similar expression pattern in Delayed Fed birds was deferred until 4D. Levels of myostatin, a negative regulator of muscle growth, increased in Fed birds starting at 2D, while levels in Delayed Fed birds began to increase at 4D. In Fed birds, levels of transcripts for two genes associated with protein catabolism, F-box protein 32 and forkhead box O3, were lower at 2D, while Delayed Fed mRNA levels did not decrease until 4D. Mechanistic target of rapamycin mRNA levels decreased from 1D through 8D in both treatments, except for a transient increase in the Delayed Fed birds between 1D and 2D. These data suggest that within breast muscle, delayed feeding alters hormonal signaling, interrupts tissue differentiation, postpones onset of growth, and may lead to increased protein catabolism. Together, these processes could ultimately contribute to a reduction in proper growth and development of birds not given feed immediately after hatch, and ultimately hinder the long-term potential of muscle accretion in meat type birds.

Metabolic Gene Expression in the Muscle and Blood Parameters of Broiler Chickens Stimulated In Ovo with Synbiotics

Simple Summary

Poultry production plays a major role in providing meat products to global markets. Hence, there is a continued interest of researchers in the possibilities of improving the production parameters of broiler chickens. A direct response from muscles and their metabolism to in ovo synbiotic stimulation on day 12 of egg incubation has already been widely documented. However, it is necessary to analyze the molecular mechanisms determining the phenotypic effects. The present research aimed to explain the molecular background of the quality of broiler chicken meat after injection of synbiotics based on Lactobacillus strains into the air chamber of the egg. Characterization of the meat quality is based on the signature of the metabolic gene expression closely related to muscles and basic physiological parameters.

Abstract

To better understand the effects of synbiotics administered at early stages of embryonic development in poultry, it is necessary to analyze direct effects (meat quality) and the molecular background. The molecular interpretation of poultry meat properties after in ovo administration of synbiotics remains to be reported. The purpose of the present study was to analyze the molecular background of meat quality based on gene expression and basic physiological parameters. Eggs were injected with (S1) Lactobacillus salivarius with galacto-oligosaccharides or (S2) Lactobacillus plantarum with raffinose family oligosaccharides. The pectoral muscle was collected at two time points (day 7 and day 42) and subjected to RNA isolation. Gene expression analysis was performed by RT-qPCR for a panel of eight genes associated with metabolism. The concentration of glucose and hormones (insulin, glucagon, and leptin (S1 p = 0.04)) was also increased. The obtained results showed that metabolic gene expression in the muscle was more differential due to synbiotic stimulation on day 7 (FST in S1 p = 0.03; PDK4 in S1 p = 0.02 and S2 p = 0.01; CEBPB in S1 p = 0.01 and S2 p = 0.008; PHKB in S1 p = 0.01; PRKAG3 in S1 p = 0.02) than on day 42 (PDK4 in S1 p = 0.04). On the basis of the results obtained, it can be concluded that in ovo stimulation with S1 triggered the most potent and favorable changes in the pectoral muscle gene expression in broiler chickens.

Impact of adipokines and myokines on fat browning

Since the discovery of leptin in 1994, the adipose tissue (AT) is not just considered a passive fat storage organ but also an extremely active secretory and endocrine organ that secretes a large variety of hormones, called adipokines, involved in energy metabolism. Adipokines may not only contribute to AT dysfunction and obesity, but also in fat browning, a process that induces a phenotypic switch from energy-storing white adipocytes to thermogenic brown fat-like cells. The fat browning process and, consequently, thermogenesis can also be stimulated by physical exercise. Contracting skeletal muscle is a metabolically active tissue that participates in several endocrine functions through the production of bioactive factors, collectively termed myokines, proposed as the mediators of physical activity-induced health benefits. Myokines affect muscle mass, have profound effects on glucose and lipid metabolism, and promote browning and thermogenesis of white AT in an endocrine and/or paracrine manner. The present review focuses on the role of different myokines and adipokines in the regulation of fat browning, as well as in the potential cross-talk between AT and skeletal muscle, in order to control body weight, energy expenditure and thermogenesis.

Roles of leptin in the recovery of muscle and bone by reloading after mechanical unloading in high fat diet-fed obese mice

Muscle and bone masses are elevated by the increased mechanical stress associated with body weight gain in obesity. However, the mechanisms by which obesity affects muscle and bone remain unclear. We herein investigated the roles of obesity and humoral factors from adipose tissue in the recovery phase after reloading from disuse-induced muscle wasting and bone loss using normal diet (ND)- or high fat diet (HFD)-fed mice with hindlimb unloading (HU) and subsequent reloading. Obesity did not affect decreases in trabecular bone mineral density (BMD), muscle mass in the lower leg, or grip strength in HU mice. Obesity significantly increased trabecular BMD, muscle mass in the lower leg, and grip strength in reloading mice over those in reloading mice fed ND. Among the humoral factors in epididymal and subcutaneous adipose tissue, leptin mRNA levels were significantly higher in reloading mice fed HFD than in mice fed ND. Moreover, circulating leptin levels were significantly higher in reloading mice fed HFD than in mice fed ND. Leptin mRNA levels in epididymal adipose tissue or serum leptin levels positively correlated with the increases in trabecular BMD, total muscle mass, and grip strength in reloading mice fed ND and HFD. The present study is the first to demonstrate that obesity enhances the recovery of bone and muscle masses as well as strength decreased by disuse after reloading in mice. Leptin may contribute to the recovery of muscle and bone enhanced by obesity in mice.

Functional Relationship between Leptin and Nitric Oxide in Metabolism

Leptin, the product of the ob gene, was originally described as a satiety factor, playing a crucial role in the control of body weight. Nevertheless, the wide distribution of leptin receptors in peripheral tissues supports that leptin exerts pleiotropic biological effects, consisting of the modulation of numerous processes including thermogenesis, reproduction, angiogenesis, hematopoiesis, osteogenesis, neuroendocrine, and immune functions as well as arterial pressure control. Nitric oxide (NO) is a free radical synthesized from L-arginine by the action of the NO synthase (NOS) enzyme. Three NOS isoforms have been identified: the neuronal NOS (nNOS) and endothelial NOS (eNOS) constitutive isoforms, and the inducible NOS (iNOS). NO mediates multiple biological effects in a variety of physiological systems such as energy balance, blood pressure, reproduction, immune response, or reproduction. Leptin and NO on their own participate in multiple common physiological processes, with a functional relationship between both factors having been identified. The present review describes the functional relationship between leptin and NO in different physiological processes.

Adipose tissue protects against sepsis-induced muscle weakness in mice: from lipolysis to ketones

Background

ICU-acquired weakness is a debilitating consequence of prolonged critical illness that is associated with poor outcome. Recently, premorbid obesity has been shown to protect against such illness-induced muscle wasting and weakness. Here, we hypothesized that this protection was due to increased lipid and ketone availability.

Methods

In a centrally catheterized, fluid-resuscitated, antibiotic-treated mouse model of prolonged sepsis, we compared markers of lipolysis and fatty acid oxidation in lean and obese septic mice (n = 117). Next, we compared markers of muscle wasting and weakness in septic obese wild-type and adipose tissue-specific ATGL knockout (AAKO) mice (n = 73), in lean septic mice receiving either intravenous infusion of lipids or standard parenteral nutrition (PN) (n = 70), and in lean septic mice receiving standard PN supplemented with either the ketone body 3-hydroxybutyrate or isocaloric glucose (n = 49).

Results

Obese septic mice had more pronounced lipolysis (p ≤ 0.05), peripheral fatty acid oxidation (p ≤ 0.05), and ketogenesis (p ≤ 0.05) than lean mice. Blocking lipolysis in obese septic mice caused severely reduced muscle mass (32% loss vs. 15% in wild-type, p < 0.001) and specific maximal muscle force (59% loss vs. 0% in wild-type; p < 0.001). In contrast, intravenous infusion of lipids in lean septic mice maintained specific maximal muscle force up to healthy control levels (p = 0.6), whereas this was reduced with 28% in septic mice receiving standard PN (p = 0.006). Muscle mass was evenly reduced with 29% in both lean septic groups (p < 0.001). Lipid administration enhanced fatty acid oxidation (p ≤ 0.05) and ketogenesis (p < 0.001), but caused unfavorable liver steatosis (p = 0.01) and a deranged lipid profile (p ≤ 0.01). Supplementation of standard PN with 3-hydroxybutyrate also attenuated specific maximal muscle force up to healthy control levels (p = 0.1), but loss of muscle mass could not be prevented (25% loss in both septic groups; p < 0.001). Importantly, this intervention improved muscle regeneration markers (p ≤ 0.05) without the unfavorable side effects seen with lipid infusion.

Conclusions

Obesity-induced muscle protection during sepsis is partly mediated by elevated mobilization and metabolism of endogenous fatty acids. Furthermore, increased availability of ketone bodies, either through ketogenesis or through parenteral infusion, appears to protect against sepsis-induced muscle weakness also in the lean.

Electronic supplementary material

The online version of this article (10.1186/s13054-019-2506-6) contains supplementary material, which is available to authorized users.

iNOS Gene Ablation Prevents Liver Fibrosis in Leptin-Deficient ob/ob Mice

The role of extracellular matrix (ECM) remodeling in fibrosis progression in nonalcoholic fatty liver disease (NAFLD) is complex and dynamic, involving the synthesis and degradation of different ECM components, including tenascin C (TNC). The aim was to analyze the influence of inducible nitric oxide synthase (iNOS) deletion on inflammation and ECM remodeling in the liver of ob/ob mice, since a functional relationship between leptin and iNOS has been described. The expression of molecules involved in inflammation and ECM remodeling was analyzed in the liver of double knockout (DBKO) mice simultaneously lacking the ob and the iNOS genes. Moreover, the effect of leptin was studied in the livers of ob/ob mice and compared to wild-type rodents. Liver inflammation and fibrosis were increased in leptin-deficient mice. As expected, leptin treatment reverted the obesity phenotype. iNOS deletion in ob/ob mice improved insulin sensitivity, inflammation, and fibrogenesis, as evidenced by lower macrophage infiltration and collagen deposition as well as downregulation of the proinflammatory and profibrogenic genes including Tnc. Circulating TNC levels were also decreased. Furthermore, leptin upregulated TNC expression and release via NO-dependent mechanisms in AML12 hepatic cells. iNOS deficiency in ob/ob mice improved liver inflammation and ECM remodeling-related genes, decreasing fibrosis, and metabolic dysfunction. The activation of iNOS by leptin is necessary for the synthesis and secretion of TNC in hepatocytes, suggesting an important role of this alarmin in the development of NAFLD.

Sarcopenia in patients with non-alcoholic fatty liver disease: is it a clinically significant entity?

Sarcopenia, described as the loss of muscle mass and/or strength, is gaining importance as it can be increasingly related to many chronic diseases. It is also associated with chronic liver disease, and recently it has been more frequently linked to non-alcoholic fatty liver disease (NAFLD) in particular. Both sarcopenia and NAFLD are subject to complex and intermingled pathophysiological processes, of which some are in common. Furthermore, it is presently unclear if sarcopenia directly contributes to NAFLD or vice versa. The mechanisms that are involved may include obesity, insulin resistance, vitamin D deficiency, aging, physical inactivity and certain cytokines. Current clinical evidence is subject to an important heterogeneity in methods and definitions, with additionally also a relative overrepresentation of evidence in Asian ethnicities. Nonetheless, all studies so far point towards the same association between sarcopenia and NAFLD, including an association with NAFLD-severity and NAFLD-related fibrosis. Since the field is in its infancy, clear definitions and further research are needed to aid to improve understanding of the association between NAFLD and sarcopenia. This can eventually lead to additional potential therapeutic interventions. This review attempts to give an overview of the current published literature that links sarcopenia to NAFLD, followed by a discussion of the presumably involved pathophysiological factors, and ends by discussing current unmet needs.

Epac2a-knockout mice are resistant to dexamethasone-induced skeletal muscle atrophy and short-term cold stress

Exchange protein directly activated by cAMP (Epac) 2a-knockout (KO) mice exhibit accelerated diet-induced obesity and are resistant to leptin-mediated adipostatic signaling from the hypothalamus to adipose tissue, with sustained food intake. However, the impact of Epac2a deficiency on hypothalamic regulation of sympathetic nervous activity (SNA) has not been elucidated. This study was performed to elucidate the response of Epac2a-KO mice to dexamethasone-induced muscle atrophy and acute cold stress. Compared to age-matched wild-type mice, Epac2a-KO mice showed higher energy expenditures and expression of myogenin and uncoupling protein-1 in skeletal muscle (SM) and brown adipose tissue (BAT), respectively. Epac2a-KO mice exhibited greater endurance to dexamethasone and cold stress. In wild-type mice, exogenous leptin mimicked the responses observed in Epac2a-KO mice. This suggests that leptin-mediated hypothalamic signaling toward SNA appears to be intact in these mice. Hence, the potentiated responses of SM and BAT may be due to their high plasma leptin levels.

The increase in fiber size in male rat gastrocnemius after chronic central leptin infusion is related to activation of insulin signaling

Insulin potentiates leptin effects on muscle accrual and glucose homeostasis. However, the relationship between leptin's central effects on peripheral insulin sensitivity and the associated structural changes remain unclear. We hypothesized that central leptin infusion modifies muscle size through activation of insulin signaling. Muscle insulin signaling, enzymes of fatty acid metabolism, mitochondrial respiratory chain complexes, proliferating cell nuclear antigen (PCNA) and fiber area were analyzed in the gastrocnemius of chronic central infused (L), pair-fed (PF) and control rats. PCNA-positive nuclei, fiber area, GLUT4 and glycogen levels and activation of Akt and mechanistic target of rapamycin were increased in L, with no changes in PF. Acetyl-CoA carboxylase-β mRNA levels and non-esterified fatty acid and triglyceride content were reduced and carnitine palmitoyltransferase-1b expression and mitochondrial complexes augmented in L. These results suggest that leptin promotes an increase in muscle size associated with improved insulin signaling favored by lipid profile.

Associations between lean mass and leptin in men with chronic spinal cord injury: Results from the FRASCI-muscle study

Leptin is an adipo-myokine that regulates appetite and energy expenditure by a neuroendocrine feedback loop. Leptin levels are positively correlated with BMI in the spinal cord injury population and leptin levels are greater in individuals with spinal cord injury compared to uninjured controls. Leptin is produced in multiple tissues, including fat, bone, and skeletal muscle and is a putative biomarker of sedentary behavior in older adults. We assessed body composition leptin, adiponectin, and IL-6 levels in 205 men with chronic spinal cord injury. We found no association between age, injury duration, injury level, injury completeness, or walking status and leptin. There was a significant positive association between lean mass and leptin in men with SCI that was independent of fat. Adjusting for body composition, leptin levels were positively associated with IL-6 and negatively associated with adiponectin levels. When considering men with SCI and sarcopenic obesity, only fat mass remained positively associated with leptin. We found no association between IL-6, adiponectin, or lean mass and leptin in the sarcopenic obesity group. Our findings suggest that lean mass is an under recognized, but substantial, source of circulating leptin. Furthermore, SCI-related sarcopenic obesity may result in dysregulated adipo-myokine metabolism with local and systemic physiologic effects.

Targeted disruption of the iNOS gene improves adipose tissue inflammation and fibrosis in leptin-deficient ob/ob mice: role of tenascin C

BACKGROUND/OBJECTIVES

Obesity is related to a dynamic extracellular matrix (ECM) remodeling, which involves the synthesis and degradation of different proteins, such as tenascin C (TNC) in the adipose tissue (AT). Given the functional relationship between leptin and inducible nitric oxide synthase (iNOS), our aim was to analyze the impact of the absence of the iNOS gene in AT inflammation and ECM remodeling in ob/ob mice.

SUBJECTS/METHODS

The expression of genes involved in inflammation and ECM remodeling was evaluated in 10-week-old male double knockout (DBKO) mice simultaneously lacking the ob and iNOS genes as well as in ob/ob mice classified into three groups [control, leptin-treated (1 mg kg^-1 day^-1) and pair-fed].

RESULTS

Leptin deficiency increased inflammation and fibrosis in AT. As expected, leptin treatment improved the obesity phenotype. iNOS deficiency in ob/ob mice improved insulin sensitivity, AT inflammation, and ECM remodeling, as evidenced by lower AT macrophage infiltration and collagen deposition, a downregulation of proinflammatory and profibrogenic genes Tnf, Emr1, Hif1a, Col6a1, Col6a3, and Tnc, as well as lower circulating TNC levels. Interestingly, leptin upregulated TNC expression and release in 3T3-L1 adipocytes, and iNOS knockdown in 3T3-L1 fat cells produced a significant decrease in basal and leptin-induced Tnc expression.

CONCLUSIONS

Ablation of iNOS in leptin-deficient mice improved AT inflammation and ECM remodeling-related genes, attenuating fibrosis, and metabolic dysfunction. The activation of iNOS by leptin is necessary for the synthesis and secretion of TNC in adipocytes, suggesting an important role of this alarmin in the development of AT inflammation and fibrosis.

Unravelling the role of fatty acid metabolism in cancer through the FOXO3-FOXM1 axis

Obesity and cachexia represent divergent states of nutritional and metabolic imbalance but both are intimately linked to cancer. There is an extensive overlap in their signalling pathways and molecular components involved such as fatty acids (FAs), which likely play a crucial role in cancer. Forkhead box (FOX) proteins are responsible of a wide range of transcriptional programmes during normal development, and the FOXO3-FOXM1 axis is associated with cancer initiation, progression and drug resistance. Free fatty acids (FFAs), FA synthesis and β-oxidation are associated with cancer development and progression. Meanwhile, insulin and some adipokines, that are up-regulated by FAs, are also involved in cancer development and poor prognosis. In this review, we discuss the role of FA metabolism in cancer and how FA metabolism integrates with the FOXO3-FOXM1 axis. These new insights may provide leads to better cancer diagnostics as well as strategies for tackling cancer development, progression and drug resistance.

Long-term PGC1β overexpression leads to apoptosis, autophagy and muscle wasting

Skeletal muscle wasting is prevalent in many chronic diseases, necessitating inquiries into molecular regulation of muscle mass. Nuclear receptor co-activator peroxisome proliferator-activated receptor co-activator 1 alpha (PGC1α) and its splice variant PGC1α4 increase skeletal muscle mass. However, the effect of the other PGC1 sub-type, PGC1β, on muscle size is unclear. In transgenic mice selectively over-expressing PGC1β in the skeletal muscle, we have found that PGC1β progressively decreases skeletal muscle mass predominantly associated with loss of type 2b fast-twitch myofibers. Paradoxically, PGC1β represses the ubiquitin-proteolysis degradation pathway genes resulting in ubiquitinated protein accumulation in muscle. However, PGC1β overexpression triggers up-regulation of apoptosis and autophagy genes, resulting in robust activation of these cell degenerative processes, and a concomitant increase in muscle protein oxidation. Concurrently, PGC1β up-regulates apoptosis and/or autophagy transcriptional factors such as E2f1, Atf3, Stat1, and Stat3, which may be facilitating myopathy. Therefore, PGC1β activation negatively affects muscle mass over time, particularly fast-twitch muscles, which should be taken into consideration along with its known aerobic effects in the skeletal muscle.

Involvement of the leptin-adiponectin axis in inflammation and oxidative stress in the metabolic syndrome

The aim of the present work was to study whether the leptin-adiponectin axis may have a pathophysiological role in the increased systemic inflammation and oxidative stress observed in patients with the metabolic syndrome (MS). Leptin, adiponectin, and markers of inflammation and oxidative stress were measured in a sample of 140 Caucasian subjects (74 males/66 females), aged 28-82 years, 60 with and 80 without the MS. Total concentrations of adiponectin as well as its multimeric forms HMW, MMW and LMW were significantly lower in individuals with the MS. The ratio adiponectin/leptin, a marker of dysfunctional adipose tissue, was dramatically decreased in the MS group. Systemic oxidative stress, as evidenced by levels of thiobarbituric acid reactive substances (TBARS), as well as markers of inflammation such as serum amyloid A (SAA), C-reactive protein (CRP) and osteopontin were significantly increased in subjects with the MS. Total adiponectin concentrations were negatively correlated with levels of TBARS and CRP levels. Furthermore, the ratio adiponectin/leptin was negatively correlated with SAA concentrations as well as with CRP levels. We concluded that a dysfunctional adipose tissue as suggested by a low adiponectin/leptin ratio may contribute to the increased oxidative stress and inflammation, hallmarks of the MS.

Normalization of adiponectin concentrations by leptin replacement in ob/ob mice is accompanied by reductions in systemic oxidative stress and inflammation

The circulating concentrations of adiponectin, an antidiabetic adipokine, have been shown to be reduced in obesity, in relation to an increase in inflammation. The aim of the present work was to assess the effect of leptin replacement on adiponectin levels and expression as well as on markers of oxidative stress and inflammation in leptin-deficient ob/ob mice. Twelve-week-old male mice (n = 7–10 per group) were treated with either saline (wild type and ob/ob mice) or leptin (ob/ob mice) for 18 days. A third group of ob/ob mice was treated with saline and pair-fed to the amount of food consumed by the leptin-treated group. Leptin replacement restored values of adiponectin (P < 0.001), reduced circulating 8-isoprostane and serum amyloid A (SAA) levels (P < 0.05 for both), and significantly downregulated the increased gene expression of osteopontin (Spp1, P < 0.05), Saa3 (P < 0.05), Cd68 (P < 0.01), Il6 (P < 0.01) and NADPH oxidase (Nox1 and Nox2, P < 0.01) in the perirenal WAT and Spp1 (P < 0.05) in the liver of ob/ob mice. In cultured adipocytes from ob/ob mice, leptin increased (P < 0.05) the mRNA expression and secretion of adiponectin. We concluded that circulating concentrations of adiponectin are positively regulated by leptin and ameliorate obesity-associated oxidative stress and inflammation in mice.

Pharmacological evaluation of aqueous extract of syzigium cumini for its antihyperglycemic and antidyslipidemic properties in diabetic rats fed a high cholesterol diet-Role of PPARγ and PPARα

In India syzygium cumini (Myrtaceae) is commonly used traditional medicine to treat diabetes. The present study was undertaken to assess an investigation of antihyperglycemic and antidyslipidemic properties of aqueous extract of Syzigium Cumini (SC) in diabetic rats fed a high cholesterol diet. The aqueous extract of SC was screened for antihyperglycemic and antidyslipidemic activity by streptozotocin induced diabetes in rats. Animals were treated with 100, 200 and 400mg/kg body weight of aqueous extract of SC. Metformin were used as reference antihyperglycemic drugs for comparison. Administration of aqueous extract of SC or metformin for 21days resulted in a significant (P<0.05) reduction in serum glucose, insulin and Homeostasis model assessment of insulin resistance (HOMA-IR) compared with diabetic controls. Treatment with 100mg/kg/day aqueous extract of SC did not result in a significant reduction in serum insulin levels, but 200mg/kg/day and 400mg/kg/day, aqueous extract of SC and metformin showed significant reductions 17.89%, 19.60% and 24.40%, respectively. Furthermore, administration of 100, 200 and 400mg/kg/day, aqueous extract of SC and metformin resulted in significant decrease in insulin resistance of 19.20%, 41.59%, 51.55% and 68.68%, respectively. In high fat diet- streptozotocin (HFD - STZ) treated rats β-cells function (HOMA-B) were markedly reduced (5.8-fold), however observed a significant (P<0.01) improvement of β-cell function with aqueous extract of SC (400mg/kg/day) and metformin. The aqueous extract of SC seeds exhibits significant insulin-sensitizing, antidyslipidemic, antioxidant, anti-inflammatory and β-cell salvaging activity in HFD-STZ-induced type 2 diabetic rats via overexpression of PPARγ and PPARα activity, affirming its potential to be used in the prevention and treatment of type 2 diabetes mellitus (T2DM). Further isolation and characterization of active components in SC seed extract are needed to explore the other possible mechanisms and pathways that are involved in its anti-diabetic effect.

Role of the Cytokine-like Hormone Leptin in Muscle-bone Crosstalk with Aging

The cytokine-like hormone leptin is a classic adipokine that is secreted by adipocytes, increases with weight gain, and decreases with weight loss. Additional studies have, however, shown that leptin is also produced by skeletal muscle, and leptin receptors are abundant in both skeletal muscle and bone-derived mesenchymal (stromal) stem cells. These findings suggest that leptin may play an important role in muscle-bone crosstalk. Leptin treatment in vitro increases the expression of myogenic genes in primary myoblasts, and leptin treatment in vivo increases the expression of microRNAs involved in myogenesis. Bone marrow adipogenesis is associated with low bone mass in humans and rodents, and leptin can reduce marrow adipogenesis centrally through its receptors in the hypothalamus as well as directly via its receptors in bone marrow stem cells. Yet, central leptin resistance can increase with age, and low circulating levels of leptin have been observed among the frail elderly. Thus, aging appears to significantly alter leptin-mediated crosstalk among various organs and tissues. Aging is associated with bone loss and muscle atrophy, contributing to frailty, postural instability, and the incidence of falls. Therapeutic interventions such as protein and amino acid supplementation that can increase muscle mass and muscle-derived leptin may have multiple benefits for the elderly that can potentially reduce the incidence of falls and fractures.

Crosstalk between adipokines and myokines in fat browning

Skeletal muscle is the largest organ determining whole-body insulin sensitivity and metabolic homoeostasis. Adaptive changes of skeletal muscle in response to physical activity include adjustments in the production and secretion of muscle-derived bioactive factors, known as myokines, such as myostatin, IL-4, IL-6, IL-7 and IL-15, myonectin, follistatin-like 1 or leukaemia inhibitory factor. These myokines not only act locally in the muscle in an autocrine/paracrine manner, but also are released to the bloodstream as endocrine factors to regulate physiological processes in other tissues. Irisin, derived from the cleavage of FNDC5 protein, constitutes a myokine that induces myogenesis and fat browning (switch of white adipocytes to brown fat-like cells) together with a concomitant increase in energy expenditure. Besides being a target for irisin actions, the adipose tissue also constitutes a production site of FNDC5. Interestingly, irisin secretion from subcutaneous and visceral fat depots is decreased by long-term exercise training and fasting, suggesting a discordant regulation of FNDC5/irisin in skeletal muscle and adipose tissue. Accordingly, our group has recently reported that the adipokine leptin differentially regulates FNDC5/irisin expression in skeletal muscle and fat, confirming the crosstalk between both tissues. Moreover, irisin secretion and function are regulated by other myokines, such as follistatin or myostatin, as well as by other adipokines, including fibroblast growth factor 21 and leptin. Taken together, myokines have emerged as novel molecular mediators of fat browning and their activity can be modulated by adipokines, confirming the crosstalk between skeletal muscle and adipose tissue to regulate thermogenesis and energy expenditure.

Fine-mapping of genes determining extrafusal fiber properties in murine soleus muscle

Muscle fiber cross-sectional area (CSA) and proportion of different fiber types are important determinants of muscle function and overall metabolism. Genetic variation plays a substantial role in phenotypic variation of these traits; however, the underlying genes remain poorly understood. This study aimed to map quantitative trait loci (QTL) affecting differences in soleus muscle fiber traits between the LG/J and SM/J mouse strains. Fiber number, CSA, and proportion of oxidative type I fibers were assessed in the soleus of 334 genotyped female and male mice of the F₃₄ generation of advanced intercross lines (AIL) derived from the LG/J and SM/J strains. To increase the QTL detection power, these data were combined with 94 soleus samples from the F₂ intercross of the same strains. Transcriptome of the soleus muscle of LG/J and SM/J females was analyzed by microarray. Genome-wide association analysis mapped four QTL (genome-wide P < 0.05) affecting the properties of muscle fibers to chromosome 2, 3, 4, and 11. A 1.5-LOD QTL support interval ranged between 2.36 and 4.67 Mb. On the basis of the genomic sequence information and functional and transcriptome data, we identified candidate genes for each of these QTL. The combination of analyses in F₂ and F₃₄ AIL populations with transcriptome and genomic sequence data in the parental strains is an effective strategy for refining QTL and nomination of the candidate genes.

The Root Extract of Pueraria lobata and Its Main Compound, Puerarin, Prevent Obesity by Increasing the Energy Metabolism in Skeletal Muscle

Radix Pueraria lobata (RP) has been reported to prevent obesity and improve glucose metabolism; however, the mechanism responsible for these effects has not been elucidated. The mechanism underlying anti-obesity effect of RP was investigated in high-fat diet (HFD) induced obese mice and skeletal muscle cells (C2C12). Five-week-old C5BL/6 mice were fed a HFD containing or not containing RP (100 or 300 mg/kg) or metformin (250 mg/kg) for 16 weeks. RP reduced body weight gain, lipid accumulation in liver, and adipocyte and blood lipid levels. In addition, RP dose-dependently improved hyperglycemia, insulinemia, and glucose tolerance, and prevented the skeletal muscle atrophy induced by HFD. Furthermore, RP increased the peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α) expression and phosphorylation of adenosine monophosphate-activated protein kinase (AMPK) in skeletal muscle tissues. RP and its main component, puerarin, increased mitochondrial biogenesis and myotube hypertrophy in C2C12 cells. The present study demonstrates that RP can prevent diet-induced obesity, glucose tolerance, and skeletal muscle atrophy in mouse models of obesity. The mechanism responsible for the effect of RP appears to be related to the upregulation of energy metabolism in skeletal muscle, which at the molecular level may be associated with PGC-1α and AMPK activation.

Lower insulin sensitivity is related to lower relative muscle cross-sectional area, lower muscle density and lower handgrip force in young and middle aged non-diabetic men

OBJECTIVES

This study investigated whether an association between insulin resistance (IR) and muscle parameters is appreciable in young healthy men, independent of obesity. Furthermore, markers of muscle metabolism and hormones/possible determinants, were explored.

METHODS

358 healthy young men were divided into a less and more insulin sensitive (LIS [age=33.2±5.4, BMI=23.4±2.3] and MIS [age=35.5±5.3, BMI=28.1±3.7]) group based on upper and lower quartile of HOMA-IR. Muscle cross-sectional area (CSA), -density, handgrip force, serum testosterone, estradiol, SHBG, Vitamin 25(OH)D, creatinine, IGF-1, IGFBP-3 and leptin levels were compared between these groups, correcting for differences in age, physical activity and fat mass. Correlations between HOMA-IR and these parameters, and between muscle measures and biochemical parameters, were calculated.

RESULTS

LIS is related to lower relative muscle CSA, muscle density, muscle/fat CSA ratio, relative handgrip force and level of physical activity. Furthermore, lower levels in SHBG, testosterone, Vitamin 25(OH)D and higher leptin, IGF-1 and IGFBP-3 levels were observed in LIS. Bio available T, FT, TE2, FE2, bioavailable E2, serum and urinary creatinine levels did not differ between groups.

CONCLUSION

Differences in muscle performance are already present in healthy men with lower insulin sensitivity and could be possibly modifiable risk factors for the development of type 2 diabetes.

Molecular Mechanisms of Obesity-Induced Osteoporosis and Muscle Atrophy

Obesity and osteoporosis are two alarming health disorders prominent among middle and old age populations, and the numbers of those affected by these two disorders are increasing. It is estimated that more than 600 million adults are obese and over 200 million people have osteoporosis worldwide. Interestingly, both of these abnormalities share some common features including a genetic predisposition, and a common origin: bone marrow mesenchymal stromal cells. Obesity is characterized by the expression of leptin, adiponectin, interleukin 6 (IL-6), interleukin 10 (IL-10), monocyte chemotactic protein-1 (MCP-1), tumor necrosis factor-alpha (TNF-α), macrophage colony stimulating factor (M-CSF), growth hormone (GH), parathyroid hormone (PTH), angiotensin II (Ang II), 5-hydroxy-tryptamine (5-HT), Advance glycation end products (AGE), and myostatin, which exert their effects by modulating the signaling pathways within bone and muscle. Chemical messengers (e.g., TNF-α, IL-6, AGE, leptins) that are upregulated or downregulated as a result of obesity have been shown to act as negative regulators of osteoblasts, osteocytes and muscles, as well as positive regulators of osteoclasts. These additive effects of obesity ultimately increase the risk for osteoporosis and muscle atrophy. The aim of this review is to identify the potential cellular mechanisms through which obesity may facilitate osteoporosis, muscle atrophy and bone fractures.

Lower Muscle Mass and Body Fat in Adolescent Idiopathic Scoliosis Are Associated With Abnormal Leptin Bioavailability

STUDY DESIGN

This was a case-control study.

OBJECTIVE

This study aimed to investigate the body composition and its correlation with leptin and soluble leptin receptor (sOB-R) levels in girls with adolescent idiopathic scoliosis (AIS) and compared with healthy controls.

SUMMARY OF BACKGROUND DATA

Patients with AIS are associated with lower body weight, taller stature, lower body mass index (BMI), and deranged bone quality. Despite the widely reported lower BMI and body weight in girls with AIS, the body composition of these patients was not thoroughly studied with sufficient sample size. Leptin is an important factor in regulating energy and bone metabolism, and has been postulated as one of the etiologic factors of AIS.

METHODS

One hundred forty-eight AIS and 116 control girls aged 12 to 14 were recruited. Body composition was measured with bioelectrical impedance analysis. Caloric intake and physical activity level were assessed by food frequency and Baecke questionnaires respectively. Serum total leptin and sOB-R levels were measured with enzyme-linked immunosorbent assay, and free leptin index was calculated.

RESULTS

AIS girls had lower body weight and BMI, other anthropometric and sexual maturity parameters were comparable with controls. There were no difference in caloric intake and physical activity levels. After adjustment for physical activity level, AIS girls had lower skeletal muscle mass, lower body fat, and %body fat. Higher sOB-R and lower free leptin index were found in AIS girls after adjusted for age and body weight. Weaker correlations between serum total leptin, FLI, and body composition parameters were observed in AIS girls.

CONCLUSION

Results suggested that the lower body weight in AIS girls was contributed by both lower skeletal muscle mass and lower body fat. Altered leptin bioavailability also exists in AIS girls and could lead to lower body weight, lower BMI, and abnormal body composition that were manifested in AIS simultaneously.

LEVEL OF EVIDENCE

4.

Body composition and energy intake - skeletal muscle mass is the strongest predictor of food intake in obese adolescents: The HEARTY trial

There has been renewed interest in examining the relationship between specific components of energy expenditure and the overall influence on energy intake (EI). The purpose of this cross-sectional analysis was to determine the strongest metabolic and anthropometric predictors of EI. It was hypothesized that resting metabolic rate (RMR) and skeletal muscle mass would be the strongest predictors of EI in a sample of overweight and obese adolescents. 304 post-pubertal adolescents (91 boys, 213 girls) aged 16.1 (±1.4) years with body mass index at or above the 95th percentile for age and sex OR at or above the 85th percentile plus an additional diabetes risk factor were measured for body weight, RMR (kcal/day) by indirect calorimetry, body composition by magnetic resonance imaging (fat free mass (FFM), skeletal muscle mass, fat mass (FM), and percentage body fat), and EI (kcal/day) using 3 day food records. Body weight, RMR, FFM, skeletal muscle mass, and FM were all significantly correlated with EI (p < 0.005). After adjusting the model for age, sex, height, and physical activity, only FFM (β = 21.9, p = 0.007) and skeletal muscle mass (β = 25.8, p = 0.02) remained as significant predictors of EI. FFM and skeletal muscle mass also predicted dietary protein and fat intake (p < 0.05), but not carbohydrate intake. In conclusion, with skeletal muscle mass being the best predictor of EI, our results support the hypothesis that the magnitude of the body's lean tissue is related to absolute levels of EI in a sample of inactive adolescents with obesity.