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Glucagon-like peptide-1 receptor agonists act via appetite suppression and caloric restriction. These treatments can result in significant muscle loss, likely due to evolutionary mechanisms protecting against food scarcity as muscle is a major energy utilizer. One mechanism that reduces muscle mass involves activation of type II activin receptors, ActRIIA/B, which yield profound muscle growth in humans when blocked. We previously demonstrated GDF8, also known as myostatin, and activin A are the two major ActRIIA/B ligands mediating muscle minimization. Here, we report that dual blockade can also prevent muscle loss associated with glucagon-like peptide-1 receptor agonists – and even increase muscle mass – in both obese mice and non-human primates; moreover, this muscle preservation enhances fat loss and is metabolically beneficial. These data raise the possibility that supplementing glucagon-like peptide-1 receptor agonist treatment with GDF8 and activin A blockade could greatly improve the quality of weight loss during the treatment of obesity in humans. Myostatin and activin A are the two primary negative regulators of muscle mass. Blocking these circulating ligands during GLP-1 therapy induces improved body composition through preservation of lean mass and enhanced fat mass loss in obese primates.

Ghrelin O-acyltransferase (GOAT) attaches octanoate to proghrelin, which is processed to ghrelin, an octanoylated peptide hormone that stimulates release of growth hormone (GH) from pituitary cells. Elimination of the gene encoding ghrelin or its receptor produces only mild phenotypes in mice. Thus, the essential function of ghrelin is obscure. Here, we eliminate the Goat gene in mice, thereby eliminating all octanoylated ghrelin from blood. On normal or high fat diets, Goat⁻/⁻ mice grew and maintained the same weights as wild-type (WT) littermates. When subjected to 60% calorie restriction, WT and Goat⁻/⁻ mice both lost 30% of body weight and 75% of body fat within 4 days. In both lines, fasting blood glucose initially declined equally. After 4 days, glucose stabilized in WT mice at 58-76 mg/dL. In Goat⁻/⁻ mice, glucose continued to decline, reaching 12-36 mg/dL on day 7. At this point, WT mice showed normal physical activity, whereas Goat⁻/⁻ mice were moribund. GH rose progressively in calorie-restricted WT mice and less in Goat⁻/⁻ mice. Infusion of either ghrelin or GH normalized blood glucose in Goat⁻/⁻ mice and prevented death. Thus, an essential function of ghrelin in mice is elevation of GH levels during severe calorie restriction, thereby preserving blood glucose and preventing death.

Background Sarcopenia is defined as age-related low muscle mass and function, and can also describe the loss of muscle mass in certain medical conditions, such as sarcopenic obesity. Sarcopenic obesity describes loss of muscle and function in obese individuals; however, as sarcopenia is an age-related condition and obesity can occur in any age group, a more accurate term is obesity with low lean muscle mass (OLLMM). Given limited data on OLLMM (particularly in those aged < 65 years), the purpose of this study was to estimate the prevalence of OLLMM in adults aged ≥ 20 years in the USA. Methods Data from the National Health and Nutrition Examination Survey (NHANES) 2017–2018 and 1999–2006 were used. OLLMM was defined as an appendicular lean mass, adjusted for body mass index (BMI), cut-off point < 0.789 for males and < 0.512 for females, measured by dual-energy X-ray absorptiometry (DXA). DXA was only measured in individuals 20–59 years old in NHANES 2017–2018; we therefore utilized logistic regression models to predict OLLMM from NHANES 1999–2006 for those aged ≥ 60 years. The prevalence of OLLMM was estimated overall, and by sex, age, race/ethnicity, and clinical subgroup (high BMI, prediabetes, type 2 diabetes mellitus [T2DM], non-alcoholic fatty liver disease [NAFLD] with fibrosis, or post-bariatric surgery). Prevalence estimates were extrapolated to the USA population using NHANES sampling weights. Results We estimated that, during 2017–2018, 28.7 million or 15.9% of the USA population had OLLMM. The prevalence of OLLMM was greater in older individuals (8.1%, aged 20–59 years vs 28.3%, aged ≥ 60 years), highest (66.6%) in Mexican-American females aged ≥ 60 years, and lowest (2.6%) in non-Hispanic Black males aged 20–59 years. There was a higher prevalence of OLLMM in adults with prediabetes (19.7%), T2DM (34.5%), NAFLD with fibrosis (25.4%), or post-bariatric surgery (21.8%), compared with those without each condition. Conclusions Overall, the burden of OLLMM in the USA is substantial, affecting almost 30 million adults. The prevalence of OLLMM increased with age, and among those with prediabetes, T2DM, NAFLD with fibrosis, or post-bariatric surgery. A unified definition of OLLMM will aid diagnosis and treatment strategies.

Oncostatin M (OSM) is a unique Interleukin 6 (IL-6) family cytokine that plays pivotal roles in numerous biological events by signaling via two types of receptor complexes. While type I OSM receptor complex is formed by glycoprotein 130 (gp130) heterodimerization with Leukemia Inhibitory Factor receptor (LIFR), type II OSM receptor complex is composed of gp130 and OSM receptor (OSMR). OSM is an important contributor to multiple inflammatory diseases and cancers while OSM inhibition has been shown to be effective at reducing symptoms, making OSM an attractive therapeutic target. Using cryogenic electron microscopy (cryo-EM), we characterize full extracellular assemblies of human type I OSM receptor complex and mouse type II OSM receptor complex. The juxtamembrane domains of both complexes are situated in close proximity due to acute bends of the receptors. The rigid N-terminal extension of OSM contributes to gp130 binding and OSM signaling. Neither glycosylation nor pro-domain cleavage of OSM affects its activity. Mutagenesis identifies multiple OSM and OSMR residues crucial for complex formation and signaling. Our data reveal the structural basis for the assemblies of both type I and type II OSM receptor complexes and provide insights for modulation of OSM signaling in therapeutics. OSM is an IL-6 family cytokine that can signal via type I receptor complex (OSM/gp130/LIFR) or type I receptor complex (OSM/gp130/OSMR). Here, the authors report cryo-EM structures of the two types of OSM receptor complexes and provide insights for modulation of OSM signaling in therapeutics.

Evolutionary pressures to protect against food scarcity likely resulted in highly-conserved pathways designed to minimize energy expenditure, one of which involves the minimization of muscle mass; these mechanisms may be counter-productive in a modern world suffering from obesity and sarcopenia. Growth differentiation factor 8 (GDF8)/myostatin, acting via ActRIIA/B receptors, is the best-characterized negative regulator of muscle mass, leading to therapeutic efforts to augment muscle growth by blocking GDF8 or ActRIIA/B. ActRIIA/B blockade approximately doubles the muscle increase of GDF8 blockade, and as ActRIIA/B responds to multiple other TGFβ-family members, this implies other ligands might also regulate muscle mass. Previously, we suggested that activin A (ActA) is the key second negative regulator acting via ActRIIA/B, as blockade of both GDF8 and ActA in mice/monkeys matches the muscle growth of ActRIIA/B blockade. Here, we extend these observations to humans in a two-part, randomized, placebo-controlled Phase 1 trial ( www.clinicaltrials.gov , NCT02943239) conducted at two sites in New Zealand. Eligible subjects included healthy postmenopausal females aged 45–70 years and males aged 35–60 years not intending to father children, with a body mass index of 18–32 kg/m 2 . Part I tested single-dose administration of anti-GDF8 alone, anti-ActA alone, several dose combinations of anti-GDF8 + anti-ActA, or placebo in healthy postmenopausal females; part II tested multiple-dose administration of anti-ActA alone or placebo in healthy postmenopausal females, combination anti-GDF8 + anti-ActA or placebo in healthy postmenopausal females, and anti-ActA alone or placebo in healthy males. The primary outcome measure was the incidence and severity of treatment-emergent adverse events through week 16 for the single-dose part of the study and through week 40 for the multiple-dose part of the study. Secondary endpoints included percent and absolute change in thigh muscle volume, percent and absolute change in total and regional body composition, pharmacokinetic profiles of the GDF8 and ActA mAbs in serum over time, changes in serum total GDF8 and total ActA levels over time, and the presence of anti-drug antibodies against the GDF8 mAb or the ActA mAb. Magnetic resonance imaging was used to quantitate changes in thigh muscle volume and dual x-ray absorptiometry was used to quantitate changes in regional body composition (total lean mass, appendicular lean body mass, android fat mass, and total fat mass). A total of 82 subjects were enrolled (48 in the single-dose part and 34 in the multiple-dose part of the study). Baseline demographic and clinical characteristics were generally balanced across the single- and multiple-dose parts of the study. Combining GDF8 and ActA blocking antibodies led to greater muscle growth than either antibody alone; increases in muscle were accompanied by reductions in fat. The observed clinical effects on muscle and fat paralleled mAb exposure in serum. The combination was generally well tolerated, and no subjects tested positive for anti-drug antibodies post-treatment. These results suggest that GDF8 and ActA are the dominant negative regulators of muscle mass in humans, and that combined blockade may be a promising therapeutic approach in muscle atrophy and obesity settings. GDF8 and activin A are the dominant negative regulators of muscle mass in animal models. This two-part, randomized, placebo-controlled Phase 1 trial suggests that GDF8 and activin A are also the dominant negative regulators of muscle mass in humans.

Recent human genome-wide association studies have identified common missense variants in MARC1 , p.Ala165Thr and p.Met187Lys, associated with lower hepatic fat, reduction in liver enzymes and protection from most causes of cirrhosis. Using an exome-wide association study we recapitulated earlier MARC1 p.Ala165Thr and p.Met187Lys findings in 540,000 individuals from five ancestry groups. We also discovered novel rare putative loss of function variants in MARC1 with a phenotype similar to MARC1 p.Ala165Thr/p.Met187Lys variants. In vitro studies of recombinant human MARC1 protein revealed Ala165Thr substitution causes protein instability and aberrant localization in hepatic cells, suggesting MARC1 inhibition or deletion may lead to hepatoprotection. Following this hypothesis, we generated Marc1 knockout mice and evaluated the effect of Marc1 deletion on liver phenotype. Unexpectedly, our study found that whole-body Marc1 deficiency in mouse is not protective against hepatic triglyceride accumulation, liver inflammation or fibrosis. In attempts to explain the lack of the observed phenotype, we discovered that Marc1 plays only a minor role in mouse liver while its paralogue Marc2 is the main Marc family enzyme in mice. Our findings highlight the major difference in MARC1 physiological function between human and mouse.

Carbohydrate response element binding protein (ChREBP) is a lipogenic transcription factor that is thought to be involved in the development of hepatic steatosis and insulin resistance. Increased ChREBP expression in liver results in increased hepatic steatosis, and the isoform ChREBPβ in adipose tissue can predict insulin sensitivity in obese humans. As ChREBP is activated by glucose, it was postulated that the composition of diet would regulate ChREBP isoform expression in metabolically relevant tissues. We compared the effects of diets with high complex carbohydrate, high fat, or a normal chow on ChREBP expression and metabolic parameters in C57BL/6 mice. We found that diets high in fat decrease ChREBP expression in adipose tissue, but isocaloric diets high in carbohydrate have no effect. Interestingly, this decrease in adipose ChREBP was associated with increased inflammatory markers. In the same animals a high carbohydrate diet induced a robust increase in hepatic ChREBPβ expression (≈2-fold; p = 0.0002), but little detectable change in the more abundant ChREBPα transcript. This change was accompanied by increased expression of target genes liver pyruvate kinase (p<0.0001), acetyl-CoA carboxylase (p = 0.0191) and stearoyl-CoA desaturase-1 (p = 0.0045). This increase in ChREBP expression was associated with increased hepatic steatosis, despite no changes in body weight or body fat when compared to chow-fed mice. Unexpectedly, mice fed a high carbohydrate diet displayed enhanced sensitivity to exogenous insulin, despite having mild glucose intolerance and increased liver steatosis. In summary, we have shown the composition of diet can selectively regulate ChREBP isoform expression in a tissue specific manner. Furthermore, we have shown a high complex carbohydrate diet selectively increases hepatic ChREBPβ expression, which associates with hepatic steatosis but not insulin resistance. In contrast, a high fat diet reduces adipose ChREBP, which associates with inflammation and insulin resistance.

The gut hormone ghrelin targets the brain to promote food intake and adiposity. The ghrelin receptor growth hormone secretagogue 1 receptor (GHSR) is present in hypothalamic centers controlling energy metabolism as well as in the ventral tegmental area (VTA), a region important for motivational aspects of multiple behaviors, including feeding. Here we show that in mice and rats, ghrelin bound to neurons of the VTA, where it triggered increased dopamine neuronal activity, synapse formation, and dopamine turnover in the nucleus accumbens in a GHSR-dependent manner. Direct VTA administration of ghrelin also triggered feeding, while intra-VTA delivery of a selective GHSR antagonist blocked the orexigenic effect of circulating ghrelin and blunted rebound feeding following fasting. In addition, ghrelin- and GHSR-deficient mice showed attenuated feeding responses to restricted feeding schedules. Taken together, these data suggest that the mesolimbic reward circuitry is targeted by peripheral ghrelin to influence physiological mechanisms related to feeding.

Multiple organs cooperate to regulate appetite, metabolism, and glucose and fatty acid homeostasis. Here, we identified and characterized lymphatic vasculature dysfunction as a cause of adult-onset obesity. We found that functional inactivation of a single allele of the homeobox gene Prox1 led to adult-onset obesity due to abnormal lymph leakage from mispatterned and ruptured lymphatic vessels. Prox1 heterozygous mice are a new model for adult-onset obesity and lymphatic vascular disease.

The gut hormone and neuropeptide ghrelin affects energy balance and growth hormone release through hypothalamic action that involves synaptic plasticity in the melanocortin system. Ghrelin binding is also present in other brain areas, including the telencephalon, where its function remains elusive. Here we report that circulating ghrelin enters the hippocampus and binds to neurons of the hippocampal formation, where it promotes dendritic spine synapse formation and generation of long-term potentiation. These ghrelin-induced synaptic changes are paralleled by enhanced spatial learning and memory. Targeted disruption of the gene that encodes ghrelin resulted in decreased numbers of spine synapses in the CA1 region and impaired performance of mice in behavioral memory testing, both of which were rapidly reversed by ghrelin administration. Our observations reveal an endogenous function of ghrelin that links metabolic control with higher brain functions and suggest novel therapeutic strategies to enhance learning and memory processes.