Myostatin regulates energy homeostasis in the heart and prevents heart failure.

RATIONALE: Myostatin is a major negative regulator of skeletal muscle mass and initiates multiple metabolic changes, including enhanced insulin sensitivity. However, the function of myostatin in the heart is barely understood, although it is upregulated in the myocardium under several pathological conditions. OBJECTIVE: Here, we aimed to decipher the role of myostatin and myostatin-dependent signaling pathways for cardiac function and cardiac metabolism in adult mice. To avoid potential counterregulatory mechanisms occurring in constitutive and germ-line-based myostatin mutants, we generated a mouse model that allows myostatin inactivation in adult cardiomyocytes. METHODS AND RESULTS: Cardiac MRI revealed that genetic inactivation of myostatin signaling in the adult murine heart caused cardiac hypertrophy and heart failure, partially recapitulating effects of the age-dependent decline of the myostatin paralog growth and differentiation factor 11. We found that myostatin represses AMP-activated kinase activation in the heart via transforming growth factor-ß-activated kinase 1, thereby preventing a metabolic switch toward glycolysis and glycogen accumulation. Furthermore, myostatin stimulated expression of regulator of G-protein signaling 2, a GTPase-activating protein that restricts Gaq and Gas signaling and thereby protects against cardiac failure. Inhibition of AMP-activated kinase in vivo rescued cardiac hypertrophy and prevented enhanced glycolytic flow and glycogen accumulation after inactivation of myostatin in cardiomyocytes. CONCLUSIONS: Our results uncover an important role of myostatin in the heart for maintaining cardiac energy homeostasis and preventing cardiac hypertrophy.

Myostatin induces interstitial fibrosis in the heart via TAK1 and p38.

Myostatin, a member of the TGF-ß superfamily of secreted growth factors, is a negative regulator of skeletal muscle growth. In the heart, it is expressed at lower levels compared to skeletal muscle but up-regulated under disease conditions. Cre recombinase-mediated inactivation of myostatin in adult cardiomyocytes leads to heart failure and increased mortality but cardiac function of surviving mice is restored after several weeks probably due to compensatory expression in non-cardiomyocytes. To study long-term effects of increased myostatin expression in the heart and to analyze the putative crosstalk between cardiomyocytes and fibroblasts, we overexpressed myostatin in cardiomyocytes. Increased expression of myostatin in heart muscle cells caused interstitial fibrosis via activation of the TAK-1-MKK3/6-p38 signaling pathway, compromising cardiac function in older mice. Our results uncover a novel role of myostatin in the heart and highlight the necessity for tight regulation of myostatin to maintain normal heart function.

Additive efficacy of a bispecific anti-TNF/IL-6 nanobody compound in translational models of rheumatoid arthritis.

Rheumatoid arthritis (RA) is one of the most common autoimmune diseases affecting primarily the joints. Despite successful therapies including antibodies against tumor necrosis factor (TNF) and interleukin-6 (IL-6) receptor, only 20 to 30% of patients experience remission. We studied whether inhibiting both TNF and IL-6 would result in improved efficacy. Using backtranslation from single-cell RNA sequencing (scRNA-seq) data from individuals with RA, we hypothesized that TNF and IL-6 act synergistically on fibroblast-like synoviocytes (FLS) and T cells. Coculture of FLS from individuals with RA and T cells supported this hypothesis, revealing effects on both disease-driving pathways and biomarkers. Combining anti-TNF and anti-IL-6 antibodies in collagen-induced arthritis (CIA) mouse models resulted in sustained long-term remission, improved histology, and effects on bone remodeling pathways. These promising data initiated the development of an anti-TNF/IL-6 bispecific nanobody compound 1, with similar potencies against TNF and IL-6. We observed additive efficacy of compound 1 in a FLS/T cell coculture affecting arthritis and T helper 17 (TH17) pathways. This nanobody compound transcript signature inversely overlapped with described RA endotypes, indicating a potential efficacy in a broader patient population. In summary, we showed superiority of a bispecific anti-TNF/IL-6 nanobody compound or combination treatment over monospecific treatments in both in vitro and in vivo models. We anticipate improved efficacy in upcoming clinical studies.

Multi-omics profiling of collagen-induced arthritis mouse model reveals early metabolic dysregulation via SIRT1 axis.

Rheumatoid arthritis (RA) is characterized by joint infiltration of immune cells and synovial inflammation which leads to progressive disability. Current treatments improve the disease outcome, but the unmet medical need is still high. New discoveries over the last decade have revealed the major impact of cellular metabolism on immune cell functions. So far, a comprehensive understanding of metabolic changes during disease development, especially in the diseased microenvironment, is still limited. Therefore, we studied the longitudinal metabolic changes during the development of murine arthritis by integrating metabolomics and transcriptomics data. We identified an early change in macrophage pathways which was accompanied by oxidative stress, a drop in NAD+ level and induction of glucose transporters. We discovered inhibition of SIRT1, a NAD-dependent histone deacetylase and confirmed its dysregulation in human macrophages and synovial tissues of RA patients. Mining this database should enable the discovery of novel metabolic targets and therapy opportunities in RA.

TNF induces glycolytic shift in fibroblast like synoviocytes via GLUT1 and HIF1A.

TNF is a central cytokine in the pathogenesis of rheumatoid arthritis (RA). Elevated level of TNF causes local inflammation that affects immune cells and fibroblast-like synoviocytes (FLS). Nowadays, only 20-30% of patients experience remission after the standard of care therapy-antibodies against TNF. Interestingly, responders show reduced levels of GLUT1 and GAPDH, highlighting a potential link to cellular metabolism. The aim of the study was to investigate whether TNF directly affects the metabolic phenotype of FLS. Real-time respirometry displayed TNF-induced upregulation of glycolysis along with a modest increase of oxidative phosphorylation in FLS from healthy donors. In addition, TNF stimulation enhanced HIF1A and GLUT1 expression. The upregulation of HIF1A and GLUT1 reflects their enriched level in FLS from RA patients (RA-FLS). The inhibition of TAK1, HIF1a and hexokinase deciphered the importance of TNF/TAK1/HIF1A/glycolysis signaling axis. To prove that inhibition of glycolysis reduced the pathogenic phenotype, we showed that 2-deoxyglucose, a hexokinase inhibitor, partially decreased secretion of RA biomarkers. In summary, we identified a direct role of TNF on glycolytic reprogramming of FLS and confirmed the potency of immunometabolism for RA. Further studies are needed to evaluate the therapeutic impact especially regarding non-responder data.

Glucose transporter 1 in rheumatoid arthritis and autoimmunity.

Knowledge about metabolism of immune cells increased almost exponentially during the last two decades and thereby created the new area immunometabolism. Increased glucose uptake and glycolysis were identified as one of the major drivers in immune cells for rapid adaptation to changes in the microenvironment or external stimuli. These metabolic switches are crucial to generate macromolecules for immune cell proliferation and activation. Glucose transporter 1 (GLUT1), a ubiquitously expressed glucose transporter, is strongly upregulated after innate and adaptive immune cell activation. Deletion or inhibition of GLUT1 blocked T cell proliferation and effector function, antibody production from B cells and reduced inflammatory responses in macrophages. Increased glucose uptake and GLUT1 expression are not only observed in proinflammatory conditions, but also in murine models of autoimmunity as well as in human patients. Rheumatoid arthritis (RA), the most common autoimmune disease, is characterized by infiltration of immune cells, hyperproliferation of fibroblast-like synoviocytes, and destruction of cartilage and bone. These processes create a hypoxic microenvironment in the synovium. Moreover, synovial samples including fibroblast-like synoviocytes from RA patients showed increased lactate level and upregulate GLUT1. Similar upregulation of GLUT1 is observed in systemic lupus erythematosus and psoriasis patients as well as in murine autoimmune models. Inhibition of GLUT1 using either T cell specific knockouts or small molecule GLUT1/glycolysis inhibitors improved phenotypes of different murine autoimmune disease models like arthritis, lupus, and psoriasis. Thereby the therapeutic potential of immunometabolism and especially interference with glycolysis was proven. This article is categorized under: Biological Mechanisms > Metabolism Translational, Genomic, and Systems Medicine > Translational Medicine Physiology > Mammalian Physiology in Health and Disease.

High throughput screening of mitochondrial bioenergetics in human differentiated myotubes identifies novel enhancers of muscle performance in aged mice.

Mitochondrial dysfunction is increasingly recognized as a contributor to age-related muscle loss and functional impairment. Therefore, we developed a high throughput screening strategy that enabled the identification of compounds boosting mitochondrial energy production in a human skeletal muscle cell model. Screening of 7949 pure natural products revealed 22 molecules that significantly increased oxygen consumption and ATP levels in myotubes. One of the most potent compounds was the flavanone hesperetin. Hesperetin (10 µM) increased intracellular ATP by 33% and mitochondrial spare capacity by 25%. Furthermore, the compound reduced oxidative stress in primary myotubes as well as muscle tissue in vivo. In aged mice administration of hesperetin (50 mg/kg/d) completely reverted the age-related decrease of muscle fiber size and improved running performance of treated animals. These results provide a novel screening platform for the discovery of drugs that can improve skeletal muscle function in patients suffering from sarcopenia or other disorders associated with mitochondrial dysfunction.