Project description:Skeletal muscle has recently arisen as a novel regulator of Central Nervous System (CNS) function and aging, secreting bioactive molecules known as myokines with metabolism-modifying functions in targeted tissues, including the CNS. Here we report the generation of a novel transgenic mouse with enhanced skeletal muscle lysosomal and mitochondrial function via targeted overexpression of Transcription Factor E-B (TFEB). We have discovered that the resulting geroprotective benefits in skeletal muscle reduces neuroinflammation and accumulation of tau-associated pathological hallmarks in a mouse model of tau pathology. Muscle TFEB overexpression also significantly ameliorates proteotoxicity, reduces neuroinflammation and promotes transcriptional remodeling of the aging CNS, preserving cognition and memory in aging mice. Our results implicate the maintenance of skeletal muscle function throughout aging to direct regulation of CNS health and disease, and suggest that skeletal-muscle originating factors may act as novel therapeutic targets against age-associated neurodegenerative disorders.
Project description:Skeletal muscle mass is an important determinant of whole-body glucose disposal. We here show that mice (M-PDK1KO mice) with skeletal muscle–specific deficiency of 3'-phosphoinositide–dependent kinase 1 (PDK1), a key component of the phosphatidylinositol 3-kinase (PI3K) signaling pathway, manifest a reduced skeletal muscle mass under the static condition as well as impairment of exercise load–induced muscle hypertrophy. Whereas exercise load-induced changes in gene expression were not affected, the phosphorylation of ribosomal protein S6 kinase (S6K) and S6 induced by exercise load was attenuated in skeletal muscle of M-PDK1KO mice, suggesting that PDK1 regulates muscle hypertrophy not through changes in gene expression but through stimulation of protein synthesis via the S6K-S6 axis.
Project description:Arrestin Domain Containing 2 and 3 (Arrdc2/3) are genes whose mRNA contents are decreased in young skeletal muscle following mechanical overload. Arrdc3 is linked to the regulation of signaling pathways in non-muscle cells that could influence skeletal muscle size. Despite a similar amino acid sequence, Arrdc2 function remains undefined. The purpose of this study was to further explore the relationship of Arrdc2/Arrdc3 expression with changes in mechanical load in young and aged muscle and define the effect of Arrdc2/3 expression on myotube diameter. In young and aged mice, mechanical load was decreased using hindlimb suspension while mechanical load was increased by reloading previously unloaded muscle or inducing high force contractions. Arrdc2 and Arrdc3 mRNAs were overexpressed in C2C12 myotubes using adenoviruses. Myotube diameter was determined 48 h post-transfection and RNA sequencing was performed on those samples. Arrdc2 and Arrdc3 mRNA content was higher in the unloaded muscle within 1 day of disuse and remained higher up through 10 days. The induction of Arrdc2 mRNA was more pronounced in aged muscle than young muscle in response to unloading. Reloading previously unloaded muscle of young and aged mice restored Arrdc2 and Arrdc3 levels to ambulatory levels. Increasing mechanical load beyond normal ambulatory levels lowered Arrdc2 but not Arrdc3 mRNA in young and aged muscle. Arrdc2, not Arrdc3, overexpression was sufficient to lower myotube diameter in C2C12 cells in part by altering the transcriptome favoring muscle atrophy. These data are consistent with Arrdc2 contributing to disuse atrophy, particularly in aged muscle.
Project description:Morphological studies of skeletal muscle tissue have provided detailed insights into the architecture of muscle fibers, the surrounding cells, and the extracellular matrix. However, a spatial proteomics analysis of the skeletal muscle, including the muscle-tendon transition zone, is lacking. Here, we prepared thin cryotome muscle sections along the longitudinal axis of the mouse soleus muscle and measured each muscle slice using short LC-MS gradients. We generated more than 3000 high-resolution longitudinal protein profiles of central to distal skeletal muscle regions and created a molecular network of different skeletal muscle regions that reveals the complex architecture of the muscle-tendon transition zone. Among the proteins that show an increasing profile from muscle to tendon, we find proteins related to neuronal activity, fatty acid biosynthesis, and the renin-angiotensin system (RAS). Blocking the RAS in cultured mouse tenocytes using losartan reduces the synthesis of extracellular matrix proteins, including collagen and fibronectin. Overall, our analysis of thin cryotome sections provides a spatial proteome of skeletal muscle and reveals that the RAS acts as an additional regulator of the matrix within muscle-tendon junctions.
Project description:Skeletal muscle dysfunction in survivors of pneumonia is a major cause of lasting morbidity that disproportionately affects older individuals. We found that skeletal muscle recovery was impaired in aged compared with young mice after influenza A virus-induced pneumonia. In young mice, recovery of muscle loss was associated with expansion of tissue-resident skeletal muscle macrophages and downregulation of MHC II expression, followed by a proliferation of muscle satellite cells. These findings were absent in aged mice and in mice deficient in Cx3cr1. Transcriptomic profiling of tissue-resident skeletal muscle macrophages from aged compared with young mice showed downregulation of pathways associated with phagocytosis and proteostasis, and persistent upregulation of inflammatory pathways. Consistently, skeletal muscle macrophages from aged mice failed to downregulate MHCII expression during recovery from influenza A virus induced pneumonia and showed impaired phagocytic function in vitro. Like aged animals, mice deficient in the phagocytic receptor Mertk showed no macrophage expansion, MHCII downregulation or satellite cell proliferation and failed to recover skeletal muscle function after influenza A pneumonia. Our data suggest that a loss of phagocytic function in a CX3CR1+ tissue-resident skeletal muscle macrophage population in aged mice precludes satellite cell proliferation and recovery of skeletal muscle function after influenza A pneumonia.
Project description:Duchenne muscular dystrophy (DMD) is caused by genetic deficiency of dystrophin and characterized by massive structural and functional changes of skeletal muscle tissue, leading to terminal muscle failure. In this project, proteomics data from skeletal muscle of a genetically engineered DMD pig model treated by somatic gene editing are shown.
Project description:Mechanosensing is required for the senses of touch and hearing, and impacts on cellular processes such as cell differentiation, migration, invasion and tissue homeostasis. Mechanical inputs give rise to p38- and JNK-signaling, which mediates adaptive physiological responses in various tissues. In muscle, fiber contraction-induced p38 and JNK signaling ensures adaptation to exercise, muscle repair and hypertrophy. However, the mechanism by which muscle fibers sense mechanical load to activate this signaling, as well as the physiological roles of mechanical stress sensing more broadly, have remained elusive. Here, we show that the upstream MAP3K ZAK is a sensor of cellular compression induced by osmotic shock and cyclic compression in vitro, and muscle contraction in vivo. This function relies on ZAK’s ability to recognize stress fibers in cells and the corresponding Z-discs in muscle fibers, when under tension. Consequently, ZAK-deficient mice present with skeletal muscle defects characterized by fibers with centralized nuclei and progressive adaptation towards a slower myosin profile. Our results highlight how cells in general sense mechanical compressive load, and how mechanical forces generated during muscle contraction are translated into MAP kinase signaling.
Project description:Skeletal muscle function is vital to movement, thermogenesis and metabolism. Muscle fibers differ in contractile ability, mitochondrial content and metabolic properties and muscle fiber transition influences muscle function. However, the molecular mechanisms regulating muscle fiber transition in muscle function are unclear. Here, in over 150 human muscle samples, we observed that markers of oxidative muscle fiber and mitochondria correlate positively with PPARGC1 and CDK4, and, negatively with CDKN2A, a locus significantly associated with type 2 diabetes. Mice expressing an overactive Cdk4 that cannot bind its inhibitor p16INK4a, a product of the CDKN2A locus, are longer, leaner, exhibit increased oxidative myofibers with superior mitochondrial energetics, display enhanced muscle glucose uptake, and are protected from obesity and diabetes. In contrast, Cdk4-deficiency, or skeletal muscle-specific deletion of Cdk4’s transcriptional target, E2F3, reduces oxidative myofiber numbers, deteriorates mitochondrial function and exercise capacity, while increasing diabetes susceptibility. E2F3 activates the PPARGC1 promoter and CDK4/E2F3/PPARGC1 levels correlate positively with exercise and fitness, and negatively with adiposity, insulin resistance and lipid accumulation in muscle. These findings provide insight into oxidative muscle fiber transition and function that is of relevance to metabolic and muscular diseases.
Project description:Caloric restriction (CR) without malnutrition appears to mitigate many detrimental effects of aging, in particular the age-related decline in skeletal muscle mitochondrial function. Although the mechanisms responsible for this protective effect remain unclear, CR is commonly believed to increase mitochondrial biogenesis; a concept that is now demanding closer scrutiny. Here we show that lifelong CR in mice prevents age-related loss of mitochondrial function, measured in isolated mitochondria and permeabilized muscle fibers. We find that these beneficial effects of CR occur without increasing mitochondrial abundance. Furthermore, whole-genome expression profiling and large-scale proteomic surveys revealed expression patterns inconsistent with increased mitochondrial biogenesis. These observations, combined with lower protein synthesis rates support an alternative hypothesis that CR preserves mitochondrial function not by increasing mitochondrial biogenesis, but rather by decreasing mitochondrial oxidant emission, increasing antioxidant scavenging, thereby minimizing oxidative damage to cellular components. Cross-sectional comparison of skeletal muscle from young (8mo), old (24mo) and old caloric restricted mice, obtained from the colony maintained on behalf of the National Institute on Aging.
Project description:To define regulation of tissue proteomes by Bmal1, daily feeding rhythm, and the interaction, we employed Bmal1-stopFL mice, which do not express the main transcriptional activator of the molecular clock, Bmal1, except in cre recombinase-expressing cells1,2 (Figure 1A). Bmal1-stopFL mice lacking cre (Bmal1 knockout, KO) are analogous to Bmal1-null mice and display severely impaired behavioral and molecular rhythms1-3. Hepatocyte-specific Alfp-cre and skeletal muscle-specific Hsa-cre genes were introduced to generate a single line wherein both hepatocyte and skeletal muscle Bmal1 were reconstituted (Liver+Muscle-RE), i.e., rescued (Smith, Koronowski et al. 2023). This approach had the benefit of analyzing liver and muscle from the same mice but comes with the qualification that the abundance of some proteins may be influenced by Bmal1 function in the other tissue, or by a synergistic effect of Bmal1 in both tissues, rather than through rescue of local Bmal1 function alone. Proteomic anlaysis was performed in liver and skeletal muscle.