Muscle biology
Abstract
Greater than 25% of all men develop an inguinal hernia in their lifetime, and more than 20 million inguinal hernia repair surgeries are performed worldwide each year. The mechanisms causing abdominal muscle weakness, the formation of inguinal hernias, or their recurrence are largely unknown. We previously reported that excessively produced estrogen in the lower abdominal muscles (LAM) triggers extensive LAM fibrosis, leading to hernia formation in a transgenic male mouse model expressing the human aromatase gene (Aromhum). To understand the cellular basis of estrogen-driven muscle fibrosis, we performed single-cell RNA-sequencing on LAM tissue from Aromhum and wild-type littermates. We found a fibroblast-like cell group comprised of six clusters, two of which were validated for their enrichment in Aromhum LAM tissue. One of the novel hernia-associated fibroblast clusters in Aromhum was enriched for the estrogen receptor-α gene (Esr1Hi). Esr1Hi fibroblasts maximally expressed estrogen target genes and seemed to serve as the progenitors of another cluster expressing ECM-altering enzymes (Mmp3Hi) and upregulate expression of pro-inflammatory, pro-fibrotic genes. The discovery of these two novel and unique hernia-associated fibroblasts may lead to the development of novel treatments that can non-surgically prevent or reverse inguinal hernias.
Authors
Tanvi Potluri, Matthew J. Taylor, Jonah J. Stulberg, Richard L. Lieber, Hong Zhao, Serdar E. Bulun
Abstract
Sex/gender disparity in asthma is recognized, and suggests a modulatory role for sex-steroids, particularly estrogen. However, studies including our own show a dichotomous role for estrogen in airway remodeling, making it unclear whether sex hormones are protective or detrimental in asthma, and suggesting a need to explore mechanisms upstream or independent of estrogen. We hypothesize that Kisspeptin (Kp)/KISS1R signaling serves this role. Airway smooth muscle (ASM) is a key structural cell type that contributes to remodeling in asthma. We explored the role of Kp/KISS1R in regulating ASM proliferation. We report novel data that Kp and KISS1R are expressed in human airways, especially ASM, with lower expression in ASM from females compared to males, and asthmatics showing lowest expression compared to non-asthmatics. Proliferation studies showed that cleaved forms of Kp, particularly Kp-10 mitigates PDGF-induced ASM proliferation. Pharmacological inhibition and shRNA knockdown of KISS1R increased basal ASM proliferation, further amplified by PDGF. The anti-proliferative effect of Kp-10 in ASM was found to be mediated by inhibition of MAPK-ERK-Akt pathways, with altered expression of PCNA, C/EBP-alpha, Ki-67, Cyclin-D1, and Cyclin-E leading to cell-cycle arrest at G0/G1 phase. Overall, we demonstrate the importance of Kp/KISS1R signaling in regulating ASM proliferation and a potentially novel therapeutic avenue to blunt remodeling in asthma.
Authors
Niyati A. Borkar, Nilesh Sudhakar Ambhore, Rama Satyanarayana Raju Kalidhindi, Christina M. Pabelick, Y.S. Prakash, Venkatachalem Sathish
Abstract
Mammalian skeletal muscle contains heterogenous myofibers with different contractile and metabolic properties that sustain muscle mass and endurance capacity. The transcriptional regulators that govern these myofiber gene programs have been elucidated. However, the hormonal cues that direct the specification of myofiber types and muscle endurance remain largely unknown. Here we uncover the secreted factor Tsukushi (TSK) as an extracellular signal that is required for maintaining muscle mass, strength, and endurance capacity, and contributes to muscle regeneration. Mice lacking TSK exhibited reduced grip strength and impaired exercise capacity. Muscle transcriptomic analysis revealed that TSK deficiency results in a remarkably selective impairment in the expression of myofibrillar genes characteristic of slow-twitch muscle fibers that is associated with abnormal neuromuscular junction formation. AAV-mediated overexpression of TSK failed to rescue these myofiber defects in adult mice, suggesting that the effects of TSK on myofibers are likely restricted to certain developmental stages. Finally, mice lacking TSK exhibited diminished muscle regeneration following cardiotoxin-induced muscle injury. These findings support a crucial role of TSK as a hormonal cue in the regulation of contractile gene expression, endurance capacity, and muscle regeneration.
Authors
Qiuyu Wang, Xiaoxue Qiu, Tongyu Liu, Cheehoon Ahn, Jeffrey F. Horowitz, Jiandie D. Lin
Abstract
Approximately 80% of pancreatic cancer patients suffer from cachexia and one-third die due to cachexia-related complications such as respiratory failure and cardiac arrest. Although there has been considerable research into cachexia mechanisms and interventions, there are, to date, no FDA-approved therapies. A major contributing factor could be the failure of animal models to accurately recapitulate the human condition. In this study, we generated an aged model of pancreatic cancer cachexia to compare cachexia progression in young versus aged tumor-bearing mice. Comparative skeletal muscle transcriptome analyses identified 3-methyladenine (3-MA) as a candidate anti-wasting compound. In vitro analyses confirmed anti-wasting capacity while in vivo analysis revealed potent anti-tumor effects. Transcriptome analyses of 3-MA-treated tumor cells implicated Perp as a 3-MA target gene. We subsequently 1) observed significantly higher expression of Perp in cancer cell lines compared to control cells, 2) noted a survival disadvantage associated with elevated Perp, and 3) found that 3-MA-associated Perp reduction inhibited tumor cell growth. Finally, we provide in vivo evidence that survival benefits conferred by 3-MA administration are independent of its effect on tumor progression. Taken together, we report a novel mechanism linking 3-MA to Perp inhibition, and further implicate PERP as a novel tumor promoting factor in pancreatic cancer.
Authors
Aneesha Dasgupta, Paige C. Arneson-Wissink, Rebecca E. Schmitt, Dong Seong Cho, Alexandra M. Ducharme, Tara L. Hogenson, Eugene W. Krueger, William R. Bamlet, Lizhi Zhang, Gina L. Razidlo, Martin E. Fernandez-Zapico, Jason D. Doles
Abstract
While current thinking posits that insulin signaling to GLUT4 exocytic translocation and glucose uptake in skeletal muscle and adipocytes is controlled by phosphorylation-based signaling, many proteins in this pathway are acetylated on lysine residues. However, the importance of acetylation and lysine acetyltransferases to insulin-stimulated glucose uptake is incompletely defined. Here, we demonstrate that combined loss of the acetyltransferases E1A binding protein p300 (p300) and cAMP response element binding protein binding protein (CBP) in mouse skeletal muscle causes a complete loss of insulin-stimulated glucose uptake. Similarly, brief (i.e. 1 h) pharmacological inhibition of p300/CBP acetyltransferase activity recapitulates this phenotype in human and rodent myotubes, 3T3-L1 adipocytes, and mouse muscle. Mechanistically, these effects are due to p300/CBP-mediated regulation of GLUT4 exocytic translocation and occurs downstream of Akt signaling. Taken together, we highlight a fundamental role for acetylation and p300/CBP in the direct regulation of insulin-stimulated glucose transport in skeletal muscle and adipocytes.
Authors
Vitor F. Martins, Samuel A. LaBarge, Alexandra Stanley, Kristoffer Svensson, Chao-Wei Hung, Omer Keinan, Theodore P. Ciaraldi, Dion Banoian, Ji E. Park, Christina Ha, Byron Hetrick, Gretchen A. Meyer, Andrew Philp, Larry L. David, Robert R. Henry, Joseph E. Aslan, Alan R. Saltiel, Carrie E. McCurdy, Simon Schenk
Abstract
BACKGROUND. Skeletal muscle maladaptation accompanies chronic kidney disease (CKD) and negatively impacts physical function. Emphasis in CKD has historically been placed on muscle fiber intrinsic deficits, such as altered protein metabolism and atrophy. However, targeted treatment of fiber intrinsic dysfunction has produced limited improvement, whereas alterations within the fiber extrinsic environment have scarcely been examined. METHODS. We investigated alterations to the skeletal muscle interstitial environment with deep cellular phenotyping of biopsies from patients with CKD compared to age-matched control participants and performed transcriptome profiling to define the molecular underpinnings of CKD-associated muscle impairments. We further examined changes in the observed muscle maladaptation following initiation of dialysis therapy for kidney failure. RESULTS. Patients with CKD exhibited a progressive fibrotic muscle phenotype, which was associated with impaired regenerative capacity and lower vascular density. The severity of these deficits was strongly associated with the degree of kidney dysfunction. Consistent with these profound deficits, CKD was associated with broad alterations to the muscle transcriptome, including altered extracellular matrix organization, downregulated angiogenesis, and altered expression of pathways related to stem cell self-renewal. Remarkably, despite the seemingly advanced nature of this fibrotic transformation, dialysis treatment rescued these deficits, restoring a healthier muscle phenotype. Furthermore, after accounting for muscle atrophy, strength and endurance improved after dialysis initiation. CONCLUSION. These data identify a dialysis-responsive muscle fibrotic phenotype in CKD and suggest that the early dialysis window presents a unique opportunity of improved muscle regenerative capacity during which targeted interventions may achieve maximal impact. TRIAL REGISTRATION. NCT01452412 FUNDING. NIH
Authors
Camille R. Brightwell, Ameya S. Kulkarni, William Paredes, Kehao Zhang, Jaclyn B. Perkins, Knubian J. Gatlin, Matthew Custodio, Hina Farooq, Bushra Zaidi, Rima Pai, Rupinder S. Buttar, Yan Tang, Michal L. Melamed, Thomas H. Hostetter, Jeffrey E. Pessin, Meredith Hawkins, Christopher S. Fry, Matthew K. Abramowitz
Abstract
Stromal interaction molecule 1 (STIM1), the sarcoplasmic reticulum (SR) transmembrane protein, activates store-operated Ca2+ entry (SOCE) in skeletal muscle and, thereby, coordinates Ca2+ homeostasis, Ca2+-dependent gene expression, and contractility. STIM1 occupies space in the junctional SR membrane of the triads and the longitudinal SR at the Z-line. How STIM1 is organized and is retained in these specific subdomains of the SR is unclear. Here, we identified desmin, the major type III intermediate filament protein in muscle, as a binding partner for STIM1 based on a yeast 2-hybrid screen. Validation of the desmin-STIM1 interaction by immunoprecipitation and immunolocalization confirmed that the CC1-SOAR domains of STIM1 interact with desmin to enhance STIM1 oligomerization yet limit SOCE. Based on our studies of desmin-KO mice, we developed a model wherein desmin connected STIM1 at the Z-line in order to regulate the efficiency of Ca2+ refilling of the SR. Taken together, these studies showed that desmin-STIM1 assembles a cytoskeletal-SR connection that is important for Ca2+ signaling in skeletal muscle.
Authors
Hengtao Zhang, Victoria Graham Bryson, Chaojian Wang, TianYu Li, Jaclyn P. Kerr, Rebecca Wilson, Deborah M. Muoio, Robert J. Bloch, Christopher Ward, Paul B. Rosenberg
Abstract
Obesity, a major healthcare issue, is characterized by metabolic abnormalities in multiple tissues, including the skeletal muscle. Although dysregulation of skeletal muscle metabolism can strongly influence the homeostasis of systemic energy, the underlying mechanism remains unclear. We found promoter hypermethylation and decreased gene expression of fibroblast growth factor 6 (FGF6) in the skeletal muscle of individuals with obesity using high-throughput sequencing. Reduced binding of the cyclic AMP responsive element binding protein-1 (CREB1) to the hypermethylated cyclic AMP (cAMP) response element, which is a regulatory element upstream of the transcription initiation site, partially contributed to the downregulation of FGF6 in patients with obesity. Overexpression of Fgf6 in mice skeletal muscle stimulated protein synthesis, activating the mammalian target of rapamycin (mTOR) pathway, and prevented the increase in weight and the development of insulin resistance in high-fat diet-fed mice. Thus, our findings highlight the role played by Fgf6 in regulating skeletal muscle hypertrophy and whole-body metabolism, indicating its potential in strategies aimed at preventing and treating metabolic diseases.
Authors
Bo Xu, Caizhi Liu, Hong Zhang, Rong Zhang, Mengyang Tang, Yan Huang, Li Jin, Lingyan Xu, Cheng Hu, Weiping Jia
Abstract
Myosin Binding Protein-C slow (sMyBP-C) comprises a subfamily of cytoskeletal proteins encoded by MYBPC1 that is expressed in skeletal muscles where it contributes to myosin thick filament stabilization and actomyosin cross-bridge regulation. Recently, our group described the causal association of dominant missense pathogenic variants in MYBPC1 with an early-onset myopathy characterized by generalized muscle weakness, hypotonia, dysmorphia, skeletal deformities, and myogenic tremor occurring in the absence of neuropathy. To mechanistically interrogate the etiologies of this MYBPC1-associated myopathy in vivo, we generated a knock-in mouse model carrying the E248K pathogenic variant. Using a battery of phenotypic, behavioral, and physiological measurements spanning neonatal to young adult life, we find that heterozygous E248K mice faithfully recapitulate the onset and progression of generalized myopathy, tremor occurrence, and skeletal deformities seen in human carriers. Moreover, using a combination of biochemical, ultrastructural, and contractile assessments at the level of the tissue, cell, and myofilaments, we show that the loss-of-function phenotype observed in mutant muscles is primarily driven by disordered and misaligned sarcomeres containing fragmented and out-of-register internal membranes that result in reduced force production and tremor initiation. Collectively, our findings provide mechanistic insights underscoring the E248K-disease pathogenesis and offer a relevant preclinical model for therapeutic discovery.
Authors
Janelle Geist Hauserman, Janis Stavusis, Humberto C. Joca, Joel C. Robinett, Laurin Hanft, Jack Vandermeulen, Runchen Zhao, Joseph P Stains, Konstantinos Konstantopoulos, Kerry S. McDonald, Christopher Ward, Aikaterini Kontrogianni-Konstantopoulos
Abstract
Spinal muscular atrophy (SMA) is a neuromuscular disorder caused by loss of survival motor neuron (SMN) protein. While SMN restoration therapies are beneficial, they are not a cure. We aimed to identify potentially novel treatments to alleviate muscle pathology combining transcriptomics, proteomics, and perturbational data sets. This revealed potential drug candidates for repurposing in SMA. One of the candidates, harmine, was further investigated in cell and animal models, improving multiple disease phenotypes, including lifespan, weight, and key molecular networks in skeletal muscle. Our work highlights the potential of multiple and parallel data-driven approaches for the development of potentially novel treatments for use in combination with SMN restoration therapies.
Authors
Katharina E. Meijboom, Viola Volpato, Jimena Monzón-Sandoval, Joseph M. Hoolachan, Suzan M. Hammond, Frank Abendroth, Olivier G. de Jong, Gareth Hazell, Nina Ahlskog, Matthew J.A. Wood, Caleb Webber, Melissa Bowerman
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