Dominant mutations in the HSP70 co-chaperone DNAJB6 cause a late onset muscle disease termed limb girdle muscular dystrophy type D1 (LGMDD1), which is characterized by protein aggregation and vacuolar myopathology. Disease mutations reside within the G/F domain of DNAJB6, but the molecular mechanisms underlying dysfunction are not well understood. Using yeast, cell culture, and mouse models of LGMDD1, we found that the toxicity associated with disease-associated DNAJB6 required its interaction with HSP70, and that abrogating this interaction genetically or with small molecules was protective. In skeletal muscle, DNAJB6 localizes to the Z-disc with HSP70. Whereas HSP70 normally diffused rapidly between the Z-disc and sarcoplasm, the rate of HSP70’s diffusion in LGMDD1 mouse muscle was diminished likely because it has an unusual affinity for the Z-disc and mutant DNAJB6. Treating LGMDD1 mice with a small molecule inhibitor of the DNAJ-HSP70 complex re-mobilized HSP70, improved strength and corrected myopathology. These data support a model in which LGMDD1 mutations in DNAJB6 are a gain-of-function disease that is, counter-intuitively, mediated via HSP70 binding. Thus, therapeutic approaches targeting HSP70:DNAJB6 may be effective in treating this inherited muscular dystrophy.
Rocio Bengoechea, Andrew R. Findlay, Ankan K. Bhadra, Hao Shao, Kevin C. Stein, Sara K. Pittman, Jill Daw, Jason E. Gestwicki, Heather L. True, Conrad C. Weihl
Facioscapulohumeral muscular dystrophy (FSHD) is caused by loss of repression of the DUX4 gene; however, the DUX4 protein is rare and difficult to detect in human muscle biopsies, and pathological mechanisms are obscure. FSHD is also a chronic disease that progresses slowly over decades. We used the sporadic, low-level, muscle-specific expression of DUX4 enabled by the iDUX4pA-HSA mouse to develop a chronic long-term muscle disease model. After 6 months of extremely low sporadic DUX4 expression, dystrophic muscle presented hallmarks of FSHD histopathology, including muscle degeneration, capillary loss, fibrosis, and atrophy. We investigated the transcriptional profile of whole muscle as well as endothelial cells and fibroadiopogenic progenitors (FAPs). Strikingly, differential gene expression profiles of both whole muscle and, to a lesser extent, FAPs, showed significant overlap with transcriptional profiles of MRI-guided human FSHD muscle biopsies. These results demonstrate a pathophysiological similarity between disease in muscles of iDUX4pA-HSA mice and humans with FSHD, solidifying the value of chronic rare DUX4 expression in mice for modeling pathological mechanisms in FSHD and highlighting the importance FAPs in this disease.
Darko Bosnakovski, Ahmed S. Shams, Ce Yuan, Meiricris T. da Silva, Elizabeth T. Ener, Cory W. Baumann, Angus J. Lindsay, Mayank Verma, Atsushi Asakura, Dawn A. Lowe, Michael Kyba
Salt inducible kinases (SIKs) are key regulators of cellular metabolism and growth, but their role in cardiomyocyte plasticity and heart failure pathogenesis remains unknown. Here, we showed that loss of SIK1 kinase activity protected against adverse cardiac remodeling and heart failure pathogenesis in rodent models and human iPSC-derived cardiomyocytes. We found that SIK1 phosphorylated and stabilized histone deacetylase 7 (HDAC7) protein during cardiac stress, an event that is required for pathologic cardiomyocyte remodeling. Gain- and loss-of-function studies of HDAC7 in cultured cardiomyocytes implicated HDAC7 as a pro-hypertrophic signaling effector that can induce c-Myc expression, indicating a functional departure from the canonical MEF2 co-repressor function of class IIa HDACs. Taken together, our findings reveal what we believe to be a previously unrecognized role for a SIK1-HDAC7 axis in regulating cardiac stress responses and implicate this pathway as a potential target in human heart failure.
Austin Hsu, Qiming Duan, Sarah McMahon, Yu Huang, Sarah A.B. Wood, Nathanael S. Gray, Biao Wang, Benoit G. Bruneau, Saptarsi M. Haldar
Understanding the circuits that promote an efficient resolution of inflammation is crucial to deciphering the molecular and cellular processes required to promote tissue repair. Macrophages play a central role in the regulation of inflammation, resolution, and repair/regeneration. Using a model of skeletal muscle injury and repair, herein we identified annexin A1 (AnxA1) as the extracellular trigger of macrophage skewing toward a pro-reparative phenotype. Brought into the injured tissue initially by migrated neutrophils, and then overexpressed in infiltrating macrophages, AnxA1 activated FPR2/ALX receptors and the downstream AMPK signaling cascade, leading to macrophage skewing, dampening of inflammation, and regeneration of muscle fibers. Mice lacking AnxA1 in all cells or only in myeloid cells displayed a defect in this reparative process. In vitro experiments recapitulated these properties, with AMPK-null macrophages lacking AnxA1-mediated polarization. Collectively, these data identified the AnxA1/FPR2/AMPK axis as an important pathway in skeletal muscle injury regeneration.
Simon McArthur, Gaëtan Juban, Thomas Gobbetti, Thibaut Desgeorges, Marine Theret, Julien Gondin, Juliana E. Toller-Kawahisa, Chris P. Reutelingsperger, Bénédicte Chazaud, Mauro Perretti, Rémi Mounier
Lamin A is a component of the inner nuclear membrane that, together with epigenetic factors, organizes the genome in higher order structures required for transcriptional control. Mutations in the Lamin A/C gene cause several diseases, belonging to the class of laminopathies, including muscular dystrophies. Nevertheless, molecular mechanisms involved in the pathogenesis of Lamin A-dependent dystrophies are still largely unknown. Polycomb group of proteins (PcG) are epigenetic repressors and Lamin A interactors, primarily involved in the maintenance of cell identity. Using a murine model of Emery-Dreifuss Muscular Dystrophy (EDMD), we showed here that Lamin A loss deregulated PcG positioning in muscle satellite stem cells leading to de-repression of non-muscle specific genes and p16INK4a, a senescence driver encoded in the Cdkn2a locus. This aberrant transcriptional programme caused impairment in self-renewal, loss of cell identity and premature exhaustion of quiescent satellite cell pool. Genetic ablation of Cdkn2a locus restored muscle stem cell properties in Lamin A/C null dystrophic mice. Our findings established a direct link between Lamin A and PcG epigenetic silencing and indicated that Lamin A-dependent muscular dystrophy can be ascribed to intrinsic epigenetic dysfunctions of muscle stem cells.
Andrea Bianchi, Chiara Mozzetta, Gloria Pegoli, Federica Lucini, Sara Valsoni, Valentina Rosti, Cristiano Petrini, Alice Cortesi, Francesco Gregoretti, Laura Antonelli, Gennaro Oliva, Marco De Bardi, Roberto Rizzi, Beatrice Bodega, Diego Pasini, Francesco Ferrari, Claudia Bearzi, Chiara Lanzuolo
The mechanisms that modulate the kinetics of muscle relaxation are critically important for muscle function. A prime example of the impact of impaired relaxation kinetics is nemaline myopathy caused by mutations in KBTBD13 (NEM6). In addition to weakness, NEM6 patients have slow muscle relaxation, compromising contractility and daily-life activities. The role of KBTBD13 in muscle is unknown, and the pathomechanism underlying NEM6 is undetermined. A combination of transcranial magnetic stimulation-induced muscle relaxation, muscle fiber- and sarcomere-contractility assays, low angle X-ray diffraction and super-resolution microscopy revealed that the impaired muscle relaxation kinetics in NEM6 patients are caused by structural changes in the thin filament, a sarcomeric microstructure. Using homology modeling, binding- and contractility assays with recombinant KBTBD13, novel Kbtbd13-knockout and Kbtbd13R408C-knockin mouse models and a GFP-labeled Kbtbd13- transgenic zebrafish model we discovered that KBTBD13 binds to actin – a major constituent of the thin filament - and that mutations in KBTBD13 cause structural changes impairing muscle relaxation kinetics. We propose that this actin-based impaired relaxation is central to NEM6 pathology.
Josine M. de Winter, Joery P. Molenaar, Michaela Yuen, Robbert van der Pijl, Shengyi Shen, Stefan Conijn, Martijn van de Locht, Menne Willigenburg, Sylvia J.P. Bogaards, Esmee S.B. van Kleef, Saskia Lassche, Malin Persson, Dilson E. Rassier, Tamar E. Sztal, Avnika A. Ruparelia, Viola Oorschot, Georg Ramm, Thomas E. Hall, Zherui Xiong, Christopher N. Johnson, Frank Li, Balazs Kiss, Noelia Lozano-Vidal, Reinier A. Boon, Manuela Marabita, Leonardo Nogara, Bert Blaauw, Richard J. Rodenburg, Benno Kϋsters, Jonne Doorduin, Alan H. Beggs, Henk Granzier, Ken Campbell, Weikang Ma, Thomas Irving, Edoardo Malfatti, Norma B. Romero, Robert J. Bryson-Richardson, Baziel G.M. van Engelen, Nicol C. Voermans, Coen A.C. Ottenheijm
Membrane repair is essential to cell survival. In skeletal muscle, injury often associates with plasma membrane disruption. Additionally, muscular dystrophy is linked to mutations in genes that produce fragile membranes or reduce membrane repair. Methods to enhance repair and reduce susceptibility to injury could benefit muscle in both acute and chronic injury settings. Annexins are a family of membrane-associated Ca2+-binding proteins implicated in repair, and annexin A6 was previously identified as a genetic modifier of muscle injury and disease. Annexin A6 forms the repair cap over the site of membrane disruption. To elucidate how annexins facilitate repair, we visualized annexin cap formation during injury. We found that annexin cap size positively correlated with increasing Ca2+ concentrations. We also found that annexin overexpression promoted external blebs enriched in Ca2+ and correlated with a reduction of intracellular Ca2+ at the injury site. Annexin A6 overexpression reduced membrane injury, consistent with enhanced repair. Treatment with recombinant annexin A6 protected against acute muscle injury in vitro and in vivo. Moreover, administration of recombinant annexin A6 in a model of muscular dystrophy reduced serum creatinine kinase, a biomarker of disease. These data identify annexins as mediators of membrane-associated Ca2+ release during membrane repair and annexin A6 as a therapeutic target to enhance membrane repair capacity.
Alexis R. Demonbreun, Katherine S. Fallon, Claire C. Oosterbaan, Elena Bogdanovic, James L. Warner, Jordan J. Sell, Patrick G. Page, Mattia Quattrocelli, David Y. Barefield, Elizabeth M. McNally
Myocardin (MYOCD) is the founding member of a class of transcriptional co-activators that bind serum response factor to activate gene expression programs critical in smooth muscle (SM) and cardiac muscle development. Insights into the molecular functions of MYOCD have been obtained from cell culture studies and, to date, knowledge about in vivo roles of MYOCD comes exclusively from experimental animals. Here, we defined an often lethal congenital human disease associated with inheritance of pathogenic MYOCD variants. This disease manifested as a massively dilated urinary bladder, or megabladder, with disrupted SM in its wall. We provided evidence that monoallelic loss-of-function variants in MYOCD caused congenital megabladder in males only, whereas biallelic variants were associated with disease in both sexes, with a phenotype additionally involving the cardiovascular system. These results were supported by co-segregation of MYOCD variants with the phenotype in four unrelated families, by in vitro transactivation studies where pathogenic variants resulted in abrogated SM gene expression, and finding megabladder in two distinct mouse models with reduced Myocd activity. In conclusion, we have demonstrated that variants in MYOCD result in human disease, and the collective findings highlight a vital role for MYOCD in mammalian organogenesis.
Arjan C. Houweling, Glenda M. Beaman, Alex V. Postma, T. Blair Gainous, Klaske D. Lichtenbelt, Francesco Brancati, Filipa M. Lopes, Ingeborg van der Made, Abeltje M. Polstra, Michael L. Robinson, Kevin D. Wright, Jamie M. Ellingford, Ashley R. Jackson, Eline Overwater, Rita Genesio, Silvio Romano, Letizia Camerota, Emanuela D'Angelo, Elizabeth J. Meijers-Heijboer, Vincent M. Christoffels, Kirk M. McHugh, Brian L. Black, William G. Newman, Adrian S. Woolf, Esther E. Creemers
Receptor activator of Nfkb ligand (RANKL) activates, while osteoprotegerin (OPG) inhibits, osteoclastogenesis. In turn a neutralizing Ab against RANKL, denosumab improves bone strength in osteoporosis. OPG also improves muscle strength in mouse models of Duchenne’s muscular dystrophy (mdx) and denervation-induce atrophy, but its role and mechanisms of action on muscle weakness in other conditions remains to be investigated. We investigated the effects of RANKL inhibitors on muscle in osteoporotic women and mice that either overexpress RANKL (HuRANKL-Tg+), or lack Pparb and concomitantly develop sarcopenia (Pparb-/-). In women, denosumab over 3 years improved appendicular lean mass and handgrip strength compared to no treatment, whereas bisphosphonate did not. HuRANKL-Tg+ mice displayed lower limb force and maximal speed, while their leg muscle mass was diminished, with a lower number of type I and II fibers. Both OPG and denosumab increased limb force proportionally to the increase in muscle mass. They markedly improved muscle insulin sensitivity and glucose uptake, and decrease anti-myogenic and inflammatory gene expression in muscle, such as myostatin and protein tyrosine phosphatase receptor-γ. Similarly, in Pparb-/-, OPG increased muscle volume and force, while also normalizing their insulin signaling and higher expression of inflammatory genes in skeletal muscle. In conclusions, RANKL deteriorates, while its inhibitor improves, muscle strength and insulin sensitivity in osteoporotic mice and humans. Hence denosumab could represent a novel therapeutic approach for sarcopenia.
Nicolas Bonnet, Lucie Bourgoin, Emmanuel Biver, Eleni Douni, Serge Ferrari
Aside from its catalytic function in protein synthesis, leucyl-tRNA synthetase (LRS) has a nontranslational function in regulating cell growth via the mammalian target of rapamycin (mTOR) complex 1 (mTORC1) pathway by sensing amino acid availability. mTOR also regulates skeletal myogenesis, but the signaling mechanism is distinct from that in cell growth regulation. A role of LRS in myogenesis has not been reported. Here we report that LRS negatively regulated myoblast differentiation in vitro. This function of LRS was independent of its regulation of protein synthesis, and it required leucine-binding but not tRNA charging activity of LRS. Local knock down of LRS accelerated muscle regeneration in a mouse injury model, and so did the knock down of Rag or Raptor. Further in vitro studies established a Rag-mTORC1 pathway, which inhibits the IRS1-PI3K-Akt pathway, to be the mediator of the nontranslational function of LRS in myogenesis. BC-LI-0186, an inhibitor reported to disrupt LRS-Rag interaction, promoted robust muscle regeneration with enhanced functional recovery, and this effect was abolished by cotreatment with an Akt inhibitor. Taken together, our findings revealed what we believe is a novel function for LRS in controlling the homeostasis of myogenesis, and suggested a potential therapeutic strategy to target a noncanonical function of a housekeeping protein.
Kook Son, Jae-Sung You, Mee-Sup Yoon, Chong Dai, Jong Hyun Kim, Nidhi Khanna, Aditi Banerjee, Susan A. Martinis, Gyoonhee Han, Jung Min Han, Sunghoon Kim, Jie Chen