Mahoudeau, A. | bioRxiv Science

bioRxiv2024

Distinct pathogenic influence of anti-HMGCR+ and anti-SRP+ immune-mediated necrotizing myopathy autoantibodies on engineered muscle function

Immune-mediated necrotizing myopathy (IMNM) is a subgroup of idiopathic inflammatory myopathies associated with anti-signal recognition particle (SRP) or anti-3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) autoantibodies. However, the demonstration of a direct pathogenic effect of IMNM patient autoantibodies on skeletal muscle contractile force, independent of the downstream activation of the complement pathway, has yet to be reported. Thus, the goal of this study was to leverage a custom 3D-human skeletal muscle microtissue (hMMT) culture platform, that enables muscle cell contractile apparatus maturation and the analysis of contractile function, to evaluate the direct effect of total immunoglobulins (IgGs) isolated from IMNM patients with amplification of anti-SRP+ or anti-HMGCR+ autoantibodies. hMMTs capable of force generation were treated with total IgGs, isolated from 3 SRP+ and 3 HMGCR+ patients plasma, and delivered in complement inactivated media for 4 days. hMMT health was then evaluated by quantifying the peak force and contraction kinetics in response to electrical field stimulation and by performing histological analysis of sarcomere and myotube structures. Treating hMMTs with total IgGs from anti-HMGCR+ patients resulted in a decline in tetanus contractile force, though sarcomere Z-line architecture analysis revealed no significant influences on sarcomere organization. hMMT treatment with total IgGs from anti-SRP+ patients induced muscle atrophy, observed via significantly smaller myotube diameter, but this did not translate to a decline in contractile function. This study demonstrates that anti-SRP and anti-HMGCR autoantibodies exert direct, but distinct influences on IMNM-associated skeletal muscle pathogenesis, which may inform IMNM therapy development.

bioengineering↗

bioRxiv2018

Guanabenz treatment improves Oculopharyngeal muscular dystrophy phenotype

Oculopharyngeal muscular dystrophy (OPMD) is a rare late onset genetic disease affecting most profoundly eyelid and pharyngeal muscles, leading respectively to ptosis and dysphagia, and proximal limb muscles at later stages. A short abnormal (GCG) triplet expansion in the polyA- binding protein nuclear 1 (PABPN1) gene leads to PABPN1-containing aggregates in the muscles of OPMD patients. It is commonly accepted that aggregates themselves, the aggregation process and/or the early oligomeric species of PABPN1 are toxic in OPMD. Decreasing PABPN1 aggregate load in animal models of OPMD ameliorates the muscle phenotype. In order to identify a potential therapeutic molecule that would prevent and reduce aggregates, we tested guanabenz acetate (GA), an FDA-approved antihypertensive drug, in OPMD cells as well as in the A17 OPMD mouse model. We demonstrate that treating mice with GA reduces the size and number of nuclear aggregates, improves muscle force, protects myofibres from the pathology-derived turnover and decreases fibrosis. GA is known to target various cell processes, including the unfolded protein response (UPR), which acts to attenuate endoplasmic reticulum (ER) stress. Here we used a cellular model of OPMD to demonstrate that GA increases both the phosphorylation of the eukaryotic translation initiator factor 2 subunit (eIF2) and the splicing of Xbp1, key components of the UPR. Altogether these data suggest that modulation of protein folding regulation can be beneficial for OPMD and support the further development of guanabenz or its derivatives for treatment of OPMD in humans.\n\nSignificance StatementOculopharyngeal muscular dystrophy (OPMD) is a rare late onset incurable genetic disease characterized by the formation of insoluble aggregates in skeletal muscles. It has been shown that the reduction of aggregates correlates with an improvement of the disease. Here we used a mouse model of OPMD to show that Guanabenz acetate, the active constituent of a marketed but recently discontinued drug for hypertension, decreases the number and the size of aggregates after systemic delivery and improves many aspects of the disease. We also describe experimental evidences explaining the mechanism behind the efficacy of such compound for OPMD.

pathology↗