Patients with neuromuscular disorders suffer from a lack of treatment options for skeletal muscle weakness and disease comorbidities. Here, we introduce as a potential therapeutic agent a heterodimeric ligand-trapping fusion protein, ActRIIB:ALK4-Fc, which comprises extracellular domains of activin-like kinase 4 (ALK4) and activin receptor type IIB (ActRIIB), a naturally occurring pair of type I and II receptors belonging to the TGF-β superfamily. By surface plasmon resonance (SPR), ActRIIB:ALK4-Fc exhibited a ligand binding profile distinctly different from that of its homodimeric variant ActRIIB-Fc, sequestering ActRIIB ligands known to inhibit muscle growth but not trapping the vascular regulatory ligand bone morphogenetic protein 9 (BMP9). ActRIIB:ALK4-Fc and ActRIIB-Fc administered to mice exerted differential effectsconcordant with SPR results -on vessel outgrowth in a retinal explant assay. ActRIIB:ALK4-Fc induced a systemic increase in muscle mass and function in wild-type mice and in murine models of Duchenne muscular dystrophy (DMD), amyotrophic lateral sclerosis (ALS), and disuse atrophy. Importantly, ActRIIB:ALK4-Fc improved neuromuscular junction abnormalities in murine models of DMD and presymptomatic ALS and alleviated acute muscle fibrosis in a DMD model. Furthermore, in combination therapy ActRIIB:ALK4-Fc increased the efficacy of antisense oligonucleotide M12-PMO on dystrophin expression and skeletal muscle endurance in an aged DMD model. ActRIIB:ALK4-Fc shows promise as a therapeutic agent, alone or in combination with dystrophin rescue therapy, to alleviate muscle weakness and comorbidities of neuromuscular disorders.
Cardiomyopathies are ascribed to a variety of etiologies, present with diverse clinical phenotypes, and lack disease-modifying treatments. Mounting evidence implicates dysregulated activin receptor signaling in heart disease and highlights inhibition of this pathway as a potential therapeutic target. Here, we explored the effects of activin ligand inhibition using ActRIIB:ALK4-Fc, a heterodimeric receptor fusion protein, in two mechanistically distinct murine models of cardiomyopathy. Treatment with ActRIIB:ALK4-Fc significantly improved systolic or diastolic function in cardiomyopathy induced by neuromuscular disease or diabetes mellitus. Moreover, ActRIIB:ALK4-Fc corrected Ca 2+ handling protein expression in diseased heart tissues, suggesting that activin signaling inhibition could alleviate cardiomyopathies in part by rebalancing aberrant intracellular Ca 2+ homeostasis-a common underlying pathomechanism in diverse heart diseases.
Genetic variation in the ACVR1C gene has been reported to be associated with decreased waist-to-hip ratio and risk of type 2 diabetes in humans. However, the effect of this naturally occurring variation on ALK7 function is unclear. Here we show that the human ACVR1C variant I195T, which displays the greatest effect on waist-to-hip ratio adjusted for body mass index, fails to signal in response to ALK7 ligands in a cell-based assay. This is consistent with observations in mice that impaired ALK7 signaling increases lipolysis and decreases adiposity. As further validation of ALK7 as an obesity target, we present data showing in the naturally occurring polygenic obese TSOD mouse a specific high affinity neutralizing monoclonal anti-ALK7 antibody (ALK7 mAb) dramatically decreases leptin levels, adipose macrophages and adiposity. The specificity of the ALK7 mAb is demonstrated by its lack of effect in genetically deficient ALK7 mice. These data along with the knowledge that normal Balb/c mice harbor a homozygous ALK7 nonsense mutation suggests that targeting ALK7 in humans should decrease obesity, susceptibility to diabetes and have minimal on-target negative consequences. Disclosure Y. Bu: None. M. Zhao: None. M. Fredericks: None. M. Cannell: None. Y. Dagon: None. C.A. Emdin: None. K. Okunishi: None. H. Wang: None. D. Sako: None. R. Castonguay: Employee; Self; Acceleron Pharma. R.N.V. Suragani: None. S. Kathiresan: Advisory Panel; Self; Regeneron Genetics Center. Consultant; Self; Color Genomics, Corvia Medical, Inc., Medgenome, Pfizer Inc. Stock/Shareholder; Self; Catabasis Pharmaceuticals, Maze Therapeutics, San THerapeutics, Verve Therapeutics. A. Grinberg: None. J. Knopf: Stock/Shareholder; Self; Acceleron Phama. R.S. Pearsall: Employee; Self; Acceleron Pharma, Inc. Stock/Shareholder; Self; Acceleron Pharma, Inc. R. Kumar: Employee; Self; Acceleron Pharma. T. Izumi: Research Support; Self; Acceleron Pharma.
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