ActRIIB:ALK4-Fc alleviates muscle dysfunction and comorbidities in murine models of neuromuscular disorders

Abstract

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.

Functionally diverse heteromeric traps for ligands of the transforming growth factor-β superfamily

“…4 B,C), consistent with previous observations 35 , 37 . These tissue alterations in the presence of IIB-Fc:ALK4-Fc are likely achieved, at least in part, through hypertrophy of individual muscle fibers, and have been reported to accompany enhanced muscle twitch force 35 . Interestingly, the selectively diminished binding to BMP9 and BMP10 by IIB-Fc:ALK4-Fc (Fig.…”

“…Similarly, IIB-Fc:ALK4-Fc treatment caused a significant increase in gastrocnemius weight (at 10 mg/kg: 234.4 ± 9, P < 0.001) and a significant reduction in body fat (at 10 mg/kg: − 3.34 ± 0.45, P < 0.001) comparable in magnitude to changes caused by IIB-Fc:IIB-Fc (gastrocnemius weight: 230.6 ± 8.66, P < 0.001; body fat: − 3.51 ± 0.33, P < 0.001) (Fig. 4 B,C), consistent with previous observations 35 , 37 . These tissue alterations in the presence of IIB-Fc:ALK4-Fc are likely achieved, at least in part, through hypertrophy of individual muscle fibers, and have been reported to accompany enhanced muscle twitch force 35 .…”

“…To assess the biologic effects of treatment on multiple tissue composition, body fat and bone mineral density were measured by nuclear magnetic resonance (NMR) imaging and dual-energy x-ray absorptiometry (DXA), respectively, at baseline (day -1) and day 27. The gastrocnemius muscle, which responds strongly to manipulation of TGF-β superfamily signaling 8 , 35 , was chosen as a representative muscle and weighed at day 28. Control experiments indicated that replacement of a human Fc domain with its murine counterpart does not affect activity of a IIB-Fc:IIB-Fc homodimeric construct tested in mice for 8 weeks (Supplemental Fig.…”

Systemic administration of monovalent follistatin-like 3-Fc-fusion protein increases muscle mass in mice

“…In this case, the bi-FSTL3-Fc protein resembles a biparatopic bispecific antibody. As shown in the case of a heterodimeric fusion protein ActRIIB:ALK4-Fc ( Li et al., 2021 ), one molecule of Fc-protein with two arms can pinch one GDF8 homodimer ( Figure 8 I). However, our data suggest that this is not a major binding form between bi-FSTL3-Fc and GDF8, possibly because of steric hindrance.…”

Myostatin/Activin-A Signaling in the Vessel Wall and Vascular Calcification

“…Finally, to broaden the discussion to the therapeutic approaches based on Act-A signaling modulation, it should be mentioned that administration of the recently developed ActRIIB:ALK4-Fc, a heterodimeric ligand-trapping fusion protein of the extracellular domains of ALK4 and ActRIIB, improved muscle dysfunction in murine models of neuromuscular disorders [108].…”