Butyrate endows extraocular muscle stem cell-like transcriptomic patterns that ameliorate satellite cell depletion and denervation to slow ALS progression.

Abstract

Amyotrophic lateral sclerosis (ALS) is a fatal neuromuscular disease that affects all voluntary muscles in the body, leading to paralysis and respiratory failure, while the extraocular muscles (EOMs) are largely spared even at the end-stage of ALS. Through whole-mount muscle imaging, we detected severe denervation along with depletion of Pax7+ satellite cells (SCs) peri-neuromuscular junction (NMJ) in hindlimb and diaphragm muscles of end-stage SOD1G93A mice (a familial ALS mouse model), but not in EOMs. Upon isolating SCs from different muscles using fluorescence activated cell sorting (FACS), the FACS profiles of hindlimb and diaphragm SCs of G93A mice exhibited activation and depletion phenotypes but not in wildtype controls. Importantly, both wildtype and G93A EOM SCs exhibited spontaneous activation behavior without significant differences in abundance. Examination of Pax7+ and Ki67+ cell ratios and RNA-Seq of SCs cultured in growth and differentiation medium revealed that EOM SCs maintained renewability and stemness better than diaphragm and hindlimb counterparts, especially in differentiation-favoring environments. Comparative functional annotation analyses indicate enrichment of axon guidance molecules, such as Cxcl12, in cultured EOM SCs. In cocultures of motor neurons and myotubes, overexpressing Cxcl12 improved NMJ formation. The unique homeostasis regulation of EOM SCs with their axon-attractive nature may explain the preservation of SCs and NMJ innervation in ALS EOMs. Intriguingly, feeding G93A mice with sodium butyrate extended the life span of G93A mice, alleviated NMJ denervation and SCs depletion. Butyrate treatment promoted renewability and stemness of cultured G93A hindlimb and diaphragm SCs, as well as Cxcl12 expression. Thus, butyrate-induced EOM SC-like transcriptomic patterns may contribute to its beneficiary effects observed in G93A mice (Funding_NIH R01NS105621).