mTOR pathway modulation improves hypercapnia-induced satellite cell autophagy arrest and dysfunctional myogenesis.

Chronic CO2 retention, or hypercapnia, occurs in pulmonary diseases and leads to skeletal muscle wasting. Muscle wasting and hypercapnia are independently associated with substantial mortality. While abnormal skeletal muscle stem -satellite- cells, contribute to impaired myogenesis in pulmonary diseases, no mechanistic data exists on hypercapnia-driven dysfunctional satellite cells and myogenesis in-vivo. Autophagy regulates satellite cell activation and myogenesis, and while elevated CO2 inhibits autophagy in inflammatory cells, it has never been evaluated in the context of hypercapnia-driven abnormal myogenesis. Using lineage tracing in pre- and post-stem cell transplantation experiments, we show that hypercapnia undermines both Pax7- and α-7 integrin-expressing satellite cells activation, replication and myogenesis. Satellite cells’ multi-omic analyses indicate that hypercapnia disrupts multiple pathways regulated by autophagy. Moreover, autophagy-specific LC3 fluorescence-reporting mouse and cellular data demonstrate that hypercapnia reduces expressions of AMPK and Ulk1, which critically participate in autophagosome formation, and has no effect on the antagonistic mTOR pathway including Ulk1 serine-757 phosphorylation. Moreover, Atg7 knockout-driven loss of autophagy function phenocopies the effects on hypercapnia. After rapamycin administration, the hypercapnia-induced myogenic deficit is corrected by a sharp AMPK activation leading to the autophagy-stimulatory Ulk1 phosphorylation at serine-555, autophagy acceleration, increased satellite cells replication and improved myogenesis post-satellite cells transplantation. Pax7-GFP reporter mice were flow sorted and collected for scRNA-Sequencing. They were immediately fixed and sequenced following 10X genomics fixed cell sequencing protocols (PN-1000414).