Rapamycin improves satellite cells’ autophagy and muscle regeneration during hypercapnia
Joseph Balnis, Emily L. Jackson, Lisa A. Drake, Diane V. Singer, Ramon Bossardi Ramos, Harold A. Singer, Ariel Jaitovich
Joseph Balnis, Emily L. Jackson, Lisa A. Drake, Diane V. Singer, Ramon Bossardi Ramos, Harold A. Singer, Ariel Jaitovich
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Research Article Pulmonology

Rapamycin improves satellite cells’ autophagy and muscle regeneration during hypercapnia

Abstract

Both CO2 retention, or hypercapnia, and skeletal muscle dysfunction predict higher mortality in critically ill patients. Mechanistically, muscle injury and reduced myogenesis contribute to critical illness myopathy, and while hypercapnia causes muscle wasting, no research has been conducted on hypercapnia-driven dysfunctional myogenesis in vivo. Autophagy flux regulates myogenesis by supporting skeletal muscle stem cell — satellite cell — activation, and previous data suggest that hypercapnia inhibits autophagy. We tested whether hypercapnia worsens satellite cell autophagy flux and myogenic potential and if autophagy induction reverses these deficits. Satellite cell transplantation and lineage-tracing experiments showed that hypercapnia undermined satellite cells’ activation, replication, and myogenic capacity. Bulk and single-cell sequencing analyses indicated that hypercapnia disrupts autophagy, senescence, and other satellite cell programs. Autophagy activation was reduced in hypercapnic cultured myoblasts, and autophagy genetic knockdown phenocopied these changes in vitro. Rapamycin stimulation led to AMPK activation and downregulation of the mTOR pathway, which are both associated with accelerated autophagy flux and cell replication. Moreover, hypercapnic mice receiving rapamycin showed improved satellite cell autophagy flux, activation, replication rate, and posttransplantation myogenic capacity. In conclusion, we have shown that hypercapnia interferes with satellite cell activation, autophagy flux, and myogenesis, and systemic rapamycin administration improves these outcomes.

Authors

Joseph Balnis, Emily L. Jackson, Lisa A. Drake, Diane V. Singer, Ramon Bossardi Ramos, Harold A. Singer, Ariel Jaitovich

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Figure 4

Postinjury satellite cells’ contribution to myogenesis is reduced in hypercapnia.

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Postinjury satellite cells’ contribution to myogenesis is reduced in hyp...
(A) Pax7-GFP reporter mice induced with tamoxifen were exposed to normo- and hypercapnia, and TA muscle was then injured (once) with CTX to observe intrinsic satellite cell participation in muscle repair by section’s MFI. (B) Preinjury MFI is elevated in HC versus NC muscles (n = 5). (C) Postinjury muscle sections showed a significantly lower change in MFI compared with NC animals, indicating less Pax7-GFP cell participation in muscle repair (n = 5). (D) Graphic illustrates experimental design of transplantation experiments. (E and F) Column-isolated α7-integrin–positive satellite cells from RFP-expressing animals showed that HC mice produce satellite cells with significantly reduced myogenic capacity in comparison with NC counterparts, as determined by counting the number of red myofibers per TA muscle section 2 weeks after transplant into a healthy NC recipient. The animals’ contralateral legs were transplanted with cells from an NC donor as a control (n = 8). All statistical comparisons were performed using Student’s t test; *P < 0.05, **P < 0.01, and ***P < 0.001. Graphics from D were constructed with clipart supplied by BioRender.com.