ATG14 and RB1CC1 play essential roles in maintaining muscle homeostasis

ABSTRACT

Defects in macroautophagy/autophagy are implicated in the pathogenesis of neuromuscular and heart diseases. To precisely define the roles of autophagy-related genes in skeletal and cardiac muscles, we generated muscle-specific rb1cc1- and atg14-conditional knockout (cKO) mice by using Ckm/Ckmm2-Cre and compared their phenotypes to those of ulk1 ulk2-conditional double-knockout (cDKO) mice. atg14-cKO mice developed hypertrophic cardiomyopathy, which was associated with abnormal accumulation of autophagic cargoes in the heart and early mortality. Skeletal muscles of both atg14-cKO and rb1cc1-cKO mice showed features of autophagic vacuolar myopathy with ubiquitin⁺ SQSTM1⁺ deposits, but only those of rb1cc1-cKO mice showed TARDBP/TDP-43⁺ pathology and other features of the inclusion body myopathy–like disease we previously described in ulk1 ulk2-cDKO mice. Herein, we highlight tissue-specific differences between skeletal and cardiac muscles in their reliance on core autophagy proteins and unique roles for ULK1-ULK2 and RB1CC1 among these proteins in the development of TARDBP⁺ pathology.

ABBREVIATIONS:AVM: autophagic vacuolar myopathy; cDKO: conditional double knockout; cKO: conditional knockout; H&E: hematoxylin and eosin; IBM: inclusion body myopathy; mtDNA: mitochondrial DNA; PFA: paraformaldehyde; RNP: ribonucleoprotein; TBST: Tris-buffered saline with 0.2% Triton X-100

KEYWORDS:

• ATG14
• autophagy
• autophagic vacuolar myopathy
• cardiomyopathy
• inclusion body myopathy
• RB1CC1
• RNA-binding protein
• ULK1
• ULK2

Acknowledgments

We are grateful to Dr. Doug Green (St. Jude) for providing the Atg14^flox/flox mouse line, to Dr. Jun-Lin Guan (University of Cincinnati) for sharing the Rb1cc1^flox/flox mouse line, and Masaaki Komatsu (Tokyo Metropolitan Institute of Medical Science) for the gift of Atg7^flox/flox mouse line. We are also grateful to the staffs in the St. Jude Veterinary Pathology Core and Cell and Tissue Imaging Core for technical assistance and to Dr. Vani Shanker and Dr. Angela J McArthur for editing the manuscript.

Disclosure statement

The authors declare that they have no competing financial interests.

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

This work was supported by the American Lebanese Syrian Associated Charities; National Institutes of Health [R01 GM132231]; National Institutes of Health [R01 MH115058]; Robert Packard Center for ALS Research, Johns Hopkins University.