DELAYED SKELETAL MUSCLE REGENERATION IN AN ACCELERATED AGEING MOUSE MODEL

Delayed skeletal muscle regeneration in an accelerated ageing mouse model. Suvham Barua 1,3; Lorenza Bodo 1; Alessio Menga 1; Daniela Talarico 2; Andrea Graziani 1,3 & Elia Angelino 1,3. 1. Molecular Biotechnology Center ‘Guido Tarone’, Department of Molecular Biotechnologies and Health Sciences, University of Torino, Turin, Italy, 2. Division of Genetics and Cell Biology, IRCCS, San Raffaele Scientific Institute, Milan, Italy, 3. Department of Translational Medicine, University of Piemonte Orientale, Novara, Italy. Introduction PolgD257A constitutive knock-in mice exhibit a premature aging phenotype between 8 to 12 months, characterized by anaemia, kyphosis, alopecia, lipodystrophy, and sarcopenia. The D257A mutation specifically impairs the DNA-proofreading activity, but not the DNA polymerase activity, of Polg, a nuclear gene encoding a DNA polymerase crucial for mitochondrial DNA repair. This impairment leads to increased mutations in mitochondrial DNA, resulting in primary mitochondrial myopathy. Additionally, PolgD257A mice display signs of immunosenescence and inflammaging by 11 months of age. In this study, we aimed to develop a model for delayed skeletal muscle regeneration associated with premature aging. This model can be used in future studies to investigate delayed regeneration due to mitochondrial dysfunction and aging, providing insights into the role of mitochondrial dysfunction in aging and its impact on muscle regeneration. Methods Male and female PolgD257A and wild-type mice, aged 3-months and 11-months, were histologically analysed to assess skeletal muscle regeneration, as well as satellite cell-autonomous and non-cell-autonomous effects. To study cell-autonomous effects, primary myoblasts were cultured ex vivo. For the regenerating environment effects, GFP+ myoblasts were transplanted into 11-month-old PolgD257A and wild-type mice. Result PolgD257A mice exhibit significantly delayed muscle regeneration at 11-months of age and moderately delayed regeneration at 3-months, compared to their age-matched controls. At both 11 and 3 months of age, PolgD257A mice show a reduction in satellite cells (SC) and Pax7+ myoblasts in both basal and regenerating muscles, respectively, when compared to age-matched wild-type mice. However, primary myoblasts from PolgD257A mice cultured ex vivo do not display any defects in proliferation or differentiation. Notably, there are fewer and smaller cross-sectional area wt-GFP+ myoblasts engrafted in the muscles of 11-month-old PolgD257A mice compared to wild-type mice. Additionally, PolgD257A mice show increased M2-macrophage infiltration and higher levels of senescence in regenerating muscles compared to wild-type mice. Conclusion Collectively, we characterized both satellite cell (SC) autonomous and non-cell autonomous factors in age-related defective skeletal muscle regeneration using a model of accelerated aging driven by mitochondrial dysfunction. Our findings indicate that non-cell autonomous factors play a significant role in the impaired muscle regeneration observed in PolgD257A mice, primarily due to the accumulation of senescent cells and other age-related factors.