Year: 2025
Type: dissertation
Abstract: Mutations in the mitochondrial DNA (mtDNA) have been linked to skeletal muscle atrophy and sarcopenia. Muscle satellite cells (MuSCs), responsible for regenerating new muscle fibres, are generally quiescent but become activated during muscle biogenesis in the course of development and growth, exercise, or damage. The regenerative capacity of MuSCs declines with age, and this is thought to be a contributing factor to sarcopenia. With the ever-increasing age of the global population, it is essential to understand the consequences of disturbed mtDNA integrity in MuSCs in the context of sarcopenia. To explore how mtDNA mutations affect the regeneration capacity of MuSCs, we employed a mouse model expressing a dominant negative mutation of TWINKLE (K320E-Twinkle), the mtDNA helicase, under the control of tamoxifen, specifically in the MuSCs or in skeletal muscle, respectively. This mutation is known to accelerate the accumulation of mtDNA alterations. Acute activation of muscle regeneration in adult mice by cardiotoxin induced degeneration of M. tibialis anterior (TA) induced the dramatic accumulation of fibres with mitochondrial dysfunction and enhanced inflammation. Our studies using the mitoTIMER reporter, along with induction of K320E-Twinkle in MuSCs in vitro, pointed to an initial increase in mitochondrial biogenesis and turnover. In contrast, when K320E-Twinkle is activated upon muscle biogenesis during normal development, we do not observe mitochondrial dysfunction. However, histological analyses showed a reduced cross-sectional area and a prominent fibre type shift, from glycolytic to oxidative in the TA. Interestingly, this was observed only in the glycolytic TA muscle and not in the predominantly oxidative M. soleus. Additionally, in vitro analysis of MuSC differentiation showed that K320E-Twinkle impairs muscle fibre differentiation by reducing mitochondrial biogenesis. Accordingly, K320E-Twinkle-C2C12 cells also showed disturbed differentiation, along with reduced myogenic fusion, respiratory chain defects, and progressive mtDNA depletion. Proximity proteomics revealed a decrease of mitochondrial proteins in the proteome of the mutant cells. In conclusion, our results demonstrate that interfering with mtDNA replication in MuSCs impairs muscle differentiation and alters muscle architecture. Our data reveals a link between mtDNA integrity and the altered metabolic shift from glycolytic to oxidative, similar to that observed in aged sarcopenic muscle of long-lived organisms.
Author: Sen, Ayesha
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W7058189218