Maintenance of mtDNA integrity in muscle stem cells

• Applicant: Dr. David Pla Martin, Ph.D.
• Subject Area: Biogerontology and Geriatric Medicine ; Anatomy and Physiology
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 445067265

Background: The regenerative capacity of muscle stem cells (MuSCs) declines with age and cell-intrinsic alterations contribute to muscle mass loss. Sarcopenia leads to physical disability, but more importantly to an increased incidence of falls followed by hospitalization, which may result in premature death. Loss of muscle mass may also contribute to insulin resistance typical for old age. Understanding aging-related alterations in MuSCs is thus essential to establish new strategies to delay the development of sarcopenia.Problem: In non-dividing cells of humans, copies of mitochondrial DNA (mtDNA) with large deletions accumulate during aging, giving rise to a tissue mosaic. Tissue stem cells are rarely dividing and may suffer the same fate. Both the copy numbers of mtDNA and mitochondrial mass must be expanded during SC differentiation, and dramatically so when upon recruitment small MuSCs give rise to large mature muscle fibers which strongly depend on mitochondrial function. Thus, intactness of mtDNA encoding thirteen essential subunits of the respiratory chain is obviously essential for differentiation of SCs, but little is known about the mechanisms maintaining mtDNA integrity, which, moreover, is likely to be compromised during aging.Strategy: To study the role of mtDNA deletions during aging, we have generated a mouse strain which expresses, upon Cre-recombination (Rosa26-Stop-construct), a dominant-negative mutant of the mitochondrial helicase Twinkle, thus enhancing the generation of deleted mtDNA species, here in MuSCs driven by Pax7-Cre. In this proposal, we will primarily determine if accumulation of mtDNA molecules with large deletions occurs during aging in MuSCs or if this is avoided by (i) either minimizing the rate of mtDNA replication and, consequently, the chance of mutation events or by (ii) "purification" for wt molecules during division. Alternatively, iii) MuSCs with high mtDNA deletion loads may be selected against during activation. In addition, the turnover and maintenance of quality of mitochondria will be investigated.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr. Rudolf Wiesner