The role of poly(ADP- ribose)polymerases in muscle stem cell fate and function

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Rationale: Recently, the critical roles for mitochondrial-linked signalling in stem cell (SC) function are becoming increasingly recognized. Despite low mitochondrial content and a reliance on mitochondrial-independent glycolytic metabolism for energy in most types of SCs, our current research has implicated mitochondrial function in SC activation, fate decisions and for defense against senescence, defined as the loss of a cells ability to divide (Zhang et al, Science 2016). Related to mitochondrial function, we have previously demonstrated that two large families of proteins, poly(ADPribose) polymerases (PARP) and Sirtuin (SIRT) enzymes, balance cell stress responses with mitochondrial homeostasis, and can have a large impact on tissue or whole body metabolism. Interestingly, each of these family of proteins require NAD+, a limited and key energy metabolite, as a cofactor for enzymatic activity and therefore compete for intracellular stores of NAD+. Interestingly, with cell stress, DNA damage, or inflammatory conditions, the PARP family of enzymes become highly activated, which results in depletion of NAD+ stores, compromised SIRT enzymatic activity leading to mitochondrial dysfunction. As a result, PARP inhibition or genetic loss of function of Parp1 in mice, for example, increases NAD+ levels and SIRT-directed mitochondrial biogenesis. Related to this, our lab recently demonstrated that PARP activity is overactive in muscle during muscular dystrophy causing metabolic dysfunction (Ryu et al, Science Translational Medicine 2016). However, the role of PARP proteins in stem cell fate, metabolism or function has yet to be revealed. Our long-term goal is to examine the precise mechanisms by which PARP activity alter tissue regenerative capacity and stem cell function with damage, disease and aging. To achieve this long-term objective, our immediate goals, which are the subject of this NSERC Discovery Grant, are to: (1) Profile the intersections of PARP-, NAD+- and mitochondrial-metabolism in muscle SCs in mice following exercise training. (2) Evaluate the role of PARP activation in muscle SCs during muscle damage-induced regeneration using cardiotoxin and downhill running or in a mouse model of muscular dystrophy. (3) Determine if PARP activation in muscle SCs is necessary for exercise-induced muscle SC proliferation/differentiation or for tissue regeneration following damage using PARP inhibitors in vivo or in cell culture. The proposed experiments will combine a variety of in vitro and mouse exercise models already established in the PI's lab. We expect data generated from the proposed experiments to identify novel PARP directed mechanisms responsible muscle stem cell fate during exercise and tissue regeneration. The proposed studies will provide unique training opportunities for students interested molecular exercise physiology and stem cell biology.