Exploring the Functions and Regulatory Mechanisms of Peroxisomes during Skeletal Muscle Development and Regeneration

Skeletal muscle (SKM) can adjust the balance between glycolytic and oxidative metabolism to meet theenergy requirement under various physiological conditions, and this adaptation relies very much on theexpression and activity of PGC-1α, a key regulator of oxidative metabolism facilitating the expression ofgenes critical for the function and biogenesis of the key oxidative organelles, mitochondria and peroxisomes.Peroxisomes are single membrane-bounded organelles that are ubiquitous and highly dynamic. Theyparticipate in the β-oxidation of vary long chain, unsaturated, and branched fatty acids as well asmetabolizing carboxylates containing a 3-methyl or 2-hydroxy group via α-oxidation. Another importantfunction of peroxisomes is removing the harmful reactive oxygen species (ROS) concomitantly generatesfrom the oxidation of substrates in mitochondria and peroxisomes, which is performed by several antioxidantenzymes, including catalase, SOD1, and PRDX5. The number of peroxisomes in a cell reflects its metabolicstatus and it is balanced by the biogenesis and autophagy processes. Defects in peroxisome biogenesis causesa spectrum of peroxisome biogenesis disorder (PBD), and the most serious one, the Zellweger syndrome, isusually neonatal lethal and shows low muscle tone (hypotonia), implying the participation of peroxisomes inthe development and function of skeletal muscle systems. A recent fly study has also demonstrated thatperoxisomes are critically required for lipid metabolism and muscle function. Besides, functional defects ofperoxisomes are implicated in the etiology of type II diabetes. Taken together, these studies have stronglysuggested the importance of peroxisomes in normal muscle metabolism, especially that of lipid; therefore,elucidating the regulatory mechanisms of their biogenesis, removal, and functions in skeletal muscle shouldpave way for therapies of these metabolic disorders in SKM. Our recently published studies showed thatthe transcription factor Bhlhe40 can directly bind to the promoter of PGC-1α to repress its expression andinteract directly with PGC-1α on PGC-1α-targeted gene promoters/enhancers, which in turn repressedPGC-1α transactivational activity on these cis-elements through recruitment of HDACs. These studiessuggest that Bhlhe40 regulates PGC-1α at both expression and activity levels, therefore, its activity shouldhave profound influence on cellular oxidative metabolism, especially on the biogenesis and metabolicactivity of the major organelles, mitochondrion and peroxisome, for oxidative metabolism. To furtherdelineate the regulatory mechanisms of peroxisome function and homeostasis by Bhlhe40 during skeletalmuscle development and regeneration, we propose to perform the following experiments in myogenicdifferentiation in vitro and in myogenic development in utero and in postnatal life development andregeneration:1. Observing peroxisome functions and dynamics of number during myogenesis in vitro.2. Observing peroxisome functions and dynamics of number during myogenesis in vivo.3. Examining the effect of Peroxisome depletion on myogensis in vitro.4. Observing peroxisome functions and dynamics of number during myogenesis in vitro in Bhlhe40over-expressed (Bhlhe40-OV) and knockdowned (Bhlhe40-KD) myoblasts .5. Observing peroxisome functions and dynamics of number during myogenesis in vivo in Bhlhe40knockout (Bhlhe40-KO) mice.6. Defining the regulatory mechanisms of peroxisome related genes by Bhlhe407. Complementation assay of Bhlhe40 targeted peroxisome related genes in peroxisome number andfunctions.