Long‐term Quercetin Treatment is Unable to Sustain Elevated PGC‐1α Pathway Activity in the mdx Diaphragm
Authors: Spaulding Hannah , Ballmann Christopher , Quindry John , Selsby Joshua 
Published: November 2023

Overexpression of PGC‐1α has been shown to attenuate disuse atrophy and reduce disease severity caused by dystrophin deficiency. Effective therapeutics for atrophy caused by prolonged exposure to microgravity and dystrophin deficiency will require long‐term interventions as these are persistent perturbations of skeletal muscle. Quercetin, a naturally occurring flavonoid, is predicted to activate the PGC‐1α pathway via SIRT‐1, which ultimately results in a shift toward a slow, oxidative muscle phenotype. We demonstrated that a 0.2% quercetin enriched diet attenuated respiratory dysfunction in mdx mice, a model of Duchenne muscular dystrophy caused by dystrophin deficiency, for 4–8 months during a 12 month study in 14 month old mice. The purpose of this investigation was to determine the extent to which chronic dietary quercetin enrichment maintained elevated PGC‐1α pathway activity in diaphragms of 14 month old mdx mice fed quercetin for 12 months. Relative protein abundance of the upstream PGC‐1α pathway regulator phosphorylated (p‐) AMPKT172, was decreased 7.1‐fold (p<0.05) in mdx compared to C57, however, quercetin increased p‐AMPKT172 3.5‐fold compared to mdx. SIRT‐1 and SIRT‐1 activity, measured by histone 3 lysine 9 acetylation, increased over 2.0‐ (p<0.05) and 3.0‐fold (p<0.05), respectively, in mdx compared to C57, but were unaltered with quercetin treatment. PGC‐1α protein abundance was increased by 1.8‐fold in mdx and 1.3‐fold in mdxQ mice compared to C57. Protein abundance of downstream pathway components leading to an oxidative phenotype, ERRα, NRF‐1 and TFAM, were increased 1.7‐fold, decreased 1.4‐fold, and decreased 6.0‐fold, respectively, in dystrophic muscle compared to C57 and were not altered by the quercetin diet. Consistent with these findings, protein abundance of cytochrome c and succinate dehydrogenase A decreased 1.7‐fold in mdx compared to C57; cytochrome c oxidase IV was not detectable in dystrophic muscle. Mitochondrial markers were similar between mdx and mdxQ. The PGC‐1α pathway also leads to a slow muscle phenotype. We found that GABPA was decreased 1.6‐fold (p<0.05) in mdx mice while utrophin and type I myosin heavy chain were increased 30‐fold (p<0.05) and 2.0‐fold (p<0.05), respectively. Relative protein abundance of GABPA, utrophin, and type I myosin heavy chain was not altered with quercetin treatment. These data suggest that following 12 months of dietary quercetin enrichment PGC‐1α pathway activity was depressed in dystrophic diaphragms compared to C57 and was similar between untreated and quercetin‐treated mdx mice. This finding is consistent with our previous functional data and supports the postulate that the transient nature of quercetin‐mediated protection of respiratory function is due to the development of quercetin insensitivity. This inhibitory mechanism will need to be characterized and overcome if quercetin is to be a successful therapy for Duchenne muscular dystrophy and atrophy caused by long‐term exposure to microgravity.Support or Funding InformationThis work was supported by the Duchenne Alliance Research Foundation and its member foundations.