Microbes, metabolites and muscle: Metagenomic and metabolomic analyses in a mouse model of muscular dystrophy
Authors: Marullo Anthony , O'Halloran Ken 
Published: May 2023

Skeletal muscle is the largest metabolic organ. The metabolic and endocrine nature of skeletal muscle allows for long-range signaling and influence over the enteric environment and the resident microbiota. Commensal microbial signaling can influence the composition and development of skeletal muscle, forming a bidirectional gut-muscle axis.Duchenne muscular dystrophy (DMD) is a fatal neuromuscular disease characterised by skeletal muscle atrophy, fibrosis, and ultimately cardiorespiratory failure. The pathways involved in muscle atrophy can be influenced via gut microbial signaling; thus we sought to characterize metabolic signaling between the gut and the diaphragm in a mouse model of DMD ( mdx) to look for potential therapeutic targets.The study was divided into two arms and conducted following institutional ethical approval. The first arm investigated metabolomic signaling. 6-month-old male BL10 wildtype (WT; n = 12) and mdx (n = 12) mice were anaesthetized (induction by 5% isoflurane) and decapitated. Following collection of trunk blood, the diaphragm was excised, and colonic/cecal contents were collected. The samples were then processed by mass-spectrometry to isolate the metabolomic profiles of semi-polar, secondary bile acid, and short chain fatty acid (SCFA) targets in the gut, plasma and diaphragm of WT and mdx mice. The second arm of the study explores the gut microbial profile and diaphragm gene expression, structure and function. 6-month-old male WT (n = 15) and mdx (n = 15) were anesthetized (induction by 5% isoflurane) followed by cervical dislocation. The diaphragm was excised, and longitudinal strips were isolated for structural analysis (i.e., histological staining and immunohistochemistry for fibre type and size), PCR gene expression, and isometric force assessment ex vivo. Additionally, fecal pellets were collected and analyzed via shotgun metagenomic sequencing to assess microbial populations.Diaphragm twitch and tetanic force are profoundly decreased in mdx mice compared to WT. Our preliminary analysis suggests a substantially altered metabolic profile within skeletal muscle affecting glycolysis and oxidative metabolism. Interestingly, mdx diaphragms have lowered expression of the Olfr78 receptor, found within the vasculature of skeletal muscle, which transduces short-chain fatty acid signaling, primarily acetate and propionate. Our analysis of faecal metabolites showed a significant decrease in acetate (which also functions as a substrate in oxidative metabolism) in mdx mice. Activation of Olfr78 receptors contributes to vasodilation which suggests that blood supply to the mdx diaphragm may be compromised. Full analysis of metabolomic data and faecal metagenomic data is currently underway.A comprehensive characterisation of the gut-muscle axis in mdx mice may pave the way for novel microbiota-directed therapeutic strategies to ameliorate gut and muscle dysfunction in DMD. Funded by Science Foundation Ireland SFI/19/6628 INSPIRE DMD. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.