Mushroom Compound Inotodiol Fights Muscle Aging via Mitochondrial Pathway

Sarcopenia—the progressive, age-driven loss of skeletal muscle mass and strength—is a major cause of frailty, disability, and mortality in older adults, yet no approved pharmacological therapies exist. Mitochondrial dysfunction and intramuscular lipid accumulation are now recognized as central drivers of this decline, making restoration of mitochondrial homeostasis a high-priority therapeutic target.

The research team first characterized the aging muscle environment using untargeted metabolomics of young versus aged mouse muscle, single-nucleus RNA sequencing of publicly available datasets, and human skeletal muscle histology from the GTEx database. Aged muscles showed marked suppression of oxidative phosphorylation, downregulation of SIRT3 and PGC-1α, reduced mitochondrial DNA content, impaired mitochondrial membrane potential (JC-1 assay), and elevated mitochondrial superoxide (MitoSOX). These findings established the metabolic and mitochondrial landscape of aging muscle and motivated the search for a corrective intervention.

Inotodiol (Ino), a lanostane-type triterpenoid mycosterol isolated from Inonotus obliquus (Chaga mushroom), was identified as the key bioactive ingredient behind previously observed muscle benefits of I. obliquus extract. In aged male mice (24 months), oral Ino administration significantly increased gastrocnemius and tibialis anterior muscle mass, improved grip strength and treadmill performance, increased myofiber cross-sectional area, and shifted fiber-type composition toward oxidative (Type I/IIA) fibers. Ino also prevented dexamethasone-induced muscle atrophy in younger mice, reduced atrogene expression (Atrogin-1, MuRF1), and suppressed protein ubiquitination.

At the cellular and molecular level, Ino enhanced mitochondrial biogenesis and function: it increased mitochondrial DNA copy number, elevated expression of electron transport chain components, restored membrane potential, boosted oxygen consumption rate and ATP production, and reduced ROS and lipid accumulation. In palmitic acid-treated myotubes modeling lipotoxic stress, Ino normalized lipid droplet accumulation and restored lipid oxidation gene expression. Mechanistically, Ino directly binds and activates LXRβ (confirmed by docking and coactivator recruitment assays), promoting its interaction with PPARδ to drive transcription of Sirt3. Elevated SIRT3 then activates PGC-1α through deacetylation, amplifying mitochondrial biogenesis and oxidative capacity. Loss-of-function experiments using LXRβ or SIRT3 knockdown abolished Ino's protective effects, confirming the LXRβ→SIRT3→PGC-1α axis as the essential signaling pathway.

These findings position Ino as a mechanistically grounded, multi-target therapeutic candidate for sarcopenia and related metabolic muscle disorders, with a natural-product origin that may favor a favorable safety profile for future clinical development.