Mouse sarcopenia model reveals sex- and age-specific differences in phenotypic and molecular characteristics.

Our study was to characterize sarcopenia in C57BL/6J mice using a clinically relevant definition to investigate the underlying molecular mechanisms. Aged male (23-32 months old) and female (27-28 months old) C57BL/6J mice were classified as non-, probable-, or sarcopenic based on assessments of grip strength, muscle mass, and treadmill running time, using 2 SDs below the mean of their young counterparts as cutoff points. A 9%-22% prevalence of sarcopenia was identified in 23-26 month-old male mice, with more severe age-related declines in muscle function than mass. Females aged 27-28 months showed fewer sarcopenic but more probable cases compared with the males. As sarcopenia progressed, a decrease in muscle contractility and a trend toward lower type IIB fiber size were observed in males. Mitochondrial biogenesis, oxidative capacity, and AMPK-autophagy signaling decreased as sarcopenia progressed in males, with pathways linked to mitochondrial metabolism positively correlated with muscle mass. No age- or sarcopenia-related changes were observed in mitochondrial biogenesis, OXPHOS complexes, AMPK signaling, mitophagy, or atrogenes in females. Our results highlight the different trajectories of age-related declines in muscle mass and function, providing insights into sex-dependent molecular changes associated with sarcopenia progression, which may inform the future development of novel therapeutic interventions.

EXT418, a novel long-acting ghrelin, mitigates Lewis lung carcinoma induced cachexia in mice.

BACKGROUND: Ghrelin is a potential therapy for cachexia due to its orexigenic properties and anabolic effects on muscle and fat. However, its clinical use is limited by the short half-life of active (acylated) ghrelin (~11 min in humans). EXT418 is a novel long-acting, constitutively active ghrelin analog created by covalently linking it to a vitamin D derivative. Here, we evaluated the effects and mechanisms of action of EXT418 on Lewis lung carcinoma (LLC)-induced cachexia in mice. METHODS: Male C57BL/6J mice (5- to 7-month-old) were implanted with 1 × 106 heat-killed (HK) or live LLC cells. When the tumour was palpable, mice were injected with vehicle (T + V) or EXT418 daily (T + 418 Daily, 0.25 mg/kg/day) or every other day (T + 418 EOD, 0.5 mg/kg/EOD) for up to 14 days, whereas HK-treated mice were given vehicle (HK + V). Subsets of T + 418 Daily or EOD-treated mice were pair-fed to the T + V group. Body composition and grip strength were evaluated before tumour implantation and at the end of the experiment. Molecular markers were probed in muscles upon termination. RESULTS: In tumour-bearing mice, administration of EXT418 daily or EOD partially prevented weight loss (T + V vs. T + 418 Daily, P = 0.030; and vs. T + 418 EOD, P = 0.020). Similar effects were observed in whole body fat and lean body mass. Grip strength in tumour-bearing mice was improved by EXT418 daily (P = 0.010) or EOD (P = 0.008) administration compared with vehicle-treated mice. These effects of EXT418 on weight and grip strength were partially independent of food intake. EXT418 daily administration also improved type IIA (P = 0.015), IIB (P = 0.037) and IIX (P = 0.050) fibre cross-sectional area (CSA) in tibialis anterior (TA) and EXT418 EOD improved CSA of IIB fibres in red gastrocnemius (GAS; P = 0.005). In skeletal muscles, tumour-induced increases in atrogenes Fbxo32 and Trim63 were ameliorated by EXT418 treatments (TA and GAS/plantaris, PL), which were independent of food intake. EXT418 administration decreased expression of the mitophagy marker Bnip3 (GAS/PL; P ≤ 0.010). Similar effects of EXT418 EOD were observed in p62 (GAS/PL; P = 0.039). In addition, EXT418 treatments ameliorated the tumour-induced elevation in muscle Il6 transcript levels (TA and GAS/PL), independently of food intake. Il-6 transcript levels in adipose tissue and circulating IL-10 were elevated in response to the tumour but these increases were not significant with EXT418 administration. Tumour mass was not altered by EXT418. CONCLUSIONS: EXT418 mitigates LLC-induced cachexia by attenuating skeletal muscle inflammation, proteolysis, and mitophagy, without affecting tumour mass and partially independent of food intake.