Mitochondrial-derived peptides MOTS-c and humanin attenuate dexamethasone-induced atrophy in human skeletal muscle cells.

In vitro study using primary human skeletal muscle myotubes

“We tested the hypothesis that the MDP S14G‐humanin (HNG) and the mitochondrial open reading frame of the 12S rRNA‐c (MOTS‐c) mitigate DEXA‐induced atrophy in human skeletal myotubes.”

Fully differentiated primary human skeletal myotubes from young sedentary donors

“Human skeletal muscle cells, isolated from the quadriceps of 2 donors from the young sedentary group as detailed in Balan et al. (Balan et al., 2020) and cryopreserved at passage 3 in the laboratory, were used for all experiments.”

3 independent cultures (N = 3) per treatment group

“Each dot represents one experiment, which was replicated in 3 independent cultures (N = 3).”

24-hour exposure to dexamethasone with 6-hour peptide pre-treatment (30 hours total)

“DEXA doses ranging from 0.1 μM to 100 μM were tested over 6, 24, and 48 h to reliably induce a significant atrophic phenotype, with 10 μM DEXA and a 24‐h exposure period selected for the main study.”

MOTS-c co-treatment preserved myotube area and fusion index, increased Akt phosphorylation, and reduced MURF1 expression and STAT3 activation compared to dexamethasone alone.

“MOTS‐c co‐treatment with DEXA completely preserved myotube area (p < 0.001) and fusion index (p = 0.02), increased Akt phosphorylation (p = 0.0015) and blunted both MURF1 upregulation (p = 0.03) and STAT3 activation (p = 0.005) compared to DEXA alone.”

HNG co-treatment preserved myotube area and blunted STAT3 activation but did not affect fusion index or E3 ligase mRNA levels.

“HNG co‐treatment with DEXA preserved myotube area (p < 0.001), blunted DEXA‐induced STAT3 activation (p = 0.027), but had no effect on fusion index or E3 ligase mRNA levels.”

Dexamethasone treatment decreased myotube size and differentiation while increasing MURF1, MAFbx, and PGC1α expression.

“DEXA decreased myotube size (area, p < 0.001) and differentiation (Fusion Index, p = 0.05). Additionally, DEXA increased both muscle ring finger protein 1 (MURF1, p < 0.001) and muscle atrophy F‐box (MAFbx, p = 0.01) as well as peroxisome proliferator‐activated receptor‐gamma coactivator‐1 alpha (PGC1α, p < 0.001).”

Small sample size (n=3) limited statistical power for variables with smaller effect sizes, increasing the risk of type II errors.

“Although typical in in vitro cell culture experiments, this small sample size limited our statistical power, particularly for variables with smaller effect sizes or greater inherent variability.”