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Myokines released by exercise are identified as factors that can influence a person's health and wellbeing. While myokine secretion in response to an acute bout of endurance and resistance-type exercise has been examined, the influence of resistance-exercise training on myokines at rest is less well established. Therefore, this study was designed to evaluate a panel of myokines at rest following a 12-week resistance-exercise training program in younger and older males. Participants (n = 15) completed a 12-week progressive resistance-exercise training program supervised by a certified fitness professional. The training protocol targeted all major muscle groups of the upper and lower body. Resting blood samples were collected before and after completion of the training program to determine concentrations of apelin, fibroblast growth factor-21 (FGF-21), interleukin (IL)-4, IL-6, IL-7, IL-15, leukemia inhibitory factor (LIF), and irisin. Two-way repeated ANOVAs were used to compare variables between time-points and age groups. There was a main effect of time found for apelin (p = 0.003) and IL-15 (p < 0.001), while no main effects for group or time were found for the other myokines (all p > 0.05). Age group × training status interactions were found for IL-6 (p = 0.04) and irisin (p = 0.014) without pairwise differences for IL-6 (p > 0.05), and younger males had higher concentrations of irisin compared to older males post-training (p = 0.036). Overall, the 12-week resistance-exercise training program significantly increased apelin and IL-15 over time but did not change the other resting myokine concentrations for the younger or older males. However, the higher concentration of irisin in younger versus older males post-training suggests a potential explanation for the anabolic resistance observed with aging. [ABSTRACT FROM AUTHOR]

Mechanical perturbation triggers activation of resident myogenic stem cells to enter the cell cycle through a cascade of events including hepatocyte growth factor (HGF) release from its extracellular tethering and the subsequent presentation to signaling‐receptor c‐met. Here, we show that with aging, extracellular HGF undergoes tyrosine‐residue (Y) nitration and loses c‐met binding, thereby disturbing muscle homeostasis. Biochemical studies demonstrated that nitration/dysfunction is specific to HGF among other major growth factors and is characterized by its locations at Y198 and Y250 in c‐met‐binding domains. Direct‐immunofluorescence microscopy of lower hind limb muscles from three age groups of rat, provided direct in vivo evidence for age‐related increases in nitration of ECM‐bound HGF, preferentially stained for anti‐nitrated Y198 and Y250‐HGF mAbs (raised in‐house) in fast IIa and IIx myofibers. Overall, findings highlight inhibitory impacts of HGF nitration on myogenic stem cell dynamics, pioneering a cogent discussion for better understanding age‐related muscle atrophy and impaired regeneration with fibrosis (including sarcopenia and frailty). [ABSTRACT FROM AUTHOR]

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This document is the cover legend for an article titled "Age-related nitration/dysfunction of myogenic stem cell activator HGF" published in the journal Aging Cell. The article, authored by Alaa Elgaabari et al., explores the impact of aging on the function of a protein called HGF, which is involved in the activation of stem cells responsible for muscle regeneration. The research suggests that age-related nitration of HGF may contribute to the decline in muscle regeneration observed in older individuals. The article includes a list of all the authors involved in the study. [Extracted from the article]

In response to peroxynitrite (ONOO - ) generation, myogenic stem satellite cell activator HGF (hepatocyte growth factor) undergoes nitration of tyrosine residues (Y198 and Y250) predominantly on fast IIa and IIx myofibers to lose its binding to the signaling receptor c-met, thereby disturbing muscle homeostasis during aging. Here we show that rat anti-HGF monoclonal antibody (mAb) 1H41C10, which was raised in-house against a synthetic peptide FTSNPEVR nitro Y 198 EV, a site well-conserved in mammals, functions to confer resistance to nitration dysfunction on HGF. 1H41C10 was characterized by recognizing both nitrated and non-nitrated HGF with different affinities as revealed by Western blotting, indicating that the paratope of 1H41C10 may bind to the immediate vicinity of Y198. Subsequent experiments showed that 1H41C10-bound HGF resists peroxynitrite-induced nitration of Y198. A companion mAb-1H42F4 presented similar immuno-reactivity, but did not protect Y198 nitration, and thus served as the control. Importantly, 1H41C10-HGF also withstood Y250 nitration to retain c-met binding and satellite cell activation functions in culture. The Fab region of 1H41C10 exerts resistivity to Y250 nitration possibly due to its localization in the immediate vicinity to Y250, as supported by an additional set of experiments showing that the 1H41C10-Fab confers Y250-nitration resistance which the Fc segment does not. Findings highlight the in vitro preventive impact of 1H41C10 on HGF nitration-dysfunction that strongly impairs myogenic stem cell dynamics, potentially pioneering cogent strategies for counteracting or treating age-related muscle atrophy with fibrosis (including sarcopenia and frailty) and the therapeutic application of investigational HGF drugs., (© 2024 The Author(s). Aging Cell published by Anatomical Society and John Wiley & Sons Ltd.)