Inhibition of High-Temperature Requirement Protein A2 Protease Activity Represses Myogenic Differentiation via UPRmt

Abstract

Skeletal muscles require muscle satellite cell (MuSC) differentiation to facilitate the replenishment and repair of muscle fibers. A key step in this process is called myogenic differentiation. The differentiation ability of MuSCs decreases with age and can result in sarcopenia. Although mitochondria have been reported to be involved in myogenic differentiation by promoting a bioenergetic remodeling, little is known about the interplay of mitochondrial proteostasis and myogenic differentiation. High-temperature-requirement protein A2 (HtrA2/Omi) is a protease that regulates proteostasis in the mitochondrial intermembrane space (IMS). Mice deficient in HtrA2 protease activity show a distinct phenotype of sarcopenia. To investigate the role of IMS proteostasis during myogenic differentiation, we treated C2C12 myoblasts with UCF101, a specific inhibitor of HtrA2 during differentiation process. A key step in this process is called myogenic differentiation. The differentiation ability of MuSCs decreases with age and can result in sarcopenia. Further, CHOP, p-eIF2α, and other mitochondrial unfolded protein response (UPRmt)-related proteins are upregulated. Therefore, we suggest that imbalance of mitochondrial IMS proteostasis acts via a retrograde signaling pathway to inhibit myogenic differentiation via the UPRmt pathway. These novel mechanistic insights may have implications for the development of new strategies for the treatment of sarcopenia.

HTRA2/OMI-Mediated Mitochondrial Quality Control Alters Macrophage Polarization Affecting Systemic Chronic Inflammation

“…HtrA2/Omi deficiency promotes the generation of unfolded proteins, in particular components of respiratory complexes on mitochondrial membranes. The current study shows that HtrA2/Omi protease deficiency leads to oxidative phosphorylation and a reduction in the number of mitochondrial genes encoding ETC subunits [14]. Moisoi et al showed that an increase in the unfolded subunits of the HtrA2/Omi KO brain mitochondrial complexes I-IV leads to systemic respiratory dysfunction [42].…”

“…HtrA2/Omi is located in the mitochondrial membrane gap and was originally described as a serine protease that induces stress responses in mammalian cells [12]. Previous studies have mostly focused on the potential regulation of apoptosis by HtrA2/Omi proteins in neurodegenerative diseases [13], sarcopenia [14], and tumors [15]. With the progress of research, another role of HtrA2/Omi proteins in cells has been gradually discovered, as a key regulator of mitochondrial molecular quality control [16].…”

Mitochondrial stress response and myogenic differentiation

“…HtrA2 is a protease located in the mitochondrial IMS that is involved in UPRmt to maintain mitochondrial homeostasis (Riar et al, 2017). Previously published results from our team (Sun et al, 2022) showed that inhibition of HtrA2 enzyme activity using UCF101 resulted in blocked differentiation of C2C12 myoblasts. Considering that the loss of HtrA2 enzyme activity-induced proteostasis imbalance and mitochondrial IMS stress are the main triggers of UPRmt, we hypothesised that UPRmt could be associated with impaired differentiation due to HtrA2 enzyme activity inhibition.…”

“…MRFs also regulate the level of myosin heavy chain (MyHC), which determines the contractile properties of myofibers (Zammit, 2017). Reduced myogenic differentiation capacity has been reported to be associated with the progression of several muscle diseases, such as sarcopenia (Sun et al, 2022), skeletal muscle atrophy (Rahman and Quadrilatero, 2023) and Duchenne muscular dystrophy (Meyer et al, 2021).…”

“…As a result, mitochondria within differentiated myotubes appear more mature, with high numbers, enhanced levels of oxidative phosphorylation and increased ATP production (Vertel and Fischman, 1977;Barbieri et al, 2011;Rahman and Quadrilatero, 2021). To further elucidate the relationship between mitochondria and myogenic differentiation, several studies have used rotenone (complex I inhibitor), trifluoroacetone (complex II inhibitor) (Chabi et al, 2021), carbonylcyanide p-trifluoromethoxy-phenylhydrazone (FCCP) (mitochondrial uncoupler) (Wang et al, 2014), mitochondrial division inhibitor-1 (Mdivi-1) (dynamin-related protein 1 (Drp1) inhibitor) (Kim et al, 2013), ethidium bromide (EB) (mitochondrial DNA transcriptional inhibitor), rifampicin (mitochondrial RNA synthesis inhibitor) (Brunk and Yaffe, 1976), chloramphenicol (mitochondrial protein synthesis inhibitor) (Seyer et al, 2011), and UCF101 (High-Temperature Requirement Protein A2(HtrA2) inhibitor) (Sun et al, 2022) and others were used in differentiation model experiments, and it was found that affecting mitochondrial function from multiple aspects can have a negative impact on myogenic differentiation, indicating that mitochondrial diversity function controls the fate of myoblast differentiation.…”