Molecular Hydrogen Manages Mitochondrial Proteostatic Stress and Induces Cellular Response

Molecular hydrogen (H2) has an anti‐oxidant effect on hundreds of animal models. However, the exact molecular mechanisms of molecular hydrogen still remains elusive. Mitochondrial unfolded protein response (mtUPR) is a known stress response to perturbed mitochondrial proteostasis caused by oxidative stress or mitochondrial dysfunction. We examined the effects of molecular hydrogen on mtUPR by examining mtUPR‐related protein expression in vivo and in vitro. Mice drinking hydrogen water showed higher expression of the HSP60 chaperone protein, which is an mtUPR marker, as well as other mtUPR‐related proteins including protein kinase R (PKR), phosphorylated eukaryotic translation initiation factor 2a (eIf2a), and activating transcription factor 5 (ATF5). Incubation of cultured cells in 10% hydrogen gas increased expression of HSP60 and some mtUPR‐related proteins in four human cell lines (A549, HeLa, HT1080, and PC3 cells, which are called “responders” hereafter), but not in three other human cell lines (HCT116, HepG2, and SH‐SY5Y cells, which are called “non‐responders”). Flowcytometric analysis disclosed that higher mitochondrial mass, higher superoxide production, higher mitochondrial membrane potential in “responders” compared to “non‐responders’. Similarly, measurement of the oxygen consumption rate revealed high spare capacity of the electron transport complex (ETC) activity in “responders”. Indeed, the gene set enrichment analysis (GSEA) of gene expression profiles in gene expression omnibus (GEO) of two groups of cell lines demonstrated that ETC‐related pathways were upregulated in “responders”. In addition, quantification of DNA synthesis by BrdU assay revealed that incubation of cultured cells in 10% hydrogen gas for 48 h induced cell proliferation, and rescued proliferation blockage by rotenone in “responders”. We report that hydrogen induces mtUPR and cellular proliferation in cell lines with higher mitochondrial ETC activity. Molecular hydrogen ameliorates a variety of diseases including Parkinson’s disease, myocardiac or cerebral infarction, and inflammatory diseases. Molecular hydrogen is thus likely to manage mitochondrial stress through activation of mtUPR, and exerts its effects on these oxidative stress‐related diseases.