NEW GENES, FUNCTIONS AND BIOMARKERS

Facio-scapulo-humeral muscular dystrophy (FSHD) is a genetically inherited disease causing progressive weakness of skeletal muscle with unique clinical features such as asymmetrically affected patterns and large varieties of disease progression. As these aspects cannot be simply explained by the causative mutation, the involvement of environmental factors should be considered. It is known that the genetic backgrounds for both FSHD type 1 (FSHD1) and FSHD type 2 (FSHD2) lead to chromatin relaxation of disease-associated genomic locus, resulting in aberrant gene expression of DUX4, a key factor of FSHD pathogenesis by exerting toxicity against muscle cells. How DUX4 expression is regulated in FSHD remains unclear. Thus, we hypothesized that environmental factors, including oxidative stress, may modulate DUX4 expression. To investigate our hypothesis, firstly we established an FSHD myocyte model by using iPSCs derived from one healthy control, FSHD1 and FSHD2 patients and also generating isogenic control clones from FSHD2 by correcting its causative SMCHD1 mutation. All those clones efficiently differentiated into myocytes. Importantly, FSHD-derived myocytes, and not healthy nor isogenic control myocytes, showed robust gene expression of DUX4 and its direct downstream targets, confirming that our FSHD model is consistent with previous genetic studies. Then, by using this FSHD myocyte model, we demonstrated that DUX4 expression was increased by oxidative stress, mediated by DNA damage response (DDR), and suppressed by inhibition of ATM, a DDR regulator kinase. We also found that other types of genotoxic stresses also increased DUX4 expression in FSHD myocytes. In summary, our study provides a new FSHD-iPSC model also applicable to drug discovery, and importantly suggests that oxidative stress and other genotoxic stresses can be risk factors against FSHD patients, which may be partially prevented even by daily behaviors.