Singleton-Merten Syndrome–like Skeletal Abnormalities in Mice with Constitutively Activated MDA5

Singleton-Merten syndrome (SMS) is a type I interferonopathy characterized by dental dysplasia, aortic calcification, skeletal abnormalities, glaucoma, and psoriasis. A missense mutation in IFIH1 encoding a cytoplasmic viral RNA sensor MDA5 has recently been identified in the SMS patients as well as in patients with a monogenic form of lupus. We previously reported tha Ifih1 gs/+ mice express a constitutively active MDA5 and spontaneously develop lupus-like nephritis. In this study, we demonstrate that the Ifih1 gs/+ mice also exhibit SMS-like bone abnormalities, including decreased bone mineral density and thin cortical bone. Histological analysis revealed a low number of osteoclasts, low bone formation rate, and abnormal development of growth plate cartilages in Ifih1 gs/+ mice. These abnormalities were not observed in Ifih1 gs/+ ・ Mavs -/- and Ifih1 gs/+ ・ Ifnar1 -/- mice, indicating the critical role of type I IFNs induced by MDA5/MAVS-dependent signaling in the bone pathogenesis of Ifih1 gs/+ mice, affecting bone turnover. Taken together, our findings suggest the inhibition of type I IFN signaling as a possible effective therapeutic strategy for bone disorders in SMS patients.