Role of SMAD2 signaling in CFC syndrome patient-derived induced pluripotent stem cells during early osteogenesis

Abstract

Cardiofaciocutaneous (CFC) syndrome is a rare genetic disorder caused by mutations in the extracellular signal-regulated kinase (ERK) signaling pathway. However, little is known about how aberrant ERK signaling is associated with the defective bone development manifested in most CFC syndrome patients. Induced pluripotent stem cells (iPSCs) were generated from dermal fibroblasts of a CFC syndrome patient having BRAF gain-of-function mutation. CFC-iPSCs were differentiated into mesenchymal stem cells (CFC-MSCs) and further induced to osteoblasts in vitro. CFC-MSCs progressed normally through chondrogenesis and adipogenesis, but osteogenesis was attenuated compared to wild-type (WT)-cells. Breifly, CFC-MSCs exhibited aberrant expression of osteogenic markers, reduced ALP activity, and low mineralization capacity during osteogenesis compared to WT-cells. In addition to activated ERK signaling due to BRAF mutation, increased p-SMAD2 and decreased p-SMAD1 were observed in CFC-MSCs during osteogenesis. The defective osteogenesis of CFC-MSCs was rescued by inhibition of ERK signaling and SMAD2 signaling or activation of SMAD1 signaling. Importantly, activation of ERK signaling and SMAD2 signaling or inhibition of SMAD1 signaling recapitulated the impaired osteogenesis in WT-MSCs. These findings indicate that SMAD2 signaling and SMAD1 signaling as well as ERK signaling are responsible for defective early bone development in CFC syndrome, providing a novel insight on the pathological mechanism and therapeutic targets.