m6A mRNA demethylase FTO promotes chondrogenic differentiation of human bone marrow mesenchymal stem cells by targeting SMAD3.

Bone marrow mesenchymal stem cells (BMSCs) have chondrogenic differentiation potential to treat cartilage injury. N6 methyladenosine (m6A), one of the most prevalent mRNA modification, has been reported to be crucial in cartilage disease. Herein, we further investigated the effects and underlying mechanisms in the modification of m6A on the chondrogenic differentiation of MSCs. This study showed that the m6A level was decreased in the chondrogenic differentiation of MSCs and m6A mRNA demethylation fat mass and obesity-associated protein (FTO) played an important role in these processes. The overexpression of FTO has been demonstrated to improve the levels of chondrogenic markers. We confirmed that FTO directly binded to SMAD3 mRNA and increased its demethylation, which promoted the chondrogenic differentiation of MSCs. We further indicated that the m6A "reader" YTHDF2 was probably related with the chondrogenic differentiation of MSCs. SiFTO attenuated the SiYTHDF2-increased mRNA stability of SMAD3, leading to the declining levels of chondrogenic markers. Collectively, these results reveal FTO could act as an important mediator of SMAD3 mRNA demethylation and improve the chondrogenic differentiation of MSCs.