The fat mass and obesity-associated gene (FTO) encodes an m6A RNA demethylase that controls mRNA processing and has been linked to both obesity and bone mineral density in humans by genome-wide association studies. To examine the role of FTO in bone, we characterized the phenotype of mice lacking Fto globally (FtoKO) or selectively in osteoblasts (FtoOcKO). Both mouse models developed age-related reductions in bone volume in both the trabecular and cortical compartments. RNA profiling in osteoblasts following acute disruption of Fto revealed changes in transcripts of Hspa1a and other genes in the DNA repair pathway containing consensus m6A motifs required for demethylation by Fto. Fto KO osteoblasts were more susceptible to genotoxic agents (UV and H2O2) and exhibited increased rates of apoptosis. Importantly, forced expression of Hspa1a or inhibition of NF-κB signaling normalized the DNA damage and apoptotic rates in Fto KO osteoblasts. Furthermore, increased metabolic stress induced in mice by feeding a high-fat diet induced greater DNA damage in osteoblast of FtoOc KO mice compared to controls. These data suggest that FTO functions intrinsically in osteoblasts through Hspa1a–NF-κB signaling to enhance the stability of mRNA of proteins that function to protect cells from genotoxic damage.

The patterning and ossification of the mammalian skeleton requires the coordinated actions of both intrinsic bone morphogens and extrinsic neurovascular signals, which function in a temporal and spatial fashion to control mesenchymal progenitor cell (MPC) fate. Here, we show the genetic inhibition of tropomyosin receptor kinase A (TrkA) sensory nerve innervation of the developing cranium results in premature calvarial suture closure, associated with a decrease in suture MPC proliferation and increased mineralization. In vitro, axons from peripheral afferent neurons derived from dorsal root ganglions (DRGs) of wild-type mice induce MPC proliferation in a spatially restricted manner via a soluble factor when cocultured in microfluidic chambers. Comparative spatial transcriptomic analysis of the cranial sutures in vivo confirmed a positive association between sensory axons and proliferative MPCs. SpatialTime analysis across the developing suture revealed regional-specific alterations in bone morphogenetic protein (BMP) and TGF-β signaling pathway transcripts in response to TrkA inhibition. RNA sequencing of DRG cell bodies, following direct, axonal coculture with MPCs, confirmed the alterations in BMP/TGF-β signaling pathway transcripts. Among these, the BMP inhibitor follistatin-like 1 (FSTL1) replicated key features of the neural-to-bone influence, including mitogenic and anti-osteogenic effects via the inhibition of BMP/TGF-β signaling. Taken together, our results demonstrate that sensory nerve-derived signals, including FSTL1, function to coordinate cranial bone patterning by regulating MPC proliferation and differentiation in the suture mesenchyme.