Suppression of TLR4 prevents diabetic bone loss by regulating FTO-mediated mA modification.

Toll-like receptor-4 (TLR4) has been implicated in the development and progression of diabetic osteoporosis. However, the mechanisms underlying TLR4-regulated bone metabolism in diabetes are yet to be fully understood. Epigenetic modifications have been indicated as a possible mechanism leading to increased risk of osteoporosis and bone fracture. As N6-methyladenosine (mA) is the most common epigenetic modification in eukaryotic mRNAs, we hypothesized that TLR4 regulates mA modification in bone tissues of diabetic rats, thereby potentially explaining the pathogenesis of diabetic bone loss. mA sequencing (mA-seq) was performed in samples of the femur of TLR4-wild type (TLR4) and TLR4-knockout (TLR4) diabetic rats to identify genes with differential mA modifications that may be associated with the bone loss phenotype. We found that in TLR4 rats, the rapid weight loss of diabetic rats was prevented, and bone mineral density (BMD) was significantly increased. mA-seq and Gene Ontology enrichment analysis revealed that mA-modified genes in the femur of TLR4 diabetic rats were associated with regulation of biological processes such as osteoclast differentiation. qRT-PCR analysis on the expression levels of the mA-modified methyltransferases and demethylases demonstrated that only the mA demethylase fat mass and obesity-associated protein（FTO）was decreased. Using an osteoclast cell model, we confirmed that TLR4-mediated osteoclast differentiation was induced by glycolipid toxicity via inhibition of FTO expression. Taken together, these results suggest that inhibition of TLR4 may prevent diabetic bone loss via regulation of FTO-mediated mA modification.