Alkbh1-mediated DNA N6-methyladenine modification regulates bone marrow mesenchymal stem cell fate during skeletal aging

Objectives: DNA N6-methyladenine (N6-mA) demethylase Alkbh1 participates in regulating osteogenic differentiation of mesenchymal stem cell (MSCs) and vascular calcification. However, the role of Alkbh1 in bone metabolism remains unclear.

Materials and methods: Bone marrow mesenchymal stem cells (BMSCs)-specific Alkbh1 knockout mice were used to investigate the role of Alkbh1 in bone metabolism. Western blot, qRT-PCR, and immunofluorescent staining were used to evaluate the expression of Alkbh1 or optineurin (optn). Micro-CT, histomorphometric analysis, and calcein double-labeling assay were used to evaluate bone phenotypes. Cell staining and qRT-PCR were used to evaluate the osteogenic or adipogenic differentiation of BMSCs. Dot blotting was used to detect the level of N6-mA in genomic DNA. Chromatin immunoprecipitation (Chip) assays were used to identify critical targets of Alkbh1. Alkbh1 adeno-associated virus was used to overexpress Alkbh1 in aged mice.

Results: Alkbh1 expression in BMSCs declined during aging. Knockout of Alkbh1 promoted adipogenic differentiation of BMSCs while inhibited osteogenic differentiation. BMSC-specific Alkbh1 knockout mice exhibited reduced bone mass and increased marrow adiposity. Mechanistically, we identified optn as the downstream target through which Alkbh1-mediated DNA m6A modification regulated BMSCs fate. Overexpression of Alkbh1 attenuated bone loss and marrow fat accumulation in aged mice.

Conclusions: Our findings demonstrated that Alkbh1 regulated BMSCs fate and bone-fat balance during skeletal aging and provided a potential target for the treatment of osteoporosis.