DNA N⁶-methyladenine demethylase ALKBH1 enhances osteogenic differentiation of human MSCs

Abstract

ALKBH1 was recently discovered as a demethylase for DNA N⁶-methyladenine (N6-mA), a new epigenetic modification, and interacts with the core transcriptional pluripotency network of embryonic stem cells. However, the role of ALKBH1 and DNA N6-mA in regulating osteogenic differentiation is largely unknown. In this study, we demonstrated that the expression of ALKBH1 in human mesenchymal stem cells (MSCs) was upregulated during osteogenic induction. Knockdown of ALKBH1 increased the genomic DNA N6-mA levels and significantly reduced the expression of osteogenic-related genes, alkaline phosphatase activity, and mineralization. ALKBH1-depleted MSCs also exhibited a restricted capacity for bone formation in vivo. By contrast, the ectopic overexpression of ALKBH1 enhanced osteoblastic differentiation. Mechanically, we found that the depletion of ALKBH1 resulted in the accumulation of N6-mA on the promoter region of ATF4, which subsequently silenced ATF4 transcription. In addition, restoring the expression of ATP by adenovirus-mediated transduction successfully rescued osteogenic differentiation. Taken together, our results demonstrate that ALKBH1 is indispensable for the osteogenic differentiation of MSCs and indicate that DNA N6-mA modifications area new mechanism for the epigenetic regulation of stem cell differentiation.

Bone development: DNA modification needed for stem cell differentiation

DNA modifications by the enzyme ALKBH1 is needed for stem cells to differentiate into bone-forming cells. Epigenetic gene regulation by the addition of chemical tags to the DNA base adenine was recently shown to be an important process in mammalian stem cells. ALKBH1 is a critical part of this newly discovered regulatory system. Shujuan Zou and colleagues from Sichuan University, Chengdu, China, investigated the role of this enzyme in bone development and found that elevated levels are present in human bone marrow-derived stem cells. ALKBH1 enhances gene expression by stripping methyl tags from adenine residues in the promoter region of the gene encoding an activating regulatory protein. The resulting elevated gene expression triggers a molecular cascade that drives differentiation of the stem cells into bone-forming cells.

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