Transcription factor SMAD5 upregulates ALG5 to alleviate osteoporosis development by inducing osteogenic differentiation.

Background: Impaired osteogenic differentiation ability of mesenchymal stem cells (MSCs) plays a pathogenic role in osteoporosis (OP). ALG5, a key glucosyltransferase, participates in the synthesis of the glucose-residue donor. However, little is known about the role of ALG5 in OP pathogenesis and osteogenic differentiation.

Methods: The GSE35956 dataset was used to observe OP-associated factors. ALG5 and SMAD5 mRNA analysis was performed by quantitative PCR. Induction of osteoblastic differentiation of human MSCs (hMSCs) was done using specific media for 14 days. The ovariectomy (OVX)-induced osteoporotic mouse model was established. Calcium deposition was detected by alkaline phosphatase (ALP) activity assay and Alizarin Red staining. Protein expression was evaluated by immunoblot analysis. The relationship of SMAD5 with the ALG5 promoter was predicted by the online tool JASPAR and validated by luciferase assay.

Results: In bone marrow of OP, ALG5 and SMAD5 levels were decreased. Overexpression of ALG5 acted for enhancement of osteogenic differentiation and autophagy of hMSCs. Mechanistically, SMAD5 enhanced ALG5 transcription to increase ALG5 expression. Moreover, increased SMAD5 expression promoted osteogenic differentiation of hMSCs through ALG5. ALG5 and SMAD5 were also underexpressed in bone samples of OVX-osteoporotic mice. Furthermore, increased SMAD5 expression alleviated OP development of OVX mice by inducing osteogenic differentiation by upregulating ALG5.

Conclusion: Our findings demonstrate that increased SMAD5 expression upregulates ALG5 to enhance osteogenic differentiation of hMSCs and thus alleviates OP development, providing novel potential approaches to combat OP.