VGLL3 Regulates DAPK2-Mediated Autophagy During Osteoblast Differentiation

Vestigial-like family member 3 (VGLL3), a transcriptional cofactor of the TEA domain family, has been previously identified as a regulator of osteoblast differentiation. Building upon our previous findings, we investigated VGLL3 function in MC3T3-E1 osteoblasts using an integrated approach combining transcriptomic analysis and functional assays to identify its downstream effectors and explore associated autophagy mechanisms. RNA-seq analysis of Vgll3-knockdown (shVgll3) cells identified death-associated protein kinase 2 (DAPK2), a regulator of autophagy, as a downstream effector. Autophagic activity was examined using transmission electron microscopy and western blot analysis of LC3-II and p62 proteins. The effects of Dapk2 knockdown (shDapk2) on osteoblast differentiation were evaluated using qPCR, western blotting, alkaline phosphatase staining, and Alizarin Red staining. Rapamycin treatment was used to determine whether pharmacologic activation of autophagy could restore osteoblast function. Vgll3 knockdown significantly suppressed autophagic flux, as evidenced by fewer autophagic vacuoles, decreased LC3-II accumulation, and increased p62 expression. A comparable reduction in autophagic activity was observed in shDapk2 cells and was accompanied by impaired osteoblast differentiation. Rapamycin treatment partially restored autophagy and osteogenic differentiation in Vgll3-deficient cells. Finally, overexpression of DAPK2 partially rescued autophagic activity and osteogenic differentiation in shVgll3 cells, supporting its role as a key downstream functional effector. FOXM1 was further implicated as a potential transcriptional regulator contributing to DAPK2 expression. Collectively, our findings suggest that VGLL3 may influence osteogenic differentiation in osteoblasts, potentially involving DAPK2-associated autophagy.