d-Pinitol Rescues Osteoblast Differentiation From Tumor Necrosis Factor-Alpha-Mediated Suppression via β-Galactoside α-2,6-Sialyltransferase 1 Induction.

d-pinitol, a naturally occurring inositol derivative found in legumes and soy-based foods, has shown various biological effects, including anti-inflammatory and insulin-sensitizing activities. However, its role in osteoblast differentiation under inflammatory conditions remains unclear. In this study, we investigated whether d-pinitol alleviates tumor necrosis factor-alpha (TNF-α)-induced suppression of osteogenic gene expression in MC3T3-E1 pre-osteoblasts. Using RT-PCR, real-time PCR, and Western blot analyses, we found that d-pinitol significantly restored the expression of osteogenic markers inhibited by TNF-α. Mechanistically, d-pinitol treatment markedly suppressed TNF-α-mediated upregulation of CREBH and Smurf1, negative regulators of osteoblast differentiation. Importantly, d-pinitol strongly induced the expression of β-galactoside α-2,6-sialyltransferase 1 (ST6Gal-1), and overexpression of ST6Gal-1 alone also decreased CREBH and Smurf1 expression. Furthermore, both d-pinitol and ST6Gal-1 overexpression attenuated TNF-α-induced endoplasmic reticulum (ER) stress markers, including ATF4, ATF6, EDEM, and BiP. These findings collectively suggest that d-pinitol promotes osteoblast differentiation under inflammatory stress by inducing ST6Gal-1 expression, thereby suppressing the CREBH-Smurf1 signaling axis and ER stress pathways. Our results highlight the potential therapeutic implications of d-pinitol in managing inflammatory bone diseases.