Diminished membrane recruitment of Akt is instrumental in alcohol-associated osteopenia via the PTEN/Akt/GSK-3β/β-catenin axis

Alcohol is considered a leading risk factor for osteopenia. Our previous research indicated that the Akt/GSK-3β/β-catenin pathway plays a critical role in the ethanol-induced antiosteogenic effect in bone mesenchymal stem cells (BMSCs). PI3K/Akt is negatively regulated by the phosphatase and tensin homolog (PTEN) phosphatase. In this study, we found that ethanol increased PTEN expression in the BMSCs and bone tissue of ethanol-treated Sprague-Dawley rats. PTEN upregulation impaired Akt recruitment to the plasma membrane and suppressed Akt phosphorylation at Ser473, thereby inhibiting Akt/GSK3β/β-catenin signaling and the expression of COL1 and OCN in BMSCs in vitro and in vivo. The results of in vivo assays indicated that PTEN inhibition protected bone tissue against ethanol. Interestingly, our data revealed that following ethanol stimulation, PTEN and PTEN pseudogene 1 (PTENP1) mRNA expression was increased in a time-dependent manner, resulting in an increased PTEN protein level. In addition, ethanol upregulated PTEN expression and decreased PTEN phosphorylation (p-PTEN), indicating an increase in functional PTEN levels. In summary, the ethanol-mediated transcriptional and post-transcriptional regulation of PTEN impaired downstream Akt/GSK3β/β-catenin signaling and BMSC osteogenic differentiation. Therefore, we propose that Akt/GSK3β/β-catenin activation via PTEN inhibition may be a potential therapeutic approach for preventing the development of alcohol-induced osteopenia.