The mechanisms by which chronic ethanol intake induces bone loss remain unclear. In females, the skeletal response to ethanol varies depending on physiologic status (e.g., cycling, pregnancy, or lactation). Ethanol-induced oxidative stress appears to be a key event leading to skeletal toxicity. In this study, ethanol-containing liquid diets were fed to postlactational female Sprague-Dawley rats intragastrically for 4 weeks beginning at weaning. Ethanol consumption decreased bone mineral density (BMD) compared with control animals during this period of bone rebuilding following the end of lactation. Coadministration of the antioxidant N-acetylcysteine (NAC) was able to block bone loss and downregulation of the bone-formation markers alkaline phosphatase and osteocalcin in serum and gene expression in bone. Real-time array analysis of total RNA isolated from bone tissue revealed that the majority of Wnt signaling components were downregulated by chronic ethanol infusion. Real-time PCR confirmed downregulated gene expression in a subset of the Wnt signaling components by ethanol. However, the Wnt antagonist DKK1 was upregulated by ethanol. The key canonical Wnt signaling molecule beta-catenin protein expression was inhibited, while glycogen synthase kinase-3-beta was dephosphorylated by ethanol in bone and preosteoblastic cells. These actions of ethanol were blocked by NAC. Ethanol treatment inactivated TCF/LEF gene transcription, eliminated beta-catenin nuclear translocation in osteoblasts, and reciprocally suppressed osteoblastogenesis and enhanced adipogenesis. These effects of ethanol on lineage commitment of mesenchymal stem cells were eliminated by NAC pretreatment. These observations are consistent with the hypothesis that ethanol inhibits bone formation through stimulation of oxidative stress to suppress Wnt signaling.
(c) 2010 American Society for Bone and Mineral Research.