Location: Arkansas Children's Nutrition CenterTitle: A role for ethanol-induced oxidative stress in controlling lineage commitment of mesenchymal stromal cells through inhibition of wnt/beta-catenin signaling Author
Submitted to: Journal of Bone and Mineral Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2009
Publication Date: 5/15/2010
Citation: Chen, J., Lazarenko, O.P., Shankar, K., Blackburn, M.L., Badger, T.M., Ronis, M.J. 2010. A role for ethanol-induced oxidative stress in controlling lineage commitment of mesenchymal stromal cells through inhibition of wnt/beta-catenin signaling. Journal of Bone and Mineral Research. 25(5):1117-1127. Interpretive Summary: Chronic alcohol drink can cause bone weak, but the mechanism of how chronic alcohol drink can affect bone forming cell, called osteoblast, is not known. In the present manuscript, we have used a rat animal model to let post lactation female rats drink alcohol for 4 weeks, and we isolated bone forming osteoblasts and investigated the response of those cells to alcohol. We have found that osteoblasts and their precursors from alcohol feeding animals were inactive to build new bone compared with their controls. Not only that, osteoblast differentiation from their early stage of cells was found to be suppressed by alcohol. There is a well known signal call Wnt/beta-catenin signal is responsible for signaling osteoblast differentiation from their early stage of cells. This signal was dramatically suppressed by giving alcohol to experimental animals. Interestingly, when osteoblast differentiation signal was suppressed, on the other hand another signal which to promote fat formation in bone marrow was activated. All these effects of alcohol on osteoblast differentiation could be reversed by single anti-oxidant agent call N-acetylcystein treatment to animals. From our experimental data, we therefore conclude that alcohol inhibits bone formation through stimulation of oxidative stress to suppress Wnt signaling.
Technical Abstract: The mechanisms by which chronic ethanol intake induces bone loss remain unclear. In females, the skeletal response to ethanol varies depending on physiologic status (viz. cycling, pregnancy, lactation). Ethanol-induced oxidative stress appears to be a key event leading to skeletal toxicity. In the current study, EtOH-containing liquid diets were fed to post-lactational female Sprague-Dawley rats i.g. for 4 weeks beginning at weaning. EtOH consumption decreased bone mineral density (BMD) compared to control animals during this period of bone rebuilding following the end of lactation. Co-administration of the antioxidant N-acetylcysteine (NAC) was able to block bone loss and down-regulation 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 down-regulated by chronic EtOH infusion. Real-time PCR confirmed down-regulated gene expression in a subset of the Wnt signaling components by EtOH. However, the Wnt antagonist DKK1 was up-regulated by EtOH. The key canonical Wnt signaling molecule beta-catenin protein expression was inhibited while glycogen synthase kinase-3-beta was de-phosphorylated by EtOH in bone and pre-osteoblastic cells. These actions of EtOH were blocked by NAC. EtOH treatment inactivated TCF/LEF gene transcription, eliminated beta-catenin nuclear translocation in osteoblasts, and reciprocally suppressed osteoblastogenesis and enhanced adipogenesis. These effects of EtOH on lineage commitment of mesenchymal stem cells were eliminated by NAC pre-treatment. These observations are consistent with the hypothesis that EtOH inhibits bone formation through stimulation of oxidative stress to suppress Wnt signaling.