Acetate derived from metabolism of ethanol affects gene expression in bone and contributes to delays in chondrogenic differentiation.

Abstract

Alcohol intake is a risk factor for development of osteopenia. Ethanol perturbs gene expression in osteoblasts and osteoclasts and disrupts growth plate morphology. Hepatic metabolism of ethanol to acetate elevates concentrations of acetate in the circulation. We investigated whether acetate could in part mediate the toxicity of ethanol in bone and on chondrocyte differentiation. When ethanol and acetate were compared by gavage for four consecutive days, none of eleven genes involved in bone homeostasis were significantly affected by acetate, but acetate responses significantly correlated with ethanol responses. Intraperitoneal injection with acetate to transiently elevate serum acetate for four consecutive days significantly increased expression of two markers of osteoclast differentiation, calcitonin receptor (Calcr) and Ocstamp. Early chondrogenic differentiation of ATDC5 cells for 7 days in vitro characterized by aggrecan (Acan) and collagen 2a1 (Col2a1) mRNA expression and proteoglycan production was inhibited by both 50 mM ethanol and 5 mM acetate. Ethanol effects were not blocked by the alcohol dehydrogenase inhibitor 4-methylpyrazole. 50 mM ethanol retarded both ATDC5 cell growth and culture medium acidification. Inhibition of chondrogenic differentiation by 5 mM acetate was associated with elevated phosphorylation of ERK1 and ERK2 and decreased expression of transcription factors Sox9 and Runx2. In acetate-exposed cells, blocking of ERK1 and ERK2 phosphorylation with Trametinib prevented further reduction of Acan and Col2a1 mRNA expression. We conclude that ethanol-derived acetate mediates at least part of the induction of Calcr and Ocstamp expression, and that acetate mimics effects of ethanol on early chondrogenic differentiation.