Pathogenesis and mechanisms of ethanol-induced limb defects .

摘要

Fetal alcohol spectrum disorders encompass a variety of structural and behavioral abnormalities attributable to maternal alcohol consumption. This study was designed to investigate the mechanistic and pathogenic role of retinoic acid (RA) in the genesis of ethanol-induced forelimb defects. The mouse limb bud has proven to be an ideal model with which to study effects of ethanol because its development is more thoroughly understood than other regions or organ systems. The hypothesis that RA-deficient mouse embryos/fetuses manifest similar limb defects and distal limb cell death patterns to those of ethanol treated dams was tested. A RA receptor (RAR) antagonist and an aldehyde dehydrogenase (ALDH) inhibitor produced limb malformations consistent with those following ethanol exposure. Similarly, cell death was observed in the same region of the limb following exposure to each chemical. Secondly, the hypothesis that exogenous RA can prevent ethanol-induced cell death in the limb was tested. A subteratogenic dose of RA was co-administered with ethanol. Limb buds exposed to ethanol and RA exhibited low levels of distal limb cell death, comparable to control limbs, demonstrating that RA acts antagonistically to ethanol in the limb and suggesting that ethanol interferes with RA-mediated development. Also, in support of this premise, the results of in situ hybridization analysis reveal that ethanol represses RA-dependant gene expression in the limb at 8 and 18 hours, post treatment. Importantly, however, microarray examination of limb buds within 2-6 hours of ethanol exposure revealed no correlation between the transcriptional changes induced by ethanol and the RAR antagonist. The lack of early RA-mediated gene changes following ethanol exposure indicates that perturbation of RA-dependent developmental pathways is NOT a proximate teratogenic effect of ethanol. Significant changes in cellular functions and pathways were evident shortly after ethanol exposure, suggesting several possible mechanisms of ethanol teratogenesis that merit future investigation.