Date of Graduation
Alcohol exposure causes developmental abnormality known as Fetal Alcohol Syndrome (FAS), featured with central nervous system (CNS) dysfunction. The cerebellum is vulnerable to ethanol toxicity. Developmental exposure to ethanol depletes the number of cerebellar granule cells; however, the underlying mechanisms are unknown. A potential mechanism for ethanol-induced neuronal depletion is to reduce the pool of neuronal progenitors. The progression of the cell cycle is regulated by a family of protein kinases called cyclin-dependent kinases (CDKs). We hypothesize that ethanol interferes with the CDK system and disrupts the cell cycle kinetics in cerebellar granule progenitors (CGPs). Pregnant rats were fed ad libitum an ethanol-containing liquid diet (Et) or pair-fed an isocaloric control diet (Ct). The expression of CDK, cyclin, or CDK inhibitor (CDKI) during development were quantified. Prenatal ethanol exposure down-regulated the expression of CDK2/cyclin as well as p27 Kip (a CDKI). In contrast, ethanol up-regulated the amount of CDK4/CDK6/cyclin D2. These findings were verified with an in vitro study. In the primary cultures of CGPs, ethanol also disrupted CDK system in a pattern similar to the in vivo observation. Analysis of cell cycle kinetics by a cumulative BrdU labeling technique demonstrated that ethanol increased the duration of the total cell cycle, S-phase, and decreased the growth fraction (the cycling population). Furthermore, ethanol caused a delayed apoptosis. To further determine the molecular mechanisms of ethanol-induced damage, we investigated the effect of ethanol on the activity of a transcription factor, AP-1 in the CGPs. AP-1 regulates many genes that are critical for cell cycle control including cyclins. The CGPs were isolated from mice expressing the AP-1-luciferase transgene. Brain-derived neurotrophic factor (BDNF) is an important trophic factor regulating the development of CGPs. We demonstrated that BDNF stimulated AP-1 activity, and ethanol blocked BDNF-stimulated activation. PI-3K/AKT and JNK signal pathways were critical for BDNF-regulated AP-1 activity, and ethanol significantly inhibited the BDNF-mediated activation of these pathways. In summary, ethanol alters the CDK system and cell cycle kinetics in CGPs; disruption of transcriptional regulation may account for ethanol-induced damage.
Li, Zheng, "The mechanisms of ethanol-induced damage to the developing cerebellum: Effects on the cerebellar granule cells." (2003). Graduate Theses, Dissertations, and Problem Reports. 9289.