107: Effects of chronic intrauterine hypoxia on mitochondrial respiratory protein function within fetal guinea pig forebrain

Abstract

Antenatal intrauterine insults are the predominant cause of neonatal hypoxic ischemic encephalopathy. Neonatal brain MRI studies demonstrate abnormal brain patterns attributed to both preterm and term intrauterine insults coexisting in the same child, showing secondary brain injury developing in fetuses compromised by an earlier intrauterine insult. Altered mitochondrial oxidative phosphorylation and ATP production plays a pivotal role in secondary brain injury. We hypothesize that the degree of mitochondrial dysfunction is dependent on timing of the initial brain injury. Using an animal model of chronic intrauterine hypoxia, we characterized mitochondrial function in the fetal forebrain after early- or late-onset hypoxia by examining the expression and activity of electron transport chain proteins (ETC). Pregnant guinea pigs were exposed to either normoxia (n=12) or hypoxia (ambient O2 10.5%) starting at 28 d (early- onset, n=6) or 50 d (late-onset, n=6) gestation until term (65d). Male fetuses were extracted from anesthetized sows, weighed and forebrains were excised. Protein expression of ETC Complexes I-V (CI-CV) and enzyme activity of Complex I (CI activity) were measured by Western Blot Analysis and Enzyme-Linked Immunoassay, respectively. Results of the hypoxic effects are means +/- SEM, with statistical comparison to normoxia by one-tailed T-Test. Hypoxia reduced fetal body weight and crown rump length while increasing brain:body ratio (Table 1). Late-onset hypoxia did not effect either CI-V expression or CI activity. In contrast, early-onset hypoxia decreased expression of CI (49%) and CII (40%). CIII-V changes were not significant (Fig.1A). CI activity in early hypoxia increased 48% compared to normoxia controls (Fig.1B). The impact of hypoxia on mitochondrial respiratory chain function in the fetal forebrain varied with the gestational age of exposure. Early exposure to significant hypoxia produced an enduring deficit in mitochondrial function exemplified by disruption of CI/II expression and dysregulation of CI activity. This likely mediates ongoing electron leakage, the base cause of oxidative stress, and ongoing brain injury.View Large Image Figure ViewerDownload Hi-res image Download (PPT)