Placental Insufficiency Alters Cerebral Bcl-2 but not P-53 and Bax Gene Expression in Asymmetrical Intrauterine Growth Retarded (IUGR) Fetal Rats• 268

Abstract

Asymmetric IUGR infants are at significant risk for perinatal ischemic neurological damage as well as neurodevelopmental delay despite sparing of brain growth. A primary source of this ischemic damage is mitochondrial free radical production which leads to subsequent lipid peroxidation (LP). Bcl-2 and P-53 response protein Bax are mitochondrial associated proteins which are linked to increased free radical production and prevent or facilitate cellular apoptosis respectively. We therefore hypothesized that cerebral gene expression of Bcl-2, P-53, and Bax would be altered and LP would be increased in term fetal rats made IUGR by maternal uterine artery ligation (a well characterized model of uteroplacental insufficiency and asymmetrical IUGR). We performed sham surgery (C) and bilateral uterine artery ligation (IUGR) on pregnant rats on day 19 of gestation (term-21d). 48 hours after surgery, a caserean section was performed and cerebral tissue RNA and protein were extracted for RT-PCR (utilizing an internal control) and western blotting. To assess levels of lipid peroxidation present in the cerebral tissue, malondialdehyde levels were quantitated. RESULTS: Cerebral Bcl-2 mRNA levels(C=1.0, IUGR Bcl-2=0.29±0.03; p < 0.05) and protein levels (C=1.0, IUGR Bcl-2= 0.40±0.05; p< 0.05) were significantly decreased in IUGR pups. In contrast, mRNA levels of P53 and Bax were not significantly different between control and IUGR fetal animals (C=1.0, IUGR P53=0.95±0.12, IUGR Bax=1.1±0.20); moreover, cerebral protein levels of P53 were not significantly different between control and IUGR pups (C=1.0, IUGR P53=1.2±0.16). Malondialdehyde levels were increased(IUGR-4.44±0.83 vs C-3.53±0.66 nmol/g tissue) though not significantly. We conclude that the intrauterine milieu associated with placental insufficiency decreases gene expression of the mitochondrial associated apoptosis protein Bcl-2, but does not significantly alter gene expression of P-53 or P-53 response protein Bax. The decreased expression of Bcl-2 is intriguing because Bcl-2 prevents apoptosis by blocking the release of Cytochrome c from the mitochondria. Cytosolic cytochrome c is necessary for the initiation of the apoptosis program. We speculate that decreased gene expression of Bcl-2 may leave the IUGR fetus susceptible to hypoxic-ischemic insults.