Abstract 2026 Poster Session II, Sunday, 5/2 (poster 236)

Uteroplacental insufficiency causes IUGR, and IUGR infants suffer an increased risk of developing ischemic neurological damage and neurodevelopmental delay. An element of neurological ischemic damage is initiated by free radical production from the mitochondrial electron transport chain, and mitochondrial DNA is particularly susceptible to damage from these free radicals. We have previously demonstrated that fetal cerebral gene expression of key mitochondrial proteins involved in electron transport is increased in a rat model of IUGR; in contrast, cerebral gene expression of these proteins is decreased in juvenile IUGR rats (Lane et al-1997 Ped Res). Mitochondrial gene expression can be influenced by mitochondrial DNA quantities. We therefore hypothesized that decreased expression of these cerebral mitochondrial genes would be associated with a parallel decrease in mitochondrial DNA. To test this hypothesis, we performed bilateral uterine artery ligation to induce IUGR and sham surgery (C) in pregnant rats on d19 of gestation (term 21d). IUGR and control DNA, protein, and RNA were isolated from brains of full term d21 fetuses (F21) and d21 juvenile animals (J21). To quantify mitochondrial DNA, we performed a PCR technique which co-amplifies an intron of genomic DNA and a non-coding region of mitochondrial D-loop DNA. Mitochondrial DNA levels were standardized to levels of genomic DNA. We also performed western blotting using an anti-human monoclonal antibody to a mitochondrial 60 kD marker protein. RESULTS: Levels of fetal cerebral mitochondrial DNA and marker protein were not significantly different between control and IUGR animals (F21 C=1.0; F21 IUGR mito DNA=0.86±0.06; F21 IUGR mito protein 0.90±0.09; p=NS) (n=12). In contrast, levels of juvenile cerebral mitochondrial DNA and protein were significantly decreased (J21 C=1.0; J21 IUGR mito DNA 63±0.04*; J21 IUGR mito protein 58±05*; *p<0.05) (n=15). To exclude the possibility that these J21 findings were a result of a nonspecific decrease in nucleotide or protein levels, we measured cerebral mRNA and protein levels of P53 in J21 pups. Neither P53 mRNA or protein levels were significantly altered in the J21 IUGR brain. We conclude that the amount of mitochondrial DNA relative to genomic DNA is unchanged in F21 IUGR brain; in contrast, cerebral mitochondrial DNA is significantly decreased relative to genomic DNA in J21 IUGR brain. Moreover, we found decreased levels of a mitochondrial marker protein in J21 IUGR brain. Mitochondrial DNA damage occurs at 10-30 times the rate of nuclear DNA under identical conditions of cellular stress. This vulnerability results from the proximity of mitochondrial DNA to oxidative phosphorylation and subsequent free radical production and a deficient DNA repair system. We speculate that the hypoxic, acidotic, and hypoglycemic intrauterine milieu of the IUGR fetus results in free radical production and subsequent mitochondrial DNA damage. As the animals mature, this damage may decrease the mitochondrial/nuclear DNA ratio as a result of the ineffective mitochondrial DNA repair system, or lead to a decrease in mitochondrial number secondary to inhibition of mitochondrial replication.