Abstract 600: Neonatal Transient Hyperoxic Exposure Leads to Persistent Vascular DNA Damage and Increased Senescence Proteins in Rats: Potential Role in Developmental Programming of Hypertension

Abstract

Background: Preterm infants have reduced antioxidant defenses vs. babies born at term and are exposed to high levels of oxygen (O2) both in intensive care and as compared to the intrauterine environment. We have shown that neonatal hyperoxic stress leads in adult rats to hypertension, endothelial dysfunction and arterial rigidity, all characteristic of vascular aging. Indeed, acutely, markers of vascular cells senescence are increased. Aim: To examine whether indices of vascular aging persists beyond neonatal hyperoxic exposure. For this purpose, vessels (aorta) are studied at 4 weeks (wks, pre-hypertension) and 16 wks (young adults-elevated blood pressure). Methods: Sprague-Dawley pups were kept at 80% O2 or in room air from postnatal days 3 to 10. Aortas were sampled at 4 and 16 wks (n=5-7 animals/group) to examine tumour suppressor p53 binding protein 1 (53BP1, indices of DNA damage) and senescence proteins (p53, p16 and p21) by immunofluorescence. Bax and bcl2 proteins (for apoptosis) were assessed by western blot at 4 wks. Results: At 4 wks, aortas of O2 exposed rats showed increased nuclear foci of 53BP1 (19.3±0.8 vs. 10.5±1.1 fluorescence intensity, p<0.0001), and increased expression of p53 (19.3±0.4 vs. 16.3±0.9, p<0.05) compared to controls. Expressions of Bax (pro-apoptotic protein) and the ratio Bax/Bcl2 were not different between groups (2±0.2 vs. 1.6±0.1, and 1.4±0.1 vs. 1.2±0.1, respectively). Bcl2 (anti-apoptotic protein) was decreased in O2 exposed rats compared to controls (1.6±0.03 vs. 1.3±0.07, p<0.01). At 16 wks, O2 exposed rats showed also increased nuclear foci of 53BP1 (23.9±3.8 vs. 14.2±0.9, p<0.05), and increased expression of p53 (21.6±1.6 vs. 13.8±0.5, p<0.01), and p16 (16.9±1.6 vs. 7.7±0.8, p<0.01), p21 was not changed (11.5±0.9 vs. 14±1.9, non significant). Conclusions: Neonatal exposure to O2 leads at 4 wks and 16 wks to DNA damage and expression of senescence associated proteins without evidence of apoptosis (at 4wks ). These changes are present before the adult consequences of neonatal exposure (i.e. hypertension and vascular dysfunction) and may contribute to their development.