MILD, PRENATAL HYPOXIA IN THE PREGNANT RAT INDUCES ALTERATIONS IN THE CARDIORESPIRATORY FUNCTION AND PROTEIN EXPRESSION OF JUVENILE OFFSPRING

Monique Youssoufian, Ulrike Mathesius, Rosemary Martin, The School of Biochemistry and Molecular Biology, Australian National University, ACT.

Pathophysiological events during prenatal life, such as fetal hypoxaemia, have long-lasting effects on postnatal health. This has been well demonstrated in the cardiovascular system, but not in other systems such as the respiratory system. In this study pregnant Wistar rats were exposed to either mild hypoxia (14% O₂) or air (controls) in late pregnancy (E17-E19). This is the time when respiratory rhythm develops. Offspring were handled from postnatal day (PN)14-20 in preparation for cardiorespiratory measurements in the awake state. Blood pressure, heart rate, and ventilation were measured from PN20-24. A subset of pups from each condition was used to analyse protein expression in brainstem and carotid body tissue by 2-d gel electrophoresis and peptide mass fingerprinting. Treated offspring had significantly higher basal heart rates and decreased inspiratory times at rest (p<0.05 for both). Furthermore, there was a significant treatment effect on protein expression in tissue from juvenile offspring. Preliminary identification of changed proteins include a diverse range of function. In the carotid bodies, treated pups showed a down regulation of tropomyosin (particularly the alpha-4 chain) and vimentin, both of which help maintain cytoskeletal integrity; and ER-60, a cysteine protease of the endoplasmic reticulum. There was an upregulation of dihydropirimidinase-2, which aids in cell migration and guidance and heat shock cognate 71, a cytosolic chaperone protein. In the brainstem, there was a dysregulation of several isoforms of mitochondrial ATP synthase beta chain, and a decrease in glial fibrillary acidic protein, a type III intermediate filament like vimentin. There was a concurrent increase in heat shock 60, a mitochondrial chaperone protein, and phosphotidylethanolamine-binding protein, whose function is still elusive but may involve membrane biosynthesis, intracellular signalling, and/or catecholaminergic transmission. Some of these changes in protein expression may represent adaptive mechanisms to limit brain damage early in development.