Effects of chronic hypoxia and AMPK activation on uteroplacental perfusion, placental metabolism and the regulation of fetal growth

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PROJECT SUMMARY The hypoxia of high-altitude (HA, >2500 m) increases the frequency of fetal growth restriction (FGR) three-fold. The normal pregnancy rise in blood flow to the uteroplacental circulation (termed “uterine” here) is also reduced in FGR at HA or at low altitude, but lower uterine blood flow is not solely responsible for FGR because O2 supply still exceeds fetal O2 consumption, even at HA. Thus, the mechanisms by which lower uterine blood flow reduces fetal growth and their temporal relationship remain unclear. Our prior work implicates AMPK in the regulation of uterine vascular function, blood flow, and fetal growth, and our preliminary data show that FGR vs. appropriate for gestational age (AGA) pregnancies in La Paz, Bolivia (3850 m) have lower third-trimester uterine blood flow; greater placental AMPK activation, suppressed mitochondrial oxidative metabolism, and metabolite profiles supporting impaired fatty acid and amino acid metabolism. We propose human and sheep studies to be conducted under chronic maternal hypoxia in order to determine whether placental AMPK signaling serves as a nexus between uteroplacental perfusion and placental metabolism to regulate fetal growth through its dual role as a potent vasodilator and metabolic sensor. In HA residents with AGA or FGR pregnancies women at unlabored C-section, we will measure blood flows, perform four-vessel sampling on both sides of the placenta, collect placental and human uteroplacental and fetoplacental arteries regulating blood flow for vasoreactivity studies, and conduct biochemical assays. Because vasodilation is impaired in FGR, we will test whether pharmacologic mediated modulators of mitochondrial oxidative metabolism and redox status restore impaired AMPK- vasorelaxation.Since access to human blood vessels and placenta are only available at delivery, we will perform parallel studies in a sheep model of hypoxia-associated FGR in order to measure these same variables but also with metabolic tracers both before and after FGR (i.e. at mid- and late-gestation respectively) in order to identify when uterine O2 supply decreases, and test the temporal relationship between O2 supply, O2 consumption, nutrient uptake, and fetoplacental metabolism relative to the initiation of FGR. As in the human studies, we will also assess the effects of AMPK activation on uterine vasoreactivity and placental nutrient metabolism, and test whether restoring mitochondrial oxidative metabolism improves vasodilation in key uterine resistance vessels. The proposed studies will enable our understanding to move beyond the conventional idea that insufficient fetal oxygenation triggers FGR to one in which we know when and how the hypoxia-associated FGR develops. Such information is essential for refining therapeutic strategies for restoring fetal growth under conditions of hypoxia, a goal that has, to date, proven elusive.