Early-stage mammalian embryos survive within a low oxygen tension environment and develop into fully functional, healthy organisms despite this hypoxic stress. This suggests that hypoxia plays a regulative role in fetal development that influences cell mobilization, differentiation, proliferation, and survival. The long-term hypoxic environment is sustained throughout gestation. Elucidation of the mechanisms by which cardiovascular stem cells survive and thrive under hypoxic conditions would benefit cell-based therapies where stem cell survival is limited in the hypoxic environment of the infarcted heart. The current study addressed the impact of long-term hypoxia on fetal Islet-1+ cardiovascular progenitor cell clones, which were isolated from sheep housed at high altitude. The cells were then cultured in vitro in 1% oxygen and compared with control Islet-1+ cardiovascular progenitor cells maintained at 21% oxygen. RT-PCR, western blotting, flow cytometry, and migration assays evaluated adaptation to long term hypoxia in terms of survival, proliferation, and signaling. Non-canonical Wnt, Notch, AKT, HIF-2α and Yap1 transcripts were induced by hypoxia. The hypoxic niche environment regulates these signaling pathways to sustain the dedifferentiation and survival of fetal cardiovascular progenitor cells.

Autonomic innervation of the pulmonary vasculature triggers vasomotor contractility predominately through activation of alpha-adrenergic receptors (α-ARs) in the fetal circulation. Long-term hypoxia (LTH) modulates pulmonary vasoconstriction potentially through upregulation of α1-AR in the vasculature. Our study aimed to elucidate the role of α-AR in phenylephrine (PE)-induced pulmonary vascular contractility, comparing the effects of LTH in the fetal and adult periods on α-AR subtypes and PE-mediated Ca2+ responses and contractions. To address this, we performed wire myography, Ca2+ imaging, and mRNA analysis of pulmonary arteries from ewes and fetuses exposed to LTH or normoxia. Postnatal maturation depressed PE-mediated contractile responses. α2-AR activation contracted fetal vessels; however, this was suppressed by LTH. α1A- and α1B-AR subtypes contributed to arterial contractions in all groups. The α1D-AR was also important to contractility in fetal normoxic vessels and LTH mitigated its function. Postnatal maturity increased the number of myocytes with PE-triggered Ca2+ responses while LTH decreased the percentage of fetal myocytes reacting to PE. The difference between myocyte Ca2+ responsiveness and vessel contractility suggests that fetal arteries are sensitized to changes in Ca2+. The results illustrate that α-adrenergic signaling and vascular function change during development and that LTH modifies adrenergic signaling. These changes may represent components in the etiology of pulmonary vascular disease and foretell the therapeutic potential of adrenergic receptor antagonists in the treatment of pulmonary hypertension.

Ca2+ oscillations are important in the regulation of many cerebral arterial functions ranging from vasoconstriction to gene transcription. Without these oscillatory waveforms, there are alterations in the signaling pathways regulated by Ca2+. Previous work has shown that long term hypoxia (LTH) due to high altitude exposure can cause cerebral vascular dysfunction including changes in reactivity and morphology in the fetus as well as adult. Studies performed in cerebral arterial preparations have illustrated that LTH in sheep fetus and adult cause whole cell Ca2+ signaling dysfunctions that compromise vascular reactivity and contribute to cerebral arterial pathologies. Based on the premise that Ca2+ oscillations, vasoconstriction, vessel morphology, and LTH mediated cerebral arterial function are interrelated we tested the hypothesis that LTH impairs Ca2+ oscillations. The impact of LTH and maturation on Ca2+ signals in cerebral arterial myocytes was examined using confocal imaging techniques of flou‐4 loaded myocytes of basilar arteries from low (700m) or high altitude (3,801m) near term fetal or adult sheep. LTH decreased the intracellular Ca2+ signals independent of age due to a faster decay in the Ca2+ signal, an effect that could impair vasoconstriction, alter tissue structure, and compromise the regulation of cerebral blood flow. Along with producing smaller Ca2+ events, the data show that LTH inhibits the cell's ability to respond with Ca2+ signals in response to 30 mM potassium‐induced depolarization in fetal as well as adult sheep. LTH and ontogeny may also play interconnected roles in Ca2+ signaling as LTH inhibits distant communication between myocytes in fetal sheep, whereas in adult sheep it stimulates local signaling. These observations illustrate that altitude and maturation each modify Ca2+ signaling behavior in ways that likely impact arterial reactivity and other mechanisms related to the regulation of cerebral blood flow.Support or Funding InformationThis work is supported by The National Institutes of Health, Eunice Kennedy Shriver National Institute of Child Health and Human Development grant number HD083132, by the National Science Foundation under Grant No. MRI 0923559, and the Loma Linda University School of Medicine.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.