Endothelial cells derived from elephant seals blunt angiogenic transcriptional signaling during hypoxia exposure

Abstract

Northern elephant seals ( Mirounga angustirostris) conduct repeated deep dives, during which arterial blood oxygen becomes depleted. Interestingly, elephant seals require little surface recovery time from these dives, and extreme hypoxemia occurs regardless of dive duration or purpose. Recent in vitro and in silica work indicates that tight regulation of the canonical hypoxia response may protect diving seals against the inflammatory injuries typically associated with repeated hypoxia exposure. In vivo assessments of these phenomena, however, remain restricted due to both technical constraints and animals' inaccessibility while diving at sea. We developed a proliferative endothelial cell culture system from expelled placental arteries to assess the real-time molecular response to hypoxia exposure in northern elephant seals. Hypoxia inducible factor 1a (HIF-1a) protein localized to the nucleus within 1 h of exposure to 1% O2 in both species[KA1]. Hypoxia increased HIF-1a protein levels to a maximum of ~70-fold over (normoxic) baseline levels in both seal and human cells (p=0.005 for both species), though the response dynamics differed between species. HIF-1a abundance in seal cells was biphasic, with an initial rapid peak occurring within 15 min of hypoxia onset. In contrast, HIF-1a levels did not peak in human cells until 1 h in hypoxia and abundance declined continuously following this peak. Interestingly, RNAseq analysis of HIF-1a target gene expression suggested that seal cells blunt angiogenic signaling and vascular remodeling during hypoxia exposure despite sustained HIF-1a protein stabilization. Seal cell expression of STC2, NHE1/SLC9A1, and PFKL lagged behind expression of these genes in human cells during hypoxia exposure, and seal cell expression of ANGPT2 and MMP14 remained stable during long term hypoxia exposure, while expression of these genes was variable or high in human cells. Cis-regulatory analyses suggested a role for altered metabolism (rather than altered oxygen delivery) in seal cells during hypoxia via FOXK1, NFKB1, JUN and ZBTB7A. In contrast, the transcriptional signature in human cells suggests altered expression of oxygen delivery pathways via homeobox A13 (HOXA13), FOS like 1 (FOSL1) and SRF, all of which regulate angiogenesis, vascular remodeling and vasodilation. Together, these data suggest that seal endothelial cells respond to hypoxia by managing metabolic factors rather than calling for increased oxygen delivery despite rapid and sustained HIF-1a stabilization. NSF GRFP and UC Berkeley startup This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.