High Altitude Specializations in Gelada Identified by Gene Expression and Cell Physiology

Mammals live in a variety of environments and struggle against various conditions. One condition that many mammals have adapted to is hypoxia. Different mammals have adapted to high-altitude, chronic hypoxia including certain populations of humans. However, these human populations emerged around 46,000 years ago, whereas other species, including primates from the genus Theropithecus have resided in the Ethiopian Highlands for at least 1 million years. Geladas (Theropithecus gelada) are baboon-like monkeys native to the Ethiopian Highlands (2350-4550m). Geladas also have a mixture of physiological and morphological adaptations including increased chest size, lower hemoglobin levels, and increased selection for hypoxia related genes. To assess mechanistic elements of hypoxia tolerance in gelada, we isolated dermal fibroblasts from ear biopsies of wild geladas (n=12) from Ethiopia as part of the Simien Mountains Gelada Research Project and compared them to dermal fibroblasts isolated from sea-level dwelling humans (ATCC). We assayed the production of reactive oxygen species (ROS) in both species using an amplex red assay. We also exposed cells to hypoxic conditions and assayed mitochondrial membrane potential upon reoxygenation using a MitoTracker fluorescent dye. Under baseline (normoxic, 21% O2) conditions, gelada fibroblasts produce 76% less ROS compared to human fibroblasts, suggesting a potential mechanism to avoid hypoxic cellular damage. We combined our approach with bulk RNAseq from both species, comparing differential gene expression and enriched pathways following a 6h and 24h exposure to hypoxic (0.5% O2) conditions. In the 24-h experiment, cells of both primates have similar numbers of differentially expressed genes (gelada: 1510 upregulated, 1922 downregulated; human: 1712 upregulated, 1456 downregulated). However in the shorter (6-h) exposure, gelada cells show a substantially reduced gene expression response with only 366 differentially expressed genes, versus 2765 in human. In the 24h exposure, upregulated genes in both species are enriched for pathways such as glycolysis and iron binding, however gelada fibroblasts additionally demonstrate enrichments in Wnt signaling and negative regulation of apoptosis, whereas human fibroblasts are enriched for ubiquitin protein conjugation and DNA damage repair. The hypoxia inducible factor (HIF) signaling pathway is also enriched in gelada fibroblasts, even after 24-h in hypoxia, but not in the human cells. This suggests that the species may differentially affect hypoxia signaling via the HIF-1 transcription factor, either in amplitude or timecourse of response. Next steps will include an evaluation of the timecourse of HIF1α in hypoxic cells from both species using western blot. Funding by NSF #2022046 This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.