UC San Diego

Chronic Mountain Sickness (CMS) occurs in high-altitude residents with major neurological symptoms such as migraine headaches, dizziness and cognitive deficits. Recent work demonstrated that highlanders have increased intracellular pH (pHi) in their brain cells, perhaps for the sake of adaptation to hypoxemia and help to facilitate glycolysis, DNA synthesis, and cell cycle progression. Since there are well adapted (non-CMS) and maladapted (CMS) high-altitude dwellers, it is not clear whether pHi is differently regulated in these two high-altitude populations. In this work, we obtained induced pluripotent stem cell (iPSC)-derived astrocytes from both CMS and non-CMS highlanders who live in the Peruvian Andes (>14,000 ft) and studied pHi regulation in these astrocytes using pH-sensitive dye BCECF. Our results show that the steady-state pHi (ss pHi) is lower in CMS astrocytes compared with non-CMS astrocytes. In addition, the acid extrusion following an acid loading is faster and the pHi dependence of H+ flux rate becomes steeper in CMS astrocytes. Furthermore, the Na+ dependency of ss pHi is stronger in CMS astrocytes and the Na+/H+ exchanger (NHE) inhibitors blunted the acid extrusion in both CMS and non-CMS astrocytes. We conclude that (a) NHE contributes to the ss pHi stabilization and mediates active acid extrusion during the cytosolic acidosis in highlanders; (b) acid extrusion becomes less pHi sensitive in non-CMS (versus CMS) astrocytes which may prevent NHE from over-activated in the hypoxia-induced intracellular acidosis and render the non-CMS astrocytes more resistant to hypoxemia challenges.