Lifelong exposure to high-altitude hypoxia in humans is associated with improved redox homeostasis and structural-functional adaptations of the neurovascular unit.

KEY POINTS: High-altitude (HA) hypoxia has the potential to alter the structural-functional integrity of the neurovascular unit (NVU) in humans. For the first time, we examined to what extent chronic and lifelong hypoxia impacts multimodal biomarkers reflecting NVU structure-function in lowlanders and native Andean highlanders. Despite lowlanders presenting with a reduction in systemic oxidative-nitrosative stress and maintained cerebral bioenergetic and cerebrovascular function during chronic hypoxia, there was evidence for increased axonal injury and cognitive impairment. Compared to lowlanders at sea-level, highlanders exhibited elevated vascular NO bioavailability, improved dynamic regulatory capacity and cerebrovascular reactivity, comparable cerebral substrate delivery, neurovascular coupling and maintained cognition. Unlike lowlanders following chronic-HA, highlanders presented with lower concentrations of S100B, neurofilament-light chain and total-tau. These findings highlight novel integrated adaptations towards the regulation of the NVU in highlanders that may represent a neuroprotective phenotype underpinning successful adaptation to the lifelong stress of HA hypoxia.

ABSTRACT: High-altitude (HA) hypoxia may alter the structural-functional integrity of the neurovascular unit (NVU). Herein, we compared male lowlanders (n = 9) at sea-level (SL) and after 14-days acclimatization to 4,300 m (chronic HA) in Cerro de Pasco (CdP), Péru (HA), against sex, age and body mass index-matched healthy highlanders (n = 9) native to CdP (lifelong-HA). Serum proteins were examined to reflect NVU integrity and venous blood assayed for free radicals and nitric oxide (NO). Regional cerebral blood flow (CBF) was examined in conjunction with cerebral substrate delivery, dynamic cerebral autoregulation (dCA), cerebrovascular reactivity to carbon dioxide (CVRCO2 ) and neurovascular coupling (NVC). Psychomotor tests were employed to examine cognitive function. Compared to lowlanders at SL, highlanders exhibited elevated plasma and red blood cell NO bioavailability (P = 0.005, d = 1.549 and P = 0.003, d = 1.681), improved anterior and posterior dCA (low frequency Gain: P = 0.029, d = -1.292 and P = 0.017, d = -1.255 respectively), elevated anterior CVRCO2 (P = 0.113, d = -0.852) and preserved cerebral substrate delivery and NVC (all P = >0.100). In highlanders, S100B, neurofilament light-chain and T-tau were consistently lower (P = 0.018, d = -1.244, P = 0.037, d = -1.075 and P = <0.001, d = -3.894, respectively) and cognition comparable (all P = >0.100) to lowlanders following chronic-HA. These findings highlight novel integrated adaptations towards regulation of the NVU in highlanders that may represent a neuroprotective phenotype underpinning successful adaptation to the lifelong stress of HA hypoxia. Abstract figure legend We determined how the hypoxia of high-altitude across the temporal continuum of chronic through to lifelong exposure impacts the neurovascular unit (NVU) phenotype and to what extent this is subject to altered redox homeostasis. Basal multimodal biomarkers reflecting NVU structure-function were determined in lowlanders at sea-level (lifelong normoxia) and after 2 weeks acclimatization to 4,300 m (chronic hypoxia) in Cerro de Pasco, Péru (CdP) and compared to age/sex-matched highlanders native to CdP (lifelong hypoxia). Compared to acclimatized lowlanders, highlanders were characterized by elevated systemic nitric oxide (NO) bioavailability, improved dynamic cerebral autoregulation (dCA) and cerebrovascular reactivity to carbon dioxide (CVRCO2 ) and lower concentrations of S100B, neurofilament-light chain (NF-L) and total tau (T-Tau) in the face of preserved cerebral bioenergetics and cognition. Collectively, our novel findings tentatively suggest that these integrated adaptations may collectively reflect a neuroprotective phenotype to cope with the lifelong stress of high-altitude hypoxia. MCA, middle cerebral artery; PCA, posterior cerebral artery; ICA, internal carotid artery; VA, vertebral artery. This article is protected by copyright. All rights reserved.