Class switching of carbonic anhydrase isoforms mediates remyelination in CA3 hippocampal neurons during chronic hypoxia

Gut microbiota's role in high-altitude cognitive impairment: the therapeutic potential of Clostridium sp. supplementation

Prolonged exposure to high-altitude environments may increase the risk of cognitive decline in young migrants. Recent studies suggest that hypobaric hypoxia-induced alterations in gut microbial composition could partly contribute to this risk. However, the absence of direct evidence from cohort studies and an unclear mechanism hinder intervention development based on this hypothesis. This study recruited 109 young male migrants living in Xizang to investigate the microbial mechanisms underlying cognitive impairment associated with high-altitude migration. Multi-omic analysis revealed distinct microbiome and metabolome features in migrants with cognitive decline, notably a reduced abundance of Clostridium species and disrupted fecal absorption of L-valine. Mechanistic studies showed that hypobaric hypoxia significantly damaged the intestinal barrier, leading to lipopolysaccharide (LPS) leakage and an influx of inflammatory factors into the peripheral blood, which activated microglia and caused neuronal injury in the hippocampus of mice. Additionally, compromised L-valine absorption due to intestinal barrier damage correlated with lower hippocampal glutamate levels and neurotrophic factors. Intervention with Clostridium sp. effectively restored the intestinal barrier and enhanced L-valine absorption, which mitigated hypobaric hypoxia-induced inflammation and hippocampal neural damage in mice. In conclusion, cognitive impairment among young migrants at high altitude may be attributed to hypobaric hypoxia-induced gut microbiota disruption and subsequent intestinal barrier dysfunction. This study may provide a promising approach for preventing and treating high-altitude-associated cognitive impairment.

Hypoxia and brain aging: Neurodegeneration or neuroprotection?

The absolute reliance of the mammalian brain on oxygen to generate ATP renders it acutely vulnerable to hypoxia, whether at high altitude or in clinical settings of anemia or pulmonary disease. Hypoxia is pivotal to the pathogeneses of myriad neurological disorders, including Alzheimer's, Parkinson's and other age-related neurodegenerative diseases. Conversely, reduced environmental oxygen, e.g. sojourns or residing at high altitudes, may impart favorable effects on aging and mortality. Moreover, controlled hypoxia exposure may represent a treatment strategy for age-related neurological disorders. This review discusses evidence of hypoxia's beneficial vs. detrimental impacts on the aging brain and the molecular mechanisms that mediate these divergent effects. It draws upon an extensive literature search on the effects of hypoxia/altitude on brain aging, and detailed analysis of all identified studies directly comparing brain responses to hypoxia in young vs. aged humans or rodents. Special attention is directed toward the risks vs. benefits of hypoxia exposure to the elderly, and potential therapeutic applications of hypoxia for neurodegenerative diseases. Finally, important questions for future research are discussed.