HIF1A and Cognitive impairment: We found that in Sprague-Dawley (SD) rats, chronic hypoxia induces cognitive impairment, and an increase in HIF-1α, tau hyperphosphorylation, and Protein Phosphatase 2A (PP2A) deficiency with a decrease of leucine carboxyl methyltransferase 1 (LCMT1, responsible for PP2A methylation and activity) in the hippocampus.