Adaptability to hypobaric hypoxia is facilitated through mitochondrial bioenergetics: an in vivo study

High-altitude pulmonary oedema (HAPE) experienced under high-altitude conditions is attributed to mitochondrial redox distress. Hence, hypobaric hypoxia (HH)-induced alteration in expression of mitochondrial biogenesis and dynamics genes was determined in rat lung. Further, such alteration was correlated with expression of mitochondrial DNA (mtDNA)-encoded oxidative phosphorylation (mtOXPHOS) genes. The prophylactic effect of dexamethasone (DEX) in counteracting the HH-induced mitochondrial distress was used as control to understand adaptation to high-altitude exposure.

Rats pretreated with DEX were exposed to normobaric normoxia (NN) or HH. HH-induced injury was assessed as an increase in lung water content, tissue damage and oxidant generation. Mitochondrial number, mtDNA content and mtOXPHOS activities were measured to determine mitochondrial function. The expression of mitochondrial biogenesis, dynamics and mtOXPHOS genes was studied.

HH-induced lung injury was associated with decreased mitochondrial number, mtDNA content and mtOXPHOS activities. HH exposure decreased the nuclear gene oestrogen-related receptor-α (ERRα), which interacts with PPAR-γ coactivator-1α (PGC-1α) in controlling mitochondrial metabolism. Consequently, mtOXPHOS transcripts are repressed under HH. Further, HH modulated mitochondrial dynamics by decreasing mitofusin 2 (Mfn2) and augmenting fission 1 (Fis1) and dynamin-related protein 1 (Drp1) expression. Nevertheless, DEX treatment under NN (i.e. adaptation to HH) did not affect mitochondrial biogenesis and dynamics, but increased mtOXPHOS transcripts. Further, mtOXPHOS activities increased together with reduced oxidant generation. Also, DEX pretreatment normalized ERRα along with mitochondrial dynamics genes and increased mtOXPHOS transcripts to elicit the mitochondrial function under HH.

HH stress (HAPE)-mediated mitochondrial dysfunction is due to repressed ERRα and mtOXPHOS transcripts. Thus, ERRα-mediated protection of mitochondrial bioenergetics might be the likely candidate required for lung adaptation to HH.