Quantitative proteomics reveal an altered pattern of protein expression in saliva of hypobaric hypoxia-induced rat model

Hypobaric hypoxia (HH), a pathophysiological condition caused by an ascent to a high altitude. It occurs due to a deficiency of oxygen at the tissue level. Saliva is an advantageous biological sample because of easy, low cost and minimally invasive sample collection and processing. Although few reports have documented the effect of long term exposure to hypobaric hypoxia on salivary proteome but short term proteome based study remains uninvestigated. In this study, age-matched male SD rats were exposed to simulated hypobaric hypoxia (~ 25,000 ft, 7620 m) for 1 day (HD1), 3 days (HD3) and 7 days (HD7) followed by iTRAQ based LCMS/MS comparison with normoxic controls. Oxidative stress being the main event of hypobaric hypoxia suggested an initial increase in levels of oxidative stress parameters such as reactive oxygen species (ROS) and lipid peroxidation; and decrease in antioxidant enzymes such as the activity of catalase and reduced glutathione. Based on iTRAQ, out of 67 differentially expressed proteins, 36 (22 up-regulated and 14 down-regulated), 45 (24 up-regulated and 21 down-regulated), and 45 (19 up-regulated and 26 down-regulated) were modulated in HD1, HD3, and HD7 group respectively. Few proteins such as BPI fold-containing family A member 2, cystatin, and carbonic anhydrase 1 showed many folds differential expression in exposed groups as compared to normoxia. Through Ingenuity Pathways analysis, we have observed glucocorticoid receptor signaling and MSP-RON pathway to be most significantly affected. Glucocorticoid receptor signaling and MSP-RON signalling being the most significant pathways involved modulated proteins such as annexin 1, hsp90, keratin, actin-beta, and kallikrein 1. These proteins were found to aid in acclimatization and survival during hypobaric hypoxia. Taken together, this study provided the proof of concept for footprints of hypobaric hypoxia-mediated events during short term exposure through rat salivary proteome.