High basal level of autophagy in high-altitude residents attenuates myocardial ischemia-reperfusion injury

Objective: Hypoxia can induce autophagy, which plays an important role in cardioprotection. The present study tested the hypothesis that patients with congenital heart disease living at a high altitude could resist ischemia-reperfusion injury better than those at a low altitude, through elevated basal autophagy by chronic hypoxia. Methods: Twelve Tibetan patients residing at a high altitude of >3000 m and 12 Han patients residing at a low altitude of <500 m with simple atrial or ventricular septal defects were prospectively recruited. All patients underwent cardiopulmonary bypass, maintaining a flowrate of approximately 2.4 to 2.8 L/min/m(2) and mean arterial pressure of >= 40 to 60 mmHg. Myocardial ischemia-reperfusion injury between the 2 groups was compared using cardiac troponin I, brain natriuretic peptide, hematoxylin eosin staining, and the terminal deoxynucleotidyl transferase dUTP nick end labeling test. Autophagy-related proteins microtubule-associated protein 1 light chain 3 II (LC3II), Beclin1, and lysosomal-associated membrane protein 2 (LAMP2) and their upstream protein BCL2/adenovirus E1B 19-kDa protein-interacting protein 3 (Bnip3) were evaluated with Western blotting. Results: The maximal cardiac troponin I concentration and increasing x-fold of brain natriuretic peptide in the high-altitude group were obviously lower than those in the low-altitude group (3.10 +/- 0.77 vs 7.10 +/- 2.28 ng/mL and 2.51 +/- 0.94 vs 14.66 +/- 6.83, respectively). The preoperative and postoperative levels of LC3II, LAMP2, and upstream Bnip3 in the high-altitude group were obviously greater. No difference was found in the Beclin1 level between the 2 groups at baseline or ischemia-reperfusion. Conclusions: Patients living at a high altitude with congenital heart disease resisted ischemia-reperfusion injury during cardiac surgery better than those at a low altitude, possibly through elevated basal autophagy induced by chronic hypoxia.