Ischemic Postconditioning Attenuates Myocardial Ischemia-Reperfusion-Induced Acute Lung Injury by Regulating Endoplasmic Reticulum Stress-Mediated Apoptosis

Abstract

Objective: To explore the effect of ischemic postconditioning on myocardial ischemia-reperfusion-induced acute lung injury (ALI).

Methods: Forty adult male C57BL/6 mice were randomly divided into sham operation group (SO group), myocardial ischemia-reperfusion group (IR group), ischemic preconditioning group (IPRE group) and ischemic postconditioning group (IPOST group) (10 mice in each group). Anterior descending coronary artery was blocked for 60 min and then reperfused for 15 min to induce myocardial IR. For the IPRE group, 3 consecutive cycles of 5 min of occlusion and 5 minutes of reperfusion of the coronary arteries were performed before ischemia. For the IPOST group, 3 consecutive cycles of 5 min reperfusion and 5 minutes of occlusion of the coronary arteries were performed before reperfusion. Pathological changes of lung tissue, lung wet-to-dry (W/D) weight ratio, inflammatory factors, oxidative stress indicators, apoptosis of lung cells and endoplasmic reticulum stress (ERS) protein were used to evaluate lung injury.

Results: After myocardial IR, lung injury worsened significantly, manifested by alveolar congestion, hemorrhage, structural destruction of alveolar septal thickening, and interstitial neutrophil infiltration. In addition, lung W/D ratio was increased, plasma inflammatory factors, including interleukin (IL)-6, tumor necrosis factor (TNF)-α, and IL-17A, were increased, malondialdehyde (MDA) activity of lung tissue was increased, and superoxide dismutase (SOD) activity was decreased after myocardial IR. It was accompanied by the increased protein expression levels of ERS-related protein glucose regulatory protein 78 (GRP78), CCAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP), and caspase-12, and the increased apoptotic indices of lung tissues.

Conclusion: IPOST can effectively improve myocardial IR-induced ALI by inhibiting ERS-induced apoptosis of alveolar epithelial cells.

Keywords: Acute Lung Injury; Alveolar Epithelial Cells; Apoptosis; Carrier Proteins; Coronary Vessels; Ischemia-Reperfusion; Ischemic Postconditioning.

Fig. 1

Effect of IPOST on the pathological changes and W/D ratio of lung tissue after myocardial IR. (A) Representative photomicrographs of HE staining of lung sections (200× magnification). (B) Histological score of lung injury. (C) Analysis of lung W/D ratio. Data were expressed as mean±standard deviation (SD). ^△ compared with SO group, P<0.05; ^▲ compared with IR group, P<0.05; ^▽ compared with IPRE group, P<0.05.

Fig. 2

Effect of IPOST on the plasma pro-inflammatory cytokine content after myocardial IR in mice. (A) Tumor necrosis factor alpha (TNF-α) levels; (B) Interleukin 6 (IL-6) levels; (C) Interleukin-17A (IL-17A) levels. Data were expressed as mean±standard deviation (SD). ^△ compared with SO group, P<0.05; ^▲ compared with IR group, P<0.05; ^▽ compared with IPRE group, P<0.05.

Fig. 3

Effects of IPOST on MDA content and SOD activity in lung tissues. (A) MDA level; (B) SOD level. Data were expressed as mean±standard deviation (SD). ^△ compared with SO group, P<0.05; ^▲ compared with IR group, P<0.05; ^▽ compared with IPRE group, P<0.05.

Fig. 4

Effect of IPOST on apoptosis of lung tissue after myocardial IR (magnification 200×). (A) Typical micrographs of lung stained with TUNEL. The number of apoptotic cells in lung tissue was significantly increased in IR group and decreased in IPRE and IPOST groups. The number of apoptotic cells in IPOST group was significantly lower than that in IPRE group. (B) The apoptosis index (AI) of lung tissue. Data were expressed as mean±standard deviation (SD). ^△ compared with SO group, P<0.05; ^▲ compared with IR group, P<0.05; ^▽ compared with IPRE group, P<0.05.

Supplementary Fig. 1

A diagram of the different group stratification.

Fig. 5

Effect of IPOST on ERS-related proteins in lung tissue after myocardial IR. Western blot was used to analyze the representative results of GRP78, CHOP and caspase-12. (A) Expression of GRP78; (B) CHOP; (C) Caspase-12. ^△ compared with SO group, P<0.05; ^▲ compared with IR group, P<0.05; ^▽ compared with IPRE group, P<0.05.