Time-course changes of remote apoptosis and necroptosis of pulmonary cells induced by acute kidney injury in mice

Abstract

Objective To explore the change patterns of apoptosis and necroptosis in lung cells over time during acute kidney injury-induced distal lung injury. Methods Thirty male C57BL/6J mice (8 weeks old) were randomly divided into Sham operation group (undergoing laparotomy only), and renal ischemia-reperfusion groups (RI/r groups, bilateral kidney ischemia for 50 min followed by reperfusion for 6, 12, 24, 36 and 48 h respectively), with 5 animals in each group. HE staining was performed to assess lung tissue injury. The serum concentrations of creatinine (Cr) and blood urea nitrogen (BUN) were determined with corresponding reagent kits. The lung cell apoptosis was detected by TUNEL. Immunofluorescence staining was used to investigate the expression of phosphorylation mixed lineage kinase domain like protein (p-MLKL), and Western blotting was employed to measure the expression levels of phosphorylation receptor-interacting protein 1 (p-RIP1), p-MLKL and cleaved Caspase-3. Results Within 24 h after renal I/R injury, the serum levels of Cr and BUN and pulmonary pathological injury score were increased in a time-dependent manner, and the severity of renal injury was positively correlated with that of lung injury. The number of apoptotic cells and the expression level of cleaved Caspase-3 in the lung were raised gradually with the elapse of time. Compared with the Sham operation group, the number of apoptotic cells was elevated in the RI/r12, 24, 36 and 48 h groups (P < 0.05), and the expression of cleaved Caspase-3 was notably up-regulated in the RI/r 24, 36 and 48 h groups (P < 0.05). The expression levels of p-MLKL and p-RIP1 were increased time-dependently, and the p-MLKL level was then declined gradually after reaching a peak at 36 h after reperfusion. Conclusion Within 48 h after renal I/R injury, lung injury is exacerbated gradually. The number of apoptotic lung cells continues to increase, but that of necroptosis is in a trend of decrease after reaching a peak at 36 h.

Keywords

• renal ischemia-reperfusion
• acute lung injury
• apoptosis
• necroptosis