Preliminary Study on the Pathogenic Mechanism of Myoglobin-induced Endoplasmic Reticulum Stress andApoptosis in Crush Syndrome

Objective To explore the pathogenic mechanism of myoglobin-induced endoplasmic reticulum stress (ERS) and apoptosis in tubular epithelial cells in acute kidney injury (AKI) mouse model of crush syndrome. Methods Eighteen C56BL/6 mice were randomly divided into control group, modeling 8 h group and modeling 24 h group. The AKI model of crush syndrome was established by intramuscular injection of 50% glycerol saline solution into thigh (8 μL/g), while equivalent volume of physiological saline was injected in control group. AKI was diagnosed when serum creatinine (sCr) level increased to double value of control group. The mice in the experimental groups were sacrificed at the time points of 8 h and 24 h after injection respectively. Serum Cr was detected and renal tissues was observed under electron microscopy. Apoptosis was detected by TUNEL technique. Marker proteins and mRNA of apoptosis and ERS were detected by immunohistochemistry and real-time PCR. Human kidney proximal tubular cell (HK-2) cells cultured in vitro were randomly divided into control, intervention 6 h and intervention 12 h groups. Control group were incubated in standard cell culture (DMEM/F12) and the two intervention groups were incubated in special DMEM/F12 in which ferrohemoglobin was added. After 6 h and 12 h incubation, the cells were collected and apoptosis was detected by flow cytometry. Results AKI model of crush syndrome was successfully established, which was proved with sCr doubling at the 8 h after the intramuscular injection of glycerol saline. Swelling of endoplasmic reticulum and mitochondria in proximal tubular epithelial cells was more obvious in the two model groups than that in control group. TUNEL staining showed the percentage of positive cells in AKI groups was higher than that in control group (P <0.05). Immunohistochemistry and real-time PCR showed the expressions of caspase3, caspase12 and CHOP in AKI groups were higher than those in control group (P <0.05).Flow cytometry showed cell apoptosis ratio was higher in model groups than control group (P <0.05). Conclusion Myoglobin induced ERS and apoptosis may be involved in the pathogenesis of AKI in crush syndrome.