[Expression and significance of c-FLIP protein in sepsis mice with acute kidney injury].

Objective: To observe the expression of cellular Fas-associated death domain-like interleukin-1β converting enzyme inhibit protein (c-FLIP) in sepsis mice with acute kidney injury (SAKI) and explore its significance.
Methods: Thirty male ICR mice were divided into the normal control group (Normal group), sham operation group (Sham group) and SAKI group by random number table method, with 10 mice in each group. The SAKI model of mice was established by cecal ligation and puncture (CLP); the Sham group was not ligated and the cecum was not punctured, and other surgical procedures were the same as the SAKI group; the Normal group did not experience any treatment. The serum and renal tissues of mice in each group were harvested 24 hours after CLP model establishment. The levels of serum creatinine (SCr) and blood urea nitrogen (BUN) were detected by enzyme linked immunosorbent assay (ELISA). The renal tissues were stained with hematoxylin-eosin (HE), and the pathological changes of renal tissues were observed under light microscope and the severity of injury was determined. The expression of c-FLIP in renal tissues was detected by immunohistochemistry. The expression of c-FLIP, Bax and caspase-3 protein in renal tissue was detected by Western Blot. The correlation between c-FLIP expression and Bax, caspase-3 protein expressions in renal tissues were analyzed by Pearson test.
Results: In the Normal group and the Sham group, the renal tubular epithelial cells were regular and intact, and no interstitial inflammatory cell infiltration was observed; the renal injury score was both 1.30±0.48; immunohistochemistry showed a large amount of c-FLIP positive expression in renal tubular epithelial cells (IA: 120.20±3.87, 116.70±3.46); Western Blot showed high expression of c-FLIP in renal tissues (c-FLIP/GAPDH: 0.99±0.01, 0.98±0.02), and low expressions of Bax and caspase-3 (Bax/GAPDH: 0.16±0.04, 0.19±0.03, caspase-3/GAPDH: 0.24±0.04, 0.23±0.05). Compared with the Sham group, in the SAKI group, renal tubular epithelial cells were degenerated and necrosis, and a large number of interstitial inflammatory cells infiltrated, the renal injury score was significantly increased (4.60±0.52 vs. 1.30±0.48, P < 0.01); the levels of SCr and BUN were significantly increased [SCr (μmol/L): 193.90±13.54 vs. 24.50±3.78, BUN (mmol/L): 81.60±7.26 vs. 5.20±0.92, both P < 0.01]; the c-FLIP positive cells in renal tissues was significantly reduced (IA: 17.11±0.82 vs. 116.70±3.46, P < 0.01); the expression of c-FLIP protein in renal tissues was significantly decreased (c-FLIP/GAPDH: 0.29±0.03 vs. 0.98±0.02, P < 0.01), while the expressions of Bax and caspase-3 protein were significantly increased (Bax/GAPDH: 0.87±0.06 vs. 0.19±0.03, caspase-3/GAPDH: 0.88±0.07 vs. 0.23±0.05, both P < 0.01]. The correlation analysis showed that the c-FLIP protein was significantly negatively correlated with Bax (r = -0.468, P = 0.029) and caspase-3 protein expressions (r = -0.663, P = 0.004).
Conclusions: The expression level of c-FLIP protein was significantly down-regulated in renal tissue of SAKI, and its down-regulation mechanism was associated with increased apoptosis of renal tubular epithelial cells, which could be an effective target for the treatment of SAKI.