[Mechanism of large-conductance calcium-activated potassium channel involved in inflammatory response in sepsis].

OBJECTIVE: To explore the mechanisms of large-conductance calcium-activated potassium channel (BKCa) involved in inflammatory response in sepsis.

METHODS: The serum levels of BKCa were measured by enzyme-linked immunosorbent assay (ELISA) in patients with sepsis (28 cases), patients with common infection (25 cases) and healthy people (25 cases). The relationship between levels of BKCa and acute physiology and chronic health evaluation II (APACHE II) were analyzed. Cultured RAW 264.7 cells were stimulated by lipopolysaccharide (LPS). In some experiments, a cell model of sepsis was constructed using Nigericin as the second stimulus signal. The mRNA and protein expressions of BKCa in RAW 264.7 cells stimulated with LPS (0, 50, 100, 1 000 μg/L) were measured by real-time fluorescence quantitative polymerase chain reaction (RT-qPCR) and Western blotting. RAW 264.7 cells were transfected with small interfering RNA of BKCa (siRNA-BKCa), and the levels of caspase-1 precursor (pro-caspase-1), interleukin-1β precursor (pro-IL-1β) in cell, and the levels of caspase-1 p20, IL-1β p17 of cell culture medium, and NOD-like receptor protein 3 (NLRP3), nuclear factor-κB (NF-κB) were measured by Western blotting. The apoptosis were detected by staining with propidium iodide (PI), the release rate of lactate dehydrogenase (LDH) were measured, and the expression of apoptotic protein Gasdermin D (GSDMD) was measured by Western blotting to evaluate the effect of silencing BKCa on cell pyrosis.

RESULTS: The level of serum BKCa in patients with sepsis was significantly higher than that in patients with common infection and health peoples (ng/L: 165.2±25.9 vs. 102.5±25.9, 98.8±20.0, both P < 0.05). In addition, the level of serum BKCa in patients with sepsis was significantly positively correlated with APACHE II score (r = 0.453, P = 0.013). LPS could construct a sepsis cell model by which LPS could promote BKCa expression in mRNA and protein with a concentration-dependent manner. The mRNA and protein expressions of BKCa in the cells stimulated by 1 000 μg/L LPS were significantly higher than that in the blank group (0 μg/L) [BKCa mRNA (2-ΔΔCt ): 3.00±0.36 vs. 1.00±0.16, BKCa/β-actin: 1.30±0.16 vs. 0.37±0.09, both P < 0.05]. Compared with the control group, the ratios of caspase-1 p20/pro-caspase-1 and IL-1β p17/pro-IL-1β in the model group were significantly increased (caspase-1 p20/pro-caspase-1: 0.83±0.12 vs. 0.27±0.05, IL-1β p17/pro-IL-1β: 0.77±0.12 vs. 0.23±0.12, both P < 0.05), however, transfection of siRNA-BKCa induced the decrease both of them (caspase-1 p20/pro-capase-1: 0.23±0.12 vs. 0.83±0.12, IL-1β p17/pro-IL-1β: 0.13±0.05 vs. 0.77±0.12, both P < 0.05). Compared with the control group, the number of apoptotic cells, LDH release rate and GSDMD expression in the model group were significantly increased [LDH release rate: (30.60±8.40)% vs. (15.20±7.10)%, GSDMD-N/GSDMD-FL: 2.10±0.16 vs. 1.00±0.16, both P < 0.05], however, transfection of siRNA-BKCa induced the decrease both of them [LDH release rate: (15.60±7.30)% vs. (30.60±8.40)%, GSDMD-N/GSDMD-FL: 1.13±0.17 vs. 2.10±0.16, both P < 0.05]. The mRNA and protein expressions of NLRP3 in sepsis cells were significantly higher than those in the control group [NLRP3 mRNA (2-ΔΔCt ): 2.06±0.17 vs. 1.00±0.24, NLRP3/GAPDH: 0.46±0.05 vs. 0.15±0.04, both P < 0.05]. However, the expression of NLRP3 after siRNA-BKCa transfection was significantly lower than that in model group [NLRP3 mRNA (2-ΔΔCt ): 1.57±0.09 vs. 2.06±0.17, NLRP3/GAPDH: 0.19±0.02 vs. 0.46±0.05, both P < 0.05]. Compared with the control group, the NF-κB p65 nuclear transfer of sepsis cell were significantly increased (NF-κB p65/Histone: 0.73±0.12 vs. 0.23±0.09, P < 0.05). However, the NF-κB p65 expression in the nucleus were decreased after siRNA-BKCa transfection (NF-κB p65/Histone: 0.20±0.03 vs. 0.73±0.12, P < 0.05).

CONCLUSIONS: BKCa is involved in the pathogenesis of sepsis, and its possible mechanism is to activate NF-κB/NLRP3/caspase-1 signaling pathway to induce inflammatory factor production and cell death.