Dexmedetomidine protects against burn-induced intestinal barrier injury via the MLCK/p-MLC signalling pathway

BACKGROUND

Evidence suggests that sedative dexmedetomidine can prevent intestinal dysfunction. However, the specific mechanisms of its protective effects against burn-induced intestinal barrier injury remain unclear. We aimed to explore the possible positive effects of dexmedetomidine on burn-induced intestinal barrier injury and the effects the myosin light chain kinase (MLCK)/phosphorylated myosin light chain (p-MLC) signalling pathway in an experimental model of burn injury.

METHODS

In this study, the plasma concentration of fluorescein isothiocyanate-labelled dextran (FITC-dextran) was measured. Histological changes were evaluated using haematoxylin and eosin (HE) staining. Tight junction proteins were evaluated by western blot and immunofluorescence analyses to assess the structural integrity of intestinal tight junctions. The level of inflammation was detected by enzyme-linked immunosorbent assay (ELISA).

RESULTS

The results shows that the increase in intestinal permeability caused by burn injury is accompanied by histological damage to the intestine, decreases in the expression of the tight junction proteins Zonula Occludens-1 (ZO-1) and Occludin, increases in inflammatory cytokine levels and elevation of both MLCK protein expression and MLC phosphorylation. After dexmedetomidine treatment, the burn-induced changes were ameliorated.

CONCLUSIONS

In conclusion, dexmedetomidine exerted an anti-inflammatory effect and protected tight junction complexes against burn‑induced intestinal barrier damage by inhibiting the MLCK/p-MLC signalling pathways.

Effects of hypoxia inducible factor-1α on expression levels of MLCK, p-MLC and ZO-1 of rat endothelial cells

OBJECTIVE

To examine the aberrant expression of endothelial permeability associated proteins including MLCK, p-MLC and ZO-1 in presence of different levels of hypoxia-inducible factor 1 alpha (HIF-1α).

METHODS

We established monolayer vascular endothelial cell model with the primary rat endothelial cells. Over-expressed or under-expressed HIF-1α cell lines were made by endothelial cells transfected with plasmid vector constructed with HIF-1α gene or HIF-1α-specific short hairpin RNA (shRNA). Levels of mRNA and protein of MLCK, p-MLC and ZO-1 were determined using Real-Time PCR and Western blot. All data were analyzed using by One-Way ANOVA method and LSD.

RESULTS

We successfully cultured the rat endothelial primary cells for four days. The mRNA and protein levels of MLCK and p-MLC were significantly increased in the HIF-1α over-expression group than that in the blank control group and the empty plasmid GV230 group (P＜0.05). ZO-1 was significantly lower in the HIF-1α over-expression group than that in the blank control group and the GV230 group. On the contrary, the mRNA and protein levels of MLCK and p-MLC were significantly lower in the HIF-1α under-expression group than that in the blank control group and the shRNA-NC group (P＜0.05). ZO-1 was significantly higher in the HIF-1α low-expression group than that in the blank control group and the shRNA-NC group.

CONCLUSION

HIF-1α positively regulates the expression of MLCK and p-MLC and negatively regulates the expression of ZO-1 in rat monolayer endothelial cells.

[Regulation of hypoxia inducible factor-1α on permeability of vascular endothelial cells and the mechanism]

Objective: To investigate the regulation of hypoxia-inducible factor-1α (HIF-1α) on permeability of rat vascular endothelial cells and the mechanism. Methods: Twelve male Sprague-Dawley rats aged 35 to 38 days were collected and vascular endothelial cells were separated and cultured. The morphology of cells was observed after 4 days of culture, and the following experiments were performed on the 2nd or 3rd passage of cells. (1) Rat vascular endothelial cells were collected and divided into blank control group, negative control group, HIF-1α interference sequence 1 group, HIF-1α interference sequence 2 group, and HIF-1α interference sequence 3 group according to the random number table (the same grouping method below), with 3 wells in each group. Cells in negative control group, HIF-1α interference sequence 1 group, HIF-1α interference sequence 2 group, and HIF-1α interference sequence 3 group were transfected with GV248 empty plasmid, recombinant plasmid respectively containing HIF-1α interference sequence 1, interference sequence 2, and interference sequence 3 with liposome 2000. Cells in blank control group were only transfected with liposome 2000. After transfection of 24 h, expression levels of HIF-1α mRNA and protein of cells in each group were respectively detected by reverse transcription real-time fluorescent quantitative polymerase chain reaction and Western blotting (the same detecting methods below) . The sequence with the highest interference efficiency was selected. (2) Another batch of rat vascular endothelial cells were collected and divided into blank control group, negative control group, and HIF-1α low expression group, with 3 wells in each group. Cells in blank control group were only transfected with liposome 2000, and cells in negative control group and HIF-1α low expression group were respectively transfected with GV248 empty plasmid and low expression HIF-1α recombinant plasmid selected in experiment (1) with liposome 2000. After 14 days of culture, the mRNA and protein expressions of HIF-1α in each group were detected. (3) Another batch of rat vascular endothelial cells were collected and divided into blank control group, negative control group, and HIF-1α high expression group, with 3 wells in each group. Cells in blank control group were transfected with liposome 2000, and cells in negative control group and HIF-1α high expression group were respectively transfected with GV230 empty plasmid and HIF-1α high expression recombinant plasmid with liposome 2000. After 14 days of culture, the mRNA and protein expressions of HIF-1α of cells in each group were detected. (4) After transfection of 24 h, cells of three groups in experiment (1) and three groups in experiment (2) were collected, and mRNA and protein expressions of myosin light chain kinase (MLCK), phosphorylated myosin light chain (p-MLC), and zonula occludens 1 (ZO-1) of cells were detected. Data were processed with one-way analysis of variance and t test. Results: After 4 days of culture, the cells were spindle-shaped, and rat vascular endothelial cells were successfully cultured. (1) The interference efficiencies of HIF-1α of cells in HIF-1α interference sequence 1 group, HIF-1α interference sequence 2 group, and HIF-1α interference sequence 3 group were 47.66%, 45.79%, and 62.62%, respectively, and the interference sequence 3 group had the highest interference efficiency. After transfection of 24 h, the mRNA and protein expression levels of HIF-1α of cells in interference sequence 3 group were significantly lower than those in blank control group (t=18.404, 9.140, P<0.01) and negative control group (t=15.099, 7.096, P<0.01). (2) After cultured for 14 days, the mRNA and protein expression levels of HIF-1α of cells in HIF-1α low expression group were significantly lower than those in blank control group (t=21.140, 5.440, P<0.01) and negative control group (t= 14.310, 5.210, P<0.01). (3) After cultured for 14 days, the mRNA and protein expression levels of HIF-1α of cells in HIF-1α high expression group were significantly higher than those in blank control group (t=19.160, 7.710, P<0.01) and negative control group (t= 19.890, 7.500, P<0.01). (4) After transfection of 24 h, the mRNA expression levels of MLCK and p-MLC of cells in HIF-1α low expression group were significantly lower than those in blank control group (t=2.709, 4.011, P<0.05 or P<0.01) and negative control group (t=2.373, 3.744, P<0.05 or P<0.01). The mRNA expression level of ZO-1 of cells in HIF-1α low expression group was significantly higher than that in blank control group and negative control group (t=4.285, 5.050, P<0.01). The mRNA expression levels of MLCK and p-MLC of cells in HIF-1α high expression group were significantly higher than those in blank control group (t=9.118, 11.313, P<0.01) and negative control group (t=9.073, 11.280, P<0.01). The mRNA expression level of ZO-1 of cells in HIF-1α high expression group was significantly lower than that in blank control group and negative control group (t=2.889, 2.640, P<0.05). (5) After transfection of 24 h, the protein expression levels of MLCK and p-MLC of cells in HIF-1α low expression group were significantly lower than those in blank control group (t=2.652, 3.983, P<0.05 or P<0.01) and negative control group (t=2.792, 4.065, P<0.05 or P<0.01). The protein expression of ZO-1 of cells in HIF-1α low expression group was significantly higher than that in blank control group and negative control group (t=3.881, 3.570, P<0.01). The protein expression levels of MLCK and p-MLC of cells in HIF-1α high expression group were 1.18±0.24 and 0.68±0.22, which were significantly higher than 0.41±0.21 and 0.35±0.14 in blank control group (t=5.011, 3.982, P<0.05 or P<0.01) and 0.43±0.20 and 0.36±0.12 in negative control group (t= 4.880, 3.862, P<0.05 or P<0.01). The protein expression level of ZO-1 of cells in HIF-1α high expression group was 0.08±0.06, which was significantly lower than 0.20±0.09 in blank control group and 0.19±0.09 in negative control group (t=4.178, 3.830, P<0.05 or P<0.01). Conclusions: HIF-1α up-regulates expressions of MLCK and p-MLC and down-regulates expression of ZO-1, thereby increasing the permeability of rat vascular endothelial cells.