The Role Of KCNQ4 Potassium Channel In Formation Of Abdominal Aortic Aneurysms

Objective: Abdominal aortic aneurysm（AAA）is a kind of vascular inflammatory disease.It has been reported that KCNQ4 ion channel is expressed in vascular smooth muscle cells.In this study,we investigated the effect of KCNQ4 on Ang II-induced AAA using KCNQ4 gene knockout mice(KCNQ4^-/-).Methods:1 Mouse AAA model10-week-old male mice were used to experiment.The genomic DNA was extracted from the ears tissues,and used to identify the genotypes by PCR.AngII（1000 ng/min/kg）or saline was administered by Alzet osmotic minipumps planted subcutaneously.At 0,7,14,21,28 day after AngII infusion,systolic blood pressure and diastolic blood pressure were measured by an intelligent noninvasive sphygmomanometer.At 28-day after AngII infusion,survivor mice underwent ultrasonography with a Veov 770 TM Imaging System in B-mode.The maximal suprarenal aortic diameter was measured at peak systole by the caliper measurement feature.2 Vascular morphologyAt 28-day after AngII infusion,the thoracoabdominal aortas were separated.HE staining was used to observe the vascular morphological changes,and elastic layer changes were observed by EVG staining.3 Immunohistochemical stainingAt 28-day after Ang II infusion,the aortic sections were prepared and used to observe the expression of the proteins by immunohistochemical and immunofluorescence staining,respectively.4 Statistical analysisAll the experimental data were processed by SPSS 20 statistical software.Data are expressed as mean ± SD from three independent experiments.Statistical significance was determined using one-way ANOVA analysis and unpaired Student’s t test.Categorical data was shown as percentage and tested with the χ2 test.P < 0.05 was considered statistically significant.Results:1 KCNQ4^-/-mice has higher blood pressure than WT mice.At 0,7 and 14 day after AngII infusion,the SBP of KCNQ4^-/-mice was significantly higher than the WT mice about 10 mmHg（P < 0.05）,while the DBP was no significant difference（P > 0.05）.However,at 21,28 day after Ang II infusion,there was no significant difference in SBP between the two genotype mice（P > 0.05）.In order to further explore the role of KCNQ4 channel in the regulation of blood pressure,we chose KCNQ channel specific opener RTG to observe its effect on blood pressure.The results showed that RTG reduced the SBP about 10 mmHg of WT mice with AngII and saline infused.However,RTG had no significant effect on KCNQ4^-/-mice.The results suggest that KCNQ4 knockout can cause the increase of blood pressure in mice,and KCNQ4 channel opener can significantly reduce the blood pressure of mice.2 Knockout of KCNQ4 inhibits AngII-induced AAA.At 28-day after stimulation,compared with the saline group and AngII infused KCNQ4^-/-group,the incidence of AAA in Ang II-infused WT group was significantly increased.Ultrasonic and HE staining results showed that the abdominal aortas of AngII-infused mice were larger than saline group.And the vessel diameter of AngII-infused WT mice was significantly increased than the Ang II infused KCNQ4^-/-mice（P < 0.05）,and the vascular wall was thickening.In addition,the results of EVG and fluorescence staining showed that the elastic layer of WT mice was significantly reduced compared with the KCNQ4^-/-mice in the AngII-infused group.Immunofluorescence staining showed that the collagen I and collagen III were significantly reduced in AngII-infused WT mice（P < 0.05）.3 The expression of KCNQ4 ion channel in WT mice.Immunohistochemical staining showed that the expression of KCNQ4 was significantly higher in AAA tissues than that in the aortas without AAA（P < 0.05）.4 Knockout of KCNQ4 inhibits AngII-induced vascular inflammation and AAA.The expression of CD68,IL-6,VCAM-1,ICAM-1,MMP2 and MMP9 were detected by immunohistochemistry and immunofluorescence staining.The results showed that: compared with the AngII-infused KCNQ4^-/-mice,the expression of CD68,IL-6,VCAM-1,ICAM-1,MMP2,MMP9 were significantly increased in AngII-infused WT mice with AAA（P < 0.05）.Conclusion:1 Knockout of KCNQ4 induces blood pressure rised,and KCNQ4 channel openers reduce blood pressure.2 Knockout of KCNQ4 reduces the incidence of AngII-induced AAA.3 Knockout of KCNQ4 inhibits the vascular inflammation.