Role Of Urethral Support Tissue AQP2 Expression In The Pathogenesis Of Female Stress Urinary Incontinence

Background:Stress urinary incontinence(SUI)is an involuntary leakage of urine when activities like sneezing,coughing,laughing,or exercise increase abdominal pressure.SUI is a common chronic disease among elderly women.It is increasingly valued because of its high incidence and serious impact on quality of life.In 2009,an epidemiological survey of six regions in China revealed that nearly one-third(30.9%)of adult females in China suffer from urinary incontinence,of which SUI accounts for about two-thirds(61%),and the number of cases is rapidly increasing in line with the aging population.Although the pathogenesis of SUI is still unknown,it is clear that some factors such as pregnancy delivery,chronic increased abdominal pressure,low estrogen lead to poor repair of the urethral support tissues,i.e,the abnormal remodeling of the extracellular matrix(ECM)of urethral support tissues.It is a key factor in its pathogenesis.Aquaporins,a family of small molecule transmembrane proteins,are widely involved in human cell migration by promoting transmembrane water transport in the pseudopodia of cells,and are associated with the repair of various tissue damages in humans.The main components of female urethral support tissues are connective tissues,which are composed of a large amount of ECM mainly composed of type Ⅰ and type Ⅲcollagen and a small number of cellular components mainly composed of fibroblasts;fibroblasts can synthesize and secrete collagen and can release matrix metalloproteinases(MMPs)to degrade collagen,which are important cells that mediate ECM remodeling.Our team’s previous study found the expression of Aquaporin 2(AQP2)in female urethral support tissue fibroblasts,but the correlation between AQP2 and pathogenesis of SUI and its role in the pathogenesis of SUI is not yet clear and no relevant literature has reported it.Objective:The purpose of this study was to investigate the expression of AQP2 in female urethral support tissues and its relationship with SUI,and to explore the molecular mechanism of AQP2 involvement in female SUI at the cellular level in vitro.Materials and methods:12 female patients with stress urinary incontinence(SUI group)and 12 women without stress urinary incontinence(non-SUI group)who were admitted to the Obstetrics and Gynecology Hospital of Zhejiang University School of Medicine from March 2013 to March 2014 were selected for the study.Subjects were obtained from the full layer of the anterior vaginal wall(ie,urethral support tissues)at a distance of 1～2 cm from the cervix.The expression of AQP2 protein in urethral support tissues was detected by immunohistochemical EnVision staining.Western Blot was used to detect the difference of AQP2 protein expression in urethral support tissues between SUI group and non-SUI group.Primary cultured urethral support tissue fibroblasts were used to construct AQP2 over-expression and low-expression urethral support tissue fibroblast models using siRNA interference technology and plasmid transfection overexpression technology.Real-time PCR and ELISA were used to detect changes in the synthesis of type Ⅰcollagen and type Ⅲ collagen in urethral support tissue fibroblasts when AQP2 was over-expressed and low-expressed.Results:1.EnVision staining of immunohistochemistry showed that there was expression of AQP2 protein in female urethral support tissues and it was strongly expressed on fibroblasts.2.The protein levels of AQP2 in the non-SUI and SUI groups were 8.10±0.90 and 2.86±0.60,respectively.Statistical analysis showed that the level of AQP2 protein in female urethral support tissues in the SUI group was significantly lower than that in the non-SUI group(p<0.05).3.After overexpression of fibroblast AQP2 in female urethral support tissues,the expression levels of type Ⅰ and type Ⅲ collagen mRNA and protein were significantly increased(p<0.05);after low expression of female urethral support tissue fibroblast AQP2,type Ⅰ and type Ⅲ collagen mRNA and protein expression levels decreased significantly(p<0.05).Conclusion:1.There is AQP2 protein expression in female urethral support tissues,and the decreased expression level is closely related to the pathogenesis of SUI.2.AQP2 protein may participate in the pathogenesis of female SUI by regulating the metabolism of type Ⅰ and type Ⅲ collagen in urethral support tissue fibroblasts.