Diabetic bladder dysfunction (DBD) is a progressive deterioration of urinary function that commonly occurs in patients with diabetes. In addition to high glucose levels, diabetes is associated with metabolic derangement and the production of numerous potentially harmful metabolites which accumulate in the circulation as well as the urine. Normally, the urothelia maintains an impenetrable barrier to protect underlying smooth muscle but this barrier is known to breakdown during diabetes. We have previously shown in a mouse model (the Akita mouse) that the NLRP3 inflammasome, a multimeric structure that activates inflammatory cascades, is responsible for diabetic bladder inflammation and dysfunction. In this study we hypothesize that NLRP3 activation may result in a decrease in the barrier function of the urothelia, thus exposing the underlying areas to high levels of harmful diabetic metabolites which, in turn, trigger increased inflammation and dysfunction. Additionally, the loss of barrier function may be a major factor in the increased susceptibility to urinary tract infections. As an initial investigation into this hypothesis, we examined changes in expression of barrier genes in diabetic mice with either intact NLRP3 or in which it has been genetically deleted.

Four groups of 15 week old female mice were used: non-diabetic control (non-diabetic, n=9), type 1 diabetic Akita mice (diabetic, n=7), non-diabetic control mice with NLRP3 knocked out (non-diabetic KO, n=12), and diabetic NLRP3 knock-out mice (diabetic KO, n=12). Previously we have shown DBD symptoms in the Akita mice at this time point. Urothelia was harvested from each mouse and used for qPCR studies. The following gene expression markers of barrier function were assessed: zona occludin 1 (ZO1), zona occludin 2 (ZO2), Claudin 4 (CL4), beta catenin (BCT), uroplakin 1b (UP1), and uroplakin 2 (UP2).

Urothelia from diabetic mice exhibit significant decreases in expression of ZO1, ZO2, CL4 and UP1 compared to non-diabetic mice. No statistically significant changes in BCT or UP2 gene expression are noted. Importantly, these changes in barrier gene expression did not occur in the diabetic KO mice.

Diabetes reduces expression of genes regulating urothelial barrier function in a NLRP3-dependent manner.

This finding provides insight into how DBD develops. In the absence of NLRP3, diabetes does not impact barrier function. Currently, there are no effective treatments for patients living with DBD. NLRP3 inhibition may provide a much needed therapeutic target to improve the quality of life of diabetic patients. Further studies are needed to determine how the NLRP3 inflammasome impacts urothelial barrier function.