Diabetic bladder dysfunction (DBD) patients present with symptoms ranging from overactive bladder to underactive bladder/decompensation and various combinations thereof. Experimental models suggest that DBD progresses from overactive to underactive bladder but this progression has not been established in humans. We have recently demonstrated the appearance of overactive bladder symptoms (decreased voided volume and increased voiding frequency during awake restrained urodynamics) in a genetic mouse model of type I diabetes (the Akita mouse) at 15 weeks.  In the present study we have extended this time frame to 30 weeks to assess progression of this complication into middle adulthood. 

Counterintuitively, the Epidemiology of Diabetes Interventions and Complications Study showed that strict glycemic control does not decrease the risk of DBD in humans. This surprising result suggests that, mechanistically, this complication must arise more from the metabolic derangement in this disease than a direct effect of high glucose levels. Building on this conclusion we have recently shown that diabetic metabolites are capable of directly activating a structure known as the NLRP3 inflammasome within cultured urothelial cells. The NLRP3 inflammasome is a multimeric complex that senses such metabolites (known as Damaged Associated Molecular Patterns or DAMPS) and triggers an inflammatory response by activating caspase-1 to cleave pro-IL-1β into its active form and promote its release where it acts as a strong pro-inflammatory cytokine. Previous studies from multiple labs have also shown that NLRP3-induced inflammation underlies several other diabetic complications such as nephropathy, neuropathy and retinopathy. Recently we have demonstrated just such a central role for NLRP3 in the production of signs of overactive bladder at 15 weeks in our Akita diabetic mice through the use of these diabetic mice in which NLRP3 has been genetically deleted (NLRP3-/-). To determine if NLRP3-mediated inflammation may drive the progression of DBD from overactive bladder to underactive bladder we have examined urodynamic function at 30 weeks in the NLRP3-/- mice.

All animal studies were approved by our Institutions Animal Care and Use Committee. Four groups were used: 1) control mice, 2) control mice with NLRP3-/- genotype, 3) diabetic mice (Akita) and 4) diabetic mice with the NLRP3-/- genotype. Mice were assessed at 30 weeks for blood glucose using a glucometer (AimStrip). Inflammation was assessed by injecting mice i.v. with 10 mg/kg Evan’s blue. 1 h later bladders were harvested and dye extracted with formamide (56oC overnight). Extravasated dye was calculated from a standard curve and normalized to bladder weight. Urinary function was assessed by awake restrained urodynamics.

30 week old diabetic mice, with or without a functional NLRP3 gene, had significantly increased blood glucose compared to controls (274 vs 128 mg/dl). Diabetes greatly increased bladder inflammation. However, this increase was completely blocked in the diabetic NLRP3 /- mice. Urodynamic analysis revealed signs of underactive bladder (an increase in voiding volume associated with a decrease in voiding frequency) in response to diabetes. These changes were not present in the diabetic mice in which NLRP3 had been deleted (NLRP3-/-).

Female Akita mice develop significant bladder inflammation and urodynamic signs of underactive bladder/decompensation after 30 weeks of age which did not develop in the absence of NLRP3.

The results demonstrate a central role for NLRP3-mediated inflammation in the development and progression of DBD