AB298. SPR-25 NLRP3/IL-1β mediates denervation during bladder outlet obstruction in rats

Objective: Bladder outlet obstruction (BOO) is a common condition resulting from benign prostatic hyperplasia, neurologic pathology, organ prolapse, etc. Long-term, obstruction is well-established to evoke denervation in the bladder which causes the detrusor to become hypocontractile, resulting in inefficient bladder emptying and consequent infections, continence issues or even renal failure. Recently, considerable attention has been paid to a role for inflammation in bladder deterioration during BOO and we have shown a central role for the NLRP3 inflammasome in triggering this inflammation. In the present study we explore a possible connection between this NLRP3-induced inflammation and bladder denervation.

Methods: Rats were divided into five groups: (I) control; (II) sham operated; (III) BOO + vehicle (1 mL, 40% ethanol in PBS, p.o.); (IV) BOO + glyburide (Gly, NLRP3 inhibitor; 10 mg/kg, p.o.); (V) BOO + anakinra (Ana, IL-1 receptor antagonist; 25 mg/kg, i.p.). BOO is constructed in female rats by inserting a 1 mm outer diameter transurethral catheter, tying a silk ligature around the urethra and removing the catheter. Medications were administered prior to surgery and once daily. At 12 days animals were sacrificed and the bladders processed for histological analysis. Transverse sections (5 µm) were stained for PGP9.5 expression (a pan-neuronal marker) using standard immunohistochemistry techniques. Entire sections were scanned, using a 10× objective, into TIFF files using Zen software (Zeiss Inc.). Images were imported into Elements software (Nikon Inc.) and the area of individual neurons designated as well as total bladder area (exclusive of the urothelium and lumen). The number of neurons and respective areas were used to calculate nerve density.

Results: Denervation in the bladder wall during BOO was significant, as measured by nerve density. This effect was attenuated by either preventing NLRP3 activation with Gly or blocking IL-1β’s action at its receptor by treatment with Ana, clearly indicating a role for NLRP3/IL-1β in bladder denervation during BOO. The effect was also apparent with the total number of nerves despite considerable changes in bladder wall area (increased in BOO, maintained by Gly or Ana). Interestingly, the mean area of individual nerves was increased in BOO. This effect was blocked by Gly or Ana suggesting a loss of smaller neurons and/or retraction of neuronal branching during BOO as a result of NLRP3/IL-1β.

Conclusions: NLRP3/IL-1b-induced inflammation leads to bladder denervation during BOO and blocking this pathway, either by preventing NLRP3 activation or inhibiting the action of IL-1B, prevents nerve loss.

Funding Source(s): NIDDK—R01DK103534 (PI-Purves)

Keywords: Inflammasome; bladder; outlet obstruction; innervation; immunostaining