Abstract 263: Toll-like Receptor 4 Involvement in Normal Bladder Smooth Muscle Contractile Function

Abstract

Overactive bladder (OAB) and bladder dysfunction are commonly associated with aging and metabolic disorders, and both hypertension and the use of anti-hypertensive medication have been correlated with OAB. Recent evidence demonstrates the involvement of the innate immune system in chronic disease conditions via Toll-like receptors (TLRs) activation by damage associated molecular patterns (DAMPs) released from injured cells. TLR4 is expressed in both urothelium and detrusor layers of the bladder and we have previously shown that TLR4 activation contributes to diabetic bladder dysfunction. Here we hypothesized that TLR4 participates in the physiological function of bladder smooth muscle cells. We used wild type (WT) and TLR4-/- (TLR4KO) adult male mice and evaluated the bladder smooth muscle contractile function. We observed that bladder weight was increased in TLR4KO compared to WT mice (% body weight: WT=0.98±0.03, TLR4KO=1.20±0.07). Contraction of urothelium-denuded bladder strips to carbacholine was increased in TLR4KO compared to WT mice (pD2: WT=5.74±0.11, TLR4KO=6.22±0.08). TLR4KO bladder also displayed a higher electrical field stimulation (EFS)-induced maximal contractile response compared to WT, both in the presence and absence of urothelium (mN force at 32 Hz: WT-uro=22.96±2.33, TLR4KO-uro=30.98±6.45, WT+uro=33.05±4.57, TLR4KO+uro=45.30±3.61). Cyclooxygenase 1 (COX1) expression was increased in bladder smooth muscle from TLR4KO compared to WT. COX inhibition by indomethacin reverted the augmented contractile response of TLR4KO bladder strips to carbacholine. No differences in basal reactive oxygen species levels were observed between bladder smooth muscle cells isolated from WT and TLR4KO. These data demonstrate that genetic ablation of TLR4 leads to bladder hypercontractility via COX activation and suggest that TLR4 contributes to the maintenance of physiological smooth muscle function of the bladder.