AB012. Involvement of elevated TRPC6 in pathogenesis of overactive bladder

Objective: Overactive bladder (OAB) syndrome is defined as urinary urgency, usually accompanied by frequency and nocturia, with or without urge urinary incontinence, in the absence of urinary tract infection or other obvious pathology. At present, the pathogenesis of OAB is little known. The number and activity of involved receptors as well as changed relationship between ion channels and receptors were the researched focuses, which increased the excitability and contractility, but reduced the relaxation and coordination of bladder smooth muscle. As we known, Ca²⁺ as an important second messenger, can be directly involved in the excitation contraction coupling of smooth muscle cell. Especially that, the Ca²⁺ influx, which is mediated by transmembrane calcium channel, is the most important factor of produced action potentials in excitable cells. TRPC6 as a kind of transmembrane calcium channel, has very close relationship with the smooth muscle cells of respiratory, digestive and circulatory system. Based on these reports and the results of preliminary study, we speculated that Ca²⁺ influx, and excitement of bladder smooth muscle cells, is mediated by over expression of TRPC6. This may be one factor of produced OAB.

Methods: We established the OAB rat model, and characterized the localization of TRPC6 with immunohistochemistry and immunofluorescence detection, as well as the protein and mRNA expression levels of TRPC6 were examined with western blot and RT-PCR detection. Using FK506, the specific inhibitors of TRPC6, we down-regulated the expression of TRPC6, and then characterized the changes of contractile function in bladder smooth muscle of OAB rats with muscle contraction test. After treatment with PDGF in BMSCs, we tested the protein expression of TRPC6 with western blot, and the expression of JNK and P38.

Results: The immunohistochemistry and immunofluorescence of bladder smooth muscles of OAB rats were shown. The positive staining of TRPC6 appeared at cell membrane of bladder smooth muscle. The western blot and RT-PCR results indicated that, the expression of TRPC6 protein and mRNA in OAB was significantly higher than the normal. After administration of FK506, the expression and mRNA of TRPC6 decreased obviously, and there were improved contraction of smooth muscle in OAB rats. TRPC6 protein could be elevated after induction of PDGF in BMSCs. And blockade with the inhibitors of JNK and P38, the protein levels of TRPC6 were decreased.

Conclusions: The expression of TRPC6 protein and mRNA in bladder smooth muscle of OAB was significantly higher than normal. Reduced the expression of TRPC6 can improve bladder function and contraction of smooth muscle in OAB. PDGF could induced TRPC6 expression in BMSCs. P38 and JNK were involved in the regulation of TRPC6 expression in BMSCs.

Keywords: Pathogenesis; overactive bladder (OAB); TRPC6