Downregulation of TRPC6 expression is a critical molecular event during FK506 treatment for overactive bladder

Purpose: It has been suggested that FK506 could improve some symptoms of OAB in both clinical settings and animal models; however, its mechanism of action is not well-understood. Here, we investigated the effect of FK506 on TRPC6 in bladder smooth muscle, and explored the possible involvement of TRPC6 in OAB.

Methods: FK506 was injected intraperitoneally into rats in which OAB was induced via BOO, and urodynamic indices were recorded. Rats and human bladder smooth muscle tissues with or without OAB were examined for TRPC6 expression by western blot, RT-PCR and IF staining. Cultured BSMCs were treated with PDGF, TRPC6 siRNAs and FK506. Then the TRPC6 expression and cellular proliferation were examined, and the Ca²⁺ influx and contractility of BSMCs were examined by time-lapse Ca²⁺ imaging and collagen gel contraction. Finally, IF and Co-IP were performed to test the effects of FK506 on NFAT translocation to the nucleus and the interaction of TRPC6 with FKBP12, respectively.

Results: FK506 improved urodynamic indices of OAB rats, and TRPC6 was expressed in rats and human bladder tissues. TRPC6 elevation in OAB rats was inhibited by FK506, and this inhibition coincided with improvements in urodynamic indices. PDGF enhanced TRPC6 expression, cellular proliferation, Ca²⁺ influx and contractility of BSMCs, and these effects were inhibited by TRPC6 siRNAs and FK506. FK506 inhibited NFAT translocation to the nucleus and disrupted the interaction of TRPC6 with FKBP12.

Conclusions: Our results collectively indicate that FK506 may be used to treat OAB, and that TRPC6 may serve as an attractive target for therapeutic intervention in OAB.