The sphingosine-1-phosphate pathway is upregulated in response to partial urethral obstruction in male rats and activates RhoA/Rho-kinase signalling

Abstract

Objectives: To examine the effect of partial urethral obstruction (PUO) on the sphingosine-1-phosphate (S1P, a bioactive lipid shown to modulate smooth muscle, SM) pathway in the bladders of male rats, and to determine the effect of PUO on the RhoA/Rho-kinase (ROK) pathway, and whether there is a molecular cross-talk with the S1P pathways associated with bladder overactivity (S1P1-S1P3, where S1P1 is associated with nitric oxide-mediated SM relaxation, and S1P2 and S1P3 receptors are associated more with SM contraction via the ROK pathway).

Materials and methods: In all, 20 male rats were divided into two groups and underwent PUO or a sham operation (control). After 2 weeks all rats were killed humanely and bladder specimens used for in vitro organ-bath physiological contractility studies, and for mRNA and protein analyses of major S1P/ROK pathway constituents via real-time polymerase chain reaction and Western blotting, respectively. In addition, early-passage SM cells were transfected with recombinant sphingosine kinase (SPHK, the enzyme that converts sphingosine to S1P).

Results: Bladders from PUO rats had greater mRNA expression of the S1P2 and S1P3 receptors, as well as SPHK1, than the sham controls (4.78, 2.04 and 2.72 times, respectively). PUO rats also had significantly greater expression of RhoA and ROKalpha (1.76 and 2.19 times, respectively). Western blotting and organ-bath contractility studies showed similar changes at the protein and in vitro functional level, with an increased contractility of bladder strips from PUO rats to exogenous S1P. Transfection of SPHK into isolated SM cells increased ROK expression.

Conclusions: We show for the first time that the S1P signalling pathway is significantly upregulated in response to PUO in male rats at both the molecular and in vitro functional levels, correlating with an activation of the RhoA/ROK pathway. Further, we provide novel data that SPHK overexpression increases ROK expression in vitro, suggesting a novel hypothesis of S1P-induced bladder overactivity in the mechanism for PUO-induced bladder dysfunction and the S1P signalling pathway as a possible therapeutic target for bladder overactivity.