807 SPHINGOSINE-1-PHOSPHATE SIGNALING PATHWAY A NOVEL MOLECULAR TARGET FOR TREATING ERECTILE DYSFUNCTION

Abstract

INTRODUCTION AND OBJECTIVES: The bioactive lipid sphingosine-1-phosphate (S1P) regulates smooth muscle (SM) contractility via three G protein-coupled receptors. The S1P1 receptor is associated with nitric oxide (NO)-mediated SM relaxation while S1P2 & S1P3 receptors are linked to SM contraction via activation of the Rho-kinase (ROK) pathway. Sphingosine kinase-1 (SphK1) is the main driver of S1P formation via phosphorylation of sphingosine. Here we determine the role the S1P signaling pathway plays in modulating corpus cavernosum (CC) SM (CCSM) tone in vitro and erectile function in vivo in both rats and humans emphasizing molecular signaling through S1P2 and S1P3 receptors. METHODS: Serum was obtained from normal adult male rats and male human donors from which S1P levels were assessed by high-performance liquid chromatography. CC from normal rats and men undergoing penile prosthesis surgery were used for molecular and physiological studies. Expression of S1P1-3 receptors and SphK1 was determined by Real-Time RT-PCR and Western blotting. In vitro organ bath contractility and in vivo cavernous nerve stimulated intracavernous pressure (ICP) increases were also measured. RESULTS: Circulating serum S1P levels were found to be 250 nM in adult male rats but only 100 nM in humans. Human and rat CC express mRNA and protein for SphK1 and all three S1P receptors with SphK1 expression increased significantly in men 60 years of age. Both exogenous S1P and the phosphorylated S1P1/S1P3 receptor agonist FTY720-P (1-10 M) contracted while the S1P2 selective antagonist JTE-013 and the S1P3 selective antagonist suramin relaxed CCSM in vitro in an NO-independent manner. Force produced by S1P and FTY720-P was similar to PE-induced contraction at low 1-5 M doses with both totally attenuated by 1 M ROK inhibitor H-1152. Intracavernous injection of FTY720-P to anesthetized rats severely inhibited cavernous nerve-induced ICP rise, while JTE-013 alone induced a strong dose-dependent increase in ICP reaching a partial-to-full erection at 500 nmoles. Finally, injection of SphK1 siRNA in vivo knocked down rat CC SphK1 by 80% and significantly potentiated ICP. CONCLUSIONS: This study provides the first clear evidences that the S1P pathway is another key component of the contractile machinery in CC and would be expected as a potential therapeutic target for priapism and erectile dysfunction (ED). Moreover, our recent publications demonstrating expression, function and obstruction-induced alteration of the S1P pathway in bladder may implicate this pathway in lower urinary tract symptoms (LUTS) associated ED.