Protease-activated receptor 2 activates CRAC-mediated Ca2+ influx to cause prostate smooth muscle contraction

Endothelial PAR2 activation evokes resistance artery relaxation

Protease-activated receptor-1 & -2 (PAR1 and PAR2) are expressed widely in cardiovascular tissues including endothelial and smooth muscle cells. PAR1 and PAR2 may regulate blood pressure via changes in vascular contraction or relaxation mediated by endothelial Ca2+ signaling, but the mechanisms are incompletely understood. By using single-cell Ca2+ imaging across hundreds of endothelial cells in intact blood vessels, we explored PAR-mediated regulation of blood vessel function using PAR1 and PAR2 activators. We show that PAR2 activation evoked multicellular Ca2+ waves that propagated across the endothelium. The PAR2-evoked Ca2+ waves were temporally distinct from those generated by muscarinic receptor activation. PAR2 activated distinct clusters of endothelial cells, and these cells were different from those activated by muscarinic receptor stimulation. These results indicate that distinct cell clusters facilitate spatial segregation of endothelial signal processing. We also demonstrate that PAR2 is a phospholipase C-coupled receptor that evokes Ca2+ release from the IP3 -sensitive store in endothelial cells. A physiological consequence of this PAR2 signaling system is endothelium-dependent relaxation. Conversely, PAR1 activation did not trigger endothelial cell Ca2+ signaling nor relax or contract mesenteric arteries. Neither did PAR1 activators alter the response to PAR2 or muscarinic receptor activation. Collectively, these results suggest that endothelial PAR2 but not PAR1 evokes mesenteric artery relaxation by evoking IP3 -mediated Ca2+ release from the internal store. Sensing mediated by PAR2 receptors is distributed to spatially separated clusters of endothelial cells.

Mast cell function in prostate inflammation, fibrosis, and smooth muscle cell dysfunction

Intraurethral inoculation of mice with uropathogenic Escherichia coli (CP1) results in prostate inflammation, fibrosis, and urinary dysfunction, recapitulating some but not all of the pathognomonic clinical features associated with benign prostatic hyperplasia (BPH) and lower urinary tract symptoms (LUTS). In both patients with LUTS and CP1-infected mice, we observed increased numbers and activation of mast cells and elevated levels of prostate fibrosis. Therapeutic inhibition of mast cells using a combination of a mast cell stabilizer, cromolyn sodium, and the histamine 1 receptor antagonist cetirizine di-hydrochloride in the mouse model resulted in reduced mast cell activation in the prostate and significant alleviation of urinary dysfunction. Treated mice showed reduced prostate fibrosis, less infiltration of immune cells, and decreased inflammation. In addition, as opposed to symptomatic CP1-infected mice, treated mice showed reduced myosin light chain-2 phosphorylation, a marker of prostate smooth muscle contraction. These results show that mast cells play a critical role in the pathophysiology of urinary dysfunction and may be an important therapeutic target for men with BPH/LUTS.NEW & NOTEWORTHY LUTS-associated benign prostatic hyperplasia is derived from a combination of immune activation, extracellular matrix remodeling, hyperplasia, and smooth muscle cell contraction in prostates of men. Using a mouse model, we describe the importance of mast cells in regulating these multiple facets involved in the pathophysiology of LUTS. Mast cell inhibition alleviates both pathology and urinary dysfunction in this model, suggesting the potential for mast cell inhibition as a therapeutic that prevents and reverses pathology and associated symptomology.

Effect of BTP2 on agonist-induced vasoconstriction in the mouse aorta in vitro

BTP2 is a potent inhibitor of store-operated Ca2+ entry (SOCE), which plays a vital role in vasoconstriction. However, the direct effect of BTP2 on the contractile response remains unclear. Here, we investigated the effects and mechanisms of action of BTP2 in the mouse aorta. Isometric tension was measured using a Multi Myograph System with two stainless steel wires. Ca2+ transient was recorded by confocal laser scanning microscope. The results showed that BTP2 markedly suppressed vasoconstriction mediated by SOCE and Ca2+ influx mediated by SOCE. The cumulative concentration of BTP2 had no effect on the baseline of mouse aortic rings, whereas it increased vasoconstriction stimulated by 3 μmol/L Phenylephrine. BTP2 (1 μmol/L) significantly increased vasoconstriction induced by 3 μmol/L Phe or cumulative concentration. BTP2 also promoted noradrenaline-induced aortic contraction. However, Phe- and noradrenaline-induced contraction was not affected by 0.3 or 3 μmol/L BTP2, and BTP2 at 10 μmol/L significantly suppressed aortic contraction. BTP2 inhibited 5-HT-evoked contraction in a concentration-dependent manner. BTP2 at higher concentrations (>3 μmol/L) inhibited CaCl2 -induced and 60 mmol/L K+ -induced contraction with progressive reduction of maximal contraction in a concentration-dependent manner. These results suggest that 1 μmol/L BTP2 increases contraction evoked by α1 adrenoreceptor activation. BTP2 at higher concentrations may inhibit Cav1.2 channels.

Effects of shRNA-mediated silencing of PDE5A3 on intracellular cGMP and free Ca2+ levels and human prostate smooth muscle cell proliferation from benign prostatic hyperplasia

Benign prostatic hyperplasia (BPH) with lower urinary tract symptoms (LUTS) is a common disease among elderly men, for which safe and effective treatment strategies remain limited. The aim of the present study was to explore the potential effects of phosphodiesterase 5A3 (PDE5A3) silencing on human prostate smooth muscle cells (HPSMCs). HPSMCs were initially obtained from patients with BPH/LUTS. Short hairpin RNA (shRNA) targeting the PDE5A3 gene was subsequently transfected into cultured HPSMCs. The expression of PDE5A3 was measured using reverse transcription-quantitative PCR and western blotting. cGMP levels were then measured using western blotting and immunocytochemical staining and intracellular Ca²⁺ concentration was measured using rhod2-AM in HPSMCs after transfection. HPSMC proliferation was also observed within 4 days. Cells transfected with PDE5A3-shRNA2 exhibited the most notable decline in PDE5A3 expression compared with that in the Control or NC groups. cGMP levels in HPSMCs transfected with PDE5A3-shRNA2 was significantly increased compared with those in the Control or NC groups, whereas intracellular Ca²⁺ concentrations in cells in the PDE5A3-shRNA2 group were decreased compared with that in the Control or NC groups. The proliferation of HPSMCs in the PDE5A3-shRNA2 group was also inhibited compared with that in the Control or NC groups after 72 h of culture. In conclusion, shRNA-mediated silencing of PDE5A3 was able to increase the levels of cGMP whilst reducing the concentration of Ca²⁺ in HPSMCs, in turn suppressing their proliferation. These findings may potentially provide a novel therapeutic target for treating BPH/LUTS.

Protease-activated receptor 2 activates CRAC-mediated Ca2+ influx to cause prostate smooth muscle contraction

Protease activated receptor 2 (PAR2) is a G-protein coupled receptor that contributes to prostate fibrosis and lower urinary tract symptoms (LUTS). In addition to fibrosis, aberrant smooth muscle tone in the prostate has been hypothesized to play a role. We therefore examined PAR2 expression in primary human prostate smooth muscle cells (PSMC) and studied the downstream signaling effects of PAR2 activation. Signaling pathways involved in the process were assessed using the PAR2 activating peptide SLIGKV-NH2. We show that PAR2 is expressed in PSMC and that PAR2 activation mediates a biphasic elevation in intracellular Ca²⁺ and phosphorylation of myosin light chain 20 (MLC20), causing cellular contraction as assessed in a gel contraction assay. Intracellular Ca²⁺ flux was inhibited by a phosphoinositide hydrolysis inhibitor, U73122, showing a requirement for phospholipase C β (PLCβ) activation. PSMC expressed mRNA for L-type voltage dependent Ca²⁺ channels (VDCC) as well as Ca²⁺ release activated channels (CRAC), a hitherto unreported finding. Secondary intracellular Ca²⁺ oscillations were abrogated only by BTP2, the CRAC channel inhibitor, but not by nifedipine, an inhibitor of VDCC. These data suggest that, PAR2 activation and subsequent Ca²⁺ entry through CRAC channels are important mechanisms in prostate smooth muscle contraction.