Signal transduction pathways of detrusor smooth muscle contraction evoked by prostanoids and isoprostanes in murine urinary bladder
Authors: Molnar Peter J. , Der Balint , Borsodi Kinga , Balla Helga , Borbas Zsofia , Molnar Krisztina , Ruisanchez Eva , Offermanns Stefan , Benyo Zoltan 
Published: April 2020

The overactive bladder (OAB) is a clinical condition characterized by symptoms of frequency, urgency with/without incontinence, with a prevalence of 16% in the developed countries. The current pharmacological treatment mainly consists of anticholinergic drugs with several side effects. According to prior experimental results the arachidonic acid (AA) derivate prostanoids and isoprotanes, the latter produced non‐enzymatically during oxidative stress, are not only biomarkers of systemic oxidative stress, but are excreting in the urine and might act directly on the detrusor muscle leading to detrusor overactivity.

Our aim was to examine the effects and the signal transduction pathways of prostanoids and isoprotanes in the urinary bladder smooth muscle, and potentially provide theoretical basis for the development of more specific medication of OAB with less adverse effects.

Detrusor muscle strips were prepared from wild type (C57BL/6) and knockout mice, deficient for the thromboxane receptor (TP) or the α‐subunits of heterotrimeric G proteins (Gαq/11‐KO, Gα12/13‐KO) without urothelium under dissection microscope. Contraction force was measured by myograph under isometric conditions and normalized to the reference contractions evoked by 124 mM K+.

The prostaglandin E2 (PGE2) and prostaglandin F2α (PGF2α), as well as the isoprostane 8‐epi‐PGE2 and 8‐iso‐PGF2α evoked contraction in the urinary bladder strips. The effect of the prostanoids was decreased, and the effect of the isoprostanes was abolished in the strips of TP KO mice, suggesting that the effect of the prostanoids is mediated partially, whereas that of the isoprostanes mainly by the TP. The TP receptor selective agonist U‐46619 evoked dose‐dependent contraction in the bladder strips, and neither the cholinerg antagonist atropine, nor the purinerg P2X‐antagonist pyridoxalphosphate‐6‐azophenyl‐2',4'‐disulfonic acid (PPADS) decreased the responses, indicating that the TP agonist has a direct effect on the detrusor muscle. The responses evoked by U‐46619 were comparable to the effect evoked by cholinergic agonist, carbachol. The contraction responses were decreased in the strips of the Gα12/13‐KO mice. Correspondingly, the responses evoked by the prostanoids and isoprostanes were reduced by the Rho‐kinase (ROCK) inhibitor Y‐27632. In the strips of the Gαq/11‐KO mice, the responses were also decreased and in the presence of Y‐27632 abolished completely.

In conclusion, the examined prostanoids and isoprostanes evokes contraction acting directly on the detrusor muscle. These responses are mediated mainly by the TP receptor and are linked to the Gαq/11 and to the Gα12/13‐Rho‐ROCK intracellular signaling pathways in the murine urinary bladder. The Gα12/13‐Rho‐ROCK signaling pathway may provide a novel, more specific pharmacological target with less adverse effects in the treatment of OAB.

Support or Funding Information

K‐112964, K‐125174 and NVKP‐16‐1‐2016‐0042 from the Hungarian National Research, Development and Innovation Office and EFOP‐3.6.3‐VEKOP‐16‐2017‐00009.