Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA347

Poster Communications

The role of beta arrestins and PDEs in smooth muscle tone regulation of vessels and airways

L. F. Lebender1,2, B. K. Fleischmann1, D. Wenzel1

1. Institute of Physiology 1, University of Bonn, Bonn, NRW, Germany. 2. University of Bonn, Research Training Group 1873, Bonn, Germany.

The regulation of smooth muscle tone in vessels and airways is essential to optimize blood and airflow. Its dysregulation can result in high blood pressure or obstructive lung disease. In order to develop alternative therapeutic strategies novel molecular targets involved in smooth muscle tone regulation need to be identified. Beta arrestins are promising candidates, because of their claimed key role in the modulation of beta adrenergic receptors (ARs) and further direct effects on cAMP signaling. Earlier reports have proposed that beta arrestins upon beta2 AR activation can recruit phosphodiesterase 4 (PDE4) to the plasma membrane in HEK 293 cells, thereby modulating local cAMP levels. Due to the relevance of cAMP for smooth muscle tone this finding suggests that beta arrestins may affect vascular tone via PDE signaling. We have investigated this aspect by performing isometric force measurements in a wire myograph in pulmonary arteries (PAs), aortas and tracheas from WT, beta arrestin 1-/- and beta arrestin 2-/- mice. After pre-constriction with the alpha1 AR agonist phenylephrine (10-7 M) dose response curves applying the beta AR agonist isoprenaline (ISO) (10-9 -10-4 M) were recorded with or without pre-treatment with the PDE 4 inhibitor roflumilast (10-5 M). In addition, qPCR experiments were performed to determine the expression levels of different PDE subtypes. Isometric force measurements revealed that ISO induced a dose-dependent relaxation of PAs, aortas and tracheas after phenylephrine-dependent pre-constriction. PAs from beta arrestin 1-/- animals show a reduced ISO-dependent relaxation compared to WT and beta arrestin 2-/- mice. In contrast, EC50 values of ISO dose response curves in aortas and tracheas of all genotypes were similar. When tissues were pre-treated with roflumilast ISO dose-response curves in PAs were shifted to the left in WT and beta arrestin 1-/-, but not in beta arrestin 2-/- animals. However, the lower potency of ISO in beta arrestin 1-/- compared to WT PAs remained unchanged. In the aortas roflumilast did not affect ISO dose response curves of all genotypes investigated, whereas it shifted all ISO dose-response curves to the left in tracheas; this was especially pronounced in beta arrestin 2 -/- tracheas. In qRT-PCR experiments no difference in the expression of PDE isoforms was detected in PAs of the different genotypes. Our results demonstrate that beta arrestin 1 and 2 affect vascular tone regulation in PAs and airways; this appears to be unrelated to the expression levels of PDEs. PDE4 inhibition unmasks enhanced cAMP signaling in tracheas, especially in beta arrestin 2-/-. This could be due to the previously reported reduction of beta2 AR internalization in beta arrestin 2 deficiency. Thus, we are planning to further explore the role of beta arrestins for tone regulation in vessels and airways in future studies.

Where applicable, experiments conform with Society ethical requirements