Angiotensin II-Induced Contraction is Mediated by Activation of Polo-Like Kinase 1 (Plk1) in Pudendal and Mesenteric Resistance Arteries of Mice.

BACKGROUND: Polo-like kinase 1 (Plk1) is a Ser/Thr protein kinase that plays a role in cell cycle regulation. Recently, Plk1 was demonstrated to be required for arterial structure organization and its absence caused aortic rupture and death, being also required for RhoA activation and vasoconstriction in aorta. In this study, we aimed to investigate the role of Plk1 in the contraction of resistance arteries in response to different classes of contractile agents. We hypothesize that agonist-mediated contraction is dependent on activation of Plk1 in resistance arteries in both males and females.

METHODS: Male and female wild type mice were used in this study. The pudendal and mesenteric resistance arteries were isolated and mounted in a wire-myograph. Contractions were obtained by concentration-response curves to phenylephrine (PE), serotonin (5-HT), thromboxane A2 analogue U46619 and angiotensin II (Ang-II). Concentration response curve to the same agonist was repeated after incubation with Plk1 inhibitor Volasertib (100 nM or 1 uM). Contractions in the presence of Volasertib were calculated as percentage of the maximal contraction evoked by its respective agonist in control conditions, which was considered 100%. Expression of Plk1 was evaluated by western blot using mesenteric artery in control conditions and after incubation with Ang-II, with or without the Plk1 inhibitor volasertib. Curves to Ang-II were also repeated in the absence of any inhibitor in order to rule out tachyphylaxis of Ang-II in the second curve. Paired Student's t-test was used for data analysis. Data are expressed as mean ± S.E.M of 3-5 mice.

RESULTS: In male, the contractile effects of PE, 5-HT, U46619 and Ang-II in the pudendal and mesenteric arteries were evaluated in the presence of the Plk1 inhibitor, Volasertib (100 nM). Plk1 inhibition did not affect the contraction induced by PE, 5-HT and U46619 in either pudendal or mesenteric arteries. On the other hand, the contraction induced by Ang-II was markedly reduced in the presence of Volasertib (100 nM) in both pudendal and mesenteric arteries (Fig 1A and 1C, respectively). However, the inhibition of the contraction was not dependent on the dose, since 1 uM of Volasertib did not cause further inhibition (Pudendal artery EMAX: 3.86 ± 0.97% vs 5.02 ± 0.48%, in the presence of 100 nM and 1 uM of Volasertib, respectively; Mesenteric artery EMAX: 0.28 ± 0.21% vs 0.36 ± 0.18%, in the presence of 100 nM and 1 uM of Volasertib, respectively). In females, only 100 nM of Volasertib was tested in the contraction induced by PE and Ang-II. In females, Volasertib did not affect the contraction induced by PE in pudendal and mesenteric arteries. In contrast, the contraction induced by Ang-II was markedly reduced in the presence of Volasertib 100 nM (Fig 1B and 1D). Plk1 is expressed in the mesenteric artery of wild type mice, however, it was not affected by incubation with either Ang-II (100 nM) or Volasertib (100 nM). However, it is possible that these treatments are affecting Plk1 phosphorylation.

CONCLUSION: Our findings are the first to demonstrate that Plk1 plays a role in Ang-II-induced contraction of the pudendal and mesenteric arteries of mice. More studies are necessary to elucidate the process of Plk1 activation and its association with vascular dysfunction in pathological conditions such as hypertension and diabetes.