Role of the PKA regulatory subunit RIα in the contractile tone of the aorta

Abstract

Protein kinase A (PKA) is a key enzyme activated by binding of cAMP. PKA induces smooth muscle relaxation and vasodilatation. The PKA-RIα knock-in heterozygous mice, [R368X]/[+] (KI), leading to the generation of a truncated RIα and the repression of PKA activation (Le Stunff et al., 2017, J Bone Miner Res ) may help decipher the contribution of PKA-RIα in vascular system which has remained elusive. Our aim is to document the expression of PKA-RIα in mouse aorta and to decipher its role in arterial tone by using wild-type (WT) and KI mice. Aortas were harvested from adult male WT and KI mice. PKA subunits expressions were studied by immunoblot. Vascular reactivity was tested by mounting the aorta on a wire-myograph. The internal circumference (IC) was recorded. Concentration-contractile responses were performed for K + (20–120 mM), U46619 (1 nM–3 μM) and phenylephrine (PE, 1 nM–3 μM). Vasorelaxant responses to acetylcholine (ACh, 1 nM–10 μM) and to L858051 (adenylate cyclase activator, 10 nM–30 μM) were studied in aorta contracted with PE. All groups included 5–6 mice. In WT aorta, the anti-PKA-RIα antibody yielded a signal at 49 kDa, as expected. In KI mice, mutant allele expression was confirmed by an additional signal at 47 kDa. RIIα and Cα expressions were similar in both strains. IC was 20% smaller in KI mice than in WT. The contractile response to K + and PE were similar in both groups, whereas the response to U46619 was stronger in mutant aorta with a higher E max . ACh and L858051 relaxed aortas similarly in both groups. These preliminary data show that PKA-RIα is expressed in mouse aorta. The smaller IC of aorta in [R368X]/[+] mice is consistent with their smaller size (Le Stunff et al.). The stronger constriction to U46619 in mutant mice may be explained by reduced PKA activity compared to WT. The similar relaxation to L858051 in mutant mice maybe due to redundancy of PKA-RIα in mouse aorta.