Role of S1P- and Rho-kinase signalling in age-related myogenic tone deficiency in murine resistance arteries

Ageing is a risk factor for cardiovascular and neurodegenerative diseases. The myogenic response in resistance arteries is responsible for basal (myogenic) tone and blood flow autoregulation. G-protein-coupled receptors and G₁₂/RhoA/Rho kinase are implicated in myogenic tone (MT), and we aimed to clarify their role in pressure sensing and ageing. We studied MT in third-order mesenteric arteries (MA) ex vivo and first–fourth order cerebral arteries (CA) in vivo in young versus middle-aged male mice. Inhibition of α₁-, AT₁-, ET_A- and TP-receptors and thromboxane synthase did not affect MT in MA from young mice. The P2Y-receptor blocker suramin inhibited MT, whereas PPADS and apyrase did not. MT in intact or endothelium-denuded MAs was not affected by the knockout of P2Y₆-receptor (P2Y₆-R). qPCR showed upregulation of P2Y₂-R in P2Y₆-deficient arteries. MT was not affected in P2Y₂-R knock-out mice. The sphingosine-kinase (SK) blocker SKI-II inhibited MT in young mice, and the sphingosine 1-phosphate receptor 2 (S1P₂-R) blocker JTE-013 inhibited MT in young and middle-aged mice. MT was impaired in middle-aged mice. Furthermore, MT was reduced in young mice carrying familial Alzheimer's disease mutations (5xFAD), and JTE-013 abolished MT in 5xFAD mice and their wild-type littermates. JTE-013 did not affect calcium signalling in cultured human coronary artery smooth muscle cells. High-resolution microangiography confirmed that infusion of JTE-013 or KD025 (a Rho-kinase 2 inhibitor) preferentially dilated small (distal) CAs, and infusion of nifedipine (an L-type channel inhibitor) dilated all CAs in all mice, independent of age. SK and S1P₂-R are crucially involved in pressure sensing in MT. RhoA/Rho-kinase signalling might be involved in age-related MT deficiency.