Background and purpose Vascular tone is regulated by the relative contractile state of vascular smooth muscle cells (VSMCs). Several integrins directly modulate VSMC contraction by regulating calcium influx through L-type voltage-gated Ca2+ channels (VGCCs). Genetic variants in ITGA9, which encodes the α9 subunit of integrin α9β1, and SVEP1, a ligand for integrin α9β1, associate with elevated blood pressure, however, neither SVEP1 nor integrin α9β1 have reported roles in vasoregulation. We therefore determined whether SVEP1 and integrin α9β1 can regulate VSMC contraction. Experimental Approach SVEP1 and integrin binding were confirmed by immunoprecipitation and cell binding assays. Human induced pluripotent stem cell-derived VSMCs were used in in vitro [Ca2+]i studies, and aortas from a Svep1+/- knockout mouse model were used in wire myography to measure vessel contraction. Key Results We confirmed the ligation of SVEP1 to integrin α9β1 and additionally found SVEP1 to directly bind to integrin α4β1. Inhibition of SVEP1, integrin α4β1 or α9β1 significantly enhanced [Ca2+]i release in isolated VSMCs to Gαq/11-vasoconstrictors. This response was confirmed in whole vessels where a greater contraction to U46619 was seen in vessels from Svep1+/- mice compared to littermate controls or when integrin α4β1 or α9β1 were inhibited. Inhibition studies suggested that this effect was mediated via VGCCs in a PKC dependent mechanism. Conclusions and Implications Our studies reveal a novel role for SVEP1 and the integrins α4β1 and α9β1 in reducing vascular hyper-contractility. This could provide an explanation for the genetic associations with blood pressure risk at the SVEP1 and ITGA9 loci.

Introduction: Sudden Cardiac Death (SCD) risk assessment is limited, particularly in patients with non-ischemic cardiomyopathies. This is the first application, in patients with non-ischemic cardiomyopathies, of two novel risk markers, Regional Restitution Instability Index (R2I2) and Peak Electrocardiogram Restitution Slope (PERS), which have been shown to be predictive of ventricular arrhythmias (VA) or death in ischemic cardiomyopathy patients. Methods and Results: Blinded retrospective study of 50 patients: 33 dilated cardiomyopathy and 17 other; undergoing electrophysiological study (EPS) for SCD risk stratification, and 29 controls with structurally normal hearts undergoing EPS. R2I2 was calculated from an EPS using ECG surrogates for action potential duration and diastolic interval. Cut-offs for high and low R2I2/PERS were predefined. R2I2 was significantly higher in study than control patients (0.99±0.05 vs. 0.63±0.04, <0.001). PERS showed a trend to higher values in the study group (1.18[0.63] vs. 1.09[0.54], p=0.07). During median follow up of 5.6 years [IQR 1.9 years] 9 study patients reached the endpoint of ventricular arrhythmia(VA)/death. Patients who experienced VA/death showed trends to higher mean R2I2 (1.14±0.07vs.0.95±0.05, p=0.12) and PERS (1.46[0.49] vs. 1.13[0.62], p=0.22). A Cox proportional hazards model using grouped markers: R2I2<1.03+PERS<1.21 / either R2I2≥1.03 or PERS≥1.21 / R2I2≥1.03+PERS≥1.21; significantly predicted VA/death (p=0.02) with a hazard ratio per positive component of 3.2 (95% confidence interval 1.2 to 8.8). Conclusion: R2I2≥1.03+PERS≥1.21 predict VA/death in patients with non-ischemic cardiomyopathies. R2I2≥1.03+PERS≥1.21 have the potential to play an important role in SCD risk stratification in non-ischemic cardiomyopathies but their validity should be confirmed in a larger study.