Abstract 2271: Deletion of the CaMK4 Gene in Mice Determines a Hypertensive Phenotype
Calcium/calmodulin-dependent kinase 4 (CaMK4) belongs to the CaMK family and is expressed in selected cellular types, where it regulates calcium-dependent signaling. In particular, its presence in the endothelium suggests a yet undisclosed role for this kinase in the regulation of vascular function. Furthermore, Genome-Wide Analysis showed an association between elevated blood pressure (BP) and the rs10491334 T/C Single Nucleotide Polymorphism of human CaMK4 gene. To evaluate the role of CaMK4 in BP homeostasis, we performed an ultrasound (US, VeVo, Visualsonics) cardiac evaluation and an invasive (Millar) arterial BP measurement in mice with deletion of the CaMK4 gene (CaMK4−/−, n=16) and wild type littermates (WT, n=14). Vasorelaxant responses to Acetylcholine (Ach, 10 nM to 10 μM), Isoproterenol (Iso, 1 nM to 1 μM) and Nitroprusside (Np, 1 nM to 10 μM) were assessed on ex vivo aortic rings preparations, pre-constricted with phenylephrine (PE, 1 μM). CaMK4−/−presented BP levels (Systolic BP 123±0.7 mmHg, Diastolic BP 90±0.3 mmHg) significantly higher (ANOVA, p< 0.05) than WT (Systolic BP 110±0.6, Diastolic BP 81±0.3 mmHg). Interestingly, the increase in BP levels paralleled the development of cardiac size (CaMK4−/− vs WT: Heart weight/body ratio 5.5±0.3 vs 4.24±0.2; Heart weight/tibia lenght: 7.4±0.4 vs 5.7±0.3;p<0.05), with worsening of US assessed cardiac function (CaMK4−/− vs WT: Shortening Fraction 0.36±0.06 vs 0.42±0.04; EndDiastolic Diameter 4.2±0.3 vs 3.3±0.4;p<0.05). CaMK4−/− vessels showed an attenuated endothelium-dependent vasore-laxation to ACh (% max vasodilation; CaMK4−/− vs WT: 23.7±0.05 vs 33.8±0.03; p<0.05) and to Iso (24.2±0.07 vs 55.8±0.05; p<0.05), while no differences were observed in endothelium independent vasorelaxant responses to Np (not shown). In cultured endothelial cells isolated from the aorta of WT mice, CaMK4 co-immunoprecipitates with eNOS and phosphorylates it in Ser 1177 in response to ionomycin or VEGF. These responses are lost in CaMk4−/− endothelial cells. We conclude that CaMK4 participates in BP homeostasis through the control of eNOS activity. This could be the underlying mechanism for the association in humans of CaMK4 gene polymorphism and essential hypertension.