Background/Methods: We have examined the hypothesis that cyst formation is key in the pathogenesis of cardiovascular disease in a Lewis polycystic kidney (LPK) model of autosomal-recessive polycystic kidney disease (ARPKD), by determining the relationship between cyst development and indices of renal function and cardiovascular disease. Results: In the LPK (n = 35), cysts appear at week 3 (1.1 ± 0.1 mm) increasing to week 24 (2.8 ± 2 mm). Immunostaining for nephron-specific segments indicate cysts develop predominantly from the collecting duct. Cyst formation preceded hypertension (160 ± 22 vs. Lewis control 105 ± 20 mm Hg systolic blood pressure (BP), n = 12) at week 6, elevated creatinine (109 ± 63 vs. 59 ± 6 µmol/l, n = 16) and cardiac mass (0.7 vs. 0.4% bodyweight, n = 15) at week 12, and left ventricular hypertrophy (2,898 ± 207 vs. 1,808 ± 192 µm, n = 14) at week 24 (all p ≤ 0.05). Plasma-renin activity and angiotensin II were reduced in 10- to 12-week LPK (2.2 ± 2.9 vs. Lewis 11.9 ± 4.9 ng/ml/h, and 25.0 ± 19.1 vs. 94.9 ± 64.4 pg/ml, respectively, n = 26, p ≤ 0.05). Ganglionic blockade (hexamethonium 3.3 mg/kg) significantly reduced mean BP in the LPK (52 vs. Lewis 4%, n = 9, p ≤ 0.05). Conclusion: Cyst formation is a key event in the genesis of hypertension while the sympathetic nervous system is important in the maintenance of hypertension in this model of ARPKD.

Integrative Physiology B lood vessels consist of 2 major cell types, endothelial and mural cells, such as pericytes and vascular smooth muscle cells (VSMC), which surround the endothelium. Regulator of G-protein signaling 5 (RGS5) is expressed in mural cells and has emerged as a crucial modulator of vascular pathology in cancer. For instance, we have demonstrated that RGS5 is highly upregulated in angiogenic tumor pericytes.1 Loss of RGS5 results in pericyte maturation and normalization of tumor vasculature.2,3 Moreover, we showed a crucial role for RGS5 in regulating vascular barrier function in tumors and in brain capillaries during ischemia, and also provided the first genetic evidence that RGS5 is involved in vascular wall remodeling in adults. 2A striking feature of RGS5 expression is its dynamic nature in various physiological and pathological states, which indicates a role in adaptive processes. 1,[4][5][6] This is consistent with RGS5 being a member of the extended family of RGS molecules, which are modulators of G-protein-coupled receptors (GPCRs). G-protein signaling pathways rely on rapid on-off kinetics, and RGS molecules act as GTPaseactivating proteins (GAP) for heterotrimeric G proteins and, as such, regulate duration and intensity of signaling events. They contain a highly conserved carboxyl-terminal RGS domain that confers the catalytic function for active Gα subunits. Members of the R4/B subfamily, which include, among others, RGS 2, 4, and 5, are the smallest RGS Original received September 21, 2012; revision received January 7, 2013; accepted January 9, 2013. In December 2012, the average time from submission to first decision for all original research papers submitted to Circulation Research was 14.5 days.