Essential hypertension is a common disease, yet its pathogenesis is not well understood. Altered control of sodium excretion in the kidney may be a key causative feature, but this has been difficult to test experimentally, and recent studies have challenged this hypothesis. Based on the critical role of the renin-angiotensin system (RAS) and the type I (AT 1) angiotensin receptor in essential hypertension, we developed an experimental model to separate AT 1 receptor pools in the kidney from those in all other tissues. Although actions of the RAS in a variety of target organs have the potential to promote high blood pressure and end-organ damage, we show here that angiotensin II causes hypertension primarily through effects on AT 1 receptors in the kidney. We find that renal AT1 receptors are absolutely required for the development of angiotensin II-dependent hypertension and cardiac hypertrophy. When AT 1 receptors are eliminated from the kidney, the residual repertoire of systemic, extrarenal AT1 receptors is not sufficient to induce hypertension or cardiac hypertrophy. Our findings demonstrate the critical role of the kidney in the pathogenesis of hypertension and its cardiovascular complications. Further, they suggest that the major mechanism of action of RAS inhibitors in hypertension is attenuation of angiotensin II effects in the kidney. transgenic mice ͉ kidney transplantation ͉ blood pressure H igh blood pressure (BP) is a highly prevalent disorder, and its complications (including heart disease, stroke, and kidney disease) are a major public health problem (1). Despite decades of scrutiny, the precise pathogenesis of essential hypertension has been difficult to delineate. Guyton and his associates suggested that defective handling of sodium by the kidney and consequent dysregulation of body fluid volumes is a requisite, final common pathway in hypertension pathogenesis (2). The powerful capacity of this pathway to modulate blood pressure is illustrated by the elegant studies of Lifton and associates showing that virtually all of the Mendelian disorders with major impact on blood pressure homeostasis are caused by genetic variants affecting salt and water reabsorption by the distal nephron (3). On the other hand, several recent studies have suggested that primary vascular defects may cause hypertension by impacting peripheral resistance without direct involvement of renal excretory functions (4-7).Among the various regulatory systems that impact blood pressure, the RAS has a key role. Inappropriate activation of the RAS, as in renal artery stenosis, leads to profound hypertension and cardiovascular morbidity (8). Moreover, in patients with essential hypertension who typically lack overt signs of RAS activation, ACE inhibitors and angiotensin receptor blockers (ARBs) effectively reduce blood pressure and ameliorate cardiovascular complications (9-11), suggesting that dysregulation of the RAS contributes to their elevated blood pressure.

The carboxypeptidase ACE2 is a homologue of angiotensin-converting enzyme (ACE). To clarify the physiological roles of ACE2, we generated mice with targeted disruption of the Ace2 gene. ACE2-deficient mice were viable, fertile, and lacked any gross structural abnormalities. We found normal cardiac dimensions and function in ACE2-deficient animals with mixed or inbred genetic backgrounds. On the C57BL/6 background, ACE2 deficiency was associated with a modest increase in blood pressure, whereas the absence of ACE2 had no effect on baseline blood pressures in 129/SvEv mice. After acute Ang II infusion, plasma concentrations of Ang II increased almost 3-fold higher in ACE2-deficient mice than in controls. In a model of Ang II-dependent hypertension, blood pressures were substantially higher in the ACE2-deficient mice than in WT. Severe hypertension in ACE2-deficient mice was associated with exaggerated accumulation of Ang II in the kidney, as determined by MALDI-TOF mass spectrometry. Although the absence of functional ACE2 causes enhanced susceptibility to Ang II-induced hypertension, we found no evidence for a role of ACE2 in the regulation of cardiac structure or function. Our data suggest that ACE2 is a functional component of the renin-angiotensin system, metabolizing Ang II and thereby contributing to regulation of blood pressure.

We develop a sampling theory for genes sampled from a population evolving with deterministically varying size. We use a coalescent approach to provide recursions for the probabilities of particular sample configurations, and describe a Monte Carlo method by which the solutions to such recursions can be approximated. We focus on infinite-alleles, infinite-sites and finite-sites models. This approach may be used to find maximum likelihood estimates of parameters of genetic interest, and to test hypotheses about the varying environment. The methods are illustrated with data from the mitochondrial control region sampled from a North American Indian tribe.

Abstract-Drugs and antibodies that interrupt vascular endothelial growth factor (VEGF) signaling pathways improve outcomes in patients with a variety of cancers by inhibiting tumor angiogenesis. A major adverse effect of these treatments is hypertension, suggesting a critical role for VEGF in blood pressure (BP) regulation. However, the physiological mechanisms underlying the control of BP by VEGF are unclear. To address this question, we administered a specific antibody against the major VEGF receptor, VEGFR2, to normal mice and assessed the consequences on BP. Compared with vehicle-treated controls, administration of the anti-VEGFR2 antibody caused a rapid and sustained increase in BP of Ϸ10 mm Hg. This increase in BP was associated with a significant reduction in renin mRNA expression in the kidney (Pϭ0.019) and in urinary excretion of aldosterone (PϽ0.05). Treatment with the anti-VEGFR2 antibody also caused a marked reduction in the expression of endothelial and neuronal NO synthases in the kidney. To examine the role of NO in the hypertension caused by blocking VEGFR2, mice were treated with N -nitro-L-arginine methyl ester (L-NAME) (20 mg/kg per day), an inhibitor of NO production. L-NAME administration abolished the difference in BP between the vehicle-and anti-VEGFR2-treated groups. Our data suggest that VEGF, acting via VEGFR2, plays a critical role in BP control by promoting NO synthase expression and NO activity. Interfering with this pathway is likely to be one mechanism underlying hypertension caused by antiangiogenic agents targeting VEGF. (Hypertension. 2009;54:652-658.)

Angiotensin II, acting through type 1 angiotensin (AT 1 ) receptors, has potent effects that alter renal excretory mechanisms. Control of sodium excretion by the kidney has been suggested to be the critical mechanism for blood pressure regulation by the renin-angiotensin system (RAS). However, since AT 1 receptors are ubiquitously expressed, precisely dissecting their physiological actions in individual tissue compartments including the kidney with conventional pharmacological or gene targeting experiments has been difficult. Here, we used a cross-transplantation strategy and AT 1A receptor-deficient mice to demonstrate distinct and virtually equivalent contributions of AT 1 receptor actions in the kidney and in extrarenal tissues to determining the level of blood pressure. We demonstrate that regulation of blood pressure by extrarenal AT 1A receptors cannot be explained by altered aldosterone generation, which suggests that AT 1 receptor actions in systemic tissues such as the vascular and/or the central nervous systems make nonredundant contributions to blood pressure regulation. We also show that interruption of the AT 1 receptor-mediated short-loop feedback in the kidney is not sufficient to explain the marked stimulation of renin production induced by global AT 1 receptor deficiency or by receptor blockade. Instead, the renin response seems to be primarily determined by renal baroreceptor mechanisms triggered by reduced blood pressure. Thus, the regulation of blood pressure by the RAS is mediated by AT 1 receptors both within and outside the kidney.

cyte responses exacerbate angiotensin II-dependent hypertension. Am J Physiol Regul Integr Comp Physiol 298: R1089-R1097, 2010. First published February 10, 2010 doi:10.1152/ajpregu.00373.2009.-Activation of the immune system by ANG II contributes to the pathogenesis of hypertension, and pharmacological suppression of lymphocyte responses can ameliorate hypertensive end-organ damage. Therefore, to examine the mechanisms through which lymphocytes mediate blood pressure elevation, we studied ANG II-dependent hypertension in scid mice lacking lymphocyte responses and wild-type controls. Scid mice had a blunted hypertensive response to chronic ANG II infusion and accordingly developed less cardiac hypertrophy. Moreover, lymphocyte deficiency led to significant reductions in heart and kidney injury following 4 wk of angiotensin. The muted hypertensive response in the scid mice was associated with increased sodium excretion, urine volumes, and weight loss beginning on day 5 of angiotensin infusion. To explore the mechanisms underlying alterations in blood pressure and renal sodium handling, we measured gene expression for vasoactive mediators in the kidney after 4 wk of ANG II administration. Scid mice and controls had similar renal expression for interferon-␥, interleukin-1␤, and interleukin-6. By contrast, lymphocyte deficiency (i.e., scid mice) during ANG II infusion led to upregulation of tumor necrosis factor-␣, endothelial nitric oxide synthase (eNOS), and cyclooxygenase-2 (COX-2) in the kidney. In turn, this enhanced eNOS and COX-2 expression in the scid kidneys was associated with exaggerated renal generation of nitric oxide, prostaglandin E2, and prostacyclin, all of which promote natriuresis. Thus, the absence of lymphocyte activity protects from hypertension by allowing blood pressure-induced sodium excretion, possibly via stimulation of eNOSand COX-2-dependent pathways.inflammation; kidney diseases; T lymphocytes THE RENIN-ANGIOTENSIN SYSTEM (RAS) is a critical regulator of blood pressure and fluid homeostasis. The principal effector molecule of this system, angiotensin II (ANG II) raises blood pressure primarily through activation of type 1 angiotensin (AT 1 ) receptors (11). The important role of AT 1 receptors in the pathogenesis of hypertension is illustrated by clinical trials that show the impressive efficacy of AT 1 receptor blockers (ARBs) in ameliorating hypertension and its complications, including chronic kidney disease (CKD) and cardiac hypertrophy (3, 13, 37).In these trials, RAS inhibition appears to protect from end-organ damage to a greater degree than can be explained solely by blood pressure reduction (3, 63). Blockade of proinflammatory cellular effects of ANG II represents one blood pressure-independent mechanism through which ARB therapy could protect against target organ injury. For example, ANG II stimulates NF-B activation and interferon-␥ expression in the kidney, and immunosuppression can reverse these effects (8,45,46). Moreover, ANG II can drive lymphocyte proliferation (48), a...

Activation of the renin-angiotensin system contributes to the progression of chronic kidney disease. Based on the known cellular effects of ANG II to promote inflammation, we posited that stimulation of lymphocyte responses by ANG II might contribute to the pathogenesis of hypertensive kidney injury. We therefore examined the effects of the immunosuppressive agent mycophenolate mofetil (MMF) on the course of hypertension and kidney disease induced by chronic infusion of ANG II in 129/SvEv mice. Although it had no effect on the severity of hypertension or cardiac hypertrophy, treatment with MMF significantly reduced albuminuria and ameliorated kidney injury, decreasing glomerulosclerosis and reducing lymphocyte infiltration into the renal interstitium. Attenuation of renal pathology with MMF was associated with reduced expression of mRNAs for the proinflammatory cytokines interferon-␥ and tumor necrosis factor-␣ and the profibrotic cytokine transforming growth factor-␤. As infiltration of the kidney by T lymphocytes was a prominent feature of ANG II-dependent renal injury, we carried out experiments examining the effects of ANG II on lymphocytes in vitro. We find that exposure of splenic lymphocytes to ANG II causes prominent rearrangements of the actin cytoskeleton. These actions require the activity of Rho kinase. Thus, ANG II exaggerates hypertensive kidney injury by stimulating lymphocyte responses. These proinflammatory actions of ANG II seem to have a proclivity for inducing kidney injury while having negligible actions in the pathogenesis of cardiac hypertrophy.inflammation; kidney diseases; T lymphocytes THE RENIN-ANGIOTENSIN SYSTEM (RAS) is a master regulator of blood pressure and fluid homeostasis. The principal effector molecule of this system, ANG II, increases blood pressure primarily through activation of type I angiotensin (AT 1 ) receptors (13). Consistent with this notion, mice lacking the AT 1A receptor, the closest functional homolog to the human AT 1 receptor, have dramatically reduced blood pressures compared with wild-type controls (29). Furthermore, pharmacologic inhibition of the AT 1 receptor yields impressive blood pressure reduction in human hypertensive patients (14).In these hypertensive patients, the capacity of AT 1 receptor activation to promote kidney injury is highlighted by the efficacy of AT 1 receptor blockers (ARBs) in slowing the progression of chronic kidney disease (7,36,59). The ability of ARBs to ameliorate renal and cardiovascular disease depends at least in part on their blood pressure-lowering effects (21,22). Clinical trials suggest that the degree of end-organ protection provided by angiotensin receptor blockade cannot be explained by blood pressure reduction alone (7, 59). One blood pressure-independent mechanism through which ARBs protect the kidney may involve direct inhibition of proinflammatory cellular actions of ANG II. For example, on a cellular level, ANG II causes lymphocyte proliferation, NF-B activation, and generation of mononuclear cell chemokines such...

Immune system activation contributes to the pathogenesis of hypertension and the resulting progression of chronic kidney disease (CKD). In this regard, we recently identified a role for pro-inflammatory Th1 T lymphocyte responses in hypertensive kidney injury. As Th1 cells generate IFN-γ and TNF-α, we hypothesized that IFN-γ and TNF-α propagate renal damage during hypertension induced by activation of the renin-angiotensin system (RAS). Therefore, after confirming that mice genetically deficient of Th1 immunity were protected from kidney glomerular injury despite a preserved hypertensive response, we subjected mice lacking IFN-γ or TNF-α to our model of hypertensive CKD. IFN-deficiency had no impact on blood pressure elevation or urinary albumin excretion during chronic angiotensin II infusion. By contrast, TNF-deficient (KO) mice had blunted hypertensive responses and reduced end-organ damage in our model. As Ang II-infused TNF KO mice had exaggerated eNOS expression in the kidney and enhanced nitric oxide (NO) bioavailability, we examined the actions of TNF-α generated from renal parenchymal cells in hypertension by transplanting wild-type or TNF KO kidneys into wild-type recipients prior to the induction of hypertension. Transplant recipients lacking TNF solely in the kidney had blunted hypertensive responses to Ang II and augmented renal eNOS expression, confirming a role for kidney-derived TNF-α to promote Ang II-induced blood pressure elevation by limiting renal NO generation.