Dietary Protein, Chronic Salt-Sensitive Hypertension, and Kidney Damage.

It has been estimated that over a fifth of deaths worldwide can be attributed to dietary risk factors. A particularly serious condition is salt-sensitive (SS) hypertension and renal damage, participants of which demonstrate increased morbidity and mortality. Notably, a large amount of evidence from humans and animals has demonstrated that other components of the diet can also modulate hypertension and associated end-organ damage. Evidence presented in this review provides support for the view that immunity and inflammation serve to amplify the development of SS hypertension and leads to malignant disease accompanied by tissue damage. Interestingly, SS hypertension is modulated by changes in dietary protein intake, which also influences immune mechanisms. Together, the evidence presented in this review from animal and human studies indicates that changes in dietary protein source have profound effects on the gut microbiota, microbiota-derived metabolites, gene expression, immune cell activation, the production of cytokines and other factors, and the development of SS hypertension and kidney damage.

Functional NADPH oxidase 2 in T cells amplifies salt-sensitive hypertension and associated renal damage.

Infiltrating T cells in the kidney amplify salt-sensitive (SS) hypertension and renal damage, but the mechanisms are not known. Genetic deletion of T cells (SSCD247-/-) or of the p67phox subunit of NADPH oxidase 2 (NOX2; SSp67phox-/-) attenuates SS hypertension in the Dahl SS rat. We hypothesized that reactive oxygen species produced by NOX2 in T cells drive the SS phenotype and renal damage. T cells were reconstituted by adoptively transferring splenocytes (∼10 million) from the Dahl SS (SS→CD247) rat, the SSp67phox-/- rat (p67phox→CD247), or only PBS (PBS→CD247) into the SSCD247-/- rat on postnatal day 5. Animals were instrumented with radiotelemeters and studied at 8 wk of age. There were no detectable differences in mean arterial pressure (MAP) or albuminuria between groups when rats were maintained on a low-salt (0.4% NaCl) diet. After 21 days of high-salt diet (4.0% NaCl), MAP and albuminuria were significantly greater in SS→CD247 rats compared with p67phox→CD247 and PBS→CD247 rats. Interestingly, there was no difference between p67phox→CD247 and PBS→CD247 rats in albuminuria or MAP after 21 days. The lack of CD3+ cells in PBS→CD247 rats and the presence of CD3+ cells in rats that received the T cell transfer demonstrated the effectiveness of the adoptive transfer. No differences in the number of CD3+, CD4+, or CD8+ cells were observed in the kidneys of SS→CD247 and p67phox→CD247 rats. These results indicate that reactive oxygen species produced by NOX2 in T cells participates in the amplification of SS hypertension and renal damage.NEW & NOTEWORTHY Our current work used the adoptive transfer of T cells that lack functional NADPH oxidase 2 into a genetically T cell-deficient Dahl salt-sensitive (SS) rat model. The results demonstrated that reactive oxygen species produced by NADPH oxidase 2 in T cells participate in the amplification of SS hypertension and associated renal damage and identifies a potential mechanism that exacerbates the salt-sensitive phenotype.

T Cells Contribute to Pathological Responses in the Non-Targeted Rat Heart following Irradiation of the Kidneys.

Heart disease is a significant adverse event caused by radiotherapy for some cancers. Identifying the origins of radiogenic heart disease will allow therapies to be developed. Previous studies showed non-targeted effects manifest as fibrosis in the non-irradiated heart after 120 days following targeted X-irradiation of the kidneys with 10 Gy in WAG/RijCmcr rats. To demonstrate the involvement of T cells in driving pathophysiological responses in the out-of-field heart, and to characterize the timing of immune cell engagement, we created and validated a T cell knock downrat on the WAG genetic backgrou nd. Irradiation of the kidneys with 10 Gy of X-rays in wild-type rats resulted in infiltration of T cells, natural killer cells, and macrophages after 120 days, and none of these after 40 days, suggesting immune cell engagement is a late response. The radiation nephropathy and cardiac fibrosis that resulted in these animals after 120 days was significantly decreased in irradiated T cell depleted rats. We conclude that T cells function as an effector cell in communicating signals from the irradiated kidneys which cause pathologic remodeling of non-targeted heart.

Gut-Immune-Kidney Axis: Influence of Dietary Protein in Salt-Sensitive Hypertension.

Humans with salt-sensitive hypertension demonstrate increased morbidity, increased mortality, and renal end-organ damage when compared with normotensive subjects or those with salt-resistant hypertension. Substantial evidence from humans and animals has also demonstrated the role of dietary components other than salt to modulate hypertension. Evidence presented in this review provides support for the view that immunity and inflammation serve to amplify the development of salt-sensitive hypertension and leads to malignant disease accompanied by end-organ damage. Interestingly, salt-sensitive disease is modulated by changes in dietary protein intake, which also influences immune mechanisms. Together, the evidence presented in this review from animal and human studies indicates that changes in dietary protein source have profound effects on the gut microbiota, microbiota-derived metabolites, DNA methylation, gene expression, immune cell activation, the production of cytokines and other factors, and the development of salt-sensitive hypertension and related disease phenotypes.

Concurrent Aspirin Use Is Associated with Improved Outcome in Rectal Cancer Patients Who Undergo Chemoradiation Therapy.

BACKGROUND: The benefit of aspirin in rectal cancer during chemoradiation therapy (CRT) and the factors affecting its efficacy are not well characterized. We compared the outcomes of rectal patients undergoing neoadjuvant CRT based on aspirin use. METHODS: Patients undergoing CRT for rectal cancer from 2010 to 2018 were evaluated. Aspirin use was determined by medication list prior to treatment. RNA sequencing and subsequent gene set enrichment analysis was performed on surgically resected specimens. RESULTS: 147 patients underwent neoadjuvant CRT with a median follow-up of 38.2 months. Forty-two patients were taking aspirin prior to CRT. Aspirin users had significantly less local and distant progression, and improved progression-free and overall survival. On RNA-sequencing, neither PI3KCA nor KRAS mutational status were associated with the benefit of aspirin use or tumor downstaging. PTGS2/COX2 expression trended lower in aspirin users, but not with tumor response. Aspirin use was associated with increases of M1 macrophages, plasma cells, CD8+ T cells, and reduction of M2 macrophages in the resected tumor. CONCLUSIONS: Concurrent aspirin use during neoadjuvant CRT was associated with improved local and distant tumor control leading to significantly improved survival. Neither mutations in KRAS or PI3CKA, nor the levels of COX-2 expression at the time of resection of the residual tumor were predictive of these aspirin benefits.

Amplification of Salt-Sensitive Hypertension and Kidney Damage by Immune Mechanisms.

Humans with salt-sensitive (SS) hypertension demonstrate increased morbidity, increased mortality, and renal end-organ damage when compared with normotensive subjects or those with salt-resistant hypertension. Increasing evidence indicates that immune mechanisms play an important role in the full development of SS hypertension and associated renal damage. Recent experimental advances and studies in animal models have permitted a greater understanding of the mechanisms of activation and action of immunity in this disease process. Evidence favors a role of both innate and adaptive immune mechanisms that are triggered by initial, immune-independent alterations in blood pressure, sympathetic activity, or tissue damage. Activation of immunity, which can be enhanced by a high-salt intake or by alterations in other components of the diet, leads to the release of cytokines, free radicals, or other factors that amplify renal damage and hypertension and mediate malignant disease.

Sexual Dimorphic Role of CD14 (Cluster of Differentiation 14) in Salt-Sensitive Hypertension and Renal Injury.

Genomic sequence and gene expression association studies in animals and humans have identified genes that may be integral in the pathogenesis of various diseases. CD14 (cluster of differentiation 14)-a cell surface protein involved in innate immune system activation-is one such gene associated with cardiovascular and hypertensive disease. We previously showed that this gene is upregulated in renal macrophages of Dahl salt-sensitive animals fed a high-salt diet; here we test the hypothesis that CD14 contributes to the elevated pressure and renal injury observed in salt-sensitive hypertension. Using CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/clustered regularly interspaced short palindromic repeat-associated 9), we created a targeted mutation in the CD14 gene on the Dahl SS (SS/JrHSDMcwi) background and validated the absence of CD14 peptides via mass spectrometry. Radiotelemetry was used to monitor blood pressure in wild-type and CD14-/- animals challenged with high salt and identified infiltrating renal immune cells via flow cytometry. Germline knockout of CD14 exacerbated salt-sensitive hypertension and renal injury in female animals but not males. CD14-/- females demonstrated increased infiltrating macrophages but no difference in infiltrating lymphocytes. Transplant of CD14+/+ or CD14-/- bone marrow was used to isolate the effects of CD14 knockout to hematopoietic cells and confirmed that the differential phenotype observed was due to knockout of CD14 in hematopoietic cells. Ovariectomy was used to remove the influence of female sex hormones, which completely abrogated the effect of CD14 knockout. These studies provide a novel treatment target and evidence of a new dichotomy in immune activation between sexes within the context of hypertensive disease where CD14 regulates immune cell activation and renal injury.

Irradiation of the kidneys causes pathologic remodeling in the nontargeted heart: A role for the immune system.

Cardiac disease is a frequent and significant adverse event associated with radiotherapy for cancer. Identifying the underlying mechanism responsible for radiation injury to the heart will allow interventions to be developed. In the present study, we tested if local kidney irradiation results in remodeling of the shielded, nontargeted heart. One kidney, two kidneys, or the total body of male WAG and Dahl SS rats were irradiated with 10 Gy of X-rays. Local kidney irradiation resulted in systemic hypertension, increased BUN, infiltration of T lymphocytes, natural killer cells, and macrophages into the renal cortex and medulla, and renal fibrosis. Local irradiation of kidneys in WAG rats resulted in remodeling in the nontargeted heart after 120 days, manifested by perivascular fibrosis and increased interventricular septal thickness, but was not seen in Dahl SS rats due to a high baseline level of fibrosis in the sham-irradiated animals. Genetic depletion of T cells mitigated the nephropathy after local kidney irradiation, indicating a role for the immune system in mediating this outcome. Local kidney irradiation resulted in a cascade of pro-inflammatory cytokines and low-molecular weight metabolites into the circulation associated with transmission of signals resulting in pathologic remodeling in the nontargeted heart. A new model is proposed whereby radiation-induced cardiac remodeling in susceptible animals is indirect, with lower hemi body organs such as the kidney exporting factors into the circulation that cause remodeling outside of the irradiated field in the shielded, nontargeted heart. This nontargeted effect appears to be mediated, in part, by the immune system.

Concurrent ß-blocker Use is Associated With Improved Outcome in Esophageal Cancer Patients Who Undergo Chemoradiation: A Retrospective Matched-pair Analysis.

BACKGROUND: ß-blocker use has been associated with improved outcomes in a number of different malignancies; however, the impact of ß-blockade in esophageal cancer is not been well characterized. We compared the outcomes of esophageal cancer patients based on ß-blocker usage. METHODS: The charts of all 418 patients treated with radiation for esophageal cancer at our institution from April 2010 to October 2018 were analyzed. Patients who underwent treatment with palliative intent or did not finish treatment were excluded. ß-blocker use was determined from the medication list at time of pretreatment consultation. RESULTS: There were 291 esophageal cancer patients who received neoadjuvant/definitive chemoradiation therapy. The median follow-up for the cohort was 22.5 months (interquartile range: 9.6 to 41.0 mo). Within the cohort, 27.8% (n=81) of patients were taking ß-blockers at the time of treatment. Those taking ß-blockers had significantly improved distant control (22.2% vs. 37.9%; P=0.035). Concomitant ß-blocker use was significantly associated with improved progression-free survival (P<0.001, hazard ratio=0.42 [0.27-0.66]) and overall survival (P=0.002, hazard ratio=0.55 [0.38-0.81]) on Cox regression analysis. Propensity score-matched pairs were created using tumor stage, nodal stage, sex, neoadjuvant versus definitive therapy, Karnofsky Performance Status, and aspirin use. This matched-pair analysis showed a significant progression-free survival (P=0.005) benefit in esophageal cancer patients taking ß-blockers. CONCLUSIONS: Concurrent ß-blocker use is common within patients receiving concurrent chemoradiation for esophageal cancer. Esophageal cancer patients who received chemoradiation while taking ß-blockers demonstrated significant benefits in survival-based outcomes.

Inflammatory macrophages in the kidney contribute to salt-sensitive hypertension.

This review will highlight recent studies that have investigated the relationship between Na+, renal macrophage polarization, and renal damage. A hyperosmotic environment drives the macrophage toward a proinflammatory phenotype and away from an anti-inflammatory phenotype. Animal models of salt-sensitive hypertension demonstrate a characteristic infiltration of macrophages into the kidney that is greatly reduced when blood pressure is lowered. Because general immunosuppression or macrophage depletion leads to a host of adverse side effects, more recent studies have modulated the interaction of specific signaling molecules, including NOD-like receptor family pyrin domain-containing 3, chemokine (C-X-C motif) ligand 16, and VEGF, to prevent the end-organ renal damage that accumulates in salt-sensitive disease.

NOX2-derived reactive oxygen species in immune cells exacerbates salt-sensitive hypertension.

Previous studies utilizing the SSp67phox-/- rat have demonstrated the importance of systemic NADPH oxidase NOX2-derived reactive oxygen species (ROS) production in the pathogenesis of Dahl Salt-Sensitive (SS) hypertension and renal damage. It is established that the immune system contributes to the development of SS hypertension and our laboratory has observed an enrichment of NOX2 subunits in infiltrating T cells. However, the contribution of immune cell-derived ROS in SS hypertension remains unknown. To assess the role of ROS in immune cells, SSp67phox-/- rats underwent total body irradiation and received bone marrow transfer from either SS (+SS) or SSp67phox-/- (+SSp67phox-/-) donor rats. Demonstrated in a respiratory burst assay, response to phorbol 12-myristate 13-acetate stimulus (135 µM) was 10.2-fold greater in peritoneal macrophages isolated from +SS rats compared to nonresponsive + SSp67phox-/- cells, validating that + SS rats were capable of producing NOX2-derived ROS in cells of hematopoietic origin. After 3 weeks of high salt challenge, there was an exacerbated increase in mean arterial pressure in +SS rats compared to + SSp67phox-/- control rats (176.1 ± 4.7 vs 147.9 ± 8.4 mmHg, respectively), which was accompanied by a significant increase in albuminuria (168.3 ± 23.7 vs 107.0 ± 20.4 mg/day) and renal medullary protein cast formation (33.2 ± 4.7 vs 8.1 ± 3.5%). Interestingly, upon analysis of renal immune cells, there was trending increase of CD11b/c + monocytes and macrophages in the kidney of +SS rats (4.7 ± 0.4 vs 3.5 ± 0.5 × 106 cells/kidney, +SS vs + SSp67phox-/-, p = 0.06). These data altogether demonstrate that immune cell production of NOX2-derived ROS is sufficient to exacerbate Dahl SS hypertension, renal damage, and renal inflammation.

Preoperative radiation as part of a multidisciplinary strategy for a medically inoperable patient with a bleeding colon cancer.

An 84-year-old man with a history of deep vein thrombosis on warfarin and coronary artery disease presented with haematochezia and was diagnosed with an ascending colon cancer. He was short of breath with lower extremity oedema at the initial surgical consultation. Evaluation revealed an acute exacerbation of congestive heart failure, and further workup and treatment were recommended by the cardiology team. After multidisciplinary discussion, he underwent radiation for the control of bleeding, followed by cardiac catheterisation and placement of a bare metal stent. The patient subsequently underwent robotic-assisted right hemicolectomy. Pathology demonstrated a complete response, and the patient recovered uneventfully. He is alive swith no evidence of disease recurrence 12 months after surgery and 18 months after initial diagnosis.

Salt-sensitive increase in macrophages in the kidneys of Dahl SS rats.

Studies of Dahl salt-sensitive (SS) rats have shown that renal CD3+ T cells and ED-1+ macrophages are involved in the development of salt-sensitive hypertension and renal damage. The present study demonstrated that the increase in renal immune cells, which accompanies renal hypertrophy and albuminuria in high-salt diet-fed Dahl SS rats, is absent in Sprague-Dawley and SSBN13 rats that are protected from the SS disease phenotype. Flow cytometric analysis demonstrated that >70% of the immune cells in the SS kidney are M1 macrophages. PCR profiling of renal myeloid cells showed a salt-induced upregulation in 9 of 84 genes related to Toll-like receptor signaling, with notable upregulation of the Toll-like receptor 4/CD14/MD2 complex. Because of the prominent increase in macrophages in the SS kidney, we used liposome-encapsulated clodronate (Clod) to deplete macrophages and assess their contribution to salt-sensitive hypertension and renal damage. Dahl SS animals were administered either Clod-containing liposomes (Clod-Lipo), Clod, or PBS-containing liposomes as a vehicle control. Clod-Lipo treatment depleted circulating and splenic macrophages by ∼50%; however, contrary to our hypothesis, Clod-Lipo-treated animals developed an exacerbated salt-sensitive response with respect to blood pressure and albuminuria, which was accompanied by increased renal T and B cells. Interestingly, those treated with Clod also demonstrated an exacerbated phenotype, but it was less severe than Clod-Lipo-treated animals and independent of changes to the number of renal immune cells. Here, we have shown that renal macrophages in Dahl SS animals sustain a M1 proinflammatory phenotype in response to increased dietary salt and highlighted potential adverse effects of Clod-Lipo macrophage depletion.

The function of SH2B3 (LNK) in the kidney.

Recent evidence indicates the adaptor protein SH2B3 has a major role in the progression of renal diseases. SH2B3 is highly expressed by hematopoietic cells and regulates cytokine signaling, inducing cell-specific effects. Additionally, its expression in other cell types suggests that SH2B3 may have a more extensive role within the kidney. Ex vivo studies have determined targets of SH2B3 cell-specific signaling, while in vivo studies have observed the SH2B3 overall affects in the progression of renal diseases. This mini-review covers the function of SH2B3-expressing cell types that contribute to renal pathologies and their regulation by SH2B3.

Interleukin-6 inhibition attenuates hypertension and associated renal damage in Dahl salt-sensitive rats.

Immune cells in the kidney are implicated in the development of hypertension and renal damage in the Dahl salt-sensitive (SS) rat. Interestingly, interleukin 6 (IL-6) mRNA is 54-fold higher in T-lymphocytes isolated from the kidney compared with circulating T-lymphocytes. The present experiments assessed the role of IL-6 in the development of SS hypertension by treating rats (n = 13-14/group) with an IL-6 neutralizing antibody or normal IgG during an 11-day period of high-salt (4.0% NaCl chow) intake. The mean arterial pressure (MAP) and urine albumin excretion rates (Ualb) were not different between the groups fed low salt (0.4% NaCl). Following 11 days of drug treatment and high salt, however, the rats receiving anti-IL-6 demonstrated a 47% reduction of IL-6 in the renal medulla compared with control SS. Moreover, the increase in MAP following 11 days of high-NaCl intake was significantly attenuated in SS administered anti-IL-6 compared with the control group (138 ± 3 vs. 149 ± 3 mmHg) as was the salt-induced increase in Ualb and glomerular and tubular damage. To investigate potential mechanisms of action, a flow cytometric analysis of immune cells in the kidney (n = 8-9/group) demonstrated that the total number of monocytes and macrophages was significantly lower in the treatment vs. the control group. The total number of T- and B-lymphocytes in the kidneys was not different between groups. These studies indicate that IL-6 production may participate in the development of SS hypertension and end-organ damage by mediating increased infiltration or proliferation of macrophages into the kidney.

Renal Tumor Necrosis Factor α Contributes to Hypertension in Dahl Salt-Sensitive Rats.

Tumor necrosis factor α (TNFα) is a major proinflammatory cytokine and its level is elevated in hypertensive states. Inflammation occurs in the kidneys during the development of hypertension. We hypothesized that TNFα specifically in the kidney contributes to the development of hypertension and renal injury in Dahl salt-sensitive (SS) rats, a widely used model of human salt-sensitive hypertension and renal injury. SS rats were chronically instrumented for renal interstitial infusion and blood pressure measurement in conscious, freely moving state. Gene expression was measured using real-time PCR and renal injury assessed with histological analysis. The abundance of TNFα in the renal medulla of SS rats, but not the salt-insensitive congenic SS.13(BN26) rats, was significantly increased when rats had been fed a high-salt diet for 7 days (n = 6 or 9, p < 0.01). The abundance of TNFα receptors in the renal medulla was significantly higher in SS rats than SS.13(BN26) rats. Renal interstitial administration of Etanercept, an inhibitor of TNFα, significantly attenuated the development of hypertension in SS rats on a high-salt diet (n = 7-8, p < 0.05). Glomerulosclerosis and interstitial fibrosis were also significantly ameliorated. These findings indicate intrarenal TNFα contributes to the development of hypertension and renal injury in SS rats.

Predictors of Pathologic Complete Response Following Neoadjuvant Chemoradiotherapy for Rectal Cancer.

BACKGROUND: Some patients with rectal cancer who receive neoadjuvant chemoradiotherapy (nCRT) achieve a pathologic complete response (pCR) and may be eligible for less radical surgery or non-operative management. The aim of this study was to identify variables that predict pCR after nCRT for rectal cancer and to examine the impact of pCR on postoperative complications. METHODS: A retrospective review was performed of the NCDB from 2006 to 2011. Patients with rectal cancer who received nCRT followed by radical resection were included in this study. Multivariable analysis of the association between clinicopathologic characteristics and pCR was performed, and propensity-adjusted analysis was used to identify differences in postoperative morbidity between pCR and non-pCR patients. RESULTS: A total of 23,747 patients were included in the study. Factors associated with pCR included lower tumor grade, lower clinical T and N stage, higher radiation dose, and delaying surgery by more than 6-8 weeks after the end of radiation, while lack of health insurance was linked with a lower likelihood of pCR. Complete response was not associated with an increased risk of major postoperative complications. CONCLUSIONS: Several clinical, pathologic, and treatment variables can help to predict which patients are most likely to have pCR after nCRT for rectal cancer. Awareness of these variables can be valuable in counseling patients regarding prognosis and treatment options.

Role of Repeat 18F-Fluorodeoxyglucose Positron Emission Tomography Examination in Predicting Pathologic Response Following Neoadjuvant Chemoradiotherapy for Esophageal Adenocarcinoma.

IMPORTANCE: Predicting complete pathologic response (CPR) preoperatively can significantly affect surgical decision making. There are conflicting data regarding positron emission tomography computed tomography (PET CT) characteristics and the ability of PET CT to predict pathologic response following neoadjuvant chemoradiotherapy in esophageal adenocarcinoma because most existing studies that include squamous histology have limited numbers and use nonstandardized PET CT imaging. OBJECTIVE: To determine if PET CT characteristics are associated with CPR in patients undergoing trimodality treatment for esophageal adenocarcinoma. DESIGN, SETTING, AND PARTICIPANTS: A retrospective medical record review was conducted at a large tertiary cancer center from a prospectively maintained database from January 1, 2005, to December 31, 2012. Inclusion criteria were patients undergoing esophagectomy for locally advanced esophageal adenocarcinoma post-neoadjuvant chemoradiotherapy with 2 standardized PET CT studies done at our institution (pre-neoadjuvant chemoradiotherapy and post-neoadjuvant chemoradiotherapy) for review. Data collected included clinical, pathologic, imaging, and treatment characteristics. MAIN OUTCOME AND MEASURE: The primary study outcome was the association of PET CT characteristics with histologic confirmed pathologic response. RESULTS: Of the total participants, 77 patients met the inclusion criteria. Twenty-two patients (28.6%) had CPR vs 55 patients (71.4%) who had incomplete pathologic response. The 2 groups were similar in age, sex, race/ethnicity, comorbid conditions, Eastern Cooperative Oncology Group status, tumor grade, chemotherapy, and radiation regimen and days between the 2 PET CTs. The mean prestandardized uptake variable (SUV; 14.5 vs 11.2; P = .05), δ SUV (10.3 vs 5.4; P = .02), and relative δ SUV (0.6 vs 0.4; P = .02) were significantly higher in those with CPR vs incomplete pathologic response. Using the Youden Index, a δ SUV value less than 45% was predictive of residual disease with a positive predictive value of 91.7% (95% CI, 73-99; P < .05). CONCLUSIONS AND RELEVANCE: To our knowledge, this is the largest study examining the role of PET CT characteristics in esophageal adenocarcinoma for patients undergoing neoadjuvant chemoradiotherapy that demonstrates that δ SUV of less than 45% is associated with patients with residual disease but not CPR. Based on the findings from our study, the current recommendation is still surgical resection regardless of the posttherapy PET SUV in the primary tumor. However, our study highlights the ability to detect patients with residual disease and the need to critically evaluate these patients for consideration of additional therapies.

Rap1b in smooth muscle and endothelium is required for maintenance of vascular tone and normal blood pressure.

OBJECTIVE: Small GTPase Ras-related protein 1 (Rap1b) controls several basic cellular phenomena, and its deletion in mice leads to several cardiovascular defects, including impaired adhesion of blood cells and defective angiogenesis. We found that Rap1b(-/-) mice develop cardiac hypertrophy and hypertension. Therefore, we examined the function of Rap1b in regulation of blood pressure. APPROACH AND RESULTS: Rap1b(-/-) mice developed cardiac hypertrophy and elevated blood pressure, but maintained a normal heart rate. Correcting elevated blood pressure with losartan, an angiotensin II type 1 receptor antagonist, alleviated cardiac hypertrophy in Rap1b(-/-) mice, suggesting a possibility that cardiac hypertrophy develops secondary to hypertension. The indices of renal function and plasma renin activity were normal in Rap1b(-/-) mice. Ex vivo, we examined whether the effect of Rap1b deletion on smooth muscle-mediated vessel contraction and endothelium-dependent vessel dilation, 2 major mechanisms controlling basal vascular tone, was the basis for the hypertension. We found increased contractility on stimulation with a thromboxane analog or angiotensin II or phenylephrine along with increased inhibitory phosphorylation of myosin phosphatase under basal conditions consistent with elevated basal tone and the observed hypertension. Cyclic adenosine monophosphate-dependent relaxation in response to Rap1 activator, Epac, was decreased in vessels from Rap1b(-/-) mice. Defective endothelial release of dilatory nitric oxide in response to elevated blood flow leads to hypertension. We found that nitric oxide-dependent vasodilation was significantly inhibited in Rap1b-deficient vessels. CONCLUSIONS: This is the first report to indicate that Rap1b in both smooth muscle and endothelium plays a key role in maintaining blood pressure by controlling normal vascular tone.