Activation of angiotensinogen gene in cardiac myocytes by angiotensin II and mechanical stretch

Counter-regulatory RAS peptides: new therapy targets for inflammation and fibrotic diseases?

The renin-angiotensin system (RAS) is an important cascade of enzymes and peptides that regulates blood pressure, volume, and electrolytes. Within this complex system of reactions, its counter-regulatory axis has attracted attention, which has been associated with the pathophysiology of inflammatory and fibrotic diseases. This review article analyzes the impact of different components of the counter-regulatory axis of the RAS on different pathologies. Of these peptides, Angiotensin-(1-7), angiotensin-(1-9) and alamandine have been evaluated in a wide variety of in vitro and in vivo studies, where not only they counteract the actions of the classical axis, but also exhibit independent anti-inflammatory and fibrotic actions when binding to specific receptors, mainly in heart, kidney, and lung. Other functional peptides are also addressed, which despite no reports associated with inflammation and fibrosis to date were found, they could represent a potential target of study. Furthermore, the association of agonists of the counter-regulatory axis is analyzed, highlighting their contribution to the modulation of the inflammatory response counteracting the development of fibrotic events. This article shows an overview of the importance of the RAS in the resolution of inflammatory and fibrotic diseases, offering an understanding of the individual components as potential treatments.

Predictive model identifies key network regulators of cardiomyocyte mechano-signaling

Mechanical strain is a potent stimulus for growth and remodeling in cells. Although many pathways have been implicated in stretch-induced remodeling, the control structures by which signals from distinct mechano-sensors are integrated to modulate hypertrophy and gene expression in cardiomyocytes remain unclear. Here, we constructed and validated a predictive computational model of the cardiac mechano-signaling network in order to elucidate the mechanisms underlying signal integration. The model identifies calcium, actin, Ras, Raf1, PI3K, and JAK as key regulators of cardiac mechano-signaling and characterizes crosstalk logic imparting differential control of transcription by AT1R, integrins, and calcium channels. We find that while these regulators maintain mostly independent control over distinct groups of transcription factors, synergy between multiple pathways is necessary to activate all the transcription factors necessary for gene transcription and hypertrophy. We also identify a PKG-dependent mechanism by which valsartan/sacubitril, a combination drug recently approved for treating heart failure, inhibits stretch-induced hypertrophy, and predict further efficacious pairs of drug targets in the network through a network-wide combinatorial search.

Common stresses such as high blood pressure or heart attack can lead to heart failure, which afflicts over 25 million people worldwide. These stresses cause cardiomyocytes to grow and remodel, which may initially be beneficial but ultimately worsen heart function. Current heart failure drugs such as beta-blockers counteract biochemical cues prompting cardiomyocyte growth, yet mechanical cues to cardiomyocytes such as stretch are just as important in driving cardiac dysfunction. However, no pharmacological treatments have yet been approved that specifically target mechano-signaling, in part because it is not clear how cardiomyocytes integrate signals from multiple mechano-responsive sensors and pathways into their decision to grow. To address this challenge, we built a systems-level computational model that represents 125 interactions between 94 stretch-responsive signaling molecules. The model correctly predicts 134 of 172 previous independent experimental observations, and identifies the key regulators of stretch-induced cardiomyocyte remodeling. Although cardiomyocytes have many mechano-signaling pathways that function largely independently, we find that cooperation between them is necessary to cause growth and remodeling. We identify mechanisms by which a recently approved heart failure drug pair affects mechano-signaling, and we further predict additional pairs of drug targets that could be used to help reverse heart failure.

Angiotensin II receptors and peritoneal dialysis-induced peritoneal fibrosis

The vasoactive hormone angiotensin II initiates its major hemodynamic effects through interaction with AT1 receptors, a member of the class of G protein-coupled receptors. Acting through its AT1R, angiotensin II regulates blood pressure and renal salt and water balance. Recent evidence points to additional pathological influences of activation of AT1R, in particular inflammation, fibrosis and atherosclerosis. The transcription factor nuclear factor κB, a key mediator in inflammation and atherosclerosis, can be activated by angiotensin II through a mechanism that may involve arrestin-dependent AT1 receptor internalization. Peritoneal dialysis is a therapeutic modality for treating patients with end-stage kidney disease. The effectiveness of peritoneal dialysis at removing waste from the circulation is compromised over time as a consequence of peritoneal dialysis-induced peritoneal fibrosis. The non-physiological dialysis solution used in peritoneal dialysis, i.e. highly concentrated, hyperosmotic glucose, acidic pH as well as large volumes infused into the peritoneal cavity, contributes to the development of fibrosis. Numerous trials have been conducted altering certain components of the peritoneal dialysis fluid in hopes of preventing or delaying the fibrotic response with limited success. We hypothesize that structural activation of AT1R by hyperosmotic peritoneal dialysis fluid activates the internalization process and subsequent signaling through the transcription factor nuclear factor κB, resulting in the generation of pro-fibrotic/pro-inflammatory mediators producing peritoneal fibrosis.

The JAK-STAT pathway in hypertrophic stress signaling and genomic stress response

The JAK-STAT signaling pathway plays a central role in transducing stress and growth signals in the hypertrophic heart. Unlike most signal transducers, JAKs and STATs signal in a number of different ways, both within the JAK-STAT pathway and in collaboration with other signaling pathways. In this review, we discuss how IL-6 activates cells lacking IL-6 receptors through trans-signaling and examine JAK-STAT pathway interaction with GPCR-linked pathways both within and between cells. Finally, we discuss recent studies showing how the JAK-STAT pathway can intersect with a general transcriptional regulatory mechanism to effect transcription of STAT-dependent stress response genes.

Deletion of the angiotensin II type 1 receptor-associated protein enhances renal sodium reabsorption and exacerbates angiotensin II-mediated hypertension

Angiotensin II type 1 receptor (AT1R)–associated protein (ATRAP) promotes AT1R internalization along with suppression of pathological activation of tissue AT1R signaling. However, the functional significance of ATRAP in renal sodium handling and blood pressure regulation under pathological stimuli is not fully resolved. Here we show the blood pressure of mice with a gene-targeted disruption of ATRAP was comparable to that of wild-type mice at baseline. However, in ATRAP-knockout mice, angiotensin II–induced hypertension was exacerbated and the extent of positive sodium balance was increased by angiotensin II. Renal expression of the sodium-proton antiporter 3, a major sodium transporter in the proximal tubules, urinary pH, renal angiotensinogen production, and angiotensin II content was unaffected. Stimulation of the renal expression and activity of the epithelial sodium channel (ENaC), a major sodium transporter in the distal tubules, was significantly enhanced by chronic angiotensin II infusion. The circulating and urinary aldosterone levels were comparable. The blood pressure response and renal ENaC expression by aldosterone were not affected. Thus, ATRAP deficiency exacerbated angiotensin II–mediated hypertension by pathological activation of renal tubular AT1R by angiotensin II. This directly stimulates ENaC in the distal tubules and enhances sodium retention in an aldosterone-independent manner.

Angiotensin II blockade and renal protection

Current national guidelines have recommended the use of renin-angiotensin system inhibitors, including angiotensin II type 1 receptor blockers (ARBs), in preference to other antihypertensive agents for treating hypertensive patients with chronic kidney disease. However, the mechanisms underlying the renoprotective effects of ARBs are multiple and complex. Blood pressure reduction by systemic vasodilation with an ARB contributes to its beneficial effects in treating kidney disease. Furthermore, ARB-induced renal vasodilation results in an increase in renal blood flow, leading to improvement of renal ischemia and hypoxia. ARBs are also effective in reducing urinary albumin excretion through a reduction in intraglomerular pressure and the protection of glomerular endothelium and/or podocyte injuries. In addition to blocking angiotensin II-induced renal cell and tissue injuries, ARBs can decrease intrarenal angiotensin II levels by reducing proximal tubular angiotensinogen and production of collecting duct renin, as well as angiotensin II accumulation in the kidney. In this review, we will briefly summarize our current understanding of the pharmacological effects of an ARB in the kidney. We will also discuss the possible mechanisms responsible for the renoprotective effects of ARBs on type 2 diabetic nephropathy.

Augmented intrarenal and urinary angiotensinogen in hypertension and chronic kidney disease

Activated intrarenal renin-angiotensin system plays a cardinal role in the pathogenesis of hypertension and chronic kidney disease. Angiotensinogen is the only known substrate for renin, which is the rate-limiting enzyme of the renin-angiotensin system. Because the levels of angiotensinogen are close to the Michaelis-Menten constant values for renin, angiotensinogen levels as well as renin levels can control the renin-angiotensin system activity, and thus, upregulation of angiotensinogen leads to an increase in the angiotensin II levels and ultimately increases blood pressure. Recent studies using experimental animal models have documented the involvement of angiotensinogen in the intrarenal renin-angiotensin system activation and development of hypertension. Enhanced intrarenal angiotensinogen mRNA and/or protein levels were observed in experimental models of hypertension and chronic kidney disease, supporting the important roles of angiotensinogen in the development and the progression of hypertension and chronic kidney disease. Urinary excretion rates of angiotensinogen provide a specific index of the intrarenal renin-angiotensin system status in angiotensin II-infused rats. Also, a direct quantitative method has been developed recently to measure urinary angiotensinogen using human angiotensinogen enzyme-linked immunosorbent assay. These data prompted us to measure urinary angiotensinogen in patients with hypertension and chronic kidney disease, and investigate correlations with clinical parameters. This short article will focus on the role of the augmented intrarenal angiotensinogen in the pathophysiology of hypertension and chronic kidney disease. In addition, the potential of urinary angiotensinogen as a novel biomarker of the intrarenal renin-angiotensin system status in hypertension and chronic kidney disease will be also discussed.

Gene expression profiling of DEHP-treated cardiomyocytes reveals potential causes of phthalate arrhythmogenicity

BACKGROUND

Di-(2-ethylhexyl)-phthalate (DEHP) is a widely used plasticizer that imparts flexibility to polyvinyl chloride. We have recently reported that clinically relevant concentrations of DEHP can affect electrical coupling between cardiac myocytes causing significant rhythm disturbances. The underlying causes for this effect are currently unknown.

OBJECTIVES

To use data on global mRNA expression as a tool to reveal possible pathways leading to arrhythmogenic effects of DEHP.

METHODS

Rat neonatal cardiomyocytes were treated with 50 μg/mL DEHP for 72 h. Extracted RNA samples were hybridized onto Affymetrix Rat Gene 1.0 ST arrays. The mRNA expression of a subset of genes was validated by qRT-PCR. In a second set of experiments, cells were treated in a concentration dependent manner to identify genes affected by low DEHP concentrations.

RESULTS

DEHP exposure is associated with global changes in mRNA expression, with differentially expressed genes overrepresented in 47 Gene Ontology categories. Modified expression was detected for genes associated with cell electrical activity, calcium handling, adhesion and microtubular transport. For a number of key proteins, including kinesin, TGFβ2, α-tubulin, and α1 & β1 integrins, changes in mRNA levels were confirmed on the level of the protein expression. A number of genes associated with cell adhesion and electrical activity were identified as early DEHP targets as they were affected by concentrations as low as 1 μg/mL.

CONCLUSIONS

Exposure of neonatal rat cardiomyocytes to clinically relevant DEHP concentrations leads to global changes in mRNA expression. These changes help to explain the arrhythmogenic effects of phthalates on these cells.

The role of local and systemic renin angiotensin system activation in a genetic model of sympathetic hyperactivity-induced heart failure in mice

Sympathetic hyperactivity (SH) and renin angiotensin system (RAS) activation are commonly associated with heart failure (HF), even though the relative contribution of these factors to the cardiac derangement is less understood. The role of SH on RAS components and its consequences for the HF were investigated in mice lacking α2Aand α2Cadrenoceptor knockout (α2A/α2CARKO) that present SH with evidence of HF by 7 mo of age. Cardiac and systemic RAS components and plasma norepinephrine (PN) levels were evaluated in male adult mice at 3 and 7 mo of age. In addition, cardiac morphometric analysis, collagen content, exercise tolerance, and hemodynamic assessments were made. At 3 mo, α2A/α2CARKO mice showed no signs of HF, while displaying elevated PN, activation of local and systemic RAS components, and increased cardiomyocyte width (16%) compared with wild-type mice (WT). In contrast, at 7 mo, α2A/α2CARKO mice presented clear signs of HF accompanied only by cardiac activation of angiotensinogen and ANG II levels and increased collagen content (twofold). Consistent with this local activation of RAS, 8 wk of ANG II AT1receptor blocker treatment restored cardiac structure and function comparable to the WT. Collectively, these data provide direct evidence that cardiac RAS activation plays a major role underlying the structural and functional abnormalities associated with a genetic SH-induced HF in mice.

Kidney-specific enhancement of ANG II stimulates endogenous intrarenal angiotensinogen in gene-targeted mice

This study was performed in transgenic mice to test the hypothesis that the selective intrarenal overproduction of ANG II increases intrarenal mouse (m) angiotensinogen (AGT) expression. We used the following three groups: 1) single transgenic mice (group A, n = 14) expressing human (h) AGT only in the kidney, 2) double-transgenic mice (group D, n = 13) expressing human renin systemically in addition to hAGT only in the kidney, and 3) wild-type (group W, n = 12) mice. Exogenous hAGT protein is inactive in group A because endogenous mouse renin cannot cleave hAGT to ANG I because of a high species specificity. All mice were monitored from 12 to 18 wk of age. Systolic blood pressure progressively increased from 116 +/- 5 mmHg (12 wk) to 140 +/- 7 (18 wk) in group D. This increase was not observed in groups A or W. Intrarenal hAGT levels were similar in groups A and D; however, hAGT was not detectable in kidneys of group W. Kidney ANG II levels were increased in group D (216 +/- 43 fmol/g) compared with groups A (117 +/- 16) and W (118 +/- 17). However, plasma ANG II concentrations were similar among the three groups. Endogenous renal mAGT mRNA was increased significantly in group D (1.46 +/- 0.19, ratio) compared with groups A (0.97 +/- 0.12) and W (1.00 +/- 0.08). Endogenous renal mAGT protein was also significantly increased in group D compared with groups A and W. Interstitial collagen-positive area, interstitial macrophage/monocyte infiltration, and afferent arteriolar wall thickness were increased significantly in group D compared with groups A and W. These data indicate for the first time that the selective stimulation of intrarenal production of ANG II from hAGT augments endogenous intrarenal mAGT mRNA and protein expression.

High-glucose-induced regulation of intracellular ANG II synthesis and nuclear redistribution in cardiac myocytes

The prevailing paradigm is that cardiac ANG II is synthesized in the extracellular space from components of the circulating and/or local renin-angiotensin system. The recent discovery of intracrine effects of ANG II led us to determine whether ANG II is synthesized intracellularly in neonatal rat ventricular myocytes (NRVM). NRVM, incubated in serum-free medium, were exposed to isoproterenol or high glucose in the absence or presence of candesartan, which was used to prevent angiotensin type 1 (AT1) receptor-mediated internalization of ANG II. ANG II was measured in cell lysates and the culture medium, which represented intra- and extracellularly synthesized ANG II, respectively. Isoproterenol increased ANG II concentration in cell lysates and medium of NRVM in the absence or presence of candesartan. High glucose markedly increased ANG II synthesis only in cell lysates in the absence and presence of candesartan. Western analysis showed increased intracellular levels of angiotensinogen, renin, and chymase in high-glucose-exposed cells. Confocal immunofluorocytometry confirmed the presence of ANG II in the cytoplasm and nucleus of high-glucose-exposed NRVM and along the actin filaments in isoproterenol-exposed cells. ANG II synthesis was dependent on renin and chymase in high-glucose-exposed cells and on renin and angiotensin-converting enzyme in isoproterenol-exposed cells. In summary, the site of ANG II synthesis, intracellular localization, and the synthetic pathway in NRVM are stimulus dependent. Significantly, NRVM synthesized and retained ANG II intracellularly, which redistributed to the nucleus under high-glucose conditions, suggesting a role for an intracrine mechanism in diabetic conditions.

Enhanced intrarenal angiotensinogen contributes to early renal injury in spontaneously hypertensive rats

This study was performed to determine whether augmented intrarenal angiotensinogen may contribute to the enhanced renal angiotensin II (Ang II) and associated tissue injury in spontaneously hypertensive rats (SHR). SHR and Wistar-Kyoto rats (WKY) were maintained on a normal diet and killed at either 7 or 14 wk of age. Two groups of SHR received either an Ang II type 1 receptor blocker (ARB; olmesartan, 5 mg/d) or a triple therapy (hydralazine 7.5 mg/d, reserpine 0.15 mg/d, and hydrochlorothiazide 3 mg/d [HRH]) during weeks 7 through 14. Systolic BP and renal Ang II were significantly increased in SHR-14 (n = 8) compared with WKY-7, WKY-14, and SHR-7 (n = 8 each), and ARB treatment prevented these increases (n = 8). However, whereas HRH treatment prevented the development of hypertension in SHR, this combination therapy failed to decrease renal Ang II (n = 8). With the use of urine samples or fixed renal sections, renal injuries in rats were quantified in a semiautomated manner by the following six parameters: (1) urinary excretion rate of total protein, (2) glomerular sclerosis, (3) interstitial expansion, (4) and (5) numbers of monocytes/macrophages in interstitium or glomeruli, and (6) arterial proliferation. Angiotensinogen mRNA and protein levels in kidney cortex, measured by real-time reverse transcriptase-PCR and Western blot analysis, respectively, and all six parameters of renal damage were changed in parallel, and ARB treatment also prevented these increases. However, HRH treatment failed to prevent these increases. These results indicate that SHR have enhanced intrarenal angiotensinogen production that contributes to increased Ang II levels leading to the development of hypertension and renal injury in this strain.

The intrarenal renin-angiotensin system in autosomal dominant polycystic kidney disease

Hypertension is a common complication of autosomal dominant polycystic kidney disease (ADPKD), often present before the onset of renal failure. A role for the renin-angiotensin system (RAS) has been proposed, but studies of systemic RAS have failed to show a correlation between plasma renin activity and blood pressure in ADPKD. Ectopic renin expression by cyst epithelium was first reported in 1992 (Torres VE, Donovan KA, Sicli G, Holley KE, Thibodeau ST, Carretero OA, Inagami T, McAteer JA, and Johnson CM. Kidney Int 42: 364-373, 1992). It is not known, however, whether other RAS components are also expressed by cysts in ADPKD. We show that, in addition to renin, angiotensinogen (AGT) is produced by some cysts and dilated tubules. Angiotensin-converting enzyme, ANG II type 1 receptor, and ANG II peptide are also present within cysts and in many tubules; and some cyst fluids contain high ANG II concentrations. Additionally, cyst-derived cells in culture continue to express the components of the RAS at both the protein and mRNA levels. We further show that renin is expressed primarily in cysts of distal tubule origin and in cyst-derived cells with distal tubule characteristics, whereas AGT is expressed primarily in cysts of proximal tubule origin and in cyst-derived cells with proximal tubule characteristics. Renin production by cyst-derived cells appears to be regulated by extracellular Na+ concentration. Based on these observations, we propose a model of an autocrine/paracrine RAS in polycystic kidney disease, whereby overactivity of the intrarenal system results in sustained increases in intratubular ANG II concentrations.

Release of preformed Ang II from myocytes mediates angiotensinogen and ET-1 gene overexpression in vivo via AT1 receptor

The role of angiotensin II in pressure overload is still debated because notwithstanding its effects on myocyte contractility angiotensin II is not an obligatory factor for the development of hypertrophy. To define the role of angiotensin II in acute pressure overload we studied the effects of AT1 blockade (valsartan 80mg per day) on myocardial contractility, cardiac growth factor gene expression, and myocardial hypertrophy in aortic banded (60mmHg) pigs. Acute pressure overload caused an abrupt reduction of myocardial contractility, measured by the end-systolic stiffness constant, and a sharp increase in end-systolic stress which rapidly normalized (within 12h) in the placebo group. In AT1-blocked animals end-systolic stiffness constant remained significantly depressed up to 24h and end-systolic stress was still elevated up to 48h (both P<0.05 vs placebo). In both groups confocal microscopy revealed that granular staining of angiotensin II in cardiomyocyte cytoplasm disappeared after 30min of pressure overload. AT1 blockade abolished following cardiac overexpression of angiotensinogen and endothelin-1 genes as shown in RT-PCR studies and the consequent angiotensin II and endothelin-1 release in the coronary circulation. Conversely, insulin-like growth factor-I and ACE mRNA overexpression, as well as the onset of left ventricular mass increase, were not significantly affected by AT1 blockade.

IN CONCLUSION

(1) mechanical stress releases preformed angiotensin II from myocyte in vivo; (2) the AT1 blockade abolishes cardiac angiotensin II and endothelin-1 production with delayed recovery of myocardial contractility; whereas (3) the overexpression of insulin-like growth factor-I gene and the development of myocardial hypertrophy are not angiotensin II-mediated effects.

Enhancement of angiotensinogen expression in angiotensin II-dependent hypertension

Chronic infusion of angiotensin (Ang) II leads to the development of hypertension and enhances intrarenal Ang II content to levels greater than can be explained from the circulating concentrations of the peptide. We previously reported that renal angiotensinogen (Ao) mRNA is enhanced in Ang II-dependent hypertension and may contribute to augmented intrarenal Ang II levels, but the Ao protein levels were not significantly increased. Because a high-salt diet (H/S) has been shown to suppress renal expression of Ao mRNA, we examined the effects of chronic Ang II infusion on kidney and liver Ao mRNA and protein levels in male Sprague-Dawley rats (n=12) maintained on an 8% salt diet. Ang II was administered via osmotic minipumps (40 ng/min) to 1 group (n=6) while the remaining rats were sham-operated. A H/S diet alone did not alter systolic blood pressure in sham animals (109+/-6 mm Hg at day 12); however, Ang II infusions to the H/S rats significantly increased systolic blood pressure (167+/-7 at day 12) and intrarenal Ang II content (459+/-107 fmol/g versus 270+/-42) despite a marked suppression of plasma renin activity (0.9+/-0.2 ng Ang I. mL(-1). h(-1) versus 2.8+/-1.3). Ang II infusions significantly increased kidney Ao mRNA compared with the H/S diet alone by 1.9+/-0.1-fold. Western blot analysis of kidney protein extracts showed that the Ang II-infused rats had increased kidney Ao protein levels compared with the H/S diet alone (1.9+/-0.1-fold). Liver Ao mRNA and protein and plasma Ao protein were also significantly increased by Ang II infusions. These data demonstrate the effects of Ang II infusion to stimulate Ao mRNA and protein. Thus, the augmented intrarenal Ang II in Ang II-dependent hypertension may result, in part, by a positive amplification mechanism to activate renal expression of AO:

Cyclic stretch and hypertension induce retinal expression of vascular endothelial growth factor and vascular endothelial growth factor receptor-2: potential mechanisms for exacerbation of diabetic retinopathy by hypertension

Systemic hypertension exacerbates diabetic retinopathy and other coexisting ocular disorders through mechanisms that remain largely unknown. Increased vascular permeability and intraocular neovascularization characterize these conditions and are complications primarily mediated by vascular endothelial growth factor (VEGF). Because systemic hypertension increases vascular stretch, we evaluated the expression of VEGF, VEGF-R2 (kinase insert domain-containing receptor [KDR]), and VEGF-R1 (fms-like tyrosine kinase [Flt]) in bovine retinal endothelial cells (BRECs) undergoing clinically relevant cyclic stretch and in spontaneously hypertensive rat (SHR) retina. A single exposure to 20% symmetric static stretch increased KDR mRNA expression 3.9 +/- 1.1-fold after 3 h (P = 0.002), with a gradual return to baseline within 9 h. In contrast, BRECs exposed to cardiac-profile cyclic stretch at 60 cpm continuously accumulated KDR mRNA in a transcriptionally mediated, time-dependent and stretch-magnitude-dependent manner. Exposure to 9% cyclic stretch increased KDR mRNA expression 8.7 +/- 2.9-fold (P = 0.011) after 9 h and KDR protein concentration 1.8 +/- 0.3-fold (P = 0.005) after 12 h. Stretched-induced VEGF responses were similar. Scatchard binding analysis demonstrated a 180 +/- 40% (P = 0.032) increase in high-affinity VEGF receptor number with no change in affinity. Cyclic stretch increased basal thymidine uptake 60 +/- 10% (P < 0.001) and VEGF-stimulated thymidine uptake by 2.6 +/- 0.2-fold (P = 0.005). VEGF-NAb reduced cyclic stretch-induced thymidine uptake by 65%. Stretched-induced KDR expression was not inhibited by AT1 receptor blockade using candesartan. Hypertension increased retinal KDR expression 67 +/- 42% (P < 0.05) in SHR rats compared with normotensive WKY control animals. When hypertension was reduced using captopril or candesartan, retinal KDR expression returned to baseline levels. VEGF reacted similarly, but Flt expression did not change. These data suggest a novel molecular mechanism that would account for the exacerbation of diabetic retinopathy by concomitant hypertension, and may partially explain the principal clinical manifestations of hypertensive retinopathy itself. Furthermore, these data imply that anti-VEGF therapies may prove therapeutically effective for hypertensive retinopathy and/or ameliorating the deleterious effects of coexistent hypertension on VEGF-associated disorders such as diabetic retinopathy.