Th1 inflammatory response with altered expression of profibrotic and vasoactive mediators in AT1A and AT1B double-knockout mice

Diverse biological functions of the renin-angiotensin system

The renin-angiotensin system (RAS) has been widely known as a circulating endocrine system involved in the control of blood pressure. However, components of RAS have been found to be localized in rather unexpected sites in the body including the kidneys, brain, bone marrow, immune cells, and reproductive system. These discoveries have led to steady, growing evidence of the existence of independent tissue RAS specific to several parts of the body. It is important to understand how RAS regulates these systems for a variety of reasons: It gives a better overall picture of human physiology, helps to understand and mitigate the unintended consequences of RAS-inhibiting or activating drugs, and sets the stage for potential new therapies for a variety of ailments. This review fulfills the need for an updated overview of knowledge about local tissue RAS in several bodily systems, including their components, functions, and medical implications.

Effect of N-Acetyl Cysteine on Renal Interstitial Fibrosis in Mice

This study examined the effect of N-acetyl cysteine (NAC), a reactive oxygen species (ROS) inhibitor, on renal interstitial fibrosis induced by unilateral ureteral obstruction (UUO) in mice. UUO led to a significant increase in the fibrotic area of obstructed kidneys, which was attenuated by NAC (84.8 mg/kg/d) in the drinking water. Renal expression of type III collagen and tumor necrosis factor (TNF)-α mRNAs was elevated in UUO mice and inhibited by NAC. Extracellular signal-regulated kinase (ERK1/2) phosphorylation was significantly elevated by UUO, and NAC significantly attenuated the elevation. UUO inhibited the activity of glutathione peroxidase, while NAC restored its activity. Together, the results of this study suggest that renal interstitial fibrosis induced by UUO was ameliorated by NAC via several mechanisms including increased glutathione peroxidase activity, reduced phosphorylation of ERK1/2, and reduced expression of TNF-α and type III collagen mRNAs.

Apparently normal kidney development in mice with conditional disruption of ANG II-AT1 receptor genes in FoxD1-positive stroma cell precursors

An intact renin-angiotensin system involving ANG II type 1 (AT₁) receptors is crucial for normal kidney development. It is still unclear in which cell types AT₁ receptor signaling is required for normal kidney development, maturation, and function. Because all kidney cells deriving from stroma progenitor cells express AT₁ receptors and because stromal cells fundamentally influence nephrogenesis and tubular maturation, we investigated the relevance of AT₁ receptors in stromal progenitors and their descendants for renal development and function. For this aim, we generated and analyzed mice with conditional deletion of AT_1A receptor in the FoxD1 cell lineage in combination with global disruption of the AT_1B receptor gene. These FoxD1-AT1ko mice developed normally. Their kidneys showed neither structural nor functional abnormalities compared with wild-type mice, whereas in isolated perfused FoxD1-AT1ko kidneys, the vasoconstrictor and renin inhibitory effects of ANG II were absent. In vivo, however, plasma renin concentration and renal renin expression were normal in FoxD1-AT1ko mice, as were blood pressure and glomerular filtration rate. These findings suggest that a strong reduction of AT₁ receptors in renal stromal progenitors and their descendants does not disturb normal kidney development.

Oxidative stress in hypertension: role of the kidney

SIGNIFICANCE

Renal oxidative stress can be a cause, a consequence, or more often a potentiating factor for hypertension. Increased reactive oxygen species (ROS) in the kidney have been reported in multiple models of hypertension and related to renal vasoconstriction and alterations of renal function. Nicotinamide adenine dinucleotide phosphate oxidase is the central source of ROS in the hypertensive kidney, but a defective antioxidant system also can contribute.

RECENT ADVANCES

Superoxide has been identified as the principal ROS implicated for vascular and tubular dysfunction, but hydrogen peroxide (H2O2) has been implicated in diminishing preglomerular vascular reactivity, and promoting medullary blood flow and pressure natriuresis in hypertensive animals.

CRITICAL ISSUES AND FUTURE DIRECTIONS

Increased renal ROS have been implicated in renal vasoconstriction, renin release, activation of renal afferent nerves, augmented contraction, and myogenic responses of afferent arterioles, enhanced tubuloglomerular feedback, dysfunction of glomerular cells, and proteinuria. Inhibition of ROS with antioxidants, superoxide dismutase mimetics, or blockers of the renin-angiotensin-aldosterone system or genetic deletion of one of the components of the signaling cascade often attenuates or delays the onset of hypertension and preserves the renal structure and function. Novel approaches are required to dampen the renal oxidative stress pathways to reduced O2(-•) rather than H2O2 selectivity and/or to enhance the endogenous antioxidant pathways to susceptible subjects to prevent the development and renal-damaging effects of hypertension.

Amelioration of cisplatin-induced mouse renal lesions by a cyclooxygenase (COX)-2 selective inhibitor

In this study, we investigated the effects of the cyclooxygenase (COX)-2 selective inhibitor, meloxicam, on cisplatin-induced inflammation, oxidative stress and renal lesions in BALB/c mice. A single cisplatin injection (13 mg/kg, i.p.) significantly increased plasma creatinine, blood urea nitrogen and urinary glucose accompanied by a concomitant increase in COX-2 mRNA and COX-2 protein levels. These changes in renal lesion parameters were diminished by simultaneous treatment of meloxicam (0.7 mg/kg/day in drinking water). The expression of oxidative stress markers, p47(phox), p67(phox), hemoxygenase-1 (HO-1), nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 2 (NOX2) and 4-hydroxy-2-nonenal (4-HNE)-modified protein were increased with cisplatin injection. Simultaneous treatment of meloxicam with cisplatin significantly inhibited the increase in p47(phox), HO-1 and 4-HNE-modified protein. The phosphorylation of extracellular regulated kinase (ERK) and c-jun-N-terminal kinase (JNK) were increased with cisplatin injection, but these changes were inhibited by meloxicam. Moreover, concomitant meloxicam treatment also prevented the cisplatin-induced infiltration of macrophages to the tubulointerstitial area. These results suggest that meloxicam can ameliorate cisplatin-induced mouse renal lesions, potentially through the inhibition of inflammatory and oxidative stress responses.

Calpain inhibition attenuates angiotensin II-induced abdominal aortic aneurysms and atherosclerosis in low-density lipoprotein receptor-deficient mice

Chronic infusion of angiotensin II (AngII) augments atherosclerosis and abdominal aortic aneurysm (AAA) formation in hypercholesterolemic mice. AngII-induced AAAs are associated with medial macrophage accumulation and matrix metalloproteinase (MMP) activation. Inhibition of calpain, a calcium-activated neutral cysteine protease, by overexpression of its endogenous inhibitor, calpastatin, attenuates AngII-induced leukocyte infiltration, perivascular inflammation, and MMP activation in mice. The purpose of this study was to define whether pharmacological inhibition of calpain influences AngII-induced AAAs in hypercholesterolemic mice. Male low-density lipoprotein receptor-/- mice were fed a fat-enriched diet and administered with either vehicle or a calpain-specific inhibitor, BDA-410 (30 mg/kg per day) for 5 weeks. After 1 week of feeding, mice were infused with AngII (1000 ng/kg per minute) for 4 weeks. AngII-infusion profoundly increased aortic calpain protein and activity. BDA-410 administration had no effect on plasma cholesterol concentrations or AngII-increased systolic blood pressure. Calpain inhibition significantly attenuated AngII-induced AAA formation and atherosclerosis development. BDA-410 administration attenuated activation of MMP12, proinflammatory cytokines (IL-6, monocyte chemoattractant protein-1), and macrophage infiltration into the aorta. BDA-410 administration significantly attenuated thioglycolate-elicited macrophage accumulation in the peritoneal cavity. We conclude that calpain inhibition using BDA-410 attenuated AngII-induced AAA formation and atherosclerosis development in low-density lipoprotein receptor-/- mice.

Synthesis and secretion of renin in mice with induced genetic mutations

The juxtaglomerular (JG) cell product renin is rate limiting in the generation of the bioactive octapeptide angiotensin II. Rates of synthesis and secretion of the aspartyl protease renin by JG cells are controlled by multiple afferent and efferent pathways originating in the CNS, cardiovascular system, and kidneys, and making critical contributions to the maintenance of extracellular fluid volume and arterial blood pressure. Since both excesses and deficits of angiotensin II have deleterious effects, it is not surprising that control of renin is secured by a complex system of feedforward and feedback relationships. Mice with genetic alterations have contributed to a better understanding of the networks controlling renin synthesis and secretion. Essential input for the setting of basal renin generation rates is provided by β-adrenergic receptors acting through cyclic adenosine monophosphate, the primary intracellular activation mechanism for renin mRNA generation. Other major control mechanisms include COX-2 and nNOS affecting renin through PGE2, PGI2, and nitric oxide. Angiotensin II provides strong negative feedback inhibition of renin synthesis, largely an indirect effect mediated by baroreceptor and macula densa inputs. Adenosine appears to be a dominant factor in the inhibitory arms of the baroreceptor and macula densa mechanisms. Targeted gene mutations have also shed light on a number of novel aspects related to renin processing and the regulation of renin synthesis and secretion.

Gene expression profiles linked to AT1 angiotensin receptors in the kidney

To characterize gene expression networks linked to AT(1) angiotensin receptors in the kidney, we carried out genome-wide transcriptional analysis of RNA from kidneys of wild-type (WT) and AT(1A) receptor-deficient mice (KOs) at baseline and after 2 days of angiotensin II infusion (1,000 ng·kg(-1)·min(-1)). At baseline, 405 genes were differentially expressed (>1.5×) between WT and KO kidneys. Of these, >80% were upregulated in the KO group including genes involved in inflammation, oxidative stress, and cell proliferation. After 2 days of angiotensin II infusion in WT mice, expression of ≈805 genes was altered (18% upregulated, 82% repressed). Genes in metabolism and ion transport pathways were upregulated while there was attenuated expression of genes protective against oxidative stress including glutathione synthetase and mitochondrial superoxide dismutase 2. Angiotensin II infusion had little effect on blood pressure in KOs. Nonetheless, expression of >250 genes was altered in kidneys from KO mice during angiotensin II infusion; 14% were upregulated, while 86% were repressed including genes involved in immune responses, angiogenesis, and glutathione metabolism. Between WT and KO kidneys during angiotensin II infusion, 728 genes were differentially expressed; 10% were increased and 90% were decreased in the WT group. Differentially regulated pathways included those involved in ion transport, immune responses, metabolism, apoptosis, cell proliferation, and oxidative stress. This genome-wide assessment should facilitate identification of critical distal pathways linked to blood pressure regulation.

Renal failure in mice with Gsalpha deletion in juxtaglomerular cells

BACKGROUND

Mice with deletion of Gsalpha in renin-producing cells (RC/FF mice) have been shown to have greatly reduced renin production and lack of responsiveness of renin secretion to acute stimuli. In addition, young RC/FF mice are hypotensive and have a vasopressin-resistant concentrating defect. In the present study we have determined the long-term effect on renal function, blood pressure, and renal pathology in this low renin and diuretic mouse model.

METHODS AND RESULTS

Urine osmolarity of RC/FF mice was decreased in all age groups. GFR measured at 7, 14 and 20 weeks of age declined progressively. Single nephron GFR similarly declined while fractional proximal fluid absorption was maintained. Expression levels of extracellular matrix proteins (collagen I, IV and fibronectin) and alpha-smooth muscle actin were increased in kidneys of RC/FF mice at 20 weeks, and this was accompanied by focal segmental glomerulosclerosis and periglomerular interstitial fibrosis. RC/FF mice showed a progressive reduction of body weight, an increase in urine albumin excretion, and an increase of blood pressure with aging.

CONCLUSION

A chronic reduction of renin production in mice may be a risk factor in its own right, and does not protect renal function against the profibrotic influence of a chronically elevated urine flow.

Cardiovascular phenotype of mice lacking all three subtypes of angiotensin II receptors

Angiotensin II activates two distinct receptors, the angiotensin II receptors type 1 (AT(1)) and type 2 (AT(2)). In rodents, two AT(1) subtypes were identified (AT(1a) and AT(1b)). To determine receptor-specific functions and possible angiotensin II effects independent of its three known receptors we generated mice deficient in either one of the angiotensin II receptors, in two, or in all three (triple knockouts). Triple knockouts were vital and fertile, but survival was impaired. Hypotension and renal histological abnormalities in triple knockouts were comparable to those in mice lacking both AT(1) subtypes. All combinations lacking AT(1a) were distinguished by reduced heart rate. AT(1a) deletion impaired the in vivo pressor response to angiotensin II bolus injection, whereas deficiency for AT(1b) and/or AT(2) had no effect. However, the additional lack of AT(1b) in AT(1a)-deficient mice further impaired the vasoconstrictive capacity of angiotensin II. Although general vasoconstrictor properties were not changed, angiotensin II failed to alter blood pressure in triple knockouts, indicating that there are no other receptors involved in direct angiotensin II pressor effects. Our data identify mice deficient in all three angiotensin II receptors as an ideal tool to better understand the structure and function of the renin-angiotensin system and to search for angiotensin II effects independent of AT(1) and AT(2).

Augmented renal vascular nNOS and renin protein expression in angiotensin type 1 receptor null mice

The present study was performed to determine the influence of absence of angiotensin type 1A (AT(1A)) and/or AT(1B) receptor feedback regulation of kidney neuronal nitric oxide synthase (nNOS) and renin protein expression. Kidneys were harvested from wild-type (WT), AT(1A)(-/-), AT(1B)(-/-), and AT(1A)(-/-)AT(1B)(-/-) mice and immunostained for nNOS and renin protein localization. AT(1A)(-/-) and AT(1A)(-/-)AT(1B)(-/-) kidneys demonstrated an increase in the percentage of glomeruli with nNOS-positive afferent and interlobular arterioles compared with WT mice. Density of vascular nNOS immunostaining was 20-fold higher in kidneys of AT(1A)(-/-) and AT(1A)(-/-)AT(1B)(-/-) compared with WT mice. Density of macula densa nNOS immunostaining was 7-fold higher in AT(1A)(-/-)AT(1B)(-/-) than in WT mice. Percent of glomeruli positive for juxtaglomerular (JG) cell renin was 3-fold higher, whereas the density of JG cell renin immunostaining was 15-fold higher in kidneys of AT(1A)(-/-) and AT(1A)(-/-)AT(1B)(-/-) compared with WT mice. Kidneys of AT(1A)(-/-) and AT(1A)(-/-)AT(1B)(-/-) mice displayed recruitment of renin protein expression along afferent and interlobular arterioles. Absence of AT(1) receptor signaling resulted in enhanced nNOS protein expression in both microvascular and tubular structures. Enhanced NO generation may contribute to the reduced renal vascular tone and blood pressure observed with blockade of the renin-angiotensin system.

Angiotensin AT1 receptor antagonists exert anti-inflammatory effects in spontaneously hypertensive rats

BACKGROUND AND PURPOSE

Although the main therapeutic effect of angiotensin AT1 receptor antagonists is to decrease blood pressure, they also exert anti-inflammatory effects in the cardiovascular system. However, the underlying mechanisms remain unclear. We investigated the inhibitory effect of AT1 antagonists on the chemokine monocyte chemoattractant protein 1 (MCP-1) and its receptor C-C chemokine receptor 2 (CCR2) in rat monocytes and aortas.

EXPERIMENTAL APPROACH

Spontaneous hypertensive rats (SHRs) were treated with the AT1 antagonists losartan or telmisartan for 4 weeks, and Wistar-Kyoto rats (WKYs) were used as normotensive controls. Systolic arterial pressure was measured, and the number of macrophages in the aortic vessel wall was assessed by anti-ED-1 antibody immunolabelling.

KEY RESULTS

Compared with WKYs, SHRs showed significantly increased ED-1 positive macrophages in the aortic wall, which were decreased after high doses of losartan or telmisartan. Low doses of losartan did not improve blood pressure significantly as did the high doses, but markedly decreased macrophage infiltration in the vessel wall. AT1 antagonists, particularly at high doses, improved aortic remodeling in SHR. At the molecular level, AT1 antagonists attenuated the expression of MCP-1 and CCR2 in the aorta and peripheral blood monocytes and lowered the serum level of MCP-1. In addition, Western blotting showed that AT1 antagonists inhibited the phosphorylation of Akt in mouse monocytes.

CONCLUSIONS AND IMPLICATIONS

AT1 antagonism inhibited vessel wall inflammation and inhibition of PI3K/Akt may be involved in the modulation of the MCP-1/CCR2 system by AT1 antagonists in SHRs.

Compromised renal microvascular reactivity of angiotensin type 1 double null mice

Angiotensin type 1A (AT(1A)) and 1B (AT(1B)) receptor deletion (AT1DKO) results in renal microvascular disease, tubulointerstitial injury, and reduced blood pressure. To test the hypothesis that renal preglomerular responses to angiotensin (ANG) II are mediated by AT(1A) and AT(1B) receptors, experiments were performed in AT1DKO mice using the in vitro blood perfused juxtamedullary nephron technique. Kidneys were harvested from AT1DKO and wild-type (WT) mice and bathed with ANG II (1-100 nM), norepinephrine (NE; 100-1,000 nM), or acetylcholine (ACh; 10 microM). Baseline diameters of afferent (19.5 +/- 0.7 and 13.9 +/- 0.7 microm, n = 17 and 16) and efferent (15.5 +/- 2.1 and 10.8 +/- 1.0 microm, n = 4 and 7) arterioles of AT1DKO were significantly larger than WT. Afferent and efferent arteriolar responses to ANG II, 100, and 300 nM NE were absent in AT1DKO; although significant constriction to 1 microM NE was observed (-17 +/- 5 and -23 +/- 6%, respectively). Afferent arterioles of WT mice dilated significantly in response to ACh (15.1 +/- 0.6 to 17.0 +/- 1.2 microm, n = 6); however, arterioles from AT1DKO tended to contract (19.9 +/- 1.2 to 17.8 +/- 1.6 microm; n = 6, P = 0.06). In summary, loss of ANG II-induced contraction, reduced vasoconstriction to NE, and endothelial cell dysfunction contribute to the renal vascular phenotype of AT1DKO mice. We conclude that ANG II signaling via the AT(1) receptor plays a pivotal role in basal renal microvascular tone and effectiveness to respond to vasoconstrictor and vasodilator agonists.

Antihypertensive therapy induces compartment-specific chemokine expression and a Th1 immune response in the clipped kidney of Goldblatt hypertensive rats

The present study examined the pathogenesis of interstitial inflammation and fibrosis in antihypertensively treated rats with two-kidney, one-clip hypertension. Hypertensive rats were randomized into four groups: no treatment and moderate, intermediate, and intensified lowering of blood pressure with increasing doses of a vasopeptidase inhibitor for 6 wk. The vasopeptidase inhibitor dose dependently lowered blood pressure. The tubulointerstitial damage was accompanied by a diffuse infiltration of mononuclear cells and circumscript mononuclear inflammatory cell cluster formation consisting mainly of T cells and to a lesser degree of macrophages and B cells. Real-time PCR analyses showed a dose-dependent induction of MCP-1 and the Th1-type chemokines IP10 and Mig as well as their receptor CXCR3 and the Th1 cytokine IFN-γ. In situ hybridization and laser microdissection revealed a strong expression of these Th1-associated transcripts in the clusters and, in the case of MCP-1, also diffusely in the interstitium. The inflammation was accompanied by the appearance of myofibroblasts and synthesis of the fibrogenic factor plasminogen activator inhibitor-1 as well as the collagenase matrix metalloproteinase-2, leading to collagen I upregulation and interstitial scarring. No inflammation or fibrosis was found in normotensive rats treated with the vasopeptidase inhibitor. The renal injury in the clipped kidney is accompanied by compartment-specific chemokine expression and cell cluster formation of Th1 specificity associated with upregulation of fibrogenic proteins and matrix metalloproteinases. These findings suggest that the Th1 chemokines IP10 and Mig as well as their receptor CXCR3 are potential targets for therapeutic interventions in ischemic nephropathy.

Evidence for nitrite reductase activity in intact mouse Leydig tumor cells

Nitric oxide (NO) supposedly derived via L-arginine-NO synthase (NOS) pathway has been implicated in inhibiting steroidogenesis by binding the heme moiety of steroidogenic enzymes. Previously, nitrite, and to a lesser extent nitrate ions inhibited steroidogenesis via NO by hitherto unknown reduction mechanism. Recently, a putative mammalian nitrite reductase activity ascribed to complex III of mitochondrial respiratory chain complexes (MRCC) has been reported, where MRCC inhibitors reduced NO production from nitrite variably. We thus studied the effects of MRCC inhibitors on testosterone production in mouse Leydig tumor cells (MLTC-1) without (basal) or with human chorionic gonadotropin (hCG) stimulation. In stimulated MLTC-1, MRCC inhibitors decreased testosterone production, order being: complex III (antimycin A and myxothiazol) > complex I (rotenone) > complex II (thenoyltrifluoroacetone), while cAMP production increased inversely. In unstimulated MLTC-1, MRCC inhibitors in same order, increased basal testosterone production, which correlated inversely with the percentage inhibition of NO production, with one exception; while antimycin A did not inhibit NO production in the nitrite reductase study mentioned above, it increased basal testosterone production in the present study. While MLTC-1 expressed mRNA for endothelial and neuronal, but not inducible NOS, various stimulators and inhibitors of L-arginine-NOS pathway had no effect on basal testosterone production in MLTC-1 or fresh Balb/c Leydig cells. Moreover, hCG increased nitrate uptake into MLTC-1, which suggests the gonadotropin aids nitrite and nitrate ions in their steroidogenesis inhibitory activity. In conclusion, this study supports the existence of a surrogate mammalian nitrite reductase and the dormancy of L-arginine-NOS pathway in MLTC-1.

Rapid pathogenesis induced by a vesicular stomatitis virus matrix protein mutant: viral pathogenesis is linked to induction of tumor necrosis factor alpha

Vesicular stomatitis virus (VSV) matrix (M) protein blocks host mRNA export from the nucleus and thereby inhibits interferon induction in infected cells. M mutants with mutations of methionine 51 (M51) lack this shutoff function. We examined pathogenesis of a VSV M mutant with a deletion of M51 (VSVDeltaM51) after intranasal infection of BALB/c mice and found an unexpected phenotype. Mice that received VSVDeltaM51 experienced a more rapid but overall less severe weight loss than mice that received the recombinant wild-type VSV (rwtVSV). Rapid weight loss was not explained by faster initial replication because VSVDeltaM51 replication was controlled faster than rwtVSV replication in the lungs and did not spread systemically like rwtVSV. This faster control of VSVDeltaM51 correlated with a more rapid induction of interferon in the lung. Because tumor necrosis factor alpha (TNF-alpha) is associated with weight loss, we examined TNF-alpha induction in mice infected with rwtVSV or VSVDeltaM51. We found more-rapid induction of TNF-alpha by the mutant at early times after infection, while rwtVSV induced more TNF-alpha later in infection. This result suggested that TNF-alpha induction might explain both the rapid weight loss caused by the mutant and the overall greater weight loss caused by the rwtVSV. Using TNF-alpha knockout mice (C57BL/6 background), we showed that weight loss following rwtVSV infection was greatly reduced in the absence of TNF-alpha. Although the rapid weight loss caused by VSVDeltaM51 was less pronounced in C57BL/6 mice, it was eliminated in the absence of TNF-alpha. These results indicate a role for TNF-alpha in the pathogenesis of VSV.

Embryonic lethality in Dear gene-deficient mice: new player in angiogenesis

The dual endothelin-1/angiotensin II receptor (Dear) binds endothelin-1 (ET-1) and angiotensin II (ANG II) with equal affinities in the Dahl S/JRHS rat strain. To elucidate its physiological significance within the context of multiple receptor isoforms and diverse ET-1 and ANG II functions spanning blood pressure regulation, tumor proliferation, and angiogenesis, we characterized mouse Dear and Dear-deficient mice. Unlike null mutant models of ET-1, ANG II, and all other ET-1 and ANG II receptors, Dear(-/-) deficiency results in impaired angiogenesis, dysregulated neuroepithelial development, and embryonic lethality by embryonic day 12.5. Interestingly, mouse Dear does not bind ANG II, similar to Dahl R/JRHS rat Dear, but binds ET-1 and vascular endothelial growth factor (VEGF) signal peptide (VEGFsp) with equal affinities, suggesting a putative novel multifunction for VEGFsp and a parsimonious mechanism for coordination of VEGF-induced and Dear-mediated pathways. Consistent with its developmental angiogenic role, Dear inhibition results in decreased tumor growth in B16-F10 melanoma cell-induced subcutaneous tumor in female Dear(+/-)/C57BL6BC10 mice, but not in males (age 3.5 mo), and in 127Cs radiation-induced orthotopic mammary tumors in Sprague-Dawley female rats (age range 3-6.5 mo). Altogether, the data identify Dear as a new player in angiogenesis during development downstream to, and nonredundant with, VEGF-mediated pathways, as well as a putative modulator of tumor angiogenesis acting within a gender-specific paradigm.