Angiotensin II regulation of vascular endothelial growth factor and receptors Flt-1 and KDR/Flk-1 in cyclosporine nephrotoxicity

The role of renin angiotensin system in the pathophysiology of rheumatoid arthritis

BACKGROUND

In rheumatoid arthritis (RA) and osteoarthritis (OA), chronic inflammatory processes lead to progresive joint destruction. The renin-angiotensin system (RAS) is involved in the pathogenesis of RA and OA. The aim of this mini-review article is to summarize evidence on the role of RAS in RA and OA.

METHODS

A non-systematic search in Pubmed included terms as "rheumatoid arthritis", "renin angiotensin system", "osteopenia", "RANKL", "DKK-1", "MMP", "inflammation", "angiogenesis", "local renin-angiotensin system", "angiotensin converting enzyme", "AT2 receptor", "Ang-(1-7)", "VEGF", "angiotensine receptor blocker", "angiotensin converting enzyme inhibitors", "renin inhibitors".

RESULTS

Both RAS axes, the classical one, formed by angiotensin converting enzyme (ACE), angiotensin (Ang) II and AT1 receptor (AT1R) and the counter-regulatory one, composed by ACE2, Ang-(1-7) and the Mas receptor, modulate inflammation and tissue damage. Ang II activates pro-inflammatory mediators and oxidative stress. Conversely, Ang-(1-7) exerts anti-inflammatory actions, decreasing cytokine release, leukocyte attraction, density of vessels, tissue damage and fibrosis. Angiogenesis facilitates inflammatory cells invasion, while osteopenia causes joint dysfunction. Up-regulated osteoclastogenisis and down-regulated osteoblastogeneses were associaed with the activation of the classical RAS axis. Three different pathways, RANKL, DKK-1 and MMPs are enhanced by classical RAS activation. The treatment of RA included methotrexate and corticosteroids, which can cause side effects. Studies with angiotensin receptor blockers (ARBs), angiotensin converting enzyme inhibitors (ACEi) and renin inhibitors have been conducted in experimental and clinical RA with promising results.

CONCLUSION

The classical RAS activation is an important mechanism in RA pathogenesis and the benefit of ARB and ACEi administration should be further investigated.

Upgrading prevascularization in tissue engineering: A review of strategies for promoting highly organized microvascular network formation

Functional and perfusable vascular network formation is critical to ensure the long-term survival and functionality of engineered tissues after their transplantation. Although several vascularization strategies have been reviewed in past, the significance of microvessel organization in three-dimensional (3D) scaffolds has been largely ignored. Advances in high-resolution microscopy and image processing have revealed that the majority of tissues including cardiac, skeletal muscle, bone, and skin contain highly organized microvessels that orient themselves to align with tissue architecture for optimum molecular exchange and functional performance. Here, we review strategies to develop highly organized and mature vascular networks in engineered tissues, with a focus on electromechanical stimulation, surface topography, micro scaffolding, surface-patterning, microfluidics and 3D printing. This review will provide researchers with state of the art approaches to engineer vascularized functional tissues for diverse applications. STATEMENT OF SIGNIFICANCE: Vascularization is one of the critical challenges facing tissue engineering. Recent technological advances have enabled researchers to develop microvascular networks in engineered tissues. Although far from translational applications, current vascularization strategies have shown promising outcomes. This review emphasizes the most recent technological advances and future challenges for developing organized microvascular networks in vitro. The next critical step is to achieve highly perfusable, dense, mature and organized microvascular networks representative of native tissues.

Role of Receptor Tyrosine Kinase Signaling in Renal Fibrosis

Renal fibrosis can be induced in different renal diseases, but ultimately progresses to end stage renal disease. Although the pathophysiologic process of renal fibrosis have not been fully elucidated, it is characterized by glomerulosclerosis and/or tubular interstitial fibrosis, and is believed to be caused by the proliferation of renal inherent cells, including glomerular epithelial cells, mesangial cells, and endothelial cells, along with defective kidney repair, renal interstitial fibroblasts activation, and extracellular matrix deposition. Receptor tyrosine kinases (RTKs) regulate a variety of cell physiological processes, including metabolism, growth, differentiation, and survival. Many studies from in vitro and animal models have provided evidence that RTKs play important roles in the pathogenic process of renal fibrosis. It is also showed that tyrosine kinases inhibitors (TKIs) have anti-fibrotic effects in basic research and clinical trials. In this review, we summarize the evidence for involvement of specific RTKs in renal fibrosis process and the employment of TKIs as a therapeutic approach for renal fibrosis.

AUF1-RGG peptides up-regulate the VEGF antagonist, soluble VEGF receptor-1 (sFlt-1)

The macrophage is essential to the innate immune response, but also contributes to human disease by aggravating inflammation. Under severe inflammation, macrophages and other immune cells over-produce immune mediators, including vascular endothelial growth factor (VEGF). The VEGF protein stimulates macrophage activation and induces macrophage migration. A natural inhibitor of VEGF, the soluble VEGF receptor (sFlt-1) is also produced by macrophages and sFlt-1 has been used clinically to block VEGF. In macrophages, we have shown that the mRNA regulatory protein AUF1/hnRNP D represses VEGF gene expression by inhibiting translation of AURE-regulated VEGF mRNA. Peptides (AUF1-RGG peptides) that are modeled on the arginine-glycine-glycine (RGG) motif in AUF1 also block VEGF expression. This report shows that the AUF1-RGG peptides reduce two other AURE-regulated genes, TNF and GLUT1. Three alternative splice variants of sFlt-1 contain AURE in their 3'UTR, and in an apparent paradox, AUF1-RGG peptides stimulate expression of these three sFlt-1 Variants. The AUF1-RGG peptides likely act by distinct mechanisms with complimentary effects to repress VEGF gene expression and over-express the endogenous VEGF blocking agent, sFlt-1. The AUF1-RGG peptides are novel reagents that reduce VEGF and other inflammatory mediators, and may be useful tools to suppress severe inflammation.

WITHDRAWN: AUF1-RGG peptides up-regulate the VEGF antagonist, soluble VEGF receptor-1 (sFlt-1)

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Long-term high salt diet causes hypertension and alters renal cytokine gene expression profiles in Sprague-Dawley rats

OBJECTIVE

The present study examines whether a long-term high salt diet causes hypertension and renal injury in normal subjects [Sprague-Dawley (SD) rats] and alters renal cytokine-related gene expression profiles.

METHODS

Four 10 week old male SD rats received a high salt diet (HS, 8%) and the other 4 SD rats received a normal salt diet (NS, 0.5%) for 8 weeks. Mean arterial pressure (MAP) and renal damages such as albuminuria and histological renal injury were determined. The relative mRNA levels of 514 cytokine-related genes (normalized by beta-actin) in rat kidneys following NS or HS were determined quantitatively through analysis of 4 sets of gene expression profiles using the mouse cDNA membrane microarrays.

RESULTS

We demonstrated that 8 weeks of HS diet increased MAP [(140.0+/-5.3) vs (112.0+/-2.2) mmHg; 1 mmHg=0.133 kPa, P<0.01], albuminuria [(41.4+/-3.2) vs (20.1+/-4.5) mg/d; P<0.01], and caused histological renal injury in SD rats, compared to NS group. Of the 514 genes in the array, there were 27 (5.25%) genes with significantly different expression in the kidney of SD rats with HS compared to those of SD rats with NS. Functional clustering analysis indicated the following functional pathways related to high salt diet-induced hypertension: (1) pro-inflammatory response ( upward arrowIL-17, CCL28; downward arrow NFkappabib); (2) endothelial dysfunction ( downward arrowVEGF-A, VEGF-B, endoglin); (3) pro-matrix formation ( upward arrowosteopontin, IGFBP-5; downward arrow IFN-gamma); and (4) attenuated cell survival and differentiation ( downward arrowCNTF, IGF-II R, ephrin-B1). Northern blot confirmed that 8 weeks of HS diet significantly decreased renal expression of VEGF mRNA, compared to NS group (P<0.01). ELISA showed that HS diet significantly decreased renal protein levels of VEGF and CCL28.

CONCLUSION

These findings support the hypothesis that hypertension can be induced in normal rats by a long-term high salt diet, which is associated with increased renal injury and marked changes in renal cytokine gene expression profiles that are closely related to the pro-inflammatory response, pro-matrix formation, endothelial dysfunction, and attenuated cell survival and differentiation.

Renal protective effects of leukotriene receptor blockers in an experimental model of cyclosporine nephrotoxicity

BACKGROUND

Chronic cyclosporine (CsA) nephrotoxicity is associated with renal fibrosis and hyaline arteriolopathy. Fibrogenic cytokines, such as transforming growth factor-beta (TGF-beta) and vascular endothelial growth factor (VEGF), play a pivotal role in CsA nephrotoxicity. Previous studies have demonstrated the possible role of leukotrienes (LT) in chronic CsA nephrotoxicity. The aim of this study was to examine the possible beneficial effects of LT blockers in attenuating the morphological and histochemical effects induced by CsA in a rat model of CsA nephrotoxicity.

MATERIALS AND METHODS

Twenty-four male Wistar rats were divided into 3 groups (n = 8). The first group (G1) was treated with vehicle intraperitoneally (IP) for 60 days. The second group (G2) was treated with 15 mg/kg CsA IP for 60 days. The third group (G3) was treated with the same dose of CsA plus 4 mg/kg montelukast administered by oral gavage for 60 days.

RESULTS

There was a statistically significant decrease in glomerular filtration rate (GFR) among G2 compared with G1 animals: 0.41 +/- 0.03 vs 1.63 +/- 0.12 mL/min (P < .001), or G3 hosts: 0.41 +/- 0.03 vs 0.95 +/- 0.05 mL/min (P < .005), respectively. The percentage of hyaline arteriolopathic changes was higher in G2 than G1 or G3: 81.66% +/- 8.2% vs 11.83% +/- 0.87% (P < .01) or 37.0% +/- 8.8% (P < .01), respectively. Fibrosis score was higher in G2 compared with G1 or G3: 1.5 +/- 0.04 vs 0.16 +/- 0.02 (P < .001) and 1.0 +/- 0.05 (P < .05), respectively. TGF-beta and VEGF immunoexpression were significantly increased in G2 compared with G1 (P < .05) or G3 (P < .05).

CONCLUSIONS

Our study suggested that LT may play a critical role in the pathogenesis of chronic CsA nephrotoxicity; the administration of montelukast, a LT receptor blocker, may prevent CsA-induced nephrotoxicity.

Congenic strains reveal the effect of the renin gene on skeletal muscle angiogenesis induced by electrical stimulation

Previous studies have indicated the importance of angiotensin II (ANG II) in skeletal muscle angiogenesis. The present study explored the effect of regulation of the renin gene on angiogenesis induced by electrical stimulation with the use of physiological, pharmacological, and genetic manipulations of the renin-angiotensin system (RAS). Transfer of the entire chromosome 13, containing the physiologically regulated renin gene, from the normotensive inbred Brown Norway (BN) rat into the background of an inbred substrain of the Dahl salt-sensitive (SS/Mcwi) rat restored renin levels and the angiogenic response after electrical stimulation. This restored response was significantly attenuated when SS-13BN/Mcwi consomic rats were treated with lisinopril or high-salt diet. The role of ANG II on this effect was confirmed by the complete restoration of skeletal muscle angiogenesis in SS/Mcwi rats infused with subpressor doses of ANG II. Congenic strains derived from the SS-13BN/Mcwi consomic were used to further verify the role of the renin gene in this response. Microvessel density was markedly increased after stimulation in congenic strains that contained the renin gene from the BN rat (congenic lines A and D). This angiogenic response was suppressed in control strains that carried regions of the BN genome just above (congenic line C) or just below (congenic line B) the renin gene. The present study emphasizes the importance of maintaining normal renin regulation as well as ANG II levels during the angiogenesis process with a combination of physiological, genetic, and pharmacological manipulation of the RAS.

Angiotensin II is a critical mediator of prazosin-induced angiogenesis in skeletal muscle

OBJECTIVE

The purpose of this study was to determine whether a high-salt diet modulates physiological angiogenesis in skeletal muscle by altering angiotensin II (ANGII) and vascular endothelial growth factor (VEGF) levels.

METHODS

Sprague-Dawley rats were placed on a control diet (0.4% NaCl by weight) or high-salt diet (4.0% NaCl) prior to treatment with the vasodilator prazosin in the drinking water. In addition, a group of animals fed high salt were infused intravenously with ANGII at a low dose to prevent ANGII suppression by high salt, and a group of rats fed control diet were treated with the angiotensin II type I (AT(1)) receptor blocker losartan and prazosin.

RESULTS

Prazosin induced significant angiogenesis in the tibialis anterior muscle after 1 week of treatment. High-salt-fed rats demonstrated a complete inhibition of this angiogenic response. Maintenance of ANGII levels restored prazosin-induced angiogenesis in animals fed a high-salt diet. In addition, losartan treatment blocked prazosin-induced angiogenesis in animals on a control diet. Western blot analysis indicated that prazosin-induced angiogenesis was independent of changes in muscle levels of VEGF.

CONCLUSIONS

This study demonstrates an inhibitory effect of high salt intake on prazosin-induced angiogenesis. Further, these results indicate that ANGII acting through the AT(1) receptor is a critical pathway in this model of angiogenesis.

Angiotensin II stimulates hypoxia-inducible factor 1alpha accumulation in glomerular mesangial cells

Hypoxia increases hypoxia-inducible factor 1alpha (HIF-1alpha) protein levels by inhibiting ubiquitination and degradation of HIF-1alpha, which regulates the transcription of many genes. Recent studies have revealed that many ligands can stimulate HIF-1alpha accumulation under nonhypoxic conditions. In this study, we show that angiotensin II (Ang II) increased HIF-1alpha protein levels in a time- and dose-dependent manner under normoxic conditions. Treatment of mesangial cells with Ang II (100 nM) increased production of reactive oxygen species (ROS). Ang II (100 nM) increased the phosphorylation of PDK-1 and Akt/PKB in glomerular mesangial cells. Ang II-stimulated HIF-1alpha accumulation was blocked by the phosphatidylinositol 3-kinase (PI-3K) inhibitors, Ly 294001, and wortmannin, suggesting that PI-3K was involved. Because increased ROS generation by Ang II may activate the PI-3K-PKB/Akt signaling pathway, these results suggest that Ang II may stimulate a ROS-dependent activation of the PI-3K-PKB/Akt pathway, which leads to HIF-1alpha accumulation.

Transforming growth factor-beta1, vascular endothelial growth factor, and bone morphogenic protein-7 expression in tacrolimus-induced nephrotoxicity in rats

The aim of our study was to investigate transforming growth factor (TGF)-beta1, vascular endothelial growth factor (VEGF), and bone morphogenic protein-7 (BMP-7) expression in the rat model of chronic tacrolimus (TAC) toxicity compared to healthy controls. Seventeen male Wistar rats were divided into two groups: group 1 animals were healthy controls and Group 2 animals were treated with TAC (1 mg/kg per day intraperitoneally for 8 weeks). At the end of the study period the animals were sacrificed following renal function studies including blood urea nitrogen (BUN), serum creatinine, and creatinine clearance, and renal tissues were examined by light microscopy for the findings of tacrolimus toxicity, specifically for afferent arteriolopathy and interstitial fibrosis. TGF-beta1, VEGF, and BMP-7 expression were assessed by semiquantitative scoring of the immunohistochemically stained specimens. Mean TAC levels were 5.53 +/- 2.38 ng/mL in group 2. BUN, creatinine levels, and creatinine clearance were 57.99 +/- 11.13 vs 39.49 +/- 5.64 mg/dL; 0.60 +/- 0.16 vs 0.65 +/- 0.09 mg/dL; 0.97 +/- 0.39 vs 1.17 +/- 0.32 mL/min in group 2 versus group 1. Only the BUN level was significantly higher in group 2 compared to group 1. Afferent arteriolopathy and interstitial fibrosis were significantly increased in group 2 compared to group 1. TGF-beta1 and VEGF expression was significantly increased while BMP-7 expression was significantly decreased in group 2 versus group 1. In conclusion, our findings suggest that TAC-induced nephrotoxicity is associated with increased TGF-beta1 and VEGF and decreased BMP-7 expression.

VEGF gene expression is regulated post-transcriptionally in macrophages

The macrophage is critical to the innate immune response and contributes to human diseases, including inflammatory arthritis and plaque formation in atherosclerosis. Vascular endothelial growth factor (VEGF) is an angiogenic cytokine that is produced by macrophages. To study the regulation of VEGF production in macrophages we show that stimulation of monocyte-macrophage-like RAW-264.7 cells by lipopolysaccharide (LPS) increases expression of VEGF mRNA and protein. Three alternative splicing VEGF mRNA isoforms are produced, and the stability of VEGF mRNA increases following cellular activation. To study post-transcriptional regulation of the VEGF gene the 3'-untranslated region (3' UTR) was introduced into the 3' UTR of the luciferase gene in a reporter construct. In both RAW-264.7 cells and thioglycollate-elicited macrophages, the 3' UTR sequence dramatically reduces reporter expression. Treatment with activators of macrophages, including LPS, lipoteichoic acid, and VEGF protein, stimulates expression of 3' UTR reporters. Finally, mapping studies of the 3' UTR of VEGF mRNA show that deletion of the heterogeneous nuclear ribonucleoprotein l binding site affects basal reporter expression in RAW-264.7 cells, but does not affect reporter activation with LPS. Together these results demonstrate that a post-transcriptional mechanism contributes to VEGF gene expression in activated macrophage cells.

Inhibition of the Renin Angiotensin System Decreases Fibrogenic Cytokine Expression in Tacrolimus Nephrotoxicity in Rats

The aim of our study was to investigate the influence of angiotensin-converting enzyme (ACE) inhibition and angiotensin II receptor blockage on the renal function by light microscopic and immunohistochemical findings in a rat model of tacrolimus nephrotoxicity. Thirty-two male Wistar rats were divided into four groups of eight: G1 = control group; G2-G3, G4 = Tacrolimus (Tac) 1 mg/kg/d intraperitoneally (ip); G3 (Tac + Q) = ip Tac and peroral quinapril 10 mg/kg; and G4 (Tac + V) = Tac and valsartan 40 mg/d. Serum blood urea nitrogen (BUN), creatinine, and creatinine clearance were measured before and at the end of the study period. Renal tissues were assessed for light microscopic findings of tacrolimus toxicity. Transforming growth factor-beta, VEGF, PDGF, BMP-7, and interleukin-6 (IL-6) expression were semiquantitatively scored after immunohistochemical staining. At the end of the study period serum BUN and creatinine levels were increased in all groups, but creatinine clearance was not significantly changed between the groups. Afferent arteriolopathy was significantly less pronounced in G3 versus G2 and G4. Interstial fibrosis was significantly less pronounced in G3 and G4 versus G2. TGF-beta, PDGF, and IL-6 expression were significantly increased in G2, G3, and G4 compared to G1, and in G2 compared to G3 and G4. BMP-7 expression was significantly decreased in G2, G3, and G4 compared to G1, whereas the differences between G2, G3, and G4 failed to reach statistical significance. In conclusion, the results of our study suggested that renin angiotensin inhibition down-regulates fibrogenic cytokine expression in rats displaying tacrolimus nephrotoxicity.

Vascular endothelial growth factor in children with nephrotic syndrome treated with cyclosporine A

AIM

To assess the effect of cyclosporine A (CyA) on the level of vascular endothelial growth factor (VEGF) in the plasma and urine of nephrotic syndrome children.

METHODS

The study material consisted of 15 children (F 6, M 9; group I) who were subjected to the following examinations: A) at the time of proteinuria relapse, before treatment with CyA, B) after 3 mo, C) after 6 mo, and D) after 12 mo of CyA administration with prednisone and convertase inhibitor. The control group (II) contained 20 healthy children. The immunoenzymatic ELISA method (R&D Quantikine) was used to determine plasma and urinary VEGF levels, while the immunofluorescence method was applied to assess CyA concentration in the plasma. The statistical program Statistica 6.0 was used for statistical analysis of the results.

RESULTS

In the present study, plasma VEGF level in examination A was higher than in the control group (p<0.01). After proteinuria regression (B), it did not differ from the level observed in healthy children (p>0.05). After 6 and 12 mo of CyA administration, VEGF concentration increased and was higher than in the control group (p<0.05). In all the examinations, urinary excretion of VEGF was higher than in the control group, increasing proportionally with the duration of treatment and plasma CyA level. A positive correlation was observed between plasma and urinary VEGF levels and between VEGF and CyA concentrations in the plasma.

CONCLUSION

Long-term CyA treatment of nephrotic syndrome children leads to an increase in plasma and urinary VEGF.

Angiotensin II infusion restores stimulated angiogenesis in the skeletal muscle of rats on a high-salt diet

Elevated dietary salt intake has previously been demonstrated to have dramatic effects on microvascular structure and function. The purpose of this study was to determine whether a high-salt diet modulates physiological angiogenesis in skeletal muscle. Male Sprague-Dawley rats were placed on a control diet (0.4% NaCl by weight) or a high-salt diet (4.0% NaCl) before implantation of a chronic electrical stimulator. After seven consecutive days of unilateral hindlimb muscle stimulation, animals on control diets demonstrated a significant increase in microvessel density in the tibialis anterior muscle of the stimulated hindlimb relative to the contralateral control leg. High salt-fed rats demonstrated a complete inhibition of this angiogenic response, as well as a significant reduction in plasma ANG II levels compared with those of control animals. To investigate the role of ANG II suppression on the inhibitory effect of high-salt diets, a group of rats that were fed high salt were chronically infused with ANG II at a low dose. Maintenance of ANG II levels restored stimulated angiogenesis to control levels in animals fed a high-salt diet. Western blot analysis indicated that inhibition of angiogenesis in high salt-fed rats was not due to changes in VEGF or VEGF receptor type 1 protein expression in response to stimulation; however, the degree to which VEGF receptor 2 protein increased with stimulation was significantly lower in high salt-fed animals. This study demonstrates an inhibitory effect of high salt intake on stimulated angiogenesis and suggests a critical role for ANG II suppression in mediating this antiangiogenic effect.

Upregulation of Transforming Growth Factor-β1 and Vascular Endothelial Growth Factor Gene and Protein Expression in Cyclosporin-Induced Overgrown Edentulous Gingiva in Rats

BACKGROUND

To examine the effects of cyclosporin A (CsA) on the expression of growth factors in induced gingival overgrowth with limited contributing factors arising from local inflammation caused by bacterial plaque, this study of gingival overgrowth was designed on the edentulous ridge of rats.

METHODS

After a 3-week healing period following maxillary molar extractions, 16 five-week-old male Sprague-Dawley rats were assigned to CsA and control groups. Animals in the CsA group were fed 30 mg/kg CsA daily, whereas the control rats received a mineral oil vehicle instead. After 4 weeks, all animals were sacrificed, and the morphology of edentulous ridges was recorded by dental impression. The gingivae on the left-hand side were dissected and stored for mRNA analysis, whereas the gingivae on the right-hand side were fixed in 4% paraformaldehyde for immunohistochemistry (IHC) analysis of transforming growth factor-beta1 (TGF-beta1), platelet-derived growth factor beta (PDGF-beta), insulin-like growth factor-1 (IGF-1), and vascular endothelial growth factor (VEGF).

RESULTS

The edentulous gingivae were enlarged and the body weights were reduced in the CsA-treated animals compared to controls. The mRNA expressions of TGF-beta1, IGF-1, and VEGF were higher in the gingivae of the CsA group than in the control group. In addition, a greater mRNA expression (7.21-fold) of VEGF was demonstrated in the CsA group than in the control group by real-time polymerase chain reaction (PCR). The percentages of cells staining positive for TGF-beta1 and VEGF were significantly greater in the CsA rats than in the control rats.

CONCLUSIONS

Greater mRNA expression and positive staining for TGF-beta1 and VEGF were observed in the edentulous gingivae of rats that received CsA. Therefore, CsA may upregulate TGF-beta1 and VEGF gene expression and protein secretion in CsA-induced gingival overgrowth.

Angiotensin II regulates vascular endothelial growth factor via hypoxia-inducible factor-1alpha induction and redox mechanisms in the kidney

Angiotensin II (AngII) is a cytokine that participates in renal damage. Vascular endothelial growth factor (VEGF) is constitutively expressed in the kidney and is involved in the progression of renal disease. The aim of this work was to investigate the relation between AngII and VEGF and the mechanisms involved in its regulation in the kidney. We have observed that in cultured tubuloepithelial cells (NRK52E cell line) AngII increased VEGF gene expression and promoter activation. Hypoxia-inducible factor-1 (HIF-1) is one of the main VEGF gene activators. AngII induces HIF-1alpha protein production and increases HIF-1 DNA-binding activity. An antisense HIF-1alpha oligodeoxynucleotide inhibited AngII-induced VEGF overexpression. The reactive oxygen species act as second messengers in kidney damage caused by AngII and mediate the induction of HIF-1 by cytokines. In tubuloepithelial cells, VEGF up-regulation and HIF-1alpha induction due to AngII were significantly diminished by antioxidants, suggesting a redox-mediated mechanism. Infusion of AngII into mice caused renal VEGF overexpression, HIF-1 activation, and oxidative stress. In summary, these data show that AngII in vivo and in vitro up-regulates renal VEGF expression by a mechanism that involves HIF-1 activation and oxidative stress.

Acute induction of gene expression in brain and liver by insulin-induced hypoglycemia

The robust neuroendocrine counterregulatory responses induced by hypoglycemia protect the brain by restoring plasma glucose, but little is known about molecular responses to hypoglycemia that may also be neuroprotective. To clarify these mechanisms, we examined gene expression in hypothalamus, cortex, and liver 3 h after induction of mild hypoglycemia by a single injection of insulin, using cDNA microarray analysis and quantitative real-time PCR. Real-time PCR corroborated the induction of six genes (angiotensinogen, GLUT-1, inhibitor of kappaB, inhibitor of DNA binding 1 [ID-1], Ubp41, and mitogen-activated protein kinase phosphatase-1 [MKP-1]) by insulin-induced hypoglycemia in the hypothalamus: five of these six genes in cortex and three (GLUT-1, angiotensinogen, and MKP-1) in liver. The induction was due to hypoglycemia and not hyperinsulinemia, since fasting (characterized by low insulin and glucose) also induced these genes. Four of these genes (angiotensinogen, GLUT-1, ID-1, and MKP-1) have been implicated in enhancement of glucose availability, which could plausibly serve a neuroprotective role during acute hypoglycemia but, if persistent, could also cause glucose-sensing mechanisms to overestimate plasma glucose levels, potentially causing hypoglycemia-induced counterregulatory failure. Although using cDNA microarrays with more genes, or microdissection, would presumably reveal further responses to hypoglycemia, these hypoglycemia-induced genes represent useful markers to assess molecular mechanisms mediating cellular responses to hypoglycemia.

The role of vascular endothelial growth factor (VEGF) in renal pathophysiology

Vascular endothelial growth factor (VEGF) is an endothelial-specific growth factor that promotes endothelial cell proliferation, differentiation and survival, mediates endothelium-dependent vasodilatation, induces microvascular hyperpermeability and participates in interstitial matrix remodeling. In the kidney, VEGF expression is most prominent in glomerular podocytes and in tubular epithelial cells, while VEGF receptors are mainly found on preglomerular, glomerular, and peritubular endothelial cells. The role of VEGF in normal renal physiology is essentially unknown. The absence of prominent effects of VEGF blockade in normal experimental animals suggests a limited function during homeostasis, although a role in the formation and maintenance of glomerular capillary endothelial fenestrations has been suggested. VEGF and its receptors are up-regulated in experimental animals and humans with type 1 and type 2 diabetes. Inhibition of VEGF has beneficial effects on diabetes-induced functional and structural alterations, suggesting a deleterious role for VEGF in the pathophysiology of diabetic nephropathy. VEGF is required for glomerular and tubular hypertrophy and proliferation in response to nephron reduction, and loss of VEGF is associated with the development of glomerulosclerosis and tubulointerstitial fibrosis in the remnant kidney. No firm conclusions on the role of VEGF in minimal change or membranous glomerulonephritis can be drawn. VEGF may be an essential mediator of glomerular recovery in proliferative glomerulonephritis. Glomerular and tubulointerstitial repair in thrombotic microangiopathy and cyclosporin nephrotoxicity may also be VEGF-dependent. In conclusion, VEGF is required for growth and proliferation of glomerular and peritubular endothelial cells. While deleterious in some, it may contribute to recovery in other forms of renal diseases.

Effect of angiotensin-converting enzyme-inhibiting therapy on the expression of vascular endothelial growth factor in hyperstimulated rat ovary

OBJECTIVE

To determine the effect of angiotensin-converting enzyme-inhibiting therapy on the expression of vascular endothelial growth factor (VEGF) in the hyperstimulated rat ovary.

DESIGN

Experimental study.

SETTING

University animal research laboratory.

ANIMAL(S)

Thirty Wistar albino adult female rats were studied; 20 rats were stimulated with gonadotropins (groups 1 and 2), and 10 were controls (group 3). Ten of the stimulated rats received additional treatment with enalapril (group 2).

INTERVENTION(S)

At the end of the treatment period, rat ovaries were subjected to immunohistochemical staining with anti-VEGF antibodies.

MAIN OUTCOME MEASURE(S)

VEGF staining intensity was graded semiquantitatively, and the H-score was calculated by light microscopic examination of the groups.

RESULT(S)

VEGF expression was found to be significantly higher in the endothelium and stroma in groups 1 and 2 compared with group 3. Although VEGF immunoreactivity was lower in the stimulation regimen plus enalapril group compared with the stimulation regimen-only group, the difference was insignificant.

CONCLUSION(S)

Enalapril does not seem to have a significant effect on VEGF expression in the hyperstimulated rat ovary. Because angiotensin II exerts its multiple actions via specific receptors, there may be other factors, such as a receptor blockade, that contribute to the VEGF expression.

Cyclosporine renal dysfunction

Cyclosporine (CsA), introduced as an immunosuppressive agent in the 1980s, quickly become the first-line treatment in organ transplantation. However, these improvements were associated with an increased incidence of renal dysfunction. CsA causes histopathological changes in renal transplants that are often difficult to distinguish from other processes, especially chronic allograft nephropathy. Enhanced angiotensin II, transforming growth factor-beta, and vascular endothelial growth factor expression together with down-regulation of nitric oxide synthesis may play roles in chronic CsA nephropathy. Efforts have recently focused upon protocols that minimize the risk of CsA nephrotoxicity while preserving low rates of acute rejection. Four types of CsA-sparing studies have emerged from recent clinical experience: (1) conversion studies in which a nonnephrotoxic drug is substituted to allow CsA reduction, (2) minimal CsA exposure studies in which reduced CsA doses are combined with nonnephrotoxic drugs, (3) withdrawal studies in which CsA is completely discontinued at some time after transplantation, and (4) CsA-free studies in which the drug is completely avoided from the time of transplantation. Monitoring of CsA immunosuppression according to C2 blood levels, which better correlate with the area under the time-concentration curve than trough concentrations, should reduce the risk for toxicity; however, the most appropriate target range has not yet been clearly established. Because of interindividual differences in CsA absorption and susceptibility to renal dysfunction, the current therapeutic drug monitoring should be supplemented with pharmacogenetic information on genetic variability of relevant genes for pharmacokinetic parameters and therapeutic targets. This approach may guide choices for immunosuppressants for particular patients, with low toxicity. Thus, despite of 20 years of its history, CsA renal dysfunction remains an important clinical challenge.