Role of VEGF in kidney development, microvascular maintenance and pathophysiology of renal disease

Evaluating different methods for kidney recellularization

This study explores a potential solution to the shortage of kidneys for transplantation in end-stage renal disease (ESRD). Currently, kidney transplantation stands as the optimal option, yet the scarcity of organs persists. Employing tissue engineering, researchers sought to assess the feasibility of generating kidneys for transplantation. Pig kidneys were utilized since they possess higher similarities to human kidneys. Cells were removed via decellularization, which maintains the organ's microarchitecture. Subsequently, pig kidney cells and human red blood cells were perfused into the vacant kidney structure to reconstitute it. The methodologies employed showed promising results, suggesting a viable approach to increase the recellularization rate in whole pig kidneys. This proof-of-concept establishes a groundwork for potentially extending this technology to human kidneys, tackling the organ shortage, thus positively enhancing outcomes for ESRD patients by increasing the availability of transplantable organs.

Klotho in pregnancy and intrauterine development-potential clinical implications: a review from the European Renal Association CKD-MBD Working Group

Intrauterine development is crucial for life-long health; therefore, elucidation of its key regulators is of interest for their potential prognostic and therapeutic implications. Originally described as a membrane-bound anti-aging protein, Klotho has evolved as a regulator of numerous functions in different organ systems. Circulating Klotho is generated by alternative splicing or active shedding from cell membranes. Recently, Klotho was identified as a regulator of placental function, and while Klotho does not cross the placental barrier, increased levels of circulating α-Klotho have been identified in umbilical cord blood compared with maternal blood, indicating that Klotho may also play a role in intrauterine development. In this narrative review, we discuss novel insights into the specific functions of the Klotho proteins in the placenta and in intrauterine development, while summarizing up-to-date knowledge about their structures and functions. Klotho plays a role in stem cell functioning, organogenesis and haematopoiesis. Low circulating maternal and foetal levels of Klotho are associated with preeclampsia, intrauterine growth restriction, and an increased perinatal risk for newborns, indicating a potential use of Klotho as biomarker and therapeutic target. Experimental administration of Klotho protein indicates a neuro- and nephroprotective potential, suggesting a possible future role of Klotho as a therapeutic agent. However, the use of Klotho as intervention during pregnancy is as yet unproven. Here, we summarize novel evidence, suggesting Klotho as a key regulator for healthy pregnancies and intrauterine development with promising potential for clinical use.

The protective effect of 1400W against ischaemia and reperfusion injury is countered by transient medullary kidney endothelial dysregulation

Renal ischaemia and reperfusion (I/R) is caused by a sudden temporary impairment of the blood flow. I/R is a prevalent cause of acute kidney injury. As nitric oxide generated by inducible nitric oxide synthase (iNOS) has detrimental effects during I/R, the pharmacological blockade of iNOS has been proposed as a potential strategy to prevent I/R injury. The aim of this study was to improve the understanding of 1400W (an iNOS inhibitor) on renal I/R as a pharmacological strategy against kidney disease. BALB/c mice received 30 min of bilateral ischaemia, followed by 48 h or 28 days of reperfusion. Vehicle or 1400W (10 mg/kg) was administered 30 min before inducing ischaemia. We found that after 48 h of reperfusion 1400W decreased the serum creatinine, blood urea nitrogen, neutrophil gelatinase-associated lipocalin and proliferating cell nuclear antigen 3 in the I/R animals. Unexpectedly, we observed mRNA upregulation of genes involved in kidney injury, cell-cycle arrest, inflammation, mesenchymal transition and endothelial activation in the renal medulla of sham animals treated with 1400W. We also explored if 1400W promoted chronic kidney dysfunction 28 days after I/R and did not find significant alterations in renal function, fibrosis, blood pressure or mortality. The results provide evidence that 1400W may have adverse effects in the renal medulla. Importantly, our data point to 1400W-induced endothelial dysfunction, establishing therapeutic limitations for its use. KEY POINTS: Acute kidney injury is a global health problem associated with high morbidity and mortality. The pharmacological blockade of inducible nitric oxide synthase (iNOS) has been proposed as a potential strategy to prevent AKI induced by ischaemia and reperfusion (I/R). Our main finding is that 1400W, a selective and irreversible iNOS inhibitor with low toxicity that is proposed as a therapeutic strategy to prevent kidney I/R injury, produces aberrant gene expression in the medulla associated to tissue injury, cell cycle arrest, inflammation, mesenchymal transition and endothelial activation. The negative effect of 1400W observed in the renal medulla at 48 h from drug administration, is transient as it did not translate into a chronic kidney disease condition.

Decellularization of porcine kidney with submicellar concentrations of SDS results in the retention of ECM proteins required for the adhesion and maintenance of human adult renal epithelial cells

When decellularizing kidneys, it is important to maintain the integrity of the acellular extracellular matrix (ECM), including associated adhesion proteins and growth factors that allow recellularized cells to adhere and migrate according to ECM specificity. Kidney decellularization requires the ionic detergent sodium dodecyl sulfate (SDS); however, this results in a loss of ECM proteins important for cell adherence, migration, and growth, particularly glycosaminoglycan (GAG)-associated proteins. Here, we demonstrate that using submicellar concentrations of SDS results in a greater retention of structural proteins, GAGs, growth factors, and cytokines. When porcine kidney ECM scaffolds were recellularized using human adult primary renal epithelial cells (RECs), the ECM promoted cell survival and the uniform distribution of cells throughout the ECM. Cells maintained the expression of mature renal epithelial markers but did not organize on the ECM, indicating that mature cells are unable to migrate to specific locations on ECM scaffolds.

Microvascular remodeling and altered angiogenic signaling in human kidneys distal to occlusive atherosclerotic renal artery stenosis

BACKGROUND

Renal artery stenosis (RAS) is an important cause of chronic kidney disease and secondary hypertension. In animal models, renal ischemia leads to downregulation of growth-factor expression and loss of intrarenal microcirculation. However, little is known about the sequelae of large vessel occlusive disease on the microcirculation within human kidneys.

METHOD

This study included 5 patients who underwent nephrectomy due to renovascular occlusion, and 7 non-stenotic discarded donor kidneys (4 deceased donors). Micro-computed tomography was performed to assess microvascular spatial densities and tortuosity, an index of microvascular immaturity. Renal protein expression, gene expression, and histology were studied in-vitro using immunoblotting, polymerase-chain-reaction, and staining.

RESULTS

RAS demonstrated loss of medium-sized vessels (0.2-0.3mm) compared to donor kidneys (p = 0.037) and increased microvascular tortuosity. RAS kidneys had greater protein expression of angiopoietin-1, hypoxia-inducible factor (HIF)-1α, and thrombospondin (TSP)-1, but lower protein expression of vascular endothelial growth factor (VEGF) than donor kidneys. Renal fibrosis, loss of peritubular capillaries (PTC) and pericyte detachment were greater in RAS, yet they had more newly-formed PTC than donor kidneys. Therefore, our study quantified significant microvascular remodeling in the post-stenotic human kidney. RAS induced renal microvascular loss, vascular remodeling, and fibrosis. Despite downregulated VEGF, stenotic kidneys upregulated compensatory angiogenic pathways related to angiopoietin-1.

CONCLUSIONS

These observations underscore the nature of human RAS as a microvascular disease distal to main vessel stenosis, and support therapeutic strategies directly targeting the post-stenotic kidney microcirculation in patients with RAS.

Cytoprotective potentialities of carvacrol and its nanoemulsion against cisplatin-induced nephrotoxicity in rats: development of nano-encasulation form

Cisplatin (Cisp) is a widely distributed chemotherapeutic drug for cancers. Nephrotoxicity is one of the most common side effects of the use of this drug. Carvacrol (CV) is a common natural compound in essential oils and extracts of medicinal plants with potent in vivo and in vitro bioactivities. The work was extended to achieve the target of investigation of the protective potentialities of CV and its nanoemulsion as a cytoprotective drug against Cisp-induced nephrotoxicity in albino rats. CV-nanoemulsion was prepared by a hydrophilic surfactant polysorbate 80 (Tween 80) and deionized water. The TEM image of the particle distribution prepared nanoemulsion is mainly spherical in shape with particle size varying between 14 and 30 nm. Additionally, the Cisp administration caused the increasing of the levels of urea and creatinine in the blood and serum. These increasing of urea and creatinine levels caused consequently the turbulence of the oxidative stress as well as the rising of hs-CRP, IL-6, and TNF-α levels in the serum. Also, histopathological changes of the kidney tissue were observed. These changes back to normal by treatment with CV-nanoemulsion. Expression levels of nephrotoxicity-related genes including LGALS3, VEGF, and CAV1 in kidney tissue using qRT-PCR were measured. The results revealed that the expression of LGALS3, VEGF and CAV1 genes was highly significantly increased in only Cisp treated group when compared with other treated groups. While, these genes expressions were significantly decreased in Cisp + CV treated group when compared with Cisp treated rats (P < 0.001). In addition, there were no significant differences between Cisp + nano-CV treated group and both negative control and nanoemulsion alone groups but it was not significant. In addition, the Western blot of protein analysis results showed that the LGALS3 and CAV1 are highly expressed only in Cisp + CV treated group compared with other groups. There was no significant difference between Cisp + nano-CV treated animals and negative control for both mRNA and protein expression. Based on these results, CV was combined with calcium alginate; a more stable capsule is formed, allowing for the formation of a double wall in the microcapsule. These results supported the therapeutic effect of CV and its nano-emulsion as cytoprotective agents against Cisp nephrotoxicity.

MicroRNA profiling in kidney in pigs fed ochratoxin A contaminated diet

OTA is a toxic metabolite produced by fungus belonging to Aspergillus and Penicillium genera. Kidney is the main target of this toxin; OTA is considered as one of the etiological factors at the origin of the human Balkan endemic nephropathy. microRNA are short non-coding transcrips (18-22 nucleotides in length) regulating key cellular processes. Various miRNAs have been established to play important roles in development of renal carcinoma and urothelial cancer. The objective of this study is to analyse the miRNA profiling in the kidney of piglets experimentally intoxicated with feed contaminated with OTA. Fifteen piglets (five pigs/group) were randomly distributed into 3 groups, fed normal diet (Group 1: control), or diets contaminated with OTA in two concentrations: 50 μg OTA/kg feed (Group 2: 50 μg OTA/kg feed) or 200 μg OTA/kg feed (Group 3: 200 μg OTA/kg feed) for 28 days. At the end of the experiment blood samples were taken for serological analyses. Animals from control group and 200 μg OTA/kg feed were sacrificed and kidney samples were taken for histological and molecular analyses. As resulted from molecular profiling study there are 8 miRNA differentially expressed in OTA kidney vs control kidney, in which five miRNA were overexpressed in the kidney of OTA intoxicated animals: miR-497 (FC = 6.34), miR-133a-3p (FC = 5.75), miR-423-3p (FC = 5.48), miR-34a (FC = 1.68), miR-542-3p (1.65) while three miRNA were downregulated: miR-421-3p (FC = -3.96); miR-490 (FC = -3.87); miR-9840-3p (FC = -2.13). The altered miRNAs as effect of OTA are strongly connected to the engine of cancer, disturbing nodal points in different pathways, as TP53 signalling. This proof-of-concept study proves the actual utility of miRNAs as biomarkers of mycotoxin exposure, including OTA.

Reabsorption in the proximal tubuli-ultrastructural evidence for a novel aspect of renal VEGF trafficking

Many clinical and experimental studies have revealed VEGF as an important factor in the pathophysiology of renal damage during diabetes mellitus (DM). Anti-VEGF therapy is in clinical use for treatment of DM and other diabetes-related (and unrelated) diseases. Nevertheless, little is known about the metabolism of VEGF in the kidneys. In order to determine the ultrastructural localization of VEGF in the kidney, we study the distribution of VEGF in the kidney of rats by using immunogold immunohistochemistry. Our light-microscopic data showed remarkable re-distribution of VEGF in proximal tubular cells (PTCs) during prolonged hyperglycemia, a DM type 2 model (DM2), which was confirmed by transmission electron microscopy (TEM) findings. TEM findings revealed an initial presence of VEGF in the vesicular transport apparatus of PTCs in healthy rats and its gradual translocation to the apical membrane of PTCs after renal damage caused by high sucrose treatment. The presented data add to our understanding of kidney VEGF trafficking, providing novel insight into the renal metabolism and pharmacodynamics of the cytokine. This could have a high impact on the use of VEGF and anti-VEGF therapy in different renal diseases.

Uteroplacental insufficiency in rats induces renal apoptosis and delays nephrogenesis completion

AIM

Uteroplacental insufficiency in rats reduces nephron endowment, leptin concentrations and programmes cardiorenal disease in offspring. Cross-fostering growth-restricted (Restricted) offspring onto a mother with normal lactation restores leptin concentrations and nephron endowment. This study aimed to determine whether the reduced nephron endowment in Restricted offspring is due to delayed glomerular formation and dysregulation of renal genes regulating branching morphogenesis, apoptosis or leptin signalling. Furthermore, we aimed to investigate whether cross-fostering Restricted offspring onto Control mothers could improve glomerular maturation and restore renal gene abundance.

METHODS

Uteroplacental insufficiency was induced by bilateral uterine vessel ligation (Restricted) or sham (Control) surgery on gestation day 18 (E18). Kidneys were collected at E20, postnatal day 1 (PN1) and PN7. An additional cohort was cross-fostered onto separate mothers at birth and kidneys collected at PN7.

RESULTS

Kidneys were lighter in the Restricted group, but weight was restored with cross-fostering. At E20, abundance of Bax, Flt1 and Vegfa was increased in Restricted offspring, while Ret and Bcl2 transcripts were increased only in Restricted females. At PN7, abundance of Gdnf and Ret was higher in Restricted offspring, as was Casp3. Restricted offspring had a wider nephrogenic zone with more immature glomeruli suggesting a delayed or extended nephrogenic period. Cross-fostering had subtle effects on gene abundance and glomerular maturity.

CONCLUSION

Uteroplacental insufficiency induced apoptosis in the developing kidney and delayed and extended nephrogenesis. Cross-fostering Restricted offspring onto Control mothers had beneficial effects on kidney growth and renal maturity, which may contribute to the restoration of nephron endowment.

Basic fibroblast growth factor reduces functional and structural damage in chronic kidney disease

Chronic kidney disease (CKD) is characterized by loss of renal function. The pathological processes involved in the progression of this condition are already known, but the molecular mechanisms have not been completely explained. Recent reports have shown the intrinsic capacity of the kidney to undergo repair after acute injury through the reexpression of repairing proteins (Villanueva S, Cespedes C, Vio CP. Am J Physiol Regul Integr Comp Physiol 290: R861-R870, 2006). Stimulation with basic fibroblast growth factor (bFGF) could accelerate this process. However, it is not known whether bFGF can induce this phenomenon in kidney cells affected by CKD. Our aim was to study the evolution of renal damage in animals with CKD treated with bFGF and to relate the amount of repairing proteins with renal damage progression. Male Sprague-Dawley rats were subjected to 5/6 nephrectomy (NPX) and treated with bFGF (30 μg/kg, NPX+bFGF); a control NPX group was treated with saline (NPX+S). Animals were euthanized 35 days after bFGF administration. Functional effects were assessed based on serum creatinine levels; morphological damage was assessed by the presence of macrophages (ED-1), interstitial α-smooth muscle actin (α-SMA), and interstitial collagen through Sirius red staining. The angiogenic factors VEGF and Tie-2 and the epithelial/tubular factors Ncam, bFGF, Pax-2, bone morphogenic protein-7, Noggin, Lim-1, Wnt-4, and Smads were analyzed. Renal stem cells were evaluated by Oct-4. We observed a significant reduction in serum creatinine levels, ED-1, α-SMA, and Sirius red as well as an important induction of Oct-4, angiogenic factors, and repairing proteins in NPX+bFGF animals compared with NPX+S animals. These results open new perspectives toward reducing damage progression in CKD.

Podocyte-specific VEGF down-regulation and pathophysiological development

It is well-known that vascular endothelial growth factor (VEGF) plays a key role in development and pathology, but its function in normal adult tissues is rarely understood. Increased use of anti-angiogenic therapies targeting VEGF in human pathologies have shown more and more adverse effects. In this report, a conditional expression model (Tet-On system) was used to down-regulate podocyte VEGF in adult mice, which resulted in many kidney problems, characterized by glomerular morphological changes, proteinuria, reduced water consumption and urination, increased urine electro-conductivity, as well as high susceptibility to BSA stress. Our findings indicated that podocyte-specific VEGF down-regulation resulted in poor kidney performance and led mice to be more susceptible to further kidney damages.

Anti-inflammatory effects of pigment epithelium-derived factor in diabetic nephropathy

Previously, we have reported that pigment epithelium-derived factor (PEDF) ameliorates albuminuria and inhibits matrix protein deposition in the kidney of streptozotocin (STZ)-induced diabetic rats, suggesting a renoprotective effect of PEDF in early stages of diabetic nephropathy. As inflammation is a major contributor to the development and progression of diabetic nephropathy, we examined in the present study whether PEDF inhibits renal inflammation in diabetic kidney. Diabetic rats received an intravenous injection of an adenovirus expressing PEDF (Ad-PEDF) or the same titer of a control virus. Three wk after the injection, diabetic rats treated with the control virus showed significantly elevated renal levels of proinflammatory factors such as ICAM-1, MCP-1, TNF-alpha, and VEGF compared with age-matched nondiabetic controls. Ad-PEDF effectively suppressed the overexpression of these proinflammatory factors in diabetic kidneys. In cultured primary human renal mesangial cells (HMC), the high-glucose medium-induced upregulation of VEGF and MCP-1 was largely blocked by PEDF. Furthermore, PEDF inhibited high glucose-induced activation of NF-kappaB, a key transcription factor mediating inflammatory responses, and hypoxia-inducible factor-1, a major activator of VEGF expression in HMC. These results suggest that the renoprotective effect of PEDF against diabetic nephropathy may be partially through its anti-inflammatory activity, likely by blocking the NF-kappaB and HIF-1 pathways.

Inhibition of bFGF-receptor type 2 increases kidney damage and suppresses nephrogenic protein expression after ischemic acute renal failure

Recovery from acute renal failure (ARF) requires the replacement of injured cells by new cells that are able to restore tubule epithelial integrity. We have recently described the expression of nephrogenic proteins [Vimentin, neural cell adhesion molecule, basic fibroblast growth factor (bFGF), Pax-2, bone morphogen protein-7, Noggin, Smad 1-5-8, p-Smad, hypoxia-inducible factor-1alpha, vascular endothelial growth factor], in a time frame similar to that observed in kidney development, after ischemic ARF induced in an ischemia-reperfusion (I/R) model. Furthermore, we show that bFGF, a morphogen involved in mesenchyme/epithelial transition in kidney development, induces a reexpression of morphogenic proteins in an earlier time frame and accelerates the recovery process after renal damage. Herein, we confirm that renal morphogenes are modulated by bFGF and hypothesized that a decrease in bFGF receptor 2 (bFGFR2) levels by the use of antisense oligonucleotides diminishes the expression of morphogenes. Male Sprague-Dawley rats submitted to ischemic injury were injected with 112 microg/kg bFGFR2 antisense oligonucleotide (bFGFR2-ASO) followed by reperfusion. Rats were killed, and the expression of nephrogenic proteins and renal marker damage was analyzed by immunohistochemistry and immunoblot. Animals subjected to I/R treated with bFGFR2-ASO showed a significant reduction in morphogen levels (P < 0.05). In addition, we observed an increase in markers of renal damage: macrophages (ED-1) and interstitial alpha-smooth muscle actin. These results confirm that bFGF participates in the recovery process and that treatment with bFGFR2-ASO induces an altered expression of morphogen proteins.

bFGF induces an earlier expression of nephrogenic proteins after ischemic acute renal failure

Recovery from acute renal failure (ARF) requires the replacement of injured cells with new cells that restore tubule epithelial integrity. We described recently the expression of a wide range of nephrogenic proteins in tubular cells after ARF induced by ischemia-reperfusion (I/R) (Villanueva S, Cespedes C, and Vio CP. Am J Physiol Regul Integr Comp Physiol 290: R861-R870, 2006). These markers, namely, Vimentin, neural cell adhesion molecules (Ncam), basic fibroblast growth factor (bFGF), paired homeobox-2 (Pax-2), bone morphogene protein-7 (BMP-7), Noggin, Lim-1, Engrailed, Smad, phospho-Smad, hypoxia-induced factor-1alpha (HIF-1alpha), VEGF, and Tie-2, are expressed in a time frame similar to that observed in normal kidney development. bFGF participates in early kidney development as a morphogen involved in mesenchyme/epithelial transition, and it is reexpressed in the recovery phase of ARF. To test the hypothesis that bFGF can accelerate the regeneration after renal damage, we used recombinant bFGF and studied the expression pattern of the above described morphogens in ARF. Male Sprague-Dawley rats were subjected to 30 min of renal ischemic injury and were injected with bFGF 30 microg/kg followed by reperfusion. Rats were killed and the expression of nephrogenic proteins were analyzed by immunohistochemistry and Western blot analysis. In the animals subjected to I/R treated with bFGF, we observed a 12- to 24-h earlier and more abundant reexpression of the proteins Ncam, bFGF, Pax-2, BMP-7, Noggin, Lim-1, Engrailed, VEGF, and Tie-2 than the I/R untreated rats. In addition, we observed a reduction in renal damage markers ED-1 and alpha-smooth muscle actin. These results indicate that bFGF can participate in the regeneration process and suggest that the treatment with bFGF can induce an earlier regeneration process after ischemic acute renal failure.

Insulin-induced vascular endothelial growth factor expression is mediated by the NADPH oxidase NOX3

Vascular endothelial growth factor (VEGF) is the most potent stimulatory factor of angiogenesis. Its expression is induced by reactive oxygen species (ROS) in hypoxic conditions and by insulin in normoxic cells. Both ROS and insulin can activate mitogen-activated protein kinases (MAPKs) and induce the transcriptional factor Sp1, components that are essential for VEGF gene expression. The aim of this study was to investigate the role of ROS producing NADPH oxidase enzymes (NOX-es) in insulin-regulated VEGF gene activation. To achieve this goal we chose HepG2 cells as our model system as these cells express the NADPH oxidase isoform NOX3 and respond to insulin stimulation with enhanced ROS production and mRNA transcription and production of VEGF. We demonstrate that in control cells insulin stimulation leads to H2O2 generation, a biphasic activation of p42/44 MAPK and the induction of both Sp1 and HIF-1alpha. Transfection of NOX3-specific siRNA abrogates H2O2 production and inhibits exclusively the second phase of p42/44 MAPK phosphorylation and Sp1 DNA binding and thus prevents upregulation of VEGF-A mRNA expression. In conclusion, our results demonstrate that NOX3, a ROS generating NADPH oxidase, plays an integral role in insulin-induced p42/44 MAPK signal transmission and VEGF-A production.

Microvascular growth, development, and remodeling in the embryonic avian kidney: the interplay between sprouting and intussusceptive angiogenic mechanisms

Embryonic development is associated with extensive vascular growth and remodeling. We used immunohistochemical, light and electron microscopical techniques, as well as vascular casting methods to study the developing chick embryo kidney with special attention to the interplay between sprouting and intussusceptive vascular growth modes. During inauguration at embryonic day 5 (E5), the early mesonephros was characterised by extensive microvascular sprouting. By E7, the vascular growth mode switched to intussusception, which contributed to rapid kidney vasculature growth up to E11, when the first obvious signs of vascular degeneration were evident. The metanephros underwent similar phases of vascular development inaugurating at E8 with numerous capillary sprouts and changing at E13 to intussusceptive growth, which was responsible for vascular amplification and remodeling. A phenomenal finding was that future renal lobules arose as large glomerular tufts, supplied by large vessels, which were split into smaller intralobular feeding and draining vessels with subsequent formation of solitary glomeruli. This glomerular duplication was achieved by intussusception, i.e., by formation of pillars in rows and their successive merging to delineate the vascular entities. Ultimately, the maturation of the vasculature was achieved by intussusceptive pruning and branching remodeling. An interesting finding was that strong VEGF expression was associated with the sprouting phase of angiogenesis while bFGF was upregulated during the phase of intussusceptive microvascular growth. We conclude that microvascular growth and remodeling in avian kidney follows an adroitly crafted pattern, which entails a precise spaciotemporal interplay between sprouting and intussusceptive angiogenic growth modes supported partly by VEGF and bFGF.

Decreased expression of pigment epithelium-derived factor is involved in the pathogenesis of diabetic nephropathy

Pigment epithelium-derived factor (PEDF) is a potent angiogenic inhibitor. Previous studies have shown that decreased ocular levels of PEDF are associated with diabetic retinopathy. However, the implication of PEDF expression in diabetic nephropathy has not been revealed. In the present study, we demonstrated for the first time that the expression of PEDF was decreased at both the mRNA and protein levels in the kidney of diabetic rats, whereas transforming growth factor-beta (TGF-beta) and fibronectin levels were increased in the same diabetic kidneys. As shown by immunohistochemistry, the decrease of PEDF expression occurs primarily in the glomeruli. In vitro studies showed that high concentrations of glucose significantly decreased PEDF secretion in primary human glomerular mesangial cells (HMCs), suggesting that hyperglycemia is a direct cause of the PEDF decrease in the kidney. Toward the function of PEDF, we showed that PEDF blocked the high-glucose-induced overexpression of TGF-beta, a major pathogenic factor in diabetic nephropathy, and fibronectin in primary HMCs, suggesting that PEDF may function as an endogenous inhibitor of TGF-beta expression and fibronectin production in glomeruli. Therefore, decreased expression of PEDF in diabetic kidneys may contribute to extracellular matrix overproduction and the development of diabetic nephropathy.

Somatostatin analogues: multiple roles in cellular proliferation, neoplasia, and angiogenesis

Angiogenesis, the development of new blood vessels is a crucial process both for tumor growth and metastatic dissemination. Additionally, dysregulation in angiogenesis has been implicated in the pathogenesis of cardiovascular disease, proliferative retinopathy, diabetic nephropathy, and rheumatoid arthritis (RA). The neuropeptide somatostatin has been shown to be a powerful inhibitor of neovascularization in several experimental models. Furthermore, somatostatin receptors (sst) are expressed on endothelial cells; particularly, sst2 has been found to be uniquely up-regulated during the angiogenic switch, from quiescent to proliferative endothelium. The present manuscript reviews the anti-angiogenic activity of somatostatin and its analogues in neoplastic and nonneoplastic disease. The role of sst subtypes particularly sst2 in mediating its angioinhibitory activity is described. Somatostatin agonists may also exert their anti-angiogenic activity indirectly by inhibition of growth factors like vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), and the growth hormone (GH)/insulin-like growth factor-I (IGF-I) axis or through its immunomodulatory effects. However, the therapeutic utility of somatostatin agonists as anti-angiogenic drugs in these diseases remains confusing because of conflicting results from different studies. More basic research, as well as patient-oriented studies, is required to firmly establish the clinical potential of somatostatin agonists in therapeutic angiogenesis. The currently available somatostatin agonists have high affinity of sst2 with lower affinities for sst3 and sst5. The emergence of novel somatostatin agonists especially bispecific analogues (agonists targeting multiple cellular receptors) and conjugates (synthesized by chemically linking somatostatin analogues with other antineoplastic agents) with improved receptor specificity signify a new generation of anti-angiogenics, which may represent novel strategies in the treatment of neovascularization-related diseases.