Angiotensinase A gene expression and enzyme activity in isolated glomeruli of diabetic rats

Knockout of aminopeptidase A in mice causes functional alterations and morphological glomerular basement membrane changes in the kidneys

Aminopeptidase A is one of the most potent enzymes within the renin-angiotensin system in terms of angiotensin II degradation. Here, we examined whether there is a kidney phenotype and any compensatory changes in other renin angiotensin system enzymes involved in the metabolism of angiotensin II associated with aminopeptidase A deficiency. Kidneys harvested from aminopeptidase A knockout mice were examined by light and electron microscopy, immunohistochemistry and immunofluorescence. Kidney angiotensin II levels and the ability of renin angiotensin system enzymes in the glomerulus to degrade angiotensin II ex vivo, their activities, protein and mRNA levels in kidney lysates were evaluated. Knockout mice had increased blood pressure and mild glomerular mesangial expansion without significant albuminuria. By electron microscopy, knockout mice exhibited a mild increase of the mesangial matrix, moderate thickening of the glomerular basement membrane but a striking appearance of knob-like structures. These knobs were seen in both male and female mice and persisted after the treatment of hypertension. In isolated glomeruli from knockout mice, the level of angiotensin II was more than three-fold higher as compared to wild type control mice. In kidney lysates from knockout mice angiotensin converting enzyme activity, protein and mRNA levels were markedly decreased possibly as a compensatory mechanism to reduce angiotensin II formation. Thus, our findings support a role for aminopeptidase A in the maintenance of glomerular structure and intra-kidney homeostasis of angiotensin peptides.

Garlic Attenuates Plasma and Kidney ACE-1 and AngII Modulations in Early Streptozotocin-Induced Diabetic Rats: Renal Clearance and Blood Pressure Implications

Raw garlic aqueous extract (GE) has ameliorative actions on the renin-angiotensin system in type-1 diabetes mellitus (DM); however its effects on plasma and kidney angiotensin I converting enzyme type-1 (ACE-1) and angiotensin II (AngII) require further elucidation. This study investigated the effect of GE on plasma and kidney ACE-1 and AngII concentrations and in relation to systemic and renal clearance indicators significant to blood pressure (BP) homeostasis in early streptozotocin- (STZ-) induced type-1 DM. Normal rats (n = 10) received 0.5 mL normal saline (NR/NS), diabetic rats (n = 10) received 0.5 mL NS (DR/NS), and treated diabetic rats (n = 10) received 50 mg/0.1 mL/100 g body weight GE (DR/GE) as daily intraperitoneal injections for 8 weeks. Compared to NR/NS, DR/NS showed a significant increase in plasma ACE-1 and AngII and conversely a decrease in kidney ACE-1 and AngII. These changes were associated with an increase in BP and clearance functions. Alternatively and compared to DR/NS, DR/GE showed normalization or attenuation in plasma and kidney ACE-1 and AngII. These GE induced rectifications were associated with moderation in BP elevation and renal clearance functions. Garlic attenuates modulations in plasma and kidney ACE-1 and AngII, in addition to BP and renal clearance function in type-1 DM.

The importance of the intrarenal renin-angiotensin system

Evidence suggests that virtually every organ system in the human body possesses a local renin-angiotensin system (RAS). These local systems seem to be independently regulated and compartmentalized from the plasma circulation, perhaps with the exception of the vascular endothelial system, which is responsible for maintaining physiological plasma levels of RAS components. Among these local RASs, the kidney RAS--the focus of this Review--seems to be of critical importance for the regulation of blood pressure and salt balance. Indeed, overactivation of the intrarenal RAS in certain disease states constitutes a pathogenic mechanism that leads to tissue injury, proliferation, fibrosis and ultimately, end-organ damage. Intrarenal levels of angiotensin peptides are considerably higher than those in plasma or any other organ tissue. Moreover, the kidney has a unique capacity to degrade angiotensin peptides, perhaps to maintain its intrinsic homeostasis. Interestingly, each local RAS has a distinct enzymatic profile resulting in different patterns of angiotensin fragment generation in different tissues. A better understanding of the autocrine and paracrine mechanisms involved in the renal RAS and other local RASs might direct future organ-specific therapy.

Regulation of renal 12(S)-hydroxyeicosatetraenoic acid in diabetes by angiotensin AT1 and AT2 receptors

Diabetes is associated with increased production of 12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE]. The mechanisms involved in this process remain unclear. We hypothesized that hyperglycemia and angiotensin II (ANG II) regulate renal 12(S)-HETE production via a balance between angiotensin AT(1) and AT(2) receptors activities. Using a microdialysis technique, renal interstitial fluid (RIF) levels of ANG II and 12(S)-HETE were monitored in normal control and streptozotocin-induced diabetic rats at baseline and then weekly thereafter for 12 wk. In a second group of normal and diabetic rats, 3 wk after development of diabetes, we monitored RIF 12(S)-HETE levels in response to acute AT(1) receptor blockade with valsartan or AT(2) receptor blockade with PD123319 individually or combined. Two weeks after induction of diabetes there was a 404% increase in ANG II (P < 0.05), a 149% increase in 12S-HETE (P < 0.05), and a 649% increase in urinary albumin excretion (P < 0.05). These levels remained elevated throughout the study. PD123319 given alone had no effect on 12(S)-HETE. Valsartan decreased 12(S)-HETE by 61.6% (P < 0.0001), a response that was abrogated when PD123319 was given with valsartan. These data demonstrate that hyperglycemia increases renal ANG II and 12(S)-HETE levels. The increase in 12(S)-HETE is mediated via AT(1) receptor. The attenuation of the effects of AT(1) receptor blockade by PD123319 suggests that AT(2) receptor contributes to the downregulation of renal 12(S)-HETE production.

AT1 and AT2 receptor in the kidney: role in health and disease

The renin angiotensin system plays an important role in the control of body fluid and electrolyte homeostasis and blood pressure regulation. Angiotensin II is the most effector hormone of this system and functions mainly through stimulation of its subtype receptors, namely, the AT1 and AT2 receptors. Most of the known physiological and pathologic effects of angiotensin II are mediated through stimulation of the AT1 receptor. The knowledge about the involvement of the AT2 receptor in physiological and pathologic processes is still evolving. In the kidney, both the AT1 and AT2 receptors contribute to the regulation of renal hemodynamic and tubular functions. Also, these receptors regulate renal cellular growth and matrix formation. However, AT2 receptor possesses functions that counteract the effects of the AT1 receptor. The balance between the AT1 and AT2 receptors can determine the renal status in health and disease.

Angiotensin III activates nuclear transcription factor-kappaB in cultured mesangial cells mainly via AT(2) receptors: studies with AT(1) receptor-knockout mice

Nuclear factor-kappaB (NF-kappaB) regulates many genes involved in renal pathophysiologic processes. It was previously demonstrated that angiotensin II (AngII) and its amino-terminal degradation product AngIII activate NF-kappaB in mesangial cells. However, which are the Ang receptor subtypes involved in the NF-kappaB pathway and whether these Ang peptides act through the same or different receptors in mesangial cells have not been evaluated. Under the culture conditions used, quiescent rat mesangial cells expressed both AT(1) and AT(2) receptors. To investigate the receptors involved in the NF-kappaB pathway, two different approaches were used, i.e., pharmacologic studies, using specific AT(1) and AT(2) receptor antagonists and agonists, and studies in AT(1) receptor-knockout mice. In cultured rat mesangial cells, both AT(1) and AT(2) receptor antagonists inhibited AngII-induced NF-kappaB DNA binding activity, whereas NF-kappaB activation elicited by AngIII was mainly blocked by the AT(2) receptor antagonist. Similar results were observed for cytosolic IkappaBalpha degradation. An AT(2) receptor agonist also activated NF-kappaB. In AT(1) receptor-knockout murine mesangial cells, AngIII and AngII increased NF-kappaB activity and degraded cytosolic IkappaBalpha; both processes were blocked by the AT(2) receptor antagonist. These data demonstrate that, in mesangial cells, NF-kappaB activation is mediated by AT(1) and AT(2) receptors, suggesting a novel intracellular signaling mechanism for AT(2) receptors in the kidney. Some differences in Ang peptide receptor-mediated responses were also observed. AngII activates NF-kappaB via AT(1) and AT(2) receptors, whereas AngIII acts mainly via AT(2) receptors. These results suggest the potential involvement of the AngIII/AT(2) receptor/NF-kappaB pathway in pathophysiologic processes in the kidney and provide a better understanding of the renin-angiotensin system.

Effects of amino acids and glucose on mesangial cell aminopeptidase a and angiotensin receptors

BACKGROUND

High protein diets and diabetes increase renal renin angiotensin system (RAS) activity, which is associated with glomerular injury. Aminopeptidase A (APA) is a cell surface metalloprotease that degrades angiotensin II (AII) in the mesangium. Mesangial cells (MC) also possess receptors for AII; the type 1 (AT1 receptor) promotes proliferation and fibrosis, while the type 2 (AT2 receptor) opposes these effects. We evaluated whether amino acids and glucose alter expression of APA, AT1 receptor and AT2 receptor in a manner that further augments RAS activity.

METHODS

Confluent rat MC were grown in serum-free media for 48 hours prior to exposing to experimental conditions: control (C), high amino acids (HA, mixed amino acid solution added to raise concentrations 5- to 6-fold over C), high glucose (HG 30, mM glucose). Semi-quantitative RT-PCR was used to assess mRNA for APA, AT1 receptor, AT2 receptor, and beta-actin. Values are expressed relative to beta actin.

RESULTS

Both HA and HG reduced APA mRNA (HG 1.13 plus minus 0.19, HA 1.12 plus minus 0.16 versus C 1.27 plus minus 0.16 P < 0.05, N = 8). HA increased AT1 receptor mRNA (HA 2.11 plus minus 0.43 versus C 1.14 plus minus 0.28 P < 0.05, N = 8). HG increased AT2 receptor mRNA (HG 1.31 plus minus 0.43 versus C 0.82 plus minus 0.33 P < 0.05, N = 6).

CONCLUSIONS

A reduction of APA, in response to high levels of amino acids or glucose, could contribute to increased AII as a result of decreased degradation in MC. The effect of amino acids to increase AT1 receptor expression may further enhance adverse hemodynamic and pro-fibrotic actions of AII. Conversely, glucose increased AT2 receptor expression, which could modulate responses mediated by the AT1 receptor.

Systemic infusion of angiotensin II into normal rats activates nuclear factor-kappaB and AP-1 in the kidney: role of AT(1) and AT(2) receptors

Recent studies have pointed out the implication of angiotensin II (Ang II) in various pathological settings. However, the molecular mechanisms and the AngII receptor (AT) subtypes involved are not fully identified. We investigated whether AngII elicited the in vivo activation of nuclear transcription factors that play important roles in the pathogenesis of renal and vascular injury. Systemic infusion of Ang II into normal rats increased renal nuclear factor (NF)-kappaB and AP-1 binding activity that was associated with inflammatory cell infiltration and tubular damage. Interestingly, infiltrating cells presented activated NF-kappaB complexes, suggesting the involvement of AngII in inflammatory cell activation. When rats were treated with AT(1) or AT(2) receptor antagonists different responses were observed. The AT(1) antagonist diminished NF-kappaB activity in glomerular and tubular cells and abolished AP-1 in renal cells, improved tubular damage and normalized the arterial blood pressure. The AT(2) antagonist diminished mononuclear cell infiltration and NF-kappaB activity in glomerular and inflammatory cells, without any effect on AP-1 and blood pressure. These data suggest that AT(1) mainly mediates tubular injury via AP-1/NF-kappaB, whereas AT(2) receptor participates in the inflammatory cell infiltration in the kidney by NF-kappaB. Our results provide novel information on AngII receptor signaling and support the recent view of Ang II as a proinflammatory modulator.

Proinflammatory actions of angiotensins

Many experimental data have suggested that the renin-angiotensin system participates in immune and inflammatory responses. Angiotensin II is involved in several steps of the inflammatory process: mononuclear cells respond to angiotensin II stimulation (cell proliferation and chemotaxis); angiotensin II regulates the recruitment of proinflammatory cells into the site of injury (mediated by the expression of vascular permeability factors, adhesion molecules and chemokines by resident cells); inflammatory cells can produce angiotensin II, and might therefore contribute to the perpetuation of tissue damage. In this review, we summarize the proinflammatory properties of angiotensin II, to demonstrate the novel role of this vasoactive peptide as a true cytokine. We will show the information obtained as a result of the pharmacological blockade of the renin angiotensin system, which has demonstrated that this system is involved in immune and inflammatory diseases. In this aspect, we discuss the molecular mechanism of angiotensin II-induced tissue damage, as well as its contribution to the pathogenesis of several diseases, including atherosclerosis, hypertension and renal damage, showing that angiotensin II plays an active role in the inflammatory response of these diseases.

Renal expression of aminopeptidase A in rats with two-kidney, one-clip hypertension

BACKGROUND

Angiotensin II (ANG II) is a major factor involved in the progression of chronic renal disease. Although the generation of this vasoactive peptide has been investigated in great detail, only a few studies have hitherto addressed the metabolism of ANG II into fragments such as angiotensin III and IV (ANG III, IV) which may exert physiological effects independent of ANG II. Aminopeptidase A (APA) is the major enzyme degrading ANG II. The aim of the current study was to evaluate glomerular APA expression in rats with two-kidney, one-clip hypertension.

METHODS

The left renal artery was restricted with a 0.2-mm silver clip. Kidneys were harvested 1 and 4 weeks after surgery. APA enzyme and protein expression was evaluated in kidney sections. Total APA enzyme activity and mRNA expression was assessed in isolated glomeruli. Degradation of exogenous ANG II by isolated glomeruli was measured with reverse-phase high-performance liquid chromatography.

RESULTS

APA enzyme activity, protein, and mRNA expression were stimulated in the clipped kidney 1 week after surgery compared with the contralateral kidney or normal controls. In contrast, 4 weeks after clipping APA activity and expression was higher in the contralateral kidney. In parallel to these findings, degradation of ANG II was greatest in isolated glomeruli obtained from the clipped kidney after 1 week. However, preparations from the contralateral kidney 4 weeks after surgery were more active in the metabolism of exogenous ANG II.

CONCLUSION

The present study provides evidence that APA is complexly regulated in in vivo situations with an activated local renin-ANG II system. ANG II appears to play a direct role in this regulation. However, since conversion of ANG II to ANG III by APA is the initial step leading to the formation of ANG IV which may exert detrimental effects not mediated through classical ANG II receptors, a local increase in APA activity may contribute to the progression of chronic renal disease even during complete AT(1)-receptor blockade.

Cell cycle regulation in diabetic nephropathy

Cell cycle regulation in diabetic nephropathy. Renal hypertrophy is one of the earliest abnormalities of diabetic nephropathy. Although selected cell populations. such as tubulointerstitial fibroblasts, may undergo sustained proliferation in the diabetic environment, most renal cells such as mesangial cells are arrested in the G1-phase of the cell cycle after actively leaving G0-phase and some self-limited early proliferation. High glucose, transforming growth factor-beta (TGF-beta), angiotensin II, and probably other factors induce inhibitors of cyclin-dependent kinases (CDK) including p21Cip1 and p27KiP1. These CDK-inhibitors bind to and inactivate G1-phase cyclin/CDK complexes. The consequence is a lack in kinase activity, underphosphorylation of the retinoblastoma gene protein, and a failure to initiate the G1-S-phase transit. The half-life of CDK-inhibitors may also be increased by serine phosphorylation mediated through activated MAP kinases. Treatment of diabetic rats with angiotensin-converting enzyme inhibitors attenuates glomerular hypertrophy and abolishes the glomerular expression of the CDK-inhibitors p16INK4 and p27KiP1, thus indicating that the cell cycle arrest can be therapeutically influenced. Cell cycle proteins may also be involved in these molecular events, leading to a limited degree of tubular apoptosis, which is a feature of diabetic nephropathy. Although not definitively proven, accumulating evidence suggests that early hypertrophy of renal cells may act as pacemaker for subsequent irreversible structural changes, such as glomerulosclerosis and tubulointerstitial fibrosis. Therefore, a better understanding of altered processes of cell cycle regulation is necessary to develop novel therapeutic strategies to prevent diabetic nephropathy. The recent observation that glomerular hypertrophy and proteinuria do not develop in diabetic p21CiP1 knockout mice indicates that this approach is feasible.

Angiotensin III increases MCP-1 and activates NF-kappaB and AP-1 in cultured mesangial and mononuclear cells

BACKGROUND

Monocyte infiltration is a common feature of renal diseases. Angiotensin II (Ang II) participates in inflammatory cell infiltration in the kidney. However, the influence of other peptides of the renin-angiotensin system, such as the N-terminal Ang II degradation product Ang III, has not been addressed.

METHODS

In cultured renal and mononuclear cells, we investigated whether Ang III is involved in monocyte recruitment through the regulation of the chemokine, monocyte chemoattractant protein-1 (MCP-1; Northern blot, Western blot, immunofluorescence, and chemotaxis), and the activation of transcription factors, nuclear factor kappaB (NF-kappaB) and activating protein-1 (AP-1; electrophoretic mobility shift assay).

RESULTS

In cultured rat mesangial and mononuclear cells, Ang III increased MCP-1 gene expression and protein levels. Supernatants from Ang III-treated mesangial cells showed increased chemoattractant activity for monocytes, which was partially inhibited by the addition of anti-MCP-1 antibody. Ang III elicited a rapid NF-kappaB activation (8-fold, after 30 min), showing a kinetics and intensity similar to that observed with Ang II and tumor necrosis factor-alpha. The maximal NF-kappaB activation was correlated with nuclear translocation of p50 and p65 subunits and disappearance of cytosolic IkappaB. Ang III also activated AP-1 (5-fold, after 18 h), while SP-1 was unchanged. Two NF-kappaB inhibitors abolished the Ang III-induced MCP-1 mRNA expression, suggesting that overexpression of this chemokine is mediated, at least in part, by NF-kappaB activation.

CONCLUSIONS

Ang III activates the transcription factors NF-kappaB and AP-1 and increases the expression of related genes, such as MCP-1. Our study describes a novel and potent proinflammatory action of this Ang degradation product, expanding the present view of the renin-angiotensin system.

Molecular mechanisms of diabetic renal hypertrophy

Altered growth of renal cells is one of the early abnormalities detected after the onset of diabetes. Cell culture studies whereby renal cells are exposed to high glucose concentrations have provided a considerable amount of insight into mechanisms of growth. In the glomerular compartment, there is a very early and self-limited proliferation of mesangial cells with subsequent hypertrophy, whereas proximal tubular cells primarily undergo hypertrophy. There is overwhelming evidence from in vivo and cell culture studies that induction of the transforming growth factor-beta (TGF-beta) system mediates the actions of high ambient glucose and that this system is pivotal for the hypertrophy of mesangial and tubular cells. Other factors such as hemodynamic forces, protein glycation products, and several mediators (for example, angiotensin II, endothelin-1, thromboxane, and platelet-derived growth factor) may further amplify the synthesis of TGF-beta and/or the expression of its receptors in the diabetic state. Cellular hypertrophy can be characterized by cell cycle arrest in the G1 phase. The molecular mechanism arresting mesangial cells in the G1 phase of the cell cycle is the induction of cyclin-dependent kinase (CdK) inhibitors such as p27Kip1 and p21, which bind to and inactivate cyclin-CdK complexes responsible for G1-phase exit. High-glucose-induced activation of protein kinase C and stimulated TGF-beta expression appear to be essential for stimulated expression of p27Kip1. In addition, a decreased turnover of protein caused by the inhibition of proteases contributes to hypertrophy. The development of irreversible renal changes in diabetes mellitus such as glomerulosclerosis and tubulointerstitial fibrosis is always preceded by the early hypertrophic processes in the glomerular and the tubular compartments. It may still be debated whether diabetic renal hypertrophy will inevitably lead to irreversible fibrotic changes in the absence of other factors such as altered intraglomerular hemodynamics and genetic predisposition. Nevertheless, understanding cellular growth on a molecular level may help design a novel therapeutic approach to prevent or treat diabetic nephropathy effectively.

Angiotensin III up-regulates genes involved in kidney damage in mesangial cells and renal interstitial fibroblasts

Angiotensin (Ang) II is considered the effector peptide of the renin-angiotensin system (RAS) that acts as a renal growth factor. Some studies have shown that the angiotensin degradation product Ang III presents some biological activities, though its role in renal pathology has not been explored. We have observed that in renal interstitial fibroblasts Ang III induces c-fos gene expression, suggesting a potential role of Ang III in the control of cell proliferation. To study the involvement of Ang III in matrix regulation, we determined whether Ang III increased TGF-beta gene expression and fibronectin production in cultured rat mesangial cells and renal interstitial fibroblasts, the main effector cells in glomerular and interstitial fibrosis, respectively. In both cell types, treatment with Ang III (10(-7) M) for six hours up-regulated gene expression of transforming growth factor-beta 1 (TGF-beta 1; 2.3- and 2.2-fold, respectively). This peptide also increased fibronectin production in renal interstitial fibroblasts. All these data suggest that Ang III could contribute to matrix accumulation. Activation of local RAS has been described during renal damage. Renal cells express angiotensinogen mRNA that was up-regulated in response to Ang II and Ang III stimulation, and therefore both peptides may participate in the generation of angiotensin peptides in the kidney. In conclusion, our results suggest that the angiotensin degradation product Ang III could participate in the pathogenesis of key events of renal diseases, supporting the hypothesis that other peptides of the RAS besides Ang II may be involved in renal injury.

Glomerular expression of p27Kip1 in diabetic db/db mouse: role of hyperglycemia

Early diabetic nephropathy is characterized by glomerular hypertrophy. Previous studies in vitro have demonstrated that mesangial cells exposed to high glucose are arrested in the G1-phase of the cell cycle and express increased levels of the cyclin-dependent kinase inhibitor p27Kip1. The present study was performed to investigate the renal expression of p27Kip1 in db/db mice, a model of diabetes mellitus type II. Glomerular p27Kip1 protein, but not mRNA expression, was strongly enhanced in diabetic db/db mice compared with non-diabetic db/+ littermates. Immunohistochemical studies revealed that this stimulated expression was mainly restricted to the nuclei of mesangial cells and podocytes, but glomerular endothelial cells occasionally also stained positively. Quantification of p27Kip1 positive glomerular cells showed a significant increase of these cells in db/db mice compared with non-diabetic db/+ animals. Although tubular cells revealed a positive staining for p27Kip1 protein, there was no difference between db/+ and db/db mice. Immunoprecipitation experiments revealed that p27Kip1 protein associates with Cdk2 and Cdk4, but not with Cdk6. To test for the influence of hyperglycemia on cell cycle arrest and p27Kip1 expression, mesangial cells were isolated from db/+ and db/db mice. There was a similar basal proliferation when these cells were grown in normal glucose-containing medium (100 mg/dl). However, raising the glucose concentration to 275 to 450 mg/dl induced cell cycle arrest in db/+ as well as db/db mesangial cells. Increasing the medium osmolarity with D-mannitol failed to induce p27Kip1 expression in mesangial cells. Transfection of cells with p27Kip1 antisense, but not missense, phosphorothioate oligonucleotides facilitated cell cycle progression equally well in db/+ and db/db mesangial cells. Furthermore, p27Kip1 expression was comparable in both cell lines in normal glucose, but increased in high glucose medium. Our studies demonstrate that p27Kip1 expression is enhanced in diabetic db/db animals. This induction appears to be due to hyperglycemia. Expression of p27Kip1 may be important in cell cycle arrest and hypertrophy of mesangial cells during early diabetic nephropathy.

Overexpression of aminopeptidase A abolishes the growth promoting effects of angiotensin II in cultured mouse mesangial cells

Angiotensin II (Ang II) has diverse effects on the glomerular tuft such as regulation of glomerular hemodynamics and stimulation of mesangial cell growth, and may be one pivotal factor in the progression of renal disease. In order to locally inactivate Ang II, we overexpressed aminopeptidase A (E.C. 3.4.11.7; ATA), a peptidase involved in the conversion of Ang II into angiotensin III, in a mouse mesangial cell line (MMC) that normally does not exhibit this enzyme. Stable transfections were selected in medium containing G418. ATA-overexpressing clones ATA5 and ATA21 revealed mRNA, protein, and enzyme activity in contrast to wild-type MMCs or mock-transfected Neo3 cells (stably transfected with expression vectors without ATA cDNA). There was no difference in the binding of Ang II to its putative receptors in all cell lines. Ang II increased intracellular inositol 1,4,5-triphosphate (IP3) in Neo3, but not in ATA5 and ATA21 cells. In contrast to MMCs and Neo3 cells, Ang II failed to stimulate proliferation in ATA5 and ATA21 clones as measured by [3H] thymidine incorporation and direct cell counts. However, ATA5 and ATA21 revealed a mitogenic response not different from MMCs after stimulation 2% or 10% of fetal calf serum. Treatment of ATA5 and ATA21 with 0.1 mM of the ATA-inhibitor amastatin or an ATA-inhibiting specific monoclonal antibody restored the proliferative effect of Ang II, suggesting that surface activity of ATA is involved in the attenuated mitogenesis in these cell. Our study demonstrates that it is feasible to overexpress Ang II-degrading enzymes in cultured mesangial cells and that this overexpression attenuated some effect of exogenous Ang II. These experiments are a first step toward the development of novel strategies to selectively antagonize locally generated Ang II in the kidney.

The role of angiotensin II in diabetic nephropathy: emphasis on nonhemodynamic mechanisms

Several systemic or intrarenal networks of cytokines and growth factors can be modulated by the diabetic state. We summarize the status of the renin-angiotensin system in diabetes mellitus and review the evidence of its involvement in the pathogenesis of diabetic nephropathy. Particular emphasis is placed on the nonhemodynamic properties of this vasoactive agent as both a renal growth factor and a profibrogenic peptide. Antagonizing the effects of angiotensin II with converting enzyme inhibitors is an established protective strategy in the management of diabetic nephropathy even in the absence of systemic hypertension. This and other indirect evidence from experimental animal studies suggest that the intrarenal concentration of angiotensin II may be increased as a result of increased synthesis and despite enhanced breakdown, that this peptide participates in the progression of diabetic nephropathy. However, down-regulation of angiotensin type 1 (AT1)-receptors is one of the abnormalities of both tubules and glomeruli in diabetic renal disease. A heightened bioactivation of the intrarenal angiotensin II system is therefore likely but not certain. Studies in cultured proximal tubular and glomerular mesangial cells have disclosed striking similarities between the effects of high glucose-containing medium and of treatment with angiotensin II on the growth properties and the induction of cytokines in these cells. There may also exist additive effects of angiotensin II and high glucose on signal-transduction pathways, such as activation of protein kinase C, although the contractile response to angiotensin II may be blunted by high glucose in mesangial cells. An important downstream mediator of the effects of both angiotensin II and high glucose is the activation of transforming growth factor-beta that can mediate at least some of the hypertrophic and profibrotic effects of either angiotensin II or high glucose in the diabetic kidney.