Endothelin antagonism prevents early EGFR transactivation but not increased matrix metalloproteinase activity in diabetes

Urinary exosome proteins PAK6 and EGFR as noninvasive diagnostic biomarkers of diabetic nephropathy

OBJECTIVE

The actin cytoskeleton plays an essential role in maintaining podocyte functions. However, whether the urinary exosome proteins related to the regulation of the actin cytoskeleton are changed in diabetic nephropathy (DN) is still unknown. This study was to investigate the possibility that related proteins can be applied as diagnostic biomarkers for DN.

METHODS

Urinary exosomes were obtained from 144 participants (Discovery phase: n = 72; Validation phase: n = 72) by size exclusion chromatography methods. Proteomic analysis of urinary exosome by LC-MS/MS. Western blot and ELISA were applied to validate the selected urinary exosome proteins. The clinical value of selected urinary exosome proteins was evaluated using correlation and receiver operating characteristic curve analyses.

RESULTS

Fifteen urinary proteins related to the regulation of the actin cytoskeleton were identified in urinary exosomes. Three upregulated proteins were selected, including Serine/threonine-protein kinase PAK6 (PAK6), Epidermal growth factor receptor (EGFR), and SHC-transforming protein 1(SHC1). The expression level of PAK6 and EGFR was negatively correlated with estimated glomerular filtration rate and positively correlated with serum creatinine levels. For diagnosing DN in the discovery phase: the area under curve (AUC) of PAK6 was 0.903, EGFR was 0.842, and the combination of two proteins was 0.912. These better performances were also observed in the validation phase (For PAK6: AUC = 0.829; For EGFR: AUC = 0.797; For PAK6 + EGFR: AUC = 0.897).

CONCLUSIONS

Urinary exosome proteins PAK6 and EGFR may be promising and noninvasive biomarkers for diagnosing DN.

Epidermal Growth Factor Receptor: A Potential Therapeutic Target for Diabetic Kidney Disease

Diabetic kidney disease (DKD) is a leading cause of end-stage renal disease worldwide and the major cause of renal failure among patients on hemodialysis. Numerous studies have demonstrated that transient activation of epidermal growth factor receptor (EGFR) pathway is required for promoting kidney recovery from acute injury whereas its persistent activation is involved in the progression of various chronic kidney diseases including DKD. EGFR-mediated pathogenesis of DKD is involved in hemodynamic alteration, metabolic disturbance, inflammatory response and parenchymal cellular dysfunction. Therapeutic intervention of this receptor has been available in the oncology setting. Targeting EGFR might also hold a therapeutic potential for DKD. Here we review the functional role of EGFR in the development of DKD, mechanisms involved and the perspective about use of EGFR inhibitors as a treatment for DKD.

Matrix Metalloproteinases in Diabetic Kidney Disease

Around the world diabetic kidney disease (DKD) is the main cause of chronic kidney disease (CKD), which is characterized by mesangial expansion, glomerulosclerosis, tubular atrophy, and interstitial fibrosis. The hallmark of the pathogenesis of DKD is an increased extracellular matrix (ECM) accumulation causing thickening of the glomerular and tubular basement membranes, mesangial expansion, sclerosis, and tubulointerstitial fibrosis. The matrix metalloproteases (MMPs) family are composed of zinc-dependent enzymes involved in the degradation and hydrolysis of ECM components. Several MMPs are expressed in the kidney; nephron compartments, vasculature and connective tissue. Given their important role in DKD, several studies have been performed in patients with DKD proposing that the measurement of their activity in serum or in urine may become in the future markers of early DKD. Studies from diabetic nephropathy experimental models suggest that a balance between MMPs levels and their inhibitors is needed to maintain renal homeostasis. This review focuses in the importance of the MMPs within the kidney and their modifications at the circulation, kidney and urine in patients with DKD. We also cover the most important studies performed in experimental models of diabetes in terms of MMPs levels, renal expression and its down-regulation effect.

Extracellular matrix roles in cardiorenal fibrosis: Potential therapeutic targets for CVD and CKD in the elderly

Whereas hypertension, diabetes, and dyslipidemia are age-related risk factors for cardiovascular disease (CVD) and chronic kidney disease (CKD), aging alone is an independent risk factor. With advancing age, the heart and kidney gradually but significantly undergo inflammation and subsequent fibrosis, which eventually results in an irreversible decline in organ physiology. Through cardiorenal network interactions, cardiac dysfunction leads to and responds to renal injury, and both facilitate aging effects. Thus, a comprehensive strategy is needed to evaluate the cardiorenal aging network. Common hallmarks shared across systems include extracellular matrix (ECM) accumulation, along with upregulation of matrix metalloproteinases (MMPs) including MMP-9. The wide range of MMP-9 substrates, including ECM components and inflammatory cytokines, implicates MMP-9 in a variety of pathological and age-related processes. In particular, there is strong evidence that inflammatory cell-derived MMP-9 exacerbates cardiorenal aging. This review explores the potential therapeutic targets against CVD and CKD in the elderly, focusing on ECM and MMP roles.

Matrix Metalloproteinases in Kidney Disease: Role in Pathogenesis and Potential as a Therapeutic Target

Matrix metalloproteinases (MMPs) are large family of proteinases. In addition to a fundamental role in the remodeling of the extracellular matrix, they also cleave a number of cell surface proteins and are involved in multiple cellular processes. MMP activity is regulated via numerous mechanisms, including inhibition by endogenous tissue inhibitors of metalloproteinases (TIMPs). Similar to MMPs, a role for TIMPs has been established in multiple cell signaling pathways. Aberrant expression of MMPs and TIMPS in renal pathophysiology has long been recognized, and with the generation of specific knockout mice, the mechanistic role of several MMPs and TIMPs is becoming more understood and has revealed both pathogenic and protective roles. This chapter will focus on the expression and localization of MMPs and TIMPs in the kidney, as well as summarizing the current information linking these proteins to acute kidney injury and chronic kidney disease. In addition, we will summarize studies suggesting that MMPs and TIMPs may be biomarkers of renal dysfunction and represent novel therapeutic targets to attenuate kidney disease.

Rethinking glomerular basement membrane thickening in diabetic nephropathy: adaptive or pathogenic?

Diabetic nephropathy (DN) is the leading cause of chronic kidney disease in the United States and is a major cause of cardiovascular disease and death. DN develops insidiously over a span of years before clinical manifestations, including microalbuminuria and declining glomerular filtration rate (GFR), are evident. During the clinically silent period, structural lesions develop, including glomerular basement membrane (GBM) thickening, mesangial expansion, and glomerulosclerosis. Once microalbuminuria is clinically apparent, structural lesions are often considerably advanced, and GFR decline may then proceed rapidly toward end-stage kidney disease. Given the current lack of sensitive biomarkers for detecting early DN, a shift in focus toward examining the cellular and molecular basis for the earliest structural change in DN, i.e., GBM thickening, may be warranted. Observed within one to two years following the onset of diabetes, GBM thickening precedes clinically evident albuminuria. In the mature glomerulus, the podocyte is likely key in modifying the GBM, synthesizing and assembling matrix components, both in physiological and pathological states. Podocytes also secrete matrix metalloproteinases, crucial mediators in extracellular matrix turnover. Studies have shown that the critical podocyte-GBM interface is disrupted in the diabetic milieu. Just as healthy podocytes are essential for maintaining the normal GBM structure and function, injured podocytes likely have a fundamental role in upsetting the balance between the GBM's synthetic and degradative pathways. This article will explore the biological significance of GBM thickening in DN by reviewing what is known about the GBM's formation, its maintenance during health, and its disruption in DN.

High Glucose Up-regulates ADAM17 through HIF-1α in Mesangial Cells

We previously showed that ADAM17 mediates high glucose-induced matrix production by kidney mesangial cells. ADAM17 expression is increased in diabetic kidneys, suggesting that its up-regulation may augment high glucose profibrotic responses. We thus studied the effects of high glucose on ADAM17 gene regulation. Primary rat mesangial cells were treated with high glucose (30 mm) or mannitol as osmotic control. High glucose dose-dependently increased ADAM17 promoter activity, transcript, and protein levels. This correlated with augmented ADAM17 activity after 24 h versus 1 h of high glucose. We tested involvement of transcription factors shown in other settings to regulate ADAM17 transcription. Promoter activation was not affected by NF-κB or Sp1 inhibitors, but was blocked by hypoxia-inducible factor-1α (HIF-1α) inhibition or down-regulation. This also prevented ADAM17 transcript and protein increases. HIF-1α activation by high glucose was shown by its increased nuclear translocation and activation of the HIF-responsive hypoxia-response element (HRE)-luciferase reporter construct. Assessment of ADAM17 promoter deletion constructs coupled with mutation analysis and ChIP studies identified HIF-1α binding to its consensus element at -607 as critical for the high glucose response. Finally, inhibitors of epidermal growth factor receptor (EGFR) and downstream PI3K/Akt, or ADAM17 itself, prevented high glucose-induced HIF-1α activation and ADAM17 up-regulation. Thus, high glucose induces ADAM17 transcriptional up-regulation in mesangial cells, which is associated with augmentation of its activity. This is mediated by HIF-1α and requires EGFR/ADAM17 signaling, demonstrating the potentiation by ADAM17 of its own up-regulation. ADAM17 inhibition thus provides a potential novel therapeutic strategy for the treatment of diabetic nephropathy.

The extracellular matrix in the kidney: a source of novel non-invasive biomarkers of kidney fibrosis?

Interstitial fibrosis is the common endpoint of end-stage chronic kidney disease (CKD) leading to kidney failure. The clinical course of many renal diseases, and thereby of CKD, is highly variable. One of the major challenges in deciding which treatment approach is best suited for a patient but also in the development of new treatments is the lack of markers able to identify and stratify patients with stable versus progressive disease. At the moment renal biopsy is the only means of diagnosing renal interstitial fibrosis. Novel biomarkers should improve diagnosis of a disease, estimate its prognosis and assess the response to treatment, all in a non-invasive manner. Existing markers of CKD do not fully and specifically address these requirements and in particular do not specifically reflect renal fibrosis. The aim of this review is to give an insight of the involvement of the extracellular matrix (ECM) proteins in kidney diseases and as a source of potential novel biomarkers of renal fibrosis. In particular the use of the protein fingerprint technology, that identifies neo-epitopes of ECM proteins generated by proteolytic cleavage by proteases or other post-translational modifications, might identify such novel biomarkers of renal fibrosis.

Inhibition of Src kinase blocks high glucose-induced EGFR transactivation and collagen synthesis in mesangial cells and prevents diabetic nephropathy in mice

Chronic exposure to high glucose leads to diabetic nephropathy characterized by increased mesangial matrix protein (e.g., collagen) accumulation. Altered cell signaling and gene expression accompanied by oxidative stress have been documented. The contribution of the tyrosine kinase, c-Src (Src), which is sensitive to oxidative stress, was examined. Cultured rat mesangial cells were exposed to high glucose (25 mmol/L) in the presence and absence of Src inhibitors (PP2, SU6656), Src small interfering RNA (siRNA), and the tumor necrosis factor-α-converting enzyme (TACE) inhibitor, TAPI-2. Src was investigated in vivo by administration of PP2 to streptozotocin (STZ)-induced diabetic DBA2/J mice. High glucose stimulated Src, TACE, epidermal growth factor receptor (EGFR), mitogen-activated protein kinases (MAPKs), extracellular signal-regulated kinase (ERK1/2, p38), and collagen IV accumulation in mesangial cells. PP2 and SU6656 blocked high glucose-stimulated phosphorylation of Src Tyr-416, EGFR, and MAPKs. These inhibitors and Src knockdown by siRNA, as well as TAPI-2, also abrogated high glucose-induced phosphorylation of these targets and collagen IV accumulation. In STZ-diabetic mice, albuminuria, increased Src pTyr-416, TACE activation, ERK and EGFR phosphorylation, glomerular collagen accumulation, and podocyte loss were inhibited by PP2. These data indicate a role for Src in a high glucose-Src-TACE-heparin-binding epidermal growth factor-EGFR-MAPK-signaling pathway to collagen accumulation. Thus, Src may provide a novel therapeutic target for diabetic nephropathy.

Combined Effects of PPAR γ Agonists and Epidermal Growth Factor Receptor Inhibitors in Human Proximal Tubule Cells

We aimed to determine whether epidermal growth factor receptor (EGFR) inhibition, in addition to a peroxisome proliferator-activated receptor gamma (PPARγ) agonist, prevents high-glucose-induced proximal tubular fibrosis, inflammation, and sodium and water retention in human proximal tubule cells exposed to normal glucose; high glucose; high glucose with the PPARγ agonist pioglitazone or with the P-EGFR inhibitor, gefitinib; or high glucose with both pioglitazone and gefitinib. We have shown that high glucose increases AP-1 and NFκB binding activity, downstream phosphorylation of EGFR and Erk1/2, and fibronectin and collagen IV expression. Pioglitazone reversed these effects but upregulated NHE3 and AQP1 expression. Gefitinib inhibited high glucose induced fibronectin and collagen IV, and EGFR and Erk1/2 phosphorylation and reversed pioglitazone-induced increases in NHE3 and AQP1 expression. Our data suggests that combination of an EGFR inhibitor and a PPARγ agonist mitigates high-glucose-induced fibrosis and inflammation and reverses the upregulation of transporters and channels involved in sodium and water retention in human proximal tubule cells. Hence EGFR blockade may hold promise, not only in limiting tubulointerstitial pathology in diabetic nephropathy, but also in limiting the sodium and water retention observed in patients with diabetes and exacerbated by PPARγ agonists.

Glibenclamide induces collagen IV catabolism in high glucose-stimulated mesangial cells

We have shown the full prevention of mesangial expansion in insulin-deficient diabetic rats by treatment with clinically-relevant dosages of glibenclamide (Glib). Studies in mesangial cells (MCs) also demonstrated reduction in the high glucose (HG)-induced accumulation of collagens, proposing that this was due to increased catabolism. In the present study, we investigated the signaling pathways that may be implicated in Glib action. Rat primary MCs were exposed to HG for 8 weeks with or without Glib in therapeutic (0.01 μM) or supratherapeutic (1.0 μM) concentrations. We found that HG increased collagen IV protein accumulation and PAI-1 mRNA and protein expression, in association with decreased cAMP generating capacity and decreased PKA activity. Low Glib increased collagen IV mRNA but fully prevented collagen IV protein accumulation and PAI-1 overexpression while enhancing cAMP formation and PKA activity. MMP2 mRNA, protein expression and gelatinolytic activity were also enhanced. High Glib was, overall, ineffective. In conclusion, low dosage/concentration Glib prevents HG-induced collagen accumulation in MC by enhancing collagen catabolism in a cAMP-PKA-mediated PAI-1 inhibition.

Cerebral myogenic reactivity and blood flow in type 2 diabetic rats: role of peroxynitrite in hypoxia-mediated loss of myogenic tone

Dysregulation of cerebral vascular function and, ultimately, cerebral blood flow (CBF) may contribute to complications such as stroke and cognitive decline in diabetes. We hypothesized that 1) diabetes-mediated neurovascular and myogenic dysfunction impairs CBF and 2) under hypoxic conditions, cerebral vessels from diabetic rats lose myogenic properties because of peroxynitrite (ONOO(-))-mediated nitration of vascular smooth muscle (VSM) actin. Functional hyperemia, the ability of blood vessels to dilate upon neuronal stimulation, and myogenic tone of isolated middle cerebral arteries (MCAs) were assessed as indices of neurovascular and myogenic function, respectively, in 10- to 12-week control and type 2 diabetic Goto-Kakizaki rats. In addition, myogenic behavior of MCAs, nitrotyrosine (NY) levels, and VSM actin content were measured under normoxic and hypoxic [oxygen glucose deprivation (OGD)] conditions with and without the ONOO(-) decomposition catalyst 5,10,15,20-tetrakis(4-sulfonatophenyl) prophyrinato iron (III), chloride (FeTPPs). The percentage of myogenic tone was higher in diabetes, and forced dilation occurred at higher pressures. Functional hyperemia was impaired. Consistent with these findings, baseline CBF was lower in diabetes. OGD reduced the percentage of myogenic tone in both groups, and FeTPPs restored it only in diabetes. OGD increased VSM NY in both groups, and although FeTPPs restored basal levels, it did not correct the reduced filamentous/globular (F/G) actin ratio. Acute alterations in VSM ONOO(-) levels may contribute to hypoxic myogenic dysfunction, but this cannot be solely explained by the decreased F/G actin ratio due to actin nitration, and mechanisms may differ between control and diabetic animals. Our findings also demonstrate that diabetes alters the ability of cerebral vessels to regulate CBF under basal and hypoxic conditions.

Endothelin and the podocyte

In the past decade, research has advanced our understanding how endothelin contributes to proteinuria and glomerulosclerosis. Data from pre-clinical and clinical studies now provide evidence that proteinuric diseases such as focal segmental glomerulosclerosis and diabetic nephropathy as well as hypertension nephropathy are sensitive to treatment with endothelin receptor antagonists (ERAs). Like blockade of the renin-angiotensin system, ERA treatment-under certain conditions-may even cause disease regression, effects that could be achieved on top of renin-angiotensin-aldosterone system blockade, suggesting independent therapeutic mechanisms by which ERAs convey nephroprotection. Beneficial effects of ERAs on podocyte function, which is essential to maintain the glomerular filtration barrier, have been identified as one of the key mechanisms by which inhibition of the endothelin ETA receptor ameliorates renal structure and function. In this article, we will review pre-clinical studies demonstrating a causal role for endothelin in proteinuric chronic kidney disease (with a particular focus on functional and structural integrity of podocytes in vitro and in vivo). We will also review the evidence suggesting a therapeutic benefit of ERA treatment on the functional integrity of podocytes in humans.

Deficient degradation of homotrimeric type I collagen, α1(I)3 glomerulopathy in oim mice

Col1a2-deficient (oim) mice synthesize homotrimeric type I collagen due to nonfunctional proα2(I) collagen chains. Our previous studies revealed a postnatal, progressive type I collagen glomerulopathy in this mouse model, but the mechanism of the sclerotic collagen accumulation within the renal mesangium remains unclear. The recent demonstration of the resistance of homotrimeric type I collagen to cleavage by matrix metalloproteinases (MMPs), led us to investigate the role of MMP-resistance in the glomerulosclerosis of Col1a2-deficient mice. We measured the pre- and post-translational expression of type I collagen and MMPs in glomeruli from heterozygous and homozygous animals. Both the heterotrimeric and homotrimeric isotypes of type I collagen were equally present in whole kidneys of heterozygous mice by immunohistochemistry and biochemical analysis, but the sclerotic glomerular collagen was at least 95-98% homotrimeric, suggesting homotrimeric type I collagen is the pathogenic isotype of type I collagen in glomerular disease. Although steady-state MMP and Col1a1 mRNA levels increased with the disease progression, we found these changes to be a secondary response to the deficient clearance of MMP-resistant homotrimers. Increased renal MMP expression was not sufficient to prevent homotrimeric type I collagen accumulation.

Sildenafil, a phosphodiesterase type 5 inhibitor, attenuates diabetic nephropathy in non-insulin-dependent Otsuka Long-Evans Tokushima Fatty rats

BACKGROUND

It is well established that the pathogenesis of diabetic nephropathy is associated with abnormalities of renal nitric oxide (NO) generation. Many of the biological actions of NO are mediated by cGMP, which is rapidly degraded by phosphodiesterases. In this study, we evaluated the renoprotective effects of sildenafil (SIL), an inhibitor of phosphodiesterase-5, in type 2 diabetic rats.

METHODS

Male Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a non-insulin-dependent diabetes model, and Long-Evans Tokushima Otsuka rats, a non-diabetic control, were treated with either SIL (2.5 mg·kg(-1) in drinking water) or undosed water for 28 weeks, starting at 30 weeks of age.

RESULTS

Sildenafil treatment significantly decreased albuminuria, attenuated glomerular hyperfiltration and resulted in a decrease in glomerular hypertrophy, in addition to a reduced glomerulosclerosis score and a dramatic decrease in the number of glomerular and tubulointerstitial proliferating cell nuclear antigen-positive cells in OLETF rats. This was accompanied by a significant reduction in renal cortical mRNA levels of collagen types I and III. The increased mRNA levels of matrix metalloproteinase (MMP)-2, MMP-9, tissue inhibitors of MMPs (TIMP)-1 and TIMP-2 in the OLETF rats were significantly or partially attenuated by SIL treatment.

CONCLUSIONS

This study suggests that SIL attenuated diabetic nephropathy due to its potent antiproliferative effects and its regulatory effects on extracellular matrix. This latter effect is thought to be a result of its ability to affect the balance between MMPs and their inhibitors.

Renal expression of proto-oncogene Ets-1 on matrix remodeling in experimental diabetic nephropathy

The molecular mechanisms of glomerulosclerosis and tubulointerstitial fibrosis in diabetic nephropathy (DN) have received scant attention. Ets-1 proto-oncogene plays a role in matrix remodeling by regulating matrix-degrading enzymes. We investigated the possible role of Ets-1 in the pathogenesis of DN. 6-week-old male Sprague-Dawley rats were divided into two experimental groups as follows: control group (n=30) and a Diabetes mellitus group (n=40) induced by injection of streptozotozin (STZ). The rats were investigated at 1, 4, 8, 12 and 16 weeks after STZ-treatment. By means of immunohistochemistry, the expression of Ets-1 in glomeruli was significantly increased in STZ-treated rat kidneys from week 1 (P<0.05) and reached the peak at week 4 (P<0.05), followed by a downward trend at subsequent time points. Similarly, the expression of Ets-1 in the tubulointerstitium was also markedly increased from week 1 (P<0.05) and reached a maximum at week 8 (P<0.05). By double immunostaining, Ets-1-positive cells were frequently found to co-express matrix metalloproteinase-2 (MMP-2) in STZ-treated rat kidneys. Increased expression of tissue inhibitor of metalloproteinase-2 (TIMP-2) coincided with increased expression of α-smooth muscle actin (α-SMA) in STZ-induced DN. A positive relationship was observed between the expression of Ets-1 in glomeruli or tubulointerstitium and the expression of MMP-2 (P<0.01; P<0.01, respectively) in STZ-treated rat kidneys. The ratio of MMP-2 and TIMP-2 in glomeruli or tubulointerstitium was negatively correlated with deposition of type IV collagen (P<0.01; P<0.01, respectively). These findings suggest that Ets-1 may play a critical role in fine-tuning matrix remodeling of STZ-induced DN.

Dual endothelin receptor antagonism prevents remodeling of resistance arteries in diabetes

Vascular remodeling, characterized by extracellular matrix deposition and increased media-to-lumen (M/L) ratio, contributes to the development of microvascular complications in diabetes. We have previously shown in type 2 diabetic Goto-Kakizaki (GK) rats that selective ETA receptor blockade prevents medial thickening of mesenteric arteries via regulation of matrix metalloproteases (MMP), whereas selective ETB receptor blockade augments this thickening. The goal of this study was to determine the effect of combined ETA and ETB receptor blockade on resistance vessel remodeling. Vessel structure, MMP activity, and extracellular matrix proteins were assessed in control Wistar and diabetic GK rats treated with vehicle or bosentan (100 mg/kg per day) for 4 weeks (n = 7-9 per group). Bosentan completely prevented the increase in M/L ratio and MMP-2 activity in diabetes but paradoxically increased M/L ratio and MMP activation in control animals. Collagenase (MMP-13) activity and protein levels were significantly decreased in diabetes. Accordingly, collagen deposition was augmented in GK rats. Dual ET receptor antagonism improved enzyme activity and normalized MMP-13 levels in diabetic animals but blunted MMP-13 activity in control animals. In summary, current findings suggest that diabetes-mediated remodeling of resistance arteries is prevented by dual blockade of ETA and ETB receptors and that the relative role of ET receptors in the regulation of vascular structure differs in the control and disease states.

HB-EGF release mediates glucose-induced activation of the epidermal growth factor receptor in mesangial cells

Glomerular matrix accumulation is a hallmark of diabetic nephropathy. We showed that transactivation of the epidermal growth factor receptor (EGFR) is an important mediator of matrix upregulation in mesangial cells (MC) in response to high glucose (HG). Here, we study the mechanism of EGFR transactivation. In primary MC, EGFR transactivation by 1 h of HG (30 mM) was unaffected by inhibitors of protein kinase C, reactive oxygen species, or the angiotensin II AT1 receptor. However, general metalloprotease inhibition, as well as specific inhibitors of heparin-binding EGF-like growth factor (HB-EGF), prevented both EGFR and downstream Akt activation. HB-EGF was released into the medium by 30 min of HG, and this depended on metalloprotease activity. One of the metalloproteases shown to cleave proHB-EGF is ADAM17 (TACE). HG, but not an osmotic control, activated ADAM17, and its inhibition prevented EGFR and Akt activation and HB-EGF release into the medium. siRNA to either ADAM17 or HB-EGF prevented HG-induced EGFR transactivation. We previously showed that EGFR/Akt signaling increases transforming growth factor (TGF)-β1 transcription through the transcription factor activator protein (AP)-1. HG-induced AP-1 activation, as assessed by EMSA, was abrogated by inhibitors of metalloproteases, HB-EGF and ADAM17. HB-EGF and ADAM17 siRNA also prevented AP-1 activation. Finally, these inhibitors and siRNA prevented TGF-β1 upregulation by HG. Thus, HG-induced EGFR transactivation in MC is mediated by the release of HB-EGF, which requires activity of the metalloprotease ADAM17. The mechanism of ADAM17 activation awaits identification. Targeting upstream mediators of EGFR transactivation including HB-EGF or ADAM17 provides novel therapeutic targets for the treatment of diabetic nephropathy.

Advanced glycation end-products activate extracellular signal-regulated kinase via the oxidative stress-EGF receptor pathway in renal fibroblasts

Advanced glycation end-products (AGEs), epidermal growth factor receptor (EGFR), reactive oxygen species (ROS), and extracellular signal-regulated kinases (ERK) are implicated in diabetic nephropathy (DN). Therefore, we asked if AGEs-induced ERK protein phosphorylation and mitogenesis are dependent on the receptor for AGEs (RAGE)-ROS-EGFR pathway in normal rat kidney interstitial fibroblast (NRK-49F) cells. We found that AGEs (100 microg/ml) activated EGFR and ERK1/2, which was attenuated by RAGE short-hairpin RNA (shRNA). AGEs also increased RAGE protein and intracellular ROS levels while RAGE shRNA and N-acetylcysteine (NAC) attenuated AGEs-induced intracellular ROS. Hydrogen peroxide (5-25 microM) increased RAGE protein level while activating both EGFR and ERK1/2. Low-dose hydrogen peroxide (5 microM) increased whereas high-dose hydrogen peroxide (100 microM) decreased mitogenesis at 3 days. AGEs-activated EGFR and ERK1/2 were attenuated by an anti-oxidant (NAC) and an EGFR inhibitor (Iressa). Moreover, AGEs-induced mitogenesis was attenuated by RAGE shRNA, NAC, Iressa, and an ERK1/2 inhibitor (PD98059). In conclusion, it was found that AGEs-induced mitogenesis is dependent on the RAGE-ROS-EGFR-ERK1/2 pathway whereas AGEs-activated ERK1/2 is dependent on the RAGE-ROS-EGFR pathway in NRK-49F cells.

Early inhibition of EGFR signaling prevents diabetes-induced up-regulation of multiple gene pathways in the mesenteric vasculature

Diabetes mellitus is associated with vascular complications including an impairment of vascular function and alterations in the reactivity of blood vessels to vasoactive hormones. However, the signaling mechanisms leading to vascular dysfunction in diabetes are not fully understood. This microarray-based study was designed to identify differential gene expression between the normal and diabetic mesenteric vasculature and to investigate the effect of inhibiting epidermal growth factor receptor (EGFR) signaling on global gene expression in the mesenteric bed of streptozotocin (STZ)-induced diabetic rats. Transcriptome analysis was performed in triplicate using oligonucleotide microarrays housing 10,000 rat genes on the mesenteric bed of normal, diabetic, and diabetic rats treated with AG1478, a selective inhibitor of EGFR. Four weeks of diabetes led to a profound alteration in gene expression within the mesenteric bed with 1167 of the 3074 annotated genes being up-regulated and 141 genes down-regulated by at least 2-fold. The up-regulated gene ontologies included receptor tyrosine kinases, G-protein coupled receptors and ion channel activity. In particular, significant overexpressions of colipase, phospholipase A2, carboxypeptidases, and receptor tyrosine kinases such as EGFR, erbB2 and fibroblast growth factor receptor were observed in diabetes mesenteric vasculature. A 4-week intraperitoneal treatment of diabetic animals with AG1478 (1.2 mg/kg/alt diem) beginning on the same day as STZ injection prevented up-regulation of the majority (approximately 95%) of the genes associated with STZ diabetes including those apparently "unrelated" to the known EGFR pathway without correction of hyperglycemia. These results suggest that activation of EGFR signaling is a key initiating step that leads to induction of multiple signaling pathways in the development of diabetes-induced vascular dysfunction. Thus, therapeutic targeting of EGFR may represent a novel strategy for the prevention and/or treatment of vascular dysfunction in diabetes.

Endothelin receptor selectivity in chronic kidney disease: rationale and review of recent evidence

Endothelin (ET) is a potent vasoconstrictory peptide with proinflammatory and profibrotic properties that exerts its biological effects through two pharmacologically distinct receptor subtypes, namely ET(A) and ET(B). In addition to its substantial contribution to normal renal function, a large body of evidence suggests that derangement of the renal ET system is involved in the initiation and progression of chronic kidney disease (CKD) in diabetes, hypertension and glomerulonephritis. Thus, the use of ET receptor antagonists (ERAs) may offer potential novel treatment strategies in CKD. Recent literature on the role of the renal ET system in the healthy kidney was reviewed. In addition, an unbiased PubMed search was performed for studies published during the last 5 years that addressed the effects of ERAs in CKD. A particular objective was to extract information regarding whether selective or nonselective ERAs may have therapeutic potential in humans. ET-1 acts primarily as an autocrine or paracrine factor in the kidney. In normal physiology, ET-1 promotes diuresis and natriuresis by local production and action through ET(B) receptors in the renal medulla. In pathology, ET-1 mediates vasoconstriction, mesangial-cell proliferation, extracellular matrix production and inflammation, effects that are primarily conveyed by ET(A) receptors. Results obtained in animal models and in humans with the use of ERAs in CKD are encouraging; nevertheless, it is still under debate which receptor subtype should be targeted. According to most studies, selective inhibition of ET(A) receptors appears superior compared with nonselective ERAs because this approach does not interfere with the natriuretic, antihypertensive and ET clearance effects of ET(B) receptors. Although preliminary data in humans are promising, the potential role of ERAs in patients with CKD and the question of which receptor subtype should be targeted can only be clarified in randomized clinical trials.

Global upregulation of gene expression associated with renal dysfunction in DOCA-salt-induced hypertensive rats occurs via signaling cascades involving epidermal growth factor receptor: a microarray analysis

Renal dysfunction is a major cause of morbidity and mortality in patients with hypertension. In an attempt to understand the molecular mechanisms leading to renal dysfunction and in particular that of epidermal growth factor receptor (EGFR) and RasGTPase signaling, we analyzed global gene expression changes in the kidneys of deoxycorticosterone acetate (DOCA)-salt-induced hypertensive rats with and without treatment with AG1478, a selective inhibitor of EGFR tyrosine kinase, or FPTIII, a farnesyl transferase inhibitor known to inhibit RasGTPase. Microarray-based global gene expression analysis was performed in triplicate for each rat kidney taken from normotensive Wistar rats, DOCA-salt hypertensive (DH) rats, DH rats treated with AG1478, or DH rats treated with FPTIII. From the initial data set of 10,163 gene spots per group, upregulation of 2398 genes and downregulation of only 50 genes by more than 2-fold was observed in hypertensive rat kidneys compared to non-diseased controls. Interestingly, treatment of animals with AG1478 or FPTIII prevented upregulation of more than 97% of genes associated with hypertension in the rat kidney. Analysis of proteinuria, renal artery responsiveness and histopathology studies confirmed that DOCA-salt hypertensive rats had developed kidney damage over the study period and that this kidney dysfunction could be significantly prevented upon AG1478 or FPTIII treatment without normalising blood pressure. Taken together, our data imply that signaling cascades involving EGFR and/or RasGTPase pathways are key contributors to the induction of renal damage in hypertension and these and potentially other downstream effector molecules may serve as novel targets for therapeutic intervention.

Matrix metalloproteinases: their potential role in the pathogenesis of diabetic nephropathy

Matrix metalloproteinases (MMPs), a family of proteinases including collagenases, gelatinases, stromelysins, matrilysins, and membrane-type MMPs, affect the breakdown and turnover of extracellular matrix (ECM). Moreover, they are major physiologic determinants of ECM degradation and turnover in the glomerulus. Renal hypertrophy and abnormal ECM deposition are hallmarks of diabetic nephropathy (DN), suggesting that altered MMP expression or activation contributes to renal injury in DN. Herein, we review and summarize recent information supporting a role for MMPs in the pathogenesis of DN. Specifically, studies describing dysregulated activity of MMPs and/or their tissue inhibitors in various experimental models of diabetes, including animal models of type 1 or type 2 diabetes, clinical investigations of human type 1 or type 2 diabetes, and kidney cell culture studies are reviewed.

Evidence for vasculoprotective effects of ETB receptors in resistance artery remodeling in diabetes

OBJECTIVE

Vascular remodeling, characterized by extracellular matrix deposition and increased media-to-lumen (M/l) ratio, contributes to the development of microvascular complications in diabetes. Matrix metalloproteinases (MMPs) play an important role in the regulation of extracellular matrix (ECM) turnover and vascular remodeling. Vasoactive factor endothelin (ET)-1 not only causes potent vasoconstriction but also exerts profibrotic and proliferative effects that change vessel architecture, which makes it a likely candidate for a key role in vascular complications of diabetes. Thus, this study investigated the regulation of MMP activity of resistance arteries under mild-to-moderate diabetes conditions, as seen in type 2 diabetes, and the relative role of ET receptors in this process.

RESEARCH DESIGN AND METHODS

Vessel structure, MMP activity, and ECM proteins were assessed in control Wistar and diabetic Goto-Kakizaki (GK) rats treated with vehicle, ET(A) receptor antagonist atrasentan (5 mg x kg(-1) x day(-1)), or ET(B) receptor antagonist A-192621 (15 mg x kg(-1) x day(-1)) for 4 weeks.

RESULTS

M/l ratio was increased in diabetes. Atrasentan prevented this increase, whereas A-192621 caused further thickening of the medial layer. Increased MMP-2 activity in diabetes was prevented by atrasentan treatment. Collagenase activity was significantly decreased in diabetes, and while ET(A) antagonism improved enzyme activity, ET(B) blockade further reduced collagenase levels. Accordingly, collagen deposition was augmented in GK rats, which was reversed by atrasentan but exacerbated with A-192621.

CONCLUSIONS

ET-1 contributes to the remodeling of mesenteric resistance arteries in diabetes via activation of ET(A) receptors, and ET(B) receptors provide vasculoprotective effects.

Increased hemorrhagic transformation and altered infarct size and localization after experimental stroke in a rat model type 2 diabetes

BACKGROUND

Interruption of flow through of cerebral blood vessels results in acute ischemic stroke. Subsequent breakdown of the blood brain barrier increases cerebral injury by the development of vasogenic edema and secondary hemorrhage known as hemorrhagic transformation (HT). Diabetes is a risk factor for stroke as well as poor outcome of stroke. The current study tested the hypothesis that diabetes-induced changes in the cerebral vasculature increase the risk of HT and augment ischemic injury.

METHODS

Diabetic Goto-Kakizaki (GK) or control rats underwent 3 hours of middle cerebral artery occlusion and 21 h reperfusion followed by evaluation of infarct size, hemorrhage and neurological outcome.

RESULTS

Infarct size was significantly smaller in GK rats (10 +/- 2 vs 30 +/- 4%, p < 0.001). There was significantly more frequent hematoma formation in the ischemic hemisphere in GK rats as opposed to controls. Cerebrovascular tortuosity index was increased in the GK model (1.13 +/- 0.01 vs 1.34 +/- 0.06, P < 0.001) indicative of changes in vessel architecture.

CONCLUSION

These findings provide evidence that there is cerebrovascular remodeling in diabetes. While diabetes-induced remodeling appears to prevent infarct expansion, these changes in blood vessels increase the risk for HT possibly exacerbating neurovascular damage due to cerebral ischemia/reperfusion in diabetes.

Differential effects of ET(A) and ET(B) receptor antagonism on oxidative stress in type 2 diabetes

Endothelin (ET-1) is chronically elevated in diabetes. However, role of ET-1 in increased oxidative stress in type 2 diabetes is less clear. This study tested the hypotheses that: 1) oxidative stress markers are increased and total antioxidant capacity is decreased in diabetes, and 2) activation of ET(A) receptors mediates oxidative stress whereas ET(B) receptors display opposing effects. Plasma total antioxidant status (TAS) and 8-isoprostane (8-iso PGF(2alpha)) as well as total nitrotyrosine levels in mesenteric resistance vessels were measured in control Wistar and diabetic Goto-Kakizaki (GK) rats (n=5-10) treated with vehicle, ET(A) antagonist (atrasentan, 5 mg/kg/day), or ET(B) receptor antagonist (A-192621, 15 or 30 mg/kg/day, low and high dose, respectively) for 4 weeks. 8-iso PGF(2alpha) (pg/ml) levels were significantly higher in low dose A-192621 treatment groups of control and diabetic rats than in atrasentan or high-dose A-192621 treated groups. Protein nitration was increased in diabetes and ET(A) receptor antagonism prevented this increase. TAS levels were similar in all experimental groups. Thus, ET-1 contributes to oxidative stress in type 2 diabetes and ET receptor antagonism with atrasentan or A-192612 displays differential effects depending on dose and receptor subtype.

Role of matrix metalloproteinases in renal pathophysiologies

Matrix metalloproteinases (MMPs) are a large family of proteinases that remodel extracellular matrix (ECM) components and cleave a number of cell surface proteins. MMP activity is regulated via a number of mechanisms, including inhibition by tissue inhibitors of metalloproteinases (TIMPs). Originally thought to cleave only ECM proteins, MMP substrates are now known to include signaling molecules (growth factor receptors) and cell adhesion molecules. Recent data suggest a role for MMPs in a number of renal pathophysiologies, both acute and chronic. This review will focus on the expression and localization of MMPs and TIMPs in the kidney, as well as summarizing the current information linking these proteins to acute kidney injury, glomerulosclerosis/tubulointerstitial fibrosis, chronic allograft nephropathy, diabetic nephropathy, polycystic kidney disease, and renal cell carcinoma.

Matrix metalloproteinase 2 and basement membrane integrity: a unifying mechanism for progressive renal injury

Chronic kidney disease (CKD) and failure are problems of increasing importance. Regardless of the primary etiology, CKD is characterized by tubular atrophy, interstitial fibrosis, and glomerulosclerosis. It has been assumed that diminished matrix metalloproteinase (MMP) activity is responsible for the accumulation of the extracellular matrix (ECM) proteins and collagens that typify the fibrotic kidney. Here we demonstrate that transgenic renal proximal tubular epithelial expression of a specific enzyme, MMP-2, is sufficient to generate the entire spectrum of pathological and functional changes characteristic of human CKD. At the earliest point, MMP-2 leads to structural alterations in the tubular basement membrane, a process that triggers tubular epithelial-mesenchymal transition, with resultant tubular atrophy, fibrosis and renal failure. Inhibition of MMP-2, specifically in the early, prefibrotic stages of disease may offer an additional approach for treatment of these disabling disorders.

Type-2 diabetes-induced changes in vascular extracellular matrix gene expression: relation to vessel size

BACKGROUND

Hyperglycemia-induced changes in vascular wall structure contribute to the pathogenesis of diabetic microvascular and macrovascular complications. Matrix metalloproteinases (MMP), a family of proteolytic enzymes that degrade extracellular matrix (ECM) proteins, are essential for vascular remodeling. We have shown that endothelin-1 (ET-1) mediates increased MMP activity and associated vascular remodeling in Type 2 diabetes. However, the effect of Type 2 diabetes and/or ET-1 on the regulation of ECM and MMP gene expression in different vascular beds remains unknown.

METHODS

Aorta and mesenteric artery samples were isolated from control, Type 2 diabetic Goto-Kakizaki (GK) rats and GK rats treated with ETA antagonist ABT-627. Gene expression profile of MMP-2, MMP-9, MT1-MMP, fibronectin, procollagen type 1, c-fos and c-jun, were determined by quantitative real-time (qRT) PCR. In addition, aortic gene expression profile was evaluated by an ECM & Adhesion Molecules pathway specific microarray approach.

RESULTS

Analysis of the qRT-PCR data demonstrated a significant increase in mRNA levels of MMPs and ECM proteins as compared to control animals after 6 weeks of mild diabetes. Furthermore, these changes were comparable in aorta and mesentery samples. In contrast, treatment with ETA antagonist prevented diabetes-induced changes in expression of MMPs and procollagen type 1 in mesenteric arteries but not in aorta. Microarray analysis provided evidence that 27 extracellular matrix genes were differentially regulated in diabetes. Further qRT-PCR with selected 7 genes confirmed the microarray data.

CONCLUSION

These results suggest that the expression of both matrix scaffold protein and matrix degrading MMP genes are altered in macro and microvascular beds in Type 2 diabetes. ETA antagonism restores the changes in gene expression in the mesenteric bed but not in aorta suggesting that ET-1 differentially regulates microvascular gene expression in Type 2 diabetes.