Wynand B.W.H. Melenhorst

Adamalysins in biology and disease

ADAMs (a disintegrin and metalloprotease) are membrane‐bound enzymes, capable of shedding a multitude of proteins from the surface of the cell. They are therefore considered crucial modulators of physiological and pathophysiological processes. The structure and function of ADAMs is related to those of a family of snake venom metalloproteases which also possess a potential adhesion domain as well as a potential protease domain. Mammalian ADAMs are involved in various biological and disease‐related processes, such as cell–cell fusion, adhesion and intracellular signalling. Functional involvement has been described in sperm–egg binding and fusion, trophoblast invasion and matrix degradation during pregnancy, angiogenesis and neovascularization. Clinically, ADAMs are implicated in pathological processes, including cancer, inflammation, neurodegeneration and fibrosis, through shedding of the apoptosis‐inducing FAS ligand, cytokines and growth factors. A second group of proteins within the ADAM family has recently been discovered. These contain several thrombospondin‐like repeats in their C‐terminal regions, in the absence of the transmembrane domain known to be present in ADAMs. These proteins were called the ADAMTS (ADAM with thrombospondin domains) family. The relevance of ADAMTS enzymes has become evident in patients with a deficiency in ADAMTS‐13, a von Willebrand factor cleaving protease. These patients develop thrombotic thrombocytopenic purpura, a devastating thrombotic disorder caused by widespread microvascular thrombi composed of platelets and von Willebrand factor (VWF). Here we focus on the genetic, developmental, functional and disease‐related aspects of ADAMs and ADAMTS. Finally we discuss the perspectives of the therapeutical potential of ADAMs in disease. Copyright

Epidermal Growth Factor Receptor Signaling in the Kidney Key Roles in Physiology and Disease

Signaling through epidermal growth factor (EGF) receptors (ErbB receptors; EGFRs) is important for fundamental cellular functions, such as proliferation, migration, growth, and differentiation.1 In human biology, ErbB signaling is involved in normal growth and development, as well as in the initiation and progression of disease. Based on the aberrant expression in a variety of malignant tumors, ErbB family members have been recognized as targets in anticancer therapy and are now used in the treatment of breast and colon malignancies. Other than tumor biology, ErbB signaling is critically involved in renal electrolyte homeostasis. Moreover, ErbB family members are implicated in the development of end organ damage, as occurs in hypertension 2 and atherosclerosis.3 Therefore, the therapeutic potential of targeting ErbB receptors and ErbB signaling pathways may go beyond the field of oncology. In this review, we report on the physiological and disease-related aspects of renal ErbB signaling, with attention to potential benefits and downsides of systemic ErbB inhibition in the healthy and diseased kidney.

ADAM17 upregulation in human renal disease: a role in modulating TGF-alpha availability?

A disintegrin and metalloproteinase (ADAM)17 sheds growth factors from the cell membrane, including epidermal growth factor receptor (EGFR) ligand transforming growth factor (TGF)-alpha. In mice, angiotensin II infusion induces renal fibrosis via ADAM17-mediated TGF-alpha shedding and subsequent EGFR activation. Pharmacological ADAM17 inhibition reduced renal fibrotic lesions and improved renal function, positioning ADAM17 as a promising target of intervention in renal disease. We studied ADAM17 expression in the human kidney. ADAM17 mRNA was constitutively expressed in normal adult kidneys, with highest expression in distal tubules. In human renal disease, ADAM17 was de novo expressed in proximal tubules, peritubular capillaries, and glomerular mesangium and upregulated in podocytes. Glomerular mesangial and endothelial ADAM17 were associated with mesangial matrix expansion, focal glomerulosclerosis, and glomerular macrophage infiltration (P < 0.01). Peritubular capillary and proximal tubular ADAM17 were associated with interstitial fibrosis and interstitial macrophage infiltration (P < 0.05). Both glomerular and interstitial ADAM17 were associated with decreased renal function (P < 0.05). In renal fibrosis, ADAM17 colocalized with TGF-alpha. Moreover, in cultured human podocytes and proximal tubular cells, pharmacological ADAM17 inhibition reduced constitutive TGF-alpha shedding by 78% (P < 0.005) and 100% (P < 0.05), respectively, and phorbol ester-induced TGF-alpha shedding by 84% (P < 0.005) and 92% (P = 0.005), respectively. Finally, ADAM17 inhibition reduced cellular proliferation. In conclusion, the ADAM17 expression pattern and its role in shedding TGF-alpha from cultured human kidney cells suggest a role in the development of fibrosis. Since EGFR signaling is implicated in renal fibrosis, targeting ADAM17 to reduce availability of EGFR ligand TGF-alpha may represent a promising way of intervention in human renal disease.

Glomerular and tubular induction of the transcription factor c-Jun in human renal disease.

The transcription factor c‐Jun regulates the expression of genes involved in proliferation and inflammation in many cell types but its role in human renal disease is largely unclear. In the current study we investigated whether c‐Jun activation is associated with human renal disease and if c‐Jun activation regulates pro‐inflammatory and pro‐fibrotic genes in renal cells. Activation of c‐Jun was quantified by scoring renal expression of phosphorylated c‐Jun (pc‐Jun) in control human renal tissue and in biopsies from patients with various renal diseases (diabetic nephropathy, focal glomerulosclerosis, hypertension, IgA nephropathy, membranous glomerulopathy, minimal change disease, membranoproliferative glomerulonephritis, systemic lupus erythematosus, acute rejection, and Wegeners granulomatosis); this was correlated with parameters of renal damage. Furthermore, we studied the functional role of c‐Jun activation in human tubular epithelial cells (HK‐2) stimulated with TGF‐β. Activated c‐Jun was present in nuclei of glomerular and tubular cells in all human renal diseases, but only sporadically in controls. Across the diseases, the extent of pc‐Jun expression correlated with the degree of focal glomerulosclerosis, interstitial fibrosis, cell proliferation, kidney injury molecule‐1 (Kim‐1) expression, macrophage accumulation, and impairment of renal function. In HK‐2 cells, TGF‐β induced c‐Jun activation after 1 h (+40%, p < 0.001) and 24 h (+160%, p < 0.001). The specific c‐Jun N‐terminal kinase (JNK) inhibitor SP600125 abolished c‐Jun phosphorylation at all time points and blunted TGF‐β‐ or BSA‐induced procollagen‐1α 1 and MCP‐1 gene expression in HK‐2 cells. We conclude that in human renal disease, the transcription factor c‐Jun is activated in glomerular and tubular cells. Activation of c‐Jun may be involved in the regulation of inflammation and/or fibrosis in human renal disease. Copyright

Expression and Response to Angiotensin-Converting Enzyme Inhibition of Matrix Metalloproteinases 2 and 9 in Renal Glomerular Damage in Young Transgenic Rats with Renin-Dependent Hypertension

Extracellular matrix expansion in the glomerular mesangium contributes to the development of glomerulosclerosis and chronic renal disease in arterial hypertension. Transforming growth factor-β1 (TGF-β1), matrix metalloproteinases (MMPs), and tissue inhibitors of MMPs (TIMPs) are involved in this process. Conflicting data are reported on the effects of angiotensin II (Ang II) and the response to angiotensin-converting enzyme inhibition on MMPs and TIMPs in early stages of hypertensive glomerular damage. We therefore investigated the effects of Ang II-dependent hypertension on MMP-2, MMP-9, TIMP-1, and TIMP-2 in isolated glomeruli of 8-week-old homozygous male rats overexpressing the mouse Ren2 gene [TGR(mRen2)27]. At this age, systolic blood pressure was already significantly elevated in Ren2 compared with Sprague-Dawley (SD) rats (197 ± 38 versus 125 ± 16 mm Hg, p < 0.01). Ren2 exhibited renal damage as determined by increased urinary albumin excretion, focal glomerulosclerosis, mesangial matrix expansion, and α-smooth muscle actin deposition. Quantification of mRNA levels in isolated glomeruli by real-time polymerase chain reaction showed a significant increase of TGF-β1, a 2.3- and a 2.6-fold increase of MMP-2 and TIMP-1 in Ren2 compared with SD (p < 0.01, respectively) and no strain differences for TIMP-2. In contrast, MMP-9 mRNA expression was markedly suppressed to 10% of control levels in Ren2 (p < 0.01). Early treatment with ramipril completely prevented renal damage in Ren2 and restored mRNA expression of TGF-β1, MMP-2, and TIMP-1 to SD control levels. Interestingly, down-regulation of MMP-9 mRNA, protein, and activity was not affected by ramipril, indicating that the protective effect of this compound is not attributable to restoration of MMP-9 in the glomerulus.

Tubular epithelial syndecan-1 maintains renal function in murine ischemia/reperfusion and human transplantation.

Syndecan-1, a heparan sulfate proteoglycan, has an important role in wound healing by binding several growth factors and cytokines. As these processes are also crucial in damage and repair after renal transplantation, we examined syndecan-1 expression in human control kidney tissue, renal allograft protocol biopsies, renal allograft biopsies taken at indication, and non-transplant interstitial fibrosis. Syndecan-1 expression was increased in tubular epithelial cells in renal allograft biopsies compared with control. Increased epithelial syndecan-1 in allografts correlated with low proteinuria and serum creatinine, less interstitial inflammation, less tubular atrophy, and prolonged allograft survival. Knockdown of syndecan-1 in human tubular epithelial cells in vitro reduced cell proliferation. Selective binding of growth factors suggests that syndecan-1 may promote epithelial restoration. Bilateral renal ischemia/reperfusion in syndecan-1-deficient mice resulted in increased initial renal failure and tubular injury compared with wild-type mice. Macrophage and myofibroblast numbers, tubular damage, and plasma urea levels were increased, and tubular proliferation reduced in the kidneys of syndecan-1 deficient compared with wild-type mice 14 days following injury. Hence syndecan-1 promotes tubular survival and repair in murine ischemia/reperfusion injury and correlates with functional improvement in human renal allograft transplantation.

ADAM17 up-regulation in renal transplant dysfunction and non-transplant-related renal fibrosis

BACKGROUND Interstitial fibrosis and tubular atrophy (IF/TA) is an important cause of renal function loss and ischaemia-reperfusion (I/R) injury is considered to play an important role in its pathophysiology. The aim of the present study was to investigate the role of a disintegrin and metalloproteinase 17 (ADAM17) in human renal allograft disease and in experimental I/R injury of the kidney. METHODS We studied the expression of ADAM17 messenger RNA (mRNA) in IF/TA and control kidneys by reverse transcription-polymerase chain reaction and in situ hybridization. Moreover, we assessed ADAM17-mediated heparin-binding epidermal growth factor (HB-EGF) shedding in immortalized human cells. Finally, we studied the effect of pharmacological ADAM17 inhibition in a model of renal I/R injury in rats. RESULTS ADAM17 mRNA was up-regulated in IF/TA when compared to control kidneys. In normal kidneys, ADAM17 mRNA was weakly expressed in proximal tubules, peritubular capillaries, glomerular endothelium and parietal epithelium. In IF/TA, tubular, capillary and glomerular ADAM17 expression was strongly enhanced with de novo expression in the mesangium. In interstitial fibrotic lesions, we observed co-localization of ADAM17 with HB-EGF protein. In vitro, inhibition of ADAM17 with TNF484 resulted in a dose-dependent reduction of HB-EGF shedding in phorbol 12-myrisate 13-acetate-stimulated cells and non-stimulated cells. In vivo, ADAM17 inhibition significantly reduced the number of glomerular and interstitial macrophages at Day 4 of reperfusion. CONCLUSIONS In conclusion, HB-EGF co-expresses with ADAM17 in renal interstitial fibrosis, suggesting a potential interaction in IF/TA. Targeting ADAM17 to reduce epidermal growth factor receptor phosphorylation could be a promising way of intervention in human renal disease.

Heparin binding epidermal growth factor in renal ischaemia/reperfusion injury†

The epidermal growth factor (EGF) receptor and its ligands are crucially involved in the renal response to ischaemia. We studied the heparin binding‐epidermal growth factor (HB‐EGF), a major ligand for the EGF receptor, in experimental and human ischaemia/reperfusion injury (IRI). HB‐EGF mRNA and protein expression was studied in rat kidneys and cultured human tubular (HK‐2) cells that were subjected to IRI and in human donor kidneys during transplantation. The effect of EGF receptor inhibition was investigated in vivo and in vitro. Furthermore, urinary HB‐EGF protein excretion was studied after renal transplantation. Finally, HB‐EGF KO and WT mice were subjected to IRI to study the role of HB‐EGF in renal injury. HB‐EGF mRNA was significantly up‐regulated in the early phase of IRI in rats, cells, and human donor biopsies. Treatment with PKI‐166 reduces macrophage accumulation and interstitial α‐SMA in the early phase of IRI in rats. In vitro, PKI‐166 causes a marked reduction in HB‐EGF‐induced cellular proliferation. Urinary HB‐EGF is increased after transplantation compared with control urines from healthy subjects. HB‐EGF KO mice subjected to IRI revealed significantly less morphological damage after IRI, compared with WT mice. We conclude that IRI results in early induction of HB‐EGF mRNA and protein in vivo and in vitro. Absence of HB‐EGF and inhibition of the EGF receptor in the early phase of IRI has protective effects, suggesting a modulating role for HB‐EGF. Copyright

Upregulation of ADAM19 in chronic allograft nephropathy

ADAM19 (a disintegrin and metalloproteinase 19) is involved in cell–cell and cell‐matrix interactions and tumor necrosis factor (TNF)‐alpha shedding. We studied ADAM19 in chronic allograft nephropathy (CAN) nephrectomies and in normal human kidneys. Reverse transcriptase (RT) PCR revealed an upregulation of ADAM19 mRNA in CAN when compared with control kidneys (p = 0.002). Using RNA in situ hybridization (ISH), we detected moderate ADAM19 mRNA expression in vascular smooth muscle cells (SMCs) and distal tubuli of control kidneys. In CAN, massive ADAM19 expression was detected in SMCs, distal tubuli, glomerular sclerotic lesions and inflammatory CD4+ cells. To determine whether ADAM19 is specifically related to CAN, we studied transplant biopsies with and without CAN, acute rejection and non‐transplant‐related kidney diseases: interstitial fibrosis (IF), interstitial atrophy, glomerular fibrosis and interstitial inflammation. In various renal structures, ADAM19 mRNA was significantly higher in CAN when compared with renal allografts without CAN or acute rejection. ADAM19 expression in renal endothelium was significantly higher in acute rejection when compared with renal allografts without CAN. When compared to CAN, ADAM19 was expressed to a similar extent in non‐transplant‐related interstitial and glomerular fibrosis, interstitial atrophy and inflammation. Although these observational data do not establish a cause and effect relationship, ADAM19 may have a modulatory role in the dysfunctional renal allograft state.