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 Wegener's 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-beta. 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-beta 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-beta- or BSA-induced procollagen-1alpha 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.

ADAM19 expression in human nephrogenesis and renal disease: associations with clinical and structural deterioration.

ADAM19, an enzyme from the ADAM (a disintegrin and metalloproteinase) family, is involved in various cell-cell and cell-matrix interactions. It can cleave epidermal growth factor (EGF)-like growth factors, such as heparin-binding (HB)-EGF and neuregulin (NRG), from the cell membrane. ADAM-mediated EGF receptor activation is crucial in the development of renal pathology. Based on these data, we studied ADAM19 in human nephrogenesis and renal disease. We collected 20 fetal kidneys and 56 biopsies from patients with various renal diseases. The unaffected part of kidneys from eight patients with renal cell carcinoma served as control. RNA in situ hybridization revealed widespread ADAM19 mRNA expression in the nephrogenic zone of human fetal kidneys. Normal human kidneys showed constitutive ADAM19 expression in distal tubules and endothelial cells, whereas proximal tubules were negative. In renal disease, ADAM19 was de novo expressed in proximal tubules and glomerular mesangium and upregulated in distal tubules and endothelial cells. ADAM19 colocalized with tubular and interstitial NRG, however, not with HB-EGF. Independent of renal disorder, mesangial ADAM19 expression was associated with glomerular damage as assessed by mesangial matrix expansion, focal glomerulosclerosis, and glomerular macrophage influx (all P<0.001). ADAM19 in proximal tubules and in peritubular capillaries was associated with interstitial fibrosis (P<0.05). Finally, increasing tubular ADAM19 was associated with declining renal function (P<0.05). The abundant ADAM19 expression during nephrogenesis points to a role in growth promotion and regulation. The high ADAM19 expression in renal disease suggests involvement in profibrotic and proinflammatory processes leading to renal deterioration.

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.