Tissue renin angiotensin system in IgA nephropathy

Abstract

The inhibition of angiotensin II (AngII) by use of angiotensin converting enzyme (ACE) inhibitor or AngII receptor blocker is effective for prevention of the progression of renal diseases including IgA nephropathy (IgAN). AngII plays a variety of biological roles via AngII receptors. Through AngII type 1 receptor (AT1R), AngII induces vasoconstriction, cellular proliferation, extracellular matrix production and fibrosis, while it leads vasodilatation, apoptosis and inhibition of cell proliferation through AngII type 2 receptor (AT2R). Recent studies showed the local production of AngII in many tissues including the heart, vessel and kidney, suggesting that local AngII may be more important than circulating AngII in tissue injury. AngII is generated from angiotensin I by ACE or ACE independent pathway, such as chymase which is a serine protease. Since chymase was shown to be synthesized 80% of AngII in human heart, chymase also may play an important role in converting to AngII in the kidney. Although it was reported that ACE was produced in renal tissue, the localization of chymase and AngII receptors is unclear in the human kidney. To research the local renin‐angiotensin system in renal tissue of patients with IgAN, we localized chymase mRNA, ACE mRNA, AT1R mRNA and AT2R mRNA by in situ hybridization and investigated the relationship between the expression of these mRNAs and tissue injury. Fresh frozen sections of renal tissue from 21 patients with IgAN were examined. The sections were fixed with 4% paraformaldehyde and hybridized with the digoxigenin (DIG)‐labelled oligonucleotide probes for chymase mRNA, ACE mRNA, AT1R mRNA and AT2R mRNA. Using anti‐DIG antibody, immunohistochemistry was performed to visualize the DIG‐labelled probe. Colour was developed by reaction with H2O2 and 3,3′diaminobenzidine/=tetrahydrochloride. As identifying the exact locations of the cells positive for chymase mRNA, ACE mRNA and AngII receptor mRNA, we stained using periodic acid‐Schiff after in situ hybridization. We classified the histological grading of the glomerular and tubulointerstitial injury. Two to five glomeruli were analysed in each biopsy tissue and the degree of injury in each glomerulus was graded from 1 to 3 based on the proportion of the lesion in the sectioned areas of each glomerulus. In the tubulointerstitium, three to five fields of cortical interstitium in each section were examined under low magnification (×200). In each designated field, we determined the degree of tubular atrophy and interstitial fibrosis from grade 1 to 3. In situ hybridization showed that the signals of chymase mRNA, ACE mRNA, AT1R mRNA and AT2R mRNA were observed in mesangial cells, glomerular epithelial cells, cells of the Bowman’s capsule, cells of crescent, tubular epithelial cells and some infiltrating mononuclear cells. In the glomeruli, the percentage of cells positive for chymase mRNA, ACE mRNA, AT1R mRNA and AT2R mRNA per glomerulus decreased as the glomerular injury progressed. Chymase mRNA and ACE mRNA were diffusely expressed i...