Up-regulation of angiotensin-converting enzyme (ACE) gene expression induces tubulointerstitial injury in reflux nephropathy

Abstract

Reflux nephropathy (RN) is the cause of end-stage renal failure in 3%-25% of children and 10%-15% of adults. Angiotensin-converting enzyme (ACE) converts the inactive decapeptide angiotensin I (Ang I) to the active octapeptide angiotensin II (Ang II), a potent vasoconstrictor. ACE is localized in highest concentrations on the luminal surface of endothelial cells, but is also found in several other cell types, including the epithelial cells of the proximal renal tubule. Recent studies have suggested that ACE increases production of the components of extracellular matrix (ECM) such as fibronectin (Fib) mediated through Ang II. Since RN is a primary tubulointerstitial disease, we hypothesized that local overexpression of ACE may induce renal fibrosis via up-regulation of Ang II. In this study, we investigated the expression of ACE in severely refluxing kidneys from eight patients (age range 6 months-14 years) with severe RN secondary to primary high-grade vesicoureteral reflux at nephrectomy. Control material included normal kidney specimens obtained from three adult patients during partial nephrectomy for an incidentaloma. Soluble enzyme immunohistochemistry was carried out using polyclonal antibodies to ACE and Fib. In-situ hybridization (ISH) was performed utilizing biotin-labelled antisense oligonucleotide probe. Reverse transcription-polymerase chain reaction (RT-PCR) was performed to evaluate the relative amount of ACE mRNA. In the refluxing kidney, there was strong ACE immunoreactivity in the glomerulus and proximal tubules and moderate-to-strong immunoreactivity in the distal tubules accompanied by strong Fib immunoreactivity in the glomerulus, proximal tubule, and interstitial space. There was strong ACE mRNA expression in the glomerulus and proximal tubules and moderate expression in the distal tubules. In the control kidneys, homogeneous weak ACE immunoreactivity and mRNA expression was demonstrated only in the proximal tubules. RT-PCR showed strong ACE expression in the refluxing kidneys compared to controls. Up-regulation of ACE in RN accompanied by an increase in ECM in the tubulointerstitial space suggests that ACE is involved in the pathogenesis of the renal parenchymal damage in patients with RN. Pharmacologic blockade of ACE may be helpful in preventing the renal fibrosis associated with RN.

Serum and urine fibronectin levels in children with vesicoureteral reflux

“…Reflux nephropathy is a tubulointerstitial disease developing as a sequel to VUR [18,19,30], which are high grade and persistent and accompanied by recurrent infections of the urinary tract [1][2][3]5]. Gordon et al [2] performed a meta-analysis of literature reports regarding the course of VUR, finding that primary reflux is not the main or sufficient cause of kidney damage and that concomitant infections should be always considered.…”

“…In recent years, researchers have focused on the involvement of extracellular matrix proteins and their inhibitors in these processes [7,8,14,18]. Accumulation of collagen IV, LN, and FN in the interstitial tissue and renal glomeruli leads to tissue fibrosis, atrophy of renal tubules and glomerulosclerosis, which in case of VUR promotes reflux nephropathy [7,8,[18][19][20]. FN plays an important role in this process [7,14,18].…”

“…The ultimate mechanism leading to kidney damage is similar, irrespective of the primary cause. It has been shown that diabetes, membranous nephropathies, various glomerulopathies, and reflux nephropathies involve increased accumulation of extracellular matrix proteins in various kidney structures, leading to interstitial tissue fibrosis, atrophy of renal tubules, and glomerulosclerosis [16][17][18][19][20]. Yoshioka et al [18], in renal biopsies obtained from eight patients with reflux nephropathy, showed increased accumulation of collagen IV, LN, and FN in mesangium of renal glomeruli, with no signs of sclerosis.…”

“…As FN is coded by various mRNAs, it has various isoforms [13][14][15]. Many literature reports have described the assessment of cellular FN expression in renal interstitial tissue, mesangium, and basement membrane of glomeruli in various glomerulopathies [16][17][18][19][20][21][22]. Research studies conducted on animals and humans with various renal diseases have shown increased expression of FN in renal interstitial tissue and in glomeruli, especially in membranous, diabetic and reflux nephropathies, and in other glomerulopathies [16][17][18][19][20][21][22].…”

Altered renin–angiotensin system gene expression causes renal hypoplasia in the rats with nitrofen-induced diaphragmatic hernia

“…Most effects of RAS are exerted by potent octapeptide angiotensin II (Ang II). Renin cleaves angiotensinogen (AGT) to the decapaptide angiotensin I. Angiotensin-converting enzyme (ACE) converts the inactive angiotensin I to the Ang II, which is a potent vasoconstrictor, vascular growth factor and facilitator of norepinephrine release from sympathetic nerve terminals [7].…”