Role of leukocyte adhesion molecules in monocyte/ macrophage infiltration in weanling rats with unilateral ureteral obstruction

Role of inflammation in túbulo-interstitial damage associated to obstructive nephropathy

Obstructive nephropathy is characterized by an inflammatory state in the kidney, that is promoted by cytokines and growth factors produced by damaged tubular cells, infiltrated macrophages and accumulated myofibroblasts. This inflammatory state contributes to tubular atrophy and interstitial fibrosis characteristic of obstructive nephropathy. Accumulation of leukocytes, especially macrophages and T lymphocytes, in the renal interstitium is strongly associated to the progression of renal injury. Proinflammatory cytokines, NF-κB activation, adhesion molecules, chemokines, growth factors, NO and oxidative stress contribute in different ways to progressive renal damage induced by obstructive nephropathy, as they induce leukocytes recruitment, tubular cell apoptosis and interstitial fibrosis. Increased angiotensin II production, increased oxidative stress and high levels of proinflammatory cytokines contribute to NF-κB activation which in turn induce the expression of adhesion molecules and chemokines responsible for leukocyte recruitment and iNOS and cytokines overexpression, which aggravates the inflammatory response in the damaged kidney. In this manuscript we revise the different events and regulatory mechanisms involved in inflammation associated to obstructive nephropathy.

Prevention of renal interstitial fibrosis via histone deacetylase inhibition in rats with unilateral ureteral obstruction

Acute rejection following renal transplantation has become manageable with the introduction of calcineurin inhibitors, FK506 and cyclosporine A. However, chronic allograft dysfunction accompanied by renal interstitial fibrosis, which induces graft loss, remains unresolved. Here, we evaluated the effect of FR276457, a pan-histone deacetylase (HDAC) inhibitor, on interstitial fibrosis in the injured kidneys of a rat model of unilateral ureteral obstruction. The injured kidneys, harvested on Day 14 following the operation, showed progression of interstitial fibrosis, increases of hydroxyproline contents, and mRNA expression of collagen type Ialpha1 and monocyte chemotactic protein 1 (MCP-1). However, these changes were found to be prevented with daily oral administration of FR276457. In addition, given that MCP-1 is believed to contribute to progressive fibrosis, we investigated the direct effect of FR276457 on MCP-1 production by activated THP-1 cells in vitro. Results showed that FR276457 administration decreased MCP-1 production in these cells in a concentration-dependent manner. Findings from the present study suggested that a pan-HDAC inhibitor may exert a prophylactic effect against renal interstitial fibrosis by inhibiting MCP-1 production.

Obstructive nephropathy: towards biomarker discovery and gene therapy

Obstructive nephropathy is a major cause of renal failure, particularly in infants and children. Cellular and molecular mechanisms responsible for the progression of the tubular atrophy and interstitial fibrosis-processes that lead to nephron loss-have been elucidated in the past 5 years. Following urinary tract obstruction and tubular dilatation, a cascade of events results in upregulation of the intrarenal renin-angiotensin system, tubular apoptosis and macrophage infiltration of the interstitium. This is followed by accumulation of interstitial fibroblasts through proliferation of resident fibroblasts and epithelial-mesenchymal transformation of renal tubular cells. Under the influence of cytokines, chemokines and other signaling molecules produced by tubular and interstitial cells, fibroblasts undergo transformation to myofibroblasts that induce expansion of the extracellular matrix. The cellular interactions that regulate development of interstitial inflammation, tubular apoptosis and interstitial fibrosis are complex. Changes in renal gene expression and protein production afford many potential biomarkers of disease progression and targets for therapeutic manipulation. These include signaling molecules and receptors involved in macrophage recruitment and proliferation, tubular death signals and survival factors, and modulators of epithelial-mesenchymal transformation. Targeted gene deletion and various forms of gene therapy have been used in experimental obstructive nephropathy, mostly rodent models of unilateral ureteral obstruction or cell culture techniques. Further refinement of these models is needed to develop a matrix of biomarkers with clinical predictive value, as well as molecular therapies that will prevent or reverse the renal structural and functional consequences of obstructive nephropathy.

Distinct roles of Mac-1 and its counter-receptors in neonatal obstructive nephropathy

Urinary tract obstruction during renal development leads to tubular atrophy and interstitial fibrosis. Inflammatory macrophages are crucial in this process, and beta2-integrins play a major role in leukocyte recruitment. We investigated the role of beta2-integrins and their major counter-receptors (intercellular adhesion molecule-1 (ICAM-1), receptor for advanced glycation endproducts (RAGE), junctional adhesion molecule (JAM)-C) in obstructive nephropathy in neonatal mice. Two-day-old beta2-integrin-deficient mice (Mac-1-/- and LFA-1-/-(deficient for leukocyte function-associated antigen-1)) and wild-type mice (C57BL/6) underwent unilateral ureteral obstruction (UUO) or sham operation. After 1, 5 or 12 days of obstruction, renal macrophage infiltration and tubulointerstitial damage were quantitated. Tissue abundance of Mac-1 and its ligands ICAM-1, RAGE and JAM-C was examined by Western blot and immunoprecipitation. Deficiency of either integrin was associated with reduced early macrophage invasion into the obstructed kidney. After 12 days of UUO, macrophage infiltration and tubulointerstitial injury were reduced only in Mac-1-/- but not in LFA-1-/- mice. Besides ICAM-1, an upregulation of two novel Mac-1 ligands, RAGE and JAM-C were observed, however, with distinct time courses. We conclude that beta2-integrins mediate macrophage infiltration in UUO. Mac-1 is the predominant leukocyte integrin involved in leukocyte recruitment after obstruction. ICAM-1 and its new ligands RAGE and JAM-C are sequentially activated in UUO. Blocking of Mac-1 and its ligands may confer synergistic renoprotective effects in neonatal obstructive nephropathy.

Soluble fibronectin induces chemokine gene expression in renal tubular epithelial cells

BACKGROUND

Increasing proteinuria in kidney disease is associated with an increased risk of renal failure. Urinary proteins such as albumin induce inflammatory signaling and gene expression in tubular epithelial cells (TECs). Fibronectin is an extracellular matrix protein that can exist in soluble form and is excreted in the urine of patients with glomerular disease.

METHODS

To explore the impact of soluble fibronectin on tubular epithelium, murine TECs were stimulated with soluble fibronectin and chemokine mRNA was determined by RNase protection assay.

RESULTS

Fibronectin induced the expression of inflammatory chemokine genes, including monocyte chemoattractant protein-1 (MCP-1) (CCL2) and macrophage inflammatory protein-2 (MIP-2) within 2 hours in a dose-dependent manner. Phosphorylation of Src family tyrosine kinases was also increased in TECs following exposure to fibronectin. Src tyrosine kinases were involved in the fibronectin activation of MCP-1 since the Src inhibitors SU6656 and PP2 effectively reduced the induction of this chemokine. Fibronectin also induced the phosphorylation of extracellular signal-regulated protein kinase (ERK1/2) within minutes in TECs. The ERK kinase (MEK1/2) inhibitor U0126 inhibited the fibronectin induction of MCP-1 mRNA suggesting that ERK1/2 was also involved in this inflammatory pathway. Furthermore, fibronectin also induced phosphorylation of IkappaBalpha within 20 minutes in TECs. The nuclear factor-kappaB (NF-kappaB) inhibitors N-acetyl-L-cysteine (NAC) and pyrrolidinecarbodithioic acid (PDTC) effectively blocked fibronectin induction of MCP-1 mRNA.

CONCLUSION

Soluble fibronectin activates MCP-1 gene expression in TECs via Src tyrosine kinases, ERK1/2 and NF-kappaB. These data provide further support to the concept that proteinuria per se contributes to the tubulointerstitial injury observed in glomerular disease.

Fasudil attenuates interstitial fibrosis in rat kidneys with unilateral ureteral obstruction

This study was designed to investigate possible effects of the Rho-kinase inhibitor, fasudil, on the progression of renal failure in rats with unilateral ureteral obstruction. The renal failure markers monitored were the extent of renal interstitial fibrosis and that of macrophage infiltration. In kidneys with unilateral ureteral obstruction, interstitial fibrosis was observed, using Sirius-Red staining, on day 16 after unilateral ureteral obstruction. Macrophage infiltration was observed by immunohistochemistry, using the antibody, ED1. Interstitial fibrosis and macrophage infiltration were significantly attenuated in fasudil-treated animals. The migration of monocytes in vitro elicited by N-formyl-methionyl-leucyl-phenylalanine was potently inhibited by fasudil and its active metabolite, hydroxyfasudil. These results suggest that inhibition of Rho-kinase produces a reduction of macrophage infiltration and represents a new therapeutic strategy for renal fibrosis, a major factor in the progression to end-stage renal failure.