Tubulointerstitial injury induced in rats by a monoclonal antibody that inhibits function of a membrane inhibitor of complement

C3 deposits worsens the prognosis in type iii extracapillary glomerulonephritis

INTRODUCTION

Type iii extracapillary glomerulonephritis (PEGN) is a common cause of rapidly progressive glomerulonephritis and it is usually associated with circulating anti-neutrophil cytoplasmic antibodies (ANCAs). Recent evidence points to complement activation as an important factor in the pathogenesis of PEGN. The aim of the present study was to assess the value of C3 deposits in the prognosis of PEGN.

METHODS

All patients diagnosed of PEGN from 1995 to 2015 (n=72) were included in this study. Progression of renal disease in patients with positive staining for C3 by immunofluorescence was compared with those with negative staining. Mean follow up was 73 months. Progression to end-stage renal disease in relation to clinical and histological variables was analyzed.

RESULTS

Positive staining for C3 was observed in 22 out of the 72 patients (30.5%). At the time of diagnosis, patients with C3 deposits had higher serum creatinine concentration than those without C3 staining (5.00 vs. 3.85mg/dl, P=0.050). Renal survival at 10 years was 36.9% in patients with positive C3 staining vs. 64.4% in patients with negative staining (P=0.005). Mortality at 10 years was higher in patients with C3 deposits than in patients without deposits (77 vs. 49.3%).

CONCLUSIONS

Thus, our study shows that PEGN with deposits of C3 is associated with worse renal prognosis and greater mortality. These results would support the hypothesis that activation of the alternative pathway complement may play an important role in the generation of renal injury associated with PEGN.

Kidney and Liver Injuries After Major Burns in Rats Are Prevented by Resolvin D2

OBJECTIVES

Innate immune dysfunction after major burn injuries increases the susceptibility to organ failure. Lipid mediators of inflammation resolution, e.g., resolvin D2, have been shown recently to restore neutrophil functionality and reduce mortality rate in a rat model of major burn injury. However, the physiological mechanisms responsible for the benefic activity of resolvin D2 are not well understood.

DESIGN

Prospective randomized animal investigation.

SETTING

Academic research setting.

SUBJECTS

Wistar male rats.

INTERVENTIONS

Animals were subjected to a full-thickness burn of 30% total body surface area. Two hours after burn, 25 ng/kg resolvin D2 was administered IV and repeated every day, for 8 days. At day 10 post burn, 2 mg/kg of lipopolysaccharide was administered IV, and the presence of renal and hepatic injuries was evaluated at day 11 post burn by histology, immunohistochemistry, and relevant blood chemistry.

MEASUREMENTS AND MAIN RESULTS

In untreated animals, we found significant tissue damage in the kidneys and liver, consistent with acute tubular necrosis and multifocal necrosis, and changes in blood chemistry, reflecting the deterioration of renal and hepatic functions. We detected less tissue damage and significantly lower values of blood urea nitrogen (26.4 ± 2.1 vs 36.0 ± 9.3 mg/dL; p ≤ 0.001), alanine aminotransferase (266.5 ± 295.2 vs 861.8 ± 813.7 U/L; p ≤ 0.01), and total bilirubin (0.13 ± 0.05 vs 0.30 ± 0.14 mg/dL; p ≤ 0.01) in resolvin D2-treated rats than in untreated animals. The mean blood pressure of all animals was above 65 mm Hg, indicating adequate tissue perfusion throughout the experiments. We measured significantly larger amounts of chromatin in the circulation of untreated than of resolvin D2-treated rats (575.1 ± 331.0 vs 264.1 ± 122.4 ng/mL; p ≤ 0.05) and identified neutrophil extracellular traps in kidney and liver tissues from untreated rats, consistent with the tissue damage.

CONCLUSIONS

Pathologic changes in kidney and liver tissues in a rat model of major burn and endotoxin insults are ameliorated by resolvin D2.

Glomerular C3d as a novel prognostic marker for renal vasculitis

Pauci-immune necrotizing crescentic glomerulonephritis is the histologic substrate of antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis. Several studies in animal models have demonstrated the crucial role of complement activation in the pathogenesis of ANCA-associated vasculitis, but only small series have analyzed the prognostic implications of complement glomerular deposits. This study aimed to assess the clinical and prognostic implications of C3d- and C4d-positive glomerular staining in renal vasculitis. Eighty-five patients with a diagnosis of pauci-immune necrotizing crescentic glomerulonephritis were included in the study. C3d and C4d were analyzed by immunohistochemical staining using a polyclonal antibody. The primary predictors were glomerular C3d- and C4d-positive staining. The primary end point was the cumulative percentage of patients who developed end-stage renal disease. Glomerular staining for C3d and C4d was observed in 42 (49.4%) of 85 biopsies and 38 (44.7%) of 85 biopsies, respectively. C3d-positive staining was associated with the severity of renal impairment and with a lower response rate to treatment (P=.003 and P=.04, respectively). Renal survival at 2 and 5 years was 60.9% and 51.8% in C3d-positive patients compared with 87.7% and 78.9% in C3d-negative patients (P=.04). C4d-positive staining did not show any impact in renal outcome. When adjusted by renal function and other histologic parameters, C3d staining remained as an independent predictor for renal survival (hazard ratio, 2.5; 95% confidence interval, 1.1-5.7; P=.03). Therefore, this study demonstrates that C3d-positive glomerular staining is an independent risk factor for the development of end-stage renal disease in ANCA-associated renal vasculitis.

Complement activation in the tubulointerstitium: AKI, CKD, and in between

Complement activation is actively regulated to prevent injudicious activation, such as on peritubular endothelia and basolateral aspects of tubules. Miao et al. studied mice in which the key complement regulator, Crry, was deleted from tubular cells. This lacked functional consequence in unmanipulated animals. Yet, following ischemia-reperfusion, there was greater injury due to alternative pathway activation of C5. When the balance between complement activation and regulation is tipped towards the former, pathologic complement activation can ensue.

C5b-9-targeted molecular MR imaging in rats with Heymann nephritis: a new approach in the evaluation of nephrotic syndrome

Membranous nephropathy (MN) is the major cause of adult nephrotic syndrome, which severely affects patients’ quality of life. Currently, percutaneous renal biopsy is required to definitively diagnose MN. However, this technique is invasive and may cause severe complications. Therefore, an urgent clinical need exists for dynamic noninvasive monitoring of the renal state. In-depth molecular imaging studies could assist in finding a solution. Membrane attack complex C5b-9 is the key factor in the development of MN, and this protein primarily deposits in the glomerulus. The present study bound polyclonal antibodies to C5b-9 with ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles to obtain C5b-9-targeted magnetic resonance molecular imaging probes. The probes were injected intravenously into rats with Heymann nephritis, a classic disease model of MN. The signal intensity in the T2*-weighted imaging of kidneys in vivo using 7.0 Tesla magnetic resonance imaging decreased significantly 24 hours after injection compared to the untargeted and control groups. This signal change was consistent with the finding of nanoparticle deposits in pathological glomeruli. This study demonstrated a novel molecular imaging technique for the assessment of MN.

Complement regulation in renal disease models

Activation of the complement system is tightly regulated by plasma and cell-associated complement regulatory proteins (CRPs), such as factor H (fH), decay-accelerating factor, and membrane cofactor protein. Animal models of disease have provided considerable insights into the important roles for CRPs in the kidney. Mice deficient in fH have excessive fluid phase C3 activation and inactivation, leading to deposition of inactivated C3b in glomerular capillary walls (GCW), comparable with dense deposit disease. In contrast, when fH lacks C-terminal surface targeting regions, local activation on the GCW leads to a disease reminiscent of thrombotic microangiopathy. The uniquely rodent protein, CR1-related y (Crry), has features analogous to human membrane cofactor protein. Defective Crry leads to unrestricted alternative pathway activation in the tubulointerstitium, resulting in pathologic features ranging from thrombotic microangiopathy (TMA), acute kidney injury, and tubulointerstitium nephritis. In the presence of initiators of the classic or lectin pathways, commonly in the form of immune complexes in human glomerular diseases, complement regulation is stressed, with the potential for recruitment of the spontaneously active alternative pathway. The threshold for this activation is set by CRPs; pathology is more likely when complement regulation is defective. Within the endocapillary region of the GCW, fH is key, while decay-accelerating factor and Crry are protective on mesangial cells and podocytes. Arguably, acquired alterations in these CRPs is a more common event, extending from pathologic states of cellular injury or production of inhibitory antibodies, to physiological fine tuning of the adaptive immune response.

Tissue-specific deletion of Crry from mouse proximal tubular epithelial cells increases susceptibility to renal ischemia-reperfusion injury

The murine cell surface protein Crry (complement receptor 1-related protein/gene y) is a key complement regulator with similar activities to human membrane cofactor protein (MCP) and decay-accelerating factor. MCP has a critical role in preventing complement-mediated tissue injury and its mutation has been implicated in several human kidney diseases. The study of Crry in mice has relevance to understanding MCP activity in human diseases; however, such efforts have been hampered by the embryonic lethality phenotype of Crry gene knockout. Here we used a conditional gene-targeting approach and deleted Crry from the mouse proximal tubular epithelial cells where Crry is prominently expressed. Absence of Crry from proximal tubular epithelial cells resulted in spontaneous C3 deposition on the basolateral surface but no apparent renal disease in unchallenged mice. However, mice deficient in Crry on proximal tubular epithelial cells developed exacerbated renal injury when subjected to renal ischemia-reperfusion, showing increased blood urea nitrogen levels, higher tubular injury scores, more tubular epithelial cell apoptosis, and inflammatory infiltrates. Renal ischemia-reperfusion injury in the Crry conditional knockout mice was prevented by blocking C3 and C5 activation using an anti-properdin or anti-C5 monoclonal antibody (mAb), respectively. Thus, Crry has a critical role in protecting proximal tubular epithelial cells during ischemia-reperfusion challenge. Our results highlight the latent risk for inflammatory kidney injury associated with defects in membrane complement regulators.

IL-22 ameliorates renal ischemia-reperfusion injury by targeting proximal tubule epithelium

IL-22 is an epithelial cell survival cytokine that is currently under development for the treatment of acute liver damage. Here, we used a mouse model of renal ischemia/reperfusion (I/R) injury to investigate whether IL-22 has therapeutic potential for the treatment of AKI. The action of IL-22 is mediated by binding to IL-22R1 and leads to STAT3 activation. Under physiologic conditions, renal expression of IL-22R1 was detected only in the brush border of the renal proximal tubular epithelial cells (RPTECs). Renal I/R elevated serum IL-22 levels slightly but did not induce STAT3 phosphorylation in RPTECs. IL-22-deficient mice had slightly increased I/R-induced injury compared with wild-type mice. In contrast, treatment with IL-22 or overexpression of IL-22 by either gene targeting (IL-22 transgenic mice) or administration of adenovirus expressing IL-22 increased STAT3 phosphorylation in RPTECs, ameliorated I/R-induced renal inflammation and tubular cell injury, and preserved renal functions. Overexpression of IL-22 increased the phosphorylation of STAT3 and Akt, upregulated antiapoptotic genes (e.g., Bcl-2), and downregulated proapoptotic genes (e.g., Bad) in the kidneys of mice subjected to I/R. Notably, phosphorylation of Akt increased and expression of Bad decreased in proximal tubular cells under these conditions. Furthermore, compared with wild-type mice, IL-22 transgenic mice had increased survival rates, whereas IL-22-deficient mice had reduced survival rates after I/R injury. In summary, renal expression of IL-22R1 is restricted to RPTECs, and treatment with IL-22 protects against renal I/R injury by activating STAT3 and AKT, suggesting that IL-22 has therapeutic potential for the treatment of AKI.

Loss of CD11b exacerbates murine complement-mediated tubulointerstitial nephritis

Acute complement activation occurs in the tubulointerstitium (TI) of kidneys transplanted from Crry^−/−C3^−/− mice into complement-sufficient wildtype mice, followed by marked inflammatory cell infiltration, tubular damage and interstitial fibrosis. We postulated iC3b-CD11b interactions were critical in this TI nephritis model. We transplanted Crry^−/−C3^−/− mouse kidneys into CD11b^−/− and wildtype C57BL/6 mice. Surprisingly, there was greater inflammation in Crry^−/−C3^−/− kidneys in CD11b^−/− recipients compared to those in wildtype hosts. Kidneys in CD11b^−/− recipients had large numbers of CD11b⁻Ly6C^hiCCR2^hiF4/80⁺ cells consistent with inflammatory (M1) macrophages recruited from circulating monocytes of the host CD11b^−/− animal. There was also an expanded population of CD11b⁺CD11c⁺Ly6C⁻F4/80^hi cells. Since these cells were CD11b⁺, they must have originated from the transplanted kidney; their surface protein expression and appearance within the kidney were consistent with the intrinsic renal mononuclear cellular population. These cells were markedly expanded relative to all relevant controls, including the contralateral donor kidney and Crry^−/−C3^−/− mouse kidneys in CD11b^+/+ wildtype recipients. Direct evidence for their in situ proliferation was the presence of nuclear Ki67 and PCNA in CD11b⁺F4/80⁺ cells. Thus, in this experimental model in which there is unrestricted C3 activation, CD11b⁺ monocytes limit their own infiltration into the kidney and prevent proliferation of endogenous mononuclear cells. This suggests a role for outside-in iC3b-CD11b signals in limiting intrinsic organ inflammation.

The role of the complement system in acute kidney injury

Acute kidney injury is a common and severe clinical problem. Patients who develop acute kidney injury are at increased risk of death despite supportive measures such as hemodialysis. Research in recent years has shown that tissue inflammation is central to the pathogenesis of renal injury, even after nonimmune insults such as ischemia/reperfusion and toxins. Examination of clinical samples and preclinical models has shown that activation of the complement system is a critical cause of acute kidney injury. Furthermore, complement activation within the injured kidney is a proximal trigger of many downstream inflammatory events within the renal parenchyma that exacerbate injury to the kidney. Complement activation also may account for the systemic inflammatory events that contribute to remote organ injury and patient mortality. Complement inhibitory drugs have now entered clinical use and may provide an important new therapeutic approach for patients suffering from, or at high risk of developing, acute kidney injury.

Curcumin alleviates immune-complex-mediated glomerulonephritis in factor-H-deficient mice

Complement factor H (Cfh) is a key regulator of the complement cascade and protects C57BL/6 mice from immune complex-mediated complement-dependent glomerulonephritis. In chronic serum sickness (CSS) there are increased deposits of immune complexes in the glomeruli with inflammation and a scarring phenotype. As cucurmin is an effective anti-inflammatory agent and reduces complement activation, we hypothesized that it should alleviate renal disease in this setting. To determine the effectiveness of curcumin, an apoferritin-induced CSS model in Cfh-deficient (Cfh(-/-)) mice was used. Curcumin treatment (30 mg/kg) given every day in parallel with apoferritin reduced glomerulonephritis and enhanced kidney function (blood urea nitrogen, 45·4 ± 7·5 versus 35·6 ± 5·1; albuminuria, 50·1 ± 7·1 versus 15·7 ± 7·1; glomerulonephritis, 2·62 + 0·25 versus 2 + 0·3, P < 0·05). In line with reduced IgG deposits in mice with CSS given curcumin, C9 deposits were reduced indicating reduced complement activation. Mice treated with curcumin had a significant reduction in the number of splenic CD19(+) B cells and the ratio of CD19 : CD3 cells (P < 0·05) with no change in the T-cell population. Myeloperoxidase assay showed reduced macrophages in the kidney. However, a significant reduction in the M2 subset of splenic macrophages by apoferritin was prevented by curcumin, suggesting a protective function. Curcumin treatment reduced mRNA expression of inflammatory proteins monocyte chemoattractant protein-1 and transforming growth factor-β and matrix proteins, fibronectin, laminin and collagen. Our results clearly illustrate that curcumin reduces glomerulosclerosis, improves kidney function and could serve as a therapeutic agent during serum sickness.

Cell cycle arrest in a model of colistin nephrotoxicity

Colistin (polymixin E) is an antibiotic prescribed with resurging frequency for multidrug resistant gram negative bacterial infections. It is associated with nephrotoxicity in humans in up to 55% of cases. Little is known regarding genes involved in colistin nephrotoxicity. A murine model of colistin-mediated kidney injury was developed. C57/BL6 mice were administered saline or colistin at a dose of 16 mg/kg/day in 2 divided intraperitoneal doses and killed after either 3 or 15 days of colistin. After 15 days, mice exposed to colistin had elevated blood urea nitrogen (BUN), creatinine, and pathologic evidence of acute tubular necrosis and apoptosis. After 3 days, mice had neither BUN elevation nor substantial pathologic injury; however, urinary neutrophil gelatinase-associated lipocalin was elevated (P = 0.017). An Illumina gene expression array was performed on kidney RNA harvested 72 h after first colistin dose to identify differentially expressed genes early in drug treatment. Array data revealed 21 differentially expressed genes (false discovery rate < 0.1) between control and colistin-exposed mice, including LGALS3 and CCNB1. The gene signature was significantly enriched for genes involved in cell cycle proliferation. RT-PCR, immunoblot, and immunostaining validated the relevance of key genes and proteins. This murine model offers insights into the potential mechanism of colistin-mediated nephrotoxicity. Further studies will determine whether the identified genes play a causative or protective role in colistin-induced nephrotoxicity.

Endotoxemia alters tight junction gene and protein expression in the kidney

Intact tight junctional (TJ) proteins are required for tubular ion transport and waste excretion. Disruption of TJs may contribute to a decreased glomerular filtration rate in acute kidney injury (AKI) via tubular backleak. The effect of LPS-mediated AKI on murine TJs has not been studied extensively. We hypothesized LPS endotoxin administration to mice would disrupt tubular TJ proteins including zonula occludens-1 (ZO-1), occludin, and claudins. ZO-1 and occludin immunofluorescence 24 h post-LPS revealed a marked change in localization from the usual circumferential fencework pattern to one with substantial fragmentation. Renal ZO-1 expression was significantly reduced 24 h after LPS (decrease of 56.1 ± 7.4%, P < 0.001), with subsequent recovery. ZO-1 mRNA expression was increased 24 h post-LPS (4.34 ± 0.87-fold, P = 0.0019), suggesting disruption of ZO-1 protein is not mediated by transcriptional regulation, but rather by degradation or changes in translation. Similarly, claudin-4 protein expression was decreased despite elevated mRNA. LPS administration resulted in dephosphorylation of occludin and fragmented tubular redistribution. Protein expression of claudin-1, and -3 was increased after LPS. ZO-1, occludin, and claudin-1, -3, and -4 gene expression were increased 48 h after LPS, suggesting a renal response to strengthen TJs following injury. Interestingly, reduced mRNA expression was found only for claudin-8. This study provides further support that LPS-induced AKI is associated with structural injury and is not merely due to hemodynamic changes.

Distinct roles for C3a and C5a in complement-induced tubulointerstitial injury

To prevent injury to host tissues, complement activation is regulated by a number of plasma and membrane-associated proteins, most of which limit C3 and C5 activation. An influx of circulating C3 from a syngeneic host into donor kidneys deficient in Crry (a membrane protein that reduces C3 convertase activity) causes spontaneous complement activation, primarily in the tubulointerstitum, leading to renal failure. To determine the roles of the C3a and C5a anaphylatoxins in tubulointerstitial inflammation and fibrosis, kidneys from Crry-/-C3-/- mice were transplanted into hosts lacking the C3a and/or C5a receptor. While unrestricted complement activation in the tubules was not affected by receptor status in the transplant recipient, C3a receptor deficiency in the recipients led to significantly reduced renal leukocyte infiltration and the extent of tubulointerstitial inflammation and fibrosis, all of which led to preserved renal function. The absence of C5a receptors in recipients was not only inconsequential, but the protective effect of C3a receptor deficiency was also eliminated, suggesting distinct roles of C3a and C5a receptor signaling in this model. There was significant infiltration of the tubulointerstitum with 7/4+F4/80+CD11b+ myelomonocytic cells and Thy1.2+ T cells along injured tubules, and interstitial collagen I and III deposition, all of which were C3a receptor dependent. Thus, blockade of C3a receptor signaling is a possible treatment to reduce renal inflammation and preserve renal function associated with complement activation.

Basigin/CD147 promotes renal fibrosis after unilateral ureteral obstruction

Regardless of their primary causes, progressive renal fibrosis and tubular atrophy are the main predictors of progression to end-stage renal disease. Basigin/CD147 is a multifunctional molecule-it induces matrix metalloproteinases and hyaluronan, for example-and has been implicated in organ fibrosis. However, the relationship between basigin and organ fibrosis has been poorly studied. We investigated basigin's role in renal fibrosis using a unilateral ureteral obstruction model. Basigin-deficient mice (Bsg(-/-)) demonstrated significantly less fibrosis after surgery than Bsg(+/+) mice. Fewer macrophages had infiltrated in Bsg(-/-) kidneys. Consistent with these in vivo data, primary cultured tubular epithelial cells from Bsg(-/-) mice produced less matrix metalloproteinase and exhibited less motility on stimulation with transforming growth factor β. Furthermore, Bsg(-/-) embryonic fibro blasts produced less hyaluronan and α-smooth muscle actin after transforming growth factor β stimulation. Together, these results demonstrate for the first time that basigin is a key regulator of renal fibrosis. Basigin could be a candidate target molecule for the prevention of organ fibrosis.

Dynamic control of the complement system by modulated expression of regulatory proteins

The complement system serves many biological functions, including the eradication of invasive pathogens and the removal of damaged cells and immune-complexes. Uncontrolled complement activation causes injury to host cells, however, so adequate regulation of the system is essential. Control of the complement system is maintained by a group of cell surface and circulating proteins referred to as complement regulatory proteins. The expression of the cell surface complement regulatory proteins varies from tissue to tissue. Furthermore, specific cell types can upregulate or downregulate the expression of these proteins in response to a variety of signals or insults. Altered regulation of the complement regulatory proteins can have important effects on local complement activation. In some circumstances this can be beneficial, such as in the setting of certain infections. In other circumstances, however, this can be a cause of complement-mediated injury of the tissue. A full understanding of the mechanisms by which the complement system is modulated at the local level can have important implications for how we diagnose and treat a wide range of inflammatory diseases.

The complement inhibitors Crry and factor H are critical for preventing autologous complement activation on renal tubular epithelial cells

Congenital and acquired deficiencies of complement regulatory proteins are associated with pathologic complement activation in several renal diseases. To elucidate the mechanisms by which renal tubular epithelial cells (TECs) control the complement system, we examined the expression of complement regulatory proteins by the cells. We found that Crry is the only membrane-bound complement regulator expressed by murine TECs, and its expression is concentrated on the basolateral surface. Consistent with the polarized localization of Crry, less complement activation was observed when the basolateral surface of TECs was exposed to serum than when the apical surface was exposed. Furthermore, greater complement activation occurred when the basolateral surface of TECs from Crry(-/-)fB(-/-) mice was exposed to normal serum compared with TECs from wild-type mice. Complement activation on the apical and basolateral surfaces was also greater when factor H, an alternative pathway regulatory protein found in serum, was blocked from interacting with the cells. Finally, we injected Crry(-/-)fB(-/-) and Crry(+/+)fB(-/-) mice with purified factor B (an essential protein of the alternative pathway). Spontaneous complement activation was seen on the tubules of Crry(-/-)fB(-/-) mice after injection with factor B, and the mice developed acute tubular injury. These studies indicate that factor H and Crry regulate complement activation on the basolateral surface of TECs and that factor H regulates complement activation on the apical surface. However, congenital deficiency of Crry or reduced expression of the protein on the basolateral surface of injured cells permits spontaneous complement activation and tubular injury.

Zymosan, but Not Lipopolysaccharide, Triggers Severe and Progressive Peritoneal Injury Accompanied by Complement Activation in a Rat Peritonitis Model

Fungal peritonitis is an important complication in peritoneal dialysis patients; either continuous or recurrent peritonitis may enhance peritoneal damage. Even when the peritoneal dialysis catheter is removed in patients with fungal peritonitis, peritoneal fibrosis can progress and evolve into encapsular peritoneal sclerosis. It is unclear why fungal infections are worse than bacterial in these respects. Zymosan is a cell wall component of yeast that strongly activates the complement system. In this study, we compared the effects of zymosan and bacterial LPS on peritoneal inflammation in a rat peritoneal injury model induced by mechanical scraping. Intraperitoneal administration of zymosan, but not LPS or vehicle, caused markedly enhanced peritonitis with massive infiltration of cells and deposition of complement activation products C3b and membrane attack complex on day 5. In rats administered zymosan and sacrificed on days 18 or 36, peritoneal inflammation persisted with accumulation of ED-1-positive cells, small deposits of C3b and membrane attack complex, exudation of fibrinogen, and capillary proliferation in subperitoneal tissues. When zymosan was administered daily for 5 days after peritoneal scrape, there was even greater peritoneal inflammation with peritoneal thickening, inflammatory cell accumulation, and complement deposition. Inhibition of systemic complement by pretreatment with cobra venom factor or local inhibition by i.p. administration of the recombinant complement regulator Crry-Ig reduced peritoneal inflammation in zymosan-treated rats. Our results show that yeast components augment inflammation in the injured peritoneum by causing complement activation within the peritoneal cavity. Local anticomplement therapy may therefore protect from peritoneal damage during fungal infection of the peritoneum.

Complement activation is involved in renal damage in human antineutrophil cytoplasmic autoantibody associated pauci-immune vasculitis

OBJECTIVE

This study was to investigate the evidence for complement activation in renal biopsy specimens of patients with myeloperoxidase (MPO)-antineutrophil cytoplasmic autoantibody (ANCA)-associated pauci-immune vasculitis.

METHODS

Renal biopsy specimens from seven patients with MPO-ANCA positive pauci-immune necrotizing crescentic glomerulonephritis (NCGN) were used to detect the staining of membrane attack complex (MAC), C3d, C4d, mannose-binding lectin (MBL), factor B and factor P using immunohistochemistry and immunofluorescence. Renal tissue from seven patients with minimal change disease (MCD) and two normal renal tissue were used as controls.

RESULTS

MAC, C3d, factor B and factor P could be detected in glomeruli and small blood vessels with active vasculitis of patients with pauci-immune AAV, but not or scarcely in patients with MCD and in normal renal tissue. C3d and factor B co-localized with MAC, factor P colocalized with C3d. MBL and C4d were not detected in patients with AAV.

CONCLUSION

The alternative pathway of the complement system is involved in renal damage of human pauci-immune AAV.

Heat shock protein 90-binding agents protect renal cells from oxidative stress and reduce kidney ischemia-reperfusion injury

Heat shock proteins (Hsps) are protective in models of transplantation, yet practical strategies to upregulate them remain elusive. The heat shock protein 90-binding agent (HBA) geldanamycin and its analogs (17-AAG and 17-DMAG) are known to upregulate Hsps and confer cellular protection but have not been investigated in a model relevant to transplantation. We examined the ability of HBAs to upregulate Hsp expression and confer protection in renal adenocarcinoma (ACHN) cells in vitro and in a mouse model of kidney ischemia-reperfusion (I/R) injury. Hsp70 gene expression was increased 30-40 times in ACHN cells treated with HBAs, and trimerization and DNA binding of heat shock transcription factor-1 (HSF1) were demonstrated. A three- and twofold increase in Hsp70 and Hsp27 protein expression, respectively, was found in ACHN cells treated with HBAs. HBAs protected ACHN cells from an H2O2-mediated oxidative stress, and HSF1 short interfering RNA was found to abrogate HBA-mediated Hsp induction and protection. In vivo, Hsp70 was upregulated in the kidneys, liver, lungs, and heart of HBA-treated mice. This was associated with a functional and morphological renal protection from I/R injury. Therefore, HBAs mediate upregulation of protective Hsps in mouse kidneys which are associated with reduced I/R injury and may be useful in reducing transplant-associated kidney injury.

Mapping quantitative trait loci for proteinuria-induced renal collagen deposition

The progression of chronic kidney disease is a complex process influenced by genetic factors. Proteinuria is a predictor of functional deterioration and an accelerator of disease progression through renal parenchymal damage and interstitial fibrosis. To determine genetic components that might mediate renal fibrosis due to proteinuria, we mapped loci influencing the phenotype of two mouse strains differing in proteinuria-induced renal type I collagen (COLI) deposition. Collagen I deposition in 129S1/svImJ and C57BL/6J mice differs significantly among tested strains. We backcrossed 120 hemi-nephrectomized (129S1/svImJ x C57BL/6J) F1 x 129S1/svImJ backcrossed mice loaded with bovine serum albumin giving rise to proteinuria and renal COLI deposition. Quantitative trait loci (QTL) mapping was performed and our analysis identified one suggestive linkage for renal COLI deposition peaking at 87 cM near D2Mit224 (logarithm of odds: 2.41) on Chr 2. In silico analysis uncovered nine candidate genes. Hence, although more studies are needed, these QTL provide an initial cue to subsequent gene discovery, which might help unravel the genetics of renal fibrosis.

The Many Effects of Complement C3- and C5-Binding Proteins in Renal Injury

The complement system is an important component of the innate immune system and a modulator of adaptive immunity. The entire complement system is focused on C3 and C5. Thus, there are proteins that activate C3 and C5, those that regulate this activation, and those that transduce the effects of C3 and C5 activation products; each can affect the kidney in renal injury. The normal kidney has the inherent capacity to protect itself from complement activation through cellular expression of decay-accelerating factor, membrane cofactor protein (in human beings), and Crry (in rodents). In addition, plasma factor H protects vascular spaces in the kidney. Although the main function of these proteins is to limit complement activation, there is now considerable evidence that they can transduce signals on engagement in immune cells. The G-protein-coupled 7-span transmembrane receptors for C3a and C5a, and the integral membrane complement receptors (CR) for C3b, iC3b, and C3dg, are expressed outside the kidney, particularly in cells of hematopoietic and immune lineage. These are important in renal injury through their infiltration of the kidney and/or by affecting kidney-directed immune responses. There is mounting evidence that intrinsic glomerular and tubular cell C3aR and C5aR expression and activation also can affect renal injury. CR1 on podocytes and the beta2 integrins CR3 and CR4 in kidney dendritic cells have functions that remain poorly defined. Cells of the kidney also have the capacity to produce and activate their own complement proteins. Thus, intrinsic renal cells express decay-accelerating factor, membrane cofactor protein, Crry, C3aR, C5aR, CR1, CR3, and CR4. These can be engaged by C3 and C5 activation products derived from systemic and local pools in renal injury. Given their capacity to provide signals that influence kidney cellular behavior, their activation can have substantial effects in renal injury. Defining these in a cell- and disease-specific fashion is an exciting challenge for future research.

Unrestricted C3 activation occurs in Crry-deficient kidneys and rapidly leads to chronic renal failure

Deficiency of the C3 convertase regulator Crry is embryonic lethal in mice unless C3 also is absent. For evaluation of the effect of local kidney Crry deficiency in the setting of an intact complement system, Crry(-/-)C3(-/-) mouse kidneys were transplanted into syngeneic C57BL/6 wild-type mice. These Crry-deficient kidneys developed marked inflammatory cell infiltration, tubular damage, and interstitial fibrosis, whereas similar changes were absent in control transplanted kidneys. Strong C3 deposition in the vessels and tubules that correlated significantly with measures of disease supported that complement activation was pathogenic in this model. Microarray studies showed upregulation of a number of chemokine and extracellular matrix genes, which were validated for CCL2 and CXCL10 mRNA and collagen III protein. The functional significance of these pathophysiologic findings was evaluated by removing both native kidneys, so the transplanted kidney alone provided renal function. Within 21 d of transplantation, seven of eight Crry-deficient kidneys in complement-sufficient wild-type hosts failed, compared with two of 13 controls (P = 0.001), with final blood urea nitrogen levels of 133.9 +/- 33.0 and 55.6 +/- 8.3 mg/dl, respectively (P = 0.015). These data show that mouse Crry is a critical complement regulator in the kidney. When absent, unrestricted complement activation occurs and quickly leads to marked inflammation and progressive renal failure, with features relevant to human diseases with underlying defects in complement regulation, such as hemolytic uremic syndrome.

The central role of the alternative complement pathway in human disease

The complement system is increasingly recognized as important in the pathogenesis of tissue injury in vivo following immune, ischemic, or infectious insults. Within the complement system, three pathways are capable of initiating the processes that result in C3 activation: classical, alternative, and lectin. Although the roles that proinflammatory peptides and complexes generated during complement activation play in mediating disease processes have been studied extensively, the relative contributions of the three activating pathways is less well understood. Herein we examine recent evidence that the alternative complement pathway plays a key and, in most instances, obligate role in generating proinflammatory complement activation products in vivo. In addition, we discuss new concepts regarding the mechanisms by which the alternative pathway is activated in vivo, as recent clinical findings and experimental results have provided evidence that continuous active control of this pathway is necessary to prevent unintended targeting and injury to self tissues.

Altered renal tubular expression of the complement inhibitor Crry permits complement activation after ischemia/reperfusion

Ischemia/reperfusion (I/R) of several organs results in complement activation, but the kidney is unique in that activation after I/R occurs only via the alternative pathway. We hypothesized that selective activation of this pathway after renal I/R could occur either because of a loss of complement inhibition or from increased local synthesis of complement factors. We examined the relationship between renal complement activation after I/R and the levels and localization of intrinsic membrane complement inhibitors. We found that loss of polarity of complement receptor 1-related protein y (Crry) in the tubular epithelium preceded activation of the alternative pathway along the basolateral aspect of the tubular cells. Heterozygous gene-targeted mice that expressed lower amounts of Crry were more sensitive to ischemic injury. Furthermore, inhibition of Crry expressed by proximal tubular epithelial cells in vitro resulted in alternative pathway-mediated injury to the cells. Thus, altered expression of a complement inhibitor within the tubular epithelium appears to be a critical factor permitting activation of the alternative pathway of complement after I/R. Increased C3 mRNA and decreased factor H mRNA were also detected in the outer medulla after I/R, suggesting that altered synthesis of these factors might further contribute to complement activation in this location.

Midkine antisense oligodeoxyribonucleotide inhibits renal damage induced by ischemic reperfusion

BACKGROUND

Midkine, a heparin-binding growth factor, is involved in the migration of inflammatory cells. The inflammatory cell migration to the tubulointerstitium of the kidney after ischemia/reperfusion (I/R) injury is attenuated in midkine gene-deficient mice, resulting in better preservation of the tubulointerstitium compared with wild-type mice. In the present investigation, we planned to evaluate the usefulness of antisense midkine for the therapy of ischemic renal failure.

METHODS

Midkine antisense phosphorothioate oligodeoxyribonucleotide (ODN) at a dose of 1 mg/kg in saline was intravenously administered to mice 1 day before or after I/R. The kidneys were removed for examination 1, 2, 3, and 7 days after I/R.

RESULTS

It was rapidly incorporated into proximal tubular epithelial cells, and inhibited midkine synthesis, leading to reduced migration of inflammatory cells to the injured epithelial layer. Consequently, the midkine antisense ODN-treated animals exhibited less severe renal damage than untreated or midkine sense ODN-treated animals 2 days after I/R as assessed by morphologic criteria and blood urea nitrogen (BUN) and serum creatinine levels. Midkine expression, BUN, and serum creatinine levels were not significantly different between injection of midkine antisense ODN before and after ischemic injury.

CONCLUSION

These results indicate that intravenous injection of midkine antisense ODN is a candidate for a novel therapeutic strategy against acute tubulointerstitial injury induced by I/R injury.

Pathogenesis of Afa/Dr diffusely adhering Escherichia coli

Over the last few years, dramatic increases in our knowledge about diffusely adhering Escherichia coli (DAEC) pathogenesis have taken place. The typical class of DAEC includes E. coli strains harboring AfaE-I, AfaE-II, AfaE-III, AfaE-V, Dr, Dr-II, F1845, and NFA-I adhesins (Afa/Dr DAEC); these strains (i) have an identical genetic organization and (ii) allow binding to human decay-accelerating factor (DAF) (Afa/Dr(DAF) subclass) or carcinoembryonic antigen (CEA) (Afa/Dr(CEA) subclass). The atypical class of DAEC includes two subclasses of strains; the atypical subclass 1 includes E. coli strains that express AfaE-VII, AfaE-VIII, AAF-I, AAF-II, and AAF-III adhesins, which (i) have an identical genetic organization and (ii) do not bind to human DAF, and the atypical subclass 2 includes E. coli strains that harbor Afa/Dr adhesins or others adhesins promoting diffuse adhesion, together with pathogenicity islands such as the LEE pathogenicity island (DA-EPEC). In this review, the focus is on Afa/Dr DAEC strains that have been found to be associated with urinary tract infections and with enteric infection. The review aims to provide a broad overview and update of the virulence aspects of these intriguing pathogens. Epidemiological studies, diagnostic techniques, characteristic molecular features of Afa/Dr operons, and the respective role of Afa/Dr adhesins and invasins in pathogenesis are described. Following the recognition of membrane-bound receptors, including type IV collagen, DAF, CEACAM1, CEA, and CEACAM6, by Afa/Dr adhesins, activation of signal transduction pathways leads to structural and functional injuries at brush border and junctional domains and to proinflammatory responses in polarized intestinal cells. In addition, uropathogenic Afa/Dr DAEC strains, following recognition of beta(1) integrin as a receptor, enter epithelial cells by a zipper-like, raft- and microtubule-dependent mechanism. Finally, the presence of other, unknown virulence factors and the way that an Afa/Dr DAEC strain emerges from the human intestinal microbiota as a "silent pathogen" are discussed.

Lack of the growth factor midkine enhances survival against cisplatin-induced renal damage

Although cisplatin acts directly on proximal tubule epithelial cells and causes cell death, little is known regarding the biological significance of its secondary effects, such as inflammation. The growth factor midkine is highly expressed in the proximal tubule and exerts ambivalent activities as to cisplatin nephrotoxicity, ie, anti-apoptotic and chemotactic ones. Here we report that midkine-deficient mice show a significantly higher survival rate than wild-type mice. The levels of blood urea nitrogen and tubular degeneration and apoptosis were higher in wild-type mice despite the anti-apoptotic activity of midkine. We found that recruitment of neutrophils was more enhanced in wild-type mice, this being consistent with the chemotactic activity of midkine. Midkine expression in wild-type mice persisted for 24 hours, and then dramatically decreased. Preadministration of midkine anti-sense oligodeoxyribonucleotide to wild-type mice suppressed midkine expression, and consequently neutrophil infiltration. It is of note that neutrophil infiltration, apoptosis, and elevation of blood urea nitrogen became conspicuous sequentially, namely 1, 2, and 3 days after cisplatin administration, respectively. These findings suggest that early molecular events involving midkine induce inflammatory response and their circuits eventually enhance the death of the proximal tubule epithelial cells. The results indicate the crucial role of inflammation in cisplatin-induced renal damage, and provide a candidate molecular target for its prevention.

Overexpression of complement inhibitor Crry does not prevent cryoglobulin-associated membranoproliferative glomerulonephritis

BACKGROUND

Mice overexpressing thymic stromal lymphopoietin (TSLP) develop mixed cryoglobulinemia with renal disease closely resembling human cryoglobulin-associated membranoproliferative glomerulonephritis (MPGN), including glomerular deposits of immunoglobulins and complement. We assessed the effect of complement inhibition through overexpression of Crry (complement receptor-1 related gene/protein Y), which blocks the classic and alternative pathway of complement activation through inhibition of the C3 convertase, in cryoglobulinemia-associated immune complex glomerulonephritis.

METHODS

TSLP transgenic mice were crossbred with animals overexpressing Crry. Mice were sacrificed after 50 days (females) or 120 days (males), and kidneys, blood, and urine were collected from seven mice of each experimental group (wild type, Crry transgenic, TSLP transgenic, and Crry/TSLP doubly transgenic).

RESULTS

TSLP/Crry doubly transgenic animals demonstrated expected serum levels of Crry. Renal involvement, both in TSLP transgenic and TSLP/Crry doubly transgenic animals, was characterized by glomerular matrix expansion, macrophage influx, activation of mesangial cells, and deposition of immunoglobulins and complement. Overexpression of Crry did not result in significant improvement of renal pathology or laboratory findings. Expression of recombinant soluble Crry was confirmed by enzyme-linked immunosorbent assay (ELISA) in Crry transgenic animals. However, formation of the membrane attack complex C5b-9 as a marker of terminal active complement components and represented by glomerular C9 staining could not be inhibited in Crry transgenic TSLP mice.

CONCLUSION

These results indicate that overexpression of Crry was not sufficient to prevent renal injury in TSLP transgenic mice. We suggest that the inhibitory capacity of Crry may be overwhelmed by chronic complement activation. Further studies need to address the role of complement in cryoglobulinemic glomerulonephritis before therapeutic complement inhibition can be attempted.

Anti-monocyte chemoattractant protein-1 gene therapy attenuates renal injury induced by protein-overload proteinuria

It has been postulated that protein filtered through glomeruli activates tubular epithelial cells, which secrete vasoactive and inflammatory substances including chemokines, leading to tubulointerstitial renal injury. The present study was designed to investigate the role of monocyte chemoattractant protein-1 (MCP-1) in this process and to evaluate the effectiveness of a kidney-targeted gene transfer technique using hydrodynamic pressure. Naked plasmid encoding 7ND (an MCP-1 antagonist) or a control plasmid was introduced into the left kidney of rats. Three days after gene transfer (day 0), intraperitoneal administration of bovine serum albumin (10 mg/g body wt per day) was started and continued for 14 or 21 d. RT-PCR showed that 7ND mRNA was expressed only in the gene-transfected kidney. Immunostaining showed that 7ND protein was localized in the interstitial cells. Macrophage infiltration was significantly reduced in the left kidney of rats treated with 7ND on days 14 and 21. In the right kidney, such effects were not observed. 7ND also attenuated tubular damage and decreased the number of apoptotic cells. Computer-assisted analysis revealed that the areas positively stained for alpha-smooth muscle actin (alpha SMA), fibronectin-EDA, type I collagen, and collagen fibrils were significantly reduced in the 7ND-treated kidney on day 21. Furthermore, 7ND gene therapy significantly reduced MCP-1 and TGF-beta 1 mRNA expression. These results demonstrate that MCP-1 plays an important role in the development of tubulointerstitial inflammation, tubular damage, and fibrosis induced by proteinuria. The fact that 7ND gene therapy had little effect on the contralateral kidney indicates that 7ND acted locally. This strategy may have a potential usefulness as a gene therapy against tubulointerstitial renal injury.

Lack of a functional alternative complement pathway ameliorates ischemic acute renal failure in mice

Ischemia/reperfusion (I/R) injury of the kidney is a common cause of acute renal failure (ARF) and is associated with high morbidity and mortality in the intensive care unit. The mechanisms underlying I/R injury are complex. Studies have shown that complement activation contributes to the pathogenesis of I/R injury in the kidney, but the exact mechanisms of complement activation have not been defined. We hypothesized that complement activation in this setting occurs via the alternative pathway and that mice deficient in complement factor B, an essential component of the alternative pathway, would be protected from ischemic ARF. Wild-type mice suffered from a decline in renal function and had significant tubular injury, particularly in the outer medulla, after I/R. We found that factor B-deficient mice (fB(-/-)) developed substantially less functional and morphologic renal injury after I/R. Furthermore, control wild-type mice had an increase in tubulointerstitial complement C3 deposition and neutrophil infiltration in the outer medulla after I/R, whereas fB(-/-) mice demonstrated virtually no C3 deposition or neutrophil infiltration. Our results demonstrate that complement activation in the kidney after I/R occurs exclusively via the alternative pathway, and that selective inhibition of this pathway provides protection to the kidneys from ischemic ARF.

Acute renal failure in endotoxemia is caused by TNF acting directly on TNF receptor-1 in kidney

Bacterial endotoxin (LPS) is responsible for much of the widespread inflammatory response seen in sepsis, a condition often accompanied by acute renal failure (ARF). In this work we report that mice deficient in TNFR1 (TNFR1(-/-)) were resistant to LPS-induced renal failure. Compared with TNFR1(+/+) controls, TNFR1(-/-) mice had less apoptosis in renal cells and fewer neutrophils infiltrating the kidney following LPS administration, supporting these as mediators of ARF. TNFR1(+/+) kidneys transplanted into TNFR1(-/-) mice sustained severe ARF after LPS injection, which was not the case with TNFR1(-/-) kidneys transplanted into TNFR1(+/+) mice. Therefore, TNF is a key mediator of LPS-induced ARF, acting through its receptor TNFR1 in the kidney.

Decay-accelerating factor confers protection against complement-mediated podocyte injury in acute nephrotoxic nephritis

SUMMARY

Decay-accelerating factor (DAF or CD55) is one of a set of regulators that function to protect self cells from deposition of autologous C3b on their surfaces. Its relative importance in vivo, however, is incompletely understood. As one approach to address this issue, we induced nephrotoxic serum (NTS) nephritis in wild-type mice and Daf1 gene-floxed mice devoid of renal DAF expression. For these experiments NTS IgG was administered at a dose (0.5 mg iv) that requires complement for glomerular injury. After 18 hours, renal injury was assessed by proteinuria and by histologic, immunohistochemical, and electron microscopic analyses of kidneys. Fifteen normal and 15 DAF-deficient mice were studied. Baseline albuminuria in the Daf1(-/-) mice was 115.9 +/- 41.4 microg/mg creatinine as compared with 85.7 +/- 32.3 microg/mg creatinine in their Daf1(+/+) littermates (p = 0.075). After administration of NTS IgG, albuminuria increased to 2001.7 +/- 688.7 microg/mg creatinine as compared with 799.7 +/- 340.5 microg/mg creatinine in the controls (p = 0.0003). Glomerular histology was similar in Daf1(-/-) and Daf1(+/+) mice, with essentially no infiltrating leukocytes. In contrast, electron microscopy revealed severe podocyte fusion in the Daf1(-/-) mice but only mild focal changes in the controls. Immunohistochemical staining showed equivalent deposition of the administered (sheep) NTS IgG in the Daf1(-/-) and Daf1(+/+) animals. This contrasted with marked deposition of autologous murine C3 in the former and minimal deposition in the latter. The results show that DAF is essential physiologically for protecting glomeruli against autologous complement attack initiated by the classical pathway.

Enhancement of the complement activating capacity of 17-1A mAb to overcome the effect of membrane-bound complement regulatory proteins on colorectal carcinoma

Adjuvant immunotherapy with 17-1A mAb directed against colorectal carcinoma is found to be effective in patients. However, 52 % of the patients treated with mAb 17-1A showed recurrence within 7 years. This high recurrence rate might be due to inhibition of complement activation by membrane-bound complement regulatory proteins (mCRP). The effect of these complement regulatory proteins might be reduced by blocking mCRP, or be overcome by activating more complement at the tumor cell membrane. In this study the complement-activating capacity of the 17-1A mAb was enlarged by conjugating it to cobra venom factor (CVF) or C3b. The most important C3 regulatory protein, CD55, was blocked using a bispecific mAb directed against the 17-1A / Ep-CAM antigen and CD55. Up to a 13-fold increase in C3 deposition was observed due to 17-1A-CVF and 17-1A-C3b, as compared to 17-1A. CD55 was shown to partly inhibit complement activation by these conjugates. The effect of the bispecific anti-17-1A / Ep-CAM*anti-CD55 mAb was compared with 17-1A conjugates with CVF or C3, and bispecific mAb were shown to be equally or more efficient in complement activation than the 17-1A-CVF or 17-1A-C3b conjugates. Therefore, 17-1A conjugates and anti-17-1A / EpCAM*anti-CD55 bispecific mAb may be promising immunotherapeutic agents for patients with colorectal cancer.

Membrane complement regulators protect against the development of type II collagen-induced arthritis in rats

OBJECTIVE

To investigate changes in the distribution patterns of membrane complement regulators (MCRs) during the development of type II collagen-induced arthritis (CIA) and to examine the protective effects of these molecules against the augmentation of CIA in the knee joint.

METHODS

Immunohistochemistry was used to examine the distribution of the MCRs Crry, DAF, and CD59 in the synovium of knee joints before and 2, 4, and 10 weeks after induction of CIA by immunization with type II collagen. In addition, at 2 or 10 weeks after induction of CIA, rats were injected intraarticularly with anti-Crry and/or anti-CD59 as the F(ab')2 fraction of monoclonal antibodies (mAb). Knee joint swelling and histologic changes in the synovium were examined 2 weeks after mAb injection.

RESULTS

Synovial expression of Crry, DAF, and CD59 decreased in parallel with increased inflammation. When Crry and CD59 were functionally blocked at 2 weeks after the induction of CIA, swelling of the knee joints was markedly increased. Blocking of either regulator alone had no effect on swelling. Thickening of the synovial surface and proliferation of subsynovial tissue were all increased after blocking Crry and CD59, whereas blocking of either MCR alone had no effect. When both Crry and CD59 were blocked, deposits of membrane attack complex were found in the synovium.

CONCLUSION

Our findings indicate that in rats with CIA and severely inflamed synovium, local expression of MCR is reduced. The MCRs Crry and CD59 appear to suppress the development of CIA.

Midkine is involved in neutrophil infiltration into the tubulointerstitium in ischemic renal injury

Midkine (MK) is a multifunctional heparin-binding protein and promotes migration of neutrophils, macrophages, and neurons. In the normal mouse kidney, MK is expressed in the proximal tubules. After renal ischemic reperfusion injury, its expression in proximal tubules was increased. Immediate increase of MK expression was found when renal proximal tubular epithelial cells in culture were exposed to 5 mM H(2)O(2). Histologically defined tubulointerstitial damage was less severe in MK-deficient (Mdk(-/-)) than in wild-type (Mdk(+/+)) mice at 2 and 7 days after ischemic reperfusion injury. Within 2 days after ischemic injury, inflammatory leukocytes, of which neutrophils were the major population, were recruited to the tubulointerstitium. The numbers of infiltrating neutrophils and also macrophages were lower in Mdk(-/-) than in Mdk(+/+) mice. Induction of macrophage inflammatory protein-2 and macrophage chemotactic protein-1, chemokines for neutrophils and macrophages, respectively, were also suppressed in Mdk(-/-) mice. Furthermore, renal tubular epithelial cells in culture expressed macrophage inflammatory protein-2 in response to exogenous MK administration. These results suggested that MK enhances migration of inflammatory cells upon ischemic injury of the kidney directly and also through induction of chemokines, and contributes to the augmentation of ischemic tissue damage.

Glomerular complement regulation is overwhelmed in passive Heymann nephritis

BACKGROUND

An injection of anti-Fx1A antibodies in rats leads to passive Heymann nephritis (PHN), a model of membranous nephropathy. Fx1A is a crude extract of renal cortex that contains megalin as a principal component. However, when rats are given anti-megalin antibodies, abnormal proteinuria does not occur. Because of the established complement dependence of PHN, we hypothesized that antibodies neutralizing complement regulatory proteins in the rat glomerulus also were required to induce PHN. Two likely targets are Crry and CD59, proteins abundant on the rat podocyte and contained within Fx1A that inhibit the C3 convertase and C5b-9 assembly, respectively.

METHODS

Rats were injected with anti-megalin monoclonal antibodies, followed by anti-Crry and/or anti-CD59 F(ab')(2) antibodies five days later. In a second group of experiments, rats were injected with anti-Fx1A or anti-Fx1A immunodepleted of reactivity against Crry and/or CD59.

RESULTS

In the setting of podocyte-associated anti-megalin monoclonal antibodies, simultaneous neutralization of Crry and CD59 function led to the development of significant proteinuria (11.0 +/- 2.1 mg/day, P < 0.001 vs. all other groups). In contrast, animals that had neither or only one of these complement regulators inhibited had normal urinary protein excretion (< or =6 mg/day). In animals given anti-Fx1A depleted of anti-Crry and/or anti-CD59, all groups developed typical PHN, characterized by heavy proteinuria and extensive glomerular deposition of C3 and C5b-9.

CONCLUSION

Crry and CD59 play an important role in restraining complement-mediated injury following subepithelial immune complex deposition; however, in PHN, their regulatory capacity is overwhelmed.

Increased susceptibility of decay-accelerating factor deficient mice to anti-glomerular basement membrane glomerulonephritis

To prevent complement-mediated autologous tissue damage, host cells express a number of membrane-bound complement inhibitors. Decay-accelerating factor (DAF, CD55) is a GPI-linked membrane complement regulator that is widely expressed in mammalian tissues including the kidney. DAF inhibits the C3 convertase of both the classical and alternative pathways. Although DAF deficiency contributes to the human hematological syndrome paroxysmal nocturnal hemoglobinuria, the relevance of DAF in autoimmune tissue damage such as immune glomerulonephritis remains to be determined. In this study, we have investigated the susceptibility of knockout mice that are deficient in GPI-anchored DAF to nephrotoxic serum nephritis. Injection of a subnephritogenic dose of rabbit anti-mouse glomerular basement membrane serum induced glomerular disease in DAF knockout mice but not in wild-type controls. When examined at 8 days after anti-glomerular basement membrane treatment, DAF knockout mice had a much higher percentage of diseased glomeruli than wild-type mice (68.8 +/- 25.0 vs 10.0 +/- 3.5%; p < 0.01). Morphologically, DAF knockout mice displayed increased glomerular volume (516 +/- 68 vs 325 +/- 18 x 10(3) microm(3) per glomerulus; p < 0.0001) and cellularity (47.1 +/- 8.9 vs 32.0 +/- 3.1 cells per glomerulus; p < 0.01). Although the blood urea nitrogen level showed no difference between the two groups, proteinuria was observed in the knockout mice but not in the wild-type mice (1.4 +/- 0.7 vs 0.02 +/- 0.01 mg/24 h albumin excretion). The morphological and functional abnormalities in the knockout mouse kidney were associated with evidence of increased complement activation in the glomeruli. These results support the conclusion that membrane C3 convertase inhibitors like DAF play a protective role in complement-mediated immune glomerular damage in vivo.

Targeted deletion of the CD59 gene causes spontaneous intravascular hemolysis and hemoglobinuria

The glycolipid-anchored glycoprotein CD59 inhibits assembly of the lytic membrane attack complex of complement by incorporation into the forming complex. Absence of CD59 and other glycolipid-anchored molecules on circulating cells in the human hemolytic disorder paroxysmal nocturnal hemoglobinuria is associated with intravascular hemolysis and thrombosis. To examine the role of CD59 in protecting host tissues in health and disease, CD59-deficient (CD59(-/-)) mice were produced by gene targeting in embryonic stem cells. Absence of CD59 was confirmed by staining cells and tissues with specific antibody. Despite the complete absence of CD59, mice were healthy and fertile. Erythrocytes in vitro displayed increased susceptibility to complement and were positive in an acidified serum lysis test. Despite this, CD59(-/-) mice were not anemic but had elevated reticulocyte counts, indicating accelerated erythrocyte turnover. Fresh plasma and urine from CD59(-/-) mice contained increased amounts of hemoglobin when compared with littermate controls, providing further evidence for spontaneous intravascular hemolysis. Intravascular hemolysis was increased following administration of cobra venom factor to trigger complement activation. CD59(-/-) mice will provide a tool for characterizing the importance of CD59 in protection of self tissues from membrane attack complex damage in health and during diseases in which complement is activated.

Enhanced expression of complement C5a receptor mRNA in human diseased kidney assessed by in situ hybridization

BACKGROUND

Anaphylatoxin C5a mediates inflammatory responses through interaction with a specific C5a receptor (C5aR), the expression of which is thought to be restricted to peripheral blood leukocytes. Although the presence of C5aR on cultured mesangial cells and tubular epithelial cells has recently been documented, the tissue distribution of C5aR in diseased kidney has not yet been determined.

METHODS

Immunohistochemistry and nonradioactive in situ hybridization for C5aR were performed in 34 tissue samples of kidneys from patients with various renal diseases, including 4 with minimal change nephrotic syndrome (MCNS), 5 with membranous nephropathy (MN), and 25 with mesangial proliferative glomerulonephritis (mesGN; 15 patients with IgA nephropathy, 5 with non-IgA mesGN, and 5 with lupus nephritis). Normal portions of surgically resected kidney served as the control.

RESULTS

In normal kidneys, C5aR protein was detected in tubular epithelial cells, while C5aR mRNA was detected in a few glomerular cells, tubular epithelial cells, and vascular endothelial and smooth muscle cells. In MCNS, the distribution of C5aR protein and mRNA was similar to that in normal kidneys. In MN and mesGN, C5aR protein and mRNA were detected in mesangial cells, glomerular epithelial and endothelial cells, Bowman's capsule cells, tubular cells, infiltrating cells, and vascular endothelial and smooth muscle cells. The glomerular expression of C5aR mRNA and protein correlated positively with the degree of mesangial hypercellularity and mesangial matrix expansion in mesGN. In the tubulointerstitium, interstitial expression of C5aR mRNA correlated positively with the degree of tubular atrophy and interstitial broadening in mesGN. Furthermore, the interstitial expression of C5aR mRNA correlated positively with the level of serum creatinine.

CONCLUSIONS

Our results indicate that renal cells produce C5aR and that activation of C5a/C5aR pathway on renal cells may be involved in tissue injury in mesGN.

Membrane complement regulatory proteins: insight from animal studies and relevance to human diseases

The complement system plays an important role in host defense. However, if not properly regulated, activated complement can also cause significant damage to host tissues. To prevent complement-mediated autologous tissue damage, host cells express a number of membrane-bound complement regulatory proteins. These include decay-accelerating factor (DAF, CD55), membrane cofactor protein (MCP, CD46) and CD59. Recent studies of membrane complement regulatory proteins from various animal species have revealed similarities as well as significant differences from the corresponding human proteins. In this review, we summarize recent advances in this area and contrast the structure, function and tissue distribution of membrane complement regulatory proteins in human and nonprimate mammalian species. We also discuss how the characterization of the animal proteins has provided important clues and might continue to show relevance to the pathogenesis and therapeutics of a number of human diseases.

The role of C5a in the development of thrombotic glomerulonephritis in rats

Thrombus formation is the important pathologic finding observed in glomerulonephritis induced by antiglomerular basement membrane (GBM) antibodies. Although strong deposition of C3 and membrane attack complex (MAC) is observed in this disease, the role of complement has not been fully elucidated. The aim of this work was to investigate the role of complement, especially an anaphylatoxin C5a, in a rat model of thrombotic glomerulonephritis. Rats were first pretreated with subclinical dose of lipopolysaccharide (LPS). Thrombotic glomerulonephritis was then induced by intravenous injection with rabbit antirat GBM (RbAGBM) (Group I). For the evaluation of the role of complement, the soluble complement receptor type 1 (sCR1) (Group II) or the C5a receptor antagonist peptide (C5aR-AP) (Group III) was intravenously administered 30 min before RbAGBM injection. For exploring the role of neutrophils, rats were pretreated with cyclophosphamide before induction of disease (Group IV). All rats were sacrificed at 6 h, and histological examination was performed. Rats in Group I developed severe glomerular thrombosis. Leucocyte accumulation and strong binding of C3 and MAC were observed in the glomeruli. In rats treated with sCR1 (Group II) and C5aR-AP (Group III), both leucocyte accumulation and thrombus formation in the glomeruli were significantly inhibited. C3 and MAC were negative in the glomeruli in Group II rats, while they were strongly observed in Group III. In neutrophil depleted rats (Group IV), there was also deposition of C3 and MAC in the glomeruli but thrombus formation was not observed. These findings indicated that glomerular thrombosis is dependent on the leucocytes, and mediated in part by the anaphylatoxin C5a but not MAC in the present model.

Expression of a soluble complement inhibitor protects transgenic mice from antibody-induced acute renal failure

Crry is a potent complement regulator in rodents that inhibits C3 convertases. In rats, intrarenal arterial injection of anti-glomerular endothelial cell (GEN) antibodies leads to complement-dependent microvascular injury and acute renal failure. In this study, a mouse variant of this model and the effects of complement inhibition were examined. Transgenic mice that overexpressed soluble Crry systemically and in their kidneys were studied. Anti-GEN IgG was injected intravenously into eight Crry transgenic mice and seven transgene-negative littermates (which were used as control animals). Thirty h after injection, blood urea nitrogen (BUN) levels were 30.3 +/- 4.4 and 114.8 +/- 23.5 mg/dl for transgene-positive and -negative animals, respectively (P = 0.012). Four of five transgene-negative animals with BUN levels of > 100 mg/dl were anuric; the remaining animal exhibited minimal albuminuria and no detectable urinary C3. In animals with renal failure, glomerular capillary collapse and tubular necrosis were observed. There was significant tubular staining for C3 in transgene-negative animals, with cellular and basal distributions, both of which were statistically greater than those in transgene-positive animals. Tubular cell C3 staining was strongly correlated with BUN values (r = 0.83, P < 0.001), as was C9 staining (r = 0.56, P = 0.037), suggesting that complement activation to the C5b-9 membrane attack complex had a casual role in renal failure. Thus, systemic injection of anti-GEN antibodies into mice leads to acute renal failure, with glomerular and tubular injury. Animals that overexpress soluble Crry in renal tubules and elsewhere are protected from the acute renal failure that occurs in this model, which ultimately seems to develop because of complement activation focused on tubules.

New pharmacologic options for renal preservation

The understanding of the cause and pathophysiology of renal failure has guided the rational development of pharmacologic renoprotective strategies. Although traditionally anesthesiologists have focused on renal hemodynamic derangements, newer information suggests that cellular interactions amplify and perpetuate the insult. Consequently, the potential renoprotective armamentarium not only encompasses the more traditional vasoactive agents but also therapeutic approaches that may modify the cellular response to injury. Although few of these agents have reached the clinical arena, preliminary work suggests that this new approach to renal injury and protection may be promising.