Increased expression of cyclooxygenase 2 contributes to aberrant renin production in connexin 40-deficient kidneys

We previously found that deletion of connexin 40 (Cx40) causes a misdirection of renin-expressing cells from the media layer of afferent arterioles to the perivascular tissue, extraglomerular mesangium, and periglomerular and peritubular interstitium. The mechanisms underlying this aberrant renin expression are unknown. Here, we questioned the relevance of cyclooxygenase-2 (COX-2) activity for aberrant renin expression in Cx40-deficient kidneys. We found that COX-2 mRNA levels were increased three-fold in the renal cortex of Cx40-deficient kidneys relative to wild-type (wt) kidneys. In wt kidneys, COX-2 immunoreactivity was minimally detected in the juxtaglomerular region, but renin expression was frequently associated with COX-2 immunoreactivity in Cx40-deficient kidneys. Treatment with COX-2 inhibitors for 1 wk lowered renin mRNA levels in wt kidneys by about 40%. In Cx40-deficient kidneys, basal renin mRNA levels were increased two-fold relative to wt kidneys, and these elevated mRNA levels were reduced to levels of untreated wt mice by COX-2 inhibitors. In parallel, renin immunoreactive areas were clearly reduced by COX-2 inhibitors such that renin expression vanished and decreased significantly in the periglomerular and peritubular extensions. Notably, COX-2 inhibitor treatment lowered plasma renin concentration (PRC) in wt kidneys by about 40% but did not affect the highly elevated PRC levels in Cx40-deficient mice. These findings suggest that aberrant renin-producing cells in Cx40-deficient kidneys express significant amounts of COX-2, which contribute to renin expression in these cells, in particular, those in the periglomerular and peritubular position. Apparently, these disseminated cells do not contribute to the enhanced renin secretion rates of Cx40-deficient kidneys.     

Involvement of mesangial cells expressing alpha-smooth muscle actin during restorative glomerular remodeling in Thy-1.1 nephritis.

The function of actin cytoskeleton in mesangial cells (MCs) during the recovering process of injured glomeruli is not fully understood. MCs in injured glomeruli express alpha-smooth muscle actin (alpha-SMA), which is not detected in normal glomeruli. We focused on the localization of alpha-SMA in MCs of Thy-1.1 nephritic rat. Expression of alpha-SMA in the injured glomeruli peaked at day 5 after antibody injection and then declined gradually. At day 5, MCs, where alpha-SMA was localized at their cytoplasmic processes situated in various positions, occupied the expanded mesangium. MCs expressing alpha-SMA tended to be located at the peripheral region close to the glomerular basement membrane (GBM) or endothelial cells at day 8. Localization of alpha-SMA within the peripheral MCs was restricted to the cytoplasmic processes radiating toward the GBM and touching it with their tips at day 8. These alpha-SMA-containing processes are suitable to transmit the contractile force to GBM and may contribute to normalize the expanded glomerular volume. In addition, an actin-binding protein, drebrin, was localized in all MC processes extending toward various directions throughout the course of nephritis, suggesting that drebrin is involved in the formation of MC processes.     

Cellular origin of fibronectin in interspecies hybrid kidneys

The cellular origin of fibronectin in the kidney was studied in three experimental models. Immunohistochemical techniques that use cross-reacting or species-specific antibodies against mouse or chicken fibronectin were employed. In the first model studied, initially avascular mouse kidneys cultured on avian chorioallantoic membranes differentiate into epithelial kidney tubules and become vascularized by chorioallantoic vessels. Subsequently, hybrid glomeruli composed of mouse podocytes and avian endothelial-mesangial cells form. In immunohistochemical studies, cross-reacting antibodies to fibronectin stained vascular walls, tubular basement membranes, interstitium, and glomeruli of mouse kidney grafts. The species-specific antibodies reacting only with mouse fibronectin stained interstitial areas and tubular basement membranes, but showed no reaction with hybrid glomeruli and avian vascular walls. In contrast, species-specific antibodies against chicken fibronectin stained both the interstitial areas and the vascular walls as well as the endothelial-mesangial areas of the hybrid glomeruli, but did not stain the mouse-derived epithelial structures of the kidneys. In the second model, embryonic kidneys cultured under avascular conditions in vitro develop glomerular tufts, which are devoid of endothelial cells. These explants showed fluorescence staining for fibronectin only in tubular basement membranes and in interstitium. The avascular, purely epithelial glomerular bodies remained unstained. Finally, in outgrowths of separated embryonic glomeruli, the cross-reacting fibronectin antibodies revealed two populations of cells: one devoid of fibronectin and another expressing fibronectin in strong fibrillar and granular patterns. These results favor the idea that the main endogenous cellular sources for fibronectin in the embryonic kidney are the interstitial and vascular cells. All experiments presented here suggest that fibronectin is not synthesized by glomerular epithelial cells in vivo.     

Demonstration of human kidney differentiation antigens with monoclonal antibodies

Six human differentiation antigens (EE24.6, EG9.11, EG14.1, EI16.1, EK8.1, EK17.1) have been defined using monoclonal antibodies obtained from mice immunized with embryonic kidney cells. Their histologic distribution was determined on frozen sections of embryonic, fetal, and adult human kidneys by immunofluorescence assay. EE24.6, an ureteral bud marker, was detected only on the germ layer of mature kidney urothelium. EG9.11 and EG14.1 were detected on the S-shaped bodies and also on the adult proximal convoluted tubule for the former and the glomerular basement membrane for the latter. EI16.1, a marker of condensed mesenchyme, was detected only on epithelial cells of adult proximal convoluted tubule. EK8.1 was found in the mesangium, connective tissue, and with particularly dense labeling in the basement membranes. This labeling pattern was present throughout renal organogenesis. EK17.1 recognized both cell and plasma human fibronectins. Staining for all antibodies was nearly identical in mesonephros and metanephros. These results demonstate that some antigens follow their embryonic destiny. They indicate an antigenic similarity between the mesonephros and the metanephros and, therefore, a very early appearance of these antigens. During differentiation, these antigens concentrate on more defined structures, and staining became increased with an increased degree of differentiation.     

Macrophage metalloelastase as a major factor for glomerular injury in anti-glomerular basement membrane nephritis

Rat anti-glomerular basement membrane (GBM) nephritis is a model of crescentic glomerulonephritis induced by injection of anti-GBM antiserum. To elucidate the mechanism of glomerular injury, we analyzed the gene expression patterns in the kidneys of anti-GBM nephritis rats using DNA arrays, and found that macrophage metalloelastase/matrix metalloproteinase (MMP)-12 was one of the highly expressed genes in the kidneys on days 3 and 7 after the injection of anti-GBM antiserum. Enhancement of MMP-12 mRNA expression was confirmed by Northern blot analysis, and in situ hybridization revealed that MMP-12 mRNA was expressed in ED-1-positive macrophages and multinuclear giant cells in the glomeruli with crescent. Moreover, these cells were positive with anti-rat rMMP-12 Ab on the section of the kidneys of anti-GBM nephritis rats on day 7. To clarify the role of MMP-12, we conducted a neutralization experiment using anti-rat rMMP-12 Ab, which had an ability to inhibit rMMP-12 activity of degrading natural substrate such as bovine elastin or human fibronectin in vitro. Anti-rat rMMP-12 Ab or control Ig was injected in each of six rats on days 0, 2, 4, and 6 after the injection of anti-GBM antiserum. Consequently, crescent formation and macrophage infiltration in the glomeruli were significantly reduced in the rats treated with anti-rat rMMP-12 Ab, and the amount of urine protein was also decreased. These results disclosed that MMP-12 played an important role in glomerular injury in a crescentic glomerulonephritis model, and inhibition of MMP-12 may lead to a new therapeutic strategy for this disease.     

Immunohistochemical distribution of type VI collagen in developing human kidney

Summary The distribution of type VI collagen was investigated immunohistochemically in the developing human kidney from 15 to 32 weeks gestational age and it was compared with that observed in the normal infantile and adult human kidney. In fetal kidney, type VI collagen was widely distributed as a fibrillar network in the subcapsularly undifferentiated mesenchyme and intertubular interstitium, and as a basement membrane-like structure around the ureteral bud branches, tubules, and collecting ducts. During nephrogenesis, type VI collagen disappeared from the induced mesenchyme close to the tips of ureteral branches, while it formed a distinct basement membrane-like structure around the early stages of nephron differentiation (comma-shaped and S-shaped bodies) and later along Bowman's capsule of capillary loop and maturing glomeruli. A strong immureactivity for type VI collagen was also found in the glomerular basement membrane and mesangial areas of capillary loop and maturing glomeruli. In infantile kidney, type VI collagen showed a distribution pattern similar to that observed during the fetal period. In adult human kidney, glomerular basement membrane showed a weak positivity for type VI collagen and the basement membrane-like staining around Bowman's capsule, tubules, and collecting ducts was less evident than in fetal and infantle kidney. Our immunohistochemical findings suggest that type VI collagen is a normal component of the glomerular and extraglomerular extracellular matrix of developing human kidney and that it undergoes changes in the expression during maturation.     

Abrogation of mercuric chloride-induced nephritis in the Brown Norway rat by treatment with antibodies against TNFalpha

HgCl(2) induces an autoimmune disease in the Brown Norway rat characterized by synthesis of autoantibodies (mainly, anti-GBM Abs), severe proteinuria and interstitial nephritis. Also, HgCl(2)- injected rats develop glomerular cell infiltrates consisting of ED1(+) cells (monocyte/macrophage), starting on day 4 and reaching a maximum on day 8. Treatment with anti-TNF-alpha antiserum had preventative effects as it reduced the urinary protein levels to close to the normal range and also blocked the influx of inflammatory cells in the renal glomeruli and interstitium, but circulating anti-GBM and lineal glomerular IgG deposits were unmodified. In addition, whole isolated glomeruli from HgCl(2)-induced nephritis secreted TNF-alpha commencing on day 8, being maximally detected on day 11 and preceding, between 2 to 3 days, the development of proteinuria. The administration of anti-TNF-alpha antiserum or anti-alpha4 integrin mAb completely abrogated the synthesis of TNF-alpha in glomeruli isolated from the respective treated groups of animals, in addition to the proteinuria. Taken together our results confirm that TNF-alpha plays an important role in the induction and development of HgCl(2)-induced nephritis and highlights the pathogenic importance of the local release of TNF in those renal diseases in which prominent glomerular macrophage accumulation is a constant feature.     

Intraglomerular fibronectin in rat experimental glomerulonephritis.

To clarify the mechanisms of glomerular pericapillary fibronectin deposition in human membranous nephropathy and mesangial proliferative glomerulonephritis, intraglomerular fibronectin distribution was examined by light and electron microscopy using the experimental rat models of Heymann and nephrotoxic serum nephritis. As previously demonstrated by immunofluorescence microscopy (Pettersson and Colvin 1978; Ikeya et al. 1985, 1986), fibronectin was distributed in the mesangial areas and occasionally on percicapillary walls of normal glomeruli, while in nephrotoxic serum nephritis and Heymann nephritis, fibronectin was diffusely located along glomerular capillary walls as well as in the mesangium. By immunoelectron microscopy using the immunogold technique, fibronectin was also noted in the mesangial areas and the lamina densa of the glomerular basement membrane (GBM) in normal glomeruli. In nephrotoxic serum nephritis, fibronectin was seen around mesangial cells situated between endothelial cells and the GBM, suggesting that pericapillary fibronectin in nephrotoxic serum nephritis reflects mesangial extension. However, in Heymann nephritis, it was found uniformly in the lamina rara interna, lamina densa and lamina rara externa of the GBM, indicating no specific relation to glomerular cells. When sections of normal and both experimental nephritis kidneys were incubated with fluorescein isothiocyanate conjugated with rat plasma fibronectin, a linear pattern of fluorescein staining along the glomerular capillary walls was observed in Heymann nephritis but not in normal or nephrotoxic serum nephritic rats. The GBM in Heymann nephritis would thus appear to have an affinity for plasma fibronectin. Based on the above findings, fibronectin in the GBM of rats with Heymann nephritis may reasonably be concluded to originate from the plasma.     

Experimental Dirofilaria immitis-associated glomerulonephritis induced in part by in situ formation of immune complexes in the glomerular capillary wall

Eight dogs were immunized with an aqueous-soluble extract of adult Dirofilaria immitis. Subsequent to at least 7-fold increases in antibody titer, the left renal artery of each dog was infused with 6 mg of D. immitis antigen. Fourteen days after infusion, the left kidney was compared to the right kidney and preinfusion biopsies. All dogs developed glomerular lesions in the left kidney characterized by 1 or more of the following: mesangial cell proliferation, neutrophil infiltration, increased periodic acid-Schiff-positive staining of the mesangium and glomerular basement membrane (GBM), fibrin deposition, and thickening of the GBM. Left kidney glomerular immunofluorescence was positive in 7 of the 8 dogs using polyclonal antisera for canine IgG and C3 in a linear or fine granular pattern. Ultrastructural lesions were present in the left kidney of all dogs and consisted of irregular GBM thickening, intramembranous and mesangial electron-dense deposits, and mesangial and endothelial cell proliferation. Antibodies directed against D. immitis antigen were demonstrated in all kidney eluates from the left kidney. The right kidneys of 3 of the dogs developed lesions; however, in comparison to the left kidney, the lesions in the right kidneys were inconsistent, mild, and focal. The histologic findings in the left kidney were similar to those observed in dogs with naturally occurring D. immitis infections. In sham-immunized control dogs, renal arterial infusion of D. immitis antigen did not cause consistent immune complex glomerulonephritis; however, antigen adherence to glomerular capillary walls was observed by immunofluorescent microscopy.(ABSTRACT TRUNCATED AT 250 WORDS)     

Severe Nephrotoxic Nephritis following Conditional and Kidney-Specific Knockdown of Stanniocalcin-1

Background

Inflammation is the hallmark of nephrotoxic nephritis. Stanniocalcin-1 (STC1), a pro-survival factor, inhibits macrophages, stabilizes endothelial barrier function, and diminishes trans-endothelial migration of leukocytes; consistently, transgenic (Tg) overexpression of STC1 protects from nephrotoxic nephritis. Herein, we sought to determine the phenotype of nephrotoxic nephritis after conditional and kidney-specific knockdown of STC1.

Methods

We used Tg mice that, express either STC1 shRNA (70% knockdown of STC1 within 4d) or scrambled shRNA (control) upon delivery of Cre-expressing plasmid to the kidney using ultrasound microbubble technique. Sheep anti-mouse GBM antibody was administered 4d after shRNA activation; and mice were euthanized 10 days later for analysis.

Results

Serum creatinine, proteinuria, albuminuria and urine output were similar 10 days after anti-GBM delivery in both groups; however, anti-GBM antibody delivery to mice with kidney-specific knockdown of STC1 produced severe nephrotoxic nephritis, characterized by severe tubular necrosis, glomerular hyalinosis/necrosis and massive cast formation, while control mice manifested mild tubular injury and crescentic glomerulonephritis. Surprisingly, the expression of cytokines/chemokines and infiltration with T-cells and macrophages were also diminished in STC1 knockdown kidneys. Staining for sheep anti-mouse GBM antibody, deposition of mouse C₃ and IgG in the kidney, and antibody response to sheep IgG were equal.

Conclusions

nephrotoxic nephritis after kidney-specific knockdown of STC1 is characterized by severe tubular and glomerular necrosis, possibly due to loss of STC1-mediated pro-survival factors, and we attribute the paucity of inflammation to diminished release of cytokines/chemokines/growth factors from the necrotic epithelium.     

Developmental modifications of sheep kidney antigens

We have used monoclonal antibodies to study the changes in the expression of four kidney antigens during organogenesis in the sheep. Two of these antibodies, EE24.6 and EJ30.1, label intensely only the adult kidney, whereas the other two, EK17.1 and EJ15.1, bind to the extracellular matrix of the embryonic kidney. For EJ15.1, the staining of the extracellular matrix decreases temporarily during the second half of intrauterine life, a period during which a light staining appears in the mesangium. For the other, EK17.1, the extracellular matrix staining in the stroma gradually decreases as the embryo grows, while staining of the mesangium and the arterial intima becomes evident. With EK17.1, fibronectin is identified in the extracellular matrix of the embryonic kidney and intracellularly in the mesangial cells after these cells have colonized the glomerulus. The mesonephros staining seems to be the same as that of the metanephros.In the adult, extraglomerular vascular endothelial cells bind EK17.1, whereas intraglomerular endothelial cells do not express fibronectin, which suggests a functional difference between endothelial cells in these two localizations.     

Expression of nestin in the podocytes of normal and diseased human kidneys

The complex cyto-architecture of the podocyte is critical for glomerular permselectivity. The present study characterizes the expression of nestin, an intermediate filament protein, in human kidneys. In normal kidneys, nestin was detected at the periphery of glomerular capillary loops. Colabeling showed nestin was expressed in WT1-positive cells. Within the podocyte, nestin immunoreactivity was present in the cell body and primary process. This was supported by immunoelectron microscopy. Nestin also colocalized with vimentin in the periphery of capillary loops but not in the mesangium. Nestin was not detected in other structures of the adult human kidney. To determine the potential role of nestin in proteinuria, nestin was examined in kidney biopsies from patients with or without proteinuria. These patients were diagnosed with IgA nephropathy with mild mesangial expansion but without proteinuria, IgA nephropathy with proteinuria, membranous nephropathy (MN), and focal segmental glomerular sclerosis (FSGS). The distribution of nestin in these biopsies was similar to that in the normal kidney. Semiquantitative analysis of immunostaining showed that glomerular nestin expression in IgA nephropathy without proteinuria was not different from normal kidney; however, nestin expression in kidneys of patients with IgA nephropathy and proteinuria, or MN and FSGS with proteinuria was significantly reduced compared with normal kidney (P < 0.01). Reduced nestin mRNA expression in the patients with IgA nephropathy with proteinuria and FSGN was also observed by quantitative real-time PCR. These studies suggest that nestin may play an important role in maintaining normal podocyte function in the human kidney.     

Mesangioproliferative Glomerulonephritis in Mink with Encephalitozoonosis

Renal specimens from 6 mink with encephalitozoonosis were studied by light and electron microscopy and immunohistochemistry. The glomeruli of affected kidneys had a mesangioproliferative glomerulonephritis which was characterized by an increase in mesangial cells and matrix in most glomeruli. Some glomeruli were partially or completely sclerosed. There were protein or granular casts in the cortical and medullary tubules. Interstitial nephritis, vasculitis and tubular cysts were found. Electron microscopy demonstrated extensive matrix and increased cellularity in the mesangial areas. Glomeruli showed segmentally thickened or wrinkled capillary basement membranes. Electron dense deposits were found in the glomerular basement membranes and mesangium. Peroxidase-anti-peroxidase immunohistochemistry demonstrated that IgG and IgM positive material was present as granular deposits in the glomerular basement membrane and occasionally in the mesangium.     

Differential Expression of Specific Dermatan Sulfate Domains in Renal Pathology

Dermatan sulfate (DS), also known as chondroitin sulfate (CS)-B, is a member of the linear polysaccharides called glycosaminoglycans (GAGs). The expression of CS/DS and DS proteoglycans is increased in several fibrotic renal diseases, including interstitial fibrosis, diabetic nephropathy, mesangial sclerosis and nephrosclerosis. Little, however, is known about structural alterations in DS in renal diseases. The aim of this study was to evaluate the renal expression of two different DS domains in renal transplant rejection and glomerular pathologies. DS expression was evaluated in normal renal tissue and in kidney biopsies obtained from patients with acute interstitial or vascular renal allograft rejection, patients with interstitial fibrosis and tubular atrophy (IF/TA), and from patients with focal segmental glomerulosclerosis (FSGS), membranous glomerulopathy (MGP) or systemic lupus erythematosus (SLE), using our unique specific anti-DS antibodies LKN1 and GD3A12. Expression of the 4/2,4-di-O-sulfated DS domain recognized by antibody LKN1 was decreased in the interstitium of transplant kidneys with IF/TA, which was accompanied by an increased expression of type I collagen, decorin and transforming growth factor beta (TGF-β), while its expression was increased in the interstitium in FSGS, MGP and SLE. Importantly, all patients showed glomerular LKN1 staining in contrast to the controls. Expression of the IdoA-Gal-NAc4SDS domain recognized by GD3A12 was similar in controls and patients. Our data suggest a role for the DS domain recognized by antibody LKN1 in renal diseases with early fibrosis. Further research is required to delineate the exact role of different DS domains in renal fibrosis.     

Serial Non-Invasive Assessment of Antibody Induced Nephritis in Mice Using Positron Emission Tomography

Mouse models of experimental anti-glomerular basement membrane (anti-GBM) nephritis provide an analytical tool for studying spontaneous lupus nephritis. The potential of Positron Emission Tomography (PET) was evaluated using 2-deoxy-2-[¹⁸F]fluoro-d-glucose (FDG) as a probe to monitor the progression of anti-GBM induced nephritis in a mouse model. The imaging results were compared to conventional measures of renal function and pathological changes. Serum and urinary vascular cell adhesion molecule-1 (VCAM-1) levels were used as measures of endothelial cell activation and inflammation. Following a challenge with anti-glomerular antibodies, mice exhibited peak changes in serum creatinine, proteinuria, and glomerulonephritis score at 14 days post-challenge (p.c.). In contrast, VCAM levels peaked at day 7 p.c. On dynamic PET images (0–60 min) of day 7, kidneys of the anti-GBM nephritis mice demonstrated a unique pattern of FDG uptake. Compared to the time activity curve (TAC) prior to challenge, a rightward shift was observed after the challenge. By day 10 p.c., kidney FDG uptake was lower than baseline and remained so until the study ended at 21 days p.c. During this time frame measures of renal dysfunction remained high but VCAM-1 levels declined. These changes were accompanied by an increase in kidney volume as measured by Computed Tomography (CT) and intra-abdominal fluid collection. Our results suggest that FDG-PET-CT can be used as a non-invasive imaging tool to longitudinally monitor the progression of renal disease activity in antibody mediated nephritis and the magnitude of renal FDG retention correlates better with early markers of renal inflammation than renal dysfunction.     

The immunoreactivity of glial fibrillary acidic protein in mesangial cells and podocytes of the glomeruli of rat kidney in vivo and in culture

In this study the presence of glial fibrillary acidic protein (GFAP) in kidney is for the first time demonstrated in cryostat sections and cultures of isolated glomerular explants derived from rat kidneys. In double immunolabelling analysis of adult rat kidney sections using antiserum against GFAP and monoclonal antibody (mAb) against vimentin or desmin, the presence of immunoreactivity for GFAP could be observed in the glomerulus of the kidney and vascular cells situated in the peritubular space which expressed vimentin and desmin. Labelling of the sections with absorbed antiserum against GFAP completely abolished the staining in all these cells. The mAb against GFAP, clone GF12.24 which is known to label GFAP both in neural and non-neural cells, recognised its antigen only in the cells located in glomeruli. The investigations performed on early 2- or 3-day-old cultures from glomerular explants revealed different patterns of staining for GFAP in mesangial cells and podocytes: weak filamentous in mesangial cells and a strong non-filamentous perinuclear pattern in podocytes. Due to prominent perinuclear expression in podocytes GFAP may be considered as a marker of these cells. A different pattern of distribution of immunoreactivity for GFAP in podocytes and mesangial cells might be due to function-related posttranslational modifications of GFAP resulting in assembly or disassembly of GFAP filaments. The different pattern of staining for GFAP in the podocytes and mesangial cells, cells which exert a different influence on the capillaries of the glomeruli, suggests a role for GFAP in regulation of the tension and permeability of vascular walls. Previous investigations and present studies hint at GFAP as being a general marker of perivascular cells.     

Increased class I and class II MHC products and mRNA in kidneys of MRL-lpr/lpr mice during autoimmune nephritis and inhibition by cyclosporine

The expression of MHC products in the kidneys of MRL-1pr/1pr mice was investigated. As previously described, these mice develop lupus-like nephritis with intraglomerular and peritubular Ig deposition, vasculitis, and interstitial mononuclear cell infiltration at about 12 wk of age. As the nephritis appeared, the expression of MHC class I and II products rose, as demonstrated by absorption and by specific binding of radiolabeled antibodies. Hybridization of kidney RNA with specific probes revealed an increase in specific mRNA for MHC class I and II genes and for beta2 microglobulin. Using rat monoclonals against mouse class I and II MHC products, and goat anti-rat Ig as second antibody, we showed that the increase in renal class I and II expression was localized to the basolateral membranes of tubular cells, and, in the case of class I, in arteries and glomeruli. The sites of tubular MHC expression corresponded closely to the sites of extensive peritubular Ig deposition. High doses of cyclosporine given for 6 to 8 wk reduced the peritubular Ig deposits, renal Ia and H-2K expression, and specific mRNA for beta 2-microglobulin and MHC genes, but did not reduce anti-DNA antibody levels in serum. Thus the peritubular Ig deposits and tubular MHC induction coincided in timing and location, and in their resolution with cyclosporine. The results raise the possibility that the increase in renal MHC expression not only accompanies the renal lesions, but may play a role in their pathogenesis.     

Serology and tissue lesions in rabbits immunized with Streptococcus mutans

Rabbits were immunized i.v. or i.d. with sterile suspensions of disrupted Streptococcus mutans strain MT703 or K1R. Indirect immunofluorescence assays indicated that sera from four of 10 rabbits immunized i.d. contained antibodies reactive with monkey and human heart and kidney components; 19 of 24 rabbits immunized i.v. had antibodies reactive with these tissues. Heart-reactive antibodies were also detected by immunoelectrophoresis and indirect radioimmunoassay. These antibodies were absorbed well by cytoplasmic membranes, a whole cell extract, and an alkali extract of S. mutans but only weakly by intact bacteria. Between 6 and 8 weeks after the first i.v. administration of S. mutans vaccines, rabbits developed proteinuria and hematuria with subsequent weight loss and lethargy. Approximately 25% of the animals died from illness between the fifth and sixth month of immunization. In 13 of 15 rabbits, immune deposits of C3 and IgG, IgM, or IgA and fibrinogen were seen in kidneys within the glomeruli, basement membranes of the peritubular capillaries, and in the interstitium. In the heart, deposits were seen along the capillaries of the myocardium. In 8 of 14 rabbits, focal deposits of S. mutans antigen were detected in glomeruli and in the kidney interstitium. The kidneys showed gross pathologic and histopathologic changes. Most kidneys were pale and enlarged. Microscopic examination revealed hypercellularity of the glomeruli, presence of neutrophils, thickening of glomerular and tubular basement membranes, tubular atrophy, edema, and fibrosis of the interstitium. The kidney disease presented features of poststreptococcal glomerulonephritis. Microscopic examination of heart sections revealed mild perivascular infiltration by polymorphonuclear leukocytes and plasma cells in some of the rabbits.     

Renal Dnase1 Enzyme Activity and Protein Expression Is Selectively Shut Down in Murine and Human Membranoproliferative Lupus Nephritis

Background

Deposition of chromatin-IgG complexes within glomerular membranes is a key event in the pathogenesis of lupus nephritis. We recently reported an acquired loss of renal Dnase1 expression linked to transformation from mild to severe membranoproliferative lupus nephritis in (NZBxNZW)F1 mice. As this may represent a basic mechanism in the progression of lupus nephritis, several aspects of Dnase1 expression in lupus nephritis were analyzed.

Methodology/Principal Findings

Total nuclease activity and Dnase1 expression and activity was evaluated using in situ and in vitro analyses of kidneys and sera from (NZBxNZW)F1 mice of different ages, and from age-matched healthy controls. Immunofluorescence staining for Dnase1 was performed on kidney biopsies from (NZBxNZW)F1 mice as well as from human SLE patients and controls. Reduced serum Dnase1 activity was observed in both mesangial and end-stage lupus nephritis. A selective reduction in renal Dnase1 activity was seen in mice with massive deposition of chromatin-containing immune complexes in glomerular capillary walls. Mice with mild mesangial nephritis showed normal renal Dnase1 activity. Similar differences were seen when comparing human kidneys with severe and mild lupus nephritis. Dnase1 was diffusely expressed within the kidney in normal and mildly affected kidneys, whereas upon progression towards end-stage renal disease, Dnase1 was down-regulated in all renal compartments. This demonstrates that the changes associated with development of severe nephritis in the murine model are also relevant to human lupus nephritis.

Conclusions/Significance

Reduction in renal Dnase1 expression and activity is limited to mice and SLE patients with signs of membranoproliferative nephritis, and may be a critical event in the development of severe forms of lupus nephritis. Reduced Dnase1 activity reflects loss in the expression of the protein and not inhibition of enzyme activity.