Immunohistochemical localization of glomerular basement membrane antigens in various renal diseases

TGF-beta1 is an autocrine mediator of renal tubular epithelial cell growth and collagen IV production

Recent studies in cultured cells have provided evidence that a variety of pathobiologic stimuli, including high glucose, angiotensin II, and thromboxane A(2), trigger a signaling pathway leading to autocrine induction of TGF-beta1. TGF-beta1 production through this pathway may profoundly affect cell growth, matrix synthesis, and response to injury. This study examines the role of autocrine versus exogenously added TGF-beta1 in cellular proliferation and collagen IV production, critical targets of TGF-beta1 signaling, using renal cells derived from TGF-beta1 knockout (KO) animals or wild-type (WT) controls. Growth of WT and KO cells was assessed by cell counting and [(3)H]thymidine uptake. Basal and TGF-beta1-stimulated collagen production was assessed by Northern and Western blotting; transcriptional activity of the alpha1(IV) collagen gene was assessed by transient transfection analysis. KO cells grew at a faster rate than WT cells carefully matched for plating density and passage number. This increased growth rate was paralleled by increases in [(3)H]thymidine uptake. KO cells expressed lower levels of the cell cycle inhibitors p21 and p27 than WT cells. KO cells failed to express TGF-beta1, as expected. Basal TGF-beta3 mRNA levels were higher in KO cells than in WT cells. WT cells expressed higher basal levels of TGF-beta2 mRNA than KO cells. Basal alpha1(IV) and alpha2(IV) collagen mRNA and protein expression were significantly lower in KO cells than WT cells. Administration of exogenous TGF-beta1 induced collagen IV production in both KO and WT cells. Although basal transcriptional activity of an alpha1(IV) collagen-CAT construct was lower in KO cells than WT cells, administration of exogenous TGF-beta1 was associated with significant increases in transcriptional activity of this construct in both KO and WT cells. These studies provide evidence that autocrine production of TGF-beta1 may play a critical role in regulation of growth and basal collagen IV production by renal tubular epithelial cells.

Alport disease: a review of the diagnostic difficulties

In patients with familial hematuria, ultrastructural study of the renal biopsy has been the gold standard for the diagnosis of Alport disease, based on characteristic findings of glomerular basement membrane thickening due to reduplication of the lamina densa. But the diagnosis has difficulties as not all biopsies from Alport disease patients have these structural changes. In adult female patients or in children, extensive thinning of the basement membrane can be the major abnormality by electron microscopy. Until the genetic mutation of collagen IV responsible for Alport disease can be demonstrated in all patients, the diagnosis will continue to be a challenge at the clinical and at the ultrastructural levels.

X-linked Alport syndrome in females

Alport syndrome (AS) is in the differential diagnosis of hematuria. Variability in clinical presentation and in the ultrastructural changes of the glomerulus can make the diagnosis of AS a challenge in female patients. The purpose of this report is to present immunostaining for glomerular basement membrane (GBM) expression of alpha5(IV) as an adjunctive diagnostic method. Renal biopsy specimens from eight female patients with clinical presentation suggestive of AS were studied. The patients were between 7 and 36 years of age; six were between 12 and 15 years. Light microscopy and immunohistochemistry using a monoclonal antibody to alpha5(IV) were performed. Controls showed a continuous linear pattern along the GBM in normal kidneys and absence in renal biopsy specimens from male X-linked AS patients. To express the variability of the ultrastructural GBM changes among the patients in the series, we developed a semi-quantitative Alport Index, obtained by quantification of severity and extent of ultrastructural GBM changes. With immunohistochemistry, we showed an interrupted, discontinuous linear pattern for alpha5(IV) in glomeruli from the eight patients in the series, confirming the diagnosis of X-linked AS. The ultrastructural Alport Index varied between 6 and 47, showing the heterogeneity in the severity of the GBM changes, even among the six patients aged between 12 and 15 years. In three of the eight biopsy specimens, the predominant change was thin GBM, and the Alport Index was below 20. Immunohistochemistry for alpha5(IV) in renal biopsy specimens can identify female patients heterozygous for X-linked AS. In this series, the method led to the diagnosis of AS in female patients in whom the predominant ultrastructural change was thin basement membrane.

Quantitative changes in the glomerular basement membrane components in human membranous nephropathy

In membranous nephropathy (MN), the glomerular basement membrane (GBM) is thickened due to accumulation of GBM material between and around the subepithelial immune deposits. Alterations in the GBM components in relation to subepithelial deposits and GBM thickening are not clearly defined. The GBM distribution of classical and novel [alpha 4(IV)] chains of type IV collagen, laminin, and fibronectin have been studied in seven patients with MN and in three normal controls by a quantitative immunogold technique. In normal kidneys, the labelling of type IV collagen or fibronectin was distributed predominantly along the endothelial side of the GBM; alpha 4(IV) was found in the lamina densa; and laminin was concentrated in the epithelial zone of the GBM (P < 0.01). In MN, there were increased immunogold densities for classical and novel type IV collagen chains, laminin, and fibronectin in the spikes of MN patients compared with controls (P < 0.05). Furthermore, gold particle labelling for the alpha 4(IV) collagen chain was increased in the middle zone (P < 0.01) and that for fibronectin was increased in the endothelial and middle zones of the GBM (P < 0.05) compared with normal controls. These findings suggest that subepithelial immune deposits stimulate glomerular epithelial cells (GEC), resulting in enhanced secretion of classical and novel type IV collagen chains, laminin, and fibronectin, forming spikes in MN; of these newly formed components, only novel type IV collagen appears to migrate towards the middle zone of the GBM, contributing to thickening of this zone. The results also suggest that fibronectin, possibly derived from the circulation, is related to thickening of the endothelial zone of the GBM, which in turn might be related to progressive glomerulosclerosis.

Collagen distribution in human membranous glomerulonephritis

In membranous glomerulonephritis (MGN), thickening of the glomerular basement membrane (GBM) is partly due to the accumulation of basement membrane material between and around immune deposits located on the epithelial aspect of the GBM. We investigated the distribution of type IV collagen chains (alpha 1/alpha 2, alpha 3, alpha 4, alpha 5, alpha 6) and of types I, III, V, and VI collagen in the glomeruli from 16 patients, by indirect immunofluorescence in 13 and the high-resolution immunogold technique in 6. No changes were detected in stage I MGN. The spiky projections of the GBM in stage II MGN and the basement membrane layers encircling immune deposits in stage III contained the alpha 3, alpha 4, and alpha 5 chains of type IV collagen. In contrast, the alpha 1/alpha 2 chains of type IV, as well as type VI collagen accumulated in the subendothelial aspect of the GBM. No significant staining for types I, III, and V collagens or for the alpha 6 chain of type IV collagen was detected. The results show that, as in the normal glomeruli, the different chains of type IV collagen are not co-distributed in the glomerular extracellular matrix in MGN. They also indicate that type IV collagen chains and type IV collagen play an important role in the thickening of the GBM in human MGN.

The glomerular basement membrane in lupus nephritis

Systemic lupus erythematosus is a disease that is particularly suited for studies of glomerular basement membrane pathology. Classification of the renal pathology of lupus nephritis is usually based on light microscopic features, combined with immunofluorescence findings and electron microscopic alterations. Study of renal biopsy helps to distinguish potentially reversible and irreversible disease, and to estimate prognosis of patients with lupus nephritis. Moreover, studies of human disease, as well as the availability of animal models and in vitro cell culture systems employing biochemical and molecular biological studies of extracellular matrix, have led to a considerable increase in knowledge of the pathogenetic events underlying derangements of the glomerular basement membrane in lupus nephritis.

Distribution of the extracellular matrix components in human glomerular lesions

Most glomerular pathologies are associated with alterations of the matrix compartment. Using reagents directed against the alpha 1/alpha 2 and alpha 3 chains of type IV collagen [alpha 1/alpha 2(IV), alpha 3(IV)], laminin, heparan sulphate proteoglycan (HPG), fibronectin, collagen I, and collagen III, we investigated the modifications of the glomerular matrix components in several human glomerular lesions compared with normal kidney. In type I membranous glomerulonephritis (MGN) (nine cases), we did not observe alterations in the matrix component distribution. In MGN types II and III (five cases), the spikes and chainettes were made of the alpha 3(IV) chain, laminin, and HPG, while the alpha 1/alpha 2(IV) chains were localized along the subendothelial side of the glomerular basement membrane (GBM). In focal and segmental glomerulosclerosis (six cases), fibronectin, alpha 1/alpha 2(IV) chains, laminin, and small amounts of interstitial collagens were detected within the collapsed capillary loops; the newly formed matrix material between the podocytes and the GBM contained the alpha 1/alpha 2(IV) chains, laminin, and HPG but not the alpha 3(IV) chain. In crescentic glomerulonephritis (six cases), fibronectin was the most abundant and, in purely cellular crescents, the unique component. A basement membrane-like network containing laminin, HPG, alpha 1/alpha 2(IV) chains, and interstitial collagens developed in a second step between the crescent cells. Interstitial collagens were present in the crescent framework, even when the integrity of Bowman's capsule was preserved.(ABSTRACT TRUNCATED AT 250 WORDS)

Altered glomerular extracellular matrix synthesis in experimental membranous nephropathy

Chronic progressive membranous nephropathy (MN) in humans is characterized by thickening of the glomerular basement membrane (GBM) with formation of spikes which contain laminin and other extracellular matrix (ECM) proteins. We have utilized two models of MN in the rat (active and passive Heymann nephritis, AICN, PHN) to define the sequential changes in composition of GBM as they relate to changes in glomerular gene expression for ECM components, altered permeability and morphological changes. Renal biopsies obtained during the course of AICN and PHN were immunostained for various ECM proteins and total glomerular RNA was hybridized with cDNA probes specific for laminin B2-chain, s-laminin, and types I and IV collagen. In addition, the ability of anti-glomerular epithelial cell (GEC) antibody and complement on rat GEC in culture to induce laminin release or laminin and s-laminin mRNA expression was determined. The results demonstrate that at weeks 12, 16, and 20 of AICN, immunostaining for laminin, s-laminin, fibronectin, entactin, and heparan sulfate proteoglycan increased in the GBM in a spike-like pattern. Concomitantly, glomerular mRNA levels of laminin B2-chain and of s-laminin increased. Type IV collagen protein and gene expression remained unchanged or decreased. No glomerular immunostaining for type I collagen occurred during AICN despite increased expression of mRNA for this collagen type. In contrast to AICN, in PHN no pronounced changes of the glomerular ECM occurred, except for transient expression of type I collagen mRNA in whole glomerular RNA and type I collagen protein the GEC cytoplasm. Stimulation of GEC in culture with anti-GEC antibody and complement also failed to induce transcription of laminin or s-laminin mRNA or the release of laminin protein. These findings suggest that the polyantigenic expansion of GBM which occurs in chronic experimental MN may be stimulated by factors different from the C5b-9 mediated processes that cause the initial proteinuria.