Immunochemical studies of the Alport antigen

Multidisciplinary Management of Alport Syndrome: Current Perspectives

Alport syndrome is a multisystem disorder that universally affects the kidney and frequently involves the inner ear and the eye. Over the course of a lifetime, addressing the health care needs of a person with Alport syndrome and their family entails the services of primary providers, nephrologists, genetic counselors, audiologists, ophthalmologists, transplant physicians, kidney dieticians, and social workers as well as other healthcare professionals. This article attempts to provide context and guidance regarding the multidisciplinary care of Alport syndrome based on the natural history of the condition.

Alport syndrome: a rare cause of uraemia

Alport syndrome (AS) is a heterogeneous basement membrane disease characterised by haematuria with progressive hereditary nephritis, high-frequency sensorineural hearing loss (SNHL) and pathognomonic ocular lesions. It is one of the spectra of diseases representing hereditary nephritis, which inevitably leads to end-stage renal disease (ESRD). Microscopic or frank haematuria persistent from childhood constitutes the clinical clue for its early recognition. It occurs as a result of genetically inherited or de novo mutations in type IV collagen genes. The most common mode of inheritance is X-linked and men are more severely affected. We report a case of a young woman, in her fourth decade of life presenting with overt nephropathy, having persistent haematuria associated with SNHL and lenticonus with dot and fleck retinopathy on detailed clinical examination, diagnosed as a previously undetected case of Alport syndrome.

Aortic abnormalities in males with Alport syndrome

BACKGROUND

There have been isolated case reports of arterial disease in males with Alport syndrome (AS), a systemic disorder of Type IV collagen. In this paper, we describe five new cases of AS associated with significant aortic disease including dissection and aneurysm.

METHODS

We present brief clinical descriptions of five males with AS and aortic disease. We performed immunohistochemical analysis of the expression of the α5 chain of Type IV collagen in skin basement membranes from a previously reported family with AS and associated aortic disease and in the aortic media of male mice with X-linked Alport syndrome (XLAS) due to a nonsense mutation in the COL4A5 gene.

RESULTS

Three of the five patients exhibited aneurysm and dissection of the thoracic aorta, occurring at 25-32 years of age, while one had aortic dilatation and another had aortic insufficiency. All five men required renal replacement therapy by age 20. Immunohistochemistry of skin biopsy specimens in previously reported male siblings with aortic disease confirmed that they had XLAS. We further found that the α5 chain of Type IV collagen is abnormally absent from aortic media of transgenic mice with XLAS.

CONCLUSIONS

Early onset aortic disease may be an unusual feature of AS. Screening of men with AS for aortic abnormalities may be clinically indicated in some families.

An unusual case of pulmonary-renal syndrome associated with defects in type IV collagen composition and anti-glomerular basement membrane autoantibodies

Commercial serological assays for the presence of anti-glomerular basement membrane (GBM) antibodies are thought to be indicative of Goodpasture's syndrome. We report a case in which commercial tests inaccurately suggested that a patient with a pulmonary-renal syndrome had Goodpasture's disease. Additional laboratory testing using recombinant type IV collagen NC1 domain proteins showed that the autoantibodies in question were not directed against the Goodpasture antigen (the alpha3NC1 domain), but against the alpha2NC1 domain of type IV collagen. Our findings represent the first known case of human autoantibodies to the alpha2NC1 domain. Further investigation showed that this patient has decreased alpha3 and alpha5 chain expression in the GBM and defects in type IV collagen, resembling abnormalities in patients with Alport's syndrome.

A human-mouse chimera of the alpha3alpha4alpha5(IV) collagen protomer rescues the renal phenotype in Col4a3-/- Alport mice

Collagen IV is a major structural component of basement membranes. In the glomerular basement membrane (GBM) of the kidney, the alpha3, alpha4, and alpha5(IV) collagen chains form a distinct network that is essential for the long-term stability of the glomerular filtration barrier, and is absent in most patients affected with Alport syndrome, a progressive inherited nephropathy associated with mutation in COL4A3, COL4A4, or COL4A5 genes. To investigate, in vivo, the regulation of the expression, assembly, and function of the alpha3alpha4alpha5(IV) protomer, we have generated a yeast artificial chromosome transgenic line of mice carrying the human COL4A3-COL4A4 locus. Transgenic mice expressed the human alpha3 and alpha4(IV) chains in a tissue-specific manner. In the kidney, when expressed onto a Col4a3(-/-) background, the human alpha3(IV) chain restored the expression of and co-assembled with the mouse alpha4 and alpha5(IV) chains specifically at sites where the human alpha3(IV) was expressed, demonstrating that the expression of all three chains is required for network assembly. The co-assembly of the human and mouse chains into a hybrid network in the GBM restores a functional GBM and rescues the Alport phenotype, providing further evidence that defective assembly of the alpha3-alpha4-alpha5(IV) protomer, caused by mutations in any of the three chains, is the pathogenic mechanism responsible for the disease. This line of mice, humanized for the alpha3(IV) collagen chain, will also provide a valuable model for studying the pathogenesis of Goodpasture syndrome, an autoimmune disease caused by antibodies against this chain.

Alport syndrome associated with diffuse leiomyomatosis: COL4A5-COL4A6 deletion associated with a mild form of Alport nephropathy

BACKGROUND

The X-linked Alport syndrome (AS) is an inherited nephropathy due to mutations in the COL4A5 gene, encoding the alpha5 chain of type IV collagen, a major component of the glomerular basement membrane (GBM). Here, we report a new kindred with the rare association of X-linked AS and diffuse leiomyomatosis (DL), which is a tumourous process involving smooth muscle cells of the oesophagus, the tracheobronchial tree and, in females, the genital tract. For this syndrome, an almost constant association of large COL4A5 rearrangements with a severe juvenile form of nephropathy has been described for male patients.

METHODS

DNA rearrangement at the COL4A5-COL4A6 locus was studied in several members of this family using polymerase chain reaction and pulsed field gel electrophoresis. Furthermore, immunohistochemical staining of tumour and skin samples was performed.

RESULTS

The affected patients in this family carry a 120 kb deletion by which the COL4A5 exon 1 and COL4A6 exons 1, 1', and 2 are removed. Immunohistochemical investigation of a skin biopsy of an affected male patient confirmed the absence of both the alpha5 and the alpha6 chains of type IV collagen in the basement membrane of the skin. Surprisingly, both affected male patients had a rather mild renal phenotype.

CONCLUSIONS

This report shows that, contrary to what has been reported to date, patients suffering from AS associated with DL can be associated with a late onset renal failure (adult) form of nephropathy.

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.

Approach to the diagnosis of thin basement membrane nephropathy in females with the use of antibodies to type IV collagen

CONTEXT

Thin basement membrane nephropathy is recognized by a diffusely thin glomerular basement membrane (GBM) ultrastructurally. In contrast to Alport syndrome (AS), there is no GBM thickening, lamellation, or granular inclusions. Morphologically, there is overlap between thin basement membrane nephropathy and AS in female patients in whom there might be only thin GBM and no pathognomonic findings of AS.

OBJECTIVE

To determine if the use of antibodies to collagen IV is helpful in making the distinction between thin basement membrane nephropathy and AS in female patients with primarily thin GBMs.

DESIGN

We examined renal biopsies from 9 adult female patients with thin GBMs for the presence of alpha1, alpha3, alpha4, and alpha5 chains of type IV collagen by immunofluorescence.

RESULTS

In 2 patients with segmental GBM staining, no suggestion for AS was found on physical examination or in their family history. In the remaining 7 patients with normal GBM staining, 4 had family members with end-stage renal disease of unknown etiology, raising the suspicion of X-linked or autosomal-recessive AS. Three patients were presumed to have thin basement membrane nephropathy.

CONCLUSION

Segmental GBM staining for alpha3, alpha4, and alpha5 chains of type IV collagen raises the suspicion of AS in the presence of adequate controls and other supporting evidence. Normal GBM staining for alpha3, alpha4, and alpha5 chains of type IV collagen, however, does not exclude AS.

Distribution of alpha-chains of type IV collagen in glomerular basement membranes with ultrastructural alterations suggestive of Alport syndrome

BACKGROUND

In Alport syndrome (AS) impaired production and/or assembly of col IV alpha-chain isoforms results in abnormal structure of glomerular basement membrane (GBM), haematuria and, frequently, progressive renal disease. We investigated the relationship between col IV alpha-chains expression and morphology of GBM, as a possible key to the better understanding of the pathogenesis of renal disease in AS.

METHODS

GBM distribution of col IV alpha1-, alpha3-, and alpha5-chain was investigated by immunohistochemistry in 32 patients (21 males and 11 females, mean age at biopsy of 11.5 years) with ultrastructural findings suggestive of AS. Ten patients had a proven COL4A5 mutation. Based on the severity of ultrastructural findings, the biopsies were grouped in three (I-III) electron microscopy (EM) classes. Significant EM changes of GBM (thinning, thickening, splitting, basket weaving of the lamina densa) were singularly evaluated using a semiquantitative scale (0-3).

RESULTS

Col IV alpha1-chain was demonstrated in GBM of all patients. Three patterns of staining for col IValpha3- and alpha5-chains were observed: positive, negative, and alpha3(IV)-positive/alpha5(IV)-negative. By chi(2)-test, EM class III lesions and complete loss of alpha3(IV)- and alpha5(IV)-antigen were significantly more frequent (P<0.05 and P<0.01) in male patients, but no significant relation was observed between EM classes and immunohistochemical patterns. GBM alterations did not correlate with staining for alpha5(IV)-chain. Intensity of alpha3(IV)-chain staining, however, had a negative correlation (P<0.05) with the severity of GBM basket weaving.

CONCLUSIONS

Our results suggest that the alpha3(IV)-chain-containing col IV-network plays a fundamental role in structural and, possibly, functional organization of GBM. Absence of alpha3(IV)-chain in GBM could indicate a more severe renal disease in AS.

Identification and localization of type IV collagen chains in the inner ear cochlea

Mutations in the genes encoding the alpha3(IV), alpha4(IV) and alpha5(IV) chains of type IV collagen have been implicated in the pathogenesis of Alport's syndrome, a hereditary disorder characterized by progressive nephropathy and sensorineural deafness. The known expression of these chains in kidney basement membranes supports the contention that they play a crucial role in the ultrafiltration function. Whether they play a role in auditory signal transduction remains unknown as heretofore, they have not been identified in the inner ear. In the present study, the expression of type IV collagen in cochlea of the inner ear of guinea pigs was determined. All six alpha-chains of type IV collagen were identified by biochemical and immunological methods. By indirect immunofluorescence, alpha1(IV) and alpha2(IV) chains were localized to the spiral limbus, basilar membrane and tectorial membrane. The alpha3(IV), alpha4(IV), alpha5(IV) and alpha6(IV) chains localized exclusively to the tectorial membrane and basilar membrane. These results suggest a possible role of type IV collagen chains in the active tuning of the basilar and tectorial membrane, an essential step in frequency discrimination and amplification of auditory signals.

Identification of two alternatively spliced forms of human tubulointerstitial nephritis antigen (TIN-Ag)

Tubulointerstitial nephritis antigen (TIN-Ag) is a recently described basement membrane glycoprotein reactive with autoantibodies in some forms of immunologically mediated human tubulointerstitial nephritis. This report presents the complete cDNA and predicted amino acid sequences of two human TIN-Ag mRNA species referred to as TIN1 and TIN2. Translation through the open reading frames of these clones indicates the presence of a signal peptide and putative pre-propeptide. TIN1 additionally contains a characteristic laminin-like epidermal growth factor (EGF) motif and significant homology within the carboxy terminus with the cysteine proteinase family of enzymes. The EGF motif bears important similarities in the positions of cysteines with two motifs in the propeptide of von Willebrand factor. The EGF motif and part of the region that is homologous with the cysteine proteinase family are removed from the TIN2 cDNA. However, the rest of the sequence is identical in these two forms, indicating an alternatively spliced TIN-Ag mRNA product. Both forms contain putative calcium-binding sites. Secondary structure predictions strongly suggest differences between TIN1 and TIN2 leading to the hypothesis that these two forms of TIN-Ag may exhibit differences in their function. Expression studies with appropriate probes demonstrate expression mainly in the kidney and in the intestinal epithelium and lack of expression in other tissues. In the kidney, both TIN1 and TIN2 transcripts are detected, however, TIN1 appears to be the predominant form.

The goodpasture autoantigen. Identification of multiple cryptic epitopes on the NC1 domain of the alpha3(IV) collagen chain

Goodpasture (GP) disease is an autoimmune disorder in which autoantibodies against the alpha3(IV) chain of type IV collagen bind to the glomerular and alveolar basement membranes, causing progressive glomerulonephritis and pulmonary hemorrhage. Two major conformational epitope regions have been identified on the noncollagenous domain of type IV collagen (NC1 domain) of the alpha3(IV) chain as residues 17-31 (E(A)) and 127-141 (E(B)) (Netzer, K.-O. et al. (1999) J. Biol. Chem. 274, 11267-11274). To determine whether these regions are two distinct epitopes or form a single epitope, three GP sera were fractionated by affinity chromatography on immobilized NC1 chimeras containing the E(A) and/or the E(B) region. Four subpopulations of GP antibodies with distinct epitope specificity for the alpha3(IV)NC1 domain were thus separated and characterized. They were designated GP(A), GP(B), GP(AB), and GP(X), to reflect their reactivity with E(A) only, E(B) only, both regions, and neither, respectively. Hence, regions E(A) and E(B) encompass critical amino acids that constitute three distinct epitopes for GP(A), GP(B), and GP(AB) antibodies, respectively, whereas the epitope for GP(X) antibodies is located in a different unknown region. The GP(A) antibodies were consistently immunodominant, accounting for 60-65% of the total immunoreactivity to alpha3(IV)NC1; thus, they probably play a major role in pathogenesis. Regions E(A) and E(B) are held in close proximity because they jointly form the epitope for Mab3, a monoclonal antibody that competes for binding with GP autoantibodies. All GP epitopes are sequestered in the hexamer configuration of the NC1 domain found in tissues and are inaccessible for antibody binding unless dissociation of the hexamer occurs, suggesting a possible mechanism for etiology of GP disease. GP antibodies have the capacity to extract alpha3(IV)NC1 monomers, but not dimers, from native human glomerular basement membrane hexamers, a property that may be of fundamental importance for the pathogenesis of the disease.

Renal basement membrane components

Renal basement membrane components. Basement membranes are specialized extracellular matrices found throughout the body. They surround all epithelia, endothelia, peripheral nerves, muscle cells, and fat cells. They play particularly important roles in the kidney, as demonstrated by the fact that defects in renal basement membranes are associated with kidney malfunction. The major components of all basement membranes are laminin, collagen IV, entactin/nidogen, and sulfated proteoglycans. Each of these describes a family of related proteins that assemble with each other in the extracellular space to form the basement membrane. Over the last few years, new basement membrane components that are expressed in the kidney have been discovered. Here, the major components and their localization in mature and developing renal basement membranes are described. In addition, the phenotypes of basement membrane component gene mutations, both naturally occurring and experimental, are discussed, as is the aberrant deposition of basement membrane proteins in the extracellular matrix in several renal diseases.

Absence of the alpha6(IV) chain of collagen type IV in Alport syndrome is related to a failure at the protein assembly level and does not result in diffuse leiomyomatosis

X-linked Alport syndrome is a progressive nephropathy associated with mutations in the COL4A5 gene. The kidney usually lacks the alpha3-alpha6 chains of collagen type IV, although each is coded by a separate gene. The molecular basis for this loss remains unclear. In canine X-linked hereditary nephritis, a model for X-linked Alport syndrome, a COL4A5 mutation results in reduced mRNA levels for the alpha3, alpha4, and alpha5 chains in the kidney, implying a mechanism coordinating the production of these 3 chains. To examine whether production of alpha6 chain is under the same control, we studied smooth muscle cells from this animal model. We determined the canine COL4A5 and COL4A6 genes are separated by 435 bp, with two first exons for COL4A6 separated by 978 bp. These two regions are >/= 78% identical to the human sequences that have promoter activity. Despite this potential basis for coordinated transcription of the COL4A5 and COL4A6 genes, the alpha6 mRNA level remained normal in affected male dog smooth muscle while the alpha5 mRNA level was markedly reduced. However, both alpha5 and alpha6 chains were absent at the protein level. Our results suggest that production of the alpha6 chain is under a control mechanism separate from that coordinating the alpha3-alpha5 chains and that the lack of the alpha6 chain in Alport syndrome is related to a failure at the protein assembly level, raising the possibility that the alpha5 and alpha6 chains are present in the same network. The lack of the alpha6 chain does not obviously result in disease, in particular leiomyomatosis, as is seen in Alport patients with deletions involving the COL4A5 and COL4A6 genes.

Identification of COL4A5 defects in Alport's syndrome by immunohistochemistry of skin

BACKGROUND

The COL4A3-COL4A4-COL4A5 network in the glomerular basement membrane is affected in the inherited renal disorder Alport's syndrome (AS). Approximately 85% of the AS patients are expected to carry a mutation in the X-chromosomal COL4A5 gene and 15% in the autosomal COL4A3 and COL4A4 genes. The COL4A5 chain is also present in the epidermal basement membrane (EBM). It is predicted that approximately 70% of the COL4A5 mutations prevent incorporation of this chain in basement membranes.

METHODS

We investigated whether or not COL4A5 defects could be detected by immunohistochemical analysis of the EBM. Punch skin biopsies were obtained from 22 patients out of 17 families and two biopsy specimens from healthy males were used as controls.

RESULTS

In four cases with the COL4A5 frameshift or missense mutations, the COL4A5 chain was either lacking from the EBM (male) or showed a focally negative pattern (female). In three other patients with a COL4A5 missense mutation, a COL4A3 and a COL4A4 mutation, respectively, the COL4A5 staining was normal. A (focally) negative EBM-COL4A5 staining was found in three patients of six families with a diagnosis of AS and in one family of a group of four families with possible AS.

CONCLUSIONS

The (focal) absence of COL4A5 in the EBM of skin biopsy specimens can be used for fast identification of COL4A5 defects. Combined with polymorphic COL4A5 markers, both postnatal and prenatal DNA diagnosis are possible in the family of the patient.

Distribution of the alpha1 to alpha6 chains of type IV collagen in bovine follicles

During follicular development the proliferative and differentiated state of the epithelioid granulosa cells changes, and the movement of fluid across the follicular basal lamina enables the formation of an antrum. Type IV collagen is an important component of many basal laminae. Each molecule is composed of three alpha chains; however, six different type IV collagen chains have been identified. It is not known which of these chains are present in the follicular basal lamina and whether the type IV collagen composition of the basal lamina changes during follicular development. Therefore, we immunolocalized each of the six chains in bovine ovaries using antibodies directed to the nonconserved non-collagenous (NC) domains. Additionally, dissected follicles were digested with collagenase to release the NC domains, and the NC1 domains were then detected by standard Western immunoblot methods. The follicular basal lamina of almost all primordial and preantral follicles was positive for all type IV collagen alpha chains. Colocalization of type IV collagen and factor VIII-related antigen allowed for discrimination between the follicular and endothelial basal laminae. Type IV collagen alpha1, alpha2, alpha3, alpha4, and alpha5 chains were present within the follicular basal lamina of only a proportion of antral follicles (17 of 22, 20 of 21, 15 of 18, 14 of 28, and 12 of 23, respectively), and staining was less intense than in the preantral follicles. Staining for the alpha1 and alpha2 chains was diffusely distributed throughout the theca in regions not associated with recognized basal laminae. The specificity of this immunostaining for alpha1 and alpha2 chains of type IV collagen was confirmed by Western immunoblots. As well as being detected in the basal lamina of approximately half of the antral follicles examined, type IV collagen alpha4 also colocalized with 3beta-hydroxysteroid dehydrogenase-immunopositive cells in the theca interna. Type IV collagen alpha6 was detected in the basal lamina of only one of the 16 antral follicles examined. Thus, the follicular basal lamina changes in composition during follicular development, with immunostaining levels being reduced for all type IV collagen chains and immunoreactivity for type IV collagen alpha6 being lost as follicle size increases. Additionally, immunoreactivity for alpha1 and alpha2 appears in the extracellular matrix of the theca as it develops.

Glomerular basement membrane. Identification of a novel disulfide-cross-linked network of alpha3, alpha4, and alpha5 chains of type IV collagen and its implications for the pathogenesis of Alport syndrome

Glomerular basement membrane (GBM) plays a crucial function in the ultrafiltration of blood plasma by the kidney. This function is impaired in Alport syndrome, a hereditary disorder that is caused by mutations in the gene encoding type IV collagen, but it is not known how the mutations lead to a defective GBM. In the present study, the supramolecular organization of type IV collagen of GBM was investigated. This was accomplished by using pseudolysin (EC 3.4.24.26) digestion to excise truncated triple-helical protomers for structural studies. Two distinct sets of truncated protomers were solubilized, one at 4 degrees C and the other at 25 degrees C, and their chain composition was determined by use of monoclonal antibodies. The 4 degrees C protomers comprise the alpha1(IV) and alpha2(IV) chains, whereas the 25 degrees C protomers comprised mainly alpha3(IV), alpha4(IV), and alpha5(IV) chains along with some alpha1(IV) and alpha2(IV) chains. The structure of the 25 degrees C protomers was examined by electron microscopy and was found to be characterized by a network containing loops and supercoiled triple helices, which are stabilized by disulfide cross-links between alpha3(IV), alpha4(IV), and alpha5(IV) chains. These results establish a conceptual framework to explain several features of the GBM abnormalities of Alport syndrome. In particular, the alpha3(IV). alpha4(IV).alpha5(IV) network, involving a covalent linkage between these chains, suggests a molecular basis for the conundrum in which mutations in the gene encoding the alpha5(IV) chain cause defective assembly of not only alpha5(IV) chain but also the alpha3(IV) and alpha4(IV) chains in the GBM of patients with Alport syndrome.

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.

Induction of anti-GBM nephritis in rats by recombinant alpha 3(IV)NC1 and alpha 4(IV)NC1 of type IV collagen

The capability of the noncollagenous (NC1) domains of the six alpha chains of human type IV collagen to induce anti-glomerular basement membrane (GBM) nephritis in WKY rats was determined. This was accomplished by using recombinant technology to express the six NC1 domains in mammalian 293 cells and to purify the proteins using an anti-Flag affinity column. All rats injected with alpha 3(IV)NC1 and alpha 4(IV)NC1 developed proteinuria and hematuria. Rats injected with alpha 5(IV)NC1 developed mild hematuria, whereas rats injected with the alpha 1(IV)NC1, alpha 2(IV)NC1 and alpha 6(IV)NC1 domains developed neither proteinuria nor hematuria. The renal lesions induced by alpha 3(IV)NC1 and alpha 4(IV)NC1 domains were characteristic of those in patients with anti-GBM nephritis and Goodpasture syndrome. The experimental nephritis is mediated by anti-basement membrane antibodies that are targeted to alpha 3(IV)NC1 and alpha 4(IV)NC1 domains and which bind to the glomerular basement membrane. The uniqueness of the alpha 3(IV)NC1 and alpha 4(IV)NC1 domains, among the six NC1 domains, to induce severe anti-GBM disease may relate to the accessibility of epitopes in the GBM for binding of antibody. The pathogenicity of the alpha 4(IV)NC1 antibodies establishes a conundrum because the pathogenic antibodies in patients are not targeted to the alpha 4(IV)NC1, but are targeted to the alpha 3(IV)NC1 domain in anti-GBM nephritis and to the alpha 3(IV)NC1 and alpha 5(IV)NC1 domains in Alport post-transplant anti-GBM nephritis.

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.

Comparative distribution of the alpha 1(IV), alpha 5(IV), and alpha 6(IV) collagen chains in normal human adult and fetal tissues and in kidneys from X-linked Alport syndrome patients

We have shown previously that the 5' ends of the genes for the alpha 5(IV) and alpha 6(IV) collagen chains lie head-to-head on Xq22 and are deleted in patients with Alport syndrome (AS)-associated diffuse leiomyomatosis. In this study, we raised a rabbit anti-human alpha 6(IV)chain antibody, demonstrated its specificity by the analysis of recombinant NC1 domains af all six type IV chains, and studied the distribution of the alpha 6(IV) chain in relation to the alpha 1(IV) and alpha 5(IV) chains in human adult and fetal tissues involved in AS and diffuse leiomyomatosis. The alpha 6(IV) chain colocalizes with the alpha 5(IV) chain in basement membranes (BMs) of many tissues, but not in glomerular BM. These data exclude the alpha 6(IV) chain as a site for AS mutations. The head-to-head genomic pairing of the alpha 5(IV) and alpha 6 (IV) genes implies coordinate transcription of the two genes. Differential localization of the alpha 5(IV) and alpha 6(IV) chains shows that the two chains are not always coordinately regulated. The alpha 6(IV) chain, together with the alpha 3(IV)-alpha 5(IV) chains, was absent from all renal BMs in eight patients with X-linked AS while the alpha 1(IV) and alpha 2(IV) chains were increased. The data support the existence of two independent collagen networks, one for the alpha 3(IV)-alpha 6(IV) chains and one for the alpha 1(IV) and alpha 2(IV) chains.

Autosomal recessive Alport syndrome: immunohistochemical study of type IV collagen chain distribution

Alport syndrome (AS) is an hereditary disease of basement membrane collagen. It is mainly transmitted as a dominant X-linked trait and caused by mutations in the COL4A5 gene encoding the alpha 5 chain of type IV collagen. However, autosomal recessive AS due to mutations in the COL4A3 or COL4A4 genes could represent up to 15% of AS. Using the immunofluorescence technique, we analyzed the distribution of the different chains of type IV collagen in renal (12 specimens) and skin (4 specimens) basement membranes of 12 AS patients belonging to 11 unrelated kindreds in which autosomal recessive inheritance had been demonstrated (3 kindreds) or was suggested by clinical and genealogic data (8 kindreds). The renal and skin distribution was normal in one patient with COL4A4 mutations. A peculiar pattern of distribution of the alpha 3-alpha 5(IV) chains was observed in the other patients. It was characterized the co-absence of the alpha 3(IV), alpha 4(IV) and alpha 5(IV) chains in the glomerular basement membrane, and the presence of the alpha 5(IV) chain in a series of extraglomerular basement membranes including capsular, collecting ducts and epidermal basement membranes, a combination never observed in X-linked AS. This immunohistochemical pattern is correlated with the specific distribution of the alpha 3-alpha 5 chains of type IV collagen chains within extraglomerular basement membranes. It could be a useful marker for the identification of autosomal recessive AS.

A COL4A3 gene mutation and post-transplant anti-alpha 3(IV) collagen alloantibodies in Alport syndrome

The X-linked Alport syndrome is associated with mutations and deletions in COL4A5 gene, one of six genes which constitute the alpha-chains of type IV collagen in basement membranes. The autosomal recessive form of Alport syndrome is characterized by mutations and deletions in the COL4A3 and COL4A4 genes. A fraction of Alport patients who undergo renal transplantation develop anti-glomerular basement membrane (GBM) nephritis, which results in loss of the renal allograft function. Recently, the target for alloantibodies from an X-linked Alport patient with complete COL4A5 gene deletion was determined to be the alpha 3 chain of type IV collagen. The present study characterized the post-transplant alloantibodies from an autosomal recessive Alport patient with anti-GBM glomerulonephritis and a COL4A3 gene mutation which predicted a loss of 85% of the alpha 3(IV) NC1 domain. The specificity of these new antibodies were studied using glomerular basement membrane constituents and recombinant type IV collagen domains. The results establish the target for the alloantibodies from an autosomal recessive Alport patient with COL4A3 deletion as principally the alpha 3(IV) collagen chain, similar to the post-transplant alloantibodies from X-linked Alport patients with COL4A5 gene deletions. The absence of alpha 3(IV) chain in the GBM of patients with both these forms of Alport syndrome, due either to a failure of synthesis or a failure of assembly, presumably leads to a loss of immunologic tolerance for the alpha 3(IV) NC1 domain in transplanted allografts.

Bull terrier hereditary nephritis: a model for autosomal dominant Alport syndrome

Bull terrier hereditary nephritis is inherited as an autosomal dominant disease and causes renal failure at variable ages in affected dogs. The aims of this study were to compare the clinical, ultrastructural and immunohistochemical features of bull terrier hereditary nephritis with the characteristics of the human forms of Alport syndrome. Many animals with bull terrier hereditary nephritis have hematuria, and some have anterior lenticonus. However, deafness is not associated with the renal disease, and affected dogs do not have the large platelets that are occasionally seen in patients with autosomal Alport syndrome. The glomerular capillary basement membrane (GCBM) in affected bull terriers has an identical ultrastructural appearance to that seen in X-linked Alport syndrome, with lamellations and intramembranous electron-dense deposits. However, both the Goodpasture and the Alport antigens, which represent parts of the alpha 3(IV) and alpha 5(IV) collagen chains, respectively, are present in the GCBM of affected dogs. Bull terrier hereditary nephritis represents an animal model for autosomal dominant Alport syndrome, and can be used to further examine how genetic mutations affect a basement membrane protein and the corresponding membrane structure.

Collagen IV alpha 3, alpha 4, and alpha 5 chains in rodent basal laminae: sequence, distribution, association with laminins, and developmental switches

Collagen IV is a major component of vertebrate basal laminae (BLs). Studies in humans have revealed a family of genes encoding alpha 1-alpha 6 collagen IV chains and implicated alpha 3-alpha 6 in disease processes (Goodpasture and Alport syndromes and diffuse leiomyomatosis). To extend studies of these components to an experimentally accessible animal, we cloned cDNAs encoding partial collagen alpha 3, alpha 4, and alpha 5(IV) chains from the mouse. Ribonuclease protection assays showed that all three genes were expressed at highest levels in kidney and lung; alpha 5(IV) was also expressed at high levels in heart. We then made antibodies specific for each collagen IV chain. Immunohistochemical studies of several tissues revealed many combinations of collagen IV chains; however, alpha 3 and alpha 4 (IV) were always coexpressed, and only appeared in BLs that were alpha 5(IV) positive. The alpha 3-alpha 5(IV) chains were frequently but not exclusively associated with the S (beta 2) chain of laminin, as were the alpha 1, 2 (IV) collagen chains with laminin B1 (beta 1). An analysis of developing rat kidney BLs showed that newly formed (S-shaped) nephrons harbored collagen alpha 1 and alpha 2(IV) and laminin B1; maturing (capillary loop stage) BLs contained collagen alpha 1-alpha 5(IV) and laminin B1 and S-laminin; and mature glomerular BLs contained mainly collagen alpha 3-alpha 5(IV) and S-laminin. Thus, collagen alpha 1 and alpha 2(IV) and laminin B1 appear to be fetal components of the glomerular BL, and there is a developmental switch to collagen alpha 3-alpha 5(IV) and S-laminin expression.

Immunohistochemical study of alpha 1-5 chains of type IV collagen in hereditary nephritis

The distribution of alpha 1-5 chains of type IV collagen [alpha 1-5(IV)] in the glomerular basement membrane (GBM) and epidermal basement membrane (EBM) of 23 families with hereditary nephritis was examined by indirect immunofluorescence. These families were divided into three clinicopathological groups. Group I (10 families) patients showed a widespread "basket weave" pattern of the GBM and a family history of nephritis was present. Group II (6 families) patients showed a widespread "basket weave" change without a family history of nephritis. Group III (7 families) patients showed a widespread attenuation of the GBM but no "basket weave" change, and had a family history of nephritis and chronic renal failure. alpha 1(IV) and alpha 2(IV) were present in all affected and unaffected family members and controls. All normal family members and controls expressed alpha 3(IV), alpha 4(IV) and alpha 5(IV) in the GBM and alpha 5(IV) in the EBM in a diffuse pattern. All group I families and three of the group II families exhibited complete loss of the alpha 5(IV) antigen from the GBM and EBM in male patients, and segmental loss of the alpha 5(IV) antigen in female patients. In these families the alpha 3(IV) and alpha 4(IV) antigens were completely lost from the GBM in male patients with severe nephritis, whereas alpha 3(IV) alpha 4(IV) were present but diminished in male patients with mild nephritis. Three group II and all group III families expressed the alpha 3-5(IV) antigens in an identical manner to that of normal controls. These findings indicate that the heterogeneity of hereditary nephritis reflects a variety of aberrant expression patterns of alpha 3-5(IV) and that immunohistochemical examination of alpha 5(IV) in the EBM is a useful method for the diagnosis of X-linked Alport syndrome.

Characterization of anti-GBM antibodies involved in Goodpasture's syndrome

Goodpasture's syndrome is a life threatening autoimmune kidney disease. The patients have autoantibodies to the glomerular basement membrane, which are specific for the C-terminal domain of type IV collagen (NC1). The major antigen has been localized to the alpha 3 (IV)-chain. We have investigated sera from 44 patients with anti-NC1 antibodies. The quantity of antibodies to four different alpha(IV)-chains of type IV collagen was measured with direct ELISA. We used affinity chromatography to separate the antibodies and their specificities were studied with ELISA. The results show that about 1% of the patients total IgG are anti-NC1 antibodies and that 90% of these antibodies are specific for the alpha 3(IV)-chain. Antibodies to the other alpha(IV)-chains were found in 80% of the patients. Furthermore, affinity purified anti-alpha 3(IV) antibodies from one patient were inhibited by antibodies from the other patients, from 4 to 72%. The antibodies, from 39 of the patients, were inhibited by a monoclonal antibody against the alpha 3(IV)-chain. The results indicate that patients with Goodpasture's syndrome can have antibodies to most of the alpha(IV)-chains, while the majority of anti-NC1 antibodies are restricted to the alpha 3(IV)-chain. Moreover the number of epitopes seems to be limited and the majority of the antibodies from most patients are against one single epitope on the alpha 3(IV)-chain.

Identification of mutations in the alpha 3(IV) and alpha 4(IV) collagen genes in autosomal recessive Alport syndrome

Alport syndrome (AS) is an hereditary disease of basement membranes characterized by progressive renal failure and deafness. Changes in the glomerular basement membrane (GBM) in AS suggest that the type IV collagen matrix, the major structural component of GBM, is disrupted. We recently isolated the genes for two type IV collagens, alpha 3(IV) and alpha 4(IV), that are encoded head-to-head on human chromosome 2. These chains are abundant in normal GBM but are sometimes absent in AS. We screened for mutations in families in which consanguinity suggested autosomal recessive inheritance. Homozygous mutations were found in alpha 3(IV) in two families and in alpha 4(IV) in two others, demonstrating that these chains are important in the structural integrity of the GBM and that there is an autosomal form of AS in addition to the previously-defined X-linked form.

A monoclonal antibody marker for Alport syndrome identifies the Alport antigen as the alpha 5 chain of type IV collagen

The nephropathy of Alport syndrome is associated with unique abnormalities of glomerular basement membranes and is caused in many families by mutations in the X-chromosomal gene COL4A5, which encodes the alpha 5 chain of type IV collagen. We have previously reported that Alport epidermal and glomerular basement membranes fail to bind a monoclonal antibody, Mab A7, that reacts with normal epidermal and glomerular basement membranes, and that this abnormality is unique to Alport syndrome. The molecule in normal tissues that reacts with Mab A7 was termed the "Alport antigen". In the present study we used recombinant carboxyterminal noncollagenous (NC1) domains of the alpha 1, alpha 2, alpha 3, alpha 4 and alpha 5 chains of type IV collagen to determine the molecular identity of the Alport antigen. Mab A7 was found to bind specifically to the NC1 domain of the alpha 5 chain of type IV collagen, by ELISA and immunoblotting studies. This finding provides a molecular explanation for the utility of Mab A7 as a marker for the Alport basement membrane defect. Mab A7 can identify the Alport basement membrane defect in those patients in whom COL4A5 mutations prevent incorporation of alpha 5(IV) into basement membranes.

COL4A5 gene deletion and production of post-transplant anti-alpha 3(IV) collagen alloantibodies in Alport syndrome

Mutations in the COL4A5 gene encoding the alpha 5(IV) chain of type IV collagen have been implicated as the primary defect in X-linked Alport syndrome. Several kinds of mutations have been reported so far, spanning point mutations to complete gene deletions. About 5% of Alport patients, who undergo renal transplantation, develop anti-glomerular basement membrane (GBM) nephritis, causing loss of allograft function. In one such patient, COL4A5 gene deletion was recently identified. In the present study, the GBM constituent, targeted by the anti-GBM alloantibodies from the patient who had complete COL4A5 gene deletion was identified. Its identity was determined on the basis of circulating antibody binding to various GBM constituents, domains of bovine type IV collagen and recombinant NC1 domain of human type IV collagen. These results establish, for the first time, the absence of the alpha 5(IV) chain in Alport GBM and, in the same patient, the production of an alloantibody that is targeted to a different chain of type IV collagen, the alpha 3(IV) chain. These findings provide further support for the hypothesis that: (1) anti-alpha 3(IV) collagen alloantibodies mediate the allograft glomerulonephritis; and (2) COL4A5 gene mutations cause defective assembly of the alpha 3(IV) collagen alloantibodies mediate the allograft glomerulonephritis; and (2) COL4A5 gene mutations cause defective assembly of the alpha 3(IV) chain in Alport GBM, as reflected by the production of anti-alpha 3(IV) alloantibodies.

Alport syndrome: from bedside to genome to bedside

Alport syndrome is a genetic disorder of basement membranes manifested clinically by a progressive nephropathy and, in many families, sensorineural hearing loss and ocular lesions. During the 1980s evidence was amassed indicating type IV (basement membrane) collagen as the defective protein in Alport This hypothesis was confirmed in 1990 by the cloning of the X-chromosomal gene COL4A5, which encodes the alpha 5 chain of type IV collagen, and the discovery of mutations in this gene in many Alport kindreds. The results of results of recent studies suggest that the alpha 5(IV) chain forms a distinct collagenous network with the alpha 3 and alpha 4 chains of type IV collagen and that mutations in alpha 5(IV) may prevent the normal incorporation of alpha 3(IV) and alpha 4(IV) into basement membranes. Renal biopsy remains an important modality for making the diagnosis of Alport syndrome, but may eventually be replaced by molecular genetic techniques. Posttransplant anti-glomerular basement membrane nephritis occurs rarely in Alport patients and may be restricted to a subgroup with particular COL4A5 mutations. It is not clear why COL4A5 mutations result in glomerulosclerosis and renal failure, or whether this process may be slowed through dietary or pharmacologic intervention.