Goodpasture antigen: expression of the full-length alpha3(IV) chain of collagen IV and localization of epitopes exclusively to the noncollagenous domain

Type IV Collagen and SOX9 Are Molecular Targets of BET Inhibition in Experimental Glomerulosclerosis

Progressive glomerulonephritis (GN) is characterized by an excessive accumulation of extracellular (ECM) proteins, mainly type IV collagen (COLIV), in the glomerulus leading to glomerulosclerosis. The current therapeutic approach to GN is suboptimal. Epigenetic drugs could be novel therapeutic options for human disease. Among these drugs, bromodomain and extra-terminal domain (BET) inhibitors (iBETs) have shown beneficial effects in experimental kidney disease and fibrotic disorders. Sex-determining region Y-box 9 (SOX9) is a transcription factor involved in regulating proliferation, migration, and regeneration, but its role in kidney fibrosis is still unclear. We investigated whether iBETs could regulate ECM accumulation in experimental GN and evaluated the role of SOX9 in this process. For this purpose, we tested the iBET JQ1 in mice with anti-glomerular basement membrane nephritis induced by nephrotoxic serum (NTS). In NTS-injected mice, JQ1 treatment reduced glomerular ECM deposition, mainly by inhibiting glomerular COLIV accumulation and Col4a3 gene overexpression. Moreover, chromatin immunoprecipitation assays demonstrated that JQ1 inhibited the recruitment and binding of BRD4 to the Col4a3 promoter and reduced its transcription. Active SOX9 was found in the nuclei of glomerular cells of NTS-injured kidneys, mainly in COLIV-stained regions. JQ1 treatment blocked SOX9 nuclear translocation in injured kidneys. Moreover, in vitro JQ1 blocked TGF-β1-induced SOX9 activation and ECM production in cultured mesangial cells. Additionally, SOX9 gene silencing inhibited ECM production, including COLIV production. Our results demonstrated that JQ1 inhibited SOX9/COLIV, to reduce experimental glomerulosclerosis, supporting further research of iBET as a potential therapeutic option in progressive glomerulosclerosis.

Rituximab in treatment of anti-GBM antibody glomerulonephritis: A case report and literature review

RATIONALE

Anti-glomerular basement membrane (GBM) disease is a T cell-mediated disease that has a poor prognosis with conventional therapy. We tested rituximab as a primary therapy to reduce anti-GBM antibody produced by B cells.

PATIENT CONCERNS

A 53-year old woman with complaints of a fever, headache and abdominal discomfort showed renal failure with elevated anti-GBM antibody, and renal biopsy revealed crescentic necrotizing glomerulonephritis with linear immunoglobulin G (IgG) 1 deposition along GBM.

DIAGNOSES

The patient's plasma contained autoantibodies against Goodpasture antigen, which is the NC domain of collagen IVα3, and CD4-positive helper T cells were found surrounding crescent glomeruli with the coexistence CD20-positive B cells.

INTERVENTIONS

Rituximab with steroid and plasma exchange.

OUTCOMES

The levels of autoantibody for Goodpasture antigen were reduced, and the patient was able to temporarily withdraw from hemodialysis.

LESSONS

B cell depletion with rituximab is effective as an initial therapy for anti-GBM disease.

Goodpasture's autoimmune disease - A collagen IV disorder

Goodpasture's (GP) disease is an autoimmune disorder characterized by the deposition of pathogenic autoantibodies in basement membranes of kidney and lung eliciting rapidly progressive glomerulonephritis and pulmonary hemorrhage. The principal autoantigen is the α345 network of collagen IV, which expression is restricted to target tissues. Recent discoveries include a key role of chloride and bromide for network assembly, a novel posttranslational modification of the antigen, a sulfilimine bond that crosslinks the antigen, and the mechanistic role of HLA in genetic susceptibility and resistance to GP disease. These advances provide further insights into molecular mechanisms of initiation and progression of GP disease and serve as a basis for developing of novel diagnostic tools and therapies for treatment of Goodpasture's disease.

Frequency of COL4A3/COL4A4 mutations amongst families segregating glomerular microscopic hematuria and evidence for activation of the unfolded protein response. Focal and segmental glomerulosclerosis is a frequent development during ageing

Familial glomerular hematuria(s) comprise a genetically heterogeneous group of conditions which include Alport Syndrome (AS) and thin basement membrane nephropathy (TBMN). Here we investigated 57 Greek-Cypriot families presenting glomerular microscopic hematuria (GMH), with or without proteinuria or chronic kidney function decline, but excluded classical AS. We specifically searched the COL4A3/A4 genes and identified 8 heterozygous mutations in 16 families (28,1%). Eight non-related families featured the founder mutation COL4A3-p.(G1334E). Renal biopsies from 8 patients showed TBMN and focal segmental glomerulosclerosis (FSGS). Ten patients (11.5%) reached end-stage kidney disease (ESKD) at ages ranging from 37-69-yo (mean 50,1-yo). Next generation sequencing of the patients who progressed to ESKD failed to reveal a second mutation in any of the COL4A3/A4/A5 genes, supporting that true heterozygosity for COL4A3/A4 mutations predisposes to CRF/ESKD. Although this could be viewed as a milder and late-onset form of autosomal dominant AS, we had no evidence of ultrastructural features or extrarenal manifestations that would justify this diagnosis. Functional studies in cultured podocytes transfected with wild type or mutant COL4A3 chains showed retention of mutant collagens and differential activation of the unfolded protein response (UPR) cascade. This signifies the potential role of the UPR cascade in modulating the final phenotype in patients with collagen IV nephropathies.

The role of necrotic cell death in the pathogenesis of immune mediated nephropathies

Necrosis, an inflammatory form of cell death, has been considered to be an accidental death and/or cell death due to injury. However, the literature in the last decade has established that necrosis is a regulated form of cell death, and that inhibition of specific molecular pathways leading to necrosis can block it and reduce inflammation. Since necrotic lesions are observed in several immune mediated human pathologies, in this review we will discuss the impact that this form of programmed cellular demise has in the pathology of immune mediated nephropathies.

Evidence for activation of the unfolded protein response in collagen IV nephropathies

Thin-basement-membrane nephropathy (TBMN) and Alport syndrome (AS) are progressive collagen IV nephropathies caused by mutations in COL4A3/A4/A5 genes. These nephropathies invariably present with microscopic hematuria and frequently progress to proteinuria and CKD or ESRD during long-term follow-up. Nonetheless, the exact molecular mechanisms by which these mutations exert their deleterious effects on the glomerulus remain elusive. We hypothesized that defective trafficking of the COL4A3 chain causes a strong intracellular effect on the cell responsible for COL4A3 expression, the podocyte. To this end, we overexpressed normal and mutant COL4A3 chains (G1334E mutation) in human undifferentiated podocytes and tested their effects in various intracellular pathways using a microarray approach. COL4A3 overexpression in the podocyte caused chain retention in the endoplasmic reticulum (ER) that was associated with activation of unfolded protein response (UPR)-related markers of ER stress. Notably, the overexpression of normal or mutant COL4A3 chains differentially activated the UPR pathway. Similar results were observed in a novel knockin mouse carrying the Col4a3-G1332E mutation, which produced a phenotype consistent with AS, and in biopsy specimens from patients with TBMN carrying a heterozygous COL4A3-G1334E mutation. These results suggest that ER stress arising from defective localization of collagen IV chains in human podocytes contributes to the pathogenesis of TBMN and AS through activation of the UPR, a finding that may pave the way for novel therapeutic interventions for a variety of collagenopathies.

Developments in purification methods for obtaining and evaluation of collagen derived endogenous angioinhibitors

Collagen constitutes one of the vital components of the basement membrane scaffolds. Non-collagenous domains (NC1) derived from collagens exhibit potent anti-angiogenic properties, thus attaining significance in regulation of angiogenesis promoted diseases. Individual NC1 domains essential for anti-angiogenic evaluations are generally obtained through purification of individual non-collagenous domains, which have undergone steady developments for enhancing the yields, purpose of biological evaluations and solubility based on the nature of different NC1 domains. This review focuses on the method developments in obtaining biologically active NC1 domains and for specific evaluations in different scenarios.

Crescentic Glomerulonephritis with Anti-GBM and p-ANCA Antibodies

We are presenting a case of renal failure with anti-GBM and p-ANCA antibodies positive. Patients with dual antibodies are considered to be a vasculitis-variant of anti-GBM antibody nephritis. These patients may have atypical presentation and it may delay diagnosis and treatment. Recurrence rate is higher in these patients. We reviewed the literature of cases and studies on cresenteric glomerulonephritis with anti-GBM and p-ANCA positive patients. We recommend that patients suspected with pulmonary-renal syndrome should be checked for anti-GBM and p-ANCA antibodies, should undergo renal biopsy and should should have close long term follow up to watch for recurrence.

Goodpasture's disease: molecular architecture of the autoantigen provides clues to etiology and pathogenesis

PURPOSE OF REVIEW

Goodpasture's disease is an autoimmune disorder characterized by the deposition of pathogenic autoantibodies in basement membranes of kidney and lung, which induces rapidly progressive glomerulonephritis and pulmonary hemorrhage. The target antigen is the α3NC1 domain of collagen IV, which is expressed in target organs as an α345 network. Recent studies of specificity and epitopes of Goodpasture's autoantibodies and discovery of novel posttranslational modification of the antigen, a sulfilimine bond, provide further insight into mechanisms of initiation and progression of Goodpasture's disease.

RECENT FINDINGS

Analysis of the specificity of Goodpasture's autoantibodies revealed a distinct subset of circulating and kidney-bound antiα5NC1 antibody, which is associated with loss of kidney function. Structural integrity of the α345NC1 hexamer is stabilized by the novel sulfilimine crosslinks conferring immune privilege to the Goodpasture's autoantigen. Native antibodies may contribute to establishment of immune tolerance to autoantigen. Structural analysis of epitopes for autoantibodies and alloantibodies indicates a critical role of conformational change in the α345NC1 hexamer in eliciting an autoimmune response in Goodpasture's disease.

SUMMARY

Understanding of the quaternary structure of the Goodpasture's autoantigen continues to provide insights into autoimmune mechanisms that serve as a basis for development of novel diagnostic tools and therapies for Goodpasture's disease.

Advances in the pathogenesis of Goodpasture's disease: from epitopes to autoantibodies to effector T cells

Goodpasture's disease, an "organ-specific" autoimmune disease is manifest by rapidly progressive glomerulonephritis and pulmonary hemorrhage. Studies into the pathogenesis of this disease have shed light on the autoantigen (the non-collagenous domain of the alpha3 chain of type IV collagen, alpha3(IV)NC1) and its epitopes, as well as the involvement of autoantibodies and cellular effectors in disease. The discovery of alpha3(IV)NC1 lead to studies that defined the structure and biology of type IV collagen and are defining B and T cell epitopes. Goodpasture autoantibody epitopes are "cryptic" in that they are structurally sequestered by adjacent non-collagenous domains of alpha4 and alpha5 type IV collagen. T cell epitope studies in rats demonstrated that a 13-mer could induce experimental autoimmune glomerulonephritis. T cells from patients with Goodpasture's recognize two epitopes, in regions which are highly susceptible in antigen processing by endosomal proteases. Goodpasture's disease is strongly associated with HLA DRB1 genes, whereby DRB1*1501 confers susceptibility and the DRB1*0701 and DRB1*0101 are dominantly protective. Experimental data implicate both autoantibodies and cell mediated immunity as disease effectors. Observations in humans suggest that regulatory T cells are associated with the development of self-immunoregulation in the convalescent phase of disease.

Goodpasture antigen-binding protein and its spliced variant, ceramide transfer protein, have different functions in the modulation of apoptosis during zebrafish development

Human Goodpasture antigen-binding protein (GPBP) is an atypical protein kinase that phosphorylates the Goodpasture auto-antigen, the alpha3 chain of collagen IV. The COL4A3BP gene is alternatively spliced producing two protein isoforms: GPBP and GPBPDelta26. The latter lacks a serine-rich domain composed of 26 amino acid residues. Both isoforms also function as ceramide transfer proteins (CERT). Here, we explored the function of Gpbp and GpbpDelta26/CERT during embryogenesis in zebrafish. We cloned both splice variants of the zebrafish gene and found that they are differentially expressed during development. We used antisense oligonucleotide-mediated loss-of-function and synthetic mRNA-based gain-of-function approaches. Our results show that the loss-of-function phenotype is linked to cell death, evident primarily in the muscle of the somites, extensive loss of myelinated tracks, and brain edema. These results indicate that disruption of the nonvesicular ceramide transport is detrimental to normal embryonic development of somites and brain because of increased apoptosis. Moreover, this phenotype is mediated by Gpbp but not GpbpDelta26/CERT, suggesting that Gpbp is an important factor for normal skeletal muscle and brain development.

Glomerulonephritis

The term glomerulonephritis encompasses a range of immune-mediated disorders that cause inflammation within the glomerulus and other compartments of the kidney. Studies with animal models have shown the crucial interaction between bone-marrow-derived inflammatory cells and cells intrinsic to the kidney that is both fundamental and unique to the pathogenesis of glomerulonephritis. The mechanisms of interaction between these cells and the mediators of their coordinated response to inflammation are being elucidated. Despite these pathophysiological advances, treatments for glomerulonephritis remain non-specific, hazardous, and only partly successful. Glomerulonephritis therefore remains a common cause of end-stage kidney failure worldwide. Molecule-specific approaches offer hope for more effective and safer treatments in the future.

Antibody response against the glomerular basement membrane protein agrin in patients with transplant glomerulopathy

Chronic allograft nephropathy (CAN) of renal allografts is still the most important cause of graft loss. A subset of these patients have transplant glomerulopathy (TGP), characterized by glomerular basement membrane (GBM) duplications, but of unknown etiology. Recently, a role for the immune system in the pathogenesis of TGP has been suggested. In 11 of 16 patients with TGP and in 3 of 16 controls with CAN in the absence of TGP we demonstrate circulating antibodies reactive with GBM isolates. The presence of anti-GBM antibodies was associated with the number of rejection episodes prior to diagnosis of TGP. Sera from the TGP patients also reacted with highly purified GBM heparan sulphate proteoglycans (HSPG). Indirect immunofluorescence with patient IgG showed a GBM-like staining pattern and colocalization with the HSPGs perlecan and especially agrin. Using patient IgG, we affinity purified the antigen and identified it as agrin. Reactivity with agrin was found in 7 of 16 (44%) of patients with TGP and in 7 of 11 (64%) patients with anti-GBM reactivity. In conclusion, we have identified a humoral response against the GBM-HSPG agrin in patients with TGP, which may play a role in the pathogenesis of TGP.

The fine specificity and cytokine profile of T-helper cells responsive to the alpha3 chain of type IV collagen in Goodpasture's disease

Goodpasture's disease is a severe nephritis characterized by autoantibodies to the alpha3 chain of type IV collagen, alpha3(IV)NC1, in the glomerular basement membrane. The disease is very strongly associated with HLA-DR15, the affinities of alpha3(IV)NC1 peptides for DR15 are known, and elution experiments have identified major naturally processed sequences. Here, the fine specificity and cytokine profile of alpha3(IV)NC1-reactive T cells from patients with Goodpasture's disease is defined. Peripheral blood mononuclear cells from patients at diagnosis proliferated in response to significantly more peptides (chi(2) = 8.6, P = 0.004) from a panel spanning the sequence of alpha3(IV)NC1 than did those from control DR15-positive donors and were highly focused (P = 0.0002, binomial distribution) on two peptides, alpha3(71-90) and alpha3(131-150). Some peptides induced interferon-gamma, but none induced IL-4. Resolution of disease was accompanied by a striking deviation of the responses from proliferation to secretion of the T-regulatory cytokine IL-10, and addition of neutralizing antibody confirmed that such IL-10 production was suppressive. The affinity of the peptides for DR15 molecules was positively correlated (chi(2) = 14.6, P = 0.00067) with the ability to elicit proliferation. However, unlike foreign antigens, this hierarchy is not due to responses against the major naturally processed peptides, which rarely stimulated proliferation and which have only intermediate affinity for DR15 molecules. It is inferred that the helper response to alpha3(IV)NC1 in Goodpasture's disease is dominated by epitopes that are normally inefficiently presented because of processing constraints.

Characterization of assembly of recombinant type IV collagen α3, α4, and α5 chains in transfected cell strains

BACKGROUND

Alport syndrome is caused by mutations in type IV collagen alpha3, alpha4, and alpha5 genes. Immunohistochemical analyses of kidney sections from normal individuals and Alport syndrome patients have suggested that the alpha3(IV), alpha4(IV), and alpha5(IV) chains form a heterotrimer in the glomerular basement membrane (GBM) and that a defect in any one of the chains disrupts the assembly of the three chains, resulting in Alport syndrome.

METHODS

We established stable transformants of HEK293 cells that expressed mouse alpha3(IV) and/or alpha4(IV) and/or alpha5(IV) chains. Using cell extracts and culture media of these cells, experiments were performed to determine whether or not the alpha3(IV) and alpha4(IV) chains were coimmunoprecipitated with the alpha5(IV) chain. Moreover, we examined complex formation of mutant alpha5(IV) chain containing either a deletion or substitution mutation with the alpha3(IV) and alpha4(IV) chains.

RESULTS

The established cell strains were named according to their transfected alpha(IV) chains. The alpha3(IV) and alpha4(IV) chains were coimmunoprecipitated with the alpha5(IV) chain in alpha345 cells but not in alpha35 and alpha45 cells. These chains were not coimmunoprecipitated with the alpha5(IV) chain, which lacked either a collagenous domain or NC1 domain. The ability of the alpha5(IV) chain with either a G1182R or C1573R substitution, corresponding to previously reported mutations in Alport syndrome patients, to form a complex with alpha3(IV) and alpha4(IV) chains was diminished.

CONCLUSION

The findings indicate that alpha3(IV), alpha4(IV), and alpha5(IV) chains form a complex, which is a heterotrimer, and that a defect in complex formation might be one of the molecular mechanisms underlying the pathogenesis of Alport syndrome.

Transfer of the alpha 5(IV) collagen chain gene to smooth muscle restores in vivo expression of the alpha 6(IV) collagen chain in a canine model of Alport syndrome

X-linked Alport syndrome is a progressive renal disease caused by mutations in the COL4A5 gene, which encodes the alpha 5(IV) collagen chain. As an initial step toward gene therapy for Alport syndrome, we report on the expression of recombinant alpha 5(IV) collagen in vitro and in vivo. A full-length cDNA-encoding canine alpha 5(IV) collagen was cloned and expressed in vitro by transfection of HEK293 cells that synthesize the alpha1(IV) and alpha2(IV), but not the alpha 3(IV) to alpha 6(IV) collagen chains. By Northern blotting, an alpha 5(IV) mRNA transcript of 5.2 kb was expressed and the recombinant protein was detected by immunocytochemistry. The chain was secreted into the medium as a 190-kd monomer; no triple helical species were detected. Transfected cells synthesized an extracellular matrix containing the alpha1(IV) and alpha2(IV) chains but the recombinant alpha 5(IV) chain was not incorporated. These findings are consistent with the concept that the alpha 5(IV) chain requires one or more of the alpha 3(IV), alpha 4(IV), or alpha 6(IV) chains for triple helical assembly. In vivo studies were performed in dogs with X-linked Alport syndrome. An adenoviral vector containing the alpha 5(IV) transgene was injected into bladder smooth muscle that lacks both the alpha 5(IV) and alpha 6(IV) chains in these animals. At 5 weeks after injection, there was expression of both the alpha 5(IV) and alpha 6(IV) chains by smooth muscle cells at the injection site in a basement membrane distribution. Thus, this recombinant alpha 5(IV) chain is capable of restoring expression of a second alpha(IV) chain that requires the presence of the alpha 5(IV) chain for incorporation into collagen trimers. This vector will serve as a useful tool to further explore gene therapy for Alport syndrome.

Immunology of anti-glomerular basement membrane disease

Anti-glomerular basement membrane disease is a form of autoimmune glomerulonephritis often accompanied by lung haemorrhage. It is characterized by circulating and deposited antibodies that bind basement membrane components in the glomerulus and lung alveolus. Since early descriptions of the deposition of immunoglobulin on the glomerular basement membrane, work has focused on the binding properties of the autoantibodies, and this has led to the identification of the autoantigen as the non-collagenous region of the alpha 3 chain of type IV collagen. Despite being thought of as a prototypic antibody mediated autoimmune disease, it is becoming apparent that both humoral and cellular immune mechanisms act in concert to initiate and perpetuate disease. Recent data have shed light on the molecular pathogenesis of anti-glomerular basement membrane disease and provided a more complete framework on which to build our understanding of autoimmune renal disease. This should lead to novel approaches to immunotherapy for patients with glomerulonephritis.

Hydrophobic amino acid residues are critical for the immunodominant epitope of the Goodpasture autoantigen. A molecular basis for the cryptic nature of the epitope

Goodpasture (GP) autoimmune disease is caused by autoantibodies to type IV collagen that bind to the glomerular basement membrane, causing rapidly progressing glomerulonephritis. The immunodominant GP(A) autoepitope is encompassed by residues 17-31 (the E(A) region) within the noncollagenous (NC1) domain of the alpha 3(IV) chain. The GP epitope is cryptic in the NC1 hexamer complex that occurs in the type IV collagen network found in tissues and inaccessible to autoantibodies unless the hexamer dissociates. In contrast, the epitope for the Mab3 monoclonal antibody is also located within the E(A) region, but is fully accessible in the hexamer complex. In this study, the identity of residues that compose the GP(A) autoepitope was determined, and the molecular basis of its cryptic nature was explored. This was achieved using site-directed mutagenesis to exchange the alpha3(IV) residues in the E(A) region with the corresponding residues of the homologous but non-immunoreactive alpha1(IV) NC1 domain and then comparing the reactivity of the mutated chimeras with GP(A) and Mab3 antibodies. It was shown that three hydrophobic residues (Ala(18), Ile(19), and Val(27)) and Pro(28) are critical for the GP(A) autoepitope, whereas two hydrophilic residues (Ser(21) and Ser(31)) along with Pro(28) are critical for the Mab3 epitope. These results suggest that the cryptic nature of the GP(A) autoepitope is the result of quaternary interactions of the alpha 3, alpha 4, and alpha 5 NC1 domains of the hexamer complex that bury the one or more hydrophobic residues. These findings provide critical information for understanding the etiology and pathogenesis of the disease as well as for designing drugs that would mimic the epitope and thus block the binding of GP autoantibodies to autoantigen.

Structure of the human type IV collagen gene COL4A3 and mutations in autosomal Alport syndrome

Mutations in either the COL4A3 or the COL4A4 genes, encoding the alpha3 and alpha4 chains of type IV collagen, are responsible for the autosomal-recessive form of Alport syndrome, a progressive hematuric nephropathy characterized by glomerular basement membrane abnormalities. Reported here are the complete COL4A3 exon-intron structure and a comprehensive screen for mutations of the 52 COL4A3 exons in 41 unrelated patients diagnosed as having autosomal Alport syndrome. This resulted in the identification of 21 mutations that are expected to be causative. Furthermore, it is shown that heterozygous COL4A3 missense mutations, when symptomatic, can be associated with a broad range of phenotypes, from familial benign hematuria to the complete features of Alport syndrome nephropathy.

Helper T cells in antibody-mediated, organ-specific autoimmunity

The production of pathogenic autoantibodies in organ-specific autoimmune diseases is largely T cell dependent. For many of these diseases, the precise specificities and cytokine profiles of the T cells that respond to the corresponding autoantigens have now been identified. This knowledge has been exploited to treat some models of antibody-mediated autoimmunity using peptides corresponding to the dominant helper epitopes, giving impetus to the development of a similar approach in the equivalent human diseases.