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

Clinical Manifestations of Alport Syndrome-Diffuse Leiomyomatosis Patients With Contiguous Gene Deletions in COL4A6 and COL4A5

Alport syndrome-diffuse leiomyomatosis is a rare type of X-linked Alport syndrome resulting from contiguous deletions of 5′ exons of COL4A5 and COL4A6. Studies have suggested that the occurrence of diffuse leiomyomatosis is associated with the characteristic localisation of the COL4A6 gene deletion break point. An electronic database was searched for all studies accessing AS-DL to analyze the clinical characteristics, gene deletion break points of patients with AS-DL, and the pathogenesis of AS-DL. It was found that the proportion of de novo mutations of AS-DL was significantly higher in female probands than male probands (78 vs. 44%). Female patients with AS-DL had a mild clinical presentation. The incidence of proteinuria and ocular abnormalities was much lower in female probands than in male probands, and there was generally no sensorineural hearing loss or chronic kidney disease (CKD), which progressed to Stage 3 in female probands. The contiguous deletion of the 5' exons of COL4A5 and COL4A6, with the break point within the intron 3 of COL4A6, was the critical genetic defect causing AS-DL. However, the pathogenesis of characteristic deletion of COL4A6 that contributes to diffuse leiomyomatosis is still unknown. In addition, characteristic contiguous deletion of COL4A5 and COL4A6 genes in AS-DL may be related to transposed elements (TEs).

Clonal overgrowth of esophageal smooth muscle cells in diffuse leiomyomatosis-Alport syndrome caused by partial deletion in COL4A5 and COL4A6 genes

This is a study of a patient who manifests all of the features of a diffuse leiomyomatosis-Alport syndrome (DL-ATS), and her two-year-old son who has already been diagnosed with Alport syndrome. Fourteen years ago, the patient underwent a partial esophageal resection followed by a replacement with jejunum. Recently, she underwent a surgical resection of the esophagus due to esophageal dysfunction. Genetic analyses of COL4A5 and COL4A6 on the X-chromosome were efficiently performed using the genomic DNA of her son. We have identified a novel deletion of 194-kb in length, encompassing COL4A5-COL4A6 promoters as well as nearly the entire large intron 1 of COL4A5 and intron 2 of COL4A6. To uncover the relationship of the esophagus-specific occurrence of the tumor and the expression of those genes, immunohistochemical analyses of type IV collagen α chains were conducted in the non-affected individuals. The esophageal smooth muscle-specific expression of α5(IV) and α6(IV) chains in the gastrointestinal tract was observed. Moreover, CAG repeat analysis of the androgen receptor gene and an immunohistochemical analysis in the leiomyoma revealed clonal overgrowth of the cells which received X-inactivation on the non-affected allele. These results may suggest that the dominant effect was caused by the partial deletion of the esophageal smooth muscle-specific genes, COL4A5 and COL4A6.

Sequential expression of type IV collagen networks: testis as a model and relevance to spermatogenesis

The six alpha chains of type IV collagen are organized into three networks: alpha1/alpha2, alpha3/alpha4/alpha5, and alpha1/alpha2/alpha5/alpha6. A shift from the alpha1/alpha2 to the alpha3/alpha4/alpha5 network occurs in the developing glomerular basement membrane, but how the alpha1/alpha2/alpha5/alpha6 network fits into this sequence is less clear, because the three networks do not colocalize. Here, we studied the seminiferous tubule basement membrane of normal canine testis where all three networks do colocalize: the alpha1/alpha2 network is expressed from birth, the alpha1/alpha2/alpha5/alpha6 network by 5-6 weeks of age, and the alpha3/alpha4/alpha5 network by 2 months of age. A canine model of Alport syndrome allowed study of the absence of alpha3/alpha4/alpha5 and alpha1/alpha2/alpha5/alpha6 networks in testis. In Alport dogs, the seminiferous tubule basement membrane was thinner than in controls. Spermatogenesis began at the same time as with normal dogs; however, the number of mature sperm was significantly reduced in Alport dogs. Thus, it would appear that alpha3/alpha4/alpha5 and alpha1/alpha2/alpha5/alpha6 networks are not essential for onset of spermatogenesis, but long-term function may be compromised by the loss of one or both networks. This situation is analogous to the glomerular basement membrane in Alport syndrome. In conclusion, testis can serve as a model system to study the sequence of type IV collagen network expression.

Smooth muscle trans-membrane sarcoglycan complex in partial bladder outlet obstruction

The urinary bladder experiences both distension and contraction as a part of the normal filling and emptying cycle. To empty properly, tension generated intracellularly in a smooth muscle cell must be smoothly and efficiently transferred across its sarcolemma to the basement membrane, which mediates its binding to both the extracellular matrix and to other cells. As a consequence of urethral obstruction, the bladder cannot generate appropriate force to contract the organ, thereby leading to inefficient emptying and associated sequelae. In this study, an animal model of urethral obstruction was utilized to study the membrane-associated structures that transfer tension across the sarcolemma of bladder smooth muscle cells. Immunohistochemical localization of key components of the smooth muscle tension transfer apparatus (TTA) was performed utilizing specific antibodies against:(1) the alpha-chains of type IV collagen, a basement membrane component, and (2) beta-sarcoglycan, an integral membrane protein that is a participant in the physical linkage between the cytoskeleton and the basement membrane. We demonstrate, in obstructed animals, that there is a pronounced disruption of the TTA with a physical displacement of these two components that can be demonstrated at the level of the light microscope using scanning confocal microscopy. Electron microscopy further demonstrates significant increases in the size of the junctional plaques between smooth muscle cells.

Regulation of collagen type IV genes is organ-specific: Evidence from a canine model of Alport syndrome

BACKGROUND

Despite advances in knowledge about collagen type IV at the protein level, little is known about expression of its six alpha chains. X-linked Alport syndrome provides a system to study collagen type IV gene expression within a setting of disturbed protein synthesis. Mutations in the alpha5 chain result in loss of the alpha3/alpha4/alpha5 and alpha1/alpha2/alpha5/alpha6 networks from the kidney, with progressive renal disease.

METHODS

We used a canine model of Alport syndrome to measure expression of the six type IV collagen chains from 11 days to 7(1/2) months of age. We determined to what extent message levels in kidney change over time, and what correlation exists with clinical and pathologic changes in glomeruli, and the primary mutation. The latter was evaluated by examining testis, an organ normally containing the same collagen type IV networks but uninvolved by disease.

RESULTS

The alpha1 to alpha6 mRNAs were expressed at all time points in normal canine kidney. By comparison to normal, in Alport dog kidney, the alpha1 and alpha2 mRNAs were up-regulated after 2 months of age, alpha3 and alpha4 mRNAs were down-regulated by 2 months of age, and the alpha5 mRNA was almost undetectable at any time. In testis, all mRNAs were expressed at comparable levels in normal and affected dogs other than the alpha5 chain, which was not expressed in affected testis.

CONCLUSION

Normal expression of collagen type IV is under control mechanisms specific to each organ and to individual chains. The altered expression in canine Alport syndrome is not the direct result of the mutation, since these changes do not occur in all organs nor are they present from birth. Instead, collagen type IV expression is influenced by disease, with down-regulation of alpha3 and alpha4 chains temporally related to the onset of proteinuria, and up-regulation of alpha1 and alpha2 chains to glomerulosclerosis. This dysregulation of the alpha3 and alpha4 chains is unique to this Alport model, and suggests an unidentified mechanism linking pathology with down-regulation of expression of these two chains.

Immunolocalization and distribution patterns of type IV collagen alpha chains in oral mucosal melanoma

The basement membrane (BM) is mainly composed of type IV collagen, which is composed of triple combinations of six distinct alpha (alpha) chains in a tissue-specific manner. The six collagen chain-specific antibodies (alpha1-alpha6) were used to examine the BMs of the oral epithelium (OE) and tumor clusters in oral mucosal melanoma (OMM). Eight OMM cases were examined. Results showed that the alpha1 and alpha2 chains were constantly detected at the BM of the normal OE as well as at the OE with atypical melanocytic proliferation and in invasive melanoma with nodular nests. The alpha1 and alpha2 chains were intermittently detected in in situ OMM, early invasive OMM and advanced invasive OMM with sheet-like nests. Gradual loss of alpha5 and alpha6 from the OE with atypical melanocyte through in situ OMM and early invasive OMM was observed. These findings suggest that changes in the immunolocalization and distribution patterns of type IV collagen alpha chains are associated with the progression of OMM. The distribution pattern of type IV collagen alpha chain varies depending on the architecture of the nest.

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.

The NC1 domain of collagen IV encodes a novel network composed of the alpha 1, alpha 2, alpha 5, and alpha 6 chains in smooth muscle basement membranes

Type IV collagen, the major component of basement membranes (BMs), is a family of six homologous chains (alpha1-alpha6) that have a tissue-specific distribution. The chains assemble into supramolecular networks that differ in the chain composition. In this study, a novel network was identified and characterized in the smooth muscle BMs of aorta and bladder. The noncollagenous (NC1) hexamers solubilized by collagenase digestion were fractionated by affinity chromatography using monoclonal antibodies against the alpha5 and alpha6 NC1 domains and then characterized by two-dimensional gel electrophoresis and Western blotting. Both BMs were found to contain a novel alpha1.alpha2.alpha5.alpha6 network besides the classical alpha1.alpha2 network. The alpha1.alpha2.alpha5.alpha6 network represents a new arrangement in which a protomer (triple-helical isoform) containing the alpha5 and alpha6 chains is linked through NC1-NC1 interactions to an adjoining protomer composed of the alpha1 and alpha2 chains. Re-association studies revealed that the NC1 domains contain recognition sequences sufficient to encode the assembly of both networks. These findings, together with previous ones, indicate that the six chains of type IV collagen are distributed in three major networks (alpha1.alpha2, alpha3.alpha4.alpha5, and alpha1.alpha2.alpha5.alpha6) whose chain composition is encoded by the NC1 domains. The existence of the alpha1.alpha2.alpha5.alpha6 network provides a molecular explanation for the concomitant loss of alpha5 and alpha6 chains from the BMs of patients with X-linked Alport's syndrome.

Diffuse esophageal leiomyomatosis with perirectal involvement mimicking Hirschsprung disease

We describe a 25-year-old woman with diffuse esophageal leiomyomatosis. During childhood, achalasia was mistakenly diagnosed in this patient. Subsequently, she underwent cardiomyotomy and developed symptoms of Hirschsprung disease. These symptoms were caused by infiltration of the esophageal and rectal walls by benign muscular hypertrophy. The pseudo-Hirschsprung disorder was manifested by chronic severe constipation, with consistent manometric findings. Clitoral hypertrophy and vulvar and periurethral leiomyoma were also present. Genetic analysis demonstrating deletion of the COL4A5/COL4A6 locus and the discovery of microscopic hematuria implied that the patient could transmit both diffuse leiomyomatosis and the Alport syndrome.

Glomerular expression of type IV collagen chains in normal and X-linked Alport syndrome kidneys

Alport syndrome is an inherited nephropathy characterized by alterations of the glomerular basement membrane because of mutations in type IV collagen genes. COL4A5 mutations, causing X-linked Alport syndrome, frequently result in the loss of the alpha5 chains of type IV collagen in basement membranes. This is associated with the absence of the alpha3(IV) and alpha4(IV) chains and increased amounts of alpha1(IV) and alpha2(IV) in glomerular basement membranes. The mechanisms resulting in such a configuration are still controversial and are of fundamental importance for understanding the pathology of the disease and for considering gene therapy. In this article we studied, for the first time, type IV collagen expression in kidneys from X-linked Alport syndrome patients, using in situ hybridization and immunohistochemistry. We show that, independent of the type of mutation and of the level of COL4A5 transcription, both COL4A3 and COL4A4 genes are actively transcribed in podocytes. Moreover, using immunofluorescence amplification, we were able to demonstrate that the alpha3 chain of type IV collagen was present in the podocytes of all patients. Finally, the alpha1(IV) chain, which accumulates within glomerular basement membranes, was found to be synthesized by mesangial/endothelial cells. These results strongly suggest that, contrary to what has been found in dogs affected with X-linked Alport syndrome, there is no transcriptional co-regulation of COL4A3, COL4A4, and COL4A5 genes in humans, and that the absence of alpha3(IV) to alpha5(IV) in glomerular basement membranes in the patients results from events downstream of transcription, RNA processing, and protein synthesis.