A model of autosomal recessive Alport syndrome in English cocker spaniel dogs

Col4a3-/- Mice on Balb/C Background Have Less Severe Cardiorespiratory Phenotype and SGLT2 Over-Expression Compared to 129x1/SvJ and C57Bl/6 Backgrounds

Alport syndrome (AS) is a hereditary renal disorder with no etiological therapy. In the preclinical Col4a3^-/- model of AS, disease progression and severity vary depending on mouse strain. The sodium-glucose cotransporter 2 (SGLT2) is emerging as an attractive therapeutic target in cardiac/renal pathologies, but its application to AS remains untested. This study investigates cardiorespiratory function and SGLT2 renal expression in Col4a3^-/- mice from three different genetic backgrounds, 129x1/SvJ, C57Bl/6 and Balb/C. male Col4a3^-/- 129x1/SvJ mice displayed alterations consistent with heart failure with preserved ejection fraction (HFpEF). Female, but not male, C57Bl/6 and Balb/C Col4a3^-/- mice exhibited mild changes in systolic and diastolic function of the heart by echocardiography. Male C57Bl/6 Col4a3^-/- mice presented systolic dysfunction by invasive hemodynamic analysis. All strains except Balb/C males demonstrated alterations in respiratory function. SGLT2 expression was significantly increased in AS compared to WT mice from all strains. However, cardiorespiratory abnormalities and SGLT2 over-expression were significantly less in AS Balb/C mice compared to the other two strains. Systolic blood pressure was significantly elevated only in mutant 129x1/SvJ mice. The results provide further evidence for strain-dependent cardiorespiratory and hypertensive phenotype variations in mouse AS models, corroborated by renal SGLT2 expression, and support ongoing initiatives to develop SGLT2 inhibitors for the treatment of AS.

Allele frequency of nonsense mutation responsible for hereditary nephropathy in English cocker spaniel dogs

Hereditary nephropathy is a primary progressive glomerular disease in dogs associated with the c.115A>T mutation in the COL4A4 gene in English cocker spaniel (ECS) dogs. The disease is inherited in an autosomal recessive manner. Hereditary nephropathy has been described in this breed since the late 1940s. To date, there are no data on the prevalence of this disease in Brazil, so the aim of this study was to evaluate the allelic frequency of this mutation in ECS dogs in this country. The DNA samples were purified from blood samples or buccal swabs from 221 ECS dogs. Fragments of the DNA containing the mutation were amplified by PCR and submitted to direct gene sequencing. The allele frequency of the mutation was 0.9%. The presence of the mutation in the ECS dog population in Brazil reveals the importance of performing the genotyping tests in these dogs as a method of diagnosing the disease and identifying heterozygous animals, aiming to reduce clinical cases of disease through mating.

COL4A6 is dispensable for autosomal recessive Alport syndrome

Alport syndrome is caused by mutations in the genes encoding α3, α4, or α5 (IV) chains. Unlike X-linked Alport mice, α5 and α6 (IV) chains are detected in the glomerular basement membrane of autosomal recessive Alport mice, however, the significance of this finding remains to be investigated. We therefore generated mice lacking both α3 and α6 (IV) chains and compared their renal function and survival with Col4a3 knockout mice of 129 × 1/Sv background. No significant difference was observed in the renal function or survival of the two groups, or when the mice were backcrossed once to C57BL/6 background. However, the survival of backcrossed double knockout mice was significantly longer than that of the mice of 129 × 1/Sv background, which suggests that other modifier genes were involved in this phenomenon. In further studies we identified two Alport patients who had a homozygous mutation in intron 46 of COL4A4. The α5 and α6 (IV) chains were focally detected in the glomerular basement membrane of these patients. These findings indicate that although α5 and α6 (IV) chains are induced in the glomerular basement membrane in autosomal recessive Alport syndrome, their induction does not seem to play a major compensatory role.

Histologic and Ultrastructural Studies of Juvenile Onset Renal Disease in Four Rottweiler Dogs

Juvenile onset renal disease is described in 2 male and 2 female young Rottweiler dogs. Histologic changes in all dogs were cystic dilatation of Bowman's space, mesangial hypercellularity, and glomerulosclerosis. Three dogs also had glomerular crescents and moderate to severe interstitial fibrosis. Electron microscopy revealed glomerular basement membranes of variable thickness, with extensive splitting or lamellation of the lamina densa. These ultrastructural findings are similar to those found in people and in other breeds of dogs with inherited defects in type IV collagen.

Pathological features of proteinuric nephropathy resembling Alport syndrome in a young Pyrenean Mountain dog

The renal biopsy tissue from a 9-month-old, male Pyrenean Mountain dog with renal disorder and severe proteinuria was examined. Ultrastructural examination revealed multilaminar splitting and fragmentation of the glomerular basement membrane (GBM) and diffuse podocyte foot process effacement. Immunofluorescent staining for α(IV) chains revealed presence of α5(IV) and complete absence of α3(IV) and α4(IV) chains in the GBM. Immunohistochemistry also revealed decreased and altered expression of nephrin and podocin in the glomeruli compared with normal canine glomeruli. These results suggested that the glomerular disease of the present case might be consistent with canine hereditary nephropathy resembling human Alport syndrome caused by genetic defect of type IV collagen, and indicated possible contribution of podocyte injury to severe proteinuria in this case.

A model of strain-dependent glomerular basement membrane maintenance and its potential ramifications in health and disease

A model is developed and analyzed for type IV collagen turnover in the kidney glomerular basement membrane (GBM), which is the primary structural element in the glomerular capillary wall. The model incorporates strain dependence in both deposition and removal of the GBM, leading to an equilibrium tissue strain at which deposition and removal are balanced. The GBM thickening decreases tissue strain per unit of transcapillary pressure drop according to the law of Laplace, but increases the transcapillary pressure drop required to maintain glomerular filtration. The model results are in agreement with the observed GBM alterations in Alport syndrome and thin basement membrane disease, and the model-predicted linear relation between the inverse capillary radius and inverse capillary thickness at equilibrium is consistent with published data on different mammals. In addition, the model predicts a minimum achievable strain in the GBM based on the geometry, properties, and mechanical environment; that is, an infinitely thick GBM would still experience a finite strain. Although the model assumptions would be invalid for an extremely thick GBM, the minimum achievable strain could be significant in diseases, such as Alport syndrome, characterized by focal GBM thickening. Finally, an examination of reasonable values for the model parameters suggests that the oncotic pressure drop-the osmotic pressure difference between the plasma and the filtrate due to large molecules-plays an important role in setting the GBM strain and, thus, leakage of protein into the urine may be protective against some GBM damage.

Characterization of the genetic basis for autosomal recessive hereditary nephropathy in the English Springer Spaniel

BACKGROUND

Autosomal recessive hereditary nephropathy (ARHN) was diagnosed in 2 English Springer Spaniels (ESS), a breed not previously reported to be affected by hereditary nephropathy (HN).

OBJECTIVE

To identify and characterize the genetic cause of ARHN in ESS.

ANIMALS

Sixty-three ESS (2 with ARHN, 2 obligate carriers, and 59 others), 2 mixed-breed dogs with X-linked HN, and 2 English Cocker Spaniels (ECS) with ARHN were included.

METHODS

ARHN was diagnosed based on transmission electron microscopy and immunostaining of kidney. DNA from affected dogs was screened for the mutation known to cause ARHN in ECS. Quantities of COL4A3, COL4A4, and COL4A5 mRNA transcripts in renal cortex were determined using quantitative reverse transcription-polymerase chain reaction (qRT-PCR) for ARHN-affected dogs and 7 other dogs. The coding regions of COL4A3 and COL4A4 were sequenced for the 2 ARHN-affected ESS and an unaffected dog. Exon 30 of COL4A4 was sequenced for all 63 ESS.

RESULTS

qRT-PCR indicated a significant reduction in transcript levels of both COL4A3 and COL4A4 mRNA in the kidney of ARHN-affected ESS. Sequencing identified a single nucleotide substitution in COL4A4 at base 2806 resulting in a premature stop codon. Thirteen of 25 related dogs were identified as carriers.

CONCLUSIONS AND CLINICAL IMPORTANCE

A mutation highly likely to cause ARHN in ESS has been identified.

Persistent haematuria and proteinuria due to glomerular disease in related Abyssinian cats

Eight cases of glomerular disease in young, related Abyssinian cats are described. Haematuria was the most consistent feature. Six cats developed the nephrotic syndrome. The short-term prognosis was good for cats with haematuria and fair for cats with the nephrotic syndrome as oedema resolved in three of the six cats. Light microscopic examination of renal biopsies from three cats was considered normal or revealed only mild abnormalities. In the three cases subjected to necropsy, histological abnormalities included mild mesangial hypercellularity and adhesions between the glomerular tuft and Bowman's capsule consistent with a focal proliferative glomerulopathy. Further investigation into this glomerulopathy will require ultrastructural and immunohistochemical studies to characterise the glomerular abnormality and genetic analyses to investigate its potential to be an inherited disease. Glomerular disease, potentially a familial one, should be considered in the investigation of persistent haematuria or proteinuria in Abyssinian and related cats.

Choosing a mouse model to study the molecular pathobiology of Alport glomerulonephritis

Alport syndrome, caused by mutations that interfere with the normal assembly of the alpha3alpha4alpha5(IV) collagen network in the glomerular basement membrane (GBM), is the most common inherited glomerular disease leading to renal failure. A detailed knowledge of the underlying pathogenic mechanisms is necessary for developing new, more specific, and effective therapeutic strategies aimed at delaying the onset and slowing disease progression. Studies of several dog and mouse models of Alport syndrome have significantly enhanced our understanding of the disease mechanisms and provided systems for testing potential therapies. In the most widely used Col4a3-/- mouse models of autosomal-recessive Alport syndrome (ARAS), the genetic background strongly affects renal survival. One contributing factor may be the strong ectopic deposition of alpha5alpha6(IV) collagen in the GBM of Col4a3-/- mice on the C57BL/6J background, which is almost undetectable on the 129/Sv background. This isoform 'switch' has not been observed in human ARAS, although it had been reported in the dog model of ARAS. In human patients as well as dog and mouse models of X-linked Alport syndrome, the alpha3-alpha6(IV) collagen chains are absent from the GBM. These biochemical differences among Alport animal models provide an opportunity to determine how the molecular makeup of the GBM affects the glomerular function. At the same time, potentially confounding influences of characteristics unique to a particular strain or model should be carefully considered in the design of studies aiming to define key events underlying the pathobiology of Alport glomerular disease.

Loss of alpha3/alpha4(IV) collagen from the glomerular basement membrane induces a strain-dependent isoform switch to alpha5alpha6(IV) collagen associated with longer renal survival in Col4a3-/- Alport mice

Mutations in COL4A3/4/5 genes that affect the normal assembly of the alpha3/4/5(IV) collagen network in the glomerular basement membrane (GBM) cause Alport syndrome. Patients progress to renal failure at variable rates that are determined by the underlying mutation and putative modifier genes. Col4a3(-/-) mice, a model for autosomal recessive Alport syndrome, progress to renal failure significantly slower on the C57BL/6 than on the 129X1/Sv background. Reported here is a novel strain-specific alternative collagen IV isoform switch that is associated with the differential renal survival in Col4a3(-/-) Alport mice. The downregulation or the absence of alpha3/4(IV) collagen chains in the GBM of Lmx1b(-/-) and Col4a3(-/-) mice was found to induce ectopic deposition of alpha5/6(IV) collagen. The GBM deposition of alpha5/6(IV) collagen was abundant in C57BL/6 Col4a3(-/-) mice but almost undetectable in 129X1/Sv Col4a3(-/-) mice. This strain difference was due to overall low expression of alpha6(IV) chain and alpha5/6(IV) protomers in the tissues of 129X1/SvJ mice, a natural Col4a6 knockdown. In (129 x B6)F1 Col4a3(-/-) mice, the amount of alpha5/6(IV) collagen in the GBM was inherited in a mother-to-son manner, suggesting that it is controlled by one or more X-linked loci, possibly Col4a6 itself. Importantly, high levels of ectopic alpha5/6(IV) collagen in the GBM were associated with approximately 46% longer renal survival. These findings suggest that alpha5/6(IV) collagen, the biologic role of which has been hitherto unknown, may partially substitute for alpha3/4/5(IV) collagen. Therapeutically induced GBM deposition of alpha5/6(IV) collagen may provide a novel strategy for delaying renal failure in patients with autosomal recessive Alport syndrome.

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.

Extracellular matrix in ovarian follicular development and disease

The ovarian follicle contains several different cell types and separate compartments and undergoes substantial development during its growth and maturation. Extracellular matrix (ECM) could be expected to play a major role in these processes. Most research on ECM in follicles has focused on the follicular basal lamina and its changing composition during folliculogenesis and on the specialised matrix formed at ovulation by the cumulus cells surrounding the oocyte and the zona pellucida. We review these aspects. Few naturally occurring gene mutations have identified unique roles for ECM molecules in follicular function. Presumably, any mutations leading to reduced fertility are eliminated quickly by natural selection and, when mutations are not eliminated, considerable redundancy occurs to ensure successful reproduction. In mice, in which the genome can be easily manipulated, the modification of matrix components associated with cumulus and oocytes has often resulted in partial infertility, suggesting redundancy. We provide an update of basal lamina components focusing on newer discoveries. In addition, we review matrix associated with the occyte and cumulus cells (excluding the zona pellucida) and other components of ECM. Where possible, we examine evidence for the role of the ECM in follicular development and diseases.

Familial hematurias: what we know and what we don't

Over the past 30 years we have learned a great deal about the molecular genetics and natural history of familial forms of hematuria. Our enhanced understanding of these conditions has yet to generate effective therapies for Alport syndrome, the form of familial hematuria associated with end-stage renal disease. This review briefly presents the current state of knowledge about familial hematuria and argues for the organization of clinical therapeutic trials in Alport syndrome.

Early diagnosis of renal disease and renal failure

The main goal of early diagnosis of renal disease and renal failure in dogs and cats is to enable timely application of therapeutic interventions that may slow or halt disease progression. Strategies for early diagnosis of renal disease use urine tests that detect proteinuria that is a manifestation of altered glomerular permselectivity or impaired urine-concentrating ability as well blood tests to evaluate plasma creatinine concentration. Animals with progressive renal disease should be carefully investigated and treated appropriately. Animals with mild, possibly nonprogressive, renal disease should be monitored adequately to detect any worsening trends,which should lead to further investigation and treatment even if the increments of change are small.

A novel basal lamina matrix of the stratified epithelium of the ovarian follicle

Basal laminas are important sheets of specialized extracellular matrix that underlie and surround groups of cells, such as epithelia or endothelia, enabling the cells to orientate their basal/apical polarity and creating a microenvironment for them. Basal laminas can also individually encapsulate whole cells, such as muscle cells, thereby forming a microenvironment but not polarizing the enclosed cells. Other mesenchymal or stromal cells exist with no basal lamina. In the course of studying the bovine follicular basal lamina which underlies the multilayered epithelium of the ovarian follicle, we identified a developmentally regulated novel extracellular matrix (which we call focimatrix for focal intra-epithelial matrix). Focimatrix is composed of basal lamina-like material deposited as plaques or aggregates between the multilayers of the epithelial granulosa cells. The focimatrix does not encapsulate individual or groups of cells and therefore does not form a microenvironment for them. Focimatrix contains collagen type IV subunits alpha1 and alpha2 (but not alpha3-alpha6), and laminin chains alpha1, beta2 and gamma1 (but not alpha2 or beta1), and nidogen-1 and perlecan (but not versican). The amount of focimatrix increases with increasing follicular size, and its appearance precedes the expression by granulosa cells of the enzymes for steroid hormone synthesis, cholesterol side-chain cleavage cytochrome P450 (SCC) and 3beta-hydroxysteroid dehydrogenase (3beta-HSD), in the days preceding ovulation. The expression in granulosa cells of two components examined, nidogen-1 and perlecan, also increases substantially when follicles enlarge to a sufficient size capable of ovulating. Following ovulation the follicular basal lamina is degraded, and presumably focimatrix is too since it is not detected in corpora lutea that develop from the ovulating follicles. During this development the granulosa cells undergo an epithelial-mesenchymal transition (EMT) into luteal cells following ovulation, and substantially increase their expression of steroidogenic enzymes in the process. During EMT epithelial cells lose polarity. Since focimatrix exists on more than one side of the granulosa cells, we propose that it disrupts the polarity induced by the follicular basal lamina in the lead up to ovulation. Hence focimatrix maybe a key part of the follicular/luteal EMT.

Effects of serial ultrasound-guided renal biopsies on kidneys of healthy adolescent dogs

Ten healthy mixed-breed dogs were used to evaluate the functional and structural effects of serial ultrasound-guided renal biopsies obtained with an automated biopsy needle. In each dog, one lateral renal cortex was biopsied at 2, 4, and 6 months of age; the other kidney was the control. Five dogs had two tissue cores and five dogs had four tissue cores taken on each biopsy occasion, and one core was examined microscopically. One week before each biopsy and a month after the final biopsy, the glomerular filtration rate (GFR) was determined by renal scintigraphy. Dogs were then euthanized for evaluation of gross and microscopic lesions attributable to the biopsies. There was no difference between GFR values for biopsied kidneys and those of control kidneys (P > 0.05). Microscopic lesions were not identified in biopsies taken at 2 and 4 months, but focal lesions were found in three of 10 specimens taken at 6 months of age. At necropsy, six of 10 biopsied kidneys had small visible capsular scars, and linear tracts < 2 mm wide were observed on cut surfaces in six of 10 biopsied kidneys cut transversely into slices 5 mm thick. Discrete light microscopic lesions were observed in 25 of 452 (5.5%) of randomly selected 6-mm-diameter sections of renal cortex from biopsied kidneys. We conclude that serial renal cortical biopsies can be obtained by our method from healthy adolescent dogs with minimal risk of inducing changes that might be confused with those of a progressive renal disease.

In vivo expression of putative LMX1B targets in nail-patella syndrome kidneys

The nail-patella syndrome (NPS) is characterized by nail and bone abnormalities, associated with glomerular involvement in approximately 40% of patients. Typical glomerular changes consist of fibrillar material in the irregularly thickened glomerular basement membrane. NPS is inherited as an autosomal dominant trait and caused by heterozygous loss of function mutations in LMX1B, a member of the LIM homeodomain protein family. Mice with homozygous inactivation of the gene exhibit nail and skeletal defects, similar to those observed in patients, associated with glomerular abnormalities. Strong reduction in the glomerular expression of the alpha3 and alpha4 chains of type IV collagen, and of podocin and CD2AP, two podocyte proteins critical for glomerular function, has been observed in Lmx1b null mice. The expression of these proteins appeared to be regulated by Lmx1b. To determine whether these changes in podocyte gene expression are involved in the development of NPS nephropathy, using immunohistological techniques, we analyzed the podocyte phenotype and the renal distribution of type IV collagen chains in the kidneys of seven NPS patients with severe glomerular disease. We also examined the nature of the fibrillar material present within the glomerular extracellular matrix. The glomerular basement membrane fibrillar material was specifically labeled with anti-type III collagen antibodies, suggesting a possible regulation of type III collagen expression by LMX1B. The expression of the alpha3 and alpha4 chains of type IV collagen, and of podocin and CD2AP, was found to be normal in the seven patients. These findings indicate that heterozygous mutations of LMX1B do not appear to dramatically affect the expression of type IV collagen chains, podocin, or CD2AP in NPS patients.

Genetic cause of X-linked Alport syndrome in a family of domestic dogs

Alport syndrome is a hereditary disease of type IV (basement membrane) collagens that occurs spontaneously in humans and dogs. In the human, X-linked Alport syndrome (XLAS) is caused by mutations in COL4A5, resulting in absence of type IV collagen alpha5 chains from the glomerular basement membrane (GBM) of affected individuals. The consequence of this defect is progressive renal failure, for which the only available treatments are dialysis and transplantation. Recent studies support the prospect of gene transfer therapy for Alport syndrome, but further development of required technologies and demonstration of safety and efficacy must be accomplished in a suitable animal model. We previously identified and have propagated a family of mixed-breed dogs with an inherited nephropathy that exhibits the clinical, immunohistochemical, pathological, and ultrastructural features of human XLAS. To identify the causative mutation, COL4A5 cDNAs from normal and affected dogs were sequenced in their entirety. Sequence analyses revealed a 10-bp deletion in exon 9 of affected dogs. This deletion causes a frame-shift that results in a premature stop codon in exon 10. Characterization of the causative mutation was followed by development of an allele-specific test for identification of dogs in this kindred that are destined to develop XLAS.

Increased expression of MMP-2, MMP-9 (type IV collagenases/gelatinases), and MT1-MMP in canine X-linked Alport syndrome (XLAS)

BACKGROUND

Alport syndrome is a group of genetic disorders resulting from mutations in either the alpha3(IV), alpha4(IV) or alpha5(IV) collagen chains. The disease is characterized by a progressive glomerulonephritis, usually associated with a high-frequency specific sensorineural hearing loss, dot and fleck retinopathy, and lens abnormalities. Dogs with naturally occurring genetic disorders of basement membrane collagen (type IV) may serve as animal models of Alport syndrome. In this study, a well-characterized naturally occurring canine model was employed to demonstrate a potential role for matrix metalloproteinases (MMPs) in Alport renal disease pathogenesis.

METHODS

Adolescent male dogs that developed renal failure were euthanized and necropsied. Clinicopathologic features of the disease were characterized, and kidneys from normal and Alport dogs were analyzed by gelatin zymography, Western blotting, in situ zymography, immunohistology, and by reverse transcription polymerase chain reaction (RT-PCR) for expression of MMP-2, MMP-9, and membrane type 1-MMP (MT1-MMP).

RESULTS

Affected dogs developed proteinuria and rapidly progressive juvenile-onset chronic renal failure. The activities of MMP-2 and MMP-9 were significantly induced in Alport kidney. In situ zymography confirmed elevated active metalloproteinases in kidney cryosections of affected dogs. The mRNAs encoding MMP-2, MMP-9 and MT1-MMP were also increased in Alport dogs suggesting that elevated expression of MMPs reflects events in the progression of Alport syndrome in dogs.

CONCLUSION

Elevated expression of MMP-2, MMP-9, and MT1-MMP is observed in fibrotic renal cortex from X-linked Alport syndrome dogs. These findings suggest that MMPs may play an important role in matrix accumulation associated with progressive renal scarring in this model.

Laminin-1 reexpression in Alport mouse glomerular basement membranes

BACKGROUND

Alport disease is a heritable basement membrane disorder caused by mutations in genes encoding the alpha3, alpha4, or alpha5 chains of type IV collagen, which normally comprise the collagenous network of mature glomerular basement membranes (GBMs). In Alport disease, the alpha3(IV), alpha4(IV), alpha5(IV) collagen network is absent and substituted for by alpha1(IV), and alpha2(IV) collagen, which normally is present only in developing, immature GBMs. The disease is marked by progressive GBM thickening and delamination, proteinuria, and renal failure. In addition to collagen IV dysregulation, abnormal GBM laminins also occur and may contribute to the pathogenesis of Alport glomerulopathy.

METHODS

To investigate laminin dysregulation in a mouse model of Alport disease, we used antibodies specific for laminin-alpha1 and -beta1 chains (to recognize laminin-1), and -alpha5 chain (to recognize laminin-11), and evaluated their distribution during glomerular development in alpha3(IV) collagen-deficient mice.

RESULTS

Developing glomeruli of infant alpha3(IV) collagen knockout mice underwent normal down-regulation of laminin-1, but laminin-1 chains were then reexpressed in maturing glomeruli, becoming concentrated in the subepithelial GBM projections typical of Alport disease. Immunoelectron microscopy showed that laminin-1 reexpression took place in both glomerular endothelial cells and podocytes.

CONCLUSIONS

The absence of a alpha3(IV), alpha4(IV), alpha5(IV) network may stimulate reexpression of laminin-1 by Alport mouse endothelial cells and podocytes. This abnormal GBM, which is more characteristic of immature glomeruli, may promote podocyte foot process effacement and reversion to a less differentiated state.

Renal pathology of polycystic kidney disease and concurrent hereditary nephritis in Bull Terriers

OBJECTIVE

To describe the renal lesions in Bull Terrier polycystic kidney disease (BTPKD), to confirm that the renal cysts in BTPKD arise from the nephron or collecting tubule, and to identify lesions consistent with concurrent BTPKD and Bull Terrier hereditary nephritis (BTHN).

DESIGN

Renal tissue from five Bull Terriers with BTPKD and eight control dogs was examined by light and transmission electron microscopy. Clinical data were collected from all dogs, and family history of BTPKD and BTHN for all Bull Terriers.

RESULTS

In BTPKD the renal cysts were lined by epithelial cells of nephron or collecting duct origin that were usually squamous or cuboidal, with few organelles. They had normal junctional complexes, and basal laminae of varying thicknesses. Glomeruli with small, atrophic tufts and dilated Bowman's capsules, tubular loss and dilation, and interstitial inflammation and fibrosis were common. Whereas the lesions seen in BTHN by light microscope were nonspecific, the presence of characteristic ultrastructural glomerular basement membrane (GMB) lesions and a family history of this disease indicated concurrent BTHN was likely in three of five cases of BTPKD.

CONCLUSION

This paper provides evidence that renal cysts in BTPKD are of nephron or collecting duct origin. In addition, GBM lesions are described that strongly suggest that BTPKD and BTHN may occur simultaneously.

Quantitative trait loci influence renal disease progression in a mouse model of Alport syndrome

Alport syndrome is a human hereditary glomerulonephritis which results in end-stage renal failure (ESRF) in most cases. It is caused by mutations in any one of the collagen alpha3(IV), alpha4(IV), or alpha5(IV) chain genes (COL4A3-COL4A5). Patients carrying identical mutations can exhibit very different disease courses, suggesting that other genes or the environment influence disease progression. We previously generated a knockout mouse model of Alport syndrome by mutating Col4a3. Here, we show that genetic background strongly influences the timing of onset of disease and rate of progression to ESRF in these mice. On the 129X1/SvJ background, Col4a3 -/- mice reached ESRF at approximately 66 days of age, while on the C57BL/6J background, the mean age at ESRF was 194 days of age. This suggests the existence of modifier genes that influence disease progression. A detailed histopathological analysis revealed that glomerular basement membrane lesions typical of Alport syndrome were significantly more frequent in homozygotes on the 129X1/SvJ background than on the C57BL/6J background as early as two weeks of age, suggesting that modifier genes act by influencing glomerular basement membrane structure. Additional data indicated that differential physiological responses to basement membrane splitting also underlie the differences in disease progression. We attempted to map the modifier genes as quantitative trait loci (QTLs) using age at ESRF as the quantitative trait. Genome scans were performed on mice at the two extremes in a cohort of mutant F1 x C57BL/6J backcross mice. Analysis with Map Manager QT revealed QTLs linked to markers on chromosomes 9 and 16. A more detailed understanding of how these QTLs act could lead to new approaches for therapy in diverse renal diseases.

Abnormal glomerular basement membrane laminins in murine, canine, and human Alport syndrome: aberrant laminin alpha2 deposition is species independent

Kidneys from mice, dogs, and humans with X-linked and autosomal-recessive forms of Alport syndrome were examined by immunofluorescence for expression of laminin alpha, beta, and gamma chains using monospecific antibodies. Laminin alpha2 chain was absent from glomerular basement membranes (GBM) in normal human, murine, and canine kidneys but was abnormally deposited in Alport GBM, regardless of species or inheritance pattern. In murine and canine Alport kidneys, laminin alpha2 seems to be deposited as part of both laminin-2 (alpha2beta1gamma1) and laminin-4 (alpha2beta2gamma1) but as part of only laminin-4 in human Alport kidneys. GBM laminin alpha2 chain deposition was not observed in a variety of non-Alport human glomerulopathies. This finding adds to the list of proteins that are aberrantly deposited in Alport GBM as a consequence of the absence of the alpha3, alpha4, and alpha5 chains of type IV collagen: (1) type IV collagen alpha1 and alpha2 chains, (2) type V collagen, (3) type VI collagen, and most recently (4) the laminin alpha2 chain and (5) the laminin alpha1 and beta1 chains in mice and dogs. These findings emphasize further the critical role played by the alpha3, alpha4, and alpha5 chains of type IV collagen in establishing and maintaining the composition, structure, and function of mature GBM.

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.

Expression of the alpha6 chain of type IV collagen in glomerular basement membranes of healthy adult dogs

OBJECTIVE

To evaluate expression of the alpha6 chain of type IV collagen in the glomerular basement membranes (GBM) of healthy dogs.

SAMPLE POPULATION

Kidney specimens from 12 healthy dogs. For comparison, kidney specimens from 8 human subjects between 25 and 83 years old also were evaluated.

PROCEDURE

Sections were immunolabeled with a monospecific antibody that cross-reacts with human and canine alpha6(IV) chains and examined by means of fluorescence microscopy.

RESULTS

Immunolabeling of the alpha6(IV) chain was not observed in GBM of 6 dogs < or = 30 months old but was observed in GBM of the remaining 6 dogs, all of which were > or = 45 months old. Expression of the alpha6(IV) chain was not observed in GBM of the human subjects, regardless of the age of the subject.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicate that the alpha6(IV) chain is expressed in GBM of healthy dogs, but the expression is age-dependent. Composition and structural organization of type IV collagen in the GBM of healthy adult dogs is different from that described for other species.

Familial glomerulonephropathy in a litter of beagles

Membranoproliferative glomerulonephropathy was diagnosed in 5 of 7 adult Beagles from the same litter. Dogs were raised in more than 1 area of the United States. One died without evidence of renal disease when it was 3 years old. At 8 years of age, 2 dogs developed signs of uremia, including polyuria, polydipsia, and infrequent episodes of anorexia and vomiting. Serum biochemical variables and urine specific gravity values were consistent with renal azotemia. Both dogs had proteinuria. Although healthy, 3 of the 4 remaining Beagles had proteinuria. Of these 3, only 1 was azotemic. Membranoproliferative glomerulonephritis was diagnosed on the basis of results of histologic examination of renal biopsy specimens from 4 of the dogs. Electron microscopy performed on 3 of the renal biopsy specimens revealed identical lesions, consisting of an extremely thickened glomerular basement membrane with multilaminar splitting. Immunoglobulin or amyloid deposits were not detected. On the basis of similar clinicopathologic abnormalities, common genetic background, and identical histopathologic and electron microscopic findings, familial renal disease was diagnosed. Additional studies involving other related Beagles are needed to identify the hereditary nature of membranoproliferative glomerulonephropathy in Beagles.

Insertional mutation of the collagen genes Col4a3 and Col4a4 in a mouse model of Alport syndrome

Mice homozygous for the transgenic insertion in line OVE250 exhibit severe progressive glomerulonephritis. Ultrastructural changes in the glomerular basement membrane (GBM) at 2 weeks of age resemble those in Alport syndrome. The transgenic insertion site was mapped by FISH to mouse chromosome 1 close to Pax3. Genetic and molecular analyses identified a deletion of genomic DNA at the transgene insertion site. Exons 1 through 12 of the collagen IV gene Col4a4, exons 1 and 2 of the adjacent Col4a3 gene, and the intergenic promoter region are deleted. Transcripts of Col4a3 and Col4a4 are undetectable in mutant kidney, and both proteins are missing from the GBM. Persistent cellular proliferation in mutant kidneys suggests that interaction with the extracellular matrix may be important for cell maturation. Evolutionarily conserved sequence elements in the promoter regions of human and mouse Col4a3 and Col4a4 include a 19-bp element that was tandemly duplicated in the human lineage and a CTC box element common to several genes encoding extracellular matrix proteins. This new animal model of Alport syndrome, Col4Delta3-4, lacks both alpha3 and alpha4 chains of collagen IV and exhibits an earlier disease onset than mice lacking alpha3 only.

Alport syndrome. An inherited disorder of renal, ocular, and cochlear basement membranes

Alport syndrome (AS) is a genetically heterogeneous disease arising from mutations in genes coding for basement membrane type IV collagen. About 80% of AS is X-linked, due to mutations in COL4A5, the gene encoding the alpha 5 chain of type IV collagen (alpha 5[IV]). A subtype of X-linked Alport syndrome (XLAS) in which diffuse leiomyomatosis is an associated feature reflects deletion mutations involving the adjacent COL4A5 and COL4A6 genes. Most other patients have autosomal recessive Alport syndrome (ARAS) due to mutations in COL4A3 or COL4A4, which encode the alpha 3(IV) and alpha 4(IV) chains, respectively. Autosomal dominant AS has been mapped to chromosome 2 in the region of COL4A3 and COL4A4. The features of AS reflect derangements of basement membrane structure and function resulting from changes in type IV collagen expression. The primary pathologic event appears to be the loss from basement membranes of a type IV collagen network composed of alpha 3, alpha 4, and alpha 5(IV) chains. While this network is not critical for normal glomerulogenesis, its absence appears to provoke the overexpression of other extracellular matrix proteins, such as the alpha 1 and alpha 2(IV) chains, in glomerular basement membranes, leading to glomerulosclerosis. The diagnosis of AS still relies heavily on histologic studies, although routine application of molecular genetic diagnosis will probably be available in the future. Absence of epidermal basement membrane expression of alpha 5(IV) is diagnostic of XLAS, so in some cases kidney biopsy may not be necessary for diagnosis. Analysis of renal expression of alpha 3(IV)-alpha 5(IV) chains may be a useful adjunct to routine renal biopsy studies, especially when ultrastructural changes in the GBM are ambiguous. There are no specific therapies for AS. Spontaneous and engineered animal models are being used to study genetic and pharmacologic therapies. Renal transplantation for AS is usually very successful. Occasional patients develop anti-GBM nephritis of the allograft, almost always resulting in graft loss.