Chronic renal failure and shortened lifespan in COL4A3+/- mice: an animal model for thin basement membrane nephropathy

Phosphate induces inflammation and exacerbates injury from cigarette smoke in the bronchial epithelium

An elevation in serum phosphate-also called hyperphosphatemia-is associated with reduced kidney function in chronic kidney disease (CKD). Reports show CKD patients are more likely to develop lung disease and have poorer kidney function that positively correlates with pulmonary obstruction. However, the underlying mechanisms are not well understood. Here, we report that two murine models of CKD, which both exhibit increased serum levels of phosphate and fibroblast growth factor (FGF) 23, a regulator of phosphate homeostasis, develop concomitant airway inflammation. Our in vitro studies point towards a similar increase of phosphate-induced inflammatory markers in human bronchial epithelial cells. FGF23 stimulation alone does not induce a proinflammatory response in the non-COPD bronchial epithelium and phosphate does not cause endogenous FGF23 release. Upregulation of the phosphate-induced proinflammatory cytokines is accompanied by activation of the extracellular-signal regulated kinase (ERK) pathway. Moreover, the addition of cigarette smoke extract (CSE) during phosphate treatments exacerbates inflammation as well as ERK activation, whereas co-treatment with FGF23 attenuates both the phosphate as well as the combined phosphate- and CS-induced inflammatory response, independent of ERK activation. Together, these data demonstrate a novel pathway that potentially explains pathological kidney-lung crosstalk with phosphate as a key mediator.

A glycine substitution in the collagenous domain of Col4a3 in mice recapitulates late onset Alport syndrome

Alport syndrome (AS) is a severe inherited glomerulopathy caused by mutations in the genes encoding the α-chains of type-IV collagen, the most abundant component of the extracellular glomerular basement membrane (GBM). Currently most AS mouse models are knockout models for one of the collagen-IV genes. In contrast, about half of AS patients have missense mutations, with single aminoacid substitutions of glycine being the most common. The only mouse model for AS with a homozygous knockin missense mutation, Col4a3-p.Gly1332Glu, was partly described before by our group. Here, a detailed in-depth description of the same mouse is presented, along with another compound heterozygous mouse that carries the glycine substitution in trans with a knockout allele. Both mice recapitulate essential features of AS, including shorten lifespan by 30–35%, increased proteinuria, increased serum urea and creatinine, pathognomonic alternate GBM thinning and thickening, and podocyte foot process effacement. Notably, glomeruli and tubuli respond differently to mutant collagen-IV protomers, with reduced expression in tubules but apparently normal in glomeruli. However, equally important is the fact that in the glomeruli the mutant α3-chain as well as the normal α4/α5 chains seem to undergo a cleavage at, or near the point of the mutation, possibly by the metalloproteinase MMP-9, producing a 35 kDa C-terminal fragment. These mouse models represent a good tool for better understanding the spectrum of molecular mechanisms governing collagen-IV nephropathies and could be used for pre-clinical studies aimed at better treatments for AS.

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Two mouse models were generated that recapitulate essential features of AS patients.

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Glomeruli and tubuli respond differently to mutant collagen IV protomers.

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The mutant colIV protomers in glomeruli probably undergo a cleavage process by MMP9.

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The two AS mouse models represent a good tool for studying collagen-IV nephropathies.

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These models could be used for pre-clinical studies aimed at better treatments.

Connectivity mapping of a chronic kidney disease progression signature identified lysine deacetylases as novel therapeutic targets

Tubulointerstitial injury is an important determinant of chronic kidney disease progression, yet treatment is limited. Accordingly, we derived a chronic kidney disease progression signature based on aging and disease in Col4a3^-/- mice, a model associated with proteinuria and progressive loss of kidney function. Computational drug repurposing with the Connectivity Map identified vorinostat, a lysine deacetylase inhibitor, as a candidate treatment to reverse progression signature gene expression. Vorinostat administration significantly increased the lifespan of Col4a3^-/- mice and attenuated tubulointerstitial fibrosis and JNK phosphorylation in the kidneys of Col4a3^-/- mice. In vitro, vorinostat reduced albumin- and angiotensin II-induced activation of canonical mitogen-activated protein kinases in kidney tubular epithelial cells. Finally, a subset of murine progression signature genes was differentially expressed across kidney transcriptomic data from patients with focal segmental glomerulosclerosis, IgA nephropathy, and diabetic nephropathy. Thus, our findings suggest that lysine deacetylase inhibition may be a novel treatment to chronic kidney disease associated with proteinuria and progressive tubulointerstitial injury.

Glomerular Basement Membrane Protein Expression and the Diagnosis and Prognosis of Autosomal Dominant Alport Syndrome

Alport syndrome is a hereditary glomerular nephritis associated with hearing loss and eye abnormalities and is classified as X-linked Alport syndrome, autosomal recessive Alport syndrome, and autosomal dominant Alport syndrome. Autosomal dominant Alport syndrome is caused by a mutation in the gene encoding type IV collagen α3 (α3[IV]); (COL4A3), or α4 (α4[IV]); (COL4A4). Autosomal dominant Alport syndrome progresses more gradually than male X-linked Alport syndrome and autosomal recessive Alport syndrome. Differentiating autosomal dominant Alport syndrome from thin basement membrane nephropathy, which shows better kidney prognosis, remains challenging. Because autosomal dominant Alport syndrome is linked to a heterozygous mutation, type IV collagen is produced by the wild-type allele, and all α(IV) chains are supposed to be normally expressed. In this study, the pathologic findings of a patient with Alport syndrome with a novel COL4A4 heterozygous nonsense mutation were investigated. We observed weaker staining of α5(IV) in the glomerular basement membrane and enhanced expressions of α2(IV), laminin, and fibronectin, which were assumed to be caused by compensatory mechanisms for lack of enough α3α4α5(IV) expression in the glomerular basement membrane. These findings may be useful not only for differentially diagnosing autosomal dominant Alport syndrome from thin basement membrane nephropathy, but also for determining the extent of progression and predicting kidney prognosis.

Transplantation of umbilical cord mesenchymal stem cells into mice with focal segmental glomerulosclerosis delayed disease manifestation

Background

Familial focal segmental glomerulosclerosis (fFSGS) is difficult to treat, and stem cell transplantation is one of the most promising approaches for treating this condition. According to the novel mutation site found in our FSGS family, we established a novel animal model of FSGS to explore the application of stem cell therapy in FSGS.

Methods

The animal model used in this experiment was p.Gly1617Valfs X15 (C57BL/6) mutant mice. This mutation was first found in a focal segmental glomerulosclerosis (FSGS) family undergoing renal biopsy in our department. The mouse model was then constructed via CRISPR/Cas9 genomic editing technology. Then, the animals were injected with human umbilical cord mesenchymal stem cells (UCMSC) through the tail vein and regularly followed up to determine phenotypic changes in urine protein quantities, serum creatinine and histological outcomes.

Results

Compared with the positive control group, the levels of urinary protein and serum creatine were decreased significantly after UCMSC transplantation. HE staining images revealed a delay in glomerular sclerosis. Moreover, the secretion of the type IV collagen α3 chain was significantly increased compared with the positive control group, as shown by using immunofluorescence microscopic observation, and electron microscopy proved that the podocytes and basement membrane recovered well from the damage. The intervention also resulted in enhanced IL-22 expression.

Conclusions

UCMSC transplantation may be a potential treatment for FSGS, and IL-22 may play an important role in this process. Further studies are needed to reveal the underlying mechanism.

Kidney Injury by Variants in the COL4A5 Gene Aggravated by Polymorphisms in Slit Diaphragm Genes Causes Focal Segmental Glomerulosclerosis

Kidney injury due to focal segmental glomerulosclerosis (FSGS) is the most common primary glomerular disorder causing end-stage renal disease. Homozygous mutations in either glomerular basement membrane or slit diaphragm genes cause early renal failure. Heterozygous carriers develop renal symptoms late, if at all. In contrast to mutations in slit diaphragm genes, hetero- or hemizygous mutations in the X-chromosomal COL4A5 Alport gene have not yet been recognized as a major cause of kidney injury by FSGS. We identified cases of FSGS that were unexpectedly diagnosed: In addition to mutations in the X-chromosomal COL4A5 type IV collagen gene, nephrin and podocin polymorphisms aggravated kidney damage, leading to FSGS with ruptures of the basement membrane in a toddler and early renal failure in heterozygous girls. The results of our case series study suggest a synergistic role for genes encoding basement membrane and slit diaphragm proteins as a cause of kidney injury due to FSGS. Our results demonstrate that the molecular genetics of different players in the glomerular filtration barrier can be used to evaluate causes of kidney injury. Given the high frequency of X-chromosomal carriers of Alport genes, the analysis of genes involved in the organization of podocyte architecture, the glomerular basement membrane, and the slit diaphragm will further improve our understanding of the pathogenesis of FSGS and guide prognosis of and therapy for hereditary glomerular kidney diseases.

Genetische Ursachen und Therapie beim Alport-Syndrom

Bei der Typ IV Kollagen-Erkrankung Alport-Syndrom (AS) handelt es sich um eine progressive hereditäre Nephropathie. Klinische Zeichen sind zunächst Hämaturie und Proteinurie, im weiteren Verlauf kommt es zu einem terminalen Nierenversagen. Zusätzlich werden extrarenale Manifestationen wie Innenohr-Schwerhörigkeit und Augenveränderungen beobachtet. Man unterscheidet drei Erbgänge: 85 % der Fälle sind X-chromosomal, ca. 10 % autosomal und weniger als 5 % digenisch. Ursächlich sind Varianten in den Kollagen Typ IV-Genen COL4A3, COL4A4 (beide autosomal) und COL4A5 (X-chromosomal). Die Symptomatik heterozygoter Anlageträger wurde früher als benigne familiäre Hämaturie bezeichnet. Da Anlageträger jedoch häufig keinen benignen Verlauf zeigen, werden sie inzwischen auch unter der Diagnose „Alport-Syndrom“ geführt.

Der Humangenetiker hat daher beim AS eine wichtige Lotsenfunktion: Bei früher Diagnose ist das AS inzwischen gut behandelbar, wodurch das terminale Nierenversagen um mehrere Jahre hinausgezögert und damit die Lebenserwartung verbessert werden kann. Aufgrund der Therapiemöglichkeiten sollte die (molekulargenetische) Diagnose bei Betroffenen, auch bei heterozygoten Anlageträgern, frühzeitig gestellt werden.

Mit diesem Artikel sollen die genetischen Ursachen des AS, mögliche genetische Einflussfaktoren auf den variablen Phänotyp, die unterschiedlichen Krankheitsstadien, Komplikationen sowie die derzeit zugelassene Behandlung aufgezeigt werden, um eine bestmögliche lebenslange Betreuung des Patienten zu gewährleisten.

COL4A3 Gene Variants and Diabetic Kidney Disease in MODY

BACKGROUND AND OBJECTIVES

Despite advances in identifying genetic factors of diabetic kidney disease (DKD), much of the heritability remains unexplained. Nine maturity-onset diabetes in young (MODY) probands with kidney biopsy-proven DKD were selected and included in this study. The probands had more severe DKD compared with their parents with MODY, with overt proteinuria or rapid progression to ESKD. We aimed to explore the contribution of the variants in susceptibility genes of DKD to the severity of kidney phenotype between the probands and their parents.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Whole-exome sequencing was performed to identify suspected MODY probands and their families. Known DKD susceptibility genes were reviewed. Variants reported to be associated with DKD, or those with minor allele frequency <0.05 and predicted to be pathogenic, were selected and analyzed. Immunofluorescence staining of COL4α3 was performed in kidney specimens of patients with DKD with or without R408H and M1209I of COL4A3 variants.

RESULTS

HNF1B-MODY, CEL-MODY, PAX4-MODY, and WFS1-MODY were diagnosed among nine families. We identified 196 selected variants of 25 DKD susceptibility genes among the participants. Analysis of phenotype between probands and parents, gene function, and protein-protein interaction networks revealed that COL4A3 variants were involved in the progression of DKD. Weak granular staining of COL4α3 was observed in the glomerular basement membrane of patients with the R408H and M1209I variants, whereas strong consecutive staining was observed in patients without these variants. Moreover, more number of DKD variants were identified in probands than in their parents with MODY.

CONCLUSIONS

The genetic effect of more pathogenic variants in various DKD susceptibility genes, especially variants in the COL4A3 gene, partially explained the more severe kidney phenotype in probands with kidney biopsy-proven DKD.

Genetic basis of adult-onset nephrotic syndrome and focal segmental glomerulosclerosis

Nephrotic syndrome (NS) is one of the most common glomerular diseases with signs of nephrosis, heavy proteinuria, hypoalbuminemia, and edema. Dysfunction of glomerular filtration barrier causes protein loss through the kidneys. Focal segmental glomerulosclerosis (FSGS) accounts for nearly 20% of NS among children and adults. Adult-onset FSGS/NS is often associated with low response to steroid treatment and immunosuppressive medication and poor renal survival. Several genes involved in NS and FSGS have been identified by linkage analysis and next-generation sequencing. Most of these genes encode proteins and are highly expressed in glomerular podocytes, which play crucial roles in slit-diaphragm signaling, regulation of actin cytoskeleton dynamics and maintenance of podocyte integrity, and cell-matrix interactions. In this review, we focus on the recently identified genes in the adult-onset NS and FSGS and discuss clinical significance of screening of these genes.

Novel mutations in COL4A3, COL4A4, and COL4A5 in Chinese patients with Alport Syndrome

Alport syndrome (AS) is a clinically and genetically heterogeneous, progressive nephropathy caused by mutations in COL4A3, COL4A4, and COL4A5, which encode type IV collagen. The large sizes of these genes and the absence of mutation hot spots have complicated mutational analysis by routine polymerase chain reaction (PCR)-based approaches. Here, in order to design a rapid and effective method for the genetic diagnosis of AS, we developed a strategy by utilizing targeted capture associated with next-generation sequencing (NGS) to analyze COL4A3, COL4A4, and COL4A5 simultaneously in 20 AS patients. All the coding exons and flanking sequences of COL4A3, COL4A4, and COL4A5 from the probands were captured followed by HiSeq 2500 sequencing. Candidate mutations were validated by classic Sanger sequencing and quantitative (q)PCR. Sixteen patients (16/20, 75%) showed X-linked inheritance, and four patients (4/20, 20%) showed autosomal recessive inheritance. None of the individuals had autosomal-dominant AS. Fifteen novel mutations, 6 known mutations, and 2 novel fragment deletions were detected by targeted capture and NGS. Of these novel mutations, 12, 3, and 2 mutations were detected in COL4A5, COL4A4, and COL4A3, respectively. A comparison of the clinical manifestations caused by different types of mutations in COL4A5 suggested that nonsense mutations and glycine substitution by an acidic amino acid are more severe than the other missense mutations. Pathogenic mutations were detected in 20 patients. These novel mutations can expand the genotypic spectrum of AS. Our results demonstrated that targeted capture and NGS technology are effective in the genetic diagnosis of AS.

A functional variant in NEPH3 gene confers high risk of renal failure in primary hematuric glomerulopathies. Evidence for predisposition to microalbuminuria in the general population

Background

Recent data emphasize that thin basement membrane nephropathy (TBMN) should not be viewed as a form of benign familial hematuria since chronic renal failure (CRF) and even end-stage renal disease (ESRD), is a possible development for a subset of patients on long-term follow-up, through the onset of focal and segmental glomerulosclerosis (FSGS). We hypothesize that genetic modifiers may explain this variability of symptoms.

Methods

We looked in silico for potentially deleterious functional SNPs, using very strict criteria, in all the genes significantly expressed in the slit diaphragm (SD). Two variants were genotyped in a cohort of well-studied adult TBMN patients from 19 Greek-Cypriot families, with a homogeneous genetic background. Patients were categorized as “Severe” or “Mild”, based on the presence or not of proteinuria, CRF and ESRD. A larger pooled cohort (HEMATURIA) of 524 patients, including IgA nephropathy patients, was used for verification. Additionally, three large general population cohorts [Framingham Heart Study (FHS), KORAF4 and SAPHIR] were used to investigate if the NEPH3-V353M variant has any renal effect in the general population.

Results and conclusions

Genotyping for two high-scored variants in 103 TBMN adult patients with founder mutations who were classified as mildly or severely affected, pointed to an association with variant NEPH3-V353M (filtrin). This promising result prompted testing in the larger pooled cohort (HEMATURIA), indicating an association of the 353M variant with disease severity under the dominant model (p = 3.0x10^-3, OR = 6.64 adjusting for gender/age; allelic association: p = 4.2x10^-3 adjusting for patients’ kinships). Subsequently, genotyping 6,531 subjects of the Framingham Heart Study (FHS) revealed an association of the homozygous 353M/M genotype with microalbuminuria (p = 1.0x10^-3). Two further general population cohorts, KORAF4 and SAPHIR confirmed the association, and a meta-analysis of all three cohorts (11,258 individuals) was highly significant (p = 1.3x10^-5, OR = 7.46). Functional studies showed that Neph3 homodimerization and Neph3-Nephrin heterodimerization are disturbed by variant 353M. Additionally, 353M was associated with differential activation of the unfolded protein response pathway, when overexpressed in stressed cultured undifferentiated podocyte cells, thus attesting to its functional significance. Genetics and functional studies support a “rare variant-strong effect” role for NEPH3-V353M, by exerting a negative modifier effect on primary glomerular hematuria. Additionally, genetics studies provide evidence for a role in predisposing homozygous subjects of the general population to micro-albuminuria.

A biomimetic gelatin-based platform elicits a pro-differentiation effect on podocytes through mechanotransduction

Using a gelatin microbial transglutaminase (gelatin-mTG) cell culture platform tuned to exhibit stiffness spanning that of healthy and diseased glomeruli, we demonstrate that kidney podocytes show marked stiffness sensitivity. Podocyte-specific markers that are critical in the formation of the renal filtration barrier are found to be regulated in association with stiffness-mediated cellular behaviors. While podocytes typically de-differentiate in culture and show diminished physiological function in nephropathies characterized by altered tissue stiffness, we show that gelatin-mTG substrates with Young’s modulus near that of healthy glomeruli elicit a pro-differentiation and maturation response in podocytes better than substrates either softer or stiffer. The pro-differentiation phenotype is characterized by upregulation of gene and protein expression associated with podocyte function, which is observed for podocytes cultured on gelatin-mTG gels of physiological stiffness independent of extracellular matrix coating type and density. Signaling pathways involved in stiffness-mediated podocyte behaviors are identified, revealing the interdependence of podocyte mechanotransduction and maintenance of their physiological function. This study also highlights the utility of the gelatin-mTG platform as an in vitro system with tunable stiffness over a range relevant for recapitulating mechanical properties of soft tissues, suggesting its potential impact on a wide range of research in cellular biophysics.

Prospective study on the potential of RAAS blockade to halt renal disease in Alport syndrome patients with heterozygous mutations

BACKGROUND

Patients with autosomal or X-linked Alport syndrome (AS) with heterozygous mutations in type IV collagen genes have a 1-20 % risk of progressing to end-stage renal disease during their lifetime. We evaluated the long-term renal outcome of patients at risk of progressive disease (chronic kidney disease stages 1-4) with/without nephroprotective therapy.

METHODS

This was a prospective, non-interventional, observational study which included data from a 4-year follow-up of AS patients with heterozygous mutations whose datasets had been included in an analysis of the 2010 database of the European Alport Registry. Using Kaplan-Meier estimates and logrank tests, we prospectively analyzed the updated datasets of 52 of these patients and 13 new datasets (patients added to the Registry after 2011). The effects of therapy, extrarenal symptoms and inheritance pattern on renal outcome were analyzed.

RESULTS

The mean prospective follow-up was 46 ± 10 months, and the mean time on therapy was 8.4 ± 4.4 (median 7; range 2-18) years. The time from the appearance of the first symptom to diagnosis was 8.1 ± 14.2 (range 0-52) years. At the time of starting therapy, 5.4 % of patients had an estimated glomerular filtration rate of <60 ml/min, 67.6 % had proteinuria and 27.0 % had microalbuminuria. Therapeutic strategies included angiotensin-converting enzymer inhibitors (97.1 %), angiotensin receptor antagonists (1 patient), dual therapy (11.8 %) and statins (8.8 %). Among patients included in the prospective dataset, prevented the need for dialysis. Among new patients, no patient at risk for renal failure progressed to the next disease stage after 4 years follow-up; three patients even regressed to a lower stage during therapy.

CONCLUSIONS

Treatment with blockers of the renin-angiotensin-aldosterone system prevents progressive renal failure in AS patients with heterozygous mutations in the genes causing AS. Considerable numbers of aging AS patients on dialysis may have heterozygous mutations in these genes (present in 1 % of total population) as underlying disease. Hence, greater alertness towards timely diagnosis and therapy has the potential to prevent progressive renal failure in most-if not all-AS patients with heterozygous mutations in the causal genes.

COL4A3 mutations cause focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is a histologically identifiable glomerular injury often leading to proteinuria and renal failure. To identify its causal genes, whole-exome sequencing and Sanger sequencing were performed on a large Chinese cohort that comprised 40 FSGS families, 50 sporadic FSGS patients, 9 independent autosomal recessive Alport's syndrome (ARAS) patients, and 190 ethnically matched healthy controls. Patients with extrarenal manifestations, indicating systemic diseases or other known hereditary renal diseases, were excluded. Heterozygous COL4A3 mutations were identified in five (12.5%) FSGS families and one (2%) sporadic FSGS patient. All identified mutations disrupted highly conserved protein sequences and none of them was found in either public databases or the 190 healthy controls. Of the FSGS patients with heterozygous COL4A3 mutations, segmental thinning of the glomerular base membrane (GBM) was only detected in the patient with electronic microscopy examination results available. Five ARAS patients (55.6%) had homozygous or compound-heterozygous mutations in COL4A3 or COL4A4. Serious changes in the GBM, hearing loss, and ocular abnormalities were found in 100%, 80%, and 40% of the ARAS patients, respectively. Overall, a new subgroup of FSGS patients resulting from heterozygous COL4A3 mutations was identified. The mutations are relatively frequent in families diagnosed with inherited forms of FSGS. Thus, we suggest screening for COL4A3 mutations in familial FSGS patients.

Carriers of Autosomal Recessive Alport Syndrome with Thin Basement Membrane Nephropathy Presenting as Focal Segmental Glomerulosclerosis in Later Life

Collagen IV nephropathies (COL4Ns) comprise benign familial microscopic hematuria, thin basement membrane nephropathy (TBMN), X-linked Alport syndrome (AS) and also autosomal recessive and dominant AS. Apart from the X-linked form of AS, which is caused by hemizygous mutations in the COL4A5 gene, the other entities are caused by mutations in the COL4A3 or COL4A4 genes. The diagnosis of these conditions used to be based on clinical and/or histological findings of renal biopsies, but it is the new molecular genetics approach that revolutionised their investigation and proved particularly instrumental, especially, in many not so clear-cut cases. More recently, the spectrum of COL4N has expanded to include late onset focal segmental glomerulosclerosis (FSGS) that develops on top of TBMN in later life. Also, other reports showed that some patients with a primary diagnosis of familial FSGS proved to have variants in COL4 genes. In the presence of a renal biopsy picture of FSGS and in the absence of either electron microscopy studies or molecular genetic studies that point to TBMN and COL4N, the patient and his family may be mistakenly diagnosed with hereditary FSGS leading to unnecessary further investigations, erroneous family counselling and improper corticosteroid treatment. TBMN is a frequent finding in the general population, and according to several recent reports, it may be the underlying cause and the explanation for many familial and sporadic cases of late-onset FSGS with non-nephrotic proteinuria. This is an important new finding that needs widespread recognition. It is anticipated that the molecular genetic analysis with next generation sequencing will certainly offer timely correct diagnosis.

Translational value of animal models of kidney failure

Acute kidney injury (AKI) and chronic kidney disease (CKD) are associated with decreased renal function and increased mortality risk, while the therapeutic armamentarium is unsatisfactory. The availability of adequate animal models may speed up the discovery of biomarkers for disease staging and therapy individualization as well as design and testing of novel therapeutic strategies. Some longstanding animal models have failed to result in therapeutic advances in the clinical setting, such as kidney ischemia-reperfusion injury and diabetic nephropathy models. In this regard, most models for diabetic nephropathy are unsatisfactory in that they do not evolve to renal failure. Satisfactory models for additional nephropathies are needed. These include anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis, IgA nephropathy, anti-phospholipase-A2-receptor (PLA2R) membranous nephropathy and Fabry nephropathy. However, recent novel models hold promise for clinical translation. Thus, the AKI to CKD translation has been modeled, in some cases with toxins of interest for human CKD such as aristolochic acid. Genetically modified mice provide models for Alport syndrome evolving to renal failure that have resulted in clinical recommendations, polycystic kidney disease models that have provided clues for the development of tolvaptan, that was recently approved for the human disease in Japan; and animal models also contributed to target C5 with eculizumab in hemolytic uremic syndrome. Some ongoing trials explore novel concepts derived from models, such TWEAK targeting as tissue protection for lupus nephritis. We now review animal models reproducing diverse, genetic and acquired, causes of AKI and CKD evolving to kidney failure and discuss the contribution to clinical translation and prospects for the future.

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.

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.

Epistatic role of the MYH9/APOL1 region on familial hematuria genes

Familial hematuria (FH) is explained by at least four different genes (see below). About 50% of patients develop late proteinuria and chronic kidney disease (CKD). We hypothesized that MYH9/APOL1, two closely linked genes associated with CKD, may be associated with adverse progression in FH. Our study included 102 thin basement membrane nephropathy (TBMN) patients with three known COL4A3/COL4A4 mutations (cohort A), 83 CFHR5/C3 glomerulopathy patients (cohort B) with a single CFHR5 mutation and 15 Alport syndrome patients (cohort C) with two known COL4A5 mild mutations, who were categorized as “Mild” (controls) or “Severe” (cases), based on renal manifestations. E1 and S1 MYH9 haplotypes and variant rs11089788 were analyzed for association with disease phenotype. Evidence for association with “Severe” progression in CFHR5 nephropathy was found with MYH9 variant rs11089788 and was confirmed in an independent FH cohort, D (cumulative p value = 0.001, odds ratio = 3.06, recessive model). No association was found with APOL1 gene. Quantitative Real time PCR did not reveal any functional significance for the rs11089788 risk allele. Our results derive additional evidence supporting previous reports according to which MYH9 is an important gene per se, predisposing to CKD, suggesting its usefulness as a prognostic marker for young hematuric patients.

Incidence of renal failure and nephroprotection by RAAS inhibition in heterozygous carriers of X-chromosomal and autosomal recessive Alport mutations

We studied here the clinical course of heterozygous carriers of X-linked Alport syndrome and a subgroup of patients with thin basement membrane disease due to heterozygous autosomal recessive Alport mutations whose prognosis may be worse than formerly thought. We analyzed 234 Alport carriers, including 29 with autosomal recessive mutations. Using Kaplan-Meier estimates and log-rank tests, autosomal and X-linked carriers were found to have similar incidences of renal replacement therapy, proteinuria, and impaired creatinine clearance. Further, age at onset of renal replacement therapy did not differ between X-chromosomal and autosomal carriers. Both groups showed an impaired life expectancy when reaching renal replacement therapy. RAAS inhibition significantly delayed the onset of end-stage renal failure. Not only carriers of X-linked Alport mutations but also heterozygous carriers of autosomal recessive mutations were found to have an increased risk for worse renal function. The risk of end-stage renal disease in both groups affected life expectancy, and this should cause a greater alertness toward patients presenting with what has been wrongly termed 'familial benign hematuria.' Timely therapy can help to delay onset of end-stage renal failure. Thus, yearly follow-up by a nephrologist is advised for X-linked Alport carriers and patients with thin basement membrane nephropathy, microalbuminuria, proteinuria, or hypertension.

Basement membranes in development and disease

Basement membranes (BMs) are specializations of the extracellular matrix that act as key mediators of development and disease. Their sheet like protein matrices typically serve to separate epithelial or endothelial cell layers from underlying mesenchymal tissues, providing both a biophysical support to overlying tissue as well as a hub to promote and regulate cell-cell and cell-protein interactions. In the latter context, the BM is increasingly being recognized as a mediator of growth factor interactions during development. In this review, we discuss recent findings regarding the structure of the BM and its roles in mediating the normal development of the embryo, and we examine congenital diseases affecting the BM which impact embryonic development and health in later life.

Deletion of von Hippel-Lindau in glomerular podocytes results in glomerular basement membrane thickening, ectopic subepithelial deposition of collagen {alpha}1{alpha}2{alpha}1(IV), expression of neuroglobin, and proteinuria

Vascular endothelial growth factor, which is critical for blood vessel formation, is regulated by hypoxia inducible transcription factors (HIFs). A component of the E3 ubiquitin ligase complex, von Hippel-Lindau (VHL) facilitates oxygen-dependent polyubiquitination and proteasomal degradation of HIFalpha subunits. Hypothesizing that deletion of podocyte VHL would result in HIFalpha hyperstabilization, we crossed podocin promoter-Cre transgenic mice, which express Cre recombinase in podocytes beginning at the capillary loop stage of glomerular development, with floxed VHL mice. Vascular patterning and glomerular development appeared unaltered in progeny lacking podocyte VHL. However, urinalysis showed increased albumin excretion by 4 weeks when compared with wild-type littermates with several sever cases (>1000 microg/ml). Many glomerular ultrastructural changes were seen in mutants, including focal subendothelial delamination and widespread podocyte foot process broadening, and glomerular basement membranes (GBMs) were significantly thicker in 16-week-old mutants compared with controls. Moreover, immunoelectron microscopy showed ectopic deposition of collagen alpha1alpha2alpha1(IV) in GBM humps beneath podocytes. Significant increases in the number of Ki-67-positive mesangial cells were also found, but glomerular WT1 expression was significantly decreased, signifying podocyte death and/or de-differentiation. Indeed, expression profiling of mutant glomeruli suggested a negative regulatory feedback loop involving the HIFalpha prolyl hydroxylase, Egln3. In addition, the brain oxygen-binding protein, Neuroglobin, was induced in mutant podocytes. We conclude that podocyte VHL is required for normal maintenance of podocytes, GBM composition and ultrastructure, and glomerular barrier properties.

Basement membranes and human disease

In 1990, the role of basement membranes in human disease was established by the identification of COL4A5 mutations in Alport's syndrome. Since then, the number of diseases caused by mutations in basement membrane components has steadily increased as has our understanding of the roles of basement membranes in organ development and function. However, many questions remain as to the molecular and cellular consequences of these mutations and the way in which they lead to the observed disease phenotypes. Despite this, exciting progress has recently been made with potential treatment options for some of these so far incurable diseases.

Clinico-pathological correlations in 127 patients in 11 large pedigrees, segregating one of three heterozygous mutations in the COL4A3/ COL4A4 genes associated with familial haematuria and significant late progression to proteinuria and chronic kidney disease from focal segmental glomerulosclerosis

BACKGROUND

Heterozygous mutations in the COL4A3/ COL4A4 genes are currently thought to be responsible for familial benign microscopic haematuria and maintenance of normal long-term kidney function.

METHODS

We report on 11 large Cypriot pedigrees with three such mutations. A total of 236 at-risk family members were genetically studied, and 127 (53.8%) carried a heterozygous mutation. Clinico-pathological correlations were available in all of these patients. Renal biopsies in 21 of these patients all showed various stages of focal, segmental glomerulosclerosis (FSGS). Thirteen of these biopsies were also studied with EM and showed thinning of the glomerular basement membrane.

RESULTS

Mutation G1334E (COL4A3) was found in six pedigrees, mutation G871C (COL4A3) in four and mutation 3854delG (COL4A4) in one pedigree. Clinical and laboratory correlations in all 127 mutation carriers (MC) showed that microscopic haematuria was the only urinary finding in patients under age 30. The prevalence of 'haematuria alone' fell to 66% between 31 and 50 years, to 30% between 51 and 70 and to 23% over age 71. Proteinuria with CRF developed on top of haematuria in 8% of all MC between 31 and 50 years, to 25% between 51 and 70 years and to 50% over 71 years. Altogether 18 of these 127 MC (14%) developed ESRD at a mean age of 60 years. Two members with different mutations married, and two of their children inherited both mutations and developed adolescent, autosomal recessive Alport syndrome (ATS), confirming that these mutations are pathogenic.

CONCLUSIONS

Our data confirm for the first time a definite association of heterozygous COL4A3/COL4A4 mutations with familial microscopic haematuria, thin basement membrane nephropathy and the late development of familial proteinuria, CRF, and ESRD, due to FSGS, indicating that the term 'benign familial haematuria' is a misnomer, at least in this cohort. A strong hypothesis for a causal relationship between these mutations and FSGS is also made. Benign familial haematuria may not be so benign as commonly thought.

A stable explant culture of HER2/neu invasive carcinoma supported by alpha-Smooth Muscle Actin expressing stromal cells to evaluate therapeutic agents

Background

To gain a better understanding of the effects of therapeutic agents on the tumor microenvironment in invasive cancers, we developed a co-culture model from an invasive lobular carcinoma. Tumor cells expressing HER2/neu organize in nests surrounded by alpha-Smooth Muscle Actin (α-SMA) expressing tumor stroma to resemble the morphology of an invading tumor. This co-culture, Mammary Adenocarcinoma Model (MAM-1) maintains a 1:1 ratio of HER2/neu positive tumor cells to α-SMA-reactive stromal cells and renews this configuration for over 20 passages in vitro.

Methods

We characterized the cellular elements of the MAM-1 model by microarray analysis, and immunocytochemistry. We developed flow cytometric assays to evaluate the relative responses of the tumor and stroma to the tyrosine kinase inhibitor, Iressa.

Results

The MAM-1 gene expression profile contains clusters that represent the ErbB-2 breast cancer signature and stroma-specific clusters associated with invasive breast cancers. The stability of this model and the ability to antigenically label the tumor and stromal fractions allowed us to determine the specificity of Iressa, a receptor tyrosine kinase inhibitor, for targeting the tumor cell population. Treatment resulted in a selective dose-dependent reduction in phospho-pMEK1/2 and pp44/42MAPK in tumor cells. Within 24 h the tumor cell fraction was reduced 1.9-fold while the stromal cell fraction increased >3-fold, consistent with specific reductions in phospho-pp44/42 MAPK, MEK1/2 and PCNA in tumor cells and reciprocal increases in the stromal cells. Erosion of the tumor cell nests and augmented growth of the stromal cells resembled a fibrotic response.

Conclusion

This model demonstrates the specificity of Iressa for HER2/neu expressing tumor cells versus the tumor associated myofibroblasts and is appropriate for delineating effects of therapy on signal transduction in the breast tumor microenvironment and improving strategies that can dually or differentially target the tumor and stromal elements in the microenvironment.

COL4A3/COL4A4 mutations link familial hematuria and focal segmental glomerulosclerosis. glomerular epithelium destruction via basement membrane thinning?

The recent description of multiple gene defects in hereditary podocytopathies and in hereditary glomerular basement membrane diseases has dramatically improved the current state of our knowledge on the renal glomerular filtration barrier. Recently described mutations in collagen IV and laminin in patients with hematuria and severe nephrotic syndrome add to other experimental data supporting the hypothesis that the glomerular basement membrane (GBM) may also have a significant role in protein filtration, a function previously attributed exclusively to the podocytes. Collagen IV heterozygous mutations were thought to cause only a mild form of renal disease (thin basement membrane nephropathy--TBMN). However, data from our laboratory show that many patients who carry such mutations may later on in life develop focal and segmental glomerulosclerosis, on top of the TBMN and the microscopic hematuria, a situation that frequently progresses to chronic renal failure or even end-stage renal disease. The role of unknown modifier genes may explain the heterogeneity of symptoms in TBMN and other glomerular diseases and in particular the selected development of chronic renal failure. The molecular communication between GBM and podocytes may also be a key factor in the search for these major genetic modifiers while their understanding may improve novel drug design for glomerular diseases.

COL4A3/COL4A4 mutations producing focal segmental glomerulosclerosis and renal failure in thin basement membrane nephropathy

Mutations in the COL4A3/COL4A4 genes of type IV collagen have been found in approximately 40% of cases of thin basement membrane nephropathy, which is characterized by microscopic hematuria and is classically thought to cause proteinuria and chronic renal failure rarely. Here we report our observations of 116 subjects from 13 Cypriot families clinically affected with thin basement membrane nephropathy. These families first came to our attention because they segregated microscopic hematuria, mild proteinuria, and variable degrees of renal impairment, but a dual diagnosis of focal segmental glomerulosclerosis (FSGS) and thin basement membrane nephropathy was made in 20 biopsied cases. Molecular studies identified founder mutations in both COL4A3 and COL4A4 genes in 10 families. None of 82 heterozygous patients had any extrarenal manifestations, supporting the diagnosis of thin basement membrane nephropathy. During follow-up of up to three decades, 31 of these 82 patients (37.8%) developed chronic renal failure and 16 (19.5%) reached end-stage renal disease. Mutations G1334E and G871C were detected in seven and three families, respectively, and were probably introduced by founders. We conclude that these particular COL4A3/COL4A4 mutations either predispose some patients to FSGS and chronic renal failure, or that thin basement membrane nephropathy sometimes coexists with another genetic modifier that is responsible for FSGS and progressive renal failure. The findings presented here do not justify the labelling of thin basement membrane nephropathy as a benign condition with excellent prognosis.

A novel mutation of COL4A3 presents a different contribution to Alport syndrome and thin basement membrane nephropathy

BACKGROUND

Alport syndrome (AS) and thin basement membrane nephropathy (TBMN) are heterogeneous renal hereditary diseases. Mutations of COL4A3 and COL4A4 genes were reported to be the underlying pathogenicity in both diseases. However, the mechanism of the same mutation causing totally different clinical processes and outcomes in AS and TBMN is still not clear.

SUBJECTS AND METHODS

Mutations of all coding exons of COL4A3 and COL4A4 were screened in a patient with autosomal recessive Alport syndrome (ARAS) of a Chinese Han consanguineous family by means of PCR and direct sequencing. Furthermore, the identified mutation was validated by restriction endonuclease AvaII in all 20 members in his family, as well as 46 patients with TBMN, 2 patients with AS from another two families, and 50 healthy controls.

RESULTS

A novel missense mutation (3725G>A, G1242D) in exon 42 of COL4A3 was identified in the proband in the homozygous form. This pathogenic mutation was demonstrated in all carriers who presented with hematuria or mild proteinuria in the heterozygous form, whereas it was not detected in others whose urinalysis was normal within the family. In addition, 10 polymorphisms, including 1 non-glycine missense variant and 9 neutral polymorphisms, were detected in COL4A3/COL4A4.

CONCLUSION

The novel mutation (3725G>A, G1242D) of COL4A3 was the underlying pathogenic role in the homozygous form in ARAS and in the heterozygous form in TBMN within an identical family. The result provided a potentially useful clue for the functional investigation of COL4A3 in these two hereditary glomerular disorders.

Laser capture microdissection-microarray analysis of focal segmental glomerulosclerosis glomeruli

Focal segmental glomerulosclerosis (FSGS) is a major cause of end-stage renal disease. In this report we used laser capture microdissection to purify diseased glomeruli, and microarrays to provide universal gene expression profiles. The results provide a deeper understanding of the molecular mechanisms of the disease process and suggest novel therapeutic strategies. Consistent with earlier studies, molecular markers of the differentiated podocyte, including WT1, nephrin, and VEGF, were dramatically downregulated in the diseased glomerulus. We also observed multiple changes consistent with increased TGF-beta signaling, including elevated expression of TGF-beta(2), TGF-beta(3), SMAD2, TGF-beta(1) receptor, and thrombospondin. In addition, there was relatively low level expression of Csf1r, a marker of macrophages, but elevated expression of the chemokines CXCL1, CXCL2, CCL3, and CXCL14. We also observed strongly upregulated expression of Sox9, a transcription factor that can drive a genetic program of chondrogenesis and fibrosis. Further, the gene with the greatest fold increase in expression in the diseased glomerulus was osteopontin, which has been previously strongly implicated in kidney fibrosis in the unilateral ureteral obstruction mouse model. These results confirm old findings, and indicate the involvement of new genetic pathways in the cause and progression of FSGS.

Alport syndrome and thin basement membrane nephropathy

Both Alport syndrome and thin basement membrane nephropathy (TBMN) can be considered as genetic diseases of the GBM involving the alpha3/alpha4/alpha5 network of type IV collagen. Mutations in any of the COL4A3, COL4A4 or COL4A5 genes can lead to total or partial loss of this network. Males with mutations in the X-linked COL4A5 gene develop Alport syndrome with progressive renal disease and sometimes extra-renal disease. Females who are heterozygous for a COL4A5 mutation are considered to be carriers for X-linked Alport syndrome. Although their clinical course and GBM ultrastructural changes can sometimes mimic TBMN, more often it tends to be more progressive than usually seen in TBMN. Males or females who are heterozygous for COL4A3 or COL4A4 mutations usually manifest as TBMN, with nonprogressive hematuria, while those who are homozygous or combined heterozygotes develop autosomal-recessive Alport syndrome. Thus, individuals with TBMN can be considered to be carriers for autosomal-recessive Alport syndrome, but there remain some exceptions in which patients heterozygous for COL4A3 or COL4A4 mutations develop autosomal-dominant Alport syndrome. Distinguishing between all these groups of patients requires a combination of family history and a renal biopsy for electron microscopic examination of the GBM and immunohistochemical staining of the GBM for the alpha3, alpha4 and alpha5 chains of type IV collagen. Mutational analysis of the COL4A3, COL4A4, and COL4A5 genes, whenever it becomes available, will be a valuable adjunct to the diagnostic workup in these patients. Novel therapeutic approaches may one day provide a treatment or cure for these patients, avoiding the need for transplantation and dialysis.