Genetic reprogramming with stem cells regenerates glomerular epithelial podocytes in Alport syndrome

Glomerular filtration relies on the type IV collagen (ColIV) network of the glomerular basement membrane, namely, in the triple helical molecules containing the α3, α4, and α5 chains of ColIV. Loss of function mutations in the genes encoding these chains (Col4a3, Col4a4, and Col4a5) is associated with the loss of renal function observed in Alport syndrome (AS). Precise understanding of the cellular basis for the patho-mechanism remains unknown and a specific therapy for this disease does not currently exist. Here, we generated a novel allele for the conditional deletion of Col4a3 in different glomerular cell types in mice. We found that podocytes specifically generate α3 chains in the developing glomerular basement membrane, and that its absence is sufficient to impair glomerular filtration as seen in AS. Next, we show that horizontal gene transfer, enhanced by TGFβ1 and using allogenic bone marrow-derived mesenchymal stem cells and induced pluripotent stem cells, rescues Col4a3 expression and revive kidney function in Col4a3-deficient AS mice. Our proof-of-concept study supports that horizontal gene transfer such as cell fusion enables cell-based therapy in Alport syndrome.

In chronic kidney disease altered cardiac metabolism precedes cardiac hypertrophy

Conduit arterial disease in chronic kidney disease (CKD) is an important cause of cardiac complications. Cardiac function in CKD has not been studied in the absence of arterial disease. In an Alport syndrome model bred not to have conduit arterial disease, mice at 225 days of life (dol) had CKD equivalent to humans with CKD stage 4-5. Parathyroid hormone (PTH) and FGF23 levels were one log order elevated, circulating sclerostin was elevated, and renal activin A was strongly induced. Aortic Ca levels were not increased, and vascular smooth muscle cell (VSMC) transdifferentiation was absent. The CKD mice were not hypertensive, and cardiac hypertrophy was absent. Freshly excised cardiac tissue respirometry (Oroboros) showed that ADP-stimulated O2 flux was diminished from 52 to 22 pmol/mg (P = 0.022). RNA-Seq of cardiac tissue from CKD mice revealed significantly decreased levels of cardiac mitochondrial oxidative phosphorylation genes. To examine the effect of activin A signaling, some Alport mice were treated with a monoclonal Ab to activin A or an isotype-matched IgG beginning at 75 days of life until euthanasia. Treatment with the activin A antibody (Ab) did not affect cardiac oxidative phosphorylation. However, the activin A antibody was active in the skeleton, disrupting the effect of CKD to stimulate osteoclast number, eroded surfaces, and the stimulation of osteoclast-driven remodeling. The data reported here show that cardiac mitochondrial respiration is impaired in CKD in the absence of conduit arterial disease. This is the first report of the direct effect of CKD on cardiac respiration.NEW & NOTEWORTHY Heart disease is an important morbidity of chronic kidney disease (CKD). Hypertension, vascular stiffness, and vascular calcification all contribute to cardiac pathophysiology. However, cardiac function in CKD devoid of vascular disease has not been studied. Here, in an animal model of human CKD without conduit arterial disease, we analyze cardiac respiration and discover that CKD directly impairs cardiac mitochondrial function by decreasing oxidative phosphorylation. Protection of cardiac oxidative phosphorylation may be a therapeutic target in CKD.

PDGF-D Is Dispensable for the Development and Progression of Murine Alport Syndrome

Alport syndrome is an inherited kidney disease, which can lead to glomerulosclerosis and fibrosis, as well as end-stage kidney disease in children and adults. Platelet-derived growth factor-D (PDGF-D) mediates glomerulosclerosis and interstitial fibrosis in various models of kidney disease, prompting investigation of its role in a murine model of Alport syndrome. In vitro, PDGF-D induced proliferation and profibrotic activation of conditionally immortalized human parietal epithelial cells. In Col4a3-/- mice, a model of Alport syndrome, PDGF-D mRNA and protein were significantly up-regulated compared with non-diseased wild-type mice. To analyze the therapeutic potential of PDGF-D inhibition, Col4a3-/- mice were treated with a PDGF-D neutralizing antibody. Surprisingly, PDGF-D antibody treatment had no effect on renal function, glomerulosclerosis, fibrosis, or other indices of kidney injury compared with control treatment with unspecific IgG. To characterize the role of PDGF-D in disease development, Col4a3-/- mice with a constitutive genetic deletion of Pdgfd were generated and analyzed. No difference in pathologic features or kidney function was observed in Col4a3-/-Pdgfd-/- mice compared with Col4a3-/-Pdgfd+/+ littermates, confirming the antibody treatment data. Mechanistically, lack of proteolytic PDGF-D activation in Col4a3-/- mice might explain the lack of effects in vivo. In conclusion, despite its established role in kidney fibrosis, PDGF-D, without further activation, does not mediate the development and progression of Alport syndrome in mice.

Ramipril therapy in integrin α1-null, autosomal recessive Alport mice triples lifespan: mechanistic clues from RNA-seq analysis

The standard of care for patients with Alport syndrome (AS) is angiotensin-converting enzyme (ACE) inhibitors. In autosomal recessive Alport (ARAS) mice, ACE inhibitors double lifespan. We previously showed that deletion of Itga1 in Alport mice [double-knockout (DKO) mice] increased lifespan by 50%. This effect seemed dependent on the prevention of laminin 211-mediated podocyte injury. Here, we treated DKO mice with vehicle or ramipril starting at 4 weeks of age. Proteinuria and glomerular filtration rates were measured at 5-week intervals. Glomeruli were analyzed for laminin 211 deposition in the glomerular basement membrane (GBM) and GBM ultrastructure was analyzed using transmission electron microscopy (TEM). RNA sequencing (RNA-seq) was performed on isolated glomeruli at all time points and the results were compared with cultured podocytes overlaid (or not) with recombinant laminin 211. Glomerular filtration rate declined in ramipril-treated DKO mice between 30 and 35 weeks. Proteinuria followed these same patterns with normalization of foot process architecture in ramipril-treated DKO mice. RNA-seq revealed a decline in the expression of Foxc2, nephrin (Nphs1), and podocin (Nphs2) mRNAs, which was delayed in the ramipril-treated DKO mice. GBM accumulation of laminin 211 was delayed in ramipril-treated DKO mice, likely due to a role for α1β1 integrin in CDC42 activation in Alport mesangial cells, which is required for mesangial filopodial invasion of the subendothelial spaces of the glomerular capillary loops. Ramipril synergized with Itga1 knockout, tripling lifespan compared with untreated ARAS mice. © 2023 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

iPSC-derived type IV collagen α5-expressing kidney organoids model Alport syndrome

Alport syndrome (AS) is a hereditary glomerulonephritis caused by COL4A3, COL4A4 or COL4A5 gene mutations and characterized by abnormalities of glomerular basement membranes (GBMs). Due to a lack of curative treatments, the condition proceeds to end-stage renal disease even in adolescents. Hampering drug discovery is the absence of effective in vitro methods for testing the restoration of normal GBMs. Here, we aimed to develop kidney organoid models from AS patient iPSCs for this purpose. We established iPSC-derived collagen α5(IV)-expressing kidney organoids and confirmed that kidney organoids from COL4A5 mutation-corrected iPSCs restore collagen α5(IV) protein expression. Importantly, our model recapitulates the differences in collagen composition between iPSC-derived kidney organoids from mild and severe AS cases. Furthermore, we demonstrate that a chemical chaperone, 4-phenyl butyric acid, has the potential to correct GBM abnormalities in kidney organoids showing mild AS phenotypes. This iPSC-derived kidney organoid model will contribute to drug discovery for AS.

X-linked Alport Syndrome with Type IV Collagen α5 Chain Staining Revealing Normal Expression in the Glomerular Basement Membrane and Negative on Bowman's Capsule and Distal Tubular Basement Membrane: A Case Report

X-linked Alport syndrome is a hereditary progressive renal disease resulting from the disruption of collagen α3α4α5 (IV) heterotrimerization caused by pathogenic variants in the COL4A5 gene. This study aimed to report a male case of X-linked Alport syndrome with a mild phenotype accompanied by an atypical expression pattern of type IV collagen α5 [α5 (IV)] chain in glomerulus. A 38-year-old male presented with proteinuria (2.3 g/day) and hematuria. He has been detected urinary protein and occult blood since childhood. A renal biopsy was performed at the age of 29 years; however, a diagnosis of Alport syndrome was not considered. A renal biopsy 9 years later revealed diffuse thinning and lamellation of the glomerular basement membrane. Α staining for α5 (IV) revealed a normal expression pattern in the glomerular basement membrane and a complete negative expression in Bowman's capsule and distal tubular basement membrane. Using next-generation sequencing, we detected a COL4A5 missense variant within exon 35 (NM_000495.5: c.3088G>A, p. G1030S). The possibility of X-linked Alport syndrome should be considered when negative expression of α5 (IV) staining on Bowman's capsule was observed.

Empagliflozin reduces podocyte lipotoxicity in experimental Alport syndrome

Sodium-glucose cotransporter-2 inhibitors (SGLT2i) are anti-hyperglycemic agents that prevent glucose reabsorption in proximal tubular cells. SGLT2i improves renal outcomes in both diabetic and non-diabetic patients, indicating it may have beneficial effects beyond glycemic control. Here, we demonstrate that SGLT2i affects energy metabolism and podocyte lipotoxicity in experimental Alport syndrome (AS). In vitro, we found that the SGLT2 protein was expressed in human and mouse podocytes to a similar extent in tubular cells. Newly established immortalized podocytes from Col4a3 knockout mice (AS podocytes) accumulate lipid droplets along with increased apoptosis when compared to wild-type podocytes. Treatment with SGLT2i empagliflozin reduces lipid droplet accumulation and apoptosis in AS podocytes. Empagliflozin inhibits the utilization of glucose/pyruvate as a metabolic substrate in AS podocytes but not in AS tubular cells. In vivo, we demonstrate that empagliflozin reduces albuminuria and prolongs the survival of AS mice. Empagliflozin-treated AS mice show decreased serum blood urea nitrogen and creatinine levels in association with reduced triglyceride and cholesterol ester content in kidney cortices when compared to AS mice. Lipid accumulation in kidney cortices correlates with a decline in renal function. In summary, empagliflozin reduces podocyte lipotoxicity and improves kidney function in experimental AS in association with the energy substrates switch from glucose to fatty acids in podocytes.

Activation of Stimulator of IFN Genes (STING) Causes Proteinuria and Contributes to Glomerular Diseases

BACKGROUND

The signaling molecule stimulator of IFN genes (STING) was identified as a crucial regulator of the DNA-sensing cyclic GMP-AMP synthase (cGAS)-STING pathway, and this signaling pathway regulates inflammation and energy homeostasis under conditions of obesity, kidney fibrosis, and AKI. However, the role of STING in causing CKD, including diabetic kidney disease (DKD) and Alport syndrome, is unknown.

METHODS

To investigate whether STING activation contributes to the development and progression of glomerular diseases such as DKD and Alport syndrome, immortalized human and murine podocytes were differentiated for 14 days and treated with a STING-specific agonist. We used diabetic db/db mice, mice with experimental Alport syndrome, C57BL/6 mice, and STING knockout mice to assess the role of the STING signaling pathway in kidney failure.

RESULTS

In vitro, murine and human podocytes express all of the components of the cGAS-STING pathway. In vivo, activation of STING renders C57BL/6 mice susceptible to albuminuria and podocyte loss. STING is activated at baseline in mice with experimental DKD and Alport syndrome. STING activation occurs in the glomerular but not the tubulointerstitial compartment in association with autophagic podocyte death in Alport syndrome mice and with apoptotic podocyte death in DKD mouse models. Genetic or pharmacologic inhibition of STING protects from progression of kidney disease in mice with DKD and Alport syndrome and increases lifespan in Alport syndrome mice.

CONCLUSION

The activation of the STING pathway acts as a mediator of disease progression in DKD and Alport syndrome. Targeting STING may offer a therapeutic option to treat glomerular diseases of metabolic and nonmetabolic origin or prevent their development, progression, or both.

Potential Renal Damage Biomarkers in Alport Syndrome—A Review of the Literature

Alport syndrome (AS) is the second most common cause of inherited chronic kidney disease. This disorder is caused by genetic variants on COL4A3, COL4A4 and COL4A5 genes. These genes encode the proteins that constitute collagen type IV of the glomerular basement membrane (GBM). The heterodimer COL4A3A4A5 constitutes the majority of the GBM, and it is essential for the normal function of the glomerular filtration barrier (GFB). Alterations in any of collagen type IV constituents cause disruption of the GMB structure, allowing leakage of red blood cells and albumin into the urine, and compromise the architecture of the GFB, inducing inflammation and fibrosis, thus resulting in kidney damage and loss of renal function. The advances in DNA sequencing technologies, such as next-generation sequencing, allow an accurate diagnose of AS. Due to the important risk of the development of progressive kidney disease in AS patients, which can be delayed or possibly prevented by timely initiation of therapy, an early diagnosis of this condition is mandatory. Conventional biomarkers such as albuminuria and serum creatinine increase relatively late in AS. A panel of biomarkers that might detect early renal damage, monitor therapy, and reflect the prognosis would have special interest in clinical practice. The aim of this systematic review is to summarize the biomarkers of renal damage in AS as described in the literature. We found that urinary Podocin and Vascular Endothelial Growth Factor A are important markers of podocyte injury. Urinary Epidermal Growth Factor has been related to tubular damage, interstitial fibrosis and rapid progression of the disease. Inflammatory markers such as Transforming Growth Factor Beta 1, High Motility Group Box 1 and Urinary Monocyte Chemoattractant Protein- 1 are also increased in AS and indicate a higher risk of kidney disease progression. Studies suggest that miRNA-21 is elevated when renal damage occurs. Novel techniques, such as proteomics and microRNAs, are promising.

Novel Keap1-Nrf2 Protein-Protein Interaction Inhibitor UBE-1099 Ameliorates Progressive Phenotype in Alport Syndrome Mouse Model

BACKGROUND

Bardoxolone methyl activates nuclear factor erythroid 2-related factor 2 (Nrf2) via covalent binding and irreversible inhibition of Kelch-like ECH-associated protein 1 (Keap1), the negative regulator of Nrf2. Ongoing clinical trials of bardoxolone methyl show promising effects for patients with CKD. However, the direct inhibition of Keap1-Nrf2 protein-protein interaction (PPI) as an approach to activate Nrf2 is less explored.

METHODS

We developed a noncovalent Nrf2 activator UBE-1099, which highly selectively inhibits Keap1-Nrf2 PPI, and evaluated its efficacy on the progressive phenotype in an Alport syndrome mouse model (Col4a5-G5X).

RESULTS

Similar to bardoxolone methyl, UBE-1099 transiently increased proteinuria and reduced plasma creatinine in Alport mice. Importantly, UBE-1099 improved the glomerulosclerosis, renal inflammation, and fibrosis, and prolonged the life span of Alport mice. UBE-1099 ameliorated the dysfunction of Nrf2 signaling in the renal tissue of Alport mice. Moreover, transcriptome analysis in the glomerulus showed that UBE-1099 induced the expression of genes associated with the cell cycle and cytoskeleton, which may explain its unique mechanism of improvement such as glomerular morphologic change.

CONCLUSIONS

UBE-1099 significantly ameliorates the progressive phenotype in Alport mice. Our results revealed the efficacy of Keap1-Nrf2 PPI inhibitor for glomerulosclerosis and present a potential therapeutic drug for CKD.

The role of discoidin domain receptor 2 in the renal dysfunction of alport syndrome mouse model

Alport syndrome (AS) is a hereditary glomerular nephritis caused by mutation in one of the type IV collagen genes α3/α4/α5 that encode the heterotrimer COL4A3/4/5. Failure to form a heterotrimer due to mutation leads to the dysfunction of the glomerular basement membrane, and end-stage renal disease. Previous reports have suggested the involvement of the receptor tyrosine kinase discoidin domain receptor (DDR) 1 in the progression of AS pathology. However, due to the similarity between DDR1 and DDR2, the role of DDR2 in AS pathology is unclear. Here, we investigated the involvement of DDR2 in AS using the X-linked AS mouse model. Mice were treated subcutaneously with saline or antisense oligonucleotide (ASO; 5 mg/kg or 15 mg/kg per week) for 8 weeks. Renal function parameters and renal histology were analyzed, and the gene expressions of inflammatory cytokines were determined in renal tissues. The expression level of DDR2 was highly elevated in kidney tissues of AS mice. Knockdown of Ddr2 using Ddr2-specific ASO decreased the Ddr2 expression. However, the DDR2 ASO treatment did not improve the proteinuria or decrease the BUN level. DDR2 ASO also did not significantly ameliorate the renal injury, inflammation and fibrosis in AS mice. These results showed that Ddr2 knockdown by ASO had no notable effect on the progression of AS indicating that DDR2 may not be critically involved in AS pathology. This finding may provide useful information and further understanding of the role of DDRs in AS.

Glomerular filtration and podocyte tensional homeostasis: importance of the minor type IV collagen network

The minor type IV collagen chain, which is a significant component of the glomerular basement membrane in healthy individuals, is known to assemble into large structures (supercoils) that may contribute to the mechanical stability of the collagen network and the glomerular basement membrane as a whole. The absence of the minor chain, as in Alport syndrome, leads to glomerular capillary demise and eventually to kidney failure. An important consideration in this problem is that the glomerular capillary wall must be strong enough to withstand the filtration pressure and porous enough to permit filtration at reasonable pressures. In this work, we propose a coupled feedback loop driven by filtration demand and tensional homeostasis of the podocytes forming the outer portion of the glomerular capillary wall. Briefly, the deposition of new collagen increases the stiffness of basement membrane, helping to stress shield the podocytes, but the new collagen also decreases the permeability of the basement membrane, requiring an increase in capillary transmural pressure drop to maintain filtration; the resulting increased pressure outweighs the increased glomerular basement membrane stiffness and puts a net greater stress demand on the podocytes. This idea is explored by developing a multiscale simulation of the capillary wall, in which a macroscopic (µm scale) continuum model is connected to a set of microscopic (nm scale) fiber network models representing the collagen network and the podocyte cytoskeleton. The model considers two cases: healthy remodeling, in which the presence of the minor chain allows the collagen volume fraction to be increased by thickening fibers, and Alport syndrome remodeling, in which the absence of the minor chain allows collagen volume fraction to be increased only by adding new fibers to the network. The permeability of the network is calculated based on previous models of flow through a fiber network, and it is updated for different fiber radii and volume fractions. The analysis shows that the minor chain allows a homeostatic balance to be achieved in terms of both filtration and cell tension. Absent the minor chain, there is a fundamental change in the relation between the two effects, and the system becomes unstable. This result suggests that mechanobiological or mechanoregulatory therapies may be possible for Alport syndrome and other minor chain collagen diseases of the kidney.

RNA-seq analysis of gene expression profiles in isolated stria vascularis from wild-type and Alport mice reveals key pathways underling Alport strial pathogenesis

Previous work demonstrates that the hearing loss in Alport mice is caused by defects in the stria vascularis. As the animals age, progressive thickening of strial capillary basement membranes (SCBMs) occurs associated with elevated levels of extracellular matrix expression and hypoxia-related gene and protein expression. These conditions render the animals susceptible to noise-induced hearing loss. In an effort to develop a more comprehensive understanding of how the underlying mutation in the COL4A3 gene influences homeostasis in the stria vascularis, we performed vascular permeability studies combined with RNA-seq analysis using isolated stria vascularis from 7-week old wild-type and Alport mice on the 129 Sv background. Alport SCBMs were found to be less permeable than wild-type littermates. RNA-seq and bioinformatics analysis revealed 68 genes were induced and 61 genes suppressed in the stria from Alport mice relative to wild-type using a cut-off of 2-fold. These included pathways involving transcription factors associated with the regulation of pro-inflammatory responses as well as cytokines, chemokines, and chemokine receptors that are up- or down-regulated. Canonical pathways included modulation of genes associated with glucose and glucose-1-PO4 degradation, NAD biosynthesis, histidine degradation, calcium signaling, and glutamate receptor signaling (among others). In all, the data point to the Alport stria being in an inflammatory state with disruption in numerous metabolic pathways indicative of metabolic stress, a likely cause for the susceptibility of Alport mice to noise-induced hearing loss under conditions that do not cause permanent hearing loss in age/strain-matched wild-type mice. The work lays the foundation for studies aimed at understanding the nature of strial pathology in Alport mice. The modulation of these genes under conditions of therapeutic intervention may provide important pre-clinical data to justify trials in humans afflicted with the disease.

CG200745, a Novel HDAC Inhibitor, Attenuates Kidney Fibrosis in a Murine Model of Alport Syndrome

Histone deacetylases have been a target of therapy for organ fibrosis. Here, we report the protective effect of CG200745 (CG), a novel histone deacetylase inhibitor, on tubulointerstitial fibrosis in Col4a3^-/- mice, a murine model of Alport syndrome. Morphological analyses revealed CG treatment markedly alleviated kidney fibrosis in Col4a3^-/- mice at the age of 7 weeks. CG prevented the activation of transforming growth factor β (TGFβ) and its downstream SMAD signaling in the kidney of Col4a3^-/- mice. As critical upstream regulators of TGFβ signaling, immunoblotting of whole kidney lysate of Col4a3^-/- mice reveled that intra-renal renin-angiotensin system (RAS) was activated with concurrent upregulation of inflammation and apoptosis, which were effectively suppressed by CG treatment. CG suppressed both activation of RAS and up-regulation of TGFβ signals in angiotensin II-stimulated HK-2 cells, a human kidney proximal tubular epithelial cell line. CG inhibited activation of TGFβ-driven signals and fibrosis in NRK-49F cells, a rat kidney fibroblast cell line, under angiotensin II-rich conditions. Collectively, CG was found to be effective both in proximal tubular epithelial cells by inhibiting local RAS and TGFβ signaling activation, as well as in fibroblasts by blocking their transition to myofibroblasts, attenuating renal fibrosis in a murine model of Alport syndrome.

Modification of an aggressive model of Alport Syndrome reveals early differences in disease pathogenesis due to genetic background

The link between mutations in collagen genes and the development of Alport Syndrome has been clearly established and a number of animal models, including knock-out mouse lines, have been developed that mirror disease observed in patients. However, it is clear from both patients and animal models that the progression of disease can vary greatly and can be modified genetically. We have identified a point mutation in Col4a4 in mice where disease is modified by strain background, providing further evidence of the genetic modification of disease symptoms. Our results indicate that C57BL/6J is a protective background and postpones end stage renal failure from 7 weeks, as seen on a C3H background, to several months. We have identified early differences in disease progression, including expression of podocyte-specific genes and podocyte morphology. In C57BL/6J mice podocyte effacement is delayed, prolonging normal renal function. The slower disease progression has allowed us to begin dissecting the pathogenesis of murine Alport Syndrome in detail. We find that there is evidence of differential gene expression during disease on the two genetic backgrounds, and that disease diverges by 4 weeks of age. We also show that an inflammatory response with increasing MCP-1 and KIM-1 levels precedes loss of renal function.

Olmesartan Attenuates Kidney Fibrosis in a Murine Model of Alport Syndrome by Suppressing Tubular Expression of TGFβ

Despite the wide use of angiotensin II receptor blockers in the treatment of Alport syndrome (AS), the mechanism as to how angiotensin II receptor blockers prevent interstitial fibrosis remains unclear. Here, we report that treatment of olmesartan effectively targets the feedback loop between the renin–angiotensin system (RAS) and transforming growth factor β (TGFβ) signals in tubular epithelial cells and preserves renal angiotensin-converting enzyme 2 (ACE2) expression in the kidney of Col4a3^–/– mice, a murine model of experimental AS. Morphology analyses revealed amelioration of kidney fibrosis in Col4a3^–/– mice by olmesartan treatment. Upregulation of TGFβ and activation of its downstream in Col4a3^–/– mice were attenuated by olmesartan in Col4a3^–/– mice. Intriguingly, TGFβ expression was preferentially upregulated in damaged tubular epithelial cells in Col4a3^–/– mice. Concurrent upregulation of TNFα-converting enzyme and downregulation of ACE2 suggested RAS activation in Col4a3^–/– mice, which was prevented by olmesartan. Mechanistically, olmesartan suppressed TGFβ-induced RAS activation in tubular epithelial cells in vitro. Collectively, we concluded that olmesartan effectively suppresses the progression of tubulointerstitial fibrosis in AS by interrupting RAS-TGFβ feedback loop to counterbalance intrarenal RAS activation.

Endothelial cell-specific collagen type IV-α3 expression does not rescue Alport syndrome in Col4a3-/- mice

The glomerular basement membrane (GBM) is a critical component of the kidney's blood filtration barrier. Alport syndrome, a hereditary disease leading to kidney failure, is caused by the loss or dysfunction of the GBM's major collagen type IV (COL4) isoform α3α4α5. The constituent COL4 α-chains assemble into heterotrimers in the endoplasmic reticulum before secretion into the extracellular space. If any one of the α3-, α4-, or α5-chains is lost due to mutation of one of the genes, then the entire heterotrimer is lost. Patients with Alport syndrome typically have mutations in the X-linked COL4A5 gene or uncommonly have the autosomal recessive form of the disease due to COL4A3 or COL4A4 mutations. Treatment for Alport syndrome is currently limited to angiotensin-converting enzyme inhibition or angiotensin receptor blockers. Experimental approaches in Alport mice have demonstrated that induced expression of COL4A3, either widely or specifically in podocytes of Col4a3-/- mice, can abrogate disease progression even after establishment of the abnormal GBM. While targeting podocytes in vivo for gene therapy is a significant challenge, the more accessible glomerular endothelium could be amenable for mutant gene repair. In the present study, we expressed COL4A3 in Col4a3-/- Alport mice using an endothelial cell-specific inducible transgenic system, but collagen-α3α4α5(IV) was not detected in the GBM or elsewhere, and the Alport phenotype was not rescued. Our results suggest that endothelial cells do not express the Col4a3/a4/a5 genes and should not be viewed as a target for gene therapy.

Hydroxypropyl-β-cyclodextrin protects from kidney disease in experimental Alport syndrome and focal segmental glomerulosclerosis

Studies suggest that altered renal lipid metabolism plays a role in the pathogenesis of diabetic kidney disease and that genetic or pharmacological induction of cholesterol efflux protects from the development of diabetic kidney disease and focal segmental glomerulosclerosis (FSGS). Here we tested whether altered lipid metabolism contributes to renal failure in the Col4a3 knockout mouse model for Alport Syndrome. There was an eight-fold increase in the cholesterol content in renal cortexes of mice with Alport Syndrome. This was associated with increased glomerular lipid droplets and cholesterol crystals. Treatment of mice with Alport Syndrome with hydroxypropyl-β-cyclodextrin (HPβCD) reduced cholesterol content in the kidneys of mice with Alport Syndrome and protected from the development of albuminuria, renal failure, inflammation and tubulointerstitial fibrosis. Cholesterol efflux and trafficking-related genes were primarily affected in mice with Alport Syndrome and were differentially regulated in the kidney cortex and isolated glomeruli. HPβCD also protected from proteinuria and mesangial expansion in a second model of non-metabolic kidney disease, adriamycin-induced nephropathy. Consistent with our experimental findings, microarray analysis confirmed dysregulation of several lipid-related genes in glomeruli isolated from kidney biopsies of patients with primary FSGS enrolled in the NEPTUNE study. Thus, lipid dysmetabolism occurs in non-metabolic glomerular disorders such as Alport Syndrome and FSGS, and HPβCD improves renal function in experimental Alport Syndrome and FSGS.

Alport syndrome and Pierson syndrome: Diseases of the glomerular basement membrane

The glomerular basement membrane (GBM) is an important component of the kidney's glomerular filtration barrier. Like all basement membranes, the GBM contains type IV collagen, laminin, nidogen, and heparan sulfate proteoglycan. It is flanked by the podocytes and glomerular endothelial cells that both synthesize it and adhere to it. Mutations that affect the GBM's collagen α3α4α5(IV) components cause Alport syndrome (kidney disease with variable ear and eye defects) and its variants, including thin basement membrane nephropathy. Mutations in LAMB2 that impact the synthesis or function of laminin α5β2γ1 (LM-521) cause Pierson syndrome (congenital nephrotic syndrome with eye and neurological defects) and its less severe variants, including isolated congenital nephrotic syndrome. The very different types of kidney diseases that result from mutations in collagen IV vs. laminin are likely due to very different pathogenic mechanisms. A better understanding of these mechanisms should lead to targeted therapeutic approaches that can help people with these rare but important diseases.

Osteopontin deficiency ameliorates Alport pathology by preventing tubular metabolic deficits

Alport syndrome is a rare hereditary renal disorder with no etiologic therapy. We found that osteopontin (OPN) is highly expressed in the renal tubules of the Alport mouse and plays a causative pathological role. OPN genetic deletion ameliorated albuminuria, hypertension, tubulointerstitial proliferation, renal apoptosis, and hearing and visual deficits in the Alport mouse. In Alport renal tubules we found extensive cholesterol accumulation and increased protein expression of dynamin-3 (DNM3) and LDL receptor (LDLR) in addition to dysmorphic mitochondria with defective bioenergetics. Increased pathological cholesterol influx was confirmed by a remarkably increased uptake of injected DiI-LDL cholesterol by Alport renal tubules, and by the improved lifespan of the Alport mice when crossed with the Ldlr-/- mice with defective cholesterol influx. Moreover, OPN-deficient Alport mice demonstrated significant reduction of DNM3 and LDLR expression. In human renal epithelial cells, overexpressing DNM3 resulted in elevated LDLR protein expression and defective mitochondrial respiration. Our results suggest a potentially new pathway in Alport pathology where tubular OPN causes DNM3- and LDLR-mediated enhanced cholesterol influx and impaired mitochondrial respiration.

Bromide supplementation exacerbated the renal dysfunction, injury and fibrosis in a mouse model of Alport syndrome

A seminal study recently demonstrated that bromide (Br-) has a critical function in the assembly of type IV collagen in basement membrane (BM), and suggested that Br- supplementation has therapeutic potential for BM diseases. Because salts of bromide (KBr and NaBr) have been used as antiepileptic drugs for several decades, repositioning of Br- for BM diseases is probable. However, the effects of Br- on glomerular basement membrane (GBM) disease such as Alport syndrome (AS) and its impact on the kidney are still unknown. In this study, we administered daily for 16 weeks 75 mg/kg or 250 mg/kg (within clinical dosage) NaBr or NaCl (control) via drinking water to 6-week-old AS mice (mouse model of X-linked AS). Treatment with 75 mg/kg NaBr had no effect on AS progression. Surprisingly, compared with 250 mg/kg NaCl, 250 mg/kg NaBr exacerbated the progressive proteinuria and increased the serum creatinine and blood urea nitrogen in AS mice. Histological analysis revealed that glomerular injury, renal inflammation and fibrosis were exacerbated in mice treated with 250 mg/kg NaBr compared with NaCl. The expressions of renal injury markers (Lcn2, Lysozyme), matrix metalloproteinase (Mmp-12), pro-inflammatory cytokines (Il-6, Il-8, Tnf-α, Il-1β) and pro-fibrotic genes (Tgf-β, Col1a1, α-Sma) were also exacerbated by 250 mg/kg NaBr treatment. Notably, the exacerbating effects of Br- were not observed in wild-type mice. These findings suggest that Br- supplementation needs to be carefully evaluated for real positive health benefits and for the absence of adverse side effects especially in GBM diseases such as AS.

Collagen IV diseases: A focus on the glomerular basement membrane in Alport syndrome

Alport syndrome is the result of mutations in any of three type IV collagen genes, COL4A3, COL4A4, or COL4A5. Because the three collagen chains form heterotrimers, there is an absence of all three proteins in the basement membranes where they are expressed. In the glomerulus, the mature glomerular basement membrane type IV collagen network, normally comprised of two separate networks, α3(IV)/α4(IV)/α5(IV) and α1(IV)/α2(IV), is comprised entirely of collagen α1(IV)/α2. This review addresses the current state of our knowledge regarding the consequence of this change in basement membrane composition, including both the direct, via collagen receptor binding, and indirect, regarding influences on glomerular biomechanics. The state of our current understanding regarding mechanisms of glomerular disease initiation and progression will be examined, as will the current state of the art regarding emergent therapeutic approaches to slow or arrest glomerular disease in Alport patients.

The Accumulation of VEGFA in the Glomerular Basement Membrane and Its Relationship with Podocyte Injury and Proteinuria in Alport Syndrome

The pathogenesis of proteinuria in Alport syndrome (AS) remains unclear. Vascular endothelial growth factor A (VEGFA) is a key regulator of the glomerular filtration barrier (GFB). This study explored the expression of VEGFA in the glomeruli and its accumulation in the glomerular basement membrane (GBM) and their relationship with podocyte injury and proteinuria in Alport syndrome (AS). Clinical data and renal tissues of control patients (11 cases) and AS patients (25 cases) were included. AS patients were further divided into 2 groups according to the quantities of their urinary protein: mild to moderate proteinuria group (proteinuria <50 mg/kg/d, 15 cases) and heavy proteinuria group (proteinuria ≥50 mg/kg/d, 10 cases). The expression and distribution of VEGFA and VEGF receptor 2 (VEGFR2) in the GFB, the phosphorylation of VEGFR2 (p-VEGFR2) and nephrin (p-nephrin), and the expression of synaptopodin and nephrin in the glomeruli were detected by immune electron microscopy and/or immunofluorescence, and their relationships to proteinuria in AS patients were analyzed. The accumulation of VEGFA in the GBM was increased in AS patients. The expression of VEGFA and the levels of p-VEGFR2 and p-nephrin in glomeruli were increased and were positively correlated with the degree of proteinuria in AS patients. The expression of synaptopodin and nephrin were decreased and were negatively correlated with the degree of proteinuria in AS patients. The over expressed VEGFA in the glomeruli and its accumulation in the GBM may activate the VEGFA-VEGFR2 and nephrin signaling pathways and lead to podocyte injury and occurrence of proteinuria in AS.

Anti-microRNA-21 oligonucleotides prevent Alport nephropathy progression by stimulating metabolic pathways

MicroRNA-21 (miR-21) contributes to the pathogenesis of fibrogenic diseases in multiple organs, including the kidneys, potentially by silencing metabolic pathways that are critical for cellular ATP generation, ROS production, and inflammatory signaling. Here, we developed highly specific oligonucleotides that distribute to the kidney and inhibit miR-21 function when administered subcutaneously and evaluated the therapeutic potential of these anti-miR-21 oligonucleotides in chronic kidney disease. In a murine model of Alport nephropathy, miR-21 silencing did not produce any adverse effects and resulted in substantially milder kidney disease, with minimal albuminuria and dysfunction, compared with vehicle-treated mice. miR-21 silencing dramatically improved survival of Alport mice and reduced histological end points, including glomerulosclerosis, interstitial fibrosis, tubular injury, and inflammation. Anti-miR-21 enhanced PPARα/retinoid X receptor (PPARα/RXR) activity and downstream signaling pathways in glomerular, tubular, and interstitial cells. Moreover, miR-21 silencing enhanced mitochondrial function, which reduced mitochondrial ROS production and thus preserved tubular functions. Inhibition of miR-21 was protective against TGF-β-induced fibrogenesis and inflammation in glomerular and interstitial cells, likely as the result of enhanced PPARα/RXR activity and improved mitochondrial function. Together, these results demonstrate that inhibition of miR-21 represents a potential therapeutic strategy for chronic kidney diseases including Alport nephropathy.

FGF23 is a novel regulator of intracellular calcium and cardiac contractility in addition to cardiac hypertrophy

Fibroblast growth factor 23 (FGF23) is a hormone released primarily by osteocytes that regulates phosphate and vitamin D metabolism. Recent observational studies in humans suggest that circulating FGF23 is independently associated with cardiac hypertrophy and increased mortality, but it is unknown whether FGF23 can directly alter cardiac function. We found that FGF23 significantly increased cardiomyocyte cell size in vitro, the expression of gene markers of cardiac hypertrophy, and total protein content of cardiac muscle. In addition, FGFR1 and FGFR3 mRNA were the most abundantly expressed FGF receptors in cardiomyocytes, and the coreceptor α-klotho was expressed at very low levels. We tested an animal model of chronic kidney disease (Col4a3(-/-) mice) that has elevated serum FGF23. We found elevations in common hypertrophy gene markers in Col4a3(-/-) hearts compared with wild type but did not observe changes in wall thickness or cell size by week 10. However, the Col4a3(-/-) hearts did show reduced fractional shortening (-17%) and ejection fraction (-11%). Acute exposure of primary cardiomyocytes to FGF23 resulted in elevated intracellular Ca(2+) ([Ca(2+)](i); F/F(o) + 86%) which was blocked by verapamil pretreatment. FGF23 also increased ventricular muscle strip contractility (67%), which was inhibited by FGF receptor antagonism. We hypothesize that although FGF23 can acutely increase [Ca(2+)](i), chronically this may lead to decreases in contractile function or stimulate cardiac hypertrophy, as observed with other stress hormones. In conclusion, FGF23 is a novel bone/heart endocrine factor and may be an important mediator of cardiac Ca(2+) regulation and contractile function during chronic kidney disease.

Upregulated expression of integrin α1 in mesangial cells and integrin α3 and vimentin in podocytes of Col4a3-null (Alport) mice

Alport disease in humans, which usually results in proteinuria and kidney failure, is caused by mutations to the COL4A3, COL4A4, or COL4A5 genes, and absence of collagen α3α4α5(IV) networks found in mature kidney glomerular basement membrane (GBM). The Alport mouse harbors a deletion of the Col4a3 gene, which also results in the lack of GBM collagen α3α4α5(IV). This animal model shares many features with human Alport patients, including the retention of collagen α1α2α1(IV) in GBMs, effacement of podocyte foot processes, gradual loss of glomerular barrier properties, and progression to renal failure. To learn more about the pathogenesis of Alport disease, we undertook a discovery proteomics approach to identify proteins that were differentially expressed in glomeruli purified from Alport and wild-type mouse kidneys. Pairs of cy3- and cy5-labeled extracts from 5-week old Alport and wild-type glomeruli, respectively, underwent 2-dimensional difference gel electrophoresis. Differentially expressed proteins were digested with trypsin and prepared for mass spectrometry, peptide ion mapping/fingerprinting, and protein identification through database searching. The intermediate filament protein, vimentin, was upregulated ∼2.5 fold in Alport glomeruli compared to wild-type. Upregulation was confirmed by quantitative real time RT-PCR of isolated Alport glomeruli (5.4 fold over wild-type), and quantitative confocal immunofluorescence microscopy localized over-expressed vimentin specifically to Alport podocytes. We next hypothesized that increases in vimentin abundance might affect the basement membrane protein receptors, integrins, and screened Alport and wild-type glomeruli for expression of integrins likely to be the main receptors for GBM type IV collagen and laminin. Quantitative immunofluorescence showed an increase in integrin α1 expression in Alport mesangial cells and an increase in integrin α3 in Alport podocytes. We conclude that overexpression of mesangial integrin α1 and podocyte vimentin and integrin α3 may be important features of glomerular Alport disease, possibly affecting cell-signaling, cell shape and cellular adhesion to the GBM.

The biodistribution of [153Gd]Gd-labeled magnetic resonance contrast agents in a transgenic mouse model of renal failure differs greatly from control mice

Nephrogenic systemic fibrosis occurs in renally impaired patients who have undergone contrast enhanced MR examination using intravenous gadolinium-based contrast agents. The effect of impaired kidney function on the biodistribution of gadolinium-based contrast agents was investigated using radiolabeled (153/Nat) gadolinium-DOTA, (153/Nat) gadolinium-DTPA, and (153/Nat) gadolinium-DTPA-BMA in a transgenic mouse model of renal impairment. Renally impaired animals had more activity associated with their tissues than did control mice, and this increase varied according to the radiotracer injected. For example, after 7 days, renally impaired animals that received (153/Nat) Gd-DOTA had 3-fold (P < 0.037) more activity in their bone tissue, whereas renally impaired animals receiving (153/Nat) Gd-DTPA and (153/Nat) Gd-DTPA-BMA had 8-fold (P < 0.0001) and 24-fold (P < 0.0001) more activity in their bone tissue, respectively. These findings demonstrate that renal impairment dramatically alters the tissue distribution of Gd(3+) ions in vivo, which are likely a critical factor in the development of nephrogenic systemic fibrosis.

Does Alport syndrome affect the basement membrane of peritoneal vessels?

Alport syndrome and encapsulating peritoneal sclerosis (EPS) are both rare diseases. Their joint occurrence is highly unlikely. Two patients at our center with Alport syndrome developed EPS. We therefore hypothesized that Alport syndrome might predispose to the development of EPS and that this predisposition might be reflected in a fast peritoneal transport rate at baseline. We compared the mass transfer area coefficient (MTAC) of creatinine and the clearances of albumin, immunoglobulin G, and alpha2-macroglobulin at baseline and for all subsequent available measurements in four patient groups: EPS patients with Alport syndrome, EPS patients without Alport syndrome, Alport patients without EPS, and long-term peritoneal dialysis (PD) patients without EPS. The transport characteristics were obtained during a standard peritoneal permeability analysis. Between July 1995 and December 2008, 5 of 417 PD patients treated at our center had Alport syndrome as their primary kidney disease, and 13 of the 417 developed EPS. Of those 13 EPS patients, 2 had Alport syndrome. We observed no differences in the baseline transport characteristics of the four groups under consideration. Taking all measures of transport characteristics into account, only the MTAC of creatinine was higher in the two EPS groups than in the other two groups (p = 0.01). We could not confirm our hypothesis that Alport syndrome affects peritoneal solute clearances.

[Correlation between ultrastructural changes of glomerular basement membrane and abnormal distribution of laminins in patients with Alport's syndrome]

OBJECTIVE

To analyse the relationship of ultrastructural changes of glomerular basement membrane (GBM) and glomerular distributions of laminin alpha1 and laminin alpha5 in patients with Alport's syndrome.

METHODS

Twenty patients with Alport's syndrome were recruited. The thickness of GBM and the extension of thickening and splitting GBM were measured under transmission electron microscope. Normal renal tissues from 6 nephrectomies of renal carcinoma were taken as controls. Paraffin embedded sections of formalin-fixed renal tissue were processed for immunohistochemistry with monoclonal antibodies to laminin alpha1 and laminin alpha5. Their distributions in GBM were evaluated by a semiquantitative scale of positive extension: absent, 0; < or =25%, 1; 25%-50%, 2; 50%-75%, 3; > or =75%, 4.

RESULTS

There were a variety of degrees of thickening or splitting GBM in patients with Alport's syndrome. Laminin alpha1 was positive in glomerular mesangial area and absolutely negative in GBM and laminin alpha5 was evenly positive in GBM in normal tissue. In Alport's syndrome, laminin alpha1 was much weaker in glomerular mesangial area, but strongly positive in GBM; laminin alpha5 in GBM was prominently reduced. There was a high negative correlation of semiquantitative scores between laminin alpha1 and laminin alpha5 (r=-0.83, P<0.001). The extension of thickening or splitting GBM was positively correlated with scores of laminin alpha1 in GBM (r=0.76, P<0.001; r=0.56, P=0.015), and was negatively correlated with scores of laminin alpha5 in GBM (r=-0.59, P=0.010; r=-0.53, P=0.025).

CONCLUSION

Abnormal distribution of laminin alpha1 and laminin alpha5 in GBM is correlated with GBM thickening and splitting in human Alport's syndrome.

Type VII collagen in Alport syndrome

BACKGROUND

Absence or segmental distribution of the alpha5(IV) collagen chain along the epidermal basement membrane (EBM) is diagnostic of X-linked Alport syndrome (X-AS), but the typical morphologic alterations usually observed along the glomerular basement membrane (GBM) are lacking. However, several differences in protein composition exist between GBM and EBM, and such differences could account for a different phenotype with the same genetic defect. Type VII collagen is one of the major collagenous components of the EBM; the purpose of this study was to investigate the modifications of protein synthesis and expression of type VII collagen in the skin of patients with X-AS.

METHODS

The distribution of type VII collagen has been studied in 15 skin biopsies (10 from X-AS patients and 5 controls) by means of electron microscopy, immunofluorescence and confocal microscopy; type VII collagen mRNA expression was also measured by RT-PCR on the same skin fragments.

RESULTS

Protein and mRNA amounts for type VII collagen were significantly higher in skin samples from X-AS patients than in controls (P < 0.001); highest values were in cases in which alpha5(IV) was completely absent.

CONCLUSIONS

Our results indicate that lack of alpha5(IV) molecule significantly alters the assembly of extracellular matrix molecules other than alphax(IV) chains also at the EBM level. We suggest that the increased synthesis and deposition of type VII collagen is likely to balance the absence of stabilizing activity normally exerted by alpha5(IV).

Laminin Compensation in Collagen α3(IV) Knockout (Alport) Glomeruli Contributes to Permeability Defects

Alport disease is caused by mutations in genes encoding the alpha3, alpha4, or alpha5 chains of type IV collagen, which form the collagenous network of mature glomerular basement membrane (GBM). In the absence of alpha3, alpha4, alpha5 (IV) collagen, alpha1, alpha2 (IV) collagen persists, which ordinarily is found only in GBM of developing kidney. In addition to dysregulation of collagen IV, Alport GBM contains aberrant laminins, which may contribute to the progressive GBM thickening and splitting, proteinuria, and renal failure seen in this disorder. This study sought to characterize further the laminin dysregulation in collagen alpha3(IV) knockout mice, a model of Alport disease. With the use of confocal microscopy, laminin alpha1 and alpha5 abundance was quantified, and it was found that they co-distributed in significantly large amounts in areas of GBM thickening. In addition, labeling of entire glomeruli for laminin alpha5 was significantly greater in Alport mice than in wild-type siblings. Reverse transcriptase-PCR from isolated glomeruli demonstrated significantly more laminin alpha5 mRNA in Alport mice than in wild-type controls, indicating upregulated transcription of Lama5. For testing glomerular barrier function, ferritin was injected into 2-wk-old Alport and control mice, and GBM was examined by electron microscopy. Highest ferritin levels were seen in Alport GBM thickenings beneath effaced podocyte foot processes, but morphologically normal GBM was significantly permeable as well. We concluded that (1) ultrastructurally normal Alport GBM residing beneath differentiated podocyte foot processes is inherently and abnormally permeable, and (2) upregulation of Lama5 transcription and concentration of laminin alpha1 and alpha5 within Alport GBM thickenings contribute to abnormal permeabilities.

Collagen α5 and α2(IV) chain coexpression: Analysis of skin biopsies of Alport patients

Alport syndrome is a collagen type IV disease caused by mutations in the COL4A5 gene with the X-linked form being most prevalent. The resultant alpha5(IV) collagen chain is a component of the glomerular and skin basement membranes (SBMs). Immunofluorescent determination of the alpha5(IV) chain in skin biopsies is the procedure of choice to identify patients. In 30% of patients, however, the mutant protein is still found in the SBM resulting in a normal staining pattern. In order to minimize or eliminate false results, we compared the distribution of the alpha2(IV) chain (another SBM component) and the alpha5(IV) chain by standard double label immunofluorescence (IF) and by confocal laser scanning microscopy. The study was performed on 55 skin biopsies of patients suspected of Alports and five normal control specimens. In normal skin, IF showed the classical linear pattern for both collagens along the basement membrane. Additionally, decreased alpha5(IV) was found in the bottom of the dermal papillary basement membrane. Confocal analysis confirmed the results and show alpha5(IV) focal interruptions. In suspected patients, both techniques showed the same rate of abnormal alpha5(IV) expression: segmental in women and absent in men. Our results show a physiological variation of alpha5(IV) location with focal interruptions and decreased expression in the bottom of the dermal basement membrane. Comparison of alpha5(IV) with alpha2(IV) expression is simple and eliminates technical artifacts.

Correlation between mRNA expression level of the mutant COL4A5 gene and phenotypes of XLAS females

Alport syndrome (AS) is a progressive hereditary glomerulonephritis presented with hematuria, progressive renal failure, sensorineural deafness, and ocular lesions. Females with X-linked Alport syndrome (XLAS) have variable phenotypes, from asymptomatic hematuria to renal failure. In order to understand the possible mechanism of different phenotypes in female XLAS, we analyzed mRNA expression level of the mutant COL4A5 gene in fibroblasts, the X-inactivation pattern in peripheral blood DNA, and the phenotype variability of XLAS females. Total RNA was isolated from cultured skin fibroblasts in five females with XLAS and confirmed deletion mutations of COL4A5 mRNA. Reverse transcription-polymerase chain reaction (PCR) was performed to amplify the fragment, including the mutation sequences of the COL4A5 gene. The PCR products were electrophoresed with 8% polyacrylamide gel. Messenger RNA expression level of the mutant COL4A5 gene was analyzed with the optical density of PCR product revealed under polyacrylamide gel. The X-inactivation analysis was performed using HpaII predigestion of peripheral blood DNA followed by PCR of the highly polymorphic CAG repeat of the androgen receptor (AR) gene. All patients in the study had persistent microscopic hematuria. Two of them had gross hematuria. Three cases had persistent and severe proteinuria of 2+~3+, and the others had discontinuous and milder proteinuria of - ~+. The patients whose mRNA expression level of the mutant COL4A5 gene was higher had persistent and more severe proteinuria (r = 0.975, P = 0.005). None of them had skewed X inactivation. Our preliminary results demonstrate that the quantity of mRNA expression level of the mutant COL4A5 gene was correlated with the phenotypic severity of females with XLAS, and this could not be explained by X-inactivation pattern in peripheral blood leukocytes.

Alphav beta6 integrin regulates renal fibrosis and inflammation in Alport mouse

The transforming growth factor (TGF)-beta-inducible integrin alpha v beta6 is preferentially expressed at sites of epithelial remodeling and has been shown to bind and activate latent precursor TGF-beta. Herein, we show that alpha v beta6 is overexpressed in human kidney epithelium in membranous glomerulonephritis, diabetes mellitus, IgA nephropathy, Goodpasture's syndrome, and Alport syndrome renal epithelium. To assess the potential regulatory role of alpha v beta6 in renal disease, we studied the effects of function-blocking alpha v beta6 monoclonal antibodies (mAbs) and genetic ablation of the beta6 subunit on kidney fibrosis in Col4A3-/- mice, a mouse model of Alport syndrome. Expression of alpha v beta6 in Alport mouse kidneys was observed primarily in cortical tubular epithelial cells and in correlation with the progression of fibrosis. Treatment with alpha v beta6-blocking mAbs inhibited accumulation of activated fibroblasts and deposition of interstitial collagen matrix. Similar inhibition of renal fibrosis was observed in beta6-deficient Alport mice. Transcript profiling of kidney tissues showed that alpha v beta6-blocking mAbs significantly inhibited disease-associated changes in expression of fibrotic and inflammatory mediators. Similar patterns of transcript modulation were produced with recombinant soluble TGF-beta RII treatment, suggesting shared regulatory functions of alpha v beta6 and TGF-beta. These findings demonstrate that alpha v beta6 can contribute to the regulation of renal fibrosis and suggest this integrin as a potential therapeutic target.

Nephroprotective effect of the HMG-CoA-reductase inhibitor cerivastatin in a mouse model of progressive renal fibrosis in Alport syndrome

BACKGROUND

Alport syndrome is caused by mutations in genes encoding for the alpha3, alpha4 or alpha5 chain of type IV collagen leading to excessive production of fibrotic tissue and end-stage renal failure. HMG-CoA-reductase-inhibitors exhibit pleiotropic effects by which they modulate the production of connective tissue. The aim of this study was to examine the anti-fibrotic effect of the HMG-CoA-reductase-inhibitor, cerivastatin, in COL4A3 knockout mice, an animal model of Alport syndrome with progressive renal fibrosis.

METHODS

Forty homozygous COL4A3 knockout mice received cerivastatin, starting 28 or 49 days after birth. Mice were sacrificed at day 52 or 66 after birth. Immunohistochemistry against laminin and fibronectin was performed. Inflammatory cell infiltration was determined by F4/80- and CD3-staining. Myofibroblasts were identified by an alpha-smooth muscle actin staining. Expression of the profibrotic cytokines, TGF-beta1 and CTGF, were determined by immunoblot.

RESULTS

The lifespan of treated COL4A3 knockout mice was increased by 28% compared with untreated animals (71+/-6 vs 91+/-9 days, P<0.01). Early cerivastatin treatment reduced cholesterol levels (113+/-13 vs 141+/-19 mmol/l in untreated animals, P<0.05) and serum urea (164 vs 235 mmol/l, day 66, P<0.05). Treatment also decreased proteinuria (5.5 vs 12 g/l at day 66, P<0.05). Deposition of laminin and fibronectin, expression of TGF-beta and CTGF was reduced. Infiltration of T-cells and macrophages as well as myofibroblasts appeared to be reduced in kidneys from cerivastatin-treated mice.

CONCLUSION

Cerivastatin prolongs the lifespan of COL4A3 knockout mice, reduces proteinuria and delays uraemia. These effects are associated with decreased renal fibrosis and a reduction of inflammatory cell infiltration.

The effect of aldosterone blockade in patients with Alport syndrome

Recent studies indicate that adding the mineralocorticoid receptor antagonist spironolactone (SP) to angiotensin converting enzyme inhibitors (ACEI) or ACEI and angiotensin receptor blocker (ARB), which is known as a triple blockade, enhances the more beneficial effects on urinary protein excretion of patients with chronic kidney diseases. In this study, we explored the effects of SP on urinary protein excretion in patients with Alport syndrome featuring persistent proteinuria in spite of the long-term use of ACEI (lisinopril) or both ACEI and ARB (candesartan). Five patients with Alport syndrome were enrolled and SP treatment (25 mg/day) was started. At the start of SP administration, all patients showed good renal function and none of them suffered from hypertension. We decided to assess the effect of SP by determining the morning urinary protein/creatinine ratio (U-P/C) and estimated glomerular filtration rate (EGFR). After SP treatment was started, U-P/C was significantly reduced at 3, 6, 12 and 18 months, while EGFR did not change. The drop in systolic and diastolic blood pressure was statistically significant and serum potassium level was slightly elevated. None of the patients showed signs of severe hyperkalemia (>5.0 mEq/l). These results suggest that aldosterone receptor blockade combined with ACEI and ARB therapy offers a valuable adjuvant treatment for the reduction of proteinuria in patients with Alport syndrome as in those with other chronic kidney diseases. SP can thus be expected to constitute a good renoprotective agent for Alport syndrome. These preliminary data indicate that large-scale trials of this therapy should be done.

Spectrum of clinical features and type IV collagen alpha-chain distribution in Chinese patients with Alport syndrome

BACKGROUND

Alport syndrome (AS) is a clinically and genetically heterogeneous nephropathy. The goal of the present study is to delineate clinical characteristics and the distribution of type IV collagen chains in Chinese AS patients and to identify any alpha(IV)-chain expression and clinical phenotype correlation.

METHODS

A total of 126 biopsy-proven patients meeting immunofluorescence criteria for the diagnosis of AS were investigated retrospectively.

RESULTS

Microscope haematuria associated with proteinuria was observed as the initial symptom in 77.8% of the patients; 59.8% showed hearing impairment and 22.9% had ocular abnormalities. Renal biopsies from 118 patients revealed mesangial proliferative glomerulonephritis (61.9%) and focal and segmental sclerosis glomerulonephritis (37.3%). Ten different distribution patterns for the type IV collagen alpha-chains were found in the kidney; six of these are presented here for the first time. Based on renal immunofluorescence findings, 113 patients (89.7%) were classified as X-linked dominant inherited AS (XLAS) and 13 (10.3%) as autosomal recessive AS (ARAS). The XLAS group was divided into typical and non-typical subgroups according to the expression patterns for the alpha3(IV)-chain. Clinical phenotypes were more severe in XLAS patients than in ARAS patients and the prognosis was poorer in typical XLAS patients than non-typical XLAS patients.

CONCLUSION

In China, the incidence of XLAS is 89.7% and 10.3% for ARAS. Chinese patients with AS have various distribution patterns of type IV collagen alpha-chains. The distribution pattern of type IV collagen alpha-chains in the kidney may correspond to the severity of the clinical phenotype.

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

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

Bone marrow-derived cells contribute to podocyte regeneration and amelioration of renal disease in a mouse model of Alport syndrome

In a model of autosomally recessive Alport syndrome, mice that lack the alpha3 chain of collagen IV (Col4alpha3(-/-)) develop progressive glomerular damage leading to renal failure. The proposed mechanism is that podocytes fail to synthesize normal glomerular basement membrane, so the collagen IV network is unstable and easily degraded. We used this model to study whether bone marrow (BM) transplantation can rectify this podocyte defect by correcting the deficiency in Col4alpha3. Female C57BL/6 Col4alpha3(-/-) (-/-) mice were transplanted with whole BM from male wild-type (+/+) mice. Control female -/- mice received BM from male -/- littermates. Serum urea and creatinine levels were significantly lower in recipients of +/+ BM compared with those of -/- BM 20 weeks post-transplant. Glomerular scarring and interstitial fibrosis were also significantly decreased. Donor-derived cells were detected by in situ hybridization (ISH) for the Y chromosome, and fluorescence and confocal microscopy indicated that some showed an apparent podocyte phenotype in mice transplanted with +/+ BM. Glomeruli of these mice showed small foci of staining for alpha3(IV) protein by immunofluorescence. alpha3(IV) mRNA was detectable by reverse transcription-polymerase chain reaction and ISH in some mice transplanted with +/+ BM but not -/- BM. However, a single injection of mesenchymal stem cells from +/+ mice to irradiated -/- recipients did not improve renal disease. Our data show that improved renal function in Col4alpha3(-/-) mice results from BM transplantation from wild-type donors, and the mechanism by which this occurs may in part involve generation of podocytes without the gene defect.

Hereditary nephritis mimicking immune complex-mediated glomerulonephritis

The defining ultrastructural features of hereditary nephritis are "basket weave" lamellation or thinning of glomerular basement membranes. Electron-dense deposits are not seen and immunofluorescence (IF) is generally negative. In this study, we report 5 cases of hereditary nephritis in which substantial amounts of glomerular electron-dense deposits were identified on electron microscopy, with corresponding positive IF staining in 4 cases, suggesting immune complex-mediated glomerulonephritis. However, no case had histological evidence of glomerular endocapillary or extracapillary proliferation or leukocyte infiltration typical of active glomerulonephritis. Four cases were diagnosed at outside institutions simply as forms of glomerulonephritis without considering the possibility of hereditary nephritis and were sent for consultation in contemplation of possible immunosuppressive therapy. All patients had negative serologies and no known underlying infectious or autoimmune disease; 4 patients had family history of hematuria or renal disease. The glomerular electron-dense deposits were predominantly mesangial (4 cases) and intramembranous (4 cases), as well as subepithelial (2 cases) or subendothelial (1 case). Corresponding IF positivity for immune reactants was identified in 4 cases, and IgG was the predominant immunoglobulin deposited. A characteristic feature was the tendency for deposits to form between the complex layers of glomerular basement membrane material, favoring a process of nonspecific entrapment of immune reactants within the thickened, lamellated basement membrane. In all cases, a diagnosis of hereditary nephritis was confirmed by demonstration of the characteristic loss of immunoreactivity for the alpha5 subunit of collagen IV (4 cases) or Goodpasture's antigen (1 case) in renal or epidermal basement membranes. These cases expand the spectrum of unusual pathological findings in hereditary nephritis and emphasize the potential for hereditary nephritis to mimic immune complex glomerulonephritis.

Distribution of type IV collagen in the cochlea in Alport syndrome

OBJECTIVE

To determine the distribution of alpha1, alpha3, and alpha5 chains of type IV collagen in the cochlea in Alport syndrome.

DESIGN

Case-control study.

PATIENTS

Two patients with sensorineural hearing loss due to Alport syndrome. Both patients had known mutations in the COL4A5 gene.

MAIN OUTCOME MEASURES

Immunostaining was used to study the distribution of type IV collagen (alpha1, alpha3, and alpha5 chains) within the cochlea. Immunostaining was also performed in the cochlear tissues of an unaffected individual used as a control.

RESULTS

In the control ear, alpha1 staining was observed in the basement membrane overlying the basilar membrane, in the basement membrane of cochlear blood vessels and Schwann cells, and within the spiral limbus. In the control ear, we also observed strong staining for alpha3 and alpha5 chains in the basement membrane overlying the basilar membrane and within the spiral ligament. In both cases with Alport syndrome, no immunostaining was observed for alpha3 or alpha5 chains within the cochlea, whereas alpha1 staining was present in locations similar to that seen in the control ear.

CONCLUSIONS

The results indicate that isotype switching does not occur within the cochlea in Alport syndrome. The results are also consistent with the hypothesis that the sensorineural hearing loss in Alport syndrome may be due to alterations in cochlear micromechanics and/or dysfunction of the spiral ligament.