Endoplasmic Reticulum Stress Activation in Alport Syndrome Varies Between Genotype and Cell Type.
ABSTRACT: Alport syndrome is a hereditary progressive chronic kidney disease caused by mutations in type IV collagen genes COL4A3/4/5. X-linked Alport syndrome (XLAS) is caused by mutations in the COL4A5 gene and is the most common form of Alport syndrome. A strong correlation between the type of COL4A5 mutation and the age developing end-stage renal disease in male patients has been found. Mutation to the ? (IV) chain causes retention of the protein to the endoplasmic reticulum lumen, which causes endoplasmic reticulum stress (ERS) and subsequent exertion of deleterious intracellular effects through the activation of ERS. The exact time point that mutant type IV collagen ? chain exerts its deleterious effects remains elusive. In this study, we explored the relationship between the COL4A5 genotype and cell type in ERS activation. We obtained skin fibroblasts from Alport syndrome patients with different COL4A5 mutation categories [i.e., a missense mutation (c.4298G > T, p.Gly1433Val) in exon 47, a splicing mutation (c.1949-1G > A) in intron 25 and an insertion (c.573_c.574insG, p. Pro193Alafs*23) in exon 10], and then reprogrammed these fibroblasts into induced pluripotent stem cells (iPSCs). Interestingly, no significant dysregulation of ERS pathway markers was observed for the three COL4A5 mutant iPSCs; however, significant activation of ERS in COL4A5 mutant fibroblasts was observed. In addition, we found that the activation levels of some ERS markers in fibroblasts varied among the three COL4A5 mutation types. Mutant COL4A5 proteins were demonstrated to have different effects on cells at different stages of ontogenesis, providing a theoretical basis for choosing the timing of intervention. The observed differences in activation of ERS by the COL4A5 mutant fibroblasts may contribute to the intracellular molecular mechanisms that describe the correlation between genotype and clinical features in XLAS.
Project description:X-linked Alport syndrome (XLAS) is a progressive kidney disease caused by genetic abnormalities of COL4A5. Lack of collagen IV ?5 chain staining and "basket-weave" by electron microscopy (EM) in glomerular basement membrane (GBM) are its typical pathology. However, the causal relationship between GBM defects and progressive nephropathy is unknown. We analyzed sequential pathology in a mouse model of XLAS harboring a human nonsense mutation of COL4A5. In mutant mice, nephropathy commenced from focal GBM irregularity by EM at 6 weeks of age, prior to exclusive crescents at 13 weeks of age. Low-vacuum scanning EM demonstrated substantial ragged features in GBM, and crescents were closely associated with fibrinoid exudate, despite lack of GBM break and podocyte depletion at 13 weeks of age. Crescents were derived from two sites by different cellular components. One was CD44?+?cells, often with fibrinoid exudate in the urinary space, and the other was accumulation of ?-SMA?+?cells in the thickened Bowman's capsule. These changes finally coalesced, leading to global obliteration. In conclusion, vulnerability of glomerular and capsular barriers to the structural defect in collagen IV may cause non-necrotizing crescents via activation of PECs and migration of interstitial fibroblasts, promoting kidney disease in this model.
Project description:BACKGROUND:Alport syndrome is an inherited renal disease caused by mutations in COL4A3, COL4A4, or COL4A5 genes. Coexisting mutations in either two of the three genes in Alport patients have been reported recently. However, the effect of heterozygous mutations in COL4A3 or COL4A4 genes in X-linked Alport syndrome (XLAS) patients is unclear. METHODS:Using targeted next-generation sequencing, six unrelated Chinese children were identified to have a combination of a pathogenic variant in COL4A5 and a heterozygous mutation in COL4A3 or COL4A4. They were three males and three females. Another three XLAS males each with only one pathogenic variant in COL4A5 were included. The clinical data were analyzed and compared between the males in two groups (group 1, males with a pathogenic variant in COL4A5 and a heterozygous pathogenic variant in COL4A3 or COL4A4; group 2, males with only one pathogenic variant in COL4A5). RESULTS:Patients with XLAS who also had heterozygous pathogenic COL4A3 or COL4A4 variants accounted for 1% of Alport syndrome. In this study, three children showed coexisting pathogenic variants in COL4A5 and COL4A3. Two children showed pathogenic variants in COL4A5 and COL4A4. One child had pathogenic variants in the three COL4A3-5 genes, in which the pathogenic variant in COL4A5 was de novo and the pathogenic variants in COL4A4 and COL4A3 were inherited independently (in trans). The site and type of mutations in COL4A5 were similar between the two groups. It was revealed that males in group 1 presented more severe proteinuria than males in group 2 (p < 0.05). CONCLUSION:The present study provides further evidence for complicated genotype in Alport syndrome. For the first time, we reported a case with three pathogenic variants in COL4A5, COL4A3, and COL4A4 genes. Moreover, we found that heterozygous pathogenic COL4A3 or COL4A4 variants are likely to make XLAS disease more serious.
Project description:Alport syndrome (AS) is an inherited disorder characterized by glomerular basement membrane (GBM) abnormality and development of chronic kidney disease at an early age. The cause of AS is a genetic mutation in type IV collagen, and more than 80% of patients have X-linked AS (XLAS) with mutation in <i>COL4A5</i>. Although the causal gene has been identified, mechanisms of progression have not been elucidated, and no effective treatment has been developed. In this study, we generated a <i>Col4a5</i> mutant mouse harboring a nonsense mutation (R471X) obtained from a patient with XLAS using clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated system. <i>Col4a5</i> mRNA and protein expressions were not observed in the kidneys of hemizygous R471X male mice. R471X mice showed proteinuria and hematuria. Pathology revealed progression of glomerulosclerosis and interstitial fibrosis by age. Electron microscopy identified irregular thickening in GBM accompanied by irregular lamination. These observations were consistent with the clinical and pathological features of patients with AS and other established models. In addition, our mice models develop end-stage renal disease at the median age of 28 weeks, much later compared to previous models much more consistent with clinical course of human XLAS. Our models have advantages for future experiments in regard with treatment for human XLAS.
Project description:X-linked Alport syndrome (XLAS) is an inherited renal disease caused by mutations in COL4A5 gene. The c.2858G>T(p.(G953V)) in COL4A5 gene (rs78972735) has been considered pathogenic previously. However, there are conflicting interpretations of its pathogenicity recently. Here we presented 19 Chinese families, out of which 36 individuals (18 probands and 18 family members) carried the c.2858G>T(p.(G953V)) in COL4A5 gene. The clinical manifestations and genetic findings of them were analyzed. We found there were no clinical features of Alport syndrome not only in six probands with c.2858G>T(p.(G953V)) in COL4A5 plus pathogenic variants in other genes (e.g., WT1, ADCK4, NPHP1, TRPC6, COL4A4, and PAX2) but also in another six probands with only the c.2858G>T(p.(G953V)) variant. The other six probands with a combination of c.2858G>T(p.(G953V)) and another pathogenic variant in COL4A5 had XLAS. Eleven family members (11/18, nine females and two males) who had only the c.2858G>T(p.(G953V)) variant were asymptomatic. These two males (at age of 42 and 35 years) had normal result of urine analysis and no more clinical traits of Alport syndrome. We conclude c.2858G>T(p.(G953V)) in COL4A5 gene is not a pathogenic variant for XLAS. Individuals should not be diagnosed as XLAS only based on the detection of c.2858G>T(p.(G953V)) in COL4A5 gene.
Project description:Optical coherence tomography (OCT) findings of temporal macular thinning are important in the diagnosis and prognosis of X-linked Alport syndrome (XLAS).To report OCT findings and severity of temporal macular thinning in a cohort with XLAS and to correlate these and other ocular findings with mutation genotype.Patients with XLAS underwent genotyping for COL4A5 mutations and complete eye examinations with retinal imaging using spectral domain OCT and fundus photography. Temporal macular thinning was calculated from OCT measurements by comparing the ratio of the retinal thickness of the temporal to the nasal subfields with a published normative database.University departments of ophthalmology and nephrology.Thirty-two patients from 24 families.Temporal thinning index calculated from spectral domain OCT scans.All study patients had a mutation associated with the X-linked COL4A5 gene. Eleven different mutations were identified. Eleven of 32 patients (34%) expressed the L1649R mutation. Of a total of 63 eyes with available OCT scans, 44 (70%) had severe pathological temporal macular thinning. The L1649R mutation was associated with the least amount of severe temporal macular thinning and later onset of renal failure.Temporal macular thinning is a prominent sign associated with XLAS, suggesting that OCT measurements are essential in the diagnosis and prognosis of the disease. The L1649R mutation in the COL4A5 gene causes a relatively mild form of XLAS characterized by late-onset renal failure and less frequent, severe temporal macular thinning relative to other COL4A5 mutations. The pathological basis for the retinal abnormalities of XLAS remains to be established.
Project description:There have been isolated case reports of arterial disease in males with Alport syndrome (AS), a systemic disorder of Type IV collagen. In this paper, we describe five new cases of AS associated with significant aortic disease including dissection and aneurysm.We present brief clinical descriptions of five males with AS and aortic disease. We performed immunohistochemical analysis of the expression of the ?5 chain of Type IV collagen in skin basement membranes from a previously reported family with AS and associated aortic disease and in the aortic media of male mice with X-linked Alport syndrome (XLAS) due to a nonsense mutation in the COL4A5 gene.Three of the five patients exhibited aneurysm and dissection of the thoracic aorta, occurring at 25-32 years of age, while one had aortic dilatation and another had aortic insufficiency. All five men required renal replacement therapy by age 20. Immunohistochemistry of skin biopsy specimens in previously reported male siblings with aortic disease confirmed that they had XLAS. We further found that the ?5 chain of Type IV collagen is abnormally absent from aortic media of transgenic mice with XLAS.Early onset aortic disease may be an unusual feature of AS. Screening of men with AS for aortic abnormalities may be clinically indicated in some families.
Project description:Currently, there are no treatments for Alport syndrome, which is the second most commonly inherited kidney disease. Here we report the development of an exon-skipping therapy using an antisense-oligonucleotide (ASO) for severe male X-linked Alport syndrome (XLAS). We targeted truncating variants in exon 21 of the COL4A5 gene and conducted a type IV collagen α3/α4/α5 chain triple helix formation assay, and in vitro and in vivo treatment efficacy evaluation. We show that exon skipping enabled trimer formation, leading to remarkable clinical and pathological improvements including expression of the α5 chain on glomerular and the tubular basement membrane. In addition, the survival period was clearly prolonged in the ASO treated mice group. This data suggests that exon skipping may represent a promising therapeutic approach for treating severe male XLAS cases.
Project description:Female carriers of X-linked Alport syndrome (XLAS) demonstrate variability in clinical phenotype that, unlike males, cannot be correlated with genotype. X-inactivation, the method by which females (XX) silence transcription from one X chromosome in order to achieve gene dosage parity with males (XY), likely modifies the carrier phenotype, but this hypothesis has not been tested directly.Using a genetically defined mouse model of XLAS, we generated two groups of Alport female (Col4a5(+/-)) carriers that differed only in the X-controlling element (Xce) allele regulating X-inactivation. We followed the groups as far as 6 months of age comparing survival and surrogate outcome measures of urine protein and plasma urea nitrogen.Preferential inactivation of the mutant Col4a5 gene improved survival and surrogate outcome measures of urine protein and plasma urea nitrogen. In studies of surviving mice, we found that X-inactivation in kidney, measured by allele-specific mRNA expression assays, correlated with surrogate outcomes.Our findings establish X-inactivation as a major modifier of the carrier phenotype in X-linked Alport syndrome. Thus, X-inactivation patterns may offer prognostic information and point to possible treatment strategies for symptomatic carriers.
Project description:PURPOSE: To describe an unusual ocular phenotype in a Chinese female patient with X-linked Alport syndrome (XLAS), and to characterize the type IV collagen alpha 5 (COL4A5) gene mutation in the patient and her son. METHODS: Detailed ophthalmologic examinations and optical coherence tomography were performed in the patient and her family members. For gene analysis of COL4A5, the entire coding region of COL4A5 mRNA from cultured skin fibroblast was analyzed by using reverse-transcription-polymerase chain reaction (RT-PCR) and direct sequencing, and genomic DNA was analyzed by using PCR and direct sequencing. RESULTS: The patient presented with progressive myopia at age 14 and bilateral giant macular holes (about 2 disc diameter) at age 28. At age 33 when presented to our hospital, slit lamp examination of the anterior segment showed bilateral anterior and posterior lenticonus; fundus photography and optical coherence tomography showed bilateral giant macular holes which were larger than photographed at age 28. Electron microscopy of renal biopsy showed irregular thinned and thickened areas of the glomerular basement membrane with splitting of the lamina densa. Her son was then found to have hematuria (at age 3), and indirect immunofluorescence of the epidermal basement membrane showed negative staining for the collagen ?5(IV) chain. However, the ophthalmological examinations of her son were unremarkable. A novel COL4A5 mutation g. 4400_4400+1del, leading to an indel in exon 45 (r. 4198delins4198+2_ 4198+72), was detected in the patient and her son. This mutation produces a shift in the reading frame, resulting in a missense sequence of 13 codons followed by a premature stop codon. Her mother was not affected with the mutation. CONCLUSIONS: Our report extends the phenotypic and genotypic spectrum of X-linked Alport syndrome.
Project description:<h4>Background</h4>X-linked Alport syndrome (XLAS), caused by mutations in the type IV collagen COL4A5 gene, accounts for approximately 80% of human Alport syndrome. Dogs with XLAS have a similar clinical progression. Prior studies in autosomal recessive Alport mice demonstrated early mesangial cell invasion as the source of laminin 211 in the glomerular basement membrane (GBM), leading to proinflammatory signaling. The objective of this study was to verify this process in XLAS dogs.<h4>Methods</h4>XLAS dogs and WT littermates were monitored with serial clinicopathologic data and kidney biopsies. Biopsies were obtained at set milestones defined by the onset of microalbuminuria (MA), overt proteinuria, onset of azotemia, moderate azotemia, and euthanasia. Kidney biopsies were analyzed by histopathology, immunohistochemistry, and electron microscopy.<h4>Results</h4>XLAS dogs showed progressive decrease in renal function and progressive increase in interstitial fibrosis and glomerulosclerosis (based on light microscopy and immunostaining for fibronectin). The only identifiable structural abnormality at the time of microalbuminuria was ultrastructural evidence of mild segmental GBM multilamination, which was more extensive when overt proteinuria developed. Co-localization studies showed that mesangial laminin 211 and integrin ?8?1 accumulated in the GBM at the onset of overt proteinuria and coincided with ultrastructural evidence of mild cellular interpositioning, consistent with invasion of the capillary loops by mesangial cell processes.<h4>Conclusion</h4>In a large animal model, the induction of mesangial filopodial invasion of the glomerular capillary loop leading to the irregular deposition of laminin 211 is an early initiating event in Alport glomerular pathology.