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Ozbek DA, Koc SC, Özkan NE, Kablan SE, Yet I, Uner M, Ozlu N, Nemutlu E, Lay I, Ayhan AS, Yildirim T, Arici M, Yilmaz SR, Erdem Y, Altun B. A comparative urinary proteomic and metabolomic analysis between renal aa amyloidosis and membranous nephropathy with clinicopathologic correlations. J Proteomics 2024; 293:105064. [PMID: 38154551 DOI: 10.1016/j.jprot.2023.105064] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2023] [Revised: 11/20/2023] [Accepted: 12/18/2023] [Indexed: 12/30/2023]
Abstract
Urinary omics has become a powerful tool for elucidating pathophysiology of glomerular diseases. However, no urinary omics analysis has been performed yet on renal AA amyloidosis. Here, we performed a comparative urine proteomic and metabolomic analysis between recently diagnosed renal AA amyloidosis (AA) and membranous nephropathy (MN) patients. Urine samples of 22 (8 AA, 8 MN and 6 healthy control) patients were analyzed with nLC-MS/MS and GC/MS for proteomic and metabolomic studies, respectively. Pathological specimens were scored for glomerulosclerosis and tubulointerstitial fibrosis grades. Functional enrichment analysis between AA and control groups showed enrichment in cell adhesion related sub-domains. Uromodulin (UMOD) was lower, whereas ribonuclease 1 (RNase1) and α-1-microglobulin/bikunin precursor (AMBP) were higher in AA compared to MN group. Correlations were demonstrated between UMOD-proteinuria (r = -0.48, p = 0.03) and AMBP-eGFR (r = -0.69, p = 0.003) variables. Metabolomic analysis showed myo-inositol and urate were higher in AA compared to MN group. A positive correlation was detected between RNase1 and urate independent of eGFR values (r = 0.63, p = 0.01). Enrichment in cell adhesion related domains suggested a possible increased urinary shear stress due to amyloid fibrils. UMOD, AMBP and myo-inositol were related with tubulointerstitial damage, whereas RNase1 and urate were believed to be related with systemic inflammation in AA amyloidosis. SIGNIFICANCE: Urinary omics studies have become a standard tool for biomarker studies. However, no urinary omics analysis has been performed yet on renal AA amyloidosis. Here, we performed a comparative urinary omics analysis between recently diagnosed renal AA amyloidosis (AA), membranous nephropathy (MN) patients and healthy controls. Pathological specimens were scored with glomerulosclerosis (G) and tubulointerstitial fibrosis (IF) grades to consolidate the results of the omics studies and correlation analyzes. Functional enrichment analysis showed enrichment in cell adhesion related sub-domains due to downregulation of cadherins; which could be related with increased urinary shear stress due to amyloid deposition and disruption of tissue micro-architecture. In comparative proteomic analyzes UMOD was lower, whereas RNase1 and AMBP were higher in AA compared to MN group. Whereas in metabolomic analyzes; myo-inositol, urate and maltose were higher in AA compared to MN group. Correlations were demonstrated between UMOD-proteinuria (r = -0.48, p = 0.03), AMBP-eGFR (r = -0.69, p = 0.003) and between RNase1-Urate independent of eGFR values (r = 0.63, p = 0.01). This study is the first comprehensive urinary omics analysis focusing on renal AA Amyloidosis to the best of our knowledge. Based on physiologic roles and clinicopathologic correlations of the molecules; UMOD, AMBP and myo-inositol were related with tubulointerstitial damage, whereas RNase1 and urate were believed to be increased with systemic inflammation and endothelial damage in AA amyloidosis.
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Affiliation(s)
- Deniz Aral Ozbek
- Hacettepe University Faculty of Medicine, Department of Internal Medicine, Ankara, Turkey.
| | - Sila Cankurtaran Koc
- Hacettepe University Faculty of Medicine, Department of Nephrology, Ankara, Turkey
| | - Nazlı Ezgi Özkan
- Koc University Research Center for Translational Medicine, Istanbul, Turkey
| | - Sevilay Erdogan Kablan
- Hacettepe University Faculty of Pharmacy, Department of Analytical Chemistry, Ankara, Turkey
| | - Idil Yet
- Hacettepe University Graduate School of Health Sciences, Department of Bioinformatics, Ankara, Turkey
| | - Meral Uner
- Hacettepe University Faculty of Medicine, Department of Pathology, Ankara, Turkey
| | - Nurhan Ozlu
- Koc University Research Center for Translational Medicine, Istanbul, Turkey
| | - Emirhan Nemutlu
- Hacettepe University Faculty of Pharmacy, Department of Analytical Chemistry, Ankara, Turkey
| | - Incilay Lay
- Hacettepe University Faculty of Medicine, Department of Biochemistry, Ankara, Turkey
| | - Arzu Saglam Ayhan
- Hacettepe University Faculty of Medicine, Department of Pathology, Ankara, Turkey
| | - Tolga Yildirim
- Hacettepe University Faculty of Medicine, Department of Nephrology, Ankara, Turkey
| | - Mustafa Arici
- Hacettepe University Faculty of Medicine, Department of Nephrology, Ankara, Turkey
| | - Seref Rahmi Yilmaz
- Hacettepe University Faculty of Medicine, Department of Nephrology, Ankara, Turkey
| | - Yunus Erdem
- Hacettepe University Faculty of Medicine, Department of Nephrology, Ankara, Turkey
| | - Bulent Altun
- Hacettepe University Faculty of Medicine, Department of Nephrology, Ankara, Turkey
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Stamellou E, Seikrit C, Tang SCW, Boor P, Tesař V, Floege J, Barratt J, Kramann R. IgA nephropathy. Nat Rev Dis Primers 2023; 9:67. [PMID: 38036542 DOI: 10.1038/s41572-023-00476-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 10/26/2023] [Indexed: 12/02/2023]
Abstract
IgA nephropathy (IgAN), the most prevalent primary glomerulonephritis worldwide, carries a considerable lifetime risk of kidney failure. Clinical manifestations of IgAN vary from asymptomatic with microscopic or intermittent macroscopic haematuria and stable kidney function to rapidly progressive glomerulonephritis. IgAN has been proposed to develop through a 'four-hit' process, commencing with overproduction and increased systemic presence of poorly O-glycosylated galactose-deficient IgA1 (Gd-IgA1), followed by recognition of Gd-IgA1 by antiglycan autoantibodies, aggregation of Gd-IgA1 and formation of polymeric IgA1 immune complexes and, lastly, deposition of these immune complexes in the glomerular mesangium, leading to kidney inflammation and scarring. IgAN can only be diagnosed by kidney biopsy. Extensive, optimized supportive care is the mainstay of therapy for patients with IgAN. For those at high risk of disease progression, the 2021 KDIGO Clinical Practice Guideline suggests considering a 6-month course of systemic corticosteroid therapy; however, the efficacy of systemic steroid treatment is under debate and serious adverse effects are common. Advances in understanding the pathophysiology of IgAN have led to clinical trials of novel targeted therapies with acceptable safety profiles, including SGLT2 inhibitors, endothelin receptor blockers, targeted-release budesonide, B cell proliferation and differentiation inhibitors, as well as blockade of complement components.
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Affiliation(s)
- Eleni Stamellou
- Department of Nephrology, School of Medicine, University of Ioannina, Ioannina, Greece
- Department of Nephrology and Clinical Immunology, RWTH Aachen University Hospital, Aachen, Germany
| | - Claudia Seikrit
- Department of Nephrology and Clinical Immunology, RWTH Aachen University Hospital, Aachen, Germany
| | - Sydney C W Tang
- Division of Nephrology, Department of Medicine, University of Hong Kong, Hong Kong, China
| | - Peter Boor
- Department of Nephrology and Clinical Immunology, RWTH Aachen University Hospital, Aachen, Germany
- Department of Pathology, RWTH Aachen University, Aachen, Germany
| | - Vladimir Tesař
- Department of Nephrology, 1st Faculty of Medicine and General University Hospital, Charles University, Prague, Czech Republic
| | - Jürgen Floege
- Department of Nephrology and Clinical Immunology, RWTH Aachen University Hospital, Aachen, Germany
| | - Jonathan Barratt
- Department of Cardiovascular Sciences, University of Leicester, Leicester, UK
| | - Rafael Kramann
- Department of Nephrology and Clinical Immunology, RWTH Aachen University Hospital, Aachen, Germany.
- Department of Internal Medicine, Nephrology and Transplantation, Erasmus Medical Center, Rotterdam, Netherlands.
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Jin L, Niu C, Ni Y. Correlation between peripheral blood α1-MG, DNMT1 expression, and the severity of diabetic nephropathy renal pathological damage. Medicine (Baltimore) 2023; 102:e35409. [PMID: 37861555 PMCID: PMC10589556 DOI: 10.1097/md.0000000000035409] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/06/2023] [Accepted: 09/05/2023] [Indexed: 10/21/2023] Open
Abstract
To explore the correlation between peripheral blood α1-microglobulin (α1-MG) and monocyte DNA methyltransferase 1 (DNMT1) expression and the severity of renal pathological damage in diabetic nephropathy (DN). The study group comprised 100 patients with DN who underwent treatment at our hospital from January 2022 to January 2023, while the control group consisted of 50 patients with uncomplicated diabetes. The relative expression levels of peripheral blood α1-MG and DNMT1 were compared between the 2 groups of patients. Additionally, the levels of vascular endothelial growth factor (VEGF) were measured, and the diagnostic value of DN was explored using ROC curves. Furthermore, the correlation between the aforementioned indicators and the severity of renal pathological damage in the patients of the study group was analyzed. Compared to the patients in the control group, the patients in the study group showed increased relative expression levels of peripheral blood α1-MG and DNMT1, as well as elevated levels of VEGF (P < .05). The diagnostic value of peripheral blood α1-MG, DNMT1 relative expression levels, and VEGF levels for DN was explored using ROC curves. The AUC values were 0.907, 0.923, and 0.936, respectively (P < .05). The relative expression levels of peripheral blood α1-MG, DNMT1, and VEGF levels in DN patients increase with the elevation of the interstitial fibrosis and tubular atrophy scoring (IFTA) score, showing a positive correlation with r-values of 0.651, 0.710, and 0.628, respectively (P < .05). The relative expression levels of peripheral blood α1-MG, DNMT1, and VEGF levels in DN patients increase with the elevation of the interstitial inflammation score, showing a positive correlation with r-values of 0.771, 0.633, and 0.678, respectively (P < .05). The relative expression levels of peripheral blood α1-MG, DNMT1, and VEGF levels in DN patients increase with the elevation of the glomerular grading, showing a positive correlation with r-values of 0.714, 0.609, and 0.677, respectively (P < .05). The expression levels of peripheral blood α1-MG, DNMT1, and VEGF are significantly elevated in patients with DN. These levels show a positive correlation with the IFTA score, interstitial inflammation score, and glomerular grading, contributing to the diagnosis and assessment of DN.
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Affiliation(s)
- Liang Jin
- Department of Hand and Foot Surgery, Xingtai People’s Hospital, Xingtai, Hebei, People’s Republic of China
| | - Chao Niu
- Department of Hand and Foot Surgery, Xingtai People’s Hospital, Xingtai, Hebei, People’s Republic of China
| | - Yulong Ni
- Department of Hand and Foot Surgery, Xingtai People’s Hospital, Xingtai, Hebei, People’s Republic of China
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Development and Evaluation of a Robust Sandwich Immunoassay System Detecting Serum WFA-Reactive IgA1 for Diagnosis of IgA Nephropathy. Int J Mol Sci 2022; 23:ijms23095165. [PMID: 35563555 PMCID: PMC9104065 DOI: 10.3390/ijms23095165] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2022] [Revised: 04/28/2022] [Accepted: 05/03/2022] [Indexed: 02/04/2023] Open
Abstract
Aberrant glycosylation of IgA1 is involved in the development of IgA nephropathy (IgAN). There are many reports of IgAN markers focusing on the glycoform of IgA1. None have been clinically applied as a routine test. In this study, we established an automated sandwich immunoassay system for detecting aberrant glycosylated IgA1, using Wisteria floribunda agglutinin (WFA) and anti-IgA1 monoclonal antibody. The diagnostic performance as an IgAN marker was evaluated. The usefulness of WFA for immunoassays was investigated by lectin microarray. A reliable standard for quantitative immunoassay measurements was designed by modifying a purified IgA1 substrate. A validation study using multiple serum specimens was performed using the established WFA-antibody sandwich automated immunoassay. Lectin microarray results showed that WFA specifically recognized N-glycans of agglutinated IgA1 in IgAN patients. The constructed IgA1 standard exhibited a wide dynamic range and high reactivity. In the validation study, serum WFA-reactive IgA1 (WFA+-IgA1) differed significantly between healthy control subjects and IgAN patients. The findings indicate that WFA is a suitable lectin that specifically targets abnormal agglutinated IgA1 in serum. We also describe an automated immunoassay system for detecting WFA+-IgA1, focusing on N-glycans.
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Zhang S, Sun H, Zhang Z, Li M, Guo Z, Ye W, Cai G, Sun W, Li M. Diagnostic Potential of Plasma IgA1 O-Glycans in Discriminating IgA Nephropathy From Other Glomerular Diseases and Healthy Participants. Front Mol Biosci 2022; 9:871615. [PMID: 35445079 PMCID: PMC9014244 DOI: 10.3389/fmolb.2022.871615] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2022] [Accepted: 03/21/2022] [Indexed: 11/30/2022] Open
Abstract
Background: Aberrant O-glycosylation of IgA1 plays an important role in IgA nephropathy pathogenesis. Previous proteomic studies analyzed O-glycans of the circulating IgA1 hinge region and found that the N-acetylgalactosamine (GalNAc) and galactose numbers in the hinge region of IgA1 of patients with IgA nephropathy were lower than those in healthy participants. However, the diagnostic performance of the O-glycosylation traits in the hinge region of plasma IgA1 for IgA nephropathy remains unelucidated. The present study aimed to determine the difference in plasma IgA1 hinge region O-glycoforms among IgA nephropathy, non-IgA nephropathy disease controls, and healthy participants, and to further evaluate the diagnostic performance of plasma IgA1 glycosylation traits. Methods: Sixty-two patients with biopsy-proven primary IgA nephropathy, 30 age- and sex-matched non-IgA nephropathy disease controls (10 patients with membranous nephropathy, 10 with focal segmental glomerulosclerosis, and 10 with minimal change disease), and 30 healthy participants were prospectively recruited. Plasma galactose deficient-IgA1 levels were measured using a KM55 kit. Plasma IgA was extracted using IgA immunoaffinity beads. After de-N-glycosylation, reduction, alkylation, trypsin digestion, and O-glycopeptide enrichment via hydrophilic interaction liquid chromatography, liquid chromatography tandem mass spectrometry (LC-MS/MS) was applied to analyze the IgA1 O-glycosylation patterns and we derived the plasma IgA1 O-glycosylation traits. Results: Plasma IgA1 O-glycosylation patterns were significantly changed in IgA nephropathy patients compared to those with non-IgA nephropathy disease controls and healthy participants. The GalNAc number was lowest in IgA nephropathy patients. In addition, a similar result was observed for the galactose number in the IgA1 hinge region. These values showed moderate potential for discriminating between IgA nephropathy and the controls. When these values were combined, the area under the curve increased compared to when they were considered individually. When further adding a clinical indicator, the area under the curve of the GalNAc-galactose-IgA panel exceed 0.9 in discriminating IgA nephropathy from the controls. Conclusion: The amount of GalNAc and galactose in plasma IgA1 hinge region identified by glycoproteomics could be used as a diagnostic biomarker for IgA nephropathy. The panel containing GalNAc, galactose, and circulating IgA displayed excellent diagnostic performance and is promising for practical clinical applications.
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Affiliation(s)
- Shuyu Zhang
- Department of Nephrology, State Key Laboratory of Complex Severe and Rare Diseases, Peking Union Medical College Hospital, Chinese Academy of Medical Science and Peking Union Medical College, Beijing, China
| | - Haidan Sun
- Core Facility of Instruments, School of Basic Medicine, Peking Union Medical College, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences, Beijing, China
| | - Zejian Zhang
- Medical Research Center, State Key Laboratory of Complex Severe and Rare Diseases, Peking Union Medical College Hospital, Chinese Academy of Medical Science and Peking Union Medical College, Beijing, China
| | - Menglin Li
- State Key Laboratory of Bioactive Substances and Functions of Natural Medicines, Institute of Materia Medica, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China
| | - Zhengguang Guo
- Core Facility of Instruments, School of Basic Medicine, Peking Union Medical College, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences, Beijing, China
| | - Wenling Ye
- Department of Nephrology, State Key Laboratory of Complex Severe and Rare Diseases, Peking Union Medical College Hospital, Chinese Academy of Medical Science and Peking Union Medical College, Beijing, China
| | - Guangyan Cai
- Department of Nephrology, The First Medical Centre, Chinese PLA General Hospital, Medical School of Chinese PLA, Beijing, China
- *Correspondence: Mingxi Li, ; Wei Sun, ; Guangyan Cai,
| | - Wei Sun
- Core Facility of Instruments, School of Basic Medicine, Peking Union Medical College, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences, Beijing, China
- *Correspondence: Mingxi Li, ; Wei Sun, ; Guangyan Cai,
| | - Mingxi Li
- Department of Nephrology, State Key Laboratory of Complex Severe and Rare Diseases, Peking Union Medical College Hospital, Chinese Academy of Medical Science and Peking Union Medical College, Beijing, China
- *Correspondence: Mingxi Li, ; Wei Sun, ; Guangyan Cai,
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Zhang X, Lv J, Liu P, Xie X, Wang M, Liu D, Zhang H, Jin J. Poly-IgA Complexes and Disease Severity in IgA Nephropathy. Clin J Am Soc Nephrol 2021; 16:1652-1664. [PMID: 34607844 PMCID: PMC8729420 DOI: 10.2215/cjn.01300121] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2021] [Accepted: 09/21/2021] [Indexed: 02/04/2023]
Abstract
BACKGROUND AND OBJECTIVES Poly-IgA immune complex formation and glomerular deposition play a key role in IgA nephropathy. Our study sought to develop a new methodology for one-step serologic detection of poly-IgA levels. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS A novel ELISA method using recombinant CD89 as a "capturing" probe was established for detecting poly-IgA immune complex in plasma. We applied semiquantitative measurements of these poly-IgA indices in patients recruited at Peking University First Hospital who had IgA nephropathy or other kidney disease types, as compared with healthy controls. The longitudinal trend of the poly-IgA index and the association with pathologic parameters and treatment responses were evaluated. Finally, we analyzed the molecular composition of poly-IgA complexes in patients by mass spectrometry. RESULTS Recombinant CD89-mounted ELISA plates specifically captured plasma poly-IgA. The levels of poly-IgA immune complex (26.7 [interquartile range (IQR) 17.1-42.6] U/ml) in IgA nephropathy were significantly higher than those in healthy controls (15.5 [IQR 10.7-20.0] U/ml; P<0.001) or in controls with non-IgA nephropathy disease (14.8 [IQR 10.5-21.9] U/ml; P<0.001). Higher levels of poly-IgA immune complex were associated with lower eGFR and worse kidney outcome. Accuracy parameters and concordant statistics showed good discrimination between IgA nephropathy and healthy controls based on poly-IgA index levels (area under the curve [AUC], 0.78; 95% confidence interval [95% CI], 0.72 to 0.83; P<0.001), significantly outperforming galactose-deficient IgA1 levels (AUC, 0.70; P=0.05). Corticosteroid and immunosuppressant treatments lowered poly-IgA indices. After a recombinant CD89-directed workflow in conjunction with mass spectrometry, we also analyzed the molecular composition of IgA immune complex in patients with IgA nephropathy. CONCLUSIONS Higher level of recombinant CD89-bound poly-IgA immune complex was associated with the severity of the disease and with treatment response to steroids and immunosuppressants.
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Affiliation(s)
- Xue Zhang
- Renal Division, Peking University First Hospital, Beijing, China,Peking University Institute of Nephrology, Beijing, China,Key Laboratory of Renal Disease, Ministry of Health of China, Beijing, China,Key Laboratory of Chronic Kidney Disease Prevention and Treatment (Peking University), Ministry of Education, Beijing, China,Research Units of Diagnosis and Treatment of Immune-Mediated Kidney Diseases, Chinese Academy of Medical Sciences, Beijing, China
| | - Jicheng Lv
- Renal Division, Peking University First Hospital, Beijing, China,Peking University Institute of Nephrology, Beijing, China,Key Laboratory of Renal Disease, Ministry of Health of China, Beijing, China,Key Laboratory of Chronic Kidney Disease Prevention and Treatment (Peking University), Ministry of Education, Beijing, China,Research Units of Diagnosis and Treatment of Immune-Mediated Kidney Diseases, Chinese Academy of Medical Sciences, Beijing, China
| | - Pan Liu
- Division of Nephrology and Feinberg Cardiovascular and Renal Research Institute, Northwestern University Feinberg School of Medicine, Chicago, Illinois
| | - Xinfang Xie
- Division of Nephrology and Feinberg Cardiovascular and Renal Research Institute, Northwestern University Feinberg School of Medicine, Chicago, Illinois
| | - Manliu Wang
- Renal Division, Peking University First Hospital, Beijing, China,Peking University Institute of Nephrology, Beijing, China,Key Laboratory of Renal Disease, Ministry of Health of China, Beijing, China,Key Laboratory of Chronic Kidney Disease Prevention and Treatment (Peking University), Ministry of Education, Beijing, China,Research Units of Diagnosis and Treatment of Immune-Mediated Kidney Diseases, Chinese Academy of Medical Sciences, Beijing, China
| | - Dan Liu
- Proteomics Laboratory, Medical and Health Analytical Center, Peking University, Beijing, China
| | - Hong Zhang
- Renal Division, Peking University First Hospital, Beijing, China,Peking University Institute of Nephrology, Beijing, China,Key Laboratory of Renal Disease, Ministry of Health of China, Beijing, China,Key Laboratory of Chronic Kidney Disease Prevention and Treatment (Peking University), Ministry of Education, Beijing, China,Research Units of Diagnosis and Treatment of Immune-Mediated Kidney Diseases, Chinese Academy of Medical Sciences, Beijing, China
| | - Jing Jin
- Division of Nephrology and Feinberg Cardiovascular and Renal Research Institute, Northwestern University Feinberg School of Medicine, Chicago, Illinois
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Pathogenesis of IgA Nephropathy: Current Understanding and Implications for Development of Disease-Specific Treatment. J Clin Med 2021; 10:jcm10194501. [PMID: 34640530 PMCID: PMC8509647 DOI: 10.3390/jcm10194501] [Citation(s) in RCA: 28] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2021] [Accepted: 09/22/2021] [Indexed: 12/20/2022] Open
Abstract
IgA nephropathy, initially described in 1968 as a kidney disease with glomerular “intercapillary deposits of IgA-IgG”, has no disease-specific treatment and is a common cause of kidney failure. Clinical observations and laboratory analyses suggest that IgA nephropathy is an autoimmune disease wherein the kidneys are damaged as innocent bystanders due to deposition of IgA1-IgG immune complexes from the circulation. A multi-hit hypothesis for the pathogenesis of IgA nephropathy describes four sequential steps in disease development. Specifically, patients with IgA nephropathy have elevated circulating levels of IgA1 with some O-glycans deficient in galactose (galactose-deficient IgA1) and these IgA1 glycoforms are recognized as autoantigens by unique IgG autoantibodies, resulting in formation of circulating immune complexes, some of which deposit in glomeruli and activate mesangial cells to induce kidney injury. This proposed mechanism is supported by observations that (i) glomerular immunodeposits in patients with IgA nephropathy are enriched for galactose-deficient IgA1 glycoforms and the corresponding IgG autoantibodies; (ii) circulatory levels of galactose-deficient IgA1 and IgG autoantibodies predict disease progression; and (iii) pathogenic potential of galactose-deficient IgA1 and IgG autoantibodies was demonstrated in vivo. Thus, a better understanding of the structure–function of these immunoglobulins as autoantibodies and autoantigens will enable development of disease-specific treatments.
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