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Activated Innate Immunity and Involvement of the CX3CR1-FKN Axis in Promoting Hematuria in IgA Nephropathy Patients

ABSTRACT: The hallmark of IgA nephropathy (IgAN) is gross hematuria (GH) coinciding with or immediately following an upper respiratory or gastrointestinal tract infection and can represent the disease triggering event. Therefore, a whole genomic screening of IgAN patients during the GH was done to clarify the link between mucosal encountered antigens and the occurrence of glomerular hematuria. The modulated genes during GH show a clear involvement of the interferon signalling, antigen presenting pathway, and the immuno-proteasome. The gene characterizing cytotoxic effector lymphocytes (CX3CR1) implicated in vascular endothelial damage, was found up-regulated at both mRNA and protein level. In vitro antigenic stimulation of PBMCs on an independent set of IgAN patients and healthy blood donors (HBS) demonstrated that patients upregulate specifically CX3CR1 in an enhanced and dose dependant manner, while an expected down-regulation occurred in HBD. This enhanced activation occurred in both patients characterized by recurrent GH and by permanent microscopic hematuria (MH). We then analyzed glomerular fractalkine (FKN) expression, since this ligand is involved in the vascular gateway for CX3CR1+ cells towards the inflamed tissues. A significantly higher FKN expression on the capillary vessels and podocytes was found in recurrent GH patients compared to permanent MH, suggesting a predisposition for cytotoxic cell extravasation in recurrent GH patients. Taken together, our findings demonstrate, for the first time, a defect in antigen handling in PBMCs of IgAN patients with a specific up-regulation of CX3CR1. Furthermore, the constitutive up regulation of glomerular FKN, suggests an involvement of the CX3CR1-FKN axis in the exacerbation of GH.

ORGANISM(S): Homo sapiens

PROVIDER: GSE27676 | GEO | 2012/03/30

SECONDARY ACCESSION(S): PRJNA138189

REPOSITORIES: GEO

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Project description:The hallmark of IgA nephropathy (IgAN) is gross hematuria (GH) coinciding with or immediately following an upper respiratory or gastrointestinal tract infection and can represent the disease triggering event. Therefore, a whole genomic screening of IgAN patients during the GH was done to clarify the link between mucosal encountered antigens and the occurrence of glomerular hematuria. The modulated genes during GH show a clear involvement of the interferon signalling, antigen presenting pathway, and the immuno-proteasome. The gene characterizing cytotoxic effector lymphocytes (CX3CR1) implicated in vascular endothelial damage, was found up-regulated at both mRNA and protein level. In vitro antigenic stimulation of PBMCs on an independent set of IgAN patients and healthy blood donors (HBS) demonstrated that patients upregulate specifically CX3CR1 in an enhanced and dose dependant manner, while an expected down-regulation occurred in HBD. This enhanced activation occurred in both patients characterized by recurrent GH and by permanent microscopic hematuria (MH). We then analyzed glomerular fractalkine (FKN) expression, since this ligand is involved in the vascular gateway for CX3CR1+ cells towards the inflamed tissues. A significantly higher FKN expression on the capillary vessels and podocytes was found in recurrent GH patients compared to permanent MH, suggesting a predisposition for cytotoxic cell extravasation in recurrent GH patients. Taken together, our findings demonstrate, for the first time, a defect in antigen handling in PBMCs of IgAN patients with a specific up-regulation of CX3CR1. Furthermore, the constitutive up regulation of glomerular FKN, suggests an involvement of the CX3CR1-FKN axis in the exacerbation of GH. Gene expression profile comparison 3 IgAN patients at two different clinical time points, the first sample during the gross hematuria episode and the second during the remission phase of the disease characterized by microscopic hematuria

Project description:Background: In a previous study of patients with assumed benign IgA nephropathy (IgAN), we have shown that 18.6% develop a progressive clinical course, which was not predicted by any known clinical nor histopathological parameters (Knoop 2017). We aim to differentiate between future progressors and non-progressors with assumed benign IgAN by using glomerular transcriptomics from diagnostic kidney biopsies and to investigate whether this can identify drugs to be used in those patients. Methods: We included adult progressors (n=15) and patients with clinical remission (non-progressors, n=21) from our previously reported IgAN cohort. Glomerular cross-sections were obtained through laser-capture microdissection from 10µm archival kidney biopsy sections for mRNA sequencing, using the SMARTer Stranded Total RNA-Seq kit – Pico Input Mammalian (Clontech Laboratories, California, USA). Key results were validated in external cohorts and on the protein level with immunohistochemistry in the discovery cohort and an internal validation cohort. We also compared our transcriptomic findings with an external genome-wide association study (GWAS) dataset (Kiryluk 2021). Results: For the statistical analyses, we studied 8 progressors and 9 non-progressors. Based on the 1,240 differentially expressed glomerular genes from the initial kidney biopsies, we were able to identify future IgAN progressors and non-progressors using a two-component classifier. The classifier predicted disease progression with 88% accuracy, 75% sensitivity and 100% specificity (AUC=0.875), more accurate than the recommended International IgAN Prediction Tool in this specific patient cohort. Among our differentially expressed genes, 10 were also found in the GWAS dataset (Kiryluk 2021). We identified 45 drug targets in the DrugBank database, including angiotensinogen, a target of sparsentan, currently investigated as therapy in IgAN (NCT03762850 and NCT04663204). The findings on upregulation of angiotensinogen, which was independent of blood pressure, were validated in an internal IgAN validation cohort. Interestingly, complement activation did not play a major role in our data. Our work suggests that LXR, FXR and macrophage activation pathways could be critically involved in the inhibition of the progression of low-risk ccRCC. Furthermore, a 10-component classifier could support an early identification of apparently low-risk ccRCC patients.

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Activated Innate Immunity and Involvement of the CX3CR1-FKN Axis in Promoting Hematuria in IgA Nephropathy Patients

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