Expression of CD19+CD5+B Cells and IgA1-positive cells in Tonsillar Tissues of IgA Nephropathy Patients

Decrypting the Pathological Pathways in IgA Nephropathy

IgAN is the most common form of glomerulonephritis affecting 2000000 people annually. The disease ultimately progresses to chronic renal failure and ESRD. In this article, we focused on a comprehensive understanding of the pathogenesis of the disease and thus identifying different target proteins that could be essential in therapeutic approaches in the management of the disease. Aberrantly glycosylated IgA1 produced by the suppression of the enzyme β-1, 3 galactosyltransferase ultimately triggered the formation of IgG autoantibodies which form complexes with Gd-IgA1. The complex gets circulated through the blood vessels through monocytes and ultimately gets deposited in the glomerular mesangial cells via CD71 receptors present locally. This complex triggers the inflammatory pathways activating the alternate complement system, various types of T Cells, toll-like receptors, cytokines, and chemokines ultimately recruiting the phagocytic cells to eliminate the Gd-IgA complex. The inflammatory proteins cause severe mesangial and podocyte damage in the kidney which ultimately initiates the repair process following chronic inflammation by an important protein named TGFβ1. TGF β1 is an important protein produced during chronic inflammation mediating the repair process via various downstream transduction proteins and ultimately producing fibrotic proteins which help in the repair process but permanently damage the glomerular cells.

Gut-kidney axis in IgA nephropathy: Role on mesangial cell metabolism and inflammation

IgA Nephropathy (IgAN) is the commonest primary glomerular disease around the world and represents a significant cause of end-stage renal disease. IgAN is characterized by mesangial deposition of IgA-immune complexes and mesangial expansion. The pathophysiological process includes an abnormally glycosylated IgA1, which is an antigenic target. Autoantibodies specifically recognize galactose-deficient IgA1 forming immune complexes that are amplified in size by the soluble IgA Fc receptor CD89 leading to deposition in the mesangium through interaction with non-classical IgA receptors. The local production of cytokines promotes local inflammation and complement system activation, besides the stimulation of mesangial proliferation. The spectrum of clinical manifestations is quite variable from asymptomatic microscopic hematuria to rapidly progressive glomerulonephritis. Despite all the advances, the pathophysiology of the disease is still not fully elucidated. The mucosal immune system is quoted to be a factor in triggering IgAN and a "gut-kidney axis" is proposed in its development. Furthermore, many recent studies have demonstrated that food intake interferes directly with disease prognosis. In this review, we will discuss how mucosal immunity, microbiota, and nutritional status could be interfering directly with the activation of intrinsic pathways of the mesangial cells, directly resulting in changes in their function, inflammation and development of IgAN.

ST6Gal1 is up-regulated and associated with aberrant IgA1 glycosylation in IgA nephropathy: An integrated analysis of the transcriptome

Galactose-deficient IgA1 (Gd-IgA1) plays a crucial role in the development of Immunoglobulin A nephropathy (IgAN), however, the underlying pathogenic mechanisms driving Gd-IgA1 production in B cells are not well understood. In this study, RNA-seq analysis identified 337 down-regulated and 405 up-regulated genes in B cells from 17 patients with IgAN and 6 healthy controls. Among them, ST6Gal1, which was associated with IgAN in a previous genome-wide association study (GWAS), was up-regulated in IgAN and significantly positive correlated with elevated Gd-IgA1. In addition, we identified increased plasma ST6Gal1 levels in 100 patients with IgAN, which were associated with higher levels of proteinuria, plasma IgA, Gd-IgA1 levels, greater degrees of systemic complement activation including C3a, Bb, C4d, MAC and a lower proportion classified as C2 grade (crescent proportion ≥25%). Interesting, in vitro, recombinant ST6Gal1 (rST6Gal1) exposure reduced the production of Gd-IgA1 in cultured peripheral blood mononuclear cells from IgAN patients. rST6Gal1 stimuli also increased expression of C1GALT1, which were well-known proportional to the decrease in galactose deficiency of IgA1. In conclusions, we identified increased plasma ST6Gal1 levels and the association of ST6Gal1 with disease severity of IgAN. Additionally, rST6Gal1 administration in vitro increased expression of C1GALT1 and reduced the production of Gd-IgA1.

The Role of Immune Modulation in Pathogenesis of IgA Nephropathy

IgA nephropathy (IgAN) is the most prevalent primary glomerulonephritis worldwide, with diverse clinical manifestations characterized by recurrent gross hematuria or microscopic hematuria, and pathological changes featuring poorly O-galactosylated IgA1 deposition in the glomerular mesangium. Pathogenesis has always been the focus of IgAN studies. After 50 years of research, most scholars agree that IgAN is a group of clinicopathological syndromes with certain common immunopathological characteristics, and multiple mechanisms are involved in its pathogenesis, including immunology, genetics, and environmental or nutritional factors. However, the precise pathogenetic mechanisms have not been fully determined. One hypothesis about the pathogenesis of IgAN suggests that immunological factors are engaged in all aspects of IgAN development and play a critical role. A variety of immune cells (e.g., dendritic cells, NK cells, macrophages, T-lymphocyte subsets, and B-lymphocytes, etc.) and molecules (e.g., IgA receptors, Toll-like receptors, complements, etc.) in innate and adaptive immunity are involved in the pathogenesis of IgAN. Moreover, the abnormality of mucosal immune regulation is the core of IgAN immunopathogenesis. The roles of tonsil immunity or intestinal mucosal immunity, which have received more attention in recent years, are supported by mounting evidence. In this review, we will explore the latest research insights on the role of immune modulation in the pathogenesis of IgAN. With a better understanding of immunopathogenesis of IgAN, emerging therapies will soon become realized.

Increased Non-switched Memory B Cells are Associated with Plasmablasts, Serum IL-6 Levels and Renal Functional Impairments in IgAN Patients

Background: Circulating B cells are crucial for the pathogenesis of IgA nephropathy (IgAN). This study aimed at investigating the relationship between frequency of different subsets of circulating B cells and clinical measures in IgAN patients.Methods: The percentages of different subsets of circulating B cells in 23 IgAN patients and 14 healthy controls (HC) were determined by flow cytometry. Their serum IL-6 levels were measured by Cytometric Bead Array (CBA). Clinical parameters in five patients were measured before and after treatment for 8-12 weeks. The potential relationship between variants was analyzed.Results: In comparison with the HC, the frequency of CD3-CD19+ CD27+ IgD+IgM+ non-switched memory B cells (P = .0038) and CD3-CD19+ CD27hiCD38hi plasmablasts (P = .0467) and serum IL-6 (P = .0392) levels significantly increased in IgAN patients. The percentages of non-switched memory B cells were positively correlated with plasmablasts (R = 0.5781, P = .0039) and serum IL-6 levels (R = 0.6663, P = .0005) in the patients. The percentages of non-switched memory B cells (R = 0.8399, P < .0001), plasmablasts (R = 0.4486, P = .0318) and the levels of serum IL-6 (R = 0.5461, P = .0070) were positively correlated with the values of 24-h urine proteins in IgAN patients. The serum levels of IL-6 were negatively correlated with the eGFR values. Following standard treatment, the frequency of non-switched memory B cells and plasmablasts and the levels of 24-h urine proteins (P = .0317, P = .0079, P < .05) significantly decreased in IgAN patients.Conclusions: Abnormally higher frequency of non-switched memory B cells and plasmablasts may contribute to the pathogenesis of IgAN and be potential biomarkers for IgAN.

Activation of the interleukin-4/signal transducer and activator of transcription 6 signaling pathway and homeodomain-interacting protein kinase 2 production by tonsillar mononuclear cells in IgA nephropathy

BACKGROUND/AIM

Clinical development and exacerbation of IgA nephropathy (IgAN) are frequently preceded by episodes of upper respiratory tract infection such as tonsillitis. This study aimed to determine the role of the interleukin-4 (IL-4)/signal transducer and activator of transcription 6 (STAT6) signaling pathway and homeodomain-interacting protein kinase 2 (HIPK2) in aberrant IgA1 O-glycosylation production, and identify potential therapeutic targets in IgAN.

METHODS

Expression levels of IL-4, STAT6, core1β1,3-galactosyltransferase (C1GALT1C1), core1β3GalT-specific molecular chaperone (Cosmc) and HIPK2 in tonsil components were examined by immunohistochemical and immunofluorescence staining. Lymphocytes isolated from 22 patients with IgAN and 24 patients with chronic tonsillitis (CT) as controls were cultured for 72 h with or without IL-4, lipopolysaccharide (LPS) and α-hemolytic streptococcus (HS) stimulation. Expression levels of STAT6, C1GALT1C1, Cosmc, HIPK2-mRNA and protein were measured by real-time PCR and Western blot analysis, respectively. The concentration of IgA1 and level of O-glycosylation were determined by ELISA and Vicia villosa (VV) lectin-binding assay. To determine the contribution of HIPK2 in IgA secretion and O-glycosylation, cells were subjected to experiments for evaluation of HIPK2 silencing by Hipk2-siRNA transfection.

RESULTS

The IL-4/STAT6 signaling pathway was highly activated in all tonsil tissues (including the germinal center and tonsillar crypt epithelium) of IgAN patients, but the gene or protein expression of β1,3-Gal transferase (C1GALT1) and COSMC decreased significantly in patients with IgAN in comparison with those with CT. Hipk2 production in the tonsils derived from IgAN patients was significantly higher than that of CT patients. HIPK2-mRNA expression significantly negatively correlated with renal function as expressed by the estimated glomerular filtration rate, and also significantly positively correlated with daily proteinuria. The level of IL-4, STAT6 and HIPK2 were closely related with Lee's pathological grading system. The levels of mRNA and protein encoding STAT6 and Hipk2 in cells coincubated with IL-4, LPS and HS were significantly higher than those in the controls without stimulation; however, in the IgAN group the levels of mRNA and protein encoding C1GALT1 and Cosmc were significantly lower compared to the controls. IgA1 concentrations of supernatants in IgAN patients were remarkably higher under conditions of external stimulation. As expected, the optical density value of VV lectin binding to IgA1 increased after external stimulation in the IgAN group. By siRNA transfection, our results clearly indicate that Hipk2 negatively regulates C1GALT1 and Cosmc expression. Importantly, HIPK2-siRNA attenuates the aberrant glycosylation of IgA1 secretion.

CONCLUSION

We identified and confirmed that activation of the IL-4/STAT6 signaling pathway has a crucial role in aberrant glycosylation of IgA1 secretion. HIPK2, a protein kinase previously unrecognized in kidney disease, may mediate the glycosylation of IgA1. We believe that HIPK2 could be a new therapeutic target for IgAN, especially as protein kinases are 'drugable' targets.