O-glycoforms of polymeric IgA1 in the plasma of patients with IgA nephropathy are associated with pathological phenotypes

GalNAc-T14 may Contribute to Production of Galactose-Deficient Immunoglobulin A1, the Main Autoantigen in IgA Nephropathy

Introduction

Immunoglobulin A1 (IgA1) with galactose-deficient O-glycans (Gd-IgA1) play a key role in the pathogenesis of IgA nephropathy (IgAN). Mucosal-tissue infections increase IL-6 production and, in patients with IgAN, are often associated with macroscopic hematuria. IgA1-secreting cell lines derived from the circulation of patients with IgAN, compared to those of healthy controls (HCs), produce more IgA1 that has O-glycans with terminal or sialylated N-acetylgalactosamine (GalNAc). GalNAc residues are added to IgA1 hinge region by some of the 20 GalNAc transferases, the O-glycosylation-initiating enzymes. Expression of GALNT2, encoding GalNAc-T2, the main enzyme initiating IgA1 O-glycosylation, is similar in cells derived from patients with IgAN and HCs. In this report, we extend our observations of GALNT14 overexpression in IgA1-producing cell lines from patients with IgAN.

Methods

GALNT14 expression was analyzed in peripheral blood mononuclear cells (PBMCs) from patients with IgAN and from HCs. Moreover, the effect of GALNT14 overexpression or knock-down on Gd-IgA1 production in Dakiki cells was assessed.

Results

GALNT14 was overexpressed in PBMCs from patients with IgAN. IL-6 increased GALNT14 expression in PBMCs from patients with IgAN and HCs. We used IgA1-producing cell line Dakiki, a previously reported model of Gd-IgA1-producing cells, and showed that overexpression of GalNAc-T14 enhanced galactose deficiency of IgA1, whereas siRNA-mediated GalNAc-T14 knock-down reduced it. GalNAc-T14 was localized in trans-Golgi network, as expected.

Conclusions

Overexpression of GALNT14 due to inflammatory signals during mucosal infections may contribute to overproduction of Gd-IgA1 in patients with IgAN.

The Presence of ANCA in IgA Crescentic Nephropathy Does Not Lead to Worse Prognosis with Intensive Rescue Treatment

BACKGROUND

Immunoglobulin A nephropathy (IgAN) is the most common glomerulonephritis worldwide. The concomitant presence of both crescentic proliferation and anti-neutrophil cytoplasmic autoantibodies (ANCA) in this pathology represents a rare coincidence. However, it is not clear to what extent the presence of ANCA (IgA or IgG) in these patients could have any clinical significance. The aim of the current work is to describe the presence of ANCA (IgA or IgG) in patients with IgAN and crescentic proliferation and its possible clinical implications.

METHODS

We retrospectively recruited all patients in our center with a histological diagnosis of IgAN with crescentic proliferation between January 2013 and December 2020. The main demographic and clinicopathologic data, fundamental histological characteristics, as well as the treatments implemented and main kidney outcomes, were collected and analyzed at a 6 and 12-month follow-up.

RESULTS

Between January 2013 and December 2020, a total of 17 adults were diagnosed with concomitant crescentic proliferation through a kidney biopsy of IgAN. Five (29.4%) patients showed ANCA, three (60%) showed IgA-ANCA and two (40%) showed IgG-ANCA. All ANCA-positive patients had some degree of crescentic proliferation. At diagnosis, the mean age of patients was 48 years old (range: 27-75). Nine of them were women (52%) and the most common clinical presentation was hypertension (71%). At the time of biopsy, the mean serum creatinine and proteinuria were 2.2 mg/dL (DS 1.42) and 3.5 g/mgCr (DS 1.22), respectively, with no statistical differences between ANCA-positive and -negative patients. Histological analyses showed that 11 out of the 12 (91%) ANCA-negative IgAN patients displayed less than 25% cellular crescents, whereas 100% of ANCA-positive IgAN patients displayed more than 25% cellular crescents (p = 0.04). Notably, five (30%) patients displayed fibrinoid necrosis, with four of them (80%) being IgAN-ANCA-positive (p = 0.01). Only one ANCA-negative patient needed renal replacement therapy (RRT) upon admission (5%). The mean serum creatinine and proteinuria were 1.94 mg/dL (DS 1.71) and 1.45 g/gCr (DS 1.78), respectively, within 6 months of immunosuppressive therapy. At 12-month follow-up, the mean creatinine was 1.57 mg/dL (DS 1). Four (23.5%) patients needed RRT at the end of the follow-up and four (23.5%) patients died.

CONCLUSIONS

Probably due to the limited number of IgAN-ANCA-positive and IgAN-ANCA-negative patients, no significant differences were found between the clinical and laboratory characteristics. IgAN-ANCA-negative patients seemed to display less extracapillary proliferation than IgAN-ANCA-positive patients, who tended to show significantly higher fibrinoid necrosis. There were no differences regarding renal prognosis and patient survival after aggressive immunosuppressive therapy within 6 and 12 months when comparing the two samples.

[Efficacy of plasma exchange in severe crescentic IgA nephropathy: A multicentered, cohort study]

OBJECTIVE

To evaluate the efficacy of plasma exchange therapy on crescentic IgA nephropathy (IgAN).

METHODS

A retrospective analysis was performed in a cohort of patients with crescentic IgAN from January 2012 to September 2020 at 9 sites across China. Clinical and pathological data, as well as therapeutic regimens, were collected. In order to minimize the effect of potential confounders in baseline characteristics, propensity score matching using a 1 ∶1 ratio nearest neighbor algorithm was performed between the adjunctive plasma exchange therapy group and the intensive immunosuppressive therapy group. The primary outcome was end-stage of kidney disease (ESKD). Kaplan-Meier method was used to compare the difference in renal survival between the two groups.

RESULTS

A total of 95 crescentic IgAN patients with acute kidney disease were included in this study, including 37 (38.9%) patients receiving adjunctive plasma exchange therapy, and 58 (61.1%) patients receiving intensive immunosuppressive therapy. In the whole cohort, the baseline eGFR was 12.77 (7.28, 21.29) mL/(min·1.73 m²), 24-hour urinary protein quantification was 5.9 (4.0, 8.9) g, and crescent percentage was 64.71% (54.55%, 73.68%). In the study, 23 patients in each group were matched after propensity score matching The median follow-up time was 7 (1, 26) months. As a whole, 29 patients (63.0%) reached ESKD, including 16 patients (69.6%) in the adjunctive plasma exchange therapy group and 13 (56.5%) patients in the intensive immunosuppressive therapy group.. There were no stastical difference between the two groups in terms of baseline eGFR [14.30 (9.31, 17.58) mL/(min·1.73 m²) vs. 11.45 (5.59, 20.79) mL/(min·1.73 m²)], 24-hour urinary protein (7.4±3.4) g vs. (6.6±3.8) g, crescent percentage 64.49%±13.23% vs. 66.41%±12.65% and the proportion of patients received steroid therapy[23 (100.0%) vs. 21 (91.3%)] (All P>0.05). Kaplan-Meier survival analysis demonstrated that there was no significant difference in renal survival rate between the two groups (Log-rank test, P=0.933).

CONCLUSION

The adjunctive plasma exchange therapy in addition to conventional intense immunosuppressive therapy did not additionally improve the prognosis of crescentic IgA nephropathy.

Site-specific N-glycosylation characterization of micro monoclonal immunoglobulins based on EThcD-sceHCD-MS/MS

Monoclonal immunoglobulin produced by clonal plasma cells is the main cause in multiple myeloma and monoclonal gammopathy of renal significance. Because of the complicated purification method and the low stoichiometry of purified protein and glycans, site-specific N-glycosylation characterization for monoclonal immunoglobulin is still challenging. To profile the site-specific N-glycosylation of monoclonal immunoglobulins is of great interest. Therefore, in this study, we presented an integrated workflow for micro monoclonal IgA and IgG purification from patients with multiple myeloma in the HYDRASYS system, in-agarose-gel digestion, LC-MS/MS analysis without intact N-glycopeptide enrichment, and compared the identification performance of different mass spectrometry dissociation methods (EThcD-sceHCD, sceHCD, EThcD and sceHCD-pd-ETD). The results showed that EThcD-sceHCD was a better choice for site-specific N-glycosylation characterization of micro in-agarose-gel immunoglobulins (~2 μg) because it can cover more unique intact N-glycopeptides (37 and 50 intact N-glycopeptides from IgA1 and IgG2, respectively) and provide more high-quality spectra than sceHCD, EThcD and sceHCD-pd-ETD. We demonstrated the benefits of the alternative strategy in site-specific N-glycosylation characterizing micro monoclonal immunoglobulins obtained from bands separated by electrophoresis. This work could promote the development of clinical N-glycoproteomics and related immunology.

Diagnostic Potential of Plasma IgA1 O-Glycans in Discriminating IgA Nephropathy From Other Glomerular Diseases and Healthy Participants

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.