The transcription factor HMGB2 indirectly regulates APRIL expression and Gd-IgA1 production in patients with IgA nephropathy

Abstract

Background

IgA nephropathy (IgAN) is the most common primary glomerulonephritis worldwide. Proliferation-inducing ligand (APRIL) was identified as an important cause of glycosylation deficiency of IgA1 (Gd-IgA1), which can ‘trigger’ IgAN. Our previous study indicated that high migration group protein B2 (HMGB2) in peripheral blood mononuclear cells from patients with IgAN was associated with disease severity, but the underlying mechanism remains unclear.

Materials and methods

The location of HMGB2 was identified by immunofluorescence. qRT-PCR and Western blotting were used to measure HMGB2, HMGA1, and APRIL expression. Gd-IgA1 levels were detected by enzyme-linked immunosorbent assay (ELISA). In addition, we used DNA pull-down, protein profiling, and transcription factor prediction software to identify proteins bound to the promoter region of the APRIL gene. RNA interference and coimmunoprecipitation (Co-IP) were used to verify the relationships among HMGB2, high mobility group AT-hook protein 1 (HMGA1), and APRIL.

Results

HMGB2 expression was greater in IgAN patients than in HCs and was positively associated with APRIL expression in B cells. DNA pull-down and protein profiling revealed that HMGB2 and HMGA1 bound to the promoter region of the APRIL gene. The expression levels of HMGA1, APRIL, and Gd-IgA1 were downregulated after HMGB2 knockdown. Co-IP indicated that HMGB2 binds to HMGA1. The Gd-IgA1 concentration in the supernatant was reduced after HMGA1 knockdown. HMGA1 binding sites were predicted in the promoter region of the APRIL gene.

Conclusion

HMGB2 expression is greater in IgAN patients than in healthy controls; it promotes APRIL expression by interacting with HMGA1, thereby inducing Gd-IgA1 overexpression and leading to IgAN.

Keywords:

• IgA nephropathy
• glycosylation-deficiency IgA1
• high migration group protein B2
• high migration group protein A1
• proliferation-inducing ligand

Acknowledgements

We would like to express our gratitude to all patients involved in this study and all colleagues in the nephrology lab and the renal pathology department. Extensively acknowledgments are given to the ACS Authoring services (https://acsauthoringservices.enago.cn/) and EditSprings (https://www.editsprings.cn) for competent correction and polishing of the text.

Ethical approval

The Medical Ethics Committee of The First Affiliated Hospital of Zhengzhou University approved the study protocol, and informed written consent was obtained from each participant. All methods reported here were carried out in accordance with the relevant guidelines and regulations of The First Affiliated Hospital of Zhengzhou University.

Author contributions

Conceived and designed experiments: Yaling Zhai and Zhanzheng Zhao; analyzed the data: Huijuan Tian, Wenhui Zhang and Shuaigang Sun; contributed reagents/materials/analysis tools: Zhanzheng Zhao; wrote the paper: Huijuan Tian and Yaling Zhai. All authors read and approved the final manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

Raw data used during the current study are available from the corresponding author on reasonable request for noncommercial use.

Additional information

Funding

The work was supported by the Natural Science Foundation of Henan Province [Grant No. 232300420034] and National Natural Science Foundation for Youths of China [Grant No. 81600555], China Postdoctoral Science Foundation [Grant No.2018M640684], National Natural Science Foundation of China [Grant Nos. 81873611], Science and Technology Innovation Team of Henan [Grant No. 17IRTSTHN020], Foundation for Leading Personnel of Central Plains of China [Grant No. 194200510006].