Role of let-7b in the regulation of<i>N</i>-acetylgalactosaminyltransferase 2 in IgA nephropathy

Abstract

BACKGROUND: IgA nephropathy (IgAN) is characterized by aberrant O-glycosylation in the hinge region of IgA1. The early step in O-glycan formation is the attachment of N-acetylgalactosamine (GalNAc) to the serine/threonine of the hinge region; the process is catalysed by UDP-N-acetyl-α-d-galactosamine:polypeptide N-acetylgalactosaminyltransferase 2 (GALNT2). In our previous work, the microarray analysis on peripheral blood mononuclear cells (PBMCs) identified an upregulated miRNA called let-7b. METHODS: To study the molecular mechanisms in which let-7b was involved, we performed a bioinformatic analysis to predict their target genes. To validate biologically let-7b targets, we performed transient transfection experiments ex vivo using PBMCs from an independent group of IgAN patients and healthy blood donors (HBDs). RESULTS: Bioinformatic analysis revealed that GALNT2 is the potential target of let-7b. We found this miRNA significantly upregulated in PBMCs of IgAN patients compared with HBDs. Then, we demonstrated in ex-vivo experiments that let-7b decreased GALNT2 levels in PBMCs of IgAN patients, whereas the loss of let-7b function in PBMCs of HBDs led to an increase of GALNT2 mRNA and its protein level. Finally, we found that upregulation of let-7b occurred also in B-lymphocytes from IgAN patients. CONCLUSIONS: Our results give novel additional information on the abnormal O-glycosylation process of IgA1 in IgAN patients. This study provides evidence for another important miRNA-based regulatory mechanism of the O-glycosylation process in which the deregulated expression of let-7b is associated with altered expression of GALNT2. This finding could be taken into consideration for new therapeutic approaches in IgAN because other serum glycosylated proteins do not display abnormal glycosylation.