Background Kidney involvement is frequent in patients with systemic lupus erythematosus, and is associated with significant co-morbidities, particularly in children. New treatment strategies with fewer side effects are much needed to improve the care of patients with lupus nephritis (LN).

MicroRNAs (miRNAS) are noncoding RNAs responsible for post-transcriptional gene silencing. Altered miRNA expression can broadly altered cell behavior, contributing to sustained pathology. The study of these regulatory molecules can, therefore, contribute to a better understanding of LN and identify new pathways that are clinically relevant.

Objectives The main goal of this study was to characterize the miRNA signature of pediatric LN and define the role of miRNAs in the pathology of the disease.

Methods RNA was extracted from 18 kidney sections of children and adolescents with LN and 8 controls (patients with post-streptococcal glomerulonephritis and kidney donors), using Qiagen™ miRNeasy FFPE kit. Direct digital detection of over 700 miRNAs was performed with the nCounter™ human miRNA assay kit. R™ was used for data analysis. miR-26a and miR-30b were further quantified by qRT-PCR, using Taqman™ miRNA assays. The miRNA pattern of different human kidney cell lines was also studied using the same methodology. HER2 expression was analyzed, by immunohistochemistry, in kidney sections from LN patients and controls and, by qRT-PCR, immunofluorescence and western-blot, in cell lines.

Results There is a LN-specific miRNA signature, as was demonstrated by the principal component analysis. This pattern mainly reflects proliferation, cell growth and inflammation, according to IPA® pathway analysis. When compared to normal tissue, a significant decrease in the expression of miR-26a was found in LN class IV (p=0.002) and LN class III (p=0.03), with similar results for miR-30b. These results were confirmed by qRT-PCR. There was an association between miR-26a and crescents in the kidney specimens (p=0.04), which is a sign of cell proliferation. Cell lines representative of human kidney tubular, mesangial and endothelial cells expressed these miRNAs, confirming their broad role in the kidney. We examined HER2 expression as a potential responder to the dysregulated miRNAs and we found it was highly increased in the glomeruli and tubular compartments of LN patients. This protein was expressed in human podocytes, tubular and mesangial cell lines.

Conclusions We described, for the first time, the kidney miRNA signature of LN, with over 700 miRNAs analyzed and with the identification of miR-26a and miR-30b as being implicated in this disease and having a possible role in the regulation of cell proliferation. Recently, it was shown that trastuzumab, a monoclonal antibody against HER2, produces therapeutic actions by up-regulating miR-26a and miR-30b in breast cancer cells. If the same effect occurs in kidneys, this may be a new promising pathway to decrease cell proliferation and damage in LN. The significant increase of HER2 expression in the kidneys of LN patients supports this hypothesis. In conclusion, this study identified aberrant expression of miR-26a and miR-30b in LN and upregulation of a potentially important downstream mediator of cell proliferation and the inflammatory response. These findings created solid foundations for the development of new treatment strategies in LN.

References PMIDs: 21420034; 22384020.

Disclosure of Interest None Declared