Background/Purpose: We have previously shown that renal expression of miR-150 correlates with chronicity index (CI) in lupus nephritis. Since fibrosis is a major histologic feature of the CI we explored the potential role of miR-150 in renal fibrosis. Our data showed a positive correlation between fibrosis and miR-150 expression, therefore we assumed that miR-150 increases the production of pro-fibrotic molecules by downregulating a regulator of fibrotic proteins. The European Bioinformatic Institute (EBI) database identified SOCS-1 (suppressor of cytokine signaling-1) as such a target of miR-150. SOCS-1 has previously been shown to decrease fibronectin in mesangial cells as well as reduce fibronectin and collagen 1 in renal tubular fibroblast. SOCS1-/- mice developed lupus nephritis-like disease. We hypothesized that miR-150 increases the synthesis of profibrotic molecules by down regulating SOCS1.

Methods: The localization of miR-150 in kidney was identified by in situ hybridization in 6 kidney needle biopsies from patients with lupus nephritis (3 from patients with high renal miR-150 and 3 from patients with low renal miR150) and 2 kidneys from autopsies without known kidney diseases. Renal collagen 1(COL1) immunofluorescent staining was performed on the same samples. Primary human renal proximal tubular epithelial cells (RPTEC) and primary human mesangial cells (MC) were used for transfection with miR-150. To confirm SOCS1 as a mir-150 target a luciferase gene linked with the 3’UTR of SOCS1 was cotransfected with miR-150 in RPTEC cells and the luciferase activity was measured 48hrs after the cotransfection. Protein expression of SOCS1 and fibrotic proteins,  COL1, collagen 3 (COL3) and fibronectin (FN) were analyzed by western blot in these cultured cells 48hr after miR-150 transfection.

Results: miR-150 predominantly localized in renal cortical proximal tubular cells. Moderate staining was seen in podocytes in kidney biopsies with high but not in those with low renal miR-150 expression. Immunofluorescent staining showed significantly increased COL1 in kidney biopsies with high renal miR-150 and high CI compared to the kidneys with low renal miR-150 and low CI. Luciferase activity linked to the 3’UTR of SOCS1 was downregulated to 68.5% (p<0.01) of control cells by miR-150 in RPTEC, confirming SOCS1 as a direct target of miR-150. miR-150 transfection significantly decreased SOCS1 signal and increased expression of FN in both RPTEC and MC whereas it led to increased levels of COL3 in RPTEC and COL1 levels in mesangial cells.       

Conclusion: miR-150 transfection increased the synthesis of pro-fibrotic molecules in two primary human renal cells by downregulating the expression of SOCS1, a negative regulator of fibrosis. These data together with the previously described obseravtion that miR-150 expression in lupus nephritis correlates with chronicity index suggest that miR-150 plays an important role in chronic kidney injury in lupus nephritis.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/mirorna-mir-150-contributes-to-chronic-kidney-injury-in-lupus-nephritis-by-increasing-the-synthesis-of-fibrotic-proteins-via-downregulation-of-socs1/