MicroRNA-148b regulates megalin expression and is associated with receptor downregulation in mice with unilateral ureteral obstruction.

Megalin is a multiligand, endocytic receptor that is important for the normal, proximal tubule reabsorption of filtered proteins, hormones, enzymes, essential nutrients, and nephrotoxins. Megalin dysfunction has been associated with acute, as well as chronic kidney diseases. Tubular proteinuria has been observed following unilateral ureteral obstruction (UUO), suggesting megalin dysfunction; however, the pathophysiological mechanism has not been determined. To identify potential regulators of megalin expression, we examined renal microRNAs (miRNAs) expression and observed an upregulation of microRNA-148b (miR-148b) in obstructed mouse kidneys 7 days after UUO, which was associated with a significant reduction in proximal tubule megalin expression and accumulation of megalin ligands. By in silico miRNA target prediction analysis, we identified megalin messenger RNA (mRNA) as a potential target of miR-148b and confirmed using a dual-luciferase reporter assay that miR-148b targeted the 3'-untranslated region of the megalin gene. Transfection of LLC-PK1 cells with miR-148b mimic reduced endogenous megalin mRNA and protein levels in a concentration-dependent manner, while transfection with miR-148b inhibitor resulted in an increase. Our findings suggest that miR-148b directly downregulates megalin expression and that miR-148b negatively regulates megalin expression in UUO-induced kidney injury. Furthermore, the identification of a miRNA regulating megalin expression may allow for targeted interventions to modulate megalin function and proximal tubule uptake of proteins, as well as other ligands.