Supplementary Material for: Up-Regulation of CD74 Expression in Parietal Epithelial Cells in a Mouse Model of Focal Segmental Glomerulosclerosis

<i>Background/Aims:</i> De novo expression of CD44 is considered as a marker of parietal epithelial cell (PEC) activation. The aim of our study was to explore CD74 expression, which can form a complex with CD44, in PECs during the progression of focal segmental glomerulosclerosis (FSGS). To clarify the role of CD74 expression and of its interaction with CD44, we generated a new mouse model with enhanced PEC activation through lipopolysaccharide (LPS) application to adriamycin (ADR)-induced nephropathy mice (LPS-treated ADR mice). <i>Methods:</i> As a new model, LPS was intraperitoneally injected into the mice 3 weeks after ADR injection. The mice were divided into 3 categories: control mice, ADR mice and LPS-treated ADR mice. Renal function parameters, histologic changes and immunohistochemical expression of CD74 and other PEC activation markers were analyzed after LPS application. <i>Results:</i>After LPS stimulation, the glomeruli were characterized by enlarged epithelial cells with strong CD74 expression, followed by pseudo-crescent formation. By double staining, CD74-positive enlarged cells showed co-expression of classical PEC markers, but not of <i>Lotus tetragonolobus</i> lectin (marker of proximal tubular cells), suggesting amplification of PEC activation. Time-course analysis displayed marked upregulation of CD74 expression during rapid PEC activation compared with CD44. Additionally, the time-dependent change in ERK phosphorylation showed a similar pattern to CD74. <i>Conclusion:</i> Our results indicate that CD74 can be a marker for PEC activation in FSGS. By modifying the ADR mouse model through LPS treatment, we found that CD74 upregulation better reflects a rapid amplification of PEC activation than CD44 expression.