Increased crystal-cell interaction in vitro under co-culture of renal tubular cells and adipocytes by in vitro co-culture paracrine systems simulating metabolic syndrome

We established an experimental co-culture system for renal tubular cells and adipocytes to investigate kidney stone formation mechanisms under metabolic syndrome (MetS) conditions and examined the interaction between these cells morphologically and genetically. M-1s and 3T3-L1s were cultured individually (control, CON), with 24-h culture media from each cell type added to the other cell type (replacement, RP) in 2-layer co-culture dishes for 24 h (transwell, TW). M-1s were then exposed to calcium oxalate monohydrate (COM) crystals, and attached C-14-labeled COM crystals were quantified. Expression of kidney stone- and adipocyte-related genes was analyzed. The radioactivity of adherent COM crystals significantly increased in TW and was relatively higher in RP compared to CON. M-1s demonstrated significant upregulation of adiponectin (Adipoq) in RP and secreted phosphoprotein 1 (Spp1) in TW compared to CON before COM crystal exposure, and significant downregulation of Spp1 in TW and upregulation of tumor necrosis factor (Tnf), interleukin 6 (Il-6), and chemokine (C-C motif) ligand 2 (Ccl2) compared to CON after COM crystal exposure. 3T3-L1s showed significant upregulation of Spp1, Adipoq, Tnf-alpha, and Ccl2 compared to CON. Enzyme-linked immunosorbent assays of co-culture medium revealed significantly increased TNF-alpha in TW. Our results highlight the potential for paracrine interactions between renal tubular cells and adipocytes and suggest that MetS conditions may lead to kidney stone formation.