Effect of processed culture supernatant (PCS) after preconditioning (by Hyp, EGF, or TNF) or control culture (Ctrl) on the proliferation and viability of epithelial cells. (A) Characteristic phase contrast microscopy of subconfluent (above) and confluent (below) murine renal tubular epithelial cells in culture (bar: 100 µm); (B) DAPI assay: cell proliferation was determined by a fluorometric assay using 4,6-diamino-2-phenylindole (DAPI), measuring the DNA content as an indirect determination of proliferation, after incubation with PCS for 72 h. Fluorescence was measured in a fluorescence reader (355 nm ex/460 nm em), and expressed as arbitrary units (mean ± SD, n = 6); (C) XTT assay: cell viability of mTEC was measured after incubation with PCS for 72 h. The XTT assay was performed and optical density (OD) was measured in a microplate reader at 490 nm vs. 650 nm (arbitrary units, mean ± SD, n = 6). * p < 0.05, ** p < 0.01, *** p < 0.001 versus control and among each preconditioning regimen.