Previous studies from our own group and others have demonstrated that cyclooxygenase-2 (COX-2) inhibitors could reduce proteinuria in some experimental models of progressive renal disease. To investigate a possible role of COX-2 in podocytes during the course of self-limited glomerular injury, we administered puromycin nucleoside (PAN) on day 1 (15 mg/100 g BW) and day 3 (30 mg/100 g BW) to wild-type and transgenic mice with podocyte-specific COX-2 expression driven by a nephrin promoter. An additional group received both PAN and the COX-2-specific inhibitor, SC58236 (6 mg/l in drinking water). There was no significant difference in the albumin (µg)/creatinine (mg) ratio between wild-type (26.3±4.2, n= 8) and transgenic (28.9±2.3, n= 8) mice under baseline conditions. PAN induced significant albuminuria only in the transgenic mice with a peak at day 3: 72.1±8.9 µg/mg creatinine (n= 12, p< 0.05, compared with basal level), which remitted by day 10 (37.4±4.4 µg/mg, n= 7, p< 0.05, compared with day 3). Electron microscopy demonstrated that PAN caused 56.7±4.2% foot process effacement in transgenic mice compared with 38.8±4.1% in wild type at day 3. PAN increased immunoreactive COX-2 in glomeruli from transgenic mice (day 3: 1.47±0.08 fold; day 10: 1.25±0.16 fold, n= 5–9, p< 0.05 compared with basal level), which was restricted to podocytes. Real time PCR indicated that endogenous COX-2 mRNA increased (2.6±0.1 fold of wild-type control at day 3 and 2.2±0.2 at day 10, n= 4, p< 0.05), while the nephrin-driven COX-2 mRNA was unchanged. Nephrin mRNA and protein expression were decreased by PAN in the transgenic mice. The COX-2-specific inhibitor, SC58236, reduced foot process effacement in transgenic mice administered PAN to 21.7±5.2% and significantly reduced the albuminuria at day 3 (42.2±3.8, n= 13, p< 0.05 compared with untreated) without significantly altering COX-2 expression. In summary, in transgenic mice with podocyte COX-2 overexpression, PAN increased albuminuria and induced foot process fusion. Thus, increased COX-2 expression increased podocyte susceptibility to further injury.