Oxalate inhibits renal proximal tubule cell proliferation via oxidative stress, p38 MAPK/JNK, and cPLA2 signaling pathways

Exposure of renal proximal tubule cells to oxalate may play an important role in cell proliferation, but the signaling pathways involved in this effect have not been elucidated. Thus the present study was performed to examine the effect of oxalate on 3H-labeled thymidine incorporation and its related signal pathway in primary cultured rabbit renal proximal tubule cells (PTCs). The effects of oxalate on [3H]thymidine incorporation, lactate dehydrogenase (LDH) release, Trypan blue exclusion, H2O2 release, activation of mitogen-activated protein kinases (MAPKs), and 3H-labeled arachidonic acid (AA) release were examined in primary cultured renal PTCs. Oxalate inhibited [3H]thymidine incorporation in a time- and dose-dependent manner. However, its analogs did not affect [3H]thymidine incorporation. Oxalate (1 mM) significantly increased H2O2 release, which was blocked by N-acetyl-l-cysteine (NAC) and catalase (antioxidants). Oxalate significantly increased p38 MAPK and stress-activated protein kinase (SAPK)/c-Jun NH2-terminal kinase (JNK) activity, not p44/42 MAPK. Oxalate stimulated [3H]AA release and translocation of cytosolic phospholipase A2 (cPLA2) from the cytosolic fraction to the membrane fraction. Indeed, oxalate significantly increased prostaglandin E2 (PGE2) production compared with control. Oxalate-induced inhibition of [3H]thymidine incorporation and increase of [3H]AA release were prevented by antioxidants (NAC), a p38 MAPK inhibitor (SB-203580), a SAPK/JNK inhibitor (SP-600125), or PLA2 inhibitors [mepacrine and arachidonyl trifluoromethyl ketone (AACOCF3)], but not by a p44/42 MAPK inhibitor (PD-98059). These findings suggest that oxalate inhibits renal PTC proliferation via oxidative stress, p38 MAPK/JNK, and cPLA2 signaling pathways.