Background.

The signaling pathways of mitogen-activated protein kinases (MAPKs) are important molecular components responsible for ischemia/reperfusion (I/R) injury in the kidneys. Preconditioning with cyclosporine A (CsA) or FK506 reduces subsequent I/R injury. We studied the effect of preconditioning with CsA or FK506 on MAPK expression in ischemic rat kidneys.

Methods.

Two separate studies were performed using Sprague-Dawley rats. First, MAPK (extracellular signal-regulated kinase [ERK], jun N-terminal kinase [JNK], p38) expressions were observed at 0, 10, 20, 30, 60, 120, and 1,440 min after I/R injury. Second, the effects of preconditioning with CsA or FK506 on MAPK expressions were observed in rat kidneys with I/R injury. I/R injury was induced by clamping both renal arteries for 45 min. Rats were pretreated with intravenous (IV) CsA (3 mg/kg) or IV FK506 (0.3 mg/kg) 6 hr before I/R injury and killed 30 min later. Expression of MAPK was measured using immunoblot and immunohistochemistry.

Results.

MAPK (ERK, JNK, p38) expressions were significantly increased in kidneys with I/R injury compared with sham-operated controls, and immunohistochemistry revealed increased MAPK immunoreactivity in renal tubules of the outer medulla. Kidneys preconditioned with low-dose CsA or FK506 showed significantly increased ERK expression compared with kidneys with I/R injury alone (CsA, 9.5-vs. 4.5-fold; FK506 10.4-vs. 4.5-fold: P< 0.05) but showed decreased JNK (CsA, 3.8-vs. 5.3-fold; FK506, 3.4-vs. 5.3-fold: P< 0.05) and p38 expression (CsA, 2.5-vs. 3.7-fold; FK506, 2.1-vs. 3.7-fold: P< 0.05).

Conclusions.

Preconditioning with CsA or FK506 differentially regulates the expression of MAPK in rat kidneys with I/R injury, and this may explain the remarkable protective effects of these agents.