Prolongation of cardiac allograft survival by inhibition of ERK1/2 signaling in a mouse model.

Background. It has been demonstrated that in vitro the presence of extracellular signal-regulated kinase I and 2 (ERK1/2) signaling inhibitor suppresses T cell activation and Th1 development. However, pharmacological interference of ERK1/2 signaling by administration of its small molecule inhibitor has not been tested as a therapeutic target in the prevention of allograft rejection. Methods. The immunosuppressive effect of targeting ERK1/2 signaling was tested on cardiac allograft survival in C57BL/6 (H-2(b)) to Balb/c (H-2(d)) murine model using PD98059 inhibitor. Phosphorylation/activation of ERK 1/2 and STAT6 proteins were assessed by Western blot. Results. Blockade of ERK1/2 using PD98059 had significant immunosuppressive effect and prolonged survival of mouse cardiac allografts from 8.3 +/- 0.5 days (vehicle) to 12.6 +/- 1.3 days (100 mg/kg PD98059; P < 0.0001). Combination therapy of PD98059 (100 mg/kg) with cyclosporine (CsA, 15 mg/kg for 20 days) additionally enhanced graft survival (34.4 +/- 1.2 days) compared to CsA (14.9 +/- 1.1 days; P < 0.0001) or PD98059 monotherapy (P < 0.0001). Attenuation of graft rejection by PD98059 correlated to reduction of intragraft ERK phosphorylation and leukocyte infiltration, and to increase in interleukin (IL)-4 or decrease in interferon-gamma production within the grafts. In vitro inhibition of ERK1/2 by PD98059 promoted Th2 differentiation by upregulation IL-4 production but not altering IL-4 stimulating STAT6 pathway. Conclusion. Targeting ERK1/2 signaling results in suppression of alloimmune responses by an unique mechanism that involves Th1/Th2 skewing, suggesting a therapeutic potential of inhibition of ERK1/2 signaling for transplant rejection, particularly in combination with CsA.