Objective. Chronic rejection of transplanted organs remains unresolved issue in organ transplantation. The chronic rejection is the most common cause of graft loss within 10 years of the transplantation. Thus, our goal is to uncover the mechanisms of chronic rejection, which will undoubtedly revolutionize transplant medicine. Major signs of chronic rejection include artery occlusion and collagen deposition (fibrosis), which are induced by macrophages that infiltrate the graft and aggregate around graft's vessels. The migration of macrophages into the allograft depends on CX3CR1/CX3CL1 (Fractalkine) pathway and actin cytoskeleton, which is under the control of small GTPase RhoA. Methods We generated mice with macrophage specific deletion of RhoA. Hearts from BALB/c (H-2d) donors were transplanted into RhoAflox/flox (no Cre), heterozygous Lyz2Cre+/-RhoA+/flox and Lyz2Cre+/-RhoAflox/flox recipients treated with CTLA4-Ig to inhibit early T cell response, and transplanted hearts were pathologically assessed for signs of chronic rejection. We studied macrophage responses to RhoA deletion using actin staining, immunostaining, PCR, Western blotting and flow cytometry. Results. Macrophage-specific deletion of RhoA in conjunction with CTLA4-Ig abrogated chronic rejection of allografts and inhibited macrophage infiltration into the grafts. RhoA deletion affected macrophage structure and down regulated expression of fractalkine receptor CX3CR1. We showed that RhoA deletion disrupts CX3CR1 receptor recycling in macrophages through disruption of actin-dependent endosomal and Golgi pathway that control receptor recycling. This in turn disrupts CX3CR1/CX3CL1 signaling, which directs macrophages to the transplanted organ. Conclusions. These novel findings indicate that interference with the RhoA pathway inhibits macrophage infiltration of the graft through disruption of CX3CR1/CX3CL1 (Fractalkine) pathway. This, in turn, will help to design novel macrophage-targeted anti-rejection therapies.

CITATION INFORMATION: Kloc M, Liu Y, Chen W, Li X, Ghobrial R. Macrophage Specific Deletion of RhoA Inhibits Fractalkine Signaling and Abrogates Chronic Rejection of Cardiac Allograft. Am J Transplant. 2017;17 (suppl 3).

« Back to 2017 American Transplant Congress