Abstract
Immunomodulatory activity of mesenchymal stem cells (MSCs) is largely mediated by paracrine factors. Our previous studies showed that activation of nuclear factor-kappa B (NF-κB) regulates cytokine/growth factor secretion by MSCs. This study aimed to elucidate the role of Rap1 (repressor/activator protein), a novel modulator involved in the NF-κB pathway, in regulating the immunomodulatory potency of MSCs in acute allograft rejection of heart transplantation. The immunosuppressive potency of wild-type MSCs (WT-MSCs) or Rap1-deficient MSCs (Rap1-/--MSCs) was examined in mice with acute allograft rejection following heart transplantation. With a combination of immunosuppressant rapamycin at a dose of 1 mg/kg/d, WT-MSCs notably prolonged the survival of the transplanted heart compared with Rap1-/--MSCs. Rap1-/--MSCs displayed a marked insensitivity to inhibit the mixed lymphocyte reaction (MLR) due to impaired cytokine production and a significantly reduced activity of NF-κB signaling in vitro. Finally, transplantation of encapsulated WT-MSCs greatly prolonged the survival of the heart allograft compared with encapsulated Rap1-/--MSCs. Our results indicate that Rap1 is essential to maintain the immunomodulatory function of MSCs. Deletion of Rap1 results in impaired immunomodulatory function of MSCs.