Knockdown of microRNA-155 in Kupffer cells results in immunosuppressive effects and prolongs survival of mouse liver allografts.

BACKGROUND: Our previous studies have shown that Kupffer cells (KCs) play a crucial role in postoperative pathologic changes. Recent reports have demonstrated that microRNA-155 (miR-155) is associated with inflammation and upregulation of proinflammatory mediators in the peripheral blood and allografts of transplant patients. However, the precise mechanism for this remains unknown.
METHODS: KCs isolated from BALB/c mice were transfected with miR-155 mimic or inhibitor. Levels of suppressor of cytokine signaling 1/Janus kinase/signal transducer and activator of transcription (SOCS1/JAK/STAT) proteins and surface molecules (MHC-II, CD40, and CD86) were then measured. T-cell proliferation and apoptosis were evaluated in mixed lymphocyte reactions. Orthotopic liver transplantation was performed in mice after miR-155 short hairpin RNA lentivirus treatment, and postoperative survival, liver function and histology, and mRNA and protein expression were analyzed.
RESULTS: miR-155 knockdown in KCs decreased MHC-II, CD40, and CD86 expression, suppressed antigen-presenting function, and affected SOCS1/JAK/STAT inflammatory pathways. In addition, KCs transfected with miR-155 inhibitor and cocultured with T lymphocytes showed reduced T-cell responses but a greater number of apoptotic T cells. Finally, miR-155 suppression in graft liver prolonged liver allograft survival and improved liver function. The changes were closely associated with the levels of T helper 1 and 2 (Th1/Th2) cytokines and T-cell apoptosis, but a direct mechanistic link in vivo was not established.
CONCLUSION: These data suggest miR-155 regulates the balance of Th1/Th2 cytokines and the maturation and function of KCs in mice. miR-155 repression in KCs positively regulates KC function toward immunosuppression and prolongs liver allograft survival.