Role of macrophage migration inhibitory factor (MIF) in peripheral nerve regeneration: anti-MIF antibody induces delay of nerve regeneration and the apoptosis of Schwann cells

Macrophage migration inhibitory factor (MIF) is a pluripotent cytokine involved in inflammation and immune responses as well as in cell growth. Although we previously demonstrated the presence of MIF in peripheral nerves, and MIF mRNA expression was up-regulated after axotomy, the role of MIF in nerve injury and regeneration has not been evaluated. To examine the potential role of MIF in nerve regeneration, we locally administered an anti-MIF polyclonal antibody into regenerating rat sciatic nerves using the silicone chamber model. The effect of the anti-MIF antibody on nerve regeneration was evaluated using an axonal reflex test. In addition, we carried out a terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling (TUNEL) assay and immunohistochemical analysis of the damaged nerve segments with regard to apoptosis-related proteins such as p53 to evaluate the effects of anti- MIF antibodies on apoptosis during the regeneration process. The regeneration length of the nerve in the anti-MIF antibody-treated group was significantly shorter than that in the non-immune rabbit IgG-treated group at weeks 2, 4 and 6 after surgery. TUNEL assay showed that a large number of apoptotic cells, mostly Schwann cells, were observed in the intratubal and distal nerve segments at weeks 4 and 6 after surgery by the anti-MIF antibody treatment. Consistent with these results, Ki-67-positive cells were significantly decreased by the anti-MIF antibody treatment. Immunohistochemical analyses revealed that p53 and, to a lesser extent, Fas were more up-regulated in the anti-MIF antibody-treated nerves than in the controls. Taken together, these results suggest that MIF plays an important role in acceleration of peripheral nerve regeneration and in prevention of Schwann cell apoptosis, mainly through overcoming the apoptotic effect of p53.