Mesenchymal stem cell transplantation modulates neuroinflammation in focal cerebral ischemia: Contribution of fractalkine and IL-5

Mesenchymal stem cells (MSCs) are reported to possess immunomodulatory properties. Previous reports have demonstrated the beneficial effects of MSC-transplantation in focal cerebral ischemia animal models. In this study, we have investigated the neuroimmunomodulatory functions of human MSCs, transplanted in a rat focal ischemia model of transient middle cerebral artery occlusion (MCAO). Our results revealed that in a human mesenchymal stem cell line, B10 cell transplantation decreased the accumulation of Iba-1+ microglia and GFAP+ astrocytes, and inhibited proinflammatory gene expression in the core and ischemic border zone (IBZ). Among the proinflammatory genes iNOS, which was expressed in microglia/macrophage, was persistently inhibited up to 7 days after MCAO. In vivo laser capture microdissection and double immunofluorescence staining, and in vitro B10 cell culture experiments showed that, in inflammatory conditions, B10 cells expressed cytokines and growth factors including IL-5, fractalkine, IGF-1, GDNF and VEGF. Fractalkine and IL-5 inhibited cytokine-induced proinflammatory gene expression including iNOS in a human microglia cell line. Thus, our results demonstrate that MSC transplantation suppresses MCAO focal ischemia-induced inflammation, possibly through expression of fractalkine and IL-5.

Research Highlights
► Mesenchymal stem cell (MSC) transplantation inhibits inflammation in an MCAO model.
► MSCs express fractalkine and IL-5 in an inflammatory condition, in vivo and in vitro.
► Fractalkine and IL-5 inhibit cytokine-induced inflammatory gene expression.
► MSC-transplantation increases fractalkine and IL-5 positive cell numbers in MCAO.