Recruitment of Regulatory T Cells with rCCL17 Promotes M2 Microglia/Macrophage Polarization Through TGFβ/TGFβR/Smad2/3 Pathway in a Mouse Model of Intracerebral Hemorrhage

Background Intracerebral hemorrhage (ICH) is a devastating neurological disease with high mortality and morbidity. The microglia activation and peripheral inflammatory cells infiltration play an important role in the ICH prognosis. Previous studies have demonstrated that regulatory T cells (Tregs) ameliorated neuroinflammation following experimental ICH. However, the specific molecular mechanism underlying such effects of Tregs remains unclear. In the present study, our aims were to examine the effect of Tregs recruitment induced by recombinant CC chemokine ligand 17(rCCL17) in an intrastriatal autologous blood mouse model of ICH and to determine whether the TGF-β/TGF-βR/Smad2/3 pathway was involved in Tregs promoted M2 microglia/macrophage polarization. Methods A total of 404 adult CD1 mice (male, eight-week-old) were subject to sham surgery or autologous blood injection of ICH. A CD25-specific mouse antibody or isotype control mAb was injected intraperitoneally 48h prior to ICH induction to deplete Tregs. Recombinant CCL17 (rCCL17), a C-C chemokine receptor 4 (CCR4), was delivered intranasally at 1 h post-ICH. SB431542, a specific inhibitor of TGF-β was administered intraperitoneally 1 h before ICH induction. Post-ICH assessments included neuro-behavior evaluation, brain edema, hematoma volume, hemoglobin content, western blotting, double immunofluorescence staining and immunohistochemistry. Results Endogenous brain expressions of CCL17 and Tregs marker Foxp3 as well as the number of Tregs in the perihematomal region were increased following ICH. The Tregs deletion by a CD25 antibody aggravated short-term neurological deficits and brain edema, increased the level of inflammatory cytokines and peripheral inflammatory cells infiltration, exacerbated hematoma expansion and increased M1phenotypes of microglia/macrophage in ICH mice. The rCCL17 treatment increased the number of Tregs in the brain, reduced hematoma expansion and brain edema, promoted microglia/macrophage polarization toward M2 phenotypes. Moreover, the expressions of brain TGF-β/phosphorylated-Smad2/3 were increased. The neuroprotective effects of rCCL17 were abolished by co-administration of the selective TGF-β inhibitor SB431542. Conclusions Our study demonstrated rCCL17 recruited of Tregs to brain in the autologous blood injection model of ICH. Tregs promoted microglia/macrophages polarization toward M2 phenotype and alleviation early brain injury, at least in part, through the TGFβ/TGFβR/Smad2/3 signaling pathway in ICH mice. Thus, rCCL17-mediated Tregs recruitment may provide a promising therapeutic strategy to reduce early brain injury after ICH.