ABSTRACT
Family members of peroxisome proliferator-activated receptors (PPARs), such as PPARγ, have been shown to be effective in regulating T helper 17 (Th17) cell differentiation. However, whether PPARα, another important family member of PPARs, contributes to Th17 cell differentiation remains controversial. In the present study, we show that PPARα may be a negative regulator of Th17 cell differentiation. In CD4+ T cells from PPARα knockout mice, PPARα deficiency enhances IL-17 and IL-6 levels and promotes Th17 cell differentiation. In contrast, in CD4+ T cells from wild type mice, PPARα activation suppresses Th17 cell differentiation. Furthermore, IL-6 neutralizing antibody dose-dependently reduces the activity of STAT3 and down-regulates the protein expression of RORγt in CD4+ T cells from PPARα knockout mice but has no effect on that of wild type mice. On the other hand, in isolated CD4+ T cells from experimental autoimmune myocarditis (EAM) rats, PPARα agonist Fenofibrate decreased the expression of IL-17 and RORγt, increased the expression of Foxp3, while PPARα antagonist MK886 reversed these effects. Importantly, in vivo activation of PPARα ameliorates EAM by suppressing Th17 cell differentiation through reducing the expression of RORγt and phosphorylated STAT3 that are upregulated in EAM hearts. These results imply that PPARα suppresses Th17 cell differentiation through IL-6/STAT3/RORγt signaling pathway and suggest that PPARα may become a molecular target for treating autoimmune myocarditis.
Subject(s)
Cell Differentiation/genetics , Myocarditis/genetics , PPAR alpha/genetics , Th17 Cells/immunology , Animals , Autoimmune Diseases/genetics , Autoimmune Diseases/immunology , Autoimmune Diseases/pathology , CD4-Positive T-Lymphocytes/immunology , Cell Differentiation/immunology , Disease Models, Animal , Humans , Interleukin-17/genetics , Interleukin-6/genetics , Lymphocyte Activation/genetics , Lymphocyte Activation/immunology , Mice , Mice, Knockout , Myocarditis/immunology , Myocarditis/pathology , Nuclear Receptor Subfamily 1, Group F, Member 3/genetics , STAT3 Transcription Factor/genetics , Signal Transduction/genetics , Th17 Cells/metabolismABSTRACT
It has been shown that cholesterol modulates activity of protein kinase C (PKC), and PKC phosphorylates connexin 43 (Cx43) to regulate its function, respectively. However, it is not known whether cholesterol modulates function of Cx43 through regulating activity of PKC. In the present study, we demonstrated that cholesterol enrichment reduced the dye transfer ability of Cx43 in cultured H9c2 cells. Western blot analysis indicated that cholesterol enrichment enhanced the phosphorylated state of Cx43. Immunofluorescent images showed that cholesterol enrichment made the Cx43 distribution from condensed to diffused manner in the interface between the cells. In cholesterol enriched cells, PKC antagonists partially restored the dye transfer ability among the cells, downregulated the phosphorylation of Cx43 and redistributed Cx43 from the diffused manner to the condensed manner in the cell interface. In addition, reduction of cholesterol level suppressed PKC activity to phosphorylate Cx43 and restored Cx43 function in PKC agonist-treated cells. Furthermore, we demonstrated that cholesterol enrichment upregulated the phosphorylated state of Cx43 at Ser368, while PKC antagonists reversed the effect. Taken together, cholesterol level in the cells plays important roles in regulating Cx43 function through activation of the PKC signaling pathway.
