Pioglitazone, a peroxisome proliferator-activated receptor γ activator, ameliorates experimental autoimmune myocarditis by modulating Th1/Th2 balance

Objectives – The aim of this study is to investigate the effect of Peroxisome proliferator-activated receptor γ (PPARγ) ligand on experimental autoimmune myocarditis (EAM). Background – Rat EAM model resembles the giant cell myocarditis in human. Recent studies have suggested that Th1 cytokines are involved in the initiation and progression of EAM, whereas Th2 cytokines are associated with the remission. PPARγ, which is a member of nuclear hormone receptor superfamily, has been known to affect not only glucose homeostasis but also immune responses, by regulating the Th1/Th2 balance. Methods – Lewis rats were immunized with cardiac myosin and divided into three groups: Group N, normal control rats (n = 16); Group E, EAM rats (n = 17); and Group P, EAM rats treated with a PPARγ activator pioglitazone (n = 20). Results – Cardiac dysfunction and remodeling were inhibited in Group P compared to Group E. Heart weight/body weight ratio and the degree of inflammation and fibrosis were significantly lower in Group P than in Group E. The mRNA levels of macrophage inflammatory protein-1α (MIP-1α), which plays an important role in the recruitment of inflammatory cells in the early stage of EAM, were upregulated in the heart of Group E, but not in the heart of Group P. Furthermore, the treatment with pioglitazone decreased the expression levels of proinflamatory cytokine (TNFα and IL-1β) genes and Th1 cytokine (IFN-γ) genes, and increased the expression levels of Th2 cytokine (IL-4) gene. Conclusions – PPARγ ligands may have beneficial effects on myocarditis by inhibiting MIP-1α expression and modulating the Th1/Th2 balance.