Objective: To examine whether transforming growth factor-β (TGF-β) pathway and adaptive T cell immunity play roles in the anti-atherosclerotic effects of pioglitazone (PIO) in ApoE-/- mice.
Methods: ApoE-/- mice with atherosclerosis induced by high-fat feeding were treated daily with PIO (20 mg/kg) or vehicle for 8 weeks. The protein expressions of TGF-β pathway in the atheromatous lesions of the aorta and the percentages of IFN-γ+ and Foxp3+ cells in the spleen of the mice were examined with immunohistochemical staining. In the in vitro experiment, primary cultured splenocytes were stimulated with oxidized low-density lipoproteins (oxLDL) and treated with PIO either alone or in combination with the PPARγ antagonist GW9662, after which the changes in percentages of CD4+IFN-γ+ cells and CD4+CD25+Foxp3+ cells were analyzed with flow cytometry.
Results: PIO treatment of ApoE-/- mice with high-fat feeding significantly attenuated the progression of atheromatous lesions (P<0.05) and resulted in increased expressions of TGFβ1 (P<0.01), TGFβRII (P<0.05), and p-Smad3 (P<0.05) and a decreased expression of Smad7 (P<0.05) in the lesions. PIO treatment also led to decreased percentage of IFN-γ+ cells (P<0.05) and increased percentage of Foxp3+ cells (P<0.01) in the spleen of the mice. In primary cultured splenocytes, PIO treatment caused significant down-regulation of IFN-γ mRNA (P<0.05) and up-regulation of Foxp3 mRNA (P<0.05) and obviously increased the percentages of CD4+IFN-γ+ cells (P<0.05) and CD4+CD25+Foxp3+ (P<0.05); the effects of PIO on CD4+IFN-γ+ and CD4+CD25+Foxp3+ cells were abolished by treatment of the cells with GW9662.
Conclusion: The anti-atherosclerotic effect of PIO is probably mediated by the TGF-β/Smad signaling pathway and PPAR-γ-dependent modulation of Th1/Treg population.