The Th17/Treg functional imbalance during atherogenesis in ApoE−/− mice
Introduction
Atherosclerosis is a chronic inflammatory disease involving T lymphocytes, particularly CD4+ T cells [1], [2], [3]. The up-regulation of T helper cell 1 (Th1) response has been found in the local atherosclerotic lesions and circulating lymphocytes in atherosclerotic animal models and patients with acute coronary syndrome [ACS, including unstable angina (UA) and acute myocardial infarction (AMI)], suggesting that Th1/Th2 imbalance plays an important role in the development of atherosclerosis and plaque rupture [4], [5], [6], [7].
CD4+ CD25+ regulatory T (Treg) cells and Th17 cells have recently been described as two distinct subsets which are different from Th1 and Th2 cells. Treg cells expressing the forkhead/winged helix transcription factor (Foxp3) have anti-inflammatory properties and maintain tolerance against self components by contact-dependent suppression or releasing anti-inflammatory cytokines [such as interleukin (IL)-10 and transforming growth factor (TGF)-β1] [8], while Th17 cells expressing retinoic acid-related orphan receptor γt (RORγt) play critical roles in the development of autoimmunity and allergic reactions by producing IL-17 and, to a lesser extent, IL-6 [9]. Therefore, the balance between Th17 and Treg cells is important in the development/prevention of inflammatory and autoimmune diseases [10]. In the previous study we reported that the Th17/Treg imbalance existed in patients with ACS, suggesting a potential role of Th17/Treg imbalance in plaque destabilization [11]. Recently, de Boer et al. reported that the frequency of naturally occurring Treg cells decreased in all developmental stages of human atherosclerotic lesions [12].
As apolipoprotein E (ApoE)-deficient mice exhibit atherosclerotic lesion formation similar to what was observed in humans, they have often been used to investigate the pathogenesis of atherosclerosis [13]. In another report, Mor et al. showed Treg numbers were reduced in atherosclerotic ApoE−/− mice compared with age-matched C57BL/6J littermates [14]. Little is known about whether the Th17/Treg imbalance existed during atherogenesis in ApoE−/− mice.
In the present study, we investigated Th17/Treg functions at different levels including cell frequencies, related cytokine secretion and key transcription factors in ApoE−/− mice and their age-matched C57BL/6J mice. The results demonstrated that ApoE−/− mice revealed significantly increased secretion of Th17 related cytokines (IL-17 and IL-6) and expression of transcription factor (RORγt) levels and obviously decreased number in Treg cells, secretion of Treg related cytokines (TGF-β1) and expression of transcription factor (Foxp3) levels as compared with age-matched C57BL/6J mice. Results indicate that Th17/Treg functional imbalance exists during atherogenesis in ApoE−/− mice, suggesting a potential role of Th17/Treg imbalance in the formation and progression of atherosclerosis.
Section snippets
Animal models
As a model of in vivo atherosclerosis, ApoE−/− mice on a C57BL/6J background and their wild-type littermates, purchased from Jackson Laboratory (Bar Harbor, Maine, USA), were bred and maintained in the Animal Center of Beijing University. The investigation conforms to the Guide for the Care and Use of Laboratory Animals published by the US National Institutes of Health (NIH Publication No. 85–23, revised 1996). All animal studies were reviewed and approved by the Animal Study Committee of
Basic physiological parameters
We have shown the body weight and plasma cholesterol gain of ApoE−/− mice and the wild-type littermates C57BL/6J mice over a 32-week period (Table 1).
Atherosclerosis lesion area
As shown in Fig. 1, ApoE−/− mice had prominent atherosclerotic lesions with progressive development whereas C57BL/6J mice nearly did not have visible atherosclerotic lesions stained with oil red O. We fed eight-week-old ApoE−/− mice with a regular diet for 4 time periods: 0, 8, 16 and 24 weeks. Atherosclerotic lesion size increased significantly
Discussion
The Th17/Treg balance controls inflammation and may be important in atherosclerosis. To investigate whether the Th17/Treg functional imbalance existed during atherogenesis in mice, we detected Th17/Treg functions comparatively between ApoE−/− mice and age-matched C57BL/6J littermates. The results demonstrated that ApoE−/− mice revealed significant increase in Th17 related cytokines (IL-17 and IL-6) and transcription factor (RORγt) levels and obvious decrease in Treg number, Treg related
Disclosures
None.
Acknowledgments
This work described in this article was supported by National Natural Science Foundation of China (No. 30600234, 30871067) and National Basic Research Program of China (973 Program) 2007CB512000; 2007CB512005.
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These authors contributed equally to this work.