Homocysteine activates vascular smooth muscle cells by DNA demethylation of platelet-derived growth factor in endothelial cells

Hyperhomocysteinemia (HHcy), as an independent risk factor of atherosclerosis, facilitates endothelial dysfunction and activation of vascular smooth muscle cells (VSMCs). However, little is known about the crosstalk between endothelial cells (ECs) and VSMCs under HHcy. We investigated whether homocysteine (Hcy) activates VSMCs by aberrant secretion of mitogen platelet-derived growth factors (PDGFs) from ECs in human and in mice. In this study, we found that increased Hcy level did not affect VSMC activity in 24 hrs until the concentration reached 500 μM. In contrast, Hcy at 100 μM significantly promoted proliferation and migration of VSMCs co-cultured with human ECs. This effect was partially reversed by pretreatment with a PDGF receptor inhibitor. Hcy concentration-dependently upregulated the mRNA level of PDGF-A, -C and -D but not PDGF-B in ECs. Hcy reduced the expression and activity of DNA methyltransferase 1, demethylation of PDGF-A, -C and -D promoters and enhanced the binding activity of transcriptional factor SP-1 to the promoter. Hcy upregulation of PDGF was confirmed in the aortic intima of mice with HHcy. Multivariate regression analysis revealed HHcy was a predictor of increased serum PDGF level in patients. Thus, Hcy upregulates PDGF level via DNA demethylation in ECs, affects cross-talk between ECs and VSMCs and leads to VSMC activation.

Hyperhomocysteinemia exaggerates adventitial inflammation and angiotensin II-induced abdominal aortic aneurysm in mice

RATIONALE

A number of epidemiological studies have suggested an association of hyperhomocysteinemia (HHcy) and abdominal aortic aneurysm (AAA), but discrepancies exist. In addition, we lack direct evidence supporting a causal role.

OBJECTIVE

We determined the association and contribution of HHcy to AAA formation.

METHODS AND RESULTS

We first performed a meta-analysis of studies involving 1489 subjects and found a strong association of HHcy and AAA (odds ratio, 7.39). Next, we used angiotensin II-infused male apolipoprotein E-deficient mice and tested whether HHcy contributes to AAA pathogenesis. Homocysteine (Hcy) supplement (1.8 g/L) in drinking water resulted in mild HHcy. Intriguingly, HHcy greatly increased the incidence of angiotensin II-induced AAA and aortic dissection in apolipoprotein E-deficient mice (vehicle versus Hcy: 50% versus 100%; P<0.05). Histology indicated HHcy markedly exaggerated aortic adventitial inflammation. Increased levels of proinflammatory interleukin-6 and monocyte chemoattractant protein-1 were preferentially colocalized within adventitial fibroblasts in HHcy plus angiotensin II mice, which suggested the importance of adventitial fibroblasts activation in Hcy-aggravated AAA. Hcy sequentially stimulated adventitial fibroblasts transformation into myofibroblasts, secretion of interleukin-6 and monocyte chemoattractant protein-1, and consequent recruitment of monocytes/macrophages to adventitial fibroblasts, which was abolished by the NADPH oxidase inhibitor diphenyliodonium. NADPH oxidase 4, but not other homologs of NADPH oxidase, was significantly upregulated by Hcy in adventitial fibroblasts, whereas NADPH oxidase 4 small interfering RNA silencing diminished Hcy-induced adventitial fibroblasts activation. Finally, folic acid supplement (0.071 μg/g per day) markedly reduced HHcy-aggravated angiotensin II-induced AAA formation in apolipoprotein E-deficient mice.

CONCLUSIONS

HHcy may aggravate AAA formation at least partially via activating adventitial fibroblast NADPH oxidase 4.

Fenofibrate inhibited the differentiation of T helper 17 cells in vitro

Uncontrolled activity of T cells mediates autoimmune and inflammatory diseases such as multiple sclerosis, inflammatory bowel diseases, rheumatoid arthritis, type 1 diabetes, and atherosclerosis. Recent findings suggest that enhanced activity of interleukin-17 (IL-17) producing T helper 17 cells (Th17 cells) plays an important role in autoimmune diseases and inflammatory diseases. Previous papers have revealed that a lipid-lowering synthetic ligand of peroxisome proliferator-activated receptor α (PPARα), fenofibrate, alleviates both atherosclerosis and a few nonlipid-associated autoimmune diseases such as autoimmune colitis and multiple sclerosis. However, the link between fenofibrate and Th17 cells is lacking. In the present study, we hypothesized that fenofibrate inhibited the differentiation of Th17 cells. Our results showed that fenofibrate inhibited transforming growth factor-β (TGF-β) and IL-6-induced differentiation of Th17 cells in vitro. However, other PPARα ligands such as WY14643, GW7647 and bezafibrate did not show any effect on Th17 differentiation, indicating that this effect of fenofibrate might be PPARα independent. Furthermore, our data showed that fenofibrate reduced IL-21 production and STAT3 activation, a critical signal in the Th17 differentiation. Thus, by ameliorating the differentiation of Th17 cells, fenofibrate might be beneficial for autoimmunity and inflammatory diseases.

Statins induce the accumulation of regulatory T cells in atherosclerotic plaque

CD4⁺CD25⁺ regulatory T cells (Tregs) mediate immune suppression and prevent autoimmune disorders. Recently, Tregs were found to present in atherosclerotic lesions and play an important role in the progression of atherosclerosis. Statins have immunomodulatory properties, and the effect of statins on atherosclerosis depends in part on their immunomodulatory mechanisms. We sought to determine whether statins exhibit an effect on Tregs in atherosclerotic plaques and in peripheral circulation of patients with acute coronary syndrome (ACS). In an in vivo experiment, we induced atherosclerotic plaques in apolipoprotein E-deficient (ApoE⁻/⁻) mice. The mice were randomly divided into two groups for 6-wk treatment: simvastatin (50 mg/kg/d) or vehicle (control). Simvastatin significantly increased the number of Tregs and the expression of Treg marker Foxp3 (Forkhead/winged helix transcription factor), transforming growth factor (TGF)-β and interleukin (IL)-10 in atherosclerotic plaques. Moreover, simvastatin played an important role in modulating the balance between antiinflammatory (Tregs and Th2 cells) and proinflammatory (Th17 and Th1 cells) subsets of T cells. In an in vitro experiment, peripheral blood mononuclear cells (PBMCs) were isolated from patients with ACS and incubated with simvastatin. After an incubation for 96 h, simvastatin significantly enhanced the frequency and functional suppressive properties of Tregs. Therefore, statin treatment may influence Tregs in atherosclerotic lesions. Furthermore, statins improved the quantity and suppressive function of Tregs in ACS patients.

Fenofibrate enhances the in vitro differentiation of foxp3(+) regulatory T cells in mice

Foxp3⁺ regulatory T cells (Tregs) play a critical role in maintaining immune self-tolerance. Reduced number and activity of Tregs are usually found in autoimmune and inflammatory diseases, and enhancing the differentiation of Tregs may be a promising therapeutic strategy. Some reports suggested an anti-inflammatory and anti-autoimmune potential for fenofibrate, a hypolipidemic drug used worldwide, whose lipid effects are mediated by the activation of peroxisome proliferator-activated receptor α (PPARα). In the present paper, we found that fenofibrate dose-dependently increased transforming growth factor-β and interleukin-2-induced Treg differentiation in vitro, by 1.96-fold from 0 to 20 μM (12.59 ± 1.34% to 24.69 ± 3.03%, P < 0.05). Other PPARα activators, WY14643 (100 μM), gemfibrozil (50 μM), and bezafibrate (30 μM), could not enhance Treg differentiation. In addition, PPARα could not upregulate the promoter activity of the Treg-specific transcription factor Foxp3. Fenofibrate might exert its function by enhancing Smad3 phosphorylation, a critical signal in Treg differentiation, via Akt suppression. Our work reveals a new PPARα independent anti-inflammatory mechanism of fenofibrate in up-regulating mouse Treg differentiation.

The role of oxidized low-density lipoprotein in breaking peripheral Th17/Treg balance in patients with acute coronary syndrome

Oxidized low-density lipoprotein (ox-LDL) is an instrumental factor in atherogenesis, however, the effects of ox-LDL on the balance of Th17/Treg in acute coronary syndrome [ACS, including unstable angina (UA) and acute myocardial infarction (AMI)] is still unclear. CD4(+)CD25(+) regulatory T (Treg) cells and Th17 cells, subsets of T-helper cells, play important roles in peripheral immunity and their imbalance leads to the development of tissue inflammation and autoimmune diseases. However, few studies have explored the effect of Th17/Treg balance in plaque destabilization and the onset of ACS. To explore the shift of Th17/Treg balance in ACS patients and the effect of ox-LDL on the balance, we examined the frequencies of Th17 and Treg cells, key transcription factors and relevant cytokines in patients with AMI, UA, stable angina (SA) and controls. We analysed the correlations of serum ox-LDL to Th17/Treg frequency, and the effects of ox-LDL on Th17/Treg cells in vitro. Our study demonstrated that ACS patients have shown a significant increase of Th17 frequency, RORgammat expression and serum Interleukin 17 (IL-17), and a obvious decline of Treg frequency, Foxp3 expression, suppressive function, and serum IL-10. Serum ox-LDL positively correlated with the frequency of Th17 cells and negatively correlated with the frequency of Treg cells. In vitro incubation of peripheral blood mononuclear cells from controls with ox-LDL resulted in a significant reduction of Treg cells and a significant elevation of Th17 cells in a dose- and time-dependant manner. Treg and Th17 cells from ACS patients were significantly more susceptible to ox-LDL-mediated alterations. Th17/Treg numerical and functional imbalance exists in ACS patients, and ox-LDL has a direct effect on Th17/Treg imbalance which may contribute to the occurrence of ACS.