T cell-specific overexpression of TGFß1 fails to influence atherosclerosis in ApoE-deficient mice.

Clinical data have indicated a negative correlation between plasma TGFß1 concentrations and the extent of atherosclerosis and have thus led to the hypothesis that the pleiotropic cytokine may have anti-atherogenic properties. T-cells are currently discussed to significantly participate in atherogenesis, but the precise role of adaptive immunity in atherogenesis remains to be elucidated. TGFß1 is known to strongly modulate the function of T-cells, however, inhibition of TGFß1 signalling in T-cells of atherosclerosis-prone knock-out mice failed to unequivocally clarify the role of the cytokine for the development of atherosclerosis. In the present study, we thus tried to specify the role of TGFß1 in atherogenesis by using the murine CD2-TGFß1 transgenic strain which represents a well characterized model of T-cell specific TGFß1 overexpression. The CD2-TGFß1 transgenic mice were crossed to ApoE knock-out mice and quantity and quality of atherosclerosis regarding number of macrophages, smooth muscle cells, CD3 positive T-cells and collagen was analyzed in CD2-TGFß1 ApoE double mutants as well as non-transgenic ApoE controls on both normal and atherogenic diet of a duration of 8, 16 or 24 weeks, respectively. In all experimental groups investigated, we failed to detect any influence of TGFß1 overexpression on disease. Total number of CD3-positive T-lymphocytes was not significantly different in atherosclerotic lesions of CD2-TGFß1 ApoE(-/-) females and isogenic ApoE(-/-) controls, even after 24 weeks on the atherogenic diet. The synopsis of these data and our previous study on TGFß1 overexpressing macrophages suggests that potential effects of TGFß1 on atherosclerosis are most probably mediated by macrophages rather than T-cells.

Overexpression of TGF-ß1 in macrophages reduces and stabilizes atherosclerotic plaques in ApoE-deficient mice.

Although macrophages represent the hallmark of both human and murine atherosclerotic lesions and have been shown to express TGF-ß1 (transforming growth factor ß1) and its receptors, it has so far not been experimentally addressed whether the pleiotropic cytokine TGF-ß1 may influence atherogenesis by a macrophage specific mechanism. We developed transgenic mice with macrophage specific TGF-ß1 overexpression, crossed the transgenics to the atherosclerotic ApoE (apolipoprotein E) knock-out strain and quantitatively analyzed both atherosclerotic lesion development and composition of the resulting double mutants. Compared with control ApoE(-/-) mice, animals with macrophage specific TGF-ß1 overexpression developed significantly less atherosclerosis after 24 weeks on the WTD (Western type diet) as indicated by aortic plaque area en face (p<0.05). Reduced atherosclerotic lesion development was associated with significantly less macrophages (p<0.05 after both 8 and 24 weeks on the WTD), significantly more smooth muscle cells (SMCs; p<0.01 after 24 weeks on the WTD), significantly more collagen (p<0.01 and p<0.05 after 16 and 24 weeks on the WTD, respectively) without significant differences of inner aortic arch intima thickness or the number of total macrophages in the mice pointing to a plaque stabilizing effect of macrophage-specific TGF-ß1 overexpression. Our data shows that macrophage specific TGF-ß1 overexpression reduces and stabilizes atherosclerotic plaques in ApoE-deficient mice.

No effect of C-reactive protein on early atherosclerosis in LDLR-/- / human C-reactive protein transgenic mice.

The association between increased concentrations of C-reactive protein (CRP) and future cardiovascular events is well established. However, it is currently unclear whether this clinical observation represents an epiphenomenon or whether the pentraxin may actively promote the development of atherosclerosis. Experimental studies with knockout mice with a defect in apolipoprotein E (ApoE(-/-)) have been used to investigate the role of CRP in atherogenesis, but the results obtained have been contradictory so far. Since knockout mice with a defect in low density lipoprotein receptor (LDLR(-/-)) may represent a better model of atherogenesis compared to ApoE(-/-) animals, we undertook experiments to investigate the atherogenic potential of CRP using LDLR(-/-) knockout mice. We crossbred CRP transgenic animals expressing the human CRP pentraxin (huCRP) to LDLR(-/-) mice, fed the resulting double mutants a pro-atherogenic Western type diet (WTD) for four, eight or 12 weeks, respectively, and quantitated atherosclerotic lesion development. Significant differences of lesion size or lesion composition could not be detected between the huCRP-positive LDLR(-/-) mice and the huCRP-negative LDLR(-/-) controls corroborating the contention that CRP does not play a pathogenetic role in early murine atherogenesis.

Interferon-gamma induces chronic active myocarditis and cardiomyopathy in transgenic mice.

Chronic heart failure is associated with an activation of the immune system characterized among other factors by the cardiac synthesis and serum expression of proinflammatory cytokines. There is unequivocal clinical and experimental evidence that the cytokine tumor necrosis factor-alpha is involved in the development of chronic heart failure, but a putative cardiotoxic potential of the proinflammatory cytokine interferon (IFN)-gamma remains primarily unknown. To investigate this issue we analyzed the cardiac phenotype of SAP-IFN-gamma transgenic mice, which constitutively express IFN-gamma in their livers and hence exhibit high circulating serum levels of this cytokine. SAP-IFN-gamma mice spontaneously developed chronic active myocarditis, characterized by the infiltration of not only CD4(+) and CD8(+) T cells but also Mac2(+) (galectin 3(+)) macrophages and CD11c(+) dendritic cells, eventually culminating in cardiomyopathy. Echocardiographic analyses exhibited a left ventricular dilation and impaired systolic function induced by IFN-gamma overexpression. IFN-gamma-mediated cardiotoxicity was associated with high-level cardiac transcription of the proinflammatory cytokines tumor necrosis factor-alpha and interleukin-12 and the macrophage-attracting chemokines MCP1 and MIP1-alpha. Myotoxic IFN-gamma effects could not be detected in smooth or striated muscle tissue, suggesting cardiomyocellular specificity of the toxic IFN-gamma effect. The precise mechanism of IFN-gamma cardiotoxicity remains to be elucidated.