Nuclear factor of activated T cells regulates osteopontin expression in arterial smooth muscle in response to diabetes-induced hyperglycemia

OBJECTIVE

Hyperglycemia is a recognized risk factor for cardiovascular disease in diabetes. Recently, we reported that high glucose activates the Ca(2+)/calcineurin-dependent transcription factor nuclear factor of activated T cells (NFAT) in arteries ex vivo. Here, we sought to determine whether hyperglycemia activates NFAT in vivo and whether this leads to vascular complications.

METHODS AND RESULTS

An intraperitoneal glucose-tolerance test in mice increased NFATc3 nuclear accumulation in vascular smooth muscle. Streptozotocin-induced diabetes resulted in increased NFATc3 transcriptional activity in arteries of NFAT-luciferase transgenic mice. Two NFAT-responsive sequences in the osteopontin (OPN) promoter were identified. This proinflammatory cytokine has been shown to exacerbate atherosclerosis and restenosis. Activation of NFAT resulted in increased OPN mRNA and protein in native arteries. Glucose-induced OPN expression was prevented by the ectonucleotidase apyrase, suggesting a mechanism involving the release of extracellular nucleotides. The calcineurin inhibitor cyclosporin A or the novel NFAT blocker A-285222 prevented glucose-induced OPN expression. Furthermore, diabetes resulted in higher OPN expression, which was significantly decreased by in vivo treatment with A-285222 for 4 weeks or prevented in arteries from NFATc3(-/-) mice.

CONCLUSIONS

These results identify a glucose-sensitive transcription pathway in vivo, revealing a novel molecular mechanism that may underlie vascular complications of diabetes.

Tumor necrosis factor-alpha does not mediate diabetes-induced vascular inflammation in mice

OBJECTIVE

Vascular inflammation is a key feature of both micro- and macrovascular complications in diabetes. Several lines of evidence have implicated the cytokine tumor necrosis factor (TNF) alpha as an important mediator of inflammation in diabetes. In the present study we evaluated the role of TNF alpha in streptozotocin (STZ)-induced diabetes on vascular inflammation in C57BL/6 wild-type and apoE-/- mice.

METHODS AND RESULTS

Diabetes increased the expression of vascular cell adhesion molecule (VCAM)-1 in cerebral arteries 150 m in diameter as well as the macrophage accumulation in aortic root atherosclerotic plaques in apoE-/- mice. A more pronounced vascular inflammatory response was observed in diabetic TNF alpha-deficient apoE-/- mice. These mice were also characterized by increased accumulation of IgG and IgM autoantibodies in atherosclerotic lesions. Diabetes also increased VCAM-1 expression and plaque formation in apoE-competent TNF alpha -/- mice, whereas no such effects were observed in C57BL/6 wild-type mice.

CONCLUSIONS

The present findings suggest that TNF alpha does not mediate diabetic-induced vascular inflammation in mice and reveal an unexpected protective role for TNF alpha. These effects are partly attributable to a direct antiinflammatory role of TNF alpha, but may also reflect a defective development of the immune system in these mice.

Nuclear factor of activated T-cells transcription factors in the vasculature: the good guys or the bad guys?

PURPOSE OF REVIEW

The nuclear factor of activated T-cells (NFAT) proteins are a family of Ca/calcineurin-dependent transcription factors that were first characterized in T-lymphocytes as inducers of cytokine gene expression. Since then, NFAT proteins have been shown to play varied roles outside of the immune system, including in the cardiovascular system. Cells in the vessel wall display a diverse array of Ca signaling modalities, which are subject to change during disease. The fact that NFAT proteins are able to decode and translate these signals into changes in gene expression makes them potential regulators of vascular pathogenesis.

RECENT FINDINGS

It is now clear that NFAT signaling is required for normal vascular patterning during embryogenesis and for vascular endothelial growth factor-induced angiogenesis. The overall role of NFAT signaling in the vasculature, however, is less clear during adult life. This review aims to give an update on mechanisms that regulate NFAT activation in vascular cells, with an emphasis on the role of mitochondria and of upstream activators such as lipids and glucose. It also addresses recent work implicating NFAT proteins as mediators of vascular disease.

SUMMARY

A better understanding of the NFAT-signaling pathway in the vasculature may open up an unexplored area for the development of new therapeutic approaches for treating vascular disease.