NFAT signaling in chronic and acute inflammation. A novel target for the treatment of diabetic vascular complications and acute pancreatitis?
Diabetic patients suffer from macro- and microvascular complications causing increased morbidity and mortality. How hyperglycemia provokes vascular damage remains unclear, but glucose is believed to fuel a harmful low-grade chronic inflammation of the vessel wall. Previous work showed that glucose activates the transcription factor Nuclear Factor of Activated T cells (NFAT) in arteries ex vivo. NFAT is a family of Ca2+-calcineurin-sensitive proteins first found to regulate inflammatory gene expression in T cells, but have since been demonstrated to play a role in other cell types, including vascular endothelium and smooth muscle cells. We hypothesized that NFAT proteins are activated by glucose in diabetic vessels where they regulate proinflammatory genes that contribute to diabetic atherosclerosis and retinopathy. We also hypothesized that NFAT proteins regulate the inflammatory disease acute pancreatitis (AP). In the thesis, we demonstrate that both acute and chronic hyperglycemia activate NFAT in large arteries and retinal microvessels of mice. We show that activation of NFAT promotes the expression of the pro-inflammatory cytokine osteopontin (OPN). In vivo inhibition of NFAT with the novel blocker A-285222 or genetic deletion of NFATc3 reduced diabetes-induced OPN expression in mouse aorta. Moreover, we showed that treatment with A-285222 abolished diabetes-induced atherosclerosis, but had no effect on atherosclerosis in non-diabetic mice. Specifically, A-285222 reduced aortic lipid and macrophage content and the expression of IL-6, OPN, monocyte chemotactic protein-1 (MCP-1), intercellular adhesion molecule 1 (ICAM-1), and tissue factor in the arterial wall. In retinal vessels in vivo, we show that both glucose and lipids up-regulate the expression of vascular cell adhesion molecule 1 ( VCAM-1), promoting endothelial activation. Furthermore, in these vessels, we demonstrate that NFAT is activated by glucose by a mechanism involving the local release of extracellular nucleotides (i.e. UTP, UDP). In vivo inhibition of NFAT prevented diabetes-induced reduction of anti-inflammatory IL-10 in whole retina and reduced OPN and ICAM-1 mRNA in retinal microvessels. Finally, in the context of the exocrine pancreas, we demonstrate that NFATc3 regulates trypsinogen activation, inflammation and tissue damage in two mouse models of AP, and that NFATc3 deletion prevents AP-induced damage. Taken together, this thesis establishes that NFAT plays important roles in diabetic vascular complications and AP. Targeting NFAT may represent a novel therapeutic approach in these inflamatory disorders.