P2Y6 receptor potentiates pro-inflammatory responses in macrophages and exhibits differential roles in atherosclerotic lesion development.

BACKGROUND: P2Y(6), a purinergic receptor for UDP, is enriched in atherosclerotic lesions and is implicated in pro-inflammatory responses of key vascular cell types and macrophages. Evidence for its involvement in atherogenesis, however, has been lacking. Here we use cell-based studies and three murine models of atherogenesis to evaluate the impact of P2Y(6) deficiency on atherosclerosis. METHODOLOGY/PRINCIPAL FINDINGS: Cell-based studies in 1321N1 astrocytoma cells, which lack functional P2Y(6) receptors, showed that exogenous expression of P2Y(6) induces a robust, receptor- and agonist-dependent secretion of inflammatory mediators IL-8, IL-6, MCP-1 and GRO1. P2Y(6)-mediated inflammatory responses were also observed, albeit to a lesser extent, in macrophages endogenously expressing P2Y(6) and in acute peritonitis models of inflammation. To evaluate the role of P2Y(6) in atherosclerotic lesion development, we used P2Y(6)-deficient mice in three mouse models of atherosclerosis. A 43% reduction in aortic arch plaque was observed in high fat-fed LDLR knockout mice lacking P2Y(6) receptors in bone marrow-derived cells. In contrast, no effect on lesion development was observed in fat-fed whole body P2Y(6)xLDLR double knockout mice. Interestingly, in a model of enhanced vascular inflammation using angiotensin II, P2Y(6) deficiency enhanced formation of aneurysms and exhibited a trend towards increased atherosclerosis in the aorta of LDLR knockout mice. CONCLUSIONS: P2Y(6) receptor augments pro-inflammatory responses in macrophages and exhibits a pro-atherogenic role in hematopoietic cells. However, the overall impact of whole body P2Y(6) deficiency on atherosclerosis appears to be modest and could reflect additional roles of P2Y(6) in vascular disease pathophysiologies, such as aneurysm formation.

11ß-hydroxysteroid dehydrogenase type 1 gene knockout attenuates atherosclerosis and in vivo foam cell formation in hyperlipidemic apoE⁻/⁻ mice.

BACKGROUND: Chronic glucocorticoid excess has been linked to increased atherosclerosis and general cardiovascular risk in humans. The enzyme 11ß-hydroxysteroid dehydrogenase type 1 (11ßHSD1) increases active glucocorticoid levels within tissues by catalyzing the conversion of cortisone to cortisol. Pharmacological inhibition of 11ßHSD1 has been shown to reduce atherosclerosis in murine models. However, the cellular and molecular details for this effect have not been elucidated. METHODOLOGY/PRINCIPAL FINDINGS: To examine the role of 11ßHSD1 in atherogenesis, 11ßHSD1 knockout mice were created on the pro-atherogenic apoE⁻/⁻ background. Following 14 weeks of Western diet, aortic cholesterol levels were reduced 50% in 11ßHSD1⁻/⁻/apoE⁻/⁻ mice vs. 11ßHSD1⁺/⁺/apoE⁻/⁻ mice without changes in plasma cholesterol. Aortic 7-ketocholesterol content was reduced 40% in 11ßHSD1⁻/⁻/apoE⁻/⁻ mice vs. control. In the aortic root, plaque size, necrotic core area and macrophage content were reduced ∼30% in 11ßHSD1⁻/⁻/apoE⁻/⁻mice. Bone marrow transplantation from 11ßHSD1⁻/⁻/apoE⁻/⁻ mice into apoE⁻/⁻ recipients reduced plaque area 39-46% in the thoracic aorta. In vivo foam cell formation was evaluated in thioglycollate-elicited peritoneal macrophages from 11ßHSD1⁺/⁺/apoE⁻/⁻ and 11ßHSD1⁻/⁻/apoE⁻/⁻ mice fed a Western diet for ∼5 weeks. Foam cell cholesterol levels were reduced 48% in 11ßHSD1⁻/⁻/apoE⁻/⁻ mice vs. control. Microarray profiling of peritoneal macrophages revealed differential expression of genes involved in inflammation, stress response and energy metabolism. Several toll-like receptors (TLRs) were downregulated in 11ßHSD1⁻/⁻/apoE⁻/⁻ mice including TLR 1, 3 and 4. Cytokine release from 11ßHSD1⁻/⁻/apoE⁻/⁻-derived peritoneal foam cells was attenuated following challenge with oxidized LDL. CONCLUSIONS: These findings suggest that 11ßHSD1 inhibition may have the potential to limit plaque development at the vessel wall and regulate foam cell formation independent of changes in plasma lipids. The diminished cytokine response to oxidized LDL stimulation is consistent with the reduction in TLR expression and suggests involvement of 11ßHSD1 in modulating binding of pro-atherogenic TLR ligands.