P2Y receptors and atherosclerosis in apolipoprotein E-deficient mice

Background and purpose:

P2Y nucleotide receptors are involved in the regulation of vascular tone, smooth muscle cell (SMC) proliferation and inflammatory responses. The present study investigated whether they are involved in atherosclerosis.

Experimental approach:

mRNA of P2Y receptors was quantified (RT-PCR) in atherosclerotic and plaque-free aorta segments of apolipoprotein E-deficient (apoE^–/–) mice. Macrophage activation was assessed in J774 macrophages, and effects of non-selective purinoceptor antagonists on atherosclerosis were evaluated in cholesterol-fed apoE^–/– mice.

Key results:

P2Y₆ receptor mRNA was consistently elevated in segments with atherosclerosis, whereas P2Y₂ receptor expression remained unchanged. Expression of P2Y₁ or P2Y₄ receptor mRNA was low or undetectable, and not influenced by atherosclerosis. P2Y₆ mRNA expression was higher in cultured J774 macrophages than in cultured aortic SMCs. Furthermore, immunohistochemical staining of plaques demonstrated P2Y₆-positive macrophages, but few SMCs, suggesting that macrophage recruitment accounted for the increase in P2Y₆ receptor mRNA during atherosclerosis. In contrast to ATP, the P2Y₆-selective agonist UDP increased mRNA expression and activity of inducible nitric oxide synthase and interleukin-6 in J774 macrophages; this effect was blocked by suramin (100–300 µM) or pyridoxal-phosphate-6-azophenyl-2′-4′-disulphonic acid (PPADS, 10–30 µM). Finally, 4-week treatment of cholesterol-fed apoE^–/– mice with suramin or PPADS (50 and 25 mg·kg⁻¹·day⁻¹ respectively) reduced plaque size, without changing plaque composition (relative SMC and macrophage content) or cell replication.

Conclusions and implications:

These results suggest involvement of nucleotide receptors, particularly P2Y₆ receptors, during atherosclerosis, and warrant further research with selective purinoceptor antagonists or P2Y₆ receptor-deficient mice.