The endothelium-derived contracting factor uridine adenosine tetraphosphate induces P2Y^sub 2^-mediated pro-inflammatory signaling by monocyte chemoattractant protein-1 formation

It is very well established that purinergic signaling plays a relevant role in vascular physiology and pathophysiology. Recently, a new purinoceptor agonist uridine adenosine tetraphosphate (Up^sub 4^A) has been identified as a highly potent endothelial-derived contracting factor (EDCF). The purpose of the study was to investigate Up^sub 4^A's influence on pro-inflammatory mechanisms. An early component of the inflammatory response in atherogenesis is the oxidative stress-induced formation of monocyte chemoattractant protein-1 (MCP-1). Here, we investigated the influence of Up^sub 4^A on MCP-1 formation and characterized the underlying signaling transduction mechanisms in rat vascular smooth muscle cells (VSMCs). Up^sub 4^A induced MCP-1 expression and secretion in VSMCs via the activation of P2Y^sub 2^ in a concentration-dependent manner. MCP-1 formation depends on generation of reactive oxygen species (ROS). To determine whether the predominant source of ROS in the vasculature, the NAD(P)H oxidase (Nox), is involved, we used different approaches. The ROS scavenger, tiron, the Nox inhibitor, apocynin and diphenyl-iodonium, as well as Nox1 knockdown, diminished the Up^sub 4^A-induced MCP-1 formation. Rac1 activation and p47^sup phox^ translocation from cytosol to the plasma membrane--both required for assembling and activation of Nox, were stimulated by Up^sub 4^A. ERK1/2 and p38 activation is essential for the intracellular signal transduction. In summary, Up^sub 4^A induced Nox1-dependent ROS generation, which further stimulated MCP-1 formation via MAPK phosphorylation in VSMCs. This process requires the activation of the G-protein coupled receptor P2Y^sub 2^. Therefore, Up^sub 4^A is not only a potent EDCF but also a potent inductor of pro-inflammatory response in the vascular wall.[PUBLICATION ABSTRACT]