Suppression of PLCβ2 by Endotoxin Plays a Role in the Adenosine A2A Receptor-Mediated Switch of Macrophages from an Inflammatory to an Angiogenic Phenotype

Toll-like receptor (TLR) 2, 4, 7, and 9 agonists, together with adenosine A(2A) receptor (A(2A)R) agonists, switch macrophages; from an inflammatory (M1) to an angiogenic (M2-like) phenotype. This switch involves induction of A(2A)Rs by TLR agonists, down-regulation of tumor necrosis factor a (TNF alpha) and interleukin-12, and up-regulation of vascular endothelial growth factor (VEGF) and interleukin-10 expression. We show here that the TLR4 agonist lipopolysaccharide (LPS) induces rapid and specific post-transcriptional down-regulation of phospholipase C(PLC)beta 1 and beta 2 expression in macrophages; by destabilizing their mRNAs. The PLC beta inhibitor U73122 down-regulates TNF alpha expression by macrophages, and in the presence of A(2A)R agonists, up-regulates VEGF, mimicking the synergistic action of LPS with A(2A)R agonists. Selective down-regulation of PLC beta 2, but not PLC beta 1, using small-interfering RNA resulted in increased VEGF expression in response to A(2A)R agonists, but did not suppress TNF alpha expression. Macrophages from PLC beta 2(-/-) mice also expressed increased VEGF in response to A(2A)R agonists. LPS-mediated suppression of PLC beta 1 and beta 2 is MyD88-dependent. in a model of endotoxic shock, LPS (35 mu g/mouse, i.p.) suppressed PLC beta 1 and beta 2 expression in spleen, liver, and lung of wild-type but not MyD88(-/-) mice. These studies indicate that LPS suppresses PLC beta 1 and beta 2 expression in macrophages in vitro and in several tissues in vivo. These results suggest that suppression of PLC)32 plays an important role in switching M1 macrophages into an M2-like state. (Am J Pathol 2009, 175:2439-245 DOI: 10.2353/ajpath.2009.090290)