LPS inhibits PI-phospholipase C but not PC-phospholipase D or phosphorylase activation by vasopressin and norepinephrine

Suppression of PLCbeta2 by endotoxin plays a role in the adenosine A(2A) 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 alpha (TNFalpha) 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)beta1 and beta2 expression in macrophages by de-stabilizing their mRNAs. The PLCbeta inhibitor U73122 down-regulates TNFalpha 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 PLCbeta2, but not PLCbeta1, using small-interfering RNA resulted in increased VEGF expression in response to A(2A)R agonists, but did not suppress TNFalpha expression. Macrophages from PLCbeta2(-/-) mice also expressed increased VEGF in response to A(2A)R agonists. LPS-mediated suppression of PLCbeta1 and beta2 is MyD88-dependent. In a model of endotoxic shock, LPS (35 microg/mouse, i.p.) suppressed PLCbeta1 and beta2 expression in spleen, liver, and lung of wild-type but not MyD88(-/-) mice. These studies indicate that LPS suppresses PLCbeta1 and beta2 expression in macrophages in vitro and in several tissues in vivo. These results suggest that suppression of PLCbeta2 plays an important role in switching M1 macrophages into an M2-like state.

Lack of effect of calcitonin gene-related peptide and amylin on major markers of glucose metabolism in hepatocytes

Effects of amylin and calcitonin gene-related peptide on several processes involved in carbohydrate metabolism were investigated in rat hepatocytes, non-parenchymal cells (Kupffer, Ito and endothelial cells) and alveolar macrophages. In hepatocytes, cAMP levels were increased 25-fold by glucagon (10 nM), less than 2-fold by calcitonin gene-related peptide (100 nM) and not at all by amylin (100 nM). In non-parenchymal cells and cultured alveolar macrophages, calcitonin gene-related peptide potently, and amylin weakly, stimulated cAMP levels. In hepatocytes neither amylin nor calcitonin gene-related peptide affected glycogen phosphorylase activity, glucose output, lactate uptake, glycogen synthesis, glycogen mass or tyrosine aminotransferase activity. The density of calcitonin gene-related peptide specific binding sites in parenchymal cells was 10-fold less then seen in non-parenchymal cells. We found no significant evidence of specific amylin binding sites. These results are consistent with the notion that amylin does not exert a direct effect in hepatocytes. However, we do not rule out that amylin may affect hepatic glucose output indirectly through Cori cycling of lactate derived from skeletal muscle or from interactions through non-parenchymal cells.