Adiponectin decreases C-reactive protein synthesis and secretion from endothelial cells: evidence for an adipose tissue-vascular loop

Abstract

Background and objective: Inflammation is pivotal in atherosclerosis. C-reactive protein (CRP), in addition to being a cardiovascular risk marker, may also be proatherogenic. We have previously shown that in addition to the liver, human aortic endothelial cells (HAECs) synthesize and secrete CRP. Whereas CRP levels are increased in obesity, metabolic syndrome, and diabetes, levels of adiponectin are reduced in these conditions. We tested the hypothesis that adiponectin reduces CRP synthesis and secretion in HAECs under normoglycemic (5.5 mmol/L glucose) and hyperglycemic conditions (15 mmol/L glucose).

Methods and results: Adiponectin dose-dependently reduced CRP mRNA and protein from HAECs. Adiponectin treatment of HAECs significantly decreased IkappaB phosphorylation and NFkappaB binding activity. There was no effect of adiponectin on STAT or C/EBP transcriptional activity. Adiponectin also activated AMP kinase resulting in decreased NFkappaB activity and decreased CRP mRNA and protein. These effects of adiponectin were mimicked by AICAR, an activator of AMPK, and reversed by inhibition of AMPK. Thus, adiponectin reduces CRP synthesis and secretion from HAECs under hyperglycemia via upregulation of AMP kinase and downregulation of NFkappaB. Similar findings were observed in rat primary hepatocytes.

Conclusions: Thus, in obesity and diabetes, the hypoadiponectinemia could exacerbate the proinflammatory state by inducing CRP production.

Figure 1

Effect of Adiponectin on HG-induced CRP synthesis and secretion (n=5). HAEC were incubated with mannitol, NG/HG (5.5/15mMglucose) in absence and presence of globular or total adiponectin. a. Representative RT-PCR with CRP/18S densitometric ratios. b. Representative Western blot with CRP/β-actin ratios. c. Secreted CRP. ; *p<0.01 vs NG; ^#p<0.05 vs HG

Figure 2

Effect of Adiponectin on HG- induced nuclear transcription factor activity: HAEC were incubated with NG/HG ± adiponectin. 2a). STAT1 and STAT3; 2b). C/EBPβ; 2c). NFκb. *p<0.01 vs control. *p<0.001 vs NG and ^#p<0.01 vs HG. 2d). A representative blot of phospho p65 expression with densitometric ratios of pp65/p65 (n=3).

Figure 3

Loss of NFκb abrogates HG-induced CRP: HAEC were transiently transfected with control or dominant negative Iκb vector for 24 hours in presence of NG or HG. 3a). Secreted CRP 3b). Representative RT-PCR gel of CRP with ratios. *p<0.001 compared to mannitol/NG; #p<0.01 vs. HG, n=3.

Figure 4

Effect of Adiponectin on HG-induced AMPK and NFκb activity in HAEC. 4a. Representative Western blot for pAMPK/AMPK with densitometric ratios. 4b. Representative CRP RT-PCR gel and densitometric ratios. 4c. Secreted CRP 4d. Nuclear NFκb DNA binding activity. *p<0.01 compared to C, NG and #p<0.01 compared to HG, n=4 experiments.

Figure 5

Effect of Adiponectin on CRP secretion in Primary Rat hepatocytes incubated with IL-1b and IL-6 in absence and presence of adiponectin. 5a. Secreted CRP levels *p<0.001 vs. IL-1+IL-6 and #p<0.05 vs. IL-1+IL-6. 5b. Nuclear C/EBP-beta, STAT1, STAT3 and NFκb activity. *p<0.001 vs.Control and #p<0.05 vs. IL-1+IL-6; n=3.