Effects of macrophage-specific adiponectin expression on lipid metabolism in vivo

Epidemiological studies have associated low circulating levels of the adipokine adiponectin with multiple metabolic disorders, including metabolic syndrome, obesity, insulin resistance, type II diabetes, and cardiovascular disease. Recently, we reported that adiponectin selectively overexpressed in mouse macrophages can improve insulin sensitivity and protect against inflammation and atherosclerosis. To further investigate the role of adiponectin and macrophages on lipid and lipometabolism in vivo, we engineered the expression of adiponectin in mouse macrophages (Ad-TG mice) and examined effects on plasma lipoproteins and on the expression levels of genes involved in lipoprotein metabolism in tissues. Compared with the wild-type (WT) mice, Ad-TG mice exhibited significantly lower levels of plasma total cholesterol (-21%, P < 0.05) due to significantly decreased LDL (-34%, P < 0.05) and VLDL (-32%, P < 0.05) cholesterol concentrations together with a significant increase in HDL cholesterol (+41%, P < 0.05). Further studies investigating potential mechanisms responsible for the change in lipoprotein cholesterol profile revealed that adiponectin-producing macrophages altered expression of key genes in liver tissue, including apoA1, apoB, apoE, the LDL receptor, (P < 0.05), and ATP-binding cassette G1 (P < 0.01). In addition, Ad-TG mice also exhibited higher total and high-molecular-weight adipnection levels in plasma and increased expression of the anti-inflammatory cytokine IL-10 as well as a decrease in the proinflammatory cytokine IL-6 in adipose tissue. These results indicate that macrophages engineered to produce adiponectin can influence in vivo gene expression in adipose tissue in a manner that reduces inflammation and macrophage infiltration and in liver tissue in a manner that alters the circulating lipoprotein profile, resulting in a decrease in VLDL and LDL and an increase in HDL cholesterol. The data support further study addressing the use of genetically manipulated macrophages as a novel therapeutic approach for treatment of cardiometabolic disease.