Loss of myeloid lipoprotein lipase exacerbates adipose tissue fibrosis with collagen VI deposition and hyperlipidemia in leptin-deficient obese mice

During obesity, tissue macrophages increase in number and become proinflammatory, thereby contributing to metabolic dysfunction. Lipoprotein lipase (LPL), which hydrolyzes triglyceride in lipoproteins, is secreted by macrophages. However, the role of macrophage-derived LPL in adipose tissue remodeling and lipoprotein metabolism is largely unknown. To clarify these issues, we crossed leptin-deficient Lep(ob/ob) mice with mice lacking the Lpl gene in myeloid cells (Lpl(m−/m−)) to generate Lpl(m−/m−);Lep(ob/ob) mice. We found the weight of perigonadal white adipose tissue (WAT) was increased in Lpl(m−/m−);Lep(ob/ob) mice compared with Lep(ob/ob) mice due to substantial accumulation of both adipose tissue macrophages and collagen that surrounded necrotic adipocytes. In the fibrotic epidydimal WAT of Lpl(m−/m−);Lep(ob/ob) mice, we observed an increase in collagen VI and high mobility group box 1, while α-smooth muscle cell actin, a marker of myofibroblasts, was almost undetectable, suggesting that the adipocytes were the major source of the collagens. Furthermore, the adipose tissue macrophages from Lpl(m−/m−);Lep(ob/ob) mice showed increased expression of genes related to fibrosis and inflammation. In addition, we determined Lpl(m−/m−);Lep(ob/ob) mice were more hypertriglyceridemic than Lep(ob/ob) mice. Lpl(m−/m−);Lep(ob/ob) mice also showed slower weight gain than Lep(ob/ob) mice, which was primarily due to reduced food intake. In conclusion, we discovered that the loss of myeloid Lpl led to extensive fibrosis of perigonadal WAT and hypertriglyceridemia. In addition to illustrating an important role of macrophage LPL in regulation of circulating triglyceride levels, these data show that macrophage LPL protects against fibrosis in obese adipose tissues.