Pro-Inflammatory Effects of HDL are Primarily Mediated by a Small HDL Subpopulation in Bone Marrow Derived Macrophages
Chau, Jessica   (University of Washington)
Mentor: Bornfeldt, Karin
HDL exhibits a variety of functions that may contribute to its cardioprotective effects, including reverse cholesterol transport and inhibition of inflammatory and oxidative processes. However, the effect of HDL on inflammatory cells, such as macrophages, is not completely understood, as HDL has been shown to inhibit or enhance the inflammatory activation of these cells in different studies. In addition, the relative effects of small, medium and large HDL subpopulations on macrophages are not known. Our goal was to clarify the effects of small, medium and large HDL on inflammatory responses in macrophages. HDL and its small (7.9 nm diameter), medium (9.3 nm diameter) and large (11.3 nm diameter) sub-fractions were isolated from transgenic mice harboring a human apolipoprotein A-I transgene. Bone marrow-derived macrophages (BMDMs) were pretreated with either total HDL (0.1-1.0 m M), or HDL sub-fractions (0.5 m M) for 4 hours before stimulation with 10 ng/ml lipopolysaccharide (LPS) in the absence of HDL. At the end of LPS treatment, cells were collected and used to measure gene expression of inflammatory mediators by real-time PCR. Our results show that total HDL dose-dependently increased LPSinduced tumor necrosis factor-a (Tnfa), IFN-?-inducible protein 10 (Cxcl10) and interferonstimulated gene 15 (Isg15) gene expression, but had no effect in the absence of LPS. Pretreatment with small HDL had the strongest pro-inflammatory effect as it significantly (p<0.05) increased the LPS-induced TNF-a (350% over LPS alone), interleukin 1b (183% over LPS alone) and ISG15 (72% over LPS alone) gene expression. Conversely, medium and large HDL had no significant effect on LPS-induced TNF-a and IL-1ß expression. Since small HDL is more effective than medium and large HDL in accumulating cellular cholesterol, changes in cellular pro-inflammatory signaling due to passive cholesterol depletion might be involved in the pro-inflammatory effect of small HDL. These studies increase our understanding of cellular effects of HDL subpopulations, which are altered in subjects with diabetes and diabetes complications.