Effects And Mechanism Of The Conditioned Media Of Hypothalamus On Endocytosis Of Ox-LDL By Macrophages

Background and ObjectiveFormation of macrophage-derived foam cells plays a critical role in the initiation and progression of atherosclerosis, oxidized low-density lipoprotein (ox-LDL) is the key element in the process. Macrophages take up oxidized lipoproteins via scavenger receptors such as CD36and scavenger receptor A (SR-A), which causes intracellular lipids accumulation and foam cells formation. The recent evidence indicates that hypothalamus can effects on the development of atherosclerosis, but the potential mechanism is still unclear. Therefore, in the current study, the conditioned media of hypothalamus was used to investigate the effects on macrophage-derived foam cell formation and discuss the molecular mechanism.Materials and Methods The hypothalamic tissues from newborn rats were taken for cellular culture and the conditioned media were collected. Macrophages were pretreated with conditioned media for one hour, and then incubated for another six hours with Dil-labeled oxidized low density lipoprotein (Dil-ox-LDL;20μmol/L), the ox-LDL uptaking ability of macrophages was evaluated by Laser scanning confocal microscope imaging system.1. As for the investigation of mechanism in the process, macrophages were separately pretreated with the conditioned media of hypothalamus for one hour and then co-cultured for another24h in the presence of ox-LDL(20μl/mL). Immunofluorescence and western blotting assay were used to detect the expression of macrophage cell-surface receptors including SR-A and CD36. 2. To identify the signaling pathways involved in the inhibitory effect of hypothalamus on foam cell formation, macrophages were pretreated for one hour with the NF-κB inhibitor PDTC before the treatment of the conditioned media of hypothalamus. The expression of SR-A and CD36was detected by western blotting assay.ResultsTreating macrophages with ox-LDL alone caused intracellular lipid accumulation in cells. The high levels of SR-A and CD36expressions induced by ox-LDL were significantly attenuated in the presence the conditioned media of hypothalamus.The decreased expression of ox-LDL receptors SR-A and CD36induced by the conditioned media of hypothalamus was reversed by NF-κB signaling pathway inhibitor PDTC.Conclusion1. The conditioned media of hypothalamus can suppress the cellular uptake ability of ox-LDL by macrophages.2. The inhibitory effect of the conditioned media of hypothalamus in suppressing cellular ox-LDL uptake is attributed to down-regulating the expressions of cell-surface ox-LDL receptors SR-A and CD36.3. The down-regulation of ox-LDL receptors SR-A and CD36by the conditioned media of hypothalamus is via NF-κB signal pathway.