Dopamine D₁-like Receptors Suppresses The Proliferation Of Macrophages Induced By Ox-LDL

Background:Atherosclerosis (AS) is the main pathology of heart and cerebrovascular diseases. Thedamage of endothelial cells, the pathological physiological process of monocytes, vascularsmooth muscle cells (VSMCs) and macrophages migration, proliferation and the release ofinflammatory cytokines and so on are believed to be the major pathophysiological processesof atherosclerosis. Macrophages phagocyte chemically modified low-density lipoprotein(LDL) by scavenger receptors, such as oxidized low-density lipoprotein (Ox–LDL) andacetylated low density lipoprotein (acetyl-LDL) become macrophage–derived foam cells, isthe early stages of atherosclerosis. Ox-LDL is the most important risk factor ofatherosclerosis durling chemically modified lipoproteins. In recent years, a growing numberof studies have found that Ox-LDL could induce macrophages proliferation by stimulatinggranulocyte–macrophage colony-stimulating factor (GM-CSF), activation of protein kinaseC (PKC) and increase the number of intracellular Ca2+or other ways. The phenomenon ofmacrophages proliferation is demonstrated play an important regulatory role in thedevelopment of atherosclerosis and may exacerbate the pathological process ofatherosclerosis.Catecholamines is a substances containing nerve catechol and amine groups, includingnorepinephrine, epinephrine, and dopamine (DA). DA is a precursor substance ofnorepinephrine and epinephrine, and as the major endogenous catecholamineneurotransmitters, DA can play a protective role by dopamine receptors. Dopaminereceptors belong to the rhodopsin class family, which is a G protein-coupled receptorsincluding two subtypes depending on its structure and pharmacological properties, namelythe dopamine D1-like receptors and the dopamine D2–like receptors. Our laboratory studiesand the previous studies of others have shown that stimulate dopamine D1-likereceptors caninhibit the process of proliferation, migration and so on in vascular smooth muscle cells mediated by platelet-derived growth factor (PDGF), norepinephrine and the insulin-likegrowth factor, which maybe have an effect of anti-atherosclerotic. As one of the major cellsin atherosclerosis, if there is dopamine D1-like receptors expressed on macrophages andwhether it will affect the proliferation of macrophage or not are still unclear. Therefore, inthis study, we observed if there is dopamine D1-like receptors expressed on macrophages,whether it will affect macrophages proliferation induced by Ox-LDL or not, and explore itsmechanism preliminary.Method:1. The culture of mouse peritoneal macrophages and RAW264.7cells.2. The expression of the dopamine D1-like receptors on macrophages were examined byImmunohistochemistry, RT-PCR, Western blot.3. The proliferation of RAW264.7cells were examined by [3H]-TdR and method ofevaluation of cell number.4. The preliminary impact mechanism of the dopamine D1-like receptors onproliferation of Ox-LDL-induced macrophage were examined by [3H]-TdR and Western blot.5. The different expressions of the dopamine D1-like receptors on mouse peritonealmacrophages between ApoE-/-mouse and C57BL/6J mouse were examined by Western blot.Results:1. The dopamine D1-like receptors(including D1and D5receptors) is expressed onmouse macrophages.2. The expression of dopamine D1-like receptors on ApoE-/-mouse peritonealmacrophages is obviously decreased compared with C57BL/6J mouse peritonealmacrophages.3. Stimulate the dopamine D1-like receptors can slightly suppress proliferation ofRAW264.7cells. Whereas, stimulate the dopamine D1-like receptors can significantly inhibitthe proliferation of RAW264.7cells induced by Ox-LDL, and this effect was depend onconcentration.4. Fenoldopam can inhibit the up-regulation of MAPK/ERK and PI3K/AKT signalpathways which is activated by Ox-LDL in RAW264.7cell.Conclusion:The dopamine D1-like receptors(including D1and D5receptor) is expressed on mouse macrophages and compared with C57/BL6J, the expression of dopamine D1-like receptors onApoE-/-mouse peritoneal macrophages is significantly decreased. Stimulate the dopamineD1-like receptors can significantly suppress the proliferation of RAW264.7cells induced byOx-LDL, which may activated the MAPK/ERK and PI3K/AKT signal pathways.