1. TGF-β inhibits the uptake of modified low density lipoprotein by human macrophages through a Smad-dependent pathway: A dominant role for Smad-2
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Daryn Robert Michael, Rebecca Claire Salter, and Dipak Purshottam Ramji
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CD36 Antigens ,Macrophage ,CD36 ,Gene Expression ,Smad2 Protein ,SMAD ,AcLDL, acetylated low density lipoprotein ,LDL, low density lipoprotein ,Small hairpin RNA ,OxLDL, oxidized low density lipoprotein ,chemistry.chemical_compound ,Transforming Growth Factor beta ,Homeostasis ,Phosphorylation ,ABCA-1, ATP-binding cassette transporter A-1 ,Cells, Cultured ,ApoE, apolipoprotein E ,Foam cell ,HMDM, human monocyte-derived macrophages ,Gene knockdown ,Lipoprotein lipase ,DiI, 1,1′-dioctadecyl-3,3,3′,3′-tetramethyllindocarbocyane perchlorate ,Scavenger Receptors, Class A ,Cell biology ,Lipoproteins, LDL ,LPL, lipoprotein lipase ,Cholesterol ,Biochemistry ,Low-density lipoprotein ,shRNA, short hairpin RNA ,Molecular Medicine ,Signal Transduction ,TGF-β ,ABCG-1, ATP-binding cassette transporter G-1 ,Biology ,ApoE−/−, apolipoprotein E deficient ,CD36, cluster of differentiation 36 ,Article ,THP-1, human acute monocytic leukemia cell line ,Humans ,Smad3 Protein ,Molecular Biology ,Macrophages ,Transforming growth factor beta ,Atherosclerosis ,Lipoprotein Lipase ,chemistry ,biology.protein ,SR-A, scavenger receptor A ,Foam Cells - Abstract
The anti-atherogenic cytokine, TGF-β, plays a key role during macrophage foam cell formation by modulating the expression of key genes involved in the control of cholesterol homeostasis. Unfortunately, the molecular mechanisms underlying these actions of TGF-β remain poorly understood. In this study we examine the effect of TGF-β on macrophage cholesterol homeostasis and delineate the role of Smads-2 and ‐3 during this process. Western blot analysis showed that TGF-β induces a rapid phosphorylation-dependent activation of Smad-2 and ‐3 in THP-1 and primary human monocyte-derived macrophages. Small interfering RNA-mediated knockdown of Smad-2/3 expression showed that the TGF-β-mediated regulation of key genes implicated in the uptake of modified low density lipoproteins and the efflux of cholesterol from foam cells was Smad-dependent. Additionally, through the use of virally delivered Smad-2 and/or Smad-3 short hairpin RNA, we demonstrate that TGF-β inhibits the uptake of modified LDL by macrophages through a Smad-dependent mechanism and that the TGF-β-mediated regulation of CD36, lipoprotein lipase and scavenger receptor-A gene expression was dependent on Smad-2. These studies reveal a crucial role for Smad signaling, particularly Smad-2, in the inhibition of foam cell formation by TGF-β through the regulation of expression of key genes involved in the control of macrophage cholesterol homeostasis., Highlights ► Anti-atherogenic cytokine TGF-β inhibits macrophage foam cell formation. ► The role of Smads in the control of macrophage cholesterol homeostasis was studied. ► Smads were found to play a key role in the TGF-β-mediated uptake of modified LDL. ► A dominant role of Smad2 was identified in the regulation of gene expression. ► The TGF-β-Smad axis may represent a powerful anti-foam cell therapeutic target.
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