TGF-β inhibits the uptake of modified low density lipoprotein by human macrophages through a Smad-dependent pathway: a dominant role for Smad-2.
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.
Cardiff School of Biosciences, Cardiff University, Cardiff, UK. MichaelDr1@cf.ac.uk
Daryn R
DR
Michael
Rebecca C
RC
Salter
Dipak P
DP
Ramji
D018955:CD36 Antigens / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D002784:Cholesterol / Q000235:genetics / Q000378:metabolism; D005487:Foam Cells / Q000378:metabolism; D015870:Gene Expression; D006706:Homeostasis; D006801:Humans; D008071:Lipoprotein Lipase / Q000235:genetics / Q000378:metabolism; D008077:Lipoproteins, LDL / Q000235:genetics / Q000378:metabolism*; D008264:Macrophages / Q000378:metabolism*; D010766:Phosphorylation; D051117:Scavenger Receptors, Class A / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D051899:Smad2 Protein / Q000235:genetics / Q000378:metabolism*; D051900:Smad3 Protein / Q000235:genetics / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism*
D018955:CD36 Antigens; D008077:Lipoproteins, LDL; C497782:SMAD2 protein, human; C497790:SMAD3 protein, human; D051117:Scavenger Receptors, Class A; D051899:Smad2 Protein; D051900:Smad3 Protein; D016212:Transforming Growth Factor beta; D002784:Cholesterol; D008071:Lipoprotein Lipase