Interaction of monocytes with vascular smooth muscle cells regulates monocyte survival and differentiation through distinct pathways.
OBJECTIVE
Vascular smooth muscle cells (VSMCs) may regulate monocyte functions within atherosclerotic lesions. We investigated the impact of VSMC/monocyte interactions on monocyte apoptosis and scavenger receptor CD36 expression, key events related to monocyte survival and differentiation.


RESULTS
Serum deprivation significantly increased THP-1 and human peripheral blood monocyte apoptosis. However, this was significantly reversed by physical binding to human VSMCs (HVSMCs). On binding to HVSMCs, antiapoptotic kinase Akt and its downstream targets were phosphorylated, and Bcl-2 expression was enhanced. Binding-mediated suppression of apoptosis and Akt phosphorylation were attenuated by a phosphoinositide 3-kinase inhibitor and also by an antibody to vascular cell adhesion molecule-1. CD36 expression was also significantly increased in THP-1 cells and in human peripheral blood monocytes after binding to HVSMCs, and this was mediated by both direct contact and soluble factors. Extracellular signal-regulated kinase 1/2 (ERK1/2) mitogen-activated protein kinase phosphorylation was increased in THP-1 cells after HVSMC coculture. Furthermore, an ERK1/2 inhibitor blocked monocyte CD36 upregulation. Contact-dependent CD36 induction and ERK1/2 phosphorylation in monocytes were inhibited by blocking vascular cell adhesion molecule-1 on HVSMC, whereas soluble factor-induced CD36 expression was attenuated by a monocyte chemoattractant protein-1 neutralizing antibody.


CONCLUSIONS
These data provide evidence of novel VSMC-dependent local regulation mechanisms for monocyte survival and differentiation in atherosclerosis.
Cai
Qiangjun
Q
Gonda Goldschmied Diabetes Center, Beckman Research Institute of City of Hope, Duarte, CalifA 91010, USA.
Lanting
Linda
L
Natarajan
Rama
R
D017209:Apoptosis / Q000502:physiology; D018955:CD36 Antigens / Q000096:biosynthesis / Q000378:metabolism; D002454:Cell Differentiation / Q000502:physiology*; D002460:Cell Line; D002470:Cell Survival / Q000502:physiology; D018932:Chemokine CCL2 / Q000502:physiology; D006801:Humans; D020935:MAP Kinase Signaling System / Q000502:physiology; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D009000:Monocytes / Q000166:cytology* / Q000201:enzymology / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000201:enzymology / Q000378:metabolism; D032389:Myocytes, Smooth Muscle / Q000201:enzymology / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis; D015854:Up-Regulation / Q000502:physiology; D019010:Vascular Cell Adhesion Molecule-1 / Q000378:metabolism / Q000502:physiology
D018955:CD36 Antigens; D018932:Chemokine CCL2; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2; D019010:Vascular Cell Adhesion Molecule-1; C494918:AKT1 protein, human