Contribution of intimal smooth muscle cells to cholesterol accumulation and macrophage-like cells in human atherosclerosis.
BACKGROUND
Intimal smooth muscle cells (SMCs) contribute to the foam cell population in arterial plaque, and express lower levels of the cholesterol exporter ATP-binding cassette transporter A1 (ABCA1) in comparison with medial arterial SMCs. The relative contribution of SMCs to the total foam cell population and their expression of ABCA1 in comparison with intimal monocyte-derived macrophages, however, are unknown. Although the expression of macrophage markers by SMCs following lipid loading has been described, the relevance of this phenotypic switch by SMCs in human coronary atherosclerosis has not been determined.


RESULTS
Human coronary artery sections from hearts explanted at the time of transplantation were processed to clearly delineate intracellular and extracellular lipids and allow costaining for cell-specific markers. Costaining for oil red O and the SMC-specific marker SM α-actin of foam cell-rich lesions revealed that 50±7% (average±standard error of the mean, n=14 subjects) of total foam cells were SMC derived. ABCA1 expression by intimal SMCs was significantly reduced between early and advanced atherosclerotic lesions, with no loss in ABCA1 expression by myeloid lineage cells. Costaining with the macrophage marker CD68 and SM α-actin revealed that 40±6% (n=15) of CD68-positive cells originated as SMCs in advanced human coronary atherosclerosis.


CONCLUSIONS
These findings suggest SMCs contain a much larger burden of the excess cholesterol in human coronary atherosclerosis than previously known, in part, because of their relative inability to release excess cholesterol via ABCA1 in comparison with myeloid lineage cells. Our results also indicate that many cells identified as monocyte-derived macrophages in human atherosclerosis are in fact SMC derived.
Departments of Medicine and Pathology and Laboratory Medicine, Centre for Heart Lung Innovation, Institute for Heart + Lung Health, Providence Health Care Research Institute at St. Paul's Hospital, University of British Columbia, Vancouver, BC, Canada (S.A., A.C.C., B.M.M., G.A.F.), and Department of Research Resources, Penn State Milton S. Hershey Medical Center, Hershey, PA (T.A.).
Sima
S
Allahverdian
Ali Cyrus
AC
Chehroudi
Bruce M
BM
McManus
Thomas
T
Abraham
Gordon A
GA
Francis
D064286:ATP Binding Cassette Transporter 1 / Q000378:metabolism; D000199:Actins / Q000378:metabolism; D015703:Antigens, CD / Q000378:metabolism; D015214:Antigens, Differentiation, Myelomonocytic / Q000378:metabolism; D015415:Biomarkers / Q000378:metabolism; D019070:Cell Lineage / Q000502:physiology; D002784:Cholesterol / Q000378:metabolism*; D003324:Coronary Artery Disease / Q000378:metabolism*; D003331:Coronary Vessels / Q000166:cytology / Q000378:metabolism*; D005487:Foam Cells / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D008264:Macrophages / Q000166:cytology / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism*; D022423:Myeloid Cells / Q000166:cytology / Q000378:metabolism; D017539:Tunica Intima / Q000166:cytology / Q000378:metabolism; D000097382:CD68 Molecule
D064286:ATP Binding Cassette Transporter 1; D000199:Actins; D015703:Antigens, CD; D015214:Antigens, Differentiation, Myelomonocytic; D015415:Biomarkers; D002784:Cholesterol; C577836:ABCA1 protein, human; C067980:CD68 antigen, human; D000097382:CD68 Molecule
atherosclerosis; cholesterol; foam cells; macrophages; myocytes, smooth muscle