Expression of macrophage (M phi) scavenger receptor, CD36, in cultured human aortic smooth muscle cells in association with expression of peroxisome proliferator activated receptor-gamma, which regulates gain of M phi-like phenotype in vitro, and its implication in atherogenesis

CD36 is one of the major receptors for oxidized low density lipoproteins be longing to macrophage (M phi) scavenger receptor (SR) class B and is though t to play an important role in the foam cell formation from monocyte-M phi in the atherosclerotic lesions. Although it has been hypothesized that smoo th muscle cells (SMCs) may be the other origin of foam cells in vivo, suppo rting data are still very limited. In the present study, we have tested the expression of a variety of SRs, including CD36, in 8 lots of primary human aortic SMCs (HASMCs) explanted from 8 different donors. Functional CD36 wa s expressed in cultured HASMCs, and the levels of expression were widely ra nged between the lots. SR class A (SR-A) was expressed abundantly in CD36-n egative lots. Other M phi markers, such as CD32 and CD68, were expressed in all lots tested. These data suggest that the cultured HASMCs gained an M p hi-like phenotype. To determine the mechanism for the above-described pheno typic change, we have tested the expression of a nuclear receptor, peroxiso me proliferator activated receptor-gamma, in those cells. This nuclear rece ptor was abundantly expressed in CD36-positive lots, whereas c-fms was expr essed abundantly in CD36-negative/SR-A-positive lots. The synthetic ligand of peroxisome proliferator activated receptor-gamma, troglitazone, upregula ted the expression of CD36 only in CD36-positive lots.-These observations d emonstrate that cultured HASMCs can gain an M phi-like phenotype, possibly classified by the expression of CD36 or SR-A. The present study may support the possibilities of transformation of HASMCs into foam cells in vivo.