Oxidized Low Density Lipoprotein and Lysophosphatidylcholine Stimulate Cell Cycle Entry in Vascular Smooth Muscle Cells

We have previously shown that oxidized low density lipoprotein (LDL) but not native LDL stimulated DNA synthesis in cultured smooth muscle cells (SMC) and that α-tocopherol (vitamin E) inhibited this proliferative response (Lafont, A., Chai, Y. C., Cornhill, J. F., Whitlow, P. L., Howe, P. H., and Chisolm, G. M. (1995) J. Clin. Invest. 95, 1018-1025). The moiety of oxidized LDL that stimulates DNA synthesis and the cellular mechanism for this potentially mitogenic effect are not known. We now report that lipid fractions containing lysophospholipids from oxidized LDL or phospholipase A2-treated native LDL stimulated SMC DNA synthesis as did palmitoyl lysophosphatidylcholine (lysoPC). Protein kinase C inhibitors and down-regulation of protein kinase C activity by phorbol ester inhibited oxidized LDL- and lysoPC-induced DNA synthesis. A neutralizing monoclonal antibody against fibroblast growth factor-2 significantly inhibited oxidized LDL and lysoPC-induced DNA synthesis in SMC; irrelevant antibodies were ineffective. Vitamin E inhibited the DNA synthesis stimulated by lysoPC, an observation that distinguished this effect from DNA synthesis induced by another detergent, digitonin. These results suggest that oxidized LDL and its lysoPC moiety stimulate SMC to enter the cell cycle via an oxidative mechanism that causes the release of fibroblast growth factor-2 and a subsequent autocrine or paracrine response.