Stimulation of glycolipid synthesis and exchange by human serum high density lipoprotein-3 in human fibroblasts and leukocytes.

Upon exposure to either human skin fibroblasts or human circulating leukocytes, the composition of human serum high density lipoprotein-3 (HDL3) was modified by the apparent loss of apolipoprotein A-II and a 2- to 4-fold increase in glycosphingolipid content. Exposure of HDL3 to leukocytes produced an increase in the content of lactosylceramide, which is the major glycolipid in leukocytes, whereas exposure of HDL3 to human skin fibroblasts produced predominantly an increase in trihexosylceramide, which is the major glycolipid in fibroblasts. Other protein components of HDL3 (such as apolipoprotein A-I) were unaffected and there were no major changes in either neutral lipid or phospholipid composition. The increase in glycosphingolipid content of both cells and reisolated HDL3 particles was HDL3 concentration-dependent up to a concentration of 1 mg/ml and appeared to be the result of a stimulation of cellular glycolipid synthesis by HDL3 and subsequent transfer to HDL3 in the medium. A similar stimulation could not be produced by either low density lipoprotein or lipoprotein-deficient human serum. The coaddition of HDL3 and lipoprotein-deficient serum reduced both the loss of apolipoprotein A-II and the change in HDL3 glycolipid content, but not the increase in cellular glycolipid content, suggesting that modification of the apolipoprotein A-II peptide may enhance the ability of HDL3 to acquire new glycolipid from cells.