Activation of Ganglioside GM3 Biosynthesis in Human Monocyte/Macrophages during Culturing
We found that GM3 levels in human peripheral blood monocytes and cultured monocyte-derived macrophages were 0.37 and 2.7 ug per million cells, respectively. GM3 synthase of monocytes and to a greater extent of monocyte-derived macrophages was shown to be able to sialylate endogenous substrate, lactosylceratnide, to form GM3. With exogenously added lactosylceramides, GM3 synthase activity was 57.1 and 563 pmol/h per mg protein in monocytes and monocyte-derived macrophages, respectively. The revealed changes in ganglioside GM3 biosynthesis are specific as the activity of some other sialyltransferases under these conditions was not altered. Human anti-GM3 synthase antibody detected in monocytes a main protein with molecular weight of 60 kD and minor proteins with molecular weights of 52 and 64 kD. In monocyte-derived macrophages the amounts of 60 kD protein and especially 64 kD protein sharply rose. Thus, the increase in ganglioside GM3 levels, GM3 synthase activity, and enzyme amounts during culturing of monocyte/macrophages may be one of the mechanisms of <i>in vivo </i>increased ganglioside GM3 levels in arterial atherosclerotic lesions.