Analysis of the mitogenic effect of fetuin preparations on arterial smooth muscle cells: The role of contaminant platelet‐derived growth factor

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Abstract
Fetuin, a major protein of fetal calf serum, partially purified by the method of Pedersen, stimulated growth of aortic smooth muscle cells. More highly purified fetuin preparations stimulated growth less than Pedersen fetuin, as previously described for other cell types, suggesting that this activity is due to a contaminant. Recently bovine alpha2‐macroglobulin or “Embryonin” has been proposed as the mitogenic component of crude fetuin preparations. We found that active fetuin preparations did contain alpha2‐macroglobulin that stimulated smooth muscle cell growth. However, alpha2‐macroglobulin purified directly from platelet‐poor bovine plasma or fetuin purified from Pedersen fetuin by gel filtration lacked appreciable mitogenic effect on smooth muscle cells. Since alpha2‐macroglobulin can bind platelet‐derived growth factor (PDGF), and since highly acidic fetuin might bind the very basic PDGF molecule non‐specifically, we measured the PDGF content of various fetuin preparations and found a good correlation between the PDGF content and mitogenic activity. Gel filtration experiments demonstrated that in Pedersen fetuin PDGF occurred both free, and in association with alpha2‐macroglobulin. We conclude that the principal mitogenic component for smooth muscle cells in crude fetuin preparations is PDGF, since purified bovine alpha2‐macroglobulin or fetuin do not appreciably affect growth of these cells. These results help to resolve a long‐standing controversy regarding the nutrition of cultured cells. In addition, we suggest that before alpha2‐macroglobulin or “Embryonin” is accepted as a bona fide growth factor for a given cell type, the role of contamination with PDGF should be assessed.