Alpha 2-macroglobulin is an astroglia-derived neurite-promoting factor for cultured neurons from rat central nervous system.

The neurite promoting factors in the astroglial conditioned medium (As-CM) were characterized by using primary cultures of embryonic rat neocortical neurons. The factors in the As-CM bind to lectins such as wheat germ agglutinin (WGA), suggesting that they contain sugar moieties. When the WGA-bound fractions were applied on a Superose 6 column, the activity was recovered mainly in two fractions, peak I and peak II. The peak II fraction was further purified by Mono Q anion exchange chromatography. A single protein band of 180 kDa was detected in the final Mono Q fraction by sodium dodecylsulfate polyacrylamide gel electrophoresis. The molecular weight coincided with that of alpha 2-macroglobulin (alpha 2M). Western blotting showed that the single protein band was reacted with anti-alpha 2M antibody but not with anti-fibronectin and anti-laminin antisera. The neurite-promoting activity of the Mono Q fraction was inhibited by anti-alpha 2M antibody. Furthermore, commercially available alpha 2M also promotes neurite outgrowth in our assay system. These results strongly suggested that alpha 2M is one of the neurite-promoting factors in the As-CM.