ALPHA-FETOPROTEIN BINDING AND UPTAKE BY PRIMARY CULTURES OF HUMAN SKELETAL-MUSCLE

alpha-Fetoprotein (AFP), a serum a-globulin mainly synthesized by the fetal liver and the yolk sac, is the major carrier of polyunsaturated fatty acids during embryo-fetal development. One property characterist ic of fetal cells undergoing growth and differentiation is their abili ty to bind and internalize AFP. In the present work, we have studied t he binding and endocytosis of AFP by human muscular cells developing i n vitro. Primary cultures of human skeletal muscle, obtained from biop sies and examined at two stages of differentiation (myoblasts and myot ubes), were incubated for different times, at 0 and 37 degrees C, with a colloidal-gold-conjugated human AFP probe and studied by light and electron microscopy, as well as by laser scanning confocal microscopy in the reflection mode. The results obtained show that (a) human myobl asts in primary culture bind and internalize the protein, probably thr ough specific AFP receptors, (b) this property is strongly reduced or lost in well-differentiated myotubes, and (c) AFP is also bound, throu ghout culture development, to the extracellular matrix of fusing myobl asts and differentiated myotubes. The physiological significance of AF P uptake by human myoblasts undergoing growth and differentiation may be based on the ability of AFP to carry and deliver fatty acids to fet al cells.