Inversely related expression of epidermal- and heart-type fatty acid binding proteins during myogenic differentiation of C2C12 myoblasts

Abstract

Following our report that heart-type (H-) fatty acid binding protein (FABP) was strongly up-regulated in differentiating myotubes, we examined the role of FABP and their effect on oleic acid uptake in the differentiation of mouse C2C12 myoblasts to myotubes in vitro. A second epidermal-type (E-) FABP is already expressed in the myoblast stage and is down-regulated at the onset of myogenic differentiation. This down-regulation is paralleled by that of β-actin, whereas mRNA expression of myogenic transcription factors and of H-FABP increases. These findings were verified at the protein level, which indicated that a basal level of FABPs, independent of the type, is always present during differentiation. Both FABPs were identified by their intracellular binding of oleic acid. This may explain that the change in oleic acid uptake into C2C12 cells at different stages of differentiation was negligible. Yet, the transition from E-FABP expressing myoblasts to H-FABP expressing myotubes was accompanied by a shift in preferential incorporation of oleic acid from triacylglycerols to phospholipids, perhaps necessary for terminal differentiation. The comparison of the expression of H-FABP with that of master myogenic transcription factors demonstrates that this fatty acid binding protein is not involved in the initiation of differentiation. The combination of a particular FABP and the cell in which it is expressed determines the fatty acid uptake. Cette etude examine le role des proteines de liaison des acides gras (FABP) de type cardiaque et leur effet sur la captation de l'acide oleique dans la differenciation de myoblastes C2C12 de souris en myotubes in vitro. Une FABP de type epidermique est exprimee au stade myoblaste et diminue au debut de la differenciation myogenique. Cette regulation est parallele a celle de la β-actine alors que l'expression de l'ARNm des facteurs de transcription myogenique et les FABP du type cardiaque augmentent. Les resultats montrent que ces proteines de liaison des acides gras ne sont pas impliquees dans la differenciation terminale.