Glycosphingolipid biosynthesis during myogenesis of rat L6 cells in vitro

Abstract

Glycosphingolipid biosynthesis was examined using [3H]-galactose as a precursor as rat L6 myoblasts fused to form multinucleated myotubes. Incorporation of label into neutral glycolipids decreased steadily as the population of myotubes increased, so that final biosynthesis was one-half that observed with myoblasts (p less than 0.02). Conversely, ganglioside biosynthesis doubled during myoblast confluency (p less than 0.02) and then decreased as myotubes formed. Qualitatively, L6 cells synthesized large amounts of ganglioside GM3 during all myogenic phases. The major neutral glycosphingolipid products were lactosylceramide and paragloboside (nLcOse4Cer). Few changes in TLC autoradiographic patterns were noted during differentiation, with the exception of a slight decrease in ganglioside GM1. The results indicate that the biosynthesis of glycosphingolipids is tightly regulated during myogenesis in vitro and suggest a role for membrane gangliosides in muscle cell differentiation.

Glycosphingolipids during skeletal muscle cell differentiation: Comparison of normal and fusion-defective myoblasts

“…A report of an increase in one particular ganglioside, GDla, during myogenesis [21] conflicts with others claiming increases in a different structure, GD3 [22], while still others found no changes in specific GSL structures but alterations in total content [23]. We have recently suggested that these discrepancies may be due to the different species of origin of the cells examined because skeletal muscle GSLs exhibit a marked species specificity [24,25]. Several studies from our laboratory have consistently reported a transient increase in the synthesis of total neutral GSLs, or gangliosides, or both during in vitro myogenesis [24][25][26].…”

“…GSL synthesis during myogenesis of E63 myoblasts was examined using [3U]-serine as a metabolic precursor and yielded results similar to those documented previously by this laboratory [24,25]. E63 cells exhibited a transient increase in total neutral GSL synthesis at the time of cell contact and membrane fusion during myogenesis.…”

“…One laboratory group has reported an increase in ganglioside GDla at the time of myoblast fusion [21]. We, analyzing the same myoblast line (rat L6), found few changes in the synthesis of specific GSL structures, including GDla, but rather an overall increase in the synthesis of total gangliosides [24]. Upon a comparative study of several myogenic cell lines, we have previously suggested that changes in the synthesis of specific GSL structures during myogenesis is solely a function of the myogenic model being studied.…”

“…We have recently suggested that these discrepancies may be due to the different species of origin of the cells examined because skeletal muscle GSLs exhibit a marked species specificity [24,25]. Several studies from our laboratory have consistently reported a transient increase in the synthesis of total neutral GSLs, or gangliosides, or both during in vitro myogenesis [24][25][26]. This increased synthesis was shown to coincide with myoblast fusion and was greatly exaggerated during differentiation of dystrophic muscle cells [25].…”

Implications for the mammalian sialidases in the physiopathology of skeletal muscle

“…Gangliosides are acidic glycosphingolipids most abundant in the nervous system [9-11], but also present in skeletal muscle [12-16]. They are anchored on the outer leaflets of cell surfaces, with the sphingosine and fatty acid chains of the ceramide moiety embedded in the plasma membrane and the sugar oligosaccharide chain with terminal sialic acid(s) protruding toward the extracellular surface [17].…”