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

Abstract

The regulation of glycosphingolipid (GSL) synthesis in culture by fusion-competent (E63) myoblasts and fusion-defective (fu-1) cells was examined. Upon reaching confluency E63 cells fused to form multinucleated myotubes and demonstrated many characteristics of developing skeletal muscle including induction of creatine kinase activity and a shift in creatine kinase isozymes to the MM isoform. The fu-1 cells displayed none of these characteristics, despite the fact that both cells were cloned from the same parental myoblast line (rat L8). There was a transient increase in the synthesis of total neutral GSLs by E63 cells at the time of membrane fusion. In contrast, neutral GSL synthesis by fu-1 cells gradually decreased with time in culture. The major GSLs synthesized by both cell types were lactosylceramide and ganglioside GM3, with more complex structures being observed with prolonged time in culture. Several glycosyltransferase activities were assayed at varying times in culture. Generally, the changes in activities fell into three groups. One group was maximally activated at the end of the culture period (GalT-3, GalNAcT-1 and GalT-6). Another group was maximally activated during the time of active membrane fusion (GlcT and SAT-1). A third group was maximally activated at the time of cell contact and the beginning of membrane fusion (GlcNAcT-1 and GalT-2). In terms of the times of maximal activation there were few differences between E63 and fu-1 cells, with one notable exception. The activity of GalT-2 (lactosylceramide synthase) in E63 cells increased dramatically upon contact and the beginning of membrane fusion, whereas there were no changes in GalT-2 activity in fu-1 cells during time in culture. These results support our hypothesis that membrane glycosphingolipids play an important role in the differentiation of skeletal muscle cells.

Ganglioside GM3 Levels Are Altered in a Mouse Model of HIBM: GM3 as a Cellular Marker of the Disease

“…ST3Gal5 is the enzyme responsible for ganglioside GM3 synthesis. So far, the possible relationship between GM3 synthesis and HIBM was never investigated, yet GM3 is a glycosphingolipid largely involved in differentiation of muscle cells [44]–[46] and, more generally, in numerous cellular pathways, such as migration, proliferation, apoptosis or insulin sensitivity [42], [43]. Therefore, an alteration of its synthesis could directly lead to a vast modification of the cell metabolism.…”

“…Among gangliosides, GM3 is of particular interest, due to its preponderance in muscles [39]. Thus, an alteration of GM3 levels in HIBM cells could lead to a variety of detrimental effects and modification of cell metabolism and draw a bridge between several past observations on HIBM cells such as impairment of myogenic terminal differentiation (Amsili et al, personal communication) or modification of the apoptotic signaling pathways [54] as GM3 is precisely involved in terminal differentiation of myoblasts [44] and the control of apoptosis [36], [55].…”

“…GM3 is the most abundant ganglioside in muscle, representing almost 70% of total ganglioside in muscle membranes [37]–[40]. Gangliosides, and particularly GM3 and GD3 are involved in regulation of numerous cellular pathways, such as migration, proliferation, senescence and apoptosis [41]–[43] and ganglioside levels change over time in muscle cells, particularly during differentiation [44]–[46]. Thus, an alteration of the capacity of GNE to effectively regulate GM3 synthesis could alter progressively the ability of muscle cells to adapt to their environment or to cope with their needs.…”

Pleiotropic effects of sphingolipids in skeletal muscle

“…In contrast, very little is known about the role of glycosphingolipids in myogenesis. Pioneering studies indeed showed that myoblast differentiation was paralleled by increased biosynthesis of lactosylceramide and ganglioside GM3 [56,57]. More recently, cytosolic sialidase Neu2 was reported to be upregulated during C2C12 myoblast differentiation and, importantly, its overexpression was found to enhance myogenesis [58].…”

Oligomerization and Topology of the Golgi Membrane Protein Glucosylceramide Synthase

“…Glucosylceramide is the common precursor of most higher order glycosphingolipids, which are important cell membrane constituents and have been implicated as important factors in development, differentiation, tumor progression, and pathogen/host interactions (5)(6)(7)(8)(9)(10)(11). Thus, GCS may play significant roles in several biological processes by regulating the overall synthesis of glucosylceramide-derived glycosphingolipids.…”