Differential expression of glucose transporter isoforms during ES cell differentiation in vitro

Abstract

The facilitative glucose transporters (GLUT) are a family of structurally related membrane glycoproteins. In mouse blastocysts five different GLUT isoforms are expressed. Whereas the GLUT expression as a cell specific marker is well characterised in adult tissues, the expression during cell differentiation processes is still not clear. We studied mRNA levels and protein abundance of five GLUT isoforms (GLUT1–4, 8) in mouse embryonic stem cell line D3 (ESC) and during spontaneous, neuronal and myogenic differentiation of embryoid bodies (EBs). Both ESC and EBs expressed GLUT1, 3 and 8, whereas GLUT 2 and 4 mRNA were solely detectable in EBs of 15 (GLUT2) or 2 (GLUT4) days. A low glucose concentration of 5mM during EB differentiation regulated GLUT RNA expression and delayed EB growth and differentiation. Using specific cell markers, expression of GLUT3 and 4 was dependent on the differentiating cell type. GLUT3 was localised in the cell membranes of undifferentiated (SSEA-1+) and differentiated (SSEA-1-) cells. In 4 to 15 days EBs the outer cell layer (=SSEA-1-; CK18+ and CK19+) of endoderm-like cells showed a high GLUT3 labelling, similar to trophoblast cells in mouse blastocysts, whereas GLUT3 mRNA was decreased and no GLUT3 labelling was detected at 20d. GLUT4 is expressed in most of the differentiated (SSEA-1-), but not in undifferentiated (SSEA-1+) cells. GLUT4 positiv cells were located in the nucleus of desmin-negative cells, and in cytoplasm and plasma membranes of desmin+/GLUT4+ cells. In differentiated neuronal or myogenic EBs, Nestin and Desmin are co-expressed with GLUT3 and 4, whereas spontaneously differentiating EBs did not express nestin or desmin, indicating that the cell-type specific GLUT3 and 4 expression in spontaneously differentiating EB is not related to a neuronal or myogenic cell type. Our data suggest that during EB differentiation the cell-type specific GLUT expression is similar to the expression pattern in the early embryo.