Inhibition of ganglioside GD1a synthesis suppresses the differentiation of human mesenchymal stem cells into osteoblasts

In this study, we investigated the regulatory role of ganglioside GD1a in the differentiation of osteoblasts from human mesenchymal stem cells (hMSCs) by using lentivirus-containing short hairpin (sh)RNA to knockdown ST3 beta-galactoside alpha-2, 3-sialyltransferase 2 (ST3Gal II) mRNA expression. After hMSCs were infected for 72 h with the lentivirus constructed with ST3Gal II shRNAs, the puromycin-resistant cells were selected and subcultured to produce hMSCs with ST3Gal II mRNA knockdown. The hMSCs established from human dental papilla abundantly expressed CD44 and CD105, but not CD45 and CD117. Osteoblasts that differentiated from normal hMSCs showed a significant increase in alkaline phosphatase (ALP) activity and ganglioside GD1a expression level compared with those in hMSCs. Lentiviral infection of hMSCs successfully induced a marked inhibition of ST3Gal II mRNA expression and caused a significant decrease in ALP activity and ganglioside GD1a expression. During osteoblastic differentiation, the increased ALP activity remarkably reduced by suppression of ganglioside GD1a expression by ST3Gal II shRNA. Ganglioside GD1a and ALP were mainly expressed in the cell body of hMSCs and osteoblasts with colocalization. The phosphorylation of extracellular signal-regulated kinases (ERK) 1/2 mitogen-activated protein (MAP) kinase and epidermal growth factor receptor (EGFR) was significantly reduced in the osteoblasts that had differentiated from the hMSCs with ST3Gal II mRNA knockdown. These results suggest that ganglioside GD1a plays an important role in the regulation of osteoblastic differentiation of hMSCs through the activation of ERK 1/2 MAP kinase and EGFR.