The heparan sulfate proteoglycan (HSPG) glypican‐3 mediates commitment of MC3T3‐E1 cells toward osteogenesis

Abstract

Heparan sulfate (HS) sugar chains attached to core proteoglycans (PGs) termed HSPGs mediate an extensive range of cell-extracellular matrix (ECM) and growth factor interactions based upon their sulfation patterns. When compared with non-osteogenic (maintenance media) culture conditions, under established osteogenic culture conditions, MC3T3-E1 cells characteristically increase their osteogenic gene expression profile and switch their dominant fibroblast growth factor receptor (FGFR) from FGFR1 (0.5-fold decrease) to FGFR3 (1.5-fold increase). The change in FGFR expression profile of the osteogenic-committed cultures was reflected by their inability to sustain an FGF-2 stimulus, but respond to BMP-2 at day 14 of culture. The osteogenic cultures decreased their chondroitin and dermatan sulfate PGs (biglycan, decorin, and versican), but increased levels of the HS core protein gene expression, in particular glypican-3. Commitment and progress through osteogenesis is accompanied by changes in FGFR expression, decreased GAG initiation but increased N- and O-sulfation and reduced remodeling of the ECM (decreased heparanase expression) resulting in the production of homogenous (21 kDa) HS chain. With the HSPG glypican-3 expression strongly upregulated in these processes, siRNA was used to knockdown this gene to examine the effect on osteogenic commitment. Reduced glypican-3 abrogated the expression of Runx2, and thus differentiation. The reintroduction of this HSPG into Runx2-null cells allowed osteogenesis to proceed. These results demonstrate the dependence of osteogenesis on specific HS chains, in particular those associated with glypican-3.

Fibroblast growth factor signaling in skeletal development and disease

“…In mesenchymal osteoprogenitor cells, FGFR1/2 are important for maintaining mesenchymal stem cell stemness by inhibiting cell senescence (Coutu et al 2011;Di Maggio et al 2012). During the osteogenic differentiation process, initially high Fgfr1/Fgfr2 expression is associated with FGF2 responsiveness and a robust proliferative response (Cowan et al 2003;Haupt et al 2009). In more mature osteoblasts, decreased expression of Fgfr1 and increased expression of Fgfr2, Fgfr3, and Fgfr4 are associated with an inability to sustain an FGF2 response ).…”

Matrix Protein Biglycan Induces Osteoblast Differentiation through Extracellular Signal-Regulated Kinase and Smad Pathways

“…7) Recent studies have found that the heparan sulfate mediates osteoblasts toward osteogenesis, and it regulates the anabolic activity of osteoblasts by triggering transient increase in Erk1/2 phosphorylation and activating Runx2. 30,31) Chondroitin sulfates involved in the osteogenic progression of osteoprogenitors are through Erk pathway. 32) This implies that GAGs may have potential ability facilitating osteoblast differentiation through Erk phosphrylation and Runx2 activity.…”

Regenerative potential of glycosaminoglycans for skin and bone

“…During osteogenic differentiation of mesenchymal stem cells (MSCs), PG expression pattern is reported to undergo continuous changes [61,62].…”