Murine osteoblasts regulate mesenchymal stem cells via WNT and cadherin pathways: mechanism depends on cell–cell contact mode

Abstract

Osteoblasts (OSTs) are derived from mesenchymal stem cells (MSCs) and coexist in close proximity with MSCs in bone during development and remodelling. Interactions between these two cell types remain obscure. Through a well-defined co-culture model, the present work demonstrated that OSTs regulate MSCs through the WNT and cadherin pathways. The regulation mechanism depends on the cell-cell contact mode (indirect or direct) between the two cell types. When physically separated (indirect contact), OSTs express WNTs and stimulate the osteogenic differentiation of MSCs through the activation of the WNT pathway and suppression of the cadherin pathway. This mechanism is evidenced by: (a) the elevation of cytoplasmic and nuclear unphosphorylated beta-catenin protein levels; (b) the suppression of beta-catenin degradation; (c) the increase in WNT-related transcription factor TCF1/LEF1; and (d) the loss of major bone-related cadherins (N-CAD and CAD11). Addition of DKK1 antagonizes the WNT pathway and diminishes the stimulatory effect of OSTs on MSCs. When in direct cell-cell contact, OSTs still secrete WNTs, whose binding still stabilizes the beta-catenin in MSCs. However, direct cell-cell contact induces the upregulation of cadherin pathway in MSCs, which suppresses the WNT pathway by containing cytoplasmic beta-catenin protein at a low level; consequently, the stimulatory effect of OSTs is negated. Regulation of cytoplasmic beta-catenin protein levels through concerted action or crosstalk between the WNT and cadherin pathways is the key to the signalling transduction in these cellular communication networks.

Osteogenic differentiation is synergistically influenced by osteoinductive treatment and direct cell–cell contact between murine osteoblasts and mesenchymal stem cells

“…The multipotent differentiation capabilities of MSCs into various types of cell lineage, such as osteoblasts, chondrocytes, and adipocytes, have been characterized in numerous studies [1,2]. Studies have used co-culture systems to further investigate the possible induction of osteogenesis of MSCs by neighbouring cells [18][19][20][21]. Osteoblasts, which are derived from bone-marrow MSCs, are the main cell type responsible for bone formation, and are one of the neighbouring cell types close to the bone marrow.…”

“…Osteoblasts, which are derived from bone-marrow MSCs, are the main cell type responsible for bone formation, and are one of the neighbouring cell types close to the bone marrow. Direct cell-cell contact co-culture models have produced further evidence that co-culture of MSCs and osteoblasts [17,20,22] or osteoblast-derived soluble factors [16,23,24] leads to osteogenesis. It is believed that interaction between bonemarrow MSCs and their neighbouring cells may lead to MSC osteogenesis via cell-cell contact or osteoblast-derived soluble factors.…”

Osteogenic differentiation of mesenchymal stem cells is regulated by osteocyte and osteoblast cells in a simplified bone niche

“…In previous studies where enhanced osteogenic differentiation of MSCs was reported, by either conditioned media or in a co-culture with bone cells, medium applied to MSC cultures was supplemented with osteogenic factors (Lu et al, 2011;Ilmer et al, 2009;Wang et al, 2007;Heino et al, 2004). In contrast, Csaki et al (2009) found a high density co-culture of osteoblasts and MSCs to produce as strong an osteogenic response as a co-culture supplemented with osteogenic medium.…”

“…There is increasing evidence that osteocytes act as the mechanotransducers for bone (Skerry et al, 1989;Cowin et al, 1995;Tatsumi et al, 2007;Burra et al, 2010) and are also instrumental for regulating osteoclast formation from monocyte precursors (You et al, 2008). Here, it has been observed that osteocytes are capable of inducing a greater osteogenic response in MSCs than osteoblasts, both in terms of an increase in ALP activity in MSCs, which is a characteristic early marker of osteogenesis, and an increase in mineral production (a later osteogenic differentiation marker).…”

Biomimetic Extracellular Matrix-Incorporated Scaffold Induces Osteogenic Gene Expression in Human Marrow Stromal Cells

“…Studies using coculture systems have shown that cell-cell interactions between osteoblasts and MSCs induce osteogenic differentiation of the MSCs. 22 We believe that interaction between the differentiating cells within the scaffold could induce signal transduction, leading to the formation of a homogeneous population of differentiating cells.…”