Canonical Wnts function as potent regulators of osteogenesis by human mesenchymal stem cells

Abstract

Genetic evidence indicates that Wnt signaling is critically involved in bone homeostasis. In this study, we investigated the functions of canonical Wnts on differentiation of adult multipotent human mesenchymal stem cells (hMSCs) in vitro and in vivo. We observe differential sensitivities of hMSCs to Wnt inhibition of osteogenesis versus adipogenesis, which favors osteoblastic commitment under binary in vitro differentiation conditions. Wnt inhibition of osteogenesis is associated with decreased expression of osteoblastic transcription factors and inhibition of c-Jun N-terminal kinase and p38 mitogen-activated protein kinase activation, which are involved in osteogenic differentiation. An hMSC subpopulation exhibits high endogenous Wnt signaling, the inhibition of which enhances osteogenic and adipogenic differentiation in vitro. In an in vivo bone formation model, high levels of Wnt signaling inhibit de novo bone formation by hMSCs. However, hMSCs with exogenous expression of Wnt1 but not stabilized β-catenin markedly stimulate bone formation by naive hMSCs, arguing for an important role of a canonical Wnt gradient in hMSC osteogenesis in vivo.

Pharmaceutical modulation of canonical Wnt signaling in multipotent stromal cells for improved osteoinductive therapy

“…Nevertheless, even the in vivo survival of GW-treated hMSCs was transient, suggesting a support role for hMSCs where the cells transiently up-regulate angiogenesis and inherent osteogenic capacity of the host's tissue. In agreement with this observation, it has recently been demonstrated that a population of hMSCs with an enhanced endogenous canonical Wnt signaling serves to enhance synergistically the ostoegenic capacity of coadministered hMSCs with a lesser degree of Wnt signaling (25).…”

“…3B). It has been speculated that arrest of canonical Wnt signaling occurs during terminal differentiation of osteoprogenitor cells, and Dkk-1 has been implicated in this process (24,25). Dkk-1 secretion was reduced in all cases, with maximal inhibition occurring at concentrations that induced highest ALP activity (Fig.…”

“…A simple interpretation of these results leads to the conclusion that endogenous canonical Wnt signaling can enhance osteogenesis. However, in light of an elegant series of experiments carried out by Liu et al (25), the mechanism seems more complex. In this instance, canonical Wnts1 and 3a could inhibit ALP and mineralization by hMSCs at high concentrations; however, when hMSCs were subjected to a bimodal culture system where adipogenic and osteogenic supplements were available, canonical Wnt signaling tipped the balance in favor of osteogenesis.…”

Opposite Spectrum of Activity of Canonical Wnt Signaling in the Osteogenic Context of Undifferentiated and Differentiated Mesenchymal Cells: Implications for Tissue Engineering

“…Our observation that Wnt3a treatment inhibits osteogenic differentiation in mesenchymal cells (e.g., ASCs and E16) is consistent with previous in vitro studies performed on other multipotent mesenchymal cells. [41][42][43][44] In addition, our study provides also in vivo evidence complementing in vitro results. It must be pointed out that in vitro Wnt3a treatment represents a constant and continuous treatment of cells, compared to in vivo treatment where calvarial bones are initially exposed to doses of Wnt3a protein, which gradually decreased overtime.…”

Development of Stepwise Osteogenesis-mimicking Matrices for the Regulation of Mesenchymal Stem Cell Functions

“…7, B and C). There are many reports that PPARG expression is suppressed by Wnt/␤-catenin signal during osteogenesis (42,43). The Wnt/␤-catenin signal may be strongly activated in the cells cultured on the stem cell matrices and early stage matrices to inhibit PPARG expression.…”