To explain this effect of GAG mimetics on bone regeneration

To explain this effect of GAG mimetics on bone regeneration, we hypothesize that it is partly due to their capacity to modulate endogenous MSC properties in vivo. Therefore, to validate this ep4 antagonist we investigated in this study whether some particular mimetics are able to potentiate effectively the properties of rat MSC (rMSC) in vitro. Two different mimetics with specific structural signatures, [OTR4120] and [OTR4131], were compared to natural GAG on their ability to modulate clonogenicity, growth, migration and osteogenic differentiation of rMSC. Each GAG mimetic was used in rMSC culture, alone or in combination with a long term treatment with FGF-2, to assess the advantages of a GAG mimetic conditioning prior to therapeutic treatment of bone defect by MSC.
Results
Discussion Bone marrow MSC are currently exploited in clinical trials as a promising cell therapeutic tool to repair damaged tissues. During regenerative processes, the properties of MSC are regulated through complex interactions between HBP and GAG harboring fine specific chemical structures (Cool and Nurcombe, 2005; Jackson et al., 2006). In the past few years, structural and functional analogs of GAG were developed and demonstrated to display regenerative properties as illustrated in animal model of bone repair (Lafont et al., 2004). Here, we studied the effect of two structurally different GAG mimetics, equally sulfated and bearing or not acetyl groups, on the properties of MSC. We hypothesize that GAG mimetics can represent potential therapeutic alternatives to treatments with exogenous growth factors, since they can modulate endogenous growth factor activities. The in vitro effects of these GAG mimetics, with or without continuous treatment with FGF-2, were studied on rMSC obtained after purification, amplification and functional characterization.
Materials and methods
Acknowledgments This work was supported by Region Ile-de-France doctoral fellowship for Dr. G. Frescaline. We thank Dr. F. Siñeriz and Pr. D. Barritault from OTR3 Inc. (Paris, France) for kindly providing GAG mimetic molecules. We thank Pr. L. Garrigue-Antar and Pr. I. Martelly for helpful readings of the manuscript.
Introduction By definition, the process of synthesizing mineralized structures performed by creatures via inorganic solid states is called biomineralization. In general, a distinction is made between “biologically induced mineralization” and “biologically controlled mineralization”. In the first process a mineral is formed as a side-product or an end-product of cellular metabolism and interaction of the cells with the environment (Lowenstam, 1981). This procedure results in heterogeneous minerals. In contrast, the second process leads to very complex structured intra- or extracellular minerals with specific properties such as bone or dentin. It is also well known that the inorganic share of biominerals in mammals formed by the abovementioned processes mainly consists of calcium phosphate (Ca–P), which is chemically the same as hydroxyl apatite (HA) (LeGeros, 2001; Dorozhkin and Epple, 2002). However, there are differences between biominerals and HA regarding the Ca/P ratios, for example, caused by Ca deficits (LeGeros, 1991). In addition, the process of biomineralization can be physiological or pathological (LeGeros, 2001). Pathological mineral formation can be seen when excessive cell growth takes place, for instance, in tumors (Skinner, 2000, 2005). In this case, dead cells disintegrate, release phosphate and, due to a higher concentration of Ca, exceed the solubility product in the extracellular space and precipitation takes place (Skinner, 2005). During the formation of minerals alongside collagen fibers, in vivo osteoblasts primarily form an extracellular matrix (ECM) consisting of collagen and proteoglycane, followed by a restructuring of the proteins at so-called “active sides” (Hohling et al., 1995, 1997; Plate et al., 1998; Wiesmann et al., 1993, 2005).