| dc.description.abstract | Endochondral bone regeneration, which consists of regenerating bone tissue based on a cartilage template, is a promising approach to treat bone defects. Cartilage constructs are engineered with mesenchymal stromal cells (MSCs) in vitro. To generate high quality cartilage tissue in vitro, the differentiation conditions for the MSCs are crucial. Among others, bone morphogenic protein 2 (BMP-2) is a common growth factor used to differentiate MSCs chondrogenically in vitro. However, it is not completely clear how BMP-2 affects chondrogenesis and extracellular matrix (ECM) production. Therefore, the effects of BMP-2 reported in literature so far on the chondrogenic differentiation of MSCs and therefore ECM composition are fundamental to be summarized to have a better understanding of the topic, in order to produce in vitro cartilage constructs which can effectively sustain bone tissue regeneration in vivo.
This article aims to provide a broad overview on the effect of BMP-2 on MSCs chondrogenesis and on cartilage ECM composition. It also provides a collection of techniques helpful to detect BMP-2 remnants after cartilage ECM constructs engineering, since it could have a collateral impact on the therapeutical effects of the cartilage construct.
It is reported that upon BMP-2 binding to its receptors, activation of different molecular pathways are ensued, where cell proliferation, cell survival and chondrogenesis are upregulated. Furthermore, the expression of chondrocyte-specific genes, such as collagen type II, aggrecan and glycosaminoglycans and hypertrophy-specific genes, such as collagen type X, alkaline phosphatase and matrix metalloproteinase are stimulated, influencing ECM composition.
In detail, BMP-2 is a soluble extracellular protein that binds to BMP-2 receptor located on the surface of the target cell. Thereafter, upon the binding, two molecular pathways within the target cell are activated, namely the Smad and Non-Smad pathway. This results in a signalling cascade that ends up with the transcription of target genes responsible for the differentiation of the MSC into chondrocyte and, if the signal is sustained, ultimately in hypertrophic chondrocyte with the respective expression of cell type-specific ECM components, such as collagen type II or type X, respectively. Indeed, it has been also shown how the combination of BMP-2 with TGF-β, another protein involved in chondrogenic differentiation of MSCs, induced chondrogenic differentiation in vitro and higher hypertrophic marker expression, compared to when these growth factors are not combined.
In this article, also different methods and techniques have been described to detect BMP-2 remnants left within the ECM construct after the engineering process. In detail, there are reported promising degrading enzymes of the cartilage matrix, in order to set free and expose its components, and also promising BMP-2 detection methods that exploit the immunogenicity (IHC, ELISA, WB) or the size (WB, MS) of the protein of interest, in order to be set it apart from the rest.
In conclusion, this knowledge may help to understand how to approach and effectively intervene in bone tissue engineering in vitro, in order to produce cartilage constructs to transplant, which successfully induce endochondral bone formation in vivo. | |
