Ruthenium Nanocomposites For Osteogenic Differentiation Of Mesenchymal Stem Cells And Its Molecular Mechanisms

Recently, an increasing trend is arising for the utilization of bone graft substitutes(BGSs). It is due to both the requirement of more than two million grafting procedures for the repair of bone damages worldwide and the well-known challenges concerning the use of autografts and allografts. An ideal BGS is considered to have the following properties:(1) osteoconductivity, which is defined as the potential of BGSs to provide a matrix or scaffold for bone formation,(2) osteoinductivity, which is the ability of a material to induce bone formation in nonosseous tissues,(3) osteogenic cells such as stem cells, progenitors, or mature osteoblasts, which produce the new bone matrix, and(4) osteointegration, which is defined as the ability of a material to bond chemically to the host tissue without formation of an intervening fibrous tissue. To evaluate the potential of BGSs, stem cells were cultured on the surface of BGSs and their proliferation and osteogenic differentiation were investigated in vitro.Multipotent mesenchymal stem cells(MSCs) have attracted particular attention in stem cell therapy and tissue engineering because they can be readily isolated and expanded ex vivo and induced either in vitro or in vivo to terminally differentiate into osteoblasts,chondrocytes, adipocytes, tenoctyes, and neural cells.Osteoblasts and adipocytes all originate from MSCs and can transform mutually.There is a reciprocal relationship between the differentiation of adipocytic and osteogenic cells in MSC culture. It was demonstrated that there was a therapeutic opportunity to either prevent or treat osteopenic disorders by inhibiting marrow adipogenesis with a concomitant increase in osteoblastogenesis.The self-renewal and differentiation of MSCs can be modulated by some nanoscale materials in vitro. Difficulties persisting with many of these known materials include lack of osteoinductive properties, poor processing abilities, and insufficient degradation.Based on the above research background, four kinds of ruthenium nanocomposites have been synthesized in this paper. The interactions of the drugs with MSCs have been examined here,which aims to explore potent drugs for bone regeneration. Three chapters are included in this thesis.In chapter 1, we firstly describe the discovery, characteristics, differentiation and tissue repair of MSCs, and then focus on the present nanoscale materials for stem cell therapy and bone tissue engineering. Finally, we give the purpose and significance of this thesis.In chapter 2, Ru nanoparticles(Ru NPs) and γ-Fe2O3@Ru nanoparticles(Fe2O3@Ru) were synthesized, and these particles were nontoxic to MSCs based on cytotoxicity assays. We demonstrate that Ru NPs and Fe2O3@Ru could induce MSCs to differentiate into osteoblasts, and in particular, Fe2O3@Ru was highly significant for promoting the osteogenic differentiation of MSCs and inhibiting adipocytic differentiation. We confirmed that the promotion of the osteogenic differentiation of MSCs may be regulated by a Smad-dependent bone morphogenetic protein(BMP) signalling pathway. We also indicated that the BMP signalling pathway is related to the Fe2O3@Ru-MSC interaction. In addition, Fe2O3@Ru caused a reduction in the expression of CD44, CD73 and CD105. The results revealed that Fe2O3@Ru-treated MSCs had already begun differentiation.In chapter 3, Although amino(-NH2)-terminated surfaces generated by silane modification nanoparticles(Si O2-NH2) can promote osteogenic differentiation of MSCs, how silica surfaces with ruthenium nanoparticles(Si O2@Ru) act in MSCs remains largely unknown. Cytotoxicity of Si O2@Ru on MSCs was assessed by MTT assays at concentrations ranging from 5 to 200 μg/ml for 24 or 72 h. Cytotoxicity of the Si O2@Ru was found to be dose dependent, not time dependent, with concentrations less than 10 μg/ml showing no significant differences compared to untreated controls. The enrichment of silica surfaces with ruthenium nanoparticles(Si O2@Ru) can be used to trigger MSCs differentiation into osteocytes, minimising the need for exogenous biological supplementation. The activation in Akt signaling pathways was observed in MSCs cultured with Si O2@Ru, and these enhancement effects could be blocked by Akt inhibitor LY294002. Si O2@Ru showed in vitro osteocompatibility that surpassed that of Si O2-NH2, as well as supported the proliferation and differentiation of MSCs. This demonstrates the potential of Si O2@Ru for use in bone regeneration.