Molecular Mechanism Of Calcium Silicate Ceramics Promoting Bone Regeneration Through Regulating The Immunosuppresive Function Of Mesenchymal Stem Cells

Bioactive silicate materials have been widely proved to be able to induce bone tissue regeneration in vivo,but the underlying molecular mechanism has not been fully elucidated.Recently,inflammatory response has been proved to be critical for tissue regeneration and many studies have proved that the ion extracts released from bioactive silicate materials can directly modulate the behaviors of macrophages and make them produce an immune microenvironment conducive to promote bone regeneration.Meanwhile,immunomodulatory effects of mesenchymal stem cells have been widely reported during bone regeneration as they can secret a variety of immune regulatory molecules to modulate the phenotype polarization of macrophages.However,whether bioactive silicate materials can indirectly regulate macrophages through affecting the immunomodulatory function of mesenchymal stem cells remains unclear.Therefore,considering the important role of mesenchymal stem cells in regulating inflammatory response,this study focuses on the effects of the ion extracts released from calcium silicate(CS),a kind of typical bioactive silicate materials,on the immunosuppressive function of human bone marrow mesenchymal stem cells(HBMSCs).In addition,the effects of direct and indirect CS ion extracts stimulation on macrophages are compared,followed by the investigation of in vitro osteogenic differentiation of HBMSCs cultured in different condition medium collected from these macrophages.The results showed that CS ion extracts could enhance the immunosuppressive function of HBMSCs by upregulating the gene expression of TSG-6,COX-2,PTGES2 and HGF through NF-κB signaling pathway,thereby indirectly promoting the polarization of macrophages towards M2 phenotype.Then,by using the condition medium collected from macrophages,the up-regulation of ALP,RUNX2,BMP-2 and COL-Ⅰgene expression in HBMSCs were observed,confirming the enhancement of in vitro osteogenic differentiation of HBMSCs.Besides,we found that CS ion extracts could promote macrophages polarize to M2 phenotype more effectively by indirect modulation,thereby eliciting an immune microenvironment conducive to the osteogenic gene expression of ALP and RUNX2 in HBMSCs.