Osteogenesis and angiogenesis induced by porous β-CaSiO3/PDLGA composite scaffold via activation of AMPK/ERK1/2 and PI3K/Akt pathways

As a potential bioactive material, β-calcium silicate (β-CS) has attracted particular attention in the field of bone regeneration. In this study, porous β-CS/Poly-D,L-Lactide-Glycolide (PDLGA) composite scaffolds were developed with the goals of controlling the degradation rate and improving the mechanical and biological properties. The compressive strength and toughness were significantly enhanced by PDLGA modification of porous β-CS ceramic scaffolds. The effects of the ionic extract from β-CS/PDLGA composite scaffolds on osteogenic differentiation of rat bone marrow-derived mesenchymal stem cells (rBMSCs), proliferation of human umbilical vein endothelial cells (HUVECs) and the related mechanisms were investigated. It was shown that bioactive ions from β-CS/PDLGA scaffolds could enhance cell viability, alkaline phosphatase (ALP) activity, calcium mineral deposition, and mRNA expression levels of osteoblast-related genes of rBMSCs without addition of extra osteogenic reagents. The activation in AMP-activated protein kinase (AMPK), extracellular signal-related kinases (ERK) 1/2 and RUNX-2 were observed in rBMSCs cultured in the extract of β-CS/PDLGA, and these effects could be blocked by AMPK inhibitor Compound C. The extracts of β-CS/PDLGA composites stimulated HUVECs proliferation that was associated with phosphorylation of protein kinase B (Akt) and endothelial nitric oxide synthase (eNOS) as well as an increase in nitric oxide (NO) production and secretion of vascular endothelial growth factor (VEGF). The inductions were abolished by the addition of phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002. The composite scaffolds were implanted in critical sized rabbit femur defects (6 × 10 mm) for 4, 12 and 20 weeks with β-tricalcium phosphate (β-TCP) as controls. Sequential histological evaluations and radiographs revealed that β-CS/PDLGA dramatically stimulated new bone formation and angiogenesis. The biodegradation rate of the β-CS/PDLGA scaffolds was lower than that of β-TCP at each time point examined, and matched the new bone formation rates. These data suggest that β-CS/PDLGA could promote bone regeneration in vivo, which might be ascribed to the enhanced osteogenic differentiation of mesenchymal stem cells (MSCs) and increased angiogenic activity of endothelial cells (ECs).