The Paracrine Effect of Hyaluronic Acid-Treated Endothelial Cells Promotes BMP-2-Mediated Osteogenesis.

The combination of hyaluronic acid (HA) and BMP-2 has been reported to promote bone regeneration. However, the interaction of endothelial cells and bone marrow mesenchymal stem cells (BMSCs) during HA + BMP-2 treatment is not fully understood. This study aimed to analyze the direct effect of HA, as well as the paracrine effect of HA-treated endothelial cells, on the BMP-2-mediated osteogenic differentiation of BMSCs. The angiogenic differentiation potential of HA at different molecular weights and different concentrations was tested. The direct effect of HA, as well as the indirect effect of HA-treated human umbilical cord endothelial cells (HUVECs, i.e., conditioned medium (CM)-based co-culture) on the BMP-2-mediated osteogenic differentiation of BMSCs was analyzed using alkaline phosphatase (ALP) staining and activity, alizarin red S (ARS) staining, and RT-qPCR of osteogenic markers. Angiogenic differentiation markers were also analyzed in HUVECs after treatment with HA + BMP-2. The bone regeneration potential of BMP-2 and HA + BMP-2 was analyzed in a rat ectopic model. We found that 1600 kDa HA at 300 µg/mL promoted tube formation by HUVECs in vitro and upregulated the mRNA expression of the angiogenic markers CD31, VEGF, and bFGF. HA inhibited, but conditioned medium from HA-treated HUVECs promoted, the BMP-2-mediated osteogenic differentiation of BMSCs, as indicated by the results of ALP staining and activity, ARS staining, and the mRNA expression of the osteogenic markers RUNX-2, ALP, COLI, and OPN. HA + BMP-2 (50 ng/mL) upregulated the expression of the angiogenesis-related genes VEGF and bFGF in HUVECs and bone regeneration in vivo compared to BMP-2 treatment. In conclusion, the paracrine effect of hyaluronic acid-treated endothelial cells promotes BMP-2-mediated osteogenesis, suggesting the application potential of HA + BMP-2 in bone tissue engineering.

Liquid Crystal Modified Polylactic Acid Improves Cytocompatibility and M2 Polarization of Macrophages to Promote Osteogenesis.

Liquid crystalline phases (LC phases) are widely present in an organism. The well-aligned domain and liquidity of the LC phases are necessary for various biological functions. How to stabilize the floating LC phases and maintain their superior biology is still under study. In addition, it is unclear whether the exogenous LC state can regulate the immune process and improve osteogenesis. In this work, a series of composite films (PLLA/LC) were prepared using cholesteryl oleyl carbonate (COC), cholesteryl pelargonate (CP), and polylactic acid (PLLA) via a controlled facile one-pot approach. The results showed that the thermo-responsive PLLA/LC films exhibited stable LC phases at human body temperature and the cytocompatibility of the composites was improved significantly after modification by the LC. In addition, the M2 polarization of macrophages (RAW264.7) was enhanced in PLLA/LC films, and the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) was improved as co-cultured with macrophages. The in vivo bone regeneration of the materials was verified by calvarial repair, in which the amount of new bone in the PLLA-30% LC group was greater than that in the PLLA group. This work revealed that the liquid crystal-modified PLLA could promote osteogenesis through immunomodulation.