RETRACTED ARTICLE: Effect of the co-culture of human bone marrow mesenchymal stromal cells with human umbilical vein endothelial cells in vitro

Directing Stem Cell Commitment by Amorphous Calcium Phosphate Nanoparticles Incorporated in PLGA: Relevance of the Free Calcium Ion Concentration

The microenvironment of mesenchymal stem cells (MSCs) is responsible for the modulation in MSC commitment. Nanocomposites with an inorganic and an organic component have been investigated, and osteogenesis of MSCs has been attributed to inorganic phases such as calcium phosphate under several conditions. Here, electrospun meshes and two-dimensional films of poly(lactic-co-glycolic acid) (PLGA) or nanocomposites of PLGA and amorphous calcium phosphate nanoparticles (PLGA/aCaP) seeded with human adipose-derived stem cells (ASCs) were analyzed for the expression of selected marker genes. In a two-week in vitro experiment, osteogenic commitment was not found to be favored on PLGA/aCaP compared to pure PLGA. Analysis of the medium revealed a significant reduction of the Ca²⁺ concentration when incubated with PLGA/aCaP, caused by chemical precipitation of hydroxyapatite (HAp) on aCaP seeds of PLGA/aCaP. Upon offering a constant Ca²⁺ concentration, however, the previously observed anti-osteogenic effect was reversed: alkaline phosphatase, an early osteogenic marker gene, was upregulated on PLGA/aCaP compared to pristine PLGA. Hence, in addition to the cell–material interaction, the material–medium interaction was also important for the stem cell commitment here, affecting the cell–medium interaction. Complex in vitro models should therefore consider all factors, as coupled impacts might emerge.

Co-transplantation of Wharton's jelly mesenchymal stem cell-derived osteoblasts with differentiated endothelial cells does not stimulate blood vessel and osteoid formation in nude mice models

A major challenge in bone tissue engineering is the lack of post-implantation vascular growth into biomaterials. In the skeletal system, blood vessel growth appears to be coupled to osteogenesis-suggesting the existence of molecular crosstalk between endothelial cells (ECs) and osteoblastic cells. The present study (performed in two murine ectopic models) was designed to determine whether co-transplantation of human Wharton's jelly mesenchymal stem cell-derived osteoblasts (WJMSC-OBs) and human differentiated ECs enhances bone regeneration and stimulates angiogenesis, relative to the seeding of WJMSC-OBs alone. Human WJMSC-OBs and human ECs were loaded into a silicate-substituted calcium phosphate (SiCaP) scaffold and then ectopically implanted at subcutaneous or intramuscular sites in nude mice. At both subcutaneous and intramuscular implantation sites, we observed ectopic bone formation and osteoids composed of host cells when WJMSC-OBs were seeded into the scaffold. However, the addition of ECs was associated with a lower level of osteogenesis, and we did not observe stimulation of blood vessel ingrowth. in vitro studies demonstrated that WJMSC-OBs lost their ability to secrete vascular endothelial growth factor and stromal cell-derived factor 1-including when ECs were present. In these two murine ectopic models, our cell-matrix environment combination did not seem to be optimal for inducing vascularized bone reconstruction.