Hypoxia Inhibits Osteogenesis in Human Mesenchymal Stem Cells through Direct Regulation of RUNX2 by TWIST

Bone loss induced by hypoxia is associated with various pathophysiological conditions, however, little is known about the effects of hypoxia and related signaling pathways on osteoblast differentiation and bone formation. Because bone marrow-derived mesenchymal stem cells (MSCs) survive under hypoxic conditions and readily differentiate into osteoblasts by standard induction protocols, they are a good in vitro model to study the effects of hypoxia on osteoblast differentiation.Using human MSCs, we discovered TWIST, a downstream target of HIF-1α, was induced under hypoxia and acted as a transcription repressor of RUNX2 through binding to the E-box located on the promoter of type 1 RUNX2. Suppression of type 1 RUNX2 by TWIST under hypoxia further inhibited the expression of BMP2, type 2 RUNX2 and downstream targets of RUNX2 in MSCs.Our findings point to the important role of hypoxia-mediated signalling in osteogenic differentiation in MSCs through direct regulation of RUNX2 by TWIST, and provide a method for modifying MSC osteogenesis upon application of these cells in fracture healing and bone reconstruction

Expansion of human mesenchymal stem cells in a fixed-bed bioreactor system based on non-porous glass carrier – Part B: Modeling and scale-up of the system

Human mesenchymal stem cells (hMSC) are a promising cell source for the manufacturing of cell therapeutic or tissue engineered implants. In part A of this publication a fixed-bed bioreactor system based on non-porous borosilicate glass spheres and procedures for the automated expansion of hMSC with high yield and vitality has been introduced. Part B of this study deals with the modeling of the process in order to transfer the bioreactors system from the laboratory to the production scale. Relevant model parameters have been obtained by fitting them to the experimental data of hMSC-TERT cultivations in scales up to 300 cm3. Scale-up calculations were carried out exemplarily for a target cell number of twenty billion cells