title: Aged human mesenchymal stem cells: the duration of bone morphogenetic protein-2 stimulation determines induction or inhibition of osteogenic differentiation.
abstract: Bone morphogenetic protein 2 (BMP-2) is a potent osteoinductive cytokine and a growing number of in vitro studies analyze its effects on human mesenchymal stem cells (hMSC) derived from aged or osteoporotic donors. In these studies the exact quantification of osteogenic differentiation capacity is of fundamental interest. Nevertheless, the experimental conditions for osteogenic differentiation of aged hMSC have not been evaluated systematically and vary to a considerable extend. Aim of the study was to assess the influence of cell density, osteogenic differentiation media (ODM) change intervals and duration of BMP-2 stimulation on osteoinduction. Furthermore, time series were carried out for osteogenic differentiation and BMP-2 concentration in ODM/BMP-2 cell culture supernatants. The experiments were performed using hMSC isolated from femoral heads of aged patients undergoing hip joint replacement. ODM change intervals of 96 hours resulted in significantly higher calcium deposition compared to shorter intervals. A cell density of 80% prior to stimulation led to stronger osteoinduction compared to higher cell densities. In ODM, aged hMSC showed a significant induction of calcium deposition after 9 days. Added to ODM, BMP-2 showed a stable concentration in the cell culture supernatants for at least 96 hours. Addition of BMP-2 to ODM for the initial 4 days led to a significantly higher induction of osteogenic differentiation compared to ODM alone. On the other hand, addition of BMP-2 for 21 days almost abrogated the osteoinductive effect of ODM. We could demonstrate that the factors investigated have a substantial impact on the extent of osteogenic differentiation of aged hMSC. Consequently, it is of upmost importance to standardize the experimental conditions in order to enable comparability between different studies. We here define standard conditions for osteogenic differentiation in regard to the specific features of aged hMSC. The finding that BMP-2 induces or inhibits osteogenic differentiation in a time dependent manner indicates an age related alteration in signal transduction of hMSC and requires further investigation.
authors.affiliation: Department of Surgery, Experimental Surgery and Regenerative Medicine, University of Munich , Germany.
authors.forename: Jostein
authors.initials: J
authors.lastname: Heggebö
authors.affiliation: Department of Surgery, Experimental Surgery and Regenerative Medicine, University of Munich , Germany.
authors.forename: Florian
authors.initials: F
authors.lastname: Haasters
authors.affiliation: Department of Surgery, Experimental Surgery and Regenerative Medicine, University of Munich , Germany.
authors.forename: Hans
authors.initials: H
authors.lastname: Polzer
authors.affiliation: Department of Surgery, Experimental Surgery and Regenerative Medicine, University of Munich , Germany.
authors.forename: Christina
authors.initials: C
authors.lastname: Schwarz
authors.affiliation: Department of Surgery, Experimental Surgery and Regenerative Medicine, University of Munich , Germany.
authors.forename: Maximilian Michael
authors.initials: MM
authors.lastname: Saller
authors.affiliation: Department of Surgery, Experimental Surgery and Regenerative Medicine, University of Munich , Germany.
authors.forename: Wolf
authors.initials: W
authors.lastname: Mutschler
authors.affiliation: Department of Surgery, Experimental Surgery and Regenerative Medicine, University of Munich , Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Schieker
authors.affiliation: Department of Surgery, Experimental Surgery and Regenerative Medicine, University of Munich , Germany.
authors.forename: Wolf Christian
authors.initials: WC
authors.lastname: Prall
keywords: BMP-2; age; in vitro; mesenchymal stem cells; osteogenic differentiation