Temporal Expression Patterns And Corresponding Protein Inductions of Early Responsive Genes in Rabbit Bone-Marrow Derived Mesenchymal Stem Cells Under Cyclic Compressive Loading

¹ Department of Biomedical Engineering, University of Miami, Coral Gables, FL
² Research Service and Geriatrics Research, Education, and Clinical Center, Veterans Affairs Medical Center, Miami, Florida

^* To whom correspondence should be addressed. E-mail: hcheung{at}med.miami.edu.

	Abstract

Our recent study suggested that cyclic compressive loading may promote chondrogenesis of rabbit bone-marrow mesenchymal stem cells (BM-MSCs) in agarose cultures through TGF- signaling pathway. It has been shown that the AP-1 (Jun-Fos) complex mediated autoinduction of TGF-1 and its binding activity was essential for promoting chondrogenesis of mesenchymal cells while Sox9 was identified as an essential transcription factor for chondrogenesis of embryonic mesenchymal cells. The objective of this study was to examine temporal expression patterns of early responsive genes (Sox9, c-Fos, c-Jun, and TGF- type I and II receptors) and induction of their corresponding proteins in agarose culture of rabbit BM-MSCs subjected to cyclic compressive loading. The rabbit BM-MSCs were obtained from the tibias and femurs of New Zealand White rabbits. Cell-agarose constructs were made by suspending BM-MSCs in 2% agarose gel (10⁷ cells/ml) for cyclic, unconfined compression tests performed in a custom-made bioreactor. In the loading experiment, specimens were subjected to sinusoidal loading with a magnitude of 15% strain at a frequency of 1 Hz for 4 hr per day. Experiments were conducted for 2 consecutive days. This study showed that cyclic compressive loading promoted gene expressions of Sox9, c-Jun, and both TGF- receptors and productions of their corresponding proteins while those gene expressions exhibited different temporal expression patterns among genes and between two days of testing. The gene expression of c-Fos was only detected in the samples subjected to one-hour dynamic compressive loading. These findings suggest that the TGF- signal transduction and activities of AP-1 and Sox9 are involved in the early stage of BM-MSC chondrogenesis promoted by dynamic compressive loading.