Expression pattern of the chromosome 21 transcription factor Ets2 in cell-seeded three-dimensional bone constructs

The use of nanoscale topography to modulate the dynamics of adhesion formation in primary osteoblasts and ERK/MAPK signalling in STRO-1+ enriched skeletal stem cells

The physiochemical characteristics of a material with in vivo applications are critical for the clinical success of the implant and regulate both cellular adhesion and differentiated cellular function. Topographical modification of an orthopaedic implant may be a viable method to guide tissue integration and has been shown in vitro to dramatically influence osteogenesis, inhibit bone resorption and regulate integrin mediated cell adhesion. Integrins function as force dependant mechanotransducers, acting via the actin cytoskeleton to translate tension applied at the tissue level to changes in cellular function via intricate signalling pathways. In particular the ERK/MAPK signalling cascade is a known regulator of osteospecific differentiation and function. Here we investigate the effects of nanoscale pits and grooves on focal adhesion formation in human osteoblasts (HOBs) and the ERK/MAPK signalling pathway in mesenchymal populations. Nanopit arrays disrupted adhesion formation and cellular spreading in HOBs and impaired osteospecific differentiation in skeletal stem cells. HOBs cultured on 10 microm wide groove/ridge arrays formed significantly less focal adhesions than cells cultured on planar substrates and displayed negligible differentiation along the osteospecific lineage, undergoing up-regulations in the expression of adipospecific genes. Conversely, osteospecific function was correlated to increased integrin mediated adhesion formation and cellular spreading as noted in HOBS cultured on 100 microm wide groove arrays. Here osteospecific differentiation and function was linked to focal adhesion growth and FAK mediated activation of the ERK/MAPK signalling pathway in mesenchymal populations.

The study of the feasibility of segmental bone defect repair with tissue- engineered bone membrane: a qualitative observation

The objective of the study was to investigate the feasibility of intramembranous osteogenesis from tissue-engineered bone membrane in vivo. Bone marrow mesenchymal stem cells (MSCs) of rabbits were harvested, expanded and some of them were induced into osteoblasts. Porcine small intestinal submucosa (SIS) was converted by a series of physical and chemical procedures into a scaffold. MSCs and induced osteoblasts were seeded separately onto the scaffold, thus fabricating two kinds of tissue-engineered bone membrane. A total of 12 New Zealand rabbits were subjected to a surgical operation; a 15 mm bone segment, including the periosteum, was resected from the radius on both sides of each rabbit to create critical bone defects. The two kinds of tissue-engineered bone membrane and SIS (as control) were implanted randomly into the site of bone defect. The animals had radiographs and were killed after 4 weeks. The specimens were harvested and histological examination performed for evidence of osteogenesis. Bone tissue had formed in defects treated by the two kinds of tissue-engineered bone membrane at 4 weeks. This was supported by the X-ray and histological examination, which confirmed the segmental gap bridged by bone. There was no attempt to bridge in the bone defect treated by SIS. Tissue-engineered bone membrane, constructed by seeding allogeneic cells on an xenogeneic and bio-derived scaffold, can repair critical bone defects successfully.

Mechanical strain induces osteogenic differentiation: Cbfa1 and Ets-1 expression in stretched rat mesenchymal stem cells

Distraction osteogenesis is an active process of bone regeneration under controlled mechanical stimulation. Osteogenic differentiation of mesenchymal stem cells (MSCs) is essential for bone formation during this process. Cbfa1 and Ets-1 (core binding factor alpha 1 and v-ets erythroblastosis virus E26 oncogene homolog 1) are transcription factors that play important roles in the differentiation of MSCs to osteoblasts. In order to mimic a single activation of a clinical distraction device, a short period of cyclic mechanical strain (40 min and 2,000 microstrains) was applied to rat MSCs. Cellular proliferation and alkaline phosphatase (ALP) activity were examined. The mRNA expression of Cbfa1 and Ets-1, as well as ALP, a specific osteoblast marker, was detected using real-time quantitative reverse transcription polymerase chain reaction. The results showed that mechanical strain can promote MSC proliferation, increase ALP activity and up-regulate the expression of Cbfa1 and Ets-1. A significant increase in Ets-1 expression was detected immediately after mechanical stimulation, but Cbfa1 expression was elevated later. The temporal expression pattern of ALP coincided perfectly with that of Cbfa1. Mechanical strain may act as a stimulator to induce differentiation of mesenchymal stem cells into osteoblasts, which is vital for bone formation in distraction osteogenesis.

Expression patterns of Ets2 protein correlate with bone-specific proteins in cell-seeded three-dimensional bone constructs

The transcription factor Ets2 and its transcriptional targets osteopontin (OPN) and osteocalcin (OC) are expressed in tissue-engineered bone constructs in vitro. Up to now little is known about the role of Ets2 in tissue-engineering applications. This study was intended to investigate the hypothesis that protein expression of Ets2 is correlated with the expression of bone-specific proteinsin tissue-engineeredbone constructs. Cell-seeded three-dimensional bone constructs manufactured with osteoblastic cells and poly(lactic-co-glycolic acid) polymer fleeces over a period of 21 days were analyzed by SDS-PAGE and Western blotting. The protein expression of OPN, OC, osteonectin and collagen type I was analyzed. Cellularity, alkaline phosphatase-specific activity and histology confirmed the osteoblastic phenotype of the constructs. Correlations between Ets2 expression and OPN and Ets2 and collagen type I expression could be detected during the phase of late osteoblastic differentiation between days 9 and 21. The correlation between OC and collagen type I was significant in this late stage of osteoblastic differentiation. These results suggest that there is a strong interplay of Ets2 with bone-specific proteins in cell-seeded three-dimensional bone constructs. This study is a crucial step to elucidate the complex interplay of bone-related proteins in the application of bone tissue engineering.