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BACKGROUND: Chondral defects show lack of proper regeneration whereas osteochondral lesions display limited regeneration capacity. Latter is probably due to immigration of chondroprogenitor cells from the subchondral bone. Known chondroprogenitor cells for cartilage tissues are multi-potent adult marrow stromal or mesenchymal stem cells (MSCs). In vitro chondrogenic differentiation of these precursor cells usually require cues from growth and signalling factors provided in vivo by surrounding tissues and cells. We hypothesise that signalling factors secreted by differentiated cartilage tissue can initiate and maintain chondrogenic differentiation status of MSCs. METHODS: To study such paracrine communication between allogenic rat articular cartilage and rat MSCs embedded in alginate beads a novel coculture system without addition of external growth factors has been established. RESULTS: Impact of cartilage on differentiating MSCs was observed at two different time points. Firstly, sustained expression of Sox9 was observed at an early stage which indicated induction of chondrogenic differentiation. Secondly, late stage repression of collagen X indicated pre-hypertrophic arrest of differentiation. In the culture supernatant we have identified vascular endothelial growth factor alpha (VEGF-164 alpha), matrix metalloproteinase (MMP) -13 and tissue inhibitors of MMPs (TIMP-1 and TIMP-2) which could be traced back either to the cartilage explant or to the MSCs under the influence of cartilage. CONCLUSION: The identified factors might be involved in regulation of collagen X gene and protein expression and therefore, may have an impact on the control and regulation of MSCs differentiation.  相似文献   
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The Cellular Transport of Magnesium in Rat Liver   总被引:1,自引:0,他引:1  
The bidirectional transport of Mg in rat liver was studied using slices labeled with 28Mg in a closed two-compartment system under steady-state conditions. The influx (Kbs) and efflux (Ksb) transfer coefficients governing transport between the extracellular phase and a rapidly exchanging cell fraction were 0.074 and 0.019 per min, respectively. An increased extracellular concentration of Mg++ caused a 30% decrease in Kbs and a 31% increase in Ksb. A decreased extracellular Mg++ had an opposite effect. At 0°C, both transfer coefficients were reduced by 65%. Increased pH and NaCN increased transport, whereas Ca++ reduced transport. Reduced pH, altered Na+:K+ ratio, Sr++, glucose deletion, iodoacetate, ethanol, and lactate had no significant influence. Dinitrophenol reduced Ksb but had no effect on Kbs. These data support the thesis that the intracellular concentration of Mg is in part regulated by a reciprocal change in the influx transfer coefficient and a parallel change in the efflux transfer coefficient in response to altered extracellular concentrations of Mg++. The qualitative and quantitative similarities of Mg and Ca transport in this system suggest that Mg and Ca share a common transport mechanism which is primarily dependent upon the binding of these divalent cations to macromolecular ligands within the cell membrane or within the cell.  相似文献   
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