Microgravity is one of the most important characteristics in space flight. Exposure to microgravity results in extensive physiological changes in humans. Bone loss is one of the changes with serious consequences: however. the mechanism retains unclear. As the origin of osteoprogenitors, mesenchymal stein cells (MSCs) may play an important role in it. After cultured under simulated microgravity (in a rotary cell culture system, RCCS), MSCs were stained using oil red O to identify adipocytes. The mRNA level of bone morphogenetic protein (BMP)-2 and peroxisome proliferators-activated receptor (PPAR) gamma 2 was determined by RT-PCR. Otherwise, MSCs were induced to osteogenic differentiation after microgravity culture, and then the activity of alkaline phosphatase (ALP) was determined by PNPP and the content of osteocalcin (OC) by ELISA. Furthermore, the telomerase activity in MSCs was measured by TRAP. The results showed that simulated microgravity inhibited osteoblastic differentiation and induced adipogenic differentiation accompanied by the change of gene expression of BMP-2 and PPAR gamma 2 in MSCs. Meanwhile, the telomerase activity decreased significantly in MSCs under simulated microgravity. The reduced bone formation in space flight may partly be due to the altered potential differentiation of MSCs associated with telomerase activity which plays a key role in regulating the lifespan of cell proliferation and differentiation. Therefore. telomerase activation/replacement may act as a potential countermeasure for microgravity-induced bone loss. (C) 2008 Elsevier Ltd. All rights reserved.
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