The Mice Drawer System Tissue Sharing Program (MDS-TSP): osteobiology in microgravity
Biticchi, Roberta ; Cancedda, Ranieri ; Cilli, Michele ; ...Pignataro, Salvatore ; et al.
Jan - 2010

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type: Conference Proceedings

Abstract
The capacity of bone tissue to alter its mass and architecture in response to mechanical request has long been known. Bone not only develops as a structure designed specifically for mechanical demands, but it can adapt during life toward more efficient mechanical performance. In partic-ular, the skeletal effects of microgravity result in the development of an osteoporotic phenotype with several bone defects including a bone mass decrease resembling the bone modifications occurring in elder people and in bed rest conditions. This is particularly true for weight bearing bones such as spine, femur and tibiae. In contrast non-weight bearing bones like calvaria etc didnt show bone mineral density decrease in weightlessness. Given the interest of our labora-tory in the microgravity induced skeleton alterations, we focused our attention on a transgenic mouse overexpressing pleiotrophin (PTN) under the control of the bone specific human os-teocalcin promoter. This protein is a heparin-binding cytokine with different functions. In particular PTN-transgenic mice (PTN-Tg) show an increase in the bone mass and mineral-ization, with a calcium content/mg bone of 10We used this mouse model in the MDS flight experiment to study the PTN potential role in counteracting bone loss in microgravity. Three PTN-transgenic mice (Tg) and three wild type (Wt) mice were housed in the MDS (Mouse Drawer System) at the ISS for three months. During these three months two wt and one tg mice died and therefore could be only frozen for subsequent skeletal analysis. The other three mice, daily checked for their health status, were viable and in good condition throughout the all three months at the ISS. At the end of November 2009 the three mice came back to Earth and after blood collection were immediately sacrificed and the different bones isolated. From blood cell analysis no major hematological alterations were noticed in the blood cell count except a slight increase in the number of erythrocytes. The serum collected from these mice is being used in a Luminex panel assay for several cytokine and bone metabolism markers. A ground replica of the flight experiment (ground control) was performed at the University of Genova from November 2009 to the second week of February 2010 during which we collected the bone samples. To study the microgravity effects on both wt and PTN-Tg mice we are performing morphological analysis by classical histological technique. A finer microarchitectural study by synchrotron and bench microCT has been initiated both at the Grenoble and the Trieste facil-ities. With this last technique we are analyzing both weight and non-weight bearing bones and we are evaluating bone mineral density, mineralization amount, trabecular architecture. We are also in the process of obtaining a holotomographic reconstruction of the trabecular and cortical bone from both the flight and the ground control mice. In addition we extracted RNA from long bones and bone marrow of the same mice and we are performing Real-time PCR analysis to determine the expression of bone marker such as osteocalcin, runx2, bone sialoprotein and of markers of bone turnover such as RankL, TRAP, cathepsin K, IL6 in the different animals.

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