ASGSB 1999 Annual Meeting Abstracts

GROWTH FACTOR RECEPTOR SIGNAL TRANSDUCTION IS MODULATED BY MICROGRAVITY IN RAT OSTEOBLASTS. Y. Kumei¹, H. Akiyama², M. Hirano², H. Shimokawa¹, S. Morita¹, C. Mukai³, and S. Nagaoka⁴. ¹Tokyo Medical and Dental Univ, ²Toray Research Center, ³NASDA/Tsukuba Space Center, and ⁴Fujita Health Univ., Japan

The purpose is to investigate the mechanism by which osteoblast function is deteriorated in microgravity. Rat osteoblasts were cultured for 4 and 5 days during Shuttle-Spacelab (STS-65) flight. After one-day treatment with 1, 25 (OH)₂ vitamin D₃, cells were fixed by guanidine isothiocyanate solution on board. The mRNA levels for PDGF- receptor, EGF receptor, the receptor adaptor protein Shc, and c-fos were determined by quantitative RT-PCR. The mRNA levels for PDGF- receptor, Shc, and c-fos were decreased to 62%, 55% and 25% on the 4th day of flight, and 47%, 40% and 43% on the 5th day, as compared to the corresponding ground controls (p<0.05).  The mRNA levels for EGF receptor were not altered by microgravity.  Microgravity down-regulates gene expression of PDGF- receptor and Shc, the immediate downstream signaling molecule of growth factor receptors.  These events result in reduction of c-fos gene expression.  Data suggest that signal transduction via growth factor receptors is modulated by microgravity in rat osteoblasts.

 (Supported by NASDA and the grant from Institute of Space and Astronautical Science in Japan)

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