Expression of PDGF-beta receptor, EGF receptor, and receptor adaptor protein Shc in rat osteoblasts during spaceflight

A number of studies have indicated that microgravity induces osteopenia and modulates functions of mammalian cells. However, the molecular mechanisms underlying these effects of microgravity are still unknown. Rat osteoblasts were cultured for 4 and 5 days during Shuttle-Spacelab flight, and fixed b y guanidine isothiocyanate solution on board after treatment with 1 alpha, 25 (OH)(2) vitamin D-3. The mRNA levels for platelet-derived growth factor (PDGF)-beta receptor, epidermal growth factor (EGF) receptor, the growth fa ctor receptor adaptor protein Shc, and c-fos were determined using the meth od of quantitative reverse transcription-polymerase chain reaction. The mRN A levels for EGF receptor were not altered by microgravity. However, the mR NA levels for PDGF-beta receptor, Shc, and c-fos were decreased to 62, 55 a nd 25% on the 4th day of flight, and 47, 40, and 43% on the 5th day, respec tively, as compared to the corresponding ground controls. Expression of the growth factor receptor and the receptor adaptor protein was modulated in r at osteoblasts during spaceflight. Data suggest that signal transduction vi a growth factor receptors in rat osteoblasts is impaired by microgravity. D ysfunction of osteoblasts might be involved in spaceflight-induced osteopen ia.