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Platelet-Activating Factor Receptor Signals in Rat Osteoblasts during Spaceflight
bGraduate School of Tokyo Medical and Dental University, Tokyo 113-8549, Japan cToray Research Center, Kamakura 248-8555, Japan
aAddress for correspondence: Dr. Yasuhiro Kumei, Biochemistry, Department of Hard Tissue Engineering, Graduate School of Tokyo Medical and Dental University, Tokyo 113-8549, Japan. Voice/fax: +81-3-5803-4555. e-mail: kumei.bch{at}tmd.ac.jp
The platelet-activating factor (PAF) is a lipid mediator. The G-protein-coupled receptor of PAF (PAF-R) is activated by inflammatory and stressful conditions in numerous cell types. PAF/PAF-R is involved in apoptotic and antiapoptotic processes. We examined microgravity effects on the expression of PAF-R and second messengers in rat osteoblasts. The PAF-R signals are transmitted via arachidonic acid, phospholipase C (PLC), protein kinase C (PKC), and mitogen-activated protein kinase. Rat osteoblasts were cultured for 4 and 5 days aboard a space shuttle and solubilized on board. PAF-R gene expression in flight cultures increased to 2-6-fold higher than in ground controls. Gene expression of the G-protein
 subunit Gq in flight cultures increased to 3-fold and higher than in ground controls. It is known that Gaq stimulates the effecter PLCß, activating PKC. The mRNA levels of PKC and PKC in flight cultures were increased to 2-5-fold higher than in ground controls. The PKC mRNA level in flight cultures was increased to 3-fold higher than in ground controls on the 4th day. Gene expression of catalytic and regulatory subunits of protein kinase A was suppressed in flight cultures. PKC and PKC are novel PKCs that can be target substrates of caspases. The PAF-R gene may act as a mechano-sensitive gene that is involved in the apoptotic and antiapoptotic processes of osteoblasts under microgravity.
Key Words: spaceflight • osteoblast • platelet-activating factor receptor • protein kinase C • G-protein • apoptosis This article has been cited by other articles:
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