Does microgravity induce apoptotic signal in rat osteoblasts via cjun-n-terminal kinase?

The mechanism of space flight-induced bone mass loss is unknown. We conducted experiments aboard the Space Shuttle using primary cultured osteoblasts. During flight, quadruplicate cultures were treated with 1 nM of 1alpha,25 dihydroxyvitamin D3 for one day, then fixed with guanidine isothiocyanate solution on board. After return to the Earth, the mRNA levels were analyzed by quantitative RT-PCR. Microgravity increased the mRNA levels of JNK, c-Jun N-terminal kinase or stress-activated protein kinase, in rat osteoblasts, as compared to the 1G ground control. Microgravity decreased the mRNA levels of the principal heat shock protein, Hsp 70. JNK is known to play a key role particularly in the stress-activated cell apoptosis. Data suggested apoptotic and anti-apoptotic effects of microgravity on rat osteoblast.