Abstract
Previously, we have shown that Ca oscillations modulate the activities of ion channels and the fluctuation of membrane potentials in human mesenchymal stem cells (hMSCs). We have also found an ATP autocrine/paracrine signaling pathway as the mechanism for Ca oscillations. In this study we further investigated whether Ca dependent transcription factors are regulated by Ca oscillations by examining the localization of NFAT and NF-κB through immunocytochemical experiments. NF-κB was found to be more abundant in the cytosol than in the nucleus in most undifferentiated hMSCs (140/151 cells). On the other hand, nuclear staining of NFAT was detected in more than 80% of hMSCs (40/48 cells). The nuclear translocation of NFAT was also confirmed by Western blotting of the cytoplasmic and nuclear fractions. These findings suggest that NFAT is constitutively activated in hMSCs. When an ATP autocrine and Ca oscillations signaling pathway was blocked, the NFAT signals in the nucleus were reduced, indicating the involvement of Ca oscillations in the regulation of NFAT activation. Using adipogenic techniques we differentiated hMSCs into adipocytes. In these adipocytes, no spontaneous Ca oscillations were observed (32/32 cells). In the immunocytochemical experiments, the nuclear staining of NFAT was not prominent. Thus, we concluded that Ca oscillations might play an important role in NFAT activation in undifferentiated hMSCs but not in derived adipocytes. [J Physiol Sci. 2006;56 Suppl:S82]
