Cyclic ADP-ribose increases human mesenchymal stem cell proliferation through the modulation of spontaneous Ca2+ oscillations

Abstract

Introdution: Human bone marrow mesenchymal stem cells (hMSCs) play an important role in the regulation of hematopoiesis. Cyclic ADP-ribose (cADPR), a universal Ca2+ mobilizer produced by hMSCs, has been demonstrated to be an important factor in the regulation of hematopoietic stem cells proliferation. However, its biological effects on hMSCs are not understood. This study was to investigate the effects of cADPR on Ca2+ signaling, cell proliferation and differentiation in hMSCs. Methods: Ca2+ activity was measured with confocal microscope. RTPCR and western blot were used to detect gene and protein expression, respectively. siRNA technique was applied to knockdown gene expression. Results: cADPR increased the frequency of spontaneous Ca2+ oscillations, and this effect was abolished by pre-treatment with the specific cADPR antagonist 8-Br-cADPR, but not by ryanodine, the classic targets of cADPR in other types of cells. RT-PCR showed no gene expression for ryanodine receptors in hMSCs. The cADPR-induced increase of spontaneous Ca2+ oscillations was abolished by the TRPM2 channel inhibitors. Knockdown of TRPM2 channels showed no significant effects on spontaneous Ca2+ oscillations; however, it abrogated the cADPR effect on spontaneous Ca2+ oscillations. We further found that cADPR increased hMSCs proliferation, but had no significant effects on osteogeneic and adipogeneic differentiation. The effect of cADPR on hMSCs proliferation was antagonized by 8-Br-cADPR or by the selective knockdown of TRPM2 channels. Conclusions: Our results demonstrate that cADPR regulate cell proliferation by modulating spontaneous Ca2+ oscillations mediated by TRPM2 channels, but has no effects on osteogeneic and adipogeneic differentiation in hMSCs.