Recently we found that vesicular monoamine transporter VMAT

Recently, we found that vesicular monoamine transporter 2 (VMAT2) regulates monoamine (including dopamine) storage by acting as a negative regulator, such that high monoamine levels inhibit the progression from Pdx1+ pancreatic progenitor Nanaomycin A to Neurog3+ endocrine progenitor cells of ESC-derived pancreatic progenitor cells and during embryonic pancreatic development (Sakano et al., 2014). VMAT2, which regulates dopamine storage, and tyrosine hydroxylase, which synthesizes dopamine, are expressed in both the embryonic pancreas and the adult islets (Persson-Sjogren et al., 2002; D.S. et al., unpublished data). Our results suggest that the VMAT2-dopamine signal plays important roles both during pancreas development and in the maintenance of β cell mass. It was previously reported that NECA promotes β cell regeneration in a zebrafish model and that adenosine kinase inhibitors increase primary β cell proliferation (Annes et al., 2012). We found that NECA functions by antagonizing dopamine signaling to increase β cell proliferation and decrease β cell apoptosis. The detailed mechanism of the crosstalk between ADORA2A and DRD2 signaling in β cell proliferation is not yet known. Adenosine signaling is mediated by ADORA2A, which is a Gαs-coupled receptor that increases cAMP. Dopamine signaling is mediated by a Gαi-coupled receptor DRD2, which decreases cAMP. Thus, ADORA2A and DRD2 exert opposing effects on cAMP levels, and they have been reported to be highly co-localized and form heterodimers in the striatum (Fuxe et al., 2001) and neuronal cells (Kamiya et al., 2003) where the heterodimer antagonizes homodimer formation of ADORA2A/ADORA2A or DRD2/DRD2, to modulate dopaminergic activity (Ferre et al., 1991; Hall and Strange, 1999). L-Dopa treatment, which activates dopamine signaling, was reported to disrupt heteromer formation (Bonaventura et al., 2014; Pinna et al., 2014). Crosstalk between adenosine and dopamine signaling through other mechanisms has also been observed. ADORA2A mediates the phosphorylation of dopamine- and cAMP-regulated phosphoprotein of Mr 32,000 (DARPP-32) at Thr34 (the cAMP-dependent protein kinase site) in striatopallidal neurons, and has been reported to oppose DRD2 signaling (Shuto et al., 2006; Yabuuchi et al., 2006). Similarly, dopamine signaling has been reported to exert opposing effects on GLP-1 through phosphorylation of the serine/threonine kinase AKT, its downstream substrate GSK3b, and several other downstream signaling molecules (Ustione et al., 2013).
Experimental Procedures
Author Contributions
Acknowledgments We thank Mr. Yuki Sonoda and Ms. Misako Katabuchi for technical assistance and helpful discussions, and Dr. Junji Hirota and the members of the Center for Biological Resources and Informatics at Tokyo Institute of Technology, and the members in the Center for Animal Resources and Development at Kumamoto University for their technical assistance. This work was supported by grants (26253059 and 26670384 to S.K., 26461638 to N.S., and 26461036 to D.S.) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) Japan. This work was also supported in part by the Takeda Science Foundation, Japanese Insulin Dependent Diabetes Mellitus (IDDM) Network Foundation, and the Program for Leading Graduate Schools ‘HIGO’ to Kumamoto University from MEXT. S.K. is a member of the HIGO Program, MEXT, Japan.
Introduction Pluripotent stem cells (PSC) have been used to study human development, model disease, and generate cellular tools for regenerative medicine. Human embryonic stem cells (hESC) have been considered the functional, genetic, and epigenetic gold standard in the field (Thomson et al., 1998). Methods of somatic cell reprogramming to generate induced PSC (iPSC) (Takahashi and Yamanaka, 2006) are continually being improved and have enabled the generation of iPSC using a variety of somatic cell sources, gene combinations, and methodologies. However, due to the intensive resources required for iPSC generation and characterization, direct comparisons of iPSC generated using a wide range of technologies and cell sources from multiple independent laboratories have rarely been performed, making it unclear whether all methodologies produce iPSC with a similar quality and stability.