Synthia H. Sun Professor

Laboratory of Glia Functions
image Synthia H. Sun   Professor

Ph.D., Dept. 
University of Missouri-Columbis, USA
Jun-Chi Lo Hsin-Chen Lu Tsan-Ting Hsu Yu-Chia Lin
image Our research interest is to elucidate the molecular mechanisms of ATP-stimulated signal transduction pathways and physiological functions of astrocytes in the central nervous system. Astrocytes form tripartite synapse with neurons thus directly involves in neurotransmission. And ATP is the most important mediator acting between neuron and astrocyte. Although astrocytes do not have action potential but are able to transmit fast signaling through Ca2+ signaling. We have established two clonal astrocytes cell lines, RBA-2 and IA-1g1. We found that these astrocytes possess several ATP P2 receptors and ATP stimulated increases in intracellular Ca2+ concentration (Ca2+ signaling). ATP is known to mediate its functions through activation of two large families of P2 receptors, P2Y G-protein-coupled metabotropic receptors and P2X ionotropic receptors, P2X containing seven subtypes and P2Y containing at least 8 subtypes, all coupled to Ca2+ signaling in astrocytes. Presently, we know that RBA-2 astrocytes possess at least three P2 receptors, P2Y1, P2X4 and P2X7 and IA-1g1 possess P2X4 receptors. We have focused on elucidation of mechanisms involving in activation of the low affinity P2X7 receptor of RBA-2 astrocytes. Currently, we aim to examine the signaling and functions of the two high affinity P2 receptors, P2Y1 and P2X4 receptors because these receptors may be physiologically important. However, no Ca2+ signaling was detected earlier using the conventional spectrophotometer Ca2+ measurement system. We’ve set up a single cell Ca2+ imaging system and found that ATP does induced Ca2+ transient and Ca2+ oscillation through activation of P2Y1 receptor. Since P2 receptors are known to play an important role in neuron-astrocyte interaction, we also examine the roles of P2 receptor in neuronal cells. We use neuroblastoma cells as our model system and found the P2 receptors expression may be functional important in these cells.
Figure 1. Cofocal photomicrographs of RBA-2 astrocytes stained immunocytochemically with GFAP (green) and actin (red).

image Elucidation of molecular mechanisms involving in P2Y1 and P2X4 mediated Ca2+ signaling and physiologicalfunctions of RBA-2 astrocytes
image Potential link between systemic inflammation and neuronal degeneration–the role of neuron-glia cross talk: Neuroimmune responses of astrocytes and their effects on neuronal functions
image Elucidation of molecular mechanisms of ATP and endothelin-1 stimulate signal transduction pathways and physiological function of astrocytes
image Elucidation of molecular mechanisms of P2X7 receptor-mediated signal transducntion pathways and physioilogical functions of RBA-2 astrocytes
image Adminiastration of Education.Human brain project, from gene to cognition: effect of stress on neural cells
image Chen H. B., *Sun S. H. (2006) Oxidized ATP (oATP) Decreased the Expression of beta-Actin and the Intracellular Superoxide concentrations independent of P2X7 receptor in RBA-2 Type 2 Astrocytes. Eur. J. Pharmacol. 550: 1–7
image Chen H. B., Chan Y-T, Hung A C., Tsai Y-C and *Sun S. H. (2006) Elucidation of ATP-stimulated stress protein expression of RBA-2 type-2 astrocytes: ATP potentiate HSP60 and Cu/Zn SOD expression and stimulates pI shift of peroxiredoxin II. J. Cell. Biochem. 97:314-326.
image Hung A C., Chu Y-J, Lin Y-H Weng J-Y, Chen H. B., Au Y-C and *Sun S. H. (2005) Roles of protein kinase C in regulation of P2X7 receptor-mediated calcium signalling of cultured type-2 astrocyte cell line, RBA-2. Cell. Signal., 17:1384-1396.
image Wang, C.-M., Chang, Y.-Y. and *Sun, S. H. (2003) Activation of P2X7 purinoceptor stimulated TGF-1 mRNA expression via PKC/MAPK pathway in the RBA-2 type-2 astrocytes. Cell. Signal., 15:1129-1137.
image Ju, Y. J., Wang, C.-M, Hung, A. C., Lo, J.-C., Lin H.-J. and *Sun, S. H. (2003) Endothelin-1 stimulated capacitative Ca2+ entry through ETA receptors of a rat brain-derived type-1 astrocyte cell line, IA-1g1 Cell. Signal., 15:197-207
image Wang, C.-M., Chang, Y.-Y., Kuo, J.-S. and *Sun, S. H. (2002) Activation of P2X7 receptors induced [3H]GABA release from RBA-2 type-2 astrocyte cell line through a Cl-/HCO3--dependent mechanism. Glia, 37:8-18.
image Hung, A. C. and *Sun, S. H. (2002) Characterization of the P2X7 receptor-mediated phosphatidylcholine-phospholipase D activities in a rat brain-derived type-2 astrocyte cell line, RBA-2: Involvement of PKC-dependent and PKC-independent pathways. Cell. Signal., 14:1-10