One of the important routes to transmit signals between cells in multicellular organisms is by exocytosis which allows the release of neurotransmitters and hormones. My laboratory has focused on the regulation of Ca2+-dependent exocytosis. By using electrochemical method and Ca2+ measurements, we have characterized the Ca2+ signaling pathways and secretions in mouse adrenal medullary chromaffin cells to provide knowledge for future studies on Ca2+ regulations and molecular mechanisms of Ca2+-dependent secretion using PC12 cells and mouse chromaffin cells as a model system.
We also study the role of Rab3A in exocytosis, especially in priming steps, and the possible molecular interactions among Rab3A, Munc13-1 and Munc18-1 by using fluorescence proteins combined with total internal reflection fluorescence microscope (TIRFM). Our results show that Rab3A involves in Munc13-1 and RIM interaction and is dissociated from vesicle membrane by interacting with Munc18-1 to regulate exocytosis.
Among the various Ca2+ pathways, we have focused on the Na+/Ca2+ exchanger (NCX) on the plasma membrane, which has been demonstrated as the predominant mechanism for exporting excess intracellular Ca2+ in excitable cells, such as cardiac muscle cells and neuronal cells. We have found that sarcomeric mitochondrial creatine kinase (sMiCK) and muscle type cytosolic isozyme of creatine kinase (CKM) are able to interact with NCX1. This interaction may be important in the recovery of NCX1 activity that lost under an energy-compromised state.
Another line of research in my laboratory is to study the mechanism that underlies the progressive degeneration of the dopaminergic neurons in Parkinson's disease. We have indentified an interaction between dopamine (DA) and Zn2+ that synergistically induces cell death. When PC12 cells were pretreated with Zn2+ before DA treatment, DA and Zn2+ synergistically increased cell death. There is a similar synergistic effect when DA and Zn2+ were co-infused into the striatum, resulting in striatal DA content depletion in vivo. Thus, both DA oxidation and Zn2+ are possibly linked to the degeneration of DA neurons. We are currently trying to elucidate the mechanism involved in the DA and Zn2+ induced death of DA neurons.
1. Lo HS, Chiang HC, Lin MY, Chiang HY, Chu YC and Kao LS (2004) Synergistic effects of dopamine and Zn2+ on the induction of PC12 cell death and dopamine depletion in the striatum: possible implication in the pathogenesis of Parkinson's disease. Neurobiol. Dis. 17, 54-61.
2. Lin CC, Huang CC, Lin KH, Cheng KH, Yang DM, Tsai YS, Ong RY, Huang YN, Kao LS. (2007) Visualization of Rab3A dissociation during exocytosis: a study by total internal reflection microscopy. J. Cell Physiol. 211(2):316-26.
3. Pan CY, Tsai LL, Jiang JH, Chen LW, Kao LS. (2008) The co-presence of Na+/Ca2+-K+ exchanger and Na+/Ca2+ exchanger in bovine adrenal chromaffin cells. J. Neurochem. 107(3):658-67.
4. Wu PC, Fann MJ, Kao LS.(2010) Characterization of Ca2+ signaling pathways in mouse adrenal medullary chromaffin cells. J Neurochem. 112(5):1210-22.
5. Yang, YC, Fann, MJ, Chang, WH, Tai, LH, Jiang, JH, and Kao, LS. (2010) Regulation of sodium-calcium exchanger activity by creatine kinase under energy-compromised conditions. J. Biol. Chem. 285, 28275-28285
6. Huang, CC, Yang, DM, Lin, CC, Kao, LS. (2011) Involvement of Rab3A in vesicle priming during exocytosis: interaction with Munc13-1 and Munc18-1. Traffic, 12(10):1356-1370. Epub 2011 Jul 20