My laboratory is focused on the molecular mechanisms which regulate exocytosis, using two models- the neuroendocrine insulin-secreting pancreatic islet beta cell and the epithelial pancreatic acinar cell which secrete digestive enzymes. We are mainly interested in SNARE proteins, originally described to regulate neurotransmitter release, but subsequently found to be highly conserved in neuroendocrine and non-excitable secretory cells to regulate secretion. We were the first to identify the combinations of SNARE proteins which mediate the distinct exocytic events in the acinar cell (apical and basolateral exocytosis, homotypic granule fusion) and the pancreatic islet beta cell. In the islet beta cell, we proceeded to demonstrate that these SNARE proteins could independently bind and regulate potassium channels which control membrane excitability, and thereby regulate the fine sequence of ionic and exocytic events leading to secretion. We are currently examining the precise functional interacting domains between these SNARE proteins and ion channels in the hope that we may identify specific drug targets to treat diseases (diabetes) which may have as their basis a dysregulation of exocytosis or ion channels. In collaboration with a team of scientists, we have now shown that the SNARE regulation of ion channels are also conserved in non-secretory cells, specifically the gastrointestinal smooth muscle and cardiac muscle, to modulate muscle excitability and contraction. Insights from these can eventually be applied to treat gastrointestinal motility and cardiovascular disorders. As well, we have begun to explore specific molecules which interact with the SNARE proteins to mediate the priming of insulin granules which could amplify insulin secretion in the sluggish diabetic islet beta cells. We have now generated or acquired several transgenic mouse models with altered expression of SNARE and associated proteins to unequivocally elucidate their function in these tissues. Insights from my research are therefore of direct impact to: 1) normal secretory biology and pathobiology, specifically in understanding (and hopefully treat) the dysregulated insulin secretion in diabetes and pathologic membrane fusion in pancreatitis; and 2) membrane ion channel biology of cardiac and gastrointestinal muscles in health and in disease.
My lab has in place molecular biological techniques to examine structure-function, gene transfer of cell lines and primary cells in culture (by adenoviruses), biochemical protein binding assays, cell biology methods (confocal microscopy, islet secretion assays), and importantly, single cell analyses by patch-clamp electrophysiology (including capacitance measurements) to directly study ion channel function, and state-of-the art fluorescent imaging techniques (TIRFM, multi-photon and spinning disc cofocal) to visualize and track single secretory granule exocytosis. Within a larger collaborative team of scientists, we have also established functional assays of gastrointestinal and cardiac muscles.