Transgenic Mouse Overexpressing Syntaxin-1A as a Diabetes Model

Transgenic Mouse Overexpressing Syntaxin-1A as a Diabetes Model Patrick P.L. Lam 1 2 , Yuk-Man Leung 1 2 , Laura Sheu 1 2 , James Ellis 3 , Robert G. Tsushima 1 2 , Lucy R. Osborne 1 4 and Herbert Y. Gaisano 1 2 1 Department of Medicine, University of Toronto, Toronto, Canada 2 Department of Physiology, University of Toronto, Toronto, Canada 3 Program in Developmental Biology, Sick Kids Hospital, Toronto, Canada 4 Department of Molecular and Medical Genetics, University of Toronto, Toronto, Canada Address correspondence and reprint requests to Herbert Y. Gaisano, MD, University of Toronto, Room 7226, Medical Science Building, 1 King’s College Circle, Toronto, Ontario, Canada M5S 1A8. E-mail: herbert.gaisano{at}utoronto.ca . Or Lucy R. Osborne, PhD, University of Toronto, Room 7238, Medical Science Building, 1 King’s College Circle, Toronto, Ontario, Canada M5S 1A8. E-mail: lucy.osborne{at}utoronto.ca Abstract Soluble N -ethylmaleimide–sensitive factor (NSF) attachment protein receptor (SNARE) protein syntaxin-1A (STX-1A) plays a role not only in exocytosis, but also binds and regulates Ca 2+ and K + (voltage-gated K + and ATP-sensitive K + channels) to influence the sequence of events leading to secretion. Islet levels of STX-1A and cognate SNARE proteins are reduced in type 2 diabetic rodents, suggesting their role in dysregulated insulin secretion contributing to the abnormal glucose homeostasis. We investigated the specific role of STX-1A in pancreatic β-cells by generating transgenic mice, which express a moderately increased level (∼30% higher) of STX-1A in pancreatic islets (hereafter called STX-1A mice). The STX-1A mice displayed fasting hyperglycemia and a more sustained elevation of plasma glucose levels after an intraperitoneal glucose tolerance test, with correspondingly reduced plasma insulin levels. Surprisingly, β-cells from the STX-1A male mice also exhibited abnormal insulin tolerance. To unequivocally determine the β-cell secretory defects, we used single-cell analyses of exocytosis by patch clamp membrane capacitance measurements and ion channel recordings. Depolarization-evoked membrane capacitance increases were reduced in the STX-1A mouse islet β-cells. The STX-1A mouse also exhibited reduced currents through the Ca 2+ channels but little change in the voltage-gated K + channel or ATP-sensitive K + channel. These results suggest that fluctuation of islet STX-1A levels in diabetes could influence the pathological and differential regula