Human Molecular Genetics Advance Access originally published online on January 7, 2008
Human Molecular Genetics 2008 17(7):1020-1030; doi:10.1093/hmg/ddm374
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DSCR1/RCAN1 regulates vesicle exocytosis and fusion pore kinetics: implications for Down syndrome and Alzheimer's disease
1 Molecular and Cellular Neuroscience Group, Department of Human Physiology and Centre for Neuroscience, Flinders University, Adelaide, Australia 2 Endocrine Cell Biology Group, Prince Henry's Institute of Medical Research, Clayton, Victoria, Australia 3 Centre for Functional Genomics and Human Disease, Monash Institute of Medical Research, Monash University, Clayton, Victoria, Australia 4 CIBER Epidemiología y Salud Pública (CIBERESP), Barcelona, Spain 5 Genes and Disease Program, Center for Genomic Regulation (CRG), UPF, Barcelona, Spain
* To whom correspondence should be addressed at: Department of Biochemistry and Molecular Biology and Department of Anatomy and Cell Biology, Monash University, Clayton, Victoria 3168, Australia. Email: melanie.pritchard{at}med.monash.edu.au
Received August 20, 2007; Accepted December 19, 2007
Genes located on chromosome 21, over-expressed in Down syndrome (DS) and Alzheimer's disease (AD) and which regulate vesicle trafficking, are strong candidates for involvement in AD neuropathology. Regulator of calcineurin activity 1 (RCAN1) is one such gene. We have generated mutant mice in which RCAN1 is either over-expressed (RCAN1ox) or ablated (Rcan1–/–) and examined whether exocytosis from chromaffin cells, a classic cellular model of neuronal exocytosis, is altered using carbon fibre amperometry. We find that Rcan1 regulates the number of vesicles undergoing exocytosis and the speed at which the vesicle fusion pore opens and closes. Cells from both Rcan1–/– and RCAN1ox mice display reduced levels of exocytosis. Changes in single-vesicle fusion kinetics are also evident resulting in the less catecholamine released per vesicle with increasing Rcan1 expression. Acute calcineurin inhibition did not replicate the effect of RCAN1 overexpression. These changes are not due to alterations in Ca2+ entry or the readily releasable vesicle pool size. Thus, we illustrate a novel regulator of vesicle exocytosis, Rcan1, which influences both exocytotic rate and vesicle fusion kinetics. If Rcan1 functions similarly in neurons then overexpression of this protein, as occurs in DS and AD brains, will reduce both the number of synaptic vesicles undergoing exocytosis and the amount of neurotransmitter released per fusion event. This has direct implications for the pathogenesis of these diseases as sufficient levels of neurotransmission are required for synaptic maintenance and the prevention of neurodegeneration and vesicle trafficking defects are the earliest hallmark of AD neuropathology.