CHOLINERGIC AGONISTS STIMULATE SECRETION OF SOLUBLE FULL-LENGTH AMYLOID PRECURSOR PROTEIN IN NEUROENDOCRINE CELLS

The AP peptide of Alzheimer disease is derived from the proteolytic pr ocessing of the amyloid precursor proteins (APP), which are considered type I transmembrane glycoproteins. Recently, however, soluble forms of full-length APP were also detected in several systems including chr omaffin granules. In this report we used antisera specific for the cyt oplasmic sequence of APP to show that primary bovine chromaffin cells secrete a soluble APP, termed solAPPcyt, of an apparent molecular mass of 130 kDa. This APP was oversecreted from Chinese hamster ovary cell s transfected with a full-length APP cDNA indicating that solAPPcyt co ntained both the transmembrane and A beta sequence. Deglycosylation of solAPPcyt showed that it contained both N- and O-linked sugars, sugge sting that this APP was transported through the endoplasmic reticulum- Golgi pathway. Secretion of solAPPcyt from primary chromaffin cells wa s temperature-, time-, and energy-dependent and was stimulated by cell depolarization in a Ca2+-dependent manner. Cholinergic receptor agoni sts, including acetylcholine, nicotine, or carbachol, stimulated the r apid secretion of solAPPcyt, a process that was inhibited by cholinerg ic antagonists. Stimulation of solAPPcyt secretion was paralleled by a stimulation of secretion in catecholamines and chromogranin A, indica ting that secretion of solAPPcyt was mediated by chromaffin granule ve sicles, Taken together, our results show that release of the potential ly amyloidogenic solAPPcyt is an active cellular process mediated by b oth the constitutive and regulated pathways. solAPPcyt was also detect ed in human cerebrospinal fluid. Combined with the neuronal physiology of chromaffin cells, our data suggest that cholinergic agonists may s timulate the release of this APP in neuronal synapses where it may exe rt its biological function(s). Moreover, vesicular or secreted solAPPc yt may serve as a soluble precursor of A beta.