Short- and long-term effect of acetylcholinesterase inhibition on the expression and metabolism of the amyloid precursor protein

Abstract

We have investigated the acute and chronic effect of metrifonate (MTF) and dichlorvos (DDVP), respectively the prodrug and active acetylcholinesterase inhibitor, on the secretory processing of the amyloid precursor protein (APP) in SH-SY5Y neuroblastoma cells. We demonstrate that the acute treatment of SH-SY5Y cells with both compounds results in an increased secretion of the soluble fragment of APP (sAPP␣) into the conditioned media of cells, with a pattern correlated to the level of acetycholinesterase inhibition. The regulation of APP processing in these conditions is mediated by an indirect cholinergic effect on muscarinic receptors, as demonstrated by inhibition with atropine. We have also followed APP expression and metabolism after long-term treatment with metrifonate. Treated cells showed reduced AChE activity after 24, 48 h and also following 7 days of repeated treatment, a time point at which increased AChE expression was detectable. At all time points sAPP␣ release was unaffected suggesting that enhanced sAPP␣ release by MTF is transitory, nevertheless the sensitivity of cholinergic receptors was unchanged, as indicated by the fact that cholinergic response can be elicited similarly in untreated and treated cells. APP gene expression was unaffected by long-term AChE inhibition suggesting that increased short-term sAPP␣ release does not elicit compensatory effects. Molecular Psychiatry (2001) 6, 520-528.

Role of protein kinase Cα in the regulated secretion of the amyloid precursor protein

“…In particular, the cholinergic receptor stimulation of sAPP release is blocked by staurosporine 12 and GF109203X. 14,20 We show here that both cell lines respond equally to carbachol in spite of the defective PKCa in the SYa4 cell line. This result suggests that the involvement of PKCa in the carbachol-regulated APP processing is not significant or at least that redundant signalling pathways are activated that can bypass the defective kinase.…”

“…These isoforms include mRNAs containing exon 7 (encoding the KPI domain) and exon 8, isoforms Protein kinase Ca in APP processing M Racchi et al containing only exon 7, and APP mRNAs where both exons are spliced out. 20 The cells respond to phorbol esters and carbachol by releasing sAPPa ranging two to three-fold above basal levels ( Figure 2). Furthermore, following simultaneous treatment with carbachol and phorbol ester, these cells secrete sAPPa to an extent that is less than the net sum of the independent effects of these two compounds.…”

“…The blockade of PLC would reduce the contribution of Ca 2+ and phosphatidylinositol, thus blocking the contribution of cofactors for the activation of PKC. As described before, the inhibition of carbachol-mediated sAPPa release can be partially obtained, with the PKC inhibitor GF109203X, 14,20 which is not selective for PKC isoforms. We show here that Gö 6976, the specific inhibitor of Ca 2+ -dependent PKC isoforms a, b, and g, did not block the effect of carbachol, thus conclusively demonstrating that PKCa is not involved in receptor-mediated sAPPa release.…”

“…6,7 The demonstration that cholinesterase inhibitors studied for AD therapy also induced sAPP release by an indirect cholinergic mechanism further substantiated this result. 20 Stimulation of G-protein-coupled receptors by neurotransmitters regulates APP processing by PKC-dependent signalling pathways. In particular, the cholinergic receptor stimulation of sAPP release is blocked by staurosporine 12 and GF109203X.…”

Multifunctional Neuroprotective Derivatives of Rasagiline as Anti-Alzheimer's Disease Drugs

“…However, this neuroprotective effect of ladostigil does not appear to result from its ChE inhibition activity only, since rasagiline or propargylamine were also able to induce PKC and ERK activation and promote sAPP␣ release. 22 Several ChEIs, such as tacrine, 80 physostigmine, 81 metrifonate, 82 ganstigmine, 83 and donepezil 84 increased sAPP␣ release in cell culture. However, the observations that phenserine 78 and tacrine, at high concentration, 85 decreased sAPP␣ release suggests that the regulation of APP processing by ChEIs is not simply associated to AChE inhibition.…”