Induction of acetylcholinesterase expression during apoptosis in various cell types

Novel dimeric acetylcholinesterase inhibitor bis7-tacrine, but not donepezil, prevents glutamate-induced neuronal apoptosis by blocking N-methyl-D-aspartate receptors

The neuroprotective properties of bis(7)-tacrine, a novel dimeric acetylcholinesterase (AChE) inhibitor, on glutamate-induced excitotoxicity were investigated in primary cultured cerebellar granule neurons (CGNs). Exposure of CGNs to 75 mum glutamate resulted in neuronal apoptosis as demonstrated by Hoechst staining, TUNEL, and DNA fragmentation assays. The bis(7)-tacrine treatment (0.01-1 mum) on CGNs markedly reduced glutamate-induced apoptosis in dose- and time-dependent manners. However, donepezil and other AChE inhibitors, even at concentrations of inhibiting AChE to the similar extents as 1 mum bis(7)-tacrine, failed to prevent glutamate-induced excitotoxicity in CGNs; moreover, both atropine and dihydro-beta-erythroidine, the cholinoreceptor antagonists, did not affect the anti-apoptotic properties of bis(7)-tacrine, suggesting that the neuroprotection of bis(7)-tacrine appears to be independent of inhibiting AChE and cholinergic transmission. In addition, ERK1/2 and p38 pathways, downstream signals of N-methyl-d-aspartate (NMDA) receptors, were rapidly activated after the exposure of glutamate to CGNs. Bis(7)-tacrine inhibited the apoptosis and the activation of these two signals with the same efficacy as the coapplication of PD98059 and SB203580. Furthermore, using fluorescence Ca(2+) imaging, patch clamp, and receptor-ligand binding techniques, bis(7)-tacrine was found effectively to buffer the intracellular Ca(2+) increase triggered by glutamate, to reduce NMDA-activated currents and to compete with [(3)H]MK-801 with an IC(50) value of 0.763 mum in rat cerebellar cortex membranes. These findings strongly suggest that bis(7)-tacrine prevents glutamate-induced neuronal apoptosis through directly blocking NMDA receptors at the MK-801-binding site, which offers a new and clinically significant modality as to how the agent exerts neuroprotective effects.

A preclinical view of cholinesterase inhibitors in neuroprotection: do they provide more than symptomatic benefits in Alzheimer's disease?

The prevalence of Alzheimer's disease (AD), a neurodegenerative condition whose greatest risk factor is old age, is expected to rise dramatically during the next five decades, along with the trend for increased longevity. Early diagnosis and intervention with therapies that halt or slow disease progress are likely to represent an important component of effective treatment. Although much progress has been made in this area, there are currently no clinically approved interventions for AD that are classed as disease modifying or neuroprotective. Cholinesterase inhibitors are a drug class used for the symptomatic treatment of AD. Recent evidence from preclinical studies indicates that these agents can attenuate neuronal damage and death from cytotoxic insults, and therefore might affect AD pathogenesis. The mechanisms by which these actions are mediated might or might not be directly related to their primary mode of action.

Blood‐cell‐specific acetylcholinesterase splice variations under changing stimuli

Developmental and trauma-induced mechanism(s) that modify inflammation and immune responses in blood cells were recently found to be regulated by acetylcholine. Here, we report corresponding blood cell-specific changes in acetylcholinesterase splice variants. Plasmon resonance and flow cytometry using acetylcholinesterase variant-specific antibody probes, revealed a progressive increase in myeloid cell fractions expressing the apoptosis-related acetylcholinesterase-S variant from newborns to adult controls and post-delivery mothers. Hematopoietic cell fractions positive for the myeloproliferative acetylcholinesterase-R variant, were similarly high in post-partum blood, both intracellular and on the cell surface. Moreover, intracellular acetylcholinesterase-S protein amounts as reflected by fluorescence intensity measurements remained unchanged in myeloid cells from post-partum mothers as compared with matched controls. Unlike brain neurons, which over-express intracellular acetylcholinesterase-R under stress, lymphocytes from post-partum mothers presented increased surface acetylcholinesterase-S and pronounced decreases in both the expression and contents of surface acetylcholinesterase-R. Peripheral stimuli-induced modulations in acetylcholine regulation may hence reflect blood cell lineage-dependent acetylcholinesterase splice variations.

Acetylcholinesterase plays a pivotal role in apoptosome formation

Although a recent study (Zhang et al. Cell Death Differ 2002; 9; 790-800) presented that acetylcholinesterase (AChE) might be an important common component in leading to various types of apoptosis, the molecular mechanism, by which AChE functions, had remained elusive before that study. We explored the role of AChE in apoptosis by silencing the AChE gene. Silencing of the AChE gene abolished the expression of AChE and prevented caspase-9 activation, decrease of cell viability, nuclear condensation and poly(adenosine diphosphate-ribose) polymerase cleavage but not mitochondrial events. Importantly, silencing of the AChE gene blocked the interaction between apoptotic protease-activating factor-1 and cytochrome c. Here we propose that AChE plays a pivotal role in the formation of apoptosome.

Role of RB and RB2/P130 genes in marrow stromal stem cells plasticity

Marrow stromal cells (MSCs) are stem-like cells having a striking somatic plasticity. In fact, besides differentiating into mesenchymal lineages (bone, cartilage, and fat), they are capable of differentiating into neurons and astrocytes in vitro and in vivo. The RB and RB2/P130 genes, belonging to the retinoblastoma gene family, play a key role in neurogenesis, and for this reason, we investigated their role in neural commitment and differentiation of MSCs. In MSCs that were either uncommitted or committed toward neural differentiation, we ectopically expressed RB and RB2/P130 genes and analyzed their role in regulating the cell cycle, apoptosis and differentiation. In uncommitted MSCs, the activity of RB and RB2/P130 appeared limited to negatively regulating cell cycle progression, having no role in apoptosis and differentiation (toward either mesenchymal or neural lineages). On the other hand, in MSCs committed toward the neural phenotype, both RB and RB2/P130 reduced cell proliferation rate and affected the apoptotic process. RB protected differentiating cells from programmed cell death. On the contrary, RB2/P130 increased the percentage of cells in apoptosis. All of these activities were accomplished mainly in an HDAC-independent way. The retinoblastoma genes also influenced differentiation in neural committed MSCs. RB2/P130 contributes mainly to the induction of generic neural properties, while RB triggers cholinergic differentiation. These differentiating activities are HDAC-dependent. Our research shows that there is a critical temporal requirement for the RB genes during neuronal differentiation of MSCs: they are not required for cell commitment but play a role in the maturation process. For the above reasons, RB and RB2/P130 may have a role in neural differentiation but not in neural determination.

The C-terminal t peptide of acetylcholinesterase forms an α helix that supports homomeric and heteromeric interactions

Acetylcholinesterase subunits of type T (AChET) possess an alternatively spliced C-terminal peptide (t peptide) which endows them with amphiphilic properties, the capacity to form various homo-oligomers and to associate, as a tetramer, with anchoring proteins containing a proline rich attachment domain (PRAD). The t peptide contains seven conserved aromatic residues. By spectroscopic analyses of the synthetic peptides covering part or all of the t peptide of Torpedo AChET, we show that the region containing the aromatic residues adopts an alpha helical structure, which is favored in the presence of lipids and detergent micelles: these residues therefore form a hydrophobic cluster in a sector of the helix. We also analyzed the formation of disulfide bonds between two different AChET subunits, and between AChET subunits and a PRAD-containing protein [the N-terminal fragment of the ColQ protein (QN)] possessing two cysteines upstream or downstream of the PRAD. This shows that, in the complex formed by four T subunits with QN (T4-QN), the t peptides are not folded on themselves as hairpins but instead are all oriented in the same direction, antiparallel to that of the PRAD. The formation of disulfide bonds between various pairs of cysteines, introduced by mutagenesis at various positions in the t peptides, indicates that this complex possesses a surprising flexibility.