Molecular form of human lymphocyte membrane-bound acetylcholinesterase

Cholinergic Modulation of the Immune System in Neuroinflammatory Diseases

Frequent diseases of the CNS, such as Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, and psychiatric disorders (e.g., schizophrenia), elicit a neuroinflammatory response that contributes to the neurodegenerative disease process itself. The immune and nervous systems use the same mediators, receptors, and cells to regulate the immune and nervous systems as well as neuro-immune interactions. In various neurodegenerative diseases, peripheral inflammatory mediators and infiltrating immune cells from the periphery cause exacerbation to current injury in the brain. Acetylcholine (ACh) plays a crucial role in the peripheral and central nervous systems, in fact, other than cells of the CNS, the peripheral immune cells also possess a cholinergic system. The findings on peripheral cholinergic signaling, and the activation of the “cholinergic anti-inflammatory pathway” mediated by ACh binding to α7 nAChR as one of the possible mechanisms for controlling inflammation, have restarted interest in cholinergic-mediated pathological processes and in the new potential therapeutic target for neuro-inflammatory-degenerative diseases. Herein, we focus on recent progress in the modulatory mechanisms of the cholinergic anti-inflammatory pathway in neuroinflammatory diseases.

Cholinergic Machinery as Relevant Target in Acute Lymphoblastic T Leukemia

Various types of non-neuronal cells, including tumors, are able to produce acetylcholine (ACh), which acts as an autocrine/paracrine growth factor. T lymphocytes represent a key component of the non-neuronal cholinergic system. T cells-derived ACh is involved in a stimulation of their activation and proliferation, and acts as a regulator of immune response. The aim of the present work was to summarize the data about components of cholinergic machinery in T lymphocytes, with an emphasis on the comparison of healthy and leukemic T cells. Cell lines derived from acute lymphoblastic leukemias of T lineage (T-ALL) were found to produce a considerably higher amount of ACh than healthy T lymphocytes. Additionally, ACh produced by T-ALL is not efficiently hydrolyzed, because acetylcholinesterase (AChE) activity is drastically decreased in these cells. Up-regulation of muscarinic ACh receptors was also demonstrated at expression and functional level, whereas nicotinic ACh receptors seem to play a less important role and not form functional channels in cells derived from T-ALL. We hypothesized that ACh over-produced in T-ALL may act as an autocrine growth factor and play an important role in leukemic clonal expansion through shaping of intracellular Ca²⁺ signals. We suggest that cholinergic machinery may be attractive targets for new drugs against T-ALL. Specifically, testing of high affinity antagonists of muscarinic ACh receptors as well as antagomiRs, which interfere with miRNAs involved in the suppression of AChE expression, may be the first choice options.

Muscular dystrophy by merosin deficiency decreases acetylcholinesterase activity in thymus of Lama2dy mice

Half of congenital muscular dystrophy cases arise from laminin alpha2 (merosin) deficiency, and merosin-deficient mice (Lama2dy) exhibit a dystrophic phenotype. The abnormal development of thymus in Lama2dy mice, the occurrence of acetylcholinesterase (AChE) in the gland and the impaired distribution of AChE molecules in skeletal muscle of the mouse mutant prompted us to compare the levels of AChE mRNAs and enzyme species in thymus of control and Lama2dy mice. AChE activity in normal thymus (mean +/- SD 1.42 +/- 0.28 micromol acetylthiocholine/h/mg protein, U/mg) was decreased by approximately 50% in dystrophic thymus (0.77 +/- 0.23 U/mg) (p = 0.007), whereas butyrylcholinesterase activity was little affected. RT-PCR assays revealed variable levels of R, H and T AChE mRNAs in thymus, bone marrow and spinal cord. Control thymus contained amphiphilic AChE dimers (G2A, 64%) and monomers (G1A, 19%), as well as hydrophilic tetramers (G4H, 9%) and monomers (G1H, 8%). The dimers consisted of glycosylphosphatidylinositol-anchored H subunits. Western blot assays with anti-AChE antibodies suggested the occurrence of inactive AChE in mouse thymus. Despite the decrease in AChE activity in Lama2dy thymus, no differences between thymuses from control and dystrophic mice were observed in the distribution of AChE forms, phosphatidylinositol-specific phospholipase C sensitivity, binding to lectins and size of AChE subunits.

Breast cancer metastasis alters acetylcholinesterase activity and the composition of enzyme forms in axillary lymph nodes

Because of the probable involvement of cholinesterases (ChEs) in tumorigenesis, this research was addressed to ascertaining whether breast cancer metastasis alters the content of acetylcholinesterase (AChE) and/or butyrylcholinesterase (BuChE) in axillary lymph nodes (LN). ChE activity was assayed in nine normal (NLN) and seven metastasis-bearing nodes (MLN) from women. AChE and BuChE forms were characterised by sedimentation analyses, hydrophobic chromatography and western blotting. The origin of ChEs in LN was studied by lectin interaction. AChE activity dropped from 21.6 mU/mg (nmol of the substrate hydrolysed per minute and per milligram protein) in NLN to 3.8 mU/mg in MLN (p < 0.001), while BuChE activity (3.6 mU/mg) was little affected. NLN contained globular amphiphilic AChE dimers (G2A, 35%), monomers (G1A, 30%), hydrophilic tetramers (G4H, 8%), and asymmetric species (A4, 23%, and A8, 4%); MLN displayed only G2A (65%) and G1A (35%) AChE forms. NLN and MLN contained G4H (79%), G4A (7%), and G1H (14%) BuChE components. Neither the binding of ChE forms with lectins and antibodies nor the subunit size were altered by metastasis. The higher level of AChE in NLN than in brain and the specific pattern of AChE forms in NLN support its role in immunity. The different profile of AChE forms in NLN and MLN may be useful for diagnosis.

Amphiphilic and hydrophilic forms of acetylcholinesterase from sheep platelets

Acetylcholinesterase (AChE, EC 3.1.1.7) was extracted from sheep platelets by successive homogenizations, yielding low-salt soluble (LSS), high-salt soluble (HSS) and detergent-soluble (DS) fractions. These accounted, respectively, for about 30%, 7% and 60% of total AChE activity. Applications of hydrophobic chromatography on phenyl-agarose to three solubilized fractions revealed that hydrophilic forms were almost exclusively located in the LSS fraction ( approximately 27% of total AChE), whereas most amphiphilic forms were present in DS extracts ( approximately 59% of total AChE), the remaining forms being distributed among aqueous soluble fractions. Enzyme molecular forms in the solubilized extracts were identified by centrifugation in 5-20% sucrose gradients containing Triton X-100 or Brij 97 to differentiate between hydrophilic or amphiphilic species. A predominance of hydrophilic dimeric forms ( approximately 22%), with small amounts of hydrophilic monomers (5%) and amphiphilic dimers and monomers (3%), was found in soluble AChE (LSS fraction). Amphiphilic AChE forms extracted in the HSS and DS fractions had a single peak in the sedimentation profiles with sedimentation coefficients of about 6S in gradients with Triton X-100; these were slightly shifted in the presence of Brij 97. After treatment with dithiothreitol, this molecular form solubilized in DS was converted to another molecular form with a lower sedimentation coefficient. Our results show that amphiphilic globular dimers are the dominant molecular form in sheep platelet AChE, suggesting a partial conversion of this membrane-bound form into soluble dimers and monomers, mainly with a hydrophilic character, through the action of either endogenous proteases and phospholipases or residual endogenous reducing agents.

Relationships between monoaminergic and cholinergic innervation of the rat thymus during aging

The present study has been undertaken in order to investigate whether aging is accompanied by alterations in the thymic autonomic innervation. The results showed that in aged rats compared to young adult rats the density of monoaminergic histofluorescent nerve profiles decreased remarkably, while their pattern of intrathymic distribution remained unchanged. The thymic concentrations of noradrenaline (NA) and dopamine (DA) also significantly decreased between the age of 12 and 18 months. However, the density of thymic autofluorescent cells (afc) markedly increased over the same period, as well as the concentration of 5-hydroxytryptamine (5-HT). The aged rat thymus seemed to be able to maintain its cholinergic innervation in terms of density and pattern of distribution, while the density of cells with intracytoplasmic acetylcholinesterase (AChE) staining even increased. The neurochemical measurement showed an increase in the activity of AChE between the age of 9 to 18 months. The results indicate an altered relation between the components of thymic autonomic innervation of aged rats that might be related to the reduced immunocompetence of their T cells.

Glycolipid-anchored acetylcholinesterases from rabbit lymphocytes and erythrocytes differ in their sensitivity to phosphatidylinositol-specific phospholipase C

The type of membrane association of acetylcholinesterase (AChE, EC 3.1.1.7) was studied in rabbit lymphocytes and erythrocytes. In both cases, the unique AChE molecular form was an amphiphilic dimer (referred to as G2a) anchored in the membrane by a glycosylphosphatidylinositol. In lymphocytes, G2a AChE was directly converted into its hydrophilic G2h counterpart by a treatment with Bacillus thuringiensis phosphatidylinositol-phospholipase C (PI-PLC, EC 3.1.4.10). In erythrocytes, AChE was resistant to PI-PLC but was rendered sensitive by a prior deacylation with alkaline hydroxylamine. This observation suggests that, as previously reported for human erythrocyte AChE, an acylation of the inositol ring in the glycolipid anchor of rabbit erythrocyte AChE (that does not occur in lymphocytes) prevents the cleavage.

Monomerization of tetrameric bovine caudate nucleus acetylcholinesterase. Implications for hydrophobic assembly and membrane anchor attachment site

Tetrameric detergent-soluble bovine caudate nucleus acetylcholinesterase (AChE) was reduced and alkylated under conditions in which at least 95% of initial activity is retained. This treatment alone did not result in monomerization of AChE, nor did it create a hydrophilic enzyme. However, in the presence of SDS the enzyme became monomerized. Incubation of AChE with trypsin in the presence of the reversible inhibitor edrophonium rendered the enzyme hydrophilic and led to catalytically active monomers being produced. SDS/PAGE of this preparation in non-reducing conditions revealed only a small decrease in the subunit molecular mass. N-Terminal sequencing of the enzyme, before and after trypsin treatment, yielded identical N-termini showing that the enzyme was monomerized subsequent to C-terminal tryptic cleavage. From our results, we conclude that the most C-terminal cysteine residue is involved in inter-subunit disulphide bonding as well as in the attachment of AChE to the membrane anchor. Furthermore, the C-terminal region in the primary structure provides an area for hydrophobic contacts between the different subunits and also between the subunits and the membrane anchor.

Origin and significance of acetylcholine and choline in plasma and serum from normal and paretic cows

Before the onset of bovine paresis a stage of hyperactivity and hypersensitivity was observed in clinical as well as in immunologically provoked cases. By gas chromatographic analysis of choline (Ch) in plasma and serum from four immunologically provoked cows this stage was verified to be an initial immuno-cholinergic hyperactivation. In the first hour after antigen challenge with 0.5 mg nematode AChE there was a very sharp rise in Ch mainly from agonist-stimulated and phospholipase mediated phosphatidylcholine (PC) breakdown. A secondary massive influx of Ca into cells was mirrored in a 1 mmol/l depression of serum-Ca values during the first hours. The hyperagonism mediated Ca-translocation brought water into cells, resulting in reduced plasma volume. The generally supposed mechanism of secondary, Ca-mediated cell damage and cell death was initiated and sometimes resulted in "Downers" with persisting paralysis. All acetylcholine (ACh)-stimulated parts from CNS to the periphery are irregularly involved explaining the very varied clinical appearance of bovine paresis, and the influence on for instance the autonomous nerve system, adrenals and pancreas. In the experimental group, ACh in plasma showed a sharp fall within the first hour, while there were fairly constant values of serum-ACh in the first four hours, possibly indicating some antibody protection. When paresis was established between 15-28 hours after challenge the general anergetic state was characterised by low ACh-levels. Also in a larger field group ACh-levels were significantly depressed in paretic compared to healthy cows. The unexpected finding in this group was considerably higher levels of ACh and especially Ch in serum compared to plasma. The origin of ACh and Ch had to be blood cells. Preliminary gas chromatographic analysis has confirmed ACh-synthesis by leucocytes and an integrated immuno-cholinergic system of great importance can be anticipated. The general feature of bovine paresis is updated by immune-etiological, pathophysiological, blood chemical, clinical-experimental and nomenclature considerations. The exact mechanism of pathogenesis is not revealed in this investigation, though many circumstances favour an anti-Id mediated hyperagonism. Other types of investigations and above all more basic knowledge of distribution and functional character of cholinergic components on immune cells are required.

Acetylcholinesterase distribution in subpopulations of murine thymocyte

The presence of acetylcholinesterase has been detected in the thymus of several species both biochemically and histochemically. In this study we have investigated the molecular forms and the level of this enzyme in separate compartments of the murine thymus and in different thymocyte subpopulations. Similar levels of acetylcholinesterase activity are present both in thymocytes and in the stromal component. Sucrose density gradient analysis revealed the presence of a single molecular form of about 5 S, presumably a dimeric form. Moreover the results demonstrate a preferential association of AChE with mature thymocyte subsets (Peanut Agglutinin negative and Corticoresistant). This finding correlates with the preferential sensitivity of these cells to cholinergic drugs and supports the hypothesis that acetylcholinesterase modulates the cholinergic effects on thymocytes.