Possible Effect of Activation of α7-Nicotinic Acetylcholine Receptors in the Mitochondrial Membrane on the Development of Apoptosis

Using flow cytometry and sandwich-immunoenzyme assay, we showed that nicotinic acetylcholine receptors with a subunit α7 (nAChRs α7) expressed in the outer mitochondrial membrane are involved in the control of mitochondria-dependent apoptosis. Pre-incubation of the mitochondria with an nAChRs α7 agonist, choline, decreased dissipation of the membrane potential of these organelles induced by the action of 0.5 mM hydrogen peroxide (H₂O₂) but did not influence the analogous effect of a high Ca²⁺ concentration (90 μM). Agonists of nAChRs α7 (choline, acetylcholine, and PNU 282987), or an inhibitor of voltage-dependent anion channels, DIDS, prevented the release of cytochrome c from the intermembrane mitochondrial space under the action of H₂O₂. In contrast, an antagonist of nAChRs α7, methyllycaconitine, promoted the release of cytochrome c and prevented the effects of agonists. The obtained data confirm the active involvement of nAChRs α7 and voltage-dependent anion channels in the process of formation of mitochondrial pores. In this case, agonists of mitochondrial nAChRs α7 subunits exert an antiapoptotic effect, while antagonists of mitochondrial nAChRs α7 subunits manifest a proapoptotic action.     

Tumor and teratoma induction in tobacco plants by debudding

Stem and root tumors and teratomata may be induced in tobacco plants (Nicotiana tabacum L., var. One Sucker) by total debudding. Intact plants or plants only decapitated produced no tumors or teratomata throughout their life time. These findings suggest a possibly important oncological relationship between normal growth and tumorous growth. Prevention of normal regeneration (apical and axillary shoot growth) incites pathological regeneration (formation of tumors and tumor shoots). Total bud killing or inactivation by ionizing radiation did not incite tumor or teratoma formation.     

Differential involvement of α4β2, α7 and α9α10 nicotinic acetylcholine receptors in B lymphocyte activation in vitro

Mouse B lymphocytes express several nicotinic acetylcholine receptor (nAChR) subtypes, their exact functions being not clearly understood. Here we show that α7 nAChR was present in about 60%, while α4β2 and α9(α10) nAChRs in about 10% and 20% of mouse spleen B lymphocytes, respectively; Balb/c and C57Bl/6 mice possessed different relative amounts of these nAChR subtypes. α4β2 and α7, but not α9(α10) nAChRs, were up-regulated upon B lymphocyte activation in vitro. Flow cytometry and sandwich ELISA studies demonstrated that α7 and α9(α10) nAChRs are coupled to CD40, whereas α4β2 nAChR is coupled to IgM. B lymphocytes of both α7(-/-) and β2(-/-) mice responded to anti-CD40 stronger than those of the wild-type mice, whereas the cells of β2(-/-) mice responded to anti-IgM worse than those of the wild-type or α7(-/-) mice. Inhibition of α7 and α9(α10) nAChRs with methyllicaconitine resulted in considerable augmentation of CD40-mediated B lymphocyte proliferation in cells of all genotypes; stimulation of α4β2 nAChRs with epibatidine increased the IgM-mediated proliferation of the wild-type and α7(-/-), but not β2(-/-) cells. Inhibition of α9(α10) nAChRs with α-conotoxin PeAI exerted weak stimulating effect on CD40-mediated proliferation. This nAChR subtype was up-regulated in α7(-/-) B-cells. α7 nAChRs were found recruited to immune synapses between human T and B lymphocytes, both of which produced acetylcholine. It is concluded that α7 nAChR fulfills inhibitory CD40-related mitogenic function, α4β2 nAChR produces a stimulatory IgM-related effect, while α9α10 nAChR is a "reserve" receptor, which partly compensates the absence of α7 nAChR in α7(-/-) cells. Acetylcholine is an additional mediator to modulate activation of interacting T and B lymphocytes.     

The role of nicotinic receptors in B-lymphocyte development and activation

We studied the binding of [(3)H]-epibatidine and [(125)I-]alpha-bungarotoxin, as well as subunit-specific antibodies with purified B lymphocytes of C57Bl/6J mice and found that these cells contained 12,200+/-3200 of alpha4(alpha5)beta2 and 3130+/-750 of alpha7(alpha5beta4) nicotinic acetylcholine receptors per cell. According to flow cytometry data, the highest expression of alpha4(alpha5)beta2 receptors was observed in immature newly generated B lymphocytes of the bone marrow, while the number of alpha7(alpha5beta4) receptors grew up along with the B cell maturation in the spleen. By using alpha4, beta2 or alpha7 knockout and chimera mice, it was shown that both receptor subtypes supported the survival of B cell precursors and increased the size of B-lymphocyte population in the bone marrow. In contrast, propagation of mature B lymphocytes in the spleen was controlled by alpha7-containing subtype only. Moreover, mature B lymphocytes became sensitive to nicotine only in the absence of beta2-containing receptors. Knockout mice had less serum IgG, IgG-producing cells and natural IgG antibodies than their wild-type counterparts, while the absence of beta2-containing receptors resulted in increased B-lymphocyte activation and antibody immune response. The data obtained indicate that nicotinic receptors are involved in regulating B-lymphocyte development and activation, possibly, by affecting expression and/or signaling of CD40, the two subtypes playing different roles.     

Non-neuronal nicotinic acetylcholine receptors: Cholinergic regulation of the immune processes

Nicotinic acetylcholine receptors (nAChRs) were initially discovered and studied as mediators of fast synaptic transmission in neuromuscular junctions and autonomic ganglia. Later on, they were found in the brain and in many nonexcitable tissues where they regulate vital cellular functions and the activity of other receptors. Primary immune organs, the bone marrow and thymus, are innervated with cholinergic nerves, which mediate the control of lymphopoiesis provided by the autonomic nervous system. In addition, lymphocytes are able to produce endogenous acetylcholine that can regulate the immune processes in an auto/paracrine way. Correspondingly, both T and B lymphocytes express functional nAChRs involved in the regulation of development and activation of these cells. This review describes the structure and roles of nAChRs in the immune system with regard to its potential regulation by the autonomic nervous system, as well as by self sources of endogenous agonists. Neirofiziologiya/Neurophysiology, Vol. 39, Nos. 4/5, pp. 307–314, July–October, 2007.     

Short chain oligogalacturonides induce ethylene production and expression of the gene encoding aminocyclopropane 1-carboxylic acid oxidase in tomato plants

Oligogalacturonic acids (OGAs), derived from plant cell wall pectin, have been implicated in a number of signal transduction pathways involved in growth, development and defense responses of higher plants. This study investigates the size range of OGAs capable of inducing ethylene synthesis in tomato plants, and demonstrates that in contrast with many other effects, only short chain OGAs are active. Oligomers across a range of DP from 2-15 were separated and purified to homogeneity by QAE-Sephadex anion exchange chromatography using a novel elution system. The OGAs were applied to tomato plants and assayed for their ability to induce ethylene gas release and changes in steady state levels of mRNA encoding the ethylene forming enzyme aminocyclopropane-1-carboxylic acid oxidase (ACO). The study demonstrated that only OGAs in the size range of DP4-6 were active both in eliciting ACO expression and in the production of ethylene.