Mitochondrial Nicotinic Acetylcholine Receptors Support Liver Cells Viability After Partial Hepatectomy

Nicotinic acetylcholine receptors in cancer: Limitations and prospects

Nicotinic acetylcholine receptors (nAChRs) have long been considered to solely mediate neurotransmission. However, their widespread distribution in the human body suggests a more diverse physiological role. Additionally, the expression of nAChRs is increased in certain cancers, such as lung cancer, and has been associated with cell proliferation, epithelial-to-mesenchymal cell transition, angiogenesis and apoptosis prevention. Several compounds that interact with these receptors have been identified as potential therapeutic agents. They have been tested as drugs for treating nicotine addiction, alcoholism, depression, pain and Alzheimer's disease. This review focuses on nAChR-mediated signalling in cancer, presenting opportunities for the development of innovative nAChR-based anticancer drugs. It displays the differences in expression of each nAChR subunit between normal and cancer cells for selected cancer types, highlighting their possible involvement in specific cases. Antagonists of nAChRs that could complement existing cancer therapies are summarised and critically discussed. We hope that this review will stimulate further research on the role of nAChRs in cancer potentially leading to innovative cancer therapies.

α7 Nicotinic acetylcholine receptors regulate translocation of HIF-1α to the cell nucleus and mitochondria upon hypoxia

Nicotinic acetylcholine receptors (nAChRs), initially characterized as ligand-gated ion channels mediating fast synaptic transmission, are now found in many non-excitable cells and mitochondria where they function in ion-independent manner and regulate vital cellular processes like apoptosis, proliferation, cytokine secretion. Here we show that the nAChRs of α7 subtype are present in the nuclei of liver cells and astrocytoma U373 cell line. As shown by lectin ELISA, the nuclear α7 nAChRs are mature glycoproteins that follow the standard rout of post-translational modifications in Golgi; however, their glycosylation profile is non-identical to that of mitochondrial nAChRs. They are exposed on the outer nuclear membrane and are found in combination with lamin B1. The nuclear α7 nAChRs are up-regulated in liver within 1 h after partial hepatectomy and in H₂O₂-treated U373 cells. As shown both in silico and experimentally, the α7 nAChR interacts with hypoxia-inducible factor HIF-1α and this interaction is impaired by α7-selective agonists PNU282987 and choline or type 2 positive allosteric modulator PNU120596, which prevent HIF-1α accumulation in the nuclei. Similarly, HIF-1α interacts with mitochondrial α7 nAChRs in U373 cells treated with dimethyloxalylglycine. It is concluded that functional α7 nAChRs influence HIF-1α translocation into the nucleus and mitochondria upon hypoxia.

Universal nature of cholinergic regulation demonstrated with nicotinic acetylcholine receptors

Mammalian nicotinic acetylcholine receptors (nAChRs) were initially discovered as ligand-gated ion channels mediating fast synaptic transmission in the neuro-muscular junctions and autonomic ganglia. They were further found to be involved in a wide range of basic biological processes within the brain and in non-excitable tissues. The present review summarizes the data obtained in our laboratory during last two decades. Investigation of autonomic ganglia with the nAChR subunit-specific antibodies was followed by identification of nAChRs in B lymphocytes, discovery of mitochondrial nAChRs and their role in mitochondrial apoptosis pathway, and revealing the role of α7 nAChRs and α7-specific antibodies in neuroinflammation-related Alzheimer disease and COVID-19. The data obtained demonstrate the involvement of nAChRs in cell survival, proliferation, cell-to-cell communication and inflammatory reaction. Together with the ability of nAChRs to function in both ionotropic and metabotropic way, these data illustrate the universal nature of cholinergic regulation mediated by nAChRs.

Mitochondrial nicotinic acetylcholine receptors: Mechanisms of functioning and biological significance

Nicotinic acetylcholine receptors mediate fast synaptic transmission in neuro-muscular junctions and autonomic ganglia and modulate survival, proliferation and neurotransmitter or cytokine release in the brain and non-excitable cells. The neuronal-type nicotinic acetylcholine receptors are expressed in the outer mitochondria membrane to regulate the release of pro-apoptotic substances like cytochrome c or reactive oxygen species. In the intracellular environment, nicotinic acetylcholine receptor signaling is ion-independent and triggers intramitochondrial kinases, similar to those activated by plasma membrane nicotinic acetylcholine receptors. The present review will describe the data obtained during the last five years including, in particular, post-translational glycosylation as a targeting signal to mitochondria, mechanisms of mitochondrial nicotinic acetylcholine receptor signaling studied with subtype-specific agonists, antagonists, positive allosteric modulators and knockout mice lacking certain nicotinic acetylcholine receptor subunits, interaction of mitochondrial nicotinic acetylcholine receptors with Bcl-2 family proteins and their involvement in important pathologies like neuroinflammation, liver damage and SARS-CoV-2 infection.

Evidence of a dual mechanism of action underlying the anti-proliferative and cytotoxic effects of ammonium-alkyloxy-stilbene-based α7- and α9-nicotinic ligands on glioblastoma cells

Glioblastomas (GBMs), the most frequent brain tumours, are highly invasive and their prognosis is still poor despite the use of combination treatment. MG624 is a 4-oxystilbene derivative that is active on α7- and α9-containing neuronal nicotinic acetylcholine receptor (nAChR) subtypes. Hybridisation of MG624 with a non-nicotinic resveratrol-derived pro-oxidant mitocan has led to two novel compounds (StN-4 and StN-8) that are more potent than MG624 in reducing the viability of GBM cells, but less potent in reducing the viability of mouse astrocytes. Functional analysis of their activity on α7 receptors showed that StN-4 is a silent agonist, whereas StN-8 is a full antagonist, and neither alters intracellular [Ca²⁺] levels when acutely applied to U87MG cells. After 72 h of exposure, both compounds decreased U87MG cell proliferation, and pAKT and oxphos ATP levels, but only StN-4 led to a significant accumulation of cells in phase G₁/G₀ and increased apoptosis. One hour of exposure to either compound also decreased the mitochondrial and cytoplasmic ATP production of U87MG cells, and this was not paralleled by any increase in the production of reactive oxygen species. Knocking down the α9 subunit (which is expressed at relatively high levels in U87MG cells) decreased the potency of the effects of both compounds on cell viability, but cell proliferation, ATP production, pAKT levels were unaffected by the presence of the noncell-permeable α7/α9-selective antagonist αBungarotoxin. These last findings suggest that the anti-tumoral effects of StN-4 and StN-8 on GBM cells are not only due to their action on nAChRs, but also to other non-nicotinic mechanisms.

Mesenchymal stem cells as a potential therapeutic tool to cure cognitive impairment caused by neuroinflammation

An established contribution of neuroinflammation to multiple brain pathologies has raised the requirement for therapeutic strategies to overcome it in order to prevent age- and disease-dependent cognitive decline. Mesenchymal stem cells (MSCs) produce multiple growth and neurotrophic factors and seem to evade immune rejection due to low expression of major histocompatibility complex class I molecules. Therefore, MSCs are widely used in experiments and clinical trials of regenerative medicine. This review summarizes recent data concerning the optimization of MSC use for therapeutic purposes with the emphasis on the achievements of the last 2 years. Specific attention is paid to extracellular vesicles secreted by MSCs and to the role of α7 nicotinic acetylcholine receptors. The reviewed data demonstrate that MSCs have a significant therapeutic potential in treating neuroinflammation-related cognitive disfunctions including age-related neurodegenerative diseases. The novel data demonstrate that maximal therapeutic effect is being achieved when MSCs penetrate the brain and produce their stimulating factors in situ. Consequently, therapeutic application using MSCs should include measures to facilitate their homing to the brain, support the survival in the brain microenvironment, and stimulate the production of neurotrophic and anti-inflammatory factors. These measures include but are not limited to genetic modification of MSCs and pre-conditioning before transplantation.

Retrograde signaling by a mtDNA-encoded non-coding RNA preserves mitochondrial bioenergetics

Alveolar epithelial type II (AETII) cells are important for lung epithelium maintenance and function. We demonstrate that AETII cells from mouse lungs exposed to cigarette smoke (CS) increase the levels of the mitochondria-encoded non-coding RNA, mito-RNA-805, generated by the control region of the mitochondrial genome. The protective effects of mito-ncR-805 are associated with positive regulation of mitochondrial energy metabolism, and respiration. Levels of mito-ncR-805 do not relate to steady-state transcription or replication of the mitochondrial genome. Instead, CS-exposure causes the redistribution of mito-ncR-805 from mitochondria to the nucleus, which correlated with the increased expression of nuclear-encoded genes involved in mitochondrial function. These studies reveal an unrecognized mitochondria stress associated retrograde signaling, and put forward the idea that mito-ncRNA-805 represents a subtype of small non coding RNAs that are regulated in a tissue- or cell-type specific manner to protect cells under physiological stress.

Different Effects of Nicotine and N-Stearoyl-ethanolamine on Episodic Memory and Brain Mitochondria of α7 Nicotinic Acetylcholine Receptor Knockout Mice

Nicotinic acetylcholine receptors of α7 subtype (α7 nAChRs) are involved in regulating neuroinflammation and cognitive functions. Correspondingly, α7-/- mice demonstrate pro-inflammatory phenotype and impaired episodic memory. In addition, nAChRs expressed in mitochondria regulate the release of pro-apoptotic factors like cytochrome c. Here we studied whether the cognitive deficiency of α7-/- mice can be cured by oral consumption of either nicotine or N-stearoylethanolamine (NSE), a lipid possessing anti-inflammatory, cannabimimetic and membrane-stabilizing activity. Mice were examined in Novel Object Recognition behavioral test, their blood, brains and brain mitochondria were tested for the levels of interleukin-6, various nAChR subtypes and cytochrome c released by ELISA. The data presented demonstrate that both substances stimulated the raise of interleukin-6 in the blood and improved episodic memory of α7-/- mice. However, NSE improved, while nicotine worsened the brain mitochondria sustainability to apoptogenic stimuli, as shown by either decreased or increased amounts of cytochrome c released. Both nicotine and NSE up-regulated α4β2 nAChRs in the brain; NSE up-regulated, while nicotine down-regulated α9-containing nAChRs in the brain mitochondria. It is concluded that the level of alternative nAChR subtypes in the brain is critically important for memory and mitochondria sustainability in the absence of α7 nAChRs.

Positive Allosteric Modulation of Alpha7 Nicotinic Acetylcholine Receptors Transiently Improves Memory but Aggravates Inflammation in LPS-Treated Mice

Neuroinflammation accompanies or even precedes the development of cognitive changes in many brain pathologies, including Alzheimer’s disease. Therefore, dampening inflammatory reactions within the brain is a promising strategy for supporting cognitive functions in elderly people and for preventing the development of neurodegenerative disorders. Nicotinic acetylcholine receptors containing α7 subunits (α7 nAChRs) are involved in regulating cell survival, inflammation, and memory. The aim of our study was to evaluate the efficiency of α7-specific therapy at different stages of inflammation and to compare the effects of orthosteric agonist PNU282987 and type 2 positive allosteric modulator (PAM) PNU120596 in mice after a single injection of lipopolysaccharide (LPS). The data presented demonstrate that PNU282987 protected mice from LPS-induced impairment of episodic memory by decreasing IL-6 levels in the blood, stabilizing the brain mitochondria and up-regulating the brain α7-, α3-, and α4-containing nAChRs. Such treatment was efficient when given simultaneously with LPS or a week after LPS injection and was not efficient if LPS had been injected 2 months before. PNU120596 also decreased IL-6, stabilized mitochondria and up-regulated the brain nAChRs. However, its memory-improving effect was transient and disappeared after the end of the injection cycle. Moreover, cessation of PNU120596 treatment resulted in a sharp increase in IL-1β and IL-6 levels in the blood. It is concluded that activating α7 nAChRs protects the mouse brain from the pathogenic effect of LPS in the early stages of inflammation but is not efficient when irreversible changes have already occurred. The use of a PAM does not improve the effect of the agonist, possibly potentiates the effect of endogenous agonists, and results in undesirable effects after treatment cessation.

Nicotinic-nAChR signaling mediates drug resistance in lung cancer

Lung cancer is the leading cause of cancer death worldwide. Cigarette smoking is the most common risk factor for lung carcinoma; other risks include genetic factors and exposure to radon gas, asbestos, secondhand smoke, and air pollution. Nicotine, the primary addictive constituent of cigarettes, contributes to cancer progression through activation of nicotinic acetylcholine receptors (nAChRs), which are membrane ligand-gated ion channels. Activation of nicotine/nAChR signaling is associated with lung cancer risk and drug resistance. We focused on nAChR pathways activated by nicotine and its downstream signaling involved in regulating apoptotic factors of mitochondria and drug resistance in lung cancer. Increasing evidence suggests that several sirtuins play a critical role in multiple aspects of cancer drug resistance. Thus, understanding the consequences of crosstalk between nicotine/nAChRs and sirtuin signaling pathways in the regulation of drug resistance could be a critical implication for cancer therapy.

Differentiating the Pharmacodynamics and Toxicology of Macrolide and Ketolide Antibiotics

This is a review of the macrolide and ketolide field focusing on differentiating the pharmacodynamics and especially the toxicology of the macrolides and ketolides. We emphasize the diversity in pharmacodynamics and toxicity of the macrolides and ketolides, resulting from even small structural changes, which makes it important to consider the various different compounds separately, not necessarily as a class. The ketolide, telithromycin, was developed because of rising bacterial macrolide resistance but was withdrawn postapproval after visual disturbances, syncope, myasthenia gravis, and hepatotoxicity were noted. These diverse adverse effects could be attributed to inhibition of nicotinic acetylcholine receptors. Solithromycin, a later generation ketolide, was effective in treating bacterial pneumonia, but it was not approved by the U.S. Food and Drug Administration owing, in part, to its structural similarity to telithromycin. This Miniperspective describes that structurally similar macrolides/ketolides have clearly mechanistically distinct effects. Understanding these effects could help in developing and securing regulatory approval of a new macrolide/ketolide that is active against macrolide-resistant pathogenic bacteria.

Mitochondria as a possible target for nicotine action

Mitochondria are multifunctional and dynamic organelles deeply integrated into cellular physiology and metabolism. Disturbances in mitochondrial function are involved in several disorders such as neurodegeneration, cardiovascular diseases, metabolic diseases, and also in the aging process. Nicotine is a natural alkaloid present in the tobacco plant which has been well studied as a constituent of cigarette smoke. It has also been reported to influence mitochondrial function both in vitro and in vivo. This review presents a comprehensive overview of the present knowledge of nicotine action on mitochondrial function. Observed effects of nicotine exposure on the mitochondrial respiratory chain, oxidative stress, calcium homeostasis, mitochondrial dynamics, biogenesis, and mitophagy are discussed, considering the context of the experimental design. The potential action of nicotine on cellular adaptation and cell survival is also examined through its interaction with mitochondria. Although a large number of studies have demonstrated the impact of nicotine on various mitochondrial activities, elucidating its mechanism of action requires further investigation.

Contribution of Mitochondrial Ion Channels to Chemo-Resistance in Cancer Cells

Mitochondrial ion channels are emerging oncological targets, as modulation of these ion-transporting proteins may impact on mitochondrial membrane potential, efficiency of oxidative phosphorylation and reactive oxygen production. In turn, these factors affect the release of cytochrome c, which is the point of no return during mitochondrial apoptosis. Many of the currently used chemotherapeutics induce programmed cell death causing damage to DNA and subsequent activation of p53-dependent pathways that finally leads to cytochrome c release from the mitochondrial inter-membrane space. The view is emerging, as summarized in the present review, that ion channels located in this organelle may account in several cases for the resistance that cancer cells can develop against classical chemotherapeutics, by preventing drug-induced apoptosis. Thus, pharmacological modulation of these channel activities might be beneficial to fight chemo-resistance of different types of cancer cells.

The α9α10 Nicotinic Acetylcholine Receptor Antagonist αO-Conotoxin GeXIVA[1,2] Alleviates and Reverses Chemotherapy-Induced Neuropathic Pain

Oxaliplatin is a third-generation platinum drug and is widely used as a first-line therapy for the treatment of colorectal cancer (CRC). However, a large number of patients receiving oxaliplatin develop dose-limiting painful neuropathy. Here, we report that αO-conotoxin GeXIVA[1,2], a highly potent and selective antagonist of the α9α10 nicotinic acetylcholine receptor (nAChR) subtype, can relieve and reverse oxaliplatin-induced mechanical and cold allodynia after single and repeated intramuscular (IM) injections in rats. Treatments were started at 4 days post oxaliplatin injection when neuropathic pain emerged and continued for 8 and 16 days. Cold score and mechanical paw withdrawal threshold (PWT) were detected by the acetone test and von Frey test respectively. GeXIVA[1,2] significantly relieved mechanical and cold allodynia in oxaliplatin-treated rats after a single injection. After repeated treatments, GeXIVA[1,2] produced a cumulative analgesic effect without tolerance and promoted recovery from neuropathic pain. Moreover, the long lasting analgesic effect of GeXIVA[1,2] on mechanical allodynia continued until day 10 after the termination of the 16-day repeated treatment procedure. On the contrary, GeXIVA[1,2] did not affect acute mechanical and thermal pain behaviors in normal rats after repeated injections detected by the von Frey test and tail flick test. GeXIVA[1,2] had no influence on rat hind limb grip strength and body weight after repeated treatments. These results indicate that αO-conotoxin GeXIVA[1,2] could provide a novel strategy to treat chemotherapy-induced neuropathic pain.

Intravenously Injected Mesenchymal Stem Cells Penetrate the Brain and Treat Inflammation-Induced Brain Damage and Memory Impairment in Mice

Neuroinflammation is regarded as one of the pathogenic factors of Alzheimer disease (AD). Previously, we showed that mice regularly injected with bacterial lipopolysaccharide (LPS) possessed the AD-like symptoms like episodic memory decline, elevated amounts of amyloid beta (Aβ) peptide (1-42), and decreased levels of nicotinic acetylcholine receptors (nAChRs) in the brain. The use of mesenchymal stem cells (MSCs), which can differentiate into multiple cell types, including neurons, is an attractive idea of regenerative medicine, in particular, for neurodegenerative disorders like AD. In the present study, we aimed to investigate whether pathogenic effect of LPS on the brain and behavior of mice can be prevented or treated by injection of MSCs or MSC-produced soluble factors. Fluorescently-labeled MSCs, injected intravenously, were found in the brain blood vessels of LPS-treated mice. Mice co-injected with LPS and MSCs did not demonstrate episodic memory impairment, Aβ (1-42) accumulation, and nAChR decrease in the brain and brain mitochondria. Their mitochondria released less cytochrome c under the effect of Ca²⁺ compared to mitochondria of LPS-only-treated mice. Moreover, MSCs could reverse the pathogenic symptoms developed 3 weeks after LPS injection. Cultured MSCs produced IL-6 in response to LPS and MSCs effect in vivo was accompanied by additional stimulation of both micro- and macroglia. Xenogeneic (human) MSCs were almost as efficient as allogeneic (mouse) ones and regular injections of human MSC-conditioned medium also produced positive effect. These data allow suggesting MSCs as a potential therapeutic tool to cure neuroinflammation-related cognitive pathology.

Proteomic Investigation of Murine Neuronal α7-Nicotinic Acetylcholine Receptor Interacting Proteins

The α7-nicotinic acetylcholine receptor (α7-nAChR) is a ligand-gated ion channel that is expressed widely in vertebrates and is the principal high-affinity α-bungarotoxin (α-bgtx) binding protein in the mammalian CNS. α7-nAChRs associate with proteins that can modulate its properties. The α7-nAChR interactome is the summation of proteins interacting or associating with α7-nAChRs in a protein complex. To identify an α7-nAChR interactome in neural tissue, we isolated α-bgtx-affinity protein complexes from wild-type and α7-nAChR knockout (α7 KO) mouse whole brain tissue homogenates using α-bgtx-affinity beads. Affinity precipitated proteins were trypsinized and analyzed with an Orbitrap Fusion mass spectrometer. Proteins isolated with the α7-nAChR specific ligand, α-bgtx, were determined to be α7-nAChR associated proteins. The α7-nAChR subunit and 120 additional proteins were identified. Additionally, 369 proteins were identified as binding to α-bgtx in the absence of α7-nAChR expression, thereby identifying nonspecific proteins for α7-nAChR investigations using α-bgtx enrichment. These results expand on our previous investigations of α7-nAChR interacting proteins using α-bgtx-affinity bead isolation by controlling for differences between α7-nAChR and α-bgtx-specific proteins, developing an improved protein isolation methodology, and incorporating the latest technology in mass spectrometry. The α7-nAChR interactome identified in this study includes proteins associated with the expression, localization, function, or modulation of α7-nAChRs, and it provides a foundation for future studies to elucidate how these interactions contribute to human disease.