Cholinergic drugs inhibit in vitro megakaryopoiesis via the alpha7-nicotinic acetylcholine receptor

α7nAChR activation in AT2 cells promotes alveolar regeneration through WNT7B signaling in acute lung injury

Reducing inflammatory damage and improving alveolar epithelium regeneration are two key approaches to promoting lung repair in acute lung injury/acute respiratory distress syndrome (ALI/ARDS). Stimulation of cholinergic α7 nicotinic acetylcholine receptor (α7nAChR, coded by Chrna7) signaling could dampen lung inflammatory injury. However, whether activation of α7nAChR in alveolar type II (AT2) cells promotes alveolar epithelial injury repair and underlying mechanisms is elusive. Here, we found that α7nAChR was expressed on AT2 cells and was upregulated in response to LPS-induced ALI. Meanwhile, deletion of Chrna7 in AT2 cells impeded lung repair process and worsened lung inflammation in ALI. Using in vivo AT2 lineage-labeled mice and ex vivo AT2 cell-derived alveolar organoids, we demonstrated that activation of α7nAChR expressed on AT2 cells improved alveolar regeneration by promoting AT2 cells to proliferate and subsequently differentiate toward alveolar type I cells. Then, we screened out the WNT7B signaling pathway by the RNA-Seq analysis of in vivo AT2 lineage-labeled cells and further confirmed its indispensability for α7nAChR activation-mediated alveolar epithelial proliferation and differentiation. Thus, we have identified a potentially unrecognized pathway in which cholinergic α7nAChR signaling determines alveolar regeneration and repair, which might provide us a novel therapeutic target for combating ALI.

Cholinergic signals preserve haematopoietic stem cell quiescence during regenerative haematopoiesis

The sympathetic nervous system has been evolutionary selected to respond to stress and activates haematopoietic stem cells via noradrenergic signals. However, the pathways preserving haematopoietic stem cell quiescence and maintenance under proliferative stress remain largely unknown. Here we found that cholinergic signals preserve haematopoietic stem cell quiescence in bone-associated (endosteal) bone marrow niches. Bone marrow cholinergic neural signals increase during stress haematopoiesis and are amplified through cholinergic osteoprogenitors. Lack of cholinergic innervation impairs balanced responses to chemotherapy or irradiation and reduces haematopoietic stem cell quiescence and self-renewal. Cholinergic signals activate α7 nicotinic receptor in bone marrow mesenchymal stromal cells leading to increased CXCL12 expression and haematopoietic stem cell quiescence. Consequently, nicotine exposure increases endosteal haematopoietic stem cell quiescence in vivo and impairs hematopoietic regeneration after haematopoietic stem cell transplantation in mice. In humans, smoking history is associated with delayed normalisation of platelet counts after allogeneic haematopoietic stem cell transplantation. These results suggest that cholinergic signals preserve stem cell quiescence under proliferative stress.

Repurposing Pilocarpine Hydrochloride for Treatment of Candida albicans Infections

Candida albicans is the most common human fungal pathogen with an estimated crude mortality rate of 40%. The ability of the organism to switch from the yeast to hyphal form and produce biofilms are important virulence factors. C. albicans infections are combatted by the host immune system. However, Candida triggers a strong inflammatory response that, if not appropriately regulated, can damage host tissues. Therefore, it is important that the host immune response eliminates the fungus but limits tissue damage. This study provides evidence that targeting cholinergic receptors cannot only curb the virulence of C. albicans by inhibiting filamentous growth and biofilm formation but can also appropriately regulate the host immune response to induce rapid clearance with limited damage to vital tissues. This article provides evidence that repurposing licensed drugs that target cholinergic receptors may offer novel therapeutic solutions for the prevention or treatment of fungal infections.

Acetylcholine modulates the virulence of Candida albicans and regulates an appropriate immune response to infection in a Galleria mellonella infection model. Indeed, the evidence suggests that C. albicans possesses a functional cholinergic receptor that can regulate filamentous growth and biofilm formation. Furthermore, G. mellonella immune cell subsets possess repertories of cholinergic receptors which regulate an effective and appropriate cellular immune response to C. albicans infection. This study aimed to investigate the cholinergic receptor subtype involved in regulation of filamentous growth and biofilm formation by C. albicans and determine the roles of cholinergic receptors in modulation of G. mellonella immune cell subsets. The general muscarinic receptor agonist, pilocarpine hydrochloride, inhibited C. albicans biofilm formation and pathogenicity, a phenomenon that could be reversed using the general muscarinic receptor antagonist, scopolamine. Pilocarpine hydrochloride protected G. mellonella larvae from C. albicans infection via inhibition of C. albicans filamentation and appropriate regulation of cellular immunity. However, scopolamine abrogated the capacity of pilocarpine hydrochloride to protect G. mellonella larvae from C. albicans infection. Furthermore, acetylcholine and pilocarpine hydrochloride exhibited differential modulatory capabilities on Galleria mellonella hemocyte responses to C. albicans. The data in this article demonstrate that a muscarinic receptor modulates C. albicans filamentation and biofilm formation. Furthermore, the results suggest that G. mellonella hemocyte subsets possess unique repertoires of cholinergic receptors that regulate their differentiation, activation, and function in contrasting manners. Therefore, targeting cholinergic receptors by repurposing currently licensed cholinergic drugs may offer novel therapeutic solutions for the prevention or treatment of fungal infections.

IMPORTANCECandida albicans is the most common human fungal pathogen with an estimated crude mortality rate of 40%. The ability of the organism to switch from the yeast to hyphal form and produce biofilms are important virulence factors. C. albicans infections are combatted by the host immune system. However, Candida triggers a strong inflammatory response that, if not appropriately regulated, can damage host tissues. Therefore, it is important that the host immune response eliminates the fungus but limits tissue damage. This study provides evidence that targeting cholinergic receptors cannot only curb the virulence of C. albicans by inhibiting filamentous growth and biofilm formation but can also appropriately regulate the host immune response to induce rapid clearance with limited damage to vital tissues. This article provides evidence that repurposing licensed drugs that target cholinergic receptors may offer novel therapeutic solutions for the prevention or treatment of fungal infections.

Inhibition of glutamate regulated calcium entry into leukemic megakaryoblasts reduces cell proliferation and supports differentiation

Human megakaryocytes release glutamate and express glutamate-gated Ca(2+)-permeable N-methyl-D-aspartate receptors (NMDARs) that support megakaryocytic maturation. While deregulated glutamate pathways impact oncogenicity in some cancers, the role of glutamate and NMDARs in megakaryocytic malignancies remains unknown. The aim of this study was to determine if NMDARs participate in Ca(2+) responses in leukemic megakaryoblasts and if so, whether modulating NMDAR activity could influence cell growth. Three human cell lines, Meg-01, Set-2 and K-562 were used as models of leukemic megakaryoblasts. NMDAR components were examined in leukemic cells and human bone marrow, including in megakaryocytic disease. Well-established NMDAR modulators (agonists and antagonists) were employed to determine NMDAR effects on Ca(2+) flux, cell viability, proliferation and differentiation. Leukemic megakaryoblasts contained combinations of NMDAR subunits that differed from normal bone marrow and the brain. NMDAR agonists facilitated Ca(2+) entry into Meg-01 cells, amplified Ca(2+) responses to adenosine diphosphate (ADP) and promoted growth of Meg-01, Set-2 and K-562 cells. Low concentrations of NMDAR inhibitors (riluzole, memantine, MK-801 and AP5; 5-100μM) were weakly cytotoxic but mainly reduced cell numbers by suppressing proliferation. The use-dependent NMDAR inhibitor, memantine (100μM), reduced numbers and proliferation of Meg-01 cells to less than 20% of controls (IC50 20μM and 36μM, respectively). In the presence of NMDAR inhibitors cells acquired morphologic and immunophenotypic features of megakaryocytic differentiation. In conclusion, NMDARs provide a novel pathway for Ca(2+) entry into leukemic megakaryoblasts that supports cell proliferation but not differentiation. NMDAR inhibitors counteract these effects, suggesting a novel opportunity to modulate growth of leukemic megakaryoblasts.

Effect of pesticide exposure on platelet indices in farm workers

We aimed to assess the effect of exposure to pesticide on platelet indices including mean platelet volume (MPV) and platelet distribution width (PDW) in farm workers. The study group consisted of 40 farm workers (4 females, 36 males; mean age 42.6 ± 9.8 years). An age-, gender- and body mass index-matched control group was composed of 38 healthy volunteers (8 females, 30 males; mean age 46.1±8.9 years). Platelet indices were assessed in farm workers exposed to pesticides. MPV values were significantly lower in farm workers than in those of controls (6.3 ± 1.1 vs. 7.6 ± 0.7 fL, respectively; p < 0.001). Platelet count was significantly lower in farm workers than those of controls (155.7 ± 35.7 vs. 271.3 ± 96.2 × 10(9)/L, respectively; p < 0.001). PDW was significantly lower in farm workers than in those of controls (8.9% ± 2.0% vs. 15.8% ± 0.8%, respectively; p < 0.001). We have found that MPV and other platelet indices were significantly lower in farm workers exposed to pesticides than those of controls. Our findings suggest that MPV may be a sensitive indicator of a pesticide-exposure effect.

The unique contribution of ion channels to platelet and megakaryocyte function

Ion channels are transmembrane proteins that play ubiquitous roles in cellular homeostasis and activation. In addition to their recognized role in the regulation of ionic permeability and thus membrane potential, some channel proteins possess intrinsic kinase activity, directly interact with integrins or are permeable to molecules up to ≈1000 Da. The small size and anuclear nature of the platelet has often hindered progress in understanding the role of specific ion channels in hemostasis, thrombosis and other platelet-dependent events. However, with the aid of transgenic mice and 'surrogate' patch clamp recordings from primary megakaryocytes, important unique contributions to platelet function have been identified for several classes of ion channel. Examples include ATP-gated P2X1 channels, Orai1 store-operated Ca2+ channels, voltage-gated Kv1.3 channels, AMPA and kainate glutamate receptors and connexin gap junction channels. Furthermore, evidence exists that some ion channels, such as NMDA glutamate receptors, contribute to megakaryocyte development. This review examines the evidence for expression of a range of ion channels in the platelet and its progenitor cell, and highlights the distinct roles that these proteins may play in health and disease.