Nicotinic acetylcholine receptor-mediated stimulation of endothelial cells results in the arrest of haematopoietic progenitor cells on endothelium

Activating α7nAChRs enhances endothelial progenitor cell function partially through the JAK2/STAT3 signaling pathway

Microvascular injury is a common pathological process in ischemia-reperfusion injury. Endothelial progenitor cells (EPCs) are vital cells for angiogenesis and endothelial repair. These cells can home to injury sites and secrete angiogenic growth factors. α7nAChRs are pivotal in cholinergic angiogenesis, which is associated with endothelial cells and EPCs. Our study was designed to determine whether activating α7nAChRs enhances the function of EPCs and to explore the underlying mechanism. EPCs were derived from the bone marrow of male Sprague-Dawley rats and treated with an α7nAChR agonist (PNU282987), an α7nAChR antagonist (MLA) and a JAK2 antagonist (AG490). We then assayed the angiogenic abilities of the EPCs, including proliferation ability, adhesion ability, migration ability and in vitro tube formation ability. The levels of total JAK2 (t-JAK2), phosphorylated JAK2 (p-JAK2), total STAT3 (t-STAT3) and phosphorylated STAT3 (p-STAT3) were estimated by western blot analysis. PNU282987 treatment facilitated the angiogenic abilities of EPCs compared with the control regimen. The western blot data suggested that PNU282987 increased the levels of p-JAK2 and p-STAT3. However, the differences in t-JAK2 levels and t-STAT3 levels between the agonist-treated group and the control group were not significant. Moreover, treating EPCs with AG490 reduced STAT3 phosphorylation and attenuated the PNU282987-induced enhancement of EPCs. We demonstrated that activating α7nAChRs can enhance EPC functions partially through the JAK2/STAT3 signaling pathway. This study reveals that α7nAChRs are potential therapeutic targets for angiogenesis and that the JAK2/STAT3 pathway plays a vital role in the associated therapeutic mechanism.

Lung fibroblasts share mesenchymal stem cell features which are altered in chronic obstructive pulmonary disease via the overactivation of the Hedgehog signaling pathway

Background

Alteration of functional regenerative properties of parenchymal lung fibroblasts is widely proposed as a pathogenic mechanism for chronic obstructive pulmonary disease (COPD). However, what these functions are and how they are impaired in COPD remain poorly understood. Apart from the role of fibroblasts in producing extracellular matrix, recent studies in organs different from the lung suggest that such cells might contribute to repair processes by acting like mesenchymal stem cells. In addition, several reports sustain that the Hedgehog pathway is altered in COPD patients thus aggravating the disease. Nevertheless, whether this pathway is dysregulated in COPD fibroblasts remains unknown.

Objectives and Methods

We investigated the stem cell features and the expression of Hedgehog components in human lung fibroblasts isolated from histologically-normal parenchymal tissue from 25 patients—8 non-smokers/non-COPD, 8 smokers-non COPD and 9 smokers with COPD—who were undergoing surgery for lung tumor resection.

Results

We found that lung fibroblasts resemble mesenchymal stem cells in terms of cell surface marker expression, differentiation ability and immunosuppressive potential and that these properties were altered in lung fibroblasts from smokers and even more in COPD patients. Furthermore, we showed that some of these phenotypic changes can be explained by an over activation of the Hedgehog signaling in smoker and COPD fibroblasts.

Conclusions

Our study reveals that lung fibroblasts possess mesenchymal stem cell-features which are impaired in COPD via the contribution of an abnormal Hedgehog signaling. These processes should constitute a novel pathomechanism accounting for disease occurrence and progression.

Cholinergic activation of hematopoietic stem cells: role in tobacco-related disease?

Tobacco use is associated with an increase in the white blood cell (WBC) count. This association has been attributed to bronchopulmonary inflammation and/or infection. It is not known if nicotine itself may play a role. The objective of this study was to determine whether nicotine itself could affect the WBC count, and to determine whether this was due to a direct effect on hematopoietic stem cells (HSC). C57Bl6J mice received nicotine orally, and measurements of the WBC count, bone marrow and spleen cellularity, and HSC count were made. To determine the functionality of HSCs, irradiated animals received bone marrow transplants from vehicle or nicotine-treated mice. Nicotine increased leukocytes in the peripheral blood, bone marrow and spleen. The peripheral red cell and platelet count were unaffected. Nicotine increased the frequency of HSC in the bone marrow. Isolated long-term HSCs from nicotine-treated mice transplanted into irradiated mice regenerated all hematopoietic cell lineages, demonstrating the functional competence of those HSCs. HSCs expressed nicotinic acetylcholine receptors (nAChRs), as documented by FITC-conjugated alpha-bungarotoxin binding. Nicotine increased soluble Kit ligand, consistent with stem cell activation. In conclusion, the data suggest a new mechanism for the increased WBC associated with tobacco use. The effect of nicotine to activate hematopoiesis may contribute to tobacco-related diseases.

Functional nicotinic and muscarinic receptors on mesenchymal stem cells

Mesenchymal stem cells (MSCs) are under the control of a large number of signaling systems. In this study, the presence and functionality of the acetylcholine (ACh) signaling system in MSCs was examined. We detected the expression of choline acetyltransferase (ChAT), acetylcholinesterase (AChE), and the presence of ACh in MSCs. MSCs also expressed the nicotinic acetylcholine receptor subunits alpha 3, alpha 5, alpha 7, and the muscarinic acetylcholine receptor 2 (M2-receptor). The M2-receptor and the nicotinic alpha 7 receptor subunits were expressed on distinct subpopulations of cells, indicating differential regulation of cholinergic signaling between MSCs. Stimulation of MSCs with the nicotinic receptor agonist nicotine and the muscarinic receptor agonist muscarine induced immediate and transient increases in intracellular Ca(2+) concentration. Furthermore, muscarine had an inhibiting effect on the production of the intracellular signaling molecule cyclic adenosine 3',5'-monophosphate (cAMP). The AChE inhibitor chlorpyrifos, which is widely used as an agricultural insecticide, had similar effects on intracellular Ca(2+) and cAMP in MSCs. Nicotine, muscarine, and chlorpyrifos induced the phosphorylation of extracellular signal-regulated kinases 1 and 2. This study demonstrates that several components of a cholinergic signaling system are present and functional in MSCs. Environmental compounds such as nicotine and agricultural insecticides can interfere with this system and may affect cellular processes in the MSC.

Adipose stem cell treatment in mice attenuates lung and systemic injury induced by cigarette smoking

RATIONALE

Adipose-derived stem cells express multiple growth factors that inhibit endothelial cell apoptosis, and demonstrate substantial pulmonary trapping after intravascular delivery.

OBJECTIVES

We hypothesized that adipose stem cells would ameliorate chronic lung injury associated with endothelial cell apoptosis, such as that occurring in emphysema.

METHODS

Therapeutic effects of systemically delivered human or mouse adult adipose stem cells were evaluated in murine models of emphysema induced by chronic exposure to cigarette smoke or by inhibition of vascular endothelial growth factor receptors.

MEASUREMENTS AND MAIN RESULTS

Adipose stem cells were detectable in the parenchyma and large airways of lungs up to 21 days after injection. Adipose stem cell treatment was associated with reduced inflammatory infiltration in response to cigarette smoke exposure, and markedly decreased lung cell death and airspace enlargement in both models of emphysema. Remarkably, therapeutic results of adipose stem cells extended beyond lung protection by rescuing the suppressive effects of cigarette smoke on bone marrow hematopoietic progenitor cell function, and by restoring weight loss sustained by mice during cigarette smoke exposure. Pulmonary vascular protective effects of adipose stem cells were recapitulated by application of cell-free conditioned medium, which improved lung endothelial cell repair and recovery in a wound injury repair model and antagonized effects of cigarette smoke in vitro.

CONCLUSIONS

These results suggest a useful therapeutic effect of adipose stem cells on both lung and systemic injury induced by cigarette smoke, and implicate a lung vascular protective function of adipose stem cell derived paracrine factors.

The cholinergic anti-inflammatory system limits T cell infiltration into the neurodegenerative CNS, but cannot counteract complex CNS inflammation

Stimulation of the nicotinic alpha7 acetylcholine receptor (nAChRalpha7) by nicotine or acetylcholine initiates the cholinergic anti-inflammatory pathway, a mechanism for neural inhibition of inflammation. The action of this pathway was initially discovered in animal models of endotoxemia and septic shock, and later described in a number of other diseases. Moreover, the action of this pathway is also implied in human degenerative diseases of the central nervous system (CNS) like amyotrophic lateral sclerosis or Alzheimer's disease. In spite of this general interest, little is known about its involvement in regulating T cell entry into, or inflammatory reactions within the CNS. We tested the action of the cholinergic anti-inflammatory pathway in nAChRalpha7-deficient mice and their wildtype counterparts in two different experimental settings: In the facial nerve axotomy model characterized by neurodegeneration and T cell infiltration, and in the experimental autoimmune encephalomyelitis (EAE) model providing a very complex scenario of CNS inflammation and demyelination. We found that the cholinergic anti-inflammatory pathway limits the site-directed influx of activated T cells into the lesioned facial motor nucleus, but cannot counteract CNS inflammation in EAE.

Nicotine increases the collagen-degrading ability of human gingival fibroblasts

BACKGROUND AND OBJECTIVE

The objective of this study was to determine the effects that nicotine and the combination of nicotine and Porphyromonas gingivalis supernatant have on human gingival fibroblast-mediated collagen degradation.

MATERIAL AND METHODS

Human gingival fibroblasts were cultured with 25-500 microg/ml of nicotine in collagen-coated six-well plates. On days 1-5, the conditioned media was collected for zymography and western blot analyses of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs). The cells were then removed and the collagen cleavage visualized by Coomassie blue staining. To examine the combined effect, 250 microg/ml of nicotine and 10% v/v culture supernatant of P. gingivalis ATCC 33277 were added to the human gingival fibroblasts. The mRNA levels of multiple MMPs and TIMPs were monitored.

RESULTS

Nicotine increased the human gingival fibroblast-mediated collagen cleavage. The MMP-14 and MMP-2 produced by the nicotine-treated human gingival fibroblasts more readily underwent zymogen activation. Nicotine treatment resulted in TIMP-2 redistribution to the cell surface. The mRNAs of multiple MMPs and TIMPs were unaltered by nicotine. An additive collagen cleavage effect was observed when the human gingival fibroblasts were treated with both nicotine and P. gingivalis.

CONCLUSION

Nicotine increased human gingival fibroblast-mediated collagen degradation, in part through the activation of membrane-associated MMPs. Nicotine and P. gingivalis had an additive effect on human gingival fibroblast-mediated collagen degradation.

Nicotine protects kidney from renal ischemia/reperfusion injury through the cholinergic anti-inflammatory pathway

Kidney ischemia/reperfusion injury (I/R) is characterized by renal dysfunction and tubular damages resulting from an early activation of innate immunity. Recently, nicotine administration has been shown to be a powerful inhibitor of a variety of innate immune responses, including LPS-induced toxaemia. This cholinergic anti-inflammatory pathway acts via the α7 nicotinic acetylcholine receptor (α7nAChR). Herein, we tested the potential protective effect of nicotine administration in a mouse model of renal I/R injury induced by bilateral clamping of kidney arteries. Renal function, tubular damages and inflammatory response were compared between control animals and mice receiving nicotine at the time of ischemia. Nicotine pretreatment protected mice from renal dysfunction in a dose-dependent manner and through the α7nAChR, as attested by the absence of protection in α7nAChR-deficient mice. Additionally, nicotine significantly reduced tubular damages, prevented neutrophil infiltration and decreased productions of the CXC-chemokine KC, TNF-α and the proinflammatory high-mobility group box 1 protein. Reduced tubular damage in nicotine pre-treated mice was associated with a decrease in tubular cell apoptosis and proliferative response as attested by the reduction of caspase-3 and Ki67 positive cells, respectively. All together, these data highlight that nicotine exerts a protective anti-inflammatory effect during kidney I/R through the cholinergic α7nAChR pathway. In addition, this could provide an opportunity to overcome the effect of surgical cholinergic denervation during kidney transplantation.

The cholinergic system is involved in regulation of the development of the hematopoietic system

Gene expression profiling demonstrated that components of the cholinergic system, including choline acetyltransferase, acetylcholinesterase and nicotinic acetylcholine receptors (nAChRs), are expressed in embryonic stem cells and differentiating embryoid bodies (EBs). Triggering of nAChRs expressed in EBs by nicotine resulted in activation of MAPK and shifts of spontaneous differentiation toward hemangioblast. In vivo, non-neural nAChRs are detected early during development in fetal sites of hematopoiesis. Similarly, in vivo exposure of the developing embryo to nicotine resulted in higher numbers of hematopoietic progenitors in fetal liver. However postpartum, the number of hematopoietic stem/progenitor cells (HSPC) was decreased, suggesting an impaired colonization of the fetal bone marrow with HSPCs. This correlated with increased number of circulating HSPC and decreased expression of CXCR4 that mediates migration of circulating cells into the bone marrow regulatory niche. In addition, protein microarrays demonstrated that nicotine changed the profile of cytokines produced in the niche. While the levels of IL1alpha, IL1beta, IL2, IL9 and IL10 were not changed, the production of hematopoiesis-supportive cytokines including G-CSF, GM-CSF, IL3, IL6 and IGFBP-3 was decreased. This correlated with the decreased repopulating ability of HSPC in vivo and diminished hematopoietic activity in bone marrow cultures treated with nicotine. Interestingly, nicotine stimulated the production of IL4 and IL5, implying a possible role of the cholinergic system in pathogenesis of allergic diseases. Our data provide evidence that the nicotine-induced imbalance of the cholinergic system during gestation interferes with normal development and provides the basis for negative health outcomes postpartum in active and passive smokers.

Sustained exposure to nicotine leads to extramedullary hematopoiesis in the spleen

The effect of sustained exposure to nicotine, a major constituent of cigarette smoke, on hematopoiesis in the bone marrow (BM) and spleen was evaluated in a murine model. BALB/c mice were exposed to nicotine subcutaneously using 21-day slow-release pellets. Exposure to nicotine had no effect on the proliferation of long-term BM cultures or on their ability to form colonies. However, there was a significant decrease in the generation of lineage-specific progenitor cells, specifically eosinophil (colony-forming unit [CFU]-Eos) progenitors, in the BM of nicotine-exposed mice compared with control mice. Surprisingly, sustained exposure of mice to nicotine was found to induce significant hematopoiesis in the spleen. There was a significant increase in total colony formation as well as eosinophil-, granulocyte-macrophage-, and B-lymphocyte-specific progenitors (CFU-Eos, CFU-GM, and CFU-B, respectively) in nicotine-exposed mice but not in control mice. Sustained exposure to nicotine was associated with significant inhibition of rolling and migration of enriched hematopoietic stem/progenitor cells (HSPCs) across BM endothelial cells (BMECs) in vitro as well as decreased expression of beta2 integrin on the surface of these cells. Although sustained exposure to nicotine has only a modest effect on BM hematopoiesis, our studies indicate that it significantly induces extramedullary hematopoiesis in the spleen. Decreased interaction of nicotine-exposed HSPCs with BMECs (i.e., rolling and migration) may result in altered BM homing of these cells, leading to their seeding and proliferation at extramedullary sites such as the spleen.

Control by cholinergic mechanisms

In the respiratory tract acetylcholine is neurotransmitter in ganglia and postganglionic parasympathetic nerves, but in addition is paracrine mediator released from various non-neuronal cells. Almost every cell type present in the respiratory tract expresses nicotinic and muscarinic receptors and therefore appears to be a target for acetylcholine. The present review describes the mechanisms of synthesis and release of acetylcholine from neuronal and non-neuronal cells and the differential control mechanisms. The different cholinoceptors, multiple nicotinic and muscarinic receptors and their signalling are outlined and their involvement in the modulation of the function of various target cells, smooth muscles, nerves, surface epithelial, secretory cells, fibroblasts and inflammatory cells is discussed in detail.