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

Hematopoietic Stem Cells as an Integrative Hub Linking Lifestyle to Cardiovascular Health

Despite breakthroughs in modern medical care, the incidence of cardiovascular disease (CVD) is even more prevalent globally. Increasing epidemiologic evidence indicates that emerging cardiovascular risk factors arising from the modern lifestyle, including psychosocial stress, sleep problems, unhealthy diet patterns, physical inactivity/sedentary behavior, alcohol consumption, and tobacco smoking, contribute significantly to this worldwide epidemic, while its underpinning mechanisms are enigmatic. Hematological and immune systems were recently demonstrated to play integrative roles in linking lifestyle to cardiovascular health. In particular, alterations in hematopoietic stem cell (HSC) homeostasis, which is usually characterized by proliferation, expansion, mobilization, megakaryocyte/myeloid-biased differentiation, and/or the pro-inflammatory priming of HSCs, have been shown to be involved in the persistent overproduction of pro-inflammatory myeloid leukocytes and platelets, the cellular protagonists of cardiovascular inflammation and thrombosis, respectively. Furthermore, certain lifestyle factors, such as a healthy diet pattern and physical exercise, have been documented to exert cardiovascular protective effects through promoting quiescence, bone marrow retention, balanced differentiation, and/or the anti-inflammatory priming of HSCs. Here, we review the current understanding of and progression in research on the mechanistic interrelationships among lifestyle, HSC homeostasis, and cardiovascular health. Given that adhering to a healthy lifestyle has become a mainstream primary preventative approach to lowering the cardiovascular burden, unmasking the causal links between lifestyle and cardiovascular health from the perspective of hematopoiesis would open new opportunities to prevent and treat CVD in the present age.

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.

Clearing the Haze: How Does Nicotine Affect Hematopoiesis before and after Birth?

Hematopoiesis is a tightly regulated process orchestrated by cell-intrinsic and cell-extrinsic cues. Over the past several decades, much effort has been focused on understanding how these cues regulate hematopoietic stem cell (HSC) function. Many endogenous key regulators of hematopoiesis have been identified and extensively characterized. Less is known about the mechanisms of long-term effects of environmental toxic compounds on hematopoietic stem and progenitor cells (HSPCs) and their mature immune cell progeny. Research over the past several decades has demonstrated that tobacco products are extremely toxic and pose huge risks to human health by causing diseases like cancer, respiratory illnesses, strokes, and more. Recently, electronic cigarettes have been promoted as a safer alternative to traditional tobacco products and have become increasingly popular among younger generations. Nicotine, the highly toxic compound found in many traditional tobacco products, is also found in most electronic cigarettes, calling into question their purported "safety". Although it is known that nicotine is toxic, the pathophysiology of disease in exposed people remains under investigation. One plausible contributor to altered disease susceptibility is altered hematopoiesis and associated immune dysfunction. In this review, we focus on research that has addressed how HSCs and mature blood cells respond to nicotine, as well as identify remaining questions.

The Impact of Sedentary Lifestyle, High-fat Diet, Tobacco Smoke, and Alcohol Intake on the Hematopoietic Stem Cell Niches

Hematopoietic stem and progenitor cells maintain hematopoiesis throughout life by generating all major blood cell lineages through the process of self-renewal and differentiation. In adult mammals, hematopoietic stem cells (HSCs) primarily reside in the bone marrow (BM) at special microenvironments called “niches.” Niches are thought to extrinsically orchestrate the HSC fate including their quiescence and proliferation. Insight into the HSC niches mainly comes from studies in mice using surface marker identification and imaging to visualize HSC localization and association with niche cells. The advantage of mouse models is the possibility to study the 3-dimensional BM architecture and cell interactions in an intact traceable system. However, this may not be directly translational to human BM. Sedentary lifestyle, unhealthy diet, excessive alcohol intake, and smoking are all known risk factors for various diseases including hematological disorders and cancer, but how do lifestyle factors impact hematopoiesis and the associated niches? Here, we review current knowledge about the HSC niches and how unhealthy lifestyle may affect it. In addition, we summarize epidemiological data concerning the influence of lifestyle factors on hematological disorders and malignancies.

The Consequence of Aqueous Extract of Tobacco Leaves (Nicotiana tabacum. L) on Feed Intake, Body Mass, and Hematological Indices of Male Wistar Rats fed under Equal Environmental Conditions

OBJECTIVE

While the dangers of consuming tobacco by smoking has been of concern, the hazardous effect of other forms of tobacco consumption (in smokeless form) on health indices are less well explored. In this paper, we explored the effect of different doses of aqueous extract of tobacco leaves on feed intake, body mass, and hematological indices of male Wistar rats under equal environmental conditions.

METHOD

Using an oral route of administration, the rats (n = 24; w = 65-85 g; 2-3 weeks old) were administered at different doses of 100, 200, 400, 0 mg/kg body weight (b.w.) per day to group A, B, C, and D for 42 days, after phytochemical and acute toxicity testing of the tobacco leaves.

RESULTS

Compared to the negative control group (D), packed cell volume, hemoglobin concentration, red blood cells, and lymphocytes reduced dose-dependently in contrast to the white blood cells, neutrophils, mean corpuscular hemoglobin concentration, mean corpuscular hemoglobin, and mean corpuscular volume. As body mass and feed intake in relation to the different doses of aqueous extract of tobacco leaves reduced significantly (p < 0.05), the reverse was observed for body mass and feed intake in relation to room temperature.

CONCLUSIONS

By influencing hematological indices, feed intake, and body mass, the extract of tobacco leaves can be hazardous to health. However, to assess safety and to come up with a conscious conclusion, future studies should explore the effect of the extract on organs histopathology, biochemical parameters, and lipid profile of the body.

The impact of donor total estimated blood volume on nucleated cell yield in bone marrow harvests for hematopoietic stem cell transplantation

BACKGROUND

Nucleated cell yields of marrow harvests depend on factors related to donors, the procedure itself, and the volume of marrow harvested. Few attempts have been made to relate donor characteristics to harvest volume. We hypothesize that the percentage of total donor blood volume accessed for harvesting impacts the nucleated cell yield per ml of marrow collected.

METHODS AND MATERIALS

We investigated 481 consecutive unrelated marrow harvests from a single center. Donor characteristics including weight, body mass index (BMI), white blood cells (WBCs), hemoglobin (Hgb), and platelet counts, as well as estimated total blood volume, were recorded and compared with nucleated cell yields and harvest volumes.

RESULTS

The percentage of donor blood volume accessed for marrow harvesting was inversely related to nucleated cell yields (r = -0.57). The donor-recipient weight differential impacted cell yields as well (r = 0.35), with heavier recipients requiring increased marrow volumes from smaller donors to satisfy their nucleated cell needs. 3.73 × 10⁸ /kg of recipient weight could be collected with 95% certainty when harvest volumes did not exceed 16.1% of donor total blood volume. In a stepwise multiple regression analysis, 45.4% of cell yield variance was explained by blood volume percentage accessed for harvesting, donor weight, and WBC. Donor sex, BMI, and platelet counts did not contribute further to cell yield variance. Smokers had higher cell yields than nonsmokers (20.4 vs. 18.3 × 10⁶ /ml; 95% confidence interval 0.62, 3.47) independent of other parameters.

CONCLUSION

Establishing the relationship between percentage of estimated donor total blood volume and recipient cell needs can facilitate donor selection for successful hematopoietic cell (HPC) transplants.

Vagal α7nAChR signaling regulates α7nAChR+Sca1+ cells during lung injury repair

Background

The distal airways of the lung and bone marrow are innervated by the vagus nerve. Vagal α7nAChR signaling plays a key role in regulating lung infection and inflammation; however, whether this pathway regulates α7nAChR⁺Sca1⁺ cells during lung injury repair remains unknown. We hypothesized that vagal α7nAChR signaling controls α7nAChR⁺Sca1⁺ cells, which contribute to the resolution of lung injury.

Methods

Pneumonia was induced by intratracheal challenge with E. coli. The bone marrow mononuclear cells (BM-MNCs) were isolated from the bone marrow of pneumonia mice for immunofluorescence. The bone marrow, blood, BAL, and lung cells were isolated for flow cytometric analysis by labeling with anti-Sca1, VE-cadherin, p-Akt1, or Flk1 antibodies. Immunofluorescence was also used to examine the coexpression of α7nAChR, VE-cadherin, and p-Akt1. Sham, vagotomized, α7nAChR knockout, and Akt1 knockout mice were infected with E. coli to study the regulatory role of vagal α7nAChR signaling and Akt1 in Sca1⁺ cells.

Results

During pneumonia, BM-MNCs were enriched with α7nAChR⁺Sca1⁺ cells, and this cell population proliferated. Transplantation of pneumonia BM-MNCs could mitigate lung injury and increase engraftment in recipient pneumonia lungs. Activation of α7nAChR by its agonist could boost α7nAChR⁺Sca1⁺ cells in the bone marrow, peripheral blood, and bronchoalveolar lavage (BAL) in pneumonia. Immunofluorescence revealed that α7nAChR, VE-cadherin, and p-Akt1 were coexpressed in the bone marrow cells. Vagotomy could reduce α7nAChR⁺VE-cadherin⁺ and VE-cadherin⁺p-Akt1⁺ cells in the bone marrow in pneumonia. Knockout of α7nAChR reduced VE-cadherin⁺ cells and p-Akt1⁺ cells in the bone marrow. Deletion of Akt1 reduced Sca1⁺ cells in the bone marrow and BAL. More importantly, 91.3 ± 4.9% bone marrow and 77.8 ± 4.9% lung α7nAChR⁺Sca1⁺VE-cadherin⁺ cells expressed Flk1, which is a key marker of endothelial progenitor cells (EPCs). Vagotomy reduced α7nAChR⁺Sca1⁺VE-cadherin⁺p-Akt1⁺ cells in the bone marrow and lung from pneumonia mice. Treatment with cultured EPCs reduced ELW compared to PBS treatment in E. coli pneumonia mice at 48 h. The ELW was further reduced by treatment with EPCs combining with α7nAChR agonist-PHA568487 compared to EPC treatments only.

Conclusions

Vagal α7nAChR signaling regulates α7nAChR⁺Sca1⁺VE-cadherin⁺ EPCs via phosphorylation of Akt1 during lung injury repair in pneumonia.

Tuberculosis and cigarette smoke exposure: An update of in vitro and in vivo studies

Tuberculosis (TB) has been declared the first cause of death by an infectious agent. Annually, 10.4 million people suffer active TB. Most infected individuals live in low-income countries, where social and economic conditions enhance the dissemination and progression of the disease. These countries have a high percentage of smokers. Thousands of studies have linked cigarette smoke (CS) with increased risk of many diseases, such as cancer and lung diseases. Numerous in vitro studies have been conducted to evaluate the general and specific toxic effects of CS in lung immune function. Smoke exposure increases the risk of TB development three-fold. However, until now, only few animal studies have been performed to analyze the association between smoke and TB. In the present work, we review in vitro and in vivo studies whose aim was to analyze the molecular basis of TB susceptibility caused by exposure to CS.

Granulocytes as models for human protein marker identification following nicotine exposure

Nicotinic acetylcholine receptors (nAChRs) are pentameric cation channels expressed in the mammalian CNS, in the peripheral nervous system, and in skeletal muscle. Neuronal-type nAChRs are also found in several non-neuronal cell types, including leukocytes. Granulocytes are a subtype of leukocytes that include basophils, eosinophils, and neutrophils. Granulocytes, also known as polymorphonuclear leukocytes, are characterized by their ability to produce, store, and release compounds from intracellular granules. Granulocytes are the most abundant type of leukocyte circulating in the peripheral blood. Granulocyte abundance, nAChR expression, and nAChR upregulation following chronic nicotine administration makes granulocytes interesting models for identifying protein markers of nicotine exposure. Nicotinic receptor subunits and several non-nAChR proteins have been identified as protein markers of granulocyte nicotine exposure. We review methods to isolate granulocytes from human tissue, summarize present data about the expression of nAChRs in the three granulocyte cell types (basophils, eosinophils, and neutrophils), describe current knowledge of the effects of nicotine exposure on human granulocyte protein expression, and highlight areas of interest for future investigation. This is an article for the special issue XVth International Symposium on Cholinergic Mechanisms.

Combined Analysis of Endothelial, Hematopoietic, and Mesenchymal Stem Cell Compartments Shows Simultaneous but Independent Effects of Age and Heart Disease

Clinical trials using stem cell therapy for heart diseases have not reproduced the initial positive results obtained with animal models. This might be explained by a decreased regenerative capacity of stem cells collected from the patients. This work aimed at the simultaneous investigation of endothelial stem/progenitor cells (EPCs), mesenchymal stem/progenitor cells (MSCs), and hematopoietic stem/progenitor cells (HSCs) in sternal bone marrow samples of patients with ischemic or valvular heart disease, using flow cytometry and colony assays. The study included 36 patients referred for coronary artery bypass grafting or valve replacement surgery. A decreased frequency of stem cells was observed in both groups of patients. Left ventricular dysfunction, diabetes, and intermediate risk in EuroSCORE and SYNTAX score were associated with lower EPCs frequency, and the use of aspirin and β-blockers correlated with a higher frequency of HSCs and EPCs, respectively. Most importantly, the distribution of frequencies in the three stem cell compartments showed independent patterns. The combined investigation of the three stem cell compartments in patients with cardiovascular diseases showed that they are independently affected by the disease, suggesting the investigation of prognostic factors that may be used to determine when autologous stem cells may be used in cell therapy.

The effects of water pipe smoking on hematological parameters in rats

OBJECTIVES

This study aimed to investigate the effect of water-pipe (WP) smoking on hematological parameters of Wistar rats.

METHODS

Thirty-five young male rats (200-250 g) were randomly assigned to five groups (n=7). The control group was exposed to room air and the experimental groups were exposed to WP smoking, using a special apparatus designed to have the ability to keep the rats for 40 minutes every day for 4, 8, 12 and 12 weeks; moreover, one of the two groups of 12 weeks of WP exposer had four following weeks of rest. Blood samples were collected to evaluate red blood cell count, hemoglobin, hematocrit, white blood cell and platelet counts.

RESULTS

The results showed that RBC count, Hb and Hct parameters were significantly higher in WP smoking rats than the control group (P< 0.001). We found that WBC counts insignificantly increased (P < 0.39) but Plt counts insignificantly decreased (P < 0.13) in WP smoking rats compared with control group.

CONCLUSION

The findings may help to raise awareness of tobacco smokers about the potential toxicities of WP; likewise, the results can be used by physicians and public health officials in tobacco prevention programs.

Cigarette Smoke Alters the Hematopoietic Stem Cell Niche

Effects of tobacco smoke on hematologic derangements have received little attention. This study employed a mouse model of cigarette smoke exposure to explore the effects on bone marrow niche function. While lung cancer is the most widely studied consequence of tobacco smoke exposure, other malignancies, including leukemia, are associated with tobacco smoke exposure. Animals received cigarette smoke exposure for 6 h/day, 5 days/week for 9 months. Results reveal that the hematopoietic stem and progenitor cell (HSPC) pool size is reduced by cigarette smoke exposure. We next examined the effect of cigarette smoke exposure on one supporting cell type of the niche, the mesenchymal stromal cells (MSCs). Smoke exposure decreased the number of MSCs. Transplantation of naïve HSPCs into irradiated mice with cigarette smoke exposure yielded fewer numbers of engrafted HSPCs. This result suggests that smoke-exposed mice possess dysfunctional niches, resulting in abnormal hematopoiesis. Co-culture experiments using MSCs isolated from control or cigarette smoke-exposed mice with naïve HSPCs in vitro showed that MSCs from cigarette smoke-exposed mice generated marked expansion of naïve HSPCs. These data show that cigarette smoke exposure decreases in vivo MSC and HSC number and also increases pro-proliferative gene expression by cigarette smoke-exposed MSCs, which may stimulate HSPC expansion. These results of this investigation are clinically relevant to both bone marrow donors with a history of smoking and bone marrow transplant (BMT) recipients with a history of smoking.

The α4 nicotinic receptor promotes CD4+ T-cell proliferation and a helper T-cell immune response

Smoking is a common addiction and a leading cause of disease. Chronic nicotine exposure is known to activate nicotinic acetylcholine receptors (nAChRs) in immune cells. We demonstrate a novel role for α4 nAChRs in the effect of nicotine on T-cell proliferation and immunity. Using cell-based sorting and proteomic analysis we define an α4 nAChR expressing helper T-cell population (α4(+)CD3(+)CD4(+)) and show that this group of cells is responsive to sustained nicotine exposure. In the circulation, spleen, bone marrow, and thymus, we find that nicotine promotes an increase in CD3(+)CD4(+) cells via its activation of the α4 nAChR and regulation of G protein subunit o, G protein regulated-inducer of neurite outgrowth, and CDC42 signaling within T cells. In particular, nicotine is found to promote a helper T cell 2 adaptive immunologic response within T cells that is absent in α4(-/-) mice. We thus present a new mechanism of α4 nAChR signaling and immune regulation in T cells, possibly accounting for the effect of smoking on the immune system.

Ion channels in hematopoietic and mesenchymal stem cells

Hematopoietic stem cells (HSCs) reside in bone marrow niches and give rise to hematopoietic precursor cells (HPCs). These have more restricted lineage potential and eventually differentiate into specific blood cell types. Bone marrow also contains mesenchymal stromal cells (MSCs), which present multilineage differentiation potential toward mesodermal cell types. In bone marrow niches, stem cell interaction with the extracellular matrix is mediated by integrin receptors. Ion channels regulate cell proliferation and differentiation by controlling intracellular Ca(2+), cell volume, release of growth factors, and so forth. Although little evidence is available about the ion channel roles in true HSCs, increasing information is available about HPCs and MSCs, which present a complex pattern of K(+) channel expression. K(+) channels cooperate with Ca(2+) and Cl(-) channels in regulating calcium entry and cell volume during mitosis. Other K(+) channels modulate the integrin-dependent interaction between leukemic progenitor cells and the niche stroma. These channels can also regulate leukemia cell interaction with MSCs, which also involves integrin receptors and affects the MSC-mediated protection from chemotherapy. Ligand-gated channels are also implicated in these processes. Nicotinic acetylcholine receptors regulate cell proliferation and migration in HSCs and MSCs and may be implicated in the harmful effects of smoking.

Nicotine and pathological angiogenesis

This paper describes the role of endothelial nicotinic acetylcholine receptors (nAChR) in diseases where pathological angiogenesis plays a role. An extensive review of the literature was performed, focusing on studies that investigated the effect of nicotine upon angiogenesis. Nicotine induces pathological angiogenesis at clinically relevant concentrations (i.e. at tissue and plasma concentrations similar to those of a light to moderate smoker). Nicotine promotes endothelial cell migration, proliferation, survival, tube formation and nitric oxide (NO) production in vitro, mimicking the effect of other angiogenic growth factors. These in vitro findings indicate that there may be an angiogenic component to the pathophysiology of major tobacco related diseases such as carcinoma, atherosclerosis, and age-related macular degeneration. Indeed, nicotine stimulates pathological angiogenesis in pre-clinical models of these disorders. Subsequently, it has been demonstrated that nicotine stimulates nAChRs on the endothelium to induce angiogenic processes, that these nAChRs are largely of the α7 homomeric type, and that there are synergistic interactions between the nAChRs and angiogenic growth factor receptors at the phosphoproteomic and genomic levels. These findings are of potential clinical relevance, and provide mechanistic insights into tobacco-related disease. Furthermore, these findings may lead to novel therapies for diseases characterized by insufficient or inappropriate angiogenesis.

Exposure to nicotine adversely affects the dendritic cell system and compromises host response to vaccination

The magnitude of Th1 cells response to vaccination is a critical factor in determining protection from clinical disease. Our previous in vitro studies suggested that exposure to the nicotine component of cigarette smoke skews the differentiation of both human and mouse dendritic cell (DC) precursors into atypical DCs (DCs differentiated ex vivo in the presence of nicotine) lacking parameters essential for the development of Th1-mediated immunity. In this study, we determined the causal relationship between nicotine-induced DC alterations and host response to vaccines. We show that animals exposed to nicotine failed to develop and maintain Ag-specific effector memory Th1 cells and Ab production to protein-based vaccine formulated with Th1 adjuvants. Accordingly, both prophylactic and therapeutic vaccines failed to protect and cure the nicotine-exposed mice from disease. More importantly, we demonstrate the nicotine-induced defects in the biological activities of in vivo DCs as an underlying mechanism. Indeed, i.v. administration of DCs differentiated in the presence of nicotine preferentially promoted the development of Ag-specific IL-4-producing effector cells in the challenged mice. In addition, DC subsets isolated from mice exposed to nicotine produced significantly less cytokines in response to Th1 adjuvants and inadequately supported the development of Ag-specific Th1 cells. Collectively, our studies suggest that nicotine-induced defects in the DC system compromises vaccine efficacy in smokers.