B lymphocyte-derived acetylcholine limits steady-state and emergency hematopoiesis

Neuroimmune circuits in the plaque and bone marrow regulate atherosclerosis

Atherosclerosis remains the leading cause of death globally. Although its focal pathology is atheroma that develops in arterial walls, atherosclerosis is a systemic disease involving contributions by many organs and tissues. It is now established that the immune system causally contributes to all phases of atherosclerosis. Recent and emerging evidence positions the nervous system as a key modulator of inflammatory processes that underly atherosclerosis. This neuro-immune crosstalk, we are learning, is bidirectional, and immune regulated afferent signaling is becoming increasingly recognized in atherosclerosis. Here, we summarize data and concepts that link the immune and nervous systems in atherosclerosis by focusing on two important sites, the arterial vessel and the bone marrow.

Neuro-immune crosstalk in hematopoiesis, inflammation, and repair

Innate immune cells are primary effectors during host defense and in sterile inflammation. Their production in the bone marrow is tightly regulated by growth and niche factors, and their activity at sites of inflammation is orchestrated by a network of alarmins and cytokines. Yet, recent work highlights a significant role of the peripheral nervous system in these processes. Sympathetic neural pathways play a key role in regulating blood cell homeostasis, and sensory neural pathways mediate pro- or anti-inflammatory signaling in a tissue-specific manner. Here, we review emerging evidence of the fine titration of hematopoiesis, leukocyte trafficking, and tissue repair via neuro-immune crosstalk, and how its derailment can accelerate chronic inflammation, as in atherosclerosis.

Insights into ionizing radiation-induced bone marrow hematopoietic stem cell injury

With the widespread application of nuclear technology across various fields, ionizing radiation-induced injuries are becoming increasingly common. The bone marrow (BM) hematopoietic tissue is a primary target organ of radiation injury. Recent researches have confirmed that ionizing radiation-induced hematopoietic dysfunction mainly results from BM hematopoietic stem cells (HSCs) injury. Additionally, disrupting and reshaping BM microenvironment is a critical factor impacting both the injury and regeneration of HSCs post radiation. However, the regulatory mechanisms of ionizing radiation injury to BM HSCs and their microenvironment remain poorly understood, and prevention and treatment of radiation injury remain the focus and difficulty in radiation medicine research. In this review, we aim to summarize the effects and mechanisms of ionizing radiation-induced injury to BM HSCs and microenvironment, thereby enhancing our understanding of ionizing radiation-induced hematopoietic injury and providing insights for its prevention and treatment in the future.

Bone marrow niches for hematopoietic stem cells: life span dynamics and adaptation to acute stress

ABSTRACT

Hematopoietic stem cells (HSCs) are instrumental for organismal survival because they are responsible for lifelong production of mature blood lineages in homeostasis and response to external stress. To fulfill their function, HSCs rely on reciprocal interactions with specialized tissue microenvironments, termed HSC niches. From embryonic development to advanced aging, HSCs transition through several hematopoietic organs in which they are supported by distinct extrinsic cues. Here, we describe recent discoveries on how HSC niches collectively adapt to ensure robust hematopoietic function during biological aging and after exposure to acute stress. We also discuss the latest strategies leveraging niche-derived signals to revert aging-associated phenotypes and enhance hematopoietic recovery after myeloablation.

Neurotransmitters: Impressive regulators of tumor progression

In contemporary times, tumors have emerged as the primary cause of mortality in the global population. Ongoing research has shed light on the significance of neurotransmitters in the regulation of tumors. It has been established that neurotransmitters play a pivotal role in tumor cell angiogenesis by triggering the transformation of stromal cells into tumor cells, modulating receptors on tumor stem cells, and even inducing immunosuppression. These actions ultimately foster the proliferation and metastasis of tumor cells. Several major neurotransmitters have been found to exert modulatory effects on tumor cells, including the ability to restrict emergency hematopoiesis and bind to receptors on the postsynaptic membrane, thereby inhibiting malignant progression. The abnormal secretion of neurotransmitters is closely associated with tumor progression, suggesting that focusing on neurotransmitters may yield unexpected breakthroughs in tumor therapy. This article presents an analysis and outlook on the potential of targeting neurotransmitters in tumor therapy.

B cells modulate lung antiviral inflammatory responses via the neurotransmitter acetylcholine

The rapid onset of innate immune defenses is critical for early control of viral replication in an infected host, yet it can also lead to irreversible tissue damage, especially in the respiratory tract. Intricate regulatory mechanisms must exist that modulate inflammation, while controlling the infection. Here, B cells expressing choline acetyl transferase (ChAT), an enzyme required for production of the metabolite and neurotransmitter acetylcholine (ACh) are identified as such regulators of the immediate early response to influenza A virus. Lung tissue ChAT + B cells are shown to interact with a7 nicotinic Ach receptor-expressing lung interstitial macrophages in mice within 24h of infection to control their production of TNFa, shifting the balance towards reduced inflammation at the cost of enhanced viral replication. Thus, innate-stimulated B cells are key participants of an immediate-early regulatory cascade that controls lung tissue damage after viral infection.

B cell-mediated antigen presentation promotes adverse cardiac remodeling in chronic heart failure

Cardiovascular disease remains the leading cause of death worldwide. A primary driver of cardiovascular mortality is ischemic heart failure, a form of cardiac dysfunction that can develop in patients who survive myocardial infarction. Acute cardiac damage triggers robust changes in the spleen with rapid migration of immune cells from the spleen to the heart. Activating this "cardio-splenic" axis contributes to progressive cardiac dysfunction. The cardio-splenic axis has, therefore, been identified as a promising therapeutic target to prevent or treat heart failure. However, our understanding of the precise mechanisms by which specific immune cells contribute to adverse cardiac remodeling within the cardio-splenic axis remains limited. Here, we show that splenic B cells contribute to the development of heart failure via MHC II-mediated antigen presentation. We found that the adoptive transfer of splenic B cells from mice with ischemic heart failure promoted adverse cardiac remodeling and splenic inflammatory changes in naïve recipient mice. Based on single-cell RNA sequencing analysis of splenic B cells from mice with ischemic heart failure, we hypothesized that B cells contributed to adverse cardiac remodeling through antigen presentation by MHC II molecules. This mechanism was confirmed using transgenic mice with B cell-specific MHC II deletion, and by analyzing circulating B cells from humans who experienced myocardial infarction. Our results broaden our understanding of B lymphocyte biology, reshape current models of immune activation in response to myocardial injury, and point towards MHC II-mediated signaling in B cells as a novel and specific therapeutic target in chronic heart failure.

B cell-mediated antigen presentation promotes adverse cardiac remodeling in chronic heart failure

Cardiovascular disease remains the leading cause of death worldwide. A primary driver of cardiovascular mortality is ischemic heart failure, a form of cardiac dysfunction that can develop in patients who survive myocardial infarction. Acute cardiac damage triggers robust changes in the spleen with rapid migration of immune cells from the spleen to the heart. Activating this "cardio-splenic" axis contributes to progressive cardiac dysfunction. The cardio-splenic axis has, therefore, been identified as a promising therapeutic target to prevent or treat heart failure. However, our understanding of the precise mechanisms by which specific immune cells contribute to adverse cardiac remodeling within the cardio-splenic axis remains limited. Here, we show that splenic B cells contribute to the development of heart failure via MHC II-mediated antigen presentation. We found that the adoptive transfer of splenic B cells from mice with ischemic heart failure promoted adverse cardiac remodeling and splenic inflammatory changes in naïve recipient mice. Based on single-cell RNA sequencing analysis of splenic B cells from mice with ischemic heart failure, we hypothesized that B cells contributed to adverse cardiac remodeling through antigen presentation by MHC II molecules. This mechanism was confirmed using transgenic mice with B cell-specific MHC II deletion, and by analyzing circulating B cells from humans who experienced myocardial infarction. Our results broaden our understanding of B lymphocyte biology, reshape current models of immune activation in response to myocardial injury, and point towards MHC II-mediated signaling in B cells as a novel and specific therapeutic target in chronic heart failure.

Systemic and local regulation of hematopoietic homeostasis in health and disease

Hematopoietic stem cells (HSCs) generate all blood cell lineages responsible for tissue oxygenation, life-long hematopoietic homeostasis and immune protection. In adulthood, HSCs primarily reside in the bone marrow (BM) microenvironment, consisting of diverse cell types that constitute the stem cell 'niche'. The adaptability of the hematopoietic system is required to respond to the needs of the host, whether to maintain normal physiology or during periods of physical, psychosocial or environmental stress. Hematopoietic homeostasis is achieved by intricate coordination of systemic and local factors that orchestrate the function of HSCs throughout life. However, homeostasis is not a static process; it modulates HSC and progenitor activity in response to circadian rhythms coordinated by the central and peripheral nervous systems, inflammatory cues, metabolites and pathologic conditions. Here, we review local and systemic factors that impact hematopoiesis, focusing on the implications of aging, stress and cardiovascular disease.

From Marrow to Bone and Fat: Exploring the Multifaceted Roles of Leptin Receptor Positive Bone Marrow Mesenchymal Stromal Cells

The bone marrow (BM) stromal cell microenvironment contains non-hematopoietic stromal cells called mesenchymal stromal cells (MSCs). MSCs are plastic adherent, form CFU-Fs, and give rise to osteogenic, adipogenic, chondrogenic progenitors, and most importantly provide HSC niche factor chemokine C-X-C motif ligand 12 (CXCL12) and stem cell factor (SCF). Different authors have defined different markers for mouse MSC identification like PDGFR+Sca-1+ subsets, Nestin+, or LepR+ cells. Of these, the LepR+ cells are the major source of SCF and CXCL12 in the BM microenvironment and play a major role in HSC maintenance and hematopoiesis. LepR+ cells give rise to most of the bones and BM adipocytes, further regulating the microenvironment. In adult BM, LepR+ cells are quiescent but after fracture or irradiation, they proliferate and differentiate into mesenchymal lineage osteogenic, adipogenic and/or chondrogenic cells. They also play a crucial role in the steady-state hematopoiesis process, as well as hematopoietic regeneration and the homing of hematopoietic stem cells (HSCs) after myeloablative injury and/or HSC transplantation. They line the sinusoidal cavities, maintain the trabeculae formation, and provide the space for HSC homing and retention. However, the LepR+ cell subset is heterogeneous; some subsets have higher adipogenic potential, while others express osteollineage-biased genes. Different transcription factors like Early B cell factor 3 (EBF3) or RunX2 help maintain this balance between the self-renewing and committed states, whether osteogenic or adipogenic. The study of LepR+ MSCs holds immense promise for advancing our understanding of HSC biology, tissue regeneration, metabolic disorders, and immune responses. In this review, we will discuss the origin of the BM resident LepR+ cells, different subtypes, and the role of LepR+ cells in maintaining hematopoiesis, osteogenesis, and BM adipogenesis following their multifaceted impact.

Circulating extracellular choline acetyltransferase regulates inflammation

BACKGROUND

Choline acetyltransferase (ChAT) is required for the biosynthesis of acetylcholine, the molecular mediator that inhibits cytokine production in the cholinergic anti-inflammatory pathway of the vagus nerve inflammatory reflex. Abundant work has established the biology of cytoplasmic ChAT in neurons, but much less is known about the potential presence and function of ChAT in the extracellular milieu.

OBJECTIVES

We evaluated the hypothesis that extracellular ChAT activity responds to inflammation and serves to inhibit cytokine release and attenuate inflammation.

METHODS

After developing novel methods for quantification of ChAT activity in plasma, we determined whether ChAT activity changes in response to inflammatory challenges.

RESULTS

Active ChAT circulates within the plasma compartment of mice and responds to immunological perturbations. Following the administration of bacterial endotoxin, plasma ChAT activity increases for 12-48 h, a time period that coincides with declining tumor necrosis factor (TNF) levels. Further, a direct activation of the cholinergic anti-inflammatory pathway by vagus nerve stimulation significantly increases plasma ChAT activity, whereas the administration of bioactive recombinant ChAT (r-ChAT) inhibits endotoxin-stimulated TNF production and anti-ChAT antibodies exacerbate endotoxin-induced TNF levels, results of which suggest that ChAT activity regulates endogenous TNF production. Administration of r-ChAT significantly attenuates pro-inflammatory cytokine production and disease activity in the dextran sodium sulfate preclinical model of inflammatory bowel disease. Finally, plasma ChAT levels are also elevated in humans with sepsis, with the highest levels observed in a patient who succumbed to infection.

CONCLUSION

As a group, these results support further investigation of ChAT as a counter-regulator of inflammation and potential therapeutic agent.

The parasitic worm product ES-62 protects against collagen-induced arthritis by resetting the gut-bone marrow axis in a microbiome-dependent manner

The parasitic worm-derived immunomodulator, ES-62 rescues defective levels of IL-10-producing regulatory B cells (Bregs) and suppresses chronic Th1/Th17-driven inflammation to protect against joint destruction in the mouse collagen-induced arthritis (CIA) model of rheumatoid arthritis. Such autoimmune arthritis is also associated with dysbiosis of the gut microbiota and disruption of intestinal barrier integrity. We recently further exploited the CIA model to show that ES-62's prevention of joint destruction is associated with protection of intestinal barrier integrity and normalization of the gut microbiota, thereby suppressing the gut pathology that precedes the onset of autoimmunity and joint damage in CIA-mice. As the status of the gut microbiota impacts on immune responses by influencing haematopoiesis, we have therefore investigated whether ES-62 harnesses the homeostatic mechanisms regulating this gut-bone marrow (BM) axis to resolve the chronic inflammation promoting autoimmunity and joint destruction in CIA. Reflecting this, ES-62 was found to counteract the BM myeloid/lymphoid bias typically associated with chronic inflammation and infection. This was achieved primarily by ES-62 acting to maintain the levels of lymphoid lineages (B220+ and CD3+ cells) observed in naïve, healthy mice but lost from the BM of CIA-mice. Moreover, ES-62's ability to prevent bone-destroying osteoclastogenesis was found to be associated with its suppression of CIA-induced upregulation of osteoclast progenitors (OCPs) in the BM. Critically, and supporting ES-62's targeting of the gut-BM axis, this rewiring of inflammatory haematopoiesis was lost in mice with a depleted microbiome. Underlining the importance of ES-62's actions in restoring steady-state haematopoiesis, the BM levels of B and T lymphoid cells were shown to be inversely correlated, whilst the levels of OCPs positively correlated, with the severity of joint damage in CIA-mice.

Cholinergic signaling via the α7 nicotinic acetylcholine receptor regulates the migration of monocyte-derived macrophages during acute inflammation

BACKGROUND

The involvement of the autonomic nervous system in the regulation of inflammation is an emerging concept with significant potential for clinical applications. Recent studies demonstrate that stimulating the vagus nerve activates the cholinergic anti-inflammatory pathway that inhibits pro-inflammatory cytokines and controls inflammation. The α7 nicotinic acetylcholine receptor (α7nAChR) on macrophages plays a key role in mediating cholinergic anti-inflammatory effects through a downstream intracellular mechanism involving inhibition of NF-κB signaling, which results in suppression of pro-inflammatory cytokine production. However, the role of the α7nAChR in the regulation of other aspects of the immune response, including the recruitment of monocytes/macrophages to the site of inflammation remained poorly understood.

RESULTS

We observed an increased mortality in α7nAChR-deficient mice (compared with wild-type controls) in mice with endotoxemia, which was paralleled with a significant reduction in the number of monocyte-derived macrophages in the lungs. Corroborating these results, fluorescently labeled α7nAChR-deficient monocytes adoptively transferred to WT mice showed significantly diminished recruitment to the inflamed tissue. α7nAChR deficiency did not affect monocyte 2D transmigration across an endothelial monolayer, but it significantly decreased the migration of macrophages in a 3D fibrin matrix. In vitro analysis of major adhesive receptors (L-selectin, β1 and β2 integrins) and chemokine receptors (CCR2 and CCR5) revealed reduced expression of integrin αM and αX on α7nAChR-deficient macrophages. Decreased expression of αMβ2 was confirmed on fluorescently labeled, adoptively transferred α7nAChR-deficient macrophages in the lungs of endotoxemic mice, indicating a potential mechanism for α7nAChR-mediated migration.

CONCLUSIONS

We demonstrate a novel role for the α7nAChR in mediating macrophage recruitment to inflamed tissue, which indicates an important new aspect of the cholinergic regulation of immune responses and inflammation.

The Impact of the Nervous System on Arteries and the Heart: The Neuroimmune Cardiovascular Circuit Hypothesis

Three systemic biological systems, i.e., the nervous, the immune, and the cardiovascular systems, form a mutually responsive and forward-acting tissue network to regulate acute and chronic cardiovascular function in health and disease. Two sub-circuits within the cardiovascular system have been described, the artery brain circuit (ABC) and the heart brain circuit (HBC), forming a large cardiovascular brain circuit (CBC). Likewise, the nervous system consists of the peripheral nervous system and the central nervous system with their functional distinct sensory and effector arms. Moreover, the immune system with its constituents, i.e., the innate and the adaptive immune systems, interact with the CBC and the nervous system at multiple levels. As understanding the structure and inner workings of the CBC gains momentum, it becomes evident that further research into the CBC may lead to unprecedented classes of therapies to treat cardiovascular diseases as multiple new biologically active molecules are being discovered that likely affect cardiovascular disease progression. Here, we weigh the merits of integrating these recent observations in cardiovascular neurobiology into previous views of cardiovascular disease pathogeneses. These considerations lead us to propose the Neuroimmune Cardiovascular Circuit Hypothesis.

Neuroanatomy of lymphoid organs: Lessons learned from whole-tissue imaging studies

Decades of extensive research have documented the presence of neural innervations of sensory, sympathetic, or parasympathetic origin in primary and secondary lymphoid organs. Such neural inputs can release neurotransmitters and neuropeptides to directly modulate the functions of various immune cells, which represents one of the essential aspects of the body's neuroimmune network. Notably, recent studies empowered by state-of-the-art imaging techniques have comprehensively assessed neural distribution patterns in BM, thymus, spleen, and LNs of rodents and humans, helping clarify several controversies lingering in the field. In addition, it has become evident that neural innervations in lymphoid organs are not static but undergo alterations in pathophysiological contexts. This review aims to update the current information on the neuroanatomy of lymphoid organs obtained through whole-tissue 3D imaging and genetic approaches, focusing on anatomical features that may designate the functional modulation of immune responses. Moreover, we discuss several critical questions that call for future research, which will advance our in-depth understanding of the importance and complexity of neural control of lymphoid organs.

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.

Pharmacological and Electroceutical Targeting of the Cholinergic Anti-Inflammatory Pathway in Autoimmune Diseases

Continuous dialogue between the immune system and the brain plays a key homeostatic role in various immune responses to environmental cues. Several functions are under the control of the vagus nerve-based inflammatory reflex, a physiological mechanism through which nerve signals regulate immune functions. In the cholinergic anti-inflammatory pathway, the vagus nerve, its pivotal neurotransmitter acetylcholine, together with the corresponding receptors play a key role in modulating the immune response of mammals. Through communications of peripheral nerves with immune cells, it modulates proliferation and differentiation activities of various immune cell subsets. As a result, this pathway represents a potential target for treating autoimmune diseases characterized by overt inflammation and a decrease in vagal tone. Consistently, converging observations made in both animal models and clinical trials revealed that targeting the cholinergic anti-inflammatory pathway using pharmacologic approaches can provide beneficial effects. In parallel, bioelectronic medicine has recently emerged as an alternative approach to managing systemic inflammation. In several studies, nerve electrostimulation was reported to be clinically relevant in reducing chronic inflammation in autoimmune diseases, including rheumatoid arthritis and diabetes. In the future, these new approaches could represent a major therapeutic strategy for autoimmune and inflammatory diseases.

Cigarette smoke stimulates clonal expansion of Jak2V617F and Tet2-/- cells

Introduction

Somatic mutations in myeloid growth factor pathway genes, such as JAK2, and genes involved in epigenetic regulation, such as TET2, in hematopoietic stem cells (HSCs) leads to clonal hematopoiesis of indeterminate potential (CHIP) which presents a risk factor for hematologic malignancy and cardiovascular disease. Smoking behavior has been repeatedly associated with the occurrence of CHIP but whether smoking is an environmental inflammatory stressor in promoting clonal expansion has not been investigated.

Methods

We performed in vivo smoke exposures in both wildtype (WT) mice and transplanted mice carrying Jak2V617F mutant and Tet2 knockout (Tet-/-) cells to determine the impact of cigarette smoke (CS) in the HSC compartment as well as favoring mutant cell expansion.

Results

WT mice exposed to smoke displayed increased oxidative stress in long-term HSCs and suppression of the hematopoietic stem and progenitor compartment but smoke exposure did not translate to impaired hematopoietic reconstitution in primary bone marrow transplants. Gene expression analysis of hematopoietic cells in the bone marrow identified an imbalance between Th17 and Treg immune cells suggesting a local inflammatory environment. We also observed enhanced survival of Jak2V617F cells exposed to CS in vivo and cigarette smoke extract (CSE) in vitro. WT bone marrow hematopoietic cells from WT/Jak2V617F chimeric mice exposed to CS demonstrated an increase in neutrophil abundance and distinct overexpression of bone marrow stromal antigen 2 (Bst2) and retinoic acid early transcript 1 (Raet1) targets. Bst2 and Raet1 are indicative of increased interferon signaling and cellular stress including oxidative stress and DNA damage, respectively. In chimeric mice containing both WT and Tet2-/- cells, we observed an increased percentage of circulating mutant cells in peripheral blood post-cigarette smoke exposure when compared to pre-exposure levels while this difference was absent in air-exposed controls.

Conclusion

Altogether, these findings demonstrate that CS results in an inflamed bone marrow environment that provides a selection pressure for existing CHIP mutations such as Jak2V617F and Tet2 loss-of-function.

The Role of Inflammation in the Initiation and Progression of Myeloid Neoplasms

Myeloid malignancies are devastating hematologic cancers with limited therapeutic options. Inflammation is emerging as a novel driver of myeloid malignancy, with important implications for tumor composition, immune response, therapeutic options, and patient survival. Here, we discuss the role of inflammation in normal and malignant hematopoiesis, from clonal hematopoiesis to full-blown myeloid leukemia. We discuss how inflammation shapes clonal output from hematopoietic stem cells, how inflammation alters the immune microenvironment in the bone marrow, and novel therapies aimed at targeting inflammation in myeloid disease.

SIGNIFICANCE

Inflammation is emerging as an important factor in myeloid malignancies. Understanding the role of inflammation in myeloid transformation, and the interplay between inflammation and other drivers of leukemogenesis, may yield novel avenues for therapy.

Cardiovascular Brain Circuits

The cardiovascular system is hardwired to the brain via multilayered afferent and efferent polysynaptic axonal connections. Two major anatomically and functionally distinct though closely interacting subcircuits within the cardiovascular system have recently been defined: The artery-brain circuit and the heart-brain circuit. However, how the nervous system impacts cardiovascular disease progression remains poorly understood. Here, we review recent findings on the anatomy, structures, and inner workings of the lesser-known artery-brain circuit and the better-established heart-brain circuit. We explore the evidence that signals from arteries or the heart form a systemic and finely tuned cardiovascular brain circuit: afferent inputs originating in the arterial tree or the heart are conveyed to distinct sensory neurons in the brain. There, primary integration centers act as hubs that receive and integrate artery-brain circuit-derived and heart-brain circuit-derived signals and process them together with axonal connections and humoral cues from distant brain regions. To conclude the cardiovascular brain circuit, integration centers transmit the constantly modified signals to efferent neurons which transfer them back to the cardiovascular system. Importantly, primary integration centers are wired to and receive information from secondary brain centers that control a wide variety of brain traits encoded in engrams including immune memory, stress-regulating hormone release, pain, reward, emotions, and even motivated types of behavior. Finally, we explore the important possibility that brain effector neurons in the cardiovascular brain circuit network connect efferent signals to other peripheral organs including the immune system, the gut, the liver, and adipose tissue. The enormous recent progress vis-à-vis the cardiovascular brain circuit allows us to propose a novel neurobiology-centered cardiovascular disease hypothesis that we term the neuroimmune cardiovascular circuit hypothesis.

Myocardial Immune Cells: The Basis of Cardiac Immunology

The mammalian heart is characterized by the presence of striated myocytes, which allow continuous rhythmic contraction from early embryonic development until the last moments of life. However, the myocardium contains a significant contingent of leukocytes from every major class. This leukocyte pool includes both resident and nonresident immune cells. Over recent decades, it has become increasingly apparent that the heart is intimately sensitive to immune signaling and that myocardial leukocytes exhibit an array of critical functions, both in homeostasis and in the context of cardiac adaptation to injury. Here, we systematically review current knowledge of all major leukocyte classes in the heart, discussing their functions in health and disease. We also highlight the connection between the myocardium, immune cells, lymphoid organs, and both local and systemic immune responses.

Neuroimmune nexus in the pathophysiology and therapy of inflammatory disorders: role of α7 nicotinic acetylcholine receptors

The α7-nicotinic acetylcholine receptor (α7nAChR) is a key protein in the cholinergic anti-inflammatory pathway (CAP) that links the nervous and immune systems. Initially, the pathway was discovered based on the observation that vagal nerve stimulation (VNS) reduced the systemic inflammatory response in septic animals. Subsequent studies form a foundation for the leading hypothesis about the central role of the spleen in CAP activation. VNS evokes noradrenergic stimulation of ACh release from T cells in the spleen, which in turn activates α7nAChRs on the surface of macrophages. α7nAChR-mediated signaling in macrophages reduces inflammatory cytokine secretion and modifies apoptosis, proliferation, and macrophage polarization, eventually reducing the systemic inflammatory response. A protective role of the CAP has been demonstrated in preclinical studies for multiple diseases including sepsis, metabolic disease, cardiovascular diseases, arthritis, Crohn's disease, ulcerative colitis, endometriosis, and potentially COVID-19, sparking interest in using bioelectronic and pharmacological approaches to target α7nAChRs for treating inflammatory conditions in patients. Despite a keen interest, many aspects of the cholinergic pathway are still unknown. α7nAChRs are expressed on many other subsets of immune cells that can affect the development of inflammation differently. There are also other sources of ACh that modify immune cell functions. How the interplay of ACh and α7nAChR on different cells and in various tissues contributes to the anti-inflammatory responses requires additional study. This review provides an update on basic and translational studies of the CAP in inflammatory diseases, the relevant pharmacology of α7nAChR-activated drugs and raises some questions that require further investigation.

Transcriptional Activation of Regenerative Hematopoiesis via Vascular Niche Sensing

Transition between activation and quiescence programs in hematopoietic stem and progenitor cells (HSC/HSPCs) is perceived to be governed intrinsically and by microenvironmental co-adaptation. However, HSC programs dictating both transition and adaptability, remain poorly defined. Single cell multiome analysis divulging differential transcriptional activity between distinct HSPC states, indicated for the exclusive absence of Fli-1 motif from quiescent HSCs. We reveal that Fli-1 activity is essential for HSCs during regenerative hematopoiesis. Fli-1 directs activation programs while manipulating cellular sensory and output machineries, enabling HSPCs co-adoptability with a stimulated vascular niche. During regenerative conditions, Fli-1 presets and enables propagation of niche-derived Notch1 signaling. Constitutively induced Notch1 signaling is sufficient to recuperate functional HSC impairments in the absence of Fli-1. Applying FLI-1 modified-mRNA transduction into lethargic adult human mobilized HSPCs, enables their vigorous niche-mediated expansion along with superior engraftment capacities. Thus, decryption of stem cell activation programs offers valuable insights for immune regenerative medicine.

Spleen fibroblastic reticular cell-derived acetylcholine promotes lipid metabolism to drive autoreactive B cell responses

Autoreactive B cell responses are essential for the development of systemic lupus erythematosus (SLE). Fibroblastic reticular cells (FRCs) are known to construct lymphoid compartments and regulate immune functions. Here, we identify spleen FRC-derived acetylcholine (ACh) as a key factor that controls autoreactive B cell responses in SLE. In SLE, CD36-mediated lipid uptake leads to enhanced mitochondrial oxidative phosphorylation in B cells. Accordingly, the inhibition of fatty acid oxidation results in reduced autoreactive B cell responses and ameliorated diseases in lupus mice. Ablation of CD36 in B cells impairs lipid uptake and differentiation of autoreactive B cells during autoimmune induction. Mechanistically, spleen FRC-derived ACh promotes lipid influx and generation of autoreactive B cells through CD36. Together, our data uncover a novel function of spleen FRCs in lipid metabolism and B cell differentiation, placing spleen FRC-derived ACh in a key position in promoting autoreactive B cells in SLE.

The roles of bone remodeling in normal hematopoiesis and age-related hematological malignancies

Prior research establishing that bone interacts in coordination with the bone marrow microenvironment (BMME) to regulate hematopoietic homeostasis was largely based on analyses of individual bone-associated cell populations. Recent advances in intravital imaging has suggested that the expansion of hematopoietic stem cells (HSCs) and acute myeloid leukemia cells is restricted to bone marrow microdomains during a distinct stage of bone remodeling. These findings indicate that dynamic bone remodeling likely imposes additional heterogeneity within the BMME to yield differential clonal responses. A holistic understanding of the role of bone remodeling in regulating the stem cell niche and how these interactions are altered in age-related hematological malignancies will be critical to the development of novel interventions. To advance this understanding, herein, we provide a synopsis of the cellular and molecular constituents that participate in bone turnover and their known connections to the hematopoietic compartment. Specifically, we elaborate on the coupling between bone remodeling and the BMME in homeostasis and age-related hematological malignancies and after treatment with bone-targeting approaches. We then discuss unresolved questions and ambiguities that remain in the field.

Mesenchymal stem cells: Emerging concepts and recent advances in their roles in organismal homeostasis and therapy

Stem cells play a crucial role in re-establishing homeostasis in the body, and the search for mechanisms by which they interact with the host to exert their therapeutic effects remains a key question currently being addressed. Considering their significant regenerative/therapeutic potential, research on mesenchymal stem cells (MSCs) has experienced an unprecedented advance in recent years, becoming the focus of extensive works worldwide to develop cell-based approaches for a variety of diseases. Initial evidence for the effectiveness of MSCs therapy comes from the restoration of dynamic microenvironmental homeostasis and endogenous stem cell function in recipient tissues by systemically delivered MSCs. The specific mechanisms by which the effects are exerted remain to be investigated in depth. Importantly, the profound cell-host interplay leaves persistent therapeutic benefits that remain detectable long after the disappearance of transplanted MSCs. In this review, we summarize recent advances on the role of MSCs in multiple disease models, provide insights into the mechanisms by which MSCs interact with endogenous stem cells to exert therapeutic effects, and refine the interconnections between MSCs and cells fused to damaged sites or differentiated into functional cells early in therapy.

SARS-CoV-2 Spike Protein Downregulates Cell Surface α7nAChR through a Helical Motif in the Spike Neck

A deficiency of the functional α7 nicotinic acetylcholine receptor (α7nAChR) impairs neuronal and immune systems. The SARS-CoV-2 spike protein (S12) facilitates virus cell entry during COVID-19 infection and can also independently disrupt cellular functions. Here, we found that S12 expression significantly downregulated surface expression of α7nAChR in mammalian cells. A helical segment of S12 (L1145-L1152) in the spike neck was identified to be responsible for the downregulation of α7nAChR, as the mutant S12AAA (L1145A-F1148A-L1152A) had minimal effects on surface α7nAChR expression. This S12 segment is homologous to the α7nAChR intracellular helical motif known for binding chaperone proteins RIC3 and Bcl-2 to promote α7nAChR surface expression. Competition from S12 for binding these proteins likely underlies suppression of surface α7nAChR. Considering the critical roles of α7nAChR in cellular functions, these findings provide a new perspective for improving mRNA vaccines and developing treatment options for certain symptoms related to long COVID.

Altered Membrane Expression and Function of CD11b Play a Role in the Immunosuppressive Effects of Morphine on Macrophages at the Nanomolar Level

Morphine, one of the most efficacious analgesics, is effective in severe pain, especially in patients with concomitant painful cancers. The clinical use of morphine may be accompanied by increased immunosuppression, susceptibility to infection and postoperative tumor metastatic recurrence, and the specific mechanisms and clinical strategies to alleviate this suppression remain to be investigated. Expression of CD11b is closely associated with the macrophage phagocytosis of xenobiotic particles, bacteria or tumor cells. Here, we find that morphine at 0.1-10 nM levels inhibited CD11b expression and function on macrophages via a μ-opioid receptor (MOR)-dependent mechanism, thereby reducing macrophage phagocytosis of tumor cells, a process that can be reversed by thymopentin (TP5), a commonly used immune-enhancing adjuvant in clinical practice. By knocking down or overexpressing MOR on macrophages and using naloxone, an antagonist of the MOR receptor, and LA1, a molecule that promotes macrophage CD11b activation, we suggest that morphine may regulate macrophage phagocytosis by inhibiting the surface expression and function of macrophage CD11b through the membrane expression and activation of MOR. The CD47/SIRPα axis, which is engaged in macrophage-tumor immune escape, was not significantly affected by morphine. Notably, TP5, when combined with morphine, reversed the inhibition of macrophage phagocytosis by morphine through mechanisms that promote membrane expression of CD11b and modulate its downstream signaling (e.g., NOS2, IFNG, IL1B and TNFA, as well as AGR1, PDGFB, IL6, STAT3, and MYC). Thus, altered membrane expression and function of CD11b may mediate the inhibition of macrophage phagocytosis by therapeutic doses of morphine, and the reversal of this process by TP5 may provide an effective palliative option for clinical immunosuppression by morphine.

Secreted immune metabolites that mediate immune cell communication and function

Metabolites are emerging as essential factors for the immune system that are involved in both metabolic circuits and signaling cascades. Accumulated evidence suggests that altered metabolic programs initiated by the activation and maturation of immune cell types are accompanied by the delivery of various metabolites into the local environment. We propose that, in addition to protein/peptide ligands, secreted immune metabolites (SIMets) are essential components of immune communication networks that fine-tune immune responses under homeostatic and pathological conditions. We summarize recent advances in our understanding of SIMets and discuss the potential mechanisms by which some metabolites engage in immunological responses through receptor-, transporter-, and post-translational-mediated regulation. These insights may contribute to understanding physiology and developing effective therapeutics for inflammatory and immune-mediated diseases.

Neuronal regulation of B-cell immunity: Anticipatory immune posturing?

The brain may sense, evaluate, modulate, and intervene in the operation of immune system, which would otherwise function autonomously in defense against pathogens. Antibody-mediated immunity is one arm of adaptive immunity that may achieve sterilizing protection against infection. Lymphoid organs are densely innervated. Immune cells supporting the antigen-specific antibody response express receptors for neurotransmitters and glucocorticoid hormones, and they are subjected to collective regulation by the neuroendocrine and the autonomic nervous system. Emerging evidence reveals a brain-spleen axis that regulates antigen-specific B cell responses and antibody-mediated immunity. In this article, we provide a synthesis of those studies as pertinent to neuronal regulation of B cell responses in secondary lymphoid organs. We propose the concept of defensive immune posturing as a brain-initiated top-down reaction in anticipation of potential tissue injury that requires immune protection.

Antipsychotic drugs induce vascular defects in hematopoietic organs

Antipsychotic agents are clinically utilized to treat schizophrenia and other mental disorders. These drugs induce neurological and metabolic side effects, but their influence on blood vessels remains largely unknown. Here, we show that haloperidol, one of the most frequently prescribed antipsychotic agents, induces vascular defects in bone marrow. Acute haloperidol treatment results in vascular dilation that is specific to hematopoietic organs. This vessel dilation is associated with disruption of hematopoiesis and hematopoietic stem/progenitor cells (HSPCs), both of which are reversible after haloperidol withdrawal. Mechanistically, haloperidol treatment blocked the secretion of vascular endothelial growth factor A (VEGF-A) from HSPCs. Genetic blockade of VEGF-A secretion from hematopoietic cells or inhibition of VEGFR2 in endothelial cells result in similar vessel dilation in bone marrow during regeneration after irradiation and transplantation. Conversely, VEGF-A gain of function rescues the bone marrow vascular defects induced by haloperidol treatment and irradiation. Our work reveals an unknown effect of antipsychotic agents on the vasculature and hematopoiesis with potential implications for drug application in clinic.

The immune system as a system of relations

Progress in neuroimmunology established that the nervous and the immune systems are two functionally related physiological systems. Unique sensory and immune receptors enable them to control interactions of the organism with the inner and the outer worlds. Both systems undergo an experience-driven selection process during their ontogeny. They share the same mediators/neurotransmitters and use synapses for intercellular communication. They keep a memory of previous experiences. Immune cells can affect nervous cells, nervous cells can affect immune cells, and they regulate each other. I however argue that the two systems differ by three major points: 1) Unlike the nervous system, the immune system has a loose anatomical structure, in which molecular and cellular events mostly occur at random; 2) The immune system can respond to molecules of the living world whereas the nervous system can respond to phenomena of the physical world; 3) Responses of the immune system act both on the organism and on the stimulus that triggered the response, whereas responses of the nervous system act on the organism only. The nervous and the immune systems therefore appear as two complementary systems of relations that closely work together, and whose reactivities are well-suited to deal with physical and biological stimuli, respectively. Its ability both to adapt the organism to the living world and to adapt the living world to the organism endows the immune system with powerful adaptive properties that enable the organism to live in peace with itself and with other living beings, whether pathogens or commensals.

Immune cell cholinergic signaling in adipose thermoregulation and immunometabolism

Research focusing on adipose immunometabolism has been expanded from inflammation in white fat during obesity development to immune cell function regulating thermogenic fat, energy expenditure, and systemic metabolism. This opinion discusses our current understanding of how resident immune cells within the thermogenic fat niche may regulate whole-body energy homeostasis. Furthermore, various types of immune cells can synthesize acetylcholine (ACh) and regulate important physiological functions. We highlight a unique subset of cholinergic macrophages within subcutaneous adipose tissue, termed cholinergic adipose macrophages (ChAMs); these macrophages interact with beige adipocytes through cholinergic receptor nicotinic alpha 2 subunit (CHRNA2) signaling to induce adaptive thermogenesis. We posit that these newly identified thermoregulatory macrophages may broaden our view of immune system functions for maintaining metabolic homeostasis and potentially treating obesity and metabolic disorders.

Gut immune cells—A novel therapeutical target for cardiovascular disease?

Despite scientific and clinical advances during the last 50 years cardiovascular disease continues to be the main cause of death worldwide. Especially patients with diabetes display a massive increased cardiovascular risk compared to patients without diabetes. Over the last two decades we have learned that cardiometabolic and cardiovascular diseases are driven by inflammation. Despite the fact that the gastrointestinal tract is one of the largest leukocyte reservoirs of our bodies, the relevance of gut immune cells for cardiovascular disease is largely unknown. First experimental evidence suggests an important relevance of immune cells in the intestinal tract for the development of metabolic and cardiovascular disease in mice. Mice specifically lacking gut immune cells are protected against obesity, diabetes, hypertension and atherosclerosis. Importantly antibody mediated inhibition of leukocyte homing into the gut showed similar protective metabolic and cardiovascular effects. Targeting gut immune cells might open novel therapeutic approaches for the treatment of cardiometabolic and cardiovascular diseases.

Differential Regulation of Allergic Airway Inflammation by Acetylcholine

Acetylcholine (ACh) from neuronal and non-neuronal sources plays an important role in the regulation of immune responses and is associated with the development of several disease pathologies. We have previously demonstrated that group 2 innate lymphoid cell (ILC2)-derived ACh is required for optimal type 2 responses to parasitic infection and therefore sought to determine whether this also plays a role in allergic inflammation. Rora^Cre+Chat^LoxP mice (in which ILC2s cannot synthesize ACh) were exposed to an allergenic extract of the fungus Alternaria alternata, and immune responses in the airways and lung tissues were analyzed. Airway neutrophilia and expression of the neutrophil chemoattractants CXCL1 and CXCL2 were enhanced 24 h after exposure, suggesting that ILC2-derived ACh plays a role in limiting excessive pulmonary neutrophilic inflammation. The effect of non-selective depletion of ACh was examined by intranasal administration of a stable parasite-secreted acetylcholinesterase. Depletion of airway ACh in this manner resulted in a more profound enhancement of neutrophilia and chemokine expression, suggesting multiple cellular sources for the release of ACh. In contrast, depletion of ACh inhibited Alternaria-induced activation of ILC2s, suppressing the expression of IL-5, IL-13, and subsequent eosinophilia. Depletion of ACh reduced macrophages with an alternatively activated M2 phenotype and an increase in M1 macrophage marker expression. These data suggest that ACh regulates allergic airway inflammation in several ways, enhancing ILC2-driven eosinophilia but suppressing neutrophilia through reduced chemokine expression.

Impaired haematopoietic stem / progenitor cell traffic and multi-organ damage in diabetes

During antenatal development, hematopoietic stem/progenitor cells (HSPCs) arise from a specialized endothelium and migrate from the extraembryonic mesoderm to the fetal liver before establishing hematopoiesis in the bone marrow (BM). It is still debated whether, in adulthood, HSPCs display such ontologic overlap with vascular cells and capacity for endothelial differentiation. Yet, adult HSPCs retain a prominent migratory activity and traffic in the bloodstream to secondary lymphoid organs and all peripheral tissues, before eventually returning to the BM. While patrolling parenchymatous organs, HSPCs locate close to the vasculature, where they establish local hematopoietic islands and contribute to tissue homeostasis by paracrine signals. Solid evidence shows that diabetes mellitus jeopardizes the traffic of HSPCs from BM to the circulation and peripheral tissues, a condition called “mobilopathy.” A reduction in the levels of circulating HSPCs is the most immediate and apparent consequence, which has been consistently observed in human diabetes, and is strongly associated with future risk for multi-organ damage, including micro- and macro-angiopathy. But the shortage of HSPCs in the blood is only the visible tip of the iceberg. Abnormal HSPC traffic results from a complex interplay among metabolism, innate immunity, and hematopoiesis. Notably, mobilopathy is mechanistically connected with diabetes-induced myelopoiesis. Impaired traffic of HSPCs and enhanced generation of pro-inflammatory cells synergize for tissue damage and impair the resolution of inflammation. We herein summarize the current evidence that diabetes affects HSPC traffic, which are the causes and consequences of such alteration, and how it contributes to the overall disease burden.

Chat-ty B cells talk down hematopoiesis

B cells produce acetylcholine that is sensed by bone marrow stromal cells and reduces hematopoiesis.

Bone Marrow Niches of Hematopoietic Stem and Progenitor Cells

The mammalian hematopoietic system is remarkably efficient in meeting an organism’s vital needs, yet is highly sensitive and exquisitely regulated. Much of the organismal control over hematopoiesis comes from the regulation of hematopoietic stem cells (HSCs) by specific microenvironments called niches in bone marrow (BM), where HSCs reside. The experimental studies of the last two decades using the most sophisticated and advanced techniques have provided important data on the identity of the niche cells controlling HSCs functions and some mechanisms underlying niche-HSC interactions. In this review we discuss various aspects of organization and functioning of the HSC cell niche in bone marrow. In particular, we review the anatomy of BM niches, various cell types composing the niche, niches for more differentiated cells, metabolism of HSCs in relation to the niche, niche aging, leukemic transformation of the niche, and the current state of HSC niche modeling in vitro.