Macrophage depletion suppresses sympathetic hyperinnervation following myocardial infarction

Neuro- and immuno-modulation mediated by the cardiac sympathetic nerve: a novel insight into the anti-ischemic efficacy of acupuncture

Communication between sympathetic nerves and the immune system is a crucial and active process during myocardial ischemia (MI), as myocardial damage and inflammatory stimuli concurrently occur. Sympathetic nerves undergo structural and functional changes after MI, leading to adverse left ventricular (LV) remodeling and heart failure (HF). The complex inflammatory response to MI, including local myocardial anti-inflammatory repair and systemic immune reactions, plays a key role in adverse LV remodeling. Here, we review the progressive structural and electrophysiological remodeling of the LV and the involvement of sympathetic tone in complex and dynamic processes that are susceptible to MI pathological conditions. Acupuncture has been reported to effectively improve cardiac function, eliminate arrhythmia, and mitigate adverse LV remodeling via somatosensory regulation after MI. Moreover, acupuncture has an anti-inflammatory effect on the pathological process of myocardial ischemia. In this Review, we aim to summarize the involvement of sympathetic nerve activation in the neuro-immune modulation of structural and functional cardiac changes after MI. As a noninvasive method for sympathetic regulation, acupuncture is an ideal option because of its anti-ischemic efficacy. A better understanding of the neural circuitry that regulates cardiac function and immune responses following MI could reveal novel targets for acupuncture treatment.

Electroacupuncture Improves Cardiac Function via Inhibiting Sympathetic Remodeling Mediated by Promoting Macrophage M2 Polarization in Myocardial Infarction Mice

Electroacupuncture (EA) at the Neiguan acupoint (PC6) has shown significant cardioprotective effects. Sympathetic nerves play an important role in maintaining cardiac function after myocardial infarction (MI). Previous studies have found that EA treatment may improve cardiac function by modulating sympathetic remodeling after MI. However, the mechanism in how EA affects sympathetic remodeling and improves cardiac function remains unclear. The aim of this study is to investigate the cardioprotective mechanism of EA after myocardial ischemic injury by improving sympathetic remodeling and promoting macrophage M2 polarization. We established a mouse model of MI by occluding coronary arteries in male C57/BL6 mice. EA treatment was performed at the PC6 with current intensity (1 mA) and frequency (2/15 Hz). Cardiac function was evaluated using echocardiography. Heart rate variability in mice was assessed via standard electrocardiography. Myocardial fibrosis was evaluated by Sirius red staining. Levels of inflammatory factors were assessed using RT-qPCR. Sympathetic nerve remodeling was assessed through ELISA, western blotting, immunohistochemistry, and immunofluorescence staining. Macrophage polarization was evaluated using flow cytometry. Our results indicated that cardiac systolic function improved significantly after EA treatment, with an increase in fractional shortening and ejection fraction. Myocardial fibrosis was significantly mitigated in the EA group. The sympathetic nerve marker tyrosine hydroxylase and the nerve sprouting marker growth-associated Protein 43 were significantly reduced in the EA group, indicating that sympathetic remodeling was significantly reduced. EA treatment also promoted macrophage M2 polarization, reduced levels of inflammatory factors TNF-α, IL-1β, and IL-6, and decreased macrophage-associated nerve growth factor in myocardial tissue. To sum up, our results suggest that EA at PC6 attenuates sympathetic remodeling after MI to promote macrophage M2 polarization and improve cardiac function.

miR-let-7a inhibits sympathetic nerve remodeling after myocardial infarction by downregulating the expression of nerve growth factor

Objective

Sympathetic hyperinnervation following myocardial infarction (MI) is one of the primary causes of ventricular arrhythmias (VAs) after MI. Nerve growth factor (NGF) is a key molecule that induces sympathetic nerve remodeling. Previous studies have confirmed that microRNA (miR)-let-7a interacts with NGF. However, whether miR-let-7a is involved in sympathetic remodeling after MI remains unknown. We aimed to investigate whether miR-let-7a was associated with the occurrence of VA after MI.

Methods and results

A rat model of myocardial infarction was established using left coronary artery ligation. miR-let-7a expression levels were analyzed by reverse transcription-quantitative PCR. Western blotting was also used to examine NGF expression levels in vivo and in M1 macrophages in vitro. The relationship between miR-let-7a and NGF levels was investigated using a luciferase reporter assay. The results revealed that the expression of miR-let-7a decreased significantly after MI, while NGF expression was significantly upregulated. In addition, overexpression of miR-let-7a effectively inhibited NGF expression in rats, which was also verified in M1 macrophages. Tyrosine hydroxylase and growth-associated protein 43 immunofluorescence results revealed that the administration of a miR-let-7a overexpression lentivirus to rats inhibited sympathetic remodeling after MI. Programmed electrical stimulation, renal sympathetic nerve activity recording, and heart rate variability measurements showed that miR-let-7a overexpression decreased sympathetic activity.

Conclusions

These findings provide novel insights into the molecular mechanisms by which miR-let-7a and NGF contribute to the progression of sympathetic nerve remodeling after MI. Therefore, miR-let-7a may be a promising therapeutic target to reduce the incidence of arrhythmia following MI.

Sympathetic hyperinnervation drives abdominal aortic aneurysm development by promoting vascular smooth muscle cell phenotypic switching

INTRODUCTION

Sympathetic hyperinnervation plays an important role in modulating the vascular smooth muscle cell (VSMC) phenotype and vascular diseases, but its role in abdominal aortic aneurysm (AAA) is still unknown.

OBJECTIVES

This study aimed to investigate the role of sympathetic hyperinnervation in promoting AAA development and the underlying mechanism involved.

METHODS

Western blotting and immunochemical staining were used to detect sympathetic hyperinnervation. We performed sympathetic denervation through coeliac ganglionectomy (CGX) and 6-OHDA administration to understand the role of sympathetic hyperinnervation in AAA and investigated the underlying mechanisms through transcriptome and functional studies. Sema4D knockout (Sema4D-/-) mice were utilized to determine the involvement of Sema4D in inducing sympathetic hyperinnervation and AAA development.

RESULTS

We observed sympathetic hyperinnervation, the most important form of sympathetic neural remodeling, in both mouse AAA models and AAA patients. Elimination of sympathetic hyperinnervation by CGX or 6-OHDA significantly inhibited AAA development and progression. We further revealed that sympathetic hyperinnervation promoted VSMC phenotypic switching in AAA by releasing extracellular ATP (eATP) and activating eATP-P2rx4-p38 signaling. Moreover, single-cell RNA sequencing revealed that Sema4D secreted by osteoclast-like cells induces sympathetic nerve diffusion and hyperinnervation through binding to Plxnb1. We consistently observed that AAA progression was significantly ameliorated in Sema4D-deficient mice.

CONCLUSIONS

Sympathetic hyperinnervation driven by osteoclast-like cell-derived Sema4D promotes VSMC phenotypic switching and accelerates pathological aneurysm progression by activating the eATP/P2rx4/p38 pathway. Inhibition of sympathetic hyperinnervation emerges as a potential novel therapeutic strategy for preventing and treating AAA.

Atorvastatin, etanercept and the nephrogenic cardiac sympathetic remodeling in chronic renal failure rats

BACKGROUND

Chronic renal failure (CRF) patients are predisposed to arrhythmias, while the detailed mechanisms are unclear. We hypothesized the chronic inflammatory state of CRF patients may lead to cardiac sympathetic remodeling, increasing the incidence of ventricular arrhythmia (VA) and sudden cardiac death. And explored the role of atorvastatin and etanercept in this process.

METHODS

A total of 48 rats were randomly divided into sham operation group (Sham group), CRF group, CRF + atorvastatin group (CRF + statin group), and CRF + etanercept group (CRF + rhTNFR-Fc group). Sympathetic nerve remodeling was assessed by immunofluorescence of growth-associated protein 43 (GAP-43) and tyrosine hydroxylase positive area fraction. Electrophysiological testing was performed to assess the incidence of VA by assessing the ventricular effective refractory period and ventricular fibrillation threshold. The levels of tumor necrosis factor-alpha (TNF-α) and interleukin-1beta were determined by Western blotting and enzyme-linked immunosorbent assay.

RESULTS

Echocardiogram showed that compared with the Sham group, left ventricular end-systolic diameter and ventricular weight/body weight ratio were significantly higher in the CRF group. Hematoxylin-eosin and Masson staining indicated that myocardial fibers were broken, disordered, and fibrotic in the CRF group. Western blotting, enzyme-linked immunosorbent assay, immunofluorescence and electrophysiological examination suggested that compared with the Sham group, GAP-43 and TNF-α proteins were significantly upregulated, GAP-43 and tyrosine hydroxylase positive nerve fiber area was increased, and ventricular fibrillation threshold was significantly decreased in the CRF group. The above effects were inhibited in the CRF + statin group and the CRF + rhTNFR-Fc group.

CONCLUSIONS

In CRF rats, TNF-α was upregulated, cardiac sympathetic remodeling was more severe, and the nephrogenic cardiac sympathetic remodeling existed. Atorvastatin and etanercept could downregulate the expression of TNF-α or inhibit its activity, thus inhibited the above effects, and reduced the occurrence of VA and sudden cardiac death.

Gabapentin attenuates cardiac remodeling after myocardial infarction by inhibiting M1 macrophage polarization through the peroxisome proliferator-activated receptor-γ pathway

OBJECTIVES

Inflammation regulates ventricular remodeling after myocardial infarction (MI), and gabapentin exerts anti-inflammatory effects. We investigated the anti-inflammatory role and mechanism of gabapentin after MI.

METHODS

Rats were divided into the sham group (n = 12), MI group (n = 20), and MI + gabapentin group (n = 16). MI was induced by left coronary artery ligation. The effects of gabapentin on THP-1-derived macrophages were examined in vitro.

RESULTS

In vivo, 1 week after MI, gabapentin significantly reduced inducible nitric oxide synthase (iNOS; M1 macrophage marker) expression and decreased pro-inflammatory factors (tumor necrosis factor [TNF]-α and interleukin [IL]-1β). Gabapentin upregulated the M2 macrophage marker arginase-1, as well as CD163 expression, and increased the expression of anti-inflammatory factors, including chitinase-like 3, IL-10, and transforming growth factor-β. Four weeks after MI, cardiac function, infarct size, and cardiac fibrosis improved after gabapentin treatment. Gabapentin inhibited sympathetic nerve activity and decreased ventricular electrical instability in rats after MI. Tyrosine hydroxylase and growth-associated protein 43 were suppressed after gabapentin treatment. Gabapentin downregulated nerve growth factor (NGF) and reduced pro-inflammatory factors (iNOS, TNF-α, and IL-1β). In vitro, gabapentin reduced NGF, iNOS, TNF-α, and IL-1β expression in lipopolysaccharide-stimulated macrophages. Mechanistic studies revealed that the peroxisome proliferator-activated receptor-γ antagonist GW9662 attenuated the effects of gabapentin. Moreover, gabapentin reduced α2δ1 expression in the macrophage plasma membrane and reduced the calcium content of macrophages.

CONCLUSION

Gabapentin attenuates cardiac remodeling by inhibiting inflammation via peroxisome proliferator-activated receptor-γ activation and preventing calcium overload.

Cardiac sympathetic hyperinnervation after myocardial infarction: a systematic review and qualitative analysis

BACKGROUND

Cardiac sympathetic hyperinnervation after myocardial infarction (MI) is associated with arrhythmogenesis and sudden cardiac death. The characteristics of cardiac sympathetic hyperinnervation remain underexposed.

OBJECTIVE

To provide a systematic review on cardiac sympathetic hyperinnervation after MI, taking into account: (1) definition, experimental model and quantification method and (2) location, amount and timing, in order to obtain an overview of current knowledge and to expose gaps in literature.

METHODS

References on cardiac sympathetic hyperinnervation were screened for inclusion. The included studies received a full-text review and quality appraisal. Relevant data on hyperinnervation were collected and qualitatively analysed.

RESULTS

Our literature search identified 60 eligible studies performed between 2000 and 2022. Cardiac hyperinnervation is generally defined as an increased sympathetic nerve density or increased number of nerves compared to another control group (100%). Studies were performed in a multitude of experimental models, but most commonly in male rats with permanent left anterior descending (LAD) artery ligation (male: 63%, rat: 68%, permanent ligation: 93%, LAD: 97%). Hyperinnervation seems to occur mainly in the borderzone. Quantification after MI was performed in regions of interest in µm2/mm2 (41%) or in percentage of nerve fibres (46%) and the reported amount showed a great variation ranging from 439 to 126,718 µm2/mm2. Hyperinnervation seems to start from three days onwards to >3 months without an evident peak, although studies on structural evaluation over time and in the chronic phase were scarce.

CONCLUSIONS

Cardiac sympathetic hyperinnervation after MI occurs mainly in the borderzone from three days onwards and remains present at later timepoints, for at least 3 months. It is most commonly studied in male rats with permanent LAD ligation. The amount of hyperinnervation differs greatly between studies, possibly due to differential quantification methods. Further studies are required that evaluate cardiac sympathetic hyperinnervation over time and in the chronic phase, in transmural sections, in the female sex, and in MI with reperfusion.

Gastrin attenuates sepsis-induced myocardial dysfunction by down-regulation of TLR4 expression in macrophages

Myocardial dysfunction is the most serious complication of sepsis. Sepsis-induced myocardial dysfunction (SMD) is often associated with gastrointestinal dysfunction, but its pathophysiological significance remains unclear. The present study found that patients with SMD had higher plasma gastrin concentrations than those without SMD. In mice, knockdown of the gastrin receptor, cholecystokinin B receptor (Cckbr), aggravated lipopolysaccharide (LPS)-induced cardiac dysfunction and increased inflammation in the heart, whereas the intravenous administration of gastrin ameliorated SMD and cardiac injury. Macrophage infiltration plays a significant role in SMD because depletion of macrophages by the intravenous injection of clodronate liposomes, 48 h prior to LPS administration, alleviated LPS-induced cardiac injury in Cckbr-deficient mice. The intravenous injection of bone marrow macrophages (BMMs) overexpressing Cckbr reduced LPS-induced myocardial dysfunction. Furthermore, gastrin treatment inhibited toll-like receptor 4 (TLR4) expression through the peroxisome proliferator-activated receptor α (PPAR-α) signaling pathway in BMMs. Thus, our findings provide insights into the mechanism of the protective role of gastrin/CCKBR in SMD, which could be used to develop new treatment modalities for SMD.

Gut microbiota and cardiac arrhythmia

One of the most prevalent cardiac diseases is cardiac arrhythmia, however the underlying causes are not entirely understood. There is a lot of proof that gut microbiota (GM) and its metabolites have a significant impact on cardiovascular health. In recent decades, intricate impacts of GM on cardiac arrythmia have been identified as prospective approaches for its prevention, development, treatment, and prognosis. In this review, we discuss about how GM and its metabolites might impact cardiac arrhythmia through a variety of mechanisms. We proposed to explore the relationship between the metabolites produced by GM dysbiosis including short-chain fatty acids(SCFA), Indoxyl sulfate(IS), trimethylamine N-oxide(TMAO), lipopolysaccharides(LPS), phenylacetylglutamine(PAGln), bile acids(BA), and the currently recognized mechanisms of cardiac arrhythmias including structural remodeling, electrophysiological remodeling, abnormal nervous system regulation and other disease associated with cardiac arrythmia, detailing the processes involving immune regulation, inflammation, and different types of programmed cell death etc., which presents a key aspect of the microbial-host cross-talk. In addition, how GM and its metabolites differ and change in atrial arrhythmias and ventricular arrhythmias populations compared with healthy people are also summarized. Then we introduced potential therapeutic strategies including probiotics and prebiotics, fecal microbiota transplantation (FMT) and immunomodulator etc. In conclusion, the GM has a significant impact on cardiac arrhythmia through a variety of mechanisms, offering a wide range of possible treatment options. The discovery of therapeutic interventions that reduce the risk of cardiac arrhythmia by altering GM and metabolites is a real challenge that lies ahead.

Autonomic nervous system and cardiac neuro-signaling pathway modulation in cardiovascular disorders and Alzheimer's disease

The heart is a functional syncytium controlled by a delicate and sophisticated balance ensured by the tight coordination of its several cell subpopulations. Accordingly, cardiomyocytes together with the surrounding microenvironment participate in the heart tissue homeostasis. In the right atrium, the sinoatrial nodal cells regulate the cardiac impulse propagation through cardiomyocytes, thus ensuring the maintenance of the electric network in the heart tissue. Notably, the central nervous system (CNS) modulates the cardiac rhythm through the two limbs of the autonomic nervous system (ANS): the parasympathetic and sympathetic compartments. The autonomic nervous system exerts non-voluntary effects on different peripheral organs. The main neuromodulator of the Sympathetic Nervous System (SNS) is norepinephrine, while the principal neurotransmitter of the Parasympathetic Nervous System (PNS) is acetylcholine. Through these two main neurohormones, the ANS can gradually regulate cardiac, vascular, visceral, and glandular functions by turning on one of its two branches (adrenergic and/or cholinergic), which exert opposite effects on targeted organs. Besides these neuromodulators, the cardiac nervous system is ruled by specific neuropeptides (neurotrophic factors) that help to preserve innervation homeostasis through the myocardial layers (from epicardium to endocardium). Interestingly, the dysregulation of this neuro-signaling pathway may expose the cardiac tissue to severe disorders of different etiology and nature. Specifically, a maladaptive remodeling of the cardiac nervous system may culminate in a progressive loss of neurotrophins, thus leading to severe myocardial denervation, as observed in different cardiometabolic and neurodegenerative diseases (myocardial infarction, heart failure, Alzheimer's disease). This review analyzes the current knowledge on the pathophysiological processes involved in cardiac nervous system impairment from the perspectives of both cardiac disorders and a widely diffused and devastating neurodegenerative disorder, Alzheimer's disease, proposing a relationship between neurodegeneration, loss of neurotrophic factors, and cardiac nervous system impairment. This overview is conducive to a more comprehensive understanding of the process of cardiac neuro-signaling dysfunction, while bringing to light potential therapeutic scenarios to correct or delay the adverse cardiovascular remodeling, thus improving the cardiac prognosis and quality of life in patients with heart or neurodegenerative disorders.

lncRNA LOC100911717-targeting GAP43-mediated sympathetic remodeling after myocardial infarction in rats

Objective

Sympathetic remodeling after myocardial infarction (MI) is the primary cause of ventricular arrhythmias (VAs), leading to sudden cardiac death (SCD). M1-type macrophages are closely associated with inflammation and sympathetic remodeling after MI. Long noncoding RNAs (lncRNAs) are critical for the regulation of cardiovascular disease development. Therefore, this study aimed to identify the lncRNAs involved in MI and reveal a possible regulatory mechanism.

Methods and results

M0- and M1-type macrophages were selected for sequencing and screened for differentially expressed lncRNAs. The data revealed that lncRNA LOC100911717 was upregulated in M1-type macrophages but not in M0-type macrophages. In addition, the lncRNA LOC100911717 was upregulated in heart tissues after MI. Furthermore, an RNA pull-down assay revealed that lncRNA LOC100911717 could interact with growth-associated protein 43 (GAP43). Essentially, immunofluorescence assays and programmed electrical stimulation demonstrated that GAP43 expression was suppressed and VA incidence was reduced after lncRNA LOC100911717 knockdown in rat hearts using an adeno-associated virus.

Conclusions

We observed a novel relationship between lncRNA LOC100911717 and GAP43. After MI, lncRNA LOC100911717 was upregulated and GAP43 expression was enhanced, thus increasing the extent of sympathetic remodeling and the frequency of VA events. Consequently, silencing lncRNA LOC100911717 could reduce sympathetic remodeling and VAs.

Macrophages in myocardial infarction

The heart contains a population of resident macrophages that markedly expands following injury through recruitment of monocytes and through proliferation of macrophages. In myocardial infarction, macrophages have been implicated in both injurious and reparative responses. In coronary atherosclerotic lesions, macrophages have been implicated in disease progression and in the pathogenesis of plaque rupture. Following myocardial infarction, resident macrophages contribute to initiation and regulation of the inflammatory response. Phagocytosis and efferocytosis are major functions of macrophages during the inflammatory phase of infarct healing, and mediate phenotypic changes, leading to acquisition of an anti-inflammatory macrophage phenotype. Infarct macrophages respond to changes in the cytokine content and extracellular matrix composition of their environment and secrete fibrogenic and angiogenic mediators, playing a central role in repair of the infarcted heart. Macrophages may also play a role in scar maturation and may contribute to chronic adverse remodeling of noninfarcted segments. Single cell studies have revealed a remarkable heterogeneity of macrophage populations in infarcted hearts; however, the relations between transcriptomic profiles and functional properties remain poorly defined. This review manuscript discusses the fate, mechanisms of expansion and activation, and role of macrophages in the infarcted heart. Considering their critical role in injury, repair, and remodeling, macrophages are important, but challenging, targets for therapeutic interventions in myocardial infarction.

Muscle contractile exercise through a belt electrode device prevents myofiber atrophy, muscle contracture, and muscular pain in immobilized rat gastrocnemius muscle

Purpose

Immobilization of skeletal muscles causes muscle atrophy, muscle contracture, and muscle pain, the mechanisms of which are related to macrophage accumulation. However, muscle contractile exercise through a belt electrode device may mitigate macrophage accumulation. We hypothesized that such exercise would be effective in preventing myofiber atrophy, muscle contracture, and muscular pain. This study tested this hypothesis in immobilized rat gastrocnemius muscle.

Materials and methods

A total of 32 rats were divided into the following control and experimental groups: immobilization (immobilized treatment only), low-frequency (LF; immobilized treatment and muscle contractile exercise with a 2 s (do) /6 s (rest) duty cycle), and high-frequency (HF; immobilized treatment and muscle contractile exercise with a 2 s (do)/2 s (rest) duty cycle). Electrical stimulation was performed at 50 Hz and 4.7 mA, and muscle contractile exercise was applied to the lower limb muscles for 15 or 20 min/session (once daily) for 2 weeks (6 times/week). After the behavioral tests, the bilateral gastrocnemius muscles were collected for analysis.

Results

The number of macrophages, the Atrogin-1 and MuRF-1 mRNA expression, and the hydroxyproline content in the HF group were lower than those in the immobilization and LF groups. The cross-sectional area (CSA) of type IIb myofibers in the superficial region, the PGC-1α mRNA expression, and the range of motion of dorsiflexion in the HF group were significantly higher than those in the immobilization and LF groups. The pressure pain thresholds in the LF and HF groups were significantly higher than that in the immobilization group, and the nerve growth factor (NGF) content in the LF and HF groups was significantly lower than that in the immobilization group.

Conclusion

Muscle contractile exercise through the belt electrode device may be effective in preventing immobilization-induced myofiber atrophy, muscle contracture, and muscular pain in the immobilized rat gastrocnemius muscle.

m6A methyltransferase METTL3 participated in sympathetic neural remodeling post-MI via the TRAF6/NF-κB pathway and ROS production

OBJECTIVE

Sudden cardiac death caused by ventricular arrhythmias (VAs) is the main cause of high mortality in patients with myocardial infarction (MI). Sympathetic neural remodeling caused by inflammation after MI is closely associated with the occurrence of VAs. METTL3, the earliest identified m⁶A methyltransferase, is critical in mediating inflammatory responses. Our aim was to investigate whether the m⁶A methyltransferase METTL3 was involved in sympathetic remodeling post-MI and its specific mechanism.

METHODS AND RESULTS

A rat MI model was established via left coronary artery ligation. The expression of METTL3, TRAF6, NOX2, and NF-κB increased at 3 days and remained elevated at 7 days after MI, as determined via Western blotting. METTL3 was primarily present in macrophages, as determined via immunofluorescence. Intramyocardial injection of lentivirus carrying METTL3-shRNA inhibited METTL3 expression in vivo. Methylated immunoprecipitation-qPCR determined the METTL3 knockdown inhibited the m⁶A level of TRAF6 mRNA 3'-UTR. The co-immunoprecipitation experiment proved that METTL3 combines with TRAF6. Western blotting showed that silencing METTL3 inhibited TRAF6 level, NF-κB activation, and ROS production; decreased cytokine release (TNF-α and IL-1β); and downregulated nerve growth factor expression. Finally, METTL3 knockdown reduced sympathetic remodeling after MI, as determined via immunofluorescence assays of tyrosine hydroxylase and growth-associated protein 43. Programmed electrical stimulation, renal sympathetic nerve activity recording, and haemodynamic measurements showed that METTL3 inhibition decreased sympathetic activity and improved cardiac function.

CONCLUSIONS

Downregulation of METTL3 expression attenuated the excessive sympathetic neural remodeling induced by MI, further reducing the incidence of VAs and improving cardiac function. This was partly associated with the inhibition of the TRAF6/NF-κB pathway and ROS production.

Immune remodeling and atrial fibrillation

Atrial fibrillation (AF) is a highly prevalent arrhythmia that causes high morbidity and mortality. However, the underlying mechanism of AF has not been fully elucidated. Recent research has suggested that, during AF, the immune system changes considerably and interacts with the environment and cells involved in the initiation and maintenance of AF. This may provide a new direction for research and therapeutic strategies for AF. In this review, we elaborate the concept of immune remodeling based on available data in AF. Then, we highlight the complex relationships between immune remodeling and atrial electrical, structural and neural remodeling while also pointing out some research gaps in these field. Finally, we discuss several potential immunomodulatory treatments for AF. Although the heterogeneity of existing evidence makes it ambiguous to extrapolate immunomodulatory treatments for AF into the clinical practice, immune remodeling is still an evolving concept in AF pathophysiology and further studies within this field are likely to provide effective therapies for AF.

Sinapic Acid Attenuated Cardiac Remodeling After Myocardial Infarction by Promoting Macrophage M2 Polarization Through the PPARγ Pathway

Background

Macrophage polarization is an important regulatory mechanism of ventricular remodeling. Studies have shown that sinapic acid (SA) exerts an anti-inflammatory effect. However, the effect of SA on macrophages is still unclear.

Objectives

The purpose of the study was to investigate the role of SA in macrophage polarization and ventricular remodeling after myocardial infarction (MI).

Methods

An MI model was established by ligating the left coronary artery. The rats with MI were treated with SA for 1 or 4 weeks after MI. The effect of SA on bone marrow-derived macrophages (BMDMs) was also observed in vitro.

Results

Cardiac systolic dysfunction was significantly improved after SA treatment. SA reduced MCP-1 and CCR2 expression and macrophage infiltration. SA decreased the levels of the inflammatory factors TNF-α, IL-1α, IL-1β, and iNOS and increased the levels of the M2 macrophage markers CD206, Arg-1, IL-10, Ym-1, Fizz-1, and TGF-β at 1 week after MI. SA significantly increased CD68⁺/CD206⁺ macrophage infiltration. Myocardial interstitial fibrosis and MMP-2 and MMP-9 levels were decreased, and the sympathetic nerve marker TH and nerve sprouting marker GAP43 were suppressed after SA treatment at 4 weeks after MI. The PPARγ level was notably upregulated after SA treatment. In vitro, SA also increased the expression of PPARγ mRNA in BMDMs and IL-4-treated BMDMs in a concentration-dependent manner. SA enhanced Arg1 and IL-10 expression in BMDMs, and the PPARγ antagonist GW9662 attenuated M2 macrophage marker expression.

Conclusions

Our results demonstrated that SA attenuated structural and neural remodeling by promoting macrophage M2 polarization via PPARγ activation after MI.

Cardiac Macrophages and Their Effects on Arrhythmogenesis

Cardiac electrophysiology is a complex system established by a plethora of inward and outward ion currents in cardiomyocytes generating and conducting electrical signals in the heart. However, not only cardiomyocytes but also other cell types can modulate the heart rhythm. Recently, cardiac macrophages were demonstrated as important players in both electrophysiology and arrhythmogenesis. Cardiac macrophages are a heterogeneous group of immune cells including resident macrophages derived from embryonic and fetal precursors and recruited macrophages derived from circulating monocytes from the bone marrow. Recent studies suggest antiarrhythmic as well as proarrhythmic effects of cardiac macrophages. The proposed mechanisms of how cardiac macrophages affect electrophysiology vary and include both direct and indirect interactions with other cardiac cells. In this review, we provide an overview of the different subsets of macrophages in the heart and their possible interactions with cardiomyocytes under both physiologic conditions and heart disease. Furthermore, we elucidate similarities and differences between human, murine and porcine cardiac macrophages, thus providing detailed information for researchers investigating cardiac macrophages in important animal species for electrophysiologic research. Finally, we discuss the pros and cons of mice and pigs to investigate the role of cardiac macrophages in arrhythmogenesis from a translational perspective.

17β-Oestradiol facilitates M2 macrophage skewing and ameliorates arrhythmias in ovariectomized female infarcted rats

Epidemiological studies have suggested a lower incidence of arrhythmia‐induced sudden cardiac death in women than in men. 17β‐oestradiol (E2) has been reported to have a post‐myocardial infarction antiarrhythmic effect, although the mechanisms have yet to be elucidated. We investigated whether E2‐mediated antioxidation regulates macrophage polarization and affects cardiac sympathetic reinnervation in rats after MI. Ovariectomized Wistar rats were randomly assigned to placebo pellets, E2 treatment, or E2 treatment +3‐morpholinosydnonimine (a peroxynitrite generator) and followed for 4 weeks. The infarct sizes were similar among the infarcted groups. At Day 3 after infarction, post‐infarction was associated with increased superoxide levels, which were inhibited by administering E2. E2 significantly increased myocardial IL‐10 levels and the percentage of regulatory M2 macrophages compared with the ovariectomized infarcted alone group as assessed by immunohistochemical staining, Western blot and RT‐PCR. Nerve growth factor colocalized with both M1 and M2 macrophages at the magnitude significantly higher in M1 compared with M2. At Day 28 after infarction, E2 was associated with attenuated myocardial norepinephrine levels and sympathetic hyperinnervation. These effects of E2 were functionally translated in inhibiting fatal arrhythmias. The beneficial effect of E2 on macrophage polarization and sympathetic hyperinnervation was abolished by 3‐morpholinosydnonimine. Our results indicated that E2 polarized macrophages into the M2 phenotype by inhibiting the superoxide pathway, leading to attenuated nerve growth factor‐induced sympathetic hyperinnervation after myocardial infarction.

Impact of Yiqi Huoxue Decoction on the Relationship between Remodeling of Cardiac Nerves and Macrophages after Myocardial Infarction in Rats

Sympathetic nerve remodeling after myocardial infarction (MI) has an indispensable role in cardiac remodeling. Numerous works have shown that sympathetic nerve remodeling can be delayed by inhibition of inflammatory response. Earlier studies have shown improvement in ventricular remodeling and inhibited chronic stage neural remodeling by Yiqi Huoxue decoction (YQHX). Therefore, the current study looked at the inhibitory effect of YQHX prescription on proinflammatory mediators and macrophages and the effect on neural remodeling at 3 and 7 days after MI. YQHX inhibited the expression of Toll-like receptor 4 (TLR4) and nuclear factor kappa B (NF-κB) proteins and macrophage infiltration within 7 days after myocardial infarction. YQHX could decrease Th-positive nerve fiber density in the area around infarction and reduce the expression of growth-associated protein 43 (GAP43), nerve growth factor (NGF), and tyrosine hydroxylase (TH) proteins, which was associated with the remodeling of sympathetic nerves. Thus, the nerve remodeling inhibition after MI due to YQHX may be through its anti-inflammatory action. These data provide direct evidence for the potential application of traditional Chinese medicine (TCM) in the remodeling of sympathetic nerves after MI.

Macrophages Can Drive Sympathetic Excitability in the Early Stages of Hypertension

Hypertension is a major health burden worldwide with many cases resistant to current treatments. Hyperactivity of the sympathetic nervous contributes to the etiology and progression of the disease, where emerging evidence suggests that inflammation may underpin the development of sympathetic dysautonomia. This study examined whether macrophages could drive the sympathetic phenotype in Spontaneously Hypertensive Rats (SHR) before animals develop high pressure. Stellate neurons from wild-type control Wistar rats and SHRs were co-cultured with blood leukocytes from their own strain, and also crossed cultured between strains. The calcium transient response to nicotinic stimulation was recorded using Fura-2 calcium imaging, where SHR neurons had a greater calcium transient compared with Wistar neurons. However, when co-cultured with leukocytes, Wistar neurons began to phenocopy the SHR sympathetic hyperactivity, while the SHR neurons themselves were unaltered. Resident leukocyte populations of the SHR and Wistar stellate ganglia were then compared using flow cytometry, where there was a shift in monocyte-macrophage subset proportions. While classical monocyte-macrophages were predominant in the Wistar, there were relatively more of the non-classical subset in the SHR, which have been implicated in pro-inflammatory roles in a number of diseases. When bone marrow-derived macrophages (BMDMs) were co-cultured with stellate neurons, they made Wistar neurons recapitulate the SHR nicotinic stimulated calcium transient. Wistar BMDMs however, had no effect on SHR neurons, even though SHR BMDMs increased SHR neuron responsiveness further above their hyper-responsive state. Taken together, these findings show that macrophages can be potent enhancers of sympathetic neuronal calcium responsiveness, and thus could conceivably play a role in peripheral sympathetic hyperactivity observed in the early stages of hypertension.

Clodronate Treatment Prevents Vaginal Hypersensitivity in a Mouse Model of Vestibulodynia

Introduction

Improved understanding of vestibulodynia pathophysiology is required to develop appropriately targeted treatments. Established features include vulvovaginal hyperinnervation, increased nociceptive signalling and hypersensitivity. Emerging evidence indicates macrophage-neuron signalling contributes to chronic pain pathophysiology. Macrophages are broadly classified as M1 or M2, demonstrating pro-nociceptive or anti-nociceptive effects respectively. This study investigates the impact of clodronate liposomes, a macrophage depleting agent, on nociceptive signalling in a mouse model of vestibulodynia.

Methods

Microinjection of complete Freund’s adjuvant (CFA) at the vaginal introitus induced mild chronic inflammation in C57Bl/6J mice. A subgroup was treated with the macrophage depleting agent clodronate. Control mice received saline. After 7 days, immunolabelling for PGP9.5, F4/80+CD11c+ and F4/80+CD206+ was used to compare innervation density and presence of M1 and M2 macrophages respectively in experimental groups. Nociceptive signalling evoked by vaginal distension was assessed using immunolabelling for phosphorylated MAP extracellular signal-related kinase (pERK) in spinal cord sections. Hyperalgesia was assessed by visceromotor response to graded vaginal distension.

Results

CFA led to increased vaginal innervation (p < 0.05), increased pERK-immunoreactive spinal cord dorsal horn neurons evoked by vaginal-distension (p < 0.01) and enhanced visceromotor responses compared control mice (p < 0.01). Clodronate did not reduce vaginal hyperinnervation but significantly reduced the abundance of M1 and M2 vaginal macrophages and restored vaginal nociceptive signalling and vaginal sensitivity to that of healthy control animals.

Conclusions

We have developed a robust mouse model of vestibulodynia that demonstrates vaginal hyperinnervation, enhanced nociceptive signalling, hyperalgesia and allodynia. Macrophages contribute to hypersensitivity in this model. Macrophage-sensory neuron signalling pathways may present useful pathophysiological targets.

Activation of Neural Modeling-Related Genes in the Heart of Mice after Gamma Irradiation

OBJECTIVE

Radiation-induced heart disease (RIHD) is a common sequela of thoracic irradiation. At the same time, nerve remodeling is involved in the progression of heart disease. However, the activation of the nerve remodeling related genes in radiation-induced heart disease is still lacking.

METHODS

In this study, C57BL/J mice was anesthetized by intraperitoneal injection with pentobarbital sodium (2%, 40 mg/kg), and radiation was delivered using a cobalt-60 (60Co) teletherapy unit (Cirus). When the mice were anesthetized, none of them showed the signs of peritonitis, pain, or discomfort. The mice hearts were exposed to a γ-radiation field of 5 mm × 5 mm. The total dose of γ-radiation was 3 Gy/day for each animal for 5 consecutive days. The mice were executed by severed neck, and its limbs were weak. Quantitative Polymerase Chain Reaction (qPCR) and immunohistochemistry were used to explore the possible mechanism of arrhythmia in patients with RIHD.

RESULTS

Our results demonstrated that Growth-Associated Protein 43 (GAP43) was increased significantly after radioactive heart injury compared with the control group. Moreover, the protein expression of Tyrosine hydroxylase (TH) and Choline acetyl-transferase (CHAT) was significantly decreased compared with the control group and gradually increased with time rend. The nerve growth factor (NGF) was remarkably increased after radiation-induced heart injury compared with the control group. Immunohistochemistry results indicated that the nerve growth factors GAP43 and NGF were significantly increased after radiation-induced heart injury.

CONCLUSIONS

Chest radiotherapy could activate the neural modeling related genes in RIHD. This may provide a new treatment plan for the future treatment of heart problems caused by chest radiotherapy.

What gets on the nerves of cardiac patients? Pathophysiological changes in cardiac innervation

The autonomic nervous system regulates cardiac function by balancing the actions of sympathetic and parasympathetic inputs to the heart. Intrinsic cardiac neurocircuits integrate these autonomic signals to fine-tune cardiac control, and sensory feedback loops regulate autonomic transmission in the face of external stimuli. These interconnected neural systems allow the heart to adapt to constantly changing circumstances that range from simple fluctuations in body position to running a marathon. The cardiac reflexes that serve to maintain homeostasis in health are disrupted in many disease states. This is often characterized by increased sympathetic and decreased parasympathetic transmission. Studies of cardiovascular disease reveal remodelling of cardiac neurocircuits at several functional and anatomical levels. Central circuits change so that sympathetic pathways become hyperactive, while parasympathetic circuits exhibit decreased activity. Peripheral sensory nerves also become hyperactive in disease, which increases patients' risk for poor cardiac outcomes. Injury and disease also alter the types of neurotransmitters and neuropeptides released by autonomic nerves in the heart, and can lead to regional hyperinnervation (increased nerve density) or denervation (decreased nerve density) of cardiac tissue. The mechanisms responsible for neural remodelling are not fully understood, but neurotrophins and inflammatory cytokines are likely involved. Areas of active investigation include the role of immune cells and inflammation in neural remodelling, as well as the role of glia in modulating peripheral neuronal activity. Our growing understanding of autonomic dysfunction in disease has facilitated development of new therapeutic strategies to improve health outcomes.

The short-chain fatty acid propionate improved ventricular electrical remodeling in a rat model with myocardial infarction

The short-chain fatty acid (SCFA) propionate (C3), a microorganism metabolite produced by gut microbial fermentation, has parasympathetic-activation effects. The cardiac autonomic rebalancing strategy is considered as an important therapeutic approach to myocardial infarction (MI)-produced ventricular arrhythmias (VAs). Thus, our research was designed to clarify the potential functions of the SCFA propionate in VAs and cardiac electrophysiology in MI rats. A hundred adult Sprague-Dawley rats were allocated to four groups: the sham group (200 mM sodium chloride), the sham + C3 group (200 mM propionate), the MI group (200 mM sodium chloride) and the MI + C3 group (200 mM propionate). In comparison with the sham group, propionate significantly increased the parasympathetic components heart rate variability (HRV) and acetylcholine levels, prolonged cardiac repolarization, induced STAT3 phosphorylation and up-regulated the c-fos expression in nodose ganglia and solitary nucleus. Propionate intake reduced the susceptibility to VAs. MI induced by coronary ligation caused a significant increase in the sympathetic components HRV, abnormal repolarization, global repolarization dispersion, norepinephrine and inflammatory cytokines, reduction and redistribution of Connexin 43 in the infarcted border zone, and activation of NFκB, which were attenuated in the MI + C3 group. Oral propionate supplementation, as a nutritional intervention, protected the heart against MI-induced VAs and cardiac electrophysiology instability partly by parasympathetic activation based on the gut-brain axis.

EphrinB2-RhoA upregulation attenuates sympathetic hyperinnervation and decreases the incidence of ventricular arrhythmia after myocardial infarction

BACKGROUND

Cardiac sympathetic hyperinnervation after myocardial infarction (MI) is associated with a high incidence of lethal arrhythmia. Erythropoietin-producing hepatoma interactor B2 (EphrinB2), a diffusible axonal chemorepellent that can induce growth cone collapse and axon repulsion of several neuronal populations, is crucial in neurodevelopment during disease development and progression. However, whether EphrinB2 could inhibit cardiac sympathetic hyperinnervation after MI remains unclear.

METHODS AND RESULTS

A rat model of MI was developed by left anterior descending coronary artery ligation. EphrinB2 expression was markedly increased in the infarcted border at 3 days after MI. Downregulation of EphrinB2 by intramyocardial injection of lentivirus carrying EphrinB2-shRNA significantly increased sympathetic hyperinnervation along with downregulated RhoA expression. In contrast, injection of EphrinB2-overexpressing lentivirus markedly upregulated EphrinB2, concomitant with inhibition of sympathetic sprouting and upregulated RhoA expression, accompanied by decreased incidence of ventricular arrhythmias (VAs). However, co-administering EphrinB2-overexpressing lentivirus and Fasudil (Rho kinase inhibitor) nearly abolished the inhibition of nerve sprouting effect. Additionally, EphrinB2 expression did not affect nerve growth factor level in the infarcted heart.

CONCLUSIONS

Overexpression of EphrinB2 may ameliorate MI-induced sympathetic hyperinnervation and further reduce the incidence of VAs, at least in part by activating RhoA-mediated axonal retraction.

Nerve-macrophage interactions in cardiovascular disease

The heart is highly innervated by autonomic neurons, and dynamic autonomic regulation of the heart and blood vessels is essential for animals to carry out the normal activities of life. Cardiovascular diseases, including heart failure and myocardial infarction, are often characterized in part by an imbalance in autonomic nervous system activation, with excess sympathetic and diminished parasympathetic activation. Notably, however, this is often accompanied by chronic inflammation within the cardiovascular tissues, which suggests there are interactions between autonomic dysregulation and inflammation. Recent studies have been unraveling the mechanistic links between autonomic nerves and immune cells within cardiovascular disease. The autonomic nervous system and immune system also act in concert to coordinate the actions of multiple organs that not only maintain homeostasis but also likely play key roles in disease-disease interactions, such as cardiorenal syndrome and multimorbidity. In this review, we summarize the physiological and pathological interactions between autonomic nerves and macrophages in the context of cardiovascular disease.

Macrophage depletion in stellate ganglia alleviates cardiac sympathetic overactivation and ventricular arrhythmogenesis by attenuating neuroinflammation in heart failure

Cardiac sympathetic overactivation is involved in arrhythmogenesis in patients with chronic heart failure (CHF). Inflammatory infiltration in the stellate ganglion (SG) is a critical factor for cardiac sympathoexcitation in patients with ventricular arrhythmias. This study aims to investigate if macrophage depletion in SGs decreases cardiac sympathetic overactivation and ventricular arrhythmogenesis in CHF. Surgical ligation of the coronary artery was used for induction of CHF. Clodronate liposomes were microinjected into bilateral SGs of CHF rats for macrophage depletion. Using cytokine array, immunofluorescence staining, and Western blot analysis, we found that macrophage expansion and expression of TNFα and IL-1β in SGs were markedly increased in CHF rats. Flow cytometry data confirmed that the percentage of macrophages in SGs was higher in CHF rats than that in sham rats. Clodronate liposomes significantly reduced CHF-elevated proinflammatory cytokine levels and macrophage expansion in SGs. Clodronate liposomes also reduced CHF-increased N-type Ca2+ currents and excitability of cardiac sympathetic postganglionic neurons and inhibited CHF-enhanced cardiac sympathetic nerve activity. ECG data from 24-h, continuous telemetry recording in conscious rats demonstrated that clodronate liposomes not only restored CHF-induced heterogeneity of ventricular electrical activities, but also decreased the incidence and duration of ventricular tachycardia/fibrillation in CHF. Macrophage depletion with clodronate liposomes attenuated CHF-induced cardiac sympathetic overactivation and ventricular arrhythmias through reduction of macrophage expansion and neuroinflammation in SGs.

Taurine Alleviates Sympathetic Innervation by Inhibiting NLRP3 Inflammasome in Postinfarcted Rats

ABSTRACT

The NLRP3 inflammasome is activated by myocardial infarction and then induces the activation of inflammatory caspase-1 activation and maturation of IL-1β, a regulator of synthesis of the nerve growth factor (NGF). Here, we studied whether taurine, 2-aminoethanesulphonic acid, can attenuate cardiac sympathetic reinnervation by modulating NLRP3 inflammasome-mediated NGF in a rat model of myocardial infarction. Male Wistar rats were subjected to coronary ligation and then randomized to either saline or taurine for 3 days or 4 weeks. Postinfarction was associated with activation of NF-κB (p65) and NLRP3 inflammasome component and increased the protein and expression of IL-1β. Macrophages at the border zone were shown to be positive for IL-1β 3 days postinfarction. Compared with vehicle, infarcted rats treated with taurine significantly attenuated myocardial messenger RNA and protein levels of NF-κB, NLRP3 inflammasome, mature caspase-1, and IL-1β. Immunofluorescent analysis, real-time quantitative reverse transcription polymerase chain reaction, and Western blotting of NGF showed that sympathetic hyperinnervation was blunted after administering taurine. Arrhythmia vulnerability in the taurine-treated infarcted rats was significantly improved than those in vehicle. Ex vivo studies showed that taurine infusion reduced myocardial IL-1β level at the extent similar to either pyrrolidine dithiocarbamate or CP-456,773, inhibitors of NF-κB and NLRP3 inflammasome, implying the key axis of NF-κB/NLRP3 inflammasome in mediating taurine-related anti-inflammation. Furthermore, administration of anti-IL-1β antibody reduced NGF levels. Taurine attenuated sympathetic innervation mainly by NLRP3 inflammasome/IL-1β-dependent pathway, which downregulated expression of NGF in infarcted rats. These findings may provide a new insight into the anti-inflammation effect of taurine.

Lack of Macrophage Migration Inhibitory Factor Reduces Susceptibility to Ventricular Arrhythmias During the Acute Phase of Myocardial Infarction

Background

Macrophages are involved in inflammatory responses and play a crucial role in aggravating ventricular arrhythmias (VAs) after myocardial infarction (MI). Macrophage migration inhibitory factor (MIF) participates in inflammatory responses during acute MI. In the present study, we hypothesized that knockout (KO) of MIF may prevent VAs during the acute phase of MI by inhibiting macrophage-derived pro-inflammatory mediators.

Methods and Results

We demonstrated that MIF-KO mice in a mouse model of MI exhibited a significant decrease in susceptibility to VAs both in vivo (84.6% vs 40.7%, P < 0.05) and ex vivo (86.7% vs 40.0%, P < 0.05) at day 3 after MI compared with that in wild-type (WT) mice. Both WT and MIF-KO mice presented similar left ventricular contractility, peri-infarct myocardial fibrosis and sympathetic reinnervation, and circulating and local norepinephrine levels during the acute phase of MI. Meanwhile, MIF-KO mice had inhibited macrophage aggregation, alleviated connexin 43 (Cx43) redistribution, and reduced level of pro-inflammatory mediators, including tumor necrosis factor-α and interleukin-1β (P < 0.05) at day 3 after MI. The differences in susceptibility to VAs, expression of pro-inflammatory mediators, and Cx43 redistribution after MI between WT and MIF-KO mice disappeared by macrophage depletion with clodronate liposomes in both groups. Furthermore, the pro-inflammatory activity of cultured peritoneal macrophages was inhibited by MIF deficiency and recovered with replenishment of exogenous MIF in vitro.

Conclusion

In conclusion, we found that lack of MIF reduced the susceptibility to VAs in mouse heart during the acute phase of MI by inhibiting pro-inflammatory activity of macrophages and improving gap-junction and electrical remodeling.

The Role of Cardiac Macrophage and Cytokines on Ventricular Arrhythmias

In the heart, cardiac macrophages have widespread biological functions, including roles in antigen presentation, phagocytosis, and immunoregulation, through the formation of diverse cytokines and growth factors; thus, these cells play an active role in tissue repair after heart injury. Recent clinical studies have indicated that macrophages or elevated inflammatory cytokines secreted by macrophages are closely related to ventricular arrhythmias (VAs). This review describes the role of macrophages and macrophage-secreted inflammatory cytokines in ventricular arrhythmogenesis.

Cardiac innervation in acute myocardial ischaemia/reperfusion injury and cardioprotection

Acute myocardial infarction (AMI) and the heart failure (HF) that often complicates this condition, are among the leading causes of death and disability worldwide. To reduce myocardial infarct (MI) size and prevent heart failure, novel therapies are required to protect the heart against the detrimental effects of acute ischaemia/reperfusion injury (IRI). In this regard, targeting cardiac innervation may provide a novel therapeutic strategy for cardioprotection. A number of cardiac neural pathways mediate the beneficial effects of cardioprotective strategies such as ischaemic preconditioning and remote ischaemic conditioning, and nerve stimulation may therefore provide a novel therapeutic strategy for cardioprotection. In this article, we provide an overview of cardiac innervation and its impact on acute myocardial IRI, the role of extrinsic and intrinsic cardiac neural pathways in cardioprotection, and highlight peripheral and central nerve stimulation as a cardioprotective strategy with therapeutic potential for reducing MI size and preventing HF following AMI. This article is part of a Cardiovascular Research Spotlight Issue entitled 'Cardioprotection Beyond the Cardiomyocyte', and emerged as part of the discussions of the European Union (EU)-CARDIOPROTECTION Cooperation in Science and Technology (COST) Action, CA16225.

Macrophages: First guards in the prevention of cardiovascular diseases

Cardiovascular diseases (CVD) remain one of the leading causes of mortality worldwide, especially in developing countries. It is widely known that severe inflammation can lead to atherosclerosis, which can cause various downstream pathologies, including myocardial injury and viral myocarditis. To date, several strategies have been proposed to prevent and cure CVD. The use of targeting macrophages has emerged as one of the most effective therapeutic approaches. Macrophages play a crucial role in eliminating senescent and dead cells while maintaining myocardial electrical activity and repairing myocardial injury. They also contribute to tissue repair and remodeling and plaque stabilization. Targeting macrophage pathways can, therefore, be advantageous in CVD care since it can lead to decreased aggregation of mononuclear cells at the injured site in the heart. Furthermore, it inhibits the development of pro-inflammatory factors, facilitates cholesterol outflow, and reduces the lipid concentration. More in-depth studies are still needed to formulate a comprehensive classification of phenotypes for different macrophages and determine their roles in the pathogenesis of CVD. In this review, we summarize the recent advances in the understanding of the role of macrophages in the prevention and cure of CVD.

Butyrate improves cardiac function and sympathetic neural remodeling following myocardial infarction in rats

Increased inflammation is found in cardiac sympathetic neural remodeling with malignant ventricular arrhythmia (VA) following myocardial infarction (MI). Butyrate, as a microbiota-derived short-chain fatty acid, can inhibit inflammation and myocardial hypertrophy. However, the role of butyrate in sympathetic neural remodeling after MI is unknown. This study aimed to investigate whether butyrate could improve cardiac dysfunction and VA following MI by regulating inflammation and sympathetic neural remodeling. MI rats were randomized to administrate the butyrate or vehicle through intraperitoneal injection to undergo the study. Our data demonstrated that butyrate treatment preserved the partial cardiac function at 7 days post-MI. Butyrate downregulated the expression of essential for inflammatory response in the infarct border zone at 3 days post-MI. Particularly, butyrate promoted expression of M2 macrophage markers. Increased expressions of nerve growth factor and norephinephrine at 7 days after MI were inhibited in butyrate-treated rats. Furthermore, butyrate significantly decreased the density of nerve fibers for growth-associated protein-43 and tyrosine hydroxylase and resulted in fewer episodes of inducible VA. In conclusion, butyrate administration ameliorated cardiac function and VA after MI possibly through promoting M2 macrophage polarization to suppress inflammatory responses and inhibit sympathetic neural remodeling and may present an effective pharmacological strategy for the prevention of MI-related remodeling.

Renal denervation restrains the inflammatory response in myocardial ischemia-reperfusion injury

Myocardial ischemia-reperfusion (I/R) injury leads to intensive sympathetic nervous system (SNS) activation and inflammatory reactions. Whether renal sympathetic denervation (RDN) could be a new therapeutic strategy to modulate I/R inflammation and reduce infarct size after myocardial I/R injury needs to be explored. First, we investigated the correlation between plasma norepinephrine concentrations and circulating myeloid cell numbers in patients with acute myocardial infarction. And then, C57BL/6 mice underwent a "two-hit" operation, with 10% phenol applied to bilateral renal nerves to abrogate sympathoexcitation, and a 45-min ligation of the left coronary artery to induce myocardial I/R injury. The effects of RDN on the mobilization of immune cells in mice following myocardial I/R injury were explored. We observed a strong association between SNS overactivation and myeloid cell excessive accumulation in patients. In animal experiments, there was a significant reduction in infarct size per area at risk in the denervated-I/R group when compared to that of the innervated-I/R group (39.2% versus 49.8%; p < 0.005), and RDN also improved the left ventricular ejection fraction by 20% after 1 week. Furthermore, the denervated-I/R group showed a decrease in the number of neutrophils and macrophages in the blood and the myocardium as reflected by immunohistochemical staining and flow cytometry analysis (p < 0.05); the decrease was associated with a significant reduction in the circulating production of IL-1, IL-6 and TNF-α (p < 0.05). In summary, our study reveals a novel link between the SNS activity and inflammatory response undergoing myocardium I/R injury and identifies RDN as a potential therapeutic strategy against myocardium I/R injury via preserving the spleen immune cells mobilization.

A novel sympathetic neuronal GABAergic signalling system regulates NE release to prevent ventricular arrhythmias after acute myocardial infarction

AIM

Overactivation of the sympathetic nerve may lead to severe ventricular arrhythmias (VAs) after myocardial infarction (MI). Thus, targeting sympathetic nerve activity is an effective strategy to prevent VAs clinically. The superior cervical ganglion (SCG), the extracardiac sympathetic ganglion innervating cardiac muscles, has been found to have a GABAergic signalling system, the physiological significance of which is obscure. We aimed to explore the functional significance of SCG post MI and whether the GABAergic signal system is involved in the process.

METHODS

Adult male Sprague-Dawley rats were divided into seven different groups. Rats in the MI groups underwent ligation of the left anterior descending coronary artery. All animals were used for electrophysiological testing, renal sympathetic nerve activity (RSNA) testing, and ELISA. Primary SCG sympathetic neurons were used for the in vitro study.

RESULTS

The GABAA receptor agonist muscimol significantly decreased the ATP-induced increase in intracellular Ca2+ (P < 0.05). GABA treatment in MI rats significantly attenuated the level of serum and cardiac norepinephrine (NE; P < 0.05). Sympathetic activity and inducible VAs were also lower in MI + GABA rats than in MI rats (P < 0.05). Knockdown of the GABAA Rs β2 subunit (GABAA Rβ2 ) in the SCG of MI rats increased the NE levels in serum and cardiac tissue, RSNA and inducible VAs compared with vehicle shRNA (P < 0.05).

CONCLUSION

The GABAergic signalling system is functionally expressed in SCG sympathetic neurons, and activation of this system suppresses sympathetic activity, thereby facilitating cardiac protection and making it a potential target to alleviate VAs.

Nerve fiber overgrowth in patients with symptomatic diverticular disease

BACKGROUND

Colonic diverticulosis is a common condition in industrialized countries. Up to 25% of patients with diverticula develop symptoms, a condition termed symptomatic uncomplicated diverticular disease (SUDD). The aim of the present study was to characterize neuroimmune interactions and nerve fiber plasticity in the colonic mucosa of patients with diverticula.

METHODS

Controls, patients with diverticulosis and with SUDD were enrolled in the study. Mucosal biopsies were obtained close to diverticula (diverticular region) and in a normal mucosa (distant site), corresponding to sigmoid and descending colon in the controls. Quantitative immunohistochemistry was used to assess mast cells, T cells, macrophages, nerve fibers, and neuronal outgrowth (growth-associated protein 43, GAP43+fibers).

KEY RESULTS

No difference emerged in mast cells and T cells among the three groups. Macrophages were increased in patients with SUDD and diverticulosis as compared to controls. Nerve fibers were enhanced in patients with SUDD and diverticulosis in comparison with controls in the diverticular region. GAP43+ fibers were increased only in patients with SUDD as compared to controls and to patients with diverticulosis in the diverticular region. In patients with SUDD, GAP43 density was increased in the diverticular region compared to distant site. Macrophages close to GAP43+ fibers were increased in the diverticular region of patients with SUDD. Significant correlations were found between GAP43+ fibers and immune cells.

CONCLUSIONS AND INFERENCES

Patients with diverticula are characterized by increased macrophage counts, while nerve fiber sprouting is increased only in the diverticular region of patients with SUDD suggesting a role in symptom generation.

Emerging Evidence of Macrophage Contribution to Hyperinnervation and Nociceptor Sensitization in Vulvodynia

Vulvodynia is an idiopathic chronic pain disorder and a leading cause of dyspareunia, or pain associated with sexual intercourse, for women. The key pathophysiological features of vulvodynia are vaginal hyperinnervation and nociceptor sensitization. These features have been described consistently by research groups over the past 30 years, but currently there is no first-line recommended treatment that targets this pathophysiology. Instead, psychological interventions, pelvic floor physiotherapy and surgery to remove painful tissue are recommended, as these are the few interventions that have shown some benefit in clinical trials. Recurrence of vulvodynia is frequent, even after vestibulectomy and questions regarding etiology remain. Vestibular biopsies from women with vulvodynia contain increased abundance of immune cells including macrophages as well as increased numbers of nerve fibers. Macrophages have multiple roles in the induction and resolution of inflammation and their function can be broadly described as pro-inflammatory or anti-inflammatory depending on their polarization state. This state is not fixed and can alter rapidly in response to the microenvironment. Essentially, M1, or classically activated macrophages, produce pro-inflammatory cytokines and promote nociceptor sensitization and mechanical allodynia, whereas M2, or alternatively activated macrophages produce anti-inflammatory cytokines and promote functions such as wound healing. Signaling between macrophages and neurons has been shown to promote axonal sprouting and nociceptor sensitization. This mini review considers emerging evidence that macrophages may play a role in nociceptor sensitization and hyperinnervation relevant to vulvodynia and considers the implications for development of new therapeutic strategies.

Local sympathetic denervation attenuates myocardial inflammation and improves cardiac function after myocardial infarction in mice

Aims

Cardiac inflammation has been suggested to be regulated by the sympathetic nervous system (SNS). However, due to the lack of methodology to surgically eliminate the myocardial SNS in mice, neuronal control of cardiac inflammation remains ill-defined. Here, we report a procedure for local cardiac sympathetic denervation in mice and tested its effect in a mouse model of heart failure post-myocardial infarction.

Methods and results

Upon preparation of the carotid bifurcation, the right and the left superior cervical ganglia were localized and their pre- and postganglionic branches dissected before removal of the ganglion. Ganglionectomy led to an almost entire loss of myocardial sympathetic innervation in the left ventricular anterior wall. When applied at the time of myocardial infarction (MI), cardiac sympathetic denervation did not affect acute myocardial damage and infarct size. In contrast, cardiac sympathetic denervation significantly attenuated chronic consequences of MI, including myocardial inflammation, myocyte hypertrophy, and overall cardiac dysfunction.

Conclusion

These data suggest a critical role for local sympathetic control of cardiac inflammation. Our model of myocardial sympathetic denervation in mice should prove useful to further dissect the molecular mechanisms underlying cardiac neural control.

Inhibition of microRNA-155 attenuates sympathetic neural remodeling following myocardial infarction via reducing M1 macrophage polarization and inflammatory responses in mice

Inflammation plays an important role in sympathetic neural remodeling induced by myocardial infarction (MI). MiR-155 is a vital regulator of inflammatory responses, and macrophage-secreted miR-155 promotes cardiac fibrosis and hypertrophy. However, whether miR-155 influences MI-induced sympathetic neural remodeling is not clear. Therefore, we examined the role of miR-155 in MI-induced sympathetic neural remodeling and the related mechanisms in both an mouse model and in lipopolysaccharide (LPS)-stimulated bone marrow-derived macrophages (BMDMs). Our data showed that miR-155 expression was significantly enhanced in the myocardial tissues of MI mice compared to sham mice. Also, MI up-regulated the electrophysiological parameters, M1 macrophage polarization, inflammatory responses, and suppressor of cytokine signaling 1 (SOCS1) expression, which coincided with the increased expression of sympathetic nerve remodeling markers(nerve growth factor, tyrosine hydroxylase and growth-associated protein 43). Except for SOCS1, these proteins were attenuated by miR-155 antagomir. In vitro, LPS-stimulation promoted miR-155 expression in BMDMs. Consistent with the in vivo findings, miR-155 antagomir diminished the LPS-induced M1 macrophage polarization, nuclear factor (NF)-κB activation, and the expression of pro-inflammatory factors and nerve growth factor; but it increased the expression of SOCS1. Inversely, miR-155 agomir significantly potentiated LPS-induced pathophysiological effects in BMDMs. MiR-155 agomir-induced effects were reversed by the NF-κB inhibitor. Mechanistically, treatment with siRNA against SOCS1 augmented the aforementioned LPS-mediated activities, which were antagonized by the addition of miR-155 antagomir. In conclusion, miR-155 inhibition downregulated NGF expression via decreasing M1 macrophage polarization and inflammatory responses dependent on the SOCS1/NF-κB pathway, subsequently diminishing MI-induced sympathetic neural remodeling and ventricular arrhythmias (VAs).

Activin A inhibition attenuates sympathetic neural remodeling following myocardial infarction in rats

Inflammation serves a critical role in driving sympathetic neural remodeling following myocardial infarction (MI), and activin A has been implicated as an important mediator of the inflammatory response post-MI. However, whether activin A impacts sympathetic neural remodeling post-MI remains unclear. In the present study, the authors assessed the effects of activin A on sympathetic neural remodeling in a rat model of MI. Rats were randomly divided into sham, MI, and MI + follistatin-300 (FS, activin A inhibitor) groups. Cardiac tissues from the peri-infarct zone were assessed for expression of sympathetic neural remodeling and inflammatory factors in rats 4 weeks post-MI by western blotting and immunohistochemical methods. Heart function was assessed by echocardiography. It is demonstrated that FS administration significantly reduced post-MI upregulation of activin A, nerve growth factor protein lever, and the density of nerve fibers with positive and protein expression of sympathetic neural remodeling markers in nerve fibers, which included growth associated protein 43 and tyrosine hydroxylase. In addition, inhibition of activin A reduced cardiac inflammation post-MI based on the reduction of i) interleukin-1 and tumor necrosis factor-α protein expression, ii) numbers and/or proportional area of infiltrating macrophages and myofibroblasts and iii) phosphorylated levels of p65 and IκBα. Furthermore, activin A inhibition lessened heart dysfunction post-MI. These results suggested that activin A inhibition reduced sympathetic neural remodeling post-MI in part through inhibition of the inflammatory response. The current study implicates activin A as a potential therapeutic target to circumvent sympathetic neural remodeling post-MI.

Amphiregulin enhances cardiac fibrosis and aggravates cardiac dysfunction in mice with experimental myocardial infarction partly through activating EGFR-dependent pathway

Cardiac fibrosis (CF), a main process of ventricular remodeling after myocardial infarction (MI), plays a crucial role in the pathogenesis of heart failure (HF) post-MI. It is known that amphiregulin (AR) is involved in fibrosis of several organs. However, the expression of AR and its role post-MI are yet to be determined. This study aimed to investigate the impact of AR on CF post-MI and related mechanisms. Significantly upregulated AR expression was evidenced in the infarct border zone of MI mice in vivo and the AR secretion was enhanced in macrophages, but not in cardiac fibroblasts. In vitro, treatment with AR increased cardiac fibroblast migration, proliferation and collagen synthesis, and upregulated the expression of epidermal growth factor receptor (EGFR) and the downstream genes such as Akt, ERK1/2 and Samd2/3 on cardiac fibroblasts. All these effects could be abrogated by pretreatment with a specific EGFR inhibitor. To verify the functions of AR in MI hearts, lentivirus-AR-shRNA and negative control vectors were delivered into the infarct border zone. After 28 days, knock-down of AR increased the survival rate and improved cardiac function, while decreasing the extent of myocardial fibrosis of MI mice. Moreover, EGFR and the downstream genes were significantly downregulated in lentivirus-AR-shRNA treated MI mice. Our results thus indicate that AR plays an important role in promoting CF after MI partly though activating the EGFR pathway. Targeting AR might be a novel therapeutic option for attenuating CF and improve cardiac function after MI.

Atrial Fibrillation Promotion in a Rat Model of Rheumatoid Arthritis

Background

The prevalence of atrial fibrillation (AF) is significantly higher in rheumatoid arthritis (RA) patients, but the underlying mechanisms remain poorly understood. The goal of this study was to assess the effects of RA on AF susceptibility and atrial arrhythmogenic remodeling in a rat model of RA.

Methods and Results

Collagen‐induced arthritis was induced in rats by immunization with type II collagen in Freund's incomplete adjuvant. Among the rats that developed arthritis, AF susceptibility and atrial remodeling were examined 8 weeks after the primary immunization. AF inducibility and duration were substantially increased in collagen‐induced arthritis rats, and AF duration was significantly and positively correlated with the serum IL‐6 and TNF‐α levels. Rats with collagen‐induced arthritis showed prolonged atrial conduction time with no changes in the atrial effective refractory period. Atrial conduction delay was accompanied by significantly increased atrial fibrosis. In addition, atrial structural and autonomic remodeling, including left atrial dilation, apoptosis and autophagy of atrial myocytes, and atrial heterogeneous sympathetic hyperinnervation, was observed. Interestingly, we found that collagen‐induced arthritis had no significant effects on connexins, Nav1.5, and the main ion channels' protein expressions in atria.

Conclusions

We demonstrated that RA increased AF susceptibility by inducing AF‐promoting atrial remodeling. This study may provide insights into mechanisms underlying RA‐induced AF and validate a model that is suitable for further mechanistic and therapeutic exploration.

P2X7 receptor inhibition attenuated sympathetic nerve sprouting after myocardial infarction via the NLRP3/IL-1β pathway

Mounting evidence supports the hypothesis that inflammation modulates sympathetic sprouting after myocardial infarction (MI). The myeloid P2X₇ signal has been shown to activate the nucleotide-binding and oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome, a master regulator of inflammation. We investigated whether P2X₇ signal participated in the pathogenesis of sympathetic reinnervation after MI, and whether NLRP3/interleukin-1β (IL-1β) axis is involved in the process. We explored the relationship between P2X₇ receptor (P2X₇ R) and IL-1β in the heart tissue of lipopolysaccharide (LPS)-primed naive rats. 3'-O-(4-benzoyl) benzoyl adenosine 5'-triphosphate (BzATP), a P2X₇ R agonist, induced caspase-1 activation and mature IL-1β release, which was further neutralized by a NLRP3 inhibitor (16673-34-0). MI was induced by coronary artery ligation. Following infarction, a marked increase in P2X₇ R was localized within infiltrated macrophages and observed in parallel with an up-regulation of NLRP3 inflammasome levels and the release of IL-1β in the left ventricle. The administration of A-740003 (a P2X₇ R antagonist) significantly prevented the NLRP3/IL-1β increase. A-740003 and/or Anakinra (an IL-1 receptor antagonist) significantly reduced macrophage infiltration as well as macrophage-based IL-1β and NGF (nerve growth factor) production and eventually blunted sympathetic hyperinnervation, as assessed by the immunofluorescence of tyrosine hydroxylase (TH) and growth-associated protein 43 (GAP 43). Moreover, the use of Anakinra partly attenuated sympathetic sprouting. This indicated that the effect of P2X₇ on neural remodelling was mediated at least partially by IL-1β. The arrhythmia score of programmed electric stimulation was in accordance with the degree of sympathetic hyperinnervation. In vitro studies showed that BzATP up-regulated secretion of nerve growth factor (NGF) in M1 macrophages via IL-1β. Together, these data indicate that P2X₇ R contributes to neural and cardiac remodelling, at least partly mediated by NLRP3/IL-1β axis. Therapeutic interventions targeting P2X₇ signal may be a novel approach to ameliorate arrhythmia following MI.

Targeted P2X7 R shRNA delivery attenuates sympathetic nerve sprouting and ameliorates cardiac dysfunction in rats with myocardial infarction

BACKGROUND

Inflammation-dominated sympathetic sprouting adjacent to the necrotic region following myocardial infarction (MI) has been implicated in the etiology of arrhythmias resulting in sudden cardiac death; however, the mechanisms responsible remain to be elucidated. Although P2X₇ R is a key immune mediator, its role has yet to be explored.

OBJECTIVE

We investigated whether P2X₇ R regulates NF-κB and affects cardiac sympathetic reinnervation in rats undergoing MI.

METHODS AND RESULTS

An adenoviral vector with a short hairpin RNA (shRNA) sequence inserted was adopted for the inhibition of P2X₇ R in vivo. Myocardial infarction was induced by left coronary artery ligation, and immediately after that, recombinant P2X₇ R-shRNA adenovirus, negative adenovirus (control), or normal saline solution (vehicle) was injected intramyocardially around the MI region and border areas. A high level of P2X₇ R was activated in the infarcted tissue at an early stage. The administration of P2X₇ R RNAi resulted in the inhibition of Akt and Erk1/2 phosphorylation and decreased the activation of NF-κB and macrophage infiltration, as well as attenuated the expression of nerve growth factor (NGF). Eventually, the NGF-induced sympathetic hyperinnervation was blunted, as assessed by the immunofluorescence of tyrosine hydroxylase (TH) and growth-associated protein 43 (GAP 43). At 7 days post-MI, the arrhythmia score of programmed electrical stimulation in the vehicle-treated infarcted rats was higher than the MI-shRNA group. Further amelioration of cardiac dysfunction was also detected.

CONCLUSIONS

The administration of P2X₇ R RNAi during the acute inflammatory response phase prevented the process of sympathetic hyperinnervation after MI, which was associated in part with inhibiting the Akt and ERK1/2 pathways and NF-κB activation.

Renal denervation in male rats with heart failure improves ventricular sympathetic nerve innervation and function

Heart failure is characterized by the loss of sympathetic innervation to the ventricles, contributing to impaired cardiac function and arrhythmogenesis. We hypothesized that renal denervation (RDx) would reverse this loss. Male Wistar rats underwent myocardial infarction (MI) or sham surgery and progressed into heart failure for 4 wk before receiving bilateral RDx or sham RDx. After additional 3 wk, left ventricular (LV) function was assessed, and ventricular sympathetic nerve fiber density was determined via histology. Post-MI heart failure rats displayed significant reductions in ventricular sympathetic innervation and tissue norepinephrine content (nerve fiber density in the LV of MI+sham RDx hearts was 0.31 ± 0.05% vs. 1.00 ± 0.10% in sham MI+sham RDx group, P < 0.05), and RDx significantly increased ventricular sympathetic innervation (0.76 ± 0.14%, P < 0.05) and tissue norepinephrine content. MI was associated with an increase in fibrosis of the noninfarcted ventricular myocardium, which was attenuated by RDx. RDx improved LV ejection fraction and end-systolic and -diastolic areas when compared with pre-RDx levels. This is the first study to show an interaction between renal nerve activity and cardiac sympathetic nerve innervation in heart failure. Our findings show denervating the renal nerves improves cardiac sympathetic innervation and function in the post-MI failing heart.