Mast cells modulate the pathogenesis of leptin-induced left stellate ganglion activation in canines

Mast cell stabilizer, an anti-allergic drug, reduces ventricular arrhythmia risk via modulation of neuroimmune interaction

Mast cells (MCs) are important intermediates between the nervous and immune systems. The cardiac autonomic nervous system (CANS) crucially modulates cardiac electrophysiology and arrhythmogenesis, but whether and how MC-CANS neuroimmune interaction influences arrhythmia remain unclear. Our clinical data showed a close relationship between serum levels of MC markers and CANS activity, and then we use mast cell stabilizers (MCSs) to alter this MC-CANS communication. MCSs, which are well-known anti-allergic agents, could reduce the risk of ventricular arrhythmia (VA) after myocardial infarction (MI). RNA-sequencing (RNA-seq) analysis to investigate the underlying mechanism by which MCSs could affect the left stellate ganglion (LSG), a key therapeutic target for modulating CANS, showed that the IL-6 and γ-aminobutyric acid (GABA)-ergic system may be involved in this process. Our findings demonstrated that MCSs reduce VA risk along with revealing the potential underlying antiarrhythmic mechanisms.

Autonomic nervous system receptor-mediated regulation of mast cell degranulation modulates the inflammation after corneal epithelial abrasion

Mast cells (MCs) regulate wound healing and are influenced by the autonomic nervous system (ANS). However, the underlying mechanisms affecting wound healing outcomes remain elusive. Here, we explored the specific role of the ANS by regulating MC degranulation following corneal epithelium abrasion. A mouse model of corneal abrasion was established by mechanically removing a 2-mm central epithelium. Wound closure, neutrophil infiltration, and transcription of injured corneas were investigated using whole-mount immunostaining, flow cytometry, and RNA-sequencing analysis, respectively. Inhibition of MC degranulation by the MC stabilizers cromolyn sodium and lodoxamide tromethamine increased the infiltration of neutrophils and delayed healing of abraded corneas. Moreover, transcriptomic profiling analysis showed that purified MCs from the limbus expressed adrenergic and cholinergic receptors. Pharmacological manipulation and sympathectomy with 6-hydroxydopamine confirmed that sympathetic nervous system signaling inhibited MC degranulation after corneal abrasion, whereas parasympathetic nervous system signaling enhanced MC degranulation. We conclude that normal degranulation of MCs in the corneal limbus and crosstalk between the ANS and MCs are crucial for the appropriate control of inflammation and the repair progress of wounded corneas. This suggests a potential approach for improving defective corneal wound healing by the administration of clinically available autonomic activity-modulating agents.

Sympathetic Nervous System Mediates Cardiac Remodeling After Myocardial Infarction in a Circadian Disruption Model

Background: Circadian rhythms have a considerable impact on the daily physiology of the heart, and their disruption causes pathology. Several studies have revealed that circadian disruption impaired cardiac remodeling after myocardial infarction (MI); however, the underlying brain-heart mechanisms remain unknown. We aim to discuss whether circadian disruption facilitates cardiac remodeling after MI by activating sympathetic nervous system.

Methods: Rats were randomly divided into three groups: Sham group (Sham), MI group (MI), and MI+ circadian disruption group (MI+Dis); rats were treated with pseudorabies virus (PRV) injections for trans-synaptic retrograde tracing; rats were randomly divided into two groups: MI+ circadian disruption + Empty Vector+ clozapine N-oxide (CNO) (Empty Vector), and MI+ circadian disruption + hM4D(Gi)+ CNO [hM4D(Gi)].

Results: Circadian disruption significantly facilitated cardiac remodeling after MI with lower systolic function, larger left ventricular volume, and aggravated cardiac fibrosis. Cardiac sympathetic remodeling makers and serum norepinephrine levels were also significantly increased by circadian disruption. PRV virus-labeled neurons were identified in the superior cervical ganglion (SCG), paraventricular nucleus (PVN), and suprachiasmatic nucleus (SCN) regions. Ganglionic blockade via designer receptors exclusively activated by designer drugs (DREADD) technique suppressed the activity of sympathetic nervous system and significantly alleviated the disruption-related cardiac dysfunction.

Conclusion: Circadian disruption adversely affected cardiac remodeling after MI possibly by activating sympathetic nervous system, and suppressing sympathetic activity can attenuate this disruption-related cardiac dysfunction.

Leptin Elicits In Vivo Eosinophil Migration and Activation: Key Role of Mast Cell-Derived PGD2

Eosinophils are key regulators of adipose tissue homeostasis, thus characterization of adipose tissue-related molecular factors capable of regulating eosinophil activity is of great interest. Leptin is known to directly activate eosinophils in vitro, but leptin ability of inducing in vivo eosinophilic inflammatory response remains elusive. Here, we show that leptin elicits eosinophil influx as well as its activation, characterized by increased lipid body biogenesis and LTC₄ synthesis. Such leptin-triggered eosinophilic inflammatory response was shown to be dependent on activation of the mTOR signaling pathway, since it was (i) inhibited by rapamycin pre-treatment and (ii) reduced in PI3K-deficient mice. Local infiltration of activated eosinophils within leptin-driven inflammatory site was preceded by increased levels of classical mast cell-derived molecules, including TNFα, CCL5 (RANTES), and PGD₂. Thus, mice were pre-treated with a mast cell degranulating agent compound 48/80 which was capable to impair leptin-induced PGD₂ release, as well as eosinophil recruitment and activation. In agreement with an indirect mast cell-driven phenomenon, eosinophil accumulation induced by leptin was abolished in TNFR-1 deficient and also in HQL-79-pretreated mice, but not in mice pretreated with neutralizing antibodies against CCL5, indicating that both typical mast cell-driven signals TNFα and PGD₂, but not CCL5, contribute to leptin-induced eosinophil influx. Distinctly, leptin-induced eosinophil lipid body (lipid droplet) assembly and LTC₄ synthesis appears to depend on both PGD₂ and CCL5, since both HQL-79 and anti-CCL5 treatments were able to inhibit these eosinophil activation markers. Altogether, our data show that leptin triggers eosinophilic inflammation in vivo via an indirect mechanism dependent on activation of resident mast cell secretory activity and mediation by TNFα, CCL5, and specially PGD₂.

Interaction between Endothelin-1 and Left Stellate Ganglion Activation: A Potential Mechanism of Malignant Ventricular Arrhythmia during Myocardial Ischemia

Endothelin-1 (ET-1) is synthesized primarily by endothelial cells. ET-1 administration in vivo enhances the cardiac sympathetic afferent reflex and sympathetic activity. Previous studies have shown that sympathetic hyperactivity promotes malignant ventricular arrhythmia (VA). The aim of this study was to investigate whether ET-1 could activate the left stellate ganglion (LSG) and promote malignant VA. Twelve male beagle dogs who received local microinjections of saline (control, n = 6) and ET-1 into the LSG (n = 6) were included. The ventricular effective refractory period (ERP), LSG function, and LSG activity were measured at different time points. VA was continuously recorded for 1 h after left anterior descending occlusion (LADO), and LSG tissues were then collected for molecular detection. Compared to that of the control group, local ET-1 microinjection significantly decreased the ERP and increased the occurrence of VA. In addition, local microinjection of ET-1 increased the function and activity of the LSG in the normal and ischemic hearts. The expression levels of proinflammatory cytokines and the protein expression of c-fos and nerve growth factor (NGF) in the LSG were also increased. More importantly, endothelin A receptor (ETA-R) expression was found in the LSG, and its signaling was significantly activated in the ET-1 group. LSG activation induced by local ET-1 microinjection aggravates LADO-induced VA. Activated ETA-R signaling and the upregulation of proinflammatory cytokines in the LSG may be responsible for these effects.