Molecular and cellular neurocardiology in heart disease.

This paper updates and builds on a previous White Paper in this journal that some of us contributed to concerning the molecular and cellular basis of cardiac neurobiology of heart disease. Here we focus on recent findings that underpin cardiac autonomic development, novel intracellular pathways and neuroplasticity. Throughout we highlight unanswered questions and areas of controversy. Whilst some neurochemical pathways are already demonstrating prognostic viability in patients with heart failure, we also discuss the opportunity to better understand sympathetic impairment by using patient specific stem cells that provides pathophysiological contextualization to study 'disease in a dish'. Novel imaging techniques and spatial transcriptomics are also facilitating a road map for target discovery of molecular pathways that may form a therapeutic opportunity to treat cardiac dysautonomia.

Chronic nicotine exposure is associated with electrophysiological and sympathetic remodeling in the intact rabbit heart.

Nicotine is the primary addictive component of tobacco products. Through its actions on the heart and autonomic nervous system, nicotine exposure is associated with electrophysiological changes and increased arrhythmia susceptibility. To assess the underlying mechanisms, we treated rabbits with transdermal nicotine (NIC, 21 mg/day) or control (CT) patches for 28 days before performing dual optical mapping of transmembrane potential (RH237) and intracellular Ca2+ (Rhod-2 AM) in isolated hearts with intact sympathetic innervation. Sympathetic nerve stimulation (SNS) was performed at the first to third thoracic vertebrae, and ß-adrenergic responsiveness was additionally evaluated following norepinephrine (NE) perfusion. Baseline ex vivo heart rate (HR) and SNS stimulation threshold were higher in NIC versus CT (P = 0.004 and P = 0.003, respectively). Action potential duration alternans emerged at longer pacing cycle lengths (PCL) in NIC versus CT at baseline (P = 0.002) and during SNS (P = 0.0003), with similar results obtained for Ca2+ transient alternans. SNS shortened the PCL at which alternans emerged in CT but not in NIC hearts. NIC-exposed hearts tended to have slower and reduced HR responses to NE perfusion, but ventricular responses to NE were comparable between groups. Although fibrosis was unaltered, NIC hearts had lower sympathetic nerve density (P = 0.03) but no difference in NE content versus CT. These results suggest both sympathetic hypoinnervation of the myocardium and regional differences in ß-adrenergic responsiveness with NIC. This autonomic remodeling may contribute to the increased risk of arrhythmias associated with nicotine exposure, which may be further exacerbated with long-term use.NEW & NOTEWORTHY Here, we show that chronic nicotine exposure was associated with increased heart rate, increased susceptibility to alternans, and reduced sympathetic electrophysiological responses in the intact rabbit heart. We suggest that this was due to sympathetic hypoinnervation of the myocardium and diminished ß-adrenergic responsiveness of the sinoatrial node following nicotine treatment. Though these differences did not result in increased arrhythmia propensity in our study, we hypothesize that prolonged nicotine exposure may exacerbate this proarrhythmic remodeling.

Unraveling the lost balance: Adrenergic dysfunction in cancer cachexia.

Cancer cachexia, characterized by muscle wasting and widespread inflammation, poses a significant challenge for patients with cancer, profoundly impacting both their quality of life and treatment management. However, existing treatment modalities remain very limited, accentuating the necessity for innovative therapeutic interventions. Many recent studies demonstrated that changes in autonomic balance is a key driver of cancer cachexia. This review consolidates research findings from investigations into autonomic dysfunction across cancer cachexia, spanning animal models and patient cohorts. Moreover, we explore therapeutic strategies involving adrenergic receptor modulation through receptor blockers and agonists. Mechanisms underlying adrenergic hyperactivity in cardiac and adipose tissues, influencing tissue remodeling, are also examined. Looking ahead, we present a perspective for future research that delves into autonomic dysregulation in cancer cachexia. This comprehensive review highlights the urgency of advancing research to unveil innovative avenues for combatting cancer cachexia and improving patient well-being.

Ischemia-reperfusion myocardial infarction induces remodeling of left cardiac-projecting stellate ganglia neurons.

Neurons in the stellate ganglion (SG) provide sympathetic innervation to the heart, brown adipose tissue (BAT), and other organs. Sympathetic innervation to the heart becomes hyperactive following myocardial infarction (MI). The impact of MI on the morphology of cardiac sympathetic neurons is not known, but we hypothesized that MI would stimulate increased cell and dendritic tree size in cardiac neurons. In this study, we examined the effects of ischemia-reperfusion MI on sympathetic neurons using dual retrograde tracing methods to allow detailed characterization of cardiac- and BAT-projecting neurons. Different fluorescently conjugated cholera toxin subunit B (CTb) tracers were injected into the pericardium and the interscapular BAT pads, respectively. Experimental animals received a 45-min occlusion of the left anterior descending coronary artery and controls received sham surgery. One week later, hearts were collected for assessment of MI infarct and SGs were collected for morphological or electrophysiological analysis. Cardiac-projecting SG neurons from MI mice had smaller cell bodies and shorter dendritic trees compared with sham animals, specifically on the left side ipsilateral to the MI. BAT-projecting neurons were not altered by MI, demonstrating the subpopulation specificity of the response. The normal size and distribution differences between BAT- and cardiac-projecting stellate ganglion neurons were not altered by MI. Patch-clamp recordings from cardiac-projecting left SG neurons revealed increased spontaneous excitatory postsynaptic currents despite the decrease in cell and dendritic tree size. Thus, increased dendritic tree size does not contribute to the enhanced sympathetic neural activity seen after MI.NEW & NOTEWORTHY Myocardial infarction (MI) causes structural and functional changes specifically in stellate ganglion neurons that project to the heart, but not in cells that project to brown adipose fat tissue.

Guidelines on the use of sex and gender in cardiovascular research.

In cardiovascular research, sex and gender have not typically been considered in research design and reporting until recently. This has resulted in clinical research findings from which not only all women, but also gender-diverse individuals have been excluded. The resulting dearth of data has led to a lack of sex- and gender-specific clinical guidelines and raises serious questions about evidence-based care. Basic research has also excluded considerations of sex. Including sex and/or gender as research variables not only has the potential to improve the health of society overall now, but it also provides a foundation of knowledge on which to build future advances. The goal of this guidelines article is to provide advice on best practices to include sex and gender considerations in study design, as well as data collection, analysis, and interpretation to optimally establish rigor and reproducibility needed to inform clinical decision-making and improve outcomes. In cardiovascular physiology, incorporating sex and gender is a necessary component when optimally designing and executing research plans. The guidelines serve as the first guidance on how to include sex and gender in cardiovascular research. We provide here a beginning path toward achieving this goal and improve the ability of the research community to interpret results through a sex and gender lens to enable comparison across studies and laboratories, resulting in better health for all.

Identifying vagal sensory neurons driving the Bezold-Jarisch reflex.

Homeostatic reflexes are crucial for life, but the subpopulations of sensory neurons that stimulate these reflexes are largely unknown. A recent paper from Lovelace, Ma, and colleagues identified a population of sensory neurons in the cardiac ventricle that underlies the Bezold-Jarisch reflex and triggers syncope (fainting).

Chronic nicotine exposure is associated with electrophysiological and sympathetic remodeling in the intact rabbit heart.

Nicotine is the primary addictive component in tobacco products. Through its actions on the heart and autonomic nervous system, nicotine exposure is associated with electrophysiological changes and increased arrhythmia susceptibility. However, the underlying mechanisms are unclear. To address this, we treated rabbits with transdermal nicotine (NIC, 21 mg/day) or control (CT) patches for 28 days prior to performing dual optical mapping of transmembrane potential (RH237) and intracellular Ca 2+ (Rhod-2 AM) in isolated hearts with intact sympathetic innervation. Sympathetic nerve stimulation (SNS) was performed at the 1 st - 3 rd thoracic vertebrae, and ß-adrenergic responsiveness was additionally evaluated as changes in heart rate (HR) following norepinephrine (NE) perfusion. Baseline ex vivo HR and SNS stimulation threshold were increased in NIC vs. CT ( P = 0.004 and P = 0.003 respectively). Action potential duration alternans emerged at longer pacing cycle lengths (PCL) in NIC vs. CT at baseline ( P = 0.002) and during SNS ( P = 0.0003), with similar results obtained for Ca 2+ transient alternans. SNS reduced the PCL at which alternans emerged in CT but not NIC hearts. NIC exposed hearts also tended to have slower and reduced HR responses to NE perfusion. While fibrosis was unaltered, NIC hearts had lower sympathetic nerve density ( P = 0.03) but no difference in NE content vs. CT. These results suggest both sympathetic hypo-innervation of the myocardium and diminished ß-adrenergic responsiveness with NIC. This autonomic remodeling may underlie the increased risk of arrhythmias associated with nicotine exposure, which may be further exacerbated with continued long-term usage. NEW & NOTEWORTHY: Here we show that chronic nicotine exposure was associated with increased heart rate, lower threshold for alternans and reduced sympathetic electrophysiological responses in the intact rabbit heart. We suggest that this was due to the sympathetic hypo-innervation of the myocardium and diminished ß- adrenergic responsiveness observed following nicotine treatment. Though these differences did not result in increased arrhythmia propensity in our study, we hypothesize that prolonged nicotine exposure may exacerbate this pro-arrhythmic remodeling.

Loss of chondroitin sulfate proteoglycan sulfation allows delayed sympathetic reinnervation after cardiac ischemia-reperfusion.

Sympathetic nerve loss in the heart predicts the risk of ventricular arrhythmias after myocardial infarction (MI) in patients. Sympathetic denervation after cardiac ischemia-reperfusion is sustained by matrix components chondroitin sulfate proteoglycans (CSPGs) in the cardiac scar. We showed that 4,6-sulfation of CSPGs was critical for preventing nerve growth into the scar. Promoting early reinnervation with therapeutics reduces arrhythmias during the first 2 weeks after MI, but the longer-term consequences of restoring innervation are unknown. Therefore, we asked if the beneficial effects of early reinnervation were sustained. We compared cardiac function and arrhythmia susceptibility 40 days after MI in mice treated on Days 3-10 with vehicle or with intracellular sigma peptide to restore innervation. Surprisingly, both groups had normal innervation density in the cardiac scar 40 days after MI, indicating delayed reinnervation of the infarct in vehicle-treated mice. That coincided with similar cardiac function and arrhythmia susceptibility in the two groups. We investigated the mechanism allowing delayed reinnervation of the cardiac scar. We found that CSPG 4,6-sulfation, which is elevated early after ischemia-reperfusion, was reduced to control levels allowing reinnervation of the infarct. Thus, remodeling of extracellular matrix weeks after injury leads to remodeling of sympathetic neurons in the heart.

Cholinergic collaterals arising from noradrenergic sympathetic neurons in mice.

The sympathetic nervous system vitally regulates autonomic functions, including cardiac activity. Postganglionic neurons of the sympathetic chain ganglia relay signals from the central nervous system to autonomic peripheral targets. Disrupting this flow of information often dysregulates organ function and leads to poor health outcomes. Despite the importance of these sympathetic neurons, fundamental aspects of the neurocircuitry within peripheral ganglia remain poorly understood. Conventionally, simple monosynaptic cholinergic pathways from preganglionic neurons are thought to activate postganglionic sympathetic neurons. However, early studies suggested more complex neurocircuits may be present within sympathetic ganglia. The present study recorded synaptic responses in sympathetic stellate ganglia neurons following electrical activation of the pre- and postganglionic nerve trunks and used genetic strategies to assess the presence of collateral projections between postganglionic neurons of the stellate ganglia. Orthograde activation of the preganglionic nerve trunk, T-2, uncovered high jitter synaptic latencies consistent with polysynaptic connections. Pharmacological inhibition of nicotinic acetylcholine receptors with hexamethonium blocked all synaptic events. To confirm that high jitter, polysynaptic events were due to the presence of cholinergic collaterals from postganglionic neurons within the stellate ganglion, we knocked out choline acetyltransferase in adult noradrenergic neurons. This genetic knockout eliminated orthograde high jitter synaptic events and EPSCs evoked by retrograde activation. These findings suggest that cholinergic collateral projections arise from noradrenergic neurons within sympathetic ganglia. Identifying the contributions of collateral excitation to normal physiology and pathophysiology is an important area of future study and may offer novel therapeutic targets for the treatment of autonomic imbalance. KEY POINTS: Electrical stimulation of a preganglionic nerve trunk evoked fast synaptic transmission in stellate ganglion neurons with low and high jitter latencies. Retrograde stimulation of a postganglionic nerve trunk evoked direct, all-or-none action currents and delayed nicotinic EPSCs indistinguishable from orthogradely-evoked EPSCs in stellate neurons. Nicotinic acetylcholine receptor blockade prevented all spontaneous and evoked synaptic activity. Knockout of acetylcholine production in noradrenergic neurons eliminated all retrogradely-evoked EPSCs but did not change retrograde action currents, indicating that noradrenergic neurons have cholinergic collaterals connecting neurons within the stellate ganglion.

Candidate biomarkers of physical frailty in heart failure: an exploratory cross-sectional study.

AIMS: Physical frailty is highly prevalent and predictive of worse outcomes in heart failure (HF). Candidate biomarker analysis may help in understanding the mechanisms underlying physical frailty in HF. We aimed to identify candidate biomarkers associated with physical frailty in HF using a multimarker strategy of distinct pathophysiological processes. METHODS AND RESULTS: We collected data and plasma samples from 113 adults with New York Heart Association Functional Class I-IV HF. Physical frailty was measured with the Frailty Phenotype Criteria. Plasma biomarkers included: N-terminal pro-B-type natriuretic peptide, norepinephrine, dihydroxyphenylglycol, soluble tumour necrosis factor alpha receptor-1, adiponectin, insulin, glucose, insulin-like growth factor-1 (IGF-1), and myostatin. Comparative statistics and multivariate linear regression were used to test group differences and associations. The average age was 63.5 ± 15.7 years, half were women (48%), and most had a non-ischaemic aetiology of HF (73%). Physical frailty was identified in 42% and associated with female sex, higher body mass index and percent body fat, more comorbidities, and HF with preserved ejection fraction. Adjusting for Seattle HF Model projected survival score, comorbidities, body composition, and sex, physical frailty was associated with significantly lower plasma adiponectin [ß ± standard error (SE) -0.28 ± 0.14, P = 0.047], IGF-1 (ß ± SE -0.21 ± 0.10, P = 0.032), and myostatin (ß ± SE -0.22 ± 0.09, P = 0.011). In sex-stratified analyses, IGF-1 and myostatin were significantly associated with physical frailty in men but not women. CONCLUSION: We identified biomarkers involved in adipose tissue and skeletal muscle development, maintenance, and function that were associated with physical frailty in HF.

Therapeutics That Promote Sympathetic Reinnervation Modulate the Inflammatory Response After Myocardial Infarction.

Myocardial infarction (MI) triggers an inflammatory response that transitions from pro-inflammatory to reparative over time. Restoring sympathetic nerves in the heart after MI prevents arrhythmias. This study investigated if reinnervation altered the immune response after MI. This study used quantitative multiplex immunohistochemistry to identify the immune cells present in the heart 2 weeks after ischemia-reperfusion. Two therapeutics stimulated reinnervation, preventing arrhythmias and shifting the immune response from inflammatory to reparative, with fewer pro-inflammatory macrophages and more regulatory T cells and reparative macrophages. Treatments did not alter macrophage phenotype in vitro, which suggested reinnervation contributed to the altered immune response.

Distinct morphology of cardiac- and brown adipose tissue-projecting neurons in the stellate ganglia of mice.

Sympathetic neurons that innervate the heart are located primarily in the stellate ganglia (SG), which also contains neurons that project to brown adipose tissue (BAT). These studies were designed to examine the morphology of these two populations (cardiac- and BAT-projecting) and their target connectivity. We examined SG neurons in C57BL/6J mice following injections of the retrograde tracer cholera toxin B (CTb) conjugated to Alexa Fluor 488 and Alexa Fluor 555, into cardiac tissue and intrascapular BAT. BAT-projecting SG neurons were widely dispersed in SG, while cardiac-projecting SG neurons were localized primarily near the inferior cardiac nerve base. SG neurons were not dual-labeled, suggesting that sympathetic innervation is specific to the heart and BAT, supporting the idea of "labeled lines" of efferents. Morphologically, cardiac-projecting SG somata had more volume and were less abundant than BAT-projecting neurons using our tracer-labeling paradigm. We found a positive correlation between the number of primary dendrites per neuron and soma volume in cardiac-projecting SG neurons, though not in BAT-projecting neurons. In both SG subpopulations, the number of cholinergic inputs marked with vesicular acetylcholine transporter (VAChT) puncta contacting the soma was positively correlated to soma volume, suggesting scaling of inputs across a range of neuronal sizes. In separate studies using dual tracing from left and right BAT, we found that BAT-projecting SG neurons were located predominately ipsilateral to the injection, but a small subset of SG neurons project bilaterally to BAT. This tracing approach will allow the assessment of cell-specific mechanisms of plasticity within subpopulations of SG neurons.

Chondroitin sulfate proteoglycan 4,6 sulfation regulates sympathetic nerve regeneration after myocardial infarction.

Sympathetic denervation of the heart following ischemia/reperfusion induced myocardial infarction (MI) is sustained by chondroitin sulfate proteoglycans (CSPGs) in the cardiac scar. Denervation predicts risk of sudden cardiac death in humans. Blocking CSPG signaling restores sympathetic axon outgrowth into the cardiac scar, decreasing arrhythmia susceptibility. Axon growth inhibition by CSPGs can depend on the sulfation status of the glycosaminoglycan (CS-GAG) side chains. Tandem sulfation of CS-GAGs at the 4th (4S) and 6th (6S) positions of n-acetyl-galactosamine inhibits outgrowth in several types of central neurons, but we don't know if sulfation is similarly critical during peripheral nerve regeneration. We asked if CSPG sulfation prevented sympathetic axon outgrowth after MI. Reducing 4S with the 4-sulfatase enzyme Arylsulfatase-B (ARSB) enhanced outgrowth of dissociated rat sympathetic neurons over CSPGs. Likewise, reducing 4S with ARSB restored axon outgrowth from mouse sympathetic ganglia co-cultured with cardiac scar tissue. We quantified enzymes responsible for adding and removing sulfation, and found that CHST15 (4S dependent 6-sulfotransferase) was upregulated, and ARSB was downregulated after MI. This suggests a mechanism for production and maintenance of sulfated CSPGs in the cardiac scar. We decreased 4S,6S CS-GAGs in vivo by transient siRNA knockdown of Chst15 after MI, and found that reducing 4S,6S restored tyrosine hydroxylase (TH) positive sympathetic nerve fibers in the cardiac scar. Reinnervation reduced isoproterenol induced arrhythmias. Our results suggest that modulating CSPG-sulfation after MI may be a therapeutic target to promote sympathetic nerve regeneration in the cardiac scar and reduce post-MI cardiac arrhythmias.

Research Opportunities in Autonomic Neural Mechanisms of Cardiopulmonary Regulation: A Report From the National Heart, Lung, and Blood Institute and the National Institutes of Health Office of the Director Workshop.

This virtual workshop was convened by the National Heart, Lung, and Blood Institute, in partnership with the Office of Strategic Coordination of the Office of the National Institutes of Health Director, and held September 2 to 3, 2020. The intent was to assemble a multidisciplinary group of experts in basic, translational, and clinical research in neuroscience and cardiopulmonary disorders to identify knowledge gaps, guide future research efforts, and foster multidisciplinary collaborations pertaining to autonomic neural mechanisms of cardiopulmonary regulation. The group critically evaluated the current state of knowledge of the roles that the autonomic nervous system plays in regulation of cardiopulmonary function in health and in pathophysiology of arrhythmias, heart failure, sleep and circadian dysfunction, and breathing disorders. Opportunities to leverage the Common Fund's SPARC (Stimulating Peripheral Activity to Relieve Conditions) program were characterized as related to nonpharmacologic neuromodulation and device-based therapies. Common themes discussed include knowledge gaps, research priorities, and approaches to develop novel predictive markers of autonomic dysfunction. Approaches to precisely target neural pathophysiological mechanisms to herald new therapies for arrhythmias, heart failure, sleep and circadian rhythm physiology, and breathing disorders were also detailed.

Untangling Peripheral Sympathetic Neurocircuits.

The sympathetic nervous system plays a critical role in regulating many autonomic functions, including cardiac rhythm. The postganglionic neurons in the sympathetic chain ganglia are essential components that relay sympathetic signals to target tissues and disruption of their activity leads to poor health outcomes. Despite this importance, the neurocircuitry within sympathetic ganglia is poorly understood. Canonically, postganglionic sympathetic neurons are thought to simply be activated by monosynaptic inputs from preganglionic cholinergic neurons of the intermediolateral cell columns of the spinal cord. Early electrophysiological studies of sympathetic ganglia where the peripheral nerve trunks were electrically stimulated identified excitatory cholinergic synaptic events in addition to retrograde action potentials, leading some to speculate that excitatory collateral projections are present. However, this seemed unlikely since sympathetic postganglionic neurons were known to synthesize and release norepinephrine and expression of dual neurochemical phenotypes had not been well recognized. In vitro studies clearly established the capacity of cultured sympathetic neurons to express and release acetylcholine and norepinephrine throughout development and even in pathophysiological conditions. Given this insight, we believe that the canonical view of ganglionic transmission needs to be reevaluated and may provide a mechanistic understanding of autonomic imbalance in disease. Further studies likely will require genetic models manipulating neurochemical phenotypes within sympathetic ganglia to resolve the function of cholinergic collateral projections between postganglionic neurons. In this perspective article, we will discuss the evidence for collateral projections in sympathetic ganglia, determine if current laboratory techniques could address these questions, and discuss potential obstacles and caveats.

Small Molecules Targeting PTPσ-Trk Interactions Promote Sympathetic Nerve Regeneration.

Chondroitin sulfate proteoglycans (CSPGs) prevent sympathetic nerve regeneration in the heart after myocardial infarction and prevent central nerve regrowth after traumatic brain injury and spinal cord injury. Currently, there are no small-molecule therapeutics to promote nerve regeneration through CSPG-containing scars. CSPGs bind to monomers of receptor protein tyrosine phosphatase sigma (PTPσ) on the surface of neurons, enhancing the ability of PTPσ to bind and dephosphorylate tropomyosin receptor kinases (Trks), inhibiting their activity and preventing axon outgrowth. Targeting PTPσ-Trk interactions is thus a potential therapeutic target. Here, we describe the development and synthesis of small molecules (HJ-01 and HJ-02) that disrupt PTPσ interactions with Trks, enhance Trk signaling, and promote sympathetic nerve regeneration over CSPGs.

A primer on incorporating sex as a biological variable into the conduct and reporting of basic and clinical research studies.

The recent move to require sex as a biological variable (SABV), which includes gender, into the reporting of research published by the American Journal of Physiology-Heart and Circulatory Physiology follows a growing, and much-needed, trend by journals. Understandably, there is concern over how to do this without adding considerable work, especially if one's primary research focus is not on elucidating sex/gender differences. The purpose of this article is to provide additional guidance and examples on how to incorporate SABV into the conduct and reporting of basic and clinical research. Using examples from our research, which includes both studies focused and not focused on sex/gender differences, we offer suggestions for how to incorporate SABV into basic and clinical research studies.

Background and Design of the Biological and Physiological Mechanisms of Symptom Clusters in Heart Failure (BIOMES-HF) Study.

BACKGROUND: Symptoms, which often cluster together, are a significant problem in heart failure (HF). There is considerable heterogeneity in symptom burden, particularly in the vulnerable transition period after a hospitalization for HF, and the biological underpinnings of symptoms during transitions are unclear. The purpose of this article is to describe the background and design of a study that addresses these knowledge gaps, entitled Biological and Physiological Mechanisms of Symptom Clusters in Heart Failure (BIOMES-HF). METHODS AND RESULTS: BIOMES-HF is a prospective gender- and age-balanced longitudinal study of 240 adults during the 6-month transition period after a HF hospitalization. The aims are to (1) identify clusters of change in physical symptoms, (2) quantify longitudinal associations between biomarkers and physical symptoms, and (3) quantify longitudinal associations between physical frailty and physical symptoms among adults with HF. We will measure multiple symptoms, biomarkers, and physical frailty at discharge and then at 1 week and 1, 3, and 6 months after hospitalization. We will use growth mixture modeling and longitudinal mediation modeling to examine changes in symptoms, biomarkers, and physical frailty after HF hospitalization and associations therein. CONCLUSIONS: This innovative study will advance HF symptom science by using a multibiomarker panel and the physical frailty phenotype to capture the multifaceted nature of HF. Using advanced quantitative modeling, we will characterize heterogeneity and identify potential mechanisms of symptoms in HF. As a result, this research will pinpoint amenable targets for intervention to provide better, individualized treatment to improve symptom burden in HF. LAY SUMMARY: Adults with heart failure may have significant symptom burden. This study is designed to shed light on our understanding of the role of biological and physiological mechanisms in explaining heart failure symptoms, particularly groups of co-occurring symptoms, over time. We explore how symptoms, biomarkers, and physical frailty change after a heart failure hospitalization. The knowledge generated from this study will be used to guide the management and self-care for adults with heart failure.

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.

Phosphorylation of Lamin A/C at serine 22 modulates Nav 1.5 function.

Variants in the LMNA gene, which encodes for Lamin A/C, are associated with cardiac conduction disease (CCD). We previously reported that Lamin A/C variants p.R545H and p.A287Lfs*193, which were identified in CCD patients, decreased peak INa in HEK-293 cells expressing Nav 1.5. Decreased peak INa in the cardiac conduction system could account for patients' atrioventricular block. We found that serine 22 (Ser 22) phosphorylation of Lamin A/C was decreased in the p.R545H variant and hypothesized that lamin phosphorylation modulated Nav 1.5 activity. To test this hypothesis, we assessed Nav 1.5 function in HEK-293 cells co-transfected with LMNA variants or treated with the small molecule LBL1 (lamin-binding ligand 1). LBL1 decreased Ser 22 phosphorylation by 65% but did not affect Nav 1.5 function. To test the complete loss of phosphorylation, we generated a version of LMNA with serine 22 converted to alanine 22 (S22A-LMNA); and a version of mutant R545H-LMNA that mimics phosphorylation via serine 22 to aspartic acid 22 substitution (S22D-R545H-LMNA). We found that S22A-LMNA inhibited Lamin-mediated activation of peak INa by 63% and shifted voltage-dependency of steady-state inactivation of Nav 1.5. Conversely, S22D-R545H-LMNA abolished the effects of mutant R545H-LMNA on voltage-dependency but not peak INa . We conclude that Lamin A/C Ser 22 phosphorylation can modulate Nav 1.5 function and contributes to the mechanism by which R545H-LMNA alters Nav 1.5 function. The differential impact of complete versus partial loss of Ser 22 phosphorylation suggests a threshold of phosphorylation that is required for full Nav 1.5 modulation. This is the first study to link Lamin A/C phosphorylation to Nav 1.5 function.