Innervating sympathetic neurons regulate heart size and the timing of cardiomyocyte cell cycle withdrawal

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.

β-Adrenergic signaling drives structural and functional maturation of mouse cardiomyocytes

Cardiac maturation represents the last phase of heart development and is characterized by morphofunctional alterations that optimize the heart for efficient pumping. Its understanding provides important insights into cardiac regeneration therapies. Recent evidence implies that adrenergic signals are involved in the regulation of cardiac maturation, but the mechanistic underpinnings involved in this process are poorly understood. Herein, we explored the role of β-adrenergic receptor (β-AR) activation in determining structural and functional components of cardiomyocyte maturation. Temporal characterization of tyrosine hydroxylase and norepinephrine levels in the mouse heart revealed that sympathetic innervation develops during the first 3 wk of life, concurrent with the rise in β-AR expression. To assess the impact of adrenergic inhibition on maturation, we treated mice with propranolol, isolated cardiomyocytes, and evaluated morphofunctional parameters. Propranolol treatment reduced heart weight, cardiomyocyte size, and cellular shortening, while it increased the pool of mononucleated myocytes, resulting in impaired maturation. No changes in t-tubules were observed in cells from propranolol mice. To establish a causal link between β-AR signaling and cardiomyocyte maturation, mice were subjected to sympathectomy, followed or not by restoration with isoproterenol treatment. Cardiomyocytes from sympathectomyzed mice recapitulated the salient immaturity features of propranolol-treated mice, with the additional loss of t-tubules. Isoproterenol rescued the maturation deficits induced by sympathectomy, except for the t-tubule alterations. Our study identifies the β-AR stimuli as a maturation promoting signal and implies that this pathway can be modulated to improve cardiac regeneration therapies.NEW & NOTEWORTHY Maturation involves a series of morphofunctional alterations vital to heart development. Its regulatory mechanisms are only now being unveiled. Evidence implies that adrenergic signaling regulates cardiac maturation, but the mechanisms are poorly understood. To address this point, we blocked β-ARs or performed sympathectomy followed by rescue experiments with isoproterenol in neonatal mice. Our study identifies the β-AR stimuli as a maturation signal for cardiomyocytes and highlights the importance of this pathway in cardiac regeneration therapies.

A modular platform to generate functional sympathetic neuron-innervated heart assembloids

The technology of human pluripotent stem cell (hPSC)-based 3D organoid/assembloid cultures has become a powerful tool for the study of human embryonic development, disease modeling and drug discovery in recent years. The autonomic sympathetic nervous system innervates and regulates almost all organs in the body, including the heart. Yet, most reported organoids to date are not innervated, thus lacking proper neural regulation, and hindering reciprocal tissue maturation. Here, we developed a simple and versatile sympathetic neuron (symN)-innervated cardiac assembloid without the need for bioengineering. Our human sympathetic cardiac assembloids (hSCAs) showed mature muscle structures, atrial to ventricular patterning, and spontaneous beating. hSCA-innervating symNs displayed neurotransmitter synthesis and functional regulation of the cardiac beating rate, which could be manipulated pharmacologically or optogenetically. We modeled symN-mediated cardiac development and myocardial infarction. This hSCAs provides a tool for future neurocardiotoxicity screening approaches and is highly versatile and modular, where the types of neuron (symN or parasympathetic or sensory neuron) and organoid (heart, lung, kidney) to be innervated may be interchanged.

NADPH oxidase 2 inhibitor GSK2795039 prevents doxorubicin-induced cardiac atrophy by attenuating cardiac sympathetic nerve terminal abnormalities and myocyte autophagy

Doxorubicin is widely used for the treatment of human cancer, but its clinical use is limited by a cumulative dose-dependent cardiotoxicity. However, the mechanism of doxorubicin-induced cardiac atrophy and failure remains to be fully understood. In this study, we tested whether the specific NADPH oxidase 2 (Nox2) inhibitor GSK2795039 attenuates cardiac sympathetic nerve terminal abnormalities and myocyte autophagy, leading to the amelioration of cardiac atrophy and dysfunction in chronic doxorubicin-induced cardiomyopathy. Mice were randomized to receive saline, doxorubicin (2.5 mg/kg, every other day, 6 times) or doxorubicin plus GSK2795039 (2.5 mg/kg, twice a day, 9 weeks). Left ventricular (LV) total wall thickness and LV ejection fraction were decreased in doxorubicin-treated mice compared with saline-treated mice and the decreases were prevented by the treatment of the specific Nox2 inhibitor GSK2795039. The ratio of total heart weight to tibia length and myocyte cross-sectional area were decreased in doxorubicin-treated mice, and the decreases were attenuated by the GSK2795039 treatment. In doxorubicin-treated mice, myocardial Nox2 and 4-hydroxynonenal levels were increased, myocardial expression of GAP43, tyrosine hydroxylase and norepinephrine transporter, markers of sympathetic nerve terminals, was decreased, and these changes were prevented by the GSK2795039 treatment. The ratio of LC3 II/I, a marker of autophagy, and Atg5, Atg12 and Atg12-Atg5 conjugate proteins were increased in doxorubicin-treated mice, and the increases were attenuated by the GSK2795039 treatment. These findings suggest that inhibition of Nox2 by GSK2795039 attenuates cardiac sympathetic nerve terminal abnormalities and myocyte autophagy, thereby ameliorating cardiac atrophy and dysfunction after chronic doxorubicin treatment.

Reprogramming of the developing heart by Hif1a-deficient sympathetic system and maternal diabetes exposure

Introduction

Maternal diabetes is a recognized risk factor for both short-term and long-term complications in offspring. Beyond the direct teratogenicity of maternal diabetes, the intrauterine environment can influence the offspring's cardiovascular health. Abnormalities in the cardiac sympathetic system are implicated in conditions such as sudden infant death syndrome, cardiac arrhythmic death, heart failure, and certain congenital heart defects in children from diabetic pregnancies. However, the mechanisms by which maternal diabetes affects the development of the cardiac sympathetic system and, consequently, heightens health risks and predisposes to cardiovascular disease remain poorly understood.

Methods and results

In the mouse model, we performed a comprehensive analysis of the combined impact of a Hif1a-deficient sympathetic system and the maternal diabetes environment on both heart development and the formation of the cardiac sympathetic system. The synergic negative effect of exposure to maternal diabetes and Hif1a deficiency resulted in the most pronounced deficit in cardiac sympathetic innervation and the development of the adrenal medulla. Abnormalities in the cardiac sympathetic system were accompanied by a smaller heart, reduced ventricular wall thickness, and dilated subepicardial veins and coronary arteries in the myocardium, along with anomalies in the branching and connections of the main coronary arteries. Transcriptional profiling by RNA sequencing (RNA-seq) revealed significant transcriptome changes in Hif1a-deficient sympathetic neurons, primarily associated with cell cycle regulation, proliferation, and mitosis, explaining the shrinkage of the sympathetic neuron population.

Discussion

Our data demonstrate that a failure to adequately activate the HIF-1α regulatory pathway, particularly in the context of maternal diabetes, may contribute to abnormalities in the cardiac sympathetic system. In conclusion, our findings indicate that the interplay between deficiencies in the cardiac sympathetic system and subtle structural alternations in the vasculature, microvasculature, and myocardium during heart development not only increases the risk of cardiovascular disease but also diminishes the adaptability to the stress associated with the transition to extrauterine life, thus increasing the risk of neonatal death.

Neural dependency in wound healing and regeneration

In response to injury, humans and many other mammals form a fibrous scar that lacks the structure and function of the original tissue, whereas other vertebrate species can spontaneously regenerate damaged tissues and structures. Peripheral nerves have been identified as essential mediators of wound healing and regeneration in both mammalian and nonmammalian systems, interacting with the milieu of cells and biochemical signals present in the post-injury microenvironment. This review examines the diverse functions of peripheral nerves in tissue repair and regeneration, specifically during the processes of wound healing, blastema formation, and organ repair. We compare available evidence in mammalian and nonmammalian models, identifying critical nerve-mediated mechanisms for regeneration and providing future perspectives toward integrating these mechanisms into a therapeutic framework to promote regeneration.

Sympathetic neuropathology is revealed in muscles affected by amyotrophic lateral sclerosis

Rationale: The anatomical substrate of skeletal muscle autonomic innervation has remained underappreciated since it was described many decades ago. As such, the structural and functional features of muscle sympathetic innervation are largely undetermined in both physiology and pathology, mainly due to methodological limitations in the histopathological analysis of small neuronal fibers in tissue samples. Amyotrophic lateral sclerosis (ALS) is a fatal neuromuscular disease which mainly targets motor neurons, and despite autonomic symptoms occurring in a significant fraction of patients, peripheral sympathetic neurons (SNs) are generally considered unaffected and, as such, poorly studied. Purpose: In this research, we compared sympathetic innervation of normal and ALS muscles, through structural analysis of the sympathetic network in human and murine tissue samples. Methods and Results: We first refined tissue processing to circumvent methodological limitations interfering with the detection of muscle sympathetic innervation. The optimized "Neuro Detection Protocol" (NDP) was validated in human muscle biopsies, demonstrating that SNs innervate, at high density, both blood vessels and skeletal myofibers, independent of the fiber metabolic type. Subsequently, NDP was exploited to analyze sympathetic innervation in muscles of SOD1^G93A mice, a preclinical ALS model. Our data show that ALS murine muscles display SN denervation, which has already initiated at the early disease stage and worsened during aging. SN degeneration was also observed in muscles of MLC/SOD1^G93A mice, with muscle specific expression of the SOD1^G93A mutant gene. Notably, similar alterations in SNs were observed in muscle biopsies from an ALS patient, carrying the SOD1^G93A mutation. Conclusion: We set up a protocol for the analysis of murine and, more importantly, human muscle sympathetic innervation. Our results indicate that SNs are additional cell types compromised in ALS and suggest that dysfunctional SOD1^G93A muscles affect their sympathetic innervation.

Impact of Non-Muscle Cells on Excitation-Contraction Coupling in the Heart and the Importance of In Vitro Models

Excitation-coupling (ECC) is paramount for coordinated contraction to maintain sufficient cardiac output. The study of ECC regulation has primarily been limited to cardiomyocytes (CMs), which conduct voltage waves via calcium fluxes from one cell to another, eliciting contraction of the atria followed by the ventricles. CMs rapidly transmit ionic flux via gap junction proteins, predominantly connexin 43. While the expression of connexin isoforms has been identified in each of the individual cell populations comprising the heart, the formation of gap junctions with nonmuscle cells (i.e., macrophages and Schwann cells) has gained new attention. Evaluating nonmuscle contributions to ECC in vivo or in situ remains difficult and necessitates the development of simple, yet biomimetic in vitro models to better understand and prevent physiological dysfunction. Standard 2D cell culture often consists of homogenous cell populations and lacks the dynamic mechanical environment of native tissue, confounding the phenotypic and proteomic makeup of these highly mechanosensitive cell populations in prolonged culture conditions. This review will highlight the recent developments and the importance of new microphysiological systems to better understand the complex regulation of ECC in cardiac tissue.

Dysregulation of hypoxia-inducible factor 1α in the sympathetic nervous system accelerates diabetic cardiomyopathy

BACKGROUND

An altered sympathetic nervous system is implicated in many cardiac pathologies, ranging from sudden infant death syndrome to common diseases of adulthood such as hypertension, myocardial ischemia, cardiac arrhythmias, myocardial infarction, and heart failure. Although the mechanisms responsible for disruption of this well-organized system are the subject of intensive investigations, the exact processes controlling the cardiac sympathetic nervous system are still not fully understood. A conditional knockout of the Hif1a gene was reported to affect the development of sympathetic ganglia and sympathetic innervation of the heart. This study characterized how the combination of HIF-1α deficiency and streptozotocin (STZ)-induced diabetes affects the cardiac sympathetic nervous system and heart function of adult animals.

METHODS

Molecular characteristics of Hif1a deficient sympathetic neurons were identified by RNA sequencing. Diabetes was induced in Hif1a knockout and control mice by low doses of STZ treatment. Heart function was assessed by echocardiography. Mechanisms involved in adverse structural remodeling of the myocardium, i.e. advanced glycation end products, fibrosis, cell death, and inflammation, was assessed by immunohistological analyses.

RESULTS

We demonstrated that the deletion of Hif1a alters the transcriptome of sympathetic neurons, and that diabetic mice with the Hif1a-deficient sympathetic system have significant systolic dysfunction, worsened cardiac sympathetic innervation, and structural remodeling of the myocardium.

CONCLUSIONS

We provide evidence that the combination of diabetes and the Hif1a deficient sympathetic nervous system results in compromised cardiac performance and accelerated adverse myocardial remodeling, associated with the progression of diabetic cardiomyopathy.

Cancer neuroscience: State of the field, emerging directions

The nervous system governs both ontogeny and oncology. Regulating organogenesis during development, maintaining homeostasis, and promoting plasticity throughout life, the nervous system plays parallel roles in the regulation of cancers. Foundational discoveries have elucidated direct paracrine and electrochemical communication between neurons and cancer cells, as well as indirect interactions through neural effects on the immune system and stromal cells in the tumor microenvironment in a wide range of malignancies. Nervous system-cancer interactions can regulate oncogenesis, growth, invasion and metastatic spread, treatment resistance, stimulation of tumor-promoting inflammation, and impairment of anti-cancer immunity. Progress in cancer neuroscience may create an important new pillar of cancer therapy.

Unlocking cardiomyocyte renewal potential for myocardial regeneration therapy

Cardiovascular disease remains the leading cause of mortality worldwide. Cardiomyocytes are irreversibly lost due to cardiac ischemia secondary to disease. This leads to increased cardiac fibrosis, poor contractility, cardiac hypertrophy, and subsequent life-threatening heart failure. Adult mammalian hearts exhibit notoriously low regenerative potential, further compounding the calamities described above. Neonatal mammalian hearts, on the other hand, display robust regenerative capacities. Lower vertebrates such as zebrafish and salamanders retain the ability to replenish lost cardiomyocytes throughout life. It is critical to understand the varying mechanisms that are responsible for these differences in cardiac regeneration across phylogeny and ontogeny. Adult mammalian cardiomyocyte cell cycle arrest and polyploidization have been proposed as major barriers to heart regeneration. Here we review current models about why adult mammalian cardiac regenerative potential is lost including changes in environmental oxygen levels, acquisition of endothermy, complex immune system development, and possible cancer risk tradeoffs. We also discuss recent progress and highlight conflicting reports pertaining to extrinsic and intrinsic signaling pathways that control cardiomyocyte proliferation and polyploidization in growth and regeneration. Uncovering the physiological brakes of cardiac regeneration could illuminate novel molecular targets and offer promising therapeutic strategies to treat heart failure.

Biomedical applications of three-dimensional bioprinted craniofacial tissue engineering

Anatomical complications of the craniofacial regions often present considerable challenges to the surgical repair or replacement of the damaged tissues. Surgical repair has its own set of limitations, including scarcity of the donor tissues, immune rejection, use of immune suppressors followed by the surgery, and restriction in restoring the natural aesthetic appeal. Rapid advancement in the field of biomaterials, cell biology, and engineering has helped scientists to create cellularized skeletal muscle-like structures. However, the existing method still has limitations in building large, highly vascular tissue with clinical application. With the advance in the three-dimensional (3D) bioprinting technique, scientists and clinicians now can produce the functional implants of skeletal muscles and bones that are more patient-specific with the perfect match to the architecture of their craniofacial defects. Craniofacial tissue regeneration using 3D bioprinting can manage and eliminate the restrictions of the surgical transplant from the donor site. The concept of creating the new functional tissue, exactly mimicking the anatomical and physiological function of the damaged tissue, looks highly attractive. This is crucial to reduce the donor site morbidity and retain the esthetics. 3D bioprinting can integrate all three essential components of tissue engineering, that is, rehabilitation, reconstruction, and regeneration of the lost craniofacial tissues. Such integration essentially helps to develop the patient-specific treatment plans and damage site-driven creation of the functional implants for the craniofacial defects. This article is the bird's eye view on the latest development and application of 3D bioprinting in the regeneration of the skeletal muscle tissues and their application in restoring the functional abilities of the damaged craniofacial tissue. We also discussed current challenges in craniofacial bone vascularization and gave our view on the future direction, including establishing the interactions between tissue-engineered skeletal muscle and the peripheral nervous system.

Impact of Neurons on Patient-Derived Cardiomyocytes Using Organ-On-A-Chip and iPSC Biotechnologies

In the heart, cardiac function is regulated by the autonomic nervous system (ANS) that extends through the myocardium and establishes junctions at the sinus node and ventricular levels. Thus, an increase or decrease in neuronal activity acutely affects myocardial function and chronically affects its structure through remodeling processes. The neuro-cardiac junction (NCJ), which is the major structure of this system, is poorly understood and only a few cell models allow us to study it. Here, we present an innovant neuro-cardiac organ-on-chip model to study this structure to better understand the mechanisms involved in the establishment of NCJ. To create such a system, we used microfluidic devices composed of two separate cell culture compartments interconnected by asymmetric microchannels. Rat PC12 cells were differentiated to recapitulate the characteristics of sympathetic neurons, and cultivated with cardiomyocytes derived from human induced pluripotent stem cells (hiPSC). We confirmed the presence of a specialized structure between the two cell types that allows neuromodulation and observed that the neuronal stimulation impacts the excitation-contraction coupling properties including the intracellular calcium handling. Finally, we also co-cultivated human neurons (hiPSC-NRs) with human cardiomyocytes (hiPSC-CMs), both obtained from the same hiPSC line. Hence, we have developed a neuro-cardiac compartmentalized in vitro model system that allows us to recapitulate the structural and functional properties of the neuro-cardiac junction and that can also be used to better understand the interaction between the heart and brain in humans, as well as to evaluate the impact of drugs on a reconstructed human neuro-cardiac system.

Dynamics of metabolism and regulation of epigenetics during cardiomyocytes maturation

Maturation is the last step of heart growth that prepares the organ over the lifetime of the mammal for powerful, effective, and sustained pumping. Structural, gene expression, physiological, and functional specialties of cardiomyocytes describe this mechanism as the heart transits from fetus to adult phases. The main cornerstones of maturation of cardiomyocytes are reviewed and primary regulatory mechanisms are summarized to facilitate and organize these cellular activities. During embryonic development, cardiomyocytes proliferate rigorously but leave the cell cycle permanently immediately after the parturition of the child and experience terminal differentiation. The activation of a host of genes specific for the mature heart is correlated with the exit from the cell cycle. Even when exposed to mitogenic stimuli, the bulk of mature cardiomyocytes do not re-join the cell cycle. The reason for this permanent exit from the cell cycle is shown to be linked with stable switching off of the genes of the cell cycle directly involved in the G2/M transition phase and cytokinesis development. Researchers also trying to explain the molecular mechanism involved in stable inhibition of the gene and described structural changes (epigenetic and chromatin) in this mechanism. Substantial developments in the future with advances in the scientific platforms used for cardiomyocyte maturation research will broaden our understanding of this mechanism and result in better maturation of cardiomyocyte-derived pluripotent stem cells and effective treatment approaches for cardiovascular diseases.

Heightened sympathetic neuron activity and altered cardiomyocyte properties in spontaneously hypertensive rats during the postnatal period

The Spontaneously Hypertensive Rat (SHR) has increased sympathetic drive to the periphery that precedes and contributes to the development of high blood pressure, making it a useful model for the study of neurogenic hypertension. Comparisons to the normotensive Wistar Kyoto (WKY) rat have demonstrated altered active and intrinsic properties of SHR sympathetic neurons shortly before the onset of hypertension. Here we examine the structural and functional plasticity of postnatal SHR and WKY sympathetic neurons cultured alone or co-cultured with cardiomyocytes under conditions of limited extrinsic signaling. SHR neurons have an increased number of structural synaptic sites compared to age-matched WKY neurons, measured by the co-localization of presynaptic vesicular acetylcholine transporter and postsynaptic shank proteins. Whole cell recordings show that SHR neurons have a higher synaptic charge than WKY neurons, demonstrating that the increase in synaptic sites is associated with increased synaptic transmission. Differences in synaptic properties are not associated with altered firing rates between postnatal WKY and SHR neurons and are not influenced by interactions with target cardiomyocytes from either strain. Both SHR and WKY neurons show tonic firing patterns in our cultures, which are depleted of non-neuronal ganglionic cells and provide limited neurotrophic signaling. This suggests that the normal mature, phasic firing of sympathetic neurons requires extrinsic signaling, with potentially differential responses in the prehypertensive SHR, which have been reported to maintain tonic firing at later developmental stages. While cardiomyocytes do not drive neuronal differences in our cultures, SHR cardiomyocytes display decreased hypertrophy compared to WKY cells and altered responses to co-cultured sympathetic neurons. These experiments suggest that altered signaling in SHR neurons and cardiomyocytes contributes to changes in the cardiac-sympathetic circuit in prehypertensive rats as early as the postnatal period.

Innervation in organogenesis

Proper innervation of peripheral organs helps to maintain physiological homeostasis and elicit responses to external stimuli. Disruptions to normal function can result in pathophysiological consequences. The establishment of connections and communication between the central nervous system and the peripheral organs is accomplished through the peripheral nervous system. Neuronal connections with target tissues arise from ganglia partitioned throughout the body. Organ innervation is initiated during development with stimuli being conducted through several types of neurons including sympathetic, parasympathetic, and sensory. While the physiological modulation of mature organs by these nerves is largely understood, their role in mammalian development is only beginning to be uncovered. Interactions with cells in target tissues can affect the development and eventual function of several organs, highlighting their significance. This chapter will cover the origin of peripheral neurons, factors mediating organ innervation, and the composition and function of organ-specific nerves during development. This emerging field aims to identify the functional contribution of innervation to development which will inform future investigations of normal and abnormal mammalian organogenesis, as well as contribute to regenerative and organ replacement efforts where nerve-derived signals may have significant implications for the advancement of such studies.

Tuning the Consonance of Microscopic Neuro-Cardiac Interactions Allows the Heart Beats to Play Countless Genres

Different from skeletal muscle, the heart autonomously generates rhythmic contraction independently from neuronal inputs. However, speed and strength of the heartbeats are continuously modulated by environmental, physical or emotional inputs, delivered by cardiac innervating sympathetic neurons, which tune cardiomyocyte (CM) function, through activation of β-adrenoceptors (β-ARs). Given the centrality of such mechanism in heart regulation, β-AR signaling has been subject of intense research, which has reconciled the molecular details of the transduction pathway and the fine architecture of cAMP signaling in subcellular nanodomains, with its final effects on CM function. The importance of mechanisms keeping the elements of β-AR/cAMP signaling in good order emerges in pathology, when the loss of proper organization of the transduction pathway leads to detuned β-AR/cAMP signaling, with detrimental consequences on CM function. Despite the compelling advancements in decoding cardiac β-AR/cAMP signaling, most discoveries on the subject were obtained in isolated cells, somehow neglecting that complexity may encompass the means in which receptors are activated in the intact heart. Here, we outline a set of data indicating that, in the context of the whole myocardium, the heart orchestra (CMs) is directed by a closely interacting and continuously attentive conductor, represented by SNs. After a roundup of literature on CM cAMP regulation, we focus on the unexpected complexity and roles of cardiac sympathetic innervation, and present the recently discovered Neuro-Cardiac Junction, as the election site of "SN-CM" interaction. We further discuss how neuro-cardiac communication is based on the combination of extra- and intra-cellular signaling micro/nano-domains, implicating neuronal neurotransmitter exocytosis, β-ARs and elements of cAMP homeostasis in CMs, and speculate on how their dysregulation may reflect on dysfunctional neurogenic control of the heart in pathology.

Sympathetic Neurons Regulate Cardiomyocyte Maturation in Culture

Embryos devoid of autonomic innervation suffer sudden cardiac death. However, whether autonomic neurons have a role in heart development is poorly understood. To investigate if sympathetic neurons impact cardiomyocyte maturation, we co-cultured phenotypically immature cardiomyocytes derived from human induced pluripotent stem cells with mouse sympathetic ganglion neurons. We found that 1) multiple cardiac structure and ion channel genes related to cardiomyocyte maturation were up-regulated when co-cultured with sympathetic neurons; 2) sarcomere organization and connexin-43 gap junctions increased; 3) calcium imaging showed greater transient amplitudes. However, sarcomere spacing, relaxation time, and level of sarcoplasmic reticulum calcium did not show matured phenotypes. We further found that addition of endothelial and epicardial support cells did not enhance maturation to a greater extent beyond sympathetic neurons, while administration of isoproterenol alone was insufficient to induce changes in gene expression. These results demonstrate that sympathetic neurons have a significant and complex role in regulating cardiomyocyte development.

The microRNA-204-5p inhibits APJ signalling and confers resistance to cardiac hypertrophy and dysfunction

BACKGROUND

MicroRNAs regulate cardiac hypertrophy development, which precedes and predicts the risk of heart failure. microRNA-204-5p (miR-204) is well expressed in cardiomyocytes, but its role in developing cardiac hypertrophy and cardiac dysfunction (CH/CD) remains poorly understood.

METHODS

We performed RNA-sequencing, echocardiographic, and molecular/morphometric analysis of the heart of mice lacking or overexpressing miR-204 five weeks after trans-aortic constriction (TAC). The neonatal rat cardiomyocytes, H9C2, and HEK293 cells were used to determine the mechanistic role of miR-204.

RESULTS

The stretch induces miR-204 expression, and miR-204 inhibits the stretch-induced hypertrophic response of H9C2 cells. The mice lacking miR-204 displayed a higher susceptibility to CH/CD during pressure overload, which was reversed by the adeno-associated virus serotype-9-mediated cardioselective miR-204 overexpression. Bioinformatic analysis of the cardiac transcriptomics of miR-204 knockout mice following pressure overload suggested deregulation of apelin-receptor (APJ) signalling. We found that the stretch-induced extracellular signal-regulated kinase 1/2 (ERK1/2) activation and hypertrophy-related genes expression depend on the APJ, and both of these effects are subject to miR-204 levels. The dynamin inhibitor dynasore inhibited both stretch-induced APJ endocytosis and ERK1/2 activation. In contrast, the miR-204-induced APJ endocytosis was neither inhibited by dynamin inhibitors (dynasore and dyngo) nor associated with ERK1/2 activation. We find that the miR-204 increases the expression of ras-associated binding proteins (e.g., Rab5a, Rab7) that regulate cellular endocytosis.

CONCLUSIONS

Our results show that miR-204 regulates trafficking of APJ and confers resistance to pressure overload-induced CH/CD, and boosting miR-204 can inhibit the development of CH/CD.

Heart neurons use clock genes to control myocyte proliferation

Neurons can regulate the development, pathogenesis, and regeneration of target organs. However, the role of neurons during heart development and regeneration remains unclear. We genetically inhibited sympathetic innervation in vivo, which resulted in heart enlargement with an increase in cardiomyocyte number. Transcriptomic and protein analysis showed down-regulation of the two clock gene homologs Period1/Period2 (Per1/Per2) accompanied by up-regulation of cell cycle genes. Per1/Per2 deletion increased heart size and cardiomyocyte proliferation, recapitulating sympathetic neuron–deficient hearts. Conversely, increasing sympathetic activity by norepinephrine treatment induced Per1/Per2 and suppressed cardiomyocyte proliferation. We further found that the two clock genes negatively regulate myocyte mitosis entry through the Wee1 kinase pathway. Our findings demonstrate a previously unknown link between cardiac neurons and clock genes in regulation of cardiomyocyte proliferation and heart size and provide mechanistic insights for developing neuromodulation strategies for cardiac regen5eration.

The sympathetic nervous system in development and disease

The sympathetic nervous system prepares the body for 'fight or flight' responses and maintains homeostasis during daily activities such as exercise, eating a meal or regulation of body temperature. Sympathetic regulation of bodily functions requires the establishment and refinement of anatomically and functionally precise connections between postganglionic sympathetic neurons and peripheral organs distributed widely throughout the body. Mechanistic studies of key events in the formation of postganglionic sympathetic neurons during embryonic and early postnatal life, including axon growth, target innervation, neuron survival, and dendrite growth and synapse formation, have advanced the understanding of how neuronal development is shaped by interactions with peripheral tissues and organs. Recent progress has also been made in identifying how the cellular and molecular diversity of sympathetic neurons is established to meet the functional demands of peripheral organs. In this Review, we summarize current knowledge of signalling pathways underlying the development of the sympathetic nervous system. These findings have implications for unravelling the contribution of sympathetic dysfunction stemming, in part, from developmental perturbations to the pathophysiology of peripheral neuropathies and cardiovascular and metabolic disorders.

Reawakening the Intrinsic Cardiac Regenerative Potential: Molecular Strategies to Boost Dedifferentiation and Proliferation of Endogenous Cardiomyocytes

Despite considerable efforts carried out to develop stem/progenitor cell-based technologies aiming at replacing and restoring the cardiac tissue following severe damages, thus far no strategies based on adult stem cell transplantation have been demonstrated to efficiently generate new cardiac muscle cells. Intriguingly, dedifferentiation, and proliferation of pre-existing cardiomyocytes and not stem cell differentiation represent the preponderant cellular mechanism by which lower vertebrates spontaneously regenerate the injured heart. Mammals can also regenerate their heart up to the early neonatal period, even in this case by activating the proliferation of endogenous cardiomyocytes. However, the mammalian cardiac regenerative potential is dramatically reduced soon after birth, when most cardiomyocytes exit from the cell cycle, undergo further maturation, and continue to grow in size. Although a slow rate of cardiomyocyte turnover has also been documented in adult mammals, both in mice and humans, this is not enough to sustain a robust regenerative process. Nevertheless, these remarkable findings opened the door to a branch of novel regenerative approaches aiming at reactivating the endogenous cardiac regenerative potential by triggering a partial dedifferentiation process and cell cycle re-entry in endogenous cardiomyocytes. Several adaptations from intrauterine to extrauterine life starting at birth and continuing in the immediate neonatal period concur to the loss of the mammalian cardiac regenerative ability. A wide range of systemic and microenvironmental factors or cell-intrinsic molecular players proved to regulate cardiomyocyte proliferation and their manipulation has been explored as a therapeutic strategy to boost cardiac function after injuries. We here review the scientific knowledge gained thus far in this novel and flourishing field of research, elucidating the key biological and molecular mechanisms whose modulation may represent a viable approach for regenerating the human damaged myocardium.

Neurohumoral Cardiac Regulation: Optogenetics Gets Into the Groove

The cardiac autonomic nervous system (ANS) is the main modulator of heart function, adapting contraction force, and rate to the continuous variations of intrinsic and extrinsic environmental conditions. While the parasympathetic branch dominates during rest-and-digest sympathetic neuron (SN) activation ensures the rapid, efficient, and repeatable increase of heart performance, e.g., during the "fight-or-flight response." Although the key role of the nervous system in cardiac homeostasis was evident to the eyes of physiologists and cardiologists, the degree of cardiac innervation, and the complexity of its circuits has remained underestimated for too long. In addition, the mechanisms allowing elevated efficiency and precision of neurogenic control of heart function have somehow lingered in the dark. This can be ascribed to the absence of methods adequate to study complex cardiac electric circuits in the unceasingly moving heart. An increasing number of studies adds to the scenario the evidence of an intracardiac neuron system, which, together with the autonomic components, define a little brain inside the heart, in fervent dialogue with the central nervous system (CNS). The advent of optogenetics, allowing control the activity of excitable cells with cell specificity, spatial selectivity, and temporal resolution, has allowed to shed light on basic neuro-cardiology. This review describes how optogenetics, which has extensively been used to interrogate the circuits of the CNS, has been applied to untangle the knots of heart innervation, unveiling the cellular mechanisms of neurogenic control of heart function, in physiology and pathology, as well as those participating to brain-heart communication, back and forth. We discuss existing literature, providing a comprehensive view of the advancement in the understanding of the mechanisms of neurogenic heart control. In addition, we weigh the limits and potential of optogenetics in basic and applied research in neuro-cardiology.

Neuregulin-1, in a Conducive Milieu with Wnt/BMP/Retinoic Acid, Prolongs the Epicardial-Mediated Cardiac Regeneration Capacity of Neonatal Heart Explants

Rationale: Cardiac sympathetic nerves are required for endogenous repair of the mammalian neonatal heart in vivo, but the underlying mechanism is unclear. Objective: We tested the hypothesis that a combination of cardiac developmental growth factors Wnt3a, BMP4 and Neuregulin (NRG-1), compensate for denervation and support cardiac regeneration in explanted neonatal mammalian hearts. Methods and Results: Hearts from 2-day old neonatal mice were harvested, lesioned at the apex and grown ex vivo for 21 days under defined conditions. Hearts grown in canonical cardiomyocyte culture media underwent complete coagulative necrosis, a process resembling ischemic cell death, by day 14. However, the addition of Wnt3a, BMP-4 and NRG-1, maintained cellular integrity and restored the endogenous regenerative program. None of these factors alone, or in any paired combination, were sufficient to induce regeneration in culture. rNRG-1 alone significantly reduced the accumulation of double strand DNA damage at Day 3; (-NRG-1: 60±12%; +NRG-1: 8±3%; P<0.01) and prevented coagulative necrosis at Day 14. Short-term addition of rWnt3a and rBMP-4 (day 0-3, NRG-1+) increased WT1 expression (a marker of epicardial cells) 7-fold, epicardial proliferation (78±17 cells vs. 21±9 cells; P<0.05), migration and recellularization (80±22 vs. zero cells; P<0.01; n=6) at the injury site on day 14. Conclusions: A novel explant culture system maintains three-dimensional neonatal mouse hearts and the mammalian neonatal cardiac regenerative program ex vivo. We identified that rNRG-1, plus short-term activation of Wnt- and BMP-signaling, promotes cardiac repair via epicardial cell activation, their proliferation and migration to the injury site, followed by putative cardiomyocyte recruitment. This novel technique will facilitate future studies of mammalian cardiac regeneration and may be useful in cardiac-specific drug testing.

The role of hormones and neurons in cardiomyocyte maturation

The heart undergoes profound morphological and functional changes as it continues to mature postnatally. However, this phase of cardiac development remains understudied. More recently, cardiac maturation research has attracted a lot of interest due to the need for more mature stem cell-derived cardiomyocytes for disease modeling, drug screening and heart regeneration. Additionally, neonatal heart injury models have been utilized to study heart regeneration, and factors regulating postnatal heart development have been associated with adult cardiac disease. Critical components of cardiac maturation are systemic and local biochemical cues. Specifically, cardiac innervation and the concentration of various metabolic hormones appear to increase perinatally and they have striking effects on cardiomyocytes. Here, we first report some of the key parameters of mature cardiomyocytes and then discuss the specific effects of neurons and hormonal cues on cardiomyocyte maturation. We focus primarily on the structural, electrophysiologic, metabolic, hypertrophic and hyperplastic effects of each factor. This review highlights the significance of underappreciated regulators of cardiac maturation and underscores the need for further research in this exciting field.

Maternal diet high in linoleic acid alters offspring fatty acids and cardiovascular function in a rat model

Linoleic acid (LA), an essential n-6 fatty acid (FA), is critical for fetal development. We investigated the effects of maternal high LA (HLA) diet on offspring cardiac development and its relationship to circulating FA and cardiovascular function in adolescent offspring, and the ability of the postnatal diet to reverse any adverse effects. Female Wistar Kyoto rats were fed low LA (LLA; 1·44 % energy from LA) or high LA (HLA; 6·21 % energy from LA) diets for 10 weeks before pregnancy and during gestation/lactation. Offspring, weaned at postnatal day 25, were fed LLA or HLA diets and euthanised at postnatal day 40 (n 6-8). Maternal HLA diet decreased circulating total cholesterol and HDL-cholesterol in females and decreased total plasma n-3 FA in males, while maternal and postnatal HLA diets decreased total plasma n-3 FA in females. α-Linolenic acid (ALA) and EPA were decreased by postnatal but not maternal HLA diets in both sexes. Maternal and postnatal HLA diets increased total plasma n-6 and LA, and a maternal HLA diet increased circulating leptin, in both male and female offspring. Maternal HLA decreased slopes of systolic and diastolic pressure-volume relationship (PVR), and increased cardiac Col1a1, Col3a1, Atp2a1 and Notch1 in males. Maternal and postnatal HLA diets left-shifted the diastolic PVR in female offspring. Coronary reactivity was altered in females, with differential effects on flow repayment after occlusion. Thus, maternal HLA diets impact lipids, FA and cardiac function in offspring, with postnatal diet modifying FA and cardiac function in the female offspring.

The Intrinsic Cardiac Nervous System and Its Role in Cardiac Pacemaking and Conduction

The cardiac autonomic nervous system (CANS) plays a key role for the regulation of cardiac activity with its dysregulation being involved in various heart diseases, such as cardiac arrhythmias. The CANS comprises the extrinsic and intrinsic innervation of the heart. The intrinsic cardiac nervous system (ICNS) includes the network of the intracardiac ganglia and interconnecting neurons. The cardiac ganglia contribute to the tight modulation of cardiac electrophysiology, working as a local hub integrating the inputs of the extrinsic innervation and the ICNS. A better understanding of the role of the ICNS for the modulation of the cardiac conduction system will be crucial for targeted therapies of various arrhythmias. We describe the embryonic development, anatomy, and physiology of the ICNS. By correlating the topography of the intracardiac neurons with what is known regarding their biophysical and neurochemical properties, we outline their physiological role in the control of pacemaker activity of the sinoatrial and atrioventricular nodes. We conclude by highlighting cardiac disorders with a putative involvement of the ICNS and outline open questions that need to be addressed in order to better understand the physiology and pathophysiology of the ICNS.

Cardio-centric hemodynamic management improves spinal cord oxygenation and mitigates hemorrhage in acute spinal cord injury

Chronic high-thoracic and cervical spinal cord injury (SCI) results in a complex phenotype of cardiovascular consequences, including impaired left ventricular (LV) contractility. Here, we aim to determine whether such dysfunction manifests immediately post-injury, and if so, whether correcting impaired contractility can improve spinal cord oxygenation (SCO₂), blood flow (SCBF) and metabolism. Using a porcine model of T2 SCI, we assess LV end-systolic elastance (contractility) via invasive pressure-volume catheterization, monitor intraparenchymal SCO₂ and SCBF with fiberoptic oxygen sensors and laser-Doppler flowmetry, respectively, and quantify spinal cord metabolites with microdialysis. We demonstrate that high-thoracic SCI acutely impairs cardiac contractility and substantially reduces SCO₂ and SCBF within the first hours post-injury. Utilizing the same model, we next show that augmenting LV contractility with the β-agonist dobutamine increases SCO₂ and SCBF more effectively than vasopressor therapy, whilst also mitigating increased anaerobic metabolism and hemorrhage in the injured cord. Finally, in pigs with T2 SCI survived for 12 weeks post-injury, we confirm that acute hemodynamic management with dobutamine appears to preserve cardiac function and improve hemodynamic outcomes in the chronic setting. Our data support that cardio-centric hemodynamic management represents an advantageous alternative to the current clinical standard of vasopressor therapy for acute traumatic SCI.

Control of cytokinesis by β-adrenergic receptors indicates an approach for regulating cardiomyocyte endowment

One million patients with congenital heart disease (CHD) live in the United States. They have a lifelong risk of developing heart failure. Current concepts do not sufficiently address mechanisms of heart failure development specifically for these patients. Here, analysis of heart tissue from an infant with tetralogy of Fallot with pulmonary stenosis (ToF/PS) labeled with isotope-tagged thymidine demonstrated that cardiomyocyte cytokinesis failure is increased in this common form of CHD. We used single-cell transcriptional profiling to discover that the underlying mechanism of cytokinesis failure is repression of the cytokinesis gene ECT2, downstream of β-adrenergic receptors (β-ARs). Inactivation of the β-AR genes and administration of the β-blocker propranolol increased cardiomyocyte division in neonatal mice, which increased the number of cardiomyocytes (endowment) and conferred benefit after myocardial infarction in adults. Propranolol enabled the division of ToF/PS cardiomyocytes in vitro. These results suggest that β-blockers could be evaluated for increasing cardiomyocyte division in patients with ToF/PS and other types of CHD.

BMAL1 regulates mitochondrial fission and mitophagy through mitochondrial protein BNIP3 and is critical in the development of dilated cardiomyopathy

Dysregulation of circadian rhythms associates with cardiovascular disorders. It is known that deletion of the core circadian gene Bmal1 in mice causes dilated cardiomyopathy. However, the biological rhythm regulation system in mouse is very different from that of humans. Whether BMAL1 plays a role in regulating human heart function remains unclear. Here we generated a BMAL1 knockout human embryonic stem cell (hESC) model and further derived human BMAL1 deficient cardiomyocytes. We show that BMAL1 deficient hESC-derived cardiomyocytes exhibited typical phenotypes of dilated cardiomyopathy including attenuated contractility, calcium dysregulation, and disorganized myofilaments. In addition, mitochondrial fission and mitophagy were suppressed in BMAL1 deficient hESC-cardiomyocytes, which resulted in significantly attenuated mitochondrial oxidative phosphorylation and compromised cardiomyocyte function. We also found that BMAL1 binds to the E-box element in the promoter region of BNIP3 gene and specifically controls BNIP3 protein expression. BMAL1 knockout directly reduced BNIP3 protein level, causing compromised mitophagy and mitochondria dysfunction and thereby leading to compromised cardiomyocyte function. Our data indicated that the core circadian gene BMAL1 is critical for normal mitochondria activities and cardiac function. Circadian rhythm disruption may directly link to compromised heart function and dilated cardiomyopathy in humans.

Optical Interrogation of Sympathetic Neuronal Effects on Macroscopic Cardiomyocyte Network Dynamics

Cardiac stimulation via sympathetic neurons can potentially trigger arrhythmias. We present approaches to study neuron-cardiomyocyte interactions involving optogenetic selective probing and all-optical electrophysiology to measure activity in an automated fashion. Here we demonstrate the utility of optical interrogation of sympathetic neurons and their effects on macroscopic cardiomyocyte network dynamics to address research targets such as the effects of adrenergic stimulation via the release of neurotransmitters, the effect of neuronal numbers on cardiac behavior, and the applicability of optogenetics in mechanistic in vitro studies. As arrhythmias are emergent behaviors that involve the coordinated activity of millions of cells, we image at macroscopic scales to capture complex dynamics. We show that neurons can both decrease and increase wave stability and re-entrant activity in culture depending on their induced activity-a finding that may help us understand the often conflicting results seen in experimental and clinical studies.

Pre-innervated tissue-engineered muscle promotes a pro-regenerative microenvironment following volumetric muscle loss

Volumetric muscle loss (VML) is the traumatic or surgical loss of skeletal muscle beyond the inherent regenerative capacity of the body, generally leading to severe functional deficit. Formation of appropriate somato-motor innervations remains one of the biggest challenges for both autologous grafts as well as tissue-engineered muscle constructs. We aim to address this challenge by developing pre-innervated tissue-engineered muscle comprised of long aligned networks of spinal motor neurons and skeletal myocytes on aligned nanofibrous scaffolds. Motor neurons led to enhanced differentiation and maturation of skeletal myocytes in vitro. These pre-innervated tissue-engineered muscle constructs when implanted in a rat VML model significantly increased satellite cell density, neuromuscular junction maintenance, graft revascularization, and muscle volume over three weeks as compared to myocyte-only constructs and nanofiber scaffolds alone. These pro-regenerative effects may enhance functional neuromuscular regeneration following VML, thereby improving the levels of functional recovery following these devastating injuries.

Innervation: the missing link for biofabricated tissues and organs

Innervation plays a pivotal role as a driver of tissue and organ development as well as a means for their functional control and modulation. Therefore, innervation should be carefully considered throughout the process of biofabrication of engineered tissues and organs. Unfortunately, innervation has generally been overlooked in most non-neural tissue engineering applications, in part due to the intrinsic complexity of building organs containing heterogeneous native cell types and structures. To achieve proper innervation of engineered tissues and organs, specific host axon populations typically need to be precisely driven to appropriate location(s) within the construct, often over long distances. As such, neural tissue engineering and/or axon guidance strategies should be a necessary adjunct to most organogenesis endeavors across multiple tissue and organ systems. To address this challenge, our team is actively building axon-based "living scaffolds" that may physically wire in during organ development in bioreactors and/or serve as a substrate to effectively drive targeted long-distance growth and integration of host axons after implantation. This article reviews the neuroanatomy and the role of innervation in the functional regulation of cardiac, skeletal, and smooth muscle tissue and highlights potential strategies to promote innervation of biofabricated engineered muscles, as well as the use of "living scaffolds" in this endeavor for both in vitro and in vivo applications. We assert that innervation should be included as a necessary component for tissue and organ biofabrication, and that strategies to orchestrate host axonal integration are advantageous to ensure proper function, tolerance, assimilation, and bio-regulation with the recipient post-implant.

Neonatal Growth Restriction Slows Cardiomyocyte Development and Reduces Adult Heart Size

Prematurity is associated with reduced cardiac dimensions and an increased risk of cardiovascular disease. While prematurity is typically associated with ex utero neonatal growth restriction (GR), the independent effect of neonatal GR on cardiac development has not been established. We tested the hypothesis that isolated neonatal GR decreases cardiomyocyte growth and proliferation, leading to long-term alterations in cardiac morphology. C57BL/6 mice were fostered in litters ranging in size from 6 to 12 pups to accentuate normal variation in neonatal growth. Regardless of litter size, GR was defined by a weight below the 10th percentile. On postnatal day 8, Ki67 immunoreactivity, cardiomyocyte nucleation status and cardiomyocyte profile area were assessed. For adult mice, cardiomyocyte area was determined, along with cardiac dimensions by echocardiography and cardiac fibrosis by Masson's trichrome stain. On day 8, cardiomyocytes from GR versus control mice were significantly smaller and less likely to be binucleated with evidence of persistent cell cycle activity. As adults, GR mice continued to have smaller cardiomyocytes, as well as decreased left ventricular volumes without signs of fibrosis. Neonatal GR reduces cardiomyocyte size, delays the completion of binucleation, and leads to long-term alterations in cardiac morphology. Clinical studies are needed to ascertain whether these results translate to preterm infants that must continue to grow and mature in the midst of the increased circulatory demands that accompany their premature transition to an ex utero existence. Anat Rec, 2018. © 2018 Wiley Periodicals, Inc.

Cardiac sympathetic innervation, from a different point of (re)view

The audience of basic and clinical scientists is familiar with the notion that the sympathetic nervous system controls heart function during stresses. However, evidence indicates that the neurogenic control of the heart spans from the maintenance of housekeeping functions in resting conditions to the recruitment of maximal performance, in the fight-or-flight responses, across a whole range of intermediate states. To perform such sophisticated functions, sympathetic ganglia integrate both peripheral and central inputs, and transmit information to the heart via 'motor' neurons, directly interacting with target cardiomyocytes. To date, the dynamics and mode of communication between these two cell types, which determine how neuronal information is adequately translated into the wide spectrum of cardiac responses, are still blurry. By combining the anatomical and structural information brought to light by recent imaging technologies and the functional evidence in cellular systems, we focus on the interface between neurons and cardiomyocytes, and advocate the existence of a specific 'neuro-cardiac junction', where sympathetic neurotransmission occurs in a 'quasi-synaptic' way. The properties of such junctional-type communication fit well with those of the physiological responses elicited by the cardiac sympathetic nervous system, and explain its ability to tune heart function with precision, specificity and elevated temporal resolution.

The Biological Role of Nestin(+)-Cells in Physiological and Pathological Cardiovascular Remodeling

The intermediate filament protein nestin was identified in diverse populations of cells implicated in cardiovascular remodeling. Cardiac resident neural progenitor/stem cells constitutively express nestin and following an ischemic insult migrate to the infarct region and participate in angiogenesis and neurogenesis. A modest number of normal adult ventricular fibroblasts express nestin and the intermediate filament protein is upregulated during the progression of reparative and reactive fibrosis. Nestin depletion attenuates cell cycle re-entry suggesting that increased expression of the intermediate filament protein in ventricular fibroblasts may represent an activated phenotype accelerating the biological impact during fibrosis. Nestin immunoreactivity is absent in normal adult rodent ventricular cardiomyocytes. Following ischemic damage, the intermediate filament protein is induced in a modest population of pre-existing adult ventricular cardiomyocytes bordering the peri-infarct/infarct region and nestin⁽⁺⁾-ventricular cardiomyocytes were identified in the infarcted human heart. The appearance of nestin⁽⁺⁾-ventricular cardiomyocytes post-myocardial infarction (MI) recapitulates an embryonic phenotype and depletion of the intermediate filament protein inhibits cell cycle re-entry. Recruitment of the serine/threonine kinase p38 MAPK secondary to an overt inflammatory response after an ischemic insult may represent a seminal event limiting the appearance of nestin⁽⁺⁾-ventricular cardiomyocytes and concomitantly suppressing cell cycle re-entry. Endothelial and vascular smooth muscle cells (VSMCs) express nestin and upregulation of the intermediate filament protein may directly contribute to vascular remodeling. This review will highlight the biological role of nestin⁽⁺⁾-cells during physiological and pathological remodeling of the heart and vasculature and discuss the phenotypic advantage attributed to the intermediate filament protein.

Cardiac neuroanatomy - Imaging nerves to define functional control

The autonomic nervous system regulates normal cardiovascular function and plays a critical role in the pathophysiology of cardiovascular disease. Further understanding of the interplay between the autonomic nervous system and cardiovascular system holds promise for the development of neuroscience-based cardiovascular therapeutics. To this end, techniques to image myocardial innervation will help provide a basis for understanding the fundamental underpinnings of cardiac neural control. In this review, we detail the evolution of gross and microscopic anatomical studies for functional mapping of cardiac neuroanatomy.

Influence of cardiac nerve status on cardiovascular regulation and cardioprotection

Neural elements of the intrinsic cardiac nervous system transduce sensory inputs from the heart, blood vessels and other organs to ensure adequate cardiac function on a beat-to-beat basis. This inter-organ crosstalk is critical for normal function of the heart and other organs; derangements within the nervous system hierarchy contribute to pathogenesis of organ dysfunction. The role of intact cardiac nerves in development of, as well as protection against, ischemic injury is of current interest since it may involve recruitment of intrinsic cardiac ganglia. For instance, ischemic conditioning, a novel protection strategy against organ injury, and in particular remote conditioning, is likely mediated by activation of neural pathways or by endogenous cytoprotective blood-borne substances that stimulate different signalling pathways. This discovery reinforces the concept that inter-organ communication, and maintenance thereof, is key. As such, greater understanding of mechanisms and elucidation of treatment strategies is imperative to improve clinical outcomes particularly in patients with comorbidities. For instance, autonomic imbalance between sympathetic and parasympathetic nervous system regulation can initiate cardiovascular autonomic neuropathy that compromises cardiac stability and function. Neuromodulation therapies that directly target the intrinsic cardiac nervous system or other elements of the nervous system hierarchy are currently being investigated for treatment of different maladies in animal and human studies.

Purinergic Signaling in the Cardiovascular System

There is nervous control of the heart by ATP as a cotransmitter in sympathetic, parasympathetic, and sensory-motor nerves, as well as in intracardiac neurons. Centers in the brain control heart activities and vagal cardiovascular reflexes involve purines. Adenine nucleotides and nucleosides act on purinoceptors on cardiomyocytes, AV and SA nodes, cardiac fibroblasts, and coronary blood vessels. Vascular tone is controlled by a dual mechanism. ATP, released from perivascular sympathetic nerves, causes vasoconstriction largely via P2X1 receptors. Endothelial cells release ATP in response to changes in blood flow (via shear stress) or hypoxia, to act on P2 receptors on endothelial cells to produce nitric oxide, endothelium-derived hyperpolarizing factor, or prostaglandins to cause vasodilation. ATP is also released from sensory-motor nerves during antidromic reflex activity, to produce relaxation of some blood vessels. Purinergic signaling is involved in the physiology of erythrocytes, platelets, and leukocytes. ATP is released from erythrocytes and platelets, and purinoceptors and ectonucleotidases are expressed by these cells. P1, P2Y₁, P2Y₁₂, and P2X1 receptors are expressed on platelets, which mediate platelet aggregation and shape change. Long-term (trophic) actions of purine and pyrimidine nucleosides and nucleotides promote migration and proliferation of vascular smooth muscle and endothelial cells via P1 and P2Y receptors during angiogenesis, vessel remodeling during restenosis after angioplasty and atherosclerosis. The involvement of purinergic signaling in cardiovascular pathophysiology and its therapeutic potential are discussed, including heart failure, infarction, arrhythmias, syncope, cardiomyopathy, angina, heart transplantation and coronary bypass grafts, coronary artery disease, diabetic cardiomyopathy, hypertension, ischemia, thrombosis, diabetes mellitus, and migraine.

Sympathetic neurons are a powerful driver of myocyte function in cardiovascular disease

Many therapeutic interventions in disease states of heightened cardiac sympathetic activity are targeted to the myocytes. However, emerging clinical data highlights a dominant role in disease progression by the neurons themselves. Here we describe a novel experimental model of the peripheral neuro-cardiac axis to study the neuron’s ability to drive a myocyte cAMP phenotype. We employed a co-culture of neonatal ventricular myocytes and sympathetic stellate neurons from normal (WKY) and pro-hypertensive (SHR) rats that are sympathetically hyper-responsive and measured nicotine evoked cAMP responses in the myocytes using a fourth generation FRET cAMP sensor. We demonstrated the dominant role of neurons in driving the myocyte ß-adrenergic phenotype, where SHR cultures elicited heightened myocyte cAMP responses during neural activation. Moreover, cross-culturing healthy neurons onto diseased myocytes rescued the diseased cAMP response of the myocyte. Conversely, healthy myocytes developed a diseased cAMP response if diseased neurons were introduced. Our results provide evidence for a dominant role played by the neuron in driving the adrenergic phenotype seen in cardiovascular disease. We also highlight the potential of using healthy neurons to turn down the gain of neurotransmission, akin to a smart pre-synaptic ß-blocker.

Studying the pathophysiologic connection between cardiovascular and nervous systems using stem cells

The cardiovascular and nervous systems are deeply connected during development, health, and disease. Both systems affect and regulate the development of each other during embryogenesis and the early postnatal period. Specialized neural crest cells contribute to cardiac structures, and a number of growth factors released from the cardiac tissue (e.g., glial cell line-derived neurotrophic factor, neurturin, nerve growth factor, Neurotrophin-3) ensure proper maturation of the incoming parasympathetic and sympathetic neurons. Physiologically, the cardiovascular and nervous systems operate in harmony to adapt to various physical and emotional conditions to maintain homeostasis through sympathetic and parasympathetic nervous systems. Moreover, neurocardiac regulation involves a neuroaxis consisting of cortex, amygdala, and other subcortical structures, which have the ability to modify lower-level neurons in the hierarchy. Given the interconnectivity of cardiac and neural systems, when one undergoes pathological changes, the other is affected to a certain extent. In addition, there are specific neurocardiac diseases that affect both systems simultaneously, such as Huntington disease, Lewy body diseases, Friedreich ataxia, congenital heart diseases, Danon disease, and Timothy syndrome. Over the last decade, in vitro modeling of neurocardiac diseases using induced pluripotent stem cells (iPSCs) has provided an invaluable opportunity to elevate our knowledge about the brain-heart connection, since previously primary cardiomyocytes and neurons had been extremely difficult to maintain long-term in vitro. Ultimately, the ability of iPSC technology to model abnormal functional phenotypes of human neurocardiac disorders, combined with the ease of therapeutic screening using this approach, will transform patient care through personalized medicine in the future. © 2016 Wiley Periodicals, Inc.

Molecular and cellular neurocardiology: development, and cellular and molecular adaptations to heart disease

The nervous system and cardiovascular system develop in concert and are functionally interconnected in both health and disease. This white paper focuses on the cellular and molecular mechanisms that underlie neural-cardiac interactions during development, during normal physiological function in the mature system, and during pathological remodelling in cardiovascular disease. The content on each subject was contributed by experts, and we hope that this will provide a useful resource for newcomers to neurocardiology as well as aficionados.

Metabolic remodeling in early development and cardiomyocyte maturation

Aberrations in metabolism contribute to a large number of diseases, such as diabetes, obesity, cancer, and cardiovascular diseases, that have a substantial impact on the mortality rates and quality of life worldwide. However, the mechanisms leading to these changes in metabolic state--and whether they are conserved between diseases--is not well understood. Changes in metabolism similar to those seen in pathological conditions are observed during normal development in a number of different cell types. This provides hope that understanding the mechanism of these metabolic switches in normal development may provide useful insight in correcting them in pathological cases. Here, we focus on the metabolic remodeling observed both in early stage embryonic stem cells and during the maturation of cardiomyocytes.