Modulation of rat parasympathetic cardiac ganglion phenotype and NGF synthesis by adrenergic nerves

A cholinergic neuroskeletal interface promotes bone formation during postnatal growth and exercise

The autonomic nervous system is a master regulator of homeostatic processes and stress responses. Sympathetic noradrenergic nerve fibers decrease bone mass, but the role of cholinergic signaling in bone has remained largely unknown. Here, we describe that early postnatally, a subset of sympathetic nerve fibers undergoes an interleukin-6 (IL-6)-induced cholinergic switch upon contacting the bone. A neurotrophic dependency mediated through GDNF-family receptor-α2 (GFRα2) and its ligand, neurturin (NRTN), is established between sympathetic cholinergic fibers and bone-embedded osteocytes, which require cholinergic innervation for their survival and connectivity. Bone-lining osteoprogenitors amplify and propagate cholinergic signals in the bone marrow (BM). Moderate exercise augments trabecular bone partly through an IL-6-dependent expansion of sympathetic cholinergic nerve fibers. Consequently, loss of cholinergic skeletal innervation reduces osteocyte survival and function, causing osteopenia and impaired skeletal adaptation to moderate exercise. These results uncover a cholinergic neuro-osteocyte interface that regulates skeletogenesis and skeletal turnover through bone-anabolic effects.

Interactive regulation of laryngeal cancer and neuroscience

Nerve fibres are distributed throughout the body along with blood and lymphatic vessels. The intrinsic morphological characteristics of nerves and the general characteristics of secretions in the tumour microenvironment provide a solid theoretical basis for exploring how neuronal tissue can influence the progression of laryngeal cancer (LC). The central nervous system (CNS) and the peripheral nervous system (PNS) jointly control many aspects of cancer and have attracted widespread attention in the study of the progression, invasion and metastasis of tumour tissue banks. Stress activates the neuroendocrine response of the human hypothalamus-pituitary-adrenal (HPA) axis. LC cells induce nerve growth in the microenvironment by releasing neurotrophic factors (NTFs), and they can also stimulate neurite formation by secreting axons and axon guides. Conversely, nerve endings secrete factors that attract LC cells; this is known as perineural invasion (PNI) and promotes the progression of the associated cancer. In this paper, we summarize the systematic understanding of the role of neuroregulation in the LC tumour microenvironment (TME) and ways in which the TME accelerates nerve growth, which is closely related to the occurrence of LC.

Pleiotropic activity of nerve growth factor in regulating cardiac functions and counteracting pathogenesis

Cardiac innervation density generally reflects the levels of nerve growth factor (NGF) produced by the heart—changes in NGF expression within the heart and vasculature contribute to neuronal remodelling (e.g. sympathetic hyperinnervation or denervation). Its synthesis and release are altered under different pathological conditions. Although NGF is well known for its survival effects on neurons, it is clear that these effects are more wide ranging. Recent studies reported both in vitro and in vivo evidence for beneficial actions of NGF on cardiomyocytes in normal and pathological hearts, including prosurvival and antiapoptotic effects. NGF also plays an important role in the crosstalk between the nervous and cardiovascular systems. It was the first neurotrophin to be implicated in postnatal angiogenesis and vasculogenesis by autocrine and paracrine mechanisms. In connection with these unique cardiovascular properties of NGF, we have provided comprehensive insight into its function and potential effect of NGF underlying heart sustainable/failure conditions. This review aims to summarize the recent data on the effects of NGF on various cardiovascular neuronal and non‐neuronal functions. Understanding these mechanisms with respect to the diversity of NGF functions may be crucial for developing novel therapeutic strategies, including NGF action mechanism‐guided therapies.

The Occurrence of Valvular Atrial Fibrillation: Involvement of NGF/TrKA Signaling Pathway

OBJECTIVE

Nerve growth factor (NGF) and tropomyosin kinase receptors A (TrKA) exert a crucial effect on the regulation of autonomic nervous system which contributes to the progress of atrial fibrillation (AF). Valvular heart disease (VHD) patients are more easily to induce the AF. We investigated whether NGF/TrKA could impact the occurrence of AF in VHD patients.

MATERIALS AND METHODS

Atrial tissues were resected from 30 VHD patients with chronic AF (n = 15, AF >6 months) or sinus rhythm (SR, n = 15). The expression of NGF, TrKA, protein kinase B (PKB/Akt), beta-isoforms of glycogen synthase kinase-3 (GSK3β), Serine473 phosphorylation of Akt (p-Ser473 Akt), Serine9 phosphorylation of GSK-3β (p-Ser9 GSK3β) in right atrial tissues and peripheral blood lymphocyte were quantified by Western blot. The localization of those genes expression was measured by immunohistochemistry. Double sandwich enzyme-linked immunosorbent assay was used to observe the trace changes of NGF-β in peripheral plasma.

RESULTS

Our results revealed that the NGF expression was markedly elevated in the tissue of right atrial appendage and peripheral blood lymphocytes from AF patients compared with the SR patients. But, the expression of TrKA, GSK3β, p-Akt and p-GSK3β were decreased. There was no difference about the expression of Akt from the AF patients and the SR patients. The NGF-β level in peripheral blood plasma of patients with AF and SR was not statistical difference.

CONCLUSION

Thus, we thought that NGF/TrKA signaling pathway may be involved in the AF in the patients with VHD, inactivation of GSK3β could increase the incidence of AF, but not relevant to phosphorylation.

Part and Parcel of the Cardiac Autonomic Nerve System: Unravelling Its Cellular Building Blocks during Development

The autonomic nervous system (cANS) is essential for proper heart function, and complications such as heart failure, arrhythmias and even sudden cardiac death are associated with an altered cANS function. A changed innervation state may underlie (part of) the atrial and ventricular arrhythmias observed after myocardial infarction. In other cardiac diseases, such as congenital heart disease, autonomic dysfunction may be related to disease outcome. This is also the case after heart transplantation, when the heart is denervated. Interest in the origin of the autonomic nerve system has renewed since the role of autonomic function in disease progression was recognized, and some plasticity in autonomic regeneration is evident. As with many pathological processes, autonomic dysfunction based on pathological innervation may be a partial recapitulation of the early development of innervation. As such, insight into the development of cardiac innervation and an understanding of the cellular background contributing to cardiac innervation during different phases of development is required. This review describes the development of the cANS and focuses on the cellular contributions, either directly by delivering cells or indirectly by secretion of necessary factors or cell-derivatives.

The biology of neurotrophins: cardiovascular function

This chapter addresses the role of neurotrophins in the development of the heart, blood vessels, and neural circuits that control cardiovascular function, as well as the role of neurotrophins in the mature cardiovascular system. The cardiovascular system includes the heart and vasculature whose functions are tightly controlled by the nervous system. Neurons, cardiomyocytes, endothelial cells, vascular smooth muscle cells, and pericytes are all targets for neurotrophin action during development. Neurotrophin expression continues throughout life, and several common pathologies that impact cardiovascular function involve changes in the expression or activity of neurotrophins. These include atherosclerosis, hypertension, diabetes, acute myocardial infarction, and heart failure. In many of these conditions, altered expression of neurotrophins and/or neurotrophin receptors has direct effects on vascular endothelial and smooth muscle cells in addition to effects on nerves that modulate vascular resistance and cardiac function. This chapter summarizes the effects of neurotrophins in cardiovascular physiology and pathophysiology.

Decreased adrenoceptor stimulation in heart failure rats reduces NGF expression by cardiac parasympathetic neurons

Postganglionic cardiac parasympathetic and sympathetic nerves are physically proximate in atrial cardiac tissue allowing reciprocal inhibition of neurotransmitter release, depending on demands from central cardiovascular centers or reflex pathways. Parasympathetic cardiac ganglion (CG) neurons synthesize and release the sympathetic neurotrophin nerve growth factor (NGF), which may serve to maintain these close connections. In this study we investigated whether NGF synthesis by CG neurons is altered in heart failure, and whether norepinephrine from sympathetic neurons promotes NGF synthesis. NGF and proNGF immunoreactivity in CG neurons in heart failure rats following chronic coronary artery ligation was investigated. NGF immunoreactivity was decreased significantly in heart failure rats compared to sham-operated animals, whereas proNGF expression was unchanged. Changes in neurochemistry of CG neurons included attenuated expression of the cholinergic marker vesicular acetylcholine transporter, and increased expression of the neuropeptide vasoactive intestinal polypeptide. To further investigate norepinephrine's role in promoting NGF synthesis, we cultured CG neurons treated with adrenergic receptor (AR) agonists. An 82% increase in NGF mRNA levels was detected after 1h of isoproterenol (β-AR agonist) treatment, which increased an additional 22% at 24h. Antagonist treatment blocked isoproterenol-induced increases in NGF transcripts. In contrast, the α-AR agonist phenylephrine did not alter NGF mRNA expression. These results are consistent with β-AR mediated maintenance of NGF synthesis in CG neurons. In heart failure, a decrease in NGF synthesis by CG neurons may potentially contribute to reduced connections with adjacent sympathetic nerves.

Autonomic cardiac innervation: development and adult plasticity

Autonomic cardiac neurons have a common origin in the neural crest but undergo distinct developmental differentiation as they mature toward their adult phenotype. Progenitor cells respond to repulsive cues during migration, followed by differentiation cues from paracrine sources that promote neurochemistry and differentiation. When autonomic axons start to innervate cardiac tissue, neurotrophic factors from vascular tissue are essential for maintenance of neurons before they reach their targets, upon which target-derived trophic factors take over final maturation, synaptic strength and postnatal survival. Although target-derived neurotrophins have a central role to play in development, alternative sources of neurotrophins may also modulate innervation. Both developing and adult sympathetic neurons express proNGF, and adult parasympathetic cardiac ganglion neurons also synthesize and release NGF. The physiological function of these “non-classical” cardiac sources of neurotrophins remains to be determined, especially in relation to autocrine/paracrine sustenance during development.

 

Cardiac autonomic nerves are closely spatially associated in cardiac plexuses, ganglia and pacemaker regions and so are sensitive to release of neurotransmitter, neuropeptides and trophic factors from adjacent nerves. As such, in many cardiac pathologies, it is an imbalance within the two arms of the autonomic system that is critical for disease progression. Although this crosstalk between sympathetic and parasympathetic nerves has been well established for adult nerves, it is unclear whether a degree of paracrine regulation occurs across the autonomic limbs during development. Aberrant nerve remodeling is a common occurrence in many adult cardiovascular pathologies, and the mechanisms regulating outgrowth or denervation are disparate. However, autonomic neurons display considerable plasticity in this regard with neurotrophins and inflammatory cytokines having a central regulatory function, including in possible neurotransmitter changes. Certainly, neurotrophins and cytokines regulate transcriptional factors in adult autonomic neurons that have vital differentiation roles in development. Particularly for parasympathetic cardiac ganglion neurons, additional examinations of developmental regulatory mechanisms will potentially aid in understanding attenuated parasympathetic function in a number of conditions, including heart failure.

Chronic Electrical Neuronal Stimulation Increases Cardiac Parasympathetic Tone by Eliciting Neurotrophic Effects

Rationale:

Recently, we provided a technique of chronic high-frequency electric stimulation (HFES) of the right inferior ganglionated plexus for ventricular rate control during atrial fibrillation in dogs and humans. In these experiments, we observed a decrease of the intrinsic ventricular rate during the first 4 to 5 months when HFES was intermittently shut off.

Objective:

We thus hypothesized that HFES might elicit trophic effects on cardiac neurons, which in turn increase baseline parasympathetic tone of the atrioventricular node.

Methods and Results:

In mongrel dogs atrial fibrillation was induced by rapid atrial pacing. Endocardial HFES of the right inferior ganglionated plexus, which contains abundant fibers to the atrioventricular node, was performed for 2 years. Sham-operated nonstimulated dogs served as control. In chronic neurostimulated dogs, we found an increased neuronal cell size accompanied by an increase of choline acetyltransferase and unchanged tyrosine hydroxylase protein expression as compared with unstimulated dogs. Moreover, β-nerve growth factor (NGF) and neurotrophin (NT)-3 were upregulated in chronically neurostimulated dogs. In vitro, HFES of cultured neurons of interatrial ganglionated plexus from adult rats increased neuronal growth accompanied by upregulation of NGF, NT-3, glial-derived neurotrophic factor (GDNF), ciliary neurotrophic factor (CNTF) and brain-derived neurotrophic factor (BDNF) expression. NGF was identified as the main growth-inducing factor, whereas NT-3 did not affect HFES-induced growth. However, NT-3 could be identified as an important acetylcholine-upregulating factor.

Conclusions:

HFES of cardiac neurons in vivo and in vitro causes neuronal cellular hypertrophy, which is mediated by NGF and boosters cellular function by NT-3–mediated acetylcholine upregulation. This knowledge may contribute to develop HFES techniques to augment cardiac parasympathetic tone.