Venous endothelin modulates responsiveness of cardiac sympathetic axons to arterial semaphorin.

Denise M Poltavski,Jianxin Hu,Alicia Duron,Takako Makita,Pauline Colombier,Brian L Black

doi:10.7554/elife.42528

Abstract

Developing neurons of the peripheral nervous system reach their targets via cues that support directional growth, a process known as axon guidance. In investigating how sympathetic axons reach the heart in mice, we discovered that a combination of guidance cues are employed in sequence to refine axon outgrowth, a process we term second-order guidance. Specifically, endothelin-1 induces sympathetic neurons expressing the receptor Ednra to project to the vena cavae leading to the heart. Endothelin signaling in turn induces expression of the repulsive receptor Plexin-A4, via induction of the transcription factor MEF2C. In the absence of endothelin or plexin signaling, sympathetic neurons misproject to incorrect competing vascular trajectories (the dorsal aorta and intercostal arteries). The same anatomical and physiological consequences occur in Ednra+/-; Plxna4+/- double heterozygotes, genetically confirming functional interaction. Second-order axon guidance therefore multiplexes a smaller number of guidance cues in sequential fashion, allowing precise refinement of axon trajectories.

Highlights

The heart is innervated by sympathetic and parasympathetic divisions of the autonomic nervous system, which regulate cardiovascular response to emotion and stress
We previously demonstrated that endothelin-1 (Edn1), which is selectively expressed by the endothelium of the cardiac veins, directs axonal growth towards and along these venous routes by the subset of stellate ganglia (STG) neurons that express the endothelin receptor Ednra (Manousiouthakis et al, 2014)
We demonstrate that venous endothelium-derived Edn1 instructs Ednra+ sympathetic axon guidance to the heart, and induces the ability of these axons to repel from competing arterial routes by upregulating the expression of Plexin-A4 in Ednra+ STG neurons

Summary

Introduction

The heart is innervated by sympathetic and parasympathetic divisions of the autonomic nervous system, which regulate cardiovascular response to emotion and stress. The functional role of endothelin signaling was demonstrated in Edn1-Ednra signaling deficient mouse embryos, which showed a significant reduction of cardiac sympathetic axons reaching the SA node and the ventricular myocardium at E15.5 This deficiency of sympathetic innervation persisted into the postnatal period, and as a consequence, mutant mice were substantially compromised in ionotropic response to sympathetic activation (i.e., amphetamine-induced increased heart rate). We demonstrate that venous endothelium-derived Edn instructs Ednra+ sympathetic axon guidance to the heart, and induces the ability of these axons to repel from competing arterial routes by upregulating the expression of Plexin-A4 in Ednra+ STG neurons Lacking this second layer of guidance, cardiac sympathetic axons misproject to ectopic targets, and as a result, cardiac sympathetic innervation and physiology are both compromised. This analysis reveals that positive axon guidance alone is insufficient to accomplish correct circuitry, and defines a molecular mechanism by which axon attraction and repulsion are coordinately controlled to synergistically accomplish proper innervation

Results

E15.5 Thorax

Discussion

Materials and methods

Funding Funder