Tiered sympathetic control of cardiac function revealed by viral tracing and single cell transcriptome profiling

Abstract

The cell bodies of postganglionic sympathetic neurons innervating the heart primarily reside in the stellate ganglion (SG), alongside neurons innervating other organs and tissues. Whether cardiac-innervating stellate ganglionic neurons (SGNs) exhibit diversity and distinction from those innervating other tissues is not known. To identify and resolve the transcriptomic profiles of SGNs innervating the heart we leveraged retrograde tracing techniques using adeno-associated virus (AAV) expressing fluorescent proteins (GFP or Td-tomato) with single cell RNA sequencing. We investigated electrophysiologic, morphologic, and physiologic roles for subsets of cardiac-specific neurons and found that three of five adrenergic SGN subtypes innervate the heart. These three subtypes stratify into two subpopulations; high (NA1a) and low (NA1b and NA1c) neuropeptide-Y (NPY) -expressing cells, exhibit distinct morphological, neurochemical, and electrophysiologic characteristics. In physiologic studies in transgenic mouse models modulating NPY signaling, we identified differential control of cardiac responses by these two subpopulations to high and low stress states. These findings provide novel insights into the unique properties of neurons responsible for cardiac sympathetic regulation, with implications for novel strategies to target specific neuronal subtypes for sympathetic blockade in cardiac disease.

Differential control of intestine function by genetically defined enteric neurons

“…The emergence of single cell and single nuclei-based transcriptomics have greatly expanded the ability of peripheral neurobiologists to taxonomize neuronal subtypes based on gene expression. In fact, multiple efforts, both large-and small-scale, have been performed on peripheral neurons from the enteric 8,9,11,12,14,15 , sensory 10,16-27 and autonomic [37][38][39][40] lineages. The boundaries between cell types are difficult, perhaps even subjective, to define in a principled manner when relying primarily on transcriptomic data.…”

“…Recent studies have transcriptionally profiled each peripheral neuron lineage (enteric 2,4,[8][9][10][11][12][13][14][15][16] , sensory 10, , autonomic 7,10,[37][38][39][40][41][42] ), defining dozens of transcriptionally distinct populations of neurons in each lineage. Although these studies used different genomic methodologies, it is evident that there is significant cellular heterogeneity in each of these systems and an emergent need to develop approaches to study uncovered subpopulations.…”

Sympathetic NPY controls glucose homeostasis, cold tolerance, and cardiovascular functions in mice

“…There are six classes (Y1–Y6) of NPY receptors, which are G-protein-coupled receptors, that are differentially expressed in several target organs including smooth muscles (Y1), the cardiovascular system (Y1, Y2, Y3, Y5), kidneys (Y1, Y2, Y5, Y6), and gastrointestinal tract (Y1, Y2, Y4), as well in sympathetic axons (Y2). 16 , 25 , 46 , 73 , 74 In future studies, it will be of interest to use cKO mice to define the specific NPY receptor(s) that mediates effects of sympathetic-neuron-derived NPY in distinct effector organs. In humans, increased circulating NPY has been documented in several pathological conditions in which sympathetic output is also increased, such as hypertension, chronic heart failure, and insulin resistance.…”

“… 5 , 19 – 22 NPY, released from sympathetic nerves, also exerts a presynaptic effect in inhibiting NE release. 21 , 23 More recent studies with genetic ablation of NPY and NE co-expressing sympathetic neurons suggest roles for these neurons in modulating inflammatory responses 24 and cardiac excitability 25 in mice. However, whether observed phenotypes were due to the loss of NPY, NE, or other neuron-derived factors could not be delineated from these studies.…”

Comparative specialization of intrinsic cardiac neurons in humans, mice, and pigs

“…The apparent density of SP/CGRP fibers was also noticeably lacking in pig intracardiac ganglia. The peptides termed NPY and VIP are commonly identified within sympathetic 53,54 and parasympathetic 35,55 neurons, respectively, and can modulate ICN activity 34,[56][57][58][59] . A network of nerve fibers immunoreactive for NPY were abundant in human ganglia, but lesser so in ganglia from mice or pigs.…”