Neurotransmitter Switching in Sympathetic Neurons Coupled to Beta‐Adrenergic Signalling in Hypertensive States
Authors: Bardsley Emma N. , Davis Harvey , Buckler Keith J. , Paterson David J. 
Published: June 2021

Introduction

Hypertension can be caused by sympathetic over‐activity1,2. β‐blockers are a main‐stay treatment strategy for conditions caused by enhanced sympathetic drive3 however, the precise mechanisms that mediate and sustain the beneficial effects of β‐blockers in disease remain unclear4,5. Conventional wisdom suggests the main beneficial effects of β‐blockers reside within the myocardium; however, emerging evidence indicates that another beneficial effect of β‐blockers in disease may reside in sympathetic neurons.

Aim

We investigated whether β‐adrenoceptors (βARs) are present on cardiac post‐ganglionic sympathetic neurons (PGSNs) in human and rat; and facilitate neurotransmission in a feed‐forward manner.

Methods

We used a combination of RNA sequencing, quantitative real‐time (qRT)‐PCR, Enzyme Linked Immunosorbent Assays (ELISAs) and immunocytochemistry to investigate whether sympathetic βARs are present on human and rat sympathetic stellate ganglia. We subsequently used Förster Resonance Energy Transfer (FRET) microscopy and Ca2+ Imaging to establish whether intracellular second messenger signalling coupled to presynaptic βARs is impaired in hypertensive states; contributing to impaired cyclic nucleotide (cN) signalling and Ca2+ dysfunction. Finally, we used high pressure liquid chromatography coupled to electrochemical detection (HPLC‐EC) to assess which neurotransmitters are present within the cardiac‐sympathetic ganglia in healthy and diseased states, to test the idea that Adr may act as the preferential sympathetic neurotransmitter in disease.

Results

We identified the presence of βARs on human and rat stellate ganglia. In diseased neurons from the rat, we measured enhanced βAR‐mediated cAMP‐PKA‐Ca2+ signalling, predominantly via β2AR activation. Moreover, we identified the presence of the adrenaline (Adr) synthesising enzyme, Phenylethanolamine‐N‐methyltransferase (PNMT) in human and rat neurons; and measured greater Adr content and evoked release in diseased rat neurons.

Conclusion

We conclude that neurotransmitter switching, resulting in enhanced Adr release, may provide presynaptic positive feedback on βARs to promote further release that leads to greater postsynaptic excitability. Targeting neuronal βAR downstream signalling could provide therapeutic opportunity to minimise end‐organ damage caused by sympathetic over‐activity.

Support or Funding Information

This project was funded by the Wellcome Trust OXION Initiative, NIH SPARC Initiative and the British Heart Foundation Centre of Research Excellence (BHF CRE). We acknowledge The High‐Throughput Genomics Group at the Wellcome Trust Centre for Human Genetics (funded by Wellcome Trust grant reference 090532/Z/09/Z) for the generation of the Sequencing data. We wish to acknowledge our collaborators Dr. Ajijola, Dr. Shivkumar and Dr. Ardell at UCLA for kindly extracting and shipping human sympathetic stellate ganglia from donor patients #19, #23 and #24. We wish to thank Dr. Threlfell in our department for her help and expertise with HPLC‐EC experimental design and protocols.

This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.