Quantitative proteomics and single-nucleus transcriptomics of the sinus node elucidates the foundation of cardiac pacemaking

Nora Linscheid,Kristoffer Lihme Egerod,Sunil Jit R J Logantha,Jonatan James Thompson,Martin J Humphries,Maren Schrölkamp,Jesper Velgaard Olsen,Pi Camilla Poulsen,Shanzhuo Zhang,Ashraf Kitmitto,Mark Boyett,Henggui Zhang,Alicia Lundby,Gina Galli,Tune H Pers

doi:10.1038/s41467-019-10709-9

Abstract

The sinus node is a collection of highly specialised cells constituting the heart’s pacemaker. The molecular underpinnings of its pacemaking abilities are debated. Using high-resolution mass spectrometry, we here quantify >7,000 proteins from sinus node and neighbouring atrial muscle. Abundances of 575 proteins differ between the two tissues. By performing single-nucleus RNA sequencing of sinus node biopsies, we attribute measured protein abundances to specific cell types. The data reveal significant differences in ion channels responsible for the membrane clock, but not in Ca2+ clock proteins, suggesting that the membrane clock underpins pacemaking. Consistently, incorporation of ion channel expression differences into a biophysically-detailed atrial action potential model result in pacemaking and a sinus node-like action potential. Combining our quantitative proteomics data with computational modeling, we estimate ion channel copy numbers for sinus node myocytes. Our findings provide detailed insights into the unique molecular make-up of the cardiac pacemaker.

Highlights

The sinus node is a collection of highly specialised cells constituting the heart’s pacemaker
This study provides a comprehensive investigation of the proteome of the natural pacemaker of the heart, the sinus node
We showed that, ~8% of all quantified proteins were differentially expressed between the sinus node and atrial muscle

Summary

Introduction

The sinus node is a collection of highly specialised cells constituting the heart’s pacemaker. Incorporation of ion channel expression differences into a biophysically-detailed atrial action potential model result in pacemaking and a sinus node-like action potential. Combining our quantitative proteomics data with computational modeling, we estimate ion channel copy numbers for sinus node myocytes. By means of high-resolution mass spectrometry, we quantify protein abundances across sinus node and neighbouring, nonpacemaking atrial muscle, enabling us to determine which proteins are differentially expressed. We find that membrane clock proteins are essentially exclusively expressed in sinus node myocytes. With this knowledge, we use our proteomics data combined with computational modeling to calculate absolute copy numbers of voltage-gated ion channels per sinus node myocyte. The information contained in this data forms a foundation to evaluate sinus node function as well as molecular changes underlying pathological states of the sinus node

Methods

Results

Conclusion