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

ABSTRACT: The sinus node is a collection of highly specialised cells constituting the heart’s pacemaker. It is keenly debated whether the so-called membrane or alternatively Ca2+ clocks provide the molecular substrate of pacemaking. By high-resolution mass spectrometry, we quantified >7,000 proteins from sinus node and neighbouring atrial muscle. The abundances of 575 proteins differed between the two tissues, including particular differences in metabolic profiles and extracellular matrix composition. Most notably, the data reveal significant differences between the tissues in the ion channels responsible for the membrane clock, but not in Ca2+ clock proteins, suggesting that the membrane clock underpins pacemaking. By performing single-nucleus RNA sequencing of sinus node biopsies, we attributed protein abundances to specific cell types. Consistent with these results, incorporation of the ion channel expression differences into a biophysically-detailed atrial action potential model resulted 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 pacemaker of the heart.

ORGANISM(S): Mus musculus

PROVIDER: GSE130710 | GEO | 2019/05/04

REPOSITORIES: GEO

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Project description:to study the effect of induced expression of TBX3 within the atrium of the heart Background: Treatment of congenital or acquired disorders of the sinus node or atrioventricular node requires insight into the molecular mechanisms for the development and homeostasis of these pacemaker tissues. In the developing heart, transcription factor TBX3 is required for pacemaker and conduction system development. Here, we explore the role of TBX3 in the adult heart and investigate whether TBX3 is able to reprogram terminally differentiated working cardiomyocytes into pacemaker cells. This would be an attractive approach in biological pacemaker formation. Methods and results: TBX3 expression was ectopically induced in cardiomyocytes of adult transgenic mice. Expression analysis revealed an efficient switch from the working myocardial expression profile to that of the pacemaker myocardium. This included suppression of genes encoding gap junction subunits (Cx40, Cx43), the cardiac Na+ channel (NaV1.5; INa) and inwardly rectifying K+ ion channels (Kir-genes; IK1). Concordantly, we observed conduction slowing in these hearts, and reductions in INa and IK1 in cardiomyocytes isolated from these hearts. The reduction in IK1 resulted in a more depolarized maximum diastolic potential, thus enabling spontaneous diastolic depolarization. Neither ectopic pacemaker activity nor pacemaker current, If, were observed. Lentiviral expression of TBX3 in ventricular cardiomyocytes resulted in conduction slowing and development of heterogeneous phenotypes, including depolarized and spontaneously active cardiomyocytes. Conclusions: TBX3 partially reprograms terminally differentiated working cardiomyocytes into pacemaker-like cells and induces important pacemaker properties. The ability of TBX3 to reduce intercellular coupling to overcome current-to-load mismatch and the ability to reduce IK1 density to enable diastolic depolarization, are very promising TBX3 characteristics for biological pacemaker formation strategies. 5 TBX3 expressing left atrial appendage samples (Tamoxifen-treated Myh6MCM;CTBX3 adult male mice) and 6 controls ((Tamoxifen-treated Myh6MCM adult male mice)

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

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