Mass spectrometric proteome profiling using a deep spectral library reveals homogenization of right and left atrial proteomes in persistent atrial fibrillation patients

<h4>Aims</h4>Pulmonary veins in the left atrium (LA) are well-established as a critical site for the initiation of atrial fibrillation (AF). Emerging evidence suggests that in persistent AF (persAF), AF triggers may extend beyond LA. However, the extent to which AF-associated remodelling involves the right atrium (RA) in persAF remains a subject of debate. To address this, we employed a proteomic approach aiming at investigating AF-associated remodelling in the RA relative to the LA in persAF.<h4>Methods and results</h4>RA and LA samples were obtained from sinus rhythm (SR) patients, patients with persAF undergoing open-heart surgery, and non-failing donor hearts rejected for transplantation. A reference spectral library representing the human cardiac proteome was employed to assess the RA and LA proteomes by data-independent acquisition mass spectrometry. Protein levels were quantified by immunoblotting of human atrial tissue. Plasma levels of NT-proANP and NT-proBNP were measured in SR and persAF patients. Fibrosis levels were quantified in paraffin-embedded sections using Masson-Goldner trichrome staining. A spectral library representing 13 539 human proteins was generated from five anatomical regions of five independent donor hearts. In persAF RA, we observed marked myolysis, excessive extracellular matrix deposition and a prominent similarity to the failing ventricular proteome, all comparable to persAF LA. Although significant proteomic differences were observed between the RA and LA from SR patients, a comparison of RA and LA proteomes in persAF patients revealed proteome homogenization between the two atrial chambers. RA contributes to this homogenization by losing RA-specific markers, while gaining LA-specific markers.<h4>Conclusion</h4>Our findings suggest that RA undergoes comparable AF-associated remodelling to LA, contributing to atrial proteome unification which represents a hallmark of persAF.