EXTRACELLULAR MATRIX REMODELLING IN AGE-RELATED SINUS NODE DISEASE

Abstract

The sinoatrial node (sinus node/SAN) is the natural pacemaker of the heart and the origin of the cardiac action potential. With advancing age, in man and all mammalian species studied, the function of the SAN is observed to decline, and consequently electronic pacemakers are primarily implanted in the elderly. This is attributed to a widely accepted, yet largely unproven concept that an age-related upregulation of extracellular matrix (ECM) deposition in the SAN drives the development of sinus node disease (SND). Information is lacking in: (1) how the SAN matrix composition remodels with age, (2) what molecular pathways are driving such remodelling and (3) whether targeting the underlying mechanisms can mitigate age-related SND. In my PhD studies I investigated this clinically relevant knowledge gap first by registering the compositional remodelling of the SAN matrix using mass spectrometry in young C57BL/6J mice (2-3 months) and aged (24 months) C57BL/6JRccHsd mice. Experiments were performed to confirm that aged mice displayed canonical features of SND including bradycardia, increased sinus node recovery time and slowed conduction velocity from the SAN to the atria. It was observed that ageing resulted in remodelling of approximately 10% of the proteome, with 378 proteins showing dysregulation. This included remodelling of 49 ECM proteins with a striking upregulation of collagen VI, the predominant SAN collagen in mice. To understand what molecular factors may be driving changes in the ECM proteome, the transcriptome of the young and aged mouse SAN was also characterised using RNA sequencing. Ageing resulted in remodelling of approximately 13% of the SAN transcriptome. Bioinformatics of differentially expressed genes revealed a striking inflammatory infiltrate in the aged SAN, accompanied by an expansion of the macrophage population. The pro-inflammatory and pro-fibrotic protein galectin-3 (LGALS3), upregulated by 67% in the aged SAN, was selected as a molecular target for further enquiry due to its well-established role in regulating cardiac fibrosis. In cultured fibroblasts LGALS3 drove collagen VI synthesis, which was inhibited with the LGALS3 blocker modified citrus pectin (MCP). In vivo LGALS3 blockade prevented sinus bradycardia and an inferior shift in the leading pacemaker site in aged mice, which was associated with a restoration of collagen VI in the aged SAN to ‘young’ levels. These data are the first registration of the ECM remodelling changes that accompany age-related SND and offer new mechanistic insight into the underlying processes.

Date of Award	1 Aug 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Halina Dobrzynski (Supervisor) & Alicia D'Souza (Supervisor)