Background: Gap junctions are intercellular communication structures responsible for electrical impulse transmission between cardiac cells. In the human ventricular myocardium, they are formed primarily by connexin 43 (CX43). CX43 amount, location within the cells and spatial distribution in the tissue are potential factors modulating its function, but little is known about how age-induced variations in such features affect human left ventricular (LV) electrophysiology, either individually and in combination with other remodeling factors like fibrosis. Here, we developed methods for automatic quantification of CX43 features and fibrosis deposition from human LV samples and we in silico assessed their role in electrical propagation and arrhythmogenicity.
Methods: We processed 44 LV fluorescent immunostaining images of 50-85 y.o. individuals to characterize CX43 quantity, degree of lateralization and spatial heterogeneity together with fibrosis deposition. The results were used to feed two-dimensional computational models of human LV electrophysiology. We evaluated the effects of variations in CX43 features alone and combined with fibrosis accumulation on conduction velocity (CV), action potential duration (APD) and proarrhythmicity.
Results: No remarkable changes in CX43 amount and lateralization were found with age in the whole population. A 45% increase in CX43 spatial heterogeneity was observed in elder versus middle-age individuals. Computational simulations showed that CV was influenced by both changes in CX43 characteristics and fibrosis accumulation, while APD was mainly affected by changes in fibrosis. Analysis of proarrhythmicity showed that reduced CX43 expression to the extent observed in some elder individuals increased 5 times the areas of high repolarization gradient. These effects were potentiated when combined with fibrosis deposition or with other CX43 remodeling characteristics like tissue heterogeneity.
Conclusions: Age makes CX43 tissue spatial distribution more heterogeneous, which, together with increased fibrosis deposition, enhance arrhythmic vulnerability.