Zonula occludens-1 and connexin 43 expression in the failing human heart

Abstract

Focal disorganization of gap junctional distribution and down-regulation of the major gap junctional protein connexin 43 are typical features of myocardial remodelling in the failing human heart. Increasing evidence indicates that connexin 43 interacts with zonula-occludens-1 (ZO-1), and it has recently been shown that ZO-1 promotes the formation and growth of gap junctional plaques. In the present study, distribution patterns of ZO-1 and connexin 43 were studied in normal and in heart failure patients using double-label immunohistochemistry and confocal microscopy. ZO-1 was found to be co-localized with connexin 43 at intercalated disks. Importantly, in patients with heart failure due to dilated or ischaemic cardiomyopathy, areas of diminished connexin 43 expression were characterized by a markedly reduced ZO-1 staining. Based on these data it is concluded that in patients with heart failure, down-regulation of ZO-1 matches the diminished expression levels of connexin 43, suggesting that ZO-1 plays an important role in gap junction formation and gap junction plaque stability.

1

Connexin 43 and ZO-1 distribution in normal human myocardium. Panel A and B: Connexin 43 and ZO-1, respectively. Panel C: A merge of Panels A and B illustrating that in myocytes ZO-1 is confined together with connexin 43 at the same intercalated disks. Note the homogeneous distribution of connexin 43 and ZO-1 throughout the myocardial tissue. Panel D is an enlargement of the boxed area in Panel C illustrating that ZO-1 is also confined to intercellular junctions of endothelial cells of intramural vessels (V). Nuclei are stained blue with DAPI.

2

Connexin 43 and ZO-1 distribution in a patient with dilated cardiomyopathy. Panel A and B: Connexin 43 and ZO-1, respectively. Note the patch of myocytes at the right side displaying reduced levels of connexin 43 and ZO-1. The patch is located next to myocytes at the left part of the micrographs which are intensely labeledlabelled for both connexin 43 and ZO-1. The difference between myocytes expressing high or reduced levels of connexin 43 and ZO-1 is even more pronounced in the superimposed image shown in Panel C. Panel D is an enlargement of the boxed area in Panel C, illustrating that ZO-1 is commonly confined to the intramural vessels (V). Note that, the intensity of ZO-1 in blood vessels in the diseased heart is apparently similar to the normal heart (compare Fig. 1D with Fig. 2D). Nuclei are stained blue with DAPI.