Induced Deletion of the N-Cadherin Gene in the Heart Leads to Dissolution of the Intercalated Disc Structure

Abstract

The structural integrity of the heart is maintained by the end-to-end connection between the myocytes called the intercalated disc. The intercalated disc contains different junctional complexes that enable the myocardium to function as a syncytium. One of the junctional complexes, the zonula adherens or adherens junction, consists of the cell adhesion molecule, N-cadherin, which mediates strong homophilic cell-cell adhesion via linkage to the actin cytoskeleton. To determine the function of N-cadherin in the working myocardium, we generated a conditional knockout containing loxP sites flanking exon 1 of the N-cadherin (Cdh2) gene. Using a cardiac-specific tamoxifen-inducible Cre transgene, N-cadherin was deleted in the adult myocardium. Loss of N-cadherin resulted in disassembly of the intercalated disc structure, including adherens junctions and desmosomes. The mutant mice exhibited modest dilated cardiomyopathy and impaired cardiac function, with most animals dying within two months after tamoxifen administration. Decreased sarcomere length and increased Z-line thickness were observed in the mutant hearts consistent with loss of muscle tension because N-cadherin was no longer available to anchor myofibrils at the plasma membrane. Ambulatory electrocardiogram monitoring captured the abrupt onset of spontaneous ventricular tachycardia, confirming that the deaths were arrhythmic in nature. A significant decrease in the gap junction protein, connexin 43, was observed in the N-cadherin-depleted hearts. This animal model provides the first demonstration of the hierarchical relationship of the structural components of the intercalated disc in the working myocardium, thus establishing N-cadherin's paramount importance in maintaining the structural integrity of the heart.

N-cadherin haploinsufficiency affects cardiac gap junctions and arrhythmic susceptibility

“…We previously demonstrated that cardiac-specific deletion of N-cadherin resulted in downregulation of Cx43-containing gap junctions and sudden arrhythmic death in mice (15,16). Based on the severity of this phenotype, we speculated that gap junctions might be affected in animals expressing half the normal levels of N-cadherin thus leading to an intermediate phenotype.…”

“…The N-cadherin mutant allele lacking exon 1 was generated as previously described (15). The N-cadherin and Cx43 heterozygous mice were intercrossed and genotypes determined by polymerase chain reaction (PCR).…”

“…We recently demonstrated that cardiac-specific loss of N-cadherin (CKO) in mice leads to disassembly of the ICD and induces SCD (15). There is a significant reduction in Cx43-containing gap junctions in the N-cadherin CKO hearts causing decreased ventricular conduction velocity (16).…”

Cellular nonmuscle myosins NMHC‐IIA and NMHC‐IIB and vertebrate heart looping

“…It is also this inner layer of cardiomyocytes that detectably sends cell processes, as well as secretes proteins, into the subjacent cardiac jelly layer. Additionally, a member of a the Caϩϩ-dependent family of adhesion molecules, N-cadherin, is responsible for the connection of actin and myofibrils between neighboring myocytes at cell-cell junctions (Linask, 1992a;Kostetskii et al, 2005) and for the cell alignment and arrangement of the two layers of the developing heart tube (Shiraishi et al, 1993). Thus, during looping, as in the earlier period of cardiac compartment formation, cross-talk between two adhesion mediated-signaling pathways, integrin and N-cadherin, is evident (Linask and Lash, 1990;Linask, 1992b;Linask et al, 2005b) and as shown here, appears to be facilitated by the actinnonmuscle myosin-II complex.…”

Adhesion Proteins, Stem Cells, and Arrhythmogenesis

“…To overcome embryonic lethality, a Cre/lox conditional knockout was generated to examine the role of N-cadherin after development of the myocardium was complete [109]. It was noted that a knockout of the N-cadherin gene also resulted in loss of α-, β-and γ-catenin, as well as desmoplakin and p120.…”