Cardiomyocyte-Specific Deletion of the Coxsackievirus and Adenovirus Receptor Results in Hyperplasia of the Embryonic Left Ventricle and Abnormalities of Sinuatrial Valves

Abstract

Abstract-The coxsackievirus and adenovirus receptor (CAR), which mediates infection by the viruses most commonly associated with myocarditis, is a transmembrane component of specialized intercellular junctions, including the myocardial intercalated disc; it is known to mediate cell-cell recognition, but its natural function is poorly understood. We used conditional gene targeting to investigate the possible functions of CAR during embryonic development, generating mice with both germline and tissue-specific defects in CAR expression. Homozygous germline deletion of CAR exon 2 or cardiomyocyte-specific gene deletion at embryonic day 10 (E10) mediated by Cre recombinase expressed under the control of the cardiac troponin T promoter resulted in death by E12.5; embryos showed marked cardiac abnormalities by E10.5, with hyperplasia of the left ventricular myocardium, distention of the cardinal veins, and abnormalities of sinuatrial valves. Within the hyperplastic left ventricle, increased numbers of proliferating cells were evident; persistent expression of N-myc in the hyperplastic myocardium and attenuated expression of the trabecular markers atrial natriuretic factor and bone morphogenic protein 10 indicated that proliferating cardiomyocytes had failed to differentiate and form normal trabeculae. In electron micrographs, individual CAR-deficient cardiomyocytes within the left ventricle appeared normal, but intercellular junctions were ill-formed or absent, consistent with the known function of CAR as a junctional molecule; myofibrils were also poorly organized. When cardiomyocyte-specific deletion occurred somewhat later (by E11, mediated by Cre under control of the ␣-myosin heavy chain promoter), animals survived to adulthood and did not have evident cardiac abnormalities. These results indicate that during a specific temporal window, CAR expression on cardiomyocytes is essential for normal cardiac development. In addition, the results suggest that CAR-mediated intercellular contacts may regulate proliferation and differentiation of cardiomyocytes within the embryonic left ventricular wall. Key Words: adhesion molecules Ⅲ cardiac development Ⅲ cardiomyopathy Ⅲ coxsackievirus receptor Ⅲ hyperplasia Ⅲ intercellular junctions Ⅲ mouse heart development T he coxsackievirus and adenovirus receptor (CAR) is a 46-kDa cell surface protein that mediates attachment and infection by group B coxsackieviruses and many adenoviruses. 1,2 CAR has been conserved during vertebrate evolution, with homologs identified in mammals, birds, frogs, and fish, 3 but its natural functions are not well understood. Recent work demonstrates that CAR mediates homotypic 4,5 and heterotypic 6 intercellular interactions and that it is a component of specialized intercellular junctions, including the epithelial tight junction 4 and the cardiac intercalated disc. 7 Although distinct CAR-mediated signals have not been defined, CAR expression in tumor cell lines leads to changes in the activity of cell cycle regulators that are associated with slower g...

Podocin Participates in the Assembly of Tight Junctions between Foot Processes in Nephrotic Podocytes

“…However, the physiologic relevance needs to be further evaluated by other approaches such as tissue-and stage-specific knockouts. 25 Podocin enhances raft association of CAR by promoting its oligomerization in an analogous mechanism to that reported for the other raft proteins. 17 Podocin forms a large oligomeric complex, 5 and its raft association is stabilized in part via its C-terminus containing a prohibitin homology domain, reportedly important for lipid-protein interactions.…”

Coxsackievirus Adenovirus Receptor Loss Impairs Adult Neurogenesis, Synapse Content, and Hippocampus Plasticity

“…Nestin-Cre mice and CAR flox/flox mice (Tronche et al, 1999;Chen et al, 2006) were crossed to generate CAR-CNS KO mice. Unless specified otherwise, experiments were performed on ϳ2-month-old CAR flox/flox and CAR flox/flox nestinCre littermates.…”

“…Because CAR plays primordial roles in other tissue such as the heart, where loss of function is embryonically lethal (Chen et al, 2006), this may preclude an association with brain diseases. However, there are posttranscriptional mechanisms that can lead to the loss of CAR: studies using nonneuronal cells and tissues suggest that CAR levels are indirectly reduced by proinflammatory cytokines (e.g., TNF and IFN-␥) (Vincent et al, 2004).…”

The Coxsackievirus–Adenovirus Receptor Reveals Complex Homophilic and Heterophilic Interactions on Neural Cells

“…The absence of CAR in mice results in lethality at embryonic day 11 because of malformations of the heart (Asher et al, 2005;Dorner et al, 2005;Chen et al, 2006). In the adult heart, ablation of CAR results in disturbed conduction of electrical activity from the atrium (A) to the ventricle (V) as indicated by a prolonged PR interval in electrocardiogram plots.…”