Highly variable expression of virus receptors in the human cardiovascular system. Implications for cardiotropic viral infections and gene therapy.

Coxsackieviruses and adenoviruses are common agents of viral heart disease. In the majority of exposed individuals they do not cause myocardial disease, however, since they are not primarily cardiotropic. Until recently the molecular basis of their anomalous tropism in patients who develop viral heart disease was unknown. An important step towards clarification of the molecular basis of cardiotropic viral infections was achieved in 1997, when a common receptor for the two structurally unrelated viruses was cloned. This coxsackievirus-adenovirus receptor (CAR) is a key determinant for the cellular uptake of both viruses and for the molecular pathogenesis of coxsackievirus and adenovirus diseases. We have mapped the CAR expression in human hearts and observed highly variable expression patterns. Healthy donor hearts had low CAR expression levels, whereas explanted hearts of patients with dilated cardiomyopathy (DCM) displayed high CAR expression in the myocardium. Remarkably, however, heart failure per se was not associated with CAR induction, since in heart failure of non-DCM origin no induction was found. Additional studies on the molecular mechanisms of CAR induction in cardiomyocytes indicated the existence of a cell-cell contact-dependent molecular mechanism regulating CAR expression, whereas cellular virus uptake and low level replication had no effect. Recombinant expression of human CAR in cardiomyocytes strongly increased their virus uptake rate suggesting that CAR induction enhances cardiac vulnerability to viral disease, whereas healthy myocardium is rather resistant to CAR-dependent viruses. Receptor induction may significantly aggravate the clinical course of viral heart disease, so that the blockade of receptor expression or receptor-virus interactions opens new therapeutic perspectives. Elucidation of the molecular mechanism of CAR induction in DCM, but not in heart failure per se, may reveal a particular pathogenetic process in this disease. A broader analysis of the cardiovascular expression patterns of receptors for other potentially cardiotropic viruses (CMV, EBV, HIV, HHV-6, Parvo-B19, etc.) should lead to a better understanding of individual risk factors for viral heart diseases and of their highly variable clinical courses, and offer new therapeutic options.