Abstract 613: Differential Expression of the Coxsackie-Adenovirus Receptor in Mice Susceptible or Resistant to Viral Myocarditis
Introduction: The coxsackie-adenovirus receptor (CAR) is the functional receptor for coxsack-ievirus B3 (CVB3) infection. We have identified a novel truncated isoform of CAR (tCAR) in murine cardiomyocytes, heart and spleen. The transmembrane and cytoplasmic regions of full length murine CAR (mCAR) are replaced by a 24 amino acid C-terminal end. We hypothesize that these CAR isoforms differentially mediate CVB3 infection and impact on susceptibility to myocarditis.
Methods: To evaluate CAR isoform expression in CVB3 myocarditis we compared mCAR and tCAR in the hearts of 2 murine strains with differential susceptibility to infection: A/J (susceptible) and C57BL/6 (resistant). Hearts were randomly harvested on days 0 (uninfected controls), 1, 2 and 4 after infection with 10 pfu CVB3 (n=5/group). Real-time PCR with Taqman probes specifically designed to distinguish between mCAR and tCAR was used for gene expression studies. Polyclonal antibodies specific to the C-termini of mCAR and tCAR were used to determine CAR isoforms by western blot. Finally, the ability of tCAR to mediate CVB3 infection was assessed by comparing infectivity of mCAR-CHO and tCAR-CHO cell lines.
Results: From day 0 to day 4 post-infection (pi) mCAR RNA expression, as determined by PCR, was significantly increased in susceptible A/J mice; no increase in mCAR expression was found in resistant C57BL/6 mice. In contrast, tCAR expression was stable from day 0 to day 4 pi in A/J mice, but increased significantly from day 0 to day 4 in C57BL/6 mice. Total mCAR protein increased pi in A/J mice, while the tCAR protein increased more significantly in C57BL/6 mice. CVB3 titres were found to be significantly lower in tCAR-CHO cells [3.2 X 104 ± 4.3 X 103; p <0.01] than in mCAR-CHO cells [3.0 X 106 ± 9.3 X 105], indicating that tCAR does not mediate productive infection.
Conclusion: We have identified a unique receptor for CVB3 (tCAR) that is differentially expressed in susceptible and resistant mouse strains. The upregulation of tCAR appears to mediate host protection from CVB3 infection. The tCAR isoform may function as a soluble receptor, binding the virus, and may have important diagnostic and therapeutic implications for viral myocarditis.