PB0769 - Platelet Activation and Expression of CAR on Cardiomyocytes and Platelets: Implication on Inflammation in Patients with Dilated Cardiomyopathy

Background: Coxsackie-adenovirus receptor (CAR), a tight junction protein, normally expressed in myocardial intercalated disc, is involved in the pathogenesis of virus-mediated myocarditis leading to dilated cardiomyopathy (DCM). CAR is also expressed on platelets; the cells known to contribute to systemic inflammation.

Aims: To evaluate the relationship of CAR expression on platelets and cardiomyocytes with local and systemic inflammation in patients with DCM.

Methods: 38 patients (mean age 39.5±11.3 years, 20 male) with DCM and clinical indications for endomyocardial biopsy (EMB) and 30 healthy subjects (HS) were recruited for the study. CAR expression in EMB samples was determined by immunohistochemistry and compared to the histological grade of myocardial inflammation. Platelet activity was analyzed by light transmission (LTA) aggregation, platelet CAR expression was assessed by immunofluorescence and platelet morphology was examined by SEM. Systemic inflammation was assessed by serum levels of tumor necrosis factor alpha (TNF α), Interleukin 6, using ELISA.

Results: CAR expression in EMB samples was not related to the intensity of inflammation. It was maximal in patients with increased IL-6 level (Figure 1A,B). Platelets of DCM patients were activated as shown by enhanced spontaneous and/or ADP induced platelet aggregation (Figure 2C) and formed microaggregates and leukocyte-platelet aggregates in blood (Figure 2A,B). Platelets’ CAR expression was >4 fold higher in DCM than HS (8.0 % vs 1.75%, p=0.0002) and was observed predominantly at sites of intercellular communications (Figure 1 C,D). CAR-positive patients showed significantly higher TNF-α and IL-6 serum levels (4.94 vs. 0 pg/ml, p=0.024) and (3.76 vs 0.19 pg/ml, p = 0.02) in CAR-negative patients.

Conclusion(s): CAR expression in myocardium is associated with systemic -not local- inflammation in DCM patients. Activated platelets express CAR at sites of intercellular communications in mircoaggregates resembling the pattern of intercalated discs of the myocardium. Platelets contribute to the inflammation seen with DCM.