PB0899 - Connexin 45 is co-localized with Coxsackievirus-adenovirus receptor forming contact membrane within platelet aggregates and filopodia

Background: Coxsackie-adenovirus receptor (CAR), a protein of tight junctions, is expressed in various cells including cardiomyocytes and platelets. In myocardium CAR can moderate expression of connexins, proteins of gap junctions which were recently also found in platelets.

Aims: We aimed to study the interaction between CAR and connexins in platelets.

Methods: 18 patients (mean age 43.5 ±10.3 years, 20 male) with dilated cardiomyopathy (DCM) and 15 healthy subjects (HS) were recruited for the study. Platelet aggregation (spontaneous and ADP-induced) was studied by simultaneous analysis of the mean aggregate size changes and light transmission using an aggregation analyzer (230LA aggregometer). Platelet CAR, connexin 43 and 45 were assessed by immunofluorescence. The number of connexin positive platelets was determined relative to the total number of platelets and expressed as a percentage.

Results: In all HS platelet aggregation was within normal whereas in the majority of DCM patients there was an increased spontaneous aggregation (83.3%). Low dose ADP-induced aggregation (0.1 μM and 1.0μM), was seen in 15 (83.3%) and 14 (77.7%) of patients respectively. The expression of connexin 43 was a rare event both in HS and DCM groups. Connexin 45 was observed in singular platelets and in platelet aggregates where it co-localizes with CAR at sites of intercellular communication, and also in leukocytes. Expression of connexin 45 on platelets was 7[5.5; 10.0]% in HS compared to 20[8.5;29.8]% in DCM group (p=0.0001). In both groups platelets revealed filopodia with substantial expression of connexin 45 but weak staining for CAR.

Conclusion(s): Gap junction protein connexin 45 is expressed in normal and hyper-aggregable platelets. Connexin 45 is expressed in platelets’ filopodia and colocalizes with CAR at sites of intercellular communications forming contact membrane between neighboring cells. This novel finding indicates a possible role in cell signaling.