Epithelial (E)-Cadherin Is a Novel Regulator of Platelet Function

Epithelial (E-) cadherin is an adhesion molecule that mediates cell-cell interactions, and is important in pluripotent stem cell reprogramming. We are investigating the role of E-cadherin in megakaryocyte differentiation and platelet function, and propose that E-cadherin mediates interactions that facilitate the essential roles of platelets. We have evidence that mature megakaryocytes and platelets express E-cadherin, and therefore generated a megakaryocyte-specific E-cadherin knockout mouse using the PF4-Cre system. E-cadherin deleted mice are viable and fertile. Despite having normal platelet counts and mean platelet volume, platelet function is abnormal. E-cadherin deletion in platelets significantly increases bleeding time in adult mice, with wild type (Ecad^w/w) bleeding times of 225±52 secs, and homozygous deletion (Ecad^f/f) times of 880±134 secs (p=0.005). In vivo platelet depletion using systemic administration of anti-CD42b antibody in the Ecad^f/f mice causes death, likely due to hemorrhage and failure of hemostasis, which is not observed in Ecad^w/w with similar levels of platelet depletion, suggesting a platelet function defect that becomes more evident under stress. We performed immunofluorescence to probe platelet structure as a potential explanation for the phenotypes, and observed disrupted b-tubulin architecture in the E-cadherin null platelets. Also, static platelet adhesion assays revealed that E-cadherin deficient platelets have impaired adhesion on fibrinogen, relative to a BSA substrate (p=0.0005). We have extended our studies to the human system, and initial studies using an E-cadherin blocking antibody in human platelets show impairment of aggregation in response to ADP, epinephrine, and thrombin. Taken together, the results demonstrate that E-cadherin contributes to the delicate balance between bleeding, hemostasis, and thrombosis. Future studies will focus on identifying how E-cadherin regulates hemostasis, with an emphasis on the interactions mediated by E-cadherin, whether between platelets, or with other cells in the blood.