Introduction: The goal was to elucidate contributions of AJAP1 to epithelial cell behaviors that are integral to formation of the epicardium. Based upon our preliminary in vivo data, we hypothesized that the reduction in cardiac Ajap1 expression acts as a catalyst to impair epicardium and, subsequently, coronary vessel formation.

Methods: We first analyzed the contribution of AJAP1 to cell behavior in an in vitro system that models mammalian epicardial cells, using the MCF7 human breast adenocarcinoma cell line as these cells retain epithelial characteristics in vitro and have endogenous AJAP1 expression. We achieved AJAP1 gene silencing through a siRNA-mediated approach that led to a significant reduction in both AJAP1 mRNA and protein expression. Next, control and AJAP1-silenced MCF7s were subjected to cell adhesion assays to assess the ability of these cells to adhere to various basement membrane matrices. Finally, we analyzed Ajap1 protein expression in embryonic and adult mouse hearts to gauge how its levels change throughout stages of cardiovascular development.

Results: Our gene-silenced epithelial cells revealed a significant difference in cell adhesion abilities between the control and AJAP1-transfected cells. Cardiac Ajap1 expression changed notably throughout mouse development and after gestation.

Conclusions: We concluded that AJAP1 contributes to the in vitro cell adhesion properties in an epithelial model system of the mammalian epicardium.