Calreticulin downregulation is associated with FGF-2-induced angiogenesis through calcineurin pathway in ischemic myocardium

Fibroblast growth factor 2 (FGF-2) plays an integral role in therapeutic angiogenesis associated with myocardial infarct healing. Calcium (Ca2(+)) is one of the most universal important signaling molecules that affect cell proliferation and angiogenesis. Calreticulin (CRT), a 46-kd Ca2(+)-binding chaperone found mainly in the endoplasmic reticulum, plays an important role in regulating calcium homeostasis. The role of CRT in FGF-2-induced angiogenesis and its signaling pathways in ischemic myocardium are not clear. For this study, two-dimensional gel electrophoresis and matrix-assisted laser desorption ionization mass spectrometry were used to analyze CRT's differential expression in myocardial microvascular endothelial cells treated with or without FGF-2. Western blotting analysis was used to detect the expression of CRT and calcineurin (CaN) in sham-operated, FGF-2-, or saline intramyocardially injected myocardium. It is found that FGF-2 induced angiogenesis after sustained ischemia with downregulation of CRT expression and upregulation of CaN expression in myocardium. The CRT expression was negatively correlated to angiogenesis. Furthermore, overexpression of CRT or inhibition of CaN with cyclosporine A abolishes FGF-2-induced microvascular endothelial cells proliferation and CaN expression. The results indicate that intramyocardial administration of FGF-2 decreases myocardial CRT expression in parallel with myocardial angiogenesis in ischemic myocardium. The study further indicates that Ca2(+)/CaN signaling pathway may be involved in CRT-related angiogenesis.