No abstract

SUMMARY:Annexins II, V, and VI belong to a family of Ca 2ϩ -dependent phospholipid-binding proteins that have been involved mainly in signal transduction, differentiation, membrane trafficking events, or binding to the extracellular matrix, or that might be effective as Ca 2ϩ -channels. They are abundant in the mammalian myocardium and might play a role in ventricular remodeling and altered calcium handling during heart failure. To test this hypothesis, we compared the expression and distribution of these annexins in nonfailing (n ϭ 9) and failing human hearts with idiopathic dilated cardiomyopathy (n ϭ 11). Northern blot and slot blot analysis were used to determine the annexin mRNA levels and Western blots were used to quantify the amounts of annexin proteins. Distribution of annexins was studied by immunohistofluorescence labeling and compared with that of a sarcolemmal marker (Na ϩ /K ϩ -ATPase) and of a myofibrillar protein (␣-actinin). We showed that nonfailing hearts contained a higher amount of annexin VI than of annexin V or II (13.5 Ϯ 1.8, 3.7 Ϯ 0.2, and 2.5 Ϯ 0.5 g/mg protein, respectively). In failing hearts, there was a parallel increase in both mRNA and protein levels of annexin II (146% and 132%, p Ͻ 0.05, respectively) and annexin V (152%, p Ͻ 0.01, 147%, p Ͻ 0.005, respectively); the protein level of annexin VI was also increased (117%, p Ͻ 0.05), whereas the increase of its mRNA level was statistically insignificant. We observed a predominant localization of annexin II in interstitium, and of annexins V and VI in cardiomyocytes at the level of the sarcolemma, T-tubules, and intercalated disks in nonfailing hearts, whereas in failing hearts enlarged interstitium contained all three annexins. Furthermore, annexin V staining at the level of cardiomyocytes almost disappeared. In conclusion, we showed that heart failure is accompanied by marked overexpression of annexins II and V, as well as translocation of annexin V from cardiomyocytes to interstitial tissue. The data suggest that annexins may contribute to ventricular remodeling and annexin V to impaired Ca 2ϩ handling in failing heart. (Lab Invest 2000, 80:123-133).

This study indicated for the first time that annexin A5 was externalized at a very early stage of apoptosis and could have a proapoptotic effect in cardiomyocytes.