Annexins in cardiac tissue: cellular localization and effect on phospholipase activity

Abstract

Stimulation of cardiac phospholipid metabolism has diverse biological effects, ranging from subtle changes in cellular function to severe cellular damage. Accordingly, knowledge of the factors governing the activity of cardiac phospholipases is of great biological importance. A possible role of annexins, intracellular proteins that bind to membranes in a calcium dependent manner, as modulators of phospholipase activity has been proposed. In this study we investigated the cell type specific distribution of Annexin V and VIII in the heart. Recombinant Annexin V was used to examine the effect of this type of Annexin on cardiac phospholipase activity. Western blot analysis shows that annexin V is abundantly present in the heart. Using isolated myocytes and cultured cardiac endothelial and fibroblast-like cells, it is demonstrated that the localization of Annexin V is confined to non-myocytes. No positive bands matching the Mw of recombinant Annexin VIII are found in any of the cell types examined. In vitro studies demonstrate that recombinant Annexin V potently inhibits the activity of cardiac membrane-bound phospholipases, acting on their natural surrounding substrate, in a calcium dependent manner. Interestingly, annexin V also inhibits triacylglycerol hydrolysis. In conclusion, the expression of annexins is cell-type specific and suggests a cell-type specific function of these proteins in the heart. The absence of Annexin V in cardiac myocytes dismisses involvement of this annexin in cardiomyocyte phospholipid metabolism. The presence of Annexin V in cardiac endothelial and fibroblasts suggests a regulating role in the phospholipid homeostasis of non-myocyte cell types in the heart.

Expression and Localization of the Annexins II, V, and VI in Myocardium from Patients with End-Stage Heart Failure

“…Taken together, our results indicated that annexin V was present in sarcolemma, and intercalated discs, and in the T-tubules connected to the terminal cisternae of sarcoplasmic reticulum -the complex in which the excitation-contraction coupling took place. Therefore, labeling of annexin V in human heart was similar to that of other species (Doubell et al, 1993;Jans et al, 1995;Luckcuck et al, 1997;Trouvé et al, 1999;Van Bilsen et al, 1992;Wang et al, 1995). Interestingly, immunofluorescence of annexin V in failing hearts (Fig.…”

“…Annexins V and VI are the major annexins in porcine (Pula et al, 1990), bovine (Iida et al, 1992;Wang et al, 1993;Zeng et al, 1993), rat (Doubell et al, 1993;Jans et al, 1995;Wang et al, 1995), and guinea pig (Trouvé et al, 1999) myocardium. Annexin V is able to form voltage-gated Ca 2ϩ channels (Pollard et al, 1992) and to modulate activity of protein kinase C and phospholipase A 2 Mira et al, 1998;Van Bilsen et al, 1992). In myocardium, the localization of annexin V is not clearly established: the presence of annexin V was first reported in endothelium and fibroblasts (Van Bilsen et al, 1992), then in myocytes in which it has been detected either in cytosol (Jans et al, 1995), in membranes (Luckcuck et al, 1997;Trouvé et al, 1999), or associated with Z-lines (Trouvé et al, 1999;Wang et al, 1995).…”

“…Annexin V is able to form voltage-gated Ca 2ϩ channels (Pollard et al, 1992) and to modulate activity of protein kinase C and phospholipase A 2 Mira et al, 1998;Van Bilsen et al, 1992). In myocardium, the localization of annexin V is not clearly established: the presence of annexin V was first reported in endothelium and fibroblasts (Van Bilsen et al, 1992), then in myocytes in which it has been detected either in cytosol (Jans et al, 1995), in membranes (Luckcuck et al, 1997;Trouvé et al, 1999), or associated with Z-lines (Trouvé et al, 1999;Wang et al, 1995). Annexin VI has been localized in rat, bovine, and guinea pig hearts mainly in sarcolemma and intercalated discs of cardiomyocytes (Doubell et al, 1993;Iida et al, 1992;Luckcuck et al, 1997;Trouvé et al, 1999).…”

The Complexity of the Phospholipid Binding Protein Annexin V

“…Another biological function described for Annexin V is an anti phospholipase A2 activity. This activity is based on the same principle as the anticoagulant function of Annexin V, namely shielding off of the negatively charged phospholipids, the substrate for phospholipase A2 (13,57,58,60,61,67,79,88,89). Based on this activity, it has been postulated that Annexins participate in inflammatory processes.…”