Skin Wound Repair Is Not Altered in the Absence of Endogenous AnxA1 or AnxA5, but Pharmacological Concentrations of AnxA4 and AnxA5 Inhibit Wound Hemostasis

Skin injury induces the cell surface exposure of phosphatidylserine (PS) on damaged and dying cells to activate coagulation and repair processes. Annexins can bind to PS and may modulate the healing response. Here, we determine the relevance of annexins for skin wound healing using AnxA1- and AnxA5-deficient mice and recombinant annexins with distinct PS binding properties. Wound inflammation, closure and the formation of granulation tissue were not altered in AnxA1- or AnxA5-deficient mice or after increasing AnxA5 serum concentrations (100 nM) in wild-type mice. Increased serum concentrations (1 µM) of AnxA5 induced massive bleeding, but wound hemostasis was not delayed by AnxA1. Both annexins interact with PS, but only AnxA5 can form 2-dimensional (2D) arrays on the cell surface. The injection of an AnxA5 mutant that binds to PS but lacks the ability of 2D array formation failed to induce bleeding. 2D lattice-forming AnxA4, with high affinity to PS also caused bleeding, while hemostasis was not affected by AnxA8 with low affinity or the AnxA8 mutant with medium affinity for PS and the lack of 2D formation. Increased concentrations of AnxA4 and AnxA5 also delayed coagulation pathway activation in vitro. This effect was attenuated for the AnxA5 mutant as well as for AnxA1 and AnxA8. In conclusion, endogenous AnxA1 and AnxA5 are dispensable for wound hemostasis and repair, but pharmacologically excessive concentrations of AnxA4 and AnxA5 inhibit hemostasis in skin wounds.

Expression and thyroid hormone regulation of annexins in the anterior pituitary

Due to their property to bind to phospholipids in a Ca(2)(+)-dependent manner, proteins of the annexin superfamily are involved in many membrane-related events and thus in various forms of physiological and pathological processes. We were therefore interested in analyzing the mRNA expression of the annexins in the severely disorganized pituitaries of the athyroid Pax8(-/-) mice in comparison with that of control animals. In neither condition was mRNA expression of the annexins A3, A7, A8, A9, A11, and A13 detectable. The annexins A2, A4, and A6 were equally expressed in wild-type and Pax8(-/-) mice. Transcript levels of A1 and A10 were highly increased and those of A5 were significantly decreased in the athyroid mutants compared with controls. Treatment of Pax8(-/-) mice with physiological doses of thyroxine for 3 days normalized the mRNA expression of A1, A5, and A10 indicating that the expression of these annexins is directly regulated by thyroid hormone (TH). Since A5 exhibits by far the highest transcript levels of all annexins in the pituitary and its regulation by TH could be also confirmed at the protein level, we analyzed the mRNA expression of pituitary hormones in A5(-/-) mice. In these mutants, only the beta-FSH mRNA expression was found to be significantly reduced, while the mRNA expression levels of the other pituitary hormones were not altered. These results support the concept that annexins might serve important albeit redundant functions as modulators of pituitary hormone secretion.

DT40 cells lacking the Ca2+-binding protein annexin 5 are resistant to Ca2+-dependent apoptosis

Annexins are widely expressed Ca(2+)-dependent phospholipid-binding proteins with poorly understood physiological roles. Proposed functions include Ca(2+) channel activity and vesicle trafficking, but neither have been proven in vivo. Here we used targeted gene disruption to generate B-lymphocytes lacking annexin 5 (Anx5) expression and show that this results in reduced susceptibility to a range of apoptotic stimuli. By comparison B-lymphocytes lacking annexin 2 (Anx2) showed no such resistance, providing evidence that this effect is specific to loss of Anx5. The defect in the ANX5(-/-) cells occurs early in the apoptotic program before nuclear condensation, caspase 3 activation, and cell shrinkage, but downstream of an initial Ca(2+) influx. Only UVA/B irradiation induced similar levels of apoptosis in wild-type and ANX5(-/-) cells. Unexpectedly, ANX5(-/-) cells permeabilized in vitro also failed to release mitochondrial cytochrome C, suggesting a possible mechanism for their resistance to apoptosis. These findings demonstrate a role for Anx5 in determining the susceptibility of B-lymphocytes to apoptosis.

The annexinopathies: a new category of diseases

The annexins are a family of highly homologous phospholipid binding proteins, which share a four-domain structure, with one member of the family - annexin VI - having a duplication consisting of eight domains. Thus far, ten annexins have been described in mammals. Although the biological functions of the annexins have not been definitively established, two human diseases involving annexin abnormalities ('annexinopathies') have been identified as of the time of writing. Overexpression of annexin II occurs in the leukocytes of a subset of patients having a hemorrhagic form of acute promyelocytic leukemia. Underexpression of annexin V occurs on placental trophoblasts in the antiphospholipid syndrome and in preeclampsia. Also, an animal model has been described in which annexin VII is underexpressed and is associated with disease, but the relevance of this animal model to human disease is not yet understood. Future research is likely to elucidate additional 'annexinopathies'.