Immunocytochemical localization of annexin V (CaBP33), a Ca(2+)-dependent phospholipid- and membrane-binding protein, in the rat nervous system and skeletal muscles and in the porcine heart

An expanded proteome of cardiac t-tubules

BACKGROUND

Transverse tubules (t-tubules) are important structural elements, derived from sarcolemma, found on all striated myocytes. These specialized organelles create a scaffold for many proteins crucial to the effective propagation of signal in cardiac excitation-contraction coupling. The full protein composition of this region is unknown.

METHODS

We characterized the t-tubule subproteome using 52,033 immunohistochemical images covering 13,203 proteins from the Human Protein Atlas (HPA) cardiac tissue microarrays. We used HPASubC, a suite of Python tools, to rapidly review and classify each image for a specific t-tubule staining pattern. The tools Gene Cards, String 11, and Gene Ontology Consortium as well as literature searches were used to understand pathways and relationships between the proteins.

RESULTS

There were 96 likely t-tubule proteins identified by HPASubC. Of these, 12 were matrisome proteins and 3 were mitochondrial proteins. A separate literature search identified 50 known t-tubule proteins. A comparison of the 2 lists revealed only 17 proteins in common, including 8 of the matrisome proteins. String11 revealed that 94 of 127 combined t-tubule proteins generated a single interconnected network.

CONCLUSION

Using HPASubC and the HPA, we identified 78 novel, putative t-tubule proteins and validated 17 within the literature. This expands and improves our knowledge of this important subcellular structure of the cardiac myocyte. This information can be used to identify new structural targets involved in excitation-contraction coupling that may be altered in disease.

Annexin V-induced rat Leydig cell proliferation involves Ect2 via RhoA/ROCK signaling pathway

This study investigated the effect of annexin V on the proliferation of primary rat Leydig cells and the potential mechanism. Our results showed that annexin V promoted rat Leydig cell proliferation and cell cycle progression in a dose- and time-dependent manner. Increased level of annexin V also enhanced Ect2 protein expression. However, siRNA knockdown of Ect2 attenuated annexin V-induced proliferation of rat Leydig cells. Taken together, these data suggest that increased level of annexin V induced rat Leydig cell proliferation and cell cycle progression via Ect2. Since RhoA activity was increased following Ect2 activation, we further investigated whether Ect2 was involved in annexin V-induced proliferation via the RhoA/ROCK pathway, and the results showed that annexin V increased RhoA activity too, and this effect was abolished by the knockdown of Ect2. Moreover, inhibition of the RhoA/ROCK pathway by a ROCK inhibitor, Y27632, also attenuated annexin V-induced proliferation and cell cycle progression. We thus conclude that Ect2 is involved in annexin V-induced rat Leydig cell proliferation through the RhoA/ROCK pathway.

Quantitative analysis of [99mTc]C2A-GST distribution in the area at risk after myocardial ischemia and reperfusion using a compartmental model

OBJECTIVE

It was recently demonstrated that the radiolabeled C2A domain of synaptotagmin I accumulates avidly in the area at risk after ischemia and reperfusion. The objective was to quantitatively characterize the dynamic uptake of radiolabeled C2A in normal and ischemically injured myocardia using a compartmental model.

METHODS

To induce acute myocardial infarction, the left descending coronary artery was ligated for 18 min, followed by reperfusion. [99mTc]C2A-GST or its inactivated form, [99mTc]C2A-GST-NHS, was injected intravenously at 2 h after reperfusion. A group of four rats was sacrificed at 10, 30, 60 and 180 after injection. Uptake of [99mTc]C2A-GST and [99mTc]C2A-GST-NHS in the area at risk and in the normal myocardium were determined by gamma counting. A compartmental model was developed to quantitatively interpret myocardial uptake kinetic data. The model consists of two physical spaces (vascular space and tissue space), with plasma activity as input. The model allows for [99mTc]C2A-GST and [99mTc]C2A-GST-NHS diffusion between vascular and tissue spaces, as well as for [99mTc]C2A-GST sequestration in vascular and tissue spaces via specific binding.

RESULTS

[99mTc]C2A-GST uptake in the area at risk was significantly higher than that for [99mTc]C2A-GST-NHS at all time points. The compartmental model separated [99mTc]C2A-GST uptake in the area at risk due to passive retention from that due to specific binding. The maximum amount of [99mTc]C2A-GST that could be sequestered in the area at risk due to specific binding was estimated at a total of 0.048 nmol/g tissue. The rate of [99mTc]C2A-GST sequestration within the tissue space of the area at risk was 0.012 ml/min. Modeling results also revealed that the diffusion rate of radiotracer between vascular and tissue spaces is the limiting factor of [99mTc]C2A-GST sequestration within the tissue space of the area at risk.

CONCLUSION

[99mTc]C2A-GST is sequestered in the ischemically injured myocardium in a well-defined dynamic profile. Model parameters will be valuable indicators for gauging and guiding the development of future-generation molecular probes.

SPECT imaging of myocardial infarction using 99mTc-labeled C2A domain of synaptotagmin I in a porcine ischemia-reperfusion model

INTRODUCTION

The C2A domain of synaptotagmin I recognizes necrotic and apoptotic cells by binding to exposed anionic phospholipids. The goal is to explore the potential imaging utility of 99mTc-labeled C2A in the detection of acute cardiac cell death in a porcine model that resembles human cardiovascular physiology.

METHODS

Ischemia (20-25 min) was induced in pigs (M/F, 20-25 kg) using balloon angioplasty. 99mTc-C2A-GST (n=7) or 99mTc-BSA (n=2) was injected intravenously 1-2 h after reperfusion. Noninfarct animals were injected with 99mTc-C2A-GST (n=4). SPECT images were acquired at 3 and 6 h postinjection. Cardiac tissues were analyzed to confirm the presence of cell death.

RESULTS

Focal uptake was detected in five out of seven subjects at 3 h and in all infarct subjects at 6 h postinjection but not in infarct animals injected with 99mTc-BSA or in noninfarct animals with 99mTc-C2A-GST. Gamma counting of infarct versus normal myocardium yielded a 10.2+/-5.7-fold elevation in absolute radioactivity, with histologically confirmed infarction.

CONCLUSIONS

We present data on imaging myocardial cell death in the acute phase of infarction in pigs. C2A holds promise and warrants further development as an infarct-avid molecular probe.

Characterization of mature rat oligodendrocytes: a proteomic approach

Oligodendrocytes are glial cells responsible for the synthesis and maintenance of myelin in the central nervous system (CNS). Oligodendrocytes are vulnerable to damage occurring in a variety of neurological diseases. Understanding oligodendrocyte biology is crucial for the dissemination of de- and remyelination mechanisms. The goal of the present study is the construction of a protein database of mature rat oligodendrocytes. Post-mitotic oligodendrocytes were isolated from mature Wistar rats and subjected to immunocytochemistry. Proteins were extracted and analyzed by means of two-dimensional gel electrophoresis and two-dimensional liquid chromatography, both coupled to mass spectrometry. The combination of the gel-based and gel-free approach resulted in confident identification of a total of 200 proteins. A minority of proteins were identified in both proteomic strategies. The identified proteins represent a variety of functional groups, including novel oligodendrocyte proteins. The results of this study emphasize the power of the applied proteomic strategy to study known or to reveal new proteins and to investigate their regulation in oligodendrocytes in different disease models.

Murine M cells express annexin V specifically

The specialized epithelium covering the lymphoid follicles of Peyer's patches in the gut mediates transcytosis of antigens to the underlying immune cells, mainly through the membranous, or M, cells. At present, the molecular processes involved in the mucosal immune response, and in antigen transport across the follicle-associated epithelium (FAE) and M cells, are poorly understood. To characterize FAE and M cells, we compared the gene expression profiles of small intestine FAE and villus epithelium (VE) in BALB/c mice by microarray analysis; 91 genes were found to be up-regulated and four down-regulated at least two-fold (p<0.01) in the FAE. The differential expression of a subset of these genes was shown to be confirmed by quantitative RT-PCR. Using immunohistochemistry on BALB/c Peyer's patches, cathepsin H and clusterin expression was increased in the FAE compared to the VE. Moreover, we demonstrated M cell-specific expression of annexin V, which has recently been reported to be important in endocytic transport and membrane scaffolding, suggesting that annexin V has a function in M cell-mediated transcytosis.

Bisecting GlcNAc mediates the binding of annexin V to Hsp47

The bisecting N-acetylglucosamine (GlcNAc) structure, formed through catalysis by UDP-N-acetylglucosamine : beta-D-mannoside beta-1,4-N-acetylglucosaminyltansferase III (GnT-III), is responsible for a variety of biological functions. We have previously shown that annexin V, a member of the calcium/phospholipid-binding annexin family of proteins, has binding activity toward the bisecting GlcNAc structure. In this study, we reported on a search for potential target glycoproteins for annexin V in a rat hepatoma cell line, M31. Using a glutathione S-transferase (GST)-annexin V immobilized sepharose 4B affinity column to trap interacting proteins produced by the GnT-III-transfected M31 cells, we isolated a 47 kDa protein. It was identified as Hsp47 by an N-terminal sequence analysis. Immunoprecipitation experiments showed that annexin V interacted with Hsp47. The association of annexin V and Hsp47 was abolished by treatment with N-glycosidase F or preincubation with sugar chains containing bisecting GlcNAc, suggesting that the bisecting GlcNAc plays an important role in the interaction. An oligosaccharide analysis of Hsp47 purified from GnT-III-transfected M31 cells was shown to have the bisecting GlcNAc structure, as detected by erythroagglutinating phytohemagglutinin (E4-PHA) and matrix assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry (MS) analysis. Surface plasmon resonance analysis showed that annexin V was bound to Hsp47, bearing a bisecting GlcNAc with a Kd of 5.5 microM, whereas no significant binding was observed in the case of Hsp47 without a bisecting GlcNAc. In addition, immunofluorescence microscopy revealed the colocalization of annexin V, Hsp47, and a bisecting GlcNAc sugar chain around the Golgi apparatus. Collectively, these results suggest that the binding of annexin V to Hsp47 is mediated by a bisecting GlcNAc oligosaccharide structure and that Hsp47 is an intracellular ligand glycoprotein for annexin V.

Localisation of annexins in the retina of the rainbow trout-light and electron microscopical investigations

We present a first description of annexin immunoreactivity within the teleost retina. Antibodies against annexins V and VI were used in light and electron microscopic sections of light- and dark-adapted retinae. Strong immunoreactivity could be found in retinal layers with high synaptic input, such as the outer and inner plexiform layers and dendritic regions within the inner plexiform layer, in cells that are involved in negative feedback control such as horizontal and amacrine cells, in the membrane metabolism of photoreceptor outer segments, and in close relation to cytoskeletal components. Our findings suggest that both annexins V and VI are involved in the regulation of transmitter release, particularly of transmitters that are not directly involved in phototransduction. The annexins appear also to be involved with structures that support morphological changes in light and dark adaptation.

Anti-annexin V antibodies: are they prothrombotic?

Annexin V inhibits prothrombin activation and is able to prevent thrombus formation under normal venous and arterial blood flow conditions. Antibodies to annexin V have been identified in association with several pathological conditions, including systemic lupus erythematosus (SLE) with or without anti-phospholipid syndrome, recurrent spontaneous abortions and systemic sclerosis (SSc). These antibodies are suspected to exert a detrimental role and interfere with annexin V function. Thus, they have been associated with the occurrence of foetal loss and venous and/or arterial thrombosis in SLE patients, as well as digital ischemia in SSc patients. However, their true pathogenic role remains to be proven.

Identification of a 35 kDa protein in rat spinal ganglia and sensory fibers

A 35 kDa protein was purified from rat spinal ganglia and sensory fibers. Combined direct trypsin digest and liquid chromatography ion trap mass spectrometry analysis, the 35 kDa protein was identified as annexin V. We then studied the distribution of serum antibodies to annexin V in patients with peripheral neuropathy. We found serum positive antibodies to annexin V only in some patients with immune-mediated neuropathy. This indicated that humoral immune responses to annexin V might play a role in the pathogenesis of autoimmune sensory neuropathy or sensory neuronopathy.

Annexin expression in inflammatory myopathies

The pathogenesis of the inflammatory myopathies is still unclear, making their treatment largely empirical. Improved understanding of the molecular mechanisms of inflammatory muscle injury may, however, lead to the development of more specific immunotherapies. To elucidate a possible pathogenic contribution of calcium-binding proteins such as the annexins, we immunohistochemically investigated muscle biopsy specimens from patients with dermatomyositis (10 cases), polymyositis (9 cases), and inclusion-body myositis (4 cases), compared to control cases comprising sarcoid myopathy (3 cases), Duchenne muscular dystrophy (DMD; 4 cases), and normal muscle (3 cases). We found expression of annexins A1, A2, A4, and A6 in the vascular endothelium of all cases. Myofibers expressed annexins A5, A6, and A7 diffusely and weakly in the cytosol, whereas annexins A5 and A7 were also particularly localized to the sarcolemma. In the inflammatory myopathies, in areas of myonecrosis in DMD, and in granulomatous lesions of sarcoid myopathy, reactivity of annexins A1, A2, A4, A5, and A6 was observed in macrophages and T-lymphocytes. Whereas the latter annexins appear to be nonspecific indicators of activation, annexin A1 upregulation may represent endogenous anti-inflammatory mechanisms that merit further investigation.

Upregulation of annexins I, II, and V after traumatic spinal cord injury in adult rats

The posttraumatic inflammatory reaction contributes to progressive tissue damage after spinal cord injury (SCI). Annexins, a family of structurally related calcium- and phospholipid-binding proteins, have potent anti-inflammatory effects by inhibiting the activity of phospholipase A(2) (PLA(2)), a key enzyme responsible for inflammation and cytotoxicity. We investigated spatiotemporal expression of annexins I, II, and V after a contusive SCI using the New York University impact device (a 10-g rod, height 12.5 mm) in adult rats. Western blot analysis revealed that annexin I expression increased at 3 days after injury, peaked at 7 days (1.75-fold above the baseline level; P < 0.01), started to decline at 14 days, and returned to the baseline level at and beyond 28 days post-injury. The expression of annexin II started to increase at 3 days, reached its maximal level at 14 days (2.73-fold; P < 0.01), remained at a high level up to 28 days, and then declined to the basal level by 56 days after injury. Annexin V expression started at 3 days, reached its maximal level at 7 days (1.61-fold; P < 0.05) and remained at this level until 56 days after injury. RT-PCR results confirmed expression of all three annexins at the mRNA level after SCI. Immunohistochemistry and immunofluorescence double-labeling analyses revealed that increased annexins I, II, and V were localized in neurons and glial cells. The present study thus revealed increased expression of the three annexin isoforms after moderate contusive SCI. The precise role of annexins in posttraumatic inflammation and neuroprotection after SCI remains to be determined.

Prolactin inhibits annexin 5 expression and apoptosis in the corpus luteum of pseudopregnant rats: involvement of local gonadotropin-releasing hormone

We investigated a specific relationship between the expression of annexin 5 and prolactin in the corpus luteum of pseudopregnant rats, with particular interest in GnRH and apoptosis of luteal cells. The expression of ovarian annexin 5 mRNA was significantly decreased at mid-pseudopregnancy and recovered at the end, whereas it remained low on the corresponding day of pregnancy. The dopamine agonist CB-154, administered at mid-pseudopregnancy (d 5), increased ovarian annexin 5 mRNA, whereas prolactin, given daily for 3 d to cycling rats, decreased it. An immunocytochemical study also showed that annexin 5 increased in the corpus luteum on d 6 and 7 of pseudopregnancy after treatment with CB-154 on d 5. The distribution of annexin 5-positive cells was not uniform in the corpus luteum and matched that of terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling (TUNEL)-positive cells. Because GnRH stimulates annexin 5 mRNA expression in the gonadotropes, involvement of the GnRH receptor was examined. Local administration of a GnRH antagonist, Cetrorelix, to hemilateral ovarian bursa of pseudopregnant rats simultaneously receiving CB-154 abrogated both the expression of annexin 5 and the TUNEL reaction. The present results clearly demonstrate that prolactin decreases annexin 5 mRNA in the luteal cells during pseudopregnancy. Prolactin is suggested to suppress the local action of GnRH, which stimulates annexin 5 synthesis and apoptosis of functional luteal cells during pseudopregnancy.

Annexin V, annexin VI, S100A1 and S100B in developing and adult avian skeletal muscles

Annexins and S100 proteins constitute two multigenic families of Ca2+-modulated proteins that have been implicated in the regulation of both intracellular and extracellular activities. Some annexins can interact with certain S100 protein dimers thereby forming heterotetramers in which an S100 dimer crosslinks two copies of the partner annexin. It is suggested that S100 protein binding to an annexin might serve the function of regulating annexin function and annexin binding to an S100 protein might regulate S100 function. In the present study, annexin V, annexin VI (or ANXA5 and ANXA6, respectively, according to a novel nomenclature), S100A1 and S100B were analyzed for their subcellular localization in developing and adult avian skeletal muscles by confocal laser scanning microscopy, immunogold cytochemistry, and western blotting, and for their ability to form annexin-S100 heterocomplex in vivo by immunoprecipitation. These four proteins displayed distinct expression patterns, ANXA5 being the first to be expressed in myotubes (i.e. at embryonic day 8), followed by ANXA6 (at embryonic day 12) and S100A1 and S100B (between embryonic day 12 and embryonic day 15). The two annexins and the two S100 proteins were found associated to different extents with the sarcolemma, membranes of the sarcoplasmic reticulum, and putative transverse tubules where they appeared to be co-localized from embryonic day 18 onwards. No one of these proteins was found associated with the contractile apparatus of the sarcomeres. Immunoprecipitation studies indicated that ANXA6/S100A1 and ANXA6/S100B complexes formed in vivo. Whereas, ANXA5 was not recovered in S100A1 or S100B immunoprecipitates. From our data we suggest that: (i) ANXA5 and ANXA6, and S100A1 and S100B can be used as markers of skeletal muscle development; (ii) ANXA6 and S100A1 and S100B appear strategically located close to or on skeletal muscle membrane organelles that are critically involved in the regulation of Ca2+ fluxes, thus supporting previous in vitro observations implicating S100A1 and ANXA6 in the stimulation of Ca2+-induced Ca2+ release; and (iii) ANXA6/S100A1 and ANXA6/S100B complexes can form in vivo thereby regulating each other activities and/or acting in concert to regulate membrane-associated activities.

EGR2 mutations in inherited neuropathies dominant-negatively inhibit myelin gene expression

The identification of EGR2 mutations in patients with neuropathies and the phenotype Egr2/Krox20(-/-) have demonstrated that the Egr2 transcription factor is critical for peripheral nerve myelination. However, the mechanism by which these mutations cause disease remains unclear, as most patients present with disease in the heterozygous state, whereas Egr2(+/-) mice are phenotypically normal. To understand the effect of aberrant Egr2 activity on Schwann cell gene expression, we performed microarray expression profiling to identify genes regulated by Egr2 in Schwann cells. These include genes encoding myelin proteins and enzymes required for synthesis of normal myelin lipids. Using these newly identified targets, we have shown that neuropathy-associated EGR2 mutants dominant-negatively inhibit wild-type Egr2-mediated expression of essential myelin genes to levels sufficiently low to result in the abnormal myelination observed in these patients.

Localization of annexin V in rat normal kidney and experimental glomerulonephritis

The localization of annexin V, a calcium binding protein, was immunochemically and immunohistologically studied in experimental rat glomerulonephritis using annexin V polyclonal antibody. Plasma and urinary annexin V levels were measured by a sandwich enzyme-linked immunosorbent assay (ELISA). Urinary annexin V level, which was correlated with urinary L-lactate dehydrogenase activity, N-acetyl-beta-D-glucosaminidase activity and protein level, increased time-dependently after the injection of nephritogenic antigen (bovine glomerular basement membrane), progressively increasing to attain a peak level at 4 weeks of 51.5 +/- 11.3 ng/h. However, plasma annexin V level showed no increase during the study period. Normal kidneys showed strong staining for annexin V in distal tubules, being particularly strong in tubules of the inner stripe of the outer medulla, but could not be detected in proximal tubules. Annexin V was seen in visceral epithelial cells. Bowman's capsule of the glomerulus, the vascular endothelium of arterioles and interlobular arteries, and vascular smooth muscle. In nephritis, the lumen of distal tubules and the luminal cell membrane were deeply stained, with leakage of annexin V being observed from tubular cells. In the present study, renal annexin V was markedly excreted into urine, and its urinary level reflected the severity of damage of renal tissue and the progression of nephritis. These changes of annexin V in the distal tubule and visceral epithelial cells may be of significance in cell injury of the kidney.

S100A1 and S100B interactions with annexins

Members of the annexin protein family interact with members of the S100 protein family thereby forming heterotetramers in which an S100 homodimer crossbridges two copies of the pertinent annexin. Previous work has shown that S100A1 and S100B bind annexin VI in a Ca(2+)-dependent manner and that annexin VI, but not annexin V, blocks the inhibitory effect of S100A1 and S100B on intermediate filament assembly. We show here that both halves of annexin VI (i.e., the N-terminal half or annexin VI-a and the C-terminal half or annexin VI-b) bind individual S100s on unique sites and that annexin VI-b, but not annexin VI-a, blocks the ability of S100A1 and S100B to inhibit intermediate filament assembly. We also show that the C-terminal extension of S100A1 (and, by analogy, S100B), that was previously demonstrated to be critical for S100A1 and S100B binding to several target proteins including intermediate filament subunits, is not part of the S100 surface implicated in the recognition of annexin VI, annexin VI-a, or annexin VI-b. Evaluation of functional properties with a liposome stability and a calcium influx assay reveals the ability of both S100 proteins to permeabilize the membrane bilayer in a similar fashion like annexins. When tested in combinations with different annexin proteins both S100 proteins mostly lead to a decrease in the calcium influx activity although not all annexin/S100 combinations behave in the same manner. Latter observation supports the hypothesis that the S100-annexin interactions differ mechanistically depending on the particular protein partners.

Annexin VI binds S100A1 and S100B and blocks the ability of S100A1 and S100B to inhibit desmin and GFAP assemblies into intermediate filaments

Annexin VI, a member of a family of Ca(2+)-dependent phospholipid- and membrane-binding proteins, interacts with the Ca(2+)-regulated EF-hand proteins, S100A1 and S100B, and blocks the ability of these two proteins to inhibit the assembly of desmin and glial fibrillary acidic protein (GFAP) into intermediate filaments in a Ca(2+)- and dose-dependent manner. S100A1 and S100B each possess one annexin VI binding site, characterized by an affinity for annexin VI in the submicromolar range. Binding of annexin VI to either S100 protein occurs at a site that appears to differ in some parts from that recognizing desmin and GFAP. As S100A1 and S100B exist in solution as homodimers in which the two monomers are related by a 2-fold symmetry axis, each of the above S100 homodimers likely crosslinks two annexin VI molecules, a situation that appears typical of all the annexin-S100 protein complexes described thus far. However, whereas in the cases of other annexin-S100 complexes the C-terminal extension of the S100 molecule appears indispensable for annexin binding, the annexin VI binding site cannot be restricted to the S100A1 and S100B C-terminal extension. We speculate that the annexin VI site on S100A1/B may only partially overlap to the desmin/GFAP site. In contrast, no effects of annexin V on the ability of S100A1 or S100B to affect the desmin and GFAP assemblies could be documented, although binding of annexin V to S100A1 and S100B could be detected at relatively high Ca2+ concentrations. The present data suggest that annexin VI might regulate S100A1 and S100B activities and vice versa.

Ovariectomy enhances the expression and nuclear translocation of annexin 5 in rat anterior pituitary gonadotrophs

An observation of abundant annexin 5, a novel calcium and phospholipid binding protein, in gonadotrophs of the anterior pituitary gland of ovariectomized rats (Kawaminami et al., 1997 (in press)) led us to investigate the effect of ovariectomy on the subcellular distribution and synthesis of annexin 5. Gonadotrophs, which were identified by immunocytochemistry with anti LHbeta antiserum, dramatically increased their size three weeks after ovariectomy. These 'castration cells' were shown to contain abundant annexin 5 associated with the plasma membrane, nuclear envelope and nucleoplasm. True localization within the nucleus was shown by optical sectioning with a confocal microscope. Northern blot analysis showed that annexin 5 mRNA in the anterior pituitary gland was increased 24 h after ovariectomy. It further increased in parallel with LHbeta mRNA at three weeks and it decreased in parallel with LHbeta mRNA when estradiol (250 microg/animal per day) was given for 3 days. These results show that the expression of pituitary annexin 5 is controlled by ovarian estradiol and imply that annexin 5 plays a physiological role in the nucleus of activated gonadotrophs.

Localization of annexin V in the adult and neonatal heart

Annexins are a major family of intracellular Ca2+-binding proteins which have been implicated in a variety of cellular functions. Several conflicting reports have been published on the location of annexin V in the heart. In this paper we have used confocal microscopy to demonstrate that annexin V is associated with the sarcolemma and intercalated discs of cardiac myocytes in sections of adult porcine and rat heart. In addition, we have used confocal microscopy of isolated rat myocytes to show that this association is stable even after cells were treated with the intracellular calcium chelator BAPTA-AM, to reduce cytosolic calcium levels to very low levels. This demonstrates that annexin V associates tightly with the sarcolemma and suggests that components in addition to phospholipid are involved in binding annexin V to the membrane. Furthermore, we show that, in sections of the neonatal rat left ventricle, annexin V has a different subcellular location than that observed in the terminally differentiated adult myocyte. In these differentiating neonatal cells, annexin V is also located in the nucleoplasm and at the periphery of the nucleus. These results demonstrate that the subcellular location of annexin V is differentially regulated and suggest that annexin V regulates calcium-dependent processes at both the sarcolemma and the nucleus.

Preferential localization of annexin V to the axon terminal

To examine the participation of annexin V, a member of Ca(2+)-dependent phospholipid-binding proteins, in the process of synaptic vesicle exocytosis, rat central nervous tissue was analysed using biochemical and morphological techniques. By both fluorescence and confocal laser scanning microscopy, immunoreactivity for annexin V was predominantly localized around neuronal somata and dendrites, and the reactivity was mostly co-labeled with that for synaptophysin. The annexin V immunoreactivity was also detectable, but less intensely, in neuronal perikarya, glial cells and endothelial cells. Both immunoblot and immunoelectron microscopic analyses with intact tissues, synaptosomes and purified synaptic vesicles showed that annexin V was expressed in neurons, preferentially concentrated in axon terminals and associated with synaptic vesicles. Purified synaptic vesicles were relatively homogeneously distributed in the medium where Ca2+ was removed and thus the amount of annexin V was reduced drastically. The vesicles tended to be clustered in the fraction where endogenous annexin V is maintained, and the clusters were more conspicuous when purified human annexin V was added. Synaptic vesicles forming the clusters were not directly fused with each other but separated by a 10-15 nm gap that corresponded well with the size of single annexin V molecules. In axon terminals, globular structures 12-13 nm in diameter, similar in dimension to annexin V molecules, were distinctly found to be attached to the cytoplasmic surface of both vesicle membranes when the two vesicles were close to each other. These results suggest that annexin V belongs to the group of synaptic vesicle-associated proteins. Although its localization and significance in non-neuronal cells were not analysed here, at least in the axon terminal annexin V may participate in the cluster formation of synaptic vesicles by linking with the cytoplasmic surface of the vesicles in a Ca(2+)-dependent manner.

Measurement of plasma annexin V by ELISA in the early detection of acute myocardial infarction

Annexin V is a calcium binding protein which is widely present in various cells and tissues. Using annexin V which we isolated and purified from human cardiac muscle, we prepared an anti-human cardiac annexin V monoclonal antibody. Identification of annexin V was made by means of partial amino acid sequences. An enzyme-linked immunosorbent assay (ELISA) was developed using this monoclonal antibody and anti-canine cardiac annexin V polyclonal antibody. With this ELISA, plasma annexin V concentration was measured in 196 normal healthy individuals, 23 acute myocardial infarction (AMI) patients who were hospitalized within 6 h after the onset of chest pain, and 130 patients with other diseases, including lung, liver and kidney disease. The plasma annexin V concentration in normal healthy individuals was 1.7 +/- 0.6 ng/ml (mean +/- S.D.), while that in AMI patients was elevated to 13.2 +/- 6.8 ng/ml (P < 0.0001) at the time of initial blood drawing, 3.2 +/- 1.5 h after onset of pain, and these values were higher than normal in 21 out of 23 cases (91.3%) of AMI. In all cases excepting 3, annexin V concentration immediately decreased after the onset of pain. The annexin V concentration in patients with old myocardial infarction, chest pain syndrome, valvular heart disease, lung disease and kidney disease was 1.8 +/- 0.8, 2.0 +/- 0.7, 1.7 +/- 1.1, 2.3 +/- 1.4 and 2.1 +/- 1.2 ng/ml, respectively, being within normal limits. The values in liver disease patients and trauma patients were 3.7 +/- 2.7 (P < 0.05) and 3.3 +/- 2.4 (P < 0.05) ng/ml, respectively, being slightly higher than that in normal healthy individuals.

Differential expression of annexins I-VI in the rat dorsal root ganglia and spinal cord

The annexins are a family of Ca(2+)-dependent phospholipid-binding proteins. In the present study, the spatial expression patterns of annexins I-VI were evaluated in the rat dorsal root ganglia (DRG) and spinal cord (SC) by using indirect immunofluorescence. Annexin I is expressed in small sensory neurons of the DRG, by most neurons of the SC, and by ependymal cells lining the central canal. Annexin II is expressed by most sensory neurons of the DRG but is primarily expressed in the SC by glial cells. Annexin III is expressed by most sensory neurons, regardless of size, by endothelial cells lining the blood vessels, and by the perineurium. In the SC, annexin III is primarily expressed by astrocytes. In the DRG and the SC, annexin IV is primarily expressed by glial cells and at lower levels by neurons. In the DRG, annexin V is expressed in relatively high concentrations in small sensory neurons in contrast to the SC, where it is expressed mainly by ependymal cells and by small-diameter axons located in the superficial laminae of the dorsal horn areas. Annexin VI is differentially expressed by sensory neurons of the DRG, being more concentrated in small neurons. In the SC, annexin VI has the most striking distribution. It is concentrated subjacent to the plasma membrane of motor neurons and their processes. The differential localization pattern of annexins in cells of the SC and DRG could reflect their individual biological roles in Ca(2+)-signal transduction within the central nervous system.

Glial calcium

This review summarizes current knowledge relating intracellular calcium and glial function. During steady state, glia maintain a low cytosolic calcium level by pumping calcium into intracellular stores and by extruding calcium across the plasma membrane. Glial Ca2+ increases in response to a variety of physiological stimuli. Some stimuli open membrane calcium channels, others release calcium from intracellular stores, and some do both. The temporal and spatial complexity of glial cytosolic calcium changes suggest that these responses may form the basis of an intracellular or intercellular signaling system. Cytosolic calcium rises effect changes in glial structure and function through protein kinases, phospholipases, and direct interaction with lipid and protein constituents. Ultimately, calcium signaling influence glial gene expression, development, metabolism, and regulation of the extracellular milieu. Disturbances in glial calcium homeostasis may have a role in certain pathological conditions. The discovery of complex calcium-based glial signaling systems, capable of sensing and influencing neural activity, suggest a more integrated neuro-glial model of information processing in the central nervous system.

Immunocytochemical analyses of annexin V (CaBP33) in a human-derived glioma cell line. Expression of annexin V depends on cellular growth state

The subcellular distribution of annexin V, a calcium-dependent phospholipid- and membrane-binding protein, in a human-derived cell line, GL15, was investigated by immunocytochemistry at light and electron microscope levels. Annexin V was found diffusely in the cytoplasm and associated with plasma membranes, membranes delimiting cytoplasmic vacuoles, membranes of the endoplasmic reticulum, and filamentous structures the identity of which remains to be established. By immunocytochemistry at the light microscope level and immunochemistry, the expression of annexin V in these cells was found to depend on cellular growth stage, being maximal soon after plating and progressively declining thereafter. However, re-expression of annexin V was observed whenever cell proliferation slowed down or arrested. These findings suggest that annexin V in glioma cells is mostly expressed in connection with cell differentiation. Also, the present ultrastructural data suggest that plasma membranes, membranes of the endoplasmic reticulum and the cytoskeleton are prominent sites of action of annexin V in vivo, thus lending support to the possibility that this protein might have a role in the regulation of cytoskeleton elements and/or of the structural organization of membranes.

Structure of chicken annexin V at 2.25-A resolution

The crystal structure of chicken annexin V has been solved by molecular replacement and refined at 2.25 A. The final R factor is 19.7% with good geometry. The chicken annexin V structure is very similar to the human annexin V structure, with four similar domains each containing five helices. The structure includes three calcium ions in domains I, II, and IV, each bound by the characteristic K-G-X-G-T-(38 residues)-D/E motif. In view of the structural similarity between human and chicken annexin V, we suggest that they have a common vital function which developed early in evolutionary history.