Up-regulation of lipocortin-1 and its mRNA in reactive astrocytes in kainate-lesioned rat cerebellum

Annexin A1 in the brain--undiscovered roles?

Annexin A1 (ANXA1) is an endogenous protein known to have potent anti-inflammatory properties in the peripheral system. It has also been detected in the brain, but its function there is still ambiguous. In this review, we have, for the first time, collated the evidence currently available on the function of ANXA1 in the brain and have proposed several possible mechanisms by which it exerts a neuroprotective or anti-neuroinflammatory function. We suggest that ANXA1, its small peptide mimetics and its receptors might be exciting new therapeutic targets in the management of a wide range of neuroinflammatory diseases, including stroke and neurodegenerative conditions.

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.

Mouse glioma gene expression profiling identifies novel human glioma-associated genes

Based on previous studies demonstrating increased RAS activity in human astrocytomas, we developed a transgenic mouse model (B8) that targets an activated RAS molecule to astrocytes. Within 3 to 4 months after birth, these mice develop high-grade astrocytomas that are histologically identical to human astrocytomas. To characterize genetic events associated with B8 mouse astrocytoma formation, we employed comparative gene expression profiling of wild-type cultured mouse astrocytes, non-neoplastic B8 astrocytes, B8 astrocytoma cultures, and two other astrocytoma cultures from independently derived RAS transgenic mouse lines. We identified several classes of gene expression changes, including those associated with the non-neoplastic state in the B8 transgenic mouse, those associated with astrocytoma formation, and those specifically associated with only one of the three independently derived transgenic mouse astrocytomas. Differential expression of several unique genes was confirmed at the protein level in both the RAS transgenic mouse astrocytomas and two human glioblastoma multiforme cell lines. Furthermore, reexpression of one of these downregulated astrocytoma-associated proteins, GAP43, resulted in C6 glioma cell growth suppression. The use of this transgenic mouse model to identify novel genetic changes that might underlie the pathogenesis of human high-grade astrocytomas provides a unique opportunity to discover future targets for brain tumor therapy.

Inflammatory regulators in Parkinson's disease: iNOS, lipocortin-1, and cyclooxygenases-1 and -2

Degeneration of dopaminergic neurons and focal gliosis are pathological hallmarks of Parkinson's disease and although the brain is described as immune-privileged focal immune reactions surround failing nigral neurons. We examined the cellular distribution of pro- and anti-inflammatory molecules in human parkinsonian and neurologically normal substantia nigra and caudate-putamen postmortem. An up-regulation of nitric oxide synthase- and cyclo-oxygenase-1- and -2-containing amoeboid microglia was found in parkinsonian but not control nigra. Astroglia contained low levels of these molecules in both groups. Lipocortin-1-immunoreactive amoeboid microglia were present within the astrocytic envelope of neurons adjacent to or within glial scars in parkinsonian nigra only. Lipocortin-1 is known to have neuroprotective and anti-inflammatory properties. Up-regulation of nitric oxide synthase is generally associated with neurodestruction whereas prostaglandin synthesis may be either neurodestructive or protective. The balance of these molecules is likely to be decisive in determining neuronal survival or demise.

Acutely isolated astrocytes as models to probe astrocyte functions

Neuroscientists have become increasingly aware and accepting of the concept that astrocytes likely have many important functions in the CNS. One limitation in establishing these functions is the usual problem of what constitutes suitable experimental approaches. A major experimental step for functional studies of astrocytes has been the widespread use of primary astrocyte cultures, an approach that Leif Hertz pioneered. However, it is now becoming clear that, building on this work, an experimental paradigm shift is now needed. Namely, to increasingly study preparations corresponding to in situ conditions, such as slices. An alternative experimental system where the cells have some of the technical advantages of primary astrocyte cultures is freshly isolated astrocytes. Recent experiments from our laboratory have shown metabotropic glutamate receptor expression by such cells. Examples are given of how functional receptor studies and channel activity measured by patch clamp electrophysiology can be combined with single cell RT-PCR to define further the receptor or channel type are described to illustrate the uses of such preparations.

De novo expression of lipocortin-1 in reactive microglia and astrocytes in kainic acid lesioned rat cerebellum

An understanding of the role of reactive glia in the neurodegenerative/regenerative process requires a knowledge of the molecules synthesised by these cells following trauma. We investigated the cellular localisation of lipocortin-1 (LC-1), a putative neuroprotective agent, in cryostat sections of normal and kainic acid lesioned rat cerebellum. In the normal cerebellum lipocortin-1 immunoreactivity was detected in Purkinje cell bodies and molecular layer interneurons. Following kainic acid (1 microg) induced lesions, it was rapidly upregulated in activated microglia, from which it appeared to be secreted. At later time points it was detected in activated astrocytes. LC-1 protein levels were quantified by a sensitive and specific ELISA. Compared to control cerebellum, LC-1 levels were dramatically elevated following lesion, peaking at 3 days: 760% of basal (unlesioned) levels. In situ hybridisation studies revealed a marked upregulation of LC-1 mRNA at 1 and 3 days following the lesion, indicating the transient de novo synthesis of this protein, consistent with a localisation to microglia. In vitro studies, on cultured astrocytes and microglia, demonstrated high levels of intracellular LC-1 in both cell types. LC-1 was detected in microglial but not astrocytic, conditioned media, confirming the in vivo observations that activated microglia may secrete LC-1. Our data show that at early time points following excitotoxic lesion to the cerebellum, it is activated microglia that synthesise and possibly secrete this protein, suggesting an important role of this cell type in immunosuppression and neuroprotection following damage to the central nervous system.

Pyrimidine nucleotide-stimulated thromboxane A2 release from cultured glia

1. Uridine triphosphate (UTP), uridine diphosphate (UDP), cytidine triphosphate (CTP), and deoxythymidine triphosphate (TTP) caused concentration-dependent increases in the release of thromboxane A2 (TXA2) from cultured glia prepared from the newborn rat cerebral cortex. Although each of the pyrimidine nucleotides displayed similar potencies, CTP and TTP were considerably less effective than either UTP or UDP. The purine nucleotide ATP was equally as potent as the pyrimidine nucleotides but was marginally less effective than either UTP or UDP. 2. The ability of UTP, UDP, TTP, and CTP to promote TXA2 release from cultured glia was inhibited in a concentration-dependent manner by suramin and was markedly reduced when incubations were performed either in Ca(2+)-free medium or on cultures which had been maintained in serum-free growth medium for 4 days prior to experimentation. 3. Challenges with UTP and UDP in combination were found to elicit a response which was no different from the effects of these nucleotides alone; in addition, their effects were reversed by the phospholipase A2 inhibitor ONO-RS-082. A slight reduction in UTP- and UDP-stimulated TXA2 release was observed in cultures grown in the presence of leucine methyl ester, a treatment reported to limit microglial survival. 4. These results suggest that glia are targets for extracellular pyrimidine nucleotides and that their ability to release eicosanoids from these cells may be important in the brain's response to damage.

Effect of annexin-1 on experimental autoimmune encephalomyelitis (EAE) in the rat

Annexin-1, a calcium-dependent phospholipid binding protein, has been shown to act as an endogenous central neuroprotectant, notably against cerebral ischaemic damage. In the present study we extend these findings to an animal model of multiple sclerosis, EAE, and report that endogenous annexin-1 is expressed in ED1+ macrophages and resident astrocytes localized within the lesions in the central nervous system (CNS). Intracerebroventricular (i.c.v.) administration of an NH2-terminal fragment spanning amino acids 1-188 of annexin-1 after the onset of the clinical symptoms significantly reduced both the neurological severity as well as weight loss of mild EAE. Immunoneutralization of endogenous brain annexin-1 failed to exacerbate the clinical features of EAE. Thus, although the role of endogenous annexin-1 in the pathogenesis of EAE remains to be determined, our findings suggest that annexin-1 may be of therapeutic benefit to the treatment of multiple sclerosis.

Reactive astrocytes: cellular and molecular cues to biological function

For several decades, the reactive gliosis that occurs after an injury to the CNS has been considered one of the major impediments to axonal regeneration. Nevertheless, recent studies have suggested that in certain conditions, reactive astrocytes may provide a permissive substratum to support axonal regrowth. The important criteria, allowing for the distinction between permissive and non-permissive gliosis, are the ultrastructural 3D organization of the scar and more importantly the recognition molecules expressed by reactive astrocytes. Reactive astrocytes express surface molecules and produce various neurotrophic factors and cytokines. The latter in turn might modulate the production of recognition molecules by reactive astrocytes, allowing them to support post-lesional axonal regrowth. Although numerous recent articles have focused on cytokines and cell adhesion molecules, scant attention has been paid to reactive astrocytes. Reactive astrocytes should be considered a key element, like neurons, of a dynamic environment, thus forming with neurons a functional unit involved in homeostasis, plasticity and neurotransmission. Attempts are in progress to identify molecular markers for reactive astrocytes.

Gliogenesis in postnatal rat optic nerve: LC1 + microglia and S100-beta + astrocytes

Lipocortin 1 (LC1) and S100-beta, two Ca(2+)-binding proteins that serve as specific markers for microglia and astrocytes, respectively, have been used to study postnatal gliogenesis in the rat optic nerve. Computerized image analysis was used to quantify and map the stained and unstained glia in transverse sections (10 microns thick) taken 1-2 mm from the chiasm in optic nerves from rat pups at postnatal day 0 (P0), P7, P14, P21, P28, P38 and adults. The number of astrocytes was remarkably constant (100 per section) at all ages. Because the area of the nerve increases 10-fold from P0 to adult, the population density of astrocytes begins al > 5000 mm-2 and drops to 400 mm-2 in the mature nerve; however, because the nerve length increases two-fold, the number of astrocytes doubles over the same period. In contrast, the number of LC1 + cells per section initially is sparse (4 at P0), increases rapidly up to 36 at P21 and levels off at 49 in adults. The microglia population density is relatively stable throughout development (200-300 mm-2) except during the peak of oligodendroblast apoptosis (P21) when it rises to 450 mm-2. Neonatally, LC1 immunoreactivity predominantly labels spherical-ameboid cells; but by P28 they are replaced by mature ramified microglia. The number of unstained cells (putative oligodendrocytes) per section increases from 11 at P0 to a peak of 308 at P21, and declines slightly to 269 in adults. While generally confirming concepts of astrocyte and oligodendrocyte ontogeny from the literature, the present report adds considerable detail regarding microglia, which often have been ignored. Microglia identified by LC1 immunoreactivity comprise 12% of the glia in adult optic nerve near the chiasm.

Immunohistochemical localization of lipocortin 1 in rat brain is sensitive to pH, freezing, and dehydration

Lipocortin 1 (LC1, annexin 1) has received considerable attention as a substrate for protein kinases, as a Ca++- and phosphatidylserine-binding protein, and as a mediator of glucocorticoid anti-inflammatory effects. However, there has been confusion over localization of LC1 immunoreactivity (LC1-ir), which reportedly localizes to neurons and/or to astrocytes or microglia in rat brain. To test whether these contradictory data arise from unusual properties of the antigen, we developed a novel brain slice model to determine fixation and staining variables. The specificity of anti-LC1 sera was ensured by pre-absorption and affinity purification with immobilized recombinant LC1. Specific LC1-ir was detected in ramified microglia of brains perfused with acidified aldehydes and embedded in paraffin. However, commonly used immunohistochemical procedures have unexpected profound effects. LC1-ir was eliminated by fixation with neutral/alkaline aldehydes, by freezing before strong acid-aldehyde fixation, or by staining without partial de/rehydration before the primary serum. The sensitivity of LC1 epitopes to proton and water activities may reflect molecular properties important to LC1's roles in vivo. True LC1-ir was not detected in normal neurons or astrocytes.

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.

Annexin 1 is overexpressed and specifically secreted during experimentally induced colitis in rats

Annexin 1 is a protein induced by glucocorticoids endowed with extracellular anti-inflammatory properties. In this study, the local expression and secretion of annexins 1-6, in rat proximal colon, were studied at different times after intracolonic administration of 30 mg trinitrobenzenesulfonic acid in 50% ethanol. Secretion was identified by incubating colonic tissues in a culture medium. The expression of annexins was detected by immunoblotting in tissue homogenates and incubation media. Inflammatory stages were evaluated by measuring myeloperoxidase activity. Annexin 1 expression in colons increased after trinitrobenzenesulfonic acid treatment and was maximal between days 1 to 9, during the cellular stage of the inflammation that corresponded to maximal myeloperoxidase activity. From 12 h to 9 days after trinitrobenzenesulfonic acid/ethanol treatment, annexin 1 was specifically secreted. Annexin 3 was also overexpressed during the cellular stage, but the expression of annexins 2, 4, 5, and 6 was unchanged; none of these annexins were secreted. Annexin 1 was shown to be physiologically secreted because its release was specific, abundant, and not correlated with cellular lysis. Annexin 1 may be considered as a putative candidate in the control of the gut inflammatory processes.