Possible functions of a new genetic marker in central nervous system: the sulfated glycoprotein-2 (SGP-2)

Quantitative serum proteome analysis using tandem mass tags in dogs with epilepsy

This study included four groups of dogs (group A: healthy controls, group B: idiopathic epilepsy receiving antiepileptic medication (AEM), group C: idiopathic epilepsy without AEM, group D: structural epilepsy). Comparative quantitative proteomic analysis of serum samples among the groups was the main target of the study. Samples were analyzed by a quantitative Tandem-Mass-Tags approach on the Q-Exactive-Plus Hybrid Quadrupole-Orbitrap mass-spectrometer. Identification and relative quantification were performed in Proteome Discoverer. Data were analyzed using R. Gene ontology terms were analyzed based on Canis lupus familiaris database. Data are available via ProteomeXchange with identifier PXD041129. Eighty-one proteins with different relative adundance were identified in the four groups and 25 were master proteins (p < 0.05). Clusterin (CLU), and apolipoprotein A1 (APOA1) had higher abundance in the three groups of dogs (groups B, C, D) compared to controls. Amine oxidase (AOC3) was higher in abundance in group B compared to groups C and D, and lower in group A. Adiponectin (ADIPOQ) had higher abundance in groups C compared to group A. ADIPOQ and fibronectin (FN1) had higher abundance in group B compared to group C and D. Peroxidase activity assay was used to quantify HP abundance change, validating and correlating with proteomic analysis (r = 0.8796). SIGNIFICANCE: The proteomic analysis of serum samples from epileptic dogs indicated potential markers of epilepsy (CLU), proteins that may contribute to nerve tissue regeneration (APOA1), and contributing factors to epileptogenesis (AOC3). AEM could alter extracellular matrix proteins (FN1). Illness (epilepsy) severity could influence ADIPOQ abundance.

Protective effect of clusterin on rod photoreceptor in rat model of retinitis pigmentosa

Retinitis Pigmentosa (RP) begins with the death of rod photoreceptors and is slowly followed by a gradual loss of cones and a rearrangement of the remaining retinal neurons. Clusterin is a chaperone protein that protects cells and is involved in various pathophysiological stresses, including retinal degeneration. Using a well-established transgenic rat model of RP (rhodopsin S334ter), we investigated the effects of clusterin on rod photoreceptor survival. To investigate the role of clusterin in S334ter-line3 retinas, Voronoi analysis and immunohistochemistry were used to evaluate the geometry of rod distribution. Additionally, immunoblot analysis, Bax activation, STAT3 and Akt phosphorylation were used to evaluate the pathway involved in rod cell protection. In this study, clusterin (10μg/ml) intravitreal treatment produced robust preservation of rod photoreceptors in S334ter-line3 retina. The mean number of rods in 1mm² was significantly greater in clusterin injected RP retinas (postnatal (P) 30, P45, P60, & P75) than in age-matched saline injected RP retinas (P<0.01). Clusterin activated Akt, STAT3 and significantly reduced Bax activity; in addition to inducing phosphorylated STAT3 in Müller cells, which suggests it may indirectly acts on photoreceptors. Thus, clusterin treatment may interferes with mechanisms leading to rod death by suppressing cell death through activation of Akt and STAT3, followed by Bax suppression. Novel insights into the pathway of how clusterin promotes the rod cell survival suggest this treatment may be a potential therapeutic strategy to slow progression of vision loss in human RP.

Development- and activity-dependent expression of clusterin in the mouse olfactory bulb

Clusterin, a protein involved in many biological processes, is expressed broadly in the central nervous system, but its functions remain largely unknown. As preparations for elucidating some possible functions, we examined the spatiotemporal expression patterns of clusterin in the mouse olfactory bulb at different developmental stages and under different neuronal activity levels. Our results revealed a dynamic expression of the protein during development. Clusterin signal was seemingly diffuse during the early stages of development, shifted to the cell somas later and then predominantly to the axons of projection neurons in the adult stage, with a transition point at approximately postnatal day 18. The effects of olfactory deficits on the clusterin expression level in an anosmic mouse model were neuron-specific: the signals increased remarkably from faint to strong in olfactory sensory neurons, reduced considerably from moderate/strong to faint in the centrifugal projection neurons, decreased moderately from moderate to faint in the local bulbar projection neurons, and remained intense in long-distance bulbar projection neurons. These results showed that clusterin expression is modulated dynamically during development and by sensory activity. These findings deepen our understanding of this broadly expressed protein.

Chapter 2: Clusterin (CLU): From one gene and two transcripts to many proteins

Clusterin (CLU) has kept many researchers engaged for a long time since its first discovery and characterization in the attempt to unravel its biological role in mammals. Although there is a general consensus on the fact that CLU is supposed to play important roles in nearly all fundamental biological phenomena and in many human diseases including cancer, after about 10 years of work CLU has been defined as an "enigmatic" protein. This sense of frustration among the researchers is originated by the fact that, despite considerable scientific production concerning CLU, there is still a lack of basic information about the complex regulation of its expression. The CLU gene is a single 9-exon gene expressed at very different levels in almost all major tissues in mammals. The gene produces at least three protein forms with different subcellular localization and diverse biological functions. The molecular mechanism of production of these protein forms remains unclear. The best known is the glycosylated mature form of CLU (sCLU), secreted with very big quantitative differences at different body sites. Hormones and growth factors are the most important regulators of CLU gene expression. Before 2006, it was believed that a unique transcript of about 1.9 kb was originated by transcription of the CLU gene. Now we know that alternative transcriptional initiation, possibly driven by two distinct promoters, may produce at least two distinct CLU mRNA isoforms differing in their unique first exon, named Isoform 1 and Isoform 2. A third transcript, named Isoform 11036, has been recently found as one of the most probable mRNA variants. Approaches like cloning, expression, and functional characterization of the different CLU protein products have generated a critical mass of information teaching us an important lesson about CLU gene expression regulation. Nevertheless, further studies are necessary to better understand the tissue-specific regulation of CLU expression and to identify the specific signals triggering the expression of different/alternative transcript isoforms and protein forms in different cell types at appropriate time.

Clusterin increases post-ischemic damages in organotypic hippocampal slice cultures

Clusterin or apolipoprotein J is a heterodimeric glycoprotein which is known to be increased during tissue involution in response to hormonal changes or injury and under circumstances leading to apoptosis. Previous studies in wild-type (WT) and clusterin-null (Clu-/-) mice indicated a protective role of clusterin over-expression in astrocytes lasting up to 90 days post-ischemia. However, in in vitro and in vivo models of neonatal hypoxia-ischemia, clusterin exacerbates necrotic cell death. We developed recombinant forms of clusterin and examined their effect on propidium iodide uptake, neuronal and synaptic markers as well as electrophysiological recordings in hippocampal slice cultures from Clu-/- and WT mice subjected to oxygen-glucose deprivation (OGD). WT mice displayed a marked up-regulation of clusterin associated with electrophysiological deficits and dramatic increase of propidium iodide uptake 5 days post-OGD. Immunocytochemical and western blot analyses revealed a substantial decrease of neuronal nuclei and synaptophysin immunoreactivity that predominated in WT mice. These findings contrasted with the relative post-OGD resistance of Clu-/- mice. The addition of biologically active recombinant forms of human clusterin for 24 h post-OGD led to the abolishment of the ischemic tolerance in Clu-/- slices. This deleterious effect of clusterin was reverted by the concomitant administration of the NMDA receptor antagonist, d-2-amino-5-phosphonopentanoate. The present data indicate that in an in vitro model of ischemia characterized by the predominance of NMDA-mediated cell death, clusterin exerts a negative effect on the structural integrity and functionality of hippocampal neurons.

Sustained astrocytic clusterin expression improves remodeling after brain ischemia

Clusterin is a glycoprotein highly expressed in response to tissue injury. Using clusterin-deficient (Clu-/-) mice, we investigated the role of clusterin after permanent middle cerebral artery occlusion (MCAO). In wild-type (WT) mice, clusterin mRNA displayed a sustained increase in the peri-infarct area from 14 to 30 days post-MCAO. Clusterin transcript was still present up to 90 days post-ischemia in astrocytes surrounding the core infarct. Western blot analysis also revealed an increase of clusterin in the ischemic hemisphere of WT mice, which culminates up to 30 days post-MCAO. Concomitantly, a worse structural restoration and higher number of GFAP-reactive astrocytes in the vicinity of the infarct scar were observed in Clu-/- as compared to WT mice. These findings go beyond previous data supporting a neuroprotective role of clusterin in early ischemic events in that they demonstrate that this glycoprotein plays a central role in the remodeling of ischemic damage.

Activation of Microglial Cells and Complement following Traumatic Injury in Rat Entorhinal-Hippocampal Slice Cultures

The complement cascade has been suggested to be involved in development of secondary brain damage following traumatic brain injury (TBI). Previous studies have shown that reactive microglia are involved in activation of the complement cascade following various injuries to the nervous system. Macrophages seem to have a significant role in this process, but it is still unclear whether these cells, as well as the complement components, are derived from reactive microglia or if these biological events only can occur as a result from the influx of plasma and monocytes via a disrupted blood-brain barrier (BBB). The aim of this study was to investigate the response of microglial cells and the complement system in the absence of plasma/blood components following a standardized crush injury in an entorhinal-hippocampal slice culture. There was a clear increase in complement component C1q and C5b-9-IR (Membrane Attack Complex, MAC) in the area near the crush injury. MAC-IR appeared as numerous dots in clusters which co-localized with anti-NeuN labelled neurons in the injury border zone. Complement C1q-IR co-localized with reactive microglia, co-labelled with OX42 antisera. These findings show activation of the complement cascade near the injury zone and in particular, formation of MAC at the surface of neurons in this area. There was a distinct activation of microglial cells (OX42-IR) near the site of injury, as well as an increase in ED-1 expressing macrophages. In the absence of blood and plasma components it is likely that ED-1-labelled cells represent reactive microglia transformed into macrophages. In addition, Neurons (Neun-IR) near the injury were found to co-localize with clusterin-IR indicating upregulation of a defense system to the endogenous complement attack. The present study provides evidence that microglia and complement is activated in the injury border zone of the tissue slice in a similar fashion as in vivo following TBI, despite the absence of plasma/blood products and cells. These findings support the hypothesis that reactive microglia have a key role in complement activation following TBI by local synthesis of complement with a potential impact on development of secondary neuronal insults.

Intracellular clusterin causes juxtanuclear aggregate formation and mitochondrial alteration

Clusterin is a puzzling protein upregulated in many diseased tissues, presented as either a survival or a death protein. The role of clusterin might depend on the final maturation and localization of the protein, which can be secreted or reside inside cells, either after in situ synthesis or uptake of extracellular clusterin. We studied the biological effects of intracellular clusterin and observed that clusterin forms containing the alpha-chain region strongly accumulated in an ubiquitinated form in juxtanuclear aggregates meeting the main criterions of aggresomes and leading to profound alterations of the mitochondrial network. The viability of cells transfected by intracellular forms of clusterin was improved by overexpression of Bcl-2, and caspase inhibition was capable of rescuing cells expressing clusterin, which presented an altered mitochondrial permeability. We propose that, although it might be an inherently pro-survival and anti-apoptotic protein expressed by cells under stress in an attempt to protect themselves, clusterin can become highly cytotoxic when accumulated in the intracellular compartment. This activity might reconcile the opposite purported influences of clusterin on cell survival and explain how clusterin can be causally involved in neurodegeneration.

Complement activation in the human brain after traumatic head injury

The complement cascade has been suggested to be involved in the development of secondary brain injuries following brain contusions, based on animal experiments. The aim of the present study was to examine the possible involvement of the complement cascade following traumatic head injury in the human brain. Sixteen patients were included in this study, 12-77 years of age, treated at the neurointensive care unit for traumatic brain contusions. All of these patients were operated with frontal or temporal lobe resection due to intractable intracranial hypertension. The resected tissue was analyzed with regard to components related to complement activation. The time interval between accident and operation was 2-82 h. Brain tissue from three patients operated with hippocampectomy due to epilepsy, including temporal lobe resection, were used as controls. We found increased immunoreactivity for complement components C1q, C3b, and C3d and the membrane attack complex (MAC), C5b-9, in the immediate vicinity of neurons in the penumbra area of the contusion. These findings constitute histological evidence for activation of the complement cascade in the penumbra of cortical contusions in the human brain. Using in situ hybridization, we also found C3-mRNA in the penumbra, suggesting a local synthesis of complement. Furthermore, upregulation of the endogenous complement regulator clusterin was found in some neurons in the same area. We suggest that unknown compounds in the debris from injured neurons or myelin breakdown products trigger complement activation, including formation of C5b-9. Activated complement components may stimulate accumulation of inflammatory cells and formation of brain edema, as well as having membrane destructive effects by the end product MAC, thereby being mediators in the development of secondary brain damage.

When X-ray-inducible proteins meet DNA double strand break repair

Cellular responses to ionizing radiation (IR) include (a) activation of signal transduction enzymes; (b) stimulation of DNA repair, most notably DNA double strand break (DSB) repair by homologous or nonhomologous recombinatorial pathways; (c) activation of transcription factors and subsequent IR-inducible transcript and protein changes; (d) cell cycle checkpoint delays in G(1), S, and G(2) required for repair or for programmed cell death of severely damaged cells; (e) activation of zymogens needed for programmed cell death (although IR is a poor inducer of such responses in epithelial cells); and (f) stimulation of IR-inducible proteins that may mediate bystander effects influencing signal transduction, DNA repair, angiogenesis, the immune response, late responses to IR, and possibly adaptive survival responses. The overall response to IR depends on the cell's inherent genetic background, as well as its ability to biochemically and genetically respond to IR-induced damage. To improve the anti-tumor efficacy of IR, our knowledge of these pleiotropic responses must improve. The most important process for the survival of a tumor cell following IR is the repair of DNA double strand breaks (DSBs). Using yeast two-hybrid analyses along with other molecular and cellular biology techniques, we cloned transcripts/proteins that are involved in, or presumably affect, nonhomologous DNA double strand break end-joining (NHEJ) repair mediated by the DNA-PK complex. Using Ku70 as bait, we isolated a number of Ku-binding proteins (KUBs). We identified the first X-ray-inducible transcript/protein (xip8, Clusterin (CLU)) that associates with DNA-PK. A nuclear form of CLU (nCLU) prevented DNA-PK-mediated end joining, and stimulated cell death in response to IR or when overexpressed in the absence of IR. Structure-function analyses using molecular and cellular (including green fluorescence-tagged protein trafficking) biology techniques showed that nCLU appears to be an inactive protein residing in the cytoplasm of epithelial cells. Following IR injury, nCLU levels increase and an as yet undefined posttranslational modification appears to alter the protein, exposing nuclear localization sequences (NLSs) and coiled-coil domains. The modified protein translocates to the nucleus and triggers cell death, presumably through its interaction specifically with Ku70. Understanding nCLU responses, as well as the functions of the KUBs, will be important for understanding DSB repair. Knowledge of DSB repair may be used to improve the antitumor efficacy of IR, as well as other chemotherapeutic agents.

Identification of osmosensitive and ammonia-regulated genes in rat astrocytes by Northern blotting and differential display reverse transcriptase-polymerase chain reaction

BACKGROUND/AIMS

The hepatic encephalopathy (HE) is in part the result of astrocyte swelling with alterations of glial function. Detoxification of ammonia may be one mechanism by which astrocyte swelling is triggered in HE.

METHODS

The differential display polymerase chain reaction (DDRT-PCR) and Northern blot analysis were used for study the functional consequence of cell volume changes and ammonia on gene expression in primary rat astrocytes.

RESULTS

Differentially expressed cDNA products were identified with about 92% homology to genes coding for mouse proline rich protein expressed in brain (PRTB), rat clusterin, elongin, and human Kelch motif containing protein. As shown by Northern blot analysis, PRTB and clusterin mRNA levels were upregulated by 19-64% after 4-8 h by both ammonia and hypoosmolarity. Elongin mRNA expression increased by 97% in response to ammonia but slightly by hypoosmolarity. Further, hypoosmotic exposure for 1-24 hours but not ammonia led to an increase of 80% in KMCP mRNA levels.

CONCLUSIONS

The identification of these genes offers the opportunity to identify unrecognized molecular mechanisms of HE. The finding that several genes are induced by both, hypoosmolarity and ammonia, supports the view that astrocyte swelling is a major, but not the only pathogenetic event in HE.

Apolipoprotein J (clusterin) and Alzheimer's disease

Apolipoprotein J (clusterin) is a ubiquitous multifunctional glycoprotein capable of interacting with a broad spectrum of molecules. In pathological conditions, it is an amyloid associated protein, co-localizing with fibrillar deposits in systemic and localized amyloid disorders. In Alzheimer's disease, the most frequent form of amyloidosis in humans and the major cause of dementia in the elderly, apoJ is present in amyloid plaques and cerebrovascular deposits but is rarely seen in NFT-containing neurons. ApoJ expression is up-regulated in a wide variety of insults and may represent a defense response against local damage to neurons. Four different mechanisms of action could be postulated to explain the role of apoJ as a neuroprotectant during cellular stress: (1) function as an anti-apoptotic signal, (2) protection against oxidative stress, (3) inhibition of the membrane attack complex of complement proteins locally activated as a result of inflammation, and (4) binding to hydrophobic regions of partially unfolded, stressed proteins, and therefore avoiding aggregation in a chaperone-like manner. This review focuses on the association of apoJ in biological fluids with Alzheimer's soluble Abeta. This interaction prevents Abeta aggregation and fibrillization and modulates its blood-brain barrier transport at the cerebrovascular endothelium.

Identification of clusterin sequences mediating renal tubular cell interactions

Expression of the glycoprotein clusterin is markedly increased following tissue injury. One function of clusterin is to promote cell interactions which are perturbed in these pathologic settings. Clusterin causes cell aggregation and adhesion in vitro yet the molecular mechanism for this effect is not known. In order to identify the active site(s) of clusterin, 34 peptides, each 15 amino acid residues in length, were synthesized from hydrophilic regions of human clusterin. When studied individually, none of the peptides caused aggregation of LLC-PK1 cells, a porcine renal epithelial cell line. However, two out of the 34 peptides inhibited clusterin-induced cell aggregation in a dose-dependent manner. Scrambled versions of these two 'active' peptides did not inhibit cell aggregation. Seven peptides promoted cell adhesion. In conclusion, these findings provide evidence for novel amino acid sequences mediating clusterin-induced renal cell interactions.

Effect of targeted expression of clusterin in photoreceptor cells on retinal development and differentiation

Clusterin expression is increased in tissues undergoing apoptosis, including neurodegenerative retina, but the causal relationships remain to be clarified. To test the hypothesis that overexpression of clusterin could induce apoptosis in neurons, transgenic mice were generated in which rat clusterin transgene was expressed in photoreceptor cells under the transcriptional control of the human interphotoreceptor retinoid-binding protein (IRBP) promoter. Photoreceptor cell death in the resulting transgenic mice was examined by histology and TUNEL techniques. The expression of the clusterin transgene was confirmed by in situ hybridization in the photoreceptor cells, and results in a complex pattern of clusterin protein distribution in the retina. A reduction in apoptotic staining in the transgenic retinas was observed from birth to postnatal day 15. These results suggest that clusterin is not causally involved in apoptotic mechanisms of photoreceptor cell death, but may relate to cytoprotective functions.

Specific inhibition of apoptosis after cold-induced brain injury by moderate postinjury hypothermia

OBJECTIVE

Apoptosis of neuronal cells plays a key role in many developmental and pathological processes of the central nervous system. Deoxyribonucleic acid (DNA) of cells undergoing apoptosis is cleaved by an endonuclease into oligonucleosoma-sized fragments. These fragments can be labeled using in situ terminal deoxynucleotidyl transferase so that the apoptotic cells can be visualized by in situ apoptotic staining. The model of cold-induced rat brain edema was used to further examine this hypothesis. The protective effect of hypothermia was also studied in this model of cold-induced brain injury.

METHODS

Using a terminal deoxynucleotidyl transferase-mediated deoxyuridine 5'-triphosphate-biotin nick end labeling technique, the neuronal cells with DNA fragmentation in different regions of the brains of rats subjected to cold-induced brain injury were detected. The internucleosomal fragments of DNA in apoptotic cells were examined using agarose gel electrophoresis. The animals were randomly divided into three groups: 1) sham (n = 8); 2) cold-induced brain injury, killed at 12, 24, 48, 72, and 168 hours after cold lesion (n = 10 for each time point); 3) hypothermia, both mean temporalis and rectal temperatures were reduced by surface cooling to 32 degrees C (standard deviation, 0.1 degrees C) for 3, 6, and 12 hours (n = 10 for each time point) beginning 1 hour after cold-induced brain injury.

RESULTS

The apoptotic cells were detectable for up to 72 hours after the initial brain injury and reached a peak at approximately 24 to 48 hours, with a mean peak value of 24.29 +/- 5.26, 15.37 +/- 4.10, 15.81 +/- 3.56, 13.94 +/- 2.48, 10.46 +/- 2.23, and 7.68 +/- 2.48% in the cortex, subcortex, white matter, CA1, CA3, and dentate gyrus, respectively, and had a significant increase, compared with the control value (mean +/- standard error, P < 0.01). Agarose gel electrophoresis of DNA extracted from cortex and hippocampus containing apoptotic cells revealed a "DNA ladder" at 180- to 200-base pair intervals. In animals subjected to the same brain injury that underwent 32 degrees C hypothermia, the numbers of apoptotic cells were reduced evidently and DNA fragmentation was inhibited.

CONCLUSION

The data suggest that apoptosis occurs after cold-induced brain injury and that DNA fragmentation may be associated with apoptotic cell death. Moderate hypothermia shows specific effect on inhibition of apoptotic cell death and cellular DNA fragmentation after cold-induced brain injury in rats.

Identification of cDNAs induced by the tumor suppressor Tsc2 gene using a conditional expression system in Tsc2 mutant (Eker) rat renal carcinoma cells

Alteration of the rat homologue of the tuberous sclerosis 2 (TSC2) gene is associated with dominantly inherited cancer in the Eker rat model, indicating a tumor suppressor nature. The ability of Tsc2 to activate signal transduction and transcription suggests that genes induced by Tsc2 may mediate its biological roles. Using a subtractive hybridization approach in combination with tetracycline operator systems, we identified a set of downstream genes affected by Tsc2. Regulated expression of wild-type Tsc2 gene in Eker renal carcinomas (RCs) resulted in marked expression of cell arrest or programmed cell-death-related genes and stress-induced genes. Thus, the data suggest that Tsc2 might contribute to regulation of the cell cycle and cell survival.

Differential regulation of astrocytic mRNAs in the rat striatum after lesions of the cortex or substantia nigra

This study evaluates the time course of expression of three astrocytic mRNAs, glial fibrillary acidic protein (GFAP), apolipoprotein E (ApoE), and clusterin, in the rat striatum (ST) following a unilateral lesion of either the cortex (CX) or the substantia nigra (SN), using Northern blot and in situ hybridization analyses. We found that while there was a time-dependent increase in astrocytic GFAP mRNA in the deafferented ST following both the CX and the SN lesions, the time course of the response was different between the two lesion paradigms. Specifically, the increase in GFAP mRNA in striatal astrocytes after the SN lesion was rapid and transient returning to control levels by 10 days postlesion, while the response was long lasting and remained increased until at least 27 days after the CX lesion. In addition, the mRNA response for both ApoE and clusterin was differentially regulated in response to the two lesions. Specifically, both clusterin and ApoE mRNAs were rapidly increased in the ST following the CX lesion while both mRNAs remained unchanged following the SN lesion. Data from this study extend information derived from previous investigations on the multifunctional role of astrocytes in the response to brain injury. Specifically, our data support the notion that while the time course of the GFAP response in striatal astrocytes may vary between lesion paradigms, the upregulation of GFAP is part of a generalized response of reactive astrocytes to diverse brain injuries. By comparison, upregulation of the mRNAs for the lipoproteins clusterin and ApoE are lesion specific and may play a role in the transport of recycled myelin lipids from dying axons to actively growing axons and dendrites in reactive synaptogenesis.

Extracellular matrix modulates mesangial cell apoptosis and mRNA expression of cathepsin-B and tissue transglutaminase

Mesangial matrix is a dynamic structure which modulates mesangial cell function. Since accumulation of matrix precedes the development of focal glomerulosclerosis, we studied the effect of different matrices on mesangial cell (MC) apoptosis. Suspended mesangial cells became apoptotic in a time dependent manner. Collagen type III did not modulate MC apoptosis when compared to cells grown on plastic. MCs grown on Matrigel, collagen type I and IV showed an increased number of apoptotic cells when compared to MCs grown on plastic. DNA end-labeling further confirmed these observations. MCs grown on Matrigel showed enhanced (P < 0.05) mRNA expression for tissue transglutaminase (TTG) and cathepsin-B. Mesangial cells grown on Matrigel also showed enhanced expression of superoxide dismutase (SOD). We conclude that mesangial cells require attachment to the matrix for their survival and alteration of the quality of matrix modulates mesangial cell apoptosis.

Morphine induces splenocyte apoptosis and enhanced mRNA expression of cathepsin-B

Morphine has been demonstrated to modulate immune function. We studied whether morphine modulates apoptosis of splenocytes. Splenocytes were isolated from control and morphine treated rats. Splenocytes isolated from morphine treated rats showed increased percentage (P < 0.001) of apoptosis when compared to splenocytes isolated from untreated rats (control, 4.7 +/- 1.0% apoptotic splenocytes/field vs. morphine, 47.8 +/- 3.4% apoptotic splenocytes/field). These results were further confirmed by gel electrophoresis as well as by end-labeling DNA of splenocytes isolated from control and morphine treated rats. Splenocytes from morphine treated rats showed a classical ladder pattern with integer multiples of 180 base pairs. Splenocytes from morphine treated rats also showed increased mRNA expression of cathepsin-B, a gene associated with active cell death. These results suggest that morphine may also be modulating immune function by enhancing apoptosis of splenocytes.

Stress-induced transcription of the clusterin/apoJ gene

Clusterin/apoJ is an intriguing gene frequently isolated by differential screening in laboratories from different areas of molecular biology, since it is overexpressed in numerous cases of degenerative diseases such as Alzheimer's disease and scrapie. While the dramatic increase of clusterin expression in injured tissues is well established, the molecular basis of the gene induction remains unclear. In this study, we have focused our attention on the only DNA region strictly conserved between clusterin gene proximal promoters from different vertebrate classes. We show that this 14-bp DNA element is specifically recognized by the HSF1 transcription factor and can mediate heat-shock-induced transcription in transient expression assays. Conversely, the avian clusterin proximal promoter, point-mutated at the level of this element, no longer transmits heat-shock activation. These findings provide a possible explanation for the high sensitivity of clusterin expression to environmental changes and allow the classification of clusterin as an extracellular version of heat-shock protein.

Optimization of PCR/lambda exonuclease-mediated synthesis of sense and antisense DNA probes for in situ hybridization

In situ hybridization experiments are stringently dependent on the quality of the probes, which should be single-stranded when efficient comparison of signals obtained with antisense and control sense probes are needed. In this report, we describe an optimized synthesis of radioactive single-stranded DNA probes, without vector cloning and requiring a unique polymerization step. The sequence region selected as probe is amplified by polymerase chain reaction in the presence of radiolabelled nucleotides. The sense and antisense probes are then yielded by the action of the lambda bacteriophage exonuclease, which can specifically eliminate one out of the two strands of the amplified fragments. In this way, sense and antisense probes with identical length and specific activity can be generated by selecting the primer to be phosphorylated. We have verified the efficiency of our probes for in situ hybridization of the clusterin transcripts within the peripheral olfactory system, after surgical lesion of its synaptic target.

Response of glial cells and activation of complement following motorneuron degeneration induced by toxic ricin

Motor nerve transection in adult rats induce a series of metabolic and structural changes in the injured neurons as well as in surrounding glial cells; however, without substantial neuronal degeneration. In the present study we found, in contrast with axotomy, a massive neuronal death in the ipsilateral hypoglossal nucleus following injection of toxic ricin (RCA) into the hypoglossal nerve, which is in line with previous observations. Injection of RCA enables examination of the glial reaction in a situation where neuronal degeneration is profound, which has been the approach in the present study. We found an increase in OX42-, GFAP-, and transferrin-immunoreactivity in microglial, astroglial, and oligodendroglial cells respectively, in the ipsilateral hypoglossal nucleus three to seven days following injection of toxic ricin in the hypoglossal nerve. Proliferation was found in astrocytes as well as in microglial cells, as shown by uptake of bromodeoxyuridine. In addition, the complement cascade was activated locally in the ipsilateral hypoglossal nucleus, as demonstrated by immunohistochemical detection of complement components C3d and C9. Complement activation may serve several effects in the glial-neuronal interactions. Stimulation of phagocytosis by reactive microglia is probably the most important one. Furthermore, the degenerative neuronal somata showed increased immunoreactivity for clusterin, which is a known complement inhibitor, but a decrease in clusterin-mRNA. In conclusion, the glial cell response was in several aspects principally different following massive motorneuron degeneration induced by toxic ricin in comparison to previous findings reported after axotomy.

Injury-induced synthesis and release of apolipoprotein E and clusterin from rat neural cells

Apolipoproteins in the brain have assumed major clinical importance since it was shown that one of the allelic forms of apolipoprotein E, apoE-4, is a risk factor for Alzheimer's disease. Using tissue culture of embryonic rat spinal cord, we examined the effect of neuronal injury on the up-regulation of two apolipoproteins, apolipoprotein E and clusterin (apoJ). In order to study the influence of neuronal cells, we exploited the specific neurotoxic effect of elevated glutamate on these cells. Overstimulation by excess glutamate induced neuronal degeneration as assessed by morphological and biochemical criteria, notably the activity of choline acetyltransferase, which serves as a marker for cholinergic neurons. High concentrations of glutamate increased mRNA synthesis and the production and secretion of both apolipoprotein E and clusterin protein. Both neuronal cell death and release of the peptides were calcium-dependent and could be blocked by the NMDA receptor antagonist MK-801. Immunohistochemical data revealed the presence of clusterin in both neuronal and non-neuronal cells whereas apolipoprotein E was mainly expressed in non-neuronal cells. The results are suggestive of concerted up-regulation of apolipoprotein E and clusterin when neural cells are subjected to injury.

Induction of sulfated glycoprotein-2 (clusterin) and glial fibrillary acidic protein (GFAP) RNA expression following transient global ischemia is differentially attenuated by LY231617

Sulfated glycoprotein-2 (SGP-2) is a secreted glycoprotein that along with GFAP has emerged as a prominent molecular marker of neurodegeneration. In the present study, we have evaluated further the relationship between SGP-2, GFAP and neurodegeneration, by examining the effects of LY231617, a potent antioxidant, on expression of SGP-2 and GFAP following four vessel occlusion (4VO). GFAP and SGP-2 RNA levels increased several fold in hippocampus and caudate nucleus in response to 30 min of 4VO. LY231617 treatment markedly attenuated the induction of GFAP RNA in both hippocampus and caudate nucleus, consistent with the significant neuroprotection observed histologically. In contrast, LY231617 treatment blunted SGP-2 RNA expression only in the hippocampus; SGP-2 RNA expression in caudate nucleus was similar to vehicle-treated 4VO, despite the marked attenuation of neuronal damage in both areas by LY231617. These data suggest region-specific differential regulation of SGP-2 and GFAP RNA induction.

Activation of the complement cascade and increase of clusterin in the brain following a cortical contusion in the adult rat

The aim of the present study was to examine the glial cell response and the possible involvement of the complement cascade following a cerebral cortical contusion. The lesion was produced using a standardized weight-drop technique in adult rats. The blood-brain barrier was damaged, as demonstrated by a decrease of immunoreactivity for a tight junction protein normally expressed by endothelial cells of small vessels in the central nervous system. Increased immunoreactivity for microglial (OX42) and astroglial cells (glial fibrillary acidic protein), as well as macrophages expressing ED1-immunoreactivity (IR) were found in the vicinity of the lesion at all postoperative survival times (2-14 days). In the present study complement factor C3d- and C9-IR was found around the lesion, indicating that activation of the complement cascade had taken place. Furthermore, immunoreactivity for the putative complement inhibitor clusterin (sulfated glycoprotein-2) was found in some of the injured neurons. The contralateral hemisphere showed no evidence of the reaction found in the ipsilateral hemisphere. The balance between complement activation and complement inhibitors may have an impact on the degenerative components in the brain following traumatic injury and in particular on the events leading to nerve cell death.

Induction of clusterin in the immature brain following a hypoxic-ischemic injury

A unilateral hypoxic-ischemic (HI) insult in the 21 day old rat has been used to assess the role of clusterin in nerve cell death. Both clusterin mRNA and protein levels were measured at various time points after moderate (15 min) and severe (60 min) HI insult using in situ hybridisation and immunocytochemistry respectively. The severe HI insult lead primarily to necrotic neuronal death and showed very little if any clusterin mRNA and protein induction on the ligated side of the brain. However, following the moderate HI insult there was a dramatic time-dependent accumulation of clusterin protein in neurons of the CA1-CA2 pyramidal cell layers in the hippocampus and cortical layers 3-5, regions undergoing delayed neuronal death. Clusterin mRNA expression, in contrast to neuronal protein accumulation, appeared to be glial in origin (probably astrocytes) with increases in mRNA in and around the hippocampal fissure and only a weak signal over the CA1-CA2 pyramidal cell layer. These results support the hypothesis that the clusterin protein is synthesised in the astrocytes, secreted and then taken up by dying neurons. Clusterin immunoreactivity and in situ DNA end-labelling performed on the same sections revealed that clusterin was accumulating in neurons destined to die by programmed cell death. However the relative time-courses of DNA fragmentation and clusterin immunoreactivity suggest that clusterin production was a result of the selective delayed neuronal death rather than being involved in the biochemical cascade of events that cause it.

Programmed cell death in brains of HIV-1-positive AIDS and pre-AIDS patients

Neuropathological studies have revealed that the brains of HIV-1-infected AIDS patients show the typical encephalitis and, in addition, neuronal loss. More recently, this neuronal cell loss has been thought to take place via programmed cell death (apoptosis) which has been demonstrated by an in situ end labelling (ISEL) technique. In this study 54 brains of HIV-1-positive patients were investigated by the ISEL technique to investigate whether apoptosis is also present in the brains of patients at the asymptomatic stage. Of these, 10 patients suffered from HIV encephalitis (HIVE), 8 had AIDS without neuropathological disorders and 36 were HIV-1-positive pre-AIDS patients. Apoptotic cells were detected in 6 of the 10 HIVE, 1 of the 8 AIDS without central nervous system (CNS) disease and 4 of the 36 asymptomatic individuals. A difference seen between the AIDS and pre-AIDS cases was that, in the latter, apoptotic cells were found in the white matter in all 4 cases, while only 2 of these 4 showed apoptotic neurons. The presence of apoptotic cells in a number, albeit small, of brains of HIV-1-positive pre-AIDS individuals, combined with abnormalities described previously in the same group of patients gives further support to the opinion that brain damage already occurs during the early stages of HIV infection.

Clusterin promotes the aggregation and adhesion of renal porcine epithelial cells

The function of clusterin, a heterodimeric glycoprotein markedly induced in renal and other organ injuries, is unclear. Since renal injury is accompanied by alterations in cell attachment, it is possible that clusterin functions to promote cell-cell and cell-substratum interactions. In this study, a single cell suspension of renal epithelial (LLC-PK1) cells was treated with purified human clusterin, resulting in time- and dose-dependent cell aggregation. Electron microscopy of the cell aggregates demonstrated cell junction and lumen formation. To determine the effect of clusterin on cell adhesion, tissue culture plates were coated with clusterin, fibronectin, PBS, or albumin. Clusterin and fibronectin promoted cell adhesion to the same extent. The adhesion to clusterin was dose dependent and specific, as a monoclonal antibody against clusterin inhibited cell adhesion to clusterin but not fibronectin. Perterbations of the cytoskeleton may underlie the alterations in cell attachment which occur in renal injury. Induction of clusterin mRNA was seen after disruption of both microtubules and microfilaments and after inhibition of cell-substratum interactions. In conclusion, clusterin is a potent renal epithelial cell aggregation and adhesion molecule. We speculate that clusterin functions to promote cell-cell and cell-substratum interactions which are perturbed in the setting of renal injury, thereby preserving the integrity of the renal epithelial barrier.

Complement and clusterin in the spinal cord dorsal horn and gracile nucleus following sciatic nerve injury in the adult rat

We provide evidence for activation of the complement cascade in the dorsal horn of the spinal cord and in the gracile nucleus in the brainstem following sciatic nerve transection in the adult rat. Immunocytochemical analyses showed immunoreactivity for endogenous immunoglobulin G as shown by immunostaining with F(ab')2 antibodies, as well as complement factors C1, C1q, C3, C3d and C9 in the appropriate central termination areas of the injured sciatic nerve. Results from double labelling immunocytochemistry showed a strong association between immunoglobulin and complement factors on the one hand and reactive microglia on the other. However, some complement immunoreactivity was also found in the neuropil, possibly representing secreted complement. In situ hybridization with an oligonucleotide probe showed a marked increase in C3 messenger RNA, indicating local synthesis of C3 protein. In parallel with activation of complement, there was an increased immunoreactivity for the putative complement inhibitor clusterin, which co-localized with glial fibrillary acidic protein-positive astrocytes. In situ hybridization showed an increased labelling of clusterin messenger RNA. These findings indicate that complement activation and up-regulation of complement inhibitors are prominent central responses to peripheral sensory nerve injury. These responses may therefore be important elements underlying so-called transganglionic degenerative changes in primary sensory axons and terminals.

Clusterin accumulates in dying neurons following status epilepticus

Clusterin is a protein that has been implicated in cell death and remodelling in a number of different tissues. To further investigate the role of clusterin in nerve cell death its expression was measured in the rat brain at various times after status epilepticus (SE) induced by 1 h of hippocampal stimulation, by using in situ hybridization, immunocytochemistry, and immunoblotting. SE lead to a dramatic time-dependent increase in clusterin mRNA in non-nerve cells resembling astrocytes in the hippocampus beginning after 24 h. There was also an earlier induction of clusterin mRNA in dentate granule cells, that survive SE. Only a low mRNA signal was observed over the CA1 pyramidal cells, which die after SE. In contrast to these mRNA results, massive clusterin-like immunoreactivity was observed in CA1 pyramidal cells and dentate hilar neurons (and both of these neuronal populations die after SE), but not in dentate granule cells. We speculate that astrocytes produce clusterin after SE and that the clusterin is then secreted and taken up by hippocampal neurons destined to die. Thus, the role of clusterin in nerve cell death/ regeneration warrants further investigation.

Clusterin: physiologic and pathophysiologic considerations

Clusterin is a heterodimeric glycoprotein produced by a wide array of tissues and found in most biologic fluids. A number of physiologic functions have been proposed for clusterin based on its distribution and in vitro properties. These include complement regulation, lipid transport, sperm maturation, initiation of apoptosis, endocrine secretion, membrane protection, and promotion of cell interactions. A prominent and defining feature of clusterin is its induction in such disease states as glomerulonephritis, polycystic kidney disease, renal tubular injury, neurodegenerative conditions including Alzheimer's disease, atherosclerosis, and myocardial infarction. The expression of clusterin in these states is puzzling, from the specific molecular species and cellular pathways eliciting such expression, to the roles subserved by clusterin once induced. This review will discuss these physiologic and pathophysiologic aspects of clusterin and speculate on its role in disease.

The role of inducible transcription factors in apoptotic nerve cell death

Recent studies have shown that certain types of nerve cell death in the brain occur by an apoptotic mechanism. Researchers have demonstrated that moderate hypoxic-ischemic (HI) episodes and status epilepticus (SE) can cause DNA fragmentation as well as other morphological features of apoptosis in neurons destined to die, whereas more severe HI episodes lead to neuronal necrosis and infarction. Although somewhat controversial, some studies have demonstrated that protein synthesis inhibition prevents HI-and SE-induced nerve cell death in the brain, suggesting that apoptotic nerve cell death in the adult brain is de novo protein synthesis-dependent (i.e., programmed). The identity of the proteins involved in HI-and SE-induced apoptosis in the adult brain is unclear, although based upon studies in cell culture, a number of potential cell death and anti-apoptosis genes have been identified. In addition, a number of studies have demonstrated that inducible transcription factors (ITFs) are expressed for prolonged periods in neurons undergoing apoptotic death following HI and SE. These results suggest that prolonged expression of ITFs (in particular c-jun) may form part of the biological cascade that induces apoptosis in adult neurons. These various studies are critically discussed and in particular the role of inducible transcription factors in neuronal apoptosis is evaluated.

The lurcher gene induces apoptotic death in cerebellar Purkinje cells

In the neurologically mutant mouse strain lurcher (Lc), heterozygous animals display cell autonomous degeneration of cerebellar Purkinje cells beginning in the second postnatal week. During the course of our studies to identify the genetic lesion responsible for this disease (Norman et al., 1991), we have formulated an hypothesis suggesting that in Lc Purkinje cells homeostasis is sufficiently perturbed to lead to the activation of programmed cell death, thus resulting in neuronal loss and the consequent neurologic disease (Heintz, 1993). To address this possibility, we have examined the properties of Lc Purkinje cells as they die during the second postnatal week. Our light and electron microscopic studies demonstrate that dying Lc Purkinje cells exhibit the characteristic morphologic features of apoptosis, including nuclear condensation, axon beading and membrane blebbing. Using an in situ end-labeling method, we have also detected nicked nuclear DNA in these cells. Furthermore, we have examined the expression of the sulfated glycoprotein 2 (SGP2), whose mRNA is induced in both T-cells and prostate epithelial cells undergoing apoptotic death. We show by in situ hybridization that SGP2 is not expressed at detectable levels in normal Purkinje cells, but that its mRNA is present in Lc Purkinje cells prior to their death. Also expression of the Kv3.3b potassium channel, which marks the terminal phase of Purkinje cell differentiation, is evident in Lc Purkinje cells prior to their death. These data demonstrate that the Lc mutation induces apoptosis in cerebellar Purkinje cells following their maturation in postnatal cerebellum. Isolation of the Lc mutation and further analysis of its action in eliciting apoptosis can provide an important opportunity for understanding the etiology of neurodegenerative disease.

Complement biosynthesis in the central nervous system

Complement is an important effector arm of the human immune response. Binding of proteolytic fragments derived from activation of complement by specific receptors leads to responses as diverse as inflammation, opsonization, and B-cell activation. The importance of characterizing the expression and regulation of complement in the CNS is highlighted by growing evidence that complement plays a significant role in the pathogenesis of a variety of neurological diseases, such as multiple sclerosis and Alzheimer's disease. In vitro studies have demonstrated that astrocytes, the predominant glial cell type in the brain, are capable of expressing or producing a majority of the components of the complement system. Expression of many complement proteins synthesized by astrocytes is regulated by both pro- and anti-inflammatory cytokines, many of which are also produced by several cell types in the CNS. In addition to astrocytes, ependymal cells, endothelial cells, microglia, and neurons have recently been shown to synthesize various complement proteins or express complement receptors on their cell surfaces. Together, these studies demonstrate that several cell types throughout the brain have the potential to express complement and, in many cases, increase expression in response to mediators of the acute phase response. These studies suggest that complement may play a greater role in CNS immune responses than previously thought, and pave the way for better understanding of the dynamics of complement expression and regulation in vivo. Such understanding may lead to therapeutic manipulation of complement host defense functions in a variety of inflammatory and degenerative diseases in the CNS.

Evidence for activation of the terminal pathway of complement and upregulation of sulfated glycoprotein (SGP)-2 in the hypoglossal nucleus following peripheral nerve injury

In a previous study, we found immunoreactivity for complement factors C3, C3d, and C4d, as well as endogenous IgG in the hypoglossal nucleus following hypoglossal nerve transection, suggesting that activation of the complement cascade had taken place in the vicinity of the axotomized motorneurons. In the present study, we found increased immunoreactivity for complement factor C1 and C1q in reactive microglia, indicating an increased potential for initiation of the classical pathway by binding of IgG to C1q. Furthermore, we found immunoreactivity for C9, which contributes to the formation of C5b-9, the final lytic product of the complement cascade close to the axotomized neurons and perineuronal glia. In addition, immunoreactivity and mRNA labeling of sulfated glycoprotein (SGP-2), a putative complement inhibitor, was increased in a subpopulation of the axotomized motorneurons. SGP-2 immunoreactivity was also increased in astroglial cells ipsilateral to the nerve injury. The results lend further support to the hypothesis that the complement cascade is activated in the vicinity of axotomized neurons, which in turn may be protected by complement inhibitors. The balance between activation of complement and complement inhibitors might have an impact on the degenerative components of the axon reaction and, in particular, the events leading to nerve cell death.

Cathepsin B, a cysteine protease implicated in metastatic progression, is also expressed during regression of the rat prostate and mammary glands

We have developed a novel library-to-library cross-screening technology to clone unique mRNAs that are expressed during tissue regression. We have cloned a number of regression selected genes (RSG) that are expressed during the regression of the mammary gland and ventral prostate of the rat after the removal of the respective trophic hormone. In this investigation, we have characterized one of these genes, RSG-2, that is homologous to cathepsin B, a thiol protease that has been previously identified as one of the extracellular proteases which is activated in metastatic cells. The steady-state levels of RSG-2 mRNA in the normal prostate are low but detectable. In the regressing prostate, RSG-2 mRNA levels peak at 3-4 days after castration, at the time that tissue regression is maximal. The gene is induced in a similar fashion in the regressing mammary gland. Using in situ hybridization, we have established that RSG-2 mRNA is expressed in the luminal epithelial cells of the prostate and mammary gland that are known to undergo active cell death, suggesting that it may be a general marker for secretory epithelial cell death. Analysis of the distribution of the cathepsin B protein by immunofluorescence microscopy demonstrates that there is diffuse, but punctate, expression of the protein in all of the luminal epithelial cells of the normal prostate and mammary gland. However, at early times after hormone ablation in both glands, the majority of the increase in cathepsin B protein appears to result from redistribution to the basal aspect of the cells. At later time points, there appears to be increased amounts of the protein which is localized to the apoptotic bodies. These results suggest that RSG-2, or cathepsin B, is required for the local degradation of the basement membrane, which is one of the earliest morphologically recognizable events of active cell death.

Selective expression of clusterin (SGP-2) and complement C1qB and C4 during responses to neurotoxins in vivo and in vitro

This study concerns expression of the genes encoding three multifunctional proteins: clusterin and two complement cascade components, C1q and C4. Previous work from this and other laboratories has established that clusterin, Clq and C4 messenger RNAs are elevated during Alzheimer's disease, and in response to deafferenting and excitotoxic brain lesion. This study addresses hippocampal clusterin, ClqB and C4 expression in response to neurotoxins that caused selective neuron death. Kainate, which preferentially kills hippocampal CA3 pyramidal neurons but not dentate gyrus granule neurons induced clusterin immunoreactivity in CA1 and CA3 pyramidal neurons and adjacent astrocytes, but not in dentate gyrus granule neurons. In contrast, colchicine, which preferentially kills the dentate gyrus granule neurons, induced clusterin immunoreactivity in the local neuropil as punctate deposits, but not in the surviving or degenerating dentate gyrus granule neurons. Clusterin messenger RNA was increased in astrocytes. ClqB and C4 messenger RNAs increased within 48 h after kainate injections, particularly in the CA3 pyramidal layer, less in the dentate gyrus-CA4, and less in CA1. Clq immunoreactivity was detected in CA1 pyramidal neurons and also as small punctate deposits in the CA1 region at eight and 14 days after kainate. The increase of both clusterin and ClqB messenger RNAs after kainate injections was blocked by barbiturates that prevented seizures and neurodegeneration. In primary hippocampal neuronal cultures treated with glutamate, a subpopulation of cultured neurons that survived glutamate toxicity also had parallel elevations of clusterin and ClqB messenger RNA. In conclusion, cytotoxins that target selective hippocampal neurons increase the expression of both clusterin and ClqB in vivo and in vitro. These results show that elevations of clusterin messenger RNA or protein can be dissociated from each other and from cell death. These increased messenger RNAs were associated with immunoreactive deposits that differed by cell type and intra- versus extracellular locations. These results suggest that the complement system is involved in brain responses to injury.

Response of striatal astrocytes to neuronal deafferentation: an immunocytochemical and ultrastructural study

This ultrastructural and light microscopic immunocytochemical study describes the time course of anatomical changes that occur in striatal astrocytes in response to neuronal deafferentation in young adult rats and the coordinate distribution of two astrocytic proteins involved in reactive synaptogenesis, glial fibrillary acidic protein and clusterin. We found that following a unilateral lesion of the cerebral cortex, striatal astrocytes undergo a rapid ultrastructural transformation from a protoplasmic to a reactive type of astroglia and are the primary cells involved in the removal of degenerating axon terminals, but not axons of passage, from the neuropil. In addition, at 10 and 27 days postlesion, processes of reactive astrocytes are also seen to occupy vacant postsynaptic spines after degenerating presynaptic terminals are removed, suggesting that they may also participate in the reinnervation of the deafferented neurons. By immunocytochemistry, reactive astrocytes were characterized by a significant increase in the intensity of glial fibrillary acidic protein staining beginning at three days postlesion and lasting for at least 27 days postlesion. Reactive astrocytes were characterized by cellular hypertrophy and an increase in the density of immunoreactive processes distributed throughout the deafferented striatum. However, our analysis of astrocyte cell number found no evidence of astrocyte proliferation in response to the deafferentation lesion. Although previous in situ hybridization studies have reported elevated clusterin messenger RNA in reactive astrocytes after decortication, clusterin immunoreactivity was not seen in the cell soma of reactive astrocytes but was distributed as punctate deposits, ranging from 1 to 2 microns in diameter, within the neuropil of the deafferented striatum. At 10 days postlesion, the distribution of clusterin staining appeared as large aggregates of immunoreactive deposits adjacent to neurons. However, by 27 days postlesion, the aggregates of clusterin reaction product were replaced by a fine scattering of individual punctate deposits distributed evenly over the dorsal part of the deafferented striatum. These data support the notion that reactive astrocytes serve multiple, time-dependent roles in response to brain injury and are involved in both the removal of degenerative debris from the lesion site as well as in reforming the synaptic circuitry of the damaged brain. Our data suggest that, in response to decortication, reactive astrocytes are the primary cells responsible for removing degenerating axon terminals, but not axons of passage, from the deafferented striatum and that the coordinate increase in glial fibrillary acidic protein may serve to stabilize the extension of reactive astrocytic processes during phagocytosis.(ABSTRACT TRUNCATED AT 400 WORDS)

Gene relaxation and aging: changes in the abundance of rat ventral prostate SGP-2 (clusterin) and ornithine decarboxylase mRNAs

Sulfated glycoprotein 2 (SGP-2) mRNA progressively increased in the ventral prostate of the aging rat, reaching, at 24 months, 4-fold higher than at 3 months. Ornithine decarboxylase (ODC) mRNA peaked at 6 months (4-fold increase), and at 12 and 24 months was maintained at higher levels than at 3 months. ODC enzymatic activity was enhanced at 6 months to a much smaller extent than its own mRNA, the values at 12 and 24 months dropping to below those at 3 months. Putrescine (Put), spermidine (Spd) and spermine (Sp) concentrations also peaked at 6 months (100% increase for Put, 50% for Sp and Spd). At 24 months, Put and Spd were diminished, and Sp was unchanged with respect to the 3-month values. Under the same conditions, glyceraldehyde-3-phosphate dehydrogenase mRNA did not undergo significant alterations.

Programmed cell death: implications for neuropsychiatric disorders

Programmed cell death, sometimes referred to as apoptosis, occurs through an active process requiring new gene transcription, in contrast to the passive cell death produced by metabolic toxins. Programmed cell death is an essential part of normal development, particularly in the nervous system. Spatial, temporal, or quantitative errors in the stimuli that initiate programmed cell death, or errors within the programmed cell death pathway itself, can result in an abnormal number of neurons and pathological neural development. Excesses and deficits in neuronal numbers have now been observed not only in typical neurodegenerative disorders such as Alzheimer's and Huntington's diseases, but also in several neurodevelopmental disorders, including schizophrenia and autism. Recent investigations into the mechanisms of cell death during C. elegans neurodevelopment thymocyte negative selection, and withdrawal of sympathetic ganglion cells trophic support provides intriguing clues to the etiology and pathophysiology of these neuropsychiatric disorders.

Molecular characterization of human TRPM-2/clusterin, a gene associated with sperm maturation, apoptosis and neurodegeneration

The TRPM-2/clusterin gene and its cognate protein has been characterized in a number of species. Although the functional role, or roles, of the TRPM-2/clusterin protein remains to be firmly established, the gene has been implicated in a variety of physiological processes, including sperm maturation, lipid transport, membrane remodelling and inhibition of the complement cascade. TRPM-2/clusterin is induced de novo during the regression of the prostate and other hormone-dependent tissues after hormone ablation, and is over-expressed in several human neurodegenerative diseases including Alzheimer's disease, epilepsy and retinitis pigmentosa. We describe the genomic structure of the human TRPM-2/clusterin gene which is organized into nine exons, ranging in size from 47 bp (exon I) to 412 bp (exon V), spanning a region of 16,580 bp. Comparison with sequences registered in the databases shows that it has extensive similarity to the human protein designated as SP-40,40 or complement-lysis inhibitor (CLI), a protein that appears to block the membrane-attack complex of complement. However, the cDNA sequences reported for SP-40,40 and CLI diverge significantly in the 5' untranslated region of the mRNA (coded for by exon I), raising the possibility that the TRPM-2/clusterin gene is present in the human genome as a small multi-gene family or that there are several alternate exon I sequences in the TRPM-2 gene. Southern analysis and fluorescent in situ hybridization suggest that the clusterin gene is a single-copy gene, and that, if alternative exon I sequences are present in the genome, they lie outside of the lambda clones that have been characterized. Analysis of the promoter region of the human TRPM-2/clusterin gene shows many similarities to the rat TRPM-2/clusterin promoter including a putative control region containing several potential regulatory elements that may regulate the complex tissue-specific control of the gene which must be constitutively expressed in some tissues but is inducible in others.

Expression of clusterin in human renal diseases

Clusterin, a glycoprotein with potent cohesive properties, is induced in a wide variety of acute and chronic experimental renal diseases. The purpose of this study was to examine clusterin expression in human renal diseases. Clusterin immunostaining was examined in nephrectomy specimens from patients with autosomal-dominant polycystic kidney disease (N = 5), autosomal-recessive polycystic kidney disease (N = 3), multilocular cyst of the kidney (N = 2), renal hypoplasia/dysplasia (N = 7), Wilms' tumor (nephroblastoma) (N = 6), renal cell carcinoma (N = 9), and acute and/or chronic renal transplant rejection (N = 15). No clusterin staining was detected in normal renal tissue distant from renal cell carcinomas. Increased expression of clusterin was found in epithelial cells lining cysts in all of the cystic disorders studied. Clusterin expression was found in some immature tubules in hypoplastic/dysplastic kidneys and in tubules of rejected renal allografts, but was not a prominent finding in renal neoplasms, although some renal cell carcinomas expressed clusterin in a focal manner. Common features of clusterin induction included exclusively epithelial production of clusterin in cysts, immature nephrons, and injured tubules, heterogeneity of clusterin expression, with only some tubules and/or cysts in a given area staining for clusterin, and uniform clusterin staining of epithelial cells in a given tubule or cyst in most cases. Based on its cohesive properties, we speculate clusterin functions to maintain cell-cell and cell-substratum interactions which become perturbed in the setting of renal injury and cystic diseases.

Transforming growth factor-beta 1 induces neuronal and astrocyte genes: tubulin alpha 1, glial fibrillary acidic protein and clusterin

Transforming growth factor-beta 1 was studied as a possible regulator of messenger RNAs in astrocytes and neurons that increase after hippocampal deafferentation by perforant path transection: tubulin alpha 1, clusterin and glial fibrillary acidic protein messenger RNA. Because transforming growth factor-beta 1 messenger RNA is increased after this lesion, we examined which messenger RNA lesion responses could be induced by transforming growth factor-beta 1 alone. Porcine transforming growth factor-beta 1 infused into the lateral ventricle elevated the messenger RNAs for tubulin alpha 1, clusterin and glial fibrillary acidic protein 24 h after infusion in the ipsilateral hippocampus. As assayed by nuclear run-on, the transcription of glial fibrillary acidic protein RNA was increased in the ipsilateral hippocampus after perforant path transection and in primary rat astrocyte cultures by transforming growth factor-beta 1. In contrast, transforming growth factor-beta 1 did not change apolipoprotein-E messenger RNA or transcription, or growth associated protein-43 messenger RNA levels. We conclude that transforming growth factor-beta 1 increases subsets of neuronal and astrocyte messenger RNAs coding for cytoskeletal proteins that are also elevated in response to experimental lesions and Alzheimer's disease. This suggests that transforming growth factor-beta 1 might be a local organizing factor of neuronal and astrocyte responses to brain injury.

Clusterin (SGP-2): a multifunctional glycoprotein with regional expression in astrocytes and neurons of the adult rat brain

Clusterin (SGP-2) is a newly described glycoprotein associated with several putative functions including responses to brain injury. This study reports the regional and cell type expression of clusterin mRNA and its encoded glycoprotein in the rat brain; a limited comparison was also done with the human brain. Using in situ hybridization combined with immunocytochemistry, we found that astrocytes and neurons may express clusterin mRNA in the normal adult brain. While astrocytes throughout the brain contained clusterin mRNA, there was regional selectivity for neuronal clusterin expression. In the striatum, clusterin mRNA was not detected in neurons. Only a subset of substantia nigra dopaminergic neurons or locus ceruleus noradrenergic neurons (tyrosine hydroxylase immunopositive) contained clusterin mRNA. However, neuronal clusterin mRNA was prevalent in pontine nuclei and in the red nucleus of the midbrain tegmentum. Similarly, clusterin mRNA was prevalent in both rat and human hippocampal neuron-specific enolase immunopositive pyramidal neurons, although rat CA1 neurons had less mRNA than CA2-CA3 neurons. Monotypic primary cell cultures from the neonatal rat showed clusterin mRNA in both neurons and astrocytes, but not in microglia. By immunocytochemistry, no clusterin immunopositive glia were observed in any region of the rat brain, confirming previous studies. However, clusterin immunopositive cells (putative neurons) were observed in the Purkinje cell layer of the cerebellum, medial and interposed cerebellar nuclei, trigeminal motor nucleus, and red nucleus. Finally, in vitro studies suggest that astrocytes, but not neurons, secrete clusterin, which is pertinent to clusterin immunodeposits found after experimental lesioning.