Sulfated glycoprotein-2 is increased in rat hippocampus following entorhinal cortex lesioning

Chaperone Proteins in the Central Nervous System and Peripheral Nervous System after Nerve Injury

Injury to axons of the central nervous system (CNS) and the peripheral nervous system (PNS) is accompanied by the upregulation and downregulation of numerous molecules that are involved in mediating nerve repair, or in augmentation of the original damage. Promoting the functions of beneficial factors while reducing the properties of injurious agents determines whether regeneration and functional recovery ensues. A number of chaperone proteins display reduced or increased expression following CNS and PNS damage (crush, transection, contusion) where their roles have generally been found to be protective. For example, chaperones are involved in mediating survival of damaged neurons, promoting axon regeneration and remyelination and, improving behavioral outcomes. We review here the various chaperone proteins that are involved after nervous system axonal damage, the functions that they impact in the CNS and PNS, and the possible mechanisms by which they act.

Clusterin/Apolipoprotein J immunoreactivity is associated with white matter damage in cerebral small vessel diseases

AIM

Brain clusterin is known to be associated with the amyloid-β deposits in Alzheimer's disease (AD). We assessed the distribution of clusterin immunoreactivity in cerebrovascular disorders, particularly focusing on white matter changes in small vessel diseases.

METHODS

Post-mortem brain tissues from the frontal or temporal lobes of a total of 70 subjects with various disorders including cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), cerebral amyloid angiopathy (CAA) and AD were examined using immunohistochemistry and immunofluorescence. We further used immunogold electron microscopy to study clusterin immunoreactivity in extracellular deposits in CADASIL.

RESULTS

Immunostaining with clusterin antibodies revealed strong localization in arterioles and capillaries, besides cortical neurones. We found that clusterin immunostaining was significantly increased in the frontal white matter of CADASIL and pontine autosomal dominant microangiopathy and leukoencephalopathy subjects. In addition, clusterin immunostaining correlated with white matter pathology severity scores. Immunostaining in axons ranged from fine punctate deposits in single axons to larger confluent areas with numerous swollen axon bulbs, similar to that observed with known axon damage markers such as non-phosphorylated neurofilament H and the amyloid precursor protein. Immunofluorescence and immunogold electron microscopy experiments showed that whereas clusterin immunoreactivity was closely associated with vascular amyloid-β in CAA, it was lacking within the granular osmiophilic material immunolabelled by NOTCH3 extracelluar domain aggregates found in CADASIL.

CONCLUSIONS

Our results suggest a wider role for clusterin associated with white matter damage in addition to its ability to chaperone proteins for clearance via the perivascular drainage pathways in several disease states.

Expression pattern of sulfated glycoprotein-2 (SGP-2) mRNA in rat testes exposed to endocrine disruptors

Sulfated glycoprotein-2 (SGP-2) is secreted in Sertoli cells and epididymal epithelial cells and plays important roles in the regulation of spermatogenesis and sperm maturation. To investigate whether endocrine disruptors affect spermatogenesis through an SGP-2-dependent mechanism, daily oral doses of testosterone (50, 200 and 1,000 microg/kg), flutamide (1, 5 and 25 mg/kg), ketoconazole (0.2, 1, 5 and 25 mg/kg), diethylhexylphthalate (10, 50 and 250 mg/kg), nonylphenol (10, 50, 100 and 250 mg/kg), octylphenol (10, 50 and 250 mg/kg), diethylstilbesterol (10, 20 and 40 microg/kg) or corn oil (control) were administered to 5 week-old, male Sprague-Dawley rats for 3 weeks. Following treatment with these endocrine disruptors, testicular expression of SGP-2 mRNA was analyzed using reverse transcription-polymerase chain reaction. Compared with the control, the lowest dose of testosterone (50 microg/kg/day) significantly increased expression of SGP-2 mRNA, whereas 200 and 1,000 microg/kg/day testosterone significantly decreased the expression (P<0.05). Flutamide, ketoconazole, diethylhexylphthalate, nonylphenol, octylphenol and diethylstilbesterol significantly decreased SGP-2 mRNA expression in testes at all doses studied, with the exception of 1 mg/kg/day flutamide (P<0.05). These results suggest that endocrine disruptors might decrease spermatogenesis in testes by decreasing expression of SGP-2 mRNA.

Progressive changes in regulation of apolipoproteins E and J in glial cultures during postnatal development and aging

Apolipoprotein (Apo) E and ApoJ are lipid- and cholesterol-carriers in the central nervous system and are implicated in age-related neurodegenerative diseases. The primary source of secreted ApoE and ApoJ (clusterin) in the brain is glia. Regulation of these apolipoproteins in mixed glial cultures from rat cerebral cortex differed most strongly between neonatal- and adult-derived glia. Basal secretion of ApoJ was two-fold greater in neonatal than adult glia. Responses to cytokines also differed by donor age. In adult glia, IL-6 increased ApoE secretion, but slightly decreased ApoJ. Both IL-1 beta and TNFalpha treatments increased ApoJ secretion from adult glia, with little effect on ApoE. In contrast to adult glia, neonatal ApoJ secretion did not respond to IL-1 beta, IL-6, or TNFalpha, and ApoE secretion from neonatal glia was slightly increased by IL-6. These differences may contribute to age-related neuroinflammatory processes, and are pertinent to the general use of neonatal-derived primary glia in models for neurodegenerative disease.

Molecules involved in reactive sprouting in the hippocampus

Denervation of the hippocampus triggers reactive responses in neurons and glial cells in their affected strata in a temporally ordered fashion. Many of these responses have been studied extensively, focusing on the one hand on glial initiation and clearing responses during the degeneration phase and, on the other, on transneuronal reorganization and the newly adjusted physiological balance. We used the entorhinal cortex lesion (ECL) as a model system to study the cues that underlie the layer-specific sprouting response. This lesion destroys the perforant path, which is a massive excitatory projection to the dentate gyrus and hippocampus proper. In the deafferented zones of the hippocampus, sprouting of the remaining unlesioned fibers occurs, which replaces the lost afferences of the perforant path. We focus on candidate molecules which govern the layer-specific sprouting of the remaining axons and, in particular, on membrane-bound cues. The fact that layer-specific sprouting occurs even in the adult central nervous system (CNS) provides a valuable model for understanding the mechanisms of reactive neuronal growth and reorganization in the adult CNS. Isolation and analysis of the molecules involved in these mechanisms are important steps in understanding the potential and limitations of regeneration in the CNS.

Alterations in ApoE and ApoJ in Relation to Degeneration and Regeneration in a Mouse Model of Entorhinal Cortex Lesion

Apolipoproteins are primarily involved in the transport of lipid and cholesterol within the central nervous system (CNS) and are thought to play a role in synaptic remodeling, repair, and regeneration after brain injury. In the present study, alterations in apolipoproteins E (apoE) and J (apoJ) were examined in the molecular layers of the dentate gyrus after unilateral chemical lesioning of the entorhinal cortex (ECL), at days 0, 1, 3, 7, 28, and 90 days following injury. Alterations in immunostaining for these proteins were assessed in relation to accumulation of silver-labeled degeneration products and alterations in synaptophysin and GAP-43 immunoreactivity. Quantitative analysis of synaptophysin and GAP-43 immunostaining highlighted synaptic loss and fiber degeneration initially (3-7 days post-ECL), with subsequent terminal sprouting and reactive synaptogenesis occurring at longer survival periods (28-90 days post-ECL). Increased apoE and apoJ immunoreactivity was evident first within the neuropil (*P < 0.05 and **P < 0.01) followed by intense glial staining by day 7 post-ECL. By day 28 apoE and apoJ immunostaining had returned almost to baseline levels. However, at day 90 post-ECL, neuropil apoE and apoJ immunoreactivity was dramatically increased compared to contralateral levels (**P < 0.01 and ***P < 0.0001, respectively). Silver-labeled degeneration products were found to be in abundance at day 3 postlesion; however, by day 7 this was reduced leaving only a thin band of material within the MML and at day 90 post-ECL, dentate silver staining was similar to that of controls. The results indicate that apoE and apoJ are upregulated after injury and parallel clearance of cholesterol and lipid debris from the site of injury. This coordinated alteration in apolipoproteins may redistribute lipid material to sprouting fibers to promote neurite extension and may play an important role in long-term plasticity changes following injury.

Spontaneous classical pathway activation and deficiency of membrane regulators render human neurons susceptible to complement lysis

This study investigated the capacity of neurons and astrocytes to spontaneously activate the complement system and control activation by expressing complement regulators. Human fetal neurons spontaneously activated complement through the classical pathway in normal and immunoglobulin-deficient serum and C1q binding was noted on neurons but not on astrocytes. A strong staining for C4, C3b, iC3b neoepitope and C9 neoepitope was also found on neurons. More than 40% of human fetal neurons were lysed when exposed to normal human serum in the presence of a CD59-blocking antibody, whereas astrocytes were unaffected. Significant reduction in neuronal cell lysis was observed after the addition of soluble complement receptor 1 at 10 microg/ml. Fetal neurons were stained for CD59 and CD46 and were negative for CD55 and CD35. In contrast, fetal astrocytes were strongly stained for CD59, CD46, CD55, and were negative for CD35. This study demonstrates that human fetal neurons activate spontaneously the classical pathway of complement in an antibody-independent manner to assemble the cytolytic membrane attack complex on their membranes, whereas astrocytes are unaffected. One reason for the susceptibility of neurons to complement-mediated damage in vivo may reside in their poor capacity to control complement activation.

Glial responses, clusterin, and complement in permanent focal cerebral ischemia in the mouse

There is considerable evidence that complement activation occurs within the CNS in inflammatory and degenerative disorders, but little is known about its involvement in the pathophysiology of cerebral ischemia. Our study sought to characterize the glial response and the expression of complement factors after permanent focal cerebral ischemia in the mouse, using semiquantitative reverse transcription-polymerase chain reaction (RT-PCR), in situ hybridization, and immunohistochemistry. mRNA expression of glial fibrillary acidic protein (GFAP) increased at day 1 and peaked 3 days after middle cerebral artery (MCA) occlusion in the perifocal area. Immunohistochemical staining for GFAP indicated that astroglia were activated the day after MCA occlusion. Microglial activation, as assessed by lectin-binding experiments, increased by 1 day after MCA occlusion in the perifocal area and peaked at 3 days postocclusion. RT-PCR experiments demonstrated an increased expression of clusterin, C1qB, and C4 mRNA in the ischemic cortex, with a peak level at 3 days after MCA occlusion. Clusterin, C1qB, and C4 mRNA were located in the perifocal area, as assessed by in situ hybridization. Reactive astrocytes within the cortex medial to the ischemic lesion were found to be strongly immunoreactive for clusterin. In addition, we observed C1q-positive macrophage-like cells within the infarcted core at 3 days postocclusion. At 7 days after the onset of ischemia, increased C4 immunostaining was restricted to perifocal neurons. We conclude that local expression of complement components may contribute to the inflammation observed in this model, thereby representing an important process in secondary injury mechanisms after focal cerebral ischemia.

Neuronal death and survival in two models of hypoxic-ischemic brain damage

Two unilateral hypoxic-ischemia (HI) models (moderate and severe) in immature rat brain have been used to investigate the role of various transcription factors and related proteins in delayed neuronal death and survival. The moderate HI model results in an apoptotic-like neuronal death in selectively vulnerable regions of the brain while the more severe HI injury consistently produces widespread necrosis resulting in infarction, with some necrosis resistant cell populations showing evidence of an apoptotic type death. In susceptible regions undergoing an apoptotic-like death there was not only a prolonged induction of the immediate early genes, c-jun, c-fos and nur77, but also of possible target genes amyloid precursor protein (APP751) and CPP32. In contrast, increased levels of BDNF, phosphorylated CREB and PGHS-2 were found in cells resistant to the moderate HI insult suggesting that these proteins either alone or in combination may be of importance in the process of neuroprotection. An additional feature of both the moderate and severe brain insults was the rapid activation and/or proliferation of glial cells (microglia and astrocytes) in and around the site of damage. The glial response following HI was associated with an upregulation of both the CCAAT-enhancer binding protein alpha (microglia only) and NFkappaB transcription factors.

The mosaic of brain glial hyperactivity during normal ageing and its attenuation by food restriction

Food restriction of adult rodents increases lifespan, with commensurate attenuation of age-related pathological lesions in many organs, as well as attenuation of normal ageing changes that are distinct from gross lesions. Previous work showed that chronic food restriction attenuated age-associated astrocyte and microglial hyperactivity in the hippocampal hilus, as measured by expression of glial fibrillary acidic protein and major histocompatibility complex II antigen (OX6). Here, we examined other markers of astrocyte and microglial activation in gray and white matter regions of ad libitum-fed (Brown Norway x Fischer 344) F1 male rats aged three and 24 months and chronic food-restricted rats aged 24 months. In situ hybridization and immunohistochemical techniques evaluated glial expression of glial fibrillary acidic protein, apolipoprotein E, apolipoprotein J (clusterin), heme oxygenase-1, complement 3 receptor (OX42), OX6 and transforming growth factor-beta1. All markers were elevated in the corpus callosum during ageing and were attenuated by food restriction, but other regions showed marked dissociation of the extent and direction of changes. Astrocytic activation, as measured with glial fibrillary acidic protein expression (coding and intron-containing RNA, immunoreactivity), increased with age in the corpus callosum, basal ganglia and hippocampus. Generally, food restriction attenuated the age-related increase in glial fibrillary acidic protein messenger RNA and immunoreactivity. Food restriction also reduced the age-related increase in apolipoprotein J and E messenger RNA and heme oxygenase-1 immunoreactivity in the basal ganglia and corpus callosum. However, astrocytes in the hilus of the hippocampus showed an age-related decrease in apolipoprotein J and E messenger RNA, which was further intensified by food restriction. The age-associated microglial activation measured by OX6 and OX42 immunoreactivity was reduced by food restriction in most subregions. The localized subsets of glial age changes and effects of food restriction comprise a mosaic of ageing consistent with the regional heterogeneity of ageing changes reported by others. In particular, age has a differential effect on astrocytic and microglial hyperactivity in gray versus white matter areas. The evident mosaic of glial ageing and responses to food restriction suggests that multiple mechanisms are at work during ageing.

Endogenous FGF-2 is important for cholinergic sprouting in the denervated hippocampus

To investigate the molecular mechanisms of cholinergic sprouting in the hippocampus after removal of entorhinal cortical inputs, we evaluated trophic factor gene expression in the denervated hippocampus. Despite the proposed role for nerve growth factor (NGF) in this sprouting, we observed no change in NGF mRNA or protein at several postlesion time points. In contrast, FGF-2 mRNA was increased within 16 hr. FGF-2 immunoreactivity was localized within GFAP-positive hypertrophic astrocytes distributed specifically within the denervated outer molecular layer after the lesion. To address the functional significance of this increase in FGF-2, we assessed the magnitude of cholinergic sprouting in animals receiving chronic intracerebroventricular infusions of neutralizing antibodies specific for FGF-2 and compared it with that observed in lesioned animals receiving infusate controls. Animals given FGF-2 antibodies displayed a marked reduction in cholinergic sprouting as compared with controls. In fact, many of these animals exhibited virtually no sprouting at all despite histological verification of complete lesions. These results suggest that endogenous FGF-2 promotes cholinergic axonal sprouting in the injured adult brain. Furthermore, immunocytochemical localization of receptors for FGF-2 (i.e., FGFR1) on projecting basal forebrain cholinergic neurons suggests that FGF-2 acts directly on these neurons to induce the lesion-induced sprouting response.

Clusterin (apolipoprotein J) protein levels are increased in hippocampus and in frontal cortex in Alzheimer's disease

We studied the multifunctional protein clusterin (apolipoprotein J, SGP-2, SP-40,40) in brain tissue using quantitative Western blotting and immunohistochemistry. The material included postmortem brains from 19 patients with Alzheimer's disease (AD), 6 with vascular dementia (VAD), and 7 age-matched control subjects. Intense clusterin staining was found in the soma of both neuronal and astroglial cells. In addition, positive staining was found in a portion of senile plaques (SP) in AD brains. Quantitative analysis showed that clusterin levels were significantly increased in AD, both in frontal cortex (150% of the control value, P = 0.002) and in the hippocampus (179% of the control value, P < 0.001), while normal clusterin levels were found in cerebellum (104% of the control value). No significant changes were found in VAD. Within the AD group, there was a significant negative correlation between clusterin levels in hippocampus and severity of dementia (r = -0.40), while no such correlation was found in frontal cortex (r = 0.12). No significant correlations were found between clusterin levels and the number of SP or neurofibrillary tangles. No significant differences in clusterin levels were found in any brain region between AD patients possessing different numbers of the ApoE4 allele. The increased clusterin levels in AD brain, together with the absence of a correlation between SP counts and clusterin levels, and the finding that clusterin is only found in a smaller portion of SP do not suggest a link between clusterin and beta-amyloid dependence. Instead we hypothesize that the increase is part of a regional response in AD brain.

Behavioural, physiological and morphological analysis of a line of apolipoprotein E knockout mouse

Using apolipoprotein E knockout mice derived from the Maeda source [Piedrahita J. A. et al. (1992) Proc. natn. Acad Sci. US.A. 89, 4471 4475], we have studied the influence of apolipoprotein E gene deletion on normal CNS function by neurological tests and water maze learning, hippocampal ultrastructure assessed by quantitative immunocytochemistry and electron microscopy, CNS plasticity, i.e. hippocampal long-term potentiation and amygdaloid kindling, and CNS repair, i.e. synaptic recovery in the hippocampus following deafferentation. In each study there was little difference between the apolipoprotein E knockout mice and wild-type controls of similar age and genetic background. Apolipoprotein E knockout mice aged eight months demonstrated accurate spatial learning and normal neurological function. Synaptophysin and microtubule-associated protein 2 immunohistochemistry and electron microscopic analysis of these animals revealed that the hippocampal synaptic and dendritic densities were similar between genotypes. The induction and maintenance of kindled seizures and hippocampal long-term potentiation were indistinguishable between groups. Finally, unilateral entorhinal cortex lesions produced a marked loss of hippocampal synaptophysin immunoreactivity in both groups and a marked up-regulation of apolipoprotein E in the wild-type group. Both apolipoprotein E knockout and wild-type groups showed immunohistochemical evidence of reactive synaptogenesis, although the apolipoprotein E knockout group may have initially shown greater synaptic loss. It is suggested that either apolipoprotein E is of no importance in the maintenance of synaptic integrity and in processes of CNS plasticity and repair, or more likely, alternative (apolipo)proteins may compensate for the loss of apolipoprotein E in the knockout animals.

Deleterious actions of chronic ethanol treatment on the glycosylation of rat brain clusterin

Clusterin is a N-glycosylated sialoglycoprotein present in rat brain cells. Clusterin, which elicits aggregation in a wide variety of cells, has been suggested to play an important role in synaptic remodeling through its cell adhesion property or lipid transport capacity in the brain. Sialic acid residues in clusterin may be responsible for its structural conformation, stability and functional ability. Maturation of clusterin is governed by the relative actions of sialyltransferases and sialidases that are present in brain microsomes, golgi bodies, cytosol and plasma membranes. We have earlier reported that chronic ethanol treatment in rats has a damaging effect on the hepatic glycosylation machinery. Others have reported increased hydrolysis of brain sialoconjugates in rats following chronic ethanol administration. Specificity of the effects of chronic ethanol treatment in the brain in relation to the glycosylation process, is still obscure. Therefore, in this investigation, we have studied the specific effects of chronic ethanol treatment on the glycosylation of rat brain clusterin and the causes that may lead to any possible defects in the glycosylation process. We have determined the effects of chronic ethanol treatment on (i) the incorporation of labeled leucine and N-acetylmannosamine into immunoprecipitable clusterin in whole brain homogenate, microsomes, golgi, cytosol, plasma membrane and synaptosomes, (ii) enzymatic activities of sialyltransferases in golgi and synaptosomes, and sialidase in brain cytosol and plasma membranes, and (iii) de novo synthetic rate of rat brain cytosolic sialidase. Our results showed that chronic ethanol treatment in rats resulted in (1) a decreased sialation index of brain clusterin by 47. 2% (p<0.001), 56.7% (p<0.05), 51.7% (p<0.05), 64.8% (p<0.001), and 54.5% (p<0.05), respectively, in whole brain homogenate, golgi, cytosol, plasma membranes, and synaptosomes; (2) a 46.1% (p<0.05) and 12.5% (p<0.05) decreased activities of brain sialyltransferases, respectively, in the golgi and the synaptosomal fractions; (3) a 70. 1% (p<0.05) and 42.6% (p<0.05) increased activities of sialidases, respectively, in the cytosol and plasma membrane fractions; and (4) a 22.2%-64.3% (p<0.001) increased incorporation of labeled leucine into brain cytosolic sialidase. Our findings have clearly established that long-term ethanol treatment in rats leads to a marked impairment in the glycosylation of rat brain clusterin as a result of altered activities of brain sialation and desialation enzymes. In particular, the specific increase noted in brain sialidase activity was due to concomitant increases in its synthetic rate. These defects in the glycosylation of brain clusterin may lead to changes in the molecular conformation of clusterin, and thus, may result in its structural instability and/or functional impairment.

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.

Life-long dietary restriction attenuates age-related increases in hippocampal glial fibrillary acidic protein mRNA

The expression of astrocyte-specific glial fibrillary acidic protein increases after experimental lesions and is elevated throughout the brain in aged rodents and primates. Clusterin (ApoJ) expression increases in astrocytes and microglia after lesions, but changes during aging have not been reported. Dietary restriction (DR) delays the onset and progression of many age-related physiological deficits in rodents. This study showed that the age-related increase in glial fibrillary acidic protein mRNA in the hippocampus was attenuated in 24-month-old male Fischer 344 rats subjected to a 50% DR beginning at 6 weeks of age. ApoJ mRNA expression in astrocytes was unchanged by DR. These results demonstrate that DR can delay neurodegeneration in aged rats as assessed by a marker of reactive astrogliosis.

The effect of estradiol-induced hypothalamic pathology on sulfated glycoprotein-2 (clusterin) expression in the hypothalamus

Sulfated glycoprotein-2 (SGP-2 or clusterin) is a complex multifunctional molecule that has been recently been implicated in neuronal degeneration and remodeling. We have shown that estradiol treatment results in a selective destruction of beta-endorphin neurons in the hypothalamic arcuate nucleus. We have used immunocytochemistry to determine the distribution of SGP-2 immunoreactivity in the rat hypothalamus and to assess the effects of the estradiol-induced destruction of beta-endorphin neurons on SGP-2 expression. We have found that SGP-2-immunopositive neurons normally occur in the medial preoptic area (MPOA), supraoptic nucleus (SON), paraventricular nucleus (PVN), dorsomedial nucleus (DM), and the lateral hypothalamic area (LHA) in both males and females. The neuropil appears free of label. Treatment with estradiol valerate results in the appearance of immunopositive punctate deposits in the neuropil in the MPOA, PVN and DM. The number and distribution of SGP-2-positive neurons are unaffected by estradiol treatment except in the MPOA, where there are twice as many SGP-2-positive neurons as in controls. These effects are precluded by treatment with vitamin E, with blocks the cytotoxic action of estradiol on beta-endorphin neurons. Thus, we interpret these changes as responses to the loss of beta-endorphin afferents.

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.

Inflammatory mechanisms in neurodegeneration and Alzheimer's disease: the role of the complement system

This review discusses key findings indicating potential roles of the complement (C)-system in chronic inflammation in Alzheimer's disease (AD) brain. Although there is no means to cure or prevent the disease, recent studies suggest that antiinflammatory drugs may delay the onset of AD dementia. One target of these drugs may be the (C)-system, which is best known for its roles in inflammatory processes in peripheral tissues. However, recent data show C-system expression and regulation in brain cells, and C-system protein deposition in AD plaques. It is still nuclear whether C-system activation contributes to neuropathology in the AD brain, as shown in multiple sclerosis (MS). New clinical studies with antiinflammatory agents are now under general consideration by the Alzheimer's Disease Cooperative Study program. In this review I outline research directions which address possible C-system contributions to neurodegeneration. Finally, I discuss potential pharmacological interventions designed to control segments of classical inflammatory cascades in which the C-system is highly implicated. These aspects are critical to the understanding of C-mediated responses in normal and pathologic brain.

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.

Role of clusterin in cell adhesion during early phases of programmed cell death in P19 embryonic carcinoma cells

This study explored the role of clusterin in mechanisms of cell adhesion and apoptosis in P19 embryonic carcinoma cells. We found that serum deprivation induced transient but dramatic elevation in cell adhesion strength to the culture substrate and eventually led to apoptotic cell death. The time course of cell-adhesion increase overlapped temporally with the elevation of clusterin mRNA (peak 8 h after serum deprivation). The coincidental elevation of clusterin expression and cell adhesion strength preceded the schedule of apoptotic cell death. Clusterin antiserum partially antagonized cell adhesion, but did not modify the course of apoptosis. These data suggest that clusterin expression may partially control cell adhesion with no influence on apoptosis in P19 cells, under defined conditions.

Association of apolipoprotein E genotype with brain levels of apolipoprotein E and apolipoprotein J (clusterin) in Alzheimer disease

This study examines the relationship between the levels of apolipoprotein E (apoE) and apolipoprotein J (apoJ, also designated as clusterin) as a function of apoE genotype in the hippocampus and cortex of Alzheimer disease (AD) subjects. These two lipophilic proteins which are involved in the maintenance of lipid homeostasis are both synthesized in the brain by astrocytes. Results indicate a reduction of apoE levels in the hippocampus and frontal cortex that is proportional to the apoE4 allele dose. Conversely, apoJ (clusterin) levels were found to increase proportionately to the number of apoE4 allele dose. These results suggest a compensatory induction of apoJ (clusterin) in the brain of apoE4 AD subjects showing low brain levels of apoE.

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.

The process of reinnervation in the dentate gyrus of adult rats: gene expression by neurons during the period of lesion-induced growth

Neurons in the hippocampal dentate gyrus are extensively reinnervated following the destruction of their normal inputs from the ipsilateral entorhinal cortex (EC). The present study evaluates gene expression by dentate granule neurons and the neurons giving rise to the sprouting connections during the period of synapse growth. Adult male rats were prepared for in situ hybridization at 2, 4, 6, 8, 10, 12, 14, 20, and 30 days following unilateral EC lesions. Sections were hybridized using 35S-labeled cRNA probes for mRNAs that encode proteins thought to be important for neuronal structure and/or synapse function, including (1) mRNAs that are normally present in dendrites--the mRNAs for the high molecular weight microtubule-associated protein 2 (MAP2) and the alpha-subunit of calcium/calmodulin-dependent protein kinase II (CAMII kinase), (2) mRNAs that are upregulated in neurons that are regenerating their axons (T alpha 1 tubulin and F1/GAP43) and (3) mRNAs for proteins that are the principal constituents of neurofilaments and microtubules (the low molecular weight neurofilament protein NF68 and beta-tubulin). Although there were small changes in the levels of labeling for the mRNAs that are normally present in dendrites, there were no dramatic increases in the levels of any of the mRNAs either in dentate granule cells or in neurons giving rise to the reinnervating fibers at any postlesion interval. These results indicate that neurons in mature animals can substantially remodel their synaptic terminals and their dendrites in the absence of large-scale changes in gene expression (at least as measured by steady-state mRNA levels at various time points).

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.

Temporally and spatially restricted expression of apolipoprotein J in the developing heart defines discrete stages of valve morphogenesis

During cardiac valve morphogenesis, a series of interactions between the mesodermal-derived myocardium and the overlying endothelium lead to condensed leaflet structure formation. At the atrioventricular (AV) canal, endocardial cells are transformed by specialized underlying myocardial cells into endocardial cushions, and then remodeled into mitral and tricuspid valves. Aortic and pulmonary valves develop by a similar mechanism in the primitive outflow tract. Few genes exhibit restricted spatiotemporal expression in these critical embryonic structures, thus limiting the clues to the sequence of molecular events necessary for valvulogenesis. Apolipoprotein J (ApoJ), a secreted glycoprotein expressed in a variety of cell types at tissue interfaces, exhibits a highly restricted and dynamic expression pattern in the developing heart. ApoJ transcripts were detected in mice at day 9.0 of gestation in the wall of the developing truncus arteriosus. By day 10, intense signal occurred in a thin layer of myocardial cells adjacent to developing endocardial cushions of both atrioventricular canal and truncus arteriosus. No apoJ mRNA was present in the overlying endocardial cushions until day 13.5 when prevalvular condensation begins. Intense expression occurred in the stromal connective tissue throughout leaflet formation. The highly restricted spatiotemporal expression pattern of apoJ in the developing heart implicates its role in the morphogenesis of the AV canal and outflow tract into cardiac valves.

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)

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.

Abnormal distribution of retinal clusterin in retinitis pigmentosa

Increased expression of clusterin mRNA is associated with neurodegenerative states, including retinas affected by retinitis pigmentosa (RP). We have investigated the distribution of immunoreactive clusterin in normal and RP-affected retinas. Reactivity at the inner limiting membrane, plexiform layers, and photoreceptors in normal retina accords well with clusterin's postulated role as a membrane protective agent. In RP-affected retina the organized distribution is lost and overall reactivity appears decreased. The changes in this case may reflect increased turnover or removal of clusterin, perhaps via interaction with components of the immune system.

Localization of sulfated glycoprotein-2/clusterin mRNA in the rat brain by in situ hybridization

Sulfated glycoprotein-2 (SGP-2) gene expression seems to be constitutively expressed in a variety of tissues and organs, although levels of expression vary widely from one tissue to the other. SGP-2, also known as clusterin, has been reported to be expressed in the central nervous system (CNS). Some possible roles for brain SGP-2 have been postulated. In order to provide a substrate for a better understanding of the functions of this glycoprotein in the CNS, we investigated the detailed anatomical and cellular distribution of SGP-2 mRNA in the adult rat brain as well as the variation in its cellular expression after excitotoxin lesion. Transcripts for SGP-2 were found to be distributed throughout the rat CNS, although regional differences in their prevalence were readily observed. The ependymal lining of the ventricles showed the highest level of expression followed by various gray matter areas, some of which contained very intensively labeled cells. These cells were mostly found among several hypothalamic and brainstem nuclei, the habenular complex, as well as in the ventral horn of the spinal cord, which displayed striking hybridization signals over motoneurons. Occasional cells expressing high levels of SGP-2 transcripts were found in fiber tracts. Highly SGP-2 mRNA-positive resting glial cells were mainly located near the glial limitans and blood vessels. Two areas of relatively low constitutive SGP-2 mRNA expression are shown to produce strong hybridization signals 10 days after the local administration of the excitotoxin kainic acid. This overexpression of SGP-2 transcripts appears to involve GFAP-positive cells. Taken together, these results indicate that in the intact adult rat CNS, various cell populations, including neurons, constitutively express SGP-2 transcripts, whereas in the injured brain, reactive astrocytes become the major producers.

Increases in sulphated glycoprotein-2 mRNA levels in the rat brain after transient forebrain ischemia or partial mesodiencephalic hemitransection

Sulphated glycoprotein-2, thought to be involved in programmed cell death in peripheral organs, has been detected at increased levels in brain degenerative states. In this paper we have investigated the regional and cellular expression of this protein during development of brain lesion. With this aim sulphated glycoprotein-2 mRNA levels were studied in models of ischemic (transient forebrain ischemia) or mechanical (partial mesodiencephalic hemitransection) brain injuries using in situ hybridization histochemistry. Marked increases in sulphated glycoprotein-2 mRNA were observed in lesioned brains in both models. In addition, we report a shift in the regional distribution of positive cells in both lesion models 1-7 days post-lesion. After transient forebrain ischemia, sulphated glycoprotein-2 mRNA increases were always localized in selectively vulnerable regions (caudate-putamen, hippocampal formation), showing a temporal change in the pattern of intraregional distribution from less to more lesioned parts. In the case of mechanical lesion at 1 day, increased labelling had a widespread distribution on the lesioned side and was also observed on the intact side near the midline. In contrast, at 7 days increased labelling was restricted to regions directly lesioned (either areas whose input and/or output connections were severed by the transection or areas which were directly affected by the mechanical lesion). Analysis at the cellular level revealed that at both time intervals and in both lesion models most cell bodies overlain by dense clusters of specific grains were non-neuronal cells. The distribution patterns and their change over time suggest that at least some of these cells are inflammatory and phagocytic cells. The majority of degenerating neuronal cells after ischemia did not show increased levels of sulphated glycoprotein-2 mRNA. However, seven days after hemitransection and at all time intervals after transient ischemia, some cells clearly identifiable as neurons exhibited increased sulphated glycoprotein-2 mRNA levels.

Astrocytic messenger RNA responses to striatal deafferentation in male rat

This investigation describes the schedule and regional distribution of astrocytic responses in striatum following deafferentation by unilateral frontal cortex ablation. In the ipsilateral deafferented striatum, glial fibrillary acidic protein and clusterin (sulfated glycoprotein-2) messengerRNA showed peak elevations by 10 days postlesioning (Northern blots). Vimentin messengerRNA responded faster, with a transient elevation by three days postlesioning. The messengerRNA for glial fibrillary acidic protein, clusterin and vimentin returned toward control levels by 27 days postlesioning. However, the neuronal marker growth-associated protein messengerRNA, was decreased at all postlesion times. By in situ hybridization, the increased glial fibrillary acidic protein messengerRNA and clusterin messengerRNA signals were localized mainly to the dorsal half of the ipsilateral deafferented striatum and followed the same schedule as found by Northern blots. Glial fibrillary acidic protein messengerRNA was widely diffused in the dorsal striatum and was excluded from fascicles of the internal capsule; a similar distribution was found for glial fibrillary acidic protein-immunopositive astrocytes. While clusterin messengerRNA signal showed a distinct clustering, its immunoreactivity appeared as deposits in the deafferented striatal neuropil; Western blots confirmed the immunocytochemical results. By in situ hybridization, vimentin messengerRNA was mostly localized to the cortical wound cavity dorsal to the deafferented striatum and overlapped the distribution of vimentin-immunopositive cells. These findings suggest a coordination of striatal astrocytic messengerRNA responses with the degeneration of corticostriatal afferents. We also compared these same parameters with those from published reports on the hippocampus after deafferenting lesions. Certain astrocyte molecular responses to deafferentation are detected about five days earlier in the hippocampus than in the striatum. This different schedule in response to decortication may pertain to differences in synaptic remodeling in the hippocampus vs striatum.

Complement C1qB and C4 mRNAs responses to lesioning in rat brain

These data show the presence of mRNAs for two complement components (C) in the adult rat brain and describe their responses to experimental lesions. Cortical deafferentation caused elevations in striatal C1qB and C4 mRNAs that coincided temporally and overlapped anatomically with the course of degeneration of corticostriatal afferent fibers. By in situ hybridization, C1qB mRNA in the lesioned striatum was colocalized to cells immunoreactive for CR3, a complement receptor found on microglia-macrophages. The mRNA for SGP-2, a putative C inhibitor in rat, showed parallel changes. Similarly, in hippocampus and other brain regions, kainic acid lesions increased C1qB mRNA. The data suggest that microglia-macrophages and possibly other cells in rat brain rapidly up-regulate C-mRNAs in response to deafferentation and local neuron injury. These experimental responses provide models to analyze changes in C components during Alzheimer's disease and other chronic neurodegenerative conditions.

Complement mRNA in the mammalian brain: Responses to Alzheimer's disease and experimental brain lesioning

This study describes evidence in the adult human and rat brain for mRNAs that encode two complement (C) proteins, C1qB and C4. C proteins are important effectors of humoral immunity and inflammation in peripheral tissues but have not been considered as normally present in brain. Previous immunocytochemical studies showed that C proteins are associated with plaques, tangles, and dystrophic neurites in Alzheimer's disease (AD), but their source is unknown. Combined immunocytochemistry and in situ hybridization techniques show C4 mRNA in pyramidal neurons and C1qB mRNA in microglia. Primary rat neuron cultures also show C1qB mRNA. In the cortex from AD brains, there were two- to threefold increases of C1qB mRNA and C4 mRNA, and increased C1qB mRNA prevalence was in part associated with microglia. As a model for AD, we examined entorhinal cortex perforant path transection in the rat brain, which caused rapid increases of C1qB mRNA in the ipsilateral, but not contralateral, hippocampus and entorhinal cortex. The role of brain-derived acute and chronic C induction during AD and experimental lesions can now be considered in relation to functions of C proteins that pertain to cell degeneration and/or cell preservation and synaptic plasticity.

Sulfated glycoprotein 2: new relationships of this multifunctional protein to neurodegeneration

Sulfated glycoprotein 2 (SGP-2) from rat, and similar molecules from cow, dog, human, pig, ram and quail are known by 11 or more acronyms. SGP-2 is associated with the responses of brain and other tissues to injury; it and related molecules are also normally secreted by the adrenal gland, the liver and the testes. The mRNA of this protein is found in increased levels in Alzheimer's disease. In rats, after perforant path or excitotoxin lesions, levels of the protein or mRNA are elevated in astrocytes, and also in neurons. In rats, brain SGP-2 is regulated by gonadal and adrenal steroids. However, these increases after brain lesions may relate to a function that is associated with the human protein, namely that of inhibiting complement-mediated cell lysis. Other activities suggested for SGP-2 are lipid transport and cell-cell interactions, which are consistent with sequence data that predict binding of dinucleotides, heparin and lipids. The emerging neurobiology of SGP-2 encompasses the subjects of cell death, synaptic remodelling, neuroendocrinology and neurodegenerative diseases.

Sulfated glycoprotein-2 expression increases in rodent brain after transient global ischemia

Sulfated glycoprotein-2 (SGP-2) is emerging as a prominent marker of neurodegeneration in mammalian brain. Regulation of brain SGP-2 was studied in adult male Wistar rats subjected to 30 min of forebrain ischemia by four vessel occlusion. By 3 days after the ischemic insult, SGP-2 RNA levels were increased two fold in caudate nucleus and hippocampus. SGP-2 protein levels assessed by immunoblots were markedly increased in both brain regions following ischemia. GFAP RNA levels also increased over 5 fold in caudate nucleus and hippocampus following the ischemic insult. Despite significant elevations in GFAP RNA, protein levels of GFAP assessed by immunoblot were only marginally affected. The elevated expression of SGP-2 in rodent brain following this and other experimental lesion paradigms (e.g., excitotoxic lesions, deafferentation) suggest some general involvement of SGP-2 in neurodegeneration and remodelling following neuronal injury.