Induction of SC1 mRNA Encoding a Brain Extracellular Matrix Glycoprotein Related to SPARC following Lesioning of the Adult Rat Forebrain

SC1 is an extracellular matrix (ECM) glycoprotein related to SPARC which exhibits anti-adhesive properties. ECM molecules are thought to play important roles in influencing cell shape, proliferation and migration during neurogenesis. Following localized injury to the adult rat forebrain, a biphasic induction of SC1 mRNA was apparent, namely a rapid, transient induction at 1 day post-lesion in cortical neurons which border the lesion site followed by a more prolonged induction in astrocytes which are proximal to the wound site. A similar SC1 induction pattern was observed in the hippocampus in response to the injury. SPARC mRNA exhibits a divergent pattern of induction because it is induced in mature blood vessels close to the lesion and in blood vessels which develop following the trauma. Thus mRNAs encoding the related ECM glycoproteins SC1 and SPARC are induced in different cell populations in the adult forebrain during the neural response to localized injury.     

Differential expression of connexin43 in foetal,adult and tumour-associated human brain endothelial cells

Connexin43 (Cx43), the main protein constituting the gap junctions between astrocytes, has previously been demonstrated in endothelial cells of somatic vessels where the intercellular coupling that it provides plays a role in endothelial proliferation and migration. In this study, Cx43 expression was analysed in human brain microvascular endothelial cells of the cortical plate of 18-week foetal telencephalon, in adult cerebral cortex and glioma (astrocytomas). The study was carried out by immunocytochemistry utilizing a Cx43 monoclonal antibody and a polyclonal antibody anti-GLUT1 (glucose transporter isoform 1) to identify the endothelial cells and to localize Cx43. Endothelial Cx43 is differently expressed in the cortical plate, cerebral cortex and astrocytoma. Within the cortical plate and tumour, Cx43 is highly expressed in microvascular endothelial cells whereas it is virtually absent in the cerebral cortex microvessels. The high expression of the gap junction protein in developing brain, as well as in brain tumours, may be related to the growth status of the microvessels during brain and tumour angiogenesis. The lack of endothelial Cx43 in the cerebral cortex is in agreement with the characteristics of the mature brain endothelial cells that are sealed by tight junctions. In conclusion, the results indicate that endothelial Cx43 expression is developmentally regulated in the normal human brain and suggest that it is controlled by the microenvironment in both normal and tumour-related conditions.     

高压氧对急性脑创伤后皮层一氧化氮合酶mRNA表达的影响

目的:拟观察高压氧(HBO)治疗对急性创伤性颅脑损伤后皮层NOSmRNA表达的影响,探讨HBO治疗急性脑损伤的机理。方法:采用自由落体法打击模型制备SD大鼠急性脑创伤,伤后1 h、12 h采用0.25 MPaHBO治疗,伤后6 h、24 h取样皮层,应用半定量逆转录聚合酶链反应(RT-PCR)观察神经元型一氧化氮合酶(nNOS)、内皮型一氧化氮合酶(eNOS)和诱导型一氧化氮合酶(iNOS)mRNA表达量变化。结果:0.25MPaHBO治疗各时间组nNOS、eNOS和iNOSmRNA较急性颅脑损伤各时间组显著下降(P<0.01),且HBO治疗24 h组较6 h组下降更明显(P<0.05,P<0.01),0.25 MPa常氧高氮各时间组与急性颅脑损伤各时间组NOSmRNA表达量无统计学意义。结论:HBO治疗可以下调nNOSmRNA、iNOSmRNA和eNOSmRNA的表达量,可能为HBO治疗脑创伤的机理之一。     

Identification of Cortexin: A Novel, Neuron-Specific, 82-Residue Membrane Protein Enriched in Rodent Cerebral Cortex

Abstract: Nucleotide sequence analysis of a cDNA clone of a rat cortex-enriched mRNA identifies a novel integral membrane protein of 82 amino acids. The encoded protein is named cortexin to reflect its enriched expression in cortex. The amino acid sequence of rat cortexin and its mouse homologue are nearly identical (98% similarity), and both contain a conserved single membrane-spanning region in the middle of each sequence. Northern blot analysis shows that cortexin mRNA is brain-specific, cortexenriched, and present at significant levels in fetal brain, with peak expression in postnatal rodent brain. In situ hybridization studies detect cortexin mRNA primarily in neurons of rodent cerebral cortex, but not in cells of the hindbrain or white matter regions. The function of cortexin may be particularly important to neurons of both the developing and adult cerebral cortex.     

Region-specific effects of hypothyroidism on the relative expression of thyroid hormone receptors in adult rat brain

The aim of this study was to determine whether changes in the circulating thyroid hormone (TH) and brain synaptosomal TH content affected the relative levels of mRNA encoding different thyroid hormone receptor (TR) isoforms in adult rat brain. Northern analysis of polyA⁺RNA from cerebral cortex, hippocampus and cerebellum of control and hypothyroid adult rats was performed in order to determine the relative expression of all TR isoforms. Circulating and synaptosomal TH concentrations were determined by radioimmunoassay. Region-specific quantitative differences in the expression pattern of all TR isoforms in euthyroid animals and hypothyroid animals were recorded. In hypothyroidism, the levels of TRα2 mRNA (non-T₃-binding isoform) were decreased in all brain regions examined. In contrast the relative expression of TRα1 was increased in cerebral cortex and hippocampus, whereas in cerebellum remained unaffected. The TRβ1 relative expression in cerebral cortex and hippocampus of hypothyroid animals was not affected, whereas this TR isoform was not detectable in cerebellum. The TR isoform mRNA levels returned to control values following T₄ intraperitoneal administration to the hypothyroid rats. The obtained results show that in vivo depletion of TH regulates TR gene expression in adult rat brain in a region-specific manner. (Mol Cell Biochem 278: 93–100, 2005)     

Differential regulation of metallothionein-I and metallothionein-II mRNA expression in the rat brain following traumatic brain injury

In this study, we investigated the expression of metallothionein (MT)-I and MT-II in the rat brain following traumatic brain injury (TBI). In the early stage, significant induction of MT-I and MT-II were observed in various regions including ventricle walls, pia mater, and dentate gyrus. At 12-24 h after TBI, strong induction of MT-I mRNA was observed in cerebral cortical layer II/III, amygdala, and piriform cortex where neurons reside. On the other hand, MT-II appeared to be expressed mainly in glial cells localized in the cerebral cortex and hippocampal formation. Three days after TBI, MTs were observed in the vimentin-positive astrocytes in the penumbra as revealed by double immunohistochemistry. The differences in expression of MT-I and MT-II in different brain regions and cell types (neuron vs. glial cells) suggests that multiple regulatory mechanisms are involved in the control of MT expression following brain injury.     

Estrogen receptor-alpha gene expression in the cortex: Sex differences during development and in adulthood

17β-estradiol is a hormone with far-reaching organizational, activational and protective actions in both male and female brains. The organizational effects of early estrogen exposure are essential for long-lasting behavioral and cognitive functions. Estradiol mediates many of its effects through the intracellular receptors, estrogen receptor-alpha (ERα) and estrogen receptor-beta (ERβ). In the rodent cerebral cortex, estrogen receptor expression is high early in postnatal life and declines dramatically as the animal approaches puberty. This decline is accompanied by decreased expression of ERα mRNA. This change in expression is the same in both males and females in the developing isocortex and hippocampus. An understanding of the molecular mechanisms involved in the regulation of estrogen receptor alpha (ERα) gene expression is critical for understanding the developmental, as well as changes in postpubertal expression of the estrogen receptor. One mechanism of suppressing gene expression is by the epigenetic modification of the promoter regions by DNA methylation that results in gene silencing. The decrease in ERα mRNA expression during development is accompanied by an increase in promoter methylation. Another example of regulation of ERα gene expression in the adult cortex is the changes that occur following neuronal injury. Many animal studies have demonstrated that the endogenous estrogen, 17β-estradiol, is neuroprotective. Specifically, low levels of estradiol protect the cortex from neuronal death following middle cerebral artery occlusion (MCAO). In females, this protection is mediated through an ERα-dependent mechanism. ERα expression is rapidly increased following MCAO in females, but not in males. This increase is accompanied by a decrease in methylation of the promoter suggesting a return to the developmental program of gene expression within neurons. Taken together, during development and in adulthood, regulation of ERα gene expression in the cortex can occur by DNA methylation and in a sex-dependent fashion in the adult brain.     

Inductin of neuron-derived orphan receptor-1 in the dentate gyrus of the hippocampal formation following transient global ischemia in the rat

Neuron-derived orphan receptor (NOR-1) is a member of the thyroid/steroid receptor superfamily that was originally identified in forebrain neuronal cells undergoing apoptosis. In addition to apoptotic stimuli, activation of several signal transduction pathways including direct neuronal depolarization regulates the expression of NOR-1. In this study we tested whether the expression of NOR-1 is changed following transient ischemic injury in the adult rat brain. NOR-1 mRNA increased rapidly in the dentate gyrus of the hippocampal formation and piriform cortex 3 h after transient global ischemia and returned to basal level at 6 h. On the other hand, oxygen-glucose deprivation of cultured cerebral cortical neurons did not alter the expression of NOR-1. These results suggest that expression of NOR-1 is differentially regulated in different brain regions in response to globally applied brain ischemia, but that hypoxia is not sufficient to induce its expression.     

Distribution of alcohol dehydrogenase mRNA in the rat central nervous system. Consequences for brain ethanol and retinoid metabolism.

The localization of alcohol dehydrogenase (ADH) in brain regions would demonstrate active ethanol metabolism in brain during alcohol consumption, which would be a new basis to explain the effects of ethanol in the central nervous system. Tissue sections from several regions of adult rat brain were examined by in situ hybridization to detect the expression of genes encoding ADH1 and ADH4, enzymes highly active with ethanol and retinol. ADH1 mRNA was found in the granular and Purkinje cell layers of cerebellum, in the pyramidal and granule cells of the hippocampal formation and in some cell types of cerebral cortex. ADH4 expression was detected in the Purkinje cells, in the pyramidal and granule cells of the hippocampal formation and in the pyramidal cells of cerebral cortex. High levels of ADH1 and ADH4 mRNAs were detected in the CNS epithelial and vascular tissues: leptomeninges, choroid plexus, ependymocytes of ventricle walls, and endothelium of brain vessels. Histochemical methods detected ADH activity in rodent cerebellar slices, while Western-blot analysis showed ADH4 protein in homogenates from several brain regions. In consequence, small but significant levels of ethanol metabolism can take place in distinct areas of the CNS following alcohol consumption, which could be related to brain damage caused by a local accumulation of acetaldehyde. Moreover, the involvement of ADH in the synthesis of retinoic acid suggests a role for the enzyme in the regulation of adult brain functions. The impairment of retinol oxidation by competitive inhibition of ADH in the presence of ethanol may be an additional origin of CNS abnormalities caused by ethanol.     

Induction of a heat shock gene at the site of tissue injury in the rat brain

Our objective was to investigate whether localized tissue injury induces expression of a gene encoding the major 70 kd heat shock protein (hsp70) in the mammalian nervous system. A small surgical cut was made in the rat cerebral cortex. By 2 hr postsurgery a dramatic and highly localized induction of hsp70 mRNA was detected at the lesion site using in situ hybridization with labeled riboprobe. By 12 hr the intensity of the signal had diminished, and by 24 hr only a few cells along the walls of the cut demonstrated a high level of hsp70 mRNA. Both neurons and glial cells at the site of the surgical cut responded to tissue injury by induction of hsp70 mRNA. Induction was not observed in other brain regions, nor was the pattern of constitutive expression affected by the surgical procedure.     

Hippocampal SPARC regulates depression‐related behavior

SPARC (secreted protein acidic and rich in cysteine) is a matricellular protein highly expressed during development, reorganization and tissue repair. In the central nervous system, glial cells express SPARC during development and in neurogenic regions of the adult brain. Astrocytes control the glutamate receptor levels in the developing hippocampus through SPARC secretion. To further characterize the role of SPARC in the brain, we analyzed the hippocampal‐dependent adult behavior of SPARC KO mice. We found that SPARC KO mice show increased levels of anxiety‐related behaviors and reduced levels of depression‐related behaviors. The antidepressant‐like phenotype could be rescued by adenoviral vector‐mediated expression of SPARC in the adult hippocampus, but anxiety‐related behavior persisted in these mice. To identify the cellular mechanisms underlying these behavioral alterations, we analyzed neuronal activity and neurogenesis in the dentate gyrus (DG). SPARC KO mice have increased levels of neuronal activity, evidenced as more neurons that express c‐Fos after a footshock. SPARC also affects cell proliferation in the subgranular zone of the DG, although it does not affect maturation and survival of new neurons. SPARC expression in the adult DG does not revert the proliferation phenotype in KO mice, but our results suggest a role of SPARC in limiting the survival of new neurons in the DG. This work suggests that SPARC could affect anxiety‐related behavior by modulating neuronal activity, and that depression‐related behavior is dependent upon the adult expression of SPARC, which affects adult brain function by mechanisms that need to be elucidated.     

Expression of cytosolic branched chain aminotransferase (BCATc) mRNA in the developing mouse brain

Branched-chain aminotransferase (BCAT) catalyzes the transamination of essential branched-chain amino acids (BCAAs: leucine, isoleucine and valine) with alpha-ketoglutarate. Through this reaction, BCAAs provide nitrogen for the synthesis of glutamate, the predominant excitatory neurotransmitter. Two BCAT isoforms have been identified: one cytosolic (BCATc) and one mitochondrial (BCATm). In adult rodents, BCATc is expressed in a wide variety of structures of the central nervous system (CNS), in neurons. So far, no data were available about the expression of BCATc in the developing CNS. Here, we analyse the expression profile of BCATc mRNA in the mouse brain from embryonic day 12.5 to adult age. BCATc mRNA gradually appears in different brain regions starting from early stages of neural development, and is maintained until adulthood. BCATc mRNA is predominantly present in the cerebral cortex, hippocampus, thalamus, ventral midbrain, raphe, cerebellum and precerebellar system. This study represents the first detailed analysis of BCATc mRNA expression in the developing mouse brain.     

Increased Expression of Apolipoprotein D Following Experimental Traumatic Brain Injury

Increasing evidence suggests that apolipoprotein D (apoD) could play a major role in mediating neuronal degeneration and regeneration in the CNS and the PNS. To investigate further the temporal pattern of apoD expression after experimental traumatic brain injury in the rat, male Sprague-Dawley rats were subjected to unilateral cortical impact injury. The animals were killed and examined for apoD mRNA and protein expression and for immunohistological analysis at intervals from 15 min to 14 days after injury. Increased apoD mRNA and protein levels were seen in the cortex and hippocampus ipsilateral to the injury site from 48 h to 14 days after the trauma. Immunohistological investigation demonstrated a differential pattern of apoD expression in the cortex and hippocampus, respectively: Increased apoD immunoreactivity in glial cells was detected from 2 to 3 days after the injury in cortex and hippocampus. In contrast, increased expression of apoD was seen in cortical and hippocampal neurons at later time points following impact injury. Concurrent histopathological examination using hematoxylin and eosin demonstrated dark, shrunken neurons in the cortex ipsilateral to the injury site. In contrast, no evidence of cell death was observed in the hippocampus ipsilateral to the injury site up to 14 days after the trauma. No evidence of increased apoD mRNA or protein expression or neuronal pathology by hematoxylin and eosin staining was detected in the contralateral cortex and hippocampus. Our results reveal induction of apoD expression in the cortex and hippocampus following traumatic brain injury in the rat. Our data also suggest that increased apoD expression may play an important role in cortical neuronal degeneration after brain injury in vivo. However, increased expression of apoD in the hippocampus may not necessarily be indicative of neuronal death.