Carbonic anhydrase II in microglia in forebrains of neonatal rats

Gangliosides in Nerve Cell Specification

The central nervous system is generated from progenitor cells that are recognized as neural stem cells (NSCs). NSCs are defined as undifferentiated neural cells that are characterized by the capacity for self-renewal and multipotency. Throughout neural development, NSCs undergo proliferation, migration, and cellular differentiation, and dynamic changes are observed in the composition of carbohydrate-rich molecules, including gangliosides. Gangliosides are sialic acid-containing glycosphingolipids with essential and multifaceted functions in brain development and NSC maintenance, which reflects the complexity of brain development. Our group has pioneered research on the importance of gangliosides for growth factor receptor signaling and epigenetic regulation of ganglioside biosynthesis in NSCs. We found that GD3 is the predominant ganglioside species in NSCs (>80%) and modulates NSC proliferation by interacting with epidermal growth factor receptor signaling. In postnatal brain, GD3 is required for long-term maintenance of NSCs. Deficiency in GD3 leads to developmental and behavioral deficits, such as depression. The synthesis of GD3 is switched to the synthesis of complex, brain-type gangliosides, namely, GM1, GD1a, GD1b, and GT1b, resulting in terminal differentiation and loss of "stemness" of NSCs. In this process, GM1 is augmented by a novel GM1-modulated epigenetic gene regulation mechanism of glycosyltransferases at a later differentiation stage. Consequently, our research suggests that stage-specific gangliosides play specific roles in maintaining NSC activities and in cell fate determination.

Reduction of CAII Expression in Gastric Cancer: Correlation with Invasion and Metastasis

OBJECTIVE

Human carbonic anhydrases II (CAII) gene plays an important role in different cancer. However, its relevance to gastric cancer (GC) remains unclear. In the present study, we aimed to investigate the expression of CAII in GC and explore its correlation with some clinicopathologic characteristics of GC.

METHODS

The expression of CAII in 20 specimens of normal gastric mucosa, 38 specimens of intraepithelial neoplasia and 112 specimens of gastric carcinoma were detected by immunohistochemical techniques. Survival in GC with CAII expression was studied.

RESULTS

The positive rate of CAII protein in normal gastric mucosa was significantly higher than that in intraepithelial neoplasia and gastric carcinoma (100% vs. 63.16% and 28.57%, P<0.001). The positive rate of CAII protein was significantly higher in gastric carcinoma at early stages than that at advanced stages (70.0% vs. 19.57%, P<0.001). The positive rate of CAII protein was significantly lower in gastric carcinoma with lymph node metastases than that without lymph node metastases (10.81% vs. 37.33%, P<0.05). Furthermore, the positive rate of CAII protein was significantly lower in poorly-differentiated gastric carcinoma than in moderately- or well-differentiated gastric carcinoma (15.94% vs. 31.03% or 60.00%, P<0.05). Moreover, CAII expression was not related with sex, age and tumor size. The patients with CAII-positive tumors showed a better survival rate than those with CAII-negative tumors (P=0.024, log-rank test).

CONCLUSION

CAII expression was related with stages and lymph node metastases in gastric carcinoma. The reduction of CAII expression in GC might promote tumor cell motility and contribute to tumor growth and metastasis.

Phagocytosis of degenerating myelin in transected feline optic nerve: an immunohistochemical study

The phagocytic activity of neuroglial cells in adult feline degenerating optic nerve was investigated by immunocytochemistry at both light and electron microscopy levels. Degeneration was initiated by unilateral eye enucleation and the segment distal to the transection showing true Wallerian degeneration was examined. Following enucleation, twelve adult domestic cats were examined over a period of seven to 215 days. All cases showed slow clearance of myelin debris and absence of proliferating monocytes throughout the post-enucleation period. All phagocytic cells present were neuroglial cells, and many of these cells expressed oligodendroglial antigens. These findings demonstrate the persistence of an active population of oligodendrocytes that might play an additional functional role during Wallerian degeneration of feline optic nerve.

Carbonic anhydrase II in the developing and adult human brain

Carbonic anhydrase II (CA II) is one of 14 isozymes of carbonic anhydrases, zinc metalloenzymes that catalyze the reversible hydration of carbon dioxide to bicarbonate. Mutations in CA II in humans lead to osteopetrosis with renal tubular acidosis and cerebral calcifications, a disorder often associated with mental retardation. Recently, new avenues in CA II research have opened as a result of discoveries that the enzyme increases bicarbonate and proton fluxes and may play an important role in brain tissue. In the human brain, CA II was localized to oligodendrocytes, myelin, and choroid plexus epithelium. Because this conclusion was based on a few fragmentary reports, we analyzed in more detail the expression of the enzyme in human telencephalon. By immunoblotting, we found a gradual increase in CA II levels from 17 weeks' gestation to childhood and adolescence. By immunohistochemistry, CA II was found to be present not only in oligodendrocytes and choroid plexus epithelium (declining with aging in both these locations), but also in a subset of neurons mostly with GABAergic phenotype, in a few astrocytes, and transiently during brain development in the endothelial cells of microvessels. The enzyme also occurred in oligodendrocyte processes in contact with myelinating axons, myelin sheaths, and axolemma, but was either absent or appeared in minute amounts in compact myelin. These findings suggest the possible involvement of CA II in a wide spectrum of biologic processes in the developing and adult human brain and may contribute to better understanding of the pathogenesis of cerebral calcifications and mental retardation caused by CA II deficiency.

Expression of carbonic anhydrases II, IV, VII, VIII and XII in rat brain after kainic acid induced status epilepticus

Carbonic anhydrases (CAs) are important enzymes in the central nervous system (CNS), where they participate in regulating cerebrospinal fluid (CSF) secretion, blood-brain barrier and glial cell function. Using RT-PCR we found CA XII mRNA in rat and mouse brain. Cloning of rat CA XII revealed 94% homology with the mouse CA XII. To map the putative functional roles of different CAs, we studied the expression and localization of CA II, CA IV, CA VII, CA-related protein (CA-RP) VIII and CA XII mRNAs in rat brain after kainic acid induced epileptic seizures using Northern blot analysis and in situ hybridization. The expression of CA IV, CA VII and CA-RP VIII was somewhat similar: they were expressed in the cortex, hippocampus and midbrain structures and their expression did not change after the kainic acid treatment. The expression of CA II was concentrated in the white matter structures, which is in line with the preferential expression of CA II in the oligodendrocytes. High levels of CA II mRNA were also detected in the choroid plexus. Surprisingly, CA II was induced 3-12 h after seizures in the vulnerable CA1 region. CA XII was expressed in dentate granule cells, cortex and choroid plexus. Kainic acid stimulated CA XII expression throughout the cortical layer I. The observed hippocampal induction of CA II may indicate a pro-apoptotic and/or epileptogenic role of CA II after prolonged seizures. The physiological significance of the observed cortical induction of CA XII remains obscure. Cytosolic CA II is known to participate in CSF secretion, and the high expression of CA XII in the choroid plexus suggests an analogous role for this membrane-bound isozyme.

Visualization of microglia in living tissues using Iba1-EGFP transgenic mice

Microglia are thought to play important roles not only in repairing injured tissue but in regulating neuronal activity, and visualizing the cells is very useful as a means of further investigating the function of microglia in vivo. We previously cloned the ionized calcium-binding adaptor molecule 1 (Iba1) gene, which is expressed selectively in microglia/microphages. To generate new transgenic mice to visualize microglia with enhanced green fluorescent protein (EGFP), we here constructed a plasmid carrying EGFP cDNA under control of the Iba1 promoter. This construct was injected into C57B/6 mouse zygotes, and the Iba1-EGFP transgenic line was developed. Fluorescent in-situ hybridization analysis revealed that the Iba1-EGFP transgene was located on chromosome 11D. No obvious defects were observed during development or in adulthood, and the EGFP fluorescence remained invariant over the course of at least four generations. Judging from the immunoreactivity with anti-Iba1 antibody, all EGFP-positive cells in the adult brain were ramified microglia. In the developing transgenic embryos, EGFP signals were detected as early as embryonic Day 10.5. The most prominent EGFP signals were found in forebrain, spinal cord, eye, foreleg, yolk sac, liver, and vessel walls. At postnatal Day 6, clear EGFP signals were observed in the supraventricular corpus callosum, known as "fountain of microglia", where ameboid microglia migrate into the brain parenchyma and mature into ramified microglia. Iba1-EGFP transgenic mice thus permit observation of living microglia under a fluorescence microscope and provide a useful tool for studying the function of microglia in vivo.

pH Microdomains in Oligodendrocytes

Oligodendrocytes (OLs) are cells that produce myelin in the central nervous system. Here we use ratiometric pH indicator dye to analyze intracellular pH in OLs in culture. The results reveal alkaline microdomains, which predominate in the perikaryon and proximal dendrites, and acidic microdomains, which predominate in distal dendrites. Spatial nonuniformity of pH is generated by differential subcellular distribution of Na(+)/H(+) exchanger (NHE), which is localized in a punctate distribution in the perikaryon and proximal processes, Na(+)/HCO(3)(-) cotransporter (NBC), which is localized in a punctate distribution in distal dendrites, and carbonic anhydrase isotype II (CAII), which is colocalized with either NHE or NBC. Inhibition of NHE activity by amiloride inhibits regeneration of alkaline microdomains after cytoplasmic acidification, whereas the inhibition of CAII activity with ethoxyzolamide inhibits acidification of dendrites. Fluorescence correlation spectroscopy analysis of CAII microinjected into OLs reveals freely diffusing protein throughout the cell as well as protein associated predominantly with NHE in the perikaryon and predominantly with NBC in the dendrites. Alkaline and acidic microdomains could be generated by transport metabolons consisting of CAII associated with NHE or NBC, respectively. This study provides the first evidence for pH microdomains in cells and describes a mechanism for how they are generated.

Calcitonin receptor antibodies in the identification of osteoclasts

Osteoclasts are the cells responsible for bone resorption, and their number and rate of formation are critical in determining bone mass. To identify and quantify osteoclasts, as well as to study their formation in bone and in osteoclastogenic cultures, osteoclast-specific cell markers are required. Only the calcitonin receptor (CTR) expression unambiguously identifies osteoclasts and distinguishes them from macrophage polykaryons. However, present autoradiographic methods for CTR detection are cumbersome and time consuming. We have developed rabbit polyclonal antibodies specific for the C-terminal intracellular domain of the mouse and rat Cla CTR. These antibodies labeled HEK-293 cells stably transfected with CTR (but not untransfected HEK-293 cells). This labeling is abrogated by preabsorbing the antibodies with the recombinant antigen. The antibodies immunostained primary mouse and rat osteoclasts as well as osteoclasts in sections of mouse bone. Osteoclasts (both mononuclear and multinucleated) formed from mouse bone marrow or spleen cells cocultured with osteoblasts in the presence of 1,25 dihydroxyvitamin D3 and prostaglandin E2 were also specifically immunostained by the CTR antibodies. Cocultures incubated under conditions that did not allow osteoclastogenesis (i.e., omission of mediators or osteoblasts, or culture for less than 4 days) were not immunostained by CTR antibodies. Autoradiographic detection of 125I-labeled salmon calcitonin combined with CTR immunohistochemistry showed that both methods labeled the same cells. A CTR polyclonal antibody and monoclonal antibody F4/80 were used in combination to show immunofluorescence labeling of murine osteoclasts and macrophage populations, respectively, in marrow/osteoblast cocultures. These results indicate that simple and rapid CTR antibody-based methods can be used to identify osteoclasts, and can be used to characterize the antigenic profile of osteoclasts by using double immunofluorescence analysis.

Binding of cholera toxin B subunit: a surface marker for murine microglia but not oligodendrocytes or astrocytes

GM1 ganglioside is a receptor for the B subunit of cholera toxin. In lymphocytes, B subunit elicits an influx of extracellular Ca++ (Dixon et al., 1987). To investigate this signaling pathway in glia, we assessed the presence of GM1 ganglioside on the surface of cultured murine central nervous system (CNS) glia by binding of fluorescein-labeled B subunit. B subunit binding was compared to binding of peanut agglutinin, wheat germ agglutinin, and Bandeiraea (Griffonia) simplicifolia lectin (BSL)I, a microglial marker. Antibodies to glial fibrillary acidic protein, A007/O4 antigens, and galactocerebroside were used to identify astrocytes, immature oligodendrocytes (OLs) and mature OLs, respectively. Binding patterns differed based on cell type and developmental stage. Wheat germ and peanut agglutinins bound to the surface of microglia, astrocytes, and immature OLs; neither lectin bound to any significant extent to the surface of membrane sheets of mature OLs, although wheat germ agglutinin was rapidly endocytosed. Cells identified as microglia by BSL I binding and morphology were the only cells to stain brightly on the surface with B subunit. Thus, surface GM1 ganglioside appears to be a highly enriched marker for microglia in these mixed glial cultures. The effects of B subunit on intracellular Ca++ were examined by laser cytometry in glial cultures loaded with Indo-1. No Ca++ responses were observed in microglia. Mature OLs were examined for Ca++ responses to B subunit before and after surface levels of GM1 ganglioside were increased by incubation with exogenous GM1 ganglioside. Again, no Ca++ responses were observed. Thus, cultured microglia and mature OLs do not have the GM1-mediated signal transduction pathway seen in lymphocytes. However, the presence of GM1 ganglioside on microglia may play a role in giving rise to antibodies to this glycolipid in some CNS inflammatory diseases.

Glial-cell cultures from brains of carbonic anhydrase II-deficient mutant mice: delay in oligodendrocyte maturation

Carbonic anhydrase II (CAII) is a multifunctional enzyme found in oligodendrocytes and astrocytes in normal mouse brains. We have begun to compare the glial cells in primary cultures from neonatal genetically CAII-deficient (Car) mice to those from normal (con) mice in order to detect developmental defects, if any, in Car glial cells. In con cultures intensely CAII-positive cells costained with antibodies against the oligodendrocytic markers, O4 and myelin basic protein (MBP), respectively. Most (82%) of the CAII-positive cells were O4-positive, but only approximately 60% were MBP-positive. Some clumps of GFAP-positive cells were CAII-positive. At each respective number of days in vitro (DIV) total numbers of O4-positive cells were similar in Car and con cultures, and total numbers of galactocerebroside-positive cells also were similar in Car and con cultures. However, compared to cells in con cultures at 7 DIV, a lower percent of Car cells in the oligodendrocyte lineage expressed MBP, and morphological differentiation also was subnormal in that the Car cells showed fewer processes and membrane sheets. Car and con cultures expressed similar numbers of MBP-positive cells by 10 DIV. The results suggest a temporary delay in the maturation of Car oligodendrocytes.

Fetal alcohol syndrome: a Japanese perspective

To estimate and prevent the effects of prenatal alcohol on the central nervous system (CNS), brain dysfunction in fetal alcohol syndrome (FAS) and fetal alcohol effects (FAE) was compared by both epidemiological and experimental studies. The FAS infants exhibited a more severe degree of CNS involvement than the FAE infants. The CNS involvement features were developmental delay and intellectual impairment in both FAS and FAE. The increased risk of low birth weight and CNS involvement were much more significant in women who were heavy drinkers or alcoholics and smoked. The beneficial effect of supplementary zinc on the fetal cerebrum of FAS or FAE rats was limited, never reaching the unexposed control level. One of the most vulnerable structures in the rat fetus exposed to ethanol in utero was the synaptic formation in the hippocampus. The consistent dysmorphogenesis of synapses during early brain development may be associated with the functional impairment of the CNS in FAS and FAE.

Characterization of a putative novel type of oligodendrocyte in cultures from rat spinal cord

Oligodendrocytes originate in different neural tube domains, within boundaries of expression of a series of patterning genes which condition the diverse morphogenetic programme of each area. Although neuronal and astrocyte heterogeneity are widely accepted, and despite accumulating evidence for oligodendrocyte heterogeneity in vivo, oligodendrocytes in vitro are currently considered as a homogeneous cell population. The present investigation demonstrates that oligodendrocyte diversity can be detected in vitro and characterizes a novel morphological class of O4-positive oligodendrocyte which is consistently identifiable in rat central nervous system cultures. These cells have a very characteristic epithelioid, unbranched and often lobulated morphology which enables their identification within 2 h of plating. Immunostaining shows that this morphological type is sometimes positive for GD3, A2B5 and vimentin, and most of the time positive for Ranscht antibody, O1 and Rip but negative for glial fibrillary acidic protein, OX-42, neuron-specific enolase, nestin and erbB2. The apparent levels and/or distributions of (i) microtubules, (ii) surface glycolipids recognized by O4, O1 and Ranscht antibody, and (iii) the less specific marker carbonic anhydrase II, typically differ from those of nearby classical, branched oligodendrocytes. Cells with this epithelioid morphology also express myelin basic protein and O10 (a proteolipid protein epitope), both of which are markers for mature oligodendrocytes. Conversely, O4+/O1- cells with this membranous appearance were also seen. Although these atypical oligodendrocytes were most abundant in spinal cord cultures (representing >10% of the O4+ population), they were not exclusive to this region and occurred at a low frequency in neonatal optic nerve cultures.