Glioma invasion in the central nervous system

Invading glioma cells seem to follow distinct anatomic structures within the central nervous system. Tumor cell dissemination may occur along structures, such as the basement membranes of blood vessels or the glial limitans externa, that contain extracellular matrix (ECM) proteins. Frequently, invasive glioma cells are also found to migrate along myelinated fiber tracts of white matter. This behavior is most likely a consequence of using constitutive extracellular ligands expressed along the pathways of preferred dissemination. The extracellular space in anatomic structures, such as blood vessel basement membranes or between myelinated axons, is profoundly different, thus suggesting that glioma cells may be able to use a multiplicity of matrix ligands, possibly activating separate mechanisms for invasion. In addition, enzymatic modification of the extracellular space or deposition of ECM by the tumor cells may also create a more permissive environment for tumor spread into the adjacent brain. Tumor cell invasion is defined as translocation of neoplastic cells through host cellular and ECM barriers. This process has been studied in other cancers, in which a cascade of events has been described that involves receptor-mediated matrix adhesion, degradation of matrix by tumor-secreted metalloproteinases, and, subsequently, active cell locomotion into the newly created space. Although some of these mechanisms may play an important role in glioma invasion, there are some significant differences that are mainly the result of the profoundly different composition of the extracellular environment within the brain. This review focuses on the composition of central nervous system ECM and the recent evidence for the use by glioma cells of multiple invasion mechanisms in response to this unique environment.

Dichotomy of astrocytoma migration and proliferation

Astrocytomas often show high rates of local invasion that lead to local recurrence of the disease. Histologically, the most highly invasive astrocytoma cells are detected in isolation rather than as nests of tumor. Our study attempted to determine whether the migratory response to extracellular substrates influences the proliferative behavior of these highly invasive cells. The preferential and specific migratory response of human astrocytoma cells to extracellular matrix proteins was assessed by a microliter scale migration assay. Growth curve studies on protein ligands permissive (merosin) for cell migration indicated that the lag phase was protracted compared with cells seeded on non-permissive proteins (vitronectin). Once a certain cell density was reached, logarithmic proliferation was indistinguishable on the different proteins. The proliferation index of populations of cells migrating on merosin and vitronectin was measured by both BrdU incorporation and MIB-1 immunocytochemistry labeling. Cells seeded on vitronectin showed higher proliferation throughout the population than cells seeded on merosin. On merosin, the more migratory cells at the periphery were less proliferative than non-migratory cells in the central region of that population. The integrin-associated signal transduction protein, p125FAK, was heavily localized in the membrane of non-migrating cells and largely absent in migrating astrocytoma cells. We conclude that temporally, proliferation and migration are mutually exclusive behaviors. Cell density or non-permissive substrates that inhibit cell motility favor a more proliferative phenotype. Conversely, active migration suppresses cell proliferation.

Migration of human glioma cells on myelin

Histoanatomically invading astrocytoma cells appear to migrate along distinct structures within the brain. Astrocytoma invasion may occur along extracellular matrix (ECM) protein-containing structures, such as blood vessels, but most frequently occurs along tracts of myelinated fibers. This behavior most likely is a consequence of the use of constitutive extracellular ligands expressed along the pathways of preferred dissemination. Enzymatic modification of the extracellular space or deposition of ECM by the tumor cells may also create a more permissive environment. Established human glioma cell lines and two preparations of primary cells isolated from glioblastoma biopsies were studied with the use of cell adhesion and monolayer migration assays to investigate whether crude human central nervous system myelin extracts present specific cell adhesion ligands that promote glioma attachment and cell migration. Two cell lines showed high levels of adhesion and migration on central nervous system myelin similar to levels of migration on the ECM protein merosin, which has previously been shown to be a highly permissive substrate for cultured astrocytoma cells. Two other cell lines showed lower but specific migratory response; one cell line did not attach or specifically migrate on crude myelin extracts. For both glioblastoma primary cell preparations, myelin and merosin were the most permissive substrates for attachment and migration. Other ECM proteins (collagen type IV, fibronectin, and vitronectin) were moderate or nonpermissive substrates. Our findings indicated that astrocytoma cells may be able to use oligodendrocyte membrane-associated ligands as well as ECM proteins of the basement membranes for invasion of normal brain.

Proliferation and motility responses of primary and recurrent gliomas related to changes in epidermal growth factor receptor expression

Astrocytic neoplasms show a high incidence of elevated or mutated epidermal growth factor receptor (EGFR) expression. Although proliferative effects from EGFR activation are well described, the role that changes in this receptor play in glioma growth and migration remain poorly addressed. This report characterizes changes in the levels of EGFR expression in three glial tumors at initial presentation (resection) and at the time of recurrence. By quantitative flow cytometry the mean level of EGFR expression increased, decreased, or remained the same in different recurrent astrocytomas relative to their primary tumor cells. Immunocytochemistry for EGFR on monolayer cells corroborated the level of expression in the recurrent tumors relative to their matched primary specimen. Immunoprecipitation indicated that 170 kd EGFR was expressed in each of the tumors, and showed normal down regulation following treatment with EGF. Proliferation response to EGF was seen in only 1/6 instances, but was concentration-dependent when observed. Stimulated migration of the cells was frequently seen and was also concentration-dependent on EGF; the magnitude of response was related to the relative level of 170 kd EGFR expression in the cells. EGFR immunostaining of tissue sections from the tumors confirmed the levels of EGFR expressed in primary and recurrent astrocytomas as was seen in the cultured cells. These results indicate that the relative levels of EGFR in early passage cell cultures from glioma specimens concurs with the measured tissue levels of expression. Human glioma cells are more responsive to migration induction than proliferation induction by EGF.

Substrates for astrocytoma invasion

A better understanding of the influences of specific extracellular substrates, including proteins, glycosaminoglycans, and parenchymal cells, on the invasive behavior of glioma cells would potentially lead to novel forms of treatment aimed at confining the tumor. A monolayer, microliter scale assay was used to investigate how different substrates influenced glioma migration. Basal or unspecific movement (range, 10-260 microns/d) was determined by observing a panel of seven established human glioma cell lines. Migration rates two to five times higher than this basal activity were referred to as preferential and specific glioma migration; these rates generally occurred on merosin and tenascin. Collagen, fibronectin, or vitronectin were less supportive of migration. The glioma cells migrated on hyaluronic acid, but they did not migrate to the extent generally found on the extracellular matrix proteins. Glioma-derived extracellular matrix also served to promote cell migration. This finding implicates a role for either glioma remodeling or synthesis of a permissive environment for local dissemination that may be independent of the constitutive matrix proteins normally found in the brain. Although the glioma cells were able to migrate over monolayers of other glioma cells, they were unable to migrate over astrocytes and fibroblasts. Our findings indicate that the invasive behavior of glioma cells in situ is most likely a consequence of the interplay between the cells' manipulation of the environment and the constitutive ligands associated with specific regions or structures of the brain.

Neuronal cell death in scrapie-infected mice is due to apoptosis

Neuronal loss is a salient yet poorly understood feature in the pathology of transmissible spongiform encephalopathies (prion diseases). Cell culture experiments with neurotoxic prion protein fragments suggest that neuronal cell death in these diseases may be due to apoptosis. To test this hypothesis in vivo we used the in situ end-labeling (ISEL) technique and electron microscopy to study cell death in an experimental scrapie system in the mouse. ISEL, which relies on the incorporation of labeled nucleotides in fragmented DNA by terminal transferase, showed labeled nuclei in the brains and retinae of mice infected with the 79A strain of scrapie, whereas no labeling was observed in control animals. In the retina the highest numbers of labeled nuclei were found in the outer nuclear layer 120 days post infection followed by massive cell loss in this layer. In the brain, labeled nuclei were mainly found in the granular layer of the cerebellum of terminally ill mice. This corresponded to the presence of small dark nuclei with condensed and occasionally fragmented chromatin at the light and electron microscopical levels. Our results support the hypothesis that neuronal loss in spongiform encephalopathies is due to apoptosis. This may explain the almost complete absence of inflammatory response in prion diseases in the face of widespread neuronal cell death, and may also have therapeutic implications in the future.

Specific attachment and migration of human astrocytoma cells on human but not murine laminin

Attachment sites and biological functions of laminin isolated from murine EHS sarcoma have been well studied. Recently several variants of laminin including human placental laminin have been shown to be distinct from EHS-laminin. This study was undertaken to determine attachment, proliferation, and migration phenomena of human astrocytoma cell lines to human and murine sarcoma EHS-laminin. Using short-term attachment assays human placental laminin was shown to be the better substrate for cell adhesion. EHS-laminin mediated approximately 30-50% of the effect observed on human laminin. The astrocytoma cells expressed beta 1, beta 3, and beta 4 subunit mRNA as determined by RT-PCR. Anti-beta 1 antibodies blocked adhesion to EHS-laminin, but antibodies against beta 1, beta 4, and alpha v subunits were all ineffective in blocking adhesion to human laminin. A migration assay showed that astrocytoma cells on human laminin dispersed from a central seeding area, while cells on EHS-laminin remained where they were seeded. The pattern of dispersion could not be accounted for by changes in growth rates of astrocytoma cells on the different proteins, since both cell lines grew equally well on the two laminins. We conclude that unique epitopes on human laminin are recognized by novel receptors on human astrocytoma cells which confer a migratory phenotype to the cells.

The role of extracellular matrix in human astrocytoma migration and proliferation studied in a microliter scale assay

Ligands in the extracellular matrix (ECM) are known to mediate migration of normal as well as tumor cells via adhesion molecules such as the integrin receptor family. We develop a microliter scale (15-20 microliters total volume) monolayer migration assay to investigate the ability of astrocytoma cells to disperse on surfaces coated with purified human ECM protein ligands. In this system the rate of radial migration of the cell population was constant over time. For human astrocytoma cell lines U-251 and SF-767, laminin and collagen type IV supported a migratory phenotype; fibronectin and vitronectin only minimally supported migration. The different ECM proteins also influenced growth rate: cells on laminin and collagen had a protracted lag phase. Furthermore, migrating cells seeded on laminin or collagen showed a lower labeling index than did stationary cells in the central, crowded region on the same substrate. This micro-scale migration assay should enable detailed molecular and biochemical studies of the determinants of migration.

Determinants of human astrocytoma migration

A unique characteristic of astrocytic malignancies is their frequent dissemination through the brain. Cellular determinants of migration include adhesion to the substratum, restructuring of the actin cytoskeleton to generate motion, and (in the setting of invasion into tissue) secretion of enzymes for remodeling interstitial space to accommodate forward motion of the migrating cell. In order to better understand these features in the context of local brain invasion by astrocytoma cells, the adhesion and migratory properties of these cells have been investigated in an in vitro monolayer system. Adhesion of 8 different astrocytoma cell lines to different purified human extracellular matrix (ECM) proteins (collagen type IV, cellular fibronectin, laminin, and vitronectin) revealed that there is no "astrocytoma-specific" ECM protein that consistently leads to high cell binding. Similarly, migration of astrocytoma cells was found to be variable and dependent on different ECM proteins. Laminin was frequently the most permissive for adhesion and migration. Adhesion to collagen, fibronectin, and vitronectin was integrin dependent and could be blocked using anti-beta 1 integrin antibodies; in contrast, attachment to laminin could not be blocked using these antibodies. A comparison of adhesion with migration for each of the cell lines on each of the 4 ECM proteins revealed that poor adhesion was associated with minimal migration and that frequently, high adhesion was correlated with rapid migration. When tested for migration on autologous, cell-derived ECM, none of the cell lines were as migratory as they were on one of the purified ECM proteins, with the exception of SF767 cells. Furthermore, it was found that ECM from SF767 cells promoted the migration of other astrocytoma cells. The results from this study indicate that migration is a constitutive behavior of glioma cells which is dependent on, or modified by, the presence or absence of permissive ligands in the environment.

[Effect of the prostaglandin E2 analog nocloprost on motility and acid clearance of the tubular esophagus in man]

The effects of the E2 prostaglandin nocloprost (9b-chloro-16,16-dimethyl-prostaglandin E2) on esophageal motility and acid clearance were evaluated in a double-blind placebo controlled study in six healthy volunteers. Motility of the tubular esophagus was measured by means of a low compliance perfusion system (four channels, recording ports 10 cm apart, the distal localized in the stomach). After eight hours fasting and a 60-minutes baseline measurement (with standardized swallowing of 5 cc water every three minutes) the volunteers swallowed on two separate days in randomized order either 200 micrograms nocloprost (solved in 50 cc water) or placebo. Then the motility of the tubular esophagus was assessed for another 60-minutes during standardized swallowing. Thereafter, the motility probe was removed and a pH-electrode placed 10 cm above the lower esophageal sphincter. In order to assess the esophageal clearance, four times 5 cc of 0.1 N HCl were infused into the esophagus 10 cm above the electrode and the time between the infusion of HCl and the increase of the pH above pH 4.0 measured.

RESULTS

In five out of six volunteers the duration of esophageal contractions were decreased after administration of nocloprost as compared to placebo (6.23 +/- 1.2 vs. 5.80 +/- 1.1 seconds, p = 0.07). In contrast, neither propagation velocity, nor amplitude of contraction or acid clearance were significantly affected by nocloprost.

CONCLUSIONS

These findings suggest that in healthy volunteers nocloprost changes the pattern of esophageal contractions (duration) without affecting amplitude, velocity of propagation or acid clearance.

Birth weight of children with congenital heart disease

Birth weights of 843 children with congenital heart disease (CHD) were compared to the respective data of a normal West German population. On average, the CHD group had significantly lower birth weights, but the weight deficit was far less pronounced than in previous studies. The decrease in birth weight was distinct only in children with tetralogy of Fallot and atrial septal defect. Compared to normal newborns, patients with CHD were more often small for gestational age (15.0%) or had a low (less than 2500 g) birth weight (8.6%). The prevalence of prematurity was not increased. Extracardiac malformations were not significantly more common in CHD patients, who were small for gestational age, than in CHD patients with normal birth weight.