Laminin supports short-term survival of rat septal neurons in low-density, serum-free cultures

Polysialic acid limits septal neurite outgrowth on laminin

Polysialic acid (PSA) is a large carbohydrate found exclusively on the neural cell adhesion molecule (NCAM). In the adult brain, PSA is re-expressed by septal axons sprouting and regenerating in an environment rich in laminin. Using an in vitro model, we tested the possibility that PSA limits septal outgrowth by preventing maximal interactions with a laminin substrate. Our results indicate that PSA removal from primary septal neurons plated on laminin significantly increased neurite outgrowth at 12 h (14%, p<0.05) and 24 h (22%, p<0.01). In contrast, the removal of PSA had no impact on septal neurite outgrowth on poly-D-lysine. PSA did not influence the plating adhesion of septal neurons on laminin or poly-D-lysine, indicating that the increase in neurite outgrowth caused by PSA removal on laminin is not related to the initial attachment of the neurons to this substrate. Neurite length on laminin was significantly reduced by the function-blocking beta1-integrin antibody in the presence of PSA (20% decrease, p<0.05), and following PSA removal (34% decrease compared to neurites treated with endoN and without the beta1-integrin antibody, p<0.01). Importantly, the beta1-integrin antibody completely abolished the neurite outgrowth promoting effect of PSA removal on laminin. The beta1-integrin antibody had no impact on septal neurite length on poly-D-lysine. Taken together, these results indicate that the removal of PSA from septal neurons increases neurite outgrowth on laminin by promoting interactions between beta1-integrin and laminin.

Laminin-like proteins are differentially regulated during cerebellar development and stimulate granule cell neurite outgrowth in vitro

The basement membrane glycoprotein laminin-1 is a potent stimulator of neurite outgrowth. Although a variety of laminin isoforms have been described in recent years, the role of alternative laminin isoforms in neural development remains largely uncharacterized. We found that a polyclonal antibody raised against the alpha1, beta1, and gamma1 chains of laminin-1 and a monoclonal antibody raised against the alpha2 chain of laminin-2 detect immunoreactive material in neuronal cell bodies in the developing mouse cerebellum. In addition, laminin-1-like immunoreactivity was found in cell types throughout the cerebellum, but laminin-alpha2-like immunoreactivity was restricted to the Purkinje cells. Purified laminin-1 and laminin-2 stimulated neurite outgrowth in primary cultures of mouse cerebellar granule neurons to a similar extent, whereas the synthetic peptides tested appeared to be active only for cell adhesion and not for stimulation of neurite outgrowth. The E8 proteolytic fragment of laminin-1 contained full neurite outgrowth activity. The identity of laminins expressed in granule neurons was also examined by Western blotting; laminin-like complexes were associated with the cell and appeared to have novel compositions. These results suggest that laminin-like complexes play important roles in cerebellar development.

Neuronal laminins and their cellular receptors

The laminins are a family of extracellular matrix glycoproteins expressed throughout developing neural tissues. The laminins are potent stimulators of neurite outgrowth in vitro for a variety of cell types, presumably reflecting an in vivo role in stimulating axon outgrowth. In recent years, the laminins have been shown to occur in several distinct isoforms; currently, the precise functional differences between the laminin variants are not well understood. A variety of neuronal surface receptors have been identified for one laminin isoform, laminin-1. These receptors include several members of the integrin family, as well as non-integrin laminin-binding proteins such as LBP-110, the 67 kDa laminin-receptor, alpha-dystroglycan, and beta 1,4 galactosyltransferase. Little is currently known about receptors for other laminin isoforms.

Astroglia-neuron interactions that promote long-term neuronal survival

Besides intrinsic determinants of cell growth, epigenetic signals have been proposed to regulate development and maintenance of neurons. Here we provide evidence that cerebral astrocytes contribute significantly to the set of environmental influences that are required for long-term survival of neurons derived from the mammalian central nervous system. Cerebral astrocytes in serum-free culture express diffusible and non-diffusible neuron-supporting signals, including cell-adhesive neurite growth-promoting glycoproteins, diffusible neurotrophic factors as well as membrane-bound molecules that mediate cell contact interactions. The combination and synergistic interaction of these environmental signals markedly enhance the survival of brain neurons. While astroglia-derived cell-adhesive substrates that include a high molecular weight complex consisting of laminin beta-chains and proteoglycan (Matthiessen et al., 1989) stimulate neurite outgrowth, they fail to enhance long-term neuronal survival when additional neurotrophic and cell-contact interactions are lacking. Astrocytes release a diffusible neurotrophic activity that, when permanently applied, maintains long-term survival of central neurons in culture. The soluble neurotrophic activity seems to interact synergistically with cell-bound signals which are also required for long-term survival and which are expressed by astrocytes and neurons, but not by fibroblasts. Among neurons from different brain areas, such as hippocampus, cerebral cortex and septum, regional differences in their responsiveness to the astroglial neurotrophic activity have been observed.

Neuronal injury evoked by depolarizing agents in rat cortical cultures

Chemical depolarization is often used to study neurotransmitter release. Three commonly used depolarizing agents, veratridine, potassium, and glutamate, were evaluated for neurotoxicity. Neuronal survival and lactate dehydrogenase efflux were measured to assay irreversible injury. In addition, video-enhanced differential interference contrast microscopy was used to measure acute neuronal swelling. We found that lactate dehydrogenase efflux and cell death associated with exposure to potassium and glutamate could be blocked by the competitive N-methyl-D-aspartate antagonist amino-phosphonovaleric acid. Neuronal swelling was observed with all three agents, and could not be blocked by amino-phosphonovaleric acid. These results suggest multiple mechanisms of neuronal injury accompanying chemical depolarization. A 60-min exposure to 100 microM veratridine increased lactate dehydrogenase appearing in the medium at the end of this exposure to 615% of control and produced a 62% loss of neurons after 20-24 h. These effects could not be blocked by amino-phosphonovaleric acid at 500 microM. Differential interference contrast imaging revealed acute neuronal swelling in response to veratridine within 5 min of exposure, and this swelling could not be blocked by amino-phosphonovaleric acid. A 60-min exposure to medium supplemented with 50 mM KCl caused a lactate dehydrogenase efflux of 204% of control and produced a 48% loss of neurons. Amino-phosphonovaleric acid blocked both the neuronal loss and the excess lactate dehydrogenase efflux. In addition, differential interference contrast monitoring showed no KCl-evoked swelling. In contrast, isotonic substitution of 50 mM KCl for NaCl resulted in acute swelling which could not be blocked by amino-phosphonovaleric acid, in addition to neuronal death and lactate dehydrogenase release. Glutamate was, as expected, neurotoxic, and as has been shown before, this toxicity could be blocked by amino-phosphonovaleric acid. Observation of neurons exposed to 300 microM glutamate revealed that this treatment was invariably associated with neuronal swelling. In the presence of amino-phosphonovaleric acid, 81% of neurons swelled to greater than 110% by 30 min exposure to glutamate. These results suggest that experimental paradigms which investigate the effects of chemical depolarization upon central neurons are likely to be associated with reversible and irreversible forms of injury. This is of special importance to any study of the mechanisms of release of substances from central neurons.

Laminin concentrations in serum and cerebrospinal fluid in aging and Alzheimer's disease

Laminin, a basement membrane protein, and a potent promoter of neurite outgrowth, surrounds all peripheral nerves. It appears in the central nervous system during development and reappears in response to injury. In Alzheimer's disease (AD), there is a progressive loss of neurons in specific areas of the brain along with the presence of an increased number of senile plaques and neurofibrillary tangles. Laminin levels have been shown to be increased in injury, so we undertook to examine levels of laminin by radioimmunoassay (RIA), in cerebrospinal fluid and serum of patients with AD and age-matched controls. No difference in the CSF and serum laminin concentrations was found between Alzheimer's disease and age-matched controls. We found a lack of correlation between severity of clinical dementia and laminin concentrations. Finally, we show that the CSF and serum laminin concentrations increase with age.

The action of CGS-19755 on the redox enhancement of NMDA toxicity in rat cortical neurons in vitro

The effects of the competitive N-methyl-D-aspartate receptor antagonist CGS-19755 (cis-4-phosphonomethyl-2-piperidine carboxylic acid) were studied in cultures of rat cerebral cortex under normal and altered redox conditions. CGS-19755 was effective in preventing delayed neuronal death produced by an acute exposure to either glutamate (500 microM) or NMDA (200 microM), but was ineffective in protecting neurons against the toxicity induced by a prolonged exposure to kainate (500 microM). We observed that the reducing agent dithiothreitol (DTT, 500 microM), could dramatically enhance toxicity and electrophysiological responses produced by 50 microM NMDA. CGS-19755 (100 microM) could effectively block both of these effects of DTT. Any toxicity produced by DTT alone was also antagonized by CGS-19755. In contrast, oxidized DTT did not enhance NMDA toxicity nor was it toxic when added alone. These results indicate that CGS-19755 is an effective and specific neuroprotectant acting at the NMDA receptor in vitro, and that the enhancement in NMDA toxicity induced by DTT is mediated by an increase in activity at this receptor complex.

A neurite-promoting factor from muscle supports the survival of cultured chicken spinal motor neurons

During embryonic development, spinal motor neurons require muscle-derived trophic factors for their survival and growth. We have recently isolated a protein from muscle that is not laminin but that still stimulates neurite outgrowth from embryonic neurons in culture. In the present study, we investigated whether this protein, which we refer to as muscle-derived neurite-promoting factor (NPF), could also promote the survival and growth of motor neurons in culture. Spinal motor neurons were isolated from 6-day-old chicken embryos by a metrizamide step-gradient centrifugation protocol. Most large cells (putative motor neurons) were found in the upper metrizamide fraction (0%-6.8% interface; fraction I). Motor neurons were identified by increased specific activity of choline acetyltransferase (CAT) and by their propensity to transport retrogradely either wheat germ agglutinin-horseradish peroxidase or the fluorescent dye, 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine per chlorate (diI), when those substances were injected into the target field. Labeled motor neurons were 2.6-fold enriched in fraction I and the specific CAT activity was 4.4-fold increased in fraction I as compared to unfractionated cells. When motor neurons were grown on muscle-derived NPF, the protein supported the survival of at least 21% of the neurons for as long as 6 days in culture. The protein showed no significant effect on either CAT specific activity or on high-affinity choline uptake by neurons. There was a substantial increase from 21% to 38% of the survival of motor neurons when a combination of muscle-derived NPF and laminin was used as the substrate. Muscle-derived NPF also promoted the survival of sensory neurons and sympathetic neurons in culture. Our results demonstrate that a neurite-promoting protein derived from muscle promotes both the survival and the outgrowth of neurites from cultured spinal motor neurons as well as from sensory and sympathetic neurons.

Oligodendroglial cell death induced by oxygen radicals and its protection by catalase

The cytotoxic effects of oxygen radicals have been studied in enriched population of mature bovine oligodendrocytes in culture. Oxygen radicals were generated enzymatically by glucose and glucose oxidase, and hypoxanthine and xanthine oxidase combinations. Cytotoxicity was assessed by trypan blue exclusion and percentage lactate dehydrogenase release into the culture media. Incubation of bovine oligodendrocytes with these oxygen radical-generating systems for 4 hr resulted in significant cell death, especially in the glucose oxidase system. The oligodendrocytes were completely protected by catalase from the cytotoxic effects of both oxygen radical generating systems. However, superoxide dismutase, dimethylsulfoxide and antioxidants such as vitamin E and glutathione did not protect oligodendrocytes from the oxidant-mediated cytotoxicity. It appears that hydrogen peroxide produced in these oxygen radical-generating systems gives rise to toxic radicals that induce the cell death of bovine oligodendrocytes in culture.

Fetal rat septal cells adhere to and extend processes on basement membrane, laminin, and a synthetic peptide from the laminin A chain sequence

Responses of rat embryonic septal cells to reconstituted basement membrane, laminin, and laminin A chain-derived synthetic peptides were studied in culture. Dissociated fetal E16/17 septal cells were grown for three days on differently coated plastic substrata. Reconstituted basement membrane (Matrigel), laminin, and a 19-amino acid synthetic peptide CSRARKQAASIKVAVSADR-NH2 (PA22-2) from the laminin A chain sequence mediated cell-substratum adhesion and promoted neurite outgrowth. In contrast, cells did not attach to or form processes on uncoated plastic or on plastic substrata coated with synthetic, laminin-derived control peptides. Polyethylenimine (PEI) supported the adhesion and survival of fetal septal cells; however, when laminin was added to the medium during cell plating or 18 hr afterward, a dose-dependent increase was observed in neurite outgrowth of cells attached to this substratum. Cells grown for 6 days on PEI in the presence of laminin showed a determined increase in the number of cholinergic neurons as marked by acetylcholinesterase staining. These data suggest that the subpopulation of cholinergic septal neurons present in the septal cells studied here were also responding to laminin. The results of this in vitro study suggest potential uses for basement membrane, laminin, or synthetic peptides, such as PA22-2, in fetal septal grafts to enhance regeneration in the damaged septo-hippocampal system.

Influence of soluble environmental factors on the development of fetal brain acetylcholinesterase-positive neurons cultured in a chemically defined medium: comparison with the effects of L-triiodothyronine (L-T3)

In cerebral hemisphere neuronal cultures derived from 15-day-old rat embryos, the addition of L-triiodothyronine (L-T3) or nerve growth factor (NGF) enhanced the expression of choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activities in a dose-dependent manner. When cultures were supplemented with both agents at maximal effective concentrations, the stimulation in ChAT and AChE activities was significantly greater than the sum of the individual effects. Conversely, when the cultures were exposed to astrocyte conditioned medium grown in the presence or absence of L-T3 (CM + L-T3 or CM-L-T3). laminin and fibroblast growth factor (FGF), ChAT and AChE activities were not stimulated above those of control cultures when added alone or in combination with L-T3. Furthermore, L-T3, NGF, CMs, laminin and FGF did not affect AChE+ cell survival, but significantly increased neurite outgrowth and branching with NGF and L-T3 being the most powerful agents followed by CMs, laminin and FGF. Additionally, the simultaneous addition of L-T3 with either laminin or FGF in culture, caused an additive effect of L-T2 in the neurite density of AChE+ cells with both agents. This study shows that (1) thyroid hormones do not act through the regulation of soluble neurotrophic factors produced by astroglial cells, (2) thyroid hormones interact with the effect of NGF on ChAT and AChE activities, (3) the regulation of ChAT and AChE activities and the neurite outgrowth are independently regulated. and (4) the regulation of ChAT and AChE activities is very specific compared with that of neurite outgrowth.(ABSTRACT TRUNCATED AT 250 WORDS)

Four patterns of laminin-immunoreactive structure in developing rat brain

Laminin has been known to promote neurite outgrowth in culture. We have recently demonstrated that laminin facilitates and guides fiber growth of grafted neurons in the brain. In this study, I report that 4 distinct patterns of laminin immunoreactivity--small and large punctiform laminin, sheath laminin, and somal laminin--were expressed in the brain, each having unique spatial and temporal distributions. They are extensively produced in the developing brain while nerve fibers and vessels are actively growing. Two patterns of laminin, small and large puncta, disappear when the brain matures; the other two, sheath laminin and somal laminin, reduce in intensity but persist through adult life. The small puncta, size less than 1 micron in diameter, frequently accumulated along acellular spaces where future fiber bundles will form, interneuronal spaces and surfaces of neurons where terminal fibers dwell, and around the microvessels where neomicrovessels form. The small puncta, which reportedly appear at the eight-cell stage, were observed in our study at stage E10. They increased in expression from E14 to 19 during the stage when many nerve fibers are navigating to their targets, and subsided in the early postnatal days (P6) when less fiber growth occurs. Large puncta, size about 2 microns in diameter, existed exclusively in the hippocampus. They appeared about E16, and ended P16. The sheath laminin is known to form wrappings on microvessels, the ependymal layer, the choroid plexus, and the surface of the brain. This pattern of laminin attaches to non-neuronal structures which associate with CNS fluid. It was detected at E10 (our youngest group), increased its distribution along with expansion of the associated structure, and persisted throughout the adult life. The somal laminin, associated mainly with the soma of neurons, was the latest appearing laminin pattern (not until E16). It also persisted through adult life in the brain. The somal laminin, which was highly associated with the appearance of neuronal groups in brain nuclei, appeared group by group along with neurons. In summary, laminin attaches with distinct groups of cells in the central nervous system with specific temporal association. This close temporal and spatial association may allow laminin to actively affect nerve growth during brain development. The detailed mapping of laminin distribution is in progress in our lab.

Growth factors and growth factor receptors in the hippocampus. Role in plasticity and response to injury

Various growth factors are present in the hippocampal formation and appear responsible for the prominent plasticity of this brain area. Although hormone-like growth-promoting polypeptides are the best known, recent studies emphasize the importance in the growth response of molecules such as laminin proteoglycans, neurotransmitters and growth inhibitors. The progress and problems in the study of these substances are reviewed.

Laminin-like antigen in rat CNS neurons: distribution and changes upon brain injury and nerve growth factor treatment

Using several antibodies against rat or human laminin and an avidin-biotin immunocytochemical protocol, laminin-like immunoreactivity was detectable in the rat nervous system in expected locations, i.e., associated with blood vessels and reactive astrocytes. However, laminin staining was also abundantly present within neuronal cell bodies in most parts of the developing and adult rat CNS. Medial septum neuronal immunoreactivity was lost after septo-hippocampal disconnection, but could be preserved or even restored by intraventricular administration of nerve growth factor. Thus, at least for medial septum neurons, this laminin-like molecule can be accumulated or produced independent of direct hippocampal (target) contact. It remains to be determined whether CNS neuronal "laminin" processes activities similar to those found for laminin in vitro.

Role of the growth cone in neuronal differentiation

Nerve growth cones are motile, exploring organelles at the tip of a growing neurite. The growth cone is a highly specialized structure, equipped with a complex machinery for reversible membrane expansion and rapid cytoskeletal reorganization, a machinery required for growth cone motility and neurite elongation. It also contains perception systems that enable the growth cone to respond to external signals, thereby steering the trailing neurite to the correct target. Soluble and substrate bound guidance molecules in the environment modulate growth cone behavior either through direct interaction or classical receptor activation coupled to second messengers. A prominent phosphoprotein of the growth cone is B-50. We propose a role for this growth-associated protein kinase C substrate in signal transduction processes in the growth cone.

GABA activated chloride currents in cultured rat hippocampal and septal region neurons can be inhibited by curare and atropine

In order to study the influence of curare and atropine on the gamma-aminobutyric acid (GABA)-evoked chloride current, we have investigated cultures of hippocampal and septal region neurons from embryonic rats (E18). The neurons were cultured under the trophic influence of spatially separated astrocytes in serum-free medium. By means of the patch clamp technique, the excitable cells displayed GABA induced chloride currents within 1-15 days in vitro. In both cultures picrotoxin or bicuculline as well as curare or atropine reversibly inhibited the chloride current in a dose dependent manner. We conclude that curare and atropine are not specifically anti-cholinergic for cultured central neurons. Our results provide evidence for common ligand binding properties shared by GABAA and acetylcholine (ACh) receptors supporting the recent concept of a receptor superfamily.

Neurotrophic effects of basic and acidic fibroblast growth factors are not mediated through glial cells

Basic and acidic fibroblast growth factors (bFGF, aFGF) increase the survival of fetal hippocampal pyramidal neurons in serum-free cultures. bFGF is also a mitogen for astrocytes either in highly purified glial cultures or as a contaminant in neuronal cultures. The possibility that bFGF enhances neuronal survival indirectly through stimulating glial proliferation is unlikely. In the presence of 1 ng/ml bFGF, the total number of contaminating astrocytes (as defined by immunohistochemical staining for glial fibrillary acidic protein (GFAP] was increased to 4.3% vs 0.9% in control hippocampal cultures. aFGF did not significantly increase astrocyte number while supporting neuronal survival. Two other agents which stimulated equal or greater astrocytic proliferation, epidermal growth factor (EGF) and 10% serum, did not support neurons, and bFGF still significantly increased neuronal survival in their presence. When glial proliferation was inhibited by aphidicolin, contamination decreased to 0.1% in controls and 1.0% with 1 ng/ml bFGF, yet the neurons remained responsive to FGF. Cultures lacking any detectable GFAP-positive cells were identified, and even in the absence of glial cells, aFGF and bFGF increased neuronal survival. Because there is no significant correlation between the neuronal response and astrocyte number, it appears that bFGF and aFGF can directly support neuronal survival.

Intraneuronal laminin-like molecule in the central nervous system: demonstration of its unique differential distribution

Laminin, an extracellular matrix glycoprotein rich in basement membrane, is a multifunctional molecule of approximately 1000 kDa and is known to possess a potent neurotrophic activity. Laminin-like immunoreactivity (LLI) was for the first time demonstrated in mouse and rat CNS neurons by a sensitive immunohistochemical technique. Transblotting of SDS-PAGE of the supernatant of the mouse and rat brain homogenate identified distinct 180 kDa and weak 380 kDa bands immunoreactive to anti-laminin and these molecules differed from authentic laminin subunits. The intraneuronal distribution of LLI disclosed two distinct patterns; LLI-1 (diffuse perikaryal stain) and LLI-2 (coarse granular stain). By immunoelectron microscopy, LLI was localized to the ERs in LLI-1 neurons, whereas it appeared to be confined to lysosomes in LLI-2 neurons. LLI-1 neurons were found predominantly in hippocampal pyramidal, granule and neocortical layers 1-3, 6 neurons, in most of the striatal and thalamic neurons, and Purkinje cells. The majority of neurons in neocortical layers 4-5, medial septal and Meynert neurons, somatic motor neurons, and neurons of the deep cerebellar nuclei were classified as LLI-2 cells. No LLI was found in hypothalamic mammillary, habenular and vagal dorsal motor neurons (LLI-3). These observations may indicate intraneuronal production of laminin-related molecules in central neurons. We speculate that the laminin-related molecules (neurolaminin) play important roles in trophic or servo mechanisms in the CNS.

Preferential adhesion of brain astrocytes to laminin and central neurites to astrocytes

Astrocytes from either fetal or newborn rat brain adhered preferentially to surfaces coated with active laminin. Neurites from septal neurons did not show a preference for active over inactive laminin. However, when given a choice between laminin and an astrocytic surface, septal cells preferred to extend neurites over astroglial processes. Hence, laminin paths can guide astrocyte migration, which, in turn, can guide neurite elongation.

Effects of entorhinal lesions on trophic activities present in rat entorhinal cortex and hippocampus as studied using primary cultures of entorhinal and septal tissues

The present study examined trophic activities in normal and injured brain which affect the survival and growth of central neurons in culture. Adult rats received bilateral lesions through the angular bundle, severing projections between the entorhinal cortex and the hippocampus. Ten days later, extracts were prepared from the entorhinal or hippocampal regions of the injured brains and compared with extract prepared from analogous regions of normal brains for trophic activities in cultures of either entorhinal or septal tissues. At least three activities were observed: (1) a trophic activity which bound to polylysine-treated wells, which was greater than 10,000 Da in size, heat labile, and sensitive to trypsin, and which supported the survival of both septal and entorhinal neurons in culture; (2) a trophic activity which did not bind to polylysine-treated wells, which was greater than 10,000 Da in size, heat labile, and sensitive to trypsin, and which, in the presence of polylysine-bindable material, facilitated the survival and growth of entorhinal cells in culture, and (3) an inhibitory activity which significantly reduced survival in entorhinal cultures when cells were plated in the presence of high concentrations of extract prepared from normal brain. These effects were not due to nonspecific effects of plating the cells in, or treating the wells with, large amounts of protein. A significant injury-related increase in non-polylysine-bindable trophic activity was also observed. Extracts prepared from either the hippocampus or the entorhinal area of the injured brains contained more non-polylysine-bindable trophic activity than extract prepared from normal brains. Injury-related changes in trophic activities were more prominent in entorhinal than in septal cultures. This increase in activity may account for the injury-related effects on the survival of entorhinal transplants reported previously [Gibbs and Cotman: Neuroscience (in press) 1987], and may represent an endogenous mechanism by which the brain attempts to selectively support the survival of injured cells following injury.

Transplantation of septal neurons maintained in long-term culture

Septal cells were maintained in culture for varying lengths of time and then transplanted to adult hippocampi from which the native septal input had been removed. Cells grafted after 1 week in culture survived transplantation to the brain and innervated the host hippocampus in a pattern comparable to the native cholinergic projection. Cells grafted after 2 weeks in culture did not survive in the brain, but did survive re-plating. In addition, the viability of cells transplanted from culture paralleled the viability of brain tissue taken from donors of equivalent ages, suggesting that changes which occur in culture and affect the viability of transplanted neurons may also occur during normal development.