Specificity and valency of concanavalin A in neuron-substratum adhesion and redistribution of cell surface receptors

Lectins implicate specific carbohydrate domains in electric field stimulated nerve growth and guidance

Both endogenous lectins and DC electric fields may control aspects of early nerve growth and nerve guidance. To test whether such endogenous cues interact, lectins of varying sugar affinity and valency were studied for effects on electric field induced growth and reorientation of cultured Xenopus neurites. Concanavalin A (Con A), succinylated concanavalin A (S-Con A), and wheat germ agglutinin all completely inhibited field-induced cathodal reorientation. Lentil and pea lectins, which share the same sugar affinity as Con A/S-Con A, were only partially effective in inhibiting reorientation. Because S-Con A does not alter lateral mobility of membrane receptors, the previously accepted notion that Con A inhibited field-induced reorientation by preventing receptors from translocating and becoming redistributed asymmetrically in the membrane may be oversimplified. There are likely to be additional steric interactions that Con A and S-Con A share that inactivate asymmetrically redistributed receptors and prevent reorientation. Additionally, nerves growing in an applied field branch more commonly toward the cathode. Con A and S-Con A alone prevented this development of asymmetric branching. All the lectins tested prevented the normal field-induced increase in nerve growth rate, while all, except peanut agglutinin, prevented the usual faster growth cathodally than anodally. We suggest that lectin interactions with electric field effects in vitro may involve modulation of neuronal nicotinic acetylcholine receptors, neurotrophin receptors, or voltage-dependent calcium channels. Similar interactions between endogenous lectins and endogenous electric fields are to be expected.

Glial-conditioned medium and attachment to ConA are essential for long-term culture of cortical neurons

Cortical brain cells from 14-day-old mouse embryos were seeded on various substrates and cultivated in serum-free medium with or without conditioned medium from astrocytes or C6 glioma cells. Poly-L-lysine was shown to be the best substrate for cell attachment followed by Concanavalin A (ConA) and adhesion particles derived from glia cells. Cells grown on ConA sprouted rapidly and formed large networks. Survival of neurons was greatly prolonged when glia-conditioned medium (GCM) was present in the culture medium. Cells grown on ConA were then viable for more than 4 weeks. Without GCM, neurons survived in culture for about 2 weeks, regardless of the substrate. Endothelial cell growth supplement or acidic fibroblast growth factor increased survival of neurons but also stimulated proliferation of astrocytes.

The extracellular matrix modulates the response of PC12 cells to nerve growth factor: cell aggregation versus neurite outgrowth on 3-dimensional laminin substrata

PC12 cells attach well to plastic culture dishes coated with laminin, collagen, polylysine or a basement membrane extract (2-dimensional substrata) and, in the presence of NGF, extend short neurites within 1-2 days. However, on gels (3-dimensional substrata) reconstituted from a basement membrane extract (RBM), PC12 cells attach extending short processes transiently and within one day, form networks of small aggregates interconnected by process-bearing cells. By 3 days the network collapses into large aggregates that, in media supplemented with NGF, extended a halo of neurites resembling dorsal root ganglia in culture. Time-lapse video recordings indicate that cell motility on RBM gel is accompanied by extensive blebbing as well as extension of processes that attach to and pull together neighbouring cells. These cellular events may contribute to the disruption of the gel underneath aggregates that is apparent when cultures are stained with Coomasie Blue. Ultrastructural studies indicated that aggregates often have zonula adherens-type junctions where cell bodies and processes come in contact. PC12 cells seeded onto gels of laminin alone behave essentially the same as on RBM gels, whereas on collagen gels they behave as on 2-dimensional substrata and extended neurites rather than aggregate. The extent of aggregation increases with greater cell density and is enhanced significantly by NGF. Antisera to NGF reduce the NGF-enhancement of aggregation but do not block aggregation in the absence of NGF. Dibutyryl cAMP or epidermal growth factor, which stimulate process extension and cell division respectively, do not enhance aggregation. However, 3A3, a monoclonal antibody to a laminin/collagen receptor on PC12 cells and antibodies (Fab fragments) to the neural cell adhesion molecule both inhibit cell aggregation.

Nerve growth factor rapidly stimulates arachidonate metabolism in PC12 cells: potential involvement in nerve fiber growth

Homogenates prepared from pheochromocytoma (PC12) cells that are extending nerve fibers in response to nerve growth factor (NGF) have an increased capacity to metabolize exogenous arachidonate compared with homogenates prepared from cells untreated with NGF. These changes are not a consequence of cell attachment, since they are also seen in NGF-treated PC12 cells grown in suspension and are not found in attached cells grown in the absence of NGF. This NGF-stimulated increase in arachidonate metabolic capacity occurs rapidly and before the extension of nerve fibers. In contrast to NGF, epidermal growth factor does not alter the metabolism of exogenous arachidonate by PC12 cells. Radioimmunoassay of medium from PC12 cultures indicates that intact cells produce and release increased amounts of prostaglandin (PGE) in response to NGF. Drugs that inhibit arachidonate liberation from membrane phospholipids (mepacrine or 4-bromphenacyl bromide) block NGF-stimulated nerve fiber growth by PC12 cells. Selective inhibitors of cyclooxygenase metabolism of arachidonate (indomethacin and aspirin) fail to block growth, but inhibitors of lipoxygenase metabolism (baicalein, BW755, and eicosatetraynoic acid) are potent blockers. In cultures of dorsal root ganglion neurons, inhibitors of arachidonate release (mepacrine, 4-bromphenacyl bromide) or its subsequent metabolism by lipoxygenases (nordihydroquaiaretic acid, eicosatetraynoic acid) also prevent the early morphological events of nerve fiber growth. Our data suggest that NGF rapidly and specifically increases the capacity of PC12 cells to synthesize arachidonate metabolites, and that arachidonate metabolism may be important in nerve fiber growth by both PC12 cells and dorsal root ganglion neurons.