Neurite Outgrowth Of Cerebellar Neurons Research Articles

Vinorelbine and epirubicin share common features with polysialic acid and modulate neuronal and glial functions.

Polysialic acid (PSA), a large, linear glycan composed of 8 to over 100 α2,8-linked sialic acid residues, modulates development of the nervous system by enhancing cell migration, axon pathfinding, and synaptic targeting and by regulating differentiation of progenitor cells. PSA also functions in developing and adult immune systems and is a signature of many cancers. In this study we identified vinorelbine, a semi-synthetic third generation vinca alkaloid, and epirubicin, an anthracycline and 4'-epimer of doxorubicin, as PSA mimetics. Similar to PSA, vinorelbine and epirubicin bind to the PSA-specific monoclonal antibody 735 and compete with the bacterial analog of PSA, colominic acid in binding to monoclonal antibody 735. Vinorelbine and epirubicin stimulate neurite outgrowth of cerebellar neurons via the neural cell adhesion molecule, via myristoylated alanine-rich C kinase substrate, and via fibroblast growth factor receptor, signaling through Erk pathways. Furthermore, the two compounds enhance process formation of Schwann cells and migration of cerebellar neurons in culture, and reduce migration of astrocytes after injury. These novel results show that the structure and function of PSA can be mimicked by the small organic compounds vinorelbine and epirubicin, thus raising the possibility to re-target drugs used in treatment of cancers to nervous system repair. Vinorelbine and epirubicin, identified as PSA mimetics, enhance, like PSA, neuronal migration, neuritogenesis, and formation of Schwann cell processes, and reduce astrocytic migration. Ablating NCAM, inhibiting fibroblast growth factor (FGFR) receptor, or adding the effector domain of myristoylated alanine-rich C kinase substrate (MARCKS) minimize the vinorelbine and epirubicin effects, indicating that they are true PSA mimetics triggering PSA-mediated functions.

The Interaction between Cell Adhesion Molecule L1, Matrix Metalloproteinase 14, and Adenine Nucleotide Translocator at the Plasma Membrane Regulates L1-Mediated Neurite Outgrowth of Murine Cerebellar Neurons

We have identified the adenine nucleotide translocator (ANT) isoforms ANT1 and ANT2 that are present in the plasma membrane of mouse cerebellar neurons as novel binding partners of the cell adhesion molecule L1. The direct interaction between ANT and L1 is mediated by sites within the fibronectin type III domains of L1 and the first and third extracellular loops of the ANT proteins. We also show that L1 interacts with the ANT binding partner matrix metalloprotease 14 (MMP14) and that the ANT proteins bind directly to the L1 interaction partner glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Moreover, we provide evidence that the functional interplay between L1, ANT proteins, MMP14, and GAPDH at the plasma membrane mediates L1-induced neurite outgrowth of cerebellar neurons. Disruption of this interplay by ANT inhibitors, ANT-derived synthetic peptides, and/or function-blocking MMP14 and ANT antibodies leads to alterations in L1-dependent neurite outgrowth. Stimulation of L1-mediated signaling in cerebellar neurons triggers transient ATP secretion via ANT proteins and leads to transient src family-dependent tyrosine phosphorylation of L1, ANT1, ANT2, and MMP14. Thus, our results indicate that plasma membrane-localized ANT1 and ANT2 regulate L1-mediated neurite outgrowth in conjunction with MMP14.

An in vitro model of the inhibition of axon growth in the lesion scar formed after central nervous system injury

After central nervous system (CNS) injury, meningeal fibroblasts migrate in the lesion center to form a fibrotic scar which is surrounded by end feet of reactive astrocytes. The fibrotic scar expresses various axonal growth-inhibitory molecules and creates a major impediment for axonal regeneration. We developed an in vitro model of the scar using coculture of cerebral astrocytes and meningeal fibroblasts by adding transforming growth factor-β1 (TGF-β1), a potent fibrogenic factor. Addition of TGF-β1 to this coculture resulted in enhanced proliferation of fibroblasts and the formation of cell clusters which consisted of fibroblasts inside and surrounded by astrocytes. The cell cluster in culture densely accumulated the extracellular matrix molecules and axonal growth-inhibitory molecules similar to the fibrotic scar, and remarkably inhibited the neurite outgrowth of cerebellar neurons. Therefore, this culture system can be available to analyze the inhibitory property in the lesion site of CNS.

O-glycosylation pattern of CD24 from mouse brain

The cell adhesion molecule CD24 is a highly glycosylated glycoprotein that plays important roles in the central nervous system, the immune system and in tumor biology. Since CD24 comprises only a short protein core of approximately 30 amino acids and low conservation among species, it has been proposed that the functions of CD24 are mediated by its glycosylation pattern. Our present study provides evidence that interaction of CD24 with the cell adhesion molecule L1 is mediated by O-linked glycans carrying alpha2,3-linked sialic acid. Furthermore, de-N-glycosylated CD24 was shown to promote or inhibit neurite outgrowth of cerebellar neurons or dorsal root ganglion neurons, respectively, to the same extent as untreated CD24. Therefore, this study is focused on the structural elucidation of the chemically released, permethylated CD24 O-glycans by electrospray ionization ion trap mass spectrometry. Our analyses revealed the occurrence of a diverse mixture of mucin-type and O-mannosyl glycans carrying, in part, functionally relevant epitopes, such as 3-linked sialic acid, disialyl motifs, Le(X), sialyl-Le(X) or HNK-1 units. Hence, our data provide the basis for further studies on the contribution of carbohydrate determinants to CD24-mediated biological activities.

L1 Is Sequentially Processed by Two Differently Activated Metalloproteases and Presenilin/γ-Secretase and Regulates Neural Cell Adhesion, Cell Migration, and Neurite Outgrowth

The immunoglobulin superfamily recognition molecule L1 plays important functional roles in the developing and adult nervous system. Metalloprotease-mediated cleavage of this adhesion molecule has been shown to stimulate cellular migration and neurite outgrowth. We demonstrate here that L1 cleavage is mediated by two distinct members of the disintegrin and metalloprotease family, ADAM10 and ADAM17. This cleavage is differently regulated and leads to the generation of a membrane bound C-terminal fragment, which is further processed through gamma-secretase activity. Pharmacological approaches with two hydroxamate-based inhibitors with different preferences in blocking ADAM10 and ADAM17, as well as loss of function and gain of function studies in murine embryonic fibroblasts, showed that constitutive shedding of L1 is mediated by ADAM10 while phorbol ester stimulation or cholesterol depletion led to ADAM17-mediated L1 cleavage. In contrast, N-methyl-d-aspartate treatment of primary neurons stimulated ADAM10-mediated L1 shedding. Both proteases were able to affect L1-mediated adhesion and haptotactic migration of neuronal cells. In particular, both proteases were involved in L1-dependent neurite outgrowth of cerebellar neurons. Thus, our data identify ADAM10 and ADAM17 as differentially regulated L1 membrane sheddases, both critically affecting the physiological functions of this adhesion protein.

The Proprotein Convertase PC5A and a Metalloprotease Are Involved in the Proteolytic Processing of the Neural Adhesion Molecule L1

The transmembrane and multidomain neural adhesion molecule L1 plays important functional roles in the developing and adult nervous system. L1 is proteolytically processed at two distinct sites within the extracellular domain, leading to the generation of different fragments. In this report, we present evidence that the proprotein convertase PC5A is the protease that cleaves L1 in the third fibronectin type III domain, whereas the proprotein convertases furin, PC1, PC2, PACE4, and PC7 are not effective in cleaving L1. Analysis of mutations revealed Arg(845) to be the site of cleavage generating the N-terminal 140-kDa fragment. This fragment was present in the hippocampus, which expresses PC5A, but was not detectable in the cerebellum, which does not express PC5A. The 140-kDa L1 fragment was found to be tightly associated with the full-length 200-kDa L1 molecule. The complex dissociated from the membrane upon cleavage by a protease acting at a more membrane-proximal site of full-length L1. This proteolytic cleavage was inhibited by the metalloprotease inhibitor GM 6001 and enhanced by a calmodulin inhibitor. L1-dependent neurite outgrowth of cerebellar neurons was inhibited by GM 6001, suggesting that proteolytic processing of L1 by a metalloprotease is involved in neurite outgrowth.

Association of the Growth-Arrest-Specific Protein Gas7 with F-Actin Induces Reorganization of Microfilaments and Promotes Membrane Outgrowth

The growth-arrest-specific gene, Gas7, is required for neurite outgrowth in cerebellar neurons. Here we report that Gas7 can induce the formation of extended cellular processes in NIH3T3 cells by interacting with actin and mediating reorganization of microfilaments. The Gas 7 protein, which increased markedly during growth arrest of NIH3T3 cells and persisted transiently at high levels upon reentry of cells into the cell cycle, localized near the plasma membrane and selectively colocalized with microfilaments in membrane ruffles. Process extensions induced by ectopic overexpression of Gas7 were blocked by the actin-depolymerizing agent cytochalasin D, suggesting that membrane extensions produced by Gas7 require actin polymerization. Association of endogenous Gas7 protein with microfilaments was verified by F-actin affinity chromatography; direct binding of purified His-Gas7 to actin also was demonstrated and shown to be mediated by the Gas7 C-terminal domain. Similarly, localization of Gas7 in membrane ruffles was mediated by the C-terminal domain, although neither this region nor the N-terminal domain was individually sufficient to induce process formation. Biochemical studies and electron microscopy showed that both full-length Gas7 protein and its C-terminal region can promote actin assembly as well as the crosslinking of actin filaments. We propose that Gas7 localized near the plasma membrane induces the assembly of actin and the membrane outgrowth.