An in vitro cell culture system for the aggregation of embryonic chick central nervous system neurons

Isolamento e cultivo de neurônios e neuroesferas de córtex cerebral aviar

Métodos de cultivo celular são convenientes na realização de análises funcionais de alterações/interações protéicas das células neuronais, auxiliando a decifrar o interactoma de proteínas chaves na neurogênese de doenças do Sistema Nervoso Central. Por esse motivo, culturas de neurônios e neuroesferas isolados do córtex cerebral aviar representam um modelo acessível para o estudo de diversas doenças neurológicas, tal como a epilepsia. A espécie aviar apresenta peculiaridades em seu proteoma neuronal, visto a presença de uma expressão diferenciada de proteínas chaves no metabolismo energético cerebral, algumas destas (VDAC1 e VDAC2) desempenham papel importante na compreensão do mecanismo da epilepsia refratária. A metodologia estabelecida no presente estudo obteve cultivo de neuroeferas, onde as células cresceram tipicamente em aglomerados atingindo, dentro de 7 dias, o diâmetro ideal de 100-200 µm. A diferenciação celular das neuroesferas foi obtida após a aderência destas às placas tratadas com poli-D-lisina, evidenciada pela migração de fibras do interior da neuroesfera. Ao contrário das neuroesferas, os neurônios em cultivo extenderam seus neuritos após 11 dias de isolamento. Tal modelo in vitro pode ser utilizado com sucesso na identificação das variáveis neuroproteômicas, propiciando uma avaliação global das alterações dinâmicas e suas interações protéicas. Tal modelo pode ter aplicações em estudos dos efeitos de indutores da morte celular e bloqueadores de canais de membrana mitocondriais em proteínas chaves do metabolismo energético cerebral.

TLR-4-dependent and -independent mechanisms of fetal brain injury in the setting of preterm birth

In this study, we sought to assess how essential activation of toll-like receptor 4 (TLR-4) is to fetal brain injury from intrauterine inflammation. Both wild-type and TLR-4 mutant fetal central nervous system cells were exposed to inflammation using lipopolysaccharide in vivo or in vitro. Inflammation could not induce neuronal injury in the absence of glial cells, in either wild-type or TLR-4 mutant neurons. However, injured neurons could induce injury in other neurons regardless of TLR-4 competency. Our results indicate that initiation of neuronal injury is a TLR-4-dependent event, while propagation is a TLR-4-independent event.

Compact self-wiring in cultured neural networks

We present a novel approach for patterning cultured neural networks in which a particular geometry is achieved via anchoring of cell clusters (tens of cells/each) at specific positions. In addition, compact connections among pairs of clusters occur spontaneously through a single non-adherent straight bundle composed of axons and dendrites. The anchors that stabilize the cell clusters are either poly-D-lysine, a strong adhesive substrate, or carbon nanotubes. Square, triangular and circular structures of connectivity were successfully realized. Monitoring the dynamics of the forming networks in real time revealed that the self-assembly process is mainly driven by the ability of the neuronal cell clusters to move away from each other while continuously stretching a neurite bundle in between. Using the presented technique, we achieved networks with wiring regions which are made exclusively of neuronal processes unbound to the surface. The resulted network patterns are very stable and can be maintained for as long as 11 weeks. The approach can be used to build advanced neuro-chips for bio-sensing applications (e.g. drug and toxin detection) where the structure, stability and reproducibility of the networks are of great relevance.

SCO-spondin, a glycoprotein of the subcommissural organ/Reissner's fiber complex: evidence of a potent activity on neuronal development in primary cell cultures

In the cattle, SCO-spondin was shown to be a brain-secreted glycoprotein specifically expressed in the subcommissural organ (SCO), an ependymal differentiation located in the roof of the Sylvian aqueduct. Furthermore, SCO-spondin makes part of Reissner's fiber (RF), a structure present in the central canal of the spinal cord. Sequencing of overlaping cDNA inserts after successive screening of a cattle SCO cDNA expression library allowed characterization of the complete sequence of this novel protein. Conserved domains were identified including twenty-six thrombospondin type 1 repeats (TSRs), nine low-density lipoprotein receptor LDLr type A domains (LDLRA), two epidermal growth factor EGF-like domains, and homologies to mucins and the von Willebrand factor were found in the amino- and carboxy- termini. In addition, SCO-spondin shows a unique arrangement "in mosaic" of these domains. The putative function of SCO-spondin in neuronal differentiation is discussed regarding these features and homologies with other developmental molecules of the central nervous system exhibiting TSR domains, and involved in axonal guidance.To correlate molecular and functional features of SCO-spondin, we tested the effect of oligopeptides whose sequences include highly conserved regions of the TSRs, LDLRA repeats, and a potent site of attachment to glycosaminoglycan, on cortical and spinal cord neurons in primary cell cultures. Peptides corresponding to SCO-spondin TSRs markedly increased adhesivity and neuritic outgrowth of cortical neurons and induced disaggregation of spinal cord neurons. Thus, SCO-spondin is a candidate to interfere with neuronal development and/or axonal guidance during ontogenesis of the central nervous system in modulating side-to-side and side-to-substratum interactions, and in promoting neuritic outgrowth. RF proper has a wide range of activity on neuronal differentiation, including survival, aggregation, and disaggregation effects and neurite extension of cortical and spinal cord neurones "in vitro." Thus, the SCO/RF complex may interact with developmental processes of the central nervous system including the posterior commissure and spinal cord differentiation.

Biosynthesis and molecular biology of the secretory proteins of the subcommissural organ

Ependymal cells are specialized in the synthesis and release of different factors into the cerebrospinal fluid (CSF). The subcommissural organ (SCO) is one of the most active areas of the ventricular walls secreting into the CSF. This gland is localized in the roof of the third ventricle covering the posterior commissure. Glycoproteins synthesized in SCO cells are released into the ventricular CSF where they aggregate, in a highly ordered fashion, forming an elongated supramacromolecular structure known as the Reissner's fiber (RF). RF grows caudally and extends along the brain aqueduct, the fourth ventricle, and the whole length of the central canal of the spinal cord. The SCO cells synthesize glycoproteins of high molecular weight. A precursor form of 540 kDa is synthesized in bovine and chick SCO cells, and a transcript of 10--14 kb is expressed selectively in the bovine SCO cells. The processing of this molecule generates at least one protein of about 450 kDa (RF-Gly-I), which, after being released, is involved in the formation of RF. Additionally, biochemical data indicate that bovine SCO cells synthesize a second precursor compound of 320 kDa, which is also detected in rat, rabbit, and dog. We postulate that RF is formed by two different complexes, one of which has a very high molecular mass (700 kDa or more) and is made up of at least six polypeptides, with the polypeptide of 450 kDa being its main component. The molecules that form RF in different species have different primary structures but they express common epitopes associated to the existence of cysteine bridges, which are probably crucial for polymerization of RF. Molecular procedures involving the use of anti-RF antibodies have led to the isolation of cDNA clones encoding two proteins known as RF-GLY-I and SCO-spondin. In the last 3 years, five partial cDNA sequences encoding SCO-spondin-like proteins have been obtained (Y08560, Y08561, AJ132107, AJ132106, AJ133488). These clones along with RF-GLY-I and SCO-spondin were computer-assembled generating a cDNA consensus sequence of 14.4 kb. Analyses of the long consensus sequence revealed an extended open reading frame (ORF-1) spanning from base 1,634 to 14,400 that encodes for a putative protein of 4,256 amino acids (approximately 450 kDa). The Mr of the predicted protein is consistent with the observed Mr of the largest protein recognized with anti-RF antibodies in SCO and RF extracts. However, the absence of consensus sequences typically present near the 5J'-end of the translation initiation site suggests the existence of a second open reading frame (ORF-2) extending from base 1 to base 14,400 in frame with the ORF-1 and probably encoding for the largest protein precursor (540 kDa). An antibody raised against a peptide sequence, deduced from the open reading frame encoded by a SCO cDNA, reacted specifically with the bovine and rat SCO-RF complex, thus indicating that the protein encoded by the cloned cDNA is part of RF. Immunoblots of bovine SCO extracts using the anti-peptide serum revealed bands of 540 kDa and 450 kDa, but it did not react with the proteins of 320 and 190 kDa. These data support the existence of two precursors for the bovine RF-glycoproteins (540 and 320 kDa) with the 450-kDa protein being a processed form of the 540-kDa precursor. We postulate that the cloned cDNAs encode for a protein that corresponds to the 540-kDa precursor and that at least part of this sequence is present in the processed form of 450 kDa that is secreted to form the RF.