Effects of phorbol ester on expression of CNTF-mRNA in cultured astrocytes from rat olfactory bulb

The role of bioactive compounds on the promotion of neurite outgrowth

Neurite loss is one of the cardinal features of neuronal injury. Apart from neuroprotection, reorganization of the lost neuronal network in the injured brain is necessary for the restoration of normal physiological functions. Neuritogenic activity of endogenous molecules in the brain such as nerve growth factor is well documented and supported by scientific studies which show innumerable compounds having neurite outgrowth activity from natural sources. Since the damaged brain lacks the reconstructive capacity, more efforts in research are focused on the identification of compounds that promote the reformation of neuronal networks. An abundancy of natural resources along with the corresponding activity profiles have shown promising results in the field of neuroscience. Recently, importance has also been placed on understanding neurite formation by natural products in relation to neuronal injury. Arrays of natural herbal products having plentiful active constituents have been found to enhance neurite outgrowth. They act synergistically with neurotrophic factors to promote neuritogenesis in the diseased brain. Therefore use of natural products for neuroregeneration provides new insights in drug development for treating neuronal injury. In this study, various compounds from natural sources with potential neurite outgrowth activity are reviewed in experimental models.

Effect of ammonia on ciliary neurotrophic factor mRNA and protein expression and its upstream signalling pathway in cultured rat astroglial cells: possible implication of c-fos, Sp1 and p38MAPK

Ciliary neurotrophic factor (CNTF) may be implicated in the pathogenetic mechanisms of hepatic encephalopathy. We tested this hypothesis by treating confluent primary cultures of rat astroglial cells with ammonium chloride for various periods and analysing the effect of ammonia on the signalling pathway that regulates CNTF mRNA and protein expression. Ammonia treatment induced a dose- and time-dependent reduction in CNTF mRNA and protein expression. Surface-enhanced laser desorption/ionization-time-of-flight mass spectrometry analysis of CNTF in the culture medium demonstrated that ammonia also induced a significant decrease in CNTF release. In addition, ammonia affected Sp1 and c-fos, transcription factors that regulate CNTF mRNA and protein expression, which showed partial dephosphorylation and significantly lower mRNA and protein levels. Total content of p38MAPK (for which Sp1 and c-fos are substrates) was unaffected by ammonia, although the diphosphorylated (active) form was significantly reduced after ammonia exposure.

(−)-3,5-Dicaffeoyl-muco-quinic acid isolated from Aster scaber contributes to the differentiation of PC12 cells: through tyrosine kinase cascade signaling

Aster scaber T. (Asteraceae) has been used in traditional Korean and Chinese medicine to treat bruises, snakebites, headaches, and dizziness. (-)-3,5-Dicaffeoyl-muco-quinic acid (DQ) isolated from A. scaber induced neurite outgrowth in PC12 cells. It has been reported that the activation of the extracellular signal regulated kinase 1/2 (Erk 1/2) and phosphoinositide 3 (PI3) kinase plays a crucial role in the NGF-induced differentiation of PC12 cells. This study showed that the effect of DQ on neurite outgrowth is mediated via the Erk 1/2 and PI3 kinase-dependent pathways like NGF. Furthermore, DQ stimulated the phosphorylation of Trk A. Overall, DQ elicited the differentiation of PC12 cells through Trk A phosphorylation followed by Erk 1/2 and PI3 kinase activation.

Phorbol ester induces CYP2E1 in astrocytes, through a protein kinase C- and tyrosine kinase-dependent mechanism

Cytochrome P450 2E1 (CYP2E1) is highly inducible in a subset of astrocytes in vivo following ischemic or mechanical injury and in vitro by lipopolysaccharide or interleukin-1beta. In the present study, phorbol-12,13-dibutyrate (PDBu) was found to induce catalytically active CYP2E1 more than fourfold in cortical glial cultures. Little induction was seen up to 12 h, and full effects only at 21-24 h of PDBu treatment. CYP2E1 expression in PDBu-treated cells was enriched in a subset of astrocytes. The protein kinase C inhibitors, staurosporine and calphostin C, and the tyrosine kinase inhibitor genistein, but not its inactive analogue daidzein, prevented the induction of CYP2E1 by PDBu. It is suggested that CYP2E1, together with interleukin-6 and ciliary neurotrophic factor, is part of a response of astrocytes to cellular stress elicited by, e.g. cerebral injury, cytokines or phorbol ester, and mediated in part through protein kinase C.

ACTH(1-24) down-regulates expression of ciliary neurotrophic factor mRNA in cultured rat astrocyte

We examined the effects on astrocytes of ACTH, which is used to treat West syndrome. We stimulated cultured rat astrocytes with ACTH(1-24), corticotropin-releasing factor, and dexamethasone, and examined changes in neurotrophic factor mRNAs by reverse transcription-PCR. Down-regulation of ciliary neurotrophic factor mRNA expression was observed by stimulation with ACTH(1-24), but the expression of nerve growth factor, brain-derived neurotrophic factor, and nerotrophin-3 mRNAs was unaffected. Northern blot analysis revealed that the decrease in ciliary neurotrophic factor mRNA occurred 4 h after stimulation with more than 10 nM of ACTH(1-24). Up-regulation of nerotrophin-3 mRNA expression was found after stimulation with 1 mM dexamethasone. These results suggest that ACTH(1-24) administrated in West syndrome may influence the expression of neurotrophic factors in astrocytes in vivo.

Protein kinase C mediates neurite guidance at an astrocyte boundary

During development, astrocytes play an active role in directing axons to their final targets. This guidance has been attributed in part to the increased expression of guidance molecules, such as tenascin-C and chondroitin sulfate proteoglycans, by boundary-forming astrocytes. We have previously used a culture model of astrocyte boundaries to demonstrate that neurites growing on permissive astrocytes alter their trajectory as they encounter less-permissive astrocytes. The present study investigated the role of the protein kinase C (PKC) family of signal transduction molecules in this form of axonal guidance. Neurons were plated onto mixed astrocyte monolayers in the presence of agents that either downregulate the phorbol ester-sensitive PKC isoforms or inhibit PKC. Both downregulation and inhibition of PKC increased the percentage of neurons that crossed onto the nonpermissive astrocytes. On astrocyte monolayers, phorbol ester modulation of PKC but not PKC inhibitors resulted in a decrease in overall neurite extension. PKC inhibitors also caused a similar alteration in the neuronal response to cell-free boundaries, at concentrations that did not inhibit neurite extension. Thus, phorbol-ester-sensitive PKC isoforms direct the guidance of neurites by astrocyte-derived matrix molecules.

Immunohistochemical localization of interleukin-2 and its receptor subunits alpha, beta and gamma in the main olfactory bulb of the rat

Endogenous interleukin-2 (IL-2) was found in the adult rat brain, however, it has not been reported whether this cytokine is present in the olfactory bulb. Immunohistochemical techniques were used to examine the cellular localization of IL-2 and its receptor subunits in the main olfactory bulb of the rat. Strong IL-2 immunoreactivity was localized in glial cells, specifically in the olfactory nerve layer, glomerular layer and external plexiform layer. IL-2 mRNA was detected in the olfactory bulb by RT-PCR. All three IL-2 receptor subunits also showed distinct laminar distributions. The IL-2Ralpha and IL-2Rbeta immunoreactivity was found both in neurons and glial cells, whereas IL-2Rgamma imunoreactivity was found in glial cells, and thus resembled IL-2 immunostaining. The present results demonstrated a wide distribution of IL-2 and its receptor subunits in the main olfactory bulb of the rat, suggesting that IL-2 might play a role in the olfactory function through autocrine or paracrine pathways. The exclusive high expression of IL-2 in glial cells in distinct laminar structures, where neuron-glia interactions are closely associated with olfactory nerve regeneration, imply that IL-2 might be involved in the process of nerve regeneration in the olfactory bulb.

Neurotrophic factors in the primary olfactory pathway

The number of identified growth factors continues to increase rapidly with many being implicated in the development of the nervous system, although for most of them the autocrine and paracrine pathways of cellular regulation still remain to be elucidated. The primary olfactory pathway, consisting of the olfactory epithelium and olfactory bulb, is presented here as a very useful model for the analysis of growth factor function. Review of the available literature suggests that a large proportion of neuroactive growth factors and their receptors are present in the olfactory epithelium or olfactory bulb. Furthermore, the primary olfactory pathway is one of the most plastic in the nervous system with neurogenesis continuing to contribute new sensory neurones in the olfactory epithelium and new interneurones in the olfactory bulb throughout adult life. The rich diversity of growth factors and their receptors in the olfactory system indicates that it will be useful in elucidating how these molecules regulate the formation of the nervous system. The olfactory epithelium in particular is proving useful as a model for the actions of growth factors in directing the neuronal lineage from stem cell to mature neurone.

The optic nerve head in glaucoma: role of astrocytes in tissue remodeling

Primary open angle glaucoma is a common eye disease characterized by loss of the axons of the retinal ganglion cells leading to progressive loss of vision. The site of damage to the axons is at the level of the lamina cribrosa in the optic nerve head. The mechanism of axonal loss is unknown but elevated intraocular pressure and age are the most common factors associated with the disease. Previous studies in human glaucoma and in experimental glaucoma in monkeys have established a relationship between chronic elevation of intraocular pressure and remodeling of the optic nerve head tissues known clinically as cupping of the optic disc. This review focuses on the astrocytes, the major cell type in the optic nerve head. Astrocytes participate actively in the remodeling of neural tissues during development and in disease. In glaucomatous optic neuropathy, astrocytes play a major role in the remodeling of the extracellular matrix of the optic nerve head, synthesize growth factors and other cellular mediators that may affect directly, or indirectly, the axons of the retinal ganglion cells. Due to the architecture of the lamina cribrosa, formed by the cells and the fibroelastic extracellular matrix, astrocytes may respond to changes in intraocular pressure in glaucoma, leading to some of the detrimental events that underlie axonal loss and retinal ganglion cell degeneration.