Distribution of cholinergic neuronal differentiation factor/leukemia inhibitory factor binding sites in the developing and adult rat nervous system in vivo

Role of leukemia inhibitory factor in the nervous system and its pathology

Leukemia inhibitory factor (LIF) is a multifunction cytokine that has various effects on different tissues and cell types in rodents and humans; however, its insufficiency has a relatively mild impact. This could explain why only some aspects of LIF activity are in the limelight, whereas other aspects are not well known. In this review, the LIF structure, signaling pathway, and primary roles in the development and function of an organism are reviewed, and the effects of LIF on stem cell growth and differentiation, which are important for its use in cell culturing, are described. The focus is on the roles of LIF in central nervous system development and on the modulation of its physiological functions as well as the involvement of LIF in the pathogenesis of brain diseases and injuries. Finally, LIF and its signaling pathway are discussed as potential targets of therapeutic interventions to influence both negative phenomena and regenerative processes following brain injury.

The metabolite GnRH-(1-5) inhibits the migration of immortalized GnRH neurons

The decapeptide GnRH is an important regulator of reproductive behavior and function. In the extracellular matrix, GnRH is metabolized by the endopeptidase EC3.4.24.15 (EP24.15) to generate the pentapeptide GnRH-(1-5). In addition to its expression in the adult hypothalamus, EP24.15 is expressed along the migratory path of GnRH-expressing neurons during development. Although we have previously demonstrated a role for EP24.15 in the generation of the biologically active pentapeptide GnRH-(1-5) in regulating GnRH expression and mediating sexual behavior during adulthood in rodents, the modulatory role of GnRH-(1-5) in the migration of GnRH neurons during development remains unknown. To address this information gap, we examined the effect of GnRH-(1-5) on the cellular migration of a premigratory GnRH-secreting neuronal cell line, the GN11 cell, using a wound-healing assay. Dose- and time-response studies demonstrated that GnRH-(1-5) significantly delayed wound closure. We then sought to identify the mechanism by which GnRH-(1-5) inhibits migration. Because the cognate GnRH receptor is a G protein-coupled receptor, we examined whether GnRH-(1-5) regulates migration by also activating a G protein-coupled receptor. Using a high-throughput β-arrestin recruitment assay, we identified an orphan G protein-coupled receptor (GPR173) that was specifically activated by GnRH-(1-5). Interestingly, small interfering RNA to GPR173 reversed the GnRH-(1-5)-mediated inhibition on migration of GN11 neurons. Furthermore, we also demonstrate that the GnRH-(1-5)-activated GPR173-dependent signal transduction pathway involves the activation of the signal transducer and activator of transcription 3 in GnRH migration. These findings indicate a potential regulatory role for GnRH-(1-5) in GnRH neuronal migration during development.

Toward cell replacement therapy: promises and caveats

Studies in animal models have suggested a role for stem cells in repair and regeneration of the nervous system. Human equivalents of stem and precursor cells have been isolated and their efficacy is being evaluated in rodent and primate models. Difficulties exist in translating results of these preclinical models to therapy in humans. Evolutionary differences among rodents, primates, and humans; fundamental differences in the anatomy and physiology; differences in immune responses in xenotransplant models; the paucity of good transplant models of chronic disease; and allelic variability in the cells themselves make any study evaluating the efficacy of cells in transplant models difficult to interpret. As no better alternatives to testing in animals exist, we suggest that at this early stage a considered step-by-step approach to testing and comparison of different transplant strategies in isolation will prepare us better for clinical trials than simple evaluation of functional outcomes in various models of disease. We emphasize that we do not recommend delaying or abandoning clinical trials; rather, we suggest that one anticipate failures and design experiments and data collection such that we learn from these failures to ensure future success in as rapid a time frame as possible.

Developmental cooperation of leukemia inhibitory factor and insulin-like growth factor I in mice is tissue-specific and essential for lung maturation involving the transcription factors Sp3 and TTF-1

The multifunctional proteins leukemia inhibitory factor (LIF) and insulin-like growth factor I (IGF-I) are expressed in overlapping patterns during development and, therefore, may act cooperatively. We show that mice doubly deficient in LIF and IGF-I all died at birth of apparent respiratory failure. Growth retardation, muscle hypoplasia and delayed ossification in IGF-I-deficient E18.5 mice were exacerbated by the absence of LIF. The transcription factor Sp3 was decreased in the skeleton of the double null mice. Pronounced depletion of olfactory bulb neurons, in contrast, was only IGF-I-dependent. The lungs displayed reduced air space in the IGF-I-deficient embryos and neonates, phenotype exacerbated in the double nulls, which showed abnormal epithelial cells and decreased Sp3 expression. In addition, the transcription factor TTF-1 and the surfactant protein B were lower in the lung of the double null neonates than in all other genotypes. LIF and IGF-I, thus, have cooperative and distinct tissue functions during development. Their essential role in bone ossification apparently involves Sp3, and in lung maturation Sp3 together with TTF-1.

Expression of leukemia inhibitory factor receptor mRNA in sensory dorsal root ganglion and spinal motor neurons of the neonatal rat

Previous studies have shown that the application of leukemia inhibitory factor to the proximal nerve stump prevents the degeneration of axotomized sensory neurons in the dorsal root ganglion and motor neurons in the spinal cord of newborn rats. This study investigated the expression of leukemia inhibitory factor receptor mRNA in these neurons using in situ hybridization. Leukemia inhibitory factor receptor mRNA was detected both in sensory neurons within the dorsal root ganglion and motor neurons of the cervical spinal cord. Twenty-four hours after axotomy these neurons continue to express leukemia inhibitory factor receptor mRNA. This pattern of leukemia inhibitory factor receptor expression provides a mechanism by which endogenous and exogenous leukemia inhibitory factor could act on injured sensory and motor neurons.

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.

Regulation of the biosynthesis and processing of chromogranins in organotypic slices: influence of depolarization, forskolin and differentiating factors

Slices from rat hippocampus in organotypic culture were used to study the biosynthesis regulation of chromogranins A and B and secretogranin II. Additionally, we investigated the proteolytic conversion of secretogranin II and the levels of prohormone convertases putatively involved. Forskolin treatment and depolarization with potassium plus BayK 8644 led to significant increases in secretogranin II mRNA in the principal cells of the hippocampus. Enhanced expression of secretogranin II was also reflected by a rise in peptide levels. Despite this induction of biosynthesis the extensive processing to secretoneurin normally observed in brain was maintained. Both forskolin and depolarization upregulated the prohormone convertase (PC)1, but not PC2, indicating that PC1 levels are critical for secretoneurin production under stimulating conditions. Results obtained for chromogranins A and B were less consistent. For chromogranin A mRNA, changes were restricted to granule cells; for chromogranin B, a response in granule cells was observed to depolarization but not to forskolin, and effects in pyramidal neurons were weak. Accordingly, we were unable to detect alterations in chromogranin A and B protein levels. Furthermore, we tested several neurotrophic growth factors and found that only basic fibroblast growth factor raised secretogranin II expression without affecting chromogranins A and B. The hippocampal slice preparation allowed well controlled treatment with identification of neuronal subpopulations and yielded data largely matching experiments in vivo and in cell culture. The pronounced regulation of secretogranin II and its effective processing underlines the importance of the resulting peptide secretoneurin as an active neuropeptide in the nervous system.

Localization of gp130 in the developing and adult mouse cerebellum

Interleukin-6 (IL-6) type cytokines show functional redundancy in the immune, hematopoietic, and nervous system, which is believed to result from sharing of the signal transducing receptor gp130. IL-6 type cytokines and their binding receptors have been localized in the adult cerebellum. However, the cellular localization and developmental regulation of gp130 in the cerebellum have not been determined. In the present study the expression pattern of gp130 in the developing and adult mouse cerebellum was investigated. At embryonic day (E)15 and E17, gp130 immunoreactivity is present primarily in fiber bundles that course from the brainstem to the cerebellum. At postnatal day (P)0, gp130 immunoreactivity first appears in the Purkinje cell layer, external granule cell layer, and cerebellar nuclei. As Purkinje cells differentiate, gp130 immunoreactivity progressively extends from the cell body along their developing dendritic arbor. All Purkinje cells show intense gp130 immunoreactivity in their cell bodies by P7. In contrast the gp130 immunoreactivity detected in fiber bundles at E15 and E17 is downregulated postnatally, and cannot be detected after P7. Granule cells show gp130 immunoreactivity at P0 in the external granule cell layer and subsequently in the internal granule cell layer. Astrocytes in the white matter express gp130 at P0, and show intense gp130 immunoreactivity between P7 and P14. As the cerebellum matures gp130 immunoreactivity in the white matter decreases. The present description of the differential spatial and temporal distribution of gp130 provides an initial step in defining specific cellular populations that are potential targets of IL-6 type cytokines during cerebellar ontogeny.

Effect of leukemia inhibitory factor (LIF) on the morphology and survival of cultured hippocampal neurons and glial cells

Leukemia inhibitory factor (LIF) is a cytokine involved in the survival, differentiation and regeneration of sympathetic, sensory and motor neurons. Its effects in the brain are less well characterized. In a previous study, we found LIF transcripts to be predominantly expressed in neurons of the adult rat brain. Highest levels were observed in the hippocampus, particularly in granular neurons of the dentate gyrus and in hilar interneurons. Here we report the effects of LIF on survival and differentiation of postnatal rat hippocampal cells in vitro. We find that LIF minimally influences the survival and differentiation of dentate gyrus neurons, causing a slight reduction of the number of dendrites per neuron. In contrast, LIF induces a pronounced increase in the number of astrocytes. This increase does not appear to be due to enhanced proliferation but rather to increased cell survival. On the other hand, epidermal growth factor (EGF) induces astrocyte proliferation, and addition of LIF inhibits the EGF effect. In summary, LIF does not appear to be crucial for the survival or differentiation of cultured dentate gyrus neurons. This cytokine increases astrocyte survival but does not enhance astrocyte proliferation, and LIF is able to counteract the growth stimulation elicited by EGF.

Differentiation of mesencephalic progenitor cells into dopaminergic neurons by cytokines

Rat progenitor cells from the germinal region of the fetal mesencephalon were isolated and expanded in media containing the mitogen epidermal growth factor. These cells remained mitotically active (up to 8 months), were immunoreactive for the progenitor cell marker nestin, and were readily infected with the BAG alpha retrovirus. When incubated in complete media containing serum in poly-L-lysine-coated plates, these cells spontaneously converted to neurons and glia but rarely expressed the dopamine (DA) neuron phenotype. Nineteen different cytokines were screened for their ability to induce the DA phenotype and only interleukin (IL)-1 was found to induce the expression of the DA neuron marker tyrosine hydroxylase (TH). The addition of IL-1, IL-11, leukemia inhibitory factor (LIF), and glial cell line-derived neurotrophic factor (GDNF) were found to further increase the number of TH immunoreactive (TH-ir) cells. The addition of mesencephalic membrane fragments and striatal culture-conditioned media along with the cytokine mixture induced the expression of morphologically mature TH-ir cells that were also immunoreactive for dopa-decarboxylase, the DA transporter, and DA itself. The DA neuron cell counts were approximately 20-25% of the overall cell population and 50% of the neurofilament population. Astrocytes and oligodendrocytes were also present. These data suggest that hematopoietic cytokines participate in the development of the DA neuron phenotype. Parallels between the function of hematopoietic cytokines in bone marrow and the central nervous system may exist and be useful in understanding the factors which regulate the differentiation of neurons in the brain.

LIF is an autocrine factor for sympathetic neurons

Leukemia inhibitory factor (LIF) alters neuronal phenotypes both in vitro and in vivo. Since it can be produced by glia and other nonneural cells, LIF is a candidate target-derived differentiation factor as well as an injury-response factor. We here provide evidence that LIF can be produced by neurons and can act on the neurons that produce it. A reverse transcriptase-polymerase chain reaction assay detects LIF mRNA in rat sympathetic neuron cultures, and in situ hybridization combined with MAP2 immunocytochemistry indicates that most of the cells expressing LIF mRNA are, in fact, neurons. The neuronal lysate as well as the conditioned medium contains proteins that are specifically recognized by anti-LIF antibodies, and these antibodies also specifically stain the cultured neurons. In addition, concentrated sympathetic neuron conditioned medium can mimic the effects of LIF, and incubation of high-density sympathetic neuron cultures with anti-LIF antibodies reduces basal expression levels of LIF target genes such as particular neuropeptides, indicating that the endogenously produced cytokine is acting on the neurons under these conditions. Since we show that LIF transcript is expressed in sympathetic and sensory neurons in vivo as well, LIF could act in an autocrine fashion under a variety of physiological conditions.

Leukemia inhibitory factor (LIF) mRNA-expressing neuronal subpopulations in adult rat basal forebrain

We have previously found leukemia inhibitory factor (LIF) mRNA in neurons of the adult rat brain. To identify which neuronal subpopulations are expressing LIF transcripts, non-radioactive in situ hybridization was combined with immunocytochemistry for various neuronal markers. Studying the rat basal forebrain and cerebral cortex, we find LIF mRNA is expressed in both cholinergic and GABAergic neurons. These data suggest a role for LIF in the function of these mature neurons.