LIF is an autocrine factor for sympathetic neurons

New insights into Chlamydia pathogenesis: Role of leukemia inhibitory factor

Chlamydia trachomatis (Ct) is the leading cause of bacterial sexually transmitted infections worldwide. Since the symptoms of Ct infection are often subtle or absent, most people are unaware of their infection until they are tested or develop severe complications such as infertility. It is believed that the primary culprit of Ct-associated tissue damage is unresolved chronic inflammation, resulting in aberrant production of cytokines, chemokines, and growth factors, as well as dysregulated tissue influx of innate and adaptive immune cells. A member of the IL-6 cytokine family, leukemia inhibitory factor (LIF), is one of the cytokines induced by Ct infection but its role in Ct pathogenesis is unclear. In this article, we review the biology of LIF and LIF receptor (LIFR)-mediated signaling pathways, summarize the physiological role of LIF in the reproductive system, and discuss the impact of LIF in chronic inflammatory conditions and its implication in Ct pathogenesis. Under normal circumstances, LIF is produced to maintain epithelial homeostasis and tissue repair, including the aftermath of Ct infection. However, LIF/LIFR-mediated signaling – particularly prolonged strong signaling – can gradually transform the microenvironment of the fallopian tube by altering the fate of epithelial cells and the cellular composition of epithelium. This harmful transformation of epithelium may be a key process that leads to an enhanced risk of infertility, ectopic pregnancy and cancer following Ct infection.

Cardiac afferent signaling partially underlies premature ventricular contraction-induced cardiomyopathy

BACKGROUND

The mechanisms underlying premature ventricular contraction (PVC)-induced cardiomyopathy (PIC) remain unknown. Transient receptor potential vanilloid-1 (TRPV1) afferent fibers are implicated in the reflex processing of cardiac stress.

OBJECTIVE

The purpose of this study was to determine whether cardiac TRPV1 afferent signaling promote PIC.

METHODS

A PIC swine model (50% PVC burden) was created via an implanted pacemaker. We selectively depleted cardiac TRPV1 afferent fibers using percutaneous epicardial application of resiniferatoxin (RTX). Animals were randomized to PVC only (n = 11), PVC+RTX (n = 11), or control (n = 6). We examined early-stage (4 weeks after implantation; n = 5) and late-stage PIC (8 weeks after implantation; n = 6). At terminal experimentation, animals underwent echocardiography, serum sampling, and physiological and autonomic reflex testing.

RESULTS

Depletion of cardiac TRPV1 afferents by RTX treatment was confirmed by absent sensory fibers and absent functional responses to TRPV1 activators. Left ventricular ejection fraction was worse in late-stage than early-stage PIC (P <.01). At 4 weeks (early stage), left ventricular ejection fraction was higher in PVC+RTX vs PVC animals (51.7% ± 1.6% vs 45.0% ± 2.1%; P = .030), whereas no significant difference between PVC and PVC+RTX was observed at 8 weeks (late stage). Histologic studies demonstrated reduced fibrosis in PVC+RTX vs PVC alone at 4 weeks (2.27% ± 0.14% vs 3.01% ± 0.21%; P = .020), suggesting that RTX mitigated profibrotic pathways induced by persistent PVCs.

CONCLUSION

TRPV1 afferent depletion alleviates left ventricular dysfunction in early- but not late-stage PIC. This temporal effect suggests that multiple pathways promote PIC, of which TRPV1 afferents are a part.

gp130 cytokines are positive signals triggering changes in gene expression and axon outgrowth in peripheral neurons following injury

Adult peripheral neurons, in contrast to adult central neurons, are capable of regeneration after axonal damage. Much attention has focused on the changes that accompany this regeneration in two places, the distal nerve segment (where phagocytosis of axonal debris, changes in the surface properties of Schwann cells, and induction of growth factors and cytokines occur) and the neuronal cell body (where dramatic changes in cell morphology and gene expression occur). The changes in the axotomized cell body are often referred to as the "cell body response." The focus of the current review is a family of cytokines, the glycoprotein 130 (gp130) cytokines, which produce their actions through a common gp130 signaling receptor and which function as injury signals for axotomized peripheral neurons, triggering changes in gene expression and in neurite outgrowth. These cytokines play important roles in the responses of sympathetic, sensory, and motor neurons to injury. The best studied of these cytokines in this context are leukemia inhibitory factor (LIF) and interleukin (IL)-6, but experiments with conditional gp130 knockout animals suggest that other members of this family, not yet determined, are also involved. The primary gp130 signaling pathway shown to be involved is the activation of Janus kinase (JAK) and the transcription factors Signal Transducers and Activators of Transcription (STAT), though other downstream pathways such as mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) may also play a role. gp130 signaling may involve paracrine, retrograde, and autocrine actions of these cytokines. Recent studies suggest that manipulation of this cytokine system can also stimulate regeneration by injured central neurons.

Cell proliferation and interleukin-6-type cytokine signaling are implicated by gene expression responses in early optic nerve head injury in rat glaucoma

PURPOSE

In glaucoma, the optic nerve head (ONH) is the principal site of initial axonal injury, and elevated intraocular pressure (IOP) is the predominant risk factor. However, the initial responses of the ONH to elevated IOP are unknown. Here the authors use a rat glaucoma model to characterize ONH gene expression changes associated with early optic nerve injury.

METHODS

Unilateral IOP elevation was produced in rats by episcleral vein injection of hypertonic saline. ONH mRNA was extracted, and retrobulbar optic nerve cross-sections were graded for axonal degeneration. Gene expression was determined by microarray and quantitative PCR (QPCR) analysis. Significantly altered gene expression was determined by multiclass analysis and ANOVA. DAVID gene ontology determined the functional categories of significantly affected genes.

RESULTS

The Early Injury group consisted of ONH from eyes with <15% axon degeneration. By array analysis, 877 genes were significantly regulated in this group. The most significant upregulated gene categories were cell cycle, cytoskeleton, and immune system process, whereas the downregulated categories included glucose and lipid metabolism. QPCR confirmed the upregulation of cell cycle-associated genes and leukemia inhibitory factor (Lif) and revealed alterations in expression of other IL-6-type cytokines and Jak-Stat signaling pathway components, including increased expression of IL-6 (1553%). In contrast, astrocytic glial fibrillary acidic protein (Gfap) message levels were unaltered, and other astrocytic markers were significantly downregulated. Microglial activation and vascular-associated gene responses were identified.

CONCLUSIONS

Cell proliferation and IL-6-type cytokine gene expression, rather than astrocyte hypertrophy, characterize early pressure-induced ONH injury.

Endogenous Wnt signaling maintains neural progenitor cell potency

Wnt signaling regulates neural stem cell (NSC) function and development throughout an individual's lifetime. Intriguingly, adult hippocampal progenitors (AHPs) produce several Wnts, and the intracellular machinery necessary to respond to them, creating the potential for an active autocrine-signaling loop within this stem cell niche. However, the standard luciferase-based Wnt assay failed to detect this signaling loop. This assay is inherently less temporally sensitive to activity among a population of unsynchronized proliferating cells because it relies on the rapidly degrading reporter luciferase. We circumvented this limitation using a promoter assay that employs green fluorescent protein (GFP), as a relatively long-lived reporter of canonical Wnt activity. We found that at baseline, AHPs secreted functional Wnt that self-stimulates low-level canonical Wnt signaling. Elimination baseline Wnt activity, via application of an extracellular Wnt antagonist promoted neurogenesis, based on a combination of unbiased gene expression analysis and cell-fate analysis. A detailed clonal analysis of progenitors transduced with specific intracellular antagonists of canonical signaling, either Axin or truncated cadherin (beta-catenin sequestering), revealed that loss of baseline signaling depletes the population of multipotent precursors, thereby driving an increasing fraction to assume a committed cell fate (i.e., unipotent progenitors). Similarly, baseline Wnt signaling repressed differentiation of human NSCs. Although the specific Wnts produced by neural precursors vary with age and between species, their effects remain remarkably consistent. In sum, this study establishes that autonomous Wnt signaling is a conserved feature of the neurogenic niche that preserves the delicate balance between NSC maintenance and differentiation.

Neuroprotective properties of ciliary neurotrophic factor for cultured adult rat dorsal root ganglion neurons

We observed that recombinant ciliary neurotrophic factor (CNTF) enhanced survival and neurite outgrowth of cultured adult rat dorsal root ganglion (DRG) neurons. Among other neurotrophic factors (NGF and GDNF) and interleukin (IL)-6 cytokine members [IL-6, LIF, cardiotrophin-1, and oncostatin M (OSM)] at the same concentration (50 ng/ml), CNTF, as well as LIF and OSM, displayed high efficacy for the promotion of the number of viable neurons and neurite-bearing cells. CNTF enhanced the number of neurite-bearing cells in both small neurons (soma diameter <30 microm) and large neurons (soma diameter > or =30 microm), whereas NGF and GDNF promoted that in only small neurons. Western blot analysis revealed that CNTF induced phosphorylation of STAT3, Akt, and ERK1/2 in the neurons. Furthermore, the neurite outgrowth-promoting activity of CNTF was diminished by co-treatment with Janus kinase (JAK) 2 inhibitor, AG490; STAT3 inhibitor, STA-21; phosphatidyl inositol-3'-phosphate-kinase (PI3K) inhibitor, LY294002; and mitogen-activated protein kinase kinase (MEK) inhibitor, PD98059, in a concentration-dependent manner. Its survival-promoting activity was also affected by AG490, STA-21, and LY294002 at higher concentrations, but not by PD98059. These findings suggest the involvement of JAK2/STAT3, PI3K/Akt, and MEK/ERK signaling pathways in CNTF-induced neurite outgrowth, where the former two pathways are thought to play major roles in mediating the survival response of neurons to CNTF.

Expression and histochemical localization of ciliary neurotrophic factor in cultured adult rat dorsal root ganglion neurons

Ciliary neurotrophic factor (CNTF) is abundantly expressed in Schwann cells in adult mammalian peripheral nerves, but not in neurons. After peripheral nerve injury, CNTF released from disrupted Schwann cells is likely to promote neuronal survival and axonal regeneration. In the present study, we examined the expression and histochemical localization of CNTF in adult rat DRG in vivo and in vitro. In contrast to the restricted expression in Schwann cells in vivo, we observed abundant CNTF mRNA and protein expression in DRG neurons after 3 h, 2, 7, and 15 days in dissociated cell culture. At later stages (7 and 15 days) of culture, CNTF immunoreactivity was detected in both neuronal cell bodies and regenerating neurites. These results suggest that CNTF is synthesized and transported to neurites in cultured DRG neurons. Since we failed to observe CNTF immunoreactivity in DRG neurons in explant culture, disruption of cell-cell interactions, rather than the culture itself, may be an inducible factor for localization of CNTF in the neurons.

Leukemia inhibitory factor is produced by myelin-reactive T cells from multiple sclerosis patients and protects against tumor necrosis factor-α-induced oligodendrocyte apoptosis

In multiple sclerosis (MS), damage to oligodendrocytes is believed to be caused by an aberrant immune response initiated by autoreactive T cells. Increasing evidence indicates that these T cells are not exclusively detrimental but might also exert protective effects. We report for the first time that myelin-reactive T-cell clones from eight MS patients (6/19) and five healthy controls (4/11) produce leukemia inhibitory factor (LIF), a member of the neuropoietic family of neurotrophins. In addition, T-cell clones specific for tetanus toxoid, CD4(+) and CD8(+) T cells, and monocytes, but not B cells, secreted LIF. LIF-producing T lymphocytes and macrophages were also identified immunohistochemically in both active and chronic-active MS lesions. We further demonstrated dose-dependent protective effects of LIF on tumor necrosis factor-alpha-induced apoptosis of oligodendrocytes. In conclusion, our data demonstrate that peripheral and CNS-infiltrating T cells from MS patients produce LIF, a protective factor for oligodendrocytes. This study emphasizes that secretion of LIF may contribute to the neuroprotective effects of autoreactive T cells.

Antibody-bound β-amyloid precursor protein stimulates the production of tumor necrosis factor-α and monocyte chemoattractant protein-1 by cortical neurons

Alzheimer's disease (AD) is an age-related neurodegenerative disorder characterized by the accumulation of extracellular depositions of fibrillar beta-amyloid (A beta), which is derived from the alternative processing of beta-amyloid precursor protein (APP). Although APP is thought to function as a cell surface receptor, its mode of action still remains elusive. In this study, we found that the culture medium derived from cortical neurons treated with an anti-APP antibody triggers the death of naive neurons. Biochemical and immunocytochemical analyses revealed the presence, both in the conditioned medium and in neurons, of increased levels of tumor necrosis factor-alpha and monocyte chemoattractant protein-1. Furthermore, the expression of these proinflammatory mediators occurred through a c-Jun N-terminal protein kinase/c-Jun-dependent mechanism. Taken together, our findings provide evidence for a novel mechanism whereby neuronal APP in its full-length configuration induces neuronal death. Such a mechanism might be relevant to neuroinflammatory processes as those observed in AD.

Reduced immobility in the forced swim test in mice with a targeted deletion of the leukemia inhibitory factor (LIF) gene

Cytokines are a large and diverse group of polypeptides that are rapidly released in response to tissue injury, infection, and inflammation. Besides their effects in the periphery, cytokines also affect the central nervous system (CNS). There has been increasing interest in the potential role of cytokines in the behavioral features of depressive disorders. One cytokine that might be a candidate for a role in the etiology of depression is leukemia inhibitory factor (LIF). LIF mRNA has been detected in the hypothalamus, hippocampus, amygdala, cerebellum, cerebral cortex, and basal forebrain nuclei. The role of LIF in the CNS has not been fully elucidated. Based upon the hypothesis that cytokines might have a role in depression, the present study characterized the behavior of mice with a targeted disruption of the LIF gene (LIF knockouts) in the forced swim test, an animal model used to measure depressive-like behavior and the response to antidepressants. It was found that LIF knockout mice show reduced immobility in the forced swim test, suggesting that LIF might have a potential role in the etiology of some forms of depression.

The role of gp130/IL-6 cytokines in the development of pulmonary fibrosis: critical determinants of disease susceptibility and progression?

Cryptogenic fibrosing alveolitis (CFA), also known as idiopathic pulmonary fibrosis (IPF), is the end stage of a heterogeneous group of disorders in which the deposition of excessive amounts of collagen results in the loss of lung function and premature death. The molecular mechanisms underlying the disease are unknown. Accordingly, there is much debate as to whether pulmonary fibrosis is the end result of (1) a chronic inflammatory process or (2) a disturbance in normal epithelium-fibroblast cross talk, or both. In addition, it appears increasingly likely that there is a genetic component in the development of pulmonary fibrosis. The IL-6 cytokine family is a group of pleiotropic mediators produced by a variety of cells in response to a inflammatory stimuli. These cytokines are grouped together on the basis of weak structural homology, overlapping functions, and shared use of the transmembrane glycoprotein beta-subunit gp130 as part of their multimeric receptor complexes. Activation of these receptor complexes results in the recruitment and phosphorylation of specific transcription factors. In addition, membrane-proximal tyrosine residues act as docking sites for molecules involved in the activation of extracellular signal-related kinase (ERK). However, studies in genetically engineered mice that overexpress members of this family have shown that while overlapping biological activities exist, there are effects specific to individual cytokines. Data from both human and animal studies are now emerging to suggest that members of this cytokine family play an important role in the pathogenesis of fibroproliferative diseases and thus represent a novel group of cytokines implicated in pulmonary fibrosis. Importantly, manipulation of signaling pathways activated by these cytokines may suppress fibrosis but leave innate cellular mechanisms necessary for host defense largely untouched. This may provide guides for the development of novel pharmacological treatment for fibroproliferative diseases.

Leukemia inhibitory factor is a key signal for injury-induced neurogenesis in the adult mouse olfactory epithelium

The mammalian olfactory epithelium (OE) is composed of primary olfactory sensory neurons (OSNs) that are renewed throughout adulthood by local, restricted neuronal progenitor cells. The molecular signals that control this neurogenesis in vivo are unknown. Using olfactory bulb ablation (OBX) in adult mice to trigger synchronous mitotic stimulation of neuronal progenitors in the OE, we show the in vivo involvement of a cytokine in the cellular events leading to the regeneration of the OE. We find that, of many potential mitogenic signals, only leukemia inhibitory factor (LIF) is induced before the onset of neuronal progenitor proliferation. The rise in LIF mRNA expression peaks at 8 hr after OBX, and in situ RT-PCR and immunocytochemistry indicate that LIF is upregulated, in part, in the injured neurons themselves. This rise in LIF is necessary for injury-induced neurogenesis, as OBX in the LIF knock-out mouse fails to stimulate cell proliferation in the OE. Moreover, delivery of exogenous LIF to the intact adult OE using an adenoviral vector stimulates BrdU labeling in the apical OE. Taken together, these results suggest that injured OSNs release LIF as a stimulus to initiate their own replacement.

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.

Opposing functions of GDNF and NGF in the development of cholinergic and noradrenergic sympathetic neurons

We identified a population of mature sympathetic neurons in which Ret, the receptor for glial cell line-derived neurotrophic factor (GDNF), is coexpressed with the neurotrophin-3 (NT3) receptor TrkC and choline acetyltransferase. In a complementary population the nerve growth factor receptor TrkA is coexpressed with the norepinephrine transporter. In accordance with these in vivo results, GDNF and neurturin promote the expression of cholinergic marker genes in sympathetic chain explants, similar to NT3 and ciliary neuronotrophic factor (CNTF). To define intracellular signaling mechanisms commonly activated by NT3, GDNF, or CNTF to promote cholinergic differentiation, we have analyzed the activation of intracellular signaling cascades. Signal transducer and activator of transcription-3 (STAT3) was strongly activated by CNTF but not by GDNF or NT3 and hence is not essential for cholinergic differentiation. We conclude that cholinergic properties can be regulated by neurotrophic factors from three different protein families, whereas noradrenergic properties are promoted by NGF.

Testosterone and nerve growth factor have distinct but interacting effects on structure and neurotransmitter expression of adult pelvic ganglion cells in vitro

Circulating testosterone has potent effects on the structure and function of many pelvic ganglion cells in adult rats in vivo. However not all androgen-sensitive pelvic neurones possess androgen receptors and testosterone effects may therefore be indirect, by an action on the target organs. Here we have examined if testosterone influences neuronal structure in vitro in pelvic ganglion cells cultured from adult male rats. We have also used multiple label immunofluorescence to monitor the expression of transmitter-synthesising enzymes and peptides under various culture conditions. Testosterone was a more potent stimulant of noradrenergic soma growth in culture than nerve growth factor. Whereas nerve growth factor increased the number, branching and length of neurites, testosterone stimulated growth of a small number of very short processes, each of which bore numerous short protrusions. Testosterone also impeded the longer neurite growth induced by nerve growth factor. Many pelvic ganglion cells altered their expression of transmitters/neuropeptides under different culture conditions. In particular, under control conditions or during nerve growth factor treatment, vasoactive intestinal peptide was up-regulated in noradrenergic and cholinergic neurones; testosterone impeded this up-regulation in noradrenergic neurones. Choline acetyltransferase immunoreactivity could only be visualised when nerve growth factor was present in the cultures, and cholinergic neurones showed less neurite outgrowth than noradrenergic neurones under all culture conditions. Nerve growth factor did not stimulate levels of this enzyme as strongly if testosterone was present. This study has shown that testosterone has potent effects on the structure of many pelvic ganglion cells in vitro. It is possible that these effects are mediated indirectly, e.g. by stimulating glial-derived substances, however our results suggest that the effects are not mediated by nerve growth factor. The results also show that testosterone influences some of the actions of nerve growth factor, suggesting that there may be complex interactions between steroid signalling and neurotrophic factors in maintaining neuronal structure and function in vivo.

The ribosomal S6 kinases, cAMP-responsive element-binding, and STAT3 proteins are regulated by different leukemia inhibitory factor signaling pathways in mouse embryonic stem cells

Mouse embryonic stem (ES) cells remain "pluripotent" in vitro in the continuous presence of leukemia inhibitory factor (LIF). In the absence of LIF, ES cells are irreversibly committed to differentiate into various lineages. In this study we have set up an in vitro assay based on the anti-apoptotic activity of LIF to distinguish pluripotent from "differentiation-committed" ES cells. We have examined the phosphorylation profiles of known (STAT3 and ERKs) and identified new (ribosomal S6 kinases (RSKs) and cAMP-responsive element-binding protein (CREB)) LIF-regulated targets in ES and in ES-derived neuronal cells. We have demonstrated that although STAT3, a crucial player in the maintenance of ES cell pluripotency, is induced by LIF in all cell types tested, the LIF-dependent activation of RSKs is restricted to ES cells. We have shown that LIF-induced phosphorylation of RSKs in ES cells is dependent on ERKs, whereas STAT3 phosphorylation is not mediated by any known MAPK activities. Our results also demonstrate that the LIF-dependent phosphorylation of CREB is partially under the control of the RSK2 kinase.

An activity-dependent neurotrophin-3 autocrine loop regulates the phenotype of developing hippocampal pyramidal neurons before target contact

Neurotrophin-3 (NT-3), its cognate receptor trkC, and voltage-gated calcium channels are coexpressed by embryonic pyramidal neurons before target contact, but their functions at this stage of development are still unclear. We show here that, in vitro, anti-NT-3 and anti-trkC antibodies blocked the increase, and NT-3 reversed the decrease in the number of calbindin-D(28k)-positive pyramidal neurons induced by, respectively, calcium channel activations and blockades. Similar results were obtained with single-neuron microcultures. In addition, voltage-gated calcium channel inhibition downregulates the extracellular levels of NT-3 in high-density cultures. Moreover, electrophysiological experiments in single-cell cultures reveal a tetrodotoxin-sensitive spontaneous electrical activity allowing voltage-gated calcium channel activation. The mouse NT-3 (-/-) mutation decreases by 40% the number of developing calbindin-D(28k)-positive pyramidal neurons, without affecting neuronal survival, both in vitro and in vivo. Thus, present results strongly support that an activity-dependent autocrine NT-3 loop provides a local, intrinsic mechanism by which, before target contact, hippocampal pyramidal-like neurons may regulate their own differentiation, a role that may be important during early CNS differentiation or after adult target disruption.

Factors controlling axonal and dendritic arbors

The sculpting and maintenance of axonal and dendritic arbors is largely under the control of molecules external to the cell. These factors include both substratum-associated and soluble factors that can enhance or inhibit the outgrowth of axons and dendrites. A large number of factors that modulate axonal outgrowth have been identified, and the first stages of the intracellular signaling pathways by which they modify process outgrowth have been characterized. Relatively fewer factors and pathways that affect dendritic outgrowth have been described. The factors that affect axonal arbors form an incompletely overlapping set with those that affect dendritic arbors, allowing selective control of the development and maintenance of these critical aspects of neuronal morphology.

Differential effects of oncostatin M and leukaemia inhibitory factor expression in astrocytoma cells

The effects of the production of two closely related cytokines, oncostatin M (OSM) and leukaemia inhibitory factor (LIF), by astrocytoma cells were investigated using the stable cell line human U373-MG, which expressed and secreted both biologically active polypeptides. The expression of LIF by these cells caused resistance to this cytokine due to loss of the LIF receptor (LIFR), from the cell surface, suggesting its retention. In contrast, cells expressing OSM were stimulated by this cytokine, utilizing an autocrine mechanism, and possessed receptors for OSM, but not LIF, on the cell surface. In these cells the continuous up-regulation of OSM-induced gene expression was found even though the Janus kinase-signal transducer and activator of transcription ('JAK/STAT') pathway was almost exhausted due to long-term autocrine stimulation of the cells by OSM. The amount of LIFR was down-regulated in both LIF- and OSM-producing cells and this effect was not found in wild-type U373-MG cells treated with externally added cytokines. To investigate the mechanism of autocrine stimulation by OSM we constructed a stable cell line expressing a form of OSM that is retained in the endoplasmic reticulum (ER). This biologically active cytokine was not secreted, but was localized in the ER. In addition, it did not stimulate the astrocytoma cells in an autocrine manner. We conclude that expression of LIF causes resistance of astrocytoma cells to this cytokine, whereas expression of OSM leads to autocrine stimulation.

Spontaneous synaptogenesis in ex vivo sympathetic ganglion and the blockade by serum treatment

Central denervation for more than 1 month has been shown to cause an increase in the number of adrenergic synapses in sympathetic ganglia in vivo. Here, we report several lines of evidence that adrenergic synapses may be generated de novo in ex vivo superior cervical ganglion (SCG) of adult rats only several hours after the isolation. Structures immunoreactive for synaptophysin, a marker of presynaptic elements, were drastically decreased 6 days after the preganglionic denervation. A significant increase in number of synaptophysin positive boutons was observed over 3-8 hours in the denervated SCGs maintained ex vivo at 36 degrees C in oxygenated physiologic saline, and this increase was blocked by adding normal serum in the saline. Electron microscopic analysis confirmed that the number of adrenergic synapses specifically labeled with 5-hydroxydopamine was increased by several-fold under the same condition. Intracellular labeling of SCG neurons revealed an increase in the incidence (from 8 to 50%) of neurons having dendritic plexus after the in vitro incubation. No evidence of axonal sprouting within the ganglion was observed. Intracellular recordings from single neurons of denervated SCGs revealed that maximum amplitudes of inhibitory postsynaptic potentials, which were completely blocked by yohimbine, an alpha2-adrenoceptor antagonist, in response to focal stimulation were increased over the several hours. These results suggest that dendrites of SCG neurons rapidly develop and exhibit local efferent characteristics that underlie the inhibitory synaptic transmission once they are subjected to serum deprivation.

Induction of electrical excitability by NGF requires autocrine action of a CNTF-like factor

The overlapping expression of neurotrophin and neural cytokine receptors indicates that most neuronal populations are responsive to both classes of factors, yet relatively little is known about how these two trophic signaling systems interact to regulate neuronal phenotype. We report here that one hallmark of NGF's effects on target cells, the induction of membrane electrical excitability, requires the intermediary action of a CNTF-like factor. We found that NGF's regulation of voltage-gated potassium channels, unlike its regulation of voltage-gated sodium and calcium channels, involves a CNTF-like autocrine/paracrine loop. We showed that NGF induces secretion of a soluble factor that mimics the action of exogenous CNTF in regulating voltage-gated potassium channels and that NGF's ability to regulate this potassium channel is blocked by three independent reagents that inhibit the signaling of CNTF and/or related factors. The identity of this autocrine factor does not appear to be CNTF itself. Thus, a CNTF-like autocrine/paracrine factor is both necessary and sufficient for the regulation of potassium channels by NGF and is a key determinant of the type of electrical excitability that NGF induces in target cells.

Leukemia inhibitory factor regulates galanin/galanin message-associated peptide expression in cultured mouse dorsal root ganglia; with a note on in situ hybridization methodology

After transection of the sciatic nerve there is a dramatic increase in both galanin/galanin message-associated peptide-like immunoreactivities and preprogalanin messenger RNA levels in rat and mouse lumbar 4 and 5 dorsal root ganglion neurons. There is strong evidence that after nerve injury leukemia inhibitor factor is a key molecule in the control of peptide expression both in sympathetic neurons and in dorsal root ganglion neurons, although the cells of origin of endogenous leukemia inhibitory factor remain to be established. We have therefore studied the effect of leukemia inhibitory factor on galanin expression in 72 h cultured dorsal root ganglion neurons from normal mice, leukemia inhibitory factor-deficient and heterozygous mice with immunohistochemistry and in situ hybridization. In cultures of leukemia inhibitory factor-deficient (-/-) mice only 13% of the dorsal root ganglion neurons expressed galanin message-associated peptide and in cultures from heterozygous (+/-) and wild-type (+/+) mice the corresponding figures were, respectively, 24 and 40%. After addition of leukemia inhibitory factor (10 or 50 ng/ml) to the culture medium, the number of neurons expressing galanin message-associated peptide was increased (up to 41%) in cultures from (-/-) animals after the high concentration and reached similar values in cultures from heterozygous animals incubated with the low concentration. These findings were supported by parallel analysis of prepro-galanin messenger RNA levels, where similar transcript levels and effects in the various cultures were observed in the non-radioactive in situ hybridization experiments. These results support the hypothesis that leukemia inhibitory factor is an important regulator of galanin/galanin message-associated peptide expression following axotomy, and may therefore be involved in the defence mechanisms against neuropathic pain at the level of dorsal root ganglion neurons.

The levels of leukemia inhibitory factor mRNA in a Schwann cell line are regulated by multiple second messenger pathways

Axotomy of sympathetic and sensory neurons leads to changes in their neuropeptide phenotypes. These changes are mediated in part by the induction of leukemia inhibitory factor (LIF) by nonneuronal cells. In the present study, we identified satellite/Schwann cells as a possible source of the injury-induced LIF. Using a Schwann cell line, SC-1 cells, we examined mechanisms of LIF induction. LIF mRNA levels increased rapidly when the cells were treated with 8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphate, phorbol 12-myristate 13-acetate (PMA), or A23187. Among these reagents, PMA was the most efficacious. Inhibition of protein kinase C (PKC) by GF-1 09203X significantly reduced the PMA-induced LIF mRNA levels. As PKC is known to activate the extracellular signal-regulated kinase (ERK) signaling pathway, the involvement of this pathway in the PMA-stimulated induction of LIF mRNA was examined. Phosphorylation of ERKs was increased following PMA treatment in SC-1 cells. Moreover, inhibition of ERK kinase activity by PD98059 dramatically reduced PMA-stimulated phosphorylation of ERKs and induction of LIF mRNA. These results indicate that LIF mRNA levels can be regulated by ERK activation via stimulation of PKC in Schwann cells.

Leukemia inhibitory factor and ciliary neurotrophic factor cause dendritic retraction in cultured rat sympathetic neurons

Dendritic retraction occurs in many regions of the developing brain and also after neural injury. However, the molecules that regulate this important regressive process remain largely unknown. Our data indicate that leukemia inhibitory factor (LIF) and ciliary neurotrophic factor (CNTF) cause sympathetic neurons to retract their dendrites in vitro, ultimately leading to an approximately 80% reduction in the size of the arbor. The dendritic retraction induced by LIF exhibited substantial specificity because it was not accompanied by changes in cell number, in the rate of axonal growth, or in the expression of axonal cytoskeletal elements. An antibody to gp130 blocked the effects of LIF and CNTF, and both cytokines induced phosphorylation and nuclear translocation of stat3. Moreover, addition of soluble interleukin-6 (IL-6) receptor to the medium endowed IL-6 with the ability to cause dendritic regression. These data indicate that ligands activating the gp130 pathway have the ability to profoundly alter neuronal cell shape and polarity by selectively causing the retraction of dendrites.

Analysis of neuronal and glial phenotypes in brains of mice deficient in leukemia inhibitory factor

Leukemia inhibitory factor (LIF) can regulate the survival and differentiation of certain neurons and glial cells in culture. To determine the role of this cytokine in the central nervous system in vivo, we examined the brains of young and adult mice in which the LIF gene was disrupted. Immunohistochemical staining of neurons for choline acetyltransferase, tyrosine hydroxylase, serotonin, parvalbumin, calbindin, neuropeptide Y, vasoactive intestinal polypeptide, and calcitonin gene-related peptide revealed no significant differences between null mutant and wild-type (WT) brains. In contrast, analysis of glial phenotypes demonstrated striking deficits in the LIF-knockout brain. Staining with several anti-glial fibrillary acidic protein (GFAP) antibodies showed that the number of GFAP-positive cells in various regions of the hippocampus in the female mutant is much lower than in the WT. The null male hippocampus also displays a significant, though less marked deficit. The number of astrocytes in the mutant hippocampus, as determined by S-100 staining, is not, however, significantly different from WT. In addition, quantification of immunohistochemical staining of female, but not male, mutants reveals a significant deficit in myelin basic protein content in three brain regions, suggesting alterations in oligodendrocytes as well. Thus, while overall brain histology appears normal, the absence of LIF in vivo leads to specific, sexually dimorphic alterations in glial phenotype.

Sympathetic neurons can produce and respond to interleukin 6

Neuronal expression of cytokines is an area of active investigation in the contexts of development, disease, and normal neural function. Although cultured rat sympathetic neurons respond very weakly to exogenous interleukin 6 (IL-6), we find that addition of soluble IL-6 receptor (sIL-6R) and IL-6 enhances neuronal survival in the absence of nerve growth factor. Neutralizing monoclonal antibodies against IL-6 block these effects. Addition of IL-6 and sIL-6R also induces a subset of neuropeptide and transmitter synthetic enzyme mRNAs identical to that demonstrated for leukemia inhibitory factor, ciliary neurotrophic factor, and oncostatin M. Both of these effects are duplicated by addition of a highly active fusion protein of sIL-6R and IL-6, covalently linked by a flexible peptide chain, which is designated H-IL-6. In addition, we show that sympathetic neurons produce IL-6. In situ hybridization indicates a neuronal localization of IL-6 mRNA in superior cervical ganglia, and bioactive IL-6 protein is detected in ganglion culture supernatants. Interestingly, the IL-6 produced by sympathetic neurons does not lead to survival of these cells in culture unless sIL-6R is added. Thus, sympathetic neurons can produce IL-6 and may respond to it in an autocrine/paracrine manner if sIL-6R is present. Moreover, the prior findings of sIL-6R in serum and inflammatory fluids now have added interest in the context of neuro-immune interactions.