Ciliary neurotrophic factor/leukemia inhibitory factor/interleukin 6/oncostatin M family of cytokines induces tyrosine phosphorylation of a common set of proteins overlapping those induced by other cytokines and growth factors

Addressing neurodegeneration in glaucoma: Mechanisms, challenges, and treatments

Glaucoma is the leading cause of irreversible blindness globally. The disease causes vision loss due to neurodegeneration of the retinal ganglion cell (RGC) projection to the brain through the optic nerve. Glaucoma is associated with sensitivity to intraocular pressure (IOP). Thus, mainstay treatments seek to manage IOP, though many patients continue to lose vision. To address neurodegeneration directly, numerous preclinical studies seek to develop protective or reparative therapies that act independently of IOP. These include growth factors, compounds targeting metabolism, anti-inflammatory and antioxidant agents, and neuromodulators. Despite success in experimental models, many of these approaches fail to translate into clinical benefits. Several factors contribute to this challenge. Firstly, the anatomic structure of the optic nerve head differs between rodents, nonhuman primates, and humans. Additionally, animal models do not replicate the complex glaucoma pathophysiology in humans. Therefore, to enhance the success of translating these findings, we propose two approaches. First, thorough evaluation of experimental targets in multiple animal models, including nonhuman primates, should precede clinical trials. Second, we advocate for combination therapy, which involves using multiple agents simultaneously, especially in the early and potentially reversible stages of the disease. These strategies aim to increase the chances of successful neuroprotective treatment for glaucoma.

Preventive putative effect of agmatine on cognitive and molecular outcomes in ventral tegmental area of male offspring following physical and psychological prenatal stress

Prenatal stress (PS) results from a maternal experience of stressful events during pregnancy, which has been associated with an increased risk of behavioral disorders including substance abuse and anxiety in the offspring. PS is known to result in heightened dopamine release in the ventral tegmental area (VTA), in part through the effects of corticotropin-releasing hormone, which directly excites dopaminergic cells. It has recently been suggested that agmatine plays a role in modulating anxiety-like behaviors. In this study, we investigated whether agmatine could reduce negative cognitive outcomes in male mice prenatally exposed to psychological/physical stress, and whether this could be associated with molecular changes in VTA. Agmatine (37.5 mg/kg) was administrated 30 min prior to PS induction in pregnant Swiss mice. Male offspring were evaluated in a series of behavioral and molecular assays. Findings demonstrated that agmatine reduced the impairment in locomotor activity induced by both psychological and physical PS. Agmatine also decreased heightened conditioned place preference to morphine seen in PS offspring. Moreover, agmatine ameliorated the anxiety-like behavior and drug-seeking behavior induced by PS in the male offspring. Molecular effects were seen in VTA as the enhanced brain-derived neurotrophic factor (BDNF) induced by PS in the VTA was reduced by agmatine. Behavioral tests indicate that agmatine exerts a protective effect on PS-induced impairments in male offspring, which could be due in part to agmatine-associated molecular alterations in the VTA. Taken together, our data suggest that prenatal treatment with agmatine exerts protective effect against negative consequences of PS on the development of affective circuits in the offspring.

Urinary Cytokines as Potential Biomarkers of Mild Cognitive Impairment and Alzheimer's Disease: A Pilot Study

Background

Alzheimer's disease (AD) is the most common form of dementia, accounting for 80% of all cases. Mild cognitive impairment (MCI) is a transitional state between normal aging and AD. Early detection is crucial, as irreversible brain damage occurs before symptoms manifest.

Objective

This study aimed to identify potential biomarkers for early detection of AD by analyzing urinary cytokine concentrations. We investigated 37 cytokines in AD, MCI, and cognitively normal individuals (NC), assessing their associations with AD development.

Methods

Urinary cytokine concentrations were measured in AD (n = 25), MCI (n = 25), and NC (n = 26) patients. IL6ST and MMP-2 levels were compared between AD and NC, while TNFRSF8, IL6ST, and IL-19 were assessed in AD versus MCI. Diagnostic models distinguished AD from NC, and in-silico analysis explored molecular mechanisms related to AD.

Results

Significant perturbations in IL6ST and MMP-2 concentrations were observed in AD urine compared to NC, suggesting their potential as biomarkers. TNFRSF8, IL6ST, and IL-19 differed significantly between AD and MCI, implicating them in disease progression. Diagnostic models exhibited promising performance (AUC: 0.59-0.79, sensitivity: 0.72-0.80, specificity: 0.56-0.78) in distinguishing AD from NC. In-silico analysis revealed molecular insights, including relevant non-coding RNAs, microRNAs, and transcription factors.

Conclusion

This study establishes significant associations between urinary cytokine concentrations and AD and MCI. IL6ST, MMP-2, TNFRSF8, IL6ST, and IL-19 emerge as potential biomarkers for early detection of AD. In-silico analysis enhances understanding of molecular mechanisms in AD. Further validation and exploration of these biomarkers in larger cohorts are warranted to assess their clinical utility.

Ciliary neurotrophic factor-mediated neuroprotection involves enhanced glycolysis and anabolism in degenerating mouse retinas

Ciliary neurotrophic factor (CNTF) acts as a potent neuroprotective cytokine in multiple models of retinal degeneration. To understand mechanisms underlying its broad neuroprotective effects, we have investigated the influence of CNTF on metabolism in a mouse model of photoreceptor degeneration. CNTF treatment improves the morphology of photoreceptor mitochondria, but also leads to reduced oxygen consumption and suppressed respiratory chain activities. Molecular analyses show elevated glycolytic pathway gene transcripts and active enzymes. Metabolomics analyses detect significantly higher levels of ATP and the energy currency phosphocreatine, elevated glycolytic pathway metabolites, increased TCA cycle metabolites, lipid biosynthetic pathway intermediates, nucleotides, and amino acids. Moreover, CNTF treatment restores the key antioxidant glutathione to the wild type level. Therefore, CNTF significantly impacts the metabolic status of degenerating retinas by promoting aerobic glycolysis and augmenting anabolic activities. These findings reveal cellular mechanisms underlying enhanced neuronal viability and suggest potential therapies for treating retinal degeneration.

Pleiotropic, Unique and Shared Responses Elicited by IL-6 Family Cytokines in Human Vascular Endothelial Cells

Vascular endothelial cells express glycoprotein 130 (gp130), which is utilized as a signaling receptor by cytokines in the interleukin-6 (IL-6) family. Several IL-6 family cytokines can be found in the circulatory system during physiological or pathological conditions, and may influence endothelial function and response. This study evaluated and compared the cellular and molecular responses induced by IL-6 family cytokines in human endothelial cells. A proteomic analysis showed that IL-6 family cytokines induce the release of a range of proteins from endothelial cells, such as C-C motif chemokine ligand 23, hepatocyte growth factor, and IL-6. Pathway analysis indicated that gp130-signaling in endothelial cells regulates several functions related to angiogenesis and immune cell recruitment. The present investigation also disclosed differences and similarities between different IL-6 family cytokines in their ability to induce protein release and regulate gene expression and intracellular signaling, in regards to which oncostatin M showed the most pronounced effect. Further, this study showed that soluble gp130 preferentially blocks trans-signaling-induced responses, but does not affect responses induced by classic signaling. In conclusion, IL-6 family cytokines induce both specific and overlapping molecular responses in endothelial cells, and regulate genes and proteins involved in angiogenesis and immune cell recruitment.

Leukemia Inhibitory Factor: An Important Cytokine in Pathologies and Cancer

Leukemia Inhibitory Factor (LIF) is a member of the IL-6 cytokine family and is expressed in almost every tissue type within the body. Although LIF was named for its ability to induce differentiation of myeloid leukemia cells, studies of LIF in additional diseases and solid tumor types have shown that it has the potential to contribute to many other pathologies. Exploring the roles of LIF in normal physiology and non-cancer pathologies can give important insights into how it may be dysregulated within cancers, and the possible effects of this dysregulation. Within various cancer types, LIF expression has been linked to hallmarks of cancer, such as proliferation, metastasis, and chemoresistance, as well as overall patient survival. The mechanisms behind these effects of LIF are not well understood and can differ between different tissue types. In fact, research has shown that while LIF may promote malignancy progression in some solid tumors, it can have anti-neoplastic effects in others. This review will summarize current knowledge of how LIF expression impacts cellular function and dysfunction to help reveal new adjuvant treatment options for cancer patients, while also revealing potential adverse effects of treatments targeting LIF signaling.

Chemokine CCL5 promotes robust optic nerve regeneration and mediates many of the effects of CNTF gene therapy

Ciliary neurotrophic factor (CNTF) is a leading therapeutic candidate for several ocular diseases and induces optic nerve regeneration in animal models. Paradoxically, however, although CNTF gene therapy promotes extensive regeneration, recombinant CNTF (rCNTF) has little effect. Because intraocular viral vectors induce inflammation, and because CNTF is an immune modulator, we investigated whether CNTF gene therapy acts indirectly through other immune mediators. The beneficial effects of CNTF gene therapy remained unchanged after deleting CNTF receptor alpha (CNTFRα) in retinal ganglion cells (RGCs), the projection neurons of the retina, but were diminished by depleting neutrophils or by genetically suppressing monocyte infiltration. CNTF gene therapy increased expression of C-C motif chemokine ligand 5 (CCL5) in immune cells and retinal glia, and recombinant CCL5 induced extensive axon regeneration. Conversely, CRISPR-mediated knockdown of the cognate receptor (CCR5) in RGCs or treating wild-type mice with a CCR5 antagonist repressed the effects of CNTF gene therapy. Thus, CCL5 is a previously unrecognized, potent activator of optic nerve regeneration and mediates many of the effects of CNTF gene therapy.

The role of the leukemia inhibitory factor receptor in neuroprotective signaling

Several neurotropic cytokines relay their signaling through the leukemia inhibitory factor receptor. This 190kDa subunit couples with the 130kDa gp130 subunit to transduce intracellular signaling in neurons and oligodendrocytes that leads to expression of genes associated with neurosurvival. Moreover, activation of this receptor alters the phenotype of immune cells to an anti-inflammatory one. Although cytokines that activate the leukemia inhibitory factor receptor have been studied in the context of neurodegenerative disease, therapeutic targeting of the specific receptor subunit has been understudied in by comparison. This review examines the role of this receptor in the CNS and immune system, and its application in the treatment in stroke and other brain pathologies.

Regulation of Stem Cell Properties of Müller Glia by JAK/STAT and MAPK Signaling in the Mammalian Retina

In humans and other mammals, the neural retina does not spontaneously regenerate, and damage to the retina that kills retinal neurons results in permanent blindness. In contrast to embryonic stem cells, induced pluripotent stem cells, and embryonic/fetal retinal stem cells, Müller glia offer an intrinsic cellular source for regenerative strategies in the retina. Müller glia are radial glial cells within the retina that maintain retinal homeostasis, buffer ion flux associated with phototransduction, and form the blood/retinal barrier within the retina proper. In injured or degenerating retinas, Müller glia contribute to gliotic responses and scar formation but also show regenerative capabilities that vary across species. In the mammalian retina, regenerative responses achieved to date remain insufficient for potential clinical applications. Activation of JAK/STAT and MAPK signaling by CNTF, EGF, and FGFs can promote proliferation and modulate the glial/neurogenic switch. However, to achieve clinical relevance, additional intrinsic and extrinsic factors that restrict or promote regenerative responses of Müller glia in the mammalian retina must be identified. This review focuses on Müller glia and Müller glial-derived stem cells in the retina and phylogenetic differences among model vertebrate species and highlights some of the current progress towards understanding the cellular mechanisms regulating their regenerative response.

AAV-mediated transfer of RhoA shRNA and CNTF promotes retinal ganglion cell survival and axon regeneration

The aim of the present study was to determine whether adeno-associated viral vector (AAV) mediated transfer of ciliary neurotrophic factor (CNTF) and RhoA shRNA has additive effects on promoting the survival and axon regeneration of retinal ganglion cells (RGCs) after optic nerve crush (ONC). Silencing effects of AAV-RhoA shRNA were confirmed by examining neurite outgrowth in PC12 cells, and by quantifying RhoA expression levels with western blotting. Young adult Fischer rats received an intravitreal injection of (i) saline, (ii) AAV green fluorescent protein (GFP), (iii) AAV-CNTF, (iv) AAV-RhoA shRNA, or (v) a combination of both AAV-CNTF and AAV-RhoA shRNA. Two weeks later, the ON was completely crushed. Three weeks after ONC, RGC survival was estimated by counting βIII-tubulin-positive neurons in retinal whole mounts. Axon regeneration was evaluated by counting GAP-43-positive axons in the crushed ON. It was found that AAV-RhoA shRNA decreased RhoA expression levels and promoted neurite outgrowth in vitro. In the ONC model, AAV-RhoA shRNA by itself had only weak beneficial effects on RGC axon regeneration. However, when combined with AAV-CNTF, AAV-RhoA shRNA significantly improved the therapeutic effect of AAV-CNTF on axon regeneration by nearly two fold, even though there was no significant change in RGC viability. In sum, this combination of vectors increases the regenerative response and can lead to more successful therapeutic outcomes following neurotrauma.

Leukemia Inhibitory Factor Protects Neurons from Ischemic Damage via Upregulation of Superoxide Dismutase 3

Leukemia inhibitory factor (LIF) has been shown to protect oligodendrocytes from ischemia by upregulating endogenous antioxidants. The goal of this study was to determine whether LIF protects neurons during stroke by upregulating superoxide dismutase 3 (SOD3). Animals were administered phosphate-buffered saline (PBS) or 125 μg/kg LIF at 6, 24, and 48 h after middle cerebral artery occlusion or sham surgery. Neurons were isolated from rat pups on embryonic day 18 and used between 7 and 15 days in culture. Cells were treated with LIF and/or 10 μM Akt inhibitor IV with PBS and 0.1 % DMSO acting as vehicle controls. Neurons transfected with scrambled or SOD3 small interfering RNA (siRNA) were subjected to 24-h ischemia after PBS or LIF treatment. LIF significantly increased superoxide dismutase activity and SOD3 expression in ipsilateral brain tissue compared to PBS. Following 24-h ischemia, LIF reduced cell death and increased SOD3 messenger RNA (mRNA) in vitro compared to PBS. Adding Akt inhibitor IV with LIF counteracted the decrease in cell death. Partially silencing the expression of SOD3 using siRNA prior to LIF treatment counteracted the protective effect of LIF-alone PBS treatment. These results indicate that LIF protects neurons in vivo and in vitro via upregulation of SOD3.

Neuronal Survival, Morphology and Outgrowth of Spiral Ganglion Neurons Using a Defined Growth Factor Combination

Objectives

The functionality of cochlear implants (CI) depends, among others, on the number and excitability of surviving spiral ganglion neurons (SGN). The spatial separation between the SGN, located in the bony axis of the inner ear, and the CI, which is inserted in the scala tympani, results in suboptimal performance of CI patients and may be decreased by attracting the SGN neurites towards the electrode contacts. Neurotrophic factors (NTFs) can support neuronal survival and neurite outgrowth.

Methods

Since brain-derived neurotrophic factor (BDNF) is well known for its neuroprotective effect and ciliary neurotrophic factor (CNTF) increases neurite outgrowth, we evaluated if the combination of BDNF and CNTF leads to an enhanced neuronal survival with extended neurite outgrowth. Both NTFs were added in effective high concentrations (BDNF 50ng/ml, CNTF 100ng/ml), alone and in combination, to cultured dissociated SGN of neonatal rats for 48 hours.

Results

The neuronal survival and neurite outgrowth were significantly higher in SGN treated with the combination of the two NTFs compared to treatment with each factor alone. Additionally, with respect to the morphology, the combination of BDNF and CNTF leads to a significantly higher number of bipolar neurons and a decreased number of neurons without neurites in culture.

Conclusion

The combination of BDNF and CNTF shows a great potential to increase the neuronal survival and the number of bipolar neurons in vitro and to regenerate retracted nerve fibers.

Ciliary neurotrophic factor (CNTF): New facets of an old molecule for treating neurodegenerative and metabolic syndrome pathologies

Ciliary neurotrophic factor (CNTF) is the most extensively studied member of the cytokine family that signal through intracellular chains of the gp130/LIFRβ receptor. The severe phenotype in patients suffering from mutations inactivating LIFRβ indicates that members of this cytokine family play key, non-redundant roles during development. Accordingly, three decades of research has revealed potent and promising trophic and regulatory activities of CNTF in neurons, oligodendrocytes, muscle cells, bone cells, adipocytes and retinal cells. These findings led to clinical trials to test the therapeutic potential of CNTF and CNTF derivatives for treating neurodegenerative and metabolic diseases. Promising results have encouraged continuation of studies for treating retinal degenerative diseases. Results of some clinical trials showed that side-effects may limit the systemically administrated doses of CNTF. Therefore, therapies being currently tested rely on local delivery of CNTF using encapsulated cytokine-secreting implants. Since the side effects of CNTF might be linked to its ability to activate the alternative IL6Rα-LIFRβ-gp130 receptor, CNTFR-specific mutants of CNTF have been developed that bind to the CNTFRα-LIFRβ-gp130 receptor. These developments may prove to be a breakthrough for therapeutic applications of systemically administered CNTF in pathologies such as multiple sclerosis or Alzheimer's disease. The "designer cytokine approach" offers future opportunities to further enhance specificity by conjugating mutant CNTF with modified soluble CNTFRα to target therapeutically relevant cells that express gp130-LIFRβ and a specific cell surface marker.

Galanin is an autocrine myelin and oligodendrocyte trophic signal induced by leukemia inhibitory factor

In order to further investigate the molecular mechanisms that regulate oligodendrocyte (OC) survival, we utilized microarrays to characterize changes in OC gene expression after exposure to the cytokines neurotrophin3, insulin, or leukemia inhibitory factor (LIF) in vitro. We identified and validated the induction and secretion of the neuropeptide galanin in OCs, specifically in response to LIF. We next established that galanin is an OC survival factor and showed that autocrine or paracrine galanin secretion mediates LIF-induced OC survival in vitro. We also revealed that galanin is up-regulated in OCs in the cuprizone model of central demyelination, and that oligodendroglial galanin expression is significantly regulated by endogenous LIF in this context. We also showed that knock-out of galanin reduces OC survival and exacerbates callosal demyelination in the cuprizone model. These findings suggest a potential role for the use of galanin agonists in the treatment of human demyelinating diseases.

Delineating the regulation of energy homeostasis using hypothalamic cell models

Attesting to its intimate peripheral connections, hypothalamic neurons integrate nutritional and hormonal cues to effectively manage energy homeostasis according to the overall status of the system. Extensive progress in the identification of essential transcriptional and post-translational mechanisms regulating the controlled expression and actions of hypothalamic neuropeptides has been identified through the use of animal and cell models. This review will introduce the basic techniques of hypothalamic investigation both in vivo and in vitro and will briefly highlight the key advantages and challenges of their use. Further emphasis will be place on the use of immortalized models of hypothalamic neurons for in vitro study of feeding regulation, with a particular focus on cell lines proving themselves most fruitful in deciphering fundamental basics of NPY/AgRP, Proglucagon, and POMC neuropeptide function.

CNTF-mediated protection of photoreceptors requires initial activation of the cytokine receptor gp130 in Müller glial cells

Ciliary neurotrophic factor (CNTF) acts as a potent neuroprotective agent in multiple retinal degeneration animal models. Recently, CNTF has been evaluated in clinical trials for the inherited degenerative disease retinitis pigmentosa (RP) and for dry age-related macular degeneration (AMD). Despite its potential as a broad-spectrum therapeutic treatment for blinding diseases, the target cells of exogenous CNTF and its mechanism of action remain poorly understood. We have shown previously that constitutive expression of CNTF prevents photoreceptor death but alters the retinal transcriptome and suppresses visual function. Here, we use a lentivirus to deliver the same secreted human CNTF used in clinical trials to a mouse model of RP. We found that low levels of CNTF halt photoreceptor death, improve photoreceptor morphology, and correct opsin mislocalization. However, we did not detect corresponding improvement of retinal function as measured by the electroretinogram. Disruption of the cytokine receptor gp130 gene in Müller glia reduces CNTF-dependent photoreceptor survival and prevents phosphorylation of STAT3 and ERK in Müller glia and the rest of the retina. Targeted deletion of gp130 in rods also demolishes neuroprotection by CNTF and prevents further activation of Müller glia. Moreover, CNTF elevates the expression of LIF and endothelin 2, thus positively promoting Müller and photoreceptor interactions. We propose that exogenous CNTF initially targets Müller glia, and subsequently induces cytokines acting through gp130 in photoreceptors to promote neuronal survival. These results elucidate a cellular mechanism for exogenous CNTF-triggered neuroprotection and provide insight into the complex cellular responses induced by CNTF in diseased retinas.

Role of cytokine signaling during nervous system development

Cytokines are signaling proteins that were first characterized as components of the immune response, but have been found to have pleiotropic effects in diverse aspects of body function in health and disease. They are secreted by numerous cells and are used extensively in intercellular communications to produce different activities, including intricate processes engaged in the ontogenetic development of the brain. This review discusses factors involved in brain growth regulation and recent findings exploring cytokine signaling pathways during development of the central nervous system. In view of existing data suggesting roles for neurotropic cytokines in promoting brain growth and repair, these molecules and their signaling pathways might become targets for therapeutic intervention in neurodegenerative processes due to diseases, toxicity, or trauma.

JAK-STAT3 and somatic cell reprogramming

Reprogramming somatic cells to pluripotency, especially by the induced pluripotent stem cell (iPSC) technology, has become widely used today to generate various types of stem cells for research and for regenerative medicine. However the mechanism(s) of reprogramming still need detailed elucidation, including the roles played by the leukemia inhibitory factor (LIF) signaling pathway. LIF is central in maintaining the ground state pluripotency of mouse embryonic stem cells (ESCs) and iPSCs by activating the Janus kinase-signal transducer and activator of transcription 3 (JAK-STAT3) pathway. Characterizing and understanding this pathway holds the key to generate naïve pluripotent human iPSCs which will facilitate the development of patient-specific stem cell therapy. Here we review the historical and recent developments on how LIF signaling pathway regulates ESC pluripotency maintenance and somatic cell reprogramming, with a focus on JAK-STAT3.

Signaling of cytokines is important in regulation of GnRH neurons

Cytokines encompass a broad class of peptides that mediate signals in a broad range of physiological situations including inflammation, infection, and obesity. The cytokine receptor-associated tyrosine kinase, Jak2, is one of the most important proteins mediating cytokine signaling pathway activation. Recently, our group has demonstrated that Jak2 signaling in the gonadotropin-releasing hormone (GnRH) neuron plays a critical role in fertility in males and females, implicating cytokine activation of the neuron in GnRH neuronal development and function. To date, the specific cytokine(s) essential for activating Jak2 during neuroendocrine development are not known. In this article, we review the evidence for the role of several class 1 cytokines in regulating GnRH neuronal development, GnRH secretion, and GnRH expression.

CNTF and retina

Ciliary neurotrophic factor (CNTF) is one of the most studied neurotrophic factors for neuroprotection of the retina. A large body of evidence demonstrates that CNTF promotes rod photoreceptor survival in almost all animal models. Recent studies indicate that CNTF also promotes cone photoreceptor survival and cone outer segment regeneration in the degenerating retina and improves cone function in dogs with congenital achromotopsia. In addition, CNTF is a neuroprotective factor and an axogenesis factor for retinal ganglion cells (RGCs). This review focuses on the effects of exogenous CNTF on photoreceptors and RGCs in the mammalian retina and the potential clinical application of CNTF for retinal degenerative diseases.

Ciliary neurotrophic factor induces genes associated with inflammation and gliosis in the retina: a gene profiling study of flow-sorted, Müller cells

Background

Ciliary neurotrophic factor (CNTF), a member of the interleukin-6 cytokine family, has been implicated in the development, differentiation and survival of retinal neurons. The mechanisms of CNTF action as well as its cellular targets in the retina are poorly understood. It has been postulated that some of the biological effects of CNTF are mediated through its action via retinal glial cells; however, molecular changes in retinal glia induced by CNTF have not been elucidated. We have, therefore, examined gene expression dynamics of purified Müller (glial) cells exposed to CNTF in vivo.

Methodology/Principal Findings

Müller cells were flow-sorted from mgfap-egfp transgenic mice one or three days after intravitreal injection of CNTF. Microarray analysis using RNA from purified Müller cells showed differential expression of almost 1,000 transcripts with two- to seventeen-fold change in response to CNTF. A comparison of transcriptional profiles from Müller cells at one or three days after CNTF treatment showed an increase in the number of transcribed genes as well as a change in the expression pattern. Ingenuity Pathway Analysis showed that the differentially regulated genes belong to distinct functional types such as cytokines, growth factors, G-protein coupled receptors, transporters and ion channels. Interestingly, many genes induced by CNTF were also highly expressed in reactive Müller cells from mice with inherited or experimentally induced retinal degeneration. Further analysis of gene profiles revealed 20–30% overlap in the transcription pattern among Müller cells, astrocytes and the RPE.

Conclusions/Significance

Our studies provide novel molecular insights into biological functions of Müller glial cells in mediating cytokine response. We suggest that CNTF remodels the gene expression profile of Müller cells leading to induction of networks associated with transcription, cell cycle regulation and inflammatory response. CNTF also appears to function as an inducer of gliosis in the retina.

Interleukin-6 enhances glucose-stimulated insulin secretion from pancreatic beta-cells: potential involvement of the PLC-IP3-dependent pathway

OBJECTIVE

Interleukin-6 (IL-6) has a significant impact on glucose metabolism. However, the effects of IL-6 on insulin secretion from pancreatic β-cells are controversial. Therefore, we analyzed IL-6 effects on pancreatic β-cell functions both in vivo and in vitro.

RESEARCH DESIGN AND METHODS

First, to examine the effects of IL-6 on in vivo insulin secretion, we expressed IL-6 in the livers of mice using the adenoviral gene transfer system. In addition, using both MIN-6 cells, a murine β-cell line, and pancreatic islets isolated from mice, we analyzed the in vitro effects of IL-6 pretreatment on insulin secretion. Furthermore, using pharmacological inhibitors and small interfering RNAs, we studied the intracellular signaling pathway through which IL-6 may affect insulin secretion from MIN-6 cells.

RESULTS

Hepatic IL-6 expression raised circulating IL-6 and improved glucose tolerance due to enhancement of glucose stimulated-insulin secretion (GSIS). In addition, in both isolated pancreatic islets and MIN-6 cells, 24-h pretreatment with IL-6 significantly enhanced GSIS. Furthermore, pretreatment of MIN-6 cells with phospholipase C (PLC) inhibitors with different mechanisms of action, U-73122 and neomycin, and knockdowns of the IL-6 receptor and PLC-β(1), but not with a protein kinase A inhibitor, H-89, inhibited IL-6-induced enhancement of GSIS. An inositol triphosphate (IP(3)) receptor antagonist, Xestospondin C, also abrogated the GSIS enhancement induced by IL-6.

CONCLUSIONS

The results obtained from both in vivo and in vitro experiments strongly suggest that IL-6 acts directly on pancreatic β-cells and enhances GSIS. The PLC-IP(3)-dependent pathway is likely to be involved in IL-6-mediated enhancements of GSIS.

Overcoming insulin resistance with ciliary neurotrophic factor

The incidence of obesity and related co-morbidities such as insulin resistance, dyslipidemia and hypertension are increasing at an alarming rate worldwide. Current interventions seem ineffective to halt this progression. With the failure of leptin as an anti-obesity therapeutic, ciliary neurotrophic factor (CNTF) has proven efficacious in models of obesity and leptin resistance, where leptin proved ineffective. CNTF is a gp130 ligand that has been found to act centrally and peripherally to promote weight loss and insulin sensitivity in both human and rodent models. Future research into novel gp130 ligands may offer new candidates for obesity-related drug therapy.

Leukemia inhibitory factor regulates trafficking of T-type Ca2+ channels

Neuropoietic cytokines such as ciliary neurotrophic factor (CNTF) and leukemia inhibitory factor (LIF) stimulate the functional expression of T-type Ca(2+) channels in developing sensory neurons. However, the molecular and cellular mechanisms involved in the cytokine-evoked membrane expression of T-type Ca(2+) channels are not fully understood. In this study we investigated the role of LIF in promoting the trafficking of T-type Ca(2+) channels in a heterologous expression system. Our results demonstrate that transfection of HEK-293 cells with the rat green fluorescent protein (GFP)-tagged T-type Ca(2+) channel α(1H)-subunit resulted in the generation of transient Ca(2+) currents. Overnight treatment of α(1H)-GFP-transfected cells with LIF caused a significant increase in the functional expression of T-type Ca(2+) channels as indicated by changes in current density. LIF also evoked a significant increase in membrane fluorescence compared with untreated cells. Disruption of the Golgi apparatus with brefeldin A inhibited the stimulatory effect of LIF, indicating that protein trafficking regulates the functional expression of T-type Ca(2+) channels. Trafficking of α(1H)-GFP was also disrupted by cotransfection of HEK-293 cells with the dominant-negative form of ADP-ribosylation factor (ARF)1 but not ARF6, suggesting that ARF1 regulates the LIF-evoked membrane trafficking of α(1H)-GFP subunits. Trafficking of T-type Ca(2+) channels required transient activation of the JAK and ERK signaling pathways since stimulation of HEK-293 cells with LIF evoked a considerable increase in the phosphorylation of the downstream JAK targets STAT3 and ERK. Pretreatment of HEK-293 cells with the JAK inhibitor P6 or the ERK inhibitor U0126 blocked ERK phosphorylation. Both P6 and U0126 also inhibited the stimulatory effect of LIF on T-type Ca(2+) channel expression. These findings demonstrate that cytokines like LIF promote the trafficking of T-type Ca(2+) channels.

Expression profile of PTPIP51 in mouse brain

This study demonstrates the expression of the novel protein protein tyrosine phophatase-interacting protein 51 (PTPIP51) in mammalian brain tissue. Serial sections of the whole adult mouse brain were analyzed for PTPIP51 protein and mRNA by immunohistochemistry, immunoblotting, RT-PCR, and in situ hybridization. Recent investigations by Yu et al. (2008) describe PTPIP51 as being capable of activating Raf-1, thereby modulating the MAPK pathway. The role of Raf-1, as well as of 14-3-3, in neurological disorders is well established. PTPIP51 expression was confined to neurons in the following structures: the piriform cortex and their connections to the anterior commissure, nucleus accumbens, paraventricular and supraoptical nuclei, neurohypophysis, superior colliculus, genu of facialis nerve, spinal trigeminal tract, inferior cerebellar peduncle, and cerebellum. In the cerebellum, a subpopulation of Purkinje cells and their dendrites was strongly PTPIP51 positive. Moreover, PTPIP51 was found to be colocalized with vasopressin and its transport protein neurophysin II in the neuroendocrine nuclei and their connections to the neurohypophysis. The data presented here suggest a role of PTPIP51 in neuronal homeostasis, axonal growth, and transport.

Function and mechanism of CNTF/LIF signaling in retinogenesis

Ciliary neurotrophic factor (CNTF) and leukemia inhibitory factor (LIF) exhibit multiple biological effects in the developing vertebrate retina. CNTF/LIF inhibits rod photoreceptor, and promotes bipolar cells and Muller glia differentiation. In addition, CNTF/LIF has been shown to have proliferative and apoptotic effects. Moreover, LIF also inhibits retinal vascular development. CNTF/LIF signaling components CNTFRalpha, LIFRbeta, gp130, and a number of STAT proteins are expressed in the retina. CNTF/LIF activates Jak-STAT, ERK, and Notch pathways during retinal development. Perturbation of CNTF induced signal transduction reveals that different combinations of CNTF/LIF signaling pathways regulate differentiation of retinal neurons and glia. Gene expression studies show that CNTF/LIF affects retinogenesis by regulating various genes involved in transcription, signal transduction, protein modification, apoptosis, protein localization, and cell ion homeostasis. Most past studies have deployed ectopic expression or addition of exogenous CNTF/LIF, thus further ana-lysis of mice with conditional mutations in CNTF/LIF signaling components will allow better understanding of in-vivo functions of CNTF/LIF associated signaling events in retinogenesis.

Stat3 and c-Myc genome-wide promoter occupancy in embryonic stem cells

Embryonic stem (ES) cell pluripotency is regulated in part by transcription factor (TF) pathways that maintain self-renewal and inhibit differentiation. Stat3 and c-Myc TFs are essential for maintaining mouse ES cell self-renewal. c-Myc, together with Oct4, Sox2, and Klf4, is a reprogramming factor. While previous studies have investigated core transcriptional circuitry in ES cells, other TF pathways that promote ES cell pluripotency have yet to be investigated. Therefore, to further understand ES cell transcriptional networks, we used genome-wide chromatin immunoprecipitation and microarray analysis (ChIP-chip) to map Stat3 and c-Myc binding targets in ES cells. Our results show that Stat3 and c-Myc occupy a significant number of genes whose expression is highly enriched in ES cells. By comparing Stat3 and c-Myc target genes with gene expression data from undifferentiated ES cells and embryoid bodies (EBs), we found that Stat3 binds active and inactive genes in ES cells, while c-Myc binds predominantly active genes. Moreover, the transcriptional states of Stat3 and c-Myc targets are correlated with co-occupancy of pluripotency-related TFs, polycomb group proteins, and active and repressive histone modifications. We also provide evidence that Stat3 targets are differentially expressed in ES cells following removal of LIF, where culture of ES cells in the absence of LIF resulted in downregulation of Stat3 target genes enriched in ES cells, and upregulation of lineage specific Stat3 target genes. Altogether, we reveal transcriptional targets of two key pluripotency-related genes in ES cells – Stat3 and c-Myc, thus providing further insight into the ES cell transcriptional network.

Central exercise action increases the AMPK and mTOR response to leptin

AMP-activated protein kinase (AMPK) and mammalian Target of Rapamycin (mTOR) are key regulators of cellular energy balance and of the effects of leptin on food intake. Acute exercise is associated with increased sensitivity to the effects of leptin on food intake in an IL-6-dependent manner. To determine whether exercise ameliorates the AMPK and mTOR response to leptin in the hypothalamus in an IL-6-dependent manner, rats performed two 3-h exercise bouts, separated by one 45-min rest period. Intracerebroventricular IL-6 infusion reduced food intake and pretreatment with AMPK activators and mTOR inhibitor prevented IL-6-induced anorexia. Activators of AMPK and fasting increased food intake in control rats to a greater extent than that observed in exercised ones, whereas inhibitor of AMPK had the opposite effect. Furthermore, the reduction of AMPK and ACC phosphorylation and increase in phosphorylation of proteins involved in mTOR signal transduction, observed in the hypothalamus after leptin infusion, were more pronounced in both lean and diet-induced obesity rats after acute exercise. Treatment with leptin reduced food intake in exercised rats that were pretreated with vehicle, although no increase in responsiveness to leptin-induced anorexia after pretreatment with anti-IL6 antibody, AICAR or Rapamycin was detected. Thus, the effects of leptin on the AMPK/mTOR pathway, potentiated by acute exercise, may contribute to appetite suppressive actions in the hypothalamus.

CNTF-evoked activation of JAK and ERK mediates the functional expression of T-type Ca2+ channels in chicken nodose neurons

Culture of chicken nodose neurons with CNTF but not BDNF causes a significant increase in T-type Ca(2+) channel expression. CNTF-induced channel expression requires 12 h stimulation to reach maximal expression and is not affected by inhibition of protein synthesis, suggesting the involvement of a post-translational mechanism. In this study, we have investigated the biochemical mechanism responsible for the CNTF-dependent stimulation of T-type channel expression in nodose neurons. Stimulation of nodose neurons with CNTF evoked a considerable increase in signal transducer and activator of transcription (STAT3) and extracellular signal-regulated kinase (ERK) phosphorylation. CNTF-evoked ERK phosphorylation was transient whereas BDNF-evoked activation of ERK was sustained. Pre-treatment of nodose neurons with the Janus tyrosine kinase (JAK) inhibitor P6 blocked STAT3 and ERK phosphorylation, whereas the ERK inhibitor U0126 prevented ERK activation but not STAT3 phosphorylation. Both P6 and U0126 inhibited the stimulatory effect of CNTF on T-type channel expression. Inhibition of STAT3 activation by the selective blocker stattic has no effect on ERK phosphorylation and T-type channel expression. These results indicate that CNTF-evoked stimulation of T-type Ca(2+) channel expression in chicken nodose neurons requires JAK-dependent ERK signaling. A cardiac tissue extract derived from E20 chicken heart was also effective in promoting T-type Ca(2+) channel expression and STAT3 and ERK phosphorylation. The ability of the heart extract to stimulate JAK/STAT and ERK activation was developmentally regulated. These findings provide further support to the idea that CNTF or a CNTF-like factor mediates normal expression of T-type channels.

Frequent in-frame somatic deletions activate gp130 in inflammatory hepatocellular tumours

Inflammatory hepatocellular adenomas are benign liver tumours defined by the presence of inflammatory infiltrates and by the increased expression of inflammatory proteins in tumour hepatocytes. Here we show a marked activation of the interleukin (IL)-6 signalling pathway in this tumour type; sequencing candidate genes pinpointed this response to somatic gain-of-function mutations in the IL6ST gene, which encodes the signalling co-receptor gp130. Indeed, 60% of inflammatory hepatocellular adenomas harbour small in-frame deletions that target the binding site of gp130 for IL-6, and expression of four different gp130 mutants in hepatocellular cells activates signal transducer and activator of transcription 3 (STAT3) in the absence of ligand. Furthermore, analysis of hepatocellular carcinomas revealed that rare gp130 alterations are always accompanied by beta-catenin-activating mutations, suggesting a cooperative effect of these signalling pathways in the malignant conversion of hepatocytes. The recurrent gain-of-function gp130 mutations in these human hepatocellular adenomas fully explains activation of the acute inflammatory phase observed in tumourous hepatocytes, and suggests that similar alterations may occur in other inflammatory epithelial tumours with STAT3 activation.

Knockdown of the co-chaperone Hop promotes extranuclear accumulation of Stat3 in mouse embryonic stem cells

A key event in the mechanism of mouse embryonic stem cell (mESC) pluripotency is phosphorylation, dimerisation and translocation to the nucleus of the signal transducer and activator of transcription3, Stat3. We used RNAi to suppress the levels of the co-chaperone Hsp70/Hsp90 organising protein (Hop) in an mESC line. Hop knockdown caused 68% depletion in Stat3 mRNA levels, decreased soluble pYStat3 levels, and led to an extranuclear accumulation of Stat3. The major binding partner of Hop, Hsp90, co-localised with a small non-nuclear fraction of Stat3 in mESCs, and both Stat3 and Hop co-precipitated with Hsp90. Hop knockdown did not affect Nanog and Oct4 protein levels; however, Nanog mRNA levels were decreased. We found that in the absence of Hop, mESCs lost their pluripotent ability to form embryoid bodies with a basement membrane. These data suggest that Hop facilitates the phosphorylation and nuclear translocation of Stat3, implying a role for the Hsp70/Hsp90 chaperone heterocomplex machinery in pluripotency signalling.

Neuropoietin attenuates adipogenesis and induces insulin resistance in adipocytes

Recent findings have implicated gp130 receptor ligands, particularly ciliary neurotrophic factor (CNTF), as potential anti-obesity therapeutics. Neuropoietin (NP) is a recently discovered cytokine in the gp130 family that shares functional and structural features with CNTF and signals via the CNTF receptor tripartite complex comprised of CNTFRalpha, LIF receptor, and gp130. NP plays a role in the development of the nervous system, but the effects of NP on adipocytes have not been previously examined. Because CNTF exerts anti-obesogenic effects in adipocytes and NP shares the same receptor complex, we investigated the effects of NP on adipocyte development and insulin action. Using cultured 3T3-L1 adipocytes, we observed that NP has the ability to block adipogenesis in a dose- and time-dependent manner. We also observed that cultured adipocytes, as well as murine adipose tissue, are highly responsive to acute NP treatment. Rodents injected with NP had a substantial increase in STAT3 tyrosine phosphorylation and ERK 1 and 2 activation. We also observed the induction of SOCS-3 mRNA in 3T3-L1 adipocytes following NP treatment. Unlike CNTF, our studies have revealed that NP also substantially attenuates insulin-stimulated glucose uptake in 3T3-L1 adipocytes. In addition, NP blocks insulin action in adipose tissue in vivo. These observations are supported by data demonstrating that NP impairs insulin signaling via decreased activation of both IRS-1 and Akt. In summary, we have observed that both adipocytes in vitro and in vivo are highly responsive to NP, and this cytokine has the ability to affect insulin signaling in fat cells. These novel observations suggest that NP, unlike CNTF, may not be a viable obesity therapeutic.

Functional immobilization of signaling proteins enables control of stem cell fate

The mode of ligand presentation has a fundamental role in organizing cell fate throughout development. We report a rapid and simple approach for immobilizing signaling ligands to maleic anhydride copolymer thin-film coatings, enabling stable signaling ligand presentation at interfaces at defined concentrations. We demonstrate the utility of this platform technology using leukemia inhibitory factor (LIF) and stem cell factor (SCF). Immobilized LIF supported mouse embryonic stem cell (mESC) pluripotency for at least 2 weeks in the absence of added diffusible LIF. Immobilized LIF activated signal transducer and activator of transcription 3 (STAT3) and mitogen-activated protein kinase (MAPK) signaling in a dose-dependent manner. The introduced method allows for the robust investigation of cell fate responses from interface-immobilized ligands.

Extrinsic regulation of T-type Ca(2+) channel expression in chick nodose ganglion neurons

Functional expression of T-type Ca(2+) channels is developmentally regulated in chick nodose neurons. In this study we have tested the hypothesis that extrinsic factors regulate the expression of T-type Ca(2+) channels in vitro. Voltage-gated Ca(2+) currents were measured using whole-cell patch clamp recordings in E7 nodose neurons cultured under various conditions. Culture of E7 nodose neurons for 48 h with a heart extract induced the expression of T-type Ca(2+) channels without any significant effect on HVA currents. T-type Ca(2+) channel expression was not stimulated by survival promoting factors such as BDNF. The stimulatory effect of heart extract was mediated by a heat-labile, trypsin-sensitive factor. Various hematopoietic cytokines including CNTF and LIF mimic the stimulatory effect of heart extract on T-type Ca(2+) channel expression. The stimulatory effect of heart extract and CNTF requires at least 12 h continuous exposure to reach maximal expression and is not altered by culture of nodose neurons with the protein synthesis inhibitor anisomycin, suggesting that T-type Ca(2+) channel expression is regulated by a posttranslational mechanism. Disruption of the Golgi apparatus with brefeldin-A inhibits the stimulatory effect of heart extract and CNTF suggesting that protein trafficking regulates the functional expression of T-type Ca(2+) channels. Heart extract- or CNTF-evoked stimulation of T-type Ca(2+) channel expression is blocked by the Jak/STAT and MAP kinase blockers, AG490 and U0126, respectively. This study provides new insights into the electrical differentiation of placode-derived sensory neurons and the role of extrinsic factors in regulating the functional expression of Ca(2+) channels.

Shp2 is involved in neuronal differentiation of hippocampal precursor cells

HiB5 is a multipotent hippocampal stem cell line whose differentiation into cells of a neuronal phenotype is promoted by neurotrophic factors such as PDGF and brain-derived neurotrophic factor (BDNF). We examined the potential role of Src homology 2 (SH2)-containing protein tyrosine phosphatase (Shp2) in this differentiation process. We found that Shp2 became tyrosine phosphorylated following PDGF treatment. Wild-type Shp2 enhanced the expression of neurofilament, synapsin I and PSD95 by PDGF and BDNF, whereas their expression was attenuated by the catalytically inactive mutants Shp2C/S and Shp2DeltaP. Formation of dendritic spine-like structures increased with wild-type Shp2, but diminished with Shp2C/S and Shp2DeltaP. PSD95, localized in the post-synaptic density region of dendritic spines, PDGFRbeta and TrkB were co-immunoprecipitated with Shp2 antibodies. These results suggest that Shp2 plays a positive role in mediating PDGF- and BDNF-activated signaling which promotes the formation of dendritic spines.

Signal transduction pathways that contribute to myeloid differentiation

The production of mature, differentiated myeloid cells is regulated by the action of hematopoietic cytokines on progenitor cells in the bone marrow. Cytokines drive the process of myeloid differentiation by binding to specific cell-surface receptors in a stage- and lineage-specific manner. Following the binding of a cytokine to its cognate receptor, intracellular signal-transduction pathways become activated that facilitate the myeloid differentiation process. These intracellular signaling pathways may promote myelopoiesis by stimulating expansion of a progenitor pool, supporting cellular survival during the differentiation process, or by directly driving the phenotypic changes associated with differentiation. Ultimately, pathways that drive the differentiation process converge on myeloid transcription factors, including PU.1 and the C/EBP family, that are critical for differentiation to proceed. While much is known about the cytokines, cytokine receptors and transcription factors that regulate myeloid differentiation, less is known about the precise roles that specific signaling mediators play in promoting myeloid differentiation. Recently, however, the application of novel pharmacologic inhibitors, siRNA strategies, and transgenic and knockout models has begun to shed light on the involvement and function of signaling pathways in normal myeloid differentiation. This review will discuss the roles that key signaling pathways and mediators play in myeloid differentiation.

gp130 receptor ligands as potential therapeutic targets for obesity

Obesity and its related cluster of pathophysiologic conditions including insulin resistance, glucose intolerance, dyslipidemia, and hypertension are recognized as growing threats to world health. It is now estimated that 10% of the world's population is overweight or obese. As a result, new therapeutic options for the treatment of obesity are clearly warranted. Recent research has focused on the role that gp130 receptor ligands may play as potential therapeutic targets in obesity. One cytokine in particular, ciliary neurotrophic factor (CNTF), acts both centrally and peripherally and mimics the biologic actions of the appetite control hormone leptin, but unlike leptin, CNTF appears to be effective in obesity and as such may have therapeutic potential. In addition, CNTF suppresses inflammatory signaling cascades associated with lipid accumulation in liver and skeletal muscle. This review examines the potential role of gp130 receptor ligands as part of a therapeutic strategy to treat obesity.