Leukemia inhibitory factor: part of a large ingathering family

Tumor Necrosis Factor-Alpha Modulates Expression of Genes Involved in Cytokines and Chemokine Pathways in Proliferative Myoblast Cells

Skeletal muscle regeneration after injury is a complex process involving inflammatory signaling and myoblast activation. Pro-inflammatory cytokines like tumor necrosis factor-alpha (TNF-α) are key mediators, but their effects on gene expression in proliferating myoblasts are unclear. We performed the RNA sequencing of TNF-α treated C2C12 myoblasts to elucidate the signaling pathways and gene networks regulated by TNF-α during myoblast proliferation. The TNF-α (10 ng/mL) treatment of C2C12 cells led to 958 differentially expressed genes compared to the controls. Pathway analysis revealed significant regulation of TNF-α signaling, along with the chemokine and IL-17 pathways. Key upregulated genes included cytokines (e.g., IL-6), chemokines (e.g., CCL7), and matrix metalloproteinases (MMPs). TNF-α increased myogenic factor 5 (Myf5) but decreased MyoD protein levels and stimulated the release of MMP-9, MMP-10, and MMP-13. TNF-α also upregulates versican and myostatin mRNA. Overall, our study demonstrates the TNF-α modulation of distinct gene expression patterns and signaling pathways that likely contribute to enhanced myoblast proliferation while suppressing premature differentiation after muscle injury. Elucidating the mechanisms involved in skeletal muscle regeneration can aid in the development of regeneration-enhancing therapeutics.

The Molecular Basis and Therapeutic Potential of Leukemia Inhibitory Factor in Cancer Cachexia

Simple Summary

The mechanism of cancer cachexia is linked to a variety of factors, and inflammatory factors are thought to play a key role. We summarize the main roles of LIF in the development of cancer cachexia, including promoting fat loss, inducing skeletal muscle atrophy and causing anorexia nervosa. The main aim of this review is to increase the understanding of the effects of LIF in cachexia and to provide new insights into the treatment of cancer cachexia.

Abstract

Cachexia is a chronic metabolic syndrome that is characterized by sustained weight and muscle mass loss and anorexia. Cachexia can be secondary to a variety of diseases and affects the prognosis of patients significantly. The increase in inflammatory cytokines in plasma is deeply related to the occurrence of cachexia. As a member of the IL-6 cytokine family, leukemia inhibitory factor (LIF) exerts multiple biological functions. LIF is over-expressed in the cancer cells and stromal cells of various tumors, promoting the malignant development of tumors via the autocrine and paracrine systems. Intriguingly, increasing studies have confirmed that LIF contributes to the progression of cachexia, especially in patients with metastatic tumors. This review combines all of the evidence to summarize the mechanism of LIF-induced cachexia from the following four aspects: (i) LIF and cancer-associated cachexia, (ii) LIF and alterations of adipose tissue in cachexia, (iii) LIF and anorexia nervosa in cachexia, and (iv) LIF and muscle atrophy in cachexia. Considering the complex mechanisms in cachexia, we also focus on the interactions between LIF and other key cytokines in cachexia and existing therapeutics targeting LIF.

Optimizing and Profiling Prostaglandin E2 as a Medical Countermeasure for the Hematopoietic Acute Radiation Syndrome

Identification of medical countermeasures (MCM) to mitigate radiation damage and/or protect first responders is a compelling unmet medical need. The prostaglandin E2 (PGE2) analog, 16,16 dimethyl-PGE2 (dmPGE2), has shown efficacy as a radioprotectant and radiomitigator that can enhance hematopoiesis and ameliorate intestinal mucosal cell damage. In this study, we optimized the time of administration of dmPGE2 for protection and mitigation against mortality from the hematopoietic acute radiation syndrome (H-ARS) in young adult mice, evaluated its activity in pediatric and geriatric populations, and investigated potential mechanisms of action. Windows of 30-day survival efficacy for single administration of dmPGE2 were defined as within 3 h prior to and 6-30 h after total-body γ irradiation (TBI). Radioprotective and radio-mitigating efficacy was also observed in 2-year-old geriatric mice and 6-week-old pediatric mice. PGE2 receptor agonist studies suggest that signaling through EP4 is primarily responsible for the radioprotective effects. DmPGE2 administration prior to TBI attenuated the drop in red blood cells and platelets, accelerated recovery of all peripheral blood cell types, and resulted in higher hematopoietic and mesenchymal stem cells in survivor bone marrow. Multiplex analysis of bone marrow cytokines together with RNA sequencing of hematopoietic stem cells indicated a pro-hematopoiesis cytokine milieu induced by dmPGE2, with IL-6 and G-CSF strongly implicated in dmPGE2-mediated radioprotective activity. In summary, we have identified windows of administration for significant radio-mitigation and radioprotection by dmPGE2 in H-ARS, demonstrated survival efficacy in special populations, and gained insight into radioprotective mechanisms, information useful towards development of dmPGE2 as a MCM for first responders, military personnel, and civilians facing radiation threats.

Reduction of Neuroinflammation by δ-Opioids Via STAT3-Dependent Pathway in Chronic Glaucoma Model

The main objective of this study was to determine the inhibition of pro-inflammatory cytokines and their associated signaling molecules by δ-opioid receptor activation by a selective ligand, SNC-121 in chronic rat glaucoma model. Intraocular pressure was raised in rat eyes by injecting 2 M hypertonic saline into the limbal veins. SNC-121 (1 mg/kg; i. p) or Stattic (5 mg/kg; i. p) was administered in Brown Norway rats daily for 7 days. The mRNA expression of IL-1β, TNF-α, Fas, IL-6, leukemia inhibitory factor, and IFN-γ was increased significantly in the retina of ocular hypertensive animals at day 7, post injury. Administration of SNC-121 (1 mg/kg; i. p. injection) for 7 days (once a day) completely inhibited the increase in the mRNA and protein expression of pro-inflammatory cytokines. Mechanistically, we provide data showing a significant increase in the phosphorylation of STAT3 at tyrosine 705 whereas a moderate but significant increase in the total STAT3 protein expression was also seen in the retina of ocular hypertensive animals. Data illustrated that SNC-121 administration completely abrogated ocular hypertension-induced increase in STAT3^Y705 phosphorylation. Interestingly, acetylation of STAT3 at lysine 685 (AcK685) was reduced in ocular hypertensive animals and subsequently increased significantly by SNC-121 treatment. Stattic, a selective STAT3 inhibitor, administration resulted in a complete attenuation in the production of IL-1β and IL-6 in ocular hypertensive animals. In conclusion, δ-opioid receptor activation suppressed the phosphorylation of STAT3 at tyrosine 705 and increased acetylation at lysine 686 and these posttranslational modifications can regulate the production of some but not all pro-inflammatory cytokines in response to glaucomatous injury.

In Vitro Maturation with Leukemia Inhibitory Factor Prior to the Vitrification of Bovine Oocytes Improves Their Embryo Developmental Potential and Gene Expression in Oocytes and Embryos

Oocyte cryopreservation has a significant impact on subsequent embryonic development. Herein, we investigated whether supplementing in vitro maturation medium with Leukemia Inhibitory Factor (LIF) prior to vitrification affects embryo development and gene expression at different embryo developmental stages. A panel of genes including maternal effect, epigenetics, apoptosis and heat stress was relatively quantified. The results show reduced cleavage rates after vitrification, regardless of the LIF treatment. Although not statistically different from control-vitrified oocytes, oocyte apoptosis and the blastocyst yield of LIF-vitrified oocytes were similar to their non-vitrified counterparts. Vitrification increased oocyte ZAR1, NPM2 and DPPA3 gene expression while its expression decreased in LIF-vitrified oocytes to similar or close levels to those of non-vitrified oocytes. With a few gene-specific exceptions, vitrification significantly increased the expression of DNMT3A, HDAC1, KAT2A, BAX and BCL2L1 in oocytes and most stages of embryo development, while comparable expression patterns for these genes were observed between LIF-vitrified and non-vitrified groups. Vitrification increased HSPA1A expression in oocytes and HSP90AA1 in 2-cell embryos. Our data suggest that vitrification triggers stage-specific changes in gene expression throughout embryonic development. However, the inclusion of LIF in the IVM medium prior to vitrification stimulates blastocyst development and several other developmental parameters and induces oocytes and embryos to demonstrate gene expression patterns similar to those derived from non-vitrified oocytes.

Leukemia Inhibitory Factor Increases Survival of Pluripotent Stem Cell-Derived Cardiomyocytes

Leukemia inhibitory factor (LIF) is a growth factor with pleiotropic biological functions. It has been reported that LIF acts at different stages during mesoderm development. Also, it has been shown that LIF has a cytoprotective effect on neonatal murine cardiomyocytes (CMs) in culture, but little is known about the role of LIF during human cardiogenesis. Thus, we analyzed the effects of LIF on human pluripotent stem cells (PSC) undergoing cardiac differentiation. We first showed that LIF is expressed in the human heart during early development. We found that the addition of LIF within a precise time window during the in vitro differentiation process significantly increased CMs viability. This finding was associated to a decrease in the expression of pro-apoptotic protein Bax, which coincides with a reduction of the apoptotic rate. Therefore, the addition of LIF may represent a promising strategy for increasing CMs survival derived from PSCs.

Retinal ganglion cell death in glaucoma: Exploring the role of neuroinflammation

In clinical glaucoma, as well as in experimental models, the loss of retinal ganglion cells occurs by apoptosis. This final event is preceded by inflammatory responses involving the activation of innate and adaptive immunity, with retinal and optic nerve resident glial cells acting as major players. Here we review the current literature on the role of neuroinflammation in neurodegeneration, focusing on the inflammatory molecular mechanisms involved in the pathogenesis and progression of the optic neuropathy.

The regulation of leukemia inhibitory factor

Leukemia inhibitory factor (LIF), a secreted cytokine, plays an important role in a wide array of biological processes including inducing differentiation of leukemia cell, inflammatory response, neuronal development, embryonic implantation, stem cell self-renewal and cancer progression, etc. LIF exerts its biological functions mainly through the activation and regulation of JAK/STAT3, AKT, EKR1/2 and mTOR signal pathways. The expression levels of LIF are regulated by many different factors under different conditions in different tissue/cell types. For example, estrogen and p53 are important regulators for the high LIF production in uterine tissues at the implantation stage. Hypoxia plays a critical role in LIF overexpression in solid tumors. Many cytokines, including IL-6, IL-1β, can also induce the LIF expression and production. In this review, we summarize the current understanding on the transcriptional regulation of LIF under various conditions.

Leukemia inhibitory factor attenuates renal fibrosis through Stat3-miR-29c

Leukemia inhibitory factory (LIF), as a member of the IL-6 family, has been reported to ameliorate myocardial fibrosis and myocardial cell death. The purpose of the present study was to investigate the effect of LIF on renal fibrosis and its underlying mechanism. Our results showed, first, that LIF inhibited collagen type 1 and collagen type 3 expression induced by ANG II in NRK-49F (rat kidney fibroblast) cells and in mice with unilateral ureteral obstruction. Second, LIF induced Stat3 Tyr(705) phosphorylation and inhibited Stat3 Tyr(705) and Ser(727) phosphorylation induced by ANG II in NRK-49F cells. Third, LIF exerted an antirenal fibrosis effect mainly through activation of Stat3 Tyr(705) phosphorylation in NRK-49F cells. These effects of LIF were not observed in Stat3(-/-) cells. Finally, LIF-Stat3 upregulated microRNA-29c expression, and the latter downregulated collagen type 1 and collagen type 3 expression in NRK-49F cells and in mice with unilateral ureteral obstruction. In conclusion, LIF played a role in antirenal fibrosis by competitively activating Stat3 Tyr(705) phosphorylation, which upregulated microRNA-29c to suppress collagen expression.

The leukemia inhibitory factor (LIF) and p21 mediate the TGFβ tumor suppressive effects in human cutaneous melanoma

BACKGROUND

Cutaneous melanoma is the most lethal skin cancer and its incidence in developed countries has dramatically increased over the past decades. Localized tumors are easily treated by surgery, but advanced melanomas lack efficient treatment and are associated with very poor outcomes. Thus, understanding the processes underlying melanoma development and progression is critical. The Transforming Growth Factor beta (TGFβ) acts as a potent tumor suppressor in human melanoma, by inhibiting cell growth and preventing cellular migration and invasion.

METHODS

In this study, we aimed at elucidating the molecular mechanisms underlying TGFβ-mediated tumor suppression. Human cutaneous melanoma cell lines, derived from different patients, were used to assess for cell cycle analysis, apoptosis/caspase activity and cell migration. Techniques involved immunoblotting, immunohistochemistry, real time PCR and luciferase reporter assays.

RESULTS

We found the leukemia inhibitory factor (LIF) to be strongly up-regulated by TGFβ in melanoma cells, defining LIF as a novel TGFβ downstream target gene in cutaneous melanoma. Interestingly, we also showed that TGFβ-mediated LIF expression is required for TGFβ-induced cell cycle arrest and caspase-mediated apoptosis, as well as for TGFβ-mediated inhibition of cell migration. Moreover, we found that TGFβ-mediated LIF expression leads to activation of transcription of the cell cycle inhibitor p21 in a STAT3-dependent manner, and further showed that p21 is required for TGFβ/LIF-mediated cell cycle arrest and TGFβ-induced gene activation of several pro-apoptotic genes.

CONCLUSIONS

Together, our results define the LIF/p21 signaling cascade as a novel tumor suppressive-like pathway in melanoma, acting downstream of TGFβ to regulate cell cycle arrest and cell death, further highlight new potential therapeutic strategies for the treatment of cutaneous melanoma.

Directional induction of dopaminergic neurons from neural stem cells using substantia nigra homogenates and basic fibroblast growth factor

To date, complex components of available reagents have been used for directional induction of neural stem cells into dopaminergic neurons, resulting in a poor ability to repeat experiments. This study sought to investigate whether a homogenate of the substantia nigra of adult rats and/or basic fibroblast growth factor could directionally induce neural stem cells derived from the subventricular zone of embryonic rats to differentiate into dopaminergic neurons. Tyrosine hydroxylase-positive cells were observed exclusively after induction with the homogenate supernatant of the substantia nigra from adult rats and basic fibroblast growth factor for 48 hours in vitro. However, in the groups treated with homogenate supernatant or basic fibroblast growth factor alone, tyrosine hydroxylase expression was not observed. Moreover, the content of dopamine in the culture medium of subventricular zone neurons was significantly increased at 48 hours after induction with the homogenate supernatant of the substantia nigra from adult rats and basic fibroblast growth factor. Experimental findings indicate that the homogenate supernatant of the substantia nigra from adult rats and basic fibroblast growth factor could directionally induce neural stem cells derived from the subventricular zone of embryonic rats to differentiate into dopaminergic neurons in the substantia nigra with the ability to secrete dopamine.

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

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

Applying chemical tools to the discovery of novel regenerative medicine

Regeneration is the process of restoring cells, tissues and structures that are lost during disease, injury or aging. Most regenerative processes involve stem or progenitor cells. However, regeneration mediated by stem or progenitor cells in adult mammalian systems is limited. Hence, small molecules that promote stem cell proliferation and/or differentiation are highly sought after, either as molecular tools to further understand stem cell biology or as drug leads for development of novel regenerative medicine.:

LIF-STAT signaling and trophoblast biology

Leukemia inhibitory factor (LIF) is a pleiotropic growth factor that regulates several biological functions. This review focuses on the LIF-dependent STAT activation and its impact on modulation of trophoblast functions during embryo implantation. LIF is mainly produced by the maternal endometrium at the time of implantation while its receptors are present both on the endometrium and trophoblasts. It might influence blastocyst attachment through STAT3 activation and expression of integrins. After attachment of the blastocyst, trophoblasts undergo proliferation and differentiation into invasive EVTs and non-invasive STBs. Under in vitro conditions, LIF regulates all these processes through activation of STAT- and MAPK-dependent signaling pathways. The observations that LIF and STAT3 knockout mice are infertile further strengthen the notion about the critical involvement of LIF-mediated signaling during embryo implantation. Hence, a better understanding of LIF-STAT signaling would help in improving fertility as use of LIF in in vitro blastocyst culture improves the implanting ability of blastocyst after IVF.

Impact of inflammation on the osteoarthritic niche: implications for regenerative medicine

Osteoarthritis (OA) is the most common form of arthritis worldwide and is the sixth leading cause of disability. It costs the UK economy approximately 1% of gross national product per annum. With an aging population, the cost of chronic conditions such as OA continues to rise. Historically, treatments for OA have been limited to painkillers, physiotherapy and joint injections. When these fail, patients are referred for joint replacement surgery. With the advent of tissue engineering strategies aimed at generating new bone and cartilage for repair of osteochondral defects, there has been considerable interest in exploiting these techniques to devise new treatments for OA. To date, little consideration has been given to the OA niche and attendant inflammatory milieu for any regenerative skeletal strategy. This review highlights the importance of understanding the osteoarthritic niche in order to modify existing tissue engineering and regenerative medicine strategies for the future treatment of OA.

LIF-dependent signaling: new pieces in the Lego

LIF, a member of the IL6 family of cytokine, displays pleiotropic effects on various cell types and organs. Its critical role in stem cell models (e.g.: murine ES, human mesenchymal cells) and its essential non redundant function during the implantation process of embryos, in eutherian mammals, put this cytokine at the core of many studies aiming to understand its mechanisms of action, which could benefit to medical applications. In addition, its conservation upon evolution raised the challenging question concerning the function of LIF in species in which there is no implantation. We present the recent knowledge about the established and potential functions of LIF in different stem cell models, (embryonic, hematopoietic, mesenchymal, muscle, neural stem cells and iPSC). We will also discuss EVO-DEVO aspects of this multifaceted cytokine.

A CD25⁻ positive population of activated B1 cells expresses LIFR and responds to LIF

B1 B cells defend against infectious microorganisms by spontaneous secretion of broadly reactive “natural” immunoglobulin that appears in the absence of immunization. Among many distinguishing characteristics, B1 B cells display evidence of activation that includes phosphorylated STAT3. In order to identify the origin of pSTAT3 we examined interleukin-2 receptor (IL-2R) expression on B1 cells. We found that some (about 1/5) B1a cells express the IL-2R α chain, CD25. Although lacking CD122 and unresponsive to IL-2, B1a cells marked by CD25 express increased levels of activated signaling intermediates, interruption of which results in diminished CD25. Further, CD25⁺ B1a cells contain most of the pSTAT3 found in the B1a population as a whole. Moreover, CD25⁺ B1a cells express leukemia inhibitory factor receptor (LIFR), and respond to LIF by upregulating pSTAT3. Together, these results define a new subset of B1a cells that is marked by activation-dependent CD25 expression, expresses substantial amounts of activated STAT3, and contains a functional LIFR.

Neuroprotective and axon growth-promoting effects following inflammatory stimulation on mature retinal ganglion cells in mice depend on ciliary neurotrophic factor and leukemia inhibitory factor

After optic nerve injury retinal ganglion cells (RGCs) normally fail to regenerate axons in the optic nerve and undergo apoptosis. However, lens injury (LI) or intravitreal application of zymosan switch RGCs into an active regenerative state, enabling these neurons to survive axotomy and to regenerate axons into the injured optic nerve. Several factors have been proposed to mediate the beneficial effects of LI. Here, we investigated the contribution of glial-derived ciliary neurotrophic factor (CNTF) to LI-mediated regeneration and neuroprotection using wild-type and CNTF-deficient mice. In wild-type mice, CNTF expression was strongly upregulated in retinal astrocytes, the JAK/STAT3 pathway was activated in RGCs, and RGCs were transformed into an active regenerative state after LI. Interestingly, retinal LIF expression was correlated with CNTF expression after LI. In CNTF-deficient mice, the neuroprotective and axon growth-promoting effects of LI were significantly reduced compared with wild-type animals, despite an observed compensatory upregulation of LIF expression in CNTF-deficient mice. The positive effects of LI and also zymosan were completely abolished in CNTF/LIF double knock-out mice, whereas LI-induced glial and macrophage activation was not compromised. In culture CNTF and LIF markedly stimulated neurite outgrowth of mature RGCs. These data confirm a key role for CNTF in directly mediating the neuroprotective and axon regenerative effects of inflammatory stimulation in the eye and identify LIF as an additional contributing factor.

Determining the LIF-sensitive period for implantation using a LIF-receptor antagonist

Uteri of Lif null mice do not support embryo implantation. Since deletion of some genes often prevents the survival of null mice to adulthood, we have used a proven inhibitor of leukaemia inhibitory factor (LIF) signalling to identify the precise window of time during which LIF is required in vivo, and assessed the cellular expression of several LIF-associated targets. On day 4 of pregnancy, mice were injected with hLIF-05 (inhibitor) into the uterine lumen, with corresponding volumes of PBS (vehicle) injected into the contralateral horn. On days 5 and 6, the number of implantation sites was recorded and the uteri processed for immunohistochemistry. Blockade of LIF on day 4 reduced embryo implantation by 50% (P≤0.0001) and was effective maximally between 0930 and 1230 h. Antagonism of LIF signalling was evidenced by a lack of phosphorylated STAT3 in the luminal epithelium (LE). Amphiregulin was absent from the LE on day 4 evening and H-type-1 antigen expression was retained in the LE on day 5 in inhibited uteri. Interleukin-1α and oncostatin M expression were reduced in the stroma on day 6, following LIF inhibition. Unexpectedly, PTGS2 expression in stroma was unaffected by LIF inhibition in vivo, in contrast to Lif null mice. In summary, this suggests that LIF signalling is effective for implantation during a discrete time window on day 4 and antagonism of LIF signalling recapitulates many features exhibited in Lif null uteri. The data presented validates the use of antagonists to investigate tissue specific and temporal cytokine signalling in reproductive function.

Three LIF-dependent signatures and gene clusters with atypical expression profiles, identified by transcriptome studies in mouse ES cells and early derivatives

Background

Mouse embryonic stem (ES) cells remain pluripotent in vitro when grown in the presence of the cytokine Leukaemia Inhibitory Factor (LIF). Identification of LIF targets and of genes regulating the transition between pluripotent and early differentiated cells is a critical step for understanding the control of ES cell pluripotency.

Results

By gene profiling studies carried out with mRNAs from ES cells and their early derivatives treated or not with LIF, we have identified i) LIF-dependent genes, highly expressed in pluripotent cells, whose expression level decreases sharply upon LIF withdrawal [Pluri genes], ii) LIF induced genes [Lifind genes] whose expression is differentially regulated depending upon cell context and iii) genes specific to the reversible or irreversible committed states. In addition, by hierarchical gene clustering, we have identified, among eight independent gene clusters, two atypical groups of genes, whose expression level was highly modulated in committed cells only. Computer based analyses led to the characterization of different sub-types of Pluri and Lifind genes, and revealed their differential modulation by Oct4 or Nanog master genes. Individual knock down of a selection of Pluri and Lifind genes leads to weak changes in the expression of early differentiation markers, in cell growth conditions in which these master genes are still expressed.

Conclusion

We have identified different sets of LIF-regulated genes depending upon the cell state (reversible or irreversible commitment), which allowed us to present a novel global view of LIF responses. We are also reporting on the identification of genes whose expression is strictly regulated during the commitment step. Furthermore, our studies identify sub-networks of genes with a restricted expression in pluripotent ES cells, whose down regulation occurs while the master knot (composed of OCT4, SOX2 and NANOG) is still expressed and which might be down-regulated together for driving cells towards differentiation.

Oogenesis: Prospects and challenges for the future

Oogenesis serves a singular role in the reproductive success of plants and animals. Of their remarkable differentiation pathway what stands out is the ability of oocytes to transform from a single cell into the totipotent lineages that seed the early embryo. As our understanding that commonalities between diverse organisms at the genetic, cellular and molecular levels are conserved to achieve successful reproduction, the notion that embryogenesis presupposes oogenesis has entered the day-to-day parlance of regenerative medicine and stem cell biology. With emphasis on the mammalian oocyte, this review will cover (1) current concepts regarding the birth, survival and growth of oocytes that depends on complex patterns of cell communication between germ line and soma, (2) the notion of "maternal inheritance" from a genetic and epigenetic perspective, and (3) the relative value of model systems with reference to current clinical and biotechnology applications.

Creating prodynorphin-expressing stem cells alerted for a high-throughput of cardiogenic commitment

BACKGROUND

The development of cell therapy for the rescue of damaged heart muscle is a major area of inquiry. Within this context, the establishment of a cardiogenic cell line may remarkably facilitate the molecular dissection of cardiac fate specification, a low-efficiency and still poorly understood process, paving the way for novel approaches in the use of stem cells for cardiac repair.

METHODS & RESULTS

We used GTR1 cells, a derivative of mouse R1 embryonic stem cells bearing the puromycin-resistance gene driven by the cardiomyocyte-specific alpha-myosin heavy chain promoter, affording a gene trapping selection of a virtually pure population of embryonic stem cell-derived cardiomyocytes. Third-generation lentiviral vectors were used to overexpress the prodynorphin gene, previously shown to orchestrate a dynorphinergic system acting as a major conductor of embryonic stem cell cardiogenesis. Lentiviral prodynorphin transduction remarkably enhanced the transcription of GATA-4 and Nkx-2.5, two cardiac lineage-promoting genes, resulting in a dramatic increase in the number of spontaneously beating cardiomyocytes. Transduced cells also exhibited a subcellular redistribution patterning of protein kinase C-beta, -delta and -epsilon, a major requirement in cardiac lineage commitment. This activation resulted from a sustained increase in the transcription of targeted protein kinase C genes. Prodynorphin transduction was selective in nature and failed to activate genes responsible for skeletal myogenesis or neuronal specification.

CONCLUSIONS

The cell line developed in this study provides a powerful in vitro model of cardiomyogenesis that may help clarify the cascade of transcriptional activation and signaling networks that push multipotent cells to take on the identity of a cardiac myocyte.

In vivo phage display selection yields atherosclerotic plaque targeted peptides for imaging

PURPOSE

Atherosclerosis is a leading cause of morbidity and mortality in the Western world, yet specific imaging agents to detect and map inflammatory plaques are still lacking.

PROCEDURES

We used in vivo phage display to interrogate early atherosclerotic lesions present in ApoE-/- mice with the goal of identifying plaque-associated endothelial cell internalized affinity ligands.

RESULTS

We identified 30 phage families with some of these families exhibiting homology to known atherosclerotic proteins, namely, leukemia inhibitory factor, transferrin, and VLA-4. VLA-4 homologous peptides [termed vascular cellular adhesion molecule-1 (VCAM-1) internalizing peptide-28 (VINP28)] bound to and were internalized by VCAM-1-expressing cells and were inhibited by soluble VCAM-1. In addition, a VINP28 modified multimodal nanoparticle showed high affinity for endothelial cells expressing VCAM-1 but low affinity for macrophages or smooth muscle cells.

CONCLUSION

The identified peptides represent a set of probes to interrogate the cell surface repertoire and potentially allow early detection of atherosclerosis.

Regulation of primordial follicle assembly and development

The assembly of the primordial follicles early in ovarian development and the subsequent development and transition of the primordial follicle to the primary follicle are critical processes in ovarian biology. These processes directly affect the number of oocytes available to a female throughout her reproductive life. Once the pool of primordial follicles is depleted a series of physiological changes known as menopause occur. The inappropriate coordination of these processes contributes to ovarian pathologies such as premature ovarian failure (POF) and infertility. Primordial follicle assembly and development are coordinated by locally produced paracrine and autocrine growth factors. Endocrine factors such as progesterone have also been identified that influence follicular assembly. Locally produced factors that promote the primordial to primary follicle transition include growth factors such as kit ligand (KL), leukaemia inhibitory factor (LIF), bone morphogenic proteins (BMP's), keratinocyte growth factor (KGF) and basic fibroblast growth factor (bFGF). Factors mediating both precursor theca-granulosa cell interactions and granulosa-oocyte interactions have been identified. A factor produced by preantral and antral follicles, Müllerian inhibitory substance, can act to inhibit the primordial to primary follicle transition. Observations suggest that a complex network of cell-cell interactions is required to control the primordial to primary follicle transition. Elucidation of the molecular and cellular control of primordial follicle assembly and the primordial to primary follicle transition provides therapeutic targets to regulate ovarian function and treat ovarian disease.

Medullary thyroid cancer: the functions of raf-1 and human achaete-scute homologue-1

Medullary thyroid cancer (MTC) is a prototypic neuroendocrine tumor of the thyroid C cells. Other than surgery, there are no curative therapies for MTC. In this review, we detail recent studies that suggest that targeting specific signaling pathways may be a viable strategy to control MTC tumor progression. Specifically, we discuss the role of the raf-1 and achaete-scute homologue-1 pathways in the MTC tumor growth and differentiation.

A p38 inhibitor allows to dissociate differentiation and apoptotic processes triggered upon LIF withdrawal in mouse embryonic stem cells

Mouse embryonic stem cells remain pluripotent when maintained in the presence of leukemia inhibitory factor (LIF). Upon LIF withdrawal, most cells differentiate into various lineages, while some die by apoptosis within 3 days. We have analyzed the activation pattern of the mitogen-activated protein kinase (MAPK) families and characterized the expression profile of selected genes modulated during differentiation or apoptosis. We show that p38 MAPKs are activated first, during the apoptotic crisis, while extracellular-regulated kinases and c-Jun N-terminal kinases are induced after the apoptotic crisis in differentiated cells. However, by using both p38 kinase inhibitors (PD169316 and SB203580) and a p38alpha(-/-) cell line, we demonstrate that p38alpha activation is rather a consequence than a cause of apoptosis. We thus reveal novel properties of PD169316, which induces cell survival without impairing cell differentiation, and identify PD169316-sensitive targets like the fibroblast growth factor-5, Brachyury and bcl-2 genes. Finally, we demonstrate that overexpression of the PD169316 - regulated bcl-2 gene prevents LIF withdrawal - induced cell death.

Leukemia Inhibitory Factor: An Important Regulator of Endometrial Function

PROBLEM

Leukemia inhibitory factor (LIF) is multifunctional cytokine that displays biological activities in different cells, including endometrial cells. The aim of this study is to describe implications of LIF on a physiological function of endometrium.

METHOD OF STUDY

The role of LIF in the endometrial function is reviewed and summarized from the available literature.

RESULTS

LIF plays an important role in a physiological function of endometrium. In human endometrial LIF expression depends on cellular localizations, steroid hormones, menstrual stages and a local cytokine network. Stronger LIF expression exists in an endometrial epithelium during a luteal phase of the menstrual cycle, which coincides with the time of an implantation. The impairments of the endometrial LIF expression may play a significant role in the pathological processes involving implantation and the infertility.

CONCLUSIONS

There is a substantial evidence that LIF is a potential regulator of the endometrial function and might be one of the factors that play a key role in human reproduction.

Soluble mannose 6-phosphate/insulin-like growth factor II (IGF-II) receptor inhibits interleukin-6-type cytokine-dependent proliferation by neutralization of IGF-II

The calcium-independent mannose 6-phosphate receptor (CIMPR) is a receptor for multiple ligands, including leukemia inhibitory factor (LIF), an IL-6 type cytokine, and IGF-II. CIMPR targets newly synthesized ligands to lysosomes and induces internalization/degradation of secreted ligands. A natural soluble form of CIMPR (sCIMPR) neutralizes IGF-II mitogenic potency on hepatocytes and fibroblasts. Herein we show that sCIMPR also inhibits LIF-driven proliferation of myeloid and lymphoid cell lines. Similar inhibition was observed with IL-6 and IL-11, two other IL-6-type cytokines that do not interact with CIMPR. Neutralizing anti-IGF-II antibodies inhibited IL-6-, IL-11-, and LIF-driven cell proliferation to the same extent as sCIMPR, suggesting that neutralization of serum IGF-II by sCIMPR plays a major role in IL-6-type cytokine-dependent cell proliferation. Confirming this idea, ERK1/2 and AKT/protein kinase B, the kinases necessary for cell proliferation and survival, were activated by IGF-II alone or by the association of IL-6-type cytokines and IGF-II. IL-6-type cytokines alone (up to 10 ng/ml) did not activate ERK1/2 or AKT, but did activate STAT3 (signal transducer and activator of transcription 3), a transcription factor necessary for the G1 to S phase cell cycle transition. Activation of ERK1/2 and AKT by IGF-II thus appears essential to sustain cellular expansion driven by IL-6-type cytokines.

The unsolved enigmas of leukemia inhibitory factor

Leukemia inhibitory factor (LIF) is a polyfunctional glycoprotein cytokine whose inducible production can occur in many, perhaps all, tissues. LIF acts on responding cells by binding to a heterodimeric membrane receptor composed of a low-affinity LIF-specific receptor and the gp130 receptor chain also used as the receptor for interleukin-6, oncostatin M, cardiotrophin-1, and ciliary neurotrophic factor. LIF is essential for blastocyst implantation and the normal development of hippocampal and olfactory receptor neurons. LIF is used extensively in experimental biology because of its key ability to induce embryonic stem cells to retain their totipotentiality. LIF has a wide array of actions, including acting as a stimulus for platelet formation, proliferation of some hematopoietic cells, bone formation, adipocyte lipid transport, adrenocorticotropic hormone production, neuronal survival and formation, muscle satellite cell proliferation, and acute phase production by hepatocytes. Unwanted actions of LIF can be minimized by circulating soluble LIF receptors and by intracellular suppression by suppressors of cytokine-signaling family members. However, the outstanding problems remain of how the induction of LIF is mediated in response to demands from such a heterogeneity of target tissues and why it makes design sense to use LIF in the regulation of such a diverse and unrelated series of biological processes.

Leukemia inhibitory factor enhances survival of cardiomyocytes and induces regeneration of myocardium after myocardial infarction

BACKGROUND

Myocardial infarction (MI) is a leading cause of cardiac morbidity and mortality in many countries; however, the treatment of MI is still limited.

METHODS AND RESULTS

We demonstrate a novel gene therapy for MI using leukemia inhibitory factor (LIF) cDNA. We injected LIF plasmid DNA into the thigh muscle of mice immediately after inducing MI. Intramuscular injection of LIF cDNA resulted in a marked increase in circulating LIF protein concentrations. Two weeks later, left ventricular remodeling, such as infarct extent and myocardial fibrosis, was markedly attenuated in the LIF cDNA-injected mice compared with vehicle-injected mice. More myocardium was preserved and cardiac function was better in the LIF-treated mice than in the vehicle-injected mice. Injection of LIF cDNA not only prevented the death of cardiomyocytes in the ischemic area but also induced neovascularization in the myocardium. Furthermore, LIF cDNA injection increased the number of cardiomyocytes in cell cycle and enhanced mobilization of bone marrow cells to the heart and their differentiation into cardiomyocytes.

CONCLUSIONS

The intramuscular injection of LIF cDNA may induce regeneration of myocardium and provide a novel treatment for MI.

Beyond neurons: evidence that immune and glial cells contribute to pathological pain states

Chronic pain can occur after peripheral nerve injury, infection, or inflammation. Under such neuropathic pain conditions, sensory processing in the affected body region becomes grossly abnormal. Despite decades of research, currently available drugs largely fail to control such pain. This review explores the possibility that the reason for this failure lies in the fact that such drugs were designed to target neurons rather than immune or glial cells. It describes how immune cells are a natural and inextricable part of skin, peripheral nerves, dorsal root ganglia, and spinal cord. It then examines how immune and glial activation may participate in the etiology and symptomatology of diverse pathological pain states in both humans and laboratory animals. Of the variety of substances released by activated immune and glial cells, proinflammatory cytokines (tumor necrosis factor, interleukin-1, interleukin-6) appear to be of special importance in the creation of peripheral nerve and neuronal hyperexcitability. Although this review focuses on immune modulation of pain, the implications are pervasive. Indeed, all nerves and neurons regardless of modality or function are likely affected by immune and glial activation in the ways described for pain.

Regulation of cardiac fibroblast cellular function by leukemia inhibitory factor

BACKGROUND

Previous studies have shown that leukemia inhibitory factor (LIF) provokes hypertrophic and cytoprotective effects in cardiac myocytes. However, the effects of LIF in cardiac fibroblasts are not known. Given that the cardiac fibroblast is the most abundant cell type in the heart, we sought to examine the functional effects of LIF on cardiac fibroblasts in vitro.

RESULTS

Short-term LIF stimulation (24h) had no effect on fibroblast proliferation and/or cell differentiation. However, longer-term LIF stimulation (48-72h) increased fibroblast proliferation, and significantly inhibited cardiac fibroblast differentiation into myofibroblasts. Moreover, 72h of LIF stimulation significantly reduced collagen content in cardiac fibroblasts cultures, as well as decreased MMP activity in fibroblast culture supernatants.

CONCLUSION

The results of this study suggest that LIF stimulation down-regulates several key components of the remodeling process, including collagen content and matrix metalloproteinase (MMP) activation, and thus suggest that LIF may play an important autocrine/paracrine role in preventing excessive extracellular matrix remodeling following acute myocardial injury.

Differentiation of pluripotent embryonic stem cells into cardiomyocytes

Embryonic stem (ES) cells have been established as permanent lines of undifferentiated pluripotent cells from early mouse embryos. ES cells provide a unique system for the genetic manipulation and the creation of knockout strains of mice through gene targeting. By cultivation in vitro as 3D aggregates called embryoid bodies, ES cells can differentiate into derivatives of all 3 primary germ layers, including cardiomyocytes. Protocols for the in vitro differentiation of ES cells into cardiomyocytes representing all specialized cell types of the heart, such as atrial-like, ventricular-like, sinus nodal-like, and Purkinje-like cells, have been established. During differentiation, cardiac-specific genes as well as proteins, receptors, and ion channels are expressed in a developmental continuum, which closely recapitulates the developmental pattern of early cardiogenesis. Exploitation of ES cell-derived cardiomyocytes has facilitated the analysis of early cardiac development and has permitted in vitro "gain-of-function" or "loss-of-function" genetic studies. Recently, human ES cell lines have been established that can be used to investigate cardiac development and the function of human heart cells and to determine the basic strategies of regenerative cell therapy. This review summarizes the current state of ES cell-derived cardiogenesis and provides an overview of how genomic strategies coupled with this in vitro differentiation system can be applied to cardiac research.

Role of mitogen-activated protein kinase family in serum-induced leukaemia inhibitory factor and interleukin-6 secretion by bone marrow stromal cells

1: In the haematopoietic microenvironment, bone marrow stromal cells play an important role in regulating haematopoiesis by expressing various cytokines, including leukaemia inhibitory factor (LIF) and interleukin-6 (IL-6). However, the intracellular signal that regulates cytokine secretion in bone marrow stromal cells has not been determined. The aim of this study was to evaluate the role of mitogen-activated protein kinase (MAPK) family in serum-induced secretion of LIF and IL-6 by bone marrow stromal cells. 2: Transformed human bone marrow stromal cells (HS-5) were stimulated with foetal calf serum (FCS) to produce LIF and IL-6. FCS also induced activation of extracellular signal-regulated kinase (ERK), p38 MAPK and c-Jun NH(2)-terminal kinase (JNK). 3: Both PD98059 (MAPK/ERK kinase inhibitor) and SB203580 (p38 MAPK inhibitor) attenuated FCS-induced LIF protein production and gene expression. SB203580 decreased IL-6 production and gene expression, but PD98059 had no effect on IL-6 production and gene expression. 4: Expression of a dominant-negative mutant form of JNK1 that blocked FCS-induced JNK activity had no effect on protein production and gene expression of these cytokines. 5: These findings demonstrate that both ERK and p38 MAPK are involved in FCS-induced LIF secretion, whereas only p38 MAPK is important for IL-6 secretion, and that FCS-induced activation of JNK has no effect on the production of LIF and IL-6. We conclude that, in spite of their similar biological effects, they are differentially regulated at the level of MAPK activity in bone marrow stromal cells.

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.

Association between immune activation and early depressive symptoms in cancer patients treated with interleukin-2-based therapy

The relationship between immune activation and the development of early depressive symptoms were studied in 33 cancer patients undergoing cytokine therapy. Patients were treated either with subcutaneous IL-2 administered alone (n=13) or in association with IFN-alpha (n=5), or with IFN-alpha alone administered subcutaneously at low doses (n=5) or intravenously at high doses (n=10). The intensity of depressive symptoms was assessed during a clinical interview carried out before the start of cytokine therapy and five days later using the Montgomery and Asberg Depression Rating Scale (MADRS). On the same days, blood samples were collected for each patient to measure serum concentrations of cytokines (IL-6, IL-10, IL-1ra) and cytokine-receptors (sIL-2R, LIF-R). Results showed that patients treated with IL-2 or IL-2+IFN-alpha displayed concomitant mood symptoms and increased serum cytokine levels during treatment. In these patients, the intensity of depressive symptoms at endpoint was positively correlated with the increases measured in serum levels of IL-10 between baseline and endpoint. IL-10 is an anti-inflammatory cytokine that is produced in response to the production of pro-inflammatory cytokines, and thereby reflects an inflammatory response. These results support the hypothesis of close relationship between depressive symptoms and the activation of the cytokine network.

Leukaemia inhibitory factor (LIF): a cytokine of emerging importance in chronic airway inflammation

Inflammation is a complex set of mechanisms by which tissues respond to an injury. These responses involve the coordinated interaction between the nervous and immune systems. An integral part of this interaction is the release of a variety of cytokines that regulate cellular and molecular responses. Leukaemia Inhibitory Factor (LIF), a member of the IL-6 family of cytokines, has been shown to be an integral component of the interface between nerves and the immune system. However, little is known about this cytokine in the context of normal lung function or indeed, inflammation. Evidence is emerging that this cytokine may play an important role in regulating the neural-immune system interaction during acute inflammatory insult and the subsequent healing and restitution process. However, LIF may act as either a pro- or antiinflammatory cytokine, depending on the cell type and a number of other variables. In this review, the role of LIF in airway inflammation and resolution of inflammation is discussed. In particular, recent work suggesting that LIF is a mediator of bi-directional cross-talk between neural tissue and the immune system is highlighted.

Paracrine promotion of cardiomyogenesis in embryoid bodies by LIF modulated endoderm

In the vertebrate embryo the heart is the first organ to form. Embryonic and extra-embryonic tissues are supposed to contribute to cardiac lineage commitment before and during gastrulation in a paracrine fashion. Evidence has accumulated that factors secreted by the anterior lateral endoderm and extra-embryonic endoderm contribute to cardiomyogenesis. Here we exploit in vitro differentiation of embryonic stem cells in embryoid bodies to study differentiation of the extraembryonic endodermal lineage, gastrulation-like processes, and the influence of endoderm on cardiomyogenesis. We demonstrate that in embryoid bodies primitive endoderm differentiates to visceral and parietal endoderm and that parietal endoderm influences onset of cardiomyogenesis in a concentration-dependent manner. Both increased concentrations of leukemia inhibitory factor and its absence in lif-/- embryoid bodies hampered parietal endoderm formation. Reduced differentiation of parietal endoderm correlated with an attenuation of cardiomyogenesis even in the presence of LIE These and previous results suggest that leukemia inhibitory factor is directly and indirectly, via endoderm formation, involved in the regulation of cardiomyogenesis. Increased proliferation of parietal endoderm in lifr -/- embryoid bodies and addition of conditioned lif -/- cell culture supernatant promoted cardiomyogenesis, demonstrating for the first time that parietal endoderm also contributes to cardiomyogenesis in embryoid bodies in a paracrine and leukemia inhibitory factor and its receptor independent pathway. New factors signaling independently of the leukemia inhibitory-factor receptor pathway may sustain cardiomyocyte cell proliferation and thus be a future target for gene therapy of cardiomyopathies and cell therapy of the myocardium.

Leukemia inhibitory factor antagonizes gonadotropin induced-testosterone synthesis in cultured porcine leydig cells: sites of action

In the present report, the action of leukemia inhibitory factor (LIF) on testicular steroid hormone formation was studied. For this purpose, the direct effects of LIF were evaluated on basal and human (h)CG-stimulated testosterone synthesis by cultured, purified Leydig cells isolated from porcine testes. LIF reduced (more than 60%) hCG-stimulated testosterone synthesis. This inhibitory effect was exerted in a dose- and time-dependent manner. The maximal and half-maximal effects were obtained with, respectively, 10 ng/ml (0.5 nM ) and 2.5 ng/ml (0.125 nM ) of LIF after a 48-h treatment of the Leydig cells. Such an effect of the cytokine was not a cytotoxic effect, because it was reversible and Leydig cells recovered most of their steroidogenic activity after the removal of LIF. Considering the sites of action of LIF in inhibiting gonadotropin-stimulated testosterone formation, it was shown that LIF significantly (P < 0.002) reduced, in a comparable range (about 60% decrease), testosterone synthesis stimulated with LH/hCG or with pharmacological agents that enhance cAMP levels (cholera toxin, forskolin, and PG E2), and testosterone synthesis stimulated with 8-bromo-cAMP. Such an observation indicates that the antigonadotropic action of the cytokine is exerted in a predominant manner at a step (or steps) located beyond cAMP formation. Furthermore, incubation of Leydig cells with 22R-hydroxycholesterol (5 microg/ml, 2 h), a cholesterol substrate derivative that does not need an assisted process to be delivered to the inner mitochondrial membrane, reversed most of the inhibitory effect of LIF on the steroid hormone formation. Such results indicate that LIF acts by reducing cholesterol substrate availability in the mitochondria. Consequently, LIF action was tested on steroidogenic acute regulatory protein and PBR (peripheral benzodiazepine receptor) shown to be potentially involved in such a cholesterol transfer. LIF reduced, in a dose- and time-dependent manner, LH/hCG-induced steroidogenic acute regulatory protein messenger RNA levels. The maximal inhibitory effect was obtained with 6.6 ng/ml of LIF after 48 h of treatment. In contrast, LIF had no effect on PBR messenger RNA expression or PBR binding. This inhibitory effect of LIF on Leydig cell steroidogenesis is probably exerted via an auto/paracrine action of the cytokine. Indeed, by immunohistochemistry, LIF and LIF receptor proteins were identified in Leydig and Sertoli cells but not in other testicular cell types, except for LIF receptor in spermatogonia. Furthermore, the presence of LIF and its receptor in Leydig cells at the neonatal and adult periods suggests that the inhibitory effect of LIF on androgen formation reported here probably occurs in both the fetal and the adult Leydig cell populations during testicular development.

Stimulation of leukemia inhibitory factor receptor degradation by extracellular signal-regulated kinase

Leukemia inhibitory factor (LIF) signals via the heterodimeric receptor complex comprising the LIF receptor alpha subunit (LIFRalpha) and the common signal transducing subunit for interleukin-6 cytokine receptors, gp130. This study demonstrates that in different cell types, the level of LIFRalpha decreases during treatment with LIF or the closely related cytokine oncostatin M (OSM). Moreover, insulin and epidermal growth factor induce a similar LIFRalpha down-regulation. The regulated loss of LIFRalpha is specific since neither gp130 nor OSM receptor beta shows a comparable change in turnover. LIFRalpha down-regulation correlates with reduced cell responsiveness to LIF. Using protein kinase inhibitors and point mutations in LIFRalpha, we demonstrate that LIFRalpha down-regulation depends on activation of extracellular signal-regulated kinase 1/2 and phosphorylation of the cytoplasmic domain of LIFRalpha at serine 185. This modification appears to promote the endosomal/lysosomal pathway of the LIFRalpha. These results suggest that extracellular signal-regulated kinase-activating factors like OSM and growth factors have the potential to lower specifically LIF responsiveness in vivo by regulating LIFRalpha half-life.

Leukemia-inhibitory factor-neuroimmune modulator of endocrine function

Leukemia-inhibitory factor (LIF) is a pleiotropic cytokine expressed by multiple tissue types. The LIF receptor shares a common gp130 receptor subunit with the IL-6 cytokine superfamily. LIF signaling is mediated mainly by JAK-STAT (janus-kinase-signal transducer and activator of transcription) pathways and is abrogated by the SOCS (suppressor-of cytokine signaling) and PIAS (protein inhibitors of activated STAT) proteins. In addition to classic hematopoietic and neuronal actions, LIF plays a critical role in several endocrine functions including the utero-placental unit, the hypothalamo-pituitary-adrenal axis, bone cell metabolism, energy homeostasis, and hormonally responsive tumors. This paper reviews recent advances in our understanding of molecular mechanisms regulating LIF expression and action and also provides a systemic overview of LIF-mediated endocrine regulation. Local and systemic LIF serve to integrate multiple developmental and functional cell signals, culminating in maintaining appropriate hormonal and metabolic homeostasis. LIF thus functions as a critical molecular interface between the neuroimmune and endocrine systems.

Leukemia inhibitory factor modulates cardiogenesis in embryoid bodies in opposite fashions

Cardiogenesis is a multistep process regulated by a hierarchy of factors defining each developmental stage of the heart. One of these factors, leukemia inhibitory factor (LIF), a member of the interleukin-6 family of cytokines, is expressed in embryonic and neonatal cardiomyocytes and induces cardiomyocyte hypertrophy. Many aspects of embryogenesis are faithfully recapitulated during in vitro differentiation of embryonic stem cells in embryoid bodies. We exploited this model to study effects of growth factors on commitment and differentiation of cardiomyocytes and on maintenance of their phenotype. We identified LIF as a factor affecting commitment and differentiation of cardiomyocytes in an opposite manner. Diffusible LIF inhibited mesoderm formation and hampered commitment of cardiomyocytes. Lack of both the diffusible and matrix-bound isoforms of LIF in lif-/- embryoid bodies did not interfere with commitment, but it severely suppressed early differentiation of cardiomyocytes. Onset of differentiation was rescued by very low concentrations of diffusible LIF; however, consecutive differentiation was attenuated in a concentration-dependent manner by diffusible LIF both in wild-type and lif-/- cardiomyocytes. Differentiation of cardiomyocytes was severely hampered but not completely blocked in lifr-/- embryoid bodies, suggesting additional, LIF-receptor ligand independent pathways for commitment and differentiation of cardiomyocytes. At the fully differentiated state, both paracrine and autocrine LIF promoted proliferation and increased longevity of cardiomyocytes. These findings suggest that both paracrine and autocrine and both diffusible and matrix-bound isoforms of LIF contribute to the modulation of cardiogenesis in a subtle, opposite, and developmental stage-dependent manner and control proliferation and maintenance of the differentiated state of cardiomyocytes.

Osteoblasts and stromal cells isolated from femora in rheumatoid arthritis (RA) and osteoarthritis (OA) patients express IL-11, leukaemia inhibitory factor and oncostatin M

We investigated both in vitro and ex vivo the role of mature osteoblasts (OB) and bone marrow stromal cells (BMSC) in RA and OA by analysing the expression of the following IL-6-type cytokines: IL-11, leukaemia inhibitory factor (LIF), oncostatin M (OSM) and IL-6. OB and BMSC were isolated from femora of RA, OA and post-traumatic (PT) patients, cultured in vitro in the presence or absence of IL-1beta and tumour necrosis factor-alpha (TNF-alpha), and assessed for the production and mRNA expression of IL-6-type cytokines. Trabecular bone biopsies were obtained from the inner portions of femoral heads and used for cytokine in situ immunostaining. Cultured OB and BMSC from different patients constitutively secreted IL-11 and IL-6 but not OSM. LIF was secreted only by BMSC, at very low levels. Interestingly, IL-11 basal production was significantly higher in BMSC than in OB in all three groups tested. IL-1beta and TNF-alpha strongly stimulated IL-6-type cytokine release (except for OSM) by both OB and BMSC. OSM was expressed only at mRNA levels in all groups studied. Cytokine immunostaining on bone biopsies confirmed the data obtained on cultured cells: IL-11, IL-6 and LIF proteins were detected both in mesenchymal (BMSC and OB) and mononuclear cells; OSM was found only in mononuclear cells. These data demonstrate that IL-6-type cytokines are constitutively expressed in the bone compartment in RA, OA and PT patients and can be secreted by bone cells at different stages of differentiation (BMSC and OB). This suggests that these cytokines may be involved in the mechanisms of bone remodelling in OA and RA.

Neurotrophic factors and neuro-muscular disease: II. GDNF, other neurotrophic factors, and future directions

This is the second of two reviews in which we discuss the essential aspects of neurotrophic factor neurobiology, the characteristics of each neurotrophic factor, and their clinical relevance to neuromuscular diseases. The previous paper reviewed the neurotrophin family and neuropoietic cytokines. In the present article, we focus on the GDNF family and other neurotrophic factors and then consider future approaches that may be utilized in neurotrophic factor treatment.