Leukemia inhibitory factor protects against experimental lethal Escherichia coli septic shock in mice

Emerging roles for IL-6 family cytokines as positive and negative regulators of ectopic lymphoid structures

IL-6 family cytokines display broad effects in haematopoietic and non-haematopoietic cells that regulate immune homeostasis, host defence, haematopoiesis, development, reproduction and wound healing. Dysregulation of these activities places this cytokine family as important mediators of autoimmunity, chronic inflammation and cancer. In this regard, ectopic lymphoid structures (ELS) are a pathological hallmark of many tissues affected by chronic disease. These inducible lymphoid aggregates form compartmentalised T cell and B cell zones, germinal centres, follicular dendritic cell networks and high endothelial venules, which are defining qualities of peripheral lymphoid organs. Accordingly, ELS can support local antigen-specific responses to self-antigens, alloantigens, pathogens and tumours. ELS often correlate with severe disease progression in autoimmune conditions, while tumour-associated ELS are associated with enhanced anti-tumour immunity and a favourable prognosis in cancer. Here, we discuss emerging roles for IL-6 family cytokines as regulators of ELS development, maintenance and activity and consider how modulation of these activities has the potential to aid the successful treatment of autoimmune conditions and cancers where ELS feature.

Induced Pluripotent Stem Cell-Derived Conditioned Medium Promotes Endogenous Leukemia Inhibitory Factor to Attenuate Endotoxin-Induced Acute Lung Injury

The conditioned medium of induced pluripotent stem cells (iPSC-CM) can attenuate neutrophil recruitment and endothelial leakage of lipopolysaccharide (LPS)-induced acute lung injury (ALI). Therefore, we investigated the mechanisms by which iPSC-CM regulate the interaction between neutrophils and the endothelium in ALI. Murine iPSCs (miPSCs) were delivered intravenously to male C57BL/6 mice (8–12 weeks old) 4 h after intratracheal LPS injection. A miPSC-derived conditioned medium (miPSC-CM) was delivered intravenously to mice after intratracheal LPS injection. DMSO-induced HL-60 cells (D-HL-60, neutrophil-like cells) and human umbilical vein endothelial cells (HUVECs) were used as in vitro models to assess the interaction of neutrophils and endothelial cells. miPSC-CM diminished the histopathological changes in the lungs and the neutrophil count in bronchoalveolar lavage fluids of ALI mice. miPSC-CM attenuated the expression of adhesion molecules in the lungs of ALI mice. Human iPSC conditioned medium (hiPSC-CM) reduced the expression of adhesion molecules in a HUVEC and D-HL-60 co-culture after LPS stimulation, which decreased the transendothelial migration (TEM) of D-HL-60. A human angiogenesis factors protein array revealed that leukemia inhibitory factor (LIF) was not detected in the absence of D-HL-60 and hiPSC-CM groups. hiPSC-CM significantly promoted the production of endogenous LIF in in vitro models. Administration of an anti-LIF antibody not only reversed the effect of iPSC-CM in ALI mice, but also blocked the effect of iPSC-CM on neutrophils TEM in in vitro models. However, a controlled IgG had no such effect. Our study demonstrated that iPSC-CM promoted endogenous LIF to inhibit neutrophils TEM and attenuate the severity of sepsis-induced ALI.

Coordination of Immune-Stroma Crosstalk by IL-6 Family Cytokines

Stromal cells are a subject of rapidly growing immunological interest based on their ability to influence virtually all aspects of innate and adaptive immunity. Present in every bodily tissue, stromal cells complement the functions of classical immune cells by sensing pathogens and tissue damage, coordinating leukocyte recruitment and function, and promoting immune response resolution and tissue repair. These diverse roles come with a price: like classical immune cells, inappropriate stromal cell behavior can lead to various forms of pathology, including inflammatory disease, tissue fibrosis, and cancer. An important immunological function of stromal cells is to act as information relays, responding to leukocyte-derived signals and instructing leukocyte behavior in kind. In this regard, several members of the interleukin-6 (IL-6) cytokine family, including IL-6, IL-11, oncostatin M (OSM), and leukemia inhibitory factor (LIF), have gained recognition as factors that mediate crosstalk between stromal and immune cells, with diverse roles in numerous inflammatory and homeostatic processes. This review summarizes our current understanding of how IL-6 family cytokines control stromal-immune crosstalk in health and disease, and how these interactions can be leveraged for clinical benefit.

Cardiotrophin-1 is an anti-inflammatory cytokine and promotes IL-4-induced M2 macrophage polarization

Macrophages play a central role in tissue remodeling, repair, and resolution of inflammation. Macrophage polarization to M1 or M2 activation status may determine the progression or resolution of the inflammatory response. We have previously reported that cardiotrophin-1 (CT-1) displays both cytoprotective and metabolic activities. The role of CT-1 in inflammation remains poorly understood. Here, we employed recombinant CT-1 (rCT-1) and used CT-1-null mice and myeloid-specific CT-1 transgenic mice to investigate whether CT-1 might play a role in the modulation of the inflammatory response. We observed that CT-1 deficiency was associated with enhanced release of inflammatory mediators and with stronger activation of NF-κB in response to LPS, whereas the inflammatory response was attenuated in CT-1 transgenic mice or by administering rCT-1 to wild-type animals prior to LPS challenge. We found that CT-1 promoted IL-6 expression only by nonhematopoietic cells, whereas LPS up-regulated IL-6 expression in both hematopoietic and nonhematopoietic cells. Notably, rCT-1 inhibited LPS-mediated soluble IL-6R induction. Using IL-6^-/- mice, we showed that rCT-1 inhibited LPS-induced TNF-α and IFN-γ response in an IL-6-independent manner. Importantly, we demonstrated that CT-1 primes macrophages for IL-4-dependent M2 polarization by inducing IL-4 receptor expression. Mechanistic analyses showed that the signal transducer and activator of transcription 3-suppressor of cytokine signaling 3 axis mediates this effect. Our findings support the notion that CT-1 is a critical regulator of inflammation and suggest that rCT-1 could be a molecule with potential therapeutic application in inflammatory conditions.-Carneros, D., Santamaría, E. M., Larequi, E., Vélez-Ortiz, J. M., Reboredo, M., Mancheño, U., Perugorria, M. J., Navas, P., Romero-Gómez, M., Prieto, J., Hervás-Stubbs, S., Bustos, M. Cardiotrophin-1 is an anti-inflammatory cytokine and promotes IL-4-induced M2 macrophage polarization.

Characterising Pre-pubertal Resistance to Death from Endotoxemia

Sepsis is a common and deadly syndrome in which a dysregulated host response to infection causes organ failure and death. The current lack of treatment options suggests that a new approach to studying sepsis is needed. Pre-pubertal children show a relative resistance to death from severe infections and sepsis. To explore this phenomenon experimentally, we used an endotoxemia model of sepsis in mice. Following intra-peritoneal injection of endotoxin, pre-pubertal mice showed greater survival than post-pubertal mice (76.3% vs. 28.6%), despite exhibiting a similar degree of inflammation after two hours. Age-associated differences in the inflammatory response only became evident at twenty hours, when post-pubertal mice showed prolonged elevation of serum cytokines and differential recruitment of peritoneal immune cells. Mechanistically, prevention of puberty by hormonal blockade or acceleration of puberty by oestrogen treatment led to increased or decreased survival from endotoxemia, respectively. Additionally, the adoptive transfer of pre-pubertal peritoneal cells improved the survival of post-pubertal recipient mice, while post-pubertal peritoneal cells or vehicle did not. These data establish a model for studying childhood resistance to mortality from endotoxemia, demonstrate that oestrogen is responsible for an increased susceptibility to mortality after puberty, and identify peritoneal cells as mediators of pre-pubertal resistance.

Review: Endotoxin and the hypothalamo-pituitary-adrenal (HPA) axis

Endotoxin is considered to be a systemic (immunological) stressor eliciting a prolonged activation of the hypothalamo-pituitary-adrenal (HPA) axis. The HPA-axis response after an endotoxin challenge is mainly due to released cytokines (IL-1, IL-6 and TNF-α) from stimulated peripheral immune cells, which in turn stimulate different levels of the HPA axis. Controversy exists regarding the main locus of action of endotoxin on glucocorticoid secretion, since the effect of endotoxin on this neuro-endocrine axis has been observed in intact animals and after ablation of the hypothalamus; however, a lack of LPS effect has been described at both pituitary and adrenocortical levels. The resulting increase in adrenal glucocorticoids has well-documented inhibitory effects on the inflammatory process and on inflammatory cytokine release. Therefore, immune activation of the adrenal gland by endotoxin is thought to occur by cytokine stimulation of corticosteroid-releasing hormone (CRH) production in the median eminence of the hypothalamus, which, in turn stimulates the secretion of ACTH from the pituitary. Acute administration of endotoxin stimulates ACTH and cortisol secretion and the release of CRH and vasopressin (AVP) in the hypophysial portal blood. During repeated endotoxemia, tolerance of both immune and HPA function develops, with a crucial role for glucocorticoids in the modulation of the HPA axis. A single exposure to a high dose of LPS can induce a long-lasting state of tolerance to a second exposure of LPS, affecting the response of plasma TNF-α and HPA hormones. Although there are gender differences in the HPA response to endotoxin and IL-1, these responses are enhanced by castration and attenuated by androgen and estrogen replacement. Estrogens attenuate the endotoxin-induced stimulation of IL-6, TNF-α and IL-1ra release and subsequent activation in postmenopausal women. There appears to be a temporal and functional relation between the HPA-axis response to endotoxin and nitric oxide formation in the neuro-endocrine hypothalamus, suggesting a stimulatory role for nitric oxide in modulating the HPA response to immune challenges.

LPS Down-Regulates Specificity Protein 1 Activity by Activating NF-κB Pathway in Endotoxemic Mice

Background

Specificity protein (Sp) 1 mediates the transcription of a large number of constitutive genes encoding physiological mediators. NF-κB mediates the expression of hundreds of inducible genes encoding pathological mediators. Crosstalk between Sp1 and NF-κB pathways could be pathophysiologically significant, but has not been studied. This study examined the crosstalk between the two pathways and defined the role of NF-κB signaling in LPS-induced down-regulation of Sp1 activity.

Methods and Main Findings

Challenge of wild type mice with samonelia enteritidis LPS (10 mg/kg, i.p.) down-regulated Sp1 binding activity in lungs in a time-dependent manner, which was concomitantly associated with an increased NF-κB activity. LPS down-regulates Sp1 activity by inducing an LPS inducible Sp1-degrading enzyme (LISPDE) activity, which selectively degrades Sp1 protein, resulting in Sp1 down-regulation. Blockade of NF-κB activation in mice deficient in NF-κB p50 gene (NF-κB-KO) suppressed LISPDE activity, prevented Sp1 protein degradation, and reversed the down-regulation of Sp1 DNA binding activity and eNOS expression (an indicator of Sp1 transactivation activity). Inhibition of LISPDE activity using a selective LISPDE inhibitor mimicked the effects of NF-κB blockade. Pretreatment of LPS-challenged WT mice with a selective LISPDE inhibitor increased nuclear Sp1 protein content, restored Sp1 DNA binding activity and reversed eNOS protein down-regulation in lungs. Enhancing tissue level of Sp1 activity by inhibiting NF-κB-mediated Sp1 down-regulation increased tissue level of IL-10 and decreased tissue level of TNF- αin the lungs.

Conclusions

NF-κB signaling mediates LPS-induced down-regulation of Sp1 activity. Activation of NF-κB pathway suppresses Sp1 activity and Sp1-mediated anti-inflammatory signals. Conversely, Sp1 signaling counter-regulates NF-κB-mediated inflammatory response. Crosstalk between NF-κB and Sp1 pathways regulates the balance between pro- and anti-inflammatory cytokines.

Progesterone is essential for protecting against LPS-induced pregnancy loss. LIF as a potential mediator of the anti-inflammatory effect of progesterone

Lipopolysaccharide (LPS) administration to mice on day 7 of gestation led to 100% embryonic resorption after 24 h. In this model, nitric oxide is fundamental for the resorption process. Progesterone may be responsible, at least in part, for a Th2 switch in the feto-maternal interface, inducing active immune tolerance against fetal antigens. Th2 cells promote the development of T cells, producing leukemia inhibitory factor (LIF), which seems to be important due to its immunomodulatory action during early pregnancy. Our aim was to evaluate the involvement of progesterone in the mechanism of LPS-induced embryonic resorption, and whether LIF can mediate hormonal action. Using in vivo and in vitro models, we provide evidence that circulating progesterone is an important component of the process by which infection causes embryonic resorption in mice. Also, LIF seems to be a mediator of the progesterone effect under inflammatory conditions. We found that serum progesterone fell to very low levels after 24 h of LPS exposure. Moreover, progesterone supplementation prevented embryonic resorption and LPS-induced increase of uterine nitric oxide levels in vivo. Results show that LPS diminished the expression of the nuclear progesterone receptor in the uterus after 6 and 12 h of treatment. We investigated the expression of LIF in uterine tissue from pregnant mice and found that progesterone up-regulates LIF mRNA expression in vitro. We observed that LIF was able to modulate the levels of nitric oxide induced by LPS in vitro, suggesting that it could be a potential mediator of the inflammatory action of progesterone. Our observations support the view that progesterone plays a critical role in a successful pregnancy as an anti-inflammatory agent, and that it could have possible therapeutic applications in the prevention of early reproductive failure associated with inflammatory disorders.

Role of acute ethanol exposure and TLR4 in early events of sepsis in a mouse model

Sepsis is a major cause of death worldwide. The associated risks and mortality are known to significantly increase on exposure to alcohol (chronic or acute). The underlying mechanisms of the association of acute ethanol ingestion and poor prognosis of sepsis are largely unknown. The study described here was designed to determine in detail the role of ethanol and TLR4 in the pathogenesis of the sepsis syndrome. The effects of acute ethanol exposure and TLR4 on bacterial clearance, spleen cell numbers, peritoneal macrophage numbers, and cytokine production were evaluated using wild-type and TLR4 hyporesponsive mice treated with ethanol and then challenged with a nonpathogenic strain of Escherichia coli. Ethanol-treated mice exhibited a decreased clearance of bacteria and produced lesser amounts of most pro-inflammatory cytokines in both strains of mice at 2h after challenge. Neither ethanol treatment nor a hyporesponsive TLR4 had significant effects on the cell numbers in the peritoneal cavity and spleen 2h postinfection. The suppressive effect of acute ethanol exposure on cytokine and chemokine production was more pronounced in the wild-type mice, but the untreated hyporesponsive mice produced less of most cytokines than untreated wild-type mice. The major conclusion of this study is that acute ethanol exposure suppresses pro-inflammatory cytokine production and that a hyporesponsive TLR4 (in C3H/HeJ mice) decreases pro-inflammatory cytokine levels, but the cytokines and other mediators induced through other receptors are sufficient to ultimately clear the infection but not enough to induce lethal septic shock. In addition, results reported here demonstrate previously unknown effects of acute ethanol exposure on leukemia inhibitory factor and eotaxin, and provide the first evidence that interleukin (IL)-9 is induced through TLR4 in vivo.

Evaluation of leukemia inhibitory factor (LIF) in a rat model of postoperative pain

Postoperative pain remains a significant problem despite optimal treatment with current pharmaceutical agents. In an effort to provide better postoperative pain control, there is a need to understand the factors that contribute to the development of pain after surgery. Leukemia inhibitory factor (LIF) is a pleiotropic cytokine released from tissues after injury. We hypothesized that LIF expression in skin, muscle, and dorsal root ganglion (DRG) would increase after plantar incision. The mRNA and protein expression of LIF and LIF receptor (LIF-R) were measured after plantar incision in the rat. Pain behaviors, immunohistochemistry, and C-fiber heat responses to LIF were also studied. LIF expression increased after incision in skin and muscle, and LIF-R was present in large and small DRG neurons. LIF administration to the hindpaw increased pain behaviors, a process that was reversed by anti-LIF. However, LIF and anti-LIF treatment at the time of incision did not augment or ameliorate pain behaviors. LIF treatment activated the second messenger system, JAK-STAT3, in cultured DRG neurons, but failed to alter spontaneous activity or heat responses in C-fiber nociceptors. In conclusion, LIF is not a target for postoperative analgesia; LIF may be important for skin and muscle repair and regeneration after incision.

PERSPECTIVE

This article highlights an incision pain model for the study of factors involved in nociception. The study demonstrates that LIF in is an unlikely target for novel early postoperative analgesics.

Therapeutic potential of LIF in multiple sclerosis

Therapies for multiple sclerosis (MS) reduce the relapse rate but are unable to stop neurological decline. Here, we evaluate the potential of leukemia inhibitory factor (LIF) as a novel therapeutic in diseases with a neurodegenerative and inflammatory component, such as MS. LIF, which can be a proinflammatory cytokine, can also modulate the immune response in a beneficial way. Recent evidence demonstrates a crucial role of LIF in neuroprotection and axonal regeneration as well as the prevention of demyelination. Finally, LIF is an important survival factor for stem cells and neuronal precursors. Therefore, we propose that LIF is a potential therapeutic candidate for MS.

Neuroinflammation facilitates LIF entry into brain: role of TNF

Leukemia inhibitory factor (LIF) is a proinflammatory cytokine mediating a variety of central nervous system (CNS) responses to inflammatory stimuli. During lipopolysaccharide (LPS)-induced inflammation, blood concentrations of LIF increase, correlating with lethality of sepsis. Circulating LIF crosses the blood-brain barrier (BBB) by a saturable transport system. Here we determine how this transport system is regulated in neuroinflammation. Using transport assays that quantify the influx rate and volume of distribution of LIF in mice, we show that LPS facilitated the permeation of LIF from the blood to the brain without compromising the paracellular permeability of the BBB as determined by coadministration of fluorescein. Concurrently, gp130 (shared by the interleukin-6 family of cytokines), but not gp190 (the specific receptor for LIF) or cilliary neutrophic factor (CNTF-Ralpha, a unique receptor for cilliary neurotrophic factor that also uses gp130 and gp190), showed increased levels of mRNA and protein expression in cerebral microvessels from the LPS-treated mice. The upregulation of gp130 by LPS was at least partially mediated by vascular tumor necrosis factor receptor (TNFR)1 and TNFR2. This was shown by elevated TNFR1 and TNFR2 mRNA and protein in cerebral microvessels after LPS and by the absence of the LPS effect on gp130 in knockout mice lacking these receptors. The results show that neuroinflammation by LPS induces endothelial signaling and enhances cytokine transport across the BBB.

Coagulation Activation by Lipopolysaccharides

Lipopolysaccharides at approximate plasma reactivities >3 ng/mL or β-glucans at >0.5-1 μg/mL are toxic for human blood; lipopolysaccharide interacts with membrane components of susceptible cells (eg, monocytes) activating phospholipase A2that destroys the cell membrane. Cell fragments (microparticles or DNA) possess polynegative niches that activate intrinsic hemostasis. Pathologic disseminated intravascular coagulation arises. Blood vessels are obstructed by disseminated thrombi, and vital organ areas become ischemic. Multiorgan failure threatens life of the patient. Diagnosis and therapy of pathologic disseminated intravascular coagulation is of extreme clinical importance. For early diagnosis of pathologic disseminated intravascular coagulation, specific activation markers of coagulation (eg, plasmatic amidolytic thrombin activity) or the plasmatic lipopolysaccharide or glucan reactivity can be measured. A new treatment target might be kallikrein or factor XIIa; 10 to 20 mM arginine is the approximate 50% inhibitory concentration against the contact phase of coagulation. The complex interaction between cell fragments and hemostasis causes pathologic disseminated intravascular coagulation in sepsis.

Induction of IL-1, in the Testes of Adult Mice, Following Subcutaneous Administration of Turpentine

PROBLEM

Interleukin-1 family is present in the testicular homogenates and its cellular compartments. It has been suggested that IL-1 is involved in physiological and pathological functions of the testicular tissues. In the present study we examined the effect of acute mostly localized inflammation, using turpentine, on the expression levels of testicular IL-1 system.

METHODS OF STUDY

Mice were subcutaneously injected with steam-distilled turpentine or saline (control). Three hours to 10 days following the injection, mice were killed and testis and spleen were homogenized and examined for interleukin (IL)-1alpha, IL-1beta, and IL-1 receptor antagonist (IL-1ra) levels by enzyme-linked immunosorbent assay and polymerase chain reaction.

RESULTS

Subcutaneous injection of turpentine induced mice systemic inflammation, as indicated by significant increase in serum IL-1beta levels, and IL-1alpha, IL-1beta and IL-1ra in spleen homogenates. The levels of IL-1alpha, IL-1beta and IL-1ra were significantly induced in testicular homogenates of adult mice following subcutaneous injection of turpentine. The significant induction of testicular IL-1alpha was detected after 3-24 hr of turpentine injection and decreased later (after 3-10 days) to levels similar to the control. However, significant induction of testicular IL-1beta was detected only after 3-10 days of turpentine injection, and for testicular IL-1ra levels was detected after 3 hr to 6 days of turpentine injection, and after 10 days the levels were similar to the control. These results were also confirmed by mRNA expression of these factors.

CONCLUSION

Our results demonstrate for the first time the distant effect of acute localized inflammation on testicular IL-1 levels. Thus, transient inflammatory response to infectious/inflammatory agents at non-testicular sites that elicit systemic IL-1 response should be considered during clinical treatment as a possible factor of male infertility.

Endogenous leukemia inhibitory factor attenuates endotoxin response

Leukemia inhibitory factor (LIF) is induced in inflammation and likely plays a regulatory role. Using LIF-deficient mice (LIF-/-), we report here that endogenous LIF has a protective role in endotoxic shock and host defence. LIF-/- mice have heightened sensitivity to LPS in a LPS/D-galactosamine (D-Gal) sensitization model compared to wild-type mice (LIF+/+), enhanced thrombocytopenia and leukopenia, with increased hepatic necrosis, neutrophil sequestration in the lung and accelerated mortality. These findings correlated with 10-fold higher tumour necrosis factor-alpha (TNFalpha) and interleukin-6 (IL-6) serum levels and reduced IL-10 production in LIF-/- mice in response to LPS. Therefore, endogenous LIF attenuates the endotoxic shock response, enhances the expression of basal acute phase proteins and IL-10 production, which downregulates TNFalpha synthesis and release and thereby confers partial protection to endotoxemia.

Pulmonary expression of leukemia inhibitory factor induces B cell hyperplasia and confers protection in hyperoxia

Leukemia inhibitory factor (LIF) is produced by a large number of pulmonary cells in response to diverse stimuli. Exaggerated levels of LIF have also been detected in the adult respiratory distress syndrome and other disorders. The biologic effects of LIF in the lung, however, have not been elucidated. To define the respiratory effects of LIF, we generated transgenic mice in which human LIF was selectively targeted to the mature lung. In these mice, transgene activation caused an impressive increase in bronchoalveolar lavage (BAL) cellularity with a significant increase in BAL and tissue B lymphocytes. LIF also conferred protection in 100% O2 where it decreased alveolar-capillary protein leak and enhanced survival. This protective effect was associated with the induction of interleukin (IL)-6 mRNA and protein. LIF transgenic mice with a null mutation in IL-6 were more sensitive to the toxic effects of 100% O2 than LIF-transgenic animals with a wild-type IL-6 locus. These studies demonstrate that LIF induces B cell hyperplasia and confers protection in hyperoxic acute lung injury. They also demonstrate that LIF induces IL-6 and that the protective effects of LIF are mediated, in part, via this inductive event. LIF may be an important regulator of B cell-mediated responses and oxidant injury in the lung.

Minireview: Neuro-immuno-endocrine modulation of the hypothalamic-pituitary-adrenal (HPA) axis by gp130 signaling molecules

The neuroendocrine and immune systems communicate bidirectionally. The neuro-immune-endocrine interface is mediated by cytokines acting as auto/paracrine or endocrine factors regulating pituitary development, cell proliferation, hormone secretion, and feedback control of the hypothalamic-pituitary-adrenal (HPA) axis. At birth or during neonatal ontogenesis, cytokines produce permanent alterations of HPA axis function and the stress response. Overexpressing IL-6 or leukemia inhibitory factor leads to significant changes in pituitary development and functions. Pituitary corticotroph POMC gene expression is regulated by CRH as well as several gp130 cytokines acting as neuro-immuno-endocrine modulators. Conversely, HPA axis functions modulate susceptibility or resistance to inflammatory disease. Cytokines (including IL-1, TNF, and members of the gp130 cytokine family) participate as mediators of a complex HPA axis response to stress and inflammation. Prolonged exposure to proinflammatory cytokines increases levels of the dominant negative glucocorticoid receptor isoform. Nonresponsiveness of the HPA axis to glucocorticoid negative feedback control provides a defense from destructive effects of cytokine excess. At the same time, gp130 cytokines stimulate pituitary suppressor of cytokine signaling (SOCS)-3, which represses cytokine signaling and abrogates cytokine-induced corticotroph POMC gene transcription and ACTH secretion.

Opposing effects of pituitary leukemia inhibitory factor and SOCS-3 on the ACTH axis response to inflammation

We have shown that leukemia inhibitory factor (LIF) and suppressor of cytokine signaling (SOCS)-3 are expressed in the hypothalamus and pituitary and that LIF induces proopiomelanocortin (POMC) and ACTH, whereas SOCS-3 abrogates corticotroph POMC gene transcription and ACTH secretion. Here, we determined the role of pituitary LIF and SOCS-3 in regulating hypothalamo-pituitary-adrenal (HPA) axis inflammatory responses. Murine pituitary LIF expression was induced up to eightfold after intraperitoneal injection of lipopolysaccharide or tumor necrosis factor-alpha, concordant with elevated plasma levels of ACTH and corticosterone. In LIF knockout (LIFKO) mice, induction of both ACTH and corticosterone were attenuated. LIF deletion was associated with elevated (P < 0.05) levels of pituitary TNF-alpha, interleukin (IL)-1beta, and IL-6 mRNA and cytokine-inducible pituitary SOCS-3 expression. Abrogation of the HPA axis stress response and higher pituitary levels of proinflammatory cytokines observed in LIFKO mice resulted in a stronger inflammatory process, as evidenced by elevated erythrocyte sedimentation rate and increased serum amyloid A levels (P < 0.05). The results indicate that, although LIF induces ACTH, SOCS-3 acts to counterregulate the HPA axis response to inflammation.

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.

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.

Renal synthesis of leukaemia inhibitory factor (LIF), under normal and inflammatory conditions

Leukaemia inhibitory factor (LIF) is a pleiotropic cytokine that is particularly involved in nephrogenesis and repair of the extracellular matrix. Transgenic mice overexpressing LIF have mesangial proliferative glomerulonephritis. Also, during local inflammatory reactions, such as kidney graft rejection or urinary tract infections, urinary LIF excretion is enhanced. The aim of the study therefore was to study LIF production by normal and inflammatory diseased kidneys (glomerulonephritis or graft rejection), maintained in short cultures. To determine the responsibility of the kidney itself in LIF synthesis, we measured LIF secretion into the culture supernatants of human mesangial or renal tubular epithelial cells. Fragments from diseased kidneys, whether grafts or not, released more LIF than normal human kidney fragments, mesangial or renal tubular epithelial cells. However, LIF production was delayed in renal transplants compared to glomerulonephritic samples taken from untreated patients. In every case, LIF production was enhanced by interleukin 1beta (IL-1beta) and inhibited by IL-4 or dexamethasone, except in two severe rejection episodes. So, LIF appeared to respond to pro- and anti-inflammatory stimuli, in vitro and in vivo. Considering its biological effects, LIF could play a role in inflammatory renal diseases.

Cardiotrophin-1 attenuates endotoxin-induced acute lung injury

Cardiotrophin-1 (CT-1) is a recently discovered member of the gp130 cytokine family, which includes IL-6, IL-11, leukemia inhibitory factor, ciliary neurotrophic factor, and oncostatin M. Recent evidence suggests that, like other members of this family, CT-1 may possess anti-inflammatory properties. We hypothesized that in vivo CT-1 administration would attenuate endotoxin (ETX)-induced acute lung injury. We studied the effects of CT-1 (100 microgram/kg ip, 10 min prior to ETX) in a rat model of ETX-induced acute lung injury (Salmonella typhimurium lipopolysaccharide, 20 mg/kg ip). Six hours after ETX, lungs were harvested for determination of neutrophil accumulation (myeloperoxidase, MPO, assay) and lung edema (wet-to-dry weight ratio). Mechanisms of pulmonary vasorelaxation were examined in isolated pulmonary artery rings at 6 h by interrogating endothelium-dependent (response to acetylcholine) and endothelium-independent (response to sodium nitroprusside) relaxation following alpha-adrenergic (phenylephrine)-stimulated preconstriction. CT-1 abrogated the endotoxin-induced lung neutrophil accumulation: 2.3 +/- 0.2 units MPO/g wet lung (gwl) vs 6. 3 +/- 0.3 units MPO/gwl in the ETX group (P < 0.05 vs ETX, P > 0.05 vs control). Similarly, CT-1 prevented ETX-induced lung edema: wet-to-dry-weight ratio, 4.473 +/- 0.039 vs 4.747 +/- 0.039 in the ETX group (P < 0.05 vs ETX, P > 0.05 vs control). Endotoxin caused significant impairment of both endothelium-dependent and -independent pulmonary vasorelaxation, and CT-1 attenuated this injury. Thus, cardiotrophin-1 possesses significant anti-inflammatory properties in a model of endotoxin-induced acute lung injury.

Leukemia inhibitory factor, Interleukin 6, and other cytokines using the GP130 transducing receptor: roles in inflammation and injury

Inflammation refers to a complex set of mechanisms by which tissues respond to injury and infection. Among the many soluble mediators associated with this process, cytokines are known to be crucial in regulating a variety of cellular and molecular events. Leukemia inhibitory factor (LIF), interleukin 6 (IL-6), IL-11, and possibly other members of this cytokine family are key mediators in various inflammatory processes such as the acute-phase reaction, tissue damage, and infection. These cytokines can act in both pro-inflammatory and anti-inflammatory ways, depending on a number of variables. We emphasize here recent work utilizing knockout mice, which has highlighted the roles of LIF and IL-6, particularly in interactions between the immune and nervous systems.

Leptin deficiency enhances sensitivity to endotoxin-induced lethality

Leptin is induced by lipopolysaccharide (LPS) and cytokines. We investigated the role of leptin in LPS-induced toxicity using leptin-deficient (ob/ob) and leptin receptor-deficient (db/db) mice. Sensitivity to LPS-induced mortality is significantly greater in ob/ob mice compared with their own lean littermates but not in db/db mice. LPS reduced serum glucose in both ob/ob and db/db mice but induced corticosterone only in db/db mice. Despite the very high basal levels of serum leptin in db/db mice, a twofold increase in serum leptin levels was observed after LPS in both db/db mice and their lean littermates. No differences were detected in LPS-induced serum levels of interleukin (IL)-1beta, tumor necrosis factor, macrophage inflammatory protein-1alpha, and interferon-gamma in ob/ob mice compared with their own littermates. In contrast, a blunted induction of IL-10 and IL-1 receptor antagonist (IL-1Ra) was observed in ob/ob mice compared with their littermates. In vitro, leptin induced IL-1Ra production and upregulated the IL-1Ra induction by LPS in macrophages. Moreover, treatment with leptin reversed the increased sensitivity to LPS-induced lethality found in ob/ob mice. These results suggest that leptin participates in the host response to inflammation by modulating the host immune and cytokine responses after LPS.

Neurohormonal host defense in endotoxin shock

Lipopolysaccharide (LPS) of gram-negative bacteria is capable of activating the immune system of higher animals, which may lead to cytokine-induced lethal shock and death. LPS has little toxicity for the frog and fish, but it kills the horseshoe crab instantly by causing intravascular blood coagulation. The response to LPS evolved from simple reactions in lower animals into an intense reaction in mammals that involves a massive immune activation leading to a profound neuroendocrine and metabolic response. This is now known as the acute-phase response (APR). During APR, LPS-binding proteins (LBP) are produced by the liver in rapidly increasing quantities under the influence of interleukin-6, glucocorticoids, and catecholamines. After combination with LPS, LPB is capable of activating monocyte-macrophages and granulocytes via the CD14 surface receptor. Other receptors (CD18, 80-kDa receptor) allow for direct action by LPS of phagocytes, B and T lymphocytes, and other cells. Numerous other acute-phase proteins are produced in the liver, including C-reactive protein, complement components, fibrinogen, enzyme inhibitors, and anti-inflammatory proteins. Similar responses may be stimulated by subtoxic doses of LPS or by detoxified LPS, which manifest in endotoxin tolerance. Tolerant animals and man show increased resistance to LPS, to infections, and to various noxious insults. Infection and various forms of tissue injury are also capable of causing APR. There is much evidence to indicate that APR, which manifests in febrile illness, is an efficient host defense reaction. It is an emergency response in cases where specific immunity fails to protect the host. Therefore, the neuroimmunoregulatory network converts the immune system to a less specific, but rapid and more efficient response, APR. The hypothesis is presented that intestinal LPS serves to amplify the APR in response to various insults, which contribute to host defense, regeneration, and healing.

gp130-Related Cytokines and Their Receptors in the Pituitary

gp130-Related cytokines such as interleukin-6 and leukemia-inhibitory factor (LIF) act on the adenohypophysis in a paracrine manner, affecting both its differentiation and the function of specific cell types, notably the proopiomelanocortin (POMC) cells. They act on POMC cells in synergism with corticotrophin-releasing hormone, inducing ACTH secretion. gp130-Related cytokines as well as their receptors are expressed in the pituitary. LIF knockout mice show reduced stress-induced ACTH secretion, which can be restored by LIF replacement, suggesting a physiologic role for LIF.

Leukemia inhibitory factor: part of a large ingathering family

Leukemia Inhibitory Factor (LIF) has a wide variety of biological activities. It regulates the differentiation of embryonic stem cells, neural cells, osteoblasts, adipocytes, hepatocytes and kidney epithelial cells. It also triggers the proliferation of myoblasts, primordial germ cells and some endothelial cells. Many of these biological functions parallel those of interleukin-6, Oncostatin M, ciliary neurotrophic factor, interleukin-11 and cardiotrophin-1. These structurally related cytokines also share subunits of their receptors which could partially explain the redundancy in this system of soluble mediators. In vivo LIF proves important in regulating the inflammatory response by fine tuning of the delicate balance of at least four systems in the body, namely the immune, the hematopoietic, the nervous and the endocrine systems. Although we are far from its therapeutic applications, the fast increasing knowledge in this field may bring new insights for the understanding of the cytokine biology in general.

Tumor necrosis factor in the heart

The heart is a tumor necrosis factor (TNF)-producing organ. Both myocardial macrophages and cardiac myocytes themselves synthesize TNF. Accumulating evidence indicates that myocardial TNF is an autocrine contributor to myocardial dysfunction and cardiomyocyte death in ischemia-reperfusion injury, sepsis, chronic heart failure, viral myocarditis, and cardiac allograft rejection. Indeed, locally (vs. systemically) produced TNF contributes to postischemic myocardial dysfunction via direct depression of contractility and induction of myocyte apoptosis. Lipopolysaccharide or ischemia-reperfusion activates myocardial P38 mitogen-activated protein (MAP) kinase and nuclear factor kappa B, which lead to TNF production. TNF depresses myocardial function by nitric oxide (NO)-dependent and NO-independent (sphingosine dependent) mechanisms. TNF activation of TNF receptor 1 or Fas may induce cardiac myocyte apoptosis. MAP kinases and TNF transcription factors are feasible targets for anti-TNF (i.e., cardioprotective) strategies. Endogenous anti-inflammatory ligands, which trigger the gp130 signaling cascade, heat shock proteins, and TNF-binding proteins, also control TNF production and activity. Thus modulation of TNF in cardiovascular disease represents a realistic goal for clinical medicine.

IL-6 is an antiinflammatory cytokine required for controlling local or systemic acute inflammatory responses

IL-6 is induced often together with the proinflammatory cytokines TNFalpha and IL-1 in many alarm conditions, and circulating IL-6 plays an important role in the induction of acute phase reactions. However, whether this endogenous IL-6 plays any additional pro- or antiinflammatory roles in local or systemic responses remains unclear. In this study, the role of IL-6 in acute inflammatory responses was investigated in animal models of endotoxic lung or endotoxemia by using IL-6+/+ and IL-6-/- mice. Aerosol exposure of endotoxin induced increased IL-6 and proinflammatory cytokines TNFalpha and MIP-2 and a neutrophilic response in the lung of IL-6+/+ mice. However, the levels of TNFalpha and MIP-2 and neutrophilia were significantly higher in the lung of IL-6-/- mice. The rate of neutrophil apoptosis in these mice was similar to that in IL-6+/+ mice. A low constitutive level of antiinflammatory cytokine IL-10 was not enhanced by endotoxin and remained similar in the lung in both IL-6+/+ and IL-6-/- mice. Systemically, intraperitoneal delivery of endotoxin resulted in much more pronounced circulating levels of TNFalpha, MIP-2, GM-CSF, and IFNgamma in IL-6-/- mice than in IL-6+/+ mice, and administration of recombinant IL-6 to IL-6-/- mice abolished these differences. In contrast, circulating IL-10 levels were induced to a similar degree in both IL-6+/+ and IL-6-/- mice. Thus, our studies reveal that endogenous IL-6 plays a crucial antiinflammatory role in both local and systemic acute inflammatory responses by controlling the level of proinflammatory, but not antiinflammatory, cytokines, and that these antiinflammatory activities by IL-6 cannot be compensated for by IL-10 or other IL-6 family members.

Oncostatin M induces the differentiation of breast cancer cells

We have recently described the action of Oncostatin M (OSM) to inhibit the proliferation of breast cancer cells. In this study we examined the action of OSM on 2 breast cancer cell lines to further characterize the nature of OSM inhibition of cellular proliferation. Treatment with OSM for 6 days resulted in an approximately 2- to 5-fold decrease in cell number, which was independent of estrogen receptor status. Consistent with this, colony formation was reduced to approximately 50% when cells were exposed to OSM in primary agar cultures. Clonogenicity was further inhibited following 7 days treatment with OSM in monolayer cultures: the total number of clonogenic cells was suppressed approximately 10-fold. Analysis of cell cycle status in OSM-treated cells demonstrated a 40% reduction in the proportion of cells in S phase within 12 hr, with an increase in cells in G0/G1. After 6 days, there was a 10-fold reduction in the absolute number of cells in S phase in OSM-treated cultures. These changes were associated with striking changes in cellular morphology, including disruption of intercellular junctions and the production of lipid droplets. There was a 5-fold increase of c-fos and c-myc mRNA within 30 min of commencing treatment with OSM. In addition, in the ER positive cells there was a decrease in ER mRNA (evident within approximately 2 hr) and ER protein expression following treatment with OSM. Conversely, there was a 5-fold increase in epidermal growth factor receptor (EGFR) mRNA within 4 hr, and a 2.5-fold rise in mRNA for transforming growth factor alpha (TGF alpha). Thus, the inhibition of breast cancer cells by OSM was associated with decreased clonogenicity, a decrease in S phase cells and a variety of phenotypic changes, all consistent with the induction of differentiation.

Interleukin-6 and CAAT/enhancer binding protein beta-deficient mice act as tools to dissect the IL-6 signalling pathway and IL-6 regulation

Interleukin-6 (IL-6) is a pleiotropic cytokine playing important roles in immunity, hemopoiesis and inflammation. IL-6 signalling is known to involve the activation of two independent transcription factors: Stat3 (through phosphorylation by Jak kinases) and C/EBP beta (through activation of the ras pathway). In addition, C/EBP beta is believed to act as a transcriptional activator of the IL-6 gene itself. Making use of IL-6-deficient mice, we have recently demonstrated that IL-6 is essential for the induction of acute phase mRNAs in the liver upon localized tissue damage, but not upon systemically induced inflammation. Here we show that the defective mRNA induction is paralleled by a defective activation of Stat3, thus establishing a direct relationship between IL-6 function, Stat3 activation and acute phase genes induction. On the other hand, making use of C/EBP beta-deficient mice, we show that the induction of IL-6 by a variety of stimuli does not require C/EBP beta activity. In contrast to the predicted activating role of C/EBP beta, IL-6 levels are increased in the C/EBP beta-deficient mice, suggesting that C/EBP beta may act as a down-modulator of the IL-6 gene. Through the generation of C/EBP beta, IL-6 double mutant mice we show that IL-6 hyperproduction is responsible for the development of the Castleman's like lymphoproliferative disease described in the C/EBP beta-deficient mice, since the disorder is completely blocked by inactivating the IL-6 gene.

Pituitary cytokine and growth factor expression and action

The complex range of pituitary regulatory mechanisms reviewed here underlies the critical function of the pituitary in sustaining all higher life forms. Thus, the ultimate net secretion of pituitary hormones is determined by signal integration from all three tiers of pituitary control. It is clear from our current knowledge that the trophic hormone cells of the anterior pituitary are uniquely specialized to respond to these signals. Unravelling their diversity and complexity will shed light upon the normal function of the master gland. Understanding these control mechanisms will lead to novel diagnosis and therapy of disordered pituitary function (357).

Cytokines and the hepatic acute phase response

The acute phase response is an orchestrated response to tissue injury, infection or inflammation. A prominent feature of this response is the induction of acute phase proteins, which are involved in the restoration of homeostasis. Cytokines are important mediators of the acute phase response. Uncontrolled and prolonged action of cytokines is potentially harmful, therefore mechanisms exist which limit the activity of cytokines; these include soluble cytokine receptors and receptor antagonists. The cytokine signal is transmitted into the cell via membrane-bound receptors. Different intracellular signalling pathways are activated by different cytokine-receptor interactions. Eventually, cytokine-inducible transcription factors interact with their response elements in the promotor region of acute phase genes and transcription is induced. Systemic inflammation results in a systemic acute phase response. However, local inflammatory or injurious processes in the liver may also induce an acute phase response, for example after partial hepatectomy and during hepatic fibrosis. The acute phase proteins induced in these conditions probably act to limit proteolytic and/or fibrogenic activity and tissue damage. The possible function of the acute phase protein alpha 2-macroglobulin in hepatic fibrosis is discussed in some detail.

Cardiotrophin-1 inhibits tumor necrosis factor production in the heart and serum of lipopolysaccharide-treated mice and in vitro in mouse blood cells

Cardiotrophin-1 (CT-1) is a member of the gp130 family of cytokines that includes interleukin-6, interleukin-11, ciliary neurotrophic factor, leukemia inhibitory factor, and oncostatin M. As interleukin-6, leukemia inhibitory factor, and ciliary neurotrophic factor were previously reported to inhibit the production of tumor necrosis factor (TNF), we studied the effect of CT-1 on serum and heart TNF levels in mice treated with lipopolysaccharide (100 ng/mouse, iv). Co-treatment with CT-1 (5 micrograms/mouse intravenously) markedly inhibit TNF production both in serum and in the heart. The effect of CT-1 seems to be direct as it also inhibited TNF production when added to whole mouse blood cultured with lipopolysaccharide. Thus, CT-1 might play a protective role in some TNF-mediated diseases.

Leukemia inhibitory factor ameliorates experimental anti-GBM Ab glomerulonephritis

Leukemia inhibitory factor (LIF) is a pleiotropic cytokine that has been identified in acute and chronic inflammatory conditions such as rheumatoid arthritis, sepsis, and renal allograft rejection. We investigated the glomerular expression of LIF at 30 minutes, and 3, 6, 9, 15 and 24 hours after administration of anti-GBM Ab (N = 3) by the RNase protection assay. Control rats received rabbit sera and were sacrificed at 30 minutes, and 6 and 24 hours. LIF mRNA relative to GAPDH mRNA was detected at low levels within the glomeruli of occasional control rats. However with the induction of anti-GBM Ab GN, there was a marked increase in LIF steady-state mRNA beginning at three hours which persisted through 24 hour. LIF mRNA was also detected in cultured mesangial cells stimulated with IL-1 beta, identifying this cell type as a potential glomerular source for this cytokine. To investigate the in vivo effect of LIF, Lewis rats were continuously infused with recombinant (r) human (h) LIF (approximately 0.5 ng/hr) or saline vehicle i.p. with ALZA osmotic pumps beginning at t = -24 hours (N = 8). All rats were injected with anti-GBM Ab intravenously at t = 0 (N = 16). LIF infusion decreased 24-hour urinary protein excretion by 85% (17 +/- 15 vs. 114 +/- 37 mg/day, P = 0.0001) and was associated with a 60% decrease in glomerular macrophage infiltration (0.8 +/- 0.2 vs. 2.0 +/- 0.6 ED-1 cells/glom, P = 0.0001). The administration of rhLIF did not affect the binding of the anti-GBM Ab to glomeruli. The beneficial effects of LIF were associated with a decrease in glomerular MCP-1 (56%), IL-1 (41%) and TNF (17%) steady state mRNA expression. The latter was associated with a 29% decrease in TNF-alpha protein expression within the glomerular lysate of nephritic rats administered LIF when compared with control rats. These data demonstrate a potential role for LIF in the therapy of anti-GBM Ab GN.

Leukemia inhibitory factor induces differentiation of pituitary corticotroph function: an immuno-neuroendocrine phenotypic switch

Leukemia inhibitory factor (LIF) promotes differentiated cell function in several systems. We recently reported LIF and LIF receptor expression in human fetal pituitary corticotrophs in vivo and demonstrated LIF stimulation of adrenocorticotrophin (ACTH) transcription in vitro, suggesting a role for LIF in corticotroph development. We therefore assessed the action of LIF on proliferating murine corticotroph cells (AtT20). LIF impairs proliferation of AtT20 cells (25% reduction versus control, P < 0.03), while simultaneously enhancing ACTH secretion (2-fold, P < 0.001) and augmenting ACTH responsiveness to corticotrophin-releasing hormone (CRH) action (4-fold, P < 0.001). This attenuation of cell growth is due to a block of cell cycle progression from G1 into S phase, as measured by flow cytometric analysis (24 +/- 0.8 versus 11.57 +/- 1.5, P < 0.001). Using bromodeoxyuridine incorporation assays, loss of cells in S phase was confirmed (25 +/- 0.08 to 9.4 +/- 1.4, P < 0.008). In contrast, CRH induced the G2/M phase (3.6 +/- 0.2 to 15.4 +/- 3, P < 0.001). This effect was blunted by LIF (P < 0.001 versus CRH alone). Cyclin A mRNA levels, which decline in S phase, were stimulated 3.5-fold by LIF and markedly suppressed by CRH. These results indicate a LIF-induced cell cycle block occurring at G1/S in corticotroph cells. Thus, LIF reduces proliferation, enhances ACTH secretion, and potentiates effects of CRH on ACTH secretion while blocking effects of CRH on the cell cycle. Responses of these three markers of differentiated corticotroph function indicate LIF to be a differentiation factor for pituitary corticotroph cells by preferential phenotypic switching from proliferative to synthetic.

LIF and CNTF, which share the gp130 transduction system, stimulate hepatic lipid metabolism in rats

We determined the effects of leukemia inhibitory factor (LIF) and ciliary neurotrophic factor (CNTF) on lipid metabolism in intact rats. Administration of LIF and CNTF increased serum triglycerides in a dose-dependent manner with peak values at 2 h. The effects of LIF and CNTF on serum cholesterol were very small, and serum glucose was unaffected. Both LIF and CNTF stimulated hepatic triglyceride secretion, hepatic de novo fatty acid synthesis, and lipolysis. Pretreatment with phenylisopropyl adenosine, which inhibits lipolysis, partially inhibited LIF- and CNTF-induced hypertriglyceridemia. Interleukin-4, which inhibits cytokine-induced hepatic fatty acid synthesis, also partially inhibited LIF- and CNTF-induced hypertriglyceridemia. These results indicate that both lipolysis and de novo fatty acid synthesis play a role in providing fatty acids for the increase in hepatic triglyceride secretion. Neither indomethacin nor adrenergic receptor antagonists affected the hypertriglyceridemia. The combination of LIF plus CNTF showed no additive effects consistent with the action of both cytokines through the gp130 transduction system. Thus LIF and CNTF have similar effects on lipid metabolism; they join a growing list of cytokines that stimulate hepatic triglyceride secretion and may mediate the changes in lipid metabolism that accompany the acute phase response.

Mouse oncostatin M: an immediate early gene induced by multiple cytokines through the JAK-STAT5 pathway

Oncostatin M (OSM) is a member of the interleukin-6 (IL6)-related cytokine subfamily that includes IL6, IL11, leukemia inhibitory factor (LIF), ciliary neurotrophic factor and cardiotrophin-1. While human OSM has been characterized and the bovine OSM gene was recently cloned, the murine counterpart had not been identified. Here we describe molecular cloning of murine OSM as an immediate early gene induced by a subset of cytokines including IL2, IL3 and erythropoietin (EPO) in myeloid and lymphoid cell lines. The induction kinetics of OSM are rapid and transient, reaching a maximal level within 30-60 min and decreasing thereafter. Induction of OSM depends on the signals generated by the membrane-proximal region of the EPO receptor as well as that of the beta chain of the IL3/GM-CSF receptor, which activate JAK2 and STAT5. About 100 bases upstream of the transcription initiation site of the OSM gene contains a possible STAT5 binding site which is essential for IL2, IL3 and EPO-dependent promoter activity of the OSM gene. Expression of STAT5 and the EPO receptor in COS cells conferred EPO-dependent activation of the OSM promoter. Moreover, the mutant IL2 receptor lacking the ability to activate STAT5 induced c-myc but failed to induce OSM. Thus OSM is one of the common targets of a subset of cytokines that activate STAT5. The murine OSM gene is located near to the LIF gene, expressed at high levels in bone marrow and possesses similar biological activity to human OSM. Identification of murine OSM as a cytokine-inducible immediate early gene provides a new insight into the physiological function of this unique cytokine.