Endotoxin-induced upregulation of type I interleukin-1 receptor mRNA expression in hepatocytes of mice: role of cytokines

Salient type 1 interleukin 1 receptor expression in peripheral non-immune cells

Interleukin 1 is a pleiotropic cytokine that mediates diverse functions through its receptor, type I interleukin 1 receptor (IL-1R1). Most previous studies have focused on the expression and function of IL-1R1 in immune cells. Here we performed a comprehensive mapping of IL-1R1 distribution in multiple peripheral tissues using our IL-1R1 reporter (IL-1R1^GR/GR) mice. This method yielded the highest sensitivity of in situ detection of IL-1R1 mRNA and protein. Besides validating previously reported IL-1R1 expression in the endocrine tissues including pituitary and pancreas, our results refuted previously reported exclusive IL-1R1 expression in neurons of the spinal cord dorsal horn and dorsal root ganglia (DRG). Instead, IL-1R1 expression was detected in endothelial cells within DRG, spinal cord, pancreas, colon, muscles and many immune organs. In addition, gp38⁺ fibroblastic reticular cells (FRCs), rather than tissue macrophages or other immune cells, were found to express high levels of IL-1R1 in colon and many immune organs. A functional test of spleen FRCs showed that they responded rapidly to systemic IL-1β stimulation in vivo. Taken together, this study provides a rigorous re-examination of IL-1R1 expression in peripheral tissues and reveals tissue FRCs as a previously unappreciated novel high IL-1R1-expressing cell type in peripheral IL-1 signaling.

[Interluekin-1: from regulation of cell proliferation to chronic inflammatory diseases]

  Interleukin 1 (IL-1) was initially defined as a factor which is produced by macrophages and exhibits proliferative activity on thymocytes and fibroblasts, B cell activation and endogenous pyrogen activity. Now IL-1 is known to exhibit pleiotropic activities on various cell types and play important roles in the regulation of immune, nervous and endocrine systems, progression of tumor cells, hematopoietic cell proliferation/differentiation and especially in inflammatory diseases. In 1985 I found that IL-1 exhibits cytocidal activity against human melanoma cells. Since then I have been engaged in the research of various aspects of IL-1. This review summarizes current knowledge of IL-1, including our research and beneficial effect of IL-1 blocking on inflammatory diseases.

Discovery of the DIGIRR gene from teleost fish: a novel Toll-IL-1 receptor family member serving as a negative regulator of IL-1 signaling

Toll-IL-1R (TIR) family members play crucial roles in a variety of defense, inflammatory, injury, and stress responses. Although they have been widely investigated in mammals, little is known about TIRs in ancient vertebrates. In this study, we report a novel double Ig IL-1R related molecule (DIGIRR) from three model fish (Tetraodon nigroviridis, Gasterosteus aculeatus, and Takifugu rubripes), adding a previously unknown homolog to the TIR family. This DIGIRR molecule contains two Ig-like domains in the extracellular region, one Arg-Tyr-mutated TIR domain in the intracellular region, and a unique subcellular distribution within the Golgi apparatus. These characteristics distinguish DIGIRR from other known family members. In vitro injection of DIGIRR into zebrafish embryos dramatically inhibited LPS-induced and IL-1β-induced NF-κB activation. Moreover, in vivo knockdown of DIGIRR by small interfering RNA significantly promoted the expression of IL-1β-stimulated proinflammatory cytokines (IL-6 and IL-1β) in DIGIRR-silenced liver and kidney tissues and in leukocytes. These results strongly suggest that DIGIRR is an important negative regulator of LPS-mediated and IL-1β-mediated signaling pathways and inflammatory responses. The Arg-Tyr-mutated site disrupted the signal transduction ability of DIGIRR TIR. Evolutionally, we propose a hypothesis that DIGIRR and single Ig IL-1R related molecule (SIGIRR) might originate from a common ancient IL-1R-like molecule that lost one (in DIGIRR) or two (in SIGIRR) extracellular Ig-like domains and intracellular Ser and Arg-Tyr amino acids. DIGIRR might be an evolutionary "transitional molecule" between IL-1R and SIGIRR, representing a shift from a potent receptor to a negative regulator. These results help define the evolutionary history of TIR family members and their associated signaling pathways and mechanisms.

TGF-β down-regulates IL-1α-induced TLR2 expression in murine hepatocytes

We have previously reported that the proinflammatory cytokine interleukin (IL)-1alpha can up-regulate functional Toll-like receptor 2 (TLR2) expression in primary-cultured murine hepatocytes, and bacterial lipopeptide (BLP) is capable of signaling through TLR2 to induce serum amyloid A (SAA) expression in hepatocytes. In the present study, we investigated the effect of the anti-inflammatory cytokine transforming growth factor-beta (TGF-beta) on TLR2 expression in primary-cultured murine hepatocytes. At the mRNA and protein levels, TGF-beta up-regulated TLR2 expression but inhibited TLR2 expression induced by IL-1alpha at 24 h. BLP-induced SAA promoter activity could be augmented by pretreatment with IL-1alpha but not TGF-beta or the combination of TGF-beta and IL-1alpha. TLR2 promoter activity and nuclear factor (NF)-kappaB activation by IL-1alpha were inhibited by TGF-beta treatment. Pretreatment with TGF-beta strongly suppressed IL-1alpha-induced TLR2 promoter activity and NF-kappaB activation, which was consistent with the down-regulation of type I IL-1 receptor (IL-1RI) mRNA expression. IL-1alpha up-regulated IL-1RI mRNA, but it was inhibited by the treatment with TGF-beta. These results suggest that TGF-beta suppresses the induction of TLR2 expression by IL-1alpha through down-regulation of IL-1RI expression. These results also demonstrate the disparity between IL-1alpha and TGF-beta in regulating TLR2-mediated SAA production in hepatocytes.

Enhancement of endotoxin-induced vascular hyporeactivity to phenylephrine in the thoracic aortas of Mg-deficient rats ex vivo

Since endotoxin lethality is enhanced by Mg deficiency in animals, we determined whether endotoxin-induced vascular hyporeactivity to phenylephrine (PE) is enhanced in Mg-deficient rats. Normal and Mg-deficient adult male Wistar rats were injected with Escherichia coli 011: B4 lipopolysaccharide (1 or 5 mg/kg, i.p.). Six h later, rings prepared from their thoracic aortas showed severe hyporeactivity to PE. This was more pronounced in the Mg-deficient rats, and was reversed by in vitro treatment with a highly selective inducible nitric oxide (NO) synthase inhibitor, 1400 W, or a highly selective soluble guanylyl cyclase inhibitor, ODQ. However, reversal required high doses of both inhibitors in Mg-deficient rats. Endotoxemia for 6 h was associated with elevated serum interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha levels, and strong TNF receptor mRNA expression in the abdominal aortas, which were significantly greater in the Mg-deficient rats. Treatment of the thoracic aortas, isolated from control and Mg-deficient rats before endotoxic challenge, with IL-1beta or TNF-alpha for 6 h in vitro caused hyporeactivity to PE, but its severity did not differ significantly between the two groups. These results suggest that high serum IL-1beta and TNF-alpha levels, and increased TNF receptor production in the vascular tissue, contribute to vascular hyporeactivity to PE in endotoxemia, and to its enhancement in Mg-deficient rats, via NO/cGMP signaling.

Lack of stearoyl-CoA desaturase-1 function induces a palmitoyl-CoA Delta6 desaturase and represses the stearoyl-CoA desaturase-3 gene in the preputial glands of the mouse

The mouse preputial gland (PG), a specialized sebaceous structure, is rich in wax esters, triglycerides, and alkyl-2,3-diacylglycerol. We have found that the mouse PG expresses the three gene isoforms (SCD1, SCD2, and SCD3) of the Delta9 stearoyl-CoA desaturase enzyme that catalyzes the biosynthesis of monounsaturated fatty acids mainly, C16:1n-7 and C18:1n-9. However, mice with a targeted disruption in the SCD1 isoform (SCD1(-/-)) have undetectable SCD3 mRNA expression in the PG while the expression of SCD2 isoform was not altered. The levels of C16:1n-7 were reduced by greater than 70% while that of C18:1n-9 were reduced by 28%. The content of the C16:1n-10 (Delta6 hexadecenoic acid) isomer and a major fatty acid of the PG was increased by greater than 2-fold, mainly in the wax ester fraction of the SCD1(-/-) mouse. We demonstrate that the increase in C16:1n-10 is due to induction of a specific palmitoyl-CoA Delta6 desaturase activity. Testosterone administration to the SCD1(-/-) mouse induced SCD3 mRNA expression and resulted in an increase in the Delta9 desaturation of 16:0-CoA, but not of 18:0-CoA. These observations demonstrate that loss of SCD1 function alters the expression of SCD3 and reveal for the first time the presence and regulation of a palmitoyl-CoA Delta6 desaturase enzyme in mammals.

Development of selective tolerance to interleukin-1beta by human chondrocytes in vitro

Interleukin-1 induces release of NO and PGE(2) and production of matrix degrading enzymes in chondrocytes. In osteoarthritis (OA), IL-1 continually, or episodically, acts on chondrocytes in a paracrine and autocrine manner. Human chondrocytes in chondron pellet culture were treated chronically (up to 14 days) with IL-1beta. Chondrons from OA articular cartilage were cultured for 3 weeks before treatment with IL-1beta (0.05-10 ng/ml) for an additional 2 weeks. Spontaneous release of NO and IL-1beta declined over the pretreatment period. In response to IL-1beta (0.1 ng/ml), NO and PGE(2) release was maximal on Day 2 or 3 and then declined to near basal level by Day 14. Synthesis was recovered by addition of 1 ng/ml IL-1beta on Day 11. Expression of inducible nitric oxide synthase (iNOS), detected by immunofluorescence, was elevated on Day 2 and declined through Day 14, which coordinated with the pattern of NO release. On the other hand, IL-1beta-induced MMP-13 synthesis was elevated on Day 3, declined on Day 5, and then increased again through Day 14. IL-1beta increased glucose consumption and lactate production throughout the treatment. IL-1beta stimulated proteoglycan degradation in the early days and inhibited proteoglycan synthesis through Day 14. Chondron pellet cultures from non-OA cartilage released the same amount of NO but produced less PGE(2) and MMP-13 in response to IL-1beta than OA cultures. Like the OA, IL-1beta-induced NO and PGE(2) release decreased over time. In conclusion, with prolonged exposure to IL-1beta, human chondrocytes develop selective tolerance involving NO and PGE(2) release but not MMP-13 production, metabolic activity, or matrix metabolism.

Cloning of a Salmo salar interleukin-1 receptor-like cDNA

The interleukin-1 receptor/toll-like receptor (IL-1R/TLR) superfamily, defined by a cytosolic Toll/IL-1R (TIR) signalling domain, participates in host responses to injury and infection. We describe in this study the cloning of a cDNA encoding a Salmo salar interleukin-1 receptor-like protein (SalIL-1RLP). SalIL-1RLP comprises a potential signal peptide, three extracellular immunoglobulin domains, a short transmembrane region and an intracellular region that contains the TIR domain. The predicted amino acid sequence of SalIL-1RLP displays 43-44% similarities and 31% identities to chicken and human IL-1RI sequences. Within the intracellular region, SalIL-1RLP displays highest similarity (59%) and identity (46%) to the chicken IL-1RI sequence. Two different 5' distal UTRs were identified among six salmon IL-1RLP clones. The six clones, however, displayed identical 5' proximal UTRs, coding regions and 3' UTRs. SalIL-1RLP expression is induced in liver, head kidney, spleen and gills upon injection of salmon with bacterial lipopolysaccharide. Sequence comparisons, protein domain structures, expression patterns and phylogenetic analyses indicate that SalIL-1RLP is most closely related to type I interleukin-1 receptors and interleukin-1 receptor related proteins.

[In vitro and in vivo study of regulation mechanisms of type I interleukin-1 receptor]

Interleukin 1 (IL-1) is one of the inflammatory cytokines, which plays a pivotal role in both host defense and homeostasis. Its signal is transduced by type I IL-1 receptor (IL-1RI). This report gives an insight into the regulatory mechanism of IL-1RI in both in vitro and in vivo. IL-1 up-regulates IL-1RI through prostaglandin E2 (PGE2) production on human fibroblasts. However, in the presence of indomethacin, IL-1 down-regulates the receptor by destabilizing IL-1 receptor mRNA. Type I and type II interferons (IFNs) up-regulate the expression of IL-1RI. This up-regulation leads to the increasing susceptibility of IL-1RI to IL-1, as the DNA binding of IL-1-induced NF-kappa B and the production of IL-1-induced IL-6 from the fibroblasts are augmented by pretreatment with IFNs. On the other hand, the expression of cell surface IL-1RI is inhibited by tyrosine kinase inhibitors, herbimycin and genistein, resulting in reduction of the kinase activity of IRAK (IL-1 receptor associated kinase) and IL-1-induced IL-6 production from the fibroblasts. Lipopolysaccharide (LPS) augments the expression of IL-1RI mRNA and cell surface molecule in the hepatocytes of mice in vivo, and the augmentation is mediated by the interaction of IL-1, IL-6, and of glucocorticoid (GC). When hepatocytes were pretreated with dexamethasone (Dex) and IL-6, the activation of IRAK was augmented in response to IL-1, indicating that IL-1 signaling is also up-regulated. In addition, IL-1 treatment ather combined administration of Dex and IL-6 into mice markedly increased the serum level of serum amyloid A. These data suggest that the expression of IL-1RI is regulated by inflammatory cytokines, PGE2, GC and LPS in vitro and in vivo. This study shows that the biological activity of IL-1 can be controlled by regulating the expression of IL-1RI, and therefore proposes the use of pharmaceutical drugs for the regulation of cytokine expression.

Endotoxin and cytokine regulation of toll-like receptor (TLR) 2 and TLR4 gene expression in murine liver and hepatocytes

Toll-like receptor (TLR) 2 and TLR4 are members of the interleukin-1 receptor (IL-1R) family and transduce similar signals as IL-1R in response to bacteria and bacterial components. In this study, we investigated the regulation of their gene expression in murine tissues, especially in the liver and hepatocytes. When mice were administered lipopolysaccharide (LPS), TLR2 mRNA was upregulated in the brain, heart, lung, liver, and kidney. In contrast, it was downregulated in the spleen. TLR4 mRNA was decreased in the brain. In the heart and lung, it increased, and it was not affected in the liver, kidney, and spleen. TLR mRNA was further analyzed in the liver and hepatocytes. Like LPS treatment, administration of IL-1, IL-6, or tumor necrosis factor (TNF) upregulated TLR2 mRNA. However, none of them affected the TLR4 mRNA level. In primary cultured hepatocytes, TLR2 mRNA was upregulated by LPS, IL-1, or TNF but not by IL-6 or dexamethasone. None of them affected TLR4 mRNA expression. Similar responses were observed in the murine hepatoma cell line Hepa 1-6. These results suggest that in infection with gram-negative bacteria, LPS and proinflammatory cytokines differentially regulate gene expression of TLR2 and TLR4 in murine hepatocytes, which may lead to pathologic and host defense reactions in the liver.

Modulation of type I interleukin-1 receptor messenger RNA followed by one and repeated endotoxin treatment in the mouse

The expression of transcripts for type 1 interleukin-1 receptors (IL-1R1) were investigated utilizing reverse transcription-polymerase chain reaction (RT-PCR) techniques in male C57BL/6 mice. First, we measured IL-1R1 mRNA 1, 2, 6, and 12 h after a single injection of endotoxin lipopolysaccharide (LPS; 30 microg/mouse). IL-1R1 mRNA was measured in relevant tissues utilizing semiquantitative RT-PCR. IL-1R1 mRNA levels were significantly increased 2 and 6 h after one LPS injection group in comparison with the saline injection group in the hippocampus and testis. Next, we investigated the effect of repeated injections of LPS on IL-1R1 expression. LPS or saline were injected at 24-h intervals for 4 consecutive days. The mice were divided into four groups: (1) LPS injections for 4 days and LPS injection on day 5 (LPS-LPS); (2) LPS injections for 4 days and saline injection on day 5 (LPS-saline); (3) saline injections for 4 days and LPS injection on day 5 (saline-LPS); (4) saline injections for 4 days and saline injection on day 5 (saline-saline). The mice were sacrificed by decapitation 2 h after the last injection. In the hippocampus and pituitary gland, significant increases of IL-1R1 mRNA levels were observed in the saline-LPS group, however, the increases were attenuated in LPS-LPS group. IL-1R1 mRNA levels in the hypothalamus were unchanged in all four groups. In the adrenal gland and testis, IL-1R1 mRNA levels were significantly increased in the LPS-LPS group as well as saline-LPS group. These data demonstrate differential regulation of IL-1R1 mRNA by one and repeated endotoxin treatment and suggest the importance of the cytokines in mediating the effects of infectious challenge on brain, endocrine and immune function during endotoxemia.

IL-1beta induced changes in hypothalamic IL-1R1 and IL-1R2 mRNA expression in the rat

Interleukin-1 receptor (IL-1R1 and IL-1R2) mRNA expression was detected within the rat hypothalamus, a primary site of IL-1 action, using RT-PCR. Levels of expression were unchanged by cardiac saline-perfusion. However, intracerebroventricular (i.c.v.) administration of IL-1beta caused changes in receptor mRNA expression in non-perfused animals that were profoundly different to those observed in their saline-perfused counterparts. This study demonstrates the importance of perfusing tissue to remove blood cells when determining changes in IL-1 receptor mRNA expression.

Mechanisms by which blood levels of interleukin-6 (IL-6) are elevated after intracerebroventricular injection of IL-1beta in the rat: neural versus humoral control

Intracerebroventricular (icv) injection of interleukin-1beta (IL-1beta) in rats induces elevated IL-6 levels in peripheral blood, exceeding those induced by iv or ip injection. Two hypotheses postulated to explain this phenomenon were tested. Mediation by peripheral sympathetic activation was excluded by showing that agents that blocked preganglionic cholinergic synapses (chlorisondamine), beta-adrenergic receptors (propanalol, butoxamine), and alpha-adrenergic receptors (phentolamine) did not prevent the IL-6 response. That the peripheral response was due to passage of the injected IL-1beta into blood from the brain was supported by several observations. Immunoreactive IL-1beta appeared in peripheral blood by 10 min after icv injection and remained constant between 10-100 min after injection; values after icv injection were virtually identical to those after iv injection at 60 and 80 min. Radioiodine-labeled IL-1beta appeared in blood as early as 5 min, and by phamacokinetic analysis was found to be transferred from the brain at a rate greater than 2% of brain content per min(-1). IL-1beta infused iv in a pattern mimicking brain to blood transfer induced IL-6 levels that were more than double the values induced by a single bolus injection and were not significantly different from the values observed after icv injection. Sustained levels of IL-1beta in blood over time contribute to the high peripheral IL-6 response. This was shown by administering the same total dose iv as a single bolus of 100 ng or in two doses of 50 ng 1 h apart. Rats given a divided dose had 6-10 times higher blood IL-6 levels at 2 h than those given a single injection. The high levels of IL-6 in blood after icv injection of IL-1beta are best explained by the reservoir function of the brain IL-1beta pool and the self-priming effect of IL-1beta in peripheral tissues.

Dynamic regulation of the proinflammatory cytokine, interleukin-1beta: molecular biology for non-molecular biologists

Interleukin-1beta (IL-1beta) is a key mediator and modulator of a wide array of physiological responses important for survival. It is created by a variety of cell types, including immune cells, glia, and neurons. It is a very potent biological molecule, acting both at the periphery as well as within the central nervous system. The production and release of IL-1beta is tightly regulated by far more complex processes than previously thought. An appreciation of this complexity is necessary for proper interpretation of apparent contradictions in the literature where different aspects of IL-1beta expression are measured. Given that many researchers are not molecular biologists by training, yet need an appreciation of the controls that regulate the function of key proteins such as IL-1beta, this review is aimed at both: (a) clarifying the multiple levels at which IL-1beta production is modulated and (b) using IL-1beta regulation to explain the dynamics of gene regulation to non-molecular biologists. Three major topics will be discussed. First, regulation of IL-1beta production will be examined at every level from extracellular signals that trigger gene activation through release of active protein into the extracellular fluid. Second, regulation of IL-1beta bioavailability and bioactivity will be discussed. This section examines the fact that even after IL-1beta is released, it may or may not be able to exert a biological action due to multiple modulatory factors. Last is the introduction of the idea that IL-1beta regulation is, at times, beyond the direct control of host; that is, when IL-1beta production becomes dysregulated by pathogens.

IL-1 receptor-type expression in relation to atopy

BACKGROUND

IL-1 has 2 receptors, type I (IL-1RI) and type II (IL-1RII), which have 2 forms each, membrane (m) and soluble (s). When IL-1 binds to mIL-1RI, the active receptor, an inflammatory response is initiated, which does not occur when IL-1 binds to mIL-1RII, the decoy receptor. Both sIL-1RI and sIL-1RII function as IL-1-mopping mechanisms. We hypothesized that the ratio of active (mIL-1RI) to inactive (mIL-1RII, sIL-1RI, and sIL-1RII) receptors is important in determining the amount of inflammation produced in allergic reactions.

OBJECTIVE

Our aim was to compare the concentrations of mIL-1RI and mIL-1RII on cultured PBLs and sIL-1RI, sIL-1RII, and IL-1beta in sera and supernatants of cultured PBMCs from atopic and nonatopic subjects.

METHODS

The membrane receptors, soluble receptors, and IL-1beta concentrations were measured by ELISA with specific mAbs.

RESULTS

Although there was no difference in the level of serum IL-1beta between the 2 groups, PBMCs from atopic persons spontaneously secreted higher levels of IL-1beta than those from nonatopic donors (P < .05). PBLs from atopic subjects compared with those from nonatopic individuals expressed higher mIL-1RI (P < .0001) and mIL-1RII (P < .05). Levels of both the soluble receptors from both serum (P < .0001) and PBMCs (P < .05) of nonatopic donors were higher than those found in atopic donors.

CONCLUSION

This augmentation of mIL-1RI concomitant with a reduction in soluble receptors may be an important contributory factor to the inflammation that occurs with allergen exposure.

Augmentation of Type I IL-1 Receptor Expression and IL-1 Signaling by IL-6 and Glucocorticoid in Murine Hepatocytes

IL-1 signal is transduced through type I receptor (IL-1RI). We have recently reported that LPS augments IL-1RI mRNA expression in the hepatocytes of mice in vivo, and the augmentation is mediated by the interaction of IL-1, IL-6, and glucocorticoid (GC). In this study, we examined whether IL-1RI mRNA expression level in the hepatocytes reflects those of cell surface molecule and IL-1 signaling. When primary cultured murine hepatocytes were treated with dexamethasone (Dex) or IL-6, these two reagents synergistically up-regulated IL-1RI mRNA expression in the cells. 125I-labeled IL-1 binding experiment showed that the level of binding was also up-regulated by the treatment with Dex and IL-6. Scatchard analysis revealed that the number of IL-1R increased. The increased binding of IL-1 was completely inhibited by an Ab against murine IL-1RI, indicating that Dex and IL-6 augmented the expression of cell surface IL-1RI molecule. When hepatocytes were pretreated with Dex and IL-6, the activation of IL-1R-associated kinase was augmented in response to IL-1, indicating that IL-1 signaling was also augmented. In addition, IL-1 treatment following administration of the combination of Dex and IL-6 into mice markedly increased the serum level of serum amyloid A. These results indicate that GC and IL-6 augment the expression of cell surface IL-1RI in hepatocytes, as well as IL-1 signaling and IL-1R-associated kinase activation, through up-regulation of IL-1RI mRNA level, which represents a novel regulatory network between IL-1, GC, and IL-6.

Regulation of IGF binding protein-1 in hep G2 cells by cytokines and reactive oxygen species

The liver is a major site of synthesis for insulin-like growth factor binding protein (IGFBP)-1. Because IGFBP-1 inhibits many anabolic actions of IGF-I, increases in IGFBP-1 may be partly responsible for the decrease in lean body mass observed in catabolic/inflammatory conditions. This study aimed to determine in Hep G2 cells 1) the sensitivity of IGFBP-1 synthesis to treatment with interleukin (IL)-1, tumor necrosis factor-alpha (TNF-alpha), and IL-6, 2) the ability of reactive oxygen species (ROS) to enhance IGFBP-1 production, and 3) the role of ROS in mediating cytokine-induced increases in IGFBP-1. Hep G2 cells responded to IL-1beta, TNF-alpha, and IL-6 with maximal 8- to 10-fold increases in IGFBP-1 production. Although the maximal responsiveness of cells treated with TNF-alpha and IL-6 was 20-30% less than that with IL-1beta, cells demonstrated a similar sensitivity to all cytokines (half-maximal responsive dose of approximately 10 ng/ml). A low concentration (3 ng/ml) of all three cytokines had an additive effect on IGFBP-1 production. Cytokines also increased IGFBP-1 mRNA. The half-life of IGFBP-1 mRNA was approximately 4 h and not altered by IL-1beta. Incubation with ROS, including H2O2 and nitric oxide (NO) donors, resulted in a relatively smaller increase in IGFBP-1. However, preincubating Hep G2 cells with various free radical scavengers and NO synthase and eicosanoid inhibitors failed to prevent or attenuate cytokine-induced increases in IGFBP-1. Finally, preincubating cells with pyrrolidinedithiocarbamate (PDTC) but not SN50 (inhibitors of nuclear factor-kappaB activation and nuclear translocation, respectively) attenuated increases in IGFBP-1 induced by IL-1. These results indicate that 1) proinflammatory cytokines directly enhance IGFBP-1 synthesis by stimulating transcription without altering mRNA stability, 2) addition of exogenous ROS also stimulates IGFBP-1 production but to a smaller extent than cytokines, and 3) the cytokine-induced increase in IGFBP-1 production is not mediated by endogenous production of ROS or eicosanoids but appears to at least partially involve a PDTC-sensitive pathway.

Decreased acid-labile subunit (ALS) levels by endotoxin in vivo and by interleukin-1beta in vitro

The production by the liver of the three subunits of the growth hormone (GH)-dependent 150 kDa complex (IGF-I, IGF-binding protein-3 and acid-labile subunit or ALS) is primarily under the control of GH. Recent data have shown that, besides GH, endotoxin (LPS) and cytokines may regulate the liver IGF-I gene. To investigate the potential regulation of ALS by LPS, we measured serum ALS by immunoblot, 5 and 10 h after IP injection of LPS (250 or 750 microg/100 g BW vs saline), in 4-week-old female Wistar rats (four per group). Ten hours after injection, serum ALS levels were reduced by 57% (delta%) with the lower dose (P<0.05) and by 81% with the higher dose (P<0.01) by comparison with saline-treated rats. The decrease in ALS levels in response to LPS was not prevented by exogenous GH. To investigate the role of interleukin (IL)-1beta in the regulation of ALS, primary cultured rat hepatocytes were exposed to increasing concentrations of IL-1beta. Cell exposure to IL-1beta markedly decreased both basal and GH-stimulated ALS levels (-70%; P<0.01) in a dose-dependent fashion, with the half-maximal inhibitory effect at concentrations of 0.1 ng/ml. Our results show that endotoxin induces a rapid decline in circulating ALS that is potentially mediated through IL-1beta. By limiting the formation of the 150 kDa complex, this reduction in circulating ALS might contribute to the rapid decline in serum IGF-I observed in sepsis.

Role of glucocorticoid in the upregulation of type I interleukin-1 receptor mRNA expression in hepatocytes of endotoxin-administrated mice

The interleukin-1 (IL-1) signal is transduced through type I IL-1 receptor (IL-1RI). We have recently reported that lipopolysaccharide (LPS) upregulated IL-1RI mRNA expression in mouse liver in vivo and that IL-1 and IL-6 directly upregulated IL-1RI mRNA expression in primary cultured mouse hepatocytes. Glucocorticoid (GC) has been reported to increase IL-1 binding to the cell surface and the expression level of IL-1R mRNA in a variety of cell types. As serum GC level is elevated in an inflammatory response, we evaluated the role of GC in LPS-induced upregulation of IL-1RI mRNA in the mouse liver. When LPS was administered to adrenalectomized (ADX) mice, IL-1RI mRNA was upregulated at a level comparable to those of untreated or sham-operated mice. A high dose of dexamethasone (Dex), however, caused upregulation of the mRNA. When primary cultured mouse hepatocytes were treated with Dex, only a weak upregulation of IL-1RI mRNA was observed. However, Dex in combination with IL-1 or IL-6 markedly enhanced the IL-1RI mRNA expression. A marked upregulation of the mRNA was also induced by treatment with a combination of IL-1 and IL-6 in the absence of Dex, reflecting the observation in ADX mice. These results suggest that the upregulation of IL-1RI mRNA in response to LPS is induced by the interaction of IL-1 and IL-6 and that GC augments their effect.