IL-6 trans-signaling via STAT3 directs T cell infiltration in acute inflammation

Interleukin (IL)-6 signaling through its soluble receptor (IL-6 transsignaling) directs transition between innate and acquired immune responses by orchestrating the chemokine-directed attraction and apoptotic clearance of leukocytes. Through analysis of mononuclear cell infiltration in WT and IL-6-deficient mice during peritoneal inflammation, we now report that IL-6 selectively governs T cell infiltration by regulating chemokine secretion (CXCL10, CCL4, CCL5, CCL11, and CCL17) and chemokine receptor (CCR3, CCR4, CCR5, and CXCR3) expression on the CD3+ infiltrate. Although blockade of IL-6 trans-signaling prevented chemokine release, chemokine receptor expression remained unaltered suggesting that this response is regulated by IL-6 itself. To dissect the signaling events promoting T cell migration, inflammation was established in knock-in mice expressing mutated forms of the universal signal-transducing element for IL-6-related cytokines gp130. In mice (gp130Y757F/Y757F) deficient in SHP2 and SOCS3 binding, but presenting hyperactivation of STAT1/3, T cell recruitment and CCL5 expression was enhanced. Conversely, both of these parameters were suppressed in mice with ablated gp130-mediated STAT1/3 activation (gp130DeltaSTAT/DeltaSTAT). T cell migration was related to STAT3 activity, because monoallelic deletion of Stat3 in gp130(Y757F/Y757F) mice (gp130Y757F/Y757F:Stat3+/-) corrected the exaggerated responses observed in gp130Y757F/Y757F mice. Consequently, STAT3 plays a defining role in IL-6-mediated T cell migration.     

Pathologic consequences of STAT3 hyperactivation by IL-6 and IL-11 during hematopoiesis and lymphopoiesis

We have previously demonstrated that STAT3 hyperactivation via the interleukin 6 (IL-6) cytokine family receptor gp130 in gp130 (Y757F/Y757F) mice leads to numerous hematopoietic and lymphoid pathologies, including neutrophilia, thrombocytosis, splenomegaly, and lymphadenopathy. Because IL-6 and IL-11 both signal via a gp130 homodimer, we report here a genetic approach to dissect their individual roles in these pathologies. Neutrophilia and thrombocytosis were absent in gp130 (Y757F/Y757F) mice lacking either IL-6 (gp130 (Y757F/Y757F): IL-6 (-/-)) or the IL-11 receptor alpha subunit (gp130 (Y757F/Y757F): IL-11Ralpha1 (-/-)), and this was associated with a normalized bone marrow compartment. The elevated myelopoiesis and megakaryopoiesis in bone marrow of gp130 (Y757F/Y757F) mice was attributable to an increase by either IL-6 or IL-11 in the STAT3-driven impairment of transforming growth factor beta (TGF-beta) signaling, which is a suppressor of these lineages. In contrast, the absence of IL-6, but not IL-11 signaling, prevented the splenomegaly, abnormal lymphopoiesis, and STAT3 hyperactivation in lymphoid organs of gp130 (Y757F/Y757F) mice. Furthermore, hyperactivation of STAT3 in lymphoid organs was associated with increased expression of IL-6Ralpha, and IL-6Ralpha expression was reduced in gp130 (Y757F/Y757F): Stat3 (+/-) mice displaying normal levels of STAT3 activity. Collectively, these data genetically define distinct roles of IL-6 and IL-11 in driving pathologic hematopoietic and lymphoid responses mediated by STAT3 hyperactivation.     

An essential role for gp130 in neointima formation following arterial injury

Interleukin (IL)-6 induced vascular smooth muscle cell (VSMC) motility in a dose-dependent manner. In addition, IL-6 stimulated tyrosine phosphorylation of gp130, resulting in the recruitment and activation of STAT-3. IL-6-induced VSMC motility was found to be dependent on activation of gp130/STAT-3 signaling. IL-6 also induced cyclin D1 expression in a time- and gp130/STAT-3-dependent manner in VSMCs. Suppression of cyclin D1 levels via the use of its small interfering RNA molecules inhibited IL-6-induced VSMC motility. Furthermore, balloon injury induced IL-6 expression both at mRNA and protein levels in rat carotid artery. Balloon injury also caused increased STAT-3 phosphorylation and cyclin D1 expression, leading to smooth muscle cell migration from the media to the intimal region. Blockade of gp130/STAT-3 signaling via adenovirus-mediated expression of dngp130 or dnSTAT-3 attenuated balloon injury-induced STAT-3 phosphorylation and cyclin D1 induction, resulting in reduced smooth muscle cell migration from media to intima and decreased neointima formation. Together, these observations for the first time suggest that IL-6/gp130/STAT-3 signaling plays an important role in vascular wall remodeling particularly in the settings of postangioplasty and thereby in neointima formation.     

Suppressor of cytokine signaling 3 regulates CD8 T-cell proliferation by inhibition of interleukins 6 and 27

Suppressor of cytokine signaling (SOCS) proteins regulate the intensity and duration of cytokine responses. SOCS3 is expressed in peripheral T cells, and recent reports have suggested that overexpression of SOCS3 modulates antigen- and/or costimulation-induced T-cell activation. To study the role of SOCS3 in the regulation of T-cell activation, we used a conditional gene-targeting strategy to generate mice that lack SOCS3 in T/natural killer T cells (Socs3(DeltaLck/DeltaLck) mice). SOCS3-deficient CD8 T cells showed greater proliferation than wild-type cells in response to T-cell receptor (TCR) ligation despite normal activation of signaling pathways downstream from TCR or CD28 receptors. Signaling in response to the gp130 cytokines interleukin (IL)-6 and IL-27 was prolonged in Socs3(DeltaLck/DeltaLck) T cells, and T cells from gp130(Y757F/Y757F) mice, in which the SOCS3-binding site on gp130 is ablated, showed a striking similarity to SOCS3-deficient CD8 T cells. Although the proliferative defect of Socs3(DeltaLck/DeltaLck) T cells was not rescued in the absence of IL-6, suppression of IL-27 signaling was found to substantially reduce anti-CD3-induced proliferation. We conclude that enhanced responses to TCR ligation by SOCS3-deficient CD8 T cells are not caused by aberrant TCR-signaling pathways but, rather, that increased IL-27 signaling drives unregulated proliferation in the absence of SOCS3.     

SHP2-mediated signaling cascade through gp130 is essential for LIF-dependent I CaL, [Ca2+]i transient, and APD increase in cardiomyocytes

Leukemia inhibitory factor (LIF), a cardiac hypertrophic cytokine, increases L-type Ca(2+) current (I(CaL)) via ERK-dependent and PKA-independent phosphorylation of serine 1829 in the Cav(1.2) subunit. The signaling cascade through gp130 is involved in this augmentation. However, there are two major cascades downstream of gp130, i.e. JAK/STAT3 and SHP2/ERK. In this study, we attempted to clarify which of these two cascades plays a more important role. Knock-in mouse line, in which the SHP2 signal was disrupted (gp130(F759/F759) group), and wild-type mice (WT group) were used. A whole-cell patch clamp experiment was performed, and intracellular Ca(2+) concentration ([Ca(2+)](i) transient) was monitored. The I(CaL) density and [Ca(2+)](i) transient were measured from the untreated cells and the cells treated with LIF or IL-6 and soluble IL-6 receptor (IL-6+sIL-6r). Action potential duration (APD) was also recorded from the ventricle of each mouse, with or without LIF. Both LIF and IL-6+sIL-6r increased I(CaL) density significantly in WT (+27.0%, n=16 p<0.05, and +32.2%, n=15, p<0.05, respectively), but not in gp130(F759/F759) (+9.4%, n=16, NS, and -6.1%, n=13, NS, respectively). Administration of LIF and IL-6+sIL-6r increased [Ca(2+)](i) transient significantly in WT (+18.8%, n=13, p<0.05, and +32.0%, n=21, p<0.05, respectively), but not in gp130(F759/F759) (-3.8%, n=7, NS, and -6.4%, n=10, NS, respectively). LIF prolonged APD(80) significantly in WT (10.5+/-4.3%, n=12, p<0.05), but not in gp130(F759/F759) (-2.1+/-11.2%, n=7, NS). SHP2-mediated signaling cascade is essential for the LIF and IL-6+sIL-6r-dependent increase in I(CaL), [Ca(2+)](i) transient and APD.     

Hematopoietic abnormalities in mice deficient in gp130-mediated STAT signaling

OBJECTIVE: Studies on mice lacking the common receptor subunit gp130 reveal that activation of gp130-dependent signaling pathways is essential for normal fetal and adult hematopoiesis. However, the extent to which hematopoiesis is dependent upon activation of a particular gp130 signaling pathway, namely STAT1/3 or SHP2/MAPK, is unknown. This study examined the specific contribution of gp130-mediated STAT1/3 signaling to the regulation of hematopoiesis. MATERIALS AND METHODS: Hematopoiesis was examined at various developmental stages in mice homozygous for a targeted carboxy-terminal truncation mutation in gp130 (gp130(delta)/(delta)) that deletes all STAT1/3 binding sites, thereby abolishing gp130-mediated STAT1/3 activation. RESULTS: Adult gp130(delta)/(delta) mice have increased numbers of immature colony-forming unit spleen progenitor cells in the bone marrow and spleen, elevated numbers of committed myeloid progenitor cells in the spleen and peripheral blood, and leukocytosis. Increased progenitor cell production was observed in gp130(delta)/(delta) fetal livers from 14 days of gestation onward. In contrast, the circulating platelet count was reduced by 30% in gp130(delta)/(delta) mice, without any corresponding decrease in the number of bone marrow and splenic megakaryocytes. In liquid cultures, megakaryocytes from gp130(delta)/(delta) mice are smaller than those from wild-type mice and do not increase in size upon stimulation with interleukin-6 or interleukin-11. Administration of either interleukin-6 or interleukin-11 to gp130(delta)/(delta) mice failed to increase platelet numbers, despite an increase in the production of megakaryocytes. CONCLUSIONS: Collectively, these results reveal that gp130-mediated STAT1/3 activation is required to maintain the normal balance of hematopoietic progenitors during fetal and adult hematopoiesis. Furthermore, they suggest two distinct roles for gp130-mediated STAT1/3 activation in hematopoiesis, one restricting the production of immature hematopoietic progenitor cells and the other promoting the functional maturation of megakaryocytes to produce platelets.     

Growth control of human biliary epithelial cells by interleukin 6, hepatocyte growth factor, transforming growth factor beta1, and activin A: comparison of a cholangiocarcinoma cell line with primary cultures of non-neoplastic biliary epithelial cells

A well characterized human cholangiocarcinoma (CC) cell line, SG231, was compared with primary cultures of normal human biliary epithelial cells (BECs) for alterations in interleukin 6 (IL-6) and hepatocyte growth factor (HGF)-mediated stimulation and transforming growth factor beta1 (TGF-beta1) and activin A-mediated inhibition of growth. Results were compared with immunolabeling of the original tumor and after injection of SG231 into the liver of BALB/cByJ-scid mice. In vitro, both BECs and CCs expressed met, gp80, and gp130 messenger RNA (mRNA) and protein, but the levels of expression were higher in the CCs than in the BECs. In both the CCs and BECs, exogenous HGF or IL-6 induced phosphorylation of met or gp130, respectively, and a concentration-dependent increase in DNA synthesis. However, the CCs but not BECs, continued to grow in basal serum-free medium (SFM) and spontaneously produced both IL-6 and HGF under these conditions, which resulted in auto-phosphorylation of gp130 and met, respectively; and neutralizing anti-HGF or anti-IL-6 alone inhibited CC growth, indicative of autocrine growth control circuits. Conversely, activin A inhibits the growth of both BECs and CCs, but does not significantly increase apoptosis. Activin-A-induced growth inhibition of both CCs and BECs can be reversed by 100 ng/mL exogenous IL-6, but not by 10 to 100 ng/mL HGF. TGF-beta1 inhibited the growth of BECs but had no mitoinhibitory or proapoptotic effects on CCs. Immunolabeling of the original tumor and after inoculation into scid mice showed positive staining for met, gp130, gp80, and IL-6. This study contributes to a further understanding of BEC growth control and derangements that can occur during cholangiocarcinogenesis.     

gp130 signaling in bone cell biology: Multiple roles revealed by analysis of genetically altered mice

The receptor subunit gp130 is utilized by a wide range of cytokines, many of which have critical functions in regulating the actions of osteoclasts and osteoblasts. In vitro studies have revealed remarkably consistent effects of many of these family members, specifically, actions on receptors in the osteoblast lineage that stimulate osteoblast differentiation and stimulate production of RANKL, thereby increasing the formation of osteoclasts. In contrast to this simple model of gp130 action on bone, deletion of cytokines or receptors that interact with gp130 reveal a range of bone phenotypes implicating critical roles for gp130 signaling in longitudinal bone growth, bone resorption and bone formation. In most cases, deletion of gp130, ligands or ligand-specific receptors interacting with gp130 causes a low level of bone formation; a high level of bone formation was only observed in gp130^Y757F/Y757F mice, gp130 signaling mutants, where it is caused by a cell-lineage autonomous increase in osteoclast formation and an IL-6-dependent coupling pathway. On the other hand, the range of gene knockouts may cause either a reduction or an increase in osteoclast formation, and in many cases alterations in osteoclast size and ability to resorb bone. Since some knockouts are neonatal lethal, interpretation of ex vivo analyses and the contribution of each component to bone remodeling are not clearly defined, and there is still much work to be done before these questions can be resolved. Taken together these results indicate multiple roles for gp130 cytokines in controlling osteoblasts and osteoclast function, including paracrine roles to mediate signaling between these two cell types.     

Functional characterization of W147A: a high-affinity interleukin-11 antagonist

IL-11 is a member of the gp130 family of cytokines, which signal via assembly of multisubunit receptor complexes containing at least one molecule of the transmembrane signaling receptor gp130. IL-11 forms a high-affinity complex, thereby inducing gp130-dependent signaling. Previous studies have identified three distinct receptor binding sites, I, II, and III, crucial for the binding of murine IL-11 (mIL-11) to both the IL-11R and gp130. In this study, we have further characterized the role of the mIL-11 site III mutant W147A. We show that W147A is a high-affinity specific antagonist of mIL-11-mediated signaling in gp130/IL-11R-transfected Ba/F3 cells. The antagonistic action of W147A is due to its ability to competitively disrupt multimeric gp130/IL-11R signaling complex formation. We also show that W147A inhibits IL-11-mediated signaling in primary human endometrial cells, thus demonstrating the potential utility of W147A in suppressing IL-11 responses in vivo.     

Lack of gp130 expression in hepatocytes promotes liver injury

BACKGROUND & AIMS: Interleukin 6 (IL-6) contributes via its signal transducer gp130 to the acute phase response (APR) in hepatocytes. Recent studies indicated that IL-6 is involved in the regulation of different pathophysiologic conditions of the liver. To define the IL-6-dependent intracellular pathways more specifically, we generated a hepatocyte-specific gp130 knockout mouse. METHODS: Hepatocyte-specific gp130-deficient mice were generated using the Cre-loxP system. Expression of the Cre recombinase was under the control of a hepatocyte-specific control element. Adult mice were challenged with IL-6, oncostatin M (OSM), and LPS. RESULTS: Cre expression started at day 10.5 postconception, and a complete deletion of gp130 in hepatocytes was found at day 14 during liver development. The adult liver of these mice showed no abnormalities; however, after IL-6 and OSM stimulation, gp130-dependent pathways (STAT3, APR gene expression) were completely blocked in the liver of these animals. Additionally, challenging hepatocyte-specific gp130 knockout animals with lipopolysaccharides (LPS) lead to an onset of acute liver injury with an increase of hepatocyte apoptosis associated with elevated tumor necrosis factor alpha (TNF-alpha) serum levels and reduced nuclear factor kappaB (NF-kappaB) activation in hepatocytes. CONCLUSIONS: Our findings demonstrate that gp130 is of minor relevance for embryonal development of hepatocytes. However, the molecule has an essential role in controlling acute phase gene expression and provides hepatocellular protection after LPS challenge.     

Acute obstructive cholangiopathy in interleukin-6 deficient mice: compensation by leukemia inhibitory factor (LIF) suggests importance of gp-130 signaling in the ductular reaction

AIM: The hypothesis that interleukin-6-IL-6/gp130 signaling is involved in liver and biliary epithelial cell (BEC) biology and growth control was tested by subjecting homozygous IL-6 deficient mice (IL-6-/-) and wild type (IL-6+/+) littermate controls to bile duct ligation (BDL). MATERIALS AND METHODS: During the first week after BDL, the two groups were compared with respect to routine liver injury tests, liver histology, BEC and hepatocyte DNA synthesis, together with the expression of mRNA and protein of IL-6 as well as related growth factors, and their receptors. RESULTS: During the first week after BDL, there was marked upregulation of IL-6 mRNA and protein in the IL-6+/+ mice only in the vicinity of the biliary tree; whereas, biliary/peri-biliary IL-6R, HGF and met mRNA and protein increased in both groups. IL-6, HGF mRNA and protein localized to periductal inflammatory cells and stellate cells, while met and IL-6R protein were upregulated in the BEC and, to a lesser extent, in hepatocytes. This occurred during maximal proliferation of the BEC. Despite the absence of IL-6 in the IL-6-/- mice, there were only mildly phenotypic differences between the two groups, and no differences in mortality. Compared to IL-6+/+ controls, IL-6-/- mice showed slightly less BEC proliferation, a trend toward more liver injury, and significantly higher total serum bilirubin (TB) levels, suggestive of impaired biliary tree integrity. These changes were associated with slightly less HGF mRNA and protein expression in the IL-6-/- mice, but the differences were not significant. Leukemia inhibitory factor (LIF), another gp-130 ligand, also showed marked peri-biliary upregulation after BDL in both groups, and also induced BEC DNA synthesis, in vitro. CONCLUSIONS: The mild phenotypical differences between IL-6+/+ and IL-6-/- mice in the acute response to BDL is most likely attributable to the redundancy of the gp-130 signaling system. However, the long-term response to BDL results in a distinct phenotype in the IL-6-/- mice, marked by a relentless rise in serum total bilirubin and an inability to maintain compensatory increase in liver mass.