Induction of interleukin-6 by interferon alfa and its abrogation by a serine protease inhibitor in patients with chronic hepatitis C

Longitudinal relationships of cytokines, depression and anhedonia in depressed adolescents

BACKGROUND

Depression has been associated with low-grade elevation of plasma cytokines (e.g. interleukin-6, IL-6; tumor necrosis factor alpha, TNFα) in both cross-sectional and longitudinal studies in adults. Preclinical and clinical studies also suggest that IL-6 and TNFα elevation are associated with anhedonia. However, few studies have examined longitudinal relationships between cytokines and depression/anhedonia in clinically depressed samples, particularly adolescents.

METHODS

Thirty-six adolescents with a depressive disorder receiving standard-of-care community treatment were assessed at a baseline and a follow-up timepoint. Self-report and clinical measures of depression and anhedonia, along with plasma IL-6 and TNFα levels, were obtained at both timepoints. Baseline cytokine measures were examined in association with baseline and follow-up clinical measures. On an exploratory basis, change in clinical measures over time was examined in relation to change in cytokine levels over time.

RESULTS

Higher baseline TNFα levels predicted higher follow-up depression severity after approximately four months (controlling for baseline depression). Higher baseline TNFα levels also associated positively with baseline anhedonia and predicted higher anhedonia at follow-up (controlling for baseline anhedonia). No association was found between change in clinical measures and change in cytokine levels over time.

CONCLUSIONS

Among adolescents receiving standard-of-care community treatment for depression, higher levels of TNFα predicted greater depressive symptoms at 4-month follow-up, suggesting this cytokine may be used to help identify patients in need of more intensive treatment. Elevated TNFα levels were also associated with concurrent and future anhedonia symptoms, suggesting a specific mechanism in which TNFα affects depression trajectories. Future studies should examine the relationships between cytokine levels and depression/anhedonia symptoms at multiple timepoints in larger cohorts of depressed adolescents.

IRF9 and unphosphorylated STAT2 cooperate with NF-κB to drive IL6 expression

We describe unexpected cooperation between two cytokines that are important in regulating the growth of cancers, namely, type I interferons (IFNs) and interleukin 6 (IL6). It is well established that IL6 is vital for the ability of many tumor types to prosper, and the work in the current paper reveals that the signaling pathway driven by IFN, which is also evident in many cancers, increases the expression of IL6 through a direct effect on the IL6 gene. The findings may help to identify new antitumor targets for therapy.

In response to IFNβ, the IL6 gene is activated, modestly at early times by ISGF3 (IRF9 plus tyrosine-phosphorylated STATs 1 and 2), and strongly at late times by U-ISGF3 (IRF9 plus U-STATs 1 and 2, lacking tyrosine phosphorylation). A classical IFN-stimulated response element (ISRE) at −1,513 to −1,526 in the human IL6 promoter is required. Pretreating cells with IFNβ or increasing the expression of U-STAT2 and IRF9 exogenously greatly enhances IL6 expression in response to the classical NF-κB activators IL1, TNF, and LPS. U-STAT2 binds tightly to IRF9, the DNA binding subunit of ISGF3, and also to the p65 subunit of NF-κB. Therefore, as shown by ChIP analyses, U-STAT2 can bridge the ISRE and κB elements in the IL6 promoter. In some cancer cells, the protumorigenic activation of STAT3 will be enhanced by the increased synthesis of IL6 that is facilitated by high expression of U-STAT2 and IRF9.

IFNα enhances the production of IL-6 by human neutrophils activated via TLR8

Recently, we reported that human neutrophils produce biologically active amounts of IL-6 when incubated with agonists activating TLR8, a receptor recognizing viral single strand RNA. In this study, we demonstrate that IFNα, a cytokine that modulates the early innate immune responses toward viral and bacterial infections, potently enhances the production of IL-6 in neutrophils stimulated with R848, a TLR8 agonist. We also show that such an effect is not caused by an IFNα-dependent induction of TLR7 and its consequent co-activation with TLR8 in response to R848, but, rather, it is substantially mediated by an increased production and release of endogenous TNFα. The latter cytokine, in an autocrine manner, leads to an augmented synthesis of the IkBζ co-activator and an enhanced recruitment of the C/EBPβ transcription factor to the IL-6 promoter. Moreover, we show that neutrophils from SLE patients with active disease state, hence displaying an IFN-induced gene expression signature, produce increased amounts of both IL-6 and TNFα in response to R848 as compared to healthy donors. Altogether, data uncover novel effects that type I IFN exerts in TLR8-activated neutrophils, which therefore enlarge our knowledge on the various biological actions which type I IFN orchestrates during infectious and autoimmune diseases.

Interdependent and independent roles of type I interferons and IL-6 in innate immune, neuroinflammatory and sickness behaviour responses to systemic poly I:C

Type I interferons (IFN-I) are expressed in the brain during many inflammatory and neurodegenerative conditions and have multiple effects on CNS function. IFN-I is readily induced in the brain by systemic administration of the viral mimetic, poly I:C (synthetic double-stranded RNA). We hypothesised that IFN-I contributes to systemically administered poly I:C-induced sickness behaviour, metabolic and neuroinflammatory changes. IFN-I receptor 1 deficient mice (IFNAR1(-/-)) displayed significantly attenuated poly I:C-induced hypothermia, hypoactivity and weight loss compared to WT C57BL/6 mice. This amelioration of sickness was associated with equivalent IL-1β and TNF-α responses but much reduced IL-6 responses in plasma, hypothalamus and hippocampus of IFNAR1(-/-) mice. IFN-β injection induced trivial IL-6 production and limited behavioural change and the poly I:C-induced IFN-β response did not preceed, and would not appear to mediate, IL-6 induction. Rather, IFNAR1(-/-) mice lack basal IFN-I activity, have lower STAT1 levels and show significantly lower levels of several inflammatory transcripts, including stat1. Basal IFN-I activity appears to play a facilitatory role in the full expression of the IL-6 response and activation of the tryptophan-kynurenine metabolism pathway. The deficient IL-6 response in IFNAR1(-/-) mice partially explains the observed incomplete sickness behaviour response. Reconstitution of circulating IL-6 revealed that the role of IFNAR in burrowing activity is mediated via IL-6, while IFN-I and IL-6 have additive effects on hypoactivity, but the role of IFN-I in anorexia is independent of IL-6. Hence, we have demonstrated both interdependent and independent roles for IFN-I and IL-6 in systemic inflammation-induced changes in brain function.

The development and compensation of biliary cirrhosis in interleukin-6-deficient mice

In an effort to understand the role of IL-6/gp130 signaling in chronic liver injury, IL-6 deficient (IL-6(-/-)) and wild-type control (IL-6(+/+)) mice were subjected to bile duct ligation (BDL) for 12 weeks. This maneuver causes chronic biomechanical stress and liver injury, fueling sustained biliary epithelial and hepatocyte proliferation. By 12 weeks after BDL, IL-6(-/-) mice develop significantly higher total serum bilirubin levels (23.2 +/- 2.3 versus 14.9 +/- 2.1 mg/dl, P < 0.0001; delta bilirubin subfraction 16.7 +/- 4.0% versus 9.2 +/- 1.8%; P < 0.002), and the majority (15/18) show "black" gallbladder bile, compared to IL-6(+/+) mice (5/16; P < 0.003). The IL-6(-/-) mice also cannot sustain the compensatory liver mass increase commonly seen with chronic obstructive cholangiopathy, because of less hepatocyte proliferation, despite a rate of hepatocyte apoptosis similar to that of IL-6(+/+) mice. Moreover, IL-6(-/-) mice show a more advanced stage of biliary fibrosis and a higher mortality rate than the IL-6(+/+) controls (51% versus 23%; P < 0.02). These phenotypic changes in the IL-6(-/-) mice are associated with decreased expression and phosphorylation of gp130 and the transcription factor STAT3, compared to IL-6(+/+) mice. Daily treatment with exogenous recombinant IL-6 for 3-6 weeks starting at 6 weeks after BDL significantly lowers the serum total bilirubin in both groups. In the IL-6(-/-) mice, exogenous IL-6 treatment also increases the level of gp130 protein expression and completely reverses the loss of liver mass by increasing the hepatocyte proliferation. In conclusion, IL-6 appears to contribute to biliary tree integrity and maintenance of hepatocyte mass during chronic injury.

The development and compensation of biliary cirrhosis in interleukin-6-deficient mice

In an effort to understand the role of IL-6/gp130 signaling in chronic liver injury, IL-6 deficient (IL-6(-/-)) and wild-type control (IL-6(+/+)) mice were subjected to bile duct ligation (BDL) for 12 weeks. This maneuver causes chronic biomechanical stress and liver injury, fueling sustained biliary epithelial and hepatocyte proliferation. By 12 weeks after BDL, IL-6(-/-) mice develop significantly higher total serum bilirubin levels (23.2 +/- 2.3 versus 14.9 +/- 2.1 mg/dl, P < 0.0001; delta bilirubin subfraction 16.7 +/- 4.0% versus 9.2 +/- 1.8%; P < 0.002), and the majority (15/18) show "black" gallbladder bile, compared to IL-6(+/+) mice (5/16; P < 0.003). The IL-6(-/-) mice also cannot sustain the compensatory liver mass increase commonly seen with chronic obstructive cholangiopathy, because of less hepatocyte proliferation, despite a rate of hepatocyte apoptosis similar to that of IL-6(+/+) mice. Moreover, IL-6(-/-) mice show a more advanced stage of biliary fibrosis and a higher mortality rate than the IL-6(+/+) controls (51% versus 23%; P < 0.02). These phenotypic changes in the IL-6(-/-) mice are associated with decreased expression and phosphorylation of gp130 and the transcription factor STAT3, compared to IL-6(+/+) mice. Daily treatment with exogenous recombinant IL-6 for 3-6 weeks starting at 6 weeks after BDL significantly lowers the serum total bilirubin in both groups. In the IL-6(-/-) mice, exogenous IL-6 treatment also increases the level of gp130 protein expression and completely reverses the loss of liver mass by increasing the hepatocyte proliferation. In conclusion, IL-6 appears to contribute to biliary tree integrity and maintenance of hepatocyte mass during chronic injury.