Date Published: July 24, 2017
Publisher: Public Library of Science
Author(s): Johannes J. Kovarik, Elisabeth Kernbauer, Markus A. Hölzl, Johannes Hofer, Guido A. Gualdoni, Klaus G. Schmetterer, Fitore Miftari, Yury Sobanov, Anastasia Meshcheryakova, Diana Mechtcheriakova, Nadine Witzeneder, Georg Greiner, Anna Ohradanova-Repic, Petra Waidhofer-Söllner, Marcus D. Säemann, Thomas Decker, Gerhard J. Zlabinger, Vladimir Trajkovic.
A crucial role of cell metabolism in immune cell differentiation and function has been recently established. Growing evidence indicates that metabolic processes impact both, innate and adaptive immunity. Since a down-stream integrator of metabolic alterations, mammalian target of rapamycin (mTOR), is responsible for controlling the balance between pro-inflammatory interleukin (IL)-12 and anti-inflammatory IL-10, we investigated the effect of upstream interference using metabolic modulators on the production of pro- and anti-inflammatory cytokines. Cytokine release and protein expression in human and murine myeloid cells was assessed after toll-like receptor (TLR)-activation and glucose-deprivation or co-treatment with 5′-adenosine monophosphate (AMP)-activated protein kinase (AMPK) activators. Additionally, the impact of metabolic interference was analysed in an in-vivo mouse model. Glucose-deprivation by 2-deoxy-D-glucose (2-DG) increased the production of IL-12p40 and IL-23p19 in monocytes, but dose-dependently inhibited the release of anti-inflammatory IL-10. Similar effects have been observed using pharmacological AMPK activation. Consistently, an inhibition of the tuberous sclerosis complex-mTOR pathway was observed. In line with our in vitro observations, glycolysis inhibition with 2-DG showed significantly reduced bacterial burden in a Th2-prone Listeria monocytogenes mouse infection model. In conclusion, we showed that fasting metabolism modulates the IL-12/IL-10 cytokine balance, establishing novel targets for metabolism-based immune-modulation.
Considerable progress has been made in understanding the complex interdependency of immune cell function and metabolism. Depending on the stage of differentiation both, lymphocytic and myeloid cells seem to use diverse metabolic pathways to cope with varying bioenergy demands during their lifecycle. Alteration of cellular metabolism has been shown to impact particular immune cell functions, such as cell trafficking and cytokine secretion. This implies a mutual dependency of metabolism and immunity [1, 2]. Consequently, shifts in immune cell metabolism may be associated with distinct pathologies. However, this can also be envisaged as a tool to redirect unfavourable immune reactivity under pathologic conditions [3, 4]. Among other adaptive mechanisms, inflammation has evolved to maintain physiological homeostasis after microbial challenge of the host. The controlled induction of both pro- and anti-inflammatory mediators such as interleukin (IL)-12, IL-23, IL-6, tumor necrosis factor (TNF)-α, and IL-10 by myeloid cells plays a key role in effective immunity [5, 6], so that a well-coordinated inflammatory response can facilitate the resolution of infections. However, this process can also be detrimental if dysregulated .
The mTOR pathway has been identified as a crucial regulator of TLR signaling in human monocytes, where direct inhibition of mTOR in LPS-activated human monocytes stimulates the production of IL-12 and IL-23 while inhibiting IL-10 . We here evaluated the role of upstream interference through induction of a fasting metabolism by glucoprivation or specific AMPK activation in this process. To our knowledge, this is the first report where, similar to rapamycin, 2-DG efficiently potentiated the production of IL-12p40 and IL-23p19 in monocytes, while inhibiting anti-inflammatory IL-10. 2-DG, a glucose analogue, is phosphorylated by hexokinase to form 2-DG-6-phosphate that cannot be further metabolized and then acts as a competitive hexokinase inhibitor, thereby reducing glucose utilization and leading to impairment of cellular energy generation and also AMPK activation [36, 37] Interestingly, in a macrophage polarization model we were able to demonstrate that 2-DG was able inhibit the generation of the heterodimer IL-12p70 while showing effects similar to the monocytic system on the generation of the other cytokines tested after M1 polarization. Expression of surface marker expression characteristic for M1 and M2 polarization was inhibited which indicates that the effect of 2-DG does not seem to be due to a general effect on macrophage polarization but rather be selective on the induction of particular cytokines.