SP10 Long-chain metabolites of α-tocopherol as regulators of adaptive stress responses

Project leaders: Stefan Lorkowski, Andreas Koberle

Background and previous work
Immune cells trigger degenerative inflammatory conditions by their massive oxidative burst and excessive release of inflammatory mediators in response to exogenous stimuli such as LPS. α-Tocopherol (α-TOH) is used to prevent inflammation-associated diseases although intervention studies in humans revealed contradictory results. Hepatic α-TOH catabolism results in intermediate formation of α-TOH long-chain metabolites (α-LCM) α-13'-OH and α-13'-COOH, which occur also in the circulation, as our group has shown. Almost nothing is known about the physiological actions of the α-LCM but our group provided convincing evidence that the α-LCM may comprise a new class of hormone-like regulatory metabolites. We synthesized the α-LCM and found that the α-LCM time- and dose-dependently block the inflammatory response and oxidative burst in LPS-stimulated macrophages, likely by inducing adaptive stress response pathways. Moreover, we identified the α-LCM as potent inhibitors of 5-lipoxygenase, a key enzyme for the biosynthesis of both pro-inflammatory and pro-resolving lipid mediators, which regulate immune cell survival, activity, differentiation and function in a hormetic and dynamic manner (unpublished data). Beside inflammation, α-LCM modulates lipid homeostasis, e.g. by inhibiting oxidised LDL uptake and lipid accumulation, due to reduced phagocytosis. Further preliminary studies show that the α-LCM induce DNA damage, but protect macrophages from lipotoxicity.

Specific aims and working programme
Our findings indicate that the α-LCM may comprise a new class of hormone-like regulatory metabolites that modulate adaptive stress responses in macrophages via pathways different from their metabolic precursor α-TOH. We propose that some of the actions of α-TOH in vivo are mediated, and are thus complicated, by the circulating α-LCM, in particular under conditions in which α-TOH is supplemented. We therefore want to explore the actions of the α-LCM (i) in vitro to get insights into the proposed adaptive stress response pathways and (ii) in mouse models of inflammatory conditions to perform proof-of-concept studies on the ability of the α-LCM to protect mice from inflammatory stress by modulating adaptive stress responses and to validate the molecular mechanisms of the α-LCM in vivo by measuring appropriate serum and tissue parameters. A particular focus will be on (i) pathways involved in the induction of tolerance (i.e. persistence response) or sensitization (i.e. resistance response), and (ii) the identification of involved lipid mediators. Depending on the results obtained until start of the project, knockout mice as well as cells obtained from these mice will be used to confirm the identified regulatory pathways involved in α-LCM-mediated adaptive stress response pathways. The choice of mouse models and assays for functional readouts depend on the results obtained until start of the project.