Wednesday, 24. June 2020, 14.15 p.m. 

Leibniz-HKI, Building A8, lecture halls Koch & Pasteur (1st floor)

Metabolic rewiring of macrophages during inflammation as studied by profiling metabolism

Prof. Dr. Karsten Hiller
(TU Braunschweig, Germany)

Current metabolomics techniques provide only a static view on metabolite amounts present inside or outside of living cells. Stable-isotope labeled tracers can be applied to obtain dynamic information on biochemical reaction networks. However, such methods like for example Metabolic Flux Analysis (MFA) only provide information on known compounds in a targeted manner and rely on extensive a priori knowledge. To shed light on yet unknown parts of the metabolism, we developed the Non-targeted Tracer Fate Detection (NTFD) methodology to detect all known and unknown compounds derived from a stable-isotope labeled tracer present in a GC/MS chromatogram. For every detected and labeled compound mass isotopomer distributions (MIDs) are determined. MIDs of known and unknown compounds are then used as input for the Mass Isotopolome Analyzer (MIA). Based on the non-targeted labeling data, this software reveals global flux changes in known and unknown parts of the metabolic network. Mass Isotopolome Analyzer Mode of Action Identification (MIAMI) is our latest software for the identification of metabolic modes of action based on a stable-isotope labeling experiment combined with a compound treatment.

We applied these tools to profile the metabolome of macrophages under inflammation and identified an intracellular and highly abundant metabolite: itaconic acid. By applying stable-isotope labeling experiments, we could demonstrate that this metabolite is produced in the tricarboxylic acid cycle from cis-aconitate by an enzyme encoded by immune response gene 1 (IRG1). Besides its antimicrobial function in the innate immune response, it turned out that itaconic acid is itself involved in metabolic regulation during inflammation. To get a better picture of the rearrangement of intracellular metabolic fluxes, we applied stable-isotope labeling and showed that a sustained flux of pyruvate through pyruvate dehydrogenase complex (PDH) is essential for macrophage polarization. A sustained and high pyruvate flux into the TCA cycle is required for the synthesis of itaconic acid and lipogenic citrate. By inhibiting the mitochondrial pyruvate transporter and thus decreasing pyruvate oxidation through PDH, we could modulate the immune response of the macrophages. This is an example on how metabolism itself is involved in cellular regulation and how detailed knowledge on such can offer therapeutic intervention points.