New insights into the role of mitochondrial respiration in macrophage functions

Zusammenfassung

The interplay between the activation of innate immune cells, in particular macrophages, and their energy metabolism has gained considerable interest in the scientific community. Macrophages play critical roles in the innate immune response and their functional capabilities are strongly influenced by their metabolic status. However, the precise impact of the mitochondrial electron transport chain (ETC) on macrophages functions is an aspect that remains poorly understood. This thesis investigates the intricate interplay between ETC complexes, in particular complex I (CI) and complex II (CII), and macrophage responses. The innovative CRISPR/Cas9 HITI technique was used to create knockout (KO) models in the mouse macrophage cell line RAW 264.7, targeting the genes Ndufs4 (complex I) and Sdha, Sdhb (complex II). The absence of Ndufs4 impaired CI activity, thereby affecting macrophage metabolism with reduced basal respiration and ATP production, coupled with an increased mitochondrial ROS levels. Ndufs4−/− macrophages displayed an altered cytokine response with increased IL-6 and decreased IL-10 production, suggesting a shift towards a pro-inflammatory state, associated with enhanced phagocytic capacity. Sdha−/− and Sdhb−/− macrophages exhibited reduced succinate dehydrogenase (SDH) activity, severe impaired respiratory capacity and an altered cytokine response. Macrophages lacking these subunits showed reduced stabilization of HIF-1α and a reduced production of the pro-inflammatory cytokine IL-1β upon LPS activation. In addition, these subunits were found to be essential for the synthesis of IL-10 following LPS stimulation, a critical cytokine that acts to dampen the macrophage inflammatory response. The study also identified important changes in key signaling pathways, highlighting the role of redox balance in Stat3-IL-10 signaling. The results reveal a complex regulatory network in which mitochondrial complexes influence macrophage metabolism, signaling pathways and ultimately immune responses.