Role for the Itaconate/Nrf2 axis in metabolic and epigenetic reprogramming of neonatal macrophages

The immune system in neonates differs quantitatively and qualitatively from adults. Neonates dispose mechanism that limit innate immune responsiveness and allow colonization with commensal bacteria. Macrophages have a central role in the immune defense as they clear pathogens but also instruct other immune cells. Moreover macrophages are very plastic and diverse; they can adopt pro- and anti- inflammatory phenotypes in response to environmental signals. There is growing evidence that mitochondrial respiration, reactive oxygen species (ROS)
production and metabolic pathways determine immune cell functions and especially macrophage phenotypes. Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) emerges to play a very central role within that context. Activated by
the immunometabolite itaconate during macrophage activation, Nrf2 exerts direct anti-inflammatory functions by suppressing transcription of inflammatory cytokines, but also regulates redox metabolism of the cell and modulates
metabolic pathways. Several studies, including our own, show that neonatal monocytes and macrophages reveal a completely altered phenotype that is characterized by a reduced production of inflammatory cytokines and reduced
glycolysis and lactate production compared to adult cells. In addition, we observed a high expression of Nrf2 in neonatal monocytes and we recently showed that Nrf2 regulates tolerance in LPS induced sepsis in vivo. Key
questions arise from these findings: Is the neonatal tolerance of benefit or even harmful for the newborn in case of infection? Which molecular and metabolic mechanisms account for these drastic altered innate immune responses? To approach these questions, we will analyze central components of the neonatal immune system, by analyzing metabolic, transcriptional and epigenetic mechanism in neonatal macrophages with a focus on the role of Nrf2. To this end we will perform metabolic profiling of neonatal macrophages with Nrf2 overexpression or knockdown by means of metabolic flux and metabolite analysis. We will furthermore perform targeted and untargeted epigenetic analysis by means of global DNA methylation analysis, assess genome-wide-chromatin accessibility by ATAC sequencing and determine Histone acetylation/methylation analysis by chromatin immunoprecipitation.
Functional relevance of so identified and Nrf2 dependent signaling pathways will be confirmed by experimental neonatal sepsis model with conditional knock-out mouse strains. This proposal will therefore provide a comprehensive analysis of molecular and metabolic regulations that determine the phenotype of neonatal
macrophages.