Heme-induced persistent innate immune training (HIPI)

• Applicant: Professor Dr. Sebastian Weis
• Subject Area: Immunology ; Medical Microbiology and Mycology, Hygiene, Molecular Infection Biology
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 529734013

Trained immunity defines long-lasting adaptations of innate immunity based on transcriptional and epigenetic modifications of myeloid cells and their bone marrow progenitors with a resulting increased immune response to subsequent infection. It is a fundamental feature of innate immune cells. Presumably, TRIM prepares the innate immune system to respond to re-challenge by a given pathogen in a more efficient manner, both in terms of targeting that pathogen for destruction and limiting the extent of associated tissue damage. Innate immune cells however do not exclusively differentiate between foreign and self. Instead, they also react to the presence of host-derived molecules. Certain host-derived molecules can activate innate immunity and induce an inflammatory response regardless, whether they are triggered by infection or by sterile inflammation. These molecules have been designated as damage or danger-associated molecular patterns (DAMPs) or "alarmins". During infection, extracellular "labile" heme, released from damaged red blood or parenchymal cells and acts as prototypical alarmin. We have previously shown that labile heme is an inducer of trained immunity. We have provided experimental evidence that heme training depends on spleen tyrosine kinase signal transduction pathway acting upstream of c-Jun N-terminal kinases. It can promote resistance to sepsis and is associated with the expansion of self-renewing hematopoietic stem cells primed toward myelopoiesis and to the occurrence of a specific myeloid cell population. From this first set of data, several further fundamental questions, that shall be addressed want with this proposal. The project consists of three Work Packages (WP) that will be investigated partially in parallel due to the long-lasting nature of some of the experiments. In WP 1 we will further investigate the molecular regulation underlying peripheral heme-TRIM in vitro, identify whether a heme-binding receptor is responsible for training or alternatively how heme promotes SYK activation, directly. In WP 2 we will characterize the epigenetic heme "fingerprint”" in vitro and reveal how long does heme-TRIM lasts and if it can be reversed. In WP 3 we aim to proof that central heme training in vivo is permanently imprinted in hematopoietic stem cells. To investigate our hypothesis, we will use a combined strategy involving chemical inhibitors, gene editing, and pull-down assays. We will evaluate histone modifications and DANN methylation by means of a wide repertoire of molecular techniques such as Dot blot, Western blot and sequencing. We will perform animal experiments for up to one year and assess invasively and non-invasively the effects of heme-induced training. We will apply bone marrow transplantations to assess imprinting of heme-training in the different compartments. Our results we provide fundamental insights in the molecular regulation underlying heme-induced trained immunity and ist physiological relevance.

• DFG Programme: Research Grants
• International Connection: Australia, Brazil
• Cooperation Partners: Boris Novakovic, Ph.D.; Professor Dr. Marcelo Torres Bozza