Myeloid cell diversity and ischemic stroke

• Applicant: Professorin Dr. Karen Gertz
• Subject Area: Molecular and Cellular Neurology and Neuropathology ; Clinical Neurology; Neurosurgery and Neuroradiology ; Molecular Biology and Physiology of Neurons and Glial Cells
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 500215821

The 'translational roadblock' in stroke medicine may in part relate to the fact that the interplay of different pathomechanisms is far more complex than previously thought. In particular, many inflammatory mechanisms, which are involved in cellular damage during the early phase of brain ischemia, may be conducive to recovery and regeneration at later stages. Upon induction of stroke, dynamic changes of cell-to-cell interactions involve microglia, the resident immune cells in the central nervous system (CNS). Microglia become activated after injury, which entails increased phagocytic ability, acquisition of an amoeboid morphology and/or increased proliferative rates. In addition, monocyte-derived, blood born macrophages (Mo/MΦ) populate the infarct, but are virtually impossible to distinguish from resident microglia based on morphological criteria alone. Importantly, modulation of these different myeloid cell types clearly influences acute and long-term post-stroke outcomes. However, the exact mechanisms shaping the cerebral microenvironment after brain ischemia and modulating myeloid cell interactions, proliferation and function are not well defined. Furthermore, information on human stroke, particularly regarding myeloid cell properties, is sparse. In this project, we therefore aim to unravel the diversity of myeloid cell subsets, particularly of microglia and Mo/MΦ in the pathogenesis of ischemic stroke. We will employ two multicolor reporter mouse strains, the so-called 'Microfetti' (Cx3cr1creER/+ R26RConfetti/+) mouse and the newly developed Ccr2creERT2/+ R26RConfetti/+ mouse, which we have termed 'Monofetti'. We will characterize myeloid cell turnover in terms of clonal expansion, cell egress, and apoptosis. Using the monoclonal 'Triggering receptor expressed on myeloid cells' (TREM)2 antibody, 4D9 or isotype control, we will test the effects of TREM2 agonism on microglia proliferation, function and stroke outcome employing complex endpoint analyses including histological and electrophysiological evaluation as well as behavioral tests. Potential mechanisms will be assessed using complementary in vitro and ex vivo approaches, including different cell culture and molecular biology techniques. In addition, using TREM1 decoy peptide LP17 and control peptide, we will modulate Mo/MΦ properties and interfere with Mo/MΦ invasion. Finally, in a translational approach, we will apply imaging mass cytometry (IMC), a novel spatial technology, to autopsy specimens from human stroke victims and compare the results to mouse IMC. Here, the local cues, which modulate cell properties and myeloid cell interactions to other CNS cells including neurons, astrocytes and oligodendrocytes after stroke will be elucidated.

• DFG Programme: Priority Programmes
• Subproject of: SPP 2395: Local and peripheral drivers of microglial diversity and function
• Co-Investigator: Professor Dr. Matthias Endres