Role of neutrophil granulocytes after stroke: mechanisms of brain entry, neutrophil-induced disturbed brain recovery and remodeling

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Polymorphonuclear neutrophil granulocytes (PMN) have been found in many instances to play an important role in the pathophysiology of ischemic stroke, one of the major causes of morbidity and mortality in industrialized countries. In this context we could demonstrate by means of antibody mediated blockade that PMN use the integrin VLA-4 for adhesion to the inflamed blood brain barrier and entry into ischemic brain. Here they are recognized by local microglia, which is able to phagocytose the cells thereby potentially ameliorating the otherwise severely neurotoxic action of PMN within the brain parenchyma. However, due to the lack of suitable tools we could not yet study, how stroke develops when PMN are permanently lacking VLA 4. Furthermore, we could not clarify the pathophysiological mechanisms by which PMN exert their neurotoxic functions. To change this, we have developed a novel mouse model that now allows PMN-selective genetic manipulation and fluorescent labelling. Using this mouse model we aim at clarifying the following questions: (1) How do PMN influence microvascular patency, microvascular remodeling and angiogenesis? How are microvascular branching and arborisation altered? Which are the consequences for regional cerebral blood flow? (2) How do brain-invading PMN interact with brain neurons? How do they alter neuronal arborisation and viability? How is this process modified by brain-resident microglia? (3) Which is the role of neutrophil extracellular traps (NETs) in PMN-associated brain injury? How does inhibition of NET formation influence microvascular patency/remodeling, neuronal degeneration and neuronal plasticity? (4) How do the molecular signatures of brain-infiltrating PMN differ from PMN in the periphery? Can these molecular signatures be experimentally targeted in order to restore neuronal survival? To study these questions, we will employ advanced microscopical imaging including intravital 2 photon and lightsheet microscopy of cleared brains. In addition, we will make use of unique and complex animal models. With this study we will get a completely new understanding on the PMN-mediated effects of stroke which hopefully will pave the way to new treatment options that are needed urgently.