Role of brain resident immune cells for the formation of traumatic brain edema

• Applicant: Dr. Susanne Schwarzmaier
• Subject Area: Molecular and Cellular Neurology and Neuropathology
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 574025649

Background: Brain edema remains a key prognostic factor for many acute neurological disorders, including traumatic brain injury (TBI). There are two major forms, i.e. vasogenic brain edema (VBE) and cytotoxic brain edema (CBE). These are based on water extravasation via a compromised blood brain barrier (BBB) and astrocytic cell swelling, respectively. Despite decades of research, detailed knowledge about the temporal and spatial profile as well as the cellular and molecular mechanisms of brain edema formation after TBI is still missing. The main reason for this knowledge gap is that the methods to assess brain edema formation have severe limitations, such as a limited temporal and/or spatial resolution and/or the lack of specify regarding the type of edema. Therefore, we ran a research program to develop methods for the investigation of brain edema formation. Methods: We developed two specific in-vivo 2-photon microscopy (2PM) approaches to investigate VBE and CBE formation on the cellular level in vivo. VBE is characterized by dynamic imaging of the extravasation of a fluorescent tracer across the BBB. To investigate CBE, astrocytes are specifically labelled in transgenic animals and cell volume, movement and interaction with blood vessels are analyzed in vivo. This approach was accomplished by a setup using “free-water” diffusion magnet resonance imaging (FWI). FWI is able to differentiate freely moving water, i.e. water in the extracellular space, from not freely moving water, that is mostly intracellular, water with two tensors. This allows the investigation of brain edema formation in the whole brain, longitudinally and noninvasively, and with a satisfactory spatial resolution. To investigate the mechanisms on a cellular and molecular level, we established novel protocols to perform cerebral vessel isolation and single nucleus RNA sequencing. These techniques will be used to investigate the mechanisms causing edema formation after TBI. Hypothesis: TBI is followed by a massive acute, subacute, and chronic inflammatory response. Inflammatory cells resident within the brain (perivascular macrophages and microglia) may be involved in the formation of acute and chronic brain edema after TBI. Objectives: The project has two objectives: A) To characterize the exact temporal and spatial profile of vasogenic and cytotoxic brain edema formation after TBI in vivo by using 2PM and FWI. B) To investigate whether brain resident innate immune cells (perivascular macrophages and microglia) are involved in the formation of brain edema after TBI by in vivo microscopy, single nucleus RNA sequencing, and immunohistochemistry. Perspective: The study will generate clinically highly relevant data. It will be clarified when, where and which type of edema formation occurs following TBI. The underlying inflammatory mechanisms will be investigated. This information is essential for the development of specific therapeutic targets for VBE and CBE.

• DFG Programme: Research Grants