Background: A novel in vivo brain organoid-based model to dissect the molecular networks that orchestrate human microglia-specific phenotypes during post-injury CNS recovery.
Hypothesis: The human brain environment is instrumental to induce the program of human microglia-specific gene expression. We speculate that alterations in these context-dependent transcriptional networks can modulate their functional response to CNS injuries. This project will leverage a novel in vivo brain organoid-based model to identify molecular checkpoints in human microglia that could be targeted to program these cells towards more beneficial and tissue-supportive functions for promoting CNS recovery.
Strategy: Here, we will employ a novel organoid-based in vivo transplantation approach that allows to investigate the phenotypic and functional properties of human glial cells within a physiologically relevant, vascularized model of the human brain.
Summary
Glial cells, in particular astrocytes and microglia, serve as highly dynamic sensors of physiological and pathological events in the central nervous system (CNS). Despite the critical role of these cells in human brain pathologies, the molecular mechanisms that govern the diverse phenotypes of human glial cells are poorly understood. Previous research has shown that the human brain environment is instrumental to sustain and orchestrate human microglia identity. However, sophisticated human model systems that allow to investigate their tissue-specific functions are currently lacking. To overcome these limitations, we have developed a novel organoid-based in vivo approach that allows to study the phenotypic and functional properties of various glial cells within a physiologically relevant, vascularized organoid model of the human brain. Our preliminary data show that the human glial cells present in this system express tissue-specific markers and gain transcriptomic signatures that closely resemble their in vivocounterparts. More importantly, in vivo two-photon imaging revealed that the organoid-resident human microglial cells actively engage in surveilling the human brain environment and are capable to react to experimentally-induced injuries. This project will take advantage of this novel organoid-based in vivo model in order to dissect the molecular checkpoints that control human microglia phenotypes during post-injury CNS recovery. For this, we will set out to characterize the cellular and molecular changes that unfold in human microglial cells in response to an experimentally-induced traumatic injury in the human brain environment using unbiased high-dimensional molecular profiling, histology and in vivo microscopy (Aim ❶). Generating these organoid-based models from genetically-modified induced pluripotent stem cell (iPSC) lines will then allow us to evaluate if Triggering Receptor Expressed On Myeloid Cells 2 (TREM2), a key player in murine microglial biology, may act as a molecular checkpoint for controlling human microglia-specific injury responses (Aim ❷). Lastly, we shall functionally dissect the transcriptional networks that orchestrate the transition of human microglia phenotypes during post-injury CNS repair using a targeted CRISPR-based genetic perturbation screen (Aim 3). This will allow us to identify novel molecular checkpoints that could be targeted to tackle the negative aspects and enhance the positive actions of human microglia during brain lesion repair. We envision to contribute to an exceptionally collaborative transregional research initiative to reveal novel and human-specific checkpoints for targeted CNS recovery.
