Deciphering the History and Diversity of White and Grey Matter Microglia in Neurodegeneration and Aging

• Applicants: Professor Dr. Özgün Gökçe; Professor Dr. Marco Prinz; Professor Dr. Mikael Jakob Simons
• Subject Area: Molecular Biology and Physiology of Neurons and Glial Cells
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 458957955

Age-related changes in brain structure are a major risk factor for several neurological diseases. The specific response of microglia to aging and neurodegeneration associated damage is an outstanding and essential question with clinical implications. We hypothesize that myelin degeneration occurring during normal aging drives microglia reactivity, specifically in the white matter. This hypothesis is based on myelin debris's unique properties, consisting of lipid-rich, tightly compacted, and therefore difficult to digest membrane stacks, which may challenge microglia phagocytic function with time. In preliminary studies using single-cell RNA sequencing (scRNAseq) and imaging, we identified white matter associated microglia (WAM), which are transcriptionally distinct from the disease-associated microglia (DAM). Our preliminary work shows that the secreted apolipoprotein, APOE, which has critical roles in lipid metabolism and immunity, is required for WAM and DAM formation in Alzheimer’s Disease (AD) models. APOE genotype is the strongest genetic risk factor for late-onset AD with apoE4 increasing risk and apoE2 decreasing risk. We hypothesize that APOE4 allele is exacerbating the brain’s innate immune responses in the setting of aging and AD to worsen injury. Thus, characterizing microglia pathways and the effects of APOE alleles on these pathways have important implications for the design of microglia-based therapies. Here, we propose to study both mouse and human microglia to identify evolutionary conserved and divergent microglial programs. First, we will improve the definition of microglial states in mouse models using a "multiome Assay", which combines Transposase Accessible Chromatin (ATAC-seq), and scRNAseq (drop-seq) on the same cell. The bioinformatic integration of these multi-omic datasets will reveal molecular mechanisms that maintain microglial identity in health and disease. We will then use tools based on scRNAseq and CRISPR-Cas9 to provide a lineage history and population dynamics of microglia in white and grey matter. To provide more spatial context to the epigenetic and fate mapping, we will use Spatial Transcriptomics (ST), which will identify gene-co expression networks linked with microglia heterogeneity. Finally, we propose to use the "multiome Assay" on live microglia obtained from epilepsy surgeries. We aim to integrate epigenetic and transcriptomic characterization of human microglia to provide lineage history, epigenetic and transcriptomic diversity of human microglia without the limitations of snRNAseq. In summary, we propose to characterize transcriptional, epigenetic programs, and lineage history of human and mouse microglia. The outcomes of this research would be applicable for understanding the etiology and the development of age-related dementias, including AD.

• DFG Programme: Research Grants