Polycomb Repressive Complexes and Chromatin Architecture in Cellular Aging of the Brain - Abstract Aging is accompanied by complex, cell type-specific epigenetic alterations, yet the impact of these changes on the dysregulation of cellular transcriptomes and functional decline remains poorly understood. Among key epigenetic modulators, Polycomb Repressive Complex 1 (PRC1) maintains gene silencing by establishing a repressive chromatin environment. Previous studies demonstrated that PRC1 complexes inhibit cellular senescence, indicating a potential role of PRC1 in aging. Mechanistically, PRC1 antagonizes senescence by repressing its target gene, CDKN2A, which encodes the CDK inhibitors p16Ink4a and p14Arf. Later research revealed reduced expression of Pcgf4, a key component of PRC1, in the aged brains of both humans and mice. Mice with a heterozygous deletion of Pcgf4 develop normally, but they show cognitive deficits and neurodegeneration during aging. Although PRC1 loss strongly correlates with brain aging, the extent to which PRC1 exerts cell type-specific effects is not fully understood. A significant barrier to understanding the role of PRC1 in aging is the cellular heterogeneity within brain tissues, which complicates in vivo studies of protein- protein and protein-chromatin interactions. To address this challenge, we have recently developed a biotinylation-mediated lineage-specific capture (BLINC) technique, enabling us to define PRC1 composition and function in defined brain cell types. Our overarching goal is to elucidate how PRC1 regulates chromatin environments and maintains cellular transcriptomes during brain aging. We will address this through two specific aims. Aim 1: Using BLINC, we will identify PRC1 composition and chromatin modifications across various brain cell types in young and aged mice. Leveraging BLINC with Affinity purification, mass spectrometry, and deep sequencing, we will reveal how PRC1-mediated chromatin changes contribute to age-related alterations in gene regulation. Aim 2: We will examine the functional consequences of PRC1 loss in glutamatergic cortical neurons using conditional knockout models. By assessing chromatin and transcriptomic changes in these neurons, we aim to uncover mechanisms by which PRC1 prevents age-associated shifts toward a pro-senescence state. By combining BLINC with proteomic and genomic analysis, our study will provide novel insights into PRC1 regulation on chromatin dynamics during aging, which may lead to novel therapeutic targets for age-related conditions.
