Exploring the fundamental cellular mechanisms driving cellular senescence in macrophages

PROJECT SUMMARY Cellular senescence is a complex cellular state characterized by cell cycle arrest resulting from DNA damage or other cellular stressors. Senescent cells play key roles in multiple biological processes, including development, tissue homeostasis, and acting as an anti-cancer mechanism. Moreover, senescent cells have been causally linked to sterile inflammation and disease due to their ability to secrete inflammatory factors known as the Senescence Associated Secretory Phenotype (SASP). Interestingly, macrophages, key innate immune cells, are emerging as a key source of senescent cells in multiple settings including tissue regeneration, wound healing, cancer, atherosclerosis, Alzheimer’s, and in the aging process. However, much is not known about the basic biology of macrophage senescence, including what genes, and signaling pathways regulate the senescent state, what biomarkers accurately define them, and the underlying biology regulating their functions including the SASP. Therefore, this proposal outlines our research goals for the next five years, which revolve around gaining a deeper understanding of the cellular and molecular mechanisms underlying senescent macrophage biology. This understanding is not only crucial for unraveling the complexities of their functions but also for comprehending how they impact biological processes in normal tissue homeostasis, and disease states. Our research project intends to delve deeper into the molecular mechanisms that govern cell cycle arrest, focusing on the role of the tumor suppressors Cdkn1a (p21) and Cdkn2a (p16), as well as other cell cycle arrest genes. To achieve this, we will employ omics-based methodologies and utilize CRISPR-Cas9 technology to uncover the complex roles of these cell cycle arrest genes in regulating macrophage senescence, SASP expression, and metabolism. Additionally, we plan to investigate the non-canonical roles of the P53-p21-CCND2 pathway in metabolism, particularly its impact on mitochondrial functions and metabolic flux in senescent macrophages. An integral part of our research will involve exploring inflammatory and metabolic pathways, such as the cGAS- STING, mTOR, and NF-κB signaling pathways, that regulate macrophage senescence and SASP production. This will include an assessment of the role of the NADase CD38 in modulating NAD+ metabolism in senescent macrophages and their influence on other cell types. Finally, we will investigate the impact of genetic variation on senescent macrophage biology by utilizing The Hybrid Mouse Diversity Panel. This will enable us to assess senescent macrophage phenotypes derived from various strains of inbred mice and determine the genetic determinants that influence senescent macrophage biology. In summary, our comprehensive research strategy is designed to enhance our understanding of cellular senescence in macrophages and its broader impacts on multiple biological areas, including general homeostasis and disease. Additionally, this research aims to pave the way for developing targeted therapies for diseases impacted by cellular senescence.