Utilizing lineage tracing and functional research techniques for cellular senescence in vivo to reveal specific functions of senescent cells in different cell types

Supported by the National Natural Science Foundation of China (Grant Nos. 82088101, and 91849202), the research team led by Professor Bin Zhou from the Center for Excellence in Molecular Cell Science, Chinese Academy of Sciences, has made progress in lineage tracing and functional research on cellular senescence. This study, entitled "Identifying specific functional roles for senescence across cell types" was published online in Cell on October 4^th, 2024. The paper link is: https://www.cell.com/cell/fulltext/S0092-8674(24)01069-9.

Cellular senescence plays a crucial role in various pathological and physiological processes, including embryonic development, cancer, aging, and other diseases. Precisely targeting senescent cells in vivo is essential for revealing their roles in aging and various pathological conditions. Currently, cyclin-dependent kinase inhibitor p16^Ink4a is one of most commonly used  markers for studying cellular senescence. Many studies have employed activation of the p16^Ink4a promoter to identify senescent cells in vivo,  leading to the creation of several genetic mouse models based on p16^Ink4a. However, these genetic strategies are non-specific, as they target all senescent cells, making it difficult to delineate the cell fate and pathophysiological roles of senescent cells in specific cell types.

The researchers constructed a reporter mouse line, p16-tdT, and by detecting the expression of tdT in various organs at different ages, they found that the types of tdT⁺ cells varied across organs, with their proportions significantly increasing with age. Additionally, these tdT⁺ cells exhibit elevated senescence-associated β-galactosidase activity, increased expression of senescence-associated secretory phenotype factors, and reduced proliferative capacity, demonstrating that p16^Ink4a+ cells exhibit senescent phenotypes. The research team created a new genetic system, Sn-cTracer (Senescent cells-Creinduced-tracer), which allows for continuous tracking and selective genetic elimination of p16^Ink4a+ cells in a cell type-specific manner. Their findings revealed that removal of p16^Ink4a+ endothelial cells resulted in a profibrotic liver environment, marked by an accumulation of fibroblasts and mesenchymal cells, leading to worsened liver fibrosis. Furthermore, the researchers also manipulated gene expression in p16^Ink4a+ cells in a cell type-specific manner, overexpressing vascular endothelial growth factor receptor 2 in p16^Ink4a+ endothelial cells in the liver fibrosis model. This reprogramming enhanced the proliferative and angiogenic capacities of p16^Ink4a+ endothelial cells, reduced the expression of senescence-associated secretory factors, , and significantly alleviated liver fibrosis (Figure).

This study established lineage tracing and functional research techniques for cellular senescence in vivo based on the dual homologous recombinase system. It systematically investigated the fate and specific roles of senescent cells of different types during liver injury and repair. This study not only open new research directions and a theoretical foundation for clinical treatment of liver diseases, but also introduce innovative technical approaches for aging and regenerative medicine research.