Advancing Single-Cell Detection of Senescent Cells: Laboratory Methods and Clinical Applications

Cellular senescence (aging) is a physiological process that plays a role in tissue remodeling, wound healing, and embryogenesis. Prolonged senescence of cells can have detrimental effects and trigger a secretory phenotype (SASP, senescence-associated secretory phenotype), degenerative disorders, cancer, and age-related diseases. Suitable biomarkers and a range of different laboratory methods are used to investigate these complex relationships in vitro and in vivo. Since a universal biomarker for cell senescence has not yet been identified, numerous biomarkers are used to identify a senescent cell. The detection and quantification of these cells and their SASP provide the basis for targeted treatment of the patient. In parallel, single-cell analysis is also required for the quantitative assessment of the therapy result. Depending on the facilities of the laboratory performing the analysis, a wide range of analysis methods are available. In this review, we provide a general overview of accessible techniques such as immunohistochemistry using microscopy and automated flow cytometry and introduce new possibilities by modern techniques like mass spectrometry or a genetic method for the detection of senescent single cells. The focus here is the use of these techniques in routine laboratories. The classical laboratory analysis with the use of enzyme immunoassays, such as the measurement of products of the SASP (IL-6, IL-8), is not part of this work. This review discusses new ideas for the visualisation of clinical and laboratory patient data for gerontology. An outlook on potential and future optimization possibilities to improve or rejuvenate the senescence status of patients on a cellular and organ-specific level is discussed.