Senescent cells accumulate lipid droplets.

Senescent cells (SnCs) are growth-arrested yet remain metabolically active and undergo extensive reprogramming to support their survival and the Senescence-Associated Secretory Phenotype (SASP). SnCs undergo key metabolic changes, including increased glycolysis, altered mitochondrial function and dysregulated lipid metabolism. While these metabolic changes are increasingly recognized, a comprehensive understanding of how they contribute to the pathophysiological effects of SnCs is still lacking. Here, through metabolic profiling, we identified elevated levels of glycolytic metabolites in SnCs, which coincided with an increased presence of lipid metabolites, specifically triacylglycerol derivatives, the precursors of lipid droplets (LDs). We show that SnCs accumulate LDs in a classical primary human fibroblast model, and that senescent microglia upregulate LDs markers in a mouse model of Alzheimer's disease (AD), where they play a pathological role. Single-nucleus analysis of brains from AD patients further revealed an elevated levels of LDs markers in senescent brain cells, including microglia. Previous studies implicated both lipid droplet-containing microglia and senescent microglia in AD pathology. Our findings provide evidence that these may represent the same cell population, in which the co-occurrence of LDs accumulation and the senescent state jointly contribute to their disease-promoting properties.