Similarities and interplay between senescent cells and macrophages

Abstract

Senescence is a cellular program that prevents the replication of old, damaged, or cancerous cells. Senescent cells become growth arrested and undergo changes in their morphology, chromatin organization, and metabolism, and produce a bioactive secretome. This secretome, the senescence-associated secretory phenotype (SASP), mediates many of the pathophysiological effects associated with senescent cells, for example, recruiting and activating immune cells such as macrophages. The relation between senescent cells and macrophages is intriguing: senescent cells recruit macrophages, can induce them to undergo senescence, or can influence their polarization. Senescent cells and macrophages share multiple phenotypic characteristics; both have a high secretory status, increased lysosome numbers, or the ability to activate the inflammasome. Senescent cells accumulate during aging and disease, and killing them results in widespread benefits. Here we discuss similarities between senescent cells and macrophages and interpret the latest developments in macrophage biology to understand the molecular mechanisms of cellular senescence. We describe evidence and effects of senescence in macrophages and speculate on the ontogeny of the senescent-like state in macrophages. Finally, we examine the macrophage-senescent cell interplay and its impact on macrophage effector functions during inflammatory conditions and in the tumor microenvironment.

Figure 1.

Macrophage maturation and senescence in non-immune cells share a multitude of cellular features. Mature macrophages (Mϕ) and senescent cells share multiple common phenotypes. Both cell types display phagocytosis, lysosomal expansion, and metabolic reprogramming; have a secretory phenotype; and are cell cycle–arrested. While macrophage maturation is a differentiation process driven by CSF-1 and other growth factors, senescence is a cellular response to stress signals such as oncogenic activation, replicative exhaustion, or drugs that cause DNA damage.