The pro-inflammatory phenotype of the human non-classical monocyte subset is attributed to senescence

Abstract

Human primary monocytes comprise a heterogeneous population that can be classified into three subsets based on CD14 and CD16 expression: classical (CD14high/CD16−), intermediate (CD14high/CD16+), and non-classical (CD14low/CD16+). The non-classical monocytes are the most pro-inflammatory in response to TLR stimulation in vitro, yet they express a remarkably high basal level of miR-146a, a microRNA known to negatively regulate the TLR pathway. This concurrence of a pro-inflammatory status and a high miR-146a level has been associated with cellular senescence in other cell types. Hence, we assessed the three monocyte subsets for evidence of senescence, including proliferative status, telomere length, cellular ROS levels, and mitochondrial membrane potential. Indeed, the non-classical subset exhibited the clearest hallmarks of senescence, followed by the intermediate and then the classical subset. In addition, the non-classical subset secreted pro-inflammatory cytokines basally in vitro. The highly pro-inflammatory nature of the non-classical monocytes could be a manifestation of the senescence-associated secretory phenotype (SASP), likely induced by a high basal NF-κB activity and IL-1α production. Finally, we observed an accumulation of the non-classical monocytes, in conjunction with higher levels of plasma TNF-α and IL-8, in the elderly. These factors may contribute to inflamm-aging and age-related inflammatory conditions, such as atherosclerosis and osteoarthritis. With our new understanding that the non-classical monocyte subset is a senescent population, we can now re-examine the role of this subset in disease conditions where this subset expands.

Senescent cells re‐engineered to express soluble programmed death receptor‐1 for inhibiting programmed death receptor‐1/programmed death ligand‐1 as a vaccination approach against breast cancer

“…The vaccine not only maintained a large number of tumor antigens, but also maintained high local cytokine concentrations. 27 In the present study, we induced 4T1 cells into senescent status and found higher concentrations of immunostimulatory cytokines, including IFN-c, TNF-a, IL-17 and IL-12P70. Meanwhile, we assessed secretion of TGF-b, IL-12P40 and IL-10.…”

“…E, Survival curves of mice in different groups remains viable and metabolically active. 27 Our study showed that an accumulation of senescent cells with various SASP would cause proinflammatory microenvironments. This suggested the possibility to exploit a novel vaccine different from conventional vaccines.…”

“…At present, cellular senescence is an area of intense investigation because of unique cell conditions. Unlike death or apoptotic cells, despite the fact that a senescent cell would no longer proliferate, it remains viable and metabolically active . Our study showed that an accumulation of senescent cells with various SASP would cause pro‐inflammatory microenvironments.…”

“…In this study, we exploited a cell‐based vaccine that consisted primarily of stress‐induced senescent tumor cells. The vaccine not only maintained a large number of tumor antigens, but also maintained high local cytokine concentrations …”

PARC: ultrafast and accurate clustering of phenotypic data of millions of single cells

“…monocytes, dendritic cells and NK cells) are not annotated by any of their known subtypes. Nevertheless, PARC is able to reveal the clusters showing high expression of CD14 (cluster 9) and CD16 (or FCGR3A) (cluster 10), markers for classical and non-classical monocytes respectively (Ong, 2018). It also identifies subsets of NK cells as inferred by the expression level of CD160 and CD16 (FCGR3A) (cluster 3 and 5), which is known to be associated to the CD56dim CD16+ cytotoxic NK cell phenotype (cluster 5) (Bouteiller, 2011).…”