Macrophage senescence impairs phagocytosis and phagosome function

巨噬细胞衰老损害吞噬作用和吞噬体功能

• 批准号: RGPIN-2021-04303
• 负责人: Bowdish, Dawn
• 金额: $ 3.64万
• 依托单位: McMaster University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2021
• 资助国家: 加拿大
• 起止时间: 2021-01-01 至 2022-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=742972
• 关键词: Macrophage; senescence; impairs; phagocytosis; phagosome

Phagocytosis is an evolutionarily ancient process, which likely originated from the need of single celled organisms to internalize and digest food, and has been preserved as the major mechanism by which macrophages recognize and remove particulates, dying or damaged cells and pathogens. Our lab has recently discovered that non-opsonic phagocytosis (i.e. phagocytosis that does not require the target to be coated by complement, antibodies or other opsonins) by macrophages decreases with age, even though expression of non-opsonic receptors does not change. Furthermore, we have also found age-related changes in the rate of phagolysosomal fusion occur without affecting the pH, proteolytic or oxidative capacity of the phagosome. This delay in phagosome fusion is sufficient to decrease bacterial killing. We have compared the delay of phagolysosomal fusion between macrophages derived from young (20 mo) wildtype (WT) mice and TNF (tumour necrosis factor alpha) knockout mice, and intriguingly, defective macrophage phagocytosis and phagolysosomal maturation does not seem to be due to chronologic age but rather the increase in the inflammatory cytokine TNF. As we age, levels of inflammatory mediators increase in the serum and tissues. Myeloid cells are particularly sensitive to age-associated inflammation. Macrophages derived from old (20+ mo) mice that are deficient in TNF do not lose phagocytic capacity or demonstrate decreased phagolysosomal fusion. By analyzing transcriptional profiles of alveolar macrophages derived from young (3 mo) and old (20+ mo) WT and TNF KO mice, we have found that negative regulators of TNF signalling increase with age in a TNF dependent manner, leading us to hypothesize that this is an adaptation to chronic TNF stimulation that ultimately makes these macrophages less responsive to acute inflammatory events. We have also found that PI3K (phosphoinositide 3-kinase) signalling is compromised in aging macrophages. Although defects in PI3K signalling have been reported in other aging immune cells, the mechanisms by which PI3K signalling is impaired with age in macrophages and the degree to which this impacts phagolysosomal function is not known. Collectively these data support our hypothesis that TNF inhibits phagolysosomal fusion and impairs phagosomal function by increasing expression of negative regulators and altering PI3K signalling pathways. We propose that macrophages do not so much undergo `senescence' (as traditionally described) but rather they adapt to lifelong exposure to the inflammatory microenvironment. This adaptation includes adapting to chronic age-associated inflammation by increasing expression of negative regulators of inflammation. By uncovering specific components of the PI3K and phagolysosomal fusion pathway that are altered by the aging microenvironment, we may uncover whether this unique senescence phenotype is amenable to manipulation.

吞噬作用是一种进化上的古老过程，它可能起源于单个细胞生物以内化和消化食物的需求，并保留为巨噬细胞识别和去除颗粒物，垂死或损害的细胞和病原体的主要机制。我们的实验室最近发现，巨噬细胞的非上吞噬作用（即不需要通过补体，抗体或其他opsonins覆盖靶标的吞噬作用）随着年龄的增长而降低，即使非上声受体的表达也不会改变。此外，我们还发现吞噬融合的速率发生了与年龄相关的变化，而不会影响吞噬体的pH，蛋白水解或氧化能力。吞噬体融合的这种延迟足以减少细菌杀伤。我们已经比较了源自年轻（20个月）野生型（WT）小鼠和TNF（肿瘤坏死因子α）敲除小鼠的巨噬细胞之间的吞噬肿瘤融合的延迟，以及令人着迷的，有缺陷的巨噬细胞吞噬和吞噬体成熟的缺陷似乎是造成的。年龄，而是炎性细胞因子TNF的增加。随着年龄的增长，炎症介质的水平在血清和组织中增加。髓样细胞对与年龄相关的炎症特别敏感。源自TNF缺乏的旧（20多个MO）小鼠的巨噬细胞不会失去吞噬能力或表现出吞噬性融合的降低。通过分析源自幼年（3个月）和年龄（20+ MO）WT和TNF KO小鼠的肺泡巨噬细胞的转录曲线，我们发现TNF信号的负调节剂以TNF依赖性的方式随着年龄的增长而增加，导致我们假设该假设是这是对慢性TNF刺激的适应，最终使这些巨噬细胞对急性炎症事件的反应较低。我们还发现，在老化的巨噬细胞中，PI3K（磷酸肌醇3-激酶）信号传导受到损害。尽管在其他衰老的免疫细胞中已经报道了PI3K信号的缺陷，但巨噬细胞中PI3K信号传导受损的机制以及影响吞噬性溶肿功能的程度尚不清楚。这些数据共同支持我们的假设，即TNF抑制吞噬体融合并通过增加负调节剂的表达和改变PI3K信号通路来抑制吞噬物体融合并损害吞噬体功能。我们建议巨噬细胞不会经历“衰老”（正如传统上描述的），而是会适应终身暴露于炎症微环境中。这种适应包括通过增加炎症负调节剂的表达来适应慢性年龄相关的炎症。通过发现由老化的微环境改变的PI3K和吞噬体融合途径的特定成分，我们可以发现这种独特的衰老表型是否可容纳这种独特的衰老表型。