PLCG2 regulates endocannabinoid and eicosanoid networks in innate immune cells

Human genetic studies have pointed to a prominent role for innate immunity and lipid pathways in human immunological and neurodegenerative disorders. Our understanding of the composition and function of immunomodulatory lipid networks in innate immune cells, however, remains incomplete. Here, we show that phospholipase C gamma 2 (PLCgamma2 or PLCG2) - mutations in which are associated with autoinflammatory disorders and Alzheimer's disease- serves as a principal source of diacylglycerol (DAG) pools that are converted into a cascade of bioactive endocannabinoid (eCB) and eicosanoid lipids by DAG lipase (DAGL) and monoacylglycerol lipase (MGLL) enzymes in innate immune cells. We show that this lipid network is tonically stimulated by disease-relevant human mutations in PLCgamma2, as well as Fc receptor activation in primary human and mouse macrophages. Genetic disruption of PLCgamma2 in mouse microglia suppressed DAGL/MGLL-mediated eCB-eicosanoid crosstalk and also caused widespread transcriptional and proteomic changes, including the reorganization of immune-relevant lipid pathways reflected in reductions in DAGLB and elevations in PLA2G4A. Despite these changes, Plcg2-/- mice showed generally normal pro-inflammatory cytokine responses to lipopolysaccharide treatment, instead displaying a more restricted deficit in microglial activation that included impairments in prostaglandin production and CD68 expression. Our findings enhance the understanding of PLCgamma2 function in innate immune cells, delineating a role in crosstalk with endocannabinoid/eicosanoid pathways and modulation of subsets of cellular responses to inflammatory stimuli. Transcriptome profiles of Plcg2+/+ and Plcg2-/- mouse neonatal microglia人类遗传学研究表明，先天免疫与脂质通路在人类免疫性及神经退行性疾病中发挥关键作用。然而，我们对先天免疫细胞中免疫调节脂质网络的组成与功能的认知仍不完善。本研究证实，磷脂酶Cγ2（phospholipase C gamma 2, PLCγ2/PLCG2）——其突变与自身炎症性疾病及阿尔茨海默病相关——是先天免疫细胞中二酰基甘油（diacylglycerol, DAG）池的主要来源；该DAG池可通过二酰基甘油脂肪酶（DAG lipase, DAGL）与单酰基甘油脂肪酶（monoacylglycerol lipase, MGLL）的催化作用，级联转化为一系列生物活性内源性大麻素（endocannabinoid, eCB）与类二十烷酸脂质。我们发现，该脂质网络会被PLCγ2上与疾病相关的人类突变，以及原代人源与小鼠巨噬细胞中的Fc受体激活所持续刺激。在小鼠小胶质细胞中敲除PLCγ2基因，可抑制DAGL/MGLL介导的eCB-类二十烷酸串扰，同时引发广泛的转录组与蛋白质组变化，包括免疫相关脂质通路的重编程：具体表现为DAGLB表达下调、PLA2G4A表达上调。尽管存在上述变化，Plcg2基因敲除（Plcg2-/-）小鼠在脂多糖（lipopolysaccharide, LPS）刺激下的促炎细胞因子应答仍基本正常，仅在小胶质细胞活化方面表现出更局限的缺陷，包括前列腺素生成受损与CD68表达下调。本研究结果加深了我们对PLCγ2在先天免疫细胞中功能的认知，明确了其在内源性大麻素/类二十烷酸通路串扰中的作用，并揭示其可调控细胞对炎症刺激的部分应答。Plcg2野生型（Plcg2+/+）与敲除型（Plcg2-/-）小鼠新生小胶质细胞的转录组图谱