TNFα and IFNγ cooperate for efficient pro- to anti-inflammatory transition of macrophages during muscle regeneration (scRNA-Seq). TNFα and IFNγ cooperate for efficient pro- to anti-inflammatory transition of macrophages during muscle regeneration (scRNA-Seq)

IFNγ is traditionally known as a pro-inflammatory cytokine with diverse roles in antimicrobial and antitumor immunity. Yet, findings regarding its sources and functions during the regeneration process following a sterile injury are conflicting. Here, we show that natural killer (NK) cells are the main source of IFNγ in regenerating muscle. Beyond this cell population, IFNγ production is limited to a small population of T cells. We further show that NK cells do not play a major role in muscle regeneration following an acute injury or in dystrophic mice. Surprisingly, the absence of IFNγ per se also has no effect on muscle regeneration following an acute injury. However, the role of IFNγ is partially unmasked when TNFα is also neutralized, suggesting a compensatory mechanism. Using transgenic mice, we showed that conditional inhibition of IFNGR1 signaling in muscle stem cells or fibro-adipogenic progenitors does not play a major role in muscle regeneration. In contrast to common belief, we found that IFNγ is not present in the early inflammatory phase of the regeneration process, but rather peaks when macrophages are acquiring an anti-inflammatory phenotype. Our further transcriptomic analysis suggests that IFNγ cooperates with TNFα to regulate the transition of macrophages from pro- to anti-inflammatory. The absence of the cooperative effect of these cytokines on macrophages, however, does not result in significant regeneration impairment likely due to the presence of other compensatory mechanisms. Our findings support the arising view of IFNγ as a pleiotropic inflammatory regulator rather than an inducer of the inflammatory response. Overall design: Dissection of the role of IFNγ in muscle regeneration and fibrosis

干扰素γ（IFNγ）传统上被认为是一种促炎细胞因子，在抗菌与抗肿瘤免疫中发挥多种功能。然而，关于其在无菌性损伤后再生过程中的来源与功能的研究结论存在矛盾。本研究发现，自然杀伤（NK）细胞是再生肌肉中干扰素γ的主要来源；除此之外，干扰素γ的产生仅局限于少量T细胞群。我们进一步证实，在急性损伤后的肌肉再生过程中，或是在肌营养不良小鼠体内，自然杀伤细胞并未发挥主要作用。令人意外的是，干扰素γ本身的缺失对急性损伤后的肌肉再生也无显著影响。但当中和肿瘤坏死因子α（TNFα）时，干扰素γ的作用会部分显现，这提示存在补偿机制。通过转基因小鼠模型，我们发现，在肌肉干细胞或脂肪成纤维祖细胞中条件性抑制干扰素γ受体1（IFNGR1）信号通路，对肌肉再生并无显著影响。与普遍认知相悖的是，我们发现干扰素γ并未出现在再生过程的早期炎症阶段，而是在巨噬细胞向抗炎表型转化的时期达到峰值。进一步的转录组学分析显示，干扰素γ可与肿瘤坏死因子α（TNFα）协同，调控巨噬细胞从促炎表型向抗炎表型的转化。不过，这两种细胞因子对巨噬细胞的协同效应缺失，并未导致明显的再生功能受损，这可能是由于存在其他补偿机制。本研究结果支持了一种新兴观点：干扰素γ作为一种多效性炎症调节因子，而非炎症反应的诱导剂。总体实验设计：解析干扰素γ在肌肉再生与纤维化进程中的作用。