Transcriptional control of tissue resident macrophage phenotype

Tissue-resident macrophages take residence in tissues during early embryogenesis, developing independently in within their final tissue resulting in tissue-specific transcriptomes. Tissue-specific transcription factor expression, such as GATA-bindingprotein-6 (GATA6) in peritoneal cavity macrophages and Spalt-like-1 (SAL1) in microglia have previously been identified. Musculoaponeurotic-fibrosarcoma oncogene homolog (Maf) transcription factor family is enriched in several tissue-resident macrophage enhancer-genes. Previously identified as important for macrophage terminal differentiation, Maf is a potent activator of interleukin-10 (Il10), with overexpression of Maf suggested to suppress interleukin-12 (Il12) transcription in macrophages. Rationale The role of Maf in tissue-resident macrophages, and what impact loss of Maf has on the transcriptome of tissue-resident populations has yet to be investigated. Experimental Approach To investigate the role of Maf, specific lentiviral overexpression constructs were generated and validated. These constructs were utilised to validate the characterisation of conditional and constitutive CX3C-chemokine receptor 1 (Cx3cr1)-restricted knockout mouse lines. The role of Maf was investigated in two populations: microglia and peritoneal tissueresident macrophages (CD11bhigh,F4/80high ,Tim4+). Results Maf was demonstrated to exhibit differential phenotypic control of these populations. Microgliosis was observed in Maffl/flCx3cr1Cre/+ compared to Maffl/flCx3cr1+/+ mice, together with loss of MHCII+CD206low border-associated macrophage (BAM) population. Interestingly, no significant changes in homeostatic phenotype and development were observed in peritoneal tissue-resident macrophages. Transcriptomic analysis of Maffl/flCx3cr1Cre/+ and Maffl/flCx3cr1+/+ mice revealed a more proinflammatory-primed transcriptome under naïve conditions, which correlated with the reduction in Il-10 expression. Whilst Maf-deficiency had little effect on naïve iv peritoneal tissue-resident macrophages, it appeared to play an important role in regulation of the inflammatory monocyte-derived macrophage transcriptome in zymosan-induced peritonitis. Implications Across multiple transcriptomic analyses several genes associated with alternativeactivation of macrophages were demonstrated to be downregulated in Maffl/flCx3cr1Cre/+ mice. Suggestive of Maf influencing an alternative-activated macrophage phenotype and transcriptome across distinct macrophage populations of different ontogenie