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Interleukin-4-induced-1 (IL4i1) is an amino acid oxidase secreted from immune cells. Recent observations have suggested that IL4i1 is pro-tumorigenic via unknown mechanisms. As IL4i1 has homologues in snake venoms (LAAO, L-amino acid oxidases), we used comparative approaches to gain insight into the mechanistic basis of how conserved amino acid oxidases regulate cell fate and function. Using mammalian expressed recombinant proteins, we found venom LAAO kills cells via hydrogen peroxide generation. By contrast, mammalian IL4i1 is non-cytotoxic and instead elicits a cell productive gene expression program inhibiting ferroptotic redox death by generating indole-3-pyruvate (I3P) from tryptophan. I3P suppresses ferroptosis by direct free radical scavenging and through the activation of an anti-oxidative gene expression program. Thus, the pro-tumor effects of IL4i1 are likely mediated by local anti-ferroptotic pathways via aromatic amino acid metabolism, arguing that an IL4i1 inhibitor may modulate tumor cell death pathways.

Lactate is an end point of Warburg-type metabolism found in inflammatory macrophages. Recently, lactate was shown to modify histones of lipopolysaccharide (LPS)–activated macrophages in a time-dependent way and promote the expression of genes linked to tissue repair, including arginase-1 (Arg1). We tested the interrelationships between histone lactylation (Kla) and tissue reparative gene expression and found that Kla was uncoupled from changes in gene expression linked to resolving M2 macrophage activation but correlated with Arg1 expression. LPS-induced Arg1 was instead dependent on autocrine-paracrine interleukin-6 (IL6) production, the IL6 receptor, and Stat3 signal transduction. We found that Kla increases as macrophages prepare to die under inflammatory stress, and Kla was absent in macrophages that cannot generate reactive nitrogen or have defects in diverse macrophage death pathways. Thus, Kla is a consequence rather than a cause of macrophage activation but occurs coincidently with an IL6- and Arg1-dependent metabolic rewiring under inflammatory duress.

Immune cells regulate tumor growth by mirroring their function as tissue repair organizers in normal tissues. To understand the different facets of immune-tumor collaboration through genetics, spatial transcriptomics, and immunological manipulation with non-invasive, longitudinal imaging, we generated a penetrant double oncogene-driven autochthonous model of neuroblastoma. Spatial transcriptomic analysis showed that CD4 + and myeloid populations colocalized within the tumor parenchyma, while CD8 + T cells and B cells were peripherally dispersed. Depletion of CD4 + T cells or CCR2 + macrophages, but not B cells, CD8 + , or NK cells, prevented tumor formation. Tumor CD4 + T cells displayed unconventional phenotypes and were clonotypically diverse and antigen-independent. Within the myeloid fraction, tumor growth required myeloid cells expressing arginase-1. Overall, these results demonstrate how argininemetabolizing myeloid cells conspire with pathogenic CD4 + T cells to create permissive conditions for tumor formation, suggesting that these pro-tumorigenic pathways could be disabled by targeting myeloid arginine metabolism. Statement of SignificanceA new model of human neuroblastoma provides ways to track tumor formation and expansion in living animals, allowing identification of CD4 + T cell and macrophage functions required for oncogenesis.

Anti-TNF therapies are a core anti-inflammatory approach for chronic diseases such as rheumatoid arthritis and Crohn’s Disease. Previously, we and others found that TNF blocks the emergence and function of alternative-activated or M2 macrophages involved in wound healing and tissue-reparative functions. Conceivably, anti-TNF drugs could mediate their protective effects in part by an altered balance of macrophage activity. To understand the mechanistic basis of how TNF regulates tissue-reparative macrophages, we used RNAseq, scRNAseq, ATACseq, time-resolved phospho-proteomics, gene-specific approaches, metabolic analysis, and signaling pathway deconvolution. We found that TNF controls tissue-reparative macrophage gene expression in a highly gene-specific way, dependent on JNK signaling via the type 1 TNF receptor on specific populations of alternative-activated macrophages. We further determined that JNK signaling has a profound and broad effect on activated macrophage gene expression. Our findings suggest that TNF’s anti-M2 effects evolved to specifically modulate components of tissue and reparative M2 macrophages and TNF is therefore a context-specific modulator of M2 macrophages rather than a pan-M2 inhibitor.

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<p>Table S4</p>

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