Derivation of novel metabolic pathway score identifies alanine metabolism as a targetable influencer of TNF-alpha signaling.

Background: Better understanding of the interaction between metabolism and immune response will be key to understanding physiology and disease. Tumor Necrosis Factor-alpha (TNFα) has been studied widely. However, despite the extensive knowledge about TNFα, the cytokine appears to induce not only variable, but often contradictory, effects on inflammation and cell proliferation. Despite advancements in the metabolomics field, it is still difficult to analyze the types of multi-dose, multi-time point studies needed for elucidating the varied immunologic responses induced by TNFα. Results: We studied the dose and time course effects of TNFα on murine fibroblast cultures and further elucidated these connections using selective blockade of the TNF receptors (TNFR1 and TNFR2). To streamline analysis, we developed a method to collate the metabolic pathway output from MetaboAnalyst into a single value for the Index of pathway significance (IPS). Using this metric, we tested dose-, time-, and receptor-dependent effects of TNFα signaling on cell metabolism. Guided by these results, we then demonstrate that alanine supplementation enriched TNFR1-related responses in both cell and mouse models. Conclusions: Our results suggest that TNFα, particularly when signaling through TNFR1, may preferentially use alanine metabolism for energy. These results are limited in by cell type used and immune outputs measured. However, we anticipate that our novel method may assist other researchers in identifying metabolic targets that influence their disease or model of interest through simplifying the analysis of multi-condition experiments. Furthermore, our results endorse the consideration of follow up studies in immunometabolism to improve outcomes in TNF-mediated diseases.