IFNγ Increases Intracellular Amino Acid Content in Human Alveolar Epithelial Cells: Role of the STAT/IRF1 Axis in the Stimulation of Transmembrane Transport

TL;DR

IFNγ increases amino acid levels in lung cells by activating a specific signaling pathway, which could link inflammation to metabolism.

Contribution

The study identifies the JAK/STAT/IRF1 axis as a key driver of IFNγ-induced amino acid transport in alveolar epithelial cells.

Findings

IFNγ increases intracellular amino acids like glutamine and glutamate in A549 cells.

IFNγ activates amino acid transport systems ASC, A, L, and y+ via upregulation of transporters ASCT2, SNAT2, LAT1, and CAT1.

The effect of IFNγ on amino acid metabolism is mediated through the JAK/STAT/IRF1 pathway.

Abstract

Interferon-γ (IFNγ), a key inflammatory cytokine that orchestrates immune responses, also emerges as a regulator of cellular metabolism; however, in alveolar epithelial cells its impact on amino acid homeostasis remains poorly defined. Here, we investigated the effects of IFNγ on intracellular amino acid content and transmembrane transport in human alveolar epithelial A549 cells, focusing on the contribution of the JAK/STAT/IRF1 signaling axis. To this end, A549 WT and IRF1 knockout (IRF1 KO) cells were used to investigate IRF1 contribution, and baricitinib to evaluate the role of the JAK/STAT pathway. HPLC analysis reveals that in WT, but not in IRF1 KO cells, IFNγ markedly increases the intracellular concentration of many amino acids, including glutamine, glutamate, and several neutral and cationic amino acids, without affecting the cell volume, thus indicating true metabolic accumulation. The measurement of the transmembrane uptake of specific radiolabeled amino acids demonstrates a concomitant increase in transport Systems ASC, A, L, and y+ activity; an upregulation of the related transporters ASCT2, SNAT2, LAT1, and CAT1 has also been observed by means of qPCR analysis. Moreover, conditioned medium from SARS-CoV-2 spike-activated macrophages recapitulates IFNγ-driven amino acid remodeling in a JAK/STAT/IRF1-dependent manner. Overall, our findings identify IFNγ as a potent regulator of intracellular amino acid availability in alveolar epithelial cells through the modulation of the activity of membrane transporters. The observed IFNγ-reprogramming is IRF1 dependent, ascribing a crucial role to this transcription factor in linking inflammation and amino acid metabolism.

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