# De novo purine synthesis reprograms the macrophage inflammatory response and the immune response in sepsis

## TL;DR

This study shows that de novo purine synthesis in macrophages affects inflammation and immune responses during sepsis, suggesting it could be a new target for treatment.

## Contribution

The study identifies de novo purine synthesis as a metabolic checkpoint regulating anti-inflammatory macrophage responses in sepsis.

## Key findings

- Blocking de novo purine synthesis in macrophages reduces anti-inflammatory mediators like IL-10 and increases TNF-α.
- Salvage pathway supplementation with hypoxanthine reverses the effects of de novo purine synthesis inhibition.
- Reduced GART and PPAT expression is observed in septic patients' PBMCs and LPS-treated macrophages.

## Abstract

Sepsis is characterized by profound immunometabolic dysregulation, yet the role of purine precursor synthesis in immune reprogramming remains poorly defined. Intracellular purine nucleotides, such as ATP, are generated by de novo synthesis, which assembles purinosomes to build inosine monophosphate (IMP) from small precursors, or by the salvage pathway, which recycles purine bases such as hypoxanthine. Here, we investigated how these pathways regulate macrophage activation and host responses in sepsis. Silencing the de novo purine enzyme glycinamide ribonucleotide transformylase (GART) in LPS-stimulated macrophages induced marked transcriptomic remodeling, suppressing anti-inflammatory mediators, including IL-10 and TIMP-1, while increasing TNF-α. These effects were reversed by hypoxanthine supplementation, indicating rescue through salvage. Similar findings were observed with silencing of phosphoribosyl pyrophosphate amidotransferase (PPAT) or pharmacological GART inhibition with azaserine or lometrexol, which also reduced intracellular ATP levels in a hypoxanthine-reversible manner. In contrast, inhibition of salvage enzymes (HPRT, APRT) did not alter IL-10 expression. De novo purine synthesis blockade increased Adora2a expression and decreased Adora3 expression without affecting MAPK signaling. Macrophages formed purinosomes under purine-depleted conditions, which disassembled in the presence of exogenous hypoxanthine. In vivo, azaserine treatment in cecal ligation and puncture–induced sepsis reduced IL-10, increased TNF-α, and elevated bacterial burden. LPS-treated macrophages and PBMCs from septic patients showed reduced GART and PPAT expression. These findings identify de novo purine synthesis as a metabolic checkpoint that sustains anti-inflammatory macrophage programming and host defense, highlighting purine metabolism as a potential translational target in sepsis.