# FSTL1 promotes dendritic cell pyroptosis and immunosuppression in sepsis by inhibiting STING autophagy

## TL;DR

This study shows how FSTL1 causes immune suppression in sepsis by triggering dendritic cell death through a specific pathway involving STING and autophagy.

## Contribution

The study reveals a novel mechanism where FSTL1 inhibits STING autophagy, leading to dendritic cell pyroptosis and immunosuppression in sepsis.

## Key findings

- FSTL1 elevation correlates with dendritic cell pyroptosis in sepsis models.
- FSTL1 inhibits STING autophagy, causing its accumulation and activation.
- STING inhibition reverses FSTL1-induced immune suppression and reduces sepsis mortality.

## Abstract

Sepsis-induced immunosuppression, characterized by dendritic cell (DC) depletion, correlates with poor outcomes. The glycoprotein FSTL1 is elevated in sepsis, but its contribution to DC pyroptosis and subsequent immune dysfunction remains unknown.

We utilized in vitro models with splenic DCs and mouse dendritic cell line DC2.4, alongside a murine cecal ligation and puncture (cecal ligation and puncture) sepsis model. The roles of STING and autophagy were probed using specific modulators (STING agonist DMXAA; STING specific inhibitor C-176; autophagy inhibitor 3-methyladenine). Pyroptosis was assessed by quantifying cleaved CASP1 and GSDMD-N via Western blotting and flow cytometry. STING pathway activation and autophagic flux were evaluated by detecting protein phosphorylation (p-STING, p-TBK1) and key markers (LC3B, P62) through Western blotting, immunofluorescence, and co-immunoprecipitation. DC-mediated T-cell responses were determined by proliferation assays and cytokine secretion analysis.

FSTL1 was found elevated and correlated withDC pyroptosis in vitro and in septic mice. Mechanistically, FSTL1 inhibited the autophagic degradation of STING, leading to its accumulation and subsequent activation. Consequently, this impaired T-cell priming capacity and resulted in immunosuppression in vivo. Inhibition of STING attenuated FSTL1-induced pyroptosis, restored DC-mediated T-cell activation, and ameliorated immunosuppression. In murine septic models, FSTL1 exacerbated multiple organ injury and increased mortality, effects that were reversed by STING inhibition.

Our findings demonstrate that FSTL1 correlates with impaired STING autophagic degradation and DC pyroptosis, suggesting a potential pathway contributing to septic immune dysfunction.