MLKL Orchestrates ER-Mitochondria Stress to Drive Dendritic Cell Pyroptosis and Immunoparalysis in Sepsis

Sepsis induces systemic inflammation and immune dysregulation, leading to immunoparalysis characterized by dendritic cells (DCs) depletion and dysfunction. Mixed lineage kinase domain-like pseudokinase (MLKL) is an oranelle stress regulator; however, its role in DCs-mediated immune regulation during sepsis remains poorly defined.

This study aimed to elucidate the role of MLKL in sepsis-associated DCs dysfunction and to determine the underlying molecular mechanisms linking MLKL to immune dysregulation and disease severity.

Cecal ligation and puncture (CLP) was used to establish sepsis in wild-type (WT) and MLKL-deficient (MLKL^-/-) mice. Primary CD11c⁺ DCs and DC2.4 cells were stimulated with lipopolysaccharide (LPS), with or without MLKL knockdown. Cell death pathways, organelle stress responses, ER-phagy, and immune function were analyzed using molecular, cellular, and in vivo approaches.

Sepsis and LPS stimulation induced time-dependent MLKL activation and necroptosis-related signaling. MLKL deficiency attenuated NLRP3-gasdermin D-mediated pyroptosis, alleviated endoplasmic reticulum and mitochondrial stress, restored ER-phagy, and reduced reactive oxygen species production. These effects preserved DCs maturation and costimulatory molecule expression, thereby enhancing CD4⁺ T-cell activation. Mechanistically, MLKL localized to mitochondria-associated membranes and interacted with mitofusin 2 (MFN2), promoting its degradation; a specific MLKL fragment was sufficient to destabilize MFN2. In vivo, MLKL ablation reshaped inflammatory cytokine profiles, reduced multi-organ injury, and improved survival following sepsis.

MLKL drives DCs dysfunction and immune dysregulation in sepsis by destabilizing MFN2 and impairing ER-phagy. Targeting the MLKL-MFN2-ER-phagy axis represents a potential therapeutic strategy for restoring immune competence in sepsis.