Targeting the AKT2-NAMPT phosphorylation axis prevents macrophage senescence to enhance bactericidal activity in septic immunosuppression.

Abstract

Macrophage immune dysregulation in sepsis contributes to secondary infections and poor outcomes. Immunosuppression, a key feature of this dysregulation, has been linked to the acquisition of cellular senescence-like features in cancer. However, the mechanistic connection between immune tolerance, a well-established cellular model of immunosuppression, and macrophage senescence remains poorly understood. Here, using an in vitro model of lipopolysaccharide (LPS)-induced tolerance, we found that immune-tolerant macrophages acquired a senescent phenotype. Unexpectedly, nicotinamide phosphoribosyltransferase (NAMPT) mRNA and protein levels were markedly upregulated in tolerant macrophages despite profound suppression of MYC proto-oncogene (MYC), a canonical transcriptional regulator of NAMPT. Mechanistically, this paradoxical accumulation of NAMPT was driven by reduced expression of the RNA helicase DEAD-box helicase 6 (DDX6), thereby enhancing NAMPT mRNA stability. However, increased NAMPT abundance was uncoupled from its enzymatic activity owing to diminished AKT serine/threonine kinase 2 (AKT2)-mediated phosphorylation. Treatment with SC79, a pan-AKT activator, restored NAMPT phosphorylation and activity, attenuated senescence-associated markers, and enhanced bactericidal function in tolerant macrophages. In a murine model of sepsis, alveolar macrophages similarly exhibited reduced DDX6 and AKT2 expression, together with elevated NAMPT abundance, corroborating the in vitro findings. Collectively, these results identify a dual-layer regulatory mechanism in which DDX6 controls NAMPT abundance, whereas AKT2 dictates its activity. The uncoupling of NAMPT abundance from its enzymatic activity drives senescence during immune tolerance, identifying AKT2-NAMPT as a potential therapeutic axis to restore immune competence in sepsis.