Targeting Matrix Metalloproteinase-9 to Alleviate T Cell Exhaustion and Improve Sepsis Prognosis.

Sepsis remains a leading global cause of death, with immune heterogeneity's molecular mechanisms poorly understood. This study analyzed 1,862 human peripheral blood samples, constructing a molecular interaction disturbance network that first revealed the network biology underlying sepsis immune heterogeneity. We identified 3 sepsis subtypes with marked different prognostic characteristics, with the C1 subtype showing the worst prognosis characterized by severe CD4+ T cell exhaustion-validated across 10 independent cohorts. Integrating single-cell transcriptomics from over 450,000 cells, proteomics, and functional validation, we identified monocyte-derived matrix metalloproteinase-9 (MMP9) as a key regulator driving CD4+ T cell dysfunction. Mechanistically, MMP9 modulates T cell exhaustion through dual mechanisms: promoting leukocyte-associated immunoglobulin-like receptor-1 (Lair-1) aggregation on T cell membranes, directly inhibiting zeta chain of T cell receptor associated protein kinase 70 (ZAP70) phosphorylation in T cell receptor signaling, while impairing Ca2+-release-activated Ca2+ channel function and intracellular calcium clearance, causing calcium dysregulation that blocks nuclear factor of activated T cells (NFAT) activation and nuclear translocation. The selective MMP9 inhibitor MMP9-in-1 effectively reversed T cell dysfunction, restored calcium homeostasis and NFAT nuclear translocation, markedly enhanced CD4+ T cell interleukin-2 and interferon-γ production, and reduced programmed cell death protein 1 expression. This work establishes a comprehensive translational framework from molecular network disturbances to clinical phenotypes, advancing sepsis immunopathophysiology understanding and providing effective targets for the treatment of sepsis patients.