LAMP2-FLOT2 interaction enhances autophagosome-lysosome fusion to protect the septic heart in response to ILC2.

Abstract

Cardiac dysfunction is a serious complication of sepsis-induced multiorgan failure in intensive care units and is characterized by an uncontrolled immune response to overwhelming infection. Type 2 innate lymphoid cells (ILC2s), as a part of the innate immune system, play a crucial role in the inflammatory process of heterogeneous cardiac disorders. However, the role of ILC2 in regulating sepsis-induced cardiac dysfunction and its underlying mechanism remain unknown. The present study demonstrated that autophagic flux blockage exacerbated inflammatory response and cardiac dysfunction, which was associated with mortality of sepsis. Using a cecal ligation and puncture (CLP) mouse sepsis model, we observed an expansion of ILC2s in the septic heart. Furthermore, IL4 derived from ILC2 mitigated cardiac inflammatory responses and improved cardiac function during sepsis. Additionally, IL4 enhanced LAMP2 (lysosomal associated membrane protein 2) expression through STAT3 (signal transducer and activator of transcription 3) activation to stabilize lysosomal homeostasis and rescue the impaired autophagic flux during sepsis. Notably, LAMP2 was preferentially bound to FLOT2 (flotillin 2) after IL4 exposure, and the interaction enhanced autophagosome-lysosome fusion in cardiac endothelial cells. Loss of FLOT2 reversed the regulatory effects of LAMP2 on autophagy mediated by IL4, leading to autophagosome accumulation and suppressed autophagosome clearance. Conclusively, these findings provide novel insights that ILC2 regulates incomplete autophagic flux to protect septic heart and expand our understanding of immunoregulation for sepsis.Abbreviation: ACTB: actin beta; ACTN: actinin, alpha; ADGRE1/F4/80: adhesion G protein-coupled receptor E1; ANXA5/annexin V: annexin A5; AO: acridine orange; BECN1/Beclin1: beclin 1, autophagy related; CKM: creatine kinase, muscle; CKB: creatine kinase, brain; CLP: cecal ligation and puncture; CO: cardiac output; CQ: chloroquine; CTS: cathepsin; DAPI: 4'6-diamidino-2-phenylindole; EC: endothelial cell; EF: ejection fraction; ELISA: enzyme-linked immunosorbent assay; FLOT: flotillin; FS: fractional shortening; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GATA3: GATA binding protein 3; GLB1/β-Gal: galactosidase, beta 1; HCMEC: human cardiac microvascular endothelial cell; IL: interleukin; ILC: innate lymphoid cell; IL1RL1/ST2: interleukin 1 receptor-like 1; IL4c: IL4 complex; IL7R/CD127: interleukin 7 receptor; KEGG: Kyoto Encyclopedia of Genes and Genomes; LAMP: lysosomal-associated membrane protein; LDH: lactate dehydrogenase; LMP: lysosome membrane permeabilization; LPS: lipopolysaccharide; LVEDd: left ventricular end-diastole diameter; LVEDV: left ventricular end-diastole volume; LVESd: left ventricular end-systolic diameter; LVESV: left ventricular end-systole volume; MAN: mannosidase alpha; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MS: mass spectrometry; PECAM1/CD31: platelet/endothelial cell adhesion molecule 1; PTPRC/CD45: protein tyrosine phosphatase receptor type C; RORC/RORγt: RAR related orphan receptor gamma; SQSTM1/p62: sequestosome 1; TBX21/T-bet: T-box 21; TEM: transmission electron microscopy; THY1/CD90.2: thymus cell antigen 1, theta; TNF/TNF-α: tumor necrosis factor; V-ATPase: vacuolar-type H⁺-translocating ATPase; VIM: vimentin.