OC 28.2 - Neutrophil-derived Factor XIII-A transglutaminase contributes to adipose tissue fibrosis and inflammation in mouse-obesity model

Background: Factor XIII-A (FXIII-A) transglutaminase, fibrin clot stabilizer, was identified as an obesity gene in humans. We demonstrated that its absence in mice on high fat diet (HFD) results in significantly decreased adipose tissue (AT) inflammation, decreased extracellular matrix (ECM) and improved insulin sensitivity of AT. Others demonstrated recently that the role of fibrin in AT inflammation depends on FXIII-A-mediated crosslinking. Our data mining of Tabula Muris scRNA seq atlas shows that F13a1 mRNA is produced by neutrophils in AT and bone marrow (BM). Neutrophils can promote macrophage infiltration via generation of neutrophil extracellular traps (NETs), known to increase in obese AT.

Aims: To examine the production and activity of FXIII-A in neutrophils, in NETosis and its role in NET-ECM (fibrin) crosslinking. To study the immunometabolic phenotype of neutrophil-specific, conditional FXIII-A knockout (F13a1-/-MRP8) on HFD.

Methods: NETosis was induced in BM neutrophil cultures with phorbol myristate acetate. FXIII-A activity was analyzed with ATTO-488-cadaverine, and exogenous fibrinogen colocalization to NETs was studied by immunofluorescence microscopy. F13a1-/-MRP8 mice were placed on HFD for 16 weeks; weight gain, insulin sensitivity, AT inflammation and fibrosis markers were assessed.

Results: FXIII-A production by BM neutrophils was confirmed. FXIII-A showed crosslinking activity and externalization in NETosis. Exogenous fibrin(ogen) colocalized to NETs and this was inhibited by TG inhibitor, NC9. Compared to control F13a1flx/flx mice, F13a1-/-MRP8 mice (male) on HFD showed significantly decreased weight gain and improved insulin sensitivity. Macrophage and inflammation markers (Adgre1, Trem2, Tlr4, Tnfa) and fibrotic ECM markers (Col1a1, Fn1) were significantly decreased in AT compared to control mice.

Conclusion(s): Our data reveal neutrophils as a novel cellular source of FXIII-A and show that FXIII-A participates in NETosis where it may promote fibrin-accumulation and NET-ECM stabilization to promote macrophage infiltration. Knocking out FXIII-A in neutrophils has positive effects on metabolic health in obese mice.