Abstract 395: The Role of Transglutaminase 2 (tg2) in Regulation of Macrophage Phenotype

Abstract

Transglutaminase 2 (TG2) expression is increased in infarcted and remodeling hearts and modulates cellular responses through enzymatic effects and non-enzymatic actions. In monocytic cells, TG2 is predominantly expressed by M2 macrophages in both mice and humans. Although TG2 is considered a preserved and reliable marker of M2 macrophages, its role in regulation of macrophage phenotype remains unknown. In order to study the role of TG2 in macrophage function in homeostasis and disease, we generated mice with myeloid cell-specific loss of TG2 (MyTG2KO), and examined their response to experimental myocardial infarction (MI). Using myeloid cell reporter CSF1R EGFP mice, we found that TG2 is highly expressed in the majority of spleen, liver and lung macrophages, and is markedly upregulated in M2-like Arg1+ macrophages infiltrating the infarcted heart in contrast to infarct neutrophils. MyTG2KO mice had no baseline defects. Following MI, MyTG2KO mice and TG2 fl/fl controls had comparable chamber dilation, systolic dysfunction and infarct size, but exhibited attenuated diastolic dysfunction and reduced atrial size, reflecting lower filling pressures. Macrophages harvested from infarcted MyTG2KO mice had comparable pro-inflammatory and anti-inflammatory cytokine synthesis, but markedly increased expression of caveolin-1, the integrins a1, b1 and b3, and of the anti-fibrotic proteoglycan decorin. In vitro, we examined the effects of TG2 loss on the transcriptomic profile of bone marrow macrophages using RNAseq. Reactome and KEGG analysis showed that TG2 loss did not affect the baseline macrophage transcriptome differences. In contrast, following TGF-b stimulation, TG2 KO and WT cells had differential expression of genes regulating focal adhesion formation and the actin cytoskeleton. Consistent with the in vivo findings, TGF-b stimulation resulted in higher caveolin-1 and decorin in TG2 KO macrophages. In summary, TG2 expression is induced in M2-like macrophages infiltrating the infarcted heart and mediates diastolic dysfunction. The effects of TG2 in macrophages are not due to actions on their inflammatory profile, but may involve modulation of focal adhesion formation and cell migration, and subsequent expression of anti-fibrotic genes.