ITIH5-mediated fibroblast/macrophage crosstalk exacerbates cardiac remodelling after myocardial infarction
Background: Myocardial infarction (MI) and subsequent ischaemic cardiomyopathy (ICM) are the primary causes of heart failure. Inter-a trypsin inhibitor heavy chain 5 (ITIH5) is an ECM protein and has been identified as a myocardial marker of ICM. However, its diagnostic value in patients with ICM and its function and molecular mechanism in regulating cardiac repair and remodelling after MI remain unknown.  Methods: Three microarray datasets including 117 ICM and 152 non-failing (NF) myocardial tissue samples were merged and analysed. Peripheral blood and clinical information were collected from 53 patients with ICM and 40 NF controls. The effects of ITIH5 on cellular interactions and cardiac remodelling was studied using ITIH5 RNAi adeno-associated virus and mouse MI model in vivo and in fibroblast–macrophage co-culture model in vitro. Results: ITIH5 was upregulated in the myocardial tissue and peripheral blood of patients with ICM and could be an independent risk factor for ICM. Experiments in mice suggested that ITIH5 promotes cardiac fibrotic remodelling at all phases after MI. Downregulation of ITIH5 increased the risk of death within 7 d after MI but inhibited ventricular remodelling and improved cardiac function on the long-term. ITIH5 promotes the primary cardiac fibroblasts (CFs) proliferation, migration, and improves survival rather than activiation. Morover, ITIH5 directly promotes macrophage tissue infiltration, maturation, and profibrotic phenotype transformation, thereby promoting fibrotic remodelling. By using fibroblast–macrophage co-culture model, we demonstrated ITIH5 enhanced the fibroblast/macrophage crosstalk manifest as macrophage profibrotic phenotype transformation and CFs activation, mainly by enhancing the hyaluronan stability, the ability of ITIH5 to bind macrophage CD44 receptors and the downstream activation of the signal transduction and activator of transcription 3 pathway in macrophages.  Conclusions: ITIH5 could be used as a diagnostic marker for ICM. Moreover, ITIH5 expression was upregulated after MI, which accelerated ECM-fibroblast-macrophage interaction, thereby promoting macrophage profibrotic phenotype transformation, CFs activation, and cardiac fibrotic remodelling. Overall design: ITIH5 may indirectly regulate post MI fibrosis by immune regulation . We  conduct mRNA sequencing  on the mice infraction myocardium in widetype and ITIH5 knockdown mouse at 7 days after MI.