Identification of myeloid-derived growth factor as a mechanically-induced, growth-promoting angiocrine signal for human hepatocytes.

Recently, we have shown that after partial hepatectomy (PHx), an increased hepatic blood flow initiates liver growth in mice by vasodilation and mechanically-triggered release of angiocrine signals. Here, we use mass spectrometry to identify a mechanically-induced angiocrine signal in human hepatic endothelial cells, that is, myeloid-derived growth factor (MYDGF). We show that it induces proliferation and promotes survival of primary human hepatocytes derived from different donors in two-dimensional cell culture, via activation of mitogen-activated protein kinase (MAPK) and signal transducer and activator of transcription 3 (STAT3). MYDGF also enhances proliferation of human hepatocytes in three-dimensional organoids. In vivo, genetic deletion of MYDGF decreases hepatocyte proliferation in the regenerating mouse liver after PHx; conversely, adeno-associated viral delivery of MYDGF increases hepatocyte proliferation and MAPK signaling after PHx. We conclude that MYDGF represents a mechanically-induced angiocrine signal and that it triggers growth of, and provides protection to, primary mouse and human hepatocytes.

Endothelial ß1 Integrin-Mediated Adaptation to Myocardial Ischemia.

BACKGROUND: Short episodes of myocardial ischemia can protect from myocardial infarction. However, the role of endothelial ß1 integrin in these cardioprotective ischemic events is largely unknown. OBJECTIVE: In this study we investigated whether endothelial ß1 integrin is required for cardiac adaptation to ischemia and protection from myocardial infarction. METHODS: Here we introduced transient and permanent left anterior descending artery (LAD) occlusions in mice. We inhibited ß1 integrin by intravenous injection of function-blocking antibodies and tamoxifen-induced endothelial cell (EC)-specific deletion of Itgb1. Furthermore, human ITGB1 was silenced in primary human coronary artery ECs using small interfering RNA. We analyzed the numbers of proliferating ECs and arterioles by immunohistochemistry, determined infarct size by magnetic resonance imaging (MRI) and triphenyl tetrazolium chloride staining, and analyzed cardiac function by MRI and echocardiography. RESULTS: Transient LAD occlusions were found to increase EC proliferation and arteriole formation in the entire myocardium. These effects required ß1 integrin on ECs, except for arteriole formation in the ischemic part of the myocardium. Furthermore, this integrin subunit was also relevant for basal and mechanically induced proliferation of human coronary artery ECs. Notably, ß1 integrin was needed for cardioprotection induced by transient LAD occlusions, and the absence of endothelial ß1 integrin resulted in impaired growth of blood vessels into the infarcted myocardium and reduced cardiac function after permanent LAD occlusion. CONCLUSION: We showed that endothelial ß1 integrin is required for adaptation of the heart to cardiac ischemia and protection from myocardial infarction.