Identification of ILK as a critical regulator of VEGFR3 signalling and lymphatic vascular growth.

Vascular endothelial growth factor receptor-3 (VEGFR3) signalling promotes lymphangiogenesis. While there are many reported mechanisms of VEGFR3 activation, there is little understanding of how VEGFR3 signalling is attenuated to prevent lymphatic vascular overgrowth and ensure proper lymph vessel development. Here, we show that endothelial cell-specific depletion of integrin-linked kinase (ILK) in mouse embryos hyper-activates VEGFR3 signalling and leads to overgrowth of the jugular lymph sacs/primordial thoracic ducts, oedema and embryonic lethality. Lymphatic endothelial cell (LEC)-specific deletion of Ilk in adult mice initiates lymphatic vascular expansion in different organs, including cornea, skin and myocardium. Knockdown of ILK in human LECs triggers VEGFR3 tyrosine phosphorylation and proliferation. ILK is further found to impede interactions between VEGFR3 and ß1 integrin in vitro and in vivo, and endothelial cell-specific deletion of an Itgb1 allele rescues the excessive lymphatic vascular growth observed upon ILK depletion. Finally, mechanical stimulation disrupts the assembly of ILK and ß1 integrin, releasing the integrin to enable its interaction with VEGFR3. Our data suggest that ILK facilitates mechanically regulated VEGFR3 signalling via controlling its interaction with ß1 integrin and thus ensures proper development of lymphatic vessels.

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.

Requirement of ß1 integrin for endothelium-dependent vasodilation and collateral formation in hindlimb ischemia.

An acute increase in blood flow triggers flow-mediated dilation (FMD), which is mainly mediated by endothelial nitric oxide synthase (eNOS). A long-term increase in blood flow chronically enlarges the arterial lumen, a process called arteriogenesis. In several common human diseases, these processes are disrupted for as yet unknown reasons. Here, we asked whether ß1 integrin, a mechanosensory protein in endothelial cells, is required for FMD and arteriogenesis in the ischemic hindlimb. Permanent ligation of the femoral artery in C57BL/6 J mice enlarged pre-existing collateral arteries and increased numbers of arterioles in the thigh. In the lower leg, the numbers of capillaries increased. Notably, injection of ß1 integrin-blocking antibody or tamoxifen-induced endothelial cell-specific deletion of the gene for ß1 integrin (Itgb1) inhibited both arteriogenesis and angiogenesis. Using high frequency ultrasound, we demonstrated that ß1 integrin-blocking antibody or endothelial cell-specific depletion of ß1 integrin attenuated FMD of the femoral artery, and blocking of ß1 integrin function did not further decrease FMD in eNOS-deficient mice. Our data suggest that endothelial ß1 integrin is required for both acute and chronic widening of the arterial lumen in response to hindlimb ischemia, potentially via functional interaction with eNOS.