Understanding the role of endothelial Zeb1 in lymphatic vessels

The formation of new blood vessels is important in cancer and diseases of the cardiovascular system. Using cells isolated from human blood vessels and grown in culture, we recently discovered a protein that can switch the metabolism of these cells so that they can mature and stop growing. This protein has been shown to be involved in development and in cancer cells, but not previously in blood vessel cells. Our experiments in cultured cells predict that this protein would control how blood vessels grow in response to cardiovascular disease, and we are working on how this is important in mice models. However, we recently discovered that the same protein is regulated in the same way in lymphatic vessels (vessels that return fluid and cells from the tissue back into the bloodstream). Excess tissue fluid causes painful and debilitating conditions such as lymphedema, and lymphatic vessels are the primary route of tumour cell metastasis and also involved in fat deposition during obesity. Therefore, understanding how lymphatic vessels normally function, and how that function is controlled is of essential importance. Lymphatic vessels (LV) are an essential component of the vascular system that control interstitial fluid balance, inflammatory processes, lipid, protein and immune cell transport throughout the body. While for most of the last hundred years or so failure of the lymphatic system has been associated with lymphoedema, more recently it has demonstrated that lymphatic growth and function is a underpins multiple diverse disease involved processes including 1) enhancing efficacy of immunotherapy, 2) reducing inflammation associated with poor revascularisation of ischaemic cardiac tissue 3) neurodegeneration 4) metastatic spread 5) renal failure and 6) metabolic diseases to name a few. For any vessel, including blood, to respond to its environment the endothelial cells (ECs) change their phenotype from a quiescent, to an activated. This has been born out most recently through the use of single cell RNASeq, which provides information regarding the different EC phenotypes that exist, but limited information regarding how they are made. Transcriptional control of different EC behaviour is therefore of key importance to understand how the different phenotypes arise. We have identified a transcription factor (called Zeb1) that is dynamically regulated during lymphatic vessel growth, and its normal signature induces a 'quiescent' rather than 'activated' phenotype. This work will expand on our in vivo and molecular characterisation to determine the impact of Zeb1 signalling in normal development and pathological models of lymphatic growth. Therefore, transcription factor activity is likely to be one of the signalling pathways in which different LEC phenotypes could arise. We speculate that Zeb1 is, the first identified transcription factor for the lymphatic system that controls LEC phenotypic heterogeneity during growth
All the above data suggests that loss of Zeb1 will prime the lymphatic endothelium by reducing lymphatic EC quiescence. We will test this hypothesis by achieving the following aims:
Aim 1: Characterisation of lymphatic vessels in an endothelial specific ZEB1 KO
Aim 2: Characterisation of pathological lymphatic remodelling in Zeb1 iECKO
Aim 3: Determination of signalling events leading to Zeb1 downregulation