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Small Artery Remodelling

Final Report Summary - SMART (Small Artery Remodelling)

SmArt is a Marie Curie Initial Training Network (ITN) on SMall ARTery remodelling extending from October 1, 2009 to September 30, 2013. The network consists of 10 partner organizations (9 academic groups and one industrial) from 7 European countries specialized in the biology of vascular cells and their surrounding extracellular matrix (ECM). 13 early stage researchers (Ph.D. students) are supported for 3 years and 1 experienced researcher (postdoctoral fellow) for 2 years.

40% of European citizens currently die of cardiovascular diseases that are mainly the result of long term hypertension or diabetes and other risk factors, including obesity and a sedentary life style. Their associated complications like stroke, heart failure or organ dysfunction also contribute to the requirement for costly long-term nursing. This is a world-wide problem that is increasing at an alarming rate in European countries. Cardiovascular diseases have a complex aetiology and originate from pathological stimuli that involve different cell types, resident in the vascular wall (endothelium, smooth muscle, pericytes) or infiltrating from the blood (leukocytes, progenitor cells), and the ECM. The adaptation of the vasculature to physiological and pathophysiological influences depends on both the communication between its cellular components and their interaction with the ECM. When subjected to elevated pressure or altered flow patterns, blood vessels undergo typical transformations in wall shape that are always associated with alterations of the ECM and cellular composition, collectively referred to as vascular remodelling. This occurs specifically in small arteries and arterioles, resulting in extreme changes in size and function. Especially in hypertensive or diabetic patients, vascular remodelling contributes to a vicious cycle resulting in organ dysfunction and progressive vascular disease.

The major TRAINING OBJECTIVE of SmArt is to provide a sound theoretical and practical integrated training in the field of vascular biology, which encompasses endothelium and smooth muscle cell physiology, biochemistry, functional genomics and cell biology. Participation in the SmArt training programme provides young researchers with additional scientific, management and communication skills that will ensure both their individual success as future leaders of their own research groups and the long-term advancement of the research field as well as its technological and clinical applications.

The primary SCIENTIFIC OBJECTIVE of the SmArt network is to determine the molecular mechanisms of cell-matrix and cell-cell interactions in small artery remodelling, aiming to aid in the development of new therapies. The main results obtained are summarized below in relation to three key areas of investigation .


SIGNALLING MECHANISMS IN ENDOTHELIAL AND SMOOTH MUSCLE CELLS. The endothelium is a permeability barrier and also senses blood flow and generates signals to the underlying smooth muscle cells. It was shown that impaired energy production by mitochondria in endothelial cells reduces the generation of new blood vessels in response to hypoxia. It was also shown that NO, an important mediator of endothelial signals, modulates signal communication between endothelial cells by a mechanism involving posttranslational modification of the gap junction protein connexin 37.

In further work, the scaffolding protein MAG1 was identified in endothelial cells and shown to be involved in mechanical coupling and cell-cell communication under negative regulation by prostaglandins and COX-2. MAG-1 expression in endothelial cells was shown to be regulated by shear stress from the blood flow and by aging suggesting a central role in angiogenesis and vascular remodelling.

The role of angiotensin II (Ang II) and its receptor AT1R on vascular remodelling induced by aging was investigated. It was shown that aging has substantial effects on Ang II-induced vasomotor responses and AT1R expression. Vessel size was shown to increase with age and to be associated with increases in extracellular matrix components, especially collagen type III.

Important signalling functions in endothelium and smooth muscle cells as well as their interactions with the ECM are fulfilled by the laminin family of basal membrane proteins. One of the major subunits (alpha5) in vascular laminins was deleted in mouse perivascular cells (smooth muscle and pericytes) and in endothelium, respectively. Laminin a5 in perivascular and endothelial cell basement membranes was found to impact on the physiological response of the resistance arteries to shear and pressure, whereas in vascular smooth muscle, laminin a5 impacts on the contractile machinery.

In summary, the studies have generated new results regarding the communication between ECM, endothelium and smooth muscle of importance for the understanding of how physical factors associated with the blood flow and pressure affect the vessel wall as a whole.


STRUCTURAL AND FUNCTIONAL REARRANGEMENTS IN THE VESSEL WALL. The transcriptional control of smooth muscle differentiation in response to stretch was shown to involve regulated expression of L-type calcium channels, requiring the presence of the microRNA miR-145. Stretch furthermore causes decreased miR-144/451 expression, inversely correlating with AMPK activity and contractile differentiation. Mesenteric resistance arteries from mice devoid of all miRNAs were shown to lack myogenic tone as a result of reduced Akt signalling. The calcium- and integrin- activated kinase PYK2 was shown to regulate smooth muscle growth without affecting stretch-sensitive differentiation.

The role of the transcription factor zyxin in hypertension-induced arterial remodelling was investigated in Zyxin-deficient mice. These show age-dependent systolic dysfunction in response to DOCA-salt treatment, associated with loss of contractility in vascular smooth muscle and development of cardiac fibrosis. TRPC3 was identified as an upstream mediator of zyxin-dependent mechanotransduction in endothelial cells.

The relations between tone, cellular matrix reorganization and remodelling of small arteries are investigated, with particular reference to transglutaminases, enzymes that regulate the cross-linking of proteins including those in the ECM. We studied contractile plasticity and its sensitivity to specific vasoconstrictors, distension and inflammation, as well as the redox control of transglutaminases and their role in intracranial haemorrhage and atherosclerotic plaques. A theoretical study integrated current understanding of remodelling. A broad study of small artery remodelling in hypertensive rat models, aims at linking age and substrains of animals to vascular gene expression, wall composition and ultrastructure, biomechanical properties, and endothelial function.

In hypertension one of the key events in the vascular wall is down-regulation of the potassium channel subtype Kv7.4 leading to vascular contraction. In coronary arterioles the Kv7.4 channel is of key importance for the metabolic regulation of the coronary perfusion. The Kv7.4 channel is downregulated in diabetic rats and mice, thereby contributing to development of hypertension. Downregulation of the L-type calcium channel in the vascular wall was shown to cause structural remodelling of the arterial wall in vivo. Major changes in the response to noradrenaline, the expression of calcium activated potassium channels and the expression of different transcription factors were seen after downregulation of the L-type calcium channel.

These studies have revealed novel mechanisms regulating differentiation and growth of vascular cells in remodelling, involving microRNAs, focal adhesion and cross-linking proteins, membrane channels and calcium signalling, all of which are potential targets for pharmacological intervention.


ROLE OF RECRUITED CELLS IN REMODELLING. Stem cell recruitment to the damaged vessel is crucial for vessel remodelling. Mouse induced pluripotent stem cells (iPSCs) differentiate to endothelial cells (ECs) under stimulation by vascular endothelial growth factor (VEGF), and this stimulation was shown to be enhanced by shear stress. The signalling pathways of VEGF receptor activation involve miR-21, which targets the PTEN/Akt and TGFβ-2 pathways, which regulate stem cell differentiation into endothelial cells. Our findings indicate that elucidation of the molecular mechanisms underlying miR-21 induced stem cell differentiation might provide the basic information for stem cell therapy during vascular remodelling/disease.

The SmArt website at http://www.smallartery.eu/ includes information about the SmArt ITN and its successor SMARTER (start 1/11/2013) with contact details for all partner PIs and fellows.