As you recall from our lesson on aging, hypertension is one of the conditions associated to aging which then causes vascular dysfunction. However, studying hypertension in vivo and elucidating the breakdown of the mechanisms causing vascular dysfunction, it's not easy. Here in the cartoon, you have a schematic representation of how hypertension causes vascular dysfunction in prolonged time exposure to it. So, there are mainly two mechanical forces that arteries are faced with in conditions of increased blood pressure. One is called shear stress which is caused by the rolling and the friction of blood particles onto the vascular wall, namely the endophelium. And with increasing blood pressure, the friction and the speed at which these particles roll onto the vascular bed is increased, thus causing an inflammatory response of the vascular bed which leads eventually to vascular dysfunction. Another mechanical force acting on to the arteries at the very same time in conditions of increased blood pressure is denominated radial strain or cyclic stretch. And these results from the fact that in conditions of increased blood pressure, the vessel is exposed to an increased pulsatility and increased volume of blood which results in an increased radial stretch or strain that the vessel is faced with. Thus, in fact, what happens is that the vascular wall, in conditions of hypertension, is increasingly stretched as compared to normal tensive of condition. As I was mentioning however, in vivo, these two mechanical structures acting on the artery, as a consequence of increased blood pressure, do so simultaneously. Thus, it is not possible to discern the effects of one versus the other. For this purpose, in our laboratory, we have this machine called the cyclic stretch machine, which reproduces one of the two mechanical stretches in arteries faced with in conditions of increased blood pressure. In particular, the radial strain or cyclic stretch. What we have here is an ordinary canonic six-well plate dish where different types of cells are cultured. In our cases, it's endophelial cells. As you can see, this culture dish is made of six different wells which are then usually filled with cells and the cells adhere onto the bottom. They're then supplemented with specific media that allow them to grow. As you can see, this is a rigid structure both on the top and most importantly in the bottom which is where cells adhere. So, in the cyclic stretch machine, we have a variant of this six-well dish plate. This is very similar from the top. As you can see, it's still made of six different wells. However, the bottom of this dish is made of an elastic lamina. And this lamina is the one where the cells once seeded into the six-well plates adhere to. And once the cells have adhered onto these, they are then mounted onto this special platform which is connected via several tubings to a suction pump. And once the suction pump is activated, what happens is that it sucks from below the elastic lamina where the cells are stuck onto resulting in a stretching downwards off the raptor. And this stretching that the cells are faced to, mimics or resembles the radial strains stretch or cyclic stretch that is observed in conditions of increased blood pressures inside arteries of hypertensive patients. So, once this set up has been completed and the suction pump is started, cells are exposed for different time periods to different conditions of cyclic stretch. Here, we can regulate the extent of the stretch and how many times it occurs within a minute to simulate different degrees of hypertension. At the end of the experiment then, the cells are isolated, they are put into a lysis buffer. Different proteins are collected, and by doing so, we can then measure how different degrees of cyclic stretch affect different proteins present inside the cells, which may be crucially involved in the pathogenesis of vascular dysfunction as observed in hypertensive patients.Thank you for your attention.
