The extracellular environment —— that is to say, the environment outside the cell —— is composed of proteins secreted by cells and is deeply involved in cell function. The same can be said of vascular cells: it has been discovered that in arteries, which are exposed to the stresses of blood pressure and blood flow, rubberlike elastic fibers principally composed of a protein called elastin, which is secreted by vascular cells called smooth muscle cells (SMCs), are deeply involved in the development of arterial diseases such as aortic aneurysm and aortic dissection. Also underway is research into biomarkers for predicting the onset of disease using the knowledge obtained on the extracellular environment.