Role of AIIt in homocysteine-mediated vascular dysfunction

A diet low in folic acid (found in leafy greens) and high in the amino acid methionine (found in many meat products), can lead to high blood levels of homocysteine (Hcy), which in turn is a risk factor for heart attack and stroke. Damage to the blood vessels that results in heart attack and stroke occurs because Hcy blocks the busting up of tiny clots that form in the blood which then accumulate in the tissues and may also grow into larger clots. My laboratory has shown that a protein, AIIt, that is present on the surface of the cells that form the blood vessels, controls the production of an enzyme, plasmin, which is responsible for busting up blood clots. Mice that have no AIIt produce much less plasmin and have a dramatic accumulation of blood clots in their tissues. We intend to show that Hcy prevents the blood vessel cells from breaking down these blood clots by binding to AIIt and blocking its ability to produce plasmin. We will test this hypothesis by feeding mice a diet that is high in methionine and low in folic acid, which will give the mice high blood levels of Hcy. We will then compare the blood clot busting ability of these mice with control mice fed a diet with normal levels of folic acid and methionine and having normal levels of Hcy. We will then see if these changes in the ability of the mouse to destroy blood clots correlate with changes in the structure of AIIt caused by Hcy. We will isolate the cells that line the blood vessels in two forms, one which has AIIt and another which does not and directly compare the effect of Hcy on the clot busting ability of these cells. We will also determine why the modification of AIIt by Hcy blocks the ability of AIIt to generate plasmin and bust up blood clots by incubating purified AIIt with Hcy in test-tubes and documenting where in AIIt Hcy binds and how this binding blocks the ability of AIIt to generate plasmin.