Analyses of homocysteine as a potential modifier in Marfan syndrome

$50,000 funded by TFF

Dr. Dieter Reinhardt

Faculty of Medicine, Department of Anatomy and Cell Biology and Faculty of Dentistry
McGill University, Montréal, Quebec

Over the last decade, basic and clinical research has advanced our understanding of the biological events that lead to the development of Marfan syndrome (MFS). Scientists have discovered in 1991 that fibrillin-1 is the defective connective tissue protein in MFS. Since then more than 1000 different fibrillin-1 gene defects (mutations) have been reported. One characteristic feature of MFS is the wide variability of clinical symptoms. From this fact, scientists and clinicians conclude that other factors, called modifiers, must exist which are able to modify the development of the clinical symptoms in MFS. Today, it is not clear what these modifiers are and how they act.

Recently, it has been reported that MFS patients with aortic dissection have increased levels of a toxic amino acid called homocysteine in their blood as compared to patients with milder symptoms. Therefore, homocysteine could be one of these modifiers in MFS. Highly elevated homocysteine levels are found in another genetic disorder called homocystinuria and the clinical symptoms in the connective tissue of these patients are remarkably similar to those found in MFS. We recently demonstrated that high homocysteine levels, similar to those found in homocystinuria patients, chemically modify fibrillin-1, which alters the physical shape of the protein. Based on these data, we propose here that moderately elevated homocysteine, in concentrations found in MFS patients experiencing aortic dissection, is able to chemically modify fibrillin-1 containing typical MFS mutations. We further predict that homocysteine-modified fibrillin-1 induces other molecular events that ultimately affect the development of the clinical symptoms in MFS.

We will use different biochemical and cell biological techniques to test our hypotheses. We will compare the function of homocysteinylated fibrillin-1 with that of normal fibrillin-1. It is planned to produce a series of fibrillin-1 proteins containing typical MFS mutations leading to the classical and to the severe neonatal form of MFS. Both groups of fibrillin-1 mutations will be compared for their protease susceptibility. The mutated proteins will be used to analyze whether homocysteine can chemically modify the proteins and whether mutated fibrillin-1 is more vulnerable to this modification as compared to the non-mutated fibrillin-1. Furthermore, we will test whether homocysteine-modified fibrillin-1 can alter other processes such as protease expression patterns that might contribute to the development of the more severe cardiovascular symptoms. Finally, fibrillin-1 will be analyzed in a mouse model with mildly elevated homocysteine levels.

We anticipate that homocysteine has a detrimental effect on functional properties of fibrillin-1. If this is indeed the case, then we expect that this project will contribute to the development of new preventive strategies for the development of the symptoms in MFS by treatment with homocysteine-reducing agents.