PATHOGENESIS OF HEREDITARY TRANSTHYRETIN AMYLOIDOSIS

Indiana Univ-Purdue Univ At Indianapolis, Indianapolis IN

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Abstract

DESCRIPTION (from abstract): The overall objective of this proposal is to define the pathophysiology of the autosomal dominant transthyretin amyloidoses. These diseases, while considered rare, are actually being recognized in increased numbers of kindreds throughout the world and especially in the United States. Transthyretin amyloidosis is usually associated with peripheral neuropathy, nephropathy, and cardiomyopathy which present as late-onset (adult) disease with high degrees of morbidity and mortality. To date at least 72 variants of transthyretin (TTR) have been found to be associated with systemic amyloidosis which is inherited as an autosomal dominant disease. Of particular concern is the fact that: 1) it has recently been shown that there are elderly individuals who develop transthyretin amyloid cardiomyopathy (senile cardiac amyloldosis) in the absence of any detectible mutation in transthyretin; and, 2) there is a high prevalence of one particular transthyretin mutation (isoleucine 122) in the American Black population and this is manifest as amyloid cardiomyopathy. These two findings suggest that, as the population ages, amyloid heart disease will become of greater significance to the American population. Previous studies have centered on determining structural changes of transthyretin which are related to amyloid formation. Structures of amyloid forming variants methionine 30, serine 84, alanine 60, arginine 10, tyrosine 77 have been compared to structures of non amyloid forming threonine 109, serine 6, methionine 119 and normal transthyretin. No common structural change has been found to explain initiation of the fibril forming process but preliminary data suggest that solvent accessability to variant transthyretin dimers may allow a proteolysis event which could lead to the initiation of fibril formation. Metabolic studies using radiolabelled variant and normal transthyretins have suggested increased plasma clearance of variant proteins. The Specific Aims will test the hypothesis that single amino acid substitutions in transthyretin result in changes in tertiary structure of the transthyretin molecule which allow alterations in metabolism of the variant molecule and its associated normal monomers to lead to amyloid formation. Transthyretin proteins isolated from tissues of patients with amyloidosis will be studied to characterize proteolytic peptides and determine if partial proteolysis with generation of carboxyl terminal peptides is a factor in amyloid fibril formation. Fibril forming potential of these fragments will be tested by producing recombinant protein of residues 49 - 127 and testing fibril formation with and without full-length transthyretin in vitro. A new Specific Aim will test the hypothesis that the ratio of the various tetrameric forms of transthyretin affects the propensity to form amyloid fibrils. To accomplish this aim a dual expression system in baculovirus coexpressing normal TTR and variant TIR has been developed. These studies are directed at developing methods to prevent amyloid formation from variant TTR proteins and, thereby providing therapeutic options for a disease which at the present time has no specific therapy other than liver transplantation.