Cardiomyopathy in elderly men can be the result of extracellular deposits of amyloid in the heart, pathology referred to as Senile Systemic (or Cardiac) Amyloidosis (SSA). In SSA, wild-type transthyretin (TTR), normally a serum protein, forms amyloid deposits which disrupt normal cardiac cell functioning. The molecular mechanisms in SSA remain undefined, but are important to determine as autopsy studies have suggested that heart failure caused by amyloidosis may be vastly unrecognized and undiagnosed in the ever expanding aging population. Based on our previous studies, we hypothesize that in SSA: (1) soluble, prefibrillar high molecular weight forms of TTR (TTRHMW) are present in serum and develop into amyloid fibrils by a mechanism mediated by chaperone proteins (possibly 1B-crystallin and/or clusterin), (2) TTRHMW are formed through interactions of TTR with biomolecules whose concentration, structure or function are specific to the serum and/or cardiac tissue of patients with SSA, and (3) the presence of TTRHMW in SSA sera is associated with more rapid cardiac disease progression. Utilizing a proteomic approach coupled to an analytical strategy which is multidisciplinary (biochemical, biophysical, histopathologic, and cardiologic), we hope to elucidate the molecular mechanisms underlying SSA, and in so doing, provide useful diagnostic information and identify novel targets for therapeutic intervention. To test our hypothesis, we propose:
Specific Aim 1 : To investigate TTR molecular associations in SSA by examining patient sera for the presence of TTRHMW using sedimentation rate analysis and characterizing purified TTRHMW by mass spectrometric (MS) analyses.
Specific Aim 2 : To link proteomic changes, TTRHMW, and amyloid formation in SSA by defining serum and cardiac (or fat) tissue proteomes in patients using 2-D gel electrophoresis and MS initially focusing on 1B- crystallin and clusterin. The amyloidogenic potential of TTRHMW and the effects of 1B-crystallin and clusterin (and other associated biomolecules identified in Aim 1) on fibril formation will be tested using an established in vitro amyloid fibrillogenesis assay and recombinant proteins.
Specific Aim 3 : To study the association of TTRHMW with more rapid disease progression in SSA by measuring TTRHMW in patient sera at baseline and annually for 3 years and correlating results with cardiac troponin I, brain natriuretic peptide, left ventricular (LV) end-diastolic and end-systolic diameters, and LV ejection fraction as measures of ongoing myocardial damage and cardiac structural remodeling.
Heart disease associated with amyloid deposits is a life threatening condition and may be a significant cause of morbidity in the aging population. It is expected that as many as 2.25 million Americans (25% of the US population over the age of 80) are afflicted with senile systemic amyloidosis (SSA), pathology of unknown etiology related to the amyloidotic aggregation of the plasma protein transthyretin (TTR). The studies proposed in this application will help us to elucidate the molecular mechanisms underlying SSA, and in so doing, provide the theoretical platform for the design of effective and non-invasive diagnostic procedures and therapeutic strategies.
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