Atrial fibrillation (AF) is the most common cardiac arrhythmia, resulting in substantial morbidity and mortality. An important risk factor for developing AF is age, with a lifetime risk of 1 in 6 for the condition. The incidence of AF is increasing in epidemic proportion as the US population ages, and currently available treatment is often ineffective. The clinical course of AF is typically progressive, due to electrical and structural remodeling in the atria with rapid stimulation that increases arrhythmia susceptibility. Oxidative stress and inflammation play an important role in generating the AF substrate and promoting this remodeling process. Recently, we showed that atrial cells rapidly stimulated in culture undergo remodeling very similar to that observed in human AF. Importantly, transcriptional profiling in paced cells exhibited striking concordance with changes seen in vivo. Unexpectedly, we observed conserved transcriptional upregulation in proteins involved in amyloidosis, a process associated with protein misfolding and deposition in multiple neurodegenerative diseases, notably Alzheimer's disease. Substantial evidence indicates that the toxic species in these disorders are soluble preamyloid oligomer intermediates, rather than the mature fibrillar, amyloid-positive deposits. Indeed, our preliminary data demonstrate striking accumulation of preamyloid oligomers in rapidly-paced atrial cells, with similar results in experimental and human AF. Taken together, these data form a strong rationale for the proposed studies. The goal of this proposal is to test the hypothesis that atrial preamyloid oligomers are pathophysiologically linked to the development of AF in humans.
In Specific Aim 1, human atrial samples obtained during routine cardiac surgery at multiple centers will be used to examine the relationship of preamyloid oligomer formation to age, the risk of postoperative AF, and established AF in humans. Indicators of oxidative stress will also be investigated in these samples.
In Specific Aim 2, we will explore the effects of potent antioxidant/anti-inflammatory compounds that are also known to inhibit soluble oligomer formation, on the generation of atrial preamyloid oligomers in response to rapid stimulation in vitro and during experimental AF. Atrial natriuretic peptide (ANP) is known to form amyloid fibrils, and it is present in isolated atrial amyloidosis, a process that increases with aging in humans. Recently, mutations in ANP were causally linked to familial AF.
In Specific Aim 3, we will determine whether these ANP mutations promote the formation of preamyloid oligomers as a potential mechanism to increase AF susceptibility. The proposed studies have substantial significance, since preamyloid oligomers may not only provide a mechanistic link between oxidative stress, aging, and AF, but they may also provide a novel therapeutic target in the treatment of this common and difficult to treat arrhythmia.
The studies described in this proposal will improve our understanding of the basic mechanisms that cause a heart rhythm disturbance known as atrial fibrillation. This is important because atrial fibrillation is common in the general population, and it causes a substantial number of strokes each year, as well as weakened heart function, or heart failure. We anticipate that we will identify new mechanisms that increase a person's susceptibility to atrial fibrillation, and thus new approaches should develop to prevent its occurrence.
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