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Rapid activation causes remodeling of atrial myocytes resembling that which occurs in experimental and human atrial fibrillation (AF). Using this cellular model, we previously observed transcriptional upregulation of proteins implicated in protein misfolding and amyloidosis. For organ-specific amyloidoses such as Alzheimer's disease, preamyloid oligomers (PAOs) are now recognized to be the primary cytotoxic species. In the setting of oxidative stress, highly-reactive lipid-derived mediators known as γ-ketoaldehydes (γ-KAs) have been identified that rapidly adduct proteins and cause PAO formation for amyloid β1-42 implicated in Alzheimer's. We hypothesized that rapid activation of atrial cells triggers oxidative stress with lipid peroxidation and formation of γ-KAs, which then rapidly crosslink proteins to generate PAOs. To investigate this hypothesis, rapidly-paced and control, spontaneously-beating atrial HL-1 cells were probed with a conformation-specific antibody recognizing PAOs. Rapid stimulation of atrial cells caused the generation of cytosolic PAOs along with a myocyte stress response (e.g., transcriptional upregulation of Nppa and Hspa1a), both of which were absent in control, unpaced cells. Rapid activation also caused the formation of superoxide and γ-KA adducts in atriomyocytes, while direct exposure of cells to γ-KAs resulted in PAO production. Increased cytosolic atrial natriuretic peptide (ANP), and the generation of ANP oligomers with exposure to γ-KAs and rapid atrial HL-1 cell stimulation, strongly suggest a role for ANP in PAO formation. Salicylamine (SA) is a small molecule scavenger of γ-KAs that can protect proteins from modification by these reactive compounds. PAO formation and transcriptional remodeling were inhibited when cells were stimulated in the presence of SA, but not with the antioxidant curcumin, which is incapable of scavenging γ-KAs. These results demonstrate that γ-KAs promote protein misfolding and PAO formation as a component of the atrial cell stress response to rapid activation, and they provide a potential mechanistic link between oxidative stress and atrial cell injury., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

During atrial fibrillation (AF), rapid stimulation causes atrial remodeling that increases arrhythmia susceptibility. Using an established atrial (HL-1) myocyte model, we investigated the transcriptional profile associated with early atrial myocyte remodeling. Spontaneously contracting HL-1 cells were cultured in the absence and presence of rapid stimulation for 24 h and RNA harvested for microarray analysis. We identified 758 genes that were significantly altered with rapid stimulation (626 up- and 132 down-regulated). Results were confirmed using real-time quantitative RT-PCR for selected genes based on physiological relevance in human AF and/or experimental atrial tachycardia (AT), and regulation in the microarray results. In some cases, transcriptional changes were rapid, occurring within 3 h. For a selected group of genes, results were validated for the expressed protein, with findings that correlated with observed transcriptional changes. Significantly regulated genes were classified using the Gene Ontology Database to permit direct comparison of our findings with previously published myocardial transcriptional profiles. For broad functional categories, there was strong concordance between rapidly stimulated HL-1 myocytes and human AF, but not for other remodeling paradigms (cardiomyopathy and exercise). Many individual gene changes were conserved with AF/AT, with marked up-regulation of genes encoding brain and atrial natriuretic peptide precursors, and heat shock proteins. For the conserved genes, both a cellular stress and survival response was evident. Our results demonstrate similarities with human AF/experimental AT with respect to large-scale patterns of transcriptional remodeling, as well as regulation of specific individual genes. Importantly, we identified novel pathways and molecules that were concordantly regulated in vivo.