Abstract 18695: Role of Autophagy in Amyloidogenic Light Chain Induced Cardiac Toxicity

Abstract

AL amyloid cardiomyopathy is characterized by the deposition of amyloid fibers from monoclonal immunoglobulin light chain proteins (AL-LC) in the heart. We and others have shown that AL-LC directly results in cardiac toxicity; however, the mechanisms underlying this toxicity remain to be determined. Morphological examinations of hearts from patients with AL amyloid cardiomyopathy reveal increased double membrane autophagosome-like structures and mitochondrial deformation. Using isolated adult rat cardiomyocytes, we therefore examined whether dysregulated autophagy mediates the development of AL-LC induced cardiac toxicity. Methods and Results: Autophagy is a dynamic process and autophagic flux is, hence, determined by measurement of LC3-II protein expression in the absence and presence of lysosome inhibitors (E64d and pepstatin A). The autophagic substrate, polyubiquitin-binding protein (p62), was also examined via immunoblotting. We found that LC3-II expression increased in the absence but decreased in the presence of lysosome inhibitors in cardiomyocytes exposed to AL-LC relative to vehicle control. Moreover, p62 expression was increased in AL-LC treated cardiomyocytes, suggesting that AL-LC resulted in impaired clearance of autophagosomes in cardiomyocytes. To define the causal relationship between dysregulated autophagic clearance and AL-LC induced cardiac toxicity, we determined the functional consequences of autophagic inhibition by treatment with 3MA (3-Methyladenine, PI3K inhibitor), or autophagic activation by treatment with rapamycin (mTOR inhibitor). Inhibition of autophagy led to worsen of AL-LC induced cardiac toxicity whereas activation of autophagy protected cardiomyocytes against AL-LC induced cardiac toxicity, as measured by ROS production and cell death. Conclusion: Our data demonstrate that AL-LC directly results in impaired autophagic clearance in cardiomyocytes, contributing to the development of amyloid cardiac toxicity and cardiomyopathy. Therapies aimed at modulation of cellular autophagy may provide new treatment approaches for patients with AL amyloid cardiomyopathy.