Sensing and Clearance of Damaged Lysosomes in Macrophages and Atherosclerosis

Project Summary / Abstract Atherosclerosis is the underlying cause of the majority of cardiovascular diseases leading to tremendous morbidity and mortality. The macrophage plays a significant role in atherosclerotic plaque progression and recent efforts to identify the culprit cellular processes in macrophages have renewed interest in the role of the autophagy-lysosomal system. Various lines of evidence demonstrate a progressive dysfunction in the lysosomes of plaque macrophages which affects their ability to clear lipids and apoptotic cells. Thus, attempts at reprogramming the degradative capacity of macrophages might be a fruitful therapeutic area. Our work with TFEB, the predominant transcription factor regulating autophagy-lysosomal biogenesis, shows that enhancing its function in macrophages is atheroprotective. We have recently determined that a critical sensor for lysosomal damage in macrophages which acts to activate TFEB and autophagy is Galectin-3 (Gal3). Gal3 has traditionally been known as a biomarker for cardiovascular disease and a secreted protein with roles in immune cell recruitment and promoting atherosclerosis. However, its intracellular role is likely protective by facilitating autophagy-lysosomal function. In addition, we have shown that macrophage inflammasome activation and ensuing pyroptosis is a major trigger for Gal3 release on par with IL-1β secretion. This raises the interesting possibility that interventions aimed at curbing Gal3 release could be dually beneficial by preventing deleterious extracellular functions while retaining it in macrophages to mediate the lysosomal damage response. In this proposal, we aim to test the hypothesis that the Gal3-TFEB/autophagy axis in macrophages ameliorates atherosclerosis by mediating the sensing, clearance, and replacement of damaged lysosomes. We will evaluate this in three aims with the first aim assessing the role of Gal3 in macrophage lysosomal damage response, the second aim assessing the mechanism of Gal3 release with the goal of shifting the balance toward its beneficial intracellular roles, and the third aim evaluating the relevance of these mechanisms in human monocytes/macrophages.