Abstract 474: Atherosclerotic Macrophages Develop a Progressive Lysosomal Dysfunction that can be Rescued by Induction of a Lysosomal Biogenesis Program

Abstract

Recent reports of the proatherogenic phenotype of mice with a macrophage-specific autophagy deficiency has renewed interest in the role of the autophagy-lysosomal system in atherosclerosis. Lysosomes have the unique role of serving to process both exogenous material including the excess of atherogenic lipids and endogenous cargo including dysfunctional proteins and organelles. Surprisingly, little is known about the effect of an atherogenic environment on macrophage lysosomes. To address this, we utilize a variety of complementary techniques to show that oxidized LDL and cholesterol crystals, two of the commonly encountered lipid species in the atherosclerotic plaque, create a profound lysosomal dysfunction in cultured peritoneal macrophages. Disruptions in lysosomal pH, enzyme activity, proteolytic capacity, membrane integrity, and morphology are readily seen when cells are incubated with such lipids. Using flow cytometry to isolate resident tissue macrophages, we show that atherosclerotic plaque macrophages show features of dysfunctional lysosomes, a process that appears to be progressive with advanced plaque formation. These observations lead us to investigate whether stimulation of lysosomal function can ameliorate some of these effects. TFEB is the only known transcription factor that acts as a master regulator of lysosomal biogenesis, although its role in macrophages has not been studied. We show that overexpression of TFEB in cultured macrophages initiates a robust prodegradative response including induction of lysosomal genes and the generation of nascent lysosomes. Interestingly, this response can rescue several deleterious effects seen with atherogenic lipid loading including reductions in the secretion of the proinflammatory cytokine IL-1β and reductions in foam cell formation. Taken together, these data demonstrate that lysosomal function is markedly impaired in atherosclerosis and suggest that induction of a lysosomal biogenesis program can have anti-atherogenic effects.