Cathepsins drive anti-inflammatory activity by regulating autophagy and mitochondrial dynamics in macrophage foam cells

Background/Aims: Atherosclerosis underlies the majority of cardiovascular events, consequent to non-resolving inflammation. Considerable evidence implicates autophagy dysfunction at the core of this inflammatory condition, but the basis of this dysfunction is not fully understood. Methods: Using an in vitro model of lipid-laden macrophages, activity-based probes and high-throughput techniques, we studied the role of the cysteine proteases cathepsins in autophagy. Results: We showed that cathepsin activity is suppressed by oxidized lipids and that cathepsin has an indispensable role in the autophagy-lysosomal degradation pathway. Accordingly, loss of cathepsin function resulted in autophagy derangement. Shotgun proteomics confirmed autophagy dysfunction and unveiled a pivotal role of cathepsin L in a putative cathepsin degradation network. At the physiological level, cathepsin inhibition resulted in mitochondrial stress, which translated into impaired oxidative metabolism, excessive production of reactive oxygen species and activation of the cellular stress response, driven by ATF4-CHOP transcription factors. In addition, transcriptomic analysis of these cells uncovered some genetic similarities with the inflammatory macrophage phenotype (a.k.a M1 macrophages) and increased expression of inflammatory cytokines. Conclusion: Our data highlight the importance of cathepsins for mitochondrial quality control mechanisms and amelioration of vascular inflammation.