CTSL and atrial fibrillation: To further investigate if lysosomal function is also altered due to mitochondrial defects as the mitochondria-lysosome function are closely related, we measured the activity of lysosomal acid hydrolase, cathepsin L. Indeed, we observed that cathepsin L activity is significantly reduced by AF (Figure 1D) and also increases the activity of pro-inflammatory caspase-1 (Figure 1E) suggesting inflammasome activation by the AF treatment.