Directly visualizing mitochondrial shrinkage and lysosomal expansion during mitophagy using super-resolution microscopy

Abstract

Mitochondria–lysosome contact (MLC) is an essential process for degradation of damaged mitochondria and clearance of these malfunctioned mitochondria is crucial to keep the cell healthy. This is achieved by a process called mitophagy, which is a pathway that eliminates damaged mitochondria by sequestering them with autophagosomes and their subsequent degradation in autolysosomes. However, the process of MLC, especially the morphological changes in mitochondria and lysosomes, is poorly understood due to the non-availability of suitable fluorescent probes that could be used in super-resolution microscopy (SRM). Here, by rationally conjugating cyanine dyes to BSA, which is known to reach lysosomes via endocytic pathways, we directly visualized the shrinkage of mitochondria and expansion of lysosomes during mitophagy using SRM. We further observed both the point and side by side contacts of lysosomes and mitochondria. The complete engulfment of mitochondria inside lysosomes was also clearly visualized.