Nanoscopic quantification of sub-mitochondrial morphology, mitophagy and mitochondrial dynamics in living cells derived from patients with mitochondrial diseases

Weiwei Zou,Jesse Slone,Li Yang,Xiaoting Lou,Jiajie Diao,Taosheng Huang,Qixin Chen

doi:10.1186/s12951-021-00882-9

Abstract

SLC25A46 mutations have been found to lead to mitochondrial hyper-fusion and reduced mitochondrial respiratory function, which results in optic atrophy, cerebellar atrophy, and other clinical symptoms of mitochondrial disease. However, it is generally believed that mitochondrial fusion is attributable to increased mitochondrial oxidative phosphorylation (OXPHOS), which is inconsistent with the decreased OXPHOS of highly-fused mitochondria observed in previous studies. In this paper, we have used the live-cell nanoscope to observe and quantify the structure of mitochondrial cristae, and the behavior of mitochondria and lysosomes in patient-derived SLC25A46 mutant fibroblasts. The results show that the cristae have been markedly damaged in the mutant fibroblasts, but there is no corresponding increase in mitophagy. This study suggests that severely damaged mitochondrial cristae might be the predominant cause of reduced OXPHOS in SLC25A46 mutant fibroblasts. This study demonstrates the utility of nanoscope-based imaging for realizing the sub-mitochondrial morphology, mitophagy and mitochondrial dynamics in living cells, which may be particularly valuable for the quick evaluation of pathogenesis of mitochondrial morphological abnormalities.

Highlights

The mitochondrion is the cellular organelle which is critical for energy metabolism in mammals and most other eukaryotes
Combined with the sub-mitochondrial structure identification/ quantification and mitochondria-lysosome interaction quantification methods developed by our group [15,16,17,18], we found that the damage of mitochondrial cristae was the most probable cause of mitochondrial dysfunction in patients with SLC25A46 mutations, and that the damaged mitochondrial cristae did not induce mitophagy
Why do the SLC25A46 mutant cells examined in our study show mitochondrial hyper-fusion but a decrease in mitochondrial respiratory function? The respiratory function of mitochondria is a series of oxidation-reduction reactions mediated by multiple complexes located on the mitochondrial inner cristae, which eventually produce adenosine triphosphate (ATP) and provide energy for the tissues and cells in living organisms [43, 44]

Summary

Introduction

The mitochondrion is the cellular organelle which is critical for energy metabolism in mammals and most other eukaryotes. SLC25A46 mutations can lead to highly fused mitochondria and decreased mitochondrial oxidative phosphorylation (OXPHOS) This result contradicts the traditional view that mitochondrial fusion is beneficial to the. With a spatial resolution of 100– 120 nm, 3D-SIM was recently developed to observe and quantify mitochondrial morphology, sub-mitochondrial structure, mitophagy, mitochondrial dynamics, and the interaction of organelles [11,12,13]. We have set out to take advantage of the live-cell nanoscope-3D-SIM to dynamically observe the mitochondrial and sub-mitochondrial morphology in the fibroblasts derived from the patients carrying biallelic mutations in SLC25A46. Combined with the sub-mitochondrial structure identification/ quantification and mitochondria-lysosome interaction quantification methods developed by our group [15,16,17,18], we found that the damage of mitochondrial cristae was the most probable cause of mitochondrial dysfunction in patients with SLC25A46 mutations, and that the damaged mitochondrial cristae did not induce mitophagy. This study indicates 3D-SIM can be used to evaluate sub-mitochondrial structural damage in living cells and identify the pathology for patients with mitochondrial disease

Methods

Results

Discussion

Conclusion