In a laboratory human cell line, MGRN1 protected transiently damaged mitochondria from degradation
In a laboratory human cell line, MGRN1 protected transiently damaged mitochondria from degradation
On September 1, Cell Reports published a study of a cellular model in which mitochondria recovered their shape and energy production after brief chemical stress. In this model, the authors found that MGRN1 restrained mitophagy, the process that delivers damaged mitochondria to lysosomes for degradation.
Mitophagy removes severely damaged mitochondria from cells. In hereditary cardiomyopathy, mitophagy removed toxic protein aggregates together with mitochondria. The authors of the new study examined an intermediate case: whether a cell can restore an organelle to function after reversible damage.
They treated laboratory-grown human U2OS cells with CCCP, a compound that rapidly disrupts mitochondrial function. After 30 minutes of exposure followed by washout, the mitochondria regained their normal shape within six hours. Respiration, production of ATP, the molecule that transfers energy within the cell, and the inner membrane folds also recovered. Recovery was largely preserved after exposures lasting from half an hour to two hours but declined substantially after four hours.
The mKeima indicator changes color when a mitochondrion enters a lysosome. After brief stress, it retained the color associated with mitochondria outside lysosomes, whereas deferiprone, which specifically induces mitophagy, produced red puncta. Together with the respiration measurements, these observations show that organelle function recovered alongside mitochondrial shape.
The authors labeled proteins near the mitochondrial outer membrane before stress, immediately afterward, and after two hours of recovery. Among the candidates, MGRN1 showed the largest increase in mitochondrial association. MFN1, a protein on the mitochondrial outer membrane, helped recruit MGRN1 there. In two independent cell lines in which MGRN1 was knocked out, mitochondria recovered more slowly after two hours of stress, and mitophagy occurred more frequently.
Blocking autophagy with 3-MA and reducing levels of GP78, a protein that promotes mitophagy, largely restored the capacity for recovery. The cells also activated antioxidant defenses. The DELE1–ATF4 and Nrf2 signaling pathways increased the activity of genes that help cells manage oxidative stress. When the researchers disrupted components of these pathways, recovery worsened. In cell lines lacking MGRN1, DELE1–ATF4 signaling subsided more slowly after washout, and mitochondrial recovery was poorer.
In this cellular model, antioxidant defenses restored mitochondrial function, while MGRN1 protected the mitochondria from premature degradation.