Degradation of altered mitochondria by autophagy is impaired in Lafora disease

Abstract

Lafora disease (LD) is a fatal neurodegenerative disorder caused mostly by mutations in either of two genes encoding laforin and malin. LD is characterized by accumulation of a poorly branched form of glycogen in the cytoplasm of neurons and other cells. We previously reported dysfunctional mitochondria in different LD models. Now, using mitochondrial uncouplers and respiratory chain inhibitors, we have investigated with human fibroblasts a possible alteration in the selective degradation of damaged mitochondria (mitophagy) in LD. By flow cytometry of MitoTracker-labelled cells and measuring the levels of various mitochondrial proteins by western blot, we found in LD fibroblasts a partial impairment in the increased mitochondrial degradation produced by these treatments. In addition, colocalization of mitochondrial and lysosomal markers decreased in LD fibroblasts. All these results are consistent with a partial impairment in the induced autophagic degradation of dysfunctional mitochondria in LD fibroblasts. However, canonical recruitment of Parkin to mitochondria under these conditions remained unaffected in LD fibroblasts, and also in SH-SY5Y cells after malin and laforin overexpression. Neither mitochondrial localization nor protein levels of Bcl-2-like protein 13, another component of the mitophagic machinery that operates under these conditions, were affected in LD fibroblasts. In contrast, although these treatments raised autophagy in both control and LD fibroblasts, this enhanced autophagy was clearly lower in the latter cells. Therefore, the autophagic degradation of altered mitochondria is impaired in LD, which is due to a partial defect in the autophagic response and not in the canonical mitophagy signalling pathways.

Oxidative Stress, a Crossroad Between Rare Diseases and Neurodegeneration

“…Since the autophagy machinery is impaired, mechanisms that require this process are also affected in cellular and animal models of the disease. In this sense, we have recently described a defect in mitophagy, most likely due to defects in the initial steps of autophagosome formation [178]. Finally, we have also reported that oxidative stress is affected in the absence of a functional laforin-malin complex [179].…”

Neuroinflammation and progressive myoclonus epilepsies: from basic science to therapeutic opportunities

“…In addition, because of impairment in autophagy, defective mitochondria were not removed by mitophagy, worsening mitochondrial dysfunction (Ref. 33). Therefore, as in the case of ULD, there is a correlation between the presence of oxidative stress and neuroinflammation in this form of PME.…”

“…It seems that the accumulation of LBs is deleterious to the cell and affects different physiological pathways, for example, LD mice present altered autophagy and mitophagy (Refs 24 , 31 – 33 ) and signs of oxidative stress (Ref. 34 ).…”

Biomedical Implications of Autophagy in Macromolecule Storage Disorders

“…Activation of mTOR in laforin-deficient cells further activated serum/glucocorticoid-induced kinase 1 (SGK1), and suppression of SGK1 activity could lower glycogen accumulation, inhibited mTOR and rescued the autophagy defect (Singh et al, 2013). Defective autophagic flux could lead to inefficient glycophagy and build-up of Lafora bodies that have neurotoxic effects (Duran et al, 2014); additionally, was also associated with impaired mitophagy, increased mitochondrial fragmentation and ROS production, and decreased ATP levels in laforin- and malin-deficient cells (Roma-Mateo et al, 2015; Upadhyay et al, 2017; Lahuerta et al, 2018).…”