ABSTRACT
Autophagy is emerging as a key regulatory process during skeletal muscle development, regeneration and homeostasis, and deregulated autophagy has been implicated in muscular disorders and age-related muscle decline. We have monitored autophagy in muscles of mdx mice and human Duchenne muscular dystrophy (DMD) patients at different stages of disease. Our data show that autophagy is activated during the early, compensatory regenerative stages of DMD. A progressive reduction was observed during mdx disease progression, in coincidence with the functional exhaustion of satellite cell-mediated regeneration and accumulation of fibrosis. Moreover, pharmacological manipulation of autophagy can influence disease progression in mdx mice. Of note, studies performed in regenerating muscles of wild-type mice revealed an essential role of autophagy in the activation of satellite cells upon muscle injury. These results support the notion that regeneration-associated autophagy contributes to the early compensatory stage of DMD progression, and interventions that extend activation of autophagy might be beneficial in the treatment of DMD. Thus, autophagy could be a 'disease modifier' targeted by interventions aimed to promote regeneration and delay disease progression in DMD.
Subject(s)
Autophagy , Muscle, Skeletal/pathology , Muscle, Skeletal/physiopathology , Muscular Dystrophy, Duchenne/pathology , Muscular Dystrophy, Duchenne/physiopathology , Regeneration , Satellite Cells, Skeletal Muscle/pathology , Animals , Biopsy , Child , Child, Preschool , Disease Progression , Humans , Male , Mice, Inbred C57BL , Mice, Inbred mdx , Muscular Dystrophy, Animal/pathology , Muscular Dystrophy, Animal/physiopathologyABSTRACT
Damaged mitochondria are eliminated by mitophagy, a selective form of autophagy whose dysfunction associates with neurodegenerative diseases. PINK1, PARKIN and p62/SQTMS1 have been shown to regulate mitophagy, leaving hitherto ill-defined the contribution by key players in 'general' autophagy. In basal conditions, a pool of AMBRA1 - an upstream autophagy regulator and a PARKIN interactor - is present at the mitochondria, where its pro-autophagic activity is inhibited by Bcl-2. Here we show that, upon mitophagy induction, AMBRA1 binds the autophagosome adapter LC3 through a LIR (LC3 interacting region) motif, this interaction being crucial for regulating both canonical PARKIN-dependent and -independent mitochondrial clearance. Moreover, forcing AMBRA1 localization to the outer mitochondrial membrane unleashes a massive PARKIN- and p62-independent but LC3-dependent mitophagy. These results highlight a novel role for AMBRA1 as a powerful mitophagy regulator, through both canonical or noncanonical pathways.
Subject(s)
Adaptor Proteins, Signal Transducing/metabolism , Autophagy/physiology , Microtubule-Associated Proteins/metabolism , Mitochondria/metabolism , Neurodegenerative Diseases/metabolism , Ubiquitin-Protein Ligases/metabolism , Animals , HEK293 Cells , HeLa Cells , Heat-Shock Proteins/metabolism , Humans , Mice , Mice, Transgenic , Sequestosome-1 Protein , TransfectionABSTRACT
Mitochondria are key organelles for the maintenance of life and death of the cell, and their morphology is controlled by continual and balanced fission and fusion dynamics. A balance between these events is mandatory for normal mitochondrial and neuronal function, and emerging evidence indicates that mitochondria undergo extensive fission at an early stage during programmed cell death in several neurodegenerative diseases. A pathway for selective degradation of damaged mitochondria by autophagy, known as mitophagy, has been described, and is of particular importance to sustain neuronal viability. In the present work, we analyzed the effect of autophagy stimulation on mitochondrial function and dynamics in a model of remote degeneration after focal cerebellar lesion. We provided evidence that lesion of a cerebellar hemisphere causes mitochondria depolarization in axotomized precerebellar neurons associated with PTEN-induced putative kinase 1 accumulation and Parkin translocation to mitochondria, block of mitochondrial fusion by Mfn1 degradation, increase of calcineurin activity and dynamin-related protein 1 translocation to mitochondria, and consequent mitochondrial fission. Here we suggest that the observed neuroprotective effect of rapamycin is the result of a dual role: (1) stimulation of autophagy leading to damaged mitochondria removal and (2) enhancement of mitochondria fission to allow their elimination by mitophagy. The involvement of mitochondrial dynamics and mitophagy in brain injury, especially in the context of remote degeneration after acute focal brain damage, has not yet been investigated, and these findings may offer new target for therapeutic intervention to improve functional outcomes following acute brain damage.
