Impairment of Proteasome and Autophagy Underlying the Pathogenesis of Leukodystrophy

Abstract

Impairment of the ubiquitin-proteasome-system (UPS) and autophagy causing cytoplasmic aggregation of ubiquitin andp62 have been implicated in the pathogenesis of most neurodegenerative disorders, yet, they have not been fully elucidated in leukodystrophies. The relationship among impairment of UPS, autophagy, and globoid cell leukodystrophy (GLD), one of the most common demyelinating leukodystrophies, is clarified in this study. We examined the ubiquitin and autophagy markers in the brains of twitcher mice, a murine model of infantile GLD, and in human oligodendrocytes incubated with psychosine. Immunohistochemical examinations showed spatiotemporal accumulation of ubiquitin- and p62-aggregates mainly in the white matter of brain and spinal cord at disease progression. Western blot analysis demonstrated a significant accumulation of ubiquitin, p62, and LC3-II in insoluble fraction in parallel with progressive demyelination and neuroinflammation in twitcher brains. In vitro study validated a dose- and time-dependent cytotoxicity of psychosine upon autophagy and UPS machinery. Inhibition of autophagy and UPS exacerbated the accumulation of insoluble ubiquitin, p62, and LC3-II proteins mediated by psychosine cytotoxicity as well as increased cytoplasmic deposition of ubiquitin- and p62-aggregates, and accumulation of autophagosomes and autolysosomes. Further, the subsequent accumulation of reactive oxygen species and reduction of mitochondrial respiration led to cell death. Our studies validate the impairment of proteasome and autophagy underlying the pathogenesis of GLD. These findings provide a novel insight into pathogenesis of GLD and suggest a specific pathomechanism as an ideal target for therapeutic approaches.

Special Issue on “Ubiquitin and Autophagy”

“…The “Ubiquitin and Autophagy” Special Issue features 13 papers: seven research articles [ 1 , 2 , 3 , 4 , 5 , 6 , 7 ] and six reviews [ 8 , 9 , 10 , 11 , 12 , 13 ]. All of them are at the intersection of ubiquitin-related processes and autophagy, including the roles of: (1) ATG and UBL proteins in the UPS and autophagy [ 2 , 3 ], (2) ubiquitin-binding autophagic receptor, p62, in autophagy signaling [ 4 ], (3) LC3-interacting region (LIR) of connexins in binding to UBL proteins [ 6 ], (4) proteasomal deubiquitinating enzyme, PSMD14, in autophagy [ 7 ], (5) sorting nexins in the UPS, autophagy and endocytosis [ 8 ], (6) ubiquitin and UBL proteins in selective autophagy [ 9 ], as well as (7) structures and interactions of the UBL proteins of Atg8-family [ 13 ].…”

“…All of them are at the intersection of ubiquitin-related processes and autophagy, including the roles of: (1) ATG and UBL proteins in the UPS and autophagy [ 2 , 3 ], (2) ubiquitin-binding autophagic receptor, p62, in autophagy signaling [ 4 ], (3) LC3-interacting region (LIR) of connexins in binding to UBL proteins [ 6 ], (4) proteasomal deubiquitinating enzyme, PSMD14, in autophagy [ 7 ], (5) sorting nexins in the UPS, autophagy and endocytosis [ 8 ], (6) ubiquitin and UBL proteins in selective autophagy [ 9 ], as well as (7) structures and interactions of the UBL proteins of Atg8-family [ 13 ]. In addition to the studies on ubiquitin and autophagy in cell culture, several groups used model organisms, such as laboratory mice [ 1 , 5 ], nematode Caenorhabditis elegans [ 2 ], and social amoeba Dictyostelium discoideum [ 3 ]. Besides, the review article of Ma and colleagues discusses the interplay between the UPS and autophagy in plants [ 10 ].…”

“…Besides, the review article of Ma and colleagues discusses the interplay between the UPS and autophagy in plants [ 10 ]. Although most of the studies explored the fundamental molecular and cellular mechanisms, some of them have interesting implications for human diseases, such as cancer [ 4 ] and leukodystrophy [ 5 ]. On top of that, the review article of Watanabe et al is dedicated to the role of ubiquitin and autophagy in neurodegenerative diseases [ 12 ].…”

“…Moreover, a fully functional UPS might depend on autophagy in the tissue- and organism-specific manner [ 2 , 3 ]. Interestingly, Lin et al described the impairment of both the UPS and autophagy in the cellular and murine (twitcher mice) models of globoid cell leukodystrophy [ 5 ].…”

“…Another underlying sub-theme of the issue revolves around p62 and its functions. While p62 serves as a ubiquitin-binding receptor for many selective autophagy pathways and accumulates on the ubiquitin-positive aggregates in the brains of twitcher mice [ 5 ], it also negatively regulates TLR4 signaling and autophagy by disrupting the intermediate TRAF6-BECN1 signaling complex and inhibiting BECN1 ubiquitination in cancer cells what reduces their migration and invasion after TLR4 stimulation [ 4 ]. Finally, Catarino et al reported an alternative, ubiquitin- and p62-independent, mechanism for bridging connexins with the UBL proteins of Atg8-family, LC3B and GABARAP.…”