Dopamine-modified α-synuclein blocks chaperone-mediated autophagy

Abstract

Altered degradation of α-synuclein (α-syn) has been implicated in the pathogenesis of Parkinson disease (PD).We have shown that α-syn can be degraded via chaperone-mediated autophagy (CMA), a selective lysosomal mechanism for degradation of cytosolic proteins. Pathogenic mutants of α-syn block lysosomal translocation, impairing their own degradation along with that of other CMA substrates. While pathogenic α-syn mutations are rare, α-syn undergoes posttranslational modifications, which may underlie its accumulation in cytosolic aggregates in most forms of PD. Using mouse ventral medial neuron cultures, SH-SY5Y cells in culture, and isolated mouse lysosomes, we have found that most of these posttranslational modifications of α-syn impair degradation of this protein by CMA but do not affect degradation of other substrates. Dopamine-modified α-syn, however, is not only poorly degraded by CMA but also blocks degradation of other substrates by this pathway. As blockage of CMA increases cellular vulnerability to stressors, we propose that dopamine-induced autophagic inhibition could explain the selective degeneration of PD dopaminergic neurons.

Chaperone-mediated autophagy: roles in disease and aging

“…Such mishandling of aberrant proteins alters proteostasis and often leads to the precipitation of protein aggregates that contribute to neuronal demise [49]. The involvement of CMA in neurodegeneration is two-fold, as it contributes to the elimination of pathogenic proteins, but also often, becomes victim of the toxic effect of these aberrant proteins [50][51][52][53]. This dual role of CMA in neurodegenerative disorders makes it necessary to analyze the status of this autophagy pathway in disease in order to determine whether interventions aimed at enhancing CMA activity could be of potential value or not, depending on the degree of compromise of this pathway and the reversibility of the CMA blockage.…”

“…Dysfunction in CMA has been described in both familial [50,52,54,55] and sporadic [51,52] PD. In the case of familial PD, sequence analysis reveals the presence of CMA-targeting motifs in the majority of PD-related proteins, supporting an important role for CMA in the control of their intracellular levels ( Figure 2A).…”

“…In the case of familial PD, sequence analysis reveals the presence of CMA-targeting motifs in the majority of PD-related proteins, supporting an important role for CMA in the control of their intracellular levels ( Figure 2A). Indeed, the two most commonly mutated proteins in patients with familial PD, α-synuclein and leucine-rich repeat kinase 2 (LRRK2), have both been demonstrated to undergo degradation in lysosomes via CMA using various experimental systems such as isolated lysosomes, primary mouse neuronal cultures, mouse models of PD and even neuronal-differentiated induced pluripotent stem cells and brains from familial [50,52,54,55] and sporadic [51,52] PD patients. In contrast, pathogenic mutant variants of α-synuclein (for example, A30P and A53T mutants) and of LRRK2 (for example, G2019S and R1441C mutants), despite being recognized by cytosolic hsc70 and successfully delivered to the lysosomal membrane, fail to reach the lysosomal lumen to be degraded by CMA [50,52] (Figure 2A).…”

“…Alterations of CMA have also been implicated in sporadic PD, which accounts for the majority of the PD cases [51,52]. Perturbation of α-synuclein degradation as a consequence of unfavorable post-translational modifications caused by environmental or cellular stressors (for example, pesticides, oxidative stress, so on) is a key event in the pathogenesis of sporadic PD and various synucleinopathies [57].…”

Protein misfolding and dysregulated protein homeostasis in autoinflammatory diseases and beyond

“…Interestingly CMA has been shown to degrade -synuclein [103]. However, the mutant, oligomeric or dopamine-treated -synuclein prevent its CMAmediated degradation by blocking uptake into lysosomes [111,112]. Winslow et al showed that -synuclein overexpression inhibited autophagosome formation in autophagy [113].…”