Parkin reverses intracellular β‐amyloid accumulation and its negative effects on proteasome function

Abstract

The significance of intracellular β-amyloid (Aβ 42 ) accumulation is increasingly recognized in Alzheimer's disease (AD) pathogenesis. Aβ removal mechanisms that have attracted attention include IDE/neprilysin degradation and antibody-mediated uptake by immune cells. However, the role of the ubiquitin-proteasome system (UPS) in the disposal of cellular Aβ has not been fully explored. The E3 ubiquitin ligase Parkin targets several proteins for UPS degradation, and Parkin mutations are the major cause of autosomal recessive Parkinson's disease. We tested whether Parkin has crossfunction to target misfolded proteins in AD for proteasome-dependent clearance in SH-SY5Y and primary neuronal cells. Wild-type Parkin greatly decreased steady-state levels of intracellular Aβ 42 , an action abrogated by proteasome inhibitors. Intracellular Aβ 42 accumulation decreased cell viability and proteasome activity. Accordingly, Parkin reversed both effects. Changes in mitochondrial ATP production from Aβ or Parkin did not account for their effects on the proteasome. Parkin knock-down led to accumulation of Aβ. In AD brain, Parkin was found to interact with Aβ and its levels were reduced. Thus, Parkin is cytoprotective, partially by increasing the removal of cellular Aβ through a proteasome-dependent pathway. Keywords amyloid; ubiquitin ligase; Parkin; Alzheimer's; proteasome Parkin is a 465-amino-acid protein containing an N-terminal ubiquitin-like (Ubl) domain linked to a C-terminal RING box (Shimura et al., 2000). Parkin functions as an E3 ubiquitin-protein ligase (Imai et al., 2000;Shimura et al., 2000; Zhang et al., 2000), facilitating the proteasomal degradation of misfolded proteins. Several Parkin gene mutations have been linked to autosomal-recessive Parkinsonism with juvenile onset (Kitada et al., 1998;Lucking et al., 2000).In cell culture systems, Parkin fusion proteins have been shown to interact with several proteins, including the α-synuclein-binding protein synphilin-1 (Chung et al., 2001) (Huynh et al., 2000), and α/β tubulin (Ren et al., 2003). Parkin has also been found to be upregulated during the integrated cellular response to misfolded protein-induced ER stress (Imai et al., 2001). Specific targets of Parkin activity having intrinsic toxic and aggregative properties include Pael-R, the Parkin-associated endothelin-like receptor (Imai et al., 2001), and possibly an O-glycosylated form of α-synuclein (Shimura et al., 2001). Thus, Parkin has been shown to suppress the toxicity of PAEL-R (Imai et al., 2001), mutated α-synuclein A30P (Petrucelli et al., 2002;Lo Bianco et al., 2004), and a poly(Q)-expanded mutant of ataxin-3 (Tsai et al., 2003). Deletions in the Parkin gene result in the accumulation of nonubiquitinated forms of α-synuclein and Pael-R in the brain (Imai et al., 2001;Shimura et al., 2001).The accumulation of neuronal β-amyloid (Aβ) is increasingly recognized as a critical factor in Alzheimer's disease (AD) and related pathologies (Hartmann, 1999;Wilson et al., 1999;Gouras et al., 2005). Solub...

Parkin Null Cortical Neuronal/Glial Cultures are Resistant to Amyloid-β1-42 Toxicity: A Role for Autophagy?

“…The UPS is abnormal in AD [68][69][70][71] and its function is impaired by A␤ 1-42 peptides [8,72,73]. In this study we found that A␤ 1-42 treatment reduces the activities of the three proteosomal enzymes in WT and parkin null cultures.…”

“…Parkin, as E3 ubiquitin ligase reduces the levels of intracellular proteins by ubiquitination and proteasomal degradation [6,8,53,61]. Parkin, acting through the ubiquitin proteosomal system and stimulating autophagy, ship off altered proteins and mitochondria [33,62].…”

Interplay between Parkin and p53 Governs a Physiological Homeostasis That Is Disrupted in Parkinson's Disease and Cerebral Cancer

“…It should be emphasized that we demonstrated that p53 regulates, and is regulated by, several members of the γ-secretase complex [29,30,31,32,33] responsible for Aβ peptides that accumulate in Alzheimer's disease-affected brains [34]. Indeed, several studies indicated that parkin could control the levels of Aβ [35,36]. It should be noted that we recently delineated a consensus binding sequence targeted by parkin that allowed us to identify presenilins 1 and 2, the catalytic cores of the γ-secretase complex [37] as new parkin transcriptional targets [38].…”

Parkin Is Dispensable for Mitochondrial Function, but Its Ubiquitin Ligase Activity Is Critical for Macroautophagy and Neurotransmitters: Therapeutic Potential beyond Parkinson's Disease

“…Parkin overexpression activates the proteasome and facilitates protein clearance in models of neurodegeneration [7,8,68,84,85,86,87]. Parkin-mediated α-synuclein degradation via the ubiquitin-proteasome pathway now appears unlikely, and mounting evidence suggests that α-synuclein is cleared via autophagy [60,69,88,89].…”

“…Insoluble Parkin accumulates with intraneuronal β-amyloid (Aβ) in the hippocampus and cortex in association with autophagic defects in AD [18], suggesting that aging contributes to Parkin instability. Wild-type (WT) and not mutant loss-of-function Parkin increases proteasome activity [85,86,87] and degrades ubiquitinated Aβ, while proteasome inhibition leads to accumulation of ubiquitinated protein. Furthermore, several neurotoxins, including rotenone and 6-hydroxydopamine as well as dopamine, alter Parkin solubility and result in its intracellular aggregation [102].…”