Parkin Protects against Mitochondrial Toxins and β-Amyloid Accumulation in Skeletal Muscle Cells

Abstract

Mutations in the ubiquitin ligase-encoding Parkin gene have been implicated in the pathogenesis of autosomal recessive Parkinson disease. Outside of the central nervous system, Parkin is prominently expressed in skeletal muscle. We have found accumulations of Parkin protein in skeletal muscle biopsies taken from patients with inclusion body myositis, a degenerative disorder in which intramyofiber accumulations of the ␤-amyloid peptide are pathognomonic. In comparing primary cultures of skeletal muscle derived from parkin knock-out and wild-type mice, we have found the absence of parkin to result in greater sensitivity to mitochondrial stressors rotenone and carbonyl cyanide 3-chlorophenylhydrazone, without any alteration in sensitivity to calcium ionophore or hydrogen peroxide. Utilizing viral expression constructs coding for the Alzheimer disease and inclusion body myositis-linked ␤-amyloid precursor protein and for its metabolic byproducts A␤42 and C100, we found that parkin knock-out muscle cells are also more sensitive to the toxic effects of intracellular A␤. We also constructed a lentiviral system to overexpress wild-type Parkin and have shown that boosting the levels of parkin expression in normal skeletal muscle cultures provides substantial protection against both mitochondrial toxins and overexpressed ␤-amyloid. Correspondingly, exogenous Parkin significantly lowered A␤ levels. These data support the hypothesis that in myocytes parkin has dual properties in the maintenance of skeletal muscle mitochondrial homeostasis and in the regulation of A␤ levels. The Parkin protein is considered an E33 ubiquitin ligase and when mutated has been linked to the development of autosomal recessive Parkinson disease (1-3). In overexpression (or in cellular) models it functions to modify specific target proteins by ubiquitination, earmarking them for proteasomal degradation (3). Putative targets of Parkin include, among others, Pael-R (Parkin-associated endothelin-like receptor) (4), synphilin-1 (5), a modified form of ␣-synuclein (6), CDCrel1 (7), and p38/JTV-1, an aminoacyl-tRNA synthetase cofactor (8). Previous reports have indicated that the cellular stress response promotes the formation of a complex between Parkin, the chaperone Hsp70, the C terminus of Hsc70 interacting protein CHIP, and Pael-R (9). Recently, Parkin has also been shown to interact with the ␣4 subunit of the 19 S proteasome, although the latter does not appear to serve as a substrate for parkin-directed ubiquitination (10). Substantial accumulations of Parkin are found associated with ␣-synuclein and ubiquitin bearing Lewy bodies in Parkinson disease and dementia with Lewy bodies (11), suggesting a role in the pathologic sequestration of proteins in these disorders. Although parkin mRNA is expressed throughout the central nervous system, it is also prominently expressed in skeletal and cardiac muscle, tissues with sustained levels of protein turnover (1).Although Parkin can be found in both cytosolic and membrane-associated compartments of the cel...

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Mitochondria as targets for chemotherapy

“…Mutations in Parkin, which is implicated in the pathogenesis of autosomal recessive PD, caused marked alterations of mitochondrial structure and function and increased sensitivity to the mitochondrial stressors, rotenone and carbonyl cyanide 3-chlorophenylhydrazone. In addition, Parkin knockout muscle cells were more sensitive to the toxic effects of intracellular b-amyloid peptides (Ab) characteristic of AD, whereas Parkin expression in normal skeletal muscle cultures provided substantial protection against both mitochondrial toxins and overexpressed Ab [50]. Further, the activity of mitochondrial respiratory enzymes in patients with Parkin gene mutations was markedly decreased [51].…”

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