The Parkinson's disease genes pink1 and parkin promote mitochondrial fission and/or inhibit fusion in Drosophila

Abstract

Mutations in PTEN-induced kinase 1 (pink1) or parkin cause autosomal-recessive and some sporadic forms of Parkinson's disease. pink1 acts upstream of parkin in a common genetic pathway to regulate mitochondrial integrity in Drosophila. Mitochondrial morphology is maintained by a dynamic balance between the opposing actions of mitochondrial fusion, controlled by Mitofusin (mfn) and Optic atrophy 1 (opa1), and mitochondrial fission, controlled by drp1. Here, we explore interactions between pink1/parkin and the mitochondrial fusion/fission machinery. Muscle-specific knockdown of the fly homologue of Mfn (Marf ) or opa1, or overexpression of drp1, results in significant mitochondrial fragmentation. Mfn-knockdown flies also display altered cristae morphology. Interestingly, knockdown of Mfn or opa1 or overexpression of drp1, rescues the phenotypes of muscle degeneration, cell death, and mitochondrial abnormalities in pink1 or parkin mutants. In the male germline, we also observe genetic interactions between pink1 and the testes-specific mfn homologue fuzzy onion, and between pink1 and drp1. Our data suggest that the pink1/parkin pathway promotes mitochondrial fission and/or inhibits fusion by negatively regulating mfn and opa1 function, and/or positively regulating drp1. However, pink1 and parkin mutant flies show distinct mitochondrial phenotypes from drp1 mutant flies, and flies carrying a heterozygous mutation in drp1 enhance the pink1-null phenotype, resulting in lethality. These results suggest that pink1 and parkin are likely not core components of the drp1-mediated mitochondrial fission machinery. Modification of fusion and fission may represent a novel therapeutic strategy for Parkinson's disease.arkinson's disease (PD), the second most common neurodegenerative disorder, is characterized by degeneration of dopaminergic neurons in the midbrain (1). Although the exact cause of PD is unclear, mitochondrial toxins such as 1-methyl 4-phenyl 1,2,3,6-tetrahydropyridine (MPTP) can selectively destroy dopaminergic neurons and cause clinical features similar to PD (2, 3). Moreover, mitochondrial respiratory dysfunction also occurs in sporadic PD (4). The most compelling evidence for a mitochondrial etiology of PD, however, derives from the study of genes mediating familial forms of the disease (4, 5). Mutations in PTEN-induced kinase 1 (Pink1; PARK6), which encodes a serine-threonine kinase localized to mitochondria, and parkin (PARK2), which encodes a RING finger-containing E3 ubiquitin ligase, have been found in recessively inherited and sporadic PD cases (6-9). Previously, we and others have reported that Drosophila pink1 and parkin function in the same genetic pathway, with pink1 acting upstream of parkin, to regulate mitochondrial integrity in testes, muscle, and dopaminergic neurons (10-12). Flies lacking pink1 or parkin function are viable and show muscle degeneration and TUNEL staining, indicative of cell death (10-13). Subsequent studies have shown that parkin can suppress mitochondrial defects caused by pink1...

PINK1 as a Molecular Checkpoint in the Maintenance of Mitochondrial Function and Integrity

“…Light microscopic observations of fly spermatids reveal that nebenkerns are swollen and fail to properly divide in PINK1 and parkin mutants. These observations indicate that PINK1 and Parkin control mitochondrial fusion -fission processes (Deng et al, 2008).…”

“…Moreover, further genetic analyses using mitochondrial fusionfission regulators demonstrated that PINK1 and parkin mutant phenotypes are successfully rescued by the overexpression of Drp1, a dynamin-related GTPase that promotes mitochondrial fission, or the downeregulation of Opa1 or Marf, which are other dynamin-related GTPases that induce mitochondrial fusion (Deng et al, 2008;Park et al, 2009;Poole et al, 2008;Yang et al, 2008). These findings suggest that PINK1 and Parkin balance mitochondrial dynamics by promoting mitochondrial fission to properly maintain mitochondrial function.…”

Revisiting oxidative stress and mitochondrial dysfunction in the pathogenesis of Parkinson disease—resemblance to the effect of amphetamine drugs of abuse

“…Therefore, defective mitophagy due to a lack of parkin recruitment to impaired mitochondria by PINK1 causes the accumulation of dysfunctional mitochondria and a subsequent enhanced ROS levels and proapoptotic proteins [257]. In addition, overexpression of PINK1 promotes mitochondrial fission, while inhibition of the protein causes an excessive fusion [258,259]. Fibroblasts from PD patients carrying homozygous PINK1 mutations had truncated mitochondria networks compared to control fibroblasts, when cultured in medium with low glucose, or in the presence of galactose to favor mitochondrial energy metabolism over glycolysis [243,260].…”

Reprint of: Revisiting oxidative stress and mitochondrial dysfunction in the pathogenesis of Parkinson disease—resemblance to the effect of amphetamine drugs of abuse

“…Therefore, defective mitophagy due to a lack of parkin recruitment to impaired mitochondria by PINK1 causes the accumulation of dysfunctional mitochondria and subsequent enhanced ROS levels and proapoptotic proteins [257]. In addition, overexpression of PINK1 promotes mitochondrial fission, whereas inhibition of the protein causes excessive fusion [258,259]. Fibroblasts from PD patients carrying homozygous PINK1 mutations had truncated mitochondria networks compared to control fibroblasts, when cultured in medium with low glucose or in the presence of galactose to favor mitochondrial energy metabolism over glycolysis [243,260].…”