Disease relevance of PINK1

• Novel PINK1 mutations in early-onset parkinsonism [1].
• Hereditary early-onset Parkinson's disease caused by mutations in PINK1 [2].
• Mechanisms by which PINK1 deficiency cause cellular dysfunction (reviewed in [3] include calcium dysregulation [4] [5], direct or indirect effects on complex I respiratory function (Morais et al. EMBO Mol Med 1: 2009, 99-111)[5], and oxidative stress, which occur upstream of mitochondrial remodeling and autophagy [6] [7].
• Progress has been made in understanding some of the mechanisms of toxicity: Parkin is an E3 ubiquitin ligase and DJ-1 and PINK1 appear to protect against mitochondrial damage [8].
• In a recent issue of Nature, two independent reports by and show that loss of Drosophila PINK1 leads to defects in mitochondrial function resulting in male sterility, apoptotic muscle degeneration, and minor loss of dopamine neurons that is rescued by overexpression of the ubiquitin E3 ligase, parkin [9].
• Indeed, overexpression of PINK1 protects neuroblastoma cells from undergoing neurotoxin-induced apoptosis [10].
• PINK1 may act as a sensor for mitochondrial function/dysfunction. Functional mitochondria import and release proteolytically processed forms of PINK1 [11]. Failure of PINK1 processing by depolarized mitochondria triggers their removal by PARK2-dependent mitophagy [12]. In contrast, processed PINK1 signals neurodifferentiation and dendrite outgrowth [13].

Psychiatry related information on PINK1

• Thus, early-onset PD with dementia may be considered PINK1-linked parkinsonism [14].
• One patient with a novel homozygous nonsense PINK1 mutation presented unusually with restless legs symptoms [15].
• PINK1 was absent in cortical Lewy bodies, in neurofibrillary tangles in Alzheimer's disease, progressive supranuclear palsy and corticobasal degeneration, and in the glial and neuronal alpha-synuclein positive inclusions in multiple system atrophy [16].
• Management: the indomitable Mr. Pink. Whistle-blowers. Interview by Toni Turner [17].

High impact information on PINK1

• Mutations in the PTEN-induced putative kinase 1 (PINK1) are a common cause of autosomal recessive Parkinson's disease [9].
• PINK1 deficiency suppresses complex I respiratory function through direct (Morais et al. EMBO Mol Med 1: 2009, 99-111) or indirect mechanisms involving mitochondrial calcium dysregulation [5].
• Parkin blushed by PINK1 [9].
• Recessively inherited mutations in parkin, DJ-1, and PINK1 have recently been linked to familial forms of parkinsonism [18].
• Generally, the T-cell clones have been obtained from immune donors, but J.R.L. Pink and F. Sinigaglia argue here that non-immune, human leukocyte antigen (HLA)-typed donors are a useful source of clones and antigen-presenting cells that can be used to assay systematically peptide-MHC associations [19].
• The molecular mechanisms responsible for postpollination changes in floral scent emission were investigated in snapdragon cv Maryland True Pink and petunia cv Mitchell flowers using a volatile ester, methylbenzoate, one of the major scent compounds emitted by these flowers, as an example [20].

Chemical compound and disease context of PINK1

• All sites of mutations were novel, suggesting that PINK1 may be the second most common causative gene next to parkin in parkinsonism with the recessive mode of inheritance [1].
• PTEN-induced kinase 1 (PINK1) is a recently identified gene, mutations of which cause levodopa-responsive parkinsonism [21].
• Juvenile-onset Parkinsonism as a result of the first mutation in the adenosine triphosphate orientation domain of PINK1 [22].
• Recently, mutations in a novel gene, PINK1, encoding a 581 amino acid protein with both mitochondrial targeting and serine/threonine kinase domains, were identified as a cause of autosomal recessive parkinsonism [16].
• Our results indicate that PARK6 pathology results in a more uniform loss of striatal dopamine terminal function than Parkinson's disease [23].

Biological context of PINK1

• They found two novel PINK1 mutations: one was a homozygous deletion (13516-18118del) and the other a homozygous missense mutation (C388R) [14].
• Naturally occurring non-coding antisense provides sophisticated mechanisms for diversifying genomes and we describe a human specific non-coding antisense expressed at the PINK1 locus (naPINK1) [24].
• The observation of concordant regulation of svPINK1 and naPINK1 during in vivo mitochondrial biogenesis was confirmed using RNAi, where selective targeting of naPINK1 results in loss of the PINK1 splice variant in neuronal cell lines [24].
• We defined the linkage disequilibrium structure of PINK1 and used this to identify a set of tagging single nucleotide polymorphisms that we estimate will efficiently represent all of the common DNA variation in the entire gene [25].
• Genotyping these tags in a set of 576 Parkinson's disease patients and 514 controls did not demonstrate a case-control partition for allele or for haplotype and thus provides evidence against the existence of a common functional variants in PINK1 that has a strong influence on PD risk [25].

Biological pathways regulated by PINK1

• Downstream pathways modulated by PINK1 include phosphorylation of the HSP90-family member TRAP1/Hsp75 [26] and indirect effects on phosphorylation of HtrA2 [27] and Drp1 (Sandebring in press).[7].
• Several studies implicate PINK1 in regulation of oxidative stress. PINK1 loss of function is associated with increased ROS detected in human cells [6][28][29] and Drosophila [30]. PINK1 transcription may be upregulated as part of a FOXO-regulated ROS defense response [31].
• Calcium dysregulation appears to be an upstream consequence of PINK1 loss of function. Mitochondria play a key role in buffering cytosolic calcium taking up calcium into the matrix through a membrane-potential dependent uniporter. A sodium-calcium antiporter releaases calcium back into the cytosol to regenerate buffering capacity. PINK1 deficient human and mouse neurons show defective antiporter activity and enhanced sensitivity to mitochondrial calcium overload [5]. Blocking mitochondrial calcium uptake protects cells expressing a PINK1 truncation mutant and A52T a-synuclein [4].
• PINK1 loss of function promotes fission in cultured mammalian cells [32][6](Sandebring in press). [Ref]. This process may involve calcium-dependent activation of calcineurin, which dephosphorylates the fission protein Drp1 (Sandebring in press), [Ref], and mitochondrial fragmentation is inhibited by antioxidants [6].
• Abnormal cristae and decreased mitochondrial membrane potential have been consistently implicated in a variety of experimental models (Reviewed in Chu in press).[33]. PINK1 may associated with complexes of the mitochondrial electron transport chain and its loss of function may have direct effects on mitochondrial complex I function (Morais 2009), although indirect effects through substrate limitation have also been shown [5].
• PINK1 levels modulate the mitochondrial fission-fusion balance, but differences are observed in Drosophila versus cultured human cells. In Drosophila, loss of PINK1 function causes enlarged mitochondria, complemented by enhancing Drp1 or suppressing Mfn/Opa [34][35][36]. In human cells, loss of PINK1 function causes mitochondrial fragmentation [32][6] (Sandebring in press), , reversed by dominant negative Drp1, Drp1 siRNA or Opa1/Mfn2 overexpression. The effects of PINK1 on mitochondrial dynamics may be indirect [34] (Sandebring in press). .
• Mitochondrial fission and mitochondrial autophagy are coordinately upregulated in PINK1 loss of function neuronal cells [6]. Inhibiting either process exacerbates cell death, implying both processes as part of a compensatory process that isolates depolarized mitochondria (and presumably reduces ROS and calcium leakage). In lysosomal storage diseases, sustained deficits in lysosomal function result in accumulation of fragmented mitochondria with impaired calcium buffering and enhanced susceptibility to injury [37].
• Protection against injury arising from PINK1 deficiency could be achieved through enhancement of compensatory adaptations (fission and autophagy), and do not necessarily imply that the normal role of PINK1 has been reconstituted by reversal of the primary deficit [3].
• Parkin overexpression protects against the effects of PINK1 deficiency in multiple experimental systems [38][32][6]. Parkin has been shown to promote autophagy of depolarized mitochondria [39]. Parkin restores steady state mitochondrial morphology in PINK1 deficient cells by enhancing mitochondrial autophagy [6].

Anatomical context of PINK1

• PINK1 is expressed abundantly in mitochondria rich tissues, such as skeletal muscle, where it plays a critical role determining mitochondrial structural integrity in Drosophila [24].
• The physiological relevance of this observation is not yet clear, but it implies that a portion of PINK1 may be exported after processing in the mitochondria [40].
• These results show that PINK1 is processed at the N terminus in a manner consistent with mitochondrial import, but the mature protein also exists in the cytosol [40].
• To study the effect of PINK1 mutations on oxidative stress, we used primary fibroblasts and immortalized lymphoblasts from three patients homozygous for G309D-PINK1 [41].
• In addition, we show that PINK1 is detected in a proportion of Lewy bodies in cases of sporadic Parkinson's disease and Parkinson's disease associated with heterozygous mutations in the PINK1 gene, which are clinically and pathologically indistinguishable from the sporadic cases [16].

Associations of PINK1 with chemical compounds

• PINK1 encodes a putative serine/threonine kinase with a mitochondrial targeting sequence [42].
• We demonstrated that, on proteasome inhibition with MG-132, PINK1 and other mitochondrial proteins localized to aggresomes [43].
• Both recombinant enzymes preferentially phosphorylate the artificial substrate histone H1 exclusively at serine and threonine residues, demonstrating that PINK1 is indeed a protein serine/threonine kinase [10].
• Furthermore, co-expression of wild-type DJ-1 and PINK1 suppresses neurotoxin 1-methyl-4-phenylpyridinium (MPP(+))-induced death of dopaminergic SH-SY5Y cells [44].
• CONCLUSIONS: Heterozygous PINK1 mutations may predispose to PD, as was previously suggested by the presence of dopamine hypometabolism in asymptomatic mutation carriers [45].
• In a large Saudi family with PD with at least 3 consanguineous marriages between first cousins, we detected a threonine to methionine substitution at codon 313 (T313M) PINK1 mutation that affected the kinase domain [46].

Physical interactions of PINK1

• In transfected cells, DJ-1 interacts with PINK1 [44].

Regulatory relationships of PINK1

• BACKGROUND: Mutations in the PTEN induced putative kinase 1 (PINK1) are implicated in early-onset Parkinson's disease [24].
• Mutations in genes encoding both DJ-1 and pten-induced kinase 1 (PINK1) are independently linked to autosomal recessive early-onset familial forms of Parkinson's disease (PD) [44].
• INTERVENTIONS: Analysis of clinical characteristics and mutation analysis of the parkin and PTEN-induced kinase (PINK1) genes by direct sequencing and gene-dosage analysis using the multiplex ligation-dependent probe amplification technique [47].

Other interactions of PINK1

• Here we show that mutations in PINK1 (PTEN-induced kinase 1) are associated with PARK6 [2].
• Overexpression of wild-type PINK1 also reduced the levels of cleaved caspase-9, caspase-3, caspase-7, and activated poly(ADP-ribose) polymerase under both basal and staurosporine-induced conditions [48].
• Recruiting new families will help cloning the defective genes at PARK6 and PARK7 loci [49].
• We here summarize the results of genetic investigations on a series of 82 parkinsonian patients from 60 families in Taiwan. We found 13 parkin patients in 7 families (12%), 2 PINK1 sibs from 1 family, and 1 LRRK2 patient from 1 family with I2012T mutation [50].

Analytical, diagnostic and therapeutic context of PINK1

• Cell culture studies suggest that PINK1 is mitochondrially located and may exert a protective effect on the cell that is abrogated by the mutations, resulting in increased susceptibility to cellular stress [2].
• To test for the presence of exon rearrangements in PINK1, we established a new quantitative duplex PCR assay [51].
• We performed sequence analysis of all the coding and exon-intron junctions of the PINK1 using specific primer sets [15].
• We describe two unrelated cases with PINK1 mutations (homozygous nonsense and heterozygous missense) that highlight issues regarding the role of heterozygous mutations and the utility of genetic screening in patient care [52].
• Using immunohistochemistry and western blotting we were able to demonstrate that PINK1 is a ubiquitous protein expressed throughout the human brain and it is found in all cell types showing a punctate cytoplasmic staining pattern consistent with mitochondrial localization [16].

References