PINK1/Park2-Mediated Mitophagy Relieve Non-Alcoholic Fatty Liver Disease

Up to now, there's a limited number of studies on the relationship between PINK1/Park2 pathway and mitophagy in NAFLD. To investigate the effect of Park2-mediated mitophagy on non-alcoholic fatty liver disease (NAFLD). Oleic acid was used for the establishment of NAFLD model. Oil red-dyed lipid drops and mitochondrial alternations were observed by transmission electron microscopy. Enzymatic kit was used to test lipid content. The levels of IL-8 and TNF-alpha were determined by ELISA. Lenti-Park2 and Park2-siRNA were designed to upregulate and downregulate Park2 expression, respectively. The changing expression of PINK and Park2 was detected by RT-qPCR and Western blot. Immunofluorescence staining was applied to measure the amount of LC3. Successful NAFLD modeling was featured by enhanced lipid accumulation, as well as the elevated total cholesterol (TC), triglyceride (TG), TNF-alpha and IL-8 levels. Mitochondria in NAFLD model were morphologically and functionally damaged. Park2 expression was upregulated by lenti-Park2 and downregulated through Park2-siRNA. The PINK1 expression showed the same trend as Park2 expression. Immunofluorescence staining demonstrated that the when Park2 was overexpressed, more LC3 protein on mitochondrial autophagosome membrane was detected, whereas Park2 knockdown impeded LC3' locating on the membrane. The transmission electron microscopy image exhibited that the extent of damage to the mitochondrial in NAFLD model was revered by enhanced Park2 expression but further exacerbated by reduced Park2 expression. Park2-mediated mitophagy could relive NAFLD and may be a novel therapeutic target for NAFLD treatment. Keywords: Non-alcoholic Fatty Liver Disease (NAFLD), Mitophagy, PINK1/Park2, Park2, PINK1.

Parkinson's Disease: Are PINK1 Activators Inching Closer to the Clinic?

The activation of PINK1 by small molecules has emerged as a promising strategy in treating Parkinson's disease (PD). Recent progress in this area has raised excitement around PINK1 activators as PD treatments, and herein we offer insight into these developments and their potential to deliver much needed novel PD treatments.

Tailoring Magnetite-Nanoparticle-Based Nanocarriers for Gene Delivery: Exploiting CRISPRa Potential in Reducing Conditions

Gene delivery has emerged as a promising alternative to conventional treatment approaches, allowing for the manipulation of gene expression through gene insertion, deletion, or alteration. However, the susceptibility of gene delivery components to degradation and challenges associated with cell penetration necessitate the use of delivery vehicles for effective functional gene delivery. Nanostructured vehicles, such as iron oxide nanoparticles (IONs) including magnetite nanoparticles (MNPs), have demonstrated significant potential for gene delivery applications due to their chemical versatility, biocompatibility, and strong magnetization. In this study, we developed an ION-based delivery vehicle capable of releasing linearized nucleic acids (tDNA) under reducing conditions in various cell cultures. As a proof of concept, we immobilized a CRISPR activation (CRISPRa) sequence to overexpress the pink1 gene on MNPs functionalized with polyethylene glycol (PEG), 3-[(2-aminoethyl)dithio]propionic acid (AEDP), and a translocating protein (OmpA). The nucleic sequence (tDNA) was modified to include a terminal thiol group and was conjugated to AEDP's terminal thiol via a disulfide exchange reaction. Leveraging the natural sensitivity of the disulfide bridge, the cargo was released under reducing conditions. Physicochemical characterizations, including thermogravimetric analysis (TGA) and Fourier-transform infrared (FTIR) spectroscopy, confirmed the correct synthesis and functionalization of the MNP-based delivery carriers. The developed nanocarriers exhibited remarkable biocompatibility, as demonstrated by the hemocompatibility, platelet aggregation, and cytocompatibility assays using primary human astrocytes, rodent astrocytes, and human fibroblast cells. Furthermore, the nanocarriers enabled efficient cargo penetration, uptake, and endosomal escape, with minimal nucleofection. A preliminary functionality test using RT-qPCR revealed that the vehicle facilitated the timely release of CRISPRa vectors, resulting in a remarkable 130-fold overexpression of pink1. We demonstrate the potential of the developed ION-based nanocarrier as a versatile and promising gene delivery vehicle with potential applications in gene therapy. The developed nanocarrier is capable of delivering any nucleic sequence (up to 8.2 kb) once it is thiolated using the methodology explained in this study. To our knowledge, this represents the first MNP-based nanocarrier capable of delivering nucleic sequences under specific reducing conditions while preserving functionality.

Is Disrupted Mitophagy a Central Player to Parkinson's Disease Pathology?

Whilst the pathophysiology at a cellular level has been defined, the cause of Parkinson's disease (PD) remains poorly understood. This neurodegenerative disorder is associated with impaired dopamine transmission in the substantia nigra, and protein accumulations known as Lewy bodies are visible in affected neurons. Cell culture models of PD have indicated impaired mitochondrial function, so the focus of this paper is on the quality control processes involved in and around mitochondria. Mitochondrial autophagy (mitophagy) is the process through which defective mitochondria are removed from the cell by internalisation into autophagosomes which fuse with a lysosome. This process involves many proteins, notably including PINK1 and parkin, both of which are known to be coded on genes associated with PD. Normally in healthy individuals, PINK1 associates with the outer mitochondrial membrane, which then recruits parkin, activating it to attach ubiquitin proteins to the mitochondrial membrane. PINK1, parkin, and ubiquitin cooperate to form a positive feedback system which accelerates the deposition of ubiquitin on dysfunctional mitochondria, resulting in mitophagy. However, in hereditary PD, the genes encoding PINK1 and parkin are mutated, resulting in proteins that are less efficient at removing poorly performing mitochondria, leaving cells more vulnerable to oxidative stress and ubiquitinated inclusion bodies, such as Lewy bodies. Current research that looks into the connection between mitophagy and PD is promising, already yielding potentially therapeutic compounds; until now, pharmacological support for the mitophagy process has not been part of the therapeutic arsenal. Continued research in this area is warranted.

Role of Rho-Associated Protein Kinase Inhibition As Therapeutic Strategy for Parkinson's Disease: Dopaminergic Survival and Enhanced Mitophagy

The GTP-binding protein, Rho, plays a significant role in the cellular pathology of Parkinson’s disease. The downstream effector of Rho, Rho-associated kinase (ROCK), performs several functions, including microglial inflammatory response and enhanced Parkin-mediated mitophagy. Its inhibition shows neuroprotective effects in carried studies. Parkinson’s disease pathology also rests on incomplete removal of damaged mitochondria, leading to neuronal impairment. ROCK has different isoforms, inhibition of which have been shown to decrease the adverse changes in microglia. There has also been evidence of a decreased release of inflammatory cytokines and a reduction in degradation of dopaminergic neurons on the addition of ROCK inhibitors. Additionally, ROCK inhibitors have recently been shown to increase the activity of hexokinase 2 (HK2), relocating it to mitochondria, and therefore leading to upregulated mitochondrial targeting. Understanding the cellular basis of ROCK activity and its inhibition may help us advance in creating new strategies for the treatment of Parkinson’s disease.

Mitophagy deficiency increases NLRP3 to induce brown fat dysfunction in mice

Although macroautophagy/autophagy deficiency causes degenerative diseases, the deletion of essential autophagy genes in adipocytes paradoxically reduces body weight. Brown adipose tissue (BAT) plays an important role in body weight regulation and metabolic control. However, the key cellular mechanisms that maintain BAT function remain poorly understood. in this study, we showed that global or brown adipocyte-specific deletion of pink1, a Parkinson disease-related gene involved in selective mitochondrial autophagy (mitophagy), induced BAT dysfunction, and obesity-prone type in mice. Defective mitochondrial function is among the upstream signals that activate the NLRP3 inflammasome. NLRP3 was induced in brown adipocyte precursors (BAPs) from pink1 knockout (KO) mice. Unexpectedly, NLRP3 induction did not induce canonical inflammasome activity. Instead, NLRP3 induction led to the differentiation of pink1 KO BAPs into white-like adipocytes by increasing the expression of white adipocyte-specific genes and repressing the expression of brown adipocyte-specific genes. nlrp3 deletion in pink1 knockout mice reversed BAT dysfunction. Conversely, adipose tissue-specific atg7 KO mice showed significantly lower expression of Nlrp3 in their BAT. Overall, our data suggest that the role of mitophagy is different from general autophagy in regulating adipose tissue and whole-body energy metabolism. Our results uncovered a new mitochondria-NLRP3 pathway that induces BAT dysfunction. The ability of the nlrp3 knockouts to rescue BAT dysfunction suggests the transcriptional function of NLRP3 as an unexpected, but a quite specific therapeutic target for obesity-related metabolic diseases.Abbreviations: ACTB: actin, beta; BAPs: brown adipocyte precursors; BAT: brown adipose tissue; BMDMs: bone marrow-derived macrophages; CASP1: caspase 1; CEBPA: CCAAT/enhancer binding protein (C/EBP), alpha; ChIP: chromatin immunoprecipitation; EE: energy expenditure; HFD: high-fat diet; IL1B: interleukin 1 beta; ITT: insulin tolerance test; KO: knockout; LPS: lipopolysaccharide; NLRP3: NLR family, pyrin domain containing 3; PINK1: PTEN induced putative kinase 1; PRKN: parkin RBR E3 ubiquitin protein ligase; RD: regular diet; ROS: reactive oxygen species; RT: room temperature; UCP1: uncoupling protein 1 (mitochondrial, proton carrier); WT: wild-type.

Mammalian BCAS3 and C16orf70 associate with the phagophore assembly site in response to selective and non-selective autophagy

Macroautophagy/autophagy is an intracellular degradation process that delivers cytosolic materials and/or damaged organelles to lysosomes. De novo synthesis of the autophagosome membrane occurs within a phosphatidylinositol-3-phosphate-rich region of the endoplasmic reticulum, and subsequent expansion is critical for cargo encapsulation. This process is complex, especially in mammals, with many regulatory factors. In this study, by utilizing PRKN (parkin RBR E3 ubiquitin protein ligase)-mediated mitochondria autophagy (mitophagy)-inducing conditions in conjunction with chemical crosslinking and mass spectrometry, we identified human BCAS3 (BCAS3 microtubule associated cell migration factor) and C16orf70 (chromosome 16 open reading frame 70) as novel proteins that associate with the autophagosome formation site during both non-selective and selective autophagy. We demonstrate that BCAS3 and C16orf70 form a complex and that their association with the phagophore assembly site requires both proteins. In silico structural modeling, mutational analyses in cells and in vitro phosphoinositide-binding assays indicate that the WD40 repeat domain in human BCAS3 directly binds phosphatidylinositol-3-phosphate. Furthermore, overexpression of the BCAS3-C16orf70 complex affects the recruitment of several core autophagy proteins to the phagophore assembly site. This study demonstrates regulatory roles for human BCAS3 and C16orf70 in autophagic activity.

Abbreviations: AO: antimycin A and oligomycin; Ash: assembly helper; ATG: autophagy-related; BCAS3: BCAS3 microtubule associated cell migration factor; C16orf70: chromosome 16 open reading frame 70; DAPI: 4‘,6-diamidino-2-phenylindole; DKO: double knockout; DMSO: dimethyl sulfoxide; ER: endoplasmic reticulum; fluoppi: fluorescent-based technology detecting protein-protein interactions; FIS1: fission, mitochondrial 1; FKBP: FKBP prolyl isomerase family member 1C; FRB: FKBP-rapamycin binding; hAG: humanized azami-green; IP: immunoprecipitation; IRES: internal ribosome entry site; KO: knockout; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MFN2: mitofusin 2; MS: mass spectrometry; MT-CO2: mitochondrially encoded cytochrome c oxidase II; mtDNA: mitochondrial DNA; OPTN: optineurin; PFA: paraformaldehyde; PE: phosphatidylethanolamine; PtdIns3K: phosphatidylinositol 3-kinase; PtdIns3P: phosphatidylinositol-3-phosphate; PtdIns(3,5)P₂: phosphatidylinositol-3,5-bisphosphate; PINK1: PTEN induced kinase 1; PRKN/Parkin: parkin RBR E3 ubiquitin protein ligase; PROPPIN: β-propellers that bind polyphosphoinositides; RB1CC1/FIP200: RB1 inducible coiled-coil 1; TOMM20: translocase of outer mitochondrial membrane 20; ULK1: unc-51 like autophagy activating kinase 1; WDR45B/WIPI3: WD repeat domain 45B; WDR45/WIPI4: WD repeat domain 45; WIPI: WD repeat domain, phosphoinositide interacting; WT: wild type; ZFYVE1/DFCP1: zinc finger FYVE-type containing 1

Chemical and Genetic Zebrafish Models to Define Mechanisms of and Treatments for Dopaminergic Neurodegeneration

The zebrafish (Danio rerio) is routinely used in biological studies as a vertebrate model system that provides unique strengths allowing applications in studies of neurodevelopmental and neurodegenerative diseases. One specific advantage is that the neurotransmitter systems are highly conserved throughout vertebrate evolution, including between zebrafish and humans. Disruption of the dopaminergic signaling pathway is linked to multiple neurological disorders. One of the most common is Parkinson’s disease, a neurodegenerative disease associated with the loss of dopaminergic neurons, among other neuropathological characteristics. In this review, the development of the zebrafish’s dopaminergic system, focusing on genetic control of the dopaminergic system, is detailed. Second, neurotoxicant models used to study dopaminergic neuronal loss, including 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), the pesticides paraquat and rotenone, and 6-hydroxydopamine (6-OHDA), are described. Next, zebrafish genetic knockdown models of dj1, pink1, and prkn established for investigating mechanisms of Parkinson’s disease are discussed. Chemical modulators of the dopaminergic system are also highlighted to showcase the applicability of the zebrafish to identify mechanisms and treatments for neurodegenerative diseases such as Parkinson’s disease associated with the dopaminergic system.

pink1, atp13a2 and uchl1 expressions are affected by inflammation in the brain

In Parkinson's disease (PD), several genes have been identified as the PD-related genes, however, the regulatory mechanisms of these gene expressions have not been fully identified. In this study, we investigated the effect of inflammation, one of the major risk factors in PD on expressions of the PD-related genes. Lipopolysaccharide (LPS) was intraperitoneally administered to mature male zebrafish and gene expressions in the brains were examined by real-time PCR. In the inflammation-related genes, expressions of tnfb, il1b and il6 were increased at 2 days post administration in the 10 μg group, and tnfb expression was also increased at 4 days post administration in the 1 μg and 10 μg group. In the PD-related genes, pink1 expression was significantly decreased at 4 days, atp13a2 expression was significantly increased at 7 days, and uchl1 expression was significantly decreased at 7 days. This suggests that pink1, atp13a2 and uchl1 expressions are regulated by inflammation, and this regulatory mechanism might be involved in the progress of PD.

PINK1 and PARK2 Suppress Pancreatic Tumorigenesis through Control of Mitochondrial Iron-Mediated Immunometabolism

Pancreatic cancer is an aggressive malignancy with changes in the tumor microenvironment. Here, we demonstrate that PINK1 and PARK2 suppressed pancreatic tumorigenesis through control of mitochondrial iron-dependent immunometabolism. Using mouse models of spontaneous pancreatic cancer, we show that depletion of Pink1 and Park2 accelerates mutant Kras-driven pancreatic tumorigenesis. PINK1-PARK2 pathway-mediated degradation of SLC25A37 and SLC25A28 increases mitochondrial iron accumulation, which leads to the HIF1A-dependent Warburg effect and AIM2-dependent inflammasome activation in tumor cells. AIM2-mediated HMGB1 release further induces expression of CD274/PD-L1. Consequently, pharmacological administration of mitochondrial iron chelator, anti-HMGB1 antibody, or genetic depletion of Hif1a or Aim2 in pink1^-/- and park2^-/- mice confers protection against pancreatic tumorigenesis. Low PARK2 expression and high SLC25A37 and AIM2 expression are associated with poor prognosis in patients with pancreatic cancer. These findings suggest that disrupted mitochondrial iron homeostasis may contribute to cancer development and hence constitute a target for therapeutic intervention.

Early-Onset Parkinsonism: Case Report and Review of the Literature

BACKGROUND

Early-onset parkinsonism can be caused by PTEN-induced putative kinase 1 (PINK1) gene defects and is usually characterized by an age of onset in the fourth decade of life, slow disease progression, resting tremor, rigidity, bradykinesia, postural instability, and levodopa-induced dyskinesia.

METHODS

We evaluated a child with early-onset symptoms and performed a literature review for previously reported examples of children aged 18 years or less with PINK1 gene defects.

RESULTS

We describe a five-year-old boy with autosomal recessive early-onset parkinsonism caused by a homozygous missense mutation in the PINK1 gene. This is the youngest individual yet reported with early-onset parkinsonism.

CONCLUSION

PINK1-type of early-onset parkinsonism can occur in very young patients, and phenotypic expression of PINK1 mutations may depend on age of onset and ethnicity.

Involvement of heat shock proteins on Mn-induced toxicity in Caenorhabditis elegans

BACKGROUND

All living cells display a rapid molecular response to adverse environmental conditions, and the heat shock protein family reflects one such example. Hence, failing to activate heat shock proteins can impair the cellular response. In the present study, we evaluated whether the loss of different isoforms of heat shock protein (hsp) genes in Caenorhabditis elegans would affect their vulnerability to Manganese (Mn) toxicity.

METHODS

We exposed wild type and selected hsp mutant worms to Mn (30 min) and next evaluated further the most susceptible strains. We analyzed survival, protein carbonylation (as a marker of oxidative stress) and Parkinson's disease related gene expression immediately after Mn exposure. Lastly, we observed dopaminergic neurons in wild type worms and in hsp-70 mutants following Mn treatment. Analysis of the data was performed by one-way or two way ANOVA, depending on the case, followed by post-hoc Bonferroni test if the overall p value was less than 0.05.

RESULTS

We verified that the loss of hsp-70, hsp-3 and chn-1 increased the vulnerability to Mn, as exposed mutant worms showed lower survival rate and increased protein oxidation. The importance of hsp-70 against Mn toxicity was then corroborated in dopaminergic neurons, where Mn neurotoxicity was aggravated. The lack of hsp-70 also blocked the transcriptional upregulation of pink1, a gene that has been linked to Parkinson's disease.

CONCLUSIONS

Taken together, our data suggest that Mn exposure modulates heat shock protein expression, particularly HSP-70, in C. elegans. Furthermore, loss of hsp-70 increases protein oxidation and dopaminergic neuronal degeneration following manganese exposure, which is associated with the inhibition of pink1 increased expression, thus potentially exacerbating the vulnerability to this metal.

[PINK1 and the related diseases]

As a kind of mitochondrial membrane protein with protein kinase activity, phosphatase and tensin homolog deleted on chromosome ten induced kinase 1 (PINK1) is involved in many biological metabolic processes. Since PINK1 had been found to be associated with Parkinson's disease, researchers have been exploring its biological function. PINK1 localizes in the outer mitochondrial membrane and regulates cell function through phosphorylating proteins. PINK1 is involved in mitochondrial function, mitochondrial morphology and mitochondrial autophagy, but the regulatory pathway is not yet clear. PINK1 is expressed widely in many tissues with a variety of biological activity, especially in tissues with high energy consumption. It may therefore be involved in the development and regulation of many diseases. Mutations in PINK1 were originally discovered to cause autosomal recessive Parkinson's disease. Recently some research has revealed that PINK1 is related to the development of neonatal hypoxic-ischemic encephalopathy, cancer, diabetes and other diseases. Studying and exploring the biological functions of PINK1 will facilitate the identification of the targets for therapeutic intervention for its related diseases. This review article mainly focuses on recent studies about the biological function and related diseases of PINK1.

[PINK1 and the related diseases]

As a kind of mitochondrial membrane protein with protein kinase activity, phosphatase and tensin homolog deleted on chromosome ten induced kinase 1 (PINK1) is involved in many biological metabolic processes. Since PINK1 had been found to be associated with Parkinson's disease, researchers have been exploring its biological function. PINK1 localizes in the outer mitochondrial membrane and regulates cell function through phosphorylating proteins. PINK1 is involved in mitochondrial function, mitochondrial morphology and mitochondrial autophagy, but the regulatory pathway is not yet clear. PINK1 is expressed widely in many tissues with a variety of biological activity, especially in tissues with high energy consumption. It may therefore be involved in the development and regulation of many diseases. Mutations in PINK1 were originally discovered to cause autosomal recessive Parkinson's disease. Recently some research has revealed that PINK1 is related to the development of neonatal hypoxic-ischemic encephalopathy, cancer, diabetes and other diseases. Studying and exploring the biological functions of PINK1 will facilitate the identification of the targets for therapeutic intervention for its related diseases. This review article mainly focuses on recent studies about the biological function and related diseases of PINK1.

Beneficial Effects of AMP-Activated Protein Kinase Agonists in Kidney Ischemia-Reperfusion: Autophagy and Cellular Stress Markers

Background: Kidney ischemia-reperfusion is a form of acute kidney injury resulting in a cascade of cellular events prompting rapid cellular damage and suppression of kidney function. A cellular response to ischemic stress is the activation of AMP-activated protein kinase (AMPK), where AMPK induces a number of homeostatic and renoprotective mechanisms, including autophagy. However, whether autophagy is beneficial or detrimental in ischemia-reperfusion remains controversial. We investigated the effects of agonist induction of AMPK activity on autophagy and cell stress proteins in the model of kidney ischemia-reperfusion. Methods: AMPK agonists, AICAR (0.1 g/kg) and metformin (0.3 g/kg), were administered 24 h prior to ischemia, with kidneys harvested at 24 h of reperfusion. Results: We observed a paradoxical decrease in AMPK activity accompanied by increases in mammalian target of rapamycin (mTOR) C1 activity and p62/SQSTM1 expression. These results led us to propose that AMPK and autophagy are insufficient to properly counter the cellular insults in ischemia-reperfusion. Agonist induction of AMPK activity with AICAR or metformin increased macroautophagy protein LC3 and normalized p62/SQSTM1 expression and mTOR activity. Ischemia-reperfusion increases in Beclin-1 and PINK1 expressions, consistent with increased mitophagy, were also mitigated with AMPK agonists. Stress-responsive and apoptotic marker expressions increase in ischemia-reperfusion and are significantly attenuated with agonist administration, as are early indicators of fibrosis. Conclusions: Our data suggest that levels of renoprotective AMPK activity and canonical autophagy are insufficient to maintain cellular homeostasis, contributing to the progression of ischemia-reperfusion injury. We further demonstrate that induction of AMPK activity can provide beneficial cellular effects in containing injury in ischemia-reperfusion. © 2014 S. Karger AG, Basel.

The pathways of mitophagy for quality control and clearance of mitochondria

Selective autophagy of mitochondria, known as mitophagy, is an important mitochondrial quality control mechanism that eliminates damaged mitochondria. Mitophagy also mediates removal of mitochondria from developing erythrocytes, and contributes to maternal inheritance of mitochondrial DNA through the elimination of sperm-derived mitochondria. Recent studies have identified specific regulators of mitophagy that ensure selective sequestration of mitochondria as cargo. In yeast, the mitochondrial outer membrane protein autophagy-related gene 32 (ATG32) recruits the autophagic machinery to mitochondria, while mammalian Nix is required for degradation of erythrocyte mitochondria. The elimination of damaged mitochondria in mammals is mediated by a pathway comprised of PTEN-induced putative protein kinase 1 (PINK1) and the E3 ubiquitin ligase Parkin. PINK1 and Parkin accumulate on damaged mitochondria, promote their segregation from the mitochondrial network, and target these organelles for autophagic degradation in a process that requires Parkin-dependent ubiquitination of mitochondrial proteins. Here we will review recent advances in our understanding of the different pathways of mitophagy. In addition, we will discuss the relevance of these pathways in neurons where defects in mitophagy have been implicated in neurodegeneration.

PINK1 stimulates interleukin-1β-mediated inflammatory signaling via the positive regulation of TRAF6 and TAK1

Parkinson's disease (PD) is characterized by a progressive loss of dopaminergic neurons in the substantia nigra. The cause of neuronal death in PD is largely unknown, but several genetic loci, including PTEN-induced putative kinase 1 (PINK1), have been linked to early onset autosomal recessive forms of familial PD. PINK1 encodes a serine/threonine kinase, which phosphorylates several substrates and consequently leads to cell protection against apoptosis induced by various stresses. In addition, research has shown that inflammation largely contributes to the pathogenesis of PD, but the functional link between PINK1 and PD-linked neuroinflammation remains poorly understood. Therefore, in the present study, we investigated the functional role of PINK1 in interleukin (IL)-1β-mediated inflammatory signaling. We show that PINK1 specifically binds to TRAF6 and TAK1, and facilitates the autodimerization and autoubiquitination of TRAF6. PINK1 also enhances the association between TRAF6 and TAK1, phosphorylates TAK1, and stimulates polyubiquitination of TAK1. Furthermore, PINK1 leads to the potentiation of IL-1β-mediated NF-κB activity and cytokine production. These findings suggest that PINK1 positively regulates two key molecules, TRAF6 and TAK1, in the IL-1β-mediated signaling pathway, consequently up-regulating their downstream inflammatory events.

PINK1 as a molecular checkpoint in the maintenance of mitochondrial function and integrity

Parkinson's disease (PD), the most prevalent neurodegenerative movement disorder, is characterized by an age-dependent selective loss of dopaminergic (DA) neurons. Although most PD cases are sporadic, more than 20 responsible genes in familial cases were identified recently. Genetic studies using Drosophila models demonstrate that PINK1, a mitochondrial kinase encoded by a PD-linked gene PINK1, is critical for maintaining mitochondrial function and integrity. This suggests that mitochondrial dysfunction is the main cause of PD pathogenesis. Further genetic and cell biological studies revealed that PINK1 recruits Parkin, an E3 ubiquitin ligase encoded by another PD-linked gene parkin, to mitochondria and regulates the mitochondrial remodeling process via the Parkin-mediated ubiquitination of various mitochondrial proteins. PINK1 also directly phosphorylates the mitochondrial proteins Miro and TRAP1, subsequently inhibiting mitochondrial transport and mitochondrial oxidative damage, respectively. Moreover, recent Drosophila genetic analyses demonstrate that the neuroprotective molecules Sir2 and FOXO specifically complement mitochondrial dysfunction and DA neuron loss in PINK1 null mutants, suggesting that Sir2 and FOXO protect mitochondria and DA neurons downstream of PINK1. Collectively, these recent results suggest that PINK1 plays multiple roles in mitochondrial quality control by regulating its mitochondrial, cytosolic, and nuclear targets.

Mitochondrial processing peptidase regulates PINK1 processing, import and Parkin recruitment

Mutations in phosphatase and tensin homologue-induced kinase 1 (PINK1) cause recessively inherited Parkinson's disease (PD), a neurodegenerative disorder linked to mitochondrial dysfunction. In healthy mitochondria, PINK1 is rapidly degraded in a process involving both mitochondrial proteases and the proteasome. However, when mitochondrial import is compromised by depolarization, PINK1 accumulates on the mitochondrial surface where it recruits the PD-linked E3 ubiquitin ligase Parkin from the cytosol, which in turn mediates the autophagic destruction of the dysfunctional organelles. Using an unbiased RNA-mediated interference (RNAi)-based screen, we identified four mitochondrial proteases, mitochondrial processing peptidase (MPP), presenilin-associated rhomboid-like protease (PARL), m-AAA and ClpXP, involved in PINK1 degradation. We find that PINK1 turnover is particularly sensitive to even modest reductions in MPP levels. Moreover, PINK1 cleavage by MPP is coupled to import such that reducing MPP activity induces PINK1 accumulation at the mitochondrial surface, leading to Parkin recruitment and mitophagy. These results highlight a new role for MPP in PINK1 import and mitochondrial quality control via the PINK1–Parkin pathway.

Mitochondrial quality control and Parkinson's disease: a pathway unfolds

Recent findings from genetic studies suggest that defective mitochondrial quality control may play an important role in the development of Parkinson's disease (PD). Such defects may result in the impairment of neuronal mitochondria, which leads to both synaptic dysfunction and cell death and results in neurodegeneration. Here, we review state-of-the-art knowledge of how pathways affecting mitochondrial quality control might contribute to PD, with a particular emphasis on the molecular mechanisms employed by PTEN-induced putative kinase 1 (PINK1), HtrA2 and Parkin to regulate mitochondrial quality control.

Recent advances in the genetics of Parkinson's disease

Genetic studies have provided valuable insight into the pathological mechanisms underlying Parkinson's disease (PD). The elucidation of genetic components to what was once largely considered a nongenetic disease has given rise to a multitude of cell and animal models enabling the dissection of molecular pathways involved in disease etiology. Here, we review advances obtained from models of dominant mutations in α-synuclein and LRRK2 as well as recessive PINK1, parkin and DJ-1 mutations. Recent genome-wide association studies have implicated genetic variability at two of these loci, α-synuclein and LRRK2, as significant risk factors for developing sporadic PD. This, coupled with the established role of mitochondrial impairment in both familial and sporadic PD, highlights the likelihood of common mechanisms fundamental to the etiology of both.

PINK1 function in health and disease

The role of mitochondria in sporadic Parkinson's disease (PD) has been debated for a little over 20 years since the description of complex I deficiency in the substantia nigra pars compacta (SNpc) of PD patients. However, the identification of recessive pathogenic mutations in the pink1 gene in familial PD cases firmly re-ignited interest in the pathophysiology of mitochondria in PD. PINK1 is a putative mitochondrial serine/threonine kinase, which protects cells against oxidative stress induced apoptosis. The mechanism by which this is achieved and the effect of the pathogenic mutations has been an area of intensive research over the past five years. Significant progress has been made and, in this review, we summarize the physiological roles that have been assigned to PINK1 and the potential mechanisms behind pathogenesis.