SREBF1 links lipogenesis to mitophagy and sporadic Parkinson disease

Mitochondrial quality control has an impact on many diseases, but intense research has focused on the action of 2 genes linked to heritable forms of Parkinson disease (PD), PINK1 and PARK2/parkin, which act in a common pathway to promote mitophagy. However, criticism has been raised that little evidence links this mechanism to sporadic PD. To gain a greater insight into the mechanisms of PINK1-PARK2 mediated mitophagy, we undertook a genome-wide RNAi screen in Drosophila and human cell models. Strikingly, we discovered several components of the lipogenesis pathway, including SREBF1, playing a conserved role in mitophagy. Our results suggest that lipids influence the stabilization of PINK1 during the initiation of mitophagy. Importantly, SREBF1 has previously been identified as a risk locus for sporadic PD, and thus implicates aberrant mitophagy as contributing to sporadic PD. Our findings suggest a role for lipid synthesis in PINK1-PARK2 mediated mitophagy, and propose a mechanistic link between familial and sporadic PD, supporting a common etiology.     

Short Mitochondrial ARF Triggers Parkin/PINK1-dependent Mitophagy

Parkinson disease (PD) is a complex neurodegenerative disease characterized by the loss of dopaminergic neurons in the substantia nigra. Multiple genes have been associated with PD, including Parkin and PINK1. Recent studies have established that the Parkin and PINK1 proteins function in a common mitochondrial quality control pathway, whereby disruption of the mitochondrial membrane potential leads to PINK1 stabilization at the mitochondrial outer surface. PINK1 accumulation leads to Parkin recruitment from the cytosol, which in turn promotes the degradation of the damaged mitochondria by autophagy (mitophagy). Most studies characterizing PINK1/Parkin mitophagy have relied on high concentrations of chemical uncouplers to trigger mitochondrial depolarization, a stimulus that has been difficult to adapt to neuronal systems and one unlikely to faithfully model the mitochondrial damage that occurs in PD. Here, we report that the short mitochondrial isoform of ARF (smARF), previously identified as an alternate translation product of the tumor suppressor p19ARF, depolarizes mitochondria and promotes mitophagy in a Parkin/PINK1-dependent manner, both in cell lines and in neurons. The work positions smARF upstream of PINK1 and Parkin and demonstrates that mitophagy can be triggered by intrinsic signaling cascades.     

BAG2 Gene-mediated Regulation of PINK1 Protein Is Critical for Mitochondrial Translocation of PARKIN and Neuronal Survival

Emerging evidence has demonstrated a growing genetic component in Parkinson disease (PD). For instance, loss-of-function mutations in PINK1 or PARKIN can cause autosomal recessive PD. Recently, PINK1 and PARKIN have been implicated in the same signaling pathway to regulate mitochondrial clearance through recruitment of PARKIN by stabilization of PINK1 on the outer membrane of depolarized mitochondria. The precise mechanisms that govern this process remain enigmatic. In this study, we identify Bcl2-associated athanogene 2 (BAG2) as a factor that promotes mitophagy. BAG2 inhibits PINK1 degradation by blocking the ubiquitination pathway. Stabilization of PINK1 by BAG2 triggers PARKIN-mediated mitophagy and protects neurons against 1-methyl-4-phenylpyridinium-induced oxidative stress in an in vitro cell model of PD. Collectively, our findings support the notion that BAG2 is an upstream regulator of the PINK1/PARKIN signaling pathway.     

Regulation by mitophagy

Eukaryotes employ elaborate mitochondrial quality control to maintain the function of the power-generating organelle. Mitochondrial quality control is particularly important for the maintenance of neural and muscular tissues. Mitophagy is specialized version of the autophagy pathway. Mitophagy delivers damaged mitochondria to lysosomes for degradation. Recently, a series of elegant studies have demonstrated that two Parkinson's disease-associated genes PINK1 and parkin are involved in the maintenance of healthy mitochondria as mitophagy. Parkin in co-operation with PINK1 specifically recognizes damaged mitochondria with reduced mitochondrial membrane potential (Δψm), rapidly isolates them from the mitochondrial network and eliminates them through the ubiquitin–proteasome and autophagy pathways. Here we introduce and review recent studies that contribute to understanding the molecular mechanisms of mitophagy such as PINK1 and Parkin-mediated mitochondrial regulation. We also discuss how defects in the PINK1–Parkin pathway may cause neurodegeneration in Parkinson's disease.     

Cytosolic cleaved PINK1 represses Parkin translocation to mitochondria and mitophagy

PINK1 is a mitochondrial kinase proposed to have a role in the pathogenesis of Parkinson''s disease through the regulation of mitophagy. Here, we show that the PINK1 main cleavage product, PINK1_52, after being generated inside mitochondria, can exit these organelles and localize to the cytosol, where it is not only destined for degradation by the proteasome but binds to Parkin. The interaction of cytosolic PINK1 with Parkin represses Parkin translocation to the mitochondria and subsequent mitophagy. Our work therefore highlights the existence of two cellular pools of PINK1 that have different effects on Parkin translocation and mitophagy.     

The ubiquitin signal and autophagy: an orchestrated dance leading to mitochondrial degradation

The quality of mitochondria, essential organelles that produce ATP and regulate numerous metabolic pathways, must be strictly monitored to maintain cell homeostasis. The loss of mitochondrial quality control systems is acknowledged as a determinant for many types of neurodegenerative diseases including Parkinson's disease (PD). The two gene products mutated in the autosomal recessive forms of familial early‐onset PD, Parkin and PINK1, have been identified as essential proteins in the clearance of damaged mitochondria via an autophagic pathway termed mitophagy. Recently, significant progress has been made in understanding how the mitochondrial serine/threonine kinase PINK1 and the E3 ligase Parkin work together through a novel stepwise cascade to identify and eliminate damaged mitochondria, a process that relies on the orchestrated crosstalk between ubiquitin/phosphorylation signaling and autophagy. In this review, we highlight our current understanding of the detailed molecular mechanisms governing Parkin‐/PINK1‐mediated mitophagy and the evidences connecting Parkin/PINK1 function and mitochondrial clearance in neurons.     

Mitochondrial proteolytic stress induced by loss of mortalin function is rescued by Parkin and PINK1

The mitochondrial chaperone mortalin was implicated in Parkinson''s disease (PD) because of its reduced levels in the brains of PD patients and disease-associated rare genetic variants that failed to rescue impaired mitochondrial integrity in cellular knockdown models. To uncover the molecular mechanisms underlying mortalin-related neurodegeneration, we dissected the cellular surveillance mechanisms related to mitochondrial quality control, defined the effects of reduced mortalin function at the molecular and cellular levels and investigated the functional interaction of mortalin with Parkin and PINK1, two PD-related proteins involved in mitochondrial homeostasis. We found that reduced mortalin function leads to: (1) activation of the mitochondrial unfolded protein response (UPR(mt)), (2) increased susceptibility towards intramitochondrial proteolytic stress, (3) increased autophagic degradation of fragmented mitochondria and (4) reduced mitochondrial mass in human cells in vitro and ex vivo. These alterations caused increased vulnerability toward apoptotic cell death. Proteotoxic perturbations induced by either partial loss of mortalin or chemical induction were rescued by complementation with native mortalin, but not disease-associated mortalin variants, and were independent of the integrity of autophagic pathways. However, Parkin and PINK1 rescued loss of mortalin phenotypes via increased lysosomal-mediated mitochondrial clearance and required intact autophagic machinery. Our results on loss of mortalin function reveal a direct link between impaired mitochondrial proteostasis, UPR(mt) and PD and show that effective removal of dysfunctional mitochondria via either genetic (PINK1 and Parkin overexpression) or pharmacological intervention (rapamycin) may compensate mitochondrial phenotypes.     

Drosophila Trap1 protects against mitochondrial dysfunction in a PINK1/parkin model of Parkinson's disease

Mitochondrial dysfunction caused by protein aggregation has been shown to have an important role in neurological diseases, such as Parkinson''s disease (PD). Mitochondria have evolved at least two levels of defence mechanisms that ensure their integrity and the viability of their host cell. First, molecular quality control, through the upregulation of mitochondrial chaperones and proteases, guarantees the clearance of damaged proteins. Second, organellar quality control ensures the clearance of defective mitochondria through their selective autophagy. Studies in Drosophila have highlighted mitochondrial dysfunction linked with the loss of the PTEN-induced putative kinase 1 (PINK1) as a mechanism of PD pathogenesis. The mitochondrial chaperone TNF receptor-associated protein 1 (TRAP1) was recently reported to be a cellular substrate for the PINK1 kinase. Here, we characterise Drosophila Trap1 null mutants and describe the genetic analysis of Trap1 function with Pink1 and parkin. We show that loss of Trap1 results in a decrease in mitochondrial function and increased sensitivity to stress, and that its upregulation in neurons of Pink1 mutant rescues mitochondrial impairment. Additionally, the expression of Trap1 was able to partially rescue mitochondrial impairment in parkin mutant flies; and conversely, expression of parkin rescued mitochondrial impairment in Trap1 mutants. We conclude that Trap1 works downstream of Pink1 and in parallel with parkin in Drosophila, and that enhancing its function may ameliorate mitochondrial dysfunction and rescue neurodegeneration in PD.     

PTEN-induced kinase 1 (PINK1) and Parkin: Unlocking a mitochondrial quality control pathway linked to Parkinson's disease

Dissection of the function of two Parkinson's disease-linked genes encoding the protein kinase, PTEN-induced kinase 1 (PINK1) and ubiquitin E3 ligase, Parkin, has illuminated a highly conserved mitochondrial quality control pathway found in nearly every cell type including neurons. Mitochondrial damage-induced activation of PINK1 stimulates phosphorylation-dependent activation of Parkin and ubiquitin-dependent elimination of mitochondria by autophagy (mitophagy). Structural, cell biological and neuronal studies are unravelling the key steps of PINK1/Parkin-dependent mitophagy and uncovering new insights into how the pathway is regulated. The emerging role for aberrant immune activation as a driver of dopaminergic neuron degeneration after loss of PINK1 and Parkin poses new exciting questions on cell-autonomous and noncell-autonomous mechanisms of PINK1/Parkin signalling in vivo.     

Parkin and PINK1 function in a vesicular trafficking pathway regulating mitochondrial quality control

Mitochondrial dysfunction has long been associated with Parkinson's disease (PD). Parkin and PINK1, two genes associated with familial PD, have been implicated in the degradation of depolarized mitochondria via autophagy (mitophagy). Here, we describe the involvement of parkin and PINK1 in a vesicular pathway regulating mitochondrial quality control. This pathway is distinct from canonical mitophagy and is triggered by the generation of oxidative stress from within mitochondria. Wild‐type but not PD‐linked mutant parkin supports the biogenesis of a population of mitochondria‐derived vesicles (MDVs), which bud off mitochondria and contain a specific repertoire of cargo proteins. These MDVs require PINK1 expression and ultimately target to lysosomes for degradation. We hypothesize that loss of this parkin‐ and PINK1‐dependent trafficking mechanism impairs the ability of mitochondria to selectively degrade oxidized and damaged proteins leading, over time, to the mitochondrial dysfunction noted in PD.     

Destructive cellular paths underlying familial and sporadic Parkinson disease converge on mitophagy

The knowledge gap separating the molecular and cellular underpinnings of Parkinson disease (PD) and its pathology hinders treatment innovation. Adding to this difficulty is the lack of a reliable biomarker for PD. Our previous studies identify a link of 2 PD proteins, PINK1/PRKN Parkin to a mitochondrial motor adaptor RHOT1/Miro-1, which mediates mitochondrial motility and mitophagy. Here we review our recent paper showing that a third PD protein, LRRK2, also targets RHOT1 and regulates mitophagy, and pathogenic LRRK2 disrupts this function. Notably, we discover impairments in RHOT1 and mitophagy in sporadic PD patients with no known genetic backgrounds, pointing to RHOT1-mediated mitophagy as a convergent pathway in PD. This novelty opens new doors in PD research toward RHOT1-based therapy and biomarker development.     

The Complex I Subunit NDUFA10 Selectively Rescues Drosophila pink1 Mutants through a Mechanism Independent of Mitophagy

Mutations in PINK1, a mitochondrially targeted serine/threonine kinase, cause autosomal recessive Parkinson''s disease (PD). Substantial evidence indicates that PINK1 acts with another PD gene, parkin, to regulate mitochondrial morphology and mitophagy. However, loss of PINK1 also causes complex I (CI) deficiency, and has recently been suggested to regulate CI through phosphorylation of NDUFA10/ND42 subunit. To further explore the mechanisms by which PINK1 and Parkin influence mitochondrial integrity, we conducted a screen in Drosophila cells for genes that either phenocopy or suppress mitochondrial hyperfusion caused by pink1 RNAi. Among the genes recovered from this screen was ND42. In Drosophila pink1 mutants, transgenic overexpression of ND42 or its co-chaperone sicily was sufficient to restore CI activity and partially rescue several phenotypes including flight and climbing deficits and mitochondrial disruption in flight muscles. Here, the restoration of CI activity and partial rescue of locomotion does not appear to have a specific requirement for phosphorylation of ND42 at Ser-250. In contrast to pink1 mutants, overexpression of ND42 or sicily failed to rescue any Drosophila parkin mutant phenotypes. We also find that knockdown of the human homologue, NDUFA10, only minimally affecting CCCP-induced mitophagy, and overexpression of NDUFA10 fails to restore Parkin mitochondrial-translocation upon PINK1 loss. These results indicate that the in vivo rescue is due to restoring CI activity rather than promoting mitophagy. Our findings support the emerging view that PINK1 plays a role in regulating CI activity separate from its role with Parkin in mitophagy.     

PARK2-mediated mitophagy is involved in regulation of HBEC senescence in COPD pathogenesis

Cigarette smoke (CS)-induced mitochondrial damage with increased reactive oxygen species (ROS) production has been implicated in COPD pathogenesis by accelerating senescence. Mitophagy may play a pivotal role for removal of CS-induced damaged mitochondria, and the PINK1 (PTEN-induced putative kinase 1)-PARK2 pathway has been proposed as a crucial mechanism for mitophagic degradation. Therefore, we sought to investigate to determine if PINK1-PARK2-mediated mitophagy is involved in the regulation of CS extract (CSE)-induced cell senescence and in COPD pathogenesis. Mitochondrial damage, ROS production, and cell senescence were evaluated in primary human bronchial epithelial cells (HBEC). Mitophagy was assessed in BEAS-2B cells stably expressing EGFP-LC3B, using confocal microscopy to measure colocalization between TOMM20-stained mitochondria and EGFP-LC3B dots as a representation of autophagosome formation. To elucidate the involvement of PINK1 and PARK2 in mitophagy, knockdown and overexpression experiments were performed. PINK1 and PARK2 protein levels in lungs from patients were evaluated by means of lung homogenate and immunohistochemistry. We demonstrated that CSE-induced mitochondrial damage was accompanied by increased ROS production and HBEC senescence. CSE-induced mitophagy was inhibited by PINK1 and PARK2 knockdown, resulting in enhanced mitochondrial ROS production and cellular senescence in HBEC. Evaluation of protein levels demonstrated decreased PARK2 in COPD lungs compared with non-COPD lungs. These results suggest that PINK1-PARK2 pathway-mediated mitophagy plays a key regulatory role in CSE-induced mitochondrial ROS production and cellular senescence in HBEC. Reduced PARK2 expression levels in COPD lung suggest that insufficient mitophagy is a part of the pathogenic sequence of COPD.     

Uncovering the roles of PINK1 and parkin in mitophagy

Parkinson disease (PD) is the second most prevalent neurodegenerative disorder, and thus elucidation of the pathogenic mechanism and establishment of a fundamental cure is essential in terms of public welfare. Fortunately, our understanding of the pathogenesis of two types of recessive familial PDs—early-onset familial PD caused by dysfunction of the PTEN-induced putative kinase 1 (PINK1) gene and autosomal recessive juvenile Parkinsonism (ARJP) caused by a mutation in the Parkin gene—has evolved and continues to expand.Key words: PINK1, parkin, ubiquitin, mitochondria, autophagy, mitophagy, membrane potential, quality controlSince the cloning of PINK1 and Parkin, numerous papers have been published about the corresponding gene products, but the mechanism by which dysfunction of PINK1 and/or Parkin causes PD remain unclear. Parkin encodes a ubiquitin ligase E3, a substrate recognition member of the ubiquitination pathway, whereas PINK1 encodes a mitochondria-targeted serine-threonine kinase that contributes to the maintenance of mitochondrial integrity. Based on their molecular functions, it is clear that Parkin-mediated ubiquitination and PINK1 phosphorylation are key events in disease pathogenesis. The underlying mechanism, however, is not as well defined and claims of pathogenicity, until recently, remained controversial. Although Parkin''s E3 activity was clearly demonstrated in vitro, we were unable to show a clear E3 activity of Parkin in cell/in vivo. In addition, despite a predicted mitochondrial localization signal for PINK1, we were unable to detect PINK1 on mitochondria by either immunoblotting or immunocytochemistry. More confusingly, overexpression of nontagged PINK1 mainly localized to the cytoplasm under steady state conditions.Work by Dr. Youle''s group at the National Institutes of Health in 2008, however, offered new insights. They reported that Parkin associated with depolarized mitochondria and that Parkin-marked mitochondria were subsequently cleared by autophagy. Soon after their publication, we also examined the function of Parkin and PINK1 following a decrease in mitochondrial membrane potential. Our findings, described below (Fig. 1), have contributed to the development of a mechanism explaining pathogenicity.Open in a separate windowFigure 1Model of mitochondrial quality control mediated by PINK1 and Parkin. Under steady-state conditions, the mature 60 kDa PINK1 is constantly cleaved by an unknown protease to a 50 kDa intermediate form that is subsequently degraded, presumably by the proteasome (upper part). The protein, however, is stabilized on depolarized mitochondria because the initial processing event is inhibited by a decrease in mitochondrial membrane potential (lower part). Accumulated PINK1 recruits cytosolic Parkin onto depolarized mitochondria resulting in activation of its E3 activity. Parkin then ubiquitinates a mitochondrial substrate(s). As a consequence, damaged mitochondria are degraded via mitophagy. Ub, ubiquitin.(1) We sought to determine the subcellular localization of endogenous PINK1, and realized that endogenous PINK1 is barely detectable under steady-state conditions. However, a decrease in mitochondrial membrane-potential following treatment with the mitochondrial uncoupler carbonyl cyanide m-chlorophenylhydrazone (CCCP) results in the gradual accumulation of endogenous PINK1 on mitochondria. Importantly, when CCCP is washed out, the accumulated endogenous PINK1 rapidly disappears (within 30 min) both in the presence and absence of cycloheximide. These results support the hypothesis that PINK1 is constantly transported to the mitochondria, but is rapidly degraded in a membrane potential-dependent manner (see below for details). We speculate that PINK1 is stabilized by a decrease in mitochondrial membrane potential and as a result accumulates on depolarized mitochondria.(2) We examined the potential role of PINK1 in the mitochondrial recruitment of Parkin. In control MEFs (PINK1^+/+), Parkin is selectively recruited to the mitochondria following CCCP treatment, and subsequently results in the selective disappearance of the mitochondria via autophagy (called mitophagy). In sharp contrast, Parkin is not translocated to the mitochondria in PINK1 knockout (PINK1^−/−) MEFs following CCCP treatment, and subsequent mitochondrial degradation is also completely impeded. These results suggest that PINK1 is “a Parkin-recruitment factor” that recruits Parkin from the cytoplasm to damaged mitochondria in a membrane potential-dependent manner for mitophagy.(3) We monitored the E3 activity of Parkin using an artificial pseudo-substrate fused to Parkin in cells. Parkin''s E3 activity was repressed under steady-state conditions; however, we find that Parkin ubiquitinates the pseudo-substrate when it is retrieved to the depolarized mitochondria, suggesting that activation of the latent Parkin E3 activity is likewise dependent on a decrease in mitochondrial membrane potential.(4) PINK1 normally exists as either a long (approximately 60 kDa) or a short (approximately 50 kDa) protein. Because the canonical mitochondrial targeting signal (matrix targeting signal) is cleaved after import into the mitochondria, the long form has been designated as the precursor and the short form as the mature PINK1. However, our subcellular localization study of endogenous PINK1 following CCCP treatment shows that the long form is recovered in the mitochondrial fraction, suggesting that it is not the pre-import precursor form. Moreover, by monitoring the degradation process of PINK1 following recovery of membrane potential, we realized that the short form of PINK1 transiently appears soon after CCCP is washed out and then later disappears, suggesting that the processed form of PINK1 is an intermediate in membrane-potential-dependent degradation. In conclusion, these results imply that PINK1 cleavage does not reflect a canonical maturation process accompanying mitochondrial import as initially thought, but rather represents constitutive degradation in healthy mitochondria by a two-step mechanism; i.e., first limited processing and subsequent complete degradation probably via the proteasome.(5) PINK1 accumulation by decrease of membrane potential and subsequent recruitment of Parkin onto mitochondria are presumably etiologically important because they are impeded for the most part by disease-linked mutations of PINK1 or Parkin.These results, together with reports by other groups, strongly suggest that recessive familial PD is caused by dysfunction of quality control for depolarized mitochondria.At present, we do not know whether the aforementioned pathogenic mechanism of recessive familial PD can be generalized to prevalent sporadic PD. However, the clinical symptoms of recessive familial PD caused by dysfunction of PINK1 or Parkin resembles that of idiopathic PD except early-onset pathogenesis, and thus it is plausible that there is a common pathogenic mechanism. We accordingly believe that our results provide solid insight into the molecular mechanisms of PD pathogenesis, not only for familial forms caused by Parkin and PINK1 mutations, but also the major sporadic form of PD.To fully understand the molecular mechanism of PINK1-Parkin-mediated mitophagy, further details need to be addressed including: identifying the protease(s) that processes PINK1 in a mitochondrial membrane-potential dependent manner and that presumably monitors mitochondrial integrity; identifying a physiological substrate(s) of PINK1; determining the molecular mechanism underlying Parkin activation; and identifying the protein(s) linking Parkin-mediated ubiquitination to mitophagy. A detailed mechanism of the aforementioned events will be the focus of future research, however, we feel our conclusion that PINK1 and Parkin function in the removal of depolarized mitochondria is evident and hope that our studies will provide a solid foundation for further studies.     

SREBF1 links lipogenesis to mitophagy and sporadic Parkinson disease

Mitochondrial quality control has an impact on many diseases, but intense research has focused on the action of 2 genes linked to heritable forms of Parkinson disease (PD), PINK1 and PARK2/parkin, which act in a common pathway to promote mitophagy. However, criticism has been raised that little evidence links this mechanism to sporadic PD. To gain a greater insight into the mechanisms of PINK1-PARK2 mediated mitophagy, we undertook a genome-wide RNAi screen in Drosophila and human cell models. Strikingly, we discovered several components of the lipogenesis pathway, including SREBF1, playing a conserved role in mitophagy. Our results suggest that lipids influence the stabilization of PINK1 during the initiation of mitophagy. Importantly, SREBF1 has previously been identified as a risk locus for sporadic PD, and thus implicates aberrant mitophagy as contributing to sporadic PD. Our findings suggest a role for lipid synthesis in PINK1-PARK2 mediated mitophagy, and propose a mechanistic link between familial and sporadic PD, supporting a common etiology.     

Zinc prevents mitochondrial superoxide generation by inducing mitophagy in the setting of hypoxia/reoxygenation in cardiac cells

Zinc plays a role in autophagy and protects cardiac cells from ischemia/reperfusion injury. This study aimed to test if zinc can induce mitophagy leading to attenuation of mitochondrial superoxide generation in the setting of hypoxia/reoxygenation (H/R) in cardiac cells. H9c2 cells were subjected to 4?h hypoxia followed by 2?h reoxygenation. Under normoxic conditions, treatments of cells with ZnCl₂ increased both the LC3-II/LC3-I ratio and GFP-LC3 puncta, implying that zinc induces autophagy. Further experiments showed that endogenous zinc is required for the autophagy induced by starvation and rapamycin. Zinc down-regulated TOM20, TIM23, and COX4 both in normoxic cells and the cells subjected to H/R, indicating that zinc can trigger mitophagy. Zinc increased ERK activity and Beclin1 expression, and zinc-induced mitophagy was inhibited by PD98059 and Beclin1 siRNA during reoxygenation. Zinc-induced Beclin1 expression was reversed by PD98059, implying that zinc promotes Beclin1 expression via ERK. In addition, zinc failed to induce mitophagy in cells transfected with PINK1 siRNA and stabilized PINK1 in mitochondria. Moreover, zinc-induced PINK1 stabilization was inhibited by PD98059. Finally, zinc prevented mitochondrial superoxide generation and dissipation of mitochondrial membrane potential (ΔΨ_m) at reoxygenation, which was blocked by both the Beclin1 and PINK1 siRNAs, suggesting that zinc prevents mitochondrial oxidative stress through mitophagy. In summary, zinc induces mitophagy through PINK1 and Beclin1 via ERK leading to the prevention of mitochondrial superoxide generation in the setting of H/R. Clearance of damaged mitochondria may account for the cardioprotective effect of zinc on H/R injury.     

The PINK1-Parkin pathway is involved in the regulation of mitochondrial remodeling process

The two Parkinson’s disease (PD) genes, PTEN-induced kinase 1 (PINK1) and parkin, are linked in a common pathway which affects mitochondrial integrity and function. However, it is still not known what this pathway does in the mitochondria. Therefore, we investigated its physiological function in Drosophila. Because Drosophila PINK1 and parkin mutants show changes in mitochondrial morphology in both indirect flight muscles and dopaminergic neurons, we here investigated whether the PINK1-Parkin pathway genetically interacts with the regulators of mitochondrial fusion and fission such as Drp1, which promotes mitochondrial fission, and Opa1 or Marf, which induces mitochondrial fusion. Surprisingly, DrosophilaPINK1 and parkin mutant phenotypes were markedly suppressed by overexpression of Drp1 or downregulation of Opa1 or Marf, indicating that the PINK1-Parkin pathway regulates mitochondrial remodeling process in the direction of promoting mitochondrial fission. Therefore, we strongly suggest that mitochondrial fusion and fission process could be a prominent therapeutic target for the treatment of PD.     

Dual role of USP30 in controlling basal pexophagy and mitophagy

USP30 is an integral protein of the outer mitochondrial membrane that counteracts PINK1 and Parkin‐dependent mitophagy following acute mitochondrial depolarisation. Here, we use two distinct mitophagy reporter systems to reveal tonic suppression by USP30, of a PINK1‐dependent component of basal mitophagy in cells lacking detectable Parkin. We propose that USP30 acts upstream of PINK1 through modulation of PINK1‐substrate availability and thereby determines the potential for mitophagy initiation. We further show that a fraction of endogenous USP30 is independently targeted to peroxisomes where it regulates basal pexophagy in a PINK1‐ and Parkin‐independent manner. Thus, we reveal a critical role of USP30 in the clearance of the two major sources of ROS in mammalian cells and in the regulation of both a PINK1‐dependent and a PINK1‐independent selective autophagy pathway.     

The PINK1/Parkin pathway: a mitochondrial quality control system?

Significant insight into the mechanisms that contribute to dopaminergic neurodegeneration in Parkinson disease has been gained from the analysis of genes linked to rare heritable forms of parkinsonism such as PINK1 and parkin, loss-of-function mutations of which cause autosomal recessive parkinsonism. PINK1 encodes a mitochondrially targeted Ser/Thr kinase and parkin encodes a ubiquitin-protein ligase. Functional studies of PINK1 and Parkin in animal and cellular model systems have shown that both proteins play important roles in maintaining mitochondrial integrity. Genetic studies of PINK1 and Parkin orthologs in flies have shown that PINK1 acts upstream from Parkin in a common pathway that appears to regulate mitochondrial morphology. Mitochondrial morphology is regulated by mitochondrial fission and fusion-promoting proteins, and is important in a variety of contexts, including mitochondrial trafficking and mitochondrial quality control. In particular, mitochondrial fission appears to promote the segregation of terminally dysfunctional mitochondria for degradation in the lysosome through a process termed mitophagy. Recent work has shown that Parkin promotes the degradation of dysfunctional mitochondria in vertebrate cell culture. Here we postulate a model whereby the PINK1/Parkin pathway regulates mitochondrial dynamics in an effort to promote the turnover of damaged mitochondria.     

PINK1 deficiency in β-cells increases basal insulin secretion and improves glucose tolerance in mice

The Parkinson''s disease (PD) gene, PARK6, encodes the PTEN-induced putative kinase 1 (PINK1) mitochondrial kinase, which provides protection against oxidative stress-induced apoptosis. Given the link between glucose metabolism, mitochondrial function and insulin secretion in β-cells, and the reported association of PD with type 2 diabetes, we investigated the response of PINK1-deficient β-cells to glucose stimuli to determine whether loss of PINK1 affected their function. We find that loss of PINK1 significantly impairs the ability of mouse pancreatic β-cells (MIN6 cells) and primary intact islets to take up glucose. This was accompanied by higher basal levels of intracellular calcium leading to increased basal levels of insulin secretion under low glucose conditions. Finally, we investigated the effect of PINK1 deficiency in vivo and find that PINK1 knockout mice have improved glucose tolerance. For the first time, these combined results demonstrate that loss of PINK1 function appears to disrupt glucose-sensing leading to enhanced insulin release, which is uncoupled from glucose uptake, and suggest a key role for PINK1 in β-cell function.