Juvenile-onset Parkinsonism Research Articles

Kufor-Rakeb syndrome-associated psychosis: a novel loss-of-function ATP13A2 variant and response to antipsychotic therapy

Biallelic (autosomal recessive) pathogenic variants in ATP13A2 cause a form of juvenile-onset parkinsonism, termed Kufor-Rakeb syndrome. In addition to motor symptoms, a variety of other neurological and psychiatric symptoms may occur in affected individuals, including supranuclear gaze palsy and cognitive decline. Although psychotic symptoms are often reported, response to antipsychotic therapy is not well described in previous case reports/series. As such, we describe treatment response in an individual with Kufor-Rakeb syndrome-associated psychosis. His disease was caused by a homozygous novel loss-of-function ATP13A2 variant (NM_022089.4, c.1970_1975del) that was characterized in this study. Our patient exhibited a good response to quetiapine monotherapy, which he has so far tolerated well. We also reviewed the literature and summarized all previous descriptions of antipsychotic treatment response. Although its use has infrequently been described in Kufor-Rakeb syndrome, quetiapine is commonly used in other degenerative parkinsonian disorders, given its lower propensity to cause extrapyramidal symptoms. As such, quetiapine should be considered in the treatment of Kufor-Rakeb syndrome-associated psychosis when antipsychotic therapy is deemed necessary.

Pathogenesis of Parkinson's disease: from hints from monogenic familial PD to biomarkers.

Twenty-five years have passed since the causative gene for familial Parkinson's disease (PD), Parkin (now PRKN), was identified in 1998; PRKN is the most common causative gene in young-onset PD. Parkin encodes a ubiquitin-protein ligase, and Parkin is involved in mitophagy, a type of macroautophagy, in concert with PTEN-induced kinase 1 (PINK1). Both gene products are also involved in mitochondrial quality control. Among the many genetic PD-causing genes discovered, discovering PRKN as a cause of juvenile-onset PD has significantly impacted other neurodegenerative disorders. This is because the involvement of proteolytic systems has been suggested as a common mechanism in neurodegenerative diseases in which inclusion body formation is observed. The discovery of the participation of PRKN in PD has brought attention to the involvement of the proteolytic system in neurodegenerative diseases. Our research group has successfully isolated and identified CHCHD2, which is involved in the mitochondrial electron transfer system, and prosaposin (PSAP), which is involved in the lysosomal system, in this Parkin mechanism. Hereditary PD is undoubtedly an essential clue to solitary PD, and at least 25 or so genes and loci have been reported so far. This number of genes indicates that PD is a very diverse group of diseases. Currently, the diagnosis of PD is based on clinical symptoms and imaging studies. Although highly accurate diagnostic criteria have been published, early diagnosis is becoming increasingly important in treatment strategies for neurodegenerative diseases. Here, we also describe biomarkers that our group is working on.

PTPA variants and impaired PP2A activity in early-onset parkinsonism with intellectual disability.

The protein phosphatase 2A complex (PP2A), the major Ser/Thr phosphatase in the brain, is involved in a number of signalling pathways and functions, including the regulation of crucial proteins for neurodegeneration, such as alpha-synuclein, tau and LRRK2. Here, we report the identification of variants in the PTPA/PPP2R4 gene, encoding a major PP2A activator, in two families with early-onset parkinsonism and intellectual disability. We carried out clinical studies and genetic analyses, including genome-wide linkage analysis, whole-exome sequencing, and Sanger sequencing of candidate variants. We next performed functional studies on the disease-associated variants in cultured cells and knock-down of ptpa in Drosophila melanogaster. We first identified a homozygous PTPA variant, c.893T>G (p.Met298Arg), in patients from a South African family with early-onset parkinsonism and intellectual disability. Screening of a large series of additional families yielded a second homozygous variant, c.512C>A (p.Ala171Asp), in a Libyan family with a similar phenotype. Both variants co-segregate with disease in the respective families. The affected subjects display juvenile-onset parkinsonism and intellectual disability. The motor symptoms were responsive to treatment with levodopa and deep brain stimulation of the subthalamic nucleus. In overexpression studies, both the PTPA p.Ala171Asp and p.Met298Arg variants were associated with decreased PTPA RNA stability and decreased PTPA protein levels; the p.Ala171Asp variant additionally displayed decreased PTPA protein stability. Crucially, expression of both variants was associated with decreased PP2A complex levels and impaired PP2A phosphatase activation. PTPA orthologue knock-down in Drosophila neurons induced a significant impairment of locomotion in the climbing test. This defect was age-dependent and fully reversed by L-DOPA treatment. We conclude that bi-allelic missense PTPA variants associated with impaired activation of the PP2A phosphatase cause autosomal recessive early-onset parkinsonism with intellectual disability. Our findings might also provide new insights for understanding the role of the PP2A complex in the pathogenesis of more common forms of neurodegeneration.

Teaching Video NeuroImage: Facial-Faucial-Finger Myoclonus in Kufor-Rakeb Syndrome.

Two Chinese Australian siblings from nonconsanguineous parents presented with adolescent-onset dystonia-parkinsonism with prominent anxiety. Examination revealed eyelid, lower facial, and distal upper extremity myoclonus (Video 1), which was recorded using surface EMG (Figure 1). Compound heterozygous pathogenic variants in ATP13A2 were identified, c.3176T>G (p.L1059R) and c.3253delC (p.L1088WfsX4), confirming the diagnosis of Kufor-Rakeb syndrome (KRS).1 KRS classically presents as juvenile-onset, levodopa-responsive parkinsonism combined with pyramidal signs, upgaze palsy, cognitive decline, and, uniquely, facial-faucial-finger minimyoclonus.2 This distinctive pattern of myoclonus is a useful clue to the diagnosis in affected individuals and distinguishes it from other forms of juvenile-onset parkinsonism.

Investigation of USP30 inhibition to enhance Parkin-mediated mitophagy: tools and approaches.

Mitochondrial dysfunction is implicated in Parkinson disease (PD). Mutations in Parkin, an E3 ubiquitin ligase, can cause juvenile-onset Parkinsonism, probably through impairment of mitophagy. Inhibition of the de-ubiquitinating enzyme USP30 may counter this effect to enhance mitophagy. Using different tools and cellular approaches, we wanted to independently confirm this claimed role for USP30. Pharmacological characterisation of additional tool compounds that selectively inhibit USP30 are reported. The consequence of USP30 inhibition by these compounds, siRNA knockdown and overexpression of dominant-negative USP30 on the mitophagy pathway in different disease-relevant cellular models was explored. Knockdown and inhibition of USP30 showed increased p-Ser65-ubiquitin levels and mitophagy in neuronal cell models. Furthermore, patient-derived fibroblasts carrying pathogenic mutations in Parkin showed reduced p-Ser65-ubiquitin levels compared with wild-type cells, levels that could be restored using either USP30 inhibitor or dominant-negative USP30 expression. Our data provide additional support for USP30 inhibition as a regulator of the mitophagy pathway.

Structural mechanisms for gating and ion selectivity of the human polyamine transporter ATP13A2

Mutations in ATP13A2, also known as PARK9, cause a rare monogenic form of juvenile-onset Parkinson's disease named Kufor-Rakeb syndrome and other neurodegenerative diseases. ATP13A2 encodes a neuroprotective P5B P-type ATPase highly enriched in the brain that mediates selective import of spermine ions from lysosomes into the cytosol via an unknown mechanism. Here we present three structures of human ATP13A2 bound to an ATP analog or to spermine in the presence of phosphomimetics determined by cryoelectron microscopy. ATP13A2 autophosphorylation opens a lysosome luminal gate to reveal a narrow lumen access channel that holds a spermine ion in its entrance. ATP13A2's architecture suggests physical principles underlying selective polyamine transport and anticipates a "pump-channel" intermediate that could function as a counter-cation conduit to facilitate lysosome acidification. Our findings establish a firm foundation to understand ATP13A2 mutations associated with disease and bring us closer to realizing ATP13A2's potential in neuroprotective therapy.

Clinical Study of 668 Indian Subjects with Juvenile, Young, and Early Onset Parkinson's Disease.

To determine the demographic pattern of juvenile-onset parkinsonism (JP, <20 years), young-onset (YOPD, 20-40 years), and early onset (EOPD, 40-50 years) Parkinson's disease (PD) in India. We conducted a 2-year, pan-India, multicenter collaborative study to analyze clinical patterns of JP, YOPD, and EOPD. All patients under follow-up of movement disorders specialists and meeting United Kingdom (UK) Brain Bank criteria for PD were included. A total of 668 subjects (M:F 455:213) were recruited with a mean age at onset of 38.7 ± 8.1 years. The mean duration of symptoms at the time of study was 8 ± 6 years. Fifteen percent had a family history of PD and 13% had consanguinity. JP had the highest consanguinity rate (53%). YOPD and JP cases had a higher prevalence of consanguinity, dystonia, and gait and balance issues compared to those with EOPD. In relation to nonmotor symptoms, panic attacks and depression were more common in YOPD and sleep-related issues more common in EOPD subjects. Overall, dyskinesias were documented in 32.8%. YOPD subjects had a higher frequency of dyskinesia than EOPD subjects (39.9% vs. 25.5%), but they were first noted later in the disease course (5.7 vs. 4.4 years). This large cohort shows differing clinical patterns in JP, YOPD, and EOPD cases. We propose that cutoffs of <20, <40, and <50 years should preferably be used to define JP, YOPD, and EOPD.

Parkin truncating variants result in a loss-of-function phenotype

Parkinson disease (PD) is the second most common neurodegenerative disorder. Most cases of PD are sporadic, while 5–10% have a known genetic basis. Variants in the PARK2 gene are the most frequent cause of autosomal recessive juvenile-onset PD. PARK2 encodes parkin, a multi-domain protein that functions as an ubiquitin E3 ligase. Numerous variants spanning all parkin domains have been identified, although the pathogenic relevance for several of those remains unclear. In this study, we aimed to functionally characterize two truncating parkin variants: N52Mfs*29, which is highly prevalent in the Portuguese and Spanish populations, and L358Rfs*77, recently identified in the Portuguese population. Our results indicate that both variants are prematurely degraded by the proteasome, even though proteins levels are still moderate. We also showed that they are aggregation-prone and lead to mislocalized parkin. Interestingly, the L358Rfs*77 variant is mislocalized to the nucleus, which was never reported for parkin variants. While N52Mfs*29 impaired self-ubiquitination activity, the L358Rfs*77 variant seemed to retain it. Both variants, however, fail to ubiquitinate p62 substrate and did not relocalize to depolarized mitochondria. Therefore, we conclude that parkin truncating variants cause loss of parkin function, thus showing their causative role in PD pathogenesis.

Juvenile onset parkinsonism-dystonia syndrome: A novel mutation in the SLC6A3 gene

The differential diagnosis for genetic dystonia parkinsonism is broad. Juvenile onset parkinsonism-dystonia, also known as dopamine transporter deficiency syndrome (DTDS), is an autosomal recessive disorder with variable neurological manifestations and age of onset. We describe DTDS with a novel mutation. Case report We identified a 19-year-old male, who presented with history of juvenile-onset parkinsonism. He had a normal birth and neonatal course with normal developmental milestones. Cognitive, motor and speech were reported to be normal in the first decade of life. At 10–11 years of age, the patient started to have tremor and progressive parkinsonian symptoms. He additionally starts to have speech difficulties. The parents are consanguineous, but there is no family history of movement disorders, Parkinson’s disease or other psychiatric illness. Other siblings (brother and sister) are unaffected. Neurological examination revealed loss of speech to single words, rigidity, generalized bradykinesia, dystonia with dystonic tremor. Gene analysis showed a novel homozygous mutation in SLC6A3 gene (g.1394863c > G) with both parents and siblings having a heterozygous mutation in the same gene. •DTDS is a rare disorder that should be considered in the differential diagnosis of genetic parkinsonism of juvenile-onset. Affected individuals show hyperkinesia with orolingual and limb dyskinesia, dystonia, and chorea with parkinsonian features.•Atypical onset in adolescence or adulthood has been described.•SLC6A3 encodes the dopamine transporter (DAT) that is expressed predominantly within the substantia nigra and in the midbrain, which has a crucial role in mediating reuptake and homeostasis of dopamine.

Genetic analysis of PODXL gene in patients with familial and young-onset Parkinson's disease in a Taiwanese population

Mutations in the podocalyxin-like gene (PODXL) have been recently identified in a consanguineous Indian family with juvenile-onset Parkinson's disease (PD) and 3 unrelated patients with PD. However, the pathogenicity of PODXL mutations in the disease and their role in other PD populations remain unclear. The aim of this study was to investigate the PODXL mutations in a Taiwanese cohort with familial and young-onset PD. Among 531 participants, including 161 probands from PD pedigrees without known PD-causative gene mutations and 370 patients with early-onset PD (age of onset <50 years), all exons and exon-intron boundary junctions of PODXL were analyzed by Sanger sequencing. We did not find any pathogenic coding variants or previously reported mutations, indicating that PODXL mutations may not play a role in familial or early-onset PD in this Taiwanese population.

PTRHD1 Loss-of-function mutation in an african family with juvenile-onset Parkinsonism and intellectual disability.

The genetic bases of PD in sub-Saharan African (SSA) populations remain poorly characterized, and analysis of SSA families with PD might lead to the discovery of novel disease-related genes. To investigate the clinical features and identify the disease-causing gene in a black South African family with 3 members affected by juvenile-onset parkinsonism and intellectual disability. Clinical evaluation, neuroimaging studies, whole-exome sequencing, homozygosity mapping, two-point linkage analysis, and Sanger sequencing of candidate variants. A homozygous 28-nucleotide frameshift deletion in the PTRHD1 coding region was identified in the 3 affected family members and linked to the disease with genome-wide significant evidence. PTRHD1 was recently nominated as the disease-causing gene in two Iranian families, each containing 2 siblings with similar phenotypes and homozygous missense mutations. Together with the previous reports, we provide conclusive evidence that loss-of-function mutations in PTRHD1 cause autosomal-recessive juvenile parkinsonism and intellectual disability. © 2018 International Parkinson and Movement Disorder Society.

Parkin negatively regulates the antiviral signaling pathway by targeting TRAF3 for degradation

Chronic neuroinflammation is a characteristic of Parkinson's disease (PD). Previous investigations have shown that Parkin gene mutations are related to the early-onset recessive form of PD and isolated juvenile-onset PD. Further, Parkin plays important roles in mitochondrial quality control and cytokine-induced cell death. However, whether Parkin regulates other cellular events is still largely unknown. In this study, we performed overexpression and knockout experiments and found that Parkin negatively regulates antiviral immune responses against RNA and DNA viruses. Mechanistically, we show that Parkin interacts with tumor necrosis factor receptor-associated factor 3 (TRAF3) to regulate stability of TRAF3 protein by promoting Lys48-linked ubiquitination. Our findings suggest that Parkin plays a novel role in innate immune signaling by targeting TRAF3 for degradation and maintaining the balance of innate antiviral immunity.

Juvenile-onset parkinsonism with pyramidal signs due to compound heterozygous mutations in the F-Box only protein 7 gene

BackgroundJuvenile-onset parkinsonism is often caused by genetic factors. Mutations in several autosomal genes, including the F-box only protein 7 (FBXO7) gene, have been found in patients suffering from juvenile-onset parkinsonism with pyramidal signs. Only five types of FBXO7 mutations have been described. Here, we present a case report about a Chinese patient presenting with juvenile-onset parkinsonism likely caused by FBXO7 mutations. MethodsThe patient was a 32-year-old Chinese male. DNA samples were extracted from the patient and his parents. Exons in parkinsonism-related genes were amplified and sequenced. ResultsThe patient began experiencing a progressive involuntary tremor in his left hand at 16 years of age, which was followed by the development of gait dysfunction, dysarthria, and rapid eye movement sleep behavior disorder. A neurological examination of the patient revealed cogwheel rigidity, bradykinesia, static and postural tremor and bilateral Babinski signs. The patient responded to dopaminergic therapies but was affected by psychiatric side effects. Further genetic analysis of the patient and his parents revealed compound heterozygous mutations of the FBXO7 gene (NM_012179.3) in the patient (a nonsense c.1408G > T (p.E470X) mutation and a missense c.152A > G (p.N51S) mutation coming from the patient's mother and father, respectively). ConclusionsThis is the first case harboring FBXO7 mutations that presented with juvenile-onset parkinsonism in the Chinese population.

Differential expression of PARK2 splice isoforms in an in vitro model of dopaminergic-like neurons exposed to toxic insults mimicking Parkinson's disease.

Mutations in PARK2 (or parkin) are responsible for 50% of cases of autosomal-recessive juvenile-onset Parkinson's disease (PD). To date, 21 alternative splice variants of the human gene have been cloned. Yet most studies have focused on the full-length protein, whereas the spectrum of the parkin isoforms expressed in PD has never been investigated. In this study, the role of parkin proteins in PD neurodegeneration was explored for the first time by analyzing their expression profile in an in vitro model of PD. To do so, undifferentiated and all-trans-retinoic-acid (RA)-differentiated SH-SY5Y cells (which thereby acquire a PD-like phenotype) were exposed to PD-mimicking neurotoxins: 1-methyl-4-phenylpyridinium (MPP+ ) and 6-hydroxydopamine (6-OHDA) are widely used in PD models, whereas carbonyl cyanide m-chlorophenyl hydrazone (CCCP) and carbobenzoxy-Leu-Leu-leucinal (MG132) interfere, respectively, with mitochondrial mitophagy and proteasomal degradation. Following treatment with each neurotoxin H1, the first parkin isoform to be cloned, was down-regulated compared to the respective controls both in undifferentiated and RA-differentiated cells. In contrast, the expression pattern of the minor splice isoforms varied as a function of the compound used: it was largely unchanged in both cell cultures (eg, H21-H6, H12, XP isoform) or it showed virtually opposite alterations in undifferentiated and RA-differentiated cells (eg, H20 and H3 isoform). This complex picture suggests that up- or down-regulation may be a direct effect of toxin exposure, and that the different isoforms may exert different actions in neurodegeneration via modulation of different molecular pathways.

Micro-NMR elucidates altered metabolites in the Parkinson’s disease-related catp-6 genotype of Caenorhabditis elegans

A severe form of Parkinson’s disease (PD) is the Kufor-Rakeb syndrome. Here mutations in the ATP13A2 (PARK9) gene lead to an early juvenile-onset Parkinsonism often accompanied by dementia. ATP13A2 encodes a lysosomal P-type ATPase. Its ortholog in Caenorhabditis elegans is the catp-6 gene where phenotypes with mutations in the alleles ok3473 and tm3190 show high mortality and low reproduction. Since PD is difficult to study in humans we wanted to investigate the potential to use C. elegans as model for the Kufor-Rakeb syndrome. As it is difficult to obtain enough catp-6 mutant worms for standard NMR metabolic profiling, we explored focused ultrasonication extraction and miniaturized NMR as techniques to overcome this limitation. One- and two-dimensional NMR experiments (1 H, JRES, TOCSY) were performed with a commercial high-resolution magic angle spinning (HR-MAS) probe (25 µL sample volume). Significant features were identified through analysis of variance (ANOVA, p 1.5), PCA, and PLS-DA. Assignment of statistically relevant peaks resulted in the identification of twenty altered metabolites. Previous studies on catp-6 mutants identified strong morphological and functional changes in their mitochondria. Our findings of altered TCA metabolites (fumarate, succinate), branched-chain amino acids (leucine, isoleucine and valine) and nucleotides (AMP, ATP and GTP), formate and hypoxanthine appear to support these findings. Highest fold changes (< −5) in wildtype relative to both catp-6 strains were found for GTP. Formic acid is known to inhibit the mitochondrial respiratory chain complex IV and high hypoxanthine in catp-6 indicates an increased nucleotide salvage pathway. Alterations in most of the remaining metabolites may be the result of the recently discovered activation of AMPK (AMP-activated protein kinase) and inhibition of mTOR (mechanistic target of rapamycin) pathways together with a catabolic response to recover energy production. If the effect of the catp-6 mutation in C. elegans at the level of metabolites is correlated to the metabolic dysfunction in the human PARK9 ortholog, then it may be possible to uncover the molecular mechanism behind Parkinsonism and the Kufor-Rakeb syndrome.

Loss-of-function mutations in the ATP13A2/PARK9 gene cause complicated hereditary spastic paraplegia (SPG78).

Hereditary spastic paraplegias are heterogeneous neurodegenerative disorders characterized by progressive spasticity of the lower limbs due to degeneration of the corticospinal motor neurons. In a Bulgarian family with three siblings affected by complicated hereditary spastic paraplegia, we performed whole exome sequencing and homozygosity mapping and identified a homozygous p.Thr512Ile (c.1535C > T) mutation in ATP13A2. Molecular defects in this gene have been causally associated with Kufor-Rakeb syndrome (#606693), an autosomal recessive form of juvenile-onset parkinsonism, and neuronal ceroid lipofuscinosis (#606693), a neurodegenerative disorder characterized by the intracellular accumulation of autofluorescent lipopigments. Further analysis of 795 index cases with hereditary spastic paraplegia and related disorders revealed two additional families carrying truncating biallelic mutations in ATP13A2. ATP13A2 is a lysosomal P5-type transport ATPase, the activity of which critically depends on catalytic autophosphorylation. Our biochemical and immunocytochemical experiments in COS-1 and HeLa cells and patient-derived fibroblasts demonstrated that the hereditary spastic paraplegia-associated mutations, similarly to the ones causing Kufor-Rakeb syndrome and neuronal ceroid lipofuscinosis, cause loss of ATP13A2 function due to transcript or protein instability and abnormal intracellular localization of the mutant proteins, ultimately impairing the lysosomal and mitochondrial function. Moreover, we provide the first biochemical evidence that disease-causing mutations can affect the catalytic autophosphorylation activity of ATP13A2. Our study adds complicated hereditary spastic paraplegia (SPG78) to the clinical continuum of ATP13A2-associated neurological disorders, which are commonly hallmarked by lysosomal and mitochondrial dysfunction. The disease presentation in our patients with hereditary spastic paraplegia was dominated by an adult-onset lower-limb predominant spastic paraparesis. Cognitive impairment was present in most of the cases and ranged from very mild deficits to advanced dementia with fronto-temporal characteristics. Nerve conduction studies revealed involvement of the peripheral motor and sensory nerves. Only one of five patients with hereditary spastic paraplegia showed clinical indication of extrapyramidal involvement in the form of subtle bradykinesia and slight resting tremor. Neuroimaging cranial investigations revealed pronounced vermian and hemispheric cerebellar atrophy. Notably, reduced striatal dopamine was apparent in the brain of one of the patients, who had no clinical signs or symptoms of extrapyramidal involvement.

Parkin Deficiency Reduces Hippocampal Glutamatergic Neurotransmission by Impairing AMPA Receptor Endocytosis.

Mutations in Parkin, a ubiquitinating enzyme, lead to the selective loss of midbrain dopaminergic neurons and juvenile-onset Parkinson's disease (PD). Parkin loss of function has also been shown to alter hippocampal glutamatergic neurotransmission, providing a potential explanation for PD-associated cognitive impairment. However, very little is known about Parkin's specific sites or mechanisms of action at glutamatergic synapses. Here, we show that Parkin deficiency leads to decreased AMPA receptor-mediated activity due to disruption of the postsynaptic endocytic zones required for maintaining proper cell-surface AMPA receptor levels. These findings demonstrate a novel role for Parkin in synaptic AMPA receptor internalization and suggest a Parkin-dependent mechanism for hippocampal dysfunction that may explain cognitive deficits associated with some forms of PD.

Versatile members of the DNAJ family show Hsp70 dependent anti-aggregation activity on RING1 mutant parkin C289G.

Parkinson’s disease is one of the most common neurodegenerative disorders and several mutations in different genes have been identified to contribute to the disease. A loss of function parkin RING1 domain mutant (C289G) is associated with autosomal-recessive juvenile-onset Parkinsonism (AR-JP) and displays altered solubility and sequesters into aggregates. Single overexpression of almost each individual member of the Hsp40 (DNAJ) family of chaperones efficiently reduces parkin C289G aggregation and requires interaction with and activity of endogenously expressed Hsp70 s. For DNAJB6 and DNAJB8, potent suppressors of aggregation of polyglutamine proteins for which they rely mainly on an S/T-rich region, it was found that the S/T-rich region was dispensable for suppression of parkin C289G aggregation. Our data implies that different disease-causing proteins pose different challenges to the protein homeostasis system and that DNAJB6 and DNAJB8 are highly versatile members of the DNAJ protein family with multiple partially non-overlapping modes of action with respect to handling disease-causing proteins, making them interesting potential therapeutic targets.

Loss of ATP13A2 impairs glycolytic function in Kufor-Rakeb syndrome patient-derived cell models

BackgroundKufor-Rakeb syndrome (KRS) is an autosomal recessive, juvenile-onset Parkinson's disease (PD) caused by loss-of-function mutations in ATP13A2 (PARK9). Impaired energy metabolism is considered a pathogenic mechanism in PD and mitochondrial dysfunction resulting from Zn2+ dyshomeostasis has been found in KRS patient-derived cells. In addition to mitochondrial energy production, glycolysis plays an important role in cellular energy metabolism and glucose hypometabolism has been reported in PD. However, glycolytic status in KRS remains undetermined despite its potential importance. MethodsWe assessed glycolytic function in ATP13A2-deficient KRS patient-derived human olfactory neurosphere cells and fibroblasts and determined the effect of pyruvate supplementation on improving cellular energy production. ResultsWe found impaired extracellular acidification, reduction in pyruvate production and a decrease in the NAD+/NADH ratio, indicative of glycolytic dysfunction. In addition, gene expression analysis revealed an altered expression profile for several glycolytic enzymes. Glycolytic dysfunction was aggravated when the intracellular Zn2+ concentration was increased, while ATP13A2 overexpression and pyruvate supplementation blocked the observed Zn2+-mediated toxicity. Moreover, supplementation with pyruvate significantly increased basal mitochondrial ATP production and abolished Zn2+-induced cell death. ConclusionsThese findings indicate that glycolytic dysfunction contributes to pathogenesis and pyruvate supplementation improves overall cellular bioenergetics in our KRS patient-derived cell model, highlighting a therapeutic potential.

F-box protein 7 mutations promote protein aggregation in mitochondria and inhibit mitophagy.

The mutations of F-box protein 7 (FBXO7) gene (T22M, R378G and R498X) are associated with a severe form of autosomal recessive juvenile-onset Parkinson's disease (PD) (PARK 15). Here we demonstrated that wild-type (WT) FBXO7 is a stress response protein and it can play both cytoprotective and neurotoxic roles. The WT FBXO7 protein is vital to cell mitophagy and can facilitate mitophagy to protect cells, whereas mutant FBXO7 inhibits mitophagy. Upon stress, the endogenous WT FBXO7 gets up-regulated, concentrates into mitochondria and forms FBXO7 aggregates in mitochondria. However, FBXO7 mutations aggravate deleterious FBXO7 aggregation in mitochondria. The FBXO7 aggregation and toxicity can be alleviated by Proline, glutathione (GSH) and coenzyme Q10, whereas deleterious FBXO7 aggregation in mitochondria can be aggravated by prohibitin 1 (PHB1), a mitochondrial protease inhibitor. The overexpression of WT FBXO7 could lead to FBXO7 protein aggregation and dopamine neuron degeneration in transgenic Drosophila heads. The elevated FBXO7 expression and aggregation were identified in human fibroblast cells from PD patients. FBXO7 can also form aggregates in brains of PD and Alzheimer's disease. Our study provides novel pathophysiologic insights and suggests that FBXO7 may be a potential therapeutic target in FBXO7-linked neuron degeneration in PD.