PLA2G6-Associated Neurodegeneration (PLAN): Review of Clinical Phenotypes and Genotypes

Emerging Disease-Modifying Therapies in Neurodegeneration With Brain Iron Accumulation (NBIA) Disorders

Neurodegeneration with Brain Iron Accumulation (NBIA) is a heterogeneous group of progressive neurodegenerative diseases characterized by iron deposition in the globus pallidus and the substantia nigra. As of today, 15 distinct monogenetic disease entities have been identified. The four most common forms are pantothenate kinase-associated neurodegeneration (PKAN), phospholipase A2 group VI (PLA2G6)-associated neurodegeneration (PLAN), beta-propeller protein-associated neurodegeneration (BPAN) and mitochondrial membrane protein-associated neurodegeneration (MPAN). Neurodegeneration with Brain Iron Accumulation disorders present with a wide spectrum of clinical symptoms such as movement disorder signs (dystonia, parkinsonism, chorea), pyramidal involvement (e.g., spasticity), speech disorders, cognitive decline, psychomotor retardation, and ocular abnormalities. Treatment remains largely symptomatic but new drugs are in the pipeline. In this review, we discuss the rationale of new compounds, summarize results from clinical trials, provide an overview of important results in cell lines and animal models and discuss the future development of disease-modifying therapies for NBIA disorders. A general mechanistic approach for treatment of NBIA disorders is with iron chelators which bind and remove iron. Few studies investigated the effect of deferiprone in PKAN, including a recent placebo-controlled double-blind multicenter trial, demonstrating radiological improvement with reduction of iron load in the basal ganglia and a trend to slowing of disease progression. Disease-modifying strategies address the specific metabolic pathways of the affected enzyme. Such tailor-made approaches include provision of an alternative substrate (e.g., fosmetpantotenate or 4′-phosphopantetheine for PKAN) in order to bypass the defective enzyme. A recent randomized controlled trial of fosmetpantotenate, however, did not show any significant benefit of the drug as compared to placebo, leading to early termination of the trials' extension phase. 4′-phosphopantetheine showed promising results in animal models and a clinical study in patients is currently underway. Another approach is the activation of other enzyme isoforms using small molecules (e.g., PZ-2891 in PKAN). There are also compounds which counteract downstream cellular effects. For example, deuterated polyunsaturated fatty acids (D-PUFA) may reduce mitochondrial lipid peroxidation in PLAN. In infantile neuroaxonal dystrophy (a subtype of PLAN), desipramine may be repurposed as it blocks ceramide accumulation. Gene replacement therapy is still in a preclinical stage.

Lipids, lysosomes and mitochondria: insights into Lewy body formation from rare monogenic disorders

Accumulation of the protein α-synuclein into insoluble intracellular deposits termed Lewy bodies (LBs) is the characteristic neuropathological feature of LB diseases, such as Parkinson's disease (PD), Parkinson's disease dementia (PDD) and dementia with LB (DLB). α-Synuclein aggregation is thought to be a critical pathogenic event in the aetiology of LB disease, based on genetic analyses, fundamental studies using model systems, and the observation of LB pathology in post-mortem tissue. However, some monogenic disorders not traditionally characterised as synucleinopathies, such as lysosomal storage disorders, iron storage disorders and mitochondrial diseases, appear disproportionately vulnerable to the deposition of LBs, perhaps suggesting the process of LB formation may be a result of processes perturbed as a result of these conditions. The present review discusses biological pathways common to monogenic disorders associated with LB formation, identifying catabolic processes, particularly related to lipid homeostasis, autophagy and mitochondrial function, as processes that could contribute to LB formation. These findings are discussed in the context of known mediators of α-synuclein aggregation, highlighting the potential influence of impairments to these processes in the aetiology of LB formation.

The Importance of Drosophila melanogaster Research to UnCover Cellular Pathways Underlying Parkinson's Disease

Parkinson's disease (PD) is a complex neurodegenerative disorder that is currently incurable. As a consequence of an incomplete understanding of the etiology of the disease, therapeutic strategies mainly focus on symptomatic treatment. Even though the majority of PD cases remain idiopathic (~90%), several genes have been identified to be causative for PD, facilitating the generation of animal models that are a good alternative to study disease pathways and to increase our understanding of the underlying mechanisms of PD. Drosophila melanogaster has proven to be an excellent model in these studies. In this review, we will discuss the different PD models in flies and key findings identified in flies in different affected pathways in PD. Several molecular changes have been identified, of which mitochondrial dysfunction and a defective endo-lysosomal pathway emerge to be the most relevant for PD pathogenesis. Studies in flies have significantly contributed to our knowledge of how disease genes affect and interact in these pathways enabling a better understanding of the disease etiology and providing possible therapeutic targets for the treatment of PD, some of which have already resulted in clinical trials.

Phospholipase iPLA2β averts ferroptosis by eliminating a redox lipid death signal

Ferroptosis, triggered by discoordination of iron, thiols and lipids, leads to the accumulation of 15-hydroperoxy (Hp)-arachidonoyl-phosphatidylethanolamine (15-HpETE-PE), generated by complexes of 15-lipoxygenase (15-LOX) and a scaffold protein, phosphatidylethanolamine (PE)-binding protein (PEBP)1. As the Ca²⁺-independent phospholipase A₂β (iPLA₂β, PLA2G6 or PNPLA9 gene) can preferentially hydrolyze peroxidized phospholipids, it may eliminate the ferroptotic 15-HpETE-PE death signal. Here, we demonstrate that by hydrolyzing 15-HpETE-PE, iPLA₂β averts ferroptosis, whereas its genetic or pharmacological inactivation sensitizes cells to ferroptosis. Given that PLA2G6 mutations relate to neurodegeneration, we examined fibroblasts from a patient with a Parkinson's disease (PD)-associated mutation (fPD^R747W) and found selectively decreased 15-HpETE-PE-hydrolyzing activity, 15-HpETE-PE accumulation and elevated sensitivity to ferroptosis. CRISPR-Cas9-engineered Pnpla9^R748W/R748W mice exhibited progressive parkinsonian motor deficits and 15-HpETE-PE accumulation. Elevated 15-HpETE-PE levels were also detected in midbrains of rotenone-infused parkinsonian rats and α-synuclein-mutant Snca^A53T mice, with decreased iPLA₂β expression and a PD-relevant phenotype. Thus, iPLA₂β is a new ferroptosis regulator, and its mutations may be implicated in PD pathogenesis.

Paroxysmal kinesigenic dyskinesia associated with a novel POLG variant: A case report

INTRODUCTION

Paroxysmal kinesigenic dyskinesia (PKD) is a rare neurological disease characterized by recurrent dyskinesia or choreoathetosis triggered by sudden movements. Pathogenic variants in PRRT2 are the main cause of PKD. However, only about half of clinically diagnosed PKD patients have PRRT2 mutations, indicating that additional undiscovered causative genes could be implicated. PKD associated with POLG variant has not been reported.

PATIENT CONCERNS

A 14-year-old boy presented with a 2-month history of involuntary dystonic movements triggered by sudden activities. He was conscious during the attacks. Neurological examination, laboratory tests, brain magnetic resonance imaging (MRI), electroencephalogram (EEG) were all normal. Genetic analysis showed a novel variant of POLG (c.440G>T, p.Ser147Ile), which was considered to be a likely pathogenic variant in this case.

DIAGNOSES

The patient was diagnosed with PKD.

INTERVENTIONS

Low dose carbamazepine was used orally for treatment.

OUTCOMES

The patient achieved complete resolution of symptoms without any dyskinesia during the 6-month follow up.

CONCLUSION

Our study identified the novel POLG variant (c.440G>T, p.Ser147Ile) to be a likely pathogenic variant in PKD.

Pluripotent Stem Cell Derived Neurons as In Vitro Models for Studying Autosomal Recessive Parkinson's Disease (ARPD): PLA2G6 and Other Gene Loci

Parkinson's disease (PD) is a neurodegenerative motor disorder which is largely sporadic; however, some familial forms have been identified. Genetic PD can be inherited by autosomal, dominant or recessive mutations. While the dominant mutations mirror the prototype of PD with adult-onset and L-dopa-responsive cases, autosomal recessive PD (ARPD) exhibit atypical phenotypes with additional clinical manifestations. Young-onset PD is also very common with mutations in recessive gene loci. The main genes associated with ARPD are Parkin, PINK1, DJ-1, ATP13A2, FBXO7 and PLA2G6. Calcium dyshomeostasis is a mainstay in all types of PD, be it genetic or sporadic. Intriguingly, calcium imbalances manifesting as altered Store-Operated Calcium Entry (SOCE) is suggested in PLA2G6-linked PARK 14 PD. The common pathways underlying ARPD pathology, including mitochondrial abnormalities and autophagic dysfunction, can be investigated ex vivo using induced pluripotent stem cell (iPSC) technology and are discussed here. PD pathophysiology is not faithfully replicated by animal models, and, therefore, nigral dopaminergic neurons generated from iPSC serve as improved human cellular models. With no cure to date and treatments aiming at symptomatic relief, these in vitro models derived through midbrain floor-plate induction provide a platform to understand the molecular and biochemical pathways underlying PD etiology in a patient-specific manner.

The role of genetics in Parkinson's disease: a large cohort study in Chinese mainland population

This study aimed to determine the mutational spectrum of familial Parkinson's disease and sporadic early-onset Parkinson's disease (sEOPD) in a mainland Chinese population and the clinical features of mutation carriers. We performed multiplex ligation-dependent probe amplification assays and whole-exome sequencing for 1676 unrelated patients with Parkinson's disease in a mainland Chinese population, including 192 probands from families with autosomal-recessive Parkinson's disease, 242 probands from families with autosomal-dominant Parkinson's disease, and 1242 sEOPD patients (age at onset ≤ 50). According to standards and guidelines from the American College of Medical Genetics and Genomics, pathogenic/likely pathogenic variants in 23 known Parkinson's disease-associated genes occurred more frequently in the autosomal-recessive Parkinson's disease cohort (65 of 192, 33.85%) than in the autosomal-dominant Parkinson's disease cohort (10 of 242, 4.13%) and the sEOPD cohort (57 of 1242, 4.59%), which leads to an overall molecular diagnostic yield of 7.88% (132 of 1676). We found that PRKN was the most frequently mutated gene (n = 83, 4.95%) and present the first evidence of an SNCA duplication and LRRK2 p.N1437D variant in mainland China. In addition, several novel pathogenic/likely pathogenic variants including LRRK2 (p.V1447M and p.Y1645S), ATP13A2 (p.R735X and p.A819D), FBXO7 (p.G67E), LRP10 (c.322dupC/p.G109Rfs*51) and TMEM230 (c.429delT/p.P144Qfs*2) were identified in our cohort. Furthermore, the age at onset of the 132 probands with genetic diagnoses (median, 31.5 years) was about 14.5 years earlier than that of patients without molecular diagnoses (i.e. non-carriers, median 46.0 years). Specifically, the age at onset of Parkinson's disease patients with pathogenic/likely pathogenic variants in ATP13A2, PLA2G6, PRKN, or PINK1 was significantly lower than that of non-carriers, while the age at onset of carriers with other gene pathogenic/likely pathogenic variants was similar to that of non-carriers. The clinical spectrum of Parkinson's disease-associated gene carriers in this mainland Chinese population was similar to that of other populations. We also detected 61 probands with GBA possibly pathogenic variants (3.64%) and 59 probands with GBA p.L444P (3.52%). These results shed insight into the genetic spectrum and clinical manifestations of Parkinson's disease in mainland China and expand the existing repertoire of pathogenic or likely pathogenic variants involved in known Parkinson's disease-associated genes. Our data highlight the importance of genetic testing in Parkinson's disease patients with age at onset < 40 years, especially in those from families with a recessive inheritance pattern, who may benefit from early diagnosis and treatment.

Initial survey of PLA2G6 missense variant causing neuroaxonal dystrophy in Papillon dogs in North America and Europe

BACKGROUND

An autosomal recessive, rapidly progressive degenerative neuropathy known as infantile neuroaxonal dystrophy (NAD) was originally reported in Papillion puppies in 1995. In 2015, a causative missense variant in the PLA2G6 gene was identified in three affected puppies. Archived samples from Papillons clinically diagnosed with NAD prior to 2015 as well as samples obtained from 660 Papillons from North America and Europe between 2015 and 2017 were screened for the presence of this PLA2G6 gene variant (XM_022424454.1:c.1579G > A) using a TaqMan assay.

RESULTS

Archived samples from affected puppies diagnosed prior to 2015 and three more recently acquired samples from Papillons clinically affected with NAD were all homozygous for the variant. SIFT analysis predicts that the PLA2G6 missense substitution (XP_022280162.1:p.Ala527Thr) will not be tolerated in the iPLA2β protein. Notably, 17.5% of the 660 tested Papillons were heterozygotes, resulting in a variant allele frequency of 0.092 in this initial survey. Since then, screening for NAD in Papillons by at least 10 other laboratories and data from the Health Committee of Papillon Club of America gathered between 2017 and 2019 reveal a variant allele frequency of 0.047.

CONCLUSIONS

This survey and data from other laboratories documents the widespread presence of the PLA2G6 variant in the Papillon population in North America and Europe. Despite the apparent declining prevalence of the PLA2G6 variant, screening of Papillons intended for breeding is still recommended to avoid inadvertent production of puppies with infantile NAD.

Association of rare heterozygous PLA2G6 variants with the risk of Parkinson's disease

The PLA2G6 gene has been identified as a causative gene for autosomal recessive early-onset dystonia-parkinsonism. Possible association was reported between single heterozygous PLA2G6 mutation and the risk of Parkinson's disease (PD), which, however, remained inconclusive. To clarify the effect of heterozygous PLA2G6 variants on the risk of PD, a total of 3710 patients with PD and 2636 controls of Chinese mainland population were recruited and genotyped by whole-exome sequencing or whole-genome sequencing. Variants in the PLA2G6 coding region were extracted and subjected to burden analysis using the optimal sequence kernel association test. In total, we identified 86 rare heterozygous variants in the PLA2G6 coding region, whereas no significant difference was found between cases and controls. Therefore, we found no supportive evidence for heterozygous PLA2G6 variants being a risk factor for PD in Chinese mainland population.

Comprehensive Analysis of Familial Parkinsonism Genes in Rapid-Eye-Movement Sleep Behavior Disorder

BACKGROUND

There is only partial overlap in the genetic background of isolated rapid-eye-movement sleep behavior disorder (iRBD) and Parkinson's disease (PD).

OBJECTIVE

To examine the role of autosomal dominant and recessive PD or atypical parkinsonism genes in the risk of iRBD.

METHODS

Ten genes, comprising the recessive genes PRKN, DJ-1 (PARK7), PINK1, VPS13C, ATP13A2, FBXO7, and PLA2G6 and the dominant genes LRRK2, GCH1, and VPS35, were fully sequenced in 1039 iRBD patients and 1852 controls of European ancestry, followed by association tests.

RESULTS

We found no association between rare heterozygous variants in the tested genes and risk of iRBD. Several homozygous and compound heterozygous carriers were identified, yet there was no overrepresentation in iRBD patients versus controls.

CONCLUSION

Our results do not support a major role for variants in these genes in the risk of iRBD. © 2020 International Parkinson and Movement Disorder Society.

Overdosing on iron: Elevated iron and degenerative brain disorders

IMPACT STATEMENT

Brain degenerative disorders, which include some neurodevelopmental disorders and age-associated diseases, cause debilitating neurological deficits and are generally fatal. A large body of emerging evidence indicates that iron accumulation in neurons within specific regions of the brain plays an important role in the pathogenesis of many of these disorders. Iron homeostasis is a highly complex and incompletely understood process involving a large number of regulatory molecules. Our review provides a description of what is known about how iron is obtained by the body and brain and how defects in the homeostatic processes could contribute to the development of brain diseases, focusing on Alzheimer's disease and Parkinson's disease as well as four other disorders belonging to a class of inherited conditions referred to as neurodegeneration based on iron accumulation (NBIA) disorders. A description of potential therapeutic approaches being tested for each of these different disorders is provided.

Brain MRI Pattern Recognition in Neurodegeneration With Brain Iron Accumulation

Most neurodegeneration with brain iron accumulation (NBIA) disorders can be distinguished by identifying characteristic changes on magnetic resonance imaging (MRI) in combination with clinical findings. However, a significant number of patients with an NBIA disorder confirmed by genetic testing have MRI features that are atypical for their specific disease. The appearance of specific MRI patterns depends on the stage of the disease and the patient's age at evaluation. MRI interpretation can be challenging because of heterogeneously acquired MRI datasets, individual interpreter bias, and lack of quantitative data. Therefore, optimal acquisition and interpretation of MRI data are needed to better define MRI phenotypes in NBIA disorders. The stepwise approach outlined here may help to identify NBIA disorders and delineate the natural course of MRI-identified changes.

Protective role of anticancer drugs in neurodegenerative disorders: A drug repurposing approach

The disease heterogeneity and little therapeutic progress in neurodegenerative diseases justify the need for novel and effective drug discovery approaches. Drug repurposing is an emerging approach that reinvigorates the classical drug discovery method by divulging new therapeutic uses of existing drugs. The common biological background and inverse tuning between cancer and neurodegeneration give weight to the conceptualization of repurposing of anticancer drugs as novel therapeutics. Many studies are available in the literature, which highlights the success story of anticancer drugs as repurposed therapeutics. Among them, kinase inhibitors, developed for various oncology indications evinced notable neuroprotective effects in neurodegenerative diseases. In this review, we shed light on the salient role of multiple protein kinases in neurodegenerative disorders. We also proposed a feasible explanation of the action of kinase inhibitors in neurodegenerative disorders with more attention towards neurodegenerative disorders. The problem of neurotoxicity associated with some anticancer drugs is also highlighted. Our review encourages further research to better encode the hidden potential of anticancer drugs with the aim of developing prospective repurposed drugs with no toxicity for neurodegenerative disorders.

PLA2G6 variants associated with the number of affected alleles in Parkinson's disease in Japan

This study aimed to evaluate genotype-phenotype correlations of Parkinson's disease (PD) patients with phospholipase A2 group V (PLA2G6) variants. We analyzed the DNA of 798 patients with PD, including 78 PD patients reported previously, and 336 in-house controls. We screened the exons and exon-intron boundaries of PLA2G6 using the Ion Torrent system and Sanger method. We identified 21 patients with 18 rare variants, such that 1, 9, and 11 patients were homozygous, heterozygous, and compound heterozygous, respectively, with respect to PLA2G6 variants. The allele frequency was approximately equal between patients with familial PD and those with sporadic PD. The PLA2G6 variants detected frequently were identified in the early-onset sporadic PD group. Patients who were homozygous for a variant showed more severe symptoms than those who were heterozygous for the variant. The most common variant was p.R635Q in our cohort, which was considered a risk variant for PD. Thus, the variants of PLA2G6 may play a role in familial PD and early-onset sporadic PD.

The identified clinical features of Parkinson's disease in homo-, heterozygous and digenic variants of PINK1

To investigate the prevalence and genotype-phenotype correlations of phosphatase and tensin homolog induced putative kinase 1 (PINK1) variants in Parkinson's disease (PD) patients, we analyzed 1700 patients (842 familial PD and 858 sporadic PD patients from Japanese origin). We screened the entire exon and exon-intron boundaries of PINK1 using Sanger sequencing and target sequencing by Ion torrent system. We identified 30 patients with heterozygous variants, 3 with homozygous variants, and 3 with digenic variants of PINK1-PRKN. Patients with homozygous variants presented a significantly younger age at onset than those with heterozygous variants. The allele frequency of heterozygous variants in patients with age at onset at 50 years and younger with familial PD and sporadic PD showed no differences. [¹²³I]meta-iodobenzylguanidine (MIBG) myocardial scintigraphy indicated that half of patients harboring PINK1 heterozygous variants showed a decreased heart to mediastinum ratio (12/23). Our findings emphasize the importance of PINK1 variants for the onset of PD in patients with age at onset at 50 years and younger and the broad spectrum of clinical symptoms in patients with PINK1 variants.

Genetic perspective on the synergistic connection between vesicular transport, lysosomal and mitochondrial pathways associated with Parkinson's disease pathogenesis

Parkinson's disease (PD) and atypical parkinsonian syndromes (APS) are symptomatically characterized by parkinsonism, with the latter presenting additionally a distinctive range of atypical features. Although the majority of patients with PD and APS appear to be sporadic, genetic causes of several rare monogenic disease variants were identified. The knowledge acquired from these genetic factors indicated that defects in vesicular transport pathways, endo-lysosomal dysfunction, impaired autophagy-lysosomal protein and organelle degradation pathways, α-synuclein aggregation and mitochondrial dysfunction play key roles in PD pathogenesis. Moreover, membrane dynamics are increasingly recognized as a key player in the disease pathogenesis due lipid homeostasis alterations, associated with lysosomal dysfunction, caused by mutations in several PD and APS genes. The importance of lysosomal dysfunction and lipid homeostasis is strengthened by both genetic discoveries and clinical epidemiology of the association between parkinsonism and lysosomal storage disorders (LSDs), caused by the disruption of lysosomal biogenesis or function. A synergistic coordination between vesicular trafficking, lysosomal and mitochondria defects exist whereby mutations in PD and APS genes encoding proteins primarily involved one PD pathway are frequently associated with defects in other PD pathways as a secondary effect. Moreover, accumulating clinical and genetic observations suggest more complex inheritance patters of familial PD exist, including oligogenic and polygenic inheritance of genes in the same or interconnected PD pathways, further strengthening their synergistic connection.Here, we provide a comprehensive overview of PD and APS genes with functions in vesicular transport, lysosomal and mitochondrial pathways, and highlight functional and genetic evidence of the synergistic connection between these PD associated pathways.

Genotype-phenotype correlations of adult-onset PLA2G6-associated Neurodegeneration: case series and literature review

Background

Phospholipase A2 group VI (PLA2G6) mutations associated with neurodegeneration (PLAN) manifest as heterogeneous neurodegenerative disorders with variable ages of onset. The genotype-phenotype correlation is not well-established. We aim to describe three adult patients with PLAN and combined these data with results from previous studies to elucidate adult-onset PLA2G6 phenotype-genotype correlations.

Case presentations

The first index patient presented with dystonia-parkinsonism starting at age 31 years, accompanied by major depression and cognitive decline. Genetic analysis using targeted next generation sequencing (NGS) panel, Sanger sequencing, and segregation analyses revealed a compound heterozygous mutation, c.991G > T (p.D331Y)/c.1077G > A (M358IfsX), in PLA2G6. The other two patients had levodopa-responsive, early-onset parkinsonism, starting in their late twenties. Both patients had homozygous c.991G > T (p.D331Y) mutations in PLA2G6. Patient characteristics of our reported 3 cases were compared to those of 32 previously described (2008 to 2019) patients with adult-onset PLAN. Among the combined cohort of 35 patients with adult-onset PLAN, 14 had dystonia-parkinsonism, 17 had early-onset Parkinson’s disease, 3 had hereditary spastic paraparesis, and one had ataxia. The c.991G > T (p. D331Y) mutation was almost exclusively found in Chinese patients, suggesting a common founder effect. All patients with homozygous p.D331Y mutations had levodopa-responsive, early-onset PD (100%); while other mutations mostly led to dystonia-parkinsonism, ataxia, spasticity, and combine psychiatric comorbidities.

Conclusions

We showed that adult-onset PLAN could present as purely parkinsonism features, without brain iron accumulation, particularly patients with homozygous p.D331Y mutations. Compound heterozygous mutations, including heterozygous p.D331Y, produced heterogeneous phenotypes, without obvious levodopa responsiveness.

INAD and Duchenne muscular dystrophy, two ends of the iPLA2β spectrum

Infantile neuroaxonal dystrophy (INAD) and Duchenne muscular dystrophy (DMD) are two deadly neuromuscular degenerative diseases of childhood. Knowledge on their pathophysiological mechanisms may direct us towards treatment or a cure. Although these diseases are caused by two totally different gene-mutations and cause different clinical pictures, in this article I propose a common disease mechanism in the two. This common mechanism is induced by defects in the response to cellular stress and injury. THE HYPOTHESIS: Depletion of iPLA2β in INAD and increased activity of iPLA2β in DMD eventually lead to similar defects in the response to cell stress and injury. According to this hypothesis, the depletion of iPLA2β in INAD primarily blocks repair mechanisms by the inability to form a mitochondrial permeability transition pore (PTP). Forming of the PTP is necessary to release mitochondrial coenzyme A (CoA) into the cytoplasm for activation of palmitoylation and massive endocytosis as a repair response. In DMD the increased activity of iPLA2β causes exhaustion of the stress signalling cascade by increased and prolonged PTP opening. Continuous leaking of mitochondrial CoA through the PTP leads to the inability of the cell to build a sufficient mitochondrial:cytoplasmic CoA gradient, also causing insufficient release of mitochondrial CoA as a response to cell stress and injury. Decreased palmitoylation capacity and decreased endocytosis and membrane remodelling are implicated in proven pathophysiological mechanisms in INAD and DMD. The described mechanism in INAD and DMD, may be considered a common mechanism of repair in case of cell stress and injury. Beside their role in INAD and DMD, they may therefore be implicated in other neurodegenerative diseases as well. Available research shows involvement of iPLA2β in other neurodegenerative diseases. We might be able to divide neurodegenerative diseases in "INAD-like disease-mechanism" or "DMD-like disease-mechanism", depending on decreased or increased iPLA2β activity.

Crosstalk between Nrf2 signaling and mitochondrial function in Parkinson's disease

Search for a definitive cure for neurodegenerative disorders like Parkinson's disease (PD) has met with little success. Mitochondrial dysfunction and elevated oxidative stress precede characteristic loss of dopamine-producing neurons from the midbrain in PD. The majority of PD cases are classified as sporadic (sPD) with an unknown etiology, whereas mutations in a handful of genes cause monogenic form called familial (fPD). Both sPD and fPD is characterized by proteinopathy and mitochondrial dysfunction leading to increased oxidative stress. These pathophysiological mechanisms create a vicious cycle feeding into each other, ultimately tipping the neurons to its demise. Effect of iron accumulation and dopamine oxidation adds an additional dimension to mitochondrial oxidative stress and apoptotic pathways affected. Nrf2 is a redox-sensitive transcription factor which regulates basal as well as inducible expression of antioxidant enzymes and proteins involved in xenobiotic detoxification. Recent advances, however, shows a multifaceted role for Nrf2 in the regulation of genes connected with inflammatory response, metabolic pathways, protein homeostasis, iron management, and mitochondrial bioenergetics. Here we review the role of mitochondria and oxidative stress in the PD etiology and the potential crosstalk between Nrf2 signaling and mitochondrial function in PD. We also make a case for the development of therapeutics that safely activates Nrf2 pathway in halting the progression of neurodegeneration in PD patients.