Lysosomal Storage of Subunit c of Mitochondrial ATP Synthase in Brain-Specific Atp13a2-Deficient Mice

ATP13A2 (PARK9) and basal ganglia function

ATP13A2 is a lysosomal protein involved in polyamine transport with loss of function mutations associated with multiple neurodegenerative conditions. These include early onset Parkinson's disease, Kufor-Rakeb Syndrome, neuronal ceroid lipofuscinosis, hereditary spastic paraplegia, and amyotrophic lateral sclerosis. While ATP13A2 mutations may result in clinical heterogeneity, the basal ganglia appear to be impacted in the majority of cases. The basal ganglia is particularly vulnerable to environmental exposures such as heavy metals, pesticides, and industrial agents which are also established risk factors for many neurodegenerative conditions. Not surprisingly then, impaired function of ATP13A2 has been linked to heavy metal toxicity including manganese, iron, and zinc. This review discusses the role of ATP13A2 in basal ganglia function and dysfunction, potential common pathological mechanisms in ATP13A2-related disorders, and how gene x environment interactions may contribute to basal ganglia dysfunction.

CHCHD2 Thr61Ile mutation impairs F1F0-ATPase assembly in in vitro and in vivo models of Parkinson's disease

Mitochondrial dysfunction is a significant pathological alteration that occurs in Parkinson's disease (PD), and the Thr61Ile (T61I) mutation in coiled-coil helix coiled-coil helix domain containing 2 (CHCHD2), a crucial mitochondrial protein, has been reported to cause Parkinson's disease. F1F0-ATPase participates in the synthesis of cellular adenosine triphosphate (ATP) and plays a central role in mitochondrial energy metabolism. However, the specific roles of wild-type (WT) CHCHD2 and T61I-mutant CHCHD2 in regulating F1F0-ATPase activity in Parkinson's disease, as well as whether CHCHD2 or CHCHD2 T61I affects mitochondrial function through regulating F1F0-ATPase activity, remain unclear. Therefore, in this study, we expressed WT CHCHD2 and T61I-mutant CHCHD2 in an MPP+-induced SH-SY5Y cell model of PD. We found that CHCHD2 protected mitochondria from developing MPP+-induced dysfunction. Under normal conditions, overexpression of WT CHCHD2 promoted F1F0-ATPase assembly, while T61I-mutant CHCHD2 appeared to have lost the ability to regulate F1F0-ATPase assembly. In addition, mass spectrometry and immunoprecipitation showed that there was an interaction between CHCHD2 and F1F0-ATPase. Three weeks after transfection with AAV-CHCHD2 T61I, we intraperitoneally injected 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine into mice to establish an animal model of chronic Parkinson's disease and found that exogenous expression of the mutant protein worsened the behavioral deficits and dopaminergic neurodegeneration seen in this model. These findings suggest that WT CHCHD2 can alleviate mitochondrial dysfunction in PD by maintaining F1F0-ATPase structure and function.

Modeling familial and sporadic Parkinson's disease in small fishes

The establishment of animal models for Parkinson's disease (PD) has been challenging. Nevertheless, once established, they will serve as valuable tools for elucidating the causes and pathogenesis of PD, as well as for developing new strategies for its treatment. Following the recent discovery of a series of PD causative genes in familial cases, teleost fishes, including zebrafish and medaka, have often been used to establish genetic PD models because of their ease of breeding and gene manipulation, as well as the high conservation of gene orthologs. Some of the fish lines can recapitulate PD phenotypes, which are often more pronounced than those in rodent genetic models. In addition, a new experimental teleost fish, turquoise killifish, can be used as a sporadic PD model, because it spontaneously manifests age-dependent PD phenotypes. Several PD fish models have already made significant contributions to the discovery of novel PD pathological features, such as cytosolic leakage of mitochondrial DNA and pathogenic phosphorylation in α-synuclein. Therefore, utilizing various PD fish models with distinct degenerative phenotypes will be an effective strategy for identifying emerging facets of PD pathogenesis and therapeutic modalities.

ATP13A2 modifies mitochondrial localization of overexpressed TOM20 to autolysosomal pathway

Mutations in ATP13A2 cause Kufor-Rakeb Syndrome (KRS), a juvenile form of Parkinson's Disease (PD). The gene product belongs to a diverse family of ion pumps and mediates polyamine influx from lysosomal lumen. While the biochemical and structural studies highlight its unique mechanics, how PD pathology is linked to ATP13A2 function remains unclear. Here we report that localization of overexpressed TOM20, a mitochondrial outer-membrane protein, is significantly altered upon ATP13A2 expression to partially merge with lysosome. Using Halo-fused version of ATP13A2, ATP13A2 was identified in lysosome and autophagosome. Upon ATP13A2 co-expression, overexpressed TOM20 was found not only in mitochondria but also within ATP13A2-containing autolysosome. This modification of TOM20 localization was inhibited by adding 1-methyl-4-phenylpyridinium (MPP+) and not accompanied with mitophagy induction. We suggest that ATP13A2 may participate in the control of overexpressed proteins targeted to mitochondrial outer-membrane.

ATP13A2 Declines Zinc-Induced Accumulation of α-Synuclein in a Parkinson’s Disease Model

Parkinson’s disease (PD) is characterized by the presence of Lewy bodies caused by α-synuclein. The imbalance of zinc homeostasis is a major cause of PD, promoting α-synuclein accumulation. ATP13A2, a transporter found in acidic vesicles, plays an important role in Zn²⁺ homeostasis and is highly expressed in Lewy bodies in PD-surviving neurons. ATP13A2 is involved in the transport of zinc ions in lysosomes and exosomes and inhibits the aggregation of α-synuclein. However, the potential mechanism underlying the regulation of zinc homeostasis and α-synuclein accumulation by ATP13A2 remains unexplored. We used α-synuclein-GFP transgenic mice and HEK293 α-synuclein-DsRed cell line as models. The spatial exploration behavior of mice was significantly reduced, and phosphorylation levels of α-synuclein increased upon high Zn²⁺ treatment. High Zn²⁺ also inhibited the autophagy pathway by reducing LAMP2a levels and changing the expression of LC3 and P62, by reducing mitochondrial membrane potential and increasing the expression of cytochrom C, and by activating the ERK/P38 apoptosis signaling pathway, ultimately leading to increased caspase 3 levels. These protein changes were reversed after ATP13A2 overexpression, whereas ATP13A2 knockout exacerbated α-synuclein phosphorylation levels. These results suggest that ATP13A2 may have a protective effect on Zn²⁺-induced abnormal aggregation of α-synuclein, lysosomal dysfunction, and apoptosis.

The regulatory mechanism between lysosomes and mitochondria in the aetiology of cardiovascular diseases

Coordinated action among various organelles maintains cellular functions. For instance, mitochondria and lysosomes are the main organelles contributing to cellular metabolism and provide energy for cardiomyocyte contraction. They also provide essential signalling platforms in the cell that regulate many key processes such as autophagy, apoptosis, oxidative stress, inflammation and cell death. Often, abnormalities in mitochondrial or lysosomal structures and functions bring about cardiovascular diseases (CVDs). Although the communication between mitochondria and lysosomes throughout the cardiovascular system is intensely studied, the regulatory mechanisms have not been completely understood. Thus, we summarize the most recent studies related to mitochondria and lysosomes' role in CVDs and their potential connections and communications under cardiac pathophysiological conditions. Further, we discuss limitations and future perspectives regarding diagnosis, therapeutic strategies and drug discovery in CVDs.

The Association Between Lysosomal Storage Disorder Genes and Parkinson's Disease: A Large Cohort Study in Chinese Mainland Population

Background: Recent years have witnessed an increasing number of studies indicating an essential role of the lysosomal dysfunction in Parkinson’s disease (PD) at the genetic, biochemical, and cellular pathway levels. In this study, we investigated the association between rare variants in lysosomal storage disorder (LSD) genes and Chinese mainland PD.

Methods: We explored the association between rare variants of 69 LSD genes and PD in 3,879 patients and 2,931 controls from Parkinson’s Disease & Movement Disorders Multicenter Database and Collaborative Network in China (PD-MDCNC) using next-generation sequencing, which were analyzed by using the optimized sequence kernel association test.

Results: We identified the significant burden of rare putative LSD gene variants in Chinese mainland patients with PD. This association was robust in familial or sporadic early-onset patients after excluding the GBA variants but not in sporadic late-onset patients. The burden analysis of variant sets in genes of LSD subgroups revealed a suggestive significant association between variant sets in genes of sphingolipidosis deficiency disorders and familial or sporadic early-onset patients. In contrast, variant sets in genes of sphingolipidoses, mucopolysaccharidoses, and post-translational modification defect disorders were suggestively associated with sporadic late-onset patients. Then, SMPD1 and other four novel genes (i.e., GUSB, CLN6, PPT1, and SCARB2) were suggestively associated with sporadic early-onset or familial patients, whereas GALNS and NAGA were suggestively associated with late-onset patients.

Conclusion: Our findings supported the association between LSD genes and PD and revealed several novel risk genes in Chinese mainland patients with PD, which confirmed the importance of lysosomal mechanisms in PD pathogenesis. Moreover, we identified the genetic heterogeneity in early-onset and late-onset of patients with PD, which may provide valuable suggestions for the treatment.

Heterozygous GBA D409V and ATP13a2 mutations do not exacerbate pathological α-synuclein spread in the prodromal preformed fibrils model in young mice

Autophagic dysregulation and lysosomal impairment have been implicated in the pathogenesis of Parkinson's disease, partly due to the identification of mutations in multiple genes involved in these pathways such as GBA, SNCA, ATP13a2 (also known as PARK9), TMEM175 and LRRK2. Mutations resulting in lysosomal dysfunction are proposed to contribute to Parkinson's disease by increasing α-synuclein levels, that in turn may promote aggregation of this protein. Here, we used two different genetic models-one heterozygous for a mutated form of the GBA protein (D409V), and the other heterozygous for an ATP13a2 loss-of-function mutation, to test whether these mutations exacerbate the spread of α-synuclein pathology following injection of α-synuclein preformed fibrils in the olfactory bulb of 12-week-old mice. Contrary to our hypothesis, we found that mice harboring GBA D409V^+/- and ATP13a2^+/- mutations did not have exacerbated behavioral impairments or histopathology (α-synuclein, LAMP2, and Iba1) when compared to their wildtype littermates. This indicates that in the young mouse brain, neither the GBA D409V mutation or ATP13a2 loss-of-function mutation accelerate the spread of α-synuclein pathology. As a consequence, we postulate that these mutations increase Parkinson's disease risk only by acting in one of the initial, upstream events in the Parkinson's disease pathogenic process. Further, the mutations, and the molecular pathways they impact, appear to play a less important role once the pathogenic process has been triggered and therefore do not specifically influence α-synuclein pathology spread.

Targeting of Lysosomal Pathway Genes for Parkinson's Disease Modification: Insights From Cellular and Animal Models

Previous genetic studies on hereditary Parkinson's disease (PD) have identified a set of pathogenic gene mutations that have strong impacts on the pathogenicity of PD. In addition, genome-wide association studies (GWAS) targeted to sporadic PD have nominated an increasing number of genetic variants that influence PD susceptibility. Although the clinical and pathological characteristics in hereditary PD are not identical to those in sporadic PD, α-synuclein, and LRRK2 are definitely associated with both types of PD, with LRRK2 mutations being the most frequent cause of autosomal-dominant PD. On the other hand, a significant portion of risk genes identified from GWAS have been associated with lysosomal functions, pointing to a critical role of lysosomes in PD pathogenesis. Experimental studies have suggested that the maintenance or upregulation of lysosomal activity may protect against neuronal dysfunction or degeneration. Here we focus on the roles of representative PD gene products that are implicated in lysosomal pathway, namely LRRK2, VPS35, ATP13A2, and glucocerebrosidase, and provide an overview of their disease-associated functions as well as their cooperative actions in the pathogenesis of PD, based on the evidence from cellular and animal models. We also discuss future perspectives of targeting lysosomal activation as a possible strategy to treat neurodegeneration.

Homeostatic p62 levels and inclusion body formation in CHCHD2 knockout mice

Inactivation of constitutive autophagy results in the formation of cytoplasmic inclusions in neurones, but the relationship between impaired autophagy and Lewy bodies (LBs) remains unknown. α-Synuclein and p62, components of LBs, are the defining characteristic of Parkinson's disease (PD). Until now, we have analyzed mice models and demonstrated p62 aggregates derived from an autophagic defect might serve as 'seeds' and can potentially be a cause of LB formation. P62 may be the key molecule for aggregate formation. To understand the mechanisms of LBs, we analyzed p62 homeostasis and inclusion formation using PD model mice. In PARK22-linked PD, intrinsically disordered mutant CHCHD2 initiates Lewy pathology. To determine the function of CHCHD2 for inclusions formation, we generated Chchd2-knockout (KO) mice and characterized the age-related pathological and motor phenotypes. Chchd2 KO mice exhibited p62 inclusion formation and dopaminergic neuronal loss in an age-dependent manner. These changes were associated with a reduction in mitochondria complex activity and abrogation of inner mitochondria structure. In particular, the OPA1 proteins, which regulate fusion of mitochondrial inner membranes, were immature in the mitochondria of CHCHD2-deficient mice. CHCHD2 regulates mitochondrial morphology and p62 homeostasis by controlling the level of OPA1. Our findings highlight the unexpected role of the homeostatic level of p62, which is regulated by a non-autophagic system, in controlling intracellular inclusion body formation, and indicate that the pathologic processes associated with the mitochondrial proteolytic system are crucial for loss of DA neurones.

ATP13A2 Gene Variants in Patients with Parkinson's Disease in Xinjiang

OBJECTIVE

To analyze the ATP13A2 gene variants in the Han and Uyghur populations residing in Xinjiang and to determine their correlation with the risk of Parkinson's disease (PD).

METHODS

Four ATP13A2 SNVs-rs56367069 (Arg294Gln), rs151117874 (Thr12Met), rs147277743 (Ala746Thr), and rs2076603-were analyzed in 218 patients (75 Uyghurs and 143 Hans) with sporadic PD and 234 healthy controls (90 Uyghurs and 144 Hans) by Sanger DNA sequencing.

RESULTS

Only one Han patient harbored the AG genotype of the rs147277743 SNV, indicating a frequency of 0.46% in the Han population. In addition, this SNV was not associated with PD risk. The rs2076603 SNV was correlated with PD development, and the A allele in particular was significantly different across ethnicity and age. The rs56367069 and rs151117874 SNVs were not detected in the entire cohort.

CONCLUSION

ATP13A2 rs2076603 SNV is associated with PD susceptibility, and the A allele is a PD protective factor in the Han population.

The contribution of multicellular model organisms to neuronal ceroid lipofuscinosis research

The NCLs (neuronal ceroid lipofuscinosis) are forms of neurodegenerative disease that affect people of all ages and ethnicities but are most prevalent in children. Commonly known as Batten disease, this debilitating neurological disorder is comprised of 13 different subtypes that are categorized based on the particular gene that is mutated (CLN1-8, CLN10-14). The pathological mechanisms underlying the NCLs are not well understood due to our poor understanding of the functions of NCL proteins. Only one specific treatment (enzyme replacement therapy) is approved, which is for the treating the brain in CLN2 disease. Hence there remains a desperate need for further research into disease-modifying treatments. In this review, we present and evaluate the genes, proteins and studies performed in the social amoeba, nematode, fruit fly, zebrafish, mouse and large animals pertinent to NCL. In particular, we highlight the use of multicellular model organisms to study NCL protein function, pathology and pathomechanisms. Their use in testing novel therapeutic approaches is also presented. With this information, we highlight how future research in these systems may be able to provide new insight into NCL protein functions in human cells and aid in the development of new therapies.

Lysosomal Dysfunction at the Centre of Parkinson's Disease and Frontotemporal Dementia/Amyotrophic Lateral Sclerosis

Parkinson's disease (PD) and frontotemporal dementia/amyotrophic lateral sclerosis (FTD/ALS) are insidious and incurable neurodegenerative diseases that represent a significant burden to affected individuals, caregivers, and an ageing population. Both PD and FTD/ALS are defined at post mortem by the presence of protein aggregates and the loss of specific subsets of neurons. We examine here the crucial role of lysosome dysfunction in these diseases and discuss recent evidence for converging mechanisms. This review draws upon multiple lines of evidence from genetic studies, human tissue, induced pluripotent stem cells (iPSCs), and animal models to argue that lysosomal failure is a primary mechanism of disease, rather than merely reflecting association with protein aggregate end-points. This review provides compelling rationale for targeting lysosomes in future therapeutics for both PD and FTD/ALS.

Complexity of Generating Mouse Models to Study the Upper Motor Neurons: Let Us Shift Focus from Mice to Neurons

Motor neuron circuitry is one of the most elaborate circuitries in our body, which ensures voluntary and skilled movement that requires cognitive input. Therefore, both the cortex and the spinal cord are involved. The cortex has special importance for motor neuron diseases, in which initiation and modulation of voluntary movement is affected. Amyotrophic lateral sclerosis (ALS) is defined by the progressive degeneration of both the upper and lower motor neurons, whereas hereditary spastic paraplegia (HSP) and primary lateral sclerosis (PLS) are characterized mainly by the loss of upper motor neurons. In an effort to reveal the cellular and molecular basis of neuronal degeneration, numerous model systems are generated, and mouse models are no exception. However, there are many different levels of complexities that need to be considered when developing mouse models. Here, we focus our attention to the upper motor neurons, which are one of the most challenging neuron populations to study. Since mice and human differ greatly at a species level, but the cells/neurons in mice and human share many common aspects of cell biology, we offer a solution by focusing our attention to the affected neurons to reveal the complexities of diseases at a cellular level and to improve translational efforts.

Mitochondrial Dysfunction in Parkinson's Disease-Cause or Consequence?

James Parkinson first described the motor symptoms of the disease that took his name over 200 years ago. While our knowledge of many of the changes that occur in this condition has increased, it is still unknown what causes this neurodegeneration and why it only affects some individuals with advancing age. Here we review current literature to discuss whether the mitochondrial dysfunction we have detected in Parkinson’s disease is a pathogenic cause of neuronal loss or whether it is itself a consequence of dysfunction in other pathways. We examine research data from cases of idiopathic Parkinson’s with that from model systems and individuals with familial forms of the disease. Furthermore, we include data from healthy aged individuals to highlight that many of the changes described are also present with advancing age, though not normally in the presence of severe neurodegeneration. While a definitive answer to this question may still be just out of reach, it is clear that mitochondrial dysfunction sits prominently at the centre of the disease pathway that leads to catastrophic neuronal loss in those affected by this disease.

ATP13A2 missense variant in Australian Cattle Dogs with late onset neuronal ceroid lipofuscinosis

The neuronal ceroid lipofuscinoses (NCLs) are lysosomal storage disorders characterized by progressive neurodegeneration and declines in neurological functions. Pathogenic sequence variants in at least 13 genes underlie different forms of NCL, almost all of which are recessively inherited. To date 13 sequence variants in 8 canine orthologs of human NCL genes have been found to occur in 11 dog breeds in which they result in progressive neurological disorders similar to human NCLs. Canine NCLs can serve as models for preclinical evaluation of therapeutic interventions for these disorders. In most NCLs, the onset of neurological signs occurs in childhood, but some forms have adult onsets. Among these is CLN12 disease, also known as Kufor-Rakeb syndrome, PARK9, and spastic paraplegia78. These disorders result from variants in ATP13A2 which encodes a putative transmembrane ion transporter important for lysosomal function. Three Australian Cattle Dogs (a female and two of her offspring) were identified with a progressive neurological disorder with an onset of clinical signs at approximately 6 years of age. The affected dogs exhibited clinical courses and histopathology characteristic of the NCLs. Whole genome sequence analysis of one of these dogs revealed a homozygous c.1118C > T variant in ATP13A2 that predicts a nonconservative p.(Thr373Ile) amino acid substitution. All 3 affected dogs were homozygous for this variant, which was heterozygous in 42 of 394 unaffected Australian Cattle Dogs, the remainder of which were homozygous for the c.1118C allele. The high frequency of the mutant allele in this breed suggests that further screening for this variant should identify additional homozygous dogs and indicates that it would be advisable to perform such screening prior to breeding Australian Cattle Dogs.

ATP13A2 facilitates HDAC6 recruitment to lysosome to promote autophagosome-lysosome fusion

Mutations in ATP13A2 cause Kufor-Rakeb syndrome, an autosomal recessive form of juvenile-onset atypical Parkinson's disease (PD). Recent work tied ATP13A2 to autophagy and other cellular features of neurodegeneration, but how ATP13A2 governs numerous cellular functions in PD pathogenesis is not understood. In this study, the ATP13A2-deficient mouse developed into aging-dependent phenotypes resembling those of autophagy impairment. ATP13A2 deficiency impaired autophagosome-lysosome fusion in cultured cells and in in vitro reconstitution assays. In ATP13A2-deficient cells or Drosophila melanogaster or mouse tissues, lysosomal localization and activity of HDAC6 were reduced, with increased acetylation of tubulin and cortactin. Wild-type HDAC6, but not a deacetylase-inactive mutant, restored autophagosome-lysosome fusion, antagonized cortactin hyperacetylation, and promoted lysosomal localization of cortactin in ATP13A2-deficient cells. Mechanistically, ATP13A2 facilitated recruitment of HDAC6 and cortactin to lysosomes. Cortactin overexpression in cultured cells reversed ATP13A2 deficiency-associated impairment of autophagosome-lysosome fusion. PD-causing ATP13A2 mutants failed to rescue autophagosome-lysosome fusion or to promote degradation of protein aggregates and damaged mitochondria. These results suggest that ATP13A2 recruits HDAC6 to lysosomes to deacetylate cortactin and promotes autophagosome-lysosome fusion and autophagy. This study identifies ATP13A2 as an essential molecular component for normal autophagy flux in vivo and implies potential treatments targeting HDAC6-mediated autophagy for PD.

Partial loss of ATP13A2 causes selective gliosis independent of robust lipofuscinosis

Loss-of-function mutations in ATP13A2 are associated with three neurodegenerative diseases: a rare form of Parkinson's disease termed Kufor-Rakeb syndrome (KRS), a lysosomal storage disorder termed neuronal ceroid lipofuscinosis (NCL), and a form of hereditary spastic paraplegia (HSP). Furthermore, recent data suggests that heterozygous carriers of mutations in ATP13A2 may confer risk for the development of Parkinson's disease, similar to the association of mutations in glucocerebrosidase (GBA) with both Parkinson's disease and Gaucher's disease, a lysosomal storage disorder. Mutations in ATP13A2 are generally thought to be loss of function; however, the lack of human autopsy tissue has prevented the field from determining the pathological consequences of losing functional ATP13A2. We and others have previously neuropathologically characterized mice completely lacking murine Atp13a2, demonstrating the presence of lipofuscinosis within the brain - a key feature of NCL, one of the diseases to which ATP13A2 mutations have been linked. To determine if loss of one functional Atp13a2 allele can serve as a risk factor for disease, we have now assessed heterozygous Atp13a2 knockout mice for key features of NCL. In this report, we demonstrate that loss of one functional Atp13a2 allele leads to both microgliosis and astrocytosis in multiple brain regions compared to age-matched controls; however, levels of lipofuscin were only modestly elevated in the cortex of heterozygous Atp13a2 knockout mice over controls. This data suggests the possibility that partial loss of ATP13A2 causes inflammatory changes within the brain which appear to be independent of robust lipofuscinosis. This study suggests that heterozygous loss-of-function mutations in ATP13A2 are likely harmful and indicates that glial involvement in the disease process may be an early event that positions the CNS for subsequent disease development.

Iron in neurodegenerative disorders: being in the wrong place at the wrong time?

Brain iron deposits have been reported consistently in imaging and histologic examinations of patients with neurodegenerative disorders. While the origins of this finding have not been clarified yet, it is speculated that impaired iron homeostasis or deficient transport mechanisms result in the accumulation of this highly toxic metal ultimately leading to formation of reactive oxygen species and cell death. On the other hand, there are also those who support that iron is just an incidental finding, a by product of neuronal loss. A literature review has been performed in order to present the key findings in support of the iron hypothesis of neurodegeneration, as well as to identify conditions causing or resulting from iron overload and compare and contrast their features with the most prominent neurodegenerative disorders. There is an abundance of experimental and observational findings in support of the hypothesis in question; however, as neurodegeneration is a rare incident of commonly encountered iron-associated disorders of the nervous system, and this metal is found in non-neurodegenerative disorders as well, it is possible that iron is the result or even an incidental finding in neurodegeneration. Understanding the underlying processes of iron metabolism in the brain and particularly its release during cell damage is expected to provide a deeper understanding of the origins of neurodegeneration in the years to come.

Loss of autophagy in dopaminergic neurons causes Lewy pathology and motor dysfunction in aged mice

Inactivation of constitutive autophagy results in the formation of cytoplasmic inclusions in neurons, but the relationship between impaired autophagy and Lewy bodies (LBs) as well as the in vivo process of formation remains unknown. Synuclein, a component of LBs, is the defining characteristic of Parkinson’s disease (PD). Here, we characterize dopamine (DA) neuron–specific autophagy-deficient mice and provide in vivo evidence for LB formation. Synuclein deposition is preceded by p62 and resulted in the formation of inclusions containing synuclein and p62. The number and size of these inclusions were gradually increased in neurites rather than soma with aging. These inclusions may facilitate peripheral failures. As a result, DA neuron loss and motor dysfunction including the hindlimb defect were observed in 120-week-old mice. P62 aggregates derived from an autophagic defect might serve as “seeds” and can potentially be cause of LB formation.

Lysosomal defects in ATP13A2 and GBA associated familial Parkinson's disease

Genes encoding lysosomal proteins, such as ATP13A2 and GBA, are associated with familial Parkinson's disease (PD). Heterozygous mutations in GBA are strongly associated with familial PD. ATP13A2, which encodes a lysosomal P-type ATPase, has been identified as the causative gene for Kufor-Rakeb syndrome. While lysosomal dysfunction due to these mutations exhibited early onset Parkinsonism, each animal model demonstrated different pathological mechanisms. Clinicogenetic and animal model studies recently identified several lysosomal alterations that play a role in the pathogenesis of PD.

Linking mitochondrial dysfunction to neurodegeneration in lysosomal storage diseases

Lysosomal storage diseases (LSD) are inborn errors of metabolism resulting in multisystem disease. Central nervous system involvement, often with progressive neurodegeneration, accounts for a large portion of the morbidity and mortality seen in many LSD. Available treatments fail to prevent or correct neurologic symptoms and decline. Emerging evidence points to an important role for mitochondrial dysfunction in the pathogenesis and progression of LSD-associated neurodegeneration. Mitochondrial dysfunction in LSD is characterized by alterations in mitochondrial mass, morphology and function. Disturbed mitochondrial metabolism in the CNS may lead to excessive production of mitochondrial reactive oxygen species and dysregulated calcium homeostasis. These metabolic disturbances ultimately result in mitochondria-induced apoptosis and neuronal degeneration. Here, we review the current evidence for mitochondrial dysfunction in neuronal models of seven LSD, including GM1-gangliosidosis, mucopolysaccharidosis IIIC, multiple sulfatase deficiency, Krabbe disease, Gaucher disease, Niemann Pick disease type C and the neural ceroid lipofuscinoses and outline current experimental therapies aimed at restoring mitochondrial function and neuroprotection in LSD.

Parkinson's disease pathogenesis from the viewpoint of small fish models

Parkinson's disease is a neurodegenerative disorder that involves movement discloses, degeneration of dopaminergic neurons, and presence of cytoplasmic inclusion bodies. Various animal models have been developed and small fish including zebrafish and medaka fish have recently been employed as a new model for Parkinson disease. In this review, we summarize fish models of Parkinson's disease mainly using our own findings and explain two major hypotheses of PD: lysosome dysfunction theory and mitochondrial dysfunction theory. Finally, we discuss the potential for future application of small fish model.

Purkinje Cells Are More Vulnerable to the Specific Depletion of Cathepsin D Than to That of Atg7

Neurologic phenotypes of cathepsin D (CTSD)-deficient mice, a murine model of neuronal ceroid lipofuscinoses, indicate the importance of CTSD for the maintenance of metabolism in central nervous system neurons. To further understand the role of CTSD in central nervous system neurons, we generated mice with a CTSD deficiency specifically in the Purkinje cells (PCs) (CTSD^Flox/Flox;GRID2-Cre) and compared their phenotypes with those of PC-selective Atg7-deficient (Atg7^Flox/Flox;GRID2-Cre) mice. In both strains of mice, PCs underwent degeneration, but the CTSD-deficient PCs disappeared more rapidly than their Atg7-deficient counterparts. When CTSD-deficient PCs died, the neuronal cell bodies became shrunken, filled with autophagosomes and autolysosomes, and had nuclei with dispersed small chromatin fragments. The dying Atg7-deficient PCs also showed similar ultrastructures, indicating that the neuronal cell death of CTSD- and Atg7-deficient PCs was distinct from apoptosis. Immunohistochemical observations showed the formation of calbindin-positive axonal spheroids and the swelling of vesicular GABA transporter-positive presynaptic terminals that were more pronounced in Atg7-deficient PCs than in CTSD-deficient PCs. An accumulation of tubular vesicles may have derived from the smooth endoplasmic reticulum; nascent autophagosome-like structures with double membranes was a common feature in the swollen axons of these PCs. These results suggested that PCs were more vulnerable to CTSD deficiency in lysosomes than to autophagy impairment, and this vulnerability does not depend on the severity of axonal swelling.

Impulse control disorder, lysosomal malfunction and ATP13A2 insufficiency in Parkinsonism

Lysosomal transport of cargos in neurons is essential for neuronal proteostasis, transmission and functional motors and behaviours. Lysosomal malfunction including storage disorders is involved in the pathogenesis of Parkinson's disease (PD). Given the unclear molecular mechanisms of diverse defects in PD phenotypes, especially behavioural deficits, this mini review explores the cellular contexts of PD impulse control disorders and the molecular aspects of lysosomal cross-membrane transports. Focuses are paid to trace metal involvements in α-synuclein assembly in Lewy bodies, the functions and molecular interactions of ATP13A2 as ATPase transporters in lysosomal membranes for cross-membrane trafficking and lysosomal homeostasis, and our current understandings of the neural circuits in ICD. Erroneously polarized distributions of cargos such as metals and lipids on each side of lysosomal membranes triggered by gene mutations and deregulated expression of ATP13A2 may thus instigate sensing protein structural changes such as aggregations, organelle degeneration, and specific neuronal ageing and death in Parkinsonism.