The pathological changes occurring in Parkinson's and several other neurodegenerative diseases are complex and poorly understood, but all clearly involve protein aggregation. Also frequently appearing in neurodegeneration is mitochondrial dysfunction which may precede, coincide or follow protein aggregation. These observations led to the concept that protein aggregation and mitochondrial dysfunction either arise from the same etiological factors or are interactive. Understanding the mechanisms and regulation of processes that lead to protein aggregation or mitochondrial dysfunction may therefore contribute to the design of better therapeutics. Clearance of protein aggregates and dysfunctional organelles is dependent on macroautophagy which is the process through which aged or damaged proteins and organelles are first degraded by the lysosome and then recycled. The macroautophagy-lysosomal pathway is essential for maintaining protein and energy homeostasis. Not surprisingly, failure of the lysosomal system has been implicated in diseases that have features of protein aggregation and mitochondrial dysfunction. This review summarizes 3 major topics: 1) the current understanding of Parkinson's disease pathogenesis in terms of accumulation of damaged proteins and reduction of cellular bioenergetics; 2) evolving insights into lysosomal function and biogenesis and the accumulating evidence that lysosomal dysfunction may cause or exacerbate Parkinsonian pathology and finally 3) the possibility that enhancing lysosomal function may provide a disease modifying therapy.
... Lysosomes are spherical-shaped, catabolic organelles that ubiquitously exist in almost all eukaryotic cells and are mainly responsible for the degradation of biological macromolecules, forming the main part of cell digestive system. [154][155][156] The structure of the phospholipid bilayer of a lysosome wall is similar to one of plasma membrane. Lysosomes maintain a lower pH value (ca. ...
... 4.5) compared to that of the cytoplasm because of the proton-importing machinery of V-type ATPases. [155][156][157] Most targeting approaches for lysosomes rely on the difference of pH between the interior of these organelles and the cytosol inside the cell. The probe design typically includes an addition of a tertiary amine fragment ( Fig. 1.4.5). ...
... The ethyl acetate layers were then combined, dried over Na2SO4 and concentrated in vacuo. Yield 155 3-(dodecylammonio)propane-1-sulfonate (3b), procedure adapted from elsewhere. 311 4g of dodecylamine were mixed with 1.2 eq. of 1,3-propanesultone in 30 mL of dry acetone. ...
Specific targeting, imaging and probing of cell plasma membranes and intracellular organelles can be addressed by rationally designed polarity-sensitive fluorescent probes. Here, a new efficient plasma membrane-targeting moiety was developed and tested in five cyanine dyes, showing excellent performance in cellular and in vivo microscopy. Next, the targeting moiety was grafted to a solvatochromic dye Prodan, yielding a plasma membrane probe with high lipid order sensitivity. Modifying a Nile Red using the moieties with varied alkyl chain lengths resulted in two solvatochromic plasma membrane probes: NR12A with high affinity to membranes for conventional microscopy, and NR4A, a low-affinity probe for PAINT super-resolution microscopy. Tethering Nile Red with organelle-targeted groups yielded an array of probes, able to sense polarity and lipid order in organelle membranes. The synthesized probes will find applications in bioimaging, cell biology, biophysics or mechanobiology.
... The fact that neuronopathic MPS II patients usually develop CNS abnormalities from early childhood highlights the importance of lysosomal function in CNS development. In particular, it is widely documented that lysosomes play a crucial role in neuronal differentiation and maintenance [32][33][34]. In this context, an RNAseq analysis performed on an MPS II mouse brain revealed dysregulation of a great number of pathways, including those involving synapse maturation, calcium signalling and axon guidance [8]. ...
Most of the patients affected by neuronopathic forms of Mucopolysaccharidosis type II (MPS II), a rare lysosomal storage disorder caused by defects in iduronate-2-sulfatase (IDS) activity, exhibit early neurological defects associated with white matter lesions and progressive behavioural abnormalities. While neuronal degeneration has been largely described in experimental models and human patients, more subtle neuronal pathogenic defects remain still underexplored. In this work, we discovered that the axon guidance receptor Deleted in Colorectal Cancer (Dcc) is significantly dysregulated in the brain of ids mutant zebrafish since embryonic stages. In addition, thanks to the establishment of neuronal-enriched primary cell cultures, we identified defective proteasomal degradation as one of the main pathways underlying Dcc upregulation in ids mutant conditions. Furthermore, ids mutant fish-derived primary neurons displayed higher levels of polyubiquitinated proteins and P62, suggesting a wider defect in protein degradation. Finally, we show that ids mutant larvae display an atypical response to anxiety-inducing stimuli, hence mimicking one of the characteristic features of MPS II patients. Our study provides an additional relevant frame to MPS II pathogenesis, supporting the concept that multiple developmental defects concur with early childhood behavioural abnormalities.
... In addition, the UPS plays roles in protein homeostasis, including stability and localization [2]. Similarly, lysosome-induced autophagy maintains protein homeostasis [12,13]. A recent study demonstrated that the UPS and the autophagy interact with each other to mutually supplement their functions [14]. ...
Ubiquitin-like modifier-activating enzyme 6 (UBA6) is a member of the E1 enzyme family, which initiates the ubiquitin–proteasome system (UPS). The UPS plays critical roles not only in protein degradation but also in various cellular functions, including neuronal signaling, myocardial remodeling, immune cell differentiation, and cancer development. However, the specific role of UBA6 in cellular functions is not fully elucidated in comparison with the roles of the UPS. It has been known that the E1 enzyme is associated with the motility of cancer cells. In this study, we verified the physiological roles of UBA6 in lung cancer cells through gene-silencing siRNA targeting UBA6 (siUBA6). The siUBA6 treatment attenuated the migration of H1975 cells, along with a decrease in lysosomal Ca2+ release. While autophagosomal proteins remained unchanged, lysosomal proteins, including TRPML1 and TPC2, were decreased in siUBA6-transfected cells. Moreover, siUBA6 induced the production of multivesicular bodies (MVBs), accompanied by an increase in MVB markers in siUBA6-transfected H1975 cells. Additionally, the expression of the exosomal marker CD63 and extracellular vesicles was increased by siUBA6 treatment. Our findings suggest that knock-down of UBA6 induces lysosomal TRPML1 depletion and inhibits endosomal trafficking to lysosome, and subsequently, leads to the accumulation of MVBs and enhanced exosomal secretion in lung cancer cells.
... The fact that neuronopathic MPS II patients usually develop CNS abnormalities from early childhood highlights the importance of lysosomal function in CNS development. In particular, it is widely documented that lysosomes play a crucial role in neuronal differentiation and maintenance [32][33][34] . In this context, an RNA-seq analysis performed on MPS II mouse brain revealed dysregulation of a great number of pathways including those involving synapse maturation, calcium signaling and axon guidance 8 . ...
Most patients affected by neuronopathic forms of Mucopolysaccharidosis type II (MPS II), a rare lysosomal storage disorder, exhibit early neurological defects associated with white matter lesions and progressive behavioural abnormalities. While neuronal degeneration has been largely described in experimental models and human patients, more subtle neuronal pathogenic defects remains still underexplored. In this work we discovered that the axon guidance receptor Deleted in Colorectal Cancer (Dcc) is significantly dysregulated in the brain of ids mutant zebrafish since embryonic stages. In addition, thanks to the establishment of neuronal-enriched primary cell cultures from embryonic dissected brains, we identified defective proteasomal degradation as one of the main pathways underlying Dcc upregulation in ids mutant conditions. Furthermore, ids mutant fish-derived primary neurons displayed higher levels of polyubiquitinated proteins and P62, suggesting a wider defect in protein degradation. Finally, we show that ids larvae display atypical response to anxiety-like stimuli, hence mimicking one of the characteristic features of MPS II patients. Our study provides an additional relevant frame to MPS II pathogenesis, supporting the concept that multiple developmental defects concur to early childhood behavioural abnormalities.
... Lysosome, an origin for degradation functionality, is also engaged in the autophagic process, owing to its interaction with the kinase-enzyme-complex, mTORC1 (mammalian target of rapamycin complex-1). The function of mTORC1 is a direct reflection of nutrition levels both within and outside the cell mTORC1 suppresses au- e d i s t r i b u t e d o r u p l o a d e d t o a n y o n e o r a n y w h e tophagy by phosphorylating the autophagy-initiating kinase Ulk1(Ser 757), which results in potent inhibition of autophagosome formation [32,33]. mTORC1 activation is required for the initiation of growth-promotive activities. ...
Background
The link between autophagy and lysosomal function has been well-recognised in recent dec-ades; defective autophagy and lysosomal function lead to various disorders, notably Lysoso-mal Storage Disorders (LSDs). The malfunction of multiple mechanistic pathways influences the contribution of LSDs. Different ways are employed in such situations, but one novel ap-proach could resolve the problem by inducing the autophagic pathway, which aids in main-taining proper autophagy and lysosomal degradation function.
Method
Autophagic Inducer functions on the activation of Transcriptional factor EB (TFEB) and its mechanism; mTOR Complex Inhibition dependently or independently may repair the mal-function of the entire mechanism. Finding a potential autophagic inducer is still a work in progress, but targeting TFEB and mTOR could redefine LSD treatment. The development of experimentally available TFEB modulators could enhance autophagic flux promote lysosomal function and increase lysosomal biogenesis and can be a promising technique for treating ill-nesses caused by ALP dysfunction, such as lysosomal storage disorder.
Result
MTORC1 suppression causes TFEB to be transported to the nucleus and transcription of mul-tiple genes involved in the formation of autophagosomes and lysosomes, indicating that MTORC1 has positive effects in treating lysosomal storage diseases such as Pompe disease, Batton disease, Fabry disease, etc. thus modulating autophagy attenuates the above condi-tion.
Conclusion
This review comprises autophagy and lysosome association, and their malfunction leads to various lysosomal diseases. Several natural products are also discussed, which can be possible treatment options.
... Research aimed at preventing and treating atherosclerosis is focused on lysosomes and mammalian target of rapamycin signaling (8). Changes in lysosome-related genes (LRGs) in Parkinson's disease inhibit the degradation of misfolded proteins and damage lysosomal function (9,10). In tumor-related diseases, the activity of lysosomes is related to the phenotype of malignant cells. ...
Background:
Lung adenocarcinoma (LUAD) is the most common subtype of lung cancer, representing 40% of all cases of this tumor. Despite immense improvements in understanding the molecular basis, diagnosis, and treatment of LUAD, its recurrence rate is still high.
Methods:
RNA-seq data from The Cancer Genome Atlas (TCGA) LUAD cohort were download from Genomic Data Commons Portal. The GSE13213 dataset from Gene Expression Omnibus (GEO) was used for external validation. Differential prognostic lysosome-related genes (LRGs) were identified by overlapping survival-related genes obtained via univariate Cox regression analysis with differentially expressed genes (DEGs). The prognostic model was built using Kaplan-Meier curves and least absolute shrinkage and selection operator (LASSO) analyses. In addition, univariate and multivariate Cox analyses were employed to identify independent prognostic factors. The responses of patients to immune checkpoint inhibitors (ICIs) were further predicted. The pRRophetic package and rank-sum test were used to compute the half maximal inhibitory concentrations (IC50) of 56 chemotherapeutic drugs and their differential effects in the low- and high-risk groups. Moreover, quantitative real-time polymerase chain reaction, Western blot, and human protein atlas (HPA) database were used to verify the expression of the four prognostic biomarkers in LUAD.
Results:
Of the nine candidate differential prognostic LRGs, GATA2, TFAP2A, LMBRD1, and KRT8 were selected as prognostic biomarkers. The prediction of the risk model was validated to be reliable. Cox independent prognostic analysis revealed that risk score and stage were independent prognostic factors in LUAD. Furthermore, the nomogram and calibration curves of the independent prognostic factors performed well. Differential analysis of ICIs revealed CD276, ICOS, PDCD1LG2, CD27, TNFRSF18, TNFSF9, ENTPD1, and NT5E to be expressed differently in the low- and high-risk groups. The IC50 values of 12 chemotherapeutic drugs, including epothilone.B, JNK.inhibitor.VIII, and AKT.inhibitor.VIII, significantly differed between the two risk groups. KRT8 and TFAP2A were highly expressed, while GATA2 and LMBRD1 were poorly expressed in LUAD cell lines. In addition, KRT8 and TFAP2A were highly expressed, while GATA2 and LMBRD1 were poorly expressed in tumor tissues.
Conclusions:
Four key prognostic biomarkers-GATA2, TFAP2A, LMBRD1, and KRT8-were used to construct a significant prognostic model for LUAD patients.
... Insufficient activity of the autophagyelysosome system may be involved in the formation of the amyloid plaques and tau aggregates which occur in Alzheimer's disease (AD) 3,4 . Cathepsin D (CTSD) is the principal lysosomal aspartate protease, and is activated in the acidic lysosomal environment 5 . In support of a unique role for CTSD, its deficiency causes human congenital neuronal ceroid lipofuscinosis (NCL). ...
The lysosome is responsible for protein and organelle degradation and homeostasis and the cathepsins play a key role in maintaining protein quality control. Cathepsin D (CTSD), is one such lysosomal protease, which when deficient in humans lead to neurolipofuscinosis (NCL) and is important in removing toxic protein aggregates. Prior studies demonstrated that CTSD germ-line knockout-CtsdKO (CDKO) resulted in accumulation of protein aggregates, decreased proteasomal activities, and postnatal lethality on Day 26 ± 1. Overexpression of wildtype CTSD, but not cathepsin B, L or mutant CTSD, decreased α-synuclein toxicity in worms and mammalian cells. In this study we generated a mouse line expressing human CTSD with a floxed STOP cassette between the ubiquitous CAG promoter and the cDNA. After crossing with Nestin-cre, the STOP cassette is deleted in NESTIN + cells to allow CTSD overexpression-CTSDtg (CDtg). The CDtg mice exhibited normal behavior and similar sensitivity to sub-chronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induced neurodegeneration. By breeding CDtg mice with CDKO mice, we found that over-expression of CTSD extended the lifespan of the CDKO mice, partially rescued proteasomal deficits and the accumulation of Aβ42 in the CDKO. This new transgenic mouse provides supports for the key role of CTSD in protecting against proteotoxicity and offers a new model to study the role of CTSD enhancement in vivo.
... They demonstrated that this particular probe (41, Scheme 5) showed good selectivity to the ER-localized Fe 3+ in HepG2 cells. A summary of the properties of the ER-targeted molecular probes is given in Table 3. Lysosomes are spherical catabolic organelles that contain more than 50 kinds of hydrolases, such as protease, phosphatase, lipase, and nuclease, which are used to metabolize and decompose a variety of endogenous and exogenous macromolecular substances, such as sugar, lipids, glycolipids, glycosaminoglycans, nucleic acids, and proteins [135]. As one of the most important digestive organelles in a cell, lysosomes have been proven to be involved in controlling the recycling and signal transduction processes of cell growth, division, differentiation, and cell death; they are vital elements in maintaining metabolic homeostasis, intracellular signal transduction, and plasma membrane repair as well as secretion [136]. ...
Fluorescent molecular probes are very powerful tools that have been generally applied in cell imaging in the research fields of biology, pathology, pharmacology, biochemistry, and medical science. In the last couple of decades, numerous molecular probes endowed with high specificity to particular organelles have been designed to illustrate intracellular images in more detail at the subcellular level. Nowadays, the development of cell biology has enabled the investigation process to go deeply into cells, even at the molecular level. Therefore, probes that can sketch a particular organelle’s location while responding to certain parameters to evaluate intracellular bioprocesses are under urgent demand. It is significant to understand the basic ideas of organelle properties, as well as the vital substances related to each unique organelle, for the design of probes with high specificity and efficiency. In this review, we summarize representative multifunctional fluorescent molecular probes developed in the last decade. We focus on probes that can specially target nuclei, mitochondria, endoplasmic reticulums, and lysosomes. In each section, we first briefly introduce the significance and properties of different organelles. We then discuss how probes are designed to make them highly organelle-specific. Finally, we also consider how probes are constructed to endow them with additional functions to recognize particular physical/chemical signals of targeted organelles. Moreover, a perspective on the challenges in future applications of highly specific molecular probes in cell imaging is also proposed. We hope that this review can provide researchers with additional conceptual information about developing probes for cell imaging, assisting scientists interested in molecular biology, cell biology, and biochemistry to accelerate their scientific studies.
As an organelle in cells, lysosomes play an important role in the degradation of biological macromolecules and pathogens. To elucidate the function of lysosomes in normal or disease states, recently, various fluorescent probes have been reported for imaging lysosomal analytes. However, because of the particularity of the lysosomal environment, most of the reported lysosomal fluorescent probes suffered from a series of practical issues such as easy diffusion, low detection signal-to-background ratio and false signal. To address these issues, based on an optimized in situ ordered assembly solid-state fluorophore HDPQ, we herein put forward a new strategy for the design of lysosomal enzymes probes. As a proof concept, we synthesized a fluorescent probe HDPQ-GLU for lysosomal enzyme β-glucuronidase (GLU). Experiment results displayed that compared with general lysosomal probe, the novel lysosomal probe not only exhibited excellent anti-pH interference ability and high signal-to-noise ratio in aqueous solution, but also has excellent long-term in situ imaging ability in the living system. Using this probe, we have realized high-fidelity and long-term in situ tracking GLU in lysosomes of living cells and evaluated the dynamic changes of GLU during the growth period of zebrafish. We anticipate that the new strategy based on the novel in situ ordered assembly solid-state fluorophore HDPQ may be a potential platform for developing fluorescent probes for high-fidelity imaging of lysosomal enzymes.
Flavinases, including monoamine oxidase (MAO‐A/MAO‐B), quinone oxidoreductase (NQO1), thioredoxin reductase (TrxR), nitroreductase (NTR) and so on, are important redox enzymes in organisms. They are considered as biomarkers of cell energy metabolism and cell vitality. Importantly, their aberrant expression is related to various disease processes. Therefore, the accurate measurement of flavinase is useful for the early diagnosis of diseases, which has aroused great concern in the scientific community. Various methods are also available for the detection of flavinases, fluorescence probes are considered to be one of the best detection methods due to their easy and accurate sensing capability. This review aims to introduce the advances in the design and application of flavinase probes in the last five years. This study focuses on analyzing the design strategies and reaction mechanisms of flavinases fluorescent probes and discusses the current challenges, which will further advance the development of diagnostic and therapeutic approaches for flavinase‐related diseases.
Action myoclonus-renal failure syndrome (AMRF) is an autosomal-recessive disorder with the remarkable combination of focal glomer-ulosclerosis, frequently with glomerular collapse, and progressive myoclonus epilepsy associated with storage material in the brain. Here, we employed a novel combination of molecular strategies to find the responsible gene and show its effects in an animal model. Utilizing only three unrelated affected individuals and their relatives, we used homozygosity mapping with single-nucleotide polymorphism chips to localize AMRF. We then used microarray-expression analysis to prioritize candidates prior to sequencing. The disorder was mapped to 4q13-21, and microarray-expression analysis identified SCARB2/Limp2, which encodes a lysosomal-membrane protein, as the likely candidate. Mutations in SCARB2/Limp2 were found in all three families used for mapping and subsequently confirmed in two other unrelated AMRF families. The mutations were associated with lack of SCARB2 protein. Reanalysis of an existing Limp2 knockout mouse showed intracellular inclusions in cerebral and cerebellar cortex, and the kidneys showed subtle glomerular changes. This study highlights that recessive genes can be identified with a very small number of subjects. The ancestral lysosomal-membrane protein SCARB2/LIMP-2 is responsible for AMRF. The heterogeneous pathology in the kidney and brain suggests that SCARB2/Limp2 has pleiotropic effects that may be relevant to understanding the pathogenesis of other forms of glomerulosclerosis or collapse and myoclonic epilepsies.
In eukaryotic cells, lysosomes represent a major site for macromolecule degradation. Hydrolysis products are eventually exported
from this acidic organelle into the cytosol through specific transporters. Impairment of this process at either the hydrolysis
or the efflux step is responsible of several lysosomal storage diseases. However, most lysosomal transporters, although biochemically
characterized, remain unknown at the molecular level. In this study, we report the molecular and functional characterization
of a lysosomal amino acid transporter (LYAAT-1), remotely related to a family of H+-coupled plasma membrane and synaptic vesicle amino acid transporters. LYAAT-1 is expressed in most rat tissues, with highest
levels in the brain where it is present in neurons. Upon overexpression in COS-7 cells, the recombinant protein mediates the
accumulation of neutral amino acids, such as γ-aminobutyric acid, l-alanine, and l-proline, through an H+/amino acid symport. Confocal microscopy on brain sections revealed that this transporter colocalizes with cathepsin D, an
established lysosomal marker. LYAAT-1 thus appears as a lysosomal transporter that actively exports neutral amino acids from
lysosomes by chemiosmotic coupling to the H+-ATPase of these organelles. Homology searching in eukaryotic genomes suggests that LYAAT-1 defines a subgroup of lysosomal
transporters in the amino acid/auxin permease family.
Mice deficient for the major lysosomal aspartic proteinase cathepsin D, generated by gene targeting, develop normally during the first 2 weeks, stop thriving in the third week and die in a state of anorexia at day 26 +/− 1. An atrophy of the ileal mucosa first observed in the third week progresses towards widespread intestinal necroses accompanied by thromboemboli. Thymus and spleen undergo massive destruction with fulminant loss of T and B cells. Lysosomal bulk proteolysis is maintained. These results suggest, that vital functions of cathepsin D are exerted by limited proteolysis of proteins regulating cell growth and/or tissue homeostasis, while its contribution to bulk proteolysis in lysosomes appears to be non‐critical.
Most soluble lysosomal proteins bind the mannose 6-phosphate receptor (M6P-R) to be sorted to the lysosomes. However, the lysosomes of I-cell disease (ICD) patients, a condition resulting from a mutation in the phosphotransferase that adds mannose 6-phosphate to hydrolases, have near normal levels of several lysosomal proteins, including the sphingolipid activator proteins (SAPs), G(M2)AP and prosaposin. We tested the hypothesis that SAPs are targeted to the lysosomal compartment via the sortilin receptor. To test this hypothesis, a dominant-negative construct of sortilin and a sortilin small interfering RNA (siRNA) were introduced into COS-7 cells. Our results showed that both the truncated sortilin and the sortilin siRNA block the traffic of G(M2)AP and prosaposin to the lysosomal compartment. This observation was confirmed by a co-immunoprecipitation, which demonstrated that G(M2)AP and prosaposin are interactive partners of sortilin. Furthermore, a dominant-negative mutant GGA prevented the trafficking of prosaposin and G(M2)AP to lysosomes. In conclusion, our results show that the trafficking of SAPs is dependent on sortilin, demonstrating a novel lysosomal trafficking.
Insulin-like growth factor-I (IGF-I), transforming growth factor (TGF) and epidermal growth factor (EGF) induced cathepsin D gene expression and reporter gene activity in MCF-7 human breast cancer cells transiently transfected with a construct (pCD1) containing a 2576 to 124 cathepsin D gene promoter insert. In contrast, IGF-I, but not TGF or EGF, induced reporter gene activity in cells cotransfected with wild-type estrogen receptor (ER) expression plasmid and a construct (pCD2) containing estrogen-responsive downstream elements from 208 to 101. Promoter deletion and mutational analysis experiments identified four GC-rich sites and an imperfect palindromic estrogen responsive element required for IGF-I acti
Classic Parkinson's disease (PD) is characterized by fibrillar alpha-synuclein inclusions known as Lewy bodies in the substantia nigra, which are associated with nigrostriatal degeneration. However, alpha-synuclein pathologies accumulate throughout the CNS in areas that also undergo progressive neurodegeneration, leading to dementia and other behavioral impairments in addition to parkinsonism. Although mutations in the alpha-synuclein gene only cause Lewy body PD in rare families, and although there are multiple other, albeit rare, genetic causes of familial parkinsonism, sporadic Lewy body PD is the most common movement disorder, and insights into mechanisms underlying alpha-synuclein-mediated neurodegeneration provide novel targets for the discovery of disease-modifying therapies for PD and related neurodegenerative alpha-synucleinopathies.
α-Synucleinopathies are neurodegenerative disorders that range pathologically from the demise of select groups of nuclei to pervasive degeneration throughout the neuraxis. Although mounting evidence suggests that α-synuclein lesions lead to neurodegeneration, this remains controversial. To explore this issue, we generated transgenic mice expressing wild-type and A53T human α-synuclein in CNS neurons. Mice expressing mutant, but not wild-type, α-synuclein developed a severe and complex motor impairment leading to paralysis and death. These animals developed age-dependent intracytoplasmic neuronal α-synuclein inclusions paralleling disease onset, and the α-synuclein inclusions recapitulated features of human counterparts. Moreover, immunoelectron microscopy revealed that the α-synuclein inclusions contained 10–16 nm wide fibrils similar to human pathological inclusions. These mice demonstrate that A53T α-synuclein leads to the formation of toxic filamentous α-synuclein neuronal inclusions that cause neurodegeneration.
Mutations in α-synuclein cause a form of familial Parkinson’s disease (PD), and wild-type α-synuclein is a major component of the intraneuronal inclusions called Lewy bodies, a pathological hallmark of PD. These observations suggest a pathogenic role for α-synuclein in PD. Thus far, however, little is known about the importance of α-synuclein in the nigral dopaminergic pathway in either normal or pathological situations. Herein, we studied this question by assessing the expression of synuclein-1, the rodent homologue of human α-synuclein, in both normal and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-intoxicated mice. In normal mice, detectable levels of synuclein mRNA and protein were seen in all brain regions studied and especially in ventral midbrain. In the latter, there was a dense synuclein-positive nerve fiber network, which predominated over the substantia nigra, and only few scattered synuclein-positive neurons. After a regimen of MPTP that kills dopaminergic neurons by apoptosis, synuclein mRNA and protein levels were increased significantly in midbrain extracts; the time course of these changes paralleled that of MPTP-induced dopaminergic neurodegeneration. In these MPTP-injected mice, there was also a dramatic increase in the number of synuclein-immunoreactive neurons exclusively in the substantia nigra pars compacta; all synuclein-positive neurons were tyrosine hydroxylase-positive, but none coexpressed apoptotic features. These data indicate that synuclein is highly expressed in the nigrostriatal pathway of normal mice and that it is up-regulated following MPTP-induced injury. In light of the synuclein alterations, it can be suggested that, by targeting this protein, one may modulate MPTP neurotoxicity and, consequently, open new therapeutic avenues for PD.
