Parkinson’s disease (PD) is one of the most common neurodegenerative disorders, affecting 1–1.5% of the total population. While progress has been made in understanding the neurodegenerative ...mechanisms that lead to cell death in late stages of PD, mechanisms for early, causal pathogenic events are still elusive. Recent developments in PD genetics increasingly point at endolysosomal (E‐L) system dysfunction as the early pathomechanism and key pathway affected in PD. Clathrin‐mediated synaptic endocytosis, an integral part of the neuronal E‐L system, is probably the main early target as evident in auxilin, RME‐8, and synaptojanin‐1 mutations that cause PD. Autophagy, another important pathway in the E‐L system, is crucial in maintaining proteostasis and a healthy mitochondrial pool, especially in neurons considering their inability to divide and requirement to function an entire life‐time. PINK1 and Parkin mutations severely perturb autophagy of dysfunctional mitochondria (mitophagy), both in the cell body and synaptic terminals of dopaminergic neurons, leading to PD. Endolysosomal sorting and trafficking is also crucial, which is complex in multi‐compartmentalized neurons. VPS35 and VPS13C mutations noted in PD target these mechanisms. Mutations in GBA comprise the most common risk factor for PD and initiate pathology by compromising lysosomal function. This is also the case for ATP13A2 mutations. Interestingly, α‐synuclein and LRRK2, key proteins involved in PD, function in different steps of the E‐L pathway and target their components to induce disease pathogenesis. In this review, we discuss these E‐L system genes that are linked to PD and how their dysfunction results in PD pathogenesis.
This article is part of the Special Issue “Synuclein”.
The endolysosomal (E‐L) system is increasingly recognized as the key pathway affected in Parkinson’s disease (PD). Clathrin‐mediated synaptic endocytosis, an integral part of the neuronal E‐L system, is probably the main early target. Autophagy, another important E‐L pathway that aids in maintaining proteostasis and a healthy mitochondrial pool is affected. Other crucial pathways such as E‐L sorting and trafficking, along with lysosomal degradation are also hampered. Key PD proteins such as α‐synuclein and LRRK2 target the E‐L components to induce pathology. Here, we comprehensively discuss these mechanisms to better understand the role of E‐L system dysfunction in PD pathogenesis.
This article is part of the Special Issue “Synuclein”.
Abstract Age being a risk factor for Parkinson's disease, assessment of age-related changes in the human substantia nigra may elucidate its pathogenesis. Increase in Marinesco bodies, α-synuclein, ...free radicals and so forth in the aging nigral neurons are clear indicators of neurodegeneration. Here, we report the glial responses in aging human nigra. The glial numbers were determined on Nissl-stained sections. The expression of glial fibrillary acidic protein, S100β, 2′, 3′-cyclic nucleotide 3′ phosphodiesterase, and Iba1 was assessed on cryosections of autopsied midbrains by immunohistochemistry and densitometry. The glial counts showed a biphasic increase, of which, the first prominent phase from fetal age to birth could be physiological gliogenesis whereas the second one after middle age may reflect mild age-related gliosis. Astrocytic morphology was altered, but glial fibrillary acidic protein expression increased only mildly. Presence of type-4 microglia suggests possibility of neuroinflammation. Mild reduction in 2′, 3′-cyclic nucleotide 3′ phosphodiesterase–labeled area denotes subtle demyelination. Stable age-related S100β expression indicates absence of calcium overload. Against the expected prominent gliosis, subtle age-related morphological alterations in human nigral glia attribute them a participatory role in aging.
Parkinson disease (PD) is a life-threatening neurodegenerative movement disorder with unmet therapeutic intervention. We have identified a small molecule autophagy modulator, 6-Bio that shows ...clearance of toxic SNCA/α-synuclein (a protein implicated in synucleopathies) aggregates in yeast and mammalian cell lines. 6-Bio induces autophagy and dramatically enhances autolysosome formation resulting in SNCA degradation. Importantly, neuroprotective function of 6-Bio as envisaged by immunohistology and behavior analyses in a preclinical model of PD where it induces autophagy in dopaminergic (DAergic) neurons of mice midbrain to clear toxic protein aggregates suggesting that it could be a potential therapeutic candidate for protein conformational disorders.
Auxilin participates in the uncoating of clathrin-coated vesicles (CCVs), thereby facilitating synaptic vesicle (SV) regeneration at presynaptic sites. Auxilin (DNAJC6/PARK19) loss-of-function ...mutations cause early-onset Parkinson’s disease (PD). Here, we utilized auxilin knockout (KO) mice to elucidate the mechanisms through which auxilin deficiency and clathrin-uncoating deficits lead to PD. Auxilin KO mice display cardinal features of PD, including progressive motor deficits, α-synuclein pathology, nigral dopaminergic loss, and neuroinflammation. Significantly, treatment with L-DOPA ameliorated motor deficits. Unbiased proteomic and neurochemical analyses of auxilin KO brains indicated dopamine dyshomeostasis. We validated these findings by demonstrating slower dopamine reuptake kinetics in vivo, an effect associated with dopamine transporter misrouting into axonal membrane deformities in the dorsal striatum. Defective SV protein sorting and elevated synaptic autophagy also contribute to ineffective dopamine sequestration and compartmentalization, ultimately leading to neurodegeneration. This study provides insights into how presynaptic endocytosis deficits lead to dopaminergic vulnerability and pathogenesis of PD.
Display omitted
•Auxilin KO mice recapitulate key features of Parkinson’s disease and respond to L-DOPA•SV sorting defects lead to cytoplasmic dopamine accumulation in dorsal striatum•DAT is trapped in the axonal deformities, leading to dopamine reuptake deficits•Increased dopaminergic synaptic autophagy may also contribute to disease pathology
Auxilin participates in clathrin uncoating to facilitate presynaptic endocytosis. Loss-of-function mutations of auxilin (PARK19) cause Parkinson’s disease. Using auxilin KO mice, Vidyadhara et al. show that synaptic vesicle sorting deficits, cytoplasmic dopamine accumulation, dopamine transporter mistrafficking, and synaptic autophagic overload may lead to pathogenesis of Parkinson’s disease in PARK19 patients.
•F1 crossbreds of C57BL/6J and CD-1 mice revealed augmented basal striatal LFPs.•MPTP induced pathological increase in C57BL/6J striatal LFPs; compensatory in CD-1.•Nigral calbindin was enhanced in ...crossbreds to maintain striatal LFPs despite MPTP.•Motor behaviour was unaffected in CD-1 and the crossbreds upon MPTP unlike C57BL/6J.•Similar nigrostriatal correlates are envisaged for heterogeneity in PD pathogenesis.
Asian-Indians are less vulnerable to Parkinson’s disease (PD) than the Caucasians. Their admixed populace has even lesser risk. Studying this phenomenon using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-susceptible C57BL/6J, MPTP-resistant CD-1 and their resistant crossbred mice revealed differences in the nigrostriatal cyto-molecular features. Here, we investigated the electrophysiological and behavioural correlates for differential MPTP-susceptibility and their outcome upon admixing. We recorded local field potentials (LFPs) from dorsal striatum and assessed motor co-ordination using rotarod and grip strength measures. Nigral calbindin-D28K expression, a regulator of striatal activity through nigrostriatal projections was evaluated using immunohistochemistry.
The crossbreds had significantly higher baseline striatal LFPs. MPTP significantly increased the neuronal activity in delta (0.5–4 Hz) and low beta (12–16 Hz) ranges in C57BL/6J; significant increase across frequency bands till high beta (0.5–30 Hz) in CD-1, and caused no alterations in crossbreds. MPTP further depleted the already low nigral calbindin-D28K expression in C57BL/6J. While in crossbreds, it was further up-regulated. MPTP affected the rotarod and grip strength performance of the C57BL/6J, while the injected CD-1 and crossbreds performed well. The increased striatal β-oscillations are comparable to that in PD patients. Higher power in CD-1 may be compensatory in nature, which were also reported in pre-symptomatic monkeys. Concurrent up-regulation of nigral calbindin-D28K may assist maintenance of striatal activity by buffering calcium overload in nigra. Thus, preserved motor behaviour in PD reminiscent conditions in CD-1 and crossbreds complement compensated/unaffected striatal LFPs. Similar electrophysiological correlates and cytomorphological features are envisaged in human phenomenon of differential PD prevalence, which are modulated upon admixing.
Parkinson disease (PD) prevalence varies by ethnicity. In an earlier study, we replicated the reduced vulnerability to PD in an admixed population, using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine ...(MPTP)-susceptible C57BL/6 J, MPTP-resistant CD-1 and their F1 crossbreds. In the present study, we investigated if the differences have a developmental origin. Substantia nigra was evaluated at postnatal days 2 (P2), P6, P10, P14, P18, and P22. C57BL/6 J mice had smaller nigra and fewer dopaminergic neurons than the CD-1 and crossbreds at P2, which persisted through development. A significant increase in numbers and nigral volume was observed across strains until P14. A drastic decline thereafter was specific to C57BL/6 J. CD-1 and crossbreds retained their numbers from P14 to stabilize with supernumerary neurons at adulthood. The neuronal size increased gradually to attain adult morphology at P10 in the resistant strains, vis-à-vis at P22 in C57BL/6 J. Accordingly, in comparison to C57BL/6 J, the nigra of CD-1 and reciprocal crossbreds possessed cytomorphological features of resilience, since birth. The considerably lesser dopaminergic neuronal loss in the CD-1 and crossbreds was seen at P2 and P14 and thereafter was complemented by attenuated developmental cell death. The differences in programmed cell death were confirmed by reduced TUNEL labelling, AIF, and caspase-3 expression. GDNF expression aligned with the cell death pattern at P2 and P14 in both nigra and striatum. Earlier maturity of nigra and its neurons appears to be better features that reflect as MPTP resistance at adulthood. Thus, variable MPTP vulnerability in mice and also differential susceptibility to PD in humans may arise early during nigral development.
•Hippocampal ET-1 infusion induced histochemical and behavioural deficits in rats.•P. lanceolata attenuated ET-1 ischemic injury induced cell loss in the hippocampus.•Plant extract treatment ...recovered ischemia induced loss of dendritic architecture.•These neuroprotective functions were exerted through plant’s antioxidant properties.•P. lanceolata is a potential source of novel treatment methods for ischemic stroke.
Ischemic brain injury is one of the leading causes of death and disability, where lack of disease modifying treatment strategies make us rely on symptomatic relief. Treatment principles from traditional systems of medicine may fill this gap and its validation in modern medicine perspective is important to bring them to mainstream. Here, we evaluated the neuroprotective efficacy of Ayurvedic medicinal herb Pluchea lanceolata in treating ischemic hippocampal injury. Focal hippocampal ischemia was modeled in Wistar rats through stereotaxic intrahippocampal injection of endothelin-1 (ET-1). Post-surgery, hydroalcoholic extract of the rhizome of Pluchea lanceolata (HAPL) was administered orally, once in a day for 14 consecutive days to ischemic rats. There were two treatment groups based on the HAPL dosage; HAPL200 (200 mg/kg body weight) and HAPL400 (400 mg/kg body weight). Comparisons were made with the ET-1 ischemic rats which received only the vehicle, and the normal surgical control. Ischemic hippocampal injury led to severe cognitive deficits as evaluated by Morris water maze and open field test, along with locomotory dysfunction noted in actophotometer test. HAPL treatment significantly attenuated these behavioural deficits in a dose dependent manner. Loss of pyramidal cells and degenerative phenotype of shrunken hyperdensed soma with pyknotic nuclei in CA1 and CA3 hippocampal neurons in ischemia were reversed after HAPL treatment. We provide first evidence for loss of dendritic architecture in ET-1 induced focal ischemic hippocampal injury using Golgi impregnation, where HAPL could salvage the dendritic branching and intersections. Intriguingly, it enhanced the dentritic arborization beyond what is noted in normal rats. Ability of HAPL to reverse oxidative stress, especially through maintaining glutathione peroxidase levels and lipid peroxidation in ischemic condition evidences that it may exert neuroprotection through its antioxidant properties. Thus, Pluchea lanceolata and its constituents provide potential alternative/adjuvant treatment strategy for ischemic hippocampal stroke.
Identification of genetic mutations in Parkinson’s disease (PD) promulgates the genetic nature of disease susceptibility. Resilience-associated genes being unknown till date, the normal genetic ...makeup of an individual may be determinative too. Our earlier studies comparing the substantia nigra (SN) and striatum of C57BL/6J, CD-1 mice, and their F1-crossbreds demonstrated the neuroprotective role of admixing against the neurotoxin MPTP. Furthermore, the differences in levels of mitochondrial fission/fusion proteins in the SN of parent strains imply effects on mitochondrial biogenesis. Our present investigations suggest that the baseline levels of apoptotic factors Bcl-2, Bax, and AIF differ across the three strains and are differentially altered in SN following MPTP administration. The reduction in complex-I levels exclusively in MPTP-injected C57BL/6J reiterates mitochondrial involvement in PD pathogenesis. The MPTP-induced increase in complex-IV, in the nigra of both parent strains, may be compensatory in nature. The ultrastructural evaluation showed fairly preserved mitochondria in the dopaminergic neurons of CD-1 and F1-crossbreds. However, in CD-1, the endoplasmic reticulum demonstrated distinct luminal enlargement, bordering onto ballooning, suggesting proteinopathy as a possible initial trigger.
The increase in α-synuclein in the pars reticulata of crossbreds suggests a supportive role for this output nucleus in compensating for the lost function of pars compacta. Alternatively, since α-synuclein over-expression occurs in different brain regions in PD, the α-synuclein increase here may suggest a similar pathogenic outcome. Further understanding is required to resolve this biological contraption. Nevertheless, admixing reduces the risk to MPTP by favoring anti-apoptotic consequences. Similar neuroprotection may be envisaged in the admixed populace of Anglo-Indians.
Synaptic terminals are the primary sites of neuronal communication. Synaptic dysfunction is a hallmark of many neuropsychiatric and neurological disorders. The characterization of synaptic ...sub-compartments by biochemical isolation is, therefore, a powerful method to elucidate the molecular bases of synaptic processes, both in health and disease. This protocol describes the isolation of synaptic terminals and synaptic sub-compartments from mouse brains by subcellular fractionation. First, sealed synaptic terminal structures, known as synaptosomes, are isolated following brain tissue homogenization. Synaptosomes are neuronal pre- and post-synaptic compartments with pinched-off and sealed membranes. These structures retain a metabolically active state and are valuable for studying synaptic structure and function. The synaptosomes are then subjected to hypotonic lysis and ultracentrifugation to obtain synaptic sub-compartments enriched for synaptic vesicles, synaptic cytosol, and synaptic plasma membrane. Fraction purity is confirmed by electron microscopy and biochemical enrichment analysis for proteins specific to sub-synaptic compartments. The presented method is a straightforward and valuable tool for studying the structural and functional characteristics of the synapse and the molecular etiology of various brain disorders.
Auxilin (DNAJC6/PARK19), an endocytic co-chaperone, is essential for maintaining homeostasis in the readily releasable pool (RRP) by aiding clathrin-mediated uncoating of synaptic vesicles. Its ...loss-of-function mutations, observed in familial Parkinson’s disease (PD), lead to basal ganglia motor deficits and cortical dysfunction. We discovered that auxilin-knockout (Aux-KO) mice exhibited impaired pre-synaptic plasticity in layer 4 to layer 2/3 pyramidal cell synapses in the primary visual cortex (V1), including reduced short-term facilitation and depression. Computational modeling revealed increased RRP refilling during short repetitive stimulation, which diminished during prolonged stimulation. Silicon probe recordings in V1 of Aux-KO mice demonstrated disrupted visual cortical circuit responses, including reduced orientation selectivity, compromised visual mismatch negativity, and shorter visual familiarity-evoked theta oscillations. Pupillometry analysis revealed an impaired optokinetic response. Auxilin-dependent pre-synaptic endocytosis dysfunction was associated with deficits in pre-synaptic plasticity, visual cortical functions, and eye movement prodromally or at the early stage of motor symptoms.
Display omitted
•Pre-synaptic short-term plasticity is impaired in Aux-KO mice•Orientation selectivity and visual mismatch responses are reduced in Aux-KO mice•Visual familiarity-induced oscillations are reduced in Aux-KO mice•Optokinetic responses are impaired in Aux-KO mice
Natural sciences; Biological sciences; Physiology; Neuroscience
PDF
