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DJ‐1, also known as Parkinson's disease protein 7 (Park7), is a multifunctional protein that regulates oxidative stress and mitochondrial function. Dysfunction of DJ‐1 is implicated in the pathogenesis of Parkinson's disease (PD). Hyperhomocysteinemia is associated with an increased risk of PD. Here we show that homocysteine thiolactone (HTL), a reactive thioester of homocysteine (Hcy), covalently modifies DJ‐1 on the lysine 182 (K182) residue in an age‐dependent manner. The N‐homocysteinylation (N‐hcy) of DJ‐1 abolishes its neuroprotective effect against oxidative stress and mitochondrial dysfunction, exacerbating cell toxicity. Blocking the N‐hcy of DJ‐1 restores its protective effect. These results indicate that the N‐hcy of DJ‐1 abolishes its neuroprotective effect and promotes the progression of PD. Inhibiting the N‐hcy of DJ‐1 may exert neuroprotective effect against PD. [ABSTRACT FROM AUTHOR]

The aggregation of α‐synuclein plays a pivotal role in the pathogenesis of Parkinson's disease (PD). Epidemiological evidence indicates that high level of homocysteine (Hcy) is associated with an increased risk of PD. However, the molecular mechanisms remain elusive. Here, we report that homocysteine thiolactone (HTL), a reactive thioester of Hcy, covalently modifies α‐synuclein on the K80 residue. The levels of α‐synuclein K80Hcy in the brain are increased in an age‐dependent manner in the TgA53T mice, correlating with elevated levels of Hcy and HTL in the brain during aging. The N‐homocysteinylation of α‐synuclein stimulates its aggregation and forms fibrils with enhanced seeding activity and neurotoxicity. Intrastriatal injection of homocysteinylated α‐synuclein fibrils induces more severe α‐synuclein pathology and motor deficits when compared with unmodified α‐synuclein fibrils. Increasing the levels of Hcy aggravates α‐synuclein neuropathology in a mouse model of PD. In contrast, blocking the N‐homocysteinylation of α‐synuclein ameliorates α‐synuclein pathology and degeneration of dopaminergic neurons. These findings suggest that the covalent modification of α‐synuclein by HTL promotes its aggregation. Targeting the N‐homocysteinylation of α‐synuclein could be a novel therapeutic strategy against PD. [ABSTRACT FROM AUTHOR]

The aggregation and prion-like propagation of α-synuclein are involved in the pathogenesis of Parkinson's disease. However, the underlying mechanisms regulating the assembly and spreading of α-synuclein fibrils remain poorly understood. Tau co-deposits with α-synuclein in the brains of Parkinson's disease patients, suggesting a pathological interplay between them. Here we show that tau interacts with α-synuclein and accelerates its aggregation. Compared with pure α-synuclein fibrils, the tau-modified α-synuclein fibrils show enhanced seeding activity, inducing mitochondrial dysfunction, synaptic impairment and neurotoxicity in vitro. Injection of the tau-modified α-synuclein fibrils into the striatum of mice induces more severe α-synuclein pathology, motor dysfunction and cognitive impairment when compared with the mice injected with pure α-synuclein fibrils. Knockout of tau attenuates the propagation of α-synuclein pathology and Parkinson's disease-like symptoms both in mice injected with α-syn fibrils and α-syn A53T transgenic mice. In conclusion, tau facilitates α-synuclein aggregation and propagation in Parkinson's disease. [ABSTRACT FROM AUTHOR]

Netrin‐1 is a chemotropic cue mediating axon growth and neural migration in neuronal development, and its receptors deletion in colorectal cancer and UNC5s act as dependence receptors regulating neuronal apoptosis. Asparagine endopeptidase (AEP) is an age‐dependent protease that cuts human alpha‐synuclein (α‐Syn) at N103 and triggers its aggregation and neurotoxicity. In the current study, it is reported that UNC5C receptor is cleaved by AEP in Parkinson's disease (PD) and facilitates dopaminergic neuronal loss. UNC5C is truncated by active AEP in human α‐SNCA transgenic mice in an age‐dependent manner or induced by neurotoxin rotenone. Moreover, UNC5C is fragmented by AEP in PD brains, inversely correlated with reduced netrin‐1 levels. Netrin‐1 deprivation in primary cultures induces AEP and caspase‐3 activation, triggering UNC5C proteolytic fragmentation and enhancing neuronal loss. Noticeably, blocking UNC5C cleavage by AEP attenuates netrin‐1 deprivation‐elicited neuronal death and motor disorders in netrin flox/flox mice. Overexpression of AEP‐truncated UNC5C intracellular fragment strongly elicits α‐Syn aggregation and dopaminergic loss, locomotor deficits in α‐SNCA transgenic mice. Hence, the findings demonstrate that netrin‐1 reduction and UNC5C truncation by AEP contribute to PD pathogenesis. [ABSTRACT FROM AUTHOR]

Thyrotropin-releasing hormone (TRH) and its analogs are able to stimulate the release of the endogenic dopamine (DA) in the central nervous system. However, this effect has not been tested in the Parkinson's disease (PD), which is characterized by the DA deficiency due to the dopaminergic neurons loss in the substantia nigra. Here, we investigated the therapeutic effect of Taltirelin, a long-acting TRH analog on 6-hydroxydopamine-lesioned hemi-Parkinsonian rat model. 1–10 mg/kg Taltirelin i.p. administration significantly improved the locomotor function and halted the electrophysiological abnormities of PD animals without inducing dyskinesia even with high-dose for 7 days treatment. Microdialysis showed that Taltirelin gently and persistently promoted DA release in the cortex and striatum, while L-DOPA induced a sharp rise of DA especially in the cortex. The DA-releasing effect of Taltirelin was alleviated by reserpine, vanoxerine (GBR12909) or AMPT, indicating a mechanism involving vesicular monoamine transporter-2 (VMAT-2), dopamine transporter (DAT) and tyrosine hydroxylase (TH). The in vivo and in vitro experiments further supported that Taltirelin affected the regulation of TH expression in striatal neurons, which was mediated by p-ERK1/2. Together, this study demonstrated that Taltirelin improved motor function of hemi-PD rats without inducing dyskinesia, thus supporting a further exploration of Taltirelin for PD treatment. [ABSTRACT FROM AUTHOR]

Dopaminergic neurons loss in the substantia nigra (SN) and dopamine (DA) content loss in the striatum correlate well with disease severity in Parkinson's disease (PD). Brain-derived neurotrophic factor (BDNF) is a member of neurotrophin family and is necessary for the survival and development of DA neurons in the SN. Deficits in BDNF/TrkB receptors signaling contribute to the dysfunction of PD. Deoxygedunin, a derivative of gedunin produced from Indian neem tree, binds TrkB receptor and activates TrkB and its downstream signaling cascades in a BDNF-independent manner, and possesses neuroprotective effects in vitro and in vivo . In this study, we tested the neuroprotective effects of deoxygedunin in 6-hydroxydopamine (6-OHDA)-lesioned rat model and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mice model of Parkinson's disease. Rats were treated with deoxygedunin 5 mg/kg (i.p.) for one month started two weeks before 6-OHDA lesion (pre-treatment), or for two weeks right after lesion (post-treatment), with isovolumetric vehicle as control and normal. Mice were given deoxygedunin 5 mg/kg (i.p.) for 2 weeks and administrated with MPTP twice at the dose of 20 mg/kg (i.p.) on day 7. The results revealed that pretreatment with deoxygedunin improved PD models' behavioral performance and reduced dopaminergic neurons loss in SN, associated with the activation of TrkB receptors and its two major signaling cascades involving mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K). Thus, our current study indicates that deoxygedunin, as a small molecule TrkB agonist, displays prominent neuroprotective properties, providing a novel therapeutic strategy for treating Parkinson's disease. [ABSTRACT FROM AUTHOR]

The histopathological hallmark of Parkinson's disease (PD) is the presence of fibrillar aggregates referred to as Lewy bodies (LBs), in which α-synuclein is the major component. Converging evidence supports the prion-like transmission of α-synuclein aggregates in the onset and progression of PD. Intracellular α-synuclein aggregates into pathological fibrils, which can be transferred from aggregate-producing cells to aggregate-free cells, triggering neuronal injury and the progression of pathology. However, the specific mechanisms mediating the aggregation and transmission of pathological α-synuclein remain unknown. Here we show that cofilin 1 binds to α-synuclein and promotes its aggregation. The mixed fibrils consist of cofilin 1 and α-synuclein are more compact and more potent than pure α-synuclein fibrils in seeding α-synuclein aggregation. Cofilin 1 also facilitates the uptake of α-synuclein fibrils and finally induces neuronal dysfunction. Together, these observations indicate that cofilin 1 acts as a crucial mediator in the aggregation and propagation of pathological α-synuclein, contributing to the pathogenesis of PD. • Cofilin 1 was highly expressed in human and mouse PD brains. • Cofilin 1 combined α-synuclein and promoted its aggregation. • Cofilin 1 facilitated the propagation of α-synuclein pathology. • Cofilin 1 enhanced the toxicity of α-synuclein fibrils. [ABSTRACT FROM AUTHOR]

L-DOPA-induced dyskinesia (LID) is a major complication of long-term dopamine replacement therapy in Parkinson's disease. Characteristic neural oscillation and abnormal activity of striatal projection neurons (SPNs) are typical pathological events of LID, which would be reliable biomarkers for assessment of novel anti-dyskinetic approach if fully profiled. Glutamate dysregulation plays a critical role in the development of LID, and the group II metabotropic glutamate receptors (mGluR2/3) is believed to regulate the release of glutamate on the presynaptic terminals and inhibits postsynaptic excitation. However, the anti-dyskinetic effect of modulating mGluR2/3 is still unclear. In this study, rats with unilateral dopaminergic lesion were injected with L-DOPA (12 mg/kg, i.p.) for seven days, while motor behavior was correlated with in vivo electrophysiology analyzing LFP and single-cell activity in both primary motor cortex and dorsolateral striatum. Our study showed that as LID established, high γ oscillation (hγ) predominated during LID, the number of unstable responses of SPN to dopamine increased, and the coherence between these patterns of oscillation and spiking activity also increased. We found that pretreatment of NMDA receptor antagonist, amantadine 60 mg/kg, i.p. (AMAN) significantly reduced abnormal involuntary movements (AIMs), in parallel with the reduction of hγ oscillation, and more markedly with a decrease in unstable responses of SPNs. In contrast, a mGluR2/3 agonist, LY354740 12 mg/kg, i.p. (LY) significantly shortened the duration of LID but merely exhibited a weak effect in diminishing the intensity of LID or reversing SPN responses. Together results indicate that AIMs in the rat model of PD are associated with abnormal corticostriatal signaling, which could be reversed by NMDAR antagonism more efficiently than mGluR2/3 agonism. • Amantadine reduces unstable responses of striatal projection neurons to dopamine. • Group II metabotropic glutamate receptors agonist LY354740 shortens LID duration. • The fluctuation of high γ oscillation is associated with LID duration. • The switch between high β and high γ oscillation suggests their distinct origins. [ABSTRACT FROM AUTHOR]

Pathologic aggregation and prion-like propagation of α-synuclein (α-syn) are the hallmarks of Parkinson's disease (PD). Emerging evidence shows that type 2 diabetes mellitus (T2DM) is a risk factor for PD. Interestingly, T2DM is characterized by the amyloid deposition of islet amyloid polypeptide (IAPP) in the pancreas. Although T2DM and PD share pathological similarities, the underlying molecular mechanisms bridging these two diseases remain unknown. Here, we report that IAPP co-deposits with α-syn in the brains of PD patients. IAPP interacts with α-syn and accelerates its aggregation. In addition, the IAPP-seeded α-syn fibrils show enhanced seeding activity and neurotoxicity compared with pure α-syn fibrils in vitro and in vivo. Strikingly, intravenous injection of IAPP fibrils into α-syn A53T transgenic mice or human SNCA transgenic mice accelerated the aggregation of α-syn and PD-like motor deficits. Taken together, these findings support that IAPP acts as a trigger of α-syn pathology in PD, and provide a mechanistic explanation for the increased risk and faster progression of PD in patients with T2DM. • IAPP interacts with α-synuclein and accelerates its aggregation. • IAPP enhances the seeding activity and neurotoxicity of α-synuclein fibrils. • Administration of IAPP promotes α-synuclein pathology and PD-like phenotypes. [ABSTRACT FROM AUTHOR]

Parkinson's disease (PD) is one of the most common neurodegenerative diseases, which is characterized by the loss of dopaminergic neurons in the nigrostriatal pathway. Synaptic dysfunction impairs dopamine turnover and contributes to the degeneration of dopaminergic neurons. However, the molecular mechanisms underlying synaptic dysfunction and dopaminergic neuronal vulnerability in PD are not clear. Here, we report that synaptojanin 1 (SYNJ1), a polyphosphoinositide phosphatase concentrated at nerve terminals, is a substrate of a cysteine proteinase, asparagine endopeptidase (AEP). SYNJ1 is cleaved by the cysteine proteinase AEP at N599 in the brains of PD patients. AEP-mediated cleavage of SYNJ1 disrupts neuronal phosphoinositide homeostasis and causes synaptic dysfunction. Overexpression of the AEP-generated fragments of SYNJ1 triggers synaptic dysfunction and the degeneration of dopaminergic neurons, inducing motor defects in the α-synuclein transgenic mice. Blockage of AEP-mediated cleavage of SYJN1 alleviates the pathological and behavioral defects in a mouse model of PD. Our results demonstrate that the fragmentation of SYNJ1 by AEP mediates synaptic dysfunction and dopaminergic neuronal degeneration in PD. • Synaptojanin 1 is a substrate of asparagine endopeptidase. • Asparagine endopeptidase cleaves synaptojanin 1 at N599 in the brains of patients with Parkinson's disease. • AEP-derived SYNJ1 fragments induce synaptic dysfunction and neuronal degeneration. • Blockage of AEP-mediated cleavage of SYJN1 alleviates the pathological and behavioral defects in a mouse model of PD. [ABSTRACT FROM AUTHOR]