Upregulation of Parkinson's disease-associated protein alpha-synuclein suppresses tumorigenesis via interaction with mGluR5 and gamma-synuclein in liver cancer.

Numerous epidemiological studies suggest a link between Parkinson's disease (PD) and cancer, indicating that PD-associated proteins may mediate the development of cancer. Here, we investigated a potential role of PD-associated protein α-synuclein in regulating liver cancer progression in vivo and in vitro. We found the negative correlation of α-synuclein with metabotropic glutamate receptor 5 (mGluR5) and γ-synuclein by analyzing the data from The Cancer Genome Atlas database, liver cancer patients and hepatoma cells with overexpressed α-synuclein. Moreover, upregulated α-synuclein suppressed the growth, migration, and invasion. α-synuclein was found to associate with mGluR5 and γ-synuclein, and the truncated N-terminal of α-synuclein was essential for the interaction. Furthermore, overexpressed α-synuclein exerted the inhibitory effect on hepatoma cells through the degradation of mGluR5 and γ-synuclein via α-synuclein-dependent autophagy-lysosomal pathway (ALP). Consistently, in vivo experiments with rotenone-induced rat model of PD also confirmed that, upregulated α-synuclein in liver cancer tissues through targeting on mGluR5/α-synuclein/γ-synuclein complex inhibited tumorigenesis involving in ALP-dependent degradation of mGluR5 and γ-synuclein. These findings give an insight into an important role of PD-associated protein α-synuclein accompanied by the complex of mGluR5/α-synuclein/γ-synuclein in distant communications between PD and liver cancer, and provide a new strategy in therapeutics for the treatment of liver cancer.

α-Synuclein Induced the Occurrence of RBD via Interaction with OX1R and Modulated Its Degradation.

Rapid eye movement (REM) sleep behavior disorder (RBD) is a powerful early sign of Parkinson's disease (PD), but the pathogenetic mechanism involved in RBD remains largely unexplored. α-Synuclein has been verified to form Lewy bodies in the orexin neurons, whose activity and function rely on the orexin 1 receptor (OX1R). Dysfunction of the OX1R may induce the occurrence of RBD. Here, we determined the role of the interaction between α-Synuclein and OX1R in the pathogenesis of RBD, in vitro and in vivo. We found that injection of α-Synuclein into the lateral hypothalamus area (LHA) damaged orexin neurons and induced the RBD-like sleep pattern, to further damage dopaminergic neurons and result in locomotor dysfunction in mice. α-Synuclein interacted with OX1R, promoting the degradation of OX1R through proteasomal and lysosomal pathways. In addition, overexpression of α-Synuclein downregulated OX1R-mediated signaling, subsequently leading to orexin neuron damage. We conclude that α-Synuclein induced the occurrence of RBD via interaction with OX1R and modulated its degradation. These findings provide evidence for a novel mechanism by which the association of α-Synuclein with OX1R was attributed to α-Synuclein-induced orexin neuron damage, which may be a new molecular target for an effective therapeutic strategy for RBD pathology.

Upregulated mGluR5 induces ER stress and DNA damage by regulating the NMDA receptor subunit NR2B.

Dysfunction caused by mGluR5 expression or activation is an important mechanism in the development of Parkinson's disease (PD). Early clinical studies on mGluR5 negative allosteric modulators have shown some limitations. It is therefore necessary to find a more specific approach to block mGluR5-mediated neurotoxicity. Here, we determined the role of N-methyl-D-aspartate (NMDA) receptor subunit NR2B in mGluR5-mediated ER stress and DNA damage. In vitro study, rotenone-induced ER stress and DNA damage were accompanied by an increase in mGluR5 expression and overexpressed or activated mGluR5 with agonist (RS)-2-chloro-5-hydroxyphenylglycine (CHPG) induced ER stress and DNA damage, while blocking mGluR5 with antagonist 2-methyl-6-(phenylethynyl) pyridine hydrochloride (MPEP) alleviated the effect. Furthermore, the damage caused by CHPG was blocked by NMDA receptor antagonist MK-801. Additionally, rotenone or CHPG increased the p-Src and p-NR2B, which was inhibited by MPEP. Blocking p-Src or NR2B with PP2 or CP101,606 alleviated CHPG-induced ER stress and DNA damage. Overactivation of mGluR5 accompanied with the increase of p-Src and p-NR2B in the ER stress and DNA damage was found in rotenone-induced PD rat model. These findings suggest a new mechanism wherein mGluR5 induces ER stress and DNA damage through the NMDA receptor and propose NR2B as the molecular target for therapeutic strategy for PD.

Metabotropic glutamate receptor 5 inhibits α-synuclein-induced microglia inflammation to protect from neurotoxicity in Parkinson's disease.

BACKGROUND: Microglia activation induced by α-synuclein (α-syn) is one of the most important factors in Parkinson's disease (PD) pathogenesis. However, the molecular mechanisms by which α-syn exerts neuroinflammation and neurotoxicity remain largely elusive. Targeting metabotropic glutamate receptor 5 (mGluR5) has been an attractive strategy to mediate microglia activation for neuroprotection, which might be an essential regulator to modulate α-syn-induced neuroinflammation for the treatment of PD. Here, we showed that mGluR5 inhibited α-syn-induced microglia inflammation to protect from neurotoxicity in vitro and in vivo. METHODS: Co-immunoprecipitation assays were utilized to detect the interaction between mGluR5 and α-syn in microglia. Griess, ELISA, real-time PCR, western blotting, and immunofluorescence assays were used to detect the regulation of α-syn-induced inflammatory signaling, cytokine secretion, and lysosome-dependent degradation. RESULTS: α-syn selectively interacted with mGluR5 but not mGluR3, and α-syn N terminal deletion region was essential for binding to mGluR5 in co-transfected HEK293T cells. The interaction between these two proteins was further detected in BV2 microglia, which was inhibited by the mGluR5 specific agonist CHPG without effect by its selective antagonist MTEP. Moreover, in both BV2 cells and primary microglia, activation of mGluR5 by CHPG partially inhibited α-syn-induced inflammatory signaling and cytokine secretion and also inhibited the microglia activation to protect from neurotoxicity. We further found that α-syn overexpression decreased mGluR5 expression via a lysosomal pathway, as evidenced by the lysosomal inhibitor, NH4Cl, by blocking mGluR5 degradation, which was not evident with the proteasome inhibitor, MG132. Additionally, co-localization of mGluR5 with α-syn was detected in lysosomes as merging with its marker, LAMP-1. Consistently, in vivo experiments with LPS- or AAV-α-syn-induced rat PD model also confirmed that α-syn accelerated lysosome-dependent degradation of mGluR5 involving a complex, to regulate neuroinflammation. Importantly, the binding is strengthened with LPS or α-syn overexpression but alleviated by urate, a potential clinical biomarker for PD. CONCLUSIONS: These findings provided evidence for a novel mechanism by which the association of α-syn with mGluR5 was attributed to α-syn-induced microglia activation via modulation of mGluR5 degradation and its intracellular signaling. This may be a new molecular target for an effective therapeutic strategy for PD pathology.