Inhibition Of STING Attenuates Neurodegeneration And Neuroinflammation In Mouse Parkinsonian Models

Research BackgroundParkinson’s disease(PD)is the second most common neurodegenerative disease in the world,and also the third major invisible killer threatening the health of middle-aged and elderly people in China,and seriously affects the quality of life of patients.According to statistics,there are currently about 3 million people with Parkinson’s disease in China,and it is expected to increase to 5 million people by 2030,accounting for half of the number of people with Parkinson’s disease worldwide.The pathogenesis of Parkinson’s disease involves many factors,among which microglia-mediated immune inflammatory response plays a key role.Activation of microglia cells may trigger an inflammatory response that leads to neuroinflammation and dopaminergic neuron damage,leading to the pathological features of Parkinson’s disease.The cGAS-STING signaling pathway is an important signaling pathway related to immune inflammatory response,and the activation of this pathway may lead to immune inflammation.The cGAS-STING signaling pathway has been extensively studied in autoimmune diseases,such as systemic lupus erythematosus and rheumatoid arthritis,and has been confirmed to play an important role.However,the role of cGAS-STING signaling pathway in neurodegenerative diseases,especially in Parkinson’s disease,needs further investigation.In order to further understand the specific role of cGAS-STING signaling pathway in Parkinson’s disease and explore the possibility of alleviating neuroinflammation and protecting dopaminergic neurons by inhibiting the activation of STING signaling pathway through pharmacological means,The objective of this experiment is to study the function of STING,a key molecule in the cGAS-STING signaling pathway,in Parkinson’s disease.By analyzing the mechanism of STING,we hope to provide a theoretical basis for the development of new treatment strategies for Parkinson’s disease,with the ultimate goal of alleviating the clinical characteristics of patients with Parkinson’s disease and improving their quality of life.Methods1.The acute MPTP PD mice model was induced by intraperitoneal injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine(MPTP).For C-176 treatment,mice were intraperitoneally injected with C-176 2 days before MPTP injection and continued for 3 days after MPTP injection,The changes of motor behavior were evaluated by rod rotation,rod climbing and suspension experiments.The degeneration of dopaminergic neurons was evaluated by Nissl staining,tyrosine hydroxylase immunohistochemical staining and Western Blot analysis;the effects of C-176 on neuroinflammation were observed using real time RT-PCR and immunofluorescence.2.The subacute MPTP PD mice model was induced by intraperitoneal injection of MPTP for 5 consecutive days.For C-176 treatment,mice were intraperitoneally injected with C-176 2 days before MPTP injection and continued for additional 5 days after MPTP injection.After 21 days of last MPTP injection,the changes of motor behavior were evaluated by rod rotation,rod climbing and suspension experiments.The degeneration of dopaminergic neurons was evaluated by immunohistochemistry,Nissl staining and Western Blot analysis.The effects of C-176 on neuroinflammation were observed using real time RT-PCR and immunofluorescence.3.BV2 microglia were pretreated with different concentrations of C-176(0.5 μM,1 μM,and 2 μM)for 2 h and then exposed to LPS(1 μg/mL)and MPP+(1 mM)for indicated time.Cells were collected at the indicated time points.The effects of pharmacological inhibition of STING on LPS/MPP+-induced inflammatory responses in BV2 microglial cells were determined by real time RT-PCR and Western Blot analysis.4.The small interfering RNA(siRNA)of STING was used to knock down the expression of STING in BV2 microglial cells,and the effects of genetic inhibition of STING on inflammatory response and activation of NLRP3 inflammasome after LPS/MPP+treatment were observed by realtime RT-PCR and Western Blot analysis.Results1.In the MPTP-induced acute PD mice model,the expression of STING protein levels were upregulated in the substantia nigra and striatum of MPTP mice.In the BV2 microglial cells,the expression of STING protein levels were also increased at 3 h and continued upregulated 24 h after LPS/MPP+ exposure.2.The STING specific inhibitor C-176 could significantly improve the movement disorder of acute MPTP PD mice,reduce the loss of TH-positive dopaminergic neurons and terminal fibers in the substantia nigra and striatum.C-176 treatment also attenuated the levels of MPTP-induced reactive microglia and astrocytes and inhibited the activation of STING and its downstream molecules.Moreover,C-176 attenuated the MPTP-induced activation of NLRP3 inflammasome.3.C-176 alleviated the inflammatory response of BV2 microglial cells induced by LPS/MPP+.Treatment of BV2 cells with C-176 also attenuated LPS/MPP+-induced STING signaling and NLRP3 inflammasome activation in BV2 microglial cells.4.C-176 also improved the movement disorder in MPTP-induced subacute PD mice,and reduced the MPTP-associated dopaminergic neurodegneration and neuroinflammation in the subacute MPTP PD mice model.5.Genetic inhibition of STING using STING siRNA alleviated the inflammatory response of BV2 microglial cells induced by LPS/MPP+.STING knockdown also attenuated LPS/MPP+-induced STING signaling activation in BV2 microglial cells.ConclusionsThe results of our study revealed that STING expression was significantly upregulated in the MPTP mouse model of PD.Pharmacological blockade of STING with C-176 attenuated MPTP-induced dopaminergic neurodegeneration and motor deficit in the acute and subacute MPTP mice model of PD.We also confirmed that C-176 treatment suppressed MPTP-induced proinflammatory cascade and NLRP3 inflammasome activation.The results of our study suggest that pharmacological blockade of STING may represent a promising therapeutic strategy to mitigate progressive dopaminergic degeneration in PD.