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Neurodegenerative diseases are characterized by a decline in neuronal function and structure, leading to neuronal death. Understanding the molecular mechanisms of neuronal death is crucial for developing therapeutics. MiRs are small noncoding RNAs that regulate gene expression by degrading target mRNAs or inhibiting translation. MiR dysregulation has been linked to many neurodegenerative diseases, but the underlying mechanisms are not well understood. As mitochondrial dysfunction is one of the common molecular mechanisms leading to neuronal death in many neurodegenerative diseases, here we studied miRs that modulate neuronal death caused by 1-methyl-4-phenylpyridinium (MPP + ), an inhibitor of complex I in mitochondria. We identified miR-593-5p, levels of which were increased in SH-SY5Y human neuronal cells, after exposure to MPP + . We found that intracellular Ca 2+ , but not of reactive oxygen species, mediated this miR-593-5p increase. Furthermore, we found the increase in miR-593-5p was due to enhanced stability, not increased transcription or miR processing. Importantly, we show the increase in miR-593-5p contributed to MPP + -induced cell death. Our data revealed that miR-593-5p inhibits a signaling pathway involving PTEN-induced putative kinase 1 (PINK1) and Parkin, two proteins responsible for the removal of damaged mitochondria from cells, by targeting the coding sequence of PINK1 mRNA. Our findings suggest that miR-593-5p contributes to neuronal death resulting from MPP + toxicity, in part, by impeding the PINK1/Parkin-mediated pathway that facilitates the clearance of damaged mitochondria. Taken together, our observations highlight the potential significance of inhibiting miR-593-5p as a therapeutic approach for neurodegenerative diseases., Competing Interests: Conflict of interest The authors declare that they have no conflicts of interest with the contents of this article., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Alpha-Synuclein (α-Syn) is an important protein in the pathogenesis of Parkinson disease (PD) as it accumulates as fibrillar inclusions in affected brain regions including dopaminergic neurons in the substantia nigra. Elevated levels of α-Syn seem to be crucial in mediating its toxicity. Thus, detailed information regarding the regulatory mechanism of α-Syn expression in several layers such as transcription, post-transcription and post-translation is needed in order to devise therapeutic interventions for PD. Previously, we reported that expression of α-Syn is repressed by microRNA-7 (miR-7) through its effect on the 3'-untranslated region (UTR) of α-Syn mRNA. Here, we show that miR-7 also accelerates the clearance of α-Syn and its aggregates by promoting autophagy in differentiated ReNcell VM cells. Further, miR-7 facilitates the degradation of pre-formed fibrils of α-Syn transported from outside the cells. This additional mechanism for reducing α-Syn levels show miR-7 to be an important molecular target for PD and other alpha-synucleinopathies., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Mitochondrial dysfunction is one of the major contributors to neurodegenerative disorders including Parkinson disease. The mitochondrial permeability transition pore is a protein complex located on the mitochondrial membrane. Under cellular stress, the pore opens, increasing the release of pro-apoptotic proteins, and ultimately resulting in cell death. MicroRNA-7 (miR-7) is a small non-coding RNA that has been found to exhibit a protective role in the cellular models of Parkinson disease. In the present study, miR-7 was predicted to regulate the function of mitochondria, according to gene ontology analysis of proteins that are down-regulated by miR-7. Indeed, miR-7 overexpression inhibited mitochondrial fragmentation, mitochondrial depolarization, cytochrome c release, reactive oxygen species generation, and release of mitochondrial calcium in response to 1-methyl-4-phenylpyridinium (MPP(+)) in human neuroblastoma SH-SY5Y cells. In addition, several of these findings were confirmed in mouse primary neurons. Among the mitochondrial proteins identified by gene ontology analysis, the expression of voltage-dependent anion channel 1 (VDAC1), a constituent of the mitochondrial permeability transition pore, was down-regulated by miR-7 through targeting 3'-untranslated region of VDAC1 mRNA. Similar to miR-7 overexpression, knockdown of VDAC1 also led to a decrease in intracellular reactive oxygen species generation and subsequent cellular protection against MPP(+). Notably, overexpression of VDAC1 without the 3'-UTR significantly abolished the protective effects of miR-7 against MPP(+)-induced cytotoxicity and mitochondrial dysfunction, suggesting that the protective effect of miR-7 is partly exerted through promoting mitochondrial function by targeting VDAC1 expression. These findings point to a novel mechanism by which miR-7 accomplishes neuroprotection by improving mitochondrial health., (© 2016 by The American Society for Biochemistry and Molecular Biology, Inc.)

Nuclear factor E2-related factor 2 (Nrf2) is a key transcription factor that regulates the expression of a number of antioxidant and detoxifying genes that provide cellular protection against various stressors including reactive oxygen species (ROS). Nrf2 activity is tightly regulated by a cytoplasmic inhibitory protein called Kelch-like ECH-associated protein 1 (Keap1). The mechanism that controls Keap1 expression, however, remains poorly understood. In the present study, we demonstrate that microRNA-7 (miR-7), which is highly expressed in the brain, represses Keap1 expression by targeting the 3'-untranslated region (UTR) of its mRNA in human neuroblastoma cells, SH-SY5Y. Subsequently, this event results in an increased Nrf2 activity, as evidenced by an increase in the expression of its transcriptional targets, heme oxygenase 1 (HO-1) and glutamate-cysteine ligase modifier subunit (GCLM), and an enhanced nuclear localization of Nrf2. In addition, miR-7 decreases the intracellular hydroperoxides level and increases the level of reduced form of glutathione, indicative of oxidative stress relief. We also demonstrate that targeted repression of Keap1 and activation of Nrf2 pathway, in part, underlies the protective effects of miR-7 against 1-methyl-4-phenylpyridinium (MPP+)-induced toxicity in SH-SY5Y and differentiated human neural progenitor cells, ReNcell VM. These findings point to a new mechanism by which miR-7 exerts cytoprotective effects by regulating the Nrf2 pathway., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Parkinson disease is associated with decreased activity of the mitochondrial electron transport chain. This defect can be recapitulated in vitro by challenging dopaminergic cells with 1-methyl-4-phenylpyridinium (MPP(+)), a neurotoxin that inhibits complex I of electron transport chain. Consequently, oxidative phosphorylation is blocked, and cells become dependent on glycolysis for ATP production. Therefore, increasing the rate of glycolysis might help cells to produce more ATP to meet their energy demands. In the present study, we show that microRNA-7, a non-coding RNA that protects dopaminergic neuronal cells against MPP(+)-induced cell death, promotes glycolysis in dopaminergic SH-SY5Y and differentiated human neural progenitor ReNcell VM cells, as evidenced by increased ATP production, glucose consumption, and lactic acid production. Through a series of experiments, we demonstrate that targeted repression of RelA by microRNA-7, as well as subsequent increase in the neuronal glucose transporter 3 (Glut3), underlies this glycolysis-promoting effect. Consistently, silencing Glut3 expression diminishes the protective effect of microRNA-7 against MPP(+). Further, microRNA-7 fails to prevent MPP(+)-induced cell death when SH-SY5Y cells are cultured in a low glucose medium, as well as when differentiated ReNcell VM cells or primary mouse neurons are treated with the hexokinase inhibitor, 2-deoxy-d-glucose, indicating that a functional glycolytic pathway is required for this protective effect. In conclusion, microRNA-7, by down-regulating RelA, augments Glut3 expression, promotes glycolysis, and subsequently prevents MPP(+)-induced cell death. This protective effect of microRNA-7 could be exploited to correct the defects in oxidative phosphorylation in Parkinson disease., (© 2015 by The American Society for Biochemistry and Molecular Biology, Inc.)

Mounting evidence suggests that microRNA (miR) dysregulation contributes to neurodegenerative disorders including Parkinson's disease (PD). MiR-34b and miR-34c have been previously shown to be down-regulated in the brains of patients with PD. Here, we demonstrate that miR-34b and miR-34c repress the expression of α-synuclein (α-syn), a key protein in PD pathogenesis. Inhibition of miR-34b and miR-34c expression in human dopaminergic SH-SY5Y cells increased α-syn levels and stimulated aggregate formation. Additionally, a single nucleotide polymorphism (SNP) in the 3'-UTR of α-syn was found to lower the miR-34b-mediated repression of the protein. Our results suggest that down-regulation of miR-34b and miR-34c in the brain, as well as an SNP in the 3'-UTR of α-syn can increase α-syn expression, possibly contributing to PD pathogenesis., (Copyright © 2014 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.)

Parkinson's disease (PD) is characterized by the progressive loss of dopaminergic neurons in the substantia nigra. Mitochondrial complex I impairment in PD is modeled in vitro by the susceptibility of dopaminergic neurons to the complex I inhibitor 1-methyl-4-phenylpyridinium (MPP+). In the present study, we demonstrate that microRNA-7 (miR-7), which is expressed in tyrosine hydroxylase-positive nigral neurons in mice and humans, protects cells from MPP+-induced toxicity in dopaminergic SH-SY5Y cells, differentiated human neural progenitor ReNcell VM cells, and primary mouse neurons. RelA, a component of nuclear factor-κB (NF-κB), was identified to be downregulated by miR-7 using quantitative proteomic analysis. Through a series of validation experiments, it was confirmed that RelA mRNA is a target of miR-7 and is required for cell death following MPP+ exposure. Further, RelA mediates MPP+-induced suppression of NF-κB activity, which is essential for MPP+-induced cell death. Accordingly, the protective effect of miR-7 is exerted through relieving NF-κB suppression by reducing RelA expression. These findings provide a novel mechanism by which NF-κB suppression, rather than activation, underlies the cell death mechanism following MPP+ toxicity, have implications for the pathogenesis of PD, and suggest miR-7 as a therapeutic target for this disease., (Copyright © 2014 the authors 0270-6474/14/3412725-13$15.00/0.)