Astrocyte-specific deletion of the transcription factor Yin Yang 1 in murine substantia nigra mitigates manganese-induced dopaminergic neurotoxicity

Abstract

Manganese (Mn)-induced neurotoxicity resembles Parkinson’s disease (PD), but the mechanisms underpinning its effects remain unknown. Mn dysregulates astrocytic glutamate transporters, GLT-1 and GLAST, and dopaminergic function, including tyrosine hydroxylase (TH). Our previous in vitro studies have shown that Mn repressed GLAST and GLT-1 via activation of transcription factor Yin Yang 1 (YY1). Here, we investigated if in vivo astrocytic YY1 deletion mitigates Mn-induced dopaminergic neurotoxicity, attenuating Mn-induced reduction in GLAST/GLT-1 expression in murine substantia nigra (SN). AAV5-GFAP-Cre-GFP particles were infused into the SN of 8-week old YY1flox/floxmice to generate a region-specific astrocytic YY1 conditional knockout (cKO) mouse model. Three weeks after AAV infusion, mice were exposed to 330 μg Mn (MnCl2 30 mg/kg, intranasal instillation, daily) for 3 weeks. After Mn exposure, motor functions were determined in open-field and rotarod tests, followed by western blot, qPCR and immunohistochemistry to assess YY1, TH, GLAST and GLT-1 levels. Infusion of AAV5-GFAP-Cre-GFP vectors into the SN resulted in region-specific astrocytic YY1 deletion and attenuation of Mn-induced (1) impairment of motor functions, (2) reduction of TH-expressing cells in SN and TH mRNA/protein levels in midbrain/striatum. Astrocytic YY1 deletion also attenuated the Mn-induced decrease in GLAST/GLT-1 mRNA/protein levels in midbrain. Moreover, YY1 deletion abrogated its interaction with HDACs in astrocytes. These results indicate that astrocytic YY1 plays a critical role in Mn-induced neurotoxicity in vivo, at least in part, by reducing astrocytic GLAST/GLT-1. Thus, YY1 might be a potential target for treatment of Mn toxicity and other neurological disorders associated with dysregulation of GLAST/GLT-1.

Molecular Targets of Manganese-Induced Neurotoxicity: A Five-Year Update

“…Mn exposure (30 mg/kg intranasal for 21 days) was shown to decrease EAAT1 (GLAST) and EAAT2 (GLT-1) promotor activities, as well as mRNA and protein levels resulting in reduced glutamate uptake in human astrocyte H4 cells as well as murine brain, being associated with neurobehavioral deficiency, reduced tyrosine hydroxylase mRNA and protein levels, as well as reduced histone H3 and H4 acetylation [ 171 ], all being reversed by valproic acid and sodium butyrate [ 172 ]. Our previous data from both in vitro (exposure to 250 μM Mn for 6 h) [ 173 , 174 ] and in vivo (exposure to 30 mg/kg intranasal for 21 days) [ 175 ] studies demonstrate that activation of Yin Yang 1 (YY1) transcription factor plays a significant role in GLAST and GLT-1 expression, whereas YY1 knockout significantly attenuated Mn-induced motor dysfunction, glutamate transporter reduction, tyrosine hydroxylase activity, as well as histone deacetylation [ 176 ]. At the same time, it has been demonstrated that a time- and dose-dependent increase in GLAST activity in chick cerebellar Bergmann glia cells in response to acute but non-toxic Mn exposure (200 µM for 30 min) may be associated with increased transporter affinity for [ 3 H]-d-aspartate [ 177 ].…”

Manganese Accumulation in the Brain via Various Transporters and Its Neurotoxicity Mechanisms

“…In addition, Mn-induced glutamate dyshomeostasis could be associated with glutamate transporter dysfunction. We have previously reported that Mn decreased the glutamate uptake in astrocytes, along with a reduced expression of glutamate aspartate transporter 1 (GLAST) and glutamate transporter 1 (GLT-1), resulting in excess extracellular glutamate levels [ 8 , 149 , 150 ]. Since GLAST and GLT-1 are predominantly expressed in astrocytes and responsible for >90% of the glutamate uptake from the extracellular space in the brain [ 145 ], this Mn-reduced GLT-1/GLAST could directly contribute to excitotoxic neuronal injury.…”

“…We have found that the Mn-decreased expression of GLT-1/GLAST was at the transcriptional level. The Mn-induced activation of the transcription factor Yin Yang 1 (YY1) was responsible for repressing GLAST and GLT-1 expression in both in vitro astrocyte cultures and in vivo mouse models [ 8 , 149 , 150 ]. Mn also modulated epigenetic modifier histone deacetylases (HDAC) to repress GLAST and GLT-1 expression by increasing the interaction of HDAC with YY1 and the subsequent histone deacetylation in astrocytes [ 149 , 150 ].…”

“…Mn also modulated epigenetic modifier histone deacetylases (HDAC) to repress GLAST and GLT-1 expression by increasing the interaction of HDAC with YY1 and the subsequent histone deacetylation in astrocytes [ 149 , 150 ]. Astrocytic YY1 was critical in Mn-induced neurotoxicity, since astrocytic YY1 deletion attenuated the Mn-induced repression of GLAST and GLT-1 in the substantia nigra, concomitantly decreasing the interaction between YY1 and HDACs in astrocytes [ 8 ]. These findings indicate that Mn promotes neuronal injury by dysregulating the glutamate signal at least in part by the dysregulation of glutamate transporters GLT-1/GLAST and the NMDA receptor.…”

“…Mn overexposure may result from environmental and/or occupational settings, such as mining, smelting, and agrochemical and biomedical industries [ 6 , 7 ]. Mn neurotoxicity is associated with Mn accumulation in various regions of the brain, including basal ganglia, frontal cortex, and cerebellum [ 8 ]. Moreover, increasing evidence reveals that Mn may also be a risk factor for several other neurodegenerative disorders, including Alzheimer’s disease (AD), dementia, and Huntington’s disease (HD), to name a few [ 9 ].…”