Manganese-induced reactive oxygen species activate IκB kinase to upregulate YY1 and impair glutamate transporter EAAT2 function in human astrocytes in vitro

Dysregulation of the astrocytic glutamate transporter excitatory amino acid transporter 2 (EAAT2) is associated with several neurological disorders, including Parkinson's disease, Alzheimer's disease, and manganism, the latter induced by chronic exposure to high levels of manganese (Mn). Mechanisms of Mn-induced neumtoxicity include impairment of EAAT2 function secondary to the activation of the transcription factor Yin Yang 1 (YY1) by nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kappa B). However, the upstream mechanisms by which Mn-induced NF-kappa B activates YY1 remain to be elucidated. In the present study, we used the H4 human astrocyte cell line to test if Mn activates YY1 through the canonical NF-kappa B signaling pathway, leading to EAAT2 repression. The results demonstrate that Mn exposure induced phosphorylation of the upstream kinase I kappa B kinase (IKK-beta), leading to NF-kappa B p65 translocation, increased YY1 promoter activity, mRNA/protein levels, and consequently repressed EAAT2. Results also demonstrated that Mn-induced oxidative stress and subsequent TNF-alpha production were upstream of IKK-beta activation, as antioxidants attenuated Mn-induced TNF-alpha production and IKK-beta activation. Moreover, TNF-alpha inhibition attenuated the Mn-induced activation of IKK-beta and YY1. Taken together, Mn-induced oxidative stress and TNF-alpha mediates activation of NF-kappa B signaling and YY1 upregulation, leading to repression of EAAT2. Thus, targeting reactive oxygen species (ROS), TNF-alpha and IKK-beta may attenuate Mn-induced YY1 activation and consequent EAAT2 repression.

Automated summary

The dysregulation of EAAT2 in neurological disorders, such as Parkinson's disease, Alzheimer's disease, and manganism induced by chronic exposure to high levels of manganese, is associated with NF-kappa B signaling pathway activation and YY1 upregulation. Mn-induced oxidative stress and TNF-alpha production play key roles in the activation of IKK-beta, which leads to the repression of EAAT2 by YY1. Targeting ROS, TNF-alpha, and IKK-beta may be potential strategies to attenuate Mn-induced YY1 activation and subsequent EAAT2 repression.