Brain region-specific vulnerability of astrocytes in response to 3-nitropropionic acid is mediated by cytochrome c oxidase isoform expression

Abstract

Brain region specificity is a feature characteristic of neurodegenerative disorders, such as Huntington's disease (HD). We have studied the brain region-specific vulnerability of striatal compared with cortical and mesencephalic astrocytes treated with 3-nitropropionic acid (NPA), an in vitro model of HD. Mitochondrial dysfunction is involved in neurodegenerative processes. We have previously demonstrated a causal relationship between NPA-induced transcription of the cytochrome c oxidase (COX) subunit IV isoform (cox4i2) and increased oxidative stress leading to higher rates of necrotic cell death in striatal astrocytes by the application of a small interfering RNA knockdown system. Here, we have investigated the correlation of COX IV-2 protein expression with intracellular ATP content, mitochondrial peroxide production, and viability of astrocytes from three different brain regions. In cortical and mesencephalic astrocytes, NPA caused an elevation of cox4i2 transcription as in striatal astroglia. However, increased COX IV-2 and decreased COX IV-1 protein expression levels have been observed only in striatal astrocytes. In agreement with our hypothesis, Striatal astrocytes showed the highest levels of peroxide production and necrotic cell death rates compared with cortical and mesencephalic astroglia. Thus, we suggest that the higher vulnerability of astrocytes from the striatum in our in vitro model of HD is, at least in part, based on brain region-specific differences of the COX IV-2/COX IV-1 protein ratios and accompanied elevated oxidative stress.

Mitochondrial Complex IV Subunit 4 Isoform 2 Is Essential for Acute Pulmonary Oxygen Sensing

“…In presence of the superoxide scavengers MitoTempol and S3QEL2 we could still detect the hypoxia-induced increase of ΔΨ m in WT cells, suggesting that alterations of ΔΨ m are independent and apparently not downstream of mitochondrial ROS release. Our findings are in line with previous reports showing that Cox4i2 increases ROS production in astrocytes (48, 49). To further investigate the underlying mechanism for the increase in ΔΨ m we found increased mitochondrial matrix pH, suggesting an increase of the proton gradient ΔpH contributing to increased ΔΨ m .…”

Cytochrome c oxidase dysfunction in oxidative stress

“…In astrocytes, hypoxic and toxin mediated induction of subunit IV i2 is thought to play a role in elevated mitochondrial peroxide production [69,137]. Knockdown of IV i2 by siRNA in these cells resulted in decreased mitochondrial peroxide formation in addition to decreasing CcO activity [96,137]. This observation is however opposite to an earlier report in which knockdown of subunit IV i2 under hypoxia increased H 2 O 2 production [59].…”

Sex‐ and brain region‐specific role of cytochrome c oxidase in 1‐methyl‐4‐phenylpyridinium‐mediated astrocyte vulnerability

“…To distinguish between apoptotic and necrotic astrocytes, MPP + ‐treated and untreated control cells were cultured on poly‐L‐ornithine‐coated coverslips and stained with a combination of Hoechst 33342 and propidium iodide as described by detail in Horvat et al (2006) and Misiak et al (2010b). Cells were first incubated in the presence of 1 μg/ml Hoechst 33342 trihydrochloride (Hoechst; Invitrogen) for 15 min under culturing conditions and subsequently washed twice with PBS.…”