Synergistic stress exacerbation in hippocampal neurons: Evidence favoring the dual‐hit hypothesis of neurodegeneration

Heinemann, Scott D.; Posimo, Jessica M.; Mason, Daniel M.; Hutchison, Daniel F.; Leak, Rehana K.

doi:10.1002/hipo.22580

Cited by 20 publications

(14 citation statements)

References 102 publications

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“…NAC has been shown to protect primary neurons and neuroblastoma cells against proteasome inhibition Jiang et al, 2013;Posimo et al, 2013;Heinemann et al, 2016). In contrast to our previous studies on neuroblastoma cells (Jiang et al, 2013), NAC did not preserve Hsp70 protein levels in primary astrocytes.…”

Section: Discussioncontrasting

confidence: 99%

“…Total GSH levels were measured by In-Cell Western analyses and expressed as a fraction of Hoechst-stained nuclei in the same well to control for differences in cell density. This GSH In-Cell Western assay has been validated in previous studies, in which the signal for GSH was successfully decreased with buthionine sulfoximine and increased with NAC (Leak et al, 2008;Unnithan et al, 2012;Posimo et al, 2013;Titler et al, 2013;Gleixner et al, 2016;Heinemann et al, 2016). Reduced GSH levels were measured by the luminescent GSH-Glo assay according to the manufacturer's instructions (cat.…”

Section: Methodsmentioning

confidence: 99%

“…NAC Protects Astrocytes Independent of Glutathione Synthesis. Previous studies have shown that NAC can increase GSH levels in MG132-treated cells and primary neurons Cheng et al, 2016;Heinemann et al, 2016) as well as untreated astrocytes (Jurkowska and Wróbel, 2008). Therefore, we assessed GSH levels in MG132and NAC-treated astrocytes.…”

Section: Nac Protects Primary Cortical Astrocytes Frommentioning

confidence: 97%

“…We recently showed that NAC protects neuroblastoma cells and primary cortical and hippocampal neurons against proteotoxic or oxidative stress, perhaps by raising the concentration of the antioxidant GSH (Unnithan et al, 2012Posimo et al, 2013;Heinemann et al, 2016). Indeed, most studies of NAC assume that it is effective because it provides a critical precursor, cysteine, for GSH biosynthesis (Martínez-Banaclocha, 2012;Pocernich and Butterfield, 2012).…”

Section: Introductionmentioning

confidence: 99%

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N-Acetyl-l-Cysteine Protects Astrocytes against Proteotoxicity without Recourse to Glutathione

et al. 2017

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-acetyl-l-cysteine (NAC) exhibits protective properties in brain injury models and has undergone a number of clinical trials. Most studies of NAC have focused on neurons. However, neuroprotection may be complemented by the protection of astrocytes because healthier astrocytes can better support the viability of neurons. Here, we show that NAC can protect astrocytes against protein misfolding stress (proteotoxicity), the hallmark of neurodegenerative disorders. Although NAC is thought to be a glutathione precursor, NAC protected primary astrocytes from the toxicity of the proteasome inhibitor MG132 without eliciting any increase in glutathione. Furthermore, glutathione depletion failed to attenuate the protective effects of NAC. MG132 elicited a robust increase in the folding chaperone heat shock protein 70 (Hsp70), and NAC mitigated this effect. Nevertheless, three independent inhibitors of Hsp70 function ablated the protective effects of NAC, suggesting that NAC may help preserve Hsp70 chaperone activity and improve protein quality control without need for Hsp70 induction. Consistent with this view, NAC abolished an increase in ubiquitinated proteins in MG132-treated astrocytes. However, NAC did not affect the loss of proteasome activity in response to MG132, demonstrating that it boosted protein homeostasis and cell viability without directly interfering with the efficacy of this proteasome inhibitor. The thiol-containing molecules l-cysteine and d-cysteine both mimicked the protective effects of NAC, whereas the thiol-lacking molecule -acetyl--methyl-l-cysteine failed to exert protection or blunt the rise in ubiquitinated proteins. Collectively, these findings suggest that the thiol group in NAC is required for its effects on glial viability and protein quality control.

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Section: Discussioncontrasting

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Nac Protects Primary Cortical Astrocytes Frommentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

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N-Acetyl-l-Cysteine Protects Astrocytes against Proteotoxicity without Recourse to Glutathione

et al. 2017

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“…Our previous report showed that neurons respond to dual hits of high concentrations of paraquat with additive cell loss (Heinemann et al, 2016), suggesting that neurons do not develop stress tolerance in response to severe oxidative toxicity. However, there are many other types of oxidative stimuli, including hydrogen peroxide.…”

Section: Resultsmentioning

confidence: 99%

Astrocytes Do Not Forfeit Their Neuroprotective Roles After Surviving Intense Oxidative Stress

Bhatia

Pant

Eckhoff

et al. 2019

Front. Mol. Neurosci.

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In order to fulfill their evolutionary role as support cells, astrocytes have to tolerate intense oxidative stress under conditions of brain injury and disease. It is well known that astrocytes exposed to mild oxidative stress are preconditioned against subsequent stress exposure in dual hit models. However, it is unclear whether severe oxidative stress leads to stress tolerance, stress exacerbation, or no change in stress resistance in astrocytes. Furthermore, it is not known whether reactive astrocytes surviving intense oxidative stress can still support nearby neurons. The data in this Brief Report suggest that primary cortical astrocytes surviving high concentrations of the oxidative toxicant paraquat are completely resistant against subsequent oxidative challenges of the same intensity. Inhibitors of multiple endogenous defenses (e.g., glutathione, heme oxygenase 1, ERK1/2, Akt) failed to abolish or even reduce their stress resistance. Stress-reactive cortical astrocytes surviving intense oxidative stress still managed to protect primary cortical neurons against subsequent oxidative injuries in neuron/astrocyte co-cultures, even at concentrations of paraquat that otherwise led to more than 80% neuron loss. Although our previous work demonstrated a lack of stress tolerance in primary neurons exposed to dual paraquat hits, here we show that intensely stressed primary neurons can resist a second hit of hydrogen peroxide. These collective findings suggest that stress-reactive astroglia are not necessarily neurotoxic, and that severe oxidative stress does not invariably lead to stress exacerbation in either glia or neurons. Therefore, interference with the natural functions of stress-reactive astrocytes might have the unintended consequence of accelerating neurodegeneration.

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Evidence for cross-hemispheric preconditioning in experimental Parkinson’s disease

et al. 2017

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Dopamine loss and motor deficits in Parkinson's disease typically commence unilaterally and remain asymmetric for many years, raising the possibility that endogenous defenses slow the cross-hemispheric transmission of pathology. It is well-established that the biological response to subtoxic stress prepares cells to survive subsequent toxic challenges, a phenomenon known as preconditioning, tolerance, or stress adaptation. Here we demonstrate that unilateral striatal infusions of the oxidative toxicant 6-hydroxydopamine (6-OHDA) precondition the contralateral nigrostriatal pathway against the toxicity of a second 6-OHDA infusion in the opposite hemisphere. 6-OHDA-induced loss of dopaminergic terminals in the contralateral striatum was ablated by cross-hemispheric preconditioning, as shown by two independent markers of the dopaminergic phenotype, each measured by two blinded observers. Similarly, loss of dopaminergic somata in the contralateral substantia nigra was also abolished, according to two blinded measurements. Motor asymmetries in floor landings, forelimb contacts with a wall, and spontaneous turning behavior were consistent with these histological observations. Unilateral 6-OHDA infusions increased phosphorylation of the kinase ERK2 and expression of the antioxidant enzyme CuZn superoxide dismutase in both striata, consistent with our previous mechanistic work showing that these two proteins mediate preconditioning in dopaminergic cells. These findings support the existence of cross-hemispheric preconditioning in Parkinson's disease and suggest that dopaminergic neurons mount impressive natural defenses, despite their reputation as being vulnerable to oxidative injury. If these results generalize to humans, Parkinson's pathology may progress slowly and asymmetrically because exposure to a disease-precipitating insult induces bilateral upregulation of endogenous defenses and elicits cross-hemispheric preconditioning.

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Synergistic stress exacerbation in hippocampal neurons: Evidence favoring the dual‐hit hypothesis of neurodegeneration

Cited by 20 publications

References 102 publications

N-Acetyl-l-Cysteine Protects Astrocytes against Proteotoxicity without Recourse to Glutathione

N-Acetyl-l-Cysteine Protects Astrocytes against Proteotoxicity without Recourse to Glutathione

Astrocytes Do Not Forfeit Their Neuroprotective Roles After Surviving Intense Oxidative Stress

Evidence for cross-hemispheric preconditioning in experimental Parkinson’s disease

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