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Rapid mitochondrial dysfunction mediates TNF-alpha-induced neurotoxicity.

ABSTRACT: Tumor necrosis factor alpha (TNF-?) is known to exacerbate ischemic brain injury; however, the mechanism is unknown. Previous studies have evaluated the effects of TNF-? on neurons with long exposures to high doses of TNF-?, which is not pathophysiologically relevant. We characterized the rapid effects of TNF-? on basal respiration, ATP production, and maximal respiration using pathophysiologically relevant, post-stroke concentrations of TNF-?. We observed a reduction in mitochondrial function as early as 1.5 h after exposure to low doses of TNF-?, followed by a decrease in cell viability in HT-22 cells and primary neurons. Subsequently, we used the HT-22 cell line to determine the mechanism by which TNF-? causes a rapid and profound reduction in mitochondrial function. Pre-treating with TNF-R1 antibody, but not TNF-R2 antibody, ameliorated the neurotoxic effects of TNF-?, indicating that TNF-? exerts its neurotoxic effects through TNF-R1. We observed an increase in caspase 8 activity and a decrease in mitochondrial membrane potential after exposure to TNF-? which resulted in a release of cytochrome c from the mitochondria into the cytosol. These novel findings indicate for the first time that an acute exposure to pathophysiologically relevant concentrations of TNF-? has neurotoxic effects mediated by a rapid impairment of mitochondrial function. This study focuses on the neurotoxic mechanism of a pro-inflammatory cytokine, tumor necrosis factor alpha (TNF-?). We demonstrate a prompt mitochondrial dysfunction followed by nerve cell loss after exposure to TNF-?. These studies may provide evidence that the immune system can rapidly and adversely affect brain function and that TNF-? signaling may be a target for neuroprotection.

SUBMITTER: Doll DN

PROVIDER: S-EPMC4459129 | biostudies-literature | 2015 Feb

REPOSITORIES: biostudies-literature

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Rapid mitochondrial dysfunction mediates TNF-alpha-induced neurotoxicity.

Doll Danielle N DN Rellick Stephanie L SL Barr Taura L TL Ren Xuefang X Simpkins James W JW

Journal of neurochemistry 20150129 4

Tumor necrosis factor alpha (TNF-α) is known to exacerbate ischemic brain injury; however, the mechanism is unknown. Previous studies have evaluated the effects of TNF-α on neurons with long exposures to high doses of TNF-α, which is not pathophysiologically relevant. We characterized the rapid effects of TNF-α on basal respiration, ATP production, and maximal respiration using pathophysiologically relevant, post-stroke concentrations of TNF-α. We observed a reduction in mitochondrial function a ...[more]

PMID: 25492727

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Project description:Growing evidences suggest that sustained neuroinflammation, caused by microglia overactivation, is implicated in the development and aggravation of several neurological and psychiatric disorders. In some pathological conditions, microglia produce increased levels of cytotoxic and inflammatory mediators, such as tumor necrosis factor alpha (TNF-α), which can reactivate microglia in a positive feedback mechanism. However, specific molecular mediators that can be effectively targeted to control TNF-α-mediated microglia overactivation, are yet to be uncovered. In this context, we aim to identify novel TNF-α-mediated micro(mi)RNAs and to dissect their roles in microglia activation, as well as to explore their impact on the cellular communication with neurons. A miRNA microarray, followed by RT-qPCR validation, was performed on TNF-α-stimulated primary rat microglia. Gain- and loss-of-function in vitro assays and proteomic analysis were used to dissect the role of miR-342 in microglia activation. Co-cultures of microglia with hippocampal neurons, using a microfluidic system, were performed to understand the impact on neurotoxicity. Stimulation of primary rat microglia with TNF-α led to an upregulation of Nos2, Tnf, and Il1b mRNAs. In addition, ph-NF-kB p65 levels were also increased. miRNA microarray analysis followed by RT-qPCR validation revealed that TNF-α stimulation induced the upregulation of miR-342. Interestingly, miR-342 overexpression in N9 microglia was sufficient to activate the NF-kB pathway by inhibiting BAG-1, leading to increased secretion of TNF-α and IL-1β. Conversely, miR-342 inhibition led to a strong decrease in the levels of these cytokines after TNF-α activation. In fact, both TNF-α-stimulated and miR-342-overexpressing microglia drastically affected neuron viability. Remarkably, increased levels of nitrites were detected in the supernatants of these co-cultures. Globally, our findings show that miR-342 is a crucial mediator of TNF-α-mediated microglia activation and a potential target to tackle microglia-driven neuroinflammation.

Project description:Aging and chronic inflammation are independent risk factors for the development of atherothrombosis and cardiovascular disease. We hypothesized that aging-associated inflammation promotes the development of platelet hyperreactivity and increases thrombotic risk during aging. Functional platelet studies in aged-frail adults and old mice demonstrated that their platelets are hyperreactive and form larger thrombi. We identified tumor necrosis factor α (TNF-α) as the key aging-associated proinflammatory cytokine responsible for platelet hyperreactivity. We further showed that platelet hyperreactivity is neutralized by abrogating signaling through TNF-α receptors in vivo in a mouse model of aging. Analysis of the bone marrow compartments showed significant platelet-biased hematopoiesis in old mice reflected by increased megakaryocyte-committed progenitor cells, megakaryocyte ploidy status, and thrombocytosis. Single-cell RNA-sequencing analysis of native mouse megakaryocytes showed significant reprogramming of inflammatory, metabolic, and mitochondrial gene pathways in old mice that appeared to play a significant role in determining platelet hyperreactivity. Platelets from old mice (where TNF-α was endogenously increased) and from young mice exposed to exogenous TNF-α exhibited significant mitochondrial changes characterized by elevated mitochondrial mass and increased oxygen consumption during activation. These mitochondrial changes were mitigated upon TNF-α blockade. Similar increases in platelet mitochondrial mass were seen in platelets from patients with myeloproliferative neoplasms, where TNF-α levels are also increased. Furthermore, metabolomics studies of platelets from young and old mice demonstrated age-dependent metabolic profiles that may differentially poise platelets for activation. Altogether, we present previously unrecognized evidence that TNF-α critically regulates megakaryocytes resident in the bone marrow niche and aging-associated platelet hyperreactivity and thrombosis.

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Rapid mitochondrial dysfunction mediates TNF-alpha-induced neurotoxicity.

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Rapid mitochondrial dysfunction mediates TNF-alpha-induced neurotoxicity.

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