HMGB1 Acts on Microglia Mac1 to Mediate Chronic Neuroinflammation That Drives Progressive Neurodegeneration

Laboratory of Toxicology and Pharmacology, National Institute of Environmental Health Sciences/National Institutes of Health, Research Triangle Park, North Carolina 27709, USA.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.34). 01/2011; 31(3):1081-92. DOI: 10.1523/JNEUROSCI.3732-10.2011
Source: PubMed


What drives the gradual degeneration of dopamine neurons in Parkinson's disease (PD), the second most common neurodegenerative disease, remains elusive. Here, we demonstrated, for the first time, that persistent neuroinflammation was indispensible for such a neurodegenerative process. 1-Methyl-4-phenylpyridinium, lipopolysaccharide (LPS), and rotenone, three toxins often used to create PD models, produced acute but nonprogressive neurotoxicity in neuron-enriched cultures. In the presence of microglia (brain immune cells), these toxins induced progressive dopaminergic neurodegeneration. More importantly, such neurodegeneration was prevented by removing activated microglia. Collectively, chronic neuroinflammation may be a driving force of progressive dopaminergic neurodegeneration. Conversely, ongoing neurodegeneration sustained microglial activation. Microglial activation persisted only in the presence of neuronal damage in LPS-treated neuron-glia cultures but not in LPS-treated mixed-glia cultures. Thus, activated microglia and damaged neurons formed a vicious cycle mediating chronic, progressive neurodegeneration. Mechanistic studies indicated that HMGB1 (high-mobility group box 1), released from inflamed microglia and/or degenerating neurons, bound to microglial Mac1 (macrophage antigen complex 1) and activated nuclear factor-κB pathway and NADPH oxidase to stimulate production of multiple inflammatory and neurotoxic factors. The treatment of microglia with HMGB1 led to membrane translocation of p47(phox) (a cytosolic subunit of NADPH oxidase) and consequent superoxide release, which required the presence of Mac1. Neutralization of HMGB1 and genetic ablation of Mac1 and gp91(phox) (the catalytic submit of NADPH oxidase) blocked the progressive neurodegeneration. Our findings indicated that HMGB1-Mac1-NADPH oxidase signaling axis bridged chronic neuroinflammation and progressive dopaminergic neurodegeneration, thus identifying a mechanistic basis for chronic PD progression.

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    • "N ADPH oxidase (NOX2) is the primary extracellular superoxide-producing enzyme in activated phagocytes, including microglia (Lambeth, 2004; Nunes et al., 2013). Studies from our group and others have demonstrated that microglial NOX2 is a key mediator in initiating and maintaining chronic neuroinflammation (Gao et al., 2011; Qin et al., 2013), which subsequently causes progressive dopaminergic neurodegeneration in rodent models of Parkinson's disease (PD) (Barnum and Tansey, 2010; Block and Hong, 2005; Block et al., 2007; Gao and Hong, 2008; Hirsch and Hunot, 2009; Hirsch et al., 2012). Elevated expression and activation of NOX2 have been found in the substantia nigra of PD patients and animal models (Qin et al., 2013; Wu et al., 2003). "
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    ABSTRACT: Activation of microglial NADPH oxidase (NOX2) plays a critical role in mediating neuroinflammation, which is closely linked with the pathogenesis of a variety of neurodegenerative diseases, including Parkinson's disease (PD). The inhibition of NOX2-generated superoxide has become an effective strategy for developing disease-modifying therapies for PD. However, the lack of specific and potent NOX2 inhibitors has hampered the progress of this approach. Diphenyleneiodonium (DPI) is a widely used, long-acting NOX2 inhibitor. However, due to its non-specificity for NOX2 and high cytotoxicity at standard doses (µM), DPI has been precluded from human studies. In this study, using ultra-low doses of DPI, we aimed to: (1) investigate whether these problems could be circumvented and (2) determine whether ultra-low doses of DPI were able to preserve its utility as a potent NOX2 inhibitor. We found that DPI at subpicomolar concentrations (10−14 and 10−13 M) displays no toxicity in primary midbrain neuron-glia cultures. More importantly, we observed that subpicomolar DPI inhibited phorbol myristate acetate (PMA)-induced activation of NOX2. The same concentrations of DPI did not inhibit the activities of a series of flavoprotein-containing enzymes. Furthermore, potent neuroprotective efficacy was demonstrated in a post-treatment study. When subpicomolar DPI was added to neuron-glia cultures pretreated with lipopolysaccharide, 1-methyl-4-phenylpyridinium or rotenone, it potently protected the dopaminergic neurons. In summary, DPI's unique combination of high specificity toward NOX2, low cytotoxicity and potent neuroprotective efficacy in post-treatment regimens suggests that subpicomolar DPI may be an ideal candidate for further animal studies and potential clinical trials. GLIA 2014
    Glia 12/2014; 62(12). DOI:10.1002/glia.22724 · 6.03 Impact Factor
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    • "Strong evidence indicates that chronic, low-grade inflammation is implicated in the pathogenesis of DR [11, 12]. Recently, it was demonstrated that HMGB1 is the main mediator bridging persistent neuroinflammation and chronic progressive dopaminergic neurodegeneration in neurodegenerative diseases, such as Parkinson's disease [13]. "
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    ABSTRACT: To test the hypothesis that increased expression of proinflammatory cytokine high-mobility group box-1 (HMGB1) in epiretinal membranes and vitreous fluid from patients with proliferative diabetic retinopathy and in retinas of diabetic rats plays a pathogenetic role in mediating diabetes-induced retinal neuropathy. Retinas of 1-month diabetic rats and HMGB1 intravitreally injected normal rats were studied using Western blot analysis, RT-PCR and glutamate assay. In addition, we studied the effect of the HMGB1 inhibitor glycyrrhizin on diabetes-induced biochemical changes in the retina. Diabetes and intravitreal injection of HMGB1 in normal rats induced significant upregulation of HMGB1 protein and mRNA, activated extracellular signal-regulated kinase 1 and 2 (ERK1/2), cleaved caspase-3 and glutamate; and significant downregulation of synaptophysin, tyrosine hydroxylase, glutamine synthetase, and glyoxalase 1. Constant glycyrrhizin intake from the onset of diabetes did not affect the metabolic status of the diabetic rats, but it significantly attenuated diabetes-induced upregulation of HMGB1 protein and mRNA, activated ERK1/2, cleaved caspase-3, and glutamate. In the glycyrrhizin-fed diabetic rats, the decrease in synaptophysin, tyrosine hydroxylase, and glyoxalase 1 caused by diabetes was significantly attenuated. These findings suggest that early retinal neuropathy of diabetes involves upregulated expression of HMGB1 and can be ameliorated by inhibition of HMGB1.
    Mediators of Inflammation 09/2014; 2014(11):746415. DOI:10.1155/2014/746415 · 3.24 Impact Factor
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    • "The receptors on cell surface engaged in HMGB1 interaction include RAGE, TLR4 and TLR2. Particularly, it has been proposed that the activated CD11b participates in the signaling events associated with HMGB-RAGE interaction [26], [40]. It is also known that whether HMGB1 acts as a cytokine or chemokine is closely related with the state of three redox-sensitive cysteine on it (C23, C45 and C106); HMGB1 with its all three cysteine in their reduced form functions as a chemokine, while HMGB1 with C23-C45 disulphide bond but leave C106 in its thiol form behaves like a cytokine [17]–[18], [41]. "
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    ABSTRACT: High mobility group box 1(HMGB1) was first recognized as a nuclear protein that increased the chromatin remodeling and regulates transcription of many genes. In recent years, HMGB1 has been identified as a critical "late" pro-inflammatory mediator due to its unique secretion pattern and lethal effects in sepsis. Therefore, preventing the active release and inhibiting the pro-inflammatory activity of HMGB1 become promising strategies for the treatment of sepsis. Here, we reported the therapeutic effects of Gu-4, a lactosyl derivative, on sepsis and the underlying molecular mechanisms. In an experimental rat model of sepsis caused by cecal ligation and puncture (CLP), Gu-4 administration prominently attenuated lung injury and improved the survival of the septic animals, which was positively correlated with the decrease of the serum HMGB1 level. Using RAW264.7 macrophage cell line, we further showed that Gu-4 significantly suppressed the lipopolysaccharide (LPS)-induced release and cytoplasmic translocation of HMGB1. Moreover, Gu-4 not only dose-dependently attenuated recombinant human (rhHMGB1)-induced production of TNF-α, IL-6, and IL-1β in THP-1 cells, but also greatly inhibited the adhesion of rhHMGB1-challenged THP-1 cells to HUVECs. Analyses of flow cytometry demonstrated that Gu-4 could effectively reduce the activation of CD11b elicited by rhHMGB1. Western blot analyses revealed that Gu-4 treatment could partially block the rhHMGB1-induced activation of ERK and NF-κB signalings. Meanwhile, CD11b knockdown also obviously attenuated the rhHMGB1-induced phosphorylations of ERK and IKKα/β. Taken together, our results suggest that Gu-4 possesses a therapeutic potential in the treatment of sepsis probably via inhibiting the LPS-induced release of HMGB1 from macrophages and via suppressing the pro-inflammatory activity of HMGB1.
    PLoS ONE 03/2014; 9(3):e89634. DOI:10.1371/journal.pone.0089634 · 3.23 Impact Factor
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