Elsevier

Brain Research

Volume 1643, 15 July 2016, Pages 130-139
Brain Research

Research Report
Inhibition of myeloid differentiation factor 88(MyD88) by ST2825 provides neuroprotection after experimental traumatic brain injury in mice

https://doi.org/10.1016/j.brainres.2016.05.003Get rights and content

Highlights

  • This is the first study to reveal the effect of MyD88 inhibitor ST2825 after TBI.

  • ST2825 reduced neural apoptosis and improved neurological function after TBI.

  • MyD88-mediated signaling may be a promising target for intervention after TBI.

Abstract

Myeloid differentiation factor 88(MyD88) is an endogenous adaptor protein that plays an important role in coordinating intracellular inflammatory responses induced by agonists of the Toll-like receptor and interleukin-1 receptor families. MyD88 has been reported to be essential for neuronal death in animal models and may represent a therapeutic target for pharmacologic inhibition following traumatic brain injury (TBI). The purpose of the current study was to investigate the neuroprotective effect of MyD88 specific inhibitor ST2825 in an experimental mouse model of TBI. Intracerebroventricular (ICV) injection of high concentration (20 μg/μL) ST2825 (15 min post TBI) attenuated the development of TBI in mice, markedly improved neurological function and reduced brain edema. Decreased neural apoptosis and increased neuronal survival were also observed. Biochemically, the high concentration of ST2825 significantly reduced the levels of MyD88, further decreased TAK1, p-TAK1, nuclear p65 and increased IκB-α. Additionally, ST2825 significantly reduced the levels of Iba-1 and inflammatory factors TNF-α and IL-1β. These data provide an experimental rationale for evaluation of MyD88 as a drug target and highlight the potential therapeutic implications of ST2825 in TBI.

Introduction

Traumatic brain injury (TBI) is recognized as one of the leading causes of morbidity and mortality, constituting a major health and socioeconomic problem throughout the world (Maas et al., 2008). A variety of biochemical and molecular mechanisms are responsible for primary and secondary brain damage (McIntosh et al., 1998). Despite intense research, an effective treatment that improves clinical outcomes is yet to be identified. Although previous studies suggested that pharmacological interventions might be neuroprotective (Tolias and Bullock, 2004), none of the currently available drugs have been shown to reduce morbidity and mortality or improve the prognosis of patients with TBI (Diaz-Arrastia et al., 2014). Therefore, the need for new therapeutic strategies is imperative.

Myeloid differentiation factor 88(MyD88) plays a central role in inflammatory pathways, acting as a downstream adaptor protein for signal transduction via the Toll-like receptor (TLR) and interleukin (IL)-1 receptor families. MyD88 contains a characteristic death domain that is essential for NF-κB activation, and an adjacent Toll/IL-1 receptor (TIR) homology domain for signal transduction (Medzhitov et al., 1998). The IL-1 receptor-induced NF-κB pathway leads to phosphorylation of IL-1 receptor-associated kinase (IRAK), followed by activation of TGF-β-associated kinase 1(TAK1). MyD88 acts as an adaptor protein for the interaction between IRAK and the IL-1 receptor. The association of TLRs or IL-1 receptors with MyD88 enhances the inflammatory response by stimulating the NF-κB pathway. This causes transcriptional up-regulation of inflammatory factors such as TNF-α and IL-1β, which may activate NF-κB by association with the IL-1 receptor and MyD88 (Dunne and O’Neill, 2003). Therefore, MyD88 is considered to function as an adaptor protein for inflammatory pathways that include signal transduction via the TLR and IL-1 receptor families.

ST2825 is a peptide-mimetic compound (Fig. 1) that interferes with MyD88 homodimerization, and recruitment of IRAK1 and IRAK4 (Loiarro et al., 2007). Inhibition of MyD88 by ST2825 was found to prevent cardiac enlargement following experimental acute myocardial infarction in mice (Van Tassell et al., 2010). Loss of MyD88 expression and/or function had an anti-inflammatory effect in several pathological situations, including early atherosclerosis (Bjorkbacka et al., 2004), arthritis (Joosten et al., 2003), and inflammatory diseases of the central nerves system such as multiple sclerosis (Prinz et al., 2006). Koedel and colleagues demonstrated that loss of MyD88 reduced acute brain injury and improved neurological status (Koedel et al., 2007). In previous studies, MyD88 expression was significantly increased after experimental TBI and in the human brain after TBI (Li et al., 2011, Li et al., 2013). To date, the potential neuroprotective effect of MyD88 inhibition following TBI has not been investigated. This study described the effect of pharmacologic inhibition of MyD88 by ST2825 after TBI in mice.

Section snippets

General observations and mortality rate

All mice survived the TBI or sham procedure. Administration of vehicle or ST2825 did not significantly alter arterial blood gas and heart rates of mice. There were no statistical differences between groups in physiological parameters (data not shown).

ST2825 improved neurologic function and reduced brain water content at both 24 h and 72 h after TBI

Neurological function, as measured by NSS scores, and brain water content were evaluated at both 24 h and 72 h after TBI. As shown in Fig. 2, NSS scores and brain water content were substantially increased after TBI compared with the sham group at

Discussion

The current study showed for the first time that inhibition of MyD88 by ST2825 significantly reduced the number of apoptotic cells, diminished neuronal damage and improved neurological recovery after TBI in mice. Consistent with these findings, Iba-1 and pro-inflammatory cytokines TNF-αand IL-1β were substantially decreased by ST2825 administration. These neuroprotective effects of ST2825 may be mediated by suppression of the MyD88/TAK1/NF-κB signaling pathway.

ST2825 is a specific MyD88

Animal and TBI model

All procedures were approved by Nanjing University Animal Care and Use Committee and performed in accordance with the Guide for the Care and Use of Laboratory Animals by the National Institute of Health. The male ICR mice, aged 6–8 weeks, weighing 28–32 g, were housed in a reversed 12 h light/12 h dark cycle controlled environment with free access to food and water. Experimental TBI (closed head injury) was induced using a weight-drop model as described previously (Adeleye et al., 2010, Biegon et

Acknowledgments

This work is supported by Grants from National Natural Science Foundation of China (No. 81171170, 81371294, 81401029), Natural Science Foundation of Jiangsu Province, China (BK2010459).

References (43)

  • J.P. Mayeux et al.

    Traumatic brain injury induces neuroinflammation and neuronal degeneration that is associated with escalated alcohol self-administration in rats

    Behav. Brain Res.

    (2015)
  • R. Medzhitov et al.

    MyD88 is an adaptor protein in the hToll/IL-1 receptor family signaling pathways

    Mol. Cell

    (1998)
  • R.L. Roof et al.

    Progesterone rapidly decreases brain edema: treatment delayed up to 24 h is still effective

    Exp. Neurol.

    (1996)
  • C.M. Tolias et al.

    Critical appraisal of neuroprotection trials in head injury: what have we learned?

    NeuroRx

    (2004)
  • D. Zhang et al.

    Inhibition of transforming growth factor beta-activated kinase 1 confers neuroprotection after traumatic brain injury in rats

    Neuroscience

    (2013)
  • D. Zhang et al.

    TLR4 inhibitor resatorvid provides neuroprotection in experimental traumatic brain injury: implication in the treatment of human brain injury

    Neurochem. Int.

    (2014)
  • A.A. Babcock et al.

    Signaling through MyD88 regulates leukocyte recruitment after brain injury

    J. Immunol.

    (2008)
  • A. Biegon et al.

    Dynamic changes in N-methyl-D-aspartate receptors after closed head injury in mice: implications for treatment of neurological and cognitive deficits

    Proc. Natl. Acad. Sci. USA

    (2004)
  • H. Bjorkbacka et al.

    Reduced atherosclerosis in MyD88-null mice links elevated serum cholesterol levels to activation of innate immunity signaling pathways

    Nat. Med.

    (2004)
  • R. Diaz-Arrastia et al.

    Pharmacotherapy of traumatic brain injury: state of the science and the road forward: report of the Department of Defense Neurotrauma Pharmacology Workgroup

    J. Neurotrauma

    (2014)
  • A. Dunne et al.

    The interleukin-1 receptor/Toll-like receptor superfamily: signal transduction during inflammation and host defense

    Sci. STKE

    (2003)
  • Cited by (28)

    • IRAK4 exacerbates traumatic brain injury via activation of TAK1 signaling pathway

      2022, Experimental Neurology
      Citation Excerpt :

      These results suggest that MYD88 plays critical role in IRAK4 phosphorylation. A growing body of evidence attributes negative influences to MYD88 activation on TBI-induced secondary injury, and targeting MYD88 alleviates TBI (Li et al., 2011; Zhang et al., 2016). Thus we hypothesized that MYD88 might participate in IRAK4 phosphorylation after TBI.

    • Bexarotene promotes microglia/macrophages - Specific brain - Derived Neurotrophic factor expression and axon sprouting after traumatic brain injury

      2020, Experimental Neurology
      Citation Excerpt :

      After the supernatant was removed, the rest positive fraction was used for following Western blot and qPCR. Neurological severity scores (NSS) of mice were evaluated prior to injury, and on day 1, 3, 7, 14 and 21 after CCI and were repeated three times in every testing day as previously described (Zhang et al., 2016). Briefly, the investigators blind to experimental grouping evaluated the ability of each mouse to perform 10 different tasks representing motor ability, alertness, balancing, and general behavior.

    • Pioglitazone ameliorates neuronal damage after traumatic brain injury via the PPARγ/NF-κB/IL-6 signaling pathway

      2020, Genes and Diseases
      Citation Excerpt :

      A standard curve of NaNO2 was established for each assay by performing these steps in an identical manner. The NSS was assessed prior to injury and was repeated three times on days 1, 3, 7, 14 and 21 after CCI as described by Zhang, H.S. et al.20 Using a double-blind approach, the researchers who were blinded to experimental grouping assessed the ability of each rat to perform 10 different tasks. These tasks represented athletic ability, alertness, balance, and general behavior.

    • Role of Toll-like receptor mediated signaling in traumatic brain injury

      2019, Neuropharmacology
      Citation Excerpt :

      It has been applied in different models of human diseases (Yan et al., 2017). In an experimental mouse model of TBI, intracerebroventricular (ICV) injection of a high concentration of ST2825 significantly reduced the level of MyD88, inhibited the activation of TAK1, IκB-α, and NFκB-p65, and decreased the production of the inflammatory cytokinesTNF-α and IL-1β (Zhang et al., 2016a). Curcumin, a natural antioxidant isolated from Curcuma longa, is a polyphenolic and a major active constituent of turmeric, which has been shown to be beneficial for neuroprotection in vivo and in vitro.

    View all citing articles on Scopus
    1

    These authors contributed equally to this work.

    2

    Conception and design

    3

    Analysis and interpretation.

    4

    Data collection.

    5

    Writing the article.

    6

    Critical revision of the article.

    7

    Obtaining funding.

    View full text