Inhibition of endogenous heat shock protein 70 attenuates inducible nitric oxide synthase induction via disruption of heat shock protein 70/Na(+) /H(+) exchanger 1-Ca(2+) -calcium-calmodulin-dependent protein kinase II/transforming growth factor β-activated kinase 1-nuclear factor-κB signals in BV-2 microglia

Wnt Pathway: An Emerging Player in Vascular and Traumatic Mediated Brain Injuries

The Wnt pathway, which comprises the canonical and non-canonical pathways, is an evolutionarily conserved mechanism that regulates crucial biological aspects throughout the development and adulthood. Emergence and patterning of the nervous and vascular systems are intimately coordinated, a process in which Wnt pathway plays particularly important roles. In the brain, Wnt ligands activate a cell-specific surface receptor complex to induce intracellular signaling cascades regulating neurogenesis, synaptogenesis, neuronal plasticity, synaptic plasticity, angiogenesis, vascular stabilization, and inflammation. The Wnt pathway is tightly regulated in the adult brain to maintain neurovascular functions. Historically, research in neuroscience has emphasized essentially on investigating the pathway in neurodegenerative disorders. Nonetheless, emerging findings have demonstrated that the pathway is deregulated in vascular- and traumatic-mediated brain injuries. These findings are suggesting that the pathway constitutes a promising target for the development of novel therapeutic protective and restorative interventions. Yet, targeting a complex multifunctional signal transduction pathway remains a major challenge. The review aims to summarize the current knowledge regarding the implication of Wnt pathway in the pathobiology of ischemic and hemorrhagic stroke, as well as traumatic brain injury (TBI). Furthermore, the review will present the strategies used so far to manipulate the pathway for therapeutic purposes as to highlight potential future directions.

Roles of glial ion transporters in brain diseases

Glial ion transporters are important in regulation of ionic homeostasis, cell volume, and cellular signal transduction under physiological conditions of the central nervous system (CNS). In response to acute or chronic brain injuries, these ion transporters can be activated and differentially regulate glial functions, which has subsequent impact on brain injury or tissue repair and functional recovery. In this review, we summarized the current knowledge about major glial ion transporters, including Na⁺ /H⁺ exchangers (NHE), Na⁺ /Ca²⁺ exchangers (NCX), Na⁺ -K⁺ -Cl^- cotransporters (NKCC), and Na⁺ -HCO₃ ^- cotransporters (NBC). In acute neurological diseases, such as ischemic stroke and traumatic brain injury (TBI), these ion transporters are rapidly activated and play significant roles in regulation of the intra- and extracellular pH, Na⁺ , K⁺ , and Ca²⁺ homeostasis, synaptic plasticity, and myelin formation. However, overstimulation of these ion transporters can contribute to glial apoptosis, demyelination, inflammation, and excitotoxicity. In chronic brain diseases, such as glioma, Alzheimer's disease (AD), Parkinson's disease (PD), and multiple sclerosis (MS), glial ion transporters are involved in the glioma Warburg effect, glial activation, neuroinflammation, and neuronal damages. These findings suggest that glial ion transporters are involved in tissue structural and functional restoration, or brain injury and neurological disease development and progression. A better understanding of these ion transporters in acute and chronic neurological diseases will provide insights for their potential as therapeutic targets.

Sulforaphane triggers a functional elongation of microglial process via the Akt signal

Microglia are a kind of innate immune cells in the nervous system. The amoeboid morphology in microglia indicates a pro-inflammatory status, while their ramified morphologies are associated with anti-neuroinflammation. Recently, we and others have reported that drugs that trigger microglial process elongation may be beneficial for neuroinflammation inhibition. In this study, we found that sulforaphane (SFN), a compound extracted from broccoli sprouts, promotes primary cultured microglial process elongation in both normal and pro-inflammatory conditions in a reversible manner. This pro-elongation effect of SFN was also observed in the prefrontal cortex in vivo and accompanied with an attenuation of pro-inflammatory response as well as an enhancement of anti-inflammatory response in primary cultured microglia. Mechanistic studies revealed that the SFN treatment increased Akt phosphorylation levels in primary cultured microglia and Akt inhibition blocked the effect of SFN on microglial process elongation, suggesting that the regulation of microglial process by SFN is mediated by Akt activation. Functional studies showed that Akt inhibition reversed the effect of SFN on both pro- and anti-inflammatory responses in lipopolysaccharide (LPS)-stimulated microglia. In an inflammation model in vivo, SFN pretreatment not only prevented LPS-induced retractions of microglial process in the prefrontal cortex, but improved LPS-induced behavioral abnormalities in mice, including the increase in immobility time in the tail suspension test and forced swim test as well as the decrease in sucrose preference. These results indicate that the SFN inhibits microglial activation and neuroinflammation-triggered behavioral abnormalities likely through triggering Akt-mediated microglial process elongation.

Regulation of microglial process elongation, a featured characteristic of microglial plasticity

Microglia, a type of glia within the brain characterized by a ramified morphology, are essential for removing neuronal debris and restricting the expansion of a lesion site. Upon moderate activation, they undergo a transformation in morphology inducing beneficial responses. However, upon strong stimulation, they mediate neuronal damage via production of pro-inflammatory cytokines. The inhibition of this cascade is considered an effective strategy for neuroinflammation-associated disorder therapy. During this pathological activation microglia also undergo a shortening of process length which contributes to the pathogenesis of such disorders. Thus, microglial plasticity should be considered to have two components: one is the production of inflammatory mediators, and the other is the dynamic changes in their processes. The former role has been well-documented in previous studies, while the latter one remains largely unknown. Recently, we and others have reported that the elongation of microglial process is associated with the transformation of microglia from a pro-inflammatory to an anti-inflammatory state, suggesting that the shortening of process length would make the microglia lose their ability to restrict pathological injury, while the elongation of microglial process would help attenuate neuroinflammation. Compared with the traditional anti-neuroinflammatory strategy, stimulating elongation of microglial process not only reduces the production of pro-inflammatory cytokines, but restores the ability of microglia to scan their surrounding environments, thus rendering their homeostasis regulation more effective. In this review, we provide a discussion of the factors that regulate microglial process elongation in vitro and in vivo, aiming to further drive the understanding of microglial process plasticity.

Pifithrin-μ modulates microglial activation and promotes histological recovery following spinal cord injury

BACKGROUND

Treatments immediately after spinal cord injury (SCI) are anticipated to decrease neuronal death, disruption of neuronal connections, demyelination, and inflammation, and to improve repair and functional recovery. Currently, little can be done to modify the acute phase, which extends to the first 48 hours post-injury. Efforts to intervene have focused on the subsequent phases - secondary (days to weeks) and chronic (months to years) - to both promote healing, prevent further damage, and support patients suffering from SCI.

METHODS

We used a contusion model of SCI in female mice, and delivered a small molecule reagent during the early phase of injury. Histological and behavioral outcomes were assessed and compared.

RESULTS

We find that the reagent Pifithrin-μ (PFT-μ) acts early and directly on microglia in vitro, attenuating their activation. When administered during the acute phase of SCI, PFT-μ resulted in reduced lesion size during the initial inflammatory phase, and reduced the numbers of pro-inflammatory microglia and macrophages. Treatment with PFT-μ during the early stage of injury maintained a stable anti-inflammatory environment.

CONCLUSIONS

Our results indicate that a small molecule reagent PFT-μ has sustained immunomodulatory effects following a single dose after injury.

Danger signals in stroke and their role on microglia activation after ischemia

Ischemic stroke is a major cause of death. Besides the direct damage resulting from oxygen and glucose deprivation, sterile inflammation plays a pivotal role in increasing cellular death. Damaged-associated molecular patterns (DAMPs) are passively released from dying cells and activate the innate immune system. Thus, they take part in the direct and rapid activation of the inflammatory response after stroke onset. In this review the role of the most important DAMPs, high mobility group box 1, heat and cold shock proteins, purines, and peroxiredoxins, are addressed. Moreover, intracellular pathways activated by DAMPs in microglia are illuminated.

Dihydrolipoic Acid Inhibits Lysosomal Rupture and NLRP3 Through Lysosome-Associated Membrane Protein-1/Calcium/Calmodulin-Dependent Protein Kinase II/TAK1 Pathways After Subarachnoid Hemorrhage in Rat

BACKGROUND AND PURPOSE

The NLRP3 (nucleotide binding and oligomerization domain-like receptor family pyrin domain-containing 3) inflammasome is a crucial component of the inflammatory response in early brain injury after subarachnoid hemorrhage (SAH). In this study, we investigated a role of dihydrolipoic acid (DHLA) in lysosomal rupture, NLRP3 activation, and determined the underlying pathway.

METHODS

SAH was induced by endovascular perforation in male Sprague-Dawley rats. DHLA was administered intraperitoneally 1 hour after SAH. Small interfering RNA for lysosome-associated membrane protein-1 and CaMKIIα (calcium/calmodulin-dependent protein kinase II α) was administered through intracerebroventricular 48 hours before SAH induction. SAH grade evaluation, short- and long-term neurological function testing, Western blot, and immunofluorescence staining experiments were performed.

RESULTS

DHLA treatment increased the expression of lysosome-associated membrane protein-1 and decreased phosphorylated CaMKIIα and NLRP3 inflammasome, thereby alleviating neurological deficits after SAH. Lysosome-associated membrane protein-1 small interfering RNA abolished the neuroprotective effects of DHLA and increased the level of phosphorylated CaMKIIα, p-TAK1 (phosphorylated transforming growth factor-β-activated kinase), p-JNK (phosphorylated c-Jun-N-terminal kinase), and NLRP3 inflammasome. CaMKIIα small interfering RNA downregulated the expression of p-TAK1, p-JNK, and NLRP3 and improved the neurobehavior after SAH.

CONCLUSIONS

DHLA treatment improved neurofunction and alleviated inflammation through the lysosome-associated membrane protein-1/CaMKII/TAK1 pathway in early brain injury after SAH. DHLA may provide a promising treatment to alleviate early brain injury after SAH.

Heat shock protein 70 suppresses neuroinflammation induced by α-synuclein in astrocytes

Neuroinflammation triggered by activation of glial cells plays an important role in the pathophysiology of several neurodegenerative diseases including Parkinson's disease (PD). Besides microglia, astrocytes are also critical in initiating and perpetuating inflammatory process associated with PD. Heat shock protein 70 (Hsp70) is originally described as intracellular chaperone, however, recent study revealed that it had anti-inflammatory effects as well. The present study is designed to investigate whether Hsp70 mediates neuroinflammation in astrocytes. By employing α-synuclein (α-Syn) (A53T) aggregates on primary cultured astrocytes of rats, we found that astrocytes were activated and neuroinflammatory response was triggered, as indicated by over-expression of glial fibrillary acidic protein (GFAP), cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS), increased production of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β). The data also showed that the neuroinflammatory response accompanied up-regulated Hsp70 expression. Moreover, over-expression of Hsp70 through transfection of Hsp70 cDNA plasmids could significantly reduce the production of TNF-α, IL-1β, and the expression of GFAP, COX-2 as well as iNOS. While inhibition of Hsp70 by VER155008 exacerbated neuroinflammatory response in astrocytes challenged by α-Syn aggregates. Further mechanistic study indicated that c-Jun N-terminal kinase (JNK) and nuclear factor-κB (NF-κB) signalings were responsible for the neuroinflammation, which was also regulated by Hsp70. These findings demonstrated that Hsp70 was an important modulator in astrocytes induced inflammation, and up-regulation of Hsp70 might be a potential regulating approach for neuroinflammation-related neurodegenerative diseases, such as PD.

Down-regulation of Na+/H+ exchanger 1 by Toll-like receptor stimulation in macrophages

The role of Na⁺/H⁺ exchanger 1 (NHE1) in various cell types, including inflammatory cells, has been extensively studied. However, regulation of NHE1 protein level in activated inflammatory cells is yet to be characterized. In this study, we investigated whether Toll-like receptor (TLR) ligands can regulate NHE1 protein level in the mouse macrophage-like RAW 264 cell line. We found that lipopolysaccharide (LPS), a TLR4 ligand, lowered NHE1 level and activity in RAW 264 cells and in primary murine macrophages. Other TLR ligands, such as zymosan A and poly(I:C), also displayed reduced NHE1 level. LPS promoted NHE1 ubiquitination and reduced the expression of calcineurin homologous protein 1 (CHP1), a regulator of NHE1 activity and stability. These responses were inhibited by c-Jun N-terminal kinase (JNK) inhibitor SP600125 and dexamethasone. A proteasome inhibitor, but not caspase-3 or lysosomal inhibitors, blocked the LPS-induced NHE1 down-regulation. These results suggested that LPS promotes the degranulation of NHE1 mediated by the ubiquitin-proteasome system and CHP1 downregulation resulting from activation of JNK.

Glioma-mediated microglial activation promotes glioma proliferation and migration: roles of Na+/H+ exchanger isoform 1

Microglia play important roles in extracellular matrix remodeling, tumor invasion, angiogenesis, and suppression of adaptive immunity in glioma. Na(+)/H(+) exchanger isoform 1 (NHE1) regulates microglial activation and migration. However, little is known about the roles of NHE1 in intratumoral microglial activation and microglia-glioma interactions. Our study revealed up-regulation of NHE1 protein expression in both glioma cells and tumor-associated Iba1(+) microglia in glioma xenografts and glioblastoma multiforme microarrays. Moreover, we observed positive correlation of NHE1 expression with Iba1 intensity in microglia/macrophages. Glioma cells, via conditioned medium or non-contact glioma-microglia co-cultures, concurrently upregulated microglial expression of NHE1 protein and other microglial activation markers (iNOS, arginase-1, TGF-β, IL-6, IL-10 and the matrix metalloproteinases MT1-MMP and MMP9). Interestingly, glioma-stimulated microglia reciprocally enhanced glioma proliferation and migration. Most importantly, inhibition of microglial NHE1 activity via small interfering RNA (siRNA) knockdown or the potent NHE1-specific inhibitor HOE642 significantly attenuated microglial activation and abolished microglia-stimulated glioma migration and proliferation. Taken together, our findings provide the first evidence that NHE1 function plays an important role in glioma-microglia interactions, enhancing glioma proliferation and invasion by stimulating microglial release of soluble factors. NHE1 upregulation is a novel marker of the glioma-associated microglial activation phenotype. Inhibition of NHE1 represents a novel glioma therapeutic strategy by targeting tumor-induced microglial activation.

Requirement for endogenous heat shock factor 1 in inducible nitric oxide synthase induction in murine microglia

Background

Inducible nitric oxide synthase (iNOS) makes a great contribution to host defense and inflammation. In many settings, lipopolysaccharide (LPS) induces iNOS expression through activation of the inhibitor of κB-α (IκB-α)-nuclear factor-κB (NF-κB) cascade, whereas interferon-γ (IFN-γ) acts through Janus kinase (JAK)-signal transducer and activator of transcription 1 (STAT1) signals. Heat shock factor 1 (HSF1), a major regulator of heat shock protein transcription, has been shown to regulate the production of pro-inflammatory cytokines such as tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6), but it remains obscure whether and how HSF1 affects iNOS induction.

Methods

Western blot was used to measure the protein expression. The mRNA level was measured by real-time PCR. Silence of HSF1 was achieved by small interfering RNA. Nitric oxide (NO) content and NF-κB binding activity were assayed by commercial kits. Chromatin immunoprecipitation (ChIP) was used to measure the binding activity of NF-κB and STAT1 to iNOS promoters.

Results

HSF1 inhibition or knockdown prevented the LPS- and/or IFN-γ-stimulated iNOS protein expression in cultured microglia. HSF1 inhibition blocked iNOS mRNA transcription. These inhibitory effects of HSF1 inhibition on iNOS expression were confirmed in brain tissues from endotoxemic mice. Further analysis showed that HSF1 inhibition had no effect on IκB-α degradation and NF-κB or STAT1 phosphorylation in LPS/IFN-γ-stimulated cells. The nuclear transport of active NF-κB or STAT1 was also not affected by HSF1 inhibition, but HSF1 inhibition reduced the binding of NF-κB and STAT1 to their DNA elements. In addition, HSF1 inhibition reduced NF-κB and STAT1 bindings to iNOS promoter inside the LPS/IFN-γ-stimulated cells.

Conclusions

This preventing effect of HSF1 inhibition on iNOS mRNA transcription presents the necessary role of HSF1 in iNOS induction.