Extracellular regulated kinase 1/2 signaling is a critical regulator of interleukin-1β-mediated astrocyte tissue inhibitor of metalloproteinase-1 expression

C/EBPβ: A transcription factor associated with the irreversible progression of Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is a neurodegenerative disorder distinguished by a swift cognitive deterioration accompanied by distinctive pathological hallmarks such as extracellular Aβ (β-amyloid) peptides, neuronal neurofibrillary tangles (NFTs), sustained neuroinflammation, and synaptic degeneration. The elevated frequency of AD cases and its proclivity to manifest at a younger age present a pressing challenge in the quest for novel therapeutic interventions. Numerous investigations have substantiated the involvement of C/EBPβ in the progression of AD pathology, thus indicating its potential as a therapeutic target for AD treatment.

AIMS

Several studies have demonstrated an elevation in the expression level of C/EBPβ among individuals afflicted with AD. Consequently, this review predominantly delves into the association between C/EBPβ expression and the pathological progression of Alzheimer's disease, elucidating its underlying molecular mechanism, and pointing out the possibility that C/EBPβ can be a new therapeutic target for AD.

METHODS

A systematic literature search was performed across multiple databases, including PubMed, Google Scholar, and so on, utilizing predetermined keywords and MeSH terms, without temporal constraints. The inclusion criteria encompassed diverse study designs, such as experimental, case-control, and cohort studies, restricted to publications in the English language, while conference abstracts and unpublished sources were excluded.

RESULTS

Overexpression of C/EBPβ exacerbates the pathological features of AD, primarily by promoting neuroinflammation and mediating the transcriptional regulation of key molecular pathways, including δ-secretase, apolipoprotein E4 (APOE4), acidic leucine-rich nuclear phosphoprotein-32A (ANP32A), transient receptor potential channel 1 (TRPC1), and Forkhead BoxO (FOXO).

DISCUSSION

The correlation between overexpression of C/EBPβ and the pathological development of AD, along with its molecular mechanisms, is evident. Investigating the pathways through which C/EBPβ regulates the development of AD reveals numerous multiple vicious cycle pathways exacerbating the pathological progression of the disease. Furthermore, the exacerbation of pathological progression due to C/EBPβ overexpression and its molecular mechanism is not limited to AD but also extends to other neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS), Parkinson's disease (PD), and multiple sclerosis (MS).

CONCLUSION

The overexpression of C/EBPβ accelerates the irreversible progression of AD pathophysiology. Additionally, C/EBPβ plays a crucial role in mediating multiple pathways linked to AD pathology, some of which engender vicious cycles, leading to the establishment of feedback mechanisms. To sum up, targeting C/EBPβ could hold promise as a therapeutic strategy not only for AD but also for other degenerative diseases.

Cognitive Deficits Found in a Pro-inflammatory State are Independent of ERK1/2 Signaling in the Murine Brain Hippocampus Treated with Shiga Toxin 2 from Enterohemorrhagic Escherichia coli

Shiga toxin 2 (Stx2) from enterohemorrhagic Escherichia coli (EHEC) produces hemorrhagic colitis, hemolytic uremic syndrome (HUS), and acute encephalopathy. The mortality rate in HUS increases significantly when the central nervous system (CNS) is involved. Besides, EHEC also releases lipopolysaccharide (LPS). Many reports have described cognitive dysfunctions in HUS patients, the hippocampus being one of the brain areas targeted by EHEC infection. In this context, a translational murine model of encephalopathy was employed to establish the deleterious effects of Stx2 and the contribution of LPS in the hippocampus. The purpose of this work is to elucidate the signaling pathways that may activate the inflammatory processes triggered by Stx2, which produces cognitive alterations at the level of the hippocampus. Results demonstrate that Stx2 produced depression-like behavior, pro-inflammatory cytokine release, and NF-kB activation independent of the ERK1/2 signaling pathway, while co-administration of Stx2 and LPS reduced memory index. On the other hand, LPS activated NF-kB dependent on ERK1/2 signaling pathway. Cotreatment of Stx2 with LPS aggravated the pathologic state, while dexamethasone treatment succeeded in preventing behavioral alterations. Our present work suggests that the use of drugs such as corticosteroids or NF-kB signaling inhibitors may serve as neuroprotectors from EHEC infection.

Covid-19 interface with drug misuse and substance use disorders

The coronavirus disease 2019 (Covid-19) pandemic intensified the already catastrophic drug overdose and substance use disorder (SUD) epidemic, signaling a syndemic as social isolation, economic and mental health distress, and disrupted treatment services disproportionally impacted this vulnerable population. Along with these social and societal factors, biological factors triggered by intense stress intertwined with incumbent overactivity of the immune system and the resulting inflammatory outcomes may impact the functional status of the central nervous system (CNS). We review the literature concerning SARS-CoV2 infiltration and infection in the CNS and the prospects of synergy between stress, inflammation, and kynurenine pathway function during illness and recovery from Covid-19. Taken together, inflammation and neuroimmune signaling, a consequence of Covid-19 infection, may dysregulate critical pathways and underlie maladaptive changes in the CNS, to exacerbate the development of neuropsychiatric symptoms and in the vulnerability to develop SUD. This article is part of the special Issue on 'Vulnerabilities to Substance Abuse'.

Inhibition of extracellular regulated kinase (ERK)-1/2 signaling pathway in the prevention of ALS: Target inhibitors and influences on neurological dysfunctions

Cell signal transduction pathways are essential modulators of several physiological and pathological processes in the brain. During overactivation, these signaling processes may lead to disease progression. Abnormal protein kinase activation is associated with several biological dysfunctions that facilitate neurodegeneration under different biological conditions. As a result, these signaling pathways are essential in understanding brain disorders' development or progression. Recent research findings indicate the crucial role of extracellular signal-regulated kinase-1/2 (ERK-1/2) signaling during the neuronal development process. ERK-1/2 is a key component of its mitogen-activated protein kinase (MAPK) group, controlling certain neurological activities by regulating metabolic pathways, cell proliferation, differentiation, and apoptosis. ERK-1/2 also influences neuronal elastic properties, nerve growth, and neurological and cognitive processing during brain injuries. The primary goal of this review is to elucidate the activation of ERK1/2 signaling, which is involved in the development of several ALS-related neuropathological dysfunctions. ALS is a rare neurological disorder category that mainly affects the nerve cells responsible for regulating voluntary muscle activity. ALS is progressive, which means that the symptoms are getting worse over time, and there is no cure for ALS and no effective treatment to avoid or reverse. Genetic abnormalities, oligodendrocyte degradation, glial overactivation, and immune deregulation are associated with ALS progression. Furthermore, the current review also identifies ERK-1/2 signaling inhibitors that can promote neuroprotection and neurotrophic effects against the clinical-pathological presentation of ALS. As a result, in the future, the potential ERK-1/2 signaling inhibitors could be used in the treatment of ALS and related neurocomplications.

Effects of innate immune receptor stimulation on extracellular α-synuclein uptake and degradation by brain resident cells

Synucleinopathies are age-related neurological disorders characterized by the progressive deposition of α-synuclein (α-syn) aggregates and include Parkinson’s disease (PD) and dementia with Lewy bodies (DLB). Although cell-to-cell α-syn transmission is thought to play a key role in the spread of α-syn pathology, the detailed mechanism is still unknown. Neuroinflammation is another key pathological feature of synucleinopathies. Previous studies have identified several immune receptors that mediate neuroinflammation in synucleinopathies, such as Toll-like receptor 2 (TLR2). However, the species of α-syn aggregates varies from study to study, and how different α-syn aggregate species interact with innate immune receptors has yet to be addressed. Therefore, we investigated whether innate immune receptors can facilitate the uptake of different species of α-syn aggregates. Here, we examined whether stimulation of TLRs could modulate the cellular uptake and degradation of α-syn fibrils despite a lack of direct interaction. We observed that stimulation of TLR2 in vitro accelerated α-syn fibril uptake in neurons and glia while delaying the degradation of α-syn in neurons and astrocytes. Internalized α-syn was rapidly degraded in microglia regardless of whether TLR2 was stimulated. However, cellular α-syn uptake and degradation kinetics were not altered by TLR4 stimulation. In addition, upregulation of TLR2 expression in a synucleinopathy mouse model increased the density of Lewy-body-like inclusions and induced morphological changes in microglia. Together, these results suggest that cell type-specific modulation of TLR2 may be a multifaceted and promising therapeutic strategy for synucleinopathies; inhibition of neuronal and astroglial TLR2 decreases pathogenic α-syn transmission, but activation of microglial TLR2 enhances microglial extracellular α-syn clearance.

New treatments for neurological disorders could target immune receptors associated with the build-up of protein aggregates in neurons. Synucleinopathies are characterized by abnormal deposition of α-synuclein, but the mechanism how α-synuclein spreads between cells is still elusive. Changyoun Kim and Eliezer Masliah at the National Institutes of Health in Bethesda, USA, and co-workers investigated indirect role of TLR2 in α-synuclein spreading. TLR2 has been known to interact with β-sheet-enriched oligomeric forms of α-synuclein, but not with fibrilar forms of α-synuclein (fibril). Herein, the authors found that TLR2 stimulation accelerated the uptake of fibrils in both neurons and glial cells, delayed degradation of internalized fibrils and worsen α-synuclein pathology in mouse brains. The study provides indirect modulation of α-synuclein spearding via innate immune receptor which might be a potential therapy for synucleinopathies.

LPS stimulation during HCV infection induces MMP/TIMP1 imbalance in macrophages

Introduction. During chronic hepatitis C virus (HCV) infections, HCV antigens establish cross-tolerance of endotoxins, but additional lipopolysaccharide (LPS) stimulation effects in this condition are poorly understood.Aim. This study aims to investigate the effects of the upregulated LPS on MMP and TIMP expression during chronic hepatitis C infection.Methodology. In the present study, we analysed the effect of HCV antigens and LPS stimulation on peripheral blood mononuclear cells (PBMCs) both in vivo and in vitro. Macrophages from HCV patients were isolated and their association with endotoxin tolerance was examined. MMP/TIMP1 expression and the related signalling pathways in macrophages were analysed. The macrophage and Huh7.5 cell co-culture model was used to analyse the effects of the cross-tolerance on collagen I deposition.Results. LPS levels were found to be significantly higher in HCV patients, particularly in those with HCV-induced liver fibrosis. In addition, although LPS serum level was occasionally upregulated in the patients, it did not induce intense immune response in PBMCs due to endotoxin cross-tolerance, and this was measured according to the changes in IL-6 and TNF-α levels. However, TIMP1 expression increased significantly during stimulation, exhibiting a tolerance/resistance phenotype, which was associated with TGF-β/Erk activation in macrophages. However, MMP levels did not increase due to endotoxin tolerance, which ultimately led to MMP/TIMP imbalance and influenced the deposition of collagen I.Conclusion. Increased LPS stimulation of macrophage during HCV antigen-induced endotoxin cross-tolerance contributes to MMP/TIMP1 imbalance and collagen I deposition.

Immunotherapy targeting toll-like receptor 2 alleviates neurodegeneration in models of synucleinopathy by modulating α-synuclein transmission and neuroinflammation

BACKGROUND

Synucleinopathies of the aging population are an heterogeneous group of neurological disorders that includes Parkinson's disease (PD) and dementia with Lewy bodies (DLB) and are characterized by the progressive accumulation of α-synuclein in neuronal and glial cells. Toll-like receptor 2 (TLR2), a pattern recognition immune receptor, has been implicated in the pathogenesis of synucleinopathies because TLR2 is elevated in the brains of patients with PD and TLR2 is a mediator of the neurotoxic and pro-inflammatory effects of extracellular α-synuclein aggregates. Therefore, blocking TLR2 might alleviate α-synuclein pathological and functional effects. For this purpose, herein, we targeted TLR2 using a functional inhibitory antibody (anti-TLR2).

METHODS

Two different human α-synuclein overexpressing transgenic mice were used in this study. α-synuclein low expresser mouse (α-syn-tg, under the PDGFβ promoter, D line) was stereotaxically injected with TLR2 overexpressing lentivirus to demonstrate that increment of TLR2 expression triggers neurotoxicity and neuroinflammation. α-synuclein high expresser mouse (α-Syn-tg; under mThy1 promoter, Line 61) was administrated with anti-TLR2 to examine that functional inhibition of TLR2 ameliorates neuropathology and behavioral defect in the synucleinopathy animal model. In vitro α-synuclein transmission live cell monitoring system was used to evaluate the role of TLR2 in α-synuclein cell-to-cell transmission.

RESULTS

We demonstrated that administration of anti-TLR2 alleviated α-synuclein accumulation in neuronal and astroglial cells, neuroinflammation, neurodegeneration, and behavioral deficits in an α-synuclein tg mouse model of PD/DLB. Moreover, in vitro studies with neuronal and astroglial cells showed that the neuroprotective effects of anti-TLR2 antibody were mediated by blocking the neuron-to-neuron and neuron-to-astrocyte α-synuclein transmission which otherwise promotes NFκB dependent pro-inflammatory responses.

CONCLUSION

This study proposes TLR2 immunotherapy as a novel therapeutic strategy for synucleinopathies of the aging population.

RAD51 inhibition in triple negative breast cancer cells is challenged by compensatory survival signaling and requires rational combination therapy

The molecular rationale to induce synthetic lethality, by targeting defective homologous recombination repair in triple negative breast cancer (TNBC), has proven to have several shortcomings. Not meeting the expected minimal outcomes in clinical trials has highlighted common clinical resistance mechanisms including; increased expression of the target gene PARP1, increased expression or reversion mutation of BRCA1, or up-regulation of the compensatory homologous recombination protein RAD51. Indeed, RAD51 has been demonstrated to be an alternative synthetic lethal target in BRCA1-mutated cancers. To overcome selective pressure on DNA repair pathways, we examined new potential targets within TNBC that demonstrate synthetic lethality in association with RAD51 depletion. We confirmed complementary targets of PARP1/2 and DNA-PK as well as a new synthetic lethality combination with p38. p38 is considered a relevant target in breast cancer, as it has been implicated in resistance to chemotherapy, including tamoxifen. We show that the combination of targeting RAD51 and p38 inhibits cell proliferation both in vitro and in vivo, which was further enhanced by targeting of PARP1. Analysis of the molecular mechanisms revealed that depletion of RAD51 increased ERK1/2 and p38 signaling. Our results highlight a potential compensatory mechanism via p38 that limits DNA targeted therapy.

IL-1β Inhibits Connexin 43 and Disrupts Decidualization of Human Endometrial Stromal Cells Through ERK1/2 and p38 MAP Kinase

Inflammation can interfere with endometrial receptivity. We examined how interleukin 1β (IL-1β) affects expression of the uterine gap junction protein connexin 43 (Cx43), which is known to be critical for embryonic implantation. We used an in vitro model of human endometrial stromal cells (ESCs), Western blotting, and a combination of validated, selective kinase inhibitors to evaluate five canonical IL-1β signaling pathways. Cx43 and two other markers of ESC differentiation (prolactin and VEGF) were inhibited predominantly via IL-1β-activated ERK1/2 and p38 MAP kinase cascades. The findings were corroborated using small interfering RNA to silence critical genes in either pathway. By contrast, upregulation of endogenous pro-IL-1α and pro-IL-1β following recombinant IL-1β treatment was mediated via the Jun N-terminal kinase pathway. The clinicopharmacological significance of our findings is that multiple signaling cascades may need to be neutralized to reverse deleterious effects of IL-1β on human endometrial function.

The extracellular signal-regulated kinase 1/2 pathway in neurological diseases: A potential therapeutic target (Review)

Signaling pathways are critical modulators of a variety of physiological and pathological processes, and the abnormal activation of some signaling pathways can contribute to disease progression in various conditions. As a result, signaling pathways have emerged as an important tool through which the occurrence and development of diseases can be studied, which may then lead to the development of novel drugs. Accumulating evidence supports a key role for extracellular signal-regulated kinase 1/2 (ERK1/2) signaling in the embryonic development of the central nervous system (CNS) and in the regulation of adult brain function. ERK1/2, one of the most well characterized members of the mitogen-activated protein kinase family, regulates a range of processes, from metabolism, motility and inflammation, to cell death and survival. In the nervous system, ERK1/2 regulates synaptic plasticity, brain development and repair as well as memory formation. ERK1/2 is also a potent effector of neuronal death and neuroinflammation in many CNS diseases. This review summarizes recent findings in neurobiological ERK1/2 research, with a special emphasis on findings that clarify our understanding of the processes that regulate the plethora of isoform-specific ERK functions under physiological and pathological conditions. Finally, we suggest some potential therapeutic strategies associated with agents acting on the ERK1/2 signaling to prevent or treat neurological diseases.

Novel Antitumor Invasive Actions of p-Cymene by Decreasing MMP-9/TIMP-1 Expression Ratio in Human Fibrosarcoma HT-1080 Cells

p-Cymene (4-isopropyltoluene) has been reported to have beneficial actions such as anti-inflammatory and antinociceptive activities. To evaluate whether p-cymene exhibits antitumor invasive actions, we examined the effects of p-cymene on the production of matrix metalloproteinase 9 (MMP-9)/gelatinase B and tissue inhibitor of metalloproteinases-1 (TIMP-1) in human fibrosarcoma HT-1080 cells. p-Cymene was found to dose-dependently inhibit the 12-O-tetradecanoylphorbol 13-acetate (TPA)-augmented production and gene expression of MMP-9 in HT-1080 cells. In contrast, p-cymene enhanced the TPA-augmented production and gene expression of TIMP-1 in HT-1080 cells. However, there was no change in the constitutive level of MMP-9 and TIMP-1 mRNAs and TIMP-1 protein in p-cymene-treated cells. In addition, we found that the in-vitro TPA-augmented invasiveness of HT-1080 cells was inhibited by p-cymene in a dose-dependent manner. Furthermore, p-cymene was found to suppress the constitutive and/or TPA-augmented phosphorylation of extracellular signal-regulated kinase (ERK)1/2 and p38 mitogen-activated protein kinase (MAPK) in HT-1080 cells. Thus, these results provide novel evidence that p-cymene is an effective candidate for the prevention of tumor invasion and metastasis through mechanisms that include the inhibition of MMP-9 expression and the augmentation of TIMP-1 production along with the suppression of ERK1/2 and p38 MAPK signal pathways in tumor cells.

HIV-1, methamphetamine and astrocytes at neuroinflammatory Crossroads

As a popular psychostimulant, methamphetamine (METH) use leads to long-lasting, strong euphoric effects. While METH abuse is common in the general population, between 10 and 15% of human immunodeficiency virus-1 (HIV-1) patients report having abused METH. METH exacerbates the severity and onset of HIV-1-associated neurocognitive disorders (HAND) through direct and indirect mechanisms. Repetitive METH use impedes adherence to antiretroviral drug regimens, increasing the likelihood of HIV-1 disease progression toward AIDS. METH exposure also directly affects both innate and adaptive immunity, altering lymphocyte numbers and activity, cytokine signaling, phagocytic function and infiltration through the blood brain barrier. Further, METH triggers the dopamine reward pathway and leads to impaired neuronal activity and direct toxicity. Concurrently, METH and HIV-1 alter the neuroimmune balance and induce neuroinflammation, which modulates a wide range of brain functions including neuronal signaling and activity, glial activation, viral infection, oxidative stress, and excitotoxicity. Pathologically, reactive gliosis is a hallmark of both HIV-1- and METH-associated neuroinflammation. Significant commonality exists in the neurotoxic mechanisms for both METH and HAND; however, the pathways dysregulated in astroglia during METH exposure are less clear. Thus, this review highlights alterations in astrocyte intracellular signaling pathways, gene expression and function during METH and HIV-1 comorbidity, with special emphasis on HAND-associated neuroinflammation. Importantly, this review carefully evaluates interventions targeting astrocytes in HAND and METH as potential novel therapeutic approaches. This comprehensive overview indicates, without a doubt, that during HIV-1 infection and METH abuse, a complex dialog between all neural cells is orchestrated through astrocyte regulated neuroinflammation.

C/EBPβ and C/EBPδ transcription factors: Basic biology and roles in the CNS

CCAAT/enhancer binding protein (C/EBP) β and C/EBPδ are transcription factors of the basic-leucine zipper class which share phylogenetic, structural and functional features. In this review we first describe in depth their basic molecular biology which includes fascinating aspects such as the regulated use of alternative initiation codons in the C/EBPβ mRNA. The physical interactions with multiple transcription factors which greatly opens the number of potentially regulated genes or the presence of at least five different types of post-translational modifications are also remarkable molecular mechanisms that modulate C/EBPβ and C/EBPδ function. In the second part, we review the present knowledge on the localization, expression changes and physiological roles of C/EBPβ and C/EBPδ in neurons, astrocytes and microglia. We conclude that C/EBPβ and C/EBPδ share two unique features related to their role in the CNS: whereas in neurons they participate in memory formation and synaptic plasticity, in glial cells they regulate the pro-inflammatory program. Because of their role in neuroinflammation, C/EBPβ and C/EBPδ in microglia are potential targets for treatment of neurodegenerative disorders. Any strategy to reduce C/EBPβ and C/EBPδ activity in neuroinflammation needs to take into account its potential side-effects in neurons. Therefore, cell-specific treatments will be required for the successful application of this strategy.

Golgin-84-associated Golgi fragmentation triggers tau hyperphosphorylation by activation of cyclin-dependent kinase-5 and extracellular signal-regulated kinase

Tau hyperphosphorylation is a critical event in Alzheimer's disease, in which the neuronal Golgi fragmentation occurs earlier than tau hyperphosphorylation. However, the intrinsic link between Golgi impairment and tau pathology is missing. By electron microscopy and western blotting, we observed in the present study that the neuronal Golgi fragmentation was increased age-dependently with a correlated tau hyperphosphorylation in the brains of C57BL/6 mice aged from 4 to 16 months. Simultaneously, golgin-84 and Golgi reassembly stacking protein 65, 2 important Golgi matrix proteins, were decreased in the brains of elder mice. Further studies in HEK293/tau cells showed that Golgi-disturbing agents, brefeldin A and nocodazole induced tau hyperphosphorylation. Knockdown of golgin-84, not Golgi reassembly stacking protein 65, by small interfering RNA was sufficient to induce tau hyperphosphorylation, while over-expressing golgin-84 arrested the brefeldin A-induced Golgi fragmentation and tau hyperphosphorylation. Finally, we demonstrated that cyclin-dependent kinase-5 and extracellular signal-regulated kinase were activated after golgin-84 knockdown, and simultaneous inhibition of these kinases abolished the golgin-84 deficit-induced tau hyperphosphorylation. These data suggest Golgi fragmentation could be an upstream event triggering tau hyperphosphorylation through golgin-84 deficit-induced activation of cyclin-dependent kinase-5 and extracellular signal-regulated kinase.

Baicalein inhibits the invasion and metastatic capabilities of hepatocellular carcinoma cells via down-regulation of the ERK pathway

Baicalein, a widely used Chinese herbal medicine, has historically been used in anti-inflammatory and anti-cancer therapies. However, the anti-metastatic effect and molecular mechanism(s) of baicalein on hepatocellular carcinoma (HCC) remain poorly understood. Therefore, the purpose of this study was to assess the anti-metastatic effects of baicalein and related mechanism(s) on HCC. Based on assays utilized in both HCC cell lines and in an animal model, we found that baicalein inhibited tumor cell metastasis in vivo and in vitro. Furthermore, after treatment with baicalein for 24 hours, there was a decrease in the levels of matrix metalloproteinase-2 (MMP-2), MMP-9 and urokinase-type plasminogen activator (u-PA) expression as well as proteinase activity in hepatocellular carcinoma MHCC97H cells. Meanwhile, the expression of tissue inhibitor of metalloproteinase-1 (TIMP-1) and TIMP-2 were increased in a dose-dependent fashion. Moreover, baicalein treatment dramatically decreased the levels of the phosphorylated forms of MEK1 and ERK1/2. MEK1 overexpression partially blocked the anti-metastatic effects of baicalein. Combined treatment with an ERK inhibitor (U0126) and baicalein resulted in a synergistic reduction in MMP-2, MMP-9 and u-PA expression and an increase in TIMP-1 and TIMP-2 expression; the invasive capabilities of MHCC97H cells were also inhibited. In conclusion, baicalein inhibits tumor cell invasion and metastasis by reducing cell motility and migration via the suppression of the ERK pathway, suggesting that baicalein is a potential therapeutic agent for HCC.

Astrocyte regulation of CNS inflammation and remyelination

Astrocytes regulate fundamentally important functions to maintain central nervous system (CNS) homeostasis. Altered astrocytic function is now recognized as a primary contributing factor to an increasing number of neurological diseases. In this review, we provide an overview of our rapidly developing understanding of the basal and inflammatory functions of astrocytes as mediators of CNS responsiveness to inflammation and injury. Specifically, we elaborate on ways that astrocytes actively participate in the pathogenesis of demyelinating diseases of the CNS through their immunomodulatory roles as CNS antigen presenting cells, modulators of blood brain barrier function and as a source of chemokines and cytokines. We also outline how changes in the extracellular matrix can modulate astrocytes phenotypically, resulting in dysregulation of astrocytic responses during inflammatory injury. We also relate recent studies describing newly identified roles for astrocytes in leukodystrophies. Finally, we describe recent advances in how adapting this increasing breadth of knowledge on astrocytes has fostered new ways of thinking about human diseases, which offer potential to modulate astrocytic heterogeneity and plasticity towards therapeutic gain. In summary, recent studies have provided improved insight in a wide variety of neuroinflammatory and demyelinating diseases, and future research on astrocyte pathophysiology is expected to provide new perspectives on these diseases, for which new treatment modalities are increasingly necessary.

C/EBPβ regulates multiple IL-1β-induced human astrocyte inflammatory genes

Background

CCAAT enhancer-binding protein (C/EBP)β regulates gene expression in multiple organ systems and cell types, including astrocytes in the central nervous system (CNS). Inflammatory stimuli, interleukin (IL)-1β, tumor necrosis factor-α, human immunodeficiency virus (HIV)-1 and lipopolysaccharide induce astrocyte C/EBPβ expression. C/EBPβ is detectable in brains of Alzheimer’s disease (AD), Parkinson’s disease (PD) and HIV-1-associated dementia (HAD) patients, yet little is known about how C/EBPβ contributes to astrocyte gene regulation during neuroinflammation.

Methods

The expression of 92 human inflammation genes was compared between IL-1β-treated primary human astrocytes and astrocytes transfected with C/EBPβ-specific small interfering (si)RNA prior to IL-1β treatment for 12 h. Transcripts altered by > two-fold compared to control were subjected to one-way analysis of variance and Newman-Keuls post-test for multiple comparisons. Expression of two genes, cyclooxygenase-2 (COX-2) and bradykinin receptor B2 (BDKRB2) was further confirmed in additional human astrocyte donors. Astrocytes were treated with mitogen-activated protein kinase-selective inhibitors, then with IL-1β for 12 or 24 h followed by COX-2 and BDKRB2, expression analyses.

Results

IL-1β altered expression of 29 of 92 human inflammation genes by at least two-fold in primary human astrocytes in 12 h. C/EBPβ knockdown affected expression of 17 out of 29 IL-1β-regulated genes by > 25%. Two genes relevant to neuroinflammation, COX-2 and BDKRB2, were robustly decreased and increased, respectively, in response to C/EBPβ knockdown, and expression was confirmed in two additional donors. COX-2 and BDKRB2 mRNA remained altered in siRNA-transfected astrocytes at 12, 24 or 72 h. Inhibiting p38 kinase (p38K) activation blocked IL-1β-induced astrocyte COX-2 mRNA and protein expression, but not IL-1β-induced astrocyte BDKRB2 expression. Inhibiting extracellular-regulated kinase (ERK)1/2 activation blocked IL-1β-induced BDKRB2 mRNA expression while increasing COX-2 expression.

Conclusion

These data support an essential role for IL-1β in the CNS and identify new C/EBPβ functions in astrocytes. Additionally, this work suggests p38K and ERK1/2 pathways may regulate gene expression in a complementary manner to fine tune the IL-1β-mediated astrocyte inflammatory response. Delineating a role for C/EBPβ and other involved transcription factors in human astrocyte inflammatory response may lead to effective therapies for AD, PD, HAD and other neurological disorders.