MAPK-activated Protein Kinase 2 Deficiency in Microglia Inhibits Pro-inflammatory Mediator Release and Resultant Neurotoxicity

Hyperosmotic Stress Induces Inflammation and Excessive Th17 Response to Blunt T-Cell Immunity in Tilapia

Despite the advances in study on osmotic physiology in bony fish, the mechanism by which the immune system, especially T-cell immunity, adapts and responds to osmotic stress remains unknown. In the current study, we investigated the response of T cells to hyperosmotic stress in the bony fish Nile tilapia (Oreochromis niloticus). As a euryhaline fish, tilapia was able to adapt to a wide range of salinities; however, hypertonic stress caused inflammation and excessive T-cell activation. Furthermore, hypertonic stress increased the expression of IL-17A in T cells, upregulated the transcription factor RORα, and activated STAT3 signaling, along with IL-6- and TGF-β1-mediated pathways, revealing an enhanced Th17 response in this early vertebrate. These hypertonic stress-induced events collectively resulted in an impaired antibacterial immune response in tilapia. Hypertonic stress elevated the intracellular ROS level, which in turn activated the p38-MK2 signaling pathway to promote IL-17A production by T cells. Both ROS elimination and the p38-MK2 axis blockade diminished the increased IL-17A production in T cells under hypertonic conditions. Moreover, the produced proinflammatory cytokines further amplified the hypertonic stress signaling via the MKK6-p38-MK2 axis-mediated positive feedback loop. To our knowledge, these findings represent the first description of the mechanism by which T-cell immunity responds to hypertonic stress in early vertebrates, thus providing a novel perspective for understanding the adaptive evolution of T cells under environmental stress.

Mag-Net: Rapid enrichment of membrane-bound particles enables high coverage quantitative analysis of the plasma proteome

Membrane-bound particles in plasma are composed of exosomes, microvesicles, and apoptotic bodies and represent ~1-2% of the total protein composition. Proteomic interrogation of this subset of plasma proteins augments the representation of tissue-specific proteins, representing a "liquid biopsy," while enabling the detection of proteins that would otherwise be beyond the dynamic range of liquid chromatography-tandem mass spectrometry of unfractionated plasma. We have developed an enrichment strategy (Mag-Net) using hyper-porous strong-anion exchange magnetic microparticles to sieve membrane-bound particles from plasma. The Mag-Net method is robust, reproducible, inexpensive, and requires <100 μL plasma input. Coupled to a quantitative data-independent mass spectrometry analytical strategy, we demonstrate that we can collect results for >37,000 peptides from >4,000 plasma proteins with high precision. Using this analytical pipeline on a small cohort of patients with neurodegenerative disease and healthy age-matched controls, we discovered 204 proteins that differentiate (q-value < 0.05) patients with Alzheimer's disease dementia (ADD) from those without ADD. Our method also discovered 310 proteins that were different between Parkinson's disease and those with either ADD or healthy cognitively normal individuals. Using machine learning we were able to distinguish between ADD and not ADD with a mean ROC AUC = 0.98 ± 0.06.

The effects of urolithin A on poly I:C-induced microglial activation

Neuroinflammation can be triggered by various stimuli, including viral infections. Viruses can directly invade the brain and infect neuronal cells or indirectly trigger a "cytokine storm" in the periphery that eventually leads to microglial activation in the brain. While this initial activation of microglial cells is important for viral clearance, chronic activation leads to excessive inflammation and oxidative stress, which can be neurotoxic. Remarkebly, recent studies have shown that certain viruses such as influenza A virus, coronavirus, herpes virus and Epstein-Barr virus may be involved in the development of neurodegenerative diseases such as Parkinson's disease, Alzheimer's disease, and multiple sclerosis. Therefore, it is important to find therapeutic strategies against chronic neuroinflammation triggered by viral infections. Here, we investigated the effects of urolithin A (UA) on microglial activation in vitro induced by a viral mimetic, poly I:C, in a triple co-culture system of neurons, astrocytes and microglial cells. Immunocytochemistry was used to perform a comprehensive single-cell analysis of the morphological changes of microglia as an indicator of their reactive state. Treatment with UA significantly prevented the poly I:C-induced reactive state of microglia, which was characterized by increased expression of the microglial activation markers CD68 and IBA-1. UA restored the poly I:C-induced morphology by restoring microglial ramification. In addition, UA was able to reduce the release of the pro-inflammatory mediators CCL2, TNF-α, and IL-1β and showed a trend toward attenuation of cellular ROS production in poly I:C-treated cultures. Overall, this study suggests that UA as a component of a healthy diet may help prevent virus-induced neuroinflammation and may have therapeutic potential for future studies to prevent or treat neurodegenerative diseases by targeting the associated neuroinflammatory processes.

Extracellular vesicles derived from monomeric α-synuclein-treated microglia ameliorate neuroinflammation by delivery of miRNAs targeting PRAK

Parkinson's disease (PD) is characterized by the formation of Lewy body, which mainly contains misfolded α-synuclein. Microglial activation plays a role in neurodegeneration. The pathologically oligomeric α-synuclein promotes inflammatory microglia, while physiologically monomeric α-synuclein induces anti-inflammatory microglia, the relationship between these two forms in activating microglia and the molecular mechanism is essentially unknown. In this study, using in vivo and in vitro models, we challenged primary or BV2 microglia with exogenous stimuli including α-synuclein. We examined microglial activation and the underlying mechanism by Western blot, RT-PCR, ELISA, IF, FCM, miRNA sequencing and bioinformatic analysis. Oligomeric α-synuclein activatedmicroglia via theinvolvement of the PRAK/MK5 pathway. The specific PRAK inhibitor GLPG0259 could mitigate microglial activation insulted by oligomeric α-synuclein. Monomeric α-synuclein regulated theanti-inflammatory microglia by delivering microglia-derived extracellular vesicles (EVs) in vitro and in vivo. Furthersequencingand bioinformatic analysis of microglial EVs-associated miRNAs indicatedthatmost of these miRNAs targeted PRAK. These results suggest that PRAK serves as an intersection in microglial activation when challenged with conformationally different α-synuclein. EVs derived from microglia treated with monomeric α-synuclein promote anti-inflammatory microglia by delivering miRNAs that target PRAK into recipient microglia.

Inflammatory signaling pathways in the treatment of Alzheimer's disease with inhibitors, natural products and metabolites (Review)

The intricate nature of Alzheimer's disease (AD) pathogenesis poses a persistent obstacle to drug development. In recent times, neuroinflammation has emerged as a crucial pathogenic mechanism of AD, and the targeting of inflammation has become a viable approach for the prevention and management of AD. The present study conducted a comprehensive review of the literature between October 2012 and October 2022, identifying a total of 96 references, encompassing 91 distinct pharmaceuticals that have been investigated for their potential impact on AD by inhibiting neuroinflammation. Research has shown that pharmaceuticals have the potential to ameliorate AD by reducing neuroinflammation mainly through regulating inflammatory signaling pathways such as NF‑κB, MAPK, NLRP3, PPARs, STAT3, CREB, PI3K/Akt, Nrf2 and their respective signaling pathways. Among them, tanshinone IIA has been extensively studied for its anti‑inflammatory effects, which have shown significant pharmacological properties and can be applied clinically. Thus, it may hold promise as an effective drug for the treatment of AD. The present review elucidated the inflammatory signaling pathways of pharmaceuticals that have been investigated for their therapeutic efficacy in AD and elucidates their underlying mechanisms. This underscores the auspicious potential of pharmaceuticals in ameliorating AD by impeding neuroinflammation.

Microglia mediated neuroinflammation in neurodegenerative diseases: A review on the cell signaling pathways involved in microglial activation

Microglia, the immune sentinels of the central nervous system (CNS), have emerged to be the central players in many neurological and neurodegenerative diseases. Recent studies on large genome databases and omics studies in fact provide support to the idea that microglial cells could be the drivers of these diseases. Microglial cells have the capacity to undergo morphological and phenotypic transformations depending on its microenvironment. From the homeostatic ramified state, they can shift their phenotypes between the two extremes, known as the proinflammatory M1 and anti-inflammatory M2 phenotype, with intermediate transitional states, characterized by different transcriptional signature and release of inflammatory mediators. The temporal regulation of the release of the inflammatory factors are critical for damage control and steering the microglia back towards homeostatic conditions. A dysregulation in these can lead to excessive tissue damage and neuronal death. Therefore, targeting the cell signaling pathways that are the underpinnings of microglial modulations are considered to be an important avenue for treatment of various neurodegenerative diseases. In this review we have discussed various signaling pathways that trigger microglial activation from its ramified state and highlight the mechanisms of microglia-mediated neuroinflammation that are associated with various neurodegenerative diseases. Most of the cellular factors that drive microglia towards a proinflammatory phenotype are components of the immune system signaling pathways and cell proliferation, along with certain ion channels. The anti-inflammatory phenotype is mainly elicited by purinoceptors, metabolic receptors and other receptors that primarily suppress the production proinflammatory mediators.

Nimbolide Targets Multiple Signalling Pathways to Reduce Neuroinflammation in BV-2 Microglia

Nimbolide, a limonoid compound found in the neem plant, was investigated for effects on neuroinflammation in BV-2 microglia activated with lipopolysaccharide (LPS). Cultured BV-2 cells were treated with nimbolide (125, 250 and 500 nM) followed by stimulation with LPS (100 ng/ml). Results showed that nimbolide caused a significant reduction in the levels of TNFα, IL-6, IFNγ, NO/iNOS and PGE2/COX-2 in LPS-activated BV-2 cells. Further experiments revealed that LPS-induced increased expression of phospho-p65 and phospho-IκBα proteins were reduced in the presence of nimbolide. Also, LPS-induced NF-κB acetylation, increased binding to consensus sites and transactivation, as well as phosphorylation of p38 and JNK MAPKs were reduced by nimbolide. Reduction of cellular ROS generation by nimbolide was accompanied by a reduction in gp91phox protein levels, while antioxidant effects were also observed through elevation in protein levels of HO-1 and NQO-1. It was observed that treatment of BV-2 microglia with nimbolide resulted in reduced levels of cytoplasmic Nrf2, which was accompanied by increased levels in the nucleus. Furthermore, treatment with this compound resulted in increased binding of Nrf2 to antioxidant responsive element (ARE) consensus sites accompanied by enhanced ARE luciferase activity. Knockdown experiments revealed a loss of anti-inflammatory activity by nimbolide in cells transfected with Nrf2 siRNA. Treatment with nimbolide resulted in nuclear accumulation of SIRT-1, while siRNA knockdown of SIRT-1 resulted in the reversal of anti-inflammatory activity of nimbolide. It is proposed that nimbolide reduces neuroinflammation in BV-2 microglia through mechanisms resulting in dual inhibition of NF-κB and MAPK pathways. It is also proposed that activation of Nrf2 antioxidant mechanisms may be contributing to its anti-inflammatory activity.

Activation of Angiotensin-converting Enzyme 2 Protects Against Lipopolysaccharide-induced Glial Activation by Modulating Angiotensin-converting Enzyme 2/Angiotensin (1-7)/Mas Receptor Axis

Neuroinflammation is associated with activation of glial cells and pro-inflammatory arm of the central Renin Angiotensin System (RAS) namely, Angiotensin-Converting Enzyme/Angiotensin II/Angiotensin Type 1 Receptor (ACE/Ang II/AT1R) axis. Apart from this, another axis of RAS also exists, Angiotensin-Converting Enzyme 2/Angiotensin (1-7)/Mas Receptor (ACE2/Ang (1-7)/MasR), which counters ACE/Ang II/AT1R axis by showing anti-inflammatory properties. However, the role of ACE2/Ang (1-7)/MasR axis has not been explored in glial activation and neuroinflammation. Hence, the present study tries to unveil the role of ACE2/Ang (1-7)/MasR axis in lipopolysaccharide (LPS)-induced neuroinflammation using diminazene aceturate (DIZE), an ACE2 activator, in astroglial (C6) and microglial (BV2) cells as well as male SD rats. We found that ACE2 activation efficiently prevented LPS-induced changes by decreasing glial activation, inflammatory signaling, cell migration, ROS generation via upregulation of ACE2/Ang (1-7)/MasR signaling. In addition, activation of ACE2/Ang (1-7)/MasR axis by DIZE significantly suppressed the pro-inflammatory ACE/Ang II/AT1R axis by reducing Ang II level in neuroinflammatory conditions induced by LPS in both in vitro and in vivo. ACE2/Ang (1-7)/MasR axis activation further decreased mitochondrial depolarization and apoptosis, hence providing neuroprotection. Furthermore, to validate that the beneficial effect of the ACE2 activator was indeed through MasR, a selective MasR antagonist (A779) was used that significantly blocked the anti-inflammatory effect of ACE2 activation by DIZE. Hence, our study demonstrated that ACE2 activation imparted neuroprotection by enhancing ACE2/Ang (1-7)/MasR signaling which in turn decreased glial activation, neuroinflammation, and apoptosis and improved mitochondrial health.

sVCAM1 in the Hippocampus Contributes to Postoperative Cognitive Dysfunction in Mice by Inducing Microglial Activation Through the VLA-4 Receptor

Postoperative cognitive dysfunction (POCD) is a severe postsurgical complication, but its underlying mechanisms remain unclear. Neuroinflammation mediated by microglial activation plays a major role in POCD pathophysiology. Upregulation of vascular cell adhesion molecule 1 (VCAM1) on brain endothelial cells is closely correlated with microglial activation in the mouse hippocampus. However, the role of VCAM1 upregulation in microglial activation remains unknown. Soluble VCAM1 (sVCAM1) activates the very late antigen-4 (VLA-4) receptor under inflammatory conditions. Therefore, we hypothesized that sVCAM1 which is shed from VCAM1 contributes to POCD by triggering hippocampal microglial activation through the VLA-4 receptor. We found that VCAM1 and sVCAM1 expression in the mouse hippocampus was upregulated after surgery, and the upregulation was accompanied by hippocampal microglial activation. sVCAM1 levels in mouse and human serum were increased after surgery. Anti-VCAM1 treatment inhibited microglial activation, proinflammatory cytokine production, VLA-4 expression and P38 mitogen-associated protein kinase (MAPK) pathway activation and attenuated hippocampal-dependent cognitive dysfunction. In vitro, recombinant sVCAM1 promoted M1 polarization in BV2 cells, increased VLA-4 expression and activated the P38 MAPK pathway. These effects were reversed by VLA-4 receptor blockade. Anti-VLA-4 treatment ameliorated hippocampal-dependent cognitive dysfunction after surgery by inhibiting microglial activation, proinflammatory cytokine production and P38 pathway activation. In conclusion, increased sVCAM1 in the hippocampus is involved in microglial activation and cognitive dysfunction induced by surgery. Inhibiting the sVCAM1-VLA-4 interaction in microglia may be a therapeutic strategy for POCD.

Piceatannol suppresses inflammation and promotes apoptosis in rheumatoid arthritis‑fibroblast‑like synoviocytes by inhibiting the NF‑κB and MAPK signaling pathways

Rheumatoid arthritis (RA) is a chronic inflammatory disease that mainly targets the synovial membrane, thus causing stiffness, deformity and dysfunction of joints. To date, no effective anti-inflammatory treatments are available for RA. Piceatannol (PIC) is a natural derivative of resveratrol, which has been reported to attenuate the inflammatory response. To evaluate the effect of PIC on RA and to determine the underlying molecular target of PIC, both in vitro and in vivo experiments were performed in the present study. A CIA rat model was established to evaluate the therapeutic effects of PIC. TNF-α, IL-1β and IL-6 levels in blood were measured by ELISA. Western blotting, immunofluorescence analysis and reverse transcription-quantitative PCR (RT-qPCR) were used to analyze the expression levels of protein and mRNA. In vitro, RA-fibroblast-like synoviocytes (FLSs) were pretreated with PIC and subsequently stimulated with TNF-α. The results revealed that PIC significantly upregulated the expression levels of proapoptotic proteins such as Bax and cleaved caspase-3. PIC also significantly reduced the production of proinflammatory cytokines, including PGE2, IL-6 and IL-1β, and significantly downregulated the expression of cyclooxygenase-2 at both the mRNA and protein expression levels. Furthermore, PIC downregulated the expression of MMP-3 and MMP-13, which have been found to be highly expressed in the synovium of patients with RA. Mechanistically, PIC was capable of significantly downregulating the expression levels of proteins involved in the NF-κB and MAPK signaling pathways. The results of the in vivo experiments using a rat collagen-induced arthritis model demonstrated that PIC decreased the arthritis score and exerted beneficial effects in cartilage and significantly reduced the expression of MMP-13. In conclusion, the findings of the present study revealed that PIC could suppress the inflammatory response, promote apoptosis, and exert a significant regulatory effect on the NF-κB and MAPK signaling pathways in RA-FLSs. Therefore, PIC may represent a potential drug for the future treatment of RA.

Dusp26 phosphatase regulates mitochondrial respiration and oxidative stress and protects neuronal cell death

The dual specificity protein phosphatases (Dusps) control dephosphorylation of mitogen-activated protein kinases (MAPKs) as well as other substrates. Here, we report that Dusp26, which is highly expressed in neuroblastoma cells and primary neurons is targeted to the mitochondrial outer membrane via its NH2-terminal mitochondrial targeting sequence. Loss of Dusp26 has a significant impact on mitochondrial function that is associated with increased levels of reactive oxygen species (ROS), reduction in ATP generation, reduction in mitochondria motility and release of mitochondrial HtrA2 protease into the cytoplasm. The mitochondrial dysregulation in dusp26-deficient neuroblastoma cells leads to the inhibition of cell proliferation and cell death. In vivo, Dusp26 is highly expressed in neurons in different brain regions, including cortex and midbrain (MB). Ablation of Dusp26 in mouse model leads to dopaminergic (DA) neuronal cell loss in the substantia nigra par compacta (SNpc), inflammatory response in MB and striatum, and phenotypes that are normally associated with Neurodegenerative diseases. Consistent with the data from our mouse model, Dusp26 expressing cells are significantly reduced in the SNpc of Parkinson's Disease patients. The underlying mechanism of DA neuronal death is that loss of Dusp26 in neurons increases mitochondrial ROS and concurrent activation of MAPK/p38 signaling pathway and inflammatory response. Our results suggest that regulation of mitochondrial-associated protein phosphorylation is essential for the maintenance of mitochondrial homeostasis and dysregulation of this process may contribute to the initiation and development of neurodegenerative diseases.

SRPK2 Expression and Beta-Amyloid Accumulation Are Associated With BV2 Microglia Activation

Introduction

The extracellular deposition of β-amyloid (Aβ) is a pathological hallmark in Alzheimer's disease (AD), which induces microglial activation in the pathology of AD. The expression of serine/threonine-protein kinase 2 (SRPK2) is increased in the brain tissues of patients with AD. In this study, we examined the effect of SRPK2 in the activation of microglia.

Methods

Microglia (BV2) cells were cultured and the expression of SRPK2 was enhanced by transfection of SRPK2 recombinant vectors or knockdown by SRPK2 small interfering RNA (siRNA). The cells were stimulated by lipopolysaccharide (LPS) + interferon-γ (IFN-γ) or Aβ in vitro, generating inflammatory cytokines [tumor necrosis factor-α (TNF-α), interleukin (IL)-10, and IL-6], which were investigated by real-time quantitative PCR (qPCR) and ELISA. The proliferation ability of the BV2 cells with/without SRPK2 expression was evaluated by WST-1 under pressure in the presence of Aβ. The effects of SRPK2 on microglia polarization were evaluated by investigating the expression of CD16/32 and CD206 by western blot and the expression of ionized calcium-binding adapter molecule-1 (IBA-1) and arginase-1 (Arg-1) by immunofluorescence. Hippocampal cells HT-22 were cultured with a BV2 cell (with/without SRPK2 expression)-derived medium stimulated by Aβ or LPS + IFN-γ, prior to the evaluation of HT-22 cytotoxicity by assessment of cell viability. Possible relationships between Akt and SRPK2 in the BV2 cells were investigated by western blot.

Results

The expression of SRPK2 was related to the phenotype polarization changes of microglia with increased expression of CD16/32 and IBA-1. The expression of proinflammatory cytokines IL-6 and TNF-α was increased, whereas the expression of anti-inflammatory cytokine IL-10 was decreased in the BV2 cells with SRPK2 overexpression. Moreover, with the expression enhancement of SRPK2, the BV2 cells had a higher proliferation rate. Aβ treatment can promote SRPK2 expression in BV2 cells. Aβ or LPS + IFN-γ promoted the production of cytokines IL-6 and TNF-α but decreased cytokine IL-10 in the BV2 cells. SRPK2 deficiency alleviated the cytotoxic effects of Aβ or LPS + IFN-γ exposed microglia on HT22 cells. In addition, the activated Akt pathway promoted the expression of SRPK2 in the BV2 cells.

Conclusion

Our data have found that enhanced SRPK2 expression contributed to the proinflammatory activation of microglia. Thus, SRPK2 may be a key modulating pathway of inflammatory mediators in AD pathology.

Therapeutic Potential of Vital Transcription Factors in Alzheimer's and Parkinson's Disease With Particular Emphasis on Transcription Factor EB Mediated Autophagy

Autophagy is an important cellular self-digestion and recycling pathway that helps in maintaining cellular homeostasis. Dysregulation at various steps of the autophagic and endolysosomal pathway has been reported in several neurodegenerative disorders such as Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington disease (HD) and is cited as a critically important feature for central nervous system (CNS) proteostasis. Recently, another molecular target, namely transcription factor EB (TFEB) has been explored globally to treat neurodegenerative disorders. This TFEB, is a key regulator of autophagy and lysosomal biogenesis pathway. Multiple research studies suggested therapeutic potential by targeting TFEB to treat human diseases involving autophagy-lysosomal dysfunction, especially neurodegenerative disorders. A common observation involving all neurodegenerative disorders is their poor efficacy in clearing and recycle toxic aggregated proteins and damaged cellular organelles due to impairment in the autophagy pathway. This dysfunction in autophagy characterized by the accumulation of toxic protein aggregates leads to a progressive loss in structural integrity/functionality of neurons and may even result in neuronal death. In recent years TFEB, a key regulator of autophagy and lysosomal biogenesis, has received considerable attention. It has emerged as a potential therapeutic target in numerous neurodegenerative disorders like AD and PD. In various neurobiology studies involving animal models, TFEB has been found to ameliorate neurotoxicity and rescue neurodegeneration. Since TFEB is a master transcriptional regulator of autophagy and lysosomal biogenesis pathway and plays a crucial role in defining autophagy activation. Studies have been done to understand the mechanisms for TFEB dysfunction, which may yield insights into how TFEB might be targeted and used for the therapeutic strategy to develop a treatment process with extensive application to neurodegenerative disorders. In this review, we explore the role of different transcription factor-based targeted therapy by some natural compounds for AD and PD with special emphasis on TFEB.

Mitogen-activated protein kinase-activated protein kinase-2 (MK2) and its role in cell survival, inflammatory signaling, and migration in promoting cancer

Cancer and the immune system share an intimate relationship. Chronic inflammation increases the risk of cancer occurrence and can also drive inflammatory mediators into the tumor microenvironment enhancing tumor growth and survival. The p38 MAPK pathway is activated both acutely and chronically by stress, inflammatory chemokines, chronic inflammatory conditions, and cancer. These properties have led to extensive efforts to find effective drugs targeting p38, which have been unsuccessful. The immediate downstream serine/threonine kinase and substrate of p38 MAPK, mitogen-activated-protein-kinase-activated-protein-kinase-2 (MK2) protects cells against stressors by regulating the DNA damage response, transcription, protein and messenger RNA stability, and motility. The phosphorylation of downstream substrates by MK2 increases inflammatory cytokine production, drives an immune response, and contributes to wound healing. By binding directly to p38 MAPK, MK2 is responsible for the export of p38 MAPK from the nucleus which gives MK2 properties that make it unique among the large number of p38 MAPK substrates. Many of the substrates of both p38 MAPK and MK2 are separated between the cytosol and nucleus and interfering with MK2 and altering this intracellular translocation has implications for the actions of both p38 MAPK and MK2. The inhibition of MK2 has shown promise in combination with both chemotherapy and radiotherapy as a method for controlling cancer growth and metastasis in a variety of cancers. Whereas the current data are encouraging the field requires the development of selective and well tolerated drugs to target MK2 and a better understanding of its effects for effective clinical use.

Understanding Abnormal c-JNK/p38MAPK Signaling Overactivation Involved in the Progression of Multiple Sclerosis: Possible Therapeutic Targets and Impact on Neurodegenerative Diseases

Demyelination, immune dysregulation, and neuroinflammation are the most common triggers of motor neuron disorders such as multiple sclerosis (MS). MS is a chronic demyelinating neurodegenerative disease of the central nervous system caused by abnormal immune activation, which causes myelin sheath damage. Cell signal transduction pathways are required for a variety of physiological and pathological processes in the brain. When these signaling systems become overactive, they can lead to disease progression. In various physiological conditions, abnormal mitogen-activated protein kinase (MAPK) activation is associated with several physiological dysfunctions that cause neurodegeneration. Previous research indicates that c-JNK and p38MAPK signaling play critical roles in neuronal growth and differentiation. c-JNK/p38MAPK is a member of the MAPK family, which regulates metabolic pathways, cell proliferation, differentiation, and apoptosis that control certain neurological activities. During brain injuries, c-JNK/p38MAPK also affects neuronal elastic properties, nerve growth, and cognitive processing. This review systematically linked abnormal c-JNK/p38MAPK signaling activation to multiple neuropathological pathways in MS and related neurological dysfunctions. MS progression is linked to genetic defects, oligodendrocyte destruction, glial overactivation, and immune dysregulation. We concluded that inhibiting both the c-JNK/p38MAPK signaling pathways can promote neuroprotection and neurotrophic effects against the clinical-pathological presentation of MS and influence other neurological disorders. As a result, the potential benefits of c-JNK/p38MAPK downregulation for the development of disease-modifying treatment interventions in the future could include MS prevention and related neurocomplications.

p38 MAPK Activity Is Required to Prevent Hyperactivation of NLRP3 Inflammasome

Inflammation contributes to the pathogenesis and morbidity of wide spectrum of human diseases. The inflammatory response must be actively controlled to prevent bystander damage to tissues. Yet, the mechanisms controlling excessive inflammatory responses are poorly understood. NLRP3 inflammasome plays an important role in innate immune response to cellular infection or stress. Its activation must be tightly regulated because uncontrolled inflammasome activation is associated with a number of human diseases. p38 MAPK signaling plays an essential role in the regulation of inflammation. The role of p38 MAPK in inflammatory response associated with the expression of proinflammatory molecules is known. However, the anti-inflammatory functions of p38 MAPK are largely unknown. In this study, we show that pharmacologic inhibition or genetic deficiency of p38 MAPK leads to hyperactivation of NLRP3 inflammasome, resulting in enhanced Caspase 1 activation and IL-1β and IL-18 production. The deficiency of p38 MAPK activity induced an increase of cytosolic Ca²⁺ and excessive mitochondrial Ca²⁺ uptake, leading to exacerbation of mitochondrial damage, which was associated with hyperactivation of NLRP3 inflammasome. In addition, mice with deficiency of p38 MAPK in granulocytes had evidence of in vivo hyperactivation of NLRP3 inflammasome and were more susceptible to LPS-induced sepsis compared with wild-type mice. Our results suggest that p38 MAPK negatively regulates NLRP3 inflammasome through control of Ca²⁺ mobilization. Hyperactivity of inflammasome in p38-deficient mice causes lung inflammation and increased susceptibility to septic shock.

When Good Kinases Go Rogue: GSK3, p38 MAPK and CDKs as Therapeutic Targets for Alzheimer's and Huntington's Disease

Alzheimer's disease (AD) is a mostly sporadic brain disorder characterized by cognitive decline resulting from selective neurodegeneration in the hippocampus and cerebral cortex whereas Huntington's disease (HD) is a monogenic inherited disorder characterized by motor abnormalities and psychiatric disturbances resulting from selective neurodegeneration in the striatum. Although there have been numerous clinical trials for these diseases, they have been unsuccessful. Research conducted over the past three decades by a large number of laboratories has demonstrated that abnormal actions of common kinases play a key role in the pathogenesis of both AD and HD as well as several other neurodegenerative diseases. Prominent among these kinases are glycogen synthase kinase (GSK3), p38 mitogen-activated protein kinase (MAPK) and some of the cyclin-dependent kinases (CDKs). After a brief summary of the molecular and cell biology of AD and HD this review covers what is known about the role of these three groups of kinases in the brain and in the pathogenesis of the two neurodegenerative disorders. The potential of targeting GSK3, p38 MAPK and CDKS as effective therapeutics is also discussed as is a brief discussion on the utilization of recently developed drugs that simultaneously target two or all three of these groups of kinases. Multi-kinase inhibitors either by themselves or in combination with strategies currently being used such as immunotherapy or secretase inhibitors for AD and knockdown for HD could represent a more effective therapeutic approach for these fatal neurodegenerative diseases.

The PKR/P38/RIPK1 Signaling Pathway as a Therapeutic Target in Alzheimer's Disease

Neuropathological lesions in Alzheimer’s disease (AD) include amyloid plaques formed by the accumulation of amyloid peptides, neurofibrillary tangles made of hyperphosphorylated tau protein, synaptic and neuronal degenerations, and neuroinflammation. The cause of AD is unknown, but according to the amyloid hypothesis, amyloid oligomers could lead to the activation of kinases such as eukaryotic translation initiation factor 2-alpha kinase 2 (PKR), p38, and receptor-interacting serine/threonine-protein kinase 1 (RIPK1), which all belong to the same stress-activated pathway. Many toxic kinase activations have been described in AD patients and in experimental models. A p38 mitogen-activated protein kinase inhibitor was recently tested in clinical trials but with unsuccessful results. The complex PKR/P38/RIPK1 (PKR/dual specificity mitogen-activated protein kinase kinase 6 (MKK6)/P38/MAP kinase-activated protein kinase 2 (MK2)/RIPK1) is highly activated in AD brains and in the brains of AD transgenic animals. To delineate the implication of this pathway in AD, we carried out a search on PubMed including PKR/MKK6/p38/MK2/RIPK1, Alzheimer, and therapeutics. The involvement of this signaling pathway in the genesis of AD lesions, including Aβ accumulations and tau phosphorylation as well as cognitive decline, is demonstrated by the reports described in this review. A future combination strategy with kinase inhibitors should be envisaged to modulate the consequences for neurons and other brain cells linked to the abnormal activation of this pathway.

The p38MAPK-MK2 Signaling Axis as a Critical Link Between Inflammation and Synaptic Transmission

p38 is a mitogen-activated protein kinase (MAPK), that responds primarily to stress stimuli. p38 has a number of targets for phosphorylation, including MAPK-activated protein kinase 2 (MK2). MK2 primarily functions as a master regulator of RNA-binding proteins, indirectly controlling gene expression at the level of translation. The role of MK2 in regulating the synthesis of pro-inflammatory cytokines downstream of inflammation and cellular stress is well-described. A significant amount of evidence, however, now points to a role for the p38^MAPK-MK2 signaling axis in mediating synaptic plasticity through control of AMPA receptor trafficking and the morphology of dendritic spines. These processes are mediated through control of cytoskeletal dynamics via the activation of cofilin-1 and possibly control of the expression of Arc/Arg3.1. There is evidence that MK2 is necessary for group I metabotropic glutamate receptors long-term depression (mGluR-LTD). Disruption of this signaling may play an important role in mediating cognitive dysfunction in neurological disorders such as fragile X syndrome and Alzheimer’s disease. To date, the role of neuronal MK2 mediating synaptic plasticity in response to inflammatory stimuli has not yet been investigated. In immune cells, it is clear that MK2 is phosphorylated following activation of a broad range of cell surface receptors for cytokines and other inflammatory mediators. We propose that neuronal MK2 may be an important player in the link between inflammatory states and dysregulation of synaptic plasticity underlying cognitive functions. Finally, we discuss the potential of the p38^MAPK-MK2 signaling axis as target for therapeutic intervention in a number of neurological disorders.

A Comprehensive Analysis of Unique and Recurrent Copy Number Variations in Alzheimer's Disease and its Related Disorders

BACKGROUND

Copy number variations (CNVs) play an important role in the genetic etiology of various neurological disorders, including Alzheimer's disease (AD). Type 2 diabetes mellitus (T2DM) and major depressive disorder (MDD) were shown to have share mechanisms and signaling pathways with AD.

OBJECTIVE

We aimed to assess CNVs regions that may harbor genes contributing to AD, T2DM, and MDD in 67 Saudi familial and sporadic AD patients, with no alterations in the known genes of AD and genotyped previously for APOE.

METHODS

DNA was analyzed using the CytoScan-HD array. Two layers of filtering criteria were applied. All the identified CNVs were checked in the Database of Genomic Variants (DGV).

RESULTS

A total of 1086 CNVs (565 gains and 521 losses) were identified in our study. We found 73 CNVs harboring genes that may be associated with AD, T2DM or MDD. Nineteen CNVs were novel. Most importantly, 42 CNVs were unique in our studied cohort existing only in one patient. Two large gains on chromosomes 1 and 13 harbored genes implicated in the studied disorders. We identified CNVs in genes that encode proteins involved in the metabolism of amyloid-β peptide (AGRN, APBA2, CR1, CR2, IGF2R, KIAA0125, MBP, RER1, RTN4R, VDR and WISPI) or Tau proteins (CACNAIC, CELF2, DUSP22, HTRA1 and SLC2A14).

CONCLUSION

The present work provided information on the presence of CNVs related to AD, T2DM, and MDD in Saudi Alzheimer's patients.

Novel scorpion venom peptide HsTx2 ameliorates cerebral ischemic brain injury in rats via the MAPK signaling pathway

Ischemic stroke is a severe threat to human health due to its high recurrence, mortality, and disability rates. As such, how to prevent and treat ischemic stroke effectively has become a research hotspot in recent years. Here, we identified a novel peptide, named HsTx2 (AGKKERAGSRRTKIVMLKCIREHGH, 2 861.855 Da), derived from the scorpion Heterometrus spinifer, which showed obvious anti-apoplectic effects in rats with ischemic stroke. Results further demonstrated that HsTx2 significantly reduced formation of infarct area and improved behavioral abnormalities in ischemic stroke rats. These protective effects were likely exerted via activation of the mitogen-activated protein kinase (MAPK) signaling pathway, i.e., up-regulation of phosphorylated ERK1/2 in both rat cerebral cortex and activated microglia (AM); up-regulation of phosphorylated p38 (p-p38) in the cerebral cortex; and inhibition of phosphorylated JNK and p-p38 levels in the AM. In conclusion, this study highlights HsTx2 as a potential neuroprotective agent for stroke.

Functions of p38 MAP Kinases in the Central Nervous System

Mitogen-activated protein (MAP) kinases are a central component in signaling networks in a multitude of mammalian cell types. This review covers recent advances on specific functions of p38 MAP kinases in cells of the central nervous system. Unique and specific functions of the four mammalian p38 kinases are found in all major cell types in the brain. Mechanisms of p38 activation and downstream phosphorylation substrates in these different contexts are outlined and how they contribute to functions of p38 in physiological and under disease conditions. Results in different model organisms demonstrated that p38 kinases are involved in cognitive functions, including functions related to anxiety, addiction behavior, neurotoxicity, neurodegeneration, and decision making. Finally, the role of p38 kinases in psychiatric and neurological conditions and the current progress on therapeutic inhibitors targeting p38 kinases are covered and implicate p38 kinases in a multitude of CNS-related physiological and disease states.

A primary neural cell culture model to study neuron, astrocyte, and microglia interactions in neuroinflammation

Background

Interactions between neurons, astrocytes, and microglia critically influence neuroinflammatory responses to insult in the central nervous system. In vitro astrocyte and microglia cultures are powerful tools to study specific molecular pathways involved in neuroinflammation; however, in order to better understand the influence of cellular crosstalk on neuroinflammation, new multicellular culture models are required.

Methods

Primary cortical cells taken from neonatal rats were cultured in a serum-free “tri-culture” medium formulated to support neurons, astrocytes, and microglia, or a “co-culture” medium formulated to support only neurons and astrocytes. Caspase 3/7 activity and morphological changes were used to quantify the response of the two culture types to different neuroinflammatory stimuli mimicking sterile bacterial infection (lipopolysaccharide (LPS) exposure), mechanical injury (scratch), and seizure activity (glutamate-induced excitotoxicity). The secreted cytokine profile of control and LPS-exposed co- and tri-cultures were also compared.

Results

The tri-culture maintained a physiologically relevant representation of neurons, astrocytes, and microglia for 14 days in vitro, while the co-cultures maintained a similar population of neurons and astrocytes, but lacked microglia. The continuous presence of microglia did not negatively impact the overall health of the neurons in the tri-culture, which showed reduced caspase 3/7 activity and similar neurite outgrowth as the co-cultures, along with an increase in the microglia-secreted neurotrophic factor IGF-1 and a significantly reduced concentration of CX3CL1 in the conditioned media. LPS-exposed tri-cultures showed significant astrocyte hypertrophy, increase in caspase 3/7 activity, and the secretion of a number of pro-inflammatory cytokines (e.g., TNF, IL-1α, IL-1β, and IL-6), none of which were observed in LPS-exposed co-cultures. Following mechanical trauma, the tri-culture showed increased caspase 3/7 activity, as compared to the co-culture, along with increased astrocyte migration towards the source of injury. Finally, the microglia in the tri-culture played a significant neuroprotective role during glutamate-induced excitotoxicity, with significantly reduced neuron loss and astrocyte hypertrophy in the tri-culture.

Conclusions

The tri-culture consisting of neurons, astrocytes, and microglia more faithfully mimics in vivo neuroinflammatory responses than standard mono- and co-cultures. This tri-culture can be a useful tool to study neuroinflammation in vitro with improved accuracy in predicting in vivo neuroinflammatory phenomena.

Attenuation of paraquat-induced inflammation by inhibitors of phosphorylation of mitogen-activated protein kinases in BV2 microglial cells

Paraquat has dopaminergic neurotoxicity and potentially contributes to Parkinson's disease (PD) as a risk factor. However, the cellular and molecular mechanisms of PQ-induced neurodegeneration have not been clearly elucidated. Studies have shown that PQ induces microglial neuroinflammation through toll-like receptor 4 (TLR4)-nuclear factor-κB pathway, resulting in neuronal cell loss. Mitogen-activated protein kinases (MAPKs) are involved in the production of pro-inflammatory cytokines in microglia, and in this study, the role of MAPKs in PQ-activated microglial inflammation was investigated. Murine BV₂ microglial cells were treated with 40 μM of PQ following pretreatment of the cells with selective inhibitor of MAPKs phosphorylation for blockage of the phosphorylation of ERK, JNK and P38, or a specific TLR4 inhibitor for blocking the activation of TLR4. The protein expression of phosphorylated ERK, JNK and p38, and the transcription expression of pro-inflammatory mediators were assessed with Western blotting and qRT-PCR technique, respectively. The results indicated that PQ significantly induced the phosphorylation of ERK, JNK and P38 in microglia, while MAPKs inhibitors suppressed PQ-induced phosphorylation of ERK, JNK and P38, and reduced the transcription level of pro-inflammatory cytokines. PQ-stimulated phosphorylation of ERK, JNK and P38 was also reduced by TLR4 inhibitor. The inhibited intensity in the level of pro-inflammatory cytokine transcription was obviously greater in TLR4 inhibitor + PQ group than in each MAPK inhibitor + PQ group. Taken together, inhibition of MAPKs phosphorylation partially attenuates PQ-induced microglial inflammation, which may become a potential intervention strategy for PQ neurotoxicity.

Intranasal MMI-0100 Attenuates Aβ1-42- and LPS-Induced Neuroinflammation and Memory Impairments via the MK2 Signaling Pathway

Background: Accumulating evidence suggests inhibiting neuroinflammation as a potential target in therapeutic or preventive strategies for Alzheimer's disease (AD). MAPK-activated protein kinase II (MK2), downstream kinase of p38 mitogen activated protein kinase (MAPK) p38 MAPK, was unveiled as a promising option for the treatment of AD. Increasing evidence points at MK2 as involved in neuroinflammatory responses. MMI-0100, a cell-penetrating peptide inhibitor of MK2, exhibits anti-inflammatory effects and is in current clinical trials for the treatment of pulmonary fibrosis. Therefore, it is important to understand the actions of MMI-0100 in neuroinflammation.

Methods: The mouse memory function was evaluated using novel object recognition (NOR) and object location recognition (OLR) tasks. Brain hippocampus tissue samples were analyzed by quantitative PCR, Western blotting, and immunostaining. Near-infrared fluorescent and confocal microscopy experiments were used to detect the brain uptake and distribution after intranasal MMI-0100 application.

Results: Central MMI-0100 was able to ameliorate the memory deficit induced by Aβ₁₋₄₂ or LPS in novel object and location memory tasks. MMI-0100 suppressed LPS-induced activation of astrocytes and microglia, and dramatically decreased a series of pro-inflammatory cytokines such as TNF-α, IL-6, IL-1β, COX-2, and iNOS via inhibiting phosphorylation of MK2, but not ERK, JNK, and p38 in vivo and in vitro. Importantly, one of the reasons for the failure of macromolecular protein or peptide drugs in the treatment of AD is that they cannot cross the blood–brain barrier. Our data showed that intranasal administration of MMI-0100 significantly ameliorates the memory deficit induced by Aβ₁₋₄₂ or LPS. Near-infrared fluorescent and confocal microscopy experiment results showed that a strong fluorescent signal, coming from mouse brains, was observed at 2 h after nasal applications of Cy7.5-MMI-0100. However, brains from control mice treated with saline or Cy7.5 alone displayed no significant signal.

Conclusions: MMI-0100 attenuates Aβ₁₋₄₂- and LPS-induced neuroinflammation and memory impairments via the MK2 signaling pathway. Meanwhile, these data suggest that the MMI-0100/MK2 system may provide a new potential target for treatment of AD.

Inhibition of calcium-calmodulin-dependent phosphodiesterase (PDE1) suppresses inflammatory responses

A novel, potent, and highly specific inhibitor of calcium-calmodulin-dependent phosphodiesterases (PDE) of the PDE1 family, ITI-214, was used to investigate the role of PDE1 in inflammatory responses. ITI-214 dose-dependently suppressed lipopolysaccharide (LPS)-induced gene expression of pro-inflammatory cytokines in an immortalized murine microglial cell line, BV2 cells. RNA profiling (RNA-Seq) was used to analyze the impact of ITI-214 on the BV2 cell transcriptome in the absence and the presence of LPS. ITI-214 was found to regulate classes of genes that are involved in inflammation and cell migration responses to LPS exposure. The gene expression changes seen with ITI-214 treatment were distinct from those elicited by inhibitors of other PDEs with anti-inflammatory activity (e.g., a PDE4 inhibitor), indicating a distinct mechanism of action for PDE1. Functionally, ITI-214 inhibited ADP-induced migration of BV2 cells through a P2Y12-receptor-dependent pathway, possibly due to increases in the extent of cAMP and VASP phosphorylation downstream of receptor activation. Importantly, this effect was recapitulated in P2 rat microglial cells in vitro, indicating that these pathways are active in native microglial cells. These studies are the first to demonstrate that inhibition of PDE1 exerts anti-inflammatory effects through effects on microglia signaling pathways. The ability of PDE1 inhibitors to prevent or dampen excessive inflammatory responses of BV2 cells and microglia provides a basis for exploring their therapeutic utility in the treatment of neurodegenerative diseases associated with increased inflammation and microglia proliferation such as Parkinson's disease and Alzheimer's disease.

Shaping the Nrf2-ARE-related pathways in Alzheimer's and Parkinson's diseases

A failure in redox homeostasis is a common hallmark of Alzheimer's Disease (AD) and Parkinson's Disease (PD), two age-dependent neurodegenerative disorders (NDD), causing increased oxidative stress, oxidized/damaged biomolecules, altered neuronal function and consequent cell death. Activation of nuclear factor erythroid 2-related factor 2 (Nrf2), a redox-regulated transcription factor, results in upregulation of cytoprotective and antioxidant enzymes/proteins, protecting against oxidative stress. Nrf2 regulation is achieved by various proteins and pathways, at both cytoplasmatic and nuclear level; however, the elaborate network of mechanisms involved in Nrf2 regulation may restrain Nrf2 pathway normal activity. Indeed, altered Nrf2 activity is involved in aging and NDD, such as AD and PD. Therefore, understanding the diversity of Nrf2 control mechanisms and regulatory proteins is of high interest, since more effective NDD therapeutics can be identified. In this review, we first introduce Keap1-Nrf2-ARE structure, function and regulation, with a special focus on the several pathways involved in Nrf2 positive and negative modulation, namely p62, PKC, PI3K/Akt/GSK-3β, NF-kB and p38 MAPK. We then briefly describe the evidences for oxidative stress and Nrf2 pathway deregulation in different stages of NDDs. Finally, we discuss the potential of Nrf2-related pathways as potential therapeutic targets to possibly prevent or slowdown NDD progression.

Improved immunohistochemical detection of phosphorylated mitogen-activated protein kinases in the injured rat optic nerve head

The activity of mitogen-activated protein kinases (MAPKs) is largely controlled by addition or removal of phosphate groups, which are carried out by kinase or phosphatase enzymes, respectively. Determining the phosphorylation status of MAPK isoenzymes, therefore, aids elucidation of the physiological and pathological roles of this enzyme. In practical terms, however, end-point procurement of appropriate experimental tissues produces conditions where MAPK phosphorylation status can rapidly alter, thus giving rise to aberrant data. We therefore attempted to instigate a means of stabilising end-point MAPK phosphorylation levels when procuring tissues for analysis. We employed a well-described rat model of ocular hypertension in which MAPK isoenzyme activation occurs in the optic nerve head (ONH), but can vary according to the level of resultant tissue pathology. Animals were appropriately treated and after 3 days were perfused in the presence or absence of a cocktail of phosphatase inhibitors (PIs), immediately prior to tissue fixation, in order to prevent dephosphorylation of phosphorylated MAPKs. Immunohistochemical labelling for phosphorylated MAPKs in untreated ONH sections was unaffected by the presence of PIs in the perfusate. MAPK activation was detected by immunohistochemistry in the treated ONH, but findings varied considerably, particularly in animals with less extensive tissue damage. The presence of PIs in the perfusate, however, significantly reduced this variation and enabled consistent changes to be detected, particularly in the animals with less extensive tissue damage. Thus, the addition of PIs to the perfusate is suggested when studying MAPK activation by immunohistochemistry, especially in the ONH.

Monoterpenes modulating cytokines - A review

Inflammatory response can be driven by cytokine production and is a pivotal target in the management of inflammatory diseases. Monoterpenes have shown that promising profile as agents which reduce the inflammatory process and also modulate the key chemical mediators of inflammation, such as pro and anti-inflammatory cytokines. The main interest focused on monoterpenes were to develop the analgesic and anti-inflammatory drugs. In this review, we summarized current knowledge on monoterpenes that produce anti-inflammatory effects by modulating the release of cytokines, as well as suggesting that which monoterpenoid molecules may be most effective in the treatment of inflammatory disease. Several different inflammatory markers were evaluated as a target of monoterpenes. The proinflammatory and anti-inflammatory cytokines were found TNF-α, IL-1β, IL-2, IL-5, IL-4, IL-6, IL-8, IL-10, IL-12 IL-13, IL-17A, IFNγ, TGF-β1 and IFN-γ. Our review found evidence that NF-κB and MAPK signaling are important pathways for the anti-inflammatory action of monoterpenes. We found 24 monoterpenes that modulate the production of cytokines, which appears to be the major pharmacological mechanism these compounds possess in relation to the attenuation of inflammatory response. Despite the compelling evidence supporting the anti-inflammatory effect of monoterpenes, further studies are necessary to fully explore their potential as anti-inflammatory compounds.

Dephosphorylated rather than hyperphosphorylated Tau triggers a pro-inflammatory profile in microglia through the p38 MAPK pathway

Tauopathies are a broad set of neurodegenerative dementias characterized by the aggregation of Tau protein. Activated microglia and elevated levels of pro-inflammatory molecules are also pathological hallmarks of tauopathies. In these diseases, intracellular Tau is secreted to the extracellular space, where it interacts with other cells, such as neurons and glia, promoting inflammation. However, the mechanism through which extracellular Tau triggers pro-inflammatory responses in microglia remains unknown. Primary microglia cultures were treated with extracellular Tau in its hyperphosphorylated, dephosphorylated or non-phosphorylated form. Protein cytokine arrays, real-time PCR, inhibition of the p38 MAPK pathway, phosphatase assays, and quantification of proteins through immunoblotting were used to analyze the effect of extracellular Tau on the pro-inflammatory response of microglia. The main finding of this work is that extracellular non-phosphorylated and dephosphorylated forms of Tau, rather than hyperphosphorylated Tau, activate the p38 MAPK pathway in microglia, thus triggering a pro-inflammatory response in these cells.

Central Nervous System Neuron-Glia co-Culture Models and Application to Neuroprotective Agents

Glial cell activation plays an important role in the pathogenesis of various neurodegenerative disorders. This article presents a protocol for the preparation of cultures consisting of rat embryonic cortical neurons grown in the presence of cortical microglia, in which the glia are present in physical contact with the neurons or separated by a semipermeable membrane barrier. An example of how such systems can be used to evaluate potential neuroprotective agents will also be described.

Serum amyloid A primes microglia for ATP-dependent interleukin-1β release

BACKGROUND

Acute-phase response is a systemic reaction to environmental/inflammatory insults and involves production of acute-phase proteins, including serum amyloid A (SAA). Interleukin-1β (IL-1β), a master regulator of neuroinflammation produced by activated inflammatory cells of the myeloid lineage, in particular microglia, plays a key role in the pathogenesis of acute and chronic diseases of the peripheral nervous system and CNS. IL-1β release is promoted by ATP acting at the purinergic P2X₇ receptor (P2X₇R) in cells primed with toll-like receptor (TLR) ligands.

METHODS

Purified (> 99%) microglia cultured from neonatal rat cortex and cerebellum were first primed with the putative TLR4/TLR2 agonist SAA (recombinant human Apo-SAA) or the established TLR4 agonist lipopolysaccharide (LPS) followed by addition of ATP. Expression of genes for the NLRP3 inflammasome, IL-1β, tumor necrosis factor-α (TNF-α), and SAA1 was measured by quantitative real-time polymerase chain reaction (q-PCR). Intracellular and extracellular amounts of IL-1β were determined by ELISA.

RESULTS

Apo-SAA stimulated, in a time-dependent manner, the expression of NLRP3, IL-1β, and TNF-α in cortical microglia, and produced a concentration-dependent increase in the intracellular content of IL-1β in these cells. A 2-h 'priming' of the microglia with Apo-SAA followed by addition of ATP for 1 h, resulting in a robust release of IL-1β into the culture medium, with a concomitant reduction in its intracellular content. The selective P2X₇R antagonist A740003 blocked ATP-dependent release of IL-1β. Microglia prepared from rat cerebellum displayed similar behaviors. As with LPS, Apo-SAA upregulated SAA1 and TLR2 mRNA, and downregulated that of TLR4. LPS was less efficacious than Apo-SAA, perhaps reflecting an action of the latter at TLR4 and TLR2. The TLR4 antagonist CLI-095 fully blocked the action of LPS, but only partially that of Apo-SAA. Although the TLR2 antagonist CU-CPT22 was inactive against Apo-SAA, it also failed to block the TLR2 agonist Pam₃CSK₄.

CONCLUSIONS

Microglia are central to the inflammatory process and a major source of IL-1β when activated. P2X₇R-triggered IL-1β maturation and export is thus likely to represent an important contributor to this cytokine pool. Given that SAA is detected in Alzheimer disease and multiple sclerosis brain, together with IL-1β-immunopositive microglia, these findings propose a link between P2X₇R, SAA, and IL-1β in CNS pathophysiology.

Effects of Resveratrol and other Polyphenols on Sirt1: Relevance to Brain Function During Aging

BACKGROUND

Classically the oxidative stress and more recently inflammatory processes have been identified as the major causes of brain aging. Oxidative stress and inflammation affect each other, but there is more information about the effects of oxidative stress on aging than regarding the contribution of inflammation on it.

METHODS

In the intense research for methods to delay or mitigate the effects of aging, are interesting polyphenols, natural molecules synthesized by plants (e.g. resveratrol). Their antioxidant and anti-inflammatory properties make them useful molecules in the prevention of aging.

RESULTS

The antiaging effects of polyphenols could be due to several related mechanisms, among which are the prevention of oxidative stress, SIRT1 activation and inflammaging modulation, via regulation of some signaling pathways, such as NF-κB.

CONCLUSION

In this review, we describe the positive effects of polyphenols on the prevention of the changes that occur during aging in the brain and their consequences on cognition, emphasizing the possible modulation of inflammaging by polyphenols through a SIRT1-mediated mechanism.

Culture of Neonatal Rodent Microglia, Astrocytes, and Oligodendrocytes from the Cortex, Spinal Cord, and Cerebellum

The protocol described in this chapter covers the preparation and culture of enriched populations of microglia, astrocytes, and oligodendrocytes from the cortex and spinal cord of neonatal rat and mouse. The procedure is based on enzymatic digestion of the tissue, followed by the culture of a mixed glial cell population which is then utilized as the starting point for the isolation, via differential attachment, of the different cell types.

Astrocyte/Microglia Cocultures as a Model to Study Neuroinflammation

Glial cell activation plays an important role in the pathogenesis of various neurodegenerative disorders as well as in chronic and neuropathic pain. This chapter describes a model which allows one to assess the individual and combined contributions of astrocytes and microglia in response to a pro-inflammatory stimulus, with emphasis on ionotropic purinergic receptors.

Increase in proapoptotic activity of inhibitory PAS domain protein via phosphorylation by MK2

Inhibitory PAS domain protein (IPAS) is a bifunctional protein that downregulates hypoxic gene expression and exerts proapoptotic activity by preventing prosurvival activity of Bcl-x_L and its related factors. Proapoptotic activity of IPAS is attenuated by the activation of the PINK1-Parkin pathway, and involved in neuronal degeneration in an experimental mouse model of Parkinson's disease. The current study shows that phosphorylation of IPAS at Ser184 by MAPK-activated protein kinase 2 (MK2 or MAPKAPK2) enhances the proapoptotic function of IPAS. Perinuclear clustering of mitochondria and activation of caspase-3 caused by the transient expression of EGFP-IPAS were increased by UVB irradiation. The C-terminal region of IPAS mediated the UVB susceptibility of IPAS. Increase in IPAS-induced mitochondrial clustering by UVB was completly inhibited by the p38 MAPK inhibitor SB203580. Mass spectrometry analysis of UVB-activated IPAS identified several phosphorylation sites in the C-terminal region containing p38 MAPK consensus phosphorylation sites at Ser219 and Ser223, and an MK2 consensus site at Ser184. Although mutations of Ser219 and Ser223 to Ala did not suppress the UVB-induced mitochondrial clustering, replacement of Ser184 with Ala blocked it. A phosphomimetic substitution at Ser184 enhanced mitochondrial clustering and activation of caspase-3 without UVB exposure. Furthermore, binding affinity to Bcl-x_L was increased by the mutation. Treatment of PC12 cells with CoCl₂ caused activation of MK2 and mitochondrial clustering. IPAS-dependent cell death induced by CoCl₂ in PC12 cells was decreased by the treatment with the MK2 inhibitor MK2 inhibitor III and by siRNA-directed silencing of MK2.

The potential role of neuroinflammation and transcription factors in Parkinson disease

Parkinson disease (PD) is a neurodegenerative disorder characterized by dopaminergic neurons affected by inflammatory processes. Post-mortem analyses of brain and cerebrospinal fluid from PD patients show the accumulation of proinflammatory cytokines, confirming an ongoing neuroinflammation in the affected brain regions. These inflammatory mediators may activate transcription factors—notably nuclear factor κB, Ying-Yang 1 (YY1), fibroblast growth factor 20 (FGF20), and mammalian target of rapamycin (mTOR)—which then regulate downstream signaling pathways that in turn promote death of dopaminergic neurons through death domain-containing receptors. Dopaminergic neurons are vulnerable to oxidative stress and inflammatory attack. An increased level of inducible nitric oxide synthase observed in the substantia nigra and striatum of PD patients suggests that both cytokine—and chemokine-induced toxicity and inflammation lead to oxidative stress that contributes to degeneration of dopaminergic neurons and to disease progression. Lipopolysaccharide activation of microglia in the proximity of dopaminergic neurons in the substantia nigra causes their degeneration, and this appears to be a selective vulnerability of dopaminergic neurons to inflammation. In this review, we will look at the role of various transcription factors and signaling pathways in the development of PD.

Potassium 2-(l-hydroxypentyl)-benzoate attenuates neuroinflammatory responses and upregulates heme oxygenase-1 in systemic lipopolysaccharide-induced inflammation in mice

A neuroinflammatory response is commonly involved in the progression of many neurodegenerative diseases. Potassium 2-(1-hydroxypentyl)-benzoate (PHPB), a novel neuroprotective compound, has shown promising effects in the treatment of ischemic stroke and Alzheimer׳s disease (AD). In the present study, the anti-inflammatory effects of PHPB were investigated in the plasma and brain of C57BL/6 mice administered a single intraperitoneal (i.p.) injection of lipopolysaccharide (LPS). Levels of iNOS and the cytokines TNFα, IL-1β and IL-10 were elevated in plasma, cerebral cortex and hippocampus after LPS injection and the number of microglia and astrocytes in cortex and hippocampus were increased. LPS also upregulated the expression of heme oxygenase-1 (HO-1) in the cortex and hippocampus. PHPB reduced the levels of iNOS and cytokines in the plasma and brain, decreased the number of microglia and astrocytes and further enhanced the upregulation of HO-1. In addition, PHPB inhibited the LPS-induced phosphorylation of ERK, P38 and JNK. These results suggest that PHPB is a potential candidate in the treatment of neurodegenerative diseases through inhibiting neuroinflammation.

Collagen-binding nanoparticles for extracellular anti-inflammatory peptide delivery decrease platelet activation, promote endothelial migration, and suppress inflammation

Peripheral artery disease is an atherosclerotic stenosis in the peripheral vasculature that is typically treated via percutaneous transluminal angioplasty. Deployment of the angioplasty balloon damages the endothelial layer, exposing the underlying collagen and allowing for the binding and activation of circulating platelets which initiate an inflammatory cascade leading to eventual restenosis. Here, we report on collagen-binding sulfated poly(N-isopropylacrylamide) nanoparticles that are able to target to the denuded endothelium. Once bound, these nanoparticles present a barrier that reduces cellular and platelet adhesion to the collagenous surface by 67% in whole blood and 59% in platelet-rich plasma under biologically relevant shear rates. In vitro studies indicate that the collagen-binding nanoparticles are able to load and release therapeutic quantities of anti-inflammatory peptides, with the particles reducing inflammation in endothelial and smooth muscle cells by 30% and 40% respectively. Once bound to collagen, the nanoparticles increased endothelial migration while avoiding uptake by smooth muscle cells, indicating that they may promote regeneration of the damaged endothelium while remaining anchored to the collagenous matrix and locally releasing anti-inflammatory peptides into the injured area. Combined, these collagen-binding nanoparticles have the potential to reduce inflammation, and the subsequent restenosis, while simultaneously promoting endothelial regeneration following balloon angioplasty.

STATEMENT OF SIGNIFICANCE

In this manuscript, we present our work on the development and characterization of a novel temperature sensitive collagen-binding nanoparticle system. We demonstrate that when bound to a collagenous matrix, the nanoparticles are able to promote endothelial migration while avoiding cellular uptake. We also show that the nanoparticles are able to reduce inflammation via the release of anti-inflammatory peptides which, when combined with its ability to inhibit platelet binding, could lead to reduced intimal hyperplasia following balloon angioplasty. The drug delivery platform presented represents a unique dual therapy biomaterial wherein the nanoparticle itself plays a crucial role in the system's overall therapeutic potential while simultaneously releasing anti-inflammatory peptides.

A Coral-Derived Compound Improves Functional Recovery after Spinal Cord Injury through Its Antiapoptotic and Anti-Inflammatory Effects

Background: Our previous in vitro results demonstrated that 11-dehydrosinulariolide significantly reduced 6-hydroxydopamine-induced cytotoxicity and apoptosis in a human neuroblastoma cell line, SH-SY5Y, and suppressed the expression of inducible NO synthase (iNOS) and cyclooxygenase 2 in lipopolysaccharide-stimulated macrophage cells. The neuroprotective and anti-inflammatory effects of 11-dehydrosinulariolide may be suitable for treating spinal cord injury (SCI). Methods: In the present study, Wistar rats were pretreated with 11-dehydrosinulariolide or saline through intrathecal injection after a thoracic spinal cord contusion injury induced using a New York University (NYU) impactor. The apoptotic cells were assessed using the terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. The expression and localization of proinflammatory, apoptosis-associated and cell survival-related pathway proteins were examined through immunoblotting and immunohistochemistry. Results: 11-Dehydrosinulariolide attenuated SCI-induced cell apoptosis by upregulating the antiapoptotic protein Bcl-2 and cell survival-related pathway proteins p-Akt and p-ERK, 8 h after SCI. Furthermore, the transcription factor p-CREB, which regulates Bcl-2 expression, was upregulated after 11-dehydrosinulariolide treatment. On day 7 after SCI, 11-dehydrosinulariolide exhibited an anti-inflammatory effect, attenuating SCI-induced upregulation of the inflammatory proteins iNOS and tumor necrosis factor-α. 11-Dehydrosinulariolide also induced an increase in the expression of arginase-1 and CD206, markers of M2 microglia, in the injured spinal cord on day 7 after SCI. Thus, the anti-inflammatory effect of 11-dehydrosinulariolide may be related to the promotion of an alternative pathway of microglia activation. Conclusion: The results show that 11-dehydrosinulariolide exerts antiapoptotic effects at 8 h after SCI and anti-inflammatory effects at 7 days after SCI. We consider that this compound may be a promising therapeutic agent for SCI.