Thrombin Mediates Migration of Rat Brain Astrocytes via PLC, Ca2+, CaMKII, PKCα, and AP-1-Dependent Matrix Metalloproteinase-9 Expression

Thrombin, a Key Driver of Pathological Inflammation in the Brain

Neurodegenerative diseases, including Alzheimer's disease (AD), are major contributors to death and disability worldwide. A multitude of evidence suggests that neuroinflammation is critical in neurodegenerative disease processes. Exploring the key mediators of neuroinflammation in AD, a prototypical neurodegenerative disease, could help identify pathologic inflammatory mediators and mechanisms in other neurodegenerative diseases. Elevated levels of the multifunctional inflammatory protein thrombin are commonly found in conditions that increase AD risk, including diabetes, atherosclerosis, and traumatic brain injury. Thrombin, a main driver of the coagulation cascade, has been identified as important to pathological events in AD and other neurodegenerative diseases. Furthermore, recent evidence suggests that coagulation cascade-associated proteins act as drivers of inflammation in the AD brain, and studies in both human populations and animal models support the view that abnormalities in thrombin generation promote AD pathology. Thrombin drives neuroinflammation through its pro-inflammatory activation of microglia, astrocytes, and endothelial cells. Due to the wide-ranging pro-inflammatory effects of thrombin in the brain, inhibiting thrombin could be an effective strategy for interrupting the inflammatory cascade which contributes to neurodegenerative disease progression and, as such, may be a potential therapeutic target for AD and other neurodegenerative diseases.

Emergent White Matter Degeneration in the rTg-DI Rat Model of Cerebral Amyloid Angiopathy Exhibits Unique Proteomic Changes

Cerebral amyloid angiopathy (CAA), characterized by cerebral vascular amyloid accumulation, neuroinflammation, microbleeds, and white matter (WM) degeneration, is a common comorbidity in Alzheimer disease and a prominent contributor to vascular cognitive impairment and dementia. WM loss was recently reported in the corpus callosum (CC) in the rTg-DI rat model of CAA. The current study shows that the CC exhibits a much lower CAA burden compared with the adjacent cortex. Sequential Window Acquisition of All Theoretical Mass Spectra tandem mass spectrometry was used to show specific proteomic changes in the CC with emerging WM loss and compare them with the proteome of adjacent cortical tissue in rTg-DI rats. In the CC, annexin A3, heat shock protein β1, and cystatin C were elevated at 4 months (M) before WM loss and at 12M with evident WM loss. Although annexin A3 and cystatin C were also enhanced in the cortex at 12M, annexin A5 and the leukodystrophy-associated astrocyte proteins megalencephalic leukoencephalopathy with subcortical cysts 1 and GlialCAM were distinctly elevated in the CC. Pathway analysis indicated neurodegeneration of axons, reflected by reduced expression of myelin and neurofilament proteins, was common to the CC and cortex; activation of Tgf-β1 and F2/thrombin was restricted to the CC. This study provides new insights into the proteomic changes that accompany WM loss in the CC of rTg-DI rats.

Anti-Inflammatory Effects of Rhamnetin on Bradykinin-Induced Matrix Metalloproteinase-9 Expression and Cell Migration in Rat Brain Astrocytes

Bradykinin (BK) has been shown to induce matrix metalloproteinase (MMP)-9 expression and participate in neuroinflammation. The BK/MMP-9 axis can be a target for managing neuroinflammation. Our previous reports have indicated that reactive oxygen species (ROS)-mediated nuclear factor-kappaB (NF-κB) activity is involved in BK-induced MMP-9 expression in rat brain astrocytes (RBA-1). Rhamnetin (RNT), a flavonoid compound, possesses antioxidant and anti-inflammatory effects. Thus, we proposed RNT could attenuate BK-induced response in RBA-1. This study aims to approach mechanisms underlying RNT regulating BK-stimulated MMP-9 expression, especially ROS and NF-κB. We used pharmacological inhibitors and siRNAs to dissect molecular mechanisms. Western blotting and gelatin zymography were used to evaluate protein and MMP-9 expression. Real-time PCR was used for gene expression. Wound healing assay was applied for cell migration. 2',7'-dichlorodihydrofluorescein diacetate (H2DCF-DA) and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) were used for ROS generation and NOX activity, respectively. Promoter luciferase assay and chromatin immunoprecipitation (ChIP) assay were applied to detect gene transcription. Our results showed that RNT inhibits BK-induced MMP-9 protein and mRNA expression, promoter activity, and cell migration in RBA-1 cells. Besides, the levels of phospho-PKCδ, NOX activity, ROS, phospho-ERK1/2, phospho-p65, and NF-κB p65 binding to MMP-9 promoter were attenuated by RNT. In summary, RNT attenuates BK-enhanced MMP-9 upregulation through inhibiting PKCδ/NOX/ROS/ERK1/2-dependent NF-κB activity in RBA-1.

Mild Traumatic Brain Injury/Concussion Initiates an Atypical Astrocyte Response Caused by Blood-Brain Barrier Dysfunction

Mild traumatic brain injury/concussion (mTBI) accounts for 70-90% of all reported TBI cases and causes long-lasting neurological consequences in 10-40% of patients. Recent clinical studies revealed increased blood-brain barrier (BBB) permeability in mTBI patients, which correlated with secondary damage after mTBI. However, the cascade of cellular events initiated by exposure to blood-borne factors resulting in sustained damage is not fully understood. We previously reported that astrocytes respond atypically to mTBI, rapidly losing many proteins essential to their homeostatic function, while classic scar formation does not occur. Here, we tested the hypothesis that mTBI-induced BBB damage causes atypical astrocytes through exposure to blood-borne factors. Using an mTBI mouse model, two-photon imaging, an endothelial cell-specific genetic ablation approach, and serum-free primary astrocyte cultures, we demonstrated that areas with atypical astrocytes coincide with BBB damage and that exposure of astrocytes to plasma proteins is sufficient to initiate loss of astrocyte homeostatic proteins. Although mTBI resulted in frequent impairment of both physical and metabolic BBB properties and leakage of small-sized blood-borne factors, deposition of the coagulation factor fibrinogen or vessel rupture were rare. Surprisingly, even months after mTBI, BBB repair did not occur in areas with atypical astrocytes. Together, these findings implicate that even relatively small BBB disturbances are sustained long term, and render nearby astrocytes dysfunctional, likely at the cost of neuronal health and function.

Calcium signaling in neuroglia

Glial cells exploit calcium (Ca²⁺) signals to perceive the information about the activity of the nervous tissue and the tissue environment to translate this information into an array of homeostatic, signaling and defensive reactions. Astrocytes, the best studied glial cells, use several Ca²⁺ signaling generation pathways that include Ca²⁺ entry through plasma membrane, release from endoplasmic reticulum (ER) and from mitochondria. Activation of metabotropic receptors on the plasma membrane of glial cells is coupled to an enzymatic cascade in which a second messenger, InsP₃ is generated thus activating intracellular Ca²⁺ release channels in the ER endomembrane. Astrocytes also possess store-operated Ca²⁺ entry and express several ligand-gated Ca²⁺ channels. In vivo astrocytes generate heterogeneous Ca²⁺ signals, which are short and frequent in distal processes, but large and relatively rare in soma. In response to neuronal activity intracellular and inter-cellular astrocytic Ca²⁺ waves can be produced. Astrocytic Ca²⁺ signals are involved in secretion, they regulate ion transport across cell membranes, and are contributing to cell morphological plasticity. Therefore, astrocytic Ca²⁺ signals are linked to fundamental functions of the central nervous system ranging from synaptic transmission to behavior. In oligodendrocytes, Ca²⁺ signals are generated by plasmalemmal Ca²⁺ influx, or by release from intracellular stores, or by combination of both. Microglial cells exploit Ca²⁺ permeable ionotropic purinergic receptors and transient receptor potential channels as well as ER Ca²⁺ release. In this contribution, basic morphology of glial cells, glial Ca²⁺ signaling toolkit, intracellular Ca²⁺ signals and Ca²⁺-regulated functions are discussed with focus on astrocytes.

Effects of Thrombin on the Neurovascular Unit in Cerebral Ischemia

Cerebral ischemia is a cerebrovascular disease with high morbidity and mortality that poses a significant burden on society and the economy. About 60% of cerebral ischemia is caused by thrombus, and the formation of thrombus proceeds from insoluble fibrin, following its transformation from liquid fibrinogen. In thrombus-induced ischemia, increased permeability of the blood-brain barrier (BBB), followed by the extravasation of blood components into the brain results in an altered brain microenvironment. Changes in the brain microenvironment affect brain function and the neurovascular unit (NVU), the working unit of the brain. Recent studies have reported that coagulation factors interact with the NVU and its components, but the specific function of this interaction is highly speculative and warrants further investigations. In this article, we reviewed the role of coagulation factors in cerebral ischemia and the role of coagulation factors in thrombosis. Additionally, the influence of thrombin on the NVU is introduced, as well as in the function of NVU, which may help to explore part of brain injury mechanism during ischemia. Lastly, we propose some novel therapeutic approaches on ischemic stroke by reducing the risk of coagulation.

Galangin Inhibits LPS-Induced MMP-9 Expression via Suppressing Protein Kinase-Dependent AP-1 and FoxO1 Activation in Rat Brain Astrocytes

Purpose

Neuroinflammation, characterized by the increased expression of inflammatory proteins such as matrix metalloproteinases (MMPs), plays a critical role in neurodegenerative disorders. Lipopolysaccharide (LPS) has been shown to upregulate MMP-9 expression through the activation of various transcription factors, including activator protein 1 (AP-1) and forkhead box protein O1 (FoxO1). The flavonoid 3,5,7-trihydroxy-2-phenyl-4H-1-benzopyran-4-one (galangin) has been demonstrated to possess antioxidant and anti-inflammatory properties in various types of cells. Here, we investigated the mechanisms underlying the inhibitory effect of galangin on LPS-induced MMP-9 expression in rat brain astrocytes (RBA-1 cells).

Methods

Pharmacological inhibitors and siRNAs were employed to explore the effects of galangin on LPS-challenged RBA-1 cells. Gelatin zymography, Western blotting, real-time PCR, and a luciferase reporter assay were used to detect MMP-9 activity, protein expression, mRNA levels, and promoter activity, respectively. The protein kinases involved in the LPS-induced MMP-9 expression were determined by Western blot. A chromatin immunoprecipitation (ChIP) assay was employed to evaluate the activity of c-Jun at the MMP-9 promoter.

Results

Galangin treatment attenuated the LPS-mediated induction of MMP-9 protein and mRNA expression, as well as the activity at the MMP-9 promoter. In addition, galangin exerted its inhibitory effects on MMP-9 expression through suppressing the LPS-stimulated activation of proline-rich tyrosine kinase (Pyk2), platelet-derived growth factor receptor beta (PDGFRβ), phosphoinositide 3-kinase (PI3K), protein kinase B (Akt), mammalian target of rapamycin (mTOR), and mitogen-activated protein kinases (MAPKs). Pretreatment with galangin attenuated the LPS-induced phosphorylation of c-Jun and FoxO1. LPS-induced cell migration was also suppressed by galangin pretreatment.

Conclusion

Galangin attenuates the LPS-induced inflammatory responses, including the induction of MMP-9 expression and cell migration, via inhibiting Pyk2/PDGFRβ/PI3K/Akt/mTOR/JNK1/JNK2 and p44/p42 MAPK cascade-dependent AP-1 and FoxO1 activities. These results provide new insights into the mechanisms through which galangin mitigates LPS-induced inflammatory responses, and suggest novel strategies for the management of LPS-related brain diseases.

Thrombin, a Mediator of Coagulation, Inflammation, and Neurotoxicity at the Neurovascular Interface: Implications for Alzheimer's Disease

The societal burden of Alzheimer’s disease (AD) is staggering, with current estimates suggesting that 50 million people world-wide have AD. Identification of new therapeutic targets is a critical barrier to the development of disease-modifying therapies. A large body of data implicates vascular pathology and cardiovascular risk factors in the development of AD, indicating that there are likely shared pathological mediators. Inflammation plays a role in both cardiovascular disease and AD, and recent evidence has implicated elements of the coagulation system in the regulation of inflammation. In particular, the multifunctional serine protease thrombin has been found to act as a mediator of vascular dysfunction and inflammation in both the periphery and the central nervous system. In the periphery, thrombin contributes to the development of cardiovascular disease, including atherosclerosis and diabetes, by inducing endothelial dysfunction and related inflammation. In the brain, thrombin has been found to act on endothelial cells of the blood brain barrier, microglia, astrocytes, and neurons in a manner that promotes vascular dysfunction, inflammation, and neurodegeneration. Thrombin is elevated in the AD brain, and thrombin signaling has been linked to both tau and amyloid beta, pathological hallmarks of the disease. In AD mouse models, inhibiting thrombin preserves cognition and endothelial function and reduces neuroinflammation. Evidence linking atrial fibrillation with AD and dementia indicates that anticoagulant therapy may reduce the risk of dementia, with targeting thrombin shown to be particularly effective. It is time for “outside-the-box” thinking about how vascular risk factors, such as atherosclerosis and diabetes, as well as the coagulation and inflammatory pathways interact to promote increased AD risk. In this review, we present evidence that thrombin is a convergence point for AD risk factors and as such that thrombin-based therapeutics could target multiple points of AD pathology, including neurodegeneration, vascular activation, and neuroinflammation. The urgent need for disease-modifying drugs in AD demands new thinking about disease pathogenesis and an exploration of novel drug targets, we propose that thrombin inhibition is an innovative tactic in the therapeutic battle against this devastating disease.

Neurons, Glia, Extracellular Matrix and Neurovascular Unit: A Systems Biology Approach to the Complexity of Synaptic Plasticity in Health and Disease

The synaptic cleft has been vastly investigated in the last decades, leading to a novel and fascinating model of the functional and structural modifications linked to synaptic transmission and brain processing. The classic neurocentric model encompassing the neuronal pre- and post-synaptic terminals partly explains the fine-tuned plastic modifications under both pathological and physiological circumstances. Recent experimental evidence has incontrovertibly added oligodendrocytes, astrocytes, and microglia as pivotal elements for synapse formation and remodeling (tripartite synapse) in both the developing and adult brain. Moreover, synaptic plasticity and its pathological counterpart (maladaptive plasticity) have shown a deep connection with other molecular elements of the extracellular matrix (ECM), once considered as a mere extracellular structural scaffold altogether with the cellular glue (i.e., glia). The ECM adds another level of complexity to the modern model of the synapse, particularly, for the long-term plasticity and circuit maintenance. This model, called tetrapartite synapse, can be further implemented by including the neurovascular unit (NVU) and the immune system. Although they were considered so far as tightly separated from the central nervous system (CNS) plasticity, at least in physiological conditions, recent evidence endorsed these elements as structural and paramount actors in synaptic plasticity. This scenario is, as far as speculations and evidence have shown, a consistent model for both adaptive and maladaptive plasticity. However, a comprehensive understanding of brain processes and circuitry complexity is still lacking. Here we propose that a better interpretation of the CNS complexity can be granted by a systems biology approach through the construction of predictive molecular models that enable to enlighten the regulatory logic of the complex molecular networks underlying brain function in health and disease, thus opening the way to more effective treatments.

Lysophosphatidylcholine-induced mitochondrial fission contributes to collagen production in human cardiac fibroblasts

Lysophosphatidylcholine (LPC) may accumulate in the heart to cause fibrotic events, which is mediated through fibroblast activation and collagen accumulation. Here, we evaluated the mechanisms underlying LPC-mediated collagen induction via mitochondrial events in human cardiac fibroblasts (HCFs), coupling application of the pharmacologic cyclooxygenase-2 (COX-2) inhibitor, celecoxib, and genetic mutations in FOXO1 on the fibrosis pathway. In HCFs, LPC caused prostaglandin E2 (PGE2)/PGE2 receptor 4 (EP4)-dependent collagen induction via activation of transcriptional activity of forkhead box protein O1 (FoxO1) on COX-2 gene expression. These responses were mediated through LPC-induced generation of mitochondrial reactive oxygen species (mitoROS), as confirmed by ex vivo studies, which indicated that LPC increased COX-2 expression and oxidative stress. LPC-induced mitoROS mediated the activation of protein kinase C (PKC)α, which interacted with and phosphorylated dynamin-related protein 1 (Drp1) at Ser616, thereby increasing Drp1-mediated mitochondrial fission and mitochondrial depolarization. Furthermore, inhibition of PKCα and Drp1 reduced FoxO1-mediated phosphorylation at Ser256 and nuclear accumulation, which suppressed COX-2/PGE2 expression and collagen production. Moreover, pretreatment with celecoxib or COX-2 siRNA suppressed WT FoxO1; mutated Ser256-to-Asp256 FoxO1-enhanced collagen induction, which was reversed by addition of PGE2 Our results demonstrate that LPC-induced generation of mitoROS regulates PKCα-mediated Drp1-dependent mitochondrial fission and COX-2 expression via a PKCα/Drp1/FoxO1 cascade, leading to PGE2/EP4-mediated collagen induction. These findings provide new insights about the role of LPC in the pathway of fibrotic injury in HCFs.

RTA 408 Inhibits Interleukin-1β-Induced MMP-9 Expression via Suppressing Protein Kinase-Dependent NF-κB and AP-1 Activation in Rat Brain Astrocytes

Neuroinflammation is characterized by the elevated expression of various inflammatory proteins, including matrix metalloproteinases (MMPs), induced by various pro-inflammatory mediators, which play a critical role in neurodegenerative disorders. Interleukin-1β (IL-1β) has been shown to induce the upregulation of MMP-9 through nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX)-reactive oxygen species (ROS)-dependent signaling pathways. N-(2-cyano-3,12-dioxo-28-noroleana-1,9(11)-dien-17-yl)-2-2-difluoropropanamide (RTA 408), a novel synthetic triterpenoid, has been shown to possess anti-oxidant and anti-inflammatory properties in various types of cells. Here, we evaluated the effects of RTA 408 on IL-1β-induced inflammatory responses by suppressing MMP-9 expression in a rat brain astrocyte (RBA-1) line. IL-1β-induced MMP-9 protein and mRNA expression, and promoter activity were attenuated by RTA 408. The increased level of ROS generation in RBA-1 cells exposed to IL-1β was attenuated by RTA 408, as determined by using 2′,7′-dichlorodihydrofluorescein diacetate (DCFH-DA) and CellROX. In addition, the inhibitory effects of RTA 408 on MMP-9 expression resulted from the suppression of the IL-1β-stimulated activation of Pyk2 (proline-rich tyrosine kinase), platelet-derived growth factor receptor β (PDGFRβ), Akt, ROS, and mitogen-activated protein kinases (MAPKs). Pretreatment with RTA 408 attenuated the IL-1β-induced c-Jun phosphorylation, mRNA expression, and promoter activity. IL-1β-stimulated nuclear factor-κB (NF-κB) p65 phosphorylation, translocation, and promoter activity were also attenuated by RTA 408. Furthermore, IL-1β-induced glial fibrillary acidic protein (GFAP) protein and mRNA expression, and cell migration were attenuated by pretreatment with RTA 408. These results provide new insights into the mechanisms by which RTA 408 attenuates IL-1β-mediated inflammatory responses and exerts beneficial effects for the management of brain diseases.

Heterologous calcium-dependent inactivation of Orai1 by neighboring TRPV1 channels modulates cell migration and wound healing

Store-operated calcium entry (SOCE) is an essential calcium influx mechanism in animal cells. One of the most important auto regulatory control systems involves calcium-dependent inactivation (CDI) of the Orai channel, which prevents excessive calcium influx. In the present study we analyze the role of two channels in the induction of CDI on Orai1. Here we show that calcium entering through freely diffusing TRPV1 channels induce strong CDI on Orai1 while calcium entering through P2X₄ channel does not. TRPV1 can induce CDI on Orai1 because both channels were found in close proximity in the cell membrane. This was not observed with P2X₄ channels. To our knowledge, this is the first study demonstrating that calcium arising from different channels may contribute to the modulation of Orai1 through CDI in freely diffusing single channels of living cells. Our results highlight the role of TRPV1-mediated CDI on Orai1 in cell migration and wound healing.

Bastián-Eugenio et al. showed that calcium entering the cell via TRPV1, but not P2X₄ channels, can induce calcium-dependent inactivation of Orai1. This inactivation impacts thrombin-induced cell migration and wound healing suggesting an important role of Orai1 modulation by TRPV1 channels.

A Perspective of Coagulation Dysfunction in Multiple Sclerosis and in Experimental Allergic Encephalomyelitis

A key role of both coagulation and vascular thrombosis has been reported since the first descriptions of multiple sclerosis (MS). Subsequently, the observation of a close concordance between perivascular fibrin(ogen) deposition and the occurrence of clinical signs in experimental allergic encephalomyelitis (EAE), an animal model of MS, led to numerous investigations focused on the role of thrombin and fibrin(ogen). Indeed, the activation of microglia, resident innate immune cells, occurs early after fibrinogen leakage in the pre-demyelinating lesion stage of EAE and MS. Thrombin has both neuroprotective and pro-apoptotic effects according to its concentration. After exposure to high concentrations of thrombin, astrocytes become reactive and lose their neuroprotective and supportive functions, microglia proliferate, and produce reactive oxygen species, IL-1β, and TNFα. Heparin inhibits the thrombin generation and suppresses EAE. Platelets play an important role too. Indeed, in the acute phase of the disease, they begin the inflammatory response in the central nervous system by producing of IL-1alpha and triggering and amplifying the immune response. Their depletion, on the contrary, ameliorates the course of EAE. Finally, it has been proven that the use of several anticoagulant agents can successfully improve EAE. Altogether, these studies highlight the role of the coagulation pathway in the pathophysiology of MS and suggest possible therapeutic targets that may complement existing treatments.

Galangin Inhibits Thrombin-Induced MMP-9 Expression in SK-N-SH Cells via Protein Kinase-Dependent NF-κB Phosphorylation

Galangin, a member of the flavonol compounds of the flavonoids, could exert anti-inflammatory effects in various cell types. It has been used for the treatment of arthritis, airway inflammation, stroke, and cognitive impairment. Thrombin, one of the regulators of matrix metalloproteinase (MMPs), has been known as a vital factor of physiological and pathological processes, including cell migration, the blood–brain barrier breakdown, brain edema formation, neuroinflammation, and neuronal death. MMP-9 especially may contribute to neurodegenerative diseases. However, the effect of galangin in combating thrombin-induced MMP-9 expression is not well understood in neurons. Therefore, we attempted to explore the molecular mechanisms by which galangin inhibited MMP-9 expression and cell migration induced by thrombin in SK-N-SH cells (a human neuroblastoma cell line). Gelatin zymography, western blot, real-time PCR, and cell migration assay were used to elucidate the inhibitory effects of galangin on the thrmbin-mediated responses. The results showed that galangin markedly attenuated the thrombin-stimulated phosphorylation of proto-oncogene tyrosine-protein kinase (c-Src), proline-rich tyrosine kinase 2 (Pyk2), protein kinase C (PKC)α/β/δ, protein kinase B (Akt), mammalian target of rapamycin (mTOR), p42/p44 mitogen-activated protein kinase (MAPK), Jun amino-terminal kinases (JNK)1/2, p38 MAPK, forkhead box protein O1 (FoxO1), p65, and c-Jun and suppressed MMP-9 expression and cell migration in SK-N-SH cells. Our results concluded that galangin blocked the thrombin-induced MMP-9 expression in SK-N-SH cells via inhibiting c-Src, Pyk2, PKCα/βII/δ, Akt, mTOR, p42/p44 MAPK, JNK1/2, p38 MAPK, FoxO1, c-Jun, and p65 phosphorylation and ultimately attenuated cell migration. Therefore, galangin may be a potential candidate for the management of brain inflammatory diseases.

Neuro-Immune Hemostasis: Homeostasis and Diseases in the Central Nervous System

Coagulation and the immune system interact in several physiological and pathological conditions, including tissue repair, host defense, and homeostatic maintenance. This network plays a key role in diseases of the central nervous system (CNS) by involving several cells (CNS resident cells, platelets, endothelium, and leukocytes) and molecular pathways (protease activity, complement factors, platelet granule content). Endothelial damage prompts platelet activation and the coagulation cascade as the first physiological step to support the rescue of damaged tissues, a flawed rescuing system ultimately producing neuroinflammation. Leukocytes, platelets, and endothelial cells are sensitive to the damage and indeed can release or respond to chemokines and cytokines (platelet factor 4, CXCL4, TNF, interleukins), and growth factors (including platelet-derived growth factor, vascular endothelial growth factor, and brain-derived neurotrophic factor) with platelet activation, change in capillary permeability, migration or differentiation of leukocytes. Thrombin, plasmin, activated complement factors and matrix metalloproteinase-1 (MMP-1), furthermore, activate intracellular transduction through complement or protease-activated receptors. Impairment of the neuro-immune hemostasis network induces acute or chronic CNS pathologies related to the neurovascular unit, either directly or by the systemic activation of its main steps. Neurons, glial cells (astrocytes and microglia) and the extracellular matrix play a crucial function in a “tetrapartite” synaptic model. Taking into account the neurovascular unit, in this review we thoroughly analyzed the influence of neuro-immune hemostasis on these five elements acting as a functional unit (“pentapartite” synapse) in the adaptive and maladaptive plasticity and discuss the relevance of these events in inflammatory, cerebrovascular, Alzheimer, neoplastic and psychiatric diseases. Finally, based on the solid reviewed data, we hypothesize a model of neuro-immune hemostatic network based on protein–protein interactions. In addition, we propose that, to better understand and favor the maintenance of adaptive plasticity, it would be useful to construct predictive molecular models, able to enlighten the regulating logic of the complex molecular network, which belongs to different cellular domains. A modeling approach would help to define how nodes of the network interact with basic cellular functions, such as mitochondrial metabolism, autophagy or apoptosis. It is expected that dynamic systems biology models might help to elucidate the fine structure of molecular events generated by blood coagulation and neuro-immune responses in several CNS diseases, thereby opening the way to more effective treatments.

Neuro-Coagulopathy: Blood Coagulation Factors in Central Nervous System Diseases

Blood coagulation factors and other proteins, with modulatory effects or modulated by the coagulation cascade have been reported to affect the pathophysiology of the central nervous system (CNS). The protease-activated receptors (PARs) pathway can be considered the central hub of this regulatory network, mainly through thrombin or activated protein C (aPC). These proteins, in fact, showed peculiar properties, being able to interfere with synaptic homeostasis other than coagulation itself. These specific functions modulate neuronal networks, acting both on resident (neurons, astrocytes, and microglia) as well as circulating immune system cells and the extracellular matrix. The pleiotropy of these effects is produced through different receptors, expressed in various cell types, in a dose- and time-dependent pattern. We reviewed how these pathways may be involved in neurodegenerative diseases (amyotrophic lateral sclerosis, Alzheimer's and Parkinson's diseases), multiple sclerosis, ischemic stroke and post-ischemic epilepsy, CNS cancer, addiction, and mental health. These data open up a new path for the potential therapeutic use of the agonist/antagonist of these proteins in the management of several central nervous system diseases.

Astrocytes in Migration

Cell migration is a fundamental phenomenon that underlies tissue morphogenesis, wound healing, immune response, and cancer metastasis. Great progresses have been made in research methodologies, with cell migration identified as a highly orchestrated process. Brain is considered the most complex organ in the human body, containing many types of neural cells with astrocytes playing crucial roles in monitoring normal functions of the central nervous system. Astrocytes are mostly quiescent under normal physiological conditions in the adult brain but become migratory after injury. Under most known pathological conditions in the brain, spinal cord and retina, astrocytes are activated and become hypertrophic, hyperplastic, and up-regulating GFAP based on the grades of severity. These three observations are the hallmark in glia scar formation-astrogliosis. The reactivation process is initiated with structural changes involving cell process migration and ended with cell migration. Detailed mechanisms in astrocyte migration have not been studied extensively and remain largely unknown. Here, we therefore attempt to review the mechanisms in migration of astrocytes.

PLC-γ1 is involved in the inflammatory response induced by influenza A virus H1N1 infection

We have previously reported that phosphoinositide-specific phospholipase γ1 (PLC-γ1) signaling is activated by influenza virus H1N1 infection and mediates efficient viral entry in human epithelial cells. In this study, we show that H1N1 also activates PLCγ-1 signaling in human promonocytic cell line -derived macrophages. Surprisingly, the activated PLCγ-1 signaling is not important for viral replication in macrophages, but is involved in the virus-induced inflammatory responses. PLC-γ1-specific inhibitor U73122 strongly inhibits the H1N1 virus-induced NF-κB signaling, blocking the up-regulation of TNF-α, IL-6, MIP-1α, and reactive oxidative species. In a positive feedback loop, IL-1β and TNF-α activate the PLCγ-1 signaling in both epithelial and macrophage cell lines. In summary, we have shown for the first time that the PLCγ-1 signaling plays an important role in the H1N1-induced inflammatory responses. Our study suggests that targeting the PLCγ-1 signaling is a potential antiviral therapy against H1N1 by inhibiting both viral replication and excessive inflammation.

Proline-rich tyrosine kinase 2 via enhancing signal transducer and activator of transcription 3-dependent cJun expression mediates retinal neovascularization

Despite the involvement of proline-rich tyrosine kinase 2 (Pyk2) in endothelial cell angiogenic responses, its role in pathological retinal angiogenesis is not known. In the present study, we show that vascular endothelial growth factor A (VEGFA) induces Pyk2 activation in mediating human retinal microvascular endothelial cell (HRMVEC) migration, sprouting and tube formation. Downstream to Pyk2, VEGFA induced signal transducer and activator of transcription 3 (STAT3) activation and cJun expression in the modulation of HRMVEC migration, sprouting and tube formation. Consistent with these observations, hypoxia induced activation of Pyk2-STAT3-cJun signaling axis and siRNA-mediated downregulation of Pyk2, STAT3 or cJun levels substantially inhibited hypoxia-induced retinal endothelial cell proliferation, tip cell formation and neovascularization. Together, these observations suggest that activation of Pyk2-mediated STAT3-cJun signaling is required for VEGFA-induced HRMVEC migration, sprouting and tube formation in vitro and hypoxia-induced retinal endothelial cell proliferation, tip cell formation and neovascularization in vivo.

Thrombin Enhanced Matrix Metalloproteinase-9 Expression and Migration of SK-N-SH Cells via PAR-1, c-Src, PYK2, EGFR, Erk1/2 and AP-1

Neuroinflammation is a hallmark of neurodegenerative disorders in the central nerve system (CNS). Thrombin has been known as one of the factors in pathological processes including migration, blood-brain barrier breakdown, brain edema formation, neuroinflammation, and neuronal death. Thrombin has been shown to be a regulator of matrix metalloproteinase (MMPs) expression leading to cell migration. Among MMPs, the elevated expression of MMP-9 has been observed in patients with brain diseases, which may contribute to the pathology of neuroinflammatory and neurodegenerative diseases. However, the mechanisms underlying thrombin-induced MMP-9 expression in SK-N-SH cells were not completely understood. Here, we used gelatin zymography, Western blot, real-time PCR, promoter activity assay, and cell migration assay to demonstrate that thrombin induced the expression of pro-form MMP-9 protein and messenger RNA (mRNA), and promoter activity in SK-N-SH cells, which were attenuated by pretreatment with the pharmacological inhibitor of protease-activated receptor-1 (PAR-1, SCH79797), Gi-coupled receptor (GPA2), c-Src (PP1), Pyk2 (PF431396), EGFR (AG1478), PI3K (LY294002), Akt (SH-5), MEK1/2 (U0126), or AP-1 (TanshinoneIIA) and transfection with small interfering RNA (siRNA) of PAR-1, Gi, c-Src, Pyk2, EGFR, Akt, p44, p42, or c-Jun. Moreover, thrombin-stimulated c-Src, Pyk2, EGFR, Akt, p42/p44 MAPK, or c-Jun phosphorylation was attenuated by their respective inhibitor of PP1, PF431396, AG1478, SH-5, U0126, or TanshinoneIIA. Finally, pretreatment with these inhibitors also blocked thrombin-induced SK-N-SH cell migration. Our results concluded that thrombin binding to PAR-1 receptor activated Gi-protein/c-Src/Pyk2/EGFR/PI3K/Akt/p42/p44 MAPK cascade, which in turn elicited AP-1 activation and ultimately evoked MMP-9 expression and cell migration in SK-N-SH cells.

Thrombin/Matrix Metalloproteinase-9-Dependent SK-N-SH Cell Migration is Mediated Through a PLC/PKC/MAPKs/NF-κB Cascade

Thrombin has been known to activate inflammatory genes including matrix metalloproteinases (MMPs). The elevated expression of MMP-9 has been observed in patients with neuroinflammatory diseases and may contribute to the pathology of brain diseases. However, the mechanisms underlying thrombin-induced MMP-9 expression in SK-N-SH cells remain unknown. The effects of thrombin on MMP-9 expression were examined in SK-N-SH cells by gelatin zymography, Western blot, real-time PCR, promoter activity assay, and cell migration assay. The detailed mechanisms were analyzed by using pharmacological inhibitors and small intefering RNA (siRNA) transfection. Here, we demonstrated that thrombin induced the expression of proform MMP-9 and migration of SK-N-SH cells, which were attenuated by pretreatment with the inhibitor of thrombin (PPACK), Gq (GPA2A), PC-PLC (D609), PI-PLC (ET-18-OCH₃), nonselective protien kinase C (PKC, GF109203X), PKCα/βII (Gö6983), PKCδ (Rottlerin), p38 mitogen-activated protein kinases (MAPK) (SB202190), JNK1/2 (SP600125), or NF-κB (Bay11-7082 or Helenalin) and transfection with siRNA of Gq, PKCα, PKCβ, PKCδ, p38, JNK1/2, IKKα, IKKβ, or p65. Moreover, thrombin-stimulated PKCα/βII, PKCδ, p38 MAPK, JNK1/2, or p65 phosphorylation was abrogated by their respective inhibitor of PPACK, GPA2A, D609, ET-18-OCH₃, Gö6983, Rottlerin, SB202190, SP600125, Bay11-7082, or Helenalin. Pretreatment with these inhibitors or transfection with MMP-9 siRNA also blocked thrombin-induced SK-N-SH cell migration. Our results show that thrombin stimulates a Gq/PLC/PKCs/p38 MAPK and JNK1/2 cascade, which in turn triggers NF-κB activation and ultimately induces MMP-9 expression and cell migration in SK-N-SH cells.

Anti-inflammatory activities of phospholipase C inhibitor U73122: Inhibition of monocyte-to-macrophage transformation and LPS-induced pro-inflammatory cytokine expression

A wide range of biological processes are controlled by phospholipase C (PLC)/Ca(2+) signaling, which could be blocked by PLC-specific inhibitor U73122. Whether inhibition of PLC with chemical inhibitor U73122 affects the inflammatory response in monocytes/macrophages is currently unknown. In this study, we demonstrated that U73122 inhibited PMA-induced in vitro differentiation of human promonocytic U937 cells into macrophages as reflected by the reduction of cell adherence and the decreased expression of macrophage specific marker CD163. It is possible that U73122 blocked PMA-induced adhesion of U937 cells partially by down regulation and inactivation of both Pyk2 and paxillin signaling. Furthermore, the expression of LPS-induced pro-inflammatory cytokines TNF-α and IL-1β was significantly blocked by U73122 in both dU937 cells and mouse primary peritoneal macrophages. These results suggest that PLC is involved in the sophisticated inflammatory response by monocytes/macrophages, and thereby chemical antagonists of PLC may be potential agents for the suppression of inflammatory response.

PKCα promotes the mesenchymal to amoeboid transition and increases cancer cell invasiveness

Background

The local invasion of tumor cells into the surrounding tissue is the first and most critical step of the metastatic cascade. Cells can invade either collectively, or individually. Individual cancer cell invasion can occur in the mesenchymal or amoeboid mode, which are mutually interchangeable. This plasticity of individual cancer cell invasiveness may represent an escape mechanism for invading cancer cells from anti-metastatic treatment.

Methods

To identify new signaling proteins involved in the plasticity of cancer cell invasiveness, we performed proteomic analysis of the amoeboid to mesenchymal transition with A375m2 melanoma cells in a 3D Matrigel matrix.

Results

In this screen we identified PKCα as an important protein for the maintenance of amoeboid morphology. We found that the activation of PKCα resulted in the mesenchymal-amoeboid transition of mesenchymal K2 and MDA-MB-231 cell lines. Consistently, PKCα inhibition led to the amoeboid-mesenchymal transition of amoeboid A375m2 cells. Next, we showed that PKCα inhibition resulted in a considerable decrease in the invading abilities of all analyzed cancer cell lines.

Conclusions

Our results suggest that PKCα is an important protein for maintenance of the amoeboid morphology of cancer cells, and that downregulation of PKCα results in the amoeboid to mesenchymal transition. Our data also suggest that PKCα is important for both mesenchymal and amoeboid invasiveness, making it an attractive target for anti-metastatic therapies.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1347-1) contains supplementary material, which is available to authorized users.

Thrombin enhances NGF-mediated neurite extension via increased and sustained activation of p44/42 MAPK and p38 MAPK

Rapid neurite remodeling is fundamental to nervous system development and plasticity. It involves neurite extension that is regulated by NGF through PI3K/AKT, p44/42 MAPK and p38 MAPK. It also involves neurite retraction that is regulated by the serine protease, thrombin. However, the intracellular signaling pathway by which thrombin causes neurite retraction is unknown. Using the PC12 neuronal cell model, we demonstrate that thrombin utilizes the PI3K/AKT pathway for neurite retraction in NGF-differentiated cells. Interestingly, however, we found that thrombin enhances NGF-induced neurite extension in differentiating cells. This is achieved through increased and sustained activation of p44/42 MAPK and p38 MAPK. Thus, thrombin elicits opposing effects in differentiated and differentiating cells through activation of distinct signaling pathways: neurite retraction in differentiated cells via PI3K/AKT, and neurite extension in differentiating cells via p44/42 MAPK and p38 MAPK. These findings, which also point to a novel cooperative role between thrombin and NGF, have significant implications in the development of the nervous system and the disease processes that afflicts it as well as in the potential of combined thrombin and NGF therapy for impaired learning and memory, and spinal cord injury which all require neurite extension and remodeling.

Phospholipase C activity increases in cerebrospinal fluid from migraineurs in proportion to the number of comorbid conditions: a case-control study

Background

Migraineurs are more often afflicted by comorbid conditions than those without primary headache disorders, though the linking pathophysiological mechanism(s) is not known. We previously reported that phosphatidylcholine-specific phospholipase C (PC-PLC) activity in cerebrospinal fluid (CSF) increased during migraine compared to the same individual’s well state. Here, we examined whether PC-PLC activity from a larger group of well-state migraineurs is related to the number of their migraine comorbidities.

Methods

In a case–control study, migraineurs were diagnosed using International Headache Society criteria, and controls had no primary headache disorder or family history of migraine. Medication use, migraine frequency, and physician-diagnosed comorbidities were recorded for all participants. Lumbar CSF was collected between the hours of 1 and 5 pm, examined immediately for cells and total protein, and stored at −80°C. PC-PLC activity in thawed CSF was measured using a fluorometric enzyme assay. Multivariable logistic regression was used to evaluate age, gender, medication use, migraine frequency, personality scores, and comorbidities as potential predictors of PC-PLC activity in CSF.

Results

A total of 18 migraineurs-without-aura and 17 controls participated. In a multivariable analysis, only the number of comorbidities was related to PC-PLC activity in CSF, and only in migraineurs [parameter estimate (standard error) = 1.77, p = 0.009].

Conclusion

PC-PLC activity in CSF increases with increasing number of comorbidities in migraine-without-aura. These data support involvement of a common lipid signaling pathway in migraine and in the comorbid conditions.