Calmodulin kinase II-dependent transactivation of PDGF receptors mediates astrocytic MMP-9 expression and cell motility induced by lipoteichoic acid

Ginsenoside Re exhibits neuroprotective effects by inhibiting neuroinflammation via CAMK/MAPK/NF‑κB signaling in microglia

Ginsenoside Re (G-Re) is a panaxatriol saponin and one of the pharmacologically active natural constituents of ginseng (Panax ginseng C.A. Meyer). G-Re has antioxidant, anti-inflammatory and antidiabetic effects. The present study aimed to investigate the effects of G-Re on neuroinflammatory responses in lipopolysaccharide (LPS)-stimulated microglia and its protective effects on hippocampal neurons. Cytokine levels were measured using ELISA and reactive oxygen species (ROS) levels were assessed using flow cytometry and fluorescence microscopy. Protein levels of inflammatory molecules and kinase activity were assessed by western blotting. Cell viability was assessed by MTT assay; apoptosis was estimated by Annexin V apoptosis assay. The results revealed that G-Re significantly inhibited the production of IL-6, TNF-α, nitric oxide (NO) and ROS in BV2 microglial cells, and that of NO in mouse primary microglia, without affecting cell viability. G-Re also inhibited the nuclear translocation of NF-κB, and phosphorylation and degradation of IκB-α. In addition, G-Re dose-dependently suppressed LPS-mediated phosphorylation of Ca²⁺/calmodulin-dependent protein kinase (CAMK)2, CAMK4, extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinases (JNK). Moreover, the conditioned medium from LPS-stimulated microglial cells induced HT22 hippocampal neuronal cell death, whereas that from microglial cells incubated with both LPS and G-Re ameliorated HT22 cell death in a dose-dependent manner. These results suggested that G-Re suppressed the production of pro-inflammatory mediators by blocking CAMK/ERK/JNK/NF-κB signaling in microglial cells and protected hippocampal cells by reducing these inflammatory and neurotoxic factors released from microglial cells. The present findings indicated that G-Re may be a potential treatment option for neuroinflammatory disorders and could have therapeutic potential for various neurodegenerative diseases.

Müller cells and astrocytes in tractional macular disorders

Tractional deformations of the fovea mainly arise from an anomalous posterior vitreous detachment and contraction of epiretinal membranes, and also occur in eyes with cystoid macular edema or high myopia. Traction to the fovea may cause partial- and full-thickness macular defects. Partial-thickness defects are foveal pseudocysts, macular pseudoholes, and tractional, degenerative, and outer lamellar holes. The morphology of the foveal defects can be partly explained by the shape of Müller cells and the location of tissue layer interfaces of low mechanical stability. Because Müller cells and astrocytes provide the structural scaffold of the fovea, they are active players in mediating tractional alterations of the fovea, in protecting the fovea from such alterations, and in the regeneration of the foveal structure. Tractional and degenerative lamellar holes are characterized by a disruption of the Müller cell cone in the foveola. After detachment or disruption of the cone, Müller cells of the foveal walls support the structural stability of the foveal center. After tractional elevation of the inner layers of the foveal walls, possibly resulting in foveoschisis, Müller cells transmit tractional forces from the inner to the outer retina leading to central photoreceptor layer defects and a detachment of the neuroretina from the retinal pigment epithelium. This mechanism plays a role in the widening of outer lameller and full-thickness macular holes, and contributes to visual impairment in eyes with macular disorders caused by conractile epiretinal membranes. Müller cells of the foveal walls may seal holes in the outer fovea and mediate the regeneration of the fovea after closure of full-thickness holes. The latter is mediated by the formation of temporary glial scars whereas persistent glial scars impede regular foveal regeneration. Further research is required to improve our understanding of the roles of glial cells in the pathogenesis and healing of tractional macular disorders.

Foveal configurations with disappearance of the foveal pit in eyes with macular pucker: Presumed role of Müller cells in the formation of foveal herniation

Many eyes with macular pucker are characterized by a centripetal displacement of the inner foveal layers which may result in a disappearance of the foveal pit. In this retrospective case series of 90 eyes with macular pucker of 90 patients, we describe using spectral-domain optical coherence tomography different foveal configurations with ectopic inner foveal layers, document the relationship between posterior vitreous detachment (PVD) and idiopathic epiretinal membrane (ERM) formation and spontaneous and postoperative morphological alterations of the fovea, and propose an active role of Müller cells in the development of foveal herniation. We found that ERM were formed during or after partial perifoveal PVD, or after foveal deformations caused by tissue edema. The ERM-mediated centripetal displacement of the inner foveal layers and in various eyes anterior hyaloidal traction caused a disappearance of the foveal pit and an anterior stretching of the foveola with a thickening of the central outer nuclear layer (ONL). After the edges of the thickened inner layers of the foveal walls moved together, continuous centripetal displacement of the inner foveal layers generated a bulge of the fovea towards the vitreous (foveal herniation). Macular pseudoholes with a herniation of the inner foveal layers show that the outer layer of the protruding foveal walls is the outer plexiform layer (OPL). If the ERM covered the foveal walls and parafova, but not the foveola, the inner layers of the foveal walls were not fully centripetally displaced and the foveal pit was present. The visual acuity of eyes with ectopic inner foveal layers was inversely correlated with the thickness of the foveal center. Spontaneous morphological alterations after disappearance of the foveal pit may include the development of cystoid macular edema or additional thickening of the foveal tissue and foveal herniation. The foveal configuration with ectopic inner layers of the foveal walls and a thick central ONL persisted over longer postoperative time periods. The data show that the centripetal displacement of the inner foveal layers in eyes with macular pucker, which results in a disappearance of the foveal pit, may also generate foveal herniation which is suggested to be caused by contraction of Müller cell processes in the OPL. The centripetal displacement of the inner foveal layers and the formation of foveal herniation are suggested to reverse the foveal pit formation during development.

LOX inhibition downregulates MMP-2 and MMP-9 in gastric cancer tissues and cells

Objective: The objective of this study was to analyze the effects of lysyl oxidase (LOX) on the expression and enzyme activity of the matrix metalloproteinases 2 (MMP-2) and 9 (MMP-9) and to study its preliminary effect mechanisms.

Methods: We collected fresh cancer specimens from 49 gastric cancer patients who underwent surgery. Immunohistochemistry was used to quantitate the protein expression levels of LOX and MMP-9 in gastric cancer tissues and to analyze their correlation. Also, six-week old nude mice were divided into a control group and a LOX inhibition group. SGC-7901 gastric cancer cells were inoculated subcutaneously into the backs of the two groups of these mice to construct a gastric cancer-bearing nude mouse model. In the LOX inhibition group, β-aminopropionitrile (BAPN) was used to inhibit LOX. Western blotting was used to quantitate the relative expression levels of MMP-2 and MMP-9 in mouse tumor tissues, and gelatin zymography was used to quantitate their enzyme activity levels. In addition, BGC-823 gastric cancer cells were cultured, then 0.1 mM, 0.2 mM, and 0.3 mM BAPN and 2.5 nM, 5 nM, and 10 nM LOX were added to treat BGC-823 cells. ELISA and gelatin zymography were used to quantitate the protein concentrations and changes in enzyme activity of MMP-2 and MMP-9 in the culture supernatant. Western blotting was used to quantitate the relative expression levels of platelet derived growth factor receptor (PDGFR) in the BGC-823 gastric cancer cells after LOX inhibition and exogenous LOX addition.

Results: In the tissues from the gastric cancer patients, the relative expression levels of LOX and MMP-9 were positively correlated (r = 0.326, P < 0.05). Compared with the control group, the tumor tissues from mice in the LOX inhibition group had reduced relative expression levels and enzyme activities of MMP-2 and MMP-9 (P < 0.05). After LOX were inhibited with different concentrations of BAPN in BGC-823 gastric cancer cells, the protein concentrations and enzyme activity levels of MMP-2 and MMP-9 in the culture supernatants were decreased (P < 0.05). In addition, the relative expression level of PDGFR in gastric cancer was decreased when BAPN concentrations increased, showing a negative dose-dependent manner (r_PDGFR-α = -0.964, r_PDGFR-β = -0.988, P < 0.05). After exogenous LOX treating BGC-823 cells, the concentrations and enzyme activity levels of MMP-2 and MMP-9 in the cell supernatant were increased (P < 0.05). Further, the relative expression of PDGFR in gastric cancer cells was increased with the increase of exogenous LOX, showing a positive dose-dependent manner (r_PDGFR-α=0.952, r_PDGFR-β=0.953, P<0.05).

Conclusions: LOX inhibition can inhibit the expression and enzyme activity of MMP-2 and MMP-9 in gastric cancer tissues and cells, and the probable mechanism is through its effects on the PDGF-PDGFR signaling pathway.

Calmodulin promotes matrix metalloproteinase 9 production and cell migration by inhibiting the ubiquitination and degradation of TBC1D3 oncoprotein in human breast cancer cells

The hominoid oncoprotein TBC1D3 enhances growth factor (GF) signaling and GF signaling, conversely, induces the ubiquitination and subsequent degradation of TBC1D3. However, little is known regarding the regulation of this degradation, and the role of TBC1D3 in the progression of tumors has also not been defined. In the present study, we demonstrated that calmodulin (CaM), a ubiquitous cellular calcium sensor, specifically interacted with TBC1D3 in a Ca²⁺-dependent manner and inhibited GF signaling-induced ubiquitination and degradation of the oncoprotein in both cytoplasm and nucleus of human breast cancer cells. The CaM-interacting site of TBC1D3 was mapped to amino acids 157~171, which comprises two 1–14 hydrophobic motifs and one lysine residue (K166). Deletion of these motifs was shown to abolish interaction between TBC1D3 and CaM. Surprisingly, this deletion mutation caused inability of GF signaling to induce the ubiquitination and subsequent degradation of TBC1D3. In agreement with this, we identified lysine residue 166 within the CaM-interacting motifs of TBC1D3 as the actual site for the GF signaling-induced ubiquitination using mutational analysis. Point mutation of this lysine residue exhibited the same effect on TBC1D3 as the deletion mutant, suggesting that CaM inhibits GF signaling-induced degradation of TBC1D3 by occluding its ubiquitination at K166. Notably, we found that TBC1D3 promoted the expression and activation of MMP-9 and the migration of MCF-7 cells. Furthermore, interaction with CaM considerably enhanced such effect of TBC1D3. Taken together, our work reveals a novel model by which CaM promotes cell migration through inhibiting the ubiquitination and degradation of TBC1D3.

The Unwanted Cell Migration in the Brain: Glioma Metastasis

Cell migration is identified as a highly orchestrated process. It is a fundamental and essential phenomenon underlying tissue morphogenesis, wound healing, and immune response. Under dysregulation, it contributes to cancer metastasis. Brain is considered to be the most complex organ in human body containing many types of neural cells with astrocytes playing crucial roles in monitoring both physiological and pathological functions. Astrocytoma originates from astrocytes and its most malignant type is glioblastoma multiforme (WHO Grade IV astrocytoma), which is capable to infiltrate widely into the neighboring brain tissues making a complete resection of tumors impossible. Very recently, we have reviewed the mechanisms for astrocytes in migration. Given the fact that astrocytoma shares many histological features with astrocytes, we therefore attempt to review the mechanisms for glioma cells in migration and compare them to normal astrocytes, hoping to obtain a better insight into the dysregulation of migratory mechanisms contributing to their metastasis in the brain.

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.

Analysis of the expression of the Wnt family of proteins and its modulatory role on cytokine expression in non activated and activated astroglial cells

Despite the essential functions of astrocytes and the emerging relevance of the Wnt family of proteins in the CNS under physiological and pathological conditions, the astroglial expression of this family of proteins and its potential modulatory role on astroglial activation is almost unknown. Thus, we have evaluated the expression of all Wnt ligands, receptors and regulators, and the activation state of Wnt-related signaling pathways in non-activated and differentially activated astroglial cultures. We found that numerous Wnt ligands, receptors and regulators were expressed in non-activated astrocytes, while the Wnt-dependent pathways were constitutively active. Moreover, the expression of most detectable Wnt-related molecules and the activity of the Wnt-dependent pathways suffered post-activation variations which frequently depended on the activation system. Finally, the analysis of the effects exerted by Wnt1 and 5a on the astroglial expression of prototypical genes related to astroglial activation showed that both Wnt ligands increased the astroglial expression of interleukin 1β depending on the experimental context, while did not modulate tumor necrosis factor α, interleukin 6, transforming growth factor β1 and glial fibrillary acidic protein expression. These results strongly suggest that the Wnt family of proteins is involved in how astrocytes modulate and respond to the physiological and pathological CNS.

Role of PDGF-D and PDGFR-β in neuroinflammation in experimental ICH mice model

OBJECTIVE

Inflammation plays a key role in the pathophysiological processes after intracerebral hemorrhage (ICH). Post-ICH macrophages infiltrate the brain and release pro-inflammatory factors (tumor necrosis factor-α), amplifying microglial activation and neutrophil infiltration. Platelet-derived growth factor receptor-β (PDGFR-β) is expressed on macrophages and it's activation induces the recruitment of macrophages. Platelet-derived growth factor-D (PDGF-D) is an agonist with a significantly higher affinity to the PDGFR-β compared to another isoform of the receptor. In this study, we investigated the role of PDGF-D in the pro-inflammatory response after ICH in mice.

METHODS

A blood injection model of ICH was used in eight-week old male CD1 mice (weight 30g). Some mice received an injection of plasmin or PDGF-D. Gleevec, a PDGFR inhibitor, was administered at 1, 3 or 6h post-ICH. Plasmin was administered with or without PDGF-D siRNAs mixture or scramble siRNA. A plasmin-antagonist, ε-Aminocaproic acid (EACA), was co-administrated with the blood. The effects of ICH and treatment on the brain injury and post-ICH inflammation were investigated.

RESULTS

ICH resulted in the overexpression of PDGF-D, associated with the infiltration of macrophages. PDGFR-inhibition decreased ICH-induced brain injury, attenuating macrophage and neutrophil infiltration, reducing microglial activation and TNF-α production. Administration of recombinant PDGF-D induced TNF-α production, and PDGFR-inhibition attenuated it. A plasmin-antagonist suppressed PDGFR-β activation and microglial activation. Plasmin increased PDGF-D expression, and PDGF-D inhibition reduced neutrophil infiltration.

CONCLUSION

ICH-induced PDGF-D accumulation contributed to post-ICH inflammation via PDGFR activation and enhanced macrophage infiltration. The inhibition of PDGFR had an anti-inflammatory effect. Plasmin is a possible upstream effector of PDGF-D. The targeting of PDGF-D may provide a novel way to decrease brain injury after ICH.

L-type voltage-operated calcium channels contribute to astrocyte activation In vitro

We have found a significant upregulation of L-type voltage-operated Ca(++) channels (VOCCs) in reactive astrocytes. To test if VOCCs are centrally involved in triggering astrocyte reactivity, we used in vitro models of astrocyte activation in combination with pharmacological inhibitors, siRNAs and the Cre/lox system to reduce the activity of L-type VOCCs in primary cortical astrocytes. The endotoxin lipopolysaccharide (LPS) as well as high extracellular K(+) , glutamate, and ATP promote astrogliosis in vitro. L-type VOCC inhibitors drastically reduce the number of reactive cells, astrocyte hypertrophy, and cell proliferation after these treatments. Astrocytes transfected with siRNAs for the Cav1.2 subunit that conducts L-type Ca(++) currents as well as Cav1.2 knockout astrocytes showed reduce Ca(++) influx by ∼80% after plasma membrane depolarization. Importantly, Cav1.2 knock-down/out prevents astrocyte activation and proliferation induced by LPS. Similar results were found using the scratch wound assay. After injuring the astrocyte monolayer, cells extend processes toward the cell-free scratch region and subsequently migrate and populate the scratch. We found a significant increase in the activity of L-type VOCCs in reactive astrocytes located in the growing line in comparison to quiescent astrocytes situated away from the scratch. Moreover, the migration of astrocytes from the scratching line as well as the number of proliferating astrocytes was reduced in Cav1.2 knock-down/out cultures. In summary, our results suggest that Cav1.2 L-type VOCCs play a fundamental role in the induction and/or proliferation of reactive astrocytes, and indicate that the inhibition of these Ca(++) channels may be an effective way to prevent astrocyte activation. GLIA 2016. GLIA 2016;64:1396-1415.

Sodium channels in astroglia and microglia

Voltage-gated sodium channels are required for electrogenesis in excitable cells. Their activation, triggered by membrane depolarization, generates transient sodium currents that initiate action potentials in neurons, cardiac, and skeletal muscle cells. Cells that have not traditionally been considered to be excitable (nonexcitable cells), including glial cells, also express sodium channels in physiological conditions as well as in pathological conditions. These channels contribute to multiple functional roles that are seemingly unrelated to the generation of action potentials. Here, we discuss the dynamics of sodium channel expression in astrocytes and microglia, and review evidence for noncanonical roles in effector functions of these cells including phagocytosis, migration, proliferation, ionic homeostasis, and secretion of chemokines/cytokines. We also examine possible mechanisms by which sodium channels contribute to the activity of glial cells, with an eye toward therapeutic implications for central nervous system disease. GLIA 2016;64:1628-1645.

Voltage-gated sodium channel Nav 1.5 contributes to astrogliosis in an in vitro model of glial injury via reverse Na+ /Ca2+ exchange

Astrogliosis is a prominent feature of many, if not all, pathologies of the brain and spinal cord, yet a detailed understanding of the underlying molecular pathways involved in the transformation from quiescent to reactive astrocyte remains elusive. We investigated the contribution of voltage-gated sodium channels to astrogliosis in an in vitro model of mechanical injury to astrocytes. Previous studies have shown that a scratch injury to astrocytes invokes dual mechanisms of migration and proliferation in these cells. Our results demonstrate that wound closure after mechanical injury, involving both migration and proliferation, is attenuated by pharmacological treatment with tetrodotoxin (TTX) and KB-R7943, at a dose that blocks reverse mode of the Na(+) /Ca(2+) exchanger (NCX), and by knockdown of Nav 1.5 mRNA. We also show that astrocytes display a robust [Ca(2+) ]i transient after mechanical injury and demonstrate that this [Ca(2+) ]i response is also attenuated by TTX, KB-R7943, and Nav 1.5 mRNA knockdown. Our results suggest that Nav 1.5 and NCX are potential targets for modulation of astrogliosis after injury via their effect on [Ca(2+) ]i .

Tenascin-C causes neuronal apoptosis after subarachnoid hemorrhage in rats

The role of tenascin-C (TNC), a matricellular protein, in brain injury is unknown. The aim of this study was to examine if TNC causes neuronal apoptosis after subarachnoid hemorrhage (SAH), a deadly cerebrovascular disorder, using imatinib mesylate (a selective inhibitor of platelet-derived growth factor receptor [PDGFR] that is reported to suppress TNC induction) and recombinant TNC. SAH by endovascular perforation caused caspase-dependent neuronal apoptosis in the cerebral cortex irrespective of cerebral vasospasm development at 24 and 72 h post-SAH, associated with PDGFR activation, mitogen-activated protein kinases (MAPKs) activation, and TNC induction in rats. PDGFR inactivation by an intraperitoneal injection of imatinib mesylate prevented neuronal apoptosis, as well as MAPKs activation and TNC induction in the cerebral cortex at 24 h. A cisternal injection of recombinant TNC reactivated MAPKs and abolished anti-apoptotic effects of imatinib mesylate. The TNC injection also induced TNC itself in SAH brain, which may internally augment neuronal apoptosis after SAH. These findings suggest that TNC upregulation by PDGFR activation causes neuronal apoptosis via MAPK activation, and that the positive feedback mechanisms may exist to augment neuronal apoptosis after SAH. TNC-induced neuronal apoptosis would be a new target to improve outcome after SAH.

Upregulation of COX-2/PGE2 by ET-1 mediated through Ca2+-dependent signals in mouse brain microvascular endothelial cells

Endothelin-1 (ET-1), a proinflammatory mediator, is elevated in the regions of several brain inflammatory disorders, implying that ET-1 may contribute to inflammatory responses. The deleterious effects of ET-1 on brain endothelial cells may aggravate brain inflammation mediated through the upregulation of cyclooxygenase-2 (COX-2)/prostaglandin E2 (PGE2) system. However, the signaling mechanisms underlying ET-1-induced COX-2 expression in mouse brain microvascular endothelial cells (bEnd.3 cells) remain unclear. Herein, we investigated the effects of Ca2+-dependent protein kinases on ET-1-induced COX-2 expression and PGE2 release in bEnd.3 cells. The data obtained with Western blotting, reverse transcription PCR, and intracellular Ca2+ analyses showed that ET-1-induced COX-2 expression was mediated through phosphatidylinositol-phospholipase C (PI-PLC) and phosphatidylcholine-phospholipase C (PC-PLC)/Ca2+-dependent activation of protein kinase C-alpha (PKC-α) and calmodulin kinase II (CaMKII) cascades. Next, we demonstrated that ET-1 stimulated intracellular Ca2+ increase, phoshorylation of PKC-α, CaMKII, and mitogen-activated protein kinases (MAPKs) (ERK1/2, p38 MAPK, and JNK1/2) and then activated the activating transcription factor 2 (ATF2)/activator protein 1 (AP-1) via Gq/i protein-coupled ETB receptors. Moreover, the data of chromatin immunoprecipitation and promoter reporter assay demonstrated that the activated ATF2/AP-1 and p300 bound to its corresponding binding sites within COX-2 promoter, thereby turning on COX-2 gene transcription. Finally, upregulation of COX-2 by ET-1 promoted PGE2 biosynthesis and release in these cells. Taken together, these results demonstrate that in bEnd.3 cells, Ca2+-dependent PKC-α and CaMKII linking to MAPKs, ATF2/AP-1, and p300 cascade is essential for ET-1-induced COX-2 upregulation. Understanding the mechanisms of COX-2/PGE2 system upregulated by ET-1 on brain microvascular endothelial cells may provide rational therapeutic interventions for brain injury and inflammatory diseases.

Traumatic scratch injury in astrocytes triggers calcium influx to activate the JNK/c-Jun/AP-1 pathway and switch on GFAP expression

Astrocyte activation is a hallmark of central nervous system injuries resulting in glial scar formation (astrogliosis). The activation of astrocytes involves metabolic and morphological changes with complex underlying mechanisms, which should be defined to provide targets for astrogliosis intervention. Astrogliosis is usually accompanied by an upregulation of glial fibrillary acidic protein (GFAP). Using an in vitro scratch injury model, we scratched primary cultures of cerebral cortical astrocytes and observed an influx of calcium in the form of waves spreading away from the wound through gap junctions. Using the calcium blocker BAPTA-AM and the JNK inhibitor SP600125, we demonstrated that the calcium wave triggered the activation of JNK, which then phosphorylated the transcription factor c-Jun to facilitate the binding of AP-1 to the GFAP gene promoter to switch on GFAP upregulation. Blocking calcium mobilization with BAPTA-AM in an in vivo stab wound model reduced GFAP expression and glial scar formation, showing that the calcium signal, and the subsequent regulation of downstream signaling molecules, plays an essential role in brain injury response. Our findings demonstrated that traumatic scratch injury to astrocytes triggered a calcium influx from the extracellular compartment and activated the JNK/c-Jun/AP-1 pathway to switch on GFAP expression, identifying a previously unreported signaling cascade that is important in astrogliosis and the physiological response following brain injury.

C-Src/Jak2/PDGFR/PKCδ-dependent MMP-9 induction is required for thrombin-stimulated rat brain astrocytes migration

Among matrix metalloproteinases (MMPs), MMP-9 has been observed in patients with brain inflammatory diseases and may contribute to the pathology of brain diseases. Thrombin has been known as a regulator of MMP-9 expression and cells migration. However, the mechanisms underlying thrombin-induced MMP-9 expression in rat brain astrocytes (RBA-1 cells) were not completely understood. Here, we demonstrated that thrombin induced the expression of pro-form MMP-9 in RBA-1 cells and cells migration which were attenuated by pretreatment with the inhibitor of receptor tyrosine kinase (Genistein), c-Src (PP1), Jak2 (AG490), PDGFR (AG1296), PI3K (LY294002), Akt (SH-5), PKCs (Ro318220), PKCδ (Rottlerin), or NF-κB (Bay11-7082) and transfection with siRNA of c-Src, PDGFR, Akt, PKCδ, ATF2, p65, IKKα, or IKKβ. In addition, thrombin-stimulated c-Src, Jak2, or PDGFR phosphorylation was inhibited by a thrombin inhibitor (PPACK), PP1, AG490, or AG1296. Thrombin further stimulated c-Src and PDGFR complex formation in RBA-1 cells. Thrombin also stimulated Akt and PKCδ phosphorylation and PKCδ translocation which were reduced by PPACK, PP1, AG490, AG1296, or LY294002. We further observed that thrombin markedly stimulated ATF2 or IκBα phosphorylation and NF-κB p65 translocation which were inhibited by Rottlerin or LY294002. Finally, thrombin stimulated in vivo binding of p65 to the MMP-9 promoter, which was reduced by pretreatment with Rottlerin or LY294002. These results concluded that in RBA-1 cells, thrombin activated a c-Src/Jak2/PDGFR/PI3K/Akt/PKCδ pathway, which in turn triggered ATF2 and NF-κB activation and ultimately induced MMP-9 expression associated with cell migration.

Pazopanib inhibits the activation of PDGFRβ-expressing astrocytes in the brain metastatic microenvironment of breast cancer cells

Brain metastases occur in more than one-third of metastatic breast cancer patients whose tumors overexpress HER2 or are triple negative. Brain colonization of cancer cells occurs in a unique environment, containing microglia, oligodendrocytes, astrocytes, and neurons. Although a neuroinflammatory response has been documented in brain metastasis, its contribution to cancer progression and therapy remains poorly understood. Using an experimental brain metastasis model, we characterized the brain metastatic microenvironment of brain tropic, HER2-transfected MDA-MB-231 human breast carcinoma cells (231-BR-HER2). A previously unidentified subpopulation of metastasis-associated astrocytes expressing phosphorylated platelet-derived growth factor receptor β (at tyrosine 751; p751-PDGFRβ) was identified around perivascular brain micrometastases. p751-PDGFRβ(+) astrocytes were also identified in human brain metastases from eight craniotomy specimens and in primary cultures of astrocyte-enriched glial cells. Previously, we reported that pazopanib, a multispecific tyrosine kinase inhibitor, prevented the outgrowth of 231-BR-HER2 large brain metastases by 73%. Here, we evaluated the effect of pazopanib on the brain neuroinflammatory microenvironment. Pazopanib treatment resulted in 70% (P = 0.023) decrease of the p751-PDGFRβ(+) astrocyte population, at the lowest dose of 30 mg/kg, twice daily. Collectively, the data identify a subpopulation of activated astrocytes in the subclinical perivascular stage of brain metastases and show that they are inhibitable by pazopanib, suggesting its potential to prevent the development of brain micrometastases in breast cancer patients.

Antisense MMP-9 RNA inhibits malignant glioma cell growth in vitro and in vivo

The matrix-degrading metalloproteinases (MMPs), particularly MMP-9, play important roles in the pathogenesis and development of malignant gliomas. In the present study, the oncogenic role of MMP-9 in malignant glioma cells was investigated via antisense RNA blockade in vitro and in vivo. TJ905 malignant glioma cells were transfected with pcDNA3.0 vector expressing antisense MMP-9 RNA (pcDNA-ASMMP9), which significantly decreased MMP-9 expression, and cell proliferation was assessed. For in vivo studies, U251 cells, a human malignant glioma cell line, were implanted subcutaneously into 4- to 6-week-old BALB/c nude mice. The mice bearing well-established U251 gliomas were treated with intratumoral pcDNA-AS-MMP9-Lipofectamine complex (AS-MMP-9-treated group), subcutaneous injection of endostatin (endostatin-treated group), or both (combined therapy group). Mice treated with pcDNA (empty vector)-Lipofectamine served as the control group. Four or eight weeks later, the volume and weight of tumor, MMP-9 expression, microvessel density and proliferative activity were assayed. We demonstrate that pcDNA-AS-MMP9 significantly decreased MMP-9 expression and inhibited glioma cell proliferation. Volume and weight of tumor, MMP-9 expression, microvessel density and proliferative activity in the antisense-MMP-9-treated and therapeutic alliance groups were significantly lower than those in the control group. The results suggest that MMP-9 not only promotes malignant glioma cell invasiveness, but also affects tumor cell proliferation. Blocking the expression of MMP-9 with antisense RNA substantially suppresses the malignant phenotype of glioma cells, and thus can be used as an effective therapeutic strategy for malignant gliomas.

NADPH oxidase 2-derived reactive oxygen species signal contributes to bradykinin-induced matrix metalloproteinase-9 expression and cell migration in brain astrocytes

Background

Matrix metalloproteinase-9 (MMP-9) plays a crucial role in pathological processes of brain inflammation, injury, and neurodegeneration. Moreover, bradykinin (BK) induces the expression of several inflammatory proteins in brain astrocytes. Recent studies have suggested that increased oxidative stress is implicated in the brain inflammation and injury. However, whether BK induced MMP-9 expression mediated through oxidative stress remains virtually unknown. Herein we investigated the role of redox signals in BK-induced MMP-9 expression in rat brain astrocytes (RBA-1 cells).

Results

In the study, we first demonstrated that reactive oxygen species (ROS) plays a crucial role in BK-induced MMP-9 expression in cultured brain astrocytes (in vitro) and animal brain tissue (in vivo) models. Next, BK-induced MMP-9 expression is mediated through a Ca²⁺-mediated PKC-α linking to p47^phox/NADPH oxidase 2 (Nox2)/ROS signaling pathway. Nox2-dependent ROS generation led to activation and up-regulation of the downstream transcriptional factor AP-1 (i.e. c-Fos and c-Jun), which bound to MMP-9 promoter region, and thereby turned on transcription of MMP-9 gene. Functionally, BK-induced MMP-9 expression enhanced astrocytic migration.

Conclusions

These results demonstrated that in RBA-1 cells, activation of AP-1 (c-Fos/c-Jun) by the PKC-α-mediated Nox2/ROS signals is essential for up-regulation of MMP-9 and cell migration enhanced by BK.

NADPH oxidase-mediated redox signal contributes to lipoteichoic acid-induced MMP-9 upregulation in brain astrocytes

BACKGROUND

Lipoteichoic acid (LTA) is a component of gram-positive bacterial cell walls and may be elevated in the cerebrospinal fluid of patients suffering from meningitis. Among matrix metalloproteinases (MMPs), MMP-9 has been observed in patients with brain inflammatory diseases and may contribute to the pathology of brain diseases. Moreover, several studies have suggested that increased oxidative stress is implicated in the pathogenesis of brain inflammation and injury. However, the molecular mechanisms underlying LTA-induced redox signal and MMP-9 expression in brain astrocytes remain unclear.

OBJECTIVE

Herein we explored whether LTA-induced MMP-9 expression was mediated through redox signals in rat brain astrocytes (RBA-1 cells).

METHODS

Upregulation of MMP-9 by LTA was evaluated by zymographic and RT-PCR analyses. Next, the MMP-9 regulatory pathways were investigated by pretreatment with pharmacological inhibitors or transfection with small interfering RNAs (siRNAs), Western blotting, and chromatin immunoprecipitation (ChIP)-PCR and promoter activity reporter assays. Moreover, we determined the cell functional changes by migration assay.

RESULTS

These results showed that LTA induced MMP-9 expression via a PKC(α)-dependent pathway. We further demonstrated that PKCα stimulated p47phox/NADPH oxidase 2 (Nox2)-dependent reactive oxygen species (ROS) generation and then activated the ATF2/AP-1 signals. The activated-ATF2 bound to the AP-1-binding site of MMP-9 promoter, and thereby turned on MMP-9 gene transcription. Additionally, the co-activator p300 also contributed to these responses. Functionally, LTA-induced MMP-9 expression enhanced astrocytic migration.

CONCLUSION

These results demonstrated that in RBA-1 cells, activation of ATF2/AP-1 by the PKC(α)-mediated Nox(2)/ROS signals is essential for upregulation of MMP-9 and cell migration enhanced by LTA.

c-Src-dependent EGF receptor transactivation contributes to ET-1-induced COX-2 expression in brain microvascular endothelial cells

Background

Endothelin-1 (ET-1) is elevated and participates in the regulation of several brain inflammatory disorders. The deleterious effects of ET-1 on endothelial cells may aggravate brain inflammation mediated through the upregulation of cyclooxygenase-2 (COX-2) gene expression. However, the signaling mechanisms underlying ET-1-induced COX-2 expression in brain microvascular endothelial cells remain unclear.

Objective

The goal of this study was to examine whether ET-1-induced COX-2 expression and prostaglandin E₂ (PGE₂) release were mediated through a c-Src-dependent transactivation of epidermal growth factor receptor (EGFR) pathway in brain microvascular endothelial cells (bEnd.3 cells).

Methods

The expression of COX-2 induced by ET-1 was evaluated by Western blotting and RT-PCR analysis. The COX-2 regulatory signaling pathways were investigated by pretreatment with pharmacological inhibitors, short hairpin RNA (shRNA) or small interfering RNA (siRNA) transfection, chromatin immunoprecipitation (ChIP), and promoter activity reporter assays. Finally, we determined the PGE₂ level as a marker of functional activity of COX-2 expression.

Results

First, the data showed that ET-1-induced COX-2 expression was mediated through a c-Src-dependent transactivation of EGFR/PI3K/Akt cascade. Next, we demonstrated that ET-1 stimulated activation (phosphorylation) of c-Src/EGFR/Akt/MAPKs (ERK1/2, p38 MAPK, and JNK1/2) and then activated the c-Jun/activator protein 1 (AP-1) via G_q/i protein-coupled ET_B receptors. The activated c-Jun/AP-1 bound to its corresponding binding sites within COX-2 promoter, thereby turning on COX-2 gene transcription. Ultimately, upregulation of COX-2 by ET-1 promoted PGE₂ biosynthesis and release in bEnd.3 cells.

Conclusions

These results demonstrate that in bEnd.3 cells, c-Src-dependent transactivation of EGFR/PI3K/Akt and MAPKs linking to c-Jun/AP-1 cascade is essential for ET-1-induced COX-2 upregulation. Understanding the mechanisms of COX-2 expression and PGE₂ release regulated by ET-1/ET_B system on brain microvascular endothelial cells may provide rational therapeutic interventions for brain injury and inflammatory diseases.

The multifunctional Ca2+/calmodulin-dependent kinase II regulates vascular smooth muscle migration through matrix metalloproteinase 9

The multifunctional CaMKII has been implicated in vascular smooth muscle cell (VSMC) migration, but little is known regarding its downstream targets that mediate migration. Here, we examined whether CaMKII regulates migration through modulation of matrix metalloproteinase 9 (MMP9). Using CaMKIIδ(-/-) mice as a model system, we evaluated migration and MMP9 regulation in vitro and in vivo. After ligation of the common carotid artery, CaMKII was activated in the neointima as determined by oxidation and autophosphorylation. We found that MMP9 was robustly expressed in the neointima and adventitia of carotid-ligated wild-type (WT) mice but was barely detectable in CaMKIIδ(-/-) mice. The perimeter of the external elastic lamina, a correlate of migration-related outward remodeling, was increased in WT but not in CaMKIIδ(-/-) mice. Migration induced by serum, platelet-derived growth factor, and tumor necrosis factor-α (TNF-α) was significantly decreased in CaMKIIδ(-/-) as compared with WT VSMCs, but migration was rescued with adenoviral overexpression of MMP9 in CaMKIIδ(-/-) VSMCs. Likewise, overexpression of CaMKIIδ in CaMKIIδ(-/-) VSMCs increased migration, whereas an oxidation-resistant mutant of CaMKIIδ did not. TNF-α strongly induced CaMKII oxidation and autophosphorylation as well as MMP9 activity, mRNA, and protein levels in WT, but not in CaMKIIδ(-/-) VSMC. Surprisingly, TNF-α strongly induced MMP9 promoter activity in WT and CaMKIIδ(-/-) VSMC. However, the MMP9 mRNA stability was significantly decreased in CaMKIIδ(-/-) VSMC. Our data demonstrate that CaMKII promotes VSMC migration through posttranscriptional regulation of MMP9 and suggest that CaMKII effects on MMP9 expression may be a therapeutic pathway in vascular injury.

Inflammation dampened by gelatinase A cleavage of monocyte chemoattractant protein-3

Tissue degradation by the matrix metalloproteinase gelatinase A is pivotal to inflammation and metastases. Recognizing the catalytic importance of substrate-binding exosites outside the catalytic domain, we screened for extracellular substrates using the gelatinase A hemopexin domain as bait in the yeast two-hybrid system. Monocyte chemoattractant protein-3 (MCP-3) was identified as a physiological substrate of gelatinase A. Cleaved MCP-3 binds to CC-chemokine receptors-1, -2, and -3, but no longer induces calcium fluxes or promotes chemotaxis, and instead acts as a general chemokine antagonist that dampens inflammation. This suggests that matrix metalloproteinases are both effectors and regulators of the inflammatory response.