Intracellular signalings underlying bradykinin-induced matrix metalloproteinase-9 expression in rat brain astrocyte-1

Kinin Receptors and Kinin-Related Gene Expression in Astrocytic Brain Tumors

Kinins are a set of peptides present in tissues that are involved in the inflammatory response and cancer progression. However, studies showing the expression of kinin receptors in human glioma samples are still incomplete and contradictory. The aim of the present study was to ascertain the expression of BDKRB1 and BDKRB2 genes, as well as the level of B1R and B2R proteins in human gliomas, depending on the degree of malignancy. Additionally, representative kinin-dependent genes with altered expression were indicated. The expression profile of kinin-dependent genes was determined using oligonucleotide microarray technique. In addition, RT-qPCR was used to assess the expression level of selected differentiating genes. The location of kinin receptors in brain gliomas was assessed using immunohistochemical methods. The oligonucleotide microarray method was used to identify 12 mRNA IDs of kinin-related genes whose expression was upregulated or downregulated in gliomas of different grades. In immunohistochemically stained samples, the concentrations of BR1 and BR2 proteins, measured by optical density, were statistically significantly higher in grade G3 vs. G2 and G4 vs. G3. Increased expression of kinin receptors BDKRB1 and BDKRB2 in brain gliomas, depending on the degree of malignancy, suggests the involvement of kinins and their receptors in the disease's pathogenesis. Quantitative assessment of mRNA BDKRB1, PRKAR1A, MAP2K, and EGFR in patients with brain tumors may hold diagnostic and therapeutic significance.

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.

Bradykinin, as a Reprogramming Factor, Induces Transdifferentiation of Brain Astrocytes into Neuron-like Cells

Kinins are endogenous, biologically active peptides released into the plasma and tissues via the kallikrein-kinin system in several pathophysiological events. Among kinins, bradykinin (BK) is widely distributed in the periphery and brain. Several studies on the neuro-modulatory actions of BK by the B₂BK receptor (B₂BKR) indicate that this neuropeptide also functions during neural fate determination. Previously, BK has been shown to induce differentiation of nerve-related stem cells into neuron cells, but the response in mature brain astrocytes is unknown. Herein, we used rat brain astrocyte (RBA) to investigate the effect of BK on cell transdifferentiation into a neuron-like cell morphology. Moreover, the signaling mechanisms were explored by zymographic, RT-PCR, Western blot, and immunofluorescence staining analyses. We first observed that BK induced RBA transdifferentiation into neuron-like cells. Subsequently, we demonstrated that BK-induced RBA transdifferentiation is mediated through B₂BKR, PKC-δ, ERK1/2, and MMP-9. Finally, we found that BK downregulated the astrocytic marker glial fibrillary acidic protein (GFAP) and upregulated the neuronal marker neuron-specific enolase (NSE) via the B₂BKR/PKC-δ/ERK pathway in the event. Therefore, BK may be a reprogramming factor promoting brain astrocytic transdifferentiation into a neuron-like cell, including downregulation of GFAP and upregulation of NSE and MMP-9 via the B₂BKR/PKC-δ/ERK cascade. Here, we also confirmed the transdifferentiative event by observing the upregulated neuronal nuclear protein (NeuN). However, the electrophysiological properties of the cells after BK treatment should be investigated in the future to confirm their phenotype.

Involvement of Bradykinin Receptor 2 in Nerve Growth Factor Neuroprotective Activity

Neurotrophin nerve growth factor (NGF) has been demonstrated to upregulate the gene expression of bradykinin receptor 2 (B2R) on sensory neurons, thus facilitating nociceptive signals. The aim of the present study is to investigate the involvement of B2R in the NGF mechanism of action in nonsensory neurons in vitro by using rat mixed cortical primary cultures (CNs) and mouse hippocampal slices, and in vivo in Alzheimer’s disease (AD) transgenic mice (5xFAD) chronically treated with NGF. A significant NGF-mediated upregulation of B2R was demonstrated by microarray, Western blot, and immunofluorescence analysis in CNs, indicating microglial cells as the target of this modulation. The B2R involvement in the NGF mechanism of action was also demonstrated by using a selective B2R antagonist which was able to reverse the neuroprotective effect of NGF in CNs, as revealed by viability assay, and the NGF-induced long-term potentiation (LTP) in hippocampal slices. To confirm in vitro observations, B2R upregulation was observed in 5xFAD mouse brain following chronic intranasal NGF treatment. This study demonstrates for the first time that B2R is a key element in the neuroprotective activity and synaptic plasticity mediated by NGF in brain cells.

The COX-2-derived PGE2 autocrine contributes to bradykinin-induced matrix metalloproteinase-9 expression and astrocytic migration via STAT3 signaling

Background

The matrix metalloproteinase-9 (MMP-9) is up-regulated by several proinflammatory mediators in the central nervous system (CNS) diseases. Increasing reports show that MMP-9 expression is an inflammatory biomarker of several CNS disorders, including the CNS inflammation and neurodegeneration. Bradykinin (BK) is a common proinflammatory mediator and elevated in several brain injury and inflammatory disorders. The raised BK may be detrimental effects on the CNS that may aggravate brain inflammation through MMP-9 up-regulation or cyclooxygenase-2 (COX-2)-derived prostaglandin E₂ (PGE₂) production in brain astrocytes. However, the relationship between BK-induced MMP-9 expression and COX-2-derived PGE₂ release in brain astrocytes remains unclear.

Methods

Herein we used rat brain astrocytes (RBA) to investigate the role of the COX-2/PGE₂ system in BK-induced MMP-9 expression. We used zymographic, RT-PCR, EIA, and Western blotting analyses to confirm that BK induces MMP-9 expression via a COX-2/PGE₂-dependent pathway.

Results

Our results show activation of native COX-2 by BK led to PGE₂ production and release. Subsequently, PGE₂ induced MMP-9 expression via PGE₂ receptor (EP)-mediated c-Src, Jak2, ERK1/2, and then activated signal transducer and activator of transcription 3 (STAT3) signaling pathway. Finally, up-regulation of MMP-9 by BK via the pathway may promote astrocytic migration.

Conclusion

These results demonstrated that a novel autocrine pathway for BK-induced MMP-9 protein expression is mediated through activation of STAT3 by native COX-2/PGE₂-mediated c-Src/Jak2/ERK cascades in brain astrocytes.

Rottlerin, a natural polyphenol compound, inhibits upregulation of matrix metalloproteinase-9 and brain astrocytic migration by reducing PKC-δ-dependent ROS signal

Background

Upregulation of matrix metalloproteinase-9 (MMP-9) has been indicated as one of the inflammatory biomarkers. In the central nervous system (CNS), the MMP-9 is induced by several proinflammatory mediators and participates in the CNS disorders, including inflammation and neurodegeneration. In addition, protein kinase Cs (PKCs) has been shown to be involved in regulation of various inflammatory factors like MMP-9 by several stimuli in many cell types. Several phytochemicals are believed to reduce the risk of several inflammatory disorders including the CNS diseases. The rottlerin, a principal phenolic compound of the Kamala plant Mallotus philippinensis, has been shown to possess an array of medicinal properties, including anti-PKC-δ, antitumor, anti-oxidative, and anti-inflammatory activities.

Methods

Herein, we used rat brain astrocytes (RBA) to demonstrate the signaling mechanisms of phorbol 12-myristate 13-acetate (PMA)-induced MMP-9 expression by zymographic, RT-PCR, subcellular isolation, Western blot, ROS detection, and promoter reporter analyses. Then, we evaluate the effects of rottlerin on PMA-induced MMP-9 expression in RBA and its influencing mechanism.

Results

We first demonstrated that PMA stimulated activation of various types of PKC, including PKC-δ in RBA. Subsequently, PMA induced MMP-9 expression via PKCδ-mediated reactive oxygen species (ROS) generation, extracellular signal-regulated kinase 1/2 (ERK1/2) activation, and then induced c-Fos/AP-1 signaling pathway. Finally, upregulation of MMP-9 by PMA via the pathway may promote astrocytic migration, and the event could be attenuated by rottlerin.

Conclusions

These data indicated that rottlerin may have anti-inflammatory activity by reducing these related pathways of PKC-δ-dependent ROS-mediated MMP-9 expression in brain astrocytes.

High glucose-induced complement component 3 up-regulation via RAGE-p38MAPK-NF-κB signalling in astrocytes: In vivo and in vitro studies

Diabetes is considered as a risk for cognitive decline, which is characterized by neurodegenerative alteration and innate immunity activation. Recently, complement 3 (C3), the critical central component of complement system, has been reported to play a key role in neurodegenerative alterations under pathological condition. Receptor for advanced glycation end products (RAGE) activation is confirmed to mediate several inflammatory cytokines production. However, whether C3 activation participates in the diabetic neuropathology and whether this process is regulated by RAGE activation remains unknown. The present study aimed to investigate the role of C3 in streptozotocin‐induced diabetic mice and high glucose‐induced primary astrocytes and the underlying modulatory mechanisms. The decreased synaptophysin density and increased C3 deposition at synapses were observed in the diabetic brain compared to the control brain. Furthermore, the elevated C3 was co‐localized with GFAP‐positive astrocytes in the diabetic brain slice in vivo and high glucose‐induced astrocytes culture in vitro. Diabetes/high glucose‐induced up‐regulation of C3 expression at gene, protein and secretion levels, which were attenuated by pre‐treatment with RAGE, p38MAPK and NF‐κB inhibitors separately. These results demonstrate that high glucose induces C3 up‐regulation via RAGE‐ p38MAPK‐NF‐κB signalling in vivo and in vitro, which might be associated with synaptic protein loss.

Implication of the Kallikrein-Kinin system in neurological disorders: Quest for potential biomarkers and mechanisms

Neurological disorders represent major health concerns in terms of comorbidity and mortality worldwide. Despite a tremendous increase in our understanding of the pathophysiological processes involved in disease progression and prevention, the accumulated knowledge so far resulted in relatively moderate translational benefits in terms of therapeutic interventions and enhanced clinical outcomes. Aiming at specific neural molecular pathways, different strategies have been geared to target the development and progression of such disorders. The kallikrein-kinin system (KKS) is among the most delineated candidate systems due to its ubiquitous roles mediating several of the pathophysiological features of these neurological disorders as well as being implicated in regulating various brain functions. Several experimental KKS models revealed that the inhibition or stimulation of the two receptors of the KKS system (B1R and B2R) can exhibit neuroprotective and/or adverse pathological outcomes. This updated review provides background details of the KKS components and their functions in different neurological disorders including temporal lobe epilepsy, traumatic brain injury, stroke, spinal cord injury, Alzheimer's disease, multiple sclerosis and glioma. Finally, this work will highlight the putative roles of the KKS components as potential neurotherapeutic targets and provide future perspectives on the possibility of translating these findings into potential clinical biomarkers in neurological disease.

Neuroprotective Effects of Dehydroepiandrosterone Sulfate Through Inhibiting Expression of Matrix Metalloproteinase-9 from Bradykinin-Challenged Astroglia

Dehydroepiandrosterone sulfate (DHEAS), one of the most important neuroactive steroids, is produced in the adrenals and the brain. DHEAS is believed to play a critical role in modulating different forms of cellular control, including processes associated with human neural systems. Its production rate and level in serum, adrenals, and brain gradually decrease with advancing age. The decline of DHEAS level was associated with age-related neuronal dysfunction and degeneration, most probably because the steroids protect the central nervous system (CNS) neurons against neurotoxic challenges. Moreover, increasing studies show that matrix metalloproteinases (MMPs), MMP-9 especially, are upregulated by proinflammatory mediators in the CNS disorders. The increased MMP-9 as an inflammatory biomarker of several CNS disorders that may participate in the CNS inflammation and neurodegeneration. Herein, we investigate the effects of DHEAS on brain inflammation by the model we have defined of bradykinin (BK)-induced MMP-9 expression in rat brain astrocyte (RBA) and its mechanism. The results showed that DHEAS significantly reduce MMP-9 induced by BK. Pretreatment with DHEAS can inhibit BK-stimulated phosphorylation of c-Src and PYK2. Moreover, DHEAS attenuated BK-stimulated NADPH oxidase (Nox)-derived reactive oxygen species (ROS) production, suggesting that DHEAS has an antioxidative effect. We further demonstrated that DHEAS blocked activation of ERK1/2, Akt, and c-Fos/AP-1 by BK. Finally, DHEAS decreased MMP-9-related events including RBA migration and neuronal apoptosis. The results will provide new insights into the anti-inflammatory action of DHEAS, supporting that DHEAS may have a neuroprotective effect in the improvement of the CNS disorders by reducing neuroinflammation.

High glucose-induced defective thrombospondin-1 release from astrocytes via TLR9 activation contributes to the synaptic protein loss

Diabetes, characterized by chronic hyperglycemia, is known to induce synaptic degeneration in the brain, thereby resulting in cognitive dysfunction. Thrombospondin-1(TSP-1), the secreted protein produced by astrocytes, plays a crucial role in promoting synapse formation. Toll-like receptor 9 (TLR9) has been widely known to initiate the innate immune response. We recently reported TLR9 activation in neurons results in tau hyperphosphorylation induced by HG in vitro. Its activation has been also considered to mediate oxidative stress and astrocytic dysfunction under pathological circumstance. However, whether astrocytic TSP-1 alteration plays a role in synaptic protein loss under high glucose condition and whether TLR9 activation is involved in this process have not been reported. In this study, we found that primary mouse astrocytes incubated in high glucose (30mM) induced a significant decreased TSP-1 secretion and increased intracellular contents of TSP-1 without affecting transcription level. Addition of conditioned medium from high glucose (30mM) treated astrocytes to the primary neurons exhibited reduced synaptic proteins expression, which was attenuated by treatment with exogenous rTSP-1. In addition, we demonstrated that TLR9 activation along with reactive oxygen species (ROS) generation in astrocytes was induced by high glucose (30mM). Furthermore, we explored the relationship between TLR9 activation and TSP-1 production. Both TLR9 deficiency and the antioxidant N-acetyl-L-cysteine treatment improved altered intra- and extracellular TSP-1 levels under high glucose condition. Together, our findings suggest that high glucose (30mM) impairs TSP-1 secretion from astrocytes, which depends on astrocytic dysfunction associated with TLR9 activation mediated ROS signaling, ultimately contributing to the synaptic proteins loss.

2-Chloroethanol Induced Upregulation of Matrix Metalloproteinase-2 in Primary Cultured Rat Astrocytes Via MAPK Signal Pathways

This study was to explore the mechanisms underlying 1,2-dichloroethane (1,2-DCE) induced brain edema by focusing on alteration of matrix metalloproteinase-2 (MMP-2) in rat astrocytes induced by 2-chloroethanol (2-CE), an intermediate metabolite of 1,2-DCE in vivo. Protein and mRNA levels of MMP-2, and the phosphorylated protein levels of p38 MAPK (p-p38), extracellular signal regulated protein kinase (p-ERK1/2) and c-Jun N-terminal kinase (p-JNK1/2) in astrocytes were examined by immunostaining, western blot or real-time RT-PCR analysis. Findings from this study disclosed that protein levels of MMP-2 were upregulated by 2-CE in astrocytes. Meanwhile, protein levels of p-p38, p-ERK1/2 and p-JNK1/2 were also increased apparently in the cells treated with 2-CE. Moreover, pretreatment of astrocytes with SB202190 (inhibitor of p38 MAPK), U0126 (inhibitor of ERK1/2) or SP600125 (inhibitor of JNK1/2) could suppress the upregulated expression of p-p38, p-ERK1/2, and p-JNK1/2. In response to suppressed protein levels of p-p38 and p-JNK1/2, the protein levels of MMP-2 also decreased significantly, indicating that activation of MAPK signal pathways were involved in the mechanisms underlying 2-CE-induced upregulation of MMP-2 expression.

Modulation of Kinin B2 Receptor Signaling Controls Aortic Dilatation and Rupture in the Angiotensin II-Infused Apolipoprotein E-Deficient Mouse

OBJECTIVE

Abdominal aortic aneurysm (AAA) is an important cause of mortality in older adults. Activity of the local kallikrein-kinin system may be important in cardiovascular disease. The effect of kinin B2 receptor (B2R) agonist and antagonist peptides on experimental AAA was investigated.

APPROACH AND RESULTS

AAA was induced in apolipoprotein E-deficient mice via infusion of angiotensin II (1.0 μg/kg per minute SC). B2R agonists or antagonists were given via injection (2 mg/kg IP) every other day. The B2R agonist (B9772) promoted aortic rupture in response to angiotensin II associated with an increase in neutrophil infiltration of the aorta in comparison to controls. Mice receiving a B2R/kinin B1 receptor antagonist (B9430) were relatively protected from aortic rupture. Neutrophil depletion abrogated the ability of the B2R agonist to promote aortic rupture. Progression of angiotensin II-induced aortic dilatation was inhibited in mice receiving a B2R antagonist (B9330). Secretion of metalloproteinase-2 and -9, osteoprotegerin, and osteopontin by human AAA explant was reduced in the presence of the B2R antagonist (B9330). B2R agonist and antagonist peptides enhanced and inhibited, respectively, angiotensin II-induced neutrophil activation and aortic smooth muscle cell inflammatory phenotype. The B2R antagonist (B9330; 5 μg) delivered directly to the aortic wall 1 week post-AAA induction with calcium phosphate in a rat model reduced aneurysm growth associated with downregulation of aortic metalloproteinase-9.

CONCLUSIONS

B2R signaling promotes aortic rupture within a mouse model associated with the ability to stimulate inflammatory phenotypes of neutrophils and vascular smooth muscle cells. B2R antagonism could be a potential therapy for AAA.

Circulating levels of matrix metalloproteinases and tissue inhibitors of matrix metalloproteinases during Japanese encephalitis virus infection

Matrix metalloproteinases (MMPs) are widely implicated in modulating blood brain barrier (BBB) integrity and affect the entry of peripheral immune cells into the central nervous system (CNS). The expression of MMPs is tightly regulated at the level of gene transcription, conversion of pro-enzyme to active MMPs and by the action of tissue inhibitors of metalloproteinases (TIMP). The crucial role of MMPs in inflammation indicates that perturbation of the MMP/TIMP balance decisively plays an important role in pathogenesis during viral encephalitis. The study was performed to evaluate the production of MMP-2, MMP-7, MMP-9, TIMP-1 and TIMP-3 in the sera of JEV i.e. GP 78668A (GP-78) infected BALB/c mouse model of encephalitis and gel zymography was performed for MMP-2 and MMP-9 activities. The estimation of MMP-2, MMP-7, MMP-9, TIMP-1, and TIMP-3 in JEV-infected mouse serum was analyzed by ELISA along with brain histopathology and immunohistochemistry. Evan's blue dye exclusion test was done to check the BBB integrity. Gelatin gel zymography was performed for MMP-2 and MMP-9 activities. We noticed an upregulated expression of MMPs in the sera of virus infected groups compared to controls at different days post inoculation (dpi). Post hoc analysis between days also reveals significant increase (p < 0.05) in virus infected groups with disease progression. In contrast, TIMPs expressions were significantly (p < 0.005) down regulated in the virus infected group. We provide preliminary evidence for a pattern of TIMP response in JEV infection distinct from that seen in acute inflammatory CNS conditions in JE, shown in our previous findings. Increased MMP-2 and MMP-9 activities were also found in a virus infected group with disease progression and are consistent with our previous finding of MMP-2 and MMP-9 activities in the CNS which clearly demonstrate worsen role of these immune mediators in JEV infection. This study will help to identify new targets for the therapeutic treatment of inflammatory mediated CNS disorders in JEV infection and may lead to the development of potential pharmacological targets in future.

Evaluation of Anti-Inflammatory Effects of Helminthostachys zeylanica Extracts via Inhibiting Bradykinin-Induced MMP-9 Expression in Brain Astrocytes

Phytochemicals present in vegetables, fruits, and herbs are believed to reduce the risk of several major diseases including cardiovascular or neurodegenerative disorders. The roots of the fern Helminthostachys zeylanica (L.) Hook. (Ophioglossaceae) have been used for centuries in the treatment of inflammation and as a folk medicine in several countries. The plant has been shown to possess an array of medicinal properties, including antioxidants and anti-inflammatory activities. Moreover, a rising level of matrix metalloproteinase-9 (MMP-9) has been found in blood fluid of these patients suffering from brain inflammatory diseases, which may be considered an inflammatory biomarker in several inflammatory diseases including the central nervous system (CNS) inflammation. Previously, we have demonstrated the signaling mechanisms of bradykinin (BK)-induced MMP-9 expression in brain astrocytes. Herein, we evaluate the effects of H. zeylanica extracts on BK-induced MMP-9 expression in brain astrocytes and its influencing mechanism. The results showed that H. zeylanica extracts, including E0, E1, and E2 significantly reduce MMP-9 induced by BK in brain astrocytes (RBA-1 cells). These H. zeylanica extracts can inhibit BK-stimulated phosphorylation of c-Src, Pyk2, and PKC(α/δ). Moreover, BK-stimulated NADPH oxidase (Nox)-derived reactive oxygen species (ROS) generation has also been attenuated by pretreatment with these extracts, suggesting that the H. zeylanica extracts have an antioxidative activity. We further demonstrated that the H. zeylanica extracts blocked activation of MAPKs (e.g., ERK1/2 and p38 MAPK) by BK. These data indicated that the H. zeylanica extracts may be has anti-inflammatory activity by reducing BK-induced ROS-dependent MMP-9 expression via these related pathways in brain astrocytes.

Adipose stem cells promote smooth muscle cells to secrete elastin in rat abdominal aortic aneurysm

Background

Abdominal aortic aneurysm (AAA) is a life-threatening disease and its prevalence rate increases with social aging. The degradation of elastic is an important factor in the formation of AAA.

Methods

Adipose derived stem cells (ADSCs) and bone marrow mesenchymal stem cells (BMSCs) were isolated from rats, and identified by Oil red O and alizarin red staining after adipogenesis and osteogenesis induction. In addition, ADSCs were also identified by flow cytometry with CD markers. AAA model in rats was established, and smooth muscle cells (SMCs) were isolated from AAA aortic wall and identified by immunohistochemistry. ADSCs or BMSCs were co-cultured with AAA aortic wall for in vitro experiment, and ADSCs were injected into AAA model for in vivo test. Then orcein staining was used for observing the morphology of elastic fiber, Western blot and real-time PCR were used respectively to detect the protein and gene expression of elastin, gelatinases spectrum analysis was used to detect the activity of matrix metalloproteinase-2 (MMP-2) and MMP-9.

Results

Lots of red lipid droplets were visible by Oil red O staining after adipogenesis induction, and black calcium nodules appeared by alizarin red staining after osteogenesis induction. The results of flow cytometry showed that ADSCs expressed CD44 and CD105, but exhibited negligible expression of CD31 and CD45. SMCs exhibited spindle-like morphology and α-actin protein was positive in cytoplasm. After co-cultured with ADSCs or BMSCs, the elastic fiber recovered normal winding shape, both the gene and protein expression of elastin increased, and the activity of MMP-2 decreased. The in vivo result was similar to that of in vitro.

Conclusions

ADSCs promote the expression of elastin in SMCs and contribute to the reconstruction of elastic fiber, which may provide new ideas for treating AAA.

Cypermethrin induces astrocyte damage: role of aberrant Ca(2+), ROS, JNK, P38, matrix metalloproteinase 2 and migration related reelin protein

Cypermethrin is a synthetic type II pyrethroid, derived from a natural pyrethrin of the chrysanthemum plant. Cypermethrin-mediated neurotoxicity is well studied; however, relatively less is known of its effect on astrocyte development and migration. Astrocytes are the major components of blood brain barrier (BBB), and astrocyte damage along with BBB dysfunction impair the tight junction (TJ) proteins resulting in altered cell migration and neurodegeneration. Here, we studied the mechanism of cypermethin mediated rat astrocyte damage and BBB disruption, and determined any change in expression of proteins associated with cell migration. Through MTT assay we found that cypermethrin reduced viability of cultured rat astrocytes. Immunolabelling with astrocyte marker, glial fibrillary acidic protein, revealed alteration in astrocyte morphology. The astrocytes demonstrated an enhanced release of intracellular Ca(++) and ROS, and up-regulation in p-JNK and p-P38 levels in a time-dependent manner. Cypermethrin disrupted the BBB (in vivo) in developing rats and attenuated the expression of the extracellular matrix molecule (ECM) and claudin-5 in cultured astrocytes. We further observed an augmentation in the levels of matrix metalloproteinase 2 (MMP2), known to modulate cellular migration and disrupt the developmental ECM and BBB. We observed an increase in the levels of reelin, involved in cell migration, in cultured rat astrocytes. The reelin receptor, α3β1integrin, and a mammalian cytosolic protein Disabled1 (Dab1) were also up-regulated. Overall, our study demonstrates that cypermethrin induces astrocyte injury via modulation in Ca(++), ROS, JNK and P38 pathways, which may alter MMP expression and reelin dependent astrocyte migration during brain development.

Orexin-A promotes cell migration in cultured rat astrocytes via Ca2+-dependent PKCα and ERK1/2 signals

Orexin-A is an important neuropeptide involved in the regulation of feeding, arousal, energy consuming, and reward seeking in the body. The effects of orexin-A have widely studied in neurons but not in astrocytes. Here, we report that OX1R and OX2R are expressed in cultured rat astrocytes. Orexin-A stimulated the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2), and then induced the migration of astrocytes via its receptor OX1R but not OX2R. Orexin-A-induced ERK1/2 phosphorylation and astrocytes migration are Ca2+-dependent, since they could be inhibited by either chelating the extracellular Ca2+ or blocking the pathway of store-operated calcium entry (SOCE). Furthermore, both non-selective protein kinase C (PKC) inhibitor and PKCα selective inhibitor, but not PKCδ inhibitor, prevented the increase in ERK1/2 phosphorylation and the migration of astrocytes, indicating that the Ca2+-dependent PKCα acts as the downstream of the OX1R activation and mediates the orexin-A-induced increase in ERK1/2 phosphorylation and cell migration. In conclusion, these results suggest that orexin-A can stimulate ERK1/2 phosphorylation and then facilitate the migration of astrocytes via PLC-PKCα signal pathway, providing new knowledge about the functions of the OX1R in astrocytes.

TNF-α induces matrix metalloproteinase-9-dependent soluble intercellular adhesion molecule-1 release via TRAF2-mediated MAPKs and NF-κB activation in osteoblast-like MC3T3-E1 cells

BACKGROUND

Matrix metalloproteinase-9 (MMP-9) has been shown to be induced by cytokines including TNF-α and may contribute to bone inflammatory diseases. However, the mechanisms underlying MMP-9 expression induced by TNF-α in MC3T3-E1 cells remain unclear.

RESULTS

We applied gelatin zymography, Western blot, RT-PCR, real-time PCR, selective pharmacological inhibitors of transcription (actinomycin D, Act.D), translation (cycloheximide, CHI), c-Src (PP1), MEK1/2 (U0126), p38 MAPK (SB202190), JNK1/2 (SP600125), and NF-κB (Bay11-7082), respective siRNAs transfection, promoter assay, immunofluorescence staining, and ELISA to investigate the MMP-9 expression and soluble ICAM-1 (sICAM-1) release induced by TNF-α in MC3T3-E1 cells. Here we demonstrated that TNF-α-induced MMP-9 expression was attenuated by Act.D, CHI, PP1, U0126, SB202190, SP600125, and Bay11-7082, and by the transfection with siRNAs for ERK2, p38 MAPK, and JNK2. TNF-α-stimulated TNFR1, TRAF2, and c-Src complex formation was revealed by immunoprecipitation and Western blot. Furthermore, TNF-α-stimulated NF-κB phosphorylation and translocation were blocked by Bay11-7082, but not by PP1, U0126, SB202190, or SP600125. TNF-α time-dependently induced MMP-9 promoter activity which was also inhibited by PP1, U0126, SB202190, SP600125, or Bay11-7082. Up-regulation of MMP-9 was associated with the release of sICAM-1 into the cultured medium, which was attenuated by the pretreatment with MMP-2/9i, an MMP-9 inhibitor.

CONCLUSIONS

In this study, we demonstrated that TNF-α up-regulates MMP-9 expression via c-Src, MAPKs, and NF-κB pathways. In addition, TNF-α-induced MMP-9 expression may contribute to the production of sICAM-1 by MC3T3-E1 cells. The interplay between MMP-9 expression and sICAM-1 release may exert an important role in the regulation of bone inflammatory diseases.

Ischemic stroke and traumatic brain injury: the role of the kallikrein-kinin system

Acute ischemic stroke and traumatic brain injury are a major cause of mortality and morbidity. Due to the paucity of therapies, there is a pressing clinical demand for new treatment options. Successful therapeutic strategies for these conditions must target multiple pathophysiological mechanisms occurring at different stages of brain injury. In this respect, the kallikrein-kinin system is an ideal target linking key pathological hallmarks of ischemic and traumatic brain damage such as edema formation, inflammation, and thrombosis. In particular, the kinin receptors, plasma kallikrein, and coagulation factor XIIa are highly attractive candidates for pharmacological development, as kinin receptor antagonists or inhibitors of plasma kallikrein and coagulation factor XIIa are neuroprotective in animal models of stroke and traumatic brain injury. Nevertheless, conflicting preclinical evaluation as well as limited and inconclusive data from clinical trials suggest caution when transferring observations made in animals into the human situation. This review summarizes current evidence on the pathological significance of the kallikrein-kinin system during ischemic and traumatic brain damage, with a particular focus on experimental data derived from animal models. Experimental findings are also compared with human data if available, and potential therapeutic implications are discussed.

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.

Blocking of bradykinin receptor B1 protects from focal closed head injury in mice by reducing axonal damage and astroglia activation

The two bradykinin receptors B1R and B2R are central components of the kallikrein-kinin system with different expression kinetics and binding characteristics. Activation of these receptors by kinins triggers inflammatory responses in the target organ and in most situations enhances tissue damage. We could recently show that blocking of B1R, but not B2R, protects from cortical cryolesion by reducing inflammation and edema formation. In the present study, we investigated the role of B1R and B2R in a closed head model of focal traumatic brain injury (TBI; weight drop). Increased expression of B1R in the injured hemispheres of wild-type mice was restricted to the later stages after brain trauma, i.e. day 7 (P<0.05), whereas no significant induction could be observed for the B2R (P>0.05). Mice lacking the B1R, but not the B2R, showed less functional deficits on day 3 (P<0.001) and day 7 (P<0.001) compared with controls. Pharmacological blocking of B1R in wild-type mice had similar effects. Reduced axonal injury and astroglia activation could be identified as underlying mechanisms, while inhibition of B1R had only little influence on the local inflammatory response in this model. Inhibition of B1R may become a novel strategy to counteract trauma-induced neurodegeneration.

Secretion of matrix metalloproteinase-9 from astrocytes by inhibition of tonic P2Y14-receptor-mediated signal(s)

Glial cells have various important roles in regulation of brain functions. For such events, extracellular nucleotides/P2 receptors have central roles. Although there have been huge amount of literature about activation of P2 receptors and glial functions, little is known about what happens in glia or the brain if glial P2 receptor is inhibited. Here we show that the inhibition of P2 receptors in astrocytes, the most abundant glial cells and cause a constitutive release of nucleotides, resulted in secretion of metalloproteinase-9 (MMP-9), a metal-dependent endopeptidase that degrades extracellular matrix molecules and is important in regulation of brain remodeling. When cultured astrocytes were treated with apyrase (ecto-nucleotidase), reactive blue 2 (P2 receptor antagonist), and pertussis toxin, they secreted MMP-9, suggesting that Gi-coupled P2Y receptor-mediated signals constitutively suppress the production of MMP-9. Among Gi-coupled P2Y receptors, we found that an inhibition of P2Y(14) receptor, a receptor for nucleotide-sugars such as UDP-glucose, is responsible for the production of MMP-9 by pharmacological and molecular biochemical analysis. As for the mechanisms, the inhibition of P2Y(14) receptors resulted in the release of tumor necrosis factor (TNF)-α which then acted on astrocytes to induce MMP-9. Taken together, our results suggest that the constitutive releases of nucleotide-sugars in astrocytes should play an important role in maintaining the normal status of the cell, through Gi-coupled P2Y(14) receptors, and when the signal is removed, the cells start to release TNF-α, which then acts on astrocytes in a feedback fashion to boost MMP-9 synthesis and secretion.

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.

Cardiac kallikrein-kinin system is upregulated in chronic volume overload and mediates an inflammatory induced collagen loss

Background

The clinical problem of a “pure volume overload” as in isolated mitral or aortic regurgitation currently has no documented medical therapy that attenuates collagen loss and the resultant left ventricular (LV) dilatation and failure. Here, we identify a potential mechanism related to upregulation of the kallikrein-kinin system in the volume overload of aortocaval fistula (ACF) in the rat.

Methodology/Principal Findings

LV interstitial fluid (ISF) collection, hemodynamics, and echocardiography were performed in age-matched shams and 4 and 15 wk ACF rats. ACF rats had LV dilatation and a 2-fold increase in LV end-diastolic pressure, along with increases in LV ISF bradykinin, myocardial kallikrein and bradykinin type-2 receptor (BK₂R) mRNA expression. Mast cell numbers were increased and interstitial collagen was decreased at 4 and 15 wk ACF, despite increases in LV ACE and chymase activities. Treatment with the kallikrein inhibitor aprotinin preserved interstitial collagen, prevented the increase in mast cells, and improved LV systolic function at 4 wk ACF. To establish a cause and effect between ISF bradykinin and mast cell-mediated collagen loss, direct LV interstitial bradykinin infusion in vivo for 24 hrs produced a 2-fold increase in mast cell numbers and a 30% decrease in interstitial collagen, which were prevented by BK₂R antagonist. To further connect myocardial stretch with cellular kallikrein-kinin system upregulation, 24 hrs cyclic stretch of adult cardiomyocytes and fibroblasts produced increased kallikrein, BK₂R mRNA expressions, bradykinin protein and gelatinase activity, which were all decreased by the kallikrein inhibitor-aprotinin.

Conclusions/Significance

A pure volume overload is associated with upregulation of the kallikrein-kinin system and ISF bradykinin, which mediates mast cell infiltration, extracellular matrix loss, and LV dysfunction–all of which are improved by kallikrein inhibition. The current investigation provides important new insights into future potential medical therapies for the volume overload of aortic and mitral regurgitation.

Japanese encephalitis virus induces matrix metalloproteinase-9 expression via a ROS/c-Src/PDGFR/PI3K/Akt/MAPKs-dependent AP-1 pathway in rat brain astrocytes

BACKGROUND

Japanese encephalitis virus (JEV) infection is a major cause of acute encephalopathy in children, which destroys central nervous system (CNS) cells, including astrocytes and neurons. Matrix metalloproteinase (MMP)-9 has been shown to degrade components of the basal lamina, leading to disruption of the blood-brain barrier (BBB) and to contribute to neuroinflammatory responses in many neurological diseases. However, the detailed mechanisms of JEV-induced MMP-9 expression in rat brain astrocytes (RBA-1 cells) are largely unclear.

METHODS

In this study, the effect of JEV on expression of MMP-9 was determined by gelatin zymography, western blot analysis, RT-PCR, and promoter assay. The involvement of AP-1 (c-Jun and c-Fos), c-Src, PDGFR, PI3K/Akt, and MAPKs in these responses were investigated by using the selective pharmacological inhibitors and transfection with siRNAs.

RESULTS

Here, we demonstrate that JEV induces expression of pro-form MMP-9 via ROS/c-Src/PDGFR/PI3K/Akt/MAPKs-dependent, AP-1 activation in RBA-1 cells. JEV-induced MMP-9 expression and promoter activity were inhibited by pretreatment with inhibitors of AP-1 (tanshinone), c-Src (PP1), PDGFR (AG1296), and PI3K (LY294002), and by transfection with siRNAs of c-Jun, c-Fos, PDGFR, and Akt. Moreover, JEV-stimulated AP-1 activation was inhibited by pretreatment with the inhibitors of c-Src, PDGFR, PI3K, and MAPKs.

CONCLUSION

From these results, we conclude that JEV activates the ROS/c-Src/PDGFR/PI3K/Akt/MAPKs pathway, which in turn triggers AP-1 activation and ultimately induces MMP-9 expression in RBA-1 cells. These findings concerning JEV-induced MMP-9 expression in RBA-1 cells imply that JEV might play an important role in CNS inflammation and diseases.

Nitric oxide production by endothelin-1 enhances astrocytic migration via the tyrosine nitration of matrix metalloproteinase-9

The deleterious effects of endothelin-1 (ET-1) in the central nervous system (CNS) include disturbance of water homeostasis and blood-brain barrier (BBB) integrity. In the CNS, ischemic injury elicits ET-1 release from astrocytes, behaving through G-protein coupled ET receptors. These considerations raise the question of whether ET-1 influences cellular functions of astrocytes, the major cell type that provides structural and functional support for neurons. Uncontrolled nitric oxide (NO) production has been implicated in sterile brain insults, neuroinflammation, and neurodegenerative diseases, which involve astrocyte activation and neuronal death. However, the detailed mechanisms of ET-1 action related to NO release on rat brain astrocytes (RBA-1) remain unknown. In this study, we demonstrate that exposure of astrocytes to ET-1 results in the inducible nitric oxide synthase (iNOS) up-regulation, NO production, and matrix metalloproteinase-9 (MMP-9) activation in astrocytes. The data obtained with Western blot, reverse transcription-PCR (RT-PCR), and immunofluorescent staining analyses showed that ET-1-induced iNOS expression and NO production were mediated through an ET(B)-dependent transcriptional activation. Engagement of G(i/o)--and G(q) -coupled ET(B) receptors by ET-1 led to activation of c-Src-dependent phosphoinositide 3-kinase (PI3K)/Akt and p42/p44 mitogen-activated protein kinase (MAPK) and then activated transcription factor nuclear factor-κB (NF-κB). The activated NF-κB was translocated into nucleus and thereby promoted iNOS gene transcription. Ultimately, NO production stimulated by ET-1 enhanced the migration of astrocytes through the tyrosine nitration of MMP-9. Taken together, these results suggested that in astrocytes, activation of NF-κB by ET(B)-dependent c-Src, PI3K/Akt, and p42/p44 MAPK signalings is necessary for ET-1-induced iNOS gene up-regulation.

Japanese encephalitis virus induces matrix metalloproteinase-9 in rat brain astrocytes via NF-κB signalling dependent on MAPKs and reactive oxygen species

BACKGROUND AND PURPOSE

Japanese encephalitis virus (JEV) is a member of the family Flaviviridae and JEV infection is a major cause of acute encephalopathy in children, which destroys cells in the CNS, including astrocytes and neurons. However, the detailed mechanisms underlying the inflammatory action of JEV are largely unclear.

EXPERIMENTAL APPROACH

The effect of JEV on the expression of matrix metalloproteinase (MMP)-9 was determined by gelatin zymography, Western blot analysis, real-time PCR and promoter assay. The involvement of the NADPH oxidase and reactive oxygen species (ROS), MAPKs, and the transcription factor NF-κB in these responses was investigated by using selective pharmacological inhibitors and transfection with appropriate siRNAs.

KEY RESULTS

JEV induced the expression of the pro-form of MMP-9 in rat brain astrocytes (RBA-1 cells). In RBA-1 cells, JEV induced MMP-9 expression and promoter activity, which was inhibited by pretreatment with inhibitors of NADPH oxidase (diphenylene iodonium chloride or apocynin), MAPKs (U0126, SB203580 or SP600125) and a ROS scavenger (N-acetylcysteine), or transfection with siRNAs of p47(phox) , ERK1, JNK2 and p38. In addition, JEV-induced MMP-9 expression was reduced by pretreatment with an inhibitor of NF-κB (helenalin) or transfection with p65 siRNA. Moreover, JEV-stimulated NF-κB activation was inhibited by pretreatment with the inhibitors of NADPH oxidase and MAPKs.

CONCLUSIONS AND IMPLICATIONS

MMP-9 expression induced by JEV infection of RBA-1 cells was mediated through the generation of ROS and activation of p42/p44 MAPK, p38 MAPK and JNK1/2, leading to NF-κB activation.

Reactive Oxygen Species-Dependent c-Fos/Activator Protein 1 Induction Upregulates Heme Oxygenase-1 Expression by Bradykinin in Brain Astrocytes

Heme oxygenase-1 (HO-1) plays a crucial role in tissue pathological changes such as brain injuries. Our previous studies have demonstrated that bradykinin (BK) induces the expression of several inflammatory proteins, including matrix metalloproteinase-9 and COX-2, via mitogen-activated protein kinases and nuclear factor-κB (NF-κB) in rat brain astrocytes (RBA-1). However, the molecular mechanisms underlying BK-induced HO-1 expression in RBA-1 cells remain poorly defined. Here we demonstrated that BK induced HO-1 expression and enzymatic activity via a B(2) BK receptor-activated reactive oxygen species (ROS)-dependent signaling pathway. NADPH oxidase (Nox)-dependent ROS generation led to activation of extracellular signal-regulated kinase 1/2 (ERK1/2) and c-Jun-N-terminal kinase (JNK) and then activated the downstream molecules NF-κB and c-Jun, respectively. The c-Fos, an activator protein 1 (AP-1) subunit, was upregulated by activation of NF-κB and c-Jun, which bound to HO-1 promoter and thereby turned on transcription of HO-1 gene. The rat HO-1 promoter containing a putative AP-1 cis-binding site was identified as a crucial domain linking to BK action. Taken together, these results suggested that in RBA-1 cells, activation of ERK/NF-κB and JNK/c-Jun cascades by a Nox/ROS-dependent event enhancing c-Fos/AP-1 activity is essential for HO-1 upregulation and activation induced by BK. Moreover, ROS-dependent NF-E2-related factor 2 activation also contributes to HO-1 induction by BK in astrocytes.

Transforming growth factor-β1 induces matrix metalloproteinase-9 and cell migration in astrocytes: roles of ROS-dependent ERK- and JNK-NF-κB pathways

BACKGROUND

Transforming growth factor-β (TGF-β) and matrix metalloproteinases (MMPs) are the multifunctional factors during diverse physiological and pathological processes including development, wound healing, proliferation, and cancer metastasis. Both TGF-β and MMPs have been shown to play crucial roles in brain pathological changes. Thus, we investigated the molecular mechanisms underlying TGF-β1-induced MMP-9 expression in brain astrocytes.

METHODS

Rat brain astrocytes (RBA-1) were used. MMP-9 expression was analyzed by gelatin zymography and RT-PCR. The involvement of signaling molecules including MAPKs and NF-κB in the responses was investigated using pharmacological inhibitors and dominant negative mutants, determined by western blot and gene promoter assay. The functional activity of MMP-9 was evaluated by cell migration assay.

RESULTS

Here we report that TGF-β1 induces MMP-9 expression and enzymatic activity via a TGF-β receptor-activated reactive oxygen species (ROS)-dependent signaling pathway. ROS production leads to activation of extracellular signal-regulated kinase 1/2 (ERK1/2) and c-Jun-N-terminal kinase (JNK) and then activation of the NF-κB transcription factor. Activated NF-κB turns on transcription of the MMP-9 gene. The rat MMP-9 promoter, containing a NF-κB cis-binding site, was identified as a crucial domain linking to TGF-β1 action.

CONCLUSIONS

Collectively, in RBA-1 cells, activation of ERK1/2- and JNK-NF-κB cascades by a ROS-dependent manner is essential for MMP-9 up-regulation/activation and cell migration induced by TGF-β1. These findings indicate a new regulatory pathway of TGF-β1 in regulating expression of MMP-9 in brain astrocytes, which is involved in physiological and pathological tissue remodeling of central nervous system.

Intracerebroventricular administration of an endothelin ET(B)-receptor agonist increases expression of matrix metalloproteinase-2 and -9 in rat brain

Matrix metalloproteinases (MMPs), a family of zinc-endopeptidases, have a critical role in the pathophysiological responses in damaged brains. MMPs are up-regulated in brain pathologies. To clarify the extracellular signals involved in brain MMP production, the effects of endothelins (ETs), a family of vasoconstricting peptides, were examined. Intracerebroventricular administration of 500 pmol/day Ala(1,3,11,15)-ET-1, an ET(B)-receptor agonist, increased the mRNAs of MMP2 and MMP9 in rat hippocampus and cerebrum. Ala(1,3,11,15)-ET-1 did not affect mRNA levels of MMP 1, 12, and 14. Administration of Ala(1,3,11,15)-ET-1 for 7 days also increased the protein content and proteolytic activities of MMP2 and MMP9 in the cerebrum. Immunohistochemical observations showed that astrocytes in the hippocampus and the cerebrum of ET-infused rats had MMP2 and MMP9 reactivities. In rat cultured astrocytes, both Ala(1,3,11,15)-ET-1 (100 nM) and ET-1 (100 nM) increased MMP2 and MMP9 mRNAs. ET-1 stimulated the protein releases and the proteolytic activities of MMP2 and MMP9 from cultured astrocytes. BQ788, an ET(B) antagonist, inhibited the effects of ET-1 on astrocytic MMP2 and MMP9. The ET-induced expression of MMP9, but not MMP2, was inhibited by pyrrolidine dithiocarbamate, proteasome inhibitor I, and MG132. These results suggest that ET stimulates astrocytic MMP2 and MMP9 production through ET(B) receptors.

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

Background

Lipoteichoic acid (LTA) is a component of Gram-positive bacterial cell walls, which has been found to be elevated in cerebrospinal fluid of patients suffering from meningitis. Moreover, matrix metalloproteinases (MMPs), MMP-9 especially, have been observed in patients with brain inflammatory diseases and may contribute to brain disease pathology. However, the molecular mechanisms underlying LTA-induced MMP-9 expression in brain astrocytes remain unclear.

Objective

The goal of this study was to examine whether LTA-induced cell migration is mediated by calcium/calmodulin (CaM)/CaM kinase II (CaMKII)-dependent transactivation of the PDGFR pathway in rat brain astrocytes (RBA-1 cells).

Methods

Expression and activity of MMP-9 induced by LTA was evaluated by zymographic, western blotting, and RT-PCR analyses. MMP-9 regulatory signaling pathways were investigated by treatment with pharmacological inhibitors or using dominant negative mutants or short hairpin RNA (shRNA) transfection, and chromatin immunoprecipitation (ChIP)-PCR and promoter activity reporter assays. Finally, we determined the cell functional changes by cell migration assay.

Results

The data show that c-Jun/AP-1 mediates LTA-induced MMP-9 expression in RBA-1 cells. Next, we demonstrated that LTA induces MMP-9 expression via a calcium/CaM/CaMKII-dependent transactivation of PDGFR pathway. Transactivation of PDGFR led to activation of PI3K/Akt and JNK1/2 and then activated c-Jun/AP-1 signaling. Activated-c-Jun bound to the AP-1-binding site of the MMP-9 promoter, and thereby turned on transcription of MMP-9. Eventually, up-regulation of MMP-9 by LTA enhanced cell migration of astrocytes.

Conclusions

These results demonstrate that in RBA-1 cells, activation of c-Jun/AP-1 by a CaMKII-dependent PI3K/Akt-JNK activation mediated through transactivation of PDGFR is essential for up-regulation of MMP-9 and cell migration induced by LTA. Understanding the regulatory mechanisms underlying LTA-induced MMP-9 expression and functional changes in astrocytes may provide a new therapeutic strategy for Gram-positive bacterial infections in brain disorders.

Bradykinin increases resensitization of purinergic receptor signaling in glioma cells

BACKGROUND

Purinergic receptor-mediated signaling plays an important role in the function of glial cells, including glial tumor cells. Bradykinin is also an important paracrine mediator which is highly expressed in brain tumors and may correlate with their pathological grade. Interaction between bradykinin and purinergic signaling may therefore be involved in the regulation of glial tumor cells.

RESULTS

We examined the effect of bradykinin on glial purinergic signaling in an immortalized glioma cell line. Confocal calcium imaging revealed that ATP evokes an increase in [Ca2+]i in the U87 human astrocytoma cell line. This response was reduced with repetitive application of ATP, likely due to receptor desensitization. However exposure to bradykinin increased the Ca2+ response to a second application of ATP, consistent with increased resensitization. The bradykinin effect on resensitization was similar in the absence of extracellular Ca2+ or in the presence of the PKC activator PMA, but was inhibited by the protein phosphatase inhibitor okadaic acid and the PI3K inhibitor LY294002.

CONCLUSIONS

Modulation of protein phosphatases and the PI3K pathway may represent a mechanism by which bradykinin potentiates purinergic signaling in glial cells.

Leptin-induced vascular smooth muscle cell proliferation via regulating cell cycle, activating ERK1/2 and NF-kappaB

Leptin is a peptide hormone primarily involved in the regulation of food intake and energy expenditure. Recent studies have suggested that leptin is one of the risk factors for cardiovascular diseases including atherosclerosis and hypertension. Vascular smooth muscle cells (VSMCs) play a vital role in arterial intimal thickening and vascular remodeling. In this study, we investigated the effect of leptin on VSMC cell-cycle regulation and the possible pathway. We found that leptin stimulated VSMC proliferation and increased cell progression to S and G2/M phases. The expression of cyclinD1, phosphorylated extracellular signal-regulated kinase 1/2 (ERK1/2), and nuclear factor (NF)-kappaBp65 was increased. Treatment of the cells with leptin antagonist triple mutant attenuated the leptininduced ERK1/2 and NF-kappaB activation. These results suggested that leptin stimulated VSMC proliferation by promoting transition from G1 to S phase and ERK1/2 and NF-kappaB pathway might contribute to this procession.

Endothelin-1 enhances cell migration via matrix metalloproteinase-9 up-regulation in brain astrocytes

The bioactivity of endothelin-1 (ET-1) has been suggested in the development of CNS diseases, including disturbance of water homeostasis and blood-brain barrier integrity. Recent studies suggest that hypoxic/ischemic injury of the brain induces release of ET-1, behaving through a G-protein coupled ET receptor family. The deleterious effects of ET-1 on astrocytes may aggravate brain inflammation. Increased plasma levels of matrix metalloproteinases (MMPs), in particular MMP-9, have been observed in patients with neuroinflammatory disorders. However, the detailed mechanisms underlying ET-1-induced MMP-9 expression remain unknown. In this study, the data obtained with zymographic, western blotting, real-time PCR, and immunofluorescent staining analyses showed that ET-1-induced MMP-9 expression was mediated through an ET(B)-dependent transcriptional activation. Engagement of G(i/o)- and G(q)-coupled ET(B) receptor by ET-1 led to activation of p42/p44 MAPK and then activated transcription factors including Ets-like kinase, nuclear factor-kappa B, and activator protein-1 (c-Jun/c-Fos). These activated transcription factors translocated into nucleus and bound to their corresponding binding sites in MMP-9 promoter, thereby turning on MMP-9 gene transcription. Eventually, up-regulation of MMP-9 by ET-1 enhanced the migration of astrocytes. Taken together, these results suggested that in astrocytes, activation of Ets-like kinase, nuclear factor-kappa B, and activator protein-1 by ET(B)-dependent p42/p44 MAPK signaling is necessary for ET-1-induced MMP-9 gene up-regulation. Understanding the mechanisms of MMP-9 expression and functional changes regulated by ET-1/ET(B) system on astrocytes may provide rational therapeutic interventions for brain injury associated with increased MMP-9 expression.

Immunomodulatory responses of peripheral blood mononuclear cells from multiple sclerosis patients upon in vitro incubation with the flavonoid luteolin: additive effects of IFN-beta

The study is aimed to determine the role of luteolin (3',4',5,7-tetrahydroxyflavone), alone and in combination with human interferon-beta (IFN-beta), in modulating the immune response(s) of peripheral blood mononuclear cells (PBMCs) isolated from multiple sclerosis (MS) patients. PBMC proliferation in the presence or absence of these drugs was determined and the production of pro-inflammatory cytokines (IL-1beta, TNF-alpha), and the ratio of cell migration mediator MMP-9, and its inhibitor, TIMP-1 was assessed in the culture supernatants. Luteolin reduced, in a dose-dependent manner, the proliferation of PBMCs, and modulated the levels of IL-1beta and TNF-alpha released by PBMCs in the culture supernatants. Luteolin reduced the MMP-9/TIMP-1 ratio via lowering MMP-9 production. In the majority of cases, luteolin, when combined with IFN-beta, had additive effects in modulating cell proliferation, IL-1beta, TNF-alpha, MMP-9 and TIMP-1.

Oxidized low-density lipoprotein-induced matrix metalloproteinase-9 expression via PKC-delta/p42/p44 MAPK/Elk-1 cascade in brain astrocytes

After ischemic injury to brain, disruption of the blood-brain barrier (BBB) raises the possibility of exposing the central nervous system (CNS) to oxidized low-density lipoprotein (oxLDL), a risk factor implicated in neurodegenerative diseases. Matrix metalloproteinases (MMPs), especially MMP-9, contribute to extracellular matrix (ECM) remodeling during the CNS diseases. However, the molecular mechanisms underlying oxLDL-induced MMP-9 expression in astrocytes remained unclear. Here, we reported that oxLDL induced MMP-9 expression via a PKC-delta/p42/p44 MAPK-dependent Elk-1 activation in rat brain astrocyte (RBA)-1 cells, revealed by gelatin zymography, RT-PCR, and Western blotting analyses. These responses were attenuated by pretreatment with pharmacological inhibitors and transfection with dominant negative mutants. Moreover, Elk-1-mediated MMP-9 gene transcription was confirmed by transfection with an Elk-1 binding site-mutated MMP-9 promoter construct (mt-Ets-MMP9), which blocked oxLDL-stimulated MMP-9 luciferase activity. Understanding the regulatory mechanisms by which oxLDL induced MMP-9 expression in astrocytes might provide a new therapeutic strategy of brain diseases.

Gene deletion of the kinin receptor B1 attenuates cardiac inflammation and fibrosis during the development of experimental diabetic cardiomyopathy

OBJECTIVE

Diabetic cardiomyopathy is associated with increased mortality in patients with diabetes. The underlying pathology of this disease is still under discussion. We studied the role of the kinin B1 receptor on the development of experimental diabetic cardiomyopathy.

RESEARCH DESIGN AND METHODS

We utilized B1 receptor knockout mice and investigated cardiac inflammation, fibrosis, and oxidative stress after induction of streptozotocin (STZ)-induced diabetes. Furthermore, the left ventricular function was measured by pressure-volume loops after 8 weeks of diabetes.

RESULTS

B1 receptor knockout mice showed an attenuation of diabetic cardiomyopathy with improved systolic and diastolic function in comparison with diabetic control mice. This was associated with a decreased activation state of the mitogen-activated protein kinase p38, less oxidative stress, as well as normalized cardiac inflammation, shown by fewer invading cells and no increase in matrix metalloproteinase-9 as well as the chemokine CXCL-5. Furthermore, the profibrotic connective tissue growth factor was normalized, leading to a reduction in cardiac fibrosis despite severe hyperglycemia in mice lacking the B1 receptor.

CONCLUSIONS

These findings suggest that the B1 receptor is detrimental in diabetic cardiomyopathy in that it mediates inflammatory and fibrotic processes. These insights might have useful implications on future studies utilizing B1 receptor antagonists for treatment of human diabetic cardiomyopathy.

Oxidized low-density lipoprotein induces matrix metalloproteinase-9 expression via a p42/p44 and JNK-dependent AP-1 pathway in brain astrocytes

Upregulation of matrix metalloproteinases (MMPs), especially MMP-9, by oxidized low-density lipoprotein (oxLDL) is implicated in many inflammatory diseases including brain injury. However, the signaling mechanisms underlying oxLDL-induced MMP-9 expression in astrocytes largely remain unknown. Here we report that oxLDL induces expression of proMMP-9 via a MAPK-dependent AP-1 activation in rat brain astrocyte (RBA)-1 cells. Results revealed by gelatin zymography, RT-PCR, and Western blotting analyses showed that oxLDL-induced proMMP-9 gene expression was mediated through Akt, JNK1/2, and p42/p44 MAPK phosphorylation in RBA-1 cells. These responses were attenuated by inhibitors of PI3K (LY294002), JNK (SP600125), and p42/p44 MAPK (PD98059), or transfection with dominant negative mutants and short hairpin RNA. Moreover, we demonstrated that AP-1 (i.e., c-Fos/c-Jun) is crucial for oxLDL-induced proMMP-9 expression which was attenuated by pretreatment with AP-1 inhibitor (curcumin). The regulation of MMP-9 gene transcription by AP-1 was confirmed by oxLDL-stimulated MMP-9 luciferase activity which was totally lost in cells transfected with the AP-1 binding site-mutated MMP-9 promoter construct (mt-AP1-MMP-9). These results suggested that oxLDL-induced proMMP-9 expression is mediated through PI3K/Akt, JNK1/2, and p42/p44 MAPK leading to AP-1 activation. Understanding the regulatory mechanisms underlying oxLDL-induced MMP-9 expression in astrocytes might provide a new therapeutic strategy of brain injuries and diseases.

Development of diabetic cardiomyopathy and the kallikrein-kinin system--new insights from B1 and B2 receptor signaling

Diabetic cardiomyopathy is a specific cardiomyopathy which develops in patients with diabetes mellitus in the absence of coronary atherosclerosis and hypertension. Despite the potential importance of this disease entity, the underlying mechanisms are only incompletely understood. Changes in calcium handling, disruption of the extracellular matrix regulation with accumulation of cardiac collagen, and furthermore cardiac inflammation may be an important mediator of this disease. This brief review focuses on the current aspects of the kallikrein-kinin system and its influence on the development of diabetic cardiomyopathy with particular regard to the kinin receptors B1 and B2, as their role in the development of this disease is still under discussion. Whether the role of the B1 receptor is similar to the well-described beneficial role of the B2 receptor or whether its function is opposed to the B2 receptor is controversial. Some recent findings suggest that the B1 receptor mediates cardiac inflammation and therefore may be detrimental for cardiac function in the setting of diabetic cardiomyopathy.

Sphingosine 1-phosphate induces EGFR expression via Akt/NF-kappaB and ERK/AP-1 pathways in rat vascular smooth muscle cells

Sphingosine 1-phosphate (S1P) has been shown to regulate expression of several genes in vascular smooth muscle cells (VSMCs) and contributes to arteriosclerosis. However, the mechanisms regulating epidermal growth factor receptor (EGFR) expression by S1P in aortic VSMCs remain unclear. Western blotting and RT-PCR analyses showed that S1P induced EGFR mRNA and protein expression in a time- and concentration-dependent manner, which was attenuated by inhibitors of MEK1/2 (U0126) and phosphatidylinositide 3-kinase (PI3K; wortmannin), and transfection with dominant negative mutants of ERK and Akt, respectively. These results suggested that S1P-induced EGFR expression was mediated through p42/p44 MAPK and PI3K/Akt pathways in VSMCs. In accordance with these findings, S1P stimulated phosphorylation of p42/p44 MAPK and Akt which was attenuated by U0126 and wortmannin, respectively. Furthermore, S1P-induced EGFR upregulation was blocked by a selective NF-kappaB inhibitor helenalin. Immunofluorescent staining and reporter gene assay revealed that S1P-induced activation of NF-kappaB was blocked by wortmannin, but not by U0126, suggesting that activation of NF-kappaB was mediated through PI3K/Akt. Moreover, S1P-induced EGFR expression was inhibited by an AP-1 inhibitor curcumin and tanshinone IIA. S1P-stimulated AP-1 subunits (c-Jun and c-Fos mRNA) expression was attenuated by U0126 and wortmannin, suggesting that MEK and PI3K/ERK cascade linking to AP-1 was involved in EGFR expression. Upregulation of EGFR by S1P may exert a phenotype modulation of VSMCs. This hypothesis was supported by pretreatment with AG1478 or transfection with shRNA of EGFR that attenuated EGF-stimulated proliferation of VSMCs pretreated with S1P, determined by XTT assay. These results demonstrated that in VSMCs, activation of Akt/NF-kappaB and ERK/AP-1 pathways independently regulated S1P-induced EGFR expression in VSMCs. Understanding the mechanisms involved in S1P-induced EGFR expression on VSMCs may provide potential therapeutic targets in the treatment of arteriosclerosis.

Bradykinin induces matrix metalloproteinase-9 expression and cell migration through a PKC-delta-dependent ERK/Elk-1 pathway in astrocytes

Many reports have shown that matrix metalloproteinase (MMP)-9 plays an important role in brain inflammation and diseases. In our previous study, bradykinin (BK) has been shown to induce proMMP-9 expression via MAPKs and NF-kappaB in rat brain astrocytes (RBA-1). However, the molecular mechanisms and physiological roles underlying BK-induced MMP-9 expression in RBA-1 remain unclear. Here we reported that BK induced proMMP-9 expression and promoted RBA-1 cell migration, via a B(2) BK receptor-activated protein kinase C-delta (PKC-delta)-dependent signaling pathway. Activation of PKC-delta led to phosphorylation and translocation of extracellular signal-regulated kinase 1/2 (ERK1/2) and then activated a transcription factor Elk-1. Phospho-Elk-1 bound to MMP-9 promoter and thereby induced transcription of MMP-9. The rat MMP-9 promoter containing an Elk-1 cis-binding site (Ets domain), that located at nucleotides -511 to -506 was identified as a crucial domain linking to BK action. Moreover, BK induced recruitment of p300 (as a transcriptional co-activator) to the MMP-9 promoter, leading to the acetylation of histone H4 in chromatin and facilitating MMP-9 gene transcription. Taken together, these results suggested that in RBA-1 cells, activation of ERK1/2 by a PKC-delta-dependent event mediated through Elk-1 pathway is essential for MMP-9 gene up-regulation and cell migration induced by BK.