Up-regulation of TNF-alpha convertase (TACE/ADAM17) after oxygen-glucose deprivation in rat forebrain slices

Blue light exposure collapses the inner blood-retinal barrier by accelerating endothelial CLDN5 degradation through the disturbance of GNAZ and the activation of ADAM17

Blue light is part of the natural light spectrum that emits high energy. Currently, people are frequently exposed to blue light from 3C devices, resulting in a growing incidence of retinopathy. The retinal vasculature is complex, and retinal vessels not only serve the metabolic needs of the retinal sublayers, but also maintain electrolyte homeostasis by forming the inner blood-retinal barrier (iBRB). The iBRB, which is primarily composed of endothelial cells, has well-developed tight junctions. However, with exposure to blue light, the risks of targeting retinal endothelial cells are currently unknown. We found that endothelial claudin-5 (CLDN5) was rapidly degraded under blue light, coinciding with the activation of a disintegrin and metalloprotease 17 (ADAM17), even at non-cytotoxic lighting. An apparently broken tight junction and a permeable paracellular cleft were observed. Mice exposed to blue light displayed iBRB leakage, conferring attenuation of the electroretinogram b-wave and oscillatory potentials. Both pharmacological and genetic inhibition of ADAM17 remarkably alleviated CLDN5 degradation induced by blue light. Under untreated condition, ADAM17 is sequestered by GNAZ (a circadian-responsive, retina-enriched inhibitory G protein), whereas ADAM17 escapes from GNAZ by blue light illuminance. GNAZ knockdown led to ADAM17 hyperactivation, CLDN5 downregulation, and paracellular permeability in vitro, and retinal damage mimicked blue light exposure in vivo. These data demonstrate that blue light exposure might impair the iBRB by accelerating CLDN5 degradation through the disturbance of the GNAZ-ADAM17 axis.

Transmembrane TNF and Its Receptors TNFR1 and TNFR2 in Mycobacterial Infections

Tumor necrosis factor (TNF) is one of the main cytokines regulating a pro-inflammatory environment. It has been related to several cell functions, for instance, phagocytosis, apoptosis, proliferation, mitochondrial dynamic. Moreover, during mycobacterial infections, TNF plays an essential role to maintain granuloma formation. Several effector mechanisms have been implicated according to the interactions of the two active forms, soluble TNF (solTNF) and transmembrane TNF (tmTNF), with their receptors TNFR1 and TNFR2. We review the impact of these interactions in the context of mycobacterial infections. TNF is tightly regulated by binding to receptors, however, during mycobacterial infections, upstream activation signalling pathways may be influenced by key regulatory factors either at the membrane or cytosol level. Detailing the structure and activation pathways used by TNF and its receptors, such as its interaction with solTNF/TNFRs versus tmTNF/TNFRs, may bring a better understanding of the molecular mechanisms involved in activation pathways which can be helpful for the development of new therapies aimed at being more efficient against mycobacterial infections.

A wake-like state in vitro induced by transmembrane TNF/soluble TNF receptor reverse signaling

Tumor necrosis factor alpha (TNF) has sleep regulatory and brain development roles. TNF promotes sleep in vivo and in vitro while TNF inhibition diminishes sleep. Transmembrane (tm) TNF and the tmTNF receptors (Rs), are cleaved by tumor necrosis factor alpha convertase to produce soluble (s) TNF and sTNFRs. Reverse signaling occurs in cells expressing tmTNF upon sTNFR binding. sTNFR administration in vivo inhibits sleep, thus we hypothesized that a wake-like state in vitro would be induced by sTNFR-tmTNF reverse signaling. Somatosensory cortical neuron/glia co-cultures derived from male and female mice lacking both TNFRs (TNFRKO), or lacking TNF (TNFKO) and wildtype (WT) mice were plated onto six-well multi-electrode arrays. Daily one-hour electrophysiological recordings were taken on culture days 4 through 14. sTNFR1 (0.0, 0.3, 3, 30, 60, and 120 ng/µL) was administered on day 14. A final one-hour recording was taken on day 15. Four measures were characterized that are also used to define sleep in vivo: action potentials (APs), burstiness index (BI), synchronization of electrical activity (SYN), and slow wave power (SWP; 0.25-3.75 Hz). Development rates of these emergent electrophysiological properties increased in cells from mice lacking TNF or both TNFRs compared to cells from WT mice. Decreased SWP, after the three lowest doses (0.3, 3 and 30 ng/µL) of the sTNFR1, indicate a wake-like state in cells from TNFRKO mice. A wake-like state was also induced after 3 ng/µl sTNFR1 treatment in cells from TNFKO mice, which express the TNFR1 ligand, lymphotoxin alpha. Cells from WT mice showed no treatment effects. Results are consistent with prior studies demonstrating involvement of TNF in brain development, TNF reverse signaling, and sleep regulation in vivo. Further, the current demonstration of sTNFR1 induction of a wake-like state in vitro is consistent with the idea that small neuronal/glial circuits manifest sleep- and wake-like states analogous to those occurring in vivo. Finally, that sTNF forward signaling enhances sleep while sTNFR1 reverse signaling enhances a wake-like state is consistent with other sTNF/tmTNF/sTNFR1 brain actions having opposing activities.

Targeting Angiotensin-Converting Enzyme-2/Angiotensin-(1-7)/Mas Receptor Axis in the Vascular Progenitor Cells for Cardiovascular Diseases

Bone marrow-derived hematopoietic stem/progenitor cells are vasculogenic and play an important role in endothelial health and vascular homeostasis by participating in postnatal vasculogenesis. Progenitor cells are mobilized from bone marrow niches in response to remote ischemic injury and migrate to the areas of damage and stimulate revascularization largely by paracrine activation of angiogenic functions in the peri-ischemic vasculature. This innate vasoprotective mechanism is impaired in certain chronic clinical conditions, which leads to the development of cardiovascular complications. Members of the renin-angiotensin system-angiotensin-converting enzymes (ACEs) ACE and ACE2, angiotensin II (Ang II), Ang-(1-7), and receptors AT1 and Mas-are expressed in vasculogenic progenitor cells derived from humans and rodents. Ang-(1-7), generated by ACE2, is known to produce cardiovascular protective effects by acting on Mas receptor and is considered as a counter-regulatory mechanism to the detrimental effects of Ang II. Evidence has now been accumulating in support of the activation of the ACE2/Ang-(1-7)/Mas receptor pathway by pharmacologic or molecular maneuvers, which stimulates mobilization of progenitor cells from bone marrow, migration to areas of vascular damage, and revascularization of ischemic areas in pathologic conditions. This minireview summarizes recent studies that have enhanced our understanding of the physiology and pharmacology of vasoprotective axis in bone marrow-derived progenitor cells in health and disease. SIGNIFICANCE STATEMENT: Hematopoietic stem progenitor cells (HSPCs) stimulate revascularization of ischemic areas. However, the reparative potential is diminished in certain chronic clinical conditions, leading to the development of cardiovascular diseases. ACE2 and Mas receptor are key members of the alternative axis of the renin-angiotensin system and are expressed in HSPCs. Accumulating evidence points to activation of ACE2 or Mas receptor as a promising approach for restoring the reparative potential, thereby preventing the development of ischemic vascular diseases.

Matrix metalloproteinases and ADAMs in stroke

Stroke is a leading cause of death and disability worldwide. However, after years of in-depth research, the pathophysiology of stroke is still not fully understood. Increasing evidence shows that matrix metalloproteinases (MMPs) and "a disintegrin and metalloproteinase" (ADAMs) participate in the neuro-inflammatory cascade that is triggered during stroke but also in recovery phases of the disease. This review covers the involvement of these proteins in brain injury following cerebral ischemia which has been widely studied in recent years, with efforts to modulate this group of proteins in neuroprotective therapies, together with their implication in neurorepair mechanisms. Moreover, the review also discusses the role of these proteins in specific forms of neurovascular disease, such as small vessel diseases and intracerebral hemorrhage. Finally, the potential use of MMPs and ADAMs as guiding biomarkers of brain injury and repair for decision-making in cases of stroke is also discussed.

Brain TACE (Tumor Necrosis Factor-α-Converting Enzyme) Contributes to Sympathetic Excitation in Heart Failure Rats

TNF-α (tumor necrosis factor-α) is initially synthesized as a transmembrane protein that is cleaved by TACE (TNF-α-converting enzyme) to release soluble TNF-α. The elevated level of TNF-α in the brain and circulation in heart failure (HF) suggests an increase in the TACE-mediated ectodomain shedding process. The present study sought to determine whether TACE is upregulated in cardiovascular/autonomic brain regions like subfornical organ and hypothalamic paraventricular nucleus in rats with ischemia-induced HF and whether TACE plays a role in TNF-α-driven sympathetic excitation. We found that TACE was expressed throughout the subfornical organ and paraventricular nucleus, with significantly higher levels in HF than in sham-operated (Sham) rats. Intracerebroventricular injection of recombinant TACE induced a mild increase in blood pressure, heart rate, and renal sympathetic nerve activity that peaked at 15 to 20 minutes in both Sham and HF rats. HF rats had a secondary prolonged increase in these variables that was prevented by the TNF-α inhibitor SPD304. Intracerebroventricular administration of the TACE inhibitor TNF-alpha protease inhibitor 1 decreased blood pressure, heart rate, and renal sympathetic nerve activity in Sham and HF rats, with an exaggerated reduction in heart rate and renal sympathetic nerve activity in the HF rats. Direct microinjection of TACE or TNF-alpha protease inhibitor 1 into paraventricular nucleus or subfornical organ of Sham and HF rats elicited blood pressure, heart rate, and renal sympathetic nerve activity responses similar to intracerebroventricular TACE or TNF-alpha protease inhibitor 1. Intracerebroventricular infusion of Ang II (angiotensin II) and IL (interleukin)-1β increased TACE expression in subfornical organ and paraventricular nucleus of normal rats. These data suggest that a TACE-mediated increase in soluble TNF-α in the brain contributes to sympathetic excitation in HF.

Hypoxic regulation of angiotensin-converting enzyme 2 and Mas receptor in human CD34+ cells

CD34⁺ hematopoietic stem/progenitor cells (HSPCs) are vasculogenic and hypoxia is a strong stimulus for the vasoreparative functions of these cells. Angiotensin-converting enzyme 2 (ACE2)/angiotensin-(1-7)/Mas receptor (MasR) pathway stimulates vasoprotective functions of CD34⁺ cells. This study tested if ACE2 and MasR are involved in the hypoxic stimulation of CD34⁺ cells. Cells were isolated from circulating mononuclear cells derived from healthy subjects (n = 46) and were exposed to normoxia (20% O₂ ) or hypoxia (1% O₂ ). Luciferase reporter assays were carried out in cells transduced with lentivirus carrying ACE2- or MasR- or a scramble-3'-untranslated region gene with a firefly luciferase reporter. Expressions or activities of ACE, angiotensin receptor Type 1 (AT1R), ACE2, and MasR were determined. In vitro observations were verified in HSPCs derived from mice undergoing hindlimb ischemia (HLI). In vitro exposure to hypoxia-increased proliferation and migration of CD34⁺ cells in basal conditions or in response to vascular endothelial growth factor (VEGF) or stromal-derived factor 1α (SDF) compared with normoxia. Expression of ACE2 or MasR was increased relative to normoxia while ACE or AT1R expressions were unaltered. Luciferase activity was increased by hypoxia in cells transfected with the luciferase reporter plasmids coding for the ACE2- or MasR promoters relatively to the control. The effects of hypoxia were mimicked by VEGF or SDF under normoxia. Hypoxia-induced ADAM17-dependent shedding of functional ACE2 fragments. In mice undergoing HLI, increased expression/activity of ACE2 and MasR were observed in the circulating HSPCs. This study provides compelling evidence for the hypoxic upregulation of ACE2 and MasR in CD34⁺ cells, which likely contributes to vascular repair.

Soluble TNF Regulates TACE via AP-2α Transcription Factor in Mouse Dendritic Cells

Dendritic cells (DCs), the essential immunoregulatory and APCs, are major producers of the central mediator of inflammation, soluble TNF-α (sTNF). sTNF is generated by TNF-α converting enzyme (TACE) proteolytic release of the transmembrane TNF (tmTNF) ectodomain. The mechanisms of TACE and sTNF regulation in DCs remain elusive. This study newly defines that sTNF regulates TACE in mouse DCs by engaging the AP-2α transcription factor. We found that the expression of AP-2α was higher, whereas the expression and activity of TACE were lower, in wild-type DCs (wtDCs) than in TNF knockout (TNFko) DCs. Exogenous sTNF rapidly and simultaneously induced increases of AP-2α expression and decreases of TACE expression and activity in wtDCs and TNFko DCs, indicating that AP-2α and TACE are inversely dependent on sTNF and are functionally associated. To define this functional association, we identified an AP-2α binding site in TACE promoter and demonstrated, using EMSAs and chromatin immunoprecipitation assays, that AP-2α could bind to TACE promoter in a TNF-dependent manner. Additionally, sTNF simultaneously enhanced AP-2α expression and decreased TACE promoter luciferase activity in DCs. Similarly, transfection of AP-2α cDNA decreased TACE promoter luciferase activity, TACE expression, and TACE enzymatic activity in wtDCs or TNFko DCs. In contrast, transfection of AP-2α small interfering RNA increased TACE promoter luciferase activity, TACE expression, and TACE enzymatic activity in wtDCs. These results show that TACE is a target of, and is downregulated by, sTNF-induced AP-2α transcription factor in DCs.

A Disintegrin and Metalloprotease 17 in the Cardiovascular and Central Nervous Systems

ADAM17 is a metalloprotease and disintegrin that lodges in the plasmatic membrane of several cell types and is able to cleave a wide variety of cell surface proteins. It is somatically expressed in mammalian organisms and its proteolytic action influences several physiological and pathological processes. This review focuses on the structure of ADAM17, its signaling in the cardiovascular system and its participation in certain disorders involving the heart, blood vessels, and neural regulation of autonomic and cardiovascular modulation.

High Glucose Up-regulates ADAM17 through HIF-1α in Mesangial Cells

We previously showed that ADAM17 mediates high glucose-induced matrix production by kidney mesangial cells. ADAM17 expression is increased in diabetic kidneys, suggesting that its up-regulation may augment high glucose profibrotic responses. We thus studied the effects of high glucose on ADAM17 gene regulation. Primary rat mesangial cells were treated with high glucose (30 mm) or mannitol as osmotic control. High glucose dose-dependently increased ADAM17 promoter activity, transcript, and protein levels. This correlated with augmented ADAM17 activity after 24 h versus 1 h of high glucose. We tested involvement of transcription factors shown in other settings to regulate ADAM17 transcription. Promoter activation was not affected by NF-κB or Sp1 inhibitors, but was blocked by hypoxia-inducible factor-1α (HIF-1α) inhibition or down-regulation. This also prevented ADAM17 transcript and protein increases. HIF-1α activation by high glucose was shown by its increased nuclear translocation and activation of the HIF-responsive hypoxia-response element (HRE)-luciferase reporter construct. Assessment of ADAM17 promoter deletion constructs coupled with mutation analysis and ChIP studies identified HIF-1α binding to its consensus element at -607 as critical for the high glucose response. Finally, inhibitors of epidermal growth factor receptor (EGFR) and downstream PI3K/Akt, or ADAM17 itself, prevented high glucose-induced HIF-1α activation and ADAM17 up-regulation. Thus, high glucose induces ADAM17 transcriptional up-regulation in mesangial cells, which is associated with augmentation of its activity. This is mediated by HIF-1α and requires EGFR/ADAM17 signaling, demonstrating the potentiation by ADAM17 of its own up-regulation. ADAM17 inhibition thus provides a potential novel therapeutic strategy for the treatment of diabetic nephropathy.

Increased neuronal survival in the brainstem during liver injury: role of γ-aminobutyric acid and serotonin chitosan nanoparticles

γ-Aminobutyric acid (GABA)- and serotonin (5-HT)-mediated cell signaling, neuronal survival enhancement, and reduced neuronal death in brainstem during liver injury followed by active liver regeneration have a critical role in maintaining routine bodily functions. In the present study, GABAB and 5-HT2A receptor functional regulation, interrelated actions of neuronal survival factors, and expression of apoptotic factors in the brainstem during GABA and 5-HT chitosan nanoparticles-induced active liver regeneration in partially hepatectomized rats were evaluated. Partially hepatectomized rats were treated with the nanoparticles, and receptor assays and confocal microscopic studies of GABAB and 5-HT2A receptors, gene expression studies of GABAB and 5-HT2A receptors, nuclear factor-κB (NF-κB), tumor necrosis factor-α (TNF-α), Akt-1, phospholipase C, Bax, and caspase-8 were performed with the brainstems of experimental animals. A significant decrease in GABAB and 5-HT2A receptor numbers and gene expressions denoted a homeostatic adjustment by the brain to trigger the sympathetic innervations during elevated DNA synthesis in the liver. The neuronal apoptosis resulting from the loss of liver function after partial hepatectomy was minimized by nanoparticle treatment in rats compared with rats with no treatment during regeneration. This was confirmed from the gene expression patterns of NF-κB, TNF-α, Akt-1, phospholipase C, Bax, and caspase-8. The present study revealed the potential of GABA and 5-HT chitosan nanoparticles for increasing neuronal survival in the brainstem during liver injury following regeneration, which avoids many neuropsychiatric problems.

In vitro evidence of dysregulation of blood-brain barrier function after acute and repeated/long-term exposure to TiO(2) nanoparticles

The effects of titanium dioxide nanoparticles (TiO(2) NPs) on blood-brain barrier (BBB) function are unknown. Here, we report such evidence of adverse effects after in vitro exposure of a rat primary cell-based BBB model to NPs. BBB integrity was studied by measuring the flux of sucrose through the monolayer. P-glycoprotein (P-gp) activity was assessed by measuring the passage of vinblastine. Transcription profiles of P-gp and other ABC transporters as well as of cytokines were investigated by real-time PCR. Electron microscopy and particle-induced X-ray emission measurements were performed. We compared several exposure modalities, from early to chronic, mimicking a brain-to-blood transport or a systemic contamination. In the first case, BBB integrity was preserved, but P-gp activity of endothelial cells (BECs) was reduced. In the second case, BBB integrity and P-gp function were impaired from 5 μg/mL for 24 h and expression of tight junction proteins and efflux transporters was modulated. An inflammatory response had repercussions on ABC transporter expression of glial cells. We demonstrate that NPs accumulated in BECs and crossed the cell monolayer. These findings suggest that there is an immunoregulatory loop between inflammatory components, BECs and glial cells in the dysfunction of the BBB during exposure to TiO(2) NPs.

ADAM-17: the enzyme that does it all

This review focuses on the role of ADAM-17 in disease. Since its debut as the tumor necrosis factor converting enzyme (TACE), ADAM-17 has been reported to be an indispensible regulator of almost every cellular event from proliferation to migration. The central role of ADAM-17 in cell regulation is rooted in its diverse array of substrates: cytokines, growth factors, and their receptors as well as adhesion molecules are activated or inactivated by their cleavage with ADAM-17. It is therefore not surprising that ADAM-17 is implicated in numerous human diseases including cancer, heart disease, diabetes, rheumatoid arthritis, kidney fibrosis, Alzheimer's disease, and is a promising target for future treatments. The specific role of ADAM-17 in the pathophysiology of these diseases is very complex and depends on the cellular context. To exploit the therapeutic potential of ADAM-17, it is important to understand how its activity is regulated and how specific organs and cells can be targeted to inactivate or activate the enzyme.

Normobaric hyperoxia induces ischemic tolerance and upregulation of glutamate transporters in the rat brain and serum TNF-alpha level

Recent studies suggest that intermittent and prolonged normobaric hyperoxia (HO) results in ischemic tolerance to reduce ischemic brain injury. In this research, we attempted to see changes in excitatory amino acid transporters (EAATs) and TNF-alpha levels following prolonged and intermittent hyperoxia preconditioning. Rats were divided into four experimental groups, each of 21 animals. The first two were exposed to 95% inspired HO for 4 h/day for 6 consecutive days (intermittent HO, InHO) or for 24 continuous hours (prolonged HO, PrHO). The second two groups acted as controls, and were exposed to 21% oxygen in the same chamber. Each main group was subdivided to middle cerebral artery occlusion (MCAO-operated), sham-operated (without MCAO), and intact (without any surgery) subgroups. After 24 h from pretreatment, MCAO-operated subgroups were subjected to 60 min of right MCAO. After 24 h reperfusion, neurologic deficit score (NDS) and infarct volume were measured in MCAO-operated subgroups. EAATs expression and serum TNF-alpha levels were assessed in sham-operated and intact subgroups. Preconditioning with prolonged and intermittent HO decreased NDS and upregulated EAAT1, EAAT2, and EAAT3 and increased serum TNF-alpha levels significantly. Although further studies are needed to clarify the mechanisms of ischemic tolerance, the intermittent and prolonged HO seems to partly exert their effects via increase serum TNF-alpha levels and upregulation of EAATs.

Tumor necrosis factor-alpha converting enzyme in the human placenta throughout gestation

Ectodomain shedding of epidermal growth factor receptor ligands such as transforming growth factor- alpha (TGF-alpha), heparin-binding epidermal growth factor-like growth factor (HBEGF), and amphiregulin (AREG) is considered to be important during implantation. Tumor necrosis factor-alpha converting enzyme (TACE) has been suggested as the major sheddase for these molecules. The objectives of this study are (1) to characterize the expression of TACE in the human placenta throughout gestation; (2) to determine the association between the expression of TACE with TGF-alpha, HBEGF, and AREG; (3) to ascertain whether TACE mediates TGF-alpha, HBEGF, and AREG shedding; and (4) to examine the effect of hypoxia on the expression of TACE. By analyzing a total of 55 villous samples representing different gestational ages, the authors found that TACE was continuously expressed in the placentas throughout gestation and that the levels of TACE were positively correlated with the levels of TGF-alpha, HBEGF, and AREG. Preadministration of a TACE inhibitor in villous explant cultures or transfection of cytotrophoblastic cells with TACE-specific small interference RNA decreased the shedding of HBEGF and AREG. Moreover, hypoxia (2% O(2)) caused an increase in the levels of TACE mRNA and protein in villous explants and primary cytotrophoblastic cells in vitro. These results indicate that oxygen regulates the expression of TACE and that TACE may be important for placental development during human pregnancy.

Leukocyte cell surface proteinases: regulation of expression, functions, and mechanisms of surface localization

A number of proteinases are expressed on the surface of leukocytes including members of the serine, metallo-, and cysteine proteinase superfamilies. Some proteinases are anchored to the plasma membrane of leukocytes by a transmembrane domain or a glycosyl phosphatidyl inositol (GPI) anchor. Other proteinases bind with high affinity to classical receptors, or with lower affinity to integrins, proteoglycans, or other leukocyte surface molecules. Leukocyte surface levels of proteinases are regulated by: (1) cytokines, chemokines, bacterial products, and growth factors which stimulate synthesis and/or release of proteinases by cells; (2) the availability of surface binding sites for proteinases; and/or (3) internalization or shedding of surface-bound proteinases. The binding of proteinases to leukocyte surfaces serves many functions including: (1) concentrating the activity of proteinases to the immediate pericellular environment; (2) facilitating pro-enzyme activation; (3) increasing proteinase stability and retention in the extracellular space; (4) regulating leukocyte function by proteinases signaling through cell surface binding sites or other surface proteins; and (5) protecting proteinases from inhibition by extracellular proteinase inhibitors. There is strong evidence that membrane-associated proteinases on leukocytes play critical roles in wound healing, inflammation, extracellular matrix remodeling, fibrinolysis, and coagulation. This review will outline the biology of membrane-associated proteinases expressed by leukocytes and their roles in physiologic and pathologic processes.

Effects of PKF242-484 and PKF241-466, novel dual inhibitors of TNF-alpha converting enzyme and matrix metalloproteinases, in a model of intestinal reperfusion injury in mice

Tumor necrosis factor (TNF)-alpha plays an important role in the mediation of reperfusion-induced tissue injury and lethality. Here, we assessed the effects of PKF242-484 and PKF241-466, two dual inhibitors of TNF-alpha converting enzyme (TACE) and matrix metalloproteinases (MMPs), in a model of ischemia and reperfusion injury in mice. Reperfused animals that received PKF242-484 or PKF241-466 treatment had a dose-dependent reduction of TNF-alpha concentrations in serum. Both drugs delayed and partially inhibited the reperfusion-associated lethality. Maximal inhibition occurred at 10 mg/kg. At this dose, both inhibitors reduced reperfusion-associated local and remote tissue injury, as assessed by changes in vascular permeability, neutrophil recruitment and hemorrhage. In addition, the compounds markedly reduced production of TNF-alpha, CXCL1 (keratinocyte-derived chemokine, KC) and CCL2 (monocyte chemoattractant protein-1, MCP-1) in intestine and lungs of animals which underwent reperfusion. FN-439, an inhibitor of MMPs which possesses no effect on TACE, decreased MMP-2 and MMP-3 activity, but failed to affect tissue injury, TNF-alpha production or lethality. Thus, combined TACE and MMP inhibitors might be effective co-adjuvants in treatments of injuries that follow reperfusion of an ischemic vascular territory. The effects of these drugs on TNF-alpha production appear to be more relevant than their effects on MMP inhibition.

Human colonic myocytes are involved in postischemic inflammation through ADAM17-dependent TNFalpha production

The aim of this study was to identify human colonic resident cells able to initiate an inflammatory response in postischemic injury. Postischemic colonic injury, a condition relevant to various clinical settings, involves an inflammatory cascade in intestinal tissues through the recruitment of circulating inflammatory cells. However, there is no information on the nature of resident cells of the different intestinal layers able to initiate a postischemic inflammatory response. It is however an important issue in the context of a pharmacological approach of the early phase of intestinal ischemia. We reasoned that maintaining the different colonic layers as explant cultures in an oxygenated medium immediately after colonic resection, that is, after an ischemic period, would allow one to identify the resident cells able to initiate an inflammatory cascade, without interference of recruited inflammatory/immune cells. To this end, we designed an explant culture system that operationally defines three compartments in surgical specimens of the human colon, based on the microdissected layers, that is, mucosa, submucosa (containing muscularis mucosae) and muscularis propria. To validate the results obtained in explant cultures in the clinical setting of ischemic colitis, eight cases of sigmoid volvulus were examined. Only the myocytes-containing explants produced tumor necrosis factor alpha (TNFalpha), via an ADAM17 (a disintegrin and metalloproteinase-17)-dependent pathway, as shown by the abrogation of TNFalpha production by the inhibitor Tapi-2. Immunofluorescence studies identified nonvascular and vascular myocytes as resident cells coexpressing TNFalpha and ADAM17, both in our postischemic explant system and in surgical specimens from ischemic colitis patients. Finally, time-course experiments on explanted tissues showed that TNFalpha production by myocytes was an early event triggered by a postischemic oxidative stress involving nuclear factor kappa B (NF-kappaB). In conclusion, this study identifies human intestinal myocytes as resident cells able to initiate an inflammatory reaction through TNFalpha production in postischemic conditions, and delineates two points of control in TNFalpha production, NF-kappaB and ADAM17, which can be targeted by pharmacological manipulation.

TIMP-3 Ameliorates Hepatic Ischemia/Reperfusion Injury Through Inhibition of Tumor Necrosis Factor-Alpha-Converting Enzyme Activity in Rats

BACKGROUND

Tumor necrosis factor (TNF)-alpha and its receptors play a critical role in the inflammatory cascade after hepatic ischemia/reperfusion injury. TNF-alpha converting enzyme (TACE) or disintegrin and metalloproteinase (ADAM)-17 is a metalloproteinase disintegrin that specifically cleaves precursor TNF-alpha to its mature form and is involved in the ectodomain shedding of TNF receptors. The regulation of TACE is poorly understood and its role in liver injury and/or regeneration is unknown.

METHODS

Male Wistar rats were subjected to 10 or 30 min of partial warm hepatic ischemia followed by 3 to 24 hr of reperfusion. Serum and/or hepatic TACE, TNF-alpha, TNF receptor 1 (TNFR1), and interleukin (IL)-6 levels were assessed by enzyme-linked immunosorbent assay, real-time reverse-transcriptase polymerase chain reaction, and/or Western blot.

RESULTS

Low levels of TACE were detected in normal liver tissue. Both 10 and 30 min warm ischemia resulted in a rise in TACE expression which peaked six hr after reperfusion. TNF-alpha, TNFR1, and IL-6 levels were up-regulated in a pattern similar to TACE messenger RNA (mRNA) levels. Moreover, selective inhibition of TACE activity by specific inhibitor tissue inhibitor of metalloproteinase (TIMP)-3 at dosages of 100 or 1000 ng/kg body weight showed significant decrease of circulating TNF-alpha and serum alanine transferase (ALT) levels and histological improvement of hepatic ischemia/reperfusion injuries.

CONCLUSIONS

TACE expression and its activity, as measured by increases in TNF-alpha, TNFR1, and IL-6 levels, are increased following hepatic ischemia/reperfusion injury, implying that TACE plays an important role in hepatic ischemia/reperfusion injury. Amelioration of hepatic ischemia/reperfusion injury after inhibition of TACE activity by TIMP-3 suggests that TACE inhibition may play an important role in preventing liver ischemia/reperfusion injury warranting further experimental and clinical study.

Upregulation of ADAM-17 expression in active lesions in multiple sclerosis

ADAM-17, a disintegrin and metalloproteinase, is the major proteinase responsible for the cleavage of membrane-bound tumour necrosis factor (TNF) as well as being an active sheddase of other cytokines, cytokine receptors, growth factors and adhesion molecules. TNF is a major proinflammatory cytokine that has been identified as having a pathogenic role in inflammatory diseases within the CNS including multiple sclerosis (MS). Here we report the cellular origin and distribution of ADAM-17 expression within clinically and neuropathologically confirmed MS and normal control white matter, assessed by immunohistochemistry, western blotting and PCR. ADAM-17 expression was associated with the blood vessel endothelium, activated macrophages/microglia and parenchymal astrocytes in MS white matter. Increased levels of ADAM-17 immunoreactivity were displayed in active lesions with evidence of recent myelin breakdown. Further studies into the functional role of ADAM-17 in the pathogenesis of MS and other inflammatory conditions are required.

Effects of anoxia and hypoxia on amyloid precursor protein processing in cerebral microvascular smooth muscle cells

Cerebral amyloid angiopathy (CAA) is characterized by the degeneration of cerebral microvascular smooth muscle cells (MV-SMC) and the replacement of normal vessel wall components by beta-amyloid (Abeta) protein. Little is known regarding the mechanisms of SMC degeneration in CAA. The effects of anoxia on the metabolism of the amyloid precursor protein (APP) were studied to investigate the MV-SMC response to anoxic stress and its possible role in the pathogenesis of CAA. MV-SMC exposed to chronic anoxia (24-48 hours) showed a decrease in expression of the 2 putative alpha-secretase enzymes, mature TACE (TNFalpha-converting enzyme) and ADAM10 (a disintegrin and metalloprotease). A concomitant decrease in the alpha-secretase cleavage products sAPPalpha and C83 was observed. Investigation of mRNA expression showed an increase in TACE and a sharp decrease in ADAM10 at 24 hours. Exposing MV-SMC to hypoxia (1% O2) revealed a different pattern of expression with no significant change in TACE protein, but an increase in TACE mRNA occurring at a later time point (48 hours). There was no change in ADAM10 mRNA expression, but a reduction in mature ADAM10 with a parallel increase in immature ADAM10 protein. These results demonstrate a requirement for oxygen in the regulation of the alpha-secretase pathway during APP metabolism.

Characterization of the neuroprotective effect of the cannabinoid agonist WIN-55212 in an in vitro model of hypoxic-ischemic brain damage in newborn rats

Brain slices from 7-d-old Wistar rats were exposed to oxygen-glucose deprivation (OGD) for 30 min. OGD slices were incubated with vehicle or with the CB1/CB2 cannabinoid agonist WIN55212 (50 microM), the CB1 agonist arachidonyl-2-chloroethylamide (ACEA) (50 microM), or the CB2 agonist JW133 (50 microM), alone or combined with the CB1 and CB2 receptor antagonist SR 141716 (50 microM) or SR 144528 (50 microM), respectively. Neuronal damage was assessed by histologic analysis and spectrophotometric determination of lactate dehydrogenase (LDH) efflux into the incubation medium. Additionally, medium glutamate levels were determined by high-performance liquid chromatography (HPLC) and those of tumor necrosis factor alpha (TNF-alpha) by enzyme-linked immunosorbent assay. Finally, inducible nitric oxide synthase (iNOS) and CB1/CB2 receptor expression were determined in slices homogenate by Western blot. Both CB1 and CB2 receptors were expressed in slices. OGD increased CB1 expression, cellular damage, LDH efflux, glutamate and TNF-alpha release, and inducible nitric oxide synthase (iNOS) expression; WIN55212 inhibited all these actions. SR141716 and SR144528 inhibited the effect of R(+)-WIN-55212-2 (WIN), as well as the reduction of LDH efflux by ACEA and JW133, respectively. In conclusion, WIN55212 afforded robust neuroprotection in the forebrain slices exposed to OGD, by acting on glutamatergic excitotoxicity, TNF-alpha release, and iNOS expression; this neuroprotective effect seemed to be mediated by CB1 and CB2 receptors.

The role of tumor necrosis factor-alpha in stress-induced worsening of cerebral ischemia in rats

Whereas stress is known to be one of the risk factors of stroke, few experimental studies have examined the possible mechanisms by which stress may affect stroke outcome. Most of the knowledge on the effects of stress on cerebrovascular disease in humans is restricted to catecholamines and glucocorticoids effects on blood pressure and/or development of atherosclerosis. By using an experimental paradigm consisting of the exposure of Fischer rats to repeated immobilization sessions (1 h daily during seven consecutive days) prior to permanent middle cerebral artery occlusion (MCAO), we have found that stress worsens behavioral outcome and increases infarct size after MCAO. These changes occur concomitantly to an increase in inducible nitric oxide synthase (iNOS) expression and to the accumulation of lipid peroxidation markers in brain tissue. The possible regulatory role of TNFalpha was studied by looking at the mechanisms of release of this cytokine as well as to the expression of its receptors (TNFR1 and 2). The results of the present study suggest an increase in TNFalpha expression and release after stress, as well as an increase in the expression of TNFR1. Pharmacological blockade of TNFalpha with anti-TNFalpha led to a decrease in the infarct size as well as in the oxidative/nitrosative biochemical parameters seen after ischemia. In summary, our results indicate that TNFalpha accounts, at least partly, for the worsening of MCAO consequences in brain of rats exposed to stress. Furthermore, the data presented here provide evidence that stress can increase brain ischemic damage and support a possible protective effect of treatment of stressful situations before and during the development of the brain ischemia.

Effect of ischemic neuronal insults on amyloid precursor protein processing

The nature of the association between ischemic stroke and Alzheimer's disease (AD) at the cellular and molecular level is still unknown. We evaluated the effect of ischemic neuronal insults on the regulation of amyloid precursor protein (APP) processing. We used an in vitro model of cerebral ischemia (oxygen-glucose deprivation) to evaluate the effect of ischemic neuronal insults on the amyloidogenic and non-amyloidogenic pathways using human neuroblastoma cell line and primary cultured cells of transgenic mice which expressed human APP (Tg2576). Ischemic neuronal insults increased the production of Abeta in Tg2576 primary culture cells compared to controls. A disintegrin and metalloprotease 10 (ADAM 10) was markedly increased in early stage of ischemic insults, which was followed by decreased level of ADAM 10 expression in later stage. The protein and mRNA expression of beta-site cleavage enzyme (BACE) and BACE activity was not significantly different between the group of ischemic insults and control. By contrast, the activity of gamma-secretase was significantly increased after 4 h of ischemic insults, as compared to controls. The present study showed that the ischemic neuronal insults increased the production of Abeta by influencing APP metabolism, which may link the role of ischemic insults to the pathogenesis of AD.

Chronic hypoxia in the human neuroblastoma SH-SY5Y causes reduced expression of the putative alpha-secretases, ADAM10 and TACE, without altering their mRNA levels

Alzheimer's disease is more frequent following an ischemic or hypoxic episode, with levels of beta-amyloid peptides elevated in brains from patients. Similar increases are found after experimental ischemia in animals. It is possible that increased beta-amyloid deposition arises from alterations in amyloid precursor protein (APP) metabolism, indeed, we have shown that exposing cells of neuronal origin to chronic hypoxia decreased the secretion of soluble APP (sAPPalpha) derived by action of alpha-secretase on APP, coinciding with a decrease in protein levels of ADAM10, a disintegrin metalloprotease which is thought to be the major alpha-secretase. In the current study, we extended those observations to determine whether the expression of ADAM10 and another putative alpha-secretase, TACE, as well as the beta-secretase, BACE1 were regulated by chronic hypoxia at the level of protein and mRNA. Using Western blotting and RT-PCR, we demonstrate that after 48 h chronic hypoxia, such that sAPPalpha secretion is decreased by over 50%, protein levels of ADAM10 and TACE and by approximately 60% and 40% respectively with no significant decrease in BACE1 levels. In contrast, no change in the expression of the mRNA for these proteins could be detected. Thus, we conclude that under CH the level of the putative alpha-secretases, ADAM10 and TACE are regulated by post-translational mechanisms, most probably proteolysis, rather than at the level of transcription.

Ischemic preconditioning: a novel target for neuroprotective therapy

Ischemic preconditioning involves a brief exposure to ischemia in order to develop a tolerance to injurious effects of prolonged ischemia. The molecular mechanisms of neuroprotection that lead to ischemic tolerance are not yet completely understood. However, it seems that two distinct phases are involved. Firstly, a cellular defense function against ischemia may be developed by the mechanisms inherent to neurons such as posttranslational modification of proteins or expression of new proteins via a signal transduction system to the nucleus. Secondly, a stress response and synthesis of stress proteins (heat shock proteins) may be activated. These mechanisms are mediated by chaperones. The objective of ischemic preconditioning research is to identify the underlying endogenous protective cellular receptors and signaling cascades, with the long-term goal of allowing therapeutic augmentation of the endogenous protective mechanisms in cerebral ischemia and possibly development of new neuroprotective strategies for ischemic stroke treatment.

L1 is sequentially processed by two differently activated metalloproteases and presenilin/gamma-secretase and regulates neural cell adhesion, cell migration, and neurite outgrowth

The immunoglobulin superfamily recognition molecule L1 plays important functional roles in the developing and adult nervous system. Metalloprotease-mediated cleavage of this adhesion molecule has been shown to stimulate cellular migration and neurite outgrowth. We demonstrate here that L1 cleavage is mediated by two distinct members of the disintegrin and metalloprotease family, ADAM10 and ADAM17. This cleavage is differently regulated and leads to the generation of a membrane bound C-terminal fragment, which is further processed through gamma-secretase activity. Pharmacological approaches with two hydroxamate-based inhibitors with different preferences in blocking ADAM10 and ADAM17, as well as loss of function and gain of function studies in murine embryonic fibroblasts, showed that constitutive shedding of L1 is mediated by ADAM10 while phorbol ester stimulation or cholesterol depletion led to ADAM17-mediated L1 cleavage. In contrast, N-methyl-d-aspartate treatment of primary neurons stimulated ADAM10-mediated L1 shedding. Both proteases were able to affect L1-mediated adhesion and haptotactic migration of neuronal cells. In particular, both proteases were involved in L1-dependent neurite outgrowth of cerebellar neurons. Thus, our data identify ADAM10 and ADAM17 as differentially regulated L1 membrane sheddases, both critically affecting the physiological functions of this adhesion protein.

Up-regulated expression of ADAM17 in human colon carcinoma: co-expression with EGFR in neoplastic and endothelial cells

The ADAM17 metalloproteinase (a disintegrin and metalloprotease 17) controls epidermal growth factor receptor (EGFR) activation through regulated shedding of EGFR ligands. With the advent of new therapeutic options targeting EGFR signalling in colon carcinoma, it was decided to determine ADAM17 status in relation to clinico-pathological parameters and EGFR status. To this end, a series of 39 colon carcinomas were analysed. Immunohistochemistry and immunofluorescence were used to localize ADAM17, EGFR, and the activated forms of EGFR. The activated form of ADAM17 was assessed in primary cancers and colon cell lines by immunoblotting. ADAM17 and EGFR mRNA levels were assessed by quantitative RT-PCR. Chromogenic in situ hybridization (CISH) was used to quantify the HER1 gene. ADAM17 was strongly expressed in all tumours, by both neoplastic and endothelial cells. It was expressed both as a pro- and as an active form in tumours and colonic cancer cell lines. ADAM17 mRNA was up-regulated in 90% of colon carcinomas relative to the paired normal mucosa, whatever the tumour grade or stage. When present, activated EGFR was co-expressed with ADAM17 by colon carcinomas, although at a variable level among tumour cells, and by endothelial cells. EGFR mRNA was overexpressed in 77% of colon carcinomas compared with the paired normal mucosa. One case showed high-level amplification of HER1. In conclusion, this study is the first demonstration that ADAM17 is overexpressed in human primary colon carcinoma, whatever the tumour stage and differentiation and whatever the level of EGFR expression. Its co-expression with EGFR, in both neoplastic and endothelial cells, suggests a role for ADAM17 in tumour growth and angiogenesis.

Protein kinase C-alpha mediates TNF release process in RBL-2H3 mast cells

1 To clarify the mechanism of mast cell TNF secretion, especially its release process after being produced, we utilized an antiallergic drug, azelastine (4-(p-chlorobenzyl)-2-(hexahydro-1-methyl-1H-azepin-4-yl)-1-(2H)- phthalazinone), which has been reported to inhibit TNF release without affecting its production in ionomycin-stimulated RBL-2H3 cells. 2 Such inhibition was associated with the suppression of an ionomycin-induced increase in membrane-associated PKC activity rather than the suppression of Ca2+ influx, suggesting that PKC might be involved in TNF release process. 3 To see whether conventional PKC family (cPKCs) are involved, we investigated the effects of a selective cPKC inhibitor (Gö6976) and an activator (thymeleatoxin) on TNF release by adding them 1 h after cell stimulation. By this time, TNF mRNA expression had reached its maximum. Gö6976 markedly inhibited TNF release, whereas thymeleatoxin enhanced it, showing a key role of cPKC in TNF post-transcriptional process, possibly its releasing step. 4 To determine which subtype of cPKCs could be affected by azelastine, Western blotting and live imaging by confocal microscopy were conducted to detect the translocation of endogenous cPKC (alpha, betaI and betaII) and transfected GFP-tagged cPKC, respectively. Both methods clearly demonstrated that 1 microM azelastine selectively inhibits ionomycin-triggered translocation of (alpha)PKC without acting on betaI or betaIIPKC. 5 In antigen-stimulated cells, such a low concentration of azelastine did not affect either (alpha)PKC translocation or TNF release, suggesting a functional link between (alpha)PKC and the TNF-releasing step. 6 These results suggest that (alpha)PKC mediates the TNF release process and azelastine inhibits TNF release by selectively interfering with the recruitment of (alpha)PKC in the pathway activated by ionomycin in RBL-2H3 cells.

Immature rat brain slices exposed to oxygen-glucose deprivation as an in vitro model of neonatal hypoxic-ischemic encephalopathy

To analyze whether exposure to oxygen-glucose deprivation (OGD) of immature rat brain slices might reproduce the main pathophysiologic events leading to neuronal death in neonatal hypoxic-ischemic encephalopathy (NHIE), 500 microm-thick brain slices were obtained from 7-day-old Wistar rats, and incubated in oxygenated physiological solution. In OGD group, oxygen and glucose were removed from the medium for 10-30 min (n = 25); then, slices were re-incubated in normal medium. In control group the medium composition remained unchanged (CG, n = 30). Medium samples were obtained every 30 min for 3 h. To analyze neuronal damage, slices were stained with Nissl and CA1 area of hippocampus and cortex were observed under microscopy. In addition, neuronal death was quantified as LDH released to the medium determined by spectrophotometry. Additionally, medium glutamate (Glu) levels were determined by HPLC and those of TNFalpha by ELISA, whereas inducible nitric oxide synthase expression was determined by Western blot performed on slices homogenate. Optimal OGD time was established in 20 min. After OGD, a significant decrease in the number of neurones in hippocampus and cortex was observed. LDH release was maximal at 30 min, when it was five-fold greater than in CG. Furthermore, medium Glu concentrations were 200 times greater than CG levels at the end of OGD period. A linear relationship between Glu and LDH release was demonstrated. Finally, 3 h after OGD a significant induction of iNOS as well as an increase in TNFalpha release were observed. In conclusion, OGD appears as a feasible and reproducible in vitro model, leading to a neuronal damage, which is physiopathologically similar to that found in NHIE.

The anti-inflammatory prostaglandin 15d-PGJ2 decreases oxidative/nitrosative mediators in brain after acute stress in rats

RATIONALE

Immobilisation stress is followed by accumulation of oxidative/nitrosative mediators in brain after the release of tumour necrosis factor-alpha (TNFalpha) and other cytokines, nuclear factor kappa B (NFkappaB) activation, nitric oxide synthase-2 (NOS-2) and cyclooxygenase-2 (COX-2) expression in the brain.

OBJECTIVES

This study was conducted to assess if some of the anti-inflammatory products of COX can modify the accumulation of oxidative/nitrosative species seen in brain after stress and to study the mechanisms by which this effect is achieved.

METHODS

Young-adult male Wistar rats were subjected to a single session of immobilisation during 6 h.

RESULTS

In stressed animals, brain levels of the anti-inflammatory 15d-PGJ2 increases concomitantly with COX-2 expression. Inhibition of COX-2 with NS-398 prevents stress-induced 15d-PGJ2 increase. Injection of supraphysiological doses of 15d-PGJ2 (80-120 microg/kg) decreases stress-induced increase in NOS-2 activity as well as the stress-induced increase in NO metabolites. On the other hand, 15d-PGJ2 decreases stress-induced malondialdehyde (an indicator of lipid peroxidation) accumulation in cortex and prevents oxidation of the main anti-oxidant glutathione. The mechanisms involved in the anti-oxidative properties of 15d-PGJ2 in stress involve NFkappaB blockade (by preventing stress-induced IkappaBalpha decrease) as well as inhibition of TNFalpha release in stressed animals. At the doses tested, 15d-PGJ2 decreases COX-2 expression and PGE2 release during stress, suggesting an alternative mechanism for this endogenous compound.

CONCLUSIONS

These findings demonstrate a role for this anti-inflammatory pathway in the brain response to stress and open the possibility for preventing accumulation of oxidative/nitrosative species and subsequent brain damage.

Peroxisome proliferator-activated receptor gamma activation decreases neuroinflammation in brain after stress in rats

BACKGROUND

A growing body of evidence has demonstrated that peroxisome proliferator-activated receptor gamma (PPARgamma) play a role in brain inflammatory conditions because various PPARgamma ligands inhibit proinflammatory mediators, such as cytokines (tumor necrosis factor alpha [TNFalpha]) and inducible nitric oxide synthase (NOS-2). As has been previously shown, immobilization stress and stress-related neuropsychologic conditions are followed by accumulation of oxidative/nitrosative mediators in brain after the release of cytokines, nuclear factor kappaB activation, and NOS-2 and cyclooxygenase 2 (COX-2) expression in the brain.

METHODS

To assess whether PPARgamma activation can modify the accumulation of oxidative/nitrosative species seen in brain after stress, and to study the mechanisms by which this effect is achieved, young-adult male Wistar rats (control and immobilized during 6 hours) were injected (IP) with the high-affinity ligand rosiglitazone (RS) at the onset of stress.

RESULTS

Stress increased PPARgamma expression in cortical neurons and glia as assessed by Western blot and immunohistochemistry. In stressed animals, RS (1-3 mg/kg) decreased stress-induced increases in NOS-2 activity. On the other hand, the PPARgamma ligand decreased stress-induced malondialdehyde (an indicator of lipid peroxidation) accumulation in cortex and prevented oxidation of the main antioxidant glutathione. The mechanisms involved in the antioxidative properties of RS in stress involve nuclear factor KB blockade (by preventing stress-induced IkappaBalpha decrease) and inhibition of TNFalpha release in stressed animals. At the doses tested, RS did not decrease COX-2 expression and prostaglandin E2 release during stress. Finally, RS also decreased chronic (repeated immobilization for 21 days) stress-induced accumulation of oxidative/nitrosative mediators.

CONCLUSIONS

Taken together, these findings suggest a role for this antiinflammatory pathway in the brain response to stress and the possibility of pharmacologic modulation for preventing accumulation of oxidative/nitrosative species and subsequent brain damage in stress-related neuropsychologic conditions.

TNFR1 upregulation mediates tolerance after brain ischemic preconditioning

A short ischemic event (ischemic preconditioning (IPC)) can result in subsequent resistance to severe ischemic injury (ischemic tolerance (IT)). The expression and neuroprotective role of tumor necrosis factor (TNF-alpha) have been described in models of IPC and we have showed the participation of its processing enzyme, the TNF-alpha convertase enzyme (TACE) in this process. We have now decided to explore the expression and localization of TNF receptors (TNFR) as well as other signalling mechanisms involved in IT. A period of 10 mins of temporary middle cerebral artery occlusion (tMCAO) was used for focal IPC. To evaluate the ability of IPC to produce IT, permanent MCAO was performed 48 hours after IPC. Ischemic preconditioning produced a reduction in infarct volume, as we showed previously. Ischemic preconditioning caused upregulation of neuronal TNFR1 that was reduced by the selective TACE inhibitor BB1101. Intracerebral administration of TNFR1 antisense oligodeoxynucleotide, which caused a reduction in TNFR1 expression, inhibited the IPC-induced protective effect, showing that TNFR1 upregulation is implicated in IT. Moreover, treatment with BB1101, TNFR1 antisense and lactacystin-a specific proteasome inhibitor-blocked IPC-induced NF-kappaB. Immunohistochemical studies showed the expression of TACE and TNFR1 in neurons. In summary, these data show that IPC produces neuronal upregulation of TACE and TNFR1, and that the pathway TACE/TNF-alpha/TNFR1/NF-kappaB is involved in IT.

Developmental expression of metalloproteases ADAM 9, 10, and 17 becomes restricted to divergent pancreatic compartments

The A Disintegrin And Metalloprotease (ADAM) family of metalloproteases affects a variety of proteins with important roles in development and disease, including growth factors and adhesion molecules. We have analyzed the expression patterns of ADAMs 9, 10, and 17 during pancreas ontogeny. All ADAMs investigated were expressed in the pancreatic anlagen but invariably became restricted to divergent pancreatic compartments. ADAM9 and 17 became restricted to the insulin-producing beta-cells and all islet cells, respectively. During embryogenesis, ADAM10 was detected predominantly in acinar cells, but in the adult, it was localized to the cell surface membrane of both endocrine and exocrine cells. In addition to ADAM9, a potential prognostic factor for ductal cancers, we describe the expression of ADAM10 and ADAM17 in the pancreatic ductal epithelium. Altogether, the dynamic expression profile of the ADAM proteases described here may reflect a functional divergence of these as mediators of pancreas biology.

TNF-alpha accounts for short-term persistence of oxidative status in rat brain after two weeks of repeated stress

Inducible nitric oxide synthase (NOS-2) accounts for the accumulation of oxidative and nitrosative mediators in brain after stress. To determine whether and when repeated exposure to immobilization stress leads to persistent oxidative status in rat brain, male Wistar rats were immobilized for 6 h/day for 7 or 14 days (S7, S14). Cerebral cortices were obtained immediately after the last session of stress or 1 day later. Stress increased NOS-2 activity after S7 or S14. This enzymatic activity returned to basal values 1 day after S7, but not 1 day after S14. Stress increased malondialdehyde (MDA) accumulation in cortex after S7 and S14. MDA levels returned to basal values 1 day after S7 but not 1 day after S14. In order to elucidate the possible mechanisms involved in this short-term persistence of oxidative status, brain levels of the cytokine tumour necrosis factor alpha (TNF-alpha) were determined. TNF-alpha levels did not increase after S7 or 1 day after S7, but increased after S14 and 1 day after S14. This was paralleled by an increase in TNF-alpha converting enzyme (TACE) activity in brain. When the increase in TNF-alpha at S14 was blocked by BB1101, an inhibitor of TACE, or its effects were blocked with anti-TNF-alpha, the accumulation of MDA and NOS-2 activity 1 day after S14 did not take place. These findings indicate that TACE and TNF-alpha account for stress-induced short-term persistence of NOS-2 activity and MDA accumulation after 14 days of repeated exposure and support a possible neuroprotective role for specific blockers of TNF-alpha in this situation.

Role of nitric oxide after brain ischaemia

Ischaemic stroke is the second or third leading cause of death in developed countries. In the last two decades substantial research and efforts have been made to understand the biochemical mechanisms involved in brain damage and to develop new treatments. The evidence suggests that nitric oxide (NO) can exert both protective and deleterious effects depending on factors such as the NOS isoform and the cell type by which NO is produced or the temporal stage after the onset of the ischaemic brain injury. Immediately after brain ischaemia, NO release from eNOS is protective mainly by promoting vasodilation; however, after ischaemia develops, NO produced by overactivation of nNOS and, later, NO release by de novo expression of iNOS contribute to the brain damage. This review article summarizes experimental and clinical data supporting the dual role of NO in brain ischaemia and the mechanisms by which NO is regulated after brain ischaemia. We also review NO-based therapeutic strategies for stroke treatment, not only those directly linked with the NO pathway such as NO donors and NOS inhibitors but also those partially related like statins, aspirin or lubeluzole.

Oral administration of Crataegus flavonoids protects against ischemia/reperfusion brain damage in gerbils

Stroke is the third leading cause of death as dementia is a main symptom of Alzheimer's disease. One of the important mechanisms in the pathogeny of stroke is free radical production during the reperfusion period, therefore the effects of a type of natural antioxidant, i.e. Crataegus flavonoids (CF), on brain ischemic insults were investigated in Mongolian gerbil stroke model. Results showed that pretreatment of the animals with CF decreased reactive oxygen species (ROS) production, thiobarbituric acid reactive substances content, and nitrite/nitrate concentration in brain homogenate, increased the brain homogenate-associated antioxidant level in a dose-dependent manner. CF pretreatment increased the amount of biologically available NO by scavenging of superoxide anion produced during reperfusion. At same time, in the process of ischemia/reperfusion brain damage, the content of nitrite/nitrate (the end product of NO) increased, and of NO detected by ESR decreased. Oral pretreatment with CF decreased the nitrite/nitrate content in the brain homogenate and increased the biologically available NO concentration in a dose-dependent manner. The increasing effect of antioxidant on NO might be due to its scavenging effect on superoxide anion, which could react with NO into peroxynitrite. iNOS was implied in delayed neuron death after brain ischemic damage and it was found that pretreatment with CF could decrease the protein level of tumor necrosis factor (TNF)-alpha and nuclear factor-kappa B (NF-kappaB), and increase the mRNA level of NOS estimated by western blotting and RT-PCR. More neurons survived and fewer cells suffered apoptosis in the hippocampal CA1 region of CF treated animal brain. These results suggest that oral administration of this antioxidant increases the antioxidant level in the brain and protects the brain against delayed cell death caused by ischemia/reperfusion injury.

Neuroprotective efficacy and therapeutic time window of peroxynitrite decomposition catalysts in focal cerebral ischemia in rats

Free radicals have been implicated in cerebral ischemia reperfusion (IR) injury. Massive production of nitric oxide and superoxide results in continuous formation of peroxynitrite even several hours after IR insult. This can produce DNA strand nicks, hydroxylation and/or nitration of cytosolic components of neuron, leading to neuronal death. Peroxynitrite decomposition catalysts 5,10,15,20-tetrakis(N-methyl-4'-pyridyl)porphyrinato iron (III) (FeTMPyP) and 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinato iron (III) (FeTPPS) have been demonstrated to protect neurons in in vitro cultures; however, their neuroprotective efficacy in cerebral IR injury has not been explored. In the present study, we investigated the efficacy and the therapeutic time window of FeTMPyP and FeTPPS in focal cerebral ischemia (FCI). FCI was induced according to the middle cerebral artery occlusion (MCAO) method. After 2 h of MCAO and 70 h of reperfusion, the extent of neurological deficits, infarct and edema volume were measured in Sprague-Dawley rats. FeTMPyP and FeTPPS were administered at different time points 2, 6, 9 and 12 h post MCAO. FeTMPyP and FeTPPS (3 mg kg(-1), i.v.) treatment at 2 and 6 h post MCAO produced significant reduction in infarct volume, edema volume and neurological deficits. However, treatment at latter time points did not produce significant neuroprotection. Significant reduction of peroxynitrite in blood and nitrotyrosine in brain sections was observed on FeTMPyP and FeTPPS treatment. As delayed treatment of FeTMPyP and FeTPPS produced neuroprotection, we tested whether treatment had any influence over the apoptotic neuronal death. DNA fragmentation and in situ nick end-labeling assays showed that FeTMPyP and FeTPPS treatment reduced IR injury-induced DNA fragmentation. In conclusion, peroxynitrite decomposition catalysts (FeTMPyP and FeTPPS) produced prominent neuroprotection even if administered 6 h post MCAO and the neuroprotective effect is at least in part due to the reduction of peroxynitrite and apoptosis.

Tumour necrosis factor-α stimulates expression of TNF-α converting enzyme in endothelial cells

Tumor necrosis factor-alpha converting enzyme (ADAM17) is a major metalloproteinase involved in the shedding of several membrane-bound cytokines and cytokine receptors. Interplay of cytokines and their soluble receptors might be an important regulatory element in the network of interactions responsible for maintaining homeostasis in the immune system. ADAM17 thus has the potential to participate in a broad range of immune reactions. We studied the mechanisms of ADAM17 activation in endothelial cells and found that pro-inflammatory cytokines (tumor necrosis factor-alpha, interleukin-1beta, interferon-gamma) and growth factors (epidermal growth factor, vascular endothelial growth factor) are able to upregulate transcription of ADAM17 and expression of ADAM17 protein. This process might constitute an important mechanism of regulation of ADAM17 activity. Stimulation of transcription, rather than increased ADAM17 mRNA stability, was responsible for increased levels of ADAM17 mRNA. Importantly, the increase in ADAM17 was accompanied by increased shedding of TNF-Receptor I (p55) in tumor necrosis factor-alpha-stimulated endothelial cells. Therefore, ADAM17-dependent depletion of membrane-bound tumor necrosis factor receptors from endothelial cells might constitute a mechanism of self-protection in states of prolonged immunostimulation.

In vitro ischemic tolerance involves upregulation of glutamate transport partly mediated by the TACE/ADAM17-tumor necrosis factor-alpha pathway

A short ischemic event [ischemic preconditioning (IPC)] can result in a subsequent resistance to severe ischemic injury (ischemic tolerance). Although tumor necrosis factor-alpha (TNF-alpha) contributes to the brain damage found after cerebral ischemia, its expression and neuroprotective role in models of IPC have also been described. Regarding the role of TNF-alpha convertase (TACE/ADAM17), we have recently shown its upregulation in rat brain after IPC induced by transient middle cerebral artery occlusion and that subsequent TNF-alpha release accounts for at least part of the neuroprotection found in this model. We have now used an in vitro model of IPC using rat cortical cultures exposed to sublethal oxygen-glucose deprivation (OGD) to investigate TACE expression and activity after IPC and the subsequent mechanisms of ischemic tolerance. OGD-induced cell death was significantly reduced in cells exposed to IPC by sublethal OGD 24 hr before, an effect that was inhibited by the TACE inhibitor BB3103 (1 microm) and anti-TNF-alpha antibody (2 microg/ml) and that was mimicked by TNF-alpha (10 pg/ml) preincubation. Western blot analysis showed that TACE expression is increased after IPC. IPC caused TNF-alpha release, an effect that was blocked by the selective TACE inhibitor BB-3103. In addition, IPC diminished the increase in extracellular glutamate caused by OGD and increased cellular glutamate uptake and expression of EAAT2 and EAAT3 glutamate transporters; however, only EAAT3 upregulation was mediated by increased TNF-alpha. These data demonstrate that neuroprotection induced by IPC involves upregulation of glutamate uptake partly mediated by TACE overexpression.

Inhibition of tumor necrosis factor-alpha-converting enzyme by a selective antagonist protects brain from focal ischemic injury in rats

Tumor necrosis factor alpha (TNFalpha) is an immunomodulatory and proinflammatory cytokine implicated in neuroinflammation and neuronal damage in response to cerebral ischemia. Tumor necrosis factor-alpha converting enzyme (TACE or ADAM17) is a key sheddase that releases TNFalpha from its inactive cell-bound precursor. Using a selective small molecule inhibitor of TACE, DPH-067517, we tested the hypothesis that inhibition of TNFalpha formation might have a salutary effect in ischemic stroke induced by embolic occlusion of the middle cerebral artery (MCAO). DPH-067517 selectively inhibited TACE enzyme activity in vitro (K(i) = 2.8 nM), and effectively suppressed ischemia-induced increase in soluble TNFalpha in brain tissue after systemic administration. DPH-067517 (3 and 30 mg/kg, i.p. administered 15 min before MCAO) produced 43% (n = 8, p = 0.16) and 58% (n = 8, p < 0.05) reduction in infarct size and 36% (p < 0.05) and 23% (p < 0.05) reduction in neurological deficits, respectively. The salutary effect of DPH-067517 in ischemic brain injury was also observed when the first dose was administrated 60 min after the onset of ischemia. Inhibition of TACE had no effect on apoptosis measured by levels of active caspase-3 expression and DNA fragmentation. Our data suggest that inhibition of TACE might be a potential therapeutic strategy for neuroprotection after focal ischemic stroke.

Brain edema induced by in vitro ischemia: causal factors and neuroprotection

Decreased cerebral blood flow, hence decreased oxygen and glucose, leads to ischemic brain injury via complex pathophysiological events, including excitotoxicity, mitochondrial dysfunction, increased intracellular Ca2+, and reactive oxygen species (ROS) generation. Each of these could also contribute to cerebral edema, which is the primary cause of patient mortality after stroke. In vitro brain slices are widely used to study ischemia. Here we introduce a slice model to investigate ischemia-induced edema. Significant water gain was induced in coronal slices of rat brain by 5 min of oxygen and glucose deprivation (OGD) at 35 degrees C, with progressive edema formation after return to normoxic, normoglycemic medium. Edema increased with increasing injury severity, determined by OGD duration (5-30 min). Underlying factors were assessed using glutamate-receptor antagonists (AP5/CNQX), blockade of mitochondrial permeability transition [cyclosporin A (CsA) versus FK506], inhibition of Na+/Ca2+ exchange (KB-R7943), and ROS scavengers (ascorbate, Trolox, dimethylthiourea, Tempol). All agents except KB-R7943 and FK506 significantly attenuated edema when applied after OGD; KB-R7943 was effective when applied before OGD. Significantly, complete prevention of ischemia-induced edema was achieved with a cocktail of AP5/CNQX, CsA and Tempo applied after OGD, which demonstrates the involvement of multiple, additive mechanisms. The efficacy of this cocktail further shows the potential value of combination therapies for the treatment of cerebral ischemia.

Altered expression of zinc finger proteins, ADAMs, and integrin-related proteins following treatment of cultured human cells with a low concentration of N-methyl-N'-nitro-N-nitrosoguanidine

Proteomic analysis is an important approach to characterize the proteome and study protein functions. It is also a powerful screening method for detecting unexpected alterations in protein expression that may be overlooked by conventional biochemical techniques. N-Methyl-N'-nitro-N-nitrosoguanidine (MNNG) is an alkylating agent that can induce nontargeted mutagenesis in treated cells, although the mechanism remains unclear. Using an efficient proteomic method, we identified several cellular proteins that are responsive to low-concentration MNNG treatment in human FL cells. After MNNG treatment, whole cellular proteins were separated using two-dimensional gel electrophoresis and visualized by silver staining; the digitized images then were analyzed with 2D analysis software. More than 60 proteins showed significant changes in MNNG-treated cells compared to control cells (DMSO treatment). Thirty-one proteins only detected in MNNG-treated or control cells were subjected to in-gel digestion with trypsin and identified by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry using peptide mass fingerprinting. Eighteen of theses proteins have been identified, including several zinc finger proteins, two members of the ADAMs (a disintegrin and metalloprotease domain) family, and two integrins. Most of these proteins have unknown functions and their involvement in the cellular responses to alkylating agents have not been reported. Therefore, our findings may offer new insights into the mechanisms of low-concentration MNNG-induced nontargeted mutagenesis and these proteins may serve as new biomarkers for detecting exposure of human populations to environmental carcinogens.

Upregulation of TACE/ADAM17 after ischemic preconditioning is involved in brain tolerance

A short ischemic event (ischemic preconditioning [IPC]) can result in a subsequent resistance to severe ischemic injury (ischemic tolerance [IT]). Although tumor necrosis factor-alpha (TNF-alpha) contributes to the brain damage, its expression and neuroprotective role in models of IPC have also been described. However, the role of TNF-alpha convertase (TACE) in IPC and IT is not known. Using in vitro models, the authors previously demonstrated that TACE is upregulated after ischemic brain damage. In the present study, the authors used a rat model of transient middle cerebral artery occlusion as IPC to investigate TACE expression, its involvement in TNF-alpha release, and its role in IT. Western blot analysis showed that TACE expression is increased after IPC. Ischemic preconditioning caused TNF-alpha release, an effect that was blocked by the selective TACE inhibitor BB-1101 (10 mg. kg(-1). day(-1); SHAM, 1,050 +/- 180; IPC, 1,870 +/- 290; IPC + BB, 1,320 +/- 260 ng/mg; n = 4, < 0.05). Finally, IPC produced a reduction in infarct volume, which was inhibited by treatment with BB-1101 and with anti-TNF-alpha (10 microg/5 doses; SHAM + permanent middle cerebral artery occlusion [pMCAO], 335 +/- 20; IPC + pMCAO, 244 +/- 14; IPC + BB + pMCAO, 300 +/- 6; IPC + anti-TNF + pMCAO, 348 +/- 22 mm3; n = 6-10, < 0.05). Taken together, these data demonstrate that TACE is upregulated after IPC, plays a major role in TNF-alpha shedding in IPC, and has a neuroprotective role in IT.

Developmental regulation and neuronal expression of the cellular disintegrin ADAM11 gene in mouse nervous system

ADAM11 is the prototype member of the predominantly CNS-associated clade of the ADAM metalloprotease-disintegrins that has been implicated in neural adhesion and axon guidance. The present study describes the spatiotemporal expression pattern of the ADAM11 gene in adult and developing mouse, and identifies the cells expressing the gene. In the adult CNS, ADAM11 mRNA was present throughout the forebrain, including different cortical fields and diencephalic nuclei. In brainstem, low to moderate expression was detected in certain midbrain nuclei, while several pontine and medullary nuclei showed a very strong signal. High expression was observed in the cerebellar cortex and spinal cord. In addition, ADAM11 was expressed in ganglia of the peripheral nervous system (PNS), retinae, testes, liver, and at lower levels in epidermal and mucosal epithelia, kidney, and salivary gland. The expression was localized to neurons in all examined CNS and PNS subfields. During pre- and perinatal development, ADAM11 was differentially expressed both in the developing PNS and CNS, as well as in heart, kidney, eyes, and brown fat. The present results suggest a widespread involvement of ADAM11 in neuron-neuron or neuron-glial cell interactions during development as well as in the adult nervous system. They provide novel complementary information to recently accumulated data on CNS integrin gene expression and offer useful clues for further studies of the neural functions of ADAMs and integrins.

TACE/ADAM17-TNF-alpha pathway in rat cortical cultures after exposure to oxygen-glucose deprivation or glutamate

The role of the tumor necrosis factor (TNF)-alpha convertase (TACE/ADAM17) in the adult nervous system remains poorly understood. The authors have previously demonstrated that TACE is upregulated in rat forebrain slices exposed to oxygen-glucose deprivation (OGD). They have now used rat mixed cortical cultures exposed to OGD or glutamate to study (1) TACE expression and localization, and (2) the effects of TNF-alpha release on cell viability. OGD-or glutamate-caused TNF-alpha release, an effect that was blocked by the TACE inhibitor BB3103 (BB) (0.1-1 micromol/L; control: 1.67 +/- 0.59; OGD: 6.59 +/- 1.52; glutamate: 3.38 +/- 0.66; OGD +/- BB0.1: 3.23 +/- 0.67; OGD +/- BB1: 1.33 +/- 0.22 pg/mL, n = 6, P < 0.05). Assay of TACE activity as well as Western blot showed that TACE expression is increased in OGD-or glutamate-exposed cells. In control cultures, TACE immunoreactivity was present in some microglial cells, whereas, after OGD or glutamate, TACE immunostaining appeared in most microglial cells and in some astrocytes. Conversely, BB3103 (0.1 micromol/L) caused apoptosis after glutamate exposure as shown by annexin and Hoechst 33342 staining and caspase-3 activity, an effect mimicked by the proteasome inhibitor MG-132 (caspase activity: glutamate: 5.1 +/- 0.1; glutamate + BB: 7.8 +/- 0.8; glutamate + MG: 11.9 +/- 0.5 pmol. min(-1) mg(-1) protein, n = 4, P < 0.05), suggesting that translocation of the transcription factor NF-kappaB mediates TNF-alpha-induced antiapoptotic effect. Taken together, these data demonstrate that, in rat mixed neuronal-glial cortical cultures exposed to OGD or glutamate, (1) TACE/ADAM17 activity accounts for the majority of TNF-alpha shedding, (2) an increase in glial TACE expression contributes to the rise in TNF-alpha, and (3) TNF-alpha release in this setting inhibits apoptosis via activation of the transcription factor NF-kappaB.