Role of mast cell activation in inducing microglial cells to release neurotrophin

The brain‐derived neurotrophic factor (BDNF) plays a critical role in pain hypersensitivity. BDNF is the ligand of P2X4 receptors (P2X4R) in the microglia. The causative factors involving the P2X4R over expression in the microglia remains unclear. Mast cell activation has a close relation with pain hypersensitivity. However, the underlying mechanism between mast cell activation and pain hypersensitivity is unknown. The present study aimed to elucidate the mechanism by which mast cell activation promoted the expression of P2X4R in the microglia. The results of present study showed that mast cell activation markedly promoted the expression of P2X4R and BDNF in microglial cells, which significantly enhanced the release of BDNF from microglial cells upon exposure to adenosine triphosphate. Mast cell‐derived tryptase activated PAR2 that resulted in promoting the expression of P2X4R in microglial cells. Pretreatment with antibodies against tryptase or PAR2, or using tryptase‐deficient HMC‐1 cells or PAR2‐deficient microglial cells abolished the increase in P2X4R expression and BDNF release. Increase in mitogen activated protein kinase phosphorylation was observed in the processes of mast cell‐induced BDNF release and P2X4R expression. We conclude that mast cell activation has the capacity to promote the expression of P2X4R and BDNF in microglial cells. © 2009 Wiley‐Liss, Inc.     

Colonic luminal proteases activate colonocyte proteinase-activated receptor-2 and regulate paracellular permeability in mice

Luminal activation of protease-activated receptors-2 (PAR(2)) on colonocytes by trypsin or PAR(2)-activating peptide increases colonic paracellular permeability (CPP). The aim of this study was to evaluate the role of proteases from endogenous and bacterial origin in the modulation of CPP and colonocyte PAR(2) expression in mice. CPP was assessed with (51)Cr-EDTA after intracolonic administration of different protease inhibitors. After 12 days of oral antibiotic treatment, measurements of colonic luminal serine protease activity (CLSPA), CPP, mucosal mouse mast cell proteinase-1 (MMCP-1) content, immunochemistry of PAR(2) and assessment of effects of PAR(2) agonist (SLIGRL) and mast cell degranulator (C48/80) on CPP in Ussing chambers were performed. Immunochemistry was repeated after intracolonic trypsin administration. Colonic infusion of protease inhibitors significantly reduced CPP. In antibiotic-treated mice, CLSPA was reduced coupled with a decrease in PAR(2) expression, but with no change in CPP and MMCP-1 content. Trypsin administration restored PAR(2) expression. The increase in CPP induced by SLIGRL and C48/80 was reduced after antibiotic treatment. Protease activity of colonic content plays an important role in the regulation of mucosal barrier through activation of PAR(2).     

Increased mast cells in the irritable bowel syndrome

Mast cells (MC) release potent mediators which alter enteric nerve and smooth muscle function and may play a role in the pathogenesis of the irritable bowel syndrome (IBS). The aim of this study was to determine if MC were increased in the colon of IBS patients compared to controls. Biopsy specimens were obtained from the caecum, ascending colon, descending colon and rectum of 28 patients: 14 IBS (Rome criteria); seven normal; and seven inflammatory controls. Tissue was stained immunohistochemically using a monoclonal mouse antibody for human mast cell tryptase (AA1). Tissue area occupied by tryptase-positive MC (volume density of mast cells) was quantified by image analysis. The number of plasma cells, lymphocytes, eosinophils, neutrophils and macrophages were each graded semiquantitatively (0-4) in haematoxylin and eosin stained sections. Mast cell volume density was significantly (P < 0.05) higher in IBS (0.91 +/- 0.18; CI 0.79; 1.0) than normal controls (0.55 +/- 0.14; CI 0.40; 0.69) in the caecum but not at other sites. Apart from MC, there was no evidence of increased cellular infiltrate in the IBS group. MC were significantly increased in the caecum of IBS patients compared to controls. The multiple effects of the intestinal mast cell alone, or as a participant of a persistent inflammatory response, may be fundamental to the pathogenesis of IBS.     

Proteinase‐activated receptor‐2 activation evokes oesophageal longitudinal smooth muscle contraction via a capsaicin‐sensitive and neurokinin‐2 receptor‐dependent pathway

Background Intraluminal acid evokes sustained oesophageal longitudinal smooth muscle (LSM) contraction and oesophageal shortening, which may play a role in oesophageal pain and the aetiology of hiatus hernia. In the opossum model, this reflex has been shown to involve mast cell activation and release of neurokinins from capsaicin‐sensitive neurons. The aim of this study was to determine whether proteinase‐activated receptor‐2 (PAR‐2) activation evokes reflex LSM contraction via similar mechanisms. Methods Tension recording studies were performed using opossum oesophageal LSM strips in the presence and absence of pharmacological agents. In addition, the effect of trypsin on single isolated LSM cells was determined using videomicroscopy, and the expression of PAR‐2 in oesophageal tissue was examined using immunohistochemistry. Key Results The PAR‐2 agonist trypsin evoked sustained, concentration‐dependent contraction of LSM muscle strips, but had no effect on isolated LSM cells. The trypsin‐induced contraction was blocked by capsaicin desensitization, substance P (SP) desensitization or application of the selective neurokinin‐2 (NK‐2) receptor antagonist MEN 10376. Immunohistochemistry revealed co‐localization of SP, calcitonin gene‐related peptide and PAR‐2 in axons of opossum oesophageal LSM. Conclusions & Inferences Longitudinal smooth muscle contraction induced by trypsin involves capsaicin‐sensitive neurons and subsequent activation of NK‐2, which is identical to the pathway involved in acid‐induced LSM contraction and oesophageal shortening. This suggests that acid‐induced LSM contraction may involve mast cell‐derived mediators that activate capsaicin‐sensitive neurons via PAR‐2.     

Protease‐activated receptor 4 activation increases the expression of calcitonin gene‐related peptide mRNA and protein in dorsal root ganglion neurons

Accumulating evidence demonstrates that nociceptor activation evokes a rapid change in mRNA and protein levels of calcitonin gene‐related peptide (CGRP) in dorsal root ganglion (DRG) neurons. Although the colocalization of CGRP and protease‐activated receptor‐4 (PAR4), a potent modulator of pain processing and inflammation, was detected in DRG neurons, the role of PAR4 activation in the expression of CGRP has not been investigated. In the present study, the expression of CGRP and activation (phosphorylation) of extracellular signal‐regulated kinases 1 and 2 (ERK1/2) in rat DRG neurons were measured by immunofluorescence, real‐time PCR, and Western blotting after AYPGKF‐NH2 (selective PAR4‐activating peptide; PAR4‐AP) intraplantar injection or treatment of cultured DRG neurons. The expression of CGRP in cultured DRG neurons was also assessed after treatment with AYPGKF‐NH2 with preaddition of PD98059 (an inhibitor for ERK1/2 pathway). Results showed that PAR4‐AP intraplantar injection or treatment of cultured DRG neurons evoked significant increases in DRG cells displaying CGRP immunoreactivity and cytoplasmic and nuclear staining for phospho‐ERK1/2 (p‐ERK1/2). Percentages of total DRG neurons expressing both CGRP and PAR4 or p‐ERK1/2 also increased significantly at 2 hr after PAR4‐AP treatment. Real‐time PCR and Western blotting showed that PAR4‐AP treatment significantly increased expression of CGRP mRNA and protein levels in DRG neurons. The PAR4 activation‐evoked CGRP expression both at mRNA and at protein levels was significantly inhibited after p‐ERK1/2 was inhibited by PD98059. These results provide evidence that activation of PAR4 upregulates the expression of CGRP mRNA and protein levels in DRG neurons via the p‐ERK1/2 signal pathway. © 2013 Wiley Periodicals, Inc.     

PAR4: A new role in the modulation of visceral nociception

Abstract  Protease-activated receptors (PARs) are a family of G-protein-coupled receptors with a widespread distribution that are involved in various physiological functions including inflammation and nociception. In a recent study in Neurogastroenterology and Motility, Augé et al. describe for the first time the presence of PAR4 on visceral primary afferent neurons and its role in modulating colonic nociceptive responses, colonic hypersensitivity and primary afferent responses to PAR2 and Transient Receptor Potential Vanilloid-4 (TRPV4). Using the model of visceromotor response (VMR) to colorectal distension (CRD), they show that a PAR4 agonist delivered into the colon lumen decreases basal visceral response to CRD and reduces the exacerbated VMR to CRD induced by treatment with PAR2 or TRPV4 agonists. In isolated sensory neurons, they show that a PAR4 agonist inhibits calcium mobilization induced by PAR2 or TRPV4 agonists. Finally, they describe increased pain behaviour evoked by luminal application of mustard oil in PAR4 deficient mice compared to wild type controls. The newly discovered role of PAR4 in modulating visceral pain adds to our growing understanding of the contribution of colonic proteases and PARs to the mechanisms involved in colonic hypersensitivity and their potential role as therapeutic targets for irritable bowel syndrome.     

ATP plays a role in neurite stimulation with activated mast cells

Previously, we showed that nerve-mast cell cross-talk can occur bidirectionally and that substance P is a mediator to activate mast cells. Here, we have studied the mediators to activate nerves cocultured with mast cells. Addition of antigen to the cocultures of superior cervical ganglia (SCG) and rat basophilic leukemia cells (RBLs) elicited Ca(2+) response in RBLs and after a lag period induced Ca(2+) signal in SCG neurites. Pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (purinergic receptor antagonist) or apyrase (ATP-hydrolyzing enzyme) reduced the Ca(2+) signals in neurites, indicating that ATP released from activated mast cells was one of important mediators to activate nerves.     

Colonic motor response to IgE-mediated mast cell degranulation in the Hooded-Lister rat

Abstract After challenge of sensitized individuals, food protein-induced colonic anaphylaxis may contribute to the symptom of diarrhoea. The aim of this study was to characterize the effect of food protein-induced anaphylaxis on colonic circular muscle in vitro, identify the mediators involved, and then evaluate the effect of antigen challenge on colonic transit in vivo. Hooded-Lister rats were sensitized by intraperitoneal injection of egg albumin and controls were sham-sensitized with saline. Rings of distal colonic tissue were suspended in standard tissue baths (mucosa intact) and circular muscle contractility was measured in response to antigen or other agents on day 14. In conscious animals, Na₂⁵¹CrO₄ was instilled alone, or with antigen, via proximal colostomy and the geometric centre of distribution of ⁵¹Cr calculated. Following antigen challenge, a contractile response occurred only in animals that were sensitized (specific IgE antibody levels ≥1:64), and was specific for the sensitizing antigen. Mast cell involvement was suggested when (1) concanavalin A (a degranulator of both mucosal and connective tissue mast cells) mimicked the antigen-induced response, and (2) Ag-induced contraction was significantly inhibited by mast cell stabilizers. The Ag-induced response was significantly and independently inhibited by a lipo-oxygenase enzyme inhibitor and by LTD₄ and platelet activating factor receptor antagonists. The antigen-induced response was resistant to histamine and 5-hydroxytryptamine receptor antagonists, indomethacin, atropine and tetrodotoxin. The geometric centre of distribution of ⁵¹Cr was significantly more distal in sensitized animals challenged with antigen rather than placebo, and only sensitized animals challenged with antigen developed diarrhoea. These results suggest that colonic antigen challenge of sensitized rats is associated with IgE-mediated mast cell activation, the release of membrane derived mediators which, in vitro, act directly on smooth muscle to induce contraction, and in vivo result in an increased rate of aboral transit and diarrhoea.     

Protease-activated receptor 2 expression in trigeminal neurons innervating the rat nasal mucosa

Protease-activated receptor 2 (PAR2) is activated by trypsin and mast cell tryptase to induce widespread inflammation by unknown mechanisms. Trypsin and tryptase were shown to activate sensory neurons to release substance-P and related peptides to mediate neurogenic inflammation. In the present study, the expression of PAR2 and tachykinins were investigated in rat trigeminal neurons that were identified by retrograde labeling with rhodamine dye from the nasal mucosa by using neuronal tracing in combination with immunohistochemistry. We found that large subpopulation of all trigeminal neurons (43.5+/-2.6%) identified by the pan-neuronal marker PGP 9.5 were stained with PAR2-immunoreactivity. Of all trigeminal neurons, 7.5+/-2.1% were immunoreactive for tachykinins and PAR2, and only 3.9+/-1.7% of all trigeminal neurons expressed tachykinins, but not PAR2-immunoreactivity. The present study also found that a large number trigeminal neurons innervating the nasal mucosa expressed PAR2-immunoreactivity. Of the rhodamine-labeled trigeminal neurons, 52.5+/-1.8% were immunoreactive for only PAR2 expression, 7.3+/-1.9% contained tachykinins and PAR2, and 3.1+/-0.4 of the rhodamine-labeled trigeminal neurons were non-immunoreactive PAR2, but were positive for tachykinins-immunoreactivity. In conclusion, based on the co-localization of PAR2 and tachykinins in trigeminal sensory neurons innervating the nasal mucosa, the present study suggests that, following an activation of PAR2 receptor in tachykinergic neurons by trypsin and mast cell tryptase, there may be a triggering of tachykinin-mediated phenomena such as neurogenic inflammation in allergic or non-allergic rhinitis.     

Colonic mucosal mediators from patients with irritable bowel syndrome excite enteric cholinergic motor neurons

Background Mediators released in the mucosal milieu have been suggested to be involved in visceral hypersensitivity and abdominal pain in patients with irritable bowel syndrome (IBS). However, their impact on myenteric neurons remains unsettled. Methods Mucosal biopsies were obtained from the descending colon of patients with IBS and controls. Mucosal mast cells were identified immunohistochemically. The impact of spontaneously released mucosal mediators on guinea pig electrically stimulated longitudinal muscle myenteric plexus (LMMP) preparations was assessed in vitro by means of selective receptor antagonists and inhibitors. Key Results Patients with IBS showed an increased mast cell count compared with controls. Application of mucosal mediators of IBS to LMMPs potentiated cholinergic twitch contractions, an effect directly correlated with mast cell counts. Enhanced contractions were inhibited by 50.3% with the prostaglandin D2 antagonist BW A868C, by 31.3% and 39% with the TRPV1 antagonists capsazepine and HC‐030031, respectively, and by 60.5% with purinergic P2X antagonist pyridoxalphosphate‐6‐azophenyl‐2′,4′‐disulfonic acid. Conversely, the serotonin1‐4, histamine1‐3, tachykinin1‐3 receptor blockade, and serine protease inhibition had no significant effect. Conclusions & Inferences Colonic mucosal mediators from patients with IBS excite myenteric cholinergic motor neurons. These effects were correlated with mast cell counts and mediated by activation of prostanoid receptors, TRPV1, and P2X receptors. These results support the role of mucosal inflammatory mediators and mast cell activation in altered motor function of IBS.     

Proteinase-activated receptor-4 evoked colorectal analgesia in mice: an endogenously activated feed-back loop in visceral inflammatory pain

Background Activation of proteinase‐activated receptor‐4 (PAR‐4) from the colonic lumen has an antinociceptive effect to colorectal distension (CRD) in mice in basal conditions. We aimed to determine the functional localization of the responsible receptors and to test their role in two different hyperalgesia models. Methods Mice received PAR‐4 activating peptide (PAR‐4‐AP, AYPGKF‐NH₂) or vehicle intraperitoneally (IP), and abdominal EMG response to CRD was measured. The next group received PAR‐4‐AP intracolonically (IC) with or without 2,4,6‐triaminopyrimidine, a chemical tight junction blocker, before CRD. The SCID mice were used to test the role of lymphocytes in the antihyperalgesic effect. The effects of PAR‐4‐AP and PAR‐4‐antagonist (P4pal‐10) were evaluated in water avoidance stress (WAS) model and low grade 2,4,6‐trinitrobenzene sulfonic acid (TNBS) colitis. Spinal Fos protein expression was visualized by immunohistochemistry. Key Results The antinociceptive effect of PAR‐4‐AP disappeared when was administrered IP, or with the blockade of colonic epithelial tight junctions, suggesting that PAR‐4‐AP needs to reach directly the nerve terminals in the colon. The CRD‐induced spinal Fos overexpression was reduced by 43% by PAR‐4‐AP. The PAR‐4‐AP was antihyperalgesic in both hyperalgesia models and in mice with impaired lymphocytes. The PAR‐4‐antagonist significantly increased the TNBS, but not the WAS‐induced colonic hyperalgesia. Conclusions & Inferences The antinociceptive effect of PAR‐4‐AP depends on its penetration to the colonic mucosa. The PAR‐4 activation is endogenously involved as a feedback loop to attenuate inflammatory colonic hyperalgesia to CRD.     

Expression and secretion of CXCL8 (IL-8), release of tryptase and transcription of histidine decarboxylase mRNA by anti-IgE-activated human umbilical cord blood-derived cultured mast cells

Activation of cytokine receptors and alterations in cytokines are thought to play important roles in neuronal dysfunction and in the pathogenesis of the nervous system diseases. CXCL8 (IL-8) is a CXC chemokine with chemotactic and inflammatory properties. Chemokines control mast cell infiltration in several inflammatory diseases, including stress and neurological dysfunctions. Using isolated human umbilical cord blood-derived cultured mast cells (HUCMC) from hematopoietic stem cells CD34+, mast cells were immunologically activated with anti-IgE at concentrations of 1, 5, 10 and 20 microg/ml leading to the dose-dependent production of IL-8 (p < 0.05). The increase in IL-8 mRNA expression was also noted when the cells were treated with anti-IgE at 10 microg/ml for 6 h. Immunologically activated HUCMC provoked the generation of tryptase in a dose- and time-dependent manner. We also found increased histidine decarboxylase (HDC) expression in activated HUCMC after 6 h of incubation, a rate-limiting enzyme responsible for the generation of histamine from histidine. Taken together, these results confirm that anti-IgE-activated mast cells release inflammatory mediators including CXCL8, a CXC chemokine which regulates several biological effects of mast cells, e.g. chemoattraction, and possibly causes cell arrest.     

Elevated mast cell tryptase in cerebrospinal fluid of multiple sclerosis patients

Multiple sclerosis (MS) lesions are associated with infiltration of T lymphocytes and macrophages that appear to mediate myelin destruction and gliosis (scarring). Mast cells are located perivascularly in the brain, are juxtaposed to neurons, and have been shown to secrete vasoactive and inflammatory mediators in response to neuropeptides and direct nerve stimulation. Mast cells have been previously identified in MS lesions, are activated by myelin basic protein, and can participate in the regulation of blood–brain barrier permeability, as well as in myelin destruction. Here, cerebrospinal fluid from MS patients and controls with other neurologic diseases was assayed for histamine, its major metabolite methylhistamine, and the specific mast cell marker tryptase. Histamine and methylhistamine were not elevated in MS. However, the mast cell specific proteolytic enzyme tryptase was significantly elevated in MS, suggesting that mast cell activation may be involved in the pathophysiology of this disease.     

Increased levels of activated T-cells and reduced levels of CD4/CD25+ cells in peripheral blood of Guillain-Barré syndrome patients compared to controls

Guillain-Barré syndrome (GBS) is a severe, self-limiting, autoimmune motor neuropathy. This study was performed to investigate the numbers of activated T-cells and regulatory T-cells, and CD95 and bcl-2 expression in GBS patients compared to controls. The percentage of cells expressing CD69 (activated T-cells) was increased in the blood of both patients with GBS and those with other neuropathies compared to healthy controls. GBS patients displayed significant decreases in the percentage of T-lymphocytes (CD3) and CD4/CD25+ cells (T regulatory cells) compared to patients with other neuropathies and a reduction in the percentage of cytotoxic/suppressor T-lymphocytes (CD8) compared to healthy controls. CD95 expression was reduced in GBS compared to patients with other neuropathies and expression of Bcl-2 was increased in GBS compared to healthy controls. We therefore suggest that in GBS there are increased activated T-cells and disturbances in regulatory T-cells and T-cell apoptosis.     

Post inflammatory damage to the enteric nervous system in diverticular disease and its relationship to symptoms

Abstract:  Some patients with colonic diverticula suffer recurrent abdominal pain and exhibit visceral hypersensitivity, though the mechanism is unclear. Prior diverticulitis increases the risk of being symptomatic while experimental colitis in animals increases expression of neuropeptides within the enteric nervous system (ENS) which may mediate visceral hypersensitivity. Our aim was to determine the expression of neuropeptides within the ENS in diverticulitis (study 1) and in patients with symptomatic disease (study 2). Study 1 – Nerves in colonic resection specimens with either acute diverticulitis (AD, n  = 16) or chronic diverticulitis (CD, n  = 16) were assessed for neuropeptide expression recording % area staining with protein gene product (PGP9.5), substance P (SP), neuropeptide K (NPK), pituitary adenylate cyclase activating polypeptide (PACAP), vasoactive intestinal polypeptide (VIP) and galanin. Study 2 – Seventeen symptomatic and 15 asymptomatic patients with colonic diverticula underwent flexible sigmoidoscopy and multiple peridiverticular mucosal biopsies. Study 1 – Neural tissue, as assessed by PGP staining was increased to a similar degree in circular muscle in both AD and CD. The CD specimens showed significant increases in the immunoreactivity of SP, NPK and galanin in both mucosal and circular muscle layer compared with controls. Study 2 – Mucosal histology was normal and PGP9.5 staining was similar between groups however patients with symptomatic diverticular disease demonstrated significantly higher levels of SP, NPK, VIP, PACAP and galanin within the mucosal plexus. Patients with symptomatic diverticular disease exhibit increased neuropeptides in mucosal biopsies which may reflect resolved prior inflammation, as it parallels the changes seen in acute and chronic diverticulitis.     

Phenotypic and functional properties of gamma delta T cells from patients with Guillain Barré syndrome

In this study we have examined the phenotypic and functional properties of circulating gamma delta T cells in patients with Guillain Barre syndrome (GBS), in normal healthy controls, and in patients with active multiple sclerosis (MS). Cells expressing the Vdelta2 T cell receptor showed elevated expression of the C-lectin receptor NKRP1A in both GBS and MS, suggestive of an activated state. However, in patients with GBS these cells failed to respond to pyrenil-pyrophosphate derivatives and Vdelta2 + T cell clones derived from these patients released lower levels of IFNgamma than Vdelta2 + clones derived from controls and MS patients. In contrast, in patients with GBS the Vdelta1 + subset was expanded, showed elevated expression of NKRPIA and Vdelta1 + clones derived from these patients secreted high levels of IL-4. Our findings of expanded NKRP-1A +, IL-4-producing Vdelta1 T cells in the GBS patients suggests the possibility that these cells are activated by the recognition of non-protein antigens in an MHC-unrestricted manner and contribute to the humoral response to glycolipids that is a hallmark of this disease.     

Activation of protease-activated receptor1 mediates induction of matrix metalloproteinase-9 by thrombin in rat primary astrocytes

Thrombin plays an important role in diverse neurological processes such as proliferation, cell migration, differentiation and neuroinflammation. In this study, we investigated the effect of thrombin on matrix metalloprotease-9 (MMP-9) expression in rat primary astrocytes. Thrombin (1–10 U/ml) induced a significant increase in MMP-9 activity as measured by gelatin zymography. Thrombin also increased MMP-9 mRNA expression. Among three isotypes of thrombin receptor, i.e. protease-activated receptor (PAR)-1, -3 and -4, PAR1 agonist (1–100 μM) but not PAR3 and PAR4 agonist induced MMP-9 expression. Inhibition of thrombin-induced MMP-9 production by SCH 79797 (10–50 nM), a selective PAR1 receptor antagonist, confirmed that PAR1 is a main receptor for thrombin-induced MMP-9 expression. In astrocytes, thrombin activated Erk1/2, and it was inhibited by PD98059. In this study, thrombin-induced MMP-9 expression was inhibited by PD98059. PAR1 agonist activated Erk1/2 and PD98059 inhibited PAR1 agonist-induced MMP-9 expression. MMP-9 promoter reporter assay confirmed the positive effect of ERK1/2 on MMP-9 expression. These results suggest that the activation of PAR1 mediates thrombin-induced MMP-9 expression through the regulation of Erk1/2.     

Microsomal prostaglandin E synthase-2: Cellular distribution and expression in Alzheimer's disease

Nonsteroidal anti-inflammatory drugs, such as cyclooxygenase (COX)-2 inhibitors, have been unsuccessful in slowing or reversing Alzheimer's disease (AD). Thus, understanding the expression patterns of the downstream effectors for the regulation of prostaglandin synthesis may be important for understanding the pathological processes involved in AD and formulating more effective pharmacotherapeutics for this disease. In this study, we used immunofluorescence, immunohistochemistry, and Western blot analysis to compare patterns of microsomal prostaglandin E synthase (mPGES)-2 expression in the middle frontal gyrus (MFG) of AD patients and age-matched controls. In control human brain sections, mPGES-2 immunoreactivity was observed in neurons, activated microglia, and endothelium, but not in resting microglia, astrocytes, or smooth muscle cells. Microsomal PGES-2 immunoreactivity was particularly elevated in the pyramidal neurons of brains from three of five sporadic and four of five familial AD patients compared with four of five age-matched control brains that showed minimal immunoreactivity. In contrast, Western blot analysis revealed no difference in mPGES-2 levels between end-stage AD brain tissue and control brain tissue. These results suggest that in human cortex, mPGES-2 is constitutive in neurons and endothelium and induced in activated microglia. Furthermore, the high immunoreactivity of mPGES-2 in pyramidal neurons of AD brains indicates that it might have a potential role in the functional replacement of cytosolic PGES or inactive mPGES-1 in later stages of AD.     

Tight junctions and IBS ‐ the link between epithelial permeability,low‐grade inflammation,and symptom generation?

In this issue of Neurogastroenterology and Motility, Dr Ewa Wilcz‐Villega and colleagues report low expression of E‐cadherin, a tight junction protein involved in the regulation of paracellular permeability, in the colonic mucosa of patients with the irritable bowel syndrome (IBS) with predominance of diarrhea (IBS‐D) or alternating symptoms (IBS‐A). These findings constitute an improvement in our knowledge of epithelial barrier disruption associated with IBS. There is mounting evidence to indicate that a compromised epithelial barrier is associated with low‐grade immune activation and intestinal dysfunction in at least a proportion of IBS patients. During the last 10 years of research, much interest has focused on the increase in the number of different types of immune cells in the gut mucosa of IBS patients including: mast cells, T lymphocytes, and other local cells such as enteroendocrine cells. The inflammatory mediators released by these cells or other luminal factors could be at the origin of altered epithelial barrier functions and enteric nervous system signaling, which lead to gut hypersensitivity. A current conceptual framework states that clinical symptoms of IBS could be associated with structural and functional abnormalities of the mucosal barrier, highlighting the crucial importance of elucidating the contributory role of epithelial barrier defects in the pathogenesis of IBS. More importantly, disruption of the epithelial barrier could also participate in the generation of persistent abdominal pain and discomfort mimicking IBS in patients with inflammatory bowel diseases considered in remission. This mini review gives a brief summary of clinical and experimental evidence concerning the mechanisms underlying epithelial barrier defects in IBS.