Tracey Hand

Neuroprotective Function of the PGE2 EP2 Receptor in Cerebral Ischemia

The cyclooxygenases COX-1 and COX-2 catalyze the first committed step of prostaglandin synthesis from arachidonic acid. Previous studies in rodent stroke models have shown that the inducible COX-2 isoform promotes neuronal injury, and the administration of COX-2 inhibitors reduces infarct volume. We investigated the function of PGE2, a principal prostaglandin product of COX-2 enzymatic activity, in neuronal survival in cerebral ischemia. PGE2 exerts its downstream effects by signaling through a class of four distinct G-protein-coupled EP receptors (for E-prostanoid: EP1, EP2, EP3, and EP4) that have divergent effects on cAMP and phosphoinositol turnover and different anatomical distributions in brain. The EP2 receptor subtype is abundantly expressed in cerebral cortex, striatum, and hippocampus, and is positively coupled to cAMP production. In vitro studies of dispersed neurons and organotypic hippocampal cultures demonstrated that activation of the EP2 receptor was neuroprotective in paradigms of NMDA toxicity and oxygen glucose deprivation. Pharmacologic blockade of EP2 signaling by inhibition of protein kinase A activation reversed this protective effect, suggesting that EP2-mediated neuroprotection is dependent on cAMP signaling. In the middle cerebral artery occlusion-reperfusion model of transient forebrain ischemia, genetic deletion of the EP2 receptor significantly increased cerebral infarction in cerebral cortex and subcortical structures. These studies indicate that activation of the PGE2 EP2 receptor can protect against excitotoxic and anoxic injury in a cAMP-dependent manner. Taken together, these data suggest a novel mechanism of neuroprotection mediated by a dominant PGE2 receptor subtype in brain that may provide a target for therapeutic intervention.

Deletion of the prostaglandin E2 EP2 receptor reduces oxidative damage and amyloid burden in a model of Alzheimer's disease.

Epidemiological studies demonstrate that chronic use of nonsteroidal anti-inflammatory drugs (NSAIDs) in normal aging populations reduces the risk of developing Alzheimers disease (AD). NSAIDs inhibit the enzymatic activity of cyclooxygenase-1 (COX-1) and inducible COX-2, which catalyze the first committed step in the synthesis of prostaglandins. These studies implicate COX-mediated inflammation as an early and potentially reversible preclinical event; however, the mechanism by which COX activity promotes development of AD has not been determined. Recent studies implicate the prostaglandin E2 (PGE2) E prostanoid subtype 2 (EP2) receptor in the development of the innate immune response in brain. Here, we report that deletion of the PGE2 EP2 receptor in the APPSwe-PS1ΔE9 model of familial AD results in marked reductions in lipid peroxidation in aging mice. This reduction in oxidative stress is associated with significant decreases in levels of amyloid-β (Aβ) 40 and 42 peptides and amyloid deposition. Aged APPSwe-PS1ΔE9 mice lacking the EP2 receptor harbor lower levels of β C-terminal fragments, the product of β-site APP cleaving enzyme (BACE1) processing of amyloid precursor protein. Increases in BACE1 processing have been demonstrated in models of aging and AD and after oxidative stress. Our results indicate that PGE2 signaling via the EP2 receptor promotes age-dependent oxidative damage and increased Aβ peptide burden in this model of AD, possibly via effects on BACE1 activity. Our findings identify EP2 receptor signaling as a novel proinflammatory and proamyloidogenic pathway in this model of AD, and suggest a rationale for development of therapeutics targeting the EP2 receptor in neuroinflammatory diseases such as AD.

A Genome-Wide Association Study on African-Ancestry Populations For Asthma

BACKGROUND Asthma is a complex disease characterized by striking ethnic disparities not explained entirely by environmental, social, cultural, or economic factors. Of the limited genetic studies performed on populations of African descent, notable differences in susceptibility allele frequencies have been observed. OBJECTIVES We sought to test the hypothesis that some genes might contribute to the profound disparities in asthma. METHODS We performed a genome-wide association study in 2 independent populations of African ancestry (935 African American asthmatic cases and control subjects from the Baltimore-Washington, DC, area and 929 African Caribbean asthmatic subjects and their family members from Barbados) to identify single-nucleotide polymorphisms (SNPs) associated with asthma. RESULTS A meta-analysis combining these 2 African-ancestry populations yielded 3 SNPs with a combined P value of less than 10(-5) in genes of potential biologic relevance to asthma and allergic disease: rs10515807, mapping to the alpha-1B-adrenergic receptor (ADRA1B) gene on chromosome 5q33 (3.57 x 10(-6)); rs6052761, mapping to the prion-related protein (PRNP) gene on chromosome 20pter-p12 (2.27 x 10(-6)); and rs1435879, mapping to the dipeptidyl peptidase 10 (DPP10) gene on chromosome 2q12.3-q14.2. The generalizability of these findings was tested in family and case-control panels of United Kingdom and German origin, respectively, but none of the associations observed in the African groups were replicated in these European studies. Evidence for association was also examined in 4 additional case-control studies of African Americans; however, none of the SNPs implicated in the discovery population were replicated. CONCLUSIONS This study illustrates the complexity of identifying true associations for a complex and heterogeneous disease, such as asthma, in admixed populations, especially populations of African descent.

Neuronal overexpression of cyclooxygenase-2 increases cerebral infarction

Increases in COX‐2 enzymatic activity and prostaglandin production have been associated with neuronal injury in both acute and age‐related degenerative neurological diseases. In this study, we tested the effects of increased COX‐2 activity in a model of transient focal ischemia using a transgenic mouse model in which human COX‐2 is constitutively expressed selectively in neurons of the striatum, cerebral cortex, and hippocampus. These COX‐2 transgenic mice harbor elevated levels of PGE2 that are 10‐fold higher than nontransgenic levels. A significant increase in infarct volume was observed after middle cerebral artery occlusion with 4 days of reperfusion in COX‐2 transgenic mice as compared with nontransgenic littermates. Pretreatment of nontransgenic mice with the selective COX‐2 inhibitor SC58236 resulted in a significant reduction of infarct volume in nontransgenic mice, consistent with previous pharmacological studies. However, transgenic COX‐2 mice treated with SC58236 did not show a significant reduction. This suggests that chronic increases in COX‐2 expression and enzymatic activity, which can occur in aging and in pathological states characterized by oxidative stress and chronic inflammatory processes, can lead to downstream cellular changes that have a negative impact on neuronal survival in cerebrovascular disease. Ann Neurol 2003

Filaggrin mutations that confer risk of atopic dermatitis confer greater risk for eczema herpeticum.

BACKGROUND Loss-of-function null mutations R501X and 2282del4 in the skin barrier gene, filaggrin (FLG), represent the most replicated genetic risk factors for atopic dermatitis (AD). Associations have not been reported in African ancestry populations. Atopic dermatitis eczema herpeticum (ADEH) is a rare but serious complication of AD resulting from disseminated cutaneous herpes simplex virus infections. OBJECTIVE We aimed to determine whether FLG polymorphisms contribute to ADEH susceptibility. METHODS Two common loss-of-function mutations plus 9 FLG single nucleotide polymorphisms were genotyped in 278 European American patients with AD, of whom 112 had ADEH, and 157 nonatopic controls. Replication was performed on 339 African American subjects. RESULTS Significant associations were observed for both the R501X and 2282del4 mutations and AD among European American subjects (P = 1.46 x 10(-5), 3.87 x 10(-5), respectively), but the frequency of the R501X mutation was 3 times higher (25% vs 9%) for ADEH than for AD without eczema herpeticum (EH) (odds ratio [OR], 3.4; 1.7-6.8; P = .0002). Associations with ADEH were stronger with the combined null mutations (OR, 10.1; 4.7-22.1; P = 1.99 x 10(-11)). Associations with the R501X mutation were replicated in the African American population; the null mutation was absent among healthy African American subjects, but present among patients with AD (3.2%; P = .035) and common among patients with ADEH (9.4%; P = .0049). However, the 2282del4 mutation was absent among African American patients with ADEH and rare (<1%) among healthy individuals. CONCLUSION The R501X mutation in the gene encoding filaggrin, one of the strongest genetic predictors of AD, confers an even greater risk for ADEH in both European and African ancestry populations, suggesting a role for defective skin barrier in this devastating condition.

Prostaglandin D2 mediates neuronal protection via the DP1 receptor

Cyclo‐oxygenases (COXs) catalyze the first committed step in the synthesis of the prostaglandins PGE2, PGD2, PGF2α, PGI2 and thomboxane A2. Expression and enzymatic activity of COX‐2, the inducible isoform of COX, are observed in several neurological diseases and result in significant neuronal injury. The neurotoxic effect of COX‐2 is believed to occur through downstream effects of its prostaglandin products. In this study, we examined the function of PGD2 and its two receptors DP1 and chemoattractant receptor‐homologous molecule expressed on Th2 cells (CRTH2) (DP2) in neuronal survival. PGD2 is the most abundant prostaglandin in brain and regulates sleep, temperature and nociception. It signals through two distinct G protein‐coupled receptors, DP1 and DP2, that have opposing effects on cyclic AMP (cAMP) production. Physiological concentrations of PGD2 potently and unexpectedly rescued neurons in paradigms of glutamate toxicity in cultured hippocampal neurons and organotypic slices. This effect was mimicked by the DP1‐selective agonist BW245C but not by the PGD2 metabolite 15d‐PGJ2, suggesting that neuroprotection was mediated by the DP1 receptor. Conversely, activation of the DP2 receptor promoted neuronal loss. The protein kinase A inhibitors H89 and KT5720 reversed the protective effect of PGD2, indicating that PGD2‐mediated neuroprotection was dependent on cAMP signaling. These studies indicate that activation of the PGD2 DP1 receptor protects against excitotoxic injury in a cAMP‐dependent manner, consistent with recent studies of PGE2 receptors that also suggest a neuroprotective effect of prostaglandin receptors. Taken together, these data support an emerging and paradoxical neuroprotective role of prostaglandins in the CNS.

Kalirin Inhibition of Inducible Nitric-oxide Synthase

Nitric oxide (NO) acts as a neurotransmitter. However, excess NO produced from neuronal NO synthase (nNOS) or inducible NOS (iNOS) during inflammation of the central nervous system can be neurotoxic, disrupting neurotransmitter and hormone production and killing neurons. A screen of a hippocampal cDNA library showed that a unique region of the iNOS protein interacts with Kalirin, previously identified as an interactor with a secretory granule peptide biosynthetic enzyme. Kalirin associates with iNOS in vitroand in vivo and inhibits iNOS activity by preventing the formation of iNOS homodimers. Expression of exogenous Kalirin in pituitary cells dramatically reduces iNOS inhibition of ACTH secretion. Thus Kalirin may play a neuroprotective role during inflammation of the central nervous system by inhibiting iNOS activity.

Genetic variants in thymic stromal lymphopoietin are associated with atopic dermatitis and eczema herpeticum

computer instead of at the patient makes care impersonal.’’ Two respondents commented that training programs for clinicians need to be meaningful and efficient, that all clinicians (and not just hospitalists) need to have access to health information technology, and that quantity and diversity made currently available information online daunting to navigate. Do physician researchers have a different perspective on desirable features in an EMR system compared with those who spend their time exclusively in the clinic? This question was explored by comparing the responses of the 2 groups to the questions ‘‘How can informatics be used to make medical care more personalized?’’ and ‘‘How can informatics help translate bench findings to clinical practice?’’ Physician researchers included the following 2 choices in their top 6 more often than those who spent their time mainly in the clinic: (1) the ability to exploit bioinformatic/genetic information to improve care (50% vs 28%; P 5 .03, x) and (2) the need to improve informatics methods (60% vs 42%; but P 5 .09). On-the-field clinical providers are valuable resources to facilitate refinement of health informatics technology to personalize medicine. Actively involving practicing physicians in the design, selection, and deployment of EMR systems is necessary for meaningful adoption and consequent improvement in health care. Deendayal Dinakarpandian, MD, PhD, MS Arthur R. Williams, PhD, MA(Econ), MPA Chitra Dinakar, MD From the School of Computing and Engineering, University of Missouri–Kansas City; the Center for Health Outcomes and Health Services Research, Children’s Mercy Hospitals and Clinics and University of Missouri Medical School, Kansas City; and the Division of Allergy and Immunology, Children’s Mercy Hospitals and Clinics, University of Missouri–Kansas City, Kansas City, Mo. E-mail: cdinakar@cmh.edu. Disclosure of potential conflict of interest: C. Dinakar is Chair of the Health Outcomes, Education, Delivery and Quality (HEDQ) Interest Section of the American Academy of Allergy, Asthma & Immunology and is on the Programming Committee of the American College of Allergy, Asthma and Immunology. The rest of the authors have declared that they have no conflict of interest.

Cycloxygenase-2 activity promotes cognitive deficits but not increased amyloid burden in a model of Alzheimer's disease in a sex-dimorphic pattern.

Administration of non-steroidal anti-inflammatory agents reduces the risk of developing Alzheimers disease in normal aging populations, an effect that may occur from inhibition of the cyclooxygenases, the rate-limiting enzymes in the formation of prostaglandins. In this study, we investigated whether increased activity of cyclooxygenase-2 (COX-2), the inducible isoform of cyclooxygenase, potentiates disease progression in a transgenic mouse model of Alzheimers disease. To study the functional effects of COX-2 activity, male and female bigenic mice (amyloid precursor protein with Swedish mutation [APPswe]-presenilin-1 protein with deletion of exon 9 [PS1dE9] and trigenic COX-2/APPswe-PS1dE9) were behaviorally tested +/-administration of the selective COX-2 inhibitor celecoxib. Behavioral testing included a three-trial Y maze that measures spatial working and recognition memories and an open field task that tested levels of hyperactivity. Overexpression of COX-2 in APPswe-PS1dE9 mice resulted in specific deficits in spatial working memory in female but not male mice. These sex-specific deficits were abolished by pharmacological inhibition of COX-2 activity. Importantly, COX-2-associated deficits were dependent on co-expression of all three transgenes since COX-2 single transgenic and APPswe-PS1dE9 bigenic mice showed normal memory. Quantification of amyloid plaque load and total Abeta 40 and 42 peptides did not reveal significant differences in trigenic versus bigenic mice treated with either vehicle or celecoxib. Taken together, these data indicate an interaction between the effects of COX-2 and Abeta peptides on cognition that occurs in a sex-specific manner in the absence of significant changes in amyloid burden. These findings suggest that pathological activation of COX-2 may potentiate the toxicity of Abeta peptides, particularly in females, without significantly affecting Abeta accumulation.

Function of COX-2 and Prostaglandins in Neurological Disease

Induction of COX-2 expression and enzymatic activity promotes neuronal injury in a number of models of neurological disease. Inhibition of COX-2 activity, either genetically or pharmacologically, has been shown to be neuroprotective in rodent models of stroke, Parkinson’s disease, and amyotrophic lateral sclerosis. Inhibition of COX activity with nonsteroidal anti-inflammatory drugs (NSAIDs) reduces inflammation and amyloid accumulation in murine transgenic models of Familial Alzheimer’s disease, and the use of NSAIDs decreases the risk of developing Alzheimer’s disease in healthy aging populations. COX-mediated neuronal injury is presumed be due to downstream effects of one or more prostaglandin products including PGE2, PGD2, PGF2α, PGI2 (prostacylin) and TXA2 (thromboxane) that effect cellular changes through activation of specific prostaglandin receptor subtypes and second messenger systems. In this proceeding, we review recent data demonstrating effects of prostaglandin signaling on neuronal viability that are paradoxically protective, when taken in the context that COX-2 induces neuronal injury in the setting of excitotoxicity. Conversely, in the context of an inflammatory stimulus, the EP2 receptor enhances neuronal injury. These findings argue for an additional level of complexity in the prostaglandin response in neurological disease.