Pellagra is a photosensitivity syndrome characterized by three “D's”: diarrhea, dermatitis, and dementia as a result of niacin deficiency. However, the molecular mechanisms of photosensitivity dermatitis, the hallmark abnormality of this syndrome, remain unclear. We prepared niacin deficient mice in order to develop a murine model of pellagra. Niacin deficiency induced photosensitivity and severe diarrhea with weight loss. In addition, niacin deficient mice exhibited elevated expressions of COX-2 and PGE syntheses (Ptges) mRNA. Consistently, photosensitivity was alleviated by a COX inhibitor, deficiency of Ptges, or blockade of EP4 receptor signaling. Moreover, enhanced PGE2 production in niacin deficiency was mediated via ROS production in keratinocytes. In line with the above murine findings, human skin lesions of pellagra patients confirmed the enhanced expression of Ptges. Niacin deficiency-induced photosensitivity was mediated through EP4 signaling in response to increased PGE2 production via induction of ROS formation.
Bioactive lipids such as the prostaglandins have been reported to have various cytoprotective or toxic properties in acute and chronic neurological conditions. The roles of PGF2α and its receptor (FP) are not clear in the pathogenesis of ischemic brain injury. Considering that this G-protein coupled receptor has been linked to intracellular calcium regulation, we hypothesized that its blockade would be protective. We used FP antagonist (AL-8810) and FP receptor knockout (FP−/−) mice in in vivo and in vitro stroke models. Mice that were treated with AL-8810 had 35.7 ± 6.3% less neurologic dysfunction and 36.4 ± 6.0% smaller infarct volumes than did vehicle-treated mice after 48 hours of permanent middle cerebral artery occlusion (pMCAO); FP−/− mice also had improved outcomes after pMCAO. Blockade of the FP receptor also protected against oxygen-glucose deprivation (OGD)-induced cell death and reactive oxygen species formation in slice cultures. Finally, we found that an FP receptor agonist dose dependently increased intracellular Ca2+ levels in cultured neurons and established that FP-related Ca2+ signaling is related to ryanodine receptor signaling. These results indicate that the FP receptor is involved in cerebral ischemia-induced damage and could promote development of drugs for treatment of stroke and acute neurodegenerative disorders.
cerebral ischemia; inflammation; receptor; stroke; oxygen glucose deprivation
Various kinds of stress are thought to precipitate psychiatric disorders, such as major depression. Whereas studies in rodents have suggested a critical role of medial prefrontal cortex (mPFC) in stress susceptibility, the mechanism of how stress susceptibility is determined through mPFC remains unknown. Here we show a critical role of prostaglandin E2 (PGE2), a bioactive lipid derived from arachidonic acid, in repeated social defeat stress in mice. Repeated social defeat increased the PGE2 level in the subcortical region of the brain, and mice lacking either COX-1, a prostaglandin synthase, or EP1, a PGE receptor, were impaired in induction of social avoidance by repeated social defeat. Given the reported action of EP1 that augments GABAergic inputs to midbrain dopamine neurons, we analyzed dopaminergic response upon social defeat. Analyses of c-Fos expression of VTA dopamine neurons and dopamine turnover in mPFC showed that mesocortical dopaminergic pathway is activated upon social defeat and attenuated with repetition of social defeat in wild-type mice. EP1 deficiency abolished such repeated stress-induced attenuation of mesocortical dopaminergic pathway. Blockade of dopamine D1-like receptor during social defeat restored social avoidance in EP1-deficient mice, suggesting that disinhibited dopaminergic response during social defeat blocks induction of social avoidance. Furthermore, mPFC dopaminergic lesion by local injection of 6-hydroxydopamine, which mimicked the action of EP1 during repeated stress, facilitated induction of social avoidance upon social defeat. Taken together, our data suggest that PGE2-EP1 signaling is critical for susceptibility to repeated social defeat stress in mice through attenuation of mesocortical dopaminergic pathway.
Stroke and Alzheimer’s disease (AD) are major age-related neurodegenerative diseases that may worsen the prognosis of each other. Our study was designed to delineate the prostaglandin E2 EP1 receptor role in AD and in the setting of cerebral ischemia. Genetic deletion of the prostaglandin EP1 receptor significantly attenuated the more severe neuronal damage (38.5 ± 10.6%) and memory loss induced by ischemic insult that observed in AD transgenic mice (percentage of viable hippocampal CA1 neurons: 11.2 ± 2.9%) when compared to wildtype mice (45.1 ± 9.1%). In addition, we found that the amyloid plaques were reduced in EP1 deleted AD mice. Aβ-induced toxicity (18.0 ± 7.1%) and Ca2+ response (91.8 ± 12.9%) were also reduced in EP1−/− neurons compared to control neurons in in vitro. Hence, EP1 might mediate most of the toxicity associated with COX-2 and contribute substantially to the cell death pathways in AD and stroke. Exploring potential therapeutic agent targeting EP1 receptor could potentially benefit treatments for stroke and AD patients.
Beta-amyloid; Cyclooxygenase; Neuroinflammation; Prostaglandin E2; Stroke
Prostaglandin E2 (PGE2) is produced in the skin and is suggested to play a role in the regulation of cutaneous immune homeostasis and responses. However, the multifaceted functions of PGE2 continue to elude our understanding, especially because of the multiplicity of PGE2 receptors—EP1, EP2, EP3, and EP4. While cAMP-elevating EP4 is known to activate the functions of cutaneous dendritic cells (DCs), including Langerhans cells (LCs) and dermal DCs, the role of cAMP-suppressing EP3 in this process remains unknown. Here we demonstrated that an EP3 receptor selective agonist, ONO-AE-248, inhibited chemotaxis and co-stimulatory molecule expressions of DCs in vitro. A suboptimal dose of antigen was sufficient to induce contact hypersensitivity in EP3-deficient mice. Intriguingly, EP3 deficiency did not impair skin inflammation at all when the antigen dose was sufficiently high. EP3 limited the functions of cutaneous DCs only when the antigen dose was low. In contrast to EP4, the observed unappreciated function of EP3 may stabilize the cutaneous DCs to halt the impetuous response to a suboptimal dose of antigen. Taken together, PGE2-EP3 signaling is essential for fine-tuning excessive skin inflammation by restricting DC functions.
Prostanoids are suggested to participate in diabetes pathology, but their roles are controversially discussed. The purpose of the current study was to examine the role of cyclooxygenase (prostaglandin synthase [PTGS]) enzymes and prostaglandin (PG) E2 signaling pathways in streptozotocin (STZ)-induced type 1 diabetes. Blood glucose, insulin, and survival rate were studied in mice with targeted disruption of the genes for PTGS and PGE receptors (PTGERs). PGE2 was found as the main prostanoid formed by the pancreas. Contrarily to PTGS-1, deficiency of PTGS-2 activity significantly amplified STZ effect, causing dramatic loss of insulin production and rise in blood glucose and death rate. STZ metabolism was unaffected by PTGS deficiency. Diabetogenicity of STZ in PTGER1−/−, PTGER2−/−, PTGER3−/−, and PTGER4−/− mice was comparable to control mice. In striking contrast, combined knockout of PTGER2 and PTGER4 by blocking PTGER4 in PTGER2−/− mice strongly enhanced STZ pathology. Treatment of PTGS-2−/− and wild-type mice with PTGER2/PTGER4 agonists partially protected against STZ-induced diabetes and restored β-cell function. Our data uncover a previously unrecognized protective role of PTGS-2–derived PGE2 in STZ-induced diabetes mediated by the receptor types PTGER2 and PTGER4. These findings offer the possibility to intervene in early progression of type 1 diabetes by using PTGER-selective agonists.
Idiopathic pulmonary fibrosis (IPF) is a devastating lung disease of unknown etiology with few current treatment options. Recently, we determined an important role of prostaglandin F2α (PGF2α) in pulmonary fibrosis by using a bleomycin-induced pulmonary fibrosis model and found an abundance of PGF2α in bronchoalveolar lavage fluid of IPF patients. We investigated the role of PGF2α in human IPF by assessing plasma concentrations of 15-keto-dihydro PGF2α, a stable metabolite of PGF2α.
We measured plasma concentrations of 15-keto-dihydro PGF2α in 91 IPF patients and compared these values with those of controls (n = 25). We further investigated the relationships of plasma 15-keto-dihydro PGF2α concentrations with disease severity and mortality.
Plasma concentrations of 15-keto-dihydro PGF2α were significantly higher in IPF patients than controls (p<0.001). Plasma concentrations of this metabolite were significantly correlated with forced expiratory volume in 1 second (Rs [correlation coefficient] = −0.34, p = 0.004), forced vital capacity (Rs = −0.33, p = 0.005), diffusing capacity for carbon monoxide (Rs = −0.36, p = 0.003), the composite physiologic index (Rs = 0.40, p = 0.001), 6-minute walk distance (Rs = −0.24, p = 0.04) and end-exercise oxygen saturation (Rs = −0.25, p = 0.04) when patients with emphysema were excluded. Multivariate analysis using stepwise Cox proportional hazards model showed that a higher composite physiologic index (relative risk = 1.049, p = 0.002) and plasma 15-keto-dihydro PGF2α concentrations (relative risk = 1.005, p = 0.002) were independently associated with an increased risk of mortality.
We demonstrated significant associations of plasma concentrations of PGF2α metabolites with disease severity and prognosis, which support a potential pathogenic role for PGF2α in human IPF.
Although hemin-mediated neurotoxicity has been linked to the production of free radicals and glutamate excitotoxicity, the role of the prostaglandin E2 (PGE2)-EP1 receptor remains unclear. Activation of the EP1 receptor in neurons results in increased intracellular calcium levels; therefore, we hypothesize that the blockade of the EP1 receptor reduces hemin neurotoxicity. Using postnatal primary cortical neurons cultured from wild-type (WT) and EP1−/− mice, we investigated the EP1 receptor role in hemin neurotoxicity measured by lactate dehydrogenase (LDH) cell survival assay. Hemin (75 μM) induced greater release of LDH in WT (34.7 ± 4.5%) than in EP1−/− (27.6 ± 3.3%) neurons. In the presence of the EP1 receptor antagonist SC-51089, the hemin-induced release of LDH decreased. To further investigate potential mechanisms of action, we measured changes in the intracellular calcium level [Ca2+]i following treatment with 17-phenyl trinor PGE2 (17-pt-PGE2) a selective EP1 agonist. In the WT neurons, 17-pt-PGE2 dose-dependently increased [Ca2+]i. However, in EP1−/− neurons, [Ca2+]i was significantly attenuated. We also revealed that hemin dose-dependently increased [Ca2+]i in WT neurons, with a significant decrease in EP1−/− neurons. Both 17-pt-PGE2 and hemin-induced [Ca2+]i were abolished by N-methyl-D-aspartic (NMDA) acid receptor and ryanodine receptor blockers. These results suggest that blockade of the EP1 receptor may be protective against hemin neurotoxicity in vitro. We speculate that the mechanism of hemin neuronal death involves [Ca2+]i mediated by NMDA acid receptor-mediated extracellular Ca2+ influx and EP1 receptor-mediated intracellular release from ryanodine receptor-operated Ca2+ stores. Therefore, blockade of the EP1 receptor could be used to minimize neuronal damage following exposure to supraphysiological levels of hemin.
calcium; GPCR; heme; neuroinflammation; prostaglandin
Regulation of the actin cytoskeleton is crucial for cell morphology and migration. One of the key molecules that regulates actin remodeling is the small GTPase Rho. Rho shuttles between the inactive GDP-bound form and the active GTP-bound form, and works as a molecular switch in actin remodeling in response to both extra- and intra-cellular stimuli. Mammalian homolog of Diaphanous (mDia) is one of the Rho effectors and produces unbranched actin filaments. While Rho GTPases activate mDia, the mechanisms of how the activity of mDia is downregulated in cells remains largely unknown. In our recent paper, we identified Liprin-α as an mDia interacting protein and found that Liprin-α negatively regulates the activity of mDia in the cell by displacing it from the plasma membrane through binding to the DID-DD region of mDia. Here, we review these findings and discuss how Liprin-α regulates the Rho-mDia pathway and how the mDia-Liprin-α complex functions in vivo.
Liprin; Rho; actin cytoskeleton; formin; mDia
Intestinal resident macrophages play an important role in gastrointestinal dysmotility by producing prostaglandins (PGs) and nitric oxide (NO) in inflammatory conditions. The causal correlation between PGs and NO in gastrointestinal inflammation has not been elucidated. In this study, we examined the possible role of PGE2 in the LPS-inducible inducible NO synthase (iNOS) gene expression in murine distal ileal tissue and macrophages. Treatment of ileal tissue with LPS increased the iNOS and cyclooxygenase (COX)-2 gene expression, which lead to intestinal dysmotility. However, LPS did not induce the expression of iNOS and COX-2 in tissue from macrophage colony-stimulating factor-deficient op/op mice, indicating that these genes are expressed in intestinal resident macrophages. iNOS and COX-2 protein were also expressed in dextran-phagocytized macrophages in the muscle layer. CAY10404, a COX-2 inhibitor, diminished LPS-dependent iNOS gene upregulation in wild-type mouse ileal tissue and also in RAW264.7 macrophages, indicating that PGs upregulate iNOS gene expression. EP2 and EP4 agonists upregulated iNOS gene expression in ileal tissue and isolated resident macrophages. iNOS mRNA induction mediated by LPS was decreased in the ileum isolated from EP2 or EP4 knockout mice. In addition, LPS failed to decrease the motility of EP2 and EP4 knockout mice ileum. EP2- or EP4-mediated iNOS expression was attenuated by KT-5720, a PKA inhibitor and PD-98059, an ERK inhibitor. Forskolin or dibutyryl-cAMP mimics upregulation of iNOS gene expression in macrophages. In conclusion, COX-2-derived PGE2 induces iNOS expression through cAMP/ERK pathways by activating EP2 and EP4 receptors in muscularis macrophages. NO produced in muscularis macrophages induces dysmotility during gastrointestinal inflammation.
inflammation; intestinal motility; nitric oxide; prostaglandins
During development of the central nervous system, the apical-basal polarity of neuroepithelial cells is critical for homeostasis of proliferation and differentiation of neural stem cells. While adherens junctions at the apical surface of neuroepithelial cells are important for maintaining the polarity, the molecular mechanism regulating integrity of these adherens junctions remains largely unknown. Given the importance of actin cytoskeleton in adherens junctions, we have analyzed the role of mDia, an actin nucleator and a Rho effector, in the integrity of the apical adherens junction. Here we show that mDia1 and mDia3 are expressed in the developing brain, and that mDia3 is concentrated in the apical surface of neuroepithelium. Mice deficient in both mDia1 and mDia3 develop periventricular dysplastic mass widespread throughout the developing brain, where neuroepithelial cell polarity is impaired with attenuated apical actin belts and loss of apical adherens junctions. In addition, electron microscopic analysis revealed abnormal shrinkage and apical membrane bulging of neuroepithelial cells in the remaining areas. Furthermore, perturbation of Rho, but not that of ROCK, causes loss of the apical actin belt and adherens junctions similarly to mDia-deficient mice. These results suggest that actin cytoskeleton regulated by Rho-mDia pathway is critical for the integrity of the adherens junctions and the polarity of neuroepithelial cells, and that loss of this signaling induces aberrant, ectopic proliferation and differentiation of neural stem cells.
The cardiovascular complications reported to be associated with cyclooxygenase inhibitor use have shifted our focus toward prostaglandins and their respective receptors. Prostaglandin D2 and its DP1 receptor have been implicated in various normal and pathologic conditions, but their role in stroke is still poorly defined. Here, we tested whether DP1 deletion aggravates N-methyl-d-aspartic acid (NMDA)-induced acute toxicity and whether DP1 pharmacologic activation protects mice from acute excitotoxicity and transient cerebral ischemia. Moreover, since the elderly are more vulnerable to stroke-related damage than are younger patients, we tested the susceptibility of aged DP1 knockout (DP1−/−) mice to brain damage. We found that intrastriatal injection of 15 nmol NMDA caused significantly larger lesion volumes (27.2 ± 6.4%) in young adult DP1−/− mice than in their wild-type counterparts. Additionally, intracerebroventricular pretreatment of wild-type mice with 10, 25, and 50 nmol of the DP1-selective agonist BW245C significantly attenuated the NMDA-induced lesion size by 19.5 ± 5.0%, 39.6 ± 7.7%, and 28.9 ± 7.0%, respectively. The lowest tested dose of BW245C also was able to reduce middle cerebral artery occlusion-induced brain infarction size significantly (21.0 ± 5.7%). Interestingly, the aggravated NMDA-induced brain damage was persistent in older DP1−/− mice as well. We conclude that the DP1 receptor plays an important role in attenuating brain damage and that selective targeting of this receptor could be considered as an adjunct therapeutic tool to minimize stroke damage.
BW245C; G-protein-coupled receptors; Mouse; Neurodegeneration; Neuroprotection; NMDA; Prostaglandins
The small GTPase Rho regulates cell morphogenesis through remodeling of the actin cytoskeleton. While Rho is overexpressed in many clinical cancers, the role of Rho signaling in oncogenesis remains unknown. mDia1 is a Rho effector producing straight actin filaments. Here we transduced mouse embryonic fibroblasts from mDia1-deficient mice with temperature-sensitive v-Src and examined the involvement and mechanism of the Rho-mDia1 pathway in Src-induced oncogenesis. We showed that in v-Src-transduced mDia1-deficient cells, formation of actin filaments is suppressed, and v-Src in the perinuclear region does not move to focal adhesions upon a temperature shift. Consequently, membrane translocation of v-Src, v-Src-induced morphological transformation, and podosome formation are all suppressed in mDia1-deficient cells with impaired tyrosine phosphorylation. mDia1-deficient cells show reduced transformation in vitro as examined by focus formation and colony formation in soft agar and exhibit suppressed tumorigenesis and invasion when implanted in nude mice in vivo. Given overexpression of c-Src in various cancers, these findings suggest that Rho-mDia1 signaling facilitates malignant transformation and invasion by manipulating the actin cytoskeleton and targeting Src to the cell periphery.
Diaphanous-related formin, mDia, is an actin nucleation/polymerization factor functioning downstream of the small GTPase Rho. We found that, in addition to the Rho GTPase-mediated activation, the interaction between mDia2 and anillin is required for the localization and function of mDia2 in cytokinesis.
Diaphanous-related formin, mDia, is an actin nucleation/polymerization factor functioning downstream of the small GTPase Rho. Although Rho is critically involved in cytokinesis, it remains elusive how Rho effectors and other regulators of cytoskeletons work together to accomplish this process. Here we focused on mDia2, an mDia isoform involved in cytokinesis of NIH 3T3 cells, and analyzed mechanisms of its localization in cytokinesis. We found that targeting of mDia2 to the cleavage furrow requires not only its binding to RhoA but also its diaphanous-inhibitory domain (DID). We then performed pulldown assays using a fragment containing the latter domain as a bait and identified anillin as a novel mDia2 interaction partner. The anillin-binding is competitive with the diaphanous autoregulatory domain (DAD) of mDia2 in its autoinhibitory interaction. A series of RNA interference and functional rescue experiments has revealed that, in addition to the Rho GTPase-mediated activation, the interaction between mDia2 and anillin is required for the localization and function of mDia2 in cytokinesis.
The prostaglandin E2 EP2 receptor has been shown to be important in dictating outcomes in various neuroinflammatory disorders. Here, we investigated the importance of the EP2 receptor in short- and long-term ischemic outcomes by subjecting wildtype (WT) and EP2 knockout (EP2-/-) mice to two distinct and complementary stroke models [transient and permanent middle cerebral artery occlusion (tMCAO and pMCAO)] and by using the EP2 receptor agonist ONO-AE1-259-01.
First, WT and EP2-/- mice were subjected to 90-min tMCAO with a monofilament followed by 4-day reperfusion. Second, WT mice were infused intracerebroventricularly with vehicle or ONO-AE1-259-01 45-50 min before being subjected to tMCAO. Finally, WT and EP2-/- mice were subjected to pMCAO and allowed to survive for an extended period of 7 days.
Infarct volumes in EP2-/- mice were 55.0 ± 9.1% larger after tMCAO and 33.3 ± 8.6% larger after pMCAO than those in WT mice. Neurobehavioral deficits also were significantly greater in the EP2-/- mice. These results suggest that EP2 is beneficial and that activation is sustained for days after the stroke. We also found that pharmacologic activation of EP2 with 1.0- and 2.0-nmol doses of ONO-AE1-259-01 was sufficient to significantly reduce the infarct volume in WT mice compared with that in vehicle-treated controls (20.1 ± 3.9% vs. 37.1 ± 4.6%). This reduction correlated with improved neurologic scores. No significant effect on physiologic parameters was observed.
Together, our results reveal that pharmacologic stimulation of the EP2 receptor has an important beneficial role in cerebral ischemia and might be considered as an adjunct therapy for ischemic stroke.
Rho GTPases are thought to mediate the action of several axonal growth inhibitors in the adult brain and spinal cord. RhoA has been targeted pharmacologically in both humans and animals to promote neurite outgrowth and functional recovery following CNS trauma. However, rat spinal cord injury studies suggest a complicated and partial benefit of inhibiting Rho or its downstream effector, Rho-associated kinase (ROCKII). This limited benefit may reflect inhibition of other kinases, poor access, or a minimal role of ROCKII in vivo. Therefore, we studied ROCKII mutant mice to probe this pathway genetically. ROCKII−/− dorsal root ganglion neurons are less sensitive to inhibition by Nogo protein or by chondroitin sulfate proteoglycan in vitro. We examined adult ROCKII−/− mice in two injury paradigms, cervical multilevel dorsal rhizotomy and midthoracic dorsal spinal cord hemisection. After dorsal root crush injury, the ROCKII−/− mice recovered use of the affected forepaw more quickly than did controls. Moreover, multiple classes of sensory axons regenerated across the dorsal root entry zone into the spinal cord of mice lacking ROCKII. After the spinal cord injury, ROCKII−/− mice showed enhanced local growth of raphespinal axons in the caudal spinal cord and corticospinal axons into the lesion site. Improved functional recovery was not observed by Basso Mouse Scale score following dorsal hemisection, likely due to developmental defects in the nervous system. Together, these findings demonstrate that the ROCKII gene product limits axonal growth after CNS trauma.
To clarify the intraocular pressure (IOP)‐lowering profile of tafluprost, a newly synthesised prostaglandin F2α analogue, in mice.
C57BL/6J, and EP1, EP2, EP3 and postaglandin F (FP) receptor‐deficient wild‐type (WT), EP1KO, EP2KO, EP3KO and FPKO, respectively mice were bred and acclimatised under a 12‐h (6:00–18:00) light–dark cycle. To evaluate effects of tafluprost (0.002%) on IOP at night, a single 3 µl drop of tafluprost solution was applied topically at 18:00 once into one eye in each mouse. IOP was measured 3 h after the application with a microneedle method. To clarify whether endogenous prostaglandin is concerned with the tafluprost‐induced IOP reduction, we applied 0.1% diclofenac Na, a cyclo‐oxygenase inhibitor or PBS 30 min before the application of tafluprost in WT and EP3KO mice and measured IOP 3 h after the tafluprost application. We also determined whether animals responded predictably to 0.1% bunazosin HCl, a drug known to increase uveoscleral outflow.
3 h after the application of 0.0015% tafluprost, mean (SEM) IOP reductions were 25.8 (2.1)% 26.3 (0.8)% 24.2 (1.4)% 16.5 (1.7)% and −0.9 (1.5)% in WT, EP1KO, EP2KO, EP3KO and FPKO mice, respectively. IOP reductions in EP3KO and FPKO mice were significantly smaller than in WT mice. Pretreatment with diclofenac Na significantly attenuated the IOP lowering effect of tafluprost in WT mice but not in EP3KO mice. Bunazosin HCl lowered IOP significantly in all genotypes by the same amount.
We conclude that tafluprost lowers IOP through the prostanoid FP receptor. A part of ocular hypotensive effect of tafluprost is attributed to FP receptor‐mediated prostaglandin production acting through the prostanoid EP3 receptor.
Ischemic stroke is one of the leading causes of mortality and morbidity in humans. During brain ischemia and the subsequent reperfusion that occurs with stroke, the generation of the so-called “proinflammatory” prostaglandin E2 (PGE2) increases significantly. Therefore, interest is growing regarding the differential functions of the individual PGE2 receptors (EP1–4) and their relative contribution to brain damage following ischemic and inflammatory stimuli. Here, we address the contribution of the EP3 receptor in dictating early outcomes after transient cerebral ischemia. An oxygen-glucose deprivation (OGD)-induced in vitro model of brain ischemia was used in mouse hippocampal slice cultures. For transient ischemia, the right middle cerebral artery (MCA) of wildtype (WT) and EP3 knockout (EP3−/−) C57BL/6 male mice was occluded for 90 min and reperfused for 48 or 96 h, after which neurobehavioral scores and infarct volumes were determined. Mean arterial blood pressure, pH, blood gases (PaO2 and PaCO2), cerebral blood flow, and body temperature were also determined before and during ischemia and reperfusion. OGD-induced cell death was significantly lower in brain slice cultures of EP3−/− mice than in those of WT mice. EP3−/− mice that underwent transient ischemia had significantly smaller infarct volumes than did WT mice at 48 h, but this difference was not sustained at 96 h. Neurological score deficits correlated with infarct volume, but no significant differences in the physiological parameters monitored were detected between the two genotypes. The results further support a role for EP3 receptors in contributing to acute ischemic stroke, but EP3 is not likely the sole contributor to the long-term detrimental consequences of PGE2.
EP3 receptor; focal cerebral ischemia; oxygen glucose deprivation; prostanoids
Cdc42 and Rac family GTPases are important regulators of morphology, motility, and polarity in a variety of mammalian cell types. However, comprehensive analysis of their roles in the morphological and behavioral aspects of chemotaxis within a single experimental system is still lacking. Here we demonstrate using a direct viewing chemotaxis assay that of all of the Cdc42/Rac1-related GTPases expressed in primary fibroblasts, Cdc42, Rac1, and RhoG are required for efficient migration towards platelet-derived growth factor (PDGF). During migration, Cdc42-, Rac1-, and RhoG-deficient cells show aberrant morphology characterized as cell elongation and cell body rounding, loss of lamellipodia, and formation of thick membrane extensions, respectively. Analysis of individual cell trajectories reveals that cell speed is significantly reduced, as well as persistence, but to a smaller degree, while the directional response to the gradient of PDGF is not affected. Combined knockdown of Cdc42, Rac1, and RhoG results in greater inhibition of cell speed than when each protein is knocked down alone, but the cells are still capable of migrating toward PDGF. We conclude that, Cdc42, Rac1, and RhoG function cooperatively during cell migration and that, while each GTPase is implicated in the control of morphology and cell speed, these and other Cdc42/Rac-related GTPases are not essential for the directional response toward PDGF.
Overexpression of prostacyclin synthase (PGIS) decreases lung tumor multiplicity in chemical and cigarette-smoke induced murine lung cancer models. Prostacyclin signals through a single G-protein coupled receptor (IP), which signals through cAMP. To determine the role of this receptor in lung cancer chemoprevention by prostacyclin, PGIS-overexpressing mice were crossed to mice that lack the IP receptor (IP (−/−)). Carcinogen-induced lung tumor incidence was similar in IP(+/+), IP(+/−) and IP(−/−) mice, and overexpression of PGIS gave equal protection in all three groups, indicating that the protective effects of prostacyclin are not mediated through activation of IP. Since prostacyclin can activate members of the PPAR family of nuclear receptors, we examined the role of PPARγ in prostacyclin’s protection against lung tumorigenesis. Iloprost, a stable prostacyclin analog, activated PPARγ in non-transformed bronchial epithelial cells and in a subset of human non-small cell lung cancer cell lines (NSCLC). Iloprost-impregnated chow fed to wild-type mice resulted in elevated lung macrophages and decreased lung tumor formation. Transgenic animals with lung specific PPARγ-overexpression also developed fewer lung tumors. This reduction was not enhanced by administration of supplemental iloprost. These studies indicate that PPARγ is a critical target for prostacyclin mediated lung cancer chemoprevention, and may also have therapeutic activity.
The mechanism of lamellipod actin turnover is still under debate. To clarify the intracellular behavior of the recently-identified actin disruption mechanism, we examined kinetics of AIP1 using fluorescent single-molecule speckle microscopy. AIP1 is thought to cap cofilin-generated actin barbed ends. Here we demonstrate a reduction in actin-associated AIP1 in lamellipodia of cells overexpressing LIM-kinase. Moreover, actin-associated AIP1 was rapidly abolished by jasplakinolide, which concurrently blocked the F-actin-cofilin interaction. Jasplakinolide also slowed dissociation of AIP1, which is analogous to the effect of this drug on capping protein. These findings provide in vivo evidence of the association of AIP1 with barbed ends generated by cofilin-catalyzed filament disruption. Single-molecule observation found distribution of F-actin-associated AIP1 throughout lamellipodia, and revealed even faster dissociation of AIP1 than capping protein. The estimated overall AIP1-associated actin disruption rate, 1.8 µM/s, was one order of magnitude faster than Arp2/3 complex-catalyzed actin nucleation in lamellipodia. This rate does not suffice the filament severing rate predicted in our previous high frequency filament severing-annealing hypothesis. Our data together with recent biochemical studies imply barbed end-preferred frequent filament disruption. Frequent generation of AIP1-associated barbed ends and subsequent release of AIP1 may be the mechanism that facilitates previously observed ubiquitous actin polymerization throughout lamellipodia.
Prostaglandin D2 is the most abundant prostaglandin in the brain. It has long been described as a modulator of the neuroinflammatory process, but little is known regarding the role of its Gαs-coupled receptor, DP1. Therefore, in this study, the effect of the DP1 receptor on the outcome of cerebral ischemia in wildtype (WT) and DP1 knockout (DP1−/−) C57Bl/6 mice was investigated. Ischemia-reperfusion injury was produced by a 90-min occlusion of the right middle cerebral artery followed by a 4-day reperfusion. Infarct size was 49.0 ± 11.0% larger in DP1−/− mice (n = 11; P < 0.01) than in WT mice (n = 9 per group). However, no differences were detected in the relative cerebral blood flow (CBF) or any of the physiological parameters measured (n = 5 per group) or in the large blood vessel anatomy (n = 3 per group). To further address whether the DP1 protective role in the brain could be extended to neurons, mouse primary corticostriatal neuronal cultures were exposed to the DP1-selective agonist, BW245C, which provided dose-dependent protection against excitotoxicity induced by glutamate. Protection was significant at a dose as low as 0.05 μm. The results indicate that the DP1 receptor is neuroprotective in both in vivo and in vitro paradigms. Development of drugs to stimulate the DP1 receptor in brain could provide a new therapeutic strategy against cerebral ischemia and potentially other neurological conditions.
BW245C; focal ischemia; mouse; neuroprotection; prostaglandins; stroke
mDia proteins are mammalian homologues of Drosophila diaphanous and belong to the formin family proteins that catalyze actin nucleation and polymerization. Although formin family proteins of nonmammalian species such as Drosophila diaphanous are essential in cytokinesis, whether and how mDia proteins function in cytokinesis remain unknown. Here we depleted each of the three mDia isoforms in NIH 3T3 cells by RNA interference and examined this issue. Depletion of mDia2 selectively increased the number of binucleate cells, which was corrected by coexpression of RNAi-resistant full-length mDia2. mDia2 accumulates in the cleavage furrow during anaphase to telophase, and concentrates in the midbody at the end of cytokinesis. Depletion of mDia2 induced contraction at aberrant sites of dividing cells, where contractile ring components such as RhoA, myosin, anillin, and phosphorylated ERM accumulated. Treatment with blebbistatin suppressed abnormal contraction, corrected localization of the above components, and revealed that the amount of F-actin at the equatorial region during anaphase/telophase was significantly decreased with mDia2 RNAi. These results demonstrate that mDia2 is essential in mammalian cell cytokinesis and that mDia2-induced F-actin forms a scaffold for the contractile ring and maintains its position in the middle of a dividing cell.
Prostaglandin E2 (PGE2) exerts its actions via four subtypes of the PGE receptor, EP1–4. We show that mice deficient in EP1 exhibited significantly attenuated Th1 response in contact hypersensitivity induced by dinitrofluorobenzene (DNFB). This phenotype was recapitulated in wild-type mice by administration of an EP1-selective antagonist during the sensitization phase, and by adoptive transfer of T cells from sensitized EP1−/− mice. Conversely, an EP1-selective agonist facilitated Th1 differentiation of naive T cells in vitro. Finally, CD11c+ cells containing the inducible form of PGE synthase increased in number in the draining lymph nodes after DNFB application. These results suggest that PGE2 produced by dendritic cells in the lymph nodes acts on EP1 in naive T cells to promote Th1 differentiation.
Trafficking of immune cells is controlled by directed migration of relevant cells toward chemotactic signals. Actin cytoskeleton undergoes continuous remodeling and serves as machinery for cell migration. The mDia family of formins and the Wiskott-Aldrich syndrome protein (WASP)–Arp2/3 system are two major actin nucleating–polymerizing systems in mammalian cells, with the former producing long straight actin filaments and the latter producing branched actin meshwork. Although much is known about the latter, the physiological functions of mDia proteins are unclear. We generated mice deficient in one mDia isoform, mDia1. Although mDia1−/− mice were born and developed without apparent abnormality, mDia1−/− T lymphocytes exhibited impaired trafficking to secondary lymphoid organs in vivo and showed reduced chemotaxis, little actin filament formation, and impaired polarity in response to chemotactic stimuli in vitro. Similarly, mDia1−/− thymocytes showed reduced chemotaxis and impaired egression from the thymus. These results suggest that mDia1 plays a distinct role in chemotaxis in T lymphocyte trafficking.