Generation of a conditional allele of the mouse prostaglandin EP4 receptor

Prostaglandin E2 acts via bone marrow macrophages to block PTH-stimulated osteoblast differentiation in vitro

Intermittent PTH is the major anabolic therapy for osteoporosis while continuous PTH causes bone loss. PTH acts on the osteoblast (OB) lineage to regulate bone resorption and formation. PTH also induces cyclooxygenase-2 (COX-2), producing prostaglandin E2 (PGE(2)) that can act on both OBs and osteoclasts (OCs). Because intermittent PTH is more anabolic in Cox-2 knockout (KO) than wild type (WT) mice, we hypothesized COX-2 might contribute to the effects of continuous PTH by suppressing PTH-stimulated differentiation of mesenchymal stem cells into OBs. We compared effects of continuous PTH on bone marrow stromal cells (BMSCs) and primary OBs (POBs) from Cox-2 KO mice, mice with deletion of PGE(2) receptors (Ptger(4) and Ptger(2) KO mice), and WT controls. PTH increased OB differentiation in BMSCs only in the absence of COX-2 expression or activity. In the absence of COX-2, PTH stimulated differentiation if added during the first week of culture. In Cox-2 KO BMSCs, PTH-stimulated differentiation was prevented by adding PGE(2) to cultures. Co-culture of POBs with M-CSF-expanded bone marrow macrophages (BMMs) showed that the inhibition of PTH-stimulated OB differentiation required not only COX-2 or PGE(2) but also BMMs. Sufficient PGE(2) to mediate the inhibitory effect was made by either WT POBs or WT BMMs. The inhibitory effect mediated by COX-2/PGE(2) was transferred by conditioned media from RANKL-treated BMMs and could be blocked by osteoprotegerin, which interferes with RANKL binding to its receptor on OC lineage cells. Deletion of Ptger(4), but not Ptger(2), in BMMs prevented the inhibition of PTH-stimulated OB differentiation. As expected, PGE(2) also stimulated OB differentiation, but when given in combination with PTH, the stimulatory effects of both were abrogated. These data suggest that PGE(2), acting via EP4R on BMMs committed to the OC lineage, stimulated secretion of a factor or factors that acted to suppress PTH-stimulated OB differentiation. This suppression of OB differentiation could contribute to the bone loss seen with continuous PTH in vivo.

Differential stem- and progenitor-cell trafficking by prostaglandin E2

To maintain lifelong production of blood cells, hematopoietic stem cells (HSC) are tightly regulated by inherent programs and extrinsic regulatory signals received from their microenvironmental niche. Long-term repopulating HSC (LT-HSC) reside in several, perhaps overlapping, niches that produce regulatory molecules/signals necessary for homeostasis and increased output following stress/injury ^1–5. Despite significant advances in specific cellular or molecular mechanisms governing HSC/niche interactions, little is understood about regulatory function within the intact mammalian hematopoietic niche. Recently, we and others described a positive regulatory role for Prostaglandin E₂ (PGE₂) on HSC function ex vivo^6,7. While exploring the role of endogenous PGE₂ we unexpectedly observed hematopoietic egress after nonsteroidal anti-inflammatory drug (NSAID) treatment. Surprisingly, this was independent of the SDF-1/CXCR4 axis. Stem and progenitor cells were found to have differing mechanisms of egress, with HSC transit to the periphery dependent on niche attenuation and reduction in the retentive molecule osteopontin (OPN). Hematopoietic grafts mobilized with NSAIDs had superior repopulating ability and long-term engraftment. Treatment of non-human primates and healthy human volunteers confirmed NSAID-mediated egress in higher species. PGE₂ receptor knockout mice demonstrated that progenitor expansion and stem/progenitor egress resulted from reduced EP4 receptor signaling. These results not only uncover unique regulatory roles for EP4 signaling in HSC retention in the niche but also define a rapidly translatable strategy to therapeutically enhance transplantation.

Cancer-induced anorexia in tumor-bearing mice is dependent on cyclooxygenase-1

It is well-established that prostaglandins (PGs) affect tumorigenesis, and evidence indicates that PGs also are important for the reduced food intake and body weight loss, the anorexia-cachexia syndrome, in malignant cancer. However, the identity of the PGs and the PG producing cyclooxygenase (COX) species responsible for cancer anorexia-cachexia is unknown. Here, we addressed this issue by transplanting mice with a tumor that elicits anorexia. Meal pattern analysis revealed that the anorexia in the tumor-bearing mice was due to decreased meal frequency. Treatment with a non-selective COX inhibitor attenuated the anorexia, and also tumor growth. When given at manifest anorexia, non-selective COX-inhibitors restored appetite and prevented body weight loss without affecting tumor size. Despite COX-2 induction in the cerebral blood vessels of tumor-bearing mice, a selective COX-2 inhibitor had no effect on the anorexia, whereas selective COX-1 inhibition delayed its onset. Tumor growth was associated with robust increase of PGE(2) levels in plasma - a response blocked both by non-selective COX-inhibition and by selective COX-1 inhibition, but not by COX-2 inhibition. However, there was no increase in PGE(2)-levels in the cerebrospinal fluid. Neutralization of plasma PGE(2) with specific antibodies did not ameliorate the anorexia, and genetic deletion of microsomal PGE synthase-1 (mPGES-1) affected neither anorexia nor tumor growth. Furthermore, tumor-bearing mice lacking EP(4) receptors selectively in the nervous system developed anorexia. These observations suggest that COX-enzymes, most likely COX-1, are involved in cancer-elicited anorexia and weight loss, but that these phenomena occur independently of host mPGES-1, PGE(2) and neuronal EP(4) signaling.

Prostaglandin E2-mediated attenuation of mesocortical dopaminergic pathway is critical for susceptibility to repeated social defeat stress in mice

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 E(2) (PGE(2)), a bioactive lipid derived from arachidonic acid, in repeated social defeat stress in mice. Repeated social defeat increased the PGE(2) 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 PGE(2)-EP1 signaling is critical for susceptibility to repeated social defeat stress in mice through attenuation of mesocortical dopaminergic pathway.

Cyclooxygenases and lipoxygenases in cancer

Cancer initiation and progression are multistep events that require cell proliferation, migration, extravasation to the blood or lymphatic vessels, arrest to the metastatic site, and ultimately secondary growth. Tumor cell functions at both primary or secondary sites are controlled by many different factors, including growth factors and their receptors, chemokines, nuclear receptors, cell-cell interactions, cell-matrix interactions, as well as oxygenated metabolites of arachidonic acid. The observation that cyclooxygenases and lipoxygenases and their arachidonic acid-derived eicosanoid products (prostanoids and HETEs) are expressed and produced by tumor cells, together with the finding that these enzymes can regulate cell growth, survival, migration, and invasion, has prompted investigators to analyze the roles of these enzymes in cancer progression. In this review, we focus on the contribution of cyclooxygenase- and lipoxygenase-derived eicosanoids to tumor cell function in vitro and in vivo and discuss hope and tribulations of targeting these enzymes for cancer prevention and treatment.

Current Perspectives on Pathobiology of the Ductus Arteriosus

The ductus arteriosus (DA) shunts blood away from the lungs during fetal life, but at birth this shunt is no longer needed and the vessel rapidly constricts. Postnatal persistence of the DA, patent ductus arteriosus (PDA), is predominantly a detrimental condition for preterm infants but is simultaneously a condition required to maintain systemic blood flow for infants born with certain severe congenital heart defects. Although PDA in preterm infants is associated with significant morbidities, there is controversy regarding whether PDA is truly causative. Despite advances in our understanding of the pathobiology of PDA, the optimal treatment strategy for PDA in preterm infants is unclear. Here we review recent studies that have continued to elucidate the fundamental mechanisms of DA development and pathogenesis.

International Union of Basic and Clinical Pharmacology. LXXXIII: classification of prostanoid receptors, updating 15 years of progress

It is now more than 15 years since the molecular structures of the major prostanoid receptors were elucidated. Since then, substantial progress has been achieved with respect to distribution and function, signal transduction mechanisms, and the design of agonists and antagonists (http://www.iuphar-db.org/DATABASE/FamilyIntroductionForward?familyId=58). This review systematically details these advances. More recent developments in prostanoid receptor research are included. The DP(2) receptor, also termed CRTH2, has little structural resemblance to DP(1) and other receptors described in the original prostanoid receptor classification. DP(2) receptors are more closely related to chemoattractant receptors. Prostanoid receptors have also been found to heterodimerize with other prostanoid receptor subtypes and nonprostanoids. This may extend signal transduction pathways and create new ligand recognition sites: prostacyclin/thromboxane A(2) heterodimeric receptors for 8-epi-prostaglandin E(2), wild-type/alternative (alt4) heterodimers for the prostaglandin FP receptor for bimatoprost and the prostamides. It is anticipated that the 15 years of research progress described herein will lead to novel therapeutic entities.

Regulation of endothelial cell functions by basement membrane- and arachidonic acid-derived products

Angiogenesis, the formation of new blood vessels from preexisting vasculature, is required for normal physiological as well as pathological events. The angiogenic process requires endothelial cells to proliferate, migrate, and undergo tubulogenesis. These multistep processes necessitate secretion of pro-angiogenic growth factors, activation of specific intracellular signaling, and interaction of endothelial cells with basement membrane (BM) extracellular matrix components. The generation and release of angiogenic molecules are highly regulated and are influenced by numerous factors, including BM-derived fragments, proteolytic enzymes, as well as metabolites of arachidonic acid (AA). The interactions between these key modulators of angiogenesis is extremely complex, as AA metabolites can regulate the synthesis of soluble angiogenic factors, BM components, as well as enzymes capable of cleaving BM components, which result in the generation of pro- and/or anti-angiogenic products. Furthermore, some BM-derived fragments can alter the expression of AA-converting enzymes and consequently the synthesis of angiogenic factors. In this review we describe the relationship between BM components and AA metabolites with respect to the regulation of endothelial cell functions in health and disease.

A maladaptive role for EP4 receptors in podocytes

Inhibition of p38 mitogen-activated protein kinase and cyclooxygenase-2 reduces albuminuria in models of chronic kidney disease marked by podocyte injury. Previously, we identified a feedback loop in podocytes whereby an in vitro surrogate for glomerular capillary pressure (i.e., mechanical stretch) along with prostaglandin E(2) stimulation of its EP4 receptor induced cyclooxygenase-2 in a p38-dependent manner. Here we asked whether stimulation of EP4 receptors would exacerbate glomerulopathies associated with enhanced glomerular capillary pressure. We generated mice with either podocyte-specific overexpression or depletion of the EP4 receptor (EP4(pod+) and EP4(pod-/-), respectively). Glomerular prostaglandin E(2)-stimulated cAMP levels were eightfold greater for EP4(pod+) mice compared with nontransgenic (non-TG) mice. In contrast, EP4 mRNA levels were >50% lower, and prostaglandin E(2)-induced cAMP synthesis was absent in podocytes isolated from EP4(pod-/-) mice. Non-TG and EP4(pod+) mice underwent 5/6 nephrectomy and exhibited similar increases in systolic BP (+25 mmHg) by 4 weeks compared with sham-operated controls. Two weeks after nephrectomy, the albumin-creatinine ratio of EP4(pod+) mice (3438 μg/mg) was significantly higher than that of non-TG mice (773 μg/mg; P < 0.0001). Consistent with more severe renal injury, the survival rate for nephrectomized EP4(pod+) mice was significantly lower than that for non-TG mice (14 versus 67%). In contrast, 6 weeks after nephrectomy, the albumin-creatinine ratio of EP4(pod-/-) mice (753 μg/mg) was significantly lower than that of non-TG mice (2516 μg/mg; P < 0.05). These findings suggest that prostaglandin E(2), acting via EP4 receptors contributes to podocyte injury and compromises the glomerular filtration barrier.

The prostaglandin E2 E-prostanoid 4 receptor exerts anti-inflammatory effects in brain innate immunity

Peripheral inflammation leads to immune responses in brain characterized by microglial activation, elaboration of proinflammatory cytokines and reactive oxygen species, and secondary neuronal injury. The inducible cyclooxygenase (COX), COX-2, mediates a significant component of this response in brain via downstream proinflammatory PG signaling. In this study, we investigated the function of the PGE2 E-prostanoid (EP) 4 receptor in the CNS innate immune response to the bacterial endotoxin LPS. We report that PGE2 EP4 signaling mediates an anti-inflammatory effect in brain by blocking LPS-induced proinflammatory gene expression in mice. This was associated in cultured murine microglial cells with decreased Akt and I-kappaB kinase phosphorylation and decreased nuclear translocation of p65 and p50 NF-kappaB subunits. In vivo, conditional deletion of EP4 in macrophages and microglia increased lipid peroxidation and proinflammatory gene expression in brain and in isolated adult microglia following peripheral LPS administration. Conversely, EP4 selective agonist decreased LPS-induced proinflammatory gene expression in hippocampus and in isolated adult microglia. In plasma, EP4 agonist significantly reduced levels of proinflammatory cytokines and chemokines, indicating that peripheral EP4 activation protects the brain from systemic inflammation. The innate immune response is an important component of disease progression in a number of neurodegenerative disorders, such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. In addition, recent studies demonstrated adverse vascular effects with chronic administration of COX-2 inhibitors, indicating that specific PG signaling pathways may be protective in vascular function. This study supports an analogous and beneficial effect of PGE2 EP4 receptor signaling in suppressing brain inflammation.

PGE2 signaling through the EP4 receptor on fibroblasts upregulates RANKL and stimulates osteolysis

Periprosthetic osteolysis is the most common cause of aseptic loosening in total joint arthroplasty. The role of inflammatory mediators such as prostaglandin E2 (PGE2) and osteoclast promoting factors including RANKL in the pathogenesis of osteolysis has been well characterized. However, the PGE2 receptor (EP1, EP2, or EP4), and cell type in which it is expressed, which is responsible for PGE2 induction of RANKL during wear debris-induced osteolysis, has yet to be elucidated. To address this, we used mice genetically deficient in these EP receptors to assess PGE2 and wear debris responses in vitro and in vivo. Wear debris-induced osteolysis and RANKL expression were observed at similar levels in WT, EP1(-/-), and EP2(-/-) mice, indicating that these receptors do not mediate PGE2 signals in this process. A conditional knockout approach was used to eliminate EP4 expression in FSP1(+) fibroblasts that are the predominant source of RANKL. In the absence of EP4, fibroblasts do not express RANKL after stimulation with particles or PGE2, nor do they exhibit high levels of osteoclasts and osteolysis. These results show that periprosthetic fibroblasts are important mediators of osteolysis through the expression of RANKL, which is induced after PGE2 signaling through the EP4 receptor.

Prostaglandin EP2 and EP4 receptors modulate expression of the chemokine CCL2 (MCP-1) in response to LPS-induced renal glomerular inflammation

The pro-inflammatory chemokine CCL2 [chemokine (Cys-Cys motif) ligand 2; also known as MCP-1 (monocyte chemotactic protein-1)] is up-regulated in the glomerular compartment during the early phase of LPS (lipopolysaccharide)-induced nephritis. This up-regulation also occurs in cultured MCs (mesangial cells) and is more pronounced in MCs lacking the PGE2 (prostaglandin E2) receptor EP2 or in MCs treated with a prostaglandin EP4 receptor antagonist. To examine a possible feedback mechanism of EP receptor stimulation on CCL2 expression, we used an in vitro model of MCs with down-regulated EP receptor expression. Selectively overexpressing the various EP receptors in these cells then allows the effects on the LPS-induced CCL2 expression to be examined. Cells were stimulated with LPS and CCL2 gene expression was examined and compared with LPS-stimulated, mock-transfected PTGS2 [prostaglandin-endoperoxide synthase 2, also known as COX-2 (cyclo-oxygenase-2)]-positive cells. Overexpression of EP1, as well as EP3, had no effect on LPS-induced Ccl2 mRNA expression. In contrast, overexpression of EP2, as well as EP4, significantly decreased LPS-induced CCL2 expression. These results support the hypothesis that PTGS2-derived prostaglandins, when strongly induced, counter-balance inflammatory processes through the EP2 and EP4 receptors in MCs.

Distinct roles for basal and induced COX-2 in podocyte injury

Transgenic mice that overexpress cyclooxygenase-2 (COX-2) selectively in podocytes are more susceptible to glomerular injury by adriamycin and puromycin (PAN). To investigate the potential roles of COX-2 metabolites, we studied mice with selective deletion of prostanoid receptors and generated conditionally immortalized podocyte lines from mice with either COX-2 deletion or overexpression. Podocytes that overexpressed COX-2 were virtually indistinguishable from wild-type podocytes but were significantly more sensitive to PAN-induced injury, produced more prostaglandin E(2) and thromboxane B(2), and had greater expression of prostaglandin E(2) receptor subtype 4 (EP(4)) and thromboxane receptor (TP). Treatment of COX-2-overexpressing podocytes with a TP antagonist reduced apoptosis, but treatment with an EP(4) antagonist did not. In contrast, podocytes from COX-2-knockout mice exhibited increased apoptosis, markedly decreased cell adhesion, and prominent stress fibers. In vivo, selective deletion of podocyte EP(4) did not alter the increased sensitivity to adriamycin-induced injury observed in mice overexpressing podocyte COX-2. In contrast, genetic deletion of TP in these mice prevented adriamycin-induced injury, with attenuated albuminuria and foot process effacement. These results suggest that basal COX-2 may be important for podocyte survival, but overexpression of podocyte COX-2 increases susceptibility to podocyte injury, which is mediated, in part, by activation of the thromboxane receptor.

Effects of global or targeted deletion of the EP4 receptor on the response of osteoblasts to prostaglandin in vitro and on bone histomorphometry in aged mice

Because global deletion of the prostaglandin EP4 receptor results in neonatal lethality, we generated a mouse with targeted EP4 receptor deletion using Cre-LoxP methodology and a 2.3 kb collagen I a1 promoter driving Cre recombinase that is selective for osteoblastic cells. We compared wild type (WT), global heterozygote (G-HET), targeted heterozygote (T-HET) and knockout (KO) mice. KO mice had one targeted and one global deletion of the EP4 receptor. All mice were in a mixed background of C57BL/6 and CD-1. Although there were one third fewer G-HET or KO mice at weaning compared to WT and T-HET mice, G-HET and KO mice appeared healthy. In cultures of calvarial osteoblasts, prostaglandin E(2) (PGE(2)) increased alkaline phosphatase (ALP) activity in cells from WT mice, and this effect was significantly decreased in cells from either G-HET or T-HET mice and further decreased in cells from KO mice. A selective agonist for EP4 receptor increased ALP activity and osteocalcin mRNA levels in cells from WT but not KO mice. A selective COX-2 inhibitor, NS-398, decreased osteoblast differentiation in WT but not KO cells. At 15 to 18 months of age there were no differences in serum creatinine, calcium, PTH, body weight or bone mineral density among the different genotypes. Static and dynamic histomorphometry showed no consistent changes in bone volume or bone formation. We conclude that expression of the EP4 receptor in osteoblasts is critical for anabolic responses to PGE(2) in cell culture but may not be essential for maintenance of bone remodeling in vivo.

Macrophage EP4 deficiency increases apoptosis and suppresses early atherosclerosis

Prostaglandin (PG) E(2), a major product of activated macrophages, has been implicated in atherosclerosis and plaque rupture. The PGE(2) receptors, EP2 and EP4, are expressed in atherosclerotic lesions and are known to inhibit apoptosis in cancer cells. To examine the roles of macrophage EP4 and EP2 in apoptosis and early atherosclerosis, fetal liver cell transplantation was used to generate LDLR(-/-) mice chimeric for EP2(-/-) or EP4(-/-) hematopoietic cells. After 8 weeks on a Western diet, EP4(-/-) --> LDLR(-/-) mice, but not EP2(-/-) --> LDLR(-/-) mice, had significantly reduced aortic atherosclerosis with increased apoptotic cells in the lesions. EP4(-/-) peritoneal macrophages had increased sensitivity to proapoptotic stimuli, including palmitic acid and free cholesterol loading, which was accompanied by suppression of activity of p-Akt, p-Bad, and NF-kappaB-regulated genes. Thus, EP4 deficiency inhibits the PI3K/Akt and NF-kappaB pathways compromising macrophage survival and suppressing early atherosclerosis, identifying macrophage EP4-signaling pathways as molecular targets for modulating the development of atherosclerosis.

Progress in gene targeting: using mutant mice to study renal function and disease

Genetic engineering in mice has provided much information about gene function in renal health and disease. This knowledge has largely come from conventional transgenic approaches. Recently, methods have been developed to control the cell type, timing and reversibility of target gene expression. Advances in identifying promoters conferring renal cell-specific gene regulation in vivo have greatly facilitated interpretation of gene targeting studies. Site-specific recombinases have permitted cell-specific knockout of genes; Cre is the preeminent recombinase, but recent progress with other recombinases, include Flp and PhiC31, will likely increase the usefulness of this class of enzymes. Temporally regulated gene expression, particularly using doxycycline- and tamoxifen-inducible systems, holds great promise for avoiding developmental effects of gene mutations as well as facilitating comparison of the same animal's phenotype before and after gene modification. RNA interference is undergoing tremendous growth and has great potential for achieving gene knockdown quickly and reversibly. To date, however, the utility of these systems in modifying renal function in transgenic mice remains unproven. Finally, new gene targeting tools are in development that may substantially simplify generation of transgenic animals. This review discusses the state-of-the-art in gene targeting in the kidney, reviewing function, indications and limitations of the molecular biologic tools.

Reduced cardiac remodeling and function in cardiac-specific EP4 receptor knockout mice with myocardial infarction

We have shown previously that cyclooxygenase-2 inhibition reduces cardiac hypertrophy and fibrosis postmyocardial infarction (MI) in a mouse model and that prostaglandin E(2) stimulates cardiomyocyte hypertrophy in vitro through its EP(4) receptor. Because the role of cardiac myocyte EP(4) in cardiac function and hypertrophy in vivo is unknown, we generated mice lacking EP(4) only in cardiomyocytes (CM- EP(4) knockout [KO]). Twelve- to 14-week-old mice were evaluated using echocardiography and histology. There were no differences in ejection fraction, myocyte cross-sectional area, and interstitial collagen fraction between KO mice and littermate controls. To test the hypothesis that EP(4) is involved in cardiac remodeling after MI, we induced MI by ligating the left anterior descending coronary artery. Two weeks later, the mice were subjected to echocardiography, and hearts were removed for histology and Western blot. There was no difference in infarct size between KO mice and controls; however, KO mice showed less myocyte cross-sectional area and interstitial collagen fraction than controls. Also, CM-EP4 KO mice had reduced ejection fraction. Because the transcription factor Stat-3 is involved in hypertrophy and protection from ischemic injury, we tested whether it was activated in control and KO mouse hearts after MI. Western blot indicated that Stat-3 was activated in control hearts after MI but not in KO hearts. Thus, CM-EP4 deletion decreased hypertrophy, fibrosis, and activation of Stat-3. However, cardiac function was unexpectedly worsened in these mice. We conclude that cardiac myocyte EP(4) plays a role in hypertrophy via activation of Stat-3, a process that seems to be cardioprotective.

Prostaglandin E2-EP4 receptor promotes endothelial cell migration via ERK activation and angiogenesis in vivo

Prostaglandin E2 (PGE(2)), a major product of cyclooxygenase, exerts its functions by binding to four G protein-coupled receptors (EP1-4) and has been implicated in modulating angiogenesis. The present study examined the role of the EP4 receptor in regulating endothelial cell proliferation, migration, and tubulogenesis. Primary pulmonary microvascular endothelial cells were isolated from EP4(flox/flox) mice and were rendered null for the EP4 receptor with adenoCre virus. Whereas treatment with PGE(2) or the EP4 selective agonists PGE(1)-OH and ONO-AE1-329 induced migration, tubulogenesis, ERK activation and cAMP production in control adenovirus-transduced endothelial EP4(flox/flox) cells, no effects were seen in adenoCre-transduced EP4(flox/flox) cells. The EP4 agonist-induced endothelial cell migration was inhibited by ERK, but not PKA inhibitors, defining a functional link between PGE(2)-induced endothelial cell migration and EP4-mediated ERK signaling. Finally, PGE(2), as well as PGE(1)-OH and ONO-AE1-329, also promoted angiogenesis in an in vivo sponge assay providing evidence that the EP4 receptor mediates de novo vascularization in vivo.

Conditional mutagenesis of G-protein coupled receptors and G-proteins

The G-protein-coupled receptor signaling system, consisting of a huge variety of receptors as well as of many G-proteins and effectors, operates in every cell and is involved in many physiological and pathological processes. The versatility of this system and the involvement of specific components makes G-protein-coupled receptors and their signaling pathways ideal targets for pharmacological interventions. Classical mouse knockout models have often provided important preliminary insights into the biological roles of individual receptors and signaling pathways and they are routinely used in the process of target validation. The recent development of efficient conditional mutagenesis techniques now allows a much more detailed analysis of G-protein-mediated signaling transduction processes. This review summarizes some of the areas in which progress has recently been made by applying conditional mutagenesis of genes coding for G-proteins and G-protein-coupled receptors.

The differential role of prostaglandin E2 receptors EP3 and EP4 in regulation of fever

The innate immune system of mammals is able to detect bacteria when they infect local tissue or enter the blood stream, and initiate an immediate immune response. Prostaglandin (PG) E2 is considered as the most important link between the peripheral immune system and the brain. Due to four PGE2 receptors (EP receptors) and their differential expression in various areas of the hypothalamus and brain stem, PGE2 mediates different components of the acute phase reaction. A fever model is discussed in which the preoptic area contains the mechanisms for both hyperthermic and hypothermic responses and EP receptors in the median preoptic area (MnPO) modulate the thermogenic system. The neuron-specific modulation of EP receptors in the MnPO can be critically tested by using Cre-recombinase-mediated DNA recombination in genetically engineered mice. A concept for mice with conditional expression of EP3R and EP4R to investigate the different roles of those receptors in lipopolysaccharide (LPS)-induced fever is presented.

Podocyte cell-specific expression of doxycycline inducible Cre recombinase in mice

Conventional silencing of many podocyte-specific genes in mice is associated with embryonic or perinatal lethality. Therefore, it would be of great importance to generate mouse models that allow the modification of genes that are expressed in podocytes at later stages of age. Herein is described a transgenic mouse with doxycycline-inducible podocyte-specific expression of Cre recombinase. For the generation of this binary system, a single transgenic construct that contained two separate genes was used: One encoding the optimized M2 version of the doxycycline-dependent transcription transactivator reverse tetracycline-controlled transcriptional activator (rtTA) under control of the human podocin (NPHS2) promoter and the other encoding the recombinase Cre under control of the rtTA/doxycycline-responsive minimal cytomegalovirus (CMV) Tet operator sequence 7 promotor. Microinjection of the JRC-CRE construct in fertilized oocytes from FVB/N mice resulted in 16 transgenic founders. Double-transgenic offspring from breeding of a selected founder with the Z/AP reporter mouse showed alkaline phosphatase staining only upon doxycycline administration and exclusively in podocytes. These data indicate that this new inducible Cre recombinase mouse line is an excellent tool in conditional, kidney glomerular podocyte-specific gene deletion in adult mice.

Mouse behavioural analysis in systems biology

Molecular techniques allowing in vivo modulation of gene expression have provided unique opportunities and challenges for behavioural studies aimed at understanding the function of particular genes or biological systems under physiological or pathological conditions. Although various animal models are available, the laboratory mouse (Mus musculus) has unique features and is therefore a preferred animal model. The mouse shares a remarkable genetic resemblance and aspects of behaviour with humans. In this review, first we describe common mouse models for behavioural analyses. As both genetic and environmental factors influence behavioural performance and need to be carefully evaluated in behavioural experiments, considerations for designing and interpretations of these experiments are subsequently discussed. Finally, common behavioural tests used to assess brain function are reviewed, and it is illustrated how behavioural tests are used to increase our understanding of the role of histaminergic neurotransmission in brain function.

Recent innovations in tissue-specific gene modifications in the mouse

Annotating the functions of individual genes in in vivo contexts has become the primary task of mouse genetics in the post-genome era. In addition to conventional approaches using transgenic technologies and gene targeting, the recent development of conditional gene modification techniques has opened novel opportunities for elucidating gene function at the level of the whole mouse to individual tissues or cell types. Tissue-specific gene modifications in the mouse have been made possible using site-specific DNA recombinases and conditional alleles. Recent innovations in this basic technology have facilitated new types of experiments, revealing novel insights into mammalian embryology. In this review, we focus on these recent innovations and new technical issues that impact the success of these conditional gene modification approaches.

Differential regulation of EP receptor isoforms during chondrogenesis and chondrocyte maturation

Regulation of chondrogenesis and chondrocyte maturation by prostaglandins has been a topic of interest during recent years. Particular focus on this area derives from the realization that inhibition of prostaglandin synthesis with non-steroidal anti-inflammatory drugs could impact these cartilage-related processes which are important in skeletal development and are recapitulated during bone healing either post-trauma or post-surgery. In addition to reviewing the relevant literature focused on prostaglandin synthesis and signaling through the G-protein coupled EP receptors, we present novel findings that establish the expression profile of EP receptors in chondroprogenitors and chondrocytes. Further, we begin to examine the signaling that may be involved with the transduction of PGE2 effects in these cells. Our findings suggest that EP2 and EP4 receptor activation of cAMP metabolism may represent a central axis of events that facilitate the impact of PGE2 on the processes of mesenchymal stem cell commitment to chondrogenesis and ultimate chondrocyte maturation.