Characterization of Astrocytes in the Minocycline-Administered Mouse Photothrombotic Ischemic Stroke Model.

Astrocytes, together with microglia, play important roles in the non-infectious inflammation and scar formation at the brain infarct during ischemic stroke. After ischemia occurs, these become highly reactive, accumulate at the infarction, and release various inflammatory signaling molecules. The regulation of astrocyte reactivity and function surrounding the infarction largely depends on intercellular communication with microglia. However, the mechanisms involved remain unclear. Furthermore, recent molecular biological studies have revealed that astrocytes are highly divergent under both resting and reactive states, whereas it has not been well reported how the communication between microglia and astrocytes affects astrocyte divergency during ischemic stroke. Minocycline, an antibiotic that reduces microglial activity, has been used to examine the functional roles of microglia in mice. In this study, we used a mouse photothrombotic ischemic stroke model to examine the characteristics of astrocytes after the administration of minocycline during ischemic stroke. Minocycline increased astrocyte reactivity and affected the localization of astrocytes in the penumbra region. Molecular characterization revealed that the induced expression of mRNA encoding the fatty acid binding protein 7 (FABP7) by photothrombosis was enhanced by the minocycline administration. Meanwhile, minocycline did not significantly affect the phenotype or class of astrocytes. The expression of Fabp7 mRNA was well correlated with that of tumor-necrosis factor α (TNFα)-encoding Tnf mRNA, indicating that a correlated expression of FABP7 from astrocytes and TNFα is suppressed by microglial activity.

Extracellular Environment-Controlled Angiogenesis, and Potential Application for Peripheral Nerve Regeneration.

Endothelial cells acquire different phenotypes to establish functional vascular networks. Vascular endothelial growth factor (VEGF) signaling induces endothelial proliferation, migration, and survival to regulate vascular development, which leads to the construction of a vascular plexuses with a regular morphology. The spatiotemporal localization of angiogenic factors and the extracellular matrix play fundamental roles in ensuring the proper regulation of angiogenesis. This review article highlights how and what kinds of extracellular environmental molecules regulate angiogenesis. Close interactions between the vascular and neural systems involve shared molecular mechanisms to coordinate developmental and regenerative processes. This review article focuses on current knowledge about the roles of angiogenesis in peripheral nerve regeneration and the latest therapeutic strategies for the treatment of peripheral nerve injury.

Prostaglandin E2-EP4 Axis Promotes Lipolysis and Fibrosis in Adipose Tissue Leading to Ectopic Fat Deposition and Insulin Resistance.

Lipolysis, the breakdown of triglyceride storage in white adipose tissue, supplies fatty acids to other tissues as a fuel under fasting conditions. In morbid obesity, fibrosis limits adipocyte expandability, resulting in enforced lipolysis, ectopic fat distribution, and ultimately insulin resistance. Although basal levels of lipolysis persist even after feeding, the regulatory mechanisms of basal lipolysis remain unclear. Here, we show the important role of adipocyte prostaglandin (PG) E2-EP4 receptor signaling in controlling basal lipolysis, fat distribution, and collagen deposition during feeding-fasting cycles. The PGE2-synthesis pathway in adipocytes, which is coupled with lipolysis, is activated by insulin during feeding. By regulating the lipolytic key players, the PGE2-EP4 pathway sustains basal lipolysis as a negative feedback loop of insulin action, and perturbation of this process leads to "metabolically healthy obesity." The potential role of the human EP4 receptor in lipid regulation was also suggested through genotype-phenotype association analyses.

Induced mRNA expression of matrix metalloproteinases Mmp-3, Mmp-12, and Mmp-13 in the infarct cerebral cortex of photothrombosis model mice.

A strong therapeutic target of ischemic stroke is controlling brain inflammation. Recent studies have implicated the critical role of C-C chemokine receptor 5 (CCR5) in neuroinflammation during ischemic stroke. It has been reported that the expression of the matrix metalloproteinases, MMP-3, MMP-12, and MMP-13, is controlled by CCR5; however, their expressional regulation in the infarct brain has not been clearly understood. This study investigated the mRNA expression of Mmp-3, -12, and -13 in the ischemic cerebral cortex of photothrombosis mouse model. The three Mmps were highly upregulated in the early stages of ischemic stroke and were expressed in different types of cells. Mmp-3 and Mmp-13 were expressed in blood vessel endothelial cells after ischemia-induction, whereas Mmp-12 was expressed in activated microglia. The expression of Mmp-13 in resting microglia and in neurons of uninjured cerebral cortex was lost in the infarct region. Therefore, the MMPs responding to CCR5 are differentially regulated during ischemic stroke.

Induced Prostanoid Synthesis Regulates the Balance between Th1- and Th2-Producing Inflammatory Cytokines in the Thymus of Diet-Restricted Mice.

Multiple external and internal factors have been reported to induce thymic involution. Involution involves dramatic reduction in size and function of the thymus, leading to various immunodeficiency-related disorders. Therefore, clarifying and manipulating molecular mechanisms governing thymic involution are clinically important, although only a few studies have dealt with this issue. In the present study, we investigated the molecular mechanisms underlying thymic involution using a murine acute diet-restriction model. Gene expression analyses indicated that the expression of T helper 1 (Th1)-producing cytokines, namely interferon-γ and interleukin (IL)-2, was down-regulated, while that of Th2-producing IL-5, IL-6, IL-10 and IL-13 was up-regulated, suggesting that acute diet-restriction regulates the polarization of naïve T cells to a Th2-like phenotype during thymic involution. mRNAs for prostanoid biosynthetic enzymes were up-regulated by acute diet-restriction. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analyses detected the increased production of prostanoids, particularly prostaglandin D2 and thromboxane B2, a metabolite of thromboxane A2, in the diet-restricted thymus. Administration of non-steroidal anti-inflammatory drugs, namely aspirin and etodolac, to inhibit prostanoid synthesis suppressed the biased expression of Th1- and Th2-cytokines as well as molecular markers of Th1 and Th2 cells in the diet-restricted thymus, without affecting the reduction of thymus size. In vitro stimulation of thymocytes with phorbol myristate acetate (PMA)/ionomycin confirmed the polarization of thymocytes from diet-restricted mice toward Th2 cells. These results indicated that the induced production of prostanoids during diet-restriction-induced thymic involution is involved in the polarization of naïve T cells in the thymus.

Essential role of prostaglandin E2 and the EP3 receptor in lymphatic vessel development during zebrafish embryogenesis.

Lymphatic endothelial cells arise from the venous endothelial cells in embryonic lymphatic development. However, the molecular mechanisms remain to be elucidated. We here report that prostaglandin (PG) E2 plays essential roles in the embryonic lymphatic development through the EP3 receptor, one of the PGE2 receptors. Knockdown of the EP3 receptor or inhibition of cyclooxygenases (COX; rate-limiting enzymes for PG synthesis) impaired lymphatic development by perturbing lymphatic specification during zebrafish development. These impairments by COX inhibition were recovered by treatment with sulprostone (EP1/3 agonist). Knockdown of the EP3 receptor further demonstrated its requirement in the expression of sex determining region Y-box 18 (sox18) and nuclear receptor subfamily 2, group F, member 2 (nr2f2), essential factors of the lymphatic specification. The EP3 receptor was expressed in the posterior cardinal vein (region of embryonic lymphatic development) and the adjacent intermediate cell mass (ICM) during the lymphatic specification. COX1 was expressed in the region more upstream of the posterior cardinal vein relative to the EP3 receptor, and the COX1-selective inhibitor impaired the lymphatic specification. On the other hand, two COX2 subtypes did not show distinct sites of expression around the region of expression of the EP3 receptor. Finally, we generated EP3-deficient zebrafish, which also showed defect in lymphatic specification and development. Thus, we demonstrated that COX1-derived PGE2-EP3 pathway is required for embryonic lymphatic development by upregulating the expression of key factors for the lymphatic specification.

Prostaglandin D2 elicits the reversible neurite retraction in hypothalamic cell line.

Prostaglandins (PGs) play important roles in diverse physiological processes in the central nervous system. PGD2 is the most abundant PG in the brain and acts through specific receptors, DP1 and CRTH2. We investigated the effects of PGD2 on the morphology of the hypothalamic cell line mHypoE-N37 (N37). In N37 cells, serum starvation induced neurite outgrowth and PGD2 elicited neurite retraction, although we failed to detect transcripts for DP1 and CRTH2. Such an effect of PGD2 was efficiently mimicked by its metabolite, 15-deoxy-Δ(12,14)-prostaglandin J2. N-acetyl cysteine completely abolished the effect of PGD2, and reactive oxygen species (ROS) were considered to be important. Notably, neurite outgrowth was restored by PGD2 removal. These results suggest that PGD2 induces reversible neurite retraction in a ROS-mediated mechanism that does not involve any known receptor.

Prostaglandin E2-induced inflammation: Relevance of prostaglandin E receptors.

Prostaglandin E2 (PGE2) is one of the most typical lipid mediators produced from arachidonic acid (AA) by cyclooxygenase (COX) as the rate-limiting enzyme, and acts on four kinds of receptor subtypes (EP1-EP4) to elicit its diverse actions including pyrexia, pain sensation, and inflammation. Recently, the molecular mechanisms underlying the PGE2 actions mediated by each EP subtype have been elucidated by studies using mice deficient in each EP subtype as well as several compounds highly selective to each EP subtype, and their findings now enable us to discuss how PGE2 initiates and exacerbates inflammation at the molecular level. Here, we review the recent advances in PGE2 receptor research by focusing on the activation of mast cells via the EP3 receptor and the control of helper T cells via the EP2/4 receptor, which are the molecular mechanisms involved in PGE2-induced inflammation that had been unknown for many years. We also discuss the roles of PGE2 in acute inflammation and inflammatory disorders, and the usefulness of anti-inflammatory therapies that target EP receptors. This article is part of a Special Issue entitled "Oxygenated metabolism of PUFA: analysis and biological relevance".

Prostanoid receptors and acute inflammation in skin.

Prostanoids such as prostaglandins (PGs) and thromboxanes exert a wide variety of actions via nine types of G protein-coupled receptors, including four PGE2 receptors (EPs) and two PGD2 receptors (DPs). Recent studies have revealed that prostanoids trigger or modulate acute inflammation in the skin via multiple mechanisms involving distinct receptors and molecules; PGE2 elicits vascular permeability and edema formation via EP3 receptor on mast cells, and PGE2 increases blood flow by eliciting vasodilatation via EP2/EP4 receptors on smooth muscle cells. PGD2-DP1 signaling plays a role in mast cell maturation and mast cell-mediated inflammation. Therefore, the local inhibition of specific prostanoid receptor signaling is expected to be an effective strategy for the prevention and treatment of acute inflammation.