Deficiency of long-chain acyl-CoA synthetase 4 leads to lipopolysaccharide-induced mortality in a mouse model of septic shock.

Long-chain acyl-CoA synthetase 4 (ACSL4) converts free highly unsaturated fatty acids (HUFAs) into their acyl-CoA esters and is important for HUFA utilization. HUFA-containing phospholipids produced via ACSL4-dependent reactions are involved in pathophysiological events such as inflammatory responses and ferroptosis as a source for lipid mediators and/or a target of oxidative stress, respectively. However, the in vivo role of ACSL4 in inflammatory responses is not fully understood. This study sought to define the effects of ACSL4 deficiency on lipopolysaccharide (LPS)-induced systemic inflammatory responses using global Acsl4 knockout (Acsl4 KO) mice. Intraperitoneal injection of LPS-induced more severe symptoms, including diarrhea, hypothermia, and higher mortality, in Acsl4 KO mice within 24 h compared with symptoms in wild-type (WT) mice. Intestinal permeability induced 3 h after LPS challenge was also enhanced in Acsl4 KO mice compared with that in WT mice. In addition, plasma levels of some eicosanoids in Acsl4 KO mice 6 h post-LPS injection were 2- to 9-fold higher than those in WT mice. The increased mortality observed in LPS-treated Acsl4 KO mice was significantly improved by treatment with the general cyclooxygenase inhibitor indomethacin with a partial reduction in the severity of illness index for hypothermia, diarrhea score, and intestinal permeability. These results suggest that ACSL4 deficiency enhances susceptibility to endotoxin at least partly through the overproduction of cyclooxygenase-derived eicosanoids.

Prostacyclin Synthase as an Ambivalent Regulator of Inflammatory Reactions.

Prostacyclin (PGI2) synthase (PGIS) and microsomal prostaglandin (PG) E synthase-1 (PGES-1) are PG terminal synthases which functionally couple with inducible cyclooxygenase-2 (COX-2) as their upstream enzymes to produce PGI2 and PGE2, respectively. Non-steroidal anti-inflammatory drugs exert their pharmacological effects by the inhibition of COX-2 and thereby suppression of the biosynthesis of these PGs. PGIS is abundantly expressed in vascular endothelial and smooth muscle cells and has been shown to be critical for regulation of platelet aggregation and vascular tone. In addition to its role in vascular regulation, PGIS has been shown to be expressed in inflammatory cells including macrophages, and the proinflammatory roles of PGIS has been demonstrated. On the other hand, several investigators have recently reported that PGIS functions as an anti-inflammatory mediator by macrophage polarization and have indicated that PGIS is an ambivalent regulator of inflammatory reactions. In this review, we summarize the current understanding of proinflammatory and anti-inflammatory functions of PGIS and discuss its potential as a novel anti-inflammatory therapeutic target.

Absence of prostacyclin greatly relieves cyclophosphamide-induced cystitis and bladder pain in mice.

Cyclophosphamide (CP) has been widely used in the treatment of various malignancies and autoimmune diseases, but acrolein, a byproduct of CP, causes severe hemorrhagic cystitis as the major side effect of CP. On the other hand, a large amount of prostacyclin (PGI2 ) is produced in bladder tissues, and PGI2 has been shown to play a critical role in bladder homeostasis. PGI2 is biosynthesized from prostaglandin (PG) H2 , the common precursor of PGs, by PGI2 synthase (PTGIS) and is known to also be involved in inflammatory responses. However, little is known about the roles of PTGIS-derived PGI2 in bladder inflammation including CP-induced hemorrhagic cystitis. Using both genetic and pharmacological approaches, we here revealed that PTGIS-derived PGI2 -IP (PGI2 receptor) signaling exacerbated CP-induced bladder inflammatory reactions. Ptgis deficiency attenuated CP-induced vascular permeability and chemokine-mediated neutrophil migration into bladder tissues and then suppressed hemorrhagic cystitis. Treatment with RO1138452, an IP selective antagonist, also suppressed CP-induced cystitis. We further found that cystitis-related nociceptive behavior was also relieved in both Ptgis-/- mice and RO1138452-treated mice. Our findings may provide new drug targets for bladder inflammation and inflammatory pain in CP-induced hemorrhagic cystitis.

Gene Deletion of Microsomal Prostaglandin E Synthase-1 Suppresses Chemically Induced Skin Carcinogenesis.

BACKGROUND/AIM: Microsomal prostaglandin (PG) E synthase-1 (mPGES-1) is a terminal enzyme in PGE2 synthesis and highly expressed in several cancers. In this study, to reveal the involvement of mPGES-1 in skin carcinogenesis, the effect of mPGES-1 deficiency on two-stage skin carcinogenesis in mice was investigated. MATERIALS AND METHODS: A two-stage skin carcinogenesis model using 7,12-dimethylbenz[a]anthracene (DMBA) as an initiator and 12-O-tetradecanoylphorbol-13-acetate (TPA) as a promoter was applied on mPGES-1 knockout (KO) mice and littermate wild-type mice of a Balb/c genetic background. RESULTS: DMBA/TPA-induced skin carcinogenesis was suppressed in mPGES-1 KO mice. The induction of IL-17 and other inflammatory cytokines by TPA was also suppressed by mPGES-1 deficiency, although DMBA-induced apoptosis was not affected. CONCLUSION: mPGES-1 promotes chemically induced skin carcinogenesis and might play an important role in the TPA-induced promotion phase of the two-stage skin carcinogenesis model. mPGES-1 inhibition may be a therapeutic target for skin cancer.

Coordinated action of microsomal prostaglandin E synthase-1 and prostacyclin synthase on contact hypersensitivity.

Microsomal prostaglandin (PG) E synthase-1 (mPGES-1) and prostacyclin (PGI2) synthase (PGIS) are PG terminal synthases that work downstream of cyclooxygenase and synthesize PGE2 and PGI2, respectively. Although the involvement of PG receptors in acquired cutaneous immune responses was recently shown, the roles of these PG terminal synthases remain unclear. To identify the pathophysiological roles of mPGES-1 and PGIS in cutaneous immune systems, we applied contact hypersensitivity (CHS) to mPGES-1 and PGIS knockout (KO) mice as a model of acquired immune responses. Mice were treated with 1-fluoro-2,4-dinitrobenzene (DNFB) and evaluated for ear thickness and histopathological features. The results showed that the severity of ear swelling in both gene-deficient mice was much lower than that in wild-type (WT) mice. Histological examination of DNFB-treated ears showed that inflammatory cell infiltration and edema in the dermis were also less apparent in both genotypic mice. LC-MS analysis further showed that the increment in PGE2 levels in DNFB-treated ear tissue was reduced in mPGES-1 KO mice, and that 6-keto PGF1α (a stable metabolite of PGI2) was not detected in PGIS KO mice. Furthermore, we made bone marrow (BM) chimera and found that transplantation of WT mouse-derived BM cells restored the impaired CHS response in mPGES-1 KO mice but did not restore the response in PGIS KO mice. These results indicated that mPGES-1 in BM-derived cells and PGIS in non-BM-derived cells might play critical roles in DNFB-induced CHS. mPGES-1-derived PGE2 and PGIS-derived PGI2 might coordinately promote acquired cutaneous immune responses.

Involvement of prostacyclin synthase in high-fat-diet-induced obesity.

Prostacyclin (PGI2) synthase (PGIS) functions downstream of inducible cyclooxygenase COX-2 in the PGI2 biosynthetic pathway. Although COX-2 and PGI2 receptor (IP) are known to be involved in adipogenesis and obesity, the involvement of PGIS has not been fully elucidated. In this study, we examined the role of PGIS in adiposity by using PGIS-deficient mice. Although PGIS deficiency did not affect in vitro adipocyte differentiation, when fed a high-fat diet (HFD), PGIS knockout (KO) mice showed reductions in both body weight gain and epididymal fat mass relative to wild-type (WT) mice. PGIS deficiency might reduce HFD-induced obesity by suppressing PGI2 production. We further found that additional gene deletion of microsomal prostaglandin (PG) E synthase-1 (mPGES-1), one of the other PG terminal synthases that also functions downstream of COX-2, emphasized the metabolic phenotypes of PGIS-deficient mice. More marked reduction in obesity and improved insulin resistance were observed in PGIS/mPGES-1 double KO (DKO) mice. Since an additive increase in PGF2α level in epididymal fat was observed in DKO mice, mPGES-1 deficiency might affect adiposity by enhancing the production of PGF2α. Our immunohistochemical analysis further revealed that in adipose tissues, PGIS was expressed in vascular and stromal cells but not in adipocytes. These results suggested that PGI2 produced from PGIS-expressed stromal tissues might enhance HFD-induced obesity by acting on IP expressed in adipocytes. The balance of expressions of PG terminal synthases and the subsequent production of prostanoids might be critical for adiposity.

Role of prostacyclin synthase in carcinogenesis.

Prostacyclin (PGI2) synthase (PGIS) and microsomal prostaglandin (PG) E synthase-1 (PGES-1) functionally couple with inducible cyclooxygenase-2 (COX-2) as their upstream enzymes to produce PGI2 and PGE2, respectively. Non-steroidal anti-inflammatory drugs exert their pharmacological effects including antitumor effects by the inhibition of COX-2 and thereby suppress this PG biosynthesis. PGIS is abundantly expressed in vascular endothelial and smooth muscle cells and was shown to be critical for the regulation of platelet aggregation and vascular tone. In addition to its role in vascular regulation, PGIS was shown to be frequently down-regulated in several types of cancers, and the involvement of PGIS in carcinogenesis has been suggested. In this review, we summarize the current understanding of the roles of PGIS and PGIS-derived PGI2 in carcinogenesis.