Lipoxin A4 antagonizes the mitogenic effects of leukotriene D4 in human renal mesangial cells. Differential activation of MAP kinases through distinct receptors

Lipoxin Mimetics and the Resolution of Inflammation

Inflammation and its timely resolution are critical to ensure effective host defense and appropriate tissue repair after injury and or infection. Chronic, unresolved inflammation typifies many prevalent pathologies. The key mediators that initiate and drive the inflammatory response are well defined and targeted by conventional anti-inflammatory therapeutics. More recently, there is a growing appreciation that specific mediators, including arachidonate-derived lipoxins, are generated in self-limiting inflammatory responses to promote the resolution of inflammation and endogenous repair mechanisms without compromising host defense. We discuss the proresolving biological actions of lipoxins and recent efforts to harness their therapeutic potential through the development of novel, potent lipoxin mimetics generated via efficient, modular stereoselective synthetic pathways. We consider the evidence that lipoxin mimetics may have applications in limiting inflammation and reversing fibrosis and the underlying mechanisms.

Mechanisms of ERK phosphorylation triggered via mouse formyl peptide receptor 2

Formyl peptide receptors (FPRs) are expressed in the cells of the innate immune system and provide binding with pathogen and damage-associated molecular patterns with subsequent activation of the phagocytes for defense reactions such as chemotaxis, secretory degranulation and ROS generation. Probably, FPR2 is one of the unique receptors in the organism; it is able to recognize numerous ligands of different chemical structure, and moreover, these ligands can trigger opposite phagocyte responses promoting either pro- or anti-inflammatory reactions. Therefore, FPR2 and its signaling pathways are of intense research interest. We found only slight activation of ERK1/2 in the response to peptide ligand WKYMVM in the accelerating phase of ROS generation and more intense ERK1/2 phosphorylation in the declining phase of it in mouse bone marrow granulocytes. Lipid agonist BML-111 did not induce significant ERK phosphorylation when applied for 10-1800 s. To some extent co-localization of ERK1/2 and NADPH oxidase subunits was observed even in the intact cells and didn't change under FPR2 stimulation by WKYMVM, while direct PKC activation by PMA resulted to more efficient interaction between ERK1/2 and p47phox/p67phox and their translocation to plasma membrane. We have shown that phosphorylation and activation of ERK1/2 in bone marrow granulocytes depended on FPR2-triggered activity of PI3K and PKC, phosphatase DUSP6, and, the most but not the least, on ROS generation. Since blocking of ROS generation led to a slowdown of ERK activation indicating a significant contribution of ROS to the secondary regulation of ERK activity.

Lipoxins and synthetic lipoxin mimetics: Therapeutic potential in renal diseases

Inflammation and its timely resolution are critical to ensuring effective host defence and appropriate tissue repair after injury. Unresolved inflammation typifies many renal pathologies. The key drivers of the inflammatory response are well defined and targeted by conventional anti-inflammatory therapeutics. However, these are associated with undesirable side effects including immune suppression. More recently, there is growing appreciation that specialized lipid mediators [SPMs] including lipoxins promote the resolution of inflammation and endogenous repair mechanisms without compromising host defence. We discuss the pro-resolving bioactions of lipoxins and recent work that aims to harness their therapeutic potential in the context of kidney disease.

Changes of lipoxin levels during pregnancy and the monthly-cycle, condition the normal course of pregnancy or pathology

OBJECTIVE AND DESIGN

The purpose of the review was to gather information on the role and possibilities of using lipoxin in the treatment of infertility and maintaining a normal pregnancy. Ovulation, menstruation, embryo implantation, and childbirth are reactions representing short-term inflammatory events involving lipoxin activities. Lipoxin A4 (LXA4) is an arachidonic acid metabolite, and in cooperation with its positional isomer lipoxin B4 (LXB4), it is a major lipoxin in mammals. Biosynthesis process occurs in two stages: in the first step, the donor cell releases the eicosanoid intermediate; secondarily, the acceptor cell gets and converts the intermediate product into LXA4 (leukocyte/platelet interaction).

RESULTS

Generating lipoxin synthesis may also be triggered by salicylic acid, which acetylates cyclooxygenase-2. Lipoxin A4 and its analogues are considered as specialized pro-resolving mediators. LXA4 is an important component for a proper menstrual cycle, embryo implantation, pregnancy, and delivery. Its level in the luteal phase is high, while in the follicular phase, it decreases, which coincides with an increase in estradiol concentration with which it competes for the receptor. LXA4 inhibits the progression of endometriosis. However, during the peri-implantation period, before pregnancy is confirmed clinically, high levels of LXA4 can contribute to early pregnancy loss and may cause miscarriage. After implantation, insufficient LXA4 levels contribute to incorrect maternal vessel remodeling; decreased, shallow trophoblastic invasion; and the immuno-energetic abnormality of the placenta, which negatively affects fetal growth and the maintenance of pregnancy. Moreover, the level of LXA4 increases in the final stages of pregnancy, allowing vessel remodeling and placental separation.

METHODS

The review evaluates the literature published in the PubMed and Embase database up to 31 December 2019. The passwords were checked on terms: lipoxin and pregnancy with combined endometriosis, menstrual cycle, implantation, pre-eclampsia, fetal growth restriction, and preterm labor.

CONCLUSIONS

Although no human studies have been performed so far, the cell and animal model study results suggest that LXA4 will be used in obstetrics and gynecology soon.

Arachidonic Acid Metabolism and Kidney Inflammation

As a major component of cell membrane lipids, Arachidonic acid (AA), being a major component of the cell membrane lipid content, is mainly metabolized by three kinds of enzymes: cyclooxygenase (COX), lipoxygenase (LOX), and cytochrome P450 (CYP450) enzymes. Based on these three metabolic pathways, AA could be converted into various metabolites that trigger different inflammatory responses. In the kidney, prostaglandins (PG), thromboxane (Tx), leukotrienes (LTs) and hydroxyeicosatetraenoic acids (HETEs) are the major metabolites generated from AA. An increased level of prostaglandins (PGs), TxA₂ and leukotriene B4 (LTB₄) results in inflammatory damage to the kidney. Moreover, the LTB₄-leukotriene B4 receptor 1 (BLT1) axis participates in the acute kidney injury via mediating the recruitment of renal neutrophils. In addition, AA can regulate renal ion transport through 19-hydroxystilbenetetraenoic acid (19-HETE) and 20-HETE, both of which are produced by cytochrome P450 monooxygenase. Epoxyeicosatrienoic acids (EETs) generated by the CYP450 enzyme also plays a paramount role in the kidney damage during the inflammation process. For example, 14 and 15-EET mitigated ischemia/reperfusion-caused renal tubular epithelial cell damage. Many drug candidates that target the AA metabolism pathways are being developed to treat kidney inflammation. These observations support an extraordinary interest in a wide range of studies on drug interventions aiming to control AA metabolism and kidney inflammation.

New Areas of Interest: Is There a Role for Omega-3 Fatty Acid Supplementation in Patients With Diabetes and Cardiovascular Disease?

PURPOSE OF REVIEW

Summarize studies on omega-3 fatty acids in prevention of albuminuria in subjects with diabetes.

RECENT FINDINGS

Several small, short-term trials suggested benefit on albuminuria in subjects with diabetes; however, results were not definitive. Welty et al. showed that eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) for 1 year slowed progression of early-stage albuminuria in subjects with diabetes with clinical coronary artery disease on an angiotensin-converting enzyme inhibitor or angiotensin-receptor blocker, the majority of whom had an albumin/creatinine ratio (ACR) < 30 μg/mg. Moreover, significantly more (3-fold) subjects on EPA and DHA had a decrease in ACR compared to control, and three on EPA and DHA had a change in category from > 30 μg/mg to < 30 μg/mg, whereas no controls did. Potential mechanisms for benefit are discussed. These results suggest that there is benefit and perhaps even reversal of albuminuria with EPA and DHA at an early stage of disease in those with ACR < 30 μg/mg and those with microalbuminuria (ACR > 30).

Lipoxins Regulate the Early Growth Response-1 Network and Reverse Diabetic Kidney Disease

Background The failure of spontaneous resolution underlies chronic inflammatory conditions, including microvascular complications of diabetes such as diabetic kidney disease. The identification of endogenously generated molecules that promote the physiologic resolution of inflammation suggests that these bioactions may have therapeutic potential in the context of chronic inflammation. Lipoxins (LXs) are lipid mediators that promote the resolution of inflammation.Methods We investigated the potential of LXA₄ and a synthetic LX analog (Benzo-LXA₄) as therapeutics in a murine model of diabetic kidney disease, ApoE^-/- mice treated with streptozotocin.Results Intraperitoneal injection of LXs attenuated the development of diabetes-induced albuminuria, mesangial expansion, and collagen deposition. Notably, LXs administered 10 weeks after disease onset also attenuated established kidney disease, with evidence of preserved kidney function. Kidney transcriptome profiling defined a diabetic signature (725 genes; false discovery rate P≤0.05). Comparison of this murine gene signature with that of human diabetic kidney disease identified shared renal proinflammatory/profibrotic signals (TNF-α, IL-1β, NF-κB). In diabetic mice, we identified 20 and 51 transcripts regulated by LXA₄ and Benzo-LXA₄, respectively, and pathway analysis identified established (TGF-β1, PDGF, TNF-α, NF-κB) and novel (early growth response-1 [EGR-1]) networks activated in diabetes and regulated by LXs. In cultured human renal epithelial cells, treatment with LXs attenuated TNF-α-driven Egr-1 activation, and Egr-1 depletion prevented cellular responses to TGF-β1 and TNF-αConclusions These data demonstrate that LXs can reverse established diabetic complications and support a therapeutic paradigm to promote the resolution of inflammation.

Specialized pro-resolving mediators in renal fibrosis

Inflammation and its timely resolution play a critical role in effective host defence and wound healing. Unresolved inflammatory responses underlie the pathology of many prevalent diseases resulting in tissue fibrosis and eventual organ failure as typified by kidney, lung and liver fibrosis. The role of autocrine and paracrine mediators including cytokines, prostaglandins and leukotrienes in initiating and sustaining inflammation is well established. More recently a physiological role for specialized pro-resolving lipid mediators [SPMs] in modulating inflammatory responses and promoting the resolution of inflammation has been appreciated. As will be discussed in this review, SPMs not only attenuate the development of fibrosis through promoting the resolution of inflammation but may also directly suppress fibrotic responses. These findings suggest novel therapeutic paradigms to treat intractable life-limiting diseases such as renal fibrosis.

Signal transduction involved in lipoxin A4‑induced protection of tubular epithelial cells against hypoxia/reoxygenation injury

Previous studies have reported that lipoxin A₄ (LXA₄) may exert a renoprotective effect on ischemia/reperfusion injury in various animal models. The underlying mechanism of LXA₄-induced renoprotection during ischemia/reperfusion injury remains to be elucidated. The present study investigated LXA₄-induced protection on renal tubular cells subjected to hypoxia/reoxygenation (H/R) injury, and determined the effects of peroxisome proliferator-activated receptor-γ (PPARγ) and heme oxygenase-1 (HO-1) on LXA₄ treatment. HK-2 human tubular epithelial cells exposed to H/R injury were pretreated with LXA₄, signal molecule inhibitors or the HO-1 inhibitor zinc protoporphyrin-IX, or were transfected with PPARγ small interfering RNA (siRNA) or nuclear factor E2-related factor 2 (Nrf2) siRNA. The protein and mRNA expression levels of PPARγ and HO-1 were analyzed using western blotting and reverse transcription-quantitative polymerase chain reaction. Binding activity of Nrf2 to the HO-1 E1 enhancer was determined using chromatin immunoprecipitation. Nrf2 binding to the HO-1 antioxidant responsive element (ARE) was assessed using electrophoretic mobility shift assay. Preincubation of cells with LXA₄ exposed to H/R injury led to a decreased production of inducible nitrogen oxide synthase, malondialdehyde, γ-glutamyl transpeptidase, leucine aminopeptidase and N-acetyl-β-glucosaminidase. In addition, LXA₄ pretreatment increased cell viability, protein and mRNA expression levels of PPARγ and HO-1 and PPARγ and HO-1 promoter activity. SB20358 is a p38 mitogen-activated protein kinase (p38 MAPK) pathway inhibitor, which reduced LXA₄-induced PPARγ expression levels. LXA₄ treatment upregulated p38 MAPK activation, Nrf2 nuclear translocation and increased binding activity of Nrf2 to HO-1 ARE and E1 enhancer in cells exposed to H/R injury. Transfection of the cells with PPARγ siRNA reduced the LXA₄-induced Nrf2 translocation. Transfection of the cells with PPARγ siRNA or Nrf2 siRNA also reduced the LXA₄-induced increase in HO-1 expression. In conclusion, LXA₄-induced protection of renal tubular cells against H/R injury was associated with the induction of PPARγ and HO-1, via activation of the p38 MAPK pathway, as well as Nrf2 nuclear translocation and binding to HO-1 ARE and E1 enhancer. Therefore, LXA₄-induced renoprotection is associated with activation of the p38 MAPK/PPARγ/Nrf2-ARE/HO-1 pathway.

BML-111 Attenuates Renal Ischemia/Reperfusion Injury Via Peroxisome Proliferator-Activated Receptor-α-Regulated Heme Oxygenase-1

We examine whether BML-111, a lipoxin receptor agonist, inhibits renal ischemia/reperfusion (I/R) injury, and whether peroxisome proliferator-activated receptor-α (PPARα) or heme oxygenase-1 (HO-1) is involved in protective effects of BML-111 on kidney against I/R injury. Rats subjected to renal I/R injury were treated with or without BML-111. Renal histological and immunohistochemical studies were performed. Expressions of phosphorylated p38 mitogen-activated protein kinase (pp38 MAPK), phosphorylated PPARα (pPPARα), and HO-1 were assessed in NRK-52E cells exposed to BML-111. The binding activity of PPARα to peroxisome proliferator-responsive element (PPRE) on HO-1 promoter in the cells was determined. BML-111 treatment resulted in a marked reduction in the severity of histological features of renal I/R injury, and attenuated the rise in renal myeloperoxidase and malondialdehyde, blood urea nitrogen and creatinine, urinary N-acetyl-β-glucosaminidase, and leucine aminopeptidase levels caused by I/R injury. BML-111 stimulated the renal expressions of pPPARα and HO-1, and cellular messenger RNA (mRNA) and protein expressions of pPPARα and HO-1 which were both blocked by GW6471, a selective PPARα antagonist, and ZnPP-IX, a specific inhibitor of HO-1 pretreatment. The pp38 MAPK inhibitor SB203580 blocked the BML-111-induced expressions of pp38 MAPK, pPPARα, and HO-1 in NRK-52E cells. The binding activity of PPARα to PPRE in nuclear extracts of NRK-52E cells was enhanced by treatment of the cells with BML-111, and was suppressed by GW6471 and SB203580. BML-111 protects the kidney against I/R injury via activation of p38 MAPK/PPARα/HO-1 pathway.

Cardioprotective potential of annexin-A1 mimetics in myocardial infarction

Myocardial infarction (MI) and its resultant heart failure remains a major cause of death in the world. The current treatments for patients with MI are revascularization with thrombolytic agents or interventional procedures. These treatments have focused on restoring blood flow to the ischemic tissue to prevent tissue necrosis and preserve organ function. The restoration of blood flow after a period of ischemia, however, may elicit further myocardial damage, called reperfusion injury. Pharmacological interventions, such as antioxidant and Ca(2+) channel blockers, have shown premises in experimental settings; however, clinical studies have shown limited success. Thus, there is a need for the development of novel therapies to treat reperfusion injury. The therapeutic potential of glucocorticoid-regulated anti-inflammatory mediator annexin-A1 (ANX-A1) has recently been recognized in a range of systemic inflammatory disorders. ANX-A1 binds to and activates the family of formyl peptide receptors (G protein-coupled receptor family) to inhibit neutrophil activation, migration and infiltration. Until recently, studies on the cardioprotective actions of ANX-A1 and its peptide mimetics (Ac2-26, CGEN-855A) have largely focused on its anti-inflammatory effects as a mechanism of preserving myocardial viability following I-R injury. Our laboratory provided the first evidence of the direct protective action of ANX-A1 on myocardium, independent of inflammatory cells in vitro. We now review the potential for ANX-A1 based therapeutics to be seen as a "triple shield" therapy against myocardial I-R injury, limiting neutrophil infiltration and preserving both cardiomyocyte viability and contractile function. This novel therapy may thus represent a valuable clinical approach to improve outcome after MI.

Potential role of Akt signaling in chronic kidney disease

Renal fibrosis, particularly tubulointerstitial fibrosis, is the common final outcome of almost all chronic kidney diseases. However, the mechanisms involved in the development of renal fibrosis are poorly understood. The Akt (also known as protein kinase B, PKB) family is serine/threonine protein kinases that play critical roles in regulating growth, proliferation, survival, metabolism and other cellular activities. Cytokines, high-glucose medium, transforming growth factor-β1 or advanced glycation end-products activate Akt in different renal cells. Increased Akt activation has been found in experimental tubulointerstitial fibrosis. In addition, Akt activation is also an important node in diverse signaling cascades involved in kidney damage. These data give evidence for a role for Akt in renal fibrosis, but no reviews are available on the role of Akt in the process. Thus, our aim is to review the role of Akt activation and signaling in renal fibrosis.

Lipoxin A4-induced heme oxygenase-1 protects cardiomyocytes against hypoxia/reoxygenation injury via p38 MAPK activation and Nrf2/ARE complex

OBJECTIVE

To investigate whether lipoxin A4 (LXA4) increases expression of heme oxygenase-1(HO-1) in cardiomyocytes, whether LXA4-induced HO-1 protects cardiomyocytes against hypoxia/reoxygenation (H/R) injury, and what are the mechanisms involved in the LXA4-induced HO-1 induction.

METHODS

Rat cardiomyocytes were exposed to H/R injury with or without preincubation with LXA4 or HO-1 inhibitor ZnPP-IX or various signal molecule inhibitors. Expressions of HO-1 protein and mRNA were analyzed by using Western blot and RT-PCR respectively. Activity of nuclear factor E2-related factor 2 (Nrf2) binding to the HO-1 E1 enhancer was assessed by chromatin immunoprecipitation. Nrf2 binding to the HO-1 antioxidant responsive element (ARE) were measured by using electrophoretic mobility shift assay.

RESULTS

Pretreatment of the cells undergoing H/R lesion with LXA4 significantly reduced the lactate dehydrogenase and creatine kinase productions, increased the cell viability, and increased the expressions of HO-1 protein and mRNA and HO-1 promoter activity. HO-1 inhibition abolished the protective role of LXA4 on the cells undergoing H/R lesion. LXA4 increased p38 mitogen-activated protein kinase (p38 MAPK) activation, nuclear translocation of Nrf2, Nrf2 binding to the HO-1 ARE and E1 enhancer in cardiomyocytes with or without H/R exposure.

CONCLUSION

The protection role of LXA4 against H/R injury of cardiomyocytes is related to upregulation of HO-1, via activation of p38 MAPK pathway and nuclear translocation of Nrf2 and Nrf2 binding to the HO-1 ARE and E1 enhancer, but not via activation of phosphatidyinositol-3-kinase or extracellular signal-regulated kinase pathway.

Involvement of K+ channel-dependant pathways in lipoxin A4-induced protective effects on hypoxia/reoxygenation injury of cardiomyocytes

Studies have shown that lipoxin A4 (LXA4) and activation of LXA4 receptor provided protection against myocardial ischemia/reperfusion injury in animal models. However, the mechanisms by which LXA4 induced protective role on myocardial ischemia/reperfusion injury remains unclear. In the present studies, we investigated the protective effects of LXA4 on H9c2 cardiomyocytes exposed to hypoxia/reoxygenation (H/R) injury and involvement of heme oxygenase-1 (HO-1)- and K(+) channel-dependant pathways in the LXA4 action. H9c2 cardiomyocytes were pretreated with or without LXA4 or HO-1 specific interfering RNA (siRNA) or various blockers and openers of K(+) channels before exposing to H/R injury. The levels of lactate dehydrogenase (LDH) and creatine kinase (CK) in cellular supernatants and necrosis factor-α (TNF-α) in cellular lysates were measured by using ELISA. Expressions of HO-1 mRNA and protein were analyzed by using RT-PCR and Western blot respectively. Pretreatment of the cells undergoing H/R injury with LXA4 significantly reduced the LDH and CK levels induced by H/R injury, and increased the expressions and activity of HO-1. However, the protective effects of LXA4 were completely blocked by transfection of the cells with HO-1 siRNA, and were partially but significantly blocked by pretreatment of the cells with various blockers of K(+) channels. The LXA4-induced expressions of HO-1 in the cells were also inhibited by HO-1 siRNA and various blockers of K(+) channels. The inhibitory effects of LXA4 on enhanced TNF-α levels induced by H/R injury were abolished by transfection of the cells with HO-1 siRNA. In conclusion, the protective role of LXA4 on cardiomyocytes against H/R injury is related to upregulation of HO-1 via reduced production of TNF-α and activation of ATP-sensitive K(+) channels and calcium-sensitive K(+) channel.

Distinct signaling cascades elicited by different formyl peptide receptor 2 (FPR2) agonists

The formyl peptide receptor 2 (FPR2) is a remarkably versatile transmembrane protein belonging to the G-protein coupled receptor (GPCR) family. FPR2 is activated by an array of ligands, which include structurally unrelated lipids and peptide/proteins agonists, resulting in different intracellular responses in a ligand-specific fashion. In addition to the anti-inflammatory lipid, lipoxin A4, several other endogenous agonists also bind FPR2, including serum amyloid A, glucocorticoid-induced annexin 1, urokinase and its receptor, suggesting that the activation of FPR2 may result in potent pro- or anti-inflammatory responses. Other endogenous ligands, also present in biological samples, include resolvins, amyloidogenic proteins, such as beta amyloid (Aβ)-42 and prion protein (Prp)_106–126, the neuroprotective peptide, humanin, antibacterial peptides, annexin 1-derived peptides, chemokine variants, the neuropeptides, vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase activating polypeptide (PACAP)-27, and mitochondrial peptides. Upon activation, intracellular domains of FPR2 mediate signaling to G-proteins, which trigger several agonist-dependent signal transduction pathways, including activation of phospholipase C (PLC), protein kinase C (PKC) isoforms, the phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) pathway, the mitogen-activated protein kinase (MAPK) pathway, p38MAPK, as well as the phosphorylation of cytosolic tyrosine kinases, tyrosine kinase receptor transactivation, phosphorylation and nuclear translocation of regulatory transcriptional factors, release of calcium and production of oxidants. FPR2 is an attractive therapeutic target, because of its involvement in a range of normal physiological processes and pathological diseases. Here, we review and discuss the most significant findings on the intracellular pathways and on the cross-communication between FPR2 and tyrosine kinase receptors triggered by different FPR2 agonists.

D-series resolvin attenuates vascular smooth muscle cell activation and neointimal hyperplasia following vascular injury

Recent evidence suggests that specialized lipid mediators derived from polyunsaturated fatty acids control resolution of inflammation, but little is known about resolution pathways in vascular injury. We sought to determine the actions of D-series resolvin (RvD) on vascular smooth muscle cell (VSMC) phenotype and vascular injury. Human VSMCs were treated with RvD1 and RvD2, and phenotype was assessed by proliferation, migration, monocyte adhesion, superoxide production, and gene expression assays. A rabbit model of arterial angioplasty with local delivery of RvD2 (10 nM vs. vehicle control) was employed to examine effects on vascular injury in vivo. Local generation of proresolving lipid mediators (LC-MS/MS) and expression of RvD receptors in the vessel wall were assessed. RvD1 and RvD2 produced dose-dependent inhibition of VSMC proliferation, migration, monocyte adhesion, superoxide production, and proinflammatory gene expression (IC50≈0.1-1 nM). In balloon-injured rabbit arteries, cell proliferation (51%) and leukocyte recruitment (41%) were reduced at 3 d, and neointimal hyperplasia was attenuated (29%) at 28 d by RvD2. We demonstrate endogenous biosynthesis of proresolving lipid mediators and expression of receptors for RvD1 in the artery wall. RvDs broadly reduce VSMC responses and modulate vascular injury, suggesting that local activation of resolution mechanisms expedites vascular homeostasis.

Omega-3 fatty acid-derived resolvins and protectins in inflammation resolution and leukocyte functions: targeting novel lipid mediator pathways in mitigation of acute kidney injury

Inflammation, in conjunction with leukocytes, plays a key role in most acute kidney injury (AKI). Non-resolving renal inflammation leads to chronic fibrosis and renal failure. Resolvin D series (RvDs) and E series (RvEs), protectins, and maresins (MaRs) are endogenous omega-3 fatty acid-derived lipid mediators (LMs) that potently promote inflammation resolution by shortening neutrophil life span and promoting macrophage (Mf) non-phelogistic phagocytosis of apoptotic cells and the subsequent exit of Mfs from inflammatory tissue. 14S,21R-dihydroxy docosahexaenoic acid (14S,21R-diHDHA), a Mf-produced autacrine, reprograms Mfs to rescue vascular endothelia. RvD1, RvE1, or 14S,21R-diHDHA also switches Mfs to the phenotype that produces pro-resolving interleukin-10. RvDs or protectin/neuroprotectin D1 (PD1/NPD1) inhibits neutrophil infiltration into injured kidneys, blocks toll-like receptor -mediated inflammatory activation of Mfs and mitigates renal functions. RvDs also repress renal interstitial fibrosis, and PD1 promotes renoprotective heme-oxygenase-1 expression. These findings provide novel approaches for targeting inflammation resolution and LMs or modulation of LM-associated pathways for developing better clinical treatments for AKI.

Lipoxin A4 is a novel estrogen receptor modulator

Inflammation is intimately linked with naturally occurring remodeling events in the endometrium. Lipoxins comprise a group of short-lived, nonclassic eicosanoids possessing potent anti-inflammatory and proresolution properties. In the present study, we investigated the role of lipoxin A(4) (LXA(4)) in the endometrium and demonstrated that 15-LOX-2, an enzyme necessary for LX biosynthesis, is expressed in this tissue. Our results establish that LXA(4) possesses robust estrogenic activity through its capacity to alter ERE transcriptional activity, as well as expression of estrogen-regulated genes, alkaline phosphatase activity, and proliferation in human endometrial epithelial cells. Interestingly, LXA(4) also demonstrated antiestrogenic potential, significantly attenuating E2-induced activity. This estrogenic activity was directly mediated through estrogen receptors (ERs). Subsequent investigations determined that the actions of LXA(4) are exclusively mediated through ERα and closely mimic those of the potent estrogen 17β-estradiol (E2). In binding assays, LXA(4) competed with E2 for ER binding, with an IC(50) of 46 nM. Furthermore, LXA(4) exhibited estrogenic activity in vivo, increasing uterine wet weight and modulating E2-regulated gene expression. These findings reveal a previously unappreciated facet of LXA(4) bioactions, implicating this lipid mediator in novel immunoendocrine crosstalk mechanisms.

Modulation of leukotriene D4 attenuates the development of seizures in mice

The present study has been designed to pharmacologically investigate the effect of Montelukast sodium, a leukotriene D(4) receptor antagonist, and 1,2,3,4, tetrahydroisoquinoline, a leukotriene D(4) synthetic pathway inhibitor, on the pathophysiological progression of seizures using mouse models of kindled epilepsy and status epilepticus induced spontaneous recurrent seizures. Pentylenetetrazole (40 mg kg(-1)) (PTZ) administration every second day for a period of 15 d was used to elicit chemically induced kindled seizure activity in mice. In a separate set of groups, fifty consecutive electroshocks were delivered to mice using corneal electrodes with continuously increasing intensity with an inter-shock interval of 40s. Severity of kindled seizures was assessed in terms of a composite kindled seizure severity score (KSSS). Pilocarpine (100 mg kg(-1)) was injected every twenty minutes until the onset of status epilepticus. A spontaneous recurrent seizure severity score (SRSSS) was recorded as a measure of quantitative assessment of the progressive development of spontaneous recurrent seizures induced after pilocarpine status epilepticus. Sub-acute PTZ administration and electroshock induced the development of severe form of kindled seizures in mice. Severity of kindled seizures was assessed in terms of a composite kindled seizure severity score. Further, pharmacological status epilepticus elicited a progressive evolution of spontaneous recurrent seizures in the animals. However, Montelukast sodium, a leukotriene D(4) receptor antagonist, as well as 1,2,3,4, tetrahydroisoquinoline, a leukotriene D(4) synthetic pathway inhibitor, markedly and dose dependently suppressed the development of kindled seizures as well as pilocarpine induced spontaneous recurrent seizures. Therefore, leukotriene D(4) may be implicated in the pathogenesis of seizures.

Serum levels of lipoxin A(4) do not predict the development of subsequent asthma among young children with acute bronchiolitis

BACKGROUND

Acute bronchiolitis frequently causes wheezing in infants and young children, although its relationship to asthma remains unclear. We hypothesized that serum lipoxin A(4) levels may be used as an early predictive biomarker of subsequent asthma in young children with acute bronchiolitis.

METHODS

We recruited 69 children who were divided into 3 groups: 47 children younger than 24 months with acute bronchiolitis as an experimental group (Group 1); 11 children aged 2-24 months with viral acute gastroenteritis as a non-allergic control group (Group 2); and 11 children older than 24 months with physician-diagnosed asthma exacerbations as an asthma control group (Group 3). We determined white blood cell counts, eosinophil counts, and serum levels of C-reactive protein, interleukin-4, interleukin-5, prostaglandin E(2), tumor necrosis factor-alpha, and lipoxin A(4).

RESULTS

The mean serum levels of lipoxin A(4) in the groups with acute bronchiolitis (1), acute gastroenteritis (2), and asthma (3) were 0.0430.028, 0.0540.015, and 0.0510.031 ng/ml, respectively. When compared by t-tests, there were no significant differences between Groups 1 and 2, or Groups 1 and 3 (p0.05), despite a significant difference between Groups 2 and 3 (p=0.0392). In a final regression model, serum lipoxin A(4) levels were positively correlated with age, female gender, white blood cell counts, and interleukin-5 levels in all patients, while asthma patients had lower serum lipoxin A(4) levels compared to the other two groups.

CONCLUSION

Serum levels of lipoxin A(4) cannot be used as an early predictive diagnostic marker for asthma in young children with acute bronchiolitis.

Expression and signaling of formyl-peptide receptors in the brain

The human formyl-peptide receptor (FPR) and its variants FPRL1 and FPRL2 belong to the G-protein coupled seven transmembrane receptor (GPCR) family sensitive to pertussis toxin. FPR and FPRL1 were first detected in phagocytic leukocytes, and FPRL2 was found in monocytes and in dendritic cells. The three receptors were subsequently identified in other cell types or tissues, including neuronal cells and brain, where FPR and FPRL1 play a key role in angiogenesis, cell proliferation, protection against and cell death, as well as in neuroendocrine functions. Binding of different agonists to FPRs triggers several signaling pathways, activates NFkB and STAT3 transcriptional factors and induces the accumulation of the CDK inhibitors p21(waf1/cip1), p16(INK4) and p27(kip1). Signaling molecules, such as ERKs, JNK, PKC, p38MAPK, PLC and PLD are involved in these intracellular cascades. In this article we briefly review FPRs expression and signaling in neuronal cells.

Functional and pathological roles of the 12- and 15-lipoxygenases

The 12/15-lipoxygenase enzymes react with fatty acids producing active lipid metabolites that are involved in a number of significant disease states. The latter include type 1 and type 2 diabetes (and associated complications), cardiovascular disease, hypertension, renal disease, and the neurological conditions Alzheimer's disease and Parkinson's disease. A number of elegant studies over the last thirty years have contributed to unraveling the role that lipoxygenases play in chronic inflammation. The development of animal models with targeted gene deletions has led to a better understanding of the role that lipoxygenases play in various conditions. Selective inhibitors of the different lipoxygenase isoforms are an active area of investigation, and will be both an important research tool and a promising therapeutic target for treating a wide spectrum of human diseases.

Lipoxins: resolutionary road

The resolution of inflammation is an active process controlled by endogenous mediators with selective actions on neutrophils and monocytes. The initial phase of the acute inflammatory response is characterized by the production of pro-inflammatory mediators followed by a second phase in which lipid mediators with pro-resolution activities may be generated. The identification of these mediators has provided evidence for the dynamic regulation of the resolution of inflammation. Among these endogenous local mediators of resolution, lipoxins (LXs), lipid mediators typically formed during cell-cell interaction, were the first to be recognized. More recently, families of endogenous chemical mediators, termed resolvins and protectins, were discovered. LXs and aspirin-triggered LXs are considered to act as 'braking signals' in inflammation, limiting the trafficking of leukocytes to the inflammatory site. LXs are actively involved in the resolution of inflammation stimulating non-phlogistic phagocytosis of apoptotic cells by macrophages. Furthermore, LXs have emerged as potential anti-fibrotic mediators that may influence pro-fibrotic cytokines and matrix-associated gene expression in response to growth factors. Here, we provide a review and an update of the biosynthesis, metabolism and bioactions of LXs and LX analogues, and the recent studies on their therapeutic potential as promoters of resolution and fibro-suppressants.

ATLa, an aspirin-triggered lipoxin A4 synthetic analog, prevents the inflammatory and fibrotic effects of bleomycin-induced pulmonary fibrosis

Despite an increase in the knowledge of mechanisms and mediators involved in pulmonary fibrosis, there are no successful therapeutics available. Lipoxins (LX) and their 15-epimers, aspirin-triggered LX (ATL), are endogenously produced eicosanoids with potent anti-inflammatory and proresolution effects. To date, few studies have been performed regarding their effect on pulmonary fibrosis. In the present study, using C57BL/6 mice, we report that bleomycin (BLM)-induced lung fibrosis was prevented by the concomitant treatment with an ATL synthetic analog, ATLa, which reduced inflammation and matrix deposition. ATLa inhibited BLM-induced leukocyte accumulation and alveolar collapse as evaluated by histology and morphometrical analysis. Moreover, Sirius red staining and lung hydroxyproline content showed an increased collagen deposition in mice receiving BLM alone that was decreased upon treatment with the analog. These effects resulted in benefits to pulmonary mechanics, as ATLa brought to normal levels both lung resistance and compliance. Furthermore, the analog improved mouse survival, suggesting an important role for the LX pathway in the control of disease establishment and progression. One possible mechanism by which ATLa restrained fibrosis was suggested by the finding that BLM-induced myofibroblast accumulation/differentiation in the lung parenchyma was also reduced by both simultaneous and posttreatment with the analog (alpha-actin immunohistochemistry). Interestingly, ATLa posttreatment (4 days after BLM) showed similar inhibitory effects on inflammation and matrix deposition, besides the TGF-beta level reduction in the lung, reinforcing an antifibrotic effect. In conclusion, our findings show that LX and ATL can be considered as promising therapeutic approaches to lung fibrotic diseases.

Lipoxin A4: anti-inflammatory and anti-angiogenic impact on endothelial cells

Lipoxins (LX) are a class of eicosanoid that possesses a wide spectrum of antiinflammatory and proresolution bioactions. Here we have investigated the impact of the endogenously produced eicosanoid LXA(4) on endothelial cell inflammatory, proliferative, and antigenic responses. Using HUVECs we demonstrate that LXA(4) inhibits vascular endothelial growth factor (VEGF)-stimulated inflammatory responses including IL-6, TNF-alpha, IFN-gamma and IL-8 secretion, as well as endothelial ICAM-1 expression. Interestingly, LXA(4) up-regulated IL-10 production from HUVECs. Consistent with these antiinflammatory and proresolution responses to LXA(4), we demonstrate that LXA(4) inhibited leukotriene D(4) and VEGF-stimulated proliferation and angiogenesis as determined by tube formation of HUVECs. We have explored the underlying molecular mechanisms and demonstrate that LXA(4) pretreatment is associated with the decrease of VEGF-stimulated VEGF receptor 2 (KDR/FLK-1) phosphorylation and downstream signaling events including activation of phospholipase C-gamma, ERK1/2, and Akt.

Lipoxins: update and impact of endogenous pro-resolution lipid mediators

Lipoxins (LXs) are endogenously produced eicosanoids that are typically generated by transcellular biosynthesis. These trihydroxytetraene-containing lipid mediators and their stable synthetic analogues possess a wide spectrum of anti-inflammatory and pro-resolution bioactions both in vitro and in vivo. More recently, LXs have emerged as potential anti-fibrotic mediators that may influence pro-fibrotic cytokines and matrix-associated gene expression in response to platelet-derived growth factor (PDGF). Here we review the biosynthesis, metabolism and bioactions of LXs and LX analogues and their therapeutic potential.

Opposing regulation of neutrophil apoptosis through the formyl peptide receptor-like 1/lipoxin A4 receptor: implications for resolution of inflammation

Neutrophils have a central role in innate immunity, and their programmed cell death and removal are critical to the optimal expression as well as to efficient resolution of inflammation. Human neutrophils express the pleiotropic receptor formyl peptide receptor-like 1/lipoxin A4 (LXA(4)) receptor that binds a variety of ligands, including the acute-phase reactant serum amyloid A (SAA), the anti-inflammatory lipids LXA(4) and aspirin-triggered 15-epi-LXA(4) (ATL), and the glucocorticoid-inducible protein annexin 1. In addition to regulation of neutrophil activation and recruitment, these ligands have a profound influence on neutrophil survival and apoptosis with contrasting actions, mediating aggravation or resolution of the inflammatory response. Thus, annexin 1 accelerates, whereas SAA rescues human neutrophils from constitutive apoptosis by preventing mitochondrial dysfunction and subsequent activation of caspase-3. Furthermore, ATL overcomes the antiapoptosis signal from SAA and redirects neutrophils to caspase-mediated cell death. We review recent developments about the molecular basis of these actions and suggest a novel mechanism by which aspirin promotes resolution of acute inflammation and tissue injury.

Resolving inflammation: dual anti-inflammatory and pro-resolution lipid mediators

Active resolution of acute inflammation is a previously unrecognized interface between innate and adaptive immunity. Once thought to be a passive process, the resolution of inflammation is now shown to involve active biochemical programmes that enable inflamed tissues to return to homeostasis. This Review presents new cellular and molecular mechanisms for the resolution of inflammation, revealing key roles for eicosanoids, such as lipoxins, and recently discovered families of endogenous chemical mediators, termed resolvins and protectins. These mediators have anti-inflammatory and pro-resolution properties, thereby protecting organs from collateral damage, stimulating the clearance of inflammatory debris and promoting mucosal antimicrobial defence.

ATL-1, an analogue of aspirin-triggered lipoxin A4, is a potent inhibitor of several steps in angiogenesis induced by vascular endothelial growth factor

BACKGROUND AND PURPOSE

Vascular endothelial growth factor (VEGF) is the most important proangiogenic protein. We have demonstrated that ATL-1, a synthetic analogue of aspirin-triggered lipoxin A(4), inhibits VEGF-induced endothelial cell (EC) migration. In the present study, we investigated the effects of ATL-1 in several other actions stimulated by VEGF.

METHODS

Human umbilical vein ECs were treated with ATL-1 for 30 min before stimulation with VEGF. Cell proliferation was measured by thymidine incorporation. Adherent cells were determined by fluorescence intensity using a Multilabel counter. Expression and activity of matrix metalloproteinases (MMP) were analysed by western blot and zymography.

KEY RESULTS

ATL-1 inhibited EC adhesion to fibronectin via interaction with its specific receptor. Furthermore, VEGF-induced MMP-9 activity and expression were reduced by pretreatment with ATL-1. Because the transcription factor NF-kappaB has been implicated in VEGF-mediated MMP expression and EC proliferation, we postulated that ATL-1 might modulate the NF-kappaB pathway and, indeed, ATL-1 inhibited NF-kappaB nuclear translocation. Pretreatment of EC with ATL-1 strongly decreased VEGF-dependent phosphorylation of phosphainositide 3-kinase (PI3-K) and extracellular signal-regulated kinase-2 (ERK-2), two signalling kinases involved in EC proliferation. Inhibition of VEGF-induced EC proliferation by ATL-1 was antagonized by sodium orthovanadate, suggesting that this inhibitory activity was mediated by a protein tyrosine phosphatase. This was confirmed by showing that ATL-1 inhibition of VEGF receptor-2 (VEGFR-2) phosphorylation correlates with SHP-1 association with VEGFR-2.

CONCLUSIONS AND IMPLICATIONS

The synthetic 15-epi-lipoxin analogue, ATL-1, is a highly potent molecule exerting its effects on multiple steps of the VEGF-induced angiogenesis.

Formyl peptide-receptor like-1 requires lipid raft and extracellular signal-regulated protein kinase to activate inhibitor-κB kinase in human U87 astrocytoma cells

Formyl peptide-receptor like-1 (FPRL-1) may possess critical roles in Alzheimer's diseases, chemotaxis and release of neurotoxins, possibly through its regulation of nuclear factor-kappaB (NFkappaB). Here we illustrate that activation of FPRL-1 in human U87 astrocytoma or Chinese hamster ovary cells stably expressing the receptor resulted in the phosphorylations of inhibitor-kappaB kinase (IKK), an onset kinase for NFkappaB signaling cascade. FPRL-1 selective hexapeptide Trp-Lys-Tyr-Met-Val-Met (WKYMVM) promoted IKK phosphorylations in time- and dose-dependent manners while pre-treatment of pertussis toxin abrogated the Galpha(i/o)-dependent stimulations. The FPRL-1-mediated IKK phosphorylation required extracellular signal-regulated protein kinase (ERK), phosphatidylinositol 3-kinase and cellular Src (c-Src), but not c-Jun N-terminal kinase and p38 mitogen-activated protein kinase. Despite its ability to mobilize Ca(2+), WKYMVM did not require Ca(2+) for the modulation of IKK phosphorylation. Activation of FPRL-1 also induced NFkappaB-driven luciferase expression. Interestingly, cholesterol depletion from plasma membrane by methyl-beta-cyclodextrin abolished the FPRL-1-stimulated IKK phosphorylation, denoting the important role of lipid raft integrity in the FPRL-1 to IKK signaling. Furthermore, we demonstrated that in U87 cells, several signaling intermediates in the FPRL-1-IKK pathway including Galpha(i2), c-Src and ERK were constitutively localized at the raft microdomains. WKYMVM administration not only resulted in higher amount of ERK recruitment to the raft region, but also specifically stimulated raft-associated c-Src and ERK phosphorylations. Taken together, these results demonstrate that FPRL-1 is capable of activating NFkappaB signaling through IKK phosphorylation and this may serve as a useful therapeutical target for FPRL-1-related diseases.

Formyl peptide receptor like 1 differentially requires mitogen-activated protein kinases for the induction of glial fibrillary acidic protein and interleukin-1α in human U87 astrocytoma cells

Mitogen-activated protein kinases (MAPKs) are not only pivotal mediators of signal transduction but they also regulate diverse biological processes ranging from survival, proliferation and differentiation to apoptosis. By using human U87 astrocytoma and transfected FPRL1/CHO cells, we have demonstrated that activation of FPRL1 with WKYMVM effectively phosphorylated JNK and ERK. Interestingly, p38 MAPK activation was only seen with FPRL1/CHO cells. The MAPK phosphorylations in response to WKYMVM were blocked by WRW(4) (a selective FPRL1 antagonist), but not cyclosporine H (a well-known FPR antagonist). The key signaling intermediates in the MAPK pathways were also delineated. G(i)/G(o) proteins, Src family tyrosine kinases, but not phosphatidylinositol-3 kinase, protein kinase C and calmodulin-dependent kinase II, were required to transmit signals from FPRL1 toward JNK, ERK and p38 MAPK. Furthermore, phospholipase Cbeta was distinctively involved in the regulation of JNK but not the other MAPKs. Importantly, WKYMVM-stimulated U87 cells triggered noticeable increases in glial fibrillary acidic protein (GFAP) and interleukin-1alpha (IL-1alpha), which are correlated with reactive astrocytosis. In contrast, GFAP expression was not altered following stimulation with N-formyl-methionyl-leucyl-phenylalanine. Moreover, inhibitions of G(i)/G(o) proteins and JNK completely abolished both GFAP and IL-1alpha upregulations by FPRL1, while blockade of the MEK/ERK cascade exclusively suppressed the GFAP production. Consistently, overexpression of MEK1 and constitutively active JNKK in U87 cells led to ERK and JNK activation, respectively, which was accompanied with markedly increased GFAP production. We have thus identified a possible linkage among FPRL1, MAPKs, astrocytic activation and the inflammatory response.

Cysteinyl-leukotrienes and their receptors in asthma and other inflammatory diseases: critical update and emerging trends

Cysteinyl-leukotrienes (cysteinyl-LTs), that is, LTC4, LTD4, and LTE4, trigger contractile and inflammatory responses through the specific interaction with G protein-coupled receptors (GPCRs) belonging to the purine receptor cluster of the rhodopsin family, and identified as CysLT receptors (CysLTRs). Cysteinyl-LTs have a clear role in pathophysiological conditions such as asthma and allergic rhinitis (AR), and have been implicated in other inflammatory conditions including cardiovascular diseases, cancer, atopic dermatitis, and urticaria. Molecular cloning of human CysLT1R and CysLT2R subtypes has confirmed most of the previous pharmacological characterization and identified distinct expression patterns only partially overlapping. Interestingly, recent data provide evidence for the immunomodulation of CysLTR expression, the existence of additional receptor subtypes, and of an intracellular pool of CysLTRs that may have roles different from those of plasma membrane receptors. Furthermore, genetic variants have been identified for the CysLTRs that may interact to confer risk for atopy. Finally, a crosstalk between the cysteinyl-LT and the purine systems is being delineated. This review will summarize and attempt to integrate recent data derived from studies on the molecular pharmacology and pharmacogenetics of CysLTRs, and will consider the therapeutic opportunities arising from the new roles suggested for cysteinyl-LTs and their receptors.

Aspirin-Triggered Lipoxins Override the Apoptosis-Delaying Action of Serum Amyloid A in Human Neutrophils: A Novel Mechanism for Resolution of Inflammation

Elevated plasma levels of the acute-phase reactant serum amyloid A (SAA) have been used as a marker and predictor of inflammatory diseases. SAA regulates leukocyte activation; however, it is not known whether it also modulates neutrophil apoptosis, which is critical to the optimal expression and resolution of inflammation. Culture of human neutrophils with SAA (0.1-20 microg/ml) markedly prolonged neutrophil longevity by delaying constitutive apoptosis. SAA evoked concurrent activation of the ERK and PI3K/Akt signaling pathways, leading to phosphorylation of BAD at Ser(112) and Ser(136), respectively, and to prevention of collapse of mitochondrial transmembrane potential, cytochrome c release, and caspase-3 activation. These actions were abrogated by pharmacological inhibition of the formyl peptide receptor, ERK or PI3K. Furthermore, aspirin-triggered 15-epi-lipoxin A(4) (15-epi-LXA(4)) and its stable analog 15-epi-16-p-fluorophenoxy-LXA(4), which binds to the same receptor as SAA, effectively overrode the antiapoptosis signal from SAA even when neutrophils were treated with 15-epi-LXA(4) at either 1 or 4 h postculture with SAA. 15-Epi-LXA(4) itself did not affect neutrophil survival and apoptosis. Our results indicate that SAA at clinically relevant concentrations promotes neutrophil survival by suppressing the apoptotic machinery, an effect that can be opposed by 15-epi-LXA(4). The opposing actions of SAA and aspirin-triggered 15-epi-LXA(4) may contribute to the local regulation of exacerbation and resolution of inflammation, respectively.

The Lipoxin A4 receptor is coupled to SHP-2 activation: implications for regulation of receptor tyrosine kinases

Mesangial cell proliferation is pivotal to the pathology of glomerular injury in inflammation. We have previously reported that lipoxins, endogenously produced eicosanoids with anti-inflammatory and pro-resolution bioactions, can inhibit mesangial cell proliferation in response to several agents. This process is associated with elaborate receptor cross-talk involving modification receptor tyrosine kinase phosphorylation (McMahon, B., Mitchell, D., Shattock, R., Martin, F., Brady, H. R., and Godson, C. (2002) FASEB J. 16, 1817-1819). Here we demonstrate that the lipoxin A(4) (LXA(4)) receptor is coupled to activation and recruitment of the SHP-2 (SH2 domain-containing tyrosine phosphatase-2) within a lipid raft microdomain. Using site-directed mutagenesis of the cytosolic domain of the platelet-derived growth factor receptor beta (PDGFRbeta), we report that mutation of the sites for phosphatidylinositol 3-kinase (Tyr(740) and Tyr(751)) and SHP-2 (Tyr(763) and Tyr(1009)) recruitment specifically inhibit the effect of LXA(4) on the PDGFRbeta signaling; furthermore inhibition of SHP-2 expression with short interfering RNA constructs blocked the effect of LXA(4) on PDGFRbeta phosphorylation. We demonstrate that association of the PDGFRbeta with lipid raft microdomains renders it susceptible to LXA(4)-mediated dephosphorylation by possible reactivation of oxidatively inactivated SHP-2. These data further elaborate on the potential mechanisms underlying the anti-inflammatory, proresolution, and anti-fibrotic bioactions of lipoxins.

Signal transduction involved in protective effects of 15(R/S)-methyl- lipoxin A(4) on mesangioproliferative nephritis in rats

Studies have shown that lipoxin A(4) (LXA(4)) inhibited proliferation of mesangial cells in vitro induced by platelet-derived growth factor, epidermal growth factor, leukotriene D(4) or tumor necrosis factor-alpha. In this study, we investigated the protective effects of 15(R/S)-methyl-LXA(4) on mesangioproliferative nephritis in rats and the signal transduction involved in actions of 15(R/S)-methyl-LXA(4). Mesangioproliferative nephritis was induced by a single intravenous injection of the mouse monoclonal anti-Thy1.1 antibodies. The nephritic rats were treated by intravenous injection of 15(R/S)-methyl-LXA(4) every 8h until the rats were sacrificed. There were increments in glomerular infiltration of leukocytes, expressions of protein and mRNA of interleukin (IL)-1beta and IL-6, activities of nuclear factor-kappaB (NF-kappaB) in nephritic rats from day 1 to 4 after induction of nephritis. The enhanced proteinuria, proliferation score of mesangial cells, glomerular proliferating cell nuclear antigen (PCNA) positive cells, activities of phosphorylated phosphoinositide 3-kinase (PI3-K), Akt(1), alpha-smooth muscle actin (alpha-SMA) and signal transducer and activator of transcription 3(STAT(3)), and reduced expression of p27(kip1) were found on day 4 after induction of nephritis. Treatment of nephritic rats with 15(R/S)-methyl-LXA(4) significantly reduced the protenuria, glomerular infiltration of leukocyte, expressions of protein and mRNA of IL-1beta and IL-6, proliferation score of mesangial cells, glomerular PCNA positive cells, activities of phosphorylated PI3-K, Akt(1), alpha-SMA, NF-kappaB and STAT(3), and ameliorated the decrement in p27(kip1) induced by anti-Thy1.1 antibodies. Protective effects of 15(R/S)-methyl-LXA(4) on nephritis induced by anti-Thy1.1 antibodies were related to PI3-K/Akt(1)/p27(kip1)/cyclin pathway, STAT(3) and NF-kappaB pathway-dependent signal transduction.

Mechanisms of Disease: leukotrienes and lipoxins in scleroderma lung disease--insights and potential therapeutic implications

Scleroderma interstitial lung disease (SLD) is a leading cause of morbidity and mortality in patients with systemic sclerosis. Although the pathogenesis of SLD is not clear, excessive fibrosis and inflammatory cell infiltration are the main histologic features of this disorder. Leukotrienes and lipoxins are two functionally different classes of lipoxygenase-derived eicosanoids. Leukotrienes are potent proinflammatory mediators and directly and indirectly stimulate fibroblast chemotaxis, proliferation, and collagen synthesis. Lipoxins counter-regulate the proinflammatory actions of leukotrienes and activate resolution of the inflammatory response. In addition, lipoxins inhibit growth-factor-induced fibroblast proliferation and collagen synthesis. Studies using bronchoalveolar lavage have revealed that there is an overproduction of proinflammatory and profibrotic leukotrienes in the lungs of patients with SLD, and that leukotriene levels correlate with inflammatory indices within the lungs. Moreover, the increased levels of leukotrienes in these patients are not balanced by an upregulation of anti-inflammatory and antifibrotic lipoxins. Unopposed actions of leukotrienes might, therefore, induce chronic inflammation and fibrosis in the lungs of SLD patients. Accordingly, pharmacologic correction of a leukotriene-lipoxin imbalance using leukotriene inhibitors or lipoxin analogs might be a new approach to the treatment of SLD.

The lipoxin receptor ALX: potent ligand-specific and stereoselective actions in vivo

Lipoxins (LXs) and aspirin-triggered LX (ATL) are trihydroxytetraene-containing eicosanoids generated from arachidonic acid that are distinct in structure, formation, and function from the many other proinflammatory lipid-derived mediators. These endogenous eicosanoids have now emerged as founding members of the first class of lipid/chemical mediators involved in the resolution of the inflammatory response. Lipoxin A(4) (LXA(4)), ATL, and their metabolic stable analogs elicit cellular responses and regulate leukocyte trafficking in vivo by activating the specific receptor, ALX. ALX was the first receptor cloned and identified as a G protein-coupled receptor (GPCR) for lipoxygenase-derived eicosanoids with demonstrated cell type-specific signaling pathways. ALX at the level of DNA has sequence homology to the N-formylpeptide receptor and as an orphan GPCR was initially referred to as the N-formylpeptide receptor-like 1. Although LXA(4) is the endogenous potent ligand for ALX activation, a number of peptides can also activate this receptor to stimulate calcium mobilization and chemotaxis in vitro. In contrast with LXA(4), the counterparts of many of these peptides in vivo remain to be established. The purpose of this review is to highlight the molecular characterization of the ALX receptor and provide an overview of the ALX-LXA(4) axis responsible for anti-inflammatory and proresolving signals in vivo. The information in this review provides further support for the initial nomenclature proposition for this GPCR as ALX.

Regulation of phosphatidylinositol 3-kinase by polyisoprenyl phosphates in neutrophil-mediated tissue injury

Neutrophils play a central role in host defense, inflammation, and tissue injury. Recent findings indicate a novel role for polyisoprenyl phosphates (PIPPs) as natural down-regulatory signals in neutrophils. The relationship between PIPPs and neutrophil early activating signals, such as phosphoinositides, has not been previously determined. Here, we establish presqualene diphosphate (PSDP) as an endogenous PIPP regulator of phosphatidylinositol 3-kinase (PI3K). In human neutrophils, leukotriene B4 (LTB4) triggered rapid decreases in PSDP and reciprocal increases in PI3K activity. In addition, PSDP was identified by gas chromatography/mass spectrometry in p110gamma-PI3K immunoprecipitates obtained 30 s after LTB4, indicating a physical interaction between PSDP and PI3K in activated neutrophils. Moreover, PSDP (0.4-800 pmol) directly inhibited recombinant human p110gamma-PI3K activity. During an experimental model of lung injury and inflammation, a reciprocal relationship was also present in vivo for lung PSDP and PI3K activity. To investigate its therapeutic potential, we developed a new PSDP structural mimetic that blocked human neutrophil activation and mouse lung PI3K activity and inflammation. Together, our findings indicate that PSDP is an endogenous PI3K inhibitor, and suggest that in inflammatory diseases characterized by excessive neutrophil activation, PIPPs can serve as structural templates in a novel antineutrophil therapeutic strategy to limit tissue injury.

CysLT1 receptor-induced human airway smooth muscle cells proliferation requires ROS generation, EGF receptor transactivation and ERK1/2 phosphorylation

Background

Cysteine-containing leukotrienes (cysteinyl-LTs) are pivotal inflammatory mediators that play important roles in the pathophysiology of asthma, allergic rhinitis, and other inflammatory conditions. In particular, cysteinyl-LTs exert a variety of effects with relevance to the aetiology of asthma such as smooth muscle contraction, eosinophil recruitment, increased microvascular permeability, enhanced mucus secretion and decreased mucus transport and, finally, airway smooth muscle cells (ASMC) proliferation. We used human ASMC (HASMC) to identify the signal transduction pathway(s) of the leukotriene D₄ (LTD₄)-induced DNA synthesis.

Methods

Proliferation of primary HASMC was measured by [³H]thymidine incorporation. Phosphorylation of EGF receptor (EGF-R) and ERK1/2 was assessed with a polyclonal anti-EGF-R or anti-phosphoERKl/2 monoclonal antibody. A Ras pull-down assay kit was used to evaluate Ras activation. The production of reactive oxygen species (ROS) was estimated by measuring dichlorodihydrofluorescein (DCF) oxidation.

Results

We demonstrate that in HASMC LTD₄-stimulated thymidine incorporation and potentiation of EGF-induced mitogenic signaling mostly depends upon EGF-R transactivation through the stimulation of CysLT₁-R. Accordingly, we found that LTD₄ stimulation was able to trigger the increase of Ras-GTP and, in turn, to activate ERK1/2. We show here that EGF-R transactivation was sensitive to pertussis toxin (PTX) and phosphoinositide 3-kinase (PI3K) inhibitors and that it occurred independently from Src activity, despite the observation of a strong impairment of LTD₄-induced DNA synthesis following Src inhibition. More interestingly, CysLT₁-R stimulation increased the production of ROS and N-acetylcysteine (NAC) abolished LTD₄-induced EGF-R phosphorylation and thymidine incorporation.

Conclusion

Collectively, our data demonstrate that in HASMC LTD₄ stimulation of a G_i/o coupled CysLT₁-R triggers the transactivation of the EGF-R through the intervention of PI3K and ROS. While PI3K and ROS involvement is an early event, the activation of Src occurs downstream of EGF-R activation and is followed by the classical Ras-ERK1/2 signaling pathway to control G1 progression and cell proliferation.

Lipoxin A4 inhibits connective tissue growth factor-induced production of chemokines in rat mesangial cells

Connective tissue growth factor (CTGF) is involved in mitogenesis, matrix production, and chemotaxis in mesenchymal cells. The effects of CTGF on the production of chemokines remain unclear. The present studies investigate the regulatory role of CTGF in the production of fractalkine, monocyte chemoattractant protein-1 (MCP-1), and RANTES (regulated upon activation, normal T cell expressed and secreted) in cultured mesangial cells of rats, and the modulatory effects of lipoxin A(4) (LXA(4)) on actions of CTGF. CTGF enhanced the mRNA expression and protein release of fractalkine, MCP-1, and RANTES, the expression of phospho (P)-p42/44 mitogen-activated protein kinase (MAPK), P-phosphoinositide 3-kinase (PI3-K), P-Akt, and activity of nuclear factor-kappaB (NF-kappaB) in mesangial cells. P-p42/44 MAPK blockade inhibited the CTGF-induced expression of P-p42/44 MAPK but not NF-kappaB, and partially decreased the levels of the above chemokines in supernatants. P-PI3-K blockade downregulated the CTGF-stimulated expression of P-PI3-K, P-Akt, and NF-kappaB but not P-p42/44 MAPK, and partially decreased the release of the above chemokines. NF-kappaB blockade abrogated the CTGF-activated NF-kappaB and partially decreased the secretion of the above chemokines. LXA(4) dose-dependently inhibited the CTGF-stimulated mRNA expression and protein release of the above chemokines, and the expression of P-p42/44MAPK, P-PI3-K, P-Akt, and NF-kappaB. In conclusion, these results demonstrate that CTGF induces production of fractalkine, MCP-1, and RANTES via the p42/44 MAPK-, PI3-K/Akt-, and NF-kappaB-dependent signal pathway, and LXA(4) downregulates the above effects of CTGF on rat mesangial cells.

Microarray and bioinformatic detection of novel and established genes expressed in experimental anti-Thy1 nephritis

BACKGROUND

Microarray technology is a powerful tool that can probe the molecular pathogenesis of renal injury. In this present study microarray analysis was used to monitor serial changes in the renal transcriptome of a rat model of mesangial proliferative glomerulonephritis. Administration of anti-Thy1 antibody results in phases of acute mesangial injury (day 2), cell proliferation (day 5), matrix expansion (days 5 and 7), and subsequent healing (day 14).

METHODS

Using Affymetrix (RAE230A) microarrays coupled with sequential primary biologic function-focused and secondary "baited" global cluster analysis, a cohort of established and putative novel modulators of mesangial cell turnover was identified.

RESULTS

Cluster analysis of proliferative genes identified a number of gene expression profiles. The most striking pattern was increased gene expression at day 5, a cluster that included platelet-derived growth factor (PDGF), cyclins and transforming growth factor-beta (TGF-beta). The gene expression patterns identified by primary focused cluster analysis were used as bioinformatic bait and resulted in the identification of novel families of genes such as the S100 family. The expression of established and novel genes was confirmed using reverse transcription-polymerase chain reaction (RT-PCR). Next, in vivo gene expression was compared to PDGF-stimulated mesangial cells in vitro revealing similar patterns of dysregulation.

CONCLUSION

Transcriptomic analysis defined both known and novel molecules involved in mesangial cell proliferation in vitro and in vivo and defined a panel of molecules that are potential contributors to mesangial cell dysfunction in glomerular disease.

Transforming growth factor-beta-regulated gene transcription and protein expression in human GFAP-negative lamina cribrosa cells

Primary open-angle glaucoma (POAG) is a progressive optic neuropathy, which is a major cause of worldwide visual impairment and blindness. Pathological hallmarks of the glaucomatous optic nerve head (ONH) include retinal ganglion cell axon loss and extracellular matrix (ECM) remodeling of the lamina cribrosa layer. Transforming growth factor-beta (TGF-beta) is an important pro-fibrotic modulator of ECM metabolism, whose levels are elevated in human POAG lamina cribrosa tissue compared with non-glaucomatous controls. We hypothesize that in POAG, lamina cribrosa (LC) glial cells respond to elevated TGF-beta, producing a remodeled ONH ECM. Using Affymetrix microarrays, we report the first study examining the effect of TGF-beta1 on global gene expression profiles in glial fibrillary acidic acid (GFAP)-negative LC glial cells in vitro. Prominent among the differentially expressed genes were those with established fibrogenic potential, including CTGF, collagen I, elastin, thrombospondin, decorin, biglycan, and fibromodulin. Independent TaqMan and Sybr Green quantitative PCR analysis significantly validated genes involved in regulation of cell proliferation (platelet-derived growth factor [PDGF-alpha]), angiogenesis (vascular endothelial growth factor [VEGF]), ECM accumulation and degradation (CTGF, IL-11, and ADAMT-S5), and growth factor binding (ESM-1). Bioinformatic analysis of the ESM-1 promoter identified putative Smad and Runx transcription factor binding sites, and luciferase assays confirmed that TGF-beta1 drives transcription of the ESM-1 gene. TGF-beta1 induces expression and release of ECM components in LC cells, which may be important in regulating matrix remodeling in the lamina cribrosa. In disease states such as POAG, the LC cell may represent an important pro-fibrotic cell type and an attractive target for novel therapeutic strategies.