Ocular immune privilege and the impact of intraocular inflammation

Immune privilege, a characteristic of the internal compartments of the eye, is a physiologic mechanism that is designed to provide the eye with protection against pathogens while protecting the delicate visual axis from the sight-destroying potential of immunogenic inflammation. It is assumed that the presence of intraocular inflammation is incompatible with the existence of immune privilege. The validity of this assumption has been tested in four animal models of intraocular inflammation-systemic and local endotoxin-induced uveitis (EIU), mycobacterial adjuvant-induced uveitis (MAIU), and experimental autoimmune uveitis (EAU). Immune privilege was assessed in inflamed eyes by growth of intracamerally injected allogeneic tumor cells, by the capacity to support immune deviation following intracameral injection of antigen (ovalbumin, OVA), by assaying protein, leukocyte, and selected cytokine content of aqueous humor (AqH), and by capacity of inflamed AqH to suppress T cell activation in vitro. The results indicate that, irrespective of the type of inflammation, tumor cells formed progressively growing tumors in inflamed eyes. Moreover, OVA injected into the anterior chamber of eyes inflamed by MAIU and EAU failed to induce immune deviation. AqH from inflamed eyes reflected breakdown of the blood:ocular barrier as well as transient loss of its immunosuppressive properties. Immunosuppressive microenvironments routinely reemerged in inflamed eyes, and the immunosuppressive agent present under these circumstances in AqH was active TGF beta2. It is concluded that immune privilege is surprisingly resistant to abolition by intraocular inflammation, and that maintenance of immune privilege in the face of ongoing inflammation depends upon the emergence of progressive and partially different immunosuppressive mechanisms.     

Lipid droplets in inflammation and cancer

Accumulation of lipid droplets (also known as lipid bodies or adiposomes) within leukocytes, epithelial cells, hepatocytes and other non-adipocytic cells is a frequently observed phenotype in infectious, neoplastic and other inflammatory conditions. Lipid droplet biogenesis is a regulated cellular process that culminates in the compartmentalization of lipids and of an array of enzymes, protein kinases and other proteins, suggesting that lipid droplets are inducible organelles with roles in cell signaling, regulation of lipid metabolism, membrane trafficking and control of the synthesis and secretion of inflammatory mediators. Enzymes involved in eicosanoid synthesis are localized at lipid droplets and lipid droplets are sites for eicosanoid generation in cells during inflammation and cancer. In this review, we discuss the current evidence related to the biogenesis and function of lipid droplets in cell metabolism and signaling in inflammation and cancer. Moreover, the potential of lipid droplets as markers of disease and targets for novel anti-inflammatory and antineoplastic therapies will be discussed.     

Lipid scavenging macrophages and inflammation

Macrophages are professional phagocytes, indispensable for maintenance of tissue homeostasis and integrity. Depending on their resident tissue, macrophages are exposed to highly diverse metabolic environments. Adapted to their niche, they can contribute to local metabolic turnover through metabolite uptake, conversion, storage and release. Disturbances in tissue homeostasis caused by infection, inflammation or damage dramatically alter the local milieu, impacting macrophage activation status and metabolism. In the case of persisting stimuli, defective macrophage responses ensue, which can promote tissue damage and disease. Especially relevant herein are disbalances in lipid rich environments, where macrophages are crucially involved in lipid uptake and turnover, preventing lipotoxicity. Lipid uptake is to a large extent facilitated by macrophage expressed scavenger receptors that are dynamically regulated and important in many metabolic diseases. Here, we review the receptors mediating lipid uptake and summarize recent findings on their role in health and disease. We further highlight the underlying pathways driving macrophage lipid acquisition and their impact on myeloid metabolic remodelling.     

L-arginine supplementation improves responses to injury and inflammation in dextran sulfate sodium colitis

Inflammatory bowel disease (IBD), consisting of Crohn's disease and ulcerative colitis (UC), results in substantial morbidity and is difficult to treat. New strategies for adjunct therapies are needed. One candidate is the semi-essential amino acid, L-arginine (L-Arg), a complementary medicine purported to be an enhancer of immunity and vitality in the lay media. Using dextran sulfate sodium (DSS) as a murine colonic injury and repair model with similarities to human UC, we assessed the effect of L-Arg, as DSS induced increases in colonic expression of the y(+) cationic amino acid transporter 2 (CAT2) and L-Arg uptake. L-Arg supplementation improved the clinical parameters of survival, body weight loss, and colon weight, and reduced colonic permeability and the number of myeloperoxidase-positive neutrophils in DSS colitis. Luminex-based multi-analyte profiling demonstrated that there was a marked reduction in proinflammatory cytokine and chemokine expression with L-Arg treatment. Genomic analysis by microarray demonstrated that DSS-treated mice supplemented with L-Arg clustered more closely with mice not exposed to DSS than to those receiving DSS alone, and revealed that multiple genes that were upregulated or downregulated with DSS alone exhibited normalization of expression with L-Arg supplementation. Additionally, L-Arg treatment of mice with DSS colitis resulted in increased ex vivo migration of colonic epithelial cells, suggestive of increased capacity for wound repair. Because CAT2 induction was sustained during L-Arg treatment and inducible nitric oxide (NO) synthase (iNOS) requires uptake of L-Arg for generation of NO, we tested the effect of L-Arg in iNOS(-/-) mice and found that its benefits in DSS colitis were eliminated. These preclinical studies indicate that L-Arg supplementation could be a potential therapy for IBD, and that one mechanism of action may be functional enhancement of iNOS activity.     

Lipid peroxidation: a mechanism for alcohol-induced testicular injury

That alcohol abuse may lead to testicular lipid peroxidation is suggested by the fact that ethanol is a known testicular toxin and its chronic use leads to both endocrine and reproductive failure. Because testicular membranes are rich in polyenoic fatty acids that are prone to undergo peroxidative decomposition, it is reasonable to consider that lipid peroxidation may contribute to the membrane injury and gonadal dysfunction that occurs as a result of alcohol abuse and/or chronic use. The present report reviews the studies supporting the concept that testicular lipid peroxidation is a metabolic consequence of chronic alcohol administration to animals and that its presence correlates with the gonadal injury present in animals ingesting ethanol for prolonged periods. Consistent with such a mechanism for putative alcohol-associated testicular toxicity are the observed reductions in the testicular content of polyenoic fatty acids and glutathione (GSH) content of the testes of alcohol-fed animals as compared to isocalorically fed controls. The later finding demonstrates that ethanol modifies the precarious antioxidant balance of testicular tissue such that enhanced peroxidation can occur. It is well known that peroxidation injury can be attenuated when it occurs in association with dietary vitamin A supplementation. Thus, it is of interest to note that vitamin A, acting as an antioxidant, stabilizes testicular membranes by reducing lipid peroxidation and prevents the alcohol-induced atrophy that occurs in animals not receiving vitamin-A-enriched diets. Taken together, these observations suggest that the enhanced peroxidation of testicular lipids that occurs following ethanol exposure may be an important factor in the pathogenesis of alcohol-associated gonadal injury.     

Oxygen-derived radicals: a link between reperfusion injury and inflammation

Oxygen-derived free radicals (superoxide and hydroxyl) and related species (hydrogen peroxide and hypohalous acids) have well-defined roles in the inflammatory process. Their actions include the killing of microorganisms as well as participation in cell-to-cell communication among phagocytes via the activation of a superoxide-dependent chemoattractant. The active oxygen species also have roles in postischemic injury brought about by the conversion during ischemia of the enzyme xanthine dehydrogenase (EC 1.1.1.204) to the radical-producing xanthine oxidase (EC 1.1.3.22). Although the enzymes responsible for producing superoxide in inflammation and ischemia are quite distinct, and are triggered by very different events, there are points of interplay in the two mechanisms whereby an ischemia/reperfusion-induced injury would lead to inflammation, and conversely whereby inflammation could lead to impairment of the circulation and hence to ischemic injury.     

Ocular immune privilege: a review

The definition of the term 'immune privilege' has evolved over the last century. Current usage refers to a state within a particular organ or tissue in which elements of normal immunity are absent. The fact that this deficiency is thought to be generally beneficial has compelled others to go a step further and venture that immune privilege acts to minimize expression of immunopathology. The purpose of this article is to review which parts of the eye hold immune privileged status, what mechanisms contribute to it, and what clinical benefits may have driven the development of these unique immune environments. The article ends with an examination of recent studies which have sought to use components of ocular immune privilege to prevent systemic autoimmune disease.     

Lipid peroxidation and endothelial cell injury: implications in atherosclerosis

Vascular endothelial cells, which play an active role in the physiological processes of vessel tone regulation and vascular permeability, form a border separating deeper layers of the blood vessel wall and cellular interstitial space from the blood and circulating cells. Damage or dysfunction of endothelial cells may reduce the effectiveness of the endothelium to act as a selectively permeable barrier to plasma components, including cholesterol-rich lipoprotein remnants. This may be involved in the etiology of atherosclerosis. Experimental evidence indicates that free radical-mediated lipid peroxidation can induce endothelial cell injury/dysfunction. Reactive oxygen species, including peroxidized lipids capable of initiating cell injury, may be generated within endothelial cells, be present in plasma components, or be derived from neutrophils or other blood-borne cells. Lipid peroxidation could initiate or promote the process of atherosclerotic lesion formation by directly damaging endothelial cells, and by enhancing the adhesion and activation of neutrophils and the susceptibility of platelets to aggregate. Endothelial cell injury by lipid hydroperoxides also could increase the uptake of LDL into the vessel wall. These events and other cellular dysfunctions may individually or collectively initiate and/or help to sustain the development of atherosclerosis.     

Modulating stress responses by the UPRosome: a matter of life and death

The accumulation of unfolded proteins in the endoplasmic reticulum (ER) triggers the unfolded protein response (UPR) through the activation of specialized sensors including inositol-requiring enzyme-1α (IRE1α). IRE1α signals by assembling a dynamic protein platform referred to as the UPRosome, where different modulator and adaptor proteins assemble to regulate the kinetics and amplitude of UPR effector responses. Conversely, chronic ER stress can cause apoptosis. Recent evidence indicates that several apoptosis-related proteins interact with IRE1α, regulating its prosurvival activities and performing a dual function in the regulation of cell death and adaptation to stress. Based on the increasing relevance of ER stress to the occurrence of diverse pathological conditions, strategies to target and modulate the assembly and composition of the UPRosome could have therapeutic benefits for disease intervention.     

Differential T cell response in central and peripheral nerve injury: connection with immune privilege.

The central nervous system (CNS), unlike the peripheral nervous system (PNS), is an immune-privileged site in which local immune responses are restricted. Whereas immune privilege in the intact CNS has been studied intensively, little is known about its effects after trauma. In this study, we examined the influence of CNS immune privilege on T cell response to central nerve injury. Immunocytochemistry revealed a significantly greater accumulation of endogenous T cells in the injured rat sciatic nerve than in the injured rat optic nerve (representing PNS and CNS white matter trauma, respectively). Use of the in situ terminal deoxytransferase-catalyzed DNA nick end labeling (TUNEL) procedure revealed extensive death of accumulating T cells in injured CNS nerves as well as in CNS nerves of rats with acute experimental autoimmune encephalomyelitis, but not in injured PNS nerves. Although Fas ligand (FasL) protein was expressed in white matter tissue of both systems, it was more pronounced in the CNS. Expression of major histocompatibility complex (MHC) class II antigens was found to be constitutive in the PNS, but in the CNS was induced only after injury. Our findings suggest that the T cell response to central nerve injury is restricted by the reduced expression of MHC class II antigens, the pronounced FasL expression, and the elimination of infiltrating lymphocytes through cell death.     

Lipid composition of human cerebral white matter and myelin in phenylketonuria

Abstract— White matter and purified myelin from cerebral tissue obtained at autopsy from four phenylketonuric and five non-phenylketonuric mentally-retarded patients were analysed for lipids, DNA and protein. The lipid composition of the white matter and myelin was compared with that of a representative non-myelin component of white matter, the crude mitochondrial fraction. The total lipid content was significantly lower and the ratio of cholesterol to galactolipid was significantly higher in the white matter from the PKU patients than in that from the non-PKU patients. The lipid compositions of the myelin and ‘mitochondrial’ fraction, although differing from each other, did not exhibit appreciable differences between the PKU and non-PKU brain samples. However, the amount of myelin recovered from the brains of the PKU patients was, on the average, 40 percent lower than that recovered from non-PKU brains. The abnormal cholesterol: galactolipid ratio of PKU white matter could be accounted for by the altered proportion of myelin to non-myelin lipid components. The finding in PKU brains of a normal composition of lipids in the purified myelin and the absence of cholesterol esters in the white matter suggest that the deficiency in myelin may reflect an early arrest of myelination.     

Inhibition of Pyk2 blocks lung inflammation and injury in a mouse model of acute lung injury

Background

Proline-rich tyrosine kinase 2 (Pyk2) is essential in neutrophil degranulation and chemotaxis in vitro. However, its effect on the process of lung inflammation and edema formation during LPS induced acute lung injury (ALI) remains unknown. The goal of the present study was to determine the effect of inhibiting Pyk2 on LPS-induced acute lung inflammation and injury in vivo.

Methods

C57BL6 mice were given either 10 mg/kg LPS or saline intratracheally. Inhibition of Pyk2 was effected by intraperitoneal administration TAT-Pyk2-CT 1 h before challenge. Bronchoalveolar lavage analysis of cell counts, lung histology and protein concentration in BAL were analyzed at 18 h after LPS treatment. KC and MIP-2 concentrations in BAL were measured by a mouse cytokine multiplex kit. The static lung compliance was determined by pressure-volume curve using a computer-controlled small animal ventilator. The extravasated Evans blue concentration in lung homogenate was determined spectrophotometrically.

Results

Intratracheal instillation of LPS induced significant neutrophil infiltration into the lung interstitium and alveolar space, which was attenuated by pre-treatment with TAT-Pyk2-CT. TAT-Pyk2-CT pretreatment also attenuated 1) myeloperoxidase content in lung tissues, 2) vascular leakage as measured by Evans blue dye extravasation in the lungs and the increase in protein concentration in bronchoalveolar lavage, and 3) the decrease in lung compliance. In each paradigm, treatment with control protein TAT-GFP had no blocking effect. By contrast, production of neutrophil chemokines MIP-2 and keratinocyte-derived chemokine in the bronchoalveolar lavage was not reduced by TAT-Pyk2-CT. Western blot analysis confirmed that tyrosine phosphorylation of Pyk2 in LPS-challenged lungs was reduced to control levels by TAT-Pyk2-CT pretreatment.

Conclusions

These results suggest that Pyk2 plays an important role in the development of acute lung injury in mice and that pharmacological inhibition of Pyk2 might provide a potential therapeutic strategy in the pretreatment for patients at imminent risk of developing acute lung injury.     

Cytokine-mediated inflammation in acute lung injury

Clinical acute lung injury (ALI) is a major cause of acute respiratory failure in critically ill patients. There is considerable experimental and clinical evidence that pro- and anti-inflammatory cytokines play a major role in the pathogenesis of inflammatory-induced lung injury from sepsis, pneumonia, aspiration, and shock. A recent multi-center clinical trial found that a lung-protective ventilatory strategy reduces mortality by 22% in patients with ALI. Interestingly, this protective ventilatory strategy was associated with a marked reduction in the number of neutrophils and the concentration of pro-inflammatory cytokines released into the airspaces of the injured lung. Further research is needed to establish the contribution of cytokines to both the pathogenesis and resolution of ALI.     

Mechanisms of inflammation in spinal cord injury

An increase in protease activity is a hallmark event of the secondary injury cascade following contusion SCI. Elevated levels of protease activity result in the degradation of cytoskeletal components and myelin proteins essential for cellular function and survival. We have shown that a member of the cathepsin protease family is affected by SCI. The excessive release and activity of cathepsin B, a fairly ubiquitous lysosomal cysteine protease, has been implicated in several pathologies including tumor metastasis and progression, arthritis and Alzheimer's disease. Thus, our goal was to characterize any SCI-induced changes in cathepsin B expression. Following a T12 laminectomy and a moderate contusion (NYU device), the gene and protein profiles of cathepsin B in rats were examined using real-time PCR and immunoblots, respectively. Both the contusion injured animals and the time-matched sham controls exhibited elevated pro-enzyme protein levels (37 kDa form) at the lesion site, with significant differences between the two groups at 48 h, 72 h and 7 days post-SCI. Furthermore, there was a surge in the active species of the protein with significant differences at 72 h and 7 days post-SCI for the 30 kDa form and at 48 h. and 7 days for the 25 kDa form. Real-time PCR revealed increases in cathepsin B mRNA levels following contusion SCI as early as 6 h postinjury. These data indicate that SCI causes an up-regulation of cathepsin gene expression and protein levels, and suggest that this protease may be involved in the secondary injury cascade perhaps for as long as 1 week postinjury.