Expression of phospholipases A2 and C in human corneal epithelial cells

Phospholipase Cγ2 is critical for Ca2+ flux and cytokine production in anti-fungal innate immunity of human corneal epithelial cells

Background

Fungal keratitis (FK) is a sight-threatening disease, accounting for a significant portion with its complex presentation, suboptimal efficacy of the existing therapies and uncontrollable excessive innate inflammation. Phospholipase C-γ2 (PLCγ2) is a non-receptor tyrosine kinase that plays an important role at the early period of innate immunity. This study aimed to identify the role of PLCγ2 in Dectin-1-mediated Ca²⁺ Flux and its effect on the expression of proinflammatory mediators at the exposure to Aspergillus fumigatus (A. fumigatus) hyphae antigens in human corneal epithelial cells (HCECs).

Methods

The HCECs were preincubated with or without different inhibitors respectively before A. fumigatus hyphae stimulation. Intracellular calcium flux in HCECs and levels of PLCγ2 and spleen-tyrosine kinase (Syk) were detected by fluorescence imaging and Western Blotting. The expression of proinflammatory mediators was determined by reverse transcriptase polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA).

Results

We demonstrated that an intracellular Ca²⁺ flux in HCECs was triggered by A. fumigatus hyphae and could be reduced by pre-treatment with PLCγ2-inhibitor U73122. A. fumigatus hyphae induced PLCγ2 phosphorylation was regulated by Dectin-1 via Syk. Furthermore, PLCγ2-deficient HCECs showed a drastic impairment in the Ca²⁺ signaling and the secretion of IL-6, CXCL1 and TNF-α.

Conclusions

PLCγ2 plays a critical role for Ca²⁺ Flux in HCECs stimulated by A. fumigatus hyphae. Syk acts upstream of PLCγ2 in the Dectin-1 signaling pathway. The expressions of proinflammatory mediators induced by A. fumigatus are regulated by the activation of Dectin-1-mediated PLCγ2 signaling pathway in HCECs.

Gabapentin Attenuates Ocular Inflammation: In vitro and In vivo Studies

To investigate the effects of gabapentin, a structural analog of γ-amino butyric acid (GABA), on the inflammatory response of lipopolysaccharide (LPS)-stimulated rabbit corneal cells (SIRC) and on endotoxin-induced uveitis (EIU) in rabbits. We investigated the LPS-induced expression of several inflammatory mediators, such as TNF-α, IL-1β, cPLA₂, COX-2, and PGE₂ in the SIRC cells with or without gabapentin treatment. Gabapentin treatment significantly (p < 0.05) attenuated cytokines production, cPLA₂ activation, COX-2 expression, and PGE₂ levels in SIRC. EIU was induced by an intraocular injection of 0.1 μg of LPS in albino rabbit eye. After 7 and 24 h from LPS injection clinical signs of ocular inflammation were examined by slit lamp with or without topical treatment of 0.5% gabapentin. Tears, aqueous, cornea, conjunctiva, and iris-ciliary body were collected and inflammatory biomarkers assessed. Topical treatment with gabapentin significantly (p < 0.05) reduced clinical signs and biomarkers of inflammation compared with the LPS group both at 7 and 24 h. In conclusion, the results generated in the present study suggest that ophthalmic formulation based on gabapentin may be useful in the treatment of inflammatory conditions associated to ocular pain such as uveitis, and that clinical studies to evaluate this possibility may be warranted.

Longitudinal changes in tear fluid lipidome brought about by eyelid-warming treatment in a cohort of meibomian gland dysfunction

Meibomian gland dysfunction (MGD) is a leading cause of evaporative dry eye and ocular discomfort characterized by an unstable tear film principally attributed to afflicted delivery of lipids to the ocular surface. Herein, we elucidated longitudinal tear lipid alterations associated with disease alleviation and symptom improvement in a cohort of MGD patients undergoing eyelid-warming treatment for 12 weeks. Remarkably, eyelid-warming resulted in stark reductions in lysophospholipids (P < 0.001 for lyso-plasmalogen phosphatidylethanolamine, lysophosphatidylcholine, and lysophosphatidylinositol), as well as numerous PUFA-containing diacylglyceride species in tears, accompanied by significant increases in several PUFA-containing phospholipids. These changes in tear lipidomes suggest that eyelid-warming leads to diminished activity of tear phospholipases that preferentially target PUFA-containing phospholipids. In addition, treatment led to appreciable increases (P < 0.001) in O-acyl-ω-hydroxy-FAs (OAHFAs), which are lipid amphiphiles critical to the maintenance of tear film stability. Longitudinal changes in the tear lipids aforementioned also significantly (P < 0.05) correlated with reduced rate of ocular evaporation and improvement in ocular symptoms. The foregoing data thus indicate that excess ocular surface phospholipase activity detrimental to tear film stability could be alleviated by eyelid warming alone without application of steroids and identify tear OAHFAs as suitable markers to monitor treatment response in MGD.

Meibum lipid composition in Asians with dry eye disease

BACKGROUND

Previous lipidomic analyses of the human meibum had largely focused on individuals from non-Asian populations, despite the higher prevalence of dysfunctional tear syndrome (DTS) observed across Asia. Information pertaining to the alterations in lipid profiles in relation to DTS onset and progression is also lacking and warrants comprehensive experimental analysis.

METHODOLOGIES/PRINCIPAL FINDINGS

We examined the meibum lipidome of 27 DTS patients and 10 control subjects for a total of 256 lipid species from 12 major lipid classes, including cholesteryl ester (CE), wax ester (WE), triacylglyceride (TAG), (O-acyl)-ω-hydroxy fatty acid (OAHFA), glycerophospholipids (phosphatidylcholine, PC; phosphatidylethanolamine, PE; phosphatidylinositol, PI; phosphatidylglycerol, PG) and sphingolipids (sphingomyelin, SM; ceramide, Cer; glucosylceramide, GluCer; dihexosylceramide, DihexCer). Neutral lipids were analysed using high-performance liquid-chromatography coupled with mass spectrometry (HPLC/MS) and tandem mass spectrometry (MS/MS) was used for the qualitative and quantitative analysis of polar lipid species. DTS patients were classified into three severity groups (i.e. mild, moderate and severe) based on the ocular surface disease index (OSDI). A significantly lower level of TAG (p<0.05) was observed in patients under the moderate category compared to the mild category. Notably, a number of OAHFA species displayed consistently decreasing levels that correlate with increasing disease severity. An attempt was also made to investigate the changes in meibum lipid profiles of DTS patients compared to normal individuals classified based on OSDI score. Several unsaturated TAG and PC species were found at significantly higher levels (p<0.05) in patients than controls.

CONCLUSION

The current study presents, for the first time, a comprehensive lipidome of meibum from individuals of an Asian ethnicity, which can potentially offer new insights into the higher prevalence of DTS observed amongst Asian populations. This study also represents an attempt towards identification of lipid species in meibum which could serve as marker for DTS.

Significance of lipid mediators in corneal injury and repair

Corneal injury induces an inflammatory reaction and damages the sensory nerves that exert trophic influences in the corneal epithelium. Alterations in normal healing disrupt the integrity and function of the tissue with undesirable consequences, ranging from dry eye and loss of transparency to ulceration and perforation. Lipids play important roles in this complex process. Whereas lipid mediators such as platelet activating factor (PAF) and cyclooxygenease-2 metabolites contribute to tissue damage and neovascularization, other mediators, such as the lipoxygenase (LOX) derivatives from arachidonic acid, 12- and 15-hydroxy/hydroperoxyeicosatetraenoic acids, and lipoxin A4, act as second messengers for epidermal growth factor to promote proliferation and repair. Stimulation of the cornea with pigment epithelial derived factor in the presence of docosahexaenoic acid gives rise to the synthesis of neuroprotectin D1, a derivative of LOX activity, and increases regeneration of corneal nerves. More knowledge about the role that lipids play in corneal wound healing can provide insight into the development of new therapeutic approaches for treating corneal injuries. PAF antagonists, lipoxins, and neuroprotectins can be effective therapeutic tools for maintaining the integrity of the cornea.

Variation near complement factor I is associated with risk of advanced AMD

A case-control association study for advanced age-related macular degeneration was conducted to explore several regions of interest identified by linkage. This analysis identified a single nucleotide polymorphism just 3' of complement factor I on chromosome 4 showing significant association (P<10(-7)). Sequencing was performed on coding exons in linkage disequilibrium with the detected association. No obvious functional variation was discovered that could be the proximate cause of the association, suggesting a noncoding regulatory mechanism.

Human secretory phospholipase A2, group IB in normal eyes and in eye diseases

PURPOSE

Secretory phospholipases A(2) (sPLA(2)) are enzymes involved in lipid turnover. We recently identified sPLA(2) group IB (GIB) in the rat retina as well as in cerebral neurons and found upregulation to occur in response to light damage and seizures, respectively. The purpose of the present study was to identify human GIB (hGIB) in the normal human eye and investigate the pattern of expression in patients with eye diseases involving hGIB-rich cells.

METHODS

Human GIB mRNA was identified in the human retina by means of in situ hybridization and polymerase chain reaction. Antibodies against hGIB were obtained and immunohistochemical staining was performed on paraffin-embedded sections of normal and pathological eyes. Donor eyes from patients with descemetization of the cornea, Fuchs' corneal endothelial dystrophy, age-related macular degeneration, malignant choroidal melanoma, retinitis pigmentosa and glaucoma were evaluated.

RESULTS

Expression of hGIB was found in various cells of the eye. The most abundant expression was found in retinal pigment epithelium (RPE) cells, the inner photoreceptor segments, ganglion cells and the corneal endothelium. We explored diseases involving hGIB-rich cells and found downregulation of hGIB in proliferating RPE cells as well as in diseased corneal endothelial cells.

CONCLUSIONS

Human GIB is highly expressed in cells with neurodermal origin. The pattern of expression of hGIB in diseases involving hGIB-rich cells demonstrated a downregulation of hGIB in migrating RPE cells and in diseased corneal endothelium.

Effect of retinoic acid on gene expression in human conjunctival epithelium: secretory phospholipase A2 mediates retinoic acid induction of MUC16

PURPOSE

How vitamin A contributes to the maintenance of the wet-surfaced phenotype at the ocular surface is not well understood. This study sought to identify vitamin A-responsive genes in ocular surface epithelia using gene microarray analysis of cultures of a human conjunctival epithelial (HCjE) cell line grown with all-trans-retinoic acid (RA). The analysis showed that secretory phospholipase A(2) group IIA (sPLA(2)-IIA) was the gene most upregulated by RA, followed by the membrane-associated mucin MUC16 at a later time point. Since eicosanoids, the product of arachidonic acid generated by the PLA(2) family, have been shown to increase mucin production, this study sought to determine whether sPLA(2) mediates the RA induction of MUC16.

METHODS

HCjE cells were cultured with or without RA for 3, 6, 24, and 48 hours. Complementary RNA prepared from RNA of the HCjE cells was hybridized to human gene chips and analyzed using commercial software. Microarray data on mucin expression were validated by real-time PCR. To investigate whether sPLA(2) is associated with RA-induced MUC16 upregulation, HCjE cells were incubated with RA and the broad-spectrum PLA(2) inhibitor aristolochic acid (ArA) or the specific sPLA(2)-IIA inhibitor LY315920, followed by analysis of MUC16 mRNA and protein by real-time PCR and Western blot analysis.

RESULTS

After RA addition, 28 transcripts were upregulated and 6 downregulated by more than twofold (P < 0.01) at both 3 and 6 hours (early phase). Eighty gene transcripts were upregulated and 45 downregulated at both 24 and 48 hours (late phase). Group IIA sPLA(2), significantly upregulated by 24 hours, and MUC16 were the most upregulated RNAs by RA at 48 hours. sPLA(2) upregulation by RA was confirmed by Western blot analysis. When HCjE cells were incubated with RA plus ArA or specific inhibitor of sPLA(2)-IIA, LY315920, the RA-induced MUC16 mRNA was significantly reduced (P < 0.01).

CONCLUSIONS

The RA-associated upregulation of membrane-associated mucin MUC16 at late phase appears to be through sPLA(2)-IIA. Upregulation of this hydrophilic membrane-associated mucin may be one of the important mechanisms by which vitamin A facilitates maintenance of the wet-surfaced phenotype on the ocular surface.