Control of chemokine production at the blood-retina barrier

Microarray analysis of gene expression in West Nile virus-infected human retinal pigment epithelium

PURPOSE

To identify key genes differentially expressed in the human retinal pigment epithelium (hRPE) following low-level West Nile virus (WNV) infection.

METHODS

Primary hRPE and retinal pigment epithelium cell line (ARPE-19) cells were infected with WNV (multiplicity of infection 1). RNA extracted from mock-infected and WNV-infected cells was assessed for differential expression of genes using Affymetrix microarray. Quantitative real-time PCR analysis of 23 genes was used to validate the microarray results.

RESULTS

Functional annotation clustering of the microarray data showed that gene clusters involved in immune and antiviral responses ranked highly, involving genes such as chemokine (C-C motif) ligand 2 (CCL2), chemokine (C-C motif) ligand 5 (CCL5), chemokine (C-X-C motif) ligand 10 (CXCL10), and toll like receptor 3 (TLR3). In conjunction with the quantitative real-time PCR analysis, other novel genes regulated by WNV infection included indoleamine 2,3-dioxygenase (IDO1), genes involved in the transforming growth factor-β pathway (bone morphogenetic protein and activin membrane-bound inhibitor homolog [BAMBI] and activating transcription factor 3 [ATF3]), and genes involved in apoptosis (tumor necrosis factor receptor superfamily, member 10d [TNFRSF10D]). WNV-infected RPE did not produce any interferon-γ, suggesting that IDO1 is induced by other soluble factors, by the virus alone, or both.

CONCLUSIONS

Low-level WNV infection of hRPE cells induced expression of genes that are typically associated with the host cell response to virus infection. We also identified other genes, including IDO1 and BAMBI, that may influence the RPE and therefore outer blood-retinal barrier integrity during ocular infection and inflammation, or are associated with degeneration, as seen for example in aging.

Novel serum proteomic signatures in a non-human primate model of retinal injury

PURPOSE

To identify candidate protein biomarkers in sera indicative of acute retinal injury.

METHODS

We used laser photocoagulation as a model of acute retinal injury in Rhesus macaques. In a paired-control study design, we collected serum from each animal (n=6) at 4 h, 1 day, and 3 days following a mock procedure and then again following retinal laser treatment that produced mild lesions. Samples were fractionated by isoelectric focusing, digested with trypsin, and analyzed by liquid chromatography/tandem mass spectrometry (LC-MS/MS). Spectral counting was used to determine relative protein abundances and identify proteins with statistically significant differences between control and treated sera.

RESULTS

Mild retinal injury was confirmed by fundus photography and histological examination. The average number of total proteins detected by LC-MS/MS was 908±82 among samples from all three time points. Following statistical analysis and employing stringent filtering criteria, a total of 19 proteins were identified as being significantly more abundant in sera following laser-induced retinal injury, relative to control sera. Many of the proteins detected were unique to one time point. However, four proteins (phosphoglycerate kinase 1, keratin 18, Lewis alpha-3-fucosyltransferase, and ephrin receptor A2) showed differences that were significant at both 4 h and 1 day after laser treatment, followed by a decrease to baseline levels by day 3.

CONCLUSIONS

A serum biomarker response to mild retinal laser injury was demonstrated in a primate model. Among the proteins detected with highest significant differences, most are upregulated within 24 h, and their appearance in the serum is transient. It is conceivable that a panel of these proteins could provide a means for detecting the acute-phase response to retinal injury. Further investigation of these candidate biomarkers and their correlation to retinal damage is warranted.

Polymorphisms of chemokine and chemokine receptor genes in idiopathic immune-mediated posterior segment uveitis

PURPOSE

Chemokines are important inflammatory mediators that play a crucial role in uveitis. Polymorphisms in chemokine genes can alter the expression of these genes in the inflammatory cells, which, in turn, can affect the clinical phenotype of the disease. The purpose of this study was to identify polymorphisms in chemokine genes that can predict visual outcome in patients with immune-mediated posterior segment uveitis.

METHODS

This is a case-control study of 141 Caucasians with idiopathic immune-mediated posterior segment uveitis and 282 controls matched by age and ethnicity. Six polymorphisms in four genes, (MCP-1-2518A/G, RANTES-403G/A, RANTES-28C/G, CCR2 V64I, CCR5-59029G/A, and CCR5 32 bp deletion) were analyzed by sequence specific primers polymerase chain reaction.

RESULTS

Patients with G allele at MCP-1-2581 developed the disease at an early age as compared to patients with A allele corrected p value pc=0.003. Also patients with A allele at RANTES-403 position developed less severe disease and had better visual outcome when compared with patients with G allele (pc=0.02) Final visual acuity after 18 months was better in patients with 32 bp deletion of the CCR5 gene and in patients with the CCR2 wild-type genotype pc=0.02 and pc=0.04, respectively. Patients with the CCR2 64I allele also had a higher risk of developing an elevated intraocular pressure as compared to patients with the wild-type genotype (pc=0.007).

CONCLUSIONS

Though the utility for prediction of disease susceptibility of the studied polymorphisms in chemokine genes is in general not robust, we have found that polymorphisms in chemokine genes can influence the outcome of patients with idiopathic immune-mediated posterior segment uveitis. These associations require further analysis in other groups of patients.

An apolipoprotein E variant may protect against age-related macular degeneration through cytokine regulation

Age-related macular degeneration (AMD) is the leading cause of visual impairment and blindness among the elderly in Western countries. Genetic factors, age, cigarette smoking, nutrition, and exposure to light have been identified as AMD risk factors. In this study, we investigated the association between ApoE C112R/R158C single nucleotide polymorphisms (which determine the E2, E3, and E4 isoforms) and age-related macular degeneration (AMD), and the mechanism underlying the association. Genomic DNA was extracted from 133 clinically screened controls, 94 volunteers with a younger mean age, 120 patients with advanced AMD, and 40 archived ocular AMD slides for single nucleotide polymorphism typing. The effects of recombinant ApoE isoforms on CCL2 (a chemokine), CX3CR1 (a chemokine receptor), and VEGF (a cytokine) expression in cultured human retinal pigment epithelium (RPE) cells were tested and serum cholesterol profiles of the clinically screened subjects were analyzed. ApoE112R (E4) distribution differed significantly between AMD patients and controls. ApoE112R allele frequency was 10.9% in the AMD group when compared with 16.5% in the younger controls and 18.8% in the clinically screened controls. The pathologically diagnosed archived AMD cases had the lowest allele frequency of 5%. No significant differences in ApoE158C (E2) distribution were observed among the groups. A meta-analysis of 8 cohorts including 4,289 subjects showed a strong association between AMD and 112R, but not 158C. In vitro studies found that recombinant ApoE suppresses CCL2 and VEGF expression in RPE cells. However, the E4 isoform showed more suppression than E3 in both cases. These results further confirm the association between ApoE112R and a decreased risk of AMD development. The underlying mechanisms may involve differential regulation of both CCL2 and VEGF by the ApoE isoforms.