IL-17A and IL-17RC Expression in the Macula of the Human Eye with Age-Related Macular Degeneration

Abstract

 

Purpose:

 

Age related macular degeneration (AMD) is the most common cause of irreversible central blindness amongst the elderly. It is thought that various genetic and environmental factors drive the dysregulation of macrophages, cytokines, chemokines and complement factors. Though the ensuing inflammation and oxidative stress have been well described, the precise pathogenesis remains unknown. Th17 cytokines are implicated in several inflammatory diseases like multiple sclerosis and uveitis. In AMD patients, complement factor C5b is capable of inducing Th17 cytokines and both their levels are significantly elevated in the peripheral blood. Preliminary data have shown that IL-17 is also locally elevated in human AMD eyes and in those of a mouse model for AMD, Ccl2-/-/Cx3cr1-/- on rd8 background. Moreover, there is an IL-17RC linked expression of CXCR4 in peripheral CD14+ monocytes and there are elevated levels of CXCL12/SDF-1 found in the normal eye. This setup may predispose to a pathologic homing of these monocytes to the eye and incite an inflammatory process. In addition, people with a methylated IL-17RC promoter seem to be protected from developing AMD. Here we further elucidate the role of IL-17 in the pathogenesis of AMD by investigating IL-17A, IL-17F and IL-17RC expression in AMD and normal maculae.

 

Methods:

 

The macular retina and choroid of 33 paraffin-embedded, archived AMD eyes and 7 age-matched normal eyes were microdissected and their RNA was isolated (Paradise reagent system) for cDNA synthesis (MX3000P QPCR system). IL-17A, IL-17F and IL-17RC mRNAs were quantitated by real time PCR monitored with SYBR green fluorescence.

 

Results:

 

40% of the 40 total microdissected samples (13 AMD and 3 normal eyes) yielded valid data. Significantly elevated relative transcript levels of IL-17A (AMD, 70.6±27.4; Normal, 4.59±3.4; p<0.034) and IL-17RC (AMD, 3260 ± 844; Normal, 50.1 ± 28.9; p<0.002) were found in AMD maculae compared to normal maculae. IL-17F mRNA was undetectable in all eyes. Of the 13 AMD samples, 3 of them had geographic atrophy while the remaining 10 had the exudative neovascular form. There was no significant difference in the relative expression of transcript levels of IL-17A and IL-17RC when geographic AMD was compared to exudative AMD.

 

Conclusions:

 

Significantly higher relative expression levels of IL-17RC and IL-17A but not IL-17F are in AMD macula compared to the controls. These findings support the aforementioned hypothesis of a monocyte driven inflammatory pathogenesis. It also suggests that IL-17A may primarily induce the inflammatory process through IL-17RC in the maculae.

 

Keywords: cytokines/chemokines • age-related macular degeneration • pathology: human