Loss of GPR109A results in RPE dysfunction, neurodegeneration and increased oxidative stress with age: Potential relevance to AMD

Abstract

Purpose : Oxidative stress and inflammation-induced damage to retinal pigmented epithelium (RPE) is central to the pathogenesis of age-related macular degeneration (AMD). We have demonstrated the G-protein coupled GPR109A, a key regulator of lipid homeostasis, exerts anti-inflammatory and neuroprotective effects in retina. Given that in retina GPR109A is expressed most robustly in RPE, here we characterized in detail age-dependent alterations in RPE morphology and function in Gpr109^-/- (knockout, KO) mice.

Methods : Wild-type (WT; Gpr109a^+/+) and knockout (KO; Gpr109a^-/-) C57BL/6J male mice were assessed at 2 months (young), 5 months (middle-aged), and 12 months (old) of age. Neuroretinal and RPE morphology was assessed in live animals by Spectral Domain Optical Coherence Tomography (SD-OCT); outer retinal function was analyzed by scotopic electroretinogram (ERG). Gene microarray coupled with Ingenuity Pathway Analysis (IPA) was performed with a focus on evaluation of alterations in immunomodulatory and oxidative stress-regulating genes. Gene changes identified by microarray/IPA were confirmed by qPCR. Cell death was assessed by TUNEL assay and Western blotting for caspase 3.

Results : Basement membrane thickening, cell death, barrier disruption and diminished scoptopic flash responses were evident in KO retinas even at young ages. These findings worsened with increased age and corresponded with an increase in the number of TUNEL- and caspase 3-positive cells and significant reductions in total retinal thickness. Microarray/IPA analyses revealed gene alterations consistent with an age-dependent increase in pro-inflammatory and pro-oxidant gene expression and coordinate decreased anti-inflammatory gene expression in KO RPE.

Conclusions : We conclude that the absence of GPR109A in vivo has deleterious effects on RPE function and overall retinal tissue homeostasis that worsens with age. We conclude that GPR109A not only plays a role in lipid metabolism, but functions as a critical regulator of inflammation. Therefore, targeting this receptor may be of therapeutic value in the management of age-related retinal diseases such as AMD.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.