An activated unfolded protein response promotes retinal degeneration and triggers an inflammatory response in the mouse retina

Abstract

Recent studies on the endoplasmic reticulum stress have shown that the unfolded protein response (UPR) is involved in the pathogenesis of inherited retinal degeneration caused by mutant rhodopsin. However, the main question of whether UPR activation actually triggers retinal degeneration remains to be addressed. Thus, in this study, we created a mouse model for retinal degeneration caused by a persistently activated UPR to assess the physiological and morphological parameters associated with this disease state and to highlight a potential mechanism by which the UPR can promote retinal degeneration. We performed an intraocular injection in C57BL6 mice with a known unfolded protein response (UPR) inducer, tunicamycin (Tn) and examined animals by electroretinography (ERG), spectral domain optical coherence tomography (SD-OCT) and histological analyses. We detected a significant loss of photoreceptor function (over 60%) and retinal structure (35%) 30 days post treatment. Analysis of retinal protein extracts demonstrated a significant upregulation of inflammatory markers including interleukin-1β (IL-1β), IL-6, tumor necrosis factor-α (TNF-α), monocyte chemoattractant protein-1 (MCP-1) and IBA1. Similarly, we detected a strong inflammatory response in mice expressing either Ter349Glu or T17M rhodopsin (RHO). These mutant rhodopsin species induce severe retinal degeneration and T17M rhodopsin elicits UPR activation when expressed in mice. RNA and protein analysis revealed a significant upregulation of pro- and anti-inflammatory markers such as IL-1β, IL-6, p65 nuclear factor kappa B (NF-kB) and MCP-1, as well as activation of F4/80 and IBA1 microglial markers in both the retinas expressing mutant rhodopsins. We then assessed if the Tn-induced inflammatory marker IL-1β was capable of inducing retinal degeneration by injecting C57BL6 mice with a recombinant IL-1β. We observed ~19% reduction in ERG a-wave amplitudes and a 29% loss of photoreceptor cells compared with control retinas, suggesting a potential link between pro-inflammatory cytokines and retinal pathophysiological effects. Our work demonstrates that in the context of an established animal model for ocular disease, the persistent activation of the UPR could be responsible for promoting retinal degeneration via the UPR-induced pro-inflammatory cytokine IL-1β.

Protective effect of sulforaphane against retinal degeneration in the Pde6rd10 mouse model of retinitis pigmentosa

“…However, when UPR cannot alleviate ER stress by self-regulation, pro-apoptotic mechanisms play the predominant role, which causes apoptosis of cells. (34,35) The present study found that a sustained dose of SFN significantly down-regulated the protein expression of GRP78/BiP in ER in rd10 retina, suggesting that SFN may inhibit ER stress and thereby reduce photoreceptor apoptosis. The data of this study confirm the protective effect of SFN in a relatively early stage of an RP mouse model.…”

Deferiprone Protects against Photoreceptor Degeneration Induced by Tunicamycin in the Rat Retina

“…Saline containing 3% dimethylsulfoxide or DFP solution containing 3% dimethylsulfoxide was injected to the contralateral eye. The final dose of tunicamycin, which was determined according to previous reports, [6][7][8][9] was 300 nmol/eye. The final dose of DFP was 0.5 nmol/eye or 5 nmol/eye.…”

“…4,5) The intravitreal tunicamycin injection model is used for an animal model of photoreceptor-specific degeneration. [6][7][8][9] Increase of reactive oxygen species (ROS) is also known to cause ER stress, Parkinson's disease, [10][11][12] Alzheimer's disease, [11][12][13] and photoreceptor degeneration. 14) These ROS are believed to be generated at least in part by Fenton reaction, producing hydroxyl radical from hydrogen peroxide.…”

Targeting Caspase-12 to Preserve Vision in Mice With Inherited Retinal Degeneration

“…Nuclear factor-jB is known to control the inflammatory response in cells, and together with TNFa, monocyte chemoattractant protein (MCP)-1, and IL-6 was found to be upregulated in P15 T17M retinas. 3 To determine if Csp-12 ablation in P30 T17M retinas elevates NF-jB signaling in response to, as an example, microbial infection and thus causes photoreceptor cell death, we analyzed the levels of NF-jB (p65). We were interested in NF-jB in particular because NFjB-promoted signaling has been shown to be activated in the Csp-12 À/À mouse experimental model of colonic inflammation.…”

“…1,2 The study of molecular mechanisms underlying the retinopathy in these mice has demonstrated that the unfolded protein response (UPR), along with inflammatory signaling, significantly contributes to the progression of retinal degeneration. 3 Thus, the activation of all three UPR branches, including protein kinase R-like endoplasmic reticulum kinase (PERK), activating transcriptional factor 6 (ATF6), and inositol-requiring enzyme 1 (IRE1), has been detected in T17M retinas as early as postnatal (P) day 15. Moreover, we have recently revealed that the rate of retinal degeneration could be significantly altered in these mice by modifying the expression of UPR hallmark proteins.…”