In Vivo Visualization of Endoplasmic Reticulum Stress in the Retina Using the ERAI Reporter Mouse

• Published in: Investigative ophthalmology & visual science Vol. 56; no. 11; pp. 6961 - 6970
• Main Authors: Alavi, Marcel V, Chiang, Wei-Chieh, Kroeger, Heike, Yasumura, Douglas, Matthes, Michael T, Iwawaki, Takao, LaVail, Matthew M, Gould, Douglas B, Lin, Jonathan H
• Format: Journal Article
• Language: English
• Published: United States The Association for Research in Vision and Ophthalmology 01-10-2015
• Subjects: Animals; Endoplasmic Reticulum - diagnostic imaging; Endoplasmic Reticulum - pathology; Endoplasmic Reticulum - physiology; Endoplasmic Reticulum Stress - drug effects; Endoplasmic Reticulum Stress - physiology; Longitudinal Studies; Membrane Proteins - analysis; Membrane Proteins - physiology; Mice; Mice, Transgenic; Ophthalmoscopy; Polymerase Chain Reaction; Protein-Serine-Threonine Kinases - analysis; Protein-Serine-Threonine Kinases - physiology; Retina - chemistry; Retina - diagnostic imaging; Retina - drug effects; Retina - pathology; Retina - physiology; Retinal Cell Biology; Signal Transduction - physiology; Tomography, Optical Coherence; Tunicamycin - pharmacology; Ultrasonography
• ISSN: 1552-5783; 0146-0404; 1552-5783
• DOI: 10.1167/iovs.15-16969

Endoplasmic reticulum (ER) stress activates inositol requiring enzyme 1 (IRE1), a key regulator of the unfolded protein response. The ER stress activated indicator (ERAI) transgenic mouse expresses a yellow fluorescent GFP variant (Venus) when IRE1 is activated by ER stress. We tested whether ERAI mice would allow for real-time longitudinal studies of ER stress in living mouse eyes.
We chemically and genetically induced ER stress, and qualitatively and quantitatively studied the Venus signal by fluorescence ophthalmoscopy. We determined retinal cell types that contribute to the signal by immunohistology, and we performed molecular and biochemical assays using whole retinal lysates to assess activity of the IRE1 pathway.
We found qualitative increase in vivo in fluorescence signal at sites of intravitreal tunicamycin injection in ERAI eyes, and quantitative increase in ERAI mice mated to RhoP23H mice expressing ER stress-inducing misfolded rhodopsin protein. As expected, we found that increased Venus signal arose primarily from photoreceptors in RhoP23H/+;ERAI mice. We found increased Xbp1S and XBP1s transcriptional target mRNA levels in RhoP23H/+;ERAI retinas compared to Rho+/+;ERAI retinas, and that Venus signal increased in ERAI retinas as a function of age.
Fluorescence ophthalmoscopy of ERAI mice enables in vivo visualization of retinas undergoing ER stress. ER stress activated indicator mice enable identification of individual retinal cells undergoing ER stress by immunohistochemistry. ER stress activated indicator mice show higher Venus signal at older ages, likely arising from amplification of basal retinal ER stress levels by GFP's inherent stability.