Abstract
Purpose :
Photoreceptors are highly metabolically active retinal cells and disturbance in photoreceptor metabolism leads to visual dysfunction and retinal degeneration. X-box binding protein 1 (XBP1) regulates a large array of genes that are involved in diverse cellular functions and processes including lipid and glucose metabolism; yet the role of XBP1 in regulation of photoreceptor metabolism remains to be investigated.
Methods :
Rod photoreceptor-specific XBP1 conditional knockout (Rho-XBP1 cKO) mice were generated by crossing a XBP1 floxed mouse line with a rhodopsin-iCre line. Rod photoreceptor cells were isolated from 1-month old wild-type (WT; n=4) mice and Rho-XBP1 cKO (n=4) mice using enzymatic digestion and mechanical dissociation. Mitochondrial respiration and glycolytic activity were assessed using a Seahorse XF Cell Mito Stress Test kit and a Glycolysis Stress Test, respectively. Changes in oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) were quantified by a Seahorse XFe24 Analyzer. Histology was performed with paraffin sections from WT (n=5) and Rho-XBP1 cKO (n=5) mice at 1 month of age.
Results :
We found no significant differences in mitochondrial respiratory functions measured by basal respiration, maximal respiration, ATP production, and spare respiratory capacity between WT and Rho-XBP1 cKO cells (all p>0.05). Likewise, there were no significant differences in glycolytic activities between the groups, despite a modest decrease in glycolysis in Rho-XBP1 cKO cells compared to WT cells (mean: 3.022 vs. 3.705, p>0.05). Histological study shows no abnormalities in retinal morphology in Rho-XBP1 cKO mice. Moreover, no significance was achieved in changes in retinal thicknesses between Rho-XBP1 cKO and WT mice: whole retina (mean: 160.1μm vs. 164.6μm; p>0.05), outer nuclear layer (mean: 35.59μm vs. 36.86μm; p>0.05), and the outer segment/inner segment (mean: 19.16μm vs. 21.70μm; p>0.05).
Conclusions :
Our results suggest that XBP1 deletion in rod photoreceptors does not affect photoreceptor metabolism in young mice. Furthermore, no significant difference was identified in photoreceptor and retinal morphology in these mice, indicating that XBP1 is not required for photoreceptor development. Future experiments will examine whether XBP1 deletion have an impact on photoreceptor metabolism in adult mice and under disease conditions related to retina degeneration.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.