Abstract
Purpose :
Thyroid hormone (TH) signaling is essential in regulating cell proliferation, differentiation, and metabolism. In the retina, it regulates opsin expression and cone photoreceptor viability. Increased TH levels result in photoreceptor degeneration. Our previous work found that genes involved in the necroptotic pathway, including receptor-interacting serine/threonine-protein kinase 3 (RIPK3), have increased expression when TH levels are elevated. This work investigates the role of RIPK3 and/or necroptosis signaling in TH-induced photoreceptor degeneration.
Methods :
Wild-type (C57BL/6J, WT) mice and mice with deficiency of necroptotic signaling components (Ripk3-/-, Mlkl-/-, Mlkl-/-Ripk3-/-) at postnatal day 30 received different doses of triiodothyronine (T3, 5, 10, or 20 µg/ml in drinking water) for 30 days, followed by evaluation of retinal function and photoreceptor survival. Serum T3 level was measured by ELISA. Retinal function was evaluated by electroretinogram (ERG). Retinal cell survival was analyzed morphometrically by hematoxylin & eosin (H&E) staining. Retinal cell death was analyzed by terminal deoxynucleotidyltransferase dUTP nick-end labeling (TUNEL). Cone density was analyzed by immunolabeling using cone markers.
Results :
Treatment with T3 increased serum T3 level by about 7-10-fold. T3-treated WT mice showed impaired retinal function, reduced cone density, damaged retinal layers/loss of rods, and retinal cell death. Deletion of Ripk3 protected rod and cone function against T3 treatment, shown as improved scotopic/photopic light responses, compared with that in WT mice. Deletion of Ripk3 also reduced T3-induced cone degeneration, shown as increased cone density, improved retinal morphology, and reduced number of TUNEL-positive cells, compared with that in WT mice. However, deletion of Mlkl protected rod but not cone ERG response and did not preserve cone density. The Mlkl-/-Ripk3-/- mice showed protection of retinal function, preservation of cone density, and maintenance of the retinal morphology, similar to Ripk3-/- mice.
Conclusions :
Excessive TH signaling induces photoreceptor degeneration and impairs retinal function. Deficiency of Ripk3 inhibits TH-induced retinal damage and protects photoreceptors. This evidence supports the view that RIPK3 signaling contributes to TH-induced photoreceptor cell death.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.