Loss of NRF-2 and PGC-1α genes leads to retinal pigment epithelium damage resembling dry age-related macular degeneration

Abstract

Age-related macular degeneration (AMD) is a multi-factorial disease that is the leading cause of irreversible and severe vision loss in the developed countries. It has been suggested that the pathogenesis of dry AMD involves impaired protein degradation in retinal pigment epithelial cells (RPE). RPE cells are constantly exposed to oxidative stress that may lead to the accumulation of damaged cellular proteins, DNA and lipids and evoke tissue deterioration during the aging process. The ubiquitin-proteasome pathway and the lysosomal/autophagosomal pathway are the two major proteolytic systems in eukaryotic cells. NRF-2 (nuclear factor-erythroid 2-related factor-2) and PGC-1α (peroxisome proliferator-activated receptor gamma coactivator-1 alpha) are master transcription factors in the regulation of cellular detoxification. We investigated the role of NRF-2 and PGC-1α in the regulation of RPE cell structure and function by using global double knockout (dKO) mice. The NRF-2/PGC-1α dKO mice exhibited significant age-dependent RPE degeneration, accumulation of the oxidative stress marker, 4-HNE (4-hydroxynonenal), the endoplasmic reticulum stress markers GRP78 (glucose-regulated protein 78) and ATF4 (activating transcription factor 4), and damaged mitochondria. Moreover, levels of protein ubiquitination and autophagy markers p62/SQSTM1 (sequestosome 1), Beclin-1 and LC3B (microtubule associated protein 1 light chain 3 beta) were significantly increased together with the Iba-1 (ionized calcium binding adaptor molecule 1) mononuclear phagocyte marker and an enlargement of RPE size. These histopathological changes of RPE were accompanied by photoreceptor dysmorphology and vision loss as revealed by electroretinography. Consequently, these novel findings suggest that the NRF-2/PGC-1α dKO mouse is a valuable model for investigating the role of proteasomal and autophagy clearance in the RPE and in the development of dry AMD.

Oxidative Stress and Dysfunctional Intracellular Traffic Linked to an Unhealthy Diet Results in Impaired Cargo Transport in the Retinal Pigment Epithelium (RPE)

“…Recent work has also described links between proteasomal clearance and autophagy, as well as the importance of these processes to retinopathy. Hence, mice lacking NRF‐2/ARE (nuclear factor‐erythroid 2‐related factor2/antioxidant response element) and PGC‐1α (peroxisome proliferator‐activated receptor γ co‐activator 1) recapitulate salient features of GA . Future studies will explore links between proteasomal clearance, autophagy, and phagocytosis, and how these overlapping but divergent pathways function in our model.…”

“…Future studies will explore links between proteasomal clearance, autophagy, and phagocytosis, and how these overlapping but divergent pathways function in our model. Impaired autophagy in the RPE also leads to inflammasome activation, angiogenesis and activation of innate immunity, linking dysfunction of cargo trafficking and clearance mechanisms with other well‐recognized features of retinal degeneration.…”

Crocetin Prevents RPE Cells from Oxidative Stress through Protection of Cellular Metabolic Function and Activation of ERK1/2

“…The degeneration of RPE cells is one of the early clinical hallmarks of AMD [17,18]. RPE cells are polarized and specialized epithelial cells that form a monolayer between the neural retina and Bruch's membrane/choroid forming the blood-retinal barrier.…”

Loss of Complement Factor H impairs antioxidant capacity and energy metabolism of human RPE cells

“…No significant differences were observed in any of the experimental conditions (Supplementary Fig 2A). Transcription factors promoting mitochondrial biogenesis like Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-Alpha (PGC1a) and Nuclear Factor, Erythroid 2 Like 2 (NRF2) have been shown to positively influence mitochondria metabolism and antioxidant response [26, 27]. To test whether FH loss leads to a dysregulation of those factors, we analyzed gene expression levels of PGC1a and NRF2 (Supplementary Fig.…”