Mitophagy in the Retinal Pigment Epithelium of Dry Age-Related Macular Degeneration Investigated in the NFE2L2/PGC-1α-/- Mouse Model

Abstract

Increased oxidative stress and mitochondrial damage are observed in protein aggregation diseases, such as age-related macular degeneration (AMD). We have recently reported elevated levels of oxidative stress markers, damaged mitochondria, accumulating lysosomal lipofuscin and extracellular drusen-like structures in the retinal pigment epithelial cells (RPE) of the dry AMD-resembling NFE2L2/PGC1α double knockout (dKO) mouse model. Here, we provide evidence of a disturbance in the autolysosomal machinery handling mitochondrial clearance in the RPE cells of one-year-old NFE2L2/PGC1α-deficient mice. Confocal immunohistochemical analysis revealed an upregulation of autophagosome marker microtubule-associated proteins 1A/1B light chain 3B (LC3B) as well as numerous mitophagy markers, such as PTE-induced putative kinase 1 (PINK1) and E3 ubiquitin ligase (PARKIN) together with damaged mitochondria. However, we detected no evidence of increased autolysosome formation in transmission electron micrographs or of colocalization of lysosomal marker LAMP2 (lysosome-associated membrane protein 2) and the mitochondrial marker ATP synthase β in confocal micrographs. Interestingly, we observed an upregulation of late autolysosomal fusion Ras-related protein (Rab7) in the perinuclear space of RPE cells together with autofluorescence aggregates. Our results reveal that there is at least a relative decrease of mitophagy in the RPE cells of NFE2L2/PGC1α dKO mice. This further supports the hypothesis that mitophagy is a putative therapy target in AMD-like pathology.

The Aging Stress Response and Its Implication for AMD Pathogenesis

“…As we reasoned in our previous work, this protein may be crucial in AMD pathogenesis due to its protective role against senescence of RPE cells in oxidative stress [ 10 ]. Mice with the manipulated expression of the PGC-1a gene were shown to mimic human retinal diseases, including AMD [ 131 , 158 , 159 , 160 , 161 ].…”

Potential Therapeutic Benefit of NAD+ Supplementation for Glaucoma and Age-Related Macular Degeneration

“…Impairments in this process have been associated with AMD and NAD + may be a potential solution for the impaired mitophagy [ 203 , 204 ]. PINK1 and PARKIN , which are responsible of the proper degradation of damaged mitochondria via mitophagy, appear to be upregulated in a mouse model of dry AMD, the erythroid 2-related factor 2/peroxisome proliferator-activated receptor gamma coactivator 1-alpha double knockdown, NFE2L2/PGC-1α −/− mouse model [ 205 ]. The analysis of NFE2L2/PGC-1α −/− RPE cells displayed an extensive upregulation of PINK and PARKIN levels along with an impaired mitochondrial clearance system, showing all the phenotypical change related to AMD [ 206 ].…”

Autophagy Genes for Wet Age-Related Macular Degeneration in a Finnish Case-Control Study

“…Clinical signs for the protein aggregation are the accumulation of lysosomal lipofuscin in RPE and extracellular drusen deposits between RPE and choriocapillaris. Currently, emerging evidence suggests that cellular proteostasis is disturbed in AMD and autophagy, as its crucial mechanism, plays an important role in the various stages of AMD development and progression [16][17][18][19][20][21].…”

“…This phenotype was manifested by RPE thickening, hypertrophy or hypotrophy, pigmentary abnormalities and the accumulation of oxidized proteins. Oxidative stress is a canonical stimulus to induce autophagy in RPE cells [19][20][21]24,25]. Studies on RPE cells from AMD donors and mice with AMD-like phenotype suggest autophagy involvement in AMD pathogenesis [20].…”

“…This study also revealed that chronic oxidative stress decreased autophagic flux. Autophagy can prevent retinal cells from the damaging effects of oxidative stress [19][20][21]26].…”