Inhibiting autophagy reduces retinal degeneration caused by protein misfolding

Abstract

Mutations in the genes necessary for the structure and function of vertebrate photoreceptor cells are associated with multiple forms of inherited retinal degeneration. Mutations in the gene encoding RHO (rhodopsin) are a common cause of autosomal dominant retinitis pigmentosa (adRP), with the Pro23His variant of RHO resulting in a misfolded protein that activates endoplasmic reticulum stress and the unfolded protein response. Stimulating macroautophagy/autophagy has been proposed as a strategy for clearing misfolded RHO and reducing photoreceptor death. We found that retinas from mice heterozygous for the gene encoding the RHO variant (hereafter called P23H) exhibited elevated levels of autophagy flux, and that pharmacological stimulation of autophagy accelerated retinal degeneration. In contrast, reducing autophagy flux pharmacologically or by rod-specific deletion of the autophagy-activating gene Atg5, improved photoreceptor structure and function. Furthermore, proteasome levels and activity were reduced in the P23H retina, and increased when Atg5 was deleted. Our findings suggest that autophagy contributes to photoreceptor cell death in P23H mice, and that decreasing autophagy shifts the degradation of misfolded RHO protein to the proteasome and is protective. These observations suggest that modulating the flux of misfolded proteins from autophagy to the proteasome may represent an important therapeutic strategy for reducing proteotoxicity in adRP and other diseases caused by protein folding defects.

Haploinsufficiency of GCP4 induces autophagy and leads to photoreceptor degeneration due to defective spindle assembly in retina

“…Thus, GCP4 may play bi-functional roles in maintenance of retinal homeostasis, through participating in assembly of γ-TuRC, on the other side, in regulating autophagy in retina. In line with these results, inhibition of autophagy reduced retinal degeneration by pharmacological treatment and Atg5 knockout in mice [30].…”

“…Further, the retinal cells were used to assess GCP4-involved autophagic flux. Hydroxychloroquine (HCQ, an autophagy flux inhibitor in vivo [30]) treatment resulted in accumulation of both LC3-II and SQSTM1 proteins in both wild-type and heterozygous retinas ( Fig. 5f-i).…”

Disrupted Plasma Membrane Protein Homeostasis in a Xenopus Laevis Model of Retinitis Pigmentosa

“…In summary, we demonstrated that mislocalized rhodopsin disrupts the PM homeostasis of rod photoreceptors through concomitant lysosome-mediated degradation of IS PM membrane protein, NKA. Lysosome-mediated degradation is associated with various photoreceptor degenerative disorders (Chen et al, 2013;Bogéa et al, 2015;Yao et al, 2018), but the context and consequences of the degradation differ among these diseases. For example, in a light-dependent photoreceptor degeneration model, activation of lysosomes and autophagy is neuroprotective (Chen et al, 2013), but in a mouse model of a class II rhodopsin gene mutation (Sakami et al, 2011(Sakami et al, , 2014, activation exacerbates the photoreceptor degeneration (Yao et al, 2018).…”

Autophagosome immunoisolation from GFP-LC3B mouse tissue

“…We have previously published the protein content of autophagosomes from retinas of the GFP-LC3 mouse (as analyzed by mass spectroscopy), as well as showing the difference in the levels of the visual transduction proteins ARR3 (arrestin 3, retinal) and transducin in the retinal autophagosomes of dark versus light-adapted mice [9]. We have also demonstrated the differential level of proteasome subunits being consumed in the retinas of the P23H mouse model of hereditary retinal degeneration as compared to wild-type [16]. Thus, we feel that this technique may be useful to other investigators wishing to explore the contents of the autophagosome under various conditions.…”