bims-mideyd 2024-08-04 papers

Issue of 2024‒08‒04
five papers selected by
Rajalekshmy “Raji” Shyam, Indiana University Bloomington

Acta Ophthalmol. 2024 Aug 01.

Autophagy in drusen biogenesis secondary to age-related macular degeneration.

Juha M T Hyttinen, Ali Koskela, Janusz Blasiak, Kai Kaarniranta.

Age-related macular degeneration (AMD) is an emerging cause of blindness in aged people worldwide. One of the key signs of AMD is the degeneration of the retinal pigment epithelium (RPE), which is indispensable for the maintenance of the adjacent photoreceptors. Because of impaired energy metabolism resulting from constant light exposure, hypoxia, and oxidative stress, accumulation of drusen in AMD-affected eyes is observed. Drusen contain damaged cellular proteins, lipoprotein particles, lipids and carbohydrates and they are related to impaired protein clearance, inflammation, and extracellular matrix modification. When autophagy, a major cellular proteostasis pathway, is impaired, the accumulations of intracellular lipofuscin and extracellular drusen are detected. As these aggregates grow over time, they finally cause the disorganisation and destruction of the RPE and photoreceptors leading to visual loss. In this review, the role of autophagy in drusen biogenesis is discussed since impairment in removing cellular waste in RPE cells plays a key role in AMD progression. In the future, means which improve intracellular clearance might be of use in AMD therapy to slow the progression of drusen formation.

Keywords: age‐related macular degeneration; degradative autophagy; drusen; lipofuscin; phagocytosis; retinal pigment epithelium; secretory autophagy

DOI: https://doi.org/10.1111/aos.16744

Cell Death Differ. 2024 Jul 30.

TIN2 modulates FOXO1 mitochondrial shuttling to enhance oxidative stress-induced apoptosis in retinal pigment epithelium under hyperglycemia.

Shimei Chen, Dandan Sun, Shuchang Zhang, Li Xu, Ning Wang, Huiming Li, Xun Xu, Fang Wei.

Progressive dysfunction of the retinal pigment epithelium (RPE) and the adjacent photoreceptor cells in the outer retina plays a pivotal role in the pathogenesis of diabetic retinopathy (DR). Here, we observed a marked increase in oxidative stress-induced apoptosis in parallel with higher expression of telomeric protein TIN2 in RPE cells under hyperglycemia in vivo and in vitro. Delving deeper, we confirm that high glucose-induced elevation of mitochondria-localized TIN2 compromises mitochondrial activity and weakens the intrinsic antioxidant defense, thereby leading to the activation of mitochondria-dependent apoptotic pathways. Mechanistically, mitochondrial TIN2 promotes the phosphorylation of FOXO1 and its relocation to the mitochondria. Such translocation of transcription factor FOXO1 not only promotes its binding to the D-loop region of mitochondrial DNA-resulting in the inhibition of mitochondrial respiration-but also hampers its availability to nuclear target DNA, thereby undermining the intrinsic antioxidant defense. Moreover, TIN2 knockdown effectively mitigates oxidative-induced apoptosis in diabetic mouse RPE by preserving mitochondrial homeostasis, which concurrently prevents secondary photoreceptor damage. Our study proposes the potential of TIN2 as a promising molecular target for therapeutic interventions for diabetic retinopathy, which emphasizes the potential significance of telomeric proteins in the regulation of metabolism and mitochondrial function. Created with BioRender ( https://www.biorender.com/ ).

DOI: https://doi.org/10.1038/s41418-024-01349-8

Stem Cells Dev. 2024 Jul 30.

Modeling Choroideremia disease with isogenic induced Pluripotent Stem Cells.

Ana Fragoso Fonseca, Rita Coelho, Mafalda Lopes-da-Silva, Luísa Lemos, Michael James Hall, Daniela Oliveira, Ana Sofia Falcão, Sandra Tenreiro, Miguel Cardoso Seabra, Pedro Antas.

Choroideremia (CHM) is a rare X-linked chorioretinal dystrophy causing progressive vision loss due to mutations in the CHM gene, leading to Rab escort protein 1 (REP1) loss of function. CHM disease is characterized by a progressive degeneration of the choroid, the retinal pigment epithelium (RPE) and the retina. The RPE is a monolayer of polarized cells that supports photoreceptors, providing nutrients, growth factors and ions, and removes retinal metabolism waste products, having a central role in CHM pathogenesis. Commonly used models such as ARPE-19 cells do not reproduce accurately the nature of RPE cells. Human induced pluripotent stem cells (hiPSC) can be differentiated into RPE cells (hiPSC-RPE) which mimic key features of native RPE, being more suited to study retinal diseases. Therefore, we took advantage of hiPSC, to generate new human-based CHM models. Two isogenic hiPSC lines were generated through CRISPR/Cas9: a CHM knock-out line from a healthy donor and a corrected CHM patient line using a knock-in approach. The differentiated hiPSC-RPE lines exhibited critical morphological and physiological characteristics of native RPE, including the presence of the tight junction markers Claudin-19 and Zonula Occludens-1, phagocytosis of photoreceptor outer segments, pigmentation, a post-mitotic state, and the characteristic polygonal shape. Additionally, all the studied cells were able to form retinal organoids. This work resulted in the establishment of isogenic hiPSC lines, representing a new and important CHM cellular model. To our knowledge, this is the first time that isogenic cell lines have been developed to model CHM disease, providing a valuable tool for studying the mechanisms at the onset of RPE degeneration.

DOI: https://doi.org/10.1089/scd.2024.0105

Invest Ophthalmol Vis Sci. 2024 Aug 01. 65(10): 5

Iron Chelator Deferiprone Restores Iron Homeostasis and Inhibits Retinal Neovascularization in Experimental Neovascular Age-Related Macular Degeneration.

Yuan Xu, Shiya Huang, Shengmei Zhou, Xin Wang, Mingyan Wei, Xiaodong Chen, Rongrong Zong, Xiang Lin, Shiying Li, Zuguo Liu, Qian Chen.

Purpose: Retinal neovascularization is a significant feature of advanced age-related macular degeneration (AMD) and a major cause of blindness in patients with AMD. However, the underlying mechanism of this pathological neovascularization remains unknown. Iron metabolism has been implicated in various biological processes. This study was conducted to investigate the effects of iron metabolism on retinal neovascularization in neovascular AMD (nAMD).Methods: C57BL/6J and very low-density lipoprotein receptor (VLDLR) knockout (Vldlr-/-) mice, a murine model of nAMD, were used in this study. Bulk-RNA sequencing was used to identify differentially expressed genes. Western blot analysis was performed to test the expression of proteins. Iron chelator deferiprone (DFP) was administrated to the mice by oral gavage. Fundus fluorescein angiography was used to evaluate retinal vascular leakage. Immunofluorescence staining was used to detect macrophages and iron-related proteins.
Results: RNA sequencing (RNA-seq) results showed altered transferrin expression in the retina and RPE of Vldlr-/- mice. Disrupted iron homeostasis was observed in the retina and RPE of Vldlr-/- mice. DFP mitigated iron overload and significantly reduced retinal neovascularization and vascular leakage. In addition, DFP suppressed the inflammation in Vldlr-/- retinas. The reduced signals of macrophages were observed at sites of neovascularization in the retina and RPE of Vldlr-/- mice after DFP treatment. Further, the IL-6/JAK2/STAT3 signaling pathway was activated in the retina and RPE of Vldlr-/- mice and reversed by DFP treatment.
Conclusions: Disrupted iron metabolism may contribute to retinal neovascularization in nAMD. Restoring iron homeostasis by DFP could be a potential therapeutic approach for nAMD.

DOI: https://doi.org/10.1167/iovs.65.10.5

Sci Rep. 2024 Jul 29. 14(1): 17469

TRPML1 activation ameliorates lysosomal phenotypes in CLN3 deficient retinal pigment epithelial cells.

D Wünkhaus, R Tang, K Nyame, N N Laqtom, M Schweizer, A Scotto Rosato, E K Krogsæter, C Wollnik, M Abu-Remaileh, C Grimm, G Hermey, R Kuhn, D Gruber-Schoffnegger, S Markmann.

Mutations in the lysosomal membrane protein CLN3 cause Juvenile Neuronal Ceroid Lipofuscinosis (JNCL). Activation of the lysosomal ion channel TRPML1 has previously been shown to be beneficial in several neurodegenerative disease models. Here, we tested whether TRPML1 activation rescues disease-associated phenotypes in CLN3-deficient retinal pigment epithelial (ARPE-19 CLN3-KO) cells. ARPE-19 CLN3-KO cells accumulate LAMP1 positive organelles and show lysosomal storage of mitochondrial ATPase subunit C (SubC), globotriaosylceramide (Gb3), and glycerophosphodiesters (GPDs), whereas lysosomal bis(monoacylglycero)phosphate (BMP/LBPA) lipid levels were significantly decreased. Activation of TRPML1 reduced lysosomal storage of Gb3 and SubC but failed to restore BMP levels in CLN3-KO cells. TRPML1-mediated decrease of storage was TFEB-independent, and we identified TRPML1-mediated enhanced lysosomal exocytosis as a likely mechanism for clearing storage including GPDs. Therefore, ARPE-19 CLN3-KO cells represent a human cell model for CLN3 disease showing many of the described core lysosomal deficits, some of which can be improved using TRPML1 agonists.

DOI: https://doi.org/10.1038/s41598-024-67479-8