bims-mideyd 2024-10-20 papers

Issue of 2024‒10‒20
four papers selected by
Rajalekshmy “Raji” Shyam, Indiana University Bloomington

Autophagy. 2024 Oct 16. 1-2

AKT2-mediated lysosomal dysfunction promotes secretory autophagy in retinal pigment epithelium (RPE) cells.

Sayan Ghosh, Stacey Hose, Debasish Sinha.

Age-related macular degeneration (AMD) is the leading cause of blindness in the elderly, with the non-neovascular or atrophic form being the most common. Current treatment options are limited, emphasizing the urgent need for new therapeutic strategies. Our key finding is that increased levels of AKT2 in the RPE cells impair lysosomal function and trigger secretory autophagy; a non-canonical macroautophagy/autophagy pathway where cellular materials are released via the plasma membrane rather than being degraded by lysosomes. We showed that this process involves a protein complex, AKT2-SYTL1-TRIM16-SNAP23, releasing factors contributing to drusen biogenesis, a clinical hallmark of AMD development. Importantly, SIRT5 can inhibit this pathway, potentially offering a protective effect. Understanding mechanisms by which this non-canonical autophagy pathway promotes extracellular waste accumulation could provide new insights into drusen biogenesis. Future therapies for atrophic AMD could focus on regulating secretory autophagy or manipulating proteins involved in this process.

Keywords: Atrophic age-related macular degeneration; drusen; inflammation; lysosomes; retinal pigment epithelium cells; secretory autophagy

DOI: https://doi.org/10.1080/15548627.2024.2413305

Exp Eye Res. 2024 Oct 15. pii: S0014-4835(24)00348-8. [Epub ahead of print]248 110126

The role of nicotinamide riboside in the preservation of retinal ganglion cells using an in vitro glutamate-induced excitotoxicity model.

Nan Zhang, Dongxiao Ji, Yixin Hu, Pengyu Zhang, Xizhi Deng, Min Zhu, Wen Zeng, Min Ke.

Delaying or preventing the loss of retinal ganglion cells (RGCs) in glaucoma is needed for vision preservation. Glutamate-mediated neurotoxicity arises from the excessive stimulation of N-methyl-D-aspartate membrane receptors by glutamate. This overstimulation, occurring specifically in RGCs, triggers a progressive deterioration of the optic nerve that ultimately leads to the vision loss in glaucoma. Our previous investigation demonstrated that nicotinamide riboside (NR) effectively preserved RGCs in multiple mouse models of glaucoma. To investigate the precise role of NR concerning RGCs which remains uncertain, a glutamate-induced excitotoxicity RGCs damage model was established using R28 cells in this study. Results showed that NR treatment could not only prevent the decrease in cell viability but also effectively inhibit the apoptosis of R28 cells induced by glutamate, as proven by flow cytometry and expression of key pro-apoptotic proteins. Additionally, it significantly attenuated oxidative stress induced by glutamate, as evaluated by the production of inflammatory factors, reactive oxygen species (ROS) and mitochondrial ROS (mtROS). Furthermore, NR elevated the intracellular nicotinamide adenine dinucleotide (NAD+) levels in R28 cells. Lastly, we used RNA-seq to reveal the underlying mechanism of NR protection. Combining the results of RNA-seq and Western blot, we found that NR also restored the decreased protein expression of sirtuin 1 (SIRT1) and peroxisome proliferator-activated receptor-gamma coactivator (PGC1α) induced by glutamate. These findings strongly indicated that NR exhibits a protective effect against R28 cell apoptosis in a glutamate-induced excitotoxicity RGCs damage model. This protective effect is likely mediated through the activation of the SIRT1/PGC1α pathway, achieved by increasing intracellular NAD + levels.

Keywords: Apoptosis; NAD+; Nicotinamide riboside; Retinal ganglion cell

DOI: https://doi.org/10.1016/j.exer.2024.110126

Diagn Pathol. 2024 Oct 15. 19(1): 138

PSAT1 is upregulated by METTL3 to attenuate high glucose-induced retinal pigment epithelial cell apoptosis and oxidative stress.

Xiaofeng Du, Yanting Wang, Fan Gao.

BACKGROUND: Diabetic retinopathy (DR) is a major ocular complication of diabetes mellitus, and a significant cause of visual impairment and blindness in adults. Phosphoserine aminotransferase 1 (PSAT1) is an enzyme participating in serine synthesis, which might improve insulin signaling and insulin sensitivity. Furthermore, it has been reported that the m6A methylation in mRNA controls gene expression under many physiological and pathological conditions. Nevertheless, the influences of m6A methylation on PSAT1 expression and DR progression at the molecular level have not been reported.METHODS: High-glucose (HG) was used to treat human retinal pigment epithelial cells (ARPE-19) to construct a cell injury model. PSAT1 and Methyltransferase-like 3 (METTL3) levels were detected by real-time quantitative polymerase chain reaction (RT-qPCR). PSAT1, B-cell lymphoma-2 (Bcl-2), Bcl-2 related X protein (Bax), and METTL3 protein levels were examined by western blot assay. Cell viability and apoptosis were detected by Cell Counting Kit-8 (CCK-8) and TUNEL assays. Reactive oxygen species (ROS), malondialdehyde (MDA), and Glutathione peroxidase (GSH-Px) levels were examined using special assay kits. Interaction between METTL3 and PSAT1 was verified using methylated RNA immunoprecipitation (MeRIP) and dual-luciferase reporter assay.
RESULTS: PSAT1 and METTL3 levels were decreased in DR patients and HG-treated ARPE-19 cells. Upregulation of PSAT1 might attenuate HG-induced cell viability inhibition and apoptosis and oxidative stress promotion in ARPE-19 cells. Moreover, PSAT1 was identified as a downstream target of METTL3-mediated m6A modification. METTL3 might improve the stability of PSAT1 mRNA via m6A methylation.
CONCLUSION: METTL3 might mitigate HG-induced ARPE-19 cell damage partly by regulating the stability of PSAT1 mRNA, providing a promising therapeutic target for DR.

Keywords: ARPE-19 cells; Diabetic retinopathy; High-glucose; Methyltransferase-like 3; Phosphoserine aminotransferase 1

DOI: https://doi.org/10.1186/s13000-024-01556-4

Exp Eye Res. 2024 Oct 16. pii: S0014-4835(24)00351-8. [Epub ahead of print] 110129

Regualtion of LAMTOR1 by Oxidative Stress in Retinal Pigment Epithelium: Implications for Age-Related Macular Degeneration Pathogenesis.

Jingjing Cai, Fei Liao, Yandie Mao, Shuyi Liu, Xiong Wu, Shiqi Tang, Simin Wang, Ge Shan, Shengzhou Wu.

Oxidative stress is a critical pathogenic factor for age-related macular degeneration (AMD). Autophagy serves as a mechanism to counteract oxidative stress. LAMTOR1 regulates mTORC1 activity by recruiting or disassembling it on the lysosome under the addition or deprivation of amino acids. This regulation inhibits or enhances autophagy. Our study investigates whether oxidative stress impacts LAMTOR1, thereby adapting to oxidative conditions. We employed oxidative stressors, menadione (VK3) and 4-hydroxynonenal (4-HNE), and observed a reduction of LAMTOR1 in both human and mouse retinal pigment epithelium (RPE) following short-term (1h) and prolonged exposures (24h). Nrf2 overexpression increased both lamtor1 mRNA and LAMTOR1 protein in the RPE. To determine if Nrf2 regulates lamtor1 transcription, we cloned the deletion mutants of the lamtor1 promoter into a luciferase reporter. Although the promoter contained antioxidant response elements, transcriptional activity depended on the interaction between Nrf2 and the constructs containing the transcriptional start site. Moreover, Nrf2-driven transcription was significantly reduced by an inhibitor of histone acetyltransferase, p300. Correspondingly, Nrf2 overexpression increased levels of acetylated histone3 and p300. The reduction in LAMTOR1 by 4-HNE was reversed by pepstatin A and NH4Cl which block lysosomal degradation. 4-HNE increased TFEB nuclear translocation which was reversed by LAMTOR1 overexpression. In vivo, LAMTOR1 levels decreased in the photoreceptor and RPE layers of NaIO3-injected mice, compared to PBS-injected controls. In conclusion, oxidative injury reduces LAMTOR1, predominantly through lysosomal degradation although Nrf2-mediated histone acetylation enhances lamtor1 transcription. This study reveals a previously unrecognized regulatory mechanism of lamtor1 by oxidative stress, suggesting a novel role for LAMTOR1 in the pathogenesis of AMD.

Keywords: Age-related macular degeneration; Autophagy; Histone acetyltransferase; Histone deacetylase; Lysosome; mTORC1

DOI: https://doi.org/10.1016/j.exer.2024.110129