bims-mideyd 2023-05-21 papers

bims-mideyd

Biomed News

on Mitochondrial dysfunction in eye diseases

Issue of 2023–05–21
six papers selected by
Rajalekshmy “Raji” Shyam, Indiana University Bloomington

SIRT6 overexpression in the nucleus protects mouse retinal pigment epithelium from oxidative stress.
Enhanced Biosafety of the Sleeping Beauty Transposon System by Using mRNA as Source of Transposase to Efficiently and Stably Transfect Retinal Pigment Epithelial Cells.
Anaphylatoxin C5a receptor signaling induces mitochondrial fusion and sensitizes retina pigment epithelial cells to oxidative stress.
Mitochondrial Quality Control and Metabolic Memory Phenomenon Associated with Continued Progression of Diabetic Retinopathy.
Mitochondrial dysfunction in glaucomatous degeneration.
The Presence of Guttae in Fuchs Endothelial Corneal Dystrophy Explants Correlates With Cellular Markers of Disease Progression.

Life Sci Alliance. 2023 Jul;pii: e202201448. [Epub ahead of print]6(7):

SIRT6 overexpression in the nucleus protects mouse retinal pigment epithelium from oxidative stress.

Xue Yang, Jin-Yong Chung, Usha Rai, Noriko Esumi.

Retinal pigment epithelium (RPE) is essential for the survival of retinal photoreceptors. To study retinal degeneration, sodium iodate (NaIO3) has been used to cause oxidative stress-induced RPE death followed by photoreceptor degeneration. However, analyses of RPE damage itself are still limited. Here, we characterized NaIO3-induced RPE damage, which was divided into three regions: periphery with normal-shaped RPE, transitional zone with elongated cells, and center with severely damaged or lost RPE. Elongated cells in the transitional zone exhibited molecular characteristics of epithelial-mesenchymal transition. Central RPE was more susceptible to stresses than peripheral RPE. Under stresses, SIRT6, an NAD+-dependent protein deacylase, rapidly translocated from the nucleus to the cytoplasm and colocalized with stress granule factor G3BP1, leading to nuclear SIRT6 depletion. To overcome this SIRT6 depletion, SIRT6 overexpression was induced in the nucleus in transgenic mice, which protected RPE from NaIO3 and partially preserved catalase expression. These results demonstrate topological differences of mouse RPE and warrant further exploring SIRT6 as a potential target for protecting RPE from oxidative stress-induced damage.

DOI: https://doi.org/10.26508/lsa.202201448
Biomolecules. 2023 Apr 07. pii: 658. [Epub ahead of print]13(4):

Enhanced Biosafety of the Sleeping Beauty Transposon System by Using mRNA as Source of Transposase to Efficiently and Stably Transfect Retinal Pigment Epithelial Cells.

Nina Harmening, Sandra Johnen, Zsuzsanna Izsvák, Zoltan Ivics, Martina Kropp, Thais Bascuas, Peter Walter, Andreas Kreis, Bojan Pajic, Gabriele Thumann.

  Neovascular age-related macular degeneration (nvAMD) is characterized by choroidal neovascularization (CNV), which leads to retinal pigment epithelial (RPE) cell and photoreceptor degeneration and blindness if untreated. Since blood vessel growth is mediated by endothelial cell growth factors, including vascular endothelial growth factor (VEGF), treatment consists of repeated, often monthly, intravitreal injections of anti-angiogenic biopharmaceuticals. Frequent injections are costly and present logistic difficulties; therefore, our laboratories are developing a cell-based gene therapy based on autologous RPE cells transfected ex vivo with the pigment epithelium derived factor (PEDF), which is the most potent natural antagonist of VEGF. Gene delivery and long-term expression of the transgene are enabled by the use of the non-viral Sleeping Beauty (SB100X) transposon system that is introduced into the cells by electroporation. The transposase may have a cytotoxic effect and a low risk of remobilization of the transposon if supplied in the form of DNA. Here, we investigated the use of the SB100X transposase delivered as mRNA and showed that ARPE-19 cells as well as primary human RPE cells were successfully transfected with the Venus or the PEDF gene, followed by stable transgene expression. In human RPE cells, secretion of recombinant PEDF could be detected in cell culture up to one year. Non-viral ex vivo transfection using SB100X-mRNA in combination with electroporation increases the biosafety of our gene therapeutic approach to treat nvAMD while ensuring high transfection efficiency and long-term transgene expression in RPE cells.

Keywords:  PEDF; RPE cells; Sleeping Beauty transposase; gene therapy; mRNA; non-viral; nvAMD

DOI:  https://doi.org/10.3390/biom13040658
Biochim Biophys Acta Gen Subj. 2023 May 13. pii: S0304-4165(23)00072-7. [Epub ahead of print] 130374

Anaphylatoxin C5a receptor signaling induces mitochondrial fusion and sensitizes retina pigment epithelial cells to oxidative stress.

Masaaki Ishii, Bärbel Rohrer.

  Mitochondrial dynamics is a morphological balance between fragmented and elongated shapes, reflecting mitochondrial metabolic status, cellular damage, and mitochondrial dysfunction. The anaphylatoxin C5a derived from complement component 5 cleavage, enhances cellular responses involved in pathological stimulation, innate immune responses, and host defense. However, the specific response of C5a and its receptor, C5a receptor (C5aR), in mitochondria is unclear. Here, we tested whether the C5a/C5aR signaling axis affects mitochondrial morphology in human-derived retinal pigment epithelial cell monolayers (ARPE-19). C5aR activation with the C5a polypeptide-induced mitochondrial elongation. In contrast, oxidatively stressed cells (H2O2) responded to C5a with an enhancement of mitochondrial fragmentation and an increase in the number of pyknotic nuclei. C5a/C5aR signaling increased the expression of mitochondrial fusion-related protein, mitofusin-1 (MFN1) and - 2 (MFN2), as well as enhanced optic atrophy-1 (Opa1) cleavage, which are required for mitochondrial fusion events, whereas the mitochondrial fission protein, dynamin-related protein-1 (Drp1), and mitogen-activated protein kinase (MAPK)-dependent extracellular signal-regulated protein kinase (Erk1/2) phosphorylation were not affected. Moreover, C5aR activation increased the frequency of endoplasmic reticulum (ER)-mitochondria contacts. Finally, oxidative stress induced in a single cell within an RPE monolayer (488 nm blue laser spot stimulation) induced a bystander effect of mitochondrial fragmentation in adjacent surrounding cells only in C5a-treated monolayers. These results suggest that C5a/C5aR signaling produced an intermediate state, characterized by increased mitochondrial fusion and ER-mitochondrial contacts, that sensitizes cells to oxidative stress, leading to mitochondrial fragmentation and cell death.

Keywords:  Anaphylatoxin; ER-mitochondria contact; G-protein coupled receptor; Mitochondrial dynamics

DOI:  https://doi.org/10.1016/j.bbagen.2023.130374
Int J Mol Sci. 2023 Apr 29. pii: 8076. [Epub ahead of print]24(9):

Mitochondrial Quality Control and Metabolic Memory Phenomenon Associated with Continued Progression of Diabetic Retinopathy.

Renu A Kowluru, Kumari Alka.

  Diabetic retinopathy continues to progress even when hyperglycemia is terminated, suggesting a 'metabolic memory' phenomenon. Mitochondrial dysfunction is closely associated with the development of diabetic retinopathy, and mitochondria remain dysfunctional. Quality control of mitochondria requires a fine balance between mitochondrial fission-fusion, removal of the damaged mitochondria (mitophagy) and formation of new mitochondria (biogenesis). In diabetes, while mitochondrial fusion protein (Mfn2) is decreased, fission protein (Drp1) is increased, resulting in fragmented mitochondria. Re-institution of normal glycemia fails to reverse mitochondrial fragmentation, and dysfunctional mitochondria continue to accumulate. Our aim was to investigate the direct effect of regulation of the mitochondrial fusion process during normal glycemia that follows a high glucose insult on mitochondrial quality control in the 'metabolic memory' phenomenon. Human retinal endothelial cells, incubated in 20 mM glucose for four days, followed by 5 mM glucose for four additional days, with or without the Mfn2 activator leflunomide, were analyzed for mitochondrial fission (live cell imaging), mitophagy (flow cytometry and immunofluorescence microscopy), and mitochondrial mass (mitochondrial copy numbers and MitoTracker labeling). Mitochondrial health was determined by quantifying mitochondrial reactive oxygen species (ROS), respiration rate (Seahorse XF96) and mitochondrial DNA (mtDNA) damage. Addition of leflunomide during normal glucose exposure that followed high glucose prevented mitochondrial fission, facilitated mitophagy and increased mitochondrial mass. Glucose-induced decrease in mitochondrial respiration and increase in ROS and mtDNA damage were also prevented. Thus, direct regulation of mitochondrial dynamics can help maintain mitochondrial quality control and interfere with the metabolic memory phenomenon, preventing further progression of diabetic retinopathy.

Keywords:  diabetic retinopathy; metabolic memory; mitochondria; mitochondrial dynamics; mitophagy

DOI:  https://doi.org/10.3390/ijms24098076
Int J Ophthalmol. 2023 ;16(5): 811-823

Mitochondrial dysfunction in glaucomatous degeneration.

Zi-Qiao Zhang, Zhi Xie, Sen-Yuan Chen, Xu Zhang.

  Glaucoma is a kind of optic neuropathy mainly manifested in the permanent death of retinal ganglion cells (RGCs), atrophy of the optic nerve, and loss of visual ability. The main risk factors for glaucoma consist of the pathological elevation of intraocular pressure (IOP) and aging. Although the mechanism of glaucoma remains an open question, a theory related to mitochondrial dysfunction has been emerging in the last decade. Reactive oxygen species (ROS) from the mitochondrial respiratory chain are abnormally produced as a result of mitochondrial dysfunction. Oxidative stress takes place when the cellular antioxidant system fails to remove excessive ROS promptly. Meanwhile, more and more studies show that there are other common features of mitochondrial dysfunction in glaucoma, including damage of mitochondrial DNA (mtDNA), defective mitochondrial quality control, ATP reduction, and other cellular changes, which are worth summarizing and further exploring. The purpose of this review is to explore mitochondrial dysfunction in the mechanism of glaucomatous optic neuropathy. Based on the mechanism, the existing therapeutic options are summarized, including medications, gene therapy, and red-light therapy, which are promising to provide feasible neuroprotective ideas for the treatment of glaucoma.

Keywords:  glaucoma; mitochondrial dynamics; mitochondrial dysfunction; mitophagy; neuroprotection; oxidative stress

DOI:  https://doi.org/10.18240/ijo.2023.05.20
Invest Ophthalmol Vis Sci. 2023 05 01. 64(5): 13

The Presence of Guttae in Fuchs Endothelial Corneal Dystrophy Explants Correlates With Cellular Markers of Disease Progression.

Sébastien Méthot, Stéphanie Proulx, Isabelle Brunette, Patrick J Rochette.

Purpose: Fuchs endothelial corneal dystrophy (FECD) is characterized by an accelerated depletion of corneal endothelial cells. There is growing evidence that mitochondrial exhaustion is central in the pathology. Indeed, endothelial cells loss in FECD forces the remaining cells to increase their mitochondrial activity, leading to mitochondrial exhaustion. This generates oxidation, mitochondrial damage, and apoptosis, fueling a vicious cycle of cells' depletion. This depletion ultimately causes corneal edema and irreversible loss of transparency and vision. Concurrently to endothelial cells loss, the formation of extracellular mass called guttae on the Descemet's membrane, is a hallmark of FECD. The pathology origins at the center of the cornea and progress outward, like the appearance of guttae.
Methods: Using corneal endothelial explants from patients with late-stage FECD at the time of their corneal transplantation, we correlated mitochondrial markers (mitochondrial mass, potential, and calcium) and the level of oxidative stress and apoptotic cells, with the area taken by guttae. The different markers have been analyzed using fluorescent-specific probes and microscopic analysis.
Results: We observed a positive correlation between the presence of guttae and the level of mitochondrial calcium and apoptotic cells. We found a negative correlation between the presence of guttae and the level of mitochondrial mass, membrane potential, and oxidative stress.
Conclusions: Taken together, these results show that the presence of guttae is correlated with negative outcome in the mitochondrial health, oxidative status, and survival of nearby endothelial cells. This study provides insight on FECD etiology that could lead to treatment targeting mitochondrial stress and guttae.

DOI: https://doi.org/10.1167/iovs.64.5.13