Involvement of endoplasmic reticulum stress in rotenone-induced leber hereditary optic neuropathy model and the discovery of new therapeutic agents

The Protective Effect of Docosahexaenoic Acid on Mitochondria in SH-SY5Y Model of Rotenone-Induced Toxicity

Background: Polyunsaturated fatty acids in particular omega-3 fatty acids, such as docosahexaenoic acid (DHA), are essential nutrients and components of the plasma membrane. They are involved in various processes, including synaptic development, functionality, integrity, and plasticity, and are therefore thought to have general neuroprotective properties. Considerable research evidence further supports the beneficial effects of omega-3 fatty acids, specifically on mitochondria, through their antioxidant and anti-apoptotic properties, making them an attractive addition in treatment options for neurodegenerative disorders in which mitochondrial alterations are commonly observed. However, precise information on the underlying protective mechanisms is still lacking. Methods: We utilized the most common neuronal cell line (SH-SY5Y) and induced mitochondrial oxidative stress through the addition of rotenone. To study the potential protective effect of DHA, the cells were additionally pre-treated with DHA prior to rotenone administration. By combining SILAC labeling, mitochondria enrichment, and subsequent proteomic analyses, we aimed to determine the capacity of DHA to alleviate mitochondrial oxidative stress in vitro and further shed light on the molecular mechanisms contributing to the proposed neuroprotective effect. Results: We confirmed a reduced cell viability and an increased abundance of reactive oxygen species upon rotenone treatment, DHA pre-treatment was shown to decrease said species. Additionally proteomic analysis revealed an increased expression of mitochondrial proteins in DHA pre-treated cells. Conclusions: With our study, we were able to define a potential compensatory mechanism by which the inhibition of complex I is overcome by an increased activity of the fatty acid beta oxidation in response to DHA.

Retinal damage promotes mitochondrial transfer in the visual system of a mouse model of Leber hereditary optic neuropathy

Lenadogene nolparvovec is a gene therapy which has been developed to treat Leber hereditary optic neuropathy (LHON) caused by a point mutation in the mitochondrial NADH dehydrogenase 4 (ND4) gene. Clinical trials have demonstrated a significant improvement of visual acuity up to 5 years after treatment by lenadogene nolparvovec but, surprisingly, unilateral treatment resulted in bilateral improvement of vision. This contralateral effect - similarly observed with other gene therapy products in development for MT-ND4-LHON - is supported by the migration of viral vector genomes and their transcripts to the contralateral eye, as reported in animals, and post-mortem samples from two patients. In this study, we used an AAV2 encoding fluorescent proteins targeting mitochondria to investigate whether these organelles themselves could transfer from the treated eye to the fellow one. We found that mitochondria travel along the visual system (optic chiasm and primary visual cortex) and reach the contralateral eye (optic nerve and retina) in physiological conditions. We also observed that, in a rotenone-induced model of retinal damage mimicking LHON, mitochondrial transfer from the healthy to the damaged eye was accelerated and enhanced. Our results thus provide a further explanation for the contralateral beneficial effect observed during clinical studies with lenadogene nolparvovec.

Inhibition of angiogenesis by the secretome from iPSC-derived retinal ganglion cells with Leber's hereditary optic neuropathy-like phenotypes

The blood supply in the retina ensures photoreceptor function and maintains regular vision. Leber's hereditary optic neuropathy (LHON), caused by the mitochondrial DNA mutations that deteriorate complex I activity, is characterized by progressive vision loss. Although some reports indicated retinal vasculature abnormalities as one of the comorbidities in LHON, the paracrine influence of LHON-affected retinal ganglion cells (RGCs) on vascular endothelial cell physiology remains unclear. To address this, we established an in vitro model of mitochondrial complex I deficiency using induced pluripotent stem cell-derived RGCs (iPSC-RGCs) treated with a mitochondrial complex I inhibitor rotenone (Rot) to recapitulate LHON pathologies. The secretomes from Rot-treated iPSC-RGCs (Rot-iPSC-RGCs) were collected, and their treatment effect on human umbilical vein endothelial cells (HUVECs) was studied. Rot induced LHON-like characteristics in iPSC-RGCs, including decreased mitochondrial complex I activity and membrane potential, and increased mitochondrial reactive oxygen species (ROS) and apoptosis, leading to mitochondrial dysfunction. When HUVECs were exposed to conditioned media (CM) from Rot-iPSC-RGCs, the angiogenesis of HUVECs was suppressed compared to those treated with CM from control iPSC-RGCs (Ctrl-iPSC-RGCs). Angiogenesis-related proteins were altered in the secretomes from Rot-iPSC-RGC-derived CM, particularly angiopoietin, MMP-9, uPA, collagen XVIII, and VEGF were reduced. Notably, GeneMANIA analysis indicated that VEGFA emerged as the pivotal angiogenesis-related protein among the identified proteins secreted by health iPSC-RGCs but reduced in the secretomes from Rot-iPSC-RGCs. Quantitative real-time PCR and western blots confirmed the reduction of VEGFA at both transcription and translation levels, respectively. Our study reveals that Rot-iPSC-RGCs establish a microenvironment to diminish the angiogenic potential of vascular cells nearby, shedding light on the paracrine regulation of LHON-affected RGCs on retinal vasculature.

Rotenone-Induced Optic Nerve Damage and Retinal Ganglion Cell Loss in Rats

Rotenone is a mitochondrial complex I inhibitor that causes retinal degeneration. A study of a rat model of rotenone-induced retinal degeneration suggested that this model is caused by indirect postsynaptic N-methyl-D-aspartate (NMDA) stimulation triggered by oxidative stress-mediated presynaptic intracellular calcium signaling. To elucidate the mechanisms by which rotenone causes axonal degeneration, we investigated morphological changes in optic nerves and the change in retinal ganglion cell (RGC) number in rats. Optic nerves and retinas were collected 3 and 7 days after the intravitreal injection of rotenone. The cross-sections of the optic nerves were subjected to a morphological analysis with axon quantification. The axons and somas of RGCs were analyzed immunohistochemically in retinal flatmounts. In the optic nerve, rotenone induced axonal swelling and degeneration with the incidence of reactive gliosis. Rotenone also significantly reduced axon numbers in the optic nerve. Furthermore, rotenone caused axonal thinning, fragmentation, and beading in RGCs on flatmounts and decreased the number of RGC soma. In conclusion, the intravitreal injection of rotenone in rats induced morphological abnormities with a reduced number of optic nerve axons and RGC axons when the RGC somas were degenerated. These findings help elucidate the pathogenesis of optic neuropathy induced by mitochondrial dysfunction.

The protective effect of anti-VEGF-A/Ang-2 bispecific antibody on retinal vein occlusion model mice

(233/250) Retinal vein occlusion (RVO) causes macular edema and retinal ischemia resulting in visual field and vision loss. A bispecific antibody that blocks VEGF-A and angiopoietin-2 (Ang-2) has been recently launched and applied clinically to treat macular edema, but the role of Ang-2 in the pathogenesis of RVO is still unclear. In this study, we investigated the effects of the anti-VEGF-A/anti-Ang-2 bispecific antibody (BsAb) in a murine RVO model. By using RVO model mice, the expression of Ang-2 gene and protein was examined in the retina through real-time qPCR and Western blotting, respectively. A significant increase in Ang-2 was detected 1 day after occlusion. Immediately after occlusion, control IgG 400 μg/mL, anti-VEGF-A antibody 200 μg/mL, anti-Ang-2 antibody 200 μg/mL, and BsAb 400 μg/mL were intravitreally administered at 2 μL. Visual function was examined using electroretinograms, and apoptosis was examined using TUNEL staining. Interestingly, BsAb partially suppressed the decrease in amplitude of a and b waves compared to control IgG. Anti-Ang-2 antibody and BsAb reduced apoptosis-positive cells 1 day after occlusion. Comprehensive gene expression profiles were also examined using RNA sequencing analysis. RNA sequencing analysis of the retinal tissues showed that BsAb suppressed expression of gene groups associated with inflammatory response and vascular development compared to anti-VEGF-A antibody. Taken together, higher expression of Ang-2 contributes to the pathophysiology of RVO, providing a possible mechanism for the efficacy of BsAb in suppressing retinal dysfunction in RVO.

HLA-Homozygous iPSC-Derived Mesenchymal Stem Cells Rescue Rotenone-Induced Experimental Leber's Hereditary Optic Neuropathy-like Models In Vitro and In Vivo

BACKGROUND

Mesenchymal stem cells (MSCs) hold promise for cell-based therapy, yet the sourcing, quality, and invasive methods of MSCs impede their mass production and quality control. Induced pluripotent stem cell (iPSC)-derived MSCs (iMSCs) can be infinitely expanded, providing advantages over conventional MSCs in terms of meeting unmet clinical demands.

METHODS

The potential of MSC therapy for Leber's hereditary optic neuropathy (LHON) remains uncertain. In this study, we used HLA-homozygous induced pluripotent stem cells to generate iMSCs using a defined protocol, and we examined their therapeutic potential in rotenone-induced LHON-like models in vitro and in vivo.

RESULTS

The iMSCs did not cause any tumorigenic incidence or inflammation-related lesions after intravitreal transplantation, and they remained viable for at least nine days in the mouse recipient's eyes. In addition, iMSCs exhibited significant efficacy in safeguarding retinal ganglion cells (RGCs) from rotenone-induced cytotoxicity in vitro, and they ameliorated CGL+IPL layer thinning and RGC loss in vivo. Optical coherence tomography (OCT) and an electroretinogram demonstrated that iMSCs not only prevented RGC loss and impairments to the retinal architecture, but they also improved retinal electrophysiology performance.

CONCLUSION

The generation of iMSCs via the HLA homozygosity of iPSCs offers a compelling avenue for overcoming the current limitations of MSC-based therapies. The results underscore the potential of iMSCs when addressing retinal disorders, and they highlight their clinical significance, offering renewed hope for individuals affected by LHON and other inherited retinal conditions.

ROS and Endoplasmic Reticulum Stress in Pulmonary Disease

Pulmonary diseases are main causes of morbidity and mortality worldwide. Current studies show that though specific pulmonary diseases and correlative lung-metabolic deviance own unique pathophysiology and clinical manifestations, they always tend to exhibit common characteristics including reactive oxygen species (ROS) signaling and disruptions of proteostasis bringing about accumulation of unfolded or misfolded proteins in the endoplasmic reticulum (ER). ER is generated by the unfolded protein response. When the adaptive unfolded protein response (UPR) fails to preserve ER homeostasis, a maladaptive or terminal UPR is engaged, leading to the disruption of ER integrity and to apoptosis, which is called ER stress. The ER stress mainly includes the accumulation of misfolded and unfolded proteins in lumen and the disorder of Ca²⁺ balance. ROS mediates several critical aspects of the ER stress response. We summarize the latest advances in of the UPR and ER stress in the pathogenesis of pulmonary disease and discuss potential therapeutic strategies aimed at restoring ER proteostasis in pulmonary disease.

Inhibition of endoplasmic reticulum stress by 4-phenylbutyrate alleviates retinal inflammation and the apoptosis of retinal ganglion cells after ocular alkali burn in mice

OBJECTIVE

Retinal ganglion cell (RGC) apoptosis is one of the most severe complications that causes permanent visual impairment following ocular alkali burn (OAB). Currently, very few treatment options exist for this condition. This study was conducted to determine the effect of 4-phenylbutyric acid (4-PBA) on endoplasmic reticulum (ER) stress after OAB using a well-established OAB mouse model.

METHODS

Ocular alkali burn was induced in C57BL/6 mouse corneas using 1 M NaOH. 4-PBA (10 mg/kg; 250 μL per injection) or saline (250 μL per injection) was injected intraperitoneally once per day for 3 days before the establishment of the OAB model. The apoptosis of retinal ganglion cells (RGCs) was assessed by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay, and the histological damage was examined by hematoxylin and eosin and immunofluorescence assay on retinal flat mounts. The key inflammatory response and the expression of ER stress-related markers in the retinal tissues were assessed by real-time PCR, western blotting and histologic analyses.

RESULTS

4-PBA significantly alleviated the apoptosis of RGCs and prevented the structural damage of the retina, as determined by the evaluation of RGC density and retinal thickness. Inhibition of ER stress by 4-PBA decreased the expression of vital proinflammatory cytokines, tumor necrosis factor alpha, and interleukin-1 beta; and suppressed the activation of retinal microglial cells and nuclear factor-kappa B (NF-κB). 4-PBA reduced the expression of the ER stress molecules, glucose-regulated protein 78, activated transcription factor 6, inositol-requiring enzyme-1 (IRE1), X-box-binding protein 1 splicing, and CCAAT/enhancer-binding protein homologous protein, in the retinal tissues and RGCs of OAB mice.

CONCLUSIONS

The present study demonstrated that the inhibition of ER stress by 4-PBA alleviates the inflammatory response via the IRE1/NF-κB signaling pathway and protects the retina and RGCs from injury in an OAB mouse model. Such findings further suggest that 4-PBA might have potential therapeutic implications for OAB treatment.

Retinal Circular RNA hsa_circ_0087207 Expression Promotes Apoptotic Cell Death in Induced Pluripotent Stem Cell-Derived Leber’s Hereditary Optic Neuropathy-like Models

Backgrounds: Leber’s hereditary optic neuropathy (LHON) is known as an inherited retinal disorder characterized by the bilateral central vision loss and degeneration of retinal ganglion cells (RGCs). Unaffected LHON carriers are generally asymptomatic, suggesting that certain factors may contribute to the disease manifestations between carriers and patients who carry the same mutated genotypes. Methods: We first aimed to establish the iPSC-differentiated RGCs from the normal healthy subject, the carrier, and the LHON patient and then compared the differential expression profile of circular RNAs (CircRNAs) among RGCs from these donors in vitro. We further overexpressed or knocked down the most upregulated circRNA to examine whether this circRNA contributes to the distinct phenotypic manifestations between the carrier- and patient-derived RGCs. Results: iPSCs were generated from the peripheral blood cells from the healthy subject, the carrier, and the LHON patient and successfully differentiated into RGCs. These RGCs carried equivalent intracellular reactive oxygen species, but only LHON-patient iPSC-derived RGCs exhibited remarkable apoptosis. Next-generation sequencing and quantitative real-time PCR revealed the circRNA hsa_circ_0087207 as the most upregulated circRNA in LHON-patient iPSC-derived RGCs. Overexpression of hsa_circ_0087207 increased the apoptosis in carrier iPSC-derived RGCs, while knockdown of hsa_circ_0087207 attenuated the apoptosis in LHON-patient iPSC-derived RGCs. Predicted by bioinformatics approaches, hsa_circ_0087207 acts as the sponge of miR-665 to induce the expression of a variety of apoptosis-related genes in LHON patient iPSC-derived RGCs. Conclusions: Our data indicated that hsa_circ_0087207 upregulation distinguishes the disease phenotype manifestations between iPSC-derived RGCs generated from the LHON patient and carrier. Targeting the hsa_circ_0087207/miR-665 axis might hold therapeutic promises for the treatment of LHON.