A pyruvate dehydrogenase kinase inhibitor prevents retinal cell death and improves energy metabolism in rat retinas after ischemia/reperfusion injury

Modeling of Retina and Optic Nerve Ischemia-Reperfusion Injury through Hypoxia-Reoxygenation in Human Induced Pluripotent Stem Cell-Derived Retinal Ganglion Cells

Retinal ganglion cells (RGCs) are specialized projection neurons that constitute part of the retina, and the death of RGCs causes various eye diseases, but the mechanism of RGC death is still unclear. Here, we induced cell death in human induced pluripotent stem cell (hiPSC)-derived RGC-rich retinal tissues using hypoxia-reoxygenation in vitro. Flow cytometry, immunochemistry, and Western blotting showed the apoptosis and necrosis of RGCs under hypoxia-reoxygenation, and they were rescued by an apoptosis inhibitor but not by a necrosis inhibitor. This revealed that the cell death induced in our model was mainly due to apoptosis. To our knowledge, this is the first model to reproduce ischemia-reperfusion in hiPSC-derived RGCs. Thus, the efficacy of apoptosis inhibitors and neuroprotective agents can be evaluated using this model, bringing us closer to clinical applications.

The GPR84 molecule is a mediator of a subpopulation of retinal microglia that promote TNF/IL-1α expression via the rho-ROCK pathway after optic nerve injury

Resident microglia are important to maintain homeostasis in the central nervous system, which includes the retina. The retinal microglia become activated in numerous pathological conditions, but the molecular signatures of these changes are poorly understood. Here, using an approach based on FACS and RNA-seq, we show that microglial gene expression patterns gradually change during RGC degeneration induced by optic nerve injury. Most importantly, we found that the microglial cells strongly expressed Tnf and Il1α, both of which are known to induce neurotoxic reactive astrocytes, and were characterized by Gpr84high -expressing cells in a particular subpopulation. Moreover, ripasudil, a Rho kinase inhibitor, significantly blunted Gpr84 expression and cytokine induction in vitro and in vivo. Finally, GPR84-deficient mice prevented RGC loss in optic nerve-injured retina. These results reveal that Rho kinase-mediated GPR84 alteration strongly contribute to microglial activation and promote neurotoxicity, suggesting that Rho-ROCK and GPR84 signaling may be potential therapeutic targets to prevent the neurotoxic microglial phenotype induced by optic nerve damage, such as occurs in traumatic optic neuropathy and glaucoma.

Glaucoma-Associated CDR1 Peptide Promotes RGC Survival in Retinal Explants through Molecular Interaction with Acidic Leucine Rich Nuclear Phosphoprotein 32A (ANP32A)

Glaucoma is a complex, multifactorial optic neuropathy mainly characterized by the progressive loss of retinal ganglion cells (RGCs) and their axons, resulting in a decline of visual function. The pathogenic molecular mechanism of glaucoma is still not well understood, and therapeutic strategies specifically addressing the neurodegenerative component of this ocular disease are urgently needed. Novel immunotherapeutics might overcome this problem by targeting specific molecular structures in the retina and providing direct neuroprotection via different modes of action. Within the scope of this research, the present study showed for the first time beneficial effects of the synthetic CDR1 peptide SCTGTSSDVGGYNYVSWYQ on the viability of RGCs ex vivo in a concentration-dependent manner compared to untreated control explants (CTRL, 50 µg/mL: p < 0.05 and 100 µg/mL: p < 0.001). Thereby, this specific peptide was identified first as a potential biomarker candidate in the serum of glaucoma patients and was significantly lower expressed in systemic IgG molecules compared to healthy control subjects. Furthermore, MS-based co-immunoprecipitation experiments confirmed the specific interaction of synthetic CDR1 with retinal acidic leucine-rich nuclear phosphoprotein 32A (ANP32A; p < 0.001 and log2 fold change > 3), which is a highly expressed protein in neurological tissues with multifactorial biological functions. In silico binding prediction analysis revealed the N-terminal leucine-rich repeat (LRR) domain of ANP32A as a significant binding site for synthetic CDR1, which was previously reported as an important docking site for protein-protein interactions (PPI). In accordance with these findings, quantitative proteomic analysis of the retinae ± CDR1 treatment resulted in the identification of 25 protein markers, which were significantly differentially distributed between both experimental groups (CTRL and CDR1, p < 0.05). Particularly, acetyl-CoA biosynthesis I-related enzymes (e.g., DLAT and PDHA1), as well as cytoskeleton-regulating proteins (e.g., MSN), were highly expressed by synthetic CDR1 treatment in the retina; on the contrary, direct ANP32A-interacting proteins (e.g., NME1 and PPP2R4), as well as neurodegenerative-related markers (e.g., CEND1), were identified with significant lower abundancy in the CDR1-treated retinae compared to CTRL. Furthermore, retinal protein phosphorylation and histone acetylation were also affected by synthetic CDR1, which are both partially controlled by ANP32A. In conclusion, the synthetic CDR1 peptide provides a great translational potential for the treatment of glaucoma in the future by eliciting its neuroprotective mechanism via specific interaction with ANP32A's N terminal LRR domain.

Ambient particulate matter exposure causes visual dysfunction and retinal neuronal degeneration

PM_2.5 pollution is related to neurotoxic and vascular effects in eye diseases such as glaucoma. This study investigates the adverse effects of PM_2.5 exposure on visual function and retinal neurons. A versatile aerosol concentration enrichment system was used to expose mice to either control air or PM_2.5 polluted air. Six months after PM_2.5 exposure, visual function was measured by electroretinography (ERG). Hematoxylin and eosin staining and immunofluorescence staining were used for histopathological analysis. Protein markers of apoptosis, astrocytic reactivity, inflammatory cytokines, lipid peroxidation, protein nitration and DNA damage response were quantified with ELISA, western blot or detected using immunofluorescence and immunohistochemistry. After six months of exposure, PM_2.5-exposed mice responded poorly to light stimuli compared with those exposed to the control air. PM_2.5 exposure caused retinal thinning and reduction in the expression of retinal ganglion cell-selective marker RNA-binding protein with multiple splicing (RBPMS). Further, positive TUNEL staining was observed in the inner nucleus and outer nuclear layers of the retinae after exposure to PM_2.5, which was accompanied by the activation of apoptosis signaling molecules p53, caspase-3 and Bax. PM_2.5 induced the release of inflammatory cytokines including tumor necrosis factor-α and cleaved interleukin-1β. Furthermore, increased levels of 8-OHdG and γ-H2AX in the mouse retinea were indicative of DNA single and double strand breaks by PM_2.5 exposure, which activated PARP-1 mediated DNA damage and repair. In conclusion, this study demonstrates sub-chronic systemic exposure to concentrated PM_2.5 causes visual dysfunction and retinal neuronal degeneration. DATA AVAILABILITY: The datasets during and/or analyzed during the current study available from the corresponding author on reasonable request.

The Regulatory NOD-Like Receptor NLRC5 Promotes Ganglion Cell Death in Ischemic Retinopathy by Inducing Microglial Pyroptosis

Retinal ischemia is a common pathological event that can result in retinal ganglion cell (RGC) death and irreversible vision loss. The pathogenic mechanisms linking retinal ischemia to RGC loss and visual deficits are uncertain, which has greatly hampered the development of effective treatments. It is increasingly recognized that pyroptosis of microglia contributes to the indirect inflammatory death of RGCs. In this study, we report a regulatory NOD-like receptor, NOD-, LRR- and CARD-containing 5 (NLRC5), as a key regulator on microglial pyroptosis and the retinal ischemia process. Through an in-depth analysis of our recently published transcriptome data, we found that NLRC5 was significantly up-regulated in retina during ischemia–reperfusion injury, which were further confirmed by subsequent detection of mRNA and protein level. We further found that NLRC5 was upregulated in retinal microglia during ischemia, while NLRC5 knockdown significantly ameliorated retinal ischemic damage and RGC death. Mechanistically, we revealed that knockdown of NLRC5 markedly suppressed gasdermin D (GSDMD) cleavage and activation of interleukin-1β (IL-1β) and caspase-3, indicating that NLRC5 promotes both microglial pyroptosis and apoptosis. Notably, we found that NLRC5 directly bound to NLRP3 and NLRC4 in inflammasomes to cooperatively drive microglial pyroptosis and apoptosis mediating retinal ischemic damage. Overall, these findings reveal a previously unidentified key contribution of NLRC5 signaling to microglial pyroptosis under ischemia or hypoxia conditions. This NLRC5-dependent pathway may be a novel therapeutic target for treatment of ischemic retinopathy.

Identification of Pyruvate Dehydrogenase E1 as a Potential Target against Magnaporthe oryzae through Experimental and Theoretical Investigation

Magnaporthe oryzae (M. oryzae) is a typical cause of rice blast in agricultural production. Isobavachalcone (IBC), an active ingredient of Psoralea corylifolia L. extract, is an effective fungicide against rice blast. To determine the mechanism of IBC against M. oryzae, the effect of IBC on the metabolic pathway of M. oryzae was explored by transcriptome profiling. In M. oryzae, the expression of pyruvate dehydrogenase E1 (PDHE1), part of the tricarboxylic acid (TCA cycle), was significantly decreased in response to treatment with IBC, which was verified by qPCR and testing of enzyme activity. To further elucidate the interactions between IBC and PDHE1, the 3D structure model of the PDHE1 from M. oryzae was established based on homology modeling. The model was utilized to analyze the molecular interactions through molecular docking and molecular dynamics simulation, revealing that IBC has π-π stacking interactions with residue TYR139 and undergoes hydrogen bonding with residue ASP217 of PDHE1. Additionally, the nonpolar residues PHE111, MET174, ILE 187, VAL188, and MET250 form strong hydrophobic interactions with IBC. The above results reveal that PDHE1 is a potential target for antifungal agents, which will be of great significance for guiding the design of new fungicides. This research clarified the mechanism of IBC against M. oryzae at the molecular level, which will underpin further studies of the inhibitory mechanism of flavonoids and the discovery of new targets. It also provides theoretical guidance for the field application of IBC.

Pyruvate dehydrogenase kinases (PDKs): an overview toward clinical applications

Pyruvate dehydrogenase kinase (PDK) can regulate the catalytic activity of pyruvate decarboxylation oxidation via the mitochondrial pyruvate dehydrogenase complex, and it further links glycolysis with the tricarboxylic acid cycle and ATP generation. This review seeks to elucidate the regulation of PDK activity in different species, mainly mammals, and the role of PDK inhibitors in preventing increased blood glucose, reducing injury caused by myocardial ischemia, and inducing apoptosis of tumor cells. Regulations of PDKs expression or activity represent a very promising approach for treatment of metabolic diseases including diabetes, heart failure, and cancer. The future research and development could be more focused on the biochemical understanding of the diseases, which would help understand the cellular energy metabolism and its regulation by pharmacological effectors of PDKs.

CircRNA expression profile and functional analysis in retinal ischemia-reperfusion injury

Retinal ischemia-reperfusion (I/R) is involved in the pathogenesis of many vision-threatening diseases. circRNAs act as key players in gene regulation and human diseases. However, the global circRNA expression profile in retinal I/R injury has not been fully uncovered. Herein, we established a murine model of retinal I/R injury and performed circRNA microarrays to identify I/R-related circRNAs. 1265 differentially expressed circRNAs were identified between I/R retinas and normal retinas. Notably, the detection of cWDR37 level in aqueous humor could discriminate glaucoma patients from cataract patients (AUC = 0.9367). cWdr37 silencing protected against hypoxic stress- or oxidative stress-induced retinal ganglion cell (RGC) injury. cWdr37 silencing alleviated IR-induced retinal neurodegeneration as shown by increased NeuN staining, reduced retinal reactive gliosis, and decreased retinal apoptosis. Collectively, this study provides a novel insight into the pathogenesis of retinal I/R injury. cWdr37 is a promising target for the diagnosis or treatment of I/R-related ocular diseases.

Metabolic Features of Mouse and Human Retinas: Rods versus Cones, Macula versus Periphery, Retina versus RPE

Photoreceptors, especially cones, which are enriched in the human macula, have high energy demands, making them vulnerable to metabolic stress. Metabolic dysfunction of photoreceptors and their supporting retinal pigment epithelium (RPE) is an important underlying cause of degenerative retinal diseases. However, how cones and the macula support their exorbitant metabolic demand and communicate with RPE is unclear. By profiling metabolite uptake and release and analyzing metabolic genes, we have found cone-rich retinas and human macula share specific metabolic features with upregulated pathways in pyruvate metabolism, mitochondrial TCA cycle, and lipid synthesis. Human neural retina and RPE have distinct but complementary metabolic features. Retinal metabolism centers on NADH production and neurotransmitter biosynthesis. The retina needs aspartate to sustain its aerobic glycolysis and mitochondrial metabolism. RPE metabolism is directed toward NADPH production and biosynthesis of acetyl-rich metabolites, serine, and others. RPE consumes multiple nutrients, including proline, to produce metabolites for the retina.

Aerobic Glycolysis in the Retina: Functional Roles of Pyruvate Kinase Isoforms

One hundred years ago, Otto Heinrich Warburg observed that postmitotic retinal cells are the highest oxygen-consuming cells in the body. He compared these cells to actively growing mitotic tumor cells since both cells reprogram glucose for anabolic processes, which include lipid, protein, and RNA/DNA synthesis, and for antioxidant metabolism. To achieve this metabolic reprogramming, cancer cells preferentially express a less active dimeric form, the M2 isoform of pyruvate kinase (PKM2), which shuttles glucose toward the accumulation of glycolytic intermediates that redirect cell activities into anabolic processes. Similar to cancer cells, retinal photoreceptors predominantly express the M2 isoform of PKM2. This isoform performs both metabolic and non-metabolic functions in photoreceptor cells. This review focuses on the metabolic and non-metabolic roles of pyruvate kinases in photoreceptor cell functions.