Sirtuin (Sirt) 3 Overexpression Prevents Retinopathy in Streptozotocin-Induced Diabetic Rats

Honokiol protects against diabetic retinal microvascular injury via sirtuin 3-mediated mitochondrial fusion

Introduction

Mitochondrial dysfunction and oxidative stress play important roles in diabetic retinal vascular injuries. Honokiol (HKL) is a small-molecule polyphenol that exhibits antioxidant effects and has a beneficial effect in diabetes. This study aimed to explore the potential ability of HKL to ameliorate vascular injury in diabetic retinopathy (DR) and its possible mechanisms of action.

Methods

The effect of HKL was evaluated in vascular injury in an in vivo type 2 diabetic (db/db) mouse model. In vitro, retinal microvascular endothelial cells were treated with high glucose (HG) to simulate the pathological diabetic environment. Cell viability, expression of apoptosis-related proteins, cellular reactive oxygen species, mitochondrial membrane potential, and morphological changes in the mitochondria were examined.

Results

The diabetic mice exhibited severe retinal vascular damage, including vascular leakage in vivo and capillary endothelial cell apoptosis in vitro. HKL reversed the retinal vascular leakage in the diabetic mice. In vitro, HKL improved retinal capillary endothelial cell viability, decreased apoptosis, and reversed the HG-induced increased cellular oxidative stress and mitochondrial fragmentation. The sirtuin 3 (SIRT3) inhibitor 3-TYP blocked all the in vivo and in vitro protective effects of HKL against diabetic retinal vascular leakage and capillary endothelium and eliminated the decrease in oxidative stress levels and reduction of mitochondrial fragmentation.

Discussion

In conclusion, these findings suggest that HKL inhibits vascular injury in DR, which was likely achieved through SIRT3-mediated mitochondrial fusion. This study provides a potential new strategy for the treatment of DR.

Sirt3 Protects Retinal Pigment Epithelial Cells From High Glucose-Induced Injury by Promoting Mitophagy Through the AMPK/mTOR/ULK1 Pathway

Purpose

The regulation of mitophagy by Sirt3 has rarely been studied in ocular diseases. In the present study, we determined the effects of Sirt3 on AMPK/mTOR/ULK1 signaling pathway-mediated mitophagy in retinal pigment epithelial (RPE) cells in a high glucose environment.

Methods

The mRNA expression levels of Sirt3, AMPK, mTOR, ULK1, and LC3B in RPE cells under varying glucose conditions were measured by real-time polymerase chain reaction (RT-PCR). The expressions of Sirt3, mitophagy protein, and AMPK/mTOR/ULK1 signaling pathway-related proteins were detected by Western blotting. Lentivirus (LV) transfection mediated the stable overexpression of Sirt3 in cell lines. The experimental groups were NG (5.5 mM glucose), hypertonic, HG (30 mM glucose), HG + LV-GFP, and HG + LV-Sirt3. Western blotting was performed to detect the expressions of mitophagy proteins and AMPK/mTOR/ULK1-related proteins in a high glucose environment during the overexpression of Sirt3. Reactive oxygen species (ROS) production in a high glucose environment was measured by DCFH-DA staining. Mitophagy was detected by labeling mitochondria and lysosomes with MitoTracker and LysoTracker probes, respectively. Apoptosis was detected by flow cytometry.

Results

Sirt3 expression was reduced in the high glucose group, inhibiting the AMPK/mTOR/ULK1 pathway, with diminished mitophagy and increased intracellular ROS production. The overexpression of Sirt3, increased expression of p-AMPK/AMPK and p-ULK1/ULK1, and decreased expression of p-mTOR/mTOR inhibited cell apoptosis and enhanced mitophagy.

Conclusions

Sirt3 protected RPE cells from high glucose-induced injury by activating the AMPK/mTOR/ULK1 signaling pathway.

Translational Relevance

By identifying new targets of action, we aimed to establish effective therapeutic targets for diabetic retinopathy treatment.

Dysregulation of histone deacetylases in ocular diseases

Ocular diseases are a growing global concern and have a significant impact on the quality of life. Cataracts, glaucoma, age-related macular degeneration, and diabetic retinopathy are the most prevalent ocular diseases. Their prevalence and the global market size are also increasing. However, the available pharmacotherapy is currently limited. These diseases share common pathophysiological features, including neovascularization, inflammation, and/or neurodegeneration. Histone deacetylases (HDACs) are a class of enzymes that catalyze the removal of acetyl groups from lysine residues of histone and nonhistone proteins. HDACs are crucial for regulating various cellular processes, such as gene expression, protein stability, localization, and function. They have also been studied in various research fields, including cancer, inflammatory diseases, neurological disorders, and vascular diseases. Our study aimed to investigate the relationship between HDACs and ocular diseases, to identify a new strategy for pharmacotherapy. This review article explores the role of HDACs in ocular diseases, specifically focusing on diabetic retinopathy, age-related macular degeneration, and retinopathy of prematurity, as well as optic nerve disorders, such as glaucoma and optic neuropathy. Additionally, we explore the interplay between HDACs and key regulators of fibrosis and angiogenesis, such as TGF-β and VEGF, highlighting the potential of targeting HDAC as novel therapeutic strategies for ocular diseases.

SIRT3 attenuates doxorubicin-induced cardiotoxicity by inhibiting NLRP3 inflammasome via autophagy

Doxorubicin (DOX) is a highly effective and extensively used chemotherapeutic drug but is limited by its cardiotoxicity. In our previous study, we showed that DOX-induced cardiotoxicity (DIC) triggers autophagy and pyroptosis. Sirtuin 3(SIRT3) is an NAD + -dependent deacetylase of the mitochondria that regulates autophagy. However, it is unknown if the protective effects of SIRT3 on DOX-induced cardiotoxicity involve the inhibition of NLRP3 inflammasome activation. In this study, we constructed in vivo and in vitro DIC models to investigate the effects and potential mechanisms of SIRT3 on DIC. We found that the overexpression of SIRT3 remarkably attenuated DIC through inhibition of the NLRP3 inflammasome. Moreover, we found that the overexpression of SIRT3 restored the dynamic balance of autophagosome/autolysosomes by targeting the mTOR/ULK1 signaling pathway. Application of the mTOR agonist MHY1485 further demonstrated that SIRT3 inhibited NLRP3 inflammasome activation by regulating autophagy. Collectively, the results suggest that SIRT3 effectively attenuates the cardiotoxicity of DOX and provides a theoretical foundation for further exploration of DIC.

Ginsenoside Rg1 Inhibits High Glucose-Induced Proliferation, Migration, and Angiogenesis in Retinal Endothelial Cells by Regulating the lncRNA SNHG7/miR-2116-5p/SIRT3 Axis

Background

Diabetic retinopathy (DR), including retinal angiogenesis and endothelial cell proliferation and migration, is a serious complication in diabetic patients. It has been reported that ginsenoside Rg1 can prevent retinal damage. However, the mechanism by which Rg1 prevents retinal damage is unknown. Therefore, the aim of the present study was to investigate the mechanism by which Rg1 inhibits high glucose-induced complications through the regulation of the lncRNA SNHG7/miR-2116-5p/SIRT3 axis.

Methods

Under high glucose (HG) conditions, human retinal endothelial cells (HRECs) were cultured to simulate a DR environment, and Rg1 was added after 48 h. Negative control (NC), miR-2116-5p mimic, si-SNHG7, pc-DNA SIRT3, and miR-2116-5p inhibitor were transfected into HRECs, and CCK-8 assay was used to detect the cell viability. Angiogenesis and transwell assays were used to evaluate angiogenesis and cell migration, respectively. qRT-PCR and Western blot were used to detect the expression of related genes and proteins. Luciferase reporter assays and bioinformatics were used to analyze the target binding sites of miR-2116-5p to lncRNA SNHG7 and SIRT3.

Results

The proliferation, migration and angiogenesis of HRECs were induced by HG. As expected, HG upregulated miR-2116-5p and VEGF expression but downregulated lncRNA SNHG7 and SIRT3 expression. Importantly, Rg1 inhibited HG-induced HREC proliferation, migration, and angiogenesis by upregulating the lncRNA SNHG7, and miR-2116-5p had a target regulatory relationship with both lncRNA SNHG7 and SIRT3.

Conclusion

Rg1 inhibits HG-induced proliferation, migration, angiogenesis, and VEGF expression in retinal endothelial cells through the lncRNA SNG7/miR-2116-5p/SIRT3 axis. This finding provides theoretical evidence for the clinical application of Rg1 in DR.

Unconventional avenues to decelerated diabetic retinopathy

Diabetic retinopathy (DR) is an important microvascular complication of diabetes mellitus (DM), causing significant visual impairment worldwide. Current gold standards for retarding the progress of DR include blood sugar control and regular fundus screening. Despite these measures, the incidence and prevalence of DR and vision-threatening DR remain high. Given its slowly progressive course and long latent period, opportunities to contain or slow DR before it threatens vision must be explored. This narrative review assesses the recently described unconventional strategies to retard DR progression. These include gut-ocular flow, gene therapy, mitochondrial dysfunction-oxidative stress, stem cell therapeutics, neurodegeneration, anti-inflammatory treatments, lifestyle modification, and usage of phytochemicals. These therapies impact DR directly, while some of them also influence DM control. Most of these strategies are currently in the preclinical stage, and clinical evidence remains low. Nevertheless, our review suggests that these approaches have the potential for human use to prevent the progression of DR.

Biochemical Functions and Clinical Characterizations of the Sirtuins in Diabetes-Induced Retinal Pathologies

Diabetic retinopathy (DR) is undoubtedly one of the most prominent causes of blindness worldwide. This pathology is the most frequent microvascular complication arising from diabetes, and its incidence is increasing at a constant pace. To date, the insurgence of DR is thought to be the consequence of the intricate complex of relations connecting inflammation, the generation of free oxygen species, and the consequent oxidative stress determined by protracted hyperglycemia. The sirtuin (SIRT) family comprises 7 histone and non-histone protein deacetylases and mono (ADP-ribosyl) transferases regulating different processes, including metabolism, senescence, DNA maintenance, and cell cycle regulation. These enzymes are involved in the development of various diseases such as neurodegeneration, cardiovascular pathologies, metabolic disorders, and cancer. SIRT1, 3, 5, and 6 are key enzymes in DR since they modulate glucose metabolism, insulin sensitivity, and inflammation. Currently, indirect and direct activators of SIRTs (such as antagomir, glycyrrhizin, and resveratrol) are being developed to modulate the inflammation response arising during DR. In this review, we aim to illustrate the most important inflammatory and metabolic pathways connecting SIRT activity to DR, and to describe the most relevant SIRT activators that might be proposed as new therapeutics to treat DR.

Contribution of Müller Cells in the Diabetic Retinopathy Development: Focus on Oxidative Stress and Inflammation

Diabetic retinopathy is a neurovascular complication of diabetes and the main cause of vision loss in adults. Glial cells have a key role in maintenance of central nervous system homeostasis. In the retina, the predominant element is the Müller cell, a specialized cell with radial morphology that spans all retinal layers and influences the function of the entire retinal circuitry. Müller cells provide metabolic support, regulation of extracellular composition, synaptic activity control, structural organization of the blood-retina barrier, antioxidant activity, and trophic support, among other roles. Therefore, impairments of Müller actions lead to retinal malfunctions. Accordingly, increasing evidence indicates that Müller cells are affected in diabetic retinopathy and may contribute to the severity of the disease. Here, we will survey recently described alterations in Müller cell functions and cellular events that contribute to diabetic retinopathy, especially related to oxidative stress and inflammation. This review sheds light on Müller cells as potential therapeutic targets of this disease.

Jabuticaba [Plinia trunciflora (O. Berg) Kausel] Protects Liver of Diabetic Rats Against Mitochondrial Dysfunction and Oxidative Stress Through the Modulation of SIRT3 Expression

Complications generated by hyperglycemia present in diabetes mellitus (DM) have been constantly related to oxidative stress and dysfunction in the mitochondrial electron transport chain (ETC). Sirtuin 3 (SIRT3), which is present in mitochondria, is responsible for regulating several proteins involved in metabolic homeostasis and oxidative stress. Studies have suggested alterations in the expression of SIRT3 in DM. The objective of this study was to evaluate the effects of phenolic compounds in jabuticaba (Plinia trunciflora), a berry native to Brazil, on the activity of mitochondrial ETC complexes, SIRT3 protein expression, and oxidative stress parameters in liver of diabetic rats induced by streptozotocin. After type 1 DM induction (streptozotocin 65 mg/kg), diabetic and healthy rats were treated with jabuticaba peel extract (JPE) by gavage (0.5 g/kg of weight) for 30 days. After treatments, those diabetic rats presented impaired activities of complexes I, II, and III of ETC along with an overexpression of SIRT3. In addition, an increase in lipid peroxidation and superoxide dismutase and catalase activities was observed in the diabetic group. The treatment with JPE was able to recover the activity of the mitochondrial complexes and reduce the expression of SIRT3. Furthermore, JPE treatment reduced oxidative damage to lipids and brought the antioxidants enzyme activities to basal levels in diabetic rats. Together, these results demonstrate that JPE can reduce oxidative stress related to DM by restoring mitochondrial complexes activity and regulating SIRT3 expression. Thus, JPE could become an alternative to reduce the development of complications related to DM.

The Protective Effects of Dexmedetomidine against Hypoxia/Reoxygenation-Induced Inflammatory Injury and Permeability in Brain Endothelial Cells Mediated by Sigma-1 Receptor

Cerebral ischemia-reperfusion injury (CIRI) mainly arises from the clinical treatment of ischemic stroke, induced by the blood-brain barrier (BBB) disruption and infiltrated inflammation. The Sigma-1 receptor (Sigma-1R) is a novel target for neuroprotection, and the α2-receptor agonist pain medication dexmedetomidine displays a neuroprotective effect through activating Sigma-1R. The present study aims to investigate the potential therapeutic effect of dexmedetomidine in a mouse stroke model and hypoxia/reoxygenation(OGD/R)-induced brain endothelial dysfunction. First, we found that Sigma-1R was significantly upregulated in middle cerebral artery occlusion (MCAO) mice by the administration of dexmedetomidine. In vivo experiments revealed that dexmedetomidine ameliorated hyperpermeability of the blood-brain barrier (BBB), lowered the expression level of Occludin, and impaired brain function as measured by neurological scores in MCAO mice. In vitro assays show that dexmedetomidine alleviated OGD/R-caused cytotoxicity, hyperpermeability, abnormal expression of Occludin, and inflammatory factors in human brain microvascular endothelial cells (HBMVECs). Moreover, blockage of Sigma-1R by its antagonist BD1047 abolished the neuroprotective property of dexmedetomidine in both animal and cell culture experiments. On the basis of these findings, we conclude that dexmedetomidine therapy shows neuroprotection in MCAO mice. Mechanistically, dexmedetomidine alleviated hypoxia/reoxygenation-induced cerebral endothelial dysfunction by activating the Sigma-1R-mediated signaling pathway.

Oxidative stress and diabetic retinopathy: Molecular mechanisms, pathogenetic role and therapeutic implications

Oxidative stress, a cytopathic outcome of excessive generation of ROS and the repression of antioxidant defense system for ROS elimination, is involved in the pathogenesis of multiple diseases, including diabetes and its complications. Retinopathy, a microvascular complication of diabetes, is the primary cause of acquired blindness in diabetic patients. Oxidative stress has been verified as one critical contributor to the pathogenesis of diabetic retinopathy. Oxidative stress can both contribute to and result from the metabolic abnormalities induced by hyperglycemia, mainly including the increased flux of the polyol pathway and hexosamine pathway, the hyper-activation of protein kinase C (PKC) isoforms, and the accumulation of advanced glycation end products (AGEs). Moreover, the repression of the antioxidant defense system by hyperglycemia-mediated epigenetic modification also leads to the imbalance between the scavenging and production of ROS. Excessive accumulation of ROS induces mitochondrial damage, cellular apoptosis, inflammation, lipid peroxidation, and structural and functional alterations in retina. Therefore, it is important to understand and elucidate the oxidative stress-related mechanisms underlying the progress of diabetic retinopathy. In addition, the abnormalities correlated with oxidative stress provide multiple potential therapeutic targets to develop safe and effective treatments for diabetic retinopathy. Here, we also summarized the main antioxidant therapeutic strategies to control this disease.

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Oxidative stress can both contribute to and result from hyperglycemia-induced metabolic abnormalities in retina.

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Genes important in regulation of ROS are epigenetically modified, increasing ROS accumulation in retina.

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Oxidative stress is closely associated with the pathological changes in the progress of diabetic retinopathy.

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Antioxidants ameliorate retinopathy through targeting multiple steps of oxidative stress.