Impairment of Autophagy Causes Superoxide Formation and Caspase Activation in 661 W Cells, a Cell Line for Cone Photoreceptors, under Hyperglycemic Conditions

Polystyrene microplastic-induced extracellular vesicles cause kidney-related effects in the crosstalk between tubular cells and fibroblasts

Plastic waste accumulation and its degradation into microplastics (MPs) and nanoplastics (NPs) pose environmental concerns. Previous studies have indicated that polystyrene (PS)-MPs harm living animals. Extracellular vesicles (EVs) are associated with metabolic reprogramming and mitochondrial dysfunction in various kidney diseases. In this article, we evaluated how PS-MPs affected tubular cells and fibroblasts. The results demonstrated that PS-MPs increased EV production in human tubular cells and caused endoplasmic reticulum (ER) stress-related proteins without inducing inflammation-related proteins in human tubular cells. The uptake of PS-MPs and incubation with the conditioned medium of PS-MPs induced reactive oxygen species (ROS) production and ER stress-related proteins in fibroblast cells. The fibroblast cells treated with the conditioned medium of PS-MPs also increased the expression of fibrosis-related proteins. Our findings suggested that the expression of EV-related markers increased in tubular cells via Beclin 1 after PS-MP treatment. In addition, PS-MPs induced ROS production in vitro and in vivo. We found that PS-MPs also altered the expression of EV markers in urine, and CD63 expression was also increased in vitro and in vivo after PS-MP treatment. In conclusion, PS-MP-induced EVs lead to ER stress-related proteins, ROS production and fibrosis-related proteins in tubular cells and fibroblasts.

Impaired Removal of the Damaged Mitochondria in the Metabolic Memory Phenomenon Associated with Continued Progression of Diabetic Retinopathy

Retinopathy fails to halt even after diabetic patients in poor glycemic control try to institute tight glycemic control, suggesting a "metabolic memory" phenomenon, and the experimental models have demonstrated that mitochondria continue to be damaged/dysfunctional, fueling into the vicious cycle of free radicals. Our aim was to investigate the role of removal of the damaged mitochondria in the metabolic memory. Using human retinal endothelial cells (HRECs), incubated in 20 mM D-glucose for 4 days, followed by 5 mM D-glucose for 4 additional days, mitochondrial turnover, formation of mitophagosome, and mitophagy flux were evaluated. Mitophagy was confirmed in a rat model of metabolic memory where the rats were kept in poor glycemic control (blood glucose ~ 400 mg/dl) for 3 months soon after induction of streptozotocin-induced diabetes, followed by 3 additional months of good control (BG < 150 mg/dl). Reversal of high glucose by normal glucose had no effect on mitochondrial turnover and mitophagosome formation, and mitophagy flux remained compromised. Similarly, 3 months of good glycemic control in rats, which had followed 3 months of poor glycemic control, had no effect on mitophagy flux. Thus, poor turnover/removal of the damaged mitochondria, initiated during poor glycemic control, does not benefit from the termination of hyperglycemic insult, and the damaged mitochondria continue to produce free radicals, suggesting the importance of mitophagy in the metabolic memory phenomenon associated with the continued progression of diabetic retinopathy.

The ideal treatment timing for diabetic retinopathy: the molecular pathological mechanisms underlying early-stage diabetic retinopathy are a matter of concern

Diabetic retinopathy (DR) is a prevalent complication of diabetes, significantly impacting patients' quality of life due to vision loss. No pharmacological therapies are currently approved for DR, excepted the drugs to treat diabetic macular edema such as the anti-VEGF agents or steroids administered by intraocular route. Advancements in research have highlighted the crucial role of early intervention in DR for halting or delaying disease progression. This holds immense significance in enhancing patients' quality of life and alleviating the societal burden associated with medical care costs. The non-proliferative stage represents the early phase of DR. In comparison to the proliferative stage, pathological changes primarily manifest as microangiomas and hemorrhages, while at the cellular level, there is a loss of pericytes, neuronal cell death, and disruption of components and functionality within the retinal neuronal vascular unit encompassing pericytes and neurons. Both neurodegenerative and microvascular abnormalities manifest in the early stages of DR. Therefore, our focus lies on the non-proliferative stage of DR and we have initially summarized the mechanisms involved in its development, including pathways such as polyols, that revolve around the pathological changes occurring during this early stage. We also integrate cutting-edge mechanisms, including leukocyte adhesion, neutrophil extracellular traps, multiple RNA regulation, microorganisms, cell death (ferroptosis and pyroptosis), and other related mechanisms. The current status of drug therapy for early-stage DR is also discussed to provide insights for the development of pharmaceutical interventions targeting the early treatment of DR.

Role of mitophagy in ocular neurodegeneration

Neurons in the central nervous system are among the most metabolically active cells in the body, characterized by high oxygen consumption utilizing glucose both aerobically and anaerobically. Neurons have an abundance of mitochondria which generate adequate ATP to keep up with the high metabolic demand. One consequence of the oxidative phosphorylation mechanism of ATP synthesis, is the generation of reactive oxygen species which produces cellular injury as well as damage to mitochondria. Mitochondria respond to injury by fusion which serves to ameliorate the damage through genetic complementation. Mitochondria also undergo fission to meet an increased energy demand. Loss of mitochondria is also compensated by increased biogenesis to generate new mitochondria. Damaged mitochondria are removed by mitophagy, an autophagic process, in which damaged mitochondria are surrounded by a membrane to form an autophagosome which ultimately fuses with the lysosome resulting in degradation of faulty mitochondria. Dysregulation of mitophagy has been reported in several central nervous system disorders, including, Alzheimer's disease and Parkinson's disease. Recent studies point to aberrant mitophagy in ocular neurodegenerative disorders which could be an important contributor to the disease etiology/pathology. This review article highlights some of the recent findings that point to dysregulation of mitophagy and it's underlying mechanisms in ocular neurodegenerative diseases, including, glaucoma, age-related macular degeneration and diabetic retinopathy.

Crosstalk between autophagy and insulin resistance: evidence from different tissues

Insulin is a critical hormone that promotes energy storage in various tissues, as well as anabolic functions. Insulin resistance significantly reduces these responses, resulting in pathological conditions, such as obesity and type 2 diabetes mellitus (T2DM). The management of insulin resistance requires better knowledge of its pathophysiological mechanisms to prevent secondary complications, such as cardiovascular diseases (CVDs). Recent evidence regarding the etiological mechanisms behind insulin resistance emphasizes the role of energy imbalance and neurohormonal dysregulation, both of which are closely regulated by autophagy. Autophagy is a conserved process that maintains homeostasis in cells. Accordingly, autophagy abnormalities have been linked to a variety of metabolic disorders, including insulin resistance, T2DM, obesity, and CVDs. Thus, there may be a link between autophagy and insulin resistance. Therefore, the interaction between autophagy and insulin function will be examined in this review, particularly in insulin-responsive tissues, such as adipose tissue, liver, and skeletal muscle.

Impaired mitochondrial dynamics and removal of the damaged mitochondria in diabetic retinopathy

Introduction

Mitochondrial dynamic plays a major role in their quality control, and the damaged mitochondrial components are removed by autophagy. In diabetic retinopathy, mitochondrial fusion enzyme, mitofusin 2 (Mfn2), is downregulated and mitochondrial dynamic is disturbed resulting in depolarized and dysfunctional mitochondria. Our aim was to investigate the mechanism of inhibition of Mfn2, and its role in the removal of the damaged mitochondria, in diabetic retinopathy.

Methods

Using human retinal endothelial cells, effect of high glucose (20mM) on the GTPase activity of Mfn2 and its acetylation were determined. Role of Mfn2 in the removal of the damaged mitochondria was confirmed by regulating its acetylation, or by Mfn2 overexpression, on autophagosomes- autolysosomes formation and the mitophagy flux.

Results

High glucose inhibited GTPase activity and increased acetylation of Mfn2. Inhibition of acetylation, or Mfn2 overexpression, attenuated decrease in GTPase activity and mitochondrial fragmentation, and increased the removal of the damaged mitochondria. Similar phenomenon was observed in diabetic mice; overexpression of sirtuin 1 (a deacetylase) ameliorated diabetes-induced inhibition of retinal Mfn2 and facilitated the removal of the damaged mitochondria.

Conclusions

Acetylation of Mfn2 has dual roles in mitochondrial homeostasis in diabetic retinopathy, it inhibits GTPase activity of Mfn2 and increases mitochondrial fragmentation, and also impairs removal of the damaged mitochondria. Thus, protecting Mfn2 activity should maintain mitochondrial homeostasis and inhibit the development/progression of diabetic retinopathy.

Autophagy in the retinal neurovascular unit: New perspectives into diabetic retinopathy

Diabetic retinopathy (DR) is one of the most prevalent retinal disorders worldwide, and it is a major cause of vision impairment in individuals of productive age. Research has demonstrated the significance of autophagy in DR, which is a critical intracellular homeostasis mechanism required for the destruction and recovery of cytoplasmic components. Autophagy maintains the physiological function of senescent and impaired organelles under stress situations, thereby regulating cell fate via various signals. As the retina's functional and fundamental unit, the retinal neurovascular unit (NVU) is critical in keeping the retinal environment's stability and supporting the needs of retinal metabolism. However, autophagy is essential for the normal NVU structure and function. We discuss the strong association between DR and autophagy in this review, as well as the many kinds of autophagy and its crucial physiological activities in the retina. By evaluating the pathological changes of retinal NVU in DR and the latest advancements in the molecular mechanisms of autophagy that may be involved in the pathophysiology of DR in NVU, we seek to propose new ideas and methods for the prevention and treatment of DR.

Research Progress on Mitochondrial Dysfunction in Diabetic Retinopathy

Diabetic Retinopathy (DR) is one of the most important microvascular complications of diabetes mellitus, which can lead to blindness in severe cases. Mitochondria are energy-producing organelles in eukaryotic cells, which participate in metabolism and signal transduction, and regulate cell growth, differentiation, aging, and death. Metabolic changes of retinal cells and epigenetic changes of mitochondria-related genes under high glucose can lead to mitochondrial dysfunction and induce mitochondrial pathway apoptosis. In addition, mitophagy and mitochondrial dynamics also change adaptively. These mechanisms may be related to the occurrence and progression of DR, and also provide valuable clues for the prevention and treatment of DR. This article reviews the mechanism of DR induced by mitochondrial dysfunction, and the prospects for related treatment.

Diabetic retinopathy: Involved cells, biomarkers, and treatments

Diabetic retinopathy (DR), a leading cause of vision loss and blindness worldwide, is caused by retinal neurovascular unit dysfunction, and its cellular pathology involves at least nine kinds of retinal cells, including photoreceptors, horizontal and bipolar cells, amacrine cells, retinal ganglion cells, glial cells (Müller cells, astrocytes, and microglia), endothelial cells, pericytes, and retinal pigment epithelial cells. Its mechanism is complicated and involves loss of cells, inflammatory factor production, neovascularization, and BRB impairment. However, the mechanism has not been completely elucidated. Drug treatment for DR has been gradually advancing recently. Research on potential drug targets relies upon clear information on pathogenesis and effective biomarkers. Therefore, we reviewed the recent literature on the cellular pathology and the diagnostic and prognostic biomarkers of DR in terms of blood, protein, and clinical and preclinical drug therapy (including synthesized molecules and natural molecules). This review may provide a theoretical basis for further DR research.

mTOR Signalling Pathway: A Potential Therapeutic Target for Ocular Neurodegenerative Diseases

Recent advances in the research of the mammalian target of the rapamycin (mTOR) signalling pathway demonstrated that mTOR is a robust therapeutic target for ocular degenerative diseases, including age-related macular degeneration (AMD), diabetic retinopathy (DR), and glaucoma. Although the exact mechanisms of individual ocular degenerative diseases are unclear, they share several common pathological processes, increased and prolonged oxidative stress in particular, which leads to functional and morphological impairment in photoreceptors, retinal ganglion cells (RGCs), or retinal pigment epithelium (RPE). mTOR not only modulates oxidative stress but is also affected by reactive oxygen species (ROS) activation. It is essential to understand the complicated relationship between the mTOR pathway and oxidative stress before its application in the treatment of retinal degeneration. Indeed, the substantial role of mTOR-mediated autophagy in the pathogenies of ocular degenerative diseases should be noted. In reviewing the latest studies, this article summarised the application of rapamycin, an mTOR signalling pathway inhibitor, in different retinal disease models, providing insight into the mechanism of rapamycin in the treatment of retinal neurodegeneration under oxidative stress. Besides basic research, this review also summarised and updated the results of the latest clinical trials of rapamycin in ocular neurodegenerative diseases. In combining the current basic and clinical research results, we provided a more complete picture of mTOR as a potential therapeutic target for ocular neurodegenerative diseases.

Autophagy: A Novel Pharmacological Target in Diabetic Retinopathy

Autophagy is the major catabolic pathway involved in removing and recycling damaged macromolecules and organelles and several evidences suggest that dysfunctions of this pathway contribute to the onset and progression of central and peripheral neurodegenerative diseases. Diabetic retinopathy (DR) is a serious complication of diabetes mellitus representing the main preventable cause of acquired blindness worldwide. DR has traditionally been considered as a microvascular disease, however this concept has evolved and neurodegeneration and neuroinflammation have emerged as important determinants in the pathogenesis and evolution of the retinal pathology. Here we review the role of autophagy in experimental models of DR and explore the potential of this pathway as a target for alternative therapeutic approaches.

Artesunate alleviates diabetic retinopathy by activating autophagy via the regulation of AMPK/SIRT1 pathway

CONTEXT

Artesunate (ART), an antimalarial drug, possesses the ability to induce autophagy and exhibits a protective effect on diabetes.

OBJECTIVE

This study aimed to evaluate the effects of ART on diabetic retinopathy (DR) and to explore the underlying mechanisms.

METHODS

Rats with streptozotocin-induced DR were given intravitreal injection of ART.

RESULTS

ART administration inhibited the increase in retinal thickness and prevented blood-retinal barrier in diabetic rats. Further, vascular leukocyte adherence, microglial activation, inflammatory cytokine, and ROS production in the retinas of diabetic rats were also inhibited by ART. Additionally, ART enhanced autophagy in the retinas of diabetic rats as demonstrated by up-regulated Beclin-1 expression and LC3II/I ratio and down-regulated p62. ART also activated AMP-activated protein kinase (AMPK)/sensor class III histone deacetylase sirtuin 1 (SIRT1) pathway.

CONCLUSIONS

ART, as an autophagy activator, has therapeutic potential in DR treatment.

Gypenoside XVII alleviates early diabetic retinopathy by regulating Müller cell apoptosis and autophagy in db/db mice

Diabetic retinopathy (DR) is a widespread vision-threatening disease in working people. Müller cells are important glial cells that participate in the blood retinal barrier and promote the maintenance of retinal physiological and structural homeostasis. Müller cell apoptosis and autophagy play an important role in the pathogenesis of DR. Gypenoside XVII (Gyp-17) exerts strong antiapoptotic and autophagic activities. However, the effect of Gyp-17 on DR and its mechanism of action have not been elucidated. This study explored the effect of Gyp-17 on early DR and Müller cell injury in db/db mice. Blood glucose and blood lipids were measured. Optical coherence tomography and fundus fluorescein angiography were applied to detect retinal thickness and vascular leakage, respectively. Hematoxylin eosin staining assessed the pathological changes of the retina. Retinal oxidative environment and cell apoptosis and autophagy were monitored using commercial kits, immunofluorescence, and Western blot assays. Results showed that Gyp-17 exerted no significant effect on blood glucose and lipid levels but maintained normal retinal permeability, physiological structure, high anti-oxidative enzyme expression, and the thickness of the inner nuclear layer compared with the model group. Moreover, Western blot analysis and TUNEL assay indicated that Gyp-17 significantly decreased pro-apoptotic-related protein expression and increased pro-autophagy-related protein expression compared with the model group. Immunofluorescence colocalization exhibited that the regulating action of Gyp-17 may focus on Müller cells. These data strongly demonstrate that Gyp-17 prevents early DR by decreasing apoptosis and increasing autophagy in Müller cells. Gyp-17 may be a candidate drug for early DR therapy.

Microfluidic and Microscale Assays to Examine Regenerative Strategies in the Neuro Retina

Bioengineering systems have transformed scientific knowledge of cellular behaviors in the nervous system (NS) and pioneered innovative, regenerative therapies to treat adult neural disorders. Microscale systems with characteristic lengths of single to hundreds of microns have examined the development and specialized behaviors of numerous neuromuscular and neurosensory components of the NS. The visual system is comprised of the eye sensory organ and its connecting pathways to the visual cortex. Significant vision loss arises from dysfunction in the retina, the photosensitive tissue at the eye posterior that achieves phototransduction of light to form images in the brain. Retinal regenerative medicine has embraced microfluidic technologies to manipulate stem-like cells for transplantation therapies, where de/differentiated cells are introduced within adult tissue to replace dysfunctional or damaged neurons. Microfluidic systems coupled with stem cell biology and biomaterials have produced exciting advances to restore vision. The current article reviews contemporary microfluidic technologies and microfluidics-enhanced bioassays, developed to interrogate cellular responses to adult retinal cues. The focus is on applications of microfluidics and microscale assays within mammalian sensory retina, or neuro retina, comprised of five types of retinal neurons (photoreceptors, horizontal, bipolar, amacrine, retinal ganglion) and one neuroglia (Müller), but excludes the non-sensory, retinal pigmented epithelium.