Time-lapse microscopy of oxidative stress demonstrates metabolic sensitivity of retinal pericytes under high glucose condition

Resilience to diabetic retinopathy

Chronic elevation of blood glucose at first causes relatively minor changes to the neural and vascular components of the retina. As the duration of hyperglycemia persists, the nature and extent of damage increases and becomes readily detectable. While this second, overt manifestation of diabetic retinopathy (DR) has been studied extensively, what prevents maximal damage from the very start of hyperglycemia remains largely unexplored. Recent studies indicate that diabetes (DM) engages mitochondria-based defense during the retinopathy-resistant phase, and thereby enables the retina to remain healthy in the face of hyperglycemia. Such resilience is transient, and its deterioration results in progressive accumulation of retinal damage. The concepts that co-emerge with these discoveries set the stage for novel intellectual and therapeutic opportunities within the DR field. Identification of biomarkers and mediators of protection from DM-mediated damage will enable development of resilience-based therapies that will indefinitely delay the onset of DR.

Role of autophagy in angiogenic potential of vascular pericytes

The vasculature system is composed of a multiplicity of juxtaposed cells to generate a functional biological barrier between the blood and tissues. On the luminal surface of blood vessels, endothelial cells (ECs) are in close contact with circulating cells while supporting basal lamina and pericytes wrap the abluminal surface. Thus, the reciprocal interaction of pericytes with ECs is a vital element in the physiological activity of the vascular system. Several reports have indicated that the occurrence of pericyte dysfunction under ischemic and degenerative conditions results in varied micro and macro-vascular complications. Emerging evidence points to the fact that autophagy, a conserved self-digestive cell machinery, can regulate the activity of several cells like pericytes in response to various stresses and pathological conditions. Here, we aim to highlight the role of autophagic response in pericyte activity and angiogenesis potential following different pathological conditions.

Demonstrating drug treatment efficacies by monitoring superoxide dynamics in human lung cancer cells with time-lapse fluorescence microscopy

Metformin hydrochloride, an antihyperglycemic agent, and sulindac, a nonsteroidal anti-inflammatory drug, are FDA-approved drugs known to exert anticancer effects. Previous studies demonstrated sulindac and metformin's anticancer properties through mitochondrial dysfunction and inhibition of mitochondrial electron transport chain complex I and key signaling pathways. In this study, various drugs were administered to A549 lung cancer cells, and results revealed that a combination of sulindac and metformin enhanced cell death compared to the administration of the drugs separately. To measure superoxide production over time, we employed a time-lapse fluorescence imaging technique using mitochondrial-targeted hydroethidine. Fluorescence microscopy data showed the most significant increases in superoxide production in the combination treatment of metformin and sulindac. Results showed significant differences between the combined drug treatment and control groups and between the positive control and control groups. This approach can be utilized to quantify the anticancer efficacy of drugs, creating possibilities for additional therapeutic options.

Optical Imaging Demonstrates Tissue-Specific Metabolic Perturbations in Mblac1 Knockout Mice

OBJECTIVE

Metabolic changes have been extensively documented in neurodegenerative brain disorders, including Parkinson's disease and Alzheimer's disease (AD). Mutations in the C. elegans swip-10 gene result in dopamine (DA) dependent motor dysfunction accompanied by DA neuron degeneration. Recently, the putative human ortholog of swip-10 (MBLAC1) was implicated as a risk factor in AD, a disorder that, like PD, has been associated with mitochondrial dysfunction. Interestingly, the AD risk associated with MBLAC1 arises in subjects with cardiovascular morbidity, suggesting a broader functional insult arising from reduced MBLAC1 protein expression and one possibly linked to metabolic alterations.

METHODS

Our current studies, utilizing Mblac1 knockout (KO) mice, seek to determine whether mitochondrial respiration is affected in the peripheral tissues of these mice. We quantified the levels of mitochondrial coenzymes, NADH, FAD, and their redox ratio (NADH/FAD, RR) in livers and kidneys of wild-type (WT) mice and their homozygous KO littermates of males and females, using 3D optical cryo-imaging.

RESULTS

Compared to WT, the RR of livers from KO mice was significantly reduced, without an apparent sex effect, driven predominantly by significantly lower NADH levels. In contrast, no genotype and sex differences were observed in kidney samples. Serum analyses of WT and KO mice revealed significantly elevated glucose levels in young and aged KO adults and diminished cholesterol levels in the aged KOs, consistent with liver dysfunction.

DISCUSSION/CONCLUSION

As seen with C. elegans swip-10 mutants, loss of MBLAC1 protein results in metabolic changes that are not restricted to neural cells and are consistent with the presence of peripheral comorbidities accompanying neurodegenerative disease in cases where MBLAC1 expression changes impact risk.

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.

The role of the mTOR pathway in diabetic retinopathy

The retina, the part of the eye, translates the light signal into an electric current that can be sent to the brain as visual information. To achieve this, the retina requires fine-tuned vascularization for its energy supply. Diabetic retinopathy (DR) causes alterations in the eye vascularization that reduce the oxygen supply with consequent retinal neurodegeneration. During DR, the mammalian target of rapamycin (mTOR) pathway seems to coordinate retinal neurodegeneration with multiple anabolic and catabolic processes, such as autophagy, oxidative stress, cell death, and the release of pro-inflammatory cytokines, which are closely related to chronic hyperglycemia. This review outlines the normal anatomy of the retina and how hyperglycemia can be involved in the neurodegeneration underlying this disease through over activation or inhibition of the mTOR pathway.

Role of glycolysis in retinal vascular endothelium, glia, pigment epithelium, and photoreceptor cells and as therapeutic targets for related retinal diseases

Glycolysis produces large amounts of adenosine triphosphate (ATP) in a short time. The retinal vascular endothelium feeds itself primarily through aerobic glycolysis with less ATP. But when it generates new vessels, aerobic glycolysis provides rapid and abundant ATP support for angiogenesis, and thus inhibition of glycolysis in endothelial cells can be a target for the treatment of neovascularization. Aerobic glycolysis has a protective effect on Müller cells, and it can provide with a target for visual protection and maintenance of the blood-retinal barrier. Under physiological conditions, the mitochondria of RPE can use lactic acid produced by photoreceptor cells as an energy source to provide ATP for survival. In pathological conditions, because RPE cells avoid their oxidative damage by increasing glycolysis, a large number of glycolysis products accumulate, which in turn has a toxic effect on photoreceptor cells. This shows that stabilizing the function of RPE mitochondria may become a target for the treatment of diseases such as retinal degeneration. The decrease of aerobic glycolysis leads to the decline of photoreceptor cell function and impaired vision; therefore, aerobic glycolysis of stable photoreceptor cells provides a reliable target for delaying vision loss. It is of great significance to study the role of glycolysis in various retinal cells for the targeted treatment of ocular fundus diseases.

Metabolic and Redox Regulation of Cardiovascular Stem Cell Biology and Pathology

Significance: Cardiovascular stem cells are important for regeneration and repair of damaged tissue. Recent Advances: Pluripotent stem cells have a unique metabolism, which is adopted for their energetic and biosynthetic demand as rapidly proliferating cells. Stem cell differentiation requires an exceptional metabolic flexibility allowing for metabolic remodeling between glycolysis and oxidative phosphorylation. Critical Issues: Respiration is associated with the generation of reactive oxygen species (ROS) by the mitochondrial respiratory chain. But also the membrane-bound protein nicotinamide adenine dinucleotide phosphate oxidase (NADPH oxidase, NOX) contributes to ROS levels. ROS not only play a significant role in stem cell differentiation and tissue renewal but also cause senescence and contribute to tissue aging. Future Directions: For utilization of stem cells in therapeutic approaches, a deep understanding of the molecular mechanisms how metabolism and the cellular redox state regulate stem cell differentiation is required. Modulating the redox state of stem cells using antioxidative agents may be suitable to enhance activity of endothelial progenitor cells. Antioxid. Redox Signal. 35, 163-181.

3D Optical Cryo-Imaging Method: A Novel Approach to Quantify Renal Mitochondrial Bioenergetics Dysfunction

Mitochondrial dysfunction contributes to various injuries and diseases. A mechanistic understanding of how dysfunctional mitochondria modulates metabolism is of paramount importance. Three-dimensional (3D) optical cryo-imager is a custom-designed device that can quantify the volumetric bioenergetics of organs in small animal models. The instrument captures the autofluorescence of bioenergetics indices (NADH and FAD) from tissues at cryogenic temperature. The quantified redox ratio (NADH/FAD) is used as an optical indicator of mitochondrial redox state.

Increased Ephrin-B2 expression in pericytes contributes to retinal vascular death in rodents

AIMS

Diabetes-induced retinal vascular cell death aggravates diabetic retinopathy (DR) to the proliferative stage and blindness. Pericytes play a crucial role in retinal capillaries survival, stability, and angiogenesis. Ephrin-B2 is a tyrosine kinase that regulates pericytes/endothelial cells communication during angiogenesis; yet, its role in DR is still unclear. We hypothesize that diabetes increases Ephrin-B2 signaling in pericytes, which contributes to inflammation and retinal vascular cell death.

METHODS

Selective inhibition of the Ephrin-B2 expression in the retinal pericytes was achieved using an intraocular injection of adeno-associated virus (AAV) with a specific pericyte promotor. Vascular death was determined by retinal trypsin digest. Pathological angiogenesis was assessed using the oxygen-induced retinopathy model in pericyte-Ephrin-B2 knockout mice, wild type, and wild type injected with AAV. Angiogenic properties, inflammatory, and apoptotic markers were measured in human retinal pericytes (HRP) grown under diabetic conditions.

KEY FINDING

Diabetes significantly increased the expression of Ephrin-B2, inflammatory, and apoptotic markers in the diabetic retinas and HRP. These effects were prevented by silencing Ephrin-B2 in HRP. Moreover, Ephrin-B2 silencing in retinal pericytes decreased pathological angiogenesis and acellular capillaries formation in diabetic retinas.

SIGNIFICANCE

Increased Ephrin-B2 expression in the pericytes contributed to diabetes-induced retinal inflammation and vascular death. These results identify pericytes-Ephrin-B2 as a therapeutic target for DR.

Fluorescence Imaging of Mitochondrial Redox State to Assess Diabetic Wounds

Background: Diabetes is known to cause delayed wound healing, and chronic non-healing lower extremity ulcers may end with lower limb amputations and mortalities. Given the increasing prevalence of diabetes mellitus worldwide, it is critical to focus on underlying mechanisms of these debilitating wounds to find novel therapeutic strategies and thereby improve patient outcome. Methods: This study aims to design a label-free optical fluorescence imager that captures metabolic indices (NADH and FAD autofluorescence) and monitors the in vivo wound healing progress noninvasively. Furthermore, 3D optical cryo-imaging of the mitochondrial redox state was utilized to assess the volumetric redox state of the wound tissue. Results: The results from our in vivo fluorescence imager and the 3D cryo-imager quantify the differences between the redox state of wounds on diabetic mice in comparison with the control mice. These metabolic changes are associated with mitochondrial dysfunction and higher oxidative stress in diabetic wounds. A significant correlation was observed between the redox state and the area of the wounds. Conclusion: The results suggest that our developed novel optical imaging system can successfully be used as an optical indicator of the complex wound healing process noninvasively.

DJ-1/PARK7 inhibits high glucose-induced oxidative stress to prevent retinal pericyte apoptosis via the PI3K/AKT/mTOR signaling pathway

Reactive oxygen species (ROS) act through multiple pathways to induce apoptosis of retinal capillary pericytes, which is an early marker and the primary cause of the progression of diabetic retinopathy. However, the specific molecular mechanisms behind ROS-induced retinal capillary pericyte loss in diabetic retinopathy remains elusive. In this study, we investigated the molecular regulation and effects of DJ-1/PARK7 on oxidative stress and injury of rat retinal pericytes (RRPs). To perform the research, RRPs were isolated from rat retina and cultured in medium with for 2 days: control group (5.6 mM glucose), high glucose group (30 mM glucose), hypertonic group (5.6 mM glucose + 24.4 mM mannitol). We found decreased expression of DJ-1 and increased apoptosis of RRPs in high glucose group. To further study the role of DJ-1, four groups were divided as follows: normal control group (5.6 mM glucose), high glucose (30 mM glucose), empty vector control group (pcDNA3.1,30 mM glucose), DJ-1 overexpression group (pcDNA3.1-myc-DJ-1,30 mM glucose). DJ-1, P53, p-P53, cleaved caspase-3, manganese superoxide dismutase (MnSOD), catalase (CAT) and PI3K/Akt/mTOR signaling pathway in each group was detected by Western Blot. RRPs apoptosis was detected by Terminal-deoxynucleoitidyl Transferase mediated Nick End Labeling (TUNEL) and 4'6- diamidino-2-phenylindole (DAPI). Mitochondrial function was detected by jc-1 and fluorescent probes DCFH-DA was used to determine reactive oxygen species (ROS). We found that high glucose (30 mM) lasting two days can induce significant apoptosis of RRPs, increase ROS production and expressions of p-p53 and active caspase-3, impair mitochondrial function, decrease the activities of MnSOD and CAT, and decrease expression of DJ-1, p-AKT and p-mTOR. In contrast, DJ-1/PARK7 overexpression significantly increases expression of DJ-1, p-AKT and p-mTOR, increases expression and activities of MnSOD and CAT, improves mitochondrial function, decreases expression of apoptotic gene protein p-p53 and active caspase-3, reduces ROS production and reduces the apoptotic rate of RRPs induced by high glucose. These results suggest that DJ-1 may play a role in protecting RRPs from high glucose induced-oxidative injury. DJ-1 might improve mitochondrial function, inhibit ROS production and enhance antioxidant capacity to reduce apoptosis of retinal pericytes through the PI3K/AKT/mTOR signaling pathway which may be related to early pathogenesis of diabetic retinopathy.

Blocking CXCR3 with AMG487 ameliorates the blood-retinal barrier disruption in diabetic mice through anti-oxidative

Oxidative stress and blood-retinal barrier (BRB) damage induced by hyperglycemia are the principal processes involved in the early stages of diabetic retinopathy (DR). CXC chemokine receptor 3 (CXCR3)-mediated inflammatory infiltration exists in many disease models. The main objective of the present study was to determine whether AMG487, a CXCR3 antagonist, can ameliorate BRB disruption and reactive oxygen species generation in the DR model. The retinal endothelial cell and ganglion cell ultrastructures were observed using a transmission electron microscope. The pericyte marker PDGFR-β, tight junction occludin, and leaking albumin were evaluated. The oxidative stress level, CCAAT-enhancer-binding protein homologous protein (CHOP), and p-p38 expression were also investigated in vivo and in vitro. The results indicated that AMG487 application might alleviate PDGFR-β and occludin loss, and decreased the residual content of retinal albumin in the streptozocin-induced DR mouse model via the inhibition of oxidative and endoplasmic reticulum stress, in which p38 activation was also involved. Thus, CXCR3 inhibition might be a target to prevent the early stage of DR injury.