The PI3K-PTEN tug-of-war, oxidative stress and retinal degeneration

The involvement of ROS-regulated programmed cell death in hepatocellular carcinoma

Reactive oxidative species (ROS) is a crucial factor in the regulation of cellular biological activity and function, and aberrant levels of ROS can contribute to the development of a variety of diseases, particularly cancer. Numerous discoveries have affirmed that this process is strongly associated with "programmed cell death (PCD)," which refers to the suicide protection mechanism initiated by cells in response to external stimuli, such as apoptosis, autophagy, ferroptosis, etc. Research has demonstrated that ROS-induced PCD is crucial for the development of hepatocellular carcinoma (HCC). These activities serve a dual function in both facilitating and inhibiting cancer, suggesting the existence of a delicate balance within healthy cells that can be disrupted by the abnormal generation of reactive oxygen species (ROS), thereby influencing the eventual advancement or regression of a tumor. In this review, we summarize how ROS regulates PCD to influence the tumorigenesis and progression of HCC. Studying how ROS-induced PCD affects the progression of HCC at a molecular level can help develop better prevention and treatment methods and facilitate the design of more effective preventative and therapeutic strategies.

Cell-free circulating mitochondrial DNA: An emerging biomarker for airborne particulate matter associated with cardiovascular diseases

The association of airborne particulate matter exposure with the deteriorating function of the cardiovascular system is fundamentally driven by the impairment of mitochondrial-nuclear crosstalk orchestrated by aberrant redox signaling. The loss of delicate balance in retrograde communication from mitochondria to the nucleus often culminates in the methylation of the newly synthesized strand of mitochondrial DNA (mtDNA) through DNA methyl transferases. In highly metabolic active tissues such as the heart, mtDNA's methylation state alteration impacts mitochondrial bioenergetics. It affects transcriptional regulatory processes involved in biogenesis, fission, and fusion, often accompanied by the integrated stress response. Previous studies have demonstrated a paradoxical role of mtDNA methylation in cardiovascular pathologies linked to air pollution. A pronounced alteration in mtDNA methylation contributes to systemic inflammation, an etiological determinant for several co-morbidities, including vascular endothelial dysfunction and myocardial injury. In the current article, we evaluate the state of evidence and examine the considerable promise of using cell-free circulating methylated mtDNA as a predictive biomarker to reduce the more significant burden of ambient air pollution on cardiovascular diseases.

The effects of crocetin on oxidative stress induced ARPE-19 cells by H2O2

The anti-apoptotic and antioxidant effects of crocetin was aimed to investigate on the oxidative damage model of ARPE-19 cells. The oxidative damage in ARPE cells was developed by H₂O₂ treatment at 800 μM. Different doses of crocetin (1-80 μM) were applied for 24 h, and the effects on viability were evaluated to find out the optimum drug dose. At first, three effective doses of crocetin (10, 20, 40 μM) on cell viability were selected for further analyses. The levels of superoxide dismutase (SOD), malondialdehyde (MDA) and glutathione (GSH) were determined, and the expression of pro-apoptotic Bax gene and anti-apoptotic Bcl-2 gene were evaluated. The most effective crocetin dose on cell viability was found to be 10 μM. After the H₂O₂ treatment, SOD and GSH were decreased and MDA were increased significantly (p = 0.011, 0.037, 0.018, respectively). Following the crocetin treatment at 10 μM, SOD and GSH activities were improved compared to the no drug group; and MDA level was declined remarkably (p = 0.022, 0.019, 0.029, respectively). The Bcl-2 level was significantly decreased (p < 0.01), while the Bax1 and Nrf2 expression and ROS level was increased significantly in the damage model group (p < 0.01). After the drug treatment, the Bax1 and Nrf2 expression level were decreased in all groups (p < 0.01). The increase in Bcl-2 expression was significant in crocetin 40 μM (p < 0.05) and the decrease in ROS level were significant in 20 μM and 40 μM doses of crocetin (p < 0.05). It has been shown that crocetin might be used as an antioxidant and anti-apoptotic agent on the hindering the effect of the oxidative damage. Following the development of the oxidative stress in the cells, crocetin reversed the damage signals. By the in vitro tests, it was shown that crocetin might be considered as an effective molecule to be used in the AMD treatment.

The transcriptome profile of RPE cells by the fullerenol against hydrogen peroxide stress

Age-related macular degeneration (AMD) causes central vision impairment with increased incidence. In the pathogenesis of AMD, reactive oxygen species (ROS) are associated with RPE cell apoptosis. H₂O₂ is an oxidative toxicant and is used to establish the AMD in vitro model. However, the mechanisms of ROS in H₂O₂-induced AMD are still unclear. Fullerenol, a promising antioxidant of nanomaterials, protects RPE cells from ROS attack. In addition to working as a scavenger, little is known about the antioxidant mechanism of fullerenol in RPE cells. In this study, transcriptome sequencing was performed to examine the global changes in mRNA transcripts induced by H₂O₂ in human ARPE-19 cells. Moreover, we comprehensively investigated the protective effects of fullerenol against H₂O₂-induced oxidative injury by RNA sequencing. Gene Ontology enrichment analysis showed that those pathways related to the release of positive regulation of DNA-templated transcription and negative regulation of apoptotic process were affected. Finally, we found that 12 hub genes were related to the oxidative-protection function of fullerenol. In summary, H₂O₂ affected these hub genes and signaling pathways to regulate the senescence of RPE cells. Moreover, fullerenol is a potent nanomaterial that protects the RPE and would be a promising approach for AMD prevention.

Interplay between Mitochondrial Metabolism and Cellular Redox State Dictates Cancer Cell Survival

Mitochondria are the main powerhouse of the cell, generating ATP through the tricarboxylic acid cycle (TCA) and oxidative phosphorylation (OXPHOS), which drives myriad cellular processes. In addition to their role in maintaining bioenergetic homeostasis, changes in mitochondrial metabolism, permeability, and morphology are critical in cell fate decisions and determination. Notably, mitochondrial respiration coupled with the passage of electrons through the electron transport chain (ETC) set up a potential source of reactive oxygen species (ROS). While low to moderate increase in intracellular ROS serves as secondary messenger, an overwhelming increase as a result of either increased production and/or deficient antioxidant defenses is detrimental to biomolecules, cells, and tissues. Since ROS and mitochondria both regulate cell fate, attention has been drawn to their involvement in the various processes of carcinogenesis. To that end, the link between a prooxidant milieu and cell survival and proliferation as well as a switch to mitochondrial OXPHOS associated with recalcitrant cancers provide testimony for the remarkable metabolic plasticity as an important hallmark of cancers. In this review, the regulation of cell redox status by mitochondrial metabolism and its implications for cancer cell fate will be discussed followed by the significance of mitochondria-targeted therapies for cancer.

Cobalt-induced oxidative stress contributes to alveolar/bronchiolar carcinogenesis in B6C3F1/N mice

Rodent alveolar/bronchiolar carcinomas (ABC) that arise either spontaneously or due to chemical exposure are similar to a subtype of lung adenocarcinomas in humans. B6C3F1/N mice and F344/NTac rats exposed to cobalt metal dust (CMD) by inhalation developed ABCs in a dose dependent manner. In CMD-exposed mice, the incidence of Kras mutations in ABCs was 67% with 80% of those being G to T transversions on codon 12 suggesting a role of oxidative stress in the pathogenesis. In vitro studies, such as DMPO (5,5-dimethyl-1-pyrroline N-oxide) immune-spin trapping assay, and dihydroethidium (DHE) fluorescence assay on A549 and BEAS-2B cells demonstrated increased oxidative stress due to cobalt exposure. In addition, significantly increased 8-oxo-dG adducts were demonstrated by immunohistochemistry in lungs from mice exposed to CMD for 90 days. Furthermore, transcriptomic analysis on ABCs arising spontaneously or due to chronic CMD-exposure demonstrated significant alterations in canonical pathways related to MAPK signaling (IL-8, ErbB, Integrin, and PAK pathway) and oxidative stress (PI3K/AKT and Melatonin pathway) in ABCs from CMD-exposed mice. Oxidative stress can stimulate PI3K/AKT and MAPK signaling pathways. Nox4 was significantly upregulated only in CMD-exposed ABCs and NOX4 activation of PI3K/AKT can lead to increased ROS levels in human cancer cells. The gene encoding Ereg was markedly up-regulated in CMD-exposed mice. Oncogenic KRAS mutations have been shown to induce EREG overexpression. Collectively, all these data suggest that oxidative stress plays a significant role in CMD-induced pulmonary carcinogenesis in rodents and these findings may also be relevant in the context of human lung cancers.

Retinoid Metabolism in the Degeneration of Pten-Deficient Mouse Retinal Pigment Epithelium

In vertebrate eyes, the retinal pigment epithelium (RPE) provides structural and functional homeostasis to the retina. The RPE takes up retinol (ROL) to be dehydrogenated and isomerized to 11-cis-retinaldehyde (11-cis-RAL), which is a functional photopigment in mammalian photoreceptors. As excessive ROL is toxic, the RPE must also establish mechanisms to protect against ROL toxicity. Here, we found that the levels of retinol dehydrogenases (RDHs) are commonly decreased in phosphatase tensin homolog (Pten)-deficient mouse RPE, which degenerates due to elevated ROL and that can be rescued by feeding a ROL-free diet. We also identified that RDH gene expression is regulated by forkhead box O (FOXO) transcription factors, which are inactivated by hyperactive Akt in the Pten-deficient mouse RPE. Together, our findings suggest that a homeostatic pathway comprising PTEN, FOXO, and RDH can protect the RPE from ROL toxicity.

Functional 3-Dimensional Retinal Organoids: Technological Progress and Existing Challenges

Stem cell scientists have developed methods for the self-formation of artificial organs, often referred to as organoids. Organoids can be used as model systems for research in multiple biological disciplines. Yoshiki Sasai’s innovation for deriving mammalian retinal tissue from in vitro stem cells has had a large impact on the study of the biology of vision. New developments in retinal organoid technology provide avenues for in vitro models of human retinal diseases, studies of pathological mechanisms, and development of therapies for retinal degeneration, including electronic retinal implants and gene therapy. Moreover, these innovations have played key roles in establishing models for large-scale drug screening, studying the stages of retinal development, and providing a human model for personalized therapeutic approaches, like cell transplants to replace degenerated retinal cells. Here, we first discuss the importance of human retinal organoids to the biomedical sciences. Then, we review various functional features of retinal organoids that have been developed. Finally, we highlight the current limitations of retinal organoid technologies.

Tsg101 Is Necessary for the Establishment and Maintenance of Mouse Retinal Pigment Epithelial Cell Polarity

The retinal pigment epithelium (RPE) forms a monolayer sheet separating the retina and choroid in vertebrate eyes. The polarized nature of RPE is maintained by distributing membrane proteins differentially along apico-basal axis. We found the distributions of these proteins differ in embryonic, post-natal, and mature mouse RPE, suggesting developmental regulation of protein trafficking. Thus, we deleted tumor susceptibility gene 101 (Tsg101), a key component of endosomal sorting complexes required for transport (ESCRT), in embryonic and mature RPE to determine whether ESCRT-mediated endocytic protein trafficking correlated with the establishment and maintenance of RPE polarity. Loss of Tsg101 severely disturbed the polarity of RPE, which forms irregular aggregates exhibiting non-polarized distribution of cell adhesion proteins and activation of epidermal growth factor receptor signaling. These findings suggest that ESCRT-mediated protein trafficking is essential for the development and maintenance of RPE cell polarity.

Cellular senescence: Silent operator and therapeutic target in cancer

The process of carcinogenesis and its progression involves an intricate interplay between a number of signaling networks, metabolic pathways and the microenvironment. These include an alteration in the cellular redox metabolism and deregulation of cell cycle checkpoints. Similar to the dichotomy of redox signaling in cancer cell fate and state determination, a diverging effect of an irreversible cell cycle arrest or senescence on carcinogenesis has been demonstrated. In this regard, while overwhelming oxidative stress has a damaging effect on tissue architecture and organ function and promotes death execution, a mild "pro-oxidant" environment is conducive for cell proliferation, growth and survival. Similarly, cellular senescence has been shown to elicit both a tumor suppressor and an oncogenic effect in a context-dependent manner. Notably, there appears to be a crosstalk between these two critical regulators of cell fate and state, particularly from the standpoint of the divergent effects on processes that promote or abate carcinogenesis. This review aims to provide an overview of these overarching themes and attempts to highlight critical intersection nodes, which are emerging as potential diagnostic and/or therapeutic targets for novel anticancer strategies.

Astilbin protects chicken peripheral blood lymphocytes from cadmium-induced necroptosis via oxidative stress and the PI3K/Akt pathway

Astilbin (ASB), a dihydroflavonol glycoside, is widely found in a variety of plants and in functional foods and acts as a powerful antioxidant. The aim of this study was to investigate the underlying mechanisms involved in the antagonistic effects of ASB on cadmium (Cd)-induced necroptosis in chicken peripheral blood lymphocytes. Peripheral blood lymphocytes were aseptically collected from Roman white hens and then randomly divided into five groups: the control group was incubated without additional reagents, while the other groups were incubated with Cd, ASB, a combination of Cd and ASB, and 0.1% DMSO. After a 24 h treatment, cell samples were collected. The results showed that some morphological changes consistent with necroptosis were observed in the Cd-treated groups, suggesting the occurrence of necroptosis. Simultaneously, antioxidant activity markers (CAT, SOD, GSH, GSH-px, and T-AOC) decreased and indicators of oxidative stress (MDA, iNOS, NO, H₂O₂, ·OH and ROS) increased. The production of ROS induced the activation of the PI3K/Akt signaling pathway, as the expression levels of PI3K, Akt and PDK1 were significantly elevated. Additionally, the expression levels of RIPK3, RIPK1, MLKL, TAK1, TAB2 and TAB3 were increased and that of Caspase-8 was decreased, which could cause the necroptosis. However, the most important our results was that ASB supplements remarkably attenuated the Cd-induced effects. We conclude that the Cd treatment promoted an imbalance of the antioxidant status and activated the PI3K/Akt pathway, leading to necroptosis in chicken peripheral blood lymphocytes, and that ASB was able to partially ameliorate the effect of Cd-induced necroptosis.

Circular Noncoding RNA NR3C1 Acts as a miR-382-5p Sponge to Protect RPE Functions via Regulating PTEN/AKT/mTOR Signaling Pathway

Age-related macular degeneration (AMD) is a universal leading cause for irreversible blindness in the elderly population. Dedifferentiation of retinal pigment epithelium (RPE) cells initiates early pathological events in atrophic AMD. Herein, we aim to investigate effects of a circular RNA derived from the NR3C1 gene (circNR3C1) on regulating RPE function and AMD pathogenesis. circNR3C1 expression was consistently upregulated along with RPE differentiation and was downregulated in dysfunctional RPE and blood serum of AMD patients. Silencing of circNR3C1 reduced RPE characteristic transcripts and proteins, interrupted phagocytosis, accelerated intracellular reactive oxygen species (ROS) generation, and promoted RPE proliferation in vitro. circN3C1 silencing also decreased expressions of RPE characteristic markers and disturbed the ultrastructure of RPE in vivo, as shown by a thickened RPE with twisted basal infoldings and outer segments. Mechanistically, circNR3C1 acted as an endogenous microRNA-382-5p (miR-382-5p) sponge to sequester its activity, which increased phosphatase and tensin homolog on chromosome 10 (PTEN) expression and inhibited the protein kinase B/mammalian target of rapamycin (AKT/mTOR) pathway. miR-382-5p overexpression and PTEN silencing mimicked effects of circNR3C1 silencing on RPE phenotypes in vivo and in vitro. In conclusion, circNR3C1 prevents AMD progression and protects RPE by directly sponging miR-382-5p to block its interaction with PTEN and subsequently blocks the AKT/mTOR pathway. Pharmacological circNR3C1 supplementations are promising therapeutic options for atrophic AMD.

PMN-MDSCs Enhance CTC Metastatic Properties through Reciprocal Interactions via ROS/Notch/Nodal Signaling

Intratumoral infiltration of myeloid-derived suppressor cells (MDSCs) is known to promote neoplastic growth by inhibiting the tumoricidal activity of T cells. However, direct interactions between patient-derived MDSCs and circulating tumors cells (CTCs) within the microenvironment of blood remain unexplored. Dissecting interplays between CTCs and circulatory MDSCs by heterotypic CTC/MDSC clustering is critical as a key mechanism to promote CTC survival and sustain the metastatic process. We characterized CTCs and polymorphonuclear-MDSCs (PMN-MDSCs) isolated in parallel from peripheral blood of metastatic melanoma and breast cancer patients by multi-parametric flow cytometry. Transplantation of both cell populations in the systemic circulation of mice revealed significantly enhanced dissemination and metastasis in mice co-injected with CTCs and PMN-MDSCs compared to mice injected with CTCs or MDSCs alone. Notably, CTC/PMN-MDSC clusters were detected in vitro and in vivo either in patients’ blood or by longitudinal monitoring of blood from animals. This was coupled with in vitro co-culturing of cell populations, demonstrating that CTCs formed physical clusters with PMN-MDSCs; and induced their pro-tumorigenic differentiation through paracrine Nodal signaling, augmenting the production of reactive oxygen species (ROS) by PMN-MDSCs. These findings were validated by detecting significantly higher Nodal and ROS levels in blood of cancer patients in the presence of naïve, heterotypic CTC/PMN-MDSC clusters. Augmented PMN-MDSC ROS upregulated Notch1 receptor expression in CTCs through the ROS-NRF2-ARE axis, thus priming CTCs to respond to ligand-mediated (Jagged1) Notch activation. Jagged1-expressing PMN-MDSCs contributed to enhanced Notch activation in CTCs by engagement of Notch1 receptor. The reciprocity of CTC/PMN-MDSC bi-directional paracrine interactions and signaling was functionally validated in inhibitor-based analyses, demonstrating that combined Nodal and ROS inhibition abrogated CTC/PMN-MDSC interactions and led to a reduction of CTC survival and proliferation. This study provides seminal evidence showing that PMN-MDSCs, additive to their immuno-suppressive roles, directly interact with CTCs and promote their dissemination and metastatic potency. Targeting CTC/PMN-MDSC heterotypic clusters and associated crosstalks can therefore represent a novel therapeutic avenue for limiting hematogenous spread of metastatic disease.

A glucagon-like peptide-1 analog, liraglutide, ameliorates endothelial dysfunction through miRNAs to inhibit apoptosis in rats

Background and Aims

Many studies have revealed that glucagon-like peptide-1 has vasoprotective effects. In this study, we investigated whether liraglutide suppressed endothelial dysfunction and explored the mechanism involved.

Methods

Experimental diabetes was induced through combined high-fat diet administration and intraperitoneal streptozotocin injections. Rats were randomly divided into the following four groups: control, diabetes, diabetes + a low liraglutide dose (0.2 mg/kg/d), and diabetes + a high liraglutide dose (0.4 mg/kg/d). Endothelial function and metabolic parameters were measured after 8 weeks of treatment. miRNA arrays were analyzed to identify the differentially expressed miRNAs.

Results

We found that liraglutide significantly improved aortic endothelial function in diabetic rats. Liraglutide inhibited miR-93-5p, miR-181a-5p and miR-34a-5p expression, and activated miR-26a-5p expression. miRNA mimic transfection experiments indicated negative relationships between miR-93-5p, miR-181a-5p, miR-34a-5p, and miR-26a-5p and Sirt1, Creb, Bcl-2, and Pten expression, respectively. Moreover, liraglutide increased Sirt1, Creb, and Bcl-2 expression levels and reduced Pten expression level.

Conclusion

Our results demonstrate the role of key miRNAs in the liraglutide-mediated regulation of endothelial cell function in diabetic rats.

A novel antioxidant Mito-Tempol inhibits ox-LDL-induced foam cell formation through restoration of autophagy flux

A bulk of cholesteryl esters accumulation in macrophage foam cells drives the occurrence and development of atherosclerosis. Evidence now shows that autophagy plays key roles in the degradation of intracellular lipid droplets via autolysosome, and also in the release of intracellular lipids via cholesterol efflux. In this study, we identified that a mitochondria-targeted antioxidant, Mito-Tempol, has protective effects against cholesteryl esters accumulation by activating autophagy. Mito-Tempol was shown to ameliorate the lipid burden for atherosclerosis, both in vitro and in vivo. In the established in vitro foam cell formation system using oxidized low-density lipoprotein (ox-LDL)-loaded THP-1 macrophages, Mito-Tempol prevented intracellular oxidative stress and attenuated lipid accumulation. Mito-Tempol rescued ox-LDL-impaired autophagic flux, thereby facilitating autophagy-mediated lipid degradation in THP-1 macrophages. Meanwhile, Mito-Tempol also increased the efflux of cholesterol via autophagy-dependent ABCA1 and ABCG1 up-regulation. The classical autophagy pathway of mTOR may be one of the effector for the autophagy restoration of Mito-Tempol. Our findings give the first insight that cardiovascular system disease may benefits more from the treatment of Mito-Tempol for its impact of reversing atherosclerosis via autophagy.

Mitochondrial ROS-derived PTEN oxidation activates PI3K pathway for mTOR-induced myogenic autophagy

Muscle differentiation is a crucial process controlling muscle development and homeostasis. Mitochondrial reactive oxygen species (mtROS) rapidly increase and function as critical cell signaling intermediates during the muscle differentiation. However, it has not yet been elucidated how they control myogenic signaling. Autophagy, a lysosome-mediated degradation pathway, is importantly recognized as intracellular remodeling mechanism of cellular organelles during muscle differentiation. Here, we demonstrated that the mtROS stimulated phosphatidylinositol 3 kinase/AKT/mammalian target of rapamycin (mTOR) cascade, and the activated mTORC1 subsequently induced autophagic signaling via phosphorylation of uncoordinated-51-like kinase 1 (ULK1) at serine 317 and upregulation of Atg proteins to prompt muscle differentiation. Treatment with MitoQ or rapamycin impaired both phosphorylation of ULK1 and expression of Atg proteins. Therefore, we propose a novel regulatory paradigm in which mtROS are required to initiate autophagic reconstruction of cellular organization through mTOR activation in muscle differentiation.

Phosphoinositide 3-Kinase/Akt Signaling and Redox Metabolism in Cancer

Metabolic rewiring and the consequent production of reactive oxygen species (ROS) are necessary to promote tumorigenesis. At the nexus of these cellular processes is the aberrant regulation of oncogenic signaling cascades such as the phosphoinositide 3-kinase and AKT (PI3K/Akt) pathway, which is one of the most frequently dysregulated pathways in cancer. In this review, we examine the regulation of ROS metabolism in the context of PI3K-driven tumors with particular emphasis on four main areas of research. (1) Stimulation of ROS production through direct modulation of mitochondrial bioenergetics, activation of NADPH oxidases (NOXs), and metabolic byproducts associated with hyperactive PI3K/Akt signaling. (2) The induction of pro-tumorigenic signaling cascades by ROS as a consequence of phosphatase and tensin homolog and receptor tyrosine phosphatase redox-dependent inactivation. (3) The mechanisms through which PI3K/Akt activation confers a selective advantage to cancer cells by maintaining redox homeostasis. (4) Opportunities for therapeutically exploiting redox metabolism in PIK3CA mutant tumors and the potential for implementing novel combinatorial therapies to suppress tumor growth and overcome drug resistance. Further research focusing on the multi-faceted interactions between PI3K/Akt signaling and ROS metabolism will undoubtedly contribute to novel insights into the extensive pro-oncogenic effects of this pathway, and the identification of exploitable vulnerabilities for the treatment of hyperactive PI3K/Akt tumors.

A2E-associated cell death and inflammation in retinal pigmented epithelial cells from human induced pluripotent stem cells

Accumulation of lipofuscin in the retinal pigmented epithelium (RPE) is observed in retinal degenerative diseases including Stargardt disease and age-related macular degeneration. Bis-retinoid N-retinyl-N-retinylidene ethanolamine (A2E) is a major component of lipofuscin. A2E has been implicated in RPE atrophy and retinal inflammation; however, mice with A2E accumulation display only a mild retinal phenotype. In the current study, human iPSC-RPE (hiPSC-RPE) cells were generated from healthy individuals to examine effects of A2E in human RPE cells. hiPSC-RPE cells displayed RPE-specific features, which include expression of RPE-specific genes, tight junction formation and ability to carry out phagocytosis. hiPSC-RPE cells demonstrated cell death and increased VEGF-A production in a time-dependent manner when they were cocultured with 10 μM of A2E. PCR array analyses revealed upregulation of 26 and 12 pro-inflammatory cytokines upon A2E and H₂O₂ exposure respectively, indicating that A2E and H₂O₂ can cause inflammation in human retinas. Notably, identified gene profiles were different between A2E- and H₂O₂-treated hiPSC-RPE cells. A2E caused inflammatory changes observed in retinal degenerative diseases more closely as compared to H₂O₂. Collectively, these data obtained with hiPSC-RPE cells provide evidence that A2E plays an important role in pathogenesis of retinal degenerative diseases in humans.

Protective effect of lutein on ARPE-19 cells upon H2O2-induced G2/M arrest

Oxidative damage is a key factor for the pathogenesis of age‑related macular degeneration (AMD), therefore, anti-oxidative stress is a valuable method for the prevention or treatment of AMD. The aim of the present study was to reveal the protective mechanism of lutein on retinal pigment epithelium (RPE) cells subjected to oxidative stress. Acute retinal pigment epithelial 19 (ARPE‑19) cells were exposed to oxidative stress induced by H2O2 following lutein pretreatment. The activities of caspases, level of intracellular reactive oxygen species (ROS) and cell cycle were analyzed using flow cytometry. The expression levels of cell cycle regulatory proteins and inflammation‑associated genes were detected using western blot and reverse transcription‑polymerase chain reaction analyses, respectively. The data showed that oxidative stress reduced cell viability, and increased total apoptosis and ROS generation, however, lutein prevented cells from oxidative stress‑induced damage. In addition, oxidative damage triggered G2/M phase arrest of the ARPE‑19 cells, which was reversed by lutein in a concentration‑dependent manner, through the activation of cyclin‑dependent kinase 1 and cell division cycle 25C, and degradation of cyclin B1. These results demonstrated that lutein may be an effective antioxidant, which can be applied in the prevention of AMD, or other age-related diseases associated with oxidative damage.

NADPH Oxidase Contributes to Photoreceptor Degeneration in Constitutively Active RAC1 Mice

Purpose

The active form of small GTPase RAC1 is required for activation of NADPH oxidase (NOX), which in turn generates reactive oxygen species (ROS) in nonphagocytic cells. We explored whether NOX-induced oxidative stress contributes to rod degeneration in retinas expressing constitutively active (CA) RAC1.

Methods

Transgenic (Tg)–CA-RAC1 mice were given apocynin (10 mg/kg, intraperitoneal), a NOX inhibitor, or vehicle daily for up to 13 weeks. Superoxide production and oxidative damage were assessed by dihydroethidium staining and by protein carbonyls and malondialdehyde levels, respectively. Outer nuclear layer (ONL) cells were counted and electroretinogram (ERG) amplitudes measured in Tg-CA-RAC1 mice. Outer nuclear layer cells were counted in wild-type (WT) mice after transfer of CA-Rac1 gene by subretinal injection of AAV8-pOpsin-CA Rac1-GFP.

Results

Transgenic-CA-RAC1 retinas had significantly fewer photoreceptor cells and more apoptotic ONL cells than WT controls from postnatal week (Pw) 3 to Pw13. Superoxide accumulation and protein and lipid oxidation were increased in Tg-CA-RAC1 retinas and were reduced in mice treated with apocynin. Apocynin reduced the loss of photoreceptors and increased the rod ERG a- and b-wave amplitudes when compared with vehicle-injected transgenic controls. Photoreceptor loss was also observed in regions of adult WT retina transduced with AAV8-pOpsin-CA Rac1-GFP but not in neighboring regions that were not transduced or in AAV8-pOpsin-GFP–transduced retinas.

Conclusions

Constitutively active RAC1 promotes photoreceptor cell death by oxidative damage that occurs, at least partially, through NOX-induced ROS. Reactive oxygen species are likely involved in multiple forms of retinal degenerations, and our results support investigating RAC1 inhibition as a therapeutic approach that targets this disease pathway.

Metabolic Syndrome as a Multifaceted Risk Factor for Oxidative Stress

SIGNIFICANCE

Metabolic syndrome (MetS) is associated with a greater risk of diabetes and cardiovascular diseases. It is estimated that this multifactorial condition affects 20%-30% of the world's population. A detailed understanding of MetS mechanisms is crucial for the development of effective prevention strategies and adequate intervention tools that could curb its increasing prevalence and limit its comorbidities, particularly in younger age groups. With advances in basic redox biology, oxidative stress (OxS) involvement in the complex pathophysiology of MetS has become widely accepted. Nevertheless, its clear association with and causative effects on MetS require further elucidation. Recent Advances: Although a better understanding of the causes, risks, and effects of MetS is essential, studies suggest that oxidant/antioxidant imbalance is a key contributor to this condition. OxS is now understood to be a major underlying mechanism for mitochondrial dysfunction, ectopic lipid accumulation, and gut microbiota impairment.

CRITICAL ISSUES

Further studies, particularly in the field of translational research, are clearly required to understand and control the production of reactive oxygen species (ROS) levels, especially in the mitochondria, since the various therapeutic trials conducted to date have not targeted this major ROS-generating system, aimed to delay MetS onset, or prevent its progression.

FUTURE DIRECTIONS

Multiple relevant markers need to be identified to clarify the role of ROS in the etiology of MetS. Future clinical trials should provide important proof of concept for the effectiveness of antioxidants as useful therapeutic approaches to simultaneously counteract mitochondrial OxS, alleviate MetS symptoms, and prevent complications. Antioxid. Redox Signal. 26, 445-461.

Genetic architecture of natural variation in visual senescence in Drosophila

Senescence, i.e., functional decline with age, is a major determinant of health span in a rapidly aging population, but the genetic basis of interindividual variation in senescence remains largely unknown. Visual decline and age-related eye disorders are common manifestations of senescence, but disentangling age-dependent visual decline in human populations is challenging due to inability to control genetic background and variation in histories of environmental exposures. We assessed the genetic basis of natural variation in visual senescence by measuring age-dependent decline in phototaxis using Drosophila melanogaster as a genetic model system. We quantified phototaxis at 1, 2, and 4 wk of age in the sequenced, inbred lines of the Drosophila melanogaster Genetic Reference Panel (DGRP) and found an average decline in phototaxis with age. We observed significant genetic variation for phototaxis at each age and significant genetic variation in senescence of phototaxis that is only partly correlated with phototaxis. Genome-wide association analyses in the DGRP and a DGRP-derived outbred, advanced intercross population identified candidate genes and genetic networks associated with eye and nervous system development and function, including seven genes with human orthologs previously associated with eye diseases. Ninety percent of candidate genes were functionally validated with targeted RNAi-mediated suppression of gene expression. Absence of candidate genes previously implicated with longevity indicates physiological systems may undergo senescence independent of organismal life span. Furthermore, we show that genes that shape early developmental processes also contribute to senescence, demonstrating that senescence is part of a genetic continuum that acts throughout the life span.

Knockout Serum Replacement Promotes Cell Survival by Preventing BIM from Inducing Mitochondrial Cytochrome C Release

Knockout serum replacement (KOSR) is a nutrient supplement commonly used to replace serum for culturing stem cells. We show here that KOSR has pro-survival activity in chronic myelogenous leukemia (CML) cells transformed by the BCR-ABL oncogene. Inhibitors of BCR-ABL tyrosine kinase kill CML cells by stimulating pro-apoptotic BIM and inhibiting anti-apoptotic BCL2, BCLxL and MCL1. We found that KOSR protects CML cells from killing by BCR-ABL inhibitors—imatinib, dasatinib and nilotinib. The protective effect of KOSR is reversible and not due to the selective outgrowth of drug-resistant clones. In KOSR-protected CML cells, imatinib still inhibited the BCR-ABL tyrosine kinase, reduced the phosphorylation of STAT, ERK and AKT, down-regulated BCL2, BCLxL, MCL1 and up-regulated BIM. However, these pro-apoptotic alterations failed to cause cytochrome c release from the mitochondria. With mitochondria isolated from KOSR-cultured CML cells, we showed that addition of recombinant BIM protein also failed to cause cytochrome c release. Besides the kinase inhibitors, KOSR could protect cells from menadione, an inducer of oxidative stress, but it did not protect cells from DNA damaging agents. Switching from serum to KOSR caused a transient increase in reactive oxygen species and AKT phosphorylation in CML cells that were protected by KOSR but not in those that were not protected by this nutrient supplement. Treatment of KOSR-cultured cells with the PH-domain inhibitor MK2206 blocked AKT phosphorylation, abrogated the formation of BIM-resistant mitochondria and stimulated cell death. These results show that KOSR has cell-context dependent pro-survival activity that is linked to AKT activation and the inhibition of BIM-induced cytochrome c release from the mitochondria.

Connection between Tumor Suppressor BRCA1 and PTEN in Damaged DNA Repair

Genomic instability finally induces cell death or apoptosis. The tumor suppressor, phosphatase and tensin homolog on chromosome 10 (PTEN), is a dual-specificity phosphatase, which has protein phosphatase activity and lipid phosphatase activity that antagonizes PI3K activity. Cells that lack PTEN have constitutively higher levels of PIP3 and activated downstream PI3K/AKT targets. BRCA1, a well-known breast cancer tumor suppressor, is to associate with breast cancer risk and genetic susceptibility. Many studies have demonstrated that PTEN, as well as BRCA1, plays a critical role in DNA damage responses. The BRCA1 functionally cooperates with PTEN and might be an essential blockage in the development of several tumors. Actually, the PTEN and BRCA1 genes are recognized as one of the most frequently deleted and/or mutated in many human cancers. The PI3K/AKT pathway is constitutively active in BRCA1-defective human cancer cells. Loss or decrease of these PTEN or BRCA1 function, by either mutation or reduced expression, has a role in various tumor developments. This review summarizes recent findings of the function of BRCA1 and PTEN involved in genomic stability and cancer cell signaling.

Decline in cellular clearance systems induces inflammasome signaling in human ARPE-19 cells

Retinal pigment epithelium (RPE) plays a major role in the maintenance of photoreceptors, and degeneration of RPE results in the development of age-related macular degeneration (AMD). Accumulation of intracellular protein aggregates, increased oxidative stress, and chronic inflammation are all factors damaging the functionality of aged RPE cells. Here, we report that inhibition of proteasomal degradation with MG-132 and autophagy with bafilomycin A1 resulted in the release of IL-1β but not that of IL-18 in human ARPE-19 cells. NLRP3 receptor became upregulated, and caspase-1, the functional component of an inflammasome complex, was activated. In addition to accumulating intracellular protein aggregates, inhibition of degradation systems induced oxidative stress which was demonstrated by elevated amounts of intracellular 4-hydroxynonenal (HNE)-protein adducts. Along with IL-1β, exposure to MG-132 and bafilomycin A1 resulted in the secretion of IL-8. A low concentration (1pg/ml) of IL-1β was capable of triggering significant IL-8 production which also became attenuated by treatment with a specific caspase-1 inhibitor. These results suggest that decline in intracellular degradation systems results not only in increased amounts of intracellular protein aggregates and oxidative stress but also in the activation of NLRP3 inflammasomes, arisen as a result of elevated production of biologically active IL-1β.

PTEN phosphorylation and nuclear export mediate free fatty acid-induced oxidative stress

AIM

Oxidative stress induced by free fatty acids (FFA) contributes to metabolic syndrome-associated development of cardiovascular diseases, yet molecular mechanisms remain poorly understood. This study aimed at establishing whether phosphatase and tensin homolog deleted on chromosome 10 (PTEN) and its subcellular location play a role in FFA-induced endothelial oxidative stress.

RESULTS

Exposing human endothelial cells (ECs) with FFA activated mammalian target of rapamycin (mTOR)/S6K pathway, and upon activation, S6K directly phosphorylated PTEN at S380. Phosphorylation of PTEN increased its interaction with its deubiquitinase USP7 in the nucleus, leading to PTEN deubiquitination and nuclear export. The reduction of PTEN in the nucleus, in turn, decreased p53 acetylation and transcription, reduced the expression of the p53 target gene glutathione peroxidase-1 (GPX1), resulting in reactive oxygen species (ROS) accumulation and endothelial damage. Finally, C57BL/6J mice fed with high-fat atherogenic diet (HFAD) showed PTEN nuclear export, decreased p53 and GPX1 protein expressions, elevated levels of ROS, and significant lesions in aortas. Importantly, inhibition of mTOR or S6K effectively blocked these effects, suggesting that mTOR/S6K pathway mediates HFAD-induced oxidative stress and vascular damage via PTEN/p53/GPX1 inhibition in vivo.

INNOVATION

Our study demonstrated for the first time that S6K directly phosphorylated PTEN at S380 under high FFA conditions, and this phosphorylation mediated FFA-induced endothelial oxidative stress. Furthermore, we showed that S380 phosphorylation affected PTEN monoubiquitination and nuclear localization, providing the first example of coordinated regulation of PTEN nuclear localization via phosphorylation and ubiquitination.

CONCLUSION

Our studies provide a novel mechanism by which hyperlipidemia causes vascular oxidative damage through the phosphorylation of PTEN, blocking of PTEN nuclear function, and inhibition of p53/GPX1 activity.

Selective inhibition of PI3K/Akt/mTOR signaling pathway regulates autophagy of macrophage and vulnerability of atherosclerotic plaque

Macrophage infiltration contributes to the instability of atherosclerotic plaques. In the present study, we investigated whether selective inhibition of PI3K/Akt/mTOR signaling pathway can enhance the stability of atherosclerotic plaques by activation of macrophage autophagy. In vitro study, selective inhibitors or siRNA of PI3K/Akt/mTOR pathways were used to treat the rabbit's peritoneal primary macrophage cells. Inflammation related cytokines secreted by macrophages were measured. Ultrastructure changes of macrophages were examined by transmission electron microscope. mRNA or protein expression levels of autophagy related gene Beclin 1, protein 1 light chain 3 II dots (LC3-II) or Atg5-Atg12 conjugation were assayed by quantitative RT-PCR or Western blot. In vivo study, vulnerable plaque models were established in 40 New Zealand White rabbits and then drugs or siRNA were given for 8 weeks to inhibit the PI3K/Akt/mTOR signaling pathway. Intravascular ultrasound (IVUS) was performed to observe the plaque imaging. The ultrastructure of the abdominal aortic atherosclerosis lesions were analyzed with histopathology. RT-PCR or Western blot methods were used to measure the expression levels of corresponding autophagy related molecules. We found that macrophage autophagy was induced in the presence of Akt inhibitor, mTOR inhibitor and mTOR-siRNA in vitro study, while PI3K inhibitor had the opposite role. In vivo study, we found that macrophage autophagy increased significantly and the rabbits had lower plaque rupture incidence, lower plaque burden and decreased vulnerability index in the inhibitors or siRNA treated groups. We made a conclusion that selective inhibition of the Akt/mTOR signal pathway can reduce macrophages and stabilize the vulnerable atherosclerotic plaques by promoting macrophage autophagy.

Toxoplasma gondii Proliferation Require Down-Regulation of Host Nox4 Expression via Activation of PI3 Kinase/Akt Signaling Pathway

Toxoplasma gondii results in ocular toxoplasmosis characterized by chorioretinitis with inflammation and necrosis of the neuroretina, pigment epithelium, and choroid. After invasion, T. gondii replicates in host cells before cell lysis, which releases the parasites to invade neighboring cells to repeat the life cycle and establish a chronic retinal infection. The mechanism by which T. gondii avoids innate immune defense, however, is unknown. Therefore, we determined whether PI3K/Akt signaling pathway activation by T. gondii is essential for subversion of host immunity and parasite proliferation. T. gondii infection or excretory/secretory protein (ESP) treatment of the human retinal pigment epithelium cell line ARPE-19 induced Akt phosphorylation, and PI3K inhibitors effectively reduced T. gondii proliferation in host cells. Furthermore, T. gondii reduced intracellular reactive oxygen species (ROS) while activating the PI3K/Akt signaling pathway. While searching for the main source of these ROS, we found that NADPH oxidase 4 (Nox4) was prominently expressed in ARPE-19 cells, and this expression was significantly reduced by T. gondii infection or ESP treatment along with decreased ROS levels. In addition, artificial reduction of host Nox4 levels with specific siRNA increased replication of intracellular T. gondii compared to controls. Interestingly, these T. gondii-induced effects were reversed by PI3K inhibitors, suggesting that activation of the PI3K/Akt signaling pathway is important for suppression of both Nox4 expression and ROS levels by T. gondii infection. These findings demonstrate that manipulation of the host PI3K/Akt signaling pathway and Nox4 gene expression is a novel mechanism involved in T. gondii survival and proliferation.

Inflammatory cytokines protect retinal pigment epithelial cells from oxidative stress-induced death

Purpose

To investigate the effects of inflammatory factors and oxidative stress on cell survival of the human retinal pigment epithelial (RPE) cell line, ARPE-19.

Methods

Confluent RPE cells were treated with peripheral blood mononuclear cells-conditioned medium (PCM), H₂O₂, NaIO₃, interferon (IFN)-γ, tumor necrosis factor (TNF)-α, or combinations of these. Cell viability was determined by viability assays and by light microscopy. Effector molecules of cell death were investigated by immunofluorescence microscopy and flow cytometry. Microarrays were performed to screen for differential expression of anti-oxidative enzymes, and protein expression was validated by immunoblotting.

Results

Viability of RPE cells was reduced by exposure to inflammatory agents (PCM, IFNγ+/-TNFα) or to oxidative agents (H₂O₂ or NaIO₃). Unexpectedly, cells treated with either H₂O₂ or NaIO₃ were partially protected from cell death by the addition of PCM. This protection was conferred, at least in part, by IFNγ and TNFα. Cell death induced by H₂O₂ or NaIO₃ was preceded by mitochondrial dysfunction and by p62 upregulation, both of which were attenuated by PCM and/or by IFNγ+TNFα. RPE cells co-cultured with activated T cells, or treated with cytokines showed increased expression of anti-oxidative genes, with upregulation of superoxide dismutase 2 protein following PCM treatment.

Conclusion

Oxidative stress-induced cell death was reduced by concomitant inflammatory stress. This is likely due to the cytokine-mediated induction of the anti-oxidative stress response, upregulating protective anti-oxidant pathway(s). These findings suggest caution for the clinical use of anti-inflammatory agents in the management of immune-associated eye diseases such as age-related macular degeneration.

Oxidative stress and myocardial injury in the diabetic heart

Reactive oxygen or nitrogen species play an integral role in both myocardial injury and repair. This dichotomy is differentiated at the level of species type, amount and duration of free radical generated. Homeostatic mechanisms designed to prevent free radical generation in the first instance, scavenge, or enzymatically convert them to less toxic forms and water, playing crucial roles in the maintenance of cellular structure and function. The outcome between functional recovery and dysfunction is dependent upon the inherent ability of these homeostatic antioxidant defences to withstand acute free radical generation, in the order of seconds to minutes. Alternatively, pre-existent antioxidant capacity (from intracellular and extracellular sources) may regulate the degree of free radical generation. This converts reactive oxygen and nitrogen species to the role of second messenger involved in cell signalling. The adaptive capacity of the cell is altered by the balance between death or survival signal converging at the level of the mitochondria, with distinct pathophysiological consequences that extends the period of injury from hours to days and weeks. Hyperglycaemia, hyperlipidaemia and insulin resistance enhance oxidative stress in the diabetic myocardium that cannot adapt to ischaemia-reperfusion. Altered glucose flux, mitochondrial derangements and nitric oxide synthase uncoupling in the presence of decreased antioxidant defence and impaired prosurvival cell signalling may render the diabetic myocardium more vulnerable to injury, remodelling and heart failure.

Redox-sensitive oxidation and phosphorylation of PTEN contribute to enhanced activation of PI3K/Akt signaling in rostral ventrolateral medulla and neurogenic hypertension in spontaneously hypertensive rats

AIMS

The activity of phosphoinositide 3-kinase (PI3K)/serine/threonine protein kinase (Akt) is enhanced under hypertension. The phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is a negative regulator of PI3K signaling, and its activity is redox-sensitive. In the rostral ventrolateral medulla (RVLM), which is responsible for the maintenance of blood pressure, oxidative stress plays a pivotal role in neurogenic hypertension. The present study evaluated the hypothesis that redox-sensitive inactivation of PTEN results in enhanced PI3K/Akt signaling in RVLM, leading to neurogenic hypertension.

RESULTS

Compared to age-matched normotensive Wistar-Kyoto (WKY) rats, PTEN inactivation in the form of oxidation and phosphorylation were greater in RVLM of spontaneously hypertensive rats (SHR). PTEN inactivation was accompanied by augmented PI3K activity and PI3K/Akt signaling, as reflected by the increase in phosphorylation of Akt and mammalian target of rapamycin. Intracisternal infusion of tempol or microinjection into the bilateral RVLM of adenovirus encoding superoxide dismutase significantly antagonized the PTEN inactivation and blunted the enhanced PI3K/Akt signaling in SHR. Gene transfer of PTEN to RVLM in SHR also abrogated the enhanced Akt activation and promoted antihypertension. Silencing PTEN expression in RVLM with small-interfering RNA, on the other hand, augmented PI3K/Akt signaling and promoted long-term pressor response in normotensive WKY rats.

INNOVATION

The present study demonstrated for the first time that the redox-sensitive check-and-balance process between PTEN and PI3K/Akt signaling is engaged in the pathogenesis of hypertension.

CONCLUSION

We conclude that an aberrant interplay between the redox-sensitive PTEN and PI3k/Akt signaling in RVLM underpins neural mechanism of hypertension.

Crumbs limits oxidase-dependent signaling to maintain epithelial integrity and prevent photoreceptor cell death

Crb fulfills a protective role during light exposure by limiting oxidative damage resulting from Rac1–NADPH oxidase complex activity.

Drosophila melanogaster Crumbs (Crb) and its mammalian orthologues (CRB1–3) share evolutionarily conserved but poorly defined roles in regulating epithelial polarity and, in photoreceptor cells, morphogenesis and stability. Elucidating the molecular mechanisms of Crb function is vital, as mutations in the human CRB1 gene cause retinal dystrophies. Here, we report that Crb restricts Rac1–NADPH oxidase-dependent superoxide production in epithelia and photoreceptor cells. Reduction of superoxide levels rescued epithelial defects in crb mutant embryos, demonstrating that limitation of superoxide production is a crucial function of Crb and that NADPH oxidase and superoxide contribute to the molecular network regulating epithelial tissue organization. We further show that reduction of Rac1 or NADPH oxidase activity or quenching of reactive oxygen species prevented degeneration of Crb-deficient retinas. Thus, Crb fulfills a protective role during light exposure by limiting oxidative damage resulting from Rac1–NADPH oxidase complex activity. Collectively, our results elucidate an important mechanism by which Crb functions in epithelial organization and the prevention of retinal degeneration.

PTEN regulates retinal interneuron morphogenesis and synaptic layer formation

The lipid phosphatase PTEN is a critical negative regulator of extracellular signal-induced PI3K activities, yet the roles of PTEN in the neural retina remain poorly understood. Here, we investigate the function of PTEN during retinal development. Deletion of Pten at the onset of neurogenesis in retinal progenitors results in the reduction of retinal ganglion cells and rod photoreceptors, but increased Müller glial genesis. In addition, PTEN deficiency leads to elevated phosphorylation of Akt, especially in the developing inner plexiform layer, where high levels of PTEN are normally expressed. In Pten mutant retinas, various subtypes of amacrine cells show severe dendritic overgrowth, causing specific expansion of the inner plexiform layer. However, the outer plexiform layer remains relatively undisturbed in the Pten deficient retina. Physiological analysis detects reduced rod function and augmented oscillatory potentials originating from amacrine cells in Pten mutants. Furthermore, deleting Pten or elevating Akt activity in individual amacrine cells is sufficient to disrupt dendritic arborization, indicating that Pten activity is required cell autonomously to control neuronal morphology. Moreover, inhibiting endogenous Akt activity attenuates inner plexiform layer formation in vitro. Together, these findings demonstrate that suppression of PI3K/Akt signaling by PTEN is crucial for proper neuronal differentiation and normal retinal network formation.

Phosphorylation/inactivation of PTEN by Akt-independent PI3K signaling in retinal pigment epithelium

Retinal pigment epithelium (RPE) plays a critical role in vertebrate vision by providing functional and structural support to the retina. Degeneration of RPE by cumulative oxidative stresses or acute injury frequently results in retinal degenerative diseases, notably age-related macular degeneration (AMD). Moreover, it has been shown that phosphorylation-mediated inactivation of PTEN (phosphatase and tensin homolog) in RPE is closely linked to AMD-like retinal degeneration in mice [1]. In this study, we used AMD mouse models, in which chemokine (C-C motif) ligand 2 (Ccl2) or chemokine (C-C motif) receptor 2 (Ccr2) were genetically ablated, to examine mechanisms linking reactive oxygen species (ROS) to phosphorylation/inactivation of PTEN in RPE. We found that ROS levels were increased in these RPE cells in association with phosphorylation/inactivation of PTEN. Both PTEN phosphorylation/inactivation and consequent Akt activation in the RPE of AMD model mice were inhibited by antioxidant treatment, indicating a functional role for elevated intracellular ROS. We further discovered that PTEN phosphorylation in oxidatively stressed RPE was repressed by a phosphoinositide 3-kinase (PI3K) inhibitor, but not by an Akt inhibitor. Taken together, these results suggest that ROS-activated PI3K potentiates AMD-related RPE pathogenesis through phosphorylation/inactivation of PTEN.

Differences in myocardial PTEN expression and Akt signalling in type 2 diabetic and nondiabetic patients undergoing coronary bypass surgery

OBJECTIVE

Patients with diabetes experience increased cardiovascular complications after cardiac surgery. Hyperglycaemia predicts increased mortality after myocardial infarction and may influence cardiovascular risk in humans. Impaired prosurvival phosphatase and tensin homologue on chromosome 10 (PTEN)-Akt signalling could be an important feature of the diabetic heart rendering it resistant to preconditioning. This study was designed to evaluate for differences and relationships of myocardial PTEN-Akt-related signalling and baseline glycaemic control marker in type 2 diabetic and nondiabetic patients undergoing coronary artery bypass surgery.

METHODS

Right atrial biopsies and coronary sinus blood were obtained from 18 type 2 diabetic and 18 nondiabetic patients intraoperatively. Expression and phosphorylation of Akt, endothelial nitric oxide synthase (eNOS), Bcl-2 and PTEN were evaluated by Western blot. Plasma 15-F(2t) -isoprostane concentrations were evaluated by liquid chromatography-mass spectrometry.

RESULTS

PTEN expression and 15-F(2t) -isoprostane concentrations were significantly higher in diabetic patients. Increased fasting blood glucose levels correlated with increased coronary sinus plasma 15-F(2t) -isoprostane concentrations. Increased cardiac 15-F(2t) -isoprostane generation was highly correlated with myocardial PTEN expression. Bcl-2 expression and eNOS phosphorylation were significantly lower in diabetic compared with nondiabetic patients. Akt phosphorylation tended to be lower in diabetic patients; however, this tendency failed to reach statistical significance.

CONCLUSION

The current results suggest that prosurvival PTEN-Akt signalling is impaired in the diseased diabetic myocardium. Hyperglycaemia and increased oxidative stress may contribute to this phenomenon. These findings strengthen the understanding of the underlying biologic mechanisms of cardiac injury in diabetic patients, which could facilitate development of new treatments to prevent cardiovascular complications in this high-risk population.

NPD1 induction of retinal pigment epithelial cell survival involves PI3K/Akt phosphorylation signaling

Neuroprotectin D1 (NPD1), a docosahexaenoic acid (DHA)-derived lipid mediator, promotes survival in cells exposed to oxidative stress by inducing the activity of anti-inflammatory mediators and suppressing the expression of pro-inflammatory genes. Though retinal pigment epithelial (RPE) cells naturally produce NPD1 from DHA, investigating the mechanisms through which exogenous NPD1 induces cell survival is essential to assess mechanisms of actions and the potential of this lipid mediator for treatment of retinal degenerative diseases. The PI3K/Akt and mTOR/p70S6K pathways are responsible for supporting cell survival upon exposure to oxidative stress. In human ARPE-19 cells pretreated with NPD1 then exposed to varying concentrations of oxidative stress or repeated exposures to oxidative stress, Akt, mTOR, and p70S6K were phosphorylated to a greater extent and for a greater duration than cells not pretreated with NPD1. In addition to increased phosphorylation, a subsequent decreased rate of apoptosis was observed upon NPD1 treatment. Thus NPD1 bioactivity in RPE cells enhances activation of these pathways and promotes cell integrity and survival.

Regulatory role of HIF-1alpha in the pathogenesis of age-related macular degeneration (AMD)

Age-related macular degeneration (AMD) is a leading cause of irreversible blindness in the elderly throughout the world. AMD is attributed to a complex interaction of genetic and environmental factors. It is characterized by degeneration involving the retinal photoreceptors, retinal pigment epithelium (RPE), and Bruch's membrane, as well as alterations in choroidal capillaries. Aging and age-associated degenerative diseases, such as AMD, are intimately associated with decreased levels of tissue oxygenation and hypoxia that may induce accumulation of detrimental RPE-associated deposits, inflammation and neovascularization processes in retina. Hypoxia-inducible factor (HIF) is the master regulator for hypoxia-induced cellular adaptation that is involved in NF-kappaB signaling and the autophagic protein clearance system. In this review, we discuss role of HIF in AMD pathology and as a possible therapeutic target.