Mitochondrial dysfunction links ceramide activated HRK expression and cell death

Metabolomics for identifying pathways involved in vesicating agent lewisite-induced corneal injury

Lewisite (LEW) is an arsenical vesicant that can be a potentially dangerous chemical warfare agent (CWA). Eyes are particularly susceptible to vesicant induced injuries and ocular LEW exposure can act swiftly, causing burning of eyes, edema, inflammation, cell death and even blindness. In our previous studies, we developed a LEW exposure-induced corneal injury model in rabbit and showed increased inflammation, neovascularization, cell death, and structural damage to rabbit corneas upon LEW exposure. In the present study, we further assessed the metabolomic changes to delineate the possible mechanisms underlying the LEW-induced corneal injuries. This information is vital and could help in the development of effective targeted therapies against ocular LEW injuries. Thus, the metabolomic changes associated with LEW exposures in rabbit corneas were assessed as a function of time, to delineate pathways from molecular perturbations at the genomic and proteomic levels. New Zealand white rabbit corneas (n = 3-6) were exposed to LEW vapor (0.2 mg/L; flow rate: 300 ml/min) for 2.5 min (short exposure; low dose) or 7.5 min (long-exposure; high dose) and then collected at 1, 3, 7, or 14 days post LEW exposure. Samples were prepared using the automated MicroLab STAR® system, and proteins precipitated to recover the chemically diverse metabolites. Metabolomic analysis was carried out by reverse phase UPLC-MS/MS and gas chromatography (GC)-MS. The data obtained were analyzed using Metabolon's software. The results showed that LEW exposures at high doses were more toxic, particularly at the day 7 post exposure time point. LEW exposure was shown to dysregulate metabolites associated with all the integral functions of the cornea and cause increased inflammation and immune response, as well as generate oxidative stress. Additionally, all important metabolic functions of the cells were also affected: lipid and nucleotide metabolism, and energetics. The high dose LEW exposures were more toxic, particularly at day 7 post LEW exposure (>10-fold increased levels of histamine, quinolinate, N-acetyl-β-alanine, GMP, and UPM). LEW exposure dysregulated integral functions of the cornea, caused inflammation and heightened immune response, and generated oxidative stress. Lipid and nucleotide metabolism, and energetics were also affected. The novel information about altered metabolic profile of rabbit cornea following LEW exposure could assist in delineating complex molecular events; thus, aid in identifying therapeutic targets to effectively ameliorate ocular trauma.

Mitochondrial gene expression signature predicts prognosis of pediatric acute myeloid leukemia patients

Introduction

Gene expression profile of mitochondrial-related genes is not well deciphered in pediatric acute myeloid leukaemia (AML). We aimed to identify mitochondria-related differentially expressed genes (DEGs) in pediatric AML with their prognostic significance.

Methods

Children with de novo AML were included prospectively between July 2016-December 2019. Transcriptomic profiling was done for a subset of samples, stratified by mtDNA copy number. Top mitochondria-related DEGs were identified and validated by real-time PCR. A prognostic gene signature risk score was formulated using DEGs independently predictive of overall survival (OS) in multivariable analysis. Predictive ability of the risk score was estimated along with external validation in The Tumor Genome Atlas (TCGA) AML dataset.

Results

In 143 children with AML, twenty mitochondria-related DEGs were selected for validation, of which 16 were found to be significantly dysregulated. Upregulation of SDHC (p<0.001), CLIC1 (p=0.013) and downregulation of SLC25A29 (p<0.001) were independently predictive of inferior OS, and included for developing prognostic risk score. The risk score model was independently predictive of survival over and above ELN risk categorization (Harrell's c-index: 0.675). High-risk patients (risk score above median) had significantly inferior OS (p<0.001) and event free survival (p<0.001); they were associated with poor-risk cytogenetics (p=0.021), ELN intermediate/poor risk group (p=0.016), absence of RUNX1-RUNX1T1 (p=0.027), and not attaining remission (p=0.016). On external validation, the risk score also predicted OS (p=0.019) in TCGA dataset.

Discussion

We identified and validated mitochondria-related DEGs with prognostic impact in pediatric AML and also developed a novel 3-gene based externally validated gene signature predictive of survival.

Nuclear Genome-Encoded Long Noncoding RNAs and Mitochondrial Damage in Diabetic Retinopathy

Retinal mitochondria are damaged in diabetes-accelerating apoptosis of capillary cells, and ultimately, leading to degenerative capillaries. Diabetes also upregulates many long noncoding RNAs (LncRNAs), including LncMALAT1 and LncNEAT1. These RNAs have more than 200 nucleotides and no open reading frame for translation. LncMALAT1 and LncNEAT1 are encoded by nuclear genome, but nuclear-encoded LncRNAs can also translocate in the mitochondria. Our aim was to investigate the role of LncMALAT1 and LncNEAT1 in mitochondrial homeostasis. Using human retinal endothelial cells, the effect of high glucose on LncMALAT1 and LncNEAT1 mitochondrial localization was examined by RNA fluorescence in situ hybridization. The role of these LncRNAs in mitochondrial membrane potential (by JC-I staining), mtDNA integrity (by extended length PCR) and in protective mtDNA nucleoids (by SYBR green staining) was examined in MALAT1- or NEAT1-siRNA transfected cells. High glucose increased LncMALAT1 and LncNEAT1 mitochondrial expression, and MALAT1-siRNA or NEAT1-siRNA ameliorated glucose-induced damage to mitochondrial membrane potential and mtDNA, and prevented decrease in mtDNA nucleoids. Thus, increased mitochondrial translocation of LncMALAT1 or LncNEAT1 in a hyperglycemic milieu plays a major role in damaging the mitochondrial structural and genomic integrity. Regulation of these LncRNAs can protect mitochondrial homeostasis, and ameliorate formation of degenerative capillaries in diabetic retinopathy.

Potential role of CFTR in bisphenol A-induced malignant transformation of prostate cells via mitochondrial apoptosis

Bisphenol A (BPA) is an environmental endocrine disruptor and a risk factor for prostate cancer. The cystic fibrosis transmembrane conductance regulator (CFTR) is proposed to be a prostate cancer suppressor in some recent researches. However, the potential role and mechanism of CFTR in BPA-induced prostate cancer cells has not been well identified. In this study, BPA decreased the viability of human normal prostate RWPE-1 cells detected with a CCK-8 kit. The capacity of the cell line on soft agar colony formation, wound healing, and transwell invasion indicated malignant transformation induced by BPA. Western blot analysis demonstrated that the levels of CFTR and Bcl-2 decreased, whereas Bax level increased, and ELISA detection showed a decreased ATP level in BPA-exposed cells. Cell apoptosis was analyzed with Annexin V-FITC Detection Kit by flow cytometry. However, no significant difference was observed in cell viability and apoptosis rates compared to normal RWPE-1 cells. Our research revealed a potential role of CFTR in BPA-induced malignant transformation via mitochondrial apoptosis of normal prostate cells.

A Systematic Review on Cornea Epithelial-Stromal Homeostasis

INTRODUCTION

This review aims to summarise the role of different cells, genes, proteins and lipid in regulating cornea epithelial-stromal homeostasis.

METHODS

We performed an Entrez PubMed literature search using keywords "human," "cornea," "epithelial," "stromal," "homeostasis," "fibrosis response," and "pathogenesis" on 24th of September 2019, resulting in 35 papers, of which 18 were chosen after filtering for "English language" and "published within 10 years" as well as curation for relevance by the authors.

RESULTS

The 18 selected papers showed that corneal epithelial cells, fibroblasts and telocytes, together with genes such as Klf4, Pax6 and Id found in the cells, play important roles in achieving homeostasis to maintain corneal integrity and transparency. Proteins classified as pro-fibrotic ligands and anti-fibrotic ligands are responsible for regulating cornea stromal fibrosis and extracellular matrix deposition, thus regulators of scar formation during wound healing. Anti-inflammatory ligands and wound repairing ligands are critical in eliciting protective inflammation and promoting epithelial healing, respectively. Protein receptors located on cellular membrane play a role in maintaining intercellular connections as well as corneal hydration.

DISCUSSION/CONCLUSION

These studies prompt development of novel therapeutic strategies such as tear drops or ointments that target certain proteins to maintain corneal homeostasis. However, more in vitro and in vivo studies are required to prove the effectiveness of exogenous administration of molecules in improving healing outcome. Hence, future investigations of the molecular pathways highlighted in this review will reveal novel therapeutic tools such as gene or cell therapy to treat corneal diseases.

JNK Signaling as a Key Modulator of Soft Connective Tissue Physiology, Pathology, and Healing

In healthy individuals, the healing of soft tissues such as skin after pathological insult or post injury follows a relatively predictable and defined series of cell and molecular processes to restore tissue architecture and function(s). Healing progresses through the phases of hemostasis, inflammation, proliferation, remodeling, and concomitant with re-epithelialization restores barrier function. Soft tissue healing is achieved through the spatiotemporal interplay of multiple different cell types including neutrophils, monocytes/macrophages, fibroblasts, endothelial cells/pericytes, and keratinocytes. Expressed in most cell types, c-Jun N-terminal kinases (JNK) are signaling molecules associated with the regulation of several cellular processes involved in soft tissue wound healing and in response to cellular stress. A member of the mitogen-activated protein kinase family (MAPK), JNKs have been implicated in the regulation of inflammatory cell phenotype, as well as fibroblast, stem/progenitor cell, and epithelial cell biology. In this review, we discuss our understanding of JNKs in the regulation of cell behaviors related to tissue injury, pathology, and wound healing of soft tissues. Using models as diverse as Drosophila, mice, rats, as well as human tissues, research is now defining important, but sometimes conflicting roles for JNKs in the regulation of multiple molecular processes in multiple different cell types central to wound healing processes. In this review, we focus specifically on the role of JNKs in the regulation of cell behavior in the healing of skin, cornea, tendon, gingiva, and dental pulp tissues. We conclude that while parallels can be drawn between some JNK activities and the control of cell behavior in healing, the roles of JNK can also be very specific modes of action depending on the tissue and the phase of healing.

Sphingolipids as Emerging Mediators in Retina Degeneration

The sphingolipids ceramide (Cer), sphingosine-1-phosphate (S1P), sphingosine (Sph), and ceramide-1-phosphate (C1P) are key signaling molecules that regulate major cellular functions. Their roles in the retina have gained increasing attention during the last decade since they emerge as mediators of proliferation, survival, migration, neovascularization, inflammation and death in retina cells. As exacerbation of these processes is central to retina degenerative diseases, they appear as crucial players in their progression. This review analyzes the functions of these sphingolipids in retina cell types and their possible pathological roles. Cer appears as a key arbitrator in diverse retinal pathologies; it promotes inflammation in endothelial and retina pigment epithelium (RPE) cells and its increase is a common feature in photoreceptor death in vitro and in animal models of retina degeneration; noteworthy, inhibiting Cer synthesis preserves photoreceptor viability and functionality. In turn, S1P acts as a double edge sword in the retina. It is essential for retina development, promoting the survival of photoreceptors and ganglion cells and regulating proliferation and differentiation of photoreceptor progenitors. However, S1P has also deleterious effects, stimulating migration of Müller glial cells, angiogenesis and fibrosis, contributing to the inflammatory scenario of proliferative retinopathies and age related macular degeneration (AMD). C1P, as S1P, promotes photoreceptor survival and differentiation. Collectively, the expanding role for these sphingolipids in the regulation of critical processes in retina cell types and in their dysregulation in retina degenerations makes them attractive targets for treating these diseases.

AG 205, a progesterone receptor membrane component 1 antagonist, ablates progesterone's ability to block oxidative stress-induced apoptosis of human granulosa/luteal cells†

The present studies were designed to determine whether progesterone (P4)-progesterone receptor membrane component 1 (PGRMC1) signaling is able to attenuate the apoptotic effects of oxidative stress induced by hydrogen peroxide (H2O2). To achieve this goal, freshly isolated human granulosa/luteal cells were maintained in culture. After several passages, the cells were treated with H2O2, which induced apoptosis within 2.5 h, while simultaneous treatment with P4 attenuated the apoptotic action of H2O2. AG 205, a PGRMC1 antagonist, eliminated P4's ability to prevent H2O2-induced apoptosis. AG 205 neither affected PGRMC1's cytoplasmic localization nor its interaction with PGRMC2, but appeared to reduce its presence within the nucleus. AG 205 also (1) increased the monomeric and decreased the higher molecular weight forms of PGRMC1 (i.e., dimers/oligomers) and (2) altered the expression of several genes involved in apoptosis. The most dramatic change was an approximate 8-fold increase in Harakiri (Hrk) mRNA. However, AG 205 did not induce apoptosis in the absence of H2O2. Taken together, these observations suggest that the higher molecular weight forms of PGRMC1 likely account in part for PGRMC1's ability to suppress the expression of Hrk. Harakiri is a BH-3 only member of the B-cell lymphoma 2 (BCL2) family that promotes apoptosis by binding to and antagonizing the antiapoptotic action of BCL2- and BCL2-like proteins. It is likely then that PGRMC1's ability to suppress Hrk is part of the mechanism through which P4-PGRMC1 signaling preserves the viability of human granulosa/luteal cells.

Nitrogen mustard-induced corneal injury involves the sphingomyelin-ceramide pathway

PURPOSE

Nitrogen mustard (NM), which simulates the effects of sulfur mustard (SM), is a potent vesicant known to cause irreversible corneal damage. This study investigates the mechanisms by which NM induces corneal damage by examining the impact of NM exposure on the morphology and lipidome of the cornea.

METHODS

Intact ex vivo rabbit eyes were placed in serum-free DMEM organ culture. NM (0, 1, 2.5, 5 or 10 mg/ml) was applied to the central cornea for 5, 10 or 15 min using a 5 mm filter disk and subsequently rinsed with DMEM. Corneas were then cultured for 3, 24, or 48 h before being fixed for morphological analysis or for 24 h before being snap frozen for lipidomic analysis.

RESULTS

No morphological changes were detected 3 h after NM exposure. Twenty-four h after exposure, 1 mg/ml NM caused erosion of the corneal epithelium, but no damage to the underlying stroma. Damage caused by 2.5 mg/ml NM extended almost two thirds through the corneal stroma, while 5 mg/ml completely penetrated the corneal stroma. An altered lipid profile occurred 24 h after corneas were exposed to NM. Specific sphingomyelins, ceramides, and diacylglycerols were increased up to 9-, 60- and 10-fold, respectively.

CONCLUSIONS

NM induces concentration- and exposure time-dependent damage to the cornea that increases in severity over time. Alterations in the sphingomyelin-ceramide pathway may contribute to the damaging effects of NM exposure.

Resveratrol induces mitochondria-mediated, caspase-independent apoptosis in murine prostate cancer cells

Found in the skins of red fruits, including grapes, resveratrol (RES) is a polyphenolic compound with cancer chemopreventive activity. Because of this activity, it has gained interest for scientific investigations. RES inhibits tumor growth and progression by targeting mitochondria-dependent or -independent pathways. However, further investigations are needed to explore the underlying mechanisms.

The present study is focused on examining the role of RES-induced, mitochondria-mediated, caspase-independent apoptosis of prostate cancer cells, namely transgenic adenocarcinoma of mouse prostate (TRAMP) cells. These cells were exposed to RES for various times, and cell killing, cell morphology, mitochondrial membrane potential (Δψm), expression of Bax and Bcl2 proteins, the role of caspase-3, and DNA fragmentation were analyzed.

TRAMP cells exposed to RES showed decreased cell viability, altered cell morphology, and disrupted Δψm, which led to aberrant expression of Bax and Bcl2 proteins. Furthermore, since the caspase-3 inhibitor, z-VAD-fmk (benzyloxycarbonyl-valine-alanine-aspartic acid-fluoromethyl ketone), had no appreciable impact on RES-induced cell killing, the killing was evidently caspase-independent. In addition, RES treatment of TRAMP-C1, TRAMP-C2, and TRAMP-C3 cells caused an appreciable breakage of genomic DNA into low-molecular-weight fragments.

These findings show that, in inhibition of proliferation of TRAMP cells, RES induces mitochondria-mediated, caspase-independent apoptosis. Therefore, RES may be utilized as a therapeutic agent to control the proliferation and growth of cancer cells.

Establishment of a 3D In Vitro Model to Accelerate the Development of Human Therapies against Corneal Diabetes

PURPOSE

To establish an in vitro model that would mirror the in vivo corneal stromal environment in diabetes (DM) patients.

METHODS

Human corneal fibroblasts from Healthy (HCFs), Type 1DM (T1DM) and Type 2DM (T2DM) donors were isolated and cultured for 4 weeks with Vitamin C stimulation in order to allow for extracellular matrix (ECM) secretion and assembly.

RESULTS

Our data indicated altered cellular morphology, increased cellular migration, increased ECM assembly, and severe mitochondrial damage in both T1DM and T2DMs when compared to HCFs. Furthermore, we found significant downregulation of Collagen I and Collagen V expression in both T1DM and T2DMs. Furthermore, a significant up regulation of fibrotic markers was seen, including α-smooth muscle actin in T2DM and Collagen III in both T1DM and T2DMs. Metabolic analysis suggested impaired Glycolysis and Tricarboxylic acid cycle (TCA) pathway.

CONCLUSION

DM has significant effects on physiological and clinical aspects of the human cornea. The benefits in developing and fully characterizing our 3D in vitro model are enormous and might provide clues for the development of novel therapeutics.

Examining impacts of ceranib-2 on the proliferation, morphology and ultrastructure of human breast cancer cells

Acid ceramidases are enzymes with a vital role in metabolizing ceramide to sphingosine-1-phosphate that is an antiproliferative metabolite in the ceramide pathway. Inhibition of exogenous ceramides with ceramidase inhibitors lead to augmented ceramide levels in cells and in turn lead to cell cycle arrest and apoptosis. Our study aimed at targeting ceramide metabolic pathway to induce apoptosis in human breast cancer cell line (MCF7) and we examined the antiproliferative and apoptotic activities of ceranib-2, an inhibitor of human ceramidase, on this cell line as well ultrastructural and mophological changes. Methods used for our examinations in this study were the colorimetric MTT assay, Annexin V/Propidium iodide and JC-1 staining, transmission electron microscopy and confocal microscopy. Ceranib-2 effectively inhibited the viability of MCF7 cells in 24 h in a dose dependent manner leading to apoptosis via the mitochondrial pathway by reducing the potential of mitochondrial membrane. Additionally, significant changes on cell morphology and ultrastructure were observed on MCF7 cells exposed to ceranib-2 indicating apoptotic cell death. Collectively, our data demonstrate that ceranib-2 exerts a great potential to be an antineoplastic compound and that the mechanism of its action rely on its apoptosis inducing ability.

Defective ceramide synthases in mice cause reduced amplitudes in electroretinograms and altered sphingolipid composition in retina and cornea

Complex sphingolipids are strongly expressed in neuronal tissue and contain ceramides in their backbone. Ceramides are synthesized by six ceramide synthases (CerS1-6). Although it is known that each tissue has a unique profile of ceramide synthase expression and ceramide synthases are implicated in several neurodegenerative disorders, the expression of ceramide synthase isoforms has not been investigated in the retina. Here we demonstrate CerS1, CerS2 and CerS4 expression in mouse retina and cornea, with CerS4 ubiquitously expressed in all retinal neurons and Müller cells. To test whether ceramide synthase deficiency affects retinal function, we compared electroretinograms and retina morphology between wild-type and CerS1-, CerS2- and CerS4-deficient mice. Electroretinograms were strongly reduced in amplitude in ceramide synthase-deficient mice, suggesting that signalling in the outer retina is affected. However, the number of photoreceptors and cone outer segment length were unaltered and no changes in retinal layer thickness or synaptic structures were found. Mass spectrometric analyses of ceramides, hexosyl-ceramides and sphingomyelins showed that C20 to C24 acyl-containing species were decreased whereas C16-containing species were increased in the retina of ceramide synthase-deficient mice. Similar but smaller changes were also found in the cornea. Thus, we hypothesize that the replacement of very long-chain fatty acyl residues by shorter C16 residues may affect the electrical properties of retina and cornea, and alter receptor-mediated signal transduction, vesicle-mediated synaptic transmission or corneal light transmission. Future studies need to identify the molecular targets of ceramides or derived sphingolipids in light signal transduction and transmission in the eye.

Derivation, Characterization, and Neural Differentiation of Integration-Free Induced Pluripotent Stem Cell Lines from Parkinson's Disease Patients Carrying SNCA, LRRK2, PARK2, and GBA Mutations

We report generation of induced pluripotent stem cell (iPSC) lines from ten Parkinson’s disease (PD) patients carrying SNCA, PARK2, LRRK2, and GBA mutations, and one age-matched control. After validation of pluripotency, long-term genome stability, and integration-free reprogramming, eight of these lines (one of each SNCA, LRRK2 and GBA, four PARK2 lines, and the control) were differentiated into neural stem cells (NSC) and subsequently to dopaminergic cultures. We did not observe significant differences in the timeline of neural induction and NSC derivation between the patient and control line, nor amongst the patient lines, although we report considerable variability in the efficiency of dopaminergic differentiation among patient lines. We performed whole genome expression analyses of the lines at each stage of differentiation (fibroblast, iPSC, NSC, and dopaminergic culture) in an attempt to identify alterations by large-scale evaluation. While gene expression profiling clearly distinguished cells at different stages of differentiation, no mutation-specific clustering or difference was observed, though consistent changes in patient lines were detected in genes associated mitochondrial biology. We further examined gene expression in a stress model (MPTP-induced dopaminergic neuronal death) using two clones from the SNCA triplication line, and detected changes in genes associated with mitophagy. Our data suggested that even a well-characterized line of a monogenic disease may not be sufficient to determine the cause or mechanism of the disease, and highlights the need to use more focused strategies for large-scale data analysis.

Mam33 promotes cytochrome c oxidase subunit I translation in Saccharomyces cerevisiae mitochondria

Expression of genes encoded by the mitochondrial genome is dependent on gene-specific translational activators. Mam33, the yeast homologue of p32/gC1qR/C1QBP/HABP1, promotes the translation of Cox1, a core catalytic subunit of respiratory chain complex IV.

Three mitochondrial DNA–encoded proteins, Cox1, Cox2, and Cox3, comprise the core of the cytochrome c oxidase complex. Gene-specific translational activators ensure that these respiratory chain subunits are synthesized at the correct location and in stoichiometric ratios to prevent unassembled protein products from generating free oxygen radicals. In the yeast Saccharomyces cerevisiae, the nuclear-encoded proteins Mss51 and Pet309 specifically activate mitochondrial translation of the largest subunit, Cox1. Here we report that Mam33 is a third COX1 translational activator in yeast mitochondria. Mam33 is required for cells to adapt efficiently from fermentation to respiration. In the absence of Mam33, Cox1 translation is impaired, and cells poorly adapt to respiratory conditions because they lack basal fermentative levels of Cox1.

Dose-Dependent AMPK-Dependent and Independent Mechanisms of Berberine and Metformin Inhibition of mTORC1, ERK, DNA Synthesis and Proliferation in Pancreatic Cancer Cells

Natural products represent a rich reservoir of potential small chemical molecules exhibiting anti-proliferative and chemopreventive properties. Here, we show that treatment of pancreatic ductal adenocarcinoma (PDAC) cells (PANC-1, MiaPaCa-2) with the isoquinoline alkaloid berberine (0.3-6 µM) inhibited DNA synthesis and proliferation of these cells and delay the progression of their cell cycle in G1. Berberine treatment also reduced (by 70%) the growth of MiaPaCa-2 cell growth when implanted into the flanks of nu/nu mice. Mechanistic studies revealed that berberine decreased mitochondrial membrane potential and intracellular ATP levels and induced potent AMPK activation, as shown by phosphorylation of AMPK α subunit at Thr-172 and acetyl-CoA carboxylase (ACC) at Ser79. Furthermore, berberine dose-dependently inhibited mTORC1 (phosphorylation of S6K at Thr389 and S6 at Ser240/244) and ERK activation in PDAC cells stimulated by insulin and neurotensin or fetal bovine serum. Knockdown of α1 and α2 catalytic subunit expression of AMPK reversed the inhibitory effect produced by treatment with low concentrations of berberine on mTORC1, ERK and DNA synthesis in PDAC cells. However, at higher concentrations, berberine inhibited mitogenic signaling (mTORC1 and ERK) and DNA synthesis through an AMPK-independent mechanism. Similar results were obtained with metformin used at doses that induced either modest or pronounced reductions in intracellular ATP levels, which were virtually identical to the decreases in ATP levels obtained in response to berberine. We propose that berberine and metformin inhibit mitogenic signaling in PDAC cells through dose-dependent AMPK-dependent and independent pathways.

Mitochondria: a possible nexus for the regulation of energy homeostasis by the endocannabinoid system?

The endocannabinoid system (ECS) regulates numerous cellular and physiological processes through the activation of receptors targeted by endogenously produced ligands called endocannabinoids. Importantly, this signaling system is known to play an important role in modulating energy balance and glucose homeostasis. For example, current evidence indicates that the ECS becomes overactive during obesity whereby its central and peripheral stimulation drives metabolic processes that mimic the metabolic syndrome. Herein, we examine the role of the ECS in modulating the function of mitochondria, which play a pivotal role in maintaining cellular and systemic energy homeostasis, in large part due to their ability to tightly coordinate glucose and lipid utilization. Because of this, mitochondrial dysfunction is often associated with peripheral insulin resistance and glucose intolerance as well as the manifestation of excess lipid accumulation in the obese state. This review aims to highlight the different ways through which the ECS may impact upon mitochondrial abundance and/or oxidative capacity and, where possible, relate these findings to obesity-induced perturbations in metabolic function. Furthermore, we explore the potential implications of these findings in terms of the pathogenesis of metabolic disorders and how these may be used to strategically develop therapies targeting the ECS.

Ceramide inhibits insulin-stimulated Akt phosphorylation through activation of Rheb/mTORC1/S6K signaling in skeletal muscle

Ceramide is a negative regulator of insulin activity. At the molecular level, it causes a decrease in insulin-stimulated Akt Ser473 phosphorylation in C2C12 myotubes. Interestingly, we found that the phosphorylation of S6K at Thr389 was increased under the same conditions. Utilizing both rapamycin to inhibit mTORC1 activity and shRNA to knock down Rheb, we demonstrated that the decrease in Akt Ser473 phosphorylation stimulated by insulin after C2-ceramide incubation can be prevented. The mechanism by which C2-ceramide impairs signaling would seem to involve a negative feedback of activated S6K via phosphorylation of insulin receptor substrate-1 at Ser636/639, since S6K inhibitor can block this phenomenon. Finally, rapamycin treatment was found not to affect C2-ceramide-induced PKCζ activation, suggesting that the pathway revealed in this study is parallel to the one involving PKCζ activation. We proposed a novel pathway/mechanism involving Rheb/mTORC1/S6K signaling to explain how C2-ceramide impairs insulin signaling via Akt phosphorylation. The existence of multiple pathways involved in insulin signaling impairment by C2-ceramide treatment implies that different strategies might be needed to ameliorate insulin resistance caused by C2-ceramide.

The plant decapeptide OSIP108 prevents copper-induced apoptosis in yeast and human cells

We previously identified the Arabidopsis thaliana-derived decapeptide OSIP108, which increases tolerance of plants and yeast cells to oxidative stress. As excess copper (Cu) is known to induce oxidative stress and apoptosis, and is characteristic for the human pathology Wilson disease, we investigated the effect of OSIP108 on Cu-induced toxicity in yeast. We found that OSIP108 increased yeast viability in the presence of toxic Cu concentrations, and decreased the prevalence of Cu-induced apoptotic markers. Next, we translated these results to the human hepatoma HepG2 cell line, demonstrating anti-apoptotic activity of OSIP108 in this cell line. In addition, we found that OSIP108 did not affect intracellular Cu levels in HepG2 cells, but preserved HepG2 mitochondrial ultrastructure. As Cu is known to induce acid sphingomyelinase activity of HepG2 cells, we performed a sphingolipidomic analysis of OSIP108-treated HepG2 cells. We demonstrated that OSIP108 decreased the levels of several sphingoid bases and ceramide species. Moreover, exogenous addition of the sphingoid base dihydrosphingosine abolished the protective effect of OSIP108 against Cu-induced cell death in yeast. These findings indicate the potential of OSIP108 to prevent Cu-induced apoptosis, possibly via its effects on sphingolipid homeostasis.

Decreased autophagy in rat heart induced by anti-β1-adrenergic receptor autoantibodies contributes to the decline in mitochondrial membrane potential

It has been recognized that changes in mitochondrial structure plays a key role in development of cardiac dysfunction, and autophagy has been shown to exert maintenance of mitochondrial homeostasis effects. Our previous study found that anti-β₁-adrenergic receptor autoantibodies (β₁-AABs) could lead to cardiac dysfunction along with abnormalities in mitochondrial structure. The present study tested the hypothesis that β₁-AABs may induce the decline in mitochondrial membrane potential (ΔΨm) by suppression of cardiac autophagy, which contributed to cardiac dysfunction. Male adult rats were randomized to receive a vehicle or peptide corresponding to the second extracellular loop of the β₁ adrenergic receptor (β₁-AAB group, 0.4 μg/g every two weeks for 12 weeks) and treated with rapamycin (RAPA, an autophagy agonist) at 5 mg/kg/day for two days before detection. At the 4th week, 8th week and 12th week of active immunization, the rats were sacrificed and cardiac function and the levels of cardiac LC3 and Beclin-1 were detected. ΔΨm in cardiac myocytes was determined by myocardial radionuclide imaging technology and JC-1 staining. In the present study, β₁-AABs caused cardiac dysfunction, reduced ΔΨm and decreased cardiac autophagy. Treatment with RAPA markedly attenuated β₁-AABs-induced cardiac injury evidenced by recovered ΔΨm. Taken together, these results suggested that β₁-AABs exerted significant decreased ΔΨm, which may contribute to cardiac dysfunction, most likely by decreasing cardiac autophagy in vivo. Moreover, myocardial radionuclide imaging technology may be needed to assess the risk in developing cardiac dysfunction for the people who have β₁-AABs in their blood.

Cadmium and cellular signaling cascades: interactions between cell death and survival pathways

Cellular stress elicited by the toxic metal Cd(2+) does not coerce the cell into committing to die from the onset. Rather, detoxification and adaptive processes are triggered concurrently, allowing survival until normal function is restored. With high Cd(2+), death pathways predominate. However, if sublethal stress levels affect cells for prolonged periods, as in chronic low Cd(2+) exposure, adaptive and survival mechanisms may deregulate, such that tumorigenesis ensues. Hence, death and malignancy are the two ends of a continuum of cellular responses to Cd(2+), determined by magnitude and duration of Cd(2+) stress. Signaling cascades are the key factors affecting cellular reactions to Cd(2+). This review critically surveys recent literature to outline major features of death and survival signaling pathways as well as their activation, interactions and cross talk in cells exposed to Cd(2+). Under physiological conditions, receptor activation generates 2nd messengers, which are short-lived and act specifically on effectors through their spatial and temporal dynamics to transiently alter effector activity. Cd(2+) recruits physiological 2nd messenger systems, in particular Ca(2+) and reactive oxygen species (ROS), which control key Ca(2+)- and redox-sensitive molecular switches dictating cell function and fate. Severe ROS/Ca(2+) signals activate cell death effectors (ceramides, ASK1-JNK/p38, calpains, caspases) and/or cause irreversible damage to vital organelles, such as mitochondria and endoplasmic reticulum (ER), whereas low localized ROS/Ca(2+) levels act as 2nd messengers promoting cellular adaptation and survival through signal transduction (ERK1/2, PI3K/Akt-PKB) and transcriptional regulators (Ref1-Nrf2, NF-κB, Wnt, AP-1, bestrophin-3). Other cellular proteins and processes targeted by ROS/Ca(2+) (metallothioneins, Bcl-2 proteins, ubiquitin-proteasome system, ER stress-associated unfolded protein response, autophagy, cell cycle) can evoke death or survival. Hence, temporary or permanent disruptions of ROS/Ca(2+) induced by Cd(2+) play a crucial role in eliciting, modulating and linking downstream cell death and adaptive and survival signaling cascades.

Ceramides in the pathophysiology of the anterior segment of the eye

PURPOSE

Sphingolipid (SL) research reached a peak in the past years. Yet this positive trend was not evident for eye research as the relative number of studies centered on SLs is decreasing. Our aim is to encourage the inclusion of SL metabolites in studies of ocular pathophysiology by summarizing recent findings and current awareness concerning ceramides in the anterior segment of the eye.

METHODS

Review of literature relating to ceramides as bioactive lipids and the extent to which their particular nature was investigated in ocular pathophysiology.

RESULTS

Ceramides are rare but indispensable lipids that influence cellular responses through their effects on membrane biophysical properties or direct interaction with target proteins. Their biological significance is increased by variability and adaptability as there are tens of enzymes designed to modulate their function. The eye offers a set of unique environments where ceramides or other SLs have not been extensively studied. Not surprisingly, ceramides were associated with apoptosis in the metabolically active tissues, while little is known about its effects on the biophysical properties of the tears or lens lipids. More so, there are still aspects of the ocular homeostasis control where SLs contribution has not been investigated to date (e.g. pathogen aggression).

CONCLUSIONS

Ceramides and SL metabolism still receive increasing attention and have proven to be a significant metabolite in many research fields (e.g. cancer, stress response and inflammation) and there are yet many questions that they will aid answer. With the present work, we seek to increase awareness of these lipids also in eye research and to highlight their importance as common regulators of various diseases.

Bioactive lipids-based pH sensitive micelles for co-delivery of doxorubicin and ceramide to overcome multidrug resistance in leukemia

PURPOSE

Construction of a novel PEGylated bioactive lipids-based micelle system for co-delivery of doxorubicin (DOX) and short chain ceramide (C6-ceramide) to overcome multidrug resistance in leukemia.

METHODS

The PEGylated bioactive lipids-based micelle system was constructed via electrostatic and hydrophobic interactions among DOX, bioactive lipids PazPC and C6-ceramide. The micellar formulation was characterized in terms of size, zeta potential, stability and release behavior, etc., and in vitro cytotoxicity, in vivo antitumor efficacy and the underlying mechanism were further evaluated.

RESULTS

This novel micellar system showed small size (~15 nm), high drug encapsulation efficiency (>90%), good stability and endosomal acid-triggered release of DOX. Synergistic cytotoxic effects between DOX and bioactive lipid C6-ceramide in P-gp overexpressing drug resistant leukemia P388/ADR cells were observed. The mechanistic studies demonstrated that modulation of drug efflux system and induction of apoptotic effects by lipids were responsible for the synergistic effects between DOX and C6-ceramide in drug resistant leukemia P388/ADR cells. Using an in-vivo P388/ADR leukemia mouse model, the median survival time of the DOX-loaded PEGylated micelles with PazPC and C6-ceramide as major components was significantly greater than that of free DOX and control group.

CONCLUSIONS

We developed a novel pH sensitive bioactive lipids-based micellar formulation which could potentially be useful in delivering chemotherapeutic drug DOX and provide a novel strategy to increase the therapeutic index for drug resistant leukemia treatment.

JNK1/2 regulates ER-mitochondrial Ca2+ cross-talk during IL-1β-mediated cell death in RINm5F and human primary β-cells

Elevated interleukin-1β (IL-1β) induces apoptosis in pancreatic β-cells through endoplasmic reticulum (ER) stress induction and subsequent c-jun-N-terminal kinase 1/2 (JNK1/2) activation. In earlier work we showed that JNK1/2 activation is initiated before ER stress and apoptotic induction in response to IL-1β. However, the detailed regulatory mechanisms are not completely understood. Because the ER is the organelle responsible for Ca(2+) handling and storage, here we examine the effects of IL-1β on cellular Ca(2+) movement and mitochondrial dysfunction and evaluate the role of JNK1/2. Our results show that in RINm5F cells and human primary β-cells, IL-1β alters mitochondrial membrane potential, mitochondrial permeability transition pore opening, ATP content, and reactive oxygen species production and these alterations are preceded by ER Ca(2+) release via IP3R channels and mitochondrial Ca(2+) uptake. All these events are prevented by JNK1/2 small interfering RNA (siRNA), indicating the mediating role of JNK1/2 in IL-1β-induced cellular alteration. This is accompanied by IL-1β-induced apoptosis, which is prevented by JNK1/2 siRNA and the IP3R inhibitor xestospongin C. This suggests a regulatory role of JNK1/2 in modulating the ER-mitochondrial-Ca(2+) axis by IL-1β in apoptotic cell death.

Hrk mediates 2-methoxyestradiol-induced mitochondrial apoptotic signaling in prostate cancer cells

Prostate cancer is one of the most prevalent cancers in males and ranks as the second most common cause of cancer-related deaths. 2-methoxyestradiol (2-ME), an endogenous estrogen metabolite, is a promising anticancer agent for various types of cancers. Although 2-ME has been shown to activate c-Jun-NH2-kinase (JNK) and mitochondrial-dependent apoptotic signaling pathways, the underlying mechanisms, including downstream effectors, remain unclear. Here, we report that the human Bcl-2 homology 3 (BH3)-only protein harakiri (Hrk) is a critical effector of 2-ME-induced JNK/mitochondria-dependent apoptosis in prostate cancer cells. Hrk mRNA and protein are preferentially upregulated by 2-ME, and Hrk induction is dependent on the JNK activation of c-Jun. Hrk knockdown prevents 2-ME-mediated apoptosis by attenuating the decrease in mitochondrial membrane potential, subsequent cytochrome c (cyt c) release, and caspase activation. Involvement of the proapoptotic protein Bak in this process suggested the possible interaction between Hrk and Bak. Thus, Hrk activation by 2-ME or its overexpression displaced Bak from the complex with antiapoptotic protein Bcl-xL, whereas deletion of the Hrk BH3 domain abolished its interaction with Bcl-xL, reducing the proapoptotic function of Hrk. Finally, Hrk is also involved in the 2-ME-mediated reduction of X-linked inhibitor of apoptosis through Bak activation in prostate cancer cells. Together, our findings suggest that induction of the BH3-only protein Hrk is a critical step in 2-ME activation of the JNK-induced apoptotic pathway, targeting mitochondria by liberating proapoptotic protein Bak.

p53 and Ceramide as Collaborators in the Stress Response

The sphingolipid ceramide mediates various cellular processes in response to several extracellular stimuli. Some genotoxic stresses are able to induce p53-dependent ceramide accumulation leading to cell death. However, in other cases, in the absence of the tumor suppressor protein p53, apoptosis proceeds partly due to the activity of this "tumor suppressor lipid", ceramide. In the current review, we describe ceramide and its roles in signaling pathways such as cell cycle arrest, hypoxia, hyperoxia, cell death, and cancer. In a specific manner, we are elaborating on the role of ceramide in mitochondrial apoptotic cell death signaling. Furthermore, after highlighting the role and mechanism of action of p53 in apoptosis, we review the association of ceramide and p53 with respect to apoptosis. Strikingly, the hypothesis for a direct interaction between ceramide and p53 is less favored. Recent data suggest that ceramide can act either upstream or downstream of p53 protein through posttranscriptional regulation or through many potential mediators, respectively.

Ceramide--antiestrogen nanoliposomal combinations--novel impact of hormonal therapy in hormone-insensitive breast cancer

Although the sphingolipid ceramide exhibits potent tumor suppressor effects, efforts to harness this have been hampered by poor solubility, uptake, bioavailability, and metabolic conversion. Therefore, identification of avenues to improve efficacy is necessary for development of ceramide-based therapies. In this study, we used mutant p53, triple-negative breast cancer (TNBC) cells, a type of breast cancer highly refractory to treatment, and cell-permeable nanoliposomal C6-ceramide in conjunction with the antiestrogen tamoxifen, which has been shown to be an effective modulator of ceramide metabolism. We show for the first time that nanoliposomal tamoxifen enhances nanoliposomal C6-ceramide cytotoxicity in cultured TNBC cells, a response that was accompanied by induction of cell-cycle arrest at G(1) and G(2), caspase-dependent induction of DNA fragmentation, and enhanced mitochondrial and lysosomal membrane permeability at 18 and 2 hours, respectively. Tamoxifen metabolites were also effective. Only tamoxifen promoted lysosomal membrane permeability. In addition, we show for the first time that tamoxifen inhibits acid ceramidase, as measured in intact cell assays; this effect was irreversible. Together, our findings show that tamoxifen magnifies the antiproliferative effects of C6-ceramide via combined targeting of cell-cycle traverse and lysosomal and mitochondrial integrity. We adduce that C6-ceramide-induced apoptosis is amplified by tamoxifen's impact on lysosomes and perhaps accompanying inhibition of acid ceramidase, which could result in decreased levels of sphingosine 1-phosphate. This drug regimen could serve as a promising therapy for chemoresistant and triple-negative types of breast cancer, and thus represents an indication for tamoxifen, irrespective of estrogen receptor status.

Multifunctional protein APPL2 contributes to survival of human glioma cells

Some endocytic proteins have recently been shown to play a role in tumorigenesis. In this study, we demonstrate that APPL2, an adapter protein with known endocytic functions, is upregulated in 40% cases of glioblastoma multiforme, the most common and aggressive cancer of the central nervous system. The silencing of APPL2 expression by small interfering RNAs (siRNAs) in glioma cells markedly reduces cell survival under conditions of low growth factor availability and enhances apoptosis (measured by executor caspase activity). Long‐term depletion of APPL2 by short hairpin RNAs (shRNAs), under regular growth factor availability, suppresses the cell transformation abilities, assessed by inhibited colony formation in soft agar and by reduced xenograft tumor growth in vivo. At the molecular level, the negative effect of APPL2 knockdown on cell survival is not due to the alterations in AKT or GSK3β activities which were reported to be modulated by APPL proteins. Instead, we attribute the reduced cell survival upon APPL2 depletion to the changes in gene expression, in particular to the upregulation of apoptosis‐related genes, such as UNC5B (a proapoptotic dependence receptor) and HRK (harakiri, an activator of apoptosis, which antagonizes anti‐apoptotic function of Bcl2). In support of this notion, the loss of glioma cell survival upon APPL2 knockdown can be rescued either by an excess of netrin‐1, the prosurvival ligand of UNC5B or by simultaneous silencing of HRK. Consistently, APPL2 overexpression reduces expression of HRK and caspase activation in cells treated with apoptosis inducers, resulting in the enhancement of cell viability. This prosurvival activity of APPL2 is independent of its endosomal localization. Cumulatively, our data indicate that a high level of APPL2 protein might enhance glioblastoma growth by maintaining low expression level of genes responsible for cell death induction.

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APPL2 protein levels are elevated in 40% cases of glioblastoma multiforme.

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Overexpression of APPL2 exhibits cytoprotective effects in glioma cells.

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APPL2 depletion reduces survival and transformation abilities of glioma cells.

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Silencing of APPL2 promotes expression of proapoptotic genes HRK and UNC5B.

Expression of NADPH oxidase (NOX) 5 in rabbit corneal stromal cells

Purpose

To determine whether NOX 5 is expressed in rabbit corneal stromal cells (RCSC). NADPH oxidases (NOXes) are enzymes that preferentially use NADPH as a substrate and generate superoxide. Several isoforms of NOXes function as multi-protein complexes while NOX5 and DUOXs do not require the accessory proteins for their activity and possess calcium binding EF hands.

Methods

Human NOX5 primers were used to amplify the rabbit NOX5 by RT-PCR. Amplified product was sequenced to confirm its identity. The protein encoded by the NOX5 was identified by western blot analysis. NOX5 siRNA was used to reduce transcript, protein, and calcium stimulated activity. In silico analyses were performed to establish the putative structure, functions, and evolution of rabbit NOX5.

Results

NOX activity was measured in RCSC with NADPH rather than NADH as a substrate. RT-PCR with NOX5 primers amplified 288 bp product using RCSC cDNA, which, when sequenced, confirmed its identity to human NOX5 mRNA. This sequence was used to predict the rabbit (Oryctolagus cuniculus) NOX5 gene. NOX5 siRNA reduced amounts of NOX5 mRNA in RCSC and reduced ionomycin stimulated superoxide production. A protein of about 65 to 70 kDa encoded by the NOX5 was detected by western blot analysis. In silico analysis predicted a putative rabbit NOX5 protein containing 801 amino acids. Motif searches predicted the presence of at least 3 putative EF-hands in N-terminus and a NOX domain in C terminal region.

Conclusions

The data document that the NOX5 gene was expressed in cells of lagomorphs unlike rodents, making the rabbit an interesting model to study NOX5 functions. The activity of the rabbit NOX5 was calcium stimulated, a trait of NOX5 in general. NOX5 may also prove to be a useful genetic marker for studying the taxonomic position of lagomorphs and the Glires classification.

Genetic analysis in Drosophila reveals a role for the mitochondrial protein p32 in synaptic transmission

Mitochondria located within neuronal presynaptic terminals have been shown to play important roles in the release of chemical neurotransmitters. In the present study, a genetic screen for synaptic transmission mutants of Drosophila has identified the first mutation in a Drosophila homolog of the mitochondrial protein P32. Although P32 is highly conserved and has been studied extensively, its physiological role in mitochondria remains unknown and it has not previously been implicated in neural function. The Drosophila P32 mutant, referred to as dp32^EC1, exhibited a temperature-sensitive (TS) paralytic behavioral phenotype. Moreover, electrophysiological analysis at adult neuromuscular synapses revealed a TS reduction in the amplitude of excitatory postsynaptic currents (EPSC) and indicated that dP32 functions in neurotransmitter release. These studies are the first to address P32 function in Drosophila and expand our knowledge of mitochondrial proteins contributing to synaptic transmission.