Perfluorooctanoic acid induces oxidative damage and mitochondrial dysfunction in pancreatic β-cells

Several environmental contaminants have been linked to the development of diabetes and increased diabetes‑associated mortality. Perfluorooctanoic acid (PFOA) is a widely used perfluoroalkane found in surfactants and lubricants, and in processing aids used in the production of polymers. Furthermore, PFOA has been detected in humans, wildlife and the environment. The present study investigated the toxic effects of PFOA on rat pancreatic β‑cell‑derived RIN‑m5F cells. Cell viability, apoptosis, reactive oxygen and nitrogen species, cytokine release and mitochondrial parameters, including membrane potential collapse, reduced adenosine triphosphate levels, cardiolipin peroxidation and cytochrome c release were assessed. PFOA significantly decreased RIN‑m5F cell viability and increased apoptosis. Exposure to PFOA increased the formation of reactive oxygen species, mitochondrial superoxide, nitric oxide and proinflammatory cytokines. Furthermore, PFOA induced mitochondrial membrane potential collapse and reduced adenosine triphosphate levels, cardiolipin peroxidation and cytochrome c release. These results indicate that PFOA is associated with the induction of apoptosis in RIN-m5F cells, and induces cytotoxicity via increased oxidative stress and mitochondrial dysfunction.

Perfluorooctanoic acid induces mitochondrial dysfunction in MC3T3-E1 osteoblast cells

Perfluorooctanoic acid (PFOA), a stable organic perfluorinated compound, is an emerging persistent organic pollutant, found widely in human and wildlife populations. Recent evidence suggests that exposure to environmental toxicants can be associated with higher risks of osteoporosis and fractures. We studied the cellular toxicology of PFOA in MC3T3-E1osteoblast cells. To examine the effect of PFOA, we measured cell viability, reactive oxygen species (ROS), mitochondrial superoxide, and mitochondrial parameters including adenosine triphosphate (ATP) level, mitochondrial membrane potential (MMP), cardiolipin content, and cytochrome c release in MC3T3-E1 cells. Incubating MC3T3-E1 cells in different concentrations of PFOA for 48 h resulted in a concentration-dependent decrease in cell viability and significant inductions of ROS and mitochondrial superoxide. Moreover, PFOA induced MMP collapse, cardiolipin peroxidation, cytochrome c release, and decreased ATP levels, which in turn induced apoptosis or necrosis. When osteoblast differentiation markers were assessed, PFOA treatment caused a significant reduction in alkaline phosphatase activity, collagen synthesis, and mineralization in the cells. In summary, we found an ROS- and mitochondria-mediated pathway for the induction of cell damage by PFOA in MC3T3-E1 cells. Together, our results indicate that mitochondrial toxicity could be a plausible mechanism for the toxic effects of PFOA on osteoblast function.

Uppsala Consensus Statement on Environmental Contaminants and the Global Obesity Epidemic

Summary: From the lectures presented at the 2nd International Workshop on Obesity and Environmental Contaminants, which was held in Uppsala, Sweden, on 8–9 October 2015, it became evident that the findings from numerous animal and epidemiological studies are consistent with the hypothesis that environmental contaminants could contribute to the global obesity epidemic. To increase awareness of this important issue among scientists, regulatory agencies, politicians, chemical industry management, and the general public, the authors summarize compelling scientific evidence that supports the hypothesis and discuss actions that could restrict the possible harmful effects of environmental contaminants on obesity.

Ethanol extract of Bupleurum falcatum and saikosaponins inhibit neuroinflammation via inhibition of NF-κB

ETHNOPHARMACOLOGICAL RELEVANCE

The root of Bupleurum falcatum L. (BF) has been used in traditional Korean and Chinese medicines for over 2000 years to treat infections, fever, and chronic liver diseases. Among the many active compounds in BF ethanol extract (BFE), saikosaponins exert pharmacological activities including anti-inflammatory effects. Activated microglial cells release a variety of pro-inflammatory substances, leading to neuronal cell death and neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease. The aim of the present study was to investigate the mechanism of the anti-neuroinflammatory effects of BFE using lipopolysaccharide (LPS)-stimulated microglial cells and LPS-intraperitoneal injected C57BL/6 mice.

MATERIALS AND METHODS

Dried roots of BF were extracted with 70% ethanol (tenfold volume) on a stirring plate for 24h at room temperature to prepare BFE. Pure saikosaponins (SB3, SB4, and SD) were prepared by solvent extraction and column chromatography fractionation. BV2 murine microglial cells were treated with BFE or saikosaponins for 4h and stimulated with LPS. Generation of nitric oxide (NO), inflammatory cytokines, and reactive oxygen species (ROS) from activated microglial cells were monitored. The effects of BFE on NF-κB activation were determined using RT-PCR, reporter assay, and immunostaining. The in vivo effects of BFE were also assessed by immunohistochemical staining of tissue sections from LPS-injected mouse brains.

RESULTS

Treatment with BFE or saikosaponins dose-dependently attenuated LPS-induced production of NO, iNOS mRNA, and ROS by 30-50%. They reduced LPS-mediated increases in the mRNA levels of IL-6, IL-1β, and TNF-α by approximately 30-70% without affecting cell viability, and decreased LPS-mediated NF-κB activity via reducing p65/RELA mRNA, transcriptional activity, and nuclear localization of NF-κB. BFE also reduced LPS-induced activation of microglia and astrocytes in the hippocampus and substantia nigra of LPS-injected mice.

CONCLUSION

Our data suggest that BFE may be effective for reducing neuroinflammation-mediated neurodegeneration through suppressing NF-κB-mediated inflammatory pathways.

Cyclophilin A regulates JNK/p38-MAPK signaling through its physical interaction with ASK1

Cyclophilin A (CypA), a member of the immunophilin family, is predominantly localized in the cytoplasm. The peptidylprolyl isomerase (PPIase) activity of CypA has been demonstrated to be involved in diverse cellular processes, including intracellular protein trafficking, mitochondrial function, pre-mRNA processing, and maintenance of multiprotein complex stability. In this study, we have demonstrated that CypA regulates apoptosis signaling-regulating kinase 1 (ASK1) through its direct binding. ASK1 is a member of MAPK kinase kinase (MAP3K) family, and selectively activates both JNK and p38 MAPK pathways. Here, we also report that CypA negatively regulates phosphorylation of ASK1 at Ser966, and that CypA reduces ASK1 and its downstream kinases of the JNK and p38 signaling. ASK1 is known to induce caspase-3 activation and apoptosis, and CypA inhibited ASK1-mediated apoptosis by decrease in caspase-3 activity under cellular stress conditions. Overall, we conclude that CypA negatively regulates ASK1 functions by its physical interaction with ASK1.

Serum aryl hydrocarbon receptor ligand activity is associated with insulin resistance and resulting type 2 diabetes

AIMS

Dioxin or dioxin-like compounds are ligands of the aryl hydrocarbon receptor (AhR), which is a ligand-activated nuclear transcription factor. There are limited studies about the association of serum AhR ligand activities and T2DM. Our objective was to investigate the association of serum AhR ligand activities with T2DM and its related metabolic parameters.

METHODS

This case-control study involved 83 subjects with T2DM as well as age-, sex-, and body mass index (BMI)-matched subjects with impaired glucose tolerance (IGT, n = 130) and normal glucose tolerance (NGT, n = 83). Serum AhR ligand activities were measured using a cell-based AhR ligand assay and standardized as 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TCDDeq, pmol/l).

RESULTS

The T2DM group had the highest AhR ligand activities compared to the IGT and NGT groups [median (interquartile range), 68.1 (53.1, 81.5), 60.2 (45.8, 75.1), and 53.3 (46.1, 63.7) pmol/l, respectively; P = 0.003]. In the multivariate analysis, the log2-transformed TCDDeq levels were significantly associated with the risk of T2DM after adjusting for age, sex, and BMI (odds ratio 2.26, 95 % confidence interval 1.34-3.82; P = 0.002). In nondiabetic subjects, serum AhR ligand activities showed a positive correlation with fasting glucose and insulin concentrations and the homeostasis model assessment of insulin resistance, but showed a negative correlation with adiponectin concentrations.

CONCLUSIONS

Serum AhR ligand activities were higher in the T2DM group and were correlated with the parameters of insulin resistance. Further investigation is required to elucidate the causal relationship between AhR ligand activity and T2DM.

Umbilical cord mesenchymal stromal cells affected by gestational diabetes mellitus display premature aging and mitochondrial dysfunction

Human umbilical cord mesenchymal stromal cells (hUC-MSCs) of Wharton's jelly origin undergo adipogenic, osteogenic, and chondrogenic differentiation in vitro. Recent studies have consistently shown their therapeutic potential in various human disease models. However, the biological effects of major pregnancy complications on the cellular properties of hUC-MSCs remain to be studied. In this study, we compared the basic properties of hUC-MSCs obtained from gestational diabetes mellitus (GDM) patients (GDM-UC-MSCs) and normal pregnant women (N-UC-MSCs). Assessments of cumulative cell growth, MSC marker expression, cellular senescence, and mitochondrial function-related gene expression were performed using a cell count assay, senescence-associated β-galactosidase staining, quantitative real-time reverse transcription-polymerase chain reaction, immunoblotting, and cell-based mitochondrial functional assay system. When compared with N-UC-MSCs, GDM-UC-MSCs showed decreased cell growth and earlier cellular senescence with accumulation of p16 and p53, even though they expressed similar levels of CD105, CD90, and CD73 MSC marker proteins. GDM-UC-MSCs also displayed significantly lower osteogenic and adipogenic differentiation potentials than N-UC-MSCs. Furthermore, GDM-UC-MSCs exhibited a low mitochondrial activity and significantly reduced expression of the mitochondrial function regulatory genes ND2, ND9, COX1, PGC-1α, and TFAM. Here, we report intriguing and novel evidence that maternal metabolic derangement during gestation affects the biological properties of fetal cells, which may be a component of fetal programming. Our findings also underscore the importance of the critical assessment of the biological impact of maternal-fetal conditions in biological studies and clinical applications of hUC-MSCs.

Preparation and application of graphene-poly (diallyldimethylammoniumchloride)-iron oxide nanoparticles buckypaper for hydrogen peroxide detection

We have reported the preparation and characterization of a novel, freestanding, paper-like graphene (G)-poly(diallyldimethylammoniumchloride) (PDDA)-Fe3O4 nanoparticles (NPs) composite. This G-based flexible buckypaper (BP) composed of stacked G-PDDA-NP platelets exhibited excellent mechanical properties, superior electrical properties, and enzyme mimetic activity, making it potentially suitable for in electrochemical sensor applications. The negatively charged NPs were immobilized on positively charged G-PDDA through the electrostatic interaction to form nanoscale G-PDDA-NP platelets, which were further assembled by flow-directed assembly to form BP. The resulting BP has macroscopic flexibility and stiffness due to the van der Waals forces between nanoscale G-PDDA-NP platelets and interlocking-tile arrangement of the platelets. The morphology and structure of the individual G-PDDA-NP platelets and the resulting BP were analyzed by using AFM, SEM and EDX. The BP was attached to an Au or Pt electrode to construct a non-enzyme H2O2 chemical sensor. The NPs acted as a "spacer" to increase the distance between the G sheets and decrease the chances of formation of a stacked graphitic structure, thereby increasing the surface area of the G electrode. The Fe3O4 NPs immobilized and embedded in the BP have intrinsic enzyme mimetic activity like natural peroxidase. The high surface area and excellent electrical conductivity of G improved the catalytic properties of NPs. The obtained H2O2, chemical sensor exhibited prominent electrocatalytic activity towards H2O2, with a wide linear range from 10 ppm (approximately 0.3 mM) to 800 ppm (approximately 23 mM), correlation coefficient of 0.986, and a high sensitivity of 218 microA mM(-1) x cm(-2). Such low-cost G-PDDA-NP composite BPs prepared by facile methods pave way towards novel sensors with better performance.

Novel cell-based assay reveals associations of circulating serum AhR-ligands with metabolic syndrome and mitochondrial dysfunction

Serum concentrations of environmental pollutants have been positively correlated with diabetes and metabolic syndrome in epidemiologic studies. In turn, abnormal mitochondrial function has been associated with the diseases. The relationships between these variables, however, have not been studied. We developed novel cell-based aryl hydrocarbon receptor (AhR) agonist bioassay system without solvent extraction process and analyzed whether low-dose circulating AhR ligands in human serum are associated with parameters of metabolic syndrome and mitochondrial function. Serum AhR ligand activities were measured as serum 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalent (sTCDDeq) in pM using 10 μL human sera from 97 Korean participants (47 with glucose intolerance and 50 matched controls, average age of 46.6 ± 9.9 years, 53 male and 45 female). sTCDDeq were higher in participants with glucose intolerance than normal controls and were positively associated (P < 0.01) with obesity, blood pressure, serum triglyceride, and fasting glucose, but not with HDL-cholesterol. Body mass index was in a positive linear relationship with serum AhR ligands in healthy participants. When myoblast cells were incubated with human sera, ATP generating power of mitochondria became impaired in an AhR ligand concentration-dependent manner. Our results support that circulating AhR ligands may directly reduce mitochondrial function in tissues, leading to weight gain, glucose intolerance, and metabolic syndrome. Our rapid cell-based assay using minute volume of human serum may provide one of the best monitoring systems for circulating AhR ligands, good clinical biomarkers for the progress of disease and therapeutic efficacy.

Serum arylhydrocarbon receptor transactivating activity is elevated in type 2 diabetic patients with diabetic nephropathy

Aims/Introduction

Evidence is emerging that exposure to persistent organic pollutants (POPs) is a risk factor for obesity‐related diseases and for diabetes mellitus (DM). We found that POPs could be measured by a cell‐based arylhydrocarbon receptor (AhR)‐dependent reporter assay. We tested if serum AhR transactivating (AHRT) activities are a risk factor for diabetic nephropathy in people with type 2 diabetes.

Materials and Methods

We enrolled diabetic patients with normoalbuminuria (n = 36), microalbuminuria (n = 29), macroalbuminuria (n = 8) and end‐stage renal disease (n = 31). Sera were tested for their AHRT activities, which were standardized by an AhR ligand, 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin (TCDD) and expressed as TCDD equivalents (TCDDeq pmol/L).

Results

Mean serum AHRT activities were higher in patients with microalbuminuria (40.1 ± 7.1 pmol/L), macroalbuminuria (37.4 ± 5.5 pmol/L) and end‐stage renal disease (59.1 ± 20.0 pmol/L) than in subjects with normoalbuminuria (12.7 ± 5.4 pmol/L; P < 0.05 for all comparisons). Serum AhR ligands showed a correlation with estimated glomerular filtration rate (eGFR; r = −0.663, P < 0.001), serum creatinine level (r = 0.635, P < 0.001), systolic blood pressure (r = 0.223, P = 0.026), glycated hemoglobim (r = 0.339, P < 0.001) and diabetic duration (r = 0.394, P < 0.001). In a multiple regression analysis, diabetic nephropathy was found to be an independent risk factor for higher AHRT activity after controlling for the confounding factors.

Conclusions

The present findings suggest serum AHRT activity, thus serum AhR ligands, is a risk factor for diabetic nephropathy. Further studies are required to clarify if an accumulation of POPs in the body is causally related to diabetic nephropathy.

Circadian regulation of low density lipoprotein receptor promoter activity by CLOCK/BMAL1, Hes1 and Hes6

Low density lipoprotein receptor (LDLR) plays an important role in the cholesterol homeostasis. We examined the possible circadian regulation of LDLR and mechanism(s) underlying it. In mice, blood glucose and plasma triglyceride, total and high density lipoprotein cholesterol varied distinctively throughout a day. In addition, LDLR mRNA oscillated in the liver in a functional clock-dependent manner. Accordingly, analysis of human LDLR promoter sequence revealed three putative E-boxes, raising the possible regulation of LDLR expression by E-box-binding transcription factors. To test this possibility, human LDLR promoter reporter constructs were transfected into HepG2 cells and the effects of CLOCK/BMAL1, Hes1, and Hes6 expression were analyzed. It was found that positive circadian transcription factor complex CLOCK/BMAL1 upregulated human LDLR promoter activity in a serum-independent manner, while Hes family members Hes1 and Hes6 downregulated it only under serum-depleted conditions. Both effects were mapped to proximal promoter region of human LDLR, where mutation or deletion of well-known sterol regulatory element (SRE) abolished only the repressive effect of Hes1. Interestingly, hes6 and hes1 mRNA oscillated in an anti-phasic manner in the wild-type but not in the per1-/-per2 -/- mouse. Comparative analysis of mouse, rat and human hes6 genes revealed that three E-boxes are conserved among three species. Transfection and site-directed mutagenesis studies with hes6 reporter constructs confirmed that the third E-box in the exon IV is functionally induced by CLOCK/BMAL1. Taken together, these results suggest that LDLR expression is under circadian control involving CLOCK/BMAL1 and Hes family members Hes1 and Hes6.

Meal time shift disturbs circadian rhythmicity along with metabolic and behavioral alterations in mice

In modern society, growing numbers of people are engaged in various forms of shift works or trans-meridian travels. Such circadian misalignment is known to disturb endogenous diurnal rhythms, which may lead to harmful physiological consequences including metabolic syndrome, obesity, cancer, cardiovascular disorders, and gastric disorders as well as other physical and mental disorders. However, the precise mechanism(s) underlying these changes are yet unclear. The present work, therefore examined the effects of 6 h advance or delay of usual meal time on diurnal rhythmicities in home cage activity (HCA), body temperature (BT), blood metabolic markers, glucose homeostasis, and expression of genes that are involved in cholesterol homeostasis by feeding young adult male mice in a time-restrictive manner. Delay of meal time caused locomotive hyperactivity in a significant portion (42%) of subjects, while 6 h advance caused a torpor-like symptom during the late scotophase. Accordingly, daily rhythms of blood glucose and triglyceride were differentially affected by time-restrictive feeding regimen with concurrent metabolic alterations. Along with these physiological changes, time-restrictive feeding also influenced the circadian expression patterns of low density lipoprotein receptor (LDLR) as well as most LDLR regulatory factors. Strikingly, chronic advance of meal time induced insulin resistance, while chronic delay significantly elevated blood glucose levels. Taken together, our findings indicate that persistent shifts in usual meal time impact the diurnal rhythms of carbohydrate and lipid metabolisms in addition to HCA and BT, thereby posing critical implications for the health and diseases of shift workers.

Aptamer-based immunosensor on the ZnO nanorods networks

This paper presents the fabrication and characteristics of a new aptamer-based electrochemical immunosensor on the patterned zinc oxide nanorod networks (ZNNs) for detecting thrombin. Aptamers are single-stranded RNA or DNA sequence that binds to target materials with high specificity and affinity. An antibody-antigen-aptamer sandwich structure was employed to this immunosensor for detecting thrombin. First, hydrothermally grown ZNNs were patterned on the patterned 0.02 cm2 Au/Ti electrodes on a glass substrate by lift-off process. The high isoelectric point (IEP, approximately 9.5) of nanostructured ZnO makes it suitable for immobilizing proteins with low IEP. Then 5 microL of the 500 nM antibody was immobilized on the ZNNs electrode. 5 micro/L of the mixture of 1 microM aptamer labeled by ferrocene (Fc) and thrombin was dropped on the electrode for antibody-antigen binding. The peak oxidation currents of the immunosensors at various thrombin concentrations were measured by using cyclic voltammetry. The peak oxidation current was observed at 340 mV versus Ag/AgCl electrode, and the peak oxidation current increased linearly from 62.26 nA to 354.13 nA with the logarithmic concentration of thrombin in the range from 100 pM to 250 nM. Fabrication of an aptamer-based immunosensor for thrombin detection is a new attempt and the characteristics of the fabricated immunosensors showed that the fabricated aptamer-baded immunosensor worked electrochemically well and had a low detection limit (approximately 91.04 pM) and good selectivity.

Immunosensor based on the ZnO nanorod networks for the detection of H1N1 swine influenza virus

This paper presents an immunosensor fabricated on patterned zinc oxide nanorod networks (ZNNs) for detecting the H1N1 swine influenza virus (H1N1 SIV). Nanostructured ZnO with a high isoelectric point (IEP, approximately 9.5) possesses good absorbability for proteins with low IEPs. Hydrothermally grown ZNNs were fabricated on a patterned Au electrode (0.02 cm2) through a lift-off process. To detect the H1N1 SIV, the sandwich enzyme-linked immunosorbent assay (ELISA) method was employed in the immunosensor. The immunosensor was evaluated in an acetate buffer solution containing 3,3',5,5'-tetramethylbenzidine (TMB) via cyclic voltammetry at various H1N1 SIV concentrations (1 pg/mL-5 ng/mL). The measurement results of the fabricated immunosensor showed that the reduction currents of TMB at 0.25 V logarithmically increased from 259.37 to 577.98 nA as the H1N1 SIV concentration changed from 1 pg/mL to 5 ng/mL. An H1N1 SIV immunosensor, based on the patterned ZNNs, was successfully realized for detecting 1 pg/mL-5 ng/mL H1N1 SIV concentrations, with a detection limit of 1 pg/mL for H1N1 SIV.

Quantitative and qualitative analysis of heart mitochondria for evaluating the degree of myocardial injury utilizing atomic force microscopy

Mitochondrial dysfunction plays a central role in mediating both the necrotic and apoptotic components of reperfusion injury. Because mitochondrial swelling is one of the most important indicators of the beginning of mitochondrial permeability transition, quantification of morphological changes in mitochondria would be useful in evaluating the degree of IR injury, as well as the protective effects of various therapies. In this study, we characterized the morphological changes in heart mitochondria caused by the duration and severity of ischemia utilizing particle shape analysis on atomic force microscopy (AFM) topographic images. We also simultaneously investigated the nano-mechanical changes in rat heart mitochondria by injury using force-distance curve measurements. Rats were randomly divided into 3 groups: control group (n=3), myocardial ischemia without reperfusion (PI group, n=3), and myocardial ischemia with reperfusion (IR group, n=4). Normal mitochondria appeared ellipsoidal with a mean area of 3551±1559 nm(2) and mean perimeter of 217.54±52.09 nm (n=60). The mean area and perimeter of mitochondria in the IR groups increased to 28,181±21,248 nm(2) and 595.74±234.29 nm (n=40, p<0.0001 vs. control group, respectively), maintaining oval in shape. But, in the PI group, all parameters showed significant differences compared to parameters of the control group (n=35, p<0.0001). In particular, the mean axial ratio and roundness were significantly different from those in the IR group. Mitochondria in the PI group looked more spherical than those of control and IR groups. Adhesion force is the force before the last event on the retraction half of force-distance curve measurements, corresponding to the point where the tip and the surface loose contact. The adhesion forces of heart mitochondria in the IR and PI groups significantly decreased to 19.56±1.08 nN (n=30, p<0.0001) and 18.65±3.18 nN (n=30, p<0.0001), compared to normal mitochondria which had an adhesion force of 27.64±0.88 nN (n=30). Adhesion force is governed by the attractive portion of the interacting forces between the surface atoms of the contacts. From the morphological and nano-mechanical changes in heart mitochondria, we suggested that the outer membranes of mitochondria were broken by myocardial ischemic injury before they became swollen, and the swelling might be correlated with the ischemic injury. We inferred that the breakage of membranes leads to uptake of water and matrix swelling. As a result, shape measurement parameters for the quantitative analysis of mitochondrial swelling could be very effective for evaluating the myocardial injury.

Insulin-dependent suppression of cholesterol 7α-hydroxylase is a possible link between glucose and cholesterol metabolisms

Cholesterol 7α-hydroxylase (CYP7A1) regulates the balance between cholesterol supply and metabolism by catalyzing the rate-limiting step of bile acid biosynthesis. The transcriptional activity of CYP7A1 is tightly controlled by various nuclear receptors. A forkhead transcription factor O1 (FOXO1) plays a critical role in metabolism, and insulin inactivates FOXO1 through Akt-dependent phosphorylation and nuclear exclusion. We investigated the role of insulin- Akt-FOXO1 signaling pathway in CYP7A1 transcriptional regulation since we found putative insulin-response elements, FOXO1 binding sequences, in both rat and human CYP7A1 promoters. However, ectopic expression of FOXO1 increased the rat CYP7A1-, but mildly reduced human CYP7A1-promoter activities in a dose-dependent manner. Similarly to bile acids, insulin treatment increased small heterodimer partner (SHP) mRNA rapidly and transiently, leading to the suppression of CYP7A1 transcription in both human and rodents. Chromatin immunoprecipitation showed that FOXO1 directly bound to rat CYP1A1 promoter in the absence of insulin. FOXO1 binding to the rat promoter was diminished by insulin treatment as well as by expression of SHP. Our results suggest that the stimulation of insulin- signaling pathway of Akt-FOXO1 and SHP expression may regulate cholesterol/bile acid metabolisms in liver, linking carbohydrate and cholesterol metabolic pathways. A prolonged exposure of insulin in hyperinsulinemic insulin resistance or diabetic status represses CYP7A1 transcription and bile acid biosynthesis through SHP induction and FOXO1 inactivation, leading to impairment of the hepatic cholesterol/bile acid metabolisms.

Endoplasmic reticulum stress impairs insulin signaling through mitochondrial damage in SH-SY5Y cells

Endoplasmic reticulum (ER) and mitochondrial stress are considered causal factors that induce neurodegenerative diseases. However, the relationship between these stresses remains poorly understood. To investigate the molecular mechanism underlying crosstalk between the ER and mitochondria in neurodegeneration, we treated SH-SY5Y human neuroblastoma cells with thapsigargin and tunicamycin, two inducers of ER stress, and atrazine, a promoter of mitochondrial stress. Each pharmacological agent caused mitochondrial dysfunction, which was characterized by reduced intracellular ATP, mitochondrial membrane potential, and endogenous cellular respiration as well as an augmentation of oxidative stress. Oligonucleotide microarray analysis followed by semiquantitative RT-PCR validation assays revealed that thapsigargin and tunicamycin downregulated the expression of most mitochondria-related genes in a manner similar to that induced by atrazine. In contrast, atrazine did not alter the expression of markers of ER stress. Three-dimensional principal component analysis showed that the gene expression profile produced by atrazine treatment was distinct from that generated by ER stress. However, all three agents impaired insulin receptor substrate-1 and Akt phosphorylation in the insulin signaling pathway. Ectopic overexpression of mitochondrial transcription factor A reversed the effects of thapsigargin on mitochondria and Akt signaling. We conclude that ER stress induces neuronal cell death through common perturbation of mitochondrial function and Akt signaling.

Inhibition of inflammation and oxidative stress by Angelica dahuricae radix extract decreases apoptotic cell death and improves functional recovery after spinal cord injury

Inflammation and oxidative stress play major roles in the pathogenesis after spinal cord injury (SCI). Here, we examined the neuroprotective effects of Angelica dahuricae radix (ADR) extract after SCI. ADR extract significantly decreased the levels of proinflammatory factors such as tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-6 (IL-6), inducible nitric oxide synthase (iNOS), and cyclooxygenase-2 (COX-2) in a lipopolysaccharide (LPS)-activated microglial cell line, BV2 cells. ADR extract also significantly alleviated the level of reactive oxygen species in LPS-activated BV2 cells. To examine the neuroprotective effect of ADR extract after SCI, spinally injured rats were administered ADR extract orally at a dose of 100 mg/kg for 14 days. ADR extract treatment significantly reduced the levels of TNF-α, IL-1β, IL-6, iNOS, and COX-2. The levels of superoxide anion (O(2·)(-)) and protein nitration were also significantly decreased by ADR extract. In addition, ADR extract inhibited p38 mitogen-activated protein kinase activation and pronerve growth factor expression in microglia after SCI. Furthermore, ADR extract significantly inhibited caspase-3 activation following apoptotic cell death of neurons and oligodendrocytes, thereby improving functional recovery after injury. Thus, our data suggest that ADR extract provides neuroprotection by alleviating inflammation and oxidative stress and can be used as an orally administered therapeutic agent for acute SCI.

Network clustering revealed the systemic alterations of mitochondrial protein expression

The mitochondrial protein repertoire varies depending on the cellular state. Protein component modifications caused by mitochondrial DNA (mtDNA) depletion are related to a wide range of human diseases; however, little is known about how nuclear-encoded mitochondrial proteins (mt proteome) changes under such dysfunctional states. In this study, we investigated the systemic alterations of mtDNA-depleted (ρ⁰) mitochondria by using network analysis of gene expression data. By modularizing the quantified proteomics data into protein functional networks, systemic properties of mitochondrial dysfunction were analyzed. We discovered that up-regulated and down-regulated proteins were organized into two predominant subnetworks that exhibited distinct biological processes. The down-regulated network modules are involved in typical mitochondrial functions, while up-regulated proteins are responsible for mtDNA repair and regulation of mt protein expression and transport. Furthermore, comparisons of proteome and transcriptome data revealed that ρ⁰ cells attempted to compensate for mtDNA depletion by modulating the coordinated expression/transport of mt proteins. Our results demonstrate that mt protein composition changed to remodel the functional organization of mitochondrial protein networks in response to dysfunctional cellular states. Human mt protein functional networks provide a framework for understanding how cells respond to mitochondrial dysfunctions.

Mitochondria are dynamic organelles that are essential for energy production and cellular processes in eukaryotic cells, and their functional failure is a major cause of age-associated degenerative diseases. To meet the specific needs of different cellular states, mitochondrial protein repertoires are adjusted. It is critical to characterize the systemic alterations of mitochondria to different cellular states to understand the dynamic organization of mitochondrial systems. In this study, we modularized the quantified proteomics data into protein functional networks to characterize gene expression changes under dysfunctional mitochondrial conditions. Our results demonstrate that mitochondrial protein repertoires changed to compensate for dysfunctional cellular states by reorganizing mitochondrial protein functional network. Through network clustering analysis, we discovered that cells respond to pathological conditions by modulating the coordinated expression/transport of mitochondrial proteins. Network analysis of mt proteins can advance our understanding of dysfunctional mitochondrial systems and elucidate the candidate mt proteins involved in human mitochondrial diseases.

Organelle stress-induced activating transcription factor-3 downregulates low-density lipoprotein receptor expression in Sk-Hep1 human liver cells

The low-density lipoprotein receptor (LDLR) plays a central role in cholesterol homeostasis. Here, we provide evidence that an increase in endoplasmic reticulum (ER) stress response or a disturbance of mitochondrial function inhibits LDLR expression in human liver Sk-Hep1 cells. Both organelle stresses triggered activation of activating transcription factor-3 (ATF3), which subsequently reduced LDLR expression. Serial deletion studies revealed that the LDLR promoter region within -234 bp was involved in the repression of LDLR by ATF3. In addition, we identified the region between -8 and -3 of LDLR promoter region as a putative binding site for ATF3 by using deletion construct lacking 6 bp nucleotide corresponding to this region. Transfection of ATF3-specific siRNA rescued LDLR expression under organelle stress, indicating that ATF3 was mainly responsible for the repression of LDLR by these stressors. Additionally, chromatin immunoprecipitation revealed that ATF3 directly binds to the LDLR promoter in a stress-dependent manner. The unique sterol-independent LDLR repression by organelle stress via ATF3 demonstrated here could be involved in obesity-related hypercholesterolemia, which can lead to insulin resistance and type 2 diabetes.