Dietary energy tissue-specifically regulates endoplasmic reticulum chaperone gene expression in the liver of mice

Characterization, Stress Response and Functional Analyses of Giant River Prawn (Macrobrachium rosenbergii) Glucose-Regulated Protein 78 (Mr-grp78) under Temperature Stress and during Aeromonas hydrophila Infection

Simple Summary

Glucose-regulated protein 78 (grp78) is classified as a member of the Hsp70 subfamily. This protein functions as a key factor in signal transduction associated with the unfolded protein response (UPR) in the endoplasmic reticulum (ER) during cellular stress and protects against cell damage caused by toxic chemicals, oxidative stress, Ca²⁺ depletion, programmed cell death and various infectious conditions. To investigate this crucial mechanism in giant river prawn (Macrobrachium rosenbergii), we analyzed the biological function of prawn grp78 at the molecular level in this study. The regulation of this gene was intensively analyzed under normal bacterial infection and heat/cold-shock inductions. A functional analysis of this gene under heat and infectious stress conditions was performed by gene knockdown. The information obtained in the current study clearly indicates the crucially significant roles of grp78 in the cellular stress responses of the target experimental animal under various stress conditions.

Abstract

The endoplasmic reticulum (ER) is an organelle important for several functions of cellular physiology. This study identified the giant river prawn’s glucose-regulated protein 78 (Mr-grp78), which is important for ER stress mechanisms. Nucleotide and amino acid analyses of Mr-grp78, as compared with other species, revealed the highest similarity scores with the grp78 genes of crustaceans. An expression analysis by quantitative RT-PCR indicated that Mr-grp78 was expressed in all tissues and presented its highest expression in the ovary (57.64 ± 2.39-fold), followed by the gills (42.25 ± 1.12), hindgut (37.15 ± 2.47), thoracic ganglia (28.55 ± 2.45) and hemocytes (28.45 ± 2.26). Expression analysis of Mr-grp78 mRNA levels under Aeromonas hydrophila induction and heat/cold-shock exposure was conducted in the gills, hepatopancreas and hemocytes. The expression levels of Mr-grp78 in these tissues were highly upregulated 12 h after bacterial infection. In contrast, under heat- and cold-shock conditions, the expression of Mr-grp78 was significantly suppressed in the gills at 24–96 h and in the hepatopancreas at 12 h (p < 0.05). A functional analysis via Mr-grp78 gene knockdown showed that Mr-grp78 transcription in the gills, hepatopancreas and muscle strongly decreased from 6 to 96 h. Furthermore, the silencing of this gene effectively increased the sensitivity of the tested prawns to heat- and pathogenic-bacterium-induced stress. The results of this study clearly demonstrate the significant functional roles of Mr-grp78 in response to both temperature and pathogen treatments.

Two calcium-binding chaperones from the fat body of the Colorado potato beetle, Leptinotarsa decemlineata (Coleoptera: Chrysomelidae) involved in diapause

Molecular chaperones are crucial for the correct folding of newly synthesized polypeptides, in particular, under stress conditions. Various studies have revealed the involvement of molecular chaperones, such as heat shock proteins, in diapause maintenance and starvation; however, the role of other chaperones in diapause and starvation relatively is unknown. In the current study, we identified two lectin-type chaperones with calcium affinity, a calreticulin (LdCrT) and a calnexin (LdCnX), that were present in the fat body of the Colorado potato beetle, Leptinotarsa decemlineata (Coleoptera: Chrysomelidae) during diapause. Both proteins possessed an N-globular domain, a P-arm domain, and a highly charged C-terminal domain, while an additional transmembrane domain was present in LdCnX. Phylogenetic analysis revealed distinction at the order level. Both genes were expressed in multiple tissues in larval and adult stages, and constitutively throughout development, though a starvation response was detected only for LdCrT. In females, diapause-related expression analysis in the whole body revealed an upregulation of both genes by post-diapause, but a downregulation by diapause only for LdCrT. By contrast, males revealed no alteration in their diapause-related expression pattern in the entire body for both genes. Fat body-specific expression analysis of both genes in relation to diapause revealed the same expression pattern with no alteration in females and downregulation in males by post-diapause. This study suggests that calcium-binding chaperones play similar and possibly gender-specific roles during diapause.

A single extra copy of Down syndrome critical region 1-4 results in impaired hepatic glucose homeostasis

Objectives

During fasting, hepatic gluconeogenesis is induced to maintain energy homeostasis. Moreover, abnormal dysregulation of hepatic glucose production is commonly observed in type 2 diabetes. However, the signaling components controlling hepatic glucose production to maintain normal glucose levels are not fully understood. Here, we examined the physiological role of Down syndrome critical region 1–4 (DSCR1-4), an endogenous calcineurin signaling inhibitor in the liver that mediates metabolic adaptation to fasting.

Methods

We assessed the effect of cyclosporine A, an inhibitor of calcineurin signaling on gluconeogenic gene expression in primary hepatocytes. DSCR1-4 expression was examined in diet- and genetically-induced mouse models of obesity. We also investigated the metabolic phenotype of a single extra copy of DSCR1-4 in transgenic mice and how DSCR1-4 regulates glucose homeostasis in the liver.

Results

Treatment with cyclosporin A increased hepatic glucose production and gluconeogenic gene expression. The expression of DSCR1-4 was induced by refeeding and overexpressed in obese mouse livers. Moreover, transgenic mice with a single extra copy of DSCR1-4 exhibited pyruvate intolerance and impaired glucose homeostasis. Mechanistically, DSCR1-4 overexpression increased phosphorylation of the cAMP response element-binding protein, which led to elevated expression levels of gluconeogenic genes and, thus, enhanced hepatic glucose production during fasting.

Conclusion

A single extra copy of DSCR1-4 results in dysregulated hepatic glucose homeostasis and pyruvate intolerance. Our findings suggest that nutrient-sensitive DSCR1-4 is a novel target for controlling hepatic gluconeogenesis in diabetes.

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DSCR1 mRNA and protein levels are increased in livers upon nutrient availability.

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DSCR1-4 is overexpressed in diet- or genetically induced obesity.

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DSCR1-4 trisomy mice exhibit impaired glucose homeostasis and pyruvate intolerance.

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Trisomy of DSCR1-4 leads to increased hepatic glucose production.

Restriction on an energy-dense diet improves markers of metabolic health and cellular aging in mice through decreasing hepatic mTOR activity

Dietary restriction (DR) on a normal low-fat diet improves metabolic health and may prolong life span. However, it is still uncertain whether restriction of an energy-dense, high-fat diet would also be beneficial and mitigate age-related processes. In the present study, we determined biomarkers of metabolic health, energy metabolism, and cellular aging in obesity-prone mice subjected to 30% DR on a high-fat diet for 6 months. Dietary-restricted mice had significantly lower body weights, less adipose tissue, lower energy expenditure, and altered substrate oxidation compared to their ad libitum-fed counterparts. Hepatic major urinary proteins (Mup) expression, which is linked to glucose and energy metabolism, and biomarkers of metabolic health, including insulin, glucose, cholesterol, and leptin/adiponectin ratio, were likewise reduced in high-fat, dietary-restricted mice. Hallmarks of cellular senescence such as Lamp2a and Hsc70 that mediate chaperone-mediated autophagy were induced and mechanistic target of rapamycin (mTOR) signaling mitigated upon high-fat DR. In contrast to DR applied in low-fat diets, anti-oxidant gene expression, proteasome activity, as well as 5'-adenosine monophosphate-activated protein kinase (AMPK) activation were not changed, suggesting that high-fat DR may attenuate some processes associated with cellular aging without the induction of cellular stress response or energy deprivation.

Fluorosis induces endoplasmic reticulum stress and apoptosis in osteoblasts in vivo

The present study investigated the effects of fluoride on endoplasmic reticulum (ER) stress (ERS) and osteoblast apoptosis in vivo. Forty-eight Wistar rats were randomly divided into four groups (12/group) and exposed to 0, 50, 100, and 150 mg/L of fluoride in drinking water for 8 weeks, respectively. Peripheral blood samples and bilateral femurs were used to monitor the progression of fluorosis in the animals. Hematoxylin and eosin (H&E) staining of the bone tissues was used to determine the severity of osteofluorosis. The expression of ERS chaperones (glucose-regulated protein 78 (GRP78), X-box binding protein l (XBP1), cysteine aspartate specific protease-12 (caspase-12), and growth arrest and DNA damage-inducible gene 153 (Gadd153/CHOP) was analyzed by immunohistochemistry staining, and osteoblast apoptosis was determined by TUNEL staining and flow cytometry. Accumulation of fluoride in bone was associated with the severity of osteofluorosis. The expression of GRP78, XBP1, caspase-12, and CHOP was increased in a dose-dependent manner. Fluoride-induced apoptosis in osteoblasts was also dose-dependent. High concentrations of fluoride induced ERS and osteoblast apoptosis in vivo. The increased expression of GRP78 and XBP1 increased the adaptation of osteoblasts to ERS to a certain extent. Caspase-12 and CHOP activation was associated with ERS and osteoblast apoptosis.

Endoplasmic reticulum stress in adipose tissue determines postprandial lipoprotein metabolism in metabolic syndrome patients

SCOPE

Our aim was to ascertain whether the quality and quantity of fat in the diet may influence the ER stress at the postprandial state in adipose tissue by analyzing the gene expression of chaperones, folding enzymes, and activators of the UPR.

METHODS AND RESULTS

A randomized, controlled trial conducted within the LIPGENE study assigned 39 MetS patients to one of four diets: high-SFA (HSFA; 38% energy (E) from fat, 16% E as SFA), high MUFA (HMUFA; 38% E from fat, 20% E as MUFA), and two low-fat, high-complex carbohydrate (LFHCC; 28% E from fat) diets supplemented with 1.24 g/day of long-chain n-3 PUFA or placebo for 12 wk each. A fat challenge reflecting the same fatty acid composition as the original diets was conducted post intervention. sXBP-1 is induced in the postprandial state irrespective of the diet consumed (p < 0.001). BiP increases postprandially after consumption of diets HMUFA (p = 0.006), LFHCC (p = 0.028), and LFHCC n-3 (p = 0.028). Postprandial mRNA expression levels of CRL, CNX, PDIA3, and GSTP1 in AT did not differ between the different types of diets.

CONCLUSION

Our results suggest that upregulation of the unfolded protein response at the postprandial state may represent an adaptive mechanism to counteract diet-induced stress.

Antioxidative responses in females and males of the spider Xerolycosa nemoralis (Lycosidae) exposed to natural and anthropogenic stressors

The aim of this study was to assess the intensity of enzymatic antioxidative parameters [i.e., superoxide dismutase (SOD), catalase (CAT), and the glutathione peroxidases each selene dependent, GPOX or selene independent, including GSTPx, glutathione S-transferase, and GST] and non-enzymatic antioxidative parameters [i.e., glutathione total (GSH-t), the heat shock proteins of Hsp70, and metallothioneins (Mt)] in the midgut glands of female and male wolf spiders Xerolycosa nemoralis (Lycosidae) exposed to natural stressors (i.e., heat shock and starvation) and anthropogenic stressors (i.e., the organophosphorous pesticide dimethoate) under laboratory conditions. The spiders were collected from two differentially polluted sites both localized in southern Poland: Olkusz, which is heavily polluted with metals, and Pilica, the reference site. In response to the stressing factors, increases in Hsp70 levels, in the concentrations of total glutathione and in the activity levels of glutathione-dependent enzymes (GPOX, GSTPx, and GST) were found in the midgut glands of males. In the females, high levels of activity of CAT and SOD were revealed, as well as an increased percentage of Mt-positive cells. Preexposed females, in comparison to the individuals from the reference site, responded with increased SOD activity, irrespective of the stressing factor. In contrast, the changes in the antioxidative parameters in the midgut glands of male X. nemoralis seem to reflect a short-term reaction to the applied stressors and do not confirm the effects of long-term selection in a polluted environment.

GRP78/BiP is a novel downstream target of IGF-1 receptor mediated signaling

Glucose regulated protein 78/immunoglobulin binding protein (GRP78/BiP) is an endoplasmic reticulum (ER) chaperone protein and master regulator of the unfolded protein response (UPR). The response of GRP78 to overt pharmacologically induced ER stress is well established, whereas the modulation of GRP78 to physiologic changes is less characterized. In this study, we examined the regulation of GRP78 in response to reduced IGF-1 growth factor signaling, a common consequence of calorie restriction (CR). ER chaperone protein expression was quantified in cell lysates prepared from the livers of calorie restricted (CR) and ad libitum fed mice, as well as MEFs grown in normal medium or serum starved. The requirement of IGF-1 signaling on GRP78 expression was studied using MEFs with IGF-1 receptor overexpression (R+) or deletion (R-), and the regulatory mechanism was examined using mTORC1 and PI3K inhibitors, as well as R- cells with knockdown of transcription factor FOXO1 compared to shRNA control. We observed a 40% reduction in GRP78 protein expression in CR mice and in serum-starved MEF cells. R- cells had drastically reduced AKT phosphorylation and exhibited lower levels of ER chaperones, in particular 80% less GRP78. Despite an 80% reduction in GRP78 expression, R- cells were not under chronic ER stress, but were fully capable of activating the UPR. Neither forced expression of FOXO1-AAA nor knockdown of FOXO1 in R- cells affected GRP78 expression. In conclusion, we report that IGF-1 receptor signaling regulates GRP78 expression via the PI3K/AKT/mTORC1 axis independent of the canonical UPR and FOXO1.

Protein disulfide isomerase in redox cell signaling and homeostasis

Thiol proteins may potentially act as redox signaling adaptor proteins, adjusting reactive oxygen species intermediates to specific signals and redox signals to cell homeostasis. In this review, we discuss redox effects of protein disulfide isomerase (PDI), a thioredoxin superfamily oxidoreductase from the endoplasmic reticulum (ER). Abundantly expressed PDI displays ubiquity, interactions with redox and nonredox proteins, versatile effects, and several posttranslational modifications. The PDI family contains >20 members with at least some apparent complementary actions. PDI has oxidoreductase, isomerase, and chaperone effects, the last not directly dependent on its thiols. PDI is a converging hub for pathways of disulfide bond introduction into ER-processed proteins, via hydrogen peroxide-generating mechanisms involving the oxidase Ero1α, as well as hydrogen peroxide-consuming reactions involving peroxiredoxin IV and the novel peroxidases Gpx7/8. PDI is a candidate pathway for coupling ER stress to oxidant generation. Emerging information suggests a convergence between PDI and Nox family NADPH oxidases. PDI silencing prevents Nox responses to angiotensin II and inhibits Akt phosphorylation in vascular cells and parasite phagocytosis in macrophages. PDI overexpression spontaneously enhances Nox activation and expression. In neutrophils, PDI redox-dependently associates with p47phox and supports the respiratory burst. At the cell surface, PDI exerts transnitrosation, thiol reductase, and apparent isomerase activities toward targets including adhesion and matrix proteins and proteases. Such effects mediate redox-dependent adhesion, coagulation/thrombosis, immune functions, and virus internalization. The route of PDI externalization remains elusive. Such multiple redox effects of PDI may contribute to its conspicuous expression and functional role in disease, rendering PDI family members putative redox cell signaling adaptors.

Assessment of potential immunotoxic effects caused by cypermethrin, fluoxetine, and thiabendazole using heat shock protein 70 and interleukin-1β mRNA expression in the anuran Xenopus laevis

The current study describes the effect of cypermethrin, fluoxetine, and thiabendazole, at environmentally relevant concentrations, on the expression of heat shock protein 70 (HSP70) and interleukin 1β (IL-1β), using Xenopus laevis larvae as animal model. Cytokines and interleukins are considered good predictors of the immunotoxic potential of xenobiotics. Tadpoles at stage 47 (normal tables of X. laevis) were exposed under static conditions to: 0.3 and 30 µg/L fluoxetine, 0.7 µg/L thiabendazole, and 0.24 µg/L cypermethrin. The effects were evaluated at 7, 24, and 72 h, and 6 and 9 d. Randomly chosen tadpoles were used as genetic material for detection of hsp70 and IL-1β mRNA induction through reverse transcription PCR. Tadpoles exposed to 30 µg/L fluoxetine showed mRNA expression of both genes at all exposure times, whereas at 0.3 µg/L a peak response for hsp70 was observed after 24 h, and the increase in IL-1β mRNA was statistically significant with respect to the control 72 h after exposure. Thiabendazole induced a high expression of mRNA for both hsp70 and IL-1β at all exposure times. Cypermethrin increased the hsp70 mRNA levels, with a peak at 24 h, and provoked high expression of IL-1β mRNA at all exposure times. Considering the relationship between HSP70 and IL-1β and their involvement (mainly of IL-1β) in immune responses, certain changes observed in their expression could be considered warning indicators of potential immunotoxic effects of these substances on Xenopus.

Reduced expression of alpha-1,2-mannosidase I extends lifespan in Drosophila melanogaster and Caenorhabditis elegans

Exposure to sub-lethal levels of stress, or hormesis, was a means to induce longevity. By screening for mutations that enhance resistance to multiple stresses, we identified multiple alleles of alpha-1,2-mannosidase I (mas1) which, in addition to promoting stress resistance, also extended longevity. Longevity enhancement is also observed when mas1 expression is reduced via RNA interference in both Drosophila melanogaster and Caenorhabditis elegans. The screen also identified Edem1 (Edm1), a gene downstream of mas1, as a modulator of lifespan. As double mutants for both mas1 and Edm1 showed no additional longevity enhancement, it appeared that both mutations function within a common pathway to extend lifespan. Molecular analysis of these mutants revealed that the expression of BiP, a putative biomarker of dietary restriction (DR), is down-regulated in response to reductions in mas1 expression. These findings suggested that mutations in mas1 may extend longevity by modulating DR.

Dephosphorylation of translation initiation factor 2alpha enhances glucose tolerance and attenuates hepatosteatosis in mice

The molecular mechanisms linking the stress of unfolded proteins in the endoplasmic reticulum (ER stress) to glucose intolerance in obese animals are poorly understood. In this study, enforced expression of a translation initiation factor 2alpha (eIF2alpha)-specific phosphatase, GADD34, was used to selectively compromise signaling in the eIF2(alphaP)-dependent arm of the ER unfolded protein response in liver of transgenic mice. The transgene resulted in lower liver glycogen levels and susceptibility to fasting hypoglycemia in lean mice and glucose tolerance and diminished hepatosteatosis in animals fed a high-fat diet. Attenuated eIF2(alphaP) correlated with lower expression of the adipogenic nuclear receptor PPARgamma and its upstream regulators, the transcription factors C/EBPalpha and C/EBPbeta, in transgenic mouse liver, whereas eIF2alpha phosphorylation promoted C/EBP translation in cultured cells and primary hepatocytes. These observations suggest that eIF2(alphaP)-mediated translation of key hepatic transcriptional regulators of intermediary metabolism contributes to the detrimental consequences of nutrient excess.

Identification of a novel adenine nucleotide transporter in the endoplasmic reticulum of Arabidopsis

Many metabolic reactions in the endoplasmic reticulum (ER) require high levels of energy in the form of ATP, which is important for cell viability. Here, we report on an adenine nucleotide transporter residing in the ER membranes of Arabidopsis thaliana (ER-ANT1). Functional integration of ER-ANT1 in the cytoplasmic membrane of intact Escherichia coli cells reveals a high specificity for an ATP/ADP antiport. Immunodetection in transgenic ER-ANT1-C-MYC-tag Arabidopsis plants and immunogold labeling of wild-type pollen grain tissue using a peptide-specific antiserum reveal the localization of this carrier in ER membranes. Transgenic ER-ANT1-promoter-beta-glucuronidase Arabidopsis lines show high expression in ER-active tissues (i.e., pollen, seeds, root tips, apical meristems, or vascular bundles). Two independent ER-ANT1 Arabidopsis knockout lines indicate a high physiological relevance of ER-ANT1 for ATP transport into the plant ER (e.g., disruption of ER-ANT1 results in a drastic retardation of plant growth and impaired root and seed development). In these ER-ANT1 knockout lines, the expression levels of several genes encoding ER proteins that are dependent on a sufficient ATP supply (i.e., BiP [for luminal binding protein] chaperones, calreticulin chaperones, Ca2+-dependent protein kinase, and SEC61) are substantially decreased.

Conserved and tissue-specific genic and physiologic responses to caloric restriction and altered IGFI signaling in mitotic and postmitotic tissues

Caloric restriction (CR), the consumption of fewer calories without malnutrition, and reduced insulin and/or IGFI receptor signaling delay many age-related physiological changes and extend the lifespan of many model organisms. Here, we present and review microarray and biochemical studies indicating that the potent anticancer effects of CR and disrupted insulin/IGFI receptor signaling evolved as a byproduct of the role of many mitotic tissues as reservoirs of metabolic energy. We argue that the longevity effects of CR are derived from repeated cycles of apoptosis and autophagic cell death in mitotically competent tissues and protein turnover and cellular repair in postmitotic tissues. We review studies showing that CR initiated late in life can rapidly induce many of the benefits of lifelong CR, including its anticancer effects. We also discuss evidence from liver and heart indicating that many benefits of lifelong CR are recapitulated in mitotic and postmitotic tissues when CR is initiated late in life.

Molecular cloning of the heat-shock cognate 70 (Hsc70) gene from the two-spotted spider mite, Tetranychus urticae, and its expression in response to heat shock and starvation

We isolated a heat shock cognate 70 (hsc70) gene from the two-spotted spider mite, Tetranychus urticae, a serious agricultural pest. The hsc70 cDNA is 2275 bp and contains a 1962 bp open reading frame. The translated amino acid sequence consists of 654 residues with a calculated molecular mass of 71,275 Da and an isoelectronic point (pI) of 5.52. It also contains the highly conserved functional motifs of the Hsp70 family. A comparison of the deduced amino acid sequence shows a high identity (81-84%) with Hsp70s/Hsc70s of insects but the highest identity is with mussel Hsc71 (86%). Northern blot hybridization indicates that the hsc70 transcript level of female adults is higher than that of male adults. We evaluated the response of hsc70 gene to stresses from temperature and starvation. The level of hsc70 mRNA was not significantly changed by heat and cold shocks nor by recovery after the shocks. However, the hsc70 mRNA level was decreased by food restriction of female mites. Analysis of nucleotide and deduced amino acid sequences of hsc70 gene from T. urticae suggests that it is a member of heat shock cognate 70 gene in the highly conserved Hsp70 family but that its expression is influenced by food restriction rather than thermal stress. This is the first molecular analysis of a heat shock protein gene in an acarid.

St. John's wort and its constituent hyperforin concordantly regulate expression of genes encoding enzymes involved in basic cellular pathways

OBJECTIVES AND METHODS

The effects of St. John's wort and hyperforin on gene expression were analysed in HepG2 cells by Affymetrix microarray hybridization and real time reverse transcription-PCR.

RESULTS

Both compounds increased mRNAs of the drug metabolizing enzymes CYP3A4, CYP1A1, CYP1A2 and the flavin containing monooxygenase FMO5, and of the multidrug resistance protein MRP2. CYP4F2 and the reduced nicotinamide adenine dinucleotide dehydrogenase NQO1 were downregulated. Expression of genes mediating cholesterol biosynthesis was decreased, while facilitated glucose transporters and glycolysis genes were induced, indicating increased glucose metabolism. Changes of a considerable number of additional transcripts corresponded to reports on gene regulation by hypoxia. Endoplasmic reticulum stress-regulated genes involved in unfolded protein response and in protection of cells from apoptosis were downregulated. Other calcium binding proteins were affected by both treatments, suggesting an increase in intracellular calcium.

CONCLUSIONS

St. John's wort and hyperforin concordantly affected expression of genes not only mediating metabolism and transport of exogenous and endogenous compounds, but also involved in energy metabolism, intracellular calcium regulation, cell proliferation and apoptosis.

The endoplasmic reticulum chaperone improves insulin resistance in type 2 diabetes

To determine the role of the endoplasmic reticulum (ER) in diabetes, Akita mice, a mouse model of type 2 diabetes, were mated with either heterozygous knockout mice or two types of transgenic mice of 150-kDa oxygen-regulated protein (ORP150), a molecular chaperone located in the ER. Systemic expression of ORP150 in Akita mice improves insulin intolerance, whereas the exclusive overexpression of ORP150 in pancreatic beta-cells of Akita mice did not change their glucose tolerance. Both an insulin tolerance test and hyperinsulinemic-euglycemic clamp revealed that ORP150 enhanced glucose uptake, accompanied by suppression of oxidized protein. Furthermore, ORP150 enhanced the insulin sensitivity of myoblast cells treated with hydrogen peroxide. These data suggest that ORP150 plays an important role in insulin sensitivity and is a potential target for the treatment of diabetes.

Feeding induces expression of heat shock proteins that reduce oxidative stress

Heat shock proteins (Hsps) are induced in response to various kinds of environmental and physiological stresses. However, it is unclear whether Hsps play roles in protecting cells in the digestive organs against xenobiotic chemicals. Here, we found that feeding induces expression of a set of Hsps specifically in the mouse liver and intestine by activating heat shock transcription factor 1 (HSF1). In the liver, HSF1 is required to suppress toxic effects of electrophiles, which are xenobiotic chemicals causing oxidative stress. We found that overexpression of Hsp27, which elevates cellular glutathione level, promotes survival of culture cells exposed to electrophiles. These results suggest a novel mechanism of cell protection against xenobiotic chemicals in the food.

Temporal linkage between the phenotypic and genomic responses to caloric restriction

Caloric restriction (CR), the consumption of fewer calories while avoiding malnutrition, decelerates the rate of aging and the development of age-related diseases. CR has been viewed as less effective in older animals and as acting incrementally to slow or prevent age-related changes in gene expression. Here we demonstrate that CR initiated in 19-month-old mice begins within 2 months to increase the mean time to death by 42% and increase mean and maximum lifespans by 4.7 (P = 0.000017) and 6.0 months (P = 0.000056), respectively. The rate of age-associated mortality was decreased 3.1-fold. Between the first and second breakpoints in the CR survival curve (between 21 and 31 months of age), tumors as a cause of death decreased from 80% to 67% (P = 0.012). Genome-wide microarray analysis of hepatic RNA from old control mice switched to CR for 2, 4, and 8 weeks showed a rapid and progressive shift toward the gene expression profile produced by long-term CR. This shift took place in the time frame required to induce the health and longevity effects of CR. Shifting from long-term CR to a control diet, which returns animals to the control rate of aging, reversed 90% of the gene expression effects of long-term CR within 8 weeks. These results suggest a cause-and-effect relationship between the rate of aging and the CR-associated gene expression biomarkers. Therefore, therapeutics mimicking the gene-expression biomarkers of CR may reproduce its physiological effects.

Protein oxidation in aging: endoplasmic reticulum as a target

Oxidatively modified proteins have been shown to correlate with the age of an organism or its tissues. An increase in tissue-susceptibility to experimentally induced protein oxidation not only depends on tissue type and age, but also on the maximum lifespan potential of the species. A general, although tissue dependent, decline in anti-oxidative defenses during aging may very well be responsible for this difference in vulnerability. In addition, the level of protein modifications also depends on the nature and the subcellular localization of the proteins involved. Damage to the endoplasmic reticulum (ER), and its subsequent impaired functionality may be involved in the process of aging. This is suggested by; (1) an upregulation of ER stress-response chaperones, (2) a preferential oxidation of ER-resident proteins and, (3) a disturbance of calcium homeostasis. Therefore, this review will focus on the putative involvement of the oxidized endoplasmic reticulum in the process of aging.

Calreticulin promotes folding/dimerization of human lipoprotein lipase expressed in insect cells (sf21)

Lipoprotein lipase (LPL) is a non-covalent, homodimeric, N-glycosylated enzyme important for metabolism of blood lipids. LPL is regulated by yet unknown post-translational events affecting the levels of active dimers. On co-expression of LPL with human molecular chaperones, we found that calreticulin had the most pronounced effects on LPL activity, but calnexin was also effective. Calreticulin caused a 9-fold increase in active LPL, amounting to about 50% of the expressed LPL protein. The total expression of LPL protein was increased less than 20%, and the secretion rates for active and inactive LPL were not significantly changed by the chaperone. Thus, the main effect was an increased specific activity of LPL both in cells and media. Chromatography on heparin-Sepharose and sucrose density gradient centrifugation demonstrated that most of the inactive LPL was monomeric and that calreticulin promoted formation of active dimers. Higher oligomers of inactive LPL were present in cell extracts, but only monomers and dimers were secreted to the medium. Interaction between LPL and calreticulin was demonstrated, and the effect of the chaperone was prevented by castanospermine, an inhibitor of N-glycan glucose trimming. Our data indicate an important role of endoplasmic reticulum-based chaperones for the folding/dimerization of LPL.

Carbonylation of ER chaperone proteins in aged mouse liver

Progressive accumulation of oxidative damage to macromolecules in aged tissues is thought to contribute to the decline in tissue function characteristic of the aged phenotype. Mitochondria are a major intracellular source of reactive oxygen species (ROS); however, other organelles are also endogenous sources of oxyradicals and oxidants, which can damage macromolecules. We, therefore, sought to examine the relationship between aging and oxidative damage to ER resident proteins, which exist in a strongly oxidizing environment necessary for disulfide bond formation. In these studies, we have fractionated young and aged liver homogenates, resolved the proteins by 2D gel electrophoresis, assayed for oxidative damage as indicated by protein carbonylation, and identified BiP/Grp78, protein disulfide isomerase (PDI), and calreticulin as exhibiting an age-associated increase in oxidative damage. Increased carbonylation of these key proteins in aged liver suggests an age-associated impairment in protein folding, disulfide crosslinking, and glycosylation in the aged mouse liver.

Postprandial induction of chaperone gene expression is rapid in mice

Molecular chaperones assist in the biosynthesis and processing of proteins. Most chaperones are induced by physiological stresses. We have shown that dietary energy restriction decreases the mRNA and protein levels of many endoplasmic reticulum chaperones in the livers of mice. Here, we have investigated the response of chaperone mRNA to feeding. Control and 50% energy-restricted C3B10RF1 mice were deprived of food for 24 h, fed, and killed 0, 1.5, 5 or 12 h after feeding. Chaperone mRNAs were strongly induced as early as 1.5 h after feeding in control and energy-restricted mice. The integrated levels of these mRNA over 24 h were significantly lower in energy-restricted mice. The mRNA response to energy intake was mirrored over the course of days in the level of chaperone protein. A similar but smaller response to feeding was found in kidney and muscle. Puromycin and cycloheximide failed to inhibit the feeding response, suggesting that feeding releases chaperone expression from an unstable inhibitor. Studies with dibutyryl-cAMP- and glucagon-supplemented, normal and streptozotocin-diabetic mice suggest that glucagon and insulin may be mediators of the feeding response. Adrenalectomy enhanced the feeding induction, but dexamethasone administration had no effect. Thus, postprandial changes in insulin and glucagon may link chaperone gene expression to feeding, possibly in several tissues including liver.

Genomic profiling of short- and long-term caloric restriction effects in the liver of aging mice

We present genome-wide microarray expression analysis of 11,000 genes in an aging potentially mitotic tissue, the liver. This organ has a major impact on health and homeostasis during aging. The effects of life- and health-span-extending caloric restriction (CR) on gene expression among young and old mice and between long-term CR (LT-CR) and short-term CR (ST-CR) were examined. This experimental design allowed us to accurately distinguish the effects of aging from those of CR on gene expression. Aging was accompanied by changes in gene expression associated with increased inflammation, cellular stress, and fibrosis, and reduced capacity for apoptosis, xenobiotic metabolism, normal cell-cycling, and DNA replication. LT-CR and just 4 weeks of ST-CR reversed the majority of these changes. LT-CR produced in young mice a pattern of gene expression that is a subset of the changes found in old LT-CR mice. It is possible that the early changes in gene expression, which extend into old age, are key to the life- and health-span-extending effects of CR. Further, ST-CR substantially shifted the "normo-aging" genomic profile of old control mice toward the "slow-aging" profile associated with LT-CR. Therefore, many of the genomic effects of CR are established rapidly. Thus, expression profiling should prove useful in quickly identifying CR- mimetic drugs and treatments.

Chaperone-mediated regulation of hepatic protein secretion by caloric restriction

Calorie restriction (CR) delays age-related physiological changes, reduces cancer incidence, and increases maximum life span in mammals. Here we show that CR decreased the expression of many hepatic molecular chaperones and concomitantly increased the rate and efficiency of serum protein secretion. Hepatocytes from calorie-restricted mice secreted twice as much albumin, 63% more alpha1-antitrypsin, and 250% more of the 31.5-kDa protein 2 h after their synthesis. A number of trivial explanations for these results, such as differential rates of protein synthesis and cell leakage during the assay, were eliminated. These novel results suggest that CR may promote the secretion of serum proteins, thereby promoting serum protein turnover. This may reduce the circulating level of damaging, glycoxidated serum proteins.

Introduction. Symposium: Calorie restriction: effects on body composition, insulin signaling and aging

At this time of increasing attention to the worldwide problem of obesity and its negative consequences for health and well being, it is timely to present a symposium on the effects of calorie restriction and the potential for calorie restriction mimetic therapies. The present symposium "Calorie Restriction: Effects on Body Composition, Insulin Signaling and Aging" was included in the Experimental Biology 2000 meeting held April 15-18, 2000 in San Diego, California. It is now recognized that calorie restriction carries with it many heretofore unrecognized consequences in addition to the life span-extending properties first described in the 1930s. This symposium addresses some of the current issues in calorie restriction and demonstrates the widespread effects that may underlie recidivism after weight loss, as well as the metabolically positive consequences for health of long-term calorie restraint.

Microarray profiling of gene expression in aging and its alteration by caloric restriction in mice

An active research area in biological gerontology concerns the mechanisms by which caloric restriction (CR) retards the aging process in laboratory rodents. We used high density oligonucleotide arrays representing 6347 genes to determine the gene expression profile of the aging process in gastrocnemius muscle of male C57BL/6 mice. Aging resulted in a differential gene expression pattern indicative of a marked stress response and lower expression of metabolic and biosynthetic genes. Most alterations were completely or partially prevented by CR. Transcriptional patterns of muscle from calorie-restricted animals suggest that CR retards the aging process by causing a metabolic shift toward increased protein turnover and decreased macromolecular damage. The use of high density oligonucleotide microarrays provides a new tool to measure biological age on a tissue-specific basis and to evaluate at the molecular level the efficacy of nutritional interventions designed to retard the aging process.

The hsp110 and Grp1 70 stress proteins: newly recognized relatives of the Hsp70s

Both the Grp170 and Hsp110 families represent relatively conserved and distinct sets of stress proteins, within a more diverse category that also includes the Hsp70s. All of these families are found in a wide variety of organisms from yeasts to humans. Although Hsp110s or Grp170s are not Hsp70s any more than Hsp70s are Hsp110s or Grp170s, it is still reasonable to refer to this combination of related families as the Hsp70 superfamily based on arguments discussed above and since no obvious prokaryotic Hsp110 or Grp170 has yet been identified. These proteins are related to their counterparts in the Hsp70/Grp78 family of eukaryotic stress proteins but are characterized by significantly larger molecular weights. The members of the Grp170 family are characterized by C-terminal ER retention sequences and are ER localized in yeasts and mammals. As a Grp, Grp170 is recognized to be coregulated with other major Grps by a well-known set of stress conditions, sometimes referred to as the unfolded protein response (Kozutsumi et al 1988; Nakaki et al 1989). The Hsp110 family members are localized in the nucleus and cytoplasm and, with other major Hsps, are also coregulated by a specific set of stress conditions, most notably including hyperthermic exposures. Hsp110 is sometimes called Hsp105, although it would be preferable to have a uniform term. The large Hsp70-like proteins are structurally similar to the Hsp70s but differ from them in important ways. In both the Grp170 and Hspl10 families, there is a long loop structure that is interposed between the peptide-binding ,-domain and the alpha-helical lid. In the Hsp110 family and Grp170, there are differing degrees of expansion in the alpha-helical domain and the addition of a C-terminal loop. This gives the appearance of much larger lid domains for Hsp110 and Grp170 compared with Hsp70. Both Hsp110 and Grp170 families have relatively conserved short sequences in the alpha-helical domain in the lid, which are conserved motifs in numerous proteins (we termed these motifs Magic and TedWylee as discussed earlier). The structural differences detailed in this review result in functional differences between the large (Grp170 and Hspl10) members of the Hsp70 superfamily, the most distinctive being an increased ability of these proteins to bind (hold) denatured polypeptides compared with Hsc70, perhaps related to the enlarged C-terminal helical domain. However, there is also a major difference between these large stress proteins; Hsp110 does not bind ATP in vitro, whereas Grp170 binds ATP avidly. The role of the Grp170 and Hsp110 stress proteins in cellular physiology is not well understood. Overexpression of Hsp110 in cultured mammalian cells increases thermal tolerance. Grp170 binds to secreted proteins in the ER and may be cooperatively involved in folding these proteins appropriately. These roles are similar to those of the Hsp70 family members, and, therefore, the question arises as to the differential roles played by the larger members of the superfamily. We have discussed evidence that the large members of the superfamily cooperate with members of the Hsp70 family, and these chaperones probably interact with a large number of chaperones and cochaperones in their functional activities. The fundamental point is that Hsp110 is found in conjunction with Hsp70 in the cytoplasm (and nucleus) and Grp170 is found in conjunction with78 in tha ER in every eucaryotic cell examined from yeast to humans. This would strongly argue that Hsp110 Grp170 exhibit functions in eucaryotes not effectively performed by Hsp70s or Grp78, respectively. Of interest in this respect is the observation that all Hsp110s loss of function or deletion mutants listed in the Drosophila deletion project database are lethal. The important task for the future is to determine the roles these conserved molecular chaperones play in normal and physiologically stressed cells.

Abundant expression of 150-kDa oxygen-regulated protein in mouse pancreatic beta cells is correlated with insulin secretion

The 150-kDa oxygen-regulated protein (ORP150) is a member of glucose-regulated proteins (GRPs), which are induced by stressful conditions such as oxygen or glucose deprivation. Here we investigated the highly abundant expression of ORP150 in mouse pancreas and its relationship with insulin secretion. Immunohistochemical analysis revealed that ORP150 expression was restricted to islets, especially to beta cells. The beta cell-specific expression was also observed in a mouse insulinoma cell line, MIN6, which secretes insulin in response to increased glucose concentration. Furthermore, ORP150 in islets dramatically diminished by fasting, concomitant with reduction of the serum insulin level. These results strongly suggest the role for ORP150 in insulin secretion.

Protein disulfide isomerase: the multifunctional redox chaperone of the endoplasmic reticulum

Protein disulfide isomerase (PDI) is a protein-thiol oxidoreductase that catalyzes the oxidation, reduction and isomerization of protein disulfides. In the endoplasmic reticulum PDI catalyzes both the oxidation and isomerization of disulfides on nascent polypeptides. Under the reducing condition of the cytoplasm, endosomes and cell surface. PDI catalyzes the reduction of protein disulfides. At those locations, PDI has been demonstrated to participate in the regulation of reception function, cell-cell interaction, gene expression, and actin filament polymerization. These activities of PDI will be discussed, as well as its activity as a chaperone and subunit of prolyl 4-hydroxylase and microsomal triglyceride transfer protein.

Stress resistance and longevity in selected lines of Drosophila melanogaster

Five independent populations (lines) of Drosophila melanogaster were selected for female starvation resistance. Females and males from the selected lines were relatively starvation resistant when compared to flies from five control lines. Moreover, flies from selected lines were resistant to other stresses: desiccation, acetone fumes, ethanol fumes, and paraquat (a source of oxygen radicals). Data from a variety of previous studies indicate an association between stress resistance and longevity. In this context, the present study addressed the question of whether flies from the stress-resistant lines were relatively long-lived. Replicate population cages from each selected and control line were used to assess longevity. Neither females nor males from the selected lines were relatively long-lived. In at least some cases, stress resistance may be necessary, but not sufficient, for longevity.

Heat-shock proteins, molecular chaperones, and the stress response: evolutionary and ecological physiology

Molecular chaperones, including the heat-shock proteins (Hsps), are a ubiquitous feature of cells in which these proteins cope with stress-induced denaturation of other proteins. Hsps have received the most attention in model organisms undergoing experimental stress in the laboratory, and the function of Hsps at the molecular and cellular level is becoming well understood in this context. A complementary focus is now emerging on the Hsps of both model and nonmodel organisms undergoing stress in nature, on the roles of Hsps in the stress physiology of whole multicellular eukaryotes and the tissues and organs they comprise, and on the ecological and evolutionary correlates of variation in Hsps and the genes that encode them. This focus discloses that (a) expression of Hsps can occur in nature, (b) all species have hsp genes but they vary in the patterns of their expression, (c) Hsp expression can be correlated with resistance to stress, and (d) species' thresholds for Hsp expression are correlated with levels of stress that they naturally undergo. These conclusions are now well established and may require little additional confirmation; many significant questions remain unanswered concerning both the mechanisms of Hsp-mediated stress tolerance at the organismal level and the evolutionary mechanisms that have diversified the hsp genes.

Glucose regulation of GRP78 gene expression

The endoplasmic reticulum chaperone glucose-regulated protein 78 (GRP78) is essential for the proper glycosylation, folding and assembly of many membrane bound and secreted proteins. GRP78 mRNA is well known to be induced in cultured cells by lowering medium glucose concentrations from 4.5 to 0 mg/ml. Here we report a study designed to determine the effects of intermediate concentrations of glucose on GRP78 mRNA abundance. Progressive reduction in culture medium glucose from 4.5 to 1.0 mg/ml progressively reduced GRP78 mRNA to approximately 30% of the initial level. Induction of GRP78 mRNA by glucose starvation was observed in medium containing less than 1 mg/ml glucose. Determination of the amount of glucose consumed in these cultures showed that reduction of glucose concentrations led first to repression of GRP78 mRNA abundance, followed by induction of the mRNA only when glucose is nearly exhausted. Caloric restriction in mice both reduces fasting and mean 24 h glucose blood concentrations and GRP78 mRNA abundance in the liver. Thus, it is possible that negative regulation of GRP78 mRNA in the liver is due directly to reduced blood glucose concentrations.

A glucose-regulated protein, GRP58, is down-regulated in C57B6 mouse liver after diethylhexyl phthalate exposure

Diethylhexyl phthalate (DEHP) is a widely used plasticizer that induces peroxisome proliferation in rodents. Prolonged exposure to DEHP results in a variety of toxic effects, the most significant of which appears to be an increased incidence of liver cancer and male reproductive toxicity in rodents. Accompanying these toxic effects is the induction of a number of genes within the liver, particularly those genes involved in peroxisomal fatty acid beta-oxidation and members of the cytochrome P450 family, CYP4A. In order to explore which additional genes may be altered by DEHP exposure, mRNA differential display was performed using total liver RNA from male C57B6 mice that were treated with either O or 2% DEHP in their diet for 7 days. In doing so, a number of partial cDNAs representing messages that are potentially differentially expressed have been isolated. One of these cDNAs was found to be similar to the previously cloned gene, GRP58. Analysis by RNase protection assay and North hybridization have shown that the transcript for GRP58 is down-regulated in the liver after DEHP exposure. Analysis of dose-response exposures to DEHP by reverse transcription (RT)-PCR confirm these results and also shows that GRP58 is not altered in kidney or testis. Immunoblot analysis using GRP58-specific antibodies also shows a decrease in GRP58 protein levels in DEHP-treated mice. Moreover, exposure of mice to another peroxisome proliferator, clofibrate, results in a slight down-regulation of GRP58 at the highest dose, 0.5%. Thus, it appears as if DEHP and clofibrate can use different pathways to affect gene expression.