Metyrapone prevents cortisone-induced preadipocyte differentiation by depleting luminal NADPH of the endoplasmic reticulum

Alternative splicing plays a nonredundant role in greater amberjack (Seriola dumerili) in acclimation to ambient salinity fluctuations

Alternative splicing (AS) is an important post-transcriptional mechanism for adaptation of fish to environmental stress. Here, we performed a genome-wide investigation to AS dynamics in greater amberjack (Seriola dumerili), an economical marine teleost, in response to hypo- (10 ppt) and hyper-salinity (40 ppt) stresses. Totally, 2267-2611 differentially spliced events were identified in gills and kidney upon the exposure to undesired salinity regimes. In gills, genes involved in energy metabolism, stimulus response and epithelial cell differentiation were differentially spliced in response to salinity variation, while sodium ion transport and cellular amide metabolism were enhanced in kidney to combat the adverse impacts of salinity changes. Most of these differentially spliced genes were not differentially expressed, and AS was found to regulate different biological processes from differential gene expression, indicative of the functionally nonredundant role of AS in modulating salinity acclimation in greater amberjack. Together, our study highlights the important contribution of post-transcriptional mechanisms to the adaptation of fish to ambient salinity fluctuations and provides theoretical guidance for the conservation of marine fishery resources against increasingly environmental challenges.

The Gut Microbiota Affects Corticosterone Production in the Murine Small Intestine

Glucocorticoids (GCs) are hormones that are released in response to stressors and exhibit many activities, including immunomodulatory and anti-inflammatory activities. They are primarily synthesized in the adrenal gland but are also produced in peripheral tissues via regeneration of adrenal 11-oxo metabolites or by de novo synthesis from cholesterol. The present study investigated the influence of the microbiota on de novo steroidogenesis and regeneration of corticosterone in the intestine of germ-free (GF) and specific pathogen-free mice challenged with a physical stressor (anti-CD3 antibody i.p. injection). In the small intestine, acute immune stress resulted in increased mRNA levels of the proinflammatory cytokines IL1β, IL6 and Tnfα and genes involved in de novo steroidogenesis (Stard3 and Cyp11a1), as well as in regeneration of active GCs from their 11-oxo metabolites (Hsd11b1). GF mice showed a generally reduced transcriptional response to immune stress, which was accompanied by decreased intestinal corticosterone production and reduced expression of the GC-sensitive marker Fkbp5. In contrast, the interaction between stress and the microbiota was not detected at the level of plasma corticosterone or the transcriptional response of adrenal steroidogenic enzymes. The results indicate a differential immune stress-induced intestinal response to proinflammatory stimuli and local corticosterone production driven by the gut microbiota.

Glucose-6-phosphatase-α participates in dopaminergic differentiation

OBJECTIVE

 Induction of dopaminergic (DA) differentiation is a cell-based therapy for Parkinson's disease (PD). Here, we explore the key factors of DA differentiation with a focus on glucose-6-phosphatase (G6Pase), a marker enzyme for the endoplasmic reticulum (ER) associated with cell differentiation.

METHODS

 We cultured SH-SY5Y human neuroblastoma cells, a model system for PD research, and added glial cell-derived neurotrophic factor (GDNF; 25, 50, or 100 ng/ml) to stimulate differentiation. Subsequently, several methods, such as microRNA/mRNA microarrays, quantitative real-time polymerase chain reaction (qRT-PCR) and western blot were used to detect target genes and proteins respectively.

RESULTS

 Light microscopy revealed that 50 ng/ml GDNF most effectively induced DA differentiation. MicroRNA/mRNA microarrays identified that G6PC mRNA was significantly upregulated, which might be influenced by three downregulated microRNAs. Follow-up qRT-PCR results were consistent with the microarray findings, and western blots also supported the results.

DISCUSSION

Taken together, our results demonstrate that G6PC, a subunit of G6Pase, participates in DA differentiation. Our findings may contribute to provide a foundation for the research on the mechanism of DA differentiation as well as cell-based therapy for PD.

Fructose, Glucocorticoids and Adipose Tissue: Implications for the Metabolic Syndrome

The modern Western society lifestyle is characterized by a hyperenergetic, high sugar containing food intake. Sugar intake increased dramatically during the last few decades, due to the excessive consumption of high-sugar drinks and high-fructose corn syrup. Current evidence suggests that high fructose intake when combined with overeating and adiposity promotes adverse metabolic health effects including dyslipidemia, insulin resistance, type II diabetes, and inflammation. Similarly, elevated glucocorticoid levels, especially the enhanced generation of active glucocorticoids in the adipose tissue due to increased 11β-hydroxysteroid dehydrogenase 1 (11β-HSD1) activity, have been associated with metabolic diseases. Moreover, recent evidence suggests that fructose stimulates the 11β-HSD1-mediated glucocorticoid activation by enhancing the availability of its cofactor NADPH. In adipocytes, fructose was found to stimulate 11β-HSD1 expression and activity, thereby promoting the adipogenic effects of glucocorticoids. This article aims to highlight the interconnections between overwhelmed fructose metabolism, intracellular glucocorticoid activation in adipose tissue, and their metabolic effects on the progression of the metabolic syndrome.

Cortisol promotes endoplasmic glucose production via pyridine nucleotide redox

Both increased adrenal and peripheral cortisol production, the latter governed by 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1), contribute to the maintenance of fasting blood glucose. In the endoplasmic reticulum (ER), the pyridine nucleotide redox state (NADP/NADPH) is dictated by the concentration of glucose-6-phosphate (G6P) and the coordinated activities of two enzymes, hexose-6-phosphate dehydrogenase (H6PDH) and 11β-HSD1. However, luminal G6P may similarly serve as a substrate for hepatic glucose-6-phophatase (G6Pase). A tacit belief is that the G6P pool in the ER is equally accessible to both H6PDH and G6Pase. Based on our inhibition studies and kinetic analysis in isolated rat liver microsomes, these two aforesaid luminal enzymes do share the G6P pool in the ER, but not equally. Based on the kinetic modeling of G6P flux, the ER transporter for G6P (T1) preferentially delivers this substrate to G6Pase; hence, the luminal enzymes do not share G6P equally. Moreover, cortisol, acting through 11β-HSD1, begets a more reduced pyridine redox ratio. By altering this luminal redox ratio, G6P flux through H6PDH is restrained, allowing more G6P for the competing enzyme G6Pase. And, at low G6P concentrations in the ER lumen, which occur during fasting, this acute cortisol-induced redox adjustment promotes glucose production. This reproducible cortisol-driven mechanism has been heretofore unrecognized.

mTOR inhibition increases cell viability via autophagy induction during endoplasmic reticulum stress - An experimental and modeling study

Unfolded or misfolded proteins in the endoplasmic reticulum (ER) trigger an adaptive ER stress response known as unfolded protein response (UPR). Depending on the severity of ER stress, either autophagy-controlled survival or apoptotic cell death can be induced. The molecular mechanisms by which UPR controls multiple fate decisions have started to emerge. One such molecular mechanism involves a master regulator of cell growth, mammalian target of rapamycin (mTOR), which paradoxically is shown to have pro-apoptotic role by mutually interacting with ER stress response. How the interconnections between UPR and mTOR influence the dynamics of autophagy and apoptosis activation is still unclear. Here we make an attempt to explore this problem by using experiments and mathematical modeling. The effect of perturbed mTOR activity in ER stressed cells was studied on autophagy and cell viability by using agents causing mTOR pathway inhibition (such as rapamycin or metyrapone). We observed that mTOR inhibition led to an increase in cell viability and was accompanied by an increase in autophagic activity. It was also shown that autophagy was activated under conditions of severe ER stress but that in the latter phase of stress it was inhibited at the time of apoptosis activation. Our mathematical model shows that both the activation threshold and temporal dynamics of autophagy and apoptosis inducers are sensitive to variation in mTOR activity. These results confirm that autophagy has cytoprotective role and is activated in mutually exclusive manner with respect to ER stress levels.

Physiologically achievable doses of resveratrol enhance 3T3-L1 adipocyte differentiation

PURPOSE

Resveratrol is a natural polyphenolic stilbene widely found in grapes, berries, and other plants. Caloric restriction-like effects of resveratrol have been associated with suppressive and apoptotic effects on adipocyte differentiation in vitro when used at high doses (≥ 20 µM), which may not be achievable in vivo. The aim of this study was to investigate the effects of resveratrol at physiologically achievable low doses (1 and 10 μM) on 3T3-L1 adipocyte differentiation.

METHODS

3T3-L1 preadipocytes were differentiated into adipocytes using a modified adipogenic cocktail in the presence or absence of resveratrol. Differentiation was determined by lipid accumulation and mRNA expression of marker genes. Activation of glucocorticoid receptor (GR) and peroxisome proliferator-activated receptor γ (PPARγ) was determined by transcription factor-mediated reporter assays and mRNA expression of target genes. Protein samples were collected for the study of AMPK activation.

RESULTS

Resveratrol at physiologically achievable doses (1 and 10 µM) significantly enhanced 3T3-L1 adipocyte differentiation although the effect was less pronounced compared with that achieved under optimal differentiation cocktail in vitro. Resveratrol (1-50 µM) dose dependently activated or synergized with the synthetic ligand or adipogenic treatment to activate GR and PPARγ. However, resveratrol induced cell death when used at doses above 10 µM in differentiating cells.

CONCLUSIONS

Our results report for the first time that resveratrol at physiologically achievable doses (1 and 10 µM) enhances 3T3-L1 adipocyte differentiation, which supports the emerging paradigm that enhanced adipocyte differentiation may be associated with caloric restriction-like metabolic effects for resveratrol.

Metyrapone alleviates deleterious effects of maternal food restriction on lung development and growth of rat offspring

Maternal food restriction (MFR) causes intrauterine growth restriction, a known risk factor for developing chronic lung disease. However, it is unknown whether this negative outcome is gender specific or preventable by blocking the MFR-induced hyperglucocorticoidism. Using a well-established rat model, we used metyrapone (MTP), an inhibitor of glucocorticoid synthesis, to study the MFR-induced lung changes on postnatal day (p) 21 in a gender-specific manner. From embryonic day 10 until delivery, pregnant dams were fed either an ad libitum diet or a 50% caloric restricted diet with or without MTP supplementation. Postnatally, the offspring were fed ad libitum from healthy dams until p21. Morphometric, Western blot, and immunohistochemical analysis of the lungs demonstrated that MTP mitigated the MFR-mediated decrease in alveolar count, decrease in adipogenic protein peroxisome proliferator-activated receptor γ, increase in myogenic proteins (fibronectin, α-smooth muscle actin, and calponin), increase in Wnt signaling intermediates (lymphoid enhancer-binding factor 1 and β-catenin), and increase in glucocorticoid receptor (GR) levels. The MFR-induced lung phenotype and the effects of MTP were similar in both genders. To elucidate the mechanism of MFR-induced shift of the adipogenic-to-myogenic phenotype, lung fibroblasts were used to independently study the effects of (1) nutrient restriction and (2) excess steroid exposure. Nutrient deprivation increased myogenic proteins, Wnt signaling intermediates, and GR, all changes blocked by protein supplementation. MTP also blocked, likely by normalizing nicotinamide adenine dinucleotide phosphate levels, the corticosterone-induced increase in myogenic proteins, but had no effect on GR levels. In summary, protein restriction and increased glucocorticoid levels appear to be the key players in MFR-induced lung disease, affecting both genders.

Depletion of luminal pyridine nucleotides in the endoplasmic reticulum activates autophagy with the involvement of mTOR pathway

It has been recently shown that redox imbalance of luminal pyridine nucleotides in the endoplasmic reticulum (ER) together with oxidative stress results in the activation of autophagy. In the present study we demonstrated that decrease of luminal NADPH/NADP(+) ratio alone by metyrapone was sufficient to promote the mechanism of "self-eating" detected by the activation of LC3. Depletion of luminal NADPH had also significant effect on the key proteins of mTOR pathway, which got inactivated by dephosphorylation. These findings were also confirmed by silencing the proteins (glucose-6-phosphate transporter and hexose-6-phosphate dehydrogenase) responsible for NADPH generation in the ER lumen. However, silencing the key components and addition of metyrapone had different effects on downstream substrates 4EBP1 and p70S6K of mTOR. The applied treatments did not compromise the viability of the cells. Our data suggest that ER stress caused by luminal NADPH depletion activates a pro-survival autophagic mechanism firmly coupled to the activation of mTOR pathway.

Inhibition of microsomal cortisol production by (-)-epigallocatechin-3-gallate through a redox shift in the endoplasmic reticulum--a potential new target for treating obesity-related diseases

Conversion of cortisone to cortisol by 11β-hydroxysteroid dehydrogenase type 1 (11βHSD1) in the endoplasmic reticulum (ER) of the target cells is a major determinant of glucocorticoid action, and plays an important role in the development of obesity-related diseases. Inhibition of 11βHSD1 activity is, therefore, considered as a promising novel strategy for the treatment of metabolic syndrome and diabetes. Tea flavanols and their major representative, epigallocatechin gallate are known as antiobesity and antidiabetic agents. Their impacts on blood glucose level, hepatic glucose production, and insulin responsiveness resemble those observed on inhibition or depletion of 11βHSD1. We aimed to study the effect of epigallocatechin gallate on 11βHSD1 activity in ER-derived rat liver microsomes by measuring cortisone and cortisol with HPLC. Cortisol production was efficiently suppressed in a concentration dependent manner in intact microsomal vesicles. However, this effect was abolished by membrane permeabilization; and the three proteins involved in the overall process (11βHSD1, hexose 6-phosphate dehydrogenase, and glucose 6-phosphate transporter) were not or only mildly affected. Further investigation revealed the oxidation of luminal NADPH to NADP⁺, which attenuates cortisone reduction and favors cortisol oxidation in this compartment. Such a redox shift in the ER lumen might contribute to the beneficial health effects of tea flavanols and should be regarded as a promising strategy for the development of novel selective 11βHSD1 inhibitors to treat obesity-related diseases.

[Importance of the 11β-hydroxysteroid dehydrogenase enzyme in clinical disorders]

Glucocorticoids play an important role in the regulation of carbohydrate and amino acid metabolism, they modulate the function of the immune system, and contribute to stress response. Increased and decreased production of glucocorticoids causes specific diseases. In addition to systemic hypo- or hypercortisolism, alteration of local synthesis and metabolism of cortisol may result in tissue-specific hypo- or hypercortisolism. One of the key enzymes participating in the local synthesis and metabolism of cortisol is the 11β-hydroxysteroid dehydrogenase enzyme. Two isoforms, type 1 and type 2 enzymes are located in the endoplasmic reticulum and catalyze the interconversion of hormonally active cortisol and inactive cortisone. The type 1 enzyme mainly works as an activator, and it is responsible for the generation of cortisol from cortisone in liver, adipose tissue, brain and bone. The gene encoding this enzyme is located on chromosome 1. The authors review the physiological and pathophysiological processes related to the function of the type 1 11β-hydroxysteroid dehydrogenase enzyme. They summarize the potential significance of polymorphic variants of the enzyme in clinical diseases as well as knowledge related to inhibitors of enzyme activity. Although further studies are still needed, inhibition of the enzyme activity may prove to be an effective tool for the treatment of several diseases such as obesity, osteoporosis and type 2 diabetes.

Effects of parabens on adipocyte differentiation

Parabens are a group of alkyl esters of p-hydroxybenzoic acid that include methylparaben, ethylparaben, propylparaben, butylparaben, and benzylparaben. Paraben esters and their salts are widely used as preservatives in cosmetics, toiletries, food, and pharmaceuticals. Humans are exposed to parabens through the use of such products from dermal contact, ingestion, and inhalation. However, research on the effects of parabens on health is limited, and the effects of parabens on adipogenesis have not been systematically studied. Here, we report that (1) parabens promote adipogenesis (or adipocyte differentiation) in murine 3T3-L1 cells, as revealed by adipocyte morphology, lipid accumulation, and mRNA expression of adipocyte-specific markers; (2) the adipogenic potency of parabens is increased with increasing length of the linear alkyl chain in the following potency ranking order: methyl- < ethyl- < propyl- < butylparaben. The extension of the linear alkyl chain with an aromatic ring in benzylparaben further augments the adipogenic ability, whereas 4-hydroxybenzoic acid, the common metabolite of all parabens, and the structurally related benzoic acid (without the OH group) are inactive in promoting 3T3-L1 adipocyte differentiation; (3) parabens activate glucocorticoid receptor and/or peroxisome proliferator-activated receptor γ in 3T3-L1 preadipocytes; however, no direct binding to, or modulation of, the ligand binding domain of the glucocorticoid receptor by parabens was detected by glucocorticoid receptor competitor assays; and lastly, (4) parabens, butyl- and benzylparaben in particular, also promote adipose conversion of human adipose-derived multipotent stromal cells. Our results suggest that parabens may contribute to obesity epidemic, and the role of parabens in adipogenesis in vivo needs to be examined further.

Tissue-specific dysregulation of hexose-6-phosphate dehydrogenase and glucose-6-phosphate transporter production in db/db mice as a model of type 2 diabetes

AIMS/HYPOTHESIS

Tissue-specific amplification of glucocorticoid action through 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) affects the development of the metabolic syndrome. Hexose-6-phosphate dehydrogenase (H6PDH) mediates intracellular NADPH availability for 11β-HSD1 and depends on the glucose-6-phosphate transporter (G6PT). Little is known about the tissue-specific alterations of H6PDH and G6PT and their contributions to local glucocorticoid action in db/db mice.

METHODS

We characterised the role of H6PDH and G6PT in pre-receptor metabolism of glucocorticoids by examining the production of the hepatic 11β-HSD1-H6PDH-G6PT system in db/db mice.

RESULTS

We observed that increased production of hepatic H6PDH in db/db mice was paralleled by upregulation of hepatic G6PT production and responded to elevated circulating levels of corticosterone. Treatment of db/db mice with the glucocorticoid antagonist RU486 markedly reduced production of both H6PDH and 11β-HSD1 and improved hyperglycaemia and insulin resistance. The reduction of H6PDH and 11β-HSD1 production by RU486 was accompanied by RU486-induced suppression of hepatic G6pt (also known as Slc37a4) mRNA. Incubation of mouse primary hepatocytes with corticosterone enhanced G6PT and H6PDH production with corresponding activation of 11β-HSD1 and PEPCK: effects that were blocked by RU486. Knockdown of H6pd by small interfering RNA showed effects comparable with those of RU486 for attenuating the corticosterone-induced H6PDH production and 11ß-HSD1 reductase activity in these intact cells. Addition of the G6PT inhibitor chlorogenic acid to primary hepatocytes suppressed H6PDH production.

CONCLUSIONS/INTERPRETATION

These findings suggest that increased hepatic H6PDH and G6PT production contribute to 11β-HSD1 upregulation of local glucocorticoid action that may be related to the development of type 2 diabetes.

Decreased prereceptorial glucocorticoid activating capacity in starvation due to an oxidative shift of pyridine nucleotides in the endoplasmic reticulum

Redox state of pyridine nucleotides of the endoplasmic reticulum (ER) lumen was determined in different nutritional conditions. NADPH-dependent cortisone reduction and NADP(+)-dependent cortisol oxidation were measured in rat liver microsomes, by utilizing the luminal 11β-hydroxysteroid dehydrogenase type 1 activity. Cortisone reduction decreased, while cortisol oxidation increased during onward starvation, showing that the luminal NADPH/NADP(+) ratio was substantially decreased. Cortisone or metyrapone addition caused a smaller decrease in NADPH fluorescence in microsomes from starved rats. The results demonstrate that nutrient supply is mirrored by the redox state of ER luminal pyridine nucleotides.

Redox control of endoplasmic reticulum function

The lumen of the endoplasmic reticulum constitutes a separate intracellular compartment with a special proteome and metabolome. The redox conditions of the organelle are also characteristically different from those of the other subcellular compartments. The luminal environment has been considered more oxidizing than the cytosol due to the presence of oxidative protein folding. However, recent observations suggest that redox systems in reduced and oxidized states are present simultaneously. The concerted action of membrane transporters and oxidoreductase enzymes maintains the oxidized state of the thiol-disulfide and the reduced state of the pyridine nucleotide redox systems, which are prerequisites for the normal redox reactions localized in the organelle. The powerful thiol-oxidizing machinery of oxidative protein folding continuously challenges the local antioxidant defense. Alterations of the luminal redox conditions, either in oxidizing or reducing direction, affect protein processing, are sensed by the accumulation of misfolded/unfolded proteins, and may induce endoplasmic reticulum stress and unfolded protein response. The activated signaling pathways attempt to restore the balance between protein loading and processing and induce programmed cell death if these attempts fail. Recent findings strongly support the involvement of redox-based endoplasmic reticulum stress in a plethora of human diseases, either as causative agents or as complications.

The glucocorticoid-activating enzyme 11beta-hydroxysteroid dehydrogenase type 1 has broad substrate specificity: Physiological and toxicological considerations

The primary function of 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) is to catalyze the conversion of inactive to active glucocorticoid hormones and to modulate local glucocorticoid-dependent gene expression. Thereby 11beta-HSD1 plays a key role in the regulation of metabolic functions and in the adaptation of the organism to energy requiring situations. Importantly, elevated 11beta-HSD1 activity has been associated with metabolic disorders, and recent investigations with rodent models of obesity and type 2 diabetes provided evidence for beneficial effects of 11beta-HSD1 inhibitors, making this enzyme a promising therapeutic target. Several earlier and recent studies, mainly performed in vitro, revealed a relatively broad substrate spectrum of 11beta-HSD1 and suggested that this enzyme has additional functions in the metabolism of some neurosteroids (7-oxy- and 11-oxyandrogens and -progestins) and 7-oxysterols, as well as in the detoxification of various xenobiotics that contain reactive carbonyl groups. While there are many studies on the effect of inhibitors on cortisone reduction and circulating glucocorticoid levels and on the transcriptional regulation of 11beta-HSD1 in obesity and diabetes, only few address the so-called alternative functions of this enzyme. We review recent progress on the biochemical characterization of 11beta-HSD1, with a focus on cofactor and substrate specificity and on possible alternative functions of this enzyme.

Altered redox state of luminal pyridine nucleotides facilitates the sensitivity towards oxidative injury and leads to endoplasmic reticulum stress dependent autophagy in HepG2 cells

Maintenance of the reduced state of luminal pyridine nucleotides in the endoplasmic reticulum - an important pro-survival factor in the cell - is ensured by the concerted action of glucose-6-phosphate transporter and hexose-6-phosphate dehydrogenase. The mechanism by which the redox imbalance leads to cell death was investigated in HepG2 cells. The chemical inhibition of the glucose-6-phosphate transporter, the silencing of hexose-6-phosphate dehydrogenase and/or the glucose-6-phosphate transporter, or the oxidation of luminal NADPH by themselves did not cause a significant loss of cell viability. However, these treatments caused ER calcium store depletion. If these treatments were supplemented with the administration of a subliminal dose of the oxidizing agent menadione, endoplasmic reticulum vacuolization and a loss of viability were observed. Combined treatments resulted in the activation of ATF6 and procaspase-4, and in the induction of Grp78 and CHOP. In spite of the presence of UPR markers and proapoptotic signaling the effector caspases - caspase-3 and caspase-7 - were not active. On the other hand, an elevation of the autophagy marker LC3B was observed. Immunohistochemistry revealed a punctuated distribution of LC3B II, coinciding with the vacuolization of the endoplasmic reticulum. The results suggest that altered redox state of endoplasmic reticulum luminal pyridine nucleotides sensitizes the cell to autophagy.

Body mass index is a major determinant of abdominal fat accumulation in pre-, peri- and post-menopausal women

OBJECTIVE

To investigate the role of menopause, body mass index (BMI) and aging on body fat distribution in women.

DESIGN

In this population-based cross-sectional study, 335 women (126 in pre-menopause, 75 in peri-menopause and 134 in post-menopause according to Stages of Reproductive Aging Workshop criteria) were evaluated for body mass composition and fat distribution by dual X-ray absorptiometry procedure. A sub-group of 79 women with similar age and BMI was extracted from the sample to examine the relative influence of BMI in body fat distribution.

RESULTS

ANCOVA analysis of total sample showed an age-independent increase of total fat mass (p < 0.001) and percentage on total weight (p < 0.001), arms fat mass (p < 0.01), legs fat mass percentage on total fat (p < 0.05) and trunk fat mass (p < 0.001) and percentage (p < 0.05) in peri- and post- with respect to pre-menopausal women. In the sub-sample including age and BMI matched women the difference of regional fat parameters among menopausal status was no more statistically significant.

CONCLUSION

BMI, and not age, is the main determinant of the increase of body fat mass (total and abdominal) observed during the menopausal transition.

Endoplasmic reticulum: nutrient sensor in physiology and pathology

The endoplasmic reticulum (ER) is a metabolic organelle and an ideal nutrient sensor. In response to hypoglycemia, hyperglycemia or fatty acid overload, the ER triggers the unfolded protein response, which represses protein synthesis, alters insulin responsiveness and favors apoptosis. In addition, the ER affects steroid hormone activation and autophagy. The primary aim of these responses is to adjust the metabolism to environmental changes. Failure of the ER to adapt to changes in nutrient availability can result in a pathological transition in ER functions, as observed in cases of obesity-related diseases. This review highlights the recent evidence that the ER has a prominent role in cellular adaptation, as well as in the pathomechanism of type 2 diabetes.