In vivo phosphoenolpyruvate carboxykinase promoter mapping identifies disrupted hormonal synergism as a target of inflammation during sepsis in mice

O-GlcNAcylated p53 in the liver modulates hepatic glucose production

p53 regulates several signaling pathways to maintain the metabolic homeostasis of cells and modulates the cellular response to stress. Deficiency or excess of nutrients causes cellular metabolic stress, and we hypothesized that p53 could be linked to glucose maintenance. We show here that upon starvation hepatic p53 is stabilized by O-GlcNAcylation and plays an essential role in the physiological regulation of glucose homeostasis. More specifically, p53 binds to PCK1 promoter and regulates its transcriptional activation, thereby controlling hepatic glucose production. Mice lacking p53 in the liver show a reduced gluconeogenic response during calorie restriction. Glucagon, adrenaline and glucocorticoids augment protein levels of p53, and administration of these hormones to p53 deficient human hepatocytes and to liver-specific p53 deficient mice fails to increase glucose levels. Moreover, insulin decreases p53 levels, and over-expression of p53 impairs insulin sensitivity. Finally, protein levels of p53, as well as genes responsible of O-GlcNAcylation are elevated in the liver of type 2 diabetic patients and positively correlate with glucose and HOMA-IR. Overall these results indicate that the O-GlcNAcylation of p53 plays an unsuspected key role regulating in vivo glucose homeostasis.

Glucocorticoids in Sepsis: To Be or Not to Be

Sepsis is a highly lethal syndrome resulting from dysregulated immune and metabolic responses to infection, thereby compromising host homeostasis. Activation of the hypothalamic–pituitary–adrenal (HPA) axis and subsequently adrenocortical glucocorticoid (GC) production during sepsis are important regulatory processes to maintain homeostasis. Multiple preclinical studies have proven the pivotal role of endogenous GCs in tolerance against sepsis by counteracting several of the sepsis characteristics, such as excessive inflammation, vascular defects, and hypoglycemia. Sepsis is however often complicated by dysfunction of the HPA axis, resulting from critical-illness-related corticosteroid insufficiency (CIRCI) and GC resistance. Therefore, GCs have been tested as an adjunctive therapy in sepsis and septic shock in different randomized clinical trials (RCTs). Nonetheless, these studies produced conflicting results. Interestingly, adding vitamin C and thiamin to GC therapy enhances the effects of GCs, probably by reducing GC resistance, and this results in an impressive reduction in sepsis mortality as was shown in two recent preliminary retrospective before–after studies. Multiple RCTs are currently underway to validate this new combination therapy in sepsis.

Detection of endotoxin in plasma of hospitalized diarrheic calves

OBJECTIVES

To investigate whether lipopolysaccharide (LPS) is present in plasma of calves with naturally occurring diarrhea. The second objective was to determine whether plasma [LPS] correlates with clinical, hematological, biochemical, and acid-base variables, and whether [LPS] differs between surviving and nonsurviving diarrheic calves.

DESIGN

Prospective observational study (January 2012-May 2014).

SETTING

Veterinary teaching hospital.

ANIMALS

Thirty-four calves <28 days old admitted for diagnosis and treatment of diarrhea and 30 healthy control calves.

MEASUREMENTS AND MAIN RESULTS

Admission demographics, physical examination, blood gas, biochemistry analysis, and outcome data were recorded. Plasma concentration of LPS was determined using a bovine LPS ELISA assay. Plasma [LPS] was detected in both healthy and diarrheic calves. Plasma [LPS] was significantly higher in diarrheic than healthy calves (median: 0.99 ng/mL; Interquartile range (IQR): 0.068, vs 0.88 ng/mL; 0.065 ng/mL, respectively; P < 0.001). Plasma [LPS] was higher in nonsurviving (1.04 ng/mL; 0.07 ng/mL) than in surviving calves (0.98 ng/mL; 0.022 ng/mL; P < 0.001). Plasma [LPS] was higher in beef (1.07 ng/mL; 0.182 ng/mL) than in dairy diarrheic calves (0.99 ng/mL; 0.022 ng/mL; P < 0.001). In diarrheic calves, plasma [LPS] correlated with [l-lactate] (r² = 0.496; P = 0.002); hypoglycemia (r² = -0.453; P = 0.007); increased unmeasured strong ions (r² = 0.332; P = 0.050), [Mg²⁺ ] (r² = 0.475; P = 0.004), and [phosphate] (r² = 0.468; P = 0.005), and increased aspartate aminotransferase activity (r² = 0.348; P = 0.003).

CONCLUSIONS

This study highlights a potential role of LPS in the pathogenesis of metabolic derangements such as hyperlactatemia, hypoglycemia, and increased concentration of unmeasured strong anions in diarrheic calves. Further investigation evaluating the effect of LPS on l-lactate and glucose metabolism in diarrheic calves is warranted.

Hypothermia Promotes Interleukin-22 Expression and Fine-Tunes Its Biological Activity

Disturbed homeostasis as a result of tissue stress can provoke leukocyte responses enabling recovery. Since mild hypothermia displays specific clinically relevant tissue-protective properties and interleukin (IL)-22 promotes healing at host/environment interfaces, effects of lowered ambient temperature on IL-22 were studied. We demonstrate that a 5-h exposure of endotoxemic mice to 4°C reduces body temperature by 5.0° and enhances splenic and colonic il22 gene expression. In contrast, tumor necrosis factor-α and IL-17A were not increased. In vivo data on IL-22 were corroborated using murine splenocytes and human peripheral blood mononuclear cells (PBMC) cultured upon 33°C and polyclonal T cell activation. Upregulation by mild hypothermia of largely T-cell-derived IL-22 in PBMC required monocytes and associated with enhanced nuclear T-cell nuclear factor of activated T cells (NFAT)-c2. Notably, NFAT antagonism by cyclosporin A or FK506 impaired IL-22 upregulation at normothermia and entirely prevented its enhanced expression upon hypothermic culture conditions. Data suggest that intact NFAT signaling is required for efficient IL-22 induction upon normothermic and hypothermic conditions. Hypothermia furthermore boosted early signal transducer and activator of transcription 3 activation by IL-22 and shaped downstream gene expression in epithelial-like cells. Altogether, data indicate that hypothermia supports and fine-tunes IL-22 production/action, which may contribute to regulatory properties of low ambient temperature.

Thyroid stimulating hormone increases hepatic gluconeogenesis via CRTC2

Epidemiological evidence indicates that thyroid stimulating hormone (TSH) is positively correlated with abnormal glucose levels. We previously reported that TSH has direct effects on gluconeogenesis. However, the underlying molecular mechanism remains unclear. In this study, we observed increased fasting blood glucose and glucose production in a mouse model of subclinical hypothyroidism (only elevated TSH levels). TSH acts via the classical cAMP/PKA pathway and CRTC2 regulates glucose homeostasis. Thus, we explore whether CRTC2 is involved in the process of TSH-induced gluconeogenesis. We show that TSH increases CRTC2 expression via the TSHR/cAMP/PKA pathway, which in turn upregulates hepatic gluconeogenic genes. Furthermore, TSH stimulates CRTC2 dephosphorylation and upregulates p-CREB (Ser133) in HepG2 cells. Silencing CRTC2 and CREB decreases the effect of TSH on PEPCK-luciferase, the rate-limiting enzyme of gluconeogenesis. Finally, the deletion of TSHR reduces the levels of the CRTC2:CREB complex in mouse livers. This study demonstrates that TSH activates CRTC2 via the TSHR/cAMP/PKA pathway, leading to the formation of a CRTC2:CREB complex and increases hepatic gluconeogenesis.

Hypothalamic AMPK activation blocks lipopolysaccharide inhibition of glucose production in mice liver

Endotoxic hypoglycaemia has an important role in the survival rates of septic patients. Previous studies have demonstrated that hypothalamic AMP-activated protein kinase (hyp-AMPK) activity is sufficient to modulate glucose homeostasis. However, the role of hyp-AMPK in hypoglycaemia associated with endotoxemia is unknown. The aims of this study were to examine hyp-AMPK dephosphorylation in lipopolysaccharide (LPS)-treated mice and to determine whether pharmacological hyp-AMPK activation could reduce the effects of endotoxemia on blood glucose levels. LPS-treated mice showed reduced food intake, diminished basal glycemia, increased serum TNF-α and IL-1β levels and increased hypothalamic p-TAK and TLR4/MyD88 association. These effects were accompanied by hyp-AMPK/ACC dephosphorylation. LPS-treated mice also showed diminished liver expression of PEPCK/G6Pase, reduction in p-FOXO1, p-AMPK, p-STAT3 and p-JNK level and glucose production. Pharmacological hyp-AMPK activation blocked the effects of LPS on the hyp-AMPK phosphorylation, liver PEPCK expression and glucose production. Furthermore, the effects of LPS were TLR4-dependent because hyp-AMPK phosphorylation, liver PEPCK expression and fasting glycemia were not affected in TLR4-mutant mice. These results suggest that hyp-AMPK activity may be an important pharmacological target to control glucose homeostasis during endotoxemia.

Interplay of the inflammatory and stress systems in a hepatic cell line: interactions between glucocorticoid receptor agonists and interleukin-6

The liver plays an important role in inflammation and stress by producing the acute phase proteins (APPs) required for resolution of inflammation as well as by delivering systemic glucose, through gluconeogenesis, required to fuel the stress response. Disruption of the interplay between interleukin 6 (IL-6) and glucocorticoids (GCs), the peripheral mediators of inflammation and stress, respectively, may lead to side-effects associated with the pharmacological use of GCs. The current study investigated the interplay between IL-6 and GCs in a hepatoma cell line (BWTG3) at protein (protein activity assays, Western blotting, and ELISA) and mRNA (qPCR) levels. Specifically, the action of dexamethasone (Dex), a known antiinflammatory drug and glucocorticoid receptor (GR) agonist, is compared to that of Compound A (CpdA), a selective glucocorticoid receptor agonist (SEGRA). CpdA, like IL-6, but unlike Dex, increases GR binding and decreases the metabolic enzymes, tyrosine aminotransferase, phosphoenolpyruvate carboxykinase, and gamma glutamyltransferase, at protein or mRNA level. Like Dex, both CpdA and IL-6 increase the positive APPs, serum amyloid A and C-reactive protein, and decrease the negative APP, corticosteroid binding globulin. The study shows that the GC, Dex, and IL-6 generally have divergent effects on the GR and metabolic enzymes, while their functions are convergent on the APPs. In contrast to Dex, CpdA has effects convergent to that of IL-6 on the GR, metabolic enzymes, and APPs. Thus these findings suggest that CpdA, like Dex, modulates APPs, leading to effective control of inflammation, while, in contrast to Dex, it is less likely to lead to GC-induced side-effects.

Role of glucocorticoids and the glucocorticoid receptor in metabolism: insights from genetic manipulations

Since the discovery of the beneficial effects of adrenocortical extracts for treating adrenal insufficiency more than 80 years ago, glucocorticoids and their cognate, intracellular receptor, the glucocorticoid receptor have been characterized as critical checkpoints in the delicate hormonal control of energy homeostasis in mammals. Whereas physiological levels of glucocorticoids are required for proper metabolic control, aberrant glucocorticoid action has been linked to a variety of pandemic metabolic diseases, such as type II diabetes and obesity. Based on its importance for human health, studies of the molecular mechanisms of within the glucocorticoid signaling axis have become a major focus in biomedical research. In particular, the understanding of tissue-specific functions of the glucocorticoid receptor pathway has been proven to be of substantial value for the development of novel therapies in the treatment of chronic metabolic disorders. Therefore, this review focuses on the consequences of endogenous and experimental modulation of glucocorticoid receptor expression for metabolic homeostasis and dysregulation, particularly emphasizing tissue-specific contributions of the glucocorticoid pathway to the control of energy metabolism.