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Glutathione S-transferase P deficiency induces glucose intolerance via JNK-dependent enhancement of hepatic gluconeogenesis.

ABSTRACT: Hepatic glutathione S-transferases (GSTs) are dysregulated in human obesity, nonalcoholic fatty liver disease, and diabetes. The multifunctional GST pi-isoform (GSTP) catalyzes the conjugation of glutathione with acrolein and inhibits c-Jun NH2-terminal kinase (JNK) activation. Herein, we tested whether GSTP deficiency disturbs glucose homeostasis in mice. Hepatic GST proteins were downregulated by short-term high-fat diet in wild-type (WT) mice concomitant with increased glucose intolerance, JNK activation, and cytokine mRNAs in the liver. Genetic deletion of GSTP did not affect body composition, fasting blood glucose levels, or insulin levels in mice maintained on a normal chow diet; however, compared with WT mice, the GSTP-null mice were glucose intolerant. In GSTP-null mice, pyruvate intolerance, reflecting increased hepatic gluconeogenesis, was accompanied by elevated levels of activated JNK, cytokine mRNAs, and glucose-6-phosphatase proteins in the liver. Treatment of GSTP-null mice with the JNK inhibitor 1,9-pyrazoloanthrone (SP600125) significantly attenuated pyruvate-induced hepatic gluconeogenesis and significantly altered correlations between hepatic cytokine mRNAs and metabolic outcomes in GSTP-null mice. Collectively, these findings suggest that hepatic GSTP plays a pivotal role in glucose handling by regulating JNK-dependent control of hepatic gluconeogenesis. Thus, hepatic GSTP-JNK dysregulation may be a target of new therapeutic interventions during early stages of glucose intolerance to prevent the worsening metabolic derangements associated with human obesity and its relentless progression to diabetes.

SUBMITTER: Ghosh Dastidar S

PROVIDER: S-EPMC6293160 | biostudies-literature | 2018 Nov

REPOSITORIES: biostudies-literature

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Glutathione S-transferase P deficiency induces glucose intolerance via JNK-dependent enhancement of hepatic gluconeogenesis.

Ghosh Dastidar Shubha S Jagatheesan Ganapathy G Haberzettl Petra P Shah Jasmit J Hill Bradford G BG Bhatnagar Aruni A Conklin Daniel J DJ

American journal of physiology. Endocrinology and metabolism 20180828 5

Hepatic glutathione S-transferases (GSTs) are dysregulated in human obesity, nonalcoholic fatty liver disease, and diabetes. The multifunctional GST pi-isoform (GSTP) catalyzes the conjugation of glutathione with acrolein and inhibits c-Jun NH<sub>2</sub>-terminal kinase (JNK) activation. Herein, we tested whether GSTP deficiency disturbs glucose homeostasis in mice. Hepatic GST proteins were downregulated by short-term high-fat diet in wild-type (WT) mice concomitant with increased glucose into ...[more]

PMID: 30153066

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Project description:ObjectiveThe mammalian target of rapamycin (mTOR)/p70 S6 kinase 1 (S6K1) pathway is a critical signaling component in the development of obesity-linked insulin resistance and operates a nutrient-sensing negative feedback loop toward the phosphatidylinositol 3-kinase (PI 3-kinase)/Akt pathway. Whereas acute treatment of insulin target cells with the mTOR complex 1 (mTORC1) inhibitor rapamycin prevents nutrient-induced insulin resistance, the chronic effect of rapamycin on insulin sensitivity and glucose metabolism in vivo remains elusive.Research design and methodsTo assess the metabolic effects of chronic inhibition of the mTORC1/S6K1 pathway, rats were treated with rapamycin (2 mg/kg/day) or vehicle for 15 days before metabolic phenotyping.ResultsChronic rapamycin treatment reduced adiposity and fat cell number, which was associated with a coordinated downregulation of genes involved in both lipid uptake and output. Rapamycin treatment also promoted insulin resistance, severe glucose intolerance, and increased gluconeogenesis. The latter was associated with elevated expression of hepatic gluconeogenic master genes, PEPCK and G6Pase, and increased expression of the transcriptional coactivator peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha) as well as enhanced nuclear recruitment of FoxO1, CRTC2, and CREB. These changes were observed despite normal activation of the insulin receptor substrate/PI 3-kinase/Akt axis in liver of rapamycin-treated rats, as expected from the blockade of the mTORC1/S6K1 negative feedback loop.ConclusionsThese findings unravel a novel mechanism by which mTORC1/S6K1 controls gluconeogenesis through modulation of several key transcriptional factors. The robust induction of the gluconeogenic program in liver of rapamycin-treated rats underlies the development of severe glucose intolerance even in the face of preserved hepatic insulin signaling to Akt and despite a modest reduction in adiposity.

Project description:Endocannabinoids regulate energy balance and lipid metabolism by stimulating the cannabinoid receptor type 1 (CB1). Genetic deletion and pharmacological antagonism have shown that CB1 signaling is necessary for the development of obesity and related metabolic disturbances. However, the sufficiency of endogenously produced endocannabinoids to cause hepatic lipid accumulation and insulin resistance, independent of food intake, has not been demonstrated. Here, we show that a single administration of isopropyl dodecylfluorophosphonate (IDFP), perhaps the most potent pharmacological inhibitor of endocannabinoid degradation, increases hepatic triglycerides (TG) and induces insulin resistance in mice. These effects involve increased CB1 signaling, as they are mitigated by pre-administration of a CB1 antagonist (AM251) and in CB1 knockout mice. Despite the strong physiological effects of CB1 on hepatic lipid and glucose metabolism, little is known about the downstream targets responsible for these effects. To elucidate transcriptional targets of CB1 signaling, we performed microarrays on hepatic RNA isolated from DMSO (control), IDFP and AM251/IDFP-treated mice. The gene for the secreted glycoprotein lipocalin 2 (lcn2), which has been implicated in obesity and insulin resistance, was among those most responsive to alterations in CB1 signaling. The expression pattern of IDFP mice segregated from DMSO mice in hierarchal cluster analysis and AM251 pre-administration reduced (>50%) the majority (303 of 533) of the IDFP induced alterations. Pathway analysis revealed that IDFP altered expression of genes involved in lipid, fatty acid and steroid metabolism, the acute phase response, and amino acid metabolism in a CB1-dependent manner. PCR confirmed array results of key target genes in multiple independent experiments. Overall, we show that acute IDFP treatment induces hepatic TG accumulation and insulin resistance, at least in part through the CB1 receptor, and identify novel cannabinoid responsive genes.

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Dataset Information

Glutathione S-transferase P deficiency induces glucose intolerance via JNK-dependent enhancement of hepatic gluconeogenesis.

Publications

Glutathione S-transferase P deficiency induces glucose intolerance via JNK-dependent enhancement of hepatic gluconeogenesis.

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