MAPK phosphatase-3 promotes hepatic gluconeogenesis through dephosphorylation of forkhead box O1 in mice

Quercetin Regulates Lipid Metabolism and Fat Accumulation by Regulating Inflammatory Responses and Glycometabolism Pathways: A Review

Fat synthesis and lipolysis are natural processes in growth and have a close association with health. Fat provides energy, maintains physiological function, and so on, and thus plays a significant role in the body. However, excessive/abnormal fat accumulation leads to obesity and lipid metabolism disorder, which can have a detrimental impact on growth and even harm one's health. Aside from genetic effects, there are a range of factors related to obesity, such as excessive nutrient intake, inflammation, glycometabolism disease, and so on. These factors could serve as potential targets for anti-obesity therapy. Quercetin is a flavonol that has received a lot of attention recently because of its role in anti-obesity. It was thought to have the ability to regulate lipid metabolism and have a positive effect on anti-obesity, but the processes are still unknown. Recent studies have shown the role of quercetin in lipid metabolism might be related to its effects on inflammatory responses and glycometabolism. The references were chosen for this review with no date restrictions applied based on the topics they addressed, and the databases PubMed and Web of Sicence was used to conduct the references research, using the following search terms: "quercetin", "obesity", "inflammation", "glycometabolism", "insulin sensitivity", etc. This review summarizes the potential mechanisms of quercetin in alleviating lipid metabolism through anti-inflammatory and hypoglycemic signaling pathways, and describes the possible signaling pathways in the interaction of inflammation and glycometabolism, with the goal of providing references for future research and application of quercetin in the regulation of lipid metabolism.

Intestinal dual-specificity phosphatase 6 regulates the cold-induced gut microbiota remodeling to promote white adipose browning

Gut microbiota rearrangement induced by cold temperature is crucial for browning in murine white adipose tissue. This study provides evidence that DUSP6, a host factor, plays a critical role in regulating cold-induced gut microbiota rearrangement. When exposed to cold, the downregulation of intestinal DUSP6 increased the capacity of gut microbiota to produce ursodeoxycholic acid (UDCA). The DUSP6-UDCA axis is essential for driving Lachnospiraceae expansion in the cold microbiota. In mice experiencing cold-room temperature (CR) transitions, prolonged DUSP6 inhibition via the DUSP6 inhibitor (E/Z)-BCI maintained increased cecal UDCA levels and cold-like microbiota networks. By analyzing DUSP6-regulated microbiota dynamics in cold-exposed mice, we identified Marvinbryantia as a genus whose abundance increased in response to cold exposure. When inoculated with human-origin Marvinbryantia formatexigens, germ-free recipient mice exhibited significantly enhanced browning phenotypes in white adipose tissue. Moreover, M. formatexigens secreted the methylated amino acid Nε-methyl-L-lysine, an enriched cecal metabolite in Dusp6 knockout mice that reduces adiposity and ameliorates nonalcoholic steatohepatitis in mice. Our work revealed that host-microbiota coadaptation to cold environments is essential for regulating the browning-promoting gut microbiome.

Ablation of Dual-Specificity Phosphatase 6 Protects against Nonalcoholic Fatty Liver Disease via Cytochrome P450 4A and Mitogen-Activated Protein Kinase

Dual-specificity phosphatase 6 (DUSP6) is a specific phosphatase for mitogen-activated protein kinase (MAPK). This study used a high-fat diet (HFD)-induced murine nonalcoholic fatty liver disease model to investigate the role of DUSP6 in this disease. Wild-type (WT) and Dusp6-haploinsufficiency mice developed severe obesity and liver pathology consistent with nonalcoholic fatty liver disease when exposed to HFD. In contrast, Dusp6-knockout (KO) mice completely eliminated these phenotypes. Furthermore, primary hepatocytes isolated from WT mice exposed to palmitic and oleic acids exhibited abundant intracellular lipid accumulation, whereas hepatocytes from Dusp6-KO mice showed minimal lipid accumulation. Transcriptome analysis revealed significant down-regulation of genes encoding cytochrome P450 4A (CYP4A), known to promote ω-hydroxylation of fatty acids and hepatic steatosis, in Dusp6-KO hepatocytes compared with that in WT hepatocytes. Diminished CYP4A expression was observed in the liver of Dusp6-KO mice compared with WT and Dusp6-haploinsufficiency mice. Knockdown of DUSP6 in HepG2, a human liver-lineage cell line, also promoted a reduction of lipid accumulation, down-regulation of CYP4A, and up-regulation of phosphorylated/activated MAPK. Furthermore, inhibition of MAPK activity promoted lipid accumulation in DUSP6-knockdown HepG2 cells without affecting CYP4A expression, indicating that CYP4A expression is independent of MAPK activation. These findings highlight the significant role of DUSP6 in HFD-induced steatohepatitis through two distinct pathways involving CYP4A and MAPK.

Hepatocyte TIPE2 is a fasting-induced Raf-1 inactivator that drives hepatic gluconeogenesis to maintain glucose homeostasis

BACKGROUND

The liver regulates metabolic balance during fasting-feeding cycle. Hepatic adaptation to fasting is precisely modulated on multiple levels. Tumor necrosis factor-α-induced protein 8-like 2 (TIPE2) is a negative regulator of immunity that reduces several liver pathologies, but its physiological roles in hepatic metabolism are largely unknown.

METHODS

TIPE2 expression was examined in mouse liver during fasting-feeding cycle. TIPE2-knockout mice, liver-specific TIPE2-knockout mice, liver-specific TIPE2-overexpressed mice were examined for fasting blood glucose and pyruvate tolerance test. Primary hepatocytes or liver tissues from these mice were evaluated for glucose production, lipid accumulation, gene expression and regulatory pathways. TIPE2 interaction with Raf-1 and TIPE2 transcription regulated by PPAR-α were examined using gene overexpression or knockdown, co-immunoprecipitation, western blot, luciferase reporter assay and DNA-protein binding assay.

RESULTS

TIPE2 expression was upregulated in fasted mouse liver and starved hepatocytes, which was positively correlated with gluconeogenic genes. Liver-specific TIPE2 deficiency impaired blood glucose homeostasis and gluconeogenic capacity in mice upon fasting, while liver-specific TIPE2 overexpression elevated fasting blood glucose and hepatic gluconeogenesis in mice. In primary hepatocytes upon starvation, TIPE2 interacted with Raf-1 to accelerate its ubiquitination and degradation, resulting in ERK deactivation and FOXO1 maintenance to sustain gluconeogenesis. During prolonged fasting, hepatic TIPE2 deficiency caused aberrant activation of ERK-mTORC1 axis that increased hepatic lipid accumulation via lipogenesis. In hepatocytes upon starvation, PPAR-α bound with TIPE2 promoter and triggered its transcriptional expression.

CONCLUSIONS

Hepatocyte TIPE2 is a PPAR-α-induced Raf-1 inactivator that sustains hepatic gluconeogenesis and prevents excessive hepatic lipid accumulation, playing beneficial roles in hepatocyte adaptation to fasting.

Acute Endoplasmic Reticulum Stress Suppresses Hepatic Gluconeogenesis by Stimulating MAPK Phosphatase 3 Degradation

Drug-induced liver injury (DILI) is a widespread and harmful disease, and is closely linked to acute endoplasmic reticulum (ER) stress. Previous reports have shown that acute ER stress can suppress hepatic gluconeogenesis and even leads to hypoglycemia. However, the mechanism is still unclear. MAPK phosphatase 3 (MKP-3) is a positive regulator for gluconeogenesis. Thus, this study was conducted to investigate the role of MKP-3 in the suppression of gluconeogenesis by acute ER stress, as well as the regulatory role of acute ER stress on the expression of MKP-3. Results showed that acute ER stress induced by tunicamycin significantly suppressed gluconeogenesis in both hepatocytes and mouse liver, reduced glucose production level in hepatocytes, and decreased fasting blood glucose level in mice. Additionally, the protein level of MKP-3 was reduced by acute ER stress in both hepatocytes and mouse liver. Mkp-3 deficiency eliminated the inhibitory effect of acute ER stress on gluconeogenesis in hepatocytes. Moreover, the reduction effect of acute ER stress on blood glucose level and hepatic glucose 6-phosphatase (G6pc) expression was not observed in the liver-specific Mkp-3 knockout mice. Furthermore, activation of protein kinase R-like ER kinase (PERK) decreased the MKP-3 protein level, while inactivation of PERK abolished the reduction effect of acute ER stress on the MKP-3 protein level in hepatocytes. Taken together, our study suggested that acute ER stress could suppress hepatic gluconeogenesis by stimulating MKP-3 degradation via PERK, at least partially. Thus, MKP-3 might be a therapeutic target for DILI-related hypoglycemia.

Gluconeogenesis Flux in Metabolic Disease

Gluconeogenesis is a critical biosynthetic process that helps maintain whole-body glucose homeostasis and becomes altered in certain medical diseases. We review gluconeogenic flux in various medical diseases, including common metabolic disorders, hormonal imbalances, specific inborn genetic errors, and cancer. We discuss how the altered gluconeogenic activity contributes to disease pathogenesis using data from experiments using isotopic tracer and spectroscopy methodologies. These in vitro, animal, and human studies provide insights into the changes in circulating levels of available gluconeogenesis substrates and the efficiency of converting those substrates to glucose by gluconeogenic organs. We highlight ongoing knowledge gaps, discuss emerging research areas, and suggest future investigations. A better understanding of altered gluconeogenesis flux may ultimately identify novel and targeted treatment strategies for such diseases.

New insights into signal transduction pathways in adrenal steroidogenesis: role of mitochondrial fusion, lipid mediators, and MAPK phosphatases

Hormone-receptor signal transduction has been extensively studied in adrenal gland. Zona glomerulosa and fasciculata cells are responsible for glucocorticoid and mineralocorticoid synthesis by adrenocorticotropin (ACTH) and angiotensin II (Ang II) stimulation, respectively. Since the rate-limiting step in steroidogenesis occurs in the mitochondria, these organelles are key players in the process. The maintenance of functional mitochondria depends on mitochondrial dynamics, which involves at least two opposite events, i.e., mitochondrial fusion and fission. This review presents state-of-the-art data on the role of mitochondrial fusion proteins, such as mitofusin 2 (Mfn2) and optic atrophy 1 (OPA1), in Ang II-stimulated steroidogenesis in adrenocortical cells. Both proteins are upregulated by Ang II, and Mfn2 is strictly necessary for adrenal steroid synthesis. The signaling cascades of steroidogenic hormones involve an increase in several lipidic metabolites such as arachidonic acid (AA). In turn, AA metabolization renders several eicosanoids released to the extracellular medium able to bind membrane receptors. This report discusses OXER1, an oxoeicosanoid receptor which has recently arisen as a novel participant in adrenocortical hormone-stimulated steroidogenesis through its activation by AA-derived 5-oxo-ETE. This work also intends to broaden knowledge of phospho/dephosphorylation relevance in adrenocortical cells, particularly MAP kinase phosphatases (MKPs) role in steroidogenesis. At least three MKPs participate in steroid production and processes such as the cellular cycle, either directly or by means of MAP kinase regulation. To sum up, this review discusses the emerging role of mitochondrial fusion proteins, OXER1 and MKPs in the regulation of steroid synthesis in adrenal cortex cells.

DUSP6 Deficiency Attenuates Neurodegeneration after Global Cerebral Ischemia

Transient global cerebral ischemia (tGCI) resulting from cardiac arrest causes selective neurodegeneration in hippocampal CA1 neurons. Although the effect is clear, the underlying mechanisms directing this process remain unclear. Previous studies have shown that phosphorylation of Erk1/2 promotes cell survival in response to tGCI. DUSP6 (also named MKP3) serves as a cytosolic phosphatase that dephosphorylates Erk1/2, but the role of DUSP6 in tGCI has not been characterized. We found that DUSP6 was specifically induced in the cytoplasm of hippocampal CA1 neurons 4 to 24 h after tGCI. DUSP6-deficient mice showed normal spatial memory acquisition and retention in the Barnes maze. Impairment of spatial memory acquisition and retention after tGCI was attenuated in DUSP6-deficient mice. Neurodegeneration after tGCI, revealed by Fluoro-Jade C and H&E staining, was reduced in the hippocampus of DUSP6-deficient mice and DUSP6 deficiency enhanced the phosphorylation and nuclear translocation of Erk1/2 in the hippocampal CA1 region. These data support the role of DUSP6 as a negative regulator of Erk1/2 signaling and indicate the potential of DUSP6 inhibition as a novel therapeutic strategy to treat neurodegeneration after tGCI.

O-GlycNacylation Remission Retards the Progression of Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is a metabolic disease spectrum associated with insulin resistance (IR), from non-alcoholic fatty liver (NAFL) to non-alcoholic steatohepatitis (NASH), cirrhosis, and hepatocellular carcinoma (HCC). O-GlcNAcylation is a posttranslational modification, regulated by O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA). Abnormal O-GlcNAcylation plays a key role in IR, fat deposition, inflammatory injury, fibrosis, and tumorigenesis. However, the specific mechanisms and clinical treatments of O-GlcNAcylation and NAFLD are yet to be elucidated. The modification contributes to understanding the pathogenesis and development of NAFLD, thus clarifying the protective effect of O-GlcNAcylation inhibition on liver injury. In this review, the crucial role of O-GlcNAcylation in NAFLD (from NAFL to HCC) is discussed, and the effect of therapeutics on O-GlcNAcylation and its potential mechanisms on NAFLD have been highlighted. These inferences present novel insights into the pathogenesis and treatments of NAFLD.

Dusp6 deficiency attenuates neutrophil-mediated cardiac damage in the acute inflammatory phase of myocardial infarction

Dual-specificity phosphatase 6 (DUSP6) serves a specific and conserved function on the dephosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2). We previously identified Dusp6 as a regenerative repressor during zebrafish heart regeneration, therefore we propose to investigate the role of this repressor in mammalian cardiac repair. Utilizing a rat strain harboring Dusp6 nonsense mutation, rat neutrophil-cardiomyocyte co-culture, bone marrow transplanted rats and neutrophil-specific Dusp6 knockout mice, we find that Dusp6 deficiency improves cardiac outcomes by predominantly attenuating neutrophil-mediated myocardial damage in acute inflammatory phase after myocardial infarction. Mechanistically, Dusp6 is transcriptionally activated by p38-C/EBPβ signaling and acts as an effector for maintaining p-p38 activity by down-regulating pERK and p38-targeting phosphatases DUSP1/DUSP16. Our findings provide robust animal models and novel insights for neutrophil-mediated cardiac damage and demonstrate the potential of DUSP6 as a therapeutic target for post-MI cardiac remodeling and other relevant inflammatory diseases.

BMP4 and Gremlin 1 regulate hepatic cell senescence during clinical progression of NAFLD/NASH

The role of hepatic cell senescence in human non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH) is not well understood. To examine this, we performed liver biopsies and extensive characterization of 58 individuals with or without NAFLD/NASH. Here, we show that hepatic cell senescence is strongly related to NAFLD/NASH severity, and machine learning analysis identified senescence markers, the BMP4 inhibitor Gremlin 1 in liver and visceral fat, and the amount of visceral adipose tissue as strong predictors. Studies in liver cell spheroids made from human stellate and hepatocyte cells show BMP4 to be anti-senescent, anti-steatotic, anti-inflammatory and anti-fibrotic, whereas Gremlin 1, which is particularly highly expressed in visceral fat in humans, is pro-senescent and antagonistic to BMP4. Both senescence and anti-senescence factors target the YAP/TAZ pathway, making this a likely regulator of senescence and its effects. We conclude that senescence is an important driver of human NAFLD/NASH and that BMP4 and Gremlin 1 are novel therapeutic targets.

Hepatic Leptin Signaling Improves Hyperglycemia by Stimulating MAPK Phosphatase-3 Protein Degradation via STAT3

BACKGROUND & AIMS

Obesity-related hyperglycemia, with hepatic insulin resistance, has become an epidemic disease. Central neural leptin signaling was reported to improve hyperglycemia. The aim of this study was to investigate the effect of hepatic leptin signaling on controlling hyperglycemia.

METHODS

First, the effect of leptin signaling on gluconeogenesis was investigated in primary mouse hepatocytes and hepatoma cells. Second, glucose tolerance, insulin tolerance, blood glucose levels, and hepatic gluconeogenic gene expression were analyzed in obese mice overexpressing hepatic OBRb. Third, expression of mitogen-activated protein kinase phosphatase (MKP)-3, phosphorylation level of signal transducer and activator of transcription (STAT) 3, and extracellular regulated protein kinase (ERK) were analyzed in hepatocytes and mouse liver. Fourth, the role of MKP-3 in hepatic leptin signaling regulating gluconeogenesis was analyzed. Lastly, the role of ERK and STAT3 in the regulation of MKP-3 protein by leptin signaling was analyzed.

RESULTS

Activation of hepatic leptin signaling suppressed gluconeogenesis in both hepatocytes and obese mouse liver, and improved hyperglycemia, insulin tolerance, and glucose tolerance in obese mice. The protein level of MKP-3, which can promote gluconeogenesis, was decreased by leptin signaling in both hepatocytes and mouse liver. Mkp-3 deficiency abolished the effect of hepatic leptin signaling on suppressing gluconeogenesis in hepatocytes. STAT3 decreased the MKP-3 protein level, while inactivation of STAT3 abolished the effect of leptin signaling on reducing the MKP-3 protein level in hepatocytes. Moreover, STAT3 could combine with MKP-3 and phospho-ERK1/2, which induced the degradation of MKP-3, and leptin signaling enhanced the combination.

CONCLUSIONS

Hepatic leptin signaling could suppress gluconeogenesis at least partially by decreasing the MKP-3 protein level via STAT3-enhanced MKP-3 and ERK1/2 combination.

The role of protein kinases as key drivers of metabolic dysfunction-associated fatty liver disease progression: New insights and future directions

Metabolic dysfunction-associated fatty liver disease (MAFLD), proposed in 2020 is a novel term for non-alcoholic fatty liver disease (NAFLD) which was coined for the first time in 1980. It is a leading cause of the most chronic liver disease and hepatic failure all over the world, and unfortunately, with no licensed drugs for treatment yet. The progress of the disease is driven by the triggered inflammatory process, oxidative stress, and insulin resistance in many pathways, starting with simple hepatic steatosis to non-alcoholic steatohepatitis, fibrosis, cirrhosis, and liver cancer. Protein kinases (PKs), such as MAPK, ErbB, PKC, PI3K/Akt, and mTOR, govern most of the pathological pathways by acting on various downstream key points in MAFLD and regulating both hepatic gluco- lipo-neogenesis and inflammation. Therefore, modulating the function of those potential protein kinases that are effectively involved in MAFLD might be a promising therapeutic approach for tackling this disease. In the current review, we have discussed the key role of protein kinases in the pathogenesis of MAFLD and performed a protein-protein interaction (PPI) network among the main proteins of each kinase pathway with MAFLD-related proteins to predict the most likely targets of the PKs in MAFLD. Moreover, we have reported the experimental, pre-clinical, and clinical data for the most recent investigated molecules that are activating p38-MAPK and AMPK proteins and inhibiting the other PKs to improve MAFLD condition by regulating oxidation and inflammation signalling.

Metabolic Impact of MKP-2 Upregulation in Obesity Promotes Insulin Resistance and Fatty Liver Disease

The mechanisms connecting obesity with type 2 diabetes, insulin resistance, nonalcoholic fatty liver disease, and cardiovascular diseases remain incompletely understood. The function of MAPK phosphatase-2 (MKP-2), a type 1 dual-specific phosphatase (DUSP) in whole-body metabolism, and how this contributes to the development of diet-induced obesity, type 2 diabetes (T2D), and insulin resistance is largely unknown. We investigated the physiological contribution of MKP-2 in whole-body metabolism and whether MKP-2 is altered in obesity and human fatty liver disease using MKP-2 knockout mice models and human liver tissue derived from fatty liver disease patients. We demonstrate that, for the first time, MKP-2 expression was upregulated in liver tissue in humans with obesity and fatty liver disease and in insulin-responsive tissues in mice with obesity. MKP-2-deficient mice have enhanced p38 MAPK, JNK, and ERK activities in insulin-responsive tissues compared with wild-type mice. MKP-2 deficiency in mice protects against diet-induced obesity and hepatic steatosis and was accompanied by improved glucose homeostasis and insulin sensitivity. Mkp-2^−/− mice are resistant to diet-induced obesity owing to reduced food intake and associated lower respiratory exchange ratio. This was associated with enhanced circulating insulin-like growth factor-1 (IGF-1) and stromal cell-derived factor 1 (SDF-1) levels in Mkp-2^−/− mice. PTEN, a negative regulator of Akt, was downregulated in livers of Mkp-2^−/− mice, resulting in enhanced Akt activity consistent with increased insulin sensitivity. These studies identify a novel role for MKP-2 in the regulation of systemic metabolism and pathophysiology of obesity-induced insulin resistance and fatty liver disease.

Hepatic transcriptional responses to fasting and feeding

Mammals undergo regular cycles of fasting and feeding that engage dynamic transcriptional responses in metabolic tissues. Here we review advances in our understanding of the gene regulatory networks that contribute to hepatic responses to fasting and feeding. The advent of sequencing and -omics techniques have begun to facilitate a holistic understanding of the transcriptional landscape and its plasticity. We highlight transcription factors, their cofactors, and the pathways that they impact. We also discuss physiological factors that impinge on these responses, including circadian rhythms and sex differences. Finally, we review how dietary modifications modulate hepatic gene expression programs.

FOXO transcription factor family in cancer and metastasis

Forkhead box O (FOXO) transcription factors regulate diverse biological processes, affecting development, metabolism, stem cell maintenance and longevity. They have also been increasingly recognised as tumour suppressors through their ability to regulate genes essential for cell proliferation, cell death, senescence, angiogenesis, cell migration and metastasis. Mechanistically, FOXO proteins serve as key connection points to allow diverse proliferative, nutrient and stress signals to converge and integrate with distinct gene networks to control cell fate, metabolism and cancer development. In consequence, deregulation of FOXO expression and function can promote genetic disorders, metabolic diseases, deregulated ageing and cancer. Metastasis is the process by which cancer cells spread from the primary tumour often via the bloodstream or the lymphatic system and is the major cause of cancer death. The regulation and deregulation of FOXO transcription factors occur predominantly at the post-transcriptional and post-translational levels mediated by regulatory non-coding RNAs, their interactions with other protein partners and co-factors and a combination of post-translational modifications (PTMs), including phosphorylation, acetylation, methylation and ubiquitination. This review discusses the role and regulation of FOXO proteins in tumour initiation and progression, with a particular emphasis on cancer metastasis. An understanding of how signalling networks integrate with the FOXO transcription factors to modulate their developmental, metabolic and tumour-suppressive functions in normal tissues and in cancer will offer a new perspective on tumorigenesis and metastasis, and open up therapeutic opportunities for malignant diseases.

FoxO1 signaling as a therapeutic target for type 2 diabetes and obesity

Glucose production and the consumption of high levels of carbohydrate increase the chance of insulin resistance, especially in cases of obesity. Therefore, maintaining a balanced glucose homeostasis might form a strategy to prevent or cure diabetes and obesity. The activation and inhibition of glucose production is complicated due to the presence of many interfering pathways. These pathways can be viewed at the downstream level because they activate certain transcription factors, which include the Forkhead-O1 (FoxO1). This has been identified as a significant agent in the pancreas, liver, and adipose tissue, which is significant in the regulation of lipids and glucose. The objective of this review is to discuss the intersecting portrayal of FoxO1 and its parallel cross-talk which highlights obesity-induced insulin susceptibility in the discovery of a targeted remedy. The review also analyses current progress and provides a blueprint on therapeutics, small molecules, and extracts/phytochemicals which are explored at the pre-clinical level.

Intricate Regulation of Phosphoenolpyruvate Carboxykinase (PEPCK) Isoforms in Normal Physiology and Disease

BACKGROUND

The phosphoenolpyruvate carboxykinase (PEPCK) isoforms are considered as rate-limiting enzymes for gluconeogenesis and glyceroneogenesis pathways. PEPCK exhibits several interesting features such as a) organelle-specific isoforms (cytosolic and a mitochondrial) in vertebrate clade, b) tissue-specific expression of isoforms and c) organism-specific requirement of ATP or GTP as a cofactor. In higher organisms, PEPCK isoforms are intricately regulated and activated through several physiological and pathological stimuli such as corticoids, hormones, nutrient starvation and hypoxia. Isoform-specific transcriptional/translational regulation and their interplay in maintaining glucose homeostasis remain to be fully understood. Mounting evidence indicates the significant involvement of PEPCK isoforms in physiological processes (development and longevity) and in the progression of a variety of diseases (metabolic disorders, cancer, Smith-Magenis syndrome).

OBJECTIVE

The present systematic review aimed to assimilate existing knowledge of transcriptional and translational regulation of PEPCK isoforms derived from cell, animal and clinical models.

CONCLUSION

Based on current knowledge and extensive bioinformatics analysis, in this review we have provided a comparative (epi)genetic understanding of PCK1 and PCK2 genes encompassing regulatory elements, disease-associated polymorphisms, copy number variations, regulatory miRNAs and CpG densities. We have also discussed various exogenous and endogenous modulators of PEPCK isoforms and their signaling mechanisms. A comprehensive review of existing knowledge of PEPCK regulation and function may enable identification of the underlying gaps to design new pharmacological strategies and interventions for the diseases associated with gluconeogenesis.

Glucose metabolism in Cushing's syndrome

PURPOSE OF REVIEW

Impairment of glucose metabolism is commonly encountered in Cushing's syndrome. It is the source of significant morbidity and mortality even after successful treatment of Cushing's. This review is to understand the recent advances in understanding the pathophysiology of diabetes mellitus from excess cortisol.

RECENT FINDINGS

In-vitro studies have led to significant advancement in understanding the molecular effects of cortisol on glucose metabolism. Some of these findings have been translated with human data. There is marked reduction in insulin action and glucose disposal with a concomitant, insufficient increase in insulin secretion. Cortisol has a varied effect on adipose tissue, with increased lipolysis in subcutaneous adipose tissue in the extremities, and increased lipogenesis in visceral and subcutaneous truncal adipose tissue.

SUMMARY

Cushing's syndrome results in marked impairment in insulin action and glucose disposal resulting in hyperglycemia. Further studies are required to understand the effect on incretin secretion and action, gastric emptying, and its varied effect on adipose tissue.

Angiotensin II-upregulated MAP kinase phosphatase-3 modulates FOXO1 and p21 in adrenocortical H295R cells

MAPK phosphatases (MKP) downregulate the activity of mitogen-activated protein kinases (MAPK), such as ERK1/2, and modulate the processes regulated by these kinases. ERK1/2 participate in a wide range of processes including tissue-specific hormone-stimulated steroidogenesis. H295R cells are a suitable model for the study of human adrenal cortex functions, particularly steroid synthesis, and respond to angiotensin II (Ang II) triggering ERK1/2 phosphorylation in a transient fashion. MKP-3 dephosphorylates ERK1/2 and, as recently reported, forkhead box protein 1 (FOXO1). Here, we analyzed MKP-3 expression in H295R cells and its putative regulation by Ang II. Results showed the expression of MKP-3 full length (L) and a short splice variant (S), and the upregulation of both isoforms by Ang II. L and S messenger and protein levels increased 30 min after Ang II stimulation and declined over the next 3 h, a temporal frame compatible with ERK1/2 dephosphorylation. In addition, FOXO1 activation is known to include its dephosphorylation and nuclear translocation. Therefore, we analyzed the effect of Ang II on FOXO1 modulation. Ang II induced FOXO1 transient phosphorylation and translocation and also the induction of p21, a FOXO1-dependent gene, whereas MKP-3 knock-down reduced both FOXO1 translocation and p21 induction. These data suggest that, through MKP-3, Ang II counteracts its own effects on ERK1/2 activity and also triggers the activation of FOXO-1 and the induction of cell cycle inhibitor p21. Taken together, the current findings reveal the participation of MKP-3 not only in turn–off but also in turn-on signals which control important cellular processes.

Expression of Adenoviral E1A in Transformed Cells as an Additional Factor of HDACi-Dependent FoxO Regulation

The adenoviral early region 1A (E1A) protein has proapoptotic and angiogenic activity, along with its chemosensitizing effect, making it the focus of increased interest in the context of cancer therapy. It was previously shown that E1A-induced chemosensitization to different drugs, including histone deacetylases inhibitors (HDACi), appears to be mediated by Forkhead box O (FoxO) transcription factors. In this study, we explore the relationship between E1A expression and the modulation of FoxO activity with HDACi sodium butyrate (NaBut). We show here that the basal FoxO level is elevated in E1A-expressing cells. Prolonged NaBut treatment leads to the inhibition of the FoxO expression and activity in E1A-expressing cells. However, in E1A-negative cells, NaBut promotes the transactivation ability of FoxO over time. A more detailed investigation revealed that the NaBut-induced decrease of FoxO activity in E1A-expressing cells is due to the NaBut-dependent decrease in E1A expression. Therefore, NaBut-induced inhibition of FoxO in E1A-positive cells can be overcome under unregulated overexpression of E1A. Remarkably, the CBP/p300-binding domain of E1Aad5 is responsible for stabilization of the FoxO protein. Collectively, these data show that the expression of E1A increases the FoxO stability but makes the FoxO level more sensitive to HDACi treatment.

Regulators of the RAS-ERK pathway as therapeutic targets in thyroid cancer

Thyroid cancer is mostly an ERK-driven carcinoma, as up to 70% of thyroid carcinomas are caused by mutations that activate the RAS/ERK mitogenic signaling pathway. The incidence of thyroid cancer has been steadily increasing for the last four decades; yet, there is still no effective treatment for advanced thyroid carcinomas. Current research efforts are focused on impairing ERK signaling with small-molecule inhibitors, mainly at the level of BRAF and MEK. However, despite initial promising results in animal models, the clinical success of these inhibitors has been limited by the emergence of tumor resistance and relapse. The RAS/ERK pathway is an extremely complex signaling cascade with multiple points of control, offering many potential therapeutic targets: from the modulatory proteins regulating the activation state of RAS proteins to the scaffolding proteins of the pathway that provide spatial specificity to the signals, and finally, the negative feedbacks and phosphatases responsible for inactivating the pathway. The aim of this review is to give an overview of the biology of RAS/ERK regulators in human cancer highlighting relevant information on thyroid cancer and future areas of research.

Diabetes-Induced DUSP4 Reduction Promotes Podocyte Dysfunction and Progression of Diabetic Nephropathy

Diabetic nephropathy (DN) remains the leading cause of end-stage renal disease. Hyperglycemia-induced podocyte dysfunction is a major contributor of renal function impairment in DN. Previous studies showed that activation of mitogen-activated protein kinase (MAPK) in diabetes promotes podocyte dysfunction and cell death. Dual specificity phosphatases (DUSPs) are a family of phosphatases mainly responsible for MAPK inhibition. In this study, we demonstrated that diabetes and high glucose exposure decreased DUSP4 expression in cultured podocytes and glomeruli. Diabetes-induced DUSP4 reduction enhanced p38 and c-Jun N-terminal kinase (JNK) activity and podocyte dysfunction. The overexpression of DUSP4 prevented the activation of p38, JNK, caspase 3/7 activity, and NADPH oxidase 4 expression induced by high glucose level exposure. Deletion of DUSP4 exacerbated albuminuria and increased mesangial expansion and glomerular fibrosis in diabetic mice. These morphological changes were associated with profound podocyte foot process effacement, cell death, and sustained p38 and JNK activation. Moreover, inhibition of protein kinase C-δ prevented DUSP4 expression decline and p38/JNK activation in the podocytes and renal cortex of diabetic mice. Analysis of DUSP4 expression in the renal cortex of patients with diabetes revealed that decreased DUSP4 mRNA expression correlated with reduced estimated glomerular filtration rate (<60 mL/min/1.73 m²). Thus, this study demonstrates that preserving DUSP4 expression could protect against podocyte dysfunction and preserve glomerular function in DN.

Dual-Specificity Phosphatase Regulation in Neurons and Glial Cells

Dual-specificity protein phosphatases comprise a protein phosphatase subfamily with selectivity towards mitogen-activated protein (MAP) kinases, also named MKPs, or mitogen-activated protein kinase (MAPK) phosphatases. As powerful regulators of the intensity and duration of MAPK signaling, a relevant role is envisioned for dual-specificity protein phosphatases (DUSPs) in the regulation of biological processes in the nervous system, such as differentiation, synaptic plasticity, and survival. Important neural mediators include nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) that contribute to DUSP transcriptional induction and post-translational mechanisms of DUSP protein stabilization to maintain neuronal survival and differentiation. Potent DUSP gene inducers also include cannabinoids, which preserve DUSP activity in inflammatory conditions. Additionally, nucleotides activating P2X7 and P2Y₁₃ nucleotide receptors behave as novel players in the regulation of DUSP function. They increase cell survival in stressful conditions, regulating DUSP protein turnover and inducing DUSP gene expression. In general terms, in the context of neural cells exposed to damaging conditions, the recovery of DUSP activity is neuroprotective and counteracts pro-apoptotic over-activation of p38 and JNK. In addition, remarkable changes in DUSP function take place during the onset of neuropathologies. The restoration of proper DUSP levels and recovery of MAPK homeostasis underlie the therapeutic effect, indicating that DUSPs can be relevant targets for brain diseases.

Higd1a Protects Cells from Lipotoxicity under High-Fat Exposure

Hypoxia-inducible gene domain family member 1A (Higd1a) has recently been reported to protect cells from hypoxia by helping to maintain normal mitochondrial function. The potential induction of Higd1a under high-fat exposure and whether it could protect cells from oxidative stress attracted our attention. Initially, 0.4 mM oleic acid and 0.2 mM palmitate were added to the growth media of HepG2 and LO2 cells for 72 hours. We discovered increased Higd1a expression, and knocking down Higd1a impaired mitochondrial transmembrane potential and induced cell apoptosis. We then identified that elevated reactive oxygen species (ROS) is responsible for increased Higd1a expression. Furthermore, we found that ROS promoted Higd1a expression by upregulating HIF-1a and PGC-1a expressions, and these two proteins could exert synergistic effects in inducing Higd1a expression. Taken together, these data suggest that Higd1a plays positive roles in protecting cells from oxidative stress, and ROS could induce Higd1a expression by upregulating PGC-1a and HIF-1a expressions.

Ubiquitous and cell type-specific transcriptomic changes triggered by dissipation of monovalent cation gradients in rodent cells: Physiological and pathophysiological implications

Elevation of [Na⁺]_i/[K⁺]_i-ratio is considered as one of the major signals triggering transcriptomic changes in various cells types. In this study, we identified ubiquitous and cell type-specific [Formula: see text] -sensitive genes by comparative analysis of transcriptomic changes in ouabain-treated rat aorta smooth muscle cells and rat aorta endothelial cells (RASMC and RAEC, respectively), rat cerebellar granule cells (RCGC), and mouse C2C12 myoblasts. Exposure of the cells to ouabain increased intracellular Na⁺ content by ~14, 8, 7, and 6-fold and resulted in appearance of 7577, 2698, 2120, and 1146 differentially expressed transcripts in RAEC, RASMC, C2C12, and RCGC, respectively. Eighty-three genes were found as the intersection of the four sets of identified transcripts corresponding to each cell type and are classified as ubiquitous. Among the 10 top upregulated ubiquitous transcripts are the following: Dusp6, Plk3, Trib1, Ccl7, Mafk, Atf3, Ptgs2, Cxcl1, Spry4, and Coq10b. Unique transcripts whose expression is cell-specific include 4897, 1523, 789, and 494 transcripts for RAEC, RASMC, C2C12, and RCGC, respectively. The role of gene expression and signal pathways induced by dissipation of transmembrane gradient of monovalent cations in the development of various diseases is discussed with special attention to cardiovascular and pulmonary illnesses.

Role of FoxO Proteins in Cellular Response to Antitumor Agents

FoxO proteins (FoxOs) are transcription factors with a common DNA binding domain that confers selectivity for DNA interaction. In human cells, four proteins (FoxO1, FoxO3, FoxO4 and FoxO6), with redundant activity, exhibit mainly a positive effect on genes involved in cell cycle, apoptosis regulation and drug resistance. Thus, FoxOs can affect cell response to antitumor agent treatment. Their transcriptional activity depends on post-translational modifications, including phosphorylation, acetylation, and mono/poly-ubiquitination. Additionally, alterations in microRNA network impact on FoxO transcripts and in turn on FoxO levels. Reduced expression of FoxO1 has been associated with resistance to conventional agents (e.g., cisplatin) and with reduced efficacy of drug combinations in ovarian carcinoma cells. FoxO3 has been shown as a mediator of cisplatin toxicity in colorectal cancer. A requirement for FoxO3-induced apoptosis has been reported in cells exposed to targeted agents (e.g., gefitinib). Recently, the possibility to interfere with FoxO1 localization has been proposed as a valuable approach to improve cell sensitivity to cisplatin, because nuclear retention of FoxO1 may favor the induction of pro-apoptotic genes. This review focuses on the role of FoxOs in drug treatment response in tumor cells and discusses the impact of the expression of these transcription factors on drug resistance/sensitivity.

Dual-specificity MAP kinase phosphatases in health and disease

It is well established that a family of dual-specificity MAP kinase phosphatases (MKPs) play key roles in the regulated dephosphorylation and inactivation of MAP kinase isoforms in mammalian cells and tissues. MKPs provide a mechanism of spatiotemporal feedback control of these key signalling pathways, but can also mediate crosstalk between distinct MAP kinase cascades and facilitate interactions between MAP kinase pathways and other key signalling modules. As our knowledge of the regulation, substrate specificity and catalytic mechanisms of MKPs has matured, more recent work using genetic models has revealed key physiological functions for MKPs and also uncovered potentially important roles in regulating the pathophysiological outcome of signalling with relevance to human diseases. These include cancer, diabetes, inflammatory and neurodegenerative disorders. It is hoped that this understanding will reveal novel therapeutic targets and biomarkers for disease, thus contributing to more effective diagnosis and treatment for these debilitating and often fatal conditions.

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A comprehensive review of the dual-specificity MAP kinase Phosphatases (MKPs)

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Focus is on MKPs in the regulation of MAPK signalling in health and disease.

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Covers roles of MKPs in inflammation, obesity/diabetes, cancer and neurodegeneration

DUSP6 mediates T cell receptor-engaged glycolysis and restrains TFH cell differentiation

Activated T cells undergo metabolic reprogramming and effector-cell differentiation but the factors involved are unclear. Utilizing mice lacking DUSP6 (DUSP6^-/-), we show that this phosphatase regulates T cell receptor (TCR) signaling to influence follicular helper T (T_FH) cell differentiation and T cell metabolism. In vitro, DUSP6^-/- CD4⁺ T_FH cells produced elevated IL-21. In vivo, T_FH cells were increased in DUSP6^-/- mice and in transgenic OTII-DUSP6^-/- mice at steady state. After immunization, DUSP6^-/- and OTII-DUSP6^-/- mice generated more T_FH cells and produced more antigen-specific IgG2 than controls. Activated DUSP6^-/- T cells showed enhanced JNK and p38 phosphorylation but impaired glycolysis. JNK or p38 inhibitors significantly reduced IL-21 production but did not restore glycolysis. TCR-stimulated DUSP6^-/- T cells could not induce phosphofructokinase activity and relied on glucose-independent fueling of mitochondrial respiration. Upon CD28 costimulation, activated DUSP6^-/- T cells did not undergo the metabolic commitment to glycolysis pathway to maintain viability. Unexpectedly, inhibition of fatty acid oxidation drastically lowered IL-21 production in DUSP6^-/- T_FH cells. Our findings suggest that DUSP6 connects TCR signaling to activation-induced metabolic commitment toward glycolysis and restrains T_FH cell differentiation via inhibiting IL-21 production.

Dual specificity phosphatase 5 and 6 are oppositely regulated in human skeletal muscle by acute exercise

Physical activity promotes specific adaptations in most tissues including skeletal muscle. Acute exercise activates numerous signaling cascades including pathways involving mitogen‐activated protein kinases (MAPKs) such as extracellular signal‐regulated kinase (ERK)1/2, which returns to pre‐exercise level after exercise. The expression of MAPK phosphatases (MKPs) in human skeletal muscle and their regulation by exercise have not been investigated before. In this study, we used mRNA sequencing to monitor regulation of MKPs in human skeletal muscle after acute cycling. In addition, primary human myotubes were used to gain more insights into the regulation of MKPs. The two ERK1/2‐specific MKPs, dual specificity phosphatase 5 (DUSP5) and DUSP6, were the most regulated MKPs in skeletal muscle after acute exercise. DUSP5 expression was ninefold higher immediately after exercise and returned to pre‐exercise level within 2 h, whereas DUSP6 expression was reduced by 43% just after exercise and remained below pre‐exercise level after 2 h recovery. Cultured myotubes express both MKPs, and incubation with dexamethasone (Dex) mimicked the in vivo expression pattern of DUSP5 and DUSP6 caused by exercise. Using a MAPK kinase inhibitor, we showed that stimulation of ERK1/2 activity by Dex was required for induction of DUSP5. However, maintaining basal ERK1/2 activity was required for basal DUSP6 expression suggesting that the effect of Dex on DUSP6 might involve an ERK1/2‐independent mechanism. We conclude that the altered expression of DUSP5 and DUSP6 in skeletal muscle after acute endurance exercise might affect ERK1/2 signaling of importance for adaptations in skeletal muscle during exercise.

Dual specificity phosphatase DUSP6 promotes endothelial inflammation through inducible expression of ICAM-1

Tumor necrosis factor (TNF)-α activates a diverse array of signaling pathways in vascular endothelial cells (ECs), leading to the inflammatory phenotype that contributes to the vascular dysfunction and neutrophil emigration in patients with sepsis. To date, it is not well understood what key regulator might coordinate signaling pathways to achieve inflammatory response in TNF-α-stimulated ECs. This study investigated the role of dual specificity phosphatase-6 (DUSP6) in the regulation of endothelial inflammation. Using knockout mice, we found that DUSP6 is important for TNF-α-induced endothelial intercellular adhesion molecule-1 (ICAM-1) expression in aorta and in vein. Moreover, genetic deletion of Dusp6 in pulmonary circulation significantly alleviated the susceptibility of mice to lung injury caused by neutrophil recruitment during experimental sepsis induced by TNF-α or lipopolysaccharide (LPS). The role of DUSP6 was further investigated in primary human umbilical vein endothelial cells (HUVECs). Employing RNAi approach in which endogenous DUSP6 was ablated, we showed a critical function of DUSP6 to facilitate TNF-α-induced ICAM-1 expression and endothelial leukocyte interaction. Interestingly, DUSP6-promoted endothelial inflammation is independent of extracellular signaling-regulated kinase (ERK) signaling. On the other hand, inducible DUSP6 leads to activation of canonical nuclear factor (NF)-κB-mediated transcription of ICAM-1 gene in TNF-α-stimulated human ECs. These results are the first to demonstrate a positive role of DUSP6 in endothelial inflammation-mediated pathological process and the underlying mechanism through which DUSP6 promotes NF-κB signaling in the inflamed ECs. Our findings suggest that manipulation of DUSP6 holds great potential for the treatment of acute inflammatory diseases.

SCP4 Promotes Gluconeogenesis Through FoxO1/3a Dephosphorylation

FoxO1 and FoxO3a (collectively FoxO1/3a) proteins regulate a wide array of cellular processes, including hepatic gluconeogenesis. Phosphorylation of FoxO1/3a is a key event that determines its subcellular location and transcriptional activity. During glucose synthesis, the activity of FoxO1/3a is negatively regulated by Akt-mediated phosphorylation, which leads to the cytoplasmic retention of FoxO1/3a. However, the nuclear phosphatase that directly regulates FoxO1/3a remains to be identified. In this study, we discovered a nuclear phosphatase, SCP4/CTDSPL2 (SCP4), that dephosphorylated FoxO1/3a and promoted FoxO1/3a transcription activity. We found that SCP4 enhanced the transcription of FoxO1/3a target genes encoding PEPCK1 and G6PC, key enzymes in hepatic gluconeogenesis. Ectopic expression of SCP4 increased, while knockdown of SCP4 inhibited, glucose production. Moreover, we demonstrated that gene ablation of SCP4 led to hypoglycemia in neonatal mice. Consistent with the positive role of SCP4 in gluconeogenesis, expression of SCP4 was regulated under pathophysiological conditions. SCP4 expression was induced by glucose deprivation in vitro and in vivo and was elevated in obese mice caused by genetic (A^vy) and dietary (high-fat) changes. Thus, our findings provided experimental evidence that SCP4 regulates hepatic gluconeogenesis and could serve as a potential target for the prevention and treatment of diet-induced glucose intolerance and type 2 diabetes.

Mitogen-Activated Protein Kinase Regulation in Hepatic Metabolism

The mitogen-activated protein kinases (MAPKs) participate in a multitude of processes that control hepatic metabolism. The liver regulates glucose and lipid metabolism, and under pathophysiological conditions such as obesity, type 2 diabetes mellitus (T2DM), and non-alcoholic fatty liver disease (NAFLD) these processes become dysfunctional. Stress responses activate the hepatic MAPKs, and this is thought to impair insulin action and lipid metabolism. The MAPKs also activate the MAPK phosphatases (MKPs) which oppose their actions. How the MAPK/MKP balance is controlled in liver metabolism and how perturbations in these activities contribute to metabolic disease remains unclear. Discussion of recent insights into the MAPK/MKP signaling role in hepatic metabolic function and disease will be the focus of this review.

Obesity Increases Mitogen-Activated Protein Kinase Phosphatase-3 Levels in the Hypothalamus of Mice

Mitogen-activated Protein Kinase Phosphatase 3 (MKP-3) has been involved in the negative regulation of insulin signaling. The absence of MKP-3 is also associated with reduced adiposity, increased energy expenditure and improved insulin sensitivity. The MKP-3 is known as the main Erk1/2 phosphatase and FoxO1 activator, which has repercussions on the gluconeogenesis pathway and hyperglycemia in obese mice. Recently, we showed that MKP-3 overexpression decreases FoxO1 phosphorylation in the hypothalamus of lean mice. However, the hypothalamic interaction between MKP-3 and FoxO1 during obesity was not investigated yet. Here, the MKP-3 expression and the effects on food intake and energy expenditure, were investigated in high-fat diet-induced obese mice. The results indicate that obesity in mice increased the MKP-3 protein content in the hypothalamus. This hypothalamic upregulation led to an increase of food intake, adiposity, and body weight. Furthermore, the obese mice with increased MKP-3 showed an insulin signaling impairment with reduction of insulin-induced FoxO1 and Erk1/2 phosphorylation in the hypothalamus. Moreover, a bioinformatics analysis of data demonstrated that hypothalamic MKP-3 mRNA levels were positively correlated with body weight and negatively correlated to oxygen consumption (VO₂) in BXD mice. Taken together, our study reports that obesity is associated with increased protein levels of hypothalamic MKP-3, which is related to the reduction of FoxO1 and Erk1/2 phosphorylation in the hypothalamus as well as to an increase in body weight and a reduction in energy expenditure.

Dual specificity phosphatase 6 deficiency is associated with impaired systemic glucose tolerance and reversible weight retardation in mice

Here, we aimed to investigate the potential role of DUSP6, a dual specificity phosphatase, that specifically inactivates extracellular signal-regulated kinase (ERK), for the regulation of body weight and glucose homeostasis. We further assessed whether metabolic challenges affect Dusp6 expression in selected brain areas or white adipose tissue. Hypothalamic Dusp6 mRNA levels remained unchanged in chow-fed lean vs. high fat diet (HFD) fed obese C57Bl/6J mice, and in C57Bl/6J mice undergoing prolonged fasting or refeeding with fat free diet (FFD) or HFD. Similarly, Dusp6 expression levels were unchanged in selected brain regions of Lep^ob mice treated with 1 mg/kg of leptin for 6 days, compared to pair-fed or saline-treated Lep^ob controls. Dusp6 expression levels remained unaltered in vitro in primary adipocytes undergoing differentiation, but were increased in eWAT of HFD-fed obese C57Bl/6J mice, compared to chow-fed lean controls. Global chow-fed DUSP6 KO mice displayed reduced body weight and lean mass and slightly increased fat mass at a young age, which is indicative for early-age weight retardation. Subsequent exposure to HFD led to a significant increase in lean mass and body weight in DUSP6 deficient mice, compared to WT controls. Nevertheless, after 26 weeks of high-fat diet exposure, we observed comparable body weight, fat and lean mass in DUSP6 WT and KO mice, suggesting overall normal susceptibility to develop obesity. In line with the increased weight gain to compensate for early-age weight retardation, HFD-fed DUSP6 KO displayed increased expression levels of anabolic genes involved in lipid and cholesterol metabolism in the epididymal white adipose tissue (eWAT), compared to WT controls. Glucose tolerance was perturbed in both chow-fed lean or HFD-fed obese DUSP6 KO, compared to their respective WT controls. Overall, our data indicate that DUSP6 deficiency has limited impact on the regulation of energy metabolism, but impairs systemic glucose tolerance. Our data are in conflict to earlier reports that propose protection from diet-induced obesity and glucose intolerance in DUSP6 deficient mice. Reasons for the discrepancies remain elusive, but may entail differential genetic backgrounds, environmental factors such as the type and source of HFD, or alterations in the gut microbiome between facilities.

Overexpression of Mitogen-activated protein kinase phosphatase-3 (MKP-3) reduces FoxO1 phosphorylation in mice hypothalamus

The mitogen-activated kinase phosphatase-3 (MKP-3) has gained great importance in the scientific community by acting as a regulator of the cell cycle through dephosphorylation of FoxO1, an important transcription factor involved in the insulin intracellular signaling cascade. When dephosphorylated and translocated to the nuclei, FoxO1 can promote the transcription of orexigenic neuropeptides (NPY/AgRP) in the hypothalamus, whereas insulin signaling is responsible for the disruption of this process. However, it is not understood if the hypothalamic activation of MKP-3 affects FoxO1 phosphorylation, and we hypothesized that MKP-3 overexpression reduces the capacity of the insulin signal to phosphorylate FoxO1. In the present study, we overexpressed the DUSP6 gene through an injection of adenovirus directly into the hypothalamic third ventricle of Swiss mice. The colocalization of the adenovirus was confirmed by the immunofluorescence assay. Then, MKP-3 overexpression resulted in a significant reduction of hypothalamic FoxO1 phosphorylation after insulin stimulation. This effect was independent of changes in Akt phosphorylation. Thus, the role of MKP-3 in the hypothalamus is closely associated with FoxO1 dephosphorylation and may provide a potential therapeutic target against hypothalamic disorders related to obesity and unbalanced food intake control.

Glucose Metabolism Abnormalities in Cushing Syndrome: From Molecular Basis to Clinical Management

An impaired glucose metabolism, which often leads to the onset of diabetes mellitus (DM), is a common complication of chronic exposure to exogenous and endogenous glucocorticoid (GC) excess and plays an important part in contributing to morbidity and mortality in patients with Cushing syndrome (CS). This article reviews the pathogenesis, epidemiology, diagnosis, and management of changes in glucose metabolism associated with hypercortisolism, addressing both the pathophysiological aspects and the clinical and therapeutic implications. Chronic hypercortisolism may have pleiotropic effects on all major peripheral tissues governing glucose homeostasis. Adding further complexity, both genomic and nongenomic mechanisms are directly induced by GCs in a context-specific and cell-/organ-dependent manner. In this paper, the discussion focuses on established and potential pathologic molecular mechanisms that are induced by chronically excessive circulating levels of GCs and affect glucose homeostasis in various tissues. The management of patients with CS and DM includes treating their hyperglycemia and correcting their GC excess. The effects on glycemic control of various medical therapies for CS are reviewed in this paper. The association between DM and subclinical CS and the role of screening for CS in diabetic patients are also discussed.

Lysophosphatidic acid counteracts glucagon-induced hepatocyte glucose production via STAT3

Hepatic glucose production (HGP) is required to maintain normoglycemia during fasting. Glucagon is the primary hormone responsible for increasing HGP; however, there are many additional hormone and metabolic factors that influence glucagon sensitivity. In this study we report that the bioactive lipid lysophosphatidic acid (LPA) regulates hepatocyte glucose production by antagonizing glucagon-induced expression of the gluconeogenic enzyme phosphoenolpyruvate carboxykinase (PEPCK). Treatment of primary hepatocytes with exogenous LPA blunted glucagon-induced PEPCK expression and glucose production. Similarly, knockout mice lacking the LPA-degrading enzyme phospholipid phosphate phosphatase type 1 (PLPP1) had a 2-fold increase in endogenous LPA levels, reduced PEPCK levels during fasting, and decreased hepatic gluconeogenesis in response to a pyruvate challenge. Mechanistically, LPA antagonized glucagon-mediated inhibition of STAT3, a transcriptional repressor of PEPCK. Importantly, LPA did not blunt glucagon-stimulated glucose production or PEPCK expression in hepatocytes lacking STAT3. These data identify a novel role for PLPP1 activity and hepatocyte LPA levels in glucagon sensitivity via a mechanism involving STAT3.

MicroRNAs in the thyroid

MicroRNAs (miRNAs) are small non-coding RNA comprising approximately 19-25 nucleotides. miRNAs can act as tumour suppressors or oncogenes, and aberrant expression of miRNAs has been reported in several human cancers and has been associated with cancer initiation and progression. Recent evidence suggests that miRNAs play a major role in thyroid carcinogenesis. In this review, we summarize the role of miRNAs in thyroid cancer and describe the oncogenic or tumour suppressor function of miRNAs as well as their clinical utility as prognostic or diagnostic markers in thyroid cancer.

Application of network construction to estimate functional changes to insulin receptor substrates 1 and 2 in Huh7 cells following infection with the hepatitis C virus

Hepatitis C virus (HCV) is closely associated with insulin resistance (IS), acting primarily by interfering with insulin signaling pathways, increasing cytokine-mediated (tumor necrosis factor α, interleukin 6) inflammatory responses and enhancing oxidative stress. In the insulin signaling pathways, the insulin receptor substrate (IRS) is one of the key regulatory factors. The present study constructed gene regulatory sub-networks specific for IRS1 and IRS2 in Huh7 cells and HCV-infected Huh7 (HCV-Huh7) cells using linear programming and a decomposition algorithm, and investigated the possible mechanisms underlying the function of IRS1/2 in HCV-induced IS in Huh7 cells. All data were obtained from GSE20948 of the Gene Expression Omnibus database from the National Center for Biotechnology Information. Genes which were significantly differentially expressed between Huh7 and HCV-Huh7 cells were analyzed using the significance analysis of microarray algorithm. The top 50 genes, including IRS1/2, were used as target genes to determine the gene regulatory networks and next the sub-networks of IRS1 and IRS2 in HCV-Huh7 and Huh7 cells using Gene Regulatory Network Inference Tool, an algorithm based on linear programming and the decomposition process. The IRS1/2 sub-networks were divided into upstream/downstream groups and activation/suppression clusters, and were further analyzed using Molecule Annotation System 3.0 and Database for Annotation, Visualization, and Integrated Discovery software, two online platforms for enrichment and clustering analysis and visualization. The results indicated that in Huh7 cells, the downstream network of IRS2 is more complex than that of IRS1, indicating that the insulin metabolism in Huh7 cells may be primarily mediated by IRS2. In HCV-Huh7 cells, the downstream pathway of IRS2 is blocked, suggesting that this may be the underlying mechanism in HCV infection that leads to insulin resistance. The present findings add a further dimension to the understanding of the pathological mechanisms of HCV infection-associated insulin resistance, and provide novel concepts for insulin resistance and glucose metabolism research.

Upregulation of lncRNA MEG3 promotes hepatic insulin resistance via increasing FoxO1 expression

BACKGROUND

Hepatic insulin resistance is a major characteristic of type 2 diabetes mellitus. LncRNA MEG3 has been shown to correlate to hepatic glucose production; however, the underlying mechanism remains unclear. This study aims to investigate the role of MEG3 in hepatic insulin resistance.

METHODS

High-fat diet mice, ob/ob mice and mice primary hepatocytes were used in this study. Expression of MEG3, FoxO1, G6pc and Pepck were determined by real-time PCR. FoxO1, G6pc, Pepck, HDAC1 and HDAC3 protein levels were analyzed by western blotting. Hepatic gluconeogenesis, glycogen accumulation, triglyceride and glycogen contents were measured by corresponding assay or kit, and body weight was monitored after an overnight fast.

RESULTS

Gene expression of MEG3 was upregulated in high-fat diet and ob/ob mice and increased by palmitate, oleate or linoleate. MEG3 overexpression significantly increased FoxO1, G6pc, Pepck mRNA expressions and hepatic gluconeogenesis and suppressed insulin-stimulated glycogen synthesis in primary hepatocytes, whereas palmitate-induced increase of FoxO1, G6pc and Pepck protein expressions could be reversed by MEG3 interference. In addition, high fat enhanced expression of lncRNA MEG3 in hepatocytes through histone acetylation. Furthermore, MEG3 interference could reverse the up-regulation of triglyceride as well as impaired glucose tolerance and down-regulation of glucogen content in high-fat diet mice or ob/ob mice.

CONCLUSION

Upregulation of lncRNA MEG3 enhances hepatic insulin resistance via increasing foxO1expression, suggesting that MEG3 may be a potential target and therapeutic strategy for diabetes.

Metabolic comorbidities in Cushing's syndrome

Cushing's syndrome (CS) patients have increased mortality primarily due to cardiovascular events induced by glucocorticoid (GC) excess-related severe metabolic changes. Glucose metabolism abnormalities are common in CS due to increased gluconeogenesis, disruption of insulin signalling with reduced glucose uptake and disposal of glucose and altered insulin secretion, consequent to the combination of GCs effects on liver, muscle, adipose tissue and pancreas. Dyslipidaemia is a frequent feature in CS as a result of GC-induced increased lipolysis, lipid mobilisation, liponeogenesis and adipogenesis. Protein metabolism is severely affected by GC excess via complex direct and indirect stimulation of protein breakdown and inhibition of protein synthesis, which can lead to muscle loss. CS patients show changes in body composition, with fat redistribution resulting in accumulation of central adipose tissue. Metabolic changes, altered adipokine release, GC-induced heart and vasculature abnormalities, hypertension and atherosclerosis contribute to the increased cardiovascular morbidity and mortality. In paediatric CS patients, the interplay between GC and the GH/IGF1 axis affects growth and body composition, while in adults it further contributes to the metabolic derangement. GC excess has a myriad of deleterious effects and here we attempt to summarise the metabolic comorbidities related to CS and their management in the perspective of reducing the cardiovascular risk and mortality overall.

MAP kinase phosphatase 2 regulates macrophage-adipocyte interaction

Objective

Inflammation is critical for the development of obesity-associated metabolic disorders. This study aims to investigate the role of mitogen-activated protein kinase phosphatase 2 (MKP-2) in inflammation during macrophage-adipocyte interaction.

Methods

White adipose tissues (WAT) from mice either on a high-fat diet (HFD) or normal chow (NC) were isolated to examine the expression of MKP-2. Murine macrophage cell line RAW264.7 stably expressing MKP-2 was used to study the regulation of MKP-2 in macrophages in response to saturated free fatty acid (FFA) and its role in macrophage M1/M2 activation. Macrophage-adipocyte co-culture system was employed to investigate the role of MKP-2 in regulating inflammation during adipocyte-macrophage interaction. c-Jun N-terminal kinase (JNK)- and p38-specific inhibitors were used to examine the mechanisms by which MKP-2 regulates macrophage activation and macrophage-adipocytes interaction.

Results

HFD changed the expression of MKP-2 in WAT, and MKP-2 was highly expressed in the stromal vascular cells (SVCs). MKP-2 inhibited the production of proinflammatory cytokines in response to FFA stimulation in macrophages. MKP-2 inhibited macrophage M1 activation through JNK and p38. In addition, overexpression of MKP-2 in macrophages suppressed inflammation during macrophage-adipocyte interaction.

Conclusion

MKP-2 is a negative regulator of macrophage M1 activation through JNK and p38 and inhibits inflammation during macrophage-adipocyte interaction.