As an important enzyme for gluconeogenesis, mitochondrial phosphoenolpyruvate carboxykinase (PCK2) has further complex functions beyond regulation of glucose metabolism. Here, we report that conditional knockout of Pck2 in osteoblasts results in a pathological phenotype manifested as craniofacial malformation, long bone loss, and marrow adipocyte accumulation. Ablation of Pck2 alters the metabolic pathways of developing bone, particularly fatty acid metabolism. However, metformin treatment can mitigate skeletal dysplasia of embryonic and postnatal heterozygous knockout mice, at least partly via the AMPK signaling pathway. Collectively, these data illustrate that PCK2 is pivotal for bone development and metabolic homeostasis, and suggest that regulation of metformin-mediated signaling could provide a novel and practical strategy for treating metabolic skeletal dysfunction.
Mice ; Animals ; Metformin/pharmacology* ; Phosphoenolpyruvate Carboxykinase (ATP)/metabolism* ; Gluconeogenesis/genetics* ; Mice, Knockout

OBJECTIVETo investigate the expressions of glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK) in the liver of mice with hyperhomocysteinemia (HHcy) and explore the mechanism of gluconeogenesis induced by homocysteine.

METHODSFifty mice were randomly divided into normal control group (n=25) and HHcy group (n=25) and fed with normal food and food supplemented with 1.5% methionine, respectively. After 3 months of feeding, the fasting blood glucose and insulin levels were determined, and HOMA insulin resistance index (HOMA-IR) was calculated. The expressions of G6Pase and PEPCK in the liver of mice were detected using RT-PCR and Western blotting.

RESULTSThe fasting blood glucose and insulin levels and HOMA-IR were significantly higher in HHcy group than in the control group (P<0.05). RT-PCR and Western blotting showed that the hepatic expressions of G6Pase and PEPCK mRNA and proteins increased significantly in HHcy group compared with those in the control group (P<0.05).

CONCLUSIONHomocysteine promotes gluconeogenesis to enhance glucose output and contribute to the occurrence of insulin resistance.

Animals ; Gluconeogenesis ; Glucose-6-Phosphatase ; metabolism ; Homocysteine ; blood ; Hyperhomocysteinemia ; metabolism ; Insulin Resistance ; Liver ; metabolism ; Male ; Mice ; Mice, Inbred Strains ; Phosphoenolpyruvate Carboxykinase (ATP) ; metabolism

OBJECTIVETo observe the effect of calorie restriction on the high fat diet rats mRNA expressions of liver forkhead box O1(FoxO1), phosphoenolpyruvate carboxykinase (PEPCK), glucose-6-phosphatase (G-6-P) and to explore the possible mechanisms.

METHODS24 normal 6-week-old male Wistar rats were randomly divided into three groups: normal chow group (NC, n = 7), high fat diet group (HF, n = 9) and calorie restriction group (CR, n = 8). They were fed for 12 weeks. At the end of the experiment, the rats were sacrificed and their fasting blood glucose (FBG), insulin (INS), triglycerides (TG), total cholesterol (TC) were measured. Their visceral fat (VF) and body weight (BW) were also measured and VF/BW was calculated. Gene expression was investigated by using semi-quantitative RT-PCR methods. Liver histology was studied with HE stained slides.

RESULTSCompared with the NC group, HF group rats developed visceral obesity which was accompanied by higher FBG, plasma INS, TG, and TC. The levels of FoxO1, PEPCK, and G-6-P increased by 18.9%, 33.8%, and 24.6%, respectively (P less than 0.01). Liver steatosis was observed with microscopy. The BW, VF FBG, INS, TG and TC of the CR group rats were lower in comparison to those of the HF group. The levels of FoxO1, PEPCK and G-6-P were lower by 26.6%, 35.0%, 34.3% (P less than 0.01). Meanwhile, liver steatosis was also milder.

CONCLUSIONCalorie restriction can inhibit the expressions of FoxO1, PEPCK and G-6-P, strengthen insulin signal conduction, suppress gluconeogenesis and thus regulate glycometabolism.

Animals ; Caloric Restriction ; Dietary Fats ; Forkhead Transcription Factors ; genetics ; Gene Expression Regulation ; Gluconeogenesis ; genetics ; Glucose-6-Phosphatase ; genetics ; Liver ; metabolism ; Male ; Nerve Tissue Proteins ; genetics ; Phosphoenolpyruvate Carboxykinase (ATP) ; genetics ; Rats ; Rats, Wistar

OBJECTIVETo study the relationship between hepatic insulin resistance induced by high fat diet and the expression of genes involving hepatic glucose output.

METHODSNormal 8-week-old male SD rats were randomly divided into two groups, i.e, normal chow group (NC, n = 10) and high fat diet group (HF, n = 10). They were fed for 28 weeks. Body weight and fasting blood glucose (FBG) were measured. At the end of the experiment, the rats were sacrificed and their fasting insulin (INS) and triglycerides (TG) were measured. Hepatic insulin sensitivity was measured by tissue uptake of 3H-2-deoxyglucose and the content of hepatic glycogen was measured using the anthrone method. Gene expression was investigated by using the semi-quantitative RT-PCR method.

RESULTSAs compared with NC group, CF group rats developed visceral obesity which was accompanied by higher plasma TG. FBG in CF group increased starting from the 18th week (NC 4.77+/-63 mmol/L vs HF 5.45+/-87 mmol/L, P < 0.05). The rate of uptake of 3H-2-deoxyglucose in livers decreased by 51% in the HF group. The content of hepatic glycogen increased by 92.4% (P < 0.01). The level of phosphoenolpyruvate carboxykinase (PEPCK) and PGC-1a mRNA increased by 41.5% and 30.8%, respectively (P < 0.05).

CONCLUSIONA high fat diet induced expressions of PGC-1a and PEPCK. It suggests that gluconeogenesis may play a role in the increase of hepatic glucose output and FBG.

Animals ; Dietary Fats ; Gene Expression Regulation ; Glucose ; metabolism ; Heat-Shock Proteins ; metabolism ; Insulin Resistance ; genetics ; Liver ; metabolism ; Liver Glycogen ; metabolism ; Male ; Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha ; Phosphoenolpyruvate Carboxykinase (ATP) ; metabolism ; Random Allocation ; Rats ; Rats, Sprague-Dawley ; Transcription Factors ; metabolism

BACKGROUNDNF-kappaB p65 was shown to inhibit transcription of phosphoenolpyruvate carboxykinase (PEPCK), a rate-limiting enzyme in gluconeogenesis in the liver. To understand the mechanism of action of NF-kappaB p65, we investigated the nuclear receptor corepressor in the regulation of PEPCK transcription.

METHODSRat H4IIE cells, human hepatoma HepG2 cells and human embryo kidney (HEK) 293 cells were used in this study. The transcriptional activity of a rat PEPCK gene promoter (-490/+100) was analyzed in HepG2 cells, a HepG2 super suppressor IkBalpha (ssIkBalpha) stable cell line, and HEK 293 cells. The effects of p65 and ssIkBalpha on a rat PEPCK gene promoter were observed using the PEPCK luciferase reporter system. The interaction of the cAMP-response- element-binding (CREB) protein, histone deacetylase 3 (HDAC3) and silencing mediator for retinoic and thyroid hormone receptors (SMRT) with the PEPCK gene promoter were investigated using the chromatin immunoprecipitation (ChIP) assay. p65 cotransfection and RNAi-mediated gene knockdown were used to determine the corepressor involved in the inhibition of PEPCK by NF-kappaB p65 and the transcriptional regulation of CREB by NF-kappaB p65.

RESULTSNF-kappaB p65 inhibited PEPCK expression and the inhibition was blocked by ssIkBalpha. The inhibitory effect of p65 was completely blocked in a HepG2 stable cell line in which ssIkBalpha was expressed. HDAC3 or SMRT knockdown led to a significant up-regulation of PEPCK reporter activity in the presence of p65 cotransfection. In the ChIP assay the interaction of HDAC3 and SMRT with the PEPCK gene promoter was induced by p65 activation, but the CREB signal was reduced. Transcriptional activity of CREB was inhibited by NF-kappaB p65 cotransfection. The inhibitory effect of NF-kappaB p65 was blocked by HDAC3 RNAi or SMRT RNAi.

CONCLUSIONSThe study showed that the inhibition of PEPCK by NF-kappaB p65 was dependent on HDAC3 and SMRT, which form a nuclear corepressor complex for transcriptional inhibition. The transcription factors NF-kappaB p65 and CREB share the same corepressor HDAC3-SMRT, and the corepressor exchange leads to inhibition of PEPCK gene transcription by NF-kappaB p65.

Animals ; Blotting, Western ; Cell Line ; Chromatin Immunoprecipitation ; Cyclic AMP Response Element-Binding Protein ; genetics ; metabolism ; Hep G2 Cells ; Histone Deacetylases ; genetics ; metabolism ; Humans ; NF-kappa B ; genetics ; metabolism ; Nuclear Receptor Co-Repressor 2 ; genetics ; metabolism ; Phosphoenolpyruvate Carboxykinase (ATP) ; genetics ; Promoter Regions, Genetic ; genetics ; Protein Binding ; genetics ; physiology ; Rats ; Reverse Transcriptase Polymerase Chain Reaction ; Transcription Factor RelA ; genetics ; metabolism

OBJECTIVEChromium is an essential mineral that is thought to be necessary for normal glucose homeostasis. Numerous studies give evidence that chromium picolinate can modulate blood glucose and insulin resistance. The main ingredient of Tianmai Xiaoke (TMXK) Tablet is chromium picolinate. In China, TMXK Tablet is used to treat type 2 diabetes. This study investigated the effect of TMXK on glucose metabolism in diabetic rats to explore possible underlying molecular mechanisms for its action.

METHODSDiabetes was induced in rats by feeding a high-fat diet and subcutaneously injection with a single dose of streptozotocin (50 mg/kg, tail vein). One week after streptozotocin-injection, model rats were divided into diabetic group, low dose of TMXK group and high dose of TMXK group. Eight normal rats were used as normal control. After 8 weeks of treatment, skeletal muscle was obtained and was analyzed using Roche NimbleGen mRNA array and quantitative polymerase chain reaction (qPCR). Fasting blood glucose, oral glucose tolerance test and homeostasis model assessment of insulin resistance (HOMA-IR) index were also measured.

RESULTSThe authors found that the administration of TMXK Tablet can reduce the fasting blood glucose and fasting insulin level and HOMA-IR index. The authors also found that 2 223 genes from skeletal muscle of the high-dose TMXK group had significant changes in expression (1 752 increased, 471 decreased). Based on Kyoto encyclopedia of genes and genomes pathway analysis, the most three significant pathways were "insulin signaling pathway", "glycolysis/gluconeogenesis" and "citrate cycle (TCA)". qPCR showed that relative levels of forkhead box O3 (FoxO3), phosphoenolpyruvate carboxykinase 2 (Pck2), and protein tyrosine phosphatase 1B (Ptp1b) were significantly decreased in the high-dose TMXK group, while v-akt murine thymoma viral oncogene homolog 1 (Akt1) and insulin receptor substrate 2 (Irs2) were increased.

CONCLUSIONOur data show that TMXK Tablet reduces fasting glucose level and improves insulin resistance in diabetic rats. The mechanism may be linked to the inactivation of PTP1B and PCK enzymes, or through intracellular pathways, such as the insulin signaling pathway.

Animals ; Blood Glucose ; analysis ; Chromium ; administration & dosage ; Diabetes Mellitus, Type 2 ; drug therapy ; metabolism ; Insulin ; physiology ; Insulin Resistance ; Male ; Medicine, Chinese Traditional ; Phosphoenolpyruvate Carboxykinase (ATP) ; antagonists & inhibitors ; Protein Tyrosine Phosphatase, Non-Receptor Type 1 ; antagonists & inhibitors ; Rats ; Rats, Sprague-Dawley ; Real-Time Polymerase Chain Reaction ; Signal Transduction ; drug effects ; Tablets