What is the difference between gluconeogenesis and gluconeogenesis

Both glycogenolysis and gluconeogenesis are governed primarily by glucagon and insulin, which upregulate and downregulate glucose production, respectively 7 , 8. When feeding is re-initiated, the insulin pathway is upregulated, which promotes CRTC2 ubiquitination and degradation, thereby terminating gluconeogenesis Our results also demonstrate that hepatic Sam68 deficiencies improve insulin sensitivity and reduce hyperglycemia in diabetic mice, which suggests that Sam68 could be a therapeutic target for the treatment of T2D.

Hepatic Sam68 deficiency was also associated with lower blood glucose levels after the injection of glucose Fig. Thus, hepatic Sam68 knockout appears to increase glucose tolerance and insulin sensitivity but reduce insulin levels.

Source data are provided as a Source Data file. Thus, the hepatic-specific deletion of Sam68 appeared to reduce blood glucose levels by both increasing insulin sensitivity and reducing hepatic glucose production. To investigate the molecular mechanism by which Sam68 promotes hepatic gluconeogenesis, we analyzed mouse liver tissues for the expression of key gluconeogenic genes. Both mRNA Fig. The early steps in glucagon signaling are initiated by the binding of glucagon to the glucagon receptor, which promotes adenylyl cyclase activity; then, activated adenylyl cyclase increases cAMP production and cAMP-mediated protein kinase A PKA activation Sam68 deficiency did not significantly alter glucagon receptor expression Fig.

Thus, the upstream portion of the glucagon signaling pathway i. To confirm that the observed declines in CRTC2 protein levels contributed to the downregulation of glucagon signaling and gluconeogenesis in Samdeficient mice, experiments were conducted in Sam68 LKO mice that had been injected with an adenovirus coding for a degradation-resistant variant of CRTC2 Ad-CRTC2 KR , which contained a LysArg mutation at its major ubiquitination site 36 and has been shown to upregulate glucagon- and cAMP-agonist-induced gluconeogenic gene expression and glucose production in WT hepatocytes 15 , The vector was administered to Sam68 LKO mice via tail-vein injection i.

Under feeding Fig. Collectively, these observations indicate that the Sam68 deletion impedes glucagon signaling, reduces gluconeogenesis, and improves insulin sensitivity by reducing CRTC2 protein but not mRNA levels and the CRTC2-mediated activation of gluconeogenic gene expression.

Because glucagon signaling induces gluconeogenesis, in part, by promoting the nuclear translocation of CRTC2 14 , we investigated whether glucagon also altered the subcellular distribution of Sam68 in the livers of WT mice Fig. Furthermore, Sam68 mediates a number of biological processes by functioning as an adaptor protein that interacts with other signaling molecules 40 , and co-immunoprecipitation co-IP experiments confirmed that endogenous CRTC2 interacted with Sam68 in WT mouse primary hepatocytes at baseline Fig.

Notably, reverse co-IP experiments confirmed SamCRTC2 interaction in mouse primary hepatocytes and further revealed that the interaction occurs in both the nucleus and cytoplasm Supplementary Fig. Furthermore, computational results from the combined text pattern search and hydropathy analyses showed that the P5 motif located near the C-terminus of Sam68 has Our observation that the Sam68 deletion lowers blood-glucose levels, and promotes insulin sensitivity by decreasing the stability of CRTC2 protein, suggests that these two molecules may also have a role in the pathogenic mechanisms of diabetes.

The elevations in blood glucose associated with T2D occur through a combination of declines in insulin sensitivity, which reduces peripheral glucose uptake, and an increase in hepatic glucose production. Many first-line therapies for T2D, target the increase in production, particularly via hepatic gluconeogenesis 2 , 42 , Thus, the therapies targeting the expression of Sam68 may be effective for normalizing blood-glucose levels in patients with diabetes.

The important role of hepatic CRTC2 in gluconeogenesis and insulin sensitivity has been extensively documented. In humans, CRTC2 polymorphisms are associated with an increased risk for T2D 44 , 45 , and when CRTC2 levels were manipulated in mice, the corresponding changes in blood-glucose measurements were consistent with our observations in Samdeficient mice: modest elevations of CRTC2 increased blood glucose levels and decreased insulin sensitivity 15 , 37 , global or liver-specific CRTC2 deletions reduced blood glucose and increased insulin sensitivity 15 , 39 , 46 , and both oligo- and siRNA-mediated CRTC2 inactivation mitigated hyperglycemia in diabetic mice 47 , CRTC2 triggers both glucose production and a compensatory mechanism that elevates insulin levels to promote glucose uptake 15 , 37 , 39 , which supports the notion that the reduced serum insulin levels in Sam68 LKO mice may be secondary to altered blood glucose.

Additionally, CRTC2 has been shown to modulate insulin sensitivity by regulating lipid metabolism 38 , and interestingly both the global Sam68 deletion 31 and the loss of hepatic CRTC2 expression activate thermogenesis Thus multiple mechanisms may contribute to the enhanced insulin sensitivity with hepatic Samdeficiency, which warrants further investigations.

The role of the C-terminus in binding was also supported by our hydropathy modeling and P5 mutagenesis experiments. However, the N-terminus of Sam68 is not predicted with a high probability to interact with CRTC2, suggesting a more complex mechanism and potential involvement of other molecular components. We observed that hepatic Sam68 protein expression is significantly upregulated in diabetic mouse models and in human subjects with diabetes, that glucagon signaling promotes Sam68 translocation from cytoplasm to nucleus, and that Sam68 interacts with CRTC2 both in the nucleus and cytoplasm.

Thus, it is likely that under diabetic conditions, deregulated metabolic signaling e. As an adaptor protein, Sam68 coordinates various cellular responses to environmental stimuli. In conclusion, the evidence presented in this report demonstrates that Sam68 promotes hepatic and gluconeogenesis by interacting with and stabilizing CRTC2 protein. The sequences of all primers and probes used for vector construction, PCR genotyping, and Southern blotting are reported in Supplementary Table 3 , and the antibodies used for Western blotting are listed in Supplementary Table 2.

Home-made catheters were filled with heparinized-glycerol locking solution, implanted under the back skin of mice, and threaded into the left carotid artery for blood sampling and the right jugular vein for infusion.

Mice were awake, unhandled, and able to move freely in a plastic container during the study. At the end of the clamp experiment, the mice were sacrificed, and the livers were snap-frozen in liquid nitrogen for measurements of glycogen content.

The insulin infusion rate was based on observations in pilot studies. The radioactivity of 3 H in hepatic glycogen was determined by digesting tissue samples in KOH and precipitating glycogen with ethanol Liver samples were obtained via surgical biopsy from patients with or without diabetes. Informed consent was obtained from all the subjects, and patient characteristics are listed in Supplementary Table 1.

After isolation, cells were cultured on collagen-coated plates in DMEM containing 4. Antibodies are listed in Supplementary Table 2. Immunoprecipitation IP was performed as previously described Primers are listed in Supplementary Table 3.

Readings were normalized to the total protein content in whole-cell lysates. For evaluation of insulin signaling, tissues were homogenized in RIPA buffer containing a protease- and phosphatase-inhibitor cocktail Sigma ; then, tissue proteins were extracted and evaluated via Western blotting with primary antibodies against SerAKT, ThrAKT, and total AKT Supplementary Table 2 as previously described Hydrophobicity map for each potential binding motif in Sam68 in both forward and reverse orientations was scanned across a hydrophobicity map for the whole protein sequence of CRTC2.

The degree of complementary hydropathy was calculated see Eq. In Eq. The degree of complementary hydropathy can range from 0 to 1. The hydropathy plot was generated according to a hydropathic score of each amino acid. GraphPad Prism8 Software was used for statistical analysis. A p -value of less than 0. All the representative Western blotting and measurements of glucose production from cultured primary hepatocytes presented in this article were repeated at least twice with similar results.

Further information on research design is available in the Nature Research Reporting Summary linked to this article. All data are included in this published article and its Supplementary information files. Source data are provided with this paper. Forbes, J. Mechanisms of diabetic complications. Rines, A. Targeting hepatic glucose metabolism in the treatment of type 2 diabetes. Drug Discov.

Magnusson, I. Increased rate of gluconeogenesis in type II diabetes mellitus. A 13C nuclear magnetic resonance study. Hunter, R. Metformin reduces liver glucose production by inhibition of fructosebisphosphatase. Madiraju, A. Metformin inhibits gluconeogenesis via a redox-dependent mechanism in vivo. Metformin suppresses gluconeogenesis by inhibiting mitochondrial glycerophosphate dehydrogenase. Nature , — Habegger, K. The metabolic actions of glucagon revisited.

Dobbins, R. Role of glucagon in countering hypoglycemia induced by insulin infusion in dogs. Iourgenko, V. Identification of a family of cAMP response element-binding protein coactivators by genome-scale functional analysis in mammalian cells. Natl Acad. USA , — Conkright, M. Cell 12 , — Luo, Q. Dentin, R. Glycogenolysis and gluconeogenesis are two processes which are involved in the formation of glucose in the animal body. The carbohydrates in the diet are broken down into glucose and other monosaccharides during digestion.

The glucose is transported into the liver and muscle cells by blood. That glucose is converted into a storage carbohydrate known as glycogen in a process called glycogenesis. The main difference between glycogenolysis and gluconeogenesis is that glycogenolysis is the production of glucose 6-phosphate by splitting a glucose monomer from glycogen by adding an inorganic phosphate whereas gluconeogenesis is the metabolic process by which glucose is formed from non-carbohydrate precursors in the liver.

Glycogenolysis is a process by which stored glycogen is broken down into glucose monomers in the liver under the influence of hormones. Glucagon and adrenaline govern the breakdown of glycogen in the liver when less glucose is available for the metabolism in the cells.

Glucagon is released in response to low glucose levels. Adrenaline is released in response to a threat or stress. The enzyme, glycogen phosphorylase produces glucose 1-phosphate by the phosphorylation of alpha 1,4 linkages.

The second enzyme, phosphoglucomutase converts glucose 1-phosphate into glucose 6-phosphate. The alpha 1,6 linkages are responsible for the branching of glycogen. The action of glycogen debranching enzyme and alpha 1,6 glucosidase enzymes are involved in the removal of the glucose molecules, which form branches in the glycogen.

The conversion of glucose 1-phosphate into glucose 6-phosphate is done by hexokinase. The phosphate group is removed by glucose 6-phosphatase during circulation and free glucose is readily available for the cells to be up taken. The first such reaction has been mentioned, the conversion of pyruvate to PEP. The second is the removal of one phosphate group from a fructose derivative, and the third is the removal of a second phosphate group from glucosephosphate to leave glucose.

The pyruvate entering gluconeogenesis can come from a variety of sources. One of these is the carbon-heavy portion of certain amino acids found in proteins , and another is from the oxidation of fatty acids. This is why foods consisting only or heavily of proteins and fats can serve as fuel sources along with carbohydrates. Glucose is of course a common feature of both glycolysis and gluconeogenesis. In the first pathway, it is the reactant, or starting point, while in the latter it is the product, or end point.

In addition, glycolysis and gluconeogenesis both occur in the cytoplasm of cells. Both make use of ATP and water. The two pathways also have a number of other molecules in common. For example, pyruvate is the main "entry point" of gluconeogenesis, whereas in glycolysis it is the primary product. The fact that these pathways have multiple steps makes it easier for the body to control their overall rates, which tend to shift greatly throughout the day owing to different patterns of eating and exercise.

The main difference between glycolysis and gluconeogenesis is in their basic function: one depletes existing glucose , while other replenishes it from both organic carbon-containing and inorganic carbon-free molecules. This makes glycolysis a catabolic process of metabolism, while gluconeogenesis is anabolic.

Also on the glycolysis vs.