Mathematical modeling of the insulin signal transduction pathway for prediction of insulin sensitivity from expression data

Expression and characterisation of human glycerol kinase: the role of solubilising agents and molecular chaperones

BACKGROUND

Glycerol kinase (GK; EC 2.7.1.30) facilitates the entry of glycerol into pathways of glucose and triglyceride metabolism and may play a potential role in Type 2 diabetes mellitus (T2DM). However, the detailed regulatory mechanisms and structure of the human GK are unknown.

METHODS

The human GK gene was cloned into the pET-24a(+) vector and over-expressed in Escherichia coli BL21 (DE3). Since the protein was expressed as inclusion bodies (IBs), various culture parameters and solubilising agents were used but they did not produce bioactive His-GK; however, co-expression of His-GK with molecular chaperones, specifically pKJE7, achieved expression of bioactive His-GK. The overexpressed bioactive His-GK was purified using coloumn chromatography and characterised using enzyme kinetics.

RESULTS

The overexpressed bioactive His-GK was purified apparently to homogeneity (∼295-fold) and characterised. The native His-GK was a dimer with a monomeric molecular weight of ∼55 kDa. Optimal enzyme activity was observed in TEA buffer (50 mM) at 7.5 pH. K+ (40 mM) and Mg2+ (2.0 mM) emerged as prefered metal ions for His-GK activity with specific activity 0.780 U/mg protein. The purified His-GK obeyed standard Michaelis-Menten kinetics with Km value of 5.022 µM (R2=0.927) for its substrate glycerol; whereas, that for ATP and PEP was 0.767 mM (R2=0.928) and 0.223 mM (R2=0.967), respectively. Other optimal parameters for the substrate and co-factors were also determined.

CONCLUSION

The present study demonstrates that co-expression of molecular chaperones assists with the expression of bioactive human GK for its characterisation.

High triglyceride-glucose index is associated with poor cardiovascular outcomes in Chinese acute coronary syndrome patients without diabetes mellitus who underwent emergency percutaneous coronary intervention with drug-eluting stents

Background

Previous research has supported the association between the triglyceride-glucose index (TyG index) and the incidence and prognosis of cardiovascular disease. However, the association between the TyG index and the prognosis of patients with acute coronary syndrome (ACS) without diabetes mellitus (DM) who underwent emergency percutaneous coronary intervention (PCI) with drug-eluting stents (DESs) has not been thoroughly investigated, and these patients may easily be neglected. Therefore, this study aimed to investigate the association between the TyG index and major adverse cardiovascular and cerebrovascular events (MACCEs) in Chinese ACS patients without DM who underwent emergency PCI with DES.

Methods

The total number of ACS patients without DM who underwent emergency PCI with DES for this study was 1650. Ln [fasting triglycerides (mg/dL) ×fasting plasma glucose (mg/dL)/2] is the formula used to calculate the TyG index. According to the TyG index, we classified the patients into two groups. The frequency of the following endpoint events was calculated and compared between the two groups: all-cause death, non-fatal myocardial infarction (MI), non-fatal ischemia stroke, ischemia-driven revascularization and cardiac rehospitalization.

Results

After a median of 47 months of follow-up [47 (40, 54)], 437 (26.5%) endpoint events were recorded in total. The TyG index was further demonstrated to be independent of MACCE by multivariable Cox regression analysis (hazard ratio [HR], 1.493; 95% confidence interval [CI], 1.230-1.812; p<0.001). The TyG index≥7.08 group had a considerably greater incidence of MACCE (30.3% vs. 22.7% in the TyG index<7.08 group, p<0.001), cardiac death (4.0% vs. 2.3% in the TyG index<7.08 group, p=0.047), and ischemia-driven revascularization (5.7% vs. 3.6% in the TyG index<7.08 group, p=0.046) than the TyG index<7.08 group. Between the two groups, there was no discernible difference in all-cause death (5.6% vs. 3.8% in the TyG index<7.08 group, p=0.080), non-fatal MI (1.0% vs. 0.2% in the TyG index<7.08 group, p=0.057), non-fatal ischemic stroke (1.6% vs. 1.0% in the TyG index<7.08 group, p=0.272), and cardiac rehospitalization (16.5% vs. 14.1% in the TyG index<7.08 group, p=0.171).

Conclusion

For ACS patients without DM who received emergency PCI with DES, the TyG index might be an independent predictor of MACCE.

Insulin Signaling Pathway Model in Adipocyte Cells

BACKGROUND

Worldwide, type 2 diabetes mellitus (T2DM) is one of the most pervasive and fastgrowing disorders, bringing long-term adverse effects. T2DM arises from pancreatic β-cells deficiency to produce enough insulin or when the body cannot effectively use the insulin produced by such cells. Accordingly, early diagnosis will decrease the long-term effects and high-healthcare costs of diabetes.

OBJECTIVE

The objective is developing an integrated mathematical model of the insulin signaling network based on Brännmark's model, which can simulate the signaling events more comprehensively with the added key components.

METHODS

In this study, a thorough mathematical model of the insulin signaling network was developed by expanding the previously validated model and incorporating the glycogen synthesis module. Parameters (69 parameters) of the integrated model were evaluated by a genetic algorithm by fitting the model predictions to eighty percent of experimental data from the literature. Twenty percent of the experimental data were used to evaluate the final optimized model.

RESULTS

The time-response curves indicate that the GS phosphorylation reaches its maximum in response to 10^-7 M insulin after 4 min, while the maximum phosphorylated GSK3 is attained within ~50 min. The doseresponse curves for the GSP and GSK3 of the insulin signaling intermediaries in response to the increased concentration of insulin, after 10 min, in the input from 0-100 nM exhibits a decreasing trend, whereas an increasing trend was observed for the GS and GSK3P. The GSK and GS phosphorylation sensitivity was enhanced by increasing the initial insulin concentration level from 0.001 to 100 nM. However, the sensitivity of GSK3 to insulin concentration changes (from 0.001 to 100 nM) was 3-fold higher than GS sensitivity.

CONCLUSION

Considerably, the trends of all signaling components simulated by the expanded model shows high compatibility with experimental data (R2 ≥ 0.9), which approves the accuracy of the proposed model. The proposed mathematical model can be used in many biological systems and combined with the whole-body model of the blood glucose regulation system for a better understanding of the causes and potential treatment of type 2 diabetes. Although, this model is not a complete description of insulin signaling, yet it can make profound contributions to improvements regarding other important components and signaling branches such as epidermal growth factor (EGF) signaling, as well as signaling in other cell types in the model structure of future works.

Pancreatic ductal adenocarcinoma progression is restrained by stromal matrix

Desmoplasia describes the deposition of extensive extracellular matrix and defines primary pancreatic ductal adenocarcinoma (PDA). The acellular component of this stroma has been implicated in PDA pathogenesis and is being targeted therapeutically in clinical trials. By analyzing the stromal content of PDA samples from numerous annotated PDA data sets and correlating stromal content with both anatomic site and clinical outcome, we found PDA metastases in the liver, the primary cause of mortality to have less stroma, have higher tumor cellularity than primary tumors. Experimentally manipulating stromal matrix with an anti-lysyl oxidase like-2 (anti-LOXL2) antibody in syngeneic orthotopic PDA mouse models significantly decreased matrix content, led to lower tissue stiffness, lower contrast retention on computed tomography, and accelerated tumor growth, resulting in diminished overall survival. These studies suggest an important protective role of stroma in PDA and urge caution in clinically deploying stromal depletion strategies.

Computational Analysis of Insulin-Glucagon Signalling Network: Implications of Bistability to Metabolic Homeostasis and Disease states

Insulin and glucagon control plasma macronutrient homeostasis through their signalling network composed of multiple feedback and crosstalk interactions. To understand how these interactions contribute to metabolic homeostasis and disease states, we analysed the steady state response of metabolic regulation (catabolic or anabolic) with respect to structural and input perturbations in the integrated signalling network, for varying levels of plasma glucose. Structural perturbations revealed: the positive feedback of AKT on IRS is responsible for the bistability in anabolic zone (glucose >5.5 mmol); the positive feedback of calcium on cAMP is responsible for ensuring ultrasensitive response in catabolic zone (glucose <4.5 mmol); the crosstalk between AKT and PDE3 is responsible for efficient catabolic response under low glucose condition; the crosstalk between DAG and PKC regulates the span of anabolic bistable region with respect to plasma glucose levels. The macronutrient perturbations revealed: varying plasma amino acids and fatty acids from normal to high levels gradually shifted the bistable response towards higher glucose range, eventually making the response catabolic or unresponsive to increasing glucose levels. The analysis reveals that certain macronutrient composition may be more conducive to homeostasis than others. The network perturbations that may contribute to disease states such as diabetes, obesity and cancer are discussed.

Stromal biology and therapy in pancreatic cancer: ready for clinical translation?

Pancreatic ductal adenocarcinoma (PDA) is notoriously aggressive and hard to treat. The tumour microenvironment (TME) in PDA is highly dynamic and has been found to promote tumour progression, metastasis niche formation and therapeutic resistance. Intensive research of recent years has revealed an incredible heterogeneity and complexity of the different components of the TME, including cancer-associated fibroblasts, immune cells, extracellular matrix components, tumour vessels and nerves. It has been hypothesised that paracrine interactions between neoplastic epithelial cells and TME compartments may result in either tumour-promoting or tumour-restraining consequences. A better preclinical understanding of such complex and dynamic network systems is required to develop more powerful treatment strategies for patients. Scientific activity and the number of compelling findings has virtually exploded during recent years. Here, we provide an update of the most recent findings in this area and discuss their translational and clinical implications for basic scientists and clinicians alike.

Reduced expression of Twist 1 is protective against insulin resistance of adipocytes and involves mitochondrial dysfunction

Insulin resistance (IR) has become a global epidemic that represents a serious hazard to public health. However, the precise mechanisms modulating IR have not been fully elucidated. The present study aimed to investigate the role of transcriptional factor Twist 1 in adipocyte IR and to further explore the molecular mechanism. An in vitro IR model based on cultured 3T3-L1 adipocytes was established under high glucose/insulin stimulation and an in vivo IR model in C57/BL6J mice induced by a high fat diet (HFD) was also developed. Lentivirus targeting Twist 1 silencing was introduced. The relationships between Twist 1 expression and IR state, mitochondrial dysfunction and the downstream insulin signaling pathway were assayed. Our results firstly showed the elevation of Twist 1 in IR adipocytes, and Twist 1 silencing attenuated IR. Then mitochondrial ultra-structural damage, elevated ROS, decreased MMP and ATP, and changes in mitochondrial biosynthesis-related genes in IR group indicated mitochondrial dysfunction. Further, the downstream IRS/PI3K/AKT/GluT4 pathway was showed involved in Twist 1-mediated IR. In total, we provide evidence of a protective role of Twist 1 silencing in relieving the IR state of adipocytes. Mitochondrial dysfunction and the downstream IRS/PI3K/AKT/GluT4 pathway were involved in this Twist 1-mediated IR.

Insulin sensitivity predictions in individuals with obesity and type II diabetes mellitus using mathematical model of the insulin signal transduction pathway

Mathematical modeling approaches have been commonly used in complex signaling pathway studies such as the insulin signal transduction pathway. Our expanded mathematical model of the insulin signal transduction pathway was previously shown to effectively predict glucose clearance rates using mRNA levels of key components of the pathway in a mouse model. In this study, we re-optimized and applied our expanded model to study insulin sensitivity in other species and tissues (human skeletal muscle) with altered protein activities of insulin signal transduction pathway components. The model has now been optimized to predict the effect of short term exercise on insulin sensitivity for human test subjects with obesity or type II diabetes mellitus. A comparison between our extended model and the original model showed that our model better simulates the GLUT4 translocation events of the insulin signal transduction pathway and glucose uptake as a clinically relevant model output. Results from our extended model correlate with O'Gorman's published in-vivo results. This study demonstrates the ability to adapt this model to study insulin sensitivity to many biological systems (human skeletal muscle and mouse liver) with minimal changes in the model parameters.

A simple method for identifying parameter correlations in partially observed linear dynamic models

Background

Parameter estimation represents one of the most significant challenges in systems biology. This is because biological models commonly contain a large number of parameters among which there may be functional interrelationships, thus leading to the problem of non-identifiability. Although identifiability analysis has been extensively studied by analytical as well as numerical approaches, systematic methods for remedying practically non-identifiable models have rarely been investigated.

Results

We propose a simple method for identifying pairwise correlations and higher order interrelationships of parameters in partially observed linear dynamic models. This is made by derivation of the output sensitivity matrix and analysis of the linear dependencies of its columns. Consequently, analytical relations between the identifiability of the model parameters and the initial conditions as well as the input functions can be achieved. In the case of structural non-identifiability, identifiable combinations can be obtained by solving the resulting homogenous linear equations. In the case of practical non-identifiability, experiment conditions (i.e. initial condition and constant control signals) can be provided which are necessary for remedying the non-identifiability and unique parameter estimation. It is noted that the approach does not consider noisy data. In this way, the practical non-identifiability issue, which is popular for linear biological models, can be remedied. Several linear compartment models including an insulin receptor dynamics model are taken to illustrate the application of the proposed approach.

Conclusions

Both structural and practical identifiability of partially observed linear dynamic models can be clarified by the proposed method. The result of this method provides important information for experimental design to remedy the practical non-identifiability if applicable. The derivation of the method is straightforward and thus the algorithm can be easily implemented into a software packet.

Electronic supplementary material

The online version of this article (doi:10.1186/s12918-015-0234-3) contains supplementary material, which is available to authorized users.

Elosulfase alfa for the treatment of mucopolysacchoridosis IVA

Mucopolysacchariodosis IVA is a lysosomal storage disorder characterized by deficiency of the enzyme N-acetylgalactosamine-6-sulfatase leading to accumulation of glycosaminoglycans. Mucopolysacchariodosis IVA affects many organs, especially the skeletal system. The disease is progressive, leads to serious cardiopulmonary problems and is severely debilitating. Enzyme replacement therapy with elosulfase alfa is the only approved treatment for this rare genetic condition. The results from a Phase III clinical trial demonstrated that elosulfase alfa at dose 2.0 mg/kg weekly given intravenously improved the walking distance in 6 min. The results of the 3-min stair climb test and respiratory function test did not show statistically significant improvement over the placebo. However, the composite end point analysis combining changes from baseline in walking distance in 6 min, 3-min stair climb test and respiratory function showed that at dose 2.0 mg/kg weekly, subjects performed better than the placebo, indicating that the effects of treatment are clinically meaningful. Serious side effects are uncommon and infusion-associated reactions are manageable.

Gestational Diabetes Associated with a Novel Mutation (378-379insTT) in the Glycerol Kinase Gene

Glycerol kinase deficiency (GKD) is an X-linked inborn error of metabolism at the interface of fat and carbohydrate metabolism. We report a male patient with GKD and a novel insertion of TT in exon 5 at position 378 of the GK cDNA (378–379insTT). This resulted in a premature stop codon and 0.8% normal GK activity. The mother is a carrier for this mutation and had gestational diabetes requiring insulin during this pregnancy but not in her previous pregnancy. Given the association between GKD and type 2 diabetes mellitus, it is interesting that the mother had gestational diabetes while carrying an affected fetus. Therefore, GKD is another disease where there may be a maternal–fetal interaction based on genotype. Further investigations may help elucidate the role of GKD in the carrier mother's gestational diabetes. In addition, these studies will provide better-informed counseling to families with GKD regarding the risk to carrier females.