Inhibition of glycogen synthase kinase 3 improves insulin action and glucose metabolism in human skeletal muscle

Uncovering the Therapeutic Potential of Lithium Chloride in Type 2 Diabetic Cardiomyopathy: Targeting Tau Hyperphosphorylation and TGF-β Signaling via GSK-3β Inhibition

Diabetic cardiomyopathy (DCM) is a major complication of type 2 diabetes mellitus (T2DM) that leads to significant morbidity and mortality. The alteration in the signaling mechanism in diabetes leading to cardiomyopathy remains unclear. The purpose of this study is to investigate the role of tauopathy in myocardial dysfunction observed in T2DM. In that regard, diabetic Sprague Dawley rats were treated with intraperitoneal injections of lithium chloride (LiCl), inhibiting tau phosphorylation. Cardiac function was evaluated, and molecular markers of myocardial fibrosis and the TGF-β signaling were analyzed. T2DM rats exhibited a decline in ejection fraction and fractional shortening that revealed cardiac function abnormalities and increased myocardial fibrosis. These changes were associated with tau hyperphosphorylation. Treating diabetic rats with LiCl attenuated cardiac fibrosis and improved myocardial function. Inhibition of GSK-3β leads to the suppression of tau phosphorylation, which is associated with a decrease in TGF-β expression and regulation of the pro-inflammatory markers, suggesting that tau hyperphosphorylation is parallelly associated with fibrosis and inflammation in the diabetic heart. Our findings provide evidence of a possible role of tau hyperphosphorylation in the pathogenesis of DCM through the activation of TGF-β and by inducing inflammation. Targeting the inhibition of tau phosphorylation may offer novel therapeutic approaches to reduce DCM burden in T2DM patients.

The redox-sensitive GSK3β is a key regulator of glomerular podocyte injury in type 2 diabetic kidney disease

Emerging evidence suggests that GSK3β, a redox-sensitive transducer downstream of insulin signaling, acts as a convergent point for myriad pathways implicated in kidney injury, repair, and regeneration. However, its role in diabetic kidney disease remains controversial. In cultured glomerular podocytes, exposure to a milieu of type 2 diabetes elicited prominent signs of podocyte injury and degeneration, marked by loss of homeostatic marker proteins like synaptopodin, actin cytoskeleton disruption, oxidative stress, apoptosis, and stress-induced premature senescence, as shown by increased staining for senescence-associated β-galactosidase activity, amplified formation of γH2AX foci, and elevated expression of mediators of senescence signaling, like p21 and p16INK4A. These degenerative changes coincided with GSK3β hyperactivity, as evidenced by GSK3β overexpression and reduced inhibitory phosphorylation of GSK3β, and were averted by tideglusib, a highly-selective small molecule inhibitor of GSK3β. In agreement, post-hoc analysis of a publicly-available glomerular transcriptomics dataset from patients with type 2 diabetic nephropathy revealed that the curated diabetic nephropathy-related gene set was enriched in high GSK3β expression group. Mechanistically, GSK3β-modulated nuclear factor Nrf2 signaling is involved in diabetic podocytopathy, because GSK3β knockdown reinforced Nrf2 antioxidant response and suppressed oxidative stress, resulting in an improvement in podocyte injury and senescence. Conversely, ectopic expression of the constitutively active mutant of GSK3β impaired Nrf2 antioxidant response and augmented oxidative stress, culminating in an exacerbated diabetic podocyte injury and senescence. Moreover, IRS-1 was found to be a cognate substrate of GSK3β for phosphorylation at IRS-1S332, which negatively regulates IRS-1 activity. GSK3β hyperactivity promoted IRS-1 phosphorylation, denoting a desensitized insulin signaling. Consistently, in vivo in db/db mice with diabetic nephropathy, GSK3β was hyperactive in glomerular podocytes, associated with IRS-1 hyperphosphorylation, impaired Nrf2 response and premature senescence. Our finding suggests that GSK3β is likely a novel therapeutic target for treating type 2 diabetic glomerular injury.

Maurice M, Donaldson WA. Synthesis and Evaluation of 5-(Heteroarylmethylene)hydantoins as Glycogen Synthase Kinase-3β Inhibitors

Glycogen synthase kinase-3 (GSK-3) is a serine/threonine kinase which plays a center role in the phosphorylation of a wide variety of proteins, generally leading to their inactivation. As such, GSK-3 is viewed as a therapeutic target. An ever-increasing number of small organic molecule inhibitors of GSK-3 have been reported. Phenylmethylene hydantoins are known to exhibit a wide range of inhibitory activities including for GSK-3β. A family of fourteen 2-heterocycle substituted methylene hydantoins (14, 17-29) were prepared and evaluated for the inhibition of GSK-3β at 25 μM. The IC50 values of five of these compounds was determined; the two best inhibitors are 5-[(4'-chloro-2-pyridinyl)methylene]hydantoin (IC50 = 2.14 ± 0.18 μM) and 5-[(6'-bromo-2-pyridinyl)methylene]hydantoin (IC50 = 3.39 ± 0.16 μM). The computational docking of the compounds with GSK-3β (pdb 1q41) revealed poses with hydrogen bonding to the backbone at Val135. The 5-[(heteroaryl)methylene]hydantoins did not strongly inhibit other metalloenzymes, demonstrating poor inhibitory activity against matrix metalloproteinase-12 at 25 μM and against human carbonic anhydrase at 200 μM, and were not inhibitors for Staphylococcus aureus pyruvate carboxylase at concentrations >1000 μM.

Sex differences in insulin regulation of skeletal muscle glycogen synthase and changes during weight loss and exercise in adults

OBJECTIVE

The authors sought to understand sex differences in muscle metabolism in 73 older men and women.

METHODS

Body composition, VO2max, and insulin sensitivity (M) by 3-hour hyperinsulinemic-euglycemic clamp with vastus lateralis muscle biopsies were measured.

RESULTS

Women had lower body weight, VO2max, and fat-free mass than men. Men had lower M, lower change (insulin minus basal) in muscle glycogen synthase (GS) activity, and lower change in AKT protein expression than women. M was associated with the change (insulin-basal) in GS activity and the change in AKT protein expression. Sex differences (n = 60) were tested with 6-month weight loss or 3×/week aerobic exercise training. The postintervention minus preintervention change (insulin-basal) (∆∆) in GS activity (fractional, independent, total) was higher in men than women in the weight loss group and ∆∆ in GS fractional activity was higher in women than men in the aerobic exercise group. In all participants, ∆∆ in GS fractional and independent activities was related to ∆∆ in AKT expression and glycogen content.

CONCLUSIONS

Sex differences in insulin sensitivity may be explained at the cellular muscle level, and to improve skeletal muscle insulin action in older adults, it may be necessary to recommend different behavioral strategies depending on the individual's sex.

Albadri A, Patel H, Kadri A, Aouadi K. Identification of dual-target isoxazolidine-isatin hybrids with antidiabetic potential: Design, synthesis, in vitro and multiscale molecular modeling approaches

In the development of novel antidiabetic agents, a novel series of isoxazolidine-isatin hybrids were designed, synthesized, and evaluated as dual α-amylase and α-glucosidase inhibitors. The precise structures of the synthesized scaffolds were characterized using different spectroscopic techniques and elemental analysis. The obtained results were compared to those of the reference drug, acarbose (IC50 = 296.6 ± 0.825 μM for α-amylase & IC50 = 780.4 ± 0.346 μM for α-glucosidase). Among the title compounds, 5d exhibited impressive α-amylase and α-glucosidase inhibitory activity with IC50 values of 30.39 ± 1.52 μM and 65.1 ± 3.11 μM, respectively, followed by 5h (IC50 = 46.65 ± 2.3 μM; IC50 = 85.16 ± 4.25 μM) and 5f (IC50 = 55.71 ± 2.78 μM; IC50 = 106.77 ± 5.31 μM). Mechanistic studies revealed that the most potent derivative 5d bearing the chloro substituent attached to the oxoindolin-3-ylidene core, and acarbose, are a competitive inhibitors of α-amylase and α-glucosidase, respectively. Structure activity relationship (SAR) was examined to guide further structural optimization of the most appropriate substituent(s). Moreover, drug-likeness qualities and ADMET prediction of the most active analogue, 5d was also performed. Subsequently, 5d was subjected to molecular docking and dynamic simulation during the progression of 120 ns analysis to check the essential ligand-receptor patterns, and to estimate its stability. In silico studies were found in good agreement with the in vitro enzymatic inhibitions results. In conclusion, we demonstrated that most potent compound 5d could be exploited as dual potential inhibitor of α-amylase and α-glucosidase for possible management of diabetes.

GSK-3 at the heart of cardiometabolic diseases: Isoform-specific targeting is critical to therapeutic benefit

Glycogen synthase kinase-3 (GSK-3) is a family of serine/threonine kinases. The GSK-3 family has 2 isoforms, GSK-3α and GSK-3β. The GSK-3 isoforms have been shown to play overlapping as well as isoform-specific-unique roles in both, organ homeostasis and the pathogenesis of multiple diseases. In the present review, we will particularly focus on expanding the isoform-specific role of GSK-3 in the pathophysiology of cardiometabolic disorders. We will highlight recent data from our lab that demonstrated the critical role of cardiac fibroblast (CF) GSK-3α in promoting injury-induced myofibroblast transformation, adverse fibrotic remodeling, and deterioration of cardiac function. We will also discuss studies that found the exact opposite role of CF-GSK-3β in cardiac fibrosis. We will review emerging studies with inducible cardiomyocyte (CM)-specific as well as global isoform-specific GSK-3 KOs that demonstrated inhibition of both GSK-3 isoforms provides benefits against obesity-associated cardiometabolic pathologies. The underlying molecular interactions and crosstalk among GSK-3 and other signaling pathways will be discussed. We will briefly review the specificity and limitations of the available small molecule inhibitors targeting GSK-3 and their potential applications to treat metabolic disorders. Finally, we will summarize these findings and offer our perspective on envisioning GSK-3 as a therapeutic target for the management of cardiometabolic diseases.

GSK3β Inhibition Reduced Vascular Calcification in Ins2Akita/+ Mice

Endothelial-mesenchymal transition (EndMT) drives the endothelium to contribute to vascular calcification in diabetes mellitus. In our previous study, we showed that glycogen synthase kinase-3β (GSK3β) inhibition induces β-catenin and reduces mothers against DPP homolog 1 (SMAD1) to direct osteoblast-like cells toward endothelial lineage, thereby reducing vascular calcification in Matrix Gla Protein (Mgp) deficiency. Here, we report that GSK3β inhibition reduces vascular calcification in diabetic Ins2^Akita/wt mice. Cell lineage tracing reveals that GSK3β inhibition redirects endothelial cell (EC)-derived osteoblast-like cells back to endothelial lineage in the diabetic endothelium of Ins2^Akita/wt mice. We also find that the alterations in β-catenin and SMAD1 by GSK3β inhibition in the aortic endothelium of diabetic Ins2^Akita/wt mice are similar to Mgp^-/- mice. Together, our results suggest that GSK3β inhibition reduces vascular calcification in diabetic arteries through a similar mechanism to that in Mgp^-/- mice.

Intrarenal and Urinary Glycogen Synthase Kinase-3 Beta Levels in Diabetic and Nondiabetic Chronic Kidney Disease

BACKGROUND

Renal glycogen synthase kinase-3 beta (GSK3β) overactivity has been associated with a diverse range of kidney diseases. GSK3β activity in urinary exfoliated cells was reported to predict the progression of diabetic kidney disease (DKD). We compared the prognostic value of urinary and intrarenal GSK3β levels in DKD and nondiabetic chronic kidney disease (CKD).

METHODS

We recruited 118 consecutive biopsy-proved DKD patients and 115 nondiabetic CKD patients. Their urinary and intrarenal GSK3β levels were measured. They were then followed for dialysis-free survival and rate of renal function decline.

RESULTS

DKD group had higher intrarenal and urinary GSK3β levels than nondiabetic CKD (p < 0.0001 for both), but their urinary GSK3β mRNA levels were similar. Urinary p-GSK3β level is statistically significantly correlated with the baseline estimated glomerular filtration rate (eGFR), but urinary GSK3β level by ELISA, its mRNA level, the p-GSK3β level, or the p-GSK3β/GSK3β ratio had no association with dialysis-free survival or the slope of eGFR decline. In contrast, the intrarenal pY216-GSK3β/total GSK3β ratio significantly correlated with the slope of eGFR decline (r = -0.335, p = 0.006) and remained an independent predictor after adjusting for other clinical factors.

CONCLUSION

Intrarenal and urinary GSK3β levels were increased in DKD. The intrarenal pY216-GSK3β/total GSK3β ratio was associated with the rate of progression of DKD. The pathophysiological roles of GSK3β in kidney diseases deserve further studies.

Comparison between low, moderate, and high intensity aerobic training with equalized loads on biomarkers and performance in rats

This study investigated the physiological and molecular responses of Wistar Hannover rats, submitted to three 5-week chronic training models, with similar training loads. Twenty-four Wistar Hanover rats were randomly divided into four groups: control (n = 6), low-intensity training (Z1; n = 6), moderate-intensity training (Z2; n = 6) and high-intensity training (Z3; n = 6). The three exercise groups performed a 5-week running training three times a week, with the same prescribed workload but the intensity and the volume were different between groups. An increase in maximal speed was observed after four weeks of training for the three groups that trained, with no difference between groups. Higher rest glycogen was also observed in the soleus muscle after training for the exercise groups compared to the control group. We also found that the Z2 group had a higher protein content of total and phosphorylated GSK3-β compared to the control group after five weeks of training. In conclusion, the present study shows that five weeks of treadmill training based on intensity zones 1, 2, and 3 improved performance and increased resting glycogen in the soleus muscle, therefore intensity modulation does not change the training program adaptation since the different program loads are equalized.

Glycogen Synthase Kinase 3β (GSK3β) Regulates Myogenic Differentiation in Skeletal Muscle Satellite Cells of Sheep

Glycogen synthase kinase 3β (GSK3β) has a vital role in the regulation of many cellular processes. However, the role of GSK3β in muscle cell differentiation in sheep remains unknown. In this study, we investigated the function of GSK3β in skeletal muscle satellite cells (SMSCs) of sheep. An overexpression of GSK3β significantly inhibited myotube formation as well as the mRNA levels of myogenic genes (MyoD, MyoG, MyHC1, and MyHC2a) in sheep SMSCs. SB216763 treatment had a time-course effect on the phosphorylation levels of sheep GSK3β. In addition, reducing the activity of GSK3β lead to the promotion of sheep SMSCs differentiation as well as the mRNA levels of myogenic genes (MyoD, MyoG, MyHC1, and MyHC2a). This study illustrated the function of GSK3β to inhibit myogenesis in sheep SMSCs, which provided evidence for studying the mechanisms involved in the regulation of sheep SMSCs differentiation by GSK3β.

HM-Chromanone, a Major Homoisoflavonoid in Portulaca oleracea L., Improves Palmitate-Induced Insulin Resistance by Regulating Phosphorylation of IRS-1 Residues in L6 Skeletal Muscle Cells

This study investigated the effect of (E)-5-hydroxy-7-methoxy-3-(2-hydroxybenzyl)-4-chromanone (HM-chromanone) on palmitate-induced insulin resistance and elucidated the underlying mechanism in L6 skeletal muscle cells. Glucose uptake was markedly decreased due to palmitate-induced insulin resistance in these cells; however, 10, 25, and 50 µM HM-chromanone remarkably improved glucose uptake in a concentration-dependent manner. HM-chromanone treatment downregulated protein tyrosine phosphatase 1B (PTP1B) and phosphorylation of c-Jun N-terminal kinase (JNK) and inhibitor of nuclear factor kappa-B kinase subunit beta (IKKβ), which increased because of palmitate mediating the insulin-resistance status in cells. HM-chromanone promoted insulin receptor substrate-1 (IRS-1) tyrosine phosphorylation and suppressed palmitate-induced phosphorylation of IRS-1 serine. This activated phosphoinositide 3-kinase (PI3K) and stimulated protein kinase B (AKT) phosphorylation. Phosphorylated AKT promoted the translocation of Glucose transporter type 4 to the plasma membrane and significantly enhanced glucose uptake into muscle cells. Additionally, HM-chromanone increased glycogen synthesis through phosphorylating glycogen synthase kinase 3 alpha/beta (GSK3 α/β) via AKT. Consequently, HM-chromanone may improve insulin resistance by downregulating the phosphorylation of IRS-1 serine through inhibition of negative regulators of insulin signaling and inflammation-activated protein kinases in L6 skeletal muscle cells.

Insulin signaling as a therapeutic mechanism of lithium in bipolar disorder

In this paper, we propose that lithium may exert its therapeutic effect in bipolar disorder by acting on insulin signaling pathways. Specifically, we assess the importance of the phosphatidylinositol 3-kinase/Protein Kinase B (PI3K/Akt) insulin signaling pathway and we assess how the action of lithium on both glycogen synthase kinase-3 (GSK3) and the phosphatidylinositol cycle may lead to mood stabilization mediated by PI3K/Akt insulin signaling. We also highlight evidence that several other actions of lithium (including effects on Akt, Protein kinase C (PKC), and sodium myo-inositol transporters) are putative mediators of insulin signaling. This novel mode of action of lithium is consistent with an emerging consensus that energy dysregulation represents a core deficit in bipolar disorder. It may also provide context for the significant co-morbidity between bipolar disorder, type 2 diabetes, and other forms of metabolic illness characterized by impaired glucose metabolism. It is suggested that developments in assessing neuronal insulin signaling using extracellular vesicles would allow for this hypothesis to be tested in bipolar disorder patients.

Designing and Synthesis of New Isatin Derivatives as Potential CDK2 Inhibitors

Tumors are still one of the main causes of death; therefore, the search for new therapeutic agents that will enable the implementation of effective treatment is a significant challenge for modern pharmacy. One of the important factors contributing to the development of neoplastic diseases is the overexpression of enzymes responsible for the regulation of cell division processes such as cyclin-dependent kinases. Numerous studies and examples of already-developed drugs confirm that isatin is a convenient basis for the development of new groups of inhibitors for this class of enzyme. Therefore, in this work, a new group of potential inhibitors of the CDK2 enzyme, utilizing isatin derivatives and substituted benzoylhydrazines, has been designed based on the application of computational chemistry methods, such as docking and molecular dynamics, and their inhibiting ability was assessed. In the cases of the selected compounds, a synthesis method was developed, and the selected physicochemical properties of the newly synthesized derivatives were estimated. As part of the completed project, new compounds are developed which are potential inhibitors of the CDK2 enzyme.

Leptin regulates glucose homeostasis via the canonical Wnt pathway in the zebrafish

Leptin is best known for its role in adipostasis, but it also regulates blood glucose levels. The molecular mechanism by which leptin controls glucose homeostasis remains largely unknown. Here, we use a zebrafish model to show that Wnt signaling mediates the glucoregulatory effects of leptin. Under normal feeding conditions, leptin regulates glucose homeostasis but not adipostasis in zebrafish. In times of nutrient excess, however, we found that leptin also regulates body weight and size. Using a Wnt signaling reporter fish, we show that leptin activates the canonical Wnt pathway in vivo. Utilizing two paradigms for hyperglycemia, it is revealed that leptin regulates glucose homeostasis via the Wnt pathway, as pharmacological inhibition of this pathway impairs the glucoregulatory actions of leptin. Our results may shed new light on the evolution of the physiological function of leptin.

Glycogen synthesis and beyond, a comprehensive review of GSK3 as a key regulator of metabolic pathways and a therapeutic target for treating metabolic diseases

Glycogen synthase kinase‐3 (GSK3) is a highly evolutionarily conserved serine/threonine protein kinase first identified as an enzyme that regulates glycogen synthase (GS) in response to insulin stimulation, which involves GSK3 regulation of glucose metabolism and energy homeostasis. Both isoforms of GSK3, GSK3α, and GSK3β, have been implicated in many biological and pathophysiological processes. The various functions of GSK3 are indicated by its widespread distribution in multiple cell types and tissues. The studies of GSK3 activity using animal models and the observed effects of GSK3‐specific inhibitors provide more insights into the roles of GSK3 in regulating energy metabolism and homeostasis. The cross‐talk between GSK3 and some important energy regulators and sensors and the regulation of GSK3 in mitochondrial activity and component function further highlight the molecular mechanisms in which GSK3 is involved to regulate the metabolic activity, beyond its classical regulatory effect on GS. In this review, we summarize the specific roles of GSK3 in energy metabolism regulation in tissues that are tightly associated with energy metabolism and the functions of GSK3 in the development of metabolic disorders. We also address the impacts of GSK3 on the regulation of mitochondrial function, activity and associated metabolic regulation. The application of GSK3 inhibitors in clinical tests will be highlighted too. Interactions between GSK3 and important energy regulators and GSK3‐mediated responses to different stresses that are related to metabolism are described to provide a brief overview of previously less‐appreciated biological functions of GSK3 in energy metabolism and associated diseases through its regulation of GS and other functions.

Glycogen synthase kinase-3 (GSK-3) a magic enzyme: it's role in diabetes mellitus and glucose homeostasis, interactions with fluroquionlones. A mini-review

Diabetes mellitus (DM) is a non-communicable disease throughout the world in which there is persistently high blood glucose level from the normal range. The diabetes and insulin resistance are mainly responsible for the morbidities and mortalities of humans in the world. This disease is mainly regulated by various enzymes and hormones among which Glycogen synthase kinase-3 (GSK-3) is a principle enzyme and insulin is the key hormone regulating it. The GSK-3, that is the key enzyme is normally showing its actions by various mechanisms that include its phosphorylation, formation of protein complexes, and other cellular distribution and thus it control and directly affects cellular morphology, its growth, mobility and apoptosis of the cell. Disturbances in the action of GSK-3 enzyme may leads to various disease conditions that include insulin resistance leading to diabetes, neurological disease like Alzheimer's disease and cancer. Fluoroquinolones are the most common class of drugs that shows dysglycemic effects via interacting with GSK-3 enzyme. Therefore, it is the need of the day to properly understand functions and mechanisms of GSK-3, especially its role in glucose homeostasis via effects on glycogen synthase.

Hypoglycemic Effect of Hydrophobic BCAA Peptides Is Associated with Altered PI3K/Akt Protein Expression

The hypoglycemic activities of the hydrophobic branched-chain amino acid (BCAA) peptides from seabuckthorn seed protein were preliminarily characterized in type 2 diabetic db/db mice. Four novel BCAA peptides (18.27 ± 0.26% (w/w): Leu/Ile-Pro-Glu-Asp-Pro, Asp-Leu/Ile-Val-Gly-Glu, Leu/Ile-Pro, and Leu/Ile-Pro-Leu/Ile) were identified in seabuckthorn seed protein. The protein content in seabuckthorn seed protein hydrolysate, obtained using 80% ethanol, was 78.8 ± 1.4% (w/w). Animal experiments revealed that oral administration of BCAA peptides (all four) significantly reversed the diabetic symptoms. Compared to the db/db group (control), body weight and insulin resistance were ameliorated after treatment with BCAA peptides (0.5, 1.0, 2.0 mg/(g d)). Also, the treatment remarkably reduced the fasting blood glucose (FBG) levels by upregulation of glucose transporter 4 (GULT4). Moreover, BCAA peptides significantly increased the muscle glycogen content (22.6 ± 0.9 nmol/mg) via the downregulation of protein kinase B (AKT) and glycogen synthase kinase-3β (GSK-3β) while increasing the activity of glycogen synthase (GS). BCAA peptides also significantly upregulated the protein levels of phosphatidylinositol 3-kinase (PI3K). We show that BCAA peptides alleviated insulin resistance associated with altered PI3K/Akt protein expression in the skeletal muscle of db/db mice.

Linking metabolic dysfunction with cardiovascular diseases: Brn-3b/POU4F2 transcription factor in cardiometabolic tissues in health and disease

Metabolic and cardiovascular diseases are highly prevalent and chronic conditions that are closely linked by complex molecular and pathological changes. Such adverse effects often arise from changes in the expression of genes that control essential cellular functions, but the factors that drive such effects are not fully understood. Since tissue-specific transcription factors control the expression of multiple genes, which affect cell fate under different conditions, then identifying such regulators can provide valuable insight into the molecular basis of such diseases. This review explores emerging evidence that supports novel and important roles for the POU4F2/Brn-3b transcription factor (TF) in controlling cellular genes that regulate cardiometabolic function. Brn-3b is expressed in insulin-responsive metabolic tissues (e.g. skeletal muscle and adipose tissue) and is important for normal function because constitutive Brn-3b-knockout (KO) mice develop profound metabolic dysfunction (hyperglycaemia; insulin resistance). Brn-3b is highly expressed in the developing hearts, with lower levels in adult hearts. However, Brn-3b is re-expressed in adult cardiomyocytes following haemodynamic stress or injury and is necessary for adaptive cardiac responses, particularly in male hearts, because male Brn-3b KO mice develop adverse remodelling and reduced cardiac function. As a TF, Brn-3b regulates the expression of multiple target genes, including GLUT4, GSK3β, sonic hedgehog (SHH), cyclin D1 and CDK4, which have known functions in controlling metabolic processes but also participate in cardiac responses to stress or injury. Therefore, loss of Brn-3b and the resultant alterations in the expression of such genes could potentially provide the link between metabolic dysfunctions with adverse cardiovascular responses, which is seen in Brn-3b KO mutants. Since the loss of Brn-3b is associated with obesity, type II diabetes (T2DM) and altered cardiac responses to stress, this regulator may provide a new and important link for understanding how pathological changes arise in such endemic diseases.

The Protein Phosphatase 1 Complex Is a Direct Target of AKT that Links Insulin Signaling to Hepatic Glycogen Deposition

Insulin-stimulated hepatic glycogen synthesis is central to glucose homeostasis. Here, we show that PPP1R3G, a regulatory subunit of protein phosphatase 1 (PP1), is directly phosphorylated by AKT. PPP1R3G phosphorylation fluctuates with fasting-refeeding cycle and is required for insulin-stimulated dephosphorylation, i.e., activation of glycogen synthase (GS) in hepatocytes. In this study, we demonstrate that knockdown of PPP1R3G significantly inhibits insulin response. The introduction of wild-type PPP1R3G, and not phosphorylation-defective mutants, increases hepatic glycogen deposition, blood glucose clearance, and insulin sensitivity in vivo. Mechanistically, phosphorylated PPP1R3G displays increased binding for, and promotes dephosphorylation of, phospho-GS. Furthermore, PPP1R3B, another regulatory subunit of PP1, binds to the dephosphorylated GS, thereby relaying insulin stimulation to hepatic glycogen deposition. Importantly, this PP1-mediated signaling cascade is independent of GSK3. Therefore, we reveal a regulatory axis consisting of insulin/AKT/PPP1R3G/PPP1R3B that operates in parallel to the GSK3-dependent pathway, controlling glycogen synthesis and glucose homeostasis in insulin signaling.

Effect of amylin on memory and central insulin resistance in a rat model of Alzheimer's disease

Context: Alzheimer's disease is strongly associated with brain insulin signalling.Objective: Investigating the effect of amylin as a novel treatment in streptozotocin (STZ) rat model of AD.Materials and methods: Alzheimer's disease (AD) was induced in albino rats by intracerebroventricular injection of STZ (3 mg/kg). Rats received either amylin analogue (Pramlintide 200 μg/kg/day) or Metformin (30 mg/kg/day) for 5 weeks.Results: Both Pramlintide and Metformin improve learning and memory through enhancing insulin signalling (p-IR and p-PI3K) which lead to lowering level of CSF glucose, phosphorylated tau proteins, and amyloid-β peptide (Aβ) in hippocampus.Conclusions: Insulin sensitisers as Metformin and Pramlintide can improve learning and memory and decrease the pathological changes in STZ induced rat model of AD. However, Pramlintide is superior to Metformin in some memory tests which related to its action as an amylin analogue. Amylin improves learning and memory through an independent effect other than insulin sensitisation.

The Role of Pi, Glutamine and the Essential Amino Acids in Modulating the Metabolism in Diabetes and Cancer

Purpose

Re-examine the current metabolic models.

Methods

Review of literature and gene networks.

Results

Insulin activates Pi uptake, glutamine metabolism to stabilise lipid membranes. Tissue turnover maintains the metabolic health. Current model of intermediary metabolism (IM) suggests glucose is the source of energy, and anaplerotic entry of fatty acids and amino acids into mitochondria increases the oxidative capacity of the TCA cycle to produce the energy (ATP). The reduced cofactors, NADH and FADH2, have different roles in regulating the oxidation of nutrients, membrane potentials and biosynthesis. Trans-hydrogenation of NADH to NADPH activates the biosynthesis. FADH2 sustains the membrane potential during the cell transformations. Glycolytic enzymes assume the non-canonical moonlighting functions, enter the nucleus to remodel the genetic programmes to affect the tissue turnover for efficient use of nutrients. Glycosylation of the CD98 (4F2HC) stabilises the nutrient transporters and regulates the entry of cysteine, glutamine and BCAA into the cells. A reciprocal relationship between the leucine and glutamine entry into cells regulates the cholesterol and fatty acid synthesis and homeostasis in cells. Insulin promotes the Pi transport from the blood to tissues, activates the mitochondrial respiratory activity, and glutamine metabolism, which activates the synthesis of cholesterol and the de novo fatty acids for reorganising and stabilising the lipid membranes for nutrient transport and signal transduction in response to fluctuations in the microenvironmental cues. Fatty acids provide the lipid metabolites, activate the second messengers and protein kinases. Insulin resistance suppresses the lipid raft formation and the mitotic slippage activates the fibrosis and slow death pathways.

Attenuation of Free Fatty Acid (FFA)-Induced Skeletal Muscle Cell Insulin Resistance by Resveratrol is Linked to Activation of AMPK and Inhibition of mTOR and p70 S6K

Insulin resistance, a main characteristic of type 2 diabetes mellitus (T2DM), is linked to obesity and excessive levels of plasma free fatty acids (FFA). Studies indicated that significantly elevated levels of FFAs lead to skeletal muscle insulin resistance, by dysregulating the steps in the insulin signaling cascade. The polyphenol resveratrol (RSV) was shown to have antidiabetic properties but the exact mechanism(s) involved are not clearly understood. In the present study, we examined the effect of RSV on FFA-induced insulin resistance in skeletal muscle cells in vitro and investigated the mechanisms involved. Parental and GLUT4myc-overexpressing L6 rat skeletal myotubes were used. [³H]2-deoxyglucose (2DG) uptake was measured, and total and phosphorylated levels of specific proteins were examined by immunoblotting. Exposure of L6 cells to FFA palmitate decreased the insulin-stimulated glucose uptake, indicating insulin resistance. Palmitate increased ser³⁰⁷ (131% ± 1.84% of control, p < 0.001) and ser^636/639 (148% ± 10.1% of control, p < 0.01) phosphorylation of IRS-1, and increased the phosphorylation levels of mTOR (174% ± 15.4% of control, p < 0.01) and p70 S6K (162% ± 20.2% of control, p < 0.05). Treatment with RSV completely abolished these palmitate-induced responses. In addition, RSV increased the activation of AMPK and restored the insulin-mediated increase in (a) plasma membrane GLUT4 glucose transporter levels and (b) glucose uptake. These data suggest that RSV has the potential to counteract the FFA-induced muscle insulin resistance.

Design, synthesis, structure, in vitro cytotoxic activity evaluation and docking studies on target enzyme GSK-3β of new indirubin-3'-oxime derivatives

The addition of chalcone and amine components into indirubin-3′-oxime resulted in 15 new derivatives with high yields. Structures of new derivatives were also elucidated through 1D, 2D-NMR and HR-MS(ESI) spectra and X-ray crystallography. All designed compounds were screened for cytotoxic activity against four human cancer cell lines (HepG2, LU-1, SW480 and HL-60) and one human normal kidney cell line (HEK-293). Compound 6f exhibited the most marked cytotoxicity meanwhile cytotoxicity of compounds 6e, 6h and 6l was more profound toward cancer cell lines than toward normal cell. These new derivatives were further analyzed via molecular docking studies on GSK-3β enzyme. Docking analysis shows that most of the derivatives exhibited potential inhibition activity against GSK-3β with characteristic interacting residues in the binding site. The fast pulling of ligand scheme was then employed to refine the binding affinity and mechanism between ligands and GSK-3β enzyme. The computational results are expected to contribute to predicting enzyme target of the trial inhibitors and their possible interaction, from which the design of new cytotoxic agents could be created in the future.

The Role of GSK-3 in Cancer Immunotherapy: GSK-3 Inhibitors as a New Frontier in Cancer Treatment

The serine/threonine kinase glycogen synthase kinase-3 (GSK-3) was initially identified because of its key role in the regulation of glycogen synthesis. However, it is now well-established that GSK-3 performs critical functions in many cellular processes, such as apoptosis, tumor growth, cell invasion, and metastasis. Aberrant GSK-3 activity has been associated with many human diseases, including cancer, highlighting its potential therapeutic relevance as a target for anticancer therapy. Recently, newly emerging data have demonstrated the pivotal role of GSK-3 in the anticancer immune response. In the last few years, many GSK-3 inhibitors have been developed, and some are currently being tested in clinical trials. This review will discuss preclinical and initial clinical results with GSK-3β inhibitors, highlighting the potential importance of this target in cancer immunotherapy. As described in this review, GSK-3 inhibitors have been shown to have antitumor activity in a wide range of human cancer cells, and they may also contribute to promoting a more efficacious immune response against tumor target cells, thus showing a double therapeutic advantage.

Deletion of Cardiomyocyte Glycogen Synthase Kinase-3 Beta (GSK-3β) Improves Systemic Glucose Tolerance with Maintained Heart Function in Established Obesity

Obesity is an independent risk factor for cardiovascular diseases (CVD), including heart failure. Thus, there is an urgent need to understand the molecular mechanism of obesity-associated cardiac dysfunction. We recently reported the critical role of cardiomyocyte (CM) Glycogen Synthase Kinase-3 beta (GSK-3β) in cardiac dysfunction associated with a developing obesity model (deletion of CM-GSK-3β prior to obesity). In the present study, we investigated the role of CM-GSK-3β in a clinically more relevant model of established obesity (deletion of CM-GSK-3β after established obesity). CM-GSK-3β knockout (GSK-3β^fl/flCre+/-) and controls (GSK-3β^fl/flCre-/-) mice were subjected to a high-fat diet (HFD) in order to establish obesity. After 12 weeks of HFD treatment, all mice received tamoxifen injections for five consecutive days to delete GSK-3β specifically in CMs and continued on the HFD for a total period of 55 weeks. To our complete surprise, CM-GSK-3β knockout (KO) animals exhibited a globally improved glucose tolerance and maintained normal cardiac function. Mechanistically, in stark contrast to the developing obesity model, deleting CM-GSK-3β in obese animals did not adversely affect the GSK-3αS21 phosphorylation (activity) and maintained canonical β-catenin degradation pathway and cardiac function. As several GSK-3 inhibitors are in the trial to treat various chronic conditions, including metabolic diseases, these findings have important clinical implications. Specifically, our results provide critical pre-clinical data regarding the safety of GSK-3 inhibition in obese patients.

Caulerpa okamurae extract attenuates inflammatory interaction, regulates glucose metabolism and increases insulin sensitivity in 3T3-L1 adipocytes and RAW 264.7 macrophages

OBJECTIVE

To examine whether Caulerpa okamurae ethanolic extract (COE) could inhibit obesity-mediated inflammation, improve glucose metabolism and increase insulin sensitivity, using in vitro cell models of RAW 264.7 macrophages and 3T3-L1 adipocytes.

METHODS

We cocultured 3T3-L1 adipocytes in direct contact with lipopolysaccharide-stimulated RAW 264.7 macrophages and induced insulin resistance in 3T3-L1 adipocytes with tumor necrosis factor-α (TNF-α) in the presence or absence of 250 µg/mL of COE. We investigated various markers of inflammation, glucose regulation and insulin sensitivity in these models using Griess reagent to measure nitric oxide (NO) production, 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) amino]-2-deoxyglucose to measure glucose uptake, Western blot analysis to quantify protein expression and reverse transcriptase-polymerase chain reaction to evaluate mRNA expression.

RESULTS

We found that COE (250 µg/mL) significantly inhibited the lipopolysaccharide-induced inflammatory response in RAW 264.7 macrophages by downregulating NO production, nitric oxide synthase 2 expression and nuclear translocation of nuclear factor-κB. COE also showed similar anti-inflammatory activity in coculture, along with decreased TNF-α, interleukin-6 and monocyte chemoattractant protein mRNA expression. In addition, COE also improved glucose uptake in coculture by upregulating glucose transporter-4 (GLUT-4) and adiponectin and reducing serine phosphorylation of insulin receptor substrate-1 (IRS1). In the TNF-α-induced insulin resistance model of 3T3-L1 adipocytes, COE significantly improved both basal and insulin-stimulated glucose uptake, accompanied by phosphorylation of IRS1 at tyrosine 632, phospho-5' adenosine monophosphate-activated protein kinase α and glycogen synthase kinase-3β (Ser9) as well as upregulation of GLUT-4.

CONCLUSION

Together, these findings suggest that COE has potential to treat or prevent obesity-induced metabolic disorders.

Urtica Dioica and Lamium Album Decrease Glycogen Synthase Kinase-3 beta and Increase K-Ras in Diabetic Rats

Objectives

The aim of the present work is evaluating the special effects of Urtica Dioica and Lamium Album on the serum level of K-Ras and GSK-3 beta in diabetic rats.

Methods

In the present experimental study, 32 male Wistar rats randomly divided into 4 groups (Group I: normal control rats; receiving daily PBS, Group 2: diabetic control rats; receiving single dose of streptozotocin (60 mg/kg) and daily PBS, Group 3: Diabetic rats treated with 100 mg/kg of hydroalcoholic extract of the U. dioica, Group 4: Diabetic rats treated with 100 mg/kg of hydroalcoholic extract of L. Album. Diabetes-induced by an intraperitoneal injection of streptozotocin (60 mg/ kg). On the 14 th day of treatment, the weight, fasting blood sugar (FBS) and on 28 th day blood glucose, K-Ras and GSK3 beta was measured.

Results

In diabetic group blood GSK-3 beta increase in comparison to control group (P < 0.05), also blood K-Ras decrease in the diabetic group (P < 0.05). Both extracts reduced GSK-3 beta level, however, this reduction was only statistically significant by U. dioica (P < 0.05). Compared to diabetic group, blood K-Ras level increased by both extract (P < 0.05). Also diabetes induction increase blood glucose levels and both extracts decrease its level significantly (P < 0.05). there is no significant differences among both extract effects on blood glucose, and K-Ras.

Conclusion

For the first time shown that both extracts by regulating GSK-3 beta and K-Ras improve blood glucose level. More studies are needed to determine all the effects of these herbs.

Comparative profiling of skeletal muscle models reveals heterogeneity of transcriptome and metabolism

Rat L6, mouse C2C12, and primary human skeletal muscle cells (HSMCs) are commonly used to study biological processes in skeletal muscle, and experimental data on these models are abundant. However, consistently matched experimental data are scarce, and comparisons between the different cell types and adult tissue are problematic. We hypothesized that metabolic differences between these cellular models may be reflected at the mRNA level. Publicly available data sets were used to profile mRNA levels in myotubes and skeletal muscle tissues. L6, C2C12, and HSMC myotubes were assessed for proliferation, glucose uptake, glycogen synthesis, mitochondrial activity, and substrate oxidation, as well as the response to in vitro contraction. Transcriptomic profiling revealed that mRNA of genes coding for actin and myosin was enriched in C2C12, whereas L6 myotubes had the highest levels of genes encoding glucose transporters and the five complexes of the mitochondrial electron transport chain. Consistently, insulin-stimulated glucose uptake and oxidative capacity were greatest in L6 myotubes. Insulin-induced glycogen synthesis was highest in HSMCs, but C2C12 myotubes had higher baseline glucose oxidation. All models responded to electrical pulse stimulation-induced glucose uptake and gene expression but in a slightly different manner. Our analysis reveals a great degree of heterogeneity in the transcriptomic and metabolic profiles of L6, C2C12, or primary human myotubes. Based on these distinct signatures, we provide recommendations for the appropriate use of these models depending on scientific hypotheses and biological relevance.

Effect of electrical stimulation combined with diet therapy on insulin resistance via mTOR signaling

Insulin resistance (IR) is the impaired insulin response that causes decreased glucose tolerance. Electrical stimulation (ES) can improve insulin sensitivity in the skeletal muscle. However, the underlying molecular mechanisms remain to be elucidated. In the present study, the effect of ES and diet therapy on IR and the role of the mammalian target of rapamycin (mTOR) pathway in the improvement of IR by ES were investigated. A total of 70 Sprague-Dawley male rats were divided into five groups: Normal (n=10), IR control (n=15), diet (n=15), ES (n=15) and ES + diet (n=15) groups. An IR rat model was established by high-fat and high-carbohydrate diet for 5 weeks and confirmed by measurement of fasting plasma glucose (FPG), insulin, insulin sensitivity index (ISI) and IR index. ES on the Zusanli (ST36), Sanyinjiao (SP 6) and Weiwanxiashu (EX-B3) acupoints and the low-fat and low-carbohydrate diet demonstrated protective effects. The body weight, concentrations of FPG, insulin, triglycerides (TG), free fatty acids (FFA) and total cholesterol (TC) of the rats were detected. Pathologic changes in the liver and pancreatic tissues were assessed. Western blotting and immunohistochemistry were performed to determine the role of PI3K/Akt/mTOR signaling. Results demonstrated that ES and diet therapy significantly increased ISI and reduced FPG, IR index, FFA, TG, TC and weight. Inflammatory cell infiltration in the liver and pancreatic tissues was ameliorated and lipid droplets and cavitation in hepatocyte were decreased after ES and diet therapy. The administration of ES and diet therapy also enhanced glucose transport by the upregulation of glucose transporter 4 and accelerated glycogen synthesis through the suppression of glycogen synthase kinase 3α/β via PI3K/Akt/mTOR signaling. Hence, the present results demonstrated that ES combined with diet therapy improved IR through PI3K/Akt/mTOR signaling. The proposed therapy was superior to the method of diet alone.

Glycogen synthase kinase 3β hyperactivity in urinary exfoliated cells predicts progression of diabetic kidney disease

Burgeoning evidence points to glycogen synthase kinase (GSK)3β as a key player in diverse kidney diseases. However, as a pivotal transducer of the insulin signaling pathway, the role of GSK3β in diabetic kidney disease remains uncertain. In db/db mice, renal expression of total and activated GSK3β was increasingly elevated. This preceded the development of diabetic kidney disease, and correlated with the progression of signs of diabetic kidney injury, including albuminuria and extracellular matrix accumulation in glomeruli and tubulointerstitia. In vitro, exposure of glomerular podocytes, mesangial cells, and renal tubular cells to a diabetic milieu induced GSK3β overexpression and hyperactivity, which seem essential and sufficient for eliciting diabetic cellular damages in kidney cells, because the cytopathic effect of the diabetic milieu was mitigated by GSK3β knockdown, but was mimicked by ectopic expression of constitutively active GSK3β even in the normal milieu. In consistency, kidney biopsy specimens procured from patients with varying stages of diabetic nephropathy revealed an amplified expression of total and activated GSK3β in glomeruli and renal tubules, associated with the severity of diabetic nephropathy. Moreover, in retrospective cohorts of type 2 diabetic patients that were followed for over five years, the relative activity of GSK3β in banked urinary exfoliated cells represented an independent risk factor for development or progression of renal impairment. Furthermore, receiver operating characteristic curve analysis demonstrated that GSK3β activity in urinary exfoliated cells provided much better power than albuminuria in discriminating diabetic patients with progressive renal impairment from those with stable kidney function. Thus, renal expression and activity of GSK3β are amplified in experimental and clinical diabetic nephropathy. Hence, GSK3β in urinary exfoliated cells may serve as a novel biomarker for predicting diabetic kidney disease progression.

Insulin Reduces Reaction of Follicular Granulosa Cells to FSH Stimulation in Women With Obesity-Related Infertility During IVF

CONTEXT

Women with obesity usually need larger doses of FSH for ovarian stimulation, resulting in poor outcomes; however, the mechanism is still unclear.

OBJECTIVE

To investigate the molecular regulation of FSH receptor (FSHR) expression associated with obesity.

DESIGN

Case-control study to improve in vitro fertilization (IVF) outcomes.

PATIENTS

Women with obesity (82) and women who were overweight (457) undergoing IVF and 1790 age-matched controls with normal weight from our reproductive medicine center.

MAIN OUTCOME MEASURES

FSHR expression was decreased in parallel with body mass index (BMI), whereas the estradiol (E2) level on the human chorionic gonadotropin (hCG) trigger day was significantly lower.

RESULTS

FSHR expression in human granulosa cells (hGCs), both mRNA (P = 0.02) and protein (P = 0.001) levels, was decreased in women who were overweight or obese. Both insulin (P < 0.001) and glucose (P = 0.0017) levels were positively correlated with BMI in fasting blood and follicle fluids (FFs) but not with FFs leptin level. We treated human granulosa-like tumor cells (KGN) cells with insulin; E2 production was compromised; the level of phosphorylated (p)-protein kinase B (p-Akt2) decreased, whereas p-glycogen synthase kinase 3 (GSK3) increased; and there were similar changes in hGCs from women with obesity. Stimulated hGCs from women with obesity with compound 21 (CP21), an inhibitor of GSK3β, resulted in upregulated β-catenin activation and increased FSHR expression. CP21 also increased the expression of insulin receptor substrate 1 and phosphatidylinositol 3-kinase (PI3K), as well as p-Akt2.

CONCLUSIONS

Women with obesity in IVF were associated with reduced FSHR expression and E2 production caused by a dysfunctional insulin pathway. Decreased FSHR expression in hGCs from women with obesity and insulin-treated KGN cells could be rescued by an inhibitor of GSK3β, which might be a potential target for the improvement of the impaired FSH-stimulation response in women with obesity.

Glycogen Synthase Kinase 3β Enhances Hepatitis C Virus Replication by Supporting miR-122

Hepatitis C virus (HCV) infection is associated with alterations in host lipid and insulin signaling cascades, which are partially explained by a dependence of the HCV life cycle on key molecules in these metabolic pathways. Yet, little is known on the role in the HCV life cycle of glycogen synthase kinase 3 (GSK3), one of the most important kinases in cellular metabolism. Therefore, the impact of GSK3 on the HCV life cycle was assessed in human hepatoma cell lines harboring subgenomic genotype 1b and 2a replicons or producing cell culture-derived HCV genotype 2a by exposure to synthetic GSK3 inhibitors, GSK3 gene silencing, overexpression of GSK3 constructs and immunofluorescence analyses. In addition, the role of GSK3 in hepatitis E virus (HEV) replication was investigated to assess virus specificity of the observed findings. We found that both inhibition of GSK3 function by synthetic inhibitors as well as silencing of GSK3β gene expression resulted in a decrease of HCV replication and infectious particle production, whereas silencing of the GSK3α isoform had no relevant effect on the HCV life cycle. Conversely, overexpression of GSK3β resulted in enhanced HCV replication. In contrast, GSK3β had no effect on replication of subgenomic HEV replicon. The pro-viral effect of GSK3β on HCV replication was mediated by supporting expression of microRNA-122 (miR-122), a micro-RNA which is mandatory for wild-type HCV replication, as GSK3 inhibitors suppressed miR-122 levels and as inhibitors of GSK3 had no antiviral effect on a miR-122-independent HCV mutant. In conclusion, we have identified GSK3β is a novel host factor supporting HCV replication by maintaining high levels of hepatic miR-122 expression.

Mechanism involved in insulin resistance via accumulation of β-amyloid and neurofibrillary tangles: link between type 2 diabetes and Alzheimer's disease

The pathophysiological link between type 2 diabetes mellitus (T2DM) and Alzheimer's disease (AD) has been suggested in several reports. Few findings suggest that T2DM has strong link in the development process of AD, and the complete mechanism is yet to be revealed. Formation of amyloid plaques (APs) and neurofibrillary tangles (NFTs) are two central hallmarks in the AD. APs are the dense composites of β-amyloid protein (Aβ) which accumulates around the nerve cells. Moreover, NFTs are the twisted fibers containing hyperphosphorylated tau proteins present in certain residues of Aβ that build up inside the brain cells. Certain factors contribute to the aetiogenesis of AD by regulating insulin signaling pathway in the brain and accelerating the formation of neurotoxic Aβ and NFTs via various mechanisms, including GSK3β, JNK, CamKII, CDK5, CK1, MARK4, PLK2, Syk, DYRK1A, PPP, and P70S6K. Progression to AD could be influenced by insulin signaling pathway that is affected due to T2DM. Interestingly, NFTs and APs lead to the impairment of several crucial cascades, such as synaptogenesis, neurotrophy, and apoptosis, which are regulated by insulin, cholesterol, and glucose metabolism. The investigation of the molecular cascades through insulin functions in brain contributes to probe and perceive progressions of diabetes to AD. This review elaborates the molecular insights that would help to further understand the potential mechanisms linking T2DM and AD.

GSK3-activated STAT5 regulates expression of SFRPs to modulate adipogenesis

Adipogenesis is a tightly regulated cellular process and is closely associated with obesity and its associated metabolic disorders, such as diabetes. Multiple transcription factors and signaling pathways are involved in the regulation of adipogenesis. Here, we report that glycogen synthase kinase (GSK3), which was reported to play an important role in many cellular processes, is essential to adipocyte differentiation at early and terminal differentiation phases. Mechanistically, GSK3 modulates adipogenesis through regulation of both canonical Wnt pathways, which involve Wnt/β-catenin signaling, and noncanonical Wnt pathways, which include JNK and Ras-related C3 botulinum toxin substrate signaling. GSK3-regulated adipogenesis is also mediated by secreted frizzled-related proteins (SFRPs), especially SFRP1, the canonical Wnt antagonist. The obesity-induced increase of Sfrp1 expression can be reversed by the GSK3 inhibitor. GSK3-regulated expression of Sfrp is mediated by signal transducer and activator of transcription 5 (STAT5). We demonstrated that GSK3 activates STAT5 through regulation of its phosphorylation to bind to the promoter of Sfrp genes and the peroxisome proliferator-activated receptor γ gene to stimulate their expression, which could ultimately lead to a modulated adipogenic process. Our findings identify a GSK3/STAT5/SFRP/Wnt regulatory axis of adipogenesis and shed light on the molecular mechanism of adipogenesis by suggesting that different pathways and adipogenic regulators coordinately modulate adipocyte differentiation.-Wang L., Wang, Y., Meng, Y., Zhang, C., Di, L. GSK3-activated STAT5 regulates expression of SFRPs to modulate adipogenesis.

Zinc stimulates glucose oxidation and glycemic control by modulating the insulin signaling pathway in human and mouse skeletal muscle cell lines

Zinc is a metal ion that is an essential cell signaling molecule. Highlighting this, zinc is an insulin mimetic, activating cellular pathways that regulate cellular homeostasis and physiological responses. Previous studies have linked dysfunctional zinc signaling with several disease states including cancer, obesity, cardiovascular disease and type 2 diabetes. The present study evaluated the insulin-like effects of zinc on cell signaling molecules including tyrosine, PRSA40, Akt, ERK1/2, SHP-2, GSK-3β and p38, and glucose oxidation in human and mouse skeletal muscle cells. Insulin and zinc independently led to the phosphorylation of these proteins over a 60-minute time course in both mouse and human skeletal muscle cells. Similarly, utilizing a protein array we identified that zinc could active the phosphorylation of p38, ERK1/2 and GSK-3B in human and ERK1/2 and GSK-3B in mouse skeletal muscle cells. Glucose oxidation assays were performed on skeletal muscle cells treated with insulin, zinc, or a combination of both and resulted in a significant induction of glucose consumption in mouse (p<0.01) and human (p<0.05) skeletal muscle cells when treated with zinc alone. Insulin, as expected, increased glucose oxidation in mouse (p<0.001) and human (0.001) skeletal muscle cells, however the combination of zinc and insulin did not augment glucose consumption in these cells. Zinc acts as an insulin mimetic, activating key molecules implicated in cell signaling to maintain glucose homeostasis in mouse and human skeletal muscle cells. Zinc is an important metal ion implicated in several biological processes. The role of zinc as an insulin memetic in activating key signaling molecules involved in glucose homeostasis could provide opportunities to utilize this ion therapeutically in treating disorders associated with dysfunctional zinc signaling.

In silico validation of microalgal metabolites against Diabetes mellitus

Aim. Present study aimed to evaluate the efficiency of microalgal metabolites as ligands for anti-diabetic target proteins viz., glucokinase, fructose-1, 6-bisphosphatase, glycogen synthase kinase, cytochrome P450, multi drug resistant protein, and peroxisome proliferator-activated receptor-(PPAR) via computational approach. Matherials and methods. Three-dimensional structures of microalgal metabolites were retrieved from PubChem database and were energy minimized. The active site of target protein was predicted through PDB sum. Molecular docking was performed with microalgae metabolites by using Hex 8.0 and DockThor server. Results. Hex docking revealed that the binding interaction of fucoxanthin was higher with fructose 1.6 bis-phosphatase (-298.31), human multidrug resistant protein 1 (-369.67), and PPAR(-404.18). DockThor docking indicated that zeaxanthin with glucokinase produced higher total energy (111.23 kcal/mol) and interaction energy (-2.99 kcal/mol). Lutein with fructose 1.6 bis phosphatase, human multidrug resistant protein, glycogen synthase kinase, PPARand cytochrome p450 produced higher total energy and interaction energy. Conclusion. Further studies will assess the anti-diabetic effect of carotenoids of microalgae especially lutein, zeaxanthin and fucoxanthin.

Testosterone insulin-like effects: an in vitro study on the short-term metabolic effects of testosterone in human skeletal muscle cells

PURPOSE

Testosterone by promoting different metabolic pathways contributes to short-term homeostasis of skeletal muscle, the largest insulin-sensitive tissue and the primary site for insulin-stimulated glucose utilization. Despite evidences indicate a close relationship between testosterone and glucose metabolism, the molecular mechanisms responsible for a possible testosterone-mediated insulin-like effects on skeletal muscle are still unknown.

METHODS

Here we used undifferentiated proliferating or differentiated human fetal skeletal muscle cells (Hfsmc) to investigate the short-term effects of testosterone on the insulin-mediated biomolecular metabolic machinery. GLUT4 cell expression, localization and the phosphorylation/activation of AKT, ERK, mTOR and GSK3β insulin-related pathways at different time points after treatment with testosterone were analyzed.

RESULTS

Independently from cells differentiation status, testosterone, with an insulin-like effect, induced Glut4-mRNA expression, GLUT4 protein translocation to the cytoplasmic membrane, while no effect was observed on GLUT4 protein expression levels. Furthermore, testosterone treatment modulated the insulin-dependent signal transduction pathways inducing a rapid and persistent activation of AKT, ERK and mTOR, and a transient inhibition of GSK3β. T-related effects were shown to be androgen receptor dependent.

CONCLUSION

All together our data indicate that testosterone through the activation of non-genomic pathways, participates in skeletal muscle glucose metabolism by inducing insulin-related effects.

Receptor and post-receptor abnormalities contribute to insulin resistance in myotonic dystrophy type 1 and type 2 skeletal muscle

Myotonic dystrophy type 1 (DM1) and type 2 (DM2) are autosomal dominant multisystemic disorders caused by expansion of microsatellite repeats. In both forms, the mutant transcripts accumulate in nuclear foci altering the function of alternative splicing regulators which are necessary for the physiological mRNA processing. Missplicing of insulin receptor (IR) gene (INSR) has been associated with insulin resistance, however, it cannot be excluded that post-receptor signalling abnormalities could also contribute to this feature in DM. We have analysed the insulin pathway in skeletal muscle biopsies and in myotube cultures from DM patients to assess whether downstream metabolism might be dysregulated and to better characterize the mechanism inducing insulin resistance. DM skeletal muscle exhibits alterations of basal phosphorylation levels of Akt/PKB, p70S6K, GSK3β and ERK1/2, suggesting that these changes might be accompanied by a lack of further insulin stimulation. Alterations of insulin pathway have been confirmed on control and DM myotubes expressing fetal INSR isoform (INSR-A). The results indicate that insulin action appears to be lower in DM than in control myotubes in terms of protein activation and glucose uptake. Our data indicate that post-receptor signalling abnormalities might contribute to DM insulin resistance regardless the alteration of INSR splicing.

Peripheral insulin resistance in ILK-depleted mice by reduction of GLUT4 expression

The development of insulin resistance is characterized by the impairment of glucose uptake mediated by glucose transporter 4 (GLUT4). Extracellular matrix changes are induced when the metabolic dysregulation is sustained. The present work was devoted to analyze the possible link between the extracellular-to-intracellular mediator integrin-linked kinase (ILK) and the peripheral tissue modification that leads to glucose homeostasis impairment. Mice with general depletion of ILK in adulthood (cKD-ILK) maintained in a chow diet exhibited increased glycemia and insulinemia concurrently with a reduction of the expression and membrane presence of GLUT4 in the insulin-sensitive peripheral tissues compared with their wild-type littermates (WT). Tolerance tests and insulin sensitivity indexes confirmed the insulin resistance in cKD-ILK, suggesting a similar stage to prediabetes in humans. Under randomly fed conditions, no differences between cKD-ILK and WT were observed in the expression of insulin receptor (IR-B) and its substrate IRS-1 expressions. The IR-B isoform phosphorylated at tyrosines 1150/1151 was increased, but the AKT phosphorylation in serine 473 was reduced in cKD-ILK tissues. Similarly, ILK-blocked myotubes reduced their GLUT4 promoter activity and GLUT4 expression levels. On the other hand, the glucose uptake capacity in response to exogenous insulin was impaired when ILK was blocked in vivo and in vitro, although IR/IRS/AKT phosphorylation states were increased but not different between groups. We conclude that ILK depletion modifies the transcription of GLUT4, which results in reduced peripheral insulin sensitivity and glucose uptake, suggesting ILK as a molecular target and a prognostic biomarker of insulin resistance.

Inhibition mechanism of CDK-2 and GSK-3β by a sulfamoylphenyl derivative of indoline-a molecular dynamics study

A good understanding of the inhibition mechanism of enzymes exhibiting high levels of similarity is the first step to the discovery of new drugs with selective potential. Examples of such proteins include glycogen synthase kinase-3 (GSK-3β) and cyclin-dependent kinase 2 (CDK-2). This article reports the mechanism of such enzyme inhibition as analyzed by an indoline sulfamylophenyl derivative (CHEMBL410072). Previous work has shown that such compounds exhibit selective properties towards their biological targets. This study used a combined procedure involving docking and molecular dynamics simulations, which allowed identification of interactions responsible for stabilization of complexes, and analysis of the dynamic stability of the systems obtained. The initial data obtained during the molecular docking stage show that the ligand molecule exhibits a similar affinity towards both active sites, which was confirmed by quantification of identified interactions and energy values. However, the data do not cover dynamic aspects of the considered systems. Molecular dynamics simulations realized for both complexes indicate significant dissimilarities in dynamics properties of both side chains of the considered ligands, especially in the case of the part containing the sulfamide group. Such increased mobility of the analyzed systems disrupts the stability of binding in the stabilized complex with GSK-3β protein, which finally affects also the binding affinity of the ligand molecule towards this enzyme.

A novel role for GSK3β as a modulator of Drosha microprocessor activity and MicroRNA biogenesis

Regulation of microRNA (miR) biogenesis is complex and stringently controlled. Here, we identify the kinase GSK3β as an important modulator of miR biogenesis at Microprocessor level. Repression of GSK3β activity reduces Drosha activity toward pri-miRs, leading to accumulation of unprocessed pri-miRs and reduction of pre-miRs and mature miRs without altering levels or cellular localisation of miR biogenesis proteins. Conversely, GSK3β activation increases Drosha activity and mature miR accumulation. GSK3β achieves this through promoting Drosha:cofactor and Drosha:pri-miR interactions: it binds to DGCR8 and p72 in the Microprocessor, an effect dependent upon presence of RNA. Indeed, GSK3β itself can immunoprecipitate pri-miRs, suggesting possible RNA-binding capacity. Kinase assays identify the mechanism for GSK3β-enhanced Drosha activity, which requires GSK3β nuclear localisation, as phosphorylation of Drosha at S³⁰⁰ and/or S³⁰²; confirmed by enhanced Drosha activity and association with cofactors, and increased abundance of mature miRs in the presence of phospho-mimic Drosha. Functional implications of GSK3β-enhanced miR biogenesis are illustrated by increased levels of GSK3β-upregulated miR targets following GSK3β inhibition. These data, the first to link GSK3β with the miR cascade in humans, highlight a novel pro-biogenesis role for GSK3β in increasing miR biogenesis as a component of the Microprocessor complex with wide-ranging functional consequences.

Glycogen Synthase Kinase 3: A Kinase for All Pathways?

Glycogen synthase kinase-3 (GSK-3) is an unusual protein-serine kinase in that it is primarily regulated by inhibition and lies downstream of multiple cell signaling pathways. This raises a variety of questions in terms of its physiological role(s), how signaling specificity is maintained and why so many eggs have been placed into one basket. There are actually two baskets, as there are two isoforms, GSK-3α and β, that are highly related and largely redundant. Their many substrates range from regulators of cellular metabolism to molecules that control growth and differentiation. In this chapter, we review the characteristics of GSK-3, update progress in understanding the kinase, and try to answer some of the questions raised by its unusual properties. Indeed, the kinase may trigger transformation in our thinking of how cellular signals are organized and controlled.

Knockdown of GSK3β increases basal autophagy and AMPK signalling in nutrient-laden human aortic endothelial cells

Suppression of the enzyme glycogen synthase kinase 3β (GSK3β) increases both the turnover of damaged cellular material and the activity of the enzyme AMP-activated protein kinase (AMPK) to potentially attenuate the damage inflicted by excess sugar and fat on blood vessels.

High concentrations of glucose and palmitate increase endothelial cell inflammation and apoptosis, events that often precede atherogenesis. They may do so by decreasing basal autophagy and AMP-activated protein kinase (AMPK) activity, although the mechanisms by which this occurs are not clear. Decreased function of the lysosome, an organelle required for autophagy and AMPK, have been associated with hyperactivity of glycogen synthase kinase 3β (GSK3β). To determine whether GSK3β affects nutrient-induced changes in autophagy and AMPK activity, we used a primary human aortic endothelial cell (HAEC) model of type 2 diabetes that we had previously characterized with impaired AMPK activity and autophagy [Weikel et al. (2015) Am. J. Phys. Cell Physiol. 308, C249–C263]. Presently, we found that incubation of HAECs with excess nutrients (25 mM glucose and 0.4 mM palmitate) increased GSK3β activity and impaired lysosome acidification. Suppression of GSK3β in these cells by treatment with a chemical inhibitor or overexpression of kinase-dead GSK3β attenuated these lysosomal changes. Under control and excess nutrient conditions, knockdown of GSK3β increased autophagosome formation, forkhead box protein O1 (FOXO1) activity and AMPK signalling and decreased Akt signalling. Similar changes in autophagy, AMPK and Akt signalling were observed in aortas from mice treated with the GSK3β inhibitor CHIR 99021. Thus, increasing basal autophagy and AMPK activity by inhibiting GSK3β may be an effective strategy in the setting of hyperglycaemia and dyslipidaemia for restoring endothelial cell health and reducing atherogenesis.

Profound hyperglycemia in knockout mutant mice identifies novel function for POU4F2/Brn-3b in regulating metabolic processes

The POU4F2/Brn-3b transcription factor has been identified as a potentially novel regulator of key metabolic processes. Loss of this protein in Brn-3b knockout (KO) mice causes profound hyperglycemia and insulin resistance (IR), normally associated with type 2 diabetes (T2D), whereas Brn-3b is reduced in tissues taken from obese mice fed on high-fat diets (HFD), which also develop hyperglycemia and IR. Furthermore, studies in C2C12 myocytes show that Brn-3b mRNA and proteins are induced by glucose but inhibited by insulin, suggesting that this protein is itself highly regulated in responsive cells. Analysis of differential gene expression in skeletal muscle from Brn-3b KO mice showed changes in genes that are implicated in T2D such as increased glycogen synthase kinase-3β and reduced GLUT4 glucose transporter. The GLUT4 gene promoter contains multiple Brn-3b binding sites and is directly transactivated by this transcription factor in cotransfection assays, whereas chromatin immunoprecipitation assays confirm that Brn-3b binds to this promoter in vivo. In addition, correlation between GLUT4 and Brn-3b in KO tissues or in C2C12 cells strongly supports a close association between Brn-3b levels and GLUT4 expression. Since Brn-3b is regulated by metabolites and insulin, this may provide a mechanism for controlling key genes that are required for normal metabolic processes in insulin-responsive tissues and its loss may contribute to abnormal glucose uptake.