Molecular basis of insulin-stimulated GLUT4 vesicle trafficking. Location! Location! Location!

Potential molecular mechanism of exercise reversing insulin resistance and improving neurodegenerative diseases

Neurodegenerative diseases are debilitating nervous system disorders attributed to various conditions such as body aging, gene mutations, genetic factors, and immune system disorders. Prominent neurodegenerative diseases include Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, and multiple sclerosis. Insulin resistance refers to the inability of the peripheral and central tissues of the body to respond to insulin and effectively regulate blood sugar levels. Insulin resistance has been observed in various neurodegenerative diseases and has been suggested to induce the occurrence, development, and exacerbation of neurodegenerative diseases. Furthermore, an increasing number of studies have suggested that reversing insulin resistance may be a critical intervention for the treatment of neurodegenerative diseases. Among the numerous measures available to improve insulin sensitivity, exercise is a widely accepted strategy due to its convenience, affordability, and significant impact on increasing insulin sensitivity. This review examines the association between neurodegenerative diseases and insulin resistance and highlights the molecular mechanisms by which exercise can reverse insulin resistance under these conditions. The focus was on regulating insulin resistance through exercise and providing practical ideas and suggestions for future research focused on exercise-induced insulin sensitivity in the context of neurodegenerative diseases.

Conditional Deletion of β-Catenin in the Mediobasal Hypothalamus Impairs Adaptive Energy Expenditure in Response to High-Fat Diet and Exacerbates Diet-Induced Obesity

β-Catenin is a bifunctional molecule that is an effector of the wingless-related integration site (Wnt) signaling to control gene expression and contributes to the regulation of cytoskeleton and neurotransmitter vesicle trafficking. In its former role, β-catenin binds transcription factor 7-like 2 (TCF7L2), which shows strong genetic associations with the pathogenesis of obesity and type-2 diabetes. Here, we sought to determine whether β-catenin plays a role in the neuroendocrine regulation of body weight and glucose homeostasis. Bilateral injections of adeno-associated virus type-2 (AAV2)-mCherry-Cre were placed into the arcuate nucleus of adult male and female β-catenin flox mice, to specifically delete β-catenin expression in the mediobasal hypothalamus (MBH-β-cat KO). Metabolic parameters were then monitored under conditions of low-fat (LFD) and high-fat diet (HFD). On LFD, MBH-β-cat KO mice showed minimal metabolic disturbances, but on HFD, despite having only a small difference in weekly caloric intake, the MBH-β-cat KO mice were significantly heavier than the control mice in both sexes (p < 0.05). This deficit seemed to be due to a failure to show an adaptive increase in energy expenditure seen in controls, which served to offset the increased calories by HFD. Both male and female MBH-β-cat KO mice were highly glucose intolerant when on HFD and displayed a significant reduction in both leptin and insulin sensitivity compared with controls. This study highlights a critical role for β-catenin in the hypothalamic circuits regulating body weight and glucose homeostasis and reveals potential mechanisms by which genetic variation in this pathway could impact on development of metabolic disease.

Involution of brown adipose tissue through a Syntaxin 4 dependent pyroptosis pathway

Aging, chronic high-fat diet feeding, or housing at thermoneutrality induces brown adipose tissue (BAT) involution, a process characterized by reduction of BAT mass and function with increased lipid droplet size. Single nuclei RNA sequencing of aged mice identifies a specific brown adipocyte population of Ucp1-low cells that are pyroptotic and display a reduction in the longevity gene syntaxin 4 (Stx4a). Similar to aged brown adipocytes, Ucp1-STX4KO mice display loss of brown adipose tissue mass and thermogenic dysfunction concomitant with increased pyroptosis. Restoration of STX4 expression or suppression of pyroptosis activation protects against the decline in both mass and thermogenic activity in the aged and Ucp1-STX4KO mice. Mechanistically, STX4 deficiency reduces oxidative phosphorylation, glucose uptake, and glycolysis leading to reduced ATP levels, a known triggering signal for pyroptosis. Together, these data demonstrate an understanding of rapid brown adipocyte involution and that physiologic aging and thermogenic dysfunction result from pyroptotic signaling activation.

Role of obesity related inflammation in pathogenesis of peripheral artery disease in patients of type 2 diabetes mellitus

Objective

Type 2 diabetes mellitus (T2DM) has emerged as one of the greatest global health challenges of twenty-first century. Visceral obesity is one of the most important determinant of insulin resistance (IR) as well as T2DM complications. Therefore this review focuses on the molecular mechanism of obesity induced inflammation, signaling pathways contributing to diabetes, as well as role of lifestyle interventions and medical therapies in the prevention and management of T2DM.

Method

Articles were searched on digital data base PubMed, Cochrane Library, and Web of Science. The key words used for search included Type 2 diabetes mellitus, obesity, insulin resistance, vascular inflammation and peripheral arterial disease.

Result

Visceral obesity is associated with chronic low grade inflammation and activation of immune systems which are involved in pathogenesis of obesity related IR and T2DM.

Conclusion

Metabolic dysregulation of adipose tissue leads to local hypoxia, misfolded/unfolded protein response and increased circulating free fatty acids, which in turn initiate inflammatory signaling cascades in the population of infiltrating cells. Mechanism that relates the role of adipocytokines with insulin sensitivity and glucose homeostasis might throw a light on the development of therapeutic interventions and subsequently might result in the reduction of vascular complications.

Computational, chemical profiling and biochemical evaluation of antidiabetic potential of Parkia biglobosa stem bark extract in type 2 model of rats

The present study investigated the antidiabetic and antioxidant capacity of hydromethanol extract from Parkia biglobosa stem bark (PBSBHM) in fructose-streptozotocin induced type 2 diabetic rats after 28 days of oral administration. Simultaneously, evaluated the phenolic profiles and mineral compositions of crude extract. Molecular docking analysis of protocatechuic acid, the most abundant phenolic acid with potential downstream partners protein kinase A (PKA), protein kinase C (PKC), and Ca²⁺/calmodulin-dependent protein kinase II (CaMK II), was investigated. The preliminary results showed that PBSBHM crude extract contained 225.2 ± 18.25 mg GAE/g of total phenolic and 99.28 ± 12.3 mg QE/g of total flavonoid. Both protocatechuic and gallic acids were identified as a prominent phenolic compound through HPLC analysis, while vanillic acid was not detected. High mineral composition of K, Mg, P, Ca while Mn and Cr as trace elements were found in PBSBHM by plasma optical emission spectroscopy. PBSBHM extracts showed a significant radical scavenging activity from a therapeutic point of view, a moderate antioxidant potential and improved glucose tolerance after 30 min of glucose loading. PBSBHM extracts significantly attenuated serum glucose level and glycosylated haemoglobin at the tested dosage. However, it elevated the hepatic hexokinase activity and glycogen level compared with the diabetic untreated rats. PBSBHM ameliorates the decreased activity of pancreatic superoxide dismutase, catalase and reduced glutathione but decreased the MDA level. Docking analysis of protocatechuic acid showed a moderate affinity for the target enzymes compared to the standard drugs. Our data showed that the stem bark extract of this botanical has antidiabetic potential and at least in part substantiates its traditional use in the management of diabetes, possibly due to the synergistic interactions of protocatechuic acid with other biologically active components.

The Mechanisms of the Potential Probiotic Lactiplantibacillus plantarum against Cardiovascular Disease and the Recent Developments in its Fermented Foods

Cardiovascular disease (CVD) has become the leading cause of death worldwide. Many recent studies have pointed out that Lactiplantibacillus plantarum (Lb. plantarum) has great potential in reducing the risk of CVD. Lb. plantarum is a kind of lactic acid bacteria (LAB) widely distributed in fermented food and the human intestinal tract, some strains of which have important effects on human health and the potential to be developed into probiotics. In this review, we summarize the mechanism of potential probiotic strains of Lb. plantarum against CVD. It could regulate the body’s metabolism at the molecular, cellular, and population levels, thereby lowering blood glucose and blood lipids, regulating blood pressure, and ultimately reducing the incidence of CVD. Furthermore, since Lb. plantarum is widely utilized in food industry, we highlight some of the most important new developments in fermented food for combating CVD; providing an insight into these fermented foods can assist scientists in improving the quality of these foods as well as alleviating patients’ CVD symptoms. We hope that in the future functional foods fermented by Lb. plantarum can be developed and incorporated into the daily diet to assist medication in alleviating CVD to some extent, and maintaining good health.

β-cells retain a pool of insulin-containing secretory vesicles regulated by adherens junctions and the cadherin binding protein p120 catenin

The β-cells of the islets of Langerhans are the sole producers of insulin in the human body. In response to rising glucose levels, insulin-containing vesicles inside β-cells fuse with the plasma membrane and release their cargo. However, the mechanisms regulating this process are only partly understood. Previous evidence indicated reductions in α-catenin elevate insulin release, while reductions in β-catenin decrease insulin release. α- and β-catenin contribute to cellular regulation in a range of ways but one is as members of the adherens junction complex and these contribute to the development of cell polarity in b-cells. Therefore, we investigated the effects of adherens junctions on insulin release. We show in INS-1E β-cells knockdown of either E- or N-cadherin had only small effects on insulin secretion, but simultaneous knockout of both cadherins resulted in a significant increase in basal insulin release to the same level as glucose-stimulated release. This double knockdown also significantly attenuated levels of p120 catenin, a cadherin binding partner involved in regulating cadherin turnover. Conversely, reducing p120 catenin levels with siRNA destabilized both E- and N-cadherin, and this was also associated with an increase in levels of insulin secreted from INS-1E cells. Furthermore, there were also changes in these cells consistent with higher insulin release, namely reductions in levels of F-actin and increased intracellular free Ca²⁺ levels in response to KCl-induced membrane depolarization. Taken together, these data provide evidence that adherens junctions play important roles in retaining a pool of insulin secretory vesicles within the cell and establish a role for p120 catenin in regulating this process.

Changing lanes: seasonal differences in cellular metabolism of adipocytes in grizzly bears (Ursus arctos horribilis)

Obesity is among the most prevalent of health conditions in humans leading to a multitude of metabolic pathologies such as type 2 diabetes and hyperglycemia. However, there are many wild animals that have large seasonal cycles of fat accumulation and loss that do not result in the health consequences observed in obese humans. One example is the grizzly bear (Ursus arctos horribilis) that can have body fat content > 40% that is then used as the energy source for hibernation. Previous in vitro studies found that hibernation season adipocytes exhibit insulin resistance and increased lipolysis. Yet, other aspects of cellular metabolism were not addressed, leaving this in vitro model incomplete. Thus, the current studies were performed to determine if the cellular energetic phenotype-measured via metabolic flux-of hibernating bears was retained in cultured adipocytes and to what extent that was due to serum or intrinsic cellular factors. Extracellular acidification rate and oxygen consumption rate were used to calculate proton efflux rate and total ATP defined as both ATP from glycolysis and from mitochondrial respiration. Hibernation adipocytes treated with hibernation serum produced less ATP and exhibited lower maximal respiration and glycolysis rates than active season adipocytes. These effects were reversed with serum from the opposite season. Insulin had little influence on total ATP production and lipolysis in both hibernation and active serum-treated adipocytes. Together, these results suggest that the metabolic suppression occurring in hibernation adipocytes are downstream of insulin signaling and likely due to a combined reduction in mitochondria number and/or function and glycolytic processes. Future elucidation of the serum components and the cellular mechanisms that enable alterations in mitochondrial function could provide a novel avenue for the development of treatments for human metabolic diseases.

Peripheral versus central insulin and leptin resistance: Role in metabolic disorders, cognition, and neuropsychiatric diseases

Insulin and leptin are classically regarded as peptide hormones that play key roles in metabolism. In actuality, they serve several functions in both the periphery and central nervous system (CNS). Likewise, insulin and leptin resistance can occur both peripherally and centrally. Metabolic disorders such as diabetes and obesity share several key features including insulin and leptin resistance. While the peripheral effects of these disorders are well-known (i.e. cardiovascular disease, hypertension, stroke, dyslipidemia, etc.), the CNS complications of leptin and insulin resistance have come into sharper focus. Both preclinical and clinical findings have indicated that insulin and leptin resistance are associated with cognitive deficits and neuropsychiatric diseases such as depression. Importantly, these studies also suggest that these deficits in neuroplasticity can be reversed by restoration of insulin and leptin sensitivity. In view of these observations, this review will describe, in detail, the peripheral and central functions of insulin and leptin and explain the role of insulin and leptin resistance in various metabolic disorders, cognition, and neuropsychiatric diseases.

Endometrial Glucose Transporters in Health and Disease

Pregnancy loss is a frequent occurrence during the peri-implantation period, when there is high glucose demand for embryonic development and endometrial decidualization. Glucose is among the most essential uterine fluid components required for those processes. Numerous studies associate abnormal glucose metabolism in the endometrium with a higher risk of adverse pregnancy outcomes. The endometrium is incapable of synthesizing glucose, which thus must be delivered into the uterine lumen by glucose transporters (GLUTs) and/or the sodium-dependent glucose transporter 1 (SGLT1). Among the 26 glucose transporters (14 GLUTs and 12 SGLTs) described, 10 (9 GLUTs and SGLT1) are expressed in rodents and 8 (7 GLUTs and SGLT1) in the human uterus. This review summarizes present knowledge on the most studied glucose transporters in the uterine endometrium (GLUT1, GLUT3, GLUT4, and GLUT8), whose data regarding function and regulation are still lacking. We present the recently discovered SGLT1 in the mouse and human endometrium, responsible for controlling glycogen accumulation essential for embryo implantation. Moreover, we describe the epigenetic regulation of endometrial GLUTs, as well as signaling pathways included in uterine GLUT’s expression. Further investigation of the GLUTs function in different endometrial cells is of high importance, as numerous glucose transporters are associated with infertility, polycystic ovary syndrome, and gestational diabetes.

Intranasal insulin and orexins to treat age-related cognitive decline

The intranasal (IN) administration of neuropeptides, such as insulin and orexins, has been suggested as a treatment strategy for age-related cognitive decline (ARCD). Because dysfunctional neuropeptide signaling is an observed characteristic of ARCD, it has been suggested that IN delivery of insulin and/or orexins may restore endogenous peptide signaling and thereby preserve cognition. IN administration is particularly alluring as it is a relatively non-invasive method that directly targets peptides to the brain. Several laboratories have examined the behavioral effects of IN insulin in young, aged, and cognitively impaired rodents and humans. These studies demonstrated improved performance on various cognitive tasks following IN insulin administration. Fewer laboratories have assessed the effects of IN orexins; however, this peptide also holds promise as an effective treatment for ARCD through the activation of the cholinergic system and/or the reduction of neuroinflammation. Here, we provide a brief overview of the advantages of IN administration and the delivery pathway, then summarize the current literature on IN insulin and orexins. Additional preclinical studies will be useful to ultimately uncover the mechanisms underlying the pro-cognitive effects of IN insulin and orexins, whereas future clinical studies will aid in the determination of the most efficacious dose and dosing paradigm. Eventually, IN insulin and/or orexin administration may be a widely used treatment strategy in the clinic for ARCD.

The mother relationship between insulin resistance and non-alcoholic steatohepatitis: Glucosinolates hydrolysis products as a promising insulin resistance-modulator and fatty liver-preventer

Non-alcoholic fatty liver disease (NFLD) is one of the present public health problems which have no specific and effective treatment. The speed of the disease progression depends on the patient's lifestyle. Due to life stresses and lack of time, a high number of people depend on fast food containing a high amount of fats which one of the main causes of insulin resistance (IR). IR is one of the metabolic disorders which strongly intersected with molecular NAFLD and leading to its progression into non-alcoholic steatohepatitis (NASH). In this review, we introduced the updated statistics of NAFLD and NASH progression all over the world shows its importance, etiologies, and pathogenesis. Also, IR and its role in NASH initiation and progression explored, and current treatments with its limitations have been explained. Glucosinolates (GLS) is a group of phytochemicals which known by its potent hydrolysis products with promising anti-cancer effect. In this review, we have collected the recent experimental studies of different GLS hydrolysis products against IR and chronic liver diseases supported by our lab finding. Finally, we recommend this group of phytochemicals as promising molecules to be studied experimentally and clinically against a wide range of chronic liver diseases with an acceptable safety margin.

Functional Characterization of Facilitative Glucose Transporter 4 With a Delay Responding to Plasma Glucose Level in Blunt Snout Bream (Megalobrama amblycephala)

Facilitative glucose transporter 4 (GLUT4) plays a central role in mediating insulin function to increase glucose uptake in glucose metabolism homeostasis. In this study, the function and localization of GLUT4 in blunt snout bream (Megalobrama amblycephala) were first investigated, and then, the response measured as carbohydrate level, was analyzed. The results showed that the cDNA sequence of GLUT4 in blunt snout bream (MaGLUT4, GenBank accession no: MT447093) was 2868 bp in length, and the corresponding mRNA contained a 5'-UTR region of 513 bp and a 3'-UTR region of 837 bp. MaGLUT4 had an open reading frame of 1518 bp and was encoded by 505 amino acids. Its theoretical isoelectric point and molecular weight was 6.41 and 55.47 kDa, respectively. A comparison of these characteristics with BLASTP results from the NCBI database showed that MaGLUT4 had the highest homology with Cypriniformes fish, with MaGLUT4 and GLUT4 of other Cypriniformes clustered in the phylogenetic tree with other GLUT1-4 amino acid sequences. Compared with the results from the homo_sapiens and mus_musculus data sets, some mutations were observed in the GLUT4 amino acid sequence of these aquatic animals, including an FQQI mutation to FQQL, LL mutation to MM, and TELEY mutation to TELDY. MaGLUT4 was constitutively expressed in the muscle, intestine, and liver, with the highest mRNA level observed in muscle. Furthermore, the predicted tertiary structure and results of immunohistochemical staining showed that MaGLUT4 was a transmembrane protein primarily located in the plasma membrane, where it accounts for 60.9% of the total expressed, according to an analysis of subcellular localization. Blood glucose level peaked within 1 h, and the insulin level peaked at 6 h, while the mRNA and protein levels of GLUT4 showed an upward trend with an increase in feeding time and decreased sharply after 12 h. These results confirmed that MaGLUT4 was mainly distributed in muscles and crosses the cell membrane. The changes in the insulin, mRNA, and protein levels of MaGUT4 lagged far behind changes in blood glucose levels. This delay in insulin level changes and GLUT4 activation might be the important reasons for glucose intolerance of this fish species.

Role of linagliptin in preventing the pathological progression of hepatic fibrosis in high fat diet and streptozotocin-induced diabetic obese rats

Liver fibrosis is a common complication of diabetes mellitus, with a major global public health concern. Linagliptin, a dipeptidyl peptidase-4 inhibitor (DPP-4), is classically used to treat type 2 diabetes mellitus and improves insulin resistance. Additional potential influences of linagliptin on liver fibrosis are still unclear. The present study was undertaken to investigate the therapeutic credit of linagliptin in hepatic fibrosis induced by a high-fat diet (HFD) and streptozotocin (STZ) in rats. Moreover, the mechanisms underline its anti-fibrotic effect were explored. To induce liver fibrosis with T2DM; male Sprague-Dawley albino rats were fed on a high-fat high-sucrose diet for 28 days then exposed to a single dose of STZ (30 mg/kg, IP). After two days of STZ injection, a diabetes confirmation test was done and all diabetic rats were constantly fed on HFD for thirty days with or without treatment with linagliptin (6 mg/kg). Hepatotoxicity markers, lipid profile screening, insulin signaling, inflammatory cytokines (TNF-α, IL-6, NF-κB p65), fibrosis markers (Collagen, α-SMA, TGF-β1) and histopathological studies including hematoxylin and eosin (H&E) as well Masson's trichrome stains were performed. In our preliminary study, linagliptin at a dose of 6 mg/kg was chosen as the optimum anti-diabetic dose in rats challenged with STZ. Linagliptin significantly improved insulin sensitivity and lipid profile and reduced inflammatory mediators, and collagen depositions in rats with liver fibrosis and T2DM. In conclusion, above and beyond its anti-diabetic effect, this study introduced linagliptin as a promising option for preventing the pathological progression of liver fibrosis associated with T2DM.

Effect of resveratrol on SNARE proteins expression and insulin resistance in skeletal muscle of diabetic rats

Objective(s):

Soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex proteins are involved in membrane trafficking. The expression of isoforms of SNAP-23, syntaxin-4, and VAMP-2 is significantly done in skeletal muscles; they control GLUT4 trafficking. It is believed that type 2 diabetes could be caused by the modifications in the expression of SNARE complex proteins. The purpose of this study was to evaluate the effect of resveratrol on the expression of these proteins in type 2 diabetes.

Materials and Methods:

Forty male Wistar rats were selected. Streptozotocin and nicotinamide were applied for the induction of type 2 diabetes. The animals were divided into five groups. Healthy and diabetic groups were set as control; resveratrol (1, 5, and 10 mg/kg body weight) was applied to treat the three groups of diabetic rats for 30 days. Real-time qRT-PCR was applied to evaluate the expression of SNARE complex proteins.

Results:

There is a link between diabetes and insulin resistance and up-regulation of SNARE proteins expression. Resveratrol improved hyperglycemia and insulin resistance along with a non-significant reduction in the expression of SNARE proteins.

Conclusion:

Increased expression of SNARE proteins was possibly a compensatory mechanism in response to insulin resistance in the skeletal muscles of diabetic rats. Resveratrol non-significantly reduced the expression of SNARE proteins by enhancing insulin sensitivity, where this effect was dose-dependent. Thus, higher doses of resveratrol and longer intervention periods could probably be more effective. Another molecular mechanism of the anti-diabetic properties of resveratrol was identified with an effect on the expression of SNARE proteins.

Goldfish adipocytes are pancreatic beta cell-like, glucose-responsive insulin-producing cells

Glucose homeostasis plays a key role in maintaining stable physiological conditions, and its dysfunction causes severe chronic health issues including diabetes. In this study, we have characterized goldfish adipocytes as cells with properties similar to that of pancreatic β-cells: they express considerable high levels of preproinsulin mRNAs, possess the necessary machinery for processing preproinsulin (prohormone convertases 1 and 2, carboxypeptidase E and trypsin) and responding to extracellular glucose (glucokinase and the glucose transporters 1, 2, and 4), produce insulin in a glucose-responsive manner and express key transcription factors typically involved in pancreas development (Pdx1, Neurogenin3, Nkx2.2, Pax6, and FOXO1A). These findings reinforce the feature of fish adipocytes as alternate sources of active insulin, holding the promise that they could eventually be developed as transplantable sources of this vital hormone.

GLUT4 Storage Vesicles: Specialized Organelles for Regulated Trafficking

Fat and muscle cells contain a specialized, intracellular organelle known as the GLUT4 storage vesicle (GSV). Insulin stimulation mobilizes GSVs, so that these vesicles fuse at the cell surface and insert GLUT4 glucose transporters into the plasma membrane. This example is likely one instance of a broader paradigm for regulated, non-secretory exocytosis, in which intracellular vesicles are translocated in response to diverse extracellular stimuli. GSVs have been studied extensively, yet these vesicles remain enigmatic. Data support the view that in unstimulated cells, GSVs are present as a pool of preformed small vesicles, which are distinct from endosomes and other membrane-bound organelles. In adipocytes, GSVs contain specific cargoes including GLUT4, IRAP, LRP1, and sortilin. They are formed by membrane budding, involving sortilin and probably CHC22 clathrin in humans, but the donor compartment from which these vesicles form remains uncertain. In unstimulated cells, GSVs are trapped by TUG proteins near the endoplasmic reticulum - Golgi intermediate compartment (ERGIC). Insulin signals through two main pathways to mobilize these vesicles. Signaling by the Akt kinase modulates Rab GTPases to target the GSVs to the cell surface. Signaling by the Rho-family GTPase TC10α stimulates Usp25m-mediated TUG cleavage to liberate the vesicles from the Golgi. Cleavage produces a ubiquitin-like protein modifier, TUGUL, that links the GSVs to KIF5B kinesin motors to promote their movement to the cell surface. In obesity, attenuation of these processes results in insulin resistance and contributes to type 2 diabetes and may simultaneously contribute to hypertension and dyslipidemia in the metabolic syndrome.

Hibernation induces widespread transcriptional remodeling in metabolic tissues of the grizzly bear

Revealing the mechanisms underlying the reversible physiology of hibernation could have applications to both human and animal health as hibernation is often associated with disease-like states. The present study uses RNA-sequencing to reveal the tissue and seasonal transcriptional changes occurring in grizzly bears (Ursus arctos horribilis). Comparing hibernation to other seasons, bear adipose has a greater number of differentially expressed genes than liver and skeletal muscle. During hyperphagia, adipose has more than 900 differentially expressed genes compared to active season. Hibernation is characterized by reduced expression of genes associated with insulin signaling, muscle protein degradation, and urea production, and increased expression within muscle protein anabolic pathways. Across all three tissues we find a subset of shared differentially expressed genes, some of which are uncharacterized, that together may reflect a common regulatory mechanism. The identified gene families could be useful for developing novel therapeutics to treat human and animal diseases.

Comparative study of testosterone and vitamin D analogue, elocalcitol, on insulin-controlled signal transduction pathway regulation in human skeletal muscle cells

PURPOSE

Skeletal muscle (Skm) plays a key role in regulating energetic metabolism through glucose homeostasis. Several hormones such as Testosterone (T) and Vitamin D (VD) have been shown to affect energy-dependent cell trafficking by determining Insulin (I)-like effects.

AIM

To elucidate possible hormone-related differences on muscular metabolic control, we analyzed and compared the effects of T and elocalcitol (elo), a VD analogue, on the activation of energy-dependent cell trafficking, metabolism-related-signal transduction pathways and transcription of gene downstream targets.

METHODS

Human fetal skeletal muscle cells (Hfsmc) treated with T or elo were analyzed for GLUT4 localization, phosphorylation/activation status of AKT, ERK1/2, IRS-1 signaling and c-MYC protein expression.

RESULTS

T, similar to elo, induced GLUT4 protein translocation likely in lipid raft microdomains. While both T and elo induced a rapid IRS-1 phosphorylation, the following dynamic in phosphorylation/activation of AKT and ERK1/2 signaling was different. Moreover, T but not elo increased c-MYC protein expression.

CONCLUSIONS

All together, our evidence indicates that whether both T and elo are able to affect upstream I-like pathway, they differently determine downstream effects in I-dependent cascade, suggesting diverse physiological roles in mediating I-like response in human skeletal muscle.

Curcumin Ameliorates the Impaired Insulin Signaling Involved in the Pathogenesis of Alzheimer's Disease in Rats

To date, dysregulation of the insulin signaling pathway in the brain has not been demonstrated unequivocally in Alzheimer's disease (AD). The purpose of the study was to examine the possible dysregulation of insulin signaling pathway in an AD rat model. Furthermore, the present study investigated the effect of Donepezil and Curcumin on insulin signaling, insulin, and glucose levels in AD rat brain. The rats were induced to develop AD by intraperitoneal administration of Scopolamine. We found that glucose levels in plasma and brain were decreased in AD rats, whereas the insulin levels was increased in plasma but decreased in brain in AD rats. In addition, insulin signaling proteins IR-β, IGF-1, IRS-1, IRS-2 p-Akt (Ser473), and Akt were markedly reduced in the AD rats. Furthermore, GLUT3 and GLUT4 levels in the brain were markedly reduced in AD rats. All these data were compared to Saline-treated control rats. Curcumin significantly increased glucose levels in plasma and in brain. However, insulin levels was decreased in plasma and was increased in AD rats' brain. Moreover, GLUT3 and GLUT4 levels were significantly increased in Curcumin-treated AD rats. All these data were compared to Scopolamine- induced AD rats. Thus amelioration of impaired insulin signaling and improved glucose regulation in AD rats by Curcumin may be beneficial in the management of AD.

Cdc42: A Novel Regulator of Insulin Secretion and Diabetes-Associated Diseases

Cdc42, a member of the Rho GTPases family, is involved in the regulation of several cellular functions including cell cycle progression, survival, transcription, actin cytoskeleton organization and membrane trafficking. Diabetes is a chronic and metabolic disease, characterized as glycometabolism disorder induced by insulin deficiency related to β cell dysfunction and peripheral insulin resistance (IR). Diabetes could cause many complications including diabetic nephropathy (DN), diabetic retinopathy and diabetic foot. Furthermore, hyperglycemia can promote tumor progression and increase the risk of malignant cancers. In this review, we summarized the regulation of Cdc42 in insulin secretion and diabetes-associated diseases. Organized researches indicate that Cdc42 is a crucial member during the progression of diabetes, and Cdc42 not only participates in the process of insulin synthesis but also regulates the insulin granule mobilization and cell membrane exocytosis via activating a series of downstream factors. Besides, several studies have demonstrated Cdc42 as participating in the pathogenesis of IR and DN and even contributing to promote cancer cell proliferation, survival, invasion, migration, and metastasis under hyperglycemia. Through the current review, we hope to cast light on the mechanism of Cdc42 in diabetes and associated diseases and provide new ideas for clinical diagnosis, treatment, and prevention.

The Effect of Intrahippocampal Insulin Infusion on Spatial Cognitive Function and Markers of Neuroinflammation in Diet-induced Obesity

Obesity and high fat diet consumption contribute to the development of metabolic disorders, insulin resistance, neuroinflammation, and cognitive impairments. CNS administration of insulin into the brain can attenuate these cognitive impairments. The present study investigated whether hippocampal-dependent spatial memory impairments in a dietary induced mouse model of obesity could be improved by the direct administration of insulin into the hippocampus and whether this was associated with markers of hippocampal inflammation. C57Bl/6J mice consumed a low fat or high fat diet for 16 weeks and continuous intrahippocampal saline or insulin infusion for the final 4 weeks, during a period of behavioral testing, before gene expression analysis was performed. The high fat diet group demonstrated poorer spatial memory performance in the Morris water maze and Y-maze, supporting the hypothesis that high fat diet leads to hippocampal dependent cognitive impairment. Insulin infusion into the hippocampus reversed the deficit of high fat diet consumption on both of the tasks. Increased expression of inflammatory markers was detected in the hippocampus in the high fat diet group and expression of these markers was ameliorated in insulin infused mice. This demonstrates that CNS insulin can improve hippocampal-dependent memory and that hippocampal inflammation may be a factor in the development of cognitive deficits associated with diet-induced obesity. Furthermore, these data suggest that insulin may act to attenuate high fat diet induced cognitive deficits by reducing neuroinflammation.

Insulin Receptor Plasma Membrane Levels Increased by the Progesterone Receptor Membrane Component 1

The insulin receptor (IR) is a ligand-activated receptor tyrosine kinase that has a key role in metabolism, cellular survival, and proliferation. Progesterone receptor membrane component 1 (PGRMC1) promotes cellular signaling via receptor trafficking and is essential for some elements of tumor growth and metastasis. In the present study, we demonstrate that PGRMC1 coprecipitates with IR. Furthermore, we show that PGRMC1 increases plasma membrane IR levels in multiple cell lines and decreases insulin binding at the cell surface. The findings have therapeutic applications because a small-molecule PGRMC1 ligand, AG205, also decreases plasma membrane IR levels. However, PGRMC1 knockdown via short hairpin RNA expression and AG205 treatment potentiated insulin-mediated phosphorylation of the IR signaling mediator AKT. Finally, PGRMC1 also increased plasma membrane levels of two key glucose transporters, GLUT-4 and GLUT-1. Our data support a role for PGRMC1 maintaining plasma membrane pools of the receptor, modulating IR signaling and function.

Isoalantolactone derivative promotes glucose utilization in skeletal muscle cells and increases energy expenditure in db/db mice via activating AMPK-dependent signaling

Augmenting glucose utilization and energy expenditure in skeletal muscle via AMP-activated protein kinase (AMPK) is an imperative mechanism for the management of type 2 diabetes. Chemical derivatives (2a-2h, 3, 4a-4d, 5) of the isoalantolactone (K007), a bioactive molecule from roots of Inula racemosa were synthesized to optimize the bioactivity profile to stimulate glucose utilization in skeletal muscle cells. Interestingly, 4a augmented glucose uptake, driven by enhanced translocation of glucose transporter 4 (GLUT4) to cell periphery in L6 rat skeletal muscle cells. The effect of 4a was independent to phosphatidylinositide-3-kinase (PI-3-K)/Akt pathway, but mediated through Liver kinase B1 (LKB1)/AMPK-dependent signaling, leading to activation of downstream targets acetyl coenzyme A carboxylase (ACC) and sterol regulatory element binding protein 1c (SREBP-1c). In db/db mice, 4a administration decreased blood glucose level and improved body mass index, lipid parameters and glucose tolerance associated with elevation of GLUT4 expression in skeletal muscle. Moreover, 4a increased energy expenditure via activating substrate utilization and upregulated the expression of thermogenic transcription factors and mitochondrial proteins in skeletal muscle, suggesting the regulation of energy balance. These findings suggest the potential implication of isoalantolactone derivatives for the management of diabetes.

Effects of Chromium-Loaded Chitosan Nanoparticles on Glucose Transporter 4, Relevant mRNA, and Proteins of Phosphatidylinositol 3-Kinase, Akt2-Kinase, and AMP-Activated Protein Kinase of Skeletal Muscles in Finishing Pigs

The study was conducted to evaluate the effects of chromium-loaded chitosan nanoparticles (Cr-CNP) on glucose transporter 4 (GLUT4), relevant messenger RNA (mRNA), and proteins involved in phosphatidylinositol 3-kinase (PI3K), Akt2-kinase, and AMP-activated protein kinase (AMPK) of skeletal muscles in finishing pigs. A total of 120 crossbred barrows (BW 65.00 ± 1.26 kg) were randomly allotted to four dietary treatments, with three pens per treatment and 10 pigs per pen. Pigs were fed the basal diet supplemented with 0, 100, 200, or 400 μg/kg of Cr from Cr-CNP for 35 days. After the feeding trials, 24 pigs were slaughtered to collect longissimus muscle samples for analysis. Cr-CNP supplementation increased GLUT4 messenger RNA (mRNA) (quadratically, P < 0.01) and total and plasma membrane GLUT4 protein contents (linearly and quadratically, P < 0.001) in skeletal muscles. Glycogen synthase kinase 3β (GSK-3β) mRNA was decreased linearly (P < 0.001) and quadratically (P < 0.001). Supplemental Cr-CNP increased insulin receptor (InsR) mRNA quadratically (P < 0.01), Akt2 total protein level linearly (P < 0.01) and quadratically (P < 0.001), and PI3K total protein was increased significantly (P < 0.05) in 200 μg/kg treatment group. The mRNA of AMPK subunit gamma-3 (PRKAG3) and protein of AMPKα₁ was significantly increased (P < 0.001) with the addition of Cr-CNP. The results indicate that dietary supplementation of Cr-CNP may promote glucose uptake by leading to recruitment of GLUT4 to the plasma membrane in skeletal muscles, and these actions may be associated with the insulin signal transduction and AMPK.

Membrane lipid alterations in the metabolic syndrome and the role of dietary oils

The metabolic syndrome is a cluster of pathological conditions, including hypertension, hyperglycemia, hypertriglyceridemia, obesity and low HDL levels that is of great concern worldwide, as individuals with metabolic syndrome have an increased risk of type-2 diabetes and cardiovascular disease. Insulin resistance, the key feature of the metabolic syndrome, might be at the same time cause and consequence of impaired lipid composition in plasma membranes of insulin-sensitive tissues like liver, muscle and adipose tissue. Diet intervention has been proposed as a powerful tool to prevent the development of the metabolic syndrome, since healthy diets have been shown to have a protective role against the components of the metabolic syndrome. Particularly, dietary fatty acids are capable of modulating the deleterious effects of these conditions, among other mechanisms, by modifications of the lipid composition of the membranes in insulin-sensitive tissues. However, there is still scarce data based of high-level evidence on the effects of dietary oils on the effects of the metabolic syndrome and its components. This review summarizes the current knowledge on the effects of dietary oils on improving alterations of the components of the metabolic syndrome. It also examines their influence in the modulation of plasma membrane lipid composition and in the functionality of membrane proteins involved in insulin activity, like the insulin receptor, GLUT-4, CD36/FAT and ABCA-1, and their effect in the metabolism of glucose, fatty acids and cholesterol, and, in turn, the key features of the metabolic syndrome. This article is part of a Special Issue entitled: Membrane Lipid Therapy: Drugs Targeting Biomembranes edited by Pablo V. Escribá.

Life in the fat lane: seasonal regulation of insulin sensitivity, food intake, and adipose biology in brown bears

Grizzly bears (Ursus arctos horribilis) have evolved remarkable metabolic adaptations including enormous fat accumulation during the active season followed by fasting during hibernation. However, these fluctuations in body mass do not cause the same harmful effects associated with obesity in humans. To better understand these seasonal transitions, we performed insulin and glucose tolerance tests in captive grizzly bears, characterized the annual profiles of circulating adipokines, and tested the anorectic effects of centrally administered leptin at different times of the year. We also used bear gluteal adipocyte cultures to test insulin and beta-adrenergic sensitivity in vitro. Bears were insulin resistant during hibernation but were sensitive during the spring and fall active periods. Hibernating bears remained euglycemic, possibly due to hyperinsulinemia and hyperglucagonemia. Adipokine concentrations were relatively low throughout the active season but peaked in mid-October prior to hibernation when fat content was greatest. Serum glycerol was highest during hibernation, indicating ongoing lipolysis. Centrally administered leptin reduced food intake in October, but not in August, revealing seasonal variation in the brain's sensitivity to its anorectic effects. This was supported by strong phosphorylated signal transducer and activator of transcription 3 labeling within the hypothalamus of hibernating bears; labeling virtually disappeared in active bears. Adipocytes collected during hibernation were insulin resistant when cultured with hibernation serum but became sensitive when cultured with active season serum. Heat treatment of active serum blocked much of this action. Clarifying the cellular mechanisms responsible for the physiology of hibernating bears may inform new treatments for metabolic disorders.

A method for assessing real time rates of dissolution and absorption of carbohydrate and other food matrices in human subjects

We prepared pasta of differing physical dimensions but identical chemical composition that contained two monosaccharide probes (lactulose and mannitol) that are absorbed passively and promptly excreted in urine. We showed that the rates of their liberation from the pasta under simulated gastric and small intestinal conditions largely depended upon the rate of digestion of the starchy matrix. We showed, in 20 female subjects, that excretion of mannitol was slower from the pasta with the larger particle size. Hence, after consumption of either the powdered pasta or the simple solution of probe sugars, the mass of mannitol excreted between 1 and 2½ hours was greater than that excreted between 2½ and 4 hours. However these masses did not differ significantly after consumption of the pasta pellets. These differences were not reflected in the concurrent patterns of variation in either serum glucose or insulin taken over 120 minutes, their levels being similar for pasta pellets and powder with their peak values occurring synchronously during the first hour. Hence feeding test foods impregnated with lactulose and mannitol probes provided a reproducible and practical means of assessing the timing of digestion of the carbohydrate matrix and showed that this was more protracted than suggested by post prandial glucose levels. Further, the transit times calculated on a basis of the ratios of the two marker sugars could identify that the prolongation of digestion of larger particles was not accompanied by retention of digesta in particular segments of the gut.

Tctex1d2 Is a Negative Regulator of GLUT4 Translocation and Glucose Uptake

Tctex1d2 (Tctex1 domain containing 2) is an open reading frame that encodes for a functionally unknown protein that contains a Tctex1 domain found in dynein light chain family members. Examination of gene expression during adipogenesis demonstrated a marked increase in Tctex1d2 protein expression that was essentially undetectable in preadipocytes and markedly induced during 3T3-L1 adipocyte differentiation. Tctex1d2 overexpression significantly inhibited insulin-stimulated glucose transporter 4 (GLUT4) translocation and 2-deoxyglucose uptake. In contrast, Tctex1d2 knockdown significantly increased insulin-stimulated GLUT4 translocation and 2-deoxyglucose uptake. However, acute insulin stimulation (up to 30 min) in 3T3-L1 adipocytes with overexpression or knockdown of Tctex1d2 had no effect on Akt phosphorylation, a critical signal transduction target required for GLUT4 translocation. Although overexpression of Tctex1d2 had no significant effect on GLUT4 internalization, Tctex1d2 was found to associate with syntaxin 4 in an insulin-dependent manner and inhibit Doc2b binding to syntaxin 4. In addition, glucose-dependent insulinotropic polypeptide rescued the Tctex1d2 inhibition of insulin-stimulated GLUT4 translocation by suppressing the Tctex1d2-syntaxin 4 interaction and increasing Doc2b-Synatxin4 interactions. Taking these results together, we hypothesized that Tctex1d2 is a novel syntaxin 4 binding protein that functions as a negative regulator of GLUT4 plasma membrane translocation through inhibition of the Doc2b-syntaxin 4 interaction.

Glucose uptake in brown fat cells is dependent on mTOR complex 2-promoted GLUT1 translocation

Brown adipose tissue is the primary site for thermogenesis and can consume, in addition to free fatty acids, a very high amount of glucose from the blood, which can both acutely and chronically affect glucose homeostasis. Here, we show that mechanistic target of rapamycin (mTOR) complex 2 has a novel role in β3-adrenoceptor-stimulated glucose uptake in brown adipose tissue. We show that β3-adrenoceptors stimulate glucose uptake in brown adipose tissue via a signaling pathway that is comprised of two different parts: one part dependent on cAMP-mediated increases in GLUT1 transcription and de novo synthesis of GLUT1 and another part dependent on mTOR complex 2-stimulated translocation of newly synthesized GLUT1 to the plasma membrane, leading to increased glucose uptake. Both parts are essential for β3-adrenoceptor-stimulated glucose uptake. Importantly, the effect of β3-adrenoceptor on mTOR complex 2 is independent of the classical insulin-phosphoinositide 3-kinase-Akt pathway, highlighting a novel mechanism of mTOR complex 2 activation.

4-Hydroxyisoleucine ameliorates fatty acid-induced insulin resistance and inflammatory response in skeletal muscle cells

The 4-hydroxyisoleucine (4-HIL), an unusual amino acid isolated from the seeds of Trigonella foenum-graecum was investigated for its metabolic effects to ameliorate free fatty acid-induced insulin resistance in skeletal muscle cells. An incubation of L6 myotubes with palmitate inhibited insulin stimulated-glucose uptake and -translocation of glucose transporter 4 (GLUT4) to the cell surface. Addition of 4-HIL strongly prevented this inhibition. We then examined the insulin signaling pathway, where 4-HIL effectively inhibited the ability of palmitate to reduce insulin-stimulated phosphorylation of insulin receptor substrate-1 (IRS-1), protein kinase B (PKB/AKT), AKT substrate of 160 kD (AS160) and glycogen synthase kinase 3β (GSK-3β) in L6 myotubes. Moreover, 4-HIL presented strong inhibition on palmitate-induced production of reactive oxygen species (ROS) and associated inflammation, as the activation of NF-κB, JNK1/2, ERK1/2 and p38 MAPK was greatly reduced. 4-HIL also inhibited inflammation-stimulated IRS-1 serine phosphorylation and restored insulin-stimulated IRS-1 tyrosine phosphorylation in the presence of palmitate, leading to enhanced insulin sensitivity. These findings suggested that 4-HIL could inhibit palmitate-induced, ROS-associated inflammation and restored insulin sensitivity through regulating IRS-1 function.

Alterations in insulin-signaling and coagulation pathways in platelets during hyperglycemia-hyperinsulinemia in healthy non-diabetic subject

INTRODUCTION

Diabetes mellitus (DM) is a prothrombotic and proinflammatory state. Hyperglycemia (HG) is encountered even in patients without DM. We have shown that combined HG and hyperinsulinemia (HI) in healthy non-diabetic subjects increased circulating tissue factor (TF) and thrombin generation. To understand the changes in platelet and monocyte pathways induced by combined HG and HI in healthy non-diabetic state, we performed whole genome expression profiling of leukocyte-depleted platelets and monocytes before and after 24 hours of combined HG (glucose ~200mg/dL) and HI by glucose infusion clamp in a healthy non-diabetic subject.

RESULTS

We defined time-dependent differential mRNA expression (24 versus 0 hour fold change (FC) ≥ 2) common to platelets and monocytes. Ingenuity Pathways Analysis revealed alterations in canonical insulin receptor signaling and coagulation pathways. A preliminary group of 9 differentially expressed genes was selected for qRT-PCR confirmation. Platelet 24 hour sample was compared to the 0 hour sample plus 4 controls. Five transcripts in platelets and 6 in monocytes were confirmed. Platelet GSK3B and PTPN1 were upregulated, and STXBP4 was downregulated in insulin signaling, and F3 and TFPI were upregulated in coagulation pathways. Monocyte, PIK3C3, PTPN11 and TFPI were downregulated. Platelet GSKβ3 and PTPN11 protein and TF antigen in platelets and monocytes was increased.

CONCLUSIONS

Even in non-diabetic state, HG+HI for 24 hours induces changes in platelets and monocytes. They suggest downregulation of insulin signaling and upregulation of TF. Further studies are needed to elucidate cellular alterations leading to the prothrombotic and proinflammatory state in DM.

Positive regulations of adipogenesis by Italian ryegrass [Lolium multiflorum] in 3T3-L1 cells

BACK GROUND

Intramuscular fat deposition in the meat animal is relatively new strategy for developing the meat quality. Fat deposition is largely depending on the adipocyte proliferation and differentiation. Therefore, we investigated the effect of chloroform extract of L. multiflorum [CELM] on cell proliferation, lipid accumulation and adipocyte differentiation in 3T3-L1 cells and body weight of mouse.

RESULTS

We identified 6,9-Octadecatrienoic acid, Hexadecanoic acid, 2-hydroxypropanoic acid, butane-2,3-diol and hexane-1,2,3,4,5,6-hexaol in CELM. L. multiflorum extract increased the cell viability, lipid accumulation, cell cycle progression and key transcriptional and secretory factors like PPRAγ2, C/CEBP-α, adiponectin, aP2, GLUT-4, FAS and SREBP-1 mRNA expression as compared with control cells. For in-vivo, mice administered with CELM significantly increased body weight throughout the experiment periods. Further, the identified fatty acids like 3, 6, 9-Octadecatrienoic acid and Hexadecanoic acid was docked with target protein [PPRAγ2] using HEX 6.12. The least binding energy considered as high affinity with target protein. The maximum affinity with the target protein was observed in the Hexadecanoic acid followed by 3, 6, 9-Octadecatrienoic acid. The binding efficacy of Hexadecanoic acid and 3, 6, 9-Octadecatrienoic acid to the active site of PPAR-γ2 may be enhanced the adipocyte differentiations.

CONCLUSION

These findings suggest that CELM stimulates adipogenesis via activating the PPARγ-mediated signaling pathway in adipocyte which could be useful for the development of meat quality in animals.

In vitro and in vivo enhancement of adipogenesis by Italian ryegrass (Lolium multiflorum) in 3T3-L1 cells and mice

Adipogenesis is very much important in improving the quality of meat in animals. The aim of the present study was to investigate the in vitro and in vivo adipogenesis regulation properties of Lolium multiflorum on 3T3-L1 pre-adipocytes and mice. Chemical composition of petroleum ether extract of L. multiflorum (PET-LM) confirmed the presence of fatty acids, such as α-linolenic acid, docosahexaenoic acid, oleic acid, docosatetraenoic acid, and caprylic acid, as the major compounds. PET-LM treatment increased viability, lipid accumulation, lipolysis, cell cycle progression, and DNA synthesis in the cells. PET-LM treatment also augmented peroxysome proliferator activated receptor (PPAR)-γ2, CCAAT/enhancer binding protein-α, adiponectin, adipocyte binding protein, glucose transporter-4, fatty acid synthase, and sterol regulatory element binding protein-1 expression at mRNA and protein levels in differentiated adipocytes. In addition, mice administered with 200 mg/kg body weight PET-LM for 8 weeks showed greater body weight than control mice. These findings suggest that PET-LM facilitates adipogenesis by stimulating PPARγ-mediated signaling cascades in adipocytes which could be useful for quality meat development in animals.

Metabolic syndrome and insulin resistance: underlying causes and modification by exercise training

Metabolic syndrome (MS) is a collection of cardiometabolic risk factors that includes obesity, insulin resistance, hypertension, and dyslipidemia. Although there has been significant debate regarding the criteria and concept of the syndrome, this clustering of risk factors is unequivocally linked to an increased risk of developing type 2 diabetes and cardiovascular disease. Regardless of the true definition, based on current population estimates, nearly 100 million have MS. It is often characterized by insulin resistance, which some have suggested is a major underpinning link between physical inactivity and MS. The purpose of this review is to: (i) provide an overview of the history, causes and clinical aspects of MS, (ii) review the molecular mechanisms of insulin action and the causes of insulin resistance, and (iii) discuss the epidemiological and intervention data on the effects of exercise on MS and insulin sensitivity.

SDF7, a group of Scoparia dulcis Linn. derived flavonoid compounds, stimulates glucose uptake and regulates adipocytokines in 3T3-F442a adipocytes

ETHNOPHARMACOLOGY RELEVANCE

Adipocytes are major tissues involved in glucose uptake second to skeletal muscle and act as the main adipocytokines mediator that regulates glucose uptake mechanism and cellular differentiation. The objective of this study were to examine the effect of the SDF7, which is a fraction consists of four flavonoid compounds (quercetin: p-coumaric acid: luteolin: apigenin=8: 26: 1: 3) from Scoparia dulcis Linn., on stimulating the downstream components of insulin signalling and the adipocytokines expression on different cellular fractions of 3T3-F442a adipocytes.

MATERIAL AND METHODS

Morphology and lipid accumulation of differentiated 3T3-F442a adipocytes by 100 nM insulin treated with different concentrations of SDF7 and rosiglitazone were examined followed by the evaluation of glucose uptake activity expressions of insulin signalling downstream components (IRS-1, PI3-kinase, PKB, PKC, TC10 and GLUT4) from four cellular fractions (plasma membrane, cytosol, high density microsome and low density microsome). Next, the expression level of adipocytokines (TNF-α, adiponectin and leptin) and immunoblotting of treated 3T3-F442 adipocytes was determined at 30 min and 480 min. Glucose transporter 4 (GLUT4) translocation of 3T3-F442a adipocytes membrane was also determined. Lastly, mRNA expression of adiponectin and PPAR-γ of 3T3-F442a adipocytes were induced and compared with basal concentration.

RESULTS

It was found that SDF7 was able to induce adipocytes differentiation with great extends of morphological changes, lipid synthesis and lipid stimulation in vitro. SDF7 stimulation of glucose transport on 3T3-F442a adipocytes are found to be dose independent, time-dependent and plasma membrane GLUT4 expression-dependent. Moreover, SDF7 are observed to be able to suppress TNF-α and leptin expressions that were mediated by 3T3-F442a adipocytes, while stimulated adiponectin secretion on the cells. There was a significant expression (p<0.01) of protein kinase C and small G protein TC10 on 3T3-F442a adipocytes upon treatment with SDF7 as compared to the control. SDF7 was also found to be effective in stimulating adiponectin and PPAR-γ mRNA upregulation at 50 µg/ml.

CONCLUSION

SDF7 exhibited good lipogenesis, adiponectinesis and glucose uptake stimulatory properties on 3T3-F442a adipocytes.

Effects of Combination of Thiazolidinediones with Melatonin in Dexamethasone-induced Insulin Resistance in Mice

In type 2 Diabetes, oxidative stress plays an important role in development and aggregation of insulin resistance. In the present study, long term administration of the dexamethasone led to the development of insulin resistance in mice. The effect of thiazolidinediones pioglitazone and rosiglitazone, with melatonin on dexamethasone-induced insulin resistance was evaluated in mice. Insulin resistant mice were treated with combination of pioglitazone (10 mg/kg/day, p.o.) or rosiglitazone (5 mg/kg/day, p.o.) with melatonin 10 mg/kg/day p.o. from day 7 to day 22. In the biochemical parameters, the serum glucose, triglyceride levels were significantly lowered (P<0.05) in the combination groups as compared to dexamethasone treated group as well as with individual groups of pioglitazone, rosiglitazone, and melatonin. There was also, significant increased (P<0.05) in the body weight gain in combination treated groups as compared to dexamethasone as well as individual groups. The combination groups proved to be effective in normalizing the levels of superoxide dismutase, catalase, glutathione reductase and lipid peroxidation in liver homogenates may be due to antioxidant effects of melatonin and decreased hyperglycemia induced insulin resistance by thiazolidinediones. The glucose uptake in the isolated hemidiaphragm of mice was significantly increased in combination treated groups (PM and RM) than dexamethasone alone treated mice as well as individual (pioglitazone, rosiglitazone, melatonin) treated groups probably via increased in expression of GLUT-4 by melatonin and thiazolidinediones as well as increased in insulin sensitivity by thiazolidinediones. Hence, it can be concluded that combination of pioglitazone and rosiglitazone, thiazolidinediones, with melatonin may reduces the insulin resistance via decreased in oxidative stress and control on hyperglycemia.

Hesperetin impairs glucose uptake and inhibits proliferation of breast cancer cells

The flavanone hesperetin is known to decrease basal glucose uptake, although the inhibitory mechanism is largely unknown. Here, we used MDA-MB-231 breast cancer cells to investigate the molecular pathways affected by hesperetin. The results indicate that the suppression of glucose uptake is caused by the down-regulation of glucose transporter 1 (GLUT1). Hesperetin was also found to inhibit insulin-induced glucose uptake through impaired cell membrane translocation of glucose transporter 4 (GLUT4). In addition, the phosphorylation of the insulin receptor-beta subunit (IR-beta) and Akt was suppressed. Hesperetin also decreased cellular proliferation, which is likely due to the inhibition of glucose uptake. Cancer cells are highly dependent on glucose and hesperetin may, therefore, have potential application as an anticancer agent.

Protein arginine methyltransferase 1 regulates hepatic glucose production in a FoxO1-dependent manner

Postprandial insulin plays a critical role in suppressing hepatic glucose production to maintain euglycemia in mammals. Insulin-dependent activation of protein kinase B (Akt) regulates this process, in part, by inhibiting FoxO1-dependent hepatic gluconeogenesis by direct phosphorylation and subsequent cytoplasmic exclusion. Previously, it was demonstrated that protein arginine methyltransferase 1 (PRMT1)-dependent arginine modification of FoxO1 interferes with Akt-dependent phosphorylation, both in cancer cells and in the Caenorhabditis elegans model, suggesting that this additional modification of FoxO1 might be critical in its transcriptional activity. In this study, we attempted to directly test the effect of arginine methylation of FoxO1 on hepatic glucose metabolism. The ectopic expression of PRMT1 enhanced messenger RNA levels of FoxO1 target genes in gluconeogenesis, resulting in increased glucose production from primary hepatocytes. Phosphorylation of FoxO1 at serine 253 was reduced with PRMT1 expression, without affecting the serine 473 phosphorylation of Akt. Conversely, knockdown of PRMT1 promoted an inhibition of FoxO1 activity and hepatic gluconeogenesis by enhancing the phosphorylation of FoxO1. In addition, genetic haploinsufficiency of Prmt1 reduced hepatic gluconeogenesis and blood-glucose levels in mouse models, underscoring the importance of this factor in hepatic glucose metabolism in vivo. Finally, we were able to observe an amelioration of the hyperglycemic phenotype of db/db mice with PRMT1 knockdown, showing a potential importance of this protein as a therapeutic target for the treatment of diabetes.

CONCLUSION

Our data strongly suggest that the PRMT1-dependent regulation of FoxO1 is critical in hepatic glucose metabolism in vivo.

Downregulation of vitamin C transporter SVCT-2 in doxorubicin-induced cardiomyocyte injury

Vitamin C (Vit C) has been shown to be protective against doxorubicin (Dox)-induced cardiotoxicity. However, Vit C uptake into cardiomyocytes is poorly understood. Furthermore, whether the antioxidant enzyme reserve is enhanced by Vit C is also not known. The present study investigated an influence of Dox on Vit C transporters, expression of endogenous antioxidant reserve as well as enzymes, oxidative stress, and apoptosis in isolated cardiomyocytes. Cardiomyocytes isolated from adult Sprague-Dawley rats were exposed to control (culture medium 199 alone), Dox (10 μM), Vit C (25 μM), and Vit C + Dox for 24 h. Vit C transporter expression and localization, oxidative stress, antioxidant enzymes, and apoptosis were studied. Expression and localization of sodium-dependent vitamin C transporter-2 (SVCT-2) in the sarcolemma was reduced by Dox, but Vit C supplementation was able to blunt this change. There was a decrease in the expression of antioxidant enzymes glutathione peroxidase (GPx), catalase, and Cu/Zn superoxide dismutase (SOD) due to Dox, but only GPx expression was completely prevented and Cu/Zn SOD was partially rescued by Vit C. Dox-induced decrease in antioxidant reserve and increase in oxidative stress were partially mitigated by Vit C. Dox-induced apoptosis was ameliorated by Vit C. It is suggested that cardioprotection offered by Vit C in Dox-induced cardiomyopathy may involve an upregulation of SVCT-2 transporter followed by a reduction in oxidative stress as well as blunting of cardiomyocyte injury.

Taurine exerts hypoglycemic effect in alloxan-induced diabetic rats, improves insulin-mediated glucose transport signaling pathway in heart and ameliorates cardiac oxidative stress and apoptosis

Hyperlipidemia, inflammation and altered antioxidant profiles are the usual complications in diabetes mellitus. In the present study, we investigated the therapeutic potential of taurine in diabetes associated cardiac complications using a rat model. Rats were made diabetic by alloxan (ALX) (single i.p. dose of 120mg/kg body weight) and left untreated or treated with taurine (1% w/v, orally, in water) for three weeks either from the day of ALX exposure or after the onset of diabetes. Animals were euthanized after three weeks. ALX-induced diabetes decreased body weight, increased glucose level, decreased insulin content, enhanced the levels of cardiac damage markers and altered lipid profile in the plasma. Moreover, it increased oxidative stress (decreased antioxidant enzyme activities and GSH/GSSG ratio, increased xanthine oxidase enzyme activity, lipid peroxidation, protein carbonylation and ROS generation) and enhanced the proinflammatory cytokines levels, activity of myeloperoxidase and nuclear translocation of NFκB in the cardiac tissue of the experimental animals. Taurine treatment could, however, result to a decrease in the elevated blood glucose and proinflammatory cytokine levels, diabetes-evoked oxidative stress, lipid profiles and NFκB translocation. In addition, taurine increased GLUT 4 translocation to the cardiac membrane by enhanced phosphorylation of IR and IRS1 at tyrosine and Akt at serine residue in the heart. Results also suggest that taurine could protect cardiac tissue from ALX induced apoptosis via the regulation of Bcl2 family and caspase 9/3 proteins. Taken together, taurine supplementation in regular diet could play a beneficial role in regulating diabetes and its associated complications in the heart.

Enhanced energy expenditure, glucose utilization, and insulin sensitivity in VAMP8 null mice

OBJECTIVE

Previous studies have demonstrated that the VAMP8 protein plays a complex role in the control of granule secretion, transport vesicle trafficking, phagocytosis, and endocytosis. The present study was aimed to investigate the role of VAMP8 in mediating GLUT4 trafficking and therefore insulin action in mice.

RESEARCH DESIGN AND METHODS

Physiological parameters were measured using Oxymax indirect calorimetry system in 12-week-old VAMP8 null mice. Dynamic analysis of glucose homeostasis was assessed using euglycemic-hyperinsulinemic clamp coupled with tracer radioactively labeled 2-deoxyglucose. Insulin stimulated GLUT4 protein expressions on muscle cell surface were examined by immunofluorescence microscopy.

RESULTS

VAMP8 null mice display reduced adiposity with increased energy expenditure despite normal food intake and reduced spontaneous locomotor activity. In parallel, the VAMP8 null mice also had fasting hypoglycemia (84 ± 11 vs. 115 ± 4) and enhanced glucose tolerance with increased insulin sensitivity due to increases in both basal and insulin-stimulated glucose uptake in skeletal muscle (0.19 ± 0.04 vs. 0.09 ± 0.01 mmol/kg/min during basal, 0.6 ± 0.04 vs. 0.31 ± 0.06 mmol/kg/min during clamp in red-gastrocnemius muscle, P < 0.05). Consistent with a role for VAMP8 in the endocytosis of the insulin-responsive GLUT4, sarcolemma GLUT4 protein levels were increased in both the basal and insulin-stimulated states without any significant change in the total amount of GLUT4 protein or related facilitative glucose transporters present in skeletal muscle, GLUT1, GLUT3, and GLUT11.

CONCLUSIONS

These data demonstrate that, in the absence of VAMP8, the relative subcellular distribution of GLUT4 is altered, resulting in increased sarcolemma levels that can account for increased glucose clearance and insulin sensitivity.

Copper promotes the trafficking of the amyloid precursor protein

Accumulation of the amyloid β peptide in the cortical and hippocampal regions of the brain is a major pathological feature of Alzheimer disease. Amyloid β peptide is generated from the sequential protease cleavage of the amyloid precursor protein (APP). We reported previously that copper increases the level of APP at the cell surface. Here we report that copper, but not iron or zinc, promotes APP trafficking in cultured polarized epithelial cells and neuronal cells. In SH-SY5Y neuronal cells and primary cortical neurons, copper promoted a redistribution of APP from a perinuclear localization to a wider distribution, including neurites. Importantly, a change in APP localization was not attributed to an up-regulation of APP protein synthesis. Using live cell imaging and endocytosis assays, we found that copper promotes an increase in cell surface APP by increasing its exocytosis and reducing its endocytosis, respectively. This study identifies a novel mechanism by which copper regulates the localization and presumably the function of APP, which is of major significance for understanding the role of APP in copper homeostasis and the role of copper in Alzheimer disease.