Regulation Of Insulin Receptors Research Articles

News on the molecular regulation and function of hepatic low-density lipoprotein receptor and LDLR-related protein 1.

Clearing of atherogenic lipoprotein particles by the liver requires hepatic low-density lipoprotein receptor (LDLR) and LDLR-related protein 1 (LRP1). This review highlights recent studies that have expanded our understanding of the molecular regulation and metabolic functions of LDLR and LRP1 in the liver. Various proteins orchestrate the intracellular trafficking of LDLR and LRP1. After internalization, the receptors are redirected via recycling endosomes to the cell surface. Several new endocytic proteins that facilitate the endosomal trafficking of LDLR and consequently the clearance of circulating LDL cholesterol have recently been reported. Mutations in some of these proteins cause hypercholesterolemia in human. In addition, LRP1 controls cellular cholesterol efflux by modulating the expression of ABCA1 and ABCG1, and hepatic LRP1 protects against diet-induced hepatic insulin resistance and steatosis through the regulation of insulin receptor trafficking. LDLR and LRP1 have prominent roles in cellular and organismal cholesterol homeostasis. Their functioning, including their trafficking in the cell, is controlled by numerous proteins. Comprehensive studies into the molecular regulation of LDLR and LRP1 trafficking have advanced our fundamental understanding of cholesterol homeostasis, and these insights may lead to novel therapeutic strategies for atherosclerosis, hyperlipidemia and insulin resistance in the future.

Shen-Yuan-Dan Capsule Inhibiting Inflammatory Reaction by Regulating Insulin Receptor Substrate 1/PI3K/Akt/NF-κB Signaling Pathway in Apoliprotein E Knockout Mice Fed with a High-Fat Diet.

Shen-Yuan-Dan Capsule (SYDC), a traditional Chinese medicine, is proposed to have the capacity to prevent angina pectoris. However, the effects and the related mechanisms of SYDC on atherosclerosis (AS) are still unknown. This study was designed to investigate the effects of SYDC on AS and inflammatory reaction in the apoliprotein E-knockout (ApoE-/-) mice fed with a high-fat diet. Thirty eight-week-old male ApoE-/- mice were randomly divided into three groups (n = 10) 6 weeks after being fed with a high-fat diet: the control group, the lipitor group, and the SYDC group. The hearts were collected for hematoxylin and eosin (HE) or Van Gieson (VG) staining, and the aortas were collected for quantitative reverse transcription polymerase chain reaction (RT-PCR) and western-blotting. The data showed that the levels of total cholesterol (TC), triglyceride (TG), low-density lipoprotein cholesterol (LDL-C), atherosclerotic indexes (AI) and the corrected areas of atherosclerotic plaque of the mice on SYDC group were significantly decreased compared with those of the mice in the control group (p < 0.01, p < 0.05). SYDC can significantly increase collagen proportion in plaques as compared to the untreated mice (p < 0.01). In addition, the messenger ribonucleic acid (mRNA) expressions of insulin receptor substrate 1 (IRS-1), PI3K, Akt, NF-κB and tumor necrosis factor-α (TNF-α) in the mice fed with a high-fat diet were significantly reduced by SYDC (p < 0.05, p < 0.01). SYDC can exert an anti-atherosclerotic effect on ApoE-/- mice fed with a high-fat diet. The action mechanism of SYDC was attributed to its ability to inhibit inflammatory reaction by regulating IRS-1/PI3K/Akt/NF-κB signaling pathway.

Alleviating VLDL overproduction is an important mechanism for Laminaria japonica polysaccharide to inhibit atherosclerosis in LDLr-/- mice with diet-induced insulin resistance.

The overproduction of very low density lipoprotein (VLDL) is an important cause for initiation and development of atherosclerosis, which is highly associated with insulin signaling. The aim of this work is to verify whether the inhibition of VLDL overproduction is an underlying mechanism for a Laminaria japonica polysaccharide (LJP61A (where LJP is L. japonica)) to resist atherosclerosis. LJP61A (50 and 200 mg/kg/day) was orally administered to a high-fat diet (HFD)-fed LDL receptor deficient mice for 14 weeks. LJP61A significantly attenuated insulin resistance, hepatic steatosis, atherosclerosis, and dyslipidemia. Meanwhile, LJP61A ameliorated the HFD-induced impairment of hepatic insulin signaling and reduced VLDL overproduction via regulating the expression of genes involved in the assembly and secretion of VLDL. To study the possibility that the inhibition of mammalian target of rapamycin complex 1 and stimulation of Forkhead box protein O1 (Foxo1) nuclear exclusion is a result of LJP61A via regulating insulin signaling, LJP61A was administrated to HepG2 cells in the presence or absence of mTOR inhibitor and Foxo1 inhibitor. Results showed that LJP61A alleviated VLDL overproduction via regulating insulin receptor substrate mediated phosphatidylinositide 3-kinase AKT mammalian target of rapamycin complex 1 and phosphatidylinositide 3-kinase AKT-Foxo1 signaling pathways. These results suggested that LJP61A ameliorated HFD-induced insulin resistance to attenuate VLDL overproduction possibly via regulating insulin signaling, leading to the inhibition of atherosclerosis.

Phosphorylation of clustered serine residues in the N-terminus of BPS domain negatively regulates formation of the complex between human Grb14 and insulin receptor.

Growth factor receptor-bound protein 14 (Grb14) is a negative regulator of insulin receptor (IR) and is involved in a negative feedback mechanism of insulin signaling. Grb14 associates with IR and inhibits its tyrosine kinase activity through the between pleckstrin homology and Src homology-2 (BPS) domain. We previously reported that the pharmacological inhibition and knockdown of glycogen synthase kinase-3 (GSK-3) facilitates the insulin-induced complex formation of human Grb14 (hGrb14) and IR, suggesting that GSK-3 suppresses hGrb14 recruitment to IR. This study further investigated a functional phosphorylation of the serine residues in hGrb14 BPS domain, identified as putative GSK-3 targets to verify an effect of GSK-3 on the hGrb14-IR complex formation. In vitro kinase assay using the motif-derived peptides showed that the serine residues located in N-terminal (Ser358, Ser362 and Ser366) and C-terminal (Ser419 and Ser423) regions of the BPS domain were phosphorylated by GSK-3. Co-immunoprecipitation and yeast two-hybrid (Y2H) experiments suggested that the negative charges genetically introduced on the Ser358, Ser362 and Ser366 suppressed the association of hGrb14 to IR. Surface plasmon resonance experiment gave Kd values of 8 nM for recombinant hGrb14 with respect to the interaction with IR β-subunit, and this affinity was lost after the replacements of the Ser358, Ser362 and Ser366 with glutamic acid residues. Y2H experiment with the BPS domain alone; however, did not show any difference owing to the same mutations. It is therefore evident that the N-terminus of the BPS domain plays an important role in the regulation of hGrb14-IR complex formation through phosphorylation, in addition to other domains.

Mesenchymal stem cell-conditioned medium promotes MDA-MB-231 cell migration and inhibits A549 cell migration by regulating insulin receptor and human epidermal growth factor receptor 3 phosphorylation.

Various in vitro and in vivo studies have linked mesenchymal stem cells (MSCs) with cancer, but little is known about the effect of MSCs on tumor progression. The present study aimed to analyze the role of the MSCs from different tissues, consisting of human bone marrow, adipose and the umbilical cord tissues, and the heterogeneity of tumors in tumor progression. By collecting the culture supernatants of MSCs as MSC-conditioned media (CMs), the present study found that MSC-CM produces no significant effect on the proliferation of MDA-MB-231 and A549 tumor cells. The migration of MDA-MB-231 cells was enhanced upon incubation with MSC-CM, while that of A549 cells was inhibited. Furthermore, the phosphorylation of insulin receptors (IRs) was upregulated in MSC-CM-treated MDA-MB-231 cells, while in MSC-CM-treated A549 cells, the phosphorylation of human epidermal growth factor receptor 3 (Her3) was downregulated. Taken together, the findings suggest that the phosphorylation of IR and Her3 may contribute to the discrepant effects of MSC-CM on the migration of the 2 cell lines.

The LDL Receptor-Related Protein 1: At the Crossroads of Lipoprotein Metabolism and Insulin Signaling.

The metabolic syndrome is an escalating worldwide public health concern. Defined by a combination of physiological, metabolic, and biochemical factors, the metabolic syndrome is used as a clinical guideline to identify individuals with a higher risk for type 2 diabetes and cardiovascular disease. Although risk factors for type 2 diabetes and cardiovascular disease have been known for decades, the molecular mechanisms involved in the pathophysiology of these diseases and their interrelationship remain unclear. The LDL receptor-related protein 1 (LRP1) is a large endocytic and signaling receptor that is widely expressed in several tissues. As a member of the LDL receptor family, LRP1 is involved in the clearance of chylomicron remnants from the circulation and has been demonstrated to be atheroprotective. Recently, studies have shown that LRP1 is involved in insulin receptor trafficking and regulation and glucose metabolism. This review summarizes the role of tissue-specific LRP1 in insulin signaling and its potential role as a link between lipoprotein and glucose metabolism in diabetes.

High fructose-mediated attenuation of insulin receptor signaling does not affect PDGF-induced proliferative signaling in vascular smooth muscle cells

Insulin resistance is associated with accelerated atherosclerosis. Although high fructose is known to induce insulin resistance, it remains unclear as to how fructose regulates insulin receptor signaling and proliferative phenotype in vascular smooth muscle cells (VSMCs), which play a major role in atherosclerosis. Using human aortic VSMCs, we investigated the effects of high fructose treatment on insulin receptor substrate-1 (IRS-1) serine phosphorylation, insulin versus platelet-derived growth factor (PDGF)-induced phosphorylation of Akt, S6 ribosomal protein, and extracellular signal-regulated kinase (ERK), and cell cycle proteins. In comparison with PDGF (a potent mitogen), neither fructose nor insulin enhanced VSMC proliferation and cyclin D1 expression. d-[14C(U)]fructose uptake studies revealed a progressive increase in fructose uptake in a time-dependent manner. Concentration-dependent studies with high fructose (5–25mM) showed marked increases in IRS-1 serine phosphorylation, a key adapter protein in insulin receptor signaling. Accordingly, high fructose treatment led to significant diminutions in insulin-induced phosphorylation of downstream signaling components including Akt and S6. In addition, high fructose significantly diminished insulin-induced ERK phosphorylation. Nevertheless, high fructose did not affect PDGF-induced key proliferative signaling events including phosphorylation of Akt, S6, and ERK and expression of cyclin D1 protein. Together, high fructose dysregulates IRS-1 phosphorylation state and proximal insulin receptor signaling in VSMCs, but does not affect PDGF-induced proliferative signaling. These findings suggest that systemic insulin resistance rather than VSMC-specific dysregulation of insulin receptor signaling by high fructose may play a major role in enhancing atherosclerosis and neointimal hyperplasia.

Metabolism: MAD interactions with insulin receptor.

Proteins of the mitotic checkpoint regulate insulin receptor internalization through clathrin-mediated endocytosis, thereby modulating insulin signalling and systemic glucose metabolism.

Abstract 175: High Glucose Pre-treatment Suppresses Rankl-induced Macrophage Activation via Down-regulation of Glucose Uptake Through Decreased Insulin Receptor and Insulin Receptor Substrate 1 Expression

Background: Previous studies have suggested that the pathogenesis of abdominal aortic aneurysm (AAA) is associated with the local proteinases activation and the degradation of matrix proteins by matrix metalloproteinases (MMPs) produced from activated macrophages. One of the major features of diabetes mellitus (DM)-induced vascular pathology is severe arterial calcification. Although recent large epidemiological studies have shown that DM is an independent negative risk factor for AAA, the effects of hyperglycemia on macrophages are still controversial. We have hypothesized that hyperglycemia suppresses macrophage activation through altered glucose transportation. Methods and Results: RAW264.7 cells, a murine macrophage cell line were cultured under high glucose conditions (HG group, 15.5 mM glucose) or normal glucose conditions (NG group, 5.5 mM glucose) for 7days. Cells from both groups were then transferred to normal glucose condition and stimulated with recombinant murine sRANKL. Macrophage activation, confirmed by TRAP staining positive cells, and MMP-9 expression were induced in NG group but were significantly suppressed in HG group. Glucose uptake was increased during osteoclastogenesis in NG group but not in HG group. To elucidate the underlying mechanism for this observation, we studied glucose transporters (GLUTs). Although GLUT-1 and GLUT-3 expression were not affected in either groups, the membrane translocation of GLUT-1 was significantly increased in NG group during macrophage activation but not in HG group. Insulin receptor and insulin receptor substrate-1 (IRS-1) mRNA, known to stimulate membrane translocation of GLUT, were both decreased in HG group compared to NG group. Conclusions: Our results showed hyperglycemia suppresses macrophage activation. Our results also indicated that under normal conditions, recombinant murine sRANKL increases glucose uptake during macrophage activation. In contrast, this increase is impaired in high glucose pre-treated cells. We conclude that this impairment is due, in part, to suppressed GLUT-1 membrane translocation through down regulation of insulin receptor and IRS-1

High Glucose Concentration Attenuates Insulin‐Stimulated Protein Kinase B Levels In Cultured Astrocytes

BACKGROUNDGlucoregulatory abnormalities have been implicated to contribute to the pathophysiology of Alzheimer‐type dementia. The brain requires insulin for supply of energy critical for processing of memory and cognition. Insulin acts on the insulin receptor initiating signaling cascades that activate protein kinase B (Akt) through phosphorylation (p‐Akt) in cultured astrocytes. However, it is not yet clear whether the insulin induced production of p‐Akt could be attenuated by high glucose concentrations through stimulation of an inhibitory signaling pathway involving activation of protein kinase C (PKC).OBJECTIVEThe objective of our study is to examine the phosphorylation of Akt in cultured neonatal astrocytes following insulin stimulation and to determine if this response could be attenuated by culturing astrocytes in high glucose media via activation of PKC.METHODSNeonatal astrocyte cultures were derived from rat hippocampus and cultured for three passages in normal (5.5 mM) or high glucose (25 mM) media. Astrocyte cultures were stimulated with increasing concentrations of insulin (10−11 to 10−6 M) and Western immunoblotting analysis was used to determine protein levels of p‐Akt and insulin receptor. Protein levels of PKC isoforms (alpha, gamma, and delta) were determined in whole cell lysates from separate astrocyte cultures grown in normal or high glucose media.RESULTSInsulin‐induced a dose‐dependent increase in p‐Akt protein level in astrocytes cultured in normal glucose. However, insulin stimulation of astrocytes cultured in high glucose media resulted in an attenuated protein level of p‐Akt (100 nM insulin: 3.6 ± 1.0 vs. 8.9 ± 1.6 fold increase compared to control), requiring more insulin to increase the protein levels of p‐Akt (interaction effect: p = 0.024). The protein levels of insulin receptor in cultured astrocytes also increased in response to stimulation with insulin. Astrocytes cultured in high glucose media exhibited increased protein levels of PKC alpha (1.5 fold increase, p &lt; 0.05) and gamma (2 fold increase, p &lt; 0.05) but not of the PKC delta isoform compared to astrocytes cultured in normal glucose media.CONCLUSIONSInsulin‐dependent intracellular signaling involving phosphorylation of Akt is attenuated in astrocytes cultured in high glucose media. Astrocytes respond to increased environmental glucose with isoform specific increases in PKC protein levels which may have resulted in negative regulation of astrocyte insulin receptor signaling.Support or Funding InformationFunding from NIH (NHLBI) T35 HL072483, R01 HL033833 and HL105997 and the Veterans Administration Research Career Scientist Award.

MiR-322 regulates insulin signaling pathway and protects against metabolic syndrome-induced cardiac dysfunction in mice

We identified murine miR-322, orthologous to human miR-424, as a new regulator of insulin receptor, IGF-1 receptor and sirtuin 4 mRNA in vitro and in vivo in the heart and found that miR-322/424 is highly expressed in the heart of mice. C57Bl/6N mice fed 10weeks of high fat diet (HFD) presented signs of cardiomyopathy and a stable miR-322 cardiac level while cardiac function was slightly affected in 11week-old ob/ob which overexpressed miR-322. We thus hypothesized that mmu-miR-322 could be protective against cardiac consequences of hyperinsulinemia and hyperlipidemia. We overexpressed or knocked-down mmu-miR-322 using AAV9 and monitored cardiac function in wild-type C57Bl/6N mice fed a control diet (CD) or a HFD and in ob/ob mice. The fractional shortening progressively declined while the left ventricle systolic diameter increased in HFD mice infected with an AAVcontrol or with an AAVsponge (decreasing miR-322 bioavailability) but also in ob/ob mice infected with AAVsponge. Similar observations were also found in CD-fed mice infected with AAVsponge. On the contrary over-expressing miR-322 with AAVmiR-322 was efficient in protecting the heart from HFD effects in C57Bl/6N mice. This cardioprotection could be associated with the regulation of identified targets IGF1R, INSR and CD1, a decrease in insulin signaling pathway and an enrichment of genes involved in mitochondrial function and fatty acid oxidation as demonstrated by transcriptome analysis. Altogether, these results emphasize miR-322 as a new potential therapeutic target against cardiac consequences of metabolic syndrome, which represents an increasing burden in the western countries.

Two triterpeniods from Cyclocarya paliurus (Batal) Iljinsk (Juglandaceae) promote glucose uptake in 3T3-L1 adipocytes: The relationship to AMPK activation

PurposeThe current study investigated the efficacy of Cyclocarya paliurus chloroform extract (CPEC) and its two specific triterpenoids (cyclocaric acid B and cyclocarioside H) on the regulation of glucose disposal and the underlying mechanisms in 3T3-L1 adipocytes. MethodsMice and adipocytes were stimulated by macrophages-derived conditioned medium (Mac-CM) to induce insulin resistance. CPEC was evaluated in mice for its ability by oral glucose tolerance test (OGTT) and insulin tolerance test (ITT). To investigate the hypoglycemic mechanisms of CPEC and its two triterpenoids, glucose uptake, AMP-activated protein kinase (AMPK) activation, inhibitor of NF-κB kinase β (IKKβ) phosphorylation and insulin signaling transduction were detected in 3T3-L1 adipocytes using 2-NBDG uptake assay and Western blot analysis. ResultsMac-CM, an inflammatory stimulus which induced the glucose and insulin intolerance, increased phosphorylation of IKKβ, reduced glucose uptake and impaired insulin sensitivity. CPEC and two triterpenoids improved glucose consumption and increased AMPK phosphorylation under basal and inflammatory conditions. Moreover, CPEC and its two triterpenoids not only enhanced glucose uptake in an insulin-independent manner, but also restored insulin-mediated protein kinase B (Akt) phosphorylation by reducing the activation of IKKβ and regulating insulin receptor substrate-1 (IRS-1) serine/tyrosine phosphorylation. These beneficial effects were attenuated by AMPK inhibitor compound C, implying that the effects may be associated with AMPK activation. ConclusionsCPEC and its two triterpenoids promoted glucose uptake in the absence of insulin, as well as ameliorated IRS-1/PI3K/Akt pathway by inhibiting inflammation. These effects were related to the regulation of AMPK activity.

Alpha-synuclein overexpression negatively regulates insulin receptor substrate 1 by activating mTORC1/S6K1 signaling

Alpha-synuclein (α-Syn) is a major component of Lewy bodies, a pathological feature of Parkinson's and other neurodegenerative diseases collectively known as synucleinopathies. Among the possible mechanisms of α-Syn-mediated neurotoxicity is interference with cytoprotective pathways such as insulin signaling. Insulin receptor substrate (IRS)-1 is a docking protein linking IRs to downstream signaling pathways such as phosphatidylinositol 3-kinase/Akt and mammalian target of rapamycin (mTOR)/ribosomal protein S6 kinase (S6K)1; the latter exerts negative feedback control on insulin signaling, which is impaired in Alzheimer's disease. Our previous study found that α-Syn overexpression can inhibit protein phosphatase (PP)2A activity, which is involved in the protective mechanism of insulin signaling. In this study, we found an increase in IRS-1 phosphorylation at Ser636 and decrease in tyrosine phosphorylation, which accelerated IRS-1 turnover and reduced insulin-Akt signaling in α-Syn-overexpressing SK-N-SH cells and transgenic mice. The mTOR complex (C)1/S6K1 blocker rapamycin inhibited the phosphorylation of IRS-1 at Ser636 in cells overexpressing α-Syn, suggesting that mTORC1/S6K1 activation by α-Syn causes feedback inhibition of insulin signaling via suppression of IRS-1 function. α-Syn overexpression also inhibited PP2A activity, while the PP2A agonist C2 ceramide suppressed both S6K1 activation and IRS-1 Ser636 phosphorylation upon α-Syn overexpression. Thus, α-Syn overexpression negatively regulated IRS-1 via mTORC1/S6K1 signaling while activation of PP2A reverses this process. These results provide evidence for a link between α-Syn and IRS-1 that may represent a novel mechanism for α-Syn-associated pathogenesis.

Demonstration of a direct interaction between β2-adrenergic receptor and insulin receptor by BRET and bioinformatics.

Glucose metabolism is under the cooperative regulation of both insulin receptor (IR) and β2-adrenergic receptor (β2AR), which represent the receptor tyrosine kinases (RTKs) and seven transmembrane receptors (7TMRs), respectively. Studies demonstrating cross-talk between these two receptors and their endogenous coexpression have suggested their possible interactions. To evaluate the effect of IR and prospective heteromerization on β2AR properties, we showed that IR coexpression had no effect on the ligand binding properties of β2AR; however, IR reduced β2AR surface expression and accelerated its internalization. Additionally, both receptors displayed a similar distribution pattern with a high degree of colocalization. To test the possible direct interaction between β2AR and IR, we employed quantitative BRET2 saturation and competition assays. Saturation assay data suggested constitutive β2AR and IR homo- and heteromerization. Calculated acceptor/donor (AD50) values as a measure of the relative affinity for homo- and heteromer formation differed among the heteromers that could not be explained by a simple dimer model. In heterologous competition assays, a transient increase in the BRET2 signal with a subsequent hyperbolical decrease was observed, suggesting higher-order heteromer formation. To complement the BRET2 data, we employed the informational spectrum method (ISM), a virtual spectroscopy method to investigate protein-protein interactions. Computational peptide scanning of β2AR and IR identified intracellular domains encompassing residues at the end of the 7th TM domain and C-terminal tail of β2AR and a cytoplasmic part of the IR β chain as prospective interaction domains. ISM further suggested a high probability of heteromer formation and homodimers as basic units engaged in heteromerization. In summary, our data suggest direct interaction and higher-order β2AR:IR oligomer formation, likely comprising heteromers of homodimers.

SOCS proteins regulate insulin receptor substrate (IRS)-2 activation in response to IL-4 and 13 in monocytes and macrophages (CCR5P.247)

Abstract Allergic asthma is a chronic lung disease driven by Th2 cytokines IL-4 and -13. In macrophages, IL-4/13 bind IL-4 receptors, which signal through IRS-2/STAT6, inducing M2 differentiation. We found that IL-4/13 stimulation of human monocytes/mouse macrophages leads to rapid tyrosine phosphorylation (pY) of IRS-2, peaking at 60min and returning to baseline by 150min. Mechanisms that regulate IRS-2 activity and M2 differentiation are not understood. Based on rapid de-phosphorylation of IRS-2, we hypothesized that SOCS proteins regulate IL-4/13 induced IRS-2 activation, thereby limiting M2s. To address this, we tracked the kinetics of SOCS induction following IL-4/13 exposure and found that SOCS1 and CIS are highly induced in human monocytes and mouse macrophages, respectively, while SOCS3 is only moderately induced. By co-immunoprecipitation, we found that SOCS1 and CIS complex with IRS-2 in response to IL-4/13. Furthermore, we found that siRNA knockdown of SOCS1 and CIS prolonged IRS-2 pY and enhanced human and mouse M2 differentiation respectively. Since SOCS proteins complex with ubiquitin ligases to promote proteasomal degradation, we examined the effect of proteasome inhibitors on IL-4/13-induced IRS-2 pY. Proteasome inhibition prolonged IRS-2 pY and enhanced M2 gene expression. These findings identify SOCS1 in human and CIS in mouse macrophages as critical negative regulators of IL-4/13-induced IRS-2 activity/M2 differentiation and are novel therapeutic targets for asthma.

Penostatin Derivatives, a Novel Kind of Protein Phosphatase 1B Inhibitors Isolated from Solid Cultures of the Entomogenous Fungus Isaria tenuipes

Protein tyrosine phosphatase 1B (PTP1B) is implicated as a negative regulator of insulin receptor (IR) signaling and a potential drug target for the treatment of type II diabetes and other associated metabolic syndromes. Therefore, small molecular inhibitors of PTP1B can be considered as an attractive approach for the design of new therapeutic agents of type II diabetes diseases. In a continuing search for new protein phosphatase inhibitors from fungi, we have isolated a new compound, named penostatin J (1), together with three known ones, penostatin C (2), penostatin A (3), and penostatin B (4), from cultures of the entomogenous fungus Isaria tenuipes. The structure of penostatin J (1) was elucidated by extensive spectroscopic analysis. We also demonstrate for the first time that penostatin derivatives exhibit the best PTP1B inhibitory action. These findings suggest that penostatin derivatives are a potential novel kind of PTP1B inhibitors.

Long term liver specific glucokinase gene defect induced diabetic cardiomyopathy by up regulating NADPH oxidase and down regulating insulin receptor and p-AMPK

BackgroundThe liver-specific glucokinase knockout (gckw/–) mouse experiences long-term hyperglycemia and insulin resistance. This study was designed to evaluate the functional and structural changes in the myocardium of 60 week-old gckw/– mice, and to investigate the effect of rosiglitazone on the myocardium in this model.Methods60 week-old gckw/– mice were randomly divided into 3 groups: gckw/–, gckw/– mice treated with insulin (1 U/kg) and gckw/– mice treated with rosiglitazone (18 mg/kg). Insulin or rosiglitazone treatment was for 4 weeks. Gckw/w litermates were used as controls. Echocardiography, electrocardiogram, biochemical, histopathological, ultrastructural, real time PCR and Western blot studies were performed to examine for structural and functional changes.ResultsLong-term liver-specific gck knockout in mice elicits hyperglycaemia and insulin resistance. Compared to age matched gckw/w mice, 60 week-old gckw/– mice showed decreased LV internal dimension, increased posterior wall thickness, lengthened PR and QRS intervals, up-regulated MLC2 protein expression, decreased SOD activity, increased MDA levels and up-regulated Cyba mRNA. Morphological studies revealed that there was an increase in the amount of PAS and Masson positively stained material, as did the number and proportion of the cell occupied by mitochondria in the gckw/– mice. Western blot analysis revealed that the levels of the insulin receptor, Akt, phosphorylated AMPK beta and phosphorylated ACC were reduced in gckw/– mice. These effects were partly attenuated or ablated by treatment with rosiglitazone.ConclusionsOur results indicate that changes in the myocardium occur in the liver-specific glucokinase knockout mouse and suggest that reduced glucokinase expression in the liver may induce diabetic cardiomyopathy by up regulating NADPH oxidase and down regulating insulin receptor and p-AMPK protein levels. Rosiglitazone treatment may protect against diabetic cardiomyopathy by altering the levels of a set of proteins involved in cardiac damage.

Therapeutic effects of globular adiponectin in diabetic rats with nonalcoholic fatty liver disease.

To explore the therapeutic role of globular adiponectin (gAd) in high-fat diet/streptozotocin (STZ)-induced type 2 diabetic rats with nonalcoholic fatty liver disease (NAFLD). Seven rats were fed a basic diet (normal control group; NC) during the experiment. Experimental rats (14 rats) were given a high-fat diet for 4 wk and were then injected with STZ to induce type 2 diabetes mellitus (T2DM) and NAFLD. Half of the T2DM/NAFLD rats were randomly injected intraperitoneally with gAd for 7 d (gAd-treated group), while the other 7 rats (T2DM/NAFLD group) received 0.9% saline. Plasma biochemical parameters and insulin concentrations were measured. Liver histopathology was examined by hematoxylin-eosin staining. Insulin receptor expression in the liver was analyzed by immunohistochemical staining, Western blot and quantitative real-time reverse transcription polymerase chain reaction analysis. Compared to the control group, the T2DM/NAFLD group had increased levels of glucolipid and decreased levels of insulin. Plasma glucose and lipid levels were decreased in the gAd-treated group, while serum insulin levels increased. The expression of insulin receptor in the T2DM/NAFLD group increased compared with the NC group, and gAd downregulated insulin receptor expression in the livers of T2DM/NAFLD rats. Steatosis of the liver was alleviated in the gAd-treated group compared to the T2DM/NAFLD group (NAS 1.39 ± 0.51 vs 1.92 ± 0.51, P < 0.05). Globular adiponectin exerts beneficial effects in T2DM rats with NAFLD by promoting insulin secretion, mediating glucolipid metabolism, regulating insulin receptor expression and alleviating hepatic steatosis.

Posttranscriptional Regulation of Insulin Family Ligands and Receptors

Insulin system including ligands (insulin and IGFs) and their shared receptors (IR and IGFR) are critical regulators of insulin signaling and glucose homeostasis. Altered insulin system is associated with major pathological conditions like diabetes and cancer. The mRNAs encoding for these ligands and their receptors are posttranscriptionally controlled by three major groups of regulators; (i) alternative splicing regulatory factors; (ii) turnover and translation regulator RNA-binding proteins (TTR-RBPs); and (iii) non-coding RNAs including miRNAs and long non-coding RNAs (lncRNAs). In this review, we discuss the influence of these regulators on alternative splicing, mRNA stability and translation. Due to the pathological impacts of insulin system, we also discussed the possibilities of discovering new potential regulators which will improve understanding of insulin system and associated diseases.

SOCS and diabetes—ups and downs of a turbulent relationship

Diabetes mellitus is one of the most emerging diseases threatening the present world. Thus, intensive investigations are carried out to better understand the mechanisms occurring in type 1 (T1D) and 2 (T2D) diabetes, and to elaborate more potent methods to fight the disease. In this aspect, the suppressors of cytokine signalling (SOCS) are one of the most studied factors of recent years. SOCS proteins have been discovered as cytokine pathway inhibitors; however, presently, their influence seems wider. Most of the known SOCS proteins are involved in the modulation of the development of insulin resistance, β-cell failure and eventually T1D and T2D. They are also involved in complications related with diabetes, such as retinopathy, nephropathy and cardiomyopathy. In T1D, SOCS proteins regulate β-cell mass, mediate resistance to damaging factors and improve pancreatic islet graft survival. Regarding insulin resistance and T2D, SOCS proteins take part in mediating signals produced by diabetogenic substances and regulate insulin receptor functioning, affecting insulin sensitivity. However, not all of the present data are consistent, and thus, further studies are required. Finally, for several pharmacologically active substances of importance regarding the treatment of diabetes, SOCS-modulating properties have already been described. Here, we review the findings of SOCS-diabetes relations of the last decade.