Regulation Of Insulin Signaling Research Articles

Morin Exerts Anti-Diabetic Effects in Human HepG2 Cells Via Down-Regulation of miR-29a.

Diabetes mellitus is a complex metabolic disease around the world that is characterized by hyperglycemia resulting from impaired insulin secretion, insulin action, or both. MicroRNA-29a is an important regulator of insulin signaling and gluconeogenesis pathways through IRS2, PI3K and PEPCK expressions which up regulates in Diabetes. Morin is a substantial bioflavonoid which has insulin mimetic effect, and interacting with nucleic acids and proteins. In this study HepG2 cells, were exposed to high glucose to induce diabetic condition. We have determined whether high glucose stimulation might promotes miR-29a expression level in HepG2 cells and subsequently evaluated the Morin treatment effects on this state. In HepG2 cells, high glucose increases miR-29a expression level and decreases its target genes, IRS2 and PI3K expression, and increases associated downstream gene in gluconeogenic pathway, PEPCK. Morin treatment down regulates miR-29a expression level and improves insulin signaling and glucose metabolism. To confirm the inhibitory effects of Morin on miR-29a, we have transfected cells with mimic and inhibitor-miR-29a. This study for the first time identifies that Morin improves diabetic condition through down regulation of the miR-29a level, and suggest that this new inhibitor of miR-29a may be a useful biomedicine to treat diabetes.

Brain metabolic and functional alterations in a liver-specific PTEN knockout mouse model.

Insulin resistance–as observed in aging, diabetes, obesity, and other pathophysiological situations, affects brain function, for insulin signaling is responsible for neuronal glucose transport and control of energy homeostasis and is involved in the regulation of neuronal growth and synaptic plasticity. This study investigates brain metabolism and function in a liver-specific Phosphatase and Tensin Homologue (Pten) knockout mouse model (Liver-PtenKO), a negative regulator of insulin signaling. The Liver-PtenKO mouse model showed an increased flux of glucose into the liver–thus resulting in an overall hypoglycemic and hypoinsulinemic state–and significantly lower hepatic production of the ketone body beta-hydroxybutyrate (as compared with age-matched control mice). The Liver-PtenKO mice exhibited increased brain glucose uptake, improved rate of glycolysis and flux of metabolites in the TCA cycle, and improved synaptic plasticity in the hippocampus. Brain slices from both control- and Liver-PtenKO mice responded to the addition of insulin (in terms of pAKT/AKT levels), thereby neglecting an insulin resistance scenario. This study underscores the significance of insulin signaling in brain bioenergetics and function and helps recognize deficits in diseases associated with insulin resistance.

PKCε contributes to lipid-induced insulin resistance through cross talk with p70S6K and through previously unknown regulators of insulin signaling

Insulin resistance drives the development of type 2 diabetes (T2D). In liver, diacylglycerol (DAG) is a key mediator of lipid-induced insulin resistance. DAG activates protein kinase C ε (PKCε), which phosphorylates and inhibits the insulin receptor. In rats, a 3-day high-fat diet produces hepatic insulin resistance through this mechanism, and knockdown of hepatic PKCε protects against high-fat diet-induced hepatic insulin resistance. Here, we employed a systems-level approach to uncover additional signaling pathways involved in high-fat diet-induced hepatic insulin resistance. We used quantitative phosphoproteomics to map global in vivo changes in hepatic protein phosphorylation in chow-fed, high-fat-fed, and high-fat-fed with PKCε knockdown rats to distinguish the impact of lipid- and PKCε-induced protein phosphorylation. This was followed by a functional siRNA-based screen to determine which dynamically regulated phosphoproteins may be involved in canonical insulin signaling. Direct PKCε substrates were identified by motif analysis of phosphoproteomics data and validated using a large-scale in vitro kinase assay. These substrates included the p70S6K substrates RPS6 and IRS1, which suggested cross talk between PKCε and p70S6K in high-fat diet-induced hepatic insulin resistance. These results identify an expanded set of proteins through which PKCε may drive high-fat diet-induced hepatic insulin resistance that may direct new therapeutic approaches for T2D.

Abietane-Type Diterpenoids Inhibit Protein Tyrosine Phosphatases by Stabilizing an Inactive Enzyme Conformation.

Protein tyrosine phosphatases (PTPs) contribute to a striking variety of human diseases, yet they remain vexingly difficult to inhibit with uncharged, cell-permeable molecules; no inhibitors of PTPs have been approved for clinical use. This study uses a broad set of biophysical analyses to evaluate the use of abietane-type diterpenoids, a biologically active class of phytometabolites with largely nonpolar structures, for the development of pharmaceutically relevant PTP inhibitors. Results of nuclear magnetic resonance analyses, mutational studies, and molecular dynamics simulations indicate that abietic acid can inhibit protein tyrosine phosphatase 1B, a negative regulator of insulin signaling and an elusive drug target, by binding to its active site in a non-substrate-like manner that stabilizes the catalytically essential WPD loop in an inactive conformation; detailed kinetic studies, in turn, show that minor changes in the structures of abietane-type diterpenoids (e.g., the addition of hydrogens) can improve potency (i.e., lower IC50) by 7-fold. These findings elucidate a previously uncharacterized mechanism of diterpenoid-mediated inhibition and suggest, more broadly, that abietane-type diterpenoids are a promising source of structurally diverse-and, intriguingly, microbially synthesizable-molecules on which to base the design of new PTP-inhibiting therapeutics.

The caveolae-associated coiled-coil protein, NECC2, regulates insulin signalling in Adipocytes.

Adipocyte dysfunction in obesity is commonly associated with impaired insulin signalling in adipocytes and insulin resistance. Insulin signalling has been associated with caveolae, which are coated by large complexes of caveolin and cavin proteins, along with proteins with membrane‐binding and remodelling properties. Here, we analysed the regulation and function of a component of caveolae involved in growth factor signalling in neuroendocrine cells, neuroendocrine long coiled‐coil protein‐2 (NECC2), in adipocytes. Studies in 3T3‐L1 cells showed that NECC2 expression increased during adipogenesis. Furthermore, NECC2 co‐immunoprecipitated with caveolin‐1 (CAV1) and exhibited a distribution pattern similar to that of the components of adipocyte caveolae, CAV1, Cavin1, the insulin receptor and cortical actin. Interestingly, NECC2 overexpression enhanced insulin‐activated Akt phosphorylation, whereas NECC2 downregulation impaired insulin‐induced phosphorylation of Akt and ERK2. Finally, an up‐regulation of NECC2 in subcutaneous and omental adipose tissue was found in association with human obesity and insulin resistance. This effect was also observed in 3T3‐L1 adipocytes exposed to hyperglycaemia/hyperinsulinemia. Overall, the present study identifies NECC2 as a component of adipocyte caveolae that is regulated in response to obesity and associated metabolic complications, and supports the contribution of this protein as a molecular scaffold modulating insulin signal transduction at these membrane microdomains.

Supplementation of scopoletin improves insulin sensitivity by attenuating the derangements of insulin signaling through AMPK.

Scopoletin (SPL), a phenolic coumarin, is reported to regulate glucose metabolism. This study is initiated to substantiate the action of SPL on the regulation of insulin signaling in insulin resistant RIN5f cells and high fat, high fructose diet (HFFD)-fed rat model. Adult male Sprague Dawley rats were fed HFFD for 45days to induce type 2 diabetes and then treated or untreated with SPL for the next 45days. The levels of glucose, insulin, lipid profile, oxidative stress markers along with insulin signaling and AMPK protein expressions were examined at the end of 90days. SPL lowered the levels of plasma glucose, insulin, and lipids which were increased in HFFD-fed rats. HFFD intake suppressed the activities of antioxidant enzymes such as superoxide dismutase, catalase, and glutathione peroxidase; however, they were reversed by SPL supplementation, which reduced TBARS, lipid hydroperoxide, and protein carbonyl levels both in plasma and pancreas. SPL supplementation significantly activated insulin receptor substrate 1 (IRS1), phosphatidyl inositol 3-kinase (PI3K), and protein kinase B (Akt) phosphorylation which was suppressed in HFFD rats due to lipotoxicity. Moreover, SPL significantly activated AMPK and enhanced the association of IRS1-PI3K-Akt compared to the control group. The results revealed that SPL alleviated T2D induced by HFFD by escalating the antioxidant levels and through insulin signaling regulation. We conclude that SPL can improve insulin signaling through AMPK, thereby confirming the role of SPL as an AMPK activator.

MicroRNA-205-5p is a modulator of insulin sensitivity that inhibits FOXO function

ObjectivesHepatic insulin resistance is a hallmark of type 2 diabetes and obesity. Insulin receptor signaling through AKT and FOXO has important metabolic effects that have traditionally been ascribed to regulation of gene expression. However, whether all the metabolic effects of FOXO arise from its regulation of protein-encoding mRNAs is unknown. MethodsTo address this question, we obtained expression profiles of FOXO-regulated murine hepatic microRNAs (miRNAs) during fasting and refeeding using mice lacking Foxo1, 3a, and 4 in liver (L-Foxo1,3a, 4). ResultsOut of 439 miRNA analyzed, 175 were differentially expressed in Foxo knockouts. Their functions were associated with insulin, Wnt, Mapk signaling, and aging. Among them, we report a striking increase of miR-205-5p expression in L-Foxo1,3a,4 knockouts, as well as in obese mice. We show that miR-205-5p gain-of-function increases AKT phosphorylation and decreases SHIP2 in primary hepatocytes, resulting in FOXO inhibition. This results in decreased hepatocyte glucose production. Consistent with these observations, miR-205-5p gain-of-function in mice lowered glucose levels and improved pyruvate tolerance. ConclusionsThese findings reveal a homeostatic miRNA loop regulating insulin signaling, with potential implications for in vivo glucose metabolism.

Social regulation of insulin signaling and the evolution of eusociality in ants.

Queens and workers of eusocial Hymenoptera are considered homologous to the reproductive and brood care phases of an ancestral subsocial life cycle. However, the molecular mechanisms underlying the evolution of reproductive division of labor remain obscure. Using a brain transcriptomics screen, we identified a single gene, insulin-like peptide 2 (ilp2), which is always up-regulated in ant reproductives, likely because they are better nourished than their nonreproductive nestmates. In clonal raider ants (Ooceraea biroi), larval signals inhibit adult reproduction by suppressing ilp2, thus producing a colony reproductive cycle reminiscent of ancestral subsociality. However, increasing ILP2 peptide levels overrides larval suppression, thereby breaking the colony cycle and inducing a stable division of labor. These findings suggest a simple model for the origin of ant eusociality via nutritionally determined reproductive asymmetries potentially amplified by larval signals.

Cbt modulates Foxo activation by positively regulating insulin signaling in Drosophila embryos

In late Drosophila embryos, the epidermis exhibits a dorsal hole as a consequence of germ band retraction. It is sealed during dorsal closure (DC), a morphogenetic process in which the two lateral epidermal layers converge towards the dorsal midline and fuse. We previously demonstrated the involvement of the Cbt transcription factor in Drosophila DC. However its molecular role in the process remained obscure. In this study, we used genomic approaches to identify genes regulated by Cbt as well as its direct targets during late embryogenesis. Our results reveal a complex transcriptional circuit downstream of Cbt and evidence that it is functionally related with the Insulin/insulin-like growth factor signaling pathway. In this context, Cbt may act as a positive regulator of the pathway, leading to the repression of Foxo activity. Our results also suggest that the DC defects observed in cbt embryos could be partially due to Foxo overactivation and that a regulatory feedback loop between Foxo and Cbt may be operating in the DC context.

Biliverdin reductase-A impairment links brain insulin resistance with increased Aβ production in an animal model of aging: Implications for Alzheimer disease

Brain insulin resistance is associated with an increased Aβ production in AD although the molecular mechanisms underlying this link are still largely unknown. Biliverdin reductase-A (BVR-A) is a unique Ser/Thr/Tyr kinase regulating insulin signalling. Studies from our group, demonstrated that BVR-A impairment is among the earliest events favoring brain insulin resistance development. Furthermore, reported a negative association between BVR-A protein levels/activation and BACE1 protein levels in the parietal cortex of aged beagles (an animal model of AD), thus suggesting a possible interaction. Therefore, we aimed to demonstrate that BVR-A impairment is a molecular bridge linking brain insulin resistance with increased Aβ production. Age-associated changes of BVR-A, BACE1, insulin signalling cascade and APP processing were evaluated in the parietal cortex of beagles and experiments to confirm the hypothesized mechanism(s) have been performed in vitro in HEK293APPswe cells. Our results show that BVR-A impairment occurs early with age and is associated with brain insulin resistance. Furthermore, we demonstrate that BVR-A impairment favors CK1-mediated Ser phosphorylation of BACE1 (known to mediate BACE1 recycling to plasma membrane) along with increased Aβ production in the parietal cortex, with age. Overall, our results suggest that the impairment of BVR-A is an early molecular event contributing to both (I) the onset of brain insulin resistance and (II) the increased Aβ production observed in AD. We, therefore, suggest that by targeting BVR-A activity it could be possible to delay the onset of brain insulin resistance along with an improved regulation of the APP processing.

The Tyrosine Phosphatase LMPTP Is a Key Promoter of Adipogenesis

The low molecular weight protein tyrosine phosphatase (LMPTP), encoded by the ACP1 gene, acts as a regulator of insulin signaling by dephosphorylating the activation motif of the insulin receptor. Multiple human genetics studies suggest that high LMPTP catalytic activity promotes metabolic syndrome and severity of obesity. We recently reported that LMPTP is a critical promoter of insulin resistance in obesity through an action on the liver and that pharmacological inhibition of LMPTP reverses obesity-associated diabetes in mice. Since LMPTP is highly expressed in adipose tissue but little is known about its function in these tissues, we examined the role of LMPTP in adipocyte biology. Intriguingly, we found that LMPTP acts as a critical promoter of adipogenesis. Our data indicate a novel role for LMPTP in promoting adipocyte differentiation and suggest that there may be additional signaling pathways under control of LMPTP in these cells. Disclosure S. Stanford: None. V. Zhang: None. N. Bottini: None.

Shared Genetic Influence on Early Growth and Type 2 Diabetes in Adulthood

Background: There is a strong evidence of association between birthweight (BW) and type 2 diabetes (T2D) in adulthood. Although shared genetics has been suggested to be a significant contributor to these associations, to date, we know very few shared genetic loci. We conducted a systematic genome-wide investigation of shared genetic effects (pleiotropy) and enrichment of biologically functional loci implicated in BW-T2D associations. Methods: We evaluated pleiotropy, enrichment of functional annotation, and association of single nucleotide polymorphisms (SNPs) using genome-wide summary statistics of 2,893,797 SNPs for BW from the Early Growth Genetics Consortium, and T2D from the DIAbetes Genetics Replication And Meta-analysis Consortium. Analyses were conducted using the Genetic analysis incorporating Pleiotropy and Annotation (GPA). Tests for enrichment of annotations from functional datasets were performed in loci associated with pairs of traits. Results: We found significant enrichment of genetic pleiotropy (P <10-30) and biologically functional loci jointly associated with BW and T2D (enrichment fold of shared vs. BW-specific vs. T2D-specific loci: 1.45 vs. 1.24 vs. 0.57; P=1.73x10-21). A total of 178 independent SNPs in genes NYAP2-IRS1, ADCY5, ST6GAL1, CDKAL1, ANK1, HHEX-ECOC6, FAT3-MTNR1B, and MPHOSPH9 were associated with both BW and T2D at a false discovery rate of 5%. The locus at NYAP2-IRS1 (rs1515098 C) associated with reduced BW and increased T2D risk was novel. Functional analysis showed that rs62188784, in strong LD with rs1515098 (r2=0.91), has potential regulatory (cis-eQTL) effect on expression of the IRS1 gene in adipose tissues. Conclusions: We found shared genetic loci that influence early growth and type 2 diabetes, including novel shared variant in the insulin receptor substrate 1 gene. Findings suggest that genetic regulation of insulin signaling in adipose tissue potentially influences the associations of early growth and type 2 diabetes later in life. Disclosure F. Tekola-Ayele: None. A. Lee: None. T. Workalemahu: None. D. Shrestha: None.

A Low-Frequency Amerindian Specific Variant in PALD1, a Negative Regulator of Insulin Signaling, Associates with Type 2 Diabetes

We recently completed a genome wide association study for type 2 diabetes (T2D) in 7659 American Indians who are predominantly of Pima Indian heritage using a custom designed Axiom array. A novel intronic variant (hg19 chr10:72276664 G>C) in PALD1 was identified that associated with T2D (risk allele frequency (RAF)=0.01, OR=2.19[1.49-3.22] per risk allele [C], P=6.6×10-5 adjusted for age, sex, birthyear, PCs 1-5 and accounting for genetic relatedness). Further analysis in a dataset of Urban American Indians (N=3029) representing several tribal groups living in the Phoenix area, identified a directionally consistent association (OR=2.32, P=0.12), but this variant was rare among the entire Urban American Indian sample (RAF=0.003). A meta-analysis of both datasets resulted in a summary OR of 2.15[1.49-3.13], P=4.9×10-5. In Pima Indians, this variant is highly concordant (r2=0.92) with a novel missense variant (hg19 chr10:72298980 C>T, p.[P568S]) in PALD1. The missense variant also had a significant association with T2D in Pima Indians (RAF=0.02, OR=1.80[1.25-2.60], P=0.002) and in Urban American Indians (RAF=0.008, OR=2.29[1.03-5.12], P=0.04). However, after conditional analysis, only the intronic variant remains significant in the Pima Indian dataset. PALD1 is a predicted phosphatase and acts as a negative regulator of insulin signaling. Overexpression of PALD1 leads to lower insulin stimulated AKT phosphorylation and insulin receptor abundance. For preliminary functional studies, a short fragment (100bp) containing each allele of the PALD1 intronic variant (C or G) was cloned upstream of a SV40 promoter luciferase vector and transfected into C2C12 myoblasts. The T2D risk allele (C) fragment had significantly (P=0.004) higher SV40 promoter mediated luciferase activity as compared to the non-risk (G) allele. This result is consistent with the possible role of PALD1 in T2D pathogenesis. Further mechanistic studies are currently ongoing. Disclosure A.K. Nair: None. J.R. Sutherland: None. G.R. Elson: None. P. Piaggi: None. S. Kobes: None. R.L. Hanson: None. C. Bogardus: None. L. Baier: None.

Regulation of Hepatic Insulin Sensitivity and Hepatic Steatosis by ULK1

Hepatic insulin resistance (IR) plays a central role in the pathophysiology of impaired glucose tolerance, type 2 diabetes and nonalcoholic fatty liver disease (NAFLD) and steatohepatitis (NASH), which is emerging as a major cause of liver failure and hepatocellular carcinoma. Impaired autophagy may also contribute to hepatic insulin resistance, but the interactions between insulin sensitivity and autophagy are incompletely understood. The Unc-51 Like Autophagy Activating Kinase 1 (ULK1) is an early stage autophagosome formation related kinase that is activated in selective autophagy and may be independent of nutrient or energy status. We observed that in addition to its role in autophagy regulation, ULK1 may also directly regulate insulin signaling by modulating AKT dephosphorylation. Specifically, silencing ULK1 significantly impairs insulin-stimulated activation of AKT and GSK3β in hepatocytes in the absence of significant changes in autophagy. To understand the role of ULK1 in hepatic insulin action ULK1 liver specific knock-out mice were generated. Body weight increased in L-ULK1KO relative to wild type mice on normal chow diet or 60% high fat diet. L-ULK1 KO mice exhibited impaired glucose tolerance and insulin resistance. Serum concentrations of insulin, triglyceride, cholesterol, AST and ALT were increased. Phosphorylation levels of FOXO1 and FOXO3a were decreased in concert with increased expression levels of PEPCK and G6pase and increased hepatic glucose production. In contrast, L-ULK2 KO mice were phenotypically normal. Thus, ULK1 independently and directly regulates hepatic insulin sensitivity and glucose homeostasis. Disclosure Y. Koo: None. M.P. Garneau: None. Q. Zhang: None. E. Abel: None.

TCPTP Regulates Insulin Signaling in AgRP Neurons to Coordinate Glucose Metabolism With Feeding.

Insulin regulates glucose metabolism by eliciting effects on peripheral tissues as well as the brain. Insulin receptor (IR) signaling inhibits AgRP-expressing neurons in the hypothalamus to contribute to the suppression of hepatic glucose production (HGP) by insulin, whereas AgRP neuronal activation attenuates brown adipose tissue (BAT) glucose uptake. The tyrosine phosphatase TCPTP suppresses IR signaling in AgRP neurons. Hypothalamic TCPTP is induced by fasting and degraded after feeding. Here we assessed the influence of TCPTP in AgRP neurons in the control of glucose metabolism. TCPTP deletion in AgRP neurons (Agrp-Cre;Ptpn2fl/fl ) enhanced insulin sensitivity, as assessed by the increased glucose infusion rates, and reduced HGP during hyperinsulinemic-euglycemic clamps, accompanied by increased [14C]-2-deoxy-d-glucose uptake in BAT and browned white adipose tissue. TCPTP deficiency in AgRP neurons promoted the intracerebroventricular insulin-induced repression of hepatic gluconeogenesis in otherwise unresponsive food-restricted mice, yet had no effect in fed/satiated mice where hypothalamic TCPTP levels are reduced. The improvement in glucose homeostasis in Agrp-Cre;Ptpn2fl/fl mice was corrected by IR heterozygosity (Agrp-Cre;Ptpn2fl/fl ;Insrfl/+ ), causally linking the effects on glucose metabolism with the IR signaling in AgRP neurons. Our findings demonstrate that TCPTP controls IR signaling in AgRP neurons to coordinate HGP and brown/beige adipocyte glucose uptake in response to feeding/fasting.

Seven-Up Is a Novel Regulator of Insulin Signaling.

Insulin resistance is associated with obesity, cardiovascular disease, non-alcoholic fatty liver disease, and type 2 diabetes. These complications are exacerbated by a high-calorie diet, which we used to model type 2 diabetes in Drosophila melanogaster Our studies focused on the fat body, an adipose- and liver-like tissue that stores fat and maintains circulating glucose. A gene regulatory network was constructed to predict potential regulators of insulin signaling in this tissue. Genomic characterization of fat bodies suggested a central role for the transcription factor Seven-up (Svp). Here, we describe a new role for Svp as a positive regulator of insulin signaling. Tissue-specific loss-of-function showed that Svp is required in the fat body to promote glucose clearance, lipid turnover, and insulin signaling. Svp appears to promote insulin signaling, at least in part, by inhibiting ecdysone signaling. Svp also impairs the immune response possibly via inhibition of antimicrobial peptide expression in the fat body. Taken together, these studies show that gene regulatory networks can help identify positive regulators of insulin signaling and metabolic homeostasis using the Drosophila fat body.

A feedback control of insulin signaling by transcription factor HMG box‐containing protein 1 (HBP1) in adipocytes

Adipocytes are sensitive to insulin control of cellular glucose utilization, thereby facilitating the maintenance of blood glucose concentration. Previously we demonstrated that transcription factor HBP1 is highly expressed in differentiated adipocytes, which, together with CCAAT/enhancer‐binding proteins C/EBPβ and C/EBPα, regulates adipocyte differentiation. To further gain insight into the biological role of HBP1 in mature adipocytes, here, we employed mouse embryonic fibroblast (MEF)‐derived adipocytes to test the hypothesis that HBP1 might regulate insulin sensitivity in adipocytes. First, suppression of HBP1 by siRNA‐mediated gene silencing significantly attenuated glucose uptake as shown by 2‐NBDG glucose uptake assay. We then examined the insulin‐signaling pathway to unravel the molecular mechanism by which HBP1 commands adipocytes to take up glucose. Under serum starvation, the transcription of insulin receptor (InR) was increased, whereas HBP1 silencing down‐regulated the expression of InR in adipocytes, indicating that HBP1 is able to promote insulin sensitivity under insulin insufficient state. However, the addition of insulin (2 nM for 6 h) led to a significant decrease in the transcription of HBP1, InR, and IRS1/2 (insulin receptor substrate 1/2). Moreover, HBP1 siRNA led to increased level of p‐S307 IRS‐1 that is associated with blockade of the insulin signaling, and also resulted in an unexpected induction of glucose transporter 4 (GLUT4). The upregulation of GLUT4 may function as a compensation mechanism for the defective insulin signaling caused by HBP1 silencing. Taken as a whole, our results reveal a key feedback control mechanism for HBP1 in regulating insulin signaling and glucose metabolism.Support or Funding InformationThis work was supported by the grant to MOST 105‐2320‐B‐039‐044‐MY2 C‐Y Huang.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Tocotrienol-rich fraction supplementation reduces hyperglycemia-induced skeletal muscle damage through regulation of insulin signaling and oxidative stress in type 2 diabetic mice

Chronic hyperglycemia induces impairment of muscle growth and development of diabetes mellitus (DM). Since skeletal muscle is the major site for disposal of ingested glucose, impaired glucose metabolism causes imbalance between protein synthesis and degradation which adversely affects physical mobility.In this study, we investigated the effect of tocotrienol-rich fraction (TRF) supplementation on skeletal muscle damage in diabetic mice. Diabetes was induced by a high-fat diet with streptozotocin (STZ) injection (100 mg/kg) in male C57BL/6J mice. After diabetes was induced (fasting blood glucose levels≥250 mg/dl), normal control (CON) and diabetic control (DMC) groups were administrated with olive oil, while TRF treatment groups were administrated with TRF (dissolved in olive oil) at low dose (100 mg/kg BW, LT) or high dose (300 mg/kg BW, HT) by oral gavage for 12 weeks.TRF supplementation ameliorated muscle atrophy, plasma insulin concentration and homeostatic model assessment estimated insulin resistance in diabetic mice. Moreover, TRF treatment up-regulated IRS-1 and Akt levels accompanied by increased translocation of GLUT4. Furthermore, TRF increased mitochondrial biogenesis by activating SIRT1, SIRT3 and AMPK in diabetic skeletal muscle. These changes were in part mechanistically explained by reduced levels of skeletal muscle proteins related to oxidative stress (4-hydroxynonenal, protein carbonyls, Nrf2 and HO-1), inflammation (NFkB, MCP-1, IL-6 and TNF-α), and apoptosis (Bax, Bcl₂ and caspase-3) in diabetic mice. Taken together, these results suggest that TRF might be useful as a beneficial nutraceutical to prevent skeletal muscle atrophy associated with diabetes by regulating insulin signaling via AMPK/SIRT1/PGC1α pathways in type 2 diabetic mice.

Th-POK regulates mammary gland lactation through mTOR-SREBP pathway.

The Th-inducing POK (Th-POK, also known as ZBTB7B or cKrox) transcription factor is a key regulator of lineage commitment of immature T cell precursors. It is yet unclear the physiological functions of Th-POK besides helper T cell differentiation. Here we show that Th-POK is restrictedly expressed in the luminal epithelial cells in the mammary glands that is upregulated at late pregnancy and lactation. Lineage restrictedly expressed Th-POK exerts distinct biological functions in the mammary epithelial cells and T cells in a tissue-specific manner. Th-POK is not required for mammary epithelial cell fate determination. Mammary gland morphogenesis in puberty and alveologenesis in pregnancy are phenotypically normal in the Th-POK-deficient mice. However, Th-POK-deficient mice are defective in triggering the onset of lactation upon parturition with large cellular lipid droplets retained within alveolar epithelial cells. As a result, Th-POK knockout mice are unable to efficiently secret milk lipid and to nurse the offspring. Such defect is mainly attributed to the malfunctioned mammary epithelial cells, but not the tissue microenvironment in the Th-POK deficient mice. Th-POK directly regulates expression of insulin receptor substrate-1 (IRS-1) and insulin-induced Akt-mTOR-SREBP signaling. Th-POK deficiency compromises IRS-1 expression and Akt-mTOR-SREBP signaling in the lactating mammary glands. Conversely, insulin induces Th-POK expression. Thus, Th-POK functions as an important feed-forward regulator of insulin signaling in mammary gland lactation.

Hsp90\u03b2 knockdown in DIO mice reverses insulin resistance and improves glucose tolerance

BackgroundInhibition of Hsp90 has been shown to improve glucose tolerance and insulin sensitivity in mouse models of diabetes. In the present report, the specific isoform Hsp90ab1, was identified as playing a major role in regulating insulin signaling and glucose metabolism.MethodsIn a diet-induced obese (DIO) mouse model of diabetes, expression of various Hsp90 isoforms in skeletal tissue was examined. Subsequent experiments characterized the role of Hsp90ab1 isoform in glucose metabolism and insulin signaling in primary human skeletal muscle myoblasts (HSMM) and a DIO mouse model.ResultsIn DIO mice Hsp90ab1 mRNA was upregulated in skeletal muscle compared to lean mice and knockdown using anti-sense oligonucleotide (ASO) resulted in reduced expression in skeletal muscle that was associated with improved glucose tolerance, reduced fed glucose and fed insulin levels compared to DIO mice that were treated with a negative control oligonucleotide. In addition, knockdown of HSP90ab1 in DIO mice was associated with reduced pyruvate dehydrogenase kinase-4 mRNA and phosphorylation of the muscle pyruvate dehydrogenase complex (at serine 232, 293 and 300), but increased phosphofructokinase 1, glycogen synthase 1 and long-chain specific acyl-CoA dehydrogenase mRNA. In HSMM, siRNA knockdown of Hsp90ab1 induced an increase in substrate metabolism, mitochondrial respiration capacity, and insulin sensitivity, providing further evidence for the role of Hsp90ab1 in metabolism.ConclusionsThe data support a novel role for Hsp90ab1 in arbitrating skeletal muscle plasticity via modulation of substrate utilization including glucose and fatty acids in normal and disease conditions. Hsp90ab1 represents a novel target for potential treatment of metabolic disease including diabetes.