Insulin Sensitivity In 3T3-L1 Adipocytes Research Articles

Effects of carnosic acid on mitochondrial biogenesis and insulin sensitivity in 3T3-L1 adipocytes are through induction of PGC-1α and ubiquitination of PARIS by parkin

The PGC-1α plays a vital role in regulating mitochondrial biogenesis and insulin sensitivity. This study investigated the role of PGC-1α in preventing the effects of carnosic acid (CA) against TNF-α-suppressed mitochondrial biogenesis and insulin signaling. Exposure of 3T3-L1 adipocytes to TNF-α decreased the proteins of PGC-1α and nuclear respiratory factor 1 (NRF1). However, pretreatment with CA improved this change. Additionally, CA led to increases in parkin protein and decreases in PARIS protein. Using immunoprecipitation assay, the protein interaction between PARIS and ubiquitin was increased and that between PARIS and parkin was decreased after CA treatment. Parkin siRNA blocked the effects of CA on PARIS, PGC-1α, and NRF1 proteins. PGC-1α siRNA abolished the capacity of CA to reverse the TNF-α-inhibited insulin signaling and membrane GLUT4 protein translocation. Therefore, CA attenuates the TNF-α induced impairment of mitochondrial biogenesis and glucose uptake through activation of PGC-1α via ubiquitination of PARIS by parkin.

Different Seasonal Collections of Ficus carica L. Leaves Diversely Modulate Lipid Metabolism and Adipogenesis in 3T3-L1 Adipocytes.

Due to the high prevalence of obesity and type 2 diabetes, adipogenesis dysfunction and metabolic disorders are common features in the elderly population. Thus, the identification of novel compounds with anti-adipogenic and lipolytic effects is highly desirable to reduce diabetes complications. Plants represent an important source of bioactive compounds. To date, the antidiabetic potential of several traditional plants has been reported, among which Ficus carica L. is one of the most promising. Considering that plant metabolome changes in response to a number of factors including seasonality, the aim of this study was to evaluate whether Ficus carica leaves extracts collected in autumn (FCa) and spring (FCs) differently modulate lipid metabolism and adipogenesis in 3T3-L1 adipocytes. The 1H-NMR profile of the extracts showed that FCs have a higher content of caffeic acid derivatives, glucose, and sucrose than FCa. In contrast, FCa showed a higher concentration of malic acid and furanocoumarins, identified as psoralen and bergapten. In vitro testing showed that only FCa treatments were able to significantly decrease the lipid content (Ctrl vs. FCa 25 μg/mL, 50 μg/mL and 80 μg/mL; p < 0.05, p < 0.01 and p < 0.001, respectively). Furthermore, FCa treatments were able to downregulate the transcriptional pathway of adipogenesis and insulin sensitivity in 3T3-L1 adipocytes. In more detail, FCa 80 μg/mL significantly decreased the gene expression of PPARγ (p < 0.05), C/EBPα (p < 0.05), Leptin (p < 0.0001), adiponectin (p < 0.05) and GLUT4 (p < 0.01). In conclusion, this study further supports an in-depth investigation of F. carica leaves extracts as a promising source of active compounds useful for targeting obesity and diabetes.

Liraglutide, the Synthetic Glucagon-like Peptide-1 Receptor Agonist, Improves Insulin Sensitivity of 3T3-L1 Adipocytes and Affects the Kinetics of Mitogenic and Inflammatory Kinases

Liraglutide, the Synthetic Glucagon-like Peptide-1 Receptor Agonist, Improves Insulin Sensitivity of 3T3-L1 Adipocytes and Affects the Kinetics of Mitogenic and Inflammatory Kinases

The synthetic glucagon-like peptide-1 receptor agonist liraglutide affects the kinetics of pro-inflammatory kinases and improves insulin sensitivity of 3T3-L1 adipocytes

Abstract Background Obesity is the main risk factor of latent inflammation, which leads to insulin resistance (IR) which can transform to type 2 diabetes mellitus (T2DM). Today several groups of drugs are used to correct T2DM and its complications. The most perspective treatment is the use of glucagon-like peptide-1 (GLP-1) receptor agonists, such as liraglutide, that affect the insulin exocytosis in pancreatic β-cells. The metabolic pathways in these cells are well studied, but liraglutide's effects on other insulin-sensitive tissues, such as adipose tissue, remain unclear. Purpose We wanted to investigate the effect of the synthetic analogue of GLP-1 liraglutide on insulin sensitivity and on inflammatory and mitogenic signaling pathways in 3T3-L1 adipocytes. Methods We studied the effects of liraglutide on the kinetics of inflammatory and mitogenic pathways and insulin sensitivity in 3T3-L1 adipocytes, which were differentiated according to standard protocol with insulin, IBMX and dexamethasone. IR was induced by treatment with 1mM free fatty acids for 24 hours. Activities of insulin, mitogenic and inflammatory signaling pathways were analyzed by Western blotting with phospho-specific antibodies. Insulin sensitivity was also assessed by insulin-stimulated [3H]-deoxyglucose uptake analysis. Results We have showed that liraglutide promotes the decrease in expression of kinases JNK and ERK. So, under these results, we had a hypothesis that liraglutide changes cAMP-dependent regulation of transcription. In order to check it we have used the inhibitor of adenylyl cyclase (SQ22536) to see whether there will be any effects of liraglutide. As we suspected there was no effect, so our hypothesis of the liraglutide-stimulated activation of cAMP-dependent pathway was confirmed. In the model of IR adipocytes liraglutide promotes the increase of total amount of IRS and Akt and increased phosphorylation of pAkt-T308. When SQ22536 was added there was no effect of liraglutide on insulin sensitivity. Conclusion These results suggest the action of liraglutide in 3T3-L1 adipocytes via transcriptional regulation and insulin sensitivity control. According to our hypothesis, GLP-1 analogue liraglutide can influence systemic insulin sensitivity via regulation of adipose tissue metabolism. Funding Acknowledgement Type of funding source: Foundation. Main funding source(s): Russian Science Foundation

1716-P: L-PGDS Inhibition Reduces Adiponectin Levels and Insulin Sensitivity in 3T3-L1 Adipocytes

The prevalence of obesity has increased steadily over the last few decades and is a major risk factor for type 2 diabetes and cardiovascular disease. Obesity is associated with alterations in adipose tissue functioning leading to metabolic dysfunction. In previous studies, we have reported the role of lipocalin-type prostaglandin D2 synthase (L-PGDS) in glucose intolerance and atherosclerosis. More recently, we demonstrated that L-PGDS KO mice develop NAFLD even on a low fat diet. Our present study explored the role of L-PGDS in adipose tissue. We found decreased expression of L-PGDS in insulin resistant 3T3-L1 adipocytes. Enzymatic inhibition of L-PGDS in 3T3-L1 adipocytes using AT56 impaired insulin signaling by reducing the phosphorylation of AKT protein and the expression and translocation of GLUT4 to plasma membrane. Furthermore, we found that inhibition of L-PGDS reduces the expression of adiponectin and AMPK phosphorylation in 3T3-L1 adipocytes. Rosiglitazone treatment in insulin resistant 3T3-L1 adipocytes significantly increased L-PGDS expression. Treatment with rosiglitazone restored the expression of adiponectin and phosphorylation of AMPK in AT56 treated 3T3-L1 adipocytes. Correspondingly, we found decreased L-PGDS expression in visceral fat of obese humans. Cumulatively, these data confirm that the absence of L-PGDS results in decreased insulin sensitivity via impaired insulin signaling and reduced adiponectin levels in 3T3-L1 adipocytes. Thus, our findings suggest that L-PGDS plays a significant role in maintaining the insulin sensitivity in 3T3-L1 adipocytes and provides a novel opportunity for therapeutic intervention of obesity-associated metabolic syndrome. Disclosure A. Srivastava: None. T. Palaia: None. J. Lee: None. C. Hall: None. M. Stevenson: None. A.G. Fernando: None. L. Ragolia: None. Funding American Heart Association (15GRNT22420001); George Link, Jr. Foundation, Inc.

WSF-7 Inhibits Obesity-Mediated PPARγ Phosphorylation and Improves Insulin Sensitivity in 3T3-L1 Adipocytes

Peroxisome proliferator-activated receptor γ (PPARγ), the molecular target for antidiabetic thiazolidinediones (TZDs), is a master regulator of preadipocyte differentiation and lipid metabolism. The adverse side effects of TZDs, arising from their potent agonistic activity, can be minimized by PPARγ partial agonists or PPARγ non-agonists without loss of insulin sensitization. In this study, we reported that WSF-7, a synthetic chemical derived from natural monoterpene α-pinene, is a partial PPARγ agonist. We found that WSF-7 binds directly to PPARγ. Activation of PPARγ by WSF-7 promotes adipogenesis, adiponectin oligomerization and insulin-induced glucose uptake. WSF-7 also inhibits obesity-mediated PPARγ phosphorylation at serine (Ser)273 and improves insulin sensitivity of 3T3-L1 adipocytes. Our study suggested that WSF-7 activates PPARγ transcription by a mechanism different from that of rosiglitazone or luteolin. Therefore, WSF-7 might be a potential therapeutic drug to treat type 2 diabetes.

Procyanidin C1, a Component of Cinnamon Extracts, Is a Potential Insulin Sensitizer That Targets Adipocytes.

Natural products are one of the main sources for discovering new lead compounds. We previously reported that cinnamon extract has a promising effect in regulating lipid tissue volume and insulin sensitivity in vivo. However, its effective component and the underlying mechanism are not known. In the present study, we analyzed the effect of different components of cinnamon on regulating insulin sensitivity in 3T3-L1 adipocytes. Functional assay revealed that, of the six major components of cinnamon extracts, the B-type procyanidin, procyanidin C1, improves the differentiation of 3T3-L1 cells (TG content: 1.10 ± 0.09 mM at a dosage of 25 μM vs 0.67 ± 0.02 mM in vehicle group, p < 0.001) and promotes insulin-induced glucose uptake (8.58 ± 1.43 at a dosage of 25 μM vs 3.05 ± 1.24 in vehicle group, p < 0.001). Mechanism studies further suggested that procyanidin C1 activates the AKT-eNOS pathway, thus up-regulating glucose uptake and enhancing insulin sensitivity in mature adipocytes. Taken together, our study identified B-type procyanidinC1, a component of cinnamon extract, that stimulates preadipocyte differentiation and acts as a potential insulin action enhancer through the AKT-eNOS pathway in mature adipocytes.

Chemical Inducers of Obesity-Associated Metabolic Stress Activate Inflammation and Reduce Insulin Sensitivity in 3T3-L1 Adipocytes.

Obesity is accompanied by dyslipidemia, hypoxia, endoplasmic reticulum (ER) stress, and inflammation, representing the major risk factor for the development of insulin resistance (IR) and type 2 diabetes. We modeled these conditions in cultured 3T3-L1 adipocytes and studied their effect on insulin signaling, glucose uptake, and inflammatory response via activation of stress-dependent JNK1/2 kinases. Decreased insulin-induced phosphorylation of the insulin cascade components IRS, Akt, and AS160 was observed under all tested conditions (lipid overloading of cells by palmitate, acute inflammation induced by bacterial lipopolysaccharide, hypoxia induced by Co2+, and ER stress induced by brefeldin A). In all the cases, except the acute inflammation, glucose uptake by adipocytes was reduced, and the kinetics of JNK1/2 activation was bi-phasic exhibiting sustained activation for 24 h. By contrast, in acute inflammation, JNK1/2 phosphorylation increased transiently and returned to the basal level within 2-3 h of stimulation. These results suggest a critical role of sustained (latent) vs. transient (acute) inflammation in the induction of IR and impairment of glucose utilization by adipose tissue. The components of the inflammatory signaling can be promising targets in the development of new therapeutic approaches for preventing IR and type 2 diabetes.

Myricanol mitigates lipid accumulation in 3T3-L1 adipocytes and high fat diet-fed zebrafish via activating AMP-activated protein kinase

Myricanol is a diarylheptanoid isolated from Chinese bayberry. Through virtual docking strategy, myricanol was discovered as an AMP-activated protein kinase (AMPK) activator among a series of structural analogs, with high affinity for the γ subunit of AMPK. Myricanol was also evaluated for regulatory effects on lipid accumulation and insulin sensitivity in 3T3-L1 adipocytes and adiposity in high-fat diet-fed zebrafish. Myricanol suppressed lipid accumulation in 3T3-L1 cells in the initial stage (days 0–2) by suppressing adipogenesis and in the terminal stage (days 4–7) by inducing lipolysis and lipid combustion through activating AMPK. Moreover, myricanol enhanced insulin-stimulated glucose uptake by activating the insulin signaling pathway. In high-fat diet-fed zebrafish, myricanol inhibited lipid accumulation by suppressing adipogenic factors including peroxisome proliferator-activated receptor γ (PPARγ) and CCAAT/enhancer binding protein α (C/EBPα). In summary, the results indicate that myricanol could be a potential therapeutic agent against obesity by activating the AMPK signaling pathway.

3,3'-Diindolylmethane Enhances Glucose Uptake Through Activation of Insulin Signaling in 3T3-L1 Adipocytes.

Indole-3-carbinol (I3C), a naturally occurring compound found in cruciferous vegetables, and its metabolite 3,3'-diindolylmethane (DIM) reduce body mass and serum glucose levels in high-fat-diet-induced obese mice. This study aimed to determine whether I3C or DIM could increase glucose uptake via enhanced insulin sensitivity in 3T3-L1 adipocytes, as well as the mechanism involved. 3T3-L1 preadipocytes were differentiated by using a mixture of adipogenic inducers, including a suboptimal concentration of insulin. DIM, but not I3C, increased adipocyte differentiation through upregulation of peroxisome proliferator-activated receptor γ and CCAAT/enhancer-binding protein α. DIM also enhanced glucose uptake by increasing expression of glucose transporter 4 in adipocytes. This was associated with DIM-enhanced phosphorylation of the signaling intermediates Akt, insulin receptor substrate-1, and insulin receptor early in differentiation. Our findings suggest that DIM may improve insulin sensitivity through the activation of the insulin signaling pathway, leading to enhanced glucose uptake.

Macrophage ubiquitin-specific protease 2 modifies insulin sensitivity in obese mice

We previously reported that ubiquitin-specific protease (USP) 2 in macrophages down-regulates genes associated with metabolic diseases, suggesting a putative anti-diabetic role for USP2 in macrophages. In this study, we evaluate this role at both cellular and individual levels. Isolated macrophages forcibly expressing Usp2a, a longer splicing variant of USP2, failed to modulate the insulin sensitivity of 3T3-L1 adipocytes. Similarly, macrophage-selective overexpression of Usp2a in mice (Usp2a transgenic mice) had a negligible effect on insulin sensitivity relative to wild type littermates following a three-month high-fat diet. However, Usp2a transgenic mice exhibited fewer M1 macrophages in their mesenteric adipose tissue. Following a six-month high-fat diet, Usp2a transgenic mice exhibited a retarded progression of insulin resistance in their skeletal muscle and liver, and an improvement in insulin sensitivity at an individual level. Although conditioned media from Usp2a-overexpressing macrophages did not directly affect the insulin sensitivity of C2C12 myotubes compared to media from control macrophages, they did increase the insulin sensitivity of C2C12 cells after subsequent conditioning with 3T3-L1 cells. These results indicate that macrophage USP2A hampers obesity-elicited insulin resistance via an adipocyte-dependent mechanism.

Short-Term Hypoxia-Induced Inhibition of Adipogenesis and Enhancement of Insulin Sensitivity in 3T3-L1 Adipocytes

Obesity is a risk factor of insulin resistance and metabolic disorders. Studies demonstrated that adipose tissue dysfunction may cause insulin resistance in obese individuals. Several pieces of evidence suggested that adipose tissues of obese individuals were in a low-oxygen status compared with the lean control. Other studies demonstrated that exercise re-arranged tissue blood flow, disposing cells to low oxygen concentration and increasing insulin sensitivity. According to the above findings, regulation of hypoxia on insulin sensitivity is still controversial. The purpose of the present study was to investigate the regulatory mechanism of hypoxia on adipogenesis and insulin sensitivity in 3T3-L1 dipocytes. To explore the effect of hypoxia on adipogenesis, 3T3-L1 preadipocytes were incubated in hypoxia status for 6 h in initial adipocyte differentiation. Differentiation efficiency was determined by intracellular triglyceride content measurement, oil red O staining of oil droplets, and expression of adipocyte lipidbinding protein (ALBP/aP2). Expressions of key transcriptional regulators, including those of preadipocyte factor-1 (pref-1), CCAAT/enhancer binding protein α (C/EBPα), and peroxisome proliferator-activated receptor-γ (PPARγ), were measured by immunoblotting. To investigate the effect of hypoxia on insulin sensitivity, differentiated 3T3-L1 adipocytes were preincubated in hypoxia status for 6 h, and then insulin-stimulated phosphorylation of insulin signaling pathways and glucose uptake were measured. To further elucidate the underlying mechanism, we clarify the involvement of hypoxia inducible factor-1α (HIF-1α) on hypoxia-regulated adipogenesis and insulin sensitivity by using HIF-1α inhibitor. Our results showed that hypoxia significantly decreased lipid accumulation and aP2 expression compared with normoxia control. Inhibitory effects of hypoxia on adipocyte differentiation were associated with increased pref-1 expression and decreased PPARγ expression. Hypoxia treatment increased insulinstimulated insulin receptor autophosphorylation and Akt phosphorylation and glucose uptake in 3T3-L1 adipocytes compared with normoxia control. Both hypoxia-inhibited adipogenesis and hypoxia-enhanced insulin sensitivity could be prevented by pretreatment with HIF-1α inhibitor, YC-1. In conclusion, short-term hypoxia suppressed adipogenesis and enhanced insulin sensitivity through HIF- 1α-dependent pathway in 3T3-L1 adipocytes.

Abstract 5435: A bioluminescent assay for measuring glucose uptake

Abstract Glucose management is a key biological process. In adipose tissue and skeletal muscle, decreased rates of glucose uptake commonly associated with diabetes mellitus lead to chronic hyperglycemia and a wide array of physiological damage. In contrast, the overexpression of glucose transporters in cancer cells results in increased rates of glucose uptake to support their high rates of proliferation. Thus, activators and inhibitors of glucose uptake are useful for both diabetes management and anticancer therapies. The standard method of assaying glucose uptake involves addition of a radioactive glucose analog (2-deoxyglucose) and measurement of the accumulation of the stable and impermeable phosphorylated derivative, 2-deoxyglucose-6-phosphate (2DG6P). However, radioactive assays are laborious, costly, and require special handling of radioactive materials and waste. A simpler assay can be made by measuring the production of NADPH through the oxidation of 2DG6P by glucose-6-phosphate dehydrogenase. We have developed a bioluminescent glucose uptake assay that is both rapid and convenient and exhibits a larger signal window than comparable fluorescent or colorimetric approaches. The utility of this assay will be demonstrated with both cancer cells and insulin-sensitive 3T3L1 adipocytes and L6 myotubes. Citation Format: Michael P. Valley, Mary Sobol, Jolanta Vidugiriene, James J. Cali. A bioluminescent assay for measuring glucose uptake. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5435. doi:10.1158/1538-7445.AM2015-5435

Role of the ubiquitin-proteasome system and autophagy in regulation of insulin sensitivity in serum-starved 3T3-L1 adipocytes.

The ubiquitin-proteasome system (UPS) and autophagy are two conserved intracellular proteolytic pathways, responsible for degradation of most cellular proteins in living cells. Currently, both the UPS and autophagy have been suggested to be associated with pathogenesis of insulin resistance and diabetes. However, underlying mechanism remains largely unknown. The purpose of the present study is to investigate the impact of the UPS and autophagy on insulin sensitivity in serum-starved 3T3-L1 adipocytes. Our results show that serum depletion resulted in activation of the UPS and autophagy, accompanied with increased insulin sensitivity. Inhibition of the UPS with bortezomib (BZM), a highly selective, reversible 26S proteasome inhibitor induced compensatory activation of autophagy but did not affect significantly insulin action. Genetic and pharmacological inhibition of autophagy dramatically mitigated serum starvation-elevated insulin sensitivity. In addition, autophagy inhibition compromised UPS function and led to endoplasmic reticulum (ER) stress and unfolded protein response (UPR). Inability of the UPS by BMZ exacerbated autophagy inhibition-induced ER stress and UPR. These results suggest that protein quality control maintained by the UPS and autophagy is required for preserving insulin sensitivity. Importantly, adaptive activation of autophagy plays a critical role in serum starvation-induced insulin sensitization in 3T3-L1 adipocytes.

Pentacyclic Triterpenoids from Spikes of Prunella vulgaris L. Inhibit Glycogen Phosphorylase and Improve Insulin Sensitivity in 3T3‐L1 Adipocytes

Phytochemical investigation of methanol extract from the spikes of Prunella vulgaris L. led to the isolation of two new pentacyclic triterpenoid glycosides Vulgasides I (1) and II (2) along with 13 known compounds (3-15). Their structures were established on the basis of nuclear magnetic resonance (1D and 2D) and mass spectroscopic data analysis. All the isolated compounds were screened for glycogen phosphorylase inhibitory activity and also evaluated for their effect on insulin sensitivity in 3T3-L1 adipocytes. Two new compounds (1, 2) did not demonstrate the glycogen phosphorylase inhibitory activity, but other compounds (3-11) exhibited varying degrees of glycogen phosphorylase inhibitory activity with IC50 values in the range from 30.69 to 68.85 μM. Compounds 3, 6, 7, 11, and 13 demonstrated markedly increased insulin-mediated glucose consumption in 3T3-L1 adipocytes.

CTRP3 improves the insulin sensitivity of 3T3-L1 adipocytes by inhibiting inflammation and ameliorating insulin signalling transduction.

C1q/TNF-related Protein-3 (CTRP3) is a novel adipokine with multiple effects such as lowering glucose levels, inhibiting glyconeogenesis in the liver, and increasing angiogenesis and anti-inflammation. But little is known about the effects of CTRP3 on insulin resistance in adipose tissue. This study aims to investigate the effects and mechanisms of CTRP3 on the insulin sensitivity of 3T3-L1 adipocytes. Insulin resistant 3T3-L1 adipocytes were induced by palmic acid cultivation. Such adipocytes were treated with recombinant CTRP3 protein at different concentrations (0, 10, 50, 1,250 ng/mL) for 12 hours, and at a concentration of 250 ng/mL for differing times (2, 6, 12, and 24 h). Another group was pre-treated with wortmannin, the special inhibitor of phosphatidylinositol-4,5- bisphosphate 3-kinase (PI3K), for 20 minutes before the treatment with 250 ng/mL CTRP3. The glucose consumption, the glucose uptake, the expression and release of tumour necrosis factor α (TNF-α) and interleukin-6(IL-6) in supernatant, and the protein relative expression of PI3K and protein kinase B (PKB)(ser437) were detected. Compared to the control group, glucose consumption in the CTRP3 intervention group at concentrations of 10, 50, 250, and 1,250 ng/mL was increased by 22.1%, 42.9%, 76.6% and 80.5% respectively (all P < 0.01); the glucose uptake was increased by 39.0%, 68.0%, 108.0% and 111.0% respectively (all P < 0.01); the content of TNF-α in the culture media of CTRP3 (10, 50, 250 ng/mL) intervention group was decreased by 7.6% (P > 0.05), 13.0% (P < 0.05) and 17.4% (P < 0.01) respectively; the content of IL-6 was decreased by 7.1%, 12.4% and 17.1% respectively (all P < 0.01); the protein relative expression of PI3K was increased by 0.63-, 1.00- and 1.36-fold respectively (all P < 0.01), and PKB(ser437) increased by 0.65-, 1.61- and 1.93-fold respectively (all P < 0.01); the mRNA relative expression of GLUT-4 was increased by 23.0%, 47.0% and 62.0% respectively (all P < 0.01). After the treatment with wortmannin, glucose consumption, glucose uptake, PI3K and PKB(ser437) protein relative expression, as well as GLUT-4 mRNA relative expression, was decreased by 53.2%, 44.7%, 43.4%, 56.1 and 30.9% respectively (all P < 0.01). CTRP3 could improve insulin sensitivity of insulin resistant 3T3-L1 adipocytes by decreasing inflammation and ameliorating insulin signalling transduction, indicating that CTRP3 may be a new target for the prevention and cure of insulin resistance and type 2 diabetes.

P53 Mediates impaired insulin signaling in 3T3‐L1 adipocytes during hyperinsulinemia

Hyperinsulinemia is being implicated in the development of insulin resistance but remains poorly understood. The present study focuses on p53-mediated impaired insulin signaling by hyperinsulinemia in 3T3-L1 adipocytes. Hyperinsulinemia impairs insulin-stimulated glucose uptake and its cellular signaling in a dose- and time-dependent manner. An increased level of reactive oxygen species (ROS) and stress response signals were observed, and quenching of the ROS by an antioxidant N-acetylcysteine (NAC) did not revert impaired insulin sensitivity. The tumor suppressor p53 has emerged as a crucial factor in the metabolic adaptation of cancer cells under nutritional starvation and is being studied in the development of insulin resistance in adipocytes at physiological level. Interestingly, we observed hyperinsulinemia-enhanced p53 level in a time-dependent manner without exhibiting cytotoxicity. Transient knockdown of p53 partially improved insulin sensitivity revealing a novel link between p53 and insulin signaling in adipocytes. The findings suggest that hyperinsulinemia-induced p53 impairs insulin sensitivity in 3T3-L1 adipocytes.

Herbal medicine as an alternative medicine for treating diabetes: the global burden.

Herbal medicine as an alternative medicine for treating diabetes: the global burden.

Ankaflavin regulates adipocyte function and attenuates hyperglycemia caused by high-fat diet via PPAR-γ activation

The effects of ankaflavin (AK) on adipokines level and insulin sensitivity were investigated. Mice were fed with high-fat diet (HFD) and AK to evaluate hyperglycemia and hyperlipidemia. Additionally, mature differentiated 3T3-L1 adipocytes were treated with AK or monascin (MS) to determine insulin signaling. Results showed that AK down-regulated serum and hepatic triacylglyceride (TG) and total cholesterol (TC) levels in mice, ameliorating hyperglycemia and hyperinsulinemia symptoms elicited by the HFD. AK elevated serum adiponectin levels in HFD-induced mice and mature 3T3-L1 adipocytes. The effect of AK on insulin sensitivity and adipokines secretion were abolished by peroxisome proliferator activated receptor-γ PPAR-γ antagonist GW9662. Moreover, we made the novel discovery that AK markedly promoted insulin receptor and Akt phosphorylation, and increased glucose uptake in mature 3T3-L1 adipocytes to a greater extent than did MS. Taken together, AK attenuated insulin resistance in HFD-induced mice and promoted insulin sensitivity in 3T3-L1 adipocytes through PPAR-γ activation.

Roles of a macrophage molecule M‐mod in type 2 diabetes

So far, we have identified a macrophage molecule, M‐mod (macrophage‐modulator), whose expression level was affected during differentiation. To explore biological roles of M‐mod, we established M‐mod knockdown (KD) cells using short hairpin RNA. Since M‐mod KD cells did not affect expression of CD11b and CD11c, M‐mod is dispensable for M1 macrophage differentiation. On the other hand, M‐mod KD potentiated expression of type2 diabetes‐associated genes such as adipocyte protein 2 (aP2), plasminogen activator inhibitor (PAI)‐1, and monocyte chemoattractant protein (MCP)‐1. In agreement, supernatant from M‐mod KD cells decreased insulin sensitivity of 3T3‐L1 adipocytes. M‐mod KD did not influenced phosphorylation of protein kinases (such as JNK, ERK, p38 and Akt) and their downstream transcriptional regulators (such as AP‐1, PPARs and NF‐κB). By contrast, M‐mod KD promoted methylation of histone H3 Lys4 at aP2 locus. Collectively, M‐mod might be an epigenetic suppressor of type2 diabetes‐associated genes in M1 macrophages. This study was supported by AstraZeneca, Ono Medical Research Foundation, and Suzuken Memorial Foundation.