Enhanced Muscle Insulin Sensitivity Research Articles

P300 or CBP are required for calorie restriction-mediated enhancement of skeletal muscle insulin sensitivity

A calorie-restricted diet robustly improves skeletal muscle insulin sensitivity and is a cornerstone lifestyle intervention for preventing and treating clinical hyperglycemia. While studies demonstrate that insulin-stimulated activation of phosphatidylinositol 3-kinase (PI3K) and RAC-beta serine/threonine-protein kinase (AKT2) are fundamental to enhanced muscle insulin sensitivity after calorie restriction (CR), the downstream signaling steps remain to be fully elucidated. We have previously demonstrated that the lysine acetyltransferases, E1A binding protein (p300) or cAMP response element binding protein binding protein (CBP) are required for insulin-stimulated glucose uptake by skeletal muscle, at both sub-maximal and maximal concentrations of insulin. Moreover, p300/CBP are phosphorylated by AKT, which increases their acetyltransferase activity. Considering these findings together, the objective of this study was to determine whether p300 or CBP are required for the ability of CR to enhance skeletal muscle insulin sensitivity. We hypothesized that combined inhibition of p300 and CBP acetyltransferase activity would prevent CR-induced enhancement of skeletal muscle insulin sensitivity. To address this objective, 8-week-old male C57BL/6NJ mice were either fed ad libitum (AL; n=16) or were fed a CR diet (60% of AL intake; n=16) diet for 20 days. Then, an ex vivo [3H]-2-deoxyglucose (2DOG) approach was used to assess basal and insulin-stimulated (60μU/mL [0.36nM]) 2DOG uptake in paired extensor digitorum longus (EDL) and soleus from fasted (4 h) mice. To define the role of p300/CBP acetyltransferase activity, paired muscles from AL- or CR-fed mice were pre-incubated for 60 minutes with either DMSO (experimental control; n=8/dietary group [AL-DMSO, CR-DMSO]) or the p300/CBP acetyltransferase activity inhibitor, ip300w (25mM; n=8/dietary group [AL-ip300w, CR-ip300w]). As expected, insulin-stimulated 2DOG uptake (i.e. Insulin 2DOG minus basal 2DOG) in DMSO incubated muscles was ~2.3-fold and ~3.3-fold higher in the soleus and EDL, respectively, from CR- vs. AL-fed mice. Remarkably, ip300w not only blocked insulin-stimulated 2DOG uptake in AL-fed mice, but it also abrogated the insulin-sensitizing effects of CR on muscle insulin sensitivity. To further define the importance of p300 and CBP to CR-induced enhancement of skeletal muscle insulin sensitivity, we studied mice with tamoxifen-inducible and skeletal muscle-specific knockout of CBP and heterozygous (HZ) loss of p300 (referred to as, i-mCKO/PHZ) or knockout of p300 and HZ loss of CBP (referred to as, i-mPKO/CHZ). In these mice, the AL diet or 20 days of CR was initiated 3 weeks after ~10 week-old mice were dosed with tamoxifen (5 consecutive days, 2 mg/day); Cre recombinase-negative littermates, who were also dosed with tamoxifen, were the experimental controls (referred to as wildtype [WT]). Interestingly, oral glucose tolerance and EDL insulin sensitivity were comparably enhanced by CR in WT and both i-mCKO/PHZ and i-mPKO/CHZ mice, thus suggesting that just one allele of p300 or CBP is suffcient for CR to enhance skeletal muscle insulin sensitivity. Taken together, these results demonstrate that p300 or CBP are essential for the ability of calorie restriction to enhance skeletal muscle insulin sensitivity. This work was supported by a grant from the National Institutes of Health (R56 DK1311211), and the Dr. Maryam Ahmadian Memorial Summer Fellowship Program (L.M.L.) and the UC San Diego Medical Scientist Training Program (L.S.F.). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

TBC1D4 Is Necessary for Enhancing Muscle Insulin Sensitivity in Response to AICAR and Contraction.

Muscle insulin sensitivity for stimulating glucose uptake is enhanced in the period after a single bout of exercise. We recently demonstrated that AMPK is necessary for AICAR, contraction, and exercise to enhance muscle and whole-body insulin sensitivity in mice. Correlative observations from both human and rodent skeletal muscle suggest that regulation of the phosphorylation status of TBC1D4 may relay this insulin sensitization. However, the necessity of TBC1D4 for this phenomenon has not been proven. Thus, the purpose of this study was to determine whether TBC1D4 is necessary for enhancing muscle insulin sensitivity in response to AICAR and contraction. We found that immediately after contraction and AICAR stimulation, phosphorylation of AMPKα-Thr172 and downstream targets were increased similarly in glycolytic skeletal muscle from wild-type and TBC1D4-deficient mice. In contrast, 3 h after contraction or 6 h after AICAR stimulation, enhanced insulin-stimulated glucose uptake was evident in muscle from wild-type mice only. The enhanced insulin sensitivity in muscle from wild-type mice was associated with improved insulin-stimulated phosphorylation of TBC1D4 (Thr649 and Ser711) but not of TBC1D1. These results provide genetic evidence linking signaling through TBC1D4 to enhanced muscle insulin sensitivity after activation of the cellular energy sensor AMPK.

A Lanosteryl triterpene from Protorhus longifolia augments insulin signaling in type 1 diabetic rats

BackgroundA substantial literature supports antidiabetic properties of the lanosteryl triterpene (methyl-3β-hydroxylanosta-9,24-dien-21-oate, RA-3) isolated from Protorhus longifolia stem bark. However, the molecular mechanism(s) associated with the antihyperglycemic properties of the triterpene remained to be explored. The current study aimed at investigating the molecular mechanism(s) through which RA-3 improves insulin signaling in streptozotocin-induced type 1 diabetic rats.MethodsThe type 1 diabetic rats were treated daily with a single oral dose of RA-3 (100 mg/kg) for 28 days. The rats were then sacrificed, and blood, skeletal muscle and pancreases were collected for biochemical, protein expression and histological analysis, respectively.ResultsPersistently high blood glucose levels in the diabetic control rats significantly increased expression of IRS-1Ser307 while the expression of p-Akt Ser473, p-GSK-3β Ser9, GLUT 4 and GLUT 2 were decreased. However, enhanced muscle insulin sensitivity, which was indicated by a decrease in the expression of IRS-1ser307 with a concomitant increase in the p-AktSer473, p-GSK-3β Ser9, GLUT 4 and GLUT 2 expression were observed in the diabetic rats treated with RA-3. The triterpene-treated animals also showed an improved pancreatic β-cells morphology, along with increased C-peptide levels. An increase in the levels of serum antioxidants such as catalase, superoxide dismutase, and reduced glutathione was noted in the rats treated with the triterpene, while their serum levels of interleukin-6 and malondialdehyde were reduced.ConclusionsIt is apparent that RA-3 is able to improve the insulin signaling in type 1 diabetic rats. Its beta (β)-cells protecting mechanism could be attributed to its ability to alleviate inflammation and oxidative stress in the cells.

H19 lncRNA Promotes Skeletal Muscle Insulin Sensitivity in Part by Targeting AMPK.

Skeletal muscle plays a pivotal role in regulating systemic glucose homeostasis in part through the conserved cellular energy sensor AMPK. AMPK activation increases glucose uptake, lipid oxidation, and mitochondrial biogenesis, leading to enhanced muscle insulin sensitivity and whole-body energy metabolism. Here we show that the muscle-enriched H19 long noncoding RNA (lncRNA) acts to enhance muscle insulin sensitivity, at least in part, by activating AMPK. We identify the atypical dual-specificity phosphatase DUSP27/DUPD1 as a potentially important downstream effector of H19. We show that DUSP27, which is highly expressed in muscle with previously unknown physiological function, interacts with and activates AMPK in muscle cells. Consistent with decreased H19 expression in the muscle of insulin-resistant human subjects and rodents, mice with genetic H19 ablation exhibit muscle insulin resistance. Furthermore, a high-fat diet downregulates muscle H19 via both posttranscriptional and epigenetic mechanisms. Our results uncover an evolutionarily conserved, highly expressed lncRNA as an important regulator of muscle insulin sensitivity.

DOC2B enhanced muscle insulin sensitivity by interacting with cytoskeletal proteins

Strategy to enhance skeletal muscle insulin sensitivity is a primary way to substantially reduce the risk of diabetes. Evidences have shown that whole‐body DOC2B over‐expressing mice have enhanced peripheral insulin sensitivity. However, the level of contribution of skeletal muscle specific DOC2B accounting for this enhancement and the underlying mechanism remain unclear. Towards this, we generated a new tetracycline/doxycycline (DOX)‐inducible skeletal muscle specific DOC2B over‐expressing mouse model and demonstrated that the DOC2B enrichment in skeletal muscle is sufficient to enhance peripheral insulin sensitivity as well as whole‐body glucose tolerance. Inaddition, DOC2B overexpressing mice exhibited an increase in insulin‐stimulated GLUT4 accumulation at the plasma membrane and this effect of DOC2B overexpression on promoting insulin stimulated GLUT4 translocation was further confirmed in L6 skeletal muscle cells. Importantly, DOC2B overexpression was sufficient to restore GLUT4 translocation in cells rendered insulin resistant. Proteomic analyses and co‐immunoprecipitation indicate that DOC2B interacts with cytoskeletal proteins. We also found that insulin stimulation phosphorylates DOC2B, which enhances the binding of DOC2B to cytoskeletal proteins to promote GLUT4 translocation and glucose uptake. These results support DOC2B as a potential drug target to restore insulin sensitivity in pre‐diabetic and type 2 diabetic individuals.Support or Funding InformationThis work was supported by grants from the NIH/NIDDK (R01 DK067912; R01 DK102233, to Dr. Debbie Thurmond and the American Heart Association (17POST33661194) to Dr. Jing Zhang. Additional financial support was provided to Dr. Debbie Thurmond.: the Ruth and Robert Lanman Endowment, the George Schaeffer award, and an Excellence award, through the City of Hope.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Enhanced Muscle Insulin Sensitivity After Contraction/Exercise Is Mediated by AMPK.

Earlier studies have demonstrated that muscle insulin sensitivity to stimulate glucose uptake is enhanced several hours after an acute bout of exercise. Using AICAR, we recently demonstrated that prior activation of AMPK is sufficient to increase insulin sensitivity in mouse skeletal muscle. Here we aimed to determine whether activation of AMPK is also a prerequisite for the ability of muscle contraction to increase insulin sensitivity. We found that prior in situ contraction of m. extensor digitorum longus (EDL) and treadmill exercise increased muscle and whole-body insulin sensitivity in wild-type (WT) mice, respectively. These effects were not found in AMPKα1α2 muscle-specific knockout mice. Prior in situ contraction did not increase insulin sensitivity in m. soleus from either genotype. Improvement in muscle insulin sensitivity was not associated with enhanced glycogen synthase activity or proximal insulin signaling. However, in WT EDL muscle, prior in situ contraction enhanced insulin-stimulated phosphorylation of TBC1D4 Thr649 and Ser711 Such findings are also evident in prior exercised and insulin-sensitized human skeletal muscle. Collectively, our data suggest that the AMPK-TBC1D4 signaling axis is likely mediating the improved muscle insulin sensitivity after contraction/exercise and illuminates an important and physiologically relevant role of AMPK in skeletal muscle.

Exercise improves adipose function and inflammation and ameliorates fatty liver disease in obese diabetic mice.

Adipose inflammation and dysfunction underlie metabolic obesity. Exercise improves glycemic control and metabolic indices, but effects on adipose function and inflammation are less clear. Accordingly, it was hypothesized that exercise improves adipose morphometry to reduce adipose inflammation in hyperphagic obese mice. Alms1 mutant foz/foz mice housed in pairs were fed an atherogenic or chow diet; half the cages were fitted with a computer-monitored wheel for voluntary exercise. Insulin-induced AKT-phosphorylation, adipocyte size distribution, and inflammatory recruitment were studied in visceral versus subcutaneous depots, and severity of fatty liver disease was determined. Exercise prevented obesity and diabetes development in chow-fed foz/foz mice and delayed their onset in atherogenic-fed counterparts. Insulin-stimulated phospho-AKT levels in muscle were improved with exercise, but not in adipose or liver. Exercise suppressed adipose inflammatory recruitment, particularly in visceral adipose, associated with an increased number of small adipocyte subpopulations, and enhanced expression of beige adipocyte factor PRDM16 in subcutaneous fat. In atherogenic-fed foz/foz mice liver, exercise suppressed development of nonalcoholic steatohepatitis and related liver fibrosis. Exercise confers metabo-protective effects in atherogenic-fed hyperphagic mice by preventing early onset of obesity and diabetes in association with enhanced muscle insulin sensitivity, improved adipose morphometry, and suppressed adipose and liver inflammation.

Proof of Concept: Matrix metalloproteinase inhibitor decreases inflammation and improves muscle insulin sensitivity in people with type 2 diabetes

BackgroundObesity is a state of subclinical inflammation resulting in loss of function of insulin receptors and decreased insulin sensitivity. Inhibition of the inflammatory enzymes, matrix metalloproteinases (MMPs), for 6 months in rodent models restores insulin receptor function and insulin sensitivity.MethodsThis 12-week double-blind, randomized, placebo (PL)-controlled proof-of-concept study was performed to determine if the MMP inhibitor (MMPI), doxycycline, decreased global markers of inflammation and enhanced muscle insulin sensitivity in obese people with type 2 diabetes (DM2). The study included non-DM2 controls (n = 15), and DM2 subjects randomized to PL (n = 13) or doxycycline 100 mg twice daily (MMPI; n = 11). All participants were evaluated on Day 1; MMPI and PL groups were also evaluated after 84 days of treatment.ResultsThere was a significant decrease in inflammatory markers C-reactive protein (P < 0.05) and myeloperoxidase (P = 0.01) in the MMPI but not PL group. The MMPI also significantly increased skeletal muscle activated/total insulin signaling mediators: 3’phosphoinositide kinase-1 (PDK1) (p < 0.03), protein kinase B (PKB/Akt) (p < 0.004), and glycogen synthase kinase 3ß (GSK3ß) (p < 0.03).ConclusionsThis study demonstrated short term treatment of people with diabetes with an MMPI resulted in decreased inflammation and improved insulin sensitivity. Larger, longer studies are warranted to determine if doxycycline can improve glucose control in people with diabetes.Trial RegistrationClinicaltrials.gov NCT01375491

Topiramate treatment causes skeletal muscle insulin sensitization and increased Acrp30 secretion in high-fat-fed male Wistar rats

We show that Topiramate (TPM) treatment normalizes whole body insulin sensitivity in high-fat diet (HFD)-fed male Wistar rats. Thus drug treatment markedly lowered glucose and insulin levels during glucose tolerance tests and caused increased insulin sensitization in adipose and muscle tissues as assessed by euglycemic clamp studies. The insulin-stimulated glucose disposal rate increased twofold (indicating enhanced muscle insulin sensitivity), and suppression of circulating FFAs increased by 200 to 300%, consistent with increased adipose tissue insulin sensitivity. There were no effects of TPM on hepatic insulin sensitivity in these TPM-treated HFD-fed rats. In addition, TPM administration resulted in a three- to fourfold increase in circulating levels of total and high-molecular-weight (HMW) adiponectin (Acrp30). Western blot analysis revealed normal AMPK (Thr(172)) phosphorylation in liver with a twofold increased phospho-AMPK in skeletal muscle in TPM-treated rats. In conclusion, 1) TPM treatment prevents overall insulin resistance in HFD male Wistar rats; 2) drug treatment improved insulin sensitivity in skeletal muscle and adipose tissue associated with enhanced AMPK phosphorylation; and 3) the tissue "specific" effects are associated with increased serum levels of adiponectin, particularly the HMW component.