Project description:Type 2 diabetes results from an impairment of insulin action. The first demonstrable abnormality of insulin signaling is a decrease of insulin-dependent glucose disposal followed by an increase in hepatic glucose production. In an attempt to dissect the relative importance of these two changes in disease progression, we have employed genetic knock-outs/knock-ins of the insulin receptor. Previously, we demonstrated that insulin receptor knock-out mice (Insr(-/-)) could be rescued from diabetes by reconstitution of insulin signaling in liver, brain, and pancreatic β cells (L1 mice). In this study, we used a similar approach to reconstitute insulin signaling in tissues that display insulin-dependent glucose uptake. Using GLUT4-Cre mice, we restored InsR expression in muscle, fat, and brain of Insr(-/-) mice (GIRKI (Glut4-insulin receptor knock-in line 1) mice). Unlike L1 mice, GIRKI mice failed to thrive and developed diabetes, although their survival was modestly extended when compared with Insr(-/-). The data underscore the role of developmental factors in the presentation of murine diabetes. The broader implication of our findings is that diabetes treatment should not necessarily target the same tissues that are responsible for disease pathogenesis.
Project description:We report for the first time movement of Correia Repeat Enclosed Elements, through inversion of the element at its chromosomal location. Analysis of Ion Torrent generated genome sequence data from Neisseria gonorrhoeae strain NCCP11945 passaged for 8 weeks in the laboratory under standard conditions and stress conditions revealed a total of 37 inversions: 24 were exclusively seen in the stressed sample; 7 in the control sample; and the remaining 3 were seen in both samples. These inversions have the capability to alter gene expression in N. gonorrhoeae through the previously determined activities of the sequence features of these elements. In addition, the locations of predicted non-coding RNAs were investigated to identify potential associations with CREE. Associations varied between strains, as did the number of each element identified. The analysis indicates a role for CREE in disrupting ancestral regulatory networks, including non-coding RNAs. RNA-Seq was used to examine expression changes related to Correia repeats in the strain
Project description:Introduction: Insulin signaling in adipose tissue has been shown to regulate insulin's effects in muscle. In muscle, perivascular adipose tissue (PVAT) and vascular insulin signaling regulate muscle perfusion. Insulin receptor substrate (IRS) 2 has been shown to control adipose tissue function and glucose metabolism, and here we tested the hypothesis that IRS2 mediates insulin's actions on the vessel wall as well as the vasoactive properties of PVAT. Methods: We studied PVAT and muscle resistance arteries (RA) from littermate IRS2+/+ and IRS2-/- mice and vasoreactivity by pressure myography, vascular insulin signaling, adipokine expression, and release and PVAT morphology. As insulin induced constriction of IRS2+/+ RA in our mouse model, we also exposed RA's of C57/Bl6 mice to PVAT from IRS2+/+ and IRS2-/- littermates to evaluate vasodilator properties of PVAT. Results: IRS2-/- RA exhibited normal vasomotor function, yet a decreased maximal diameter compared to IRS2+/+ RA. IRS2+/+ vessels unexpectedly constricted endothelin-dependently in response to insulin, and this effect was absent in IRS2-/- RA due to reduced ERK1/2activation. For evaluation of PVAT function, we also used C57/Bl6 vessels with a neutral basal effect of insulin. In these experiments insulin (10.0 nM) increased diameter in the presence of IRS2+/+ PVAT (17 ± 4.8, p = 0.014), yet induced a 10 ± 7.6% decrease in diameter in the presence of IRS2-/- PVAT. Adipocytes in IRS2-/- PVAT (1314 ± 161 μm2) were larger (p = 0.0013) than of IRS2+/+ PVAT (915 ± 63 μm2). Adiponectin, IL-6, PAI-1 secretion were similar between IRS2+/+ and IRS2-/- PVAT, as were expression of pro-inflammatory genes (TNF-α, CCL2) and adipokines (adiponectin, leptin, endothelin-1). Insulin-induced AKT phosphorylation in RA was similar in the presence of IRS2-/- and IRS2+/+ PVAT. Conclusion: In muscle, IRS2 regulates both insulin's vasoconstrictor effects, mediating ERK1/2-ET-1 activation, and its vasodilator effects, by mediating the vasodilator effect of PVAT. The regulatory role of IRS2 in PVAT is independent from adiponectin secretion.
Project description:Metabolic fuels regulate insulin secretion by generating second messengers that drive insulin granule exocytosis, but the biochemical pathways involved are incompletely understood. Here we demonstrate that stimulation of rat insulinoma cells or primary rat islets with glucose or glutamine + 2-aminobicyclo-(2,2,1)-heptane-2-carboxylic acid (Gln + BCH) induces reductive, "counter-clockwise" tricarboxylic acid (TCA) cycle flux of glutamine to citrate. Molecular or pharmacologic suppression of isocitrate dehydrogenase-2 (IDH2), which catalyzes reductive carboxylation of 2-ketoglutarate to isocitrate, results in impairment of glucose- and Gln + BCH-stimulated reductive TCA cycle flux, lowering of NADPH levels, and inhibition of insulin secretion. Pharmacologic suppression of IDH2 also inhibits insulin secretion in living mice. Reductive TCA cycle flux has been proposed as a mechanism for generation of biomass in cancer cells. Here we demonstrate that reductive TCA cycle flux also produces stimulus-secretion coupling factors that regulate insulin secretion, including in non-dividing cells.
Project description:BackgroundTissue-engineered muscles ("myobundles") offer a promising platform for developing a human in vitro model of healthy and diseased muscle for drug development and testing. Compared to traditional monolayer cultures, myobundles better model the three-dimensional structure of native skeletal muscle and are amenable to diverse functional measures to monitor the muscle health and drug response. Characterizing the metabolic function of human myobundles is of particular interest to enable their utilization in mechanistic studies of human metabolic diseases, identification of related drug targets, and systematic studies of drug safety and efficacy.MethodsTo this end, we studied glucose uptake and insulin responsiveness in human tissue-engineered skeletal muscle myobundles in the basal state and in response to drug treatments.ResultsIn the human skeletal muscle myobundle system, insulin stimulates a 50% increase in 2-deoxyglucose (2-DG) uptake with a compiled EC50 of 0.27 ± 0.03 nM. Treatment of myobundles with 400 µM metformin increased basal 2-DG uptake 1.7-fold and caused a significant drop in twitch and tetanus contractile force along with decreased fatigue resistance. Treatment with the histone deacetylase inhibitor 4-phenylbutyrate (4-PBA) increased the magnitude of insulin response from a 1.2-fold increase in glucose uptake in the untreated state to a 1.4-fold increase after 4-PBA treatment. 4-PBA treated myobundles also exhibited increased fatigue resistance and increased twitch half-relaxation time.ConclusionAlthough tissue-engineered human myobundles exhibit a modest increase in glucose uptake in response to insulin, they recapitulate key features of in vivo insulin sensitivity and exhibit relevant drug-mediated perturbations in contractile function and glucose metabolism.
Project description:AIMS/HYPOTHESIS:Increased extracellular matrix (ECM) collagen is a characteristic of muscle insulin resistance. Matrix metalloproteinase (MMP) 9 is a primary enzyme that degrades collagen IV (ColIV). As a component of the basement membrane, ColIV plays a key role in ECM remodelling. We tested the hypotheses that genetic deletion of MMP9 in mice increases muscle ColIV, induces insulin resistance in lean mice and worsens diet-induced muscle insulin resistance. METHODS:Wild-type (Mmp9(+/+)) and Mmp9-null (Mmp9(-/-)) mice were chow or high-fat (HF) fed for 16 weeks. Insulin action was measured by the hyperinsulinaemic-euglycaemic clamp in conscious weight-matched surgically catheterised mice. RESULTS:Mmp9(-/-) and HF feeding independently increased muscle ColIV. ColIV in HF-fed Mmp9(-/-) mice was further increased. Mmp9(-/-) did not affect fasting insulin or glucose in chow- or HF-fed mice. The glucose infusion rate (GIR), endogenous glucose appearance (EndoRa) and glucose disappearance (Rd) rates, and a muscle glucose metabolic index (Rg), were the same in chow-fed Mmp9(+/+) and Mmp9(-/-) mice. In contrast, HF-fed Mmp9(-/-) mice had decreased GIR, insulin-stimulated increase in Rd and muscle Rg. Insulin-stimulated suppression of EndoRa, however, remained the same in HF-fed Mmp9(-/-) and Mmp9(+/+) mice. Decreased muscle Rg in HF-fed Mmp9(-/-) was associated with decreased muscle capillaries. CONCLUSIONS/INTERPRETATION:Despite increased muscle ColIV, genetic deletion of MMP9 does not induce insulin resistance in lean mice. In contrast, this deletion results in a more profound state of insulin resistance, specifically in the skeletal muscle of HF-fed mice. These results highlight the importance of ECM remodelling in determining muscle insulin resistance in the presence of HF diet.
Project description:Skeletal muscle insulin resistance is a key component of the etiology of type 2 diabetes. Caloric restriction (CR) enhances the sensitivity of skeletal muscle to insulin. However, the molecular signals within skeletal muscle linking CR to improved insulin action remain largely unknown. Recently, the mammalian ortholog of Sir2, sirtuin 1 (Sirt1), has been identified as a potential transducer of perturbations in cellular energy flux into subsequent metabolic adaptations, including modulation of skeletal muscle insulin action. Here, we have demonstrated that CR increases Sirt1 deacetylase activity in skeletal muscle in mice, in parallel with enhanced insulin-stimulated phosphoinositide 3-kinase (PI3K) signaling and glucose uptake. These adaptations in skeletal muscle insulin action were completely abrogated in mice lacking Sirt1 deacetylase activity. Mechanistically, Sirt1 was found to be required for the deacetylation and inactivation of the transcription factor Stat3 during CR, which resulted in decreased gene and protein expression of the p55α/p50α subunits of PI3K, thereby promoting more efficient PI3K signaling during insulin stimulation. Thus, these data demonstrate that Sirt1 is an integral signaling node in skeletal muscle linking CR to improved insulin action, primarily via modulation of PI3K signaling.
Project description:Ossification of the posterior longitudinal ligament (OPLL) is formed by heterogeneous ossification of posterior longitudinal ligament. The patho-mechanism of OPLL is still largely unknown. MicroRNAs are small nucleatides that function as regulators of gene expression in almost any biological process. However, few microRNAs are reported to have a role in the pathological process of OPLL. Therefore, we performed high-throughput microRNA sequencing and transcriptome sequencing of primary OPLL and PLL cells in order to decipher the interacting network of microRNAs in OPLL. MRNA and microRNA profiles were done using primary culture cells of human ossification of the posterior longitudinal ligament (OPLL) tissue and normal posterior longitudinal ligament (PLL) tissue.