| 1. |
- Dehvari, Nodi, et al.
(author)
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β2‐Adrenoceptors increase translocation of GLUT4 via GPCR kinase sites in the receptor C‐terminal tail
- 2012
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In: British Journal of Pharmacology. - : Wiley. - 0007-1188 .- 1476-5381. ; 165:5, s. 1442-1456
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Journal article (peer-reviewed)abstract
- BACKGROUND AND PURPOSEbeta-Adrenoceptor stimulation induces glucose uptake in several insulin-sensitive tissues by poorly understood mechanisms.EXPERIMENTAL APPROACHWe used a model system in CHO-K1 cells expressing the human beta(2)-adrenoceptor and glucose transporter 4 (GLUT4) to investigate the signalling mechanisms involved.KEY RESULTSIn CHO-K1 cells, there was no response to b-adrenoceptor agonists. The introduction of b2-adrenoceptors and GLUT4 into these cells caused increased glucose uptake in response to beta-adrenoceptor agonists. GLUT4 translocation occurred in response to insulin and beta(2)-adrenoceptor stimulation, although the key insulin signalling intermediate PKB was not phosphorylated in response to beta(2)-adrenoceptor stimulation. Truncation of the C-terminus of the beta(2)-adrenoceptor at position 349 to remove known phosphorylation sites for GPCR kinases (GRKs) or at position 344 to remove an additional PKA site together with the GRK phosphorylation sites did not significantly affect cAMP accumulation but decreased beta(2)-adrenoceptor-stimulated glucose uptake. Furthermore, inhibition of GRK by transfection of the bARKct construct inhibited beta(2)-adrenoceptor-mediated glucose uptake and GLUT4 translocation, and overexpression of a kinase-dead GRK2 mutant (GRK2 K220R) also inhibited GLUT4 translocation. Introducing beta(2)-adrenoceptors lacking phosphorylation sites for GRK or PKA demonstrated that the GRK sites, but not the PKA sites, were necessary for GLUT4 translocation.CONCLUSIONS AND IMPLICATIONSGlucose uptake in response to activation of beta(2)-adrenoceptors involves translocation of GLUT4 in this model system. The mechanism is dependent on the C-terminus of the beta(2)-adrenoceptor, requires GRK phosphorylation sites, and involves a signalling pathway distinct from that stimulated by insulin.
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| 2. |
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| 3. |
- Olsen, Jessica M., et al.
(author)
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Glucose uptake in brown fat cells is dependent on mTOR complex 2-promoted GLUT1 translocation
- 2014
-
In: Journal of Cell Biology. - : Rockefeller University Press. - 0021-9525 .- 1540-8140. ; 207:3
-
Journal article (peer-reviewed)abstract
- Brown adipose tissue is the primary site for thermogenesis and can consume, in addition to free fatty acids, a very high amount of glucose from the blood, which can both acutely and chronically affect glucose homeostasis. Here, we show that mechanistic target of rapamycin (mTOR) complex 2 has a novel role in β3-adrenoceptor-stimulated glucose uptake in brown adipose tissue. We show that β3-adrenoceptors stimulate glucose uptake in brown adipose tissue via a signaling pathway that is comprised of two different parts: one part dependent on cAMP-mediated increases in GLUT1 transcription and de novo synthesis of GLUT1 and another part dependent on mTOR complex 2-stimulated translocation of newly synthesized GLUT1 to the plasma membrane, leading to increased glucose uptake. Both parts are essential for β3-adrenoceptor-stimulated glucose uptake. Importantly, the effect of β3-adrenoceptor on mTOR complex 2 is independent of the classical insulin-phosphoinositide 3-kinase-Akt pathway, highlighting a novel mechanism of mTOR complex 2 activation.
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| 4. |
- Sato, Masaaki, et al.
(author)
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Improving type 2 diabetes through a distinct adrenergic signaling pathway involving mTORC2 that mediates glucose uptake in skeletal muscle
- 2014
-
In: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 63:12, s. 4115-4129
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Journal article (peer-reviewed)abstract
- There is an increasing worldwide epidemic of type 2 diabetes that poses major health problems. We have identified a novel physiological system that increases glucose uptake in skeletal muscle but not in white adipocytes. Activation of this system improves glucose tolerance in Goto-Kakizaki rats or mice fed a high-fat diet, which are established models for type 2 diabetes. The pathway involves activation of β2-adrenoceptors that increase cAMP levels and activate cAMP-dependent protein kinase, which phosphorylates mammalian target of rapamycin complex 2 (mTORC2) at S2481. The active mTORC2 causes translocation of GLUT4 to the plasma membrane and glucose uptake without the involvement of Akt or AS160. Stimulation of glucose uptake into skeletal muscle after activation of the sympathetic nervous system is likely to be of high physiological relevance because mTORC2 activation was observed at the cellular, tissue, and whole-animal level in rodent and human systems. This signaling pathway provides new opportunities for the treatment of type 2 diabetes.
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| 5. |
- Chia, Ling Yeong, et al.
(author)
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Adrenoceptor regulation of the mechanistic target of rapamycin in muscle and adipose tissue
- 2019
-
In: British Journal of Pharmacology. - : Wiley. - 0007-1188 .- 1476-5381. ; 176:14, s. 2433-2448
-
Research review (peer-reviewed)abstract
- A vital role of adrenoceptors in metabolism and energy balance has been well documented in the heart, skeletal muscle, and adipose tissue. It has been only recently demonstrated, however, that activation of the mechanistic target of rapamycin (mTOR) makes a significant contribution to various metabolic and physiological responses to adrenoceptor agonists. mTOR exists as two distinct complexes named mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2) and has been shown to play a critical role in protein synthesis, cell proliferation, hypertrophy, mitochondrial function, and glucose uptake. This review will describe the physiological significance of mTORC1 and 2 as a novel paradigm of adrenoceptor signalling in the heart, skeletal muscle, and adipose tissue. Understanding the detailed signalling cascades of adrenoceptors and how they regulate physiological responses is important for identifying new therapeutic targets and identifying novel therapeutic interventions. Linked Articles This article is part of a themed section on Adrenoceptors-New Roles for Old Players. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.14/issuetoc
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| 6. |
- Dehvari, Nodi, et al.
(author)
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The metabolic effects of mirabegron are mediated primarily by beta(3)-adrenoceptors
- 2020
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In: Pharmacology Research & Perspectives. - : Wiley. - 2052-1707. ; 8:5
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Journal article (peer-reviewed)abstract
- The beta(3)-adrenoceptor agonist mirabegron is approved for use for overactive bladder and has been purported to be useful in the treatment of obesity-related metabolic diseases in humans, including those involving disturbances of glucose homeostasis. We investigated the effect of mirabegron on glucose homeostasis with in vitro and in vivo models, focusing on its selectivity at beta-adrenoceptors, ability to cause browning of white adipocytes, and the role of UCP1 in glucose homeostasis. In mouse brown, white, and brite adipocytes, mirabegron-mediated effects were examined on cyclic AMP, UCP1 mRNA, [H-3]-2-deoxyglucose uptake, cellular glycolysis, and O(2)consumption. Mirabegron increased cyclic AMP levels, UCP1 mRNA content, glucose uptake, and cellular glycolysis in brown adipocytes, and these effects were either absent or reduced in white adipocytes. In brite adipocytes, mirabegron increased cyclic AMP levels and UCP1 mRNA content resulting in increased UCP1-mediated oxygen consumption, glucose uptake, and cellular glycolysis. The metabolic effects of mirabegron in both brown and brite adipocytes were primarily due to actions at beta(3)-adrenoceptors as they were largely absent in adipocytes derived from beta(3)-adrenoceptor knockout mice. In vivo, mirabegron increased whole body oxygen consumption, glucose uptake into brown and inguinal white adipose tissue, and improved glucose tolerance, all effects that required the presence of the beta(3)-adrenoceptor. Furthermore, in UCP1 knockout mice, the effects of mirabegron on glucose tolerance were attenuated. Thus, mirabegron had effects on cellular metabolism in adipocytes that improved glucose handling in vivo, and were primarily due to actions at the beta(3)-adrenoceptor.
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| 7. |
- Evans, Bronwyn A., et al.
(author)
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Adrenoceptors in white, brown, and brite adipocytes
- 2019
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In: British Journal of Pharmacology. - : Wiley. - 0007-1188 .- 1476-5381. ; 176:14, s. 2416-2432
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Research review (peer-reviewed)abstract
- Adrenoceptors play an important role in adipose tissue biology and physiology that includes regulating the synthesis and storage of triglycerides (lipogenesis), the breakdown of stored triglycerides (lipolysis), thermogenesis (heat production), glucose metabolism, and the secretion of adipocyte-derived hormones that can control whole-body energy homeostasis. These processes are regulated by the sympathetic nervous system through actions at different adrenoceptor subtypes expressed in adipose tissue depots. In this review, we have highlighted the role of adrenoceptor subtypes in white, brown, and brite adipocytes in both rodents and humans and have included detailed analysis of adrenoceptor expression in human adipose tissue and clonally derived adipocytes. We discuss important considerations when investigating adrenoceptor function in adipose tissue or adipocytes.
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| 8. |
- Ham, Seungmin, et al.
(author)
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Role of G protein-coupled receptor kinases (GRKs) in β2-adrenoceptor-mediated glucose uptake
- 2024
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In: Pharmacology Research & Perspectives. - 2052-1707. ; 12:1
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Journal article (peer-reviewed)abstract
- Truncation of the C-terminal tail of the beta(2)-AR, transfection of beta ARKct or over-expression of a kinase-dead GRK mutant reduces isoprenaline-stimulated glucose uptake, indicating that GRK is important for this response. We explored whether phosphorylation of the beta(2)-AR by GRK2 has a role in glucose uptake or if this response is related to the role of GRK2 as a scaffolding protein. CHO-GLUT4myc cells expressing wild-type and mutant beta(2)-ARs were generated and receptor affinity for [H-3]-CGP12177A and density of binding sites determined together with the affinity of isoprenaline and BRL37344. Following receptor activation by beta(2)-AR agonists, cAMP accumulation, GLUT4 translocation, [H-3]-2-deoxyglucose uptake, and beta(2)-AR internalization were measured. Bioluminescence resonance energy transfer was used to investigate interactions between beta(2)-AR and beta-arrestin2 or between beta(2)-AR and GRK2. Glucose uptake after siRNA knockdown or GRK inhibitors was measured in response to beta(2)-AR agonists. BRL37344 was a poor partial agonist for cAMP generation but displayed similar potency and efficacy to isoprenaline for glucose uptake and GLUT4 translocation. These responses to beta(2)-AR agonists occurred in CHO-GLUT4myc cells expressing beta(2)-ARs lacking GRK or GRK/PKA phosphorylation sites as well as in cells expressing the wild-type beta(2)-AR. However, beta(2)-ARs lacking phosphorylation sites failed to recruit beta-arrestin2 and did not internalize. GRK2 knock-down or GRK2 inhibitors decreased isoprenaline-stimulated glucose uptake in rat L6 skeletal muscle cells. Thus, GRK phosphorylation of the beta(2)-AR is not associated with isoprenaline- or BRL37344-stimulated glucose uptake. However, GRKs acting as scaffold proteins are important for glucose uptake as GRK2 knock-down or GRK2 inhibition reduces isoprenaline-stimulated glucose uptake.
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| 9. |
- Hutchinson, Dana S., et al.
(author)
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Diphenylene iodonium stimulates glucose uptake in skeletal muscle cells through mitochondrial complex I inhibition and activation of AMP-activated protein kinase
- 2007
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In: Cellular Signalling. - : Elsevier BV. - 0898-6568 .- 1873-3913. ; 19:7, s. 1610-1620
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Journal article (peer-reviewed)abstract
- NADPH oxidase inhibitors such as diphenylene iodonium (DPI) and apocynin lower whole body and blood glucose levels and improve diabetes when administered to rodents. Skeletal muscle has an important role in managing glucose homeostasis and we have used L6 cells, C2C12 cells and primary muscle cells as model systems to investigate whether these drugs regulate glucose uptake in skeletal muscle cells. The data presented in this study show that apocynin does not affect glucose uptake in skeletal muscle cells in culture. Tat gp91ds, a chimeric peptide that inhibits NADPH oxidase activity, also failed to affect glucose uptake and we found no significant evidence of NADPH oxidase (subunits tested were Nox4, p22phox, gp91phox and p47phox mRNA) in skeletal muscle cells in culture. However, DPI increases basal and insulin-stimulated glucose uptake in L6 cells, C2C12 cells and primary muscle cells. Detailed studies on L6 cells demonstrate that the increase of glucose uptake is via a mechanism independent of phosphoinositide-3 kinase (PI3K)/Akt but dependent on AMP-activated protein kinase (AMPK). We postulate that DPI through inhibition of mitochondrial complex 1 and decreases in oxygen consumption, leading to decreases of ATP and activation of AMPK, stimulates glucose uptake in skeletal muscle cells.
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| 10. |
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| 11. |
- Mattsson, Charlotte L., et al.
(author)
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β₁-Adrenergic receptors increase UCP1 in human MADS brown adipocytes and rescue cold-acclimated β₃-adrenergic receptor-knockout mice via nonshivering thermogenesis
- 2011
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In: American Journal of Physiology. Endocrinology and Metabolism. - : American Physiological Society. - 0193-1849 .- 1522-1555. ; 301:6, s. E1108-E1118
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Journal article (peer-reviewed)abstract
- With the finding that brown adipose tissue is present and negatively correlated to obesity in adult man, finding the mechanism(s) of how to activate brown adipose tissue in humans could be important in combating obesity, type 2 diabetes, and their complications. In mice, the main regulator of nonshivering thermogenesis in brown adipose tissue is norepinephrine acting predominantly via β(3)-adrenergic receptors. However, vast majorities of β(3)-adrenergic agonists have so far not been able to stimulate human β(3)-adrenergic receptors or brown adipose tissue activity, and it was postulated that human brown adipose tissue could be regulated instead by β(1)-adrenergic receptors. Therefore, we have investigated the signaling pathways, specifically pathways to nonshivering thermogenesis, in mice lacking β(3)-adrenergic receptors. Wild-type and β(3)-knockout mice were either exposed to acute cold (up to 12 h) or acclimated for 7 wk to cold, and parameters related to metabolism and brown adipose tissue function were investigated. β(3)-knockout mice were able to survive both acute and prolonged cold exposure due to activation of β(1)-adrenergic receptors. Thus, in the absence of β(3)-adrenergic receptors, β(1)-adrenergic receptors are effectively able to signal via cAMP to elicit cAMP-mediated responses and to recruit and activate brown adipose tissue. In addition, we found that in human multipotent adipose-derived stem cells differentiated into functional brown adipocytes, activation of either β(1)-adrenergic receptors or β(3)-adrenergic receptors was able to increase UCP1 mRNA and protein levels. Thus, in humans, β(1)-adrenergic receptors could play an important role in regulating nonshivering thermogenesis.
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| 12. |
- Merlin, Jon, et al.
(author)
-
Could burning fat start with a brite spark? Pharmacological and nutritional ways to promote thermogenesis
- 2016
-
In: Molecular Nutrition & Food Research. - : Wiley. - 1613-4125 .- 1613-4133. ; 60:1, s. 18-42
-
Research review (peer-reviewed)abstract
- There are two types of adipose tissue with distinct functions-white adipose tissue stores chemical energy as triglycerides, whereas brown adipose tissue consumes energy and releases heat (thermogenesis) in response to sympathetic nerve activity. In humans, treatments that promote greater brown adipose tissue deposition and/or activity would be highly beneficial in regimes aimed at reducing obesity. Adult humans have restricted populations of prototypical brown adipocytes in the neck and chest areas, but recent advances have established that adipocytes with similar properties, termed brite adipocytes, can be recruited in subcutaneous depots thought to be primarily white adipose tissue. These brite adipocytes express the protein machinery required for thermogenesis, but to assess brite adipocytes as viable therapeutic targets we need to understand how to promote conversion of white adipocytes to brite adipocytes and ways to increase optimal energy consumption and thermogenesis in these brite adipocytes. This can be accomplished by pharmacological and nutritional therapies to differing degrees, as reviewed in detail here.
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| 13. |
- Merlin, Jon, et al.
(author)
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Rosiglitazone and a beta(3)-Adrenoceptor Agonist Are Both Required for Functional Browning of White Adipocytes in Culture
- 2018
-
In: Frontiers in Endocrinology. - : Frontiers Media SA. - 1664-2392. ; 9
-
Journal article (peer-reviewed)abstract
- The recruitment of brite (or beige) adipocytes has been advocated as a means to combat obesity, due to their ability to phenotypically resemble brown adipocytes (BA). Lineage studies indicate that brite adipocytes are formed by differentiation of precursor cells or by direct conversion of existing white adipocytes, depending on the adipose depot examined. We have systematically compared the gene expression profile and a functional output (oxygen consumption) in mouse adipocytes cultured from two contrasting depots, namely interscapular brown adipose tissue, and inguinal white adipose tissue (iWAT), following treatment with a known browning agent, the peroxisome proliferator-activated receptor (PPAR gamma) activator rosiglitazone. Prototypical BA readily express uncoupling protein (UCP)1, and upstream regulators including the beta(3)-adrenoceptor and transcription factors involved in energy homeostasis. Adipocytes from inguinal WAT display maximal UCP1 expression and mitochondrial uncoupling only when treated with a combination of the PPAR. activator rosiglitazone and a beta(3)-adrenoceptor agonist. In conclusion, brite adipocytes are fully activated only when a browning agent (rosiglitazone) and a thermogenic agent (beta(3)-adrenoceptor agonist) are added in combination. The presence of rosiglitazone throughout the 7-day culture period partially masks the effects of beta(3)-adrenoceptor signaling in inguinal white adipocyte cultures, whereas including rosiglitazone only for the first 3 days promotes robust beta(3)-adrenoceptor expression and provides an improved window for detection of beta(3)-adrenoceptor responses.
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| 14. |
- Merlin, Jon, et al.
(author)
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The M3-muscarinic acetylcholine receptor stimulates glucose uptake in L6 skeletal muscle cells by a CaMKK-AMPK-dependent mechanism
- 2010
-
In: Cellular Signalling. - : Elsevier BV. - 0898-6568 .- 1873-3913. ; 22:7, s. 1104-13
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Journal article (peer-reviewed)abstract
- The role of muscarinic acetylcholine receptors (mAChRs) in regulating glucose uptake in L6 skeletal muscle cells was investigated. [(3)H]-2-Deoxyglucose uptake was increased in differentiated L6 cells by insulin, acetylcholine, oxotremorine-M and carbachol. mAChR-mediated glucose uptake was inhibited by the AMPK inhibitor Compound C. Whole cell radioligand binding using [(3)H]-N-methyl scopolamine chloride identified mAChRs in differentiated but not undifferentiated L6 cells and M(3) mAChR mRNA was detected only in differentiated cells. M(3) mAChRs are Gq-coupled, and cholinergic stimulation by the mAChR agonists acetylcholine, oxotremorine-M and carbachol increased Ca(2+) in differentiated but not undifferentiated L6 cells. This was due to muscarinic but not nicotinic activation as responses were antagonised by the muscarinic antagonist atropine but not the nicotinic antagonist tubocurarine. Western blotting showed that both carbachol and the AMPK activator AICAR increased phosphorylation of the AMPKalpha subunit at Thr172, with responses to carbachol blocked by Compound C and the CaMKK inhibitor STO609 but not by the PI3K inhibitor wortmannin. AICAR-stimulated AMPK phosphorylation was not sensitive to STO-609, confirming that this compound inhibits CaMKK but not the classical AMPK kinase LKB1. The TAK1 inhibitor (5Z)-7-oxozeaenol and the G(i) inhibitor pertussis toxin both failed to block AMPK phosphorylation in response to carbachol. Using CHO-K1 cells stably expressing each of the mAChR subtypes (M(1)-M(4)), it was determined that only the M(1) and M(3) mAChRs phosphorylate AMPK, confirming a G(q)-dependent mechanism. This study demonstrates that activation of M(3) mAChRs in L6 skeletal muscle cells stimulates glucose uptake via a CaMKK-AMPK-dependent mechanism, independent of the insulin-stimulated pathway.
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| 15. |
- Merlin, Jon, et al.
(author)
-
The PPAR gamma agonist rosiglitazone promotes the induction of brite adipocytes, increasing beta-adrenoceptor-mediated mitochondrial function and glucose uptake
- 2018
-
In: Cellular Signalling. - : Elsevier BV. - 0898-6568 .- 1873-3913. ; 42, s. 54-66
-
Journal article (peer-reviewed)abstract
- Recruitment and activation of brite (or beige) adipocytes has been advocated as a potential avenue for manipulating whole-body energy expenditure. Despite numerous studies illustrating the differences in gene and protein markers between brown, brite and white adipocytes, there is very little information on the adrenergic regulation and function of these brite adipocytes. We have compared the functional (cyclic AMP accumulation, oxygen consumption rates, mitochondrial function, glucose uptake, extracellular acidification rates, calcium influx) profiles of mouse adipocytes cultured from three contrasting depots, namely interscapular brown adipose tissue, and inguinal or epididymal white adipose tissues, following chronic treatment with the peroxisome proliferator-activated receptor gamma (PPAR gamma) agonist rosiglitazone. Prototypical brown adipocytes readily express beta(3)-adrenoceptors, and beta(3)-adrenoceptor stimulation increases cyclic AMP accumulation, oxygen consumption rates, mitochondrial function, glucose uptake, and extracellular acidification rates. Treatment of brown adipocytes with rosiglitazone increases uncoupling protein 1 (UCP1) levels, and increases beta(3)-adrenoceptor mitochondrial function but does not affect glucose uptake responses. In contrast, inguinal white adipocytes only express UCP1 and beta(3)-adrenoceptors following rosiglitazone treatment, which results in an increase in all beta(3)-adrenoceptor-mediated functions. The effect of rosiglitazone in epididymal white adipocytes, was much lower compared to inguinal white adipocytes. Rosiglitazone also increased alpha(1)-adrenoceptor mediated increases in calcium influx and glucose uptake (but not mitochondrial function) in inguinal and epididymal white adipocytes. In conclusion, the PPAR gamma agonist rosiglitazone promotes the induction and function of brite adipocytes cultured from inguinal and epididymal white adipose depots.
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| 16. |
- Mukaida, Saori, et al.
(author)
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Adrenoceptors promote glucose uptake into adipocytes and muscle by an insulin-independent signaling pathway involving mechanistic target of rapamycin complex 2
- 2017
-
In: Pharmacological Research. - : Elsevier BV. - 1043-6618 .- 1096-1186. ; 116, s. 87-92
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Journal article (peer-reviewed)abstract
- Uptake of glucose into skeletal muscle and adipose tissue plays a vital role in metabolism and energy balance. Insulin released from beta-islet cells of the pancreas promotes glucose uptake in these target tissues by stimulating translocation of CLUT4 transporters to the cell surface. This process is complex, involving signaling proteins including the mechanistic (or mammalian) target of rapamycin (mTOR) and Akt that intersect with multiple pathways controlling cell survival, growth and proliferation. mTOR exists in two forms, mTOR complex 1 (mTORC1), and mTOR complex 2 (mTORC2). mTORC1 has been intensively studied, acting as a key regulator of protein and lipid synthesis that integrates cellular nutrient availability and energy balance. Studies on mTORC2 have focused largely on its capacity to activate Akt by phosphorylation at Ser473, however recent findings demonstrate a novel role for mTORC2 in cellular glucose uptake. For example, agonists acting at beta(2)-adrenoceptors (ARs) in skeletal muscle or beta(3)-ARs in brown adipose tissue increase glucose uptake in vitro and in vivo via mechanisms dependent on mTORC2 but not Akt. In this review, we will focus on the signaling pathways downstream of beta-ARs that promote glucose uptake in skeletal muscle and brown adipocytes, and will highlight how the insulin and adrenergic pathways converge and interact in these cells. The identification of insulin-independent mechanisms that promote glucose uptake should facilitate novel treatment strategies for metabolic disease.
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| 17. |
- Olsen, Jessica M., et al.
(author)
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Acute β-adrenoceptor mediated glucose clearance in brown adipose tissue; a distinct pathway independent of functional insulin signaling
- 2019
-
In: Molecular Metabolism. - : Elsevier BV. - 2212-8778. ; 30, s. 240-249
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Journal article (peer-reviewed)abstract
- Objective: β-adrenoceptor mediated activation of brown adipose tissue (BAT) has been associated with improvements in metabolic health in models of type 2 diabetes and obesity due to its unique ability to increase whole body energy expenditure, and rate of glucose and free fatty acid disposal. While the thermogenic arm of this phenomenon has been studied in great detail, the underlying mechanisms involved in β-adrenoceptor mediated glucose uptake in BAT are relatively understudied. As β-adrenoceptor agonist administration results in increased hepatic gluconeogenesis that can consequently result in secondary pancreatic insulin release, there is uncertainty regarding the importance of insulin and the subsequent activation of its downstream effectors in mediating β-adrenoceptor stimulated glucose uptake in BAT. Therefore, in this study, we made an effort to discriminate between the two pathways and address whether the insulin signaling pathway is dispensable for the effects of β-adrenoceptor activation on glucose uptake in BAT.Methods: Using a specific inhibitor of phosphoinositide 3-kinase α (PI3Kα), which effectively inhibits the insulin signaling pathway, we examined the effects of various β-adrenoceptor agonists, including the physiological endogenous agonist norepinephrine on glucose uptake and respiration in mouse brown adipocytes in vitro and on glucose clearance in mice in vivo.Results: PI3Kα inhibition in mouse primary brown adipocytes in vitro, did not inhibit β-adrenoceptor stimulated glucose uptake, GLUT1 synthesis, GLUT1 translocation or respiration. Furthermore, β-adrenoceptor mediated glucose clearance in vivo did not require insulin or Akt activation but was attenuated upon administration of a β3-adrenoceptor antagonist.Conclusions: We conclude that the β-adrenergic pathway is still functionally intact upon the inhibition of PI3Kα, showing that the activation of downstream insulin effectors is not required for the acute effects of β-adrenoceptor agonists on glucose homeostasis or thermogenesis.
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| 18. |
- Sato, Masaaki, et al.
(author)
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alpha(1A)-Adrenoceptors activate mTOR signalling and glucose uptake in cardiomyocytes
- 2018
-
In: Biochemical Pharmacology. - : Elsevier BV. - 0006-2952 .- 1356-1839. ; 148, s. 27-40
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Journal article (peer-reviewed)abstract
- The capacity of G protein-coupled receptors to modulate mechanistic target of rapamycin (mTOR) activity is a newly emerging paradigm with the potential to link cell surface receptors with cell survival. Cardiomyocyte viability is linked to signalling pathways involving Akt and mTOR, as well as increased glucose uptake and utilization. Our aim was to determine whether the am-adrenoceptor (AR) couples to these protective pathways, and increased glucose uptake. We characterised alpha(1A)-AR signalling in CHO-K1 cells co-expressing the human alpha(1A)-AR and GLUT4 (CHO alpha(1A)GLUT4myc) and in neonatal rat ventricular cardiomyocytes (NRVM), and measured glucose uptake, intracellular Ga2* mobilization, and phosphorylation of mTOR, Akt, 5' adenosine monophosphate-activated kinase (AMPK) and S6 ribosomal protein (S6rp). In both systems, noradrenaline and the alpha(1A)-AR selective agonist A61603 stimulated glucose uptake by parallel pathways involving mTOR and AMPK, whereas another alpha(1A)-AR agonist oxymetazoline increased glucose uptake predominantly by mTOR. All agonists promoted phosphorylation of mTOR at Ser2448 and Ser2481, indicating activation of both mTORC1 and mTORC2, but did not increase Akt phosphorylation. In CHO alpha(1A)GLUT4myc cells, siRNA directed against rictor but not raptor suppressed alpha(1A)-AR mediated glucose uptake. We have thus identified mTORC2 as a key component in glucose uptake stimulated by alpha(1A)-AR agonists. Our findings identify a novel link between the alpha(1A)-AR, mTORC2 and glucose uptake, that have been implicated separately in cardiomyocyte survival. Our studies provide an improved framework for examining the utility of alpha(1A)-AR selective agonists as tools in the treatment of cardiac dysfunction.
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| 19. |
- Sato, Masaaki, et al.
(author)
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Interaction with Caveolin-1 Modulates G Protein Coupling of Mouse beta(3)-Adrenoceptor
- 2012
-
In: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 287:24, s. 20674-20688
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Journal article (peer-reviewed)abstract
- Caveolins act as scaffold proteins in multiprotein complexes and have been implicated in signaling by G protein-coupled receptors. Studies using knock-out mice suggest that beta(3)-adrenoceptor (beta(3)-AR) signaling is dependent on caveolin-1; however, it is not known whether caveolin-1 is associated with the beta(3)-AR or solely with downstream signaling proteins. We have addressed this question by examining the impact of membrane rafts and caveolin-1 on the differential signaling of mouse beta(3a)- and beta(3b)-AR isoforms that diverge at the distal C terminus. Only the beta(3b)-AR promotes pertussis toxin (PTX)-sensitive cAMP accumulation. When cells expressing the beta(3a)-AR were treated with filipin III to disrupt membrane rafts or transfected with caveolin-1 siRNA, the cyclic AMP response to the beta(3)-AR agonist CL316243 became PTX-sensitive, suggesting G alpha(i/o) coupling. The beta(3a)-AR C terminus, S (P-384) under bar PLNR (P-389) under bar DG (Y-392) under bar EGARP (P-398) under bar PT, resembles a caveolin interaction motif. Mutant beta(3a)-ARs (F389A/Y392A/F398A or P384S/F389A) promoted PTX-sensitive cAMP responses, and in situ proximity assays demonstrated an association between caveolin-1 and the wild type beta(3a)-AR but not the mutant receptors. In membrane preparations, the beta(3b)-AR activated G alpha(o) and mediated PTX-sensitive cAMP responses, whereas the beta(3a)-AR did not activate G alpha(i/o) proteins. The endogenous beta(3a)-AR displayed G alpha(i/o) coupling in brown adipocytes from caveolin-1 knock-out mice or in wild type adipocytes treated with filipin III. Our studies indicate that interaction of the beta(3a)-AR with caveolin inhibits coupling to G alpha(i/o) proteins and suggest that signaling is modulated by a raft-enriched complex containing the beta(3a)-AR, caveolin-1, G alpha(s), and adenylyl cyclase.
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| 20. |
- Scheele, Camilla, et al.
(author)
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Altered regulation of the PINK1 locus: a link between Type 2 diabetes and neurodegeneration?
- 2007
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In: The FASEB Journal. - : Wiley. - 0892-6638 .- 1530-6860. ; 21:13, s. 3653-3665
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Journal article (peer-reviewed)abstract
- Mutations in PINK1 cause the mitochondrial-related neurodegenerative disease Parkinson’s. Here we investigate whether obesity, type 2 diabetes, or inactivity alters transcription from the PINK1 locus. We utilized a cDNA-array and quantitative real-time PCR for gene expression analysis of muscle from healthy volunteers following physical inactivity, and muscle and adipose tissue from nonobese or obese subjects with normal glucose tolerance or type 2 diabetes. Functional studies of PINK1 were performed utilizing RNA interference in cell culture models. Following inactivity, the PINK1 locus had an opposing regulation pattern (PINK1 was down-regulated while natural antisense PINK1 was up-regulated). In type 2 diabetes skeletal muscle, all transcripts from the PINK1 locus were suppressed and gene expression correlated with diabetes status. RNA interference of PINK1 in human neuronal cell lines impaired basal glucose uptake. In adipose tissue, mitochondrial gene expression correlated with PINK1 expression although remained unaltered following siRNA knockdown of Pink1 in primary cultures of brown preadipocytes. In conclusion, regulation of the PINK1 locus, previously linked to neurodegenerative disease, is altered in obesity, type 2 diabetes and inactivity, while the combination of RNAi experiments and clinical data suggests a role for PINK1 in cell energetics rather than in mitochondrial biogenesis.
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| 21. |
- Wu, Xifeng, et al.
(author)
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A genome-wide association study identifies a novel susceptibility locus for renal cell carcinoma on 12p11.23
- 2012
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In: Human Molecular Genetics. - : Oxford University Press (OUP). - 0964-6906 .- 1460-2083. ; 21:2, s. 456-462
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Journal article (peer-reviewed)abstract
- Renal cell carcinoma (RCC) is the most lethal urologic cancer. Only two common susceptibility loci for RCC have been confirmed to date. To identify additional RCC common susceptibility loci, we conducted an independent genome- wide association study (GWAS). We analyzed 533 191 single nucleotide polymorphisms (SNPs) for association with RCC in 894 cases and 1516 controls of European descent recruited from MD Anderson Cancer Center in the primary scan, and validated the top 500 SNPs in silico in 3772 cases and 8505 controls of European descent involved in the only published GWAS of RCC. We identified two common variants in linkage disequilibrium, rs718314 and rs1049380 (r(2) = 0.64, D' = 0.84), in the inositol 1,4,5-triphosphate receptor, type 2 (ITPR2) gene on 12p11.23 as novel susceptibility loci for RCC (P = 8.89 x 10(-10) and P = 6.07 x 10(-9), respectively, in meta-analysis) with an allelic odds ratio of 1.19 [95% confidence interval (CI): 1.13-1.26] for rs718314 and 1.18 (95% CI: 1.12-1.25) for rs1049380. It has been recently identified that rs718314 in ITPR2 is associated with waist-hip ratio (WHR) phenotype. To our knowledge, this is the first genetic locus associated with both cancer risk and WHR.
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- Öberg, Anette I., et al.
(author)
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Shikonin Increases Glucose Uptake in Skeletal Muscle Cells and Improves Plasma Glucose Levels in Diabetic Goto-Kakizaki Rats
- 2011
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In: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 6:7, s. e22510-
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Journal article (peer-reviewed)abstract
- Background: There is considerable interest in identifying compounds that can improve glucose homeostasis. Skeletal muscle, due to its large mass, is the principal organ for glucose disposal in the body and we have investigated here if shikonin, a naphthoquinone derived from the Chinese plant Lithospermum erythrorhizon, increases glucose uptake in skeletal muscle cells. Methodology/Principal Findings: Shikonin increases glucose uptake in L6 skeletal muscle myotubes, but does not phosphorylate Akt, indicating that in skeletal muscle cells its effect is medaited via a pathway distinct from that used for insulin-stimulated uptake. Furthermore we find no evidence for the involvement of AMP-activated protein kinase in shikonin induced glucose uptake. Shikonin increases the intracellular levels of calcium in these cells and this increase is necessary for shikonin-mediated glucose uptake. Furthermore, we found that shikonin stimulated the translocation of GLUT4 from intracellular vesicles to the cell surface in L6 myoblasts. The beneficial effect of shikonin on glucose uptake was investigated in vivo by measuring plasma glucose levels and insulin sensitivity in spontaneously diabetic Goto-Kakizaki rats. Treatment with shikonin (10 mg/kg intraperitoneally) once daily for 4 days significantly decreased plasma glucose levels. In an insulin sensitivity test (s.c. injection of 0.5 U/kg insulin), plasma glucose levels were significantly lower in the shikonin-treated rats. In conclusion, shikonin increases glucose uptake in muscle cells via an insulin-independent pathway dependent on calcium. Conclusions/Significance: Shikonin increases glucose uptake in skeletal muscle cells via an insulin-independent pathway dependent on calcium. The beneficial effects of shikonin on glucose metabolism, both in vitro and in vivo, show that the compound possesses properties that make it of considerable interest for developing novel treatment of type 2 diabetes.
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