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- Mukaida, Saori, et al.
(author)
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BRL37344 stimulates GLUT4 translocation and glucose uptake in skeletal muscle via beta(2)-adrenoceptors without causing classical receptor desensitization
- 2019
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In: American Journal of Physiology. Regulatory Integrative and Comparative Physiology. - : American Physiological Society. - 0363-6119 .- 1522-1490. ; 316:5, s. R666-R677
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Journal article (peer-reviewed)abstract
- The type 2 diabetes epidemic makes it important to find insulinin-dependent ways to improve glucose homeostasis. This study examines the mechanisms activated by a dual beta(2)-/beta(3)-adrenoceptor agonist, BRL37344, to increase glucose uptake in skeletal muscle and its effects on glucose homeostasis in vivo. We measured the effect of BRL37344 on glucose uptake, glucose transporter 4 (GLUT4) translocation, cAMP levels, beta(2)-adrenoceptor desensitization, beta-arrestin recruitment, Akt, AMPK, and mammalian target of rapamycin (mTOR) phosphorylation using L6 skeletal muscle cells as a model. We further tested the ability of BRL37344 to modulate skeletal muscle glucose metabolism in animal models (glucose tolerance tests and in vivo and ex vivo skeletal muscle glucose uptake). In L6 cells, BRL37344 increased GLUT4 translocation and glucose uptake only by activation of beta(2)-adrenoceptors, with a similar potency and efficacy to that of the nonselective beta-adrenoceptor agonist isoprenaline, despite being a partial agonist with respect to cAMP generation. GLUT4 translocation occurred independently of Akt and AMPK phosphorylation but was dependent on mTORC2. Furthermore, in contrast to isoprenaline, BRL37344 did not promote agonist-mediated desensitization and failed to recruit beta-arrestin1/2 to the beta(2)-adrenoceptor. In conclusion, BRL37344 improved glucose tolerance and increased glucose uptake into skeletal muscle in vivo and ex vivo through a beta(2)-adrenoceptor-mediated mechanism independently of Akt. BRL37344 was a partial agonist with respect to cAMP, but a full agonist for glucose uptake, and importantly did not cause classical receptor desensitization or internalization of the receptor.
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| 2. |
- Sato, Masaaki, et al.
(author)
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alpha(1A)-Adrenoceptors activate mTOR signalling and glucose uptake in cardiomyocytes
- 2018
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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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