1
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Chan MP, Takenaka N, Satoh T. Impaired Insulin Signaling Mediated by the Small GTPase Rac1 in Skeletal Muscle of the Leptin-Deficient Obese Mouse. Int J Mol Sci 2023; 24:11531. [PMID: 37511290 PMCID: PMC10380855 DOI: 10.3390/ijms241411531] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2023] [Revised: 07/05/2023] [Accepted: 07/12/2023] [Indexed: 07/30/2023] Open
Abstract
Insulin-stimulated glucose uptake in skeletal muscle is mediated by the glucose transporter GLUT4. The small GTPase Rac1 acts as a switch of signal transduction that regulates GLUT4 translocation to the plasma membrane following insulin stimulation. However, it remains obscure whether signaling cascades upstream and downstream of Rac1 in skeletal muscle are impaired by obesity that causes insulin resistance and type 2 diabetes. In an attempt to clarify this point, we investigated Rac1 signaling in the leptin-deficient (Lepob/ob) mouse model. Here, we show that insulin-stimulated GLUT4 translocation and Rac1 activation are almost completely abolished in Lepob/ob mouse skeletal muscle. Phosphorylation of the protein kinase Akt2 and plasma membrane translocation of the guanine nucleotide exchange factor FLJ00068 following insulin stimulation were also diminished in Lepob/ob mice. On the other hand, the activation of another small GTPase RalA, which acts downstream of Rac1, by the constitutively activated form of Akt2, FLJ00068, or Rac1, was partially abrogated in Lepob/ob mice. Taken together, we conclude that insulin-stimulated glucose uptake is impaired by two mechanisms in Lepob/ob mouse skeletal muscle: one is the complete inhibition of Akt2-mediated activation of Rac1, and the other is the partial inhibition of RalA activation downstream of Rac1.
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Affiliation(s)
| | | | - Takaya Satoh
- Laboratory of Cell Biology, Department of Biological Chemistry, Graduate School of Science, Osaka Metropolitan University, Sakai 599-8531, Japan; (M.P.C.); (N.T.)
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2
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Chau DDL, Li W, Chan WWR, Sun JKL, Zhai Y, Chow HM, Lau KF. Insulin stimulates atypical protein kinase C-mediated phosphorylation of the neuronal adaptor FE65 to potentiate neurite outgrowth by activating ARF6-Rac1 signaling. FASEB J 2022; 36:e22594. [PMID: 36250347 DOI: 10.1096/fj.202200757r] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2022] [Revised: 08/21/2022] [Accepted: 09/26/2022] [Indexed: 11/11/2022]
Abstract
Neurite outgrowth is a fundamental process in neurons that produces extensions and, consequently, neural connectivity. Neurite damage and atrophy are observed in various brain injuries and disorders. Understanding the intrinsic pathways of neurite outgrowth is essential for developing strategies to stimulate neurite regeneration. Insulin is a pivotal hormone in the regulation of glucose homeostasis. There is increasing evidence for the neurotrophic functions of insulin, including the induction of neurite outgrowth. However, the associated mechanism remains elusive. Here, we demonstrate that insulin potentiates neurite outgrowth mediated by the small GTPases ADP-ribosylation factor 6 (ARF6) and Ras-related C3 botulinum toxin substrate 1 (Rac1) through the neuronal adaptor FE65. Moreover, insulin enhances atypical protein kinase Cι/λ (PKCι/λ) activation and FE65 phosphorylation at serine 459 (S459) in neurons and mouse brains. In vitro and cellular assays show that PKCι/λ phosphorylated FE65 at S459. Consistently, insulin potentiates FE65 S459 phosphorylation only in the presence of PKCι/λ. Phosphomimetic studies show that an FE65 S459E mutant potently activates ARF6, Rac1, and neurite outgrowth. Notably, this phosphomimetic mutation enhances the FE65-ARF6 interaction, a process that promotes ARF6-Rac1-mediated neurite outgrowth. Likewise, insulin treatment and PKCι/λ overexpression potentiate the FE65-ARF6 interaction. Conversely, PKCι/λ knockdown suppresses the stimulatory effect of FE65 on ARF6-Rac1-mediated neurite outgrowth. The effect of insulin on neurite outgrowth is also markedly attenuated in PKCι/λ knockdown neurons, in the presence and absence of FE65. Our findings reveal a novel mechanism linking insulin with ARF6-Rac1-dependent neurite extension through the PKCι/λ-mediated phosphorylation of FE65.
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Affiliation(s)
- Dennis Dik-Long Chau
- School of Life Sciences, Faculty of Science, The Chinese University of Hong Kong, Hong Kong, China
| | - Wen Li
- School of Life Sciences, Faculty of Science, The Chinese University of Hong Kong, Hong Kong, China.,Research Laboratory for Biomedical Optics and Molecular Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China
| | - Wai Wa Ray Chan
- School of Life Sciences, Faculty of Science, The Chinese University of Hong Kong, Hong Kong, China
| | - Jacquelyne Ka-Li Sun
- School of Life Sciences, Faculty of Science, The Chinese University of Hong Kong, Hong Kong, China
| | - Yuqi Zhai
- School of Life Sciences, Faculty of Science, The Chinese University of Hong Kong, Hong Kong, China
| | - Hei-Man Chow
- School of Life Sciences, Faculty of Science, The Chinese University of Hong Kong, Hong Kong, China
| | - Kwok-Fai Lau
- School of Life Sciences, Faculty of Science, The Chinese University of Hong Kong, Hong Kong, China
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3
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Effting PS, Thirupathi A, Müller AP, Pereira BC, Sepa-Kishi DM, Marqueze LFB, Vasconcellos FTF, Nesi RT, Pereira TCB, Kist LW, Bogo MR, Ceddia RB, Pinho RA. Resistance Exercise Training Improves Metabolic and Inflammatory Control in Adipose and Muscle Tissues in Mice Fed a High-Fat Diet. Nutrients 2022; 14:nu14112179. [PMID: 35683979 PMCID: PMC9182921 DOI: 10.3390/nu14112179] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2022] [Revised: 05/19/2022] [Accepted: 05/20/2022] [Indexed: 12/13/2022] Open
Abstract
This study investigates whether ladder climbing (LC), as a model of resistance exercise, can reverse whole-body and skeletal muscle deleterious metabolic and inflammatory effects of high-fat (HF) diet-induced obesity in mice. To accomplish this, Swiss mice were fed for 17 weeks either standard chow (SC) or an HF diet and then randomly assigned to remain sedentary or to undergo 8 weeks of LC training with progressive increases in resistance weight. Prior to beginning the exercise intervention, HF-fed animals displayed a 47% increase in body weight (BW) and impaired ability to clear blood glucose during an insulin tolerance test (ITT) when compared to SC animals. However, 8 weeks of LC significantly reduced BW, adipocyte size, as well as glycemia under fasting and during the ITT in HF-fed rats. LC also increased the phosphorylation of AktSer473 and AMPKThr172 and reduced tumor necrosis factor-alpha (TNF-α) and interleukin 1 beta (IL1-β) contents in the quadriceps muscles of HF-fed mice. Additionally, LC reduced the gene expression of inflammatory markers and attenuated HF-diet-induced NADPH oxidase subunit gp91phox in skeletal muscles. LC training was effective in reducing adiposity and the content of inflammatory mediators in skeletal muscle and improved whole-body glycemic control in mice fed an HF diet.
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Affiliation(s)
- Pauline S. Effting
- Faculty of Sports Science, Ningbo University, Ningbo 315211, China;
- Graduate Program in Health Science, Medical School, Universidade do Extremo Sul Catarinense, Criciúma 88806-000, SC, Brazil;
| | - Anand Thirupathi
- Faculty of Sports Science, Ningbo University, Ningbo 315211, China;
- Correspondence: (A.T.); (R.A.P.)
| | - Alexandre P. Müller
- Graduate de Pós-graduação em Farmacologia, Universidade Federal de Santa Catarina, Florianópolis 88020-302, SC, Brazil;
| | - Bárbara C. Pereira
- Graduate Program in Health Science, Medical School, Universidade do Extremo Sul Catarinense, Criciúma 88806-000, SC, Brazil;
| | - Diane M. Sepa-Kishi
- Health Research Centre, School of Kinesiology and Health Science, York University, Toronto, ON M3J 1P3, Canada; (D.M.S.-K.); (R.B.C.)
| | - Luis F. B. Marqueze
- Laboratory of Exercise Biochemistry in Health, Graduate Program in Health Sciences, School of Medicine, Pontifícia Universidade Católica do Paraná, Curitiba 80215-901, PR, Brazil; (L.F.B.M.); (F.T.F.V.); (R.T.N.)
| | - Franciane T. F. Vasconcellos
- Laboratory of Exercise Biochemistry in Health, Graduate Program in Health Sciences, School of Medicine, Pontifícia Universidade Católica do Paraná, Curitiba 80215-901, PR, Brazil; (L.F.B.M.); (F.T.F.V.); (R.T.N.)
| | - Renata T. Nesi
- Laboratory of Exercise Biochemistry in Health, Graduate Program in Health Sciences, School of Medicine, Pontifícia Universidade Católica do Paraná, Curitiba 80215-901, PR, Brazil; (L.F.B.M.); (F.T.F.V.); (R.T.N.)
| | - Talita C. B. Pereira
- Graduate Program in Cellular and Molecular Biology, School of Health and Life Sciences, Pontifical Catholic University of Rio Grande do Sul, Porto Alegre 90619-900, RS, Brazil; (T.C.B.P.); (L.W.K.); (M.R.B.)
| | - Luiza W. Kist
- Graduate Program in Cellular and Molecular Biology, School of Health and Life Sciences, Pontifical Catholic University of Rio Grande do Sul, Porto Alegre 90619-900, RS, Brazil; (T.C.B.P.); (L.W.K.); (M.R.B.)
| | - Maurício R. Bogo
- Graduate Program in Cellular and Molecular Biology, School of Health and Life Sciences, Pontifical Catholic University of Rio Grande do Sul, Porto Alegre 90619-900, RS, Brazil; (T.C.B.P.); (L.W.K.); (M.R.B.)
- Graduate Program in Medicine and Health Sciences, School of Medicine, Pontifical Catholic University of Rio Grande do Sul, Porto Alegre 90619-900, RS, Brazil
| | - Rolando B. Ceddia
- Health Research Centre, School of Kinesiology and Health Science, York University, Toronto, ON M3J 1P3, Canada; (D.M.S.-K.); (R.B.C.)
| | - Ricardo A. Pinho
- Faculty of Sports Science, Ningbo University, Ningbo 315211, China;
- Laboratory of Exercise Biochemistry in Health, Graduate Program in Health Sciences, School of Medicine, Pontifícia Universidade Católica do Paraná, Curitiba 80215-901, PR, Brazil; (L.F.B.M.); (F.T.F.V.); (R.T.N.)
- Correspondence: (A.T.); (R.A.P.)
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Hasegawa K, Takenaka N, Tanida K, Chan MP, Sakata M, Aiba A, Satoh T. Atrophy of White Adipose Tissue Accompanied with Decreased Insulin-Stimulated Glucose Uptake in Mice Lacking the Small GTPase Rac1 Specifically in Adipocytes. Int J Mol Sci 2021; 22:ijms221910753. [PMID: 34639094 PMCID: PMC8509237 DOI: 10.3390/ijms221910753] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2021] [Revised: 09/28/2021] [Accepted: 09/29/2021] [Indexed: 12/03/2022] Open
Abstract
Insulin stimulates glucose uptake in adipose tissue and skeletal muscle by inducing plasma membrane translocation of the glucose transporter GLUT4. Although the small GTPase Rac1 is a key regulator downstream of phosphoinositide 3-kinase (PI3K) and the protein kinase Akt2 in skeletal muscle, it remains unclear whether Rac1 also regulates glucose uptake in white adipocytes. Herein, we investigated the physiological role of Rac1 in white adipocytes by employing adipocyte-specific rac1 knockout (adipo-rac1-KO) mice. Subcutaneous and epididymal white adipose tissues (WATs) in adipo-rac1-KO mice showed significant reductions in size and weight. Actually, white adipocytes lacking Rac1 were smaller than controls. Insulin-stimulated glucose uptake and GLUT4 translocation were abrogated in rac1-KO white adipocytes. On the other hand, GLUT4 translocation was augmented by constitutively activated PI3K or Akt2 in control, but not in rac1-KO, white adipocytes. Similarly, to skeletal muscle, the involvement of another small GTPase RalA downstream of Rac1 was demonstrated. In addition, mRNA levels of various lipogenic enzymes were down-regulated in rac1-KO white adipocytes. Collectively, these results suggest that Rac1 is implicated in insulin-dependent glucose uptake and lipogenesis in white adipocytes, and reduced insulin responsiveness due to the deficiency of Rac1 may be a likely explanation for atrophy of WATs.
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Affiliation(s)
- Kiko Hasegawa
- Laboratory of Cell Biology, Department of Biological Science, Graduate School of Science, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan; (K.H.); (N.T.); (K.T.); (M.P.C.); (M.S.)
| | - Nobuyuki Takenaka
- Laboratory of Cell Biology, Department of Biological Science, Graduate School of Science, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan; (K.H.); (N.T.); (K.T.); (M.P.C.); (M.S.)
| | - Kenya Tanida
- Laboratory of Cell Biology, Department of Biological Science, Graduate School of Science, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan; (K.H.); (N.T.); (K.T.); (M.P.C.); (M.S.)
| | - Man Piu Chan
- Laboratory of Cell Biology, Department of Biological Science, Graduate School of Science, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan; (K.H.); (N.T.); (K.T.); (M.P.C.); (M.S.)
| | - Mizuki Sakata
- Laboratory of Cell Biology, Department of Biological Science, Graduate School of Science, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan; (K.H.); (N.T.); (K.T.); (M.P.C.); (M.S.)
| | - Atsu Aiba
- Laboratory of Animal Resources, Center for Disease Biology and Integrative Medicine, Graduate School of Medicine, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan;
| | - Takaya Satoh
- Laboratory of Cell Biology, Department of Biological Science, Graduate School of Science, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan; (K.H.); (N.T.); (K.T.); (M.P.C.); (M.S.)
- Correspondence: ; Tel.: +81-72-254-7650
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Ramos PA, Lytle KA, Delivanis D, Nielsen S, LeBrasseur NK, Jensen MD. Insulin-Stimulated Muscle Glucose Uptake and Insulin Signaling in Lean and Obese Humans. J Clin Endocrinol Metab 2021; 106:e1631-e1646. [PMID: 33382888 PMCID: PMC7993573 DOI: 10.1210/clinem/dgaa919] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/11/2020] [Indexed: 12/29/2022]
Abstract
PURPOSE Skeletal muscle is the primary site for insulin-stimulated glucose disposal, and muscle insulin resistance is central to abnormal glucose metabolism in obesity. Whether muscle insulin signaling to the level of Akt/AS160 is intact in insulin-resistant obese humans is controversial. METHODS We defined a linear range of insulin-stimulated systemic and leg glucose uptake in 14 obese and 14 nonobese volunteers using a 2-step insulin clamp (Protocol 1) and then examined the obesity-related defects in muscle insulin action in 16 nonobese and 25 obese male and female volunteers matched for fitness using a 1-step, hyperinsulinemic, euglycemic clamp coupled with muscle biopsies (Protocol 2). RESULTS Insulin-stimulated glucose disposal (Si) was reduced by > 60% (P < 0.0001) in the obese group in Protocol 2; however, the phosphorylation of Akt and its downstream effector AS160 were not different between nonobese and obese groups. The increase in phosphorylation of Akt2 in response to insulin was positively correlated with Si for both the nonobese (r = 0.53, P = 0.03) and the obese (r = 0.55, P = 0.01) groups. Total muscle GLUT4 protein was 17% less (P < 0.05) in obese subjects. CONCLUSIONS We suggest that reduced muscle glucose uptake in obesity is not due to defects in the insulin signaling pathway at the level of Akt/AS160, which suggests there remain significant gaps in our knowledge of muscle insulin resistance in obesity. Our data imply that models of acute lipotoxicity do not replicate the pathophysiology of obesity.
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Affiliation(s)
- Paola A Ramos
- Endocrine Research Unit, Mayo Clinic, Rochester, MN, USA
| | - Kelli A Lytle
- Endocrine Research Unit, Mayo Clinic, Rochester, MN, USA
| | | | - Søren Nielsen
- Steno Diabetes Center Aarhus, Aarhus University Hospital, Aarhus C, Denmark
| | | | - Michael D Jensen
- Endocrine Research Unit, Mayo Clinic, Rochester, MN, USA
- Correspondence: Michael D. Jensen, MD, Division of Endocrinology, Mayo Clinic, 200 First St SW, Joseph Rm 5–194, Rochester MN 55905, USA.
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6
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Complexin-2 redistributes to the membrane of muscle cells in response to insulin and contributes to GLUT4 translocation. Biochem J 2021; 478:407-422. [DOI: 10.1042/bcj20200542] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2020] [Revised: 12/11/2020] [Accepted: 01/04/2021] [Indexed: 11/17/2022]
Abstract
Insulin stimulates glucose uptake in muscle cells by rapidly redistributing vesicles containing GLUT4 glucose transporters from intracellular compartments to the plasma membrane (PM). GLUT4 vesicle fusion requires the formation of SNARE complexes between vesicular VAMP and PM syntaxin4 and SNAP23. SNARE accessory proteins usually regulate vesicle fusion processes. Complexins aide in neuro-secretory vesicle-membrane fusion by stabilizing trans-SNARE complexes but their participation in GLUT4 vesicle fusion is unknown. We report that complexin-2 is expressed and homogeneously distributed in L6 rat skeletal muscle cells. Upon insulin stimulation, a cohort of complexin-2 redistributes to the PM. Complexin-2 knockdown markedly inhibited GLUT4 translocation without affecting proximal insulin signalling of Akt/PKB phosphorylation and actin fiber remodelling. Similarly, complexin-2 overexpression decreased maximal GLUT4 translocation suggesting that the concentration of complexin-2 is finely tuned to vesicle fusion. These findings reveal an insulin-dependent regulation of GLUT4 insertion into the PM involving complexin-2.
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7
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Takenaka N, Nakao M, Hasegawa K, Chan MP, Satoh T. The guanine nucleotide exchange factor FLJ00068 activates Rac1 in adipocyte insulin signaling. FEBS Lett 2020; 594:4370-4380. [PMID: 32978791 DOI: 10.1002/1873-3468.13939] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Revised: 08/31/2020] [Accepted: 09/10/2020] [Indexed: 12/26/2022]
Abstract
Insulin stimulates glucose uptake via the translocation of the glucose transporter GLUT4 to the plasma membrane in adipocytes. Several lines of evidence suggest that the small GTPase Rac1 plays an important role in insulin-stimulated glucose uptake in skeletal muscle and adipocytes. The purpose of this study is to investigate the mechanisms whereby Rac1 is regulated in adipocyte insulin signaling. Here, we show that knockdown of the guanine nucleotide exchange factor FLJ00068 inhibits Rac1 activation and GLUT4 translocation by insulin and a constitutively activated form of the protein kinase Akt2. Furthermore, constitutively activated FLJ00068 induced Rac1 activation and Rac1-dependent GLUT4 translocation. Collectively, these results suggest the involvement of FLJ00068 downstream of Akt2 in insulin-stimulated glucose uptake signaling in adipocytes.
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Affiliation(s)
- Nobuyuki Takenaka
- Laboratory of Cell Biology, Department of Biological Science, Graduate School of Science, Osaka Prefecture University, Sakai, Japan
| | - Mika Nakao
- Laboratory of Cell Biology, Department of Biological Science, Graduate School of Science, Osaka Prefecture University, Sakai, Japan
| | - Kiko Hasegawa
- Laboratory of Cell Biology, Department of Biological Science, Graduate School of Science, Osaka Prefecture University, Sakai, Japan
| | - Man Piu Chan
- Laboratory of Cell Biology, Department of Biological Science, Graduate School of Science, Osaka Prefecture University, Sakai, Japan
| | - Takaya Satoh
- Laboratory of Cell Biology, Department of Biological Science, Graduate School of Science, Osaka Prefecture University, Sakai, Japan
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8
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Satoh T, Takenaka N. A critical role for the small GTPase Rac1 in insulin signaling that regulates glucose uptake in skeletal muscle. RESEARCH ON CHEMICAL INTERMEDIATES 2019. [DOI: 10.1007/s11164-019-03976-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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9
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A Crucial Role for the Small GTPase Rac1 Downstream of the Protein Kinase Akt2 in Insulin Signaling that Regulates Glucose Uptake in Mouse Adipocytes. Int J Mol Sci 2019; 20:ijms20215443. [PMID: 31683681 PMCID: PMC6861951 DOI: 10.3390/ijms20215443] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2019] [Accepted: 10/29/2019] [Indexed: 01/10/2023] Open
Abstract
Insulin-stimulated glucose uptake is mediated by translocation of the glucose transporter GLUT4 to the plasma membrane in adipocytes and skeletal muscle cells. In both types of cells, phosphoinositide 3-kinase and the protein kinase Akt2 have been implicated as critical regulators. In skeletal muscle, the small GTPase Rac1 plays an important role downstream of Akt2 in the regulation of insulin-stimulated glucose uptake. However, the role for Rac1 in adipocytes remains controversial. Here, we show that Rac1 is required for insulin-dependent GLUT4 translocation also in adipocytes. A Rac1-specific inhibitor almost completely suppressed GLUT4 translocation induced by insulin or a constitutively activated mutant of phosphoinositide 3-kinase or Akt2. Constitutively activated Rac1 also enhanced GLUT4 translocation. Insulin-induced, but not constitutively activated Rac1-induced, GLUT4 translocation was abrogated by inhibition of phosphoinositide 3-kinase or Akt2. On the other hand, constitutively activated Akt2 caused Rac1 activation, and insulin-induced Rac1 activation was suppressed by an Akt2-specific inhibitor. Moreover, GLUT4 translocation induced by a constitutively activated mutant of Akt2 or Rac1 was diminished by knockdown of another small GTPase RalA. RalA was activated by a constitutively activated mutant of Akt2 or Rac1, and insulin-induced RalA activation was suppressed by an Akt2- or Rac1-specific inhibitor. Collectively, these results suggest that Rac1 plays an important role in the regulation of insulin-dependent GLUT4 translocation downstream of Akt2, leading to RalA activation in adipocytes.
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10
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Jaiswal N, Gavin MG, Quinn WJ, Luongo TS, Gelfer RG, Baur JA, Titchenell PM. The role of skeletal muscle Akt in the regulation of muscle mass and glucose homeostasis. Mol Metab 2019; 28:1-13. [PMID: 31444134 PMCID: PMC6822261 DOI: 10.1016/j.molmet.2019.08.001] [Citation(s) in RCA: 88] [Impact Index Per Article: 17.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/14/2019] [Revised: 07/29/2019] [Accepted: 08/01/2019] [Indexed: 12/15/2022] Open
Abstract
OBJECTIVE Skeletal muscle insulin signaling is a major determinant of muscle growth and glucose homeostasis. Protein kinase B/Akt plays a prominent role in mediating many of the metabolic effects of insulin. Mice and humans harboring systemic loss-of-function mutations in Akt2, the most abundant Akt isoform in metabolic tissues, are glucose intolerant and insulin resistant. Since the skeletal muscle accounts for a significant amount of postprandial glucose disposal, a popular hypothesis in the diabetes field suggests that a reduction in Akt, specifically in skeletal muscle, leads to systemic glucose intolerance and insulin resistance. Despite this common belief, the specific role of skeletal muscle Akt in muscle growth and insulin sensitivity remains undefined. METHODS We generated multiple mouse models of skeletal muscle Akt deficiency to evaluate the role of muscle Akt signaling in vivo. The effects of these genetic perturbations on muscle mass, glucose homeostasis and insulin sensitivity were assessed using both in vivo and ex vivo assays. RESULTS Surprisingly, mice lacking Akt2 alone in skeletal muscle displayed normal skeletal muscle insulin signaling, glucose tolerance, and insulin sensitivity despite a dramatic reduction in phosphorylated Akt. In contrast, deletion of both Akt isoforms (M-AktDKO) prevented downstream signaling and resulted in muscle atrophy. Despite the absence of Akt signaling, in vivo and ex vivo insulin-stimulated glucose uptake were normal in M-AktDKO mice. Similar effects on insulin sensitivity were observed in mice with prolonged deletion (4 weeks) of both skeletal muscle Akt isoforms selectively in adulthood. Conversely, short term deletion (2 weeks) of skeletal muscle specific Akt in adult muscles impaired insulin tolerance paralleling the effect observed by acute pharmacological inhibition of Akt in vitro. Mechanistically, chronic ablation of Akt induced mitochondrial dysfunction and activation of AMPK, which was required for insulin-stimulated glucose uptake in the absence of Akt. CONCLUSIONS Together, these data indicate that chronic reduction in Akt activity alone in skeletal muscle is not sufficient to induce insulin resistance or prevent glucose uptake in all conditions. Therefore, since insulin-stimulated glucose disposal in skeletal muscle is markedly impaired in insulin-resistant states, we hypothesize that alterations in signaling molecules in addition to skeletal muscle Akt are necessary to perturb glucose tolerance and insulin sensitivity in vivo.
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Affiliation(s)
- N Jaiswal
- Institute for Diabetes, Obesity, and Metabolism, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
| | - M G Gavin
- Institute for Diabetes, Obesity, and Metabolism, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
| | - W J Quinn
- Institute for Diabetes, Obesity, and Metabolism, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
| | - T S Luongo
- Institute for Diabetes, Obesity, and Metabolism, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
| | - R G Gelfer
- Institute for Diabetes, Obesity, and Metabolism, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
| | - J A Baur
- Institute for Diabetes, Obesity, and Metabolism, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA; Department of Physiology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
| | - P M Titchenell
- Institute for Diabetes, Obesity, and Metabolism, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA; Department of Physiology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA.
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11
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Takenaka N, Araki N, Satoh T. Involvement of the protein kinase Akt2 in insulin-stimulated Rac1 activation leading to glucose uptake in mouse skeletal muscle. PLoS One 2019; 14:e0212219. [PMID: 30735546 PMCID: PMC6368313 DOI: 10.1371/journal.pone.0212219] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2018] [Accepted: 01/29/2019] [Indexed: 11/27/2022] Open
Abstract
Translocation of the glucose transporter GLUT4 to the sarcolemma accounts for glucose uptake in skeletal muscle following insulin administration. The protein kinase Akt2 and the small GTPase Rac1 have been implicated as essential regulators of insulin-stimulated GLUT4 translocation. Several lines of evidence suggest that Rac1 is modulated downstream of Akt2, and indeed the guanine nucleotide exchange factor FLJ00068 has been identified as an activator of Rac1. On the other hand, the mechanisms whereby Akt2 and Rac1 are regulated in parallel downstream of phosphoinositide 3-kinase are also proposed. Herein, we aimed to provide additional evidence that support a critical role for Akt2 in insulin regulation of Rac1 in mouse skeletal muscle. Knockdown of Akt2 by RNA interference abolished Rac1 activation following intravenous administration of insulin or ectopic expression of a constitutively activated phosphoinositide 3-kinase mutant. The activation of another small GTPase RalA and GLUT4 translocation to the sarcolemma following insulin administration or ectopic expression of a constitutively activated form of phosphoinositide 3-kinase, but not Rac1, were also diminished by downregulation of Akt2 expression. Collectively, these results strongly support the notion that Rac1 acts downstream of Akt2 leading to the activation of RalA and GLUT4 translocation to the sarcolemma in skeletal muscle.
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Affiliation(s)
- Nobuyuki Takenaka
- Laboratory of Cell Biology, Department of Biological Science, Graduate School of Science, Osaka Prefecture University, Sakai, Osaka, Japan
| | - Natsumi Araki
- Laboratory of Cell Biology, Department of Biological Science, Graduate School of Science, Osaka Prefecture University, Sakai, Osaka, Japan
| | - Takaya Satoh
- Laboratory of Cell Biology, Department of Biological Science, Graduate School of Science, Osaka Prefecture University, Sakai, Osaka, Japan
- * E-mail:
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12
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Hu F, Li N, Li Z, Zhang C, Yue Y, Liu Q, Chen L, Bilan PJ, Niu W. Electrical pulse stimulation induces GLUT4 translocation in a Rac-Akt-dependent manner in C2C12 myotubes. FEBS Lett 2018; 592:644-654. [PMID: 29355935 DOI: 10.1002/1873-3468.12982] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2017] [Revised: 01/07/2018] [Accepted: 01/15/2018] [Indexed: 12/12/2022]
Abstract
Muscle contraction increases skeletal muscle glucose uptake, but the underlying mechanisms are not fully elucidated. While important for insulin-stimulated glucose uptake, the role of Akt in contraction-stimulated muscle glucose uptake is controversial. In our study, C2C12 skeletal muscle myotubes were contracted by electrical pulse stimulation (EPS). We found that EPS leads to Akt phosphorylation on sites S473 and T308 in a time-dependent manner. The Akt inhibitor MK2206 partly reduces EPS-stimulated GLUT4 translocation without affecting EPS-stimulated AMPK phosphorylation. EPS activates Rac1 GTP-binding, and EPS-stimulated GLUT4 translocation is partly inhibited by Rac1 inhibitor II and siRac1. Interestingly, both Rac1 inhibitor II and siRac1 inhibit EPS-stimulated Akt phosphorylation on sites S473 and T308. Our findings implicate a Rac1-Akt signaling pathway in EPS-stimulated GLUT4 translocation in C2C12 myotubes.
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Affiliation(s)
- Fang Hu
- Department of Immunology, Key Laboratory of Immune Microenvironment and Disease (Ministry of Education), Tianjin Key Laboratory of Metabolic Diseases, Tianjin Metabolic Diseases Hospital, Tianjin Medical University, China
| | - Nana Li
- Department of Immunology, Key Laboratory of Immune Microenvironment and Disease (Ministry of Education), Tianjin Key Laboratory of Metabolic Diseases, Tianjin Metabolic Diseases Hospital, Tianjin Medical University, China
| | - Zhu Li
- Department of Immunology, Key Laboratory of Immune Microenvironment and Disease (Ministry of Education), Tianjin Key Laboratory of Metabolic Diseases, Tianjin Metabolic Diseases Hospital, Tianjin Medical University, China
| | - Chang Zhang
- Department of Immunology, Key Laboratory of Immune Microenvironment and Disease (Ministry of Education), Tianjin Key Laboratory of Metabolic Diseases, Tianjin Metabolic Diseases Hospital, Tianjin Medical University, China
| | - Yingying Yue
- Department of Immunology, Key Laboratory of Immune Microenvironment and Disease (Ministry of Education), Tianjin Key Laboratory of Metabolic Diseases, Tianjin Metabolic Diseases Hospital, Tianjin Medical University, China
| | - Qian Liu
- Department of Immunology, Key Laboratory of Immune Microenvironment and Disease (Ministry of Education), Tianjin Key Laboratory of Metabolic Diseases, Tianjin Metabolic Diseases Hospital, Tianjin Medical University, China
| | - Liming Chen
- Department of Immunology, Key Laboratory of Immune Microenvironment and Disease (Ministry of Education), Tianjin Key Laboratory of Metabolic Diseases, Tianjin Metabolic Diseases Hospital, Tianjin Medical University, China
| | - Philip J Bilan
- Cell Biology Program, The Hospital for Sick Children, Toronto, ON, Canada
| | - Wenyan Niu
- Department of Immunology, Key Laboratory of Immune Microenvironment and Disease (Ministry of Education), Tianjin Key Laboratory of Metabolic Diseases, Tianjin Metabolic Diseases Hospital, Tianjin Medical University, China
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13
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Latva-Rasku A, Honka MJ, Stančáková A, Koistinen HA, Kuusisto J, Guan L, Manning AK, Stringham H, Gloyn AL, Lindgren CM, Collins FS, Mohlke KL, Scott LJ, Karjalainen T, Nummenmaa L, Boehnke M, Nuutila P, Laakso M. A Partial Loss-of-Function Variant in AKT2 Is Associated With Reduced Insulin-Mediated Glucose Uptake in Multiple Insulin-Sensitive Tissues: A Genotype-Based Callback Positron Emission Tomography Study. Diabetes 2018; 67:334-342. [PMID: 29141982 PMCID: PMC5780065 DOI: 10.2337/db17-1142] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/21/2017] [Accepted: 11/07/2017] [Indexed: 12/30/2022]
Abstract
Rare fully penetrant mutations in AKT2 are an established cause of monogenic disorders of glucose metabolism. Recently, a novel partial loss-of-function AKT2 coding variant (p.Pro50Thr) was identified that is nearly specific to Finns (frequency 1.1%), with the low-frequency allele associated with an increase in fasting plasma insulin level and risk of type 2 diabetes. The effects of the p.Pro50Thr AKT2 variant (p.P50T/AKT2) on insulin-stimulated glucose uptake (GU) in the whole body and in different tissues have not previously been investigated. We identified carriers (N = 20) and matched noncarriers (N = 25) for this allele in the population-based Metabolic Syndrome in Men (METSIM)study and invited these individuals back for positron emission tomography study with [18F]-fluorodeoxyglucose during euglycemic hyperinsulinemia. When we compared p.P50T/AKT2 carriers to noncarriers, we found a 39.4% reduction in whole-body GU (P = 0.006) and a 55.6% increase in the rate of endogenous glucose production (P = 0.038). We found significant reductions in GU in multiple tissues-skeletal muscle (36.4%), liver (16.1%), brown adipose (29.7%), and bone marrow (32.9%)-and increases of 16.8-19.1% in seven tested brain regions. These data demonstrate that the p.P50T substitution of AKT2 influences insulin-mediated GU in multiple insulin-sensitive tissues and may explain, at least in part, the increased risk of type 2 diabetes in p.P50T/AKT2 carriers.
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Affiliation(s)
| | | | - Alena Stančáková
- Internal Medicine, Institute of Clinical Medicine, University of Eastern Finland, Kuopio, Finland
| | - Heikki A Koistinen
- University of Helsinki and Department of Medicine, Helsinki University Central Hospital, Helsinki, Finland
- Minerva Foundation Institute for Medical Research, Helsinki, Finland
| | - Johanna Kuusisto
- Internal Medicine, Institute of Clinical Medicine, University of Eastern Finland, Kuopio, Finland
- Department of Medicine, Kuopio University Hospital, Kuopio, Finland
| | - Li Guan
- Department of Biostatistics and Center for Statistical Genetics, University of Michigan, Ann Arbor, MI
| | - Alisa K Manning
- Program in Medical and Population Genetics, Broad Institute, Cambridge, MA
- Clinical and Translational Epidemiology Unit, Massachusetts General Hospital, Boston, MA
- Department of Medicine, Harvard Medical School, Boston, MA
| | - Heather Stringham
- Department of Biostatistics and Center for Statistical Genetics, University of Michigan, Ann Arbor, MI
| | - Anna L Gloyn
- Wellcome Trust Centre for Human Genetics, Nuffield Department of Medicine, University of Oxford, Oxford, U.K
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Radcliffe Department of Medicine, University of Oxford, Oxford, U.K
- National Institute for Health Research Oxford Biomedical Research Centre, Oxford University Hospitals NHS Foundation Trust, Oxford, U.K
| | - Cecilia M Lindgren
- Program in Medical and Population Genetics, Broad Institute, Cambridge, MA
- Wellcome Trust Centre for Human Genetics, Nuffield Department of Medicine, University of Oxford, Oxford, U.K
- Big Data Institute, Li Ka Shing Centre for Health Information and Discovery, University of Oxford, Oxford, U.K
| | | | - Francis S Collins
- National Human Genome Research Institute, National Institutes of Health, Bethesda, MD
| | - Karen L Mohlke
- Department of Genetics, University of North Carolina at Chapel Hill, Chapel Hill, NC
| | - Laura J Scott
- Department of Biostatistics and Center for Statistical Genetics, University of Michigan, Ann Arbor, MI
| | | | - Lauri Nummenmaa
- Turku PET Centre, University of Turku, Turku, Finland
- Department of Psychology, University of Turku, Finland
| | - Michael Boehnke
- Department of Biostatistics and Center for Statistical Genetics, University of Michigan, Ann Arbor, MI
| | - Pirjo Nuutila
- Turku PET Centre, University of Turku, Turku, Finland
- Department of Endocrinology, Turku University Hospital, Turku, Finland
| | - Markku Laakso
- Internal Medicine, Institute of Clinical Medicine, University of Eastern Finland, Kuopio, Finland
- Department of Medicine, Kuopio University Hospital, Kuopio, Finland
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14
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In situ detection of the activation of Rac1 and RalA small GTPases in mouse adipocytes by immunofluorescent microscopy following in vivo and ex vivo insulin stimulation. Cell Signal 2017; 39:108-117. [PMID: 28821441 DOI: 10.1016/j.cellsig.2017.08.004] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2017] [Revised: 07/15/2017] [Accepted: 08/14/2017] [Indexed: 01/01/2023]
Abstract
Rac1 has been implicated in insulin-dependent glucose uptake by mechanisms involving plasma membrane translocation of the glucose transporter GLUT4 in skeletal muscle. Although the uptake of glucose is also stimulated by insulin in adipose tissue, the role for Rac1 in adipocyte insulin signaling remains controversial. As a step to reveal the role for Rac1 in adipocytes, we aimed to establish immunofluorescent microscopy to detect the intracellular distribution of activated Rac1. The epitope-tagged Rac1-binding domain of a Rac1-specific target was utilized as a probe that specifically recognizes the activated form of Rac1. Rac1 activation in response to ex vivo and in vivo insulin stimulations in primary adipocyte culture and mouse white adipose tissue, respectively, was successfully observed by immunofluorescent microscopy. These Rac1 activations were mediated by phosphoinositide 3-kinase. Another small GTPase RalA has also been implicated in insulin-stimulated glucose uptake in skeletal muscle and adipose tissue. Similarly to Rac1, immunofluorescent microscopy using an activated RalA-specific polypeptide probe allowed us to detect intracellular distribution of insulin-activated RalA in adipocytes. These novel approaches to visualize the activation status of small GTPases in adipocytes will largely contribute to the understanding of signal transduction mechanisms particularly for insulin action.
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15
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Jaldin-Fincati JR, Pavarotti M, Frendo-Cumbo S, Bilan PJ, Klip A. Update on GLUT4 Vesicle Traffic: A Cornerstone of Insulin Action. Trends Endocrinol Metab 2017; 28:597-611. [PMID: 28602209 DOI: 10.1016/j.tem.2017.05.002] [Citation(s) in RCA: 180] [Impact Index Per Article: 25.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/20/2017] [Revised: 05/08/2017] [Accepted: 05/09/2017] [Indexed: 12/20/2022]
Abstract
Glucose transport is rate limiting for dietary glucose utilization by muscle and fat. The glucose transporter GLUT4 is dynamically sorted and retained intracellularly and redistributes to the plasma membrane (PM) by insulin-regulated vesicular traffic, or 'GLUT4 translocation'. Here we emphasize recent findings in GLUT4 translocation research. The application of total internal reflection fluorescence microscopy (TIRFM) has increased our understanding of insulin-regulated events beneath the PM, such as vesicle tethering and membrane fusion. We describe recent findings on Akt-targeted Rab GTPase-activating proteins (GAPs) (TBC1D1, TBC1D4, TBC1D13) and downstream Rab GTPases (Rab8a, Rab10, Rab13, Rab14, and their effectors) along with the input of Rac1 and actin filaments, molecular motors [myosinVa (MyoVa), myosin1c (Myo1c), myosinIIA (MyoIIA)], and membrane fusion regulators (syntaxin4, munc18c, Doc2b). Collectively these findings reveal novel events in insulin-regulated GLUT4 traffic.
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Affiliation(s)
| | - Martin Pavarotti
- Cell Biology Program, The Hospital for Sick Children, Toronto, ON M5J 2L4, Canada; IHEM, Universidad Nacional de Cuyo, CONICET, Mendoza 5500, Argentina
| | - Scott Frendo-Cumbo
- Cell Biology Program, The Hospital for Sick Children, Toronto, ON M5J 2L4, Canada; Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Philip J Bilan
- Cell Biology Program, The Hospital for Sick Children, Toronto, ON M5J 2L4, Canada
| | - Amira Klip
- Cell Biology Program, The Hospital for Sick Children, Toronto, ON M5J 2L4, Canada; Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada; Department of Biochemistry, University of Toronto, Toronto, ON M5S 1A8, Canada.
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16
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Deshmukh AS. Insulin-stimulated glucose uptake in healthy and insulin-resistant skeletal muscle. Horm Mol Biol Clin Investig 2017; 26:13-24. [PMID: 26485752 DOI: 10.1515/hmbci-2015-0041] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2015] [Accepted: 09/14/2015] [Indexed: 11/15/2022]
Abstract
Skeletal muscle is the largest tissues in the human body and is considered the primary target for insulin-stimulated glucose disposal. In skeletal muscle, binding of the insulin to insulin receptor (IR) initiates a signaling cascade that results in the translocation of the insulin-sensitive glucose transporter protein 4 (GLUT4) to the plasma membrane which leads to facilitated diffusion of glucose into the cell. Understanding the precise signaling events guiding insulin-stimulated glucose uptake is pivotal, because impairment in these signaling events leads to development of insulin resistance and type 2 diabetes. This review summarizes current understanding of insulin signaling pathways mediating glucose uptake in healthy and insulin-resistant skeletal muscle.
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17
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Tunduguru R, Thurmond DC. Promoting Glucose Transporter-4 Vesicle Trafficking along Cytoskeletal Tracks: PAK-Ing Them Out. Front Endocrinol (Lausanne) 2017; 8:329. [PMID: 29209279 PMCID: PMC5701999 DOI: 10.3389/fendo.2017.00329] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/05/2017] [Accepted: 11/06/2017] [Indexed: 12/27/2022] Open
Abstract
Glucose is the principal cellular energy source in humans and maintenance of glucose homeostasis is critical for survival. Glucose uptake into peripheral skeletal muscle and adipose tissues requires the trafficking of vesicles containing glucose transporter-4 (GLUT4) from the intracellular storage compartments to the cell surface. Trafficking of GLUT4 storage vesicles is initiated via the canonical insulin signaling cascade in skeletal muscle and fat cells, as well as via exercise-induced contraction in muscle cells. Recent studies have elucidated steps in the signaling cascades that involve remodeling of the cytoskeleton, a process that underpins the mechanical movement of GLUT4 vesicles. This review is focused upon an alternate phosphoinositide-3 kinase-dependent pathway involving Ras-related C3 botulinum toxin substrate 1 signaling through the p21-activated kinase p21-activated kinase 1 and showcases related signaling events that co-regulate both the depolymerization and re-polymerization of filamentous actin. These new insights provide an enriched understanding into the process of glucose transport and yield potential new targets for interventions aimed to improve insulin sensitivity and remediate insulin resistance, pre-diabetes, and the progression to type 2 diabetes.
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Affiliation(s)
- Ragadeepthi Tunduguru
- Department of Molecular and Cellular Endocrinology, Diabetes and Metabolism Research Institute of City of Hope, Duarte, CA, United States
| | - Debbie C. Thurmond
- Department of Molecular and Cellular Endocrinology, Diabetes and Metabolism Research Institute of City of Hope, Duarte, CA, United States
- *Correspondence: Debbie C. Thurmond,
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18
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Zhou X, Shentu P, Xu Y. Spatiotemporal Regulators for Insulin-Stimulated GLUT4 Vesicle Exocytosis. J Diabetes Res 2017; 2017:1683678. [PMID: 28529958 PMCID: PMC5424486 DOI: 10.1155/2017/1683678] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/26/2017] [Revised: 03/21/2017] [Accepted: 04/03/2017] [Indexed: 11/30/2022] Open
Abstract
Insulin increases glucose uptake and storage in muscle and adipose cells, which is accomplished through the mobilization of intracellular GLUT4 storage vesicles (GSVs) to the cell surface upon stimulation. Importantly, the dysfunction of insulin-regulated GLUT4 trafficking is strongly linked with peripheral insulin resistance and type 2 diabetes in human. The insulin signaling pathway, key signaling molecules involved, and precise trafficking itinerary of GSVs are largely identified. Understanding the interaction between insulin signaling molecules and key regulatory proteins that are involved in spatiotemporal regulation of GLUT4 vesicle exocytosis is of great importance to explain the pathogenesis of diabetes and may provide new potential therapeutic targets.
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Affiliation(s)
- Xiaoxu Zhou
- Department of Biomedical Engineering, Key Laboratory for Biomedical Engineering of Ministry of Education, Zhejiang Provincial Key Laboratory of Cardio-Cerebral Vascular Detection Technology and Medicinal Effectiveness Appraisal, Zhejiang University, Hangzhou 310027, China
| | - Ping Shentu
- Department of Biomedical Engineering, Key Laboratory for Biomedical Engineering of Ministry of Education, Zhejiang Provincial Key Laboratory of Cardio-Cerebral Vascular Detection Technology and Medicinal Effectiveness Appraisal, Zhejiang University, Hangzhou 310027, China
| | - Yingke Xu
- Department of Biomedical Engineering, Key Laboratory for Biomedical Engineering of Ministry of Education, Zhejiang Provincial Key Laboratory of Cardio-Cerebral Vascular Detection Technology and Medicinal Effectiveness Appraisal, Zhejiang University, Hangzhou 310027, China
- *Yingke Xu:
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19
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Wang C, Guelfi KJ, Yang HX. Exercise and its role in gestational diabetes mellitus. Chronic Dis Transl Med 2016; 2:208-214. [PMID: 29063044 PMCID: PMC5643755 DOI: 10.1016/j.cdtm.2016.11.006] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2016] [Indexed: 12/15/2022] Open
Abstract
Gestational diabetes mellitus (GDM) refers to diabetes diagnosed in the second or third trimester of pregnancy that is not clearly either type 1 or type 2 diabetes. GDM is a common medical complication in pregnancy that has been rapidly increasing worldwide. GDM is associated with both short- and long-term health issues for both mothers and offspring. Consistent with type 2 diabetes, peripheral insulin resistance contributes to the hyperglycemia associated with GDM. Accordingly, it is important to identify strategies to reduce the insulin resistance associated with GDM. To date, observational studies have shown that exercise can be a non-invasive therapeutic option for preventing and managing GDM that can be readily applied to the antenatal population. However, the relevant mechanisms for these outcomes are yet to be fully elucidated. The present review aimed to explain the potential mechanisms of exercise from the perspective of reducing the insulin resistance, which is the root cause of GDM. Exercise recommendations and opinions of exercise during pregnancy are briefly summarized.
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Affiliation(s)
- Chen Wang
- Department of Obstetrics and Gynecology of Peking University First Hospital, Beijing 100034, China
| | - Kym Janese Guelfi
- Exercise Physiology and Biochemistry, The University of Western Australia, Perth, Western Australia 6009, Australia
| | - Hui-Xia Yang
- Department of Obstetrics and Gynecology of Peking University First Hospital, Beijing 100034, China
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20
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Genome-wide landscape of DNA methylomes and their relationship with mRNA and miRNA transcriptomes in oxidative and glycolytic skeletal muscles. Sci Rep 2016; 6:32186. [PMID: 27561200 PMCID: PMC4999948 DOI: 10.1038/srep32186] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2016] [Accepted: 08/02/2016] [Indexed: 12/15/2022] Open
Abstract
The physiological, biochemical and functional differences between oxidative and glycolytic muscles play important roles in human metabolic health and in animal meat quality. To explore these differences, we determined the genome-wide landscape of DNA methylomes and their relationship with the mRNA and miRNA transcriptomes of the oxidative muscle psoas major (PMM) and the glycolytic muscle longissimus dorsi (LDM). We observed the hypo-methylation of sub-telomeric regions. A high mitochondrial content contributed to fast replicative senescence in PMM. The differentially methylated regions (DMRs) in promoters (478) and gene bodies (5,718) were mainly enriched in GTPase regulator activity and signaling cascade-mediated pathways. Integration analysis revealed that the methylation status within gene promoters (or gene bodies) and miRNA promoters was negatively correlated with mRNA and miRNA expression, respectively. Numerous genes were closely related to distinct phenotypic traits between LDM and PMM. For example, the hyper-methylation and down-regulation of HK-2 and PFKFB4 were related to decrease glycolytic potential in PMM. In addition, promoter hypo-methylation and the up-regulation of miR-378 silenced the expression of the target genes and promoted capillary biosynthesis in PMM. Together, these results improve understanding of muscle metabolism and development from genomic and epigenetic perspectives.
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21
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Varshney P, Dey CS. P21-activated kinase 2 (PAK2) regulates glucose uptake and insulin sensitivity in neuronal cells. Mol Cell Endocrinol 2016; 429:50-61. [PMID: 27040307 DOI: 10.1016/j.mce.2016.03.035] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/07/2016] [Revised: 03/25/2016] [Accepted: 03/29/2016] [Indexed: 12/15/2022]
Abstract
P21-activated kinases (PAKs) are recently reported as important players of insulin signaling and glucose homeostasis in tissues like muscle, pancreas and liver. However, their role in neuronal insulin signaling is still unknown. Present study reports the involvement of PAK2 in neuronal insulin signaling, glucose uptake and insulin resistance. Irrespective of insulin sensitivity, insulin stimulation decreased PAK2 activity. PAK2 downregulation displayed marked enhancement of GLUT4 translocation with increase in glucose uptake whereas PAK2 over-expression showed its reduction. Treatment with Akti-1/2 and wortmannin suggested that Akt and PI3K are mediators of insulin effect on PAK2 and glucose uptake. Rac1 inhibition demonstrated decreased PAK2 activity while inhibition of PP2A resulted in increased PAK2 activity, with corresponding changes in glucose uptake. Taken together, present study demonstrates an inhibitory role of insulin signaling (via PI3K-Akt) and PP2A on PAK2 activity and establishes PAK2 as a Rac1-dependent negative regulator of neuronal glucose uptake and insulin sensitivity.
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Affiliation(s)
- Pallavi Varshney
- Kusuma School of Biological Sciences, Indian Institute of Technology-Delhi, Hauz Khas, New Delhi 110016, India
| | - Chinmoy Sankar Dey
- Kusuma School of Biological Sciences, Indian Institute of Technology-Delhi, Hauz Khas, New Delhi 110016, India.
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22
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Takenaka N, Nihata Y, Satoh T. Rac1 Activation Caused by Membrane Translocation of a Guanine Nucleotide Exchange Factor in Akt2-Mediated Insulin Signaling in Mouse Skeletal Muscle. PLoS One 2016; 11:e0155292. [PMID: 27163697 PMCID: PMC4862641 DOI: 10.1371/journal.pone.0155292] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2016] [Accepted: 04/27/2016] [Indexed: 11/25/2022] Open
Abstract
Insulin-stimulated glucose uptake in skeletal muscle is mediated by the glucose transporter GLUT4, which is translocated to the plasma membrane following insulin stimulation. Several lines of evidence suggested that the protein kinase Akt2 plays a key role in this insulin action. The small GTPase Rac1 has also been implicated as a regulator of insulin-stimulated GLUT4 translocation, acting downstream of Akt2. However, the mechanisms whereby Akt2 regulates Rac1 activity remain obscure. The guanine nucleotide exchange factor FLJ00068 has been identified as a direct regulator of Rac1 in Akt2-mediated signaling, but its characterization was performed mostly in cultured myoblasts. Here, we provide in vivo evidence that FLJ00068 indeed acts downstream of Akt2 as a Rac1 regulator by using mouse skeletal muscle. Small interfering RNA knockdown of FLJ00068 markedly diminished GLUT4 translocation to the sarcolemma following insulin administration or ectopic expression of a constitutively activated mutant of either phosphoinositide 3-kinase or Akt2. Additionally, insulin and these constitutively activated mutants caused the activation of Rac1 as shown by immunofluorescent microscopy using a polypeptide probe specific to activated Rac1 in isolated gastrocnemius muscle fibers and frozen sections of gastrocnemius muscle. This Rac1 activation was also abrogated by FLJ00068 knockdown. Furthermore, we observed translocation of FLJ00068 to the cell periphery following insulin stimulation in cultured myoblasts. Localization of FLJ00068 in the plasma membrane in insulin-stimulated, but not unstimulated, myoblasts and mouse gastrocnemius muscle was further affirmed by subcellular fractionation and subsequent immunoblotting. Collectively, these results strongly support a critical role of FLJ00068 in Akt2-mediated Rac1 activation in mouse skeletal muscle insulin signaling.
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Affiliation(s)
- Nobuyuki Takenaka
- Laboratory of Cell Biology, Department of Biological Science, Graduate School of Science, Osaka Prefecture University, Sakai, Osaka, Japan
| | - Yuma Nihata
- Laboratory of Cell Biology, Department of Biological Science, Graduate School of Science, Osaka Prefecture University, Sakai, Osaka, Japan
| | - Takaya Satoh
- Laboratory of Cell Biology, Department of Biological Science, Graduate School of Science, Osaka Prefecture University, Sakai, Osaka, Japan
- * E-mail:
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23
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Silva Frederico MJ, Mascarello A, Castro AJG, Da Luz G, Altenhofen D, Mendes CP, Leal PC, Yunes RA, Nunes RJ, Silva FRMB. Incretinomimetic and Insulinomimetic Effect of (2E)-N′-(1′-Naphthyl)-3,4,5-Trimethoxybenzohydrazide for Glycemic Homeostasis. J Cell Biochem 2015; 117:1199-209. [DOI: 10.1002/jcb.25403] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2015] [Accepted: 10/06/2015] [Indexed: 12/29/2022]
Affiliation(s)
- Marisa Jádna Silva Frederico
- Departamento de Bioquímica; Universidade Federal de Santa Catarina; Centro de Ciências Biológicas; Campus Universitário; Bairro Trindade; Cx. Postal 5069, CEP: 88040-970 Florianópolis SC Brazil
| | - Alessandra Mascarello
- Departamento de Química; Universidade Federal de Santa Catarina; Centro de Ciências Físicas e Matemáticas; Campus Universitário; Bairro Trindade; CEP: 88040-900 Florianópolis SC Brazil
| | - Allisson Jhonatan Gomes Castro
- Departamento de Bioquímica; Universidade Federal de Santa Catarina; Centro de Ciências Biológicas; Campus Universitário; Bairro Trindade; Cx. Postal 5069, CEP: 88040-970 Florianópolis SC Brazil
| | - Gabrielle Da Luz
- Departamento de Bioquímica; Universidade Federal de Santa Catarina; Centro de Ciências Biológicas; Campus Universitário; Bairro Trindade; Cx. Postal 5069, CEP: 88040-970 Florianópolis SC Brazil
| | - Delsi Altenhofen
- Departamento de Bioquímica; Universidade Federal de Santa Catarina; Centro de Ciências Biológicas; Campus Universitário; Bairro Trindade; Cx. Postal 5069, CEP: 88040-970 Florianópolis SC Brazil
| | - Camila Pires Mendes
- Departamento de Bioquímica; Universidade Federal de Santa Catarina; Centro de Ciências Biológicas; Campus Universitário; Bairro Trindade; Cx. Postal 5069, CEP: 88040-970 Florianópolis SC Brazil
| | - Paulo Cesar Leal
- Departamento de Química; Universidade Federal de Santa Catarina; Centro de Ciências Físicas e Matemáticas; Campus Universitário; Bairro Trindade; CEP: 88040-900 Florianópolis SC Brazil
| | - Rosendo Augusto Yunes
- Departamento de Química; Universidade Federal de Santa Catarina; Centro de Ciências Físicas e Matemáticas; Campus Universitário; Bairro Trindade; CEP: 88040-900 Florianópolis SC Brazil
| | - Ricardo José Nunes
- Departamento de Química; Universidade Federal de Santa Catarina; Centro de Ciências Físicas e Matemáticas; Campus Universitário; Bairro Trindade; CEP: 88040-900 Florianópolis SC Brazil
| | - Fátima Regina Mena Barreto Silva
- Departamento de Bioquímica; Universidade Federal de Santa Catarina; Centro de Ciências Biológicas; Campus Universitário; Bairro Trindade; Cx. Postal 5069, CEP: 88040-970 Florianópolis SC Brazil
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24
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Abstract
The small GTPase RalA is required for Rac1-mediated glucose uptake and activated by Rac1 in mouse skeletal muscle fibres. This might be the first demonstration of the involvement of RalA in Rac1-mediated insulin signalling in mature skeletal muscle.
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25
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Sylow L, Møller LLV, Kleinert M, Richter EA, Jensen TE. Stretch-stimulated glucose transport in skeletal muscle is regulated by Rac1. J Physiol 2015; 593:645-56. [PMID: 25416624 DOI: 10.1113/jphysiol.2014.284281] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2014] [Accepted: 11/13/2014] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Rac1 regulates stretch-stimulated (i.e. mechanical stress) glucose transport in muscle. Actin depolymerization decreases stretch-induced glucose transport in skeletal muscle. Rac1 is a required part of the mechanical stress-component of the contraction-stimulus to glucose transport in skeletal muscle. ABSTRACT An alternative to the canonical insulin signalling pathway for glucose transport is muscle contraction/exercise. Mechanical stress is an integrated part of the muscle contraction/relaxation cycle, and passive stretch stimulates muscle glucose transport. However, the signalling mechanism regulating stretch-stimulated glucose transport is not well understood. We recently reported that the actin cytoskeleton regulating GTPase, Rac1, was activated in mouse muscle in response to stretching. Rac1 is a regulator of contraction- and insulin-stimulated glucose transport, however, its role in stretch-stimulated glucose transport and signalling is unknown. We therefore investigated whether stretch-induced glucose transport in skeletal muscle required Rac1 and the actin cytoskeleton. We used muscle-specific inducible Rac1 knockout mice as well as pharmacological inhibitors of Rac1 and the actin cytoskeleton in isolated soleus and extensor digitorum longus muscles. In addition, the role of Rac1 in contraction-stimulated glucose transport during conditions without mechanical load on the muscles was evaluated in loosely hanging muscles and muscles in which cross-bridge formation was blocked by the myosin ATPase inhibitors BTS and Blebbistatin. Knockout as well as pharmacological inhibition of Rac1 reduced stretch-stimulated glucose transport by 30-50% in soleus and extensor digitorum longus muscle. The actin depolymerizing agent latrunculin B similarly decreased glucose transport in response to stretching by 40-50%. Rac1 inhibition reduced contraction-stimulated glucose transport by 30-40% in tension developing muscle but did not affect contraction-stimulated glucose transport in muscles in which force development was prevented. Our findings suggest that Rac1 and the actin cytoskeleton regulate stretch-stimulated glucose transport and that Rac1 is a required part of the mechanical stress-component of the contraction-stimulus to glucose transport in skeletal muscle.
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Affiliation(s)
- Lykke Sylow
- Molecular Physiology Group, Department of Nutrition, Exercise and Sports, University of Copenhagen, Denmark
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Tropomodulin3 is a novel Akt2 effector regulating insulin-stimulated GLUT4 exocytosis through cortical actin remodeling. Nat Commun 2015; 6:5951. [PMID: 25575350 PMCID: PMC4354152 DOI: 10.1038/ncomms6951] [Citation(s) in RCA: 68] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2014] [Accepted: 11/25/2014] [Indexed: 12/19/2022] Open
Abstract
Akt2 and its downstream effectors mediate insulin-stimulated GLUT4-storage vesicle (GSV) translocation and fusion with the plasma membrane (PM). Using mass spectrometry, we identify actin-capping protein Tropomodulin 3 (Tmod3) as an Akt2-interacting partner in 3T3-L1 adipocytes. We demonstrate that Tmod3 is phosphorylated at Ser71 on insulin-stimulated Akt2 activation, and Ser71 phosphorylation is required for insulin-stimulated GLUT4 PM insertion and glucose uptake. Phosphorylated Tmod3 regulates insulin-induced actin remodelling, an essential step for GSV fusion with the PM. Furthermore, the interaction of Tmod3 with its cognate tropomyosin partner, Tm5NM1 is necessary for GSV exocytosis and glucose uptake. Together these results establish Tmod3 as a novel Akt2 effector that mediates insulin-induced cortical actin remodelling and subsequent GLUT4 membrane insertion. Our findings suggest that defects in cytoskeletal remodelling may contribute to impaired GLUT4 exocytosis and glucose uptake.
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Role of the guanine nucleotide exchange factor in Akt2-mediated plasma membrane translocation of GLUT4 in insulin-stimulated skeletal muscle. Cell Signal 2014; 26:2460-9. [DOI: 10.1016/j.cellsig.2014.07.002] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2014] [Accepted: 07/09/2014] [Indexed: 11/23/2022]
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Satoh T. Molecular mechanisms for the regulation of insulin-stimulated glucose uptake by small guanosine triphosphatases in skeletal muscle and adipocytes. Int J Mol Sci 2014; 15:18677-92. [PMID: 25325535 PMCID: PMC4227239 DOI: 10.3390/ijms151018677] [Citation(s) in RCA: 74] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2014] [Revised: 09/28/2014] [Accepted: 09/30/2014] [Indexed: 12/11/2022] Open
Abstract
Insulin is a hormone that regulates the blood glucose level by stimulating various physiological responses in its target tissues. In skeletal muscle and adipose tissue, insulin promotes membrane trafficking of the glucose transporter GLUT4 from GLUT4 storage vesicles to the plasma membrane, thereby facilitating the uptake of glucose from the circulation. Detailed mechanisms underlying insulin-dependent intracellular signal transduction for glucose uptake remain largely unknown. In this article, I give an overview on the recently identified signaling network involving Rab, Ras, and Rho family small guanosine triphosphatases (GTPases) that regulates glucose uptake in insulin-responsive tissues. In particular, the regulatory mechanisms for these small GTPases and the cross-talk between protein kinase and small GTPase cascades are highlighted.
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Affiliation(s)
- Takaya Satoh
- Laboratory of Cell Biology, Department of Biological Science, Graduate School of Science, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, Japan.
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Abstract
Insulin is secreted into blood vessels from β cells of pancreatic islets in response to high blood glucose levels. Insulin stimulates an array of physiological responses in target tissues, including liver, skeletal muscle, and adipose tissue, thereby reducing the blood glucose level. Insulin-dependent glucose uptake in skeletal muscle and adipose tissue is primarily mediated by the redistribution of the glucose transporter type 4 from intracellular storage sites to the plasma membrane. Evidence for the participation of the Rho family GTPase Rac1 in glucose uptake signaling in skeletal muscle has emerged from studies using cell cultures and genetically engineered mice. Herein, recent progress in understanding the function and regulation of Rac1, especially the cross-talk with the protein kinase Akt2, is highlighted. In addition, the role for another Rho family member TC10 and its regulatory mechanism in adipocyte insulin signaling are described.
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Affiliation(s)
- Takaya Satoh
- Laboratory of Cell Biology; Department of Biological Science; Graduate School of Science; Osaka Prefecture University; Osaka, Japan
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Abstract
Insulin regulates glucose uptake by controlling the subcellular location of GLUT4 glucose transporters. GLUT4 is sequestered within fat and muscle cells during low-insulin states, and is translocated to the cell surface upon insulin stimulation. The TUG protein is a functional tether that sequesters GLUT4 at the Golgi matrix. To stimulate glucose uptake, insulin triggers TUG endoproteolytic cleavage. Cleavage accounts for a large proportion of the acute effect of insulin to mobilize GLUT4 to the cell surface. During ongoing insulin exposure, endocytosed GLUT4 recycles to the plasma membrane directly from endosomes, and bypasses a TUG-regulated trafficking step. Insulin acts through the TC10α GTPase and its effector protein, PIST, to stimulate TUG cleavage. This action is coordinated with insulin signals through AS160/Tbc1D4 and Tbc1D1 to modulate Rab GTPases, and with other signals to direct overall GLUT4 targeting. Data support the idea that the N-terminal TUG cleavage product, TUGUL, functions as a novel ubiquitin-like protein modifier to facilitate GLUT4 movement to the cell surface. The C-terminal TUG cleavage product is extracted from the Golgi matrix, which vacates an "anchoring" site to permit subsequent cycles of GLUT4 retention and release. Together, GLUT4 vesicle translocation and TUG cleavage may coordinate glucose uptake with physiologic effects of other proteins present in the GLUT4-containing vesicles, and with potential additional effects of the TUG C-terminal product. Understanding this TUG pathway for GLUT4 retention and release will shed light on the regulation of glucose uptake and the pathogenesis of type 2 diabetes.
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Affiliation(s)
- Jonathan P Belman
- Section of Endocrinology and Metabolism, Department of Internal Medicine, and Department of Cell Biology, Yale University School of Medicine, 333 Cedar Street, Box 208020, New Haven, CT, 06520-8020, USA
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Takenaka N, Izawa R, Wu J, Kitagawa K, Nihata Y, Hosooka T, Noguchi T, Ogawa W, Aiba A, Satoh T. A critical role of the small GTPase Rac1 in Akt2-mediated GLUT4 translocation in mouse skeletal muscle. FEBS J 2014; 281:1493-1504. [DOI: 10.1111/febs.12719] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2013] [Revised: 12/27/2013] [Accepted: 01/12/2014] [Indexed: 11/29/2022]
Affiliation(s)
- Nobuyuki Takenaka
- Laboratory of Cell Biology; Department of Biological Science; Graduate School of Science; Osaka Prefecture University; Sakai Osaka Japan
| | - Rumi Izawa
- Laboratory of Cell Biology; Department of Biological Science; Graduate School of Science; Osaka Prefecture University; Sakai Osaka Japan
| | - Junyuan Wu
- Laboratory of Cell Biology; Department of Biological Science; Graduate School of Science; Osaka Prefecture University; Sakai Osaka Japan
| | - Kaho Kitagawa
- Laboratory of Cell Biology; Department of Biological Science; Graduate School of Science; Osaka Prefecture University; Sakai Osaka Japan
| | - Yuma Nihata
- Laboratory of Cell Biology; Department of Biological Science; Graduate School of Science; Osaka Prefecture University; Sakai Osaka Japan
| | - Tetsuya Hosooka
- Division of Diabetes and Endocrinology; Department of Internal Medicine; Kobe University Graduate School of Medicine; Hyogo Japan
| | - Tetsuya Noguchi
- Division of Diabetes and Endocrinology; Department of Internal Medicine; Kobe University Graduate School of Medicine; Hyogo Japan
| | - Wataru Ogawa
- Division of Diabetes and Endocrinology; Department of Internal Medicine; Kobe University Graduate School of Medicine; Hyogo Japan
| | - Atsu Aiba
- Laboratory of Animal Resources; Center for Disease Biology and Integrative Medicine; The University of Tokyo; Japan
| | - Takaya Satoh
- Laboratory of Cell Biology; Department of Biological Science; Graduate School of Science; Osaka Prefecture University; Sakai Osaka Japan
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Cloning and functional analysis of goat glucose transporter 4. Mol Biol Rep 2014; 41:757-68. [PMID: 24381100 DOI: 10.1007/s11033-013-2915-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2012] [Accepted: 12/17/2013] [Indexed: 12/12/2022]
Abstract
OBJECTIVES Glucose transporter (GLUT) 4 is a major mediator of blood glucose levels and a key regulator of whole-body glucose homeostasis. This study aimed at evaluating the function of goat GLUT4 on glucose absorption and the effect of GLUT4 on lactose synthesis in goat mammary gland epithelial (GMGE) cells. METHODS Currently, the cDNA of GLUT4, a putative facilitative GLUT, was cloned from goat. To investigate the function of goat GLUT4, we constructed the eukaryotic expression vector pcDNA3.1-GLUT4 and used it to transfect GMGE cells, and then GLUT4 transfected GMGE (G4T-GMGE) cells were generated. The deduced GLUT4 sequence comprised 509 amino acids, what meant that a putative protein with a molecular weight of approximately 55 kDa would be produced. Both glucose uptake and lactose synthesis increased in the G4T-GMGE cells compared with the GMGE cells. At the transcriptional level, GLUT4 expression increased by nearly 55-fold in the G4T-GMGE cells, and the expression of amino acid transporters (SLC1A5, SLC3A2 and SLC7A5) enhanced as well; in contrast, GLUT1 expression decreased by more than 50 % in the G4T-GMGE cells. CONCLUSION These results suggest that goat GLUT4 functions in the transport of glucose and it may play a positive role in amino acid uptake in mammary glands.
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Abstract
GLUT4 is regulated by its intracellular localization. In the absence of insulin, GLUT4 is efficiently retained intracellularly within storage compartments in muscle and fat cells. Upon insulin stimulation (and contraction in muscle), GLUT4 translocates from these compartments to the cell surface where it transports glucose from the extracellular milieu into the cell. Its implication in insulin-regulated glucose uptake makes GLUT4 not only a key player in normal glucose homeostasis but also an important element in insulin resistance and type 2 diabetes. Nevertheless, how GLUT4 is retained intracellularly and how insulin acts on this retention mechanism is largely unclear. In this review, the current knowledge regarding the various molecular processes that govern GLUT4 physiology is discussed as well as the questions that remain.
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Abstract
A signaling cascade is activated in podocytes to induce survival and cope with stress during advanced glomerular disease, a new study shows. The findings may also explain why the immunosuppressor sirolimus, an inhibitor of this pathway, can cause proteinuria in a subset of patients with chronic kidney disease (pages 1288–1296).
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