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Serotonin regulates glucose-stimulated insulin secretion from pancreatic ? cells during pregnancy.

ABSTRACT: In preparation for the metabolic demands of pregnancy, ? cells in the maternal pancreatic islets increase both in number and in glucose-stimulated insulin secretion (GSIS) per cell. Mechanisms have been proposed for the increased ? cell mass, but not for the increased GSIS. Because serotonin production increases dramatically during pregnancy, we tested whether flux through the ionotropic 5-HT3 receptor (Htr3) affects GSIS during pregnancy. Pregnant Htr3a(-/-) mice exhibited impaired glucose tolerance despite normally increased ? cell mass, and their islets lacked the increase in GSIS seen in islets from pregnant wild-type mice. Electrophysiological studies showed that activation of Htr3 decreased the resting membrane potential in ? cells, which increased Ca(2+) uptake and insulin exocytosis in response to glucose. Thus, our data indicate that serotonin, acting in a paracrine/autocrine manner through Htr3, lowers the ? cell threshold for glucose and plays an essential role in the increased GSIS of pregnancy.

SUBMITTER: Ohara-Imaizumi M

PROVIDER: S-EPMC3845121 | biostudies-literature | 2013 Nov

REPOSITORIES: biostudies-literature

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Serotonin regulates glucose-stimulated insulin secretion from pancreatic β cells during pregnancy.

Ohara-Imaizumi Mica M Kim Hail H Yoshida Masashi M Fujiwara Tomonori T Aoyagi Kyota K Toyofuku Yukiko Y Nakamichi Yoko Y Nishiwaki Chiyono C Okamura Tadashi T Uchida Toyoyoshi T Fujitani Yoshio Y Akagawa Kimio K Kakei Masafumi M Watada Hirotaka H German Michael S MS Nagamatsu Shinya S

Proceedings of the National Academy of Sciences of the United States of America 20131111 48

In preparation for the metabolic demands of pregnancy, β cells in the maternal pancreatic islets increase both in number and in glucose-stimulated insulin secretion (GSIS) per cell. Mechanisms have been proposed for the increased β cell mass, but not for the increased GSIS. Because serotonin production increases dramatically during pregnancy, we tested whether flux through the ionotropic 5-HT3 receptor (Htr3) affects GSIS during pregnancy. Pregnant Htr3a(-/-) mice exhibited impaired glucose tole ...[more]

PMID: 24218571

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Project description:AIMS/HYPOTHESIS:Rho GTPases (Ras-related C3 botulinum toxin substrate 1 [Rac1] and cell division cycle 42 [Cdc42]) have been shown to regulate glucose-stimulated insulin secretion (GSIS) via cytoskeletal remodelling, trafficking and fusion of insulin-secretory granules with the plasma membrane. GTP loading of these G proteins, which is facilitated by GDP/GTP exchange factors, is a requisite step in the regulation of downstream effector proteins. Guanine nucleotide exchange factor VAV2 (VAV2), a member of the Dbl family of proteins, has been identified as one of the GDP/GTP exchange factors for Rac1. Despite recent evidence on the regulatory roles of VAV2 in different cell types, roles of this guanine nucleotide exchange factor in the signalling events leading to GSIS remain undefined. Using immunological, short interfering RNA (siRNA), pharmacological and microscopic approaches we investigated the role of VAV2 in GSIS from islet beta cells. METHODS:Co-localisation of Rac1 and VAV2 was determined by Triton X-114 phase partition and confocal microscopy. Glucose-induced actin remodelling was quantified by live cell imaging using the LifeAct-GFP fluorescent biosensor. Rac1 activation was determined by G protein linked immunosorbent assay (G-LISA). RESULTS:Western blotting indicated that VAV2 is expressed in INS-1 832/13 beta cells, normal rat islets and human islets. Vav2 siRNA markedly attenuated GSIS in INS-1 832/13 cells. Ehop-016, a newly discovered small molecule inhibitor of the VAV2-Rac1 interaction, or siRNA-mediated knockdown of VAV2 markedly attenuated glucose-induced Rac1 activation and GSIS in INS-1 832/13 cells. Pharmacological findings were recapitulated in primary rat islets. A high glucose concentration promoted co-localisation of Rac1 and VAV2. Real-time imaging in live cells indicated a significant inhibition of glucose-induced cortical actin remodelling by Ehop-016. CONCLUSIONS/INTERPRETATION:Our data provide the first evidence to implicate VAV2 in glucose-induced Rac1 activation, actin remodelling and GSIS in pancreatic beta cells.

Dataset Information

Serotonin regulates glucose-stimulated insulin secretion from pancreatic ? cells during pregnancy.

Publications

Serotonin regulates glucose-stimulated insulin secretion from pancreatic β cells during pregnancy.

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