α7 Nicotinic Acetylcholine Receptor Regulates the Function and Viability of L Cells

Endocrinology. 2018 Sep 1;159(9):3132-3142. doi: 10.1210/en.2018-00433.

Abstract

Enteroendocrine L cells secrete the incretin hormone glucagon-like peptide-1 (GLP-1), and they also express the α7 nicotinic acetylcholine receptor (α7nAChR), which may regulate GLP-1 secretion. Here, GTS-21, a selective α7nAChR agonist, was used to examine the effect of α7nAChR activation in L-cell lines, mouse intestinal primary cell cultures, and C57BL/6 mice. GTS-21 stimulated GLP-1 secretion in vitro, and this effect was attenuated by an α7nAChR antagonist or by α7nAChR-specific small interfering RNA. Under in vitro cell culture conditions of glucotoxicity, GTS-21 restored GLP-1 secretion and improved L-cell viability while also acting in vivo to raise levels of circulating GLP-1 in mice. To assess potential signaling mechanisms underlying these actions of GTS-21, we first monitored Ca2+, cAMP, and phosphatidylinositol 3-kinase (PI3K) activity. As expected for a GLP-1 secretagogue promoting Ca2+ influx through α7nAChR cation channels, [Ca2+]i increased in response to GTS-21, but [cAMP]i was unchanged. Surprisingly, pharmacological inhibition of growth factor signaling pathways revealed that GTS-21 also acts on the PI3K-protein kinase B-mammalian target of rapamycin pathway to promote L-cell viability. Moreover, the Ca2+ chelator BAPTA-AM counteracted GTS-21‒stimulated PI3K activity, thereby indicating unexpected crosstalk of L-cell Ca2+ and growth factor signaling pathways. Collectively, these data demonstrate that α7nAChR activation enhances GLP-1 secretion by increasing levels of cytosolic Ca2+ while also revealing Ca2+- and PI3K-dependent processes of α7nAChR activation that promote L-cell survival.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Benzylidene Compounds / pharmacology
  • Calcium / metabolism*
  • Cell Line
  • Cell Survival / drug effects
  • Cell Survival / physiology*
  • Cells, Cultured
  • Chelating Agents / pharmacology
  • Cyclic AMP / metabolism
  • Egtazic Acid / analogs & derivatives
  • Egtazic Acid / pharmacology
  • Enteroendocrine Cells / drug effects
  • Enteroendocrine Cells / metabolism*
  • Glucagon-Like Peptide 1 / drug effects
  • Glucagon-Like Peptide 1 / metabolism*
  • In Vitro Techniques
  • Mice
  • Mice, Inbred C57BL
  • Phosphatidylinositol 3-Kinase / drug effects
  • Phosphatidylinositol 3-Kinase / metabolism*
  • Proto-Oncogene Proteins c-akt / drug effects
  • Proto-Oncogene Proteins c-akt / metabolism
  • Pyridines / pharmacology
  • Signal Transduction / drug effects
  • TOR Serine-Threonine Kinases / drug effects
  • TOR Serine-Threonine Kinases / metabolism
  • alpha7 Nicotinic Acetylcholine Receptor / agonists
  • alpha7 Nicotinic Acetylcholine Receptor / metabolism*

Substances

  • Benzylidene Compounds
  • Chelating Agents
  • Chrna7 protein, mouse
  • Pyridines
  • alpha7 Nicotinic Acetylcholine Receptor
  • 1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester
  • Egtazic Acid
  • Glucagon-Like Peptide 1
  • 3-(2,4-dimethoxybenzylidene)anabaseine
  • Cyclic AMP
  • TOR Serine-Threonine Kinases
  • Phosphatidylinositol 3-Kinase
  • Proto-Oncogene Proteins c-akt
  • Calcium