Glucagon receptor inactivation leads to α-cell hyperplasia in zebrafish.

Abstract

Glucagon antagonism is a potential treatment for diabetes. One potential side effect is α-cell hyperplasia, which has been noted in several approaches to antagonize glucagon action. To investigate the molecular mechanism of the α-cell hyperplasia and to identify the responsible factor, we created a zebrafish model in which glucagon receptor (gcgr) signaling has been interrupted. The genetically and chemically tractable zebrafish, which provides a robust discovery platform, has two gcgr genes (gcgra and gcgrb) in its genome. Sequence, phylogenetic, and synteny analyses suggest that these are co-orthologs of the human GCGR. Similar to its mammalian counterparts, gcgra and gcgrb are mainly expressed in the liver. We inactivated the zebrafish gcgra and gcgrb using transcription activator-like effector nuclease (TALEN) first individually and then both genes, and assessed the number of α-cells using an α-cell reporter line, Tg(gcga:GFP). Compared to WT fish at 7 days postfertilization, there were more α-cells in gcgra-/-, gcgrb-/-, and gcgra-/-;gcgrb-/- fish and there was an increased rate of α-cell proliferation in the gcgra-/-;gcgrb-/- fish. Glucagon levels were higher but free glucose levels were lower in gcgra-/-, gcgrb-/-, and gcgra-/-;gcgrb-/- fish, similar to Gcgr-/- mice. These results indicate that the compensatory α-cell hyperplasia in response to interruption of glucagon signaling is conserved in zebrafish. The robust α-cell hyperplasia in gcgra-/-;gcgrb-/- larvae provides a platform to screen for chemical and genetic suppressors, and ultimately to identify the stimulus of α-cell hyperplasia and its signaling mechanism.

• Authors: Mingyu Li, E Danielle Dean, Liyuan Zhao, Wendell E Nicholson, Alvin C Powers, Wenbiao Chen
• Journal: The Journal of endocrinology (J Endocrinol) Vol. 227 Issue 2 Pg. 93-103 (Nov 2015) ISSN: 1479-6805 [Electronic] England
• PMID: 26446275 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, U.S. Gov't, Non-P.H.S.)
• Copyright: © 2015 Society for Endocrinology.

Chemical References

• Receptors, Glucagon

Topics

• Animals
• Animals, Genetically Modified
• Cell Proliferation (genetics)
• Cloning, Molecular
• Embryo, Nonmammalian
• Gene Expression Regulation, Developmental
• Gene Silencing
• Glucagon-Secreting Cells (metabolism, pathology)
• Hyperplasia (genetics)
• Receptors, Glucagon (genetics, metabolism)
• Zebrafish