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

ABSTRACT: Glucagon antagonism is a potential treatment for diabetes. One potential side effect is ?-cell hyperplasia, which has been noted in several approaches to antagonize glucagon action. To investigate the molecular mechanism of the ?-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 ?-cells using an ?-cell reporter line, Tg(gcga:GFP). Compared to WT fish at 7 days postfertilization, there were more ?-cells in gcgra-/-, gcgrb-/-, and gcgra-/-;gcgrb-/- fish and there was an increased rate of ?-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 ?-cell hyperplasia in response to interruption of glucagon signaling is conserved in zebrafish. The robust ?-cell hyperplasia in gcgra-/-;gcgrb-/- larvae provides a platform to screen for chemical and genetic suppressors, and ultimately to identify the stimulus of ?-cell hyperplasia and its signaling mechanism.

SUBMITTER: Li M 

PROVIDER: S-EPMC4598637 | biostudies-literature | 2015 Nov

REPOSITORIES: biostudies-literature