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Disruption of the glucagon receptor increases glucagon expression beyond α-cell hyperplasia in zebrafish
Qi Kang1, Jihong Zheng2, Jianxin Jia1
1School of Pharmaceutical Sciences and School of Life Sciences, Xiamen University, Xiamen, China; Fujian Provincial Key Laboratory of Innovative Drug Target Research, School of Pharmaceutical Sciences, Xiamen University, Xiamen, China.
Abstract:
The glucagon receptor (GCGR) is a potential target for diabetes therapy. Several emerging GCGR antagonism-based therapies are under preclinical and clinical development. However, GCGR antagonism, as well as genetically engineered GCGR deficiency in animal models, are accompanied by α-cell hyperplasia and hyperglucagonemia, which may limit the application of GCGR antagonism. To better understand the physiological changes in α cells following GCGR disruption, we performed single cell sequencing of α cells isolated from control and gcgr-/- (glucagon receptor deficient) zebrafish. Interestingly, beyond the α-cell hyperplasia, we also found that the expression of gcga, gcgb, pnoca, and several glucagon-regulatory transcription factors were dramatically increased in one cluster of gcgr-/- α cells. We further confirmed that glucagon mRNA was upregulated in gcgr-/- animals by in situ hybridization and that glucagon promoter activity was increased in gcgr-/-;Tg(gcga:GFP) reporter zebrafish. We also demonstrated that gcgr-/- α cells had increased glucagon protein levels and increased granules after GCGR disruption. Intriguingly, the increased mRNA and protein levels could be suppressed by treatment with high-level glucose or knockdown of the pnoca gene. In conclusion, these data demonstrated that GCGR deficiency not only induced α-cell hyperplasia but also increased glucagon expression in α cells, findings which provide more information about physiological changes in α-cells when the GCGR is disrupted.
Insights
Glucagon receptor (GCGR) deficiency in zebrafish causes alpha cell hyperplasia and increased glucagon production. High glucose or pnoca gene knockdown can suppress this effect, offering insights into diabetes therapy targets.
Area of Science:
- Endocrinology
- Molecular Biology
- Zebrafish Models
Background:
- The glucagon receptor (GCGR) is a key target for diabetes treatment.
- GCGR antagonism can lead to alpha cell hyperplasia and hyperglucagonemia, potentially limiting therapeutic efficacy.
- Understanding physiological changes in alpha cells upon GCGR disruption is crucial.
Purpose of the Study:
- To investigate the physiological consequences of glucagon receptor (GCGR) disruption on alpha cells.
- To elucidate the molecular mechanisms underlying alpha cell hyperplasia and hyperglucagonemia in GCGR-deficient models.
Main Methods:
- Single-cell RNA sequencing of alpha cells from control and GCGR-deficient (gcgr-/-) zebrafish.
- In situ hybridization to confirm glucagon mRNA expression.
- Reporter zebrafish (Tg(gcga:GFP)) to assess glucagon promoter activity.
- Assessment of glucagon protein levels and granule content.
Main Results:
- GCGR deficiency in zebrafish resulted in alpha cell hyperplasia.
- A subset of GCGR-deficient alpha cells exhibited significantly increased expression of gcga, gcgb, pnoca, and glucagon-regulatory transcription factors.
- Glucagon mRNA and protein levels were elevated in GCGR-deficient alpha cells.
- Increased glucagon expression was suppressed by high-level glucose treatment or pnoca gene knockdown.
Conclusions:
- GCGR deficiency induces not only alpha cell hyperplasia but also enhances glucagon expression.
- These findings provide novel insights into the complex physiological adaptations of alpha cells following GCGR disruption.
- Understanding these mechanisms may inform the development of safer and more effective diabetes therapies targeting the GCGR pathway.
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