Dynamic glucoregulation and mammalian-like responses to metabolic and developmental disruption in zebrafish

University of Massachusetts Medical School, Diabetes Center of Excellence, 373 Plantation Street, Suite 218, Worcester, MA 01605, USA.
General and Comparative Endocrinology (Impact Factor: 2.47). 10/2010; 170(2):334-45. DOI: 10.1016/j.ygcen.2010.10.010
Source: PubMed


Zebrafish embryos are emerging as models of glucose metabolism. However, patterns of endogenous glucose levels, and the role of the islet in glucoregulation, are unknown. We measured absolute glucose levels in zebrafish and mouse embryos, and demonstrate similar, dynamic glucose fluctuations in both species. Further, we show that chemical and genetic perturbations elicit mammalian-like glycemic responses in zebrafish embryos. We show that glucose is undetectable in early zebrafish and mouse embryos, but increases in parallel with pancreatic islet formation in both species. In zebrafish, increasing glucose is associated with activation of gluconeogenic phosphoenolpyruvate carboxykinase1 (pck1) transcription. Non-hepatic Pck1 protein is expressed in mouse embryos. We show using RNA in situ hybridization, that zebrafish pck1 mRNA is similarly expressed in multiple cell types prior to hepatogenesis. Further, we demonstrate that the Pck1 inhibitor 3-mercaptopicolinic acid suppresses normal glucose accumulation in early zebrafish embryos. This shows that pre- and extra-hepatic pck1 is functional, and provides glucose locally to rapidly developing tissues. To determine if the primary islet is glucoregulatory in early fish embryos, we injected pdx1-specific morpholinos into transgenic embryos expressing GFP in beta cells. Most morphant islets were hypomorphic, not a genetic, but embryos still exhibited persistent hyperglycemia. We conclude from these data that the early zebrafish islet is functional, and regulates endogenous glucose. In summary, we identify mechanisms of glucoregulation in zebrafish embryos that are conserved with embryonic and adult mammals. These observations justify use of this model in mechanistic studies of human metabolic disease.

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Available from: Agata Jurczyk
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    • "Most importantly, we identified that activation of glucagon is required for β cell regeneration from both precursor pools. Furthermore, our results demonstrate that key physiological actions of glucagon in regulating blood glucose are conserved with mammals, just as for insulin (Kinkel and Prince, 2009; Jurczyk et al., 2011; Andersson et al., 2012); in particular, we found that in zebrafish glucagon activity is correlated with blood glucose levels, and that glucagon expression is upregulated in the absence of β cells. These findings further validate zebrafish as a model for studying human metabolic disease. "
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    • "Metformin was added to the water. Glucose measurements were performed using a fluorescence-based enzymatic detection kit (Biovision, Mountain View, CA, USA) as previously described (Jurczyk et al. 2011). "
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    • "These two peaks coincide with the two periods when the animals exhibit an increase in glucose levels [8], [16], suggesting that high glucose levels stimulate a compensatory increase in beta-cell number. Whether glucose exerts a direct effect on beta-cell proliferation or whether the increase in proliferation is the result of transient insulin resistance during these two periods, as shown in mouse models [5], [16], remains to be determined. Importantly, these analyses also revealed that from 72 to 96 hpf, a majority of beta-cells enter a period of quiescence. "
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