Obesity is often associated with hyperinsulinemia due to insulin resistance. In mice models of hyperinsulinemia, adenovirus-derived E4orf1 protein promotes glucose disposal via insulin-independent pathway, and reduces insulin response to glucose load, described as its “Insulin Sparing Action”. This is likely because less insulin is needed for disposing glucose in presence of E4orf1, however, there are other potential possibilities. This study determined if E4orf1 reduces insulin response to glucose load because it a) suppresses the ability of pancreatic β-cells to secret insulin, or b) upregulates glucagon production by the pancreas.
C57BL/6J wild type (control) and transgenic C57BL/6J (E4orf1) mice that express E4orf1 protein in adipose tissue upon doxycycline feeding, were used. Post-doxycycline feeding, insulin and glucagon secretion in response to glibenclamide or phenylephrine were compared between the two groups. The pancreases were examined for histological changes.
In response to glibenclamide, E4orf1 mice secreted more insulin and exhibited lower blood glucose compared to control (47.4 ± 4.4 vs 27.4 ± 3.7 mg/dl, p < 0.003), but showed no difference in glucagon secretion. Post-phenylephrine injection, no differences were observed between the two groups for glucagon or insulin, except E4orf1 mice had a lower blood glucose rise after 10-min of injection compared to the control (39.7 ± 4.7 vs. 58.3 ± 7.5 mg/dl, p < 0.05). E4orf1 mice had significantly larger pancreatic islets and higher number of islets per mm2 tissue area. Neither the size nor the number of islets met the criteria of hypertrophy or hyperplasia.
E4orf1 retains and may enhance the ability of the pancreases to secret insulin in response to insulin secretagogue. Glucagon does not seem to play a role in the Insulin Sparing Action of E4orf1. Overall, the histology studies support better pancreatic islet health in presence of E4orf1, compared to that in control mice. The “insulin-independent” role of E4orf1 has potential therapeutic implications in addressing hyperinsulinemia in obesity.
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The authors thank Jeremy Warner and Marisa Sanchez of Reveal Biosciences for their technical assistance.
NVD has received several patents in viral obesity and adenovirus 36, including uses for E1A, E4ORF1 gene and protein, and AKT1inhibitor, and has received past grant support from Vital Health Interventions for determining anti-diabetic properties of E4‐ORF1 protein. Drs. Dhurandhar and Hegde recently received funding from Insparin Inc, which is a company created to advance the development of E4orf1 as a therapeutic agent. NVD owns shares in Insparin Ins. Funding from Insparin was not received for this study. Other authors did not have any conflict of interest.
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Akheruzzaman, M., Hegde, V., Siddik, M.A.B. et al. E4orf1-induced reduction in endogenous insulin level is independent of pancreas endocrine function. Int J Obes 46, 918–925 (2022). https://doi.org/10.1038/s41366-021-01062-3