An adenovirus-derived protein: A novel candidate for anti-diabetic drug development

Abstract

Aims Exposure to human adenovirus Ad36 is causatively and correlatively linked with better glycemic control in animals and humans, respectively. Although the anti-hyperglycemic property of Ad36 may offer some therapeutic potential, it is impractical to use an infectious agent for therapeutic benefit. Cell- based studies identified that Ad36 enhances cellular glucose disposal via its E4orf1 protein. Ability to improve glycemic control in vivo is a critical prerequisite for further investigating the therapeutic potential of E4orf1. Therefore, the aim of this study was to determine the ability of E4orf1 to improve glycemic control independent of insulin despite high fat diet. Materials & Methods 8–9wk old male C57BL/6J mice fed a high-fat diet (60% kcal) were injected with a retrovirus plasmid expressing E4orf1, or a null vector (Control). Glycemic control was determined by glucose and insulin tolerance test. Islet cell size, amount of insulin and glucagon were determined in formalin-fixed pancreas. Rat insulinoma cell line (832/13) was infected with E4orf1 or control to determine changes in glucose stimulated insulin secretion. Protein from flash frozen adipose tissue depots, liver and muscle was used to determine molecular signaling by western blotting. Results In multiple experiments, retrovirus-mediated E4orf1 expression in C57BL/6J mice significantly and reproducibly improved glucose excursion following a glucose load despite a high fat diet (60% energy). Importantly, E4orf1 improved glucose clearance without increasing insulin sensitivity, production or secretion, underscoring its insulin-independent effect. E4orf1 modulated molecular signaling in mice tissue, which included greater protein abundance of adiponectin, p-AKT and Glucose transporter Glu4. Conclusions This study provides the proof of concept for translational development of E4orf1 as a potential anti-diabetic agent. High fat intake and impaired insulin signaling are often associated with obesity, diabetes and insulin resistance. Hence, the ability of E4orf1 to improve glycemic control despite high fat diet and independent of insulin, is particularly attractive.

Reducing endogenous insulin is linked with protection against hepatic steatosis in mice

“…This study confirms previous findings that E4orf1 improves glucose clearance in mice in the presence of HF diet and exhibits its insulin sparing action [13][14][15][16]18 . The activation of E4orf1 reduced insulin requirement during glucose load in chow-dox diet, which later continued in HF-dox diet, whereas WT mice exhibited continued increase throughout the study.…”

“…Generally, in vivo reduction in insulin concomitant with an improvement in glycemic control is due to the improvement in insulin sensitivity. However, E4orf1 upregulates cellular glucose uptake independent of proximal insulin signaling 18,19 and does not improve insulin sensitivity [16][17][18] , yet it reduces endogenous insulin response 17 . The E4orf1-mediated reduction in insulin is not due to pancreatic beta cell damage or due to reduced ability of beta cells to secrete insulin 16,17 .…”

“…Subsequently, the E4orf1 protein of Ad36 was identified to have a similar anti-diabetic effect and reduced hepatic steatosis in high-fat (HF) diet-fed mice 13,14 . In mice, the expression of E4orf1 by transgenic approach or via viral vector reduces hepatic steatosis, improves glycemic control, and reduces the endogenous insulin response to glucose load 13,15,16 . This reduction in insulin is not due to an increase in insulin sensitivity 16,17 but due to the reduced requirement for insulin 6 .…”

“…We hypothesized that, in the mouse model of E4orf1 expression in adipose tissue, reduced levels of insulin, a lipogenic hormone, will be associated with reduced hepatic lipogenesis and steatosis. Another important aspect of the metabolic effects of E4orf1 is its potential as a drug to treat type 1 or type 2 diabetes [13][14][15][16]18,19 . While the effect of E4orf1 on HF-diet induced hyperglycemia is reported [13][14][15] , it is unclear whether E4orf1 will further reduce glucose levels in normoglycemic mice on a chow diet.…”

Twenty‐five years of research about adipogenic adenoviruses: A systematic review

“…Although cell culture studies showed that the E4orf1 gene of Ad36 is necessary and sufficient to induce adipogenesis in cells, studies that expressed E4orf1 in mice by transgenic approach or with the help of virus vectors did not show weight gain in mice expressing E4orf1. It is possible that the expression site and intensity of E4orf1 differs when expressed as a part of Ad36 infection.…”