A Novel Animal Model in Diabetes: Regeneration of β cells in the Axolotl Salamander?

Abstract

Diabetes is an ever‐growing health issue affecting an estimate of 463 million people worldwide. Type 1 diabetes is characterized by hyperglycemia and loss of pancreatic β cell mass. Currently, there is no curative treatment of β cell loss. Humans have a poor natural ability to regenerate β cells, empathizing the importance of conducting research in regenerative medicine. However, this field of study is limited by the animal models available due to their inadequate intrinsic ability to regenerate, size and/or remoteness from humans. As the axolotl salamander (Ambystoma mexicanum) has an intrinsic ability to regenerate limbs and organs throughout life, it is an advantageous animal model for studying the physiological and molecular mechanisms of regeneration. Compared to zebrafish, a well‐established regenerative animal model of diabetes, the size of the axolotl (up to 150 g) is fit for pre‐clinical imaging systems and serial blood samples throughout an experiment without causing any detrimental effects.We hypothesize that the axolotl has the ability to regenerate β cells, giving it the potential of becoming a new regenerative animal model of diabetes. To generate a diabetes‐like axolotl, streptozotocin, a cytotoxic glucose analogue targeting β cells specifically, was injected intraperitoneally. Initially, a protocol inspired by studies of zebrafish were used, in which 0.35 mg/g body mass was given at day 0, 1, 2, 11, and 18 to group 1 (n=12). However, this dosage caused high mortality, and the experiment was terminated prematurely. Therefore, three new dosage regimes inspired by rodent studies were investigated. For group 2 (n=3), animals were treated with 0.05 mg/g body mass at 5 consecutive days, group 3 (n=3) was given 0.05 mg/g body mass at day 0, 2, 4, 12, and 19, and group 4 (n=3) was given a single dose of 0.2 mg/g body mass at day 0. Disease development was detected by glucose tolerance tests and will further be investigated with immunofluorescence. Potential off target effects of streptozotocin will be characterized by examining changes in red blood cell morphology and the histology of liver and kidney.We found that the treatment given to group 2 and 3 resulted in diabetes‐like symptoms when compared to a control group. Group 3 resulted in low‐grade hyperglycemia, whereas the 5 consecutive injections given to group 2 caused moderate hyperglycemia.Our results demonstrate that the axolotl is able to develop diabetes‐like symptoms by streptozotocin treatment. We anticipate that further adjustments to the dosage regime given to group 2 will result in severe hyperglycemia and thus model a diabetic axolotl, and that this animal model will be able to regenerate the lost β cells. Thus, this animal model will be useful for studying the cellular source of the regenerated cells and the molecular mechanisms of regeneration.