Effect of a treat-to-target insulin therapy on ER crowding, proinsulin maturation and glucose tolerance.

<p>Mice were treated with a treat-to-target insulin therapy for a month and tested with intraperitoneal glucose tolerance test. Pancreatic sections were imaged with a transmission electron microscope and pancreatic islets were collected 48 hours after therapy withdrawal. A. Electron microscope images of insulin producing β-cells in pre-diabetic hProC(A7)Y-CpepGFP mice (insulin Detemir and vehicle treated) compared to wild-type controls. B. Western blotting of islets lysate in reducing SDS-PAGE gel showing the steady state levels of endogenous proinsulin (proinsulin), endogenous insulin (insulin), GFP-labeled mutant proinsulin (hProC(A7)Y-CpepGFP), fully processed GFP labeled C-peptide (CpepGFP), BIP, and α-tubulin for internal control. The lower panel shows graphic representation of endogenous insulin/proinsulin ratio. Three samples were used from each group. Representative samples are from two different vehicle treated pre-diabetic hProC(A7)Y-CpepGFP mice (left panel) and two different insulin treated pre-diabetic hProC(A7)Y-CpepGFP mice (middle panel). hProCpepGFP transgenic mouse and transfected HEK293 cells were used as controls to identify the location of specific bands. C. Intraperitoneal glucose tolerance test 48 hours and a week after insulin withdrawal in the same mice. Alleviation of ER crowding increased endogenous insulin/proinsulin ratio in pre-diabetic hProC(A7)Y-CpepGFP mice and temporarily normalized glucose tolerance.