Pancreatic islets were isolated from the pancreas of C57/B6 mice (female, 6 to 8 weeks old, Charles River Laboratories, USA), as we previously described (28 (link)). Briefly, mice were anesthetized and then euthanized by cervical dislocation. The abdomen was opened, the bowel was moved to the left side, and the pancreas and common duct were then exposed. A hemostat clamp was placed on either side of the small intestine, and the pancreas was inflated through the bile duct with a 30-gauge needle and a 5-ml syringe containing 3 ml of cold collagenase solution. The pancreas was then removed from the body and placed in a vial containing 2 ml of collagenase. Digestion lasted for 10 min, and then the pellet was resuspended in Ficoll of different densities. The islet layer was identified, picked, and washed with Hanks’ balanced salt solution (Gibco, USA) supplemented with 0.1% bovine serum albumin (Gibco, USA). Islets were then individually counted and picked manually under a microscope.