Insulin resistance and diabetes might promote neurodegenerative disease, but a molecular link between these disorders is unknown. Many factors are responsible for brain growth, patterning, and survival, including the insulin-insulin-like growth factor (IGF)-signaling cascades that are mediated by tyrosine phosphorylation of insulin receptor substrate (IRS) proteins. Irs2 signaling mediates peripheral insulin action and pancreatic β-cell function, and its failure causes diabetes in mice. In this study, we reveal two important roles for Irs2 signaling in the mouse brain. First, disruption of the Irs2 gene reduced neuronal proliferation during development by 50%, which dissociated brain growth from Irs1-dependent body growth. Second, neurofibrillary tangles containing phosphorylated tau accumulated in the hippocampus of old Irs2 knock-out mice, suggesting that Irs2 signaling is neuroprotective. Thus, dysregulation of the Irs2 branch of the insulin-Igf-signaling cascade reveals a molecular link between diabetes and neurodegenerative disease.

Sodium–glucose cotransporter (SGLT) inhibitors are new oral antidiabetes medications shown to effectively reduce glycated hemoglobin (A1C) and glycemic variability, blood pressure, and body weight without intrinsic properties to cause hypoglycemia in people with type 1 diabetes. However, recent studies, particularly in individuals with type 1 diabetes, have demonstrated increases in the absolute risk of diabetic ketoacidosis (DKA). Some cases presented with near-normal blood glucose levels or mild hyperglycemia, complicating the recognition/diagnosis of DKA and potentially delaying treatment. Several SGLT inhibitors are currently under review by the U.S. Food and Drug Administration and European regulatory agencies as adjuncts to insulin therapy in people with type 1 diabetes. Strategies must be developed and disseminated to the medical community to mitigate the associated DKA risk. This Consensus Report reviews current data regarding SGLT inhibitor use and provides recommendations to enhance the safety of SGLT inhibitors in people with type 1 diabetes.

Regulation of adult β-cell mass in pancreatic islets is essential to preserve sufficient insulin secretion in order to appropriately regulate glucose homeostasis. In many tissues mitogens influence development by stimulating D-type cyclins (D1, D2, or D3) and activating cyclin-dependent kinases (CDK4 or CDK6), which results in progression through the G₁ phase of the cell cycle. Here we show that cyclins D2 and D1 are essential for normal postnatal islet growth. In adult murine islets basal cyclin D2 mRNA expression was easily detected, while cyclin D1 was expressed at lower levels and cyclin D3 was nearly undetectable. Prenatal islet development occurred normally in cyclin D2^−/− or cyclin D1^+/− D2^−/− mice. However, β-cell proliferation, adult mass, and glucose tolerance were decreased in adult cyclin D2^−/− mice, causing glucose intolerance that progressed to diabetes by 12 months of age. Although cyclin D1^+/− mice never developed diabetes, life-threatening diabetes developed in 3-month-old cyclin D1^−/+ D2^−/− mice as β-cell mass decreased after birth. Thus, cyclins D2 and D1 were essential for β-cell expansion in adult mice. Strategies to tightly regulate D-type cyclin activity in β cells could prevent or cure diabetes.