p16Ink4a-induced senescence of pancreatic beta cells enhances insulin secretion

As beta cells age their levels of p16 rise, and the cells become senescent; rather than leading to dysfunction, this results in an increased capacity of the beta cells for glucose-stimulated insulin secretion. Cellular senescence is thought to contribute to age-associated deterioration of tissue physiology. The senescence effector p16 Ink4a is expressed in pancreatic beta cells during aging and limits their proliferative potential; however, its effects on beta cell function are poorly characterized. We found that beta cell–specific activation of p16 Ink4a in transgenic mice enhances glucose-stimulated insulin secretion (GSIS). In mice with diabetes, this leads to improved glucose homeostasis, providing an unexpected functional benefit. Expression of p16 Ink4a in beta cells induces hallmarks of senescence—including cell enlargement, and greater glucose uptake and mitochondrial activity—which promote increased insulin secretion. GSIS increases during the normal aging of mice and is driven by elevated p16 Ink4a activity. We found that islets from human adults contain p16 Ink4a -expressing senescent beta cells and that senescence induced by p16 Ink4a in a human beta cell line increases insulin secretion in a manner dependent, in part, on the activity of the mechanistic target of rapamycin (mTOR) and the peroxisome proliferator-activated receptor (PPAR)-γ proteins. Our findings reveal a novel role for p16 Ink4a and cellular senescence in promoting insulin secretion by beta cells and in regulating normal functional tissue maturation with age.