Novel findings explain indirect regulation of glucose homeostasis
The hormone secreting islets of Langerhans in the pancreas have a unique cyto-architecture that allows functional interrelationships between the different cell types. Somatostatin is secreted by the delta cell and is an effective inhibitor of the insulin-secreting beta cell and the glucagon-secreting alpha cell. According to a novel study from Sweden's Karolinska Instiutet, published in the journal Nature Communications, the delta cell can thereby indirectly affect glucose homeostasis in health and disease.
Our results provide important insight into the activity of the delta cell in health and pre-diabetes and a possible mechanism for how somatostatin can so effectively exert its potent suppressive effects within the islet of Langerhans," says senior author Professor Per-Olof Berggren of the Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet in Sweden, who is also a visiting professor at Lee Kong Chian School of Medicine, Singapore.
Most delta cells are elongated and have a well-defined cell soma and a filopodia-like structure. Using in vivo optogenetics and high-speed Ca2+ imaging, Per-Olof Berggren and his colleagues show that these filopodia are dynamic structures that contain a secretory machinery, enabling the delta cell to reach large numbers of beta cells within the islet.
This provides for efficient regulation of beta cell activity and is modulated by endogenous IGF-1/VEGF-A signaling. In pre-diabetes, delta cells undergo morphological changes that may be a compensation to maintain paracrine regulation of the beta cell.
"It has long been a mystery how delta cells so effectively regulate the function of alpha and beta cells, only constituting a minority among the hormone secreting cells," says Per-Olof Berggren. "These are fundamental data explaining an important structure/function relationship between delta cells and other hormone-secreting cells, and provides the basis for how delta cells, despite being in minority, can act as efficient modulators of glucose homeostasis."