Malin Fex,

Hjelt Grant Holder 2021,

Lund University.

Metabolism of nutrients in our body is regulated mainly by two hormones; insulin and glucagon. These hormones are secreted from beta and alpha-cells respectively, that are located in small spherical dense cell clusters, termed islets of Langerhans, in the pancreas. Type 2 diabetes (T2D) is a disease resulting from a combination of reduced circulating insulin and a decline in the action of the hormone in peripheral tissues. This results in increased blood glucose levels, a perturbation that over time becomes life-threatening. In addition, glucagon secretion from alpha cells becomes dysregulated in T2D and this contributes even further to high blood glucose concentrations. Therefore, understanding how both these cell types and their hormones act are essential to understand the disease.

The causes of T2D are pleiotropic (e.g., a combination of genetic predisposition and life style), where obesity and a sedentary life style are considered as the main risk factors. Our research aims to understand how genetic risk is associated with T2D and how dysfunction of insulin- and glucagon-producing cells is connected to these events. More specifically, we aim to understand the underlying molecular mechanisms of genetic variants that cause disease under certain conditions. One such gene variant currently studied by us is located in a gene encoding a receptor protein that mediates signals of the hormone melatonin (a molecule that binds melatonin – called melatonin receptor 1B (MTNR1B)). Melatonin is a hormone secreted from the pineal gland in the brain and it regulates sleep and wake patterns in humans. Melatonin can bind and signal via two melatonin receptors, the MTNR1B or the MTNR1A. In addition to regulating sleep-wake cycles, melatonin is involved in regulating the body’s energy demand. Furthermore, the receptors binding melatonin are present on beta and alpha cells. As such, the how and when of melatonin signaling in the insulin- and glucagon-producing cells is of great importance for understanding how T2D evolves.

To understand the properties of melatonin signaling in beta and alpha cells, we will use patient-specific human induced pluripotent stem cells (hiPSCs), which are differentiated to alpha- and beta-like cells.  A small skin biopsy (2mm) is taken from the arm of the individuals included in the study. These skin cells are reprogrammed by adding specific factors that reprogram skin cells to stem cells, the hiPSCs. hiPSCs have the capacity to become almost any cell type if treated with the right factors. The past two years, our research team has refined this technique, and we are now able to make beta- and alpha-like cells from human skin cells. This is a tremendous opportunity for our studies, as we now can investigate specific diabetes genes from humans in a cell culture dish.  We will utilize skin biopsies from patients with T2D that carry the MTNR1B risk variant, as well healthy individuals that do not carry this variant. The next steps involve so called “genetic scissors” to change the risk variant in the MTNR1B gene to a non-risk variant in the hiPSCs. In addition, we will create cells where we completely delete/knock out the two melatonin receptors. This will enable us to study regulation of insulin and glucagon secretion in our genetically modified beta and alpha like cells.

Presently, we have differentiated skin cells from seven individuals to commence functional studies of beta- and alpha-like cells, by high resolution microscopy techniques. We have utilized genetic scissors to modify the risk variant of MTNR1B to non-risk variants in cells from two patients and confirmed that they are viable and functional. Our next steps are to create beta- and alpha-like cells that completely lack the two receptors for melatonin (MTNR1B and MTNR1A) to even further understand the role of melatonin in regulating insulin and glucagon secreting cells, as well as to more fully understand the genetic contribution of the MTNR1B variant in the disease. We strongly believe that our studies will deepen our understanding of how T2D evolves. Additionally, our models can be utilized, not only to determine genetic influence and the role of melatonin in T2D, but the cell models we create will allow for screening of pharmacological compounds targeting melatonin signaling. This information can in turn be utilized to provide novel precision medicine tools and thus innovative therapeutic strategies to combat T2D.