OHSU scientist Carsten Schultz: Illuminating insulin release

Worldwide, rates of type 2 diabetes quadrupled between 1980 and 2016. That growth, reported by the World Health Organization last April, reflects the urgent need for prevention and improved treatment of diabetes. In current treatments of individuals with diabetes, measuring insulin levels is a fundamental tool.

Confocal images of MIN6 β cells expressing RINS1. Enlargement of the selected square (top right). Merged images (top), single channels (bottom), mCherry (magenta), sfGFP (green).
Confocal images of MIN6 β cells expressing RINS1. Enlargement of the selected square (top right). Merged images (top), single channels (bottom), mCherry (magenta), sfGFP (green).

Until now, laboratory tests have measured the total amount of insulin secreted by a large number of cells. But exploring the fundamental biology behind this process—and accurately testing drugs that could potentially control levels of insulin secretion—requires an understanding of how this works at the single-cell level.

Carsten Schultz, Ph.D., chair of the OHSU School of Medicine’s Department of Physiology and Pharmacology, led a multi-institution study that may give us a new optical method to measure the rate of insulin release from single cells in real time. The method was reported in Cell Chemical Biology.

Pancreatic beta cells produce proinsulin, the protein from which insulin is made. Proinsulin comprises an A chain, B chain, and a C-peptide that together form insulin. The C-peptide separates from the A and B chains during insulin formation. Once insulin and the C-peptide are separated, a normal beta cell releases both molecules at the same time

Using mouse beta cells, Schultz’s team tagged the A chain in a beta cell with a green fluorescent protein, and attached a molecule of a red fluorescent protein—mCherry—to the C-peptide. Unexpectedly, in the modified system, only the insulin tagged with the green fluorescent protein was released, while the C-peptide tagged with mCherry remained inside the cell.

Taking the ratio of green to red fluorescence provides a new way to measure the rate of insulin release that is a significant advance over existing methods, mainly because natural cell-to-cell variability can be addressed by this method.

The new tool is likely to be useful in observing the effects of drugs or drug candidates on the release of insulin, which is important in developing treatments for type 2 diabetes.

Co-authors of the paper are Martina Schifferer, Dmytro A. Yushchenko, Frank Stein, and Andrey Bolbat. The project was supported by the European Molecular Biology Laboratory; the EMBL Interdisciplinary Postdoc Program (M.S. and D.A.Y.); the EU Marie-Curie Program (EU grant 229597 for D.A.Y.); the Institute of Organic Chemistry and Biochemistry of the Czechoslovak Academy of Sciences (D.A.Y.); and the German Research Foundation (TRR186 for C.S.).