Insulin is secreted from pancreatic islets in a pulsatile manner due to alternating periods of cellular activity and rest. The resulting pulses of insulin are critical for proper hormonal signaling and blood glucose regulation by the liver. To recreate the interaction between the endocrine pancreas and the liver using primary murine tissue, we have designed 3D printed microfluidic platforms that hold hepatocytes downstream of islets. Islets no longer oscillate in sync once isolated from the pancreas, so the cumulative insulin released is non-pulsatile as demonstrated by taking the average intracellular calcium levels of multiple islets (Figure A, top). To force islets to secrete synchronized insulin pulses in vitro, we use programable syringe pumps that flow alternating high (11mM) and low (3mM) glucose solutions over isolated mouse islets. The syringe pump system aligns the oscillations which results in synchronized insulin release (Figure A, bottom). Next, we exposed primary murine hepatocytes to either 100nM pulses of insulin in three-minute periods or constant 50nM insulin in a microfluidic system (Figure B). Both groups were exposed to the same amount of insulin, just in a different pattern. Hepatocytes treated with pulsatile insulin for 4 hours contained significantly more glycogen compared to those treated with continuous 50nM insulin (Plt;0.05, Nf4). Future experiments will add hepatocytes downstream of the islets on the same platform to investigate the effect of pulsatile insulin and glucagon secretion on liver function. Exploring the interaction between pancreatic islets and hepatocytes will lead to a deeper understanding of the loss of pulsatile hormone secretion during the progression of type 2 diabetes.
Supported by NIDDK 1R15DK121247-01 to CSN and the John J. Kopchick Research Fellowship Award.
Islets no longer oscillate in sync once isolated as shown by calcium imaging. Taking the average of all islets shows the cumulative insulin secreted would not be pulsatile (top). Exposing islets to alternating high (11mM) and low (3mM) glucose synchronizes oscillations (bottom). B.) Hepatocytes were treated with constant 50nM insulin or three-minute pulses of 100nM insulin. After 4 hours, glycogen content was significantly higher in the group exposed to pulsatile insulin (P <0.05, N=4).
