The level of secreted insulin determines whether nutrients are metabolized for storage, or storage complexes are broken down for generation of energy. Failure to produce insulin -or to properly respond to it- results in diabetes, an illness of epidemic proportions in the US. Insulin is secreted from pancreatic Langerhans' islets in response to high levels of glucose, further potentiated by fatty acids. This requires a rise in intracellular Ca2+ concentration, generated by L-type voltage dependent Ca2+ channels (VDCC). Insulin secretion from beta cells is modulated by signals released from A and D cells, and recent evidence suggests that this may also involve signaling mediated by glutamate, the major excitatory neurotransmitter in brain. Activation of neuronal NMDA- and AMPA-type glutamate receptors leads to Ca2+ influx (directly or via VDCC activation), and thus may contribute to Ca2+ signals also in islet cells. The Ca2+/calmodulin dependent protein kinase II (CaMKII) is established as a key mediator of neuronal Ca2+ signals. CaMKII may also be required for insulin secretion, however, this is largely based on experiments that used inhibitors which also affect other kinases as well as VDCCs. Currently, even the expression of CaMKII isoforms and glutamate-receptor types in Langerhans' islets and their distribution among the different cell types is unclear or controversial. The CaMKII isoforms can differ in their subcellular targeting and their ability to interact with other proteins (including NMDA receptors and possibly VDCCs). The subunit composition of ionotropic glutamate receptors determines channel properties (including Ca2+ conductance) and regulation of targeting. The CaMKII isoform and glutamate receptor subunit composition would thus affect the connection with other signaling molecules and pathways. Our ultimate goal is to determine if and how CaMKII, VDCCs, and glutamate receptors function together in the regulation of nutrient-induced insulin secretion from pancreatic beta cells. Understanding the mechanisms of insulin secretion regulation will allow to devise new therapeutic avenues for treatment of diabetes. In this proposal we will: (1) Determine expression pattern of CaMKII and glutamate receptor isoforms among islet cells. (2) Determine regulation of insulin secretion by CaMKII in isolated islets and in beta cell lines. (3) Test feasibility of methods to study function of specific CaMKII isoforms in beta cells and islets.

R21DK070735

2006-02-01

2009-01-31