Description:

Lipids are essential for normal insulin release in response to elevated glucose. Islets depleted of their triglyceride stores exhibit markedly reduced glucose-stimulated insulin secretion (GSIS) when assayed in vitro. This defect is corrected by the addition of exogenous free factty acids (FFA). Paradoxically, chronic elevation of serum FFA also impairs GSIS and may account for changes in secretion seen in either type 2 diabetes (T2D) or T2D with obesity. Increased cytosolic Ca²⁺ and protein kinase C activation are positive signals for insulin secretion. In vitro, exogenous FFA dramatically potentiates GSIS while their intracellular products stimulate PKC activity. Agents that potentiate, but do not initiate secretion, are known as incretins and include second messengers like cAMP as well as activators of PKC. Little is known of the intracellular steps within the beta cell linking increased FFA levels to the potentiation of GSIS.

Current progress:

Our preliminary studies have used two of the imaging technologies in the Biocurents Research Center: the Zeiss confocal microscope system and the Perkin-Elmer spinning disk confocal technology. First, preliminary studies using fluorescently tagged PKC-alpha show a dramatic, rapid and reversible intracellular redistribution following fatty acid addition to pancreatic beta cells using the Zeiss system. In the future we would like to take advantage of the heated and gassed perifusion chamber fitted to this scope to examine our responses under more physiological conditions and perhaps directly correlate them to insulin release. Secondly, using fluo-4 loaded beta cells and the Perkin-Elmer system to measure intracellular Ca²⁺ demonstrated spontaneous and random oscillations in intracellular Ca²⁺ with the cells at rest. Fatty acid application rapidly increased this parameter and markedly altered the pattern of oscillations. In the future we would like to take advantage of the time and spatial resolution of this system to examine the intracellular origins of these changes in calcium metabolism.

Our long-term goal is to understand how the incretin action of FFA is altered in T2D with obesity by first understanding its function and mechanism in normal physiology. Therefore, our immediate goal is to understand how an acute rise in long-chain FFA potentiates GSIS.