DESCRIPTION (provided by applicant): β-Cells secrete insulin within a dynamic range sufficient to clear high blood sugar [glucose-stimulated insulin secretion (GSIS)] but resulting in no hypoglycemia; this requires tight coordination between insulin granule storage and secretion. In this collaborative project, we propose to test our hypothesis that cytoskeletal polymers microtubules are overall coordinators of insulin granule allocation to reserve versus readily- releasable pools. Though microtubules have been considered as direct tracks for insulin granule transport to the cell edge, we unexpectedly found that microtubules exert negative GSIS regulation. Interestingly, our preliminary data indicate that high glucose stimuli cause dynamic rearrangement of the MT network, which makes insulin granules available for release. In the proposed experiments, we will determine the mechanisms of insulin granule restrain by microtubule network and physiological cues that modulate this restrain. We plan to dissect the place of microtubule remodeling in GSIS regulation by studying which glucose-dependent signaling pathway(s) and which microtubule-regulating molecule(s) are essential for this process. Since β-cell dysfunction is a strong factor contributing to T2DM, we will test whether microtubule rearrangements play a role in disease development, and whether microtubules might serve as druggable targets in diabetes therapies. Overall, this proposal will reveal a new role for the microtubule network in β cells, which extends far beyond simple transportation of granules. Our Specific Aims will determine: (1) the mechanisms whereby MTs regulate the availability of insulin granules for release; (2) pathways and mechanisms downstream of glucose that trigger MT destabilization; and (3) pathways and mechanisms downstream of glucose that control Golgi-derived MT nucleation. This study will be pursued as a close collaboration between Dr. Kaverina's and Gu's laboratories, who specialize in MT biology and β-cell development and function, respectively.