Novel components of mitochondrial regulation of insulin secretion in type 2 diabetes

PROJECT SUMMARY The success of preventive and supportive approaches in type 2 diabetes mellitus (T2D) depends on the spontaneous recovery of β-cell function. A central component of β-cell function, glucose metabolism, is impaired in T2D. Its causes, and how this impairment might lead to functional failure of β-cells, remain unknown. Until delineated, targeting of the dysfunctional pathways and addressing the cause of the ab- normality are unlikely and therapies remain supportive rather than disease-modifying. The overall objec- tive is to identify components of human β-cell metabolism that are critical for insulin secretion in healthy individuals and fail to support physiological secretion in T2D, and to identify components mediating β-cell compensation. We have identified a novel intramitochondrial metabolic activation phenomenon as such a component, and intend to determine its mechanism and role. The central hypothesis of the project is that in T2D β-cells a metabolic rearrangement impairs the response of β-cells to glucose by limiting the acti- vation of succinate dehydrogenase (SDH), and triggers an upregulation of amplification pathways, alter- ing the physiological dynamics of insulin secretion in T2D. Using human organ donor islets and micro- scale bioenergetic and cell physiology assaying together with genetic (CRISPR) and pharmacological modulation of metabolism, 1) The mechanism of bioenergetic activation of normal human β-cells during glucose-stimulated insulin secretion (GSIS) will be identified. We hypothesize that the activation of SDH is required for GSIS, and this is conveyed by metabolic coupling factor pathways through regulating ma- trix oxaloacetate, malonate or the flux control by SDH. 2) The mechanism of T2D β-cell compensation and its effects in the context of impaired bioenergetic activation will be determined. Here, our hypothesis is that T2D β-cells compensate for the loss of bioenergetic control by upregulating amplification path- ways, and this alters characteristics of secretion. 3) The beta-cell-specific gene expression pattern re- quired for the bioenergetic activation and compensation will be determined. Our hypothesis is that the mitochondrial activation mechanism is a network-level phenomenon, requiring a particular gene expres- sion pattern. Harnessing cell-to-cell and individual-to-individual heterogeneity, mitochondrial function and nuclear gene expression will be correlated on the single-cell level. The proposed research represents a substantial departure from the status quo by recognizing a novel mitochondrial regulation mechanism as the controlling entity of glucose metabolism and insulin secretion. Furthermore, it departs from the tradi- tional dichotomy of triggering and amplification pathways controlling GSIS by determining how these pathways converge in bioenergetic regulation. This work will be significant because combining the identi- fication of abnormalities in T2D β-cell energy metabolism with knowledge of related compensatory mech- anisms, will allow targeting of these pathways to support β-cell function.