200-OR: Role of Insulin-Degrading Enzyme (IDE) in the Tubulin–Primary Cilium Axis to Regulate Glucagon Secretion

Hyperglucagonemia is a hallmark of T2D, although molecular mechanisms underlying glucagon secretion dysregulation are poorly understood. We have recently reported that genetic ablation of IDE in α-cells (A-IDE-KO mouse) leads to constitutive glucagon secretion, hypertrophy, hyperplasia and increased proliferation. αTC1.9-KD-IDE cells (~30% IDE-knock-down) displayed reduced tubulin and acetylated-α-tubulin protein levels, impaired primary cilium and increased proliferation. Thus, we aimed to elucidate the role of IDE in α-cells tubulin network and ciliogenesis, and how this axis may be part of the glucagon secretion machinery. We have studied by western-blot IDE, tubulin, acetylated-α-tubulin and Arl13b (primary cilium marker) levels in αTC1.9 cells under low- and high-glucose conditions. We have found that high-glucose lowers IDE protein levels by 50% compared to low-glucose conditions, leading to a similar decrease in tubulin, acetylated-α-tubulin and Arl13b protein levels. These findings agree with our previous results using αTC1.9-KD-IDE cells, suggesting a relevant role of IDE in microtubule dynamics to control glucagon granules exocytosis. On the other hand, αTC1.9-KD-Arl13b cells (~70% Arl13b-knock-down) were used as a model of impaired ciliogenesis, showing 50% decrease in tubulin, and dysregulated glucagon secretion, mimicking αTC1.9-KD-IDE cells phenotype. In parallel, insulin-mediated inhibition of glucagon secretion is lost and insulin receptor protein levels were decreased by 40% in both, αTC1.9-KD-IDE and αTC1.9-KD-Arl13b cells, showing the relevance of IDE and primary cilium in the paracrine regulation of α-cells. Furthermore, these results have been reproduced in A-IDE-KO mice isolated islets. In conclusion, our results show that IDE-tubulin-primary cilium axis is regulated during glucose-stimulated glucagon secretion, this axis is also required for the paracrine action of insulin on α-cells to inhibit glucagon secretion.