Role of NumbL:Mig6 Interactions in Beta-Cell Death during Glucolipotoxicity

Abstract

As the development of type 2 diabetes (T2D) requires a loss of functional beta cell mass, preserving functional beta cell mass is essential for preventing T2D. We have focused our efforts on EGF receptor (EGFR) signaling because it controls cellular proliferation, survival, and repair mechanisms—all features relevant to maintaining beta cell mass—and is dampened during glucolipotoxic conditions (GLT) similar to those in T2D. We have established that Mig6, an endogenous feedback inhibitor of EGFR, is induced in both rodent islets cultured in GLT and human T2D islets. In addition, GLT impairs EGFR signaling in rodent and human islets. Further, Mig6 overexpression promotes apoptosis in both rodent beta cell lines and islets. Because Mig6 is an adapter protein and likely functions as a molecular scaffold, here we aimed to define the molecular mechanisms of Mig6 in GLT by identifying the interacting partners of Mig6. We performed mass spectrometry analysis using low-level, flag-tagged Mig6 expression with immunoprecipitation from Ins1-derived 832/13 cells cultured in normal conditions and GLT. We identified that Mig6 interacted with Numb and NumbL, regulators of Notch signaling, in a context dependent manner. Specifically, Mig6 interacted with Numb and NumbL in normal glucose conditions whereas these interactions were disrupted by GLT. However, roles for Numb and NumbL in beta cell function or death are largely unknown. We observed that Numb and NumbL are expressed in both rodent and human islets, and whereas their expression is not altered in GLT, their localization and aforementioned interactions were. To examine their impact in beta cell death, we used siRNA-mediated suppression of Numb and NumbL in 832/13 cells during control and GLT conditions. Whereas Numb suppression had no effect, NumbL suppression reduced apoptosis in GLT. These results suggest that NumbL plays an important role in beta cell survival. Hence, the differential interactions of Mig6 and NumbL may determine beta cell fate during stress. Disclosure H.D. Basavarajappa: None. J.M. Irimia-Dominguez: None. P.T. Fueger: None.