Mechanisms of ADAM17 activation and mediated impairment of insulin signaling in endothelial cells
Board Location: #164
Discipline: Biological Sciences
Subcategory: Physiology and Health
Session: 4
Morgan Williams - University of Missouri
Co-Author(s): Larissa Ferreira-Santos, University of Columbia, MO; Zayd Kdesh, University of Columbia, MO; Camila Manrique-Acevedo, University of Columbia, MO; Jaume Padilla, University of Columbia, MO; Luis A. Martinez-Lemus, University of Columbia, MO.
Insulin signaling dysregulation is a major factor in the pathogenesis of type 2 diabetes (T2D). T2D is an important risk factor for cardiovascular disease, the main cause of death worldwide. Thus, identification of targetable molecular mechanisms to prevent and treat insulin signaling dysfunction are much needed. Recently, our research group showed that A Disintegrin And Metalloproteinase-17 (ADAM17) is increased in the vasculature of subjects with T2D. Whereas, insulin receptor α-subunit (IRα) is decreased in the vasculature of subjects with T2D, and ADAM17 shedding of IRα leads to impaired insulin-induced vasodilation. Externalization of phosphatidylserine (PS) from the inner to the outer leaflet of the plasmalemma has been proposed as a mandatory step in the activation of ADAM17. However, whether PS externalization increases ADAM17 activity, and consequently decreases insulin-induced vasodilation via IRα shedding is not known. We hypothesized that neuraminidase (Neu), an enzyme we showed is upregulated in T2D, leads to endothelial PS externalization via induction of Ca2+ influx and subsequent ADAM17 shedding of IRα. To determine the effect of Neu exposure, we used cultured endothelial cells (EC) which were used to observe changes in sialic acid, Ca2+ influx, PS externalization, ADAM17 activity, and insulin signaling. Western blotting was used to measure Akt phosphorylation, and immunofluorescence assays measured Neu activity, sialic acid, PS externalization, insulin signaling, and ADAM17 activity. We report that EC that have been exposed to Neu have increased levels of Ca2+ influx, PS externalization, and ADAM17 activity. We also find that Neu decreases IRα content on the EC surface and leads impaired insulin signaling. All reported differences are statistically significant at P< 0.05. These results show that in addition to an increase in sialic acid, Ca2+ influx, PS externalization, and ADAM17 activity, ECs also have a decrease in IR-α and insulin-induced Akt phosphorylation. The decrease in insulin-induced Akt phosphorylation leads to impaired insulin-induced vasodilation. These findings suggest that Neu causes Ca2+ influx in ECs, promotes flipping PS to the outer cell membrane leaflet and, consequently, increases ADAM17 shedding of IRα. We propose that therapeutical targeting of Neu and/or ADAM17 activity holds extraordinary promise for restoring endothelial insulin sensitivity in T2D.
Funder Acknowledgement(s): This research project was funded by the NIH.
Faculty Advisor: Luis A. Martinez-Lemus, martinezlemusl@missouri.edu
Role: Within this research project, I examined insulin induced Akt phosphorylation using Western Blot assays. These assays were used to identify Akt within the endothelial cells and revealed that endothelial cells exposed to neuraminidase have decreased levels of insulin induced AKT phosphorylation than in endothelial cells that are not. The decrease of AKT phosphorylation causes impaired insulin induced vasodilation.