AMP deaminase-2- and adenosine deaminase-mediated disposal of β-cell intracellular adenosine protects against multiple low-dose streptozotocin-induced type 1 diabetes

Abstract

Objective: To evaluate the importance of AMPD2 and ADA, two adenosine disposal enzymes, for β-cell survival and the development of T1D.

Methods: The nucleotide metabolism in EndoC-βH1 cells was compared with that of α-TC1-6 cells using HPLC and enzyme activity analysis. AMPD2 and ADA activities were modulated using a synthetic target site blocker (TSB) in vitro and in vivo. The multiple low-dose streptozotocin (MLDSTZ) mouse model was used to study T1D.

Results: EndoC-βH1 cells contained higher AMP and P-AMPK levels than α-TC1-6 cells, and these levels were further increased during stress. ADA and AMPD enzyme activities were lower in β-cells. Extracellular adenosine lowered human islet insulin contents without affecting glucagon contents. Downregulation of AMPD2 resulted in lower inosine levels and increased cell death. An AMPD2 miR141-3p miRNA TSB increased AMPD2 levels, reduced adenosine levels, and decreased β-cell death. Treatment of MLDSTZ mice with the AMPD2 TSB resulted in lower blood glucose and higher serum insulin levels, an increased β-cell area and reduced activated caspase-3. The AMPD2 TSB treatment resulted in decreased expression of IFN-γ, IL-17 and IL-10 in CD8⁺ T-cells on day 7, and an increase in IL-10⁺ macrophages on day 21. An ADA miR140-3p TSB protected partially against T1D, an effect which was further increased when combined with the AMPD2 TSB.

Conclusions: β-cells differ from α-cells in terms of the metabolism and disposal of intracellular adenosine, which makes β-cells more vulnerable to ATP-depleting stress, and therefore also more prone to being attacked by the immune system in T1D.

Keywords: AMP deaminase-2; Adenosine; Multi low-dose STZ; Type 1 diabetes; β-cell death.