Inhibition of AMP-activated protein kinase protects pancreatic β-cells from cytokine-mediated apoptosis and CD8⁺ T cell-induced cytotoxicity

Abstract

Objective: Apoptotic destruction of insulin-producing pancreatic β-cells is involved in the aetiology of both type 1 and type 2 diabetes. AMP-activated protein kinase (AMPK) is a sensor of cellular energy charge whose sustained activation has recently been implicated in pancreatic β-cell apoptosis and in islet cell death post-transplantation. Here, we examine the importance of β-cell AMPK in cytokine-induced apoptosis and in the cytotoxic action of CD8⁺ T cells.

Research Design and Methods: Clonal MIN6 β-cells or CD1 mouse pancreatic islets were infected with recombinant adenoviruses encoding enhanced green fluorescent protein (eGFP/Null), constitutively-active AMPK (AMPK CA), or dominant-negative AMPK (AMPK DN) and exposed or not to tumour necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and interferon-γ (IFN-γ). Apoptosis was detected by monitoring the cleavage of caspase-3 and DNA fragmentation. The cytotoxic effect of CD8⁺ purified T cells was examined against pancreatic islets from NOD mice infected with either Null or the AMPK DN-expressing adenoviruses.

Results: Exposure to cytokines, or expression of AMPK CA, induced apoptosis in clonal MIN6 β-cells and CD1 mouse pancreatic islets. By contrast, over-expression of AMPK DN protected against the proapoptotic effect of these agents, in part by preventing decreases in cellular ATP, and lowered the cytotoxic effect of CD8⁺ T cells towards NOD mouse islets.

Conclusions: Inhibition of AMPK activity enhances islet survival in the face of assault by either cytokines or T cells. AMPK may therefore represent an interesting therapeutic target to suppress immune mediated β-cell destruction, and may increase the efficacy of islet allografts in Type 1 diabetes.