Direct optical nanoscopy unveils signatures of cytokine-induced β-cell structural and functional stress

Here we exploit a combination of advanced optical-microscopy tools and fluorescently-labeled molecular targets in rat Insulinoma 1E β-cells exposed to proinflammatory cytokines. Expansion microscopy (ExM) is used to achieve the spatial resolution (~50 nm) needed to analyze the structural features of key subcellular targets, i.e. insulin secretory granules (ISGs), microtubules, actin filaments, and mitochondria; time-lapse live-cell microscopy, on the other hand, provides complementary information on key dynamic and metabolic subcellular parameters. It is found that 24-hours exposure to proinflammatory cytokines induces a neat decrease in the number of ISGs and alteration in the dynamics of the residual pool, marked depolymerization of microtubules, change in mitochondrial morphology and metabolic activity, and decreased cell responsiveness to glucose stimulation. This is accompanied by clear signatures of the production of reactive oxygen species. Reported results provide direct evidence that proinflammatory cytokines act as potent stimulators of insulin secretion and, concomitantly, as cell stressors.