Evidence for a Highly Cytokine-Sensitive Network of Iron-Associated Genes in Islets.

Among the complex factors contributing to beta-cell failure is inflammation. Elevated levels of proinflammatory cytokines in obese individuals, such as interleukin (IL)-1beta and IL-6, increases the risk of developing type-2 diabetes (T2D), and there is evidence that these low levels of circulating cytokines lead to islet dysfunction. Iron is closely connected to both the inflammatory response and diabetes. High levels of dietary iron increase risk of developing T2D, and excessive iron uptake by beta-cells can cause oxidative stress and inhibit function. In this study, islets were treated for 48h with 10 pg/mL IL-1beta + 20 pg/mL IL-6 as a model of low-grade inflammation. Analysis of gene microarray data identified three iron-associated genes among the most cytokine-sensitive: HAMP, STEAP4, and LCN2. These proteins are all involved directly or indirectly with increasing and/or sequestering cellular iron. RT-PCR following exposure to various stressors known to induce beta-cell failure revealed upregulation of HAMP, STEAP4, and LCN2 to be cytokine-specific. Overexpression of STEAP4 induced upregulation of HAMP and LCN2, while ferritin and ferroportin expression were unaffected. Beta-cells scanned by synchrotron X-Ray fluorescence provided data showing cytokine exposure alters iron distribution. Iron was found in discrete structures (area ~0.15-0.45 µm ) that were significantly smaller and more iron-dense in cytokine-treated beta-cells, consistent with the sequestering function of identified iron-associated genes. These data suggest a network of iron-regulating genes in beta-cells plays a role in sequestering iron in response to low-grade inflammation.