Graduate Student Ohio University Athens, Ohio, United States
Kira Slepchenko (Ohio University)| Si Chen (Advanced Photon Source)| Grace Counts (Ohio University)| Kathryn Corbin (Ohio University)| Robert Colvin (Ohio University)| Craig Nunemaker (Ohio University)
Pancreatic beta-cells secrete insulin, a hormone that maintains blood glucose homeostasis. The dysfunction of beta-cells leads to development of type2 diabetes (T2D). The causes of beta-cell dysfunction in T2D are complex. In obese individuals, increases in circulating proinflammatory cytokines IL-6 and IL-1beta are linked to a higher risk of developing diabetes, suggesting that these cytokines can be diabetes-promoting. When used at circulating concentrations found in obese individuals, these cytokines have been shown to alter calcium homeostasis in mouse beta-cells. In addition, changes in homeostasis of zinc and iron have been reported in diabetic individuals. The central hypothesis of this study: exposure to diabetes-promoting cytokines, at concentrations found in obese individuals, leads to changes in metal intracellular concentrations or distributions in beta-cells. Mouse primary beta-cells were exposed for 48 hours to cytokines: 10pg/mL IL-1beta and 20pg/mL IL-6. After cytokine exposure the cells were chemically fixed and synchrotron X-Ray fluorescence (SXRF) was employed, to investigate intracellular distributions and concentrations of zinc, calcium and iron. SXRF estimated the total cellular iron content to be 30.44 ± 12.18 (fg), and after acute exposure to cytokines the iron content was slightly increased to 47.21 ± 36.44 (fg) (mean ± S.D.). High concentrations of iron were localized in puncta structures, which were observed throughout the cytosol in all beta-cells and further analysis of the iron puncta revealed that iron was found at higher density in puncta of cells after they were exposed to cytokines, suggesting iron accumulation in these structures. The total cellular zinc content was 158.69 ± 57.68 (fg) in control cells and was significantly decreased to 65.73 ± 29.65 (fg) in cells after exposure to cytokines (mean ± S.D.) (Welch’s t-test, t(28.97) = 6.655, P<0.0001). Zinc was localized to a perinuclear space of the cells in control cells and was evenly distributed after exposure to cytokines, suggesting that cytokines had a significant effect on zinc homeostasis in beta-cells. Calcium was also observed in perinuclear space of beta-cells before cytokine exposure and was localized to similar cellular compartments as zinc. Synchrotron X-ray fluorescence estimated total cellular calcium to be 216.10 ± 67.37 femtograms (fg) control cells and was significantly decreased to 154.28 ± 68.66 (fg) after the exposure to cytokines (mean ± S.D.), (Two sample t-test, t(43)=3.040, P=0.0040). In conclusion, the synchrotron X-ray fluorescence identified significant changes to zinc, calcium and iron metallomes of pancreatic beta-cells after exposure to cytokines, which warrant further investigation.
Support or Funding Information
NIH DK089182 and DK121247 to CSN and the Ohio University Heritage College for Osteopathic Medicine.
Cellular distribution of zinc, calcium and iron in pancreatic beta-cells as detected by synchrotron X-ray fluorescence. Cells were exposed to 48 hours of cytokines (10pg/mL IL-1beta and 20pg/mL IL-6).