Resistance to type 1 diabetes induction in 12-lipoxygenase knockout mice

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Abstract

Leukocyte 12-lipoxygenase (12-LO) gene expression in pancreatic β cells is upregulated by cytotoxic cytokines like IL-1β. Recent studies have demonstrated that 12-LO inhibitors can prevent glutamate-induced neuronal cell death when intracellular glutathione stores are depleted. Therefore, 12-LO pathway inhibition may prevent β-cell cytotoxicity. To evaluate the role of 12-LO gene expression in immune-mediated islet destruction, we used 12-LO knockout (12-LO KO) mice. Male homozygous 12-LO KO mice and control C57BL/6 mice received 5 consecutive daily injections of low-dose streptozotocin to induce immune-mediated diabetes. Fasting serum glucose and insulin levels were measured at 7-day intervals, and the mice were followed up for 28 days. 12-LO KO mice were highly resistant to diabetes development compared with control mice and had higher serum insulin levels on day 28. Isolated pancreatic islets were treated with IL-1β, TNF-α, and IFN-γ for 18 hours. Glucose-stimulated insulin secretion in cytokine-treated islets from C57/BL6 mice decreased 54% from that of untreated islets. In marked contrast, the same cytokine mix led to only a 26% decrease in islets from 12-LO KO mice. Furthermore, cytokine-induced 12-hydroxyeicosatetraenoic acid (12-HETE) production was absent in 12-LO KO islets but present in C57/BL6 islets. Isolated peritoneal macrophages were stimulated for 48 hours with IFN-γ + LPS and compared for nitrate/nitrite generation. 12-LO KO macrophages generated 50% less nitrate/nitrite when compared with C57BL/6 macrophages. In summary, elimination of leukocyte 12-LO in mice ameliorates low dose streptozotocin–induced diabetes by increasing islet resistance to cytokines and decreasing macrophage production of nitric oxide.

Authors

David Bleich, Songyuan Chen, Brian Zipser, Duxin Sun, Colin D. Funk, Jerry L. Nadler