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

Abstract

The leukocyte 12-lipoxygenase (12-LO) gene is expressed in pancreatic β cells and macrophages. Products of the 12-LO enzyme are proinflammatory and may be involved in immune-mediated conditions, but formal proof of this hypothesis is lacking. Leukocyte 12-LO is preferentially expressed over 5-and 15-lipoxygenase in pancreatic β cells and may be involved in cytokine-mediated β-cell damage through generation of the lipid hydroperoxide 12-hydroperoxyeicosatetraenoic acid (12-HPETE) (1-7). Reduction of 12-HPETE to 12-hydroxyeicosatetraenoic acid (12-HETE) is facilitated by the enzyme glutathione peroxidase, and recent work has demonstrated that 12-LO inhibitors can prevent glutamate-induced neuronal cell death when intracellular glutathione stores are depleted (8). Both neuronal cell death and peroxide generation required 12-LO activity in this model and were prevented by treatment with a lipoxygenase inhibitor, baicalein (10 µM). Furthermore, the proinflammatory cytokine IL-1β was shown to increase 12-LO product formation in pancreatic islets (9, 10), whereas nordihydroguaiaretic, a lipoxygenase inhibitor, protected rat islet cells from cytokine-induced destruction (11). Given that 12-HPETE and/or other 12-LO products may damage pancreatic β cells through lipid peroxidation, it is possible that inhibition of the 12-LO pathway may protect pancreatic β cells from cytotoxic conditions.To test this hypothesis, we administered low-dose streptozotocin (STZ) to 12-LO knockout (12-LO KO) mice and genetic controls to evaluate the development of diabetes. In addition, we isolated pancreatic islets and tested them for sensitivity to cytokine-induced dysfunction. We also evaluated the capacity of macrophages to generate nitric oxide (NO) and superoxide when stimulated. We chose the low dose STZ-induced diabetic model because previous studies have demonstrated that β-cell destruction is mediated in part by generation of free radicals and lipid hydroperoxides as well as by immune activation (12, 13). 12-LO KO mice were generated by homologous recombination in embryonic stem cells, as described previously (14).In the present study, we found that 12-LO KO mice were significantly more resistant to STZ-induced diabetes than were C57BL/6 controls and that islets purified from 12-LO KO mice were protected from cytokine-induced dysfunction. Furthermore, macrophages from 12-LO KO mice generated ∼50% of the nitrate/nitrite compared with macrophages from control C57BL/6 mice. 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 glutamateinduced 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-...

Role of uncoupling protein UCP2 in cell-mediated immunity: How macrophage-mediated insulitis is accelerated in a model of autoimmune diabetes

“…Macrophages mediate islet damage through ROS, NO, and cytokine production. Therefore, suppression of macrophages or inhibition of their activity was shown to slow insulitis progression in NOD mice (29) or prevent MLDS-induced diabetes (22,30,31). We recently reported that increased mitochondrial ROS production in Ucp2-KO macrophages allows quicker and stronger p38 and ERK signaling, leading to increased cell activity (8).…”

Tissue Inhibitor of Metalloproteinase-1 Prevents Cytokine-Mediated Dysfunction and Cytotoxicity in Pancreatic Islets and β-cells

“…All animal studies were performed in accordance with guidelines set forth by the Research Animal Care Committee of City of Hope National Medical Center. Islet isolation and culturing techniques have been previously detailed (29). Male Sprague-Dawley rats weighing 250 -300 g were used for islet isolation.…”

Mechanisms by which diabetes increases cardiovascular disease

“…Also, 12(S)-HETE, one of the products of 12-LO, promotes monocyte-adhesion to endothelial cells, probably in part by inducing the fibronectin splice variant CS-1 and VCAM-1 on endothelial cells [8]. Interestingly, 12-LO deficient mice are resistant to STZ-induced diabetes suggesting not only a role for 12-LO in diabetes-induced atherosclerosis but also in pathogenesis of diabetes itself [36]. This notion is supported by the findings that the LO-inhibitor masoprocol can improve insulin sensitivity in a rat model of type 2 diabetes…”