Deletion of 12/15-Lipoxygenase Alters Macrophage and Islet Function in NOD-Alox15null Mice, Leading to Protection against Type 1 Diabetes Development

Abstract

AimsType 1 diabetes (T1D) is characterized by autoimmune depletion of insulin-producing pancreatic beta cells. We showed previously that deletion of the 12/15-lipoxygenase enzyme (12/15-LO, Alox15 gene) in NOD mice leads to nearly 100 percent protection from T1D. In this study, we test the hypothesis that cytokines involved in the IL-12/12/15-LO axis affect both macrophage and islet function, which contributes to the development of T1D.Methods12/15-LO expression was clarified in immune cells by qRT-PCR, and timing of expression was tested in islets using qRT-PCR and Western blotting. Expression of key proinflammatory cytokines and pancreatic transcription factors was studied in NOD and NOD-Alox15null macrophages and islets using qRT-PCR. The two mouse strains were also assessed for the ability of splenocytes to transfer diabetes in an adoptive transfer model, and beta cell mass.Results12/15-LO is expressed in macrophages, but not B and T cells of NOD mice. In macrophages, 12/15-LO deletion leads to decreased proinflammatory cytokine mRNA and protein levels. Furthermore, splenocytes from NOD-Alox15null mice are unable to transfer diabetes in an adoptive transfer model. In islets, expression of 12/15-LO in NOD mice peaks at a crucial time during insulitis development. The absence of 12/15-LO results in maintenance of islet health with respect to measurements of islet-specific transcription factors, markers of islet health, proinflammatory cytokines, and beta cell mass.ConclusionsThese results suggest that 12/15-LO affects islet and macrophage function, causing inflammation, and leading to autoimmunity and reduced beta cell mass.

Polarization of Macrophages toward M2 Phenotype Is Favored by Reduction in iPLA2β (Group VIA Phospholipase A2)

“…Collectively, these findings suggest that iPLA 2 ␤ deficiency mitigates polarization of macrophages toward an M1 phenotype. (42)(43)(44)(45). Consistent with this, we find that both ALOX-12 ( Fig.…”

“…12-S-hydroxyeicosatetraenoic acid) and is not detected in healthy islets but is in both T1D and T2D islets (42), is induced to a much higher level in WT macrophages than in iPLA 2 ␤-deficient macrophages. The importance of 12-LO in promoting macrophage recruitment and activation and causing detrimental effects on islet function and ␤-cell mass is supported by the reports that deletion of 12-LO protects against T1D development (44,45). Our findings, therefore, suggest that iPLA 2 ␤ activation, in addition to skewing macrophage polarization toward M1, may also preserve functionality of downstream lipidmetabolizing enzymes.…”

Selective inhibition of 12-lipoxygenase protects islets and beta cells from inflammatory cytokine-mediated beta cell dysfunction

“…Review of 12-lipoxygenase and links to biological systems highlights the important role of 12-lipoxygenase in the development of type 1 diabetes [11,15,17,23,33,34]. Studies of mouse models with transgenic deletion of 12-lipoxygenase suggest that activity of the 12-lipoxygenase enzyme strongly associates with beta cell dysfunction [17,19,33].…”

“…Deletion of 12-lipoxygenase protects mice against hyperglycaemia induced with low dose streptozotocin. In the NOD mouse, 12-lipoxygenase deletion confers a near complete protection against type 1 diabetes and also reduces immune cell activation [17,23]. Interestingly, two independent groups have shown that 12-lipoxygenase activation also participates in high-fat-induced insulin resistance and adipose tissue inflammation [24,25].…”

“…Products of 12-lipoxygenase lead to ER stress, oxidative stress and generation of proinflammatory cytokines [11,13,14,26]. Very recent evidence has shown that 12-lipoxygenase can generate IL-12 production in the islet [23,27]. Local IL-12 production may propagate an immune inflammatory state that further induces beta cell damage [27].…”