IL-33 promotes pancreatic β-cell survival and insulin secretion under diabetogenic conditions through PPARγ

Pancreatic β-cell dysfunction plays a vital role in the development of diabetes. IL-33 exerts anti-diabetic effects via its anti-inflammatory properties and has been demonstrated to increase insulin secretion in animal models. However, IL-33, as a pleiotropic cytokine, may also exert a deleterious effect on β-cells, which has not been rigorously studied. In the present study, we found that IL-33 promoted cell survival and insulin secretion in MIN6 (a mouse pancreatic β-cell line) cells under diabetogenic conditions. IL-33 increased the expression of its receptor ST2 and the transcription factor PPARγ, whereas PPARγ inhibition impaired IL-33-mediated β-cell survival and insulin release. IL-33 did not repress the expression of pro-inflammatory mediators, including Tf, Icam1, Cxcl10, and Il1b, whereas it significantly reduced the expression of Ccl2. IL-33 decreased TNF-α secretion and increased IL-10 secretion; these effects were completely reversed by PPARγ inhibition. IL-33 increased glucose uptake and expression of Glut2. It upregulated the expression of glycolytic enzyme genes, namely, Pkm2, Hk2, Gpi1, and Tpi, and downregulated the expression of Gck, Ldha, and Mct4. However, it did not alter hexokinase activity. Moreover, IL-33 increased the number and activity of mitochondria, accompanied by increased ATP production and reduced accumulation of ROS. IL-33 upregulated the expression of PGC-1α and cytochrome c, and mitochondrial fission- and fusion-associated genes, including Mfn1, Mfn2, and Dnm1l. IL-33-mediated mitochondrial homeostasis was partially reversed by PPARγ inhibition. Altogether, IL-33 protects β-cell survival and insulin secretion that could be partially driven via PPARγ, which regulates glucose uptake and promotes mitochondrial function and anti-inflammatory responses.