Obesity represents a low-grade chronic inflammation status, which is associated with compromised adaptive thermogenesis. However, the mechanisms underlying the defective activation of thermogenesis in chronic inflammation remain unclear. Here, a chronic inflammatory model is first estabolished by injecting mice with low-dose lipopolysaccharide (LPS) before cold exposure, and then it is verified that LPS treatment can decrease the core body temperature of mice and alter the microbial distribution in epididymal white adipose tissue (eWAT). An adipose tissue-resident bacterium Sphingomonas paucimobilis is identified as a potential inhibitor on the activation of brown fat and browning of inguinal WAT, resulting in defective adaptive thermogenesis. Mechanically, LPS and S. paucimobilis inhibit the production and release of 15-HETE by suppressing its main metabolic enzyme 12 lipoxygenase (12-LOX) and 15- Hydroxyeicosatetraenoic acid (15-HETE) rescues the impaired thermogenesis. Interestingly, 15-HETE directly binds to AMP-activated protein kinase α (AMPKα) and elevates the phosphorylation of AMPK, leading to the activation of uncoupling protein 1 (UCP1) and mitochondrial oxidative phosphorylation (OXPHOS) complexes. Further analysis with human obesity subjects reveals that individuals with high body mass index displayed lower 15-HETE levels. Taken together, this work improves the understanding of how chronic inflammation impairs adaptive thermogenesis and provides novel targets for alleviating obesity.
Hongyan Xue,Yuannan Huo,Yu Hu,Jinlong Zhang,Chengchen Deng,Jiaojiao Zhang,Xianzhong Wang
Heat stress reduces the number of Sertoli cells and impairs spermatogenesis . Mounting evidence indicates that lipid homeostasis is fundamental to cell survival. However, little is known about the role of lipid peroxides in the heat stress-induced apoptosis of Sertoli cells. In the present study, we used metabolomics to explore the changes of lipid peroxides in porcine Sertoli cells under heat stress using liquid chromatograph-mass spectrometry. These results showed a notable increase in the content of 8-hydroxyeicosatetraenoic acid (8-HETE), and 15-hydroxyeicosatetraenoic acid (15-HETE). Furthermore, we found that among arachidonate lipoxygenases , heat stress significantly increased the expression of arachidonate 15-lipoxygenase type B (ALOX15B). Moreover, baicalein, a specific inhibitor of ALOX15B, reduced the content of 8-HETE and 15-HETE, and decreased the apoptosis rate in heat stress-treated porcine Sertoli cells. In addition, baicalein and small interfering RNAs targeting ALOX15B increased the content of 8-HETE and 15-HETE, and activated the p38-p53 pathway, causing apoptosis in heat stress treated porcine Sertoli cells. Interestingly, a p38 inhibitor decreased the expression of ALOX15B, reduced the content of 8-HETE and 15-HETE, and decreased the expression of p53 and the apoptosis rate in heat stress treated porcine Sertoli cells. A p53 inhibitor had similar effect on Sertoli cells. These results indicated that heat stress enhanced the expression of ALOX15B, increased the content of 8-HETE and 15-HETE, and activated the p38-p53 pathway to cause apoptosis. ALOX15B and lipid peroxides obtained feedback from the p38-p53 pathway. Our findings will help to reveal the mechanism of lipid metabolism in Sertoli cells, and could provide a new targeted substrate for anti-heat stress strategies.
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