Chelerythrine enhances anti-fungi immunity in <i>Caenorhabditis elegans</i> via DAF-16 and NHR-49 mediated fatty acid metabolism.

Chelerythrine is a natural benzophenanthridine alkaloid with various pharmacological activities. However, whether Chelerythrine can influence innate immunity and its underlying molecular mechanisms remain unclear. In this study, we found that 10 μM Chelerythrine significantly extended the lifespan of <i>Caenorhabditis elegans</i> infected with <i>Candida albicans</i> (<i>C. albicans</i>) and inhibited the proliferation of <i>C. albicans</i>. This enhanced host resistance to infection was not achieved by reducing the intestinal fungal burden. Transcriptomic sequencing analysis revealed that Chelerythrine activates the FoxO and Fatty acid metabolism pathways in <i>C. elegans</i>. Interestingly, the lifespan-extending effect of Chelerythrine was completely abolished in <i>daf-16</i> and <i>nhr-49</i> mutants. Similarly, mutations in the fatty acid desaturase genes <i>fat-5</i>, <i>fat-6</i>, and <i>fat-7</i> also blocked this protective effect. RT-qPCR results confirmed that Chelerythrine treatment significantly upregulated the expression of FoxO pathway downstream genes (<i>sod-3</i>, <i>thn-2</i>, <i>lys-7</i>) and fatty acid metabolism-related genes (<i>nhr-49</i>, <i>mdt-15</i>, <i>fat-5</i>, <i>fat-6</i>, <i>fat-7</i>). Fluorescent reporter gene assays further demonstrated that Chelerythrine promotes the nuclear localization of DAF-16::GFP and enhances the fluorescence expression of SOD-3::GFP, FAT-5::GFP, FAT-6::GFP, and FAT-7::GFP. Additionally, broad-spectrum antibacterial assays showed that 10 μM Chelerythrine had no direct inhibitory activity against various pathogens, including <i>Listeria monocytogenes</i>, <i>Enterococcus faecalis</i>, <i>Pseudomonas aeruginosa</i>, and <i>Salmonella enterica</i>, indicating that it does not enhance host immunity by directly suppressing pathogen growth. In summary, this study demonstrates that Chelerythrine enhances the innate immune response of <i>C. elegans</i> against <i>C. albicans</i> by activating the DAF-16/FoxO pathway and the NHR-49-mediated fatty acid metabolism pathway. Our work reveal that Chelerythrine is a potential therapeutic candidate for the treatment of <i>C. albicans</i> infections.