Glucose dose-dependently modulates antimicrobial peptide genes expression through the ERK/PI3K-NF-κB/FOXO signaling in Chinese mitten crab (Eriocheir sinensis).

The molting cycle of crustaceans involves dramatic physiological changes, yet whether metabolic substrates such as glucose fluctuate with molt stages and contribute to immune regulation remains unclear. In this study, haemolymph glucose concentrations were measured in Chinese mitten crab (Eriocheir sinensis), revealing significant stage-dependent variations, with the highest concentrations at the inter-molt stage, intermediate at the pre-molt stage, and lowest at the post-molt stage, suggesting a link between glucose availability and molt-related immune status. To examine the effects of glucose on immune-related molecular responses, crabs at inter-molt stage were challenged with different doses of glucose. Glucose regulated the mRNA expression of antimicrobial peptide genes (EsALF1, EsALF2 and EsALF3) in a dose- and time-dependent manner. The low-dose glucose (0.1 mg/g) elicited the strongest transcriptional response at 12 h, whereas higher doses (0.5 and 2 mg/g) produced weaker or suppressive effects. Following Aeromonas hydrophila challenge, low-dose glucose was associated with the greatest increase in EsALF expression, whereas this response was attenuated at higher glucose doses. Glucose also increased NF-κB and FOXO phosphorylation in a dose-dependent manner that paralleled EsALFs expression. Moreover, inhibition of PI3K or ERK signaling significantly suppressed EsALF transcription and reduced NF-κB and p-FOXO phosphorylation levels. These findings support the involvement of PI3K/ERK and NF-κB/FOXO-associated signaling in glucose-mediated regulation of EsALF expression. This study provides new insights into the metabolic regulation of innate immunity in crustaceans.