Tissue-specific biochemical and molecular responses associated with red pigment-concentrating hormone gene knockdown in Litopenaeus vannamei.

In decapod crustaceans, red pigment-concentrating hormone (RPCH) is considered an ortholog of insect adipokinetic hormone (AKH); both belong to the conserved arthropod AKH/RPCH neuropeptide family. Research on crustacean RPCH has focused primarily on pigmentary functions, but the tissue-level roles of RPCH beyond its role in pigmentation are poorly understood. In this study, we used RNA interference to knock down the rpch gene in Litopenaeus vannamei (Lv-rpch) and integrated transcriptomic analysis, reverse transcription quantitative polymerase chain reaction (RT-qPCR) validation, biochemical assays, and histological examination to characterize responses in the gill and hepatopancreas. The two tissues exhibited distinct differentially expressed gene (DEG) profiles, comprising 190 DEGs in the hepatopancreas and 768 in the gill. Gill DEGs were enriched mainly in defense-related processes, lysosome-associated categories, structural components, and carbohydrate metabolism pathways. In the hepatopancreas, enrichment primarily involved transport, protein processing, oxidoreductase activity, xenobiotic metabolism, and carbohydrate and lipid metabolism. Biochemical assays revealed lower superoxide dismutase (SOD) activity and malondialdehyde (MDA) content in both tissues, higher gill lysozyme (LYS) activity, and lower hepatopancreatic lipase activity. Trypsin activity did not change. Histological examination indicated morphological alterations in both tissues after Lv-rpch knockdown. Taken as a whole, these results link Lv-rpch knockdown to tissue-specific transcriptomic, biochemical, and histological responses in L. vannamei, although the underlying causal mechanisms remain to be established.