PPAR is a positive transcription factor of the Δ5 fatty acyl desaturase gene in abalone Haliotis discus hannai Ino

The potential role of peroxisome proliferator-activated receptor (PPAR) in regulating the biosynthesis of long-chain polyunsaturated fatty acids (LCPUFA) has not been explored in marine gastropod. In this study, we identified and characterized a PPAR gene from the abalone species Haliotis discus hannai Ino. This gene encodes a peptide consisting of 469 amino acids and comprises typical four domains: A/B domain, DNA-binding domain, D domain, and ligand-binding domain. Highest homology with that of the Patella depressa (51.08 %) from multiple alignments and phylogenetic tree analyses revealed it is a direct orthologue of the vertebrate PPAR. Tissue distribution analysis demonstrated that PPAR was highly expressed in muscle and gill, with lower expression observed in the kidney, female gonad, and hepatopancreas. Dual-luciferase reporter assays indicated that abalone PPAR significantly up-regulated the promoter activity of Δ5 fatty acyl desaturase (Δ5fad), a crucial enzyme in LCPUFA biosynthesis. Furthermore, C18PUFA significantly increased the expressions of Δ5fad and PPAR in the hepatopancreas of abalone compared to the control group fed with an LCPUFA-rich diet. These findings suggest that PPAR acts as a positive transcription factor for the fad gene, contributing to the transcriptional regulation of LCPUFA biosynthesis in abalone.