Short Oral Presentation Nutrition Society of Australia 50th Annual Scientific Meeting 2026

A fatty acid melting-point gradient reveals n-3 PUFA metabolism and lipid remodelling in zebrafish liver cells (147090)

Manxi Zhao 1 , Sara M Pinho 1 , Gio Fidelito 2 , Matthew Jago 3 , Michael G Leeming 4 , Matthew J Watt 2 , Giovanni M Turchini 1
  1. School of Agriculture, Food and Ecosystem Sciences, Faculty of Science, University of Melbourne, Melbourne, VIC, Australia
  2. Department of Anatomy and Physiology, Faculty of Medicine, Dentistry and Health Sciences, University of Melbourne, Melbourne, VIC, Australia
  3. School of Life and Environmental Sciences, Deakin University, Geelong, VIC, Australia
  4. Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Melbourne, VIC, Australia

The increasing replacement of fish oil with terrestrial oils in aquafeeds is altering the fatty acid supply of farmed fish (1). As components of membrane phospholipids, fatty acids are key determinants of membrane fluidity, which is essential to membrane function and cellular homeostasis. Cells can respond to disturbances in fluidity by remodelling membrane lipids to maintain an appropriate physical state (2). Recent work in Atlantic salmon showed that dietary fatty acid melting point influences omega-3 metabolism in vivo (3). However, how this occurs at the cellular level remains unclear. To address this, the zebrafish (Danio rerio) liver cell line ZFL was used as an in vitro model of hepatic lipid metabolism. A fatty acid melting-point gradient (8.5–48.1 ℃) was generated by replacing oleic acid (C18:1n-9) with palmitic acid (C16:0) at OA:PA ratios of 5:0, 4:1, 3:2, 2:3, 1:4 and 0:5, while maintaining the substrate α-linolenic acid (C18:3n-3) constant. Cells were exposed to six mixtures at 28 ℃ for 24 h (n = 3 per treatment). Cellular and medium fatty acids were quantified by GC-FID, and the cellular lipidome by HPLC–MS/MS. Trends were assessed by linear regression (n = 18). The lipidome was remodelled across the gradient. Triacylglycerol abundance increased 3.70-fold, and in membrane phospholipids (PC, PE, PS and PI) the saturated fraction increased and the monounsaturated fraction decreased (R² > 0.80, p < 0.001), consistent with replacement of C18:1n-9 by C16:0. Despite the lack of eicosapentaenoic acid (EPA; C20:5n-3) and docosahexaenoic acid (DHA; C22:6n-3) in the medium, cellular EPA increased 2.27-fold (R² = 0.89, p < 0.001), together with the intermediate C20:4n-3 (R² = 0.73, p < 0.001), whereas DHA remained unchanged (R² = 0.00), indicating endogenous conversion of α-linolenic acid to EPA within 24 h, but no further to DHA. EPA was selectively enriched in PE, increasing from 3.1% to 8.0% of acyl chains (R² = 0.99, p < 0.001), while total PE abundance was unchanged (R² = 0.08, n.s.), indicating compositional remodelling rather than pool expansion. At the transcriptional level, the elongases elovl2 and elovl5 were most strongly upregulated with increasing melting point (R² = 0.75 and 0.68, p < 0.001), with elovl4a and elovl4b showing similar trends, whereas the desaturase Δ6Δ5fads2 was unchanged (R² = 0.02, n.s.). The lipogenic regulator srebp1 was also upregulated (R² = 0.59, p < 0.001), indicating a transcriptional response centred on fatty acid elongation and lipid biosynthesis. These findings show that zebrafish liver cells actively regulate n-3 long-chain polyunsaturated fatty acid (LC-PUFA) metabolism and membrane lipid composition rather than passively reflecting fatty acid supply. Understanding these responses may inform the development of terrestrial-oil-based aquafeeds while supporting the preservation of the n-3 LC-PUFA content of farmed fish for human consumers.

  1. Tocher DR (2015) Aquaculture 449, 94–107.
  2. Hazel JR (1995) Annu Rev Physiol 57, 19–42.
  3. Turchini GM, Conlan JA, Emery JA et al. (2024) Aquaculture 578, 740141.