Chitosan-Mediated Expression of <em>Caenorhabditis elegans fat-1 </em>and <em>fat-2 </em>in <em>Sparus aurata</em>: Short-Term Effects on the Hepatic Fatty Acid Profile, Intermediary Metabolism, and Proinflammatory Factors

A single dose of chitosan-tripolyphosphate (TPP) nanoparticles carrying expression plasmids for fish codon-optimized <em>Caenorhabditis elegans fat-1</em> and <em>fat-2</em> was intraperitoneally administered to gilthead seabream (<em>Sparus aurata</em>) to stimulate the biosynthesis of omega-3 long-chain polyunsaturated fatty acids (<em>n</em>-3 LC-PUFA) and evaluate subsequent short-term effects on liver intermediary metabolism and immunity. Seventy-two hours post-injection, the upregulation of <em>fat-1</em> elevated eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and total <em>n</em>-3 fatty acids in the liver, while <em>fat-2</em> enhanced DHA and <em>n</em>-3 fatty acids. Co-expression of <em>fat-1</em> and <em>fat-2</em> increased EPA, DHA, PUFA, and the total <em>n</em>-6 and <em>n</em>-3 LC-PUFA, while reducing plasma triglycerides. The expression of <em>fat-1</em> and <em>fat-2</em> suppressed hepatic lipogenesis by downregulating <em>srebf1 </em>and <em>pparg</em>, and consequently key genes in fatty acid synthesis (<em>acaca</em>, <em>acacb</em>, <em>fasn</em>, <em>scd1</em>, and <em>fads2</em>). In contrast, the co-expression of <em>fat-1</em> and <em>fat-2</em> upregulated <em>hnf4a</em>, <em>chrebp</em>, and <em>pfkl</em>, a rate-limiting enzyme in glycolysis. Furthermore, <em>fat-1</em> and <em>fat-2</em> reduced hepatic proinflammatory markers such as <em>tnfa</em> and <em>nfkb1</em>. In addition to enhancing EPA and DHA biosynthesis, promoting glycolysis, and suppressing lipogenesis, our findings suggest that the short-term expression of <em>C. elegans fat-1</em> and <em>fat-2</em> in the liver may also reduce inflammation and, therefore, could impact the health and growth performance of cultured fish.