EXERCISE DIFFERENTIALLY MODULATES THE MOLECULAR MACHINERY OF OMEGA-3 LONG-CHAIN POLYUNSATURATED FATTY ACIDS BIOSYNTHESIS UNDER FLAXSEED OIL SUPPLEMENTATION IN MALE MICE

The effects of exercise on endogenous omega-3 (n3) long-chain polyunsaturated fatty acids (LC-PUFA) biosynthesis remain unclear. This study investigated whether acute and chronic exercise modulate genes involved in LC-PUFA biosynthesis and tissue fatty acid composition under flaxseed oil (FO) supplementation. 48 male C57BL/6J mice were assigned to four groups (24 animals for the chronic design and 24 animals for the acute design, n= 6 per group): sedentary + saline; sedentary + FO; exercised + saline; and exercised + FO. No animals were lost during the experimental period. Acute (24 h) and chronic (6 weeks) exercise protocols consisted of treadmill running performed at 60% of peak workload for 60 min without incline. All the procedures were approved by the Ethics Committee on the Use of Laboratory Animals (CEUA:6411-1/2024). At the end of the protocols, liver, soleus muscle, hypothalamus, and serum were collected for RT-qPCR analysis of Fads1, Fads2, Elovl2, and Elovl5 and gas chromatography–mass spectrometry (GC–MS) determination of ALA, EPA, and DHA. Data were analyzed using two-way ANOVA, with statistical significance set at P < 0.05. All results will be presented in the following order: sedentary + saline; sedentary + FO; exercised + saline; and exercised + FO. FO supplementation increased ALA (chronic liver: 0.09, 1.16, 0.09, 0.93; chronic serum: 0.01, 0.12, 0.01, 0.12; acute liver: 0.10, 1.34, 0.10, 1.31, acute serum: 0.03, 0.09, 0.01, 0.14) and EPA (chronic liver: 0.08, 0.68, 0.11, 0.60; chronic serum: 0.006, 0.042, 0.008, 0.051; acute liver: 0.122, 0.418, 0.120, 0.487, acute serum: 0.02, 0.04, 0.01, 0.05) levels. Although FO also increased ALA (0.29, 1.07, 0.30,1.66) and EPA (0.12, 0.31, 0.13, 0.32) levels in the soleus following chronic exercise, under the acute protocol it increased only ALA levels (0.14, 0.48, 0.14, 0.41). Chronic exercise differentially regulated genes involved in LC-PUFA biosynthesis, decreasing hepatic Fads2 expression (1.00, 1.08, 0.89, 0.42). This downregulation may reflect a negative feedback mechanism, as n3 were already abundantly available, there was no need to further activate the biosynthetic pathway. Likewise, chronic exercise reduced hepatic Elovl2 expression (1.00, 1.02, 0.47, 0.35), suggesting exercise-induced remodeling of hepatic lipid metabolism rather than suppression of n3 metabolism. The increase in hypothalamic Fads2 (1.00, 1.05, 1.47, 1.59) suggests that exercise enhances LC-PUFA biosynthesis, where local synthesis is essential due to tightly regulated peripheral DHA availability. A chronic exercise × FO interaction increased Elovl5 expression in the soleus muscle (1.00, 0.76, 0.37, 1.19). It indicates that exercise enhances the elongation step of the biosynthetic pathway only when substrate availability is sufficient, supporting coordinated metabolic adaptation rather than constitutive activation of the pathway. Exercise induced tissue-specific remodeling of n3 metabolism, while FO differentially regulated LC-PUFA biosynthesis, suppressing it in the liver and enhancing it in the soleus.