Oleic Acid Promotes Milk Fat Synthesis by Stimulating GPR40-Gα _q -PI3K/Akt-SREBP1-Dependent Fatty Acid Uptake

Milk fat is a rich source of long-chain fatty acids (LCFAs) including oleic, linoleic, palmitic, and stearic acid, although their specific contributions to lactational lipid synthesis remain incompletely characterized. This study aimed to clarify the role of oleic acid in mammary milk fat production and to delineate its underlying molecular mechanisms. Using a combination of in vitro and in vivo approaches, this study investigated how oleic acid regulates triglyceride synthesis. Treatment with oleic acid significantly upregulated the lipogenic transcription factor SREBP1 and key fatty acid transporters (CD36, FATP4, and FABP4), enhancing fatty acid uptake and triglyceride accumulation in mammary epithelial cells (<i>P</i> < 0.05). Mechanistic studies employing siRNA-mediated knockdown and pharmacological inhibition demonstrated that oleic acid acts through the GPR40-Gα_q-PI3K/Akt-SREBP1 signaling axis to drive transporter expression and triglyceride synthesis. In lactating mice, administration of the GPR40 antagonist GW1100 suppressed milk fat content, reduced mammary lipid deposition, and attenuated phosphorylation of Akt/mTOR, along with downregulating SREBP1 and transporter expression (<i>P</i> < 0.05), confirming the pathway's physiological relevance. Collectively, these results establish that oleic acid enhances milk fat synthesis by activating the GPR40-Gα_q-PI3K/Akt-SREBP1 cascade, thereby promoting fatty acid transport and triglyceride assembly in mammary epithelial cells.