Stearic Acid Activates the PI3K-mTOR-4EBP1/S6K and mTOR-SREBP-1 Signaling Axes through FATP4-CDK1 To Promote Milk Synthesis in Primary Bovine Mammary Epithelial Cells

Abstract

Stearic acid (SA), an 18-carbon long-chain saturated fatty acid, has great potential for promoting lactation. Therefore, this study investigates the effects and mechanism of SA on milk synthesis in primary bovine mammary epithelial cells (BMECs). In our study, we found that SA significantly increased β-casein and triglycerides, and the effect was most significant at 100 μM. Signaling pathway studies have found that SA affects milk synthesis by upregulating cyclin-dependent kinase 1 (CDK1) to activate PI3K-mTOR-4EBP1/S6K and mTOR-SREBP-1 pathways. Furthermore, we detected fatty acid transport proteins (FATPs) when BMECs were treated with SA; the mRNA levels of FATP3 (3.713 ± 0.583) and FATP4 (40.815 ± 8.959) were significantly upregulated at 100 μM. Subsequently, we constructed FATP4-siRNA and found that SA was transported by FATP4 into BMECs, promoting milk synthesis. Collectively, these results revealed that SA activated PI3K-mTOR-4EBP1/S6K and mTOR-SREBP-1 signaling axes through FATP4-CDK1 to promote milk synthesis in BMECs.

Acylated Ghrelin Activates PI3K/mTOR Signaling Pathway by Promoting ThPOK Acetylation to Promote Milk Fat Synthesis in Bovine Mammary Epithelial Cells

“…Upon activation, this signaling pathway facilitates milk fat synthesis by regulating multiple pathways such as eIF4E, S6K, and SREBP1. 32,40,41 This study found that AG increased milk fat synthesis by activating the PI3K/ mTOR signaling pathway and upregulating the expression levels of SREBP1 and FASN. Moreover, inhibition of PI3K and mTOR blocked the promoting effect of AG on milk fat synthesis and expression of SREBP1 and FASN proteins.…”

“…36−38 The PI3K/mTOR signaling pathway regulates the proliferation and milk synthesis of mammary epithelial cells. 32,39 In addition, the PI3K/mTOR signaling pathway is involved in the regulation of lipid synthesis. Upon activation, this signaling pathway facilitates milk fat synthesis by regulating multiple pathways such as eIF4E, S6K, and SREBP1.…”

ARID3A plays a key regulatory role in palmitic acid‐stimulated milk fat synthesis in mouse mammary epithelial cells

“…The PI3K signaling is one of the most important intracellular signaling sensing nutrients to regulate multiple cellular functions, including cell proliferation, differentiation, and expression of many genes (Tsalikis et al, 2013; Wang et al, 2022). Fatty acids can promote milk fat synthesis in mammary epithelial cells through the PI3K signaling (Jin et al, 2022; F. Li et al, 2022). The SREBP1 signaling can be regulated by the PI3K/AKT signal pathway (L. Li et al, 2021; Wu et al, 2021).…”

“…Fatty acids including PA are not only substrate for the synthesis of TGs, but also signals for SREBP1 expression and maturation (Jin et al, 2022;P. Li et al, 2018;F. Li et al, 2022).…”

“…SREBP1 is formed firstly as the premature form (full length of SREBP1, fSREBP1) and can be activated in the Golgi apparatus into a truncated mature form (nuclear SREBP1, nSREBP1) and enter nucleus to regulate gene expression (Loregger et al, 2020; Shimano & Sato, 2017). Fatty acids including PA are not only substrate for the synthesis of TGs, but also signals for SREBP1 expression and maturation (Jin et al, 2022; P. Li et al, 2018; F. Li et al, 2022). Phosphoinositide 3‐kinase (PI3K) is well known an early stage signaling molecule sensing extracellular stimuli, and we previously have shown that PA can stimulate SREBP1 expression and maturation through activating PI3K (Jin et al, 2022; P. Li et al, 2018).…”