Serotonin promotes calcium accumulation and inhibits lipid accumulation in cultured goat mammary epithelial cells through HTR2A.

Objective: Fatty acids and calcium are both important nutrients in goat milk. Investigating the upstream molecular regulatory mechanisms that control the synthesis of milk fat and milk calcium in the mammary gland can help improve the quality of milk at its source. The objective of this study was to investigate the effects and regulatory pathways of serotonin (5-hydroxytryptamine, 5-HT) and its receptors on lipid synthesis and calcium ion levels in goat mammary epithelial cells (GMECs).

Methods: GMECs isolated from live goats were treated with serotonin, overexpression of Serotonin receptor 2A (HTR2A), Sarpogrelate ([SAR] the specific antagonist of HTR2A), or a combination of these agents. The expression of genes related to de novo lipid synthesis in GMECs were detected using the Quantitative Real-Time polymerase chain reaction, the content of lipid droplets was detected using the BODIPY assay, and the calcium content was detected using the calcium chelating probe Fluo-3AM assay.

Results: 5-HT dose-dependently promotes the activity of GEMCs, significantly inhibits the mRNA expression of key genes involved in de novo lipid synthesis such as ACC, FASN, SREBP1, SCD1 and ELOVL6 at a concentration of 100 μM, reduces triglyceride and total cholesterol content, suppresses lipid droplet accumulation in cells, and simultaneously promotes calcium accumulation in cells. Furthermore, overexpression of HTR2A in GMECs also induces an increase in cellular calcium levels and inhibits lipid synthesis and accumulation in cells. However, treatment of cells with SAR, the specific antagonist of HTR2A, significantly increases the levels of triglycerides, total cholesterol, and lipid droplet accumulation in cells.

Conclusion: 5-HT inhibits lipid synthesis in GMECs while promoting an increase in cellular calcium levels, and this effect is mediated by the HTR2A receptor. Furthermorey, antagonists targeting HTR2A can reverse the inhibition of lipid synthesis and accumulation in cells.