Decrease of lactogenic hormones induce epithelial-mesenchymal transition via TGFβ1 and arachidonic acid during mammary gland involution

During mammary gland involution, the epithelial mesenchymal transition (EMT) process plays an important role in tissue remodelling and in the termination of milk production. Transforming growth factor beta (TGF beta) has been known as a central inducer to EMT and contributor to the mammary gland involution. However, the whole mechanism has accomplished the EMT process in mammary gland is still unclear. Here, we show that arachidonic acid, one of the major products in milk, is new player to control the EMT together with TGF beta during mammary gland involution. Firstly, we observed decrease in CDH1 (epithelial marker gene) expression and increases in VIM and TWIST1(mesenchymal marker genes), TGFB1, and PLCG2 (arachidonic acid synthesis gene) at involution. In epithelial cells culture experiments, depletion of lactogenic hormones to mimic the involution induced TGF beta 1 and PLCG2 expressions. Treatment with arachidonic acid in epithelial cells increased VIM and TWIST1 expressions without decrease of CDH1 expression, while TGF beta 1 decreased CDH1 and increased VIM and TWIST]; more importantly, TGF beta 1 induced the expression of PLCG2, but arachidonic acid did not induce the expression of TGFB1. Finally, arachidonic acid accelerated the TGF beta 1 increasing VIM and TWIST/expressions, meanwhile arachidonic acid synthase inhibitor partially blocked the TGF beta 1 increasing VIMand TWIST/expressions. In conclusion, TGE beta 1 stimulates arachidonic acid synthesis and the arachidonic acid has a function to postulate the EMT process together with TGF beta 1 during mammary gland involution.