EXPRESSION OF FATTY-ACID SYNTHASE IS CLOSELY LINKED TO PROLIFERATION AND STROMAL DECIDUALIZATION IN CYCLING ENDOMETRIUM

Estrogen-driven proliferative phase growth is the most rapid physiolog ical proliferative process that occurs in the adult. The tissue growth that occurs during this phase of the menstrual cycle requires incorpo ration of a substantial quantity of fatty acid into the structural lip ids of cell membranes. Fatty acid synthase (FAS) is the major biosynth etic enzyme required for de novo synthesis of fatty acids. In this imm unohistochemical study, we have observed that human endometrium displa ys distinct patterns of FAS expression in the proliferative and secret ory phases of the normal menstrual cycle. Proliferative endometrial gl ands and stroma show high FAS expression that closely correlates with expression of Ki-67, estrogen and progesterone receptors, supporting t he view that FAS expression plays a role in cellular proliferation in response to estrogen. FAS expression declines during early to midsecre tory phase, then reappears in decidualized stromal cells in late secre tory phase as well as in the decidua of pregnancy. The second wave of FAS expression correlates with progesterone-receptor localization in t he decidual cells, a finding suggesting a second induction of FAS expr ession in the endometrium, associated with differentiation, that may b e regulated by progesterone.