Plasma growth arrest-specific protein 6 levels in premenopausal and postmenopausal women: the role of endogenous estrogen

Growth arrest-specific 6 (Gas6) is a vitamin K-dependent protein that interacts with receptor tyrosine kinases of the Tyro-3, AXL, Mer (TAM) family. The Gas6/TAM system contributes to the regulation of cell survival and proliferation, cell adhesion and migration, and inflammatory cytokines release. Plasma Gas6 plays an important role in the inflammatory process, and is involved in diverse human diseases. Few studies have investigated gender-specific variations in plasma Gas6 concentration. Hence, the aim of this study was to determine whether plasma Gas6 levels are associated with sex hormones in premenopausal and postmenopausal women. A total of 103 premenopausal and 135 postmenopausal women were recruited. Plasma Gas6 concentration, estradiol (E2), and sex hormone-binding globulin were assayed. The free estrogen index (FEI) was calculated. The results showed significantly lower Gas6 levels in the postmenopausal compared to the premenopausal women (P < 0.005). Plasma Gas6 levels were positively correlated with E2 levels in the pre- and postmenopausal women (r = 0.359, P < 0.001 and r = 0.261, P = 0.002, respectively). Gas6 levels were also correlated with FEI in the pre- and postmenopausal women (r = 0.234, P = 0.017 and r = 0.188, P = 0.029, respectively). After adjusting for confounders, the correlations still remained significant. In multiple stepwise regression analysis, only E2 in premenopausal and both age and E2 in postmenopausal women were independently correlated with the plasma Gas6 levels (all P < 0.001). These results suggest that plasma Gas6 is associated with sex hormones in both pre- and postmenopausal women, indicating a potential role of sex hormones in the Gas6/TAM system.