Estrogen and obesity synergistically suppress Protein S via HIF1α, enhancing thrombotic potential

Venous thromboembolism (VTE) is a leading cause of morbidity and mortality, with risk heightened in premenopausal women who are obese or use estrogen-based oral contraceptives. When both risk factors are present, thrombosis risk increases substantially. Protein S (PS), an essential anticoagulant cofactor, is downregulated by both estrogen and obesity, but the molecular basis for this suppression remains poorly defined. We investigated the impact of estrogen and obesity on PS expression using plasma samples from 157 women stratified by body mass index and contraceptive use, alongside 40 mice categorized as lean or obese with or without estrogen pellet. The levels of PS were reduced by either estrogen or obesity alone, and the combined effect increased thrombin generation. In HepG2 hepatocytes, hypoxic conditions (1%–10% O₂) mimicking obesity, with or without 17 β-estradiol, suppressed PROS1 transcription and promoter activity. Chromatin immunoprecipitation confirmed direct binding of hypoxia-inducible factor 1α (HIF1α) to the PROS1 promoter, repressing gene expression. These findings define a mechanistic pathway through which estrogen and obesity converge to suppress PS synthesis, providing insight into the elevated thrombotic risk observed in obese women using estrogen-based contraceptives. Knowing that pre-menopausal women who use estrogen-based oral contraceptives have higher incidence of venous thromboembolism, and that venous thromboembolism is associated with obesity, we used in vivo and in vitro systems to investigate the molecular mechanisms responsible for estrogen- and obesity-induced Protein S downregulation, under lean and obese conditions.