Venous thromboembolism (VTE) is a leading cause of preventable deaths in hospitals, and its incidence is not decreasing despite extensive efforts in clinical and laboratory research. Venous thrombi are primarily formed in the valve pockets of deep veins, where activated monocytes play a crucial role in bridging innate immune activation and
hemostatic pathways through the production of inflammatory
cytokines,
chemokines, and
tissue factor (TF) - a principal initiator of coagulation. In the valve pocket
inflammation and
hypoxia (sustained/intermittent) coexist, however their combined effects on immunothrombotic processes are poorly understood.
Inflammation is strongly associated with VTE, while the additional contribution of
hypoxia remains largely unexplored. To investigate this, we modelled the intricate conditions of the venous valve pocket using a state-of-the-art
hypoxia chamber with software-controlled
oxygen cycling. We comprehensively studied the effects of sustained and intermittent
hypoxia alone, and in combination with VTE-associated inflammatory stimuli on primary monocytes. TF expression and activity was measured in monocytes subjected to sustained and intermittent
hypoxia alone, or in combination with IL-1β. Monocyte responses were further analyzed in detailed by
RNA sequencing and validated by ELISA. Stimulation with IL-1β alone promoted both transcription and activity of TF. Interestingly, the stimulatory effect of IL-1β on TF was attenuated by sustained
hypoxia, but not by intermittent
hypoxia. Our transcriptome analysis further confirmed that sustained
hypoxia limited the pro-inflammatory response induced by IL-1β, and triggered a metabolic shift in monocytes. Intermittent
hypoxia alone had a modest effect on monocyte transcript. However, in combination with IL-1β intermittent
hypoxia significantly altered the expression of 2207 genes and enhanced the IL-1β-stimulatory effects on several
chemokine and
interleukin genes (e.g., IL-19, IL-24, IL-32, MIF), as well as genes involved in coagulation (
thrombomodulin) and fibrinolysis (VEGFA, MMP9, MMP14 and PAI-1). Increased production of CCL2,
IL-6 and TNF following stimulation with intermittent
hypoxia and IL-1β was confirmed by ELISA. Our findings provide valuable insights into how the different hypoxic profiles shape the immunothrombotic response of monocytes and shed new light on the early events in the pathogenesis of
venous thrombosis.