Endothelial cell responses to hypoxic stress

Adaptive responses of the endothelium to stress

It is now established that endothelial cells acquire several functional properties in response to a diverse array of extracellular stimuli. This expression of an altered phenotype is referred to as endothelial cell activation, and it includes several activities that promote inflammation and coagulation. While it is recognized that endothelial cell activation has a principal role in host defense, recent studies also demonstrate that endothelial cells are capable of complex molecular responses that protect the endothelium against various forms of stress including heat shock, hypoxia, oxidative stress, shock, ischemia-reperfusion injury, toxins, wounds, and mechanical stress. In this review, we examine endothelial cell genotypic and phenotypic responses to stress. Also, we highlight important cellular stress responses that, although not yet demonstrated directly in endothelial cells, likely exist as part of the repertoire of stress responses in endothelium. A detailed understanding of the molecular mechanisms mediating the adaptive responses of endothelial cells to stress should facilitate the development of novel therapeutics to aid in the management of diverse surgical diseases and their complications.

ERK activation upon hypoxia: involvement in HIF-1 activation

Hypoxia-inducible factor-1 (HIF-1) is a transcription factor activated by hypoxia. The HIF-1 activation transduction pathway is poorly understood. In this report, we investigated the activation of extracellular regulated kinases (ERK) in hypoxia and their involvement in HIF-1 activation. We demonstrated that in human microvascular endothelial cells-1 (HMEC-1), ERK kinases are activated during hypoxia. Using dominant negative mutants, we showed that ERK1 is needed for hypoxia-induced HIF-1 transactivation activity. Moreover, using a kinase assay and Western blot experiments, we showed that HIF-1alpha is phosphorylated in hypoxia by an ERK-dependent pathway. These results evidence the role of mitogen-activated protein kinase in the transcriptional response to hypoxia.

Microcirculatory dysfunction in sepsis: a pathogenetic basis for therapy?

Sepsis is a frequent complication of multiple organ dysfunction syndrome and remains a major problem of intensive care medicine. It is also a common factor in the final cause of death in hospital populations. Clinical observations, assisted by invasive monitoring techniques as well as pathological-anatomical studies, clearly indicate that microcirculatory dysfunction lies at the centre of sepsis pathogenesis. Numerous animal models, from rodents to primates, many of which employ bacteria or their toxins, especially endotoxins, have helped to shed light on the pathomechanisms leading to this dysregulation in the peripheral circulation. Among these are activation of humoral and cellular inflammatory mediator systems, with special emphasis on neutrophil-endothelial interactions, affecting endothelial barrier function and vasoregulation and ultimately leading to severely perturbed oxygen transport and utilization. In vitro studies have provided more insight into the molecular mechanisms involved in this microcirculatory dysfunction, although much more attention must be directed towards microvascular endothelial cells and the role of heterogeneity of response in various vascular beds. These experimental data must in turn be validated by comparing with the human in situ situation, both clinical and morphological. This review aims at a critical appraisal of the clinical and experimental evidence for sepsis-induced dysregulation of the microcirculation and how knowledge of the underlying cellular and molecular pathology could be used to make therapy more rational and effective. To date, therapeutic approaches, such as anti-cytokine and anti-oxidant regimens, which have been highly successful in experimental models, have failed to demonstrate clinical efficacy. Newer approaches, such as targeting the coagulation system, nitric oxide synthesis or intracellular signal transduction, are also discussed. The necessity to focus on the role of anti-inflammatory mediators, as well as the pathogenetic significance of important molecular groups, such as the heat shock proteins, which until now have been given scant attention, will be stressed.