Mechanical strain triggers a variety of cellular responses, but the underlying mechanotransduction process has not been established. Endothelial cells (EC) respond to mechanical strain by upregulating adhesion molecule expression through a signaling process involving reactive oxygen species (ROS), but the site of their generation is unknown. Mitochondria anchor to the cytoskeleton and could function as mechanotransducers by releasing ROS during cytoskeletal strain. In human umbilical vein EC (HUVEC), ROS production increased 221 +/- 17% during 6 h of cyclic strain vs. unstrained controls. Mitochondrial inhibitors diphenylene iodonium or rotenone abrogated this response, whereas inhibitors of nitric oxide (NO) synthase (L-nitroarginine), xanthine oxidase (allopurinol), or NAD(P)H oxidase (apocynin) had no effect. The antioxidants ebselen and diethyldithiocarbamate inhibited the increase in ROS, but the NO scavenger Hb had no effect. Thus strain induces ROS release from mitochondria. In other studies, HUVEC were rendered mitochondria deficient (rho0 EC) to determine the requirement for electron transport in the response to strain. Strain-induced 2'7'-dichlorofluorescein fluorescence was attenuated by >80% in rho0 EC compared with HUVEC (43 +/- 7 vs. 221 +/- 17%). Treatment with cytochalasin D abrogated strain-induced ROS production, indicating a requirement for the actin cytoskeleton. Cyclic strain (6 h) increased VCAM-1 expression in wild-type but not rho0 EC. Increases in NF-kappaB activation and VCAM-1 mRNA expression during strain were prevented by antioxidants. These findings demonstrate that mitochondria function as mechanotransducers in endothelium by increasing ROS signaling, which is required for strain-induced increase in VCAM-1 expression via NF-kappaB.

Abstract-Endothelial cells increase their secretion of the cytokine interleukin-6 (IL-6) during hypoxia, which then acts in an autocrine fashion to increase the permeability of cell monolayers. These responses are attenuated by antioxidants, suggesting that reactive oxygen species (ROS) participate in signaling in hypoxic endothelium. We tested whether mitochondria are responsible for these ROS in human umbilical vein endothelial cells exposed to hypoxia. Oxidation of the probe 2Ј,7Ј-dichlorodihydrofluorescein to fluorescent dichlorofluorescein or the probe dihydroethidium was used to assess oxidant signaling, whereas permeability was assessed by using transendothelial electrical resistance. Hypoxia elicited increases in dichlorofluorescein and dihydroethidium fluorescence that were abrogated by the mitochondrial electron transport (ET) inhibitors rotenone (2 mol/L) and diphenyleneiodonium (5 mol/L). The same ET inhibitors also attenuated hypoxia-induced increases in nuclear factor-B (NF-B) activation, although they did not abrogate NF-B activation in response to endotoxin (lipopolysaccharide). ET inhibition also abolished the hypoxia-induced increases in IL-6 mRNA expression, hypoxia-stimulated IL-6 secretion into the media, and the hypoxia-induced increases in transendothelial electrical resistance of human umbilical vein endothelial cell monolayers. By contrast, the above responses to hypoxia were not significantly affected by treatment with the NAD(P)H oxidase inhibitor apocynin (30 mol/L), the xanthine oxidase inhibitor allopurinol (100 mol/L), or the NO synthase inhibitor N-nitro-L-arginine (100 mol/L). We conclude that ROS signals originating from the mitochondrial ET chain trigger the increase in NF-B activation, the transcriptional activation of IL-6, the secretion of IL-6 into the cell culture media, and the increases in endothelial permeability observed during hypoxia. These responses are essential for increases in the adhesion of polymorphonuclear leukocytes and the regulated increases in the trafficking of inflammatory cells across the endothelial barrier. Hypoxic stress often precedes or accompanies tissue inflammation, and previous studies have shown that tissue hypoxia can induce manifestations of the inflammatory response. In this regard, hypoxia augments the upregulation of endothelial cell surface receptors and the regulated increases in endothelial barrier permeability. 4 -6 However, the mechanistic link between cellular hypoxia and the initiation of these responses has not been clearly established. See page 525Recent studies have suggested that reactive oxygen species (ROS) may be important intracellular signaling messengers linking tissue hypoxia to the subsequent inflammatory responses. For example, in mesenteric venules of rats exposed to systemic hypoxia, Wood et al 7 found evidence of increased ROS generation that contributed to the stimulation of leukocyte-endothelial cell adhesion. We recently reported that ROS participate in the signaling responsible for the transient increase in en...

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A drawback of robotic lobectomy is the inability of the operating surgeon to perform stapler division of the pulmonary vessels and bronchi. With the advent of the robotic stapler, the surgeon is able to control this instrument from the console. The robotic stapler presents certain challenges. This article outlines techniques to use the robotic stapler for the safe and predictable performance of lobectomies.