The endothelium plays a pivotal role in the maintenance of vascular homeostasis and its dysregulation promotes vascular complications. This thesis proposes that heme oxygenase-1 (HO-1), an anti-inflammatory enzyme with antioxidant properties, is endothelial protective factor that prevents endothelial injury induced by cisplatin or activated neutrophils. Specifically, this thesis aimed to test (i) that overexpression of HO-1 prevents cisplatin-induced endothelial injury and suppresses caspase activity; (ii) whether neutrophil-endothelial cell activation resulted in the release of soluble Flt-1 (sFlt-1) and soluble endoglin (sEng), the two anti-angiogenic factors known to induce the clinical signs of preeclampsia; (iii) whether HO-1 prevented activated neutrophils from stimulating the release of these factors from the endothelium; (iv) the relative contribution and the co-dependency of neutrophil activation and anti-angiogenic growth factors in preeclampsia where systemic endothelial dysfunction is known to occur. This thesis shows that cisplatin inhibited human umbilical vein endothelial cells (HUVEC) metabolism as measured by MTT assay and resulted in the release of placenta growth factor (PlGF). Immunoblotting confirmed that cisplatin increased cleaved caspase-3 expression in HUVEC. These effects of cisplatin were attenuated in HUVEC infected with adenovirus encoding HO-1 and the effects were exacerbated when HO-1 was silenced by siRNA. Furthermore, cisplatin stimulated PlGF release was suppressed by the overexpression of HO-1. In addition, HO-1 overexpression inhibited angiogenesis as determined by vascular endothelial growth factor-induced capillary tube formation on Matrigel coated plates. Thus these studies indicate that agents which upregulate HO-1 could increase the effectiveness and tolerability to cisplatin in cancer treatment. Although neutrophils are early contributors to endothelial cell activation, no studies have determined their contribution to the release of sFlt-1 and sEng. We therefore investigated the effect of activated neutrophils on the release of sFlt-1 and sEng in endothelial/neutrophil co-cultures and in the circulation of women with normal pregnancy and preeclampsia. LPS-mediated neutrophil activation stimulated the release of sEng but not sFlt-1 from endothelial cells in culture. In the absence of neutrophils, overexpression of HO-1 in HUVEC downregulated the release of sEng. In contrast, HO-1 overexpression failed to inhibit the release of sEng in the presence of activated neutrophils. The release of sEng by activated neutrophils-endothelial cell cocultures appears to be mediated by metalloproteinases (MMP) as the broad-spectrum MMP inhibitor (GM6001) attenuated sEng release. Clinical studies demonstrated that sEng, pro-inflammatory interleukin-6 (IL-6) and the soluble markers of neutrophil activation (α-defensins and calprotectin) were all elevated in women with preeclampsia. We identified a direct correlation between neutrophil activation and IL-6 release. However, no correlation could be established between these factors and sEng release in preeclampsia. Hence, these results provide compelling clinical evidence to show that the increase in neutrophil activation and IL-6 release during preeclampsia are unlikely to significantly contribute to the clinical signs of preeclampsia as they fail to correlate directly with the anti-angiogenic factors, which form the final common pathway to the clinical signs of preeclampsia and systemic endothelial dysfunction.

Junctional adhesion molecule C (JAM-C) is a component of endothelial cell (EC) tight junctions that has been implicated in a number of endothelial functions, such as angiogenesis and trafficking of leukocytes through the endothelium during inflammation. Work within our lab has identified that loss of JAM-C at EC junctions results in increased reverse transendothelial migration (rTEM) of neutrophils back into the circulation, a response that has been associated with the dissemination of inflammation to distant organs. Whilst the mechanism by which JAM-C is lost or redistributed away from EC junctions has begun to be elucidated, little is known about how loss of endothelial JAM-C impacts the functions of ECs. As such, this thesis aimed to investigate the effect of JAM-C deficiency on EC functions to unravel possible molecular and cellular mechanisms of mediating neutrophil rTEM. To address the effect of JAM-C deficiency on EC functions, an in vitro RNA interference (RNAi) approach was used to efficiently knock-down (KD) JAM-C in human umbilical vein ECs (HUVECs). Importantly, KD of JAM-C did not affect expression of other key EC junctional markers such as JAM-A and VE-Cadherin and cell proliferation and apoptosis were similarly unaffected. Gene expression profiling using microarrays revealed that JAM-C depleted HUVECs exhibited a pro-inflammatory phenotype under basal conditions that was characterised by increased expression of pro-inflammatory genes such as ICAM1 and IL8. Following IL-1β-induced inflammation, no difference in expression of pro-inflammatory genes was detected between control and JAM-C KD HUVECs. However, protein levels of secreted chemokines such as IL-8 were reduced in JAM-C KD HUVECs following stimulation with IL-1β. This was corroborated by in vivo studies demonstrating reduced levels of secreted chemokines in the plasma of mice where JAM-C was conditionally deleted from ECs. A novel finding of this work is the demonstration that JAM-C KD HUVECs exhibit increased autophagy under basal conditions. This might provide a potential mechanism for the reduced chemokine secretion that is observed in this system, whereby chemokines are preferentially trafficked for autophagosome-mediated degradation. Taken together, these findings indicate a multi-functional role for JAM-C in regulating EC homeostasis under basal conditions. JAM-C KD ECs respond aberrantly to inflammatory stimuli by secreting reduced chemokine levels, a consequence that could provide novel insights into the mechanisms of neutrophil rTEM under conditions of endothelial JAM-C loss.

Disruptions in the response of endothelial progenitor cells to changes in oxygen environment may present a possible mechanism behind multiple pediatric pulmonary disease models, such as bronchopulmonary dysplasia. Using high-throughput fixed single-cell protein and RNA imaging, we have created "stop-motion" movies of Thymosin. 4 (T beta 4) and Hypoxia Inducible Factor 1 alpha (HIF-1 alpha) protein expression and vascular endothelial growth factor (vegf) and endothelial nitric oxide synthase (eNOS) mRNA in human umbilical cord-derived endothelial colony-forming cells (ECFC). ECFC were grown in vitro under both room air and hyperoxia (50% O-2). We find elevated basal T beta 4 protein expression in ECFC derived from prematurely born infants versus full term infants. T beta 4 is a potent growth hormone that additionally acts as an actin sequestration protein and regulates the stability of HIF-1 alpha. This basal level increase of T beta 4 is associated with lower HIF1 alpha nuclear localization in preterm versus term ECFC upon exposure to hyperoxia. We find altered expression in the pro-angiogenic genes vegf and eNOS, two genes that HIF-1 alpha acts as a transcription factor for. This provides a potential link between a developmentally regulated protein and previously observed impaired function of preterm ECFC in response to hyperoxia.