The vascular effects of arsenic in drinking water are a global public health concern that contribute to disease in millions of people worldwide. However, the cellular and molecular mechanisms for these pathogenic effects of arsenic are not well defined. This dissertation examined the hypothesis that arsenic stimulates pathogenic signals through surface receptors on liver sinusoidal endothelial cells (LSECs) to stimulate NADPH oxidase (NOX) activity that is required for arsenic-stimulated LSEC capillarization. In mice and isolated LSECs, we demonstrated that exposure to arsenic promoted capillarization and increased expression of platelet endothelial cell adhesion molecule (PECAM-1) through a time and dose dependent mechanism.

Superoxide generating NOX enzyme complexes participate in vascular remodeling and angiogenesis and are central to arsenic stimulated cell signaling. LSEC arsenic exposure increased NOX dependent superoxide generation that was inhibited using gp91ds-tat protein, NSC23766, a Rae1-GTPase inhibitor, or quenched by the intracellular superoxide scavenger, Tempol. These inhibitors also blocked arsenic-stimulated LSEC PECAM-1 expression and defenestration. In vivo arsenic exposures failed to promote LSEC capillarization in p47^phox knockout mice. These data demonstrated that arsenic stimulates capillarization through a NOX dependent mechanism.

Given that arsenic rapidly activates NOX in vascular cells, we hypothesized that signaling for these responses was receptor mediated. Since arsenic-stimulated LSEC defenestration and capillarization is Rac1 and NOX dependent, we examined whether a g-protein coupled receptor (GPCR) upstream of Rac1 initiated these effects. Pre-treatment LSECs with Pertussis toxin (PTX), an inhibitor of Gi/o, prevented arsenic-stimulated defenestration. Since capillarization is a gain in barrier function, LSEC expression of the sphingosine-1-phosphate type 1 (S1P₁) receptor, a major Gi/o linked regulator of endothelial barrier function, and its role in arsenic-stimulated defenestration were investigated. S1P₁ was highly expressed in LSECs relative to large vessels. In ex vivo studies, inhibiting LSEC S1P₁ with a selective antagonist, VPC23109, blocked arsenic-stimulated superoxide generation, defenestration, and PECAM-1 expression. These data demonstrated that arsenic targets a specific LSEC GPCR to promote vascular remodeling, and the first demonstrating that S1P₁ regulates oxidant-dependent LSEC capillarization. Taken together, these data demonstrate that S1P₁ activated NOX stimulates LSEC capillarization, which aids in our understanding of mechanisms underlying arsenic-induced liver disease.