The role of CX3 CL1/CX3 CR1 in pulmonary angiogenesis and intravascular monocyte accumulation in rat experimental hepatopulmonary syndrome

Background & Aims Hepatopulmonary syndrome (HPS), classically attributed to intrapulmonary vascular dilatation, occurs in 15–30% of cirrhotics and causes hypoxemia and increases mortality. In experimental HPS after common bile duct ligation (CBDL), monocytes adhere in the lung vasculature and produce vascular endothelial growth factor (VEGF)-A and angiogenesis ensues and contribute to abnormal gas exchange. However, the mechanisms for these events are unknown. The chemokine fractalkine (CX3 CL1) can directly mediate monocyte adhesion and activate VEGF-A and angiogenesis via its receptor CX3 CR1 on monocytes and endothelium during inflammatory angiogenesis. We explored whether pulmonary CX3 CL1/CX3 CR1 alterations occur after CBDL and influence pulmonary angiogenesis and HPS. Methods Pulmonary CX3 CL1/CX3 CR1 expression and localization, CX3 CL1 signaling pathway activation, monocyte accumulation, and development of angiogenesis and HPS were assessed in 2- and 4-week CBDL animals. The effects of a neutralizing antibody to CX3 CR1 (anti-CX3 CR1 Ab) on HPS after CBDL were evaluated. Results Circulating CX3 CL1 levels and lung expression of CX3 CL1 and CX3 CR1 in intravascular monocytes and microvascular endothelium increased in 2- and 4-week CBDL animals as HPS developed. These events were accompanied by pulmonary angiogenesis, monocyte accumulation, activation of CX3 CL1 mediated signaling pathways (Akt, ERK) and increased VEGF-A expression and signaling. Anti-CX3 CR1 Ab treatment reduced monocyte accumulation, decreased lung angiogenesis and improved HPS. These events were accompanied by inhibition of CX3 CL1 signaling pathways and a reduction in VEGF-A expression and signaling. Conclusions Circulating CX3 CL1 levels and pulmonary CX3 CL1/CX3 CR1 expression and signaling increase after CBDL and contribute to pulmonary intravascular monocyte accumulation, angiogenesis and development of experimental HPS.