Increased number and function of endothelial progenitor cells stimulate angiogenesis by resident liver sinusoidal endothelial cells (SECs) in cirrhosis through paracrine factors

Abstract

Recent studies have shown a pathological role of angiogenesis in the progression of chronic liver diseases (CLDs). The present study focused on numbers and angiogenic functions of circulating endothelial progenitor cells (EPCs) in patients with cirrhosis. Circulating EPCs were counted by flow-cytometry, and correlated with different parameters of liver disease. They were cultured in patients and controls to compare colony-formation, proliferation and tube formation. Interactions of EPCs with hepatic stellate cells (HSCs) and sinusoidal endothelial cells (SECs) were examined by indirect and direct co-cultures in presence of EPCs and EPC-conditioned medium, respectively. ELISA and inhibition assays were performed to assess the role of EPC-derived angiogenic factors. The number of circulating EPCs was substantially higher in cirrhotic patients compared to controls (p<0.05), and showed good correlation with hepatic disease severity. Functional assays revealed that colonies and proliferation of EPCs were significantly increased in patients compared to controls (p<0.05). Direct and indirect co-cultures of patients' EPCs showed an increase in tube formation by SECs as compared to that observed with control EPCs (p<0.05). There was, however, no tube formation in HSC-EPC co-cultures. Levels of PDGF-BB and VEGF were substantially increased in patients' EPC media and inhibition of these factors by neutralizing antibodies led to a significant reduction in SECs proliferation. Mobilization and proliferation of EPCs are significantly enhanced in cirrhotic patients in comparison to controls. EPCs may play an important paracrine role in liver angiogenesis by stimulating resident SECs in cirrhosis.