Fibrocytes induce an angiogenic phenotype in cultured endothelial cells and promote angiogenesis in vivo.

Angiogenesis is an ordered process requiring the inter-play of numerous cellular and humoral factors. Studies over the past 20 years have identified several growth factors, cytokines, and enzymes that promote blood vessel formation. Most have revealed how individual factors promote an angiogenic phenotype in endothelial cells in vitro or contribute to blood vessel formation in vivo. However, the fundamental question that remains unanswered is how the cellular microenvironment contributes to angiogenesis. Fibrocytes are a recently characterized mesenchymal cell type isolated from peripheral blood that rapidly enter subcutaneously implanted wound chambers and sites of tissue injury. Here we describe the induction of an angiogenic phenotype in microvascular endothelial cells in vitro and promotion of angiogenesis in vivo by cultured fibrocytes. Fibrocytes constitutively secrete extracellular matrix-degrading enzymes, primarily matrix metalloproteinase 9, which promotes endothelial cell invasion. In addition, fibrocytes secrete several proangiogenic factors including VEGF, bFGF, IL-8, PDGF, and hematopoietic growth factors that promote endothelial cell migration, proliferation, and/or tube formation. By contrast, they do not produce representative antiangiogenic factors. Finally, both autologous fibrocytes and fibrocyte-conditioned media were found to induce blood vessel formation in vivo using the Matrigel angiogenesis model.

Expression of functional delta opioid receptors in vascular smooth muscle.

We evaluated smooth muscle from human internal mammary artery and rat aorta for the presence of delta opioid receptors. Radioligand receptor competition studies using the delta-receptor selective agonist, [3H]-[D-Ala2, Met5] enkephalinamide (DAMA) suggested the expression of a high affinity binding site in rat and human blood vessels that was consistent with the delta-2 opioid receptor subtype. Using RT-PCR with primers to the cloned delta opioid receptor (DOR), a cDNA fragment identical to the known DOR sequence was obtained from the smooth muscle cell line, A-10. Stimulation of A-10 cells with DAMA resulted in a significant mobilization of intracellular calcium and membrane depolarization. Exposure of aortic rings denuded of endothelium to DAMA induced a naltrindole-senstive increase in contractile tone. These data demonstrate the presence of a functional DOR in vascular smooth muscle and a direct impact of opioids on vascular contractile tone.