The Influence of Nerve Growth Factor (NGF) on Distribution of Perivascular Nerves in Tumor Neovasculatures of Mouse Corneal

Abstract

Angiogenesis, or new blood vessel formation, is critical for the growth and spread of tumors. The vascular tone and tissue blood flow are maintained and regulated by perivascular nerves. However, many studies have reported that tumor neovascular vessels have no innervation of perivascular nerves. We have shown that nerve growth factor (NGF) facilitated perivascular innervation and suppressed the tumor growth. From these results, we hypothesized that the neuronal regulation of blood flow toward tumors via perivascular nerves may lead suppression of the tumor growth. Therefore, the aim of this study is to investigate effect of NGF on distribution of perivascular nerves and neovessel form in tumor tissues, which were generated by mouse corneal micropocket method. A gel, which contained DU145 prostate carcinoma cells, was implanted into the mouse corneal. NGF or saline was subcutaneously administered using an osmotic mini-pump. After 1 week, the distribution of perivascular nerves in mouse corneal were immunohistochemically studied. Also, the density of neovessels (immunocytochemically stained CD31) and smooth muscles (α-smooth muscle actin; SMA) in tumor tissues was quantified by the computer-assisted image processing. Four days after implantation of tumor cells in mouse corneal, many neovessels generated from corneal limbal vessels were observed in tumor tissues. Treatment of mouse with NGF resulted in innervation of perivascular nerves around tumor neovessels, but not observed in saline-treated group. NGF treatment increased SMA-, but not CD31-, immunopositive cells. These results suggest that NGF may facilitate innervations of perivascular nerve to regulate the blood flow in tumor neovessels.