Effect of Nerve Growth Factor on Innervation of Perivascular Nerves in Neovasculatures of Mouse Cornea.

Angiogenesis, which is the generation of new vascular networks from existing blood vessels, occurs under normal and pathophysiological conditions. Perivascular nerves, which innervate mature vasculatures, maintain vascular tone and regulate tissue blood flow. However, little is known whether perivascular nerves innervate newborn blood vessels. Therefore, the aim of this study was to investigate the distribution and characterization of perivascular nerves in neovasculatures, which were generated by the mouse corneal micropocket method. Under anesthesia, a pellet containing basic fibroblast growth factor (bFGF) (100 ng/pellet) was implanted into a mouse cornea in one side of the eyeball. Nerve growth factor (NGF) was locally (2 or 20 ng) applied with the pellet, or subcutaneously (40 ng/h for 7 d) administered with an osmotic mini-pump. After the implantation, vascular endothelial cells, smooth muscle cells, and perivascular nerves in the cornea were immunohistochemically studied. Neovessels generated from existing limbal vessels were observed in pellet-implanted cornea. Immunostaining of neovasculatures showed the presence of CD31-like immunoreactive (LI) endothelial cells and α-smooth muscle actin-LI vascular smooth muscles. Perivascular nerves immunostained by protein gene product (PGP) 9.5, an axonal marker, were found in the existing limbal vessels, but they were not observed in neovasculatures. Local and subcutaneous treatment of NGF inhibits bFGF-derived angiogenesis and resulted in loop-shaped vessels that had many anastomoses, and produced innervation of PGP 9.5-LI perivascular nerves around bFGF-derived neovessels. These findings suggest that neovasculatures have no innervation of perivascular nerves, and that NGF facilitates innervations of perivascular nerves to regulate the blood flow in neovessels.

Nerve Growth Factor Facilitates the Innervation of Perivascular Nerves in Tumor-Derived Neovasculature in the Mouse Cornea.

BACKGROUND: Tumor neovascular vessels are not innervated by perivascular nerves. This study was an investigation of the effects of the nerve growth factor (NGF) on the distribution of perivascular nerves and neovessel formation in tumor tissues. METHODS: A gel containing DU145 prostate carcinoma cells or HT1080 fibrosarcoma cells was implanted into mouse corneas. NGF was subcutaneously administered using an osmotic mini-pump. The distribution of perivascular nerves in mouse corneas and densities of CD31-immunopositive neovessels and smooth muscles (α-smooth muscle actin, α-SMA) in tumor tissues were quantified. SUMMARY: Neovessels generated from corneal limber arteries in tumor tissues were observed 4-14 days after the implantation of tumor cells. The density of CD31-immunopositive cells in endothelium increased after the implantation of DU145 or HT1080 cells, while that of α-SMA-immunopositive cells slightly increased. The NGF treatment significantly increased the density of α-SMA- but not that of CD31-immunopositive cells (except for DU145 cells) and resulted in the innervation of perivascular nerves around tumor-derived neovessels, whereas no innervation was observed in the control group. Key Messages: These results suggest that NGF facilitates the innervation of perivascular nerves to regulate blood flow into tumor-derived neovessels.

[Influence of nerve growth factor (NGF) on distribution of perivascular nerves in tumor neovasculatures of mouse corneal].

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.