Genetic modulation of pigment epithelium–derived factor (PEDF) expression does not alter normal or pathological angiogenesis in the eye, or tumor growth.

Abstract

Abstract: : Purpose: To evaluate the putative role of PEDF in normal vascular development and pathological angiogenesis, utilizing PEDF–null mice and tumor cells engineered to overexpress PEDF. Methods: PEDF null mice were generated as described (Renard et al, IOVS, 44:E2888). Angioarchitecture and microvascular density were evaluated in the retina and diverse extra–ocular tissues in sections stained for PECAM. Retinal angiogenesis also was evaluated in flat–mounts stained with fluorescieinated lectin following transient exposed to hyperoxia to induce retinal neovascularization. Corneal neovascularization following placement of intrastromal sutures, and the regression of neovessels following suture removal, were evaluated in corneal flat–mounts stained with fluorescinated lectin. Finally, the effect of PEDF over–expression on tumor development was investigated in a xenograft model in which C6 glioma cells engineered to over–express PEDF, or control cells, were implanted subcutaneously in SCID mice. Two weeks after implantation, tumors were measured ex vivo. The vasculature of PEDF–expressing and control tumors was compared in tissue sections stained with PECAM. Results: As reported, PEDF null mice were born in the expected ratios and were overtly healthy. PEDF expression patterns, as determined by reporter gene expression and in situ hybridization, were not correlated with vascular boundaries and no abnormalities were evident in the vascular architecture of the retina, cornea, or extraocular tissues examined. Quantitative studies revealed no differences in the density of the superficial or deep retinal vascular beds of PEDF null mice compared with wild–type (WT) controls, or in vascular density of the pancreas or kidney. Following exposure to hyperoxia, retinal neovascularization was provoked to an equivalent extent in PEDF–/– mice and WT littermates. Similarly, the magnitude of neovascular response seen following the placement of intrastromal sutures was indistinguishable in PEDF null and WT mice, as was the extent of regression following suture removal. C6 cells engineered to over–expressing PEDF produced tumors that were indistinguishable from controls in terms of size, intrinsic vessel density and vessel morphology. Conclusions: These results do not support the hypothesis that PEDF functions as an important modulator of normal vascular development, or as an inhibitor of pathological angiogenesis.

Keywords: transgenics/knock–outs • neovascularization • retina