Developmental basis of nanophthalmos: MFRP Is required for both prenatal ocular growth and postnatal emmetropization.

BACKGROUND: Nanophthalmos is a genetic disorder characterized by very small, hyperopic eyes that are without gross structural defects. Recessive nanophthalmos is caused by severe mutations in the MFRP gene, which encodes a Frizzled-related transmembrane protein that is selectively expressed in the retinal pigment epithelium (RPE) and ciliary body. RESULTS: For two MFRP -/- adults, we have obtained records of refraction that begin in early childhood. At the age of 6 months, one patient's eyes already had a refractive error of +12.25 D, and over the next 20 years this slowly increased to +17.50 D. Adults homozygous for null mutations in MFRP have eyes with axial lengths shorter than those of normal newborns. Furthermore, the unusually high curvature of their corneas is consistent with eyes that had been smaller than normal during late fetal development. MFRP protein was first detected at 14 weeks of gestation, when it was restricted to the posterior pole RPE. By 20 weeks gestation, MFRP expression had spread laterally, and was found throughout the RPE. MFRP protein was detected in both posterior and lateral RPE of the adult eye. CONCLUSIONS: Embryonic function of the MFRP gene appears necessary for the eye to reach its full size at birth. Its onset of expression in the RPE during mid-gestation suggests that MFRP does not participate in early formation of the optic cup, and is consistent with a role in later growth and development of the eye. Patients without MFRP gene function exhibit no correction of refractive error during childhood, which suggests that this gene is essential for emmetropization, a complex process by which vision regulates axial growth of the eye.

The embryonic human choriocapillaris develops by hemo-vasculogenesis.

The purpose of this study was to characterize normal human choroidal vascular development from 6-23 weeks gestation (WG). Markers of endothelial cells (EC) (CD34, CD31, vWf), angioblasts and EC (CD39), leukocytes (CD45), erythroblasts (epsilon chain of hemoglobin, Hb-e), proliferating cells (Ki67), and VEGFR-2 were employed. At 6-7 WG, many erythroblasts were observed within islands of precursor cells in the choriocapillaris layer and others were independent from the islands. Many erythroblasts (Hb-epsilon(+)) were also positive for EC markers and/or VEGFR-2. By 8-12 WG, most of the Hb-epsilon cells had disappeared and vascular lumens became apparent. At 14-23 WG, some EC were proliferating on the scleral side of choriocapillaris in association with forming deeper vessels. In conclusion, embryonic choriocapillaris appears to form initially by hemo-vasculogenesis (blood vessels and blood cells form simultaneously from common precursors) while angiogenesis appears to be the mode of intermediate and large choroidal vessel development in the fetus.

Hyperoxia inhibits several critical aspects of vascular development.

Normal human retinal vascular development uses angiogenesis and vasculogenesis, both of which are interrupted in the vaso-obliteration phase of retinopathy of prematurity (ROP). Canine oxygen-induced retinopathy (OIR) closely resembles human ROP. Canine retinal endothelial cells (ECs) and angioblasts were used to model OIR and characterize the effects of hyperoxia on angiogenesis and vasculogenesis. Cell cycle analysis showed that hyperoxia reduced the number of G1 phase cells and showed increased arrest in S phase for both cell types. Migration of ECs was significantly inhibited in hyperoxia (P < 0.01). Hyperoxia disrupted the cytoskeleton of angioblasts but not ECs after 2 days. Differentiation of angioblasts into ECs (determined by acetylated low-density lipoprotein uptake) was evaluated after basic fibroblast growth factor treatment. Differentiation of angioblasts into pericytes was determined by smooth muscle actin expression after treatment with platelet-derived growth factor. Differentiation into ECs was significantly inhibited by hyperoxia (P < 0.0001). The percentage of CXCR4(+) cells (a marker for retinal vascular precursors) increased in both treatment groups after hyperoxia. These data show novel mechanisms of hyperoxia-induced disruption of vascular development.

Caspase activation and amyloid precursor protein cleavage in rat ocular hypertension.

PURPOSE: Retinal ganglion cell (RGC) death in glaucoma involves apoptosis. Activation of caspases and abnormal processing of amyloid precursor protein (APP) are important events in other chronic neurodegenerations, such as Alzheimer's disease (AD). The retinal expression and activation of caspases and the patterns of caspase-3-mediated APP processing in ocular hypertensive models of rat glaucoma were investigated. METHODS: RGC death was produced in one eye by chronic exposure to increased intraocular pressure (IOP) or by optic nerve transection. Elevated IOP was produced by obstruction of aqueous humor outflow with laser coagulation or limbal hypertonic saline injection. Caspase activity and APP processing in the retina were examined by RNase protection assay (RPA), immunocytochemistry, immunoblot assay, and colorimetric assay. RESULTS: RPA revealed elevations of caspase-3 mRNA, as well as other apoptosis-related mRNAs. Immunocytochemistry showed caspase-3 activation in RGCs damaged by ocular hypertension. The generation of the caspase-3-mediated APP cleavage product (DeltaC-APP) was also increased in ocular hypertensive RGCs. Western immunoblot assay and colorimetry revealed significantly more activated caspase-3 in ocular hypertensive retinas than in control retinas. The activated form of caspase-8, an initiator caspase, and amyloid-beta, a product of APP proteolysis and a component of senile plaques in AD, were detected in RGCs by immunohistochemistry significantly more often in ocular hypertensive than in control retinas. The amounts of full-length APP were reduced and amyloid-beta-containing fragments were increased in ocular hypertensive retinas by Western immunoblot assay. CONCLUSIONS: Rat RGCs subjected to chronic ocular hypertension demonstrate caspase activation and abnormal processing of APP, which may contribute to the pathophysiology of glaucoma.