Endothelial precursor cells (EPCs

We asked whether the hypoxia-regulated factor, insulin-like growth factor binding protein-3 (IGFBP3), could modulate stem cell factor receptor (c-kit ؉ ), stem cell antigen-1 (sca-1 ؉ ), hematopoietic stem cell (HSC), or CD34 ؉ endothelial precursor cell (EPC) function. Exposure of CD34 ؉ EPCs to IGFBP3 resulted in rapid differentiation into endothelial cells and dose-dependent increases in cell migration and capillary tube formation. IGFBP3-expressing plasmid was injected into the vitreous of neonatal mice undergoing the oxygeninduced retinopathy (OIR) model. In separate studies, GFP-expressing HSCs were transfected with IGFBP3 plasmid and injected into the vitreous of OIR mice. Administering either IGFBP3 plasmid alone or HSCs transfected with the plasmid resulted in a similar reduction in areas of vasoobliteration, protection of the developing vasculature from hyperoxia-induced regression, and reduction in preretinal neovascularization compared to control plasmid or HSCs transfected with control plasmid. In conclusion, IGFBP3 mediates EPC migration, differentiation, and capillary formation in vitro. Targeted expression of IGFBP3 protects the vasculature from damage and promotes proper vascular repair after hyperoxic insult in the OIR model. IGFBP3 expression may represent a physiological adaptation to ischemia and potentially a therapeutic target for treatment of ischemic conditions. IGFBP3 ͉ angiogenesis ͉ retinopathy of prematurity V ascular damage associated with diabetic retinopathy and retinopathy of prematurity (ROP) results from tissue ischemia, and, subsequently, this ischemia leads to development of pathological neovascularization. Insulin-like growth factor 1 (IGF1) is required for normal retinal vascular development because vascular development is arrested in its absence despite the presence of VEGF (1). Development of ROP is associated with low levels of IGF1 (2) because the lack of IGF1 in the early neonatal period leads to the development of avascular retina, which results in ROP (3). However, unregulated IGF1 expression can lead to pathological neovascularization (4-13), and IGF1 receptor (IGF1R) antagonists are able to suppress retinal neovascularization in vivo by inhibiting VEGF signaling (1).The effects of IGF1 are mediated by IGF1R and modulated by complex interactions with IGF binding proteins (IGFBPs), which are also modulated at multiple levels. Six IGFBPs function as transporter proteins and storage pools for IGF1 in a tissue-and developmental stage-specific manner. Phosphorylation, proteolysis, polymerization (8), and cell or matrix association (9) regulates the functions of IGFBPs. Specific IGFBPs have been shown to either stimulate or inhibit IGF1 action (10).IGFBP3, the best studied and most abundant of these binding proteins, carries Ն75% of serum IGF1 and IGF2 in heterotrimeric complexes. Besides its endocrine effects, IGFBP3 has auto-and paracrine actions affecting cell mobility, adhesion, apoptosis, survival, and the cell cycle (14,15). Like the other IGFBPs, IGFBP3 has IGF1-in...

Adult stem cells are recruited to the choroid in a model of CNV, where they contribute to forming aberrant new vessels. This observation suggests that targeting stem cell recruitment to the eye may offer a novel therapeutic strategy for ARMD.

No abstract

The ability to control the differentiation of adult hematopoietic stem cells (HSCs) would promote development of new cell-based therapies to treat multiple degenerative diseases. Systemic injection of NaIO(3) was used to ablate the retinal pigment epithelial (RPE) layer in C57Bl6 mice and initiate neural retinal degeneration. HSCs infected ex vivo with lentiviral vector expressing the RPE-specific gene RPE65 restored a functional RPE layer, with typical RPE phenotype including coexpression of another RPE-specific marker, CRALBP, and photoreceptor outer segment phagocytosis. Retinal degeneration was prevented and visual function, as measured by electroretinography (ERG), was restored to levels similar to that found in normal animals. None of the controls (no HSCs, HSCs alone and HSCs infected with lentiviral vector expressing LacZ) showed these effects. In vitro gene array studies demonstrated that infection of HSC with RPE65 increased adenylate cyclase mRNA. In vitro exposure of HSCs to a pharmacological agonist of adenylate cyclase also led to in vitro differentiation of HSCs to RPE-like cells expressing pigment granules and the RPE-specific marker, CRALBP. Our data confirm that expression of the cell-specific gene RPE65 promoted fate determination of HSCs toward RPE for targeted tissue repair, and did so in part by activation of adenylate cyclase signaling pathways. Expression by HSCs of single genes unique to a differentiated cell may represent a novel experimental paradigm to influence HSC plasticity, force selective differentiation, and ultimately lead to identification of pharmacological alternatives to viral gene delivery.