Nilanjana Sengupta

Ischemic vascular damage can be repaired by healthy, but not diabetic, endothelial progenitor cells.

Endothelial precursor cells (EPCs) play a key role in vascular repair and maintenance, and their function is impeded in diabetes. We previously demonstrated that EPCs isolated from diabetic patients have a profound inability to migrate in vitro. We asked whether EPCs from normal individuals are better able to repopulate degenerate (acellular) retinal capillaries in chronic (diabetes) and acute (ischemia/reperfusion [I/R] injury and neonatal oxygen-induced retinopathy [OIR]) animal models of ocular vascular damage. Streptozotocin-induced diabetic mice, spontaneously diabetic BBZDR/Wor rats, adult mice with I/R injury, or neonatal mice with OIR were injected within the vitreous or the systemic circulation with fluorescently labeled CD34+ cells from either diabetic patients or age- and sex-matched healthy control subjects. At specific times after administering the cells, the degree of vascular repair of the acellular capillaries was evaluated immunohistologically and quantitated. In all four models, healthy human (hu)CD34+ cells attached and assimilated into vasculature, whereas cells from diabetic donors uniformly were unable to integrate into damaged vasculature. These studies demonstrate that healthy huCD34+ cells can effectively repair injured retina and that there is defective repair of vasculature in patients with diabetes. Defective EPCs may be amenable to pharmacological manipulation and restoration of the cells’ natural robust reparative function.

IGF binding protein-3 regulates hematopoietic stem cell and endothelial precursor cell function during vascular development

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 oxygen-induced 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.

Paracrine Modulation of CXCR4 by IGF-1 and VEGF: Implications for Choroidal Neovascularization

PURPOSE Modulators of angiogenesis typically work in an orchestrated manner. The authors examined the interaction between insulinlike growth factor (IGF)-1, vascular endothelial growth factor (VEGF), and stromal derived factor (SDF)-1 in vivo and in vitro using angiogenesis models. METHODS The angiogenic effect of SDF-1, alone or in combination with IGF-1 and VEGF, was assessed in human lung microvascular endothelial cells using capillary tube formation and thymidine incorporation. Immunohistochemical analysis for CD31, SDF-1, and CXCR4 was performed on mouse eyes 2 weeks after the initiation of laser rupture of Bruchs membrane, a choroidal neovascularization (CNV) model. CXCR4 antagonist and CXCR4 blocking antibody were tested on inhibition of CNV lesion size in this model. Real-time PCR was used to determine mRNA levels for SDF-1, VEGF, IGF-1, and their cognate receptors in the retinal pigment epithelium/choroid complex of mice that underwent this CNV model. RESULTS IGF-1 and VEGF demonstrated an additive effect on SDF-1-induced in vitro angiogenesis. CXCR4 immunoreactivity was present in both normal and laser-injured mice at the laser burn site and at the ganglion cell layer, the anterior portion of the inner nuclear layer, photoreceptors, and choroidal stroma. SDF-1 was observed in identical locations but was not seen in photoreceptors. mRNA levels for SDF-1, VEGF, and IGF-1 and their receptors were increased after laser injury. CXCR4-neutralizing antibody reduced neovascularization when injected subretinally but not intraperitoneally or intravitreally. CONCLUSIONS The potent proangiogenic factors IGF-1 and VEGF both stimulate SDF-1-induced angiogenesis. Local inhibition of CXCR4 is required for an antiangiogenic effect in CNV lesions.

Regulation of Adult Hematopoietic Stem Cells Fate for Enhanced Tissue-specific Repair

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.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 NaIO3 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.

Bone Marrow–Derived Cell Recruitment to the Neurosensory Retina and Retinal Pigment Epithelial Cell Layer Following Subthreshold Retinal Phototherapy

Purpose We investigated whether subthreshold retinal phototherapy (SRPT) was associated with recruitment of bone marrow (BM)–derived cells to the neurosensory retina (NSR) and RPE layer. Methods GFP chimeric mice and wild-type (WT) mice were subjected to SRPT using a slit-lamp infrared laser. Duty cycles of 5%, 10%, 15%, and 20% (0.1 seconds, 250 mW, spot size 50 μm) with 30 applications were placed 50 to 100 μm from the optic disc. In adoptive transfer studies, GFP+ cells were given intravenously immediately after WT mice received SRPT. Immunohistochemistry was done for ionized calcium-binding adapter molecule-1 (IBA-1+), CD45, Griffonia simplicifolia lectin isolectin B4, GFP or cytokeratin). Expression of Ccl2, Il1b, Il6, Hspa1a, Hsp90aa1, Cryab, Hif1a, Cxcl12, and Cxcr4 mRNA and flow cytometry of the NSR and RPE-choroid were performed. Results Within 12 to 24 hours of SRPT, monocytes were detected in the NSR and RPE-choroid. Detection of reparative progenitors in the RPE occurred at 2 weeks using flow cytometry. Recruitment of GFP+ cells to the RPE layer occurred in a duty cycle–dependent manner in chimeric mice and in mice undergoing adoptive transfer. Hspa1a, Hsp90aa1, and Cryab mRNAs increased in the NSR at 2 hours post laser; Hif1a, Cxcl12, Hspa1a increased at 4 hours in the RPE-choroid; and Ccl2, Il1b, Ifng, and Il6 increased at 12 to 24 hours in the RPE-choroid. Conclusions SRPT induces monocyte recruitment to the RPE followed by hematopoietic progenitor cell homing at 2 weeks. Recruitment occurs in a duty cycle–dependent manner and potentially could contribute to the therapeutic efficacy of SRPT.

Stem and Progenitor Cells in the Retina

Regardless of the debate regarding moral issues of using stem cells in research, they are unequivocally useful for understanding pathological angiogenesis, particularly so in the retina. Some importan

Circulating Endothelial Progenitor Cells and Adult Vasculogenesis

Postnatal neovascularization (NV) has previously been considered synonymous with proliferation and migration of pre-existing, fully differentiated endothelial cells resident within parent vessels. The finding that circulating endothelial progenitor cells (EPCs) may home to sites of NV and differentiate in situ is consistent with vasculogenesis, a critical paradigm for the establishment of vascular networks in the embryo. While the percent contributions of angiogenesis and vasculogenesis to postnatal NV remain to be clarified, our observations in the eye, together with recent reports from other investigators in other tissues and pathologies, support that growth and development of new blood vessels in the adult are not restricted to angiogenesis but encompass both embryonic and adult mechanisms. As a corollary, augmented or retarded NV, whether endogenous or iatrogenic, likely includes enhancement or impairment of vasculogenesis. In this chapter, the molecular and cellular factors that play a role in EPC involvement in NV are discussed.

Hematopoietic Stem Cells in Vascular Development and Ocular Neovascularization

Neovascular diseases of the eye include retinopathy of prematurity (ROP), proliferative diabetic retinopathy (PDR), and the exudative or “wet” form of age-related macular degeneration (ARMD). Together these diseases affect all age groups and are the leading causes of vision impairment in developed nations [77].