Analysis of Stem Cell Populations Circulating in Peripheral Blood in Preterm Infants: Circulating Endothelial Progenitior Cells and Plasma VEGF and HGF Level as a Novel Prognostic Factors for Development of Retinopathy of Prematurity.

Abstract 4592

Retinopathy of prematurity (ROP) is a result of increased pathological neoangiogenesis of retina in preterm infants. The source of cells that are responsible for pathogenesis of ROP is still controversial, and some evidence indicates that they may be bone marrow (BM) derived. BM similarly as other tissues contains a subset of stem cells (SCs) which give rise to non-hematopoietic lineages. These non-hematopoietic stem cells appear heterogeneous and can be mobilized from the BM and other non-hematopoietic niches in response to tissue injury into peripheral blood (PB). Based on this we become interested in SCs populations that circulate in peripheral blood in preterm infants, to see whether their level and lineage commitment plays a role and has a prognostic value for development of ROP. Totally eighty-eight subjects were involved in this study: 29 preterm infants with ROP, 29 preterm infants without ROP, and 30 healthy control full-term infants. We investigated the association between i) different populations of SCs circulating in PB, ii) level of selected growth factors/chemokines regulating SCs migration/mobilization, and iii) the incidence of ROP. PB samples were collected 10 weeks after delivery and analyzed by employing flow cytometry (FACS), epimmunofluorescence staining, real time-PCR (RQ-PCR) and ELISA. We analyzed various cell populations enriched in: i) pluripotent very small embryonic-like stem cells, VSELs (lin^-CXCR4⁺CD45^-), ii) hematopoietic stem cells, HSCs (lin^-CXCR4⁺CD45⁺), and iii) early endothelial progenitor cells, EPCs (CD34⁺CD133⁺CD144⁺). In parallel we measured serum concentration of VEGF, bFGF, HGF, and SDF-1, factors that regulate trafficking of SCs. We found that the number of circulating EPCs and VSELs were significantly increased in PB of the preterm infants (almost 5- and 2-times, respectively). Moreover, the number of EPCs in the PB was significantly higher in the preterm infants with ROP as compared to preterm infants without retinopathy. At the same time we observed in preterm infants with ROP an increase in the serum concentrations of VEGF and HGF. The increased EPCs levels along with elevated levels of VEGF and HGF in preterm infants with ROP suggest that circulating EPCs and pro-angiopoietic factors may play a role in the development and progression of ROP. We conclude that EPCs mobilized into PB contribute to development of ROP in preterm children, and increase in number of these cells correlates with development of this serious complication. In addition, the observed by us increase in number of circulating VSELs in preterm infants suggest that the growth and development of immature tissues and organs may require mobilization and recruitment of pluripotent stem cells that are important in regeneration processes to reestablish proper organ function.