Critical Role of Vascular Endothelial Growth Factor Secreted by Mesenchymal Stem Cells in Hyperoxic Lung Injury

Abstract

Intratracheal transplantation of human umbilical cord blood (UCB)-derived mesenchymal stem cells (MSCs) protects against neonatal hyperoxic lung injury by a paracrine rather than a regenerative mechanism. However, the role of paracrine factors produced by the MSCs, such as vascular endothelial growth factor (VEGF), has not been delineated. This study examined whether VEGF secreted by MSCs plays a pivotal role in protecting against neonatal hyperoxic lung injury. VEGF was knocked down in human UCB-derived MSCs by transfection with small interfering RNA specific for human VEGF. The in vitro effects of MSCs with or without VEGF knockdown or neutralizing antibody were evaluated in a rat lung epithelial (L2) cell line challenged with H2O2. To confirm these results in vivo, newborn Sprague-Dawley rats were exposed to hyperoxia (90% O2) for 14 days. MSCs (1 × 10(5) cells) with or without VEGF knockdown were administered intratracheally at postnatal Day 5. Lungs were serially harvested for biochemical and histologic analyses. VEGF knockdown and antibody abolished the in vitro benefits of MSCs on H2O2-induced cell death and the up-regulation of inflammatory cytokines in L2 cells. VEGF knockdown also abolished the in vivo protective effects of MSCs in hyperoxic lung injury, such as the attenuation of impaired alveolarization and angiogenesis, reduction in the number of terminal deoxynucleotidyl transferase dUTP nick end labeling-positive and ED-1-positive cells, and down-regulation of proinflammatory cytokine levels. Our data indicate that VEGF secreted by transplanted MSCs is one of the critical paracrine factors that play seminal roles in attenuating hyperoxic lung injuries in neonatal rats.

Intratracheal transplantation of mesenchymal stem cells simultaneously attenuates both lung and brain injuries in hyperoxic newborn rats

“…Lung inflammatory cytokines and VEGF levels showed significant positive and negative correlations with brain weight, respectively, at P14. We have shown that the protective effects of MSC transplantation may primarily be mediated by a paracrine rather than a regenerative mechanism, and have highlighted the critical role of growth factors, including VEGF, in mediating the antioxidative, anti-inflammatory, and antiapoptotic paracrine effects of MSC transplantation (20). Taken together, these findings suggest that the neuroprotective …”

Strategies to enhance paracrine potency of transplanted mesenchymal stem cells in intractable neonatal disorders

“…In addition, TLR-4 in MSCs plays pivotal roles in eliminating pathogens by augmenting antibacterial effects and reducing host tissue injuries by attenuating the inflammatory response (90,91). Collectively, these studies suggest that key paracrine factors secreted by MSCs from the same source play important roles in mediating the therapeutic effects of MSCs in different preclinical disease models (11,13,48), suggesting that there is a crosstalk and interplay between the host tissue and transplanted MSCs (61,92). Therefore, unlike drug treatments that deliver a single agent at a specific dose, transplanted MSCs act as a "paracrine factors factory" that sense the microenvironment of the injury site and secrete various paracrine factors that exert several reparative functions, including antiapoptotic, anti-inflammatory, antioxidative, antifibrotic, and/or antibacterial effects in response to local microenvironmental cues to enhance the regeneration of damaged tissue (86).…”

“…Therefore, a multifaceted therapeutic agent might be necessary to improve outcomes of patients with these intractable neonatal disorders. The pleiotropic beneficial effects of stem cell therapy, such as antiapoptotic, anti-inflammatory, antifibrotic, and antioxidative effects, have been observed in various animal models of BPD (5)(6)(7)(8)10), severe IVH (13-15), or HIE (11,25,26). Furthermore, in addition to their beneficial antiinflammatory effects, antibacterial activity of transplanted stem cells were observed in an animal model of Escherichia coli pneumonia (27).…”

Mesenchymal Stem Cells for Severe Intraventricular Hemorrhage in Preterm Infants: Phase I Dose-Escalation Clinical Trial

“…Various preclinical data support the therapeutic potential of transplantation with mesenchymal stem cells (MSCs) for treating various intractable neonatal disorders including bronchopulmonary dysplasia (BPD) 11, 12, 13, 14 and hypoxic ischemic encephalopathy (HIE) 15. Human umbilical cord blood (UCB) is a promising source of MSCs.…”