Adult Bone Marrow–Derived Progenitor Cells Promote Vascular Rescue in a Mouse Model of Oxygen–Induced Retinopathy

Abstract

Abstract: : Purpose: To examine whether a subpopulation of adult bone marrow–derived progenitor cells, previously shown to increase vascular and neural survival in models of retinal degeneration, can also promote vascular rescue in a model of oxygen–induced retinopathy (OIR). Methods: Bone marrow (BM) was extracted from adult actGFP C57BL/6J mice, and different subpopulations of cells were sorted. At post–natal day 2 (P2) – P7, over 160 C57BL/6J mice were intravitreally injected with PBS, 1–2 x 10⁵ BM–derived Lineage negative hematopoietic stem cells (Lin–HSCs) or CD31, 34 and 11b–negative cells (CD–). The mice were exposed to hyperoxia (75% O₂) between P7 – P12 followed by return to room air. Retinas were isolated at different time points, the vasculature stained, confocal images of retinal whole mounts acquired, and the area of vascular obliteration as well as extent of pre–retinal neovascularization (NV) quantified. Immunohistochemistry was used to identify cell types associated with the healing process. To obtain mechanistic insight, microarray gene expression analysis was performed on the different BM cell sub–populations and on retinas from the different experimental groups. Results: Injection of Lin– cells, but not CD– cells or PBS, dramatically enhanced vascular recovery following exposure to hyperoxia. At P17, 57% of the Lin– injected eyes exhibited fully developed superficial and deep vascular networks with few abnormal neovascular tufts. Only 12% of CD– and 4% of PBS–injected contralateral eyes demonstrated such full recovery. At P17, the average area of obliteration was reduced by over 75% in the Lin– injected eyes. Long term (up to 6 months) follow–up revealed only occasional rosettes, no tumor formation, and histological preservation of the neural retina in Lin– injected eyes. Increased accumulation of macrophages was observed in rescued retinas. Using gene array analysis, Lin– BM cells showed markedly elevated levels of heat shock protein genes, and retinas and RPE from Lin– injected eyes differed in their expression profiles from control retinas. Conclusions: Intravitreal injection of Lin–HSCs markedly accelerates vascular healing of OIR, with reduced abnormal NV, rapid revascularization of the retina, and no significant long–term toxicity. While the mechanism underlying this rescue effect is complex and not yet clear, the findings support the concept of cell therapy using subpopulations of BM–derived cells in ischemic retinopathies.

Keywords: retinopathy of prematurity • retinal neovascularization