Transdifferentiated Transplanted Bone–Marrow Stem Cells Cluster in the Retina of a Mouse Model of Oxygen Induced Retinopathy and May Integrate Into the Vasculature

Abstract

Purpose: : To evaluate the transdifferentiation capacity of transplanted bone marrow–derived cells in the retina of a mouse model of oxygen induced retinopathy (OIR).

Methods: : C57BL/6J mice were exposed to 75% oxygen from postnatal day 7 (P7) to day 12 (P12) and recovered at room air thereafter. Bone marrow was harvested from C57BL/6J mice expressing GFP under control of an ß–actin promoter. At postnatal day 13 or 17 approximately 1 Million cells were injected into the sinus cavernosus. The retinal vasculature was examined on postnatal day 26/27, P50/54 and P75/76 after perfusion with Rhodamine–Concanavalin A. The number of GFP⁺ donor cells in the retina was counted and vascular and avascular area, blood vessel tufts, and main vessel turtuosity were quantified by density slicing.

Results: : About 21 days after transplantation at least 70 % of the blood leukocytes in the recipient mice were determined to be GFP⁺ by FACS analysis. The transplantation of bone marrow–derived cells does not change the vascularization pattern in oxygen treated C57BL/6J mice when measured at P17/18 and P26/27. There was a high variability in the GFP⁺ cell number in the recipient vasculature and neuroretina, although the majority of cells were found in the extravasal compartment. GFP⁺ donor cells incorporated into the vasculature were demonstrated on P54. The morphology of most of the cells outside of the vasculature resembles macrophages and microglia cells as was confirmed by immunostaining. We counted from 20 to over 900 GFP⁺ cells per retina. At the earlier hypoxic phase until P26/27 more cells were found in the retina of oxygen treated mice compared to cells in the retina of untreated mice (416.3 ± 275.9 versus 91.2 ± 31, P = 0.004). Nevertheless, there was no association of GFP⁺ cells with the edges of the avascular zones. When oxygen treated mice at P50/54 were compared with untreated controls no significant difference was found.

Conclusions: : Injection of bone marrow cells into the sinus cavernosus of young mice is a suitable method for a successful engrafting. Bone marrow–derived cells can be incorporated into the endothelial layer of the retinal vasculature, but the majority of the cells transdifferentiate into microglia cells or macrophages and are not associated with the edges of the avascular zones in a mouse model of oxygen induced retinopathy.

Keywords: retinal neovascularization • hypoxia • retinopathy of prematurity