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

PUSPOSE. 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 mu m) with 30 applications were placed 50 to 100 mu m 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-I+), CD45, Griffonia simplicifolia lectin isolectin B4, GFP or cytokeratin). Expression of Ccl2, I1b, 116, Hspala, Hsp90aal, Cryab, Hif1a, Cxcll2, 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. Hspala, Hsp90aa1, and Cryab mRNAs increased in the NSR at 2 hours post laser; Hifla, Cxcll2, Hspala increased at 4 hours in the RPE-choroid; and Ccl2, Illb, Ifng, and 116 increased at 12 to 24 hours in the RPE-choroid. CONCLUSIONS. SRPT induces monocyte recruitment to the RPE followed by hematopoictic progenitor cell homing at 2 weeks. Recruitment occurs in a duty cycle-dependent manner and potentially could contribute to the therapeutic efficacy of SRPT.