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Feng Lin, Dawn Smith, Qing Li, Ram Nagaraj, Timothy Kern, Yan Li; Complement Mediated Retinal Pericyte Injury. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2412.
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Loss of retinal pericytes is a hallmark of early stage diabetic retinopathy, but the mechanisms underlying retinal pericytes loss in diabetes are unclear. Our purpose was to test the hypotheses that complement activated by retinal pericyte-reactive autoantibodies leads to retinal pericytes cytotoxicity, and that inhibiting complement activation by upregulating endogenous cell surface complement regulators or by administering exogenous complement inhibitors is a novel approach to protect retinal pericytes from autoantibodies-induced injury, and to prevent the development of diabetic retinopathy
Human primary retinal pericytes were cultured in media containing normal and high levels of glucose, then incubated with human sera in the presence of a retinal pericyte-reactive antibody. Complement-mediated cellular injury was assessed by a conventional BCECF leakage-based cytotoxicity assay. The presence of intrinsic cell surface complement regulators on retinal pericytes was determined by flow cytometry. The presence of CD38, a diabetes-associated cell surface autoantigen, on retinal pericytes was examined by RT-PCR and flow cytometry. To test the effectiveness of inhibiting complement activation for protecting retinal pericytes, a CD55-expressing recombinant adenovirus was constructed and used to transfect retinal pericytes, and an anti-C5 IgG was employed to inhibit membrane attack complex (MAC) formation in the same cytotoxicity assays.
In the presence of a retinal pericyte-reactive antibody, retinal pericytes were injured by complement despite the presence of all three intrinsic cell surface complement regulators, i.e., CD55, CD46 and CD59. CD38 was expressed by primary retinal pericytes, and upregulated by TNFα/IFNγ, inflammatory cytokines that are associated with the development of diabetic retinopathy. Hyperglycemic culture conditions rendered retinal pericytes more susceptible to complement mediated attack with minimal effects on expression levels of the cell surface complement inhibitors. Upregulating CD55 expression levels on retinal pericytes, or inhibiting MAC formation by an anti-C5 antibody protected retinal pericytes from the autoantibodies-induced cellular injury.
The autoantibody- activated complement could be a mechanism underlying the loss of retinal pericytes in diabetic patients. Inhibiting complement activation by upregulating levels of intrinsic cell surface complement inhibitors, or by administering exogenous complement inhibitors, could reduce the loss of retinal pericytes, and help to prevent the development of diabetic retinopathy.
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