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B. Rohrer, B. Coughlin, Q. Long, G. S. Gilkeson, S. Tomlinson, K. Takahashi, V. M. Holers; Multifactorial Contributions of Complement Initiation Pathways to Mouse Laser-Induced Choroidal Neovascularization. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3501.
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© ARVO (1962-2015); The Authors (2016-present)
Human genetic studies have demonstrated that polymorphisms in different complement proteins each increase the risk for developing AMD. There are three pathways of complement activation, classical (CP), alternative (AP), and lectin (LP), which all activate a final common pathway. The proteins encoded by the risk genes participate in the AP, CP or in the final common pathway. Here we tested which pathway is essential in mouse laser-induced CNV.
CNV was analyzed using single knockouts (i.e., eliminating one complement pathway at a time), followed by double knockouts, in which only the AP pathway is present and the CP and LP are disabled, using molecular, histological and electrophysiological readouts.
First, single-gene knockouts were analyzed and compared to wildtype mice; C1q-/- for CP, MBL-A/C-/- for LP, and CFB-/- for AP activation. Six days after the laser-induced lesion, mice without a functional AP had reduced CNV progression (P<0.001) and preserved ERG amplitudes, whereas those without a functional CP or LP were indistinguishable from the wild type controls (P>0.3). Second, double-gene knockout mice were used to investigate whether AP signaling is sufficient for triggering C3 activation and CNV development. While C1q-/- MBL-A/C-/- mice, having only a functional AP, were found to be sensitive to developing CNV, the size of the lesion was reduced when compared to C57BL/6 mice (P<0.05).
The analysis of complement initiation pathways in mouse laser-induced CNV allows for the following conclusions. Comparing the single pathway knockouts with those having only a functional AP showed (1) that the AP activation is necessary but not sufficient for injury; and (2) that the LP and CP can compensate for each other, requiring elimination of both to reveal an effect. While these data demonstrate a unique role of the AP in the generation of complement-dependent injury in the RPE and choroid, CP- and LP-triggered complement activation appears to contribute to the disease. Improving our understanding of the local regulation of this pathway in the retina is essential to developing improved treatment approaches for AMD.
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