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Susie E. Barker, Ulrich F. Luhmann, Jill A. Cowing, Scott J. Robbie, Alexander J. Smith, Robin R. Ali; Dysregulation Of Alternative Pathway Complement Components In Mice Leads To An Increased Susceptibility To Tissue Damage. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1234.
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Age-related macular degeneration (AMD) is the most common cause of late-onset blindness in the developed world. The importance of the complement system in AMD pathogenesis is well established, and AMD-like symptoms are seen in patients with other complement dysregulation diseases. We investigated the complement alternative pathway (AP) in wildtype, CFH+/- and CFH-/- mice to characterize how the lack of CFH changes the local and systemic activation of the AP components, and in response to acute retinal injury.
Liver and whole eyes from C57Bl/6, CFH+/- and CFH-/- mice were analysed by western blot and quantitative RT-PCR to compare local versus systemic production of C3,CFB, CFD, CFP and CFH. We performed serum C3a ELISA to analyse the levels of activation of the complement cascade. The injury response was tested by subretinal injection of PBS and eyes were assessed histologically for retinal pathology.
We observed a significant decrease in serum levels of CFH, correlating with the number of functional CFH alleles (p<0.05). As a consequence of CFH depletion, C3 and CFB were significantly decreased consistent with the CFH genotype of the mice (p<0.05). There was no difference between CFH genotypes in the mRNA levels of C3, CFB, CFD or CFP in liver or eyes. There was no difference in whole C3 protein levels within liver or eye, but CFB was depleted in the CFH-/- mice. C3a levels were significantly reduced in the serum of CFH+/- and -/- mice (p<0.05), but there was no significant difference between genotypes in C3a levels in liver or eye. Scoring of histological sections showed that CFH+/- and -/- mice had significantly higher levels of RPE damage following subretinal injection of PBS compared to wild types (p<0.05).
C3 and CFB are dysregulated in CFH deficient mice despite normal levels of gene expression, indicating that the AP is continuously activated, leading to increased degradation of C3 and CFB. CFH-/- mice show a greater injury response to subretinal injection, suggesting a greater inflammatory reaction at the site of injection that is less controlled than in wild types due to the lack of CFH. Therefore our data suggests that CFH protects tissues from damage that may be due to lack of control of AP activation.
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