Browsing by Subject "lipoprotein"

Complement factor H (CFH) is a major susceptibility gene for age-related macular degeneration (AMD); however, its impact on AMD pathobiology is unresolved. Here, the role of CFH in the development of AMD pathology in vivo was interrogated by analyzing aged Cfh+/- and Cfh-/- mice fed a high fat, cholesterol-enriched diet. Strikingly, decreased levels of CFH led to increased sub-retinal pigmented epithelium (RPE) deposit formation, specifically basal laminar deposits, following high fat diet. Mechanistically, our data show that deposits are due to CFH competition for lipoprotein binding sites in Bruch’s membrane. Interestingly and despite sub-RPE deposit formation occurring in both Cfh+/- and Cfh-/- mice, RPE damage accompanied by loss of vision occurred only in old Cfh+/- mice. We demonstrate that such pathology is a function of excess complement activation and C5a production, associated with monocyte recruitment, in Cfh+/- mice versus complement deficiency in Cfh-/- animals. Due to the CFH dependent increase in sub-RPE deposit height we interrogated the potential of CFH as a novel regulator of Bruch’s membrane lipoprotein binding and show, using human Bruch’s membrane explants, that CFH removes endogenous human lipoproteins in aged donors. Interestingly, although the CFH H402 variant shows altered binding to BrM, this does not affect its ability to remove endogenous lipoproteins. This new understanding of the complicated interactions of CFH in AMD-like pathology provides an improved foundation for the development of targeted therapies for AMD.

Age-related macular degeneration (AMD) is a complex retinal degeneration present in elderly populations of first world countries with limited available therapeutic interventions. Risk for AMD is strongly conferred by advanced aging but is also modulated by genetic variants and environmental stresses. One of the most replicated genetic variants associated with AMD is the Complement Factor H (CFH) Y402H polymorphism. CFH is a critical regulator of the complement cascade but how the H402 variant impairs its function and contributes to AMD development is unclear. Herein, the role of the H402 variant in the development of AMD-like pathologies was interrogated using two different mouse models based on advanced aging, CFH perturbation and environmental stress.

First, aged CFH hemizygous knockout (Cfh+/-) mice were fed a high fat, cholesterol-enriched (HFC) diet for eight weeks to induce AMD-like pathologies such as vision loss, increased retinal pigmented epithelium (RPE) damage, increased sub-RPE deposit formation and immune cell recruitment to the RPE/choroid interface. To determine if the recruitment of immune cells drives the formation of the AMD-like pathologies in aged Cfh+/-~HFC mice, aged Cfh+/- mice were concurrently treated with a systemic anti-C5a therapy during the eight week HFC diet treatment to block the complement-mediated recruitment of immune cells to the eye. However, the ocular phenotype was unchanged in aged Cfh+/-~HFC mice treated with the anti-C5a therapy despite the decrease of recruited immune cells to the posterior eye. This data suggests the risk associated with the H402 CFH variant is not solely attributable to complement-mediated immune cell recruitment to the posterior eye.

Second, aged transgenic mice expressing equal concentrations of the normal human CFH Y402 (CFH-Y:Cfh-/-) or risk-associated CFH H402 (CFH-HH:Cfh-/-) protein were fed an eight week HFC diet. Remarkably, vision loss, increased RPE damage and increased sub-RPE deposit formation was only observed in aged CFH-HH:Cfh-/- mice following diet treatment. Biochemical analysis of aged CFH:Cfh-/- mice revealed differences in plasma and ocular lipoproteins, but not complement, between aged CFH-Y:Cfh-/-~HFC and CFH-HH:Cfh-/-~HFC mice. Thus, we targeted plasma lipoprotein levels through dietary intervention in aged CFH-HH:Cfh-/- mice and observed visual loss in these mice that coincided with dietary cholesterol-induced increases of plasma LDL. Based on our findings we hypothesize that the risk-associated with the H402 CFH variant and AMD is due to the interaction of CFH with lipoproteins and not its complement regulatory roles. These new insights may help explain why current therapies targeting complement inhibition for AMD have failed and, importantly, support targeting lipoprotein metabolism, as a treatment for AMD.