Abstract
The retinal pigment epithelium (RPE) is considered one of the main targets of age-related macular degeneration (AMD), the leading cause of irreversible vision loss among the ageing population worldwide. Persistent low grade inflammation and oxidative stress eventually lead to RPE dysfunction and disruption of the outer blood-retinal barrier (oBRB). Increased levels of circulating pentameric C-reactive protein (pCRP) are associated with higher risk of AMD. The monomeric form (mCRP) has been detected in drusen, the hallmark deposits associated with AMD, and we have found that mCRP induces oBRB disruption. However, it is unknown how mCRP is generated in the subretinal space. Using a Transwell model we found that both pCRP and mCRP can cross choroidal endothelial cells and reach the RPE in vitro and that mCRP, but not pCRP, is able to cross the RPE monolayer in ARPE-19 cells. Alternatively, mCRP can originate from the dissociation of pCRP in the surface of lipopolysaccharide-damaged RPE in both ARPE-19 and primary porcine RPE lines. In addition, we found that the proinflammatory phenotype of mCRP in the RPE depends on its topological localization. Together, our findings further support mCRP contribution to AMD progression enhancing oBRB disruption.
Highlights
Age-related macular degeneration (AMD) is the primary cause of irreversible vision loss among the ageing population worldwide
We first interrogated whether circulating C-reactive protein (CRP) could reach the subretinal space using a Transwell model, in which confluent monolayers of primary porcine choroidal endothelial cells (CECs) were grown on porous filters with their apical and basolateral surfaces exposed to separate chambers (Figure 1A)
Immunofluorescence imaging showed that monomeric CRP (mCRP) delivered to the apical compartment was extensively bound to the CEC surface compared to pentameric C-reactive protein (pCRP) and to CRP delivered in the basolateral chamber (Figure 1E–1G)
Summary
Age-related macular degeneration (AMD) is the primary cause of irreversible vision loss among the ageing population worldwide. AMD is a degenerative and progressive disease involving multiple genetic and environmental factors, age being the primary risk factor. The retinal pigment epithelium (RPE) monolayer is believed to be among the initial targets of early disease. AMD presents RPE cell abnormalities, disruption of the outer blood-retinal-barrier (oBRB), and degeneration of photoreceptors, which require a normally functioning www.aging-us.com. Prior research has implicated strong roles for inflammation, oxidative stress, lipid abnormalities, and RPE dysfunction in AMD pathobiology, but their precise mechanisms and their relative contribution are unclear [4]. A multitude of systemic changes occur with ageing that contribute to the initiation and development of inflammation. The immune system of elderly individuals is characterized by a basal systemic inflammatory state [5]
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