Activation of C-reactive protein proinflammatory phenotype in the blood retinal barrier in vitro: implications for age-related macular degeneration

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 bloodretinal 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.

Interlink between Inflammation and Oxidative Stress in Age-Related Macular Degeneration: Role of Complement Factor H

“…Moreover, mononuclear cell migration increased when exposed to conditioned medium from mCRP-treated RPE cells, but not in pCRP-or control-treated conditioned media [78]. Interestingly, topological localization of mCRP determines the RPE pro-inflammatory response as RPE disruption is only observed when mCRP is exposed to the apical domain [77]. These findings together with the fact that there is no transcription of CRP in the retinal tissue, led us to study how CRP isoforms could accumulate in the subretinal space.…”

“…In line with this study, we showed that mCRP, but not pCRP, induces oBRB disruption, at least in vitro. Monomeric CRP disrupts the RPE barrier function by disturbing the expression and distribution of tight junctions and increasing paracellular permeability [77]. Likewise, mCRP upregulates the production of IL-8 and monocyte chemotactic protein-1 in RPE cells.…”

“…Interestingly, mCRP, but not pCRP, is able to cross a compromised RPE monolayer but not a highly polarized RPE monolayer. Alternatively, mCRP can also originate from the dissociation of pCRP in the surface of lipopolysaccharide-damaged RPE [77]. Whether these in vitro findings translate to disease or not require validation but there is increasing evidence that supports mCRP contribution to AMD progression.…”

Monomeric C-Reactive Protein: Current Perspectives for Utilization and Inclusion as a Prognostic Indicator and Therapeutic Target

“…There are a number of other inflammation-driven pathological conditions that mCRP has recently been inextricably linked to. mCRP was shown to be present in drusen aggregates-the hallmark of age-related macular degeneration concomitant with an increased inflammatory activation of the retinal pigment epithelium and disruption of the outer blood-retinal barrier; mCRP was suggested to be involved in enhancing disruption and inflammation-associated progression of the disease (23). The plasma from a group of patients with sepsis, showed significantly higher levels of EVs bound to mCRP associated with enhanced IL-8 secretion compared with healthy individuals indicating a direct mechanism for perpetuation of the condition, whilst apheresis and removal of the mCRP was sufficient to reduce circulating cytokine levels (24); whilst, in autoimmune diseases such as lupus nephritis, highest levels of mCRP-antibodies in the serum was associated with worse symptomatic disease, increased expression of IL-6 and TNF-a, and clinical evidence of systemic lupus erythematosus (25).…”

Sensing of C-Reactive Protein Using an Extended-Gate Field-Effect Transistor with a Tungsten Disulfide-Doped Peptide-Imprinted Conductive Polymer Coating

“…CRP has also been implicated in the breakdown of important biological barriers. For example, monomeric CRP can cross the retinal pigment endothelium and may cause macular degeneration through the disruption of the outer blood-retinal barrier [ 7 ]. Moreover, C-reactive protein (CRP) has been demonstrated to induce blood brain barrier (BBB) disruption in a process involving NAD(P)H-oxidase dependent oxidative stress [ 8 ].…”