Properdin Modulates Complement Component Production in Stressed Human Primary Retinal Pigment Epithelium Cells

Abstract

The retinal pigment epithelium (RPE) maintains visual function and preserves structural integrity of the retina. Chronic dysfunction of the RPE is associated with retinal degeneration, including age-related macular degeneration (AMD). The AMD pathogenesis includes both increased oxidative stress and complement dysregulation. Physiological sources of oxidative stress in the retina are well known, while complement sources and regulation are still under debate. Using human primary RPE (hpRPE) cells, we have established a model to investigate complement component expression on transcript and protein level in AMD-risk and non-risk hpRPE cells. We evaluated the effect of properdin, a complement stabilizer, on the hpRPE cell-dependent complement profile exposed to oxidative stress. hpRPE cells expressed complement components, receptors and regulators. Complement proteins were also stored and secreted by hpRPE cells. We associated AMD-risk single nucleotide polymorphisms with an increased secretion of complement factors D (CFD) and I (CFI). Furthermore, we detected hpRPE cell-associated complement activation products (C3a, C5a) independent of any extracellularly added complement system. Exogenous properdin increased the mRNA expression of CFI and CFD, but decreased levels of complement components (C1Q, C3), receptors (C3AR, C5AR1, CD11B) and inflammation-associated transcripts (NLRP3, IL1B) in hpRPE cells exposed to oxidative stress. This properdin effect was time-dependently counter regulated. In conclusion, our data unveiled a local, genotype-associated complement component production in hpRPE cells, regulated by exogenous properdin. The local complement production and activation via blood-independent mechanisms can be a new therapeutic target for AMD.

Complement Factor H-Related 3 induces inflammation and complosome activation in human RPE cells

“…Complement components are locally expressed by different retinal cell types and by ARPE-19 cells (27,30,31,39). Here, we showed that the complement regulator FHR3 enhanced complement expression and secretion of RPE cells (Fig.…”

“…We showed that FHR-3 is an in ammatory stimulator and may serve as a damage-associated sensing molecule for RPE cells (59). Just recently, we identi ed RPE cells as one of the major sources of complement expression in the mouse retina (39), hpRPE cells (27,31) and in ARPE-19 cells (30). Here, we reported that FHR3 induced complement activation in cultured RPE cells.…”

“…Further, the C3 fragment receptor CR3, has been also associated with NLRP3 in ammasome activation in human primary RPE cells (65). Besides recently shown for ARPE-19 (30) and hpRPE cells (27), CR3 expression has been mainly associated with macrophages (66) so far.…”

“…In RPE cells, in ammasome activation is so far mainly related to stress and complement receptor signaling (25)(26)(27), but not to FHR-binding. RPE cells autonomously produce and activate numerous complement components independently from blood-derived complement proteins (26,27), which can than bind to complement receptors. This local complement expression and secretion by RPE cells is modulated by external stress (27)(28)(29)(30)(31).…”

“…RPE cells autonomously produce and activate numerous complement components independently from blood-derived complement proteins (26,27), which can than bind to complement receptors. This local complement expression and secretion by RPE cells is modulated by external stress (27)(28)(29)(30)(31). Stress-related activation of the in ammasome is associated with a pro-in ammatory secretion phenotype of RPE cells (25,30,32,33), which in return correlates with complement activation (30).…”