Complement component C3aR constitutes a novel regulator for chick eye morphogenesis

Abstract

Complement components have been implicated in a wide variety of functions including neurogenesis, proliferation, cell migration, differentiation, cancer, and more recently early development and regeneration. Following our initial observations indicating that C3a/C3aR signaling induces chick retina regeneration, we analyzed its role in chick eye morphogenesis. During eye development, the optic vesicle (OV) invaginates to generate a bilayer optic cup (OC) that gives rise to the retinal pigmented epithelium (RPE) and neural retina. We show by immunofluorescence staining that C3 and the receptor for C3a (the cleaved and active form of C3), C3aR, are present in chick embryos during eye morphogenesis in the OV and OC. Interestingly, C3aR is mainly localized in the nuclear compartment at the OC stage. Loss of function studies at the OV stage using morpholinos or a blocking antibody targeting the C3aR (anti-C3aR Ab), causes eye defects such as microphthalmia and defects in the ventral portion of the eye that result in coloboma. Such defects were not observed when C3aR was disrupted at the OC stage. Histological analysis demonstrated that microphthalmic eyes were unable to generate a normal optic stalk or a closed OC. The dorsal/ventral patterning defects were accompanied by an expansion of the ventral markers Pax2, cVax and retinoic acid synthesizing enzyme raldh-3 (aldh1a3) domains, an absence of the dorsal expression of Tbx5 and raldh-1 (aldh1a1) and a re-specification of the ventral RPE to neuroepithelium. In addition, the eyes showed overall decreased expression of Gli1 and a change in distribution of nuclear β-catenin, suggesting that Shh and Wnt pathways have been affected. Finally, we observed prominent cell death along with a decrease in proliferating cells, indicating that both processes contribute to the microphthalmic phenotype. Together our results show that C3aR is necessary for the proper morphogenesis of the OC. This is the first report implicating C3aR in eye development, revealing an unsuspected hitherto regulator for proper chick eye morphogenesis.

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

“…This can be carried out either by enzyme complexes formed by different complement proteins (convertases) or by specific proteases, e.g., cathepsin L or cathepsin B [ 11 , 69 ]. This results in high levels of anaphylatoxins C3a and C5a, which have been associated with physiological and pathological processes in the retina [ 27 , 70 , 71 ]: Eye morphogenesis [ 31 ], sub-RPE depositions [ 32 ], pro-inflammatory RPE reaction [ 33 , 34 , 35 ], PI3/Akt-pathway activation [ 29 ], and ER stress-mediated lipid accumulation [ 36 ].…”

“…Recently, it was reported, that endogenous CFH and anaphylatoxins contribute to transcriptional and metabolic homeostasis of RPE cells [ 28 , 29 , 30 ]. In RPE cells complement anaphylatoxins receptor signaling is involved in eye morphogenesis [ 31 ], sub-RPE deposits [ 32 ], pro-inflammatory RPE reaction [ 33 , 34 , 35 ], PI3/Akt-pathway activation [ 29 ], and stress-mediated lipid accumulation in RPE cells [ 36 ]. Together this indicates an involvement of autocrine complement reactivity in housekeeping mechanisms maintaining RPE physiology.…”

Significance of Complement System in Ischemic Stroke: A Comprehensive Review

“…In the CNS, microglia, astrocytes, oligodendrocytes, and neurons express C3aR, among which the neurons were identified as the principle cell type expressing C3aR under physiological conditions [164-167]. It has been shown that C3aR is involved in chick eye morphogenesis and rat cerebellar cortex histogenesis during development and facilitates mouse skeletal muscle regeneration after cardiotoxin-induced muscle injury [168-170]. However, in multiple CNS diseases, C3aR expression was increased in the brain, contributing to the exacerbation of inflammation and disease progression.…”

Pathological significance of C3aR signaling in the tumor cells of clear cell renal cell carcinoma: a clinical observation

“…However, increasing evidence from the last two decades has demonstrated that C3aR is also expressed by many non-immune cells and participates in various physiological and pathological processes. For examples, C3aR signaling was reported to participate in the regulation of eye morphogenesis [16], neural development [17][18], embryonic chick retina [19] and cardiac resident cell [20] regeneration, astroglial cell differentiation [21] and survival [22], diet-induced obesity and metabolic dysfunction [23], and tau hyperphosphorylation in Alzheimer's Disease [24]. Also, C3aR signaling was found to be involved in the induction of in ammatory cytokines [25], proliferation of mesangial [11] and carcinoma cells [12] and EMT of tubular epithelial cells [10].…”