Co-distribution of von Willebrand factor and fibronectin in cultured rhesus endothelial cells

Secretory proteostasis of the retinal pigmented epithelium: Impairment links to age-related macular degeneration

Secretory proteostasis integrates protein synthesis, processing, folding and trafficking pathways that are essential for efficient cellular secretion. For the retinal pigment epithelium (RPE), secretory proteostasis is of vital importance for the maintenance of the structural and functional integrity of apical (photoreceptors) and basal (Bruch's membrane/choroidal blood supply) sides of the environment it resides in. This integrity is achieved through functions governed by RPE secreted proteins, which include extracellular matrix modelling/remodelling, angiogenesis and immune response modulation. Impaired RPE secretory proteostasis affects not only the extracellular environment, but leads to intracellular protein aggregation and ER-stress with subsequent cell death. Ample recent evidence implicates dysregulated proteostasis as a key factor in the development of age-related macular degeneration (AMD), the leading cause of blindness in the developed world, and research aiming to characterise the roles of various proteins implicated in AMD-associated dysregulated proteostasis unveiled unexpected facets of the mechanisms involved in degenerative pathogenesis. This review analyses cellular processes unveiled by the study of the top 200 transcripts most abundantly expressed by the RPE/choroid in the light of the specialised secretory nature of the RPE. Functional roles of these proteins and the mechanisms of their impaired secretion, due to age and genetic-related causes, are analysed in relation to AMD development. Understanding the importance of RPE secretory proteostasis in relation to maintaining retinal health and how it becomes impaired in disease is of paramount importance for the development and assessment of future therapeutic advancements involving gene and cell therapies.

Cysteine-rich 61 (CYR61) is up-regulated in proliferative diabetic retinopathy

BACKGROUND

To investigate the role of CYR61 as a retinal angiogenic factor in proliferative diabetic retinopathy (PDR).

METHODS

Effects of CYR61 on RF/6A cell proliferation, migration and angiogenesis were observed by MTT assay, Transwell assay, and tube formation assay. The expression and distribution of CYR61 on retina layers of diabetic mouse were demonstrated by immunohistochemistry. The expression of Cyr61 mRNA in diabetic mouse retina was evaluated by reverse transcription-polymerase chain reaction (RT-PCR). Vitreous CYR61 levels of PDR and non-diabetic patients were measured by enzyme-linked immunosorbent assay (ELISA). Expression and distribution of CYR61 on epiretinal membrane of PDR, proliferative vitreoretinopathy (PVR) and idiopathic epiretinal membrane were evaluated by immunohistochemistry.

RESULTS

RF/6A cell proliferation, migration and tube formation capacity increased with increased concentration of CYR61 (p = 0.000). Anti-CYR61 antibody could inhibit cell migration and tube formation promoted by CYR61. In diabetic mouse, CYR61 was expressed in retina layers just as normal mouse, but the staining was stronger than normal in ganglion cell layer and inner plexiform layer. The Cyr61 mRNA expression in retina of diabetic mouse was more than that in normal mouse (p = 0.009). Vitreous CYR61 level was higher in patients with PDR than non-diabetic patients (p = 0.000). PDR patients with plenty of neovasculature on retina and epiretinal membranes had higher level of vitreous CYR61 than patients with little neovasculature (p = 0.001). CYR61 expressed in the cytoplasm of epiretinal membranes in PDR, especially in the wall cells of the tube-like structure.

CONCLUSIONS

CYR61 are likely to be involved in the pathogenesis of diabetic retinopathy, and may play a role in the course of neovasculation.

Robo1: a potential role in ocular angiogenesis

PURPOSE

Robo1, a member of the roundabout (Robo) family, serves as neuronal guidance receptors and has been reported to mediate tumor angiogenesis. In this study, we investigated the function of Robo1 and its possible role in retinal angiogenesis in vitro and in vivo.

METHODS

Expression of Robo1 in relation to retinal neovascularization was studied in an animal model of retinopathy of prematurity (ROP). siRNA technology was used to knockdown Robo1 expression to study its effects on monkey choroidal retinal endothelial cells (RF/6A) in vitro. Cell proliferation, migration, spreading, cycling, and apoptosis were assessed with the methyl thiazolyl tetrazolium (MTT), Boyden chamber, immunohistochemistry, and flow cytometry assay. Tube formation by RF/6A on Matrigel was also analyzed.

RESULTS

Robo1 expression was elevated in the ROP murine eyes (P < 0.01). Knockdown of Robo1 expression inhibited cell proliferation and migration. Tube formation by RF/6A was also disturbed.

CONCLUSIONS

Our results show that Robo1 inhibits choroidal and retinal angiogenesis in vitro. Further studies are ongoing to evaluate Robo1 as a potential target for the treatment of choroidal or retinal angiogenesis.

Quercetin inhibits choroidal and retinal angiogenesis in vitro

BACKGROUND

Quercetin is a natural substance found abundantly in grapes, red wine and other food products. In this study, we examined the effect of quercetin on choroidal and retinal angiogenesis in vitro using rhesus choroids-retina endothelial cell line (RF/6A).

METHODS

RF/6A cells were cultured in Dulbecco's Modified Eagle's Medium (DMEM) containing 10% fetal bovine serum. Then cells were treated with different concentrations (from 0 to 100 microM) of quercetin. The cell proliferation was assessed using choromogenic methylthiazol tetrazolium bromide (MTT) dye after 24, 48 and 72 hours. Cell migration after 24-hour incubation with quercetin was investigated by wound assay. Following exposure to the various concentrations of quercetin for 24 hours, tube formation on matrigel by endothelial cells was also analyzed. Apoptosis was measured by flow cytometry using annexin V-FITC and propidium iodide staining.

RESULTS

Quercetin inhibits endothelial cell proliferation in a dose-dependent fashion; 10.1%, 42.6% and 65.2% inhibition on treating with 10, 50 and 100 microM Quercetin respectively. The migration and tube formation of RA/6A cells were also significantly inhibited by quercetin in a dose-dependent manner. Flow cytometric analysis showed that the percentages of apoptotic cells were slightly increased only in 100 microM quercetin-treated cells.

CONCLUSIONS

Our results show that quercetin inhibits choroidal and retinal angiogenesis in vitro. Further studies are ongoing to evaluate this drug as a potential candidate for the treatment of choroidal or retinal neovascularization.

In vivo endothelial cell infection by Anaplasma marginale

Anaplasma marginale has recently been shown to infect endothelial cells in vitro, but it remains unknown as to whether endothelial infection also occurs in vivo. In this report, we demonstrate through dual fluorescence microscopy that A marginale, detected by the monoclonal antibody ANAF16C1, co-localizes with the endothelial cell marker, von Willebrand factor, in tissue sections from an experimentally inoculated calf. The results indicate that A marginale infection includes endothelial cells and has implications for both pathogenesis and immune mechanisms.

Tubedown-1 in remodeling of the developing vitreal vasculature in vivo and regulation of capillary outgrowth in vitro

Tubedown-1 (tbdn-1) is a mammalian homologue of the N-terminal acetyltransferase subunit NAT1 of Saccharomyces cerevisiae and copurifies with an acetyltransferase activity. Tbdn-1 expression in endothelial cells becomes downregulated during the formation of capillary-like structures in vitro and is regulated in vivo in a manner which suggests a functional role in dampening blood vessel development. Here we show that tbdn-1 is expressed highly in the vitreal vascular network (tunica vasculosa lentis and vasa hyaloidea propria) during the pruning and remodeling phases of this transient structure. The vitreal blood vessels of mice harboring a targeted inactivation of TGF-beta2 fail to remodel and abnormally accumulate, a phenomenon reminiscent of the ocular pathology resembling persistent fetal vasculature (PFV) in humans. Since suppression of normal tbdn-1 expression has been previously observed in retinal vessel proliferation, we analyzed vitreal vascular changes and tbdn-1 expression in TGF-beta2(-/-) eyes. The nuclei of vitreal vessel endothelial cells in TGF-beta2(-/-) eyes express proliferating cell nuclear antigen (PCNA) and exhibit increased levels of active (P42/44)mitogen-activated protein kinase (phospho-(P42/44)MAPK), characteristics consistent with proliferative endothelial cells. In contrast to normal vitreal vessels, collagen IV expression exhibited a disorganized pattern in the TGF-beta2(-/-) vitreal vessels, suggesting vessel disorganization and possibly a breakdown of vessel basal laminae. Moreover, vitreal vessels of TGF-beta2(-/-) mice lack expression of pericyte markers (CD13, alpha smooth muscle actin) and show ultrastructural changes consistent with pericyte degeneration. The accumulating vitreal blood vessels of TGF-beta2(-/-) mice, while maintaining expression of the endothelial marker von Willebrand Factor, show a significant decrease in the expression of tbdn-1. We addressed the functional role of tbdn-1 in the regulation of vitreal blood vessels using an in vitro model of choroid-retina capillary outgrowth. Clones of the RF/6A fetal choroid-retina endothelial cell line showing suppression of tbdn-1 levels after overexpression of an antisense TBDN-1 cDNA display a significant increase in the formation of capillary-like structures in vitro compared with controls. These findings suggest that tbdn-1 inhibits capillary-like formation in vitro and may serve to dampen vitreal blood vessel formation preceding the regression of the vitreal vasculature during development. Our results also suggest that tbdn-1 may participate with TGF-beta2 in regulating normal development of the vitreal vasculature.