Inhibition of vascular endothelial cell growth and trypsin activity by vitreous

Experimental evaluation of the viscoelasticity of porcine vitreous

This study aims to estimate the material properties of the porcine vitreous while testing it in close to its natural physiological conditions. Eighteen porcine eyes were tested within 48 h post-mortem. A custom-built computer-controlled test rig was designed to support, load and monitor the behaviour of eye globes while being subjected to dynamic rotation cycles mimicking saccade eye movement. Specimens were glued to the base of a container, surrounded by gelatin, frozen and cut in half to expose the vitreous. After thawing, the container was subjected to concentric dynamic rotations of up to 5°, 10° or 15°, while taking 50 MP photos of the specimen every 2 ms. The images were analysed by a digital image correlation algorithm to trace the movement of marked points on the vitreous surface with different radii from the centre of the posterior chamber. The initial camera image was used in building a finite-element model of the test set-up, which was used in an inverse analysis exercise to estimate the material properties of the vitreous. Angular displacements of the monitored points were up to 3.3°, 4.1° and 3.9° in response to eye rotations of 5°, 10° and 15°, respectively. With the experimental relationships between eye rotation and angular displacements used as target behaviour, the inverse analysis exercise estimated the initial shear modulus, the long-term shear modulus and the viscoelastic decay constant of the porcine vitreous as 2.10 ± 0.15 Pa, 0.50 ± 0.04 Pa and 1.20 ± 0.09 s^-1, respectively. Consideration of the viscoelasticity of the vitreous was essential to represent its experimental behaviour. Testing the vitreous in close to its normal physiological conditions produced estimations of the initial shear modulus and long-term shear modulus that were, respectively, smaller and larger than reported values (Zimberlin et al. 2010 Soft Matter 6, 3632-3635. (doi:10.1039/b925407b), Liu et al. 2013 J. Biomech. 46, 1321-7. (doi:10.1016/j.jbiomech.2013.02.006), Rossi et al. 2011 Invest. Ophthalmol. Vis. Sci. 52, 3994-4002. (doi:10.1167/iovs.10-6477)).

Normal vitreous promotes angiogenesi via the epidermal growth factor receptor

Vitreous, a transparent tissue in our body, contains anti-angiogenesis factors. Our previous work reported that vitreous activates the signaling pathway of epidermal growth factor receptor (EGFR), which plays a critical role in angiogenesis. The aim of this study was to determine the role of EGFR in vitreous-induced angiogenesis-related cellular responses in vitro. Using a pharmacologic and molecular approach, we found that vitreous increased proliferation and migration via EGFR in human umbilical vein endothelial cells (HUVECs). Furthermore, we demonstrated that vitreous promoted tube formation via EGFR in HUVECs. Subsequently, depletion of EGFR using CRISPR/Cas9 and blockage with EGFR inhibitor AG1478 suppressed vitreous-induced Akt activation and cell proliferation, migration, and tube formation in HUVECs. The significance of the angiogenic effect derived from vitreous demonstrates the importance of vitreous in the ocular physiology and the pathobiology of angiogenesis-related ophthalmic diseases, such as proliferative diabetic retinopathy.

Pooling aqueous humor samples: bias in 2D-LC-MS/MS strategy?

The proteomic analysis of body fluids presents a major challenge in studies of human diseases. Traditional techniques for protein separation require large volumes and large amounts of protein, which may be difficult to obtain for certain fluids, such as the aqueous humor (AH). Two-dimensional liquid chromatography (2D-LC-MS/MS), adapted for peptides separation from complex protein mixtures, provides an alternative approach in proteomic analysis with a potential utility in biomarker research. We investigated several different 2D-LC-MS/MS methods for use with the AH of patients with cataract, traditionally used as a control group in studies of ocular diseases. We compared analyses of individual samples with analyses of pools of proteins or peptides, and found that the investigation strategy used strongly influenced protein identification. We identified 71 proteins related to extracellular proteins highly abundant in serum (e.g., albumin or transferrin) and involved in various functions, such as transport and metabolism, together with intracellular (myeloblastin) or organelle-specific proteins (cytochrome c). An evaluation of the advantages and disadvantages of each method suggested that individual analyses and the use of peptide mixtures should be favored as complementary techniques in the search for biomarkers in ocular diseases.

Hyaluronan production regulation from porcine hyalocyte cell line by cytokines

The objective of this study were to establish a cell line derived from porcine hyalocytes and to investigate the regulation of hyaluronan (HA) synthesis in response to cytokines. After 50 passages of the cells derived from porcine vitreous tissue, a cell line was generated. The immortalized cells showed fibroblastic morphology. The cell doubling time was 56.9h. In the mRNA level, the cells expressed plate-derived growth factor (PDGF) alpha receptor, PDGF beta receptor, transforming growth factor-beta (TGF-beta) type I receptor, TGF-beta type II receptor, CD44, collagen type I, collagen type II, glial fibrillary acidic protein (GFAP), hyaluronan synthase (HAS) 2, HAS 3 and beta-actin. In the protein level, GFAP was expressed in this cell line. S-100 protein and cytokeratin were not detected. Stimulation with TGF-beta1 and/or PDGF-BB induced a marked increase in the expression level of HAS2 mRNA, and induced HA production. TGF-beta1 stimulated HAS2 expression through the signal transduction pathway including Smad 2,3,4. In summary, this report constitutes the first successful immortalization of porcine hyalocyte cells. The production of HA was induced from the generated porcine hyalocyte cell line under the stimulation of TGF-beta1 and/or PDGF-BB, which may be related to the pathogenesis of proliferative membrane formation in proliferative vitreo-retinal diseases.

The characterisation of hyalocytes: the origin, phenotype, and turnover

AIM

To determine the characterisation of hyalocytes: the origin, phenotype, and turnover in the rodent.

METHODS

To characterise the ultrastructure and distribution of hyalocytes, transmission and scanning electron microscopy was performed in rat eyes. Immunophenotypical analysis was performed by either anti-ED1 or ED2 antibodies. To examine the origin of the hyalocytes, the chimeric mice were created and were used to transplant the bone marrow (BM) cells from enhanced green fluorescent protein (EGFP) transgenic mice. The turnover of hyalocytes was examined at 0, 4, 6, 7, and 12 months after BM transplantation.

RESULTS

Hyalocytes were distributed especially in the vitreous cortex and had an irregular shape with a spherical granule. Immunophenotypical studies demonstrated that most of the hyalocytes in rat eyes expressed ED2 but not ED1. In the chimeric mice, the hyalocytes were GFP negative right after BM transplantation. Interestingly, more than 60% of hyalocytes were replaced within 4 months and approximately 90% within 7 months after BM transplantation.

CONCLUSIONS

The rodent hyalocytes were shown to express tissue macrophage marker, were derived from BM, and totally replaced within 7 months. These data provide the characterisation of hyalocytes in physiological conditions, especially their origin, distribution, and turnover, and may contribute to the better understanding of the pathogenesis of vitreoretinal disease.

Structural macromolecules and supramolecular organisation of the vitreous gel

The vitreous gel is a transparent extracellular matrix that fills the cavity behind the lens of the eye and is surrounded by and attached to the retina. This gel liquefies during ageing and in 25-30% of the oppulation the residual gel structure eventually collapses away from the posterior retina in a process called posterior retina in a process called posterior vitreous detachment. This process plays a pivotal role in a number of common blinding conditions including rhegmatogenous retinal detachment, proliferative diabetic retinopathy and macular hole formation. In order to understand the molecular events underlying vitreous liquefaction and posterior vitreous detachment and to develop new therapies it is important to understand the molecular basis of normal vitreous gel structure and how this is altered during ageing. It has previously been established that a dilute dispersion of thin (heterotypic) collagen fibrils is essential to the gel structure and that age-related vitreous liquefaction is intimately related to a process whereby these collagen fibrils aggregate. Collagen fibrils have a natural tendency to aggregate so a key question that has to be addressed is: what normally maintains the spacing of the collagen fibrils? In mammalian vitreous a network of hyaluronan normally fills the spaces between these collagen fibrils. This hyaluronan network can be removed without destroying the gel structure, so the hyaluronan is not essential for maintaining the spacing of the collagen fibrils although it probably does increase the mechanical resilience of the gel. The thin heterotypic collagen fibrils have a coating of non-covalently bound macromolecules which, along with the surface features of the collagen fibrils themselves, probably play a fundamental role in maintaining gel stability. They are likely to both maintain the short-range spacing of vitreous collagen fibrils and to link the fibrils together to form a contiguous network. A collagen fibril-associated macromolecule that may contribute to the maintenance of short-range spacing is opticin, a newly discovered extracellular matrix leucine-rich repeat protein. In addition, surface features of the collagen fibrils such as the chondroitin sulphate glycosaminoglycan chains of type IX collagen proteoglycan may also play an important role in maintaining fibril spacing. Furthering our knowledge of these and other components related to the surface of the heterotypic collagen fibrils will allow us to make important strides in understanding the macromolecular organisation of this unique and fascinating tissue. In addition, it will open up new therapeutic opportunities as it will allow the development of therapeutic reagents that can be used to modulate vitreous gel structure and thus treat a number of common, potentially blinding, ocular conditions.

Anti-angiogenic effect of TGFbeta in aqueous humor

Neovascularization is mediated by various factors in ocular tissues. Recent studies have emphasized the role of vascular endothelial growth factor in the induction of angiogenesis. We have previously reported that aqueous humor (AH) suppressed vascular endothelial cell growth and angiogenesis. We speculated that the anti-angiogenic effect of AH is mediated by transforming growth factor beta (TGFbeta). In order to clarify the presence of TGFbeta in bovine AH, we applied it on the heparin-sepharose affinity column and prepared two fractions (bound and unbound fractions). We measured TGFbeta concentration in each fraction and examined how the anti-TGFbeta antibody decreased the inhibitory effect of AH on human umbilical vein endothelial cell growth and on in vitro angiogenesis. We found the presence of TGFbeta2, but not TGFbeta1, in the heparin bound fraction, and the inhibitory effect was detected in the heparin-bound fraction. Anti-TGFbeta antibody completely and dose-dependently extinguished the inhibitory effect of AH. We propose that the inhibitory effect of AH on endothelial cell growth and in vitro angiogenesis are both mediated by TGFbeta2. Our results indicate TGFbeta2 is normally present in AH and protects the eye tissue against abnormal neovascularization.

Angiostatic role of astrocytes: suppression of vascular endothelial cell growth by TGF-beta and other inhibitory factor(s)

Our previous in vivo analyses have suggested that astrocytes play a key role in retinal vascularization by inducing endothelial cell differentiation. Here we demonstrate that medium conditioned by cultured rat brain astrocytes (ACM) contains factors, including transforming growth factor-beta (TGF-beta), that inhibit endothelial cell growth. Serum-free medium conditioned for 1-3 days was tested on exponentially growing bovine retinal microvascular endothelial, aortic endothelial, mink lung epithelial CCL-64, and Swiss mouse 3T3 fibroblast cells. The growth of all four cell types was inhibited in a dose- and time-dependent manner. CCL cells, which are used as a model for assaying TGF-beta activity, were more sensitive than the endothelial cells, suggesting that ACM contains TGF-beta. Moreover, acid treatment significantly increased the inhibitory activity of ACM, indicating that TGF-beta in ACM is predominantly in the latent form. Mouse fibroblasts, which are not affected by TGF-beta treatment under the same conditions, were also inhibited by ACM. This suggests that other inhibitory factors in addition to TGF-beta may be involved. Adsorption by an anti-TGF-beta polyclonal antibody column substantially reduced but did not eliminate the inhibitory activity of ACM for CCL and endothelial cells. Western blot analysis of ACM and proteins eluted from the affinity column revealed a 25 kDa band that co-migrates with TGF-beta. Comparative densitometry of the 25 kDa bands on Western blot indicated that the amount of TGF-beta in ACM is not sufficient to account for the total growth-inhibitory activity. These experiments demonstrate directly that rat brain astrocytes express TGF-beta. They also indicate that astrocytes may produce other growth-inhibitory factor(s) yet to be identified.

Effects of glucose on migration, proliferation and tube formation by vascular endothelial cells

In order to elucidate the association between hyperglycemia and the vascular complications of diabetes, the effects of high glucose concentrations on the migration, proliferation and tube formation of bovine carotid artery endothelial cells were investigated. Cells treated with 16.7 and 33.3 mM glucose for 6 days showed 1.69- and 1.75-fold increase in serum-induced migration compared with cells treated with 5.6 mM glucose (p less than 0.05). The effect of glucose on cell proliferation was affected by serum concentration. When this was below 0.5%, a high glucose concentration stimulated cell growth to a maximum of 1.73 times that at a serum concentration of 0.05% (p less than 0.01) whereas at a serum concentration of 10%, growth was inhibited (p less than 0.05). Tube formation was studied by culturing the cells between two layers of collagen gel. Ultrastructurally, tubular structures were composed of one to several endothelial cells containing pinocytotic vesicles and cytoplasmic projections, and linked by junctional complexes. A basal lamina-like structure surrounded the abluminal surface. Treatment of the cells with 16.7 and 27.8 mM glucose for 4 days stimulated tubular elongation 1.85 and 1.71 times, respectively (p less than 0.01). Other osmogenic molecules such as mannitol and sucrose did not affect tube formation. These data imply that high glucose concentrations mimicking diabetic hyperglycemia may not inhibit the repair of endothelial injury and could act as a stimulator of neovascularization.

Phosphorylation of small molecular weight polypeptides in the iris-ciliary complex, aqueous humor and vitreous humor

The polypeptides of vitreous humor, aqueous humor and iris-ciliary complex cells of eyes were phosphorylated with [gamma-32P]ATP without exogenous protein kinase. Phosphorylated polypeptides were analyzed by sodium dodecyl sulfate gel electrophoresis and autoradiography. The phosphorylated polypeptides of rabbit vitreous humor showed many high molecular weight prominent bands, but no detectable phosphoproteins were found in the 12 kDa or lower range. Bovine vitreous humor has predominantly acidic polypeptides and some of them are below 20 kDa. Rabbit and bovine iris-ciliary complex and rabbit aqueous humor showed a prominent common 4 kDa phosphopolypeptide which could also be synthesized by cloned populations of cells from the bovine iris and the rabbit iris-ciliary body. It is possible that the 4 kDa phosphopolypeptide of the aqueous humor is synthesized by the iris-ciliary complex cells.

Increased procollagenase activating angiogenic factor in the vitreous humour of oxygen treated kittens

Previous studies have demonstrated an increase in a low molecular weight angiogenic factor (ESAF) present in the retinae of kittens with oxygen induced retinopathy. The present paper describes differences in the quantity of ESAF extracted from the vitreous humour of control and oxygen treated animals and proposes a mechanism for the induction of intravitreal neovascularisation.