Biochemistry of connective tissue of the vertebrate eye

Alterations in protein expression in tree shrew sclera during development of lens-induced myopia and recovery

PURPOSE

During the development of, and recovery from, negative lens-induced myopia there is regulated remodeling of the scleral extracellular matrix (ECM) that controls the extensibility of the sclera. Difference gel electrophoresis (DIGE) was used to identify and categorize proteins whose levels are altered in this process.

METHODS

Two groups of five tree shrews started monocular lens wear 24 days after eye opening (days of visual experience [VE]). The lens-induced myopia (LIM) group wore a -5 D lens for 4 days. The recovery (REC) group wore a -5 D lens for 11 days and then recovered for 4 days. Two normal groups (28 and 39 days of VE; n = 5 each) were also examined, age-matched to each of the treatment groups. Refractive and A-scan measures confirmed the effect of the treatments. Scleral proteins were isolated and resolved by DIGE. Proteins that differed in abundance were identified by mass spectrometry. Ingenuity pathway analysis was used to investigate potential biological pathway interactions.

RESULTS

During normal development (28-39 days of VE), eight proteins decreased and one protein increased in relative abundance. LIM-treated eyes were myopic and longer than control eyes; LIM-control eyes were slightly myopic compared with 28N eyes, indicating a yoking effect. In both the LIM-treated and the LIM-control eyes, there was a general downregulation from normal of proteins involved in transcription, cell adhesion, and protein synthesis. Additional proteins involved in cell adhesion, actin cytoskeleton, transcriptional regulation, and ECM structural proteins differed in the LIM-treated eyes versus normal but did not differ in the control eyes versus normal. REC-treated eyes were recovering from the induced myopia. REC-control eye refractions were not significantly different from the 39N eyes, and few proteins differed from age-matched normal eyes. The balance of protein expression in the REC-treated eyes, compared with normal eyes and REC-control eyes, shifted toward upregulation or a return to normal levels of proteins involved in cell adhesion, cell division, cytoskeleton, and ECM structural proteins, including upregulation of several cytoskeleton-related proteins not affected during myopia development.

CONCLUSIONS

The DIGE procedure revealed new proteins whose abundance is altered during myopia development and recovery. Many of these are involved in cell-matrix adhesions, cytoskeleton, and transcriptional regulation and extend our understanding of the remodeling that controls the extensibility of the sclera. Reductions in these proteins during minus lens wear may produce the increased scleral viscoelasticity that results in faster axial elongation. Recovery is not a mirror image of lens-induced myopia-many protein levels, decreased during LIM, returned to normal, or slightly above normal, and additional cytoskeleton proteins were upregulated. However, no single protein or pathway appeared to be responsible for the scleral changes during myopia development or recovery.

Progressive myopia and intraocular pressure: what is the linkage? A literature review

Progressive myopia may result from an inherited biomechanical weakness of the sclera that allows it to stretch (creep) in response to stress. Increased intraocular pressure could be the mediator of stress produced by the inclined head position and the accommodation/convergence aspects of near work. This paper reviews data that relate to this hypothesis including work on sclera, intraocular pressure, animal models of myopia, and attempts at human treatment. Although the weight of evidence appears to support the proposed notion, no firm conclusion can be drawn due to imperfections in the design of prior studies. A future research agenda is proposed, including a controlled clinical trial of pharmacologically sustained ocular hypotension in young progressive myopes.

Fabrication and characterization of porous hyaluronic acid-collagen composite scaffolds

Hyaluronic acid (HA) plays a vital role in many tissues, influencing water content and mechanical function, and has been shown to have positive biological effects on cell behavior in vitro. To begin to determine whether these benefits can be accessed if HA is incorporated into collagen-based scaffolds for tissue engineering, HA-collagen composite matrices were prepared and selected properties evaluated. HA-collagen scaffolds were cross-linked with carbodiimide and loss rates of HA in culture medium assessed. Scaffold pore structures were evaluated by light and electron microscopy. Adult canine chondrocytes were grown in selected HA-collagen scaffolds to assess the effects of HA on cell behavior. Homogenous HA-collagen slurries were achieved when polyionic complexes were suppressed. HA was uniformly distributed through the scaffolds, which demonstrated honeycomb-like pores with interconnectivity among pores increasing as HA content increased. Virtually all of the HA added to the collagen slurry was incorporated into the composite scaffolds that underwent a 7-day cross-linking protocol. After 5 days in culture medium, the HA content in the scaffolds was 5-7% regardless of initial HA loading. After only 2 weeks in culture cartilaginous tissue was found in the chondrocyte-seeded HA-collagen scaffolds. This study contributes to the understanding of the effects of HA content, pH, and cross-link treatment on pore characteristics and degradation behavior essential for the design of HA-collagen scaffolds. The demonstration that these scaffolds can be populated by chondrocytes and support in vitro formation of cartilaginous tissue warrants further investigation of this material system for tissue engineering.

Pilocarpine permeability across ocular tissues and cell cultures: influence of formulation parameters

In vitro permeation studies of drugs across biological barriers are promising tools for estimating the quality and quantity of drug transport in vivo. The objective of this work was to compare the permeability of the hydrophilic model drug pilocarpine-HCl (P-HCl) through different ocular tissues and cell cultures: isolated pig cornea (PCr) and sclera (PSc), rabbit conjunctiva (RCo), and rabbit conjunctival (RCoEC) or corneal epithelial cell culture (RCrEC). Furthermore, the study included investigations about the influence of the excipients benzalkonium chloride (BAC) and ethylene diamine tetra acetic acid disodium salt (EDTA) on the permeability of the small drug. In general, BAC caused a facilitated drug transport, while EDTA hardly influenced the P-HCl concentration on the acceptor side, except for RCoEC. Additionally, the impact of variation in buffer solution pH and tonicity on drug transport in both cell cultures was tested. The higher the tonicity of the buffer solution (80, 300, and 600 mOsm/kg) the lower the permeability coefficient (P(eff)). At different pH values (6.4, 7.4, and 8.4) the P(eff) showed a directly proportional demeanor. In summary, a good correlation between the isolated tissues and cell cultures with regard to P-HCl transport could be observed.

Immunocytochemical localization of chondroitin sulfates in the interphotoreceptor matrix of the normal and dystrophic rat retina

The interphotoreceptor matrix (IPM) is a mixture of proteoglycans and glycoproteins through which metabolites must pass in transit between the retinal pigment epithelium (RPE) and the photoreceptor cells. In order to localize various species of chondroitin sulfates in the IPM of the normal and dystrophic rat retina, we have used monoclonal antibodies directed against 6-sulfated chondroitin sulfate (6S), 4-sulfated chondroitin sulfate (4S) and unsulfated chondroitin (0S). Immunofluorescence and immuno-peroxidase methods were carried out on frozen and wax-embedded sections of rat eyes. In the normal rat retina, strong labeling with the 6S antibody was observed in the basal IS/OS zone and, to a lesser extent, in the photoreceptor interstices extending to the apical RPE surface. In the RCS retina, the IPM in the basal IS/OS zone and much of the outer segment debris zone were labeled intensely with 6S antibody, but no strong labeling was present at the apical RPE surface. The labeling pattern with 0S antibody was similar to that of the 6S antibody for both normal and RCS retinas. We failed to detect any 4S antibody labeling of the IPM in both the normal and RCS retinas using these methods. These results indicate that in the rat retina, the IPM contains 6-sulfated chondroitin sulfate and unsulfated chondroitin proteoglycans that are most concentrated in the basal IS/OS zone and, to a lesser degree, between the photoreceptor outer segments. Furthermore, it appears that the rat IPM contains little or no 4-sulfated chondroitin sulfate or dermatan sulfate proteoglycan.

Differences between two fractions of glycosaminoglycans of the corneal stroma in their structural relation to collagen

Glycosaminoglycans (GAG) of bovine cornea were sequentially extracted by 0.15 M NaCl and by 1 M CaCl2, pH 8. The amounts of hexosamine (HexN) and hexuronic acid (HexUA), specific hexoses (Hex), and protein were determined in the extracts. The ultrastructure of the corneal stroma after NaCl and NaCl/CaCl2 extraction was also studied. Approximately 70% of the Hex-HexN extractable by 0.15 M NaCl is removed in the first NaCl extract, with the amount decreasing rapidly to the fifth NaCl extract. Only 20-30% of the extractable HexUA-HexN is removed in the first NaCl extract; subsequent extraction removes successively less HexUA-HexN. There is a sharp increase, however, in both Hex-HexN and HexUA-HexN removed in the first 1 M CaCl2 extract, ranging from 25 to 40% of the total extractable with NaCl. The stroma retained lamellar organization and normal spacing, diameter, and length of collagen fibers after NaCl extraction. Visibility of the 64-nm periodicity was enhanced because of loss of density in the ground substance. CaCl2 extraction led to loss of lamellar organization and apparent disruption of the collagen fibers. Only short thin fibrils remained, embedded in a material having the density and very fine fibrillar organization of basal lamina. Disruption of the collagen fibers is probably due to removal of a specific GAG component necessary to maintain the collagen as an extended morphologic structure but may also be due to a specific degradative effect of CaCl2 on collagen no longer covered by a protective layer of GAG and glycoproteins.

Mapping of the loci involved in the catabolic oxidation of L-hydroxyproline in Pseudomonas aeruginosa PAO

Genes specifying the oxidative utilization of hydroxyproline (Hyp) in P. aeruginosa PAO were located on the chromosome, around 19th minute by conjugation experiments. A map order of his-68-his-07-Hyp was assigned. Confirmation of this gene order was also demonstrated by transductional mapping studies. All the genes determining the enzymes of Hyp dissimiliatory pathway were closely linked.

Electron-microscopic histochemistry of the most peripheral retinal vessels

The reaction of Thiéry (periodic acid-thiocarbohydrazide-silver proteinate) has been applied for histochemical analysis of the structures composing the halo of the most peripheral human retinal vessels. It is suggested that glycoproteins lie in the ground substance of the halo as well as well as in the basement membranes of endothelial cells, pericytes, and Müller cells. Glycogen particles were found in endothelial cells, in pericytes and especially in Müller cells.