Age-dependent changes in the expression of matrix components in the mouse eye

BCLA CLEAR presbyopia: Management with scleral techniques, lens softening, pharmaceutical and nutritional therapies

The aging eye undergoes the same progressive crosslinking which occurs throughout the body, resulting in increased rigidity of ocular connective tissues including the lens and the sclera which impact ocular functions. This offers the potential for a scleral treatment that is based on restoring normal biomechanical movements. Laser Scleral Microporation is a laser therapy that evaporates fractional areas of crosslinked tissues in the sclera, reducing ocular rigidity over critical anatomical zones of the accommodation apparatus, restoring the natural dynamic range of focus of the eye. Although controversial and challenged, an alternative theory for presbyopia is Schachar's theory that suggests a reduction in the space between the ciliary processes and the crystalline lens. Widening of this space with expansion bands has been shown to aid near vision in people with presbyopia, a technique that has been used in the past but seems to be obsolete now. The use of drugs has been used in the treatment of presbyopia, either to cause pupil miosis to increase depth of focus, or an alteration in refractive error (to induce myopia in one eye to create monovision). Drugs and laser ablation of the crystalline lens have been used with the aim of softening the hardened lens. Poor nutrition and excess exposure to ultraviolet light have been implicated in the onset of presbyopia. Dietary nutritional supplements, lifestyle changes have also been shown to improve accommodation and the question arises whether these could be harnessed in a treatment for presbyopia as well.

Understanding how ageing impacts ganglion cell susceptibility to injury in glaucoma

Glaucoma is a leading cause of blindness worldwide, with a marked increase in prevalence with advancing age. Due to the multifactorial nature of glaucoma pathogenesis, dissecting how ageing impacts upon glaucoma risk requires analysis and synthesis of evidence from a vast literature. While there is a wealth of human clinical studies examining glaucoma pathogenesis and why older patients have increased risk, many aspects of the disease such as adaptations of retinal ganglion cells to stress, autophagy and the role of glial cells in glaucoma, require the use of animal models to study the complex cellular processes and interactions. Additionally, the accelerated nature of ageing in rodents facilitates the longitudinal study of changes that would not be feasible in human clinical studies. This review article examines evidence derived predominantly from rodent models on how the ageing process impacts upon various aspects of glaucoma pathology from the retinal ganglion cells themselves, to supporting cells and tissues such as glial cells, connective tissue and vasculature, in addition to oxidative stress and autophagy. An improved understanding of how ageing modifies these factors may lead to the development of different therapeutic strategies that target specific risk factors or processes involved in glaucoma.

Regulatory T Cells: Therapeutic Opportunities in Uveitis

Regulatory T cells (Tregs) are critical for the maintenance of immune tolerance and the suppression of excessive inflammation. Many inflammatory autoimmune disorders, including autoimmune uveitis, involve the loss of the suppressive capacities of Tregs. Over the past decade, Tregs' therapeutic potential in uveitis has garnered increasing attention. Specific subsets of Tregs, including TIGIT+ and PD-1+ Tregs, have emerged as potent immunosuppressors that may be particularly well-suited to cell-based therapeutics. Studies have elucidated the interaction between Treg development and the gut microbiome as well as various intracellular signaling pathways. Numerous cell-based therapies and therapeutic molecules have been proposed and investigated using the murine experimental autoimmune uveitis (EAU) model. However, certain challenges remain to be addressed. Studies involving the use of Tregs in human patients with uveitis are lacking, and there are concerns regarding Tregs' production and purification for practical use, their plasticity towards inflammatory phenotypes, immunogenicity, and tumorigenicity. Nevertheless, recent research has brought Tregs closer to yielding viable treatment options for uveitis.

Scleral necrosis after brachytherapy for uveal melanoma: Analysis of risk factors

BACKGROUND

Radiation-induced scleral necrosis (RISN) is a rare, but a serious complication of brachytherapy for uveal melanoma. We aimed at analysing the incidence, timing and risk factors associated with development of RISN in a large institutional series.

METHODS

All consecutive cases with brachytherapy for uveal melanoma treated by the Departments of Ophthalmology and Radiotherapy at University Hospital Essen between 1999 and 2016 were eligible. Development of RISN during the post-treatment follow-up was recorded. A 1:2 propensity score matched case-control study was performed for the evaluation of the prognostic value of different tumour- and treatment-associated parameters.

RESULTS

RISN was documented in 115 (2.9%) of 3960 patients with uveal melanoma included in the final analysis, and occurred at the mean 30.3 months (range: 1.26-226 months) after brachytherapy. In the whole cohort, younger age (p = 0.042), plaque type (p = 0.001) and ciliary body involvement (p < 0.0001) were independently associated with the RISN occurrence. In the case-control study, multivariable weighted proportional hazard analysis discovered the association of the following additional tumour- and treatment-associated characteristics with RISN: posterior tumour margin anterior to equatorial region (p = 0.0003), extraocular tumour extension (p = <0.0001), scleral contact dose (p = <0.0001), conjunctival dehiscence after therapy (p = 0.0001), disinsertion of the superior rectus muscle (p = 0.001) and the glaucoma medication (p = 0.014).

CONCLUSIONS

Our study confirms RISN as a rare complication, which might occur even years later after the brachytherapy for uveal melanoma. Alongside with scleral dose five other tumour and therapy related factors predict the risk of RISN after brachytherapy for uveal melanoma were established.

COL2A1 protective variant reduces sporadic rhegmatogenous retinal detachment severity

Rhegmatogenous retinal detachment (RRD) is the most common type of RD, the separation of neurosensory retina from the underlying retinal pigment epithelium. The RRD patients can be benefited from appropriate treatment if detected early, especially for the people predicted at high risk. In this study, we aimed to investigate the genetic association and clinical correlation of collagen type II alpha 1 (COL2A1) variants with sporadic RRD in a southern Chinese population. Totally 156 RRD patients and 254 control subjects were recruited, and 12 COL2A1 tag single nucleotide polymorphisms were genotyped by the TaqMan assay. The RRD patients had poorer visual acuity (P < 0.001) and lower intraocular pressure (IOP; P < 0.001) in their surgical eyes compared to the fellow eyes. The COL2A1 rs1793958 variant was significantly associated with RRD in the genotypic (P = 0.024), allelic (P = 0.011, odds ratio (OR) = 0.669), recessive (P = 0.011, OR = 0.384) and homozygous models (P = 0.007, OR = 0.348). RRD patients carrying the rs1793958 G allele had smaller retinal detachment area (P = 0.041) and smaller IOP differences (P = 0.046) between the surgical and fellow eyes compared to those carrying the wildtype AA genotype. In summary, this study revealed that the COL2A1 rs1793958 variant is associated with reduced risk of sporadic RRD, and patients carrying rs1793958 G allele have lower RRD severity.

Experimental scleral cross-linking increases glaucoma damage in a mouse model

The purpose of this study was to assess the effect of a scleral cross-linking agent on susceptibility to glaucoma damage in a mouse model.CD1 mice underwent 3 subconjunctival injections of 0.5 M glyceraldehyde (GA) in 1 week, then had elevated intraocular pressure (IOP) induced by bead injection. Degree of cross-linking was measured by enzyme-linked immunosorbent assay (ELISA), scleral permeability was measured by fluorescence recovery after photobleaching (FRAP), and the mechanical effects of GA exposure were measured by inflation testing. Control mice had buffer injection or no injection in 2 separate glaucoma experiments. IOP was monitored by Tonolab and retinal ganglion cell (RGC) loss was measured by histological axon counting. To rule out undesirable effects of GA, we performed electroretinography and detailed histology of the retina. GA exposure had no detectable effects on RGC number, retinal structure or function either histologically or electrophysiologically. GA increased cross-linking of sclera by 37% in an ELISA assay, decreased scleral permeability (FRAP, p = 0.001), and produced a steeper pressure-strain behavior by in vitro inflation testing. In two experimental glaucoma experiments, GA-treated eyes had greater RGC axon loss from elevated IOP than either buffer-injected or control eyes, controlling for level of IOP exposure over time (p = 0.01, and 0.049, multivariable regression analyses). This is the first report that experimental alteration of the sclera, by cross-linking, increases susceptibility to RGC damage in mice.

The contribution of lysosomotropism to autophagy perturbation

Autophagy refers to the catabolic process in eukaryotic cells that delivers cytoplasmic material to lysosomes for degradation. This highly conserved process is involved in the clearance of long-lived proteins and damaged organelles. Consequently, autophagy is important in providing nutrients to maintain cellular function under starvation, maintaining cellular homeostasis, and promoting cell survival under certain conditions. Several pathways, including mTOR, have been shown to regulate autophagy. However, the impact of lysosomal function impairment on the autophagy process has not been fully explored. Basic lipophilic compounds can accumulate in lysosomes via pH partitioning leading to perturbation of lysosomal function. Our hypothesis is that these types of compounds can disturb the autophagy process. Eleven drugs previously shown to accumulate in lysosomes were selected and evaluated for their effects on cytotoxicity and autophagy using ATP depletion and LC3 assessment, respectively. All eleven drugs induced increased staining of endogenous LC3 and exogenous GFP-LC3, even at non toxic dose levels. In addition, an increase in the abundance of SQSTM1/p62 by all tested compounds denotes that the increase in LC3 is due to autophagy perturbation rather than enhancement. Furthermore, the gene expression profile resulting from in vitro treatment with these drugs revealed the suppression of plentiful long-lived proteins, including structural cytoskeletal and associated proteins, and extracellular matrix proteins. This finding indicates a retardation of protein turnover which further supports the notion of autophagy inhibition. Interestingly, upregulation of genes containing antioxidant response elements, e.g. glutathione S transferase and NAD(P)H dehydrogenase quinone 1 was observed, suggesting activation of Nrf2 transcription factor. These gene expression changes could be related to an increase in SQSTM1/p62 resulting from autophagy deficiency. In summary, our data indicate that lysosomal accumulation due to the basic lipophilic nature of xenobiotics could be a general mechanism contributing to the perturbation of the autophagy process.

Collagen cross-linking: Strengthening the unstable cornea

Corneal ectasia, a weakening of corneal integrity, occurs both due to acquired and congenital conditions such as keratoconus. It is a progressing condition that affects both visual acuity, and corneal stability. Various methods exist for correcting this impairment, however none address the inherit pathology, an increase laxity of the corneal stroma. Collagen cross-linking, a new, minimally invasive method, aims to strengthen the stroma by inducing cross links between neighboring collagen fibers. This method results in an increase in corneal tensile strength, with no medium term adverse effects on its normal architecture. Clinically, treated patients display improvement in both visual acuity and keratometric readings. This method may provide clinicians with easily accessible tools to stop the progression, and even correct visual deterioration due to corneal ectasia. Here we review the current information regarding this new method, as well as discuss its potential benefits and downfalls.

The in vitro inflation response of mouse sclera

The purpose of this research was to develop a reliable and repeatable inflation protocol to measure the scleral inflation response of mouse eyes to elevations in intraocular pressure (IOP), comparing the inflation response exhibited by the sclera of younger and older C57BL/6 mice. Whole, enucleated eyes from younger (2 month) and older (11 month) C57BL/6 mice were mounted by the cornea on a custom fixture and inflated according to a load-unload, ramp-hold pressurization regimen via a cannula connected to a saline-filled programmable syringe pump. First, the tissue was submitted to three load-unload cycles from 6 mmHg to 15 mmHg at a rate of 0.25 mmHg/s with ten minutes of recovery between cycles. Next the tissue was submitted to a series of ramp-hold tests to measure the creep behavior at different pressure levels. For each ramp-hold test, the tissue was loaded from 6 mmHg to the set pressure at a rate of 0.25 mmHg/s and held for 30 min, and then the specimens were unloaded to 6 mmHg for 10 min. This sequence was repeated for set pressures of: 10.5, 15, 22.5, 30, 37.5, and 45 mmHg. Scleral displacement was measured using digital image correlation (DIC), and fresh scleral thickness was measured optically for each specimen after testing. For comparison, scleral thickness was measured on untested fresh tissue and epoxy-fixed tissue from age-matched animals. Comparing the apex displacement of the different aged specimens, the sclera of older animals had a statistically significant stiffer response to pressurization than the sclera of younger animals. The stiffness of the pressure-displacement response of the apex measured in the small-strain (6-15 mmHg) and the large-strain (37.5-45 mmHg) regime, respectively, were 287 ± 100 mmHg/mm and 2381 ± 191 mmHg/mm for the older tissue and 193 ± 40 mmHg/mm and 1454 ± 93 mmHg/mm for the younger tissue (Student t-test, p<0.05). The scleral thickness varied regionally, being thickest in the peripapillary region and thinnest at the equator. Fresh scleral thickness did not differ significantly by age in this group of animals. This study presents a reliable inflation test protocol to measure the mechanical properties of mouse sclera. The inflation methodology was sensitive enough to measure scleral response to changes in IOP elevations between younger and older C57BL/6 mice. Further, the specimen-specific scleral displacement profile and thickness measurements will enable future development of specimen-specific finite element models to analyze the inflation data for material properties.

Are ancient proteins responsible for the age-related decline in health and fitness?

There are a number of sites in the body where proteins are present for decades and sometimes for all of our lives. Over a period of many years, such proteins are subject to two types of modifications. The first results from the intrinsic instability of certain amino acid residues and leads to deamidation, racemization, and truncation. The second type can be traced to relentless covalent modification of such ancient proteins by reactive biochemicals produced during cellular metabolism.The accumulation of both types of posttranslational modifications over time may have important consequences for the properties of tissues that contain such proteins. It is proposed that the age-related decline in function of organs such as the eye, heart, brain, and lung, as well as skeletal components, comes about, in part, from the posttranslational modification of these long-lived proteins. Examples are provided in which this may be an important factor in the etiology of age-related conditions. As the properties of these proteins alter inexorably over time, the molecular changes contribute to a gradual decline in the function of individual organs and also tissues such as joints. This cumulative degeneration of old proteins at multiple sites in the body may also constrain the ultimate life span of the individual. The human lens may be particularly useful for discovering which reactive metabolites in the body are of most importance for posttranslational modification of long-lived proteins.

The polycomb group gene Bmi1 regulates antioxidant defenses in neurons by repressing p53 pro-oxidant activity

Aging may be determined by a genetic program and/or by the accumulation rate of molecular damages. Reactive oxygen species (ROS) generated by the mitochondrial metabolism have been postulated to be the central source of molecular damages and imbalance between levels of intracellular ROS and antioxidant defenses is a characteristic of the aging brain. How aging modifies free radicals concentrations and increases the risk to develop most neurodegenerative diseases is poorly understood, however. Here we show that the Polycomb group and oncogene Bmi1 is required in neurons to suppress apoptosis and the induction of a premature aging-like program characterized by reduced antioxidant defenses. Before weaning, Bmi1(-/-) mice display a progeroid-like ocular and brain phenotype, while Bmi1(+/-) mice, although apparently normal, have reduced lifespan. Bmi1 deficiency in neurons results in increased p19(Arf)/p53 levels, abnormally high ROS concentrations, and hypersensitivity to neurotoxic agents. Most Bmi1 functions on neurons' oxidative metabolism are genetically linked to repression of p53 pro-oxidant activity, which also operates in physiological conditions. In Bmi1(-/-) neurons, p53 and corepressors accumulate at antioxidant gene promoters, correlating with a repressed chromatin state and antioxidant gene downregulation. These findings provide a molecular mechanism explaining how Bmi1 regulates free radical concentrations and reveal the biological impact of Bmi1 deficiency on neuronal survival and aging.

Bruch's membrane changes in transgenic mice overexpressing the human biglycan and apolipoprotein b-100 genes

Age-Related Macular Degeneration (AMD) is characterized by the accumulation of lipid- and protein-rich deposits in Bruch's Membrane (BrM). A consequent decrease in hydraulic conductivity and impairment of transport through BrM may play a central role in the pathogenesis of AMD. The mechanism of deposit formation in AMD had been suggested to show similarities to the formation of atherosclerotic plaques in which the interactions of extracellular matrix proteoglycans with apolipoprotein-B 100 (apoB-100) play an important role. A prime candidate for this interaction is the small leucin-rich proteoglycan biglycan. The aim of our study was to test the effect of the simultaneous overexpression of human apoB-100 and biglycan genes in combination with a high-cholesterol diet on BrM morphology in transgenic mice. Six-weeks-old homozygous apoB-100 or biglycan, hemizygous apoB-100/biglycan transgenic and wild-type C57Bl/6 mice were fed either a standard chow or a diet supplemented with 2% cholesterol for 17 weeks. Animals were sacrificed, serum lipid levels were measured and eyes were processed for transmission electron microscopy (TEM) according to standard protocol. Morphometric analysis of digitally acquired TEM images of BrM showed that in apoB-100 and double transgenic animals fed a high-cholesterol diet, the BrM thickness was significantly increased compared to wild-type animals. Both groups had electron-lucent profiles in clusters, scattered throughout the collagenous layers of BrM, and focal nodules of an amorphous material of intermediate electron-density between the plasma and basement membranes of the retinal pigment epithelium (RPE). BrM thickness in these two groups correlated well with elevated cholesterol levels. Unexpectedly, animals overexpressing biglycan alone showed a marked, diet-independent increase in BrM thickness associated with a layer of a basement membrane-like material in outer BrM. The effects of biglycan overexpression are intriguing and further investigations are needed to elucidate the underlying mechanisms.

Genetic and epigenetic factors at COL2A1 and ABCA4 influence clinical outcome in congenital toxoplasmosis

Background

Primary Toxoplasma gondii infection during pregnancy can be transmitted to the fetus. At birth, infected infants may have intracranial calcification, hydrocephalus, and retinochoroiditis, and new ocular lesions can occur at any age after birth. Not all children who acquire infection in utero develop these clinical signs of disease. Whilst severity of disease is influenced by trimester in which infection is acquired by the mother, other factors including genetic predisposition may contribute.

Methods and Findings

In 457 mother-child pairs from Europe, and 149 child/parent trios from North America, we show that ocular and brain disease in congenital toxoplasmosis associate with polymorphisms in ABCA4 encoding ATP-binding cassette transporter, subfamily A, member 4. Polymorphisms at COL2A1 encoding type II collagen associate only with ocular disease. Both loci showed unusual inheritance patterns for the disease allele when comparing outcomes in heterozygous affected children with outcomes in affected children of heterozygous mothers. Modeling suggested either an effect of mother's genotype, or parent-of-origin effects. Experimental studies showed that both ABCA4 and COL2A1 show isoform-specific epigenetic modifications consistent with imprinting.

Conclusions

These associations between clinical outcomes of congenital toxoplasmosis and polymorphisms at ABCA4 and COL2A1 provide novel insight into the molecular pathways that can be affected by congenital infection with this parasite.

A mouse model for Stickler's syndrome: ocular phenotype of mice carrying a targeted heterozygous inactivation of type II (pro)collagen gene (Col2a1)

The influences of targeted heterozygous inactivation of type II (pro)collagen gene (Col2a1) on eye structures in the 15-month-old C57BL/6JOlaHsd mouse was studied. The eyes were collected from C57BL mice heterozygous for a targeted inactivation of one allele of the Col2a1 gene (Col2a1(+/-) mice). The eyes of C57BL mice with normal gene alleles were used as controls (Col2a1(+/+) mice). Ocular histology was analyzed from tissue sections, stained with hematoxylin and eosin, toluidine blue and alcian blue. Type II collagen was localized by immunohistochemistry. Hyaluronan (HA) was stained utilizing the biotinylated complex of the hyaluronan-binding region of aggrecan and link protein (bHABC). The anterior segment of the eye was well-formed in both genotypes, but typical folding of ciliary processes was decreased, while increased stromal extracellular matrix vacuolization was seen in the Col2a1(+/-) mice. In the lens of these mice, subcapsular extracellular matrix changes were observed. Differences in retinal structures or the number of the eyes with retinal detachment were not detected between the genotypes. In Col2a1(+/-) mice, staining for type II collagen was weaker in cornea, ciliary body, iris, lens, vitreous, retina, choroid and sclera than in the control mice. HA staining was detected in the extraocular tissues, ciliary body, iris and the choroid of both genotypes. HA staining was observed only in the vitreous body of the control animals. Heterozygous inactivation of Col2a1 gene causes structural defects in the murine eye. The observed structural changes in the ciliary body, lens and vitreous of the Col2a1(+/-) mice may represent ocular features found in the human Stickler syndrome, where the abnormalities result from COL2A1 gene mutations which lead to functional haploinsufficiency.

Vitreous collagen metabolism before and after vitrectomy

PURPOSE

To assess vitreous metabolism by measuring C-propeptide levels of type II procollagen (pCOL-II-C) and hyaluronan levels in the vitreous and in the vitreous fluid after vitrectomy for macular hole.

METHODS

We obtained 1-ml vitreous samples during vitrectomy from 34 patients (34 eyes) with a macular hole (age range 50-77 years, mean 64 years). After vitrectomy, we performed fluid-air exchange in six eyes because of unresolved macular holes and collected 4-ml fluid samples. Gel-filtration high-performance liquid chromatography (HPLC) was used to determine the molecular weight of pCOL-II-C in the samples. The pCOL-II-C level was measured by sandwich enzyme immunoassay and hyaluronan by sandwich binding protein assay.

RESULTS

HPLC showed that pCOL-II-C in the vitreous samples corresponded to purified pCOL-II-C from cartilage. The vitreous pCOL-II-C level (4.7+/-0.3 ng/ml) was similar to reported synovial fluid levels. In six eyes that underwent fluid-air exchange, pCOL-II-C in the fluid samples remained at a level similar to that in the vitreous samples, while hyaluronan levels in the fluid samples were significantly lower than in the vitreous samples.

CONCLUSIONS

The molecular weight and concentrations of pCOL-II-C in the vitreous are similar to those in joint fluid. In patients with a macular hole, type II procollagen may be secreted persistently into the vitreous cavity before and after vitrectomy.

Collagens and collagen-related matrix components in the human and mouse eye

The three-dimensional structure of the eye plays an important role in providing a correct optical environment for vision. Much of this function is dependent on the unique structural features of ocular connective tissue, especially of the collagen types and their supramolecular structures. For example, the organization of collagen fibrils is largely responsible for transparency and refraction of cornea, lens and vitreous body, and collagens present in the sclera are largely responsible for the structural strength of the eye. Phylogenetically, most of the collagens are highly conserved between different species, which suggests that collagens also share similar functions in mice and men. Despite considerable differences between the mouse and the human eye, particularly in the proportion of the different tissue components, the difficulty of performing systematic histologic and molecular studies on the human eye has made mouse an appealing alternative to studies addressing the role of individual genes and their mutations in ocular diseases. From a genetic standpoint, the mouse has major advantages over other experimental animals as its genome is better known than that of other species and it can be manipulated by the modern techniques of genetic engineering. Furthermore, it is easy, quick and relatively cheap to produce large quantities of mice for systematic studies. Thus, transgenic techniques have made it possible to study consequences of specific mutations in genes coding for structural components of ocular connective tissues in mice. As these changes in mice have been shown to resemble those in human diseases, mouse models are likely to provide efficient tools for pathogenetic studies on human disorders affecting the extracellular matrix. This review is aimed to clarify the role of collagenous components in the mouse and human eye with a closer look at the new findings of the collagens in the cartilage and the eye, the so-called "cartilage collagens".

Scleral structure, organisation and disease. A review

Although disease of the sclera is unusual, when it occurs it can rapidly destroy both the eye and vision. However, normally the sclera provides an opaque protective coat for the intraocular tissues and a stable support during variations in internal pressure and eye movements, which would otherwise perturb the visual process through distortion of the retina and the lens/iris diaphragm. This stability, which is vital for clear vision is made possible by the organisation and viscoelastic properties of scleral connective tissue. Microscopically, the sclera displays distinct concentric layers including, from outside, Tenon's capsule, episclera, the scleral stroma proper and lamina fusca, melding into underlying choroid. Two sites exhibit specialised structure and function: the perilimbal trabecular meshwork, through which aqueous filters into Schlemm's canal, and the lamina cribrosa, which permits axons of the optic nerve to exit the posterior sclera. Throughout, sclera is densely collagenous, the stroma consisting of fibrils with various diameters combining into either interlacing fibre bundles or defined lamellae in outer zones. Scleral fibrils are heterotypic structures made of collagen types I and III, with small amounts of types V and VI also present. Scleral elastic fibres are especially abundant in lamina fusca and trabecular meshwork. The interfibrillar matrix is occupied by small leucine-rich proteoglycans, decorin and biglycan, containing dermatan and dermatan/chondroitin sulphate glycosaminoglycans, together with the large proteoglycan, aggrecan, which also carries keratan sulphate sidechains. Decorin is closely associated with the collagen fibrils at specific binding sites situated close to the C-terminus of the collagen molecules. Proteoglycans influence hydration, solute diffusion and fluid movement through the sclera, both from the uvea and via the trabecular meshwork. As the sclera is avascular, nutrients come from the choroid and vascular plexi in Tenon's capsule and episclera, where there is an artery to artery anastomosis in which blood oscillates, rather than flows rapidly. This predisposes to the development of vasculitis causing a spectrum of inflammatory conditions of varying intensity which, in the most severe form, necrotising scleritis, may destroy all of the structural and cellular components of the sclera. Scleral cells become fibroblastic and the stroma is infiltrated with inflammatory cells dominated by macrophages and T-lymphocytes. This process resembles, and may be concurrent with, systemic disease affecting other connective tissues, particularly the synovial joints in rheumatoid arthritis. Current views support an autoimmune aetiology for scleritis. Whilst the role of immune complexes and the nature of initial pro-inflammatory antigen(s) remain unknown, the latter may reside in scleral tissue components which are released or modified by viral infection, injury or surgical trauma.

Collagen gene expression and the altered accumulation of scleral collagen during the development of high myopia

The development of high myopia is associated with reduced scleral collagen accumulation, scleral thinning, and loss of scleral tissue, in both humans and animal models. Reduced collagen fibril diameter is also observed in the sclera of eyes with high myopia. The present study investigated aspects of scleral collagen synthesis and degradation, in a mammalian model of high myopia, to elucidate the factors underlying scleral changes. General synthesis and degradation of scleral collagen was investigated in monocularly deprived tree shrews, through the in vivo administration of [(3)H]proline and subsequent assay of scleral tissue for [(3)H]collagen. In addition, PCR enriched cDNA, produced from tree shrew scleral mRNA, was used to synthesize probes for hybridization to custom gene arrays consisting of partial sequences for 11 collagen subtypes. Finally, real-time reverse transcriptase-PCR was employed to investigate collagen type I, III, and V mRNA expression in the sclera of myopic, contralateral control, and normal tree shrew eyes. Scleral [(3)H]proline incorporation was reduced at the posterior pole of myopic eyes following 5 days of monocular deprivation (-36 +/- 4%), whereas [(3)H]proline content was similar in treated and control eyes before myopia induction (-1 +/- 8%) but was reduced in myopic eyes following 5 (-8 +/- 2%), 12 (-15 +/- 4%), and 24 (-10 +/- 4%) days of myopia induction. The majority of the collagens investigated were found to be expressed in the sclera, with 11 subtypes being identified. Collagen type I mRNA expression was reduced in the sclera of myopic eyes (-20 +/- 7%), however, collagen type III (+2 +/- 9%) and type V (-1 +/- 6%) expression was unchanged relative to control, resulting in a net increase in the ratio of expression of collagen type III/type I and collagen type V/type I (22 and 25%, respectively). These results show that reduced scleral collagen accumulation in myopic eyes is a result of both decreased collagen synthesis and accelerated collagen degradation. Furthermore, changes in collagen synthesis are driven by reduced type I collagen production. Short term increases in the ratio of newly synthesized collagen type III/type I and type V/type I are likely to be important in the increasing frequency of small diameter scleral collagen fibrils observed in high myopia and may be important in the subsequent development of posterior staphyloma in humans with pathological myopia.

Expression of Sox9 and type IIA procollagen during ocular development and aging in transgenic Del1 mice with a mutation in the type II collagen gene

PURPOSE

To study the expression and distribution of transcription factor Sox9 and type IIA procollagen in the developing and aging eyes of normal and transgenic Dell mice carrying pro(alpha)1(II) collagen transgenes with a short deletion mutation, which cause ocular abnormalities in this mouse line.

METHODS

The eyes of Del1 mice were studied on embryonic days E14.5, E16.5 and E18.5, and at the ages of 4 and nine months, using their nontransgenic littermates as controls. Sox9 and pro(alpha)1(IIA) collagen were detected by RNase protection assay and immunohistochemistry.

RESULTS

RNase protection assay revealed Sox9 transcripts in the eyes of Del1 and control mice during development and aging. The mRNA for type IIA procollagen had a similar temporal expression pattern. On embryonic days E14.5, E16.5 and E18.5, Sox9 was located by immunohistochemistry in the nuclei and type IIA procollagen in the extracellular space of the developing retina. During growth and aging, the ocular expression of Sox9 mRNA and the immunohistochemical reaction for Sox9 antibody diminished, concomitant with the reduction in type II procollagen mRNA. However, at the age of nine months, levels of Sox9 and type IIA procollagen mRNAs were higher in the degenerating eyes of Del1 and control mice.

CONCLUSIONS

The similarities in the temporo-spatial distribution of Sox9 and type IIA procollagen suggest that this transcription factor is involved in the activation of type II collagen expression in the eye, as has been demonstrated in prechondrogenic mesenchyme and immature cartilage. The increased production of Sox9 and type IIA procollagen in the aging retina and vitreous is analogous to degenerating articular cartilage where attempted tissue repair has also been observed.

The role of the posterior ciliary body in the biosynthesis of vitreous humour

Recently, several groups have published new information regarding the origins and structure of the vitreous humour, and the inner limiting lamina (ILL) of the retina. This short article provides an overview of this new information. It is proposed that vitreous proteins are derived from several different cell types with the posterior half of the non-pigmented ciliary epithelium being prominent in the expression of several connective tissue macromolecules. In addition, some basement membrane macromolecules are also expressed by the ciliary body and may subsequently be assembled on the surface of the Müller cells to form the ILL. New data suggest that the posterior half of the non-pigmented ciliary epithelium has substantial secretory activity and is likely to play a pivotal role in eye development.