Immunogold ultrastructural localization of collagens in the aged human outflow system

Development of Cell Culture Platforms for Study of Trabecular Meshwork Cells and Glaucoma Development

BACKGROUND

Various cell culture platforms that could display native environmental cue-mimicking stimuli were developed, and effects of environmental cues on cell behaviors were studied with the cell culture platforms. Likewise, various cell culture platforms mimicking native trabecular meshwork (TM) composed of juxtacanalicular, corneoscleral and uveal meshwork located in internal scleral sulcus were used to study effects of environmental cues and/or drug treatments on TM cells and glaucoma development. Glaucoma is a disease that could cause blindness, and cause of glaucoma is not clearly identified yet. It appears that aqueous humor (AH) outflow resistance increased by damages on pathway of AH outflow can elevate intraocular pressure (IOP). These overall possibly contribute to development of glaucoma.

METHODS

For the study of glaucoma, static and dynamic cell culture platforms were developed. Particularly, the dynamic platforms exploiting AH outflow-mimicking perfusion or increased IOP-mimicking increased pressure were used to study how perfusion or increased pressure could affect TM cells. Overall, potential mechanisms of glaucoma development, TM structures and compositions, TM cell culture platform types and researches on TM cells and glaucoma development with the platforms were described in this review.

RESULTS AND CONCLUSION

This will be useful to improve researches on TM cells and develop enhanced therapies targeting glaucoma.

Trabecular meshwork's collagen network formation is inhibited by non-pigmented ciliary epithelium-derived extracellular vesicles

The present research aims to determine whether the application of non‐pigmented ciliary epithelium cells derived extracellular vesicles to human trabecular meshwork cells affects the formation and secretion of collagen type I to the extracellular matrix formation. Following the extraction of non‐pigmented ciliary epithelium derived extracellular vesicles by a precipitation method, their size and concentration were determined using tunable resistive pulse sensing technology. Extracellular vesicles were incubated with trabecular meshwork cells for 3 days. Morphological changes of collagen type I in the extracellular matrix of trabecular meshwork cells were visualized using confocal microscopy and scanning electron microscopy. A Sirius Red assay was used to determine the total amount of collagen. Finally, collagen type I expression levels in the extracellular matrix of trabecular meshwork cells were quantified by cell western analysis. We found that non‐pigmented ciliary epithelium extracellular vesicles were very effective at preventing collagen fibres formation by the trabecular meshwork cells, and their secretion to the extracellular matrix was significantly reduced (P < .001). Morphological changes in the extracellular matrix of trabecular meshwork cells were observed. Our study indicates that non‐pigmented ciliary epithelium extracellular vesicles can be used to control collagen type I fibrillogenesis in trabecular meshwork cells. These fibrils net‐like structure is responsible for remodelling the extracellular matrix. Moreover, we suggest that targeting collagen type I fibril assembly may be a viable treatment for primary open‐angle glaucoma abnormal matrix deposition of the extracellular matrix.

The lymphangiogenic and hemangiogenic privilege of the human sclera

PURPOSE

Most organs of the human body are supplied with a dense network of blood and lymphatic vessels. However, some tissues are either hypovascular or completely devoid of vessels for proper function, such as the ocular tissues sclera and cornea, cartilage and tendons. Since many pathological conditions are affecting the human sclera, this review is focussing on the lymphangiogenic and hemangiogenic privilege in the human sclera.

METHODS

This article gives an overview of the current literature based on a PubMed search as well as observations and experience from clinical practice.

RESULTS

The healthy human sclera is the outer covering layer of the eye globe consisting mainly of collagenous extracellular matrix and fibroblasts. Physiologically, the sclera shows only a superficial network of blood vessels and a lack of lymphatic vessels. This vascular privilege is actively regulated by balancing anti- and proangiogenic factors expressed by cells within the sclera. In pathological situations, such as open globe injuries or ciliary body melanomas with extraocular extension, lymphatic vessels can secondarily invade the sclera and the inner eye. This mechanism most likely is important for tumor cell metastasis, wound healing, immunologic defense against intruding microorganism, and autoimmune reactions against intraocular antigens.

CONCLUSIONS

The human sclera is characterized by a tightly regulated vascular network that can be compromised in pathological situations, such as injuries or intraocular tumors affecting healing outcomes Therefore, the molecular and cellular mechanisms underlying wound healing following surgical interventions deserve further attention, in order to devise more effective therapeutic strategies.

The Peculiar Pattern of Type IV Collagen Deposition in Epiretinal Membranes

Idiopathic epiretinal membranes are sheets of tissue that develop in the vitreoretinal interface. They are formed by cells and extracellular matrix, and they are considered the expression of a fibrotic disorder of the eye. Confocal and immunoelectron microscopy of the extracellular matrix of excised membranes, revealed high contents of type IV collagen. It was distributed within epiretinal membranes in basement membrane-like structures associated with cells and in interstitial deposits. In both cases, type IV collagen was always associated with type I collagen. Col IV was also coupled with Col VI and laminin. At high magnification, type IV collagen immunolabelling was associated with interstitial deposits and showed a reticular appearance due to the intersection of beaded microfilaments. The microfilaments are about 12 nm in diameter with interbead distance of 30-40 nm. Cells of the epiretinal membranes showed intracellular lysosome-like bodies heavily labeled for type IV collagen suggesting an active role in membrane remodeling. Hence, type IV collagen is not necessarily always associated with basement membranes; the molecular interactions that it may develop when not incorporated in basement membranes are still unknown. It is conceivable, however, that they might have implications in the progression of epiretinal membranes and other fibrotic disorders.

How many aqueous humor outflow pathways are there?

The aqueous humor (AH) outflow pathways definition is still matter of intense debate. To date, the differentiation between conventional (trabecular meshwork) and unconventional (uveoscleral) pathways is widely accepted, distinguishing the different impact of the intraocular pressure on the AH outflow rate. Although the conventional route is recognized to host the main sites for intraocular pressure regulation, the unconventional pathway, with its great potential for AH resorption, seems to act as a sort of relief valve, especially when the trabecular resistance rises. Recent evidence demonstrates the presence of lymphatic channels in the eye and proposes that they may participate in the overall AH drainage and intraocular pressure regulation, in a presumably adaptive fashion. For this reason, the uveolymphatic route is increasingly thought to play an important role in the ocular hydrodynamic system physiology. As a result of the unconventional pathway characteristics, hydrodynamic disorders do not develop until the adaptive routes cannot successfully counterbalance the increased AH outflow resistance. When their adaptive mechanisms fail, glaucoma occurs. Our review deals with the standard and newly discovered AH outflow routes, with particular attention to the importance they may have in opening new therapeutic strategies in the treatment of ocular hypertension and glaucoma.

Rho-associated protein kinase inhibitor induced morphological changes in type VI collagen in the human trabecular meshwork

Aims

To investigate morphological changes in type VI collagen in the human trabecular meshwork associated with the rho kinase inhibitor ripasudil.

Methods

This cross-sectional study evaluated the effects of ripasudil eye drop administration (RA) or no ripasudil eye drop administration (NRA) in patients with primary open-angle glaucoma (POAG; age range 60–80 years) who underwent conventional outflow reconstruction between December 2015 and September 2016 at Tokai University Hachioji Hospital. The juxtacanalicular tissue was removed and imaged using transmission electron microscopy. Type VI collagen comprises cross-banded aggregates with transverse bands 30 nm apart repeating every 105 nm. The transverse bands are called the outer rod-like region (ORR) and the intervals are called the inner rod-like region (IRR). The waveform intensity in the type VI collagen was analysed in electron micrographs using Fourier transformation to detect the IRR and ORR borders.

Results

Ten eyes of 10 patients were included (n=5/group). The baseline characteristics did not differ significantly between groups. ORR width was significantly smaller in the RA group (37.85±3.43 nm) than in the NRA group (50.62±5.23 nm, p<0.05), whereas IRR width was significantly greater in the RA group (70.68±10.84 nm) than in the NRA group (58.19±5.34 nm, p<0.05). Morphological changes in the type VI collagen total width tended to correlate with the duration of ripasudil administration (r=0.9, p=0.08).

Conclusions

Ripasudil administration in patients with POAG induced morphological changes in type VI collagen. Patients with POAG administered RA had a significantly smaller ORR width and a significantly greater IRR width than patients with POAG not administered RA.

Histological investigation of human glaucomatous eyes: Extracellular fibrotic changes and galectin 3 expression in the trabecular meshwork and optic nerve head

Glaucoma is a leading cause of irreversible vision loss and is associated with fibrotic changes in two ocular tissues-the optic nerve head (ONH) and trabecular meshwork (TM). We investigated the differences in extracellular matrix components (ECM) including collagen, elastin, transforming growth factor beta-2, type-II receptor (TGFβRII) and Galectin3 (Gal3) in the glaucomatous human eyes to quantify fibrotic changes in ONH and TM. Glaucomatous and control human donor eyes were prepared for chemical and immunological staining to quantify ECM protein expression in the TM and ONH. Chemical staining included: Trichrome (collagen), Vernhoeff-Van Giesen (elastin) and Sirius Red (collagen). Immunohistochemistry was used to determine levels of Gal3 and TGFβ2RII. Quantitative analyses were performed using Image J software. Student's t-test was used to compare groups and Pearson's test was used to determine correlations P-values of 0.05 (or less) were considered statistically significant. Deposition of ECM proteins was elevated in glaucomatous tissues. There was increased collagen (P = 0.0469), Gal3 (P < 0.0001) and TGFβ2RII (P = 0.0005) in the TM of glaucomatous eyes. Likewise, collagen (P = 0.0517) and Galectin3 (P = 0.041) were increased in the ONH glaucomatous eyes. There was a correlation of TGFβRII with Gal3 in the TM (P < 0.0001) and optic nerve (P = 0.0003). The TM and ONH of glaucomatous eyes showed increased expression of ECM proteins supporting a fibrotic pathology. Galectin3 and TGFβ-2R II showed a positive correlation in TM and optic nerve supporting co-localization and suggesting their potential role in the glaucoma fibrotic process. Clin. Anat. 31:1031-1049, 2018. © 2018 The Authors. Clinical Anatomy published by Wiley Periodicals, Inc. on behalf of American Association of Clinical Anatomists.

TGF-β induces phosphorylation of phosphatase and tensin homolog: implications for fibrosis of the trabecular meshwork tissue in glaucoma

Fundamental cell signaling mechanisms that regulate dynamic remodeling of the extracellular matrix (ECM) in mechanically loaded tissues are not yet clearly understood. Trabecular meshwork (TM) tissue in the eye is under constant mechanical stress and continuous remodeling of ECM is crucial to maintain normal aqueous humor drainage and intraocular pressure (IOP). However, excessive ECM remodeling can cause fibrosis of the TM as in primary open-angle glaucoma (POAG) patients, and is characterized by increased resistance to aqueous humor drainage, elevated IOP, optic nerve degeneration and blindness. Increased levels of active transforming growth factor-β2 (TGF-β2) in the aqueous humor is the main cause of fibrosis of TM in POAG patients. Herein, we report a novel finding that, in TM cells, TGF-β-induced increase in collagen expression is associated with phosphorylation of phosphatase and tensin homolog (PTEN) at residues Ser380/Thr382/383. Exogenous overexpression of a mutated form of PTEN with enhanced phosphatase activity prevented the TGF-β-induced collagen expression by TM cells. We propose that rapid alteration of PTEN activity through changes in its phosphorylation status could uniquely regulate the continuous remodeling of ECM in the normal TM. Modulating PTEN activity may have high therapeutic potential to alleviating the fibrosis of TM in POAG patients.

Smad-independent TGF-β2 signaling pathways in human trabecular meshwork cells

Aberrant expression and signaling of Transforming Growth Factor (TGF)-β is strongly associated with development of elevated intraocular pressure (IOP) and primary open-angle glaucoma (POAG). In cells of the trabecular meshwork, a key component of the conventional outflow pathway, TGF-β is well-known to promote expression of multiple ocular hypertensive mediators, including genes associated with fibrosis as well as cellular contractility. These effects are mediated by induction of canonical (Smad) as well as non-canonical (MAPK, Rho GTPase) signaling cascades. In the present review, we will highlight the non-canonical, Smad-independent signaling pathways activated by TGF-β2 in human TM cells, as well as the genes known to be induced by non-canonical TGF-β2 signaling.

The exit strategy: Pharmacological modulation of extracellular matrix production and deposition for better aqueous humor drainage

Primary open angle glaucoma (POAG) is an optic neuropathy and an irreversible blinding disease. The etiology of glaucoma is not known but numerous risk factors are associated with this disease including aging, elevated intraocular pressure (IOP), race, myopia, family history and use of steroids. In POAG, the resistance to the aqueous humor drainage is increased leading to elevated IOP. Lowering the resistance and ultimately the IOP has been the only way to slow disease progression and prevent vision loss. The primary drainage pathway comprising of the trabecular meshwork (TM) is made up of relatively large porous beams surrounded by extracellular matrix (ECM). Its juxtacanalicular tissue (JCT) or the cribriform meshwork is made up of cells embedded in dense ECM. The JCT is considered to offer the major resistance to the aqueous humor outflow. This layer is adjacent to the endothelial cells forming Schlemm's canal, which provides approximately 10% of the outflow resistance. The ECM in the TM and the JCT undergoes continual remodeling to maintain normal resistance to aqueous humor outflow. It is believed that the TM is a major contributor of ECM proteins and evidence points towards increased ECM deposition in the outflow pathway in POAG. It is not clear how and from where the ECM components emerge to hinder the normal aqueous humor drainage. This review focuses on the involvement of the ECM in ocular hypertension and glaucoma and the mechanisms by which various ocular hypotensive drugs, both current and emerging, target ECM production, remodeling, and deposition.

Functional Anatomy of the Outflow Facilities

In order to understand the pathophysiology, select optimal therapeutic options for patients and provide clients with honest expectations for cases of canine glaucoma, clinicians should be familiar with a rational understanding of the functional anatomy of the ocular structures involved in this group of diseases. The topographical extension and the structural and humoral complexity of the regions involved with the production and the outflow of aqueous humor undergo numerous changes with aging and disease. Therefore, the anatomy relative to the fluid dynamics of aqueous has become a pivotal yet flexible concept to interpret the different phenotypes of glaucoma.

Walking through trabecular meshwork biology: Toward engineering design of outflow physiology

According to the World Health Organization, glaucoma remains the second leading cause of blindness in the world. Glaucoma belongs to a group of optic neuropathies that is characterized by chronic degeneration of the optic nerve along with its supporting glia and vasculature. Despite significant advances in the field, there is no available cure for glaucoma. The trabecular meshwork has been implicated as the primary site for regulation of intraocular pressure, the only known modifiable factor in glaucoma development. In this review, we describe the current models for glaucoma studies, primary culture, anterior eye segments, and animal studies and their limitations. These models, especially anterior eye segments and animal tissues, often require careful interpretation given the inter-species variation and are cumbersome and expensive. The lack of an available in vitro 3D model to study trabecular meshwork cells and detailed mechanisms of their regulation of intraocular pressure has limited progress in the field of glaucoma research. In this paper, we review the current status of knowledge of the trabecular meshwork and how the current advances in tissue engineering techniques might be applied in an effort to engineer a synthetic trabecular meshwork as a 3D in vitro model to further advance glaucoma research. In addition, we describe strategies for selection and design of biomaterials for scaffold fabrication as well as extracellular matrix components to mimic and support the trabecular architecture. We also discuss possible uses for a bioengineered trabecular meshwork for both developing a fundamental understanding of trabecular meshwork biology as well as high-throughput screening of glaucoma drugs.

Tissue-based imaging model of human trabecular meshwork

We have developed a tissue-based model of the human trabecular meshwork (TM) using viable postmortem corneoscleral donor tissue. Two-photon microscopy is used to optically section and image deep in the tissue to analyze cells and extracellular matrix (ECM) within the original three-dimensional (3D) environment of the TM. Multimodal techniques, including autofluorescence (AF), second harmonic generation (SHG), intravital dye fluorescence, and epifluorescence, are combined to provide unique views of the tissue at the cellular and subcellular level. SHG and AF imaging are non-invasive tissue imaging techniques with potential for clinical application, which can be modeled in the system. We describe the following in the tissue-based model: analysis of live cellularity to determine tissue viability; characteristics of live cells based on intravital labeling; features and composition of the TM's structural ECM; localization of specific ECM proteins to regions such as basement membrane; in situ induction and expression of tissue markers characteristic of cultured TM cells relevant to glaucoma; analysis of TM actin and pharmacological effects; in situ visualization of TM, inner wall endothelium, and Schlemm's canal; and application of 3D reconstruction, modeling, and quantitative analysis to the TM. The human model represents a cost-effective use of valuable and scarce yet available human tissue that allows unique cell biology, pharmacology, and translational studies of the TM.

The collagen matrix of the human trabecular meshwork is an extension of the novel pre-Descemet's layer (Dua's layer)

BACKGROUND

The trabecular meshwork (TM) located at the angle of the anterior chamber of the eye contributes to aqueous drainage. A novel layer in the posterior part of the human cornea has recently been reported (the pre-Descemet's layer (Dua's layer (PDL)). We examined the peripheral part of this layer in relation to the origin of the TM.

METHODS

The PDL and TM of 19 human donor eyes and one exenterated sample were studied. Samples were examined by light and electron microscopy (EM) for tissue architecture and by immunohistology for four matricellular proteins, five collagen types and CD34.

RESULTS

EM revealed that beams of collagen emerged from the periphery of PDL on the anterior surface of the Descemet's membrane and divided and subdivided to continue as the beams of the TM. Long-spacing collagen was seen in the PDL and TM. Trabecular cells (CD34-ve) associated with basement membrane were seen in the peripheral part of the PDL and corresponded to the start of the separation of the collagen lamellae of PDL. Collagen VI was present continuously in PDL and extended into the TM. Matricellular proteins were seen predominantly in the TM with only laminin extending into the periphery of PDL.

CONCLUSIONS

This study provides an insight into the origins of the collagen core of the TM as an extension of the PDL of the cornea. This finding adds to the knowledge base of the TM and cornea and has the potential to impact future research into the TM and glaucoma.

Tissue plasminogen activator in trabecular meshwork attenuates steroid induced outflow resistance in mice

Tissue plasminogen activator, a serine protease encoded by the PLAT gene is present in the trabecular meshwork (TM) and other ocular tissues and has been reported to be downregulated by treatment with steroids in vitro. Steroids are known to cause changes in outflow facility of aqueous humor in many species. In the present study, we tested whether overexpression of PLAT can prevent and/or reverse the outflow facility of mouse eyes treated with steroids. Animals received bilateral injection with 20 µl of triamcinolone acetonide (TA) (40 mg/ml) suspension subconjunctivally to induce outflow facility changes. Some animals received unilateral intracameral injection with 2 µl of adenoviral suspension [3-4 x 10(12) virus genomes per milliliter (vg/ml)] carrying sheep PLAT cDNA (AdPLAT) either concurrently with TA injection or one week after TA injection, whereas others received bilateral intracameral injection with 2 µl of adenoviral suspension (9 x 10(12) vg/ml) carrying no transgene (AdNull) concurrently with TA injection. Animals were sacrificed one week after AdPLAT or AdNull treatment. Endogenous mRNA expression levels of mouse PAI-1 and MMP-2, -9 and -13 were also measured using qRT-PCR. Outflow facility one week after AdPLAT administration was increased by 60% and 63% respectively for animals that had not or had been pretreated with steroids. Overexpression of PLAT significantly upregulated expression of PAI-1, MMP-2, -9 and -13 compared to the levels found in TA only treated eyes. These findings suggest that overexpression of PLAT in TM of mouse eyes can both prevent and reverse the decrease in outflow facility caused by steroid treatment and is associated with upregulation of MMPs.

Sources of structural autofluorescence in the human trabecular meshwork

PURPOSE

In situ 2-photon excitation fluorescence (TPEF) of the human trabecular meshwork (TM) reveals beams of heterogeneous autofluorescence (AF) comprising high intensity fluorescent fibers (AF-high) on a background of lower intensity fluorescence (AF-low). To determine the sources of this AF heterogeneity, we imaged human TM to characterize AF, second harmonic generation (SHG) for collagen, and eosin-labeled fluorescence identifying elastin.

METHODS

Corneoscleral rims retained after corneal transplantation were incubated with and without eosin, and imaged by TPEF. TPEF was collected through multiphoton bandpass filters to obtain AF, SHG (collagen bandwidth), and eosin-labeled fluorescence images. For qualitative comparisons, near-simultaneous image acquisition pairs of AF-SHG (+/-eosin coincubation), AF-eosin, and SHG-eosin were captured. For quantitative comparisons, multiple regions of interest (ROI) were defined in separate TM beam regions within the uveal and corneoscleral meshwork for image acquisition pairs of AF-SHG (without eosin coincubation) and SHG-eosin. We defined 18 ROI within each acquisition pair as the basis for Manders colocalization analysis. Perfect colocalization was defined as a Manders coefficient (Mcoeff) of 1.

RESULTS

Qualitatively and quantitatively, AF-low colocalized with SHG (Mcoeff=1), but not SHG signal-voids. AF-high colocalized with SHG signal-voids (Mcoeff=1), but not the SHG signal. Like AF-high, eosin-labeled fluorescence qualitatively and quantitatively colocalized (Mcoeff=1) with SHG signal-voids, but not the SHG signal.

CONCLUSIONS

Heterogeneous AF in human TM is comprised of high intensity signal originating from elastin fibers in beam cores and lower intensity signal originating from collagen. These findings are relevant to interpreting structural extracellular matrix signals in AF images of the TM.

In situ autofluorescence visualization of human trabecular meshwork structure

PURPOSE

To characterize the three-dimensional (3-D) structure of the human trabecular meshwork (TM) by two-photon excited (TPEF) autofluorescence (AF) and optical sectioning without conventional histologic embedding and sectioning.

METHODS

Viable human ex vivo explants of the anterior chamber angle containing the aqueous humor drainage tissue in situ were imaged by TPEF to localize AF and Hoechst 33342 nuclear fluorescence. An autofluorescent marker in Schlemm's Canal (SC) aided SC situ visualization. En face and orthogonal views of the TM were generated.

RESULTS

In the innermost uveal TM, AF signals outlined an intricate 3-D network of fine branching beams with large openings between the beams. In the adjacent corneoscleral TM, beams were thicker and coalesced as plate-like structures with pore-like openings. Linear and coiled AF fibers were visible on the background AF of beams. Deeper, in the external TM, this organization changed to fine fiber arrays orientated in the tissue's longitudinal axis, reminiscent of the cribriform plexus of the juxtacanalicular TM (JCT). In the outermost JCT, AF of fine fibers was sparse, then undetectable as optical sections approached the inner wall of SC. Cell nuclei were closely associated with the TM structural extracellular matrix.

CONCLUSIONS

We have used TPEF and optical sectioning to exploit AF as a useful method to visualize the structure of the human conventional aqueous drainage pathway in situ. Ancillary nuclear staining allowed cell association with the AF structures to be seen. This approach revealed a unique 3-D perspective of the TM that is consistent with known TM structural characteristics.

The trabecular meshwork outflow pathways: structural and functional aspects. Exp Eye Res. 2009;88:648-655. [PMID: 19239914 DOI: 10.1016/j.exer.2009.02.007]

The major drainage structures for aqueous humor (AH) are the conventional or trabecular outflow pathways, which are comprised of the trabecular meshwork (made up by the uveal and corneoscleral meshworks), the juxtacanalicular connective tissue (JCT), the endothelial lining of Schlemm's canal (SC), the collecting channels and the aqueous veins. The trabecular meshwork (TM) outflow pathways are critical in providing resistance to AH outflow and in generating intraocular pressure (IOP). Outflow resistance in the TM outflow pathways increases with age and primary open-angle glaucoma. Uveal and corneoscleral meshworks form connective tissue lamellae or beams that are covered by flat TM cells which rest on a basal lamina. TM cells in the JCT are surrounded by fibrillar elements of the extracellular matrix (ECM) to form a loose connective tissue. In contrast to the other parts of the TM, JCT cells and ECM fibrils do not form lamellae, but are arranged more irregularly. SC inner wall endothelial cells form giant vacuoles in response to AH flow, as well as intracellular and paracellular pores. In addition, minipores that are covered with a diaphragm are observed. There is considerable evidence that normal AH outflow resistance resides in the inner wall region of SC, which is formed by the JCT and SC inner wall endothelium. Modulation of TM cell tone by the action of their actomyosin system affects TM outflow resistance. In addition, the architecture of the TM outflow pathways and consequently outflow resistance appear to be modulated by contraction of ciliary muscle and scleral spur cells. The scleral spur contains axons that innervate scleral spur cells or that have the ultrastructural characteristics of mechanosensory nerve endings.

Connective tissue growth factor induces extracellular matrix deposition in human trabecular meshwork cells

The major structural change in the human trabecular meshwork (TM) of eyes with primary open-angle glaucoma (POAG) is an increase in extracellular matrix (ECM) in the juxtacanalicular region of the TM. There is evidence that treatment with TGF-beta2 causes an induction of ECM deposition in cultured human TM cells and that TGF-beta2 is causatively involved in the JCT ECM increase in POAG. In the present study, we investigated the effects of connective tissue growth factor (CTGF) on the biology of cultured human TM cells. CTGF is a downstream mediator of TGF-beta2-signaling, which is expressed at high amounts in the human TM in situ. HEK293 cells were transfected with an eukaryotic expression plasmid containing the coding sequences of human CTGF. Secreted CTGF was isolated and purified by chromatography. Primary human TM cells were incubated for 24 h with CTGF at concentrations of 2.5-100 ng/ml. Following treatment with CTGF, the expression of various ECM components that are expressed in the JCT, matrix metalloproteinases (MMPs) and integrins was investigated by real-time RT-PCR and western blot analyses. In addition, the activity of MMPs was investigated by gelatine zymography. The effect of CTGF silencing on TGF-beta2-induced gene expression was investigated by transfection of immortalized HTM cells with CTGF-specific small interfering (si)RNA before TGF-beta2 treatment. CTGF-treated human TM cells showed an increase in the expression of fibronectin, collagen types I, III, IV and VI, as well as in the integrin subunits aV and beta1. Lower concentrations of CTGF caused an autoinduction of CTGF expression. No effects were observed on the expression and activity of MMP-2, MMP-9 and plasminogen activator inhibitor-1 (PAI-1). Transfection with CTGF-specific siRNA inhibited the TGF-beta2-induced upregulation of CTGF and fibronectin. Our results indicate that treatment of human TM cells with recombinant CTGF causes distinct changes in gene expression and that CTGF is a critical mediator of the effects of TGF-beta2 on ECM synthesis in human TM cells. An intriguing aspect supported by the data of the present work is that the pharmacologic modulation of CTGF might be a useful approach to develop novel therapeutic strategies to prevent or to reverse the structural changes that occur in the TM of eyes with POAG.

Structural changes of the trabecular meshwork in different kinds of glaucoma. Exp Eye Res. 2009;88:769-775. [PMID: 19114037 DOI: 10.1016/j.exer.2008.11.025]

The morphology of the trabecular meshwork in three types of open angle glaucoma: primary open angle glaucoma (POAG), corticosteroid-induced glaucoma and pigmentary glaucoma (PG) are described. Ageing is one major risk factor for development of POAG. It is assumed that preexisting age-related changes of the trabecular meshwork (TM) play a role for the development of increased outflow resistance and intraocular pressure (IOP) in various types of glaucoma. These age-related changes in the TM develop concomitant with that of presbyopia. Therefore the functional relationship between ciliary muscle (CM) and TM and the age-related changes in morphology of the outflow system are described first. One main finding in the ageing TM concerns changes of the elastic fiber network and the anterior elastic tendons of the CM. There is an increase in thickness of the sheath of the elastic fibers. Cross-sections through these fibers with their sheath appear as extracellular plaques and were therefore termed "sheath derived plaques" (SD-plaques). Morphologically, the TM changes in POAG resemble that of the ageing TM, but in POAG there is a significant increase in SD-plaques compared to age-matched controls. This increase is due to fine fibrils and other components of the extracellular matrix (ECM) that adhere to the sheaths of the elastic fibers and their connections to the inner wall endothelium. In POAG eyes there is also a marked loss of TM cells, at places leading to fusion and thickening of trabecular lamellae. In steroid-induced glaucoma there is also an increase in fine fibrillar material in the subendothelial region of SC. In contrast to POAG eyes these fibrils do not adhere to the sheath of the elastic fibers but are deposited underneath the inner wall endothelium. The main finding in steroid-induced glaucoma is an accumulation of basement membrane-like material staining for type IV collagen. These accumulations are found throughout all layers of the TM. In pigmentary glaucoma loss of cells was more prominent than in POAG eyes. Presumably, this cell loss occurs after overload of TM cells with pigment granules. Denuded TM lamellae fuse and the TM collapses. In the subendothelial region of these collapsed TM areas an increase in ECM presumably due to underperfusion was observed. At other places SC was occluded and the cribriform region appeared disorganized. In most parts of the circumference of the eye, the TM cells contained pigment granules. Occlusion of TM spaces by pigment granules or cells loaden with pigment was not seen in eyes with PG.

Melanoma associated spongiform scleropathy: characterization, biochemical and immunohistochemical studies

SUMMARY

Melanoma associated spongiform scleropathy (MASS) is a non-inflammatory scleral change with a spongiotic morphology seen in association with uveal melanoma. MASS is seen as whitish spindle shaped areas within the sclera that is adjacent to and in contact with a choroidal or ciliary body melanoma. This change can be seen as small scattered lesions in the inner scleral layers or as extensive areas along the whole extent of contact between the tumour and the sclera and involves most of the scleral thickness. MASS changes of different grades of severity were seen in 38% of 363 melanoma eyes investigated. The presence of MASS showed a statistical correlation with age. A significant high incidence of MASS was found in old age groups. This might due to the fact that MASS needs a longer period of contact between the tumour and the sclera to develop. It is also possible that age-related changes of the extracellular matrix might alter its response to melanoma produced factors leading to the development of MASS. The development of MASS and its severity are influenced by the extent of contact between the tumour and the sclera. This is supported by the significant statistical relation between the largest basal diameter of the tumours and the severity of MASS. Statistical correlation was found between MASS and scleral and extrascleral tumour extension. More than 90% of 82 specimens that showed tumour extension were associated with MASS. A biochemical analysis of scleral samples taken from areas with severe MASS showed a significant reduction of the main amino acids of collagen type I, which is the main scleral collagen. The amounts of total scleral proteins were significantly reduced. This scleral protein reduction is associated with an increase in glycosaminoglycans. These findings indicate a collagen degradation process. Immunohistochemical studies were performed to investigate the expression of matrix metalloproteinases (MMPs). In situ hybridization showed a significantly more frequent and more intense expression of MMP-2 by scleral fibroblasts in areas with MASS compared with areas without MASS. This was also seen by immunohistochemical staining. Similar high frequency and intense expression of MMP-2 were seen in tumour infiltrating macrophages. The results of biochemical and immunohistochemical studies indicate a collagen degradation process. This degradation may be the result of the proteolytic enzyme MMP-2 expressed by scleral fibroblasts under the effect of tumour humeral factors and/or tumour infiltrating macrophages. This scleral degradation results in fragmentation of the scleral collagen fibrils. This along with the accumulation of water in the sclera, as a result of the increase in the production of glycosaminoglycans, results in increase of scleral thickness in MASS areas and forms the histopathological picture of MASS. The scleral degradation may facilitate tumour invasion and may explain the statistical relation between MASS and scleral tumour invasion. MASS was found in a few of the eyes that had received pre-enucleation radiation. The possible explanation is that radiation might cause destruction of scleral fibroblasts reducing their ability to produce MMP-2, thus decreasing the development of MASS. No relation between MASS and survival was found. This is probably explained by the fact that the main cause of death due to uveal melanoma is distant metastasis. MASS changes are found to be associated with local tumour invasion but not statistically correlated to survival.

Extracellular matrix in the trabecular meshwork

The extracellular matrix (ECM) of the trabecular meshwork (TM) is thought to be important in regulating intraocular pressure (IOP) in both normal and glaucomatous eyes. IOP is regulated primarily by a fluid resistance to aqueous humor outflow. However, neither the exact site nor the identity of the normal resistance to aqueous humor outflow has been established. Whether the site and nature of the increased outflow resistance, which is associated with open-angle glaucoma, is the same or different from the normal resistance is also unclear. The ECMs of the TM beams, juxtacanalicular region (JCT) and Schlemm's canal (SC) inner wall are comprised of fibrillar and non-fibrillar collagens, elastin-containing microfibrils, matricellular and structural organizing proteins, glycosaminoglycans (GAGs) and proteoglycans. Both basement membranes and stromal ECM are present in the TM beams and JCT region. Cell adhesion proteins, cell surface ECM receptors and associated binding proteins are also present in the beams, JCT and SC inner wall region. The outflow pathway ECM is relatively dynamic, undergoing constant turnover and remodeling. Regulated changes in enzymes responsible for ECM degradation and biosynthetic replacement are observed. IOP homeostasis, triggered by pressure changes or mechanical stretching of the TM, appears to involve ECM turnover. Several cytokines, growth factors and drugs, which affect the outflow resistance, change ECM component expression, mRNA alternative splicing, cellular cytoskeletal organization or all of these. Changes in ECM associated with open-angle glaucoma have been identified.

Cochlin in the eye: functional implications

Aqueous humor is actively produced in the ciliary epithelium of the anterior chamber and has important functions for the eye. Under normal physiological conditions, the inflow and outflow of the aqueous humor are tightly regulated, but in the pathologic state this balance is lost. Aqueous outflow involves structures of the anterior chamber and experiences most resistance at the level of the trabecular meshwork (TM) that acts as a filter. The modulation of the TM structure regulates the filter and its mechanism remains poorly understood. Proteomic analyses have identified cochlin, a protein of poorly understood function, in the glaucomatous TM but not in healthy control TM from human cadaver eyes. The presence of cochlin has subsequently been confirmed by Western and immunohistochemical analyses. Functionally, cochlin undergoes multimerization induced by shear stress and other changes in the microenvironment. Cochlin along with mucopolysaccharide deposits has been found in the TM of glaucoma patients and in the inner ear of subjects affected by the hearing disorder DNFA9, a late-onset, progressive disease that also involves alterations in fluid shear regimes. In vitro, cochlin induces aggregation of primary TM cells suggesting a role in cell adhesion, possibly in mechanosensation, and in modulation of the TM filter.

'What controls aqueous humour outflow resistance?'

The bulk of aqueous humour outflow resistance is generated in or near the inner wall endothelium of Schlemm's canal in normal eyes, and probably also in glaucomatous eyes. Fluid flow through this region is controlled by the location of the giant vacuoles and pores found in cells of the endothelium of Schlemm's canal, but the flow resistance itself is more likely generated either in the extracellular matrix of the juxtacanalicular connective tissue or the basement membrane of Schlemm's canal. Future studies utilizing in vitro perfusion studies of inner wall endothelial cells may give insights into the process by which vacuoles and pores form in this unique endothelium and why inner wall pore density is greatly reduced in glaucoma.

Changes in aqueous humor dynamics with age and glaucoma

Changes in aqueous humor dynamics with age and in glaucoma have been studied for several decades. More recently, techniques have been developed which confirm earlier studies showing that outflow facility decreases with age and in glaucoma and add the newer finding that uveoscleral outflow also decreases. Morphologic studies in aging and glaucoma eyes have shown an increase in accumulation of extracellular material in both the trabecular meshwork and ciliary muscle and a loss of trabecular meshwork cells, which contribute to this reduction in outflow and result in an increase in intraocular pressure. A reduction in hyaluronic acid and increases in fibronectin and thrombospondin contribute to the change in the extracellular environment. Imbalances in responses to age-related stresses such as oxidative damage to long-lived molecules, protein cross-linking and loss of elasticity could trigger excess production of factors such as transforming growth factor beta, interleukin-1 and CD44S that could stimulate pathways leading to increases in fibronectin, transformation of trabecular meshwork cells to a myoepithelial state and decrease the breakdown in extracellular matrix material, allowing excess to accumulate. Ultimately trabecular outflow and uveoscleral outflow are reduced and intraocular pressure becomes elevated, adding more stress and perpetuating the pathological condition. Future research to identify additional factors and clarify their roles in these processes could lead to alternative therapies for age and glaucoma related changes in the eye.

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.

Confocal microscopic examination of trabecular meshwork removed during ab externo trabeculectomy

AIMS

The aim of the ab externo trabeculectomy (AET) is to remove the external portion of the trabecular meshwork (ETM) responsible for the main aqueous outflow resistance in glaucoma patients, with no opening of the anterior chamber. ETM characteristics were evaluated with a confocal microscope.

METHODS

A prospective comparative observational case series was performed in 60 consecutive medically treated patients with primary open angle glaucoma and eight postmortem normal donors' eyes that underwent AET. Once deroofing the Schlemm' s canal (SC), a deeper dissection led to removal of a coherent membrane (ETM) which allowed satisfactory aqueous egress through the remaining intact internal trabecular meshwork (TM) layers. After fixation with acetone and immunostaining with anti-vimentin antibody, ETM were analysed with a confocal microscope.

RESULTS

Glaucomatous ETM (mean thickness: 29.5 (7.6) micro m) were characterised by a severe paucicellularity compared with the controls (respectively 37.3 (9.7) cells/area and 167.5 (24.9) cells/area, p<10(-4)). ETM analysis showed involvement of both cribriform and corneoscleral layers. ETM cell density was significantly decreased in case of preoperative fluorometholone instillation.

CONCLUSION

Paucicellularity of glaucomatous TM is confirmed by this original technique. Structural characteristics of the ETM, whose removal allows satisfactory aqueous egress, suggest that aqueous outflow resistance not only involves inner wall of SC and juxtacanalicular meshwork but also corneoscleral trabecular layers.

Functional morphology of the trabecular meshwork in primate eyes

The trabecular meshwork forms most of the resistance to aqueous humor outflow needed for maintenance of a pressure gradient between intraocular pressure of approximately 17 mmHg and venous pressure of approximately 10 mmHg. The composition of the extracellular material in the subendothelial or cribriform layer seems to be mainly responsible for outflow resistance. The aqueous humor pathways through the subendothelial layer can be influenced by ciliary muscle contraction and presumably also by contractile elements recently found both in trabecular meshwork and scleral spur. Pharmacologically induced disconnection of inner wall and cribriform cells leads to wash out of extracellular material through breaks of the endothelial lining of Schlemm's canal and to increase of outflow facility. In glaucomatous eyes the resistance to aqueous humor outflow is increased due to an increase in different forms of extracellular material deposited within the cribriform layer. The amount of this newly developed extracellular material is correlated with loss of axons in the optic nerve, indicating that a common factor is responsible for both changes. To investigate the effect of various factors on the biology of trabecular cells monolayer cultures derived from cribriform and corneoscleral trabecular meshwork have been established. The two cell lines can be differentiated because cribriform cells in vivo as in vitro stain for alphabeta-crystallin whereas the corneoscleral cells remain unstained. The effect of TGFbeta, a growth factor increased in aqueous humor of glaucomatous eyes and glycocorticoids on trabecular meshwork cells show typical changes in formation of extracellular matrix components and of stress proteins. Dexamethasone and oxidative damage also lead to increase of trabecular meshwork inducible glucocorticoid response (TIGR) protein. A mutation of the TIGR-gene family has recently been found in families with juvenile and chronic simple glaucoma. Future research has to clarify the significance of these genetic factors for the pathophysiology of glaucoma and the role of trabecular cell activity in this respect.

Glycoproteins of trabecular meshwork, cornea and sclera

PURPOSE

To analyse high-molecular-weight matrix glycoproteins in trabecular meshwork, cornea and sclera using SDS/PAGE and immuno- and lectin blotting.

METHOD

Extracts of normal trabecular meshwork (TM), cornea and sclera were analysed under reducing conditions on SDS/ PAGE. Western blots were stained for total protein, and major high-molecular-weight components were identified by immunoblotting with antibodies to fibronectin (FN) and type VI collagen. Lectin blotting with PSA, MPA and DSA identified some of the glycoprotein glycans.

RESULTS

FN antibody bound to the 240 kDa band in TM, cornea and sclera. Type VI collagen antibody bound more strongly to one band and less so to two other bands at approximately 200 kDA in normal TM and to a ladder of bands in cornea and sclera. PSA and DSA bound at 240, 200 and 140 kDa in TM, cornea and sclera. MPA bound at 240, 200 and 140 kDa in TM and at 240, 200 and approximately 120 kDA in cornea and sclera.

CONCLUSIONS

FN is a component of the band at 240 kDA in TM, cornea and sclera. Normal TM was found to contain relatively more of one of the isoforms of the alpha 3 (VI) chain whilst cornea and sclera contained all the alpha 3 (VI) isoforms. Complex N-linked bi/tri-antennary glycans were localised in FN and the alpha 1, alpha 2 and alpha 3 (VI) chains in TM, cornea and sclera. O-linked glycans (identified by MPA binding) were located in FN and alpha 3 (VI) chains of TM, cornea and sclera.

The extracellular matrix and its modulation in the trabecular meshwork

The extracellular matrix (ECM) in the trabecular meshwork is is believed to be essential for maintenance of the normal outflow system. Excessive, abnormal accumulations of ECM materials have been noted in the trabecular meshwork of eyes obtained from patients with primary open angle glaucoma. This review summarizes the current knowledge regarding the composition of this matrix and the receptors for ECM proteins in the trabecular meshwork. Modulations of the ECM elements by constituents in the aqueous humor after phagocytic challenges and by glucocorticoids are also described. The ECM is known to regulate cell differentiation and cell behavior in a number of systems. It will thus be of particular interest to establish the relationship between the modulated ECM and the functional status of trabecular meshwork cells and to examine the possible relevance of such modulation to outflow resistance.

Human scleral elastic system: an immunoelectron microscopic study

An immunocytochemical study was conducted on elastic components in the sclera of seven aged human eyes. By conventional electron microscopy, elastic tissue consists of three distinct fibre types--elastic fibres, elaunin fibres, and oxytalan fibres. The distribution of six components associated with the elastic system (elastin, amyloid P component, laminin, fibronectin, gp 115, and vitronectin) were studied by immunogold transmission electron microscopy. The codistribution of amyloid P component and laminin was further studied by double immunolabelling. Both elastic and elaunin fibres contained elastin. The microfibrillar sheaths of elastic fibres labelled for amyloid P component, those of elaunin fibres for amyloid P and laminin, and those of oxytalan fibres for laminin only. No labelling was observed for fibronectin, gp 115, and vitronectin. In terms of the proteins investigated, the biochemical profile of the three fibre types was not completely identical and was manifest as different affinities in the binding of serum amyloid P component and an association with laminin.

Immunogold study of non-collagenous matrix components in normal and exfoliative iris

The present investigation was undertaken to determine if some of the components of exfoliation material in iris tissue were unique to exfoliation or were part of normal iris architecture. Eleven normal iris specimens and 10 exfoliative iris specimens were processed for cryoultramicrotomy and London resin white embedding. Immunogold electron microscopy was used to investigate the fine structural distribution of amyloid P component, elastin, entactin, fibronectin, gp115, and vitronectin in normal iris and their association with exfoliation material. Exfoliation material was positive for amyloid P component and possibly gp115, neither of which were present in normal iris tissue. Elastin and fibronectin were present in the normal iris stroma but were not associated with exfoliation material. The distribution of amyloid P component in the vessel lumen and wall led to the conclusion that amyloid P is a serum contaminant. The presence of gp115 in exfoliation material represents the synthesis of a component novel to the iris vascular cell synthetic repertoire.

Localisation of alpha(2,3) and alpha(2,6) linked terminal sialic acid groups in human trabecular meshwork

Sialic acid specific lectins were used to localise isomers of sialyl glycosides in human trabecular meshwork (TM) at the ultrastructural level. A lectin immunogold method demonstrated that sialic groups were concentrated on the endothelial surface of Schlemm's canal (SC) and in the adjacent juxta-canalicular tissue (JCT). One sialyl glycoside, alpha(2,6) linked N-acetyl neuraminic acid, was present mainly on the luminal aspect of the SC endothelium and in the cytoplasm of the JCT cells. Another, alpha(2,3) linked N-acetyl neuraminic acid, was localised predominantly to the extracellular fibrillar material of the JCT. The existence of a topographical segregation of these two sialyl glycosides within the TM supports the view that highly charged anionic molecules may be of significance in regulating aqueous outflow.

Collagens in the aged human macula

Immunogold cytochemistry was used to investigate the fine structural distribution of collagen types I-VI in Bruch's membrane and choroid of the aged human macula. Macular tissue was obtained from ten eyes, and processed for cryoultramicrotomy and London Resin white embedding. Striated collagen fibrils within the inner and outer collagenous layers were found to contain collagen types I, III and V. In addition, type V collagen was also present in the basement membrane of the choriocapillaris. Gross thickening of the choriocapillaris basement membrane was attributed to the deposition of type IV collagen. However, type IV collagen appeared to be absent from the basement membrane of the retinal pigment epithelium. The interesting location of type VI collagen on the choroidal side of the choriocapillaris suggested that its function is to anchor the choriocapillaris onto the choroid. The collagens studied were absent from fibrous banded material, long-spacing collagen, the elastic layer and amorphous granular material. It was concluded that, of the collagen types studied, only the deposition of type IV collagen contributes to the age-related thickening of Bruch's membrane.

Collagens in the aged human macular sclera

Scleral tissue from the region of the human macula was studied by the immunogold labeling technique (cryoultramicrotomy and LR white resin embedding) in an attempt to identify the fine structural distribution of collagen types I-VI. Labeling of the striated collagen fibrils suggested colocalisation of collagen types I, III and V with type V occurring at the fibril surface. Both types V and VI collagen were localised to filamentous strands in the interfibrillar matrix. Collagen types II and IV were absent from the scleral stroma.

Type IV collagen and laminin in Bruch's membrane and basal linear deposit in the human macula

Tissue obtained from the macula in 10 human eyes (53-77 years) was used for an investigation into the extracellular matrices of the retinal pigment epithelium (RPE), Bruch's membrane, and the choriocapillaris. The ultrastructural distribution of type IV collagen and laminin was documented using immunogold labelling. Labelling for type IV collagen was strongly positive in all the specimens in the basement membranes of the choriocapillaris but not that of the RPE where labelling was either weak or absent. Laminin was localised to deposits of granular material in Bruch's membrane but was absent from the basement membrane of the RPE and the choriocapillaris. Basal linear deposit, observed in three cases, demonstrated labelling for laminin but not for type IV collagen. The series was too small for correlation of these morphological changes with age.

Iris vasculopathy in exfoliation syndrome. An immunocytochemical study

Samples of control iris tissue obtained from seven enucleated eyes and nine exfoliative iridectomy specimens were prepared for an immunocytochemical study of the matrix in the walls of iris vessels. The distribution of collagen types I, IV and laminin was studied in normal and exfoliative vessels. Laminin was an integral component of exfoliation material and was present mainly in the matrix of the outer surface of normal vascular cohort cells. The laminin content in the latter location was reduced in vessels in which exfoliation aggregates were not visible. Collagen type IV was absent from exfoliation material. While type I was present in the deposits, it was considered to represent a residue of native normal tissue. Exfoliation deposits appeared to stimulate the synthesis of collagen types I and IV at an early stage of the disease.