Corneal collagens

Corneal aberrations are associated with low-energy meniscus injuries

BACKGROUND

Visual impairment can cause balance problems. Therefore, visual impairment caused by an increase in corneal deviations can lead to sudden and unstable loads in the lower extremities. We aimed to investigate the possible relationship between low-energy meniscal injuries and corneal structural measures.

METHODS

This prospective, observational study included individuals aged between 18-40 years with a normal body-mass index. The study group consisted of 54 patients with grade 2 or 3 meniscus injuries after low-energy activity. The control group consisted of 54 healthy individuals without any complaints in the knee joint. The corneal parameters of all participants were evaluated with a Scheimpflug corneal topography and specular microscopy device. Simulated keratometry (SimK), minimum central corneal thickness (MCCT), cylindrical diopter (ClyD), corneal volume (CVol) spheric aberrations (SphAbb), high-order aberration (HOA), coma values, and endothelial parameters were recorded.

RESULTS

The research and control groups were similar in terms of age, body mass index, and gender distribution. There was no significant difference between the groups in the corneal SimK and CylD, parameters. However, HOA, Coma, SphAbb, and cell variability (Cv) values were significantly higher in the study group, and contrarily MCCT, CVol, and endothelial count (Cd) values were significantly lower.

CONCLUSIONS

Our findings suggest that individuals with relatively lower MCCT values tend to develop meniscal damage after low-energy activity. Hence, the loss of corneal strength in these patients may be a sign of possible weakness in the meniscus. The HOA value above 0.26, the coma value above 0.16, and the SphAbb value above 0.1 may significantly increase the possible meniscus injury.

Application of biomaterials and nanotechnology in corneal tissue engineering

Corneal diseases are among the most common causes of blindness worldwide. Regardless of the etiology, corneal opacity- or globe integrity-threatening conditions may necessitate corneal replacement procedures. Several procedure types are currently available to address these issues, based on the complexity and extent of injury. Corneal allograft or keratoplasty is considered to be first-line treatment in many cases. However, a significant proportion of the world's population are reported to have no access to this option due to limitations in donor preparation. Thus, providing an appropriate, safe, and efficient synthetic implant (e.g., artificial cornea) may revolutionize this field. Nanotechnology, with its potential applications, has garnered a lot of recent attention in this area, however, there is seemingly a long way to go. This narrative review provides a brief overview of the therapeutic interventions for corneal pathologies, followed by a summary of current biomaterials used in corneal regeneration and a discussion of the nanotechnologies that can aid in the production of superior implants.

Myopic regression and recurrent Salzmann nodule degeneration after laser in situ keratomileusis in Ehlers Danlos Syndrome

PURPOSE

We describe the first case of Ehlers Danlos Syndrome (EDS) reported in the English language ophthalmic literature to have undergone Laser In Situ Keratomileusis (LASIK) surgery.

OBSERVATIONS

We review our patient's specific postoperative complications of myopic regression, Salzmann nodular degeneration, and dry eye syndrome, as well as the risks and consequences of performing LASIK on patients with this collagen disorder.

CONCLUSIONS AND IMPORTANCE

Refractive errors may prompt EDS patients to seek laser vision correction, placing them at increased risk for complications such as myopic regression, keratectasia, and dry eye syndrome. Aberrant wound healing and collagen dysfunction may have influenced our patient's myopic regression and Salzmann nodule degeneration post-LASIK. Currently, EDS is considered a relative contraindication in LASIK due to a presumed higher risk of postoperative keratectasia; however, we believe it is possible that not all forms of EDS need to be an absolute contraindication to LASIK. More research is warranted to determine preoperative risk stratification for laser vision surgery in each subtype of EDS.

Development of Transparent Acellular Dermal Matrix as Tissue-Engineered Stroma Substitute for Central Lamellar Keratoplasty

Purpose

To improve the transparency of the acellular dermal matrix (ADM) and investigate the optical, mechanical and histologic properties and biocompatibility of transparent ADM (TADM) in lamellar keratoplasty.

Methods

A stepwise sectioning strategy was applied to determine the transparency distribution of the ADM, and TADM was fabricated accordingly. Transmittance measurements, uniaxial tension testing, and histologic staining were applied to detect its properties. Lamellar keratoplasty was performed in rabbits with TADM, and postoperative evaluations were conducted including the transmittance of the transplant area and histologic staining.

Results

The transmittance of the ADM increased with increasing depth, and TADM was isolated mechanically at the deepest level. There was a significant improvement in the transmittance of the TADM compared with the ADM, and no significant difference in transmittance between dehydrated TADM and cornea was observed. The elastic modulus of TADM was significantly stronger than that of normal cornea (P = 0.004). TADM consisted of dense collagen fibrils, mainly collagen type I, and the collagen fibril diameter and interfibrillar spacing were determined to be larger than corneal stroma. After lamellar keratoplasty in rabbits, the TADM was well integrated with the host cornea, and transparent cornea without neovascularization was observed at 6 months. Re-epithelization was completed at 1 month, and keratocyte repopulation and collagen remodeling were observed in the graft 3 and 6 months after surgery.

Conclusions

This study presents the transparency distribution of the ADM and a method for obtaining TADM, which demonstrates ideal transparency, strong mechanical properties, and satisfactory biocompatibility when applied in lamellar keratoplasty.

Effect of congenital blepharoptosis on corneal biomechanical properties and changes after ptosis surgery

OBJECTIVES

We studied the difference in the corneal biomechanical parameters of ptotic and fellow eyes in patients with congenital blepharoptosis. The correlations between corneal biomechanical parameters and demographic or ocular parameters, and the changes after surgery were also researched.

METHODS

The corneal biomechanical parameters were measured by Corvis ST tonometry. The central corneal thickness (CCT), axial length (AL) and keratometry measurements were performed with LenStar LS900, and intraocular pressure (IOP) by non-contact applanation tonometry. The parameters were evaluated for the effect of ptosis and the relationship of corneal biomechanical parameters. These examinations were repeated 6 months after blepharoptosis surgery.

RESULTS

Twenty-nine patients were enroled. The Corvis ST parameters (Deformation amplitude [DA], A1 times, and A1 velocity), CCT, IOP with NCT, IOP with corrected, differed significantly between ptotic and fellow eyes. CCT was significantly positively correlated with Length A1 and IOP with Corvis, and negatively correlated with IOP corrected by Corvis of the ptotic eyes. The same tendency was found in the fellow eyes. Six months after the ptosis surgery, the differences in corneal biomechanics parameters between ptotic eyes and fellow eyes were not significantly changed.

CONCLUSIONS

Congenital blepharoptosis causes significant corneal biomechanical changes measured by Corvis ST. The ptotic eyes had thicker and less deformable corneas. The differences in corneal biomechanics between ptotic eyes and fellow eyes were mostly related to CCT changes. Six months after surgery, these differences in corneal biomechanics did not change significantly.

An Update on Corneal Biomechanics and Architecture in Diabetes

In the last decade, we have witnessed substantial progress in our understanding of corneal biomechanics and architecture. It is well known that diabetes is a systemic metabolic disease that causes chronic progressive damage in the main organs of the human body, including the eyeball. Although the main and most widely recognized ocular effect of diabetes is on the retina, the structure of the cornea (the outermost and transparent tissue of the eye) can also be affected by the poor glycemic control characterizing diabetes. The different corneal structures (epithelium, stroma, and endothelium) are affected by specific complications of diabetes. The development of new noninvasive diagnostic technologies has provided a better understanding of corneal tissue modifications. The objective of this review is to describe the advances in the knowledge of the corneal alterations that diabetes can induce.

Endogenous fluorescence can differentiate the keratoconic cornea

The purpose of the study was to investigate the endogenous fluorescence of the keratoconic cornea in order to analyze changes in the spectra due to the keratoconic stroma abnormalities. Twenty-two corneal buttons obtained from patients with keratoconus (KC, N = 22) at the time of penetrating keratoplasty were used. As a reference, twelve normal corneas (N = 12): ten from the Eye Bank and two from enucleated eyes due to choroidal melanoma were used. The fluorescence excitation/emission matrices (EEM) in the ranges of 250-400/260-600 nm were recorded. Healthy cornea, keratoconic cornea and sclera showed three main EEM bands, which correspond to the following fluorophores: tryptophan residues in the proteoglycan fraction of corneal/scleral stromas, naturally occurring collagen cross-links and the NAD(P)H fraction present in the metabolically active cells. Relative intensity factors S₁, S₂ and S₃ describing the contribution of each kind of fluorophore to the total fluorescence of the tissue were calculated. Normal and keratoconic corneas show qualitatively similar fluorescence matrices, but the statistically significant differences in the mean values of the S₁, S₂ and S₃ parameters for the KC and normal corneas were observed indicating changes in contribution of different fluorophores to the whole fluorescence of the tissue. Moreover, differences between multidimensional distribution of the relative intensity factors S₁, S₂ and S₃ between these groups were demonstrated (p < 0.001). In conclusions: Differences in the relative intensity factors calculated on a basis of the fluorescence spectra can correspond to the changes found in the KC stroma regarding natural collagen cross-links and the proteoglycan fraction. These parameters well differentiate the KC and normal corneas that could serve as an additional tool for the keratoconus characterization.

Unravelling the stromal-nerve interactions in the human diabetic cornea

Corneal defects due to diabetes mellitus (DM) may cause severe vision impairments. Current studies focus on the corneal epithelium and nerve defects neglecting the corneal stroma. The aim of this study was to develop a 3D in vitro model to examine the interactions between corneal stroma and nerves in the context of DM. Primary human corneal stromal fibroblasts isolated from healthy (HCFs), Type 1 (T1DM) and Type 2 (T2DM) patients were stimulated with stable ascorbic acid to secrete and assemble an extracellular matrix (ECM). Human neuronal cells were then seeded on top and differentiated to create the 3D co-cultures. Our data revealed successful co-culture of stromal fibroblasts and neuronal cells with large elongated neuron extensions. T2DM showed significant upregulation of Collagen III and IGF1 when compared to T1DM. Interestingly, upon nerve addition, those markers returned to HCF levels. Neuronal markers were also differentially modulated with T2DM co-cultures expressing high levels of βIII tubulin where T1DM co-cultures expressed Substance P. . Overall, our unique 3D co-culture model provides us with a tool that can be utilized for both molecular and therapeutic studies for diabetic keratopathy.

Manipulating mammalian cell morphologies using chemical-mechanical polished integrated circuit chips

Tungsten chemical-mechanical polished integrated circuits were used to study the alignment and immobilization of mammalian (Vero) cells. These devices consist of blanket silicon oxide thin films embedded with micro- and nano-meter scale tungsten metal line structures on the surface. The final surfaces are extremely flat and smooth across the entire substrate, with a roughness in the order of nanometers. Vero cells were deposited on the surface and allowed to adhere. Microscopy examinations revealed that cells have a strong preference to adhere to tungsten over silicon oxide surfaces with up to 99% of cells adhering to the tungsten portion of the surface. Cells self-aligned and elongated into long threads to maximize contact with isolated tungsten lines as thin as 180 nm. The orientation of the Vero cells showed sensitivity to the tungsten line geometric parameters, such as line width and spacing. Up to 93% of cells on 10 μm wide comb structures were aligned within ± 20° of the metal line axis. In contrast, only ~22% of cells incubated on 0.18 μm comb patterned tungsten lines were oriented within the same angular interval. This phenomenon is explained using a simple model describing cellular geometry as a function of pattern width and spacing, which showed that cells will rearrange their morphology to maximize their contact to the embedded tungsten. Finally, it was discovered that the materials could be reused after cleaning the surfaces, while maintaining cell alignment capability.

Establishment of a 3D In Vitro Model to Accelerate the Development of Human Therapies against Corneal Diabetes

PURPOSE

To establish an in vitro model that would mirror the in vivo corneal stromal environment in diabetes (DM) patients.

METHODS

Human corneal fibroblasts from Healthy (HCFs), Type 1DM (T1DM) and Type 2DM (T2DM) donors were isolated and cultured for 4 weeks with Vitamin C stimulation in order to allow for extracellular matrix (ECM) secretion and assembly.

RESULTS

Our data indicated altered cellular morphology, increased cellular migration, increased ECM assembly, and severe mitochondrial damage in both T1DM and T2DMs when compared to HCFs. Furthermore, we found significant downregulation of Collagen I and Collagen V expression in both T1DM and T2DMs. Furthermore, a significant up regulation of fibrotic markers was seen, including α-smooth muscle actin in T2DM and Collagen III in both T1DM and T2DMs. Metabolic analysis suggested impaired Glycolysis and Tricarboxylic acid cycle (TCA) pathway.

CONCLUSION

DM has significant effects on physiological and clinical aspects of the human cornea. The benefits in developing and fully characterizing our 3D in vitro model are enormous and might provide clues for the development of novel therapeutics.

Corneal regenerative medicine

Recently, regenerative medicine has become a highlighted field because it has great potential to induce a paradigm shift of supportive conventional therapy into definitive treatment. The cornea is the avascular, transparent, dome-shaped outermost layer of the eyeball, and it consists of three layers: epithelium, stroma, and endothelium. Conventional corneal transplantation, known as keratoplasty, has two main problems, a donor shortage and immunological rejection. Therefore, regenerative medicine has been applied to overcome these challenges. Regenerative medicine involving the corneal epithelium has been clinically applied, along with an understanding of corneal epithelial stem cell biology, earlier than that of the corneal stroma or endothelium. Thus, the effectiveness and safety of cultivated corneal or oral mucosal epithelial cell sheet transplantation have been reported by many researchers. Clinical studies on regenerative medicine for corneal stroma or endothelium have begun after basic and nonclinical study. Translational research has been performed to make corneal regenerative medicine a universal therapy. This article reviews corneal regenerative medicine.

A novel explanation of corneal clouding in a bone marrow transplant-treated patient with Hurler syndrome

One common complication of mucopolysaccharidosis I-Hurler (MPS1-H) is corneal clouding, which occurs despite current treatments, including bone marrow transplantation. Human corneas were obtained from a 14 year old subject with MPS1-H and visual disability from progressive corneal clouding despite a prior bone marrow transplant at age 2. This was compared to a cornea from a 17 year old donated to our eye bank after his accidental death. The corneas were analyzed microscopically after staining with Alcian blue, antibodies to collagen I, IV, VI, and α-smooth muscle actin. Differences in levels of expression of the indicated molecules were assessed. Corneas from Hurler and control mice were examined similarly to determine potential mechanistic overlap. The MPS1-H subject cornea showed elevations in mucopolysaccharide deposition. The MPS1-H and Hurler mice corneas showed increased and disorganized expression of collagen I and IV relative to the control corneas. The MPS1-H corneas also showed increased and disordered expression of collagen VI. Positive expression of α-smooth muscle actin indicated myofibroblast conversion within the MPS1-H cornea in both the patient and mutant mouse material compared to normal human and control mouse cornea. Increased deposition of collagens and smooth muscle actin correlate with corneal clouding, providing a potential mechanism for corneal clouding despite bone marrow transplantation in MPS1-H patients. It might be possible to prevent or slow the onset of corneal clouding by treating the cornea with drugs known to prevent myofibroblast conversion.

Inhibition by all-trans retinoic acid of collagen degradation mediated by corneal fibroblasts

BACKGROUND

We examined the effect of all-trans retinoic acid on collagen degradation mediated by corneal fibroblasts.

METHODS

Rabbit corneal fibroblasts were cultured with or without all-trans retinoic acid in a three-dimensional collagen gel, and the extent of collagen degradation was determined by measurement of hydroxyproline in acid hydrolysates of culture supernatants. Matrix metalloproteinase expression was examined by immunoblot analysis and gelatin zymography. The abundance and phosphorylation state of the endogenous nuclear factor-kappaB inhibitor IκB-α were examined by immunoblot analysis. Corneal ulceration was induced by injection of lipopolysaccharide into the central corneal stroma of rabbits and was assessed by observation with a slitlamp microscope.

RESULTS

All-trans retinoic acid inhibited interleukin-1β-induced collagen degradation by corneal fibroblasts in a concentration- and time-dependent manner. It also attenuated the release and activation of matrix metalloproteinases as well as the phosphorylation and degradation of IκB-α induced by interleukin-1β in these cells. Topical application of all-trans retinoic acid suppressed corneal ulceration induced by injection of lipopolysaccharide into the corneal stroma.

CONCLUSIONS

All-trans retinoic acid inhibited collagen degradation mediated by corneal fibroblasts exposed to interleukin-1β, with this effect being accompanied by suppression of nuclear factor-kappaB signalling as well as of matrix metalloproteinase release and activation in these cells. All-trans retinoic acid also attenuated lipopolysaccharide-induced corneal ulceration in vivo. Our results therefore suggest that all-trans retinoic acid might prove effective for the treatment of patients with corneal ulceration.

New insight into the shortening of the collagen fibril D-period in human cornea

Collagen fibrils type I display a typical banding pattern, so-called D-periodicity, of about 67 nm, when visualized by atomic force or electron microscopy imaging. Herein we report on a significant shortening of the D-period for human corneal collagen fibrils type I (21 ± 4 nm) upon air-drying, whereas no changes in the D-period were observed for human scleral collagen fibrils type I (64 ± 4 nm) measured under the same experimental conditions as the cornea. It was also found that for the corneal stroma fixed with glutaraldehyde and air-dried, the collagen fibrils show the commonly accepted D-period of 61 ± 8 nm. We used the atomic force microscopy method to image collagen fibrils type I present in the middle layers of human cornea and sclera. The water content in the cornea and sclera samples was varying in the range of .066-.085. Calculations of the D-period using the theoretical model of the fibril and the FFT approach allowed to reveal the possible molecular mechanism of the D-period shortening in the corneal collagen fibrils upon drying. It was found that both the decrease in the shift and the simultaneous reduction in the distance between tropocollagen molecules can be responsible for the experimentally observed effect. We also hypothesize that collagen type V, which co-assembles with collagen type I into heterotypic fibrils in cornea, could be involved in the observed shortening of the corneal D-period.

The tissue-engineered human cornea as a model to study expression of matrix metalloproteinases during corneal wound healing

Corneal injuries remain a major cause of consultation in the ophthalmology clinics worldwide. Repair of corneal wounds is a complex mechanism that involves cell death, migration, proliferation, differentiation, and extracellular matrix (ECM) remodeling. In the present study, we used a tissue-engineered, two-layers (epithelium and stroma) human cornea as a biomaterial to study both the cellular and molecular mechanisms of wound healing. Gene profiling on microarrays revealed important alterations in the pattern of genes expressed by tissue-engineered corneas in response to wound healing. Expression of many MMPs-encoding genes was shown by microarray and qPCR analyses to increase in the migrating epithelium of wounded corneas. Many of these enzymes were converted into their enzymatically active form as wound closure proceeded. In addition, expression of MMPs by human corneal epithelial cells (HCECs) was affected both by the stromal fibroblasts and the collagen-enriched ECM they produce. Most of all, results from mass spectrometry analyses provided evidence that a fully stratified epithelium is required for proper synthesis and organization of the ECM on which the epithelial cells adhere. In conclusion, and because of the many characteristics it shares with the native cornea, this human two layers corneal substitute may prove particularly useful to decipher the mechanistic details of corneal wound healing.

Corneal Collagen Cross-Linking in the Treatment of Progressive Keratoconus: A Randomized Controlled Contralateral Eye Study

BACKGROUND

To assess the short-term efficacy and safety of corneal collagen cross-linking (CXL) in preventing the progression of keratoconus (KCN).

MATERIALS AND METHODS

This randomized controlled clinical trial enrolled 26 patients diagnosed with bilateral progressive KCN and were eligible for CXL. In each patient, one eye was randomly selected for treatment, and the contralateral eye served as the control. The patients underwent CXL with riboflavin drops and ultraviolet radiation in the treated eye. One year follow-up data are presented. Postoperatively, patients were assessed for progression of KCN, visual changes, and other findings. The main outcome measures were maximum simulated keratometry (K-max), best spectacle-corrected visual acuity (BSCVA), and average simulated keratometry. P <0.05 was considered as statistically significant.

RESULTS

In the treated eyes, the mean K-max values decreased by 0.22 D at 1-year postoperatively and increased by 0.41 D in the control group. This difference was statistically significant (P < 0.001). BSCVA improved slightly (a decrease of 0.13 LogMAR) and decreased slightly in the control group (a 0.01 LogMAR increase). The difference between groups was statistically significant (P = 0.014). There was no decrease in visual acuity attributable to complications of CXL in the treated eyes. At 1-year, the keratometry in 3 (12%) treated eyes increased by more than 0.50 D and were considered cases of failed treatment.

CONCLUSION

Preliminary and 1-year results indicate CXL can halt the progression of KCN in most cases without causing serious complications.

Expression Profiles of Neuropeptides, Neurotransmitters, and Their Receptors in Human Keratocytes In Vitro and In Situ

Keratocytes, the quiescent cells of the corneal stroma, play a crucial role in corneal wound healing. Neuropeptides and neurotransmitters are usually associated with neuronal signaling, but have recently been shown to be produced also by non-neuronal cells and to be involved in many cellular processes. The aim of this study was to assess the endogenous intracellular and secreted levels of the neuropeptides substance P (SP) and neurokinin A (NKA), and of the neurotransmitters acetylcholine (ACh), catecholamines (adrenaline, noradrenaline and dopamine), and glutamate, as well as the expression profiles of their receptors, in human primary keratocytes in vitro and in keratocytes of human corneal tissue sections in situ. Cultured keratocytes expressed genes encoding for SP and NKA, and for catecholamine and glutamate synthesizing enzymes, as well as genes for neuropeptide, adrenergic and ACh (muscarinic) receptors. Keratocytes in culture produced SP, NKA, catecholamines, ACh, and glutamate, and expressed neurokinin-1 and -2 receptors (NK-1R and NK-2R), dopamine receptor D₂, muscarinic ACh receptors, and NDMAR1 glutamate receptor. Human corneal sections expressed SP, NKA, NK-1R, NK-2R, receptor D₂, choline acetyl transferase (ChAT), M₃, M₄ and M₅ muscarinic ACh receptors, glutamate, and NMDAR1, but not catecholamine synthesizing enzyme or the α₁ and β₂ adrenoreceptors, nor M₁ receptor. In addition, expression profiles assumed significant differences between keratocytes from the peripheral cornea as compared to those from the central cornea, as well as differences between keratocytes cultured under various serum concentrations. In conclusion, human keratocytes express an array of neuropeptides and neurotransmitters. The cells furthermore express receptors for neuropeptides/neurotransmitters, which suggests that they are susceptible to stimulation by these substances in the cornea, whether of neuronal or non-neuronal origin. As it has been shown that neuropeptides/neurotransmitters are involved in cell proliferation, migration, and angiogenesis, it is possible that they play a role in corneal wound healing.

Human Keratoconus Cell Contractility is Mediated by Transforming Growth Factor-Beta Isoforms

Keratoconus (KC) is a progressive disease linked to defects in the structural components of the corneal stroma. The extracellular matrix (ECM) is secreted and assembled by corneal keratocytes and regulated by transforming growth factor-β (TGF-β). We have previously identified alterations in the TGF-β pathway in human keratoconus cells (HKCs) compared to normal corneal fibroblasts (HCFs). In our current study, we seeded HKCs and HCFs in 3D-collagen gels to identify variations in contractility, and expression of matrix metalloproteases (MMPs) by HKCs in response the TGF-β isoforms. HKCs showed delayed contractility with decreased Collagen I:Collagen V ratios. TGF-β1 significantly increased ECM contraction, Collagen I, and Collagen V expression by HKCs. We also found that HKCs have significantly decreased Collagen I:Collagen III ratios suggesting a potential link to altered collagen isoform expression in KC. Our findings show that HKCs have significant variations in collagen secretion in a 3D collagen gel and have delayed contraction of the matrix compared to HCFs. For the first time, we utilize a collagen gel model to characterize the contractility and MMP expression by HKCs that may contribute to the pathobiology of KC.

A genetic anomaly of oriented collagen biosynthesis and cross-linking: Keratoconus

Oriented collagen biosynthesis is one of the major mechanisms involved in tissue and organ formation during development. Corneal biogenesis is one example. Defects in this process lead to anomalies in tissue structure and function. The transparency of cornea and its achievement are a good example as well as its pathological modifications. Keratoconus is one example of this type of pathologies, involving also inappropriate cross-linking of collagen fibers. Among the tentatives to correct this anomaly, the riboflavin-potentiated UV-cross-linking (CXL) of keratoconus corneas appears clinically satisfactory, although none of the experiments and clinical results published prove effective cross-linking. The published results are reviewed in this article.

In-body tissue-engineered collagenous connective tissue membranes (BIOSHEETs) for potential corneal stromal substitution

There is a severe shortage of donor cornea for transplantation in many countries. Collagenous connective tissue membranes, named BIOSHEETs, grown in vivo were successfully implanted in rabbit corneal stroma for in vivo evaluation of their suitability as a corneal stromal substitute to solve this global donor shortage. BIOSHEETs were prepared by embedding silicone moulds into dorsal subcutaneous pouches in rabbits for 1 month and stored in glycerol. After re-swelling in saline and trephining, disk-shaped BIOSHEETs (4 mm diameter) were allogeneically implanted into stromal pockets prepared in the right cornea of seven rabbits. Clinical tests for corneal thickness and transparency, and tissue analyses were performed. Because the BIOSHEETs (thickness, 131 ± 14 µm) obtained were opaque immediately after implantation, the transparency of the cornea decreased. The total thickness of the BIOSHEET-implanted cornea increased from 364 ± 21.0 µm to 726 ± 131 µm. After 4 weeks' implantation, the thickness of the cornea stabilized (493 ± 80 µm at 4 weeks and 447 ± 46 µm at 8 weeks). The transparency of the cornea increased progressively with time of implantation. The random orientation of collagen fibrils in the original BIOSHEETs tended to be homogeneous, similar to that of the native stroma. No inflammatory cells accumulated and fibroblast-like cells infiltrated the implant. The BIOSHEETs showed high biocompatibility with stromal tissues; however, further studies are needed to test its functional aspects. Although this research is only intended as a proof of concept, BIOSHEETs may be considered a feasible corneal stromal replacement, especially for treating visual impairment caused by stromal haze. Copyright © 2013 John Wiley & Sons, Ltd.

Fibronectin antibody labels corneal stromal collagen fibrils in situ along their length and circumference and demonstrates distinct staining along the cell and stromal interfaces of Descemet's membrane

PURPOSE/AIM OF THE STUDY

An immunoperoxidase cytochemical study of fibronectin localization in the rat corneal stroma and Descemet's membrane was conducted following organ culture to determine whether stromal swelling allowed better primary antibody penetration into the normally tough fibrous corneal stroma.

MATERIALS AND METHODS

Following 24 h organ culture, corneas were fixed in 4% paraformaldehyde, washed and stained overnight at 4 °C in anti-fibronectin followed by washing and incubation in an appropriate secondary antibody and exposure to protein A-HRP. Cytochemical processing was carried out in a DAB-containing medium followed by dehydration and Epon embedding.

RESULTS

Observations of the stromal lamellae revealed the presence of a novel punctate staining pattern along the length of the collagen fibrils that extended around the fibril's circumference. Measurements on the peroxidase reaction product spacing indicated a periodicity of approximately 20.69 ± 3.57 nm along the fibril's length. Light microscopic immunocytochemistry revealed the presence of fibronectin staining occurred within the endothelial cell layer but only along the DM/stromal interface. Electron microscopic observations however, revealed that fibronectin staining occurred in distinct linear patterns along the length of both the endothelial and stromal DM interfaces.

DISCUSSION

Results indicate that organ culture mediated swelling helps facilitate the penetration of primary antibody into the corneal stroma. Observations suggest a novel association exists between fibronectin and stromal collagen fibrils that helps to mediate the arrangement and organization of the stromal extracellular matrix. Results also definitively indicate that fibronectin is deposited along both DM interfaces suggesting that it plays a role in the adhesion of both the endothelial cell layer and stroma to Descemet's membrane to help maintain the tissue architecture within this region of the cornea.

Resistance of corneal RFUVA–cross-linked collagens and small leucine-rich proteoglycans to degradation by matrix metalloproteinases

PURPOSE

Extracellular matrix metalloproteinases (MMPs) are thought to play a crucial role in corneal degradation associated with the pathological progression of keratoconus. Currently, corneal cross-linking by riboflavin and ultraviolet A (RFUVA) has received significant attention for treatment of keratoconus. However, the extent to which MMPs digest cross-linked collagen and small leucine-rich proteoglycans (SLRPs) remains unknown. In this study, the resistance of RFUVA-cross-linked collagens and SLRPs to MMPs has been investigated.

METHODS

To investigate the ability of MMPs to digest cross-linked collagen and SLRPs, a model reaction system using purified collagen type I, type IV, and nonglycosylated, commercially available recombinant SLRPs, keratocan, lumican, mimecan, decorin, and biglycan in solution in vitro has been compared using reactions inside an intact bovine cornea, ex vivo.

RESULTS

Our data demonstrate that corneal cross-linked collagen type I and type IV are resistant to cleavage by MMP-1, MMP-2, MMP-9, and MMP-13, whereas non-cross-linked collagen I, IV, and natively glycosylated SLRPs are susceptible to degradation by MMPs. In addition, both cross-linked SLRPs themselves and cross-linked polymers of SLRPs and collagen appear able to resist degradation. These results suggest that the interactions between SLRPs and collagen caused by RFUVA protect both SLRPs and collagen fibrils from cleavage by MMPs.

CONCLUSIONS

A novel approach for understanding the biochemical mechanism whereby RFUVA cross-linking stops keratoconus progression has been achieved.

Spatiotemporal expression of the dermatopontin gene in zebrafish Danio rerio

There has been significant interest in the expression and function of dermatopontin (DPT) in mammals owing to recent evidence pointing to its critical role in collagen fibrillogenesis. Despite this interest, limited information is available about the site/s of DPT mRNA expression or changes in expression in vivo. We used reverse-transcription polymerase chain reaction and in situ hybridization to evaluate the spatial and temporal pattern of DPT mRNA expression in zebrafish, Danio rerio, a widely used vertebrate model. We observed that DPT transcripts were expressed in zebrafish embryos at all developmental stages in a range of tissues, including the brain and optic neuron cells. Based on our results, we hypothesize that DPT may also play a role in neural functions in vivo.

Corneal reinforcement using an acellular dermal matrix for an analysis of biocompatibility, mechanical properties, and transparency

The aim of this study was to analyze the viability of using an acellular dermal matrix (ADM) as a reinforcement material for peripheral corneal thinning disease. The complete removal of cell components was confirmed by hematoxylin and eosin (H&E) and 4',6-diamidino-2-phenylindole (DAPI) staining. Transmission electron microscopy determined that the stromal structure was well preserved. Uniaxial tests revealed that the ADM had strong mechanical properties. After being implanted into rabbit cornea the ADM showed no sign of rejection and even achieved good transparency 24weeks post-surgery. H&E staining demonstrated that keratocytes grew in the ADM and the ADM-cornea interface became blurry. Picrosirius red staining revealed great changes of collagen in the ADM. Uniaxial testing of the reinforced cornea showed better mechanical strength than the normal rabbit cornea, but this did not exhibit statistical significance. These results suggest that ADM is a worthy candidate for future exploration as a reinforcement material for peripheral corneal thinning problems.

[Eye connective tissues: cornea and vitreous body]

The authors, ophtalmologist (Y.P.) and basic scientists (J.L.-R and L.R.), collaborated on eye-research since 1962 on normal and pathological aspects of eye tissues, considered as specialized forms of connective tissues, and on specific aspects of the physiology and pathology of the eye. This date coincides with the foundation of the French Society of Connective Tissues, which celebrates the 50th anniversary of its creation. We shall present here some of our work on the ontogenetic and phylogenetic aspects of the cornea, on its structure, function and regulation in normal and pathological states, taken from a large number of publications of our laboratories. Our work on cornea started with the study of the morphogenesis of its lamellar structure, made of collagen fibers and proteoglycans. This led us to the isolation and characterization of structural (or matrix) glycoproteins, a new class of matrix components, present also in all other connective tissues, and to the study of their biosynthesis by keratocytes. Corneal wounds and regeneration were also studied, as well as some corneal pathologies such as keratoconus. The confrontation of quantitative morphological methods with biochemical procedures were to yield important results on the mechanisms of the maintenance of corneal structure and function. Another series of studies concerned the vitreous where we detected, besides previously characterized components, such as hyaluronan and collagens, fibronectin which plays an important role in the adhesion of hyaluronan to the collagen network. Its age-dependent modifications were also studied, with a special focus on the role of reactive oxygen species (ROS)-mediated degradation of hyaluronan, especially important for the aging of the vitreous.

Central corneal thickness in patients with systemic sclerosis: a controlled study

PURPOSE

To compare the central corneal thickness (CCT) of patients with systemic sclerosis (SSc) and control subjects.

METHODS

The study group comprised 37 consecutive patients with SSc, and the control group comprised 23 healthy individuals similar in age and sex. CCT value was measured by ultrasound pachymetry.

RESULTS

In the SSc group, the mean CCT in the right eye was 534.9 ± 33.5 μm and 536.9 ± 32.4 μm in the left eye. In the control group, the mean CCT was 533.0 ± 32.9 μm in the right eye and 533.1 ± 33.6 μm in the left eye. The mean CCT was not significantly different in the SSc group compared with the control group for both the right (P = 0.83) and left (P = 0.67) eyes.

CONCLUSIONS

CCT measurements do not significantly differ in patients with SSc compared with healthy control subjects.

Rapid isothermal substrate microfabrication of a biocompatible thermoplastic elastomer for cellular contact guidance

The use of microstructured substrates to study and influence cell orientation, which plays an important role in tissue functionality, has been of great interest lately. Silicon and poly(dimethylsiloxane) substrates have typically been used, but long processing times and exogenous protein surface coating, required to enhance cell viability, limit their use as large-scale platforms. There is thus a need for a non-biodegradable biocompatible substrate that allows rapid and low cost microfabrication. In this paper a styrene-(ethylene/butylene)-styrene block co-polymer (SEBS) microstructured by a rapid replication technique using low pressure an isothermal hot embossing approach has been demonstrated. SEBS substrates were treated with oxygen plasma to enhance cell adhesion and sterilized using ethylene oxide gas. While cell adhesion to and proliferation on these substrates was as good as on tissue culture polystyrene, cellular alignment on microstructured SEBS was also very high (97.7±0.5%) when calculated within a 10° angle variation from the longitudinal axis. Furthermore, tissue sheets on microstructured SEBS have been produced and exhibited cellular alignment within the engineered tissue. In addition, these results were obtained without coating the material with exogenous proteins. Such substrates should be helpful in the culture of tissue engineered substitutes with an intrinsic orientation and to elucidate questions in cell biology.

Effects of ultraviolet-A and riboflavin on the interaction of collagen and proteoglycans during corneal cross-linking

Corneal cross-linking using riboflavin and ultraviolet-A (RFUVA) is a clinical treatment targeting the stroma in progressive keratoconus. The stroma contains keratocan, lumican, mimecan, and decorin, core proteins of major proteoglycans (PGs) that bind collagen fibrils, playing important roles in stromal transparency. Here, a model reaction system using purified, non-glycosylated PG core proteins in solution in vitro has been compared with reactions inside an intact cornea, ex vivo, revealing effects of RFUVA on interactions between PGs and collagen cross-linking. Irradiation with UVA and riboflavin cross-links collagen α and β chains into larger polymers. In addition, RFUVA cross-links PG core proteins, forming higher molecular weight polymers. When collagen type I is mixed with individual purified, non-glycosylated PG core proteins in solution in vitro and subjected to RFUVA, both keratocan and lumican strongly inhibit collagen cross-linking. However, mimecan and decorin do not inhibit but instead form cross-links with collagen, forming new high molecular weight polymers. In contrast, corneal glycosaminoglycans, keratan sulfate and chondroitin sulfate, in isolation from their core proteins, are not cross-linked by RFUVA and do not form cross-links with collagen. Significantly, when RFUVA is conducted on intact corneas ex vivo, both keratocan and lumican, in their natively glycosylated form, do form cross-links with collagen. Thus, RFUVA causes cross-linking of collagen molecules among themselves and PG core proteins among themselves, together with limited linkages between collagen and keratocan, lumican, mimecan, and decorin. RFUVA as a diagnostic tool reveals that keratocan and lumican core proteins interact with collagen very differently than do mimecan and decorin.

Effect of aging on corneal biomechanical parameters using the ocular response analyzer

PURPOSE

To assess the effect of aging on corneal biomechanical parameters in a normal population.

METHODS

We prospectively examined 204 normal eyes of 204 healthy Japanese volunteers (68 men, 136 women; mean age 46.7+/-19.4 years [range: 19 to 89 years]). Corneal hysteresis, corneal resistance factor, corneal-compensated intraocular pressure (IOP(cc)), and Goldmann-correlated intraocular pressure (IOP(G)) were qualitatively assessed using a Reichert Ocular Response Analyzer. Central corneal thickness was measured using an ultrasound pachymeter. This measurement was performed 3 times, and the mean value obtained was used for statistical analysis. The relationships between patient age and corneal biomechanical parameters, or age and intraocular pressure (IOP), were investigated.

RESULTS

Mean corneal hysteresis and corneal resistance factor were 10.1+/-1.5 mmHg and 10.1+/-1.6 mmHg, respectively. Mean central corneal thickness was 539.1+/-30.9 microm. A weak, but significant, negative correlation was found between age and corneal hysteresis (Pearson's correlation coefficient r=-0.17, P=.02) and corneal resistance factor (r=-0.18 P=.01). On the other hand, no significant correlation was found between age and central corneal thickness (r=-0.06, P=.41), age and IOP(cc) (r=-0.02, P=.82), or age and IOP(G) (r=-0.11, P=.11).

CONCLUSIONS

Corneal biomechanical parameters are significantly decreased by aging without significant changes in central corneal thickness or IOP, suggesting that age-related structural changes resulting from collagen cross-linking may lead to a reduction of corneal biomechanical variables independent of central corneal thickness or IOP.

The structure and possible functions of the milkfish Chanos chanos adipose eyelid

Basic histological sections (with different staining methods) and scanning electron microscopy (SEM) examinations showed that there were three distinctive layers in the adipose eyelid of milkfish Chanos chanos, which is found in the cephalie region and covers the entire eye. The outer and inner layers were epithelial tissues and the middle layer was composed of connective tissue formed by type I collagen fibrils. No adipose tissue was found in any of the three layers of the so-called adipose eyelid. Examination by transmission spectrophotometer showed that the adipose tissue could filter out ambient light with a wavelength shorter than 305 nm. A photoretinoscope was used to investigate whether the adipose eyelid influenced the mechanism of eye focusing. Eye diopter values did not differ before or after eyelid removal, which indicated that the adipose eyelid did not play a role in eye focusing. In light of these findings, it is suggested that the adipose eyelid serves to block exposure of harmful ultraviolet light into eyes and may also to offer some protection against impact to the eye in the aquatic environment.

Development of a hemicornea from human primary cell cultures for pharmacotoxicology testing

We report the reconstruction and characterization of a hemicornea (epithelialized stroma), using primary human cells, for use in research and as an alternative to the use of animals in pharmacotoxicology testing. To create a stromal equivalent, keratocytes from human corneas were cultured in collagen-glycosaminoglycan-chitosan foams. Limbal stem cell-derived epithelial cells were seeded on top of these, giving rise to hemi-corneas. The epithelium appeared morphologically similar to its physiological counterpart, as shown by the basal cell expression of p63 isoforms including, in some cases, the stem cell marker p63DeltaNalpha, and the expression of keratin 3 and 14-3-3sigma in the upper cell layers. In addition, the cuboidal basal epithelial cells were anchored to a basement membrane containing collagen IV, laminin 5, and hemidesmosomes. In the stromal part, the keratocytes colonized the porous scaffold, formed a network of interconnecting cells, and synthesized an ultrastructurally organized extracellular matrix (ECM) containing collagen types I, V, and VI. Electron microscopy showed the newly synthesized collagen fibrils to have characteristic periodic striations, with diameters and interfibril spacings similar to those found in natural corneas. Compared to existing models for corneal pharmacotoxicology testing, this new model more closely approaches physiological conditions by including the inducing effects of mesenchyme and cell-matrix interactions on epithelial cell morphogenesis.

Impact of age, systemic glucocorticoids, and progressive knee arthritis on specific mRNA levels in different areas of the rabbit cornea

PURPOSE

To determine the influence of factors such as age, osteoarthritis (OA), and glucocorticoid treatment on total RNA and mRNA regulation in the cornea and how these factors differ between prepupillary and peripheral areas of the cornea.

METHODS

Molecular analyses of corneal tissue were performed using rabbits of different age groups and skeletally mature animals that had undergone anterior cruciate ligament (ACL) transection, an established model of knee OA. Systemic glucocorticoids were administered to cohorts of the osteoarthritic and control animals to determine the influence of distal joint disease on the corneal response. Corneal tissue was analyzed for changes in mRNA levels for several relevant genes: collagen I, collagen III, collagen V, decorin core protein, cyclooxygenase-2 (COX-2), glucocorticoid receptor, and the housekeeping gene beta-actin.

RESULTS

The corneal tissue was found to have diminishing total RNA with age, which is consistent with previous studies in the literature. Interestingly, in skeletally mature animals, distal joint OA was found to affect corneal mRNA levels for several important structural and inflammatory genes (collagen I, decorin core protein, and COX-2) in a manner that progressed with OA progression. Although systemic glucocorticoid treatment did not alter mRNA levels in the normal cornea, it did counteract the changes observed early after OA induction (3 weeks) while having less of an effect in later, more established arthritis (6 weeks).

CONCLUSIONS

This study reveals that distal joint OA can affect mRNA levels for several structural and inflammatory genes of the cornea, changes that seem to be suppressed by systemic glucocorticoid treatment. These findings indicate that OA has associated systemic factors that influence corneal cell metabolism.

Effect of High Glucose Concentration on Corneal Collagen Biosynthesis

The effect of high glucose concentration (3 g/l) on bovine corneal total protein and collagen biosynthesis was studied, using 3H-proline incorporation in explant cultures with protein and collagen determinations. The high glucose concentration increased the incorporation of 3H-proline in total corneal proteins as well as in collagens. The specific radioactivity of stromal collagens was strongly increased in these conditions. Mannitol was used to control the osmotic effect of the high glucose concentration, both at 1 and 3 g/l concentrations. Mannitol did not increase the incorporation of 3H-proline in total proteins or collagens, but on the contrary decreased it. The high glucose concentration decreased the excretion of neosynthesized proteins and collagens in the culture medium, but did not affect the total protein or collagen content of the corneas. The strong increase in the specific radioactivity of corneal collagens in the presence of 3 g/l glucose suggests an increased turnover of collagens in diabetic corneas. The increased biosynthesis of collagens together with their decreased elimination in the extracellular compartment can create the conditions for the formation and accumulation of advanced glycation endproducts by the Maillard reaction. This can induce and stimulate the liquefaction of the vitreous body leading to sight-threatening disorders such as diabetic retinopathy, retinal detachment, glaucoma, cataract formation and age-related macular degeneration.

Characterization of collagen fibers in Bruch’s membrane using chemical force microscopy

Bruch's membrane is a layer composed of collagen fibers located just beneath the retina. This study validates a strategy used to map the morphological and adhesion characteristics of collagen fibers in Bruch's membrane. Atomic force microscopy tips were functionalized with different chemical groups and used to map the hydrophilic and hydrophobic regions on the surface of the eye tissue. The largest adhesion forces were observed when tips functionalized with NH(2) groups were used. The trend in the adhesion forces was rationalized based on the distribution of different functional groups in the triple-helical structure of the collagen fibers. The results of this study can be used to design more effective strategies to treat eye diseases such as age-related macular degeneration.

Fritz Verzár was born 120 years ago: his contribution to experimental gerontology through the collagen research as assessed after half a century

F. Verzár's experiments on the age-dependent increase of cross-linking of rat tail tendons in the 1950s represented the first demonstration of age-dependent modifications of extracellular matrix (ECM) macromolecules. This discovery preceded by several years the demonstration of cell-aging and showed that body constituents considered as metabolically "inert" do exhibit age-dependent modifications at the molecular level. Progressively the physiological mechanisms of collagen cross-linking were elucidated and it became clear that this mechanism does not explain the Verzár phenomenon. It was progressively elucidated that the Maillard reaction was involved in the age-dependent cross-linking of collagen. The role of advanced glycation end products (AGEs) in collagen cross-linking, as well as their reaction with other macromolecules was convincingly demonstrated as an important factor of age-dependent modifications of cells and tissues. The Verzár phenomenon completed by the detailed chemistry of the Maillard reaction became thus a dominant paradigm in tissue aging. Verzár's name and discovery should therefore remain associated with these important progresses in aging research. The purpose of this review is to recall some of the details of Verzár's work which paved the way to his discovery and extended well beyond collagen aging.

An aligned nanofibrous collagen scaffold by electrospinning and its effects onin vitro fibroblast culture

Fabrication of nanofibrous scaffolds with well-defined architecture mimicking native extracellular matrix analog has significant potentials for many specific tissue engineering and organs regeneration applications. The fabrication of aligned collagen nanofibrous scaffolds by electrospinning was described in this study. The structure and in vitro properties of these scaffolds were compared with a random collagen scaffold. All the collagen scaffolds were first crosslinked in glutaraldehyde vapor to enhance the biostability and keep the initial nano-scale dimension intact. From in vitro culture of rabbit conjunctiva fibroblast, the aligned scaffold exhibited lower cell adhesion but higher cell proliferation because of the aligned orientation of fibers when compared with the random scaffold. And the alignment of the fibers may control cell orientation and strengthen the interaction between the cell body and the fibers in the longitudinal direction of the fibers.

Étude de l’effet des oligomères procyanidoliques sur la fibrillogénèse de la cornée

PURPOSE

We showed in a previous study that procyanidolic oligomers (PCOs) from grape seeds effectively protect corneal stroma against degradation by bacterial collagenase. Here we report the study of the effect of PCOs on protein and collagen composition of cornea and on the biosynthesis of corneal collagens.

METHODS

Bovine corneas were used in explant cultures. We quantitatively determined total proteins and collagen as well as the incorporation of 3H-proline in separated collagen types. Collagens type I, V, and VI were separated and quantitated. In order to understand some of the results obtained, we studied the interaction of PCO with collagen type I separately.

RESULTS

In the absence of PCOs, collagen typing and 3H-proline incorporation yielded the expected results for a normal cornea, with the usual proportion of the three major types of collagens. In presence of PCOs at 1 mg/ml and after 24 h incubation, total proteins and collagens decreased, as did papain-extractable collagens. Proteins in the final residue solubilized in 1 M KOH-80% v/v aqueous ethanol increased. The proportion of the three principal collagens was also modified: type I became preponderant, and the proportions of the two others (type V and VI) decreased. The study of the interaction of collagen type I with PCOs showed that 30% of total PCOs do not interact with collagen, 20% interact reversibly, and 50% of PCOs are strongly and irreversibly fixed. This strongly fixed fraction could not be separated from collagen by either column chromatography or collagenase or KOH in aqueous ethanol.

CONCLUSIONS

Bovine corneas in explant cultures in presence of PCOs undergo a modification of their protein and collagen content, with a concurrent modification of the proportion of collagens types I, V, and VI. Collagen type I predominates, and the two other types decrease. Study of the collagen type I-PCO interaction showed that roughly 50% of PCOs become irreversibly fixed to collagen, resisting collagenase or other methods of separation. This strong PCO-collagen type I interaction explains the decrease in solubility.

Formation of collagen-glycosaminoglycan blended nanofibrous scaffolds and their biological properties

The development of blended collagen and glycosaminoglycan (GAG) scaffolds can potentially be used in many soft tissue engineering applications since the scaffolds mimic the structure and biological function of native extracellular matrix (ECM). In this study, we were able to obtain novel nanofibrous collagen-GAG scaffolds by electrospinning collagen blended with chondroitin sulfate (CS), a widely used GAG, in a mixed solvent of trifluoroethanol and water. The electrospun collagen-GAG scaffold with 4% CS (COLL-CS-04) exhibited a uniform fiber structure with nanoscale diameters. A second collagen-GAG scaffold with 10% CS consisted of smaller diameter fibers but exhibited a broader diameter distribution due to the different solution properties in comparison with COLL-CS-04. After cross-linking with glutaraldehyde vapor, the collagen-GAG scaffolds became more biostable and were resistant to collagenase degradation. This is evidently a more favorable environment allowing increased proliferation of rabbit conjunctiva fibroblast on the scaffolds. Incorporation of CS into collagen nanofibers without cross-linking did not increase the biostability but still promoted cell growth. The potential of applying the nanoscale collagen-GAG scaffold in tissue engineering is significant since the nanodimension fibers made of natural ECM mimic closely the native ECM found in the human body. The high surface area characteristic of this scaffold may maximize cell-ECM interaction and promote tissue regeneration faster than other conventional scaffolds.

Mapping the type I collagen-binding site on pigment epithelium-derived factor. Implications for its antiangiogenic activity

Pigment epithelium-derived factor (PEDF), a neurotrophic and antiangiogenic serpin, is identified in tissues rich in collagen, e.g. cornea, vitreous, bone, and cartilage. We show that recombinant human PEDF formed complexes with collagens from the bovine cornea and vitreous. We have examined the direct binding of PEDF to collagen I and found that interactions were ionic in nature and occurred when PEDF and collagen I were both in solution, when either one was immobilized, or even when collagen I was denatured under reducing conditions. (125)I-PEDF bound to immobilized collagen I in a saturable fashion (K(D) = 123 nm). Compared with neurotrophic PEDF-derived peptides, ovalbumin and angiogenic inhibitors, only full-length PEDF competed efficiently with (125)I-PEDF for the binding to immobilized collagen I (EC(50) = 3 microg/ml). The collagen-binding region was analyzed using controlled proteolysis and chemically modified PEDF. Cleavage of the serpin exposed loop did not prevent binding to collagen I. Conjugation of lysines with fluorescein increased the collagen binding affinity. However, treatment of PEDF with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide abolished it, implicating the PEDF aspartic and/or glutamic acid residues in its interaction with collagen I. A negatively charged region on the surface of the PEDF molecule is rich in acidic residues (Glu(41), Glu(42), Glu(43), Asp(44), Asp(64), Asp(256), Asp(258), Glu(290), Glu(291), Glu(296), Asp(300), Glu(304)) available to interact directly with positively charged areas of collagen. This represents the first collagen-binding site described for a serpin, which in PEDF, is distinct from its heparin-binding region, neurotrophic active site, and its serpin exposed loop. The collagen-binding property of PEDF may play a role in surface localization and modulation of its antiangiogenic effects in the eye and bone.