Endogenous TSG-6 modulates corneal inflammation following chemical injury

PURPOSE

Tumor necrosis factor (TNF)-stimulated gene-6 (TSG-6) is upregulated in various pathophysiological contexts, where it has a diverse repertoire of immunoregulatory functions. Herein, we investigated the expression and function of TSG-6 during corneal homeostasis and after injury.

METHODS

Human corneas, eyeballs from BALB/c (TSG-6+/+), TSG-6+/- and TSG-6-/- mice, human immortalized corneal epithelial cells and murine corneal epithelial progenitor cells were prepared for immunostaining and real time PCR analysis of endogenous expression of TSG-6. Mice were subjected to unilateral corneal debridement or alkali burn (AB) injuries and wound healing assessed over time using fluorescein stain, in vivo confocal microscopy and histology.

RESULTS

TSG-6 is endogenously expressed in the human and mouse cornea and established corneal epithelial cell lines and is upregulated after injury. A loss of TSG-6 has no structural and functional effect in the cornea during homeostasis. No differences were noted in the rate of corneal epithelial wound closure between BALB/c, TSG-6+/- and TSG-6-/- mice. TSG-6-/- mice presented decreased inflammatory response within the first 24 h of injury and accelerated corneal wound healing following AB when compared to control mice.

CONCLUSION

TSG-6 is endogenously expressed in the cornea and upregulated after injury where it propagates the inflammatory response following chemical injury.

In vitro Assay to Examine the Function of Tears on Corneal Epithelial Cells

Tears contain numerous secreted factors, enzymes, and proteins that help in maintaining the homeostatic condition of the eye and also protect it from the external environment. However, alterations to these enzymes and/or proteins during pathologies such as mechanical injury and viral or fungal infections can disrupt the normal ocular homeostasis, further contributing to disease development. Several tear film components have a significant role in curbing disease progression and promoting corneal regeneration. Additionally, several factors related to disease progression are secreted into the tear film, thereby serving as a valuable reservoir of biomarkers. Tears are readily available and can be collected via non-invasive techniques or simply from contact lenses. Tears can thus serve as a valuable and easy source for studying disease-specific biomarkers. Significant advancements have been made in recent years in the field of tear film proteomics, lipidomics, and transcriptomics to allow a better understanding of how tears can be utilized to gain insight into the etiology of diseases. These advancements have enabled us to study the pathophysiology of various disease states using tear samples. However, the mechanisms by which tears help to maintain corneal homeostasis and how they are able to form the first line of defense against pathogens remain poorly understood and warrant detailed in vitro studies. Herein, we have developed an in vitro assay to characterize the functional importance of patient isolated tears and their components on corneal epithelial cells. This novel approach closely mimics real physiological conditions and could help the researchers gain insight into the underlying mechanisms of ocular pathologies and develop new treatments. Key features • This method provides a new technique for analyzing the effect of tear components on human corneal epithelial cells. • The components of the tears that are altered in response to diseases can be used as a biomarker for detecting ocular complications. • This procedure can be further employed as an in vitro model for assessing the efficacy of drugs and discover potential therapeutic interventions.

Age related changes in hyaluronan expression leads to Meibomian gland dysfunction

The prevalence of dry eye disease (DED) ranges from ∼5 to 50 % and its associated symptoms decrease productivity and reduce the quality of life. Approximately 85 % of all DED cases are caused by Meibomian gland dysfunction (MGD). As humans and mice age, their Meibomian glands (MGs) undergo age-related changes resulting in age related-MGD (ARMGD). The precise cause of ARMGD remains elusive, which makes developing therapies extremely challenging. We previously demonstrated that a hyaluronan (HA)-rich matrix exists surrounding the MG, regulating MG morphogenesis and homeostasis. Herein, we investigated whether changes to the HA matrix in the MG throughout life contributes towards ARMGD, and whether altering this HA matrix can prevent ARMGD. For such, HA synthase (Has) knockout mice were aged and compared to age matched wild type (wt) mice. MG morphology, lipid production, PPARγ expression, basal cell proliferation, stem cells, presence of atrophic glands and MG dropout were analyzed at 8 weeks, 6 months, 1 year and 2 years of age and correlated with the composition of the HA matrix. We found that as mice age, there is a loss of HA expression in and surrounding the MGs of wt mice, while, in contrast, Has1-/-Has3-/- mice present a significant increase in HA expression through Has2 upregulation. At 1 year, Has1-/-Has3-/- mice present significantly enlarged MGs, compared to age-matched wt mice and compared to all adult mice. Thus, Has1-/-Has3-/- mice continue to develop new glandular tissue as they age, instead of suffering MG atrophy. At 2 years, Has1-/-Has3-/- mice continue to present significantly larger MGs compared to age-matched wt mice. Has1-/-Has3-/- mice present increased lipid production, increased PPARγ expression and an increase in the number of proliferating cells when compared to wt mice at all-time points analyzed. Taken together, our data shows that a loss of the HA matrix surrounding the MG as mice age contributes towards ARMGD, and increasing Has2 expression, and consequently HA levels, prevents ARMGD in mice.

Characterization of the Limbal Epithelial Stem Cell Niche

Purpose

Limbal epithelial stem cells (LESCs) reside within a LSC niche (LSCN). We recently identified that hyaluronan (HA) is a major constituent of the LSCN, and that HA is necessary for maintaining LESCs in the "stem cell" state, both in vitro and in vivo. Herein, we characterized the LSCN to identify key components of the HA-specific LSCN.

Methods

The cornea and limbal rim were dissected from mouse corneas, subjected to mRNA extraction, and sequenced using a NextSeq 500 (Illumina) and data processed using CLC Genomics Workbench 20 (Qiagen) and the STRING database to identify key components of the LSCN. Their expression was confirmed by real-time PCR, Western blotting, and immunohistochemistry. Furthermore, the differential expression of key compounds in different corneal cell types were determined with single-cell RNA sequencing.

Results

We identified that the hyaladherins inter-alpha-inhibitor (IαI), TSG-6 and versican are highly expressed in the limbus. Specifically, HA/HC complexes are present in the LSCN, in the stroma underlying the limbal epithelium, and surrounding the limbal vasculature. For IαI, heavy chains 5 and 2 (HC5 and HC2) were found to be the most highly expressed HCs in the mouse and human limbus and were associate with HA-forming HA/HC-specific matrices.

Conclusions

The LSCN contains HA/HC complexes, which have been previously correlated with stem cell niches. The identification of HA/HC complexes in the LSCN could serve as a new therapeutic avenue for treating corneal pathology. Additionally, HA/HC complexes could be used as a substrate for culturing LESCs before LESC transplantation.

Recent advances in age-related meibomian gland dysfunction (ARMGD)

Meibomian glands (MGs), located within the tarsal plate of the eyelid, secrete meibum which is the lipid-rich secretion necessary for stabilizing the tear film and preventing tear evaporation. Changes in the quality and quantity of meibum produced causes MG dysfunction (MGD), the leading cause of evaporative dry eye disease (EDED). MGD is an underdiagnosed disease and it is estimated that, in the US, approximately 70 % of the population over 60 have MGD. Three forms of MGD occur based on their meibum secretion: hyposecretory, obstructive, and hypersecretory MGD. The pathophysiology of MGD remains poorly understood, however aging is the primary risk factor. With age, MGs undergo various age-related changes, including decreased acinar basal cell proliferation, hyperkeratinization, MG atrophy, and eventual MG drop-out, leading to age-related MGD (ARMGD). Additionally, studies have suggested that MGs can suffer inflammatory cell infiltration and changes innervation patterns with aging, which could also contribute towards ARMGD. This review focuses on how the aging process affects the MG, and more importantly, how age-related changes to the MG can lead to MG atrophy and MG drop-out, ultimately leading to ARMGD. This review also highlights the most recent developments in potential therapeutic interventions for ARMGD.

Conditional deletion of CD25 in the corneal epithelium reveals sex differences in barrier disruption

PURPOSE

IL-2 promotes activation, clonal expansion, and deletion of T cells. IL-2 signals through its heterotrimeric receptor (IL-2R) consisting of the CD25, CD122 and CD132 chains. CD25 knockout (KO) mice develop Sjögren Syndrome-like disease. This study investigates whether corneal CD25/IL-2 signaling is critical for ocular health.

METHODS

Eyes from C57BL/6 mice were collected and prepared for immunostaining or in-situ hybridization. Bulk RNA sequencing was performed on the corneal epithelium from wild-type and CD25KO mice. We generated a conditional corneal-specific deletion of CD25 in the corneal epithelium (CD25Δ/ΔCEpi). Corneal barrier function was evaluated based on the uptake of a fluorescent dye. Mice were subjected to unilateral corneal debridement, followed by epithelial closure over time.

RESULTS

In C57BL/6 mice, CD25 mRNA was expressed in ocular tissues. Protein expression of CD25, CD122, and CD132 was confirmed in the corneal epithelium. Delayed corneal re-epithelization was seen in female but not male CD25KO mice. There were 771 differentially expressed genes in the corneal epithelium of CD25KO compared to wild-type mice. While barrier function is disrupted in CD25Δ/ΔCEpi mice, re-epithelialization rates are not delayed.

CONCLUSIONS

All three chains of the IL-2R are expressed in the corneal epithelium. Our results indicate for the first time, deleting CD25 systemically in all tissues in the mouse and deleting CD25 locally in just the corneal epithelium compromises corneal epithelial barrier function, leading to dry eye disease in female mice. Future studies are needed to delineate the pathways used by IL-2 signaling to influence cornea homeostasis.

Rational design and synthesis of lumican stapled peptides for promoting corneal wound healing

PURPOSE

Lumican is a major extracellular matrix (ECM) component in the cornea that is upregulated after injury and promotes corneal wound healing. We have recently shown that peptides designed based on the 13 C-terminal amino acids of lumican (LumC13 and LumC13C-A) are able to recapitulate the effects of lumican on promoting corneal wound healing. Herein we used computational chemistry to develop peptide mimetics derived from LumC13C-A with increased stability and half-life that are biologically active and non-toxic, thereby promoting corneal wound healing with increased pharmacological potential.

METHODS

Different peptides staples were rationalized using LumC13C-A sequence by computational chemistry, docked to TGFβRI and the interface binding energies compared. Lowest scoring peptides were synthesized, and the toxicity of peptides tested using CCK8-based cell viability assay. The efficacy of the stapled peptides at promoting corneal wound healing was tested using a proliferation assay, an in vitro scratch assay using human corneal epithelial cells and an in vivo murine corneal debridement wound healing model.

RESULTS

Binding free energies were calculated using MMGBSA algorithm, and peptides LumC13C and LumC13S5 displayed superior binding to ALK5 compared to the non-stapled peptide LumC13C-A. The presence of the hydrocarbon staple in LumC13C enhances the stability of the α-helical conformation, thereby facilitating more optimal interactions with the ALK5 receptor. The stapled peptides do not present cytotoxic effects on human corneal epithelial cells at a 300 nM concentration. Similar to lumican and LumC13C-A, both C13C and LumC13S5 significantly promote corneal wound healing both in vitro and in vivo.

CONCLUSIONS

Highly stable and non-toxic stapled peptides designed based on LumC13, significantly promote corneal wound healing. As a proof of principle, our data shows that more stable and pharmacologically relevant peptides can be designed based on endogenous peptide sequences for treating various corneal pathologies.

ROS-Mediated Fragmentation Alters the Effects of Hyaluronan on Corneal Epithelial Wound Healing

A buildup of reactive oxygen species (ROS) occurs in virtually all pathological conditions. Hyaluronan (HA) is a major extracellular matrix component and is susceptible to oxidation by reactive oxygen species (ROS), yet the precise chemical structures of oxidized HA products (oxHA) and their physiological properties remain largely unknown. This study characterized the molecular weight (MW), structures, and physiological properties of oxHA. For this, high-molecular-weight HA (HMWHA) was oxidized using increasing molar ratios of hydrogen peroxide (H2O2) or hypochlorous acid (HOCl). ROS lead to the fragmentation of HA, with the oxHA products produced by HOCl exhibiting an altered chemical structure while those produced by H2O2 do not. HMWHA promotes the viability of human corneal epithelial cells (hTCEpi), while low MWHA (LMWHA), ultra-LMWHA (ULMWHA), and most forms of oxHA do not. HMWHA and LMWHA promote hTCEpi proliferation, while ULMWHA and all forms of oxHA do not. LMWHA and some forms of oxHA promote hTCEpi migration, while HMWHA does not. Finally, all native forms of HA and oxHA produced by HOCl promote in vivo corneal wound healing, while oxHA produced by H2O2 does not. Taken together, our results show that HA fragmentation by ROS can alter the physiological activity of HA by altering its MW and structure.

Meibomian gland development: Where, when and how?

The Meibomian gland (MG) is an indispensable adnexal structure of eye that produces meibum, an important defensive component for maintaining ocular homeostasis. Normal development and maintenance of the MGs is required for ocular health since atrophic MGs and disturbances in composition and/or secretion of meibum result in major ocular pathologies, collectively termed as Meibomian gland dysfunction (MGD). Currently available therapies for MGD merely provide symptomatic relief and do not treat the underlying deficiency of the MGs. Hence, a thorough understanding of the timeline of MG development, maturation and aging is required for regenerative purposes along with signaling molecules & pathways controlling proper differentiation of MG lineage in mammalian eye. Understanding the factors that contribute to the development of MGs, developmental abnormalities of MGs, and changes in the quality & quantity of meibum with developing phases of MGs are essential for developing potential treatments for MGD. In this review, we compiled a timeline of events and the factors involved in the structural and functional development of MGs and the associated developmental defects of MGs during development, maturation and aging.

Small leucine rich proteoglycans: Biology, function and their therapeutic potential in the ocular surface

Small leucine rich proteoglycans (SLRPs) are the largest family of proteoglycans, with 18 members that are subdivided into five classes. SLRPs are small in size and can be present in tissues as glycosylated and non-glycosylated proteins, and the most studied SLRPs include decorin, biglycan, lumican, keratocan and fibromodulin. SLRPs specifically bind to collagen fibrils, regulating collagen fibrillogenesis and the biomechanical properties of tissues, and are expressed at particularly high levels in fibrous tissues, such as the cornea. However, SLRPs are also very active components of the ECM, interacting with numerous growth factors, cytokines and cell surface receptors. Therefore, SLRPs regulate major cellular processes and have a central role in major fundamental biological processes, such as maintaining corneal homeostasis and transparency and regulating corneal wound healing. Over the years, mutations and/or altered expression of SLRPs have been associated with various corneal diseases, such as congenital stromal corneal dystrophy and cornea plana. Recently, there has been great interest in harnessing the various functions of SLRPs for therapeutic purposes. In this comprehensive review, we describe the structural features and the related functions of SLRPs, and how these affect the therapeutic potential of SLRPs, with special emphasis on the use of SLRPs for treating ocular surface pathologies.

Novel Peptides with Dual Properties for Treating Pseudomonas aeruginosa Keratitis: Antibacterial and Corneal Wound Healing

The corneal epithelium is a layer in the anterior part of eye that contributes to light refraction onto the retina and to the ocular immune defense. Although an intact corneal epithelium is an excellent barrier against microbial pathogens and injuries, corneal abrasions can lead to devastating eye infections. Among them, Pseudomonas aeruginosa-associated keratitis often results in severe deterioration of the corneal tissue and even blindness. Hence, the discovery of new drugs able not only to eradicate ocular infections, which are often resistant to antibiotics, but also to elicit corneal wound repair is highly demanded. Recently, we demonstrated the potent antipseudomonal activity of two peptides, Esc(1-21) and its diastereomer Esc(1-21)-1c. In this study, by means of a mouse model of P. aeruginosa keratitis and an in vivo corneal debridement wound, we discovered the efficacy of these peptides, particularly Esc(1-21)-1c, to cure keratitis and to promote corneal wound healing. This latter property was also supported by in vitro cell scratch and ELISA assays. Overall, the current study highlights Esc peptides as novel ophthalmic agents for treating corneal infection and injury, being able to display a dual function, antimicrobial and wound healing, rarely identified in a single peptide at the same micromolar concentration range.

Characterization of the Molecular Weight of Hyaluronan in Eye Products Using a Novel Method of Size Exclusion High-Pressure Liquid Chromatography

Purpose

Hyaluronan (HA) exists in two forms, high molecular weight HA (HMWHA) and low molecular weight HA (LMWHA), which have distinct physiological functions. Therefore it is imperative to know the form of HA within pharmaceutical products, including eye products. This study developed an accurate, sensitive, and quantitative method to characterize the form of HA in eye products. Thereafter, the effects of the HA-containing eye products on corneal wound healing were investigated.

Methods

The MW distributions and concentrations of HA in over the counter eye products were determined by size exclusion chromatography (SEC) high-pressure liquid chromatography (HPLC). The effects of the eye products containing HA on corneal wound healing were characterized both in vitro and in vivo using the scratch assay and the debridement wound model, respectively.

Results

The concentrations and MWs of HA were successfully determined within a range of 0.014 to 0.25 mg/mL using SEC HPLC. The concentrations of HA in the ophthalmic products varied from 0.14 to 4.0 mg/mL and the MWs varied from ∼100 kDa to >2500 kDa. All but one HA-containing eye product had an inhibitory effect on corneal wound healing, whereas pure HA promoted corneal wound healing.

Conclusions

A novel SEC-HPLC method was developed for quantifying and characterizing the MW of HA in eye products. Although HA promoted corneal wound healing, HA-containing eye products inhibited corneal wound healing, likely caused by preservatives.

Translational Relevance

SEC-HPLC could be implemented as a routine method for determining the form of HA in commercially available ophthalmic products.

Hyaluronan Modulates the Biomechanical Properties of the Cornea

Purpose

Hyaluronan (HA) is a major constituent of the extracellular matrix (ECM) that has high viscosity and is essential for maintaining tissue hydration. In the cornea, HA is enriched in the limbal region and is a key component of the limbal epithelial stem cell niche. HA is upregulated after injury participating in the formation of the provisional matrix, and has a key role in regulating the wound healing process. This study investigated whether changes in the distribution of HA before and after injury affects the biomechanical properties of the cornea in vivo.

Methods

Corneas of wild-type (wt) mice and mice lacking enzymes involved in the biosynthesis of HA were analyzed before, immediately after, and 7 and 14 days after a corneal alkali burn (AB). The corneas were evaluated using both a ring light and fluorescein stain by in vivo confocal microscopy, optical coherence elastography (OCE), and immunostaining of corneal whole mounts.

Results

Our results show that wt mice and mice lacking HA synthase (Has)1 and 3 present an increase in corneal stiffness 7 and 14 days after AB without a significant increase in HA expression and absence of scarring at 14 days after AB. In contrast, mice lacking Has2 present a significant decrease in corneal stiffness, with a significant increase in HA expression and scarring at 14 days after AB.

Conclusions

Our findings show that the mechanical properties of the cornea are significantly modulated by changes in HA distribution following alkali burn.

Hyaluronan supports the limbal stem cell phenotype during ex vivo culture

BACKGROUND

Hyaluronan (HA) has previously been identified as an integral component of the limbal stem cell niche in vivo. In this study, we investigated whether a similar HA matrix is also expressed in vitro providing a niche supporting limbal epithelial stem cells (LESCs) during ex vivo expansion. We also investigated whether providing exogenous HA in vitro is beneficial to LESCs during ex vivo expansion.

METHOD

Human LESCs (hLESCs) were isolated from donor corneas and a mouse corneal epithelial progenitor cell line (TKE2) was obtained. The HA matrix was identified surrounding LESCs in vitro using immunocytochemistry, flow cytometry and red blood exclusion assay. Thereafter, LESCs were maintained on HA coated dishes or in the presence of HA supplemented in the media, and viability, proliferation, cell size, colony formation capabilities and expression of putative stem cell markers were compared with cells maintained on commonly used coated dishes.

RESULTS

hLESCs and TKE2 cells express an HA-rich matrix in vitro, and this matrix is essential for maintaining LESCs. Further supplying exogenous HA, as a substrate and supplemented to the media, increases LESC proliferation, colony formation capabilities and the expression levels of putative limbal stem cell markers.

CONCLUSION

Our data show that both exogenous and endogenous HA help to maintain the LESC phenotype. Exogenous HA provides improved culture conditions for LESC during ex vivo expansion. Thus, HA forms a favorable microenvironment for LESCs during ex vivo expansion and, therefore, could be considered as an easy and cost-effective substrate and/or supplement for culturing LESCs in the clinic.

Anti-inflammatory protein TNFα-stimulated gene-6 (TSG-6) reduces inflammatory response after brain injury in mice

BACKGROUND

Current research suggests that the glial scar surrounding penetrating brain injuries is instrumental in preserving the surrounding uninjured tissue by limiting the inflammatory response to the injury site. We recently showed that tumor necrosis factor (TNF)-stimulated gene-6 (TSG-6), a well-established anti-inflammatory molecule, is present within the glial scar. In the present study we investigated the role of TSG-6 within the glial scar using TSG-6 null and littermate control mice subjected to penetrating brain injuries.

RESULTS

Our findings show that mice lacking TSG-6 present a more severe inflammatory response after injury, which was correlated with an enlarged area of astrogliosis beyond the injury site.

CONCLUSION

Our data provides evidence that TSG-6 has an anti-inflammatory role within the glial scar.

Extracellular Matrix Deposition and Remodeling after Corneal Alkali Burn in Mice

Corneal transparency relies on the precise arrangement and orientation of collagen fibrils, made of mostly Type I and V collagen fibrils and proteoglycans (PGs). PGs are essential for correct collagen fibrillogenesis and maintaining corneal homeostasis. We investigated the spatial and temporal distribution of glycosaminoglycans (GAGs) and PGs after a chemical injury. The chemical composition of chondroitin sulfate (CS)/dermatan sulfate (DS) and heparan sulfate (HS) were characterized in mouse corneas 5 and 14 days after alkali burn (AB), and compared to uninjured corneas. The expression profile and corneal distribution of CS/DSPGs and keratan sulfate (KS) PGs were also analyzed. We found a significant overall increase in CS after AB, with an increase in sulfated forms of CS and a decrease in lesser sulfated forms of CS. Expression of the CSPGs biglycan and versican was increased after AB, while decorin expression was decreased. We also found an increase in KS expression 14 days after AB, with an increase in lumican and mimecan expression, and a decrease in keratocan expression. No significant changes in HS composition were noted after AB. Taken together, our study reveals significant changes in the composition of the extracellular matrix following a corneal chemical injury.

Epithelial Cell Migration and Proliferation Patterns During Initial Wound Closure in Normal Mice and an Experimental Model of Limbal Stem Cell Deficiency

Purpose

Establishing the dynamics of corneal wound healing is of vital importance to better understand corneal inflammation, pathology, and corneal regeneration. Numerous studies have made great strides in investigating multiple aspects of corneal wound healing; however, some aspects remain to be elucidated. This study worked toward establishing (1) if epithelial limbal stem cells (LSCs) are necessary for healing all corneal wounds, (2) the mechanism by which epithelial cells migrate toward the wound, and (3) if centrifugal epithelial cell movement exists.

Methods

To establish different aspects of corneal epithelial wound healing we subjected mice lacking hyaluronan synthase 2 (previously shown to lack LSCs) and wild-type mice to different corneal debridement injury models.

Results

Our data show that both LSCs and corneal epithelial cells contribute toward closure of corneal wounds. In wild-type mice, removal of the limbal rim delayed closure of 1.5-mm wounds, and not of 0.75-mm wounds, indicating that smaller wounds do not rely on LSCs as do larger wounds. In mice shown to lack LSCs, removal of the limbal rim did not affect wound healing, irrespective of the wound size. Finally, transient amplifying cells and central epithelial cells move toward a central corneal wound in a centripetal manner, whereas central epithelial cells may move in a centrifugal manner to resurface peripheral corneal wounds.

Conclusions

Our findings show the dimensions of the corneal wound dictate involvement of LSCs. Our data suggest that divergent findings by different groups on the dynamics of wound healing can be in part owing to differences in the wounding models used.

Distribution and Function of Glycosaminoglycans and Proteoglycans in the Development, Homeostasis and Pathology of the Ocular Surface

The ocular surface, which forms the interface between the eye and the external environment, includes the cornea, corneoscleral limbus, the conjunctiva and the accessory glands that produce the tear film. Glycosaminoglycans (GAGs) and proteoglycans (PGs) have been shown to play important roles in the development, hemostasis and pathology of the ocular surface. Herein we review the current literature related to the distribution and function of GAGs and PGs within the ocular surface, with focus on the cornea. The unique organization of ECM components within the cornea is essential for the maintenance of corneal transparency and function. Many studies have described the importance of GAGs within the epithelial and stromal compartment, while very few studies have analyzed the ECM of the endothelial layer. Importantly, GAGs have been shown to be essential for maintaining corneal homeostasis, epithelial cell differentiation and wound healing, and, more recently, a role has been suggested for the ECM in regulating limbal stem cells, corneal innervation, corneal inflammation, corneal angiogenesis and lymphangiogenesis. Reports have also associated genetic defects of the ECM to corneal pathologies. Thus, we also highlight the role of different GAGs and PGs in ocular surface homeostasis, as well as in pathology.

Hyaluronan Derived From the Limbus is a Key Regulator of Corneal Lymphangiogenesis

Purpose

We recently reported that the glycosaminoglycan hyaluronan (HA), which promotes inflammatory angiogenesis in other vascular beds, is an abundant component of the limbal extracellular matrix. Consequently, we have explored the possibility that HA contributes to lymphangiogenesis in the inflamed cornea.

Methods

To study the role of HA on lymphangiogenesis, we used mice lacking the hyaluronan synthases and injury models that induce lymphangiogenesis.

Results

Here we report that HA regulates corneal lymphangiogenesis, both during post-natal development and in response to adult corneal injury. Furthermore, we show that injury to the cornea by alkali burn upregulates both HA production and lymphangiogenesis and that these processes are ablated in HA synthase 2 deficient mice.

Conclusion

These findings raise the possibility that therapeutic blockade of HA-mediated lymphangiogenesis might prevent the corneal scarring and rejection that frequently results from corneal transplantation.

Structural basis of oligosaccharide processing by glycosaminoglycan sulfotransferases

Heparan sulfate (HS) is a sulfated polysaccharide that plays a key role in morphogenesis, physiology and pathogenesis. The biosynthesis of HS takes place in the Golgi apparatus by a group of enzymes that polymerize, epimerize and sulfate the sugar chain. This biosynthetic process introduces varying degrees of sulfate substitution, which are tightly regulated and directly dictate binding specificity to different cytokines, morphogens and growth factors. Here, we report the use of molecular dynamics simulations to investigate the dynamics of substrate recognition of two glycosaminoglycan (GAG) sulfotransferases, N-deacetylase-N-sulfotransferase and 2-O-sulfotransferase to the HS chain during the biosynthetic process. We performed multiple simulations of the binding of the sulfotransferase domains to both the HS oligosaccharide substrate and sulfate donor, 3'-phosphoadenosine-5'-phosphosulfate. Analysis of extended simulations provide detailed and useful insights into the atomic interactions that are at work during oligosaccharide processing. The fast information matching method was used to detect the enzyme global dynamics and to predict the pairwise contact of residues responsible for GAG-enzyme binding and unbinding. The correlation between HS displacement and the location of the modified GAG chain were calculated, indicating a possible route for HS and heparin during sulfotransferase processing. Our data also show sulfotransferases contain a conserved interspaced positively charged amino acid residues that form a patch which controls the protein-GAG binding equilibrium. Together, our findings provide further understanding on the fine-tuned complex mechanism of GAG biosynthesis. Our findings can also be extrapolated to other systems for calculating rates of protein-GAG binding.

Hyaluronan Regulates Eyelid and Meibomian Gland Morphogenesis

Purpose

The Meibomian gland (MG) produces the lipid layer of the tear film, and changes to the MG that lead to a decrease or alteration in lipid quality/content may lead to MG dysfunction, a major cause of evaporative dry eye disease with prevalence ranging from 39% to 50%. Little is known about the developmental cues that regulate MG morphogenesis and homeostasis. Our study investigates the role of hyaluronan (HA), a major extracellular matrix component, in eyelid formation and MG development and function.

Methods

Hyaluronan synthase (Has) knockout mice were used to determine the role of HA in the eyelid and MG. Eyelids were obtained during different developmental stages and MG morphology was analyzed. Tet-off H2B-GFP/K5tTA mice and 5-ethynyl-2'-deoxyurdine (EdU) incorporation were used to determine the role of HA in maintaining slow-cycling and proliferating cells within the MG, respectively. Data were confirmed using an in vitro proliferation assay, differentiation assay and spheroid cultures.

Results

Has knockout mice present precocious MG development, and adult mice present MG hyperplasia and dysmorphic MGs and eyelids, with hyperplastic growths arising from the palpebral conjunctiva. Our data show that a highly organized HA network encompasses the MG, and basal cells are embedded within this HA matrix, which supports the proliferating cells. Spheroid cultures showed that HA promotes acini formation.

Conclusions

HA plays an important role in MG and eyelid development. Our findings suggest that Has knockout mice have abnormal HA synthesis, which in turn leads to precocious and exacerbated MG morphogenesis culminating in dysmorphic eyelids and MGs.

Hyaluronan Rich Microenvironment in the Limbal Stem Cell Niche Regulates Limbal Stem Cell Differentiation

Purpose

Limbal epithelial stem cells (LSCs), located in the basal layer of the corneal epithelium in the corneal limbus, are vital for maintaining the corneal epithelium. LSCs have a high capacity of self-renewal with increased potential for error-free proliferation and poor differentiation. To date, limited research has focused on unveiling the composition of the limbal stem cell niche, and, more important, on the role the specific stem cell niche may have in LSC differentiation and function. Our work investigates the composition of the extracellular matrix in the LSC niche and how it regulates LSC differentiation and function.

Methods

Hyaluronan (HA) is naturally synthesized by hyaluronan synthases (HASs), and vertebrates have the following three types: HAS1, HAS2, and HAS3. Wild-type and HAS and TSG-6 knockout mice-HAS1-/-;HAS3-/-, HAS2Δ/ΔCorEpi, TSG-6-/--were used to determine the importance of the HA niche in LSC differentiation and specification.

Results

Our data demonstrate that the LSC niche is composed of a HA rich extracellular matrix. HAS1-/-;HAS3-/-, HAS2Δ/ΔCorEpi, and TSG-6-/- mice have delayed wound healing and increased inflammation after injury. Interestingly, upon insult the HAS knock-out mice up-regulate HA throughout the cornea through a compensatory mechanism, and in turn this alters LSC and epithelial cell specification.

Conclusions

The LSC niche is composed of a specialized HA matrix that differs from that present in the rest of the corneal epithelium, and the disruption of this specific HA matrix within the LSC niche leads to compromised corneal epithelial regeneration. Finally, our findings suggest that HA has a major role in maintaining the LSC phenotype.

Lumican Peptides: Rational Design Targeting ALK5/TGFBRI

Lumican, a small leucine rich proteoglycan (SLRP), is a component of extracellular matrix which also functions as a matrikine regulating multiple cell activities. In the cornea, lumican maintains corneal transparency by regulating collagen fibrillogenesis, promoting corneal epithelial wound healing, regulating gene expression and maintaining corneal homeostasis. We have recently shown that a peptide designed from the 13 C-terminal amino acids of lumican (LumC13) binds to ALK5/TGFBR1 (type1 receptor of TGFβ) to promote wound healing. Herein we evaluate the mechanism by which this synthetic C-terminal amphiphilic peptide (LumC13), binds to ALK5. These studies clearly reveal that LumC13-ALK5 form a stable complex. In order to determine the minimal amino acids required for the formation of a stable lumican/ALK5 complex derivatives of LumC13 were designed and their binding to ALK5 investigated in silico. These LumC13 derivatives were tested both in vitro and in vivo to evaluate their ability to promote corneal epithelial cell migration and corneal wound healing, respectively. These validations add to the therapeutic value of LumC13 (Lumikine) and aid its clinical relevance of promoting the healing of corneal epithelium debridement. Moreover, our data validates the efficacy of our computational approach to design active peptides based on interactions of receptor and chemokine/ligand.

Coupling of vinculin to F-actin demands Syndecan-4 proteoglycan

Syndecans are heparan sulfate proteoglycans characterized as transmembrane receptors that act cooperatively with the cell surface and extracellular matrix proteins. Syn4 knockdown was performed in order to address its role in endothelial cells (EC) behavior. Normal EC and shRNA-Syn4-EC cells were studied comparatively using complementary confocal, super-resolution and non-linear microscopic techniques. Confocal and super-resolution microscopy revealed that Syn4 knockdown alters the level and arrangement of essential proteins for focal adhesion, evidenced by the decoupling of vinculin from F-actin filaments. Furthermore, Syn4 knockdown alters the actin network leading to filopodial protrusions connected by VE-cadherin-rich junction. shRNA-Syn4-EC showed reduced adhesion and increased migration. Also, Syn4 silencing alters cell cycle as well as cell proliferation. Moreover, the ability of EC to form tube-like structures in matrigel is reduced when Syn4 is silenced. Together, the results suggest a mechanism in which Syndecan-4 acts as a central mediator that bridges fibronectin, integrin and intracellular components (actin and vinculin) and once silenced, the cytoskeleton protein network is disrupted. Ultimately, the results highlight Syn4 relevance for balanced cell behavior.

Tumor Necrosis Factor-stimulated Gene-6 (TSG-6) Is Constitutively Expressed in Adult Central Nervous System (CNS) and Associated with Astrocyte-mediated Glial Scar Formation following Spinal Cord Injury

Tumor necrosis factor (TNF)-stimulated gene-6 (TSG-6) binds to hyaluronan and can reorganize/stabilize its structure, also enhancing the binding of this glycosaminoglycan to its cell surface receptor, CD44. TSG-6 is rapidly up-regulated in response to inflammatory cytokines protecting tissues from the damaging effects of inflammation. Despite TSG-6 treatment having been shown to improve outcomes in an experimental model of traumatic brain injury, TSG-6 expression has not been extensively studied in the central nervous system (CNS). We hereby analyzed the expression profile of TSG-6 in the developing CNS and following injury. We show that TSG-6 is expressed in the rat CNS by GFAP(+) and CD44(+) astrocytes, solely in the mature brain and spinal cord, and is not present during the development of the CNS. TSG-6(-/-) mice present a reduced number of GFAP(+) astrocytes when compared with the littermate TSG-6(+/-) mice. TSG-6 expression is drastically up-regulated after injury, and the TSG-6 protein is present within the glial scar, potentially coordinating and stabilizing the formation of this hyaluronan-rich matrix. This study shows that TSG-6 is expressed in the CNS, suggesting a role for TSG-6 in astrocyte activation and tissue repair. We hypothesize that within this context TSG-6 could participate in the formation of the glial scar and confer anti-inflammatory properties. Further studies are required to elucidate the therapeutic potential of targeting TSG-6 after CNS injury to promote its protective effects while reducing the inhibitory properties of the glial scar in axon regeneration.

Extrinsic and Intrinsic Mechanisms by Which Mesenchymal Stem Cells Suppress the Immune System

Mesenchymal stem cells (MSCs) are a group of fibroblast-like multipotent mesenchymal stromal cells that have the ability to differentiate into osteoblasts, adipocytes, and chondrocytes. Recent studies have demonstrated that MSCs possess a unique ability to exert suppressive and regulatory effects on both adaptive and innate immunity in an autologous and allogeneic manner. A vital step in stem cell transplantation is overcoming the potential graft-versus-host disease, which is a limiting factor to transplantation success. Given that MSCs attain powerful differentiation capabilities and also present immunosuppressive properties, which enable them to survive host immune rejection, MSCs are of great interest. Due to their ability to differentiate into different cell types and to suppress and modulate the immune system, MSCs are being developed for treating a plethora of diseases, including immune disorders. Moreover, in recent years, MSCs have been genetically engineered to treat and sometimes even cure some diseases, and the use of MSCs for cell therapy presents new perspectives for overcoming tissue rejection. In this review, we discuss the potential extrinsic and intrinsic mechanisms that underlie MSCs' unique ability to modulate inflammation, and both innate and adaptive immunity.

"GAG-ing with the neuron": The role of glycosaminoglycan patterning in the central nervous system

Proteoglycans (PGs) are a diverse family of proteins that consist of one or more glycosaminoglycan (GAG) chains, covalently linked to a core protein. PGs are major components of the extracellular matrix (ECM) and play critical roles in development, normal function and damage-response of the central nervous system (CNS). GAGs are classified based on their disaccharide subunits, into the following major groups: chondroitin sulfate (CS), heparan sulfate (HS), heparin (HEP), dermatan sulfate (DS), keratan sulfate (KS) and hyaluronic acid (HA). All except HA are modified by sulfation, giving GAG chains specific charged structures and binding properties. While significant neuroscience research has focused on the role of one PG family member, chondroitin sulfate proteoglycan (CSPG), there is ample evidence in support of a role for the other PGs in regulating CNS function in normal and pathological conditions. This review discusses the role of all the identified PG family members (CS, HS, HEP, DS, KS and HA) in normal CNS function and in the context of pathology. Understanding the pleiotropic roles of these molecules in the CNS may open the door to novel therapeutic strategies for a number of neurological conditions.

DNA and bone structure preservation in medieval human skeletons

Morphological and ultrastructural data from archaeological human bones are scarce, particularly data that have been correlated with information on the preservation of molecules such as DNA. Here we examine the bone structure of macroscopically well-preserved medieval human skeletons by transmission electron microscopy and immunohistochemistry, and the quantity and quality of DNA extracted from these skeletons. DNA technology has been increasingly used for analyzing physical evidence in archaeological forensics; however, the isolation of ancient DNA is difficult since it is highly degraded, extraction yields are low and the co-extraction of PCR inhibitors is a problem. We adapted and optimised a method that is frequently used for isolating DNA from modern samples, Chelex(®) 100 (Bio-Rad) extraction, for isolating DNA from archaeological human bones and teeth. The isolated DNA was analysed by real-time PCR using primers targeting the sex determining region on the Y chromosome (SRY) and STR typing using the AmpFlSTR(®) Identifiler PCR Amplification kit. Our results clearly show the preservation of bone matrix in medieval bones and the presence of intact osteocytes with well preserved encapsulated nuclei. In addition, we show how effective Chelex(®) 100 is for isolating ancient DNA from archaeological bones and teeth. This optimised method is suitable for STR typing using kits aimed specifically at degraded and difficult DNA templates since amplicons of up to 250bp were successfully amplified.

On the catalytic mechanism of polysaccharide lyases: evidence of His and Tyr involvement in heparin lysis by heparinase I and the role of Ca2+

The structurally diverse polysaccharide lyase enzymes are distributed from plants to animals but share common catalytic mechanisms. One, heparinase I (F. heparinum), is employed in the production of the major anticoagulant drug, low molecular weight heparin, and is a mainstay of cell surface proteoglycan analysis. We demonstrate that heparinase I specificity and efficiency depend on the cationic form of the substrate. Ca(2+)-heparin, in which α-L-iduronate-2-O-sulfate residues adopt (1)C4 conformation preferentially, is a substrate, while Na(+)-heparin is an inhibitor. His and Tyr residues are identified in the catalytic step and a model based on molecular dynamics and docking is proposed, in which deprotonated His203 initiates β-elimination by abstracting the C5 proton of the α-L-iduonate-2-O-sulfate residue in the substrate, and protonated Tyr357 provides the donor to the hexosamine leaving group.

Lumican expression, localization and antitumor activity in prostate cancer

The stromal reaction surrounding tumors leads to the formation of a tumor-specific microenvironment, which may play either a restrictive role or a supportive role in the growth and progression of the tumors. Lumican, a small leucine-rich proteoglycan (SLRP) of the extracellular matrix (ECM), regulates collagen fibrillogenesis. Recently, lumican has also been shown to regulate cell behavior during embryonic development, tissue repair and tumor progression. The role of lumican in cancer varies according to the type of tumor. In this study we analyze the role of lumican in the pathogenesis of prostate cancer both in vivo and in vitro. Overall lumican up-regulation was observed in the primary tumors analyzed through both real-time PCR and immunostaining. The increase in lumican expression was observed in the reactive stroma surrounding prostate primary tumors with fibrotic deposition surrounding the acinar glands. In vitro analysis demonstrated that lumican inhibited both the migration and invasion of metastatic prostate cancer cells isolated from lymph node, bone and brain. Moreover, prostate cancer cells seeded on lumican presented a decrease in the formation of cellular projections, lamellipodia detected by a decreased rearrangement in ZO-1, keratin 8/18, integrin β1 and MT1-MMP, and invadopodia detected by disruption of α-smooth muscle actin, cortactin and N-WASP. Moreover, a significant increase in prostate cancer cell invasion was observed through the peritoneum of lumican knockout mice, further demonstrating the restrictive role lumican present in the ECM has on prostate cancer invasion. In conclusion, lumican present in the reactive stroma surrounding prostate primary tumors plays a restrictive role on cancer progression, and we therefore postulate that lumican could be a valuable marker in prostate cancer staging.

Inhibitory peptides of the sulfotransferase domain of the heparan sulfate enzyme, N-deacetylase-N-sulfotransferase-1

N-Deacetylase-N-sulfotransferase 1 (Ndst1) catalyzes the initial modification of heparan sulfate and heparin during their biosynthesis by removal of acetyl groups from subsets of N-acetylglucosamine units and subsequent sulfation of the resulting free amino groups. In this study, we used a phage display library to select peptides that interact with Ndst1, with the aim of finding inhibitors of the enzyme. The phage library consisted of cyclic random 10-mer peptides expressed in the phage capsid protein pIII. Selection was based on the ability of engineered phage to bind to recombinant murine Ndst1 (mNdst1) and displacement with heparin. Peptides that were enriched through multiple cycles of binding and disassociation displayed two specific sequences, CRGWRGEKIGNC and CNMQALSMPVTC. Both peptides inhibited mNdst1 activity in vitro, however, by distinct mechanisms. The peptide CRGWRGEKIGNC presents a chemokine-like repeat motif (BXX, where B represents a basic amino acid and X is a noncharged amino acid) and binds to heparan sulfate, thus blocking the binding of substrate to the enzyme. The peptide NMQALSMPVT inhibits mNdst1 activity by direct interaction with the enzyme near the active site. The discovery of inhibitory peptides in this way suggests a method for developing peptide inhibitors of heparan sulfate biosynthesis.

Differences in the expression of glycosaminoglycans in human fibroblasts derived from gingival overgrowths is related to TGF-beta up-regulation

Glycosaminoglycans (GAGs) play important roles in cell behavior and have the ability to bind and modulate cytokines. Using primary cultured fibroblasts from hereditary gingival fibromatosis (HGF), normal gingiva (NG), and NG treated with cyclosporin-A (NGc) we show changes in the expression and structural characteristics of GAGs as well as in the expression of enzymes involved in their biosynthesis and degradation. In addition, we show the over-expression of TGF-beta1 and TGF-beta type II receptor in HGF and NGc. There is an increase in the GAGs retained in the cellular fraction, and the fine structure of galactosaminoglycans show a decrease in alpha-l-iduronic acid content in HGF and NGc. Elevated extracellular levels of low molecular weight hyaluronan (HA) are found in HGF due to increase in the expression of HA synthase 3 and hyaluronidases 1 and 2. The results bring new insights to the accumulation of extracellular matrix related to TGF-beta over-expression.

Adult bone marrow-derived mononuclear cells expressing chondroitinase AC transplanted into CNS injury sites promote local brain chondroitin sulphate degradation

Injury to the CNS of vertebrates leads to the formation of a glial scar and production of inhibitory molecules, including chondroitin sulphate proteoglycans. Various studies suggest that the sugar component of the proteoglycan is responsible for the inhibitory role of these compounds in axonal regeneration. By degrading chondroitin sulphate chains with specific enzymes, denominated chondroitinases, the inhibitory capacity of these proteoglycans is decreased. Chondroitinase administration involves frequent injections of the enzyme at the lesion site which constitutes a rather invasive method. We have produced a vector containing the gene for Flavobacterium heparinum chondroitinase AC for expression in adult bone marrow-derived cells which were then transplanted into an injury site in the CNS. The expression and secretion of active chondroitinase AC was observed in vitro using transfected Chinese hamster ovarian and gliosarcoma cells and in vivo by immunohistochemistry analysis which showed degraded chondroitin sulphate coinciding with the location of transfected bone marrow-derived cells. Immunolabelling of the axonal growth-associated protein GAP-43 was observed in vivo and coincided with the location of degraded chondroitin sulphate. We propose that bone marrow-derived mononuclear cells, transfected with our construct and transplanted into CNS, could be a potential tool for studying an alternative chondroitinase AC delivery method.