Engineering of a Secretory Active Three-Dimensional Lacrimal Gland Construct on the Basis of Decellularized Lacrimal Gland Tissue

Enhancement of lacrimal gland cell function by decellularized lacrimal gland derived hydrogel

Sustainable treatment of aqueous deficient dry eye (ADDE) represents an unmet medical need and therefore requires new curative and regenerative approaches based on appropriatein vitromodels. Tissue specific hydrogels retain the individual biochemical composition of the extracellular matrix and thus promote the inherent cell´s physiological function. Hence, we created a decellularized lacrimal gland (LG) hydrogel (dLG-HG) meeting the requirements for a bioink as the basis of a LG model with potential forin vitroADDE studies. Varying hydrolysis durations were compared to obtain dLG-HG with best possible physical and ultrastructural properties while preserving the original biochemical composition. A particular focus was placed on dLG-HG´s impact on viability and functionality of LG associated cell types with relevance for a futurein vitromodel in comparison to the unspecific single component hydrogel collagen type-I (Col) and the common cell culture substrate Matrigel. Proliferation of LG epithelial cells (EpC), LG mesenchymal stem cells, and endothelial cells cultured on dLG-HG was enhanced compared to culture on Matrigel. Most importantly with respect to a functionalin vitromodel, the secretion capacity of EpC cultured on dLG-HG was higher than that of EpC cultured on Col or Matrigel. In addition to these promising cell related properties, a rapid matrix metalloproteinase-dependent biodegradation was observed, which on the one hand suggests a lively cell-matrix interaction, but on the other hand limits the cultivation period. Concluding, dLG-HG possesses decisive properties for the tissue engineering of a LGin vitromodel such as cytocompatibility and promotion of secretion, making it superior to unspecific cell culture substrates. However, deceleration of biodegradation should be addressed in future experiments.

Polymers and Biomaterials for Posterior Lamella of the Eyelid and the Lacrimal System

The application of biopolymers in the reconstruction of the posterior lamella of the eyelid and the lacrimal system marks a significant fusion of biomaterial science with clinical advancements. This review assimilates research spanning 2015 to 2023 to provide a detailed examination of the role of biopolymers in reconstructing the posterior lamella of the eyelid and the lacrimal system. It covers the anatomy and pathophysiology of eyelid structures, the challenges of reconstruction, and the nuances of surgical intervention. This article progresses to evaluate the current gold standards, alternative options, and the desirable properties of biopolymers used in these intricate procedures. It underscores the advancements in the field, from decellularized grafts and acellular matrices to innovative natural and synthetic polymers, and explores their applications in lacrimal gland tissue engineering, including the promise of 3D bioprinting technologies. This review highlights the importance of multidisciplinary collaboration between material scientists and clinicians in enhancing surgical outcomes and patient quality of life, emphasizing that such cooperation is pivotal for translating benchtop research into bedside applications. This collaborative effort is vital for restoring aesthetics and functionality for patients afflicted with disfiguring eyelid diseases, ultimately aiming to bridge the gap between innovative materials and their clinical translation.

[Cell technologies as a basis for the development of regenerative principles for the treatment of lacrimal gland diseases]

The lacrimal gland (LG) is a tubuloacinar exocrine gland composed of acinar, ductal, and myoepithelial cells. Three-dimensional distribution of acinar lobules, ducts, and myoepithelial cells is necessary for the effective functioning of the organ. LG is the main organ of immune surveillance of the ocular surface system. The embryogenesis of the gland is regulated by the interaction of genetic mechanisms, internal epigenetic (enzyme systems, hormones) and exogenous factors. There is no doubt that there is a clear genetic program for the implementation of the complex process of embryonic development. The mechanisms regulating LG organogenesis initiate the work of a huge number of structural oncogenes, transcription and growth factors, etc. Studying the expression and selective activity of regulatory genes during organ development, their participation in the differentiation of different cell types is a current trend at the nexus of clinical genetics, molecular biology, embryology and immunocytochemistry. Due to its relatively simple structure and accessibility, human LG is a suitable object for potential application in regenerative medicine. Development of a universal protocol for obtaining functional differentiated secretory epithelium of LG capable of expressing tissue-specific markers is an urgent task. Determining the nature and origin of stem cells and progenitor cells will allow the isolation and multiplication of these cells in culture. After obtaining a functionally active culture of LG cells, it is possible to create a model of autoimmune diseases.

Eye drops of human origin-Current status and future needs: Report on the workshop organized by the ISBT Working Party for Cellular Therapies

BACKGROUND AND OBJECTIVES

Serum eye drops (SEDs) are used to treat ocular surface disease (OSD) and to promote ocular surface renewal. However, their use and production are not standardized, and several new forms of human eye drops have been developed.

MATERIALS AND METHODS

The International Society for Blood Transfusion Working Party (ISBT WP) for Cellular Therapies held a workshop to review the current types of eye drops of human origin (EDHO) status and provide guidance.

RESULTS

The ISBT WP for Cellular Therapies introduced the new terminology 'EDHO' to emphasize that these products are analogous to 'medical products of human origin'. This concept encompasses their source (serum, platelet lysate, and cord blood) and the increasingly diverse spectrum of clinical usage in ophthalmology and the need for traceability. The workshop identified the wide variability in EDHO manufacturing, lack of harmonized quality and production standards, distribution issues, reimbursement schemes and regulations. EDHO use and efficacy is established for the treatment of OSD, especially for those refractory to conventional treatments.

CONCLUSION

Production and distribution of single-donor donations are cumbersome and complex. The workshop participants agreed that allogeneic EDHO have advantages over autologous EDHO although more data on clinical efficacy and safety are needed. Allogeneic EDHOs enable more efficient production and, when pooled, can provide enhanced standardization for clinical consistency, provided optimal margin of virus safety is ensured. Newer products, including platelet-lysate- and cord-blood-derived EDHO, show promise and benefits over SED, but their safety and efficacy are yet to be fully established. This workshop highlighted the need for harmonization of EDHO standards and guidelines.

Microvascular anastomosis of the human lacrimal gland: a concept study towards transplantation of the human lacrimal gland

Introduction

Severe aqueous tear deficiency is caused by primary or secondary main lacrimal gland insufficiency. The transplantation of a human lacrimal gland could become a potential treatment option to provide physiological tears with optimal properties. To this end, we performed an ex vivo study to develop a surgical strategy that would ensure a vascular supply for a lacrimal gland transplant using microvascular techniques.

Material and methods

Five cadaver heads were used to perform a lateral orbitotomy in order to identify the vascular pedicle and the lacrimal gland itself. The principal feasibility and the time of the required surgical steps for an intraorbital microvascular re-anastomosis of the human lacrimal gland were documented. Patency and potential leakage of the anastomosis were tested with hematoxylin intraoperatively. Postoperatively, routine histological, as well as scanning electron microscopy (SEM) of the gland and vascular anastomosis, were performed.

Results

The vascular pedicle of all five glands could be isolated over a minimum stretch of at least 1 cm, severed, and successfully reanastmosed microsurgically. Time for arterial anatomization (n = 4) was 23 ± 7 min and 22 ± 3 min for the vein (p = 0.62). The total time for the entire microvascular anastomosis was 46 ± 9 min. All anastomosis were patent upon testing. SEM revealed well-aligned edges of the anastomosis with tight sutures in place.

Conclusion

Our study demonstrates as proof of principle the feasibility of intraorbital microvascular re-anastomosis of a human lacrimal gland within the presumed window of ischemia of this tissue. This should encourage orbital surgeons to attempt lacrimal gland transplantation in humans in vivo.

Current approaches for the regeneration and reconstruction of ocular surface in dry eye

Significant research revealed the preocular tear film composition and regulations that remain vital for maintaining Ocular surface functional integrity. Inflammation triggered by many factors is the hallmark of Ocular surface disorders or dry eyes syndrome (DES). The tear deficiencies may lead to ocular surface desiccation, corneal ulceration and/or perforation, higher rates of infectious disease, and the risk of severe visual impairment and blindness. Clinical management remains largely supportive, palliative, and frequent, lifelong use of different lubricating agents. However, few advancements such as punctal plugs, non-steroidal anti-inflammatory drugs, and salivary gland autografts are of limited use. Cell-based therapies, tissue engineering, and regenerative medicine, have recently evolved as long-term cures for many diseases, including ophthalmic diseases. The present article focuses on the different regenerative medicine and reconstruction/bioengineered lacrimal gland formation strategies reported so far, along with their limiting factors and feasibility as an effective cure in future.

Lacrimal gland regeneration: The unmet challenges and promise for dry eye therapy

DED (Dry eye disease) is a common multifactorial disease of the ocular surface and the tear film. DED has gained attention globally, with millions of people affected.. Although treatment strategies for DED have shifted towards Tear Film Oriented Therapy (TFOT), all the existing strategies fall under standard palliative care when addressed as a long-term goal. Therefore, different approaches have been explored by various groups to uncover alternative treatment strategies that can contribute to a full regeneration of the damaged lacrimal gland. For this, multiple groups have investigated the role of lacrimal gland (LG) cells in DED based on their regenerating, homing, and differentiating capabilities. In this review, we discuss in detail therapeutic mechanisms and regenerative strategies that can potentially be applied for lacrimal gland regeneration as well as their therapeutic applications. This review mainly focuses on Aqueous Deficiency Dry Eye Disease (ADDE) caused by lacrimal gland dysfunction and possible future treatment strategies. The current key findings from cell and tissue-based regenerative therapy modalities that could be utilised to achieve lacrimal gland tissue regeneration are summarized. In addition, this review summarises the available literature from in vitro to in vivo animal studies, their limitations in relation to lacrimal gland regeneration and the possible clinical applications. Finally, current issues and unmet needs of cell-based therapies in providing complete lacrimal gland tissue regeneration are discussed.

Development of high-throughput lacrimal gland organoid platforms for drug discovery in dry eye disease

Dysfunction and damage of the lacrimal gland (LG) results in ocular discomfort and dry eye disease (DED). Current therapies for DED do not fully replenish the necessary lubrication to rescue optimal vision. New drug discovery for DED has been limited perhaps because in vitro models cannot mimic the biology of the native LG. The existing platforms for LG organoid culture are scarce and still not ready for consistency and scale up production towards drug screening. The magnetic three-dimensional (3D) bioprinting (M3DB) is a novel system for 3D in vitro biofabrication of cellularized tissues using magnetic nanoparticles to bring cells together. M3DB provides a scalable platform for consistent handling of spheroid-like cell cultures facilitating consistent biofabrication of organoids. Previously, we successfully generated innervated secretory epithelial organoids from human dental pulp stem cells with M3DB and found that this platform is feasible for epithelial organoid bioprinting. Research targeting LG organogenesis, drug discovery for DED has extensively used mouse models. However, certain inter-species differences between mouse and human must be considered. Porcine LG appear to have more similarities to human LG than the mouse counterparts. We have conducted preliminary studies with the M3DB for fabricating LG organoids from primary cells isolated from murine and porcine LG, and found that this platform provides robust LG organoids for future potential high-throughput analysis and drug discovery. The LG organoid holds promise to be a functional model of tearing, a platform for drug screening, and may offer clinical applications for DED.

Scaffold-based developmental tissue engineering strategies for ectodermal organ regeneration

Tissue engineering (TE) is a multidisciplinary research field aiming at the regeneration, restoration, or replacement of damaged tissues and organs. Classical TE approaches combine scaffolds, cells and soluble factors to fabricate constructs mimicking the native tissue to be regenerated. However, to date, limited success in clinical translations has been achieved by classical TE approaches, because of the lack of satisfactory biomorphological and biofunctional features of the obtained constructs. Developmental TE has emerged as a novel TE paradigm to obtain tissues and organs with correct biomorphology and biofunctionality by mimicking the morphogenetic processes leading to the tissue/organ generation in the embryo. Ectodermal appendages, for instance, develop in vivo by sequential interactions between epithelium and mesenchyme, in a process known as secondary induction. A fine artificial replication of these complex interactions can potentially lead to the fabrication of the tissues/organs to be regenerated. Successful developmental TE applications have been reported, in vitro and in vivo, for ectodermal appendages such as teeth, hair follicles and glands. Developmental TE strategies require an accurate selection of cell sources, scaffolds and cell culture configurations to allow for the correct replication of the in vivo morphogenetic cues. Herein, we describe and discuss the emergence of this TE paradigm by reviewing the achievements obtained so far in developmental TE 3D scaffolds for teeth, hair follicles, and salivary and lacrimal glands, with particular focus on the selection of biomaterials and cell culture configurations.

Organoids and organ chips in ophthalmology

Recent advances have driven the development of stem cell-derived, self-organizing, three-dimensional miniature organs, termed organoids, which mimic different eye tissues including the retina, cornea, and lens. Organoids and engineered microfluidic organ-on-chips (organ chips) are transformative technologies that show promise in simulating the architectural and functional complexity of native organs. Accordingly, they enable exploration of facets of human disease and development not accurately recapitulated by animal models. Together, these technologies will increase our understanding of the basic physiology of different eye structures, enable us to interrogate unknown aspects of ophthalmic disease pathogenesis, and serve as clinically-relevant surrogates for the evaluation of ocular therapeutics. Both the burden and prevalence of monogenic and multifactorial ophthalmic diseases, which can cause visual impairment or blindness, in the human population warrants a paradigm shift towards organoids and organ chips that can provide sensitive, quantitative, and scalable phenotypic assays. In this article, we review the current situation of organoids and organ chips in ophthalmology and discuss how they can be leveraged for translational applications.

Decellularized porcine conjunctiva as an alternative substrate for tissue-engineered epithelialized conjunctiva

PURPOSE

The long-term success of visual rehabilitation in patients with severe conjunctival scarring is reliant on the reconstruction of the conjunctiva with a suitable substitute. The purpose of this study is the development and investigation of a re-epithelialized conjunctival substitute based on porcine decellularized conjunctiva (PDC).

METHODS

PDC was re-epithelialized either with pre-expanded human conjunctival epithelial cells (PDC + HCEC) or with a human conjunctival explant placed directly on PDC (PDC + HCEx). Histology and immunohistochemistry were performed to evaluate epithelial thickness, proliferation (Ki67), apoptosis (Caspase 3), goblet cells (MUC5AC), and progenitor cells (CK15, ΔNp63, ABCG2). The superior construct (PDC + HCEx) was transplanted into a conjunctival defect of a rabbit (n = 6). Lissamine green staining verified the epithelialization in vivo. Orbital tissue was exenterated on day 10 and processed for histological and immunohistochemical analysis to examine the engrafted PDC + HCEx. A human-specific antibody was used to detect the transplanted cells.

RESULTS

From day-14 in vitro onward, a significantly thicker epithelium and greater number of cells expressing Ki67, CK15, ΔNp63, and ABCG2 were noted for PDC + HCEx versus PDC + HCEC. MUC5AC-positive cells were found only in PDC + HCEx. The PDC + HCEx-grafted rabbit conjunctivas were lissamine-negative during the evaluation period, indicating epithelial integrity. Engrafted PDC + HCEx showed preserved progenitor cell properties and an increased number of goblet cells comparable to those of native conjunctiva.

CONCLUSION

Placing and culturing a human conjunctival explant directly on PDC (PDC + HCEx) enables the generation of a stable, stratified, goblet cell-rich construct that could provide a promising alternative conjunctival substitute for patients with extensive conjunctival stem and goblet cell loss.

Decellularized human corneal stromal cell sheet as a novel matrix for ocular surface reconstruction

The shortage of donor corneas as well as the limitations of tissue substitutes leads to the necessity to develop alternative materials for ocular surface reconstruction. Corneal surface substitutes must fulfill specific requirements such as high transparency, low immunogenicity, and mechanical stability combined with elasticity. This in vitro study evaluates a decellularized matrix secreted from human corneal fibroblasts (HCF) as an alternative material for ocular surface reconstruction. HCF from human donors were cultivated with the supplementation of vitamin C to form a stable and thick matrix. Furthermore, due to enhanced cultivation time, a three-dimensional like multilayered construct which partly mimics the complex structure of the corneal stroma could be generated. The formed human cell-based matrices (so-called cell sheets [CS]) were subsequently decellularized. The complete cell removal, collagen content, ultrastructure, and cell toxicity of the decellularized CS (DCS) as well as biomechanical properties were analyzed. Surgical feasibility was tested on enucleated porcine eyes. After decellularization and sterilization, a transparent, thick, cell free, and sterile tissue substitute resulted, which allowed expansion of limbal epithelial stem cells with no signs of cytotoxicity, and good surgical feasibility. DCS seem to be a promising new corneal tissue substitute derived from human cells without the limitation of donor material; however, future in vivo studies are necessary to further elucidate its potential for ocular surface reconstruction.

Towards Lacrimal Gland Regeneration: Current Concepts and Experimental Approaches

Dry eye disease (DED) is a complex and multifactorial disease resulting in a continual cycle of tear hyperosmolarity and inflammation. Patients suffering from DED experience severe pain and visual impairments leading to a reduced quality of life. Aqueous-deficient dry eye (ADDE), mainly caused through a loss of functional lacrimal gland tissue, results in the most severe forms of DED. Despite a high prevalence, the current treatments remain palliative and may be insufficient to alleviate the symptoms. Consequently, investigations on experimental approaches for in situ lacrimal gland regeneration are of great clinical interest. This article reviews the current knowledge about processes involved in lacrimal gland regeneration, about lacrimal gland resident stem cells, and offers deductions about possible concepts for in situ lacrimal gland regeneration. Promising starting points might be the utilization of therapeutic proteins, such as bone morphogenetic protein 7, mesenchymal stem cells (MSC) or MSC-based treatments such as conditioned medium, lyophilized cell extracts or adult acinar cells. This review further summarizes current experimental approaches for the treatment of ADDE in animal models and patients. Approaches investigating side population stem cells, epithelial progenitor cells and MSC showed that the transplantation of these cells had therapeutic effects on ADDE. However, the most promising and best-studied experimental approach is the use of MSC for induction/enhancement of in situ lacrimal gland regeneration. Their immunomodulatory effects, low immunogenicity, promotion of tissue regeneration and involvement during spontaneous lacrimal regeneration are favorable traits for clinical applications. In addition, the efficacy and safety of allogeneic MSC transplantation have already been demonstrated in a small patient cohort.

Analysis of lacrimal gland derived mesenchymal stem cell secretome and its impact on epithelial cell survival

In situ regeneration of lacrimal gland (LG) tissue would be a promising approach to curatively treat dry eye disease (DED). Mesenchymal stem cells (MSC) exhibit therapeutic effects in a variety of pathological conditions and our group recently reported that their number increases in regenerating mouse LG. Since the therapeutic effects are suggested to arise from secreted trophic factors, the application of MSC-secreted proteins seems to be a promising approach to induce/enhance LG regeneration. Therefore, this study aims to optimize the isolation of murine LG-MSC and analyze their secretome to investigate its potential for LG epithelial cell survival in vitro. For optimization, LG-MSC were isolated by an explant technique or cell sorting and their secretome was investigated under normal and inflammatory conditions. Results showed that the secretome of MSC had beneficial effects on the viability of ethanol-damaged LG epithelial cells. Additional, Lipocalin-2, prosaposin, ras GTPase-activating protein-binding protein 1 (Rac1) and signal transducer and activator of transcription 1 (STAT1), proteins that were up-regulated under inflammatory conditions, further improved the cell survival of ethanol-damaged LG epithelial cells. Interestingly, recovery of cell viability was highest, when the cells were incubated with STAT1. Summarizing, this study identified promising proteins for further studies on LG regeneration.

Advances in Functional Restoration of the Lacrimal Glands

The lacrimal glands produce tears to support a healthy homeostatic environment on the ocular surface. The lacrimal gland dysfunction characteristic of dry eye disease causes ocular discomfort and visual disturbances and in severe cases can result in a loss of vision. The demand for adequate restoration of lacrimal gland function has been intensified due to advances in stem cell biology, developmental biology, and bioengineering technologies. In addition to conventional therapies, including artificial tears, tear alternatives (such as autologous serum eye drops) and salivary gland transplantation, a regenerative medicine approach has been identified as a novel strategy to restore the function of the lacrimal gland. Recent studies have demonstrated the potential of progenitor cell injection therapy to repair the tissue of the lacrimal glands. A current three-dimensional (3D) tissue engineering technique has been shown to regenerate a secretory gland structure by reproducing reciprocal epithelial-mesenchymal interactions during ontogenesis in vitro and in vivo. A novel direct reprogramming method has suggested a possibility to induce markers in the lacrimal gland developmental process from human pluripotent stem cells. The development of this method is supported by advances in our understanding of gene expression and regulatory networks involved in the development and differentiation of the lacrimal glands. Engineering science has proposed a medical device to stimulate tearing and a bio-hybrid scaffold to reconstruct the 3D lacrimal gland structure. In this review, we will summarize recent bioengineering advances in lacrimal gland regeneration toward the functional restoration of the lacrimal glands as a future dry eye therapy.

Generation and characterisation of decellularised human corneal limbus

PURPOSE

Limbal epithelial stem cells (LESC) reside in a niche in the corneo-scleral transition zone. Deficiency leads to pain, corneal opacity, and eventually blindness. LESC transplantation of ex-vivo expanded human LESC on a carrier such as human amniotic membrane is a current treatment option. We evaluated decellularised human limbus (DHL) as a potential carrier matrix for the transplantation of LESC.

METHODS

Human corneas were obtained from the local eye bank. The limbal tissue was decellularised by sodium desoxychelate and DNase solution and sterilised by γ-irradiation. Native limbus- and DHL-surface structures were assessed by scanning electron microscopy and collagen ultrastructure using transmission electron microscopy. Presence and preservation of limbal basement membrane proteins in native limbus and DHL were analysed immunohistochemically. Absence of DNA after decellularisation was assessed by Feulgen staining and DNA quantification. Presence of immune cells was explored by CD45 staining, and potential cytotoxicity was tested using a cell viability assay.

RESULTS

In the DHL, the DNA content was reduced from 1.5 ± 0.3 μg/mg to 0.15 ± 0.01 μg/mg; the three-dimensional structure and the arrangement of the collagen fibrils were preserved. Main basement membrane proteins such as collagen IV, laminin, and fibronectin were still present after decellularisation and γ-irradiation. CD45-expressing cells were evident neither in the native limbus nor in the DHL. DHL did not convey cytotoxicity.

CONCLUSIONS

The extracellular matrix (ECM) of the limbus provides a tissue specific morphology and three-dimensionality consisting of particular ECM proteins. It therefore represents a substantial component of the stem cell niche. The DHL provides a specific limbal niche surrounding, and might serve as an easily producible carrier matrix for LESC transplantation.

Decellularised conjunctiva for ocular surface reconstruction

Conjunctival reconstruction is an integral component of ocular surface restoration. Decellularised tissues are frequently used clinically for tissue engineering. This study identifies porcine decellularised conjunctiva (PDC) and human decellularised conjunctiva (HDC) as promising substitutes for conjunctival reconstruction. PDC and HDC were nearly DNA-free, structurally intact and showed no cytotoxic effects in vitro, which was confirmed by DNA quantification, histology, transmission electron microscopy, collagen quantification and cytotoxicity assay. Comparing the biomechanical properties to amniotic membrane (AM), the most frequently applied matrix for ocular surface reconstruction today, the decellularised conjunctiva was more extensible and elastic but exhibited less tensile strength. The in vivo application in a rabbit model proofed significantly enhanced transplant stability and less suture losses comparing PDC and HDC to AM while none of the matrices induced considerable inflammation. Ten days after implantation, all PDC, 4 of 6 HDC but none of the AM transplants were completely integrated into the recipient conjunctiva with a partially multi-layered epithelium. Altogether, decellularised conjunctivas of porcine and human origin were superior to AM for conjunctival reconstruction after xenogeneic application in vivo.

STATEMENT OF SIGNIFICANCE

Conjunctival integrity is essential for a healthy ocular surface and clear vision. Its reconstruction is required in case of immunological diseases, after trauma, chemical or thermal burns or surgery involving the conjunctiva. Due to limitations of currently used substitute tissues such as amniotic membrane, there is a need for the development of new matrices for conjunctival reconstruction. Decellularised tissues are frequently applied clinically for tissue engineering. The present study identifies porcine and human decellularised conjunctiva as biocompatible and well tolerated scaffolds with superior integration into the recipient conjunctiva compared to amniotic membrane. Decellularised conjunctiva depicts a promising substitute for conjunctival reconstruction in ophthalmology.

Lacrimal gland development: From signaling interactions to regenerative medicine

The lacrimal gland plays a pivotal role in keeping the ocular surface lubricated, and protecting it from environmental exposure and insult. Dysfunction of the lacrimal gland results in deficiency of the aqueous component of the tear film, which can cause dryness of the ocular surface, also known as the aqueous-deficient dry eye disease. Left untreated, this disease can lead to significant morbidity, including frequent eye infections, corneal ulcerations, and vision loss. Current therapies do not treat the underlying deficiency of the lacrimal gland, but merely provide symptomatic relief. To develop more sustainable and physiological therapies, such as in vivo lacrimal gland regeneration or bioengineered lacrimal gland implants, a thorough understanding of lacrimal gland development at the molecular level is of paramount importance. Based on the structural and functional similarities between rodent and human eye development, extensive studies have been undertaken to investigate the signaling and transcriptional mechanisms of lacrimal gland development using mouse as a model system. In this review, we describe the current understanding of the extrinsic signaling interactions and the intrinsic transcriptional network governing lacrimal gland morphogenesis, as well as recent advances in the field of regenerative medicine aimed at treating dry eye disease. Developmental Dynamics 246:970-980, 2017. © 2017 Wiley Periodicals, Inc.

An In Vitro Model for the Ocular Surface and Tear Film System

Dry eye is a complicated ocular surface disease whose exact pathogenesis is not yet fully understood. For the therapeutic evaluation and pathogenesis study of dry eye, we established an in vitro three-dimensional (3D) coculture model for the ocular surface. It is composed of rabbit conjunctival epithelium and lacrimal gland cell spheroids, and recapitulates the aqueous and mucin layers of the tear film. We first investigated the culture conditions for both cell types to optimize their secretory functions, by employing goblet cell enrichment, air-lifting culture, and 3D spheroid formation techniques. The coculture of the two cell components leads to elevated secretion and higher expression of tear secretory markers. We also compared several coculture systems, and found that direct cell contact between the two cell types significantly increased tear secretion. Inflammation was induced to mimic dry eye disease in the coculture model system. Our results showed that the coculture system provides a more physiologically relevant therapeutic response compared to monocultures. Our work provides a complex 3D model as a recapitulation of the ocular surface and tear film system, which can be further developed as a model for dry eye disease and therapeutic evaluation.

Histatin-1 Expression in Human Lacrimal Epithelium

Background

Study of human lacrimal cell biology is limited by poor access to tissue samples, heterogeneous cell composition of tissue and a lack of established lacrimal epithelial markers. In order to further our understanding of lacrimal cell biology, we sought to find a better marker for human lacrimal epithelial cells, compared to what has been reported in the literature.

Methods

We utilized human Muller’s muscle conjunctival resection (MMCR) specimens containing accessory lacrimal gland (ALG) and cadaveric main lacrimal gland (MLG) as sources of lacrimal tissue. Candidate markers were sought using human ALG tissue from MMCR specimens, isolated by laser capture microdissection (LCM). Affymetrix® analysis was performed on total RNA isolated from FFPE samples to profile transcription in ALG. MMCR tissue sections were assessed by immunofluorescence using antibodies for histatin-1, lactoferrin, E-cadherin (E-cad) and alpha-smooth muscle actin (ASMA). Reverse transcriptase polymerase chain reaction (RT-PCR) analysis was performed to analyze the expression of histatin-1, E-cad and lactoferrin from cadaveric MLG.

Results

Histatin-1 is expressed in ALG and MLG, localizes to lacrimal epithelium, and to a greater degree than do other putative lacrimal epithelial markers.

Conclusions

Histatin-1 is a good marker for human lacrimal epithelium in ALG and MLG and can be used to identify lacrimal cells in future studies.