Revisiting rabbit models for keratoconus: A long-term study on collagenase-induced disease progression

Keratoconus (KC) is a degenerative disorder resulting from the degradation of the stromal collagen fibril network in the cornea, leading to its thinning and conical deformation. Various studies have established animal models of KC by using the collagenase type II enzyme to gain a better understanding of the pathogenesis, however, long-term monitoring or follow-up of the models have not been reported so far. This study evaluates the long-term stability of collagenase type II-induced KC in a rabbit model. Six New Zealand rabbits were divided into 4 study groups with 3 eyes per group. The groups were control (group 1), 0.5% proparacaine + 5 min collagenase treatment on day 0 and day 30 (group 2), 0.5% proparacaine + 10 min collagenase treatment on day 0 (group 3) and, mechanical debridement + 2 min collagenase treatment on day 0 (group 4). Inflammation was observed in group 4 till week 10. Significant decrease in the central corneal thickness was observed in group 3 by week 4 (p < 0.001) however, the thickness was regained in the subsequent follow-ups in all the groups. Keratography results showed no changes in Km values but an increased astigmatic power in all groups. Scanning electron microscopy images revealed thinner collagen fibrils arranged in a mesh-like pattern above the uniform layer of the collagen lamellae in the central part of the treated corneas. Similarly, histological staining revealed loosely packed stromal fibrils in the anterior portion of the cornea which corroborates with the immunofluorescent staining results. This study revealed the remodeling of the corneal structure by eight weeks of collagenase treatment. Consequently, the possibility of creating a rabbit keratoconus model induced by collagenase may warrant further consideration.

Human Lacrimal Gland Derived Mesenchymal Stem Cells - Isolation, Propagation, and Characterization

Purpose

The existing treatment options for dry eye disease (DED) due to lacrimal gland (LG) dysfunction are mainly palliative. Mesenchymal stem cells (MSCs) based therapies and 3D-LG organoids have been explored as a curative option for LG regeneration in animal models. Human LG epithelial cultures are previously established and, here, we aim to isolate and characterize the spindle-shaped cells obtained from primary human LG cultures in order to unveil its MSC property.

Methods

Normal human lacrimal glands were obtained from individuals undergoing LG debulking surgery. The conditions for human LG-MSC culture were standardized to obtain pure population of LG-MSCs at passage 3. Population doubling time (PDT), expression of phenotypic markers, tri-lineage differentiation, colony forming potential, and gene expression analysis were carried out to assess the phenotypic and genotypic characteristics compared to bone marrow-MSCs (BM-MSCs).

Results

Our data show that these spindle-shaped cells exhibit similar phenotypic expression, colony-forming ability, and trilineage differentiation like BM-MSCs. Moreover, the gene expression also did not show any significant difference, except for increased IL1-β in LG-MSCs. The LG-MSCs do not express any lacrimal epithelial markers unlike LG tissue.

Conclusions

This study reveals the first-time evidence for the presence of MSC population within the human LGs, and these cells might play a role in maintaining healthy microenvironment within normal LG and repair in diseased LGs.

Expansion and characterization of human limbus-derived stromal/mesenchymal stem cells in xeno-free medium for therapeutic applications

BACKGROUND

Mesenchymal stem cells (MSCs) have been proven to prevent and clear corneal scarring and limbal stem cell deficiency. However, using animal-derived serum in a culture medium raises the ethical and regulatory bar. This study aims to expand and characterize human limbus-derived stromal/mesenchymal stem cells (hLMSCs) for the first time in vitro in the xeno-free medium.

METHODS

Limbal tissue was obtained from therapeutic grade corneoscleral rims and subjected to explant culture till tertiary passage in media with and without serum (STEM MACS XF; SM), to obtain pure hLMSCs. Population doubling time, cell proliferation, expression of phenotypic markers, tri-lineage differentiation, colony-forming potential and gene expression analysis were carried out to assess the retention of phenotypic and genotypic characteristics of hLMSCs.

RESULTS

The serum-free medium supported the growth of hLMSCs, retaining similar morphology but a significantly lower doubling time of 23 h (*p < 0.01) compared to the control medium. FACS analysis demonstrated ≥ 90% hLMSCs were positive for CD90⁺, CD73⁺, CD105⁺, and ≤ 6% were positive for CD45^-, CD34^- and HLA-DR^-. Immunofluorescence analysis confirmed similar expression of Pax6⁺, COL IV⁺, ABCG2⁺, ABCB5⁺, VIM⁺, CD90⁺, CD105⁺, CD73⁺, HLA-DR^- and CD45^-, αSMA^- in both the media. Tri-lineage differentiation potential and gene expression of hLMSCs were retained similarly to that of the control medium.

CONCLUSION

The findings of this study demonstrate successful isolation, characterization and culture optimization of hLMSCs for the first time in vitro in a serum-free environment. This will help in the future pre-clinical and clinical applications of MSCs in translational research.

A review of rabbit models of meibomian gland dysfunction and scope for translational research

Dry eye disease (DED) is an emerging global health concern with meibomian gland dysfunction (MGD) being the most common subtype of DED. Despite being quite prevalent, the pathophysiological mechanisms governing MGD are poorly understood. Animal models for MGD can be a valuable resource to advance our understanding of this entity and explore novel diagnostic and therapeutic modalities. Although a lot of literature on rodent MGD models exists, a comprehensive review on rabbit animal models is lacking. Rabbits offer a great advantage over other animals as models for studying both DED and MGD. Rabbits have a widely exposed ocular surface and meibomian gland anatomy comparable with humans, which makes performing dry eye diagnostic tests possible using clinically validated imaging platforms. The existing MGD models in rabbits can broadly be classified as pharmacologically induced and surgically induced models. Most models show keratinization of the meibomian gland orifice with plugging as the final common pathway for developing MGD. Thus, understanding the advantages and disadvantages of each rabbit MGD model can help researchers choose the appropriate experimental plan based on the objective of the study. In this review, we discuss the comparative anatomy of the meibomian glands in humans and rabbits, various rabbit models of MGD, translational applications, unmet needs, and future directions in developing MGD models in rabbits.

New Frontier in the Management of Corneal Dystrophies: Basics, Development, and Challenges in Corneal Gene Therapy and Gene Editing

ABSTRACT

Corneal dystrophies represent a group of heterogeneous hereditary disorders causing progressive corneal opacification and blindness. Current corneal transplant management for corneal dystrophies faces the challenges of repeated treatments, complex surgical procedures, shortage of appropriate donor cornea, and, more importantly, graft rejection. Genetic medicine could be an alternative treatment regime to overcome such challenges. Cornea carries promising scope for a gene-based therapy involving gene supplementation, gene silencing, and gene editing in both ex vivo and in vivo platforms. In the cornea, ex vivo gene therapeutic strategies were attempted for corneal graft survival, and in vivo gene augmentation therapies aimed to prevent herpes stromal keratitis, neovascularization, corneal clouding, and wound healing. However, none of these studies followed a clinical trial-based successful outcome. CRISPR/Cas system offers a broad scope of gene editing and engineering to correct underlying genetic causes in corneal dystrophies. Corneal tissue--specific gene correction in vitro with minimal off-target effects and optimal gene correction efficiency followed by their successful surgical implantation, or in vivo CRISPR administration targeting pathogenic genes finds a way to explore therapeutic intervention for corneal dystrophies. However, there are many limitations associated with such CRISPR-based corneal treatment management. This review will look into the development of corneal gene therapy and CRISPR-based study in corneal dystrophies, associated challenges, potential approaches, and future directions.

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.

Cytokeratin profile and keratinocyte gene expression in keratinized lid margins of patients with chronic Stevens-Johnson syndrome

PURPOSE

To study the cytokeratin profile and keratinization-related gene expression in keratinized lid margins of chronic Stevens-Johnson syndrome (SJS) patients.

METHODS

Posterior eyelid margins from 24 chronic SJS patients undergoing mucous membrane grafting and six healthy margins (orbital exenteration, fresh body donors) were studied using immunofluorescence staining (CK10, CK1, filaggrin, transglutaminase 1 (TGM1), (CK19, MUC5AC)) and quantitative PCR (keratinization-related genes-HBEGF, KGF, EGF, TGFα, TGFβ, and TNFα). The staining and gene expression were studied separately in the lid margin epidermis (LME) and lid margin conjunctiva (LMC).

RESULTS

The expression of CK 1/10, filaggrin, and TGM1 in the LMC was similar to the LME in SJS patients. CK19 was expressed only in the basal epithelial layer of the LMC with loss of MUC5AC expression. Increased expression of KGF (p ≤ 0.056), TNFα (p ≤ 0.02), and TGFα (p ≤ 0.01) was observed in the LME of SJS patients compared to normal LME. LMC of SJS patients showed an increased expression of HBEGF (p ≤ 0.002), EGF (p ≤ 0.0002), KGF (p ≤ 0.02), TNFα (p ≤ 0.04), TGFα (p ≤ 0.003), and TGFβ (p ≤ 0.001) compared to normal LMC. Significant differences were observed in the expression of these genes between LME and LMC of SJS patients. These genes were validated using String analysis, which revealed the positive regulation of keratinization.

CONCLUSION

In lid margins of SJS, there is an increased expression of keratinization-related genes compared to the normal lid margin. Keratinized LMC shares similar cytokeratin profile and keratinization gene expression as seen in cutaneous epithelium of SJS patients, indicating the possibility of the cutaneous epithelium as a source for keratinized LMC.

Clinical, histological and immunohistochemistry characteristics of cornea in the sequelae stage of chronic vernal keratoconjunctivitis

Purpose:

To report the clinical outcomes and histopathological and immunohistochemistry (IHC) features in eyes with the sequelae stage of vernal keratoconjunctivitis (VKC).

Methods:

Investigative study of corneal samples obtained following surgical intervention for vision restoration in four eyes of three patients with VKC. Patient 1 (an 11-year-old boy) had deep anterior lamellar keratoplasty in both eyes, Patient 2 (a 24-year-old male) underwent superficial keratectomy followed by penetrating keratoplasty, and Patient 3 (a 22-year-old male) underwent penetrating keratoplasty. The corneal samples retrieved after surgical intervention were assessed for histology features and immunohistochemistry (IHC) studies.

Results:

The grafts were clear till the follow-up of 2–18 months. Histopathology of all four corneal samples showed epithelial hyperplasia, absent Bowman layer, thick hyalinized stromal lamellae, vascularization, and chronic inflammatory cells such as lymphocytes and plasma cells. IHC showed strong expression of CK 3 in both eyes of Patient 1 and no expression in Patients 2 and 3. The marker for limbal stem cells, ABCG2, was absent in all four samples; however, p63α was expressed strongly in Patients 2 and 3, moderately in the right eye of Patient 1, and marginally expressed in the left eye of Patient 1.

Conclusion:

The eyes in the sequelae stage of VKC (having corneal scarring and 360° hypertrophied limbus) can be managed favorably with keratoplasty and amniotic membrane transplantation without allogenic/cadaveric stem cell transplantation. The expression of transient progenitor cells in the scarred corneas of VKC patients in the sequelae stage suggests that the limbal stem cell dysfunction is more likely partial and self-renewal of limbal stem cells is a plausibility in these eyes.

Differential expression of tear film cytokines in Stevens-Johnson syndrome patients and comparative review of literature

To investigate the differential expression of tear cytokine levels among chronic Stevens–Johnson syndrome (SJS) patients to better understand the role of significantly altered cytokines in disease development. Tear samples were collected using Schirmer strips in 24 eyes of chronic SJS, 24 eyes of age and gender-matched controls, and 14 eyes of aqueous deficiency dry eye disease (DED) patients. The cytokine analysis was performed among 18 analytes which include pro-inflammatory, anti-inflammatory factors, and ELR-negative CXC chemokines. String analysis was performed for the significantly altered cytokines to understand their co-expression and role in the disease development. Additionally, a literature review was conducted to identify the signature cytokines present in chronic SJS tears. The differential expression of IL-6 (p ≤ 0.029), CXCL8/IL-8 (p ≤ 0.009), IL-1β (p ≤ 0.041), IL-2 (p ≤ 0.025), IL-10 (p ≤ 0.053), and CXCL-10 (p ≤ 0.044) were observed in chronic SJS patients and healthy controls. Whereas, IL-6 (p ≤ 0.029), CXCL8/IL-8 (p ≤ 0.058), CCL4 (p ≤ 0.056), GM-CSF (p ≤ 0.0001) IL-10 (p ≤ 0.025), and CXCL-10 (p ≤ 0.010), were differentially expressed in SJS as compared to severe DED patients. String analysis of the significantly altered cytokines revealed the involvement of several biological processes including the chronic inflammatory response, nitric oxide synthesis, angiogenesis, and cellular response to drugs. Among all the cytokines evaluated, the expression of CXCL8/IL-8 and CXCL10 levels were consistently reported in the literature. There was a differential expression of tear cytokines in SJS when compared to DED and healthy controls. The differential expression of CXCL8/IL-8 and CXCL10 was in line with existing literature and their role in chronic SJS pathogenesis merits further evaluation.