Human limbal epithelial stem cell regulation, bioengineering and function

https://doi.org/10.1016/j.preteyeres.2021.100956Get rights and content

Highlights

  • The limbal niche consists of unique cellular and molecular components.

  • Wnt signaling pathways play a critical role in the survival and regulation of LSCs.

  • Notch signaling regulates the differentiation and stratification of corneal epithelia.

  • Xenobiotic-free cGMP LSC cultivation could raise the safety standards.

  • Standardized LSCD diagnosis and staging criteria are necessary.

Abstract

The corneal epithelium is continuously renewed by limbal stem/progenitor cells (LSCs), a cell population harbored in a highly regulated niche located at the limbus. Dysfunction and/or loss of LSCs and their niche cause limbal stem cell deficiency (LSCD), a disease that is marked by invasion of conjunctival epithelium into the cornea and results in failure of epithelial wound healing. Corneal opacity, pain, loss of vision, and blindness are the consequences of LSCD. Successful treatment of LSCD depends on accurate diagnosis and staging of the disease and requires restoration of functional LSCs and their niche. This review highlights the major advances in the identification of potential LSC biomarkers and components of the LSC niche, understanding of LSC regulation, methods and regulatory standards in bioengineering of LSCs, and diagnosis and staging of LSCD. Overall, this review presents key points for researchers and clinicians alike to consider in deepening the understanding of LSC biology and improving LSCD therapies.

Section snippets

Introduction and background

The cornea and conjunctiva, which are separated by the junctional zone called the limbus, are the main tissues of the ocular surface. The limbus contains a population of self-renewing stem cells called limbal epithelial stem/progenitor cells (LSCs) that are responsible for maintenance of the integrity of the corneal surface and continuous renewal of the corneal epithelium (Tseng, 1989). Under homeostatic conditions, LSCs maintain a slow cell cycle and can increase in proliferative capacity in

Molecular and phenotypic markers of limbal stem cells

The search for a marker(s) of LSCs has been an intense area of research since the introduction of the concept of LSCs in the early 1980s. Many proteins are preferentially expressed in basal limbal epithelial cells (Chee et al., 2006; Chen et al., 2004; Schlotzer-Schrehardt and Kruse, 2005) as identified through differential transcriptome and immunohistochemistry studies in both mouse (Sartaj et al., 2017) and human (Collin et al., 2020). These putative markers have been reviewed extensively (

Regulatory pathways in human limbal stem/progenitor cells

Our initial microarray data identified cell adhesion, wound healing, cell proliferation, cell migration, and cell differentiation as the top differentially expressed biological functions in the limbus versus the cornea and conjunctiva (Nakatsu et al., 2013). This section will highlight past and ongoing studies of the roles of Wnt and Notch signaling, which are integrally involved in these biological functions, in LSC regulation by using primary human LSCs cultivated on mouse NIH-3T3-J2 (3T3

Bioengineering of limbal stem/progenitor cells

Transplantation of LSCs is an effective treatment to restore a normal corneal epithelial surface in eyes that lack LSCs. LSCs can be transplanted by using tissues or cultivated LSCs from the patient (autograft) (Deng et al., 2020a; Holland, 2015; Kolli et al., 2010; Rama et al., 2010; Sangwan et al., 2011) or a donor (allograft) (Borderie et al., 2019; Shortt et al., 2014; Zakaria et al., 2014). LSC therapies have a lower risk of complications than keratoprostheses, and autologous transplants

Evaluation of in vivo LSC function

The function of LSCs in vivo is represented by the phenotype of epithelial cells and epithelial wound healing capacity on the corneal surface, i.e., the degree of LSCD. The initial diagnosis of LSCD can be made by slit-lamp examination when the clinical history is evocative and the typical stippled fluorescein staining in a vortex pattern is detected (Fig. 15, upper 2 rows). These findings suggest a conjunctival epithelium phenotype on the cornea, the hallmark of LSCD (Deng et al., 2019).

Conclusion and future directions

Significant advances have been made in the understanding of LSC biology, and LSCD pathophysiology and treatment over the last several decades. The advancements in the field of LSC research has been built on the studies of corneal epithelial homeostasis and wound healing, LSC maintenance and niche regulation, and biomarker identification. The first global consensus on the definition, diagnosis, classification, staging, and management of LSCD has set general guidelines for ophthalmologists and

Disclosure

SXD is a consultant for Dompe US. All other authors: none.

We would like to thank Ms. Alis Balayan and Ms. Jennifer Sunga for their assistance in compiling the manuscript. Editing service was provided by Julia C. Jones, PharmD, PhD.

CRediT authorship contribution statement

Clémence Bonnet: Writing – original draft, Writing – review & editing. Sheyla González: Writing – original draft, Writing – review & editing. JoAnn S. Roberts: Writing – original draft, Writing – review & editing. Sarah Y.T. Robertson: Writing – original draft, Writing – review & editing. Maxime Ruiz: Writing – original draft, Writing – review & editing. Jie Zheng: Writing – review & editing. Sophie X. Deng: Writing – review & editing, Conceptualization.

Acknowledgments

Funding source: SXD received grant support from the National Eye Institute (NEI, 2R01 EY021797 and R01 EY028557) and the California Institute for Regenerative Medicine (TR2-01768, CLIN1-08686, CLIN2-11650). JZ received grant support from the NEI (R01 EY028557). JSR received a Diversity Supplement from the NEI (R01 EY028557). This work is supported in part by an unrestricted grant from Research to Prevent Blindness to the Department of Ophthalmology at the University of California, Los Angeles.

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    Percentage of work contributed by each author in the production of the manuscript is as follows: C. Bonnet, S. Gonzalez, J. S. Roberts; S. Robertson and M. Ruiz all completed literature searches, wrote and edited the manuscript, as well as created and compiled the figures and tables. Each of these authors contributed a section of the manuscript which is up to 15% of the work. J. Zheng contributed to revision and editing the entire manuscript. He contributed 5% of the work. S. Deng conceptualized, wrote and edited the entire manuscript. She contributed 20%.

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