Transcription factors Runx1 to 3 are expressed in the lacrimal gland epithelium and are involved in regulation of gland morphogenesis and regeneration

Advanced Biomaterials for Lacrimal Tissue Engineering: A Review

The lacrimal gland (LG) is vital for ocular health, producing tears that lubricate and protect the eye. Dysfunction of the LG leads to aqueous-deficient dry eye disease (DED), significantly impacting quality of life. Current treatments mainly address symptoms rather than the underlying LG dysfunction, highlighting the need for regenerative therapies. Tissue engineering offers a promising solution, with biomaterials playing crucial roles in scaffolding and supporting cell growth for LG regeneration. This review focuses on recent advances in biomaterials used for tissue engineering of the lacrimal gland. We discuss both natural and synthetic biomaterials that mimic the extracellular matrix and provide structural support for cell proliferation and differentiation. Natural biomaterials, such as Matrigel, decellularized extracellular matrices, chitosan, silk fibroin hydrogels, and human amniotic membrane are evaluated for their biocompatibility and ability to support lacrimal gland cells. Synthetic biomaterials, like polyethersulfone, polyesters, and biodegradable polymers (PLLA and PLGA), are assessed for their mechanical properties and potential to create scaffolds that replicate the complex architecture of the LG. We also explore the integration of growth factors and stem cells with these biomaterials to enhance tissue regeneration. Challenges such as achieving proper vascularization, innervation, and long-term functionality of engineered tissues are discussed. Advances in 3D bioprinting and scaffold fabrication techniques are highlighted as promising avenues to overcome current limitations.

RUN(X) out of blood: emerging RUNX1 functions beyond hematopoiesis and links to Down syndrome

BACKGROUND

RUNX1 is a transcription factor and a master regulator for the specification of the hematopoietic lineage during embryogenesis and postnatal megakaryopoiesis. Mutations and rearrangements on RUNX1 are key drivers of hematological malignancies. In humans, this gene is localized to the 'Down syndrome critical region' of chromosome 21, triplication of which is necessary and sufficient for most phenotypes that characterize Trisomy 21.

MAIN BODY

Individuals with Down syndrome show a higher predisposition to leukemias. Hence, RUNX1 overexpression was initially proposed as a critical player on Down syndrome-associated leukemogenesis. Less is known about the functions of RUNX1 in other tissues and organs, although growing reports show important implications in development or homeostasis of neural tissues, muscle, heart, bone, ovary, or the endothelium, among others. Even less is understood about the consequences on these tissues of RUNX1 gene dosage alterations in the context of Down syndrome. In this review, we summarize the current knowledge on RUNX1 activities outside blood/leukemia, while suggesting for the first time their potential relation to specific Trisomy 21 co-occurring conditions.

CONCLUSION

Our concise review on the emerging RUNX1 roles in different tissues outside the hematopoietic context provides a number of well-funded hypotheses that will open new research avenues toward a better understanding of RUNX1-mediated transcription in health and disease, contributing to novel potential diagnostic and therapeutic strategies for Down syndrome-associated conditions.

The First Transcriptomic Atlas of the Adult Lacrimal Gland Reveals Epithelial Complexity and Identifies Novel Progenitor Cells in Mice

The lacrimal gland (LG) secretes aqueous tears. Previous studies have provided insights into the cell lineage relationships during tissue morphogenesis. However, little is known about the cell types composing the adult LG and their progenitors. Using scRNAseq, we established the first comprehensive cell atlas of the adult mouse LG to investigate the cell hierarchy, its secretory repertoire, and the sex differences. Our analysis uncovered the complexity of the stromal landscape. Epithelium subclustering revealed myoepithelial cells, acinar subsets, and two novel acinar subpopulations: Tfrchi and Car6hi cells. The ductal compartment contained Wfdc2+ multilayered ducts and an Ltf+ cluster formed by luminal and intercalated duct cells. Kit+ progenitors were identified as: Krt14+ basal ductal cells, Aldh1a1+ cells of Ltf+ ducts, and Sox10+ cells of the Car6hi acinar and Ltf+ epithelial clusters. Lineage tracing experiments revealed that the Sox10+ adult populations contribute to the myoepithelial, acinar, and ductal lineages. Using scRNAseq data, we found that the postnatally developing LG epithelium harbored key features of putative adult progenitors. Finally, we showed that acinar cells produce most of the sex-biased lipocalins and secretoglobins detected in mouse tears. Our study provides a wealth of new data on LG maintenance and identifies the cellular origin of sex-biased tear components.

Distinct Inflammatory and Oxidative Effects of Diabetes Mellitus and Hypothyroidism in the Lacrimal Functional Unit

Diabetes mellitus (DM) and hypothyroidism (HT) are prevalent diseases associated with dry eye (DE). Their impact on the lacrimal functional unit (LFU) is poorly known. This work evaluates the changes in the LFU in DM and HT. Adult male Wistar rats had the disease induced as follows: (a) DM: streptozotocin and (b) HT: methimazole. The tear film (TF) and blood osmolarity were measured. Cytokine mRNA was compared in the lacrimal gland (LG), trigeminal ganglion (TG), and cornea (CO). Oxidative enzymes were evaluated in the LG. The DM group showed lower tear secretion (p = 0.02) and higher blood osmolarity (p < 0.001). The DM group presented lower mRNA expression of TRPV1 in the cornea (p = 0.03), higher Il1b mRNA expression (p = 0.03), and higher catalase activity in the LG (p < 0.001). The DM group presented higher Il6 mRNA expression in the TG (p = 0.02). The HT group showed higher TF osmolarity (p < 0.001), lower expression of Mmp9 mRNA in the CO (p < 0.001), higher catalase activity in the LG (p = 0.002), and higher expression of Il1b mRNA in the TG (p = 0.004). The findings revealed that DM and HT induce distinct compromises to the LG and the entire LFU.

Lacrimal Gland Epithelial Cells Shape Immune Responses through the Modulation of Inflammasomes and Lipid Metabolism

Lacrimal gland inflammation triggers dry eye disease through impaired tear secretion by the epithelium. As aberrant inflammasome activation occurs in autoimmune disorders including Sjögren's syndrome, we analyzed the inflammasome pathway during acute and chronic inflammation and investigated its potential regulators. Bacterial infection was mimicked by the intraglandular injection of lipopolysaccharide (LPS) and nigericin, known to activate the NLRP3 inflammasome. Acute injury of the lacrimal gland was induced by interleukin (IL)-1α injection. Chronic inflammation was studied using two Sjögren's syndrome models: diseased NOD.H2^b compared to healthy BALBc mice and Thrombospondin-1-null (TSP-1^-/-) compared to TSP-1^WTC57BL/6J mice. Inflammasome activation was investigated by immunostaining using the R26^ASC-citrine reporter mouse, by Western blotting, and by RNAseq. LPS/Nigericin, IL-1α and chronic inflammation induced inflammasomes in lacrimal gland epithelial cells. Acute and chronic inflammation of the lacrimal gland upregulated multiple inflammasome sensors, caspases 1/4, and interleukins Il1b and Il18. We also found increased IL-1β maturation in Sjögren's syndrome models compared with healthy control lacrimal glands. Using RNA-seq data of regenerating lacrimal glands, we found that lipogenic genes were upregulated during the resolution of inflammation following acute injury. In chronically inflamed NOD.H2^b lacrimal glands, an altered lipid metabolism was associated with disease progression: genes for cholesterol metabolism were upregulated, while genes involved in mitochondrial metabolism and fatty acid synthesis were downregulated, including peroxisome proliferator-activated receptor alpha (PPARα)/sterol regulatory element-binding 1 (SREBP-1)-dependent signaling. We conclude that epithelial cells can promote immune responses by forming inflammasomes, and that sustained inflammasome activation, together with an altered lipid metabolism, are key players of Sjögren's syndrome-like pathogenesis in the NOD.H2^b mouse lacrimal gland by promoting epithelial dysfunction and inflammation.

Lens Epithelial Explants Treated with Vitreous Humor Undergo Alterations in Chromatin Landscape with Concurrent Activation of Genes Associated with Fiber Cell Differentiation and Innate Immune Response

Lens epithelial explants are comprised of lens epithelial cells cultured in vitro on their native basement membrane, the lens capsule. Biologists have used lens epithelial explants to study many different cellular processes including lens fiber cell differentiation. In these studies, fiber differentiation is typically measured by cellular elongation and the expression of a few proteins characteristically expressed by lens fiber cells in situ. Chromatin and RNA was collected from lens epithelial explants cultured in either un-supplemented media or media containing 50% bovine vitreous humor for one or five days. Chromatin for ATAC-sequencing and RNA for RNA-sequencing was prepared from explants to assess regions of accessible chromatin and to quantitatively measure gene expression, respectively. Vitreous humor increased chromatin accessibility in promoter regions of genes associated with fiber differentiation and, surprisingly, an immune response, and this was associated with increased transcript levels for these genes. In contrast, vitreous had little effect on the accessibility of the genes highly expressed in the lens epithelium despite dramatic reductions in their mRNA transcripts. An unbiased analysis of differentially accessible regions revealed an enrichment of cis-regulatory motifs for RUNX, SOX and TEAD transcription factors that may drive differential gene expression in response to vitreous.

Generation of 3D lacrimal gland organoids from human pluripotent stem cells

Lacrimal glands are the main exocrine glands of the eyes. Situated within the orbit, behind the upper eyelid and towards the temporal side of each eye, they secrete lacrimal fluid as a major component of the tear film. Here we identify cells with characteristics of lacrimal gland primordia that emerge in two-dimensional eye-like organoids cultured from human pluripotent stem cells¹. When isolated by cell sorting and grown under defined conditions, the cells form a three-dimensional lacrimal-gland-like tissue organoid with ducts and acini, enabled by budding and branching. Clonal colony analyses indicate that the organoids originate from multipotent ocular surface epithelial stem cells. The organoids exhibit notable similarities to native lacrimal glands on the basis of their morphology, immunolabelling characteristics and gene expression patterns, and undergo functional maturation when transplanted adjacent to the eyes of recipient rats, developing lumina and producing tear-film proteins.

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.

Exocrine gland structure-function relationships

Fluid secretion by exocrine glandular organs is essential to the survival of mammals. Each glandular unit within the body is uniquely organized to carry out its own specific functions, with failure to establish these specialized structures resulting in impaired organ function. Here, we review glandular organs in terms of shared and divergent architecture. We first describe the structural organization of the diverse glandular secretory units (the end-pieces) and their fluid transporting systems (the ducts) within the mammalian system, focusing on how tissue architecture corresponds to functional output. We then highlight how defects in development of end-piece and ductal architecture impacts secretory function. Finally, we discuss how knowledge of exocrine gland structure-function relationships can be applied to the development of new diagnostics, regenerative approaches and tissue regeneration.

Prognostic importance of RUNX1 expression for head and neck adenoid cystic carcinoma

OBJECTIVE

In the present study, we aimed to investigate the prognostic value of RUNX1 expression in 76 patients with adenoid cystic carcinoma (ACC).

MATERIALS AND METHODS

All cases were arranged in tissue microarray blocks and submitted to immunohistochemistry against RUNX1. These results were statistically correlated with clinicopathologic features, including age, gender, tumour site, tumour size, lymph node status, AJCC clinical stage, distant metastasis, treatment, recurrences, follow-up, histologic pattern, vascular and neural invasion, all of which obtained from patient's medical records.

RESULTS

RUNX1 was expressed in the nuclei of tumour cells, with a mean of 18.1% of positivity. Nuclear RUNX1 expression was significantly associated with AJCC clinical stage (p < .0001), solid histologic pattern (p < .0001), vascular invasion (p < .0001) and presence of local recurrence (p < .0001). Using univariate and multivariate analyses, RUNX1 nuclear expression was significantly associated with a lower disease-free survival (p < .0001 and p = .028, respectively) and disease-specific survival (p < .0001 and p = .018, respectively) rates.

CONCLUSION

In summary, RUNX1 nuclear expression may represent an indicator of unfavourable outcome for patients affected by head and neck ACC.

Origin and Lineage Plasticity of Endogenous Lacrimal Gland Epithelial Stem/Progenitor Cells

The lacrimal gland (LG) is an exocrine organ responsible for the secretion of aqueous tear film. Regenerative and stem cell therapies that target LG repair are coming to the fore, although our understanding of LG cell lineage hierarchy is still incomplete. We utilize the analysis of label-retaining cells (LRCs) and genetic lineage tracing to define LG cell lineage hierarchy. Our study suggests that embryonic LG contains unique long-lived multipotent stem cells that give rise to all postnatal epithelial cell types. Following birth, lineages become established and the fate of progenitor cell descendants becomes restricted. However, some cell lineages retain plasticity after maturation and can trans-differentiate into other cell types upon injury. The demonstration that the LG contains progenitor cells with different levels of plasticity has profound implications for our understanding of LG gland function in homeostasis and disease and will be helpful for developing stem cell-based therapies in the future.

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Multipotent stem cells differentiate into distal Sox10+ and proximal Sox10− lineages

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Lineage-restricted progenitor cells sustain the long-term lacrimal gland maintenance

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Label-retaining cells are localized in the intercalated ducts and excretory ducts

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Some cell lineages in the adult lacrimal gland retain plasticity

Establishment of long-term serum-free culture for lacrimal gland stem cells aiming at lacrimal gland repair

BACKGROUND

Aqueous-deficient dry eye disease (ADDED) resulting from dysfunction of the lacrimal gland (LG) is currently incurable. Although LG stem/progenitor cell-based therapy is considered to be a promising strategy for ADDED patients, the lack of a reliable serum-free culture method to obtain enough lacrimal gland stem cells (LGSCs) and the basic standard of LGSC transplantation are obstacles for further research.

METHODS

Adult mouse LGSCs were cultured in Matrigel-based 3D culture under serum-free culture condition, which contained EGF, FGF10, Wnt3A, and Y-27632. LGSCs were continuously passaged over 40 times every 7 days, and the morphology and cell numbers were recorded. LGSCs were induced to differentiate to ductal cells by reducing Matrigel rigidity, while fetal bovine serum was used for the induction of acinar cells. RT-PCR or qRT-PCR analysis, RNA-sequence analysis, H&E staining, and immunofluorescence were used for characterization and examining the differentiation of LGSCs. LGSCs were allotransplanted into diseased LGs to examine the ability of repairing the damage. The condition of eye orbits was recorded using a camera, the tear production was measured using phenol red-impregnated cotton threads, and the engraftments of LGSCs were examined by immunohistochemistry.

RESULTS

We established an efficient 3D serum-free culture for adult mouse LGSCs, in which LGSCs could be continuously passaged for long-term expansion. LGSCs cultured from both the healthy and ADDED mouse LGs expressed stem/progenitor cell markers Krt14, Krt5, P63, and nestin, had the potential to differentiate into acinar or ductal-like cells in vitro and could engraft into diseased LGs and relieve symptoms of ADDED after orthotopic injection of LGSCs.

CONCLUSION

We successfully established an efficient serum-free culture for adult mouse LGSCs aiming at LG repair for the first time. Our approach provides an excellent theoretical and technical reference for future clinical research for ADDED stem cell therapy.

RUNX transcription factors: orchestrators of development

RUNX transcription factors orchestrate many different aspects of biology, including basic cellular and developmental processes, stem cell biology and tumorigenesis. In this Primer, we introduce the molecular hallmarks of the three mammalian RUNX genes, RUNX1, RUNX2 and RUNX3, and discuss the regulation of their activities and their mechanisms of action. We then review their crucial roles in the specification and maintenance of a wide array of tissues during embryonic development and adult homeostasis.

Molecular regulation of ocular gland development

The tear film is produced by two ocular glands, the lacrimal glands, which produce the aqueous component of this film, and the meibomian glands, which secrete the lipidic component that is key to reduce evaporation of the watery film at the surface of the eye. Embryonic development of these exocrine glands has been mostly studied in mice, which also develop Harderian glands, a third type of ocular gland whose role is still not well understood. This review provides an update on the signalling pathways, transcription factors andextracellular matrix components that have been shown to play a role in ocular gland development.

A microRNA/Runx1/Runx2 network regulates prostate tumor progression from onset to adenocarcinoma in TRAMP mice

While decades of research have identified molecular pathways inducing and promoting stages of prostate cancer malignancy, studies addressing dynamic changes of cancer-related regulatory factors in a prostate tumor progression model are limited. Using the TRAMP mouse model of human prostate cancer, we address mechanisms of deregulation for the cancer-associated transcription factors, Runx1 and Runx2 by identifying microRNAs with reciprocal expression changes at six time points during 33 weeks of tumorigenesis. We molecularly define transition stages from PIN lesions to hyperplasia/neoplasia and progression to adenocarcinoma by temporal changes in expression of human prostate cancer markers, including the androgen receptor and tumor suppressors, Nkx3.1 and PTEN. Concomitant activation of PTEN, AR, and Runx factors occurs at early stages. At late stages, PTEN and AR are downregulated, while Runx1 and Runx2 remain elevated. Loss of Runx-targeting microRNAs, miR-23b-5p, miR-139-5p, miR-205-5p, miR-221-3p, miR-375-3p, miR-382-5p, and miR-384-5p, contribute to aberrant Runx expression in prostate tumors. Our studies reveal a Runx/miRNA interaction axis centered on PTEN-PI3K-AKT signaling. This regulatory network translates to mechanistic understanding of prostate tumorigenesis that can be developed for diagnosis and directed therapy.

Manipulation of Panx1 Activity Increases the Engraftment of Transplanted Lacrimal Gland Epithelial Progenitor Cells

Purpose

Sjögren's syndrome is a systemic chronic autoimmune inflammatory disease that primarily targets the salivary and lacrimal glands (LGs). Currently there is no cure; therefore, cell-based regenerative therapy may be a viable option. LG inflammation is facilitated by extracellular ATP and mediated by the Pannexin-1 (Panx1) membrane channel glycoprotein. We propose that suppression of inflammation through manipulation of Panx1 activity can stimulate epithelial cell progenitor (EPCP) engraftment.

Methods

The expression of pannexins in the mouse and human LG was assayed by qRT-PCR and immunostaining. Acute LG inflammation was induced by interleukin-1α (IL1α) injection. Prior to EPCP transplantation, IL1α-injured or chronically inflamed LGs of thrombospondin-1–null mice (TSP-1^−/−) were treated with the Panx1-specific blocking peptide (¹⁰panx) or the self-deliverable RNAi (sdRNAi). The efficacy of cell engraftment and the area of inflammation were analyzed by microscopy.

Results

Panx1 and Panx2 were detected in the mouse and human LGs. Panx1 and proinflammatory factors were upregulated during acute inflammation at days 1 to 3 after the IL1α injection. The analysis of EPCP engraftment demonstrated a significant and reproducible positive correlation between the ¹⁰panx peptide or Panx1 sdRNAi treatment and the number of engrafted cells. Similarly, treatment of the LG of the TSP-1^−/− mouse (mouse model of chronic LG inflammation) by either Panx1 or Caspase-4 (also known as Casp11) sdRNAi showed a significant decrease in expression of proinflammatory markers and the lymphocyte infiltration.

Conclusions

Our results suggest that blocking Panx1 and/or Casp4 activities is a beneficial strategy to enhance donor cell engraftment and LG regeneration through the reduction of inflammation.

Runx1 mediates the development of the granular convoluted tubules in the submandibular glands

The mouse granular convoluted tubules (GCTs), which are only located in the submandibular gland (SMG) are known to develop and maintain their structure in an androgen-dependent manner. We previously demonstrated that the GCTs are involuted by the epithelial deletion of core binding factor β (CBFβ), a transcription factor that physically interacts with any of the Runt-related transcription factor (RUNX) proteins (RUNX1, 2 and 3). This result clearly demonstrates that the Runx /Cbfb signaling pathway is indispensable in the development of the GCTs. However, it is not clear which of the RUNX proteins plays useful role in the development of the GCTs by activating the Runx /Cbfb signaling pathway. Past studies have revealed that the Runx /Cbfb signaling pathway plays important roles in various aspects of development and homeostatic events. Moreover, the Runx genes have different temporospatial requirements depending on the biological situation. In the present study, the GCTs of the SMG showed a remarkable phenotype of, which phenocopied the epithelial deletion of Cbfb, in epithelial-specific Runx1 conditional knock-out (cKO) mice. The results indicate that Runx1 works as a partner of Cbfb during the development of the GCTs. We also discovered that the depletion of Runx1 resulted in the reduced secretion of saliva in male mice. Consistent with this finding, one of the water channels, Aquaporin-5 (AQP5) was mislocalized in the cytoplasm of the Runx1 mutants, suggesting a novel role of Runx1 in the membrane trafficking of AQP5. In summary, the present findings demonstrated that RUNX1 is essential for the development of the GCTs. Furthermore, RUNX1 could also be involved in the membrane trafficking of the AQP5 protein of the acinar cells in the SMG in order to allow for the proper secretion of saliva.

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.

RNA-Seq and CyTOF immuno-profiling of regenerating lacrimal glands identifies a novel subset of cells expressing muscle-related proteins

The purpose of the present studies was to use CyTOF and RNA-Seq technologies to identify cells and genes involved in lacrimal gland repair that could be targeted to treat diseases of lacrimal gland dysfunction. Lacrimal glands of female BALB/c mice were experimentally injured by intra-glandular injection of interleukin 1 alpha (IL-1α). The lacrimal glands were harvested at various time points following injury (1 to 14 days) and used to either prepare single cell suspensions for CyTOF immuno-phenotyping analyses or to extract RNA for gene expression studies using RNA-Seq. CyTOF immuno-phenotyping identified monocytes and neutrophils as the major infiltrating populations 1 and 2 days post injury. Clustering of significantly differentially expressed genes identified 13 distinct molecular signatures: 3 associated with immune/inflammatory processes included genes up-regulated at days 1–2 and 3 associated with reparative processes with genes up-regulated primarily between days 4 and 5. Finally, clustering identified 65 genes which were specifically up-regulated 2 days post injury which was enriched for muscle specific genes. The expression of select muscle-related proteins was confirmed by immunohistochemistry which identified a subset of cells expressing these proteins. Double staining experiments showed that these cells are distinct from the myoepithelial cells. We conclude that experimentally induced injury to the lacrimal gland leads to massive infiltration by neutrophils and monocytes which resolved after 3 days. RNAseq and immunohistochemistry identified a group of cells, other than myoepithelial cells, that express muscle-related proteins that could play an important role in lacrimal gland repair.

Defining epithelial cell dynamics and lineage relationships in the developing lacrimal gland

The tear-producing lacrimal gland is a tubular organ that protects and lubricates the ocular surface. The lacrimal gland possesses many features that make it an excellent model in which to investigate tubulogenesis, but the cell types and lineage relationships that drive lacrimal gland formation are unclear. Using single-cell sequencing and other molecular tools, we reveal novel cell identities and epithelial lineage dynamics that underlie lacrimal gland development. We show that the lacrimal gland from its earliest developmental stages is composed of multiple subpopulations of immune, epithelial and mesenchymal cell lineages. The epithelial lineage exhibits the most substantial cellular changes, transitioning through a series of unique transcriptional states to become terminally differentiated acinar, ductal and myoepithelial cells. Furthermore, lineage tracing in postnatal and adult glands provides the first direct evidence of unipotent KRT5⁺ epithelial cells in the lacrimal gland. Finally, we show conservation of developmental markers between the developing mouse and human lacrimal gland, supporting the use of mice to understand human development. Together, our data reveal crucial features of lacrimal gland development that have broad implications for understanding epithelial organogenesis.

Strategies for Regenerating the Lacrimal Gland

Purpose of review

Aqueous deficient dry eye disease, a significant cause of morbidity worldwide, is due to dysfunction of the main and accessory lacrimal glands. Recent advances in efforts to regenerate lacrimal gland are reviewed.

Recent findings

Several strategies are being explored: ex vivo culture models of human and non-human lacrimal gland epithelial and myoepithelial cells, isolation and characterization of adult precursor cells within lacrimal glands, directed differentiation of stem cells to lacrimal gland cells, and organogenesis and engraftment techniques.

Summary

Conditions for primary cell culture and expansion are being established and will help in the characterization of lacrimal cells. Presumed adult precursor cells have been isolated, laying down foundations for regeneration. Stem cells have been induced to express features of lacrimal gland cells. Engraftment of ex vivo cultured lacrimal tissue is proof of concept that lacrimal gland regeneration and repopulation is possible.

Human Lacrimal Gland Gene Expression

BACKGROUND

The study of human lacrimal gland biology and development is limited. Lacrimal gland tissue is damaged or poorly functional in a number of disease states including dry eye disease. Development of cell based therapies for lacrimal gland diseases requires a better understanding of the gene expression and signaling pathways in lacrimal gland. Differential gene expression analysis between lacrimal gland and other embryologically similar tissues may be helpful in furthering our understanding of lacrimal gland development.

METHODS

We performed global gene expression analysis of human lacrimal gland tissue using Affymetrix ® gene expression arrays. Primary data from our laboratory was compared with datasets available in the NLM GEO database for other surface ectodermal tissues including salivary gland, skin, conjunctiva and corneal epithelium.

RESULTS

The analysis revealed statistically significant difference in the gene expression of lacrimal gland tissue compared to other ectodermal tissues. The lacrimal gland specific, cell surface secretory protein encoding genes and critical signaling pathways which distinguish lacrimal gland from other ectodermal tissues are described.

CONCLUSIONS

Differential gene expression in human lacrimal gland compared with other ectodermal tissue types revealed interesting patterns which may serve as the basis for future studies in directed differentiation among other areas.

The Emerging Roles of RUNX Transcription Factors in Epithelial-Mesenchymal Transition

Epithelial-mesenchymal transition (EMT) is an evolutionary conserved morphogenetic program necessary for the shaping of the body plan during development. It is guided precisely by growth factor signaling and a dedicated network of specialised transcription factors. These are supported by other transcription factor families serving auxiliary functions during EMT, beyond their general roles as effectors of major signaling pathways. EMT transiently induces in epithelial cells mesenchymal properties, such as the loss of cell-cell adhesion and a gain in cell motility. Together, these newly acquired properties enable their migration to distant sites where they eventually give rise to adult epithelia. However, it is now recognized that EMT contributes to the pathogenesis of several human diseases, notably in tissue fibrosis and cancer metastasis. The RUNX family of transcription factors are important players in cell fate determination during development, where their spatio-temporal expression often overlaps with the occurrence of EMT. Furthermore, the dysregulation of RUNX expression and functions are increasingly linked to the aberrant induction of EMT in cancer. The present chapter reviews the current knowledge of this emerging field and the common themes of RUNX involvement during EMT, with the intention of fostering future research.

Alteration in cellular turnover and progenitor cell population in lacrimal glands from thrombospondin 1-/- mice, a model of dry eye

The purpose of this study was to investigate the changes that occur in the lacrimal glands (LGs) in female thrombospondin 1 knockout (TSP1^-/-) mice, a mouse model of the autoimmune disease Sjogren's syndrome. The LGs of 4, 12, and 24 week-old female TSP1^-/- and C57BL/6J (wild type, WT) mice were used. qPCR was performed to measure cytokine expression. To study the architecture, LG sections were stained with hematoxylin and eosin. Cell proliferation was measured using bromo-deoxyuridine and immunohistochemistry. Amount of CD47 and stem cell markers was analyzed by western blot analysis and location by immunofluorescence microscopy. Expression of stem cell transcription factors was performed using Mouse Stem Cell Transcription Factors RT² Profiler PCR Array. Cytokine levels significantly increased in LGs of 24 week-old TSP1^-/- mice while morphological changes were detected at 12 weeks. Proliferation was decreased in 12 week-old TSP1^-/- mice. Three transcription factors were overexpressed and eleven underexpressed in TSP1^-/- compared to WT LGs. The amount of CD47, Musashi1, and Sox2 was decreased while the amount of ABCG2 was increased in 12 week-old TSP1^-/- mice. We conclude that TSP1 is necessary for maintaining normal LG homeostasis. Absence of TSP1 alters cytokine levels and stem cell transcription factors, LG cellular architecture, decreases cell proliferation, and alters amount of stem cell markers.

Lacrimal Gland Repair Using Progenitor Cells

In humans, the lacrimal gland (LG) is the primary contributor to the aqueous layer of the tear film. Production of tears in insufficient quantity or of inadequate quality may lead to aqueous‐deficiency dry eye (ADDE). Currently there is no cure for ADDE. The development of strategies to reliably isolate LG stem/progenitor cells from the LG tissue brings great promise for the design of cell replacement therapies for patients with ADDE. We analyzed the therapeutic potential of epithelial progenitor cells (EPCPs) isolated from adult wild‐type mouse LGs by transplanting them into the LGs of TSP‐1^−/− mice, which represent a novel mouse model for ADDE. TSP‐1^−/− mice are normal at birth but progressively develop a chronic form of ocular surface disease, characterized by deterioration, inflammation, and secretory dysfunction of the lacrimal gland. Our study shows that, among c‐kit‐positive epithelial cell adhesion molecule (EpCAM⁺) populations sorted from mouse LGs, the c‐kit⁺dim/EpCAM⁺/Sca1⁻/CD34⁻/CD45⁻ cells have the hallmarks of an epithelial cell progenitor population. Isolated EPCPs express pluripotency factors and markers of the epithelial cell lineage Runx1 and EpCAM, and they form acini and ducts when grown in reaggregated three‐dimensional cultures. Moreover, when transplanted into injured or “diseased” LGs, they engraft into acinar and ductal compartments. EPCP‐injected TSP‐1^−/− LGs showed reduction of cell infiltration, differentiation of the donor EPCPs within secretory acini, and substantial improvement in LG structural integrity and function. This study provides the first evidence for the effective use of adult EPCP cell transplantation to rescue LG dysfunction in a model system. Stem Cells Translational Medicine2017;6:88–98

Lacrimal Gland Inflammation Deregulates Extracellular Matrix Remodeling and Alters Molecular Signature of Epithelial Stem/Progenitor Cells

PURPOSE

The adult lacrimal gland (LG) is highly regenerative and is able to repair itself even after substantial damage; however, this ability to regenerate is lost with the development of dry eye conditions in chronically inflamed LGs.This study compares changes in the cell adhesion and cell matrix molecules and stem cell transcription factors in the LGs of healthy mice and of two mouse models of Sjögren's syndrome: nonobese diabetic (NOD) and MRL-lpr/lpr (MRL/lpr) mice during the early stage of inflammation.

METHODS

The LGs from 12- to 13-week-old female MRL/lpr and male NOD mice along with their respective control strains were harvested and divided into three pieces and processed for quantitative (q) RT-PCR and qRT-PCR Arrays, histology, immunohistochemistry, and Western blotting.

RESULTS

The extracellular matrix (ECM) and adhesion molecules RT2-PCR array combined with protein expression data revealed changes in the expression of integrins, matrix metalloproteinases, and other molecules, which are associated largely with invasion, attachment, and expansion of the lymphocytic cells, whereas changes in the stem cell transcription factors revealed substantial decrease in expression of transcription factors associated with epithelial stem/progenitor cell lineage.

CONCLUSIONS

We concluded that the expression of several important ECM components is significantly deregulated in the LG of two murine models of Sjögren's syndrome, suggesting an alteration of the epithelial stem/progenitor cell niche. This may result in profound effects on localization, activation, proliferation, and differentiation of the LG stem/progenitor cells and, therefore, LG regeneration.

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.

Three-Dimensional Culture of Functional Adult Rabbit Lacrimal Gland Epithelial Cells on Decellularized Scaffold

Aqueous tear-deficient dry eye disease is a multifactorial chronic disorder, in which the lacrimal gland fails to produce enough tears to maintain a healthy ocular surface. Some severe cases may develop corneal damage and significant vision loss. Treatment primarily involves palliation using ocular surface lubricants, but can only provide temporary relief. Construction of a bioengineered lacrimal gland having functional secretory epithelial cells is a potentially promising option for providing long-term relief to severe dry eye patients. Using sphere-forming culture techniques, we cultured adult rabbit lacrimal gland progenitor cells and prepared a lacrimal gland scaffold by decellularization. When progenitor cells were seeded onto the decellularized scaffold, they formed duct- and acinar-like structures in the three-dimensional culture system. Lacrimal gland epithelial cells showed good cell viability, cell differentiation, and secretory function in decellularized lacrimal gland matrix, as indicated by morphology, immunostaining, and β-hexosaminidase secretion assay. This study demonstrated the potential suitability of utilizing tissue-specific progenitor cells and a tissue-derived bioscaffold for lacrimal gland restoration.

Runx1 promotes proliferation and neuronal differentiation in adult mouse neurosphere cultures

Traumatic brain injury alters the signaling environment of the adult neurogenic niche and may activate unique proliferative cell populations that contribute to the post-injury neurogenic response. Runx1 is not normally expressed by adult neural stem or progenitor cells (NSPCs) but is induced in a subpopulation of putative NSPCs after brain injury in adult mice. In order to investigate the role of Runx1 in NSPCs, we established neurosphere cultures of adult mouse subventricular zone NSPCs. We show that Runx1 is basally expressed in neurosphere culture. Removal of the mitogen bFGF or addition of 1% FBS decreased Runx1 expression. Inhibition of endogenous Runx1 activity with either Ro5-3335 or shRNA-mediated Runx1 knockdown inhibited NSPC proliferation without affecting differentiation. Lentiviral mediated over-expression of Runx1 in neurospheres caused a significant change in cell morphology without reducing proliferation. Runx1-overexpressing neurospheres changed from floating spheres to adherent colonies or individual unipolar or bipolar cells. Flow cytometry analysis indicated that Runx1 over-expression produced a significant increase in expression of the neuronal marker TuJ1 and a minor increase in the astrocytic marker S100β. Thus, Runx1 expression drove adult NSPC differentiation, predominantly toward a neuronal lineage. These data suggest that Runx1 could be manipulated after injury to promote neuronal differentiation to facilitate repair of the CNS.

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

Lacrimal gland (LG) insufficiency is a main cause for severe dry eye leading to pain, visual impairment, and eventually loss of sight. Engineering of transplantable LG tissue with secretory capacity is a desirable goal. In this study, a three-dimensional decellularized LG (DC-LG) scaffold with preserved LG morphology was generated by treatment with 1% sodium deoxycholate and DNase solution using porcine LG tissue. To address clinical applicability, the primary in vitro culture of secretory active LG cells from a small tissue biopsy of 1.5 mm diameter was introduced and compared with an established isolation method by enzymatic digestion. Cells from both isolation methods depicted an epithelial phenotype, maintained their secretory capacity for up to 30 days, and exhibited progenitor cell capacity as measured by aldehyde dehydrogenase-1 activity, side population assay, and colony-forming units. Cells from passage 0 were reseeded into the DC-LG and secretory active cells migrated into the tissue. The cells resembled an LG-like morphology and the constructs showed secretory activity. These results demonstrate the possibility of engineering a secretory competent, three-dimensional LG construct using LG cells expanded from a small tissue biopsy and DC-LG as a matrix that provides the native structure and physiological niche for these cells.

Myoepithelial Cells: Their Origin and Function in Lacrimal Gland Morphogenesis, Homeostasis, and Repair

Lacrimal gland (LG) is an exocrine tubuloacinar gland that secretes the aqueous layer of the tear film. LG epithelium is composed of ductal, acinar, and myoepithelial cells (MECs) bordering the basal lamina and separating the epithelial layer from the extracellular matrix. Mature MECs have contractile ability and morphologically resemble smooth muscle cells; however, they exhibit features typical for epithelial cells, such as the presence of specific cytokeratin filaments. Increasing evidence supports the assertion that myoepithelial cells (MECs) play key roles in the lacrimal gland development, homeostasis, and stabilizing the normal structure and polarity of LG secretory acini. MECs take part in the formation of extracellular matrix gland and participate in signal exchange between epithelium and stroma. MECs have a high level of plasticity and are able to differentiate into several cell lineages. Here, we provide a review on some of the MEC characteristics and their role in LG morphogenesis, maintenance, and repair.

Runx1 exon 6-related alternative splicing isoforms differentially regulate hematopoiesis in mice

RUNX1 is an important transcription factor for hematopoiesis. There are multiple alternatively spliced isoforms of RUNX1. The best known isoforms are RUNX1a from use of exon 7A and RUNX1b and c from use of exon 7B. RUNX1a has unique functions due to its lack of C-terminal regions common to RUNX1b and c. Here, we report that the ortholog of human RUNX1a was only found in primates. Furthermore, we characterized 3 Runx1 isoforms generated by exon 6 alternative splicing. Runx1bEx6(-) (Runx1b without exon 6) and a unique mouse Runx1bEx6e showed higher colony-forming activity than the full-length Runx1b (Runx1bEx6(+)). They also facilitated the transactivation of Runx1bEx6(+). To gain insight into in vivo functions, we analyzed a knock-in (KI) mouse model that lacks isoforms Runx1b/cEx6(-) and Runx1bEx6e. KI mice had significantly fewer lineage-Sca1(+)c-Kit(+) cells, short-term hematopoietic stem cells (HSCs) and multipotent progenitors than controls. In vivo competitive repopulation assays demonstrated a sevenfold difference of functional HSCs between wild-type and KI mice. Together, our results show that Runx1 isoforms involving exon 6 support high self-renewal capacity in vitro, and their loss results in reduction of the HSC pool in vivo, which underscore the importance of fine-tuning RNA splicing in hematopoiesis.