Characterization of immortalized rabbit lacrimal gland epithelial cells

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.

Non-invasive in vivo molecular imaging of intra-articularly transplanted immortalized bone marrow stem cells for osteoarthritis treatment

Pathophysiology of osteoarthritis (OA) is characterized by progressive loss of articular cartilage in the knee-joints. To impart regenerative ability in lowly metabolizing chondrocytes, the bone marrow stem cells (BMSCs) has recently been recognized as a superior alternative treatment for OA. However, study of primary BMSCs-mediated chondrogenesis is difficult due to progressive cellular aging and replicative senescence. To obtain a therapeutic cell population for OA, BMSCs were immortalized by human papilloma virus (HPV)-16 E6/E7 along with mCherry luciferase (mCL), a gene marker for non-invasive imaging, and designated as iBMSCs-mCL. Next, their cell morphology, population doubling time (PDT) and colony forming ability (CFU) were evaluated. Furthermore, pluripotency and immunophenotypic markers were investigated. To deduce therapeutic ability, iBMSCs-mCL were intra-articularly injected into right knee of anterior cruciate ligament transaction (ACLT)-OA mice model and tracked through non-invasive bioluminescence imaging. Cell morphology of iBMSCs-mCL was similar to parental BMSCs. PDT and CFU ability of iBMSCs-mCLs were significantly increased. Pluripotency and immunophenotypic markers were highly expressed in iBMSC-mCL. Long-term survival and tri-lineage differentiation particularly chondrogenic potential of iBMSCs-mCL were also demonstrated in vitro and then in vivo which was monitored through non-invasive imaging. Intensive bioluminescent signals in iBMSCs-mCL administered knee-joint indicated a marked in vivo survival and proliferation of iBMSCs-mCL. Immunohistochemical staining for type II collagen (IHC of Col II) and alcian blue & safranin o staining of proteoglycans also corroborated cartilage regeneration by iBMSCs-mCL. Conclusively, iBMSCs-mCL maintains stemness and in vivo cartilage regeneration potential suggesting a promising avenue for development of OA therapeutics.

Challenges and Strategies for Regenerating the Lacrimal Gland

The lacrimal gland produces the aqueous component of tears, including electrolytes, peptides, and glycoproteins necessary to maintain homeostasis and optical properties of the ocular surface. Stem cells that contribute to the homeostasis of the lacrimal gland are under extensive study. It is still unclear whether such stem cells are of mesenchymal or epithelial origin. It is also possible that a unique epithelial stem cell undergoes epithelial-mesenchymal transition and contributes to the mesenchyme. Developmental studies in mice have shown that a network of growth factors contributes to epithelial-mesenchymal interaction during morphogenesis of the lacrimal gland. Recently, the developmental process was successfully recapitulated in vitro, providing a valuable tool for study of lacrimal gland development and possibly opening doors to regenerative therapy. While further studies are required to identify and appreciate the potential of lacrimal gland stem cells, advances in stem cell biology in general should become a catalyst towards developing regenerative therapy of the lacrimal gland.

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.

Sjogrens syndrome as failed local immunohomeostasis: prospects for cell-based therapy

Sjogrens syndrome has been estimated to affect between 0.2% and 2% or more of the population. It is an autoimmune disease with the hallmark histopathology of focal, periductal, and perivascular CD4(+) cell infiltration of the lacrimal and salivary glands. The immunohistopathology is typically associated with severe lacrimal and salivary dysfunctions, which contribute to debilitating ocular surface and oral symptoms. The quality of life of patients with Sjogrens syndrome often is degraded further by serious, multisystemic manifestations, and they are subject to a forty-fold increased risk of developing B cell lymphomas. In normal lacrimal glands, secretory epithelial cells, autoimmune effector lymphocytes, and regulatory lymphocytes can be seen as collaborating to maintain a local immunohomeostasis. The epithelium contributes by secreting immunomodulatory paracrine factors and also by continuously exposing autoantigens, which thereby become available for uptake by professional antigen presenting cells (APCs). Local or systemic perturbations may initiate autoimmune pathophysiology by impairing the replacement of normally-turning-over regulatory cells, by altering epithelial production of immunomodulatory paracrine factors, by inducing intact epithelial cells to begin secreting previously cryptic epitopes (epitopes that previously were not available to bind to major histocompatibility complex (MHC) molecules and so could not be recognized by T cell antigen receptors), and by inducing epithelial cells to begin expressing MHC Class II molecules and presenting formerly cryptic epitopes directly to CD4(+) cells. This process has been modeled ex vivo with mixed cell reactions comprised of isolated epithelial cells and autologous lymphocytes. This development has occurred as studies of anterior chamber-associated immune deviation (ACAID) and other immunoregulatory phenomena have elucidated the origins and functions of several different kinds of regulatory lymphocytes and shown that regulatory lymphocytes can be generated ex vivo. It now is possible to envision strategies for exploiting each possible mode of epithelial autoantigen exposure to produce therapeutic regulatory cells that might be capable of re-establishing normal immunohomeostasis. Consideration of the hypothetical therapies identifies a number of basic questions that warrant investigation.

Current status of gene delivery and gene therapy in lacrimal gland using viral vectors

Gene delivery is one of the biggest challenges in the field of gene therapy. It involves the efficient transfer of transgenes into somatic cells for therapeutic purposes. A few major drawbacks in gene delivery include inefficient gene transfer and lack of sustained transgene expression. However, the classical method of using viral vectors for gene transfer has circumvented some of these issues. Several kinds of viruses, including retrovirus, adenovirus, adeno-associated virus, and herpes simplex virus, have been manipulated for use in gene transfer and gene therapy applications. The transfer of genetic material into lacrimal epithelial cells and tissues, both in vitro and in vivo, has been critical for the study of tear secretory mechanisms and autoimmunity of the lacrimal gland. These studies will help in the development of therapeutic interventions for autoimmune disorders such as Sjögren's syndrome and dry eye syndromes which are associated with lacrimal dysfunction. These studies are also critical for future endeavors which utilize the lacrimal gland as a reservoir for the production of therapeutic factors which can be released in tears, providing treatment for diseases of the cornea and posterior segment. This review will discuss the developments related to gene delivery and gene therapy in the lacrimal gland using several viral vector systems.

Polyethersulfone dead-end tube as a scaffold for artificial lacrimal glandsin vitro

Polyethersulfone (PES) dead-end tubes were fabricated by means of a phase inversion technique, and then were used as scaffolds for artificial lacrimal glands. The wall of the dead-end tubes could allow nutrients such as ascorbic acid, L-tryptophan, and glucose to pass through, but prevents rat IgG from passing through. Lacrimal acinar epithelial cells of Sprague-Dawley rats were cultured in vitro, and cell-associated secretory component was detected with an immunofluorescence technique to identify the acinar cells. The second passage of the cells showed high degree of cellular differentiation, and was used to seed on the PES tubes. The results showed that the PES tube could support the attachment, the growth, and the proliferation of the rat lacrimal acinar cells. Thus, PES is a substrate for the growth of lacrimal acinar cells and may be a useful scaffolding biomaterial for tissue engineering, such as a scaffold for artificial lacrimal glands.

Sensory denervation modulates eIF-2 alpha kinase expression in the rabbit lacrimal gland

PURPOSE

To investigate the hypothesis that sensory denervation of the rabbit lacrimal gland results in dysregulation of protein synthesis. We used differential display of mRNA to identify genes associated with protein synthesis and secretion that may be altered in this situation.

METHODS

New Zealand white rabbits underwent unilateral sensory denervation by the ablation of the trigeminal ganglion. After 7 days, the denervated and contralateral control lacrimal glands were removed. The effects of denervation on gene expression were carried out using differential mRNA display. Northern and Western blot analyses were used to verify differential gene expression.

RESULTS

Differential mRNA display identified the gene heme-regulated inhibitor eukaryotic initiation factor-2 alpha kinase (HRI eIF-2a kinase) in the lacrimal gland, the expression of which was reduced in the denervated lacrimal gland. The sequenced fragment from differential display showed 94% identity to rabbit HRI eIF-2a kinase. The decreased expression of HRI eIF-2a kinase was confirmed by Northern and Western blots, and measurement of HRI eIF-2a kinase phosphorylation activity in the lacrimal gland after ablation of sensory neurons showed that it was significantly decreased compared with that of normal and control lacrimal glands.

CONCLUSIONS

The results suggest that loss of sensory innervation has a role in the lacrimal gland, contributing to the expression of HRI eIF-2a kinase, a pivotal negative regulator of protein synthesis. A reduction in control of protein synthesis may lead to the translation of repressed messages associated with cell stress responses.

Peroxisome proliferator-activated receptor agonists inhibit interleukin-1beta-mediated nitric oxide production in cultured lacrimal gland acinar cells

Development of dry eye disease often occurs in individuals with autoimmune disorders such as Sjögren's syndrome. The cause of dry eye in these patients is thought to be due, at least in part, to lymphocytic infiltration of the lacrimal glands, with subsequent loss of secretion of the aqueous component of tear film. How this lymphocytic infiltration leads to loss of secretion is not fully understood. We have previously shown that the proinflammatory cytokine, interleukin-1beta (IL-1beta), can stimulate the production of nitric oxide (NO) in cultured lacrimal gland acinar cells. It is possible that IL-1beta, produced by the infiltrating macrophages, stimulates production of inducible nitric oxide synthase (iNOS), and subsequently excessive production of NO. Peroxynitrate and other radical byproducts associated with excessive synthesis of NO may be detrimental to normal function of the lacrimal gland. Here we show that the peroxisome proliferator-activated receptor (PPAR)alpha and gamma agonists can inhibit NO production in cultured lacrimal gland acinar cells. Further, this is accomplished without loss of iNOS expression or tetrahydrobiopterin. These data suggest that the use of ointments or eye drops containing these PPAR agonists may provide an effective therapeutic intervention for the prevention of dry eye in Sjögren's syndrome patients.

Induction of nitric oxide synthase and over-production of nitric oxide by interleukin-1beta in cultured lacrimal gland acinar cells

PURPOSE

Inflammation of the lacrimal gland is one of the major causative factors in aqueous tear-deficient dry eye syndrome. Pro-inflammatory cytokine production is upregulated in lacrimal gland autoimmune disease (i.e. Sjögren's syndrome) and is associated with cell death. The expression of inducible nitric oxide synthase (iNOS/NOS-2) is known to be induced in the presence of pro-inflammatory cytokines in several secretory epithelial cell types. We hypothesize that pro-inflammatory cytokines, such as interleukin-1beta (IL-1beta), cause a marked increase in nitric oxide (NO) production via induction of iNOS in lacrimal gland epithelial cells and that this may be a significant pathophysiological pathway of dry eye syndrome.

METHODS

Cultured immortalized rabbit lacrimal gland acinar cells were incubated with IL-1beta, iNOS inhibitor, or IL-1 receptor antagonist (IL-1ra). Colorimetric detection of NO(2)(-) and NO(3)(-) in the media, measured by the Griess reaction, was used as an index of NO production. Expression of iNOS was determined by SDS-PAGE and Western blot.

RESULTS

IL-1beta stimulated a concentration-dependent and time-dependent increase in NO production. IL-1beta-induced NO production was significantly antagonized by co-incubation with IL-1ra or the iNOS-specific inhibitor, 1400W. Expression of iNOS protein was greatest at 4hr after addition of IL-1beta, and was nearly undetectable at 12hr. IL-1ra greatly reduced IL-1beta-induced iNOS expression.

CONCLUSIONS

Lacrimal gland acinar cells are able to produce iNOS in response to the pro-inflammatory cytokine IL-1beta. The amount of iNOS expressed and the subsequent levels of NO that are produced by lacrimal cells are far lower than those seen in macrophages, but are consistent with those reported for other cell types in the literature. This pathway of iNOS induction and overproduction of NO may be a factor in lacrimal gland cell death in dry eye syndrome. Inhibitors of iNOS or IL-1 receptor may be beneficial for controlling lacrimal gland inflammation.

Regulatory pathways in lacrimal gland epithelium

Tears are a complex fluid that continuously cover the exposed surface of the eye, namely the cornea and conjunctiva. Tears are secreted in response to the multitude of environmental stresses that can harm the ocular surface such as cold, mechanical stimulation, physical injury, noxious chemicals, as well as infections from various organisms. Tears also provide nutrients and remove waste from cells of the ocular surface. Because of the varied function of tears, tears are complex and are secreted by several different tissues. Tear secretion is under tight neural control allowing tears to respond rapidly to changing environmental conditions. The lacrimal gland is the main contributor to the aqueous portion of the tear film and the regulation of secretion from this gland has been well studied. Despite multiple redundencies in pathways to stimulate secretion from the lacrimal gland, defects can occur resulting in dry eye syndromes. These diseases can have deleterious effects on vision. In this review, we summarize the latest information regarding the regulatory pathways, which control secretion from the lacrimal gland, and their roles in the pathogenesis of dry eye syndromes.

Down-regulation of androgen receptor expression and inhibition of lacrimal gland cell proliferation by retinoic acid

Androgens and retinoids are known to be involved in control of lacrimal gland function. Because retinoids generally antagonize androgen function it was the purpose of this study to investigate interactions of retinoic acid and androgens in rabbit lacrimal acinar cells in culture by determining effects of retinoic acid on androgen receptor (AR) mRNA expression, AR protein levels and androgen-stimulated cell proliferation. Experiments were conducted using primary rabbit lacrimal acinar cells and a transformed rabbit lacrimal acinar cell line. Exposure of primary lacrimal acinar cells in culture to 10(-10)-10(-6)M all-trans retinoic acid for 4-24hr causes an approximately 50% decrease in AR mRNA expression. Expression of AR protein in primary and transformed rabbit lacrimal acinar cells was confirmed by immunohistochemistry. Exposure of the primary cells to 10(-6)M retinoic acid for 24hr caused a 40% decrease in AR protein levels as determined by measurement of binding of(3) [H]-dihydrotestosterone (DHT) to cells in culture and Scatchard analysis. Exposure to 10(-9)-10(-6)M DHT stimulates proliferation of transformed rabbit lacrimal acinar cells. This effect is receptor mediated since it is blocked by the AR antagonist, flutamide. Proliferation of the lacrimal acinar cells is inhibited by retinoic acid, as compared to control, and retinoic acid also completely inhibits androgen stimulation of cell proliferation. This study supports the hypothesis that androgens play a supportive role in lacrimal gland function. The antagonistic influences of androgens and retinoic acid suggests that, under physiologic conditions there is a balance between the effects of androgens and retinoids in the lacrimal gland. A decrease in androgen levels in a dry eye patient may alter the balance between the effects of these important controllers of gene expression. The antagonistic effect of retinoids on androgens in the lacrimal gland must also be considered when devising pharmaceutical treatments for dye eye.

Nitric oxide and cyclic GMP-mediated protein secretion from cultured lacrimal gland acinar cells

PURPOSE

Nitric oxide (NO) donors and NO synthase (NOS) substrates were tested for their use to stimulate protein secretion from cultured lacrimal gland acinar cells, through activation of guanylate cyclase.

METHOD

Rabbit lacrimal gland epithelial cells (RLG cells) were incubated with NO donors and/or NOS substrates and the protein released into culture medium was determined with bicinchoninic acid assay. Guanylate cyclase activation by NO precursors was determined by measurement of c-GMP produced.

RESULTS

Both NO donors and NOS substrates were able to stimulate protein release from RLG cells. Among 6 compounds studied, sodium nitroprusside, isosorbide dinitrate and N(a)-benzoyl L-arginine ethyl ester (BAEE) were most potent to release protein over 100% of the basal release. The guanylate cyclase activity was stimulated by these NO precursors and was inhibited by guanylate cyclase inhibitor, [1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ).

CONCLUSION

NO donors and NOS substrates were able to stimulate protein release from RLG cells via activation of guanylate cyclase and c-GMP release, which was blocked by guanylate cyclase inhibitor, ODQ. It indicates that NO donors and NOS substrates could be used for the treatment of dry eye syndrome if the same holds true in dry eye animal models.

Intermediate filament, laminin and integrin expression in lacrimal gland acinar cells: comparison of an immortalized cell line to primary cells, and their response to retinoic acid

PURPOSE

The goal of this study was to characterize intermediate filament, integrin and laminin expression by rabbit lacrimal gland acinar cells in culture, to determine whether retinoic acid (RA) alters expression of these proteins and to compare primary cells to an immortalized rabbit lacrimal gland acinar cell line using flow cytometric analysis.

METHODS

Primary cells, maintained in serum free medium, were exposed to 10(-6) M retinoic acid for 24 hours. Immortalized cells were grown in defined medium with Nu-Serum and exposed to retinoic acid. Cells were labeled with monoclonal antibodies to cytokeratins (AE1, AE2, AE3, AE5, CK10/13, CK18), integrins (alpha(3), alpha(6), alpha(V), beta(1), beta(2), beta(3) and beta(4)), laminin, or vimentin and with FITC-conjugated secondary antibodies. Cells were analyzed for antigen expression by flow cytometry and immunocytochemistry.

RESULTS

Primary and immortalized cells expressed type I and type II epithelial cytokeratins (AE1 and AE3), cytokeratin 18, and cytokeratin 3 (AE5) Both cell types were negative to AE2 and CK10/13. Primary and immortalized cells expressed vimentin in culture, with immortalized cells expressing this protein at higher levels. Lacrimal acinar cells appear to synthesize laminin which was detected intracellularly in both cells types. Integrins alpha(6) (CD49f) and alpha(V) (CD51) were expressed by primary and immortalized cells. Expression of integrin alpha(6) was 10-fold higher in immortalized cells compared to primary cells. Retinoic acid increased integrin alpha( V) expression by primary and immortalized cells 1.3-fold and 3-fold, respectively, and caused a slight increase in integrin alpha(6) expression by primary cells. Both cell types also expressed integrins beta( 1), beta(2) and beta(3), but beta(4) was detected only in immortalized cells. Lacrimal acinar cells do not express integrin alpha(3).

CONCLUSIONS

Expression of cytokeratins, laminin and integrins by primary and immortalized cells was similar, suggesting that the immortalized cell line is a good model for the study of lacrimal structure and function. Since retinoic acid up-regulated only integrin alpha(V), but not cytokeratins, these cells appear to be highly differentiated. Flow cytometry is a useful method for analysis of protein expression by lacrimal acinar cells.