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

FGF Gradient Controls Boundary Position Between Proliferating and Differentiating Cells and Regulates Lacrimal Gland Growth Dynamics

Fibroblast growth factor (FGF) signaling plays an important role in controlling cell proliferation, survival, and cell movements during branching morphogenesis of many organs. In mammals branching morphogenesis is primarily regulated by members of the FGF7-subfamily (FGF7 and FGF10), which are expressed in the mesenchyme, and signal to the epithelial cells through the “b” isoform of fibroblast growth factor receptor-2 (FGFR2). Our previous work demonstrated that FGF7 and FGF10 form different gradients in the extracellular matrix (ECM) and induce distinct cellular responses and gene expression profiles in the lacrimal and submandibular glands. The last finding was the most surprising since both FGF7 and FGF10 bind signal most strongly through the same fibroblast growth factor receptor-2b isoform (FGFR2b). Here we revisit this question to gain an explanation of how the different FGFs regulate gene expression. For this purpose, we employed our ex vivo epithelial explant migration assay in which isolated epithelial explants are grown near the FGF loaded beads. We demonstrate that the graded distribution of FGF induces activation of ERK1/2 MAP kinases that define the position of the boundary between proliferating “bud” and differentiating “stalk” cells of growing lacrimal gland epithelium. Moreover, we showed that gene expression profiles of the epithelial explants exposed to distinct FGFs strictly depend on the ratio between “bud” and “stalk” area. Our data also suggests that differentiation of “stalk” and “bud” regions within the epithelial explants is necessary for directional and persistent epithelial migration. Gaining a better understanding of FGF functions is important for development of new approaches to enhance tissue regeneration.

Comparative study of four interleukin 17 cytokines of tongue sole Cynoglossus semilaevis: Genomic structure, expression pattern, and promoter activity

The interleukin (IL)-17 cytokine family participates in the regulation of many cellular functions. In the present study, we analyzed the genomic structure, expression, and promoter activity of four IL-17 members from the teleost fish tongue sole (Cynoglossus semilaevis), i.e. CsIL-17C CsIL-17D, CsIL-17F, and IL-17F like (IL-17Fl). We found that CsIL-17C, CsIL-17D, CsIL-17F, and CsIL-17Fl share 21.2%-28.6% overall sequence identities among themselves and 31.5%-71.2% overall sequence identities with their counterparts in other teleost. All four CsIL-17 members possess an IL-17 domain and four conserved cysteine residues. Phylogenetic analysis classified the four CsIL-17 members into three clusters. Under normal physiological conditions, the four CsIL-17 expressed in multiple tissues, especially non-immune tissues. Bacterial infection upregulated the expression of all four CsIL-17, while viral infection upregulated the expression of CsIL-17D and CsIL-17Fl but downregulated the expression of CsIL-17C and CsIL-17F. The 1.2 kb 5'-flanking regions of the four CsIL-17 exhibited apparent promoter activity and contain a number of putative transcription factor-binding sites. Furthermore, the promoter activities of CsIL-17C, CsIL-17D, and CsIL-17F, but not CsIL-17Fl, were modulated to significant extents by lipopolysaccharide, PolyI:C, and PMA. This study provides the first evidence that in teleost, different IL-17 members differ in expression pattern and promoter activity.

Comparison of gene expression profiles of conjunctival cell lines with primary cultured conjunctival epithelial cells and human conjunctival tissue

Human conjunctival cell lines are useful tools for modeling ocular surface disease and evaluation of ocular drugs and cosmetics. However, gene expression in these cells may not be comparable to primary cultured cells, raising doubts that they could be used as a substitute. We aimed to ascertain the similarities of global gene expression between commonly used cell lines and primary cells using a microarray approach. The Affymetrix U133A chip (>22,000 genes) was used to investigate conjunctival tissue (CT), primary conjunctival epithelial cells (PCEC), two conjunctival epithelial cell lines (IOBA-NHC and ChWK), and HCEC-T, a human corneal epithelial cell line (control). Using principal component analysis, the PCEC profile was clustered more closely to conjunctival tissue than either of the two cell lines. Certain extracellular matrix genes were differentially upregulated in CT compared to PCEC, suggesting presence of fibroblasts in addition to epithelial cells in CT. Overall, 67.3% (95% CI: 66.7-67.9) of transcripts in IOBA-NHC were within 1.5-fold of the corresponding transcripts in PCEC, but only 62.2% (95% CI: 61.5-62.9) in the case of ChWK. In HCEC-T, the proportion was only 58.8% (95% CI 58.1-59.4), suggesting less resemblance to PCEC than the conjunctival epithelial cell lines. The IOBA-NHC profile was more similar to PCEC than ChWK, for all genes and genes concerned with membrane association, communication, development, and regulation of metabolism, especially protein and nucleic acid metabolism. The correlation of normalized gene expression levels was high between either the IOBA-NHC or ChWK and PCEC for genes concerned with cell defense, viral life cycle, antigen presentation, antioxidation, or ubiquitin ligation. In order to evaluate the functional significance of the altered gene expression in IOBA-NHC cells, we evaluated a few proteins important for epithelial differentiation or defense, corresponding to the transcripts for S100A9, TGM2, and TLR4. Protein levels of S100A9 and TGM2 were indeed raised, and TLR4 decreased, in IOBA-NHC compared to PCEC. Gene expression in conjunctival cell lines differs from primary cells, but the profile varies according to functional gene categories. Depending on the methodology of proposed studies, if there is limited availability of PCEC, NHC-IOBA may be more suitable than ChWK, but even then, epithelial differentiation and innate immunity functions in NHC-IOBA may differ from primary cells.

Tearful relationships? Sex, hormones, the lacrimal gland, and aqueous-deficient dry eye

Sex and the endocrine system exert a significant influence on the physiology and pathophysiology of the lacrimal gland. The purpose of this article is to briefly review the nature and magnitude of these interactions between sex, hormones and lacrimal tissue, and to address how they may relate to the pathogenesis of aqueous-deficient dry eye. Towards this end, this article has a 3-fold approach: first, to summarize the influence of androgens, estrogens, glucocorticoids, mineralocorticoids, retinoic acid, prolactin, alpha-melanocyte stimulating hormone, adrenocorticotropic hormone, luteinizing hormone, follicle-stimulating hormone, growth hormone, thyroid-stimulating hormone, arginine vasopressin, oxytocin, thyroxine, parathyroid hormone, insulin, glucagon, melatonin, human chorionic gonadotropin and cholecystokinin on the structure and function of the lacrimal gland; second, to discuss the mechanism of action of each hormone on lacrimal tissue; and third, to discuss the clinical relevance of the endocrine-lacrimal gland interrelationship, with a particular focus on each hormone's role (i.e. if relevant) in the development of aqueous-tear deficiency.

Integrin adhesion in regulation of lacrimal gland acinar cell secretion

The extracellular microenvironment regulates lacrimal gland acinar cell secretion. Culturing isolated rabbit lacrimal gland acinar cells on different extracellular matrix proteins revealed that laminin enhances carbachol-stimulated secretion to a greater extent than other extracellular matrix proteins investigated. Furthermore, immunofluorescence indicated that integrin subunits, potentially functioning as laminin receptors are present in acinar cells. Among these, the integrin alpha6 and beta1 subunit mRNA expression was also confirmed by RT-PCR and sequence analysis. Secretion assays, which measured beta-hexosaminidase activity released in the culture media, demonstrated that function-blocking integrin alpha6 and beta1 monoclonal antibodies (mAbs) induce a rapid, transient and dose-dependent secretory response in cultured cells. To determine the intracellular pathways by which integrin alpha6 and beta1 mAbs could induce secretion, selected second messenger molecules were inhibited. Although inhibitors of protein kinase C and IP(3)-induced Ca(2+) mobilization attenuated carbachol-stimulated secretion, no effect on integrin mAb-induced release was observed. In addition, protein tyrosine kinases do not appear to have a role in transducing signals arising from mAb interactions. Our data clearly demonstrate, though, that cell adhesion through integrins regulates secretion from lacrimal gland acinar cells. The fact that the integrin mAbs affect the cholinergic response differently and that the integrin beta1 mAb secretion, but not the alpha6, was attenuated by the phosphatase inhibitor, sodium orthovanadate, suggests that each subunit utilizes separate intracellular signaling pathways to induce exocytosis. The results also indicate that the secretory response triggered by the beta1 integrin mAb is generated through dephosphorylation events.

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.

Identification of cytokeratin 18 as a bronchial epithelial autoantigen associated with nonallergic asthma

The allergic response to common environmental agents (allergens) has been regarded as an important mechanism in the development of airway inflammation of patients with asthma. However, allergic sensitization cannot be detected in a significant number of adult patients with asthma. The etiologic mechanism responsible for nonallergic asthma has not yet been identified. The idea of a possible involvement of autoimmunity in the pathogenesis of nonallergic asthma has been proposed by earlier studies. To test for the possible presence of an autoimmune response to bronchial epithelial cell antigens in nonallergic asthma, we examined circulating autoantibodies to cultured human bronchial epithelial cells (BEAS-2B) in sera from patients with nonallergic asthma by immunoblot analysis. IgG autoantibodies to the 49-kD bronchial epithelial cell antigen were detected in 10 of 23 patients with nonallergic asthma (43%), 3 of 27 patients with allergic asthma (11%), 2 of 20 patients with systemic lupus erythematosus (10%), and 3 of 34 healthy volunteers (9%) (p < 0.005). The 49-kD auto-antigen was purified and identified as cytokeratin 18 by amino acid sequencing. In this study, we identified cytokeratin 18 as a bronchial epithelial autoantigen associated with nonallergic asthma. Further studies are needed to determine the significance of autoimmunity in nonallergic asthma.