H. Yamagami

Androgen Deficiency, Meibomian Gland Dysfunction, and Evaporative Dry Eye

Abstract: Objective. We have recently discovered that women with primary and secondary Sjögrens syndrome are androgen‐deficient. We hypothesize that this hormone insufficiency contributes to the meibomian gland dysfunction, tear film instability, and evaporative dry eye that are characteristic of this autoimmune disorder. If our hypothesis is correct, we predict: (1) that androgens regulate meibomian gland function, control the quality and/or quantity of lipids produced by this tissue, and promote the formation of the tear films lipid layer; and (2) that androgen deficiency, due to an attenuation in androgen synthesis (e.g., during Sjögrens syndrome, menopause, aging, complete androgen‐insensitivity syndrome [CAIS] and anti‐androgen use), will lead to meibomian gland dysfunction and evaporative dry eye. The following studies were designed to test these predictions. Methods. Experimental procedures included clinical studies, animal models, and histological, biochemical, molecular biological, and biomedical engineering techniques. Results. Our results demonstrate that: (1) androgens regulate the meibomian gland. This tissue contains androgen receptor mRNA, androgen receptor protein within acinar epithelial cell nuclei, and Types 1 and 2 5α‐reductase mRNAs. Moreover, androgens appear to modulate lipid production and gene expression in mouse and/or rabbit meibomian glands; and (2) androgen deficiency may lead to meibomian gland dysfunction, altered lipid profiles in meibomian gland secretions, tear film instability, and evaporative dry eye. Thus, we have found that anti‐androgen therapy in men is associated with meibomian gland disease, a decreased tear film breakup time, and functional dry eye. Furthermore, we have discovered that androgen receptor dysfunction in women with CAIS is associated with meibomian gland changes and a significant increase in the signs and symptoms of dry eye. Of interest, we have also found that androgen deficiency is associated with significant and striking alterations in the neutral and polar lipid patterns of human meibomian gland secretions. Conclusions. Our findings show that the meibomian gland is an androgen target organ and that androgen deficiency may promote meibomian gland dysfunction and evaporative dry eye. Overall, these results support our hypothesis that androgen deficiency may be an important etiologic factor in the pathogenesis of evaporative dry eye in women with Sjögrens syndrome.

Sex steroids, the meibomian gland and evaporative dry eye.

Our recent research has led to our hypothesis that gender and sex steroid hormones are critical factors in the regulation of the meibomian gland and pathogenesis of evaporative dry eye. The objective of this article is to briefly summarize the experimental basis for this hypothesis.

Androgen control of gene expression in the rabbit meibomian gland.

Meibomian gland function is extremely important in promoting the health and integrity of the ocular surface.1–5 This gland, through its synthesis and secretion of lipids, enhances the stability and prevents the evaporation of the tear film.1–5 Meibomian gland dysfunction, in turn, leads to lipid insufficiency, tear film instability and evaporative dry eye.1–5 In fact, meibomian gland dysfunction is thought to be the primary cause of dry eye syndromes throughout the world.6 However, despite the importance of the meibomian gland in maintaining the well-being of the eye, very little research has been published concerning the physiological regulation of this tissue.

Gender-associated differences in gene expression of the meibomian gland.

Previous research has shown that a sex-related difference exists in the casual level of meibomian gland lipids on the lid margin, with women having lower amounts than men from puberty to menopause.1 We hypothesize that this difference may possibly reflect a gender-associated variation in gene expression, and consequent function, of the meibomian gland. Moreover, we hypothesize that this sex-related difference may relate in part to the influence of androgens, which are known to modulate the meibomian gland.2–9 The purpose of this study was to begin to test these hypotheses.

Androgen regulation of gene expression in the mouse lacrimal gland.

The objective of this study was to determine the nature and extent of androgen influence on gene expression in the lacrimal gland. Lacrimal glands were obtained from orchiectomized mice that had been treated with testosterone or vehicle for 2 weeks, as well as from testicular feminized mice and their Tabby controls. Samples were pooled according to experiment, processed for the isolation of RNA, and analyzed for differentially expressed mRNAs by using primarily CodeLink Bioarrays, GEM 1 and 2 gene chips and quantitative real-time PCR (qPCR) procedures. Gene chip data were analyzed with GeneSifter.Net software. Our results demonstrate that testosterone regulates the expression of over 2000 genes in the lacrimal gland. Gene ontologies most affected by androgen treatment included those related to cell growth, proliferation and metabolism, cell communication and transport, nucleic acid binding, signal transduction and receptor activities. Our findings also indicate that androgen action may be mediated, at least in part, through classical androgen receptors, and may contribute to the sex-related differences in gene expression of lacrimal tissue. Overall, these results support our working hypothesis that androgen action on the lacrimal gland is mediated primarily through a receptor-associated regulation of gene transcription.

Androgen Influence on Gene Expression in the Meibomian Gland

Our previous research has demonstrated that the meibomian gland is an androgen target organ.1 This tissue contains androgen receptor mRNA, androgen receptor protein within acinar epithelial cell nuclei and the mRNAs for both Types 1 and 2 5±-reductase, an enzyme that converts testosterone and dehydroepiandrosterone into the potent androgen, 5a-dihydrotestosterone.2,3 Our studies also indicate that androgens, as well as gender, may influence gene expression in the rabbit and/or mouse meibomian glands.4,5 The purpose of this study was to identify androgen-regulated genes that may depend upon the presence of functional androgen receptors, and that may mediate the gender-related differences in gene expression in the meibomian gland.

Estrogen and Progesterone Effects on the Morphology of the Mouse Meibomian Gland

One of the most compelling epidemiological features of dry eye syndromes is that they occur predominantly in women.1–3 In fact, the female gender has been termed a risk factor for the development of dry eye.4 This gender-related prevalence is not surprising, given that over 90% of the individuals with Sjogren’s syndrome are women,5–7 and that dry eye often occurs during menopause and aging.8–10 We hypothesize that this gender-related difference in the prevalence of dry eye syndromes is due, at least in part, to the influence of estrogens. We also hypothesize that this hormone effect is mediated primarily through estrogen action on the meibomian gland. This tissue is a large sebaceous gland,11 and estrogens are known to suppress sebaceous gland function throughout the body.11–17 To begin to test these hypotheses, we sought in the present study to determine whether estrogens, as compared to other sex steroids, influence the morphology of the meibomian gland.

Sex-Related Effect on Gene Expression in the Mouse Meibomian Gland

Purpose: Sex-related differences have been identified in the anatomy and physiology of the meibomian gland. We hypothesize that these differences are due, at least in part, to variations in gene expression. This studys objective was to determine whether sex-related differences do exist in meibomian gland gene expression. We also sought to elucidate whether such differences, if any, might be (a) analogous to those known to occur in the lacrimal gland and (b) due to the effect of sex steroids. Methods: Meibomian glands were obtained from young adult male and female BALB/c mice (n = 7 to 15 mice per sex per experiment), pooled according to sex and processed for the isolation of RNA. Samples were evaluated for differentially expressed mRNAs by using CodeLink Bioarrays and GEM 1 and 2 gene chips. Bioarray data were analyzed with GeneSifter. Net software and also compared with microarray data in GEO and GeneSifter databases. Results: Our results demonstrate that sex has a significant influence on the expression of 164 genes in the mouse meibomian gland. These genes are involved in a broad spectrum of biological processes, molecular functions, and cellular components, including such activities as metabolism, catalysis, cell growth and maintenance, membrane architecture, nucleic acid binding, transcription, and signal transduction. In addition, the nature of the sex-related variations in meibomian gland gene expression is quite different from those in the lacrimal gland and appear to be mediated in part by the action of androgens, but not estrogens or progestins. Conclusions: These findings support our hypothesis that sex-related differences exist in gene expression of the meibomian gland.

Identification of androgen-regulated genes in the lacrimal gland.

Androgens exert a significant influence on the cellular architecture, protein synthesis, immune function and secretory activity of the lacrimal gland.1 In fact, these hormone effects appear to account for many of the gender-related differences that occur in the anatomy, biochemistry, physiology and immunology of lacrimal tissue in a variety of species.1 We hypothesize that androgen actions are mediated primarily through androgen receptors, which exist in lacrimal gland epithelial cells,2–4 and involve the regulation of specific target genes. The purpose of this investigation was to identify the genes controlled by androgens in lacrimal tissue.