Robin S. Kelleher

Androgens and Dry Eye in Sjögren's Syndromea

ABSTRACT: Sjögrens syndrome is an extremely complex and currently incurable autoimmune disorder, which occurs primarily in females, and is associated with lacrimal gland inflammation, meibomian gland dysfunction, and severe dry eye. We hypothesize that androgen deficiency, which reportedly occurs in primary and secondary Sjögrens syndrome (e.g., systemic lupus erythematosus, rheumatoid arthritis), is a critical etiologic factor in the pathogenesis of dry eye syndromes. We further hypothesize that androgen treatment to the ocular surface will promote both lacrimal and meibomian gland function and alleviate both “aqueous‐deficient” and “evaporative” dry eye. Our results demonstrate that androgens regulate both lacrimal and meibomian gland function, and suggest that topical androgen administration may serve as a safe and effective therapy for the treatment of dry eye in Sjögrens syndrome.

Influence of Gender, Sex Steroid Hormones, and the Hypothalamic-Pituitary Axis on the Structure and Function of the Lacrimal Gland

Throughout the twentieth century it has become increasingly apparent that males and females are different, and not just in terms of physical characteristics. Scientists have discovered that fundamental, gender-related differences exist in almost every cell, tissue and organ of the body, including those associated with respiration, digestion, metabolism, circulation, renal function, and neural and endocrine activity. Indeed, during a recent five year period, at least 8,159 scientific reports were published that addressed the basic and/or clinical influence of gender on health and disease (Table 1).

Influence of gender and the endocrine environment on the distribution of androgen receptors in the lacrimal gland

Androgens are known to regulate both the structure and function of lacrimal tissue in a variety of species. To explore the endocrine basis for this hormone action, the following study was designed to: (1) determine the cellular distribution of androgen receptors in the lacrimal gland; and (2) examine the influence of gender and the endocrine environment on the glandular content of these binding sites. Lacrimal glands were obtained from intact, castrated, hypophysectomized, diabetic or sham-operated male or female adult rats, mice or hamsters, as well as from orchiectomized rats exposed to placebo compounds or physiological levels of testosterone. The cellular location of androgen receptors was evaluated by utilizing an immunoperoxidase protocol, in which a purified rabbit polyclonal antibody to the rat androgen receptor was used as the first antibody. Our findings with lacrimal glands showed that: (1) androgen receptors are located almost exclusively in nuclei of epithelial cells; (2) the cellular distribution or intranuclear density of these binding sites is far more extensive in glands of males, as compared to females; (3) orchiectomy or hypophysectomy, but not sham-surgery or diabetes, lead to a dramatic reduction in the immunocytochemical expression of androgen receptors; and (4) testosterone administration to orchiectomized rats induces a marked increase in androgen receptor content, relative to that in placebo-exposed glands. Our results also reveal that a 10 kb androgen receptor mRNA exists in the rat lacrimal gland. Overall, these findings demonstrate that gender and the endocrine system may significantly influence the distribution of androgen binding sites in rat lacrimal tissue. Moreover, our results show that androgens up-regulate their own lacrimal gland receptors.

Identification and endocrine control of sex steroid binding sites in the lacrimal gland

Previous research has indicated that the lacrimal gland may be a target organ for sex steroids and that androgen effects on this tissue may be inhibited by pituitary deficiency or diabetes. To extend these findings, the objectives of the current investigation were 3-fold: [a] to determine whether specific and high-affinity binding sites for androgens and estrogens exist in rat lacrimal tissue; [b] to assess whether the number and affinity of androgen binding sites in the lacrimal gland may be influenced by hypophysectomy or acute diabetes; and [c] to examine whether androgen receptor mRNA may be detected in lacrimal tissues of a variety of species. Following the collection of lacrimal gland samples, tissues were processed for the conduct of equilibrium binding methods or molecular biological techniques. Our results demonstrated that a single class of saturable, high-affinity and stereochemically selective binding sites for androgens exist in lacrimal tissues of male and female rats. These sites possessed a dissociation constant of approximately 1 nM and were also present in isolated acinar epithelial cells. In contrast, we were unable to find any evidence for the presence of specific or high-affinity receptors for estrogens in the rat lacrimal gland. With regard to changes in the endocrine environment, hypophysectomy led to an increase in the number and affinity of androgen binding sites in rat lacrimal tissue cytosol, whereas diabetes reduced the total quantity of these sites. Of interest, androgen receptor mRNA was detected in lacrimal glands of mice, rats, hamsters, guinea pigs, rabbits and humans. Overall, our findings show that the lacrimal gland is a target organ for androgens and that androgen action in this tissue may be mediated through an interaction with specific and high-affinity binding sites.

Neural-Endocrine Control of Secretory Component Synthesis by Lacrimal Gland Acinar Cells: Specificity, Temporal Characteristics and Molecular Basis

The ocular surface appears to be protected from bacterial and viral pathogens by polymeric IgA antibodies.1 These antibodies, which are produced by plasma cells in the lacrimal gland, bind to secretory component (SC) in the basolateral membrane of acinar epithelial cells, and are then transported to the apical membrane and secreted into tears.2 Of interest, the lacrimal secretion of sIgA, as well as free SC, appears to be significantly influenced by gender and hormones from the hypothalamic-pituitary-gonadal axis.2 Thus, almost 10 years ago, it was found that the concentrations of free SC and IgA in the tears of male rats were 2 to 5-fold higher than those in tears of female rats. These gender-associated differences in tear SC and IgA were shown to be caused by androgens.2 For example, castration led to a significant reduction in SC levels in tears of males, while having no impact on SC content in tears of females. In addition, administration of testosterone for 4 days to castrated male or female rats significantly increased tear SC levels. These studies showed that exposure of castrated rats to androgens resulted in alterations of lacrimal SC production.2 Moreover, later experiments demonstrated that this androgen control of SC, as well as IgA, is modulated by factors from the hypothalamus and pituitary.2 However, this research did not address whether androgens act directly on lacrimal tissue to change SC or IgA, or indirectly via an androgen-sensitive site, which in tum acts to modulate lacrimal SC and IgA.

Neural, Endocrine and Immune Regulation of Secretory Component Production by Lacrimal Gland Acinar Cells

Our previous research has shown that the endocrine, nervous and immune systems regulate the production of secretory component (SC), the polymeric immunoglobulin receptor, by acinar (epithelial) cells from the rat lacrimal gland.1 Thus, acinar cell exposure in vitro to androgens (e. g., dihydrotestosterone [DHT]), vasoactive intestinal peptide (VIP), the adrenergic agonist, isoproterenol, cyclic AMP analogues (e. g., 8-bromoadenosine 3’:5’- cyclic monophosphate [bcAMP]), cyclic AMP inducers (e. g., cholera toxin, PGE2), phosphodiesterase inhibitors (e. g., 3-isobutyl-l-methylxanthine), IL-lα, IL-lβ, or TNF-α results in a significant increase in SC output.2-4 Conversely, cellular treatment with the cholinergic agent, carbachol, causes a significant suppression of both androgen-induced and basal SC release by acinar cells.3,4

Binding Characteristics, Immunocytochemical Location and Hormonal Regulation of Androgen Receptors in Lacrimal Tissue

During the past five decades, researchers have found that distinct, gender-related differences exist in the morphology, histochemistry, biochemistry, immunology and molecular biology of the lacrimal gland in a variety of species, including mice, rats, guinea pigs, hamsters, rabbits and humans.1 These differences include striking variations in acinar cell characteristics (e.g. area, shape, membrane appearance, vesicle and nucleoli densities, nuclear size), lymphocyte populations, messenger RNA levels, enzyme and glycoprotein content, collagen amounts, adrenergic receptor expression, hormone responsiveness, and specific protein secretion.1 The underlying basis for this sexual dimorphism appears to be due almost entirely to the selective influence of androgens on the lacrimal gland.1 In contrast, sex steroids such as estrogens or progestins seem to have minimal, or no, direct effect on lacrimal tissue.1