Growth Hormone Influence on the Morphology and Size of the Mouse Meibomian Gland

Models for Meibomian gland dysfunction: In vivo and in vitro

Meibomian gland dysfunction (MGD) is a chronic abnormality of the Meibomian glands (MGs) that is recognized as the leading cause of evaporative dry eye worldwide. Despite its prevalence, however, the pathophysiology of MGD remains elusive, and effective disease management continues to be a challenge. In the past 50 years, different models have been developed to illustrate the pathophysiological nature of MGD and the underlying disease mechanisms. An understanding of these models is crucial if researchers are to select an appropriate model to address specific questions related to MGD and to develop new treatments. Here, we summarize the various models of MGD, discuss their applications and limitations, and provide perspectives for future studies in the field.

Treatment of Severe Dry Eye in Stevens-Johnson Syndrome with Umbilical Cord Serum Eye Drops

PURPOSE

To evaluate the efficacy and safety of umbilical cord serum eye drops for dry eyes in ocular Stevens-Johnson Syndrome (SJS).

PATIENTS AND METHODS

A pre-post test study with umbilical cord serum (UCS) eye drop for ocular SJS patient with moderate to severe dry eyes. Study was conducted at Kirana Cipto Mangunkusumo General Hospital from June 2020 to December 2020. A total of five patients (five eyes) with a diagnosis of SJS more than 6 months, dry eye symptoms, and abnormal tear stability test results were included in the study. Each patient was asked to instill UCS drop into the affected eye six times daily. Evaluation of ocular symptoms with ocular surface disease index (OSDI) questionnaires, non-invasive tear break-up time (NIBUT), Schirmer I, and keratoepitheliopathy scores was administered before applying UCS drop and at week 2 and 4 of eye drop use.

RESULTS

From June 2020 to December 2020, five eyes of five patients were evaluated in this study. Patients were aged from 22 to 71 years old with history of SJS over periods from 1 to 35 years. Three patients underwent ocular surgeries prior to the study. After four weeks of treatment, symptoms score, Schirmer I, and keratoepitheliopathy scores improved significantly, while NIBUT scores improved insignificantly. No side effects were noted during treatment.

CONCLUSION

Administration of UCS eye drop was effective in improving symptoms and signs of dry eye in chronic SJS patients.

Mice with gene alterations in the GH and IGF family

Much of our understanding of GH's action stems from animal models and the generation and characterization of genetically altered or modified mice. Manipulation of genes in the GH/IGF1 family in animals started in 1982 when the first GH transgenic mice were produced. Since then, multiple laboratories have altered mouse DNA to globally disrupt Gh, Ghr, and other genes upstream or downstream of GH or its receptor. The ability to stay current with the various genetically manipulated mouse lines within the realm of GH/IGF1 research has been daunting. As such, this review attempts to consolidate and summarize the literature related to the initial characterization of many of the known gene-manipulated mice relating to the actions of GH, PRL and IGF1. We have organized the mouse lines by modifications made to constituents of the GH/IGF1 family either upstream or downstream of GHR or to the GHR itself. Available data on the effect of altered gene expression on growth, GH/IGF1 levels, body composition, reproduction, diabetes, metabolism, cancer, and aging are summarized. For the ease of finding this information, key words are highlighted in bold throughout the main text for each mouse line and this information is summarized in Tables 1, 2, 3 and 4. Most importantly, the collective data derived from and reported for these mice have enhanced our understanding of GH action.

Sex Hormones, Growth Hormone, and the Cornea

The growth and maintenance of nearly every tissue in the body is influenced by systemic hormones during embryonic development through puberty and into adulthood. Of the ~130 different hormones expressed in the human body, steroid hormones and peptide hormones are highly abundant in circulation and are known to regulate anabolic processes and wound healing in a tissue-dependent manner. Of interest, differential levels of sex hormones have been associated with ocular pathologies, including dry eye disease and keratoconus. In this review, we discuss key studies that have revealed a role for androgens and estrogens in the cornea with focus on ocular surface homeostasis, wound healing, and stromal thickness. We also review studies of human growth hormone and insulin growth factor-1 in influencing ocular growth and epithelial regeneration. While it is unclear if endogenous hormones contribute to differential corneal wound healing in common animal models, the abundance of evidence suggests that systemic hormone levels, as a function of age, should be considered as an experimental variable in studies of corneal health and disease.

Topographic and specular microscopic evaluation of cornea and meibomian gland morphology in children with isolated growth hormone deficiency

PURPOSE

To evaluate whether the anterior segment topographic measurements, meibomian gland (MG), and non-invasive tear film break-up time (NITFBUT) differ between healthy children and children with isolated growth hormone deficiency (GHD).

METHODS

A total of 74 eyes of 37 children with GHD and 84 eyes of 42 age- and sex-matched healthy children were included in the study. The spherical equivalence (SE), mean keratometry (Km), corneal thickness, corneal volume (CV), anterior chamber depth (ACD), topographic NITFBUT, qualitative and quantitative MG measurements, corneal endothelial cell density (CD), and proportion of hexagonal cells (HG) were analysed.

RESULTS

The mean SE level of GHD group was similar between groups (p = 0.017). Back Km values were insignificantly steep in children with GHD (p = 0.004, with Bonferroni correction). Specular microscopy analysis was not different between groups. MG loss of GHD group were higher than control group (p < 0.001). The MG morphology analysis and distortion grade were not different between groups (p > 0.05).

CONCLUSIONS

Our results showed that the growth hormone (GH) may have an important role on the anterior segment parameters; however, it is not clear that this misregulation leads to a clinical scenario in childhood. Future studies investigating GHD and/or GH therapy on the ocular surface system are required to clearly demonstrate basic mechanism of GH action.

Meibomian Gland Dysfunction: What Have Animal Models Taught Us?

Studies have estimated that currently 344 million people worldwide and 16.4 million adults in the US have some form of dry eye disease (DED). It is believed that approximately 70% of DED cases are due to some form of evaporative dry eye, for which Meibomian gland dysfunction (MGD) is the major cause. Unfortunately, currently there is no effective treatment for MGD, and solely palliative care is available. Given the importance of MGD in DED, there has been a growing interest in studying Meibomian gland development, homeostasis and pathology, and, also, in developing therapies for treating and/or preventing MGD. For such, animal models have shown to be a vital tool. Much of what is known today about the Meibomian gland and MGD was learnt from these important animal models. In particular, canine and rabbit models have been essential for studying the physiopathology and progression of DED, and the mouse model, which includes different knockout strains, has enabled the identification of specific pathways potentially involved in MGD. Herein, we provide a bibliographic review on the various animal models that have been used to study Meibomian gland development, Meibomian gland homeostasis and MGD, primarily focusing on publications between 2000 and 2020.

Are BALB/c Mice Relevant Models for Understanding Sex-Related Differences in Gene Expression in the Human Meibomian Gland?

BACKGROUND

A compelling feature of dry eye disease is that it occurs predominantly in women. We hypothesize that this female prevalence is linked to sex-related differences in the meibomian gland (MG). This gland plays a critical role in maintaining the tear film, and its dysfunction is a major cause of dry eye disease. To understand the factors that underlie MG sexual dimorphism and promote dry eye in women, we seek to identify an optimal model for the human MG. Our goal was to determine whether a murine MG is such a model. Toward that end, we examined whether sex differences in MG gene expression are the same in BALB/c mice and humans.

METHODS

Eyelid tissues were collected from humans (n = 5-7/sex) and BALB/c mice (n = 9/sex). MGs were isolated and processed for the evaluation of gene expression by using microarrays and bioinformatics software.

RESULTS

Our analysis of the 500 most highly expressed genes from human and mouse MGs showed that only 24.4% were the same. Our comparison of 100 genes with the greatest sex-associated differences in human and mouse MGs demonstrated that none were the same. Sex also exerted a significant impact on numerous ontologies, Kyoto Encyclopedia of Genes and Genomes pathways, and chromosomes, but these effects were primarily species-specific.

CONCLUSIONS

Our results indicate that BALB/c mice are not optimal models for understanding sex-related differences in gene expression of the human MG.

Meibomian glands, meibum, and meibogenesis

Meibum is a lipid-rich secretion that is produced by fully differentiated meibocytes in the holocrine Meibomian glands (MG) of humans and most mammals. The secretion is a part of a defense mechanism that protects the ocular surface from hazardous environmental factors, and from desiccation. Meibomian lipids that have been identified in meibum are very diverse and unique in nature. The lipid composition of meibum is different from virtually any other lipid pool found in the human body. In fact, meibum is quite different from sebum, which is the closest secretion that is produced by anatomically, physiologically, and biochemically related sebaceous glands. However, meibum of mice have been shown to closely resemble that of humans, implying similar biosynthetic mechanisms in MG of both species. By analyzing available genomic, immunohistochemical, and lipidomic data, we have envisioned a unifying network of enzymatic reactions that are responsible for biosynthesis of meibum, which we call meibogenesis. Our current theory is based on an assumption that most of the biosynthetic reactions of meibogenesis are catalyzed by known enzymes. However, the main features that make meibum unique - the ratio of identified classes of lipids, the extreme length of its components, extensive ω-hydroxylation of fatty acids and alcohols, iso- and anteiso-branching of meibomian lipids (e.g. waxes), and the presence of rather unique complex lipids with several ester bonds - make it possible that either the activity of known enzymes is altered in MG, or some unknown enzymes contribute to the processes of meibogenesis, or both. Studies are in progress to elucidate meibogenesis on molecular level.

Factors influencing growth hormone levels of Bali cattle in Bali, Nusa Penida, and Sumbawa Islands, Indonesia

AIM

Bali cattle (Bos javanicus) are an Indonesian's native cattle breed that distributed in Asia to Australia. The scientific literature on these cattle is scarce. The growth hormone (GH) of Bali cattle is investigated from three separated islands, namely, Bali, Nusa Penida, and Sumbawa.

MATERIALS AND METHODS

Forty plasma samples were collected from each island, and the GH was measured using a commercial enzyme-linked immunosorbent assay kit. The data were analyzed based on the origin, sex, and cattle raising practices.

RESULTS

We found that the GH level (bovine GH [BGH]) of animal kept in stall 1.72±0.70 µg/ml was higher than free-grazing animal 1.27±0.81 µg/ml. The GH level was lower in female (1.22±0.62 µg/ml) compared to male animals (1.77±0.83 µg/ml).

CONCLUSION

We conclude that the level of BGH in Bali cattle was low and statistically equal from all origins. The different level was related to sex and management practices. Further validation is needed through observing the growth rate following BGH administration and discovering the inbreeding coefficient of the animal in Indonesia.

TFOS DEWS II Sex, Gender, and Hormones Report

One of the most compelling features of dry eye disease (DED) is that it occurs more frequently in women than men. In fact, the female sex is a significant risk factor for the development of DED. This sex-related difference in DED prevalence is attributed in large part to the effects of sex steroids (e.g. androgens, estrogens), hypothalamic-pituitary hormones, glucocorticoids, insulin, insulin-like growth factor 1 and thyroid hormones, as well as to the sex chromosome complement, sex-specific autosomal factors and epigenetics (e.g. microRNAs). In addition to sex, gender also appears to be a risk factor for DED. "Gender" and "sex" are words that are often used interchangeably, but they have distinct meanings. "Gender" refers to a person's self-representation as a man or woman, whereas "sex" distinguishes males and females based on their biological characteristics. Both gender and sex affect DED risk, presentation of the disease, immune responses, pain, care-seeking behaviors, service utilization, and myriad other facets of eye health. Overall, sex, gender and hormones play a major role in the regulation of ocular surface and adnexal tissues, and in the difference in DED prevalence between women and men. The purpose of this Subcommittee report is to review and critique the nature of this role, as well as to recommend areas for future research to advance our understanding of the interrelationships between sex, gender, hormones and DED.

TFOS DEWS II pathophysiology report

The TFOS DEWS II Pathophysiology Subcommittee reviewed the mechanisms involved in the initiation and perpetuation of dry eye disease. Its central mechanism is evaporative water loss leading to hyperosmolar tissue damage. Research in human disease and in animal models has shown that this, either directly or by inducing inflammation, causes a loss of both epithelial and goblet cells. The consequent decrease in surface wettability leads to early tear film breakup and amplifies hyperosmolarity via a Vicious Circle. Pain in dry eye is caused by tear hyperosmolarity, loss of lubrication, inflammatory mediators and neurosensory factors, while visual symptoms arise from tear and ocular surface irregularity. Increased friction targets damage to the lids and ocular surface, resulting in characteristic punctate epithelial keratitis, superior limbic keratoconjunctivitis, filamentary keratitis, lid parallel conjunctival folds, and lid wiper epitheliopathy. Hybrid dry eye disease, with features of both aqueous deficiency and increased evaporation, is common and efforts should be made to determine the relative contribution of each form to the total picture. To this end, practical methods are needed to measure tear evaporation in the clinic, and similarly, methods are needed to measure osmolarity at the tissue level across the ocular surface, to better determine the severity of dry eye. Areas for future research include the role of genetic mechanisms in non-Sjögren syndrome dry eye, the targeting of the terminal duct in meibomian gland disease and the influence of gaze dynamics and the closed eye state on tear stability and ocular surface inflammation.

Meibomian glands, meibum, and meibogenesis

Meibum is a lipid-rich secretion that is produced by fully differentiated meibocytes in the holocrine Meibomian glands (MG) of humans and most mammals. The secretion is a part of a defense mechanism that protects the ocular surface from hazardous environmental factors, and from desiccation. Meibomian lipids that have been identified in meibum are very diverse and unique in nature. The lipid composition of meibum is different from virtually any other lipid pool found in the human body. In fact, meibum is quite different from sebum, which is the closest secretion that is produced by anatomically, physiologically, and biochemically related sebaceous glands. However, meibum of mice have been shown to closely resemble that of humans, implying similar biosynthetic mechanisms in MG of both species. By analyzing available genomic, immunohistochemical, and lipidomic data, we have envisioned a unifying network of enzymatic reactions that are responsible for biosynthesis of meibum, which we call meibogenesis. Our current theory is based on an assumption that most of the biosynthetic reactions of meibogenesis are catalyzed by known enzymes. However, the main features that make meibum unique - the ratio of identified classes of lipids, the extreme length of its components, extensive ω-hydroxylation of fatty acids and alcohols, iso- and anteiso-branching of meibomian lipids (e.g. waxes), and the presence of rather unique complex lipids with several ester bonds - make it possible that either the activity of known enzymes is altered in MG, or some unknown enzymes contribute to the processes of meibogenesis, or both. Studies are in progress to elucidate meibogenesis on molecular level.

Dry Eye Management: Targeting the Ocular Surface Microenvironment

Dry eye can damage the ocular surface and result in mild corneal epithelial defect to blinding corneal pannus formation and squamous metaplasia. Significant progress in the treatment of dry eye has been made in the last two decades; progressing from lubricating and hydrating the ocular surface with artificial tear to stimulating tear secretion; anti-inflammation and immune regulation. With the increase in knowledge regarding the pathophysiology of dry eye, we propose in this review the concept of ocular surface microenvironment. Various components of the microenvironment contribute to the homeostasis of ocular surface. Compromise in one or more components can result in homeostasis disruption of ocular surface leading to dry eye disease. Complete evaluation of the microenvironment component changes in dry eye patients will not only lead to appropriate diagnosis, but also guide in timely and effective clinical management. Successful treatment of dry eye should be aimed to restore the homeostasis of the ocular surface microenvironment.

A Novel Model of Meibomian Gland Dysfunction Induced with Complete Freund's Adjuvant in Rabbits

A novel meibomian gland dysfunction (MGD) model induced by the injection of complete Freund’s adjuvant (CFA) in rabbits was developed to facilitate the understanding of the pathophysiology of MGD with meibomitis. In addition, we sought to evaluate treatment with steroid eye drops in this model. Male Japanese white rabbits were subcutaneously injected with CFA into the upper eyelid margin. The eyelid margins of the rabbits were chronologically observed through slit lamp examination. The development of meibomitis was assessed through histopathology. We evaluated the effects of topically applied tobramycin/dexamethasone (Tob/Dex) eye drops on the plugged orifices and telangiectasia. After the injection of CFA, slit lamp examination revealed markedly plugged orifices, telangiectasia around the orifices and a toothpaste-like meibum, as compared with the normal eyelids. Histopathology revealed granulation tissue with infiltration of inflammatory cells, hyperkeratinization of the ductal epithelium, and cystic dilatation of ducts in the meibomian gland. The orifices were plugged with a proteinaceous substance. Tob/Dex eye drops significantly suppressed the plugging and telangiectasia around the orifices. Through the injection of CFA, we successfully established a novel rabbit MGD that mimics the symptoms observed in humans meibomitis. This model should be useful in the evaluation of the efficacy of drug candidates.