The Role of Hypoxia-Inducible Factor 1α in the Regulation of Human Meibomian Gland Epithelial Cells

Efficacy and safety of intense pulsed light of upper and lower eyelids in Meibomian gland dysfunction: A prospective multicentric study

PURPOSE

To demonstrate that intense pulsed light therapy (IPL) of the upper and lower eyelids with meibomian gland expression (MGX) is effective in improving dry eye disease due to meibomian gland dysfunction (MGD).

METHODS

Patients with ocular discomfort (Ocular Surface Disease Index -OSDI- above 13) and signs of MGD were recruited. All patients underwent OSDI, visual acuity (VA), intraocular pressure, Schirmer test, meibography, non-invasive tear breakup time (NITBUT), slit-lamp examination (corneal and conjunctival staining, hyperemia, gland expressibility, and meibum quality), tear osmolarity and lipid layer thickness. IPL was performed with Optima IPL (Lumenis Ltd.) following a standardized protocol on upper and lower eyelids of both eyes, with inferior eyelid MGX. Patients received four sessions separated by two weeks each. Four weeks after, examinations were repeated.

RESULTS

160 patients (320 eyes) were included, of which 108 (67.5%) were women and mean age was 59.2 ± 15.08 (range 20-89). After four sessions, VA, OSDI, tear osmolarity, lipid layer thickness, NITBUT, hyperemia, corneal and conjunctival staining, gland expressibility, meibum quality, inferior eyelid Meiboscore and Schirmer test improved (all, p < 0.027). Changes in OSDI, initial and average NITBUT increased with dry eye disease severity (according to OSDI). Increased pre-treatment OSDI, hyperemia, corneal and conjunctival staining and Schirmer test were associated with an improvement in OSDI (all, p < 0.040). No adverse events were noted.

CONCLUSIONS

The combination of IPL on upper and lower eyelids with MGX is safe and effective for the treatment of MGD. Patients with severe dry eye disease present greater improvements.

Comparison of different lipid staining methods in human meibomian gland epithelial cells

This study aimed to compare the utility of four different dyes for intracellular lipid detection in immortalized human meibomian gland epithelial cells (IHMGECs). IHMGECs were cultured in a serum-containing medium for 10 days in the presence or absence of Roxadustat (Roxa), a known inducer of IHMGEC differentiation. Cells were then fixed and stained with Oil Red O (ORO), Sudan III (SIII), LipidTOX green (LT), or Nile Red (NR). IHMGECs were evaluated for the number, size, and area of stained intracellular lipid vesicles or the intensity of staining using bright field (ORO, SIII) or fluorescence (LT, NR) microscopy. Data were captured with ImageJ and analyzed with Student's two-tailed t-test. Our findings demonstrate that different staining methods can yield significantly different patterns of intracellular lipid quantity and/or distribution in IHMGECs. ORO and SIII significantly increased the size and area of lipid-containing vesicles in Roxa-treated cells. Neither stain showed a change in the number of vesicles during IHMGEC differentiation. Vesicle size was significantly greater in cells stained with ORO, as compared to SIII. In addtion, LT, but not NR, showed a significant increase in intracellular lipid intensity in IHMGECs following Roxa -induced differentiation. Our results demonstrate significant differences in the distribution patterns and intensities of lipid-containing vesicles in IHMGECs after staining with ORO, SIII, LT, and NR. ORO, SIII, and LT, but not NR staining, are helpful methods to help identify and quantitate the extent of intracellular lipid accumulation during IHMGEC differentiation.

Gene expression signatures in conjunctival fornix aspirates of patients with dry eye disease associated with Meibomian gland dysfunction. A proof-of-concept study

BACKGROUND

Meibomian gland dysfunction (MGD) is one of the most common conditions in ophthalmic practice and the most frequent cause of evaporative dry eye disease (DED). However, the immune mechanisms leading to this pathology are not fully understood and the diagnostic tests available are limited. Here, we used the nCounter technology to analyze immune gene expression in DED-MGD that can be used for developing diagnostic signatures for DED.

METHODS

Conjunctival cell samples were obtained by aspiration from patients with DED-MGD (n = 27) and asymptomatic controls (n = 22). RNA was purified, converted to cDNA, preamplified and analyzed using the Gene Expression Human Immune V2 panel (NanoString), which includes 579 target and 15 housekeeping genes. A machine learning (ML) algorithm was applied to design a signature associated with DED-MGD.

RESULTS

Forty-five immune genes were found upregulated in DED-MGD vs. controls, involved in eight signaling pathways, IFN I/II, MHC class I/II, immunometabolism, B cell receptor, T Cell receptor, and T helper-17 (Th-17) differentiation. Additionally, statistically significant correlations were found between 31 genes and clinical characteristics of the disease such as lid margin or tear osmolarity (Pearson's r < 0.05). ML analysis using a recursive feature elimination (RFE) algorithm selected a 4-gene mRNA signature that discriminated DED-MGD from control samples with an area under the ROC curve (AUC ROC) of 0.86 and an accuracy of 77.5%.

CONCLUSIONS

Multiplexed mRNA analysis of conjunctival cells can be used to analyze immune gene expression patterns in patients with DED-MGD and to generate diagnostic signatures.

Zebrafish and inherited photoreceptor disease: Models and insights

Photoreceptor dysfunctions and degenerative diseases are significant causes of vision loss in patients, with few effective treatments available. Targeted interventions to prevent or reverse photoreceptor-related vision loss are not possible without a thorough understanding of the underlying mechanism leading to disease, which is exceedingly difficult to accomplish in the human system. Cone diseases are particularly challenging to model, as some popular genetically modifiable model animals are nocturnal with a rod-dominant visual system and cones that have dissimilarities to human cones. As a result, cone diseases, which affect visual acuity, colour perception, and central vision in patients, are generally poorly understood in terms of pathology and mechanism. Zebrafish (Danio rerio) provide the opportunity to model photoreceptor diseases in a diurnal vertebrate with a cone-rich retina which develops many macular degeneration-like pathologies. Zebrafish undergo external development, allowing early-onset retinal diseases to be detected and studied, and many ophthalmic tools are available for zebrafish visual assessment during development and adulthood. There are numerous zebrafish models of photoreceptor disease, spanning the various types of photoreceptor disease (developmental, rod, cone, and mixed photoreceptor diseases) and genetic/molecular cause. In this review, we explore the features of zebrafish that make them uniquely poised to model cone diseases, summarize the established zebrafish models of inherited photoreceptor disease, and discuss how disease in these models compares to the human presentation, where applicable. Further, we highlight the contributions of these zebrafish models to our understanding of photoreceptor biology and disease, and discuss future directions for utilising and investigating these diverse models.

Clinical Potential of Hypoxia Inducible Factors Prolyl Hydroxylase Inhibitors in Treating Nonanemic Diseases

Hypoxia inducible factors (HIFs) and their regulatory hydroxylases the prolyl hydroxylase domain enzymes (PHDs) are the key mediators of the cellular response to hypoxia. HIFs are normally hydroxylated by PHDs and degraded, while under hypoxia, PHDs are suppressed, allowing HIF-α to accumulate and transactivate multiple target genes, including erythropoiesis, and genes participate in angiogenesis, iron metabolism, glycolysis, glucose transport, cell proliferation, survival, and so on. Aiming at stimulating HIFs, a group of small molecules antagonizing HIF-PHDs have been developed. Of these HIF-PHDs inhibitors (HIF-PHIs), roxadustat (FG-4592), daprodustat (GSK-1278863), vadadustat (AKB-6548), molidustat (BAY 85-3934) and enarodustat (JTZ-951) are approved for clinical usage or have progressed into clinical trials for chronic kidney disease (CKD) anemia treatment, based on their activation effect on erythropoiesis and iron metabolism. Since HIFs are involved in many physiological and pathological conditions, efforts have been made to extend the potential usage of HIF-PHIs beyond anemia. This paper reviewed the progress of preclinical and clinical research on clinically available HIF-PHIs in pathological conditions other than CKD anemia.

Human meibomian gland epithelial cell culture models: Current progress, challenges, and future directions

The widely used immortalised human meibomian gland epithelia cell (iHMGEC) line has made possible extensive studies of the biology and pathophysiology of meibomian glands (MG). Tissue culture protocols for iHMGEC have been revised and modified to optimise the growth conditions for cell differentiation and lipid accumulation. iHMGEC proliferate in serum-free medium but require serum or other appropriate exogenous factors to differentiate. Several supplements can enhance differentiation and neutral lipid accumulation in iHMGEC grown in serum-containing medium. In serum-free medium, rosiglitazone, a peroxisome proliferator activator receptor-γ (PPARγ) agonist, is reported to induce iHMGEC differentiation, neutral lipid accumulation and expression of key biomarkers of differentiation. iHMGEC cultured in serum-containing medium under hypoxia or with azithromycin increases DNAse 2 activity, a biomarker of terminal differentiation in sebocytes. The production of lipids with composition similar to meibum has not been observed in vitro and this remains a major challenge for iHMGEC culture. Innovative methodologies such as 3D ex vivo culture of MG and generation of MG organoids from stem cells are important for further developing a model that more closely mimics the in vivo biology of human MG and to facilitate the next generation of studies of MG disease and dry eye.

Comparative influence of differentiation and proliferation on gene expression in human meibomian gland epithelial cells

We recently discovered that by changing environmental signals, differentiated immortalized human meibomian gland epithelial cells (IHMGECs) de-differentiate into proliferating cells. We also discovered that following exposure to appropriate stimuli, these proliferative cells re-differentiate into differentiated IHMGECs. We hypothesize that this plasticity of differentiated and proliferative IHMGECs is paralleled by very significant alterations in cellular gene expression. To begin to test this hypothesis, we compared the gene expression patterns of IHMGECs during differentiation and proliferation. IHMGECs were cultured for four days in either differentiating or proliferating media. After four days of culture, cells were processed for the analysis of gene expression by using Illumina BeadChips and bioinformatic software. Our study identified significant differences in the expression of more than 9200 genes in differentiated and proliferative IHMGECs. Differentiation was associated with significant increases in the expression of specific genes (e.g. S100 calcium binding protein P; 7,194,386-fold upregulation) and numerous ontologies (e.g. 83 biological process [bp] ontologies with ≥100 genes were upregulated), such as those related to development, transport and lysosomes. Proliferation also led to a significant rise in specific gene expressions (e.g. cathelicidin antimicrobial peptide; 859,100-fold upregulation) and many ontologies (115 biological process [bp] ontologies with ≥100 genes were upregulated), with most of the highly significant ontologies related to cell cycle (z scores > 13.9). Our findings demonstrate that gene expression in differentiated and proliferative IHMGECs is extremely different. These results may have significant implications for the regeneration of HMGECs and the reversal of MG dropout in MG dysfunction.

Zebrafish Models of Photoreceptor Dysfunction and Degeneration

Zebrafish are an instrumental system for the generation of photoreceptor degeneration models, which can be utilized to determine underlying causes of photoreceptor dysfunction and death, and for the analysis of potential therapeutic compounds, as well as the characterization of regenerative responses. We review the wealth of information from existing zebrafish models of photoreceptor disease, specifically as they relate to currently accepted taxonomic classes of human rod and cone disease. We also highlight that rich, detailed information can be derived from studying photoreceptor development, structure, and function, including behavioural assessments and in vivo imaging of zebrafish. Zebrafish models are available for a diversity of photoreceptor diseases, including cone dystrophies, which are challenging to recapitulate in nocturnal mammalian systems. Newly discovered models of photoreceptor disease and drusenoid deposit formation may not only provide important insights into pathogenesis of disease, but also potential therapeutic approaches. Zebrafish have already shown their use in providing pre-clinical data prior to testing genetic therapies in clinical trials, such as antisense oligonucleotide therapy for Usher syndrome.