The Primary Cilium as a Therapeutic Target in Ocular Diseases

Refractive errors in patients with Bardet Biedl syndrome

PURPOSE

Bardet-Biedl Syndrome (BBS) is a rare autosomal recessive ciliopathy. Within corneal development, primary cilia serve a critical role. We sought to investigate the association of BBS with corneal astigmatism among a cohort of patients with BBS.

METHODS

This was a cross-sectional, retrospective study performed at a pediatric ophthalmology department of a tertiary hospital. The study enrolled 45 patients with genetically confirmed Bardet-Biedl syndrome, encompassing a total of 90 eyes observed from February 2011 to August 2021. Spherical and cylindrical refractive errors and keratometry outcome measures, including diopter (D) values at the flattest and steepest axes, were recorded. Corneal astigmatism of greater than 3D is considered extreme corneal astigmatism based on previously published data.

RESULTS

Among 45 patients (M:26; F:19), the mean age was 16.4 ± 8.2 years, and the mean best-corrected visual acuity was 20/60. The most common molecular diagnosis was BBS1, seen in 24 of 45 (53.3%). Among all the patients, the mean spherical refractive error was -2.9 ± 3.8D. The mean cylindrical refractive error was 2.6 ± 1.5D. The mean keratometry values at the flattest axis was 43.5 ± 5.3D (39.4-75.0) and at the steepest axis was 47.2 ± 7.3D(41.5-84.0). Among all the patients with BBS, the mean corneal astigmatism was 3.7 ± 1.0D(0.5-7.1), which is considered extreme.

CONCLUSION

A cohort of individuals with BBS demonstrated high corneal astigmatism. These results suggest an association between corneal astigmatism and primary ciliary dysfunction and may assist in clinical management and future therapeutic targets among BBS and other corneal disorders.

Dynamic changes of endothelial and stromal cilia are required for the maintenance of corneal homeostasis

Primary cilia are distributed extensively within the corneal epithelium and endothelium. However, the presence of cilia in the corneal stroma and the dynamic changes and roles of endothelial and stromal cilia in corneal homeostasis remain largely unknown. Here, we present compelling evidence for the presence of primary cilia in the corneal stroma, both in vivo and in vitro. We also demonstrate dynamic changes of both endothelial and stromal cilia during corneal development. In addition, our data show that cryoinjury triggers dramatic cilium formation in the corneal endothelium and stroma. Furthermore, depletion of cilia in mutant mice lacking intraflagellar transport protein 88 compromises the corneal endothelial capacity to establish the effective tissue barrier, leading to an upregulation of α-smooth muscle actin within the corneal stroma in response to cryoinjury. These observations underscore the essential involvement of corneal endothelial and stromal cilia in maintaining corneal homeostasis and provide an innovative strategy for the treatment of corneal injuries and diseases.

Impact of Equine Ocular Surface Squamous Neoplasia on Interactions between Ocular Transcriptome and Microbiome

Ocular surface squamous neoplasia (OSSN) represents the most common conjunctival tumor in horses and frequently results in vision loss and surgical removal of the affected globe. Multiple etiologic factors have been identified as contributing to OSSN progression, including solar radiation exposure, genetic mutations, and a lack of periocular pigmentation. Response to conventional treatments has been highly variable, though our recent work indicates that these tumors are highly responsive to local immunotherapy. In the present study, we extended our investigation of OSSN in horses to better understand how the ocular transcriptome responds to the presence of the tumor and how the ocular surface microbiome may also be altered by the presence of cancer. Therefore, we collected swabs from the ventral conjunctival fornix from 22 eyes in this study (11 with cytologically or histologically confirmed OSSN and 11 healthy eyes from the same horses) and performed RNA sequencing and 16S microbial sequencing using the same samples. Microbial 16s DNA sequencing and bulk RNA sequencing were both conducted using an Illumina-based platform. In eyes with OSSN, we observed significantly upregulated expression of genes and pathways associated with inflammation, particularly interferon. Microbial diversity was significantly reduced in conjunctival swabs from horses with OSSN. We also performed interactome analysis and found that three bacterial taxa (Actinobacillus, Helcococcus and Parvimona) had significant correlations with more than 100 upregulated genes in samples from animals with OSSN. These findings highlight the inflammatory nature of OSSN in horses and provide important new insights into how the host ocular surface interacts with certain microbial populations. These findings suggest new strategies for the management of OSSN in horses, which may entail immunotherapy in combination with ocular surface probiotics or prebiotics to help normalize ocular cell and microbe interactions.

Sirt3 Protects Retinal Pigment Epithelial Cells From High Glucose-Induced Injury by Promoting Mitophagy Through the AMPK/mTOR/ULK1 Pathway

Purpose

The regulation of mitophagy by Sirt3 has rarely been studied in ocular diseases. In the present study, we determined the effects of Sirt3 on AMPK/mTOR/ULK1 signaling pathway-mediated mitophagy in retinal pigment epithelial (RPE) cells in a high glucose environment.

Methods

The mRNA expression levels of Sirt3, AMPK, mTOR, ULK1, and LC3B in RPE cells under varying glucose conditions were measured by real-time polymerase chain reaction (RT-PCR). The expressions of Sirt3, mitophagy protein, and AMPK/mTOR/ULK1 signaling pathway-related proteins were detected by Western blotting. Lentivirus (LV) transfection mediated the stable overexpression of Sirt3 in cell lines. The experimental groups were NG (5.5 mM glucose), hypertonic, HG (30 mM glucose), HG + LV-GFP, and HG + LV-Sirt3. Western blotting was performed to detect the expressions of mitophagy proteins and AMPK/mTOR/ULK1-related proteins in a high glucose environment during the overexpression of Sirt3. Reactive oxygen species (ROS) production in a high glucose environment was measured by DCFH-DA staining. Mitophagy was detected by labeling mitochondria and lysosomes with MitoTracker and LysoTracker probes, respectively. Apoptosis was detected by flow cytometry.

Results

Sirt3 expression was reduced in the high glucose group, inhibiting the AMPK/mTOR/ULK1 pathway, with diminished mitophagy and increased intracellular ROS production. The overexpression of Sirt3, increased expression of p-AMPK/AMPK and p-ULK1/ULK1, and decreased expression of p-mTOR/mTOR inhibited cell apoptosis and enhanced mitophagy.

Conclusions

Sirt3 protected RPE cells from high glucose-induced injury by activating the AMPK/mTOR/ULK1 signaling pathway.

Translational Relevance

By identifying new targets of action, we aimed to establish effective therapeutic targets for diabetic retinopathy treatment.

Novel ancestry-specific primary open-angle glaucoma loci and shared biology with vascular mechanisms and cell proliferation

Primary open-angle glaucoma (POAG), a leading cause of irreversible blindness globally, shows disparity in prevalence and manifestations across ancestries. We perform meta-analysis across 15 biobanks (of the Global Biobank Meta-analysis Initiative) (n = 1,487,441: cases = 26,848) and merge with previous multi-ancestry studies, with the combined dataset representing the largest and most diverse POAG study to date (n = 1,478,037: cases = 46,325) and identify 17 novel significant loci, 5 of which were ancestry specific. Gene-enrichment and transcriptome-wide association analyses implicate vascular and cancer genes, a fifth of which are primary ciliary related. We perform an extensive statistical analysis of SIX6 and CDKN2B-AS1 loci in human GTEx data and across large electronic health records showing interaction between SIX6 gene and causal variants in the chr9p21.3 locus, with expression effect on CDKN2A/B. Our results suggest that some POAG risk variants may be ancestry specific, sex specific, or both, and support the contribution of genes involved in programmed cell death in POAG pathogenesis.

Resveratrol and quercetin protect from Benzo(a)pyrene-induced autophagy in retinal pigment epithelial cells

PURPOSE

This study aims to investigate the role of Resveratrol (RES) and quercetin (QR) treatments against Benzo(a)pyrene (B(a)p)-induced autophagy in retinal pigment epithelial cells.

METHODS

The IC50 doses of B(a)p, RES and QR in retinal pigment epithelial cells were determined by MTT assay and the relevant agents were administered singly or in combinations to ARPE-19 cells for 24 h. Occurrence of autophagy in the cells was verified by detection of autophagosomes using fluorescence microscope. Also, the mRNA expression levels of LC3 and Beclin 1 genes were analyzed by RT-PCR to collect further data on autophagy. Caspase-3 and IL-1β levels in lysed cells were analyzed by ELISA.

RESULTS

Autophagosomes were detected in B(a)p-treated ARPE-19 cell lines, as well as a 1.787-fold increase in LC3 mRNA expression levels. No autophagosome occurred in RES and QR treatments, and a significant decrease in their percentage amounts were observed in B(a)p + RES and B(a)p + QR. The mRNA expression levels of LC3 and Beclin 1 also supported these findings. B(a)p had no effect on Caspase-3 levels in ARPE-19 cells, but combined with RES and QR, it increased Caspase-3 levels significantly.IL-1β levels were higher in B(a)p, B(a)p + QR, B(a)p + RES, RES and QR than control group. This rise in IL-1β levels was correlated with suppression of mRNA expression levels of Beclin 1.

CONCLUSION

B(a)p exposure caused autophagy in ARPE-19 cells, but did not induce apoptosis. RES and QR treatments prevented B(a)p-induced autophagy. Therefore, RES and QR treatments showed protective effect against potential degenerative diseases caused by chronic exposure to B(a)p.

Usher Syndrome on the Island of Ireland: A Genotype-Phenotype Review

Purpose

Usher syndrome (USH) is a genetically heterogeneous group of autosomal recessive (AR) syndromic inherited retinal degenerations (IRDs) representing 50% of deaf-blindness. All subtypes include retinitis pigmentosa, sensorineural hearing loss, and vestibular abnormalities. Thorough phenotyping may facilitate genetic diagnosis and intervention. Here we report the clinical/genetic features of an Irish USH cohort.

Methods

USH patients were selected from the Irish IRD registry (Target 5000). Patients were examined clinically (deep-phenotyping) and genetically using a 254 IRD-associated gene target capture sequencing panel, USH2A exon, and whole genome sequencing.

Results

The study identified 145 patients (24.1% USH1 [n = 35], 73.8% USH2 [n = 107], 1.4% USH3 [n = 2], and 0.7% USH4 [n = 1]). A genetic diagnosis was reached in 82.1%, the majority (80.7%) being MYO7A or USH2A genotypes. Mean visual acuity and visual field (VF) were 0.47 ± 0.58 LogMAR and 31.3° ± 32.8°, respectively, at a mean age of 43 years. Legal blindness criteria were met in 40.7%. Cataract was present in 77.4%. ADGRV1 genotypes had the most VF loss, whereas USH2A patients had greater myopia and CDH23 had the most astigmatism. Variants absent from gnomAD non-Finnish Europeans and ClinVar represented more than 20% of the variants identified and were detected in ADGRV1, ARSG, CDH23, MYO7A, and USH2A.

Conclusions

USH is a genetically diverse group of AR IRDs that have a profound impact on affected individuals and their families. The prevalence and phenotype/genotype characteristics of USH in Ireland have, as yet, gone unreported. Understanding the genotype of Irish USH patients may guide clinical and genetic characterization facilitating access to existing/novel therapeutics.

Genome-wide screening reveals the genetic basis of mammalian embryonic eye development

BACKGROUND

Microphthalmia, anophthalmia, and coloboma (MAC) spectrum disease encompasses a group of eye malformations which play a role in childhood visual impairment. Although the predominant cause of eye malformations is known to be heritable in nature, with 80% of cases displaying loss-of-function mutations in the ocular developmental genes OTX2 or SOX2, the genetic abnormalities underlying the remaining cases of MAC are incompletely understood. This study intended to identify the novel genes and pathways required for early eye development. Additionally, pathways involved in eye formation during embryogenesis are also incompletely understood. This study aims to identify the novel genes and pathways required for early eye development through systematic forward screening of the mammalian genome.

RESULTS

Query of the International Mouse Phenotyping Consortium (IMPC) database (data release 17.0, August 01, 2022) identified 74 unique knockout lines (genes) with genetically associated eye defects in mouse embryos. The vast majority of eye abnormalities were small or absent eyes, findings most relevant to MAC spectrum disease in humans. A literature search showed that 27 of the 74 lines had previously published knockout mouse models, of which only 15 had ocular defects identified in the original publications. These 12 previously published gene knockouts with no reported ocular abnormalities and the 47 unpublished knockouts with ocular abnormalities identified by the IMPC represent 59 genes not previously associated with early eye development in mice. Of these 59, we identified 19 genes with a reported human eye phenotype. Overall, mining of the IMPC data yielded 40 previously unimplicated genes linked to mammalian eye development. Bioinformatic analysis showed that several of the IMPC genes colocalized to several protein anabolic and pluripotency pathways in early eye development. Of note, our analysis suggests that the serine-glycine pathway producing glycine, a mitochondrial one-carbon donator to folate one-carbon metabolism (FOCM), is essential for eye formation.

CONCLUSIONS

Using genome-wide phenotype screening of single-gene knockout mouse lines, STRING analysis, and bioinformatic methods, this study identified genes heretofore unassociated with MAC phenotypes providing models to research novel molecular and cellular mechanisms involved in eye development. These findings have the potential to hasten the diagnosis and treatment of this congenital blinding disease.

Functions and Diseases of the Retinal Pigment Epithelium

The retinal pigment epithelium is a fundamental component of the retina that plays essential roles in visual functions. Damage to the structure and function of the retinal pigment epithelium leads to a variety of retinopathies, and there is currently no curative therapy for these disorders. Therefore, studying the relationship between the development, function, and pathobiology of the retinal pigment epithelium is important for the prevention and treatment of retinopathies. Here we review the function of the retinal pigment epithelium and its relevance to the pathobiology, and discuss potential strategies for the treatment of retinopathies. In doing so, we provide new viewpoints outlining new ideas for the future study and treatment of retinopathies.