A single EFEMP1 mutation associated with both Malattia Leventinese and Doyne honeycomb retinal dystrophy

Exploring ocular fibulin-3 (EFEMP1): Anatomical, age-related, and species perspectives

Fibulin-3 (FBLN3, aka EFEMP1) is a secreted extracellular matrix (ECM) glycoprotein implicated in ocular diseases including glaucoma and age-related macular degeneration. Yet surprisingly, little is known about its native biology, expression patterns, and localization in the eye. To overcome these shortcomings, we conducted gene expression analysis and immunohistochemistry for FBLN3 in ocular tissues from mice, pigs, non-human primates, and humans. Moreover, we evaluated age-related changes in FBLN3 and FBLN3-related ECM remodeling enzymes/inhibitors in aging mice. We found that FBLN3 displayed distinct staining patterns consistent across the mouse retina, particularly in the ganglion cell layer and inner nuclear layer (INL). In contrast, human retinas exhibited a unique staining pattern, with enrichment of FBLN3 in the retinal pigment epithelium (RPE), INL, and outer nuclear layer (ONL) in the peripheral retina. This staining transitioned to the outer plexiform layer (OPL) in the central retina/macula, and was accompanied by reduced RPE immunoreactivity approaching the fovea. Surprisingly, we found significant age-related increases in FBLN3 expression and protein abundance in the mouse retina which was paralleled by reduced transcript levels of FBLN3-degrading enzymes (i.e., Mmp2 and Htra1). Our findings highlight important species-dependent, retinal region-specific, and age-related expression and localization patterns of FBLN3 which favor its accumulation during aging. These findings contribute to a better understanding of FBLN3's role in ocular pathology and provide valuable insights for future FBLN3 research.

A Long-Term Retrospective Natural History Study of EFEMP1-Associated Autosomal Dominant Drusen

Purpose

To analyze the natural history of EFEMP1-associated autosomal dominant drusen (ADD).

Methods

In this retrospective observational study of molecularly confirmed patients with ADD, data and retinal imaging were extracted from an in-house database. The main outcome measurements were best-corrected visual acuity (BCVA), refraction, and retinal imaging, including quantitative analyses of the outer nuclear layer (ONL) thickness and pigmented epithelium detachment area, as well as qualitative analyses.

Results

The study included 44 patients (34 females and 10 males). The mean ± SD age of symptom onset was 40.1 ± 6.59 years of age (range, 25-52). Fourteen patients were asymptomatic during their entire follow-up. The most common symptoms at presentation were reduced vision (70%) and distortion in central vision (53%). Most subjects were emmetropic. The mean BCVA (logMAR) at baseline was 0.27 ± 0.41 (range, -0.1 to 2.1) in right eyes and was 0.19 ± 0.32 (range, -0.2 to 1.3) in left eyes. After a mean follow-up of 7.9 years, BCVA was reduced to 0.59 ± 0.66 (range, -0.1 to 2.1) in right eyes and 0.5 ± 0.72 (range, -0.1 to 2.4) in left eyes, values that were significantly different than baseline (P < 0.0001 and P < 0.0014, respectively). Fifteen eyes showed active or inactive choroidal neovascularization (CNV). BCVA differed significantly (P = 0.0004) between eyes with and without CNV at a comparable mean age. The ONL had a slow rate of thinning longitudinally, which significantly correlated with BCVA.

Conclusions

Despite the late onset and relatively good prognosis of ADD, CNVs are more frequent than previously reported and are associated with a worse prognosis. Further research is necessary to elucidate gender associations.

EFEMP1 haploinsufficiency causes a Marfan-like hereditary connective tissue disorder

Phenotypic features of a hereditary connective tissue disorder, including craniofacial characteristics, hyperextensible skin, joint laxity, kyphoscoliosis, arachnodactyly, inguinal hernia, and diverticulosis associated with biallelic pathogenic variants in EFEMP1 have been previously described in four patients. Genome sequencing on a proband and her mother with comparable phenotypic features revealed that both patients were heterozygous for a stop-gain variant c.1084C>T (p.Arg362*). Complementary RNA-seq on fibroblasts revealed significantly reduced levels of mutant EFEMP1 transcript. Considering the absence of other molecular explanations, we extrapolated that EFEMP1 could be the cause of the patient's phenotypes. Furthermore, nonsense-mediated decay was demonstrated for the mutant allele as the principal mechanism for decreased levels of EFEMP1 mRNA. We provide strong clinical and genetic evidence for the haploinsufficiency of EFEMP1 due to nonsense-medicated decay to cause severe kyphoscoliosis, generalized hypermobility of joints, high and narrow arched palate, and potentially severe diverticulosis. To the best of our knowledge, this is the first report of an autosomal dominant EFEMP1-associated hereditary connective tissue disorder and therefore expands the phenotypic spectrum of EFEMP1 related disorders.

Optical Coherence Tomography in Inherited Macular Dystrophies: A Review

Macular dystrophies (MDs) constitute a collection of hereditary retina disorders leading to notable visual impairment, primarily due to progressive macular atrophy. These conditions are distinguished by bilateral and relatively symmetrical abnormalities in the macula that significantly impair central visual function. Recent strides in fundus imaging, especially optical coherence tomography (OCT), have enhanced our comprehension and diagnostic capabilities for MD. OCT enables the identification of neurosensory retinal disorganization patterns and the extent of damage to retinal pigment epithelium (RPE) and photoreceptor cells in the dystrophies before visible macular pathology appears on fundus examinations. It not only helps us in diagnostic retinal and choroidal pathologies but also guides us in monitoring the progression of, staging of, and response to treatment. In this review, we summarize the key findings on OCT in some of the most common MD.

Multi-tissue transcriptome-wide association study identifies novel candidate susceptibility genes for cataract

Introduction

Cataract is the leading cause of blindness among the elderly worldwide. Twin and family studies support an important role for genetic factors in cataract susceptibility with heritability estimates up to 58%. To date, 55 loci for cataract have been identified by genome-wide association studies (GWAS), however, much work remains to identify the causal genes. Here, we conducted a transcriptome-wide association study (TWAS) of cataract to prioritize causal genes and identify novel ones, and examine the impact of their expression.

Methods

We performed tissue-specific and multi-tissue TWAS analyses to assess associations between imputed gene expression from 54 tissues (including 49 from the Genotype Tissue Expression (GTEx) Project v8) with cataract using FUSION software. Meta-analyzed GWAS summary statistics from 59,944 cataract cases and 478,571 controls, all of European ancestry and from two cohorts (GERA and UK Biobank) were used. We then examined the expression of the novel genes in the lens tissue using the iSyTE database.

Results

Across tissue-specific and multi-tissue analyses, we identified 99 genes for which genetically predicted gene expression was associated with cataract after correcting for multiple testing. Of these 99 genes, 20 (AC007773.1, ANKH, ASIP, ATP13A2, CAPZB, CEP95, COQ6, CREB1, CROCC, DDX5, EFEMP1, EIF2S2, ESRRB, GOSR2, HERC4, INSRR, NIPSNAP2, PICALM, SENP3, and SH3YL1) did not overlap with previously reported cataract-associated loci. Tissue-specific analysis identified 202 significant gene-tissue associations for cataract, of which 166 (82.2%), representing 9 unique genes, were attributed to the previously reported 11q13.3 locus. Tissue-enrichment analysis revealed that gastrointestinal tissues represented one of the highest proportions of the Bonferroni-significant gene-tissue associations (21.3%). Moreover, this gastrointestinal tissue type was the only anatomical category significantly enriched in our results, after correcting for the number of tissue donors and imputable genes for each reference panel. Finally, most of the novel cataract genes (e.g., Capzb) were robustly expressed in iSyTE lens data.

Discussion

Our results provide evidence of the utility of imputation-based TWAS approaches to characterize known GWAS risk loci and identify novel candidate genes that may increase our understanding of cataract etiology. Our findings also highlight the fact that expression of genes associated with cataract susceptibility is not necessarily restricted to lens tissue.

Macular neovascularization in inherited retinal diseases: A review

Inherited retinal diseases (IRDs) are the most common cause of blindness in working-age adults. Macular neovascularization (MNV) may be a presenting feature or occurs as a late-stage complication in several IRDs. We performed an extensive literature review on MNV associated with IRDs. MNV is a well-known complication of Sorsby fundus dystrophy and pseudoxanthoma elasticum. Those with late-onset Stargardt disease may masquerade as exudative age-related macular degeneration (AMD) when MNV is the presenting feature. Peripherinopathies may develop MNV that responds well to a short course of anti-vascular endothelial growth factor (anti-VEGF) therapy, while bestrophinopathies tend to develop MNV in the early stages of the disease without vision loss. Enhanced S-cone syndrome manifests type 3 MNV that typically regresses into a subfoveal fibrotic nodule. MNV is only a rare complication in choroideraemia and rod-cone dystrophies. Most IRD-related MNVs exhibit a favorable visual prognosis requiring less intensive regimens of anti-vascular endothelial growth factor therapy compared to age-related macular degeneration. We discuss the role of key imaging modalities in the diagnosis of MNV across a wide spectrum of IRDs and highlight the gaps in our knowledge with respect to the natural history and prognosis to pave the way for future directions of research.

Novel mutation in EFEMP1 identified from two Chinese POAG families differentially activated endoplasmic reticulum stress markers and induced glaucoma in mouse

Primary open-angle glaucoma (POAG) is the most common type of glaucoma. Using whole-exome sequencing, we identified two independent families diagnosed as POAG from the China with a novel EFEMP1 variant (Exon3, c.175A>C p.Met59Leu); Three previously reported variants c.1160G>A p.R387Q, c.1189T>C p.Y397H, and c.1429C>T p.R477C in EFEPM1 from 55 sporadic POAG individuals were also identified. The variant c.175A>C p.Met59Leu co-segregated with the disease phenotype within the families. Immunoprecipitation and western blot assays showed that all three EFEMP1 mutants (p.Met59Leu, pArg140Trp, pArg345Trp) increased intracellular protein aggregations, and pMet59Leu and pArg140Arg also enhanced their extracellular proteins secretion, compared to WT in HEK293T. The differential regulations to endoplasmic reticulum (ER) stress markers ATF4, GPR78/94, and CHOP, and differential phosphorylation activations to CREB at Ser133, AKT at Ser473, p44/42 at Thr202/Tyr204, and STAT3 at Tyr705, were also detected among the mutants and WT. Finally, we revealed a significant increment of intraocular pressure and obvious reduction of RGC cells at the sixth week following intravitreal injection of adenovirus 5 (Ad5) expressing in pMet59Leu compared to WT and GFP controls. Together, variant c.175A>C p.Met59Leu in EFEMP1 is pathogenic and different mutants in EFEMP1 triggered distinct signaling pathways, explaining the reason of mutation-dependent disease phenotypes of EFEMP1.

Advances in the engineering of the outer blood-retina barrier: From in-vitro modelling to cellular therapy

The outer blood-retina barrier (oBRB), crucial for the survival and the proper functioning of the overlying retinal layers, is disrupted in numerous diseases affecting the retina, leading to the loss of the photoreceptors and ultimately of vision. To study the oBRB and/or its degeneration, many in vitro oBRB models have been developed, notably to investigate potential therapeutic strategies against retinal diseases. Indeed, to this day, most of these pathologies are untreatable, especially once the first signs of degeneration are observed. To cure those patients, a current strategy is to cultivate in vitro a mature oBRB epithelium on a custom membrane that is further implanted to replace the damaged native tissue. After a description of the oBRB and the related diseases, this review presents an overview of the oBRB models, from the simplest to the most complex. Then, we propose a discussion over the used cell types, for their relevance to study or treat the oBRB. Models designed for in vitro applications are then examined, by paying particular attention to the design evolution in the last years, the development of pathological models and the benefits of co-culture models, including both the retinal pigment epithelium and the choroid. Lastly, this review focuses on the models developed for in vivo implantation, with special emphasis on the choice of the material, its processing and its characterization, before discussing the reported pre-clinical and clinical trials.

GSK3 inhibition reduces ECM production and prevents age-related macular degeneration-like pathology

Malattia Leventinese/Doyne Honeycomb Retinal Dystrophy (ML/DHRD) is an age-related macular degeneration (AMD)-like retinal dystrophy caused by an autosomal dominant R345W mutation in the secreted glycoprotein, fibulin-3 (F3). To identify new small molecules that reduce F3 production from retinal pigmented epithelium (RPE) cells, we knocked-in a luminescent peptide tag (HiBiT) into the endogenous F3 locus which enabled simple, sensitive, and high throughput detection of the protein. The GSK3 inhibitor, CHIR99021 (CHIR), significantly reduced F3 burden (expression, secretion, and intracellular levels) in immortalized RPE and non-RPE cells. Low-level, long-term CHIR treatment promoted remodeling of the RPE extracellular matrix (ECM), reducing sub-RPE deposit-associated proteins (e.g., amelotin, complement component 3, collagen IV, and fibronectin), while increasing RPE differentiation factors (e.g., tyrosinase, and pigment epithelium derived factor). In vivo, treatment of 8 mo R345W+/+ knockin mice with CHIR (25 mg/kg i.p., 1 mo) was well tolerated and significantly reduced R345W F3-associated AMD-like basal laminar deposit number and size, thereby preventing the main pathological feature in these mice. This is the first demonstration of small molecule-based prevention of AMD-like pathology in ML/DHRD mice and may herald a rejuvenation of interest in GSK3 inhibition for the treatment of neurodegenerative diseases, including, potentially AMD itself.

Treatment Strategy With Gene Editing for Late-Onset Retinal Degeneration Caused by a Founder Variant in C1QTNF5

Purpose

Genome editing is an emerging group of technologies with the potential to ameliorate dominant, monogenic human diseases such as late-onset retinal degeneration (L-ORD). The goal of this study was to identify disease stages and retinal locations optimal for evaluating the efficacy of a future genome editing trial.

Methods

Twenty five L-ORD patients (age range, 33-77 years; median age, 59 years) harboring the founder variant S163R in C1QTNF5 were enrolled from three centers in the United Kingdom and United States. Patients were examined with widefield optical coherence tomography (OCT) and chromatic perimetry under dark-adapted and light-adapted conditions to derive phenomaps of retinal disease. Results were analyzed with a model of a shared natural history of a single delayed exponential across all subjects and all retinal locations.

Results

Critical age for the initiation of photoreceptor loss ranged from 48 years at the temporal paramacular retina to 74 years at the inferior midperipheral retina. Subretinal deposits (sRET-Ds) became more prevalent as critical age was approached. Subretinal pigment epithelial deposits (sRPE-Ds) were detectable in the youngest patients showing no other structural or functional abnormalities at the retina. The sRPE-D thickness continuously increased, reaching 25 µm in the extrafoveal retina and 19 µm in the fovea at critical age. Loss of light sensitivity preceded shortening of outer segments and loss of photoreceptors by more than a decade.

Conclusions

Retinal regions providing an ideal treatment window exist across all severity stages of L-ORD.

Lysolipids are prominent in subretinal drusenoid deposits, a high-risk phenotype in age-related macular degeneration

Introduction

Age related macular degeneration (AMD) causes legal blindness worldwide, with few therapeutic targets in early disease and no treatments for 80% of cases. Extracellular deposits, including drusen and subretinal drusenoid deposits (SDD; also called reticular pseudodrusen), disrupt cone and rod photoreceptor functions and strongly confer risk for advanced disease. Due to the differential cholesterol composition of drusen and SDD, lipid transfer and cycling between photoreceptors and support cells are candidate dysregulated pathways leading to deposit formation. The current study explores this hypothesis through a comprehensive lipid compositional analysis of SDD.

Methods

Histology and transmission electron microscopy were used to characterize the morphology of SDD. Highly sensitive tools of imaging mass spectrometry (IMS) and nano liquid chromatography tandem mass spectrometry (nLC-MS/MS) in positive and negative ion modes were used to spatially map and identify SDD lipids, respectively. An interpretable supervised machine learning approach was utilized to compare the lipid composition of SDD to regions of uninvolved retina across 1873 IMS features and to automatically discern candidate markers for SDD. Immunohistochemistry (IHC) was used to localize secretory phospholipase A2 group 5 (PLA2G5).

Results

Among the 1873 detected features in IMS data, three lipid classes, including lysophosphatidylcholine (LysoPC), lysophosphatidylethanolamine (LysoPE) and lysophosphatidic acid (LysoPA) were observed nearly exclusively in SDD while presumed precursors, including phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidic acid (PA) lipids were detected in SDD and adjacent photoreceptor outer segments. Molecular signals specific to SDD were found in central retina and elsewhere. IHC results indicated abundant PLA2G5 in photoreceptors and retinal pigment epithelium (RPE).

Discussion

The abundance of lysolipids in SDD implicates lipid remodeling or degradation in deposit formation, consistent with ultrastructural evidence of electron dense lipid-containing structures distinct from photoreceptor outer segment disks and immunolocalization of secretory PLA2G5 in photoreceptors and RPE. Further studies are required to understand the role of lipid signals observed in and around SDD.

Transcriptomic and Chromatin Accessibility Analysis of the Human Macular and Peripheral Retinal Pigment Epithelium at the Single-Cell Level

Some human retinal diseases are characterized by pathology that is restricted to specific cell types and to specific regions of the eye. Several disease entities either selectively affect or spare the macula, the retina region at the center of the posterior pole. Photoreceptor cells in the macula are involved in high-acuity vision and require metabolic support from non-neuronal cell types. Some macular diseases involve the retinal pigment epithelium (RPE), an epithelial cell layer with several metabolic-support functions essential for the overlying photoreceptors. In the current study, the ways in which RPE confers region-specific disease susceptibility were determined by examining heterogeneity within RPE tissue from human donors. RPE nuclei from the macular and peripheral retina were profiled using joint single-nucleus RNA and ATAC sequencing. The expression of several genes differed between macular and peripheral RPE. Region-specific ATAC peaks were found, suggesting regulatory elements used exclusively by macular or peripheral RPE. Across anatomic regions, subpopulations of RPE were identified that appeared to have differential levels of expression of visual cycle genes. Finally, loci associated with age-related macular degeneration were examined for a better understanding of RPE-specific disease phenotypes. These findings showed variations in the regulation of gene expression in the human RPE by region and subpopulation, and provide a source for a better understanding of the molecular basis of macular disease.

Extracellular vesicles from retinal pigment epithelial cells expressing R345W-Fibulin-3 induce epithelial-mesenchymal transition in recipient cells

We have shown previously that expression of R345W-Fibulin-3 induces epithelial-mesenchymal transition (EMT) in retinal pigment epithelial (RPE) cells. The purpose of the current study was to determine if extracellular vesicles (EVs) derived from RPE cells expressing R345W-Fibulin-3 mutation are sufficient to induce EMT in recipient cells. ARPE-19 cells were infected with luciferase-tagged wild-type (WT)- Fibulin-3 or luciferase-tagged R345W-Fibulin-3 (R345W) using lentiviruses. EVs were isolated from the media by ultracentrifugation or density gradient ultracentrifugation. Transmission electron microscopy and cryogenic electron microscopy were performed to study the morphology of the EVs. The size distribution of EVs were determined by nanoparticle tracking analysis (NTA). EV cargo was analysed using LC-MS/MS based proteomics. EV-associated transforming growth factor beta 1 (TGFβ1) protein was measured by enzyme-linked immunosorbent assay. The capacity of EVs to stimulate RPE migration was evaluated by treating recipient cells with WT- or R345W-EVs. The role of EV-bound TGFβ was determined by pre-incubation of EVs with a pan-TGFβ blocking antibody or IgG control. EM imaging revealed spherical vesicles with two subpopulations of EVs: a group with diameters around 30 nm and a group with diameters over 100 nm, confirmed by NTA analysis. Pathway analysis revealed that members of the sonic hedgehog pathway were less abundant in R345W- EVs, while EMT drivers were enriched. Additionally, R345W-EVs had higher concentrations of TGFβ1 compared to control. Critically, treatment with R345W-EVs was sufficient to increase EMT marker expression, as well as cell migration in recipient cells. This EV-increased cell migration was significantly inhibited by pre-incubation of EVs with pan-TGFβ-neutralising antibody. In conclusion, the expression of R345W-Fibulin-3 alters the size and cargo of EVs, which are sufficient to enhance the rate of cell migration in a TGFβ dependent manner. These results suggest that EV-bound TGFβ plays a critical role in the induction of EMT in RPE cells.

Fibulin7 Mediated Pathological Cardiac Remodeling through EGFR Binding and EGFR-Dependent FAK/AKT Signaling Activation

Adverse remodeling after myocardial infarction (MI) result in heart failure and sudden cardiac death. Fibulin7 (FBLN7) is an adhesion protein excreted into the extracellular matrix that functions in multiple biological processes. However, whether and how FBLN7 affects post-MI cardiac remodeling remains unclear. Here, the authors identify FBLN7 as a critical profibrotic regulator of adverse cardiac remodeling. They observe significantly upregulated serum FBLN7 levels in MI patients with left ventricular remodeling compared to those without MI. Microarray dataset analysis reveal FBLN7 is upregulated in human heart samples from patients with dilated and hypertrophic cardiomyopathy compared with non-failing hearts. The authors demonstrate that FBLN7 deletion attenuated post-MI cardiac remodeling, leading to better cardiac function and reduced myocardial fibrosis, whereas overexpression of FBLN7 results in the opposite effects. Mechanistically, FBLN7 binds to the epidermal growth factor receptor (EGFR) through its EGF-like domain, together with the EGF-like calcium-binding domain, and induces EGFR autophosphorylation at tyrosine (Y) 1068 and Y1173, which activates downstream focal adhesion kinase/AKT signaling, thereby leading to fibroblast-to-myofibroblast transdifferentiation. In addition, FBLN7-EGFR mediates this signal transduction, and the fibrotic response is effectively suppressed by the inhibition of EGFR activity. Taken together, FBLN7 plays an important role in cardiac remodeling and fibrosis after MI.

Age-related macular degeneration

Age-related macular degeneration is an increasingly important public health issue due to ageing populations and increased longevity. Age-related macular degeneration affects individuals older than 55 years and threatens high-acuity central vision required for important tasks such as reading, driving, and recognising faces. Advances in retinal imaging have identified biomarkers of progression to late age-related macular degeneration. New treatments for neovascular age-related macular degeneration offer potentially longer-lasting effects, and progress is being made towards a treatment for atrophic late age-related macular degeneration. An effective intervention to slow progression in the earlier stages of disease, or to prevent late age-related macular degeneration development remains elusive, and our understanding of underlying mechanistic pathways continues to evolve.

Electrophysiological Evaluation of Macular Dystrophies

Macular dystrophies are a heterogeneous group of genetic disorders that often severely threatens the bilateral central vision of the affected patient. While advances in molecular genetics have been instrumental in the understanding and diagnosis of these disorders, there remains significant phenotypical variation among patients within any particular subset of macular dystrophies. Electrophysiological testing remains a vital tool not only to characterize vision loss for differential diagnosis but also to understand the pathophysiology of these disorders and to monitor the treatment effect, potentially leading to therapeutic advances. This review summarizes the application of electrophysiological testing in macular dystrophies, including Stargardt disease, bestrophinopathies, X-linked retinoschisis, Sorsby fundus dystrophy, Doyne honeycomb retina dystrophy, autosomal dominant drusen, occult macular dystrophy, North Carolina macular dystrophy, pattern dystrophy, and central areolar choroidal dystrophy.

Cellular and Molecular Mechanisms of Pathogenesis Underlying Inherited Retinal Dystrophies

Inherited retinal dystrophies (IRDs) are congenital retinal degenerative diseases that have various inheritance patterns, including dominant, recessive, X-linked, and mitochondrial. These diseases are most often the result of defects in rod and/or cone photoreceptor and retinal pigment epithelium function, development, or both. The genes associated with these diseases, when mutated, produce altered protein products that have downstream effects in pathways critical to vision, including phototransduction, the visual cycle, photoreceptor development, cellular respiration, and retinal homeostasis. The aim of this manuscript is to provide a comprehensive review of the underlying molecular mechanisms of pathogenesis of IRDs by delving into many of the genes associated with IRD development, their protein products, and the pathways interrupted by genetic mutation.

Mouse Choroid Proteome Revisited: Focus on Aging

Age is a major risk factor for age-related macular degeneration (AMD), and age has a role in the disease phenotypes of heritable macular dystrophies. The proteomes of C57Bl6/J mouse choroids at 2 ages were analyzed to identify biochemical processes affected by aging. Proteins of interest were identified as those contributing most to the variance in principal component analysis and those showing the largest significant differences between ages. These proteins implicated altered ECM composition, immune system function, and lipid metabolism.

The extracellular microenvironment in immune dysregulation and inflammation in retinal disorders

Inherited retinal dystrophies (IRDs) as well as genetically complex retinal phenotypes represent a heterogenous group of ocular diseases, both on account of their phenotypic and genotypic characteristics. Therefore, overlaps in clinical features often complicate or even impede their correct clinical diagnosis. Deciphering the molecular basis of retinal diseases has not only aided in their disease classification but also helped in our understanding of how different molecular pathologies may share common pathomechanisms. In particular, these relate to dysregulation of two key processes that contribute to cellular integrity, namely extracellular matrix (ECM) homeostasis and inflammation. Pathological changes in the ECM of Bruch's membrane have been described in both monogenic IRDs, such as Sorsby fundus dystrophy (SFD) and Doyne honeycomb retinal dystrophy (DHRD), as well as in the genetically complex age-related macular degeneration (AMD) or diabetic retinopathy (DR). Additionally, complement system dysfunction and distorted immune regulation may also represent a common connection between some IRDs and complex retinal degenerations. Through highlighting such overlaps in molecular pathology, this review aims to illuminate how inflammatory processes and ECM homeostasis are linked in the healthy retina and how their interplay may be disturbed in aging as well as in disease.

A loss-of-function cysteine mutant in fibulin-3 (EFEMP1) forms aberrant extracellular disulfide-linked homodimers and alters extracellular matrix composition

Fibulin-3 (F3 or EFEMP1) is a disulfide-rich, secreted glycoprotein necessary for maintaining extracellular matrix (ECM) and connective tissue integrity. Three studies have identified distinct autosomal recessive F3 mutations in individuals with Marfan Syndrome-like phenotypes. Herein, we characterize how one of these mutations, c.163T>C; p.Cys55Arg (C55R), disrupts F3 secretion, quaternary structure, and function by forming unique extracellular disulfide-linked homodimers. Dual cysteine mutants suggest that the C55R-induced disulfide species forms because of the new availability of Cys70 on adjacent F3 monomers. Surprisingly, mutation of single cysteines located near Cys55 (i.e., Cys29, Cys42, Cys48, Cys61, Cys70, Cys159, and Cys171) also produced similar extracellular disulfide-linked dimers, suggesting that this is not a phenomenon isolated to the C55R mutant. To assess C55R functionality, F3 knockout (KO) retinal pigmented epithelial (RPE) cells were generated, followed by reintroduction of wild-type (WT) or C55R F3. F3 KO cells produced lower levels of the ECM remodeling enzyme, matrix metalloproteinase 2, and reduced formation of collagen VI ECM filaments, both of which were partially rescued by WT F3 overexpression. However, C55R F3 was unable to compensate for these same ECM-related defects. Our results highlight the unique behavior of particular cysteine mutations in F3 and uncover potential routes to restore C55R F3 loss-of-function.

Complement factor B is critical for sub-RPE deposit accumulation in a model of Doyne honeycomb retinal dystrophy with features of age-related macular degeneration

EFEMP1 R345W is a dominant mutation causing Doyne honeycomb retinal dystrophy/malattia leventinese (DHRD/ML), a rare blinding disease with clinical pathology similar to age-related macular degeneration (AMD). Aged Efemp1  R345W/R345W knock-in mice (Efemp1ki/ki) develop microscopic deposits on the basal side of retinal pigment epithelial cells (RPE), an early feature in DHRD/ML and AMD. Here, we assessed the role of alternative complement pathway component factor B (FB) in the formation of these deposits. RNA-seq analysis of the posterior eyecups revealed increased unfolded protein response, decreased mitochondrial function in the neural retina (by 3 months of age) and increased inflammatory pathways in both neural retina and posterior eyecups (at 17 months of age) of Efemp1ki/ki mice compared with wild-type littermate controls. Proteomics analysis of eye lysates confirmed similar dysregulated pathways as detected by RNA-seq. Complement activation was increased in aged Efemp1ki/ki eyes with an approximately 2-fold elevation of complement breakdown products iC3b and Ba (P < 0.05). Deletion of the Cfb gene in female Efemp1ki/ki mice partially normalized the above dysregulated biological pathway changes and oral dosing of a small molecule FB inhibitor from 10 to 12 months of age reduced sub-RPE deposits by 65% (P = 0.029). In contrast, male Efemp1ki/ki mice had fewer sub-RPE deposits than age-matched females, no elevation of ocular complement activation and no effect of FB inhibition on sub-RPE deposits. The effects of FB deletion or inhibition on Efemp1ki/ki mice supports systemic inhibition of the alternative complement pathway as a potential treatment of dry AMD and DHRD/ML.

Oxidative stress differentially impacts apical and basolateral secretion of angiogenic factors from human iPSC-derived retinal pigment epithelium cells

The retinal pigment epithelium (RPE) is a polarized monolayer that secretes growth factors and cytokines towards the retina apically and the choroid basolaterally. Numerous RPE secreted proteins have been linked to the pathogenesis of age-related macular degeneration (AMD). The purpose of this study was to determine the differential apical and basolateral secretome of RPE cells, and the effects of oxidative stress on directional secretion of proteins linked to AMD and angiogenesis. Tandem mass tag spectrometry was used to profile proteins in human iPSC-RPE apical and basolateral conditioned media. Changes in secretion after oxidative stress induced by H2O2 or tert-butyl hydroperoxide (tBH) were investigated by ELISA and western analysis. Out of 926 differentially secreted proteins, 890 (96%) were more apical. Oxidative stress altered the secretion of multiple factors implicated in AMD and neovascularization and promoted a pro-angiogenic microenvironment by increasing the secretion of pro-angiogenic molecules (VEGF, PTN, and CRYAB) and decreasing the secretion of anti-angiogenic molecules (PEDF and CFH). Apical secretion was impacted more than basolateral for PEDF, CRYAB and CFH, while basolateral secretion was impacted more for VEGF, which may have implications for choroidal neovascularization. This study lays a foundation for investigations of dysfunctional RPE polarized protein secretion in AMD and other chorioretinal degenerative disorders.

CLEC3B is a novel causative gene for macular-retinal dystrophy

PURPOSE

Macular degeneration is the leading cause of blindness worldwide. In this study, we aimed to define a new subtype of macular-retinal dystrophy and its genetic predisposition in 5 families.

METHODS

Exome sequencing was performed to determine the putative disease-causing genes in patients with inherited macular disorders confirmed through comprehensive ophthalmic examinations. To validate its functional consequence, adeno-associated virus-mediated mutant gene was delivered into the murine retina, and both structural and functional tests were performed to investigate its pathological effects in vivo.

RESULTS

In total, 5 multigenerational families diagnosed with autosomal dominant maculoretinopathy were found to carry a pathogenic variant in a new gene, CLEC3B, which encodes tetranectin, a plasminogen kringle-4 binding protein. Consistent with the disease phenotypes of patients, mice that received subretinal injections with the CLEC3B variant displayed multiple subretinal hyperreflective deposits, reduced retinal thickness, and decreased electroretinographic responses. Moreover, the optokinetic tracking response indicated that spatial frequency was significantly lower (P < .05), implying impaired visual function in these mice.

CONCLUSION

We have presented a new subtype of macular-retinal dystrophy in 5 families as well as a new pathogenic gene, CLEC3B, providing new insights into maculoretinopathy etiology.

EFEMP1 rare variants cause familial juvenile-onset open-angle glaucoma

Juvenile open-angle glaucoma (JOAG) is a severe type of glaucoma with onset before age 40 and dominant inheritance. Using exome sequencing we identified 3 independent families from the Philippines with novel EFEMP1 variants (c.238A>T, p.Asn80Tyr; c.1480T>C, p.Ter494Glnext*29; and c.1429C>T, p.Arg477Cys) co-segregating with disease. Affected variant carriers (N = 34) exhibited severe disease with average age of onset of 16 years and with 76% developing blindness. To investigate functional effects, we transfected COS7 cells with vectors expressing the three novel EFEMP1 variants and showed that all three variants found in JOAG patients caused significant intracellular protein aggregation and retention compared to wild type and also compared to EFEMP1 variants associated with other ocular phenotypes including an early-onset form of macular degeneration, Malattia Leventinese/Doyne's Honeycomb retinal dystrophy. These results suggest that rare EFEMP1 coding variants can cause JOAG through a mechanism involving protein aggregation and retention, and that the extent of intracellular retention correlates with disease phenotype. This is the first report of EFEMP1 variants causing JOAG, expanding the EFEMP1 disease spectrum. Our results suggest that EFEMP1 mutations appear to be a relatively common cause of JOAG in Filipino families, an ethnically diverse population.

The Role of the Stromal Extracellular Matrix in the Development of Pterygium Pathology: An Update

Pterygium is a benign fibrovascular lesion of the bulbar conjunctiva with frequent involvement of the corneal limbus. Its pathogenesis has been mainly attributed to sun exposure to ultraviolet-B radiation. Obtained evidence has shown that it is a complex and multifactorial process which involves multiple mechanisms such as oxidative stress, dysregulation of cell cycle checkpoints, induction of inflammatory mediators and growth factors, angiogenic stimulation, extracellular matrix (ECM) disorders, and, most likely, viruses and hereditary changes. In this review, we aim to collect all authors’ experiences and our own, with respect to the study of fibroelastic ECM of pterygium. Collagen and elastin are intrinsic indicators of physiological and pathological states. Here, we focus on an in-depth analysis of collagen (types I and III), as well as the main constituents of elastic fibers (tropoelastin (TE), fibrillins (FBNs), and fibulins (FBLNs)) and the enzymes (lysyl oxidases (LOXs)) that carry out their assembly or crosslinking. All the studies established that changes in the fibroelastic ECM occur in pterygium, based on the following facts: An increase in the synthesis and deposition of an immature form of collagen type III, which showed the process of tissue remodeling. An increase in protein levels in most of the constituents necessary for the development of elastic fibers, except FBLN4, whose biological roles are critical in the binding of the enzyme LOX, as well as FBN1 for the development of stable elastin. There was gene overexpression of TE, FBN1, FBLN5, and LOXL1, while the expression of LOX and FBLN2 and -4 remained stable. In conclusion, collagen and elastin, as well as several constituents involved in elastic fiber assembly are overexpressed in human pterygium, thus, supporting the hypothesis that there is dysregulation in the synthesis and crosslinking of the fibroelastic component, constituting an important pathogenetic mechanism for the development of the disease.

Inherited retinal diseases: Linking genes, disease-causing variants, and relevant therapeutic modalities

Inherited retinal diseases (IRDs) are a clinically complex and heterogenous group of visual impairment phenotypes caused by pathogenic variants in at least 277 nuclear and mitochondrial genes, affecting different retinal regions, and depleting the vision of affected individuals. Genes that cause IRDs when mutated are unique by possessing differing genotype-phenotype correlations, varying inheritance patterns, hypomorphic alleles, and modifier genes thus complicating genetic interpretation. Next-generation sequencing has greatly advanced the identification of novel IRD-related genes and pathogenic variants in the last decade. For this review, we performed an in-depth literature search which allowed for compilation of the Global Retinal Inherited Disease (GRID) dataset containing 4,798 discrete variants and 17,299 alleles published in 31 papers, showing a wide range of frequencies and complexities among the 194 genes reported in GRID, with 65% of pathogenic variants being unique to a single individual. A better understanding of IRD-related gene distribution, gene complexity, and variant types allow for improved genetic testing and therapies. Current genetic therapeutic methods are also quite diverse and rely on variant identification, and range from whole gene replacement to single nucleotide editing at the DNA or RNA levels. IRDs and their suitable therapies thus require a range of effective disease modelling in human cells, granting insight into disease mechanisms and testing of possible treatments. This review summarizes genetic and therapeutic modalities of IRDs, provides new analyses of IRD-related genes (GRID and complexity scores), and provides information to match genetic-based therapies such as gene-specific and variant-specific therapies to the appropriate individuals.

The second Japanese family with Malattia Leventinese/Doyne honeycomb retinal dystrophy

PURPOSE

To describe the clinical and genetic findings of patients in the second Japanese family with Malattia Leventinese/Doyne honeycomb retinal dystrophy (ML/DHRD).

METHODS

Two patients (a 41-year-old male proband and his third son) underwent comprehensive ophthalmic examinations, including full-field and multifocal electroretinography (ERG). Sanger sequencing was performed to detect an EFEMP1 gene variant (p.Arg345Trp), which was identified as the only causative pathogenic variant.

RESULTS

Genetic analysis revealed that both patients carried the heterozygous variant, but the other unaffected family members did not. Although the proband exhibited innumerable radially distributed drusen in both the posterior poles and good visual acuity at initial presentation, bilateral choroidal neovascularization (CNV) developed during the 15-year follow-up. The proband received 15 intravitreal anti-vascular endothelial growth factor (VEGF) injections in the left eye (LE) and two injections in the right eye (RE). At 56 years of age, his decimal best-corrected visual acuity was 0.1 and 1.2 in the LE and RE, respectively. Full-field ERG showed that while the rod and combined responses were within normal amplitudes, the cone and 30-Hz flicker responses had slightly decreased amplitudes. Multifocal ERG revealed attenuated central responses in the LE and decreased temporal responses in the RE. In the 20-year-old son, multifocal ERG showed normal responses in both eyes.

CONCLUSION

This is the first report of ML/DHRD in a patient who developed bilateral CNV and received anti-VEGF treatment in both eyes. Although multifocal ERG exhibited worsening of macular function, the generalized photoreceptor function was preserved until middle age.

Targeting Lipid Metabolism for the Treatment of Age-Related Macular Degeneration: Insights from Preclinical Mouse Models

Age-related macular degeneration (AMD) is a major leading cause of irreversible visual impairment in the world with limited therapeutic interventions. Histological, biochemical, genetic, and epidemiological studies strongly implicate dysregulated lipid metabolism in the retinal pigmented epithelium (RPE) in AMD pathobiology. However, effective therapies targeting lipid metabolism still need to be identified and developed for this blinding disease. To test lipid metabolism-targeting therapies, preclinical AMD mouse models are needed to establish therapeutic efficacy and the role of lipid metabolism in the development of AMD-like pathology. In this review, we provide a comprehensive overview of current AMD mouse models available to researchers that could be used to provide preclinical evidence supporting therapies targeting lipid metabolism for AMD. Based on previous studies of AMD mouse models, we discuss strategies to modulate lipid metabolism as well as examples of studies evaluating lipid-targeting therapeutics to restore lipid processing in the RPE. The use of AMD mouse models may lead to worthy lipid-targeting candidate therapies for clinical trials to prevent the blindness caused by AMD.

Cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL)

A 44-year-old Caucasian man presented with seizures and cognitive impairment. He had marked retinal drusen, and MR brain scan showed features of cerebral small vessel disease; he was diagnosed with a leukoencephalopathy of uncertain cause. He died at the age of 46 years and postmortem brain examination showed widespread small vessel changes described as a vasculopathy of unknown cause. Seven years postmortem, whole-genome sequencing identified a homozygous nonsense HTRA1 mutation (p.Arg302Ter), giving a retrospective diagnosis of cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy.

Identification of Estrogen Signaling in a Prioritization Study of Intraocular Pressure-Associated Genes

Elevated intraocular pressure (IOP) is the only modifiable risk factor for primary open-angle glaucoma (POAG). Herein we sought to prioritize a set of previously identified IOP-associated genes using novel and previously published datasets. We identified several genes for future study, including several involved in cytoskeletal/extracellular matrix reorganization, cell adhesion, angiogenesis, and TGF-β signaling. Our differential correlation analysis of IOP-associated genes identified 295 pairs of 201 genes with differential correlation. Pathway analysis identified β-estradiol as the top upstream regulator of these genes with ESR1 mediating 25 interactions. Several genes (i.e., EFEMP1, FOXC1, and SPTBN1) regulated by β-estradiol/ESR1 were highly expressed in non-glaucomatous human trabecular meshwork (TM) or Schlemm’s canal (SC) cells and specifically expressed in TM/SC cell clusters defined by single-cell RNA-sequencing. We confirmed ESR1 gene and protein expression in human TM cells and TM/SC tissue with quantitative real-time PCR and immunofluorescence, respectively. 17β-estradiol was identified in bovine, porcine, and human aqueous humor (AH) using ELISA. In conclusion, we have identified estrogen receptor signaling as a key modulator of several IOP-associated genes. The expression of ESR1 and these IOP-associated genes in TM/SC tissue and the presence of 17β-estradiol in AH supports a role for estrogen signaling in IOP regulation.

Diagnostic definition of malattia leventinese in a family from Colombia

The malattia leventinese is an autosomal dominant inherited disease whose symptoms appear between the second and fourth decades of life. It is characterized by the appearance of drusen located between the retinal pigment epithelium and the Bruch membrane. It is usually associated with low vision and may progress to blindness. The pathogenic variant p.Arg345Trp in the EFEMP1 gene has been associated with this disease. We characterized clinically and molecularly a family with malattia leventinese using a comprehensive approach that involved ophthalmologists, pediatricians, and geneticists. This approach is of great importance since the phenotype of this disease is often confused with acular degeneration. All family members underwent ophthalmological evaluation and DNA extraction from a peripheral blood sample. All exons of the EFEMP1 gene were amplified and sequenced. The pathogenic variant p.Arg345Trp was identified in affected individuals in this family. This is the first report of malattia leventinese in a family with the p.Arg345Trp pathogenic variant in Colombia. The molecular diagnosis of retinal dystrophies is essential to differentiate this type of pathology.

Age-related amyloidosis outside the brain: A state-of-the-art review

Inside and outside the brain, accumulation of amyloid fibrils plays key roles in the pathogenesis of fatal age-related diseases such as Alzheimer's and Parkinson's diseases and wild-type transthyretin amyloidosis. Although the incidence of all amyloidoses increases with age, for some types of amyloidosis aging is known as the main direct risk factor, and these types are typically diseases of elderly people. More than 10 different precursor proteins are known to cause age-associated amyloidosis; these proteins include amyloid β protein, α-synuclein, transthyretin, islet amyloid polypeptide, atrial natriuretic factor, and the newly discovered epidermal growth factor-containing fibulin-like extracellular matrix protein 1. Except for intracerebral amyloidoses, most age-related amyloidoses have been little studied. Indeed, in view of the increasing life expectancy in our societies, understanding how aging is involved in the process of amyloid fibril accumulation and the effects of amyloid deposits on the aging body is extremely important. In this review, we summarize current knowledge about the nature of amyloid precursor proteins, the prevalence, clinical manifestations, and pathogenesis of amyloidosis, and recent advances in our understanding of age-related amyloidoses outside the brain.

AMD-Like Substrate Causes Epithelial Mesenchymal Transition in iPSC-Derived Retinal Pigment Epithelial Cells Wild Type but Not C3-Knockout

The Bruch's membrane (BrM) is a five-layered extracellular matrix (ECM) that supports the retinal pigment epithelium (RPE). Normal age-related changes in the BrM may lead to RPE cell damage and ultimately to the onset and progression of age-related macular degeneration (AMD), which is the most common cause of visual loss among the elderly. A role for the complement system in AMD pathology has been established, but the disease mechanisms are poorly understood, which hampers the design of efficient therapies to treat millions of patients. In an effort to identify the mechanisms that lead from normal aging to pathology, we have developed a cell-based model using complement deficient human induced pluripotent stem cell (iPSC)-derived RPE cells cultured on an AMD-like ECM that mimics BrM. The data present evidence that changes in the ECM result in loss of differentiation and promote epithelial mesenchymal transition (EMT) of healthy RPE cells. This pathological process is mediated by complement activation and involves the formation of a randomly oriented collagen meshwork that drives the dedifferentiation of the RPE monolayer. Genetic ablation of complement component 3 has a protective effect against EMT but does not prevent the abnormal deposition of collagens. These findings offer new insights into the sequence of events that initiate AMD and may guide the design of efficient therapies to treat this disease with unmet medical needs.

Utility of EFEMP1 in the Prediction of Oncologic Outcomes of Urothelial Carcinoma

Urothelial carcinoma (UC) of the upper tract (UTUC) and urinary bladder (UBUC) is a heterogeneous malignancy. Through transcriptomic profiling of the Gene Expression Omnibus UBUC dataset (GSE31684), we discovered that epidermal growth factor-containing fibulin-like extracellularmatrix protein 1 (EFEMP1) was the most upregulated gene during metastatic development. EFEMP1 is an important component of basement membranes and acts as an enzyme regulator in extracellular matrix biology. Initially, evaluation of EFEMP1 mRNA expression in 50 UBUCs showed significantly upregulated levels in high stage UC. We further validated the clinical significance of EFEMP1 in 340 UTUC and 295 UBUC using immunohistochemistry, evaluated by H-score. High EFEMP1 immunoexpression significantly correlated with high pathologic stage, high histological grade, lymph node metastasis, vascular invasion, perineural invasion and high mitosis (all p < 0.05). After adjusting for established clinicopathological factors, EFEMP1 expression status retained its prognostic impact on disease-specific survival and metastasis-free survival in UTUC and UBUC (all p < 0.01). Furthermore, Ingenuity Pathway Analysis showed that actin cytoskeleton signaling, tumor microenvironment pathway and mitochondrial dysfunction were significantly enriched by EFEMP1 dysregulation. In conclusion, high EFEMP1 expression was associated with adverse pathological features in UC and independently predicted worse outcomes, suggesting its roles in clinical decision-making and risk stratification.

Characterization of age-related macular degeneration in Indian donor eyes

Purpose:

The purpose of this study was to test the reliability of fundus stereomicroscopy in postmortem eyes to assign severity of age-related macular degeneration (AMD) using the Minnesota grading and confirmation by histology using Alabama and Sarks grading scales and to assess the incidence of AMD pathology in donor eyes from a South Indian population.

Methods:

Eyes (199) from 153 donors (55–95 years) after obtaining fundus images were processed for histology. Fundus images were graded according to the Minnesota grading system based on drusen size, area of depigmentation, and atrophy. At least one eye from each donor displaying the AMD phenotypes were subjected to histological examination. The fundus grading was correlated with histology and the stages of AMD assigned for early AMD by the Alabama AMD grading system and for both early and advanced AMD by the Sarks classification.

Results:

Stereoscopic examination of the fundus found that 10 of the 153 donors had features of early AMD and 3 advanced AMD. Following histological examination, one of the early AMD eyes was reclassified as advanced AMD. Early AMD features that were observed on histology included soft drusen (>63 μm), basal laminar deposits, photoreceptor outer segment degeneration, disorganization of retinal pigment epithelium (RPE), Bruch's membrane thickening. Advanced AMD features observed in histology are extensive atrophy of RPE, choroidal neovascularization and disciform scar formation.

Conclusion:

Identification of either early or advanced AMD using stereomicroscopic assessment (SMA) showed high sensitivity and specificity. However, misclassification between AMD stages can occur when only SMA is used.

Complement C5 is not critical for the formation of sub-RPE deposits in Efemp1 mutant mice

The complement system plays a role in the formation of sub-retinal pigment epithelial (RPE) deposits in early stages of age-related macular degeneration (AMD). But the specific mechanisms that connect complement activation and deposit formation in AMD patients are unknown, which limits the development of efficient therapies to reduce or stop disease progression. We have previously demonstrated that C3 blockage prevents the formation of sub-RPE deposits in a mouse model of EFEMP1-associated macular degeneration. In this study, we have used double mutant Efemp1R345W/R345W:C5-/- mice to investigate the role of C5 in the formation of sub-RPE deposits in vivo and in vitro. The data revealed that the genetic ablation of C5 does not eliminate the formation of sub-RPE deposits. Contrarily, the absence of C5 in RPE cultures promotes complement dysregulation that results in increased activation of C3, which likely contributes to deposit formation even in the absence of EFEMP1-R345W mutant protein. The results also suggest that genetic ablation of C5 alters the extracellular matrix turnover through an effect on matrix metalloproteinases in RPE cell cultures. These results confirm that C3 rather than C5 could be an effective therapeutic target to treat early AMD.

Measuring the Contributions of Basal Laminar Deposit and Bruch's Membrane in Age-Related Macular Degeneration

Purpose

Basal laminar deposit (BLamD) is a consistent finding in age-related macular degeneration (AMD). We quantified BLamD thickness, appearance, and topography in eyes of aged donors with and without AMD and evaluated its relationship to other components of the retinal pigment epithelium-basal lamina/Bruch's membrane (RPE-BL-BrM) complex.

Methods

Donor eyes (n = 132) were classified as normal (n = 54), early to intermediate AMD (n = 24), geographic atrophy (GA; n = 13), and neovascular AMD (NV; n = 41). In high-resolution histology, we assessed RPE, BLamD, and BrM thicknesses and phenotypes at 3309 predefined locations in the central (foveal and perifovea) and superior (perifoveal) sections. Pre-mortem optical coherence tomography (OCT) imaging of a 90-year-old woman was compared to postmortem histopathology.

Results

In non-atrophic areas of AMD eyes, the RPE-BLamD is thick (normal = 13.7 µm, early-intermediate = 16.8 µm, GA = 17.4 µm, NV = 18.7 µm), because the BLamD is thick (normal = 0.3 µm, early-intermediate = 5.5 µm, GA = 4.1 µm, NV = 5.3 µm). RPE layer thickness is similar across these stages. Disease-associated variants of BLamD (thick, late, basal mounds) cluster subfoveally. A thick BLamD is visible on OCT as a hyporeflective split in the RPE-BL-BrM complex. BrM is thin (3.5 µm) in NV (normal = 4.2 µm, early to intermediate = 4.4 µm, and GA = 4.2 µm).

Conclusions

The RPE-BL-BrM complex is thick in AMD, driven by the accumulation and expansion of BLamD rather than expansion of either three-layer BrM, RPE-BL, or RPE. BLamD is clinically appreciable by OCT in some patients as a non-neovascular "split RPE-BL-BrM complex" or "double-layer sign." BLamD may contribute toward the formation and progression of high-risk drusen yet also exhibit protective properties.

Impaired cholesterol efflux in retinal pigment epithelium of individuals with juvenile macular degeneration

Macular degeneration (MD) is characterized by the progressive deterioration of the macula and represents one of the most prevalent causes of blindness worldwide. Abnormal intracellular accumulation of lipid droplets and pericellular deposits of lipid-rich material in the retinal pigment epithelium (RPE) called drusen are clinical hallmarks of different forms of MD including Doyne honeycomb retinal dystrophy (DHRD) and age-related MD (AMD). However, the appropriate molecular therapeutic target underlying these disorder phenotypes remains elusive. Here, we address this knowledge gap by comparing the proteomic profiles of induced pluripotent stem cell (iPSC)-derived RPEs (iRPE) from individuals with DHRD and their isogenic controls. Our analysis and follow-up studies elucidated the mechanism of lipid accumulation in DHRD iRPE cells. Specifically, we detected significant downregulation of carboxylesterase 1 (CES1), an enzyme that converts cholesteryl ester to free cholesterol, an indispensable process in cholesterol export. CES1 knockdown or overexpression of EFEMP1R345W, a variant of EGF-containing fibulin extracellular matrix protein 1 that is associated with DHRD and attenuated cholesterol efflux and led to lipid droplet accumulation. In iRPE cells, we also found that EFEMP1R345W has a hyper-inhibitory effect on epidermal growth factor receptor (EGFR) signaling when compared to EFEMP1WT and may suppress CES1 expression via the downregulation of transcription factor SP1. Taken together, these results highlight the homeostatic role of cholesterol efflux in iRPE cells and identify CES1 as a mediator of cholesterol efflux in MD.

Role of Fibulins in Embryonic Stage Development and Their Involvement in Various Diseases

The extracellular matrix (ECM) plays an important role in the evolution of early metazoans, as it provides structural and biochemical support to the surrounding cells through the cell–cell and cell–matrix interactions. In multi-cellular organisms, ECM plays a pivotal role in the differentiation of tissues and in the development of organs. Fibulins are ECM glycoproteins, found in a variety of tissues associated with basement membranes, elastic fibers, proteoglycan aggregates, and fibronectin microfibrils. The expression profile of fibulins reveals their role in various developmental processes such as elastogenesis, development of organs during the embryonic stage, tissue remodeling, maintenance of the structural integrity of basement membrane, and elastic fibers, as well as other cellular processes. Apart from this, fibulins are also involved in the progression of human diseases such as cancer, cardiac diseases, congenital disorders, and chronic fibrotic disorders. Different isoforms of fibulins show a dual role of tumor-suppressive and tumor-promoting activities, depending on the cell type and cellular microenvironment in the body. Knockout animal models have provided deep insight into their role in development and diseases. The present review covers details of the structural and expression patterns, along with the role of fibulins in embryonic development and disease progression, with more emphasis on their involvement in the modulation of cancer diseases.

Proline metabolism and transport in retinal health and disease

The retina is one of the most energy-demanding tissues in the human body. Photoreceptors in the outer retina rely on nutrient support from the neighboring retinal pigment epithelium (RPE), a monolayer of epithelial cells that separate the retina and choroidal blood supply. RPE dysfunction or cell death can result in photoreceptor degeneration, leading to blindness in retinal degenerative diseases including some inherited retinal degenerations and age-related macular degeneration (AMD). In addition to having ready access to rich nutrients from blood, the RPE is also supplied with lactate from adjacent photoreceptors. Moreover, RPE can phagocytose lipid-rich outer segments for degradation and recycling on a daily basis. Recent studies show RPE cells prefer proline as a major metabolic substrate, and they are highly enriched for the proline transporter, SLC6A20. In contrast, dysfunctional or poorly differentiated RPE fails to utilize proline. RPE uses proline to fuel mitochondrial metabolism, synthesize amino acids, build the extracellular matrix, fight against oxidative stress, and sustain differentiation. Remarkably, the neural retina rarely imports proline directly, but it uptakes and utilizes intermediates and amino acids derived from proline catabolism in the RPE. Mutations of genes in proline metabolism are associated with retinal degenerative diseases, and proline supplementation is reported to improve RPE-initiated vision loss. This review will cover proline metabolism in RPE and highlight the importance of proline transport and utilization in maintaining retinal metabolism and health.

Loss-of-Function Variants in EFEMP1 Cause a Recognizable Connective Tissue Disorder Characterized by Cutis Laxa and Multiple Herniations

Hereditary disorders of connective tissue (HDCT) compromise a heterogeneous group of diseases caused by pathogenic variants in genes encoding different components of the extracellular matrix and characterized by pleiotropic manifestations, mainly affecting the cutaneous, cardiovascular, and musculoskeletal systems. We report the case of a 9-year-old boy with a discernible connective tissue disorder characterized by cutis laxa (CL) and multiple herniations and caused by biallelic loss-of-function variants in EFEMP1. Hence, we identified EFEMP1 as a novel disease-causing gene in the CL spectrum, differentiating it from other HDCT.

First reported case of Doyne honeycomb retinal dystrophy (Malattia Leventinese/autosomal dominant drusen) in Scandinavia

BACKGROUND

Doyne honeycomb retinal dystrophy (DHRD)/malattia leventinese (ML) is an autosomal dominant, progressive retinal disorder characterized by massive central retinal drusen often partly coalescent forming a characteristic honeycomb-like pattern. Debut of vision loss often occurs in early to mid-adulthood, and the degree varies. A single variant in EFEMP1: c.1033C>T (R345W) has been identified as the cause in all cases.

METHODS

Following DNA isolation, exome sequencing was performed in seven genes associated with flecked retina. Direct sequencing was used for variant verification.

RESULTS

We report the first Scandinavian case of molecular genetically verified DHRD/ML: a 57-year-old woman debuting with vision loss and metamorphopsia. On both eyes, ophthalmological findings included massive hard drusen in the macular region and nasal to the optic disc as well as macular hyperpigmentation. Secondary choroidal neovascularizations were identified on both eyes, and anti-vascular endothelial growth factor was administered, without effect.

CONCLUSION

Molecular genetic investigation revealed heterozygosity for the known pathogenic missense variant in EFEMP1: c.1033C>T (R345W) previously reported in relation to DHRD/ML. Family history revealed no other cases of similar visual impairment suggesting a de novo mutation. Furthermore, there was no correlation between the unique DHRD/ML haplotypes reported in the literature and our patient.

Clinically-identified C-terminal mutations in fibulin-3 are prone to misfolding and destabilization

Distinct mutations in the secreted extracellular matrix protein, fibulin-3 (F3), have been associated with a number of ocular diseases ranging from primary open angle glaucoma to cuticular age-related macular degeneration to a rare macular dystrophy, Malattia Leventinese (ML). The R345W F3 mutation that causes ML leads to F3 misfolding, inefficient secretion and accumulation at higher intracellular steady state levels in cultured cells. Herein, we determined whether fifteen other clinically-identified F3 mutations also led to similar levels of misfolding and secretion defects, which might provide insight into their potential pathogenicity. Surprisingly, we found that only a single F3 variant, L451F, presented with a significant secretion defect (69.5 ± 2.4% of wild-type (WT) F3 levels) and a corresponding increase in intracellular levels (226.8 ± 25.4% of WT F3 levels). Upon follow-up studies, when this conserved residue (L451) was mutated to a charged (Asp or Arg) or bulky (Pro, Trp, Tyr) residue, F3 secretion was also compromised, indicating the importance of small side chains (Leu, Ala, or Gly) at this residue. To uncover potential inherent F3 instability not easily observed under typical culture conditions, we genetically eliminated the sole stabilizing N-linked glycosylation site (N249) from select clinically-identified F3 mutants. This removal exacerbated R345W and L451F secretion defects (19.8 ± 3.0% and 12.4 ± 1.2% of WT F3 levels, respectively), but also revealed a previously undiscovered secretion defect in another C-terminal variant, Y397H (42.0 ± 10.1% of WT F3 levels). Yet, glycan removal did not change the relative secretion of the N-terminal mutants tested (D49A, R140W, I220F). These results highlight the uniqueness and molecular similarities between the R345W and L451F variants and also suggest that previously identified disease-associated mutations (e.g., R140W) are indistinguishable from WT with respect to secretion, hinting that they may lead to disease by an alternative mechanism.

Long-Range PCR-Based NGS Applications to Diagnose Mendelian Retinal Diseases

The purpose of this study was to develop a flexible, cost-efficient, next-generation sequencing (NGS) protocol for genetic testing. Long-range polymerase chain reaction (PCR) amplicons of up to 20 kb in size were designed to amplify entire genomic regions for a panel (n = 35) of inherited retinal disease (IRD)-associated loci. Amplicons were pooled and sequenced by NGS. The analysis was applied to 227 probands diagnosed with IRD: (A) 108 previously molecularly diagnosed, (B) 94 without previous genetic testing, and (C) 25 undiagnosed after whole-exome sequencing (WES). The method was validated with 100% sensitivity on cohort A. Long-range PCR-based sequencing revealed likely causative variant(s) in 51% and 24% of proband from cohorts B and C, respectively. Breakpoints of 3 copy number variants (CNVs) could be characterized. Long-range PCR libraries spike-in extended coverage of WES. Read phasing confirmed compound heterozygosity in 5 probands. The proposed sequencing protocol provided deep coverage of the entire gene, including intronic and promoter regions. Our method can be used (i) as a first-tier assay to reduce genetic testing costs, (ii) to elucidate missing heritability cases, (iii) to characterize breakpoints of CNVs at nucleotide resolution, (iv) to extend WES data to non-coding regions by spiking-in long-range PCR libraries, and (v) to help with phasing of candidate variants.

Utility of pattern recognition and multimodal imaging in the diagnosis and management of doyne honeycomb retinal dystrophy complicated with type one choroidal neovascular membrane

A 44-year-old woman presented with decreased vision in both eyes. The retina in both eyes had drusen distributed along vascular arcades, central macula and in peripapillary region. Macula had pigmented scarring and exudation. Fundus autofluorescence showed drusen. Optical coherence tomography showed drusen, subretinal and intraretinal fluid. Fundus fluorescein and indocyanine green angiography showed drusen, retinal pigment epithelial atrophy and vascular network. Younger age at presentation, bilateral symmetry, typical distribution of drusen along the arcades in a radiating pattern, peripapillary involvement, scarring and atrophy at macula were suggestive of doyne honeycomb retinal dystrophy. The reduced vision was due to macular atrophy and an active choroidal neovascular membrane. The patient was treated with antivascular endothelial growth factor injections for choroidal neovascular membrane. Our case highlights the importance of pattern recognition and multimodal imaging for diagnosing the type of macular dystrophy as doyne honeycomb retinal dystrophy, while simultaneously managing choroidal neovascular membrane.

The interplay of oxidative stress and ARMS2-HTRA1 genetic risk in neovascular AMD

Age-related macular degeneration (AMD) is the leading cause of vision loss in adults over 60 years old globally. There are two forms of advanced AMD: “dry” and “wet”. Dry AMD is characterized by geographic atrophy of the retinal pigment epithelium and overlying photoreceptors in the macular region; whereas wet AMD is characterized by vascular penetrance from the choroid into the retina, known as choroidal neovascularization (CNV). Both phenotypes eventually lead to loss of central vision. The pathogenesis of AMD involves the interplay of genetic polymorphisms and environmental risk factors, many of which elevate retinal oxidative stress. Excess reactive oxygen species react with cellular macromolecules, forming oxidation-modified byproducts that elicit chronic inflammation and promote CNV. Additionally, genome-wide association studies have identified several genetic variants in the age-related maculopathy susceptibility 2/high-temperature requirement A serine peptidase 1 (ARMS2-HTRA1) locus associated with the progression of late-stage AMD, especially the wet subtype. In this review, we will focus on the interplay of oxidative stress and HTRA1 in drusen deposition, chronic inflammation, and chronic angiogenesis. We aim to present a multifactorial model of wet AMD progression, supporting HTRA1 as a novel therapeutic target upstream of vascular endothelial growth factor (VEGF), the conventional target in AMD therapeutics. By inhibiting HTRA1’s proteolytic activity, we can reduce pro-angiogenic signaling and prevent proteolytic breakdown of the blood-retina barrier. The anti-HTRA1 approach offers a promising alternative treatment option to wet AMD, complementary to anti-VEGF therapy.

EFEMP1 Overexpression Contributes to Neovascularization in Age-Related Macular Degeneration

Purpose: Age-related macular degeneration (AMD) is one of the leading causes of blindness, and choroidal neovascularization (CNV) in AMD can lead to serious visual impairment. Gene expression profiling of human ocular tissues have a great potential to reveal the pathophysiology of AMD. This study aimed to identify novel molecular biomarkers and gene expression signatures of AMD. Methods: We analyzed transcriptome profiles in retinal-choroid tissues derived from donor patients with AMD in comparison with those from healthy controls using a publicly available dataset (GSE29801). We focused on the EFEMP1 gene, which was found to be differentially upregulated in AMD, especially in wet AMD eyes. Serological validation analysis was carried out to verify the expression of EFEMP1 in 39 wet AMD patients and 39 age- and gender-matched cataract controls, using an enzyme-linked immunosorbent assay (ELISA). We then investigated the role of EFEMP1 in angiogenesis through in vitro experiments involving EFEMP1 overexpression (OE) and knockdown in human umbilical vein endothelial cells (HUVECs). Results: An increase in EFEMP1 expression was observed in the retinal-choroid tissues of eyes with AMD, which was more significant in wet AMD than in dry AMD. In addition, there was a significant increase in serum fibulin-3 (EFEMP1 encoded protein) concentration in patients with wet AMD compared with that in the controls. Tube formation and proliferation of EFEMP1-OE HUVECs increased significantly, whereas those of EFEMP1 knockdown HUVECs decreased significantly compared with those of the control. Additional extracellular fibulin-3 treatments did not increase tube formation and proliferation of wildtype and EFEMP1 knockdown HUVECs, indicating that the proangiogenic properties of EFEMP1 are of cell origin. We also found that vascular endothelial growth factor expression in HUVECs was upregulated by EFEMP1 overexpression and downregulated by EFEMP1 knockdown. Conclusion: Our findings demonstrate EFEMP1 as a novel biomarker for CNV in AMD, providing a new target for the development of wet AMD-directed pharmaceuticals and diagnostics.

PERIPHERAL RETINAL DRUSEN-LIKE DEPOSITS IN GUCY2C CONGENITAL SECRETORY DIARRHEA SYNDROME

PURPOSE

To report the presence of drusen in infancy, in a patient with Type 1 retinopathy of prematurity and a rare congenital sodium diarrhea secondary to a sporadic GUCY2C mutation.

METHODS

A case report generated by review of clinical course, with imaging of 1 patient and literature review.

RESULTS

A 1.075-kg infant born at gestation age 27 weeks was admitted to our institution with respiratory distress and secretory diarrhea. During screening for retinopathy of prematurity, peripheral drusen-like subretinal deposits were identified. There were no similar findings in either parent or family history of ocular pathologies. Their distribution is atypical for that seen in other causes of early onset drusen such as autosomal dominant drusen or Sorsby fundus dystrophy. Retinopathy of prematurity was identified, which progressed to Type 1, and was treated with bilateral indirect peripheral retinal photocoagulation at gestational age of 40 weeks. Fluorescein angiography was performed and was consistent with peripheral drusen. Optical coherence tomography of the central macula and an awake electroretinogram at 6 months were normal. Serial examinations confirmed no progression in the drusen-like deposits or in retinopathy of prematurity, with clinically appropriate visual development observed during close follow-up.

CONCLUSION

We identify a unique ocular phenotype of retinal drusen-like deposits in an infant with a rare, sporadic GUCY2C mutation.