Pathogenesis and treatments of TGFBI corneal dystrophies

Evaluation of TGFBI corneal dystrophy and molecular diagnostic testing

To date, 70 different TGFBI mutations that cause epithelial-stromal corneal dystrophies have been described. At present one commercially available test examines for the five most common of these mutations: R124H, R124C, R124L, R555W, and R555Q. To expand the capability of identifying the causative mutation in the remaining cases, 57 mutations would need to be added. The aim of this study was to obtain a better understanding of the worldwide distribution and population differences of TGFBI mutations and to assess which mutations could be included or excluded from any potential assay. A total of 184 published papers in Human Gene Mutation Database (HGMD) and PubMed from 34 countries worldwide reporting over 1600 corneal dystrophy cases were reviewed. Global data from 600,000 samples using the commercially available test were analyzed. Case studies by University College of London (UCL), Moorfield’s Corneal Dystrophy Study data and 19 samples from patients with clinical abnormality or uncertainty for which the current test detected no mutation were used to predict an achievable detection rate. Data from the literature search showed no difference in the spectrum and frequency of each mutation in different populations or geographical locations. According to our analysis, an increase to the worldwide detection rate in all populations from 75 to 90% could be achieved by the addition of six mutations—H626R, A546D, H572R, G623D, R124S, and M502V—to the currently available test and that may be beneficial for LASIK pre-screening worldwide.

Analysis of TGFBI Gene Mutations in Three Chinese Families with Corneal Dystrophy

Objective

To identify the types of TGFBI (transforming growth factor, beta-induced) gene mutations in three Chinese families with Reis-Bücklers corneal dystrophy (RBCD), lattice corneal dystrophy type I (LCDI), or Avellino corneal dystrophy (ACD) and to investigate the relationship between the phenotypes and genotypes of corneal dystrophy.

Methods

Peripheral blood was collected from 24 patients and 76 phenotypically normal members in three Chinese families as well as from 100 healthy controls. Genomic DNA was extracted. All 17 exons of the TGFBI gene, and the exon-intron junctions were examined by polymerase chain reaction (PCR) and direct DNA sequencing to identify and analyse gene mutations. In addition, all members of the three families were subjected to detailed clinical examinations.

Results

The heterozygous c.371G > T (p.R124L) mutation was detected in exon 4 of the TGFBI gene in nine patients from the family with RBCD. In contrast, this mutation was not found in the phenotypically normal members of the family. The heterozygous c.370C > T (p.R124C) mutation was found in exon 4 of the TGFBI gene in 11 patients from the family with LCDI. This mutation was not found in the phenotypically normal members of the family. The heterozygous c.371G > A (p.R124H) mutation was detected in exon 4 of the TGFBI gene in four patients from the family with ACD. Again, this mutation was not found in the phenotypically normal members of the family. The TGFBI gene mutations cosegregated with the disease phenotypes in the three families and exhibited an autosomal dominant mode of inheritance. No TGFBI gene mutations were detected in the 100 healthy controls.

Conclusion

There is a high degree of correlation between the phenotypes and genotypes of TGFBI-linked corneal dystrophies. R124 represents a mutational hotspot in the TGFBI gene. Gene mutation analysis provides a reliable basis for the definitive diagnosis of corneal dystrophy.

Downregulation of IL-7 and IL-7R Reduces Membrane-Type Matrix Metalloproteinase 14 in Granular Corneal Dystrophy Type 2 Keratocyte

Purpose

Granular corneal dystrophy type 2 (GCD2) is caused by a point mutation (R124H) in the TGF-β-induced gene (TGFBI). However, the mechanisms underlying the accumulation of TGF-β-induced protein (TGFBIp) are poorly understood. Therefore, we evaluated the signaling cascade affecting the expression of TGFBIp using patient-derived cells.

Methods

Keratocyte primary cultures were prepared from corneas from the eye bank or from heterozygous or homozygous patients with GCD2 after penetrating or lamellar keratoplasty. GCD2 diagnoses were based on the results of a DNA analysis for the R124H TGFβI mutation. Keratocytes were treated with various cytokines and then analyzed using quantitative PCR (qPCR) array, qPCR, flow cytometry, ELISA, and Western blotting.

Results

TGFBI expression was counterregulated by IL-7 in corneal fibroblasts. IL-7 expression was significantly reduced in corneal fibroblasts from patients with GCD2. TGF-β and TGFBI expression were reduced on IL-7 treatment in corneal fibroblasts. Interestingly, the interplay between TGF-β and IL-7 was regulated by the RANKL/RANK signaling cascade. Also, IL-7 regulates the expression of a membrane-type matrix metalloproteinase (MT-MMP), which plays a crucial role in migration and neovascularization in the cornea.

Conclusions

These studies demonstrate that impaired IL-7 expression in patients with GCD2 affects disease pathogenesis via a failure to control TGF-β expression. The RANKL/RANK axis regulates TGF-β and TGFBI expression via IL-7-mediated MT-MMP regulation in corneal fibroblasts. These findings improve our understanding of the pathogenesis of GCD2.

Corneal cell therapy: with iPSCs, it is no more a far-sight

Human-induced pluripotent stem cells (hiPSCs) provide a personalized approach to study conditions and diseases including those of the eye that lack appropriate animal models to facilitate the development of novel therapeutics. Corneal disease is one of the most common causes of blindness. Hence, significant efforts are made to develop novel therapeutic approaches including stem cell-derived strategies to replace the diseased or damaged corneal tissues, thus restoring the vision. The use of adult limbal stem cells in the management of corneal conditions has been clinically successful. However, its limited availability and phenotypic plasticity necessitate the need for alternative stem cell sources to manage corneal conditions. Mesenchymal and embryonic stem cell-based approaches are being explored; nevertheless, their limited differentiation potential and ethical concerns have posed a significant hurdle in its clinical use. hiPSCs have emerged to fill these technical and ethical gaps to render clinical utility. In this review, we discuss and summarize protocols that have been devised so far to direct differentiation of human pluripotent stem cells (hPSCs) to different corneal cell phenotypes. With the summarization, our review intends to facilitate an understanding which would allow developing efficient and robust protocols to obtain specific corneal cell phenotype from hPSCs for corneal disease modeling and for the clinics to treat corneal diseases and injury.

Long-term Clinical Outcomes of Phototherapeutic Keratectomy in Corneas With Granular Corneal Dystrophy Type 2 Exacerbated After LASIK

PURPOSE

To investigate the long-term clinical outcomes and recurrence patterns of phototherapeutic keratectomy (PTK) in patients with granular corneal dystrophy type 2 (GCD2) exacerbated after LASIK.

METHODS

Fifty-one patients (76 eyes) with GCD2 exacerbated after LASIK who underwent PTK between January 2007 and February 2017 were included. Participants underwent ophthalmic examination, including slit-lamp microscopy, corrected distance visual acuity (CDVA), slit-lamp photography, and Fourier domain optical coherence tomography at preoperative and postoperative visits. PTK was performed using VISX S4 IR (VISX, Inc., Santa Clara, CA). Visual acuity, complications, interval, and contributing factors of recurrence were evaluated.

RESULTS

The follow-up period ranged from 1 to 108 months (mean: 35.22 months). The mean logMAR CDVA was 0.55 ± 0.43 (Snellen equivalent 20/80) preoperatively and 0.09 ± 0.43 (Snellen equivalent 20/25) at 3 months postoperatively. Forty-five (61.6%) eyes developed biomicroscopic recurrence at a mean of 18.6 months after PTK; 20 (27.4%) eyes developed significant recurrence at a mean of 31.3 months after PTK. The flap removal group demonstrated better CDVA at 3 years after surgery and lower recurrence and complication rates than the flap conservation group. Multivariate analysis revealed that flap removal remarkably reduced the risk of both any sign of and significant recurrence.

CONCLUSIONS

PTK improved corneal transparency and visual acuity in patients with GCD2 exacerbated after LASIK, although GCD2 eventually recurred. PTK with flap removal was superior to PTK with flap conservation in terms of visual acuity, recurrence, and complications. [J Refract Surg. 2018;34(2):132-139.].

Fascinating Fasciclins: A Surprisingly Widespread Family of Proteins that Mediate Interactions between the Cell Exterior and the Cell Surface

The Fasciclin 1 (FAS1) domain is an ancient structural motif in extracellular proteins present in all kingdoms of life and particularly abundant in plants. The FAS1 domain accommodates multiple interaction surfaces, enabling it to bind different ligands. The frequently observed tandem FAS1 arrangement might both positively and negatively regulate ligand binding. Additional protein domains and post-translational modifications are partially conserved between different evolutionary clades. Human FAS1 family members are associated with multiple aspects of health and disease. At the cellular level, mammalian FAS1 proteins are implicated in extracellular matrix structure, cell to extracellular matrix and cell to cell adhesion, paracrine signaling, intracellular trafficking and endocytosis. Mammalian FAS1 proteins bind to the integrin family of receptors and to protein and carbohydrate components of the extracellular matrix. FAS1 protein encoding plant genes exert effects on cellulosic and non-cellulosic cell wall structure and cellular signaling but to establish the modes of action for any plant FAS1 protein still requires biochemical experimentation. In fungi, eubacteria and archaea, the differential presence of FAS1 proteins in closely related organisms and isolated biochemical data suggest functions in pathogenicity and symbiosis. The inter-kingdom comparison of FAS1 proteins suggests that molecular mechanisms mediating interactions between cells and their environment may have evolved at the earliest known stages of evolution.

Lithium chloride (LiCl) induced autophagy and downregulated expression of transforming growth factor β-induced protein (TGFBI) in granular corneal dystrophy

This study evaluated whether lithium chloride (LiCl) prevents cytoplasmic accumulation of mutant-transforming growth factor β-induced protein (Mut-TGFBI) in granular corneal dystrophy (GCD) via activation of the autophagy pathway. Levels of TGFBI and microtubule-associated protein 1A/1B-light chain 3 (LC3) in 3 GCD patients and healthy controls were analyzed by immunohistochemistry (IHC) staining and Western blot. Primary corneal fibroblasts were isolated and transfected with wild type or mutant type TGFBI over-expressed vectors, and then treated with LiCl and/or autophagy inhibitor 3-methyladenine (3-MA). Then, levels of TGFBI, glycogen synthase kinase-3 (GSK-3) and LC3-I/-II were detected. Cell viability and transmission electron microscopy assay were also performed. Levels of TGFBI and LC3 were significantly increased in GCD patients. Over-expression of mutant type TGFBI inhibited cell viability and induced autophagy in corneal fibroblasts. LiCl downregulated the expression of TGFBI in mutant type TGFBI over-expressed cells in a dose- and time-dependent manner. LiCl enhanced autophagy in mutant type TGFBI over-expressed cells and recovered cell viability in those cells. However, the effects of LiCl were partly attenuated when autophagy was suppressed by 3-MA. To summarize, treatment with LiCl inhibited the expression of TGFBI and recovery the inhibitory of mutant type TGFBI in cell viability, at least part through enhancing of autophagy. These data strongly suggest that LiCl may be useful in the treatment of GCD.

Towards personalised allele-specific CRISPR gene editing to treat autosomal dominant disorders

CRISPR/Cas9 holds immense potential to treat a range of genetic disorders. Allele-specific gene disruption induced by non-homologous end-joining (NHEJ) DNA repair offers a potential treatment option for autosomal dominant disease. Here, we successfully delivered a plasmid encoding S. pyogenes Cas9 and sgRNA to the corneal epithelium by intrastromal injection and acheived long-term knockdown of a corneal epithelial reporter gene, demonstrating gene disruption via NHEJ in vivo. In addition, we used TGFBI corneal dystrophies as a model of autosomal dominant disease to assess the use of CRISPR/Cas9 in two allele-specific systems, comparing cleavage using a SNP-derived PAM to a guide specific approach. In vitro, cleavage via a SNP-derived PAM was found to confer stringent allele-specific cleavage, while a guide-specific approach lacked the ability to distinguish between the wild-type and mutant alleles. The failings of the guide-specific approach highlights the necessity for meticulous guide design and assessment, as various degrees of allele-specificity are achieved depending on the guide sequence employed. A major concern for the use of CRISPR/Cas9 is its tendency to cleave DNA non-specifically at “off-target” sites. Confirmation that S. pyogenes Cas9 lacks the specificity to discriminate between alleles differing by a single base-pair regardless of the position in the guide is demonstrated.

Structural and Functional Implications of Human Transforming Growth Factor β-Induced Protein, TGFBIp, in Corneal Dystrophies

A major cause of visual impairment, corneal dystrophies result from accumulation of protein deposits in the cornea. One of the proteins involved is transforming growth factor β-induced protein (TGFBIp), an extracellular matrix component that interacts with integrins but also produces corneal deposits when mutated. Human TGFBIp is a multi-domain 683-residue protein, which contains one CROPT domain and four FAS1 domains. Its structure spans ∼120 Å and reveals that vicinal domains FAS1-1/FAS1-2 and FAS1-3/FAS1-4 tightly interact in an equivalent manner. The FAS1 domains are sandwiches of two orthogonal four-stranded β sheets decorated with two three-helix insertions. The N-terminal FAS1 dimer forms a compact moiety with the structurally novel CROPT domain, which is a five-stranded all-β cysteine-knot solely found in TGFBIp and periostin. The overall TGFBIp architecture discloses regions for integrin binding and that most dystrophic mutations cluster at both molecule ends, within domains FAS1-1 and FAS1-4.

Melatonin reduces endoplasmic reticulum stress and corneal dystrophy-associated TGFBIp through activation of endoplasmic reticulum-associated protein degradation

Endoplasmic reticulum (ER) stress is emerging as a factor for the pathogenesis of granular corneal dystrophy type 2 (GCD2). This study was designed to investigate the molecular mechanisms underlying the protective effects of melatonin on ER stress in GCD2. Our results showed that GCD2 corneal fibroblasts were more susceptible to ER stress-induced death than were wild-type cells. Melatonin significantly inhibited GCD2 corneal cell death, caspase-3 activation, and poly (ADP-ribose) polymerase 1 cleavage caused by the ER stress inducer, tunicamycin. Under ER stress, melatonin significantly suppressed the induction of immunoglobulin heavy-chain-binding protein (BiP) and activation of inositol-requiring enzyme 1α (IRE1α), and their downstream target, alternative splicing of X-box binding protein 1(XBP1). Notably, the reduction in BiP and IRE1α by melatonin was suppressed by the ubiquitin-proteasome inhibitor, MG132, but not by the autophagy inhibitor, bafilomycin A1, indicating involvement of the ER-associated protein degradation (ERAD) system. Melatonin treatment reduced the levels of transforming growth factor-β-induced protein (TGFBIp) significantly, and this reduction was suppressed by MG132. We also found reduced mRNA expression of the ERAD system components HRD1 and SEL1L, and a reduced level of SEL1L protein in GCD2 cells. Interestingly, melatonin treatments enhanced SEL1L levels and suppressed the inhibition of SEL1L N-glycosylation caused by tunicamycin. In conclusion, this study provides new insights into the mechanisms by which melatonin confers its protective actions during ER stress. The results also indicate that melatonin might have potential as a therapeutic agent for ER stress-related diseases including GCD2.

TGFBI functions similar to periostin but is uniquely dispensable during cardiac injury

Extracellular matrix production and accumulation stabilize the heart under normal conditions as well as form a protective scar after myocardial infarction injury, although excessive extracellular matrix accumulation with long-standing heart disease is pathological. In the current study we investigate the role of the matricellular protein, transforming growth factor beta-induced (TGFBI), which is induced in various forms of heart disease. Additionally, we sought to understand whether TGFBI is functionally redundant to its closely related family member periostin, which is also induced in the diseased heart. Surgical models of myocardial infarction and cardiac pressure overload were used in mice with genetic loss of Postn and/or Tgfbi to examine the roles of these genes during the fibrotic response. Additionally, cardiac-specific TGFBI transgenic mice were generated and analyzed. We observed that deletion of Tgfbi did not alter cardiac disease after myocardial infarction in contrast to greater ventricular wall rupture in Postn gene-deleted mice. Moreover, Tgfbi and Postn double gene-deleted mice showed a similar post-myocardial infarction disease phenotype as Postn-deleted mice. Over-expression of TGFBI in the hearts of mice had a similar effect as previously shown in mice with periostin over-expression. Thus, TGFBI and periostin act similarly in the heart in affecting fibrosis and disease responsiveness, although TGFBI is not seemingly necessary in the heart after myocardial infarction injury and is fully compensated by the more prominently expressed effector periostin.

Vortex Pattern of Corneal Deposits in Granular Corneal Dystrophy Associated With the p.(Arg555Trp) Mutation in TGFBI

PURPOSE

To describe 2 unrelated families with multiple members demonstrating a less commonly recognized vortex pattern of corneal deposits confirmed to be granular corneal dystrophy type 1 (GCD1) after identification of the p.(Arg555Trp) mutation in the transforming growth factor β-induced gene (TGFBI).

METHODS

A slit-lamp examination was performed on individuals from 2 families, one of Mexican descent and a second of Italian descent. After DNA extraction from affected individuals and their unaffected relatives, TGFBI screening was performed.

RESULTS

Eight of 20 individuals in the Mexican family and 20 of 55 in the Italian family demonstrated corneal stromal opacities. Seven of the 8 affected individuals in the Mexican family and 4 of the 20 affected individuals in the Italian family demonstrated a phenotype characterized by a "sea fan" or vortex pattern of superficial stromal corneal deposits originating from the inferior aspect of the cornea. Screening of TGFBI in both families revealed a heterozygous missense mutation [p.(Arg555Trp)] in exon 12, confirming the diagnosis of GCD1.

CONCLUSIONS

Our findings demonstrate that GCD1 may present with a vortex pattern of anterior stromal deposits. Although this pattern of dystrophic deposits is not recognized by clinicians as a typical phenotype of GCD1, it is consistent with the production of the majority of the TGFBI protein by the corneal epithelium.

Genome-wide association analyses of sleep disturbance traits identify new loci and highlight shared genetics with neuropsychiatric and metabolic traits

Chronic sleep disturbances, associated with cardiometabolic diseases, psychiatric disorders and all-cause mortality, affect 25-30% of adults worldwide. Although environmental factors contribute substantially to self-reported habitual sleep duration and disruption, these traits are heritable and identification of the genes involved should improve understanding of sleep, mechanisms linking sleep to disease and development of new therapies. We report single- and multiple-trait genome-wide association analyses of self-reported sleep duration, insomnia symptoms and excessive daytime sleepiness in the UK Biobank (n = 112,586). We discover loci associated with insomnia symptoms (near MEIS1, TMEM132E, CYCL1 and TGFBI in females and WDR27 in males), excessive daytime sleepiness (near AR-OPHN1) and a composite sleep trait (near PATJ (INADL) and HCRTR2) and replicate a locus associated with sleep duration (at PAX8). We also observe genetic correlation between longer sleep duration and schizophrenia risk (rg = 0.29, P = 1.90 × 10-13) and between increased levels of excessive daytime sleepiness and increased measures for adiposity traits (body mass index (BMI): rg = 0.20, P = 3.12 × 10-9; waist circumference: rg = 0.20, P = 2.12 × 10-7).

TGF-β Signaling in Gastrointestinal Cancers: Progress in Basic and Clinical Research

Transforming growth factor (TGF)-β superfamily proteins have many important biological functions, including regulation of tissue differentiation, cell proliferation, and migration in both normal and cancer cells. Many studies have reported that TGF-β signaling is associated with disease progression and therapeutic resistance in several cancers. Similarly, TGF-β-induced protein (TGFBI)—a downstream component of the TGF-β signaling pathway—has been shown to promote and/or inhibit cancer. Here, we review the state of basic and clinical research on the roles of TGF-β and TGFBI in gastrointestinal cancers.

4-Phenylbutyric acid reduces mutant-TGFBIp levels and ER stress through activation of ERAD pathway in corneal fibroblasts of granular corneal dystrophy type 2

Granular corneal dystrophy type 2 (GCD2) is caused by a point mutation (R124H) in the transforming growth factor β-induced (TGFBI) gene. In GCD2 corneal fibroblasts, secretion of the accumulated mutant TGFBI-encoded protein (TGFBIp) is delayed via the endoplasmic reticulum (ER)/Golgi-dependent secretory pathway. However, ER stress as the pathogenic mechanism underlying GCD2 has not been fully characterized. The aim of this study was to confirm whether ER stress is linked to GCD2 pathogenesis and whether the chemical chaperone, 4-phenylbutyric acid (4-PBA), could be exploited as a therapy for GCD2. We found that the ER chaperone binding immunoglobulin protein (BiP) and the protein disulfide isomerase (PDI) were elevated in GCD2. Western bolt analysis also showed a significant increase in both the protein levels and the phosphorylation of the key ER stress kinases, inositol-requiring enzyme 1α (IRE1α) and double stranded RNA activated protein kinase (PKR)-like ER kinase, as well as in levels of their downstream targets, X box-binding protein 1 (XBP1) and activating transcription factor 4, respectively, in GCD2 corneal fibroblasts. GCD2 cells were found to be more susceptible to ER stress-induced cell death than were wild-type corneal fibroblasts. Treatment with 4-PBA considerably reduced the levels of BiP, IRE1α, and XBP1 in GCD2 cells; notably, 4-PBA treatment significantly reduced the levels of TGFBIp without change in TGFBI mRNA levels. In addition, TGFBIp levels were significantly reduced under ER stress and this reduction was considerably suppressed by the ubiquitin proteasome inhibitor MG132, indicating TGFBIp degradation via the ER-associated degradation pathway. Treatment with 4-PBA not only protected against the GCD2 cell death induced by ER stress but also significantly suppressed the MG132-mediated increase in TGFBIp levels under ER stress. Together, these results suggest that ER stress might comprise an important factor in GCD2 pathophysiology and that the effects of 4-PBA treatment might have important implications for the development of GCD2 therapeutics.