Loss of foxc1 in zebrafish reduces optic nerve size and cell number in the retinal ganglion cell layer

Exploring the Genetic Landscape of Childhood Glaucoma

Childhood glaucoma, a significant cause of global blindness, represents a heterogeneous group of disorders categorized into primary or secondary forms. Primary childhood glaucoma stands as the most prevalent subtype, comprising primary congenital glaucoma (PCG) and juvenile open-angle glaucoma (JOAG). Presently, multiple genes are implicated in inherited forms of primary childhood glaucoma. This comprehensive review delves into genetic investigations into primary childhood glaucoma, with a focus on identifying causative genes, understanding their inheritance patterns, exploring essential biological pathways in disease pathogenesis, and utilizing animal models to study these mechanisms. Specifically, attention is directed towards genes such as CYP1B1 (cytochrome P450 family 1 subfamily B member 1), LTBP2 (latent transforming growth factor beta binding protein 2), TEK (TEK receptor tyrosine kinase), ANGPT1 (angiopoietin 1), and FOXC1 (forkhead box C1), all associated with PCG; and MYOC (myocilin), associated with JOAG. Through exploring these genetic factors, this review aims to deepen our understanding of the intricate pathogenesis of primary childhood glaucoma, thereby facilitating the development of enhanced diagnostic and therapeutic strategies.

Prolonged Supplementation of Ozonated Sunflower Oil Bestows an Antiaging Effect, Improves Blood Lipid Profile and Spinal Deformities, and Protects Vital Organs of Zebrafish (Danio rerio) against Age-Related Degeneration: Two-Years Consumption Study

Ozonated sunflower oil (OSO) is renowned for its diverse therapeutic benefits. Nonetheless, the consequences of extended dietary intake of OSO have yet to be thoroughly investigated. Herein, the effect of 2-year dietary supplementation of OSO was examined on the survivability, obesity, skeletal deformities, swimming behavior, and liver, kidney, ovary, and testis function of zebrafish. Results showed that the zebrafish feed supplemented with 20% (wt/wt) OSO for 2 years emerged with higher survivability and body weight management compared to sunflower oil (SO) and normal diet (ND)-supplemented zebrafish. Radio imaging (X-ray)-based analysis revealed 2.6° and 15.2° lower spinal curvature in the OSO-supplemented groups than in the SO and ND-supplemented groups; consistently, OSO-supplemented zebrafish showed better swimming behavior. The histology analysis of the liver revealed the least fatty liver change and interleukin (IL)-6 generation in the OSO-supplemented group. Additionally, a significantly lower level of reactive oxygen species (ROS), apoptotic, and senescent cells were observed in the liver of the OSO-supplemented zebrafish. Also, no adverse effect on the kidney, testis, and ovary morphology was detected during 2 years of OSO consumption. Moreover, lower senescence with diminished ROS and apoptosis was noticed in the kidney and ovary in response to OSO consumption. The OSO supplementation was found to be effective in countering age-associated dyslipidemia by alleviating total cholesterol (TC), triglycerides (TG), low-density lipoproteins (LDL-C) and elevating high-density lipoproteins (HDL-C)/TC levels. Conclusively, prolonged OSO consumption showed no adverse effect on the morphology and functionality of vital organs; in fact, OSO supplementation displayed a protective effect against age-associated detrimental effects on spinal deformities, vital organ functionality, cell senescence, and the survivability of zebrafish.

Long-Term Supplementation of Ozonated Sunflower Oil Improves Dyslipidemia and Hepatic Inflammation in Hyperlipidemic Zebrafish: Suppression of Oxidative Stress and Inflammation against Carboxymethyllysine Toxicity

Ozonated sunflower oil (OSO) is a well-known functional oil with antioxidant, antimicrobial, anti-allergic, and skin-moisturizing properties. However, studies on the effects of OSO on high-cholesterol diet (HCD)-induced metabolic disorders have been scarce. In the current study, we aimed to determine the anti-inflammatory effects of OSO on lipid metabolism in adult hypercholesterolemic zebrafish and its embryos. Microinjection of OSO (final 2%, 10 nL) into zebrafish embryos under the presence of carboxymethyllysine (CML, 500 ng) protected acute embryo death up to 61% survival, while sunflower oil (final 2%) showed much less protection at around 42% survival. The microinjection of OSO was more effective than SO to inhibit reactive oxygen species (ROS) production and apoptosis in the CML induced embryo toxicity. Intraperitoneal injection of OSO under the presence of CML protected acute death from CML-induced neurotoxicity with improved hepatic inflammation, less detection of ROS and interleukin (IL)-6, and lowering blood total cholesterol (TC) and triglyceride (TG), while the SO-injected group did not protect the CML-toxicity. Long-term supplementation of OSO (final 20%, wt/wt) with HCD for 6 months resulted in higher survivability than the HCD alone group or HCD + SO group (final 20%, wt/wt) with significant lowering of plasma TC and TG levels. The HCD + OSO group showed the least hepatic inflammation, fatty liver change, ROS, and IL-6 production. In conclusion, short-term treatment of OSO by injection exhibited potent anti-inflammatory activity against acute neurotoxicity of CML in zebrafish and their embryo. Long-term supplementation of OSO in the diet also revealed the highest survivability and blood lipid-lowering effect through potent antioxidant and anti-inflammatory activity.

Mutation of foxl1 Results in Reduced Cartilage Markers in a Zebrafish Model of Otosclerosis

Bone diseases such as otosclerosis (conductive hearing loss) and osteoporosis (low bone mineral density) can result from the abnormal expression of genes that regulate cartilage and bone development. The forkhead box transcription factor FOXL1 has been identified as the causative gene in a family with autosomal dominant otosclerosis and has been reported as a candidate gene in GWAS meta-analyses for osteoporosis. This potentially indicates a novel role for foxl1 in chondrogenesis, osteogenesis, and bone remodelling. We created a foxl1 mutant zebrafish strain as a model for otosclerosis and osteoporosis and examined jaw bones that are homologous to the mammalian middle ear bones, and mineralization of the axial skeleton. We demonstrate that foxl1 regulates the expression of collagen genes such as collagen type 1 alpha 1a and collagen type 11 alpha 2, and results in a delay in jawbone mineralization, while the axial skeleton remains unchanged. foxl1 may also act with other forkhead genes such as foxc1a, as loss of foxl1 in a foxc1a mutant background increases the severity of jaw calcification phenotypes when compared to each mutant alone. Our zebrafish model demonstrates atypical cartilage formation and mineralization in the zebrafish craniofacial skeleton in foxl1 mutants and demonstrates that aberrant collagen expression may underlie the development of otosclerosis.

Animal Model Contributions to Primary Congenital Glaucoma

Primary congenital glaucoma (PCG) is an ocular disease characterized by congenital anterior segmental maldevelopment with progressive optic nerve degeneration. Certain genes, such as cytochrome P450 family 1 subfamily B member 1 and latent TGF-β-binding protein 2, are involved in the pathogenesis of PCG, but the exact pathogenic mechanism has not yet been fully elucidated. There is an urgent need to determine the etiology and pathophysiology of PCG and develop new therapeutic methods to stop disease progression. Animal models can simulate PCG and are essential to study the pathogenesis and treatment of PCG. Various animal species have been used in the study of PCG, including rabbits, rats, mice, cats, zebrafish, and quails. These models are formed spontaneously or by combining with genetic engineering technology. The focus of the present study is to review the characteristics and potential applications of animal models in PCG and provide new approaches to understand the mechanism and develop new treatment strategies for patients with PCG.

Mechanistic Insights into Axenfeld-Rieger Syndrome from Zebrafish foxc1 and pitx2 Mutants

Axenfeld-Rieger syndrome (ARS) encompasses a group of developmental disorders that affect the anterior segment of the eye, as well as systemic developmental defects in some patients. Malformation of the ocular anterior segment often leads to secondary glaucoma, while some patients also present with cardiovascular malformations, craniofacial and dental abnormalities and additional periumbilical skin. Genes that encode two transcription factors, FOXC1 and PITX2, account for almost half of known cases, while the genetic lesions in the remaining cases remain unresolved. Given the genetic similarity between zebrafish and humans, as well as robust antisense inhibition and gene editing technologies available for use in these animals, loss of function zebrafish models for ARS have been created and shed light on the mechanism(s) whereby mutations in these two transcription factors cause such a wide array of developmental phenotypes. This review summarizes the published phenotypes in zebrafish foxc1 and pitx2 loss of function models and discusses possible mechanisms that may be used to target pharmaceutical development and therapeutic interventions.

Zebrafish Model in Ophthalmology to Study Disease Mechanism and Drug Discovery

Visual impairment and blindness are common and seriously affect people’s work and quality of life in the world. Therefore, the effective therapies for eye diseases are of high priority. Zebrafish (Danio rerio) is an alternative vertebrate model as a useful tool for the mechanism elucidation and drug discovery of various eye disorders, such as cataracts, glaucoma, diabetic retinopathy, age-related macular degeneration, photoreceptor degeneration, etc. The genetic and embryonic accessibility of zebrafish in combination with a behavioral assessment of visual function has made it a very popular model in ophthalmology. Zebrafish has also been widely used in ocular drug discovery, such as the screening of new anti-angiogenic compounds or neuroprotective drugs, and the oculotoxicity test. In this review, we summarized the applications of zebrafish as the models of eye disorders to study disease mechanism and investigate novel drug treatments.

The Axenfeld-Rieger Syndrome Gene FOXC1 Contributes to Left-Right Patterning

Precise spatiotemporal expression of the Nodal-Lefty-Pitx2 cascade in the lateral plate mesoderm establishes the left–right axis, which provides vital cues for correct organ formation and function. Mutations of one cascade constituent PITX2 and, separately, the Forkhead transcription factor FOXC1 independently cause a multi-system disorder known as Axenfeld–Rieger syndrome (ARS). Since cardiac involvement is an established ARS phenotype and because disrupted left–right patterning can cause congenital heart defects, we investigated in zebrafish whether foxc1 contributes to organ laterality or situs. We demonstrate that CRISPR/Cas9-generated foxc1a and foxc1b mutants exhibit abnormal cardiac looping and that the prevalence of cardiac situs defects is increased in foxc1a^−/−; foxc1b^−/− homozygotes. Similarly, double homozygotes exhibit isomerism of the liver and pancreas, which are key features of abnormal gut situs. Placement of the asymmetric visceral organs relative to the midline was also perturbed by mRNA overexpression of foxc1a and foxc1b. In addition, an analysis of the left–right patterning components, identified in the lateral plate mesoderm of foxc1 mutants, reduced or abolished the expression of the NODAL antagonist lefty2. Together, these data reveal a novel contribution from foxc1 to left–right patterning, demonstrating that this role is sensitive to foxc1 gene dosage, and provide a plausible mechanism for the incidence of congenital heart defects in Axenfeld–Rieger syndrome patients.

Insights into the regulatory molecules involved in glaucoma pathogenesis

Glaucoma is an important cause of irreversible blindness, characterized by optic nerve anomalies. Increased intraocular pressure (IOP) and aging are major risk factors. Retinal ganglion cells and trabecular meshwork cells are certainly involved in the etiology of glaucoma. Glaucoma is usually a complex disease, and various genes and functions may contribute to its etiology. Among these may be genes that encode regulatory molecules. In this review, regulatory molecules including 18 transcription factors (TFs), 195 microRNAs (miRNAs), 106 long noncoding RNAs (lncRNAs), and two circular RNAs (circRNAs) that are reasonable candidates for having roles in glaucoma pathogenesis are described. The targets of the regulators are reported. Glaucoma-related features including apoptosis, stress responses, immune functions, ECM properties, IOP, and eye development are affected by the targeted genes. The targeted genes that are frequently targeted by multiple regulators most often affect apoptosis and the related features of cell death and cell survival. BCL2, CDKN1A, and TP53 are among the frequent targets of three types of glaucoma-relevant regulators, TFs, miRNAs, and lncRNAs. TP53 was itself identified as a glaucoma-relevant TF. Several of the glaucoma-relevant TFs are themselves among frequent targets of regulatory molecules, which is consistent with existence of a complex network involved in glaucoma pathogenesis.

FOXC1 variant in a family with anterior segment dysgenesis and normal-tension glaucoma

Our study describes the glaucoma phenotype in a family with Axenfeld-Rieger syndrome (ARS) and a FOXC1 variant. Included were 20 subjects from a large three generation family of Jewish Indian ancestry. Subjects underwent a comprehensive ophthalmic examination including automated perimetry and optical coherence tomography. Eight subjects were available for molecular analysis which included whole genome sequencing on selected patients and Sanger sequencing for variant screening. Eleven patients demonstrated a wide spectrum of Axenfeld-Rieger anomaly signs and symptoms. These ranged from subtle angle abnormalities to remarkable anterior segment abnormalities such as corectopia, iris adhesions and strands. Among them, six had glaucoma and two were glaucoma suspects. Of the six subjects with glaucoma three had high-tension glaucoma and two had normal-tension glaucoma. Molecular analysis revealed a previously described pathogenic variant in the FOXC1 gene (c.378C > G p.I126M; rs104893958), in six affected patients which was not identified in two healthy siblings. Molecular analysis also revealed a PITX2 missense variant (c.28T > A p.L10M; rs755864040) which did not segregate with clinical findings and was considered likely benign. In conclusion, patients with ARS due to FOXC1 variants may present with glaucomatous optic nerve damage without apparent elevation in IOP. Normal-tension glaucoma is less commonly reported in individuals with ARS and a comprehensive glaucoma assessment may be warranted in these individuals even with normal IOP. These findings raise the possibility that glaucomatous damage associated with FOXC1 is not only due to high IOP.

Embryonic ethanol exposure alters expression of sox2 and other early transcripts in zebrafish, producing gastrulation defects

Ethanol exposure during prenatal development causes fetal alcohol spectrum disorder (FASD), the most frequent preventable birth defect and neurodevelopmental disability syndrome. The molecular targets of ethanol toxicity during development are poorly understood. Developmental stages surrounding gastrulation are very sensitive to ethanol exposure. To understand the effects of ethanol on early transcripts during embryogenesis, we treated zebrafish embryos with ethanol during pre-gastrulation period and examined the transcripts by Affymetrix GeneChip microarray before gastrulation. We identified 521 significantly dysregulated genes, including 61 transcription factors in ethanol-exposed embryos. Sox2, the key regulator of pluripotency and early development was significantly reduced. Functional annotation analysis showed enrichment in transcription regulation, embryonic axes patterning, and signaling pathways, including Wnt, Notch and retinoic acid. We identified all potential genomic targets of 25 dysregulated transcription factors and compared their interactions with the ethanol-dysregulated genes. This analysis predicted that Sox2 targeted a large number of ethanol-dysregulated genes. A gene regulatory network analysis showed that many of the dysregulated genes are targeted by multiple transcription factors. Injection of sox2 mRNA partially rescued ethanol-induced gene expression, epiboly and gastrulation defects. Additional studies of this ethanol dysregulated network may identify therapeutic targets that coordinately regulate early development.

foxc1 is required for embryonic head vascular smooth muscle differentiation in zebrafish

Vascular smooth muscle of the head derives from neural crest, but developmental mechanisms and early transcriptional drivers of the vSMC lineage are not well characterized. We find that in early development, the transcription factor foxc1b is expressed in mesenchymal cells that associate with the vascular endothelium. Using timelapse imaging, we observe that foxc1b expressing mesenchymal cells differentiate into acta2 expressing vascular mural cells. We show that in zebrafish, while foxc1b is co-expressed in acta2 positive smooth muscle cells that associate with large diameter vessels, it is not co-expressed in capillaries where pdgfrβ positive pericytes are located. In addition to being an early marker of the lineage, foxc1 is essential for vSMC differentiation; we find that foxc1 loss of function mutants have defective vSMC differentiation and that early genetic ablation of foxc1b or acta2 expressing populations blocks vSMC differentiation. Furthermore, foxc1 is expressed upstream of acta2 and is required for acta2 expression in vSMCs. Using RNA-Seq we determine an enriched intersectional gene expression profile using dual expression of foxc1b and acta2 to identify novel vSMC markers. Taken together, our data suggests that foxc1 is a marker of vSMCs and plays a critical functional role in promoting their differentiation.