Different gene knockout/transgenic mouse models manifesting persistent fetal vasculature: Are integrins to blame for this pathological condition?

Intraoperative OCT Angiography in Pediatric Patients with Persistent Fetal Vasculature

PURPOSE

To describe abnormalities of the optic nerve microvasculature in patients with persistent fetal vasculature (PFV) and their fellow eyes using OCT angiography (OCTA).

DESIGN

Cross-sectional study.

SUBJECTS

Fifty eyes of 25 patients with PFV who underwent prospective imaging using supine OCTA during examination under anesthesia at Bascom Palmer Eye Institute from March 1, 2019, to December 31, 2022.

METHODS

OCT angiography images of the optic nerve of the included patients were analyzed with a primary focus on blood flow. Demographic, clinical, and treatment factors were compared with morphologic changes in the optic disc microvasculature.

MAIN OUTCOME MEASURES

Prevalence of optic nerve microvascular abnormalities on OCTA in the affected and fellow eyes of patients with PFV.

RESULTS

A total of 50 eyes from 25 patients were reviewed, and 28% (7/25) met image quality criteria for OCTA analysis. Optic nerve OCTA showed a persistent hyaloid artery (PHA) in all (7/7) PFV eyes analyzed. Of these, flow on OCTA was detectable in 57% (4/7). A Bergmeister papilla was evident in 100% (25/25) fellow eyes, of which flow was detected in 68% (17/25). Fluorescein angiography (FA) demonstrated blood flow within the stalk in 40% (10/25) of PFV eyes and within the Bergmeister papilla in 25% (6/25) of fellow eyes. Similar findings of abnormal blood flow and presence of fibrovascular stalk were seen in both treatment-naïve and treated groups.

CONCLUSIONS

OCT angiography allows for high-resolution visualization of subtle vascular abnormalities that are not readily apparent using RetCam FA and may serve as a useful noninvasive test to confirm the patency of the PHA and Bergmeister papilla in children. The results of the present study suggest that PFV may be a bilateral and asymmetric process.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Single-Cell Characterization of the Frizzled 5 (Fz5) Mutant Mouse and Human Persistent Fetal Vasculature (PFV)

Purpose

Persistent fetal vasculature (PFV) is a pathological condition accounting for 4.8% of children's blindness in the United States. However, the PFV cell composition and pathogenetic mechanisms are poorly understood. This study aims to characterize PFV cell composition and associated molecular features and attempts to lay a foundation for further understanding the disease.

Methods

Immunohistochemistry was conducted to characterize cell types at the tissue level. Single-cell RNA sequencing (sc-RNAseq) was performed on the vitreous cells derived from normal and Fz5 mutant mice at two early postnatal ages and human PFV samples. Bioinformatic tools were used to cluster cells and analyze their molecular features and functions.

Results

The findings of this study are as follows: (1) a total of 10 defined and one undefined cell types were characterized in both the hyaloid vessel system and PFV by sc-RNAseq and immunohistochemistry; (2) neural crest-derived melanocytes, astrocytes, and fibroblasts were specifically retained in the mutant PFV; (3) Fz5 mutants were found to possess more vitreous cells at early postnatal age 3 but returned to similar levels as the wild type at postnatal age 6; (4) altered phagocytic and proliferation environments and cell-cell interactions were detected in the mutant vitreous; (5) the human PFV samples shared fibroblast, endothelial and macrophage cell types with the mouse, but having distinct immune cells including T cells, NK cells and Neutrophils; and last, (6) some neural crest features were also shared between certain mouse and human vitreous cell types.

Conclusions

We characterized PFV cell composition and associated molecular features in the Fz5 mutant mice and two human PFV samples. The excessively migrated vitreous cells, intrinsic molecular properties of these cells, phagocytic environment, and cell-cell interactions may together contribute to PFV pathogenesis. Human PFV shares certain cell types and molecular features with the mouse.

Peripheral Vascular Abnormalities Detected by Fluorescein Angiography in Contralateral Eyes of Patients With Persistent Fetal Vasculature

BACKGROUND AND OBJECTIVE

To describe peripheral retinal vascular abnormalities in the contralateral eyes of patients with unilateral persistent fetal vasculature (PFV).

PATIENTS AND METHODS

Retrospective medical record review of fluorescein angiography (FA) findings of patients with unilateral PFV. Width of the temporal peripheral avascular retina in contralateral eyes was measured in disc diameters (DD). Vascular abnormalities were described.

RESULTS

In 45 included patients, mean width of temporal peripheral avascular areas in contralateral eyes was 1.87 ± 0.71 DD. Forty-three patients (95.6%) had temporal peripheral avascular areas of 1 DD or greater in contralateral eyes, with 16 having temporal peripheral avascular areas of 2 DD or greater. Vessel shunts, vascular tortuosity and dilatation, circumferential vessels, and abnormal capillary beds in the peripheral retina were observed in 23 (51.1%) contralateral eyes of patients with unilateral PFV.

CONCLUSION

PFV patients should undergo careful evaluations of both eyes, preferably with FA, to identify vascular changes that are not visible clinically. [Ophthalmic Surg Lasers Imaging Retina. 2020;51:506-511.].

Widefield Fluorescein Angiography in the Fellow Eyes of Patients with Presumed Unilateral Persistent Fetal Vasculature

PURPOSE

To examine the retinal vascular findings on widefield fluorescein angiography (FA) in the fellow eyes of patients with unilateral persistent fetal vasculature (PFV).

DESIGN

Retrospective case series.

PARTICIPANTS

Consecutive patients with unilateral PFV evaluated by a single physician at an academic medical center from February 1, 2011, to November 30, 2018.

METHODS

Clinical and demographic information, including age, gender, race, ethnicity, affected eye, subtype, stalk origin, complications on presentation, length of follow-up, and examination findings, was reviewed using the electronic medical record. Fluorescein angiograms of the affected and fellow eyes were reviewed by 2 authors for characteristic retinal vascular abnormalities. Agreement between the authors' scores was analyzed using Cohen's Kappa.

MAIN OUTCOME MEASURES

Fluorescein angiography abnormalities, including peripheral vessel avascularity, aberrant circumferential vessels, terminal supernumerary branching, regional capillary dropout, terminal bulbing, abnormal choroidal flush, abnormal vessel straightening, and peripheral vessel leakage or dilation.

RESULTS

Inclusion criteria were met by 41 patients. The average age at initial visit was 10.0 months. The average length of follow-up was 36.4 months. Abnormalities on FA were seen in 31 (75.6%) fellow eyes: peripheral vessel avascularity in 27.5 (67.1%), aberrant circumferential vessels in 20 (48.8%), terminal supernumerary branching in 17 (41.5%), regional capillary dropout in 9 (22.0%), terminal bulbing in 6 (14.6%), abnormal choroidal flush in 3.5 (8.5%), and abnormal vessel straightening and peripheral vessel leakage in 2.5 (6.1%). Statistical analysis disclosed an overall observed agreement of 93.4% among the raters (κ = 0.84, P < 0.0001).

CONCLUSIONS

Retinal vascular abnormalities seen in patients with unilateral PFV were present in the majority of fellow eyes. This suggests that unilateral PFV may in fact be a bilateral, asymmetric process, but the clinical significance of these subtle findings is not known.

Modulating EGFR-MTORC1-autophagy as a potential therapy for persistent fetal vasculature (PFV) disease

Persistent fetal vasculature (PFV) is a human disease that results from failure of the fetal vasculature to regress normally. The regulatory mechanisms responsible for fetal vascular regression remain obscure, as does the underlying cause of regression failure. However, there are a few animal models that mimic the clinical manifestations of human PFV, which can be used to study different aspects of the disease. One such model is the Nuc1 rat model that arose from a spontaneous mutation in the Cryba1 (crystallin, beta 1) gene and exhibits complete failure of the hyaloid vasculature to regress. Our studies with the Nuc1 rat indicate that macroautophagy/autophagy, a process in eukaryotic cells for degrading dysfunctional components to ensure cellular homeostasis, is severely impaired in Nuc1 ocular astrocytes. Further, we show that CRYBA1 interacts with EGFR (epidermal growth factor receptor) and that loss of this interaction in Nuc1 astrocytes increases EGFR levels. Moreover, our data also show a reduction in EGFR degradation in Nuc1 astrocytes compared to control cells that leads to over-activation of the mechanistic target of rapamycin kinase complex 1 (MTORC1) pathway. The impaired EGFR-MTORC1-autophagy signaling in Nuc1 astrocytes triggers abnormal proliferation and migration. The abnormally migrating astrocytes ensheath the hyaloid artery, contributing to the pathogenesis of PFV in Nuc1, by adversely affecting the vascular remodeling processes essential to regression of the fetal vasculature. Herein, we demonstrate in vivo that gefitinib (EGFR inhibitor) can rescue the PFV phenotype in Nuc1 and may serve as a novel therapy for PFV disease by modulating the EGFR-MTORC1-autophagy pathway.

ABBREVIATIONS

ACTB: actin, beta; CCND3: cyclin 3; CDK6: cyclin-dependent kinase 6; CHQ: chloroquine; COL4A1: collagen, type IV, alpha 1; CRYBA1: crystallin, beta A1; DAPI: 4'6-diamino-2-phenylindole; EGFR: epidermal growth factor receptor; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GFAP: glial fibrillary growth factor; KDR: kinase insert domain protein receptor; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MKI67: antigen identified by monoclonal antibody Ki 67; MTORC1: mechanistic target of rapamycin kinase complex 1; PARP: poly (ADP-ribose) polymerase family; PCNA: proliferating cell nuclear antigen; PFV: persistent fetal vasculature; PHPV: persistent hyperplastic primary vitreous; RPE: retinal pigmented epithelium; RPS6: ribosomal protein S6; RPS6KB1: ribosomal protein S6 kinase, polypeptide 1; SQSTM1/p62: sequestome 1; TUBB: tubulin, beta; VCL: vinculin; VEGFA: vascular endothelial growth factor A; WT: wild type.

An immune response to the avascular lens following wounding of the cornea involves ciliary zonule fibrils

The lens and central cornea are avascular. It was assumed that the adult lens had no source of immune cells and that the basement membrane capsule surrounding the lens was a barrier to immune cell migration. Yet, microfibril‐associated protein‐1 (MAGP1)‐rich ciliary zonules that originate from the vasculature‐rich ciliary body and extend along the surface of the lens capsule, form a potential conduit for immune cells to the lens. In response to cornea debridement wounding, we find increased expression of MAGP1 throughout the central corneal stroma. The immune cells that populate this typically avascular region after wounding closely associate with this MAGP1‐rich matrix. These results suggest that MAGP1‐rich microfibrils support immune cell migration post‐injury. Using this cornea wound model, we investigated whether there is an immune response to the lens following cornea injury involving the lens‐associated MAGP1‐rich ciliary zonules. Our results provide the first evidence that following corneal wounding immune cells are activated to travel along zonule fibers that extend anteriorly along the equatorial surface of the lens, from where they migrate across the anterior lens capsule. These results demonstrate that lens‐associated ciliary zonules are directly involved in the lens immune response and suggest the ciliary body as a source of immune cells to the avascular lens.

Vitreous and Vision Degrading Myodesopsia

Macromolecules comprise only 2% of vitreous, yet are responsible for its gel state, transparency, and physiologic function(s) within the eye. Myopia and aging alter collagen and hyaluronan association causing concurrent gel liquefaction and fibrous degeneration. The resulting vitreous opacities and collapse of the vitreous body during posterior vitreous detachment are the most common causes for the visual phenomenon of vitreous floaters. Previously considered innocuous, the vitreous opacities that cause floaters sometimes impact vision by profoundly degrading contrast sensitivity function and impairing quality-of-life. While many people adapt to vitreous floaters, clinically significant cases can be diagnosed with Vision Degrading Myodesopsia based upon echographic assessment of vitreous structure and by measuring contrast sensitivity function. Perhaps due to the ubiquity of floaters, the medical profession has to date largely ignored the plight of those with Vision Degrading Myodesopsia. Improved diagnostics will enable better disease staging and more accurate identification of severe cases that merit therapy. YAG laser treatments may occasionally be slightly effective, but vitrectomy is currently the definitive cure. Future developments will usher in more informative diagnostic approaches as well as safer and more effective therapeutic strategies. Improved laser treatments, new pharmacotherapies, and possibly non-invasive optical corrections are exciting new approaches to pursue. Ultimately, enhanced understanding of the underlying pathogenesis of Vision Degrading Myodesopsia should result in prevention, the ultimate goal of modern Medicine.

Bush-like integrin filament networks associated with hyaloid vasculature in murine neonate eyes

The vitreous of perinatal mice temporarily develops a unique vascular system, called the vasa hyaloidea propria (VHP). Observations showed the vessels possessed an extracellular matrix including the basement membrane in their entire length. Immunostaining of whole mount preparations of VHP with integrin β₁ antibody displayed a bush-like network consisting of long and straight fibers which were associated with the VHP but extended apart from the blood vessels. Electron microscopically, each fiber was composed of a bundle of thin filaments different from collagen fibrils. Macrophages associated with the VHP appeared to be arrested by the integrin bushes. The integrin bushes fragmented and disappeared by postnatal day 10, just before the regression of the VHP. Macrophages were involved in the digestion and clearance of integrin bushes. The vitreous integrin bushes appear to provide a scaffold for architectural maintenance of the hyaloid vessels and macrophages.

In vivo detecting mouse persistent hyperplastic primary vitreous by Spectralis Optical Coherence Tomography

To identify imaging characteristics of mouse persistent hyperplastic primary vitreous (PHPV) by Spectralis Optical Coherence Tomography (OCT), as well as to assess and compare the sensitivity and precision of OCT with color photography (CP) and Fundus Fluorescein Angiography (FFA) imaging in detecting mouse PHPV. Notch4^-/- C57BL/6J mice (224 eyes) aged from 3 months to 7 months were examined in this study. CP, FFA and OCT imaging were utilized to examine vitreous cavity and retina of mouse eyes. Horizontal and radial OCT scan volume was centered on the optic nerve head. Hematoxylin and eosin (H&E) staining was performed to validate PHPV. For color photography and FFA imaging, retrolental irregular fibrovascular membrane-like tissues were found in 33 eyes with/without blood vessels in vitreous cavity. Among them, 31 eyes were visualized with lateral and oblique linear hyperreflective opacities in vitreous cavity using Spectralis OCT. Position of PHPV in posterior segment of eyes was also measured via OCT. Mouse PHPV was validated by H&E staining. Typical hyperreflective opacities in vitreous cavity were detected in PHPV mouse using Spectralis OCT. Spectralis OCT imaging can effectively detect mouse PHPV as color photography and FFA.

Histochemical characteristics of regressing vessels in the hyaloid vascular system of neonatal mice: Novel implication for vascular atrophy

The hyaloid vasculature constitutes a transitory system nourishing the internal structures of the developing eye, but the mechanism of vascular regression and its cell biological characteristics are not fully understood. The present study aimed to reveal the specificity of the hyaloid vessels by a systematic immunohistochemical approach for marker substances of myeloid cells and the extracellular matrix (ECM) in neonatal mice. Macrophages immunoreactive for F4/80, cathepsin D, and LYVE-1 gathered around the vasa hyaloidea propria (VHP), while small round cells in vascular lumen of VHP were selectively immunoreactive for galectin-3; their segmented nuclei and immunoreactivities for Ly-6G, CD11b, and myeloperoxidase indicated their neutrophilic origin. VHP possessed thick ECM and a dense pericyte envelope as demonstrated by immunostaining for laminin, type IV collagen, integrin β1, and NG2. The galectin-3⁺ cells loosely aggregated with numerous erythrocytes in the lumen of hyaloid vessels in a manner reminiscent of vascular congestion. Galectin-3 is known to polymerize and form a complex with ECM and NG2 as well as recruit leukocytes on the endothelium. Observation of galectin-3 KO mice implicated the involvement of galectin-3 in the regression of hyaloid vasculature. Since macrophages may play central roles including blocking of the blood flow and the induction of apoptosis in the regression, galectin-3⁺ neutrophils may play a supportive role in the macrophage-mediated involution of the hyaloid vascular system.

Myosin-X knockout is semi-lethal and demonstrates that myosin-X functions in neural tube closure, pigmentation, hyaloid vasculature regression, and filopodia formation

Myosin-X (Myo10) is an unconventional myosin best known for its striking localization to the tips of filopodia. Despite the broad expression of Myo10 in vertebrate tissues, its functions at the organismal level remain largely unknown. We report here the generation of KO-first (Myo10^tm1a/tm1a), floxed (Myo10^tm1c/tm1c), and KO mice (Myo10^tm1d/tm1d). Complete knockout of Myo10 is semi-lethal, with over half of homozygous KO embryos exhibiting exencephaly, a severe defect in neural tube closure. All Myo10 KO mice that survive birth exhibit a white belly spot, all have persistent fetal vasculature in the eye, and ~50% have webbed digits. Myo10 KO mice that survive birth can breed and produce litters of KO embryos, demonstrating that Myo10 is not absolutely essential for mitosis, meiosis, adult survival, or fertility. KO-first mice and an independent spontaneous deletion (Myo10^m1J/m1J) exhibit the same core phenotypes. During retinal angiogenesis, KO mice exhibit a ~50% decrease in endothelial filopodia, demonstrating that Myo10 is required to form normal numbers of filopodia in vivo. The Myo10 mice generated here demonstrate that Myo10 has important functions in mammalian development and provide key tools for defining the functions of Myo10 in vivo.