Forkhead box transcription factor FoxC1 preserves corneal transparency by regulating vascular growth. Proc Natl Acad Sci U S A. 2012;109:2015-2020. [PMID: 22171010 DOI: 10.1073/pnas.1109540109]

Bioinformatics analysis for constructing a cellular senescence-related age-related macular degeneration diagnostic model and identifying relevant disease subtypes to guide treatment

Age-related macular degeneration (AMD) is a condition causing progressive central vision loss. Growing evidence suggests a link between cellular senescence and AMD. However, the exact mechanism by which cellular senescence leads to AMD remains unclear. Employing machine learning, we established an AMD diagnostic model. Through unsupervised clustering, two distinct AMD subtypes were identified. GO, KEGG, and GSVA analyses explored the diverse biological functions associated with the two subtypes. By WGCNA, we constructed a coexpression network of differential genes between the subtypes, revealing the regulatory role of hub genes at the level of transcription factors and miRNAs. We identified 5 genes associated with inflammation for the construction of the AMD diagnostic model. Additionally, we observed that the level of cellular senescence and pathways related to programmed cell death (PCD), such as ferroptosis, necroptosis, and pyroptosis, exhibited higher expression levels in subtype B than A. Immune microenvironments also differed between the subtypes, indicating potentially distinct pathogenic mechanisms and therapeutic targets. In summary, by leveraging cellular senescence-associated gene expression, we developed an AMD diagnostic model. Furthermore, we identified two subtypes with varying expression patterns of senescence genes, revealing their differential roles in programmed cell death, disease progression, and immune microenvironments within AMD.

Primary Cilium in Neural Crest Cells Crucial for Anterior Segment Development and Corneal Avascularity

Purpose

Intraflagellar transport 46 (IFT46) is an integral subunit of the IFT-B complex, playing a key role in the assembly and maintenance of primary cilia responsible for transducing signaling pathways. Despite its predominant expression in the basal body of cilia, the precise role of Ift46 in ocular development remains undetermined. This study aimed to elucidate the impact of neural crest (NC)-specific deletion of Ift46 on ocular development.

Methods

NC-specific conditional knockout mice for Ift46 (NC-Ift46F/F) were generated by crossing Ift46F mice with Wnt1-Cre2 mice, enabling the specific deletion of Ift46 in NC-derived cells (NCCs). Sonic Hedgehog (Shh) and Notch signaling activities in NC-Ift46F/F mice were evaluated using Gli1lacZ and CBF:H2B-Venus reporter mice, respectively. Cell fate mapping was conducted using ROSAmTmG reporter mice.

Results

The deletion of Ift46 in NCCs resulted in a spectrum of ocular abnormalities, including thickened corneal stroma, hypoplasia of the anterior chamber, irregular iris morphology, and corneal neovascularization. Notably, this deletion led to reduced Shh signal activity in the periocular mesenchyme, sustained expression of key transcription factors Foxc1, Foxc2 and Pitx2, along with persistent cell proliferation. Additionally, it induced increased Notch signaling activity and the development of ectopic neovascularization within the corneal stroma.

Conclusions

The absence of primary cilia due to Ift46 deficiency in NCCs is associated with anterior segment dysgenesis (ASD) and corneal neovascularization, suggesting a potential link to Axenfeld-Rieger syndrome, a disorder characterized by ASD. This underscores the pivotal role of primary cilia in ensuring proper anterior segment development and maintaining an avascular cornea.

Leger AJ, Swamynathan SK. The Secreted Ly6/uPAR-Related Protein 1 (Slurp1) Modulates Corneal Angiogenic Inflammation Via NF-κB Signaling

Purpose

Previously we demonstrated that the secreted Ly-6/uPAR related protein 1 (SLURP1), abundantly expressed in the corneal epithelium (CE) and secreted into the tear fluid, serves as an antiangiogenic molecule. Here we describe the Slurp1-null (Slurp1X-/-) mouse corneal response to silver nitrate (AgNO3) cautery.

Methods

Five days after AgNO3 cautery, we compared the wild-type (WT) and Slurp1X-/- mouse (1) corneal neovascularization (CNV) and immune cell influx by whole-mount immunofluorescent staining for CD31 and CD45, (2) macrophage and neutrophil infiltration by flow cytometry, and (3) gene expression by quantitative RT-PCR. Quantitative RT-PCR, immunofluorescent staining, and immunoblots were employed to evaluate the expression, phosphorylation status, and subcellular localization of NF-κB pathway components.

Results

Unlike the WT, the Slurp1X-/- corneas displayed denser CNV in response to AgNO3 cautery, with more infiltrating macrophages and neutrophils and greater upregulation of the transcripts encoding VEGFA, MMP2, IL-1b, and vimentin. At 2, 7, and 10 days after AgNO3 cautery, Slurp1 expression was significantly downregulated in the WT corneas. Compared with the WT, naive Slurp1X-/- CE displayed increased phosphorylation of IKK(a/b), elevated phosphorylation of IκB with decreased amounts of total IκB, and higher phosphorylation of NF-κB, suggesting that NF-κB signaling is constitutively active in naive Slurp1X-/- corneas.

Conclusions

Enhanced angiogenic inflammation in AgNO3 cauterized Slurp1X-/- corneas and constitutively active status of NF-κB signaling in the absence of Slurp1 suggest that Slurp1 modulates corneal angiogenic inflammation via NF-κB signaling.

Alternative Genetic Diagnoses in Axenfeld-Rieger Syndrome Spectrum

Axenfeld-Rieger anomaly (ARA) is a specific ocular disorder that is frequently associated with other systemic abnormalities. PITX2 and FOXC1 variants explain the majority of individuals with Axenfeld-Rieger syndrome (ARS) but leave ~30% unsolved. Here, we present pathogenic/likely pathogenic variants in nine families with ARA/ARS or similar phenotypes affecting five different genes/regions. USP9X and JAG1 explained three families each. USP9X was recently linked with syndromic cognitive impairment that includes hearing loss, dental defects, ventriculomegaly, Dandy-Walker malformation, skeletal anomalies (hip dysplasia), and other features showing a significant overlap with FOXC1-ARS. Anterior segment anomalies are not currently associated with USP9X, yet our cases demonstrate ARA, congenital glaucoma, corneal neovascularization, and cataracts. The identification of JAG1 variants, linked with Alagille syndrome, in three separate families with a clinical diagnosis of ARA/ARS highlights the overlapping features and high variability of these two phenotypes. Finally, intragenic variants in CDK13, BCOR, and an X chromosome deletion encompassing HCCS and AMELX (linked with ocular and dental anomalies, correspondingly) were identified in three additional cases with ARS. Accurate diagnosis has important implications for clinical management. We suggest that broad testing such as exome sequencing be applied as a second-tier test for individuals with ARS with normal results for PITX2/FOXC1 sequencing and copy number analysis, with attention to the described genes/regions.

Identification of the regulatory circuit governing corneal epithelial fate determination and disease

The transparent corneal epithelium in the eye is maintained through the homeostasis regulated by limbal stem cells (LSCs), while the nontransparent epidermis relies on epidermal keratinocytes for renewal. Despite their cellular similarities, the precise cell fates of these two types of epithelial stem cells, which give rise to functionally distinct epithelia, remain unknown. We performed a multi-omics analysis of human LSCs from the cornea and keratinocytes from the epidermis and characterized their molecular signatures, highlighting their similarities and differences. Through gene regulatory network analyses, we identified shared and cell type-specific transcription factors (TFs) that define specific cell fates and established their regulatory hierarchy. Single-cell RNA-seq (scRNA-seq) analyses of the cornea and the epidermis confirmed these shared and cell type-specific TFs. Notably, the shared and LSC-specific TFs can cooperatively target genes associated with corneal opacity. Importantly, we discovered that FOSL2, a direct PAX6 target gene, is a novel candidate associated with corneal opacity, and it regulates genes implicated in corneal diseases. By characterizing molecular signatures, our study unveils the regulatory circuitry governing the LSC fate and its association with corneal opacity.

Up-to-date molecular medicine strategies for management of ocular surface neovascularization

Ocular surface neovascularization and its resulting pathological changes significantly alter corneal refraction and obstruct the light path to the retina, and hence is a major cause of vision loss. Various factors such as infection, irritation, trauma, dry eye, and ocular surface surgery trigger neovascularization via angiogenesis and lymphangiogenesis dependent on VEGF-related and alternative mechanisms. Recent advances in antiangiogenic drugs, nanotechnology, gene therapy, surgical equipment and techniques, animal models, and drug delivery strategies have provided a range of novel therapeutic options for the treatment of ocular surface neovascularization. In this review article, we comprehensively discuss the etiology and mechanisms of corneal neovascularization and other types of ocular surface neovascularization, as well as emerging animal models and drug delivery strategies that facilitate its management.

Differential roles of FOXC2 in the trabecular meshwork and Schlemm's canal in glaucomatous pathology

Impaired development and maintenance of Schlemm's canal (SC) are associated with perturbed aqueous humor outflow and intraocular pressure. The angiopoietin (ANGPT)/TIE2 signaling pathway regulates SC development and maintenance, whereas the molecular mechanisms of crosstalk between SC and the neural crest (NC)-derived neighboring tissue, the trabecular meshwork (TM), are poorly understood. Here, we show NC-specific forkhead box (Fox)c2 deletion in mice results in impaired SC morphogenesis, loss of SC identity, and elevated intraocular pressure. Visible-light optical coherence tomography analysis further demonstrated functional impairment of the SC in response to changes in intraocular pressure in NC-Foxc2 -/- mice, suggesting altered TM biomechanics. Single-cell RNA-sequencing analysis identified that this phenotype is predominately characterized by transcriptional changes associated with extracellular matrix organization and stiffness in TM cell clusters, including increased matrix metalloproteinase expression, which can cleave the TIE2 ectodomain to produce soluble TIE2. Moreover, endothelial-specific Foxc2 deletion impaired SC morphogenesis because of reduced TIE2 expression, which was rescued by deleting the TIE2 phosphatase VE-PTP. Thus, Foxc2 is critical in maintaining SC identity and morphogenesis via TM-SC crosstalk.

FoxC1 activates limbal epithelial stem cells following corneal epithelial debridement

Limbal epithelial stem cells are not only critical for corneal epithelial homeostasis but also have the capacity to change from a relatively quiescent mitotic phenotype to a rapidly proliferating cell in response to population depletion following corneal epithelial wounding. Pax6+/- mice display many abnormalities including corneal vascularization and these aberrations are consistent with a limbal stem cell deficiency (LSCD) phenotype. FoxC1 has an inhibitory effect on corneal avascularity and a positive role in stem cell maintenance in many tissues. However, the role of FoxC1 in limbal epithelial stem cells remains unknown. To unravel FoxC1's role(s) in limbal epithelial stem cell homeostasis, we utilized an adeno-associated virus (AAV) vector to topically deliver human FOXC1 proteins into Pax6 +/- mouse limbal epithelium. Under unperturbed conditions, overexpression of FOXC1 in the limbal epithelium had little significant change in differentiation (PAI-2, Krt12) and proliferation (BrdU, Ki67). Conversely, such overexpression resulted in a marked increase in the expression of putative limbal epithelial stem cell markers, N-cadherin and Lrig1. After corneal injuries in Pax6 +/- mice, FOXC1 overexpression enhanced the behavior of limbal epithelial stem cells from quiescence to a highly proliferative status. Overall, the treatment of AAV8-FOXC1 may be beneficial to the function of limbal epithelial stem cells in the context of a deficiency of Pax6 function.

Induced Pluripotent Stem Cell-Derived Corneal Cells: Current Status and Application

Deficiency and dysfunction of corneal cells leads to the blindness observed in corneal diseases such as limbal stem cell deficiency (LSCD) and bullous keratopathy. Regenerative cell therapies and engineered corneal tissue are promising treatments for these diseases [1]. However, these treatments are not yet clinically feasible due to inadequate cell sources. The discovery of induced pluripotent stem cells (iPSCs) by Shinya Yamanaka has provided a multitude of opportunities in research because iPSCs can be generated from somatic cells, thus providing an autologous and unlimited source for corneal cells. Compared to other stem cell sources such as mesenchymal and embryonic, iPSCs have advantages in differentiation potential and ethical concerns, respectively. Efforts have been made to use iPSCs to model corneal disorders and diseases, drug testing [2], and regenerative medicine [1]. Autologous treatments based on iPSCs can be exorbitantly expensive and time-consuming, but development of stem cell banks with human leukocyte antigen (HLA)- homozygous cell lines can provide cost- and time-efficient allogeneic alternatives. In this review, we discuss the early development of the cornea because protocols differentiating iPSCs toward corneal lineages rely heavily upon recapitulating this development. Differentiation of iPSCs toward corneal cell phenotypes have been analyzed with an emphasis on feeder-free, xeno-free, and well-defined protocols, which have clinical relevance. The application, challenges, and potential of iPSCs in corneal research are also discussed with a focus on hurdles that prevent clinical translation.

Foxc1a regulates zebrafish vascular integrity and brain vascular development through targeting amotl2a and ctnnb1

Accumulating evidences have pointed that foxc1a is essential for vascular development and integrity maintenance through regulating the expression of downstream genes and interacting with signaling pathways. However, the underling cellular and molecular mechanisms of foxc1a in regulating vascular development remain undetermined. Based on two different foxc1a mutant zebrafish lines (foxc1a^nju18 and foxc1a^nju19 which generated predicted truncated foxc1a proteins with 50aa and 315aa respectively), we found that around 30 % of foxc1a^nju18 zebrafish exhibited severe vascular developmental defects with obvious hemorrhage in hindbrain and trunk at embryonic stages. Confocal imaging analysis revealed that the formation of middle cerebral vein (MCeV), intra-cerebral central arteries (CtAs) and dorsal longitudinal vein (DLV) of brain vessels was significantly blocked in foxc1a^nju18enbryos. Injection of exogenous full length and foxc1a^nju19 truncated foxc1a mRNA both rescued the deficiency of foxc1a^nju18 embryos. Transcriptome analysis revealed 186 DEGs in foxc1a^nju18 zebrafish among which amotl2a and ctnnb1 expression were reduced and functionally associated with adherens junctions. Dual-Luciferase assays validated amotl2a and ctnnb1 were both directly transactivated by foxc1a. Rescue experiments demonstrated that amotl2a was mainly responsible for the vascular integrity caused by foxc1a mutation and also coordinated with ctnnb1 to regulate brain vascular development. Our data point to a novel clue that foxc1a regulates vascular integrity and brain vascular development through targeting amotl2a and ctnnb1.

Disruption of foxc1 genes in zebrafish results in dosage-dependent phenotypes overlapping Axenfeld-Rieger syndrome

The Forkhead Box C1 (FOXC1) gene encodes a forkhead/winged helix transcription factor involved in embryonic development. Mutations in this gene cause dysgenesis of the anterior segment of the eye, most commonly Axenfeld-Rieger syndrome (ARS), often with other systemic features. The developmental mechanisms and pathways regulated by FOXC1 remain largely unknown. There are two conserved orthologs of FOXC1 in zebrafish, foxc1a and foxc1b. To further examine the role of FOXC1 in vertebrates, we generated foxc1a and foxc1b single knockout zebrafish lines and bred them to obtain various allelic combinations. Three genotypes demonstrated visible phenotypes: foxc1a-/- single homozygous and foxc1-/- double knockout homozygous embryos presented with similar characteristics comprised of severe global vascular defects and early lethality, as well as microphthalmia, periocular edema and absence of the anterior chamber of the eye; additionally, fish with heterozygous loss of foxc1a combined with homozygosity for foxc1b (foxc1a+/-;foxc1b-/-) demonstrated craniofacial defects, heart anomalies and scoliosis. All other single and combined genotypes appeared normal. Analysis of foxc1 expression detected a significant increase in foxc1a levels in homozygous and heterozygous mutant eyes, suggesting a mechanism for foxc1a upregulation when its function is compromised; interestingly, the expression of another ARS-associated gene, pitx2, was responsive to the estimated level of wild-type Foxc1a, indicating a possible role for this protein in the regulation of pitx2 expression. Altogether, our results support a conserved role for foxc1 in the formation of many organs, consistent with the features observed in human patients, and highlight the importance of correct FOXC1/foxc1 dosage for vertebrate development.

C/EBPα Regulates FOXC1 to Modulate Tumor Growth by Interacting with PPARγ in Hepatocellular Carcinoma

BACKGROUND

Forkhead box C1 (FOXC1) is an important cancer-associated gene in tumor. PPAR-γ and C/EBPα are both transcriptional regulators involved in tumor development.

OBJECTIVE

We aimed to clarify the function of PPAR-γ, C/EBPα in hepatocellular carcinoma (HCC) and the relationship of PPAR-γ, C/EBPα and FOXC1 in HCC.

METHODS

Western blotting, immunofluorescent staining, and immunohistochemistry were used to evaluate protein expression. qRT-PCR was used to assess mRNA expression. Co-IP was performed to detect the protein interaction. And ChIP and fluorescent reporter detection were used to determine the binding between protein and FOXC1 promoter.

RESULTS

C/EBPα could bind to FOXC1 promoter and PPAR-γ could strengthen C/EBPα's function. Expressions of C/EBPα and PPAR-γ were both negatively related to FOXC1 in human HCC tissue. Confocal displayed that C/EBPα was co-located with FOXC1 in HepG2 cells. C/EBPα could bind to FOXC1 promoter by ChIP. Luciferase activity detection exhibited that C/EBPα could inhibit FOXC1 promoter activity, especially FOXC1 promoter from -600 to -300 was the critical binding site. Only PPAR-γ could not influence luciferase activity but strengthen inhibited effect of C/EBPα. Further, the Co-IP displayed that PPAR-γ could bind to C/EBPα. When C/EBPα and PPAR-γ were both high expressed, cell proliferation, migration, invasion, and colony information were inhibited enormously. C/EBPα plasmid combined with or without PPAR-γ agonist MDG548 treatment exhibited a strong tumor inhibition and FOXC1 suppression in mice.

CONCLUSION

Our data establish C/EBPα targeting FOXC1 as a potential determinant in the HCC, which supplies a new pathway to treat HCC. However, PPAR-γ has no effect on FOXC1 expression.

Molecular identity of human limbal heterogeneity involved in corneal homeostasis and privilege

PURPOSE

The corneal limbus maintains the homeostasis, immune and angiogenic privilege of cornea. This study aimed to depict the landscape of human limbal tissues by single-cell RNA sequencing (scRNA-seq).

METHODS

Single cells of human limbus collected from donor corneas were subjected to 10x scRNA-seq, followed by clustering cell types through the t-distributed stochastic neighbor embedding (t-SNE) and unbiased computational informatic analysis. Immunofluorescent staining was performed using human corneas to validate the analysis results.

RESULTS

47,627 cells acquired from six human limbal tissues were collected and subjected to scRNA-seq. 14 distinct clusters were identified and 8 cell types were annotated with representative markers. In-depth dissection revealed three limbal epithelial cell subtypes and refined the X-Y-Z hypothesis of corneal epithelial maintenance. We further unveiled two cell states with higher stemness (TP63⁺ and CCL20⁺ cells), and two other differentiated cell states (GPHA2⁺ and KRT6B ⁺ cells) in homeostatic limbal stem/progenitor cells (LSPCs) that differ in transcriptional profiles. Cell-cell communication analysis revealed the central role of LSPCs and their bidirectional regulation with various niche cells. Moreover, comparative analysis between limbus and skin deciphered the pivotal contribution of limbal immune cells, vascular and lymphatic endothelial cells to corneal immune and angiogenic privilege.

CONCLUSIONS

The human limbus atlas provided valuable resources and foundations for understanding corneal biology, disease and potential interventions.

The Ocular Neural Crest: Specification, Migration, and Then What?

During vertebrate embryonic development, a population of dorsal neural tube-derived stem cells, termed the neural crest (NC), undergo a series of morphogenetic changes and extensive migration to become a diverse array of cell types. Around the developing eye, this multipotent ocular NC cell population, called the periocular mesenchyme (POM), comprises migratory mesenchymal cells that eventually give rise to many of the elements in the anterior of the eye, such as the cornea, sclera, trabecular meshwork, and iris. Molecular cell biology and genetic analyses of congenital eye diseases have provided important information on the regulation of NC contributions to this area of the eye. Nevertheless, a complete understanding of the NC as a contributor to ocular development remains elusive. In addition, positional information during ocular NC migration and the molecular pathways that regulate end tissue differentiation have yet to be fully elucidated. Further, the clinical challenges of ocular diseases, such as Axenfeld-Rieger syndrome (ARS), Peters anomaly (PA) and primary congenital glaucoma (PCG), strongly suggest the need for better treatments. While several aspects of NC evolution have recently been reviewed, this discussion will consolidate the most recent current knowledge on the specification, migration, and contributions of the NC to ocular development, highlighting the anterior segment and the knowledge obtained from the clinical manifestations of its associated diseases. Ultimately, this knowledge can inform translational discoveries with potential for sorely needed regenerative therapies.

Loss of FOXC1 contributes to the corneal epithelial fate switch and pathogenesis

Forkhead box C1 (FOXC1) is required for neural crest and ocular development, and mutations in FOXC1 lead to inherited Axenfeld-Rieger syndrome. Here, we find that FOXC1 and paired box 6 (PAX6) are co-expressed in the human limbus and central corneal epithelium. Deficiency of FOXC1 and alternation in epithelial features occur in patients with corneal ulcers. FOXC1 governs the fate of the corneal epithelium by directly binding to lineage-specific open promoters or enhancers marked by H3K4me2. FOXC1 depletion not only activates the keratinization pathway and reprograms corneal epithelial cells into skin-like epithelial cells, but also disrupts the collagen metabolic process and interferon signaling pathways. Loss of interferon regulatory factor 1 and PAX6 induced by FOXC1 dysfunction is linked to the corneal ulcer. Collectively, our results reveal a FOXC1-mediated regulatory network responsible for corneal epithelial homeostasis and provide a potential therapeutic target for corneal ulcer.

Organogenesis and distribution of the ocular lymphatic vessels in the anterior eye

Glaucoma surgeries, such as trabeculectomy, are performed to lower intraocular pressure to reduce risk of vision loss. These surgeries create a new passage in the eye that reroutes the aqueous humor outflow to the subconjunctival space, where the fluid is presumably absorbed by the conjunctival lymphatics. Here, we characterized the development and function of the ocular lymphatics using transgenic lymphatic reporter mice and rats. We found that the limbal and conjunctival lymphatic networks are progressively formed from a primary lymphatic vessel that grows from the nasal-side medial canthus region at birth. This primary lymphatic vessel immediately branches out, invades the limbus and conjunctiva, and bidirectionally encircles the cornea. As a result, the distribution of the ocular lymphatics is significantly polarized toward the nasal side, and the limbal lymphatics are directly connected to the conjunctival lymphatics. New lymphatic sprouts are produced mainly from the nasal-side limbal lymphatics, posing the nasal side of the eye as more responsive to fluid drainage and inflammatory stimuli. Consistent with this polarized distribution of the ocular lymphatics, a higher drainage efficiency was observed in the nasal side than the temporal side of the eye when injected with a fluorescent tracer. In contrast, blood vessels are evenly distributed at the anterior surface of the eyes. Also, we found that these distinct vascular distribution patterns were conserved in human eyes. Together, our study demonstrated that the ocular surface lymphatics are more densely present in the nasal side and uncovered the potential clinical benefits in selecting the nasal side as a glaucoma surgery site to improve fluid drainage.

FoxC1-Induced Vascular Niche Improves Survival and Myocardial Repair of Mesenchymal Stem Cells in Infarcted Hearts

Aims

Forkhead box C1 (FoxC1) is essential for maintaining the hair follicle stem cell niche. The role of FoxC1 in maintaining mesenchymal stem cell (MSC) niches after myocardial infarction (MI) has not been directly determined to date. In this study, we determined to explore the possible roles and mechanisms of FoxC1 on MSC survival and function in the ischemic niche.

Methods and Results

MI model was established in this study, and expression level of FoxC1 was overexpressed or knocked down through efficient delivery of FoxC1 transfection or siFoxC1. Fifteen days later, the animals were allocated randomly to receive phosphate-buffered saline (PBS) injection or MSC transplantation. We identified FoxC1 as a key regulator of maintaining the vascular niche in the infarcted hearts (IHs) by driving proangiogenic and anti-inflammatory cytokines while repressing inflammatory and fibrotic factor expression. This vascular niche improved MSC survival and capacity in the IHs. Importantly, FoxC1 interacted with MSCs and was required for vessel specification and differentiation of engrafted MSCs in the ischemic niches, promoting myocardial repair. Inhibiting FoxC1 abolished these effects.

Conclusion

These results definitively implicate FoxC1 signaling in maintaining ischemic vascular niche, which may be helpful in myocardial repair induced by MSC therapy.

Tissue Engineering of Axially Vascularized Soft-Tissue Flaps with a Poly-(ɛ-Caprolactone) Nanofiber-Hydrogel Composite

Objective: To develop a novel approach for tissue engineering of soft-tissue flaps suitable for free microsurgical transfer, using an injectable nanofiber hydrogel composite (NHC) vascularized by an arteriovenous (AV) loop. Approach: A rat AV loop model was used for tissue engineering of vascularized soft-tissue flaps. NHC or collagen-elastin (CE) scaffolds were implanted into isolation chambers together with an AV loop and explanted after 15 days. Saphenous veins were implanted into the scaffolds as controls. Neoangiogenesis, ultrastructure, and protein expression of SYNJ2BP, EPHA2, and FOXC1 were analyzed by immunohistochemistry and compared between the groups. Rheological properties were compared between the two scaffolds and native human adipose tissue. Results: A functional neovascularization was evident in NHC flaps with its amount being comparable with CE flaps. Scanning electron microscopy revealed a strong mononuclear cell infiltration along the nanofibers in NHC flaps and a trend toward higher fiber alignment compared with CE flaps. SYNJ2BP and EPHA2 expression in endothelial cells (ECs) was lower in NHC flaps compared with CE flaps, whereas FOXC1 expression was increased in NHC flaps. Compared with the stiffer CE flaps, the NHC flaps showed similar rheological properties to native human adipose tissue. Innovation: This is the first study to demonstrate the feasibility of tissue engineering of soft-tissue flaps with similar rheological properties as human fat, suitable for microsurgical transfer using an injectable nanofiber hydrogel composite. Conclusions: The injectable NHC scaffold is suitable for tissue engineering of axially vascularized soft-tissue flaps with a solid neovascularization, strong cellular infiltration, and biomechanical properties similar to human fat. Our data indicate that SYNJ2BP, EPHA2, and FOXC1 are involved in AV loop-associated angiogenesis and that the scaffold material has an impact on protein expression in ECs.

Construction and Comprehensive Analysis of Dysregulated Long Noncoding RNA-Associated Competing Endogenous RNA Network in Moyamoya Disease

BACKGROUND

Moyamoya disease (MMD) is a rare cerebrovascular disease characterized by chronic progressive stenosis or occlusion of the bilateral internal carotid artery (ICA), the anterior cerebral artery (ACA), and the middle cerebral artery (MCA). MMD is secondary to the formation of an abnormal vascular network at the base of the skull. However, the etiology and pathogenesis of MMD remain poorly understood.

METHODS

A competing endogenous RNA (ceRNA) network was constructed by analyzing sample-matched messenger RNA (mRNA), long non-coding RNA (lncRNA), and microRNA (miRNA) expression profiles from MMD patients and control samples. Then, a protein-protein interaction (PPI) network was constructed to identify crucial genes associated with MMD. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes pathway (KEGG) enrichment analyses were employed with the DAVID database to investigate the underlying functions of differentially expressed mRNAs (DEmRNAs) involved in the ceRNA network. CMap was used to identify potential small drug molecules.

RESULTS

A total of 94 miRNAs, 3649 lncRNAs, and 2294 mRNAs were differentially expressed between MMD patients and control samples. A synergistic ceRNA lncRNA-miRNA-mRNA regulatory network was constructed. Core regulatory miRNAs (miR-107 and miR-423-5p) and key mRNAs (STAT5B, FOSL2, CEBPB, and CXCL16) involved in the ceRNA network were identified. GO and KEGG analyses indicated that the DEmRNAs were involved in the regulation of the immune system and inflammation in MMD. Finally, two potential small molecule drugs, CAY-10415 and indirubin, were identified by CMap as candidate drugs for treating MMD.

CONCLUSIONS

The present study used bioinformatics analysis of candidate RNAs to identify a series of clearly altered miRNAs, lncRNAs, and mRNAs involved in MMD. Furthermore, a ceRNA lncRNA-miRNA-mRNA regulatory network was constructed, which provides insights into the novel molecular pathogenesis of MMD, thus giving promising clues for clinical therapy.

Conditional inactivation of Foxc1 and Foxc2 in neural crest cells leads to cardiac abnormalities

Cardiac neural crest cells (cNCCs) are required for normal heart development. cNCCs are a multipotent and migratory cell lineage that differentiates into multiple cell types. cNCCs migrate into the developing heart to contribute to the septation of the cardiac outflow tract (OFT). Foxc1 and Foxc2 are closely related members of the FOX (Forkhead box) transcription factor family and are expressed in cNCC during heart development. However, the precise role of Foxc1 and Foxc2 in cNCCs has yet to be fully described. We found that compound NCC-specific Foxc1;Foxc2 mutant embryos exhibited persistent truncus arteriosus (PTA), ventricular septal defects (VSDs), and thinning of the ventricular myocardium. Loss of Foxc1/c2 expression in cNCCs resulted in abnormal patterns of cNCC migration into the OFT without the formation of the aorticopulmonary septum. Further, loss of Foxc1 expression in cNCCs resulted in normal OFT development but abnormal ventricular septal formation. In contrast, loss of Foxc2 expression in NCCs led to no obvious cardiac abnormalities. Together, we provide evidence that Foxc1 and Foxc2 in cNCCs are cooperatively required for proper cNCC migration, the formation of the OFT septation, and the development of the ventricles. Our data also suggests that Foxc1 expression may play a larger role in ventricular development compared to Foxc2.

Primary cilia deficiency in neural crest cells models anterior segment dysgenesis in mouse

Defects affecting tissues of the anterior segment (AS) of the eye lead to a group of highly debilitating disorders called Anterior Segment Dysgenesis (ASD). Despite the identification of some causative genes, the pathogenesis of ASD remains unclear. Interestingly, several ciliopathies display conditions of the AS. Using conditional targeting of Ift88 with Wnt1-Cre, we show that primary cilia of neural crest cells (NCC), precursors of most AS structures, are indispensable for normal AS development and their ablation leads to ASD conditions including abnormal corneal dimensions, defective iridocorneal angle, reduced anterior chamber volume and corneal neovascularization. Mechanistically, NCC cilia ablation abolishes hedgehog (Hh) signaling in the periocular mesenchyme (POM) canonically activated by choroid-secreted Indian Hh, reduces proliferation of POM cells surrounding the retinal pigment epithelium and decreases the expression of Foxc1 and Pitx2, two transcription factors identified as major ASD causative genes. Thus, we uncovered a signaling axis linking cilia and ASD.

The Spectrum of PAX6 Mutations and Genotype-Phenotype Correlations in the Eye

The transcription factor PAX6 is essential in ocular development in vertebrates, being considered the master regulator of the eye. During eye development, it is essential for the correct patterning and formation of the multi-layered optic cup and it is involved in the developing lens and corneal epithelium. In adulthood, it is mostly expressed in cornea, iris, and lens. PAX6 is a dosage-sensitive gene and it is highly regulated by several elements located upstream, downstream, and within the gene. There are more than 500 different mutations described to affect PAX6 and its regulatory regions, the majority of which lead to PAX6 haploinsufficiency, causing several ocular and systemic abnormalities. Aniridia is an autosomal dominant disorder that is marked by the complete or partial absence of the iris, foveal hypoplasia, and nystagmus, and is caused by heterozygous PAX6 mutations. Other ocular abnormalities have also been associated with PAX6 changes, and genotype-phenotype correlations are emerging. This review will cover recent advancements in PAX6 regulation, particularly the role of several enhancers that are known to regulate PAX6 during eye development and disease. We will also present an updated overview of the mutation spectrum, where an increasing number of mutations in the non-coding regions have been reported. Novel genotype-phenotype correlations will also be discussed.

Transformation of the Transcriptomic Profile of Mouse Periocular Mesenchyme During Formation of the Embryonic Cornea

Purpose

Defects in neural crest development are a major contributing factor in corneal dysgenesis, but little is known about the genetic landscape during corneal development. The purpose of this study was to provide a detailed transcriptome profile and evaluate changes in gene expression during mouse corneal development.

Methods

RNA sequencing was used to uncover the transcriptomic profile of periocular mesenchyme (pNC) isolated at embryonic day (E) 10.5 and corneas isolated at E14.5 and E16.5. The spatiotemporal expression of several differentially expressed genes was validated by in situ hybridization.

Results

Analysis of the whole-transcriptome profile between pNC and embryonic corneas identified 3815 unique differentially expressed genes. Pathway analysis revealed an enrichment of differentially expressed genes involved in signal transduction (retinoic acid, transforming growth factor-β, and Wnt pathways) and transcriptional regulation.

Conclusions

Our analyses, for the first time, identify a large number of differentially expressed genes during progressive stages of mouse corneal development. Our data provide a comprehensive transcriptomic profile of the developing cornea. Combined, these data serve as a valuable resource for the identification of novel regulatory networks crucial for the advancement of studies in congenital defects, stem cell therapy, bioengineering, and adult corneal diseases.

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.

The Diverse Consequences of FOXC1 Deregulation in Cancer

Forkhead box C1 (FOXC1) is a transcription factor with essential roles in mesenchymal lineage specification and organ development during normal embryogenesis. In keeping with these developmental properties, mutations that impair the activity of FOXC1 result in the heritable Axenfeld-Rieger Syndrome and other congenital disorders. Crucially, gain of FOXC1 function is emerging as a recurrent feature of malignancy; FOXC1 overexpression is now documented in more than 16 cancer types, often in association with an unfavorable prognosis. This review explores current evidence for FOXC1 deregulation in cancer and the putative mechanisms by which FOXC1 confers its oncogenic effects.

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

Mutation of FOXC1 causes Axenfeld-Rieger Syndrome (ARS) with early onset or congenital glaucoma. We assessed retinal ganglion cell (RGC) number in zebrafish due to CRISPR-mediated mutation and antisense inhibition of two-forkhead box transcription factors, foxc1a and foxc1b. These genes represent duplicated homologues of human FOXC1. Using a CRISPR induced null mutation in foxc1b, in combination with antisense inhibition of foxc1a, we demonstrate reduced cell number in the retinal ganglion cell layer of developing zebrafish eyes. As early as 5 days post fertilization (dpf), fewer RGCs are found in foxc1b homozygous mutants injected with foxc1a morpholinos, and a thinner optic nerve results. Our data illustrates that foxc1 is required for the expression of atonal homolog 7 (atoh7), a gene that is necessary for RGC differentiation. As markers of differentiated RGCs (pou4f2) are downregulated in foxc1b-/- mutants injected with foxc1a morpholinos and no cell death is observed, our results are consistent with defects in the differentiation of RGCs leading to reduced cell number, as opposed to increased cell death of RGCs or off targets effects of morpholino injection. Our zebrafish model demonstrates that aberrant regulation of RGC number could act in concert with other known glaucoma risk factors to influence the development of congenital and early onset glaucoma due to FOXC1 mutation.

MicroRNA-regulated pathways of flow-stimulated angiogenesis and vascular remodeling in vivo

BACKGROUND

Vascular shear stress promotes endothelial cell sprouting in vitro. The impact of hemodynamic forces on microRNA (miRNA) and gene expression within growing vascular networks in vivo, however, remain poorly investigated. Arteriovenous (AV) shunts are an established model for induction of neoangiogenesis in vivo and can serve as a tool for analysis of hemodynamic effects on miRNA and gene expression profiles over time.

METHODS

AV shunts were microsurgically created in rats and explanted on postoperative days 5, 10 and 15. Neoangiogenesis was confirmed by histologic analysis and micro-computed tomography. MiRNA and gene expression profiles were determined in tissue specimens from AV shunts by microarray analysis and quantitative real-time polymerase chain reaction and compared with sham-operated veins by bioinformatics analysis. Changes in protein expression within AV shunt endothelial cells were determined by immunohistochemistry.

RESULTS

Samples from AV shunts exhibited a strong overexpression of proangiogenic cytokines, oxygenation-associated genes (HIF1A, HMOX1), and angiopoetic growth factors. Significant inverse correlations of the expressions of miR-223-3p, miR-130b-3p, miR-19b-3p, miR-449a-5p, and miR-511-3p which were up-regulated in AV shunts, and miR-27b-3p, miR-10b-5p, let-7b-5p, and let-7c-5p, which were down-regulated in AV shunts, with their predicted interacting targets C-X-C chemokine receptor 2 (CXCR2), interleukin-1 alpha (IL1A), ephrin receptor kinase 2 (EPHA2), synaptojanin-2 binding protein (SYNJ2BP), forkhead box C1 (FOXC1) were present. CXCL2 and IL1A overexpression in AV shunt endothelium was confirmed at the protein level by immunohistochemistry.

CONCLUSIONS

Our data indicate that flow-stimulated angiogenesis is determined by an upregulation of cytokines, oxygenation associated genes and miRNA-dependent regulation of FOXC1, EPHA2 and SYNJ2BP.

Emerging insights from the genetics of cerebral small-vessel disease

Cerebral small-vessel disease (cSVD) is a common cause of stroke, functional decline, vascular cognitive impairment, and dementia. Pathological processes in the brain's microcirculation are tightly interwoven with pathology in the brain parenchyma, and this interaction has been conceptualized as the neurovascular unit (NVU). Despite intensive research efforts to decipher the NVU's structure and function to date, molecular mechanisms underlying cSVD remain poorly understood, which hampers the development of cSVD-specific therapies. Important steps forward in understanding the disease mechanisms underlying cSVD have been made using genetic approaches in studies of both monogenic and sporadic SVD. We provide an overview of the NVU's structure and function, the implications for cSVD, and the underlying molecular mechanisms of dysfunction that have emerged from recent genetic studies of both monogenic and sporadic diseases of the small cerebral vasculature.

Eye organogenesis: A hierarchical view of ocular development

This chapter provides an overview of the early developmental origins of six ocular tissues: the cornea, lens, ciliary body, iris, neural retina, and retina pigment epithelium. Many of these tissue types are concurrently specified and undergo a complex set of morphogenetic movements that facilitate their structural interconnection. Within the context of vertebrate eye organogenesis, we also discuss the genetic hierarchies of transcription factors and signaling pathways that regulate growth, patterning, cell type specification and differentiation.

Meta-analysis of the likelihood of FOXC1 expression in early- and late-stage tumors

Background

Aberrations in the expression of the transcription factor forkhead box C1 (FOXC1) have been linked to a number of malignancies. Here, we characterized the relationship between FOXC1 and cancer progression by conducting a meta-analysis of studies that reported the frequency of FOXC1 expression in tumors of different stages (T1, T2, T3, T4).

Materials and Method

Relevant articles were retrieved from the Medline database by searching for the terms “FOXC1” and “cancer”; then, the retrieved articles were reviewed individually, and studies that were of multivariate cohort design, evaluated FOXC1 expression via immunohistochemical staining, and assessed the relationship between FOXC1 expression and cancer T-stage were included in our meta-analysis.

Results

Our search terms identified 128 studies, 5 of which met all inclusion criteria. A total of 850 tumor samples were evaluated in the 5 studies; 452 samples were from early-stage (T1-T2) tumors, and 398 were from late-stage (T3-T4) tumors. FOXC1 was expressed in 60.7% (516/850) of all samples, in 54.6% (247/452) of early-stage tumor samples, and in 67.5% (269/398) of late-stage tumor samples. When calculated relative to early-stage samples, the pooled risk for FOXC1 expression in late-stage samples was 1.238 (95% CI = 1.061–1.444, p = 0.007).

Conclusions

The results from our meta-analysis of 5 studies indicate that FOXC1 is 23.8% more likely to be expressed in late-stage tumors than in early-stage tumors.

Therapeutic implication of vascular endothelial growth factor receptor-1 (VEGFR-1) targeting in cancer cells and tumor microenvironment by competitive and non-competitive inhibitors

The vascular endothelial growth factor receptor-1 (VEGFR-1) is a tyrosine kinase receptor for VEGF-A, VEGF-B, and placental growth factor (PlGF) ligands that is expressed in endothelial, myelomonocytic and tumor cells. VEGF-B and PlGF exclusively bind to VEGFR-1, whereas VEGF-A also binds to VEGFR-2. At variance with VEGFR-2, VEGFR-1 does not play a relevant role in physiological angiogenesis in the adult, while it is important in tumor-associated angiogenesis. VEGFR-1 and PlGF are expressed in a variety of tumors, promote invasiveness and contribute to resistance to anti-VEGF-A therapy. The currently approved antiangiogenic therapies for the treatment of a variety of solid tumors hamper VEGF-A signaling mediated by both VEGFR-2 and VEGFR-1 [i.e., the monoclonal antibody (mAb) anti-VEGF-A bevacizumab, the chimeric molecule aflibercept and several small molecule tyrosine kinase inhibitors] or exclusively by VEGFR-2 (i.e., the mAb anti-VEGFR-2 ramucirumab). However, molecules that interfere with VEGF-A/VEGFR-2 signaling determine severe adverse effects due to inhibition of physiological angiogenesis and their efficacy is hampered by tumor infiltration of protumoral myeloid cells. Blockade of VEGFR-1 may exert anti-tumor activity by multiple mechanisms: a) inhibition of tumor-associated angiogenesis; b) reduction of myeloid progenitor mobilization and tumor infiltration by VEGFR-1 expressing M2 macrophages, which contribute to tumor progression and spreading; c) inhibition of invasiveness, vasculogenic mimicry and survival of VEGFR-1 positive tumor cells. As a consequence of these properties, molecules targeting VEGFR-1 are expected to produce less adverse effects and to counteract resistance towards anti-VEGF-A therapies. More interestingly, selective VEGFR-1 inhibition might enhance the efficacy of immunotherapy with immune checkpoint inhibitors. In this review, we will examine the experimental evidence available so far that supports targeting VEGFR-1 signal transduction pathway for cancer treatment by competitive inhibitors that prevent growth factor interaction with the receptor and non-competitive inhibitors that hamper receptor activation without affecting ligand binding.

Photostable and Biocompatible Fluorescent Silicon Nanoparticles-Based Theranostic Probes for Simultaneous Imaging and Treatment of Ocular Neovascularization

Ocular neovascularization can result in devastating diseases that lead to marked vision impairment and eventual visual loss. In clinical implementation, neovascular eye diseases are first diagnosed by fluorescein angiography and then treated by multiple intravitreal injections, which nevertheless involves vision-threatening complications, as well as lack of real-time monitoring disease progression and timely assessment of therapeutic outcomes. To address this critical issue, we herein present a kind of theranostic agents made of peptide-functionalized silicon nanoparticles (SiNPs), suitable for simultaneous ocular neovascularization imaging and therapy. Typically, in addition to negligible toxicity and high specific binding ability to human retinal microvascular endothelial cells tube formation, the cyclo-(Arg-Gly-Asp-d-Tyr-Cys) ( c-(RGDyC))-conjugated SiNPs (SiNPs-RGD) features efficacious antiangiogenic ability in wound healing migration, transwell migration, transwell invasion, and tube formation assays. Taking advantage of these unique merits, we further employ the SiNPs-RGD for labeling angiogenic blood vessels and neovascularization suppression, demonstrating obvious inhibition of new blood vessels formation in mouse corneas. These results suggest the SiNPs-RGD as a novel class of high-quality theranostic probes is suitable for simultaneous diagnosis and treatment in ocular neovascular diseases.

Limbal stem cells: identity, developmental origin, and therapeutic potential

The cornea is our window to the world and our vision is critically dependent on corneal clarity and integrity. Its epithelium represents one of the most rapidly regenerating mammalian tissues, undergoing full-turnover over the course of approximately 1-2 weeks. This robust and efficient regenerative capacity is dependent on the function of stem cells residing in the limbus, a structure marking the border between the cornea and the conjunctiva. Limbal stem cells (LSC) represent a quiescent cell population with proliferative capacity residing in the basal epithelial layer of the limbus within a cellular niche. In addition to LSC, this niche consists of various cell populations such as limbal stromal fibroblasts, melanocytes and immune cells as well as a basement membrane, all of which are essential for LSC maintenance and LSC-driven regeneration. The LSC niche's components are of diverse developmental origin, a fact that had, until recently, prevented precise identification of molecularly defined LSC. The recent success in prospective LSC isolation based on ABCB5 expression and the capacity of this LSC population for long-term corneal restoration following transplantation in preclinical in vivo models of LSC deficiency underline the considerable potential of pure LSC formulations for clinical therapy. Additional studies, including genetic lineage tracing of the developmental origin of LSC will further improve our understanding of this critical cell population and its niche, with important implications for regenerative medicine. WIREs Dev Biol 2018, 7:e303. doi: 10.1002/wdev.303 This article is categorized under: Adult Stem Cells, Tissue Renewal, and Regeneration > Stem Cells and Disease Adult Stem Cells, Tissue Renewal, and Regeneration > Tissue Stem Cells and Niches Adult Stem Cells, Tissue Renewal, and Regeneration > Regeneration.

Human corneal cell culture models for drug toxicity studies

In vivo toxicity and absorption studies of topical ocular drugs are problematic, because these studies involve invasive tissue sampling and toxic effects in animal models. Therefore, different human corneal models ranging from simple monolayer cultures to three-dimensional models have been developed for toxicological prediction with in vitro models. Each system has its own set of advantages and disadvantages. Use of non-corneal cells, inadequate characterization of gene-expression profiles, and accumulation of genomic aberrations in human corneal models are typical drawbacks that decrease their reliability and predictive power. In the future, further improvements are needed for verifying comparable expression profiles and cellular properties of human corneal models with their in vivo counterparts. A rapidly expanding stem cell technology combined with tissue engineering may give future opportunities to develop new tools in drug toxicity studies. One approach may be the production of artificial miniature corneas. In addition, there is also a need to use large-scale profiling approaches such as genomics, transcriptomics, proteomics, and metabolomics for understanding of the ocular toxicity.

Foxc1 and Foxc2 in the Neural Crest Are Required for Ocular Anterior Segment Development

Purpose

The large Forkhead (Fox) transcription factor family has essential roles in development, and mutations cause a wide range of ocular and nonocular disease. One member, Foxc2 is expressed in neural crest (NC)-derived periocular mesenchymal cells of the developing murine eye; however, its precise role in the development, establishment, and maintenance of the ocular surface has yet to be investigated.

Methods

To specifically delete Foxc2 from NC-derived cells, conditional knockout mice for Foxc2 (NC-Foxc2^−/−) were generated by crossing Foxc2^F mice with Wnt1-Cre mice. Similarly, we also generated compound NC-specific mutations of Foxc2 and a closely related gene, Foxc1 (NC-Foxc1^−/−;NC-Foxc2^−/−) in mice.

Results

Neural crest-Foxc2^−/− mice show abnormal thickness in the peripheral-to-central corneal stroma and limbus and displaced pupils with irregular iris. The neural crest-specific mutation in Foxc2 also leads to ectopic neovascularization in the cornea, as well as impaired ocular epithelial cell identity and corneal conjunctivalization. Compound, NC-specific Foxc1; Foxc2 homozygous mutant mice have more severe defects in structures of the ocular surface, such as the cornea and eyelids, accompanied by significant declines in the expression of another key developmental factor, Pitx2, and its downstream effector Dkk2, which antagonizes canonical Wnt signaling.

Conclusions

The neural crest-Foxc2 mutation is associated with corneal conjunctivalization, ectopic corneal neovascularization, and disrupted ocular epithelial cell identity. Furthermore, Foxc2 and Foxc1 cooperatively function in NC-derived mesenchymal cells to ensure proper morphogenesis of the ocular surface via the regulation of Wnt signaling. Together, Foxc2 is required in the NC lineage for mesenchymal-epithelial interactions in corneal and ocular surface development.

New insights into mononuclear phagocyte biology from the visual system

Major advances in mononuclear phagocyte biology have been made but key questions pertinent to their roles in health and disease remain, including in the visual system. One problem concerns how dendritic cells can trigger immune responses from certain tightly regulated immune- privileged sites of the eye. Another, albeit separate, problem involves whether there are functional specializations for microglia versus monocytes in retinal neurodegeneration. In this Review, we examine novel insights in eye immune privilege and, separately, we discuss recent inroads concerning retinal degeneration. Both themes have been extensively studied in the visual system and show parallels with recent findings concerning mononuclear phagocytes in the central nervous system and in the periphery.

New insights into mechanisms of small vessel disease stroke from genetics

Cerebral small vessel disease (SVD) is a common cause of lacunar strokes, vascular cognitive impairment (VCI) and vascular dementia. SVD is thought to result in reduced cerebral blood flow, impaired cerebral autoregulation and increased blood–brain barrier (BBB) permeability. However, the molecular mechanisms underlying SVD are incompletely understood. Recent studies in monogenic forms of SVD, such as cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), and ‘sporadic’ SVD have shed light on possible disease mechanisms in SVD. Proteomic and biochemical studies in post-mortem monogenic SVD patients, as well as in animal models of monogenic disease have suggested that disease pathways are shared between different types of monogenic disease, often involving the impairment of extracellular matrix (ECM) function. In addition, genetic studies in ‘sporadic’ SVD have also shown that the disease is highly heritable, particularly among young-onset stroke patients, and that common variants in monogenic disease genes may contribute to disease processes in some SVD subtypes. Genetic studies in sporadic lacunar stroke patients have also suggested distinct genetic mechanisms between subtypes of SVD. Genome-wide association studies (GWAS) have also shed light on other potential disease mechanisms that may be shared with other diseases involving the white matter, or with pathways implicated in monogenic disease. This review brings together recent data from studies in monogenic SVD and genetic studies in ‘sporadic’ SVD. It aims to show how these provide new insights into the pathogenesis of SVD, and highlights the possible convergence of disease mechanisms in monogenic and sporadic SVD.

Long noncoding RNA expression profile of infantile hemangioma identified by microarray analysis

Infantile hemangioma (IH) is one of the most common vascular tumors of childhood. Long noncoding RNAs (lncRNAs) play a critical role in angiogenesis, but their involvement in hemangioma remains unknown. This study aimed to assess the expression profiles of lncRNAs in IH and adjacent normal tissue samples, exploring the biological functions of lncRNAs as well as their involvement in IH pathogenesis. The lncRNA expression profiles were determined by lncRNA microarrays. A total of 1259 and 857 lncRNAs were upregulated and downregulated in IH, respectively, at a fold change cutoff of 2.0 (p < 0.05); in addition, 1469 and 1184 messenger RNAs (mRNAs) were upregulated and downregulated, respectively (fold change cutoff of 2.0; p < 0.05). A total of 292 differentially expressed mRNAs were targeted by the lncRNAs with altered expression in hemangioma, including 228 and 64 upregulated and downregulated, respectively (cutoff of 2.0, p < 0.05). Gene ontology (GO) analyses revealed several angiogenesis-related pathways. An lncRNA-mRNA co-expression network for differentially expressed lncRNAs revealed significant associations of the lncRNAs MEG3, MEG8, FENDRR, and Linc00152 with their related mRNAs. The validation results of nine differentially expressed lncRNAs (MALAT1, MEG3, MEG8, p29066, p33867, FENDRR, Linc00152, p44557_v4, p8683) as well as two mRNAs (FOXF1, EGFL7) indicated that the microarray data correlated well with the QPCR results. Interestingly, MALAT1 knockdown induced apoptosis and S-phase cell cycle arrest in human umbilical vein endothelial cells (HUVECs). Overall, this study revealed the lncRNA expression profile of IH and that lncRNAs likely regulate several genes with important roles in angiogenesis.

Foxc1 Ablated Mice Are Anhidrotic and Recapitulate Features of Human Miliaria Sweat Retention Disorder

Sweat glands are critical for thermoregulation. The single tubular structure of sweat glands has a lower secretory portion and an upper reabsorptive duct leading to the secretory pore in the skin. Genes that determine sweat gland structure and function are largely unidentified. Here we report that a Fox family transcription factor, Foxc1, is obligate for appreciable sweat duct activity in mice. When Foxc1 was specifically ablated in skin, sweat glands appeared mature, but the mice were severely hypohidrotic. Morphologic analysis revealed that sweat ducts were blocked by hyperkeratotic or parakeratotic plugs. Consequently, lumens in ducts and secretory portions were dilated, and blisters and papules formed on the skin surface in the knockout mice. The phenotype was strikingly similar to the human sweat retention disorder miliaria. We further show that Foxc1 deficiency ectopically induces the expression of keratinocyte terminal differentiation markers in the duct luminal cells, which most likely contribute to keratotic plug formation. Among those differentiation markers, we show that Sprr2a transcription is directly repressed by overexpressed Foxc1 in keratinocytes. In summary, Foxc1 regulates sweat duct luminal cell differentiation, and mutant mice mimic miliaria and provide a possible animal model for its study.

A Novel Homozygous Mutation in FOXC1 Causes Axenfeld Rieger Syndrome with Congenital Glaucoma

BACKGROUND

Anterior segment dysgenesis (ASD) disorders are a group of clinically and genetically heterogeneous phenotypes in which frequently cornea, iris, and lens are affected. This study aimed to identify novel mutations in PAX6, PITX2 and FOXC1 in families with anterior segment dysgenesis disorders.

METHODS

We studied 14 Pakistani and one Mexican family with Axenfeld Rieger syndrome (ARS; n = 10) or aniridia (n = 5). All affected and unaffected family members underwent full ophthalmologic and general examinations. Total genomic DNA was isolated from peripheral blood. PCR and Sanger sequencing were performed for the exons and intron-exon boundaries of the FOXC1, PAX6, and PITX2 genes.

RESULTS

Mutations were identified in five of the 15 probands; four variants were novel and one variant was described previously. A novel de novo variant (c.225C>A; p.Tyr75*) was identified in the PAX6 gene in two unrelated probands with aniridia. In addition, a known variant (c.649C>T; p.Arg217*) in PAX6 segregated in a family with aniridia. In the FOXC1 gene, a novel heterozygous variant (c.454T>C; p.Trp152Arg) segregated with the disease in a Mexican family with ARS. A novel homozygous variant (c.92_100del; p.Ala31_Ala33del) in the FOXC1 gene segregated in a Pakistani family with ARS and congenital glaucoma.

CONCLUSIONS

Our study expands the mutation spectrum of the PAX6 and FOXC1 genes in individuals with anterior segment dysgenesis disorders. In addition, our study suggests that FOXC1 mutations, besides typical autosomal dominant ARS, can also cause ARS with congenital glaucoma through an autosomal recessive inheritance pattern. Our results thus expand the disease spectrum of FOXC1, and may lead to a better understanding of the role of FOXC1 in development.

Foxc1 and Foxc2 deletion causes abnormal lymphangiogenesis and correlates with ERK hyperactivation

The lymphatic vasculature is essential for maintaining interstitial fluid homeostasis, and dysfunctional lymphangiogenesis contributes to various pathological processes, including inflammatory disease and tumor metastasis. Mutations in FOXC2 are dominantly associated with late-onset lymphedema; however, the precise role of FOXC2 and a closely related factor, FOXC1, in the lymphatic system remains largely unknown. Here we identified a molecular cascade by which FOXC1 and FOXC2 regulate ERK signaling in lymphatic vessel growth. In mice, lymphatic endothelial cell-specific (LEC-specific) deletion of Foxc1, Foxc2, or both resulted in increased LEC proliferation, enlarged lymphatic vessels, and abnormal lymphatic vessel morphogenesis. Compared with LECs from control animals, LECs from mice lacking both Foxc1 and Foxc2 exhibited aberrant expression of Ras regulators, and embryos with LEC-specific deletion of Foxc1 and Foxc2, alone or in combination, exhibited ERK hyperactivation. Pharmacological ERK inhibition in utero abolished the abnormally enlarged lymphatic vessels in FOXC-deficient embryos. Together, these results identify FOXC1 and FOXC2 as essential regulators of lymphangiogenesis and indicate a new potential mechanistic basis for lymphatic-associated diseases.

Conditional deletion of AP-2β in mouse cranial neural crest results in anterior segment dysgenesis and early-onset glaucoma

Anterior segment dysgenesis (ASD) encompasses a group of developmental disorders in which a closed angle phenotype in the anterior chamber of the eye can occur and 50% of patients develop glaucoma. Many ASDs are thought to involve an inappropriate patterning and migration of the periocular mesenchyme (POM), which is derived from cranial neural crest cells (NCCs) and mesoderm. Although, the mechanism of this disruption is not well understood, a number of transcriptional regulatory molecules have previously been implicated in ASDs. Here, we investigate the function of the transcription factor AP-2β, encoded by Tfap2b, which is expressed in NCCs and their derivatives. Wnt1-Cre-mediated conditional deletion of Tfap2b in NCCs resulted in post-natal ocular defects typified by opacity. Histological data revealed that the conditional AP-2β NCC knockout (KO) mutants exhibited dysgenesis of multiple structures in the anterior segment of the eye including defects in the corneal endothelium, corneal stroma, ciliary body and disruption in the iridocorneal angle with adherence of the iris to the cornea. We further show that this phenotype leads to a significant increase in intraocular pressure and a subsequent loss of retinal ganglion cells and optic nerve degeneration, features indicative of glaucoma. Overall, our findings demonstrate that AP-2β is required in the POM for normal development of the anterior segment of the eye and that the AP-2β NCC KO mice might serve as a new and exciting model of ASD and glaucoma that is fully penetrant and with early post-natal onset.

Summary: Tissue-specific deletion of transcription factor AP-2β in the neural-crest-derived periocular mesenchyme generates a novel model of anterior segment dysgenesis and early onset glaucoma in mice.

Characterization of Kidney and Skeleton Phenotypes of Mice Double Heterozygous for Foxc1 and Foxc2

Foxc1 and Foxc2 play key roles in mouse development. Foxc1 mutant mice develop duplex kidneys with double ureters, and lack calvarial and sternal bones. Foxc2 null mice have been reported to have glomerular abnormalities in the kidney and axial skeletal anomalies. Expression patterns of Foxc1 and Foxc2 overlap extensively and are believed to have interactive roles. However, cooperative roles of these factors in glomerular and skeletal development are unknown. Therefore, we examined the kidneys and skeleton of mice that were double heterozygous for Foxc1 and Foxc2. Double heterozygotes were generated by mating single heterozygotes for Foxc1 and Foxc2. Newborn double heterozygous mice showed many anomalies in the kidney and urinary tract resembling Foxc1 phenotypes, including duplex kidneys, double ureters, hydronephrosis and mega-ureter. Some mice had hydronephrosis alone. In addition to these macroscopic anomalies, some mice had abnormal glomeruli and disorganized glomerular capillaries observed in Foxc2 phenotypes. Interestingly, these mice also showed glomerular cysts not observed in the single-gene knockout of either Foxc1 or Foxc2 but observed in conditional knockout of Foxc2 in the kidney. Serial section analysis revealed that all cystic glomeruli were connected to proximal tubules, precluding the possibility of atubular glomeruli resulting in cyst formation. Dorsally opened vertebral arches and malformations of sternal bones in the double heterozygotes were phenotypes similar to Foxc1 null mice. Absent or split vertebral bodies in the double heterozygotes were phenotypes similar to Foxc2 null mice, whilst hydrocephalus noted in the Foxc1 phenotype was not observed. Thus, Foxc1 and Foxc2 have a role in kidney and axial skeleton development. These transcription factors might interact in the regulation of the embryogenesis of these organs.

Wholemount imaging reveals abnormalities of the aqueous outflow pathway and corneal vascularity in Foxc1 and Bmp4 heterozygous mice

Mutations in the FOXC1/Foxc1 gene in humans and mice and Bmp4 in mice are associated with congenital anterior segment dysgenesis (ASD) and the development of the aqueous outflow structures throughout the limbus. The aim of this study was to advance our understanding of anterior segment abnormalities in mouse models of ASD using a 3-D imaging approach. Holistic imaging information combined with quantitative measurements were carried out on PECAM-1 stained individual components of the aqueous outflow vessels and corneal vasculature of Foxc1(+/-) on the C57BL/6Jx129 and ICR backgrounds, Bmp4(+/-) ICR mice, and wildtype mice from each background. In both wildtype and heterozygotes, singular, bifurcated and plexus forms of Schlemm's canal were noted. Of note, missing portions of the canal were seen in the heterozygous groups but not in wildtype animals. In general, we found the number of collector channels to be reduced in both heterozygotes. Lastly, we found a significant increase in the complexity of the corneal arcades and their penetration into the cornea in heterozygotes as compared with wild types. In conclusion, our 3-D imaging studies have revealed a more complex arrangement of both the aqueous vessels and corneal arcades in Foxc1(+/-) and Bmp4(+/-) heterozygotes, and further advance our understanding of how such abnormalities could impact on IOP and the aetiology of glaucoma.

FGF2 mediates hepatic progenitor cell formation during human pluripotent stem cell differentiation by inducing the WNT antagonist NKD1

Twaroski et al. identified naked cuticle homolog 1 (NKD1) as being directly regulated by FGFR activity during the transition from endoderm to hepatic progenitor cell. Loss of NKD1 suppresses the formation of hepatic progenitor cells from human induced pluripotent stem cells, and this phenotype can be rescued by using a pharmacological antagonist of canonical WNT signaling.

Fibroblast growth factors (FGFs) are required to specify hepatic fate within the definitive endoderm through activation of the FGF receptors (FGFRs). While the signaling pathways involved in hepatic specification are well understood, the mechanisms through which FGFs induce hepatic character within the endoderm are ill defined. Here we report the identification of genes whose expression is directly regulated by FGFR activity during the transition from endoderm to hepatic progenitor cell. The FGFR immediate early genes that were identified include those encoding transcription factors, growth factors, and signaling molecules. One of these immediate early genes encodes naked cuticle homolog 1 (NKD1), which is a repressor of canonical WNT (wingless-type MMTV integration site) signaling. We show that loss of NKD1 suppresses the formation of hepatic progenitor cells from human induced pluripotent stem cells and that this phenotype can be rescued by using a pharmacological antagonist of canonical WNT signaling. We conclude that FGF specifies hepatic fate at least in large part by inducing expression of NKD1 to transiently suppress the canonical WNT pathway.

AP-2β Is a Downstream Effector of PITX2 Required to Specify Endothelium and Establish Angiogenic Privilege During Corneal Development

PURPOSE

The homeodomain transcription factor, PITX2, is at the apex of a genetic pathway required for corneal development, but the critical effector genes regulated by the PITX2 remain unknown. The purpose of this study was to discover and validate PITX2-dependent mechanisms required for specifying cell lineages and establishing angiogenic privilege within the developing cornea.

METHODS

Microarrays were used to compare gene expression in corneas isolated from temporal Pitx2 knockout embryos and control littermates. Quantitative RT-PCR and immunohistochemistry was used to further validate Tfap2b expression differences in Pitx2 knockout versus control corneas. In situ hybridization and protein immunohistochemistry were used to assay eyes of a Tfap2b allelic series of embryos to identify differentiated cellular lineages in the cornea, blood vessel endothelium, or lymphatic vessel endothelium.

RESULTS

We show that PITX2 is required for the expression of Tfap2b, encoding the AP-2β transcription factor, in the neural crest during corneal development. Markers of differentiated corneal epithelium and stroma are expressed in the absence of AP-2β. In contrast, markers of differentiated corneal endothelium are not expressed in the absence of AP-2β. Endomucin+ blood vessels are present throughout the developing corneal stroma in the absence of AP-2β, whereas LYVE1+ lymphatic vessels are not found.

CONCLUSIONS

The AP-2β transcription factor is an important effector of PITX2 function during corneal development, required for differentiation of corneal endothelium and establishment of angiogenic privilege. Unlike PITX2, AP-2β is not required for the early expression of available lineage specific markers for the corneal epithelium and stroma during embryogenesis, nor establishment of lymphangiogenic privilege. Therefore, additional PITX2-dependent factors likely regulate these latter processes during embryonic development. These results extend our understanding of the genetic mechanisms regulating cornea development.