The tumor suppressor gene Trp53 protects the mouse lens against posterior subcapsular cataracts and the BMP receptor Acvr1 acts as a tumor suppressor in the lens

Activin receptors in human cancer: Functions, mechanisms, and potential clinical applications

Activins are members of the transforming growth factor-β (TGF-β) superfamily and act as key regulators in various physiological processes, such as follicle and embryonic development, as well as in multiple human diseases, including cancer. They have been established to signal through three type I and two type II serine/threonine kinase receptors, which, upon ligand binding, form a final signal-transducing receptor complex that activates downstream signaling and governs gene expression. Recent research highlighted the dysregulation of the expression or activity of activin receptors in multiple human cancers and their critical involvement in cancer progression. Furthermore, expression levels of activin receptors have been associated with clinicopathological features and patient outcomes across different cancers. However, there is currently a paucity of comprehensive systematic reviews of activin receptors in cancer. Thus, this review aimed to consolidate existing knowledge concerning activin receptors, with a primary emphasis on their signaling cascade and emerging biological functions, regulatory mechanisms, and potential clinical applications in human cancers in order to provide novel perspectives on cancer prognosis and targeted therapy.

Noncancer Effects of Ionizing Radiation Exposure on the Eye, the Circulatory System and beyond: Developments made since the 2011 ICRP Statement on Tissue Reactions

For radiation protection purposes, noncancer effects with a threshold-type dose-response relationship have been classified as tissue reactions (formerly called nonstochastic or deterministic effects), and equivalent dose limits aim to prevent occurrence of such tissue reactions. Accumulating evidence demonstrates increased risks for several late occurring noncancer effects at doses and dose rates much lower than previously considered. In 2011, the International Commission on Radiological Protection (ICRP) issued a statement on tissue reactions to recommend a threshold of 0.5 Gy to the lens of the eye for cataracts and to the heart and brain for diseases of the circulatory system (DCS), independent of dose rate. Literature published thereafter continues to provide updated knowledge. Increased risks for cataracts below 0.5 Gy have been reported in several cohorts (e.g., including in those receiving protracted or chronic exposures). A dose threshold for cataracts is less evident with longer follow-up, with limited evidence available for risk of cataract removal surgery. There is emerging evidence for risk of normal-tension glaucoma and diabetic retinopathy, but the long-held tenet that the lens represents among the most radiosensitive tissues in the eye and in the body seems to remain unchanged. For DCS, increased risks have been reported in various cohorts, but the existence or otherwise of a dose threshold is unclear. The level of risk is less uncertain at lower dose and lower dose rate, with the possibility that risk per unit dose is greater at lower doses and dose rates. Target organs and tissues for DCS are also unknown, but may include heart, large blood vessels and kidneys. Identification of potential factors (e.g., sex, age, lifestyle factors, coexposures, comorbidities, genetics and epigenetics) that may modify radiation risk of cataracts and DCS would be important. Other noncancer effects on the radar include neurological effects (e.g., Parkinson's disease, Alzheimer's disease and dementia) of which elevated risk has increasingly been reported. These late occurring noncancer effects tend to deviate from the definition of tissue reactions, necessitating more scientific developments to reconsider the radiation effect classification system and risk management. This paper gives an overview of historical developments made in ICRP prior to the 2011 statement and an update on relevant developments made since the 2011 ICRP statement.

Multi-omics therapeutic perspective on ACVR1 gene: from genetic alterations to potential targeting

Activin A receptor type I (ACVR1), a transmembrane serine/threonine kinase, belongs to the transforming growth factor-β superfamily, which signals via phosphorylating the downstream effectors and SMAD transcription factors. Its central role in several biological processes and intracellular signaling is well known. Genetic variation in ACVR1 has been associated with a rare disease, fibrodysplasia ossificans progressive, and its somatic alteration is reported in rare cancer diffuse intrinsic pontine glioma. Furthermore, altered expression or variation of ACVR1 is associated with multiple pathologies such as polycystic ovary syndrome, congenital heart defects, diffuse idiopathic skeletal hyperostosis, posterior fossa ependymoma and other malignancies. Recent advancements have witnessed ACVR1 as a potential pharmacological target, and divergent promising approaches for its therapeutic targeting have been explored. This review highlights the structural and functional characteristics of receptor ACVR1, associated signaling pathways, genetic variants in several diseases and cancers, protein-protein interaction, gene expression, regulatory miRNA prediction and potential therapeutic targeting approaches. The comprehensive knowledge will offer new horizons and insights into future strategies harnessing its therapeutic potential.

ATM and TP53 Polymorphisms Modified Susceptibility to Radiation-Induced Lens Opacity in Natural High Background Radiation Area, China

Purpose: A population-based case-control study was conducted in Yangjiang and Enping areas in South China to assess whether the risk of lens opacity induced by natural high background radiation exposure is modulated by polymorphisms of ATM and TP53.Materials and methods: A total of 133 cases who were diagnosed with cortical and posterior subcapsular (PSC) opacity were recruited, and 419 healthy controls were selected through counter-matching in terms of radiation status. Genomic DNA from all the participants was genotyped with the Illumina platform for four single nucleotide polymorphisms of ATM (rs189037, rs373759, and rs4585) and TP53 (rs1042522). The cumulative lens dose received during the entire life was estimated based on annual indoor and outdoor radiation doses and gender- and age-specific occupancy factors. Non-conditional logistic regression was performed to calculate odds ratio (OR) and 95% confidence intervals (95% CI).Results: ATM rs189037 and TP53 rs1042522 were significantly related to cortical and PSC opacity. The risk of opacity was higher when individuals carried the A allele of ATM rs189037 and C allele of TP53 rs1042522, compared with GG genotype. ATM rs189037 A allele carriers (AG/AA) and TP53 rs1042522 C allele carriers (CG/CC) combined with a cumulative lens dose of 100 mGy or higher showed statistically significant opacity risks (OR =5.51, 95% CI: 1.47-20.66; OR =2.69, 95% CI: 1.10-6.60).Conclusion: The A allele of ATM rs189037 and C allele of TP53 rs1042522 increase the risk of lens opacity induced by radiation. These polymorphisms in ATM and TP53 might modify the risk of cortical and PSC opacity induced by chronic and prolonged low-dose radiation.

The roles of mouse double minute 2 (MDM2) oncoprotein in ocular diseases: A review

Mouse double minute 2 (MDM2), an E3 ubiquitin ligase and the primary negative regulator of the tumor suppressor p53, cooperates with its structural homolog MDM4/MDMX to control intracellular p53 level. In turn, overexpression of p53 upregulates and forms an autoregulatory feedback loop with MDM2. The MDM2-p53 axis plays a pivotal role in modulating cell cycle control and apoptosis. MDM2 itself is regulated by the PI3K-AKT and RB-E2F-ARF pathways. While amplification of the MDM2 gene or overexpression of MDM2 (due to MDM2 SNP T309G, for instance) is associated with various malignancies, numerous studies have shown that MDM2/p53 alterations may also play a part in the pathogenetic process of certain ocular disorders (Fig. 1). These include cancers (retinoblastoma, uveal melanoma), fibrocellular proliferative diseases (proliferative vitreoretinopathy, pterygium), neovascular diseases, degenerative diseases (cataract, primary open-angle glaucoma, age-related macular degeneration) and infectious/inflammatory diseases (trachoma, uveitis). In addition, MDM2 is implicated in retinogenesis and regeneration after optic nerve injury. Anti-MDM2 therapy has shown potential as a novel approach to treating these diseases. Despite major safety concerns, there are high expectations for the clinical value of reformative MDM2 inhibitors. This review summarizes important findings about the role of MDM2 in ocular pathologies and provides an overview of recent advances in treating these diseases with anti-MDM2 therapies.

Upregulation of oncogene Activin A receptor type I by Helicobacter pylori infection promotes gastric intestinal metaplasia via regulating CDX2

BACKGROUND

Activin A receptor type I (ACVR1) is involved in tumorigenesis. However, the underlying molecular mechanisms of ACVR1 in gastric cancer (GC) and its association with Helicobacter pylori remained unclear.

MATERIALS AND METHODS

The Cancer Genome Atlas (TCGA) and Gene Expression Profiling Interactive Analysis (GEPIA) database were utilized to explore the ACVR1 expression in GC and normal control and its association with survival. The ACVR1 was knocked out using CRISPR/Cas-9; RNA sequencing analysis was performed in AGS cells with ACVR1 knockout and normal control. Functional experiments (CCK-8, colony-forming, and transwell assays) were conducted to demonstrate the role of ACVR1 in cell proliferation, invasion, and metastasis. H. pylori-infected C57/BL6 models were established. ACVR1, p-Smad1/5, and CDX2 were detected in AGS cells cocultured with H. pylori strains. The CDX2 and key elements of BMP signaling pathway were detected in AGS cells with ACVR1 knockout and normal control. In addition, Immunohistochemistry was performed to detect the ACVR1 and CDX2 expression in gastric samples.

RESULTS

ACVR1 expression was higher in GC than normal control from TCGA, GEPIA, and samples collected from our hospital (p < 0.05). ACVR1 promoted cell proliferation, migration, and invasion in vitro. Both cagA⁺ and cagA^- H. pylori could upregulate the expression ACVR1 (p < 0.05). Downregulation of ACVR1 inhibited the H. pylori-induced cell proliferation, migration, and invasion (p < 0.05). H. pylori increased the expression of p-Smad 1/5 and CDX2. The CDX2 and key elements of BMP signaling pathway were downregulated in AGS cells with ACVR1 knockout. ACVR1 and CDX2 were upregulated in the stage of intestinal metaplasia (IM). Moreover, ACVR1 and CDX2 expressions were higher in H. pylori-positive group than H. pylori-negative group (p < 0.05).

CONCLUSION

Our data indicate that H. pylori infection increases ACVR1 expression, promoting gastric IM via regulating CDX2, which is an essential step in H. pylori carcinogenesis.

Insights into Bone Morphogenetic Protein-(BMP-) Signaling in Ocular Lens Biology and Pathology

Bone morphogenetic proteins (BMPs) are a diverse class of growth factors that belong to the transforming growth factor-beta (TGFβ) superfamily. Although originally discovered to possess osteogenic properties, BMPs have since been identified as critical regulators of many biological processes, including cell-fate determination, cell proliferation, differentiation and morphogenesis, throughout the body. In the ocular lens, BMPs are important in orchestrating fundamental developmental processes such as induction of lens morphogenesis, and specialized differentiation of its fiber cells. Moreover, BMPs have been reported to facilitate regeneration of the lens, as well as abrogate pathological processes such as TGFβ-induced epithelial-mesenchymal transition (EMT) and apoptosis. In this review, we summarize recent insights in this topic and discuss the complexities of BMP-signaling including the role of individual BMP ligands, receptors, extracellular antagonists and cross-talk between canonical and non-canonical BMP-signaling cascades in the lens. By understanding the molecular mechanisms underlying BMP activity, we can advance their potential therapeutic role in cataract prevention and lens regeneration.

Leukocyte chemotactic receptor Fpr1 protects against aging-related posterior subcapsular cataract formation

Cataracts are a common consequence of aging; however, pathogenesis remains poorly understood. Here, we observed that after 3 months of age mice lacking the G protein-coupled leukocyte chemotactic receptor Fpr1 (N-formyl peptide receptor 1) began to develop bilateral posterior subcapsular cataracts that progressed to lens rupture and severe degeneration, without evidence of either systemic or local ocular infection or inflammation. Consistent with this, Fpr1 was detected in both mouse and human lens in primary lens epithelial cells (LECs), the only cell type present in the lens; however, expression was confined to subcapsular LECs located along the anterior hemispheric surface. To maximize translucency, LECs at the equator proliferate and migrate posteriorly, then differentiate into lens fiber cells by nonclassical apoptotic signaling, which results in loss of nuclei and other organelles, including mitochondria which are a rich source of endogenous N-formyl peptides. In this regard, denucleation and posterior migration of LECs were abnormal in lenses from Fpr1-/- mice, and direct stimulation of LECs with the prototypic N-formyl peptide agonist fMLF promoted apoptosis. Thus, Fpr1 is repurposed beyond its immunoregulatory role in leukocytes to protect against cataract formation and lens degeneration during aging.

Association of rs12997 variant in the ACVR1 gene: a member of bone morphogenic protein signaling pathway with primary open-angle glaucoma in a Saudi cohort

We investigated the association between variants rs12997 in activin A receptor type I (ACVR1) and rs1043784 in BMP6 located in the 3' untranslated region, and primary open-angle glaucoma (POAG). The retrospective case-control study used TaqMan real-time PCR assay to genotype 400 subjects, including 150 patients with POAG and 250 controls. The minor 'G' allele of rs12997 in ACVR1 showed significant association with POAG (p=0.027, OR=1.39, 95% CI=1.03 to 1.87). Likewise, rs12997 genotypes showed moderate association with POAG in recessive (p=0.048, OR=1.80, 95% CI=1.01 to 3.20) and log-additive models (p=0.030, OR=1.39, 95% CI=1.03 to 1.87), but did not survive Bonferroni correction. Rs1043784 in BMP6 showed no associations. Furthermore, rs12997 G/G genotype significantly (p=0.033) increased the risk of POAG (twofolds) independent of age, sex and rs1043784 genotypes in regression analysis. However, clinical variables such as intraocular pressure and cup/disc ratio showed no association with both the polymorphisms. To conclude, the study shows a modest association between rs12997 in the ACVR1 gene, a member of the bone morphogenic protein signaling pathway and POAG. However, the results need further replication in large population-based cohorts and different ethnicities to validate its role as an important genetic biomarker.

Association analysis of polymorphisms rs12997 in ACVR1 and rs1043784 in BMP6 genes involved in bone morphogenic protein signaling pathway in primary angle-closure and pseudoexfoliation glaucoma patients of Saudi origin

Background

Glaucoma is a polygenic neurodegenerative disease and the second most common cause of blindness in Saudi Arabia. To test the hypothesis that genetic variants in the genes involved in the bone morphogenic protein (BMP) signaling pathway may be associated with glaucoma, we investigated the association between 3′ untranslated region variants, rs12997 in ACVR1 and rs1043784 in BMP6, and primary angle-closure glaucoma (PACG) and pseudoexfoliation glaucoma (PXG).

Methods

In a case-control study, TaqMan® real-time PCR-based genotyping was done in 444 subjects consisting of 250 controls, 101 PACG and 95 PXG cases, and tested for genetic association with glaucoma-types and other clinical phenotypes.

Results

Rs12997[G] allele in ACVR1 exhibited significant 2-fold increased risk of PACG (p = 0.005) in women but not in men. Similarly, genotype analysis also showed that subjects carrying rs12997[G/G] genotype were at > 2-fold risk of PACG that remained significant after adjustment for age, sex, and Bonferroni correction in the recessive model. Furthermore, this effect was also significant in women only. In PXG, the rs12997[G/G] genotype showed a significant trend towards increased risk of the disease (OR = 2.04, 95% CI = 0.99–4.18, p = 0.049) but did not survive the Bonferroni correction. Regression analysis showed that rs12997[G/G] genotype was a significant predictor of PACG independent of age, sex, and rs1043784 genotypes. Likewise, age and rs12997[G/G] genotype showed significant effect on PXG outcome. The rs12997[A/G] genotype showed significant association with cup/disc ratio as compared to wild-type (p = 0.005) in PXG. Genotype and allele frequencies of rs1043784 in BMP6 did not show any significant association either with PACG or PXG.

Conclusions

Our results suggest that the polymorphism rs12997 in the ACVR1 gene involved in the BMP signaling pathway is significantly associated with PACG and PXG in a Saudi cohort. This is the first study to associate this variant/gene with PACG and PXG. However, further studies would be needed to replicate these findings in a large population-based cohort.

Reduced NGF Level Promotes Epithelial-Mesenchymal Transition in Human Lens Epithelial Cells Exposed to High Dexamethasone Concentrations

Purpose: To investigate the protective effects of nerve growth factor (NGF) against steroid-induced cataract formation in dexamethasone (Dex)-treated human lens epithelial B-3 (HLE-B3) cells and the possible molecular mechanisms underlying this protection.Materials and Methods: HLE-B3 cells were treated with Dex, and cell viability was assessed using the Cell Counting Kit-8 (CCK-8) assay. The levels of expression of NGF, fibronectin, α-smooth muscle actin (α-SMA), and E-cadherin mRNAs were measured by real-time quantitative polymerase chain reaction (qPCR), and the levels of NGF, fibronectin, α-SMA, E-cadherin, tropomyosin receptor kinase A (TrkA), and Akt proteins were measured by Western blot analysis. Gene expression profiles of growth factors in Dex-treated HLE-B3 cells were determined by PCR arrays. In addition, anterior capsule tissue was obtained during cataract surgery, and the specimens were also examined expressions of NGF.Results: NGF was expressed in HLE-B3 cells and also in lens epithelial cells of anterior lens capsules. Dex treatment of HLE-B3 cells increased their expression of epithelial-mesenchymal transition (EMT) markers and migration activity, while markedly downregulating the expression of NGF. NGF treatment significantly reduced the expression of α-SMA and fibronectin, as well as cell proliferation. The decreased phosphorylation of p38 MAPK and Akt induced by Dex treatment was significantly reversed by treatment with NGF.Conclusion: NGF/TrkA may repress EMT by targeting the p38 MAPK and pAkt pathways in Dex-treated HLE-B3 cells. NGF may be a novel therapeutic target for patients with steroid-induced cataract.

ACVR1 Function in Health and Disease

Activin A receptor type I (ACVR1) encodes for a bone morphogenetic protein type I receptor of the TGFβ receptor superfamily. It is involved in a wide variety of biological processes, including bone, heart, cartilage, nervous, and reproductive system development and regulation. Moreover, ACVR1 has been extensively studied for its causal role in fibrodysplasia ossificans progressiva (FOP), a rare genetic disorder characterised by progressive heterotopic ossification. ACVR1 is linked to different pathologies, including cardiac malformations and alterations in the reproductive system. More recently, ACVR1 has been experimentally validated as a cancer driver gene in diffuse intrinsic pontine glioma (DIPG), a malignant childhood brainstem glioma, and its function is being studied in other cancer types. Here, we review ACVR1 receptor function and signalling in physiological and pathological processes and its regulation according to cell type and mutational status. Learning from different functions and alterations linked to ACVR1 is a key step in the development of interdisciplinary research towards the identification of novel treatments for these pathologies.

Identification of Novel Gata3 Distal Enhancers Active in Mouse Embryonic Lens

BACKGROUND

The tissue-specific transcriptional programs during normal development require tight control by distal cis-regulatory elements, such as enhancers, with specific DNA sequences recognized by transcription factors, coactivators, and chromatin remodeling enzymes. Gata3 is a sequence-specific DNA-binding transcription factor that regulates formation of multiple tissues and organs, including inner ear, lens, mammary gland, T-cells, urogenital system, and thyroid gland. In the eye, Gata3 has a highly restricted expression domain in the posterior part of the lens vesicle; however, the underlying regulatory mechanisms are unknown.

RESULTS

Here we describe the identification of a novel bipartite Gata3 lens-specific enhancer located ∼18 kb upstream from its transcriptional start site. We also found that a 5-kb Gata3 promoter possesses low activity in the lens. The bipartite enhancer contains arrays of AP-1, Ets-, and Smad1/5-binding sites as well as binding sites for lens-associated DNA-binding factors. Transient transfection studies of the promoter with the bipartite enhancer showed enhanced activation by BMP4 and FGF2.

CONCLUSIONS

These studies identify a novel distal enhancer of Gata3 with high activity in lens and indicate that BMP and FGF signaling can up-regulate expression of Gata3 in differentiating lens fiber cells through the identified Gata3 enhancer and promoter elements. Developmental Dynamics 247:1186-1198, 2018. © 2018 The Authors. Developmental Dynamics published by Wiley Periodicals, Inc. on behalf of American Association of Anatomists.

Lifetime study in mice after acute low-dose ionizing radiation: a multifactorial study with special focus on cataract risk

Because of the increasing application of ionizing radiation in medicine, quantitative data on effects of low-dose radiation are needed to optimize radiation protection, particularly with respect to cataract development. Using mice as mammalian animal model, we applied a single dose of 0, 0.063, 0.125 and 0.5 Gy at 10 weeks of age, determined lens opacities for up to 2 years and compared it with overall survival, cytogenetic alterations and cancer development. The highest dose was significantly associated with increased body weight and reduced survival rate. Chromosomal aberrations in bone marrow cells showed a dose-dependent increase 12 months after irradiation. Pathological screening indicated a dose-dependent risk for several types of tumors. Scheimpflug imaging of the lens revealed a significant dose-dependent effect of 1% of lens opacity. Comparison of different biological end points demonstrated long-term effects of low-dose irradiation for several biological end points.

HSF4 regulates lens fiber cell differentiation by activating p53 and its downstream regulators

Cataract refers to opacities of the lens that impede the passage of light. Mutations in heat shock transcription factor 4 (HSF4) have been associated with cataract; however, the mechanisms regarding how mutations in HSF4 cause cataract are still obscure. In this study, we generated an hsf4 knockout zebrafish model using TALEN technology. The mutant zebrafish developed an early-onset cataract with multiple developmental defects in lens. The epithelial cells of the lens were overproliferated, resulting in the overabundance of lens fiber cells in hsf4^null zebrafish lens. Consequently, the arrangement of the lens fiber cells became more disordered and irregular with age. More importantly, the terminal differentiation of the lens fiber cell was interrupted as the organelles cannot be cleaved in due time. In the cultured human lens epithelial cells, HSF4 could stabilize and retain p53 in the nucleus to activate its target genes such as fas cell surface death receptor (Fas) and Bcl-2-associated X apoptosis regulator (Bax). In the hsf4^null fish, both p53 and activated-caspase3 were significantly decreased. Combined with the finding that the denucleation defect could be partially rescued through microinjection of p53, fas and bax mRNA into the mutant embryos, we directly proved that HSF4 promotes lens fiber cell differentiation by activating p53 and its downstream regulators. The data we presented suggest that apoptosis-related genes are involved in the lens fiber cell differentiation. Our finding that HSF4 functions in the upstream to activate these genes highlighted the new regulatory modes of HSF4 in the terminal differentiation of lens fiber cell.

Signaling and Gene Regulatory Networks in Mammalian Lens Development

Ocular lens development represents an advantageous system in which to study regulatory mechanisms governing cell fate decisions, extracellular signaling, cell and tissue organization, and the underlying gene regulatory networks. Spatiotemporally regulated domains of BMP, FGF, and other signaling molecules in late gastrula-early neurula stage embryos generate the border region between the neural plate and non-neural ectoderm from which multiple cell types, including lens progenitor cells, emerge and undergo initial tissue formation. Extracellular signaling and DNA-binding transcription factors govern lens and optic cup morphogenesis. Pax6, c-Maf, Hsf4, Prox1, Sox1, and a few additional factors regulate the expression of the lens structural proteins, the crystallins. Extensive crosstalk between a diverse array of signaling pathways controls the complexity and order of lens morphogenetic processes and lens transparency.

Ionizing radiation response of primary normal human lens epithelial cells

Whilst the cataractogenic potential of ionizing radiation has been known for over the past 120 years, little is known about radiation responses of lens cells. Our previous work was the first to evaluate the radiosensitivity of lens cells with the clonogenic assay, documenting that the survival of HLEC1 human lens epithelial cells is comparable to that of WI-38 human lung fibroblasts. Moreover, HLEC1 cells were found to contain subsets where irradiation stimulates proliferation or facilitates formation of abortive colonies with fewer cells than human fibroblasts. This study aims to gain insights into these mechanisms. Irradiation of HLEC1 cells with 10% survival dose caused a growth delay but did not reduce viability. HLEC1 cells at high cumulative population doubling level were more susceptible to radiogenic premature senescence than WI-38 cells. Concerning p53 binding protein 1 (53BP1) foci, HLEC1 cells harbored less spontaneous foci but more radiogenic foci than in WI-38 cells, and the focus number returned to spontaneous levels within 48 h postirradiation both in HLEC1 and WI-38. The chemical inhibition of DNA repair kinases ataxia telangiectasia mutated, DNA-dependent protein kinase or both delayed and attenuated the appearance and disappearance of radiogenic 53BP1 foci, increased radiogenic premature senescence and enhanced clonogenic inactivation. The DNA microarray analysis suggested both radiogenic stimulation and inhibition of cell proliferation. Treatment with conditioned medium from irradiated cells did not change growth and the plating efficiency of nonirradiated cells. These results partially explain mechanisms of our previous observations, such that unrepaired or incompletely repaired DNA damage causes a growth delay in a subset of HLEC1 cells without changing viability through induction of premature senescence, thereby leading to clonogenic inactivation, but that growth is stimulated in another subset via as yet unidentified mechanisms, warranting further studies.

Transforming Growth Factor β Superfamily Signaling in Development of Colorectal Cancer

Transforming growth factor (TGF)-β cytokines signal via a complex network of pathways to regulate proliferation, differentiation, adhesion, migration, and other functions in many cell types. A high percentage of colorectal tumors contain mutations that disrupt TGF-β family member signaling. We review how TGF-β family member signaling is altered during development of colorectal cancer, models of study, interaction of pathways, and potential therapeutic strategies.

Chromatin remodeling enzyme Snf2h regulates embryonic lens differentiation and denucleation

Ocular lens morphogenesis is a model for investigating mechanisms of cellular differentiation, spatial and temporal gene expression control, and chromatin regulation. Brg1 (Smarca4) and Snf2h (Smarca5) are catalytic subunits of distinct ATP-dependent chromatin remodeling complexes implicated in transcriptional regulation. Previous studies have shown that Brg1 regulates both lens fiber cell differentiation and organized degradation of their nuclei (denucleation). Here, we employed a conditional Snf2h(flox) mouse model to probe the cellular and molecular mechanisms of lens formation. Depletion of Snf2h induces premature and expanded differentiation of lens precursor cells forming the lens vesicle, implicating Snf2h as a key regulator of lens vesicle polarity through spatial control of Prox1, Jag1, p27(Kip1) (Cdkn1b) and p57(Kip2) (Cdkn1c) gene expression. The abnormal Snf2h(-/-) fiber cells also retain their nuclei. RNA profiling of Snf2h(-/) (-) and Brg1(-/-) eyes revealed differences in multiple transcripts, including prominent downregulation of those encoding Hsf4 and DNase IIβ, which are implicated in the denucleation process. In summary, our data suggest that Snf2h is essential for the establishment of lens vesicle polarity, partitioning of prospective lens epithelial and fiber cell compartments, lens fiber cell differentiation, and lens fiber cell nuclear degradation.

Attenuation assessment of medical protective eyewear: the AVEN experience

The goal of this paper is to test the attenuation capability of seven models of protective eyewear used in routine clinical practice. Scattered radiation from a standard patient was simulated by using a water tank located over the treatment couch of a GE Innova 3100 x-ray angiography system. Seven protective eyewear models were tested using an anthropomorphic phantom mimicking the first operator. At each test, 4 thermoluminiscent dosimeters were placed on the phantom (respectively in front of the protective eyewear, under the eyewear, on the left earpiece and at chest level) in order to have an eyewear-independent reference. A test session without glasses was also acquired. Each model was tested with standard posterior-anterior (PA) projections and the two most common protective eyewear were tested using LAO90° and LAO45°CRA30° projections. A worst-case scenario was created to be sure of having an upper limit for the assessment of eyewear attenuation in routine clinical practice. In PA projections, the absolute attenuation value ranged between 71% and 81%, while relative attenuation between dose measured at eye lens and that measured at eyewear earpiece ranged from 67% to 85%. The slightly wider range was probably due to scatter radiation variability; anyway, differences are still included in the variable uncertainty of experimental measurements. It is worth noting that #3 eyewear model (the one without lateral protection) allows an attenuation similar to that of #5 eyewear model (with 0.5 mm lead lateral protection) in LAO90° and LAO45°CRA30° projections. Despite the experimental limitations, a description of the radiation properties of protective eyewear concerning radiation attenuation can be useful to rely on protection devices which can be used in routine clinical practice.

Concise Review: Patient-Specific Stem Cells to Interrogate Inherited Eye Disease

Heritable diseases of the retina are major causes of blindness worldwide. The recent success of gene augmentation trials for the treatment of RPE65-associated Leber congenital amaurosis has underscored the need for model systems that accurately recapitulate disease. How induced pluripotent stem cell technology is being used to confirm the pathogenesis of novel genetic variants, interrogate the pathophysiology of disease, and accelerate the development of patient-centered treatments is discussed.

Whether we are driving to work or spending time with loved ones, we depend on our sense of vision to interact with the world around us. Therefore, it is understandable why blindness for many is feared above death itself. Heritable diseases of the retina, such as glaucoma, age-related macular degeneration, and retinitis pigmentosa, are major causes of blindness worldwide. The recent success of gene augmentation trials for the treatment of RPE65-associated Leber congenital amaurosis has underscored the need for model systems that accurately recapitulate disease. With the advent of patient-specific induced pluripotent stem cells (iPSCs), researchers are now able to obtain disease-specific cell types that would otherwise be unavailable for molecular analysis. In the present review, we discuss how the iPSC technology is being used to confirm the pathogenesis of novel genetic variants, interrogate the pathophysiology of disease, and accelerate the development of patient-centered treatments.

Significance

Stem cell technology has created the opportunity to advance treatments for multiple forms of blindness. Researchers are now able to use a person’s cells to generate tissues found in the eye. This technology can be used to elucidate the genetic causes of disease and develop treatment strategies. In the present review, how stem cell technology is being used to interrogate the pathophysiology of eye disease and accelerate the development of patient-centered treatments is discussed.

The cellular and molecular mechanisms of vertebrate lens development

The ocular lens is a model system for understanding important aspects of embryonic development, such as cell specification and the spatiotemporally controlled formation of a three-dimensional structure. The lens, which is characterized by transparency, refraction and elasticity, is composed of a bulk mass of fiber cells attached to a sheet of lens epithelium. Although lens induction has been studied for over 100 years, recent findings have revealed a myriad of extracellular signaling pathways and gene regulatory networks, integrated and executed by the transcription factor Pax6, that are required for lens formation in vertebrates. This Review summarizes recent progress in the field, emphasizing the interplay between the diverse regulatory mechanisms employed to form lens progenitor and precursor cells and highlighting novel opportunities to fill gaps in our understanding of lens tissue morphogenesis.

Aberrant activation of p53 due to loss of MDM2 or MDMX causes early lens dysmorphogenesis

Although forming a heterodimer or heterooligomer is essential for MDM2 and MDMX to fully control p53 during early embryogenesis, deletion of either MDM2 or MDMX in specific tissues using the loxp-Cre system reveals phenotypic diversity during organ morphogenesis, which can be completely rescued by loss of p53, suggesting the spatiotemporal independence and specificity of the regulation of p53 by MDM2 and MDMX. In this study, we investigated the role of the MDM2-MDMX-p53 pathway in the developing lens that is a relatively independent region integrating cell proliferation, differentiation and apoptosis. Using the mice expressing Cre recombinase specifically in the lens epithelial cells (LECs) beginning at E9.5, we demonstrated that deletion of either MDM2 or MDMX induces apoptosis of LEC and reduces cell proliferation, resulting in lens developmental defect that finally progresses into aphakia. Specifically, the lens defect caused by MDM2 deletion was evident at E10, occurring earlier than that caused by MDMX deletion. These lens defects were completely rescued by loss of two alleles of p53, but not one allele of p53. These results demonstrate that both MDM2 and MDMX are required for monitoring p53 activity during lens development, and they may function independently or synergistically to control p53 and maintain normal lens morphogenesis.

Emerging issues in radiogenic cataracts and cardiovascular disease

In 2011, the International Commission on Radiological Protection issued a statement on tissue reactions (formerly termed non-stochastic or deterministic effects) to recommend lowering the threshold for cataracts and the occupational equivalent dose limit for the crystalline lens of the eye. Furthermore, this statement was the first to list circulatory disease (cardiovascular and cerebrovascular disease) as a health hazard of radiation exposure and to assign its threshold for the heart and brain. These changes have stimulated various discussions and may have impacts on some radiation workers, such as those in the medical sector. This paper considers emerging issues associated with cataracts and cardiovascular disease. For cataracts, topics dealt with herein include (i) the progressive nature, stochastic nature, target cells and trigger events of lens opacification, (ii) roles of lens protein denaturation, oxidative stress, calcium ions, tumor suppressors and DNA repair factors in cataractogenesis, (iii) dose rate effect, radiation weighting factor, and classification systems for cataracts, and (iv) estimation of the lens dose in clinical settings. Topics for cardiovascular disease include experimental animal models, relevant surrogate markers, latency period, target tissues, and roles of inflammation and cellular senescence. Future research needs are also discussed.

Ionizing irradiation not only inactivates clonogenic potential in primary normal human diploid lens epithelial cells but also stimulates cell proliferation in a subset of this population

Over the past century, ionizing radiation has been known to induce cataracts in the crystalline lens of the eye, but its mechanistic underpinnings remain incompletely understood. This study is the first to report the clonogenic survival of irradiated primary normal human lens epithelial cells and stimulation of its proliferation. Here we used two primary normal human cell strains: HLEC1 lens epithelial cells and WI-38 lung fibroblasts. Both strains were diploid, and a replicative lifespan was shorter in HLEC1 cells. The colony formation assay demonstrated that the clonogenic survival of both strains decreases similarly with increasing doses of X-rays. A difference in the survival between two strains was actually insignificant, although HLEC1 cells had the lower plating efficiency. This indicates that the same dose inactivates the same fraction of clonogenic cells in both strains. Intriguingly, irradiation enlarged the size of clonogenic colonies arising from HLEC1 cells in marked contrast to those from WI-38 cells. Such enhanced proliferation of clonogenic HLEC1 cells was significant at ≥2 Gy, and manifested as increments of ≤2.6 population doublings besides sham-irradiated controls. These results suggest that irradiation of HLEC1 cells not only inactivates clonogenic potential but also stimulates proliferation of surviving uniactivated clonogenic cells. Given that the lens is a closed system, the stimulated proliferation of lens epithelial cells may not be a homeostatic mechanism to compensate for their cell loss, but rather should be regarded as abnormal. This is because these findings are consistent with the early in vivo evidence documenting that irradiation induces excessive proliferation of rabbit lens epithelial cells and that suppression of lens epithelial cell divisions inhibits radiation cataractogenesis in frogs and rats. Thus, our in vitro model will be useful to evaluate the excessive proliferation of primary normal human lens epithelial cells that may underlie radiation cataractogenesis, warranting further investigations.

A genetic variant in microRNA target site of TGF-β signaling pathway increases the risk of colorectal cancer in a Chinese population

Evidence shows that single-nucleotide polymorphisms in microRNA (miRNA) target sites can create, destroy, or modify the miRNA/mRNA binding, therefore modulating gene expression and affecting cancer susceptibility. The transforming growth factor-β (TGF-β) signaling pathway plays a pivotal role in tumor initiation and progression. Intriguingly, recent advances of genome-wide association studies have identified multiple risk loci in this pathway to be associated with risk of colorectal cancer (CRC). To test the hypothesis that genetic variants in miRNA target sites in genes of the TGF-β signaling pathway may also be associated with CRC risk, we first systematically scanned the single-nucleotide polymorphisms (SNPs) in genes of TGF-β signaling pathway which potentially affect the miRNA/mRNA bindings. Through a series of filters, we narrowed down these candidates to four SNPs. Then, we conducted a case-control study with 600 CRC patients and 638 controls in Han Chinese population. We observed that compared with A carriers (AA + AG), the GG genotype of rs12997:ACVR1 is associated with a significantly higher risk of CRC (OR = 1.52, 95% confidence interval (95% CI) = 1.04-2.21, P = 0.031), particularly in nonsmokers with a higher OR of 1.63 (95% CI = 1.04-2.55, P = 0.032). Our study suggested that SNPs in miRNA target sites could contribute to the likelihood of CRC susceptibility and emphasized the important role of polymorphisms at miRNA-regulatory elements in carcinogenesis.

p53 E3 ubiquitin protein ligase homolog regulates p53 in vivo in the adult mouse eye lens

PURPOSE

p53 is a transcription factor that plays an important role in preventing cancer development. p53 participates in relevant aspects of cell biology, including apoptosis and cell cycle control and must be strictly regulated to maintain normal tissue homeostasis. p53 E3 ubiquitin protein ligase homolog (Mdm2) is an important negative regulator of p53. The purpose of this study was to determine if Mdm2 regulates p53 in vivo in the adult lens.

METHODS

We analyzed mice expressing human p53 transgene (Tgp53) selectively in the lens in the presence or absence of Mdm2. Mice with the required genotypes were obtained by crossing transgenic, mdm2 (+/-), and p53 (-/-) mice. Eye phenotype and lens histology and ultrastructure were analyzed in adult mice.

RESULTS

In a wild-type genetic background (mdm2 (+/+)), lens damage and microphthalmia were observed only in mice homozygous for Tgp53 ((t/t)). However, in an mdm2 null background, just one allele of Tgp53 (mdm2 (-/-)/Tgp53 (t/0) mice) was sufficient to cause lens damage and microphthalmia. Furthermore, Mdm2 in only one allele was sufficient to rescue these deleterious effects, since the mdm2 (+/-)/Tgp53 (t/0) mice had eye size and lens morphology similar to the control mice.

CONCLUSIONS

Mdm2 regulates p53 in the adult lens in vivo. This information may have relevance for analyzing normal and pathological conditions of the lens, and designing cancer therapies targeting Mdm2-p53 interaction.

Regulation of mouse lens maturation and gene expression by Krüppel-like factor 4

Conditional disruption of Klf4 in the surface ectoderm-derived tissues of the eye results in defective cornea, conjunctiva and the lens. This report describes the effects of disruption of Klf4 in the lens in greater detail. Expression of Klf4, first detected in the embryonic day-12 (E12) mouse lens, peaked at E16 and was decreased in later stages. Early embryonic disruption of Klf4 resulted in a smaller lens with cortical vacuolation and nuclear opacity. Microarray comparison of Klf4CN and WT lens transcriptomes revealed fewer changes in the E16.5 (59 increases, 20 decreases of >1.5-fold) than the PN56 Klf4CN lens (239 increases, 182 decreases of >2-fold). Klf4-target genes in the lens were distinct from those previously identified in the cornea, suggesting disparate functions for Klf4 in these functionally related tissues. Transcripts encoding different crystallins were down-regulated in the Klf4CN lens. Shsp/αB-crystallin promoter activity was stimulated upon co-transfection with pCI-Klf4. Mitochondrial density was significantly higher in the Klf4CN lens epithelial cells, consistent with mitochondrial dysfunction being the most significantly affected pathway within the PN56 Klf4CN lens. The Klf4CN lens contained elevated levels of Alox12 and Alox15 transcripts, less reduced glutathione (GSH) and more oxidized glutathione (GSSG) than the WT, suggesting that it is oxidatively stressed. Although the expression of 2087 genes was modulated during WT lens maturation, transcripts encoding crystallins were abundant at E16.5 and remained stable at PN56. Among the 1065 genes whose expression increased during WT lens maturation, there were 104 Klf4-target genes (9.8%) with decreased expression in the PN56 Klf4CN lens. Taken together, these results demonstrate that Klf4 expression is developmentally regulated in the mouse lens, where it controls the expression of genes associated with lens maturation and redox homeostasis.