Mutations in CYP1B1 cause primary congenital glaucoma by reduction of either activity or abundance of the enzyme

Hypomorphic variants in inherited retinal and ocular diseases: A review of the literature with clinical cases

Hypomorphic variants decrease, but do not eliminate, gene function via a reduction in the amount of mRNA or protein product produced by a gene or by production of a gene product with reduced function. Many hypomorphic variants have been implicated in inherited retinal diseases (IRDs) and other genetic ocular conditions; however, there is heterogeneity in the use of the term "hypomorphic" in the scientific literature. We searched for all hypomorphic variants reported to cause IRDs and ocular disorders. We also discuss the presence of hypomorphic variants in the patient population of our ocular genetics department over the past decade. We propose that standardized criteria should be adopted for use of the term "hypomorphic" to describe gene variants to improve genetic counseling and patient care outcomes.

Next-generation sequencing-based gene panel tests for the detection of rare variants and hypomorphic alleles associated with primary open-angle glaucoma

Primary open-angle glaucoma (POAG) is a complex disease with a strong hereditably component. Several genetic variants have recently been associated with POAG, partially due to technological improvements such as next-generation sequencing (NGS). The aim of this study was to genetically analyze patients with POAG to determine the contribution of rare variants and hypomorphic alleles associated with glaucoma as a future method of diagnosis and early treatment. Seventy-two genes potentially associated with adult glaucoma were studied in 61 patients with POAG. Additionally, we sequenced the coding sequence of CYP1B1 gene in 13 independent patients to deep analyze the potential association of hypomorphic CYP1B1 alleles in the pathogenesis of POAG. We detected nine rare variants in 16% of POAG patients studied by NGS. Those rare variants are located in CYP1B1, SIX6, CARD10, MFN1, OPTC, OPTN, and WDR36 glaucoma-related genes. Hypomorphic variants in CYP1B1 and SIX6 genes have been identified in 8% of the total POAG patient assessed. Our findings suggest that NGS could be a valuable tool to clarify the impact of genetic component on adult glaucoma. However, in order to demonstrate the contribution of these rare variants and hypomorphic alleles to glaucoma, segregation and functional studies would be necessary. The identification of new variants and hypomorphic alleles in glaucoma patients will help to configure the genetic identity of these patients, in order to make an early and precise molecular diagnosis.

Genetics in primary congenital glaucoma: Implications in disease management and counseling

Primary congenital glaucoma is an important cause of visual impairment in children. It can develop both pre- and postnatally. Angle surgery is the first line treatment modality. If the disease remains untreated or if the diagnosis is delayed, it can lead to irreversible visual loss and blindness. The genetics of primary congenital glaucoma are complex and not yet entirely understood. At present multiple disease-causing genes have been identified. CYP1B1 is the most well known gene causing autosomal recessive congenital glaucoma. Other genes have been found to play a role through recessive, dominant or polygenic mechanisms. Here we provide an overview of the known genes and mechanisms described in patients with PCG. Furthermore, we provide a practical counseling and follow-up guideline for relatives of a proband.

Biological roles of cytochrome P450 1A1, 1A2, and 1B1 enzymes

Human cytochrome P450 enzymes (CYPs) play a critical role in various biological processes and human diseases. CYP1 family members, including CYP1A1, CYP1A2, and CYP1B1, are induced by aryl hydrocarbon receptors (AhRs). The binding of ligands such as polycyclic aromatic hydrocarbons activates the AhRs, which are involved in the metabolism (including oxidation) of various endogenous or exogenous substrates. The ligands that induce CYP1 expression are reported to be carcinogenic xenobiotics. Hence, CYP1 enzymes are correlated with the pathogenesis of cancers. Various endogenous substrates are involved in the metabolism of steroid hormones, eicosanoids, and other biological molecules that mediate the pathogenesis of several human diseases. Additionally, CYP1s metabolize and activate/inactivate therapeutic drugs, especially, anti-cancer agents. As the metabolism of drugs determines their therapeutic efficacy, CYP1s can determine the susceptibility of patients to some drugs. Thus, understanding the role of CYP1s in diseases and establishing novel and efficient therapeutic strategies based on CYP1s have piqued the interest of the scientific community.

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.

Screening of West Siberian patients with primary congenital glaucoma for CYP1B1 gene mutations

Primary congenital glaucoma (PСG) is a visual organ pathology that leads to progressive blindness and poor vision in children. Its main cause is an anomaly of the anterior chamber angle. Most cases of PСG are sporadic, but familial cases with an autosomal recessive (predominantly) and autosomal dominant (rare) type of inheritance have been described. Congenital glaucoma is a rare condition (1 case per 10,000–20,000 newborns), but its prevalence is substantially higher (up to 1 case per 250 newborns) in countries where consanguineous marriages are common. Mutations in the CYP1B1 gene, which encodes cytochrome P450 1B1, are the most common cause of autosomal recessive primary congenital glaucoma. This enzyme is known to be involved in retinoic acid metabolism and is necessary for normal eye development. The aim of this work was to assess the polymorphism of the CYP1B1 gene among West Siberian patients with primary congenital glaucoma. Direct automatic Sanger sequencing of exons and adjacent splicing sites of the CYP1B1 gene was carried out in 28 people with the PCG phenotype from a West Siberian region. As a result, in the sample of the white population we examined, pathogenic variants previously described in other ethnic groups were revealed: E387K (rs55989760), R444* (rs377049098), R444Q (rs72549376), and P437L (rs56175199), as well as novel single-nucleotide deletion p.F114Lfs*38 in the CYP1B1 gene. The latter can cause a frame shift, changed amino acid composition, and a formation of truncated in the protein. None of the detected mutations were found in the control sample of ophthalmologically examined individuals without PCG (100 people). Variants R444* (rs377049098) and R444Q (rs72549376) were not found in the general population sample either (576 randomly selected West Siberia residents). All the detected mutations caused the development of the autosomal recessive form of primary congenital glaucoma. The most severe clinical phenotype was observed in carriers of mutations in codon 444 of the gene. Consequently, in children with signs of increased intraocular pressure, molecular genetic analysis of the CYP1B1 gene is advisable for early diagnosis and timely initiation of PCG therapy.

Updates on the molecular genetics of primary congenital glaucoma (Review)

Primary congenital glaucoma (PCG) is one of the primary causes of blindness in children and is characterized by congenital trabecular meshwork and anterior chamber angle dysplasia. While being a rare condition, PCG severely impairs the quality of life of affected patients. However, the pathogenesis of PCG remains to be fully elucidated. It has previously been indicated that genetic factors serve a critical role in the pathogenesis of PCG, although patients with PCG exhibit significant genetic heterogeneity. Mutations in the cytochrome P450 family 1 subfamily B member 1 gene have been implicated in PCG and further genes that have been reported to be involved in PCG are myocilin, forkhead box C1, collagen type I α1 chain and latent transforming growth factor β binding protein 2. The present review aims to provide an up to date understanding of the genes associated with PCG and the use of molecular technologies in the identification of such genes and mutations. This may pave the way for the development of preventative methods, early diagnosis and improved therapeutic strategies in PCG.

Exome Sequencing in a Swiss Childhood Glaucoma Cohort Reveals CYP1B1 and FOXC1 Variants as Most Frequent Causes

Purpose

The aim of this study was to investigate the molecular basis of childhood glaucoma in Switzerland to recommend future targeted genetic analysis in the Swiss population.

Methods

Whole-exome sequencing and copy number variation (CNV) analysis was performed in a Swiss cohort of 18 patients from 14 unrelated families. Identified variants were validated by Sanger sequencing and multiplex ligation-dependent probe amplification. Breakpoints of structural variants were determined by a microarray. A minigene assay was conducted for functional analysis of a splice site variant.

Results

A diagnosis of primary congenital glaucoma was made in 14 patients, of which six (43%) harbored pathogenic variants in CYP1B1, one (7%) a frameshift variant in FOXC1, and seven (50%) remained without a genetic diagnosis. Three patients were diagnosed with glaucoma associated with nonacquired ocular anomalies, of which two patients with mild ocular features of Axenfeld-Rieger syndrome harbored a FOXC1 duplication plus an additional FOXC1 missense variant, and one patient with a Barkan membrane remained without genetic diagnosis. A diagnosis of juvenile open-angle glaucoma was made in one patient, and genetic analysis revealed a FOXC1 duplication.

Conclusions

Sequencing of CYP1B1 and FOXC1, as well as analysis of CNVs in FOXC1, should be performed before extended gene panel sequencing.

Translational Relevance

The identification of the molecular cause of childhood glaucoma is a prerequisite for genetic counseling and personalized care for patients and families.

Investigation of CYP1B1 Gene Involvement in Primary Congenital Glaucoma in Iraqi Children

PURPOSE

Primary congenital glaucoma (PCG) is a severe type of glaucoma that occurs early in life. PCG is usually inherited in an autosomal recessive pattern. Cytochrome P450, family 1, subfamily B, polypeptide 1 (CYP1B1) gene is reported to be PCG-related gene. It codes for the CYP1B1 enzyme which is considered as phase I xenobiotic-metabolizing enzyme and its function is related to the eye oxidative homeostasis and correspondingly to the normal development of the eye. This is the first genetic study in Iraq that investigates the CYP1B1 polymorphisms behind the PCG disease.

METHODS

Genomic DNA was extracted from the whole blood of 100 unrelated Iraqi PCG patients and 100 healthy children, all of them were aged between 1 month and 3 years. All the coding sequence of CYP1B1 gene was amplified using polymerase chain reaction; restriction fragment length polymorphism was used to follow G61E and E229K mutations. Direct sequencing was performed to screen for other mutations.

RESULTS

CYP1B1 mutations were identified in 78 (78%) of the patients. We detected a total of eight mutations: Four missense mutations (c.182G>A, c.685G>A, g.6813G>A, and g.6705G>A), one silence mutation (D449D) and three insertions (g.10068ins10069, g.10138ins10139, and g.10191ins10192). Five mutations (g.6813G>A, g.6705G>A, g.10068ins10069, g.10138ins10139, and g.10191ins10192) are novel. G61E is the only mutation that was detected in patients merely.

CONCLUSIONS

CYP1B1 mutation (G61E) is considered as PCG-related allele in the Iraqi population.

CYP1B1 prevents proteasome-mediated XIAP degradation by inducing PKCε activation and phosphorylation of XIAP

Cytochrome P450 1B1 (CYP1B1) is a key enzyme that catalyzes the metabolism of 17β-estradiol (E2) into catechol estrogens, such as 2-hydroxyestradiol (2-OHE2) and 4-hydroxyestradiol (4-OHE2). CYP1B1 is related to tumor formation and is over-expressed in a variety of cancer cells. In particular, CYP1B1 is highly expressed in hormone-related cancers such as breast cancer, ovarian cancer, or prostate cancer compared to other cancers. However, the detailed mechanisms involving this protein remain unclear. In this study, we demonstrate that CYP1B1 affects X-linked inhibitor of apoptosis protein (XIAP) expression. When CYP1B1 was over-expressed in cells, there was significant increase in the XIAP protein level, whereas the XIAP mRNA level was not affected by CYP1B1 expression. Treatment with 4-OHE2, mainly formed by CYP1B1 activity, also increased XIAP protein levels, whereas treatment with 2-OHE2 did not have a significant effect. Treatment with 4-OHE2 significantly prevented proteasome-mediated XIAP degradation. In addition, phosphorylation of XIAP on serine 87, which is known to stabilize XIAP, was up-regulated by 4-OHE2, indicating that 4-OHE2 affects XIAP stability through XIAP phosphorylation. We also found that phosphorylation of protein kinase C (PKC)ε, which is required for XIAP phosphorylation, increased when cells were treated with 4-OHE2. In summary, our data show that CYP1B1 may play an important role in preventing ubiquitin-proteasome-mediated XIAP degradation through the activation of PKCε signaling in cancer cells.

Cyp1B1 expression patterns in the developing chick inner ear

BACKGROUND

Retinoic acid (RA) plays an important role in organogenesis as a paracrine signal through transcriptional regulation of an increasing number of known downstream target genes, regulating cell proliferation, and differentiation. During the development of the inner ear, RA directly governs the morphogenesis and specification processes mainly by means of RA-synthesizing retinaldehyde dehydrogenase (RALDH) enzymes. Interestingly, CYP1B1, a cytochrome P450 enzyme, is able to mediate the oxidative metabolisms also leading to RA generation, its expression patterns being associated with many known sites of RA activity.

RESULTS

This study describes for the first time the presence of CYP1B1 in the developing chick inner ear as a RALDH-independent RA-signaling mechanism. In our in situ hybridization analysis, Cyp1B1 expression was first observed in a domain located in the ventromedial wall of the otic anlagen, being included within the rostralmost aspect of an Fgf10-positive pan-sensory domain. As development proceeds, all identified Fgf10-positive areas were Cyp1B1 stained, with all sensory patches being Cyp1B1 positive at stage HH34, except the macula neglecta.

CONCLUSIONS

Cyp1B1 expression suggested a possible contribution of CYP1B1 action in the specification of the lateral-to-medial and dorsal-to-ventral axes of the developing chick inner ear.

Compound heterozygous mutations in CYP1B1 gene leads to severe primary congenital glaucoma phenotype

AIM

To identify the novel mutation alleles in the CYP1B1 gene of primary congenital glaucoma (PCG) patients at Shandong Province of China, and investigate their correlation with glaucomatous features.

METHODS

The DNA from the peripheral blood of 13 congenital glaucoma patients and 50 ethnically matched healthy controls from the affiliated hospital of Qingdao University were extracted. The coding region of the CYP1B1 gene was amplified by PCR and direct DNA sequencing was performed. Disease causing-variants were analyzed by comparing the sequences and the structures of wild type and mutant CYP1B1 proteins by PyMOL software.

RESULTS

Two missense mutations, including A330F caused by c.988G>T&c.989C>T, and R390H caused by c.1169G>A, were identified in one of the 13 PCG patients analyzed in our study. A330F mutation was observed to be novel in the Chinese Han population, which dramatically altered the protein structure of CYP1B1 gene, including the changes in the ligand-binding pocket. Furthermore, R390H mutation caused the changes in heme-protein binding site of this gene. In addition, the clinical phenotype displayed by PCG patient with these mutations was more pronounced than other PCG patients without these mutations. Multiple surgeries and combined drug treatment were not effective in reducing the elevated intraocular pressure in this patient.

CONCLUSION

A novel A330F mutation is identified in the CYP1B1 gene of Chinese PCG patient. Moreover, in combination with other mutation R390H, this PCG patient shows significant difference in the CYP1B1 protein structure, which may specifically contribute to severe glaucomatous phenotype.

Novel CYP1B1 mutations and a possible prognostic use for surgical management of congenital glaucoma

AIM

To identify CYP1B1 gene mutations and evaluate their possible role as a prognostic factor for success rates in the surgical management of Egyptian congenital glaucoma patients.

METHODS

Totally 42 eyes of 29 primary congenital glaucoma patients were operated on with combined trabeculotomy/trabeculectomy with mitomycin-C and followed up at 1d, 1wk, 1, 6 and 12mo postoperatively. Genomic DNA was extracted from peripheral blood leukocytes. Coding regions of CYP1B1 gene were amplified using 13 pairs of primers, screened for mutations using single-strand conformation polymorphism followed by sequencing of both strands. Efficacy of the operation was graded as either a success [maintaining intraocular pressure (IOP) less than 21 mm Hg with or without anti-glaucoma medication], or a failure (IOP more than 21 mm Hg with topical antiglaucoma medications).

RESULTS

Seven novel mutations out of a total of 15 different mutations were found in the CYP1B1 genes of 14 patients (48.2%). The presence of CYP1B1 gene mutations did not correlate with the failure of the surgery (P=0.156, odds ratio=3.611, 95%CI, 0.56 to 22.89); while the positive consanguinity strongly correlated with failure of the initial procedure (P=0.016, odds ratio=11.25, 95%CI, 1.57 to 80.30). However, the Kaplan-Meier survival analysis revealed a significantly lower time of IOP control in the subgroup with mutations in CYP1B1 versus the congenital primary glaucoma group without mutations (log rank test, P=0.015).

CONCLUSION

Seven new CYP1B1 mutations are identified in Egyptian patients. Patients harboring confirmed mutations suffered from early failure of the initial surgery. CYP1B1 mutations could be considered as a prognostic factor for surgery in primary congenital glaucoma.

Analysis of CYP1B1 sequence alterations in patients with primary open-angle glaucoma of Saudi origin

Cytochrome P450 Family 1 Subfamily B Member 1 (CYP1B1; OMIM# 601771) gene encodes one of the cytochrome P450 family of enzymes. CYP1B1 mutations have been associated primarily with primary congenital glaucoma (PCG). Similar studies were reported in juvenile open-angle glaucoma, Rieger’s and Peters anomalies. Reports of likely pathogenic sequence alterations in families affected with adult-onset primary open-angle glaucoma (POAG) triggered this investigation. We screened unrelated POAG cases and healthy controls for mutations in CYP1B1 using automated Sanger sequencing to identify five known polymorphisms and one CYP1B1 mutation (p.G61E) in a heterozygous status. The p.G61E mutation is known to cause PCG in a homozygous or compound heterozygous form, and thus, its presence here in a heterozygous form indicates carrier status. These findings suggest that CYP1B1 may have no major role in the pathogenesis of POAG, at least, in the Saudi population. However, further investigations are needed to validate these findings in a larger cohort.

Bioinformatics analysis of CYP1B1 mutation hotspots in Chinese primary congenital glaucoma patients

Primary congenital glaucoma (PCG) is an inherited blinding eye disease. The CYP1B1 gene was identified as a causal gene for PCG, and many mutations have been found, but no studies have focussed on the molecular epidemiology of CYP1B1 in Chinese populations. We aimed to explore the CYP1B1 mutation hotspots in Chinese PCG patients and the possible impact of these mutations on the protein structure and function. First, we performed a meta-analysis on seven datasets of Chinese populations and found L107V and R390H to be the most common CYP1B1 mutations with allele frequencies of 3.19% and 3.09%, respectively. Then, a series of bioinformatics tools were applied to determine the sequence conservative properties, model the 3D structures, and study the dynamics changes. L107 and R390 are highly conserved residues in close proximity to the hemoglobin-binding region and the active site cavity (ASC), respectively. The mutations changed the distribution of hydrogen bonds and the local electrostatic potential. Long-term molecular dynamics (MD) simulations demonstrated the destabilization of the mutant proteins, especially at the ASC, whose solvent-accessible surface areas (SASAs) were significantly decreased. Compared with the wild-type (WT) protein, the overall structures of the mutants are associated with subtle but significant changes, and the ASC seems to adopt such structures that are not able to perform the WT-like functionality. Therefore, L107V and R390H might be the most important pathogenic mutations in Chinese PCG patients.

Genetic testing for Mendelian glaucoma

We studied the scientific literature and disease guidelines in order to summarize the clinical utility of genetic testing for Mendelian glaucomas, a large heterogeneous group of inherited disorders, classified according to age of onset as congenital glaucoma, juvenile glaucoma and age-related glaucoma. Variations in the TEK, MYOC, ASB10, NTF4, OPA1, WDR36 and OPTN genes are inherited in an autosomal dominant manner and variations in the CYP1B1 and LTBP2 genes have autosomal recessive inheritance. The prevalence of congenital glaucoma is estimated at 1-9 per 100 000, that of juvenile glaucoma at 1 per 50 000, while there is insufficient data to establish the prevalence of age-related glaucoma. Clinical diagnosis is based on clinical findings, age of onset, family history, ophthalmological examination, intraocular pressure, gonioscopy and fundoscopy. The genetic test is useful for confirming diagnosis, and for differential diagnosis, couple risk assessment and access to clinical trials.

Primary congenital and developmental glaucomas

Glaucoma is the leading cause of irreversible blindness worldwide. Although most glaucoma patients are elderly, congenital glaucoma and glaucomas of childhood are also important causes of visual disability. Primary congenital glaucoma (PCG) is isolated, non-syndromic glaucoma that occurs in the first three years of life and is a major cause of childhood blindness. Other early-onset glaucomas may arise secondary to developmental abnormalities, such as glaucomas that occur with aniridia or as part of Axenfeld-Rieger syndrome. Congenital and childhood glaucomas have strong genetic bases and disease-causing mutations have been discovered in several genes. Mutations in three genes (CYP1B1, LTBP2, TEK) have been reported in PCG patients. Axenfeld-Rieger syndrome is caused by mutations in PITX2 or FOXC1 and aniridia is caused by PAX6 mutations. This review discusses the roles of these genes in primary congenital glaucoma and glaucomas of childhood.

Cyp1b1 Regulates Ocular Fissure Closure Through a Retinoic Acid-Independent Pathway

Purpose

Mutations in the CYP1B1 gene are the most commonly identified genetic causes of primary infantile-onset glaucoma. Despite this disease association, the role of CYP1B1 in eye development and its in vivo substrate remain unknown. In the present study, we used zebrafish to elucidate the mechanism by which cyp1b1 regulates eye development.

Methods

Zebrafish eye and neural crest development were analyzed using live imaging of transgenic zebrafish embryos, in situ hybridization, immunostaining, TUNEL assay, and methylacrylate sections. Cyp1b1 and retinoic acid (RA) levels were genetically (morpholino oligonucleotide antisense and mRNA) and pharmacologically manipulated to examine gene function.

Results

Using zebrafish, we observed that cyp1b1 was expressed in a specific spatiotemporal pattern in the ocular fissures of the developing zebrafish retina and regulated fissure patency. Decreased Cyp1b1 resulted in the premature breakdown of laminin in the ventral fissure and altered subsequent neural crest migration into the anterior segment. In contrast, cyp1b1 overexpression inhibited cell survival in the ventral ocular fissure and prevented fissure closure via an RA-independent pathway. Cyp1b1 overexpression also inhibited the ocular expression of vsx2, pax6a, and pax6b and increased the extraocular expression of shha. Importantly, embryos injected with human wild-type but not mutant CYP1B1 mRNA also showed colobomas, demonstrating the evolutionary and functional conservation of gene function between species.

Conclusions

Cyp1b1 regulation of ocular fissure closure indirectly affects neural crest migration and development through an RA-independent pathway. These studies provide insight into the role of Cyp1b1 in eye development and further elucidate the pathogenesis of primary infantile-onset glaucoma.

Goniodysgenesis variability and activity of CYP1B1 genotypes in primary congenital glaucoma

Mutations in the CYP1B1 gene are currently the main known genetic cause of primary congenital glaucoma (PCG), a leading cause of blindness in children. Here, we analyze for the first time the CYP1B1 genotype activity and the microscopic and clinical phenotypes in human PCG. Surgical pieces from trabeculectomy from patients with PCG (n = 5) and sclerocorneal rims (n = 3) from cadaver donors were processed for transmission electron microscopy. Patients were classified into three groups depending on goniodysgenesis severity, which was influenced by CYP1B1 enzymatic activity. The main histological changes observed in the outflow pathway of patients with PCG and mutations in CYP1B1 were: i) underdeveloped collector channels and the Schlemm’s canal; ii) abnormal insertion of the ciliary muscle; iii) death of the trabecular endothelial cells. Our findings could be useful in improving treatment strategy of PCG associated with CYP1B1 mutations.

Functional characterization of eight rare missense CYP1B1 variants involved in congenital glaucoma and their association with null genotypes

PURPOSE

To evaluate the function of eight missense CYP1B1 single nucleotide variants (SNVs) previously identified in patients with primary congenital glaucoma (PCG).

METHODS

The eight variants were obtained by site-directed mutagenesis and transiently expressed in human embryonic kidney 293-T (HEK-293T) cells. The catalytic activity, protein stability and subcellular localization of the different recombinant CYP1B1 variants were assessed in this cell line.

RESULTS

Six of the mutant CYP1B1 proteins (p.L89P, p.A106D, p.R390S, p.P437L, p.C470Y and S485F) showed catalytic activity values ranging from 0% to 4% of those of the wild-type protein and were considered null variants. The activity values of the two remaining variants (p.F123L and p.A237E) were close to 20% of that of the wild-type enzyme and were classified as hypomorphic variants. Reduced protein stability contributed partially to the decreased catalytic activity of two of the mutant enzymes (p.L89P and p.A106D). None of the CYP1B1 variants showed intracellular aggregation and they all displayed a normal subcellular localization in the endoplasmic reticulum, suggesting that they had folded into a wild-type-like structure. The enzymatic activity associated with the different genotypes in which these CYP1B1 variants were present was estimated to range from 0% to 10% of that of the wild-type genotype.

CONCLUSION

These results confirm the pathogenicity of the analysed missense CYP1B1 variants and further support the concept that either absent or very low CYP1B1 activity levels are the primary molecular defect involved in PCG pathogenesis.

CYP1B1 Enhances Cell Proliferation and Metastasis through Induction of EMT and Activation of Wnt/β-Catenin Signaling via Sp1 Upregulation

Cytochrome P450 1B1 (CYP1B1) is a major E₂ hydroxylase involved in the metabolism of potential carcinogens. CYP1B1 expression has been reported to be higher in tumors compared to normal tissues, especially in hormone-related cancers including breast, ovary, and prostate tumors. To explore the role of CYP1B1 in cancer progression, we investigated the action of CYP1B1 in cells with increased CYP1B1 via the inducer 7,12-dimethylbenz[α]anthracene (DMBA) or an overexpression vector, in addition to decreased CYP1B1 via the inhibitor tetramethoxystilbene (TMS) or siRNA knockdown. We observed that CYP1B1 promoted cell proliferation, migration, and invasion in MCF-7 and MCF-10A cells. To understand its molecular mechanism, we measured key oncogenic proteins including β-catenin, c-Myc, ZEB2, and matrix metalloproteinases following CYP1B1 modulation. CYP1B1 induced epithelial-mesenchymal transition (EMT) and activated Wnt/β-catenin signaling via upregulation of CTNNB1, ZEB2, SNAI1, and TWIST1. Sp1, a transcription factor involved in cell growth and metastasis, was positively regulated by CYP1B1, and suppression of Sp1 expression by siRNA or DNA binding activity using mithramycin A blocked oncogenic transformation by CYP1B1. Therefore, we suggest that Sp1 acts as a key mediator for CYP1B1 action. Treatment with 4-hydroxyestradiol (4-OHE₂), a major metabolite generated by CYP1B1, showed similar effects as CYP1B1 overexpression, indicating that CYP1B1 activity mediated various oncogenic events in cells. In conclusion, our data suggests that CYP1B1 promotes cell proliferation and metastasis by inducing EMT and Wnt/β-catenin signaling via Sp1 induction.

PROXIMAL: a method for Prediction of Xenobiotic Metabolism

Background

Contamination of the environment with bioactive chemicals has emerged as a potential public health risk. These substances that may cause distress or disease in humans can be found in air, water and food supplies. An open question is whether these chemicals transform into potentially more active or toxic derivatives via xenobiotic metabolizing enzymes expressed in the body. We present a new prediction tool, which we call PROXIMAL (Prediction of Xenobiotic Metabolism) for identifying possible transformation products of xenobiotic chemicals in the liver. Using reaction data from DrugBank and KEGG, PROXIMAL builds look-up tables that catalog the sites and types of structural modifications performed by Phase I and Phase II enzymes. Given a compound of interest, PROXIMAL searches for substructures that match the sites cataloged in the look-up tables, applies the corresponding modifications to generate a panel of possible transformation products, and ranks the products based on the activity and abundance of the enzymes involved.

Results

PROXIMAL generates transformations that are specific for the chemical of interest by analyzing the chemical’s substructures. We evaluate the accuracy of PROXIMAL’s predictions through case studies on two environmental chemicals with suspected endocrine disrupting activity, bisphenol A (BPA) and 4-chlorobiphenyl (PCB3). Comparisons with published reports confirm 5 out of 7 and 17 out of 26 of the predicted derivatives for BPA and PCB3, respectively. We also compare biotransformation predictions generated by PROXIMAL with those generated by METEOR and Metaprint2D-react, two other prediction tools.

Conclusions

PROXIMAL can predict transformations of chemicals that contain substructures recognizable by human liver enzymes. It also has the ability to rank the predicted metabolites based on the activity and abundance of enzymes involved in xenobiotic transformation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12918-015-0241-4) contains supplementary material, which is available to authorized users.

A translational bioinformatic approach in identifying and validating an interaction between Vitamin A and CYP19A1

INTRODUCTION

One major challenge in personalized medicine research is to identify the environmental factors that can alter drug response, and to investigate their molecular mechanisms. These environmental factors include co-medications, food, and nutrition or dietary supplements. The increasing use of dietary supplements and their potential interactions with cytochrome P450 (CYP450) enzymes is a highly significant personalized medicine research domain, because most of the drugs on the market are metabolized through CYP450 enzymes.

METHODS

Initial bioinformatics analysis revealed a number of regulators of CYP450 enzymes from a human liver bank gene expression quantitative loci data set. Then, a compound-gene network was constructed from the curated literature data. This network consisted of compounds that interact with either CYPs and/or their regulators that influence either their gene expression or activity. We further evaluated this finding in three different cell lines: JEG3, HeLa, and LNCaP cells.

RESULTS

From a total of 868 interactions we were able to identify an interesting interaction between retinoic acid (i.e. Vitamin A) and the aromatase gene (i.e. CYP19A1). Our experimental results showed that retinoic acid at physiological concentration significantly influenced CYP19A1 gene expressions.

CONCLUSIONS

These results suggest that the presence of retinoic acid may alter the efficacy of agents used to suppress aromatase expression.

Neural crest derivatives in ocular development: discerning the eye of the storm

Neural crest cells (NCCs) are vertebrate-specific transient, multipotent, migratory stem cells that play a crucial role in many aspects of embryonic development. These cells emerge from the dorsal neural tube and subsequently migrate to different regions of the body, contributing to the formation of diverse cell lineages and structures, including much of the peripheral nervous system, craniofacial skeleton, smooth muscle, skin pigmentation, and multiple ocular and periocular structures. Indeed, abnormalities in neural crest development cause craniofacial defects and ocular anomalies, such as Axenfeld-Rieger syndrome and primary congenital glaucoma. Thus, understanding the molecular regulation of neural crest development is important to enhance our knowledge of the basis for congenital eye diseases, reflecting the contributions of these progenitors to multiple cell lineages. Particularly, understanding the underpinnings of neural crest formation will help to discern the complexities of eye development, as these NCCs are involved in every aspect of this process. In this review, we summarize the role of ocular NCCs in eye development, particularly focusing on congenital eye diseases associated with anterior segment defects and the interplay between three prominent molecules, PITX2, CYP1B1, and retinoic acid, which act in concert to specify a population of neural crest-derived mesenchymal progenitors for migration and differentiation, to give rise to distinct anterior segment tissues. We also describe recent findings implicating this stem cell population in ocular coloboma formation, and introduce recent evidence suggesting the involvement of NCCs in optic fissure closure and vascular development.

CYP1B1 Gene Analysis and Phenotypic Correlation in Portuguese Children with Primary Congenital Glaucoma

Purpose

To investigate the prevalence of CYP1B1 mutations in Portuguese children with primary congenital glaucoma (PCG) and to study the possible correlations between the mutation status and clinical features of the disease.

Methods

DNA sequencing analysis of the CYP1B1 gene was used to screen 21 children with PCG followed on Paediatric Ophthalmology and Medical Genetics consultations at D. Estefania's Hospital (Centro Hospitalar de Lisboa Central, Portugal). The effect of mutations on the phenotype of the patients was also assessed. Presence and type of mutations in CYP1B1 gene, age at diagnosis, bilaterality, age at first surgery, postoperative intraocular pressure and corneal diameter, final visual acuity, number of surgical reinterventions, and number of antiglaucoma medications required postoperatively were noted.

Results

Mutations in the CYP1B1 gene in 6 patients (28.57%) were detected, all compound heterozygotes. Seven types of mutations were identified: c.182G>A, c.317C>A, c.535delG, c.1064_1076del, c.1159G>A, c.1310C>T, and c.1390dupT. All patients with these mutations developed bilateral PCG, whereas in the group without mutations only 7 (46.67%) showed bilateral disease. Age at diagnosis was lower in the group of patients with these mutations (0.0 ± 0.00 vs 4.5 ± 2.63 months, p<0.01). In the remaining variables (age at first surgery, postoperative intraocular pressure and corneal diameter, final visual acuity, number of surgical reinterventions and antiglaucoma medications required postoperatively), no significant differences between the groups were detected (p>0.05 for all comparisons).

Conclusions

This study is the first to report the variety of mutations in the CYP1B1 gene in a group of Portuguese children with PCG and to describe 2 new mutations. Genetic analysis of PCG must be carried out, although it has not yet been possible to establish a genotype-phenotype correlation, with the exception of bilaterality and early age at diagnosis.

Indoor air pollution and neural tube defects: effect modification by maternal genes

BACKGROUND

Gene-environment interactions have been implicated in the development of neural tube defects (NTDs).

METHODS

We conducted a case-control study to investigate (1) the association of aryl hydrocarbon receptor (AHR) genetic variants and phase I metabolic enzymes with the risk of NTDs and (2) the interaction of these variants with maternal exposure to indoor air pollution from smoking and coal combustion or with placental polycyclic aromatic hydrocarbons (PAHs). Blood samples were collected from 534 mothers of fetuses or newborns with NTDs and 534 control mothers who had healthy term newborns and were assayed for 12 polymorphisms in the AHR and cytochrome P450 (CYP) genes. Information on maternal exposure was collected, and placental levels of PAHs were analyzed.

RESULTS

Maternal exposure to indoor air pollution was associated with an increased NTD risk. However, no increased NTD risk was observed for individual genetic variants. For mothers with the CYP1B1 rs2855658 GG variant, exposure to indoor air pollution led to a dose-response relationship for NTD risk, with odds ratios (ORs) of 3.0 (95% confidence interval = 1.6-5.7) and 8.1 (3.8-17) for medium and high levels of exposure, respectively. For mothers with GA or AA genotypes, this trend was less apparent. Placental PAHs were associated with an increased risk of NTDs, with an OR of 16 (3.3-75) for high levels compared with low levels of exposure among mothers with the GG genotype; there was no association for mothers with GA or AA genotypes.

CONCLUSIONS

The CYP1B1 variant modifies the effect of indoor air pollution on NTD risk.

Kuwaiti population subgroup of nomadic Bedouin ancestry-Whole genome sequence and analysis

Kuwaiti native population comprises three distinct genetic subgroups of Persian, "city-dwelling" Saudi Arabian tribe, and nomadic "tent-dwelling" Bedouin ancestry. Bedouin subgroup is characterized by presence of 17% African ancestry; it owes it origin to nomadic tribes of the deserts of Arabian Peninsula and North Africa. By sequencing whole genome of a Kuwaiti male from this subgroup at 41X coverage, we report 3,752,878 SNPs, 411,839 indels, and 8451 structural variations. Neighbor-joining tree, based on shared variant positions carrying disease-risk alleles between the Bedouin and other continental genomes, places Bedouin genome at the nexus of African, Asian, and European genomes in concordance with geographical location of Kuwait and Peninsula. In congruence with participant's medical history for morbid obesity and bronchial asthma, risk alleles are seen at deleterious SNPs associated with obesity and asthma. Many of the observed deleterious 'novel' variants lie in genes associated with autosomal recessive disorders characteristic of the region.

Mutation spectrum of CYP1B1 in Chinese patients with primary open-angle glaucoma

PURPOSE

The CYP1B1 gene has been shown to be related to primary open-angle glaucoma (POAG). This study aimed to identify the mutation profile of CYP1B1 in Chinese individuals with POAG.

METHODS

The study included 416 unrelated cases diagnosed as POAG by standard ophthalmological examinations, and 657 unrelated healthy controls in a Chinese population. Genomic DNA was collected from peripheral blood of all the participants. The coding sequence of CYP1B1 was amplified by PCR from genomic DNA, followed by direct DNA sequencing.

RESULTS

Among 416 patients with POAG, 13 missense mutations, including nine reported mutations and four novel mutations (p.P93S, p.R259C, p.A295T, p.L475P), were detected in 25 patients. All these mutations were found as heterozygotes and the reported mutations have been previously found in primary congenital glaucoma and/or POAG patients. Three of them (p.L107V, p.E229K, p.V320L) were also found in healthy controls. In addition, six previously reported single nucleotide polymorphisms (p.R48G, p.A119S, p.V243V, p.V432L, p.D449D, p.N453S) were also observed in POAG patients and controls, and they showed no obvious frequency difference between patients and controls.

CONCLUSIONS

This study provides a mutation spectrum of CYP1B1 resulting in POAG development in a Chinese population, which may demonstrate an involvement of the gene in a proportion of subjects with POAG and help to improve our understanding of the pathogenesis of CYP1B1-associated POAG.

A novel methodology for enhanced and consistent heterologous expression of unmodified human cytochrome P450 1B1 (CYP1B1)

Cytochrome P450 1B1 (CYP1B1) is a universal cancer marker and is implicated in many other disorders. Mutations in CYP1B1 are also associated with childhood blindness due to primary congenital glaucoma (PCG). To understand the CYP1B1 mediated etiopathology of PCG and pathomechanism of various cancers, it is important to carry out its functional studies. Heterologous expression of CYP1B1 in prokaryotes is imperative because bacteria yield a higher amount of heterologous proteins in lesser time and so the expressed protein is ideal for functional studies. In such expression system there is no interference by other eukaryotic proteins. But the story is not that simple as expression of heterologous CYP1B1 poses many technical difficulties. Investigators have employed various modifications/deletions of CYP N-terminus to improve CYP1B1 expression. However, the drawback of these studies is that it changes the original protein and, as a result, invalidates functional studies. The present study examines the role of various conditions and reagents in successful and consistent expression of sufficient quantities of unmodified/native human CYP1B1 in E. coli. We aimed at expressing CYP1B1 in various strains of E. coli and in the course developed a protocol that results in high expression of unmodified protein sufficient for functional/biophysical studies. We examined CYP1B1 expression with respect to different expression vectors, bacterial strains, types of culture media, time, Isopropyl β-D-1-thiogalactopyranoside concentrations, temperatures, rotations per minute, conditioning reagents and the efficacy of a newly described technique called double colony selection. We report a protocol that is simple, easy and can be carried out in any laboratory without the requirement of a fermentor. Though employed for CYP1B1 expression, this protocol can ideally be used to express any eukaryotic membrane protein.

Ocular cytochrome P450s and transporters: roles in disease and endobiotic and xenobiotic disposition

Drug metabolism and transport processes in the liver, intestine and kidney that affect the pharmacokinetics and pharmacodynamics of therapeutic agents have been studied extensively. In contrast, comparatively little research has been conducted on these topics as they pertain to the eye. Recently, however, catalytic functions of ocular cytochrome P450 enzymes have gained increasing attention, in large part due to the roles of CYP1B1 and CYP4V2 variants in primary congenital glaucoma and Bietti's corneoretinal crystalline dystrophy, respectively. In this review, we discuss challenges to ophthalmic drug delivery, including Phase I drug metabolism and transport in the eye, and the role of three specific P450s, CYP4B1, CYP1B1 and CYP4V2 in ocular inflammation and genetically determined ocular disease.

Glaucomics: a call for systems diagnostics for 21(st) century ophthalmology and personalized visual health

This article analyzes and theorizes the current knowledge silos at the intersection of omics science, ophthalmology, personalized medicine, and global visual health. Visual disorders represent one of the largest health care expenditures in the United States, costing $139 billion per year. In middle-income and industrialized countries, glaucoma is a World Health Organization priority category eye disease, known for difficulties in its early diagnosis, chronic progressive nature, and large person-to-person differences in drug efficacy and safety. A complex disease, glaucoma is best conceptualized as a syndrome displaying an ostensibly common clinical end-point, but with vastly heterogeneous molecular underpinnings and host-environment interactions. About 12% of all global blindness is attributable to glaucoma. Glaucomics is a term that we coin here so as to introduce omics science and systems diagnostics to ophthalmology, a field that can benefit enormously from personalized medicine, and which has sadly lagged behind in systems diagnostics compared to fields such as oncology. We define glaucomics as the integrated use of multi-omics and systems science approaches towards rational discovery, development, and tandem applications of diagnostics and therapeutics, for glaucoma specifically, and for personalized visual health, more broadly. We propose that glaucoma is one of the neglected lowest hanging fruits and actionable targets for omics and systems diagnostics in 21(st) century ophthalmology for the salient reasons we describe here. Additionally, we offer an analysis on two of the most pertinent neglected tropical diseases (NTDs), trachoma and river blindness, which continue to plague visual health in developing countries. We conclude with a call for research on omics applications in glaucoma and personalized visual health.

Exome sequencing in developmental eye disease leads to identification of causal variants in GJA8, CRYGC, PAX6 and CYP1B1

Developmental eye diseases, including cataract/microcornea, Peters anomaly and coloboma/microphthalmia/anophthalmia, are caused by mutations encoding many different signalling and structural proteins in the developing eye. All modes of Mendelian inheritance occur and many are sporadic cases, so provision of accurate recurrence risk information for families and affected individuals is highly challenging. Extreme genetic heterogeneity renders testing for all known disease genes clinically unavailable with traditional methods. We used whole-exome sequencing in 11 unrelated developmental eye disease patients, as it provides a strategy for assessment of multiple disease genes simultaneously. We identified five causative variants in four patients in four different disease genes, GJA8, CRYGC, PAX6 and CYP1B1. This detection rate (36%) is high for a group of patients where clinical testing is frequently not undertaken due to lack of availability and cost. The results affected clinical management in all cases. These variants were detected in the cataract/microcornea and Peters anomaly patients. In two patients with coloboma/microphthalmia, variants in ABCB6 and GDF3 were identified with incomplete penetrance, highlighting the complex inheritance pattern associated with this phenotype. In the coloboma/microphthalmia patients, four other variants were identified in CYP1B1, and CYP1B1 emerged as a candidate gene to be considered as a modifier in coloboma/microphthalmia.

CYP1B1 genotype influences the phenotype in primary congenital glaucoma and surgical treatment

AIMS

The aim of the present work was to investigate CYP1B1 gene mutations in patients of Han Chinese ethnicity with primary congenital glaucoma (PCG), and explore the clinical characteristics associated with operative effects.

METHODS

Peripheral blood genomic DNA was extracted from patients with PCG to act as a PCR template. CYP1B1 mutations were identified from the amplified coding sequences of CYP1B1. A total of 238 patients, including 116 patients described previously, were used to examine the CYP1B1 mutation frequency. Of the 238 patients, 192 patients (306 eyes) who underwent first operative treatment from January 1991 to September 2007 in the Eye, Ear, Nose & Throat Hospital of Fudan University were analysed to investigate the relationship between clinical characteristics (including CYP1B1 mutation status) and surgical effect via statistical analyses (multivariate logistic regression and Cox regression).

RESULTS

The frequency of CYP1B1 mutation carriers in Chinese patients with PCG is 17.2%, and nine novel CYP1B1 mutations were discovered. The median of onset age for patients with CYP1B1 mutations (2 months) is earlier than in patients without mutations (6 months). We identified that the mutant CYP1B1 gene, as well as poorer corneal transparency, was associated with better surgical outcome.

CONCLUSIONS

Patients with CYP1B1 mutations tend to have a higher operative success rate in terms of better intraocular pressure control effect. The combination of the CYP1B1 genotype (with or without mutations) and preoperative corneal opacity score can partially predict the outcome of PCG surgery.

Cytochrome P450 enzymes in drug metabolism: regulation of gene expression, enzyme activities, and impact of genetic variation

Cytochromes P450 (CYP) are a major source of variability in drug pharmacokinetics and response. Of 57 putatively functional human CYPs only about a dozen enzymes, belonging to the CYP1, 2, and 3 families, are responsible for the biotransformation of most foreign substances including 70-80% of all drugs in clinical use. The highest expressed forms in liver are CYPs 3A4, 2C9, 2C8, 2E1, and 1A2, while 2A6, 2D6, 2B6, 2C19 and 3A5 are less abundant and CYPs 2J2, 1A1, and 1B1 are mainly expressed extrahepatically. Expression of each CYP is influenced by a unique combination of mechanisms and factors including genetic polymorphisms, induction by xenobiotics, regulation by cytokines, hormones and during disease states, as well as sex, age, and others. Multiallelic genetic polymorphisms, which strongly depend on ethnicity, play a major role for the function of CYPs 2D6, 2C19, 2C9, 2B6, 3A5 and 2A6, and lead to distinct pharmacogenetic phenotypes termed as poor, intermediate, extensive, and ultrarapid metabolizers. For these CYPs, the evidence for clinical significance regarding adverse drug reactions (ADRs), drug efficacy and dose requirement is rapidly growing. Polymorphisms in CYPs 1A1, 1A2, 2C8, 2E1, 2J2, and 3A4 are generally less predictive, but new data on CYP3A4 show that predictive variants exist and that additional variants in regulatory genes or in NADPH:cytochrome P450 oxidoreductase (POR) can have an influence. Here we review the recent progress on drug metabolism activity profiles, interindividual variability and regulation of expression, and the functional and clinical impact of genetic variation in drug metabolizing P450s.

Null CYP1B1 genotypes in primary congenital and nondominant juvenile glaucoma

PURPOSE

To assess the mutation spectrum, enzymatic activity, and phenotypic features associated with CYP1B1 genotypes in primary congenital glaucoma (PCG) and nondominant juvenile glaucoma (ndJG).

DESIGN

CYP1B1 genotyping, segregation analysis, and functional evaluation of mutations in a cohort of patients.

PARTICIPANTS

A total of 177 probands clinically diagnosed with PCG (161) or ndJG (16).

METHODS

Automatic DNA sequencing of the promoter (-1 to -867) and the 3 CYP1B1 exons. CYP1B1 enzymatic activity was evaluated using an ethoxyresorufin O-deethylation assay in transfected HEK-293T cells.

MAIN OUTCOME MEASURES

Screening and functional evaluation of CYP1B1 mutations. Glaucoma diagnosis based on slit-lamp examination, measurement of intraocular pressure, gonioscopy, and fundus examination.

RESULTS

Thirty-one different mutations were identified in 56 PCG and 7 ndJG index cases. To the best of our knowledge, 3 of the identified mutations were novel (-337G>T, F123L, and I399_P400del). Approximately 56% of all mutation carriers were compound heterozygotes, 25% were homozygotes, and both groups inherited glaucoma as an autosomal recessive trait. Nineteen percent of carriers were heterozygotes and showed non-Mendelian segregation. In vitro and inferred functional analysis showed that no less than approximately 74% of the recessive genotypes result in null enzymatic activity. We detected variable expressivity in relation to age of onset and a possible case of incomplete penetrance in 3 of 6 families (50%), with more than 1 affected child or more than 1 subject carrying 2 CYP1B1 mutant alleles. Altogether, these data support that PCG is not a simple monogenic disease. In addition, most patients with PCG carrying null or putative null genotypes showed severe bilateral phenotypes featured by early disease onset, frequently at birth. The mean number of trabeculectomies per eye was significantly higher in carriers than in noncarriers.

CONCLUSIONS

This is the largest analysis of CYP1B1 mutations performed in European patients with PCG to date. Our data show that null CYP1B1 genotypes, and therefore complete absence of CYP1B1 activity, frequently lead to severe phenotypes. Our results support that CYP1B1 glaucoma is not a simple monogenic disease and that CYP1B1 activity levels could influence the phenotype.

Molecular basis for involvement of CYP1B1 in MYOC upregulation and its potential implication in glaucoma pathogenesis

CYP1B1 has been implicated in primary congenital glaucoma with autosomal recessive mode of inheritance. Mutations in CYP1B1 have also been reported in primary open angle glaucoma (POAG) cases and suggested to act as a modifier of the disease along with Myocilin (MYOC). Earlier reports suggest that over-expression of myocilin leads to POAG pathogenesis. Taken together, we propose a functional interaction between CYP1B1 and myocilin where 17β estradiol acts as a mediator. Therefore, we hypothesize that 17β estradiol can induce MYOC expression through the putative estrogen responsive elements (EREs) located in its promoter and CYP1B1 could manipulate MYOC expression by metabolizing 17β estradiol to 4-hydroxy estradiol, thus preventing it from binding to MYOC promoter. Hence any mutation in CYP1B1 that reduces its 17β estradiol metabolizing activity might lead to MYOC upregulation, which in turn might play a role in glaucoma pathogenesis. It was observed that 17β estradiol is present in Human Trabecular Meshwork cells (HTM) and Retinal Pigment Epithelial cells (RPE) by immunoflouresence and ELISA. Also, the expression of enzymes related to estrogen biosynthesis pathway was observed in both cell lines by RT-PCR. Subsequent evaluation of the EREs in the MYOC promoter by luciferase assay, with dose and time dependent treatment of 17β estradiol, showed that the EREs are indeed active. This observation was further validated by direct binding of estrogen receptors (ER) on EREs in MYOC promoter and subsequent upregulation in MYOC level in HTM cells on 17β estradiol treatment. Interestingly, CYP1B1 mutants with less than 10% enzymatic activity were found to increase the level of endogenous myocilin in HTM cells. Thus the experimental observations are consistent with our proposed hypothesis that mutant CYP1B1, lacking the 17β estradiol metabolizing activity, can cause MYOC upregulation, which might have a potential implication in glaucoma pathogenesis.

Systematic genetic and genomic analysis of cytochrome P450 enzyme activities in human liver

Liver cytochrome P450s (P450s) play critical roles in drug metabolism, toxicology, and metabolic processes. Despite rapid progress in the understanding of these enzymes, a systematic investigation of the full spectrum of functionality of individual P450s, the interrelationship or networks connecting them, and the genetic control of each gene/enzyme is lacking. To this end, we genotyped, expression-profiled, and measured P450 activities of 466 human liver samples and applied a systems biology approach via the integration of genetics, gene expression, and enzyme activity measurements. We found that most P450s were positively correlated among themselves and were highly correlated with known regulators as well as thousands of other genes enriched for pathways relevant to the metabolism of drugs, fatty acids, amino acids, and steroids. Genome-wide association analyses between genetic polymorphisms and P450 expression or enzyme activities revealed sets of SNPs associated with P450 traits, and suggested the existence of both cis-regulation of P450 expression (especially for CYP2D6) and more complex trans-regulation of P450 activity. Several novel SNPs associated with CYP2D6 expression and enzyme activity were validated in an independent human cohort. By constructing a weighted coexpression network and a Bayesian regulatory network, we defined the human liver transcriptional network structure, uncovered subnetworks representative of the P450 regulatory system, and identified novel candidate regulatory genes, namely, EHHADH, SLC10A1, and AKR1D1. The P450 subnetworks were then validated using gene signatures responsive to ligands of known P450 regulators in mouse and rat. This systematic survey provides a comprehensive view of the functionality, genetic control, and interactions of P450s.

Molecular complexity of primary open angle glaucoma: current concepts

Glaucoma is a group of heterogeneous optic neuropathies with complex genetic basis. Among the three principle subtypes of glaucoma, primary open angle glaucoma (POAG) occurs most frequently. Till date, 25 loci have been found to be linked to POAG. However, only three underlying genes (Myocilin, Optineurin and WDR36) have been identified. In addition, at least 30 other genes have been reported to be associated with POAG. Despite strong genetic influence in POAG pathogenesis, only a small part of the disease can be explained in terms of genetic aberration. Current concepts of glaucoma pathogenesis suggest it to be a neurodegenerative disorder which is triggered by different factors including mechanical stress due to intra-ocular pressure, reduced blood flow to retina, reperfusion injury, oxidative stress, glutamate excitotoxicity, and aberrant immune response. Here we present a mechanistic overview of potential pathways and crosstalk between them operating in POAG pathogenesis.

CYP1B1, a developmental gene with a potential role in glaucoma therapy

The association of CYP1B1 gene alterations in primary congenital glaucoma individuals has been known for about a decade. Recent evidence has shown the involvement of CYP1B1 mutations in a number of forms of glaucoma and anterior segment disorders. This suggests a wide role for CYP1B1 in ocular physiology. Histochemical studies of eyes from individuals with primary congenital glaucoma revealed abnormalities in the anterior chamber angle, the region between the cornea and the iris, containing the trabecular meshwork. The cells of the trabecular meshwork serve as a filter to allow drainage of the aqueous humour, the fluid formed by the ciliary body that fills the anterior chamber. Mutations in CYP1B1 that affect its activity have frequently been shown to influence development of the trabecular meshwork, and it is thought that CYP1B1, a monooxygenase, acts to form or degrade some endobiotic compound that is necessary for proper development of the filtering structures. The rapidly developing area of stem cell research suggests a potential therapeutic approach for glaucomas resulting from deleterious mutations in CYP1B1, that is, the transfer of stem cells, differentiated to a specific lineage, containing wild-type CYP1B1 to specific regions of the eye, where they will develop into normal cells of that region and rectify the defect.

Functional analysis of CYP1B1 mutations and association of heterozygous hypomorphic alleles with primary open-angle glaucoma

Glaucoma is an inherited complex and heterogeneous disease, and one of the most prevalent causes of definitive blindness in the world. Recent reports have indicated that heterozygous mutations of the CYTOCHOROME P4501B1 (CYP1B1) gene are present in 4-10% of patients with primary open-angle glaucoma (POAG). To further evaluate the role of CYP1B1 mutations in POAG we extended our previous association study and carried out a functional analysis of the mutations identified by polymerase chain reaction (PCR) DNA sequencing of the three exons of the gene in a total of 245 unrelated Spanish patients and 326 control subjects. Eight of nine different mutations identified in these patients were cloned and functionally assessed by measuring ethoxyresorufin O-deethylation activity and CYP1B1 stability in transiently transfected HEK-293T cells. All these mutants showed reduced catalytic activity, ranging from 20% to 60% of wild-type and/or decreased protein stability and, therefore, they were classified as hypomorphic alleles. No null alleles were identified in these patients. We found heterozygous hypomorphic CYP1B1 mutations in 17 (6.7%) patients and in seven controls (2.1%) showing that these mutations are associated with an increased risk of POAG (p = 0.005; odds ratio = 3.2; 95% confidence interval = 1.30-9.19). Our data suggest that hypomorphic CYP1B1 mutations are, to date, the main known genetic risk factor in POAG.