CYP4V2 in Bietti's crystalline dystrophy: ocular localization, metabolism of ω-3-polyunsaturated fatty acids, and functional deficit of the p.H331P variant

Presence of corneal crystals confirms an unusual presentation of Bietti's retinal dystrophy

Background: Bietti crystalline corneoretinal dystrophy (BCD) (OMIM 210370) is a rare autosomal recessive retinal dystrophy typically characterized by multiple intraretinal crystals over the posterior pole of the retina. Degeneration of the retina and sclerosis of the choroidal vessels results in progressive night blindness and central visual field loss.Methods: Detailed ophthalmic and genetic testing of the patient and his father were performed.Results: We report on a 41-year-old male patient with advanced chorioretinal dystrophy at the posterior pole extending into the peripheral retina. His sister and his father were similarly affected with nyctalopia and decreased visual acuity, although his father had a milder phenotype of a typical macular dystrophy. On close slit-lamp examination, however, both patient and his father had multiple yellow-white crystals in the peripheral cornea. Corneal findings and consanguinity of the patient's parents lead to suspicion of BCD. Molecular genetic results of the patient and his father showed homozygous for CYP4V2, c. 197T>G p.(Met66Arg) confirming the diagnosis of BCD.Conclusions: The patient's pedigree shows pseudodominant inheritance due to consanguineous parents. However, careful examination of the corneal findings strengthened the clinical suspicion of BCD, facilitating the molecular genetic confirmation of this autosomal recessive disease.

Molecular Functionality of Cytochrome P450 4 (CYP4) Genetic Polymorphisms and Their Clinical Implications

Enzymes in the cytochrome P450 4 (CYP4) family are involved in the metabolism of fatty acids, xenobiotics, therapeutic drugs, and signaling molecules, including eicosanoids, leukotrienes, and prostanoids. As CYP4 enzymes play a role in the maintenance of fatty acids and fatty-acid-derived bioactive molecules within a normal range, they have been implicated in various biological functions, including inflammation, skin barrier, eye function, cardiovascular health, and cancer. Numerous studies have indicated that genetic variants of CYP4 genes cause inter-individual variations in metabolism and disease susceptibility. Genetic variants of CYP4A11, 4F2 genes are associated with cardiovascular diseases. Mutations of CYP4B1, CYP4Z1, and other CYP4 genes that generate 20-HETE are a potential risk for cancer. CYP4V2 gene variants are associated with ocular disease, while those of CYP4F22 are linked to skin disease and CYP4F3B is associated with the inflammatory response. The present study comprehensively collected research to provide an updated view of the molecular functionality of CYP4 genes and their associations with human diseases. Functional analysis of CYP4 genes with clinical implications is necessary to understand inter-individual variations in disease susceptibility and for the development of alternative treatment strategies.

Current perspectives in Bietti crystalline dystrophy

Bietti crystalline dystrophy (BCD) is a rare-inherited disease caused by mutations in the CYP4V2 gene and characterized by the presence of multiple shimmering yellow-white deposits in the posterior pole of the retina in association with atrophy of the retinal pigment epithelium (RPE) and chorioretinal atrophy. The additional presence of glittering dots located at the corneal limbus is also a frequent finding. The CYP4V2 protein belongs to the cytochrome P450 subfamily 4 and is mainly expressed in the retina and the RPE and less expressed in the cornea. The disease has its metabolic origin in the diminished transformation of fatty acid substrates into n-3 polyunsaturated fatty acids due to a dysregulation of the lipid metabolism. In this review, we provide updated insights on clinical and molecular characteristics of BCD including underlying mechanisms of BCD, genetic diagnosis, progress in the identification of causative genetic and epigenetic factors, available techniques of exploration and development of novel therapies. This information will help clinicians to improve accuracy of BCD diagnosis, providing the patient reliable information regarding prognosis and clinical prediction of the disease course.

Progesterone effects on extracellular vesicles in the sheep uterus

Progesterone (P4) acts via the endometrium to promote conceptus growth and implantation for pregnancy establishment. Many cells release extracellular vesicles (EVs) that are membrane-bound vesicles of endosomal and plasma membrane origin. In sheep, endometrial-derived EVs were found to traffic to the conceptus trophectoderm. Thus, EVs are hypothesized to be an important mode of intercellular communication by transferring select RNAs, proteins, and lipids between the endometrium and conceptus. Electron microscopy analysis found that the endometrial luminal and glandular epithelia were the primary source of EVs in the uterus of cyclic sheep. Size exclusion chromatography and nanoparticle tracking analysis (NTA) found that total EV number in the uterine lumen increased from day 10 to 14 in cyclic sheep. Next, ewes were ovariectomized and hormone replaced to determine effects of P4 on the endometrium and EVs in the uterine lumen. Transcriptome analyses found that P4 regulated 1611 genes and nine miRNAs in the endometrium. Total EV number in the uterine lumen was increased by P4 treatment. Small RNA sequencing of EVs detected expression of 768 miRNAs and determined that P4 regulated seven of those miRNAs. These studies provide fundamental new information on how P4 influences endometrial function to regulate conceptus growth for pregnancy establishment in sheep.

CYP4V2 mutation screening in an Iranian Bietti crystalline dystrophy pedigree and evidence for clustering of CYP4V2 mutations

Purpose

To report the genetic analysis of an Iranian Bietti crystalline dystrophy (BCD)-affected family, and to review previously reported mutations in the gene and assess the distribution of affected amino acids in the encoded protein.

Methods

The eleven exons of CYP4V2 were sequenced in the DNA of the proband of the Iranian BCD family. The putative disease-causing variation was screened in all affected and non-affected members. BCD causing CYP4V2 mutations previously reported in the literature were compiled, and positions of amino acids affected by nonsense and missense mutations were mapped onto the primary structure of the CYP4V2 protein.

Results

C.1219G > T in CYP4V2 that causes p.Glu407* was identified as cause of BCD in the Iranian family. The mutation segregated with disease status. Clinical presentations were similar among affected members, except that one patient presented with retinal macular hole. Twelve nonsense and 47 missense mutations in CYP4V2 were compiled. Inspection of distribution of amino acids affected by the mutations suggested non-random distribution and clustering of affected amino acids in nine regions of the protein, including regions that contain the heme binding site, the metal binding site, and a region between these binding sites. The most C-terminus proximal nonsense mutation affected position 482.

Conclusions

This study presents results of the genetic analysis of an Iranian BCD family. Protein regions affected by mutations within the nine mutation clusters include regions well conserved among orthologous proteins and human CYP4 proteins, some of which are associated with known functions. The findings may serve to identify reasonable candidate gene region targets for gene editing therapy approaches.

Identification of novel CYP4V2 genotypes associated with Bietti crystalline dystrophy and atypical anterior segment phenotypes in Spanish patients

PURPOSE

To identify the spectrum of disease-causing CYP4V2 variants in Spanish patients with clinically diagnosed Bietti crystalline dystrophy (BCD) over an 8-year period and to analyse the phenotype-genotype correlation of the identified variants.

METHODS

Four unrelated Spanish probands with a clinical diagnosis of BCD were recruited. Ophthalmological examination included visual acuity (VA), slit lamp examination, in vivo corneal confocal microscopy, funduscopy and fluoresceinic angiography. Genomic DNA was obtained from blood samples, and the exons and flanking intron sequences of the CYP4V2 gene were screened by Sanger sequencing. Family members of the patients with mutations in CYP4V2 gene were subsequently studied.

RESULTS

Clinical examination revealed retinal and corneal patterns compatible with BCD in all the participants. We identified a total of six CYP4V2 variants among the four carriers. As far as we know, the variant p.(Trp244Cysfs*33) has not previously been reported. This variant along with p.(Ala204Thr) and p.(Arg443Trp) were combined in three novel pathogenic phenotypes that share the presence of bilateral limbic glistening deposits, severe retinal damage and visual impairment and a fast rate of progression of the disease.

CONCLUSION

To the best of our knowledge, this study represents the largest effort to determine the genetic alterations underlying BCD in Spain to date. Our results show that analysis of CYP4V2 variants is required for a reliable diagnosis of BCD. We report a high prevalence of anterior segment changes in this Spanish BCD cohort, which we consider representative of the Spanish patients.

Models and Approaches Describing the Metabolism, Transport, and Toxicity of Drugs Administered by the Ocular Route

The eye is a complex organ with a series of anatomic barriers that provide protection from physical and chemical injury while maintaining homeostasis and function. The physiology of the eye is multifaceted, with dynamic flows and clearance mechanisms. This review highlights that in vitro ocular transport and metabolism models are confined by the availability of clinically relevant absorption, distribution, metabolism, and excretion (ADME) data. In vitro ocular transport models used for pharmacology and toxicity poorly predict ocular exposure. Although ocular cell lines cannot replicate in vivo conditions, these models can help rank-order new chemical entities in discovery. Historic ocular metabolism of small molecules was assumed to be inconsequential or assessed using authentic standards. While various in vitro models have been cited, no single system is perfect, and many must be used in combination. Several studies document the use of laboratory animals for the prediction of ocular pharmacokinetics in humans. This review focuses on the use of human-relevant and human-derived models which can be utilized in discovery and development to understand ocular disposition of new chemical entities. The benefits and caveats of each model are discussed. Furthermore, ADME case studies are summarized retrospectively and capture the ADME data collected for health authorities in the absence of definitive guidelines. Finally, we discuss the novel technologies and a hypothesis-driven ocular drug classification system to provide a holistic perspective on the ADME properties of drugs administered by the ocular route.

Comprehensive screening of CYP4V2 in a cohort of Chinese patients with Bietti crystalline dystrophy

PURPOSE

Bietti crystalline dystrophy (BCD) is an autosomal recessive retinal degeneration disorder caused by mutations in CYP4V2. The aim of this study is to describe the genetic and clinical findings in 128 unrelated Chinese patients diagnosed with BCD.

METHODS

Ophthalmological evaluations were performed in all patients. All coding regions of CYP4V2 were amplified and sequenced directly. Real-time quantitative PCR was performed to detect copy number variations. Haplotype analysis was performed in 70 patients with c.802-8_810del17insGC and in 93 normal controls.

RESULTS

A total of 28 mutations in CYP4V2, including eight novel mutations, were identified in 125 patients. The most common mutation was c.802-8_810del17insGC, with an allele frequency of 62.6%, followed by p.H331P (8.7%) and c.1091-2A>G (7.5%). A novel large deletion encompassing exon 8 of CYP4V2 was detected. Haplotype analysis revealed four common haplotypes in patients with c.802-8_810del17insGC. A 17.6 kb haplotype CT(delCT)TA(Indel)A was the most common and was observed in 34.5% of the c.802-8_810del17insGC mutant alleles. The patients with mutations in CYP4V2 showed wide intra- and interfamilial variability in clinical severity.

CONCLUSIONS

The findings expand the mutational spectrum of CYP4V2 and further confirm the c.802-8_810del17insGC mutation was due to a founder effect in a large cohort of Chinese patients.

Profiling cytochrome P450 family 4 gene expression in human hepatocellular carcinoma

Cytochrome P450 family 4 (CYP4) enzymes are known as microsomal omega (ω)-hydroxylases that metabolize fatty acids, eicosanoids, vitamin D and carcinogens. Thus, CYP4 enzymes may influence tumor development and progression. The aim of the present study was to evaluate the CYP4 expression profile in hepatocellular carcinoma (HCC) and its clinical relevance. The present study obtained CYP4 mRNA expression data for 377 HCC cases from The Cancer Genome Atlas cohort and performed Kaplan‑Meier survival, Gene Ontology functional enrichment, and gene set enrichment analysis (GSEA). In addition, the level of CYP4F2 protein expression was evaluated in matched pairs of HCC and non‑tumor tissue samples and the results were correlated with the clinicopathological characteristics of HCC (n=113). HCC survival analyses indicated better overall survival in patients with high CYP4F2, CYP4F12 and CYP4V2 mRNA expression levels; the results for histological grade and Tumor‑Node‑Metastasis stage supported these results. GSEA revealed high levels of CYP4F2, CYP4F12 and CYP4V2 mRNA expression to be negatively correlated with the expression of cell cycle‑associated genes. CYP4F2 protein expression was higher in non‑neoplastic liver tissue than in HCC tissue and positively correlated with favorable pathological tumor stage (I vs. II‑IV; P=0.022) and was a good independent prognostic factor for overall survival (P=0.004). These results demonstrate that the expression levels of the genes CYP4F2, CYP4F12 and CYPV2 are favorable prognostic factors in HCC and suggest the potential predictive diagnostic and prognostic roles of CYP4F2, CYP4F12 and CYPV2 gene expression in HCC.

Secretome Screening Reveals Fibroblast Growth Factors as Novel Inhibitors of Viral Replication

Cellular antiviral programs can efficiently inhibit viral infection. These programs are often initiated through signaling cascades induced by secreted proteins, such as type I interferons, interleukin-6 (IL-6), or tumor necrosis factor alpha (TNF-α). In the present study, we generated an arrayed library of 756 human secreted proteins to perform a secretome screen focused on the discovery of novel modulators of viral entry and/or replication. The individual secreted proteins were tested for the capacity to inhibit infection by two replication-competent recombinant vesicular stomatitis viruses (VSVs) with distinct glycoproteins utilizing different entry pathways. Fibroblast growth factor 16 (FGF16) was identified and confirmed as the most prominent novel inhibitor of both VSVs and therefore of viral replication, not entry. Importantly, an antiviral interferon signature was completely absent in FGF16-treated cells. Nevertheless, the antiviral effect of FGF16 is broad, as it was evident on multiple cell types and also on infection by coxsackievirus. In addition, other members of the FGF family also inhibited viral infection. Thus, our unbiased secretome screen revealed a novel protein family capable of inducing a cellular antiviral state. This previously unappreciated role of the FGF family may have implications for the development of new antivirals and the efficacy of oncolytic virus therapy.IMPORTANCE Viruses infect human cells in order to replicate, while human cells aim to resist infection. Several cellular antiviral programs have therefore evolved to resist infection. Knowledge of these programs is essential for the design of antiviral therapeutics in the future. The induction of antiviral programs is often initiated by secreted proteins, such as interferons. We hypothesized that other secreted proteins may also promote resistance to viral infection. Thus, we tested 756 human secreted proteins for the capacity to inhibit two pseudotypes of vesicular stomatitis virus (VSV). In this secretome screen on viral infection, we identified fibroblast growth factor 16 (FGF16) as a novel antiviral against multiple VSV pseudotypes as well as coxsackievirus. Subsequent testing of other FGF family members revealed that FGF signaling generally inhibits viral infection. This finding may lead to the development of new antivirals and may also be applicable for enhancing oncolytic virus therapy.

Reduction of lipid accumulation rescues Bietti's crystalline dystrophy phenotypes

Bietti’s crystalline dystrophy (BCD) is an autosomal recessive, progressive chorioretinal degenerative disease. Retinal pigment epithelium (RPE) cells are impaired in patients with BCD, but the underlying mechanisms of RPE cell damage have not yet been determined because cells from lesions cannot be readily acquired from patients with BCD. In the present study, we successfully generated a human in vitro model of BCD, BCD patient-specific iPSC-RPE cells, and demonstrated that the accumulation of free cholesterol caused RPE cell damage and subsequent cell death via the induction of lysosomal dysfunction and impairment of autophagy flux in BCD-affected cells. We believe these findings provide evidence of the possible therapeutic efficacy of reducing intracellular free cholesterol in BCD.

Bietti’s crystalline dystrophy (BCD) is an intractable and progressive chorioretinal degenerative disease caused by mutations in the CYP4V2 gene, resulting in blindness in most patients. Although we and others have shown that retinal pigment epithelium (RPE) cells are primarily impaired in patients with BCD, the underlying mechanisms of RPE cell damage are still unclear because we lack access to appropriate disease models and to lesion-affected cells from patients with BCD. Here, we generated human RPE cells from induced pluripotent stem cells (iPSCs) derived from patients with BCD carrying a CYP4V2 mutation and successfully established an in vitro model of BCD, i.e., BCD patient-specific iPSC-RPE cells. In this model, RPE cells showed degenerative changes of vacuolated cytoplasm similar to those in postmortem specimens from patients with BCD. BCD iPSC-RPE cells exhibited lysosomal dysfunction and impairment of autophagy flux, followed by cell death. Lipidomic analyses revealed the accumulation of glucosylceramide and free cholesterol in BCD-affected cells. Notably, we found that reducing free cholesterol by cyclodextrins or δ-tocopherol in RPE cells rescued BCD phenotypes, whereas glucosylceramide reduction did not affect the BCD phenotype. Our data provide evidence that reducing intracellular free cholesterol may have therapeutic efficacy in patients with BCD.

CHOROIDAL AND RETINAL ATROPHY OF BIETTI CRYSTALLINE DYSTROPHY PATIENTS WITH CYP4V2 MUTATIONS COMPARED TO RETINITIS PIGMENTOSA PATIENTS WITH EYS MUTATIONS

PURPOSE

To compare atrophy of the choroid and retina between Bietti crystalline dystrophy (BCD) patients and EYS-related retinitis pigmentosa (RP) patients with a similar degree of central visual field defects, age, and axial length (AL).

METHODS

Nine eyes of nine BCD patients with CYP4V2 mutations (BCD group) were examined. Moreover, we selected 10 eyes of 10 RP patients with EYS mutations matched for age, axial length, and mean deviation (measured with the 10-2 SITA standard program; EYS-RP group), and 10 eyes of 10 normal volunteers matched for age and axial length (control group). Macular thicknesses of the choroid and retina were measured via swept-source optical coherence tomography.

RESULTS

The macular choroid was significantly thinner in the BCD group than in the EYS-RP and control groups, although the thickness did not significantly differ between the EYS-RP and control groups. The macular retina was significantly thinner in the BCD and EYS-RP groups than in the control group, although the thickness did not significantly differ between the BCD and EYS-RP groups at most sites.

CONCLUSION

Bietti crystalline dystrophy patients with CYP4V2 mutations showed more severe macular choroid atrophy as compared to EYS-related RP patients. These different damage patterns suggest differences in choroidal expression between CYP4V2 and EYS.

Choriocapillaris flow deficit in Bietti crystalline dystrophy detected using optical coherence tomography angiography

Background/Aims

This study aimed to evaluate blood flow in the choriocapillaris in patients with Bietti crystalline dystrophy (BCD) with CYP4V2 mutations using optical coherence tomography angiography (OCTA), and to explore the parameters associated with visual function.

Methods

This prospective case-series study included 13 eyes of 13 consecutive patients with BCD with CYP4V2 mutations and 20 healthy eyes. Using OCTA, we obtained en face images of blood flow in the choriocapillaris. The residual choriocapillaris area on en face images in a 10°×10° macular cube was manually measured and graded according to whether the choriocapillaris remained at the subfovea. We also investigated factors associated with visual acuity (VA) and the mean deviation (MD) value using a Humphrey field analyser with a 10–2 Swedish Interactive Threshold Algorithm standard program among OCTA-derived parameters.

Results

Choriocapillaris blood flow deficit was observed in 12 eyes (92%), whereas this was observed in none of healthy eyes. The adjusted residual choriocapillaris area was 2.47±1.79 mm2. The presence of the choriocapillaris at the subfovea was significantly correlated with VA and the MD value (P=0.006, r=0.71; P=0.04, r=−0.59, respectively).

Conclusions

Using OCTA, choriocapillaris blood flow deficit could be observed in most patients with BCD with CYP4V2 mutations. The presence of the choriocapillaris at the subfovea was significantly correlated with visual function in these patients. Analysis of choriocapillaris blood flow using OCTA allows non-invasive assessment of the patient’s state.

Expression and Functional Characterization of Breast Cancer-Associated Cytochrome P450 4Z1 in Saccharomyces cerevisiae

CYP4Z1 is an "orphan" cytochrome P450 (P450) enzyme that has provoked interest because of its hypothesized role in breast cancer through formation of the signaling molecule 20-hydroxyeicosatetraenoic acid (20-HETE). We expressed human CYP4Z1 in Saccharomyces cerevisiae and evaluated its catalytic capabilities toward arachidonic and lauric acids (AA and LA). Specific and sensitive mass spectrometry assays enabled discrimination of the regioselectivity of hydroxylation of these two fatty acids. CYP4Z1 generated 7-, 8-, 9-, 10-, and 11-hydroxy LA, whereas the 12-hydroxy metabolite was not detected. HET0016, the prototypic CYP4 inhibitor, only weakly inhibited laurate metabolite formation (IC50 ∼15 μM). CYP4Z1 preferentially oxidized AA to the 14(S),15(R)-epoxide with high regioselectivity and stereoselectivity, a reaction that was also insensitive to HET0016, but neither 20-HETE nor 20-carboxy-AA were detectable metabolites. Docking of LA and AA into a CYP4Z1 homology model was consistent with this preference for internal fatty acid oxidation. Thus, human CYP4Z1 has an inhibitor profile and product regioselectivity distinct from most other CYP4 enzymes, consistent with CYP4Z1's lack of a covalently linked heme. These data suggest that, if CYP4Z1 modulates breast cancer progression, it does so by a mechanism other than direct production of 20-HETE.

Specific regulation of thermosensitive lipid droplet fusion by a nuclear hormone receptor pathway

Nuclear receptors play important roles in regulating fat metabolism and energy production in humans. The regulatory functions and endogenous ligands of many nuclear receptors are still unidentified, however. Here, we report that CYP-37A1 (ortholog of human cytochrome P450 CYP4V2), EMB-8 (ortholog of human P450 oxidoreductase POR), and DAF-12 (homolog of human nuclear receptors VDR/LXR) constitute a hormone synthesis and nuclear receptor pathway in Caenorhabditis elegans This pathway specifically regulates the thermosensitive fusion of fat-storing lipid droplets. CYP-37A1, together with EMB-8, synthesizes a lipophilic hormone not identical to Δ7-dafachronic acid, which represses the fusion-promoting function of DAF-12. CYP-37A1 also negatively regulates thermotolerance and lifespan at high temperature in a DAF-12-dependent manner. Human CYP4V2 can substitute for CYP-37A1 in C. elegans This finding suggests the existence of a conserved CYP4V2-POR-nuclear receptor pathway that functions in converting multilocular lipid droplets to unilocular ones in human cells; misregulation of this pathway may lead to pathogenic fat storage.

Expression of CYP4V2 in human THP1 macrophages and its transcriptional regulation by peroxisome proliferator-activated receptor gamma

Because macrophages respond to a variety of pathological and pharmacological reagents, understanding the role of P450s in macrophages is important for therapeutic intervention. There has been a lack of research on CYP4 in macrophages, but fatty acid accumulation and lipid trafficking in macrophages have been suggested to be a main cause of atherosclerosis. All human CYP4 genes (n=12) were screened in THP1 macrophages by gene-specific reverse transcriptase-polymerase chain reaction (RT-PCR). Only CYP4V2 exhibited strong expression of both mRNA and protein. Expression levels of both CYP4V2 mRNA and protein were significantly reduced after treatment with peroxisome proliferator-activated receptor gamma (PPARγ) antagonist GW9662. However, the expression levels of CYP4V2 were not changed by PPARα antagonist (GW6471) and liver X receptor alpha antagonist (22-S hydroxycholesterol). A metabolite of the CYP4V2 enzyme, 12-hydroxydodecanoic acid, was detected in THP1 macrophages, and this metabolite was significantly decreased after treatment with the PPARγ inhibitor GW9662 (>80% decreased, p<0.05). In summary, fatty acid metabolizing protein CYP4V2 was identified in human THP1 macrophages, and its expression was regulated by PPARγ. Further study is required to understand the role of CYP4V2 with regard to fat accumulation in the activated macrophage and atherosclerotic plaque development.

Longitudinal characterisation of function and structure of Bietti crystalline dystrophy: report on a novel homozygous mutation in CYP4V2

BACKGROUND

Bietti crystalline dystrophy (BCD) is a rare inherited disorder characterised by fine crystalline deposits in the corneal limbus and retinal posterior pole. In 2004, mutations in the CYP4V2 gene were identified as the cause of BCD. Here, we describe the report of a homozygous point mutation in a patient with BCD and provide detailed characterisation of functional and structural changes over 20 years.

METHODS

At regular intervals, the patient underwent repeat ophthalmic evaluations. DNA was extracted from buccal swabs, amplified by standard PCR and analysed for homology to the CYP4V2 sequence. Homology modelling was conducted using Iterative Threading ASSEmbly Refinement and molecular dynamics simulations using GROningen MAchine for Chemical Simulations.

RESULTS

The proband, a 47-year-old woman of German ancestry was diagnosed with crystalline retinopathy at age 25. Over the next 20 years, visual acuity and function gradually declined with progression of retinal pigment epithelium and choroidal atrophy. When first tested at 39 years of age, the multifocal electroretinogram (ERG) was markedly abnormal, more so for the right eye, whereas the full-field ERG was more symmetrical and lagged other measures of visual function. Gene sequencing showed a single C>T point mutation in exon 9 encoding a R400C amino acid change. Computational modelling suggests the mutation impairs function due to loss of a hydrogen bonding interaction with the propionate side chains of the haeme prosthetic group.

CONCLUSION

This is the first report of a homozygous R400C mutation in CYP4V2 with protein modelling showing high likelihood of enzyme dysfunction. The comprehensive long-term clinical follow-up provides insight into disease progression and highlights possible anti-inflammatory modulation of disease severity.

The Crystal Structure of Cytochrome P450 4B1 (CYP4B1) Monooxygenase Complexed with Octane Discloses Several Structural Adaptations for ω-Hydroxylation

P450 family 4 fatty acid ω-hydroxylases preferentially oxygenate primary C-H bonds over adjacent, energetically favored secondary C-H bonds, but the mechanism explaining this intriguing preference is unclear. To this end, the structure of rabbit P450 4B1 complexed with its substrate octane was determined by X-ray crystallography to define features of the active site that contribute to a preference for ω-hydroxylation. The structure indicated that octane is bound in a narrow active-site cavity that limits access of the secondary C-H bond to the reactive intermediate. A highly conserved sequence motif on helix I contributes to positioning the terminal carbon of octane for ω-hydroxylation. Glu-310 of this motif auto-catalytically forms an ester bond with the heme 5-methyl, and the immobilized Glu-310 contributes to substrate positioning. The preference for ω-hydroxylation was decreased in an E310A mutant having a shorter side chain, but the overall rates of metabolism were retained. E310D and E310Q substitutions having longer side chains exhibit lower overall rates, likely due to higher conformational entropy for these residues, but they retained high preferences for octane ω-hydroxylation. Sequence comparisons indicated that active-site residues constraining octane for ω-hydroxylation are conserved in family 4 P450s. Moreover, the heme 7-propionate is positioned in the active site and provides additional restraints on substrate binding. In conclusion, P450 4B1 exhibits structural adaptations for ω-hydroxylation that include changes in the conformation of the heme and changes in a highly conserved helix I motif that is associated with selective oxygenation of unactivated primary C-H bonds.

Identification and population history of CYP4V2 mutations in patients with Bietti crystalline corneoretinal dystrophy

To identify known and novel CYP4V2 mutations in patients with Bietti crystalline cornea (BCD), expand the spectrum of CYP4V2 mutations, and characterize the population history of the c.802-8_810del17insGC mutation common in Asian populations, genomic DNA was isolated from peripheral blood samples from 58 unrelated patients with clinical diagnoses of BCD. Exons and flanking intronic regions of the CYP4V2 gene were dideoxy DNA sequenced. Nonpathogenic polymorphisms were excluded and known mutations were identified by sequencing 192 unaffected individuals from similar ethnic backgrounds and examination of online databases. The age of the c.802-8_810del17insGC mutation was estimated using three independent approaches. A total of 28 CYP4V2 mutations, 9 of which were novel, were detected in the 58 patients with BCD. These included 19 missense, 4 nonsense, 2 deletion, 2 splice site, and 1 insertion-deletion mutations. Two missense variants of uncertain significance were also detected. The age of the c.802-8_810del17insGC mutation was estimated to be 1040-8200 generations in the Chinese and 300-1100 generations in the Japanese populations. These results expand the mutation spectrum of CYP4V2, and provide insight into the origin of the c.802-8_810del17insGC mutation in the Chinese population and its transmission to the Japanese population.

A genome-wide association meta-analysis on apolipoprotein A-IV concentrations

Apolipoprotein A-IV (apoA-IV) is a major component of HDL and chylomicron particles and is involved in reverse cholesterol transport. It is an early marker of impaired renal function. We aimed to identify genetic loci associated with apoA-IV concentrations and to investigate relationships with known susceptibility loci for kidney function and lipids. A genome-wide association meta-analysis on apoA-IV concentrations was conducted in five population-based cohorts (n = 13,813) followed by two additional replication studies (n = 2,267) including approximately 10 M SNPs. Three independent SNPs from two genomic regions were significantly associated with apoA-IV concentrations: rs1729407 near APOA4 (P = 6.77 × 10 ^{-  44}), rs5104 in APOA4 (P = 1.79 × 10^-24) and rs4241819 in KLKB1 (P = 5.6 × 10^-14). Additionally, a look-up of the replicated SNPs in downloadable GWAS meta-analysis results was performed on kidney function (defined by eGFR), HDL-cholesterol and triglycerides. From these three SNPs mentioned above, only rs1729407 showed an association with HDL-cholesterol (P = 7.1 × 10 ^{-  07}). Moreover, weighted SNP-scores were built involving known susceptibility loci for the aforementioned traits (53, 70 and 38 SNPs, respectively) and were associated with apoA-IV concentrations. This analysis revealed a significant and an inverse association for kidney function with apoA-IV concentrations (P = 5.5 × 10^-05). Furthermore, an increase of triglyceride-increasing alleles was found to decrease apoA-IV concentrations (P = 0.0078). In summary, we identified two independent SNPs located in or next the APOA4 gene and one SNP in KLKB1 The association of KLKB1 with apoA-IV suggests an involvement of apoA-IV in renal metabolism and/or an interaction within HDL particles. Analyses of SNP-scores indicate potential causal effects of kidney function and by lesser extent triglycerides on apoA-IV concentrations.

Genetics of Bietti Crystalline Dystrophy

Bietti crystalline dystrophy (BCD) is an inherited retinal degenerative disease characterized by crystalline deposits in the retina, followed by progressive atrophy of the retinal pigment epithelium (RPE), choriocapillaris, and photoreceptors. CYP4V2 has been identified as the causative gene for BCD. The CYP4V2 gene belongs to the cytochrome P450 superfamily and encodes for fatty acid ω-hydroxylase of both saturated and unsaturated fatty acids. The CYP4V2 protein is localized most abundantly within the endoplasmic reticulum in the RPE and is postulated to play a role in the physiological lipid recycling system between the RPE and photoreceptors to maintain visual function. Electroretinographic assessments have revealed progressive dysfunction of rod and cone photoreceptors in patients with BCD. Several genotypes have been associated with more severe phenotypes based on clinical and electrophysiological findings. With the advent of multimodal imaging with spectral domain optical coherence tomography, fundus autofluorescence, and adaptive optics scanning laser ophthalmoscopy, more precise delineation of BCD severity and progression is now possible, allowing for the potential future development of targets for gene therapy.

Detailed functional and structural phenotype of Bietti crystalline dystrophy associated with mutations in CYP4V2 complicated by choroidal neovascularization

PURPOSE

To describe in detail the phenotype of a patient with Bietti crystalline dystrophy (BCD) complicated by choroidal neovascularization (CNV) and the response to intravitreal Bevacizumab (Avastin^®; Genentech/Roche).

METHODS

A 34-year-old woman with BCD and mutations in CYP4V2 (c.802-8_806del13/p.H331P:c992A>C) underwent a complete ophthalmic examination, full-field flash electroretinography (ERG), kinetic and two-color dark-adapted perimetry, and dark-adaptometry. Imaging was performed with spectral domain optical coherence tomography (SD-OCT), near infrared (NIR) and short wavelength (SW) fundus autofluorescence (FAF), and fluorescein angiography (FA).

RESULTS

Best-corrected visual acuity (BCVA) was 20/20 and 20/60 for the right and left eye, respectively. There were corneal paralimbal crystal-like deposits. Kinetic fields were normal in the peripheral extent. Retinal crystals were most obvious on NIR-reflectance and corresponded with hyperreflectivities within the RPE on SD-OCT. There was parafoveal/perifoveal hypofluorescence on SW-FAF and NIR-FAF. Rod > cone sensitivity loss surrounded fixation and extended to ~10° of eccentricity corresponding to regions of photoreceptor outer segment-retinal pigmented epithelium (RPE) interdigitation abnormalities. The outer nuclear layer was normal in thickness. Recovery of sensitivity following a ~76% rhodopsin bleach was normal. ERGs were normal. A subretinal hemorrhage in the left eye co-localized with elevation of the RPE on SD-OCT and leakage on FA, suggestive of CNV. Three monthly intravitreal injections of Bevacizumab led to restoration of BCVA to baseline (20/25).

CONCLUSION

crystals in BCD were predominantly located within the RPE. Photoreceptor outer segment and apical RPE abnormalities underlie the relatively extensive retinal dysfunction observed in relatively early-stage BCD. Intravitreal Bevacizumab was effective in treating CNV in this setting.

Evaluation of Photoreceptors in Bietti Crystalline Dystrophy with CYP4V2 Mutations Using Adaptive Optics Scanning Laser Ophthalmoscopy

PURPOSE

To evaluate photoreceptors in Bietti crystalline dystrophy patients with CYP4V2 mutations using high-resolution images of the macula obtained with adaptive optics scanning laser ophthalmoscopy (AO-SLO).

DESIGN

Prospective observational case series with comparison to healthy controls.

METHODS

Seven eyes of 7 Bietti crystalline dystrophy patients with CYP4V2 mutations and 12 normal eyes of 12 age- and axial length-matched healthy volunteers were studied. All participants underwent ophthalmologic examinations and AO-SLO assessments. All patients underwent spectral-domain optical coherence tomography, fundus autofluorescence, Humphrey field analysis, and electroretinography. AO-SLO images were analyzed 0.5 mm and 1.0 mm from the center of the fovea in the superior, inferior, nasal, and temporal quadrants.

RESULTS

Mean ± standard deviation cone density (cells/mm(2)) 0.5 mm from the center of the fovea was 17,209 ± 2276 in patients and 20 493 ± 2758 in controls, which was statistically different (P = .001); however, mean cone density 1.0 mm from the center of the fovea was 15 685 ± 2302 in patients and 15 705 ± 1848 in controls, which was not statistically different (P = .20). There was no correlation between cone density and mean deviation measured using a Humphrey field analysis or visual acuity in patients.

CONCLUSIONS

In Bietti crystalline dystrophy patients with CYP4V2 mutations, cone density remained for visual dysfunction by evaluation using high-resolution AO-SLO. These findings support the theory that disorder of the retinal pigment epithelium and the photoreceptors in the patients are the primary and secondary pathologic changes, respectively. This is consistent with results from previous basic studies.

Relapse of choroidal neovascularization in Bietti's crystalline retinopathy following anti-vascular endothelial growth factor therapy: A case report

Choroidal neovascularization secondary to retinitis pigmentosa is rarely observed in clinical practice. The present study describes a case of atypical retinitis pigmentosa, crystalline retinal pigmentary degeneration, complicated by choroidal neovascularization (CNV) in a 26-year-old man presenting with blurred vision in the right eye. Heidelberg multimodality imaging was performed to achieve a confirmed diagnosis. Bevacizumab was injected once intravitreally. The 3-month follow-up included visualization of the lesion's regression with spectral domain optical coherence tomography (SD-OCT). However, at 3 months after the injection, the CNV reoccurred. To the best of our knowledge, this is the first time that a case of CNV secondary to retinitis pigmentosa, in which the diagnosis was confirmed via multimodality imaging and the therapeutic efficacy was evaluated by SD-OCT, has been reported in China.

Characterization of an Additional Splice Acceptor Site Introduced into CYP4B1 in Hominoidae during Evolution

CYP4B1 belongs to the cytochrome P450 family 4, one of the oldest P450 families whose members have been highly conserved throughout evolution. The CYP4 monooxygenases typically oxidize fatty acids to both inactive and active lipid mediators, although the endogenous ligand(s) is largely unknown. During evolution, at the transition of great apes to humanoids, the CYP4B1 protein acquired a serine instead of a proline at the canonical position 427 in the meander region. Although this alteration impairs P450 function related to the processing of naturally occurring lung toxins, a study in transgenic mice suggested that an additional serine insertion at position 207 in human CYP4B1 can rescue the enzyme stability and activity. Here, we report that the genomic insertion of a CAG triplet at the intron 5–exon 6 boundary in human CYP4B1 introduced an additional splice acceptor site in frame. During evolution, this change occurred presumably at the stage of Hominoidae and leads to two major isoforms of the CYP4B1 enzymes of humans and great apes, either with or without a serine 207 insertion (insSer207). We further demonstrated that the CYP4B1 enzyme with insSer207 is the dominant isoform (76%) in humans. Importantly, this amino acid insertion did not affect the 4-ipomeanol metabolizing activities or stabilities of the native rabbit or human CYP4B1 enzymes, when introduced as transgenes in human primary cells and cell lines. In our 3D modeling, this functional neutrality of insSer207 is compatible with its predicted location on the exterior surface of CYP4B1 in a flexible side chain. Therefore, the Ser207 insertion does not rescue the P450 functional activity of human CYP4B1 that has been lost during evolution.

CCND1-CDK4-mediated cell cycle progression provides a competitive advantage for human hematopoietic stem cells in vivo

Maintenance of stem cell properties is associated with reduced proliferation but it is unknown whether the transition kinetics through distinct cell cycle phases influences the function of HSCs. Mende et al examine the effects of increasing two cell cycle complexes CCND1–CDK4 and CCNE1–CDK2 on the transition kinetics of human HSCs and their maintenance and functional alterations in vivo.

Maintenance of stem cell properties is associated with reduced proliferation. However, in mouse hematopoietic stem cells (HSCs), loss of quiescence results in a wide range of phenotypes, ranging from functional failure to extensive self-renewal. It remains unknown whether the function of human HSCs is controlled by the kinetics of cell cycle progression. Using human HSCs and human progenitor cells (HSPCs), we report here that elevated levels of CCND1–CDK4 complexes promoted the transit from G0 to G1 and shortened the G1 cell cycle phase, resulting in protection from differentiation-inducing signals in vitro and increasing human leukocyte engraftment in vivo. Further, CCND1–CDK4 overexpression conferred a competitive advantage without impacting HSPC numbers. In contrast, accelerated cell cycle progression mediated by elevated levels of CCNE1–CDK2 led to the loss of functional HSPCs in vivo. Collectively, these data suggest that the transition kinetics through the early cell cycle phases are key regulators of human HSPC function and important for lifelong hematopoiesis.

Cytochrome P450 ω-Hydroxylases in Inflammation and Cancer

Cytochrome P450-dependent ω-hydroxylation is a prototypic metabolic reaction of CYP4 family members that is important for the elimination and bioactivation of not only therapeutic drugs, but also endogenous compounds, principally fatty acids. Eicosanoids, derived from arachidonic acid, are key substrates in the latter category. Human CYP4 enzymes, mainly CYP4A11, CYP4F2, and CYP4F3B, hydroxylate arachidonic acid at the omega position to form 20-HETE, which has important effects in tumor progression and on angiogenesis and blood pressure regulation in the vasculature and kidney. CYP4F3A in myeloid tissue catalyzes the ω-hydroxylation of leukotriene B4 to 20-hydroxy leukotriene B4, an inactivation process that is critical for the regulation of the inflammatory response. Here, we review the enzymology, tissue distribution, and substrate selectivity of human CYP4 ω-hydroxylases and their roles as catalysts for the formation and termination of the biological effects of key eicosanoid metabolites in inflammation and cancer progression.

Identification of amino acid determinants in CYP4B1 for optimal catalytic processing of 4-ipomeanol

Mammalian CYP4B1 enzymes are cytochrome P450 mono-oxygenases that are responsible for the bioactivation of several exogenous pro-toxins including 4-ipomeanol (4-IPO). In contrast with the orthologous rabbit enzyme, we show here that native human CYP4B1 with a serine residue at position 427 is unable to bioactivate 4-IPO and does not cause cytotoxicity in HepG2 cells and primary human T-cells that overexpress these enzymes. We also demonstrate that a proline residue in the meander region at position 427 in human CYP4B1 and 422 in rabbit CYP4B1 is important for protein stability and rescues the 4-IPO bioactivation of the human enzyme, but is not essential for the catalytic activity of the rabbit CYP4B1 protein. Systematic substitution of native and p.S427P human CYP4B1 with peptide regions from the highly active rabbit enzyme reveals that 18 amino acids in the wild-type rabbit CYP4B1 protein are key for conferring high 4-IPO metabolizing activity. Introduction of 12 of the 18 amino acids that are also present at corresponding positions in other human CYP4 family members into the p.S427P human CYP4B1 protein results in a mutant human enzyme (P+12) that is as stable and as active as the rabbit wild-type CYP4B1 protein. These 12 mutations cluster in the predicted B-C loop through F-helix regions and reveal new amino acid regions important to P450 enzyme stability. Finally, by minimally re-engineering the human CYP4B1 enzyme for efficient activation of 4-IPO, we have developed a novel human suicide gene system that is a candidate for adoptive cellular therapies in humans.

The clinical spectrum of inherited diseases involved in the synthesis and remodeling of complex lipids. A tentative overview

Over one hundred diseases related to inherited defects of complex lipids synthesis and remodeling are now reported. Most of them were described within the last 5 years. New descriptions and phenotypes are expanding rapidly. While the associated clinical phenotype is currently difficult to outline, with only a few patients identified, it appears that all organs and systems may be affected. The main clinical presentations can be divided into (1) Diseases affecting the central and peripheral nervous system. Complex lipid synthesis disorders produce prominent motor manifestations due to upper and/or lower motoneuron degeneration. Motor signs are often complex, associated with other neurological and extra-neurological signs. Three neurological phenotypes, spastic paraparesis, neurodegeneration with brain iron accumulation and peripheral neuropathies, deserve special attention. Many apparently well clinically defined syndromes are not distinct entities, but rather clusters on a continuous spectrum, like for the PNPLA6-associated diseases, extending from Boucher-Neuhauser syndrome via Gordon Holmes syndrome to spastic ataxia and pure hereditary spastic paraplegia; (2) Muscular/cardiac presentations; (3) Skin symptoms mostly represented by syndromic (neurocutaneous) and non syndromic ichthyosis; (4) Retinal dystrophies with syndromic and non syndromic retinitis pigmentosa, Leber congenital amaurosis, cone rod dystrophy, Stargardt disease; (5) Congenital bone dysplasia and segmental overgrowth disorders with congenital lipomatosis; (6) Liver presentations characterized mainly by transient neonatal cholestatic jaundice and non alcoholic liver steatosis with hypertriglyceridemia; and (7) Renal and immune presentations. Lipidomics and molecular functional studies could help to elucidate the mechanism(s) of dominant versus recessive inheritance observed for the same gene in a growing number of these disorders.

Generation and characterization of a murine model of Bietti crystalline dystrophy

PURPOSE

Bietti crystalline dystrophy (BCD) is a rare, autosomal recessive, progressive, degenerative eye disease caused by mutations in the CYP4V2 gene, for which no treatments are currently available. Cyp4v3 is the murine ortholog to CYP4V2, and to better understand the molecular pathogenesis of this disease we have established a Cyp4v3-null mouse line.

METHODS

Cyp4v3(-/-) mice were generated by homologous recombination in embryonic stem cells. Ocular morphologic characteristics were evaluated via fundus imaging, plasma lipid profiling, and histologic analysis via Oil Red O reactivity, hematoxylin and eosin staining, and transmission electron microscopy.

RESULTS

The Cyp4v3(-/-) mouse recapitulates the characteristic features of corneoretinal crystal accumulation and systemic dyslipidemia seen in BCD. The Cyp4v3(-/-) mice behave normally and are viable and fertile when maintained under specific pathogen-free (SPF) housing conditions.

CONCLUSIONS

Cyp4v3(-/-) mice represent a promising preclinical model that may be used to better understand the disease etiology and to evaluate pharmacotherapies for this devastating condition.

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.

Association of F11 polymorphism rs2289252 with deep vein thrombosis and related phenotypes in population of Latvia

INTRODUCTION

Deep vein thrombosis (DVT) has a strong inherited predisposition that is partly explained by the strong genetic risk factors such as mutations in factor V, prothrombin, antithrombin III, protein C and S genes. Only recently the first GWAS have been performed on DVT resulting in discovery of novel genetic variants, however, the information on the common polymorphisms predisposing to the risk of DVT is still scarce.

MATERIALS AND METHODS

Here we selected six SNPs (rs5361 in SELE, rs2066865 in FGG, rs2227589 in SERPINC1, rs1613662 in GP6, rs13146272 in CYP4V2, rs2289252 in F11) reported to be associated with venous thrombosis conditions and studied the association of these common variants in selected case (n=177) and control (n=235) groups from population of Latvia. Genotyping was performed using TaqMan hybridization probe SNP genotyping assay.

RESULTS

Patients with DVT had a significantly higher frequency of F11 rs2289252 polymorphism (p=0.001; OR [95%CI]=1.61 [1.20-2.14]). When stratified by recurrence of DVT the tendency was observed that the same SNP had higher OR value in group of DVT patients with repeated episodes of DVT compared to patients with single DVT episode (p=0.009; OR [95%CI]=2.27[1.22-4.21] and p=0.009; OR [95%CI]=1.52[1.11-2.08] respectively), but due to limited group of cases this finding should be replicated.

CONCLUSION

We conclude that F11 gene variant rs2289252 contribute to inherited forms of DVT incidence and correlation of other analysed SNPs should be explored in populations with greater sample size and associated with various thrombosis related traits.

Molecular analysis and phenotypic study in 14 Chinese families with Bietti crystalline dystrophy

Purpose

To investigate the clinical features and cytochrome P450 family 4 subfamily V polypeptide 2 (CYP4V2) gene mutations in 14 Chinese families with Bietti crystalline dystrophy (BCD).

Methods

Seventeen patients from 14 unrelated Chinese families with BCD were recruited for complete clinical ophthalmic examination and genetic study. The 11 exons of CYP4V2 were amplified from genomic DNA of all patients and their family members by polymerase chain reaction (PCR) and then sequenced. Exons of TIMP3 were also sequenced in BCD patient associated with choroidal neovascularization (CNV). One hundred and seventy unrelated healthy Chinese subjects were screened for mutations in CYP4V2.

Results

All 17 patients with BCD had mutations in CYP4V2; one of these mutations was novel (c.219T>A, p.F73L) and four other mutations had been reported. The p.F73L mutation was a commonly detected mutation in our study (seven out of 34 alleles), either in the homozygous state or in the heterozygous state. Among the patients, considerable phenotypic variability was detected, both within and between families. Screening of TIMP3 did not find any mutation in the BCD patient associated with CNV.

Conclusion

The novel CYP4V2 c.219T>A (p.F73L) mutation may be another recurrent mutation in Chinese patients with BCD. Our study expands the mutation spectrum of CYP4V2 and characterizes novel genotype–phenotype associations in Chinese patients with BCD.

Gestational diabetes induces alterations in the function of neonatal endothelial colony-forming cells

BACKGROUND

Children born to mothers with gestational diabetes mellitus (GDM) experience increased risk of developing hypertension, type 2 diabetes mellitus, and obesity. Disrupted function of endothelial colony-forming cells (ECFCs) may contribute to this enhanced risk. The goal of this study was to determine whether cord blood ECFCs from GDM pregnancies exhibit altered functionality.

METHODS

ECFCs isolated from the cord blood of control and GDM pregnancies were assessed for proliferation, senescence, and Matrigel network formation. The requirement for p38MAPK in hyperglycemia-induced senescence was determined using inhibition and overexpression studies.

RESULTS

GDM-exposed ECFCs were more proliferative than control ECFCs. However, GDM-exposed ECFCs exhibited decreased network-forming ability in Matrigel. Aging of ECFCs by serial passaging led to increased senescence and reduced proliferation of GDM-exposed ECFCs. ECFCs from GDM pregnancies were resistant to hyperglycemia-induced senescence compared with those from controls. In response to hyperglycemia, control ECFCs activated p38MAPK, which was required for hyperglycemia-induced senescence. In contrast, GDM-exposed ECFCs showed no change in p38MAPK activation under equivalent conditions.

CONCLUSION

Intrauterine exposure of ECFCs to GDM induces unique phenotypic alterations. The resistance of GDM-exposed ECFCs to hyperglycemia-induced senescence and decreased p38MAPK activation suggest that these progenitor cells have undergone changes that induce tolerance to a hyperglycemic environment.

Cytochrome P450-dependent catabolism of vitamin K: ω-hydroxylation catalyzed by human CYP4F2 and CYP4F11

Vitamin K plays an essential role in many biological processes including blood clotting, maintenance of bone health, and inhibition of arterial calcification. A menaquinone form of vitamin K, MK4, is increasingly recognized for its key roles in mitochondrial electron transport, as a ligand for the nuclear receptor SXR, which controls the expression of genes involved in transport and metabolism of endo- and xenobiotics, and as a pharmacotherapeutic in the treatment of osteoporosis. Although cytochrome P450 (CYP) 4F2 activity is recognized as an important determinant of phylloquinone (K1) metabolism, the enzymes involved in menaquinone catabolism have not been studied previously. CYP4F2 and CYP4F11 were expressed and purified and found to be equally efficient as in vitro catalysts of MK4 ω-hydroxylation. CYP4F2, but not CYP4F11, catalyzed sequential metabolism of MK4 to the ω-acid without apparent release of the intermediate aldehyde. The ω-alcohol could also be metabolized to the acid by microsomal NAD(+)-dependent alcohol and aldehyde dehydrogenases. LC-MS/MS analysis of trypsinized human liver microsomes (using a surrogate peptide approach) revealed the mean concentrations of CYP4F2 and CYP4F11 to be 14.3 and 8.4 pmol/mg protein, respectively. Microsomal MK4 ω-hydroxylation activities correlated with the CYP4F2 V433M genotype but not the CYP4F11 D446N genotype. Collectively, these data expand the lexicon of vitamin K ω-hydroxylases to include the 'orphan' P450 CYP4F11 and identify a common variant, CYP4F2 (rs2108622), as a major pharmacogenetic variable influencing MK4 catabolism.

A heterogeneous mixture of F-series prostaglandins promotes sperm guidance in the Caenorhabditis elegans reproductive tract

The mechanisms that guide motile sperm through the female reproductive tract to oocytes are not well understood. We have shown that Caenorhabditis elegans oocytes synthesize sperm guiding F-series prostaglandins from polyunsaturated fatty acid (PUFA) precursors provided in yolk lipoprotein complexes. Here we use genetics and electrospray ionization tandem mass spectrometry to partially delineate F-series prostaglandin metabolism pathways. We show that omega-6 and omega-3 PUFAs, including arachidonic and eicosapentaenoic acids, are converted into more than 10 structurally related F-series prostaglandins, which function collectively and largely redundantly to promote sperm guidance. Disruption of omega-3 PUFA synthesis triggers compensatory up-regulation of prostaglandins derived from omega-6 PUFAs. C. elegans F-series prostaglandin synthesis involves biochemical mechanisms distinct from those in mammalian cyclooxygenase-dependent pathways, yet PGF_2α stereoisomers are still synthesized. A comparison of F-series prostaglandins in C. elegans and mouse tissues reveals shared features. Finally, we show that a conserved cytochrome P450 enzyme, whose human homolog is implicated in Bietti's Crystalline Dystrophy, negatively regulates prostaglandin synthesis. These results support the model that multiple cyclooxygenase-independent prostaglandins function together to promote sperm motility important for fertilization. This cyclooxygenase-independent pathway for F-series synthesis may be conserved.

A fundamental question in cell and developmental biology is how motile cells find their target destinations. One of the most important cell targeting mechanisms involves the sperm and oocyte, which unite during fertilization to produce the next generation of offspring. We have been using the nematode C. elegans to delineate these mechanisms. Our prior studies have shown that oocytes secrete F-series prostaglandins that stimulate sperm motility. Prostaglandins are widespread signaling molecules derived from polyunsaturated fatty acids or PUFAs. Mammals are not capable of synthesizing PUFAs and must receive them in the diet. C. elegans was not thought to synthesize prostaglandins because the genome lacks cyclooxygenases, enzymes that catalyze the rate-limiting step in mammalian prostaglandin synthesis. Here we show that C. elegans oocytes synthesize a heterogenous mixture of structurally related F-series prostaglandins derived from different PUFA classes, including the enantiomer of PGF_2α. These prostaglandins function collectively and redundantly to guide sperm to the fertilization site. Our results indicate that F-series prostaglandins can be synthesized independent of cyclooxygenase enzymes. This novel pathway may be evolutionarily conserved. Evidence is emerging that prostaglandins regulate sperm motility in the female reproductive tract of humans.