Biallelic ATP8B3 variants cause male infertility and fertilization failure in humans.
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Letter↗
Biomedical subjects
Xiaodong Wang
Publications and source records attributed to Xiaodong Wang.
S-adenosyl-L-methionine attenuates hepatotoxicity induced by agonistic Jo2 Fas antibody following CYP2E1 induction in mice.
S-Adenosyl-l-methionine (SAM) has been shown to be hepatoprotective against many toxic agents. Its possible effectiveness in protecting against CYP2E1-dependent toxicity is not known. We recently reported that treatment of mice with pyrazole to induce CYP2E1 increased hepatotoxicity produced by Fas agonistic Jo2 antibody. The current study was designed to investigate the effect of exogenous administration of SAM on the synergistic hepatotoxicity produced by Fas agonistic Jo2 antibody plus CYP2E1 following pyrazole pretreatment in C57BL/6 mice. Suboptimal administration of Jo2 Fas antibody combined with pyrazole pretreatment caused severe hepatotoxicity as determined by elevations in serum transaminase levels and histopathology. Exogenous administration of SAM (50 mg i.p./kg body weight every 12 h for 3 days) significantly decreased serum transaminases and ameliorated morphological changes of the liver. Addition of SAM elevated hepatic SAM and total reduced glutathione levels and inhibited CYP2E1 activity. SAM also lowered the elevated oxidative stress (lipid peroxidation, protein carbonyls, and superoxide production) and nitrosative stress (induction of inducible nitric-oxide synthase and 3-nitrotyrosine adducts) and increases in caspase-8 and -3 activation produced by the pyrazole plus Jo2 treatment. SAM did not prevent the increase in serum TNF-alpha levels or the decrease in catalase activity in this model. These results indicate that SAM can have an important hepatoprotective role as an effective reagent against Fas plus CYP2E1-induced hepatotoxicity by lowering oxidative and nitrosative stress.
Animals↗
The bZip proteins CES-2 and ATF-2 alter the timing of transcription for a cell-specific target gene in C. elegans.
The Caenorhabditis elegans basic leucine zipper (bZip) protein CES-2 regulates the transcription of different genes in different cells. Here, we show that CES-2 mediates its effects in one cell (the excretory duct cell) together with another bZip protein, ATF-2. Both proteins influence transactivation of a target gene, lin-48. Although lin-48 is required for both anatomical and physiological features of the excretory duct cell, ces-2 and atf-2 mutants only exhibit anatomical defects. We show that CES-2 and ATF-2 modify the temporal transcription of lin-48, acting to initiate embryonic expression required for normal excretory system development and anatomy. In contrast, CES-2 and ATF-2 do not influence post-embryonic lin-48 expression. We provide evidence that CES-2 and ATF-2 can interact with each other, and that they cooperate to form a complex on lin-48 regulatory sequences. Thus, the two bZip proteins function together as one of several inputs that influence the spatial and temporal regulation of lin-48.
Activating Transcription Factor 2↗
Dietary flavonoids: effects on xenobiotic and carcinogen metabolism.
Flavonoids are present in fruits, vegetables and beverages derived from plants (tea, red wine), and in many dietary supplements or herbal remedies including Ginkgo Biloba, Soy Isoflavones, and Milk Thistle. Flavonoids have been described as health-promoting, disease-preventing dietary supplements, and have activity as cancer preventive agents. Additionally, they are extremely safe and associated with low toxicity, making them excellent candidates for chemopreventive agents. The cancer protective effects of flavonoids have been attributed to a wide variety of mechanisms, including modulating enzyme activities resulting in the decreased carcinogenicity of xenobiotics. This review focuses on the flavonoid effects on cytochrome P450 (CYP) enzymes involved in the activation of procarcinogens and phase II enzymes, largely responsible for the detoxification of carcinogens. A number of naturally occurring flavonoids have been shown to modulate the CYP450 system, including the induction of specific CYP isozymes, and the activation or inhibition of these enzymes. Some flavonoids alter CYPs through binding to the aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor, acting as either AhR agonists or antagonists. Inhibition of CYP enzymes, including CYP 1A1, 1A2, 2E1 and 3A4 by competitive or mechanism-based mechanisms also occurs. Flavones (chrysin, baicalein, and galangin), flavanones (naringenin) and isoflavones (genistein, biochanin A) inhibit the activity of aromatase (CYP19), thus decreasing estrogen biosynthesis and producing antiestrogenic effects, important in breast and prostate cancers. Activation of phase II detoxifying enzymes, such as UDP-glucuronyl transferase, glutathione S-transferase, and quinone reductase by flavonoids results in the detoxification of carcinogens and represents one mechanism of their anticarcinogenic effects. A number of flavonoids including fisetin, galangin, quercetin, kaempferol, and genistein represent potent non-competitive inhibitors of sulfotransferase 1A1 (or P-PST); this may represent an important mechanism for the chemoprevention of sulfation-induced carcinogenesis. Importantly, the effects of flavonoids on enzymes are generally dependent on the concentrations of flavonoids present, and the different flavonoids ingested. Due to the low oral bioavailability of many flavonoids, the concentrations achieved in vivo following dietary administration tend to be low, and may not reflect the concentrations tested under in vitro conditions; however, this may not be true following the ingestion of herbal preparations when much higher plasma concentrations may be obtained. Effects will also vary with the tissue distribution of enzymes, and with the species used in testing since differences between species in enzyme activities also can be substantial. Additionally, in humans, marked interindividual variability in drug-metabolizing enzymes occurs as a result of genetic and environmental factors. This variability in xenobiotic metabolizing enzymes and the effect of flavonoid ingestion on enzyme expression and activity can contribute to the varying susceptibility different individuals have to diseases such as cancer. As well, flavonoids may also interact with chemotherapeutic drugs used in cancer treatment through the induction or inhibition of their metabolism.
Animals↗
Three-dimensional structure of a double apoptosome formed by the Drosophila Apaf-1 related killer.
The Drosophila Apaf-1 related killer (Dark) forms an apoptosome that activates Dronc, an apical procaspase in the intrinsic cell death pathway. To study this process, we assembled a large Dark complex in the presence of dATP. Remarkably, we found that cytochrome c was not required for assembly and when added, cytochrome c did not bind to the Dark complex. We then determined a 3D structure of the Dark complex at 18.8A resolution using electron cryo-microscopy and single particle methods. In the structure, eight Dark subunits form a wheel-like particle and two of these rings associate face-to-face. In contrast, Apaf-1 forms a single ring that is comprised of seven subunits and each Apaf-1 binds a molecule of cytochrome c. We then used relevant crystal structures to model the Dark complex. This analysis shows that a single Dark ring and the Apaf-1 apoptosome share many key features. When taken together, the data suggest that a single ring in the Dark complex may represent the Drosophila apoptosome. Thus, our analysis provides a domain model of this complex and gives insights into its function.
Animals↗
Argonaute2 cleaves the anti-guide strand of siRNA during RISC activation.
The mRNA-cleavage step of RNA interference is mediated by an endonuclease, Argonaute2 (Ago2), within the RNA-induced silencing complex (RISC). Ago2 uses one strand of the small interfering (si) RNA duplex as a guide to find messenger RNAs containing complementary sequences and cleaves the phosphodiester backbone at a specific site measured from the guide strand's 5' end. Here, we show that both strands of siRNA get loaded onto Ago2 protein in Drosophila S2 cell extracts. The anti-guide strand behaves as a RISC substrate and is cleaved by Ago2. This cleavage event is important for the removal of the anti-guide strand from Ago2 protein and activation of RISC.
Adenosine Triphosphate↗
Formation of apoptosome is initiated by cytochrome c-induced dATP hydrolysis and subsequent nucleotide exchange on Apaf-1.
Apoptosis in metazoans is executed by a group of intracellular proteases named caspases. One of the caspase-activating pathways in mammals is initiated by the release of cytochrome c from mitochondria to cytosol, where it binds to Apaf-1 to form a procaspase-9-activating heptameric protein complex named apoptosome. We report here the reconstitution of this pathway with purified recombinant Apaf-1, procaspase-9, procaspase-3, and cytochrome c from horse heart. Apaf-1 contains a dATP as a cofactor. Cytochrome c binding to Apaf-1 induces hydrolysis of dATP to dADP, which is subsequently replaced by exogenous dATP. The dATP hydrolysis and exchange on Apaf-1 are two required steps for apoptosome formation.
Animals↗
Flavonoids as a novel class of human organic anion-transporting polypeptide OATP1B1 (OATP-C) modulators.
Flavonoids are a class of polyphenolic compounds widely present in the diet and herbal products. The interactions of flavonoids with some major efflux transporters [e.g., P-glycoprotein, multidrug resistance-associated protein 1 (MRP1), and breast cancer resistance protein] have been reported; however, their interactions with uptake transporters are largely unknown. Organic anion-transporting polypeptide OATP1B1 is a liver-specific uptake transporter important in hepatic drug disposition. Our objective was to evaluate the effects of 20 naturally occurring flavonoids, and some of their corresponding glycosides, on the uptake of [3H]dehydroepiandrosterone sulfate (DHEAS) in OATP1B1-expressing and OATP1B1-negative HeLa cells. Many of the tested flavonoids (including biochanin A, genistein, and epigallocatechin-3-gallate) significantly inhibited [3H]DHEAS uptake in a concentration-dependent manner in OATP1B1-expressing cells, with biochanin A being one of the most potent inhibitors with an IC50 of 11.3 +/- 3.22 microM. The flavonoids had negligible or small effects in OATP1B1-negative cells. Four of the eight pairs of tested flavonoids and their glycosides, namely, genistein/genistin, diosmetin/diosmin, epigallocatechin/epigallocatechin-3-gallate, and quercetin/rutin, exhibited distinct effects on [3H]DHEAS uptake. For example, genistin did not inhibit DHEAS uptake, whereas genistein did, and rutin stimulated uptake, whereas quercetin had no effect. [3H]Biochanin A uptake was similar in OATP1B1-expressing and OATP1B1-negative cells, suggesting that it is not a substrate for OATP1B1. A kinetic study revealed that biochanin A inhibited [3H]DHEAS uptake in a noncompetitive manner, with a Ki of 10.2 +/- 1.89 microM. Taken together, these results indicate that flavonoids are a novel class of OATP1B1 modulators, suggesting the potential for diet-drug interactions.
Biological Transport↗
Preparation and self-assembly of uniform TiO2/SiO2 composite submicrospheres.
Monodisperse spheres of silica were uniformly coated with titania through the hydrolysis of titanium alkoxide in order to increase the refractive index of complex submicrospheres and keep their monodispersity as well as their surface morphology. On the basis of the hydrolysis of tetrabutyl orthotitanate (TBOT), a continuous-feeding procedure was used to fabricate 10-nm titania coatings on monodisperse colloidal silica submicrospheres of diameter 200 nm. The TiO2/SiO2 composite spheres were assembled to achieve structures with three-dimensional order by gravity sedimentation and vertical deposition. The complex sphere composition, quality, and morphology were characterized by different techniques.
Journal Article↗
Mule/ARF-BP1, a BH3-only E3 ubiquitin ligase, catalyzes the polyubiquitination of Mcl-1 and regulates apoptosis.
The elimination of Mcl-1, an anti-apoptotic Bcl-2 family member, is an early and required step for DNA damage-induced apoptosis. The degradation of Mcl-1 can be blocked by proteasome inhibitors, suggesting a role for the ubiquitin proteasome pathway in apoptosis. Here, we demonstrate that Mcl-1 is ubiquinated at five lysines. Biochemical fractionation of cell extracts allowed us to identify a 482 kDa HECT-domain-containing ubiquitin ligase named Mule (Mcl-1 ubiquitin ligase E3) that is both required and sufficient for the polyubiquitination of Mcl-1. Mule also contains a region similar to the Bcl-2 homology region 3 (BH3) domain that allows Mule to specifically interact with Mcl-1. Elimination of Mule expression by RNA interference stabilizes Mcl-1 protein, resulting in an attenuation of the apoptosis induced by DNA-damage agents. Thus, Mule is a unique BH3-containing E3 ubiquitin ligase apical to Bcl-2 family proteins during DNA damage-induced apoptosis.
Amino Acid Sequence↗
Specific ablation of the apoptotic functions of cytochrome C reveals a differential requirement for cytochrome C and Apaf-1 in apoptosis.
As components of the apoptosome, a caspase-activating complex, cytochrome c (Cyt c) and Apaf-1 are thought to play critical roles during apoptosis. Due to the obligate function of Cyt c in electron transport, its requirement for apoptosis in animals has been difficult to establish. We generated "knockin" mice expressing a mutant Cyt c (KA allele), which retains normal electron transfer function but fails to activate Apaf-1. Most KA/KA mice displayed embryonic or perinatal lethality caused by defects in the central nervous system, and surviving mice exhibited impaired lymphocyte homeostasis. Although fibroblasts from the KA/KA mice were resistant to apoptosis, their thymocytes were markedly more sensitive to death stimuli than Apaf-1(-/-) thymocytes. Upon treatment with gamma irradiation, procaspases were efficiently activated in apoptotic KA/KA thymocytes, but Apaf-1 oligomerization was not observed. These studies indicate the existence of a Cyt c- and apoptosome-independent but Apaf-1-dependent mechanism(s) for caspase activation.
Animals↗
Dog sciatic nerve regeneration across a 30-mm defect bridged by a chitosan/PGA artificial nerve graft.
We have developed a dual-component artificial nerve graft comprising an outer microporous conduit of chitosan and internal oriented filaments of polyglycolic acid (PGA). The novel graft was used for bridging sciatic nerve across a 30-mm defect in six Beagle dogs, which were used as a chitosan/PGA graft group. The other Beagle dogs were divided into an autograft group (n = 6) as the positive control and a non-grafted group (n = 5) as the negative control. All animals of three groups were monitored for changes in their appearance and locomotion activities after surgery. Their posture and gait were recorded regularly with the aid of photographs and videotapes for each dog. Six months post-operatively, a combination of electrophysiological examination, FluoroGold retrograde tracing, histological assessment including light microscopy and transmission electron microscopy, immunohistochemistry as well as morphometric analyses to both regenerated nerves and target muscles was utilized to investigate the nerve repair effects of our artificial nerve graft. The results demonstrated that, in the chitosan/PGA graft group, the dog sciatic nerve trunk had been reconstructed with restoration of nerve continuity and functional recovery, and its target skeletal muscle had been re-innervated, improving locomotion activities of the operated limb. This study proves the feasibility of the chitosan/PGA artificial nerve graft for peripheral nerve regeneration by bridging a longer defect in a large animal model.
Action Potentials↗
Lipopolysaccharide-induced liver injury in rats treated with the CYP2E1 inducer pyrazole.
Elevated LPS and elevated cytochrome P-450 2E1 (CYP2E1) in liver are two major independent risk factors in alcoholic liver disease. We investigated possible synergistic effects of the two risk factors in causing oxidative stress and liver injury. Sprague-Dawley rats were injected intraperitoneally with pyrazole (inducer of CYP2E1) for 2 days, and then LPS was injected via tail vein. Other rats were treated with pyrazole alone or LPS alone or saline. Eight hours later, blood was collected and livers were excised. Pathological evaluation showed severe inflammatory responses and necroses only in liver sections from rats in the pyrazole plus LPS group; blood transaminase levels were significantly elevated only in the combination group. Activities of caspase-3 and -9 and positive terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling staining were highest in the LPS alone and the LPS plus pyrazole group, with no significant difference between the two groups. Lipid peroxidation and protein carbonyls in liver homogenate as well as in situ superoxide production were maximally elevated in the LPS plus pyrazole group. Levels of nitrite plus nitrate and inducible nitric oxide (NO) synthase (iNOS) content were comparably elevated in LPS alone and the LPS plus pyrazole group; however, 3-nitrotyrosine adducts were elevated in the combined group but not the LPS group. It is likely that LPS induction of iNOS, which produces NO, coupled to pyrazole induction of CYP2E1 which produces superoxide, sets up conditions for maximal peroxynitrite formation and production of 3-nitrotyrosine adducts. CYP2E1 activity and content were elevated in the pyrazole and the LPS plus pyrazole groups. Immunohistochemical staining indicated that distribution of CYP2E1 was in agreement with that of necrosis and production of superoxide. These results show that pyrazole treatment enhanced LPS-induced necrosis, not apoptosis. The enhanced liver necrosis appears to involve an increase in oxidative and nitrosative stress generated by the combination of LPS plus elevated CYP2E1 levels.
Animals↗
Induction of cytochrome P450 2E1 increases hepatotoxicity caused by Fas agonistic Jo2 antibody in mice.
Cytochrome P450 2E1 (CYP2E1) may be a central pathway in generating oxidative stress, reactive oxygen species, and causing hepatotoxic injury by alcohol and various hepatotoxins. This study evaluated the ability of CYP2E1 to potentiate or synergize the hepatotoxicity of Fas in vivo. C57BL/6 mice were injected intraperitoneally with pyrazole (Pyr) to induce CYP2E1. Then, 16-hour fasted mice were administered agonistic Jo2 anti-Fas antibody ip. Other mice were treated with Pyr or Jo2 alone. Levels of serum aminotransferase were 8.3- and 6.3-fold higher in the Pyr/Jo2 group compared with Jo2 alone, respectively. Histological evaluation of liver showed more extensive acidophilic necrosis and severe pathological changes in the Pyr/Jo2-treated mice. DNA fragmentation and caspase-8 and -3 activities were more elevated in the Pyr/Jo2 group compared with Jo2 alone. CYP2E1 activity and protein levels were higher in the Pyr/Jo2 group than in Jo2 alone. Levels of inducible nitric oxide synthase, 3-nitrotyrosine protein adducts, malondialdehyde, and protein carbonyls were also higher in the Pyr/Jo2 group compared with Jo2 alone. Glutathione and activities of catalase and Cu-Zn superoxide dismutase were decreased in the Pyr/Jo2 group. Administration of chlormethiazole, an inhibitor of CYP2E1, to the Pyr/Jo2-treated mice caused a significant decrease of alanine aminotransferase and liver pathological changes in association with a decrease in CYP2E1 protein and activity. In conclusion, enhanced hepatotoxicity of Fas was found in mice with elevated levels of CYP2E1. We speculate that overexpression of CYP2E1 might synergize and increase the susceptibility to Fas induced-liver injury.
Animals↗
Alteration of the DNA binding domain disrupts distinct functions of the C. elegans Pax protein EGL-38.
The paired-domain-containing Pax transcription factors play an important role in the development of a range of organ, tissue and cell types. Although DNA binding elements and target genes for Pax proteins have been identified, how these proteins identify appropriate DNA elements and regulate different genes in different cellular contexts is not well understood. To investigate the relationship between Pax proteins and their targets, we have studied the in vivo and in vitro properties associated with wild-type and different mutant variants of the Caenorhabditis elegans Pax protein EGL-38. Here, we characterize the properties of four mutations that result in an amino acid substitution in the DNA binding domain of EGL-38. We find that animals bearing the different mutant alleles exhibit tissue-preferential defects in egl-38 function. The mutant proteins are also altered in their activity in an ectopic expression assay and in their in vitro DNA binding properties. Using in vitro selection, we have identified binding sites for EGL-38. However, we show that selected sites function poorly in vivo as EGL-38 response elements, indicating that sequence features in addition to DNA binding determine the efficacy of Pax response elements. The distinction between DNA binding and activity is consistent with the model that other factors commonly play a role in mediating Pax protein target site selection and function in vivo.
Alleles↗
A structure of the human apoptosome at 12.8 A resolution provides insights into this cell death platform.
Apaf-1 and cytochrome c coassemble in the presence of dATP to form the apoptosome. We have determined a structure of the apoptosome at 12.8 A resolution by using electron cryomicroscopy and single-particle methods. We then docked appropriate crystal structures into the map to create an accurate domain model. Thus, we found that seven caspase recruitment domains (CARDs) form a central ring within the apoptosome. At a larger radius, seven copies of the nucleotide binding and oligomerization domain (NOD) associate laterally to form the hub, which encircles the CARD ring. Finally, an arm-like helical domain (HD2) links each NOD to a pair of beta propellers, which bind a single cytochrome c. This model provides insights into the roles of dATP and cytochrome c in assembly. Our structure also reveals how a CARD ring and the central hub combine to create a platform for procaspase-9 activation.
Apoptosis↗
Focused beam control for ultrasound surgery with spherical-section phased array: sound field calculation and genetic optimization algorithm.
This study aims at a sound field calculation for the spherical-section phased array and an optimization algorithm for the focus patterns of phased array ultrasound surgery. An efficient field calculation formula represented as an explicit expression is derived by the strategies of projection and binomial expansion. An optimization algorithm based on genetic algorithm is constructed by the suitable fitness function and the selection strategies. The simulation results of 256-element spherical-section phased array show the capability of controlling focus accurately and effectively with the combined method made up of the explicit expression method and the genetic optimization algorithm. The simulation results of single focus, multiple foci, on-axial focus, and off-axial focus further convince the feasibility of three-dimensional (3-D) focus steering with excellent acoustic performances. A single focus with the focus dimension of 1.25 mm x 1.25 mm x 7 mm and with the intensity of 6080 W/cm2 is formed. The multiple-focus pattern can enlarge the treatment volume 22 times larger than that of single focus with a sonication. In addition, a comparison between the explicit expression approach and the point source approach testifies to the applicability of the explicit expression approach. The experiment and simulation results of 16-element array actually confirm the feasibility of the combined method.
Algorithms↗
Acoustic characteristics of Mandarin esophageal speech.
The present study attempted to investigate the acoustic characteristics of Mandarin laryngeal and esophageal speech. Eight normal laryngeal and seven esophageal speakers participated in the acoustic experiments. Results from acoustic analyses of syllables /ma/and /ba/ indicated that, F0, intensity, and signal-to-noise ratio of laryngeal speech were significantly higher than those of esophageal speech. However, opposite results were found for vowel duration, jitter, and shimmer. Mean F0, intensity, and word per minute in reading were greater but number of pauses was smaller in laryngeal speech than those in esophageal speech. Similar patterns of F0 contours and vowel duration as a function of tone were found between laryngeal and esophageal speakers. Long-time spectra analysis indicated that higher first and second formant frequencies were associated with esophageal speech than that with normal laryngeal speech.
Aged↗