Mitochondrial oxidative damage contributes to a wide range of pathologies. One therapeutic strategy to treat these disorders is targeting antioxidants to mitochondria by conjugation to the lipophilic triphenylphosphonium (TPP) cation. To date only hydrophobic antioxidants have been targeted to mitochondria; however, extending this approach to hydrophilic antioxidants offers new therapeutic and research opportunities. Here we report the development and characterization of MitoC, a mitochondria-targeted version of the hydrophilic antioxidant ascorbate. We show that MitoC can be taken up by mitochondria, despite the polarity and acidity of ascorbate, by using a sufficiently hydrophobic link to the TPP moiety. MitoC reacts with a range of reactive species, and within mitochondria is rapidly recycled back to the active ascorbate moiety by the glutathione and thioredoxin systems. Because of this accumulation and recycling MitoC is an effective antioxidant against mitochondrial lipid peroxidation and also decreases aconitase inactivation by superoxide. These findings show that the incorporation of TPP function can be used to target polar and acidic compounds to mitochondria, opening up the delivery of a wide range of bioactive compounds. Furthermore, MitoC has therapeutic potential as a new mitochondria-targeted antioxidant, and is a useful tool to explore the role(s) of ascorbate within mitochondria.
•A mitochondria-targeted ascorbate, MitoC, has been developed•MitoC is taken up by energized mitochondria and there recycled•Mitochondrial oxidative damage is decreased by MitoC•MitoC is a useful reagent to explore mitochondrial oxidative stress
ACR, accumulation ratio; AO, ascorbate oxidase; AFR, ascorbyl free radical; DHA, dehydroascorbic acid; DTPA, diethylenetriaminepenta-acetic acid; FCCP, carbonylcyanide p-(trifluoromethoxy)phenylhydrazone; FCS, foetal calf serum; GSH, glutathione; LAH, linoleic acid hydroperoxide; Δψm, mitochondrial membrane potential; MitoC, mitochondria-targeted ascorbate; MitoDHA, mitochondria-targeted dehydroascorbate; TBARS, thiobarbituric acid reactive species; TFA, trifluoroacetic acid; TPMP, methyltriphenylphosphonium; TPP, triphenylphosphonium; RET, reverse electron transport; RLM, rat liver mitochondria; ROS, reactive oxygen species; RP-HPLC, reverse-phase HPLC; XO, xanthine oxidase; Lipophilic cation; Lipid peroxidation; Mitochondria; Mitochondrial targeting; Ascorbic acid; MitoPerox; MitoC
A series of mitochondria-targeted antioxidants comprising a lipophilic triphenylphosphonium cation attached to the antioxidant chroman moiety of vitamin E by an alkyl linker have been prepared. The synthesis of a series of mitochondria-targeted vitamin E derivatives with a range of alkyl linkers gave compounds of different hydrophobicities. This work will enable the dependence of antioxidant defence on hydrophobicity to be determined in vivo.
Mitochondria; Mitochondria-targeted antioxidant; Lipid peroxidation; Vitamin E; MitoE
Cypridoidean ostracods are one of a number of animal taxa that reproduce with giant sperm, up to 10 000 µm in length, but they are the only group to have aflagellate, filamentous giant sperm. The evolution and function of this highly unusual feature of reproduction with giant sperm are currently unknown. The hypothesis of long-term evolutionary persistence of this kind of reproduction has never been tested. We here report giant sperm discovered by propagation phase contrast X-ray synchrotron micro- and nanotomography, preserved in five Miocene ostracod specimens from Queensland, Australia. The specimens belong to the species Heterocypris collaris Matzke-Karasz et al. 2013 (one male and three females) and Newnhamia mckenziana Matzke-Karasz et al. 2013 (one female). The sperm are not only the oldest petrified gametes on record, but include three-dimensional subcellular preservation. We provide direct evidence that giant sperm have been a feature of this taxon for at least 16 Myr and provide an additional criterion (i.e. longevity) to test hypotheses relating to origin and function of giant sperm in the animal kingdom. We further argue that the highly resistant, most probably chitinous coats of giant ostracod sperm may play a role in delaying decay processes, favouring early mineralization of soft tissue.
Cypridoidea; synchrotron radiation tomography; fossil gametes; soft body preservation; bat guano
Schizophrenia affects prefrontal and temporal-limbic networks. These regions were examined by contrasting regional cerebral blood flow (rCBF) during executive (Wisconsin Card Sorting Test [WCST]), and declarative memory tasks (Paired Associate Recognition Test [PART]). The tasks, and a resting baseline, were administered to 15 patients with schizophrenia and 15 healthy controls during 10 min positron emission tomography 15O-water measures of rCBF. Patients were worse on both tasks. Controls activated inferior frontal, occipitotemporal, and temporal pole regions for both tasks. Similar results were obtained for controls matched to level of patient performance. Patients showed no activation of hypothesized regions during the WCST and activated the dorsolateral prefrontal cortex during the PART. On the PART, occipitotemporal activation correlated with better performance for controls only. Better WCST performance correlated with CBF increase in prefrontal regions for controls and in the parahippocampal gyrus for patients. Results suggest that schizophrenia may involve a breakdown in the integration of a frontotemporal network that is responsive to executive and declarative memory demands in healthy individuals.
Despite advances in screening and treatment over the past several years, breast cancer remains a leading cause of cancer-related death among women in the United States. A major goal in breast cancer treatment is to develop safe and clinically useful therapeutic agents that will prevent the recurrence of breast cancers after front-line therapeutics have failed. Ideally, these agents would have relatively low toxicity against normal cells, and will specifically inhibit the growth and proliferation of cancer cells. Our group and others have previously demonstrated that breast cancer cells exhibit increased mitochondrial oxygen consumption compared with non-tumorigenic breast epithelial cells. This suggests that it may be possible to deliver redox active compounds to the mitochondria to selectively inhibit cancer cell metabolism. To demonstrate proof-of-principle, a series of mitochondria-targeted soft electrophiles (MTSEs) has been designed which selectively accumulate within the mitochondria of highly energetic breast cancer cells and modify mitochondrial proteins. A prototype MTSE, IBTP, significantly inhibits mitochondrial oxidative phosphorylation, resulting in decreased breast cancer cell proliferation, cell attachment, and migration in vitro. These results suggest MTSEs may represent a novel class of anti-cancer agents that prevent cancer cell growth by modification of specific mitochondrial proteins.
Functional and anatomical relationships between working and declarative memory were investigated by contrasting regional cerebral blood flow (rCBF) change during standard working (Wisconsin Card Sorting Test, WCST) and declarative memory (Paired Associate Recognition Test, PART) tasks using identical stimulus–response modalities. The tasks and a resting baseline were administered to 30 participants (16 men, 14 women) during successive 10-min positron emission tomography 15O-water measures of rCBF. For both tasks, rCBF increased over baseline in inferior frontal and occipitotemporal regions, with more consistent dorsolateral prefrontal activation for WCST than PART. Additional orbitofrontal increases and dorsomedial decreases were seen for the PART. Activation patterns diverged when performance was considered. For the WCST, high performers activated dorsolateral and inferior frontal regions, whereas top PART performers activated only the occipitotemporal region. These results suggest operation of a frontotemporal network subserving both types of memory function that becomes more focal as performance increases.
Neuropsychological studies have shown that deficits in verbal episodic memory in schizophrenia occur primarily during encoding and retrieval stages of information processing. The current study used positron emission tomography to examine the effect of schizophrenia on change in cerebral blood flow (CBF) during these memory stages.
CBF was measured in 23 healthy comparison subjects and 23 patients with schizophrenia during four conditions: resting baseline, motor baseline, word encoding, and word recognition. The motor baseline was used as a reference that was subtracted from encoding and recognition conditions by using statistical parametric mapping.
Patients’ performance was similar to that of healthy comparison subjects. During word encoding, patients showed reduced activation of left prefrontal and superior temporal regions. Reduced left prefrontal activation in patients was also seen during word recognition, and additional differences were found in the left anterior cingulate, left mesial temporal lobe, and right thalamus. Although patients’ performance was similar to that of healthy comparison subjects, left inferior prefrontal activation was associated with better performance only in the comparison subjects.
Left frontotemporal activation during episodic encoding and retrieval, which is associated with better recognition in healthy people, is disrupted in schizophrenia despite relatively intact recognition performance and right prefrontal function. This may reflect impaired strategic use of semantic information to organize encoding and facilitate retrieval.
The limb is widely used as a model developmental system and changes to gene expression patterns in its signaling centers, notably the zone of polarizing activity (ZPA) and the apical ectodermal ridge (AER), are known to cause limb malformations and evolutionary differences in limb morphology. Although several genes that define these limb signaling centers have been described, the identification of regulatory elements that are active within these centers has been limited. By dissecting mouse E11.5 limbs that fluorescently mark the ZPA or AER, followed by fluorescence-activated cell sorting and low-cell H3K27ac ChIP-seq, we identified thousands of specific signaling-center enhancers. Our ChIP-seq datasets show strong correlation with ZPA- and AER-expressed genes, previously characterized functional ZPA and AER enhancers and enrichment for relevant biological terms related to limb development and malformation for the neighboring genes. Using transgenic assays, we show that several of these sequences function as ZPA and AER enhancers. Our results identify novel ZPA and AER enhancers that could be important regulators of genes involved in the establishment of these specialized regions and the patterning of tetrapod limbs.
Enhancer; AER; ZPA; Limb; Mouse
In addition to their protein coding function, exons can also serve as transcriptional enhancers. Mutations in these exonic-enhancers (eExons) could alter both protein function and transcription. However, the functional consequence of eExon mutations is not well known. Here, using massively parallel reporter assays, we dissect the enhancer activity of three liver eExons (SORL1 exon 17, TRAF3IP2 exon 2, PPARG exon 6) at single nucleotide resolution in the mouse liver. We find that both synonymous and non-synonymous mutations have similar effects on enhancer activity and many of the deleterious mutation clusters overlap known liver-associated transcription factor binding sites. Carrying a similar massively parallel reporter assay in HeLa cells with these three eExons found differences in their mutation profiles compared to the liver, suggesting that enhancers could have distinct operating profiles in different tissues. Our results demonstrate that eExon mutations could lead to multiple phenotypes by disrupting both the protein sequence and enhancer activity and that enhancers can have distinct mutation profiles in different cell types.
Exons that code for protein can also have additional functions, such as regulating gene transcription through enhancer activity. Here, we changed every nucleotide in three different exons that also function as enhancers, and examined their enhancer activity to test whether nucleotide changes in these exons can affect both the protein sequence and enhancer function. We found that mutations with a significant effect on enhancer function can reside both in regions that change the protein sequence (non-synonymous) and regions that do not change it (synonymous). When we conducted a similar analysis in a different cell type, we observed a difference in the nucleotide changes that cause a significant effect on enhancer activity, suggesting that the enhancer functional units can differ between tissues.
Licensed human papillomavirus (HPV) vaccines provide near complete protection against the types of HPV that most commonly cause anogenital and oropharyngeal cancers (HPV 16 and 18) when administered to individuals naive to these types. These vaccines, like most other prophylactic vaccines, appear to protect by generating antibodies. However, almost nothing is known about the immunological memory that forms following HPV vaccination, which is required for long-term immunity. Here, we have identified and isolated HPV 16-specific memory B cells from female adolescents and young women who received the quadrivalent HPV vaccine in the absence of pre-existing immunity, using fluorescently conjugated HPV 16 pseudoviruses to label antigen receptors on the surface of memory B cells. Antibodies cloned and expressed from these singly sorted HPV 16-pseudovirus labeled memory B cells were predominantly IgG (>IgA>IgM), utilized diverse variable genes, and potently neutralized HPV 16 pseudoviruses in vitro despite possessing only average levels of somatic mutation. These findings suggest that the quadrivalent HPV vaccine provides an excellent model for studying the development of B cell memory; and, in the context of what is known about memory B cells elicited by influenza vaccination/infection, HIV-1 infection, or tetanus toxoid vaccination, indicates that extensive somatic hypermutation is not required to achieve potent vaccine-specific neutralizing antibody responses.
There is an urgent need to better understand how to reliably generate effective vaccines, particularly subunit vaccines, as certain pathogens are considered to pose too great of a safety risk to be developed as live, attenuated or killed vaccines (e.g., HIV-1). The human papillomavirus (HPV) vaccines are two of the most effective subunit vaccines ever developed and have continued to show protection against HPV associated disease up to and beyond five years post-vaccination. Moreover, the target population for these vaccines have essentially no pre-existing immunity to the HPV types covered by the vaccine; therefore, these vaccines provide an excellent model for studying the immunity elicited by a highly effective subunit vaccine. As the HPV vaccines, like most vaccines, protect by generating antibodies, we are interested in characterizing the memory B cells elicited by the HPV vaccine. Memory B cells help to sustain antibody levels over time by rapidly differentiating into antibody secreting cells upon pathogen re-exposure. Although previous studies have provided evidence that the HPV vaccines elicit memory B cells, they did not characterize these cells. Here, we have isolated HPV-specific memory B cells from adolescent females and women who received the quadrivalent HPV vaccine and have cloned antibodies from these cells. Importantly, we find that these antibodies potently inhibit HPV and that the memory B cells from which they derive exhibit hallmarks of long-lived memory B cells.
Inter-individual variation in gene regulatory elements is hypothesized to play a causative role in adverse drug reactions and reduced drug activity. However, relatively little is known about the location and function of drug-dependent elements. To uncover drug-associated elements in a genome-wide manner, we performed RNA-seq and ChIP-seq using antibodies against the pregnane X receptor (PXR) and three active regulatory marks (p300, H3K4me1, H3K27ac) on primary human hepatocytes treated with rifampin or vehicle control. Rifampin and PXR were chosen since they are part of the CYP3A4 pathway, which is known to account for the metabolism of more than 50% of all prescribed drugs. We selected 227 proximal promoters for genes with rifampin-dependent expression or nearby PXR/p300 occupancy sites and assayed their ability to induce luciferase in rifampin-treated HepG2 cells, finding only 10 (4.4%) that exhibited drug-dependent activity. As this result suggested a role for distal enhancer modules, we searched more broadly to identify 1,297 genomic regions bearing a conditional PXR occupancy as well as all three active regulatory marks. These regions are enriched near genes that function in the metabolism of xenobiotics, specifically members of the cytochrome P450 family. We performed enhancer assays in rifampin-treated HepG2 cells for 42 of these sequences as well as 7 sequences that overlap linkage-disequilibrium blocks defined by lead SNPs from pharmacogenomic GWAS studies, revealing 15/42 and 4/7 to be functional enhancers, respectively. A common African haplotype in one of these enhancers in the GSTA locus was found to exhibit potential rifampin hypersensitivity. Combined, our results further suggest that enhancers are the predominant targets of rifampin-induced PXR activation, provide a genome-wide catalog of PXR targets and serve as a model for the identification of drug-responsive regulatory elements.
Drug response varies between individuals and can be caused by genetic factors. Nucleotide variation in gene regulatory elements can have a significant effect on drug response, but due to the difficulty in identifying these elements, they remain understudied. Here, we used various genomic assays to analyze human liver cells treated with or without the antibiotic rifampin and identified drug-induced regulatory elements genome-wide. The testing of numerous active promoters in human liver cells showed only a few to be induced by rifampin treatment. A similar analysis of enhancers found several of them to be induced by the drug. Nucleotide variants in one of these enhancers were found to alter its activity. Combined, this work identifies numerous novel gene regulatory elements that can be activated due to drug response and thus provides candidate sequences in the human genome where nucleotide variation can lead to differences in drug response. It also provides a universally applicable method to detect these elements for other drugs.
We have previously demonstrated that lipopolysaccharide (LPS) induces depressive-like behavior by activating indoleamine 2,3 dioxygenase (IDO; O'Connor et al, 2009c). IDO degrades tryptophan along the kynurenine pathway. Using mass-spectrometry (LC-MS) analysis of kynurenine metabolites in the brain of mice injected at the periphery with 1 mg/kg LPS, we show that LPS activates the kynurenine 3-monooxygenase pathway that ultimately degrades kynurenine into quinolinic acid. As quinolinic acid acts as an N-methyl-𝒟-aspartate (NMDA) receptor agonist, we used the NMDA receptor antagonist ketamine to assess the role of NMDA receptor activation in LPS-induced depressive-like behavior. Here, we report that a low dose of ketamine (6 mg/kg, intraperitoneally) immediately before administration of LPS (0.83 mg/kg, intraperitoneally) in C57Bl/6 J mice abrogated the development of LPS-induced depressive-like behavior, without altering LPS-induced sickness measured by body weight loss, decreased motor activity, and reduced food intake. Depressive-like behavior was measured 24 h after LPS by decreased sucrose preference and increased immobility in the forced swim test (FST). Ketamine had no effect on LPS-induced cytokine expression in the liver and brain, IDO activation, and brain-derived neurotrophic factor (BDNF) transcripts. The ability of ketamine to abrogate LPS-induced depressive-like behavior independently of a possible interference with LPS-induced inflammatory signaling was confirmed when ketamine was administered 10 h after LPS instead of immediately before LPS. In contrast, ketamine had no effect when administered 24 h before LPS. To confirm that NMDA receptor antagonism by ketamine mediates the antidepressant-like activity of this compound in LPS-treated mice, mice were pretreated with the α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor antagonist 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(f)quinoxaline-2,3-dione (NBQX) to block enhanced AMPA receptor glutamatergic neurotransmission after NMDA receptor antagonism by ketamine. NBQX administered at the dose of 10 mg/kg intraperitoneally 15 min before ketamine in mice treated with LPS 24 h earlier restored LPS-induced decreased sucrose preference. These findings indicate that LPS-induced depressive-like behavior is mediated by NMDA receptor activation, probably as a consequence of formation of quinolinic acid.
AMPA receptor; animal models; behavioral science; biological psychiatry; depression; depression; unipolar/bipolar; inflammation; ketamine; NMDA receptor; ketamine; depression; NMDA receptor; AMPA receptor; lipopolysaccharide; inflammation
Loss of p53 gene function, which occurs in most colon cancer cells, has been shown to abolish the apoptotic response to 5-fluorouracil (5-FU). To identify genes downstream of p53 that might mediate these effects, we assessed global patterns of gene expression following 5-FU treatment of isogenic cells differing only in their p53 status. The gene encoding mitochondrial ferredoxin reductase (protein, FR; gene, FDXR) was one of the few genes significantly induced by p53 after 5-FU treatment. The FR protein was localized to mitochondria and suppressed the growth of colon cancer cells when over-expressed. Targeted disruption of the FDXR gene in human colon cancer cells showed that it was essential for viability, and partial disruption of the gene resulted in decreased sensitivity to 5-FU-induced apoptosis. These data, coupled with the effects of pharmacologic inhibitors of reactive oxygen species, indicate that FR contributes to p53-mediated apoptosis through the generation of oxidative stress in mitochondria.
Oxidative damage from elevated production of reactive oxygen species (ROS) contributes to ischemia-reperfusion injury in myocardial infarction and stroke. The mechanism by which the increase in ROS occurs is not known, and it is unclear how this increase can be prevented. A wide variety of nitric oxide donors and S-nitrosating agents protect the ischemic myocardium from infarction, but the responsible mechanisms are unclear1–6. Here we used a mitochondria-selective S-nitrosating agent, MitoSNO, to determine how mitochondrial S-nitrosation at the reperfusion phase of myocardial infarction is cardioprotective in vivo in mice. We found that protection is due to the S-nitrosation of mitochondrial complex I, which is the entry point for electrons from NADH into the respiratory chain. Reversible S-nitrosation of complex I slows the reactivation of mitochondria during the crucial first minutes of the reperfusion of ischemic tissue, thereby decreasing ROS production, oxidative damage and tissue necrosis. Inhibition of complex I is afforded by the selective S-nitrosation of Cys39 on the ND3 subunit, which becomes susceptible to modification only after ischemia. Our results identify rapid complex I reactivation as a central pathological feature of ischemia-reperfusion injury and show that preventing this reactivation by modification of a cysteine switch is a robust cardioprotective mechanism and hence a rational therapeutic strategy.
We have previously found abrogated ischemia-induced coronary collateral growth in Zucker obese fatty rats (ZOF) compared to Zucker lean rats (ZLN). Because ZOF have structural abnormalities in their mitochondria suggesting dysfunction, and also show increased production of O2ׄ−, we hypothesized that mitochondrial dysfunction, caused by oxidative stress impairs coronary collateral growth in ZOF.
Methods and Results
Increased levels of ROS were observed in aortic endothelium and smooth muscle cells in ZOF compared to ZLN. ROS levels were decreased by the mitochondria-targeted antioxidants MitoQuinone (MQ) and MitoTempol (MT) as assessed by MitoSox Red and DHE staining. Lipid peroxides (a marker of oxidized lipids) were increased in ZOF by ∼47 % compared to ZLN. The elevation in oxidative stress was accompanied by increased antioxidant enzymes, except GPx-1, and by increased uncoupling protein-2 in ZOF vs ZLN. In addition, elevated respiration rates were also observed in the obese compared to leans. Administration of MQ significantly normalized the metabolic profiles and reduced lipid peroxides in ZOF to the same level observed in leans. The protective effect of MQ also suppressed the induction of UCP-2 in the obese rats. Resolution of mitochondrial oxidative stress by MQ or MT restored coronary collateral growth to the same magnitude observed in ZLN in response to repetitive ischemia.
We conclude that mitochondrial oxidative stress and dysfunction play a key role in disrupting coronary collateral growth in obesity and the metabolic syndrome, and elimination of the mitochondrial oxidative stress with MQ or MT rescues collateral growth.
MitoQuinone; MitoTempol; metabolic syndrome; arteriogenesis; uncoupling protein-2; lipid peroxidation
The biological and mechanical function of connective tissues is largely determined by controlled cellular alignment and therefore it seems appropriate that tissue-engineered constructs should be architecturally similar to the in vivo tissue targeted for repair or replacement. Collagen organisation dictates the tensile properties of most tissues and so monitoring the deposition of cell-secreted collagen as the construct develops is essential for understanding tissue formation. In this study, electrospun fibres with a random or high degree of orientation, mimicking two types of tissue architecture found in the body, were used to culture human fibroblasts for controlling cell alignment. The minimally-invasive technique of second harmonic generation was used with the aim of monitoring and profiling the deposition and organisation of collagen at different construct depths over time while construct mechanical properties were also determined over the culture period. It was seen that scaffold fibre organisation affected cell migration and orientation up to 21 days which in turn had an effect on collagen organisation. Collagen in random fibrous constructs was deposited in alternating configurations at different depths however a high degree of organisation was observed throughout aligned fibrous constructs orientated in the scaffold fibre direction. Three-dimensional second harmonic generation images showed that deposited collagen was more uniformly distributed in random constructs but aligned constructs were more organised and had higher intensities. The tensile properties of all constructs increased with increasing collagen deposition and were ultimately dictated by collagen organisation. This study highlights the importance of scaffold architecture for controlling the development of well-organised tissue engineered constructs and the usefulness of second harmonic generation imaging for monitoring collagen maturation in a minimally invasive manner.
The glycation of protein and nucleic acids that occurs as a consequence of hyperglycemia disrupts cell function and contributes to many pathologies, including those associated with diabetes and aging. Intracellular glycation occurs after the generation of the reactive 1,2-dicarbonyls methylglyoxal and glyoxal, and disruption of mitochondrial function is associated with hyperglycemia. However, the contribution of these reactive dicarbonyls to mitochondrial damage in pathology is unclear owing to uncertainties about their levels within mitochondria in cells and in vivo. To address this we have developed a mitochondria-targeted reagent (MitoG) designed to assess the levels of mitochondrial dicarbonyls within cells. MitoG comprises a lipophilic triphenylphosphonium cationic function, which directs the molecules to mitochondria within cells, and an o-phenylenediamine moiety that reacts with dicarbonyls to give distinctive and stable products. The extent of accumulation of these diagnostic heterocyclic products can be readily and sensitively quantified by liquid chromatography–tandem mass spectrometry, enabling changes to be determined. Using the MitoG-based analysis we assessed the formation of methylglyoxal and glyoxal in response to hyperglycemia in cells in culture and in the Akita mouse model of diabetes in vivo. These findings indicated that the levels of methylglyoxal and glyoxal within mitochondria increase during hyperglycemia both in cells and in vivo, suggesting that they can contribute to the pathological mitochondrial dysfunction that occurs in diabetes and aging.
•A mitochondria-targeted mass spectrometric probe, MitoG, has been developed to measure glyoxal and methylglyoxal.•Using MitoG we show that mitochondrial glyoxal and methylglyoxal can be measured in hyperglycemic cells.•MitoG can also be used in vivo to infer mitochondrial glyoxal and methylglyoxal production in a mouse model of type I diabetes.•These findings suggest that the accumulation of glyoxal and methylglyoxal within mitochondria may contribute to mitochondrial dysfunction in diabetes.
Mitochondria; Exomarker; Methylglyoxal; Glyoxal; Hyperglycemia; MitoG; Free radicals
Bone turnover in vivo is regulated by mechanical forces such as shear stress originating from interstitial oscillatory fluid flow (OFF), and bone cells in vitro respond to mechanical loading. However, the mechanisms by which bone cells sense mechanical forces, resulting in increased mineral deposition, are not well understood. The aim of this study was to investigate the role of the primary cilium in mechanosensing by osteoblasts. MLO-A5 murine osteoblasts were cultured in monolayer and subjected to two different OFF regimens: 5 short (2 h daily) bouts of OFF followed by morphological analysis of primary cilia; or exposure to chloral hydrate to damage or remove primary cilia and 2 short bouts (2 h on consecutive days) of OFF. Primary cilia were shorter and there were fewer cilia per cell after exposure to periods of OFF compared with static controls. Damage or removal of primary cilia inhibited OFF-induced PGE2 release into the medium and mineral deposition, assayed by Alizarin red staining. We conclude that primary cilia are important mediators of OFF-induced mineral deposition, which has relevance for the design of bone tissue engineering strategies and may inform clinical treatments of bone disorders causes by load-deficiency.—Delaine-Smith, R. M., Sittichokechaiwut, A., Reilly, G. C. Primary cilia respond to fluid shear stress and mediate flow-induced calcium deposition in osteoblasts.
mechanotransduction; oscillatory fluid flow; osteogenesis; extracellular matrix
Gene expression is controlled by proximal promoters and distal regulatory elements such as enhancers. While the activity of some promoters can be invariant across tissues, enhancers tend to be highly tissue-specific.
We compiled sets of tissue-specific promoters based on gene expression profiles of 79 human tissues and cell types. Putative transcription factor binding sites within each set of sequences were used to train a support vector machine classifier capable of distinguishing tissue-specific promoters from control sequences. We obtained reliable classifiers for 92% of the tissues, with an area under the receiver operating characteristic curve between 60% (for subthalamic nucleus promoters) and 98% (for heart promoters). We next used these classifiers to identify tissue-specific enhancers, scanning distal non-coding sequences in the loci of the 200 most highly and lowly expressed genes. Thirty percent of reliable classifiers produced consistent enhancer predictions, with significantly higher densities in the loci of the most highly expressed compared to lowly expressed genes. Liver enhancer predictions were assessed in vivo using the hydrodynamic tail vein injection assay. Fifty-eight percent of the predictions yielded significant enhancer activity in the mouse liver, whereas a control set of five sequences was completely negative.
We conclude that promoters of tissue-specific genes often contain unambiguous tissue-specific signatures that can be learned and used for the de novo prediction of enhancers.
Despite continual progress in the cataloging of vertebrate regulatory elements, little is known about their organization and regulatory architecture. Here we describe a massively parallel experiment to systematically test the impact of copy number, spacing, combination and order of transcription factor binding sites on gene expression. A complex library of ~5,000 synthetic regulatory elements containing patterns from 1 2 liver-specific transcription factor binding sites was assayed in mice and in HepG2 cells. We find that certain transcription factors act as direct drivers of gene expression in homotypic clusters of binding sites, independent of spacing between sites, whereas others function only synergistically. Heterotypic enhancers are stronger than their homotypic analogs and favor specific transcription factor binding site combinations, mimicking putative native enhancers. Exhaustive testing of binding site permutations suggests that there is flexibility in binding site order. Our findings provide quantitative support for a flexible model of regulatory element activity and suggest a framework for the design of synthetic tissue-specific enhancers.
Large-scale annotation efforts have improved our ability to coarsely predict regulatory elements throughout vertebrate genomes. However, it is unclear how complex spatiotemporal patterns of gene expression driven by these elements emerge from the activity of short, transcription factor binding sequences.
We describe a comprehensive promoter extension assay in which the regulatory potential of all 6 base-pair (bp) sequences was tested in the context of a minimal promoter. To enable this large-scale screen, we developed algorithms that use a reverse-complement aware decomposition of the de Bruijn graph to design a library of DNA oligomers incorporating every 6-bp sequence exactly once. Our library multiplexes all 4,096 unique 6-mers into 184 double-stranded 15-bp oligomers, which is sufficiently compact for in vivo testing. We injected each multiplexed construct into zebrafish embryos and scored GFP expression in 15 tissues at two developmental time points. Twenty-seven constructs produced consistent expression patterns, with the majority doing so in only one tissue. Functional sequences are enriched near biologically relevant genes, match motifs for developmental transcription factors, and are required for enhancer activity. By concatenating tissue-specific functional sequences, we generated completely synthetic enhancers for the notochord, epidermis, spinal cord, forebrain and otic lateral line, and show that short regulatory sequences do not always function modularly.
This work introduces a unique in vivo catalog of short, functional regulatory sequences and demonstrates several important principles of regulatory element organization. Furthermore, we provide resources for designing compact, reverse-complement aware k-mer libraries.
Mitochondrial dysfunction contributes to degenerative neurological disorders, consequently there is a need for mitochondria-targeted therapies that are effective within the brain. One approach to deliver pharmacophores is by conjugation to the lipophilic triphenylphosphonium (TPP) cation that accumulates in mitochondria driven by the membrane potential. While this approach has delivered TPP-conjugated compounds to the brain, the amounts taken up are lower than by other organs.
To discover why uptake of hydrophobic TPP compounds by the brain is relatively poor, we assessed the role of the P-glycoprotein (Mdr1a/b) and breast cancer resistance protein (Bcrp) ATP binding cassette (ABC) transporters, which drive the efflux of lipophilic compounds from the brain thereby restricting the uptake of lipophilic drugs. We used a triple transgenic mouse model lacking two isoforms of P-glycoprotein (Mdr1a/1b) and the Bcrp.
There was a significant increase in the uptake into the brain of two hydrophobic TPP compounds, MitoQ and MitoF, in the triple transgenics following intra venous (IV) administration compared to control mice. Greater amounts of the hydrophobic TPP compounds were also retained in the liver of transgenic mice compared to controls. The uptake into the heart, white fat, muscle and kidneys was comparable between the transgenic mice and controls.
Efflux of hydrophobic TPP compounds by ABC transporters contributes to their lowered uptake into the brain and liver.
These findings suggest that strategies to bypass ABC transporters in the BBB will enhance delivery of mitochondria-targeted antioxidants, probes and pharmacophores to the brain.
► Brain accumulation of triphenylphosphonium cations is decreased by ABC transporters. ► ABC-transporter inactivation increases brain uptake of triphenylphosphonium cations. ► Bypassing ABC transporters may increase the effectiveness of mitochondrial therapies.
ABC proteins, ATP binding cassette proteins; BBB, blood–brain barrier; Bcrp, breast cancer resistance protein; CsA, cyclosporin A; IP, intra peritoneal; IV, intra venous; Mdr1, multi drug resistance 1; MitoF, 11-fluoroundecyltriphenylphosphonium mesylate; MitoQ, [10-(4,5-dimethoxy-2-methyl-3,6-dioxo-1,4-cyclohexadien-1-yl)decyl]triphenylphosphonium mesylate; MPTP, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine; TPB, tetraphenylborate; TPP, triphenylphosphonium cation; ROS, reactive oxygen species; TPMP, methyltriphenylphosphonium; Mitochondria; Lipophilic cation; Blood–brain barrier; ABC transporters; MitoQ
Regulatory elements play an important role in the variability of individual responses to drug treatment. This has been established through studies on three classes of elements that regulate RNA and protein abundance: promoters, enhancers and microRNAs. Each of these elements, and genetic variants within them, are being characterized at an exponential pace by next-generation sequencing (NGS) technologies. In this review, we outline examples of how each class of element affects drug response via regulation of drug targets, transporters and enzymes. We also discuss the impact of NGS technologies such as chromatin immunoprecipitation sequencing (ChIP-Seq) and RNA sequencing (RNA-Seq), and the ramifications of new techniques such as high-throughput chromosome capture (Hi-C), chromatin interaction analysis by paired-end tag sequencing (ChIA-PET) and massively parallel reporter assays (MPRA). NGS approaches are generating data faster than they can be analyzed, and new methods will be required to prioritize laboratory results before they are ready for the clinic. However, there is no doubt that these approaches will bring about a systems-level understanding of the interplay between genetic variants and drug response. An understanding of the importance of regulatory variants in pharmacogenomics will facilitate the identification of responders versus non-responders, the prevention of adverse effects and the optimization of therapies for individual patients.
ChIP-Seq; enhancers; miRNA; next-generation sequencing; pharmacogenomics; promoters; RNA-Seq
We have successfully delivered a reactive alkylating agent, chlorambucil (Cbl), to the mitochondria of mammalian cells. Here, we characterize the mechanism of cell death for mitochondria-targeted chlorambucil (mt-Cbl) in vitro and assess its efficacy in a xenograft mouse model of leukemia. Using a ρ° cell model, we show that mt-Cbl toxicity is not dependent on mitochondrial DNA damage. We also illustrate that re-targeting Cbl to mitochondria results in a shift in the cell death mechanism from apoptosis to necrosis, and that this behavior is a general feature of mitochondria-targeted Cbl. Despite the change in cell death mechanisms, we show that mt-Cbl is still effective in vivo and has an improved pharmacokinetic profile compared to the parent drug. These findings illustrate that mitochondrial rerouting changes the site of action of Cbl and also alters the cell death mechanism drastically without compromising in vivo efficacy. Thus, mitochondrial delivery allows the exploitation of Cbl as a promiscuous mitochondrial protein inhibitor with promising therapeutic potential.
How should funding agencies enable researchers to explore high-risk but potentially high-reward science? One model that appears to work is the NSF-funded synthesis center, an incubator for community-led, innovative science.