Ferredoxin C2 is required for chlorophyll biosynthesis and accumulation of photosynthetic antennae in Arabidopsis

Ferredoxins (Fd) are small iron-sulphur proteins, with sub-types that have evolved for specific redox functions. Ferredoxin C2 (FdC2) proteins are essential Fd homologues conserved in all photosynthetic organisms and a number of different FdC2 functions have been proposed in angiosperms. Here we use RNAi silencing in Arabidopsis thaliana to generate a viable fdC2 mutant line with near-depleted FdC2 protein levels. Mutant leaves have ~50% less chlorophyll a and b, and chloroplasts have poorly developed thylakoid membrane structure. Transcriptomics indicates upregulation of genes involved in stress responses. Although fdC2 antisense plants show increased damage at photosystem II (PSII) when exposed to high light, PSII recovers at the same rate as wild type in the dark. This contradicts literature proposing that FdC2 regulates translation of the D1 subunit of PSII, by binding to psbA transcript. Measurement of chlorophyll biosynthesis intermediates revealed a build-up of Mg-protoporphyrin IX, the substrate of the aerobic cyclase. We localise FdC2 to the inner chloroplast envelope and show that the FdC2 RNAi line has a disproportionately lower protein abundance of antennae proteins, which are nuclear-encoded and must be refolded at the envelope after import.

The function of glutaredoxin GRXS15 is required for lipoyl-dependent dehydrogenases in mitochondria

Iron-sulfur (Fe-S) clusters are ubiquitous cofactors in all life and are used in a wide array of diverse biological processes, including electron transfer chains and several metabolic pathways. Biosynthesis machineries for Fe-S clusters exist in plastids, the cytosol, and mitochondria. A single monothiol glutaredoxin (GRX) is involved in Fe-S cluster assembly in mitochondria of yeast and mammals. In plants, the role of the mitochondrial homolog GRXS15 has only partially been characterized. Arabidopsis (Arabidopsis thaliana) grxs15 null mutants are not viable, but mutants complemented with the variant GRXS15 K83A develop with a dwarf phenotype similar to the knockdown line GRXS15amiR. In an in-depth metabolic analysis of the variant and knockdown GRXS15 lines, we show that most Fe-S cluster-dependent processes are not affected, including biotin biosynthesis, molybdenum cofactor biosynthesis, the electron transport chain, and aconitase in the tricarboxylic acid (TCA) cycle. Instead, we observed an increase in most TCA cycle intermediates and amino acids, especially pyruvate, glycine, and branched-chain amino acids (BCAAs). Additionally, we found an accumulation of branched-chain α-keto acids (BCKAs), the first degradation products resulting from transamination of BCAAs. In wild-type plants, pyruvate, glycine, and BCKAs are all metabolized through decarboxylation by mitochondrial lipoyl cofactor (LC)-dependent dehydrogenase complexes. These enzyme complexes are very abundant, comprising a major sink for LC. Because biosynthesis of LC depends on continuous Fe-S cluster supply to lipoyl synthase, this could explain why LC-dependent processes are most sensitive to restricted Fe-S supply in grxs15 mutants.

Encapsidation of Viral RNA in Picornavirales: Studies on Cowpea Mosaic Virus Demonstrate Dependence on Viral Replication

To elucidate the linkage between replication and encapsidation in Picornavirales, we have taken advantage of the bipartite nature of a plant-infecting member of this order, cowpea mosaic virus (CPMV), to decouple the two processes. RNA-free virus-like particles (empty virus-like particles [eVLPs]) can be generated by transiently coexpressing the RNA-2-encoded coat protein precursor (VP60) with the RNA-1-encoded 24,000-molecular-weight (24K) protease, in the absence of the replication machinery (K. Saunders, F. Sainsbury, and G. P. Lomonossoff, Virology 393:329-337, 2009, https://doi.org/10.1016/j.virol.2009.08.023). We have made use of the ability to produce assembled capsids of CPMV in the absence of replication to examine the putative linkage between RNA replication and packaging in the Picornavirales We have created a series of mutant RNA-1 and RNA-2 molecules and have assessed the effects of the mutations on both the replication and packaging of the viral RNAs. We demonstrate that mutations that affect replication have a concomitant impact on encapsidation and that RNA-1-mediated replication is required for encapsidation of both RNA-1 and RNA-2. This close coupling between replication and encapsidation provides a means for the specific packaging of viral RNAs. Moreover, we demonstrate that this feature of CPMV can be used to specifically encapsidate custom RNA by placing a sequence of choice between the RNA-2 sequences required for replication.IMPORTANCE The mechanism whereby members of the order Picornavirales specifically package their genomic RNAs is poorly understood. Research with monopartite members of the order, such as poliovirus, indicated that packaging is linked to replication, although the presence of "packaging signals" along the length of the viral RNA has also been suggested. Thanks to the bipartite nature of the CPMV genome, which allows the manipulation of RNA-1 without modifying RNA-2, we show here that this specificity is due to a functional link between the two processes of viral replication and encapsidation. This has important implications for our understanding of the fundamental molecular biology of Picornavirales and opens the door to novel research and therapeutic applications in the field of custom RNA packaging and delivery technologies.

Improvement of an Atomic Clock using Squeezed Vacuum

Since the pioneering work of Ramsey, atom interferometers are employed for precision metrology, in particular to measure time and to realize the second. In a classical interferometer, an ensemble of atoms is prepared in one of the two input states, whereas the second one is left empty. In this case, the vacuum noise restricts the precision of the interferometer to the standard quantum limit (SQL). Here, we propose and experimentally demonstrate a novel clock configuration that surpasses the SQL by squeezing the vacuum in the empty input state. We create a squeezed vacuum state containing an average of 0.75 atoms to improve the clock sensitivity of 10000 atoms by 2.05_{-0.37}^{+0.34}  dB. The SQL poses a significant limitation for today's microwave fountain clocks, which serve as the main time reference. We evaluate the major technical limitations and challenges for devising a next generation of fountain clocks based on atomic squeezed vacuum.

Arabidopsis glutaredoxin S17 and its partner, the nuclear factor Y subunit C11/negative cofactor 2α, contribute to maintenance of the shoot apical meristem under long-day photoperiod

Glutaredoxins (GRXs) catalyze the reduction of protein disulfide bonds using glutathione as a reductant. Certain GRXs are able to transfer iron-sulfur clusters to other proteins. To investigate the function of Arabidopsis (Arabidopsis thaliana) GRXS17, we applied a strategy combining biochemical, genetic, and physiological approaches. GRXS17 was localized in the nucleus and cytosol, and its expression was elevated in the shoot meristems and reproductive tissues. Recombinant GRXS17 bound Fe2S2 clusters, a property likely contributing to its ability to complement the defects of a Baker's yeast (Saccharomyces cerevisiae) strain lacking the mitochondrial GRX5. However, a grxs17 knockout Arabidopsis mutant exhibited only a minor decrease in the activities of iron-sulfur enzymes, suggesting that its primary function is as a disulfide oxidoreductase. The grxS17 plants were sensitive to high temperatures and long-day photoperiods, resulting in elongated leaves, compromised shoot apical meristem, and delayed bolting. Both environmental conditions applied simultaneously led to a growth arrest. Using affinity chromatography and split-Yellow Fluorescent Protein methods, a nuclear transcriptional regulator, the Nuclear Factor Y Subunit C11/Negative Cofactor 2α (NF-YC11/NC2α), was identified as a GRXS17 interacting partner. A mutant deficient in NF-YC11/NC2α exhibited similar phenotypes to grxs17 in response to photoperiod. Therefore, we propose that GRXS17 interacts with NF-YC11/NC2α to relay a redox signal generated by the photoperiod to maintain meristem function.

A conserved mitochondrial ATP-binding cassette transporter exports glutathione polysulfide for cytosolic metal cofactor assembly

An ATP-binding cassette transporter located in the inner mitochondrial membrane is involved in iron-sulfur cluster and molybdenum cofactor assembly in the cytosol, but the transported substrate is unknown. ATM3 (ABCB25) from Arabidopsis thaliana and its functional orthologue Atm1 from Saccharomyces cerevisiae were expressed in Lactococcus lactis and studied in inside-out membrane vesicles and in purified form. Both proteins selectively transported glutathione disulfide (GSSG) but not reduced glutathione in agreement with a 3-fold stimulation of ATPase activity by GSSG. By contrast, Fe²⁺ alone or in combination with glutathione did not stimulate ATPase activity. Arabidopsis atm3 mutants were hypersensitive to an inhibitor of glutathione biosynthesis and accumulated GSSG in the mitochondria. The growth phenotype of atm3-1 was strongly enhanced by depletion of the mitochondrion-localized, GSH-dependent persulfide oxygenase ETHE1, suggesting that the physiological substrate of ATM3 contains persulfide in addition to glutathione. Consistent with this idea, a transportomics approach using mass spectrometry showed that glutathione trisulfide (GS-S-SG) was transported by Atm1. We propose that mitochondria export glutathione polysulfide, containing glutathione and persulfide, for iron-sulfur cluster assembly in the cytosol.

Decreased oxidative stress in patients with idiopathic dilated cardiomyopathy one year after immunoglobulin adsorption

OBJECTIVES

In a substudy to a recently reported investigation that demonstrated the benefit of immunoglobulin adsorption (immunoadsorption) for patients with idiopathic dilated cardiomyopathy (IDC), we tested whether this benefit is associated with a reduction of oxidative stress.

BACKGROUND

The progression of cardiomyopathy is believed to be related to the increase of oxidative stress. Therefore, reduction of oxidative stress could be one of the effects of immunoadsorption for improvement of cardiac performance and clinical status.

METHODS

Plasma markers for oxidative stress-thiobarbituric acid-reactive substances (TBARS), lipid peroxides (LPO), anti-oxidized low-density lipoprotein-autoantibodies (anti-oxLDL-AB), thiol groups and vitamin E-were compared in 31 patients, of whom 16 underwent immunoadsorption and 15 received conventional treatment (controls). All patients received a daily supplement of vitamins, minerals and trace elements.

RESULTS

After one year, TBARS (p = 0.026), LPO (p = 0.026) and anti-oxLD

Consequences of long-term selenium-deficient diet on the prostacyclin and thromboxane release from rat aorta

It is known that peroxides, which are increased during Se deficiency because of reduced glutathione peroxidase (GSH-Px) activity, can influence the prostacyclin I2/thromboxane A2 (PGI2/TXA2) ratio. In this study we analyzed the PGI2 and TXA2 formation of aortas of long-term Se-deficient rats. Despite low GSH-Px activity in the Se-deficient group, the basal PGI2 and TXA2 formation was not different versus control animals (PGI2: 2295+/-1134 pg/mg vs 2940+/-1134 pg/mg; TXA2: 3.83+/-1.06 pg/mg vs 5.67+/-2.99 pg/mg). However, we checked the capacity of the aortas of Se-deficient rats to compensate for a suddenly increased peroxide concentration. After peroxide stimulation, the PGI2 release was significantly lower in the Se-deficient group compared to the control group (PGI2: 3507+/-1829 pg/mg vs 7986+/-2636 pg/mg). Again, the TXA2 release did not show any differences. The release ratio of PGI2/TXA2 decreased under peroxide stress in Se-deficient animals. Although long-term Se deficiency showed a relatively well-balanced metabolism under resting conditions, sudden stress, accompanied by an excessive radical production, cannot be compensated.

Increased level of HSP27 but not of HSP72 in human heart allografts in relation to acute rejection

BACKGROUND

Increased expression of heat shock proteins (HSPs) was assumed during cardiac allograft rejection. To find evidence for this in man, we quantified HSP27 and HSP72 in cardiac allograft biopsies.

METHODS

In parallel to histological assessment of rejection, HSP27 was quantified by Western blotting in a total of 43 biopsies sampled from 3 patients. HSP72 was analyzed in parallel in 30 of the 43 cases. For comparison, HSPs were analyzed in myocardium.

RESULTS

HSP27 was significantly higher in rejecting cardiac allografts than in non-rejecting allografts and non-failing myocardium (1.52 +/- 0.25 vs. 0.83 +/- 0.11 vs. 0.50 +/- 0.05 microg/mg protein). Similarity for HSP72 (6.27 +/- 1.54 vs. 4.06 +/- 1.03 vs. 6.27 +/- 0.76 microg/mg protein) was not found.

CONCLUSION

For the first time in humans with cardiac allograft rejection, increased expression of HSP27, which could be important for cardiac self-protection, was demonstrated. For the lack of increased HSP72 expression, the influence of the cyclosporine A treatment was discussed.

The ratio of formation of prostacyclin/thromboxane A2 in HUVEC decreased in each subsequent passage

In this study, we analyzed the antioxidative potential (SOD-, GSH-Px-activity) and the basal, H2O2- and ATP-stimulated formation of PGI2 and TXA2 in human umbilical vein endothelial cells (HUVEC) of different passages. The subcultivation of cells partly represents the process of aging. Both subcultivation of the cells and the H2O2 incubation did not significantly influence the activity of SOD and GSH-Px. H2O2 (0.1 mM and 1.0 mM) stimulated the generation of PGI2 and TXA2 in the cell passages time dependently. The formation ratio of PGI/TXA2 changed from 640:1 (0.1 mM H2O2) or 430:1 (1.0 mM H2O2, 40 min incubation) at the 1st passage, to 13:1 and 17:1, respectively, at the 4th passage. This resulted from the reduction of the PGI2 synthesis connected with more pronounced TXA2 formation. The same behavior was found in the basal and ATP-stimulated eicosanoid formation. Based on this, the age-dependent activation of the oxygen radical formation could be responsible for the modified eicosanoid metabolism resulting in vascular complications in the elderly.

Atrial inhibited pacing in the sick sinus node syndrome: clinical value and the demand for rate responsiveness

A consecutive series of 66 patients (males = 32; mean age +/- SD = 71 +/- 9 years) given atrial inhibited pacemakers for sick sinus nodes were followed to study the incidence of lead failures, chronic atrial tachyarrhythmias, and atrioventricular conduction disturbances. The need for rate responsive pacing was also assessed. Pre and postoperative investigation could include carotid sinus massage, Holter monitoring, exercise testing, and invasive electrophysiology. The mean follow-up time +/- SD was 32 +/- 29 months (median = 26 months). Three patients (5%) had their pacemakers replaced due to lead failures (loss of sensing = 2; exit block = 1). Two pacemakers (3%) were replaced after 5 and 22 months due to atrial fibrillation. Four patients (6%) received new pacemakers because of development of second-degree or complete atrioventricular block after 1, 6, 12, and 31 months, respectively. During exercise, most patients (76%) responded with an increase in sinus rate at least as marked as that achievable with the currently available rate responsive pacemakers. Assuming careful patient selection, atrial inhibited pacing is well suited for many patients with sinus node dysfunction and preserved atrioventricular conduction. There is a limited need for rate responsive pacemakers in these patients.

[Kidney function in the course of compensatory hypertrophy following unilateral nephrectomy in the Wistar rat]

Unilateral nephrectomy was performed in 109 male Wistar rats, 35 animals served as controls. Determinations of glomerular filtration rate (GFR) using slope clearance of 99mTc-DTPA and of tubular function using an orally water-loading test were made. The tests were performed 2 and 5 days as well as 2, 4, 5 and 6 weeks after nephrectomy. In all examinations the GFR was more than 50% of the level of two-kidney control animals. Fractional maximum diuresis was increased in the first 2 examinations after nephrectomy from 8.9 +/- 2.1 to 15.4 +/- 4.2% of the GFR and fractional clearance of osmotically free water from 6.8 +/- 1.9 to 10.9 +/- 3.5%. In the fourth and sixth week the proximal tubular reabsorption was increased and the glomerulo-tubular balance had been recovered. However, the minimal urine osmolarity was increased to 107.8 +/- 17.7 mmol/l and the osmotic load of the nephrons remained elevated. Possible clinical implications of the results are discussed.

Rate-responsive pacing by means of activity sensing versus single rate ventricular pacing: a double-blind cross-over study

The clinical applicability of rate-responsive pacing (RRP) by means of activity sensing has been tested in 15 patients. The patients (ages 24-85) had sinus node dysfunction (2), atrial fibrillation (7), or sinus rhythm (6) combined with complete atrioventricular block. Exercise capacity was investigated on a bicycle ergometer and on a treadmill in a double-blind cross-over study design following one week each of fixed rate ventricular pacing (70 bpm) and rate-responsive pacing (60/125-150 bpm). The patients answered a questionnaire concerning subjective symptoms. A Holter ECG was recorded during 24 hours of all day activity on rate-responsive pacing. During exercise in the rate-responsive mode, heart rate increased more on the treadmill than on the bicycle. A majority of the patients (13 of 15) preferred rate-responsive pacing mainly due to less dyspnea and tiredness. Exercise capacity improved significantly both on bicycle (+7%; p less than 0.01) and on treadmill (+19%; p less than 0.01) during rate-responsive pacing. There were no complications during the follow-up period. In conclusion, the activity-sensing pacemaker is a valuable supplement to existing types of pacemakers. It should be used in patients in whom an atrial electrogram cannot be used for rate triggering.

[Bacteriologic, histologic and functional studies of the kidney in 5 days' therapy of experimental E. coli pyelonephritis with gentamycin. Comparison with 9 days' therapy]

Short-term antibiotic treatment is recommended in infections of the lower urinary tract but its effectiveness is questioned in the upper urinary tract infections. We compared a 5 and a 9 day treatment of experimental E. coli 022 pyelonephritis after unilateral nephrectomy in 127 mal Wistar rats. We used 9 mg gentamycin per kg b.w. twice daily. I131 hippurat excretion was not decreased during the 5 day treatment but was only temporarily diminished during the 9 day treatment. Histologically the severe acute pyelonephritis was decreased after the 9 day treatment but not after 5 days of treatment. Bacteriologically almost all the kidneys were sterile after the 9 day treatment but the majority of the kidneys showed the injected strain of E. coli after the 5 day treatment. The results indicated that the shortened treatment was much less effective in our acute experimental pyelonephritis.

A new transvenous lead for both atrial and ventricular pacing

A new transvenous tined unipolar lead (Medtronic SP 342) has been implanted in 56 patients; 35 leads were positioned in the atrium and 34 in the ventricle. The lead comprises a trifilar DBS-conductor within an insulation of polyurethane, four symetrically placed polyurethane tines furnished with scallops and a platinum-iridium ring-tipped electrode. The scallops in the tines ensure flexibility and a small effective diameter of the lead which makes the choice of vein less critical than with most previous tined leads. It allows use of the same normally sized vein for a second lead for dual-chamber sensing pacing. Mean atrial and ventricular electrogram amplitudes (+/-SD) were 4.6 +/- 1.2 mV and 8.8 +/- 4.4 mV; mean atrial and ventricular stimulation thresholds were 0.8 +/- 0.3 V and 0.4 +/- 0.2 V; and mean atrial and ventricular lead impendances were 415 +/- 114 ohms and 456 +/- 105 ohms, respectively. The results of this study show that the SP 342 lead is useful especially in dual chamber systems.

Timing markers showing pacemaker behavior to aid in the follow-up of a physiological pacemaker

In the present study a multiprogrammable, atrial synchronous, ventricular inhibited pacemaker (Enertrax) was used in six patients. This pacer makes it possible to evaluate pacemaker performance non-invasively and facilitates the correct interpretation of the difficult ECGs produced by these complex pacemakers.

Pacemaker-induced arrhythmias

The pacemaker ECG with different types of pacemakers used for the treatment of bradyarrhythmias is considered. The arrhythmias induced or interfered with by the pacemakers receive special consideration. The normal function of the most common types of pacing systems is schematically presented.

A comparison of the acute and long-term hemodynamic effects of ventricular inhibited and atrial synchronous ventricular inhibited pacing

Sixteen patients treated with a noninvasively programmable pacemaker were examined after a prolonged period of ventricular inhibited (VVI) and atrial synchronous ventricular inhibited (VDD) pacing. Maximal working capacity was determined by bicycle ergometry. Atrial and ventricular rates, brachial artery cuff pressure and breathing rate were determined at rest and during exercise. There was a mean increase in working capacity of 24% with VDD compared with VVI pacing (p less than 0.001). Thirteen of the patients were catheterized. During VDD pacing, cardiac output was significantly higher, particularly during exercise (+/- 32%) due to the capability of heart rate increase and despite a substantial compensatory stroke volume increase during VVI pacing. Arteriovenous oxygen difference was much higher during VVI pacing, reaching 164 +/- 14 ml/l during the highest work load, while the corresponding level during VDD pacing was 140 +/- 14 ml/l (p less than 0.001). During exercise, arterial blood lactate was significantly higher during VVI than during VDD pacing. Heart size was significantly smaller, 568 +/- 98 vs 530 +/- 96 ml/m2 BSA (p less than 0.05), during VDD pacing a questionnaire was completed by the patients to evaluate subjective symptoms and pacemaker preference. This part of the study favored the VDD mode of pacing. The conclusion of this study is that VDD pacing is superior to VVI pacing.

Comparison of physical work capacity and systolic time intervals with ventricular inhibited and atrial synchronous ventricular inhibited pacing

Sixteen patients with a non-invasively programmable pacemaker (Medtronic 2409) were examined with the unit in ventricular inhibited (VVI) and atrial synchronous ventricular inhibited (VDT/I) mode, respectively. Maximal exercise capacity was determined by means of bicycle ergometry. Work load was increased in steps of 10 watts each minute. Atrial and ventricular rates, brachial artery pressure, and respiratory rate were studied at rest and during exercise while systolic time intervals were determined at rest. There was an important increase in maximal exercise capacity when changing from VVI to VDT/I pacing. The extent of improvement was the same for patients above and below the age of 65 years. At comparable work loads VDT/I pacing resulted in significantly lower atrial rates than VVI pacing. Systolic time intervals did not differ between VVI and VDT/I pacing apart from an increase in left ventricular ejection time index with VDT/I pacing. Systolic time intervals and maximal exercise capacity with VVI pacing did not correlate with the increase in exercise capacity induced by VDT/I pacing. Physical performance can be significantly improved by VDT/I pacing in both young and old patients. Exercise capacity on VVI pacing cannot predict the possible benefit of change to VDT/I pacing.

Clinical evaluation of atrial synchronous ventricular inhibited pacemakers

The technical specifications and the operation of two atrial synchronous ventricular inhibited (ASVIP) pacemaker designs are described along with the results of clinical evaluation of these pacemakers in 30 patients. Clinical advantages of such pacemakers are contrasted with the performance of A-V sequential (DVI) and atrial synchronous (VAT) systems.

Clinical and electrophysiological characteristics of a transvenous atrial lead

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