Subunits of mitochondrial complex I exist as part of matrix- and membrane-associated subcomplexes in living cells

Mitochondrial complex I (CI) is a large assembly of 45 different subunits, and defects in its biogenesis are the most frequent cause of mitochondrial disorders. In vitro evidence suggests a stepwise assembly process involving pre-assembled modules. However, whether these modules also exist in vivo is as yet unresolved. To answer this question, we here applied submitochondrial fluorescence recovery after photobleaching to HEK293 cells expressing 6 GFP-tagged subunits selected on the basis of current CI assembly models. We established that each subunit was partially present in a virtually immobile fraction, possibly representing the holo-enzyme. Four subunits (NDUFV1, NDUFV2, NDUFA2, and NDUFA12) were also present as highly mobile matrix-soluble monomers, whereas, in sharp contrast, the other two subunits (NDUFB6 and NDUFS3) were additionally present in a slowly mobile fraction. In the case of the integral membrane protein NDUFB6, this fraction most likely represented one or more membrane-bound subassemblies, whereas biochemical evidence suggested that for the NDUFS3 protein this fraction most probably corresponded to a matrix-soluble subassembly. Our results provide first time evidence for the existence of CI subassemblies in mitochondria of living cells.     

Maternal transmission of risk for atherosclerosis

PURPOSE OF REVIEW: In the last 20 years, an increasing amount of epidemiological and pathological evidence has become available illustrating the relationship between an adverse in-utero environment and increased risk of vascular disease in the offspring. It is now generally accepted that epigenetic phenomena, such as either DNA methylation or chromatin modifications or both mediate the long-term memory and thus developmental programming of cells and tissues. RECENT FINDINGS: In utero, the placenta and fetus are exposed to the metabolic, antioxidant and pro-inflammatory and anti-inflammatory signals from the mother and will likely respond specifically. In the fetus, these responses may lead to permanent changes either in DNA methylation or chromatin modification or both and these changes may lead to increased atherosclerosis susceptibility in adulthood. However, the molecular mechanisms responsible for the translation of an adverse maternal environment into permanent epigenetic changes are poorly understood. SUMMARY: In this review, we briefly summarize the possible signals crossing the placental barrier and discuss the molecular mechanisms of epigenetic programming in the developing fetus leading to increased athero-susceptibility of the vessel wall.     

Mitigation of NADH: ubiquinone oxidoreductase deficiency by chronic Trolox treatment

Deficiency of mitochondrial NADH:ubiquinone oxidoreductase (complex I), is associated with a variety of clinical phenotypes such as Leigh syndrome, encephalomyopathy and cardiomyopathy. Circumstantial evidence suggests that increased reactive oxygen species (ROS) levels contribute to the pathogenesis of these disorders. Here we assessed the effect of the water-soluble vitamin E derivative Trolox on ROS levels, and the amount and activity of complex I in fibroblasts of six children with isolated complex I deficiency caused by a mutation in the NDUFS1, NDUFS2, NDUFS7, NDUFS8 or NDUFV1 gene. Patient cells displayed increased ROS levels and a variable decrease in complex I activity and amount. For control cells, the ratio between activity and amount was 1 whereas for the patients this ratio was below 1, indicating a defect in intrinsic catalytic activity of complex I in the latter cells. Trolox treatment dramatically reduced ROS levels in both control and patient cells, which was paralleled by a substantial increase in the amount of complex I. Although the ratio between the increase in activity and amount of complex I was exactly proportional in control cells it varied between 0.1 and 0.8 for the patients. Our findings suggest that the expression of complex I is regulated by ROS. Furthermore, they provide evidence that both the amount and intrinsic activity of complex I are decreased in inherited complex I deficiency. The finding that Trolox treatment increased the amount of complex I might aid the future development of antioxidant treatment strategies for patients. However, such treatment may only be beneficial to patients with a relatively small reduction in intrinsic catalytic defect of the complex.     

Organic-walled dinoflagellate cyst production in relation to upwelling intensity and lithogenic influx in the Cape Blanc region (off north-west Africa)

Fossil dinoflagellate cyst assemblages are increasingly used in paleoclimatic research to establish paleoenvi‐ronmental reconstructions. To obtain reliable reconstructions, it is essential to know which physical factors influence the cyst production. Most information about the relationship between variations in physical parameters and cyst production is known from middle and higher latitudes. Information from the (sub)tropics is rare. To increase this information, the temporal variation in cyst assemblages from the upwelling area off north‐west Africa (off Mauritania) has been compared to environmental conditions of the upper water column. Samples were collected by the sediment trap CB9, off north‐west Africa (Cape Blanc, 21°15′2″N, 20°42′2″W) between 11 June 1998 and 7 November 1999 at 27.5‐day intervals. Off Cape Blanc, upwelling occurs throughout the year with variable intensity. This region is also characterized by frequently occurring Saharan dust storms. Seasonal variations in dust input, upwelling intensity and sea surface temperature are reflected by the production of organic‐walled dinoflagellate cyst assemblages. Several cyst taxa are produced throughout the sampling interval, with the highest fluxes at times of strongest upwelling relaxation and/or dust input (Echinidinium aculeatum Zonneveld, Echini‐din ium delicatum Zonneveld, Echinidinium granulaturn Zonneveld, Echinidinium spp., Impagidinium aculeatum (Wall) Lentin et Williams, Impagidinium sphaeri‐cum (Wall) Lentin et Williams, Protoperidinium americanum (Gran et Braarud) Balech, Protoperidinium stellatum (Wall in Wall et Dale) Rochon etal., Protoperidinium spp., Selenopemphix nephroides (Benedek) Benedek et Sarjeant and Selenopemphix quanta (Bradford) Matsuoka). Species such as, for example, Bitectatodinium spongium (Zonneveld) Zonneveld et Jurkschat and Impagidinium patulum (Wall) Stover et Evitt do not show any production pattern related to a particular season of the year or to specific environmental conditions in the upper water column. The production of cysts of Protoperidinium monospinum (Paulsen) Zonneveld et Dale is restricted to intervals with increased nutrient concentrations in upper waters when sea surface temperatures at the sampling site is below approximately 24°C.     

The creatine kinase system is essential for optimal refill of the sarcoplasmic reticulum Ca2+ store in skeletal muscle.

Muscle function depends on an adequate ATP supply to sustain the energy consumption associated with Ca(2+) cycling and actomyosin sliding during contraction. In this regulation of energy homeostasis, the creatine kinase (CK) circuit for high energy phosphoryl transfer between ATP and phosphocreatine plays an important role. We earlier established a functional connection between the activity of the CK system and Ca(2+) homeostasis during depolarization and contractile activity of muscle. Here, we show how CK activity is coupled to the kinetics of spontaneous and electrically induced Ca(2+) transients in the sarcoplasm of myotubes. Using the UV ratiometric Ca(2+) probe Indo-1 and video-rate confocal microscopy in CK-proficient and -deficient cultured cells, we found that spontaneous and electrically induced transients were dependent on ryanodine-sensitive Ca(2+) release channels, sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase pumps, extracellular calcium, and functional mitochondria in both cell types. However, at increasing sarcoplasmic Ca(2+) load (induced by electrical stimulation at 0.1, 1, and 10 Hz), the Ca(2+) removal rate and the amount of Ca(2+) released per transient were gradually reduced in CK-deficient (but not wild-type) myotubes. We conclude that the CK/phosphocreatine circuit is essential for efficient delivery of ATP to the sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase pumps and thereby directly influences sarcoplasmic reticulum refilling and the kinetics of the sarcoplasmic Ca(2+) signals.     

Membrane-initiated Ca(2+) signals are reshaped during propagation to subcellular regions.

An important aspect of Ca(2+) signaling is the ability of cells to generate intracellular Ca(2+) waves. In this study we have analyzed the cellular and subcellular kinetics of Ca(2+) waves in a neuroendocrine transducer cell, the melanotrope of Xenopus laevis, using the ratiometric Ca(2+) probe indo-1 and video-rate UV confocal laser-scanning microscopy. The purpose of the present study was to investigate how local Ca(2+) changes contribute to a global Ca(2+) signal; subsequently we quantified how a Ca(2+) wave is kinetically reshaped as it is propagated through the cell. The combined kinetics of all subcellular Ca(2+) signals determined the shape of the total cellular Ca(2+) signal, but each subcellular contribution to the cellular signal was not constant in time. Near the plasma membrane, [Ca(2+)](i) increased and decreased rapidly, processes that can be described by a linear and exponential function, respectively. In more central parts of the cell slower kinetics were observed that were best described by a Hill equation. This reshaping of the Ca(2+) wave was modeled with an equation derived from a low-pass RC filter. We propose that the differences in spatial kinetics of the Ca(2+) signal serves as a mechanism by which the same cellular Ca(2+) signal carries different regulatory information to different subcellular regions of the cell, thus evoking differential cellular responses.     

Zinc supplementation increases bone alkaline phosphatase in healthy men.

Zinc takes part in the metabolism of bone as a constituent of the matrix and as an activator of several metallo-enzymes. Animal in vitro and in vivo studies strongly suggest that zinc supplementation could stimulate bone formation and inhibit bone resorption but data in humans remain rare. The biological effects of 50 mg zinc given orally as gluconate in 20 healthy male volunteers were investigated in a 12 weeks double-blind placebo-controlled randomized trial. To investigate bone turnover, total alkaline phosphatases activity (ALP), bone specific alkaline phosphatase activity (BAPE) and BAP mass (BAP-M) concentration were measured as parameters of bone formation while urine calcium and C-terminal collagen peptide were determined as parameters of bone resorption. Samples were obtained in fasting subjects at baseline and after 6 and 12 weeks. In zinc treated subjects, a significant increase was observed at least after 12 weeks in total ALP (p < 0.01), BAP-M (p < 0.05) and BAP-E (p < 0.02). These parameters did not significantly change in the placebo group. Urine zinc/creatinine ratio significantly increased after 6 (p < 0.03) and 12 weeks (p < 0.04) in the zinc-treated group and was significantly different from the placebo group (p < 0.002). There was no significant effect of zinc supplementation on parameters of bone resorption. In conclusion, zinc supplementation at supraphysiological doses increased parameters of bone formation in healthy men while parameters of bone resorption remained unchanged.     

A critical assessment of two species distribution models: a case study of the vervet monkey (Cercopithecus aethiops)

Aim Species distribution models are invaluable tools in biogeographical, ecological and applied biological research, but specific concerns have been raised in relation to different modelling techniques in terms of their validity. Here we compare two fundamentally different approaches to species distribution modelling, one based on simple occurrence data where the lack of an ecological framework has been criticized, and the other firmly based in socio‐ecological theory but requiring highly detailed behavioural information that is often limited in availability. Location (Sub‐Saharan) Africa. Methods We used two distinct techniques to predict the realized distribution of a model species, the vervet monkey (Cercopithecus aethiops Linnaeus, 1758). A maximum entropy model was produced taking 13 environmental variables and presence‐only data from 174 sites throughout Africa as input, with an additional 58 sites retained to test the model. A time‐budget model considering the same environmental variables was constructed from detailed behavioural data on 20 groups representing 14 populations, with presence‐only data from the remaining 218 sites reserved to test model predictions on vervet monkey occurrence. Both models were further validated against a reference species distribution map as drawn up by the African Mammals Databank. Results Both models performed well, with the time budget and maximum entropy algorithms correctly predicting vervet monkey presence at 78.4% and 91.4% of their respective test sites. Similarly, the time‐budget model correctly predicted presence and absence at 87.4% of map pixels against the reference distribution map, and the maximum entropy model achieved a success rate of 81.8%. Finally, there was a high level of agreement (81.6%) between the presence–absence maps produced by the two models, and the environmental variables identified as most strongly driving vervet monkey distribution were the same in both models. Main conclusions The time‐budget and maximum entropy models produced accurate and remarkably similar species distribution maps, despite fundamental differences in their conceptual and methodological approaches. Such strong convergence not only provides support for the credibility of current results, but also relieves concerns about the validity of the two modelling approaches.