Inhibition of chymotrypsin-like activity of the proteasome by ixazomib prevents mitochondrial dysfunction during myocardial ischemia

The heart is critically dependent on mitochondrial respiration for energy supply. Ischemia decreases oxygen availability, with catastrophic consequences for cellular energy systems. After a few minutes of ischemia, the mitochondrial respiratory chain halts, ATP levels drop and ion gradients across cell membranes collapse. Activation of cellular proteases and generation of reactive oxygen species by mitochondria during ischemia alter mitochondrial membrane permeability, causing mitochondrial swelling and fragmentation and eventually cell death. The mitochondria, therefore, are important targets of cardioprotection against ischemic injury. We have previously shown that ixazomib (IXA), a proteasome inhibitor used for treating multiple myeloma, effectively reduced the size of the infarct produced by global ischemia in isolated rat hearts and prevented degradation of the sarcoplasmic reticulum calcium release channel RyR2. The aim of this work was to further characterize the protective effect of IXA by determining its effect on mitochondrial morphology and function after ischemia. We also quantified the effect of IXA on levels of mitofusin-2, a protein involved in maintaining mitochondrial morphology and mitochondria-SR communication. We found that mitochondria were significantly preserved and functional parameters such as oxygen consumption, the ability to generate a membrane potential, and glutathione content were improved in mitochondria isolated from hearts perfused with IXA prior to ischemia. IXA also blocked the release of cytochrome c observed in ischemia and significantly preserved mitofusin-2 integrity. These beneficial effects resulted in a significant decrease in the left ventricular end diastolic pressure upon reperfusion and a smaller infarct in isolated hearts.

Mitochondrial Nanotunnels

Insight into the regulation of complex physiological systems emerges from understanding how biological units communicate with each other. Recent findings show that mitochondria communicate at a distance with each other via nanotunnels, thin double-membrane protrusions that connect the matrices of non-adjacent mitochondria. Emerging evidence suggest that mitochondrial nanotunnels are generated by immobilized mitochondria and transport proteins. This review integrates data from the evolutionarily conserved structure and function of intercellular projections in bacteria with recent developments in mitochondrial imaging that permit nanotunnel visualization in eukaryotes. Cell type-specificity, timescales, and the selective size-based diffusion of biomolecules along nanotunnels are also discussed. The joining of individual mitochondria into dynamic networks of communicating organelles via nanotunnels and other mechanisms has major implications for organelle and cellular behaviors.

Mitochondria fine-tune the slow Ca(2+) transients induced by electrical stimulation of skeletal myotubes

Mitochondria sense cytoplasmic Ca(2+) signals in many cell types. In mammalian skeletal myotubes, depolarizing stimuli induce two independent cytoplasmic Ca(2+) signals: a fast signal associated with contraction and a slow signal that propagates to the nucleus and regulates gene expression. How mitochondria sense and possibly affect these cytoplasmic Ca(2+) signals has not been reported. We investigated here (a) the emergence of mitochondrial Ca(2+) signals in response to electrical stimulation of myotubes, (b) the contribution of mitochondrial Ca(2+) transients to ATP generation and (c) the influence of mitochondria as modulators of cytoplasmic and nuclear Ca(2+) signals. Rhod2 and Fluo3 fluorescence determinations revealed composite Ca(2+) signals associated to the mitochondrial compartment in electrically stimulated (400 pulses, 45 Hz) skeletal myotubes. Similar Ca(2+) signals were detected when using a mitochondria-targeted pericam. The fast mitochondrial Ca(2+) rise induced by stimulation was inhibited by pre-incubation with ryanodine, whereas the phospholipase C inhibitor U73122 blocked the slow mitochondrial Ca(2+) signal, showing that mitochondria sense the two cytoplasmic Ca(2+) signal components. The fast but not the slow Ca(2+) transient enhanced mitochondrial ATP production. Inhibition of the mitochondrial Ca(2+) uniporter prevented the emergence of mitochondrial Ca(2+) transients and significantly increased the magnitude of slow cytoplasmic Ca(2+) signals after stimulation. Precluding mitochondrial Ca(2+) extrusion with the Na(+)/Ca(2+) exchanger inhibitor CGP37157 decreased mitochondrial potential, increased the magnitude of the slow cytoplasmic Ca(2+) signal and decreased the rate of Ca(2+) signal propagation from one nucleus to the next. Over expression of the mitochondrial fission protein Drp-1 decreased mitochondrial size and the slow Ca(2+) transient in mitochondria, but enhanced cytoplasmic and nuclear slow transients. The present results indicate that mitochondria play a central role in the regulation of Ca(2+) signals involved in gene expression in myotubes.

Parallel activation of Ca(2+)-induced survival and death pathways in cardiomyocytes by sorbitol-induced hyperosmotic stress

Hyperosmotic stress promotes rapid and pronounced apoptosis in cultured cardiomyocytes. Here, we investigated if Ca(2+) signals contribute to this response. Exposure of cardiomyocytes to sorbitol [600 mosmol (kg water)(-1)] elicited large and oscillatory intracellular Ca(2+) concentration increases. These Ca(2+) signals were inhibited by nifedipine, Cd(2+), U73122, xestospongin C and ryanodine, suggesting contributions from both Ca(2+) influx through voltage dependent L-type Ca(2+) channels plus Ca(2+) release from intracellular stores mediated by IP(3) receptors and ryanodine receptors. Hyperosmotic stress also increased mitochondrial Ca(2+) levels, promoted mitochondrial depolarization, reduced intracellular ATP content, and activated the transcriptional factor cyclic AMP responsive element binding protein (CREB), determined by increased CREB phosphorylation and electrophoretic mobility shift assays. Incubation with 1 mM EGTA to decrease extracellular [Ca(2+)] prevented cardiomyocyte apoptosis induced by hyperosmotic stress, while overexpression of an adenoviral dominant negative form of CREB abolished the cardioprotection provided by 1 mM EGTA. These results suggest that hyperosmotic stress induced by sorbitol, by increasing Ca(2+) influx and raising intracellular Ca(2+) concentration, activates Ca(2+) release from stores and causes cell death through mitochondrial function collapse. In addition, the present results suggest that the Ca(2+) increase induced by hyperosmotic stress promotes cell survival by recruiting CREB-mediated signaling. Thus, the fate of cardiomyocytes under hyperosmotic stress will depend on the balance between Ca(2+)-induced survival and death pathways.

Changes in mitochondrial dynamics during ceramide-induced cardiomyocyte early apoptosis

AIMS

In cells, mitochondria are organized as a network of interconnected organelles that fluctuate between fission and fusion events (mitochondrial dynamics). This process is associated with cell death. We investigated whether activation of apoptosis with ceramides affects mitochondrial dynamics and promotes mitochondrial fission in cardiomyocytes.

METHODS AND RESULTS

Neonatal rat cardiomyocytes were incubated with C(2)-ceramide or the inactive analog dihydro-C(2)-ceramide for up to 6 h. Three-dimensional images of cells loaded with mitotracker green were obtained by confocal microscopy. Dynamin-related protein-1 (Drp-1) and mitochondrial fission protein 1 (Fis1) distribution and levels were studied by immunofluorescence and western blot. Mitochondrial membrane potential (DeltaPsi(m)) and cytochrome c (cyt c) distribution were used as indexes of early activation of apoptosis. Cell viability and DNA fragmentation were determined by propidium iodide staining/flow cytometry, whereas cytotoxicity was evaluated by lactic dehydrogenase activity. To decrease the levels of the mitochondrial fusion protein mitofusin 2, we used an antisense adenovirus (AsMfn2). C(2)-ceramide, but not dihydro-C(2)-ceramide, promoted rapid fragmentation of the mitochondrial network in a concentration- and time-dependent manner. C(2)-ceramide also increased mitochondrial Drp-1 and Fis1 content, Drp-1 colocalization with Fis1, and caused early activation of apoptosis. AsMfn2 accentuated the decrease in DeltaPsi(m) and cyt c redistribution induced by C(2)-ceramide. Doxorubicin, which induces cardiomyopathy and apoptosis through ceramide generation, also stimulated mitochondrial fragmentation.

CONCLUSION

Ceramides stimulate mitochondrial fission and this event is associated with early activation of cardiomyocyte apoptosis.

Tumor necrosis factor-alpha activates nuclear factor-kappaB but does not regulate progesterone production in cultured human granulosa luteal cells

BACKGROUND

The role of tumor necrosis factor-alpha (TNF-alpha) in granulosa luteal cell function and steroidogenesis is still controversial. Our aim was to examine the steroidogenic response, together with the simultaneous expression and activation of nuclear factor-kappaB (NF-kappaB), in cultured human granulosa luteal cells (GLCs) following administration of TNF-alpha.

MATERIALS AND METHODS

This prospective controlled study was conducted in the Human Reproduction Division at the Institute of Maternal and Child Research, Faculty of Medicine, University of Chile and the San Borja Arriarán Hospital, National Health Service, Santiago, Chile. GLCs were obtained from aspirates of follicles from women undergoing in vitro fertilization (IVF). Thirty-two women undergoing IVF for tubal-factor and/or male-factor infertility participated in this study. Protein levels of NF-kappaB, the NF-kappaB inhibitor IkappaBalpha and steroidogenic acute regulatory protein (StAR) were determined by Western blot and localization of NF-kappaB was studied by indirect immunofluorescence. Progesterone production was determined by radioimmunoassay.

RESULTS

TNF-alpha did not affect the expression of StAR protein or the synthesis of progesterone. NF-kappaB was expressed in the GLCs and activated by TNF-alpha, resulting in degradation of IkappaBalpha and mobilization of the p65 NF-kappaB subunit into the nucleus.

CONCLUSIONS

These results indicate that TNF-alpha did not modulate steroidogenesis in cultured human GLCs. However, NF-kappaB was activated by TNF-alpha. Therefore the activation of NF-kappaB via the TNF-alpha pathway is likely associated with other preovulatory granulosa cell processes important for human ovarian function.

The risk of low birthweight

Descriptive analyses of birthweight for single live births in the United States during 1974, using birth certificate information, show that several factors are associated with a high incidence of low birthweight babies. Multivariate analyses were performed to determine correlates of low birthweight. When other factors are held constant, race not white, previous reproductive loss, short interpregnancy interval, out-of-wedlock birth, no prenatal care, and maternal age under 18 years or over 35 years each increase the risk of having an infant of low birthweight. High birth order and maternal education under 12 years of schooling were not consistent risk factors for low birthweight. Odds ratios are presented and the method for combining these, to estimate the risk for an individual mother having a low-birthweight infant, is illustrated.

Improvement in infant and perinatal mortality in the United States, 1965--1973: I. Priorities for intervention

Changes in United States infant and perinatal mortality in the period 1965--1973 were examined by race, age at death or length of gestation, and degree of urbanization. The decline of postneonatal mortality rates was greater than the declines of fetal and neonatal mortality rates. Other-than white infant and fetal mortality rates improved more than the white rates, except in the first day of life. Postneonatal mortality rates improved more in rural than in urban areas, while neonatal and perinatal mortality rates improved more in urban areas than in rural. These improvements in mortality rates have occurred at the same time as changes in medical techniques and the organization and availability of health services, improvements in economic conditions and standards of living, and changes in the demographic characteristics of the child-bearing population of the United States. Each of these changes was in a direction expected to have a favorable effect on infant and perinatal mortality. Nevertheless, the improvement of infant mortality rates has not changed the relative position of the United States in comparison with other countries. Programs to improve infant and perinatal mortality can use the data in this study to define high priority target groups using a method based on the size of the problem in the target group, the severity of the problem, and the amount and direction of change.

Availability and usefulness of selected health and socioeconomic data for community planning

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