Cardioprotective strategies preserve the stability of respiratory chain supercomplexes and reduce oxidative stress in reperfused ischemic hearts

Electron leakage from dysfunctional respiratory chain and consequent superoxide formation leads to mitochondrial and cell injury during ischemia and reperfusion (IR). In this work we evaluate if the supramolecular assembly of the respiratory complexes into supercomplexes (SCs) is associated with preserved energy efficiency and diminished oxidative stress in post-ischemic hearts treated with the antioxidant N-acetylcysteine (NAC) and the cardioprotective maneuver of Postconditioning (PostC). Hemodynamic variables, infarct size, oxidative stress markers, oxygen consumption and the activity/stability of SCs were compared between groups. We found that mitochondrial oxygen consumption and the activity of respiratory complexes are preserved in mitochondria from reperfused hearts treated with both NAC and PostC. Both treatments contribute to recover the activity of individual complexes. NAC reduced oxidative stress and maintained SCs assemblies containing Complex I, Complex III, Complex IV and the adapter protein SCAFI more effectively than PostC. On the other hand, the activities of CI, CIII and CIV associated to SCs assemblies were preserved by this maneuver, suggesting that the activation of other cardioprotective mechanisms besides oxidative stress contention might participate in maintaining the activity of the mitochondrial respiratory complexes in such superstructures. We conclude that both the monomeric and the SCs assembly of the respiratory chain contribute to the in vivo functionality of the mitochondria. However, although the ROS-induced damage and the consequent increased production of ROS affect the assembly of SCs, other levels of regulation as those induced by PostC, might participate in maintaining the activity of the respiratory complexes in such superstructures.

New complexes containing the internal alternative NADH dehydrogenase (Ndi1) in mitochondria of Saccharomyces cerevisiae

Mitochondria of Saccharomyces cerevisiae lack the respiratory complex I, but contain three rotenone-insensitive NADH dehydrogenases distributed on both the external (Nde1 and Nde2) and internal (Ndi1) surfaces of the inner mitochondrial membrane. These enzymes catalyse the transfer of electrons from NADH to ubiquinone without the translocation of protons across the membrane. Due to the high resolution of the Blue Native PAGE (BN-PAGE) technique combined with digitonin solubilization, several bands with NADH dehydrogenase activity were observed on the gel. The use of specific S. cerevisiae single and double mutants of the external alternative elements (ΔNDE1, ΔNDE2, ΔNDE1/ΔNDE2) showed that the high and low molecular weight complexes contained the Ndi1. Some of the Ndi1 associations took place with complexes III and IV, suggesting the formation of respirasome-like structures. Complex II interacted with other proteins to form a high molecular weight supercomplex with a molecular mass around 600 kDa. We also found that the majority of the Ndi1 was in a dimeric form, which is in agreement with the recently reported three-dimensional structure of the protein.

Escherichia coli-induced temporal and differential secretion of heat-shock protein 70 and interleukin-1β by human fetal membranes in a two-compartment culture system

INTRODUCTION

Escherichia coli is recognized as an etiological bacteria associated with chorioamnionitis and the preterm premature rupture of fetal membranes. This pathological condition induces pro-inflammatory cytokines and degradative metalloproteinases, which are considered biological markers secreted in an acute stage of infection. Heat-shock proteins (HSPs) are an important component of the innate immunity response and are found in different pathological conditions. They have not been previously measured in human fetal membranes in response to infectious conditions. We hypothesized that the choriodecidual tissue and amniotic epithelium secreted temporal and differential Hsp-60, Hsp-70, and interleukin (IL)-1β mediated by E. coli infection.

METHODS

Fetal membranes were mounted in a two-compartment culture system and infected with two passes of live E. coli at different doses (10², 10⁴, 10⁵, and 10⁶ colony-forming units (CFU)/mL) and intervals of incubation (3, 6, and 24 h). The culture medium was collected, and Hsp-60, Hsp-70, and IL-1β were assessed using the enzyme-linked immunosorbent assay (ELISA) method.

RESULTS

After 3 and 6 h of infection, E. coli induced an increase in Hsp-70 secretion in the choriodecidual tissue. However, after 24 h of incubation, Hsp-70 was downregulated and we observed an increase in IL-1β secretion. By contrast, E. coli induced a lower Hsp-60 secretion in the amnion compared to Hsp-70.

DISCUSSION

Human fetal membranes responded actively to E. coli infection, with an increase in Hsp-70 during the first hours of infection. After 24 h, there was an increase in the liberation of IL-1β.

PKA tightly bound to human placental mitochondria participates in steroidogenesis and is not modified by cAMP

INTRODUCTION

Protein phosphorylation plays an important role in the modulation of steroidogenesis and it depends on the activation of different signaling cascades. Previous data showed that PKA activity is related to steroidogenesis in mitochondria from syncytiotrophoblast of human placenta (HPM). PKA localization and contribution in progesterone synthesis and protein phosphorylation of HPM was assessed in this work.

METHODS

Placental mitochondria and submitochondrial fractions were used. Catalytic and regulatory PKA subunits were identified by Western blot. PKA activity was determined by the incorporation of (32)P into proteins in the presence or absence of specific inhibitors. The effect of PKA activators and inhibitors on steroidogenesis and protein phosphorylation in HPM was tested by radioimmunoassay and autoradiography.

RESULTS

The PKAα catalytic subunit was distributed in all the submitochondrial fractions whereas βII regulatory subunit was the main isoform observed in both the outer and inner membranes of HPM. PKA located in the inner membrane showed the highest activity. Progesterone synthesis and mitochondrial protein phosphorylation are modified by inhibitors of PKA catalytic subunit but are neither sensitive to inhibitors of the regulatory subunit nor to activators of the holoenzyme.

DISCUSSION

The lack of response in the presence of PKA activators and inhibitors of the regulatory subunit suggests that the activation of intramitochondrial PKA cannot be prevented or further activated.

CONCLUSIONS

The phosphorylating activity of PKA inside HPM could be an important component of the steroidogenesis transduction cascade, probably exerting its effects by direct phosphorylation of its substrates or by modulating other kinases and phosphatases.

Mitochondrial heat shock protein participates in placental steroidogenesis

The human placenta, which does not express the StAR protein, synthesizes large amounts of progesterone. The rate-limiting step for steroidogenesis is the transport of cholesterol which is divided into two steps: 1) cholesterol flux from cytoplasm to outer membrane mitochondria, and 2) cholesterol transport from outer to inner mitochondrial membrane. The proteins mediating placental cholesterol influx have not been clearly identified. We investigated the proteins involved in the transport of cholesterol in syncytiotrophoblast mitochondria from human placenta. Two proteins, one of 30 kDa, and another of 60 kDa, were identified using anti-MLN64 antibodies. The 30 kDa protein corresponds to a fragment of MLN64, and the 60 kDa protein was identified as a heat shock protein. During steroidogenesis, mitochondria released MLN64 protein to supernatant. When this supernatant was added to fresh isolated mitochondria, progesterone synthesis increased; a similar result was obtained with the addition of the recombinant MLN64-START protein. In the presence of flurescein-5-maleimide or N-ethyl-maleimide, the mitochondrial synthesis of progesterone was inhibited in a dose-dependent fashion without changes in mitochondrial respiration. 2D-electrophoretic pattern showed that flurescein-5-maleimide- fluorescence was associated with HSP60. Both MLN64 and HSP60 were identified in mitochondrial contact sites. The results suggest that HSP60 is involved in the steroidogenic metabolism of human placenta. A tight association between MLN64 and HSP60 is suggested for cholesterol transport in the human placenta.

5'-p-Fluorosulfonylbenzoyl adenosine inhibits progesterone synthesis in human placental mitochondria

The human placental mitochondria have an ATP-diphosphohydrolase (apyrase) activity. In this paper we characterized the effect of 5'-p-fluorosulfonylbenzoyl adenosine (FSBA) on placental apyrase, and its repercussion on progesterone synthesis and oxygen consumption. Apyrase activity was inhibited by FSBA. Nucleosides tri- and diphosphates protected against FSBA inactivation, but divalent cations did not, indicating that FSBA attaches itself to an ATP-binding site of apyrase. In mitochondria, the inactivation of apyrase by FSBA was associated with inhibition of progesterone synthesis. Also, the oxygen consumption induced by ATP but not by ADP, was inhibited, clearly showing that FSBA exclusively inactivated the apyrase in human placental mitochondria. It is concluded that the apyrase activity is closely related to progesterone synthesis, probably associated with the cholesterol transport between mitochondrial membranes.

A novel ATP-diphosphohydrolase from human term placental mitochondria

This report describes an ATP-diphosphohydrolase activity associated with the inner membrane of human term placental mitochondria. An enriched fraction containing 30 per cent of the total protein and 80 per cent of the total ATP-diphosphohydrolase activity was obtained from submitochondrial particles. ATP-diphosphohydrolase activity was characterized in this fraction. The enzyme had a pH optimum of 8 and catalysed the hydrolysis of triphospho- and diphosphonucleosides other than ATP or ADP. Pyrophosphate was also hydrolysed, but AMP or other monoester phosphates were not. The activity of ATP-diphosphohydrolase was dependent on Mg(2 + ), Ca(2 + )or Mn(2 + )and the enzyme substrate was the cation-nucleotide complex. An excess of free cation produced inhibition.ATP-diphosphohydrolase activity was stimulated at micromolar concentrations of calcium or magnesium in the presence of La-PPi. Negative cooperativity kinetics was observed with all substrates tested. The V(max)ranged from 150 to 300nmol of Pi released/mg/min. The [S](0.5)for nucleotides was 1-10m m and 182m m for PPi. The enzyme was inhibited by orthovanadate, but not by l -phenylalanine, oligomycin, sodium azide, P(1),P(5)-di(adenosine-5')pentaphosphate or sodium fluoride.The experimental evidence showing absence of inhibition by sodium azide and sodium fluoride, hydrolysis of pyrophosphate but not of monoester phosphates, and negative cooperativity suggested that this enzyme was a novel ATP-diphosphohydrolase.

Differences in cholesterol incorporation into mitochondria from hepatoma AS-30D and human term placenta

Cholesterol transport for steroidogenesis in the human placental mitochondria is an enigma as, contrary to other steroidogenic tissues, the human placenta does not express steroidogenic acute regulatory protein (StAR), a protein known to be required for efficient utilization of cholesterol by adrenal and gonadal mitochondria. These observations suggest the possibility that cholesterol transport in human placental mitochondria involves a similar system to that present in other non-steroidogenic tissues. We studied cholesterol incorporation into mitochondria isolated from AS-30D hepatoma cells and the human placenta. Mitochondria from both sources incorporated cholesterol in vitro. There were no differences in cholesterol incorporation into hepatoma mitochondria treated with or without trypsin. In contrast, the human placental mitochondria treated with trypsin did not incorporate exogenous cholesterol. The presence of ATP increased the uptake of cholesterol by human placental mitochondria. This increase was inhibited by vanadate. These results suggest that cholesterol incorporation into human placental mitochondria is mediated by protein(s).

Presence of two enzymes, different from the F1F0-ATPase, hydrolyzing nucleotides in human term placental mitochondria

The hydrolysis of ATP, ADP or GTP was characterized in mitochondria and submitochondrial particles since a tightly-bound ATPase associated with the inner mitochondrial membrane from the human placenta has been described. Submitochondrial particles, which are basically inner membranes, were used to define the location of this enzyme. Mitochondria treated with trypsin and specific inhibitors were also used. The oxygen consumption stimulated by ATP or ADP was 100% inhibited in intact mitochondria by low concentrations of oligomycin (0.5 microgram/mg) or venturicidine (0.1 microgram/mg), while the hydrolysis of ATP or ADP was insensitive to higher concentrations of these inhibitors but it was inhibited by vanadate. Oligomycin or venturicidine showed a different inhibition pattern in intact mitochondria in relation to the hydrolysis of ATP, ADP or GTP. When submitochondrial particles were isolated from mitochondria incubated with oligomycin or venturicidine, no further inhibition of the nucleotide hydrolysis was observed, contrasting with the partial inhibition observed in the control. By incubating the placental mitochondria with trypsin, a large fraction of the hydrolysis of nucleotides was eliminated. In submitochondrial particles obtained from mitochondria treated with trypsin or trypsin plus oligomycin, the hydrolysis of ATP was 100% sensitive to oligomycin at low concentrations, resembling the oxygen consumption; however, this preparation still showed some ADP hydrolysis. Native gel electrophoresis showed two bands hydrolyzing ADP, suggesting at least two enzymes involved in the hydrolysis of nucleotides, besides the F1F0-ATPase. It is concluded that human placental mitochondria possesses ADPase and ATP-diphosphohydrolase activities (247).

Characterization of the F1F0-ATPase and the tightly-bound ATPase activities in submitochondrial particles from human term placenta

In a previous study we demonstrated the existence of a tightly-bound ATPase in the human placental mitochondria (Martínez et al., 1993). The current study characterizes the ATP hydrolysis produced by the F1F0-ATPase and the tightly-bound ATPase in submitochondrial particles from the human term placenta. Both enzymes were not differentiated by pH. Inhibitors were necessary to distinguish the activity of each enzyme. The kinetic of the total ATP hydrolysis fitted into a model of two enzymes. During the characterization, it was observed that the tightly-bound ATPase activity was partially inhibited by vanadate and Mg2+, whereas the F1F0-ATPase was totally inhibited by Mg2+. Different nucleotides were hydrolyzed by the tightly-bound ATPase; the F1F0-ATPase hydrolyzed exclusively ATP. Glucose-6-phosphate, p-nitrophenylphosphate, or pyrophosphate were not hydrolyzed by the F1F0-ATPase, although some hydrolysis was observed with the tightly-bound ATPase. It is concluded that the tightly-bound ATPase activity corresponded to a 5'-nucelotidase, and that the human placental mitochondria could participate in the metabolism of nucleotides.

The effect of osmolarity on human placental mitochondria function

Human placental explants survive large changes in osmolarity, but the mechanism for this property is unknown. The goal of this work was to examine the effect of osmolarity on human placental mitochondria. Mitochondria from human term placenta were isolated by differential centrifugation, and incubated in the presence of different concentrations of sucrose or KCl, to modify the osmolarity of the media. Rat liver mitochondria were used as control. The parameters studied were: respiration rate, adenine nucleotide hydrolysis, calcium transport, membrane potential, and mitochondrial morphology. Stimulation of the mitochondrial respiration rate and an increase in Ca2+ transport was observed in the presence of K+. With sucrose, Ca2+ transport showed a complex kinetic behavior, whereas the respiratory control was slightly diminished. Although the ATPase activity was enhanced in the absence of a respiratory substrate, no change in ATP hydrolysis due to osmolarity was observed. ADP hydrolysis was inhibited by a high K+ concentration, but not by sucrose. The membrane potential was not modified by osmolarity, even in the absence of sucrose or K+ in the medium. Mitochondria isolated with KCl showed aggregation, whereas dispersed mitochondria were observed with sucrose. This study showed that sucrose-induced changes in osmolarity, does not modify metabolic and transport properties of human placental mitochondria, whereas KCl-induced osmolarity changes does affect these functions.

Calcium transport in human term placental mitochondria

The kinetic characteristics of the transport of Ca2+ in the human term placental mitochondria previously depleted of their intramitochondrial calcium, was studied. Maximal Ca2+ uptake was observed in the presence of inorganic phosphate and ADP. Ca2+ transport showed a Michaelis-Menten behavior, with a Vmax of 61 nmol mg-1 min-1 and a Km of 118 microM. Ruthenium red inhibited mitochondrial Ca2+ uptake. Under optimal conditions of Ca2+ uptake, the cation inhibited progesterone synthesis in placental mitochondria. The kinetic parameters of Ca2+ transport agree with the physiological role of mitochondria in the human placenta.

Respiratory control induced by ATP in human term placental mitochondria

Oxygen uptake in human placental mitochondria was stimulated by ATP addition. ATP-induced respiration was supported by malate, alpha-keto glutarate, and succinate, and inhibited by oligomycin and carboxytractyloside. This phenomenon was not caused by contamination with unspecific phosphatases or alkaline phosphatase, since NaF, L-phenyl alanine, or P1, P5-di-(adenosine-5') pentaphosphate failed to inhibit oxygen uptake induced by ATP. The stimulation of respiration was caused by an ATPase activity tightly bound to mitochondria, which yields ADP that is responsible for the oxygen uptake. The stimulation was not an uncoupling effect because ATP addition produced a transition between state 3 and 4 of respiration, indicating that ATP was not released from mitochondria.