Mitochondrial calcium spiking: a transduction mechanism based on calcium-induced permeability transition involved in cell calcium signalling

Heat Shock Protein 70 Is Involved in the Efficiency of Preconditioning with Cyclosporine A in Renal Ischemia Reperfusion Injury by Modulating Mitochondrial Functions

Cyclosporine A (CsA) preconditioning is known to target mitochondrial permeability transition pore and protect renal function after ischemia reperfusion (IR). The upregulation of heat-shock protein 70 (Hsp70) expression after CsA injection is thought to be associated with renal protection. The aim of this study was to test the effect of Hsp70 expression on kidney and mitochondria functions after IR. Mice underwent a right unilateral nephrectomy and 30 min of left renal artery clamping, performed after CsA injection and/or administration of the Hsp70 inhibitor. Histological score, plasma creatinine, mitochondrial calcium retention capacity, and oxidative phosphorylation were assessed after 24 h of reperfusion. In parallel, we used a model of hypoxia reoxygenation on HK2 cells to modulate Hsp70 expression using an SiRNA or a plasmid. We assessed cell death after 18 h of hypoxia and 4 h of reoxygenation. CsA significantly improved renal function, histological score, and mitochondrial functions compared to the ischemic group but the inhibition of Hsp70 repealed the protection afforded by CsA injection. In vitro, Hsp70 inhibition by SiRNA increased cell death. Conversely, Hsp70 overexpression protected cells from the hypoxic condition, as well as the CsA injection. We did not find a synergic association between Hsp70 expression and CsA use. We demonstrated Hsp70 could modulate mitochondrial functions to protect kidneys from IR. This pathway may be targeted by drugs to provide new therapeutics to improve renal function after IR.

The mitochondrial permeability transition pore in Ca2+ homeostasis

The mitochondrial Permeability Transition Pore (PTP) can be defined as a Ca²⁺ activated mega-channel involved in mitochondrial damage and cell death, making its inhibition a hallmark for therapeutic purposes in many PTP-related paradigms. Although long-lasting PTP openings have been widely studied, the physiological implications of transient openings (also called "flickering" behavior) are still poorly understood. The flickering activity was suggested to play a role in the regulation of Ca²⁺ and ROS homeostasis, and yet this hypothesis did not reach general consensus. This state of affairs might arise from the lack of unquestionable experimental evidence, due to limitations of the available techniques for capturing transient PTP activity and to a still partial understanding of its molecular identity. In this review we will focus on possible implications of the PTP in physiology, in particular its role as a Ca²⁺ release pathway, discussing the consequences of its forced inhibition. We will also consider the recent hypothesis of the existence of more permeability pathways and their potential involvement in mitochondrial physiology.

Non-conventional mitochondrial permeability transition: Its regulation by mitochondrial dynamics

Mitochondrial permeability transition (MPT) is a phenomenon that the inner mitochondrial membrane (IMM) loses its selective permeability, leading to mitochondrial dysfunction and cell injury. Electrophysiological evidence indicates the presence of a mega-channel commonly called permeability transition pore (PTP) whose opening is responsible for MPT. However, the molecular identity of the PTP is still under intensive investigations and debates, although cyclophilin D that is inhibited by cyclosporine A (CsA) is the established regulatory component of the PTP. PTP can also open transiently and functions as a rapid mitochondrial Ca2+ releasing mechanism. Mitochondrial fission and fusion, the main components of mitochondrial dynamics, control the number and size of mitochondria, and have been shown to play a role in regulating MPT directly or indirectly. Studies by us and others have indicated the potential existence of a form of transient MPT that is insensitive to CsA. This "non-conventional" MPT is regulated by mitochondrial dynamics and may serve a protective role possibly by decreasing the susceptibility for a frequent or sustained PTP opening; hence, it may have a therapeutic value in many disease conditions involving MPT.

Mild Therapeutic Hypothermia Protects from Acute and Chronic Renal Ischemia-Reperfusion Injury in Mice by Mitigated Mitochondrial Dysfunction and Modulation of Local and Systemic Inflammation

Renal ischemia-reperfusion (IR) injury can lead to acute kidney injury, increasing the risk of developing chronic kidney disease. We hypothesized that mild therapeutic hypothermia (mTH), 34 °C, applied during ischemia could protect the function and structure of kidneys against IR injuries in mice. In vivo bilateral renal IR led to an increase in plasma urea and acute tubular necrosis at 24 h prevented by mTH. One month after unilateral IR, kidney atrophy and fibrosis were reduced by mTH. Evaluation of mitochondrial function showed that mTH protected against IR-mediated mitochondrial dysfunction at 24 h, by preserving CRC and OX-PHOS. mTH completely abrogated the IR increase of plasmatic IL-6 and IL-10 at 24 h. Acute tissue inflammation was decreased by mTH (IL-6 and IL1-β) in as little as 2 h. Concomitantly, mTH increased TNF-α expression at 24 h. One month after IR, mTH increased TNF-α mRNA expression, and it decreased TGF-β mRNA expression. We showed that mTH alleviates renal dysfunction and damage through a preservation of mitochondrial function and a modulated systemic and local inflammatory response at the acute phase (2–24 h). The protective effect of mTH is maintained in the long term (1 month), as it diminished renal atrophy and fibrosis, and mitigated chronic renal inflammation.

Theoretical approaches used in the modelling of reversible and irreversible mitochondrial swelling in vitro

Existing theoretical approaches were considered that allow modelling of mitochondrial swelling (MS) dynamics. Simple phenomenological kinetic models were reviewed. Simple and extended biophysical and bioenergetic models that ignore mechanical properties of inner mitochondrial membrane (IMM), and similar models that include these mechanical properties were also reviewed. Limitations of these models we considered, as regards correct modelling of MS dynamics. It was found that simple phenomenological kinetic models have significant limitations, due to dependence of the kinetic parameter values estimated by fitting of the experimental data on the experimental conditions. Additionally, such simple models provide no understanding of the detailed mechanisms behind the MS dynamics, nor of the dynamics of various system parameters during MS. Thus, biophysical and bioenergetic models ignoring IMM mechanical properties can't be used to model the transition between reversible and irreversible MS. However, simple and extended biophysical models that include IMM mechanical properties allow modelling the transition to irreversible swelling. These latter models are still limited due to significantly simplified description of biochemistry, compared to those of bioenergetic models. Finally, a strategy of model development is proposed, towards correct interpretation of the mitochondrial life cycle, including the effects of MS dynamics.

Reversible and irreversible mitochondrial swelling in vitro

Mitochondrial activity as regards ATP production strongly depends on mitochondrial swelling (MS) mode. Therefore, this work analyzes reversible and irreversible MS using a detailed biophysical model. The reported model includes mechanical properties of the inner mitochondrial membrane (IMM). The model describes MS dynamics for spherically symmetric, axisymmetric ellipsoidal and general ellipsoidal mitochondria. Mechanical stretching properties of the IMM were described by a second-rank rigidity tensor. The tensor components were estimated by fitting to the earlier reported results of in vitro experiments. The IMM rigidity constant of ca. 0.008 dyn/nm was obtained for linear deformations. The model also included membrane bending effects, which were small compared to those of membrane stretching. The model was also tested by simulation of the earlier reported experimental data and of the system dynamics at different initial conditions, predicting the system behavior. The transition criteria from reversible to irreversible swelling were determined and tested. The presently developed model is applicable directly to the analysis of in vitro experimental data, while additional improvements are necessary before it could be used to describe mitochondrial swelling in vivo. The reported theoretical model also provides an idea of physically consistent mechanism for the permeability transport pore (PTP) opening, which depends on the IMM stretching stress. In the current study, this idea is discussed briefly, but a detailed theoretical analysis of these ideas will be performed later. The currently developed model provides new understanding of the detailed MS mechanism and of the conditions for the transition between reversible and irreversible MS modes. On the other hand, the current model provides useful mathematical tools, that may be successfully used in mitochondrial biophysics research, and also in other applications, predicting the behavior of mitochondria in different conditions of the surrounding media in vitro or cellular cyto(sarco)plasm in vivo. These mathematical tools are based on real biophysical processes occurring in mitochondria. Thus, we note a significant progress in the theoretical approach, which may be used in real biological systems, compared to the earlier reported models. Significance of this study derives from inclusion of IMM mechanical properties, which directly impact the reversible and irreversible mitochondrial swelling dynamics. Reversible swelling corresponds to reversible IMM deformations, while irreversible swelling corresponds to irreversible deformations, with eventual membrane disruption. The IMM mechanical properties are directly dependent on the membrane biochemical composition and structure. The IMM deformationas are induced by osmotic pressure created by the ionic/neutral solute imbalance between the mitochondrial matrix media and the bulk solution in vitro, or cyto(sarco)plasm in vivo. The novelty of the reported model is in the biophysical mechanism detailing ionic and neutral solute transport for a large number of solutes, which were not taken into account in the earlier reported biophysical models of MS. Therefore, the reported model allows understanding response of mitochondria to the changes of initial concentration(s) of any of the solute(s) included in the model. Note that the values of all of the model parameters and kinetic constants have been estimated and the resulting complete model may be used for quantitative analysis of mitochondrial swelling dynamics in conditions of real in vitro experiments.

Mitochondrial Cyclosporine A-Independent Palmitate/Ca2+-Induced Permeability Transition Pore (PA-mPT Pore) and Its Role in Mitochondrial Function and Protection against Calcium Overload and Glutamate Toxicity

A sharp increase in the permeability of the mitochondrial inner membrane known as mitochondrial permeability transition (or mPT) occurs in mitochondria under the conditions of Ca²⁺ and ROS stress. Permeability transition can proceed through several mechanisms. The most common mechanism of mPT is based on the opening of a cyclosporine A (CSA)-sensitive protein channel in the inner membrane. In addition to the CSA-sensitive pathway, mPT can occur through the transient opening of lipid pores, emerging in the process of formation of palmitate/Ca²⁺ complexes. This pathway is independent of CSA and likely plays a protective role against Ca²⁺ and ROS toxicity. The review considers molecular mechanisms of formation and regulation of the palmitate/Ca²⁺-induced pores, which we designate as PA-mPT to distinguish it from the classical CSA-sensitive mPT. In the paper, we discuss conditions of its opening in the biological membranes, as well as its role in the physiological and pathophysiological processes. Additionally, we summarize data that indicate the involvement of PA-mPT in the protection of mitochondria against calcium overload and glutamate-induced degradation in neurons.

Cardiac ischemia/reperfusion stress reduces inner mitochondrial membrane protein (mitofilin) levels during early reperfusion

Mitochondrial inner membrane protein (Mitofilin or Mic60) is a mitochondria-shaping protein that plays a key role in maintaining mitochondrial cristae structure and remodeling. We recently showed that Mitofilin knockdown in H9c2 myoblasts induces mitochondrial structural damage resulting in mitochondrial dysfunction that is responsible for cell death via apoptosis. Here, we investigated the role of Mitofilin regulation in ischemia/reperfusion (I/R) injury and studied the relationship between Mitofilin and Cyclophilin (CypD), a key regulator of mitochondrial permeability transition pore (mPTP) opening. C57Bl6 male mice hearts were subjected to different ischemia times (15, 30, or 45 min) followed by a 2 h reperfusion period, or 45 min ischemia followed by 0, 15, 30, 60, or 120 min reperfusion to determine the impact of ischemia or reperfusion times on Mitofilin levels and its interaction with CypD. We found that the increase in myocardial infarct size and the reduction of mitochondrial calcium retention capacity were concomitant with Mitofilin reduction as a function of ischemic duration. We also found that 15 min reperfusion after 45 min ischemia was sufficient to cause a reduction of Mitofilin levels compared to sham, while 45 min ischemia alone was not enough to cause a significant decrease of Mitofilin. We revealed that the c-terminus coiled-coiled domain of Mitofilin is important for its interaction with CypD and the deletion of this identified sequence resulted in a loss of Mitofilin-CypD link, dissipation of mitochondrial membrane potential and increase in cell death. A decrease of the levels of Mitofilin was also associated with mitochondrial structural integrity damage, increased reactive oxygen species (ROS) production, and calpain activity. Our results indicate that Mitofilin physically binds to CypD in the inner mitochondrial membrane and the disruption of this interaction may play a critical role in the increase of mitochondrial dysfunction and initiation of myocytes' death after I/R injury.

Mitochondrial DNA-Induced Inflammatory Responses and Lung Injury in Thermal Injury Murine Model: Protective Effect of Cyclosporine-A

Burn trauma is generally associated with profound inflammation and organ injuries, especially the lung. Damage-associated molecular patterns (DAMPs), such as mitochondrial DNA (mtDNA), released after tissue injuries, play a crucial role in the development of the inflammation. The aim of our study was to investigate the protective profiles of cyclosporine-A (CsA) in murine models with thermal injury. We studied 24 C57BL/6 mice which were randomly subjected to four groups: a sham-operation group (SO group, n = 6), an experiment group (a full-thickness thermal injury covered 30% of the TBSA, n = 6), a low-CsA group (injection of 2.5 mg/kg of CsA 15 min before the thermal injury, n = 6) and a high-CsA group (injection of 25 mg/kg of CsA 15 min before the thermal injury, n = 6). Systemic inflammatory mediators and plasma mtDNA were measured while lung injury was evaluated pathologically and cytosolic cytochrome c and mtDNA were detected. Noticeable increases in concentration of mtDNA and inflammatory mediators were obtained in the experiment group and two CsA groups comparing with the SO group (P < .05). There were significant decreases in the concentrations of mtDNA and inflammatory mediators with increasing doses of CsA (P < .05). Similarly, severity of lung injury was mitigated with increasing doses of CsA. Meanwhile, CsA also attenuated oxidative stress and release of cytochrome c and mtDNA in the lung tissue on a dose-dependent manner (P < .05). Our results suggested mtDNA contributes to the development of thermal injury-induced inflammation and lung injury. CsA might exert dual protective effects, reducing the release of mtDNA and limiting the mtDNA-induced mitochondrial dysfunction in the lung, on the thermal injury-induced acute lung injury.

EP4 activation ameliorates liver ischemia/reperfusion injury via ERK1/2‑GSK3β‑dependent MPTP inhibition

Prostaglandin E receptor subtype 4 (EP4) is widely distributed in the heart, but its role in hepatic ischemia/reperfusion (I/R), particularly in mitochondrial permeability transition pore (MPTP) modulation, is yet to be elucidated. In the present study, an EP4 agonist (CAY10598) was used in a rat model to evaluate the effects of EP4 activation on liver I/R and the mechanisms underlying this. I/R insult upregulated hepatic EP4 expression during early reperfusion. In addition, subcutaneous CAY10598 injection prior to the onset of reperfusion significantly increased hepatocyte cAMP concentrations and decreased serum ALT and AST levels and necrotic and apoptotic cell percentages, after 6 h of reperfusion. Moreover, CAY10598 protected mitochondrial morphology, markedly inhibited mitochondrial permeability transition pore (MPTP) opening and decreased liver reactive oxygen species levels. This occurred via activation of the ERK1/2-GSK3β pathway rather than the janus kinase (JAK)2-signal transducers and activators of transcription (STAT)3 pathway, and resulted in prevention of mitochondria-associated cell injury. The MPTP opener carboxyatractyloside (CATR) and the ERK1/2 inhibitor PD98059 also partially reversed the protective effects of CAY10598 on the liver and mitochondria. The current findings indicate that EP4 activation induces ERK1/2-GSK3β signaling and subsequent MPTP inhibition to provide hepatoprotection, and these observations are informative for developing new molecular targets and preventative therapies for I/R in a clinical setting.

Mitochondrial Ca2+ Transport: Mechanisms, Molecular Structures, and Role in Cells

Mitochondria are among the most important cell organelles involved in the regulation of intracellular calcium homeostasis. During the last decade, a number of molecular structures responsible for the mitochondrial calcium transport have been identified including the mitochondrial Ca2+ uniporter (MCU), Na+/Ca2+ exchanger (NCLX), and Ca2+/H+ antiporter (Letm1). The review summarizes the data on the structure, regulation, and physiological role of such structures. The pathophysiological mechanism of Ca2+ transport through the cyclosporine A-sensitive mitochondrial permeability transition pore is discussed. An alternative mechanism for the mitochondrial pore opening, namely, formation of the lipid pore induced by saturated fatty acids, and its role in Ca2+ transport are described in detail.

Attenuation of Lipopolysaccharide-Induced Acute Lung Injury by Cyclosporine-A via Suppression of Mitochondrial DNA

Background

Lipopolysaccharide (LPS) is generally associated with sepsis, which causes multiple system injuries and systemic inflammatory response. Mitochondrial DNA (mtDNA) is of great importance in mediation of inflammation. The aim of this study was to investigate the protective profiles of Cyclosporine-A (CsA) in LPS-induced acute lung injury (ALI) and systemic inflammation by the inhibition of mtDNA and Toll-like receptor.

Material/Methods

Twenty-four C57BL/6 mice were randomly assigned to 4 groups: a sham group (n=6); an experiment group (ALI induced through intraperitoneal injection of 10 mg/ml LPS, n=6); a low-CsA group (injection of 2.5 mg/kg of CsA 15 min after injection of LPS, n=6); and a high-CsA group (injection of 25 mg/kg of CsA 15 min after injection of LPS, n=6). Lung tissue, bronchoalveolar lavage fluid (BALF), and blood samples were collected at 6 h for further analyses.

Results

CsA treatment significantly attenuated LPS-induced lung histopathological changes (P<.05), myeloperoxidase (MPO) activity (P<.05) and lung wet-to-dry weight ratio (P<.05). In addition, injection of CsA decreased total cells (P<.05), neutrophils (P<.05), and total protein (P<.05) in BALF and inflammatory mediators, including tumor necrosis factor-α (TNF-α, P<.05) and interleukin-6 (IL-6, P<.05) in a dose-dependent manner. A significant decrease in mtDNA was observed in the CsA group when compared with controls (P<.05). Furthermore, we demonstrated that there was a significant difference between the high-CsA group and low-CsA group in lung injury score (P<.05), mtDNA (P<.05), and MPO (P<.05).

Conclusions

The evidence from this study suggests that CsA attenuated lung inflammation after LPS injection, and the protective mechanism may at least in part involve decreasing the release of inflammatory cytokines and mtDNA.

Activation of G protein-coupled oestrogen receptor 1 at the onset of reperfusion protects the myocardium against ischemia/reperfusion injury by reducing mitochondrial dysfunction and mitophagy

Background and Purpose

Recent evidence indicates that GPER (G protein‐coupled oestrogen receptor 1) mediates acute pre‐ischaemic oestrogen‐induced protection of the myocardium from ischaemia/reperfusion injury via a signalling cascade that includes PKC translocation, ERK1/2/ GSK‐3β phosphorylation and inhibition of the mitochondrial permeability transition pore (mPTP) opening. Here, we investigated the impact and mechanism involved in post‐ischaemic GPER activation in ischaemia/reperfusion injury. We determined whether GPER activation at the onset of reperfusion confers cardioprotective effects by protecting against mitochondrial impairment and mitophagy.

Experimental Approach

In vivo rat hearts were subjected to ischaemia followed by reperfusion with oestrogen (17β‐oestradiol, E2), E2 + G15, a GPER antagonist, or vehicle. Myocardial infarct size, the threshold for the opening of mPTP, mitophagy, mitochondrial membrane potential, ROS production, proteins ubiquitinated including cyclophilin D, and phosphorylation levels of ERK and GSK‐3β were measured.

Results

We found that post‐ischaemic E2 administration to both male and female ovariectomized‐rats reduced myocardial infarct size. Post‐ischaemic E2 administration preserved mitochondrial structural integrity and this was associated with a decrease in ROS production and increased mitochondrial membrane potential, as well as an increase in the mitochondrial Ca²⁺ load required to induce mPTP opening via activation of the MEK/ERK/GSK‐3β axis. Moreover, E2 reduced mitophagy via the PINK1/Parkin pathway involving LC3I, LC3II and p62 proteins. All these post‐ischaemic effects of E2 were abolished by G15 suggesting a GPER‐dependent mechanism.

Conclusion

These results indicate that post‐ischaemic GPER activation induces cardioprotective effects against ischaemia/reperfusion injury in males and females by protecting mitochondrial structural integrity and function and reducing mitophagy.

Different approaches to modeling analysis of mitochondrial swelling

Mitochondria are critical players involved in both cell life and death through multiple pathways. Structural integrity, metabolism and function of mitochondria are regulated by matrix volume due to physiological changes of ion homeostasis in cellular cytoplasm and mitochondria. Ca²⁺ and K⁺ presumably play a critical role in physiological and pathological swelling of mitochondria when increased uptake (influx)/decreased release (efflux) of these ions enhances osmotic pressure accompanied by high water accumulation in the matrix. Changes in the matrix volume in the physiological range have a stimulatory effect on electron transfer chain and oxidative phosphorylation to satisfy metabolic requirements of the cell. However, excessive matrix swelling associated with the sustained opening of mitochondrial permeability transition pores (PTP) and other PTP-independent mechanisms compromises mitochondrial function and integrity leading to cell death. The mechanisms of transition from reversible (physiological) to irreversible (pathological) swelling of mitochondria remain unknown. Mitochondrial swelling is involved in the pathogenesis of many human diseases such as neurodegenerative and cardiovascular diseases. Therefore, modeling analysis of the swelling process is important for understanding the mechanisms of cell dysfunction. This review attempts to describe the role of mitochondrial swelling in cell life and death and the main mechanisms involved in the maintenance of ion homeostasis and swelling. The review also summarizes and discusses different kinetic models and approaches that can be useful for the development of new models for better simulation and prediction of in vivo mitochondrial swelling.

Dose and timing of injections for effective cyclosporine A pretreatment before renal ischemia reperfusion in mice

Background

There is experimental evidence that lethal ischemia-reperfusion injury (IRI) is largely due to mitochondrial permeability transition pore (mPTP) opening, which can be prevented by cyclosporine A (CsA). The aim of our study is to show that a higher dose of CsA (10 mg/kg) injected just before ischemia or a lower dose of CsA (3 mg/kg) injected further in advance of ischemia (1 h) protects the kidneys and improves mitochondrial function.

Methods

All mice underwent a right unilateral nephrectomy followed by 30 min clamping of the left renal artery. Mice in the control group did not receive any pharmacological treatment. Mice in the three groups treated by CsA were injected at different times and with different doses, namely 3 mg/kg 1 h or 10 min before ischemia or 10 mg/kg 10 min before ischemia. After 24 h of reperfusion, the plasma creatinine level were measured, the histological score was assessed and mitochondria were isolated to calculate the calcium retention capacity (CRC) and level of oxidative phosphorylation.

Results

Mortality and renal function was significantly higher in the CsA 10 mg/kg-10 min and CsA 3mg/kg-1 h groups than in the CsA 3mg/kg-10 min group. Likewise, the CRC was significantly higher in the former two groups than in the latter, suggesting that the improved renal function was due to a longer delay in the opening of the mPTP. Oxidative phosphorylation levels were also higher 24 h after reperfusion in the protected groups.

Conclusions

Our results suggest that the protection afforded by CsA is likely limited by its availability. The dose and timing of the injections are therefore crucial to ensure that the treatment is effective, but these findings may prove challenging to apply in practice.

Lebetin 2, a Snake Venom-Derived Natriuretic Peptide, Attenuates Acute Myocardial Ischemic Injury through the Modulation of Mitochondrial Permeability Transition Pore at the Time of Reperfusion

Cardiac ischemia is one of the leading causes of death worldwide. It is now well established that natriuretic peptides can attenuate the development of irreversible ischemic injury during myocardial infarction. Lebetin 2 (L2) is a new discovered peptide isolated from Macrovipera lebetina venom with structural similarity to B-type natriuretic peptide (BNP). Our objectives were to define the acute cardioprotective actions of L2 in isolated Langendorff-perfused rat hearts after regional or global ischemia-reperfusion (IR). We studied infarct size, left ventricular contractile recovery, survival protein kinases and mitochondrial permeability transition pore (mPTP) opening in injured myocardium. L2 dosage was determined by preliminary experiments at its ability to induce cyclic guanosine monophosphate (cGMP) release without changing hemodynamic effects in normoxic hearts. L2 was found to be as effective as BNP in reducing infarct size after the induction of either regional or global IR. Both peptides equally improved contractile recovery after regional IR, but only L2 increased coronary flow and reduced severe contractile dysfunction after global ischemia. Cardioprotection afforded by L2 was abolished after isatin or 5-hydroxydecanote pretreatment suggesting the involvement of natriuretic peptide receptors and mitochondrial K_ATP (mitoK_ATP) channels in the L2-induced effects. L2 also increased survival protein expression in the reperfused myocardium as evidenced by phosphorylation of signaling pathways PKCε/ERK/GSK3β and PI3K/Akt/eNOS. IR induced mitochondrial pore opening, but this effect was markedly prevented by L2 treatment. These data show that L2 has strong cardioprotective effect in acute ischemia through stimulation of natriuretic peptide receptors. These beneficial effects are mediated, at least in part, by mitoK_ATP channel opening and downstream activated survival kinases, thus delaying mPTP opening and improving IR-induced mitochondrial dysfunction.

Postconditioning with cyclosporine a reduces early renal dysfunction by inhibiting mitochondrial permeability transition

BACKGROUND

Ischemia-reperfusion (IR) injury leads to mitochondrial permeability transition pore opening, which contributes to cell death. The aim of this study is to determine whether ischemic or pharmacological postconditioning with cyclosporine A (CsA) might protect the kidney from lethal reperfusion injury.

METHODS

Male mice underwent a unilateral (right) nephrectomy followed by 30 minutes of contralateral (left) clamping of the renal artery. We studied 4 groups at 20 minutes and 24 hours of reperfusion: a sham group (n = 4), an ischemic group (n = 6), CsA-postconditioned group (postcond-CsA, injection of 3 mg/kg of CsA 5 minutes before the end of ischemia, (n = 6), and an ischemic postconditioning (IPC) group (n = 6), consisting of 3 cycles of 30 seconds of renal ischemia with 30 seconds intervening reperfusion. After 24 hours of reperfusion, we measured plasma creatinine, urea, and histological kidney injury. The kidney mitochondria were isolated to assess the mitochondria calcium retention capacity and oxidative phosphorylation.

RESULTS

At 24 hours after reperfusion, serum creatinine decreased in postcond-CsA and IPC compared to ischemic group. The histological score was also significantly improved with postcond-CsA and IPC. At 20 minutes and 24 hours of reperfusion, calcium retention capacity was decreased significantly in the ischemic group. The mitochondrial respiration stay decreased in the ischemic group at 24 hours of reperfusion, whereas the respiration was improved significantly in the postcond-CsA and IPC group. Bax and cleaved caspase 3 decreased in PostCsA and IPC group.

CONCLUSIONS

Our results suggest that IPC and CsA, administered immediately before reperfusion, protect the kidney from lethal injury.

Accelerated recovery of mitochondrial membrane potential by GSK-3β inactivation affords cardiomyocytes protection from oxidant-induced necrosis

Loss of mitochondrial membrane potential (ΔΨ_m) is known to be closely linked to cell death by various insults. However, whether acceleration of the ΔΨ_m recovery process prevents cell necrosis remains unclear. Here we examined the hypothesis that facilitated recovery of ΔΨ_m contributes to cytoprotection afforded by activation of the mitochondrial ATP-sensitive K⁺ (mK_ATP) channel or inactivation of glycogen synthase kinase-3β (GSK-3β). ΔΨ_m of H9c2 cells was determined by tetramethylrhodamine ethyl ester (TMRE) before or after 1-h exposure to antimycin A (AA), an inducer of reactive oxygen species (ROS) production at complex III. Opening of the mitochondrial permeability transition pore (mPTP) was determined by mitochondrial loading of calcein. AA reduced ΔΨ_m to 15±1% of the baseline and induced calcein leak from mitochondria. ΔΨ_m was recovered to 51±3% of the baseline and calcein-loadable mitochondria was 6±1% of the control at 1 h after washout of AA. mK_ATP channel openers improved the ΔΨ_m recovery and mitochondrial calcein to 73±2% and 30±7%, respectively, without change in ΔΨ_m during AA treatment. Activation of the mK_ATP channel induced inhibitory phosphorylation of GSK-3β and suppressed ROS production, LDH release and apoptosis after AA washout. Knockdown of GSK-3β and pharmacological inhibition of GSK-3β mimicked the effects of mK_ATP channel activation. ROS scavengers administered at the time of AA removal also improved recovery of ΔΨ_m. These results indicate that inactivation of GSK-3β directly or indirectly by mK_ATP channel activation facilitates recovery of ΔΨ_m by suppressing ROS production and mPTP opening, leading to cytoprotection from oxidant stress-induced cell death.

Inhibition of glycogen synthase kinase 3 ameliorates liver ischemia/reperfusion injury via an energy-dependent mitochondrial mechanism

BACKGROUND & AIMS

The mechanisms of glycogen synthase kinase-3 (GSK-3)-mediated cytoprotection during liver ischemia/reperfusion (I/R) remain controversial, particularly in older organs. This study explores the role and potential mechanisms of GSK-3 in young and aging livers.

METHODS

A rodent partial warm I/R model was used to evaluate the therapeutic potential of GSK-3 modulation during hepatic I/R in young and aging Sprague-Dawley rats.

RESULTS

GSK-3 inhibition through IPC or SB216763 (SB21) preconditioning protected young rats from I/R-induced liver injury. This protection was absent in old animals but could be restored by glucose infusion prior to the I/R insult. The protection conferred by GSK-3 inhibition depended on mitochondrial metabolism regulation. Indeed, the inhibition of GSK-3 suppressed mitochondrial permeability transition pore (MPTP) opening, triggering mitohormesis in young animals, whereas insufficient fuel suppressed mitochondrial metabolism and inactivated the GSK-3-related protection in old animals. SB21 and glucose reactivated the mitochondrial F0F1-ATPase and subsequent protective cascades in the senescent liver. These effects were antagonized by an ATPase inhibitor and by an MPTP opener.

CONCLUSIONS

The protection conferred by GSK-3 inhibition during hepatic I/R insult is energy dependent, particularly in senescent livers. These findings demonstrate a key role for GSK-3-related mitochondrial energy homeostasis, which may shed new light on the clinical use of GSK-3 inhibitors to protect liver function in surgical settings, particularly for older patients.

Calcium signaling in the liver

Intracellular free Ca(2+) ([Ca(2+)]i) is a highly versatile second messenger that regulates a wide range of functions in every type of cell and tissue. To achieve this versatility, the Ca(2+) signaling system operates in a variety of ways to regulate cellular processes that function over a wide dynamic range. This is particularly well exemplified for Ca(2+) signals in the liver, which modulate diverse and specialized functions such as bile secretion, glucose metabolism, cell proliferation, and apoptosis. These Ca(2+) signals are organized to control distinct cellular processes through tight spatial and temporal coordination of [Ca(2+)]i signals, both within and between cells. This article will review the machinery responsible for the formation of Ca(2+) signals in the liver, the types of subcellular, cellular, and intercellular signals that occur, the physiological role of Ca(2+) signaling in the liver, and the role of Ca(2+) signaling in liver disease.

Oxidative stress defines the neuroprotective or neurotoxic properties of androgens in immortalized female rat dopaminergic neuronal cells

Males have a higher risk for developing Parkinson's disease and parkinsonism after ischemic stroke than females. Although estrogens have been shown to play a neuroprotective role in Parkinson's disease, there is little information on androgens' actions on dopamine neurons. In this study, we examined the effects of androgens under conditions of oxidative stress to determine whether androgens play a neuroprotective or neurotoxic role in dopamine neuronal function. Mitochondrial function, cell viability, intracellular calcium levels, and mitochondrial calcium influx were examined in response to androgens under both nonoxidative and oxidative stress conditions. Briefly, N27 dopaminergic cells were exposed to the oxidative stressor, hydrogen peroxide, and physiologically relevant levels of testosterone or dihydrotestosterone, applied either before or after oxidative stress exposure. Androgens, alone, increased mitochondrial function via a calcium-dependent mechanism. Androgen pretreatment protected cells from oxidative stress-induced cell death. However, treatment with androgens after the oxidative insult increased cell death, and these effects were, in part, mediated by calcium influx into the mitochondria. Interestingly, the negative effects of androgens were not blocked by either androgen or estrogen receptor antagonists. Instead, a putative membrane-associated androgen receptor was implicated. Overall, our results indicate that androgens are neuroprotective when oxidative stress levels are minimal, but when oxidative stress levels are elevated, androgens exacerbate oxidative stress damage.

Hydrogen sulfide preconditioning protects rat liver against ischemia/reperfusion injury by activating Akt-GSK-3β signaling and inhibiting mitochondrial permeability transition

Hydrogen sulfide (H2S) is the third most common endogenously produced gaseous signaling molecule, but its impact on hepatic ischemia/reperfusion (I/R) injury, especially on mitochondrial function, remains unclear. In this study, rats were randomized into Sham, I/R, ischemia preconditioning (IPC) or sodium hydrosulfide (NaHS, an H2S donor) preconditioning groups. To establish a model of segmental (70%) warm hepatic ischemia, the hepatic artery, left portal vein and median liver lobes were occluded for 60 min and then unclamped to allow reperfusion. Preconditioning with 12.5, 25 or 50 μmol/kg NaHS prior to the I/R insult significantly increased serum H2S levels, and, similar to IPC, NaHS preconditioning decreased alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels in the plasma and prevented hepatocytes from undergoing I/R-induced necrosis. Moreover, a sub-toxic dose of NaHS (25 μmol/kg) did not disrupt the systemic hemodynamics but dramatically inhibited mitochondrial permeability transition pore (MPTP) opening and thus prevented mitochondrial-related cell death and apoptosis. Mechanistic studies revealed that NaHS preconditioning markedly increased the expression of phosphorylated protein kinase B (p-Akt), phosphorylated glycogen synthase kinase-3 beta (p-GSK-3β) and B-cell lymphoma-2 (Bcl-2) and decreased the release of mitochondrial cytochrome c and cleaved caspase-3/9 levels. Therefore, NaHS administration prior to hepatic I/R ameliorates mitochondrial and hepatocellular damage through the inhibition of MPTP opening and the activation of Akt-GSK-3β signaling. Furthermore, this study provides experimental evidence for the clinical use of H2S to reduce liver damage after perioperative I/R injury.

Changes in the mitochondrial permeability transition pore in aging and age-associated diseases

Aging is a biological process associated with impairment of mitochondrial bioenergetic function, increased oxidative stress, attenuated ability to respond to stresses and increased risk in contracting age-associated diseases. When mitochondria are subjected to oxidative stress, accompanied by calcium overload and ATP depletion, they undergo "a permeability transition", characterized by sudden induced change of the inner mitochondrial membrane permeability for water as well as for low-molecular weight solutes (≤1.5kDa), resulting in membrane depolarization and uncoupling of oxidative phosphorylation. Research interest in the entity responsible for this phenomenon, the "mitochondrial permeability transition pore" (MPTP) has dramatically increased after demonstration that it plays a key role in the life and death decision in cells. The molecular structure and identity of MPTP is not yet known, although the pore is thought to exist as multiprotein complex. Some evidence indicate that the sensitivity of mitochondria to Ca(2+)-induced MPTP opening increases with aging; however the basis of this difference is unknown. Changes in MPTP structure and/or function may have important implications in the aging process and aged-associated diseases. This article examines data relevant to this issue. The important role of a principal lipidic counter-partner of the MPTP, cardiolipin, will also be discussed.

Flurbiprofen, a cyclooxygenase inhibitor, protects mice from hepatic ischemia/reperfusion injury by inhibiting GSK-3β signaling and mitochondrial permeability transition

Flurbiprofen acts as a nonselective inhibitor for cyclooxygenases (COX-1 and COX-2), but its impact on hepatic ischemia/reperfusion (I/R) injury remains unclear. Mice were randomized into sham, I/R and flurbiprofen (Flurb) groups. The hepatic artery and portal vein to the left and median liver lobes were occluded for 90 min and unclamped for reperfusion to establish a model of segmental (70%) warm hepatic ischemia. Pretreatment of animals with flurbiprofen prior to I/R insult significantly decreased serum alanine aminotransferase (ALT), aspartate aminotransferase (AST) and lactate dehydrogenase (LDH), and prevented hepatocytes from I/R-induced apoptosis/necrosis. Moreover, flurbiprofen dramatically inhibited mitochondrial permeability transition (MPT) pore opening, and thus prevented mitochondrial-related cell death and apoptosis. Mechanistic studies revealed that flurbiprofen markedly inhibited glycogen synthase kinase (GSK)-3β activity and increased phosphorylation of GSK-3β at Ser9, which, consequently, could modulate the adenine nucleotide translocase (ANT)-cyclophilin D (CyP-D) complex and the susceptibility to MPT induction. Therefore, administration of flurbiprofen prior to hepatic I/R ameliorates mitochondrial and hepatocellular damage through inhibition of MPT and inactivation of GSK-3β, and provides experimental evidence for clinical use of flurbiprofen to protect liver function in surgical settings in addition to its conventional use for pain relief.

Calcium transport across the inner mitochondrial membrane: molecular mechanisms and pharmacology

Growing evidence supports that mitochondrial calcium uptake is important for cell metabolism, signaling and survival. However, both the molecular nature of the mitochondrial Ca(2+) transport sites and the calcium signals they respond to remained elusive. Recent RNA interference studies have identified new candidate proteins for Ca(2+) transport across the inner mitochondrial membrane, including LETM1, MCU, MICU1 and NCLX. The sensitivity of these factors to several drugs has been tested and in parallel, some new inhibitors of mitochondrial Ca(2+) uptake have been described. This paper provides an update on the pharmacological aspects of the molecular mechanisms of the inner mitochondrial membrane Ca(2+) transport.

A novel role for mitochondrial sphingosine-1-phosphate produced by sphingosine kinase-2 in PTP-mediated cell survival during cardioprotection

Although mitochondria are key determinants of myocardial injury during ischemia-reperfusion (I/R), their interaction with critical cytoprotective signaling systems is not fully understood. Sphingosine-1-phosphate (S1P) produced by sphingosine kinase-1 protects the heart from I/R damage. Recently a new role for mitochondrial S1P produced by a second isoform of sphingosine kinase, SphK2, was described to regulate complex IV assembly and respiration via interaction with mitochondrial prohibitin-2. Here we investigated the role of SphK2 in cardioprotection by preconditioning. Littermate (WT) and sphk2 (-/-) mice underwent 45 min of in vivo ischemia and 24 h reperfusion. Mice received no intervention (I/R) or preconditioning (PC) via 5 min I/R before the index ischemia. Despite the activation of PC-cytoprotective signaling pathways in both groups, infarct size in sphk2 (-/-) mice was not reduced by PC (42 ± 3% PC vs. 43 ± 4% I/R, p = ns) versus WT (24 ± 3% PC vs. 43 ± 3% I/R, p < 0.05). sphk2 (-/-) mitochondria exhibited decreased oxidative phosphorylation and increased susceptibility to permeability transition (PTP). Unlike WT, PC did not prevent ischemic damage to electron transport or the increased susceptibility to PTP. To evaluate the direct contribution to the resistance of mitochondria to cytoprotection, SphK2, PHB2 or cytochrome oxidase subunit IV was depleted in cardiomyoblasts. PC protection was abolished by each knockdown concomitant with decreased PTP resistance. These results point to a new action of S1P in cardioprotection and suggest that the mitochondrial S1P produced by SphK2 is required for the downstream protective modulation of PTP as an effector of preconditioning protection.

Brain energy metabolism and mitochondrial dysfunction in acute and chronic hepatic encephalopathy

One proposed mechanism for acute and chronic hepatic encephalopathy (HE) is a disturbance in cerebral energy metabolism. It also reviews the current status of this mechanism in both acute and chronic HE, as well as in other hyperammonemic disorders. It also reviews abnormalities in glycolysis, lactate metabolism, citric acid cycle, and oxidative phosphorylation as well as associated energy impairment. Additionally, the role of mitochondrial permeability transition (mPT), a recently established factor in the pathogenesis of HE and hyperammonemia, is emphasized. Energy failure appears to be an important pathogenetic component of both acute and chronic HE and a potential target for therapy.

Interaction between cytokines and ammonia in the mitochondrial permeability transition in cultured astrocytes

Hepatic encephalopathy (HE) is the major neurological complication occurring in patients with acute and chronic liver failure. Elevated levels of blood and brain ammonia are characteristic of HE, and astrocytes are the primary target of ammonia toxicity. In addition to ammonia, recent studies suggest that inflammation and associated cytokines (CKs) also contribute to the pathogenesis of HE. It was previously established that ammonia induces the mitochondrial permeability transition (mPT) in cultured astrocytes. As CKs have been shown to cause mitochondrial dysfunction in other conditions, we examined whether CKs induce the mPT in cultured astrocytes. Cultures treated with tumor necrosis factor-α, interleukin-1β, interleukin-6, and interferon-γ, individually or in a mixture, resulted in the induction of the mPT in a time-dependent manner. Simultaneous treatment of cultures with a mixture of CKs and ammonia showed a marked additive effect on the mPT. As oxidative stress (OS) is known to induce the mPT, so we examined the effect of CKs and ammonia on hemeoxygenase-1 (HO-1) protein expression, a marker of OS. Such treatment displayed a synergistic effect in the upregulation of HO-1. Antioxidants significantly blocked the additive effects on the mPT by CKs and ammonia, suggesting that OS represents a major mechanism in the induction of the mPT. Treatment of cultures with minocycline, an antiinflammatory agent, which is known to inhibit OS, also diminished the additive effects on the mPT caused by CKs and ammonia. Induction of the mPT in astrocytes appears to represent a major pathogenetic factor in HE, in which CKs and ammonia are critically involved.

Mitochondrial structure and function are disrupted by standard isolation methods

Mitochondria regulate critical components of cellular function via ATP production, reactive oxygen species production, Ca²⁺ handling and apoptotic signaling. Two classical methods exist to study mitochondrial function of skeletal muscles: isolated mitochondria and permeabilized myofibers. Whereas mitochondrial isolation removes a portion of the mitochondria from their cellular environment, myofiber permeabilization preserves mitochondrial morphology and functional interactions with other intracellular components. Despite this, isolated mitochondria remain the most commonly used method to infer in vivo mitochondrial function. In this study, we directly compared measures of several key aspects of mitochondrial function in both isolated mitochondria and permeabilized myofibers of rat gastrocnemius muscle. Here we show that mitochondrial isolation i) induced fragmented organelle morphology; ii) dramatically sensitized the permeability transition pore sensitivity to a Ca²⁺ challenge; iii) differentially altered mitochondrial respiration depending upon the respiratory conditions; and iv) dramatically increased H₂O₂ production. These alterations are qualitatively similar to the changes in mitochondrial structure and function observed in vivo after cellular stress-induced mitochondrial fragmentation, but are generally of much greater magnitude. Furthermore, mitochondrial isolation markedly altered electron transport chain protein stoichiometry. Collectively, our results demonstrate that isolated mitochondria possess functional characteristics that differ fundamentally from those of intact mitochondria in permeabilized myofibers. Our work and that of others underscores the importance of studying mitochondrial function in tissue preparations where mitochondrial structure is preserved and all mitochondria are represented.

Activation of the mitochondrial permeability transition pore modulates Ca2+ responses to physiological stimuli in adult neurons

The participation of mitochondria in cellular and neuronal Ca(2+) homeostatic networks is now well accepted. Yet, critical tests of specific mitochondrial pathways in neuronal Ca(2+) responses have been hampered because the identity of mitochondrial proteins that must be integrated within this dynamic system remain uncertain. One putative pathway for Ca(2+) efflux from mitochondria exists through the formation of the permeability transition pore (PTP) that is often associated with cellular and neuronal death. Here, we have evaluated neuronal Ca(2+) dynamics and the PTP in single adult neurons in wild-type mice and those missing cyclophilin D (CyPD), a key regulator of the PTP. Using high-resolution time-lapse imaging, we demonstrate that PTP opening only follows simultaneous activation with two physiological stimuli that generate critical threshold levels of cytosolic and mitochondrial Ca(2+) . Our results are the first to demonstrate CyPD-dependent PTP opening in normal neuronal Ca(2+) homeostatic mechanisms not leading to activation of cell death pathways. As neurons in mice lacking CyPD are protected in a number of neurodegenerative disease models, the results suggest that improved viability of CyPD-knockout animals in these pathological states may be due to the transient, rather than persistent, activation of the PTP in mutant mitochondria, thereby shielding neurons from cytoplasmic Ca(2+) overload.

Mitochondrial functional impairment with aging is exaggerated in isolated mitochondria compared to permeabilized myofibers

Mitochondria regulate cellular bioenergetics and apoptosis and have been implicated in aging. However, it remains unclear whether age-related loss of muscle mass, known as sarcopenia, is associated with abnormal mitochondrial function. Two technically different approaches have mainly been used to measure mitochondrial function: isolated mitochondria and permeabilized myofiber bundles, but the reliability of these measures in the context of sarcopenia has not been systematically assessed before. A key difference between these approaches is that contrary to isolated mitochondria, permeabilized bundles contain the totality of fiber mitochondria where normal mitochondrial morphology and intracellular interactions are preserved. Using the gastrocnemius muscle from young adult and senescent rats, we show marked effects of aging on three primary indices of mitochondrial function (respiration, H(2) O(2) emission, sensitivity of permeability transition pore to Ca(2+) ) when measured in isolated mitochondria, but to a much lesser degree when measured in permeabilized bundles. Our results clearly demonstrate that mitochondrial isolation procedures typically employed to study aged muscles expose functional impairments not seen in situ. We conclude that aging is associated with more modest changes in mitochondrial function in sarcopenic muscle than suggested previously from isolated organelle studies.

A bioenergetic model of the mitochondrial population undergoing permeability transition

Mitochondrial permeability transition (MPT) is a highly regulated complex phenomenon that is a type of ischemia/reperfusion injury that can lead to cell death and ultimately organ dysfunction. A novel population transition and detailed permeability transition pore regulation model were integrated with an existing bioenergetics model to describe MPT induction under a variety of conditions. The framework of the MPT induction model includes the potential states of the mitochondria (aggregated, orthodox and post-transition), their transitions from one state to another as well as their interaction with the extra-mitochondrial environment. The model encodes the three basic necessary conditions for MPT: a high calcium load, alkaline matrix pH and circumstances which favor de-energization. The MPT induction model was able to reproduce the expected bioenergetic trends observed in a population of mitochondria subjected to conditions that favor MPT. The model was corroborated and used to predict that MPT in an acidic environment is mitigated by an increase in activity of the mitochondrial potassium/hydrogen exchanger. The model was also used to present the beneficial impact of reducing the duration mitochondria spend in the orthodox state on preserving the extra-mitochondrial ATP levels. The model serves as a tool for investigators to use to understand the MPT induction phenomenon, explore alternative hypotheses for PTP regulation, as well as identify endogenous pharmacological targets and evaluate potential therapeutics for MPT mitigation.

Inhibition of mitochondrial permeability transition to prevent the post-cardiac arrest syndrome: a pre-clinical study

AIMS

Resuscitated cardiac arrest (CA), leading to harmful cardiovascular dysfunction and multiple organ failure, includes a whole-body hypoxia-reoxygenation phenomenon. Opening of the mitochondrial permeability transition pore (mPTP) appears to be a pivotal event in ischaemia-reperfusion injury. We hypothesized that pharmacological inhibition of mPTP opening may prevent the post-CA syndrome.

METHODS AND RESULTS

Anaesthetized New Zealand White rabbits underwent a 15 min primary asphyxial CA and 120 min of reperfusion following resuscitation. At reflow, animals received an intravenous bolus of either cyclosporine A (CsA, 5 mg/kg) or NIM 811 (2.5 mg/kg), two potent inhibitors of mPTP opening, or the CsA vehicle (control). Short-term survival, haemodynamics, regional (sonomicrometry), and global cardiac function (dP/dt and aortic flow) were assessed. We measured markers of cellular injuries and/or organ failure, including troponin Ic release, lacticodehydrogenase, lactate, creatinine, and alanine aminotransferase. Cyclosporine A and NIM 811 significantly improved short-term survival, post-resuscitation cardiac function, as well as liver and kidney failure (P < 0.05). CsA and NIM 811 both attenuated in vitro mPTP opening (calcium retention capacity by spectrofluorimetry) and restored oxidative phosphorylation when compared with controls (P < 0.05).

CONCLUSION

These data suggest that pharmacological inhibition of mPTP opening, added to basic life support, attenuates the post-CA syndrome and improves short-term outcomes in the rabbit model.

Second-generation sulfonylureas preserve inhibition of mitochondrial permeability transition by the mitochondrial K+(ATP) opener nicorandil in experimental myocardial infarction

Openers of K+(ATP) channels protect the myocardium from I/R injury. Sulfonylureas are known as potent blockers of K(ATP) channels. We investigated whether 1) mitochondrial permeability transition pore may be involved in the protection afforded by the mitoK+(ATP) opener nicorandil and 2) whether sulfonylureas may prevent this beneficial effect. Anesthetized New Zealand White rabbits underwent 30 min of coronary artery occlusion, followed by 60 (isolated mitochondria) or 240 min (infarct size) of reperfusion. They received an administration of either saline (control) or nicorandil (0.5 mg kg(-1), i.v.) 15 min before ischemia. Each control and nicorandil group was divided in four subgroups pretreated by either saline, glibenclamide (Glib; 1 mg kg(-1)), gliclazide (Glic; 1 mg kg(-1)), or glimepiride (Glim; 5 microg kg(-1)) 10 min before this. Infarct size was assessed by triphenyltetrazolium chloride staining. Mitochondria were isolated from the area at risk for further assessment of the calcium retention capacity. Glibenclamide (35 +/- 8), but neither Glic (61 +/- 9) nor Glim (48 +/- 7), reversed the improvement in calcium retention capacity due to nicorandil (58 +/- 10 vs. 27 +/- 8 nmoles CaCl2 mg(-1) proteins in control). Infarct size reduction by nicorandil (32% +/- 6% vs. 65% +/- 6% of area at risk) was abolished by Glib (55 +/- 5) but not by Glic (37 +/- 3) or Glim (31 +/- 5). These data suggest that 1) the protective effect of nicorandil involves the inhibition of the mitochondrial permeability transition pore and 2) that unlike Glib, second-generation sulfonylureas preserve this cardioprotection.

Alterations in mitochondrial function as a harbinger of cardiomyopathy: lessons from the dystrophic heart

While compelling evidence supports the central role of mitochondrial dysfunction in the pathogenesis of heart failure, there is comparatively less information available on mitochondrial alterations that occur prior to failure. Building on our recent work with the dystrophin-deficient mdx mouse heart, this review focuses on how early changes in mitochondrial functional phenotype occur prior to overt cardiomyopathy and may be a determinant for the development of adverse cardiac remodelling leading to failure. These include alterations in energy substrate utilization and signalling of cell death through increased permeability of mitochondrial membranes, which may result from abnormal calcium handling, and production of reactive oxygen species. Furthermore, we will discuss evidence supporting the notion that these alterations in the dystrophin-deficient heart may represent an early "subclinical" signature of a defective nitric oxide/cGMP signalling pathway, as well as the potential benefit of mitochondria-targeted therapies. While the mdx mouse is an animal model of Duchenne muscular dystrophy (DMD), changes in the structural integrity of dystrophin, the mutated cytoskeletal protein responsible for DMD, have also recently been implicated as a common mechanism for contractile dysfunction in heart failure. In fact, altogether our findings support a critical role for dystrophin in maintaining optimal coupling between metabolism and contraction in the heart.

Mitochondria and energetic depression in cell pathophysiology

Mitochondrial dysfunction is a hallmark of almost all diseases. Acquired or inherited mutations of the mitochondrial genome DNA may give rise to mitochondrial diseases. Another class of disorders, in which mitochondrial impairments are initiated by extramitochondrial factors, includes neurodegenerative diseases and syndromes resulting from typical pathological processes, such as hypoxia/ischemia, inflammation, intoxications, and carcinogenesis. Both classes of diseases lead to cellular energetic depression (CED), which is characterized by decreased cytosolic phosphorylation potential that suppresses the cell's ability to do work and control the intracellular Ca(2+) homeostasis and its redox state. If progressing, CED leads to cell death, whose type is linked to the functional status of the mitochondria. In the case of limited deterioration, when some amounts of ATP can still be generated due to oxidative phosphorylation (OXPHOS), mitochondria launch the apoptotic cell death program by release of cytochrome c. Following pronounced CED, cytoplasmic ATP levels fall below the thresholds required for processing the ATP-dependent apoptotic cascade and the cell dies from necrosis. Both types of death can be grouped together as a mitochondrial cell death (MCD). However, there exist multiple adaptive reactions aimed at protecting cells against CED. In this context, a metabolic shift characterized by suppression of OXPHOS combined with activation of aerobic glycolysis as the main pathway for ATP synthesis (Warburg effect) is of central importance. Whereas this type of adaptation is sufficiently effective to avoid CED and to control the cellular redox state, thereby ensuring the cell survival, it also favors the avoidance of apoptotic cell death. This scenario may underlie uncontrolled cellular proliferation and growth, eventually resulting in carcinogenesis.

Persistent inhibition of mitochondrial permeability transition by preconditioning during the first hours of reperfusion

Mitochondrial permeability transition pore (mPTP) opening is a crucial event in cardiomyocyte death after I/R. We questioned whether preconditioning (PC) may inhibit mPTP opening during ischemia and/or during reperfusion and whether this effect would persist as reperfusion evolves. Anesthetized New Zealand white rabbits underwent a test ischemia followed by reperfusion. Ischemia lasted either 10 or 30 min, whereas reperfusion duration varied from 5 to 20, 60 and up to 240 min. For each duration of ischemia and reperfusion, animals were randomized as either control or PC. Preconditioning was induced by 5 min of ischemia followed by 5 min of reperfusion. Mitochondria were isolated from myocardium at risk for assessment of the calcium retention capacity (CRC) (potentiometric technique) used here as an index of sensitivity of the mPTP to Ca2+ loading. In controls, the CRC was moderately reduced after ischemia alone, but reperfusion severely and time-dependently accelerated further CRC reduction. Preconditioning failed to modify mPTP opening during ischemia alone, but significantly improved CRC during reperfusion. This protective effect persisted as reperfusion evolved. These data suggest that (a) reperfusion strikingly increases the susceptibility to Ca2+-induced mPTP opening, and that (b) PC inhibits mPTP opening at reflow and throughout the first hours of reperfusion.

The mitochondrial phenotype of peripheral muscle in chronic obstructive pulmonary disease: disuse or dysfunction?

RATIONALE

Peripheral muscle alterations have been recognized to contribute to disability in chronic obstructive pulmonary disease (COPD).

OBJECTIVES

To describe the mitochondrial phenotype in a moderate to severe COPD population and age-matched controls.

METHODS

Three primary aspects of mitochondrial function were assessed in permeabilized locomotor muscle fibers.

MEASUREMENTS AND MAIN RESULTS

Respiration rates per milligram of fiber weight were significantly lower in COPD muscle compared with healthy age-matched control muscle under various respiratory states. However, when variations in mitochondrial volume were taken into account by normalizing respiration per unit of citrate synthase activity, differences between the two groups were abolished, suggesting the absence of specific mitochondrial respiratory impairment in COPD. H(2)O(2) production per mitochondrion was higher both under basal and ADP-stimulated states, suggesting that mitochondria from COPD muscle have properties that potentiate H(2)O(2) release. Direct assessment of mitochondrial sensitivity to Ca(2+)-induced opening of the permeability transition pore (PTP) indicated that mitochondria from patients with COPD were more resistant to PTP opening than their counterparts in control subjects.

CONCLUSIONS

Comparison of these results with those of studies comparing healthy glycolytic with oxidative muscle suggests that these differences may be attributable to greater type II fiber expression in COPD muscle, as mitochondria within this fiber type have respiratory function similar to that of mitochondria from type I fibers, and yet are intrinsically prone to greater release of H(2)O(2) and more resistant to PTP opening. These results thus argue against the presence of pathological mitochondrial alterations in this category of patients with COPD.

Inhibition of GSK3β by Postconditioning Is Required to Prevent Opening of the Mitochondrial Permeability Transition Pore During Reperfusion

Background— Opening of the mitochondrial permeability transition pore (mPTP) is a crucial event in lethal reperfusion injury. Phosphorylation (inhibition) of glycogen synthase kinase-3β (GSK3β) has been involved in cardioprotection. We investigated whether phosphorylated GSK3β may protect the heart via the inhibition of mPTP opening during postconditioning.

Methods and Results— Wild-type and transgenic GSK3β-S9A mice (the cardiac GSK3β activity of which cannot be inactivated) underwent 60 minutes of ischemia and 24 hours of reperfusion. At reperfusion, wild-type and GSK3β-S9A mice received no intervention (control), postconditioning (3 cycles of 1 minute ischemia and 1 minute of reperfusion), the mPTP inhibitor cyclosporine A (CsA; 10 mg/kg IV), or the GSK3β inhibitor SB216763 (SB21; 70 μg/kg IV). Infarct size was assessed by triphenyltetrazolium chloride staining. The resistance of the mPTP to opening after Ca 2+ loading was assessed by spectrofluorometry on mitochondria isolated from the area at risk. In wild-type mice, infarct size was significantly reduced by postconditioning, CsA, and SB21, averaging 39±2%, 35±5%, and 37±4%, respectively, versus 58±5% of the area at risk in control mice ( P <0.05). In GSK3β-S9A mice, only CsA, but not postconditioning or SB21, reduced infarct size. Postconditioning, CsA, and SB21 all improved the resistance of the mPTP in wild-type mice, but only CsA did so in GSK3β-S9A mice.

Conclusion— These results suggest that S9-phosphorylation of GSK3β is required for postconditioning and likely acts by inhibiting the opening of the mitochondrial permeability transition pore.

IP3 receptors in cell survival and apoptosis: Ca2+ release and beyond

Inositol 1,4,5-trisphosphate receptors (IP(3)Rs) serve to discharge Ca(2+) from ER stores in response to agonist stimulation. The present review summarizes the role of these receptors in models of Ca(2+)-dependent apoptosis. In particular we focus on the regulation of IP(3)Rs by caspase-3 cleavage, cytochrome c, anti-apoptotic proteins and Akt kinase. We also address the evidence that some of the effects of IP(3)Rs in apoptosis may be independent of their ion-channel function. The role of IP(3)Rs in delivering Ca(2+) to the mitochondria is discussed from the perspective of the factors determining inter-organellar dynamics and the spatial proximity of mitochondria and ER membranes.

Increased mitochondrial calcium coexists with decreased reperfusion injury in postconditioned (but not preconditioned) hearts

Ca(2+) is the main trigger for mitochondrial permeability transition pore opening, which plays a key role in cardiomyocyte death after ischemia-reperfusion. We investigated whether a reduced accumulation of mitochondrial Ca(2+) might explain the attenuation of lethal reperfusion injury by postconditioning. Anesthetized New Zealand White rabbits underwent 30 min of ischemia, followed by either 240 (infarct size protocol) or 60 (mitochondria protocol) min of reperfusion. They received either no intervention (control), preconditioning by 5-min ischemia and 5-min reperfusion, postconditioning by four cycles of 1-min reperfusion and 1-min ischemia at the onset of reflow, or pharmacological inhibition of the transition pore opening by N-methyl-4-isoleucine-cyclosporin (NIM811; 5 mg/kg iv) given at reperfusion. Area at risk and infarct size were assessed by blue dye injection and triphenyltetrazolium chloride staining. Mitochondria were isolated from the risk region for measurement of 1) Ca(2+) retention capacity (CRC), and 2) mitochondrial content of total (atomic absorption spectrometry) and ionized (potentiometric technique) calcium concentration. CRC averaged 0.73 +/- 0.16 in control vs. 4.23 +/- 0.17 mug Ca(2+)/mg proteins in shams (P < 0.05). Postconditioning, preconditioning, or NIM811 significantly increased CRC (P < 0.05 vs. control). In the control group, total and free mitochondrial calcium significantly increased to 2.39 +/- 0.43 and 0.61 +/- 0.10, respectively, vs. 1.42 +/- 0.09 and 0.16 +/- 0.01 mug Ca(2+)/mg in sham (P < 0.05). Surprisingly, whereas total and ionized mitochondrial Ca(2+) decreased in preconditioning, it significantly increased in postconditioning and NIM811 groups. These data suggest that retention of calcium within mitochondria may explain the decreased reperfusion injury in postconditioned (but not preconditioned) hearts.