The interaction between tBid and cardiolipin or monolysocardiolipin

Lipidomics: An excellent tool for chronic disease detection

It has been known as almost all the cells consists a lipid molecule which has a considerable impact in various biological processes. Lipids have been investigated with a potential role for the formation of cellular membrane and thereby maintaining the structural integrity. Omics has placed as a combined technologies utilized for an exploaration of mechanistic actions in several kinds of molecules that make up the cells of an organism. Lipidomics has been recognized as a newly emerged branch of omics technology. This technology has the captivating factors to classify and characterize almost all the cellular lipids with the help of various analytical techniques and computational biological plateform. In lipidomics studies, structural display of several lipid biomarkers could also be analyzed and considered for actual disease diagnosis procedures. This could also replace certain traditional diagnostics method at all over the globe. Our review focuses how important this lipidomics particularly in disease diagnosis and also covers various analytical techniques and computational methods or bioinformatics tools in for the diagnosis of disease. In addtion, we also pinponted the possible role of lipids in several kinds of cellular disorders including cancer, neurodegenerative diseases, cardiovascular diseases, diabetes and obesity in human population. .

Resveratrol alleviates acute lung injury through regulating PLSCR-3-mediated mitochondrial dysfunction and mitophagy in a cecal ligation and puncture model

Sepsis is considered as a life-threatening organ dysfunction caused by a dysregulated response of the host to an infection. Acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is a life-threatening condition, and is the type of organ injury that is most commonly induced by sepsis. Resveratrol (RSV) has been shown to exert a wide range of therapeutic effects due to its anti-inflammatory and anti-oxidant properties. The present study aimed to investigate whether RSV could mitigate sepsis-induced ALI/ARDS, and also to unravel the underlying mechanism. The model of sepsis was established by applying the cecal ligation and puncture (CLP) method, and mitochondria from the lung tissue were isolated to assess mitochondrial function, as determined from measuring mitochondrial superoxide production using MitoSOX red mitochondrial superoxide indicator and the membrane potential. It was found that RSV could exert a protective role in CLP-induced ALI/ARDS, as evidenced by moderate levels of inflammatory cell infiltration and interstitial edema, as well as decreased levels of C-reactive protein (P<0.01), interleukin (IL)-6 (P<0.01), IL-1β (P<0.01) and tumor necrosis factor-α (P<0.01). Moreover, phospholipid scramblase 3 (PLSCR-3)-mediated mitochondrial dysfunction and mitophagy were shown to contribute towards the CLP-caused lung damage, which was reversed upon RSV administration, as demonstrated by improved mitochondrial function and markedly reduced increases in the protein levels of autophagy related (ATG)5 (P<0.01), ATG7 (P<0.05) and microtubule-associated protein 1A/1B-light chain 3 (LC3-Ⅰ/Ⅱ) (P<0.01), and a significantly increased expression of P62 (P<0.05). In addition, with regard to the CLP-induced lung injury in the mouse model, overexpression of PLSCR-3 was found to remove the beneficial effects observed upon RSV treatment. Taken together, the results of the present study have uncovered a novel molecular mechanism through which RSV may alleviate ALI/ARDS via regulating PLSCR-3-mediated mitochondrial dysfunction and mitophagy in CLP-induced mouse model.

Monolysocardiolipin (MLCL) interactions with mitochondrial membrane proteins

Monolysocardiolipin (MLCL) is a three-tailed variant of cardiolipin (CL), the signature lipid of mitochondria. MLCL is not normally found in healthy tissue but accumulates in mitochondria of people with Barth syndrome (BTHS), with an overall increase in the MLCL:CL ratio. The reason for MLCL accumulation remains to be fully understood. The effect of MLCL build-up and decreased CL content in causing the characteristics of BTHS are also unclear. In both cases, an understanding of the nature of MLCL interaction with mitochondrial proteins will be key. Recent work has shown that MLCL associates less tightly than CL with proteins in the mitochondrial inner membrane, suggesting that MLCL accumulation is a result of CL degradation, and that the lack of MLCL–protein interactions compromises the stability of the protein-dense mitochondrial inner membrane, leading to a decrease in optimal respiration. There is some data on MLCL–protein interactions for proteins involved in the respiratory chain and in apoptosis, but there remains much to be understood regarding the nature of MLCL–protein interactions. Recent developments in structural, analytical and computational approaches mean that these investigations are now possible. Such an understanding will be key to further insights into how MLCL accumulation impacts mitochondrial membranes. In turn, these insights will help to support the development of therapies for people with BTHS and give a broader understanding of other diseases involving defective CL content.

Evidence of proteolipid domain formation in an inner mitochondrial membrane mimicking model

BACKGROUND

Mitochondrial creatine kinase (mtCK) is highly abundant in mitochondria; its quantity is equimolecular to the Adenylic Nucleotide Translocator and represents 1% of the mitochondrial proteins. It is a multitask protein localized in the mitochondria intermembrane space where it binds to the specific cardiolipin (CL) phospholipid. If mtCK was initially thought to be exclusively implicated in energy transfer between mitochondria and cytosol through a mechanism referred to as the phosphocreatine shuttle, several recent studies suggested an additional role in maintaining mitochondria membrane structure.

METHODS

To further characterized mtCK binding process we used multiphoton excitation fluorescence microscopy coupled with Giant Unilamellar Vesicles (GUV) and laurdan as fluorescence probe.

RESULTS

We gathered structural and dynamical information on the molecular events occurring during the binding of mtCK to the mitochondria inner membrane. We present the first visualization of mtCK-induced CL segregation on a bilayer model forming micrometer-size proteolipid domains at the surface of the GUV. Those microdomains, which only occurred when CL is included in the lipid mixture, were accompanied by the formation of protein multimolecular assembly, vesicle clamping, and changes in both vesicle curvature and membrane fluidity CONCLUSION: Those results highlighted the importance of the highly abundant mtCK in the lateral organization of the mitochondrial inner membrane.

GENERAL SIGNIFICANCE

Microdomains were induced in mitochondria-mimicking membranes composed of natural phospholipids without cholesterol and/or sphingolipids differing from the proposed cytoplasmic membrane rafts. Those findings as well as membrane curvature modification were discussed in relation with protein-membrane interaction and protein cluster involvement in membrane morphology.

Initiation and perpetuation of NLRP3 inflammasome activation and assembly

The NLRP3 (NOD-like receptor family, pyrin domain containing 3) inflammasome is a multiprotein complex that orchestrates innate immune responses to infection and cell stress through activation of caspase-1 and maturation of inflammatory cytokines pro-interleukin-1β (pro-IL-1β) and pro-IL-18. Activation of the inflammasome during infection can be protective, but unregulated NLRP3 inflammasome activation in response to non-pathogenic endogenous or exogenous stimuli can lead to unintended pathology. NLRP3 associates with mitochondria and mitochondrial molecules, and activation of the NLRP3 inflammasome in response to diverse stimuli requires cation flux, mitochondrial Ca(2+) uptake, and mitochondrial reactive oxygen species accumulation. It remains uncertain whether NLRP3 surveys mitochondrial integrity and senses mitochondrial damage, or whether mitochondria simply serve as a physical platform for inflammasome assembly. The structure of the active, caspase-1-processing NLRP3 inflammasome also requires further clarification, but recent studies describing the prion-like properties of ASC have advanced the understanding of how inflammasome assembly and caspase-1 activation occur while raising new questions regarding the propagation and resolution of NLRP3 inflammasome activation. Here, we review the mechanisms and pathways regulating NLRP3 inflammasome activation, discuss emerging concepts in NLRP3 complex organization, and expose the knowledge gaps hindering a comprehensive understanding of NLRP3 activation.

C11orf83, a mitochondrial cardiolipin-binding protein involved in bc1 complex assembly and supercomplex stabilization

Mammalian mitochondria may contain up to 1,500 different proteins, and many of them have neither been confidently identified nor characterized. In this study, we demonstrated that C11orf83, which was lacking experimental characterization, is a mitochondrial inner membrane protein facing the intermembrane space. This protein is specifically associated with the bc1 complex of the electron transport chain and involved in the early stages of its assembly by stabilizing the bc1 core complex. C11orf83 displays some overlapping functions with Cbp4p, a yeast bc1 complex assembly factor. Therefore, we suggest that C11orf83, now called UQCC3, is the functional human equivalent of Cbp4p. In addition, C11orf83 depletion in HeLa cells caused abnormal crista morphology, higher sensitivity to apoptosis, a decreased ATP level due to impaired respiration and subtle, but significant, changes in cardiolipin composition. We showed that C11orf83 binds to cardiolipin by its α-helices 2 and 3 and is involved in the stabilization of bc1 complex-containing supercomplexes, especially the III2/IV supercomplex. We also demonstrated that the OMA1 metalloprotease cleaves C11orf83 in response to mitochondrial depolarization, suggesting a role in the selection of cells with damaged mitochondria for their subsequent elimination by apoptosis, as previously described for OPA1.

Phosphatidic acid mediates the targeting of tBid to induce lysosomal membrane permeabilization and apoptosis

Upon apoptotic stimuli, lysosomal proteases, including cathepsins and chymotrypsin, are released into cytosol due to lysosomal membrane permeabilization (LMP), where they trigger apoptosis via the lysosomal-mitochondrial pathway of apoptosis. Herein, the mechanism of LMP was investigated. We found that caspase 8-cleaved Bid (tBid) could result in LMP directly. Although Bax or Bak might modestly enhance tBid-triggered LMP, they are not necessary for LMP. To study this further, large unilamellar vesicles (LUVs), model membranes mimicking the lipid constitution of lysosomes, were used to reconstitute the membrane permeabilization process in vitro. We found that phosphatidic acid (PA), one of the major acidic phospholipids found in lysosome membrane, is essential for tBid-induced LMP. PA facilitates the insertion of tBid deeply into lipid bilayers, where it undergoes homo-oligomerization and triggers the formation of highly curved nonbilayer lipid phases. These events induce LMP via pore formation mechanisms because encapsulated fluorescein-conjugated dextran (FD)-20 was released more significantly than FD-70 or FD-250 from LUVs due to its smaller molecular size. On the basis of these data, we proposed tBid-PA interactions in the lysosomal membranes form lipidic pores and result in LMP. We further noted that chymotrypsin-cleaved Bid is more potent than tBid at binding to PA, inserting into the lipid bilayer, and promoting LMP. This amplification mechanism likely contributes to the culmination of apoptotic signaling.

Hyperthermia-induced apoptosis in Tca8113 cells is inhibited by heat shock protein 27 through blocking phospholipid scramblase 3 phosphorylation

PURPOSE

Hyperthermia induces tumour cell apoptosis through the mitochondrial apoptotic pathway; however, the signal transduction mechanism underlying this process still needs to be fully elucidated. Phospholipid scramblase 3 (PLS3), a target of protein kinase C-delta (PKC-delta), resides in mitochondria and plays pivotal roles in regulating apoptotic response. Activated PLS3 facilitates cardiolipin (CL) translocation from the mitochondrial inner membrane to the outer leaflet of the mitochondrial outer membrane and triggers apoptosis.

MATERIALS AND METHODS

The tongue squamous cell carcinoma Tca8113 cells were transfected or co-transfected using Lipofectamine 2000 with plasmids pCMV-6xHis-PLS3, pCMV-6xHis-PLS3 (T21A), pHA-PKC-delta, pHA-PKC-delta-KD (K376R), pHA-Hsp27, and empty control plasmid pcDNA3.1. The transfected cells were heated in water bath at 43 degrees C for 20 min, 40 min and 60 min. Assessments of apoptosis and redistribution of mitochondrial cardiolipin were performed by flow cytometry. PLS3, PKC-delta, Hsp27, phosphorylation of PLS3 and PLS3/PKC-delta interaction were detected by western blotting.

RESULTS

In our study the results show that elevated levels of the wild-type PLS3, but not the PLS3 (T21A) mutant, is able to increase hyperthermia-induced CL translocation and apoptosis. Wild-type PKC-delta facilitates PLS3 phosphorylation, PKC-delta/PLS3 interaction, and CL translocation, which consequently promote apoptosis. In contrast, heat shock protein 27 (Hsp27) blocks PKC-delta-induced PLS3 phosphorylation, suppresses PKC-delta/PLS3 interaction and CL translocation, and inhibits apoptosis.

CONCLUSIONS

Our findings suggest that phosphorylation of PLS3 by PKC-delta is involved in the hyperthermia-induced apoptotic signal transduction pathway in Tca8113 cells, and that Hsp27 blocks this pathway to suppress hyperthermia-induced apoptosis.

Monolysocardiolipin: improved preparation with high yield

A simple, high-yielding preparation of monolysocardiolipin (MLCL) by phospholipase A2 hydrolysis of cardiolipin (CL) in methanol on a semi-preparative scale is described. In methanol, phospholipase A2 preferentially hydrolyzes CL to MLCL. This selectivity results in ∼80% yield of MLCL. The synthesized MLCL and dilysocardiolipin were characterized by NMR and ESI-MS/MS. Only the sn-2 position of CL was hydrolyzed by phospholipase A2 in methanol.

Mitochondrial monolysocardiolipin acyltransferase is elevated in the surviving population of H9c2 cardiac myoblast cells exposed to 2-deoxyglucose-induced apoptosis

Cardiolipin (CL) is a major mitochondrial membrane phospholipid in the mammalian heart and the remodeling of CL is essential to maintain its unique unsaturated fatty acyl composition. We examined CL de novo biosynthesis and remodeling in the surviving population of H9c2 cardiac myoblast cells exposed to 2-deoxyglucose (2-DG). H9c2 cells were incubated in the absence or presence of 2-DG for 16 h with [1,3-3H]glycerol or [1-14C]linoleic acid (bound to albumin in a 1:1 molar ratio). Dead cells were removed and radioactivity was incorporated into CL. Its pool size, fatty acid composition, and the activities of the CL biosynthesis and remodeling enzymes were determined. The CL pool size, its fatty acid composition, and [1,3-3H]glycerol or [1-14C]linoleic acid incorporated into CL were unaltered in the surviving population of 2-DG-treated cells compared with controls. In addition, the activities of the CL de novo biosynthetic enzymes were unaltered. Cleaved caspase-3 and poly(ADP-ribose) polymerase were slightly elevated in the surviving population of 2-DG-treated cells compared with controls, indicating that apoptosis induction was occurring in these cells. Mitochondrial phospholipase A2 and monolysocardiolipin acyltransferase (MLCL AT) activities increased 33% (p < 0.05) and 63% (p < 0.05), respectively, in 2-deoxyglucose-treated cells compared with controls. In contrast, the activity of ALCAT1, an endoplasmic reticulum MLCL AT, decreased 77% (p < 0.05), but this was not due to a reduction in ALCAT1 mRNA expression. The mRNA expression of the Barth syndrome gene TAZ, encoding a mitochondrial CL transacylase, was unaltered in 2-DG treated cells. The increase in mitochondrial MLCL AT activity was due to an elevated expression in MLCL AT protein. Thus, an increase in MLCL AT activity and expression occurs to maintain the CL pool in the surviving population of H9c2 cells as a compensatory mechanism for the elevated phospholipase A2 activity seen in 2-DG-induced apoptosis. We hypothesize that increased mitochondrial MLCL AT activity and its expression, and hence, elevated CL resynthesis, may be a protective mechanism against monolysocardiolipin-mediated apoptosis.

Bid binding to negatively charged phospholipids may not be required for its pro-apoptotic activity in vivo

Bid is a ubiquitous pro-apoptotic member of the Bcl-2 family that has been involved in a variety of pathways of cell death. Unique among pro-apoptotic proteins, Bid is activated after cleavage by the apical caspases of the extrinsic pathway; subsequently it moves to mitochondria, where it promotes the release of apoptogenic proteins in concert with other Bcl-2 family proteins like Bak. Diverse factors appear to modulate the pro-apoptotic action of Bid, from its avid binding to mitochondrial lipids (in particular, cardiolipin) to multiple phosphorylations at sites that can modulate its caspase cleavage. This work addresses the question of how the lipid interactions of Bid that are evident in vitro actually impact on its pro-apoptotic action within cells. Using site-directed mutagenesis, we identified mutations that reduced mouse Bid lipid binding in vitro. Mutation of the conserved residue Lys157 specifically decreased the binding to negatively charged lipids related to cardiolipin and additionally affected the rate of caspase cleavage. However, this lipid-binding mutant had no discernable effect on Bid pro-apoptotic function in vivo. The results are interpreted in relation to an underlying interaction of Bid with lysophosphatidylcholine, which is not disrupted in any mutant retaining pro-apoptotic function both in vitro and in vivo.

Cardiolipin acts as a mitochondrial signalling platform to launch apoptosis

Cardiolipin (CL) is a unique anionic phospholipid specific to the mitochondria. CL influences the activity of electron transport chain enzyme complexes as well as members of the Bcl-2 family. Interactions between Bcl-2 family members and other pro-apoptotic enzymes have been shown to be crucial for the transduction of the apoptotic signalling cascades during programmed cell death. Targeting of tBid to the mitochondria, which is necessary for Bax/Bak oligomerization and cristae remodelling, is dependent on the exposure of CL at contact sites between the inner and outer mitochondrial membranes. Also, the mobilization of cytochrome c, another key apoptotic event, is tightly regulated by the oxidative state of cardiolipin. Moreover, CL has been shown to be essential for translocation and autoprocessing of caspase-8 on the mitochondria after death receptor stimulation. Deficiencies in CL inhibit the formation of tBid and prevent apoptosis by removing an essential activation platform for the autoprocessing of caspase-8. It is now apparent that CL acts as a crucial signalling platform from which it orchestrates apoptosis by integrating signals from a variety of death inducing proteins.

Mitochondrial kinases and their molecular interaction with cardiolipin

Mitochondrial isoforms of creatine kinase (MtCK) and nucleoside diphosphate kinase (NDPK-D) are not phylogenetically related but share functionally important properties. They both use mitochondrially generated ATP with the ultimate goal of maintaining proper nucleotide pools, are located in the intermembrane/cristae space, have symmetrical oligomeric structures, and show high affinity binding to anionic phospholipids, in particular cardiolipin. The structural basis and functional consequences of the cardiolipin interaction have been studied and are discussed in detail in this review. They mainly result in a functional interaction of MtCK and NDPK-D with inner membrane adenylate translocator, probably by forming proteolipid complexes. These interactions allow for privileged exchange of metabolites (channeling) that ultimately regulate mitochondrial respiration. Further functions of the MtCK/membrane interaction include formation of cardiolipin membrane patches, stabilization of mitochondria and a role in apoptotic signaling, as well as in case of both kinases, a role in facilitating lipid transfer between two membranes. Finally, disturbed cardiolipin interactions of MtCK, NDPK-D and other proteins like cytochrome c and truncated Bid are discussed more generally in the context of apoptosis and necrosis.

ALCAT1 is a polyglycerophospholipid acyltransferase potently regulated by adenine nucleotide and thyroid status

Acyl-CoA:lysocardiolipin acyltransferase-1 (ALCAT1) catalyzes acylation of lysocardiolipin back to cardiolipin, an important step in cardiolipin remodeling. The present study reports the catalytic properties of ALCAT1 in vitro and its regulation by thyroid hormone status in mouse liver and heart. Recombinant ALCAT1 expressed in Sf9 cells preferred basic pH conditions and did not require divalent cations or integrity of the subcellular membrane for its enzymatic activity. Recombinant ALCAT1 was potently inhibited by ADP and ATP, but not by adenosine nucleotide analogs or other nucleotides, such as UTP and GTP, suggesting that ALCAT1 does not require ATP hydrolysis for its enzyme activity. In addition to cardiolipin, ALCAT1 also catalyzed acylation of other members of the polyglycerophospholipid family, including phosphatidylglycerol, a precursor for cardiolipin synthesis, and bis(monoacylglycero)phosphate, a structural isomer of lysophosphatidylglycerol and a metabolic intermediate of cardiolipin. These findings suggest that ALCAT1 plays a role in the remodeling of other polyglycerophospholipids. In support of a regulatory role of ALCAT1 in cardiolipin remodeling in response to oxidative stress, ALCAT1 expression in liver and heart was significantly downregulated in mice with hypothyroidism and upregulated in mice treated with thyroid hormone, which is known to stimulate mitochondrial activity, oxidative stress, and cardiolipin remodeling.

Cardiolipin provides an essential activating platform for caspase-8 on mitochondria

Cardiolipin is a mitochondria-specific phospholipid known to be intimately involved with apoptosis. However, the lack of appropriate cellular models to date restricted analysis of its role in cell death. The maturation of cardiolipin requires the transacylase tafazzin, which is mutated in the human disorder Barth syndrome. Using Barth syndrome patient-derived cells and HeLa cells in which tafazzin was knocked down, we show that cardiolipin is required for apoptosis in the type II mitochondria-dependent response to Fas stimulation. Cardiolipin provides an anchor and activating platform for caspase-8 translocation to, and embedding in, the mitochondrial membrane, where it oligomerizes and is further activated, steps that are necessary for an efficient type II apoptotic response.

The nucleoside diphosphate kinase D (NM23-H4) binds the inner mitochondrial membrane with high affinity to cardiolipin and couples nucleotide transfer with respiration

Nucleoside diphosphate kinase (NDPK/Nm23), responsible for intracellular di- and triphosphonucleoside homeostasis, plays multiple roles in cellular energetics, signaling, proliferation, differentiation and tumor invasion. The only human NDPK with a mitochondrial targeting sequence is NDPK-D, the NME4 gene product, which is a peripheral protein of mitochondrial membranes. Subfractionation of rat liver and HEK 293 cell mitochondria revealed that NDPK-D is essentially bound to the inner membrane. Surface plasmon resonance analysis of the interaction using recombinant NDPK-D and model liposomes showed that NDPK-D interacts electrostatically with anionic phospholipids, with highest affinity observed for cardiolipin. Mutation of the central arginine (Arg-90) in a surface-exposed basic RRK motif unique to NDPK-D strongly reduced interaction with anionic phospholipids. Due to its symmetrical hexameric structure, NDPK-D was able to cross-link anionic phospholipid-containing liposomes, suggesting that NDPK-D could promote intermembrane contacts. Latency assays with isolated mitochondria and antibody binding to mitoplasts indicated a dual orientation for NDPK-D. In HeLa cells, stable expression of wild type but not of the R90D mutant led to membrane-bound enzyme in vivo. Respiration was significantly stimulated by the NDPK substrate TDP in mitochondria containing wild-type NDPK-D, but not in those expressing the R90D mutant, which is catalytically equally active. This indicates local ADP regeneration in the mitochondrial intermembrane space and a tight functional coupling of NDPK-D with oxidative phosphorylation that depends on its membrane-bound state.

Identification of Alix-type and Non-Alix-type ALG-2-binding sites in human phospholipid scramblase 3: differential binding to an alternatively spliced isoform and amino acid-substituted mutants

ALG-2, a prototypic member of the penta-EF-hand protein family, interacts with Alix at its C-terminal Pro-rich region containing four tandem PXY repeats. Human phospholipid scramblase 3 (PLSCR3) has a similar sequence (ABS-1) in its N-terminal region. In the present study, we found that ALG-2 interacts with PLSCR3 expressed in HEK293 cells in a Ca(2+)-dependent manner by co-immunoprecipitation, pulldown with glutathione S-transferase (GST) fused ALG-2 and an overlay assay using biotin-labeled ALG-2. The GST fusion protein of an alternatively spliced isoform of ALG-2, GST-ALG-2(DeltaGF122), pulled down green fluorescent protein (GFP)-fused PLSCR3 but not GFP Alix. Deletion of a region containing ABS-1 was not sufficient to abrogate the binding. A second ALG-2-binding site (ABS-2) was essential for interaction with ALG-2(DeltaGF122). Real-time interaction analyses with a surface plasmon resonance biosensor using synthetic oligopeptides and recombinant proteins corroborated direct Ca(2+)-dependent binding of ABS-1 to ALG-2 and that of ABS-2 to ALG-2 as well as to ALG-2(DeltaGF122). The sequence of ABS-2 contains multiple prolines and two phenylalanines, among which Phe(49) was found to be critical, because its substitution with Ala or Tyr caused a loss of binding ability by pulldown assays using oligopeptide-immobilized beads. ALG-2-interacting proteins were classified into two groups based on binding ability to ALG-2(DeltaGF122): (i) isoform-non-interactive (ABS-1) types, including Alix, annexin A7, annexin A11, and TSG101 and (ii) isoform-interactive (ABS-2) types including PLSCR3, PLSCR4 and Sec31A. GST-pulldown assays using single amino acid-substituted ALG-2 mutants revealed differences in binding specificities between the two groups, suggesting structural flexibility in ALG-2-ligand complex formation.

Mitochondrial carriers and pores: key regulators of the mitochondrial apoptotic program?

Mitochondria play a pivotal role in the process of apoptosis. Alterations in mitochondrial structure and function during apoptosis are regulated by proteins of the BCL-2 family, however their exact mechanism of action is largely unknown. Mitochondrial carriers and pores play an essential role in maintaining the normal function of mitochondria, and BCL-2 family members were shown to interact with several mitochondrial carriers/pores and to affect their function. This review focuses on the involvement of several of these mitochondrial carriers/pores in the regulation of the mitochondrial death pathway.

Cardiolipin: setting the beat of apoptosis

Cardiolipin (CL) is a mitochondria-specific phospholipid which is known to be intimately linked with the mitochondrial bioenergetic machinery. Accumulating evidence now suggests that this unique lipid also has active roles in several of the mitochondria-dependent steps of apoptosis. CL is closely associated with cytochrome c at the outer leaflet of the mitochondrial inner membrane. This interaction makes the process of cytochrome c release from mitochondria more complex than previously assumed, requiring more than pore formation in the mitochondrial outer membrane. While CL peroxidation could be crucial for enabling cytochrome c dissociation from the mitochondrial inner membrane, cytochrome c itself catalyzes CL peroxidation. Moreover, peroxy-CL directly activates the release of cytochrome c and other apoptogenic factors from the mitochondria. CL is also directly involved in mitochondrial outer membrane permeabilization by enabling docking and activation of pro-apoptotic Bcl-2 proteins. It appears therefore that CL has multiple roles in apoptosis and that CL metabolism contributes to the complexity of the apoptotic process.

Oxidative phosphorylation and aging

This review addresses the data that support the presence and contribution of decreased mitochondrial oxidative phosphorylation during aging to impaired cellular metabolism. Aging impairs substrate oxidation, decreases cellular energy production and increases the production of reactive intermediates that are toxic to the cell. First, the basic principles of mitochondrial oxidative physiology are briefly reviewed. Second, the focus on the relationship of altered mitochondrial respiration to the increased production of reactive oxygen species that are employed by the "rate of living" and the "uncoupling to survive" theories of aging are discussed. Third, the impairment of function of respiration in aging is reviewed using an organ-based approach in mammalian systems. Fourth, the current state of knowledge regarding aging-induced alterations in the composition and function of key mitochondrial constituents is addressed. Model organisms, including C. elegans and D. melanogaster are included where pertinent. Fifth, these defects are related to knowledge regarding the production of reactive oxygen species from specific sites of the electron transport chain.

Mitochondria and cancer: is there a morphological connection?

Mitochondria are key players in several cellular functions including growth, division, energy metabolism, and apoptosis. The mitochondrial network undergoes constant remodelling and these morphological changes are of direct relevance for the role of this organelle in cell physiology. Mitochondrial dysfunction contributes to a number of human disorders and may aid cancer progression. Here, we summarize the recent contributions made in the field of mitochondrial dynamics and discuss their impact on our understanding of cell function and tumorigenesis.

Bid, a BH3-only multi-functional molecule, is at the cross road of life and death

Bid, BH3-interacting domain death agonist, was initially cloned based in its ability to interact with both Bcl-2 and Bax. Bid contains only the BH3 domain, which is required for its interaction with the Bcl-2 family proteins and for its pro-death activity. Bid is susceptible to proteolytic cleavage by caspases, calpains, Granzyme B and cathepsins. Bid is important to cell death mediated by these proteases and thus is the sentinel to protease-mediated death signals. Protease-cleaved Bid is able to induce multiple mitochondrial dysfunctions, including the release of the inter-membrane space proteins, cristae reorganization, depolarization, permeability transition and generation of reactive oxygen species. Thus Bid is the molecular linker bridging various peripheral death pathways to the central mitochondria pathway. Recent studies further indicate that Bid may be more than just a killer molecule. Deletion of Bid inhibits carcinogenesis in the liver, although this genetic alteration promotes tumorigenesis in the myeloid cells. This is likely related to the function of Bid to promote cell cycle progression into S phase. Bid could be also involved in the maintenance of genomic stability by engaging at mitosis checkpoint. These novel findings indicate that this BH3-only Bcl-2 family protein has a diverse array of functions that are important to both the life and death of the cell.

Pro-apoptotic effect of maize lipid transfer protein on mammalian mitochondria

To assess the effect of lipids and lipid exchange in the pro-apoptotic release of cytochrome c, we investigated the ability of a plant lipid transfer protein (LTP) to initiate the apoptotic cascade at the mitochondrial level. The results show that maize LTP is able to induce cytochrome c release from the intermembrane space of mouse liver mitochondria without significant mitochondrial swelling, similarly to mouse full-length Bid. This effect is influenced by the presence of specific lipids, since addition of lysolipids like lysophosphatidylcholine strongly stimulates the LTP-induced release of cytochrome c while it is inhibited by removal of endogenous free lipids with a complete suppression of the LTP-induced release of cytochrome c. The results are discussed in light of the possible role of lipid exchange in apoptosis.

Survey of the year 2005 commercial optical biosensor literature

We identified 1113 articles (103 reviews, 1010 primary research articles) published in 2005 that describe experiments performed using commercially available optical biosensors. While this number of publications is impressive, we find that the quality of the biosensor work in these articles is often pretty poor. It is a little disappointing that there appears to be only a small set of researchers who know how to properly perform, analyze, and present biosensor data. To help focus the field, we spotlight work published by 10 research groups that exemplify the quality of data one should expect to see from a biosensor experiment. Also, in an effort to raise awareness of the common problems in the biosensor field, we provide side-by-side examples of good and bad data sets from the 2005 literature.