Synthetic and natural polyanions induce cytochrome c release from mitochondria in vitro and in situ

A PETase enzyme synthesised in the chloroplast of the microalga Chlamydomonas reinhardtii is active against post-consumer plastics

Polyethylene terephthalate hydrolases (PETases) are a newly discovered and industrially important class of enzymes that catalyze the enzymatic degradation of polyethylene terephatalate (PET), one of the most abundant plastics in the world. The greater enzymatic efficiencies of PETases compared to close relatives from the cutinase and lipase families have resulted in increasing research interest. Despite this, further characterization of PETases is essential, particularly regarding their possible activity against other kinds of plastic. In this study, we exploited for the first time the use of the microalgal chloroplast for more sustainable synthesis of a PETase enzyme. A photosynthetic-restoration strategy was used to generate a marker-free transformant line of the green microalga Chlamydomonas reinhardtii in which the PETase from Ideonella sakaiensis was constitutively expressed in the chloroplast. Subsequently, the activity of the PETase against both PET and post-consumer plastics was investigated via atomic force microscopy, revealing evidence of degradation of the plastics.

Csseverin inhibits apoptosis through mitochondria-mediated pathways triggered by Ca2 + dyshomeostasis in hepatocarcinoma PLC cells

Background

Numerous experimental and epidemiological studies have demonstrated a link between Clonorchis sinensis (C. sinensis) infestation and cholangiocarcinoma (CCA) as well as hepatocellular carcinoma (HCC). The underlying molecular mechanism involved in the malignancy of CCA and HCC has not yet been addressed. Csseverin, a component of the excretory/secretory products of C. sinensis (CsESPs), was confirmed to cause obvious apoptotic inhibition in the human HCC cell line PLC. However, the antiapoptotic mechanism is unclear. In the present study, we investigated the cellular features of the antiapoptotic mechanism upon transfection of the Csseverin gene.

Methods

In the present study, we evaluated the effects of Csseverin gene overexpression on the apoptosis of PLC cells using an Annexin PE/7-AAD assay. Western blotting was applied to quantify the activation of caspase-3 and caspase-9, the mitochondrial translocation of Bax and the release of Cyt c upon Csseverin overexpression in PLC cells. Laser scanning confocal microscopy was used to analyze the changes of intracellular calcium. Fluorescence assay and immunofluorescence assays were performed to observe the changes of the mitochondrial permeability transition pore (MPTP).

Results

The overexpression of Csseverin in PLC cells showed apoptosis resistance after the induction of apoptosis. Additionally, the activation of caspase-3 and caspase-9 was specifically weakened in Csseverin overexpression PLC cells. The overexpression of Csseverin reduced the increase in intracellular free Ca2+, thereby inhibiting MPTP opening in PLC cells. Moreover, Bax mitochondrial translocation and the subsequent release of Cyt c were downregulated in apoptotic Csseverin overexpression PLC cells.

Conclusions

The present findings suggest that Csseverin, a component of CsESPs, confers protection from human HCC cell apoptosis via the inactivation of membranous Ca²⁺ channels. Csseverin might be involved in the process of HCC through C. sinensis infestation in affected patients.

Multiple studies have contributed to the association between Clonorchis sinensis (C. sinensis) infestation and cholangiocarcinoma (CCA) as well as hepatocellular carcinoma (HCC) in past years. However, studies on the underlying pathogenic mechanisms of C. sinensis lag behind those of other parasitic diseases. The excretory/secretory products of C. sinensis (CsESPs) are pathogenic, as these products promote cell proliferation, suppress cell apoptosis and stimulate inflammation. Csseverin, a component of CsESPs, inhibited the apoptosis of the human HCC cell line PLC in our previous study. The present study illustrated that Csseverin conferred human HCC cells protection from apoptosis via an intrinsic pathway (mitochondrial-mediated) triggered by the inactivation of membranous Ca²⁺ channels.

A cross-platform metabolomics workflow for volume-restricted tissue samples: application to an animal model for polycystic kidney disease

Metabolic profiling provides an unbiased view of the physiological status of an organism as a “function” of the metabolic composition of a measured sample.

Linking Inflammation and Parkinson Disease: Hypochlorous Acid Generates Parkinsonian Poisons

Inflammation is a common feature of Parkinson Disease and other neurodegenerative disorders. Hypochlorous acid (HOCl) is a reactive oxygen species formed by neutrophils and other myeloperoxidase-containing cells during inflammation. HOCl chlorinates the amine and catechol moieties of dopamine to produce chlorinated derivatives collectively termed chlorodopamine. Here, we report that chlorodopamine is toxic to dopaminergic neurons both in vivo and in vitro Intrastriatal administration of 90 nmol chlorodopamine to mice resulted in loss of dopaminergic neurons from the substantia nigra and decreased ambulation-results that were comparable to those produced by the same dose of the parkinsonian poison, 1-methyl-4-phenylpyridinium (MPP+). Chlorodopamine was also more toxic to differentiated SH SY5Y cells than HOCl. The basis of this selective toxicity is likely mediated by chlorodopamine uptake through the dopamine transporter, as expression of this transporter in COS-7 cells conferred sensitivity to chlorodopamine toxicity. Pharmacological blockade of the dopamine transporter also mitigated the deleterious effects of chlorodopamine in vivo The cellular actions of chlorodopamine included inactivation of the α-ketoglutarate dehydrogenase complex, as well as inhibition of mitochondrial respiration. The latter effect is consistent with inhibition of cytochrome c oxidase. Illumination at 670 nm, which stimulates cytochrome c oxidase, reversed the effects of chlorodopamine. The observed changes in mitochondrial biochemistry were also accompanied by the swelling of these organelles. Overall, our findings suggest that chlorination of dopamine by HOCl generates toxins that selectively kill dopaminergic neurons in the substantia nigra in a manner comparable to MPP+.

Induction of Ca2+-dependent cyclosporin A-insensitive nonspecific permeability of the inner membrane of liver mitochondria and cytochrome c release by α,ω-hexadecanedioic acid in media of varying ionic strength

In liver mitochondria loaded with Ca2+ or Sr(2+), α,ω-hexadecanedioic acid (HDA) can induce nonspecific permeability of the inner membrane (mitochondrial pore) by the mechanism insensitive to cyclosporin A (CsA). In this work we studied the effect of ionic strength of the incubation medium on the kinetics of the processes that accompany Ca2+-dependent induction of the mitochondrial pore by fatty acid: organelle swelling, Ca2+ release from the matrix, changes in transmembrane potential (Δψ) and rate of oxygen consumption, and the release of cytochrome c from the intermembrane space. Two basic incubation media were used: sucrose medium and isotonic ionic medium containing KCl without sucrose. We found that 200 μM Ca2+ and 20 μM HDA in the presence of CsA effectively induce high-amplitude swelling of mitochondria both in the case of sucrose and in the ionic incubation medium. In the presence of CsA, mitochondria can rapidly absorb Ca2+ and retain it in the matrix for a while without reducing Δψ. Upon incubation in the ionic medium, mitochondria retain most of the added Ca2+ in the matrix for a short time without reducing the Δψ. In both cases the addition of HDA to the mitochondria 2 min after the introduction of Ca2+ leads to the rapid release of these ions from the matrix and total drop in Δψ. The mitochondrial swelling induced by Ca2+ and HDA in non-ionic medium is accompanied by almost maximal stimulation of respiration. Under the same conditions, but during incubation of mitochondria in the ionic medium, it is necessary to add cytochrome c for significant stimulation of respiration. The mitochondrial swelling induced by Ca2+ and HDA leads to the release of cytochrome c in a larger amount in the case of ionic medium than for the sucrose medium. We conclude that high ionic strength of the incubation medium determines the massive release of cytochrome c from mitochondria and liberates it from the respiratory chain, which leads to blockade of electron transport along the respiratory chain and consequently to disruption of the energy functions of the organelles.

Inhibition of JAK2/STAT3 signalling induces colorectal cancer cell apoptosis via mitochondrial pathway

Abnormalities in the JAK2/STAT3 pathway are involved in the pathogenesis of colorectal cancer (CRC), including apoptosis. However, the exact mechanism by which dysregulated JAK2/STAT3 signalling contributes to the apoptosis has not been clarified. To investigate the role of both JAK2 and STAT3 in the mechanism underlying CRC apoptosis, we inhibited JAK2 with AG490 and depleted STAT3 with a small interfering RNA. Our data showed that inhibition of JAK2/STAT3 signalling induced CRC cellular apoptosis via modulating the Bcl-2 gene family, promoting the loss of mitochondrial transmembrane potential (Δψm) and the increase of reactive oxygen species. In addition, our results demonstrated that the translocation of cytochrome c (Cyt c), caspase activation and cleavage of poly (ADP-ribose) polymerase (PARP) were present in apoptotic CRC cells after down-regulation of JAK2/STAT3 signalling. Moreover, inhibition of JAK2/STAT3 signalling suppressed CRC xenograft tumour growth. We found that JAK2/STAT3 target genes were decreased; meanwhile caspase cascade was activated in xenograft tumours. Our findings illustrated the biological significance of JAK2/STAT3 signalling in CRC apoptosis, and provided novel evidence that inhibition of JAK2/STAT3 induced apoptosis via the mitochondrial apoptotic pathway. Therefore, JAK2/STAT3 signalling may be a potential target for therapy of CRC.

Inorganic polyphosphate is a potent activator of the mitochondrial permeability transition pore in cardiac myocytes

Mitochondrial dysfunction caused by excessive Ca²⁺ accumulation is a major contributor to cardiac cell and tissue damage during myocardial infarction and ischemia–reperfusion injury (IRI). At the molecular level, mitochondrial dysfunction is induced by Ca²⁺-dependent opening of the mitochondrial permeability transition pore (mPTP) in the inner mitochondrial membrane, which leads to the dissipation of mitochondrial membrane potential (ΔΨ_m), disruption of adenosine triphosphate production, and ultimately cell death. Although the role of Ca²⁺ for induction of mPTP opening is established, the exact molecular mechanism of this process is not understood. The aim of the present study was to test the hypothesis that the adverse effect of mitochondrial Ca²⁺ accumulation is mediated by its interaction with inorganic polyphosphate (polyP), a polymer of orthophosphates linked by phosphoanhydride bonds. We found that cardiac mitochondria contained significant amounts (280 ± 60 pmol/mg of protein) of short-chain polyP with an average length of 25 orthophosphates. To test the role of polyP for mPTP activity, we investigated kinetics of Ca²⁺ uptake and release, ΔΨ_m and Ca²⁺-induced mPTP opening in polyP-depleted mitochondria. polyP depletion was achieved by mitochondria-targeted expression of a polyP-hydrolyzing enzyme. Depletion of polyP in mitochondria of rabbit ventricular myocytes led to significant inhibition of mPTP opening without affecting mitochondrial Ca²⁺ concentration by itself. This effect was observed when mitochondrial Ca²⁺ uptake was stimulated by increasing cytosolic [Ca²⁺] in permeabilized myocytes mimicking mitochondrial Ca²⁺ overload observed during IRI. Our findings suggest that inorganic polyP is a previously unrecognized major activator of mPTP. We propose that the adverse effect of polyphosphate might be caused by its ability to form stable complexes with Ca²⁺ and directly contribute to inner mitochondrial membrane permeabilization.

VDAC blockage by phosphorothioate oligonucleotides and its implication in apoptosis

Apoptosis is a crucial process that regulates the homeostasis of multicellular organisms. Impaired apoptosis contributes to cancer development, while enhanced apoptosis is detrimental in neurodegenerative diseases. The intrinsic apoptotic pathway is initiated by cytochrome c release from mitochondria. Research published in the recent decade has suggested that cytochrome c release can be influenced by the conducting states of VDAC, the channel in the mitochondrial outer membrane (MOM) responsible for metabolite flux. This review will describe the evidence that VDAC gating or blockage and subsequent changes in MOM permeability influence cytochrome c release and the onset of apoptosis. The blockage of VDAC by G3139, a proapoptotic phosphorothioate oligonucleotide, provides strong evidence for the role of VDAC in the initiation of apoptosis. The proapoptotic activity and VDAC blockage are linked in that both require the PS (phosphorothioate) modification, both are enhanced by an increase in oligonucleotide length, and both are insensitive to the nucleotide sequence. Thus, the mitochondrial outer membrane permeability regulated by VDAC gating may play an important role in mitochondrial function and in the control of apoptosis. This article is part of a Special Issue entitled: VDAC structure, function, and regulation of mitochondrial metabolism.