Calcium, mitochondria and apoptosis studied by fluorescence measurements

Methods to Evaluate Changes in Mitochondrial Structure and Function in Cancer

Mitochondria are regulators of key cellular processes, including energy production and redox homeostasis. Mitochondrial dysfunction is associated with various human diseases, including cancer. Importantly, both structural and functional changes can alter mitochondrial function. Morphologic and quantifiable changes in mitochondria can affect their function and contribute to disease. Structural mitochondrial changes include alterations in cristae morphology, mitochondrial DNA integrity and quantity, and dynamics, such as fission and fusion. Functional parameters related to mitochondrial biology include the production of reactive oxygen species, bioenergetic capacity, calcium retention, and membrane potential. Although these parameters can occur independently of one another, changes in mitochondrial structure and function are often interrelated. Thus, evaluating changes in both mitochondrial structure and function is crucial to understanding the molecular events involved in disease onset and progression. This review focuses on the relationship between alterations in mitochondrial structure and function and cancer, with a particular emphasis on gynecologic malignancies. Selecting methods with tractable parameters may be critical to identifying and targeting mitochondria-related therapeutic options. Methods to measure changes in mitochondrial structure and function, with the associated benefits and limitations, are summarized.

Analysis of Bacteriophage Behavior of a Human RNA Virus, SARS-CoV-2, through the Integrated Approach of Immunofluorescence Microscopy, Proteomics and D-Amino Acid Quantification

SARS-CoV-2, one of the human RNA viruses, is widely studied around the world. Significant efforts have been made to understand its molecular mechanisms of action and how it interacts with epithelial cells and the human microbiome since it has also been observed in gut microbiome bacteria. Many studies emphasize the importance of surface immunity and also that the mucosal system is critical in the interaction of the pathogen with the cells of the oral, nasal, pharyngeal, and intestinal epithelium. Recent studies have shown how bacteria in the human gut microbiome produce toxins capable of altering the classical mechanisms of interaction of viruses with surface cells. This paper presents a simple approach to highlight the initial behavior of a novel pathogen, SARS-CoV-2, on the human microbiome. The immunofluorescence microscopy technique can be combined with spectral counting performed at mass spectrometry of viral peptides in bacterial cultures, along with identification of the presence of D-amino acids within viral peptides in bacterial cultures and in patients' blood. This approach makes it possible to establish the possible expression or increase of viral RNA viruses in general and SARS-CoV-2, as discussed in this study, and to determine whether or not the microbiome is involved in the pathogenetic mechanisms of the viruses. This novel combined approach can provide information more rapidly, avoiding the biases of virological diagnosis and identifying whether a virus can interact with, bind to, and infect bacteria and epithelial cells. Understanding whether some viruses have bacteriophagic behavior allows vaccine therapies to be focused either toward certain toxins produced by bacteria in the microbiome or toward finding inert or symbiotic viral mutations with the human microbiome. This new knowledge opens a scenario on a possible future vaccine: the probiotics vaccine, engineered with the right resistance to viruses that attach to both the epithelium human surface and gut microbiome bacteria.

Calcium signaling induced by 15-deoxy-prostamide-J2 promotes cell death by activating PERK, IP3R, and the mitochondrial permeability transition pore

Melanoma is the deadliest form of skin cancer in the US. Although immunotherapeutic checkpoint inhibitors and small-molecule kinase inhibitors have dramatically increased the survival of patients with melanoma, new or optimized therapeutic approaches are still needed to improve outcomes. 15-deoxy-Δ^12,14-prostamide J₂ (15d-PMJ₂) is an investigational small-molecule that induces ER stress-mediated apoptosis selectively in tumor cells. Additionally, 15d-PMJ2 reduces melanoma growth in vivo. To assess the chemotherapeutic potential of 15d-PMJ₂, the current study sought to uncover molecular pathways by which 15d-PMJ₂ exerts its antitumor activity. B16F10 melanoma and JWF2 squamous cell carcinoma cell lines were cultured in the presence of pharmacological agents that prevent ER or oxidative stress as well as Ca²⁺ channel blockers to identify mechanisms of 15d-PMJ₂ cell death. Our data demonstrated the ER stress protein, PERK, was required for 15d-PMJ₂-induced death. PERK activation triggered the release of ER-resident Ca²⁺ through an IP₃R sensitive pathway. Increased calcium mobilization led to mitochondrial Ca²⁺ overload followed by mitochondrial permeability transition pore (mPTP) opening and the deterioration of mitochondrial respiration. Finally, we show the electrophilic double bond located within the cyclopentenone ring of 15d-PMJ₂ was required for its activity. The present study identifies PERK/IP3R/mPTP signaling as a mechanism of 15d-PMJ₂ antitumor activity.

Mitochondria modulate ameloblast Ca2+ signaling

The role of mitochondria in enamel, the most mineralized tissue in the body, is poorly defined. Enamel is formed by ameloblast cells in two main sequential stages known as secretory and maturation. Defining the physiological features of each stage is essential to understand mineralization. Here, we analyzed functional features of mitochondria in rat primary secretory and maturation-stage ameloblasts focusing on their role in Ca²⁺ signaling. Quantification of the Ca²⁺ stored in the mitochondria by trifluoromethoxy carbonylcyanide phenylhydrazone stimulation was comparable in both stages. The release of endoplasmic reticulum Ca²⁺ pools by adenosine triphosphate in rhod2AM-loaded cells showed similar mitochondrial Ca²⁺ (_m Ca²⁺ ) uptake. However, _m Ca²⁺ extrusion via Na⁺ -Li⁺ -Ca²⁺ exchanger was more prominent in maturation. To address if _m Ca²⁺ uptake via the mitochondrial Ca²⁺ uniporter (MCU) played a role in cytosolic Ca²⁺ (_c Ca²⁺ ) buffering, we stimulated Ca²⁺ influx via the store-operated Ca²⁺ entry (SOCE) and blocked MCU with the inhibitor Ru265. This inhibitor was first tested using the enamel cell line LS8 cells. Ru265 prevented _c Ca²⁺ clearance in permeabilized LS8 cells like ruthenium red, and it did not affect ΔΨm in intact cells. In primary ameloblasts, SOCE stimulation elicited a significantly higher _m Ca²⁺ uptake in maturation ameloblasts. The uptake of Ca²⁺ into the mitochondria was dramatically decreased in the presence of Ru265. Combined, these results suggest an increased mitochondrial Ca²⁺ handling in maturation but only upon stimulation of Ca²⁺ influx via SOCE. These functional studies provide insights not only on the role of mitochondria in ameloblast Ca²⁺ physiology, but also advance the concept that SOCE and _m Ca²⁺ uptake are complementary processes in biological mineralization.

In Vitro Study of Calcium Microsecond Electroporation of Prostate Adenocarcinoma Cells

Electroporation, applied as a non-thermal ablation method has proven to be effective for focal prostate treatment. In this study, we performed pre-clinical research, which aims at exploring the specific impact of this so-called calcium electroporation on prostate cancer. First, in an in-vitro study of DU 145 cell lines, microsecond electroporation (μsEP) parameters were optimized. We determined hence the voltage that provides both high permeability and viability of these prostate cancer cells. Subsequently, we compared the effect of μsEP on cells' viability with and without calcium administration. For high-voltage pulses, the cell death's mechanism was evaluated using flow-cytometry and confocal laser microscopy. For lower-voltage pulses, the influence of electroporation on prostate cancer cell mobility was studied using scratch assays. Additionally, we applied calcium-binding fluorescence dye (Fluo-8) to observe the calcium uptake dynamic with the fluorescence microscopy. Moreover, the molecular dynamics simulation visualized the process of calcium ions inflow during μsEP. According to our results calcium electroporation significantly decreases the cells viability by promoting apoptosis. Furthermore, our data shows that the application of pulsed electric fields disassembles the actin cytoskeleton and influences the prostate cancer cells' mobility.

In vitro cytotoxicity studies of smart pH-sensitive lamivudine-loaded CaAl-LDH magnetic nanoparticles against Mel-Rm and A-549 cancer cells

In this study, an effective nano-drug delivery system was prepared by the co-precipitation method via two steps; the preparation of Fe₃O₄ magnetic nanoparticles and its surface modification with layered double hydroxide (LDH) and loading lamivudine on this nanocarrier (Fe₃O₄@CaAl-LDH@Lamivudine). The developed nanoparticles (NPs) were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray analysis, Fourier-transformed infrared spectroscopy, vibrating-sample magnetometry, thermogravimetric analysis, X-ray photoelectron spectroscopy and Brunauer-Emmett-Teller. The prepared system demonstrated an average size of 130 nm. Also, the drug entrapment efficiency was estimated at ∼70%. In vitro, drug release investigations showed a controlled and pH-dependent lamivudine release over 300 min. The in vitro cytotoxic activity of Fe₃O₄@CaAl-LDH@Lamivudine NPs was explored against Mel-Rm and A-549 cancer cell lines in comparison with lamivudine and nanocarrier using lactate dehydrogenase colorimetric and MTT assay. The results of the MTT assay revealed that the Fe₃O₄@CaAl-LDH@Lamivudine NPs significantly inhibited the proliferation of Mel-Rm and A-549 cells in a dose-dependent manner. The influences of Fe₃O₄@CaAl-LDH@Lamivudine on the cancer cell lines by different therapeutic investigation illustrated the remarkable effect in comparison with free drug. Finally, the achieved consequences confirm the anticancer properties of Fe₃O₄@CaAl-LDH@Lamivudine and indicate that they may be a cost-effective substitute in the treatment of lung and skin cancer.Communicated by Ramaswamy H. Sarma.

Polycystin 2 regulates mitochondrial Ca2+ signaling, bioenergetics, and dynamics through mitofusin 2

Mitochondria and the endoplasmic reticulum (ER) have an intimate functional relationship due to tethering proteins that bring their membranes in close (~30 nm) apposition. One function of this interorganellar junction is to increase the efficiency of Ca²⁺ transfer into mitochondria, thus stimulating mitochondrial respiration. Here, we showed that the ER cation-permeant channel polycystin 2 (PC2) functions to reduce mitochondria-ER contacts. In cell culture models, PC2 knockdown led to a 50% increase in mitofusin 2 (MFN2) expression, an outer mitochondrial membrane GTPase. Live-cell super-resolution and electron microscopy analyses revealed enhanced MFN2-dependent tethering between the ER and mitochondria in PC2 knockdown cells. PC2 knockdown also led to increased ER-mediated mitochondrial Ca²⁺ signaling, bioenergetic activation, and mitochondrial density. Mutation or deletion of the gene encoding for PC2 results in autosomal dominant polycystic kidney disease (ADPKD), a condition characterized by numerous fluid-filled cysts. In cell culture models and mice with kidney-specific PC2 knockout, knockdown of MFN2 rescued defective mitochondrial Ca²⁺ transfer and diminished cell proliferation in kidney cysts. Consistent with these results, cyst-lining epithelial cells from human ADPKD kidneys had a twofold increase in mitochondria and MFN2 expression. Our data suggest that PC2 normally serves to limit key mitochondrial proteins at the ER-mitochondrial interface and acts as a checkpoint for mitochondrial biogenesis and bioenergetics. Loss of this regulation may contribute to the increased oxidative metabolism and aberrant cell proliferation typical of kidney cysts in ADPKD.

Activation of Ca2+-sensing receptor as a protective pathway to reduce Cadmium-induced cytotoxicity in renal proximal tubular cells

Cadmium (Cd), as an extremely toxic metal could accumulate in kidney and induce renal injury. Previous studies have proved that Cd impact on renal cell proliferation, autophagy and apoptosis, but the detoxification drugs and the functional mechanism are still in study. In this study, we used mouse renal tubular epithelial cells (mRTECs) to clarify Cd-induced toxicity and signaling pathways. Moreover, we proposed to elucidate the prevent effect of activation of Ca²⁺ sensing receptor (CaSR) by Calcimimetic (R-467) on Cd-induced cytotoxicity and underlying mechanisms. Cd induced intracellular Ca²⁺ elevation through phospholipase C-inositol 1, 4, 5-trisphosphate (PLC) followed stimulating p38 mitogen-activated protein kinases (MAPK) activation and suppressing extracellular signal-regulated kinase (ERK) activation, which leaded to increase apoptotic cell death and inhibit cell proliferation. Cd induced p38 activation also contribute to autophagic flux inhibition that aggravated Cd induced apoptosis. R-467 reinstated Cd-induced elevation of intracellular Ca²⁺ and apoptosis, and it also increased cell proliferation and restored autophagic flux by switching p38 to ERK pathway. The identification of the activation of CaSR-mediated protective pathway in renal cells sheds light on a possible cellular protective mechanism against Cd-induced kidney injury.

Ultraviolet-Ray-Induced Sea Cucumber (Stichopus japonicus) Melting Is Mediated by the Caspase-Dependent Mitochondrial Apoptotic Pathway

Sea cucumber body-wall melting occurs under certain circumstances. We have shown that apoptosis but not autolysis plays a critical role in the initial stage. However, it is still unclear how apoptosis is triggered in this process. In this study, we examined the levels of reactive oxygen species (ROS), the levels of B-cell lymphoma 2 (Bcl-2) and Bcl-2-associated X (Bax) proteins, the depolarization of mitochondrial transmembrane potentials, and cytochrome c (Cyt c) release during sea cucumber melting induced by ultraviolet (UV) exposure. We also investigated the contribution of caspase in this process by injecting a pan-caspase inhibitor. Our data showed that UV exposure stimulates ROS production, dysfunction of mitochondria, and the release of Cyt c in sea cucumber coelomic fluid cells and body walls. We found a decrease of Bcl-2 and increase of Bax in the mitochondria after UV exposure. We also demonstrated that these changes are associated with elevated caspase-9 and -3 activity. Finally, our data showed that the inhibition of caspases-9 and -3 using an inhibitor suppresses UV-induced sea cucumber melting. These results suggest that apoptosis during sea cucumber melting is mediated by mitochondrial dysfunction and follows the activation of the caspase-signaling pathway. This study presents a novel insight into the mechanism of sea cucumber melting.

In vitro characterization of alkylaminophenols-induced cell death

Alkylaminophenols are synthetic derivatives well known for their anticancer activity. In the previous studies, we described the activity of the series of Alkylaminophenols derivatives and their ability to induce cell death for many cancer cell lines. However, temporal heterogeneity in cell death induced by lead compounds, N-(2-hydroxy-5-nitrophenyl (4'-methylphenyl) methyl) indoline (Compound I) and 2-((3,4-dihydroquinolin-1(2H)-yl) (4-methoxyphenyl) methyl) phenol (Compound II), has never been tested on osteosarcoma cells (U2OS). Here, we address the level of cell-to-cell heterogeneity by examine whether differences in the type of compounds could influence its effects on cell death of U2OS. Here, we applied imaging, computational methods and biochemical methods to study heterogeneity, apoptosis, reactive oxygen species and caspase. Our results demonstrate that the Hill coefficient of dose-response curve of Compound II is greater than compound I in treated U2OS cells. Both Compounds trigger not only apoptotic cell death but also necro-apoptotic and necrotic cell death. The percentage of these sub-populations varies depending on compounds in which greater variance is induced by compound II than Compound I. We also identified the accumulation of compounds-induced reactive oxygen species during the treatment. This resulted in caspase 3/7 activation in turn induced apoptosis. In summary, the screening of Compound I and II molecules for heterogeneity, apoptosis, reactive oxygen species and caspase has identified compound II as promising anti-osteosarcoma cancer agent. Compound II could be a promising lead compound for future antitumor agent development.

Calcium efflux from the endoplasmic reticulum regulates cisplatin-induced apoptosis in human cervical cancer HeLa cells

The function of calcium efflux from the endoplasmic reticulum (ER) in cisplatin-induced apoptosis is not fully understood in cancer cells. The present study used western blot analysis, flow cytometry, immunofluorescence and 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide assay to investigate calcium signaling in human cervical cancer cells exposed to cisplatin. In the present study, treatment with cisplatin increased free Ca²⁺ levels in the cytoplasm and mitochondria of human cervical cancer HeLa cells, which further triggers the mitochondria-mediated and ER stress-associated apoptosis pathways. Notably, blocking calcium signaling using the calcium chelating agent bis-(o-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid acetoxymethyl ester inhibited cisplatin-induced apoptosis via downregulation of the calcium-dependent proteases, the calpains, and innate apoptosis proteins, such as caspsae-3, caspase-4 and C/EBP homologous protein (CHOP). In addition, use of the inositol triphosphate receptor inhibitor, 2-aminoethyl diphenylborinate, to inhibit calcium efflux from the ER resulted in similar effects. This data indicated that calcium efflux from the ER plays a significant role in cisplatin-induced apoptosis in human cervical cancer HeLa cells, which provides further mechanistic insights into the tumor cell-killing effect of cisplatin and potential therapeutic strategies to improve cisplatin chemotherapy.

Calcium homeostasis in mitochondrion-mediated apoptosis of chick embryo cecal epithelial cells induced by Eimeria tenella infection

In this study, the process of Eimeria tenella-induced apoptosis and the effect of calcium homeostasis were investigated in chick embryo cecal epithelial cells. In particular, we examined cytochrome c release into the cytoplasm, mitochondrial permeability transition pore (MPTP) opening, and changes in [Ca(2+)]c and apoptosis in host cells. Apoptosis, MPTP opening, cytochrome c release, and [Ca(2+)]c in host cells increased following infection. This trend was reversed by blocking the increase in [Ca(2+)]c using BAPTA/AM and EGTA (intra- and extracellular chelators of Ca(2+), respectively) and by applying heparin sodium and ryanodine (blockers of the inositol triphosphate and ryanodine receptors of the endoplasmic reticulum, respectively). These results indicate that [Ca(2+)]c plays a significant role in host cell mitochondrial apoptosis, which is induced via modulation of extracellular Ca(2+) levels and endoplasmic reticulum Ca(2+) channels. Thus, agents that restore Ca(2+) homeostasis may be useful for managing E. tenella infection in chickens.

Necrostatin-1 mitigates mitochondrial dysfunction post-spinal cord injury

Necrostatin-1 (Nec-1) is an inhibitor of necroptosis, playing an important role in inhibition of pathological death in the central nervous system (CNS). Our earlier study suggests that Nec-1 protects the injured spinal cord. In this study, we found that Nec-1 reduces the elevated Ca(2+) concentration in mitochondria post-injury and preserves the remarkably decreased mitochondrial membrane potential (MMP) level post-spinal cord injury (SCI). It also increases the generation of adenosine triphosphate (ATP) by promoting the activity of mitochondrial respiratory chain complex I instead of other complexes, which are significantly decreased due to the injury. Nec-1 also inhibits the release of cytochrome c in the mitochondria and protects the spinal cord from mitochondrial swelling post-SCI. Nec-1 promotes mitochondrial biogenesis by up-regulating mitochondrial transcription factor A (Tfam), in accordance with the mtDNA content. It also inhibits the up-regulation of mitochondrial fusion genes Mnf1, Mnf2 within 6h post-injury and adjusts the abnormal expression of mitochondrial fission gene Fis1. All these results indicate the improvement of mitochondrial functions in injured spinal cord after the treatment of Nec-1. This research revealed the mechanisms of functional protection of Nec-1 by mitigating mitochondrial dysfunction post-SCI.

A polysaccharide from Sanguisorbae radix induces caspase-dependent apoptosis in human leukemia HL-60 cells

One polysaccharide (SRP) was purified from Sanguisorbae radix by DEAE-cellulose-52 anion-exchange and Sephacryl S-400 gel filtration chromatography. The aim of this study was to evaluate the anticancer efficacy of SRP on human leukemia HL-60 cells in vitro and unveil the underlying mechanisms. Our results showed that SRP was able to suppress the proliferation of HL-60 cells in a dose-dependent manner by the mechanism involved in the induction of apoptosis. The increase in SRP-induced apoptosis was correlated with a rapid and sustained loss of mitochondrial transmembrane potential (ΔΨm) and a release of cytochrome c from the mitochondria into the cytosol. Furthermore, Western blot and RT-PCR analysis revealed that the protein and mRNA levels of antiapoptotic Bcl-2 were downregulated, whereas those of pro-apoptotic Bax were upregulated. Besides, caspase-9 and caspase-3 were activated, while caspase-8 was intact. Additionally, the apoptotic cells by SRP were significantly inhibited by a caspase-3 inhibitor (z-DEVD-fmk) or a caspase-9 inhibitor (Z-LETD-FMK), demonstrating the important role of caspase-9 and -3 in the process. Taken together, these findings provided evidence that SRP induced the apoptosis of HL-60 cells through an intrinsic mitochondria-mediated signaling pathway and SRP may be a promising chemotherapeutic agent for treatment of leukemia.

Real-time single-cell imaging of protein secretion

Protein secretion, a key intercellular event for transducing cellular signals, is thought to be strictly regulated. However, secretion dynamics at the single-cell level have not yet been clarified because intercellular heterogeneity results in an averaging response from the bulk cell population. To address this issue, we developed a novel assay platform for real-time imaging of protein secretion at single-cell resolution by a sandwich immunoassay monitored by total internal reflection microscopy in sub-nanolitre-sized microwell arrays. Real-time secretion imaging on the platform at 1-min time intervals allowed successful detection of the heterogeneous onset time of nonclassical IL-1β secretion from monocytes after external stimulation. The platform also helped in elucidating the chronological relationship between loss of membrane integrity and IL-1β secretion. The study results indicate that this unique monitoring platform will serve as a new and powerful tool for analysing protein secretion dynamics with simultaneous monitoring of intracellular events by live-cell imaging.

A degenerative retinal process in HIV-associated non-infectious retinopathy

HIV retinopathy is the most common non-infectious complication in the eyes of HIV-positive individuals. Oncotic lesions in the retinal nerve fiber layer, referred to as cotton wool spots (CWS), and intraretinal (IR) hemorrhages are frequently observed but are not unique to this pathology. HIV-positive patients have impaired color vision and contrast sensitivity, which worsens with age. Evidence of inner-retinal lesions and damage have been documented ophthalmoscopically, however their long term structural effect has not been investigated. It has been hypothesized that they may be partially responsible for loss of visual function and visual field. In this study we utilized clinical data, retinal imaging and transcriptomics approaches to comprehensively interrogate non-infectious HIV retinopathy. The methods employed encompassed clinical examinations, fundus photography, indirect ophthalmoscopy, Farmsworth-Munsell 100 hue discrimination testing and Illumina BeadChip analyses. Here we show that changes in the outer retina, specifically in the retinal pigment epithelium (RPE) and photoreceptor outer segments (POS) contribute to vision changes in non-infectious HIV retinopathy. We find that in HIV-positive retinae there is an induction of rhodopsin and other transcripts (including PDE6A, PDE6B, PDE6G, CNGA1, CNGB1, CRX, NRL) involved in visual transduction, as well as structural components of the rod photoreceptors (ABCA4 and ROM1). This is consistent with an increased rate of renewal of rod outer segments induced via increased phagocytosis by HIV-infected RPE previously reported in culture. Cone-specific transcripts (OPN1SW, OPN1LW, PDE6C, PDE6H and GRK7) are uniformly downregulated in HIV positive retina, likely due to a partial loss of cone photoreceptors. Active cotton wool spots and intraretinal hemorrhages (IRH) may not affect photoreceptors directly and the interaction of photoreceptors with the aging RPE may be the key to the progressive vision changes in HIV-positive patients.

Cell wall degradation and the dynamic changes of Ca2+ and related enzymes in the developing aerenchyma of wheat (Triticum aestivum L.) under waterlogging

This research was aimed to study the cell wall degradation and the dynamic changes of Ca2+ and related enzymes in developing aerenchyma of wheat root under waterlogging. An examination of morphological development by light and electron microscope revealed that the structure of cell wall in middle cortical cells remained intact after 12 h of waterlogging and turned thinner after waterlogging for 24 h. At 48 h, the aerenchyma has been formed. The cellulase activity gradually increased in middle cortical cells within 24 h of waterlogging, and decreased with the formation of aerenchyma. Fluorescence detection and subcellular localization of Ca2+ showed the dynamic changing of Ca2+ at the cellular and subcellular levels during the development of aerenchyma. The activity of Ca2+-ATPase enhanced markedly in intercellular space, plasma membrane and tonoplast of some middle cortical cells after 8 h of waterlogging and remained high after 24 h, but it decreased after 48 h of waterlogging. All these suggests that cellulase, Ca2+ and Ca2+-ATPase show a dynamic distribution during the aerenchyma development which associated with the cell wall degradation of middle cortical cells. Moreover, there is a feedback regulation between Ca2+ and Ca2+-ATPase.

High temporal resolution fluorescence measurements of a mitochondrial dye for detection of early stage apoptosis

In the present study, early stage apoptosis is explored with high temporal resolution. In addition to monitoring early apoptosis induction in single cells by ultrasensitive confocal fluorescence microscopy (UCFM), the mitochondrial protein release kinetics was explored. The current study shows development and optimization of a novel, rapid apoptosis assay to explore the earliest changes in cells by the intrinsic apoptosis pathway. We show that early apoptotic changes in the mitochondria begin nearly simultaneously with the addition of an apoptosis-inducing drug, such as staurosporine. With a temporal resolution of five minutes, this non-invasive analytical technique can elucidate the earliest apoptotic events in living cells. Moreover, our results show that the mitochondrial inter-membrane proteins are not involved in the extrinsic pathway of Ramos cells mediated by an anti-CD95 antibody. Additional techniques such as light microscopy and flow cytometry were employed to confirm the results obtained by ultrasensitive confocal fluorescence microscopy. The results of this study help to understand the earliest mechanisms of apoptosis induction in cells, enabling new methods of drug testing and dose-response analyses.

Membrane associated complexes in calcium dynamics modelling

Mitochondria not only govern energy production, but are also involved in crucial cellular signalling processes. They are one of the most important organelles determining the Ca(2+) regulatory pathway in the cell. Several mathematical models explaining these mechanisms were constructed, but only few of them describe interplay between calcium concentrations in endoplasmic reticulum (ER), cytoplasm and mitochondria. Experiments measuring calcium concentrations in mitochondria and ER suggested the existence of cytosolic microdomains with locally elevated calcium concentration in the nearest vicinity of the outer mitochondrial membrane. These intermediate physical connections between ER and mitochondria are called MAM (mitochondria-associated ER membrane) complexes. We propose a model with a direct calcium flow from ER to mitochondria, which may be justified by the existence of MAMs, and perform detailed numerical analysis of the effect of this flow on the type and shape of calcium oscillations. The model is partially based on the Marhl et al model. We have numerically found that the stable oscillations exist for a considerable set of parameter values. However, for some parameter sets the oscillations disappear and the trajectories of the model tend to a steady state with very high calcium level in mitochondria. This can be interpreted as an early step in an apoptotic pathway.

Mitochondria and heart disease

Mitochondria play a key role in the normal functioning of the heart, and in the pathogenesis and development of various types of heart disease. Physiologically, mitochondrial ATP supply needs to be matched to the often sudden changes in ATP demand of the heart, and this is mediated to a large extent by the mitochondrial Ca(2+) transport pathways allowing elevation of mitochondrial [Ca(2+)] ([Ca(2+)](m)). In turn this activates dehydrogenase enzymes to increase NADH and hence ATP supply. Pathologically, [Ca(2+)](m) is also important in generation of reactive oxygen species, and in opening of the mitochondrial permeability transition pore (MPTP); factors involved in both ischaemia-reperfusion injury and in heart failure. The MPTP has proved a promising target for protective strategies, with inhibitors widely used to show cardioprotection in experimental, and very recently human, studies. Similarly mitochondrially-targeted antioxidants have proved protective in various animal models of disease and await clinical trials. The mitochondrial Ca(2+) transport pathways, although in theory promising therapeutic targets, cannot yet be targeted in human studies due to non-specific effects of drugs used experimentally to inhibit them. Finally, specific mitochondrial cardiomyopathies due to mutations in mtDNA have been identified, usually in a gene for a tRNA, which, although rare, are almost always very severe once the mutation has exceeded its threshold.

Calcium overload is associated with lipofuscin formation in human retinal pigment epithelial cells fed with photoreceptor outer segments

PURPOSE

To investigate the role of Ca²(+) in lipofuscin formation in human retinal pigment epithelial (RPE) cells that phagocytize bovine photoreceptor outer segments (POSs).

METHODS

Cultured human RPE cells fed with 2 × 10⁷per l bovine POS were treated with flunarizine, an antagonist of Ca²(+) channel, or/and centrophenoxine, a lipofuscin scavenger. The Ca²(+) changes and lipofuscin formation were measured with fluoresence dye Fluo-3/AM ester, laser scanning confocal microscopy (LSCM) and flow cytometry (FCM). The activity of RPE cells was measured by methyl thiazolyl tetrazolium (MTT) assay and argyrophilic nucleolar organizer regions (AgNORs) assay.

RESULTS

The Ca²(+) fluorescence intensity (CFI) of RPE cells fed with POS was significantly increased compared with the controls (165.36 ± 29.92 U). It reached a peak with 777.33 ± 63.86 U (P<0.01) at 12 h, and then decreased but still maintained a high level of 316.90 ± 36.07 U (P<0.01) for 4 days. Flunarizine and centrophenoxine significantly decreased the Ca²(+) overload to 227.18 ± 14.00 U at 12 h and 211.06 ± 20.45 U at 4 days. FCM confirmed these changes. The drugs also showed an inhibitory effect on the lipofuscin formation. The proliferation rate of the cells fed with POS increased significantly. Both drugs had inhibitory effects on the activity of the cultured cells. This tendency was confirmed by AgNORs assay.

CONCLUSIONS

The Ca²(+) inflow initiated lipofuscin accumulation in RPE cells fed with POS. Flunarizine and centrophenoxine can decrease Ca²(+) overload and lipofuscin formation in RPE cells, accompanied by maintaining cellular vitality.

Quantitative analysis of intracellular calcium and mitochondrial kinetic fluorescence changes in GSNO-induced thymocyte early apoptosis

A fluorescence microscopy imaging technique was applied to observe the single-cell kinetic changes of intracellular Ca(2+) concentration ([Ca(2+)](i)) and mitochondrial membrane potential (ΔΨ(m)) during the early stage of S-nitrosoglutathione (GSNO)-induced thymocytes apoptosis. The kinetic features of [Ca(2+)](i) and ΔΨ(m) were quantitatively analyzed and compared by fitting the fluorescence intensity data. The mathematical parameter, inflection point which indicated the time point when [Ca(2+)](i) or ΔΨ(m) changed the most rapidly, was proposed to analyze the fitting curve. The results revealed that the inflection point of [Ca(2+)](i) always appeared prior to that of ΔΨ(m) during apoptosis induced by a certain GSNO concentration. Both the [Ca(2+)](i) and ΔΨ(m) changed in a GSNO concentration-dependent manner. Another parameter, half-max effect point was also employed and displayed the similar results. Such quantitative analyses of real-time observations at the single-cell level are useful for interpreting the sequence of the biological events operating in GSNO-induced thymocyte apoptosis.

Screening for calcium channel modulators in CLN3 siRNA knock down SH-SY5Y neuroblastoma cells reveals a significant decrease of intracellular calcium levels by selected L-type calcium channel blockers

BACKGROUND

Defects of the CLN3 gene on chromosome 16p12.1 lead to the juvenile form of neuronal ceroid-lipofuscinosis (JNCL, Batten Disease), the most common recessive inherited neurodegenerative disorder in children. Dysregulation of intracellular calcium homeostasis in the absence of a functional CLN3 protein (CLN3P, Battenin) has been linked to synaptic dysfunction and accelerated apoptosis in vulnerable neuronal cells. Prolonged increase of intracellular calcium concentration is considered to be a significant trigger for neuronal apoptosis and cellular loss in JNCL.

METHODS

We examined the potential effect of 41 different calcium channel modulators on intracellular calcium concentration in CLN3 siRNA knock down SH-SY5Y neuroblastoma cells.

RESULTS

Six drugs belonging to the group of voltage dependent L-type channel blockers show significant lowering of the increased intracellular calcium levels in CLN3 siRNA knock down cells.

CONCLUSIONS

Our studies provide important new data suggesting possible beneficial effects of the tested drugs on calcium flux regulated pathways in neuronal cell death. Therapeutic intervention in this untreatable disease will likely require drugs that cross the blood-brain barrier as did all of the positively screened drugs in this study.

GENERAL SIGNIFICANCE

Better comprehension of the mechanism of neurodegeneration in rare recessive disorders, such as neuronal ceroid-lipofuscinoses, is likely to help to better understand mechanisms involved in more complex genetic neurodegenerative conditions, such as those associated with aging.

Ca2+ overload and mitochondrial permeability transition pore activation in living delta-sarcoglycan-deficient cardiomyocytes

Muscular dystrophies are often associated with significant cardiac disease that can be the prominent feature associated with gene mutations in sarcoglycan. Cardiac cell death is a main feature of cardiomyopathy in sarcoglycan deficiency and may arise as a cardiomyocyte intrinsic process that remains unclear. Deficiency of delta-sarcoglycan (delta-SG) induces disruption of the dystrophin-associated glycoprotein complex, a known cause of membrane instability that may explain cardiomyocytes cytosolic Ca2+ increase. In this study we assessed the hypothesis that cytosolic Ca2+ increase triggers cardiomyocyte death through mitochondrial Ca2+ overload and dysfunction in the delta-SG-deficient CHF147 hamster. We showed that virtually all isolated CHF147 ventricular myocytes exhibited elevated cytosolic and mitochondrial Ca2+ levels by the use of the Fura-2 and Rhod-2 fluorescent probes. Observation of living cells with Mito-Tracker red lead to the conclusion that approximately 15% of isolated CHF147 cardiomyocytes had disorganized mitochondria. Transmission electron microscope imaging showed mitochondrial swelling associated with crest and membrane disruption. Analysis of the mitochondrial permeability transition pore (MPTP) activity using calcein revealed that mitochondria of CHF147 ventricular cells were twofold leakier than wild types, whereas reactive oxygen species production was unchanged. Bax, Bcl-2, and LC3 expression analysis by Western blot indicated that the intrinsic apoptosis and the cell death associated to autophagy pathways were not significantly activated in CHF147 hearts. Our results lead to conclusion that cardiomyocytes death in delta-SG-deficient animals is an intrinsic phenomenon, likely related to Ca2+-induced necrosis. In this process Ca2+ overload-induced MPTP activation and mitochondrial disorganization may have an important role.

Mitochondrial Ca2+ channels: Great unknowns with important functions

Mitochondria process local and global Ca(2+) signals. Thereby the spatiotemporal patterns of mitochondrial Ca(2+) signals determine whether the metabolism of these organelles is adjusted or cell death is executed. Mitochondrial Ca(2+) channels of the inner mitochondrial membrane (IMM) actually implement mitochondrial uptake from cytosolic Ca(2+) rises. Despite great efforts in the past, the identity of mitochondrial Ca(2+) channels is still elusive. Numerous studies aimed to characterize mitochondrial Ca(2+) uniport channels and provided a detailed profile of these great unknowns with important functions. This mini-review revisits previous research on the mechanisms of mitochondrial Ca(2+) uptake and aligns them with most recent findings.

Can Drug Safety be Predicted and Animal Experiments Reduced by Using Isolated Mitochondrial Fractions?

Mitochondrial toxicity has resulted in the withdrawal of several drugs from the market. One particular example is nefazodone, an anti-depressant withdrawn in the USA due to hepatoxicity caused by drug-induced mitochondrial dysfunction. Drug development and safety testing can involve the use of large numbers of laboratory animals, which, without a decisive pre-screening for mitochondrial toxicity, are often unable to pre-empt higher mortality rates in some patient groups. The use of isolated mitochondria as a screening tool for drug safety can decrease the number of laboratory animals used in pre-clinical studies, thus improving animal welfare and healthcare outcomes and costs. Novel techniques involving high-throughput methods can be used to investigate whether a molecule is a mitochondrial toxicant. Moreover, these screens are mechanistically-based, since the effects of the drug on oxidative phosphorylation, calcium homeostasis and mitochondrial genetics can be assessed. This review is intended to demonstrate that isolated mitochondrial fractions are suitable for predicting drug and general chemical safety in toxicological screenings, thus contributing to the refinement and reduction of animal use in laboratory research.

Mitochondrial calcium as a key regulator of mitochondrial ATP production in mammalian cells

Mitochondrial Ca(2+) transport was initially considered important only in buffering of cytosolic Ca(2+) by acting as a "sink" under conditions of Ca(2+) overload. The main regulator of ATP production was considered to be the relative concentrations of high energy phosphates. However, work by Denton and McCormack in the 1970s and 1980s showed that free intramitochondrial Ca(2+) ([Ca(2+)](m)) activated dehydrogenase enzymes in mitochondria, leading to increased NADH and hence ATP production. This leads them to propose a scheme, subsequently termed a "parallel activation model" whereby increases in energy demand, such as hormonal stimulation or increased workload in muscle, produced an increase in cytosolic [Ca(2+)] that was relayed by the mitochondrial Ca(2+) transporters into the matrix to give an increase in [Ca(2+)](m). This then stimulated energy production to meet the increased energy demand. With the development of methods for measuring [Ca(2+)](m) in living cells that proved [Ca(2+)](m) changed over a dynamic physiological range rather than simply soaking up excess cytosolic [Ca(2+)], this model has now gained widespread acceptance. However, work by ourselves and others using targeted probes to measure changes in both [Ca(2+)] and [ATP] in different cell compartments has revealed variations in the interrelationships between these two in different tissues, suggesting that metabolic regulation by Ca(2+) is finely tuned to the demands and function of the individual organ.