Mitochondria as playmakers of apoptosis, autophagy and senescence

Growth factor stimulation and oncogenic transformation lead to increased glucose metabolism that may provide resistance to cell death. We have previously demonstrated that elevated glucose metabolism characteristic of stimulated or cancerous cells can stabilize the anti-apoptotic Bcl-2 family protein Mcl-1 through inhibition of GSK-3. Here we show that the pro-apoptotic Bcl-2 family protein, Puma, is also metabolically regulated. Growth factor deprivation led to the loss of glucose uptake and induction of Puma. Maintenance of glucose uptake after growth factor withdrawal by expression of the glucose transporter, Glut1, however, suppressed Puma up-regulation and attenuated growth factor withdrawal-induced activation of Bax, DNA fragmentation, and cell death. Conversely, glucose deprivation led to Puma induction even in the presence of growth factor. This regulation of Puma expression was a central component in cell death as a consequence of growth factor or glucose deprivation because Puma deficiency suppressed both of these cell death pathways. Puma induction in growth factor or glucose withdrawal was dependent on p53 in cell lines and in activated primary T lymphocytes because p53 deficiency suppressed Puma induction and delayed Bax and caspase activation, DNA fragmentation, and loss of clonogenic survival. Importantly, although p53 levels did not change or were slightly reduced, p53 activity was suppressed by elevated glucose metabolism to inhibit Puma induction after growth factor withdrawal. These data show that p53 is metabolically regulated and that glucose metabolism initiates a signaling mechanism to inhibit p53 activation and suppress Puma induction, thus promoting an anti-apoptotic balance to Bcl-2 family protein expression that supports cell survival.

Myocardial structural remodeling, a progressive, often self-perpetuating process, is an important marker of progressive heart failure. Myocardial cell loss, through any number of mechanisms mediating cellular death, is an important component in its genesis.1 Traditionally, necrosis has been regarded as the pathological hallmark of myocardial cell death. However, there is accumulating evidence that cells can die through a number of other mechanisms including programmed and nonprogrammed cell death. The elegant study in this issue of Circulation Research by Kostin and colleagues2 makes an important addition to the list of intriguing ways that life or death decisions are made in the failing heart. They found that in addition to apoptosis and necrosis,R3-128044 3,4 cardiac cells can also die through autophagy associated with ubiquitylated protein accumulation. Apart from mechanistic insights, these kinds of new data might have a therapeutic potential. A broad look at cell survival or death and its implications may thus be in order. Traditionally, distinct types of cell death have been identified based on morphological characteristics.4 Cells were considered to have died due to necrosis if there were severe disruption of cellular membranes and cell contents. Apoptosis was thought to involve a genetically programmed cell death with preserved cell boundary and minimal inflammatory response. Other forms of cell death, with a less clear morphology or mechanism, were then identified including lysosome- or proteosome-mediated cell death. These distinctions were reinforced when reproducible mechanisms were found to underlie the different morphologies of cell death. This classification also offered the promise that therapeutic strategies could be designed to selectively influence some of these pathogenetic mechanisms. A number of findings have raised the possibility that various forms of death may be a part of the same spectrum. For one, multiple morphologies of cell death may coexist in the same microscopic …

The process of autophagy is situated at the intersection of multiple cell signaling pathways, including cell metabolism, growth, and death, and hence is subject to multiple forms of regulation. We previously reported that inhibition of isoprenylcysteine carboxylmethyltransferase (Icmt), which catalyzes the final step in the post-translational prenylation of so-called CAAX proteins, results in the induction of autophagy which enhances cell death in some cancer cells. In this study, using siRNA-mediated knockdown of a group of small GTPases that are predicted Icmt substrates, we identify Rac3 GTPase as a negative regulator of the process of autophagy. Knockdown of Rac3, but not the closely related isoforms Rac1 and Rac2, results in induction of autophagy. Ectopic expression of Rac3, significantly rescues cells from autophagy and cell death induced by Icmt inhibition, strengthening the notion of an isoform-specific autophagy regulatory function of Rac3. This role of Rac3 was observed in multiple cell lines with varying Rac subtype expression profiles, suggesting its broad involvement in the process. The identification of this less-studied Rac member as a novel regulator provides new insight into autophagy and opens opportunities in identifying additional regulatory inputs of the process.

Transgenic mice expressing high levels of the BclxL or Bcl2 proteins in the male germinal cells show a highly abnormal adult spermatogenesis accompanied by sterility. This appears to result from the prevention of an early and massive wave of apoptosis in the testis, which occurs among germinal cells during the first round of spermatogenesis. In contrast, sporadic apoptosis among spermatogonia, which occurs in normal adult testis, is not prevented in adult transgenic mice. The physiological early apoptotic wave in the testis is coincident, in timing and localization, with a temporary high expression of the apoptosis-promoting protein Bax, which disappears at sexual maturity. The critical role played by the intracellular balance, probably hormonally controlled, of the BclxL and Bax proteins (Bcl2 is apparently not expressed in normal mouse testis) in this early apoptotic wave is shown by the occurrence of a comparable testicular syndrome in mice defective in the bax gene. The apoptotic wave appears necessary for normal mature spermatogenesis to develop, probably because it maintains a critical cell number ratio between some germinal cell stages and Sertoli cells, whose normal functions and differentiation involve an elaborate network of communication.

Autophagy, which is one of the most important ways to maintain cell homeostasis plays an important regulatory role in cell survival and death. Currently, it is agreed that autophagy promotes or inhibits cell death depending on the internal and external environment and cell type. On the one hand, under normal nutritional conditions autophagy regulates cell survival by energy sensing through the main energy sensing cascade kinases. On the other hand, autophagy regulates the process of cell death. mTOR, Beclin 1, caspases, FLIPs, DAPK, and Tp53 play important regulatory roles in autophagy and apoptosis highlighting the crosstalk between the mechanisms underlying the two death modes. However, energy deficiency caused by PARP1 over-activation and DAPK-PKD pathway activation induces necrosis and autophagy, highlighting the interaction between the two pathways. In addition, autophagy regulates cell death through epigenetic regulation such as histone modification. More investigations on the relationship between autophagy and cell death is ongoing. In the future, there will be more challenges in the study of the relationship between autophagy and cell survival and death. As research increasingly focuses on cell death, the relationship between autophagy and existing and newly discovered cell death types is likely to become more complex. The elucidation of the regulatory role of autophagy in cell survival and death requires more research. Some research results are likely to provide hot topics for further investigations on diseases related to cell death disorders and an experimental basis for the targeted regulation of autophagy for specific treatment of diseases.

A Role of RIP3-Mediated Macrophage Necrosis in Atherosclerosis Development

The Australasian Cell Death Society (ACDS): celebrating 50 years of Australasian cell death research

ER stress: Can the liver cope?

Stem Cell Engraftment and Survival in the Ischemic Heart

Cell life-or-death events in osteoporosis: All roads lead to mitochondrial dynamics

This special issue on Cell Stress and Cell Death is aimed at bringing together recent developments in the fields of cellular stress and cell death and, in particular, the interplay between cell stress responses and cell death. The special issue opens with a review by S. Fulda et al. which provides an overview of how cells can respond to stress in a variety of ways ranging from the activation of survival pathways to the initiation of cell death that eventually eliminates damaged cells. Whether cells mount a protective response or succumb to death depends to a large extent on the nature and duration of the stress as well as the cell type. For example, milder stresses can lead to protection through activation of the heat shock response or the unfolded protein response (UPR). This review also describes several types of cell death (e.g., apoptosis, necrosis, pyroptosis, or autophagic cell death) and the mechanism by which a cell dies often depends on various exogenous factors as well as the cell's ability to handle the stress to which it is exposed. The implications of cellular stress responses for human physiology and disease are multifold and are discussed in this review in the context of some major world health issues such as diabetes, Parkinson's disease, myocardial infarction, and cancer. There are many molecules and cellular processes that play critical roles in normal cell signaling and survival responses, while also having a dual role in inducing cell death. A number of papers in this special issue, covering endoplasmic reticulum (ER) stress and Ca2+, address this topic. In recent years there has been a significant increase in the number of papers in the field dealing with ER stress and ER stress-induced cell death. This reflects the growing recognition of the importance of the ER in cell stress and in different modes of cell death. The ER is the site of folding of membrane and secreted proteins in the cell. Physiological or pathological processes that disturb protein folding in the ER initiate a complex intracellular signal transduction pathway, known as the UPR. This response is an attempt to reestablish ER homeostasis, although it can also lead to cell death. The review by A. Samali et al. provides a comprehensive overview of current methodologies for monitoring the UPR and ER stress, and it puts together a set of criteria to assess this response, which will be useful for researchers who wish to examine these phenomena in different model systems. The UPR is essentially tailored to reestablish ER homeostasis and it can also signal through other adaptive mechanisms involving the stimulation of autophagy. However, when ER stress is persistent, the cytoprotective functions of the UPR and autophagy can switch to cell death-promoting mechanisms. A review by T. Verfaillie et al. discusses the relationship between ER stress and autophagy and the implications for cancer therapy. Recently, a variety of anticancer therapies have been linked to the induction of ER stress in cancer cells, envisaging strategies that stimulate prodeath function or block its prosurvival function, to improve tumoricidial action. A better understanding of the molecular mechanisms that determine the final outcome of UPR and autophagy activation by chemotherapeutic agents will offer new opportunities to improve existing cancer therapies as well as revealing novel targets for cancer treatment. Prolonged or severe ER stress has been linked to induction of apoptosis. Caspase activation is one of the key steps in commitment of cells to apoptosis and is dependent on mitochondrial outer membrane permeabilization (MOMP) and the release of cytochrome c from the mitochondria. The research article by S. Gupta et al. investigates the mechanism of ER stress-induced MOMP using thapsigargin as an inducer of ER stress. They genetically dissected the role of caspase-9, -3, and -2 in the induction of MOMP by ER stress using embryonic fibroblasts derived from knockout mice and also treated cells with chemical and molecular inhibitors of the mitochondrial permeability transition. Their results suggest that caspase-9 and -2, Bcl-2 family members, and the mitochondrial permeability transition pore all play a role in MOMP during ER stress-induced apoptosis. Ca2+ is an important second messenger which is also poised at the intersection between cell survival and cell death. The review by C. Cerella et al. examines the events that occur during Ca2+ toxicity and how reparative or death pathways can be activated. They also discuss the observations that while Ca2+ can elicit these opposing responses, it also plays a role as a second messenger in signal transduction associated with cell death and survival. Knowledge of cell stress and cell death pathways, and the interplay between these, beneficially provides us with new ways to tackle diseases, particularly cancers and degenerative disease. Resistance to apoptosis is a feature of many cancer cells and this is the subject of the review by S. Fulda which summarizes the main mechanisms by which cancer cells evade the intrinsic and extrinsic apoptosis pathways. Generally, altered ratios of key pro- and antiapoptotic proteins are responsible for resistance to cell death; for example, altered ratios of Bcl-2 family proteins as well as increased expression of caspase inhibitors (IAPs) regulate the intrinsic pathway, while reduced sensitivity of extrinsic pathways occurs due to decreased expression of death receptors on the plasma membrane and increased expression of intracellular decoy proteins. Given this increased resistance to cell death pathways, the search for novel molecules to induce cell death in cancer cells is an important goal. Histone deacetylase inhibitors have become a promising new avenue for cancer therapy, and many are currently in clinical trials for various tumor types. The research article by N. Rivera-Del Valle et al. demonstrates that a novel hydroxamic acid histone deacetylase inhibitor, PCI-24781, exerts cytotoxicity and histone alterations in leukemia cells, via a mechanism that is dependent on caspase-8 and Fas-associated death domain. Another avenue for identifying novel therapeutic targets for cancers is study of inflammation, since many human malignancies have been strongly linked with chronic inflammation. The review by C. Sobolewski et al. describes the role of cyclooxygenase-2 in these diseases. This enzyme is a member of a family, which catalyzes the rate-limiting step of prostaglandin biosynthesis. Cyclooxygenase-2 is upregulated during both inflammation and cancer, and has been described to modulate cell proliferation and apoptosis mainly in solid tumors and more recently in hematological malignancies. Thus, the use of cyclooxygenase-2 inhibitors, together with other therapeutic strategies, may further improve the efficiency of anticancer treatments in the clinic. In contrast to cancers, an important aim of research into degenerative diseases is to discover novel ways to inhibit cell death. One such disease is Parkinson's disease, where there are currently no therapies which halt the degeneration of dopaminergic neurons. In the research article by K. Mnich et al. the ability of the endogenous cannabinoid, anandamide, to inhibit apoptotic cell death by the Parkinson mimetic, 6-hydroxydopamine, was shown. The protection provided by anandamide involved activation of phosphatidylinositol 3-kinase and prevention of 6-hydroxydopamine induced activation of c-Jun-NH2-terminal kinase (JNK). These data add to the growing body of literature concerning cannabinoids and Parkinson's disease. Certain other neurodegenerative diseases, termed tauopathies, feature filamentous tau-positive protein inclusions in neurons and glia, which are characterized by the expression of stress response proteins, particularly heat shock proteins (Hsps), in these inclusions. The article by L. Schwarz et al. investigated the contribution of small Hsps, Hsp27, and αB-crystallin, to neurodegenerative diseases by analyzing the association of Hsp27 with pathological lesions of tauopathies. Their results suggest distinct mechanisms for Hsp27 action in glial and neuronal cells, with prominent expression in unstressed astrocytes but with low expression observed in neurons even after stress situations. We hope that this special issue will alert researchers to some new developments in the fields of cell stress and cell death, particularly the interplay between prosurvival and prodeath responses, and how our knowledge of these can direct our efforts in discovering new therapeutic strategies for the treatment of cancers and degenerative diseases. Afshin Samali Simone Fulda Adrienne M. Gorman Osamu Hori Srinivasa M. Srinivasula

All biological processes associated with high sports performance, including energy metabolism, are influenced by genetics. DNA sequence variations in such genes, single nucleotide variants (SNVs), could confer genetic advantages that can be exploited to achieve optimal athletic performance. Ignorance of these features can create genetic “barriers” that prevent professional athletes from pursuing a career in sports. Predictive Genomic DNA Profiling reveals single nucleotide variations (SNV) that may be associated with better suitability for endurance, strength and speed sports. (1) Background: To conduct a research on candidate genes associated with regulation of skeletal muscle energy metabolism among athletes. (2) Methods: We have searched for articles in SCOPUS, Web of Science, Google Scholar, Clinical keys, PubMed, e-LIBRARY databases for the period of 2010–2020 using keywords and keywords combinations; (4) Conclusions: Identification of genetic markers associated with the regulation of energy metabolism in skeletal muscles can help sports physicians and coaches develop personalized strategies for selecting children, teenagers and young adults for endurance, strength and speed sports (such as jogging, middle or long distance runs). However, the multifactorial aspect of sport performances, including impact of genetics, epigenetics, environment (training and etc.), is important for personalized strategies for selecting of athletes. This approach could improve sports performance and reduce the risk of sports injuries to the musculoskeletal system.

Divide and die another day

Arachidonic acid (AA) generated by cytosolic phospholipase A2 (cPLA2) has been suggested to function as a second messenger in tumor necrosis factor (TNF)-induced death signaling. Here, we show that cathepsin B-like proteases are required for the TNF-induced AA release in transformed cells. Pharmaceutical inhibitors of cathepsin B blocked TNF-induced AA release in human breast (MCF-7S1) and cervix (ME-180as) carcinoma as well as murine fibrosarcoma (WEHI-S) cells. Furthermore, TNF-induced AA release was significantly reduced in cathepsin B-deficient immortalized murine embryonic fibroblasts. Employing cPLA2-deficient MCF-7S1 cells expressing ectopic cPLA2 or cPLA2-deficient immortalized murine embryonic fibroblasts, we showed that cPLA2 is dispensable for TNF-induced AA release and death in these cells. Furthermore, TNF-induced cathepsin B-dependent AA release could be dissociated from the cathepsin B-independent cell death in MCF-7S1 cells, whereas both events required cathepsin B activity in other cell lines tested. These data suggest that cathepsin B inhibitors may prove useful not only in the direct control of cell death but also in limiting the damage-associated inflammation.

he heart has a high mitochondrial content to generate the vast amount of ATP that is needed to provide the energy that is required for the continuous mechanical workload.Cellular ATP is predominantly used to support the contraction-relaxation cycle within the myocardium.Although cardiac mitochondria are flexible in using substrates to generate energy, the conversion of free fatty acids and glucose accounts for most of the ATP production in the healthy adult heart. 1 However, during advanced stages of heart failure there is an imbalance between energy demand and availability, accompanied by a downregulation of fatty acid oxidation and an increase in glycolysis. 2 Glucose becomes an important preferential substrate in the failing heart, and it is suggested that the derangement of the cardiac energy substrate metabolism plays a key role in the pathogenesis of heart failure. 3Manipulations that improve the oxidative capacity of the heart during disease might be beneficial for cardiac function and slow the progression of heart failure.MicroRNAs (miRNAs) are small, noncoding pieces of RNA that regulate gene expression by binding to recognition sequences that are usually located within the 3ʹ-untranslated region (3ʹ-UTR) of target genes.Binding of the miRNA to these sequences blocks the translational activity of these transcripts, leading to a reduction in protein formation. 4As is true for many aspects of heart disease, miRNAs have previously also been shown to be involved in the regulation of energy metabolism during heart failure. 5 miRNA that has been linked to mitochondrial dysfunction of the heart is miR-181c.MiR-181c has been proposed to function in the mitochondrial compartment of cardiomyocytes by targeting mt-COX1 mRNA.Overexpression of miR-181c induced a loss of mt-COX1 expression, which led to an increase in mt-COX2 levels and subsequent remodeling of mitochondrial respiratory complex IV.The imbalance in components of complex IV induced an increase in mitochondrial respiration and the generation of reactive oxygen species, resulting in mitochondrial dysfunction.On the contrary, genetic deletion of miR-181c/d resulted in a smaller infarct size and maintenance of cardiac function in an ischemic heart failure model by improving the mitochondrial response to oxidative stress.6 These data indicate that mitochondrial perturbations induced by miR-181c could have important consequences in myocardial pathophysiology.Another example of miRNAs influencing cardiac energy metabolism is the miR-199a/miR-214 cluster.This miRNA cluster was found to be induced in heart failure in humans and mice.Both miR-199a and miR-214 coordinately regulate peroxisome proliferator-activated receptor δ, which is a critical regulator of cardiac energy metabolism that influences the metabolic shift toward glycolysis during heart failure.The importance of these miRNAs and the role of energy metabolism in heart disease were further underscored by the fact that therapeutic inhibition of both miRNAs was able to restore mitochondrial free fatty acid metabolism in a MicroRNA-146a as a Regulator of Cardiac Energy Metabolism